The Copper Deposits of Michigan (PP 144)
The classic study of the Keweenaw Peninsula native copper district — one of the world's largest copper producers from 1845 through World War I. 51 plates…
Public-domain full text preserved in the Mountain Man Mining Library. Original source: pubs.usgs.gov.
U. S. GEOLOGICAL SURVEY George Otis Smith, Director Professional Paper 144 THE COPPER DEPOSITS OF MICHIGAN BY B. BUTLER and W. . B RBA K IN COLI,ABORATIO WITH T. 1. BROD RIC , L. . GRATO , C. D. HOHL, CHARLE P iA HE M. J. , H LZ, ALFRED W DKE, a'nd R. C. ·wELL UNITED STATES GOVERNMENT PRINTING OFFICE WASIDNGTON
u.s. G£.0L()I;iiCAl ~il t ' V t 0 MAY 14 1929 LIBRAk t ADDITIONAL COPIES OF 1'BIS P UBLICATION MAY BE PROCURED FROM TilE SUPERlNTENDENT OF DOCU MEI'OTS U.S.COVERNMENT PRINTING Ot">"ICE WASBI:NGTON, D. C. AT $2.50 PER COPY
Contents
Outline of report_ - - XJ Lava tops or amygdaloid - -- -- Oxidation of l avas- - -- --- xn xn xn xu Mineralized fissure -- --- xn xrr XJI Part 1. General feature Bibliography J ographY TopographY Broader relation haract r of th ro k g and r lation diments Fel ite conglom rate - - Extent and Lhi kn of bed Character of underlying bed_ Part 1. General features-Continued. Bedrock geology-Continued. tra.tigraphy- Continued. Paa-e Extru ive rock -- - - -- Porpbyrites --- - Melaphyr - Dolerite -- - - Relation of texture to comp iti n Di tribution of the different Amygdaloid --- - -- --- - Fragmental or brecciated top -- - -- - Alteration of t rap Red color of amygdaloid top tatement of tbe problem Red tops of unaJtered we tern flow Oxidation in mooth-top flows of Oxidation and oncentration in urface weathering imm - Atmo pheric oxidation of hot top Magmatic segregation Fumarolic alteration . cti n of gase fr m the
TV Part 1. General features- Continued. Bedrock geology-Continu'ed. Stratigraphy-Continued. Igneous rocks-Continued. Copper content of the ba alt - Intrusive rocks General features tructure- - --- -- - - - - -- -- Age and cause of folding and faulting Rock-forming period - Part 2. Ore depo it-- --- -- -- - - - - - CO TENTS Page 1Q1 Part 2. Ore deposit - ontinu d . opper depo it ontinued. Amygdaloid lode Cont inued . ellular amygdaloid lode - 7 - -- Distribution of copp r in a mygdaloid lode - Di tribution of shoots in the lode Distribution of copp r in t h shoot Richne Di tributionof copperinv in o evidence tha t t h lodes a r po r at the 1!2 Evergr en and uc ding lode --- o evidence of leaching and removal of 01 per o evidence of enrichment at the salt-water Conditions determining position of ore Features common t o all typ s JJ !J Direction of movemen J25 Means of access of the solution Ascent from contact of the '125 Ascent from the Keweenaw fa ult. Causes and conditions of precipitation Precipitation by reducing action Precipitation in consequence of
Part 2. Ore depositsontinued. Genesis of the deposit - ontinucd. Hypotheses of originContinued. D eposition by ascending solutions- Con. auses and condition of precipitaLionContinu d. Precipitation by oxidationCon. Presence of an oxidizing Destruction of oxidizing agen 'hcmi try of the depo ition of native copper from a cending olution , by R. ummary of gene i -- - --
oro Triassic of ber pper Whit River, AI Zwick.au .\lp;odon s, Permian " R d 13 ds" of Llic ,'outhw :;(, . r Lie anada Lik lihood f finding n wore bodi -- Distribution of depo.i --- -- - - -- - Exploration of lod s haracLcr of amygdaloid Joel Mineralogy as a guide in exploration and Mineralogic guides in amygdaloid Mineralogic guid s in conglom rate Fold - -- --- - CONTENTS Page Part 2. Ore depo itsContinued. Application of geology to mining- 'ontinued. Ore shoots- Continued. Barriersontinued. Transverse versus longitudinal ugg stion for fu ure geologic work in the opper Geophysical methods applied to exploration and geologic mapping, by T. M. Broderick and C. D. Hobl. Direct conductivity and resistance Indirect application of geophysics to copper Application of geophysical methods to geologic rumerous geologic checks available._ Favorable geographic and topographic Page
Part 2. Ore depo it -Conti nued. G ophy ical method applied , etc.- ontinued. Application of g oph_vsical method , tc.- Con . Theory and practice of magnetic surveying_ Fundamental principle History of work in the Lake uperior Keweenawan rocks - Early ob en ·ations. -- - Recent work within the copper di trict_-- Work in 1925 Determination of trike .. Tracing beds at specific horizons Location of faults, folds, and fissure Other relations of magnetic feature Present attitude toward magnetic surveying Part 3. Detailed de cription of Iones and fissures Mineralogic and textural influence Location and topography -- - White Pine Extension mine -- - - Prod:.JCt,ion - - -- -- -- - - --- Lodes of t he Hancock m ine Pewabic amygdaloid l odes_ :: :: :::::::·- Character of flows Mineralization Rock alteratio~~: : :::::::: :::::: Mineralization in different lodes "Main" branch - Pewabic Far W~t J~d;;~ :::::::: Franklin Jr. mine CONTENTS Page Part 3. Detailed description of I des aud fissure ·-Con. Lodes in 1 Iron oxide in th alum t e' Hecla Changes in the iron oxid Faults - - - - - - - - --- - - Distribution of the copper_ I nfluence of faults and fi ures - -- Mineralization of the walls Change in grade of ore - Map bowing " copp r per uni ar a Cause of convergence of solutions and influence of barriers Copper boulder and kull -- - Alteration and m ineralization of the lode - - Alteration and mineralization later than Distribution through thicknes of the
CONTENTS Part 3. Detailed d escripti~n of lodes and fissuresCon. Page Kearsai·ge lode-Contmued. Oxidation - Alteration accompanying mineralization Probable causes of rich and poor ground I nfluence of fi sure on the lod --- --- audition favorable to mineralization in the known productive portion of the Kear arge Effect of depth on the opper content of the ,\layflower-Old Extent and correlation Hanging-wall trap -- -- Di tribution of type -- - -- --- - --- - Xew Arcadian lod --- -- \Vyandot o. Evergreen and succeeding lod baracter of flows - - --- kuctur - - - - --- Character of amygdaloid Relation of mineralization to character of lode_ Mass mine-- - -- - --- - Adventure mine - Part 3. Detailed description of lodes and fissure -Con. Page Evergreen and succeeding lodes-Continued. Evergreen lode- ontinued. Folds -- -- - -- --- - 2 1 Cro · fat:lts and ·lips- --- - --- - - --- - --- - trike fi urc -- - Relation 0f minerali?.ation to character of uperior lodes - - - · -- --- ·· Hi torY -- Fi sure n.ines and pro pects of Keweenaw
CO 'l'E 'f Part 3. Detailed de ·cription of lod ·s 1Lnd f·i · urcs- Con. Puge Fi ·sure depositsContinued. Part a. Detttiled dcscrit tion of lod. ILOd fi ·sures- on. Page Fissure deposit ·- ontinued. Fissur mines and prospllCts of K eweenaw Fi ure mines and pro pects of Ke' e naw < Ontonagon ountie - Continued. ative Copper_ WinthrOP and Ontonagon ounties-Continued. Pho nix fissure ort h Albion-Manhattan.-- ·enid - Mincsot.a and 13ranc h ·ure and alico lode , ILL STRATIO Page 2. General geologic map and sections of t he Keweenawan and as ociated rocks in the Lake uperior copper 9. · Geologic map of 10. Geologic map of Copper Range from Atlantic to 16. Geologic section in T. 58 17. ~anitou and orth Cliff geologic ections --- --- - - In pocket. 19. Geologic sections in Tps. 56 and 57 N., R. 32 W -- In pocket. 20. Geologic sections in T. 56 ., Rs. 32 and 33 W--- -- - - --- - --- - -- --- In pocket. 21. Geologic sections in T. 56 ., R. 33 W - -- --- - --- -- In pocket. 22. Geologic sections in Tps. 55 and 56 N., R. 33 W -- --- - - In pocket. 23. Geologic sections in Quincy mine, T. 55 ., R. 34 W - - - In pocket. 25. Geologic sections in T. 53 ., R. 35 W., and T . 54 ., R. 34 W - --- -- - - - - - In pocket. 26. Geologic sections of Copper Range diamond-drill holes, T. 53 27. Geologic sections in T. 52 N., R. 36 W., and T. 53 28. Geologic sections in Elm River & Contact Copper Co.'s mLne , T. 52 29. Geologic sections in T. 52 N.; R. 36 W., and T. 51 32. Geologic sections in T. 49 ., Rs. 40, 41, and 42 W- - -- - - - --- -- -- - - - - -- -- -- -- - - In pocket.
CONTENTS Page 40. Longitudinal section of Kearsarge lode In pocket. 42. Longitudinal sections of Old Arcadian and Winona lode -- In pocket. 44. Longitudinal section of Ogima lode ·- -- --- - In pocket. 49. Longitudinal section of Baltic and Baltic West lodes - - -- --- In pock t . 53. Ridge produced by resi taut flows· - --- -- -- - 54. A, Dougla Houghton Falls; B, Drill core improperly stored; C, Glaciated surface howing re i tance of 56. Texture of lava a 57. Texture of lava as hown in micro copic ection - -- - - 5 . Texture of flow top a een in lodes· --- -- -- -- - - -- 59. Texture of flow tops as een in specimens- - --- -- -- 60. Texture of flow top as seen in diamond-drill core -- - - -- -- - - - -- 62. Iron oxide in flow tops as een in polished ections. 63. Iron oxides in rocks a 67. A , Intergrowth of copper and ilver; 8 , F i ure breccia partly replaced by datolite; C, ative ilver on native ulphideveins - -- --- -- - - --- --- - - 73. Bleaching of amygdaloid lode a ociated with copper and sulphide ... - 74. A, o. 2 shaft hou e, Quincy mine; B, haft hou es, Baltic mine; C, View looking north from I le Royale mine to Quincy Hill over Portage Lake -- - -- --- - --- -- --- -- - --- 75. A, haft on I earsarge lode; B, Shaft on Winona lode; C, orth Bluff and shafts and dumps of Calico and Mine ota lode , Michigan mine; D, Calumet, showing haJts on alumet & Hecla conglomerate and Osceola amygdaloid_ Fw RE 1. Variation in thickne of I ear arge Bow -- --- - - --- 2. Change in iron in lava top at Twin Fall, Idaho - - --- - - - 4. Iron content of Kea arge Bow --- -- -- - 5. Gai'ns and lo es in con tituents in oxidized top, a compar d with trap pQrtion of flow. --- - 7. Stability relation for the quation FeaO.+CO;::t3FeO+C02--- - -- --- --- --- -- - -- 9. Possible development of the Keweenaw fault --- - - 10. Possible development of the Kew cnaw fault-- -- -- -- 11. Paragenesis of mi.Oeral of Michigan copper depo it - - : 15. Variation in copper content per foot of depth, Calumet & HeQla mine- , -- - 16. Influence of varying permeability of rock on flow of solution and formation of ore hoot --- -- -- Composition of bleached and unbleached rock --- --- - -
OUTLINE OF REPORT The copper di trict of Keweenaw Point, in the northern peninsula of Michigan, i the econd largest producer of copper in the world. The output of the district ince 1 45 has been more than 7,500,000,000 pounds and showed a rather steady and con i tent increa e from the beginning of production to the end of the World War in 191 , ince which there has been a marked decrease. GEOLOGY General jeatures.- In Keweenawan time a eries of basaltic flows accumulated to a depth of thou ands of feet. Interbedded with the flows are felsite conglomerates. In the lower part of the eries the conglomerates are rather abundant and thick; in the middl part they are relatively few and thin but persist for long di ianc ·; in ihe upper part they make up the bulk of the rock. Intruded into and probably also interbedded with the basalt and conglomeraies ar ·iliceou ·, felsitic, and porphyritic rocks of similar compo ition to the material that makes up the conglomerates. The location of the fi · ure from which the igneous material, both extru ive and intru ive, pre umably came is unknown, but there are orne r a on for uppo ing that they were ituated toward the center f the Lake uperior structural basin, under the present lake, and that the flow outward from them was in a direction opposite to the pre ent dip of the beds. Probably the felsite bodies from which the conglomerates were derived lay in the arne directi n the fi ures, and the material was carried down the same slop as the lavas. Both the flows and the diments ar believed to have accumulated on a land urface, though probably ome, e pecially of the later sediments, were laid down in bodic of water. The flows range in thickness from a few feet to 1,300 feet and in extent along the trike from a few hundred feet to at least 40 miles. arly all of them are basaltic, but there are differences in compo ition, expr ed in textural differences, which make it po ible to divide tho flows into everal general groups. The intru ive rock are mainly silic ous fel ites or porphyries, but there are orne, like those of Mount Boh mia and others toward the Michigan- Wiscon in boundary, that approach the Duluth gabbro in compo ition and t xture, and these and the felsite also w re probably derived from the arne source as that rock. Laua tops or amygdaloids.- The d nse rock that forms the greater part of most of the thick flow ' is commonly called "trap"; it i everywhere overlain by more open-textured material, which is known as "amygdaloid." The cellular tops were formed by the action of gas which wa contained in the ' lava and was liberated during the progress of flow and consolidation. Part of this gas e cap d from the stu·face, and part waa caught as bubble in the vi cous top of the lava and thus formed a cellular mass which was later converted into amygdaloid by the filling of ti1e ve icles. vera! types of top are recognized. The most common is the cellular top, which was produced by the simple freezing in of individual bubbles of gas. Coalescing amygdaloid has re ulted when many bubbles collected into au irregular layer of ga separated by material in which cavities were relatively few. This gave I ng connected passages in the tops. Fragmental top is due to the breaking up of the cellular top, during olidification and flow, into angular fragments which became so jumbled a to form an irregular hummocky surface. Where the fragment are piled above the general surface they also sink into the flow, so that lava top of this kind varies abruptly and irregularly in thickne . Scoriaceous top results from a working over of any of t.he other types by the process of erosion and edimentation. It very commonly underlies felsite conglomerate but occurs also where there is little or no felsite sediment. From comparison with other region it i thought that th different types have re ulted from differ nt condition f the lava a it reached the. urface. Lava that i ·ued at a high t mperature and had a low gas content producer! cellular top. Lava that i ued at a low temperature and had a high gas content produced fragmental top. Coale ·cing top was formed on lava intermediate between the other t wo. Oxidation of lavas.-The tops of nearly all th flow. are di - tiuctly red, and the fragmental top arc decidedly r d. hemical a nalyse show that there i: in general a tcacly decreas in the proportion of ferric iron and an lncrea c in f rrou · iron from the top of a flow nearly to he bottom. In the fragr,nental flows there i also more total iron in the top-a much a 40 per nt more than in the compact portion of the flow. It i thought that the oxidation and concentration of Lhe iron were accompli hed in large part by the gase given off by the lava during solidification. The evidence indicate that at the temperature at which the lava emerged the inclosed ga e were either neutral or reducing in their action on ferric oxide, but as they cooled in their a cent through the flow they became strongly oxidizing toward ferrous oxide. Copper in trap.-An examination of the fre he t traps confirm previou ob ervation that the · contain copper in mall amount. Both native copper and chalcopyrite are pre ent. It eem probable that at lea t a part of the copper i a primary con tituent of the trap . Structure.-The Michigan copper region i on the outhern rim of the Lake uperior syncline or ba in, wh.ich wa probably formed during Keweenawan time. The early Keweenawan ;ock of Keweenaw Point dip steeply and th later one progre ively le teeply northwe tward, toward the center of the ba. in. Tran vel· e to the general strike of the Lake up rior yncline are anticlines and synclin s that pitch down the lip of the larger fo~d; among the folds are he Keweenaw anticline, the Ontonagon yncline, and the Be emer anticline. On the e broader anticlin and sync! in are . ev ral "ubordinate folds of imilar trend, uch as the ·Allouez anticlin , the I le Royal yncline, and the Baltic and Mass anticline . The greatest fault of the region i the Keweenaw fault, whi h bound the oopp r-bearing erie on the outh from the end of I eweenaw Point to Lake Gogebic. This i · a r v r c fault of northwesterly dip, along which the ba altic erie ha been thru t over the "Eastern " ( am brian) and tone. Th dip of the fault i nearly parallel to the flows, and it al o follow · the major anticlinal and ynclinal tructure of the rook . Many branch faults and fi sure are as ociat!ld with the I eweenaw fault. Relatively mall t ran verse fault and fi ure are al o pr ent around the ere ·t of the anticline . The mov ment on th Keweenaw fault probably did not begin till late KewconaXI
OUTLINE OF REPORT wan time, and much of it occurred after the "Ea tern" sandstone was deposited. The trao v r e folding and faulting probably followed the I eweenltw faulting and preced d the period of mineralization. ORE DEPOSI'l'S The copper deposits are of two main classe - lode deposits and fissure deposits.1 The lode deposits consi t of conglomerate lodes, which are mineralized beds of felsite conglomerate interbedded with the lava flow , and amygdaloid lodes, which are the mineralized ve icular or brecciated tops of the lava flows. The fissure depo its are veins along fractures that are in part parallel and in part transver e to the beds; all of them are of narrow tabular form. The commercially important known deposits with one exception are confined to the portion of the Keweenawan series composed predominantly of lava flows. They are distributed through most of that portion of the series. The more productive lode , from the base upward, are the Baltic amygdaloid, Isle Royale amygdaloid, Kear arge amygdaloid, Osceola amygdaloid, Calumet & Hecla conglomerate, Allouez conglomerate, Pewabic amygdaloid, and A bbed amygdaloid. The one uch lode, named for the formation that contain it, is in the upper sedimentary portion of the serie . The fi ure deposits are in the ame portion of the serie as mo. t of the lodes. Conglomerate lodes.-Only two of the conglomerate beds have been extensively explored, the Calumet & Hecla and the Allouez. The Calumet & Hecla conglomerate over most of it known extent is a sandy or '" scoriaceous" bed with a little fel ite sand at the top. At Calumet it opens into a well-developed felsite conglomerate lens that increa es in thickness and extent with increased depth. The Allouez conglomerate is thicker and more persistent than the Calumet & Hecla but in places is represented only by a clay seam. The valuable mineralized portion of the Calumet & Hecla conglomerate is confined to the conglomerate lens, and the copper content decreases abruptly where the conglomerate changes to sand. The copper occurs a native metal and mainly replaces the finer matrix of the conglomerate. The common minerals associated with the copper are feldspar and epidote, mainly deposited earlier than the copper, and quartz and calcite, contemporaneous with the copper. Zeolites are conspicuously absent. The characteristic rock alteration effected by the ore-bearing solutions was the removal of hematite, with a resultant bleaching of the lode from brown to pinkish. Amygdaloid lodes.- Ail but two of the largely productive amygdaloid lodes, as well as most of those that have given some encouragement, are of the fragmental type. One, the Pewabic, is mainly of the coalescing type, though in part it is !"ragmen tal, and the Ash bed is mainly a "scoriaceous" lode ' though locally fragmental. o mines have been found in th~ cellular amygdaloids, which are by far the most abundant. A greater variety of minerals is associated with the copper in the amygdaloid lodes than in the conglomerates. Chlorite, feldspar, epidote, and pumpellyite are the abundant minerals that mainly preceded the copper in deposition. Abundant quartz and calcite and orne prehnite and datolite were locally deposited with the copper; the zeolites laumontite and analcite, together with saponite and other minerals in small amount were deposited later than the copper. Sericite was deposited apparently both with and later than the copper. to ferr us oxid and recombination to form ferrous and r . compounds such as pumpellyite, chl rite, and epidote. erne Ore shoots.- The minable copper occurs in shoots, of which many are large but a ll far less extensive than the lodes th 1 contain them. Th ore of the shoots was. deposited in l~e more permeabl parts of the lodes by solutiOns whose move. ment was directed by barriers of relatively impermeabl material. Two types of environm nt have most common!~ favored the formation of shoots- a "bed," conglomerate amygdaloid, that is prevailingly impermeal le but contains permeable portions of great downward extension, like the alumet & Hecla onglom rate shoot and the Kearsarge amygdaloid shoot, and a" bed," su has the sceola amygdaloid that is prevailingly permeabl but contains impermeabl~ streaks which cause a cone ntration f s lutions beneath them. Mineralized fi sures.- Most of the v ins in the north end of the distri t are in cross fissures on the K weenaw and Allouez anticlines. The mineralization of th fissures bas occurred near the intersections with strong amygdaloids and under the "slide" at th base f the Greenstone flow. The 'fissures at the south end of the district are mainly strike fissur s dipping more steeply than th b ds; they also are mineralized n n.r the intersf'rtion with strong conglomerates or amygdaloids. Chang with d pth.- II the larger kno' n ore shoots have had as rich or at som place n ar their outcrop as at any greater depth. Any changes in grade to the pr sent depth of development may be attributed more to changes in the character of the lode rock than to distance from the outcrop. Decrease in grade in the fissures and possibly in some of the lodes may be due mainly to depth. Genesi of the depo it .- Tw differing explanations of the genesis of the deposits have been advanced. One assumes that they are due to descending solutions, that the copper was derived from the lavas or from overlying beds, and that reaction of the oxidized copper-bearing solutions with the ferrous iron of the lavas produced metallic copper and ferric compounds. The other assumes that they were formed by ascending po· tential sulphide-bearing solutions which derived their copper from an igneous source, and that the reaction of these solutions with the ferric iron of the rocks resulted in the oxidation of the solutions, the reduction of the ferric iron, and the precipitation of native copper. The theory of deposition by descending waters appears untenable for several reasons. There is, in the first plAce, no adequate source of the copper, for although copper is present in the traps there is no evidence of its removal. It is difficult, also, to believe that gravity circulation could have been ade· quate to form the deposits, for the gravity circulation of solu· tiona in the deep levels of the mines is almost nil, and many of the deposits are on the under sides of impermeable barriers. The deposits, moreover, were formed in beds rich in ferric iron and poor in ferrous iron. The ferric iron was partly removed and partly reduced to the ferrous stat a reaction which does not seem likely to occur in the presence of oxidized solutions. In the ascensional hypothesis it is assumed that the copper solutions originated in the underlying Duluth gabbro and that they either entered the lode-forming layers directly where the downward extensions of these layers were in contact with the magma or passed from the magma to the places of deposition by way of fissures. elutions thus originating must have been highly heated, in the early stages gaseous, and under great pressure, and they could therefore easily make their way along fissures aud permeable layers. The principal facts that cause the authors to favor this }lypotbesis are that the solutions became concentrated and The rock alteration effected during the formation of the amygdaloid lodes was of two types- a removal of hematite similar to that in the conglomerate, and a partial rem'oya.l of the iron of hematite and a partial chemical reduction of ferric oxide ' deposited ore on the under sides of barriers and that they were reducing in character- they carried sulphides, and they de· posited native copper in beds rich in ferric iron, which they partly reduced or removed. I The terms " lode" and "fissure" aro here applied according to local usage; lor deflnitious see section on ore ,(eposits, p. 101.
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THE COPPER DEPO, IT OF MICHIGA By B. . BuTLER and W. . BuRBANK In collaboration with T. M. RRODERI K, L. C. GRATO , C. D. H oaL, HARLES PALACHE, M. J. C ROLZ, A !.FRED W A ' DK E 1 and R. . WELLS P RT 1. GENERAL FEATURE INTRODUCTION FIELD WORK AND AUTHORSHIP The field work on which this report is based wa begun in the pring of 1920 by the Calumet & Hecla Consolidated Copper Co. under the supervi ion of Prof. L. C. Graton. The work done under these ·onditions was continued till the spring of 1924. T. M. Broderick, B. . Butl r, C. D. Hohl, and Alfr d Wandkc were engaged in the survey for the greater part or all of the period ; Prof. Charle Palache for the umm rs of 1920 and 1921. Professor Graton pent each ummer and hort period at ther ea ons in the district. Me srs. Brod rick, Butler, and Hob.! worked mainly on the general field problems, Professor Palache o-ave pecial attention to mineralogy, and Mr. Wa1~dke worked partly in the field but gave special attention to the petrographic and mineralogic studie in the labomtory. Robert Hoffman pent the summer of 1920 and E. R. L v 11 th ummer of 1921 in the work. By a. coo p era ~iv arrangem nt between Harvard niver ity, the I at10nal R arch ouncil, and th nited tate Geological ur e , R. . W lis at th arne time made a tud of th chemi try of th formation of native copper. The chemi t of the alum t & Hecla Co. contributed analy e and other chemical data especially in the early stages of the inv tio-ation: Augu tu Locke was in fr quent con ultation with the other worke1 , and short p riod wer spent on the w?rk by J. olney Lewis, William Burn , and G. N. Bjorg . W. 0. Hotchki s and H. R. Aldrich, who have been working on the geology of the Kewe nawan ro~ks for the Wisconsin Geological and Nat ural tory Survey, visited the district and made intere tmg contribution to the discu ion of th broader r.elations of the Keweenawan. Prof. A. C. Lane . likewise gave th b nefit of his long xperience in the district. . On. the completion of the Calumet & Hecla. investigation m the spring of 1924, a.n arrangement had been made by the nited tates eological urvey after con ultation with the other compani s of th district, by which the general geologic re ults of the alumet & Hecla study were turned o er to the Geolocical urvey, which extended the tudy throughout"' the pr~du ctive part of the di trict. Mr. Butler, r appomted on the Geologi al uTvey, and W. . Burbank were as igned to thi work, which wa anied on till Augu t, 1925. A large part of this field work wa. done in as ociation with th o-eologi a! department of the Calumet & He la o. During th la t few Srear ertain le tricalmethod of pro pecting have been tried in the di trict with indifferent re ult , and in onnection with thi wol'k i e 1 . Broderi k and Hob! tarted dip-needle urv whi h were uc e ful in incli a.ting th tr nd of difl' r nt formation on the bedrock urface beneath the extenive coverino- of glacial drift. The re ult obtained were of uch general mterest that the e gentlemen have kindly prepared a chapter on "geophysical methods applied to exploration and geologic mapping," which has be n in orporated in thi report. Mi Marie J. cholz compiled roo t of the stati tical data for both the alum t & Hecla onsolidated opper o. and the Geologi al urvey and did most of the clerical work on the Teport. The drafting of the udace map and con iderable of the other drafting was done by Carlos V. Rawlings. The general features of the geology and the occurrence of the copper and much of the detail for the north end of the district, a presented in this report, were mainly work d out during the Calumet & Hecla inve tigation by the m n engag d in that work. The name of all the e men appear in the title-page with th addition of W. S. Burbank. The report as it now tands wa prepared by B. . Butler and W. S. Burbank. SCQPE OF REPORT The difficulty and high cost of obtaining geologic data in this generally drift-covered district has made it desirable to collect and· to put on record all such da.ta. that are available. Field observation ha' e therefore been presented in the text and on the map n,nd sections in greater detail than ha be n cu tomary in r ports of this character. The attempt ha been.
THE COPPER DEPOSITS OF MI HIGAN made al o to how on the map all known developments in the di ·trict, with the hope that this would promote the mo t ffective planning of future developments. The fact of the occurr nee of copper have been et forth a they have been a certained, and a general di cussion of the origin of the ores is given. The attempt has been made to keep fact and speculation eli tinct, and it is hoped that the reader will draw his own onclusions from the facts rather than unq unlifiedly a cept tho e here pre eDtcd. In the ection on the application of geology to mining are de. cribed methods in the earch for ore depo its that seem to give mo t promi e of ucces . ACKNOWLEDGMENTS It i hardly neces ary to say that any geologic report on an old district i likely to be but one of a eries each ba ed on the data accumulated by rnany others in addition to the authors, up to the time that it wa made. Thi report i no exception to the rul and contain much information derived from earlier report. . The last general account of the region, however, was written about 15 year ago, and the mining developments that ha e been ca.rried on, at time very actively, during the period that has ince elap ed have added greatly to the body of geologic fact that was then available. The main sources of information, apart from the work of the authors, have been the reports of the Michigan Geological Survey, previous reports by the United States Geological Surve.y, and the data accumulated by the operating companies. The Michigan Geological urvey generously furnished all material in its po session. All the mining companie of the di trict gave that hearty cooperation which was essential to the succe s of the report and without the assurance of which the urvey would not have been undertaken. The h lp given by the different companie ha , of cow· e, not been equal. Tho e who had much gave much; orne had little and could give no more than tb,ey had. The Calumet & Hecla Consolidated Copper Co. made the outstanding contribution, starting the work, and paying for a large part of it; and without this cooperation the report by the Geological urvey would not have been undertaken. Whatever of usefulness comes to the district from this report should be largely credited to that company. Acknowledgment to individuals who have published the results of their investigations is made under the he~d~g ."Previous investigations." Acknowledgment to rnd1V1duals for the data coming from companies is not easy, because information on any one topic, has u ually been accumulated over a long period and has been gathered by several individuals. The authors trust that they will be pardoned, therefore, if they do _try to accredit each borrowed fact to its original ' Soo noto on p. 233. author but merg their acl nowl dgments of indebtedness .in on . ex pre ion of m t ordial thanks to the official of the ompani . veral ngineer of the district, peciaUy Mr. R. R. eeb r and . 1r. Berman Fe ing, have furni hed data for companie with which they wer formerl connect d but which at the tim of the inve tigation w r not operating. Mr. A. H. Meuch contributed m1tny data on the south end . of the di tri t oll t d b th while he was a memb r of the Mi higan Geologi al urvey and later. Chemi t f Lhe 11lum L & H cla o. have helped both by their interest and by analy e . For analy " the authors are ind bted to Me rs. W. F. Hillenbrand and H. C. Kenney. In addi ion to the acknowledgment for contribution to the r port, th author wi h to expre appreciation for court ie · xt nded, e pecially by · th alumet c ' Hecla o., t th Ge logical urvey aDd to them per onally, which add d much to the conv nience and ffectiv u f th work. To ~vlr. F. alkin , of the Geologi al w·vey, the author ar indebted for a ritical ·reading of the report, whi h re ulted in many h lpful ugge tion . PREVIOUS INVESTIGATIONS Few other di trict of the country have received uch nwnerous and repeated examination by geologists and engineer a have been made in the copper country of 1ichigan. Altogether a vast amount of information has been as embled regarding thi district. Of that which ha.: b n publli hed, mo t has been afforded by the tate urvey of Mi bigan, Wiconsin, and Minne ota and by th nited ta Geological urvey. All known publication on the geology of the di trict are li ted in th bibliograph , but the contribution of several groups of worke are of so outstanding importance as to d erv pocial mention. Douglass Houghton/a in 1 41, first brought the district effectively to the attention of mining men. His valuable work ' as terminated in it midst four years later by his death. The next general report was made by Raphael Pwnpelly and his associate, A. R. Marvin ,Z who laid the foundation for the sy tematic study of the stratigraphy. of. the d~strict,. studied the mineralogy of tho deposits rn deta1l, and set up a theory of the deposition ?f the ores that for 50 years has exerted a controlling .uence on geologic thought regarding the district. The value of Pumpelly's pioneer work in mineralogy and rock alteration is too well recognized to need extended comment. The work of R. D. Irving 3 and his associates gave a broad view of the copper-bearing rocks and their stratigraphic and structural relations an<Ladded much Houghton, Doug!~, Michigan State Oe;;;-ogist (Fourth] Ann. Rept.: H. R. Doc. 27, 1841. : Michigan Oeol. Survey, vol. 1, pt. 2, 1 73. Mo~.vi~~S:.' D., Tbe copper-bearing rocks of Lake Superior: U. s. Oeot. SurvoY
BIBLIOGRAPHY to the knowledge of the mineralogy and petrography of these formations. 1. L. Hubbard/ a State geologi t, contributed especially to our knowledge of the felsite rna ses and the general structure in the north end of the district, and later, as an operator, he wa successful in applying geology to the location of profitable lodes, notably in the Champion mine. The final report by A. C. Lan ,S a tate geologist, brought together the result of year of tudy by himself and other members of the Michigan Geological urvey. This report is the great storehou of fact concerning the stratigraphy of the district. In it is pre ented a theory of the origin of the copper deposits consid rably modifying that et forth by Pumpelly. The value of thi report i too well known to require comment. Van Hise and Leith,6 in their monograph on Lake uperior geology, made evident the setting of the copper di trict in the larger province. They definitely broke away from the Pumpelly theory of formation of the ores. Many others have contributed to our knowledge of the district, as will app ar in the followi.nO' page and ,a can be een by coo ·ulting the bibliography. orne of them, notably Prof. A. E. eaman, have made a far more exten ive and intimate tudy of the di trict than the bibliography would indicate. BIBLIOGRAPHY [ eo also p. 2331 ACKERMANN, HERMAN W. Die Kupferfuhrenden chichten am Lake uperior: raturw. Gesell. I i Dre den itzungsber. 1 75, pp. 101- 105 1 76. AGA SIZ, AI,E ANDER. On th po iti n of th . and ·tone of the outhern lope of a portion of K w enaw Point, Lake uperior: Boston oc. at. Hi t. Proc., vol. 11, pp. 244-246, 1 67. On underground tempera.tur s at great depth: Am. Jour. ci., 3d er., vol. 50, pp. 503-504, 1 95. AoAs Iz, GEoROE R ussELL. Alexander Aga iz, 1 3 1910: Le ters and publications of Alexander Agas iz, with a. ketch of hi life and work, Boston and ew York, Houghton Mifflin Co., 1913. AGASsiz, Lours. Lake uperior; its physical character , vegetation, and animal , Boston, 42 pp., 1 50. On Marcou's "Geology of orth America.": Am. Jour. ci., 2d er ., vol. 27, pp. 134-137, 1 59. ALDRICH, H. R. Magnetic surveying on the copper-bearing rocks of Wisconsin: Econ. Geology, vol. 18, pp. 562-574, 1923. ALLEN, ROLLAND CRATEN. Progress of the geological urvey of Michigan; g ology and topography: Michigan Aca.d. ci. Rept. 13, pp. 69- 78, 1911. (and Ruthven, A. G.) Progre s of the geological and biological survey of Michigan: Michigan cad. Rept. 14, pp. 33- 36, 1912. 'Rub bard, L. L., Michigan Oeol. Survey, vol. 6, 1 98. 1 Laue, A. C., Tbo Keweenaw series of Miobigau: Michigan Gaol. and Bioi. Survey Pub. 6, 2 vols., 1911. 1 Van Rise, C . .R., and Leith, C. K., Tbe geology of the Luke Superior region: U. 8. Oeol. Survey Mou. 52, 1911. ALLE , RoLLA D CRATE -Continued . (and others) li neral resource of Michigan, with tati - tical tables of production and value of mineral products for 1910 and prior years: Michigan Geol. urvey Pub. 8 (Geol. ser. 6), 465 pp., 1912. Biennial report of the director: Michigan Geol. Survey Pub. 17 (Geol. ser. 14), 104 pp., map, 1914. (and Barrett, L. P.) A revision of the equence and structure of the pre-Keweenawan formations of the eastern Gogebic iron range of Michigan: Michigan Geol. Survey Pub. 18 (Geol. ser. 15), pp. 33- 61, map, 1915; [in part], Jour. Geology, vol. 23, pp. 6 9-703, map, 1915. (and Barrett, L. P.) Contribution to the pre-Cambrian geology of northern Michigan and Wisconsin: Michigan Geol. Survey Pub. 1 (Geol. ser. 15) , pp. 13- 164, map, (and Smith, R. A., and Barrett, L. P .) Geological map of Michigan, scale 1 : 750,000 : Michigan Geol. Survey Pub. 23, 1916. Mineral resources of Michigan, with stati tical tables of production and value of mineral products for 1912 and prior years: Michigan Geol. Sun·ey Pub. 13 (Geol. ser. 10), 255 pp., 1913. Idem for 1913, Pub. 16 (Geol. r. 13) , 150 pp., 1914; for 1914, Pub. 19 (Geol. ser. 16), 359 pp., 1915; for 1915, Pub. 21 (Geol. ser. 17), 402 pp., map, 1916; for 1916, Pub. 24 (Geol. ser. 20), 291 pp., 1917; for 1917, Pub. 27 (Geol. ser. 22), 225 pp., map, 191 ; for 191 , Pub. 29 (0 ol. ser. 24), 214 pp., 4 figs. , 1920. A 0 YMOUS. The silver of the Lake 'uperior minerctl region : Min . Mng., vol. 1, pp. 447- 454, 1 53. BARNEs, GEORGE OnviLLE. Field notes ... on t e Out.ouagou district [Lake uperior region]: 31st Cong., 1st ses ., . Ex. Doc. 1, pt. 3, and H . Ex. Doc. 5, pt. 3, pp. 627- 636, 1849. BARRETT, L. P . (See Allen, R . C., and Smith, R. A.) I BAUERMANN, HILARY. Remarks on the copper mines of the State of Michigan : Geol. Soc. London Quart. Jour., vol. 22, pp. 44 463, 1866; a.b tract, Geol. Mag., vol. 3, pp. 22 226, 1 66. BAYFIELD, H. w. Outlines of the geology of L.a.ke uperior: Quebec Lit. and Hist. oc. Trans., vol. 1, pp. 1- 43, 1829. BAYLEY, WILLIAM HIRLEY. Basic massive rocks: Jour. Geology, vol. 1, pp. 433-456, 587- 596, 1893. The Sturgeon River tongue [Michigan]: U. . Geol. Survey Mon. 36, pp. 45 4 7, 1. 99; Nineteenth Ann. Rept., pt. 3, pp. 146-151, 1 99. BELL, RoBERT. Geology of Lakes Superior and 1p1gon: Canada Geol. Survey Rept. Progress for 1866-1869, pp. 313- 364, 1870. Report on the country north of Lake Superior, between the Nipigon and Michipicoten Rivers: Canada Geol. Survey Rept. Progress for 187Q-1871, pp. 322-351, 1872. Report on the country between Lake Superior and Lake Winnipeg: Canada. Geol. l!iurvey Rept. Progress for 1872-1873, pp. 7- 111, 1 73. The mineral region of Lake Superior: Canadian aturalist and Geologist, 2d er., vol. 7, pp. 49-51, 1875. Report on an exploration in 1 75, between James Bay and Lakes Superior and Huron: Canada. Geol. urvey Rept. Progress for 1 7 5-1 76, pp. 294-342, 1 77. Report on geological researches north of Lake Huron and east of Lake Superior: an ada Geol. urvey Rept. Progre s for 1 (6-1 77, pp. 193- 220, 1 7 .
THE COPPER DEPO IT OF MICHIGAN BENEDICT, . H. & (and Kenny, H. C.) Ammonia leaching of Calumet Hecla tailings: Am. Inst. Min. Eng. Trans., vol. 70, PP· 595- 610, 1924. Calumet & Hecla reclamation plant: Lake Superior Min. Inst. Bull., 1925. BERKEY, CHARLES PETER. The occurrence of datolite on the north shore of Lake Superior [abstract]: iinne ota Acad. at. Sci. Bull., vol. 4, pp. 42-43, 1896. The occurrence of copper minerals in hematite ore, Montana mine, oudan, Minn.: Lake uperior Min. In t. Proo., vol. 4, pp. 73- 79, 1 96; Minnesota Univ. Eng. Year Book, vol. 5, pp. llQ-117, 1 97. n the occurrence of native copper and other copper minerals in the hematite ore of the Montana mine, Soudan, Minn. [abstract]: Science, new ser., vol. 6, pp. 363-364, 1897. BIGSBY, JoHN JEREMIAH. Notes on the geography and geology of Lake uperior: Quart. Jour. ci., vol. 1 , pp. 1- 34, 228- 269, 1824--25; abstract, Bull. sci. nat., Pari , vol. 7, pp. 8- 13, 1 26. On the physical geography, geology, and commercial resource of Lake uperior: Edinburgh I ew Philo . Jour., vol. 53, pp. 55- 62, 1 52. BLAlCE, WILLIAM P. Review of a portion of the geological map of the nited States and British provinces, by Jules Marcou: Am. Jour. ci., 2d ser., vol. 22, pp. 3 3- 3 8, 1 56. BLANDY, JOHN F. Topography with especial reference to the Lake Superior copper district: Am. Inst. Min. Eng. Trans., vol. 1, pp. 75-82, 1873. The origin of the native copper in the Michigan deposits: Eng. and Min. Jour., vol. 70, pp. 278-279, 1900. ( ee al o Williams, C. P.) BooTH, JoH (and Hulburt, E. J.) Geologic~~tl and topographical map of the mineral district of Lake Superior, Mich., ew York, 1855. BomE, JULES. Notice sur le lac uperieur et ses mines de cuivre de Ia rive americai·ne: Soc. ind. min. Bull., vol. 6, pp. 233-284, 1860; vol. 7, pp. 185- 251, 1861; vol. 8, pp. 27Q-271, 1862; Allgem. Berg- u. hi.ittenm. Zeitung, vol. 4, pp. 44 - 450, 457-460, 469- 471, 1862. BRAD! H, ALVA. Memoir of Douglass Houghton, first State geologist of Michigan; with an appendix containing reports or abstracts of the first geological survey, and a chronological tatement of the progress of geological exploration in Michigan, 302 pp., Detroit, 1889. BRAUNS, R. Native copper in basalt: Zeitschr. Kryst. Min., 1911, p. 493; Centralbl. Mineralogie, 1908, pp. 705- 709. BRI sMADE, RoBERT BnucE. The Michigan copper mines and methods: Min. World, vol. 32, pp. 549-552, 1910. BRISTOL, T. W. (See Houghton, Jacob, jr.) BRODERICK, THOMAS Mo TETTH. The relation of the titaniferous magnetites of northeastern Minnesota to the Duluth gabbro: Econ. Geology, vol. 12, pp. 663-696, 1917. BROOKS, THOMAS BENTON. On the youngest Huronian rocks south of Lake Superior, and the age of the copper-bearing series: Am. Jour. Sci., 3d er., vol. 11, pp. 206- 211, 1876. Classified li t of the rooks observed in the Huronian series outh of Lake Superior: Am. Jour. Sci., 3d ser., vol. 12, pp. 194--204, 1876. BROOKS, THOMAS BE TO - ontinu d. (and Pumpelly, R.) On the age of the copper-bearing rock of Lake Superior: m. Jour. ci., 3d ser., vol. 3, pp. 42 - 432, 1 72. (and Julien, A. A.) Lithology [of the pper Peninsula): Michigan Geol. urvey, vol. 2, pp. 199-212, 1873. BROUGHTON, AMUEL H. Remarks on the mining interest and deta1ls of the geology of Ontonagon unty [Mich.], 24 pp., map, Philadel· phia, 1 63. BunT, WILLIAM Topography and geology of the survey of a district of town. hip lin , outh of Lake uperior, 1 45 : 29th Cong., It se s., . Ex. Doc. 357, pp. 2- 19, 1 46. Geological report of survey [in Lake Superior region]: 31 t Cong., 1 t e s., . Ex. Doc. 1, pt. 3, and H. Ex. Doc. 5, pt. 3, pp. 11- 32, 4275, 933- 935, maps, 1849. CALLE DER, JoH The Lake uperior copper mine : Min. Mag., vol. 2, pp. 249- 253, 1 54. CAMPBELL, J. B. [Lake uperior region]: 2 th ong., pee. e ., S. Ex. Doc. 1751 pp. 4-- CASE, ERMI E CowLES. (and Robin on, W. I.) The geology of Limestone Mountain and herman Hill, in Houghton Count , Mich.: Michigan Geol. urvey Pub. 1 (Geol. er. 15), pp. 16&- 1 1, 1915: Jour. Geology, vol. 23, pp. 256-260, 1915. CHAMBERLIN, THOMAS HROWDillR. The copper-bearing serie of Lake uperior: Science, vol. 1, pp. 453-455, 1 3. (and trong, Mo es) Geology of the upper St. Croix dis· trict: Geology of Wi consin, vol. 3, pp. 363- 42 , 1880. (See also Irving, Roland Duer.) CLARKE, RoBERT E. ote from the copper region [Lake uperior): Harpers Mag., vol. 6, pp. 433-44 , 577-5 , 1 53. CLEMENTS, JULIUS MORGAN. A contribution to the study of contact metamorphi m: Am. Jour. ci., 4th ser., vol. 7, pp. 1- 91, 1 99. CoRDIER, Louis. ote sur une masse de cuivre natif provenant de rives du lac Sup6rieur aux ~tats-Unis d' Amerique: Compt. Rend., vol. 28, pp. 161-162, 1849. ConEY, G. W. The Nonesuch sand tone [Porcupine district, Mich.): Eng. and Min. Jour., vol. 2, p. 778, 1906. CREDNER, HERMANN. Die Giiederung der eozoischen ( vorsilurischen) Formations· gruppe ord Ameri.kas: Zeitscbr. ges. aturwiss., Band 32, pp. 353-405,' 1 6 . Die vorsilurischen Gebilde der " Ohern Halbinsel von Michigan" in ord Amerika: Deutsch. geol. Ge ell. Zeitschr., Band 21, pp. 516- 554, 1869. Beschreibung einiger charakteristischer Vorkommen des gediegenen Kupfers auf Keweenaw Point am Oberen See ord-Amerika's: eues Jahrb., 1869, pp. 1-14. Gewaltige Kupfermassen am Lake Superior: Neues Jahrb., 1870, p. 86. Ueber Nordamerikanische chieferporphyroide: Jahrb. Mineralogie, 1870, pp. 970- 984. Elemente der Geologie, 4th ed., 726 pp., 1 7 . CRooKs, H. F. (See Savage, T. E.) DAWSON, JOHN w. On the geological structure and mineral deposits of the promontory of Mamainse, Lake Superior: Canadian Naturalist, vol. 2, pp. 1- 12, 1857. DERoux, H. Die Kupfergruben des Oberen See's Lake Superior: Berg- u. hiittenm. Zeitung, vol. 20, pp. 305-307, 329-381, 1861.
BIBLIOGRAPHY DESOR, EDO UARD. [On the clay and drift deposits in the vicinity of Lake Superior]: Boston Soc. Nat. Hist. Proc., vol. 3, pp. 235236, 1850. [On the sand dunes of Lake Superior]: Boston Soc. at. Hist. Proc., vol. 3, p. 207, 1 50; vol. 4, pp. 41- 42, 1851. [On he origin of some of the elements of the so-called Tertiary or drift of Lake uperior] : Bo ton Soc. at. Hi t. Proc., vol. 4, pp. 28- 29, 1 51. On the ilurian rocks of the La e Superior land di trict: Am. As oc. Adv. ci. Proc. 5th meeting, pp. 64, 65. 1 51. On the superficial depo its of this district, in Foster, J. W., and Whitney, J . D ., Report on the geology of the Lake uperior land di trict, pt. 2: 32d Cong., spec. ess., S. Ex. Doc. 41, pp. 232-270, 1851; in part, Am. Jour. ci., 2d ser., vol. 13, pp. 93- 109, 1 52. DrcKENSON, GEORGE J. [Report on Isle Royale]: 31st Cong., 1st sess., S. Ex. Doc. 1, pt . 3, and H. Ex. Doc. 5, pt. 3, pp. 503- 506, 1 49. DrEFFE BACH, OTTo. Bemerkungen i.iber den Kupferbergbau in den Vereinigten taaten von ordamerika: Berg- u. hi.ittenm. Zeitung, Band 17, pp. 47- 4 , 66-6 , 75-76, 1 5 . DouGLASS, JAMES. The native copper mines of Lake uperior: Quart. Jour. Sci., vol. 11, pp. 162-180, 1874; Canadian aturali t, new ser., vol. 7, pp. 318-336, 1 74. The copper resource of the United tates: ci. Am. uppl. vol. 34, pp. 141 3-141 6, 1 93. DUPAJW, LOUIS. ote sur la region cuprif~re de 1 'extremite nord-est de la peninsule de Keweenaw (Lac Superieur) : Arch. phys. nat., 4th er., vol. 10, pp. 51 - 538, 1900. DUPEE, J. A. [On copper deposits of Keweenaw Point, Lake Superior] : Bo ton Soc. Nat. Hist. Proc., vol. 5, pp. 279-2 0, 1 56. DUTTON, T . R. Observations on the basaltic formation on the northern shore of Lake uperior: Am. Jour. ci., 2d er., vol. 4, pp. 11 - 119, 1 47. EAMES, HENRY H. Geological reconnai ance of the northern, middle, and other counties of Minne ota, 5 pp., t. Paul, 1866. Report of the tate geologist on the metalliferous region bordering on Lake uperior, 21 pp.; 2d ed., 23 pp., t. Paul, 1 66. EGLESTO , THOMAS. Copper mining on Lake uperior: Am. Inst. Min. Eng. Trans., vol. 6, pp. 275-312, 1 79. [The conglomerates of the Lake uperior copper region]: Am. Inst. Min. Eng. Tran ., vol. 6, pp. 606-611, 1 79. EIGHTS, JAMES. Outlines of the geological structure of Lake uperior mineral region: New York and Lake Superior Mining Co. First Ann. Rept., appendLx, 21 pp., Albany, 1846. Er,FTMA , AnTaun Huoo. The geology of the Keweenawan area in northeastern Minnesota: Am. Geologist, vol. 21, pp. 9Q-109, map, 175-188; vol. 22, pp. 131- 149, map, 1 9 . t:LrE DE BEAUMONT, LtoNcE. [On the age of the Lake uperior sandstone]: Soc. geol. France BulY., 2d ser., vol. 7, p. 209, 1850. EMMONS, EBE EZER. (Copper mines of Lake Superior), American geology, vol. 1 , 1,pp. 171-173, 185~ FrNLAY, J. R. Appraisal of mining properties of Michigan by the tate Board of Tax Commissioners, 1911. FOSHAO, WILLIAM F. (and Lar en, E. .) Eakleite from Isle Royale, Mich.: Am. Mineralogist, 7th ser., vol. 2, pp. 23- 24, 1922. FosTER, J oaN WELLs. [Report of field work in the Lake uperior land di trict] : 30th Coug., 2d sess., . E x. Doc. 2, pp. 159-163, 1 49. (and Whitney, J. D.) ynopsi of the explorations . in the Lake Superior land di trict in the northern penin- . sula of Michigan; 31 t Cong., 1st se s., . Ex. Doc. 1, pt. 3, and H . Ex. Doc. 5, pt. 3, pp. 605-626, maps, 1 49. [Field notes of work in Lake uperior region]: Idem, pp. (and Hill, . W.) Statistic of the mine of Keweenaw Point: Idem, pp. 759-765. (and Whitney, J. D .) Mineral report [Lake uperior land district]: 31st Cong., 2d sess., H . Ex. Doc. 9 (Gen. Land Office Rept., 1 50), pp. 147- 152, 1 50. (and Whitney, J. D.) Report on the geology and topography of a portion of the Lake Superior land district in the tate of Michigan, pt. 1, Copper lands: 31 t Cong., 1st sess., H . Ex. Doc. 69, 224 pp., map , 1850. (and Whitney, J. D .) On the age of the sandstone of Lake Superior, with a description of the phenomena of the a sociation of igneou rock : Am. Assoc. Adv. ci. Proc., vol. 5, pp. 22- 3 , 1 51. (and Whitney, J . D .) ur le terrain iluriens du district metallif~re dulac uperieur: oc. Geol. France Bull., 2d er. , vol. , pp. 9-100, 1 51. Catalog of rocks, minerals, etc., collected by J. ' · . Foster: mithsonian Rept., 1 54, pp. 3 4-3 7. (and Whitney, J. D.) On the origin and stratigraphical relations of the trappea.n rocks of Lake Superior (abstract) : Ann. ci. Discovery for 1 61, p. 285, 1861. GAY & STURGIS (publi hers). Copper, a weekly review of the Lake Superior mines (A. L. Carnahan, editor), vols. 1, 2, and 3, Apr. 4, 1908, to ov. 19, 1910. GORDON, w. c. The Black River section near Bessemer [Mich.]: Michigan Acad. Sci. Rept. 7, pp. 1 - 195, i905. (assisted by Lane, A geological section from Bessemer down Black River: Michigan Geol. urvey Rept. for 1906, pp. 397- 507, map, 1907. GRANT, u.S. ote on the Keweenawan rocks of Grand Portage Island, north coast of Lake Superior: Am. Geologist, vol. 13, pp. 437-439, 1 94; abstract, Minnesota Univ. Quart. Bull., vol. 2, p. 92, 1 94. Preliminary report on the copper-bearing rocks of Douglas County, Wis.: Wisconsin Geol. Survey Bull. 6 (Econ. ser. 33) , 525 pp. maps, Madison, Wis., 1900. Junction of Lake Superior sandstone and Keweenawan traps in Wisconsin (abstract) : Geol. Soc. America Bull., vol. 13, pp. 6-9, 1901. GRAY, A. B. Mineral lands of Lake Superior region: 28th Cong., spec. sess., S. Ex. Doc. 175, pp. 14-22, 1845. Report on mineral lands on Lake Superior: 29th Cong., 1st se s., H. Doc. 211, 23 pp., map, 1846. GROUT, FRANK FITCH. Keweenawan copper deposits: Econ. Geology, vol. 5, pp. 471-476, 1910. (and Soper, E. K.) Geology of Minnesota: U. S. Geol. Survey Bu 1. 67 , pp. 7Q-105, 2 pls. (incl. map) , 3 figs., Contribution to the petrography of the Keweenawan: Jour. Geology, vol. 18, pp. 633- 657, map, 1910. The pegmatites of the Duluth gabbro: Econ. Geology, vol. 13, pp. 1 5-197, 191 .
THE COPPER DEPOSITS OF MICHIGA GnouT, FRANK FI'l'Ca-Continued. The lopolith, an igneou form exemplified by the Duluth gabbro: Am. Jour. ci ., 4th ser., vol. 46, pp. 516- 522, Internal tructure of igneous rocks; their significance and origin; with pecial reference to the Duluth gabb;o: Jour. Geology, vol. 26, pp. 439-45 , 1918; abstract, w1th discu sions by W. J. Miller and M. E. WiL·on : G ol. Soc. America Bull., vol. 29, pp. 100- 101, 191 G cK, HoM~m. Geology of the Michigan copper districL: Eng. and Min. Jour., vol. 10 , pp. 948- 949, 1919. HAl,L, CHRISTOPHER Vi7EBBER. Field report: Minnesota Geol. urvey 'eventh Ann. Rept., pp. 26-29, 187 . Report of Profe or . W. Hall, Minnesota Geol. urvey Eighth Ann. Rept., pp. 126-13 , 1879. A brief history of copper mining in iinoesota: Minnesota Acad. Nat. ci. Bull., vol. 3, pp. 105- 111, 1 9; ab tract, Minnesota niv. Quart. Bull., vol. 1, p. 91, 1893. Keweenawan area of eastern Mione ota: Ceo!. o . America Bull., vol. 12, pp. 313- 342, map, 1901. HALT., J AM]!; On the il urian sy -tem of the Lake Superior region: Am. Jour. ci., 2d er., OI. 17, pp. 1 1- 194, 1 54 . HAYES, A GUS'l' ALT,EN. On the occurrence of ma i \·e datolite in the mines of Lake Superior: l3o ·ton oc. Nat. Hi ·t. Proc., vol. , pp. 62-64, J-fgNwooD, WILLIAM JOitY. On the native copper of Lake uperior: Royal Geol. Soc. Cornwall Trans., vol. 8, pp. 3 5- 4 9, 1 71. HrLL, SaMUEL W. (See Foster, John Well .) HoDGE, JAMES THACHER. On the mineral region of Lake Superior: Am. A oc. Adv. Sci. Proc., vol. 2, pp. 301-308, 1850. HoPPER, WALTER E. Michigan copper indu try in 1915: Michigan Geol. Survey Pub. 21, (Geol. ser. 17), i)p. 11- 56, 1916. l! o Ju;, REGrNAr,o Eowr . In the Michigan copper count.ry: Canadian Min . .Jour., \'Ol. 30, pp. 421- 422, 1909. The copper-mining industry of Michigan: Min. World, vol. 36, pp. 601- 603, 656- 658, 707- 710, 763- 767, 1912. The copper indu tr · of Michigan: Michigan Geol. Survey Pub. 8 (Geol. ser. 6), pp. 15-115, 1912. The Michigan copper industry in 1913: Michigan Geol urvey Pub. 16 (Geol. ser. 13), pp. 11- 37, 1914. Michigan copper deposits: Michigan Geol. Sur;ey Pub. 19, pp. 19- 161, 1915. HoTCHKiss, WILLIAM OTis. Mining and mineral resources of Wisconsin: Am. Min. Cong. 9th An!f. Sess. Rept. Proc., pp. 220- 225, 1907. Report of the Director of the Survey: Wisconsin Geol. and Nat. Hist. Survey Twelfth Bienn. Rept., 37 pp., 2 figs., The Lake Superior geosyncline: Geol. Soc. America Bull., vol. 34, pp. 669-678, 1923. (1:5ee also Thwaites, F. T.) HouoaToN, DouGLAss. Report of the State geologist: Michigan H. Doc. 14, . Doc. 16, 37 pp., 1 3 . 'econd annual report of the State geologist of the State of Michigan, 39, 123 pp., Detroit, 1839. · Third annual report of the State geologist of the State of Michigan: Michigan H. Doc. , 124 pp., map, 184.0. Fifth annual report of the State geologist: Michigan H. Doc. 2, se s. 1 42, pp. 436-441, 1 42. HouGHTON, Douor,A s-· -Conti.oued. Metallif rous vein of the northern penin ula of Michigan: Am. Jou r. ci., vol. 41, pp. 1 3- 1 6, 1 41; Assoc. Am. Geologi ts RepL., 1 43, pp. 35- 3 . ixth annunl report of the tate geologist: Michigan Legisl. Doc. , . es . 1 43, pp. 39 402, 1 43. eventh nnnual report of th tate g ologi. t: Michigan Legis!. t 44, Joint Doc. 11, 3 pp., l 44. Copper on Lak uperior: Am. J ur. ci., vol. 47, pp. 107, 132, 1 44. Fourth annual report of the 'tate geologist: Michigan .H. Doc. 27, l 4 pp., 1 41. In part, with title General geology f the · pper Peninsula: 29th Cong., 2d sess., H. Rept. 591, pp. 6- 3 , map, 1 46. Report on the copp r of Lake Superior, in choolcraft, H. R., arrative of an expedition through the upper [i i. . ippi to Ita ca Lake, pp. 2 7- 292 ew York, 1 34; also in choolcraft, H. 1 R., Summary narrative, pp. 526-531, Philad Iphia, 1 55. Lithology [of the pper Peninsula]: Michigan Geol. , ur· vey, vol. 2, pp. 239- 246, 1 73. HouGHTO , JACOB, jr. (and Bristol, T. W.) Reports of Wm. A. Burt and Bela Hubbard on the geography, top graphy, and geology . .. of the south shore of Lake uperior, 109 pp., map, De· troit, 1846. The ancient copp r min s of Lake Superior: Wisconsin Hist. Soc. Coli., vol. , pp. 140- 151, 1 79. llOVEY, EDMUND 0'l'I . An analcite copper boulder from the I eweenaw Range, Michigan: cieuce, vol. 22, p. 96, 1 93. HuBBARD, BELA. General observations upou the geology and topography of the district south of Lake uperior: 29th Cong., 1st sess., . Ex. Doc. 357, pp. 20-29, 1 46. Geological report [of field work in Lake uperior land district]: 3lst Cong., 1st ., , '. Ex. Doc. 1, pt. 3, and H. Ex. Doc. 5, pt. 3, pp. 3 42, 2-932, 1 49. H u.s sA no, Luc1u LEE. Macroscopic minerals of Michigan: Michigan G I. urvey Rept. for 1 91- 92, pp. 17 176, 1 93. Two new geological cross sections of Keweenaw Point: Lake Superior Min. Inst. Proc., vol. 2, pp. 79- 96, l 94. The relation of the vein at the Central mine, Keweenaw Point, to the Kearsarge conglomerate: Lake uperior Min. lost. Proc., vol. 3, pp. 74-83, 1895. Keweenaw Point with particular reference to the felsit.es and their associated rocks: Michigan Geol. urvey, vol. 6, pt. 2, 155 pp., maps, 189 . Sixth annual report of the State geologist, 9 pp., Lansing, Work of the Geological Survey in the ppor Peninsula: Michigan Miner, vol. 3, No. 3, p. 9, 1901. Geological notes on the Lake Superior copper formation: Lake Superior Min. Inst. Proc., vol. 17, pp. 9-11, 1912. In the Lake Superior area what influence, if any, did the thickness and contour of footwall beds have upon the subsequent deposition and distribution of copper in overlying beds? [with discussion] : Lake Superior Min. Inst. Proc., vol. 17, pp. 227-237, 1912. (See also Koenig, G. A.) HuLBERT, E. J. (See Booth, John C.) HUNT, T. STERRY. On some points in American geology: Am. Jour. Sci., 2d ser., vol. 31, pp. 392-414, 1861. The geognostical history of the metals: Am. Inst. Min. Eng. Trans.,.v'ol. 1, pp. 313-334, 1873. The origin of metalliferous deposits: Idem, pp. 413-426.
BIBLIOGRAPHY HuNT, T. TERRY-Continued. The geology of the north shore of Lake Superior (supplementary note): ~m. Inst. Min. Eng. Trans., vol. 2, pp. 58-59, 1873. Azoic rocks, part 1: econd Pennsylvania Geol. Survey Rept. E, 253 pp., 1 7 . The history of some pre- ambrian rocks in America and Europe: Am. Jour. Sci., 3rl ser., vol. 19, pp. 268-2 3, JRVINO, RoLA ND DuEn. On the age of the copper-bearing rocks of Lake uperi or and on the westward continuation of the Lake Superior synclinal: Am. Jour. Sci., 3d ser., vol. 8, pp. 4 56, map, 1874. On some points in the geology of northern Wisconsin: Wisconsin Acad. Sci. Trans., vol. 2, pp. 107- 119, 1874. Note on the age of the crystalline rocks of Wisconsin: Am. Jour. Sci., 3d ser., vol. 13, pp. 307-309, 1 77. ote on the stratigraphy of the Huronian series of northern Wisconsin and on the equivalency of the Huronian of the Marquette and Penokee districts: Am. Jour. ci., 3d ser., vol. 17, pp. 393- 39 , 1 79. Geological structure of northern Wisconsin, with maps: Wisconsin Geol. urvey, vol. 3, pt. 1, pp. 1- 25, 1 Geology of the ea tern Lake uperior district, v.ith atlas: Wisconsin Geol. urvey, vol. 3, pt. 3, pp. 51-23 , The copper-bearing rocks of Lake uperior: . S. Geol. urvey Mon. 5, xvi, 464 pp., maps, 1 3; Third Ann. Rept., pp. 9-1 , map, 1 3. The copper-bearing rocks of Lake uperior : cience, vol. 1, pp. 14G-141, 359-360, 422, 18 3. The copper-bearing rocks of Lake Superior: Am. Jour. ci., 3d ser., vol. 29, pp. 258-259, 1885. (and Chamberlin, T. C.) Observations on the junction between the Eastern sandstone and the Keweenaw aerie on Keweenaw Point, Lake uperior: . Geol. urv y Bull. 23, 124 pp., 1 5; review, Am. Geologi t, vol. 1, pp. 4 57, 1 n the classification of the early ambrian and pre- ambrian formations : U. Ge l. urvey eventh no. R pt., pp. 365-454, 1 JA 'KSO ' CRARLJ; THOMAS. [On min ralsfrom I eweenaw Point, Lake up rior] : Bo.-ton oc. at. Hi t. Proc., vol. 1, p. 203, 1 45. [On copp r ore of the Lake uperior region]: Bo ton oo. at. Hist. Proc., vol. 2, pp. 57- 5 , 1 45. On the copper and ilver of Kew enaw Point, Lake uperior [with discussion by C. . h pard): Am. Jour. ci., vol. 49, pp. 1- 93, 1 45; s oc. Am. Geologi ts Proc., vol. 6, pp. 53- 61, 1 45. ur le gisement de cuivre et d'argent natif de bords du lac up~rieur: Compt. Rend., vol. 20, pp. 593-595, 1 45; Soc. g~ol. France Bull., 2d ser., vol. 2, pp. 317-319, 1 45; abstract, Neues Jahrb., 1845, pp. 479-4 0. [On the copper and silver ores of the Lake Superior region] : Boston Soc. Nat. Hist. Proc., vol. 2, pp. llG-114, 1846. Chemical analyses of the [copper] ores [of the Lake Superior region]: 29th Cong., 1st se s., H. Rept. 591, ru>· 38- 44, Ores and minerals from Lake Superior: Boston oc. at. Hist. 1'roc., vol. 2, pp. 256, 259, 260, 1 47. Mineral lands of Lake Sup rior: 30th Cong., 2d seas., ' . Ex. Doc. 2, o. 2, pp. 153- 163, 1847. [Report on the survey of the mineral lands in Michigan]: Idem, pp. 175-230. Report on the progress of the geological survey of the mineral lands of the United States in Michigan: Idem, pp. 185-191. JAcKso , CHARLES THOMAs-Continued. [ otes on the Lake uperior region]: Bo ton oc. Nat. Hist. Proc., vol. 3, pp. 76-77, 22 , 1 4 . Report on the geological and mineralogical survey of the mineral lands of the nited tates in the tate of Michigan : 31st Cong., 1 t se s., . Ex. Doc. 1, pt. 3, nd H. Ex. D oc. 5, pt. 3, pp. 371- 502, map , 1 49. opper of the Lake uperior region: Am. Jour. ci., 2cl er., vol. 7, pp. 2 6- 2 7, 1 49. On the g ological tructure of Keweenaw Point: Am. A oc. dv. ci. Proc., vol. 2, pp. 2 301, l 50; Am. Jour. ci., 2d er., vol. 10, pp. 65-77, 1 49; Annales des mines, 4th ser., vol. 17, pp. 103- 115, 1 50. Remark on the geology, mineralogy, and mine of Lake uperior: Am. A soc. Adv. ci. Proc., vol. 2, pp. 2 3- 2 7, 1 50; oc. g~ol. France Bull., 2d ser., vol. 7, 1 p. 667- 673, Analy es of pitchstone porphyry from Isle Royale and of a. crystal of pho phate of lime from Hurdstown, N. J.: Bo ton oc. at. Hist. Proc., vol. 4, pp. 3 41, 1 51; Am. Jour. ci., 2d ser., vol. 11, pp. 401-403, 1 51. On the age of the and tone. of the United tates: Boston oc. Nat. Hi t. Proc., vol. 3, pp. 335- 339, 1 50. Rain-drop and air-bubble impres ion : Bo ton oc. 1 at. Hi t. Proc., vol. 4, pp. 131- 132, 1 53. Igneous origin of calcite veins : Idem, pp. 30 309. Geology, tuineralogy, and topography of the lands around Lake uperior: 32d ong., 1st se s., . Ex. Doc. 112, pp. 232--244, 1 53. eber den Metall-ftihrenden Di -trikt am Oberen ee im taa.te Michigan: Archiv Mineralogie, vol. 25, pp. 656-667, 1 53. b ervations sur quelque mine de l!:tat - ni et sur le gres rouge du lac uperieur: Compt. Rend., vol. 39, pp. 03- 07, 1 54. Catalog of rock , minerals, and ores collected dming the years 1 47 and 1 4 on the geological survey of the United tates mineral land in Michigan: Smith onian In t. Ann. Rept., vol. 9, pp. 33 367, 1 55. [Trap dike:]: Bo ton oc. at. Hist. Proc., vol. 6, pp. 23- 24 1 56. [On the A hbed and the origin of the copper): Bo ton oc. at. Hi t. Proc., vol. 5, pp. 2 0- 281, 1 56; vol. 7, p. 31, ge of the Lake uperior andstone: Bo ton oc. at. Hi t. l'roc., vol. 7, pp. 396-39 , 1 60. On domeykite from the vicinity of Portage Lake, Lake uperior: Boston oc. at. Hist. Proc., vol. 8, p. 25 , Surles mines de cuivre du lac Sup~rieur et ur un nouveau gi ement d ' ~tain dans l'Etat du Maine: Compt. Rend., vol. 69, pp. 10 2--10 3 1869. JACKSO ' J. F . Copper mining in pper Michigan, a de cription of the region, mines, and some of the methods and machinery used : Mines and Minerals, vol. 23, pp. 535-540, 1903. J oY, CHARLES A. Examination of a few American minerals: New York Lye. Nat. Hist. Annals, vol. 8, pp. 12G-125, 1865. JULIEN, ALEXIS A ASTAY. Litho ogy: Michigan Geol. Survey, Upper Peninsula, vol. 2, pp. 1- 197, 1873. Microscopical examination of eleven rocks from Ashland ounty, Wi .: Wi cousin Geol. Survey, vol. 3, pp. 224-238, 1 0. rote on a. feldspar from the Calumet copper mine, Keweenaw Point, Mich. [abstract): cience, new ser., vol. 9, p. 719, 1 99; ew York Acad. ci. Annals, vol. 12, pp. 650-654, 1900. (See also Brooks, Thomas Benton.)
THE COPPER DEPOSITS OF MICHIGAN KELLER, H. F. (and Lane, A. C.) Chloritoid von Champion, Mich., . S. A.: Zeitschr. Kryst. Min., vol. 19, pp. 3 3- 3 5, (See also Lane, A. C.) KLoos, J . H. ( ee treng, A.) KENNY, H. (See Benedict, C. H.) I<ocrr, FnrEDRICH KARL LuDwro. Die Mineralgegenden der Vereinigten Staaten ordAmerikas am Lake Superior, 72 pp., Gottingen, 1 51. Kupfer- und Eisenerze am Lake Superior: Deutsch. geol. Ge ell. Zeitschr., vol. 3, pp. 355--358, 1851. Die Mineral-Regionen der obern Halbinsel Michigan's ( . A.) am Lake Superior und die Isle Royale, 24 pp., map, Gottingen, 1 52; Gottingischer Ver. bergmii.nnischer Freunde (J. F. L. Hausmann) tudien, vol. 6, pp. 1- 248, map, 1 54; abstract, Min. Mag., vol. 1, pp. 261- 268, 1853. ' KOENIG, GEORGE AuGo Tos. (and Hubbard, L. L.) On powellite from a new locality [Houghton County, Mich.]: Am. Jour. ci., 3d ser., vol. 46, pp. 356-35 , 1 93; Zeitschr. Kry t. Min., vol. 22, pp. 463- 466, 1 94. eber Mohawkit, t ibiodomeykit, Domeykit, Algodonit und inige kiin t liche I<upferar enide: Zeitschr. Kry t. Min., vol. 34, pp. 67- 77, 1901; m. Jour. ci., 4th ser., vol. 10, pp. 439- 44 , 1900 (tran lation?) . · On the new specie · melat ochalcite and keweenawite, with notes on some other known species: Am. Jour. ci., 4th ser., vol. 14, pp. 404--416, 1902. On artificial production of crystallized domeykite, algodonite, argentodomeykite, and stibiodomeykite : Am. Philos. Soc. Proc., vol. 42, pp. 219- 237, 1903. Knaus, EDWARD HENRY. Occurrence and distribution of celestite-bearing rocks: Am. Jour. Sci., 4th ser., vol. 19, pp. 286--293, 1905; abstract, Am. Geologist, vol. 35, p. 130, 1905; Geol. Soc. America Bull., vol. 16, p. 574, 1906; ci. Am. uppl., vol. 59, p. 24326, 1905. LA E, ALFRED CHURCH. (and Keller, H. F., a'nd Sharpless, F. F.) otes on Michigan minerals: Am. Jour. Sci., 3d ser., vol. 42, pp. 499--508, 1891. (and Keller, H. F.) Chloritoid von Champion, Mich., U. S. A.: Zeitschr. Kryst. Min., vol. 19, pp. 383- 385, Microscopic characters of rocks and minerals of Michigan: Michigan Geol. Survey Rept. for 1891- 92, pp. 176--183, The geology of Lower Michigan with reference to deep borings [edited from notes of C. E. Wright]: Michigan Geol. Survey, vol. 5, pt. 2, 100 pp., map, 1895. Geological report on Isle Royale, Mich.: Michigan Geol. Survey, vol. 6, pt. 1, 281 pp., map, 1898. Isle Royale; what has been accomplished in unearthing its mineral wealth: Michigan Miner, vol. 1, o. 11, pp. 1 21; No. 12, pp. 14--18, 1899. The geothermal gradient in Michigan: Am. Jour. Sci., 4th ser., vol. 9, pp. 434--438, 1900. The Geological Survey; annual report of the State geologist for the year ending Dec. 31, 1899: Michigan Miner, vol. 2, No. 3, pp. 9- 13, 1900. Suggestions from the State geologist: Michigan Miner, vol. 3, o. 10, p. 9, 1901. Suggested changes in nomenclature of Michigan formations: Michigan Miner, vol. 3, o. 10, p. 9, 1901. The economic geology of Michigan in its relations to the 1 busines world: Michigan Miner, vol. 4, No. 1, pp. 9-15, E ALFRED CHURCH- ontinued. Annual report of th tate geologi t [for 1900): Michigan Miner, vol. 3, o. 2, pp. 13- 21, 1901. Third annual r port of the tat geologi t ... for the year 1901 : Michigan Geol. urvey R. pt. for 1901, 304 pp., maps, 1902. Recent work of the G ological urvey: Michigan Acad. oi. Rept., vol. 3, pp. 3 39, 1902. Geothermal gradient: Michigan Geol. urvey Rept., for 1901, pp. 24 251, 1902. Economic g o~ogy [of Michigan]: iichigan Geol. Survey Rept. for 1901, pp. 121- 137, 1902. Variation of geothermal gradient in Michigan [abstract]: cience, new er., vol. 15, p. , 1902; Geol. oc. America Bull., vol. 13, pp. 52 - 529, 1903. nnual report Geological urvey of Michigan [for 1902]: Michigan Miner, vol. 5, o. 2, pp. 16- 26 (reprinted, 26 pp., map), 1903. The economic geology of 1ichigan [ab tract): cience, new ser., vol. 17, p. 21 , 1903; Eng. and Min. Jour., vol. 75, p. 152, 1903; ci. Am. uppl., vol. 55, p. 22666, 1903. Fifth annual report of the tate geologi t, for the year 1903: Michigan Geol. urvey Rept. for 1903, 342 pp., maps, 1905; ixth ... for 1904 : Idem for 1904; pp. 113- 16 , 1905; Seventh ... for 1905: Idem for 1905, pp. 535--571 , 1906; Eighth ... for 1906: Idem for 1906, pp. 573- 594, 1907; Tinth ... for 1907: Idem for 1907, pp. 3- 31, 190 ; Tenth .. . for 1908: Idem for 190 , pp. 1- 19, map, 1909. Magnetic phenomena around deep boring : Michigan A cad. ci. Rept., vol. 4, pp. 16 167, 1904. Hi torical review of the geology of Michigan: Michigan Acad. ci. Rept., vol. 5, pp. 184--195, 1904. The theory of copper depo ition: 1ichigan Miner, vol. 6, To. 2, pp. 9-11, o. 3, pp. 9-11, 1904; Am. Geologist, vol. 34, pp. 297- 309, 1904; Michigan Geol. urvey Rept. for 1903, pp. 239-249, 1905. Water of the Upper Penin ula of Michigan : Michigan Geol. urvey Rept. for 1903; pp. 111- 167, 1905. The Tamarack mine cro s section and the I eweenawan lodes: Michigan Geol. , urvey Rept. for 1903, pp. 251270, 1905. Comment on the " Report of the special committee on the Lake Superior region": Jour. Geology, vol. 13, pp. 457461, 1905. Underground waters of Michigan: ol. urvey Water-Supply Paper 114, pp. 242-247, map, 1905. Black River work: Michigan Geol. urvey R pt. for 1904, pp. 158-162, 1905. The geology of Keweenaw Point, a brief de cription: Lake Superior Min. lost. Proc., vol. 12, pp. 1- 104, 1907; abstract, Mines and Minerals, vol. 27, pp. 20. 206, 1906. The formation of Lake Superior copper: ci.ence, new er., vol. 25, p. 589, 1907. . Different manifestations of the ophitic texture [abstract]: Science, new ser., vol. 25, pp. 774--775, 1907. (and Seaman, A. E.) Notes on the geological section of Michigan; Part I, The pre-Ordovician : Jour. Geology, vol. 15, pp. 680-695, 1907. 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BIBLIOGRAPHY f,ANE, ALFRED CHuRCH-Continued. otes on the geological section of Michigan; Part II, From the t. Peters up: Michigan Geol. Survey Rept. for 1908, pp. 43-105, 1909. Geology of the Porcupine Mountains: Michigan Min· World, vol. 30, pp. 1115-1117, 1909. Mine waters and their field assay: Geol. oc. America Bull., vol. 19, pp. 501- 512, 1909. The decomposition of a boulder in the Calumet & Hecla conglomerate, and its bearing on the distribution of copper in the Lake Superior copper lodes as indicating the trend and characters of the waters forming the chute: Econ. Geology, vol. 4, pp. 15 - 173, 1909. Michigan iron mines and their mine waters: Min. World, vol. 31, pp. 413- 416, 1909. (and eaman, A. E.) otes on the geological section of Michigan for geologists, teachers, and drillers, Part I, The Ordovician: Michigan Geol. urvey Rept. for 190 , pp. 21- 42, 1909. The Keweenaw series of Michigan: Michigan Geol. urvey Pub. 6 (Geol. ser. 4), 2 vols., 9 3 pp., maps, 1911. 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Proc., ol. 23, pp. 20 - 212, 1 The outh Trap Range of the I ew enawan series: Am. Jour. ci., 3d ser., vol. 42, pp. 417- 419 1 91. Report of the tat geologist for 1 9: Michigan Geol. urvey Rept. for 1 91- 92, pp. 39- 44, 1 93; . .. for 1 99- 90: Idem, pp. 45-49; . .. for 1 90- 91: Idem, pp. 51-57; ... for 1 91- 92: Idem, pp. 59- 73. A sketch of the geology of th Marqu tt and Keweenawan di tricts, in Ralph, Julian, Along the south shore of Lake Superior, pp. 63- 2, copyrighted by C. B. HilJ. bard, of the Duluth, outh hor & Atlantic Ry. , 1 90; 2d ed., pp. 75-99, 1 91. The relations of the Eastern sandstone of Kew naw Point to the Lower ilurian limestone : cience, vol. 1 , p. 25, 1 91; Am. Jour. ci., 3d ser., vol. 42, pp. J7Q-171, ubdivisions of the Azoic or Archean in northem lichigan: cience, vol. 20) p. 355, 1 92; Am. Jour. i., 3d ser., vol. 45, pp. 72-73, 1 92. A sketch of the geology of the iron, gold, and copper districts of Michigan [abstract]: Geol. Mag., dec. 3, vol. 9, pp. 571-572, 1892. A sketch of the geology of the iron, gold, and copper districts of Michigan: Michigan Geol. urvey Rept. for 1891- 92; pp. 75- 174, 1893. The copper deposits of Michigan: Geol. Mag., dec. 4, vol. 3, pp. 2G-23, 1 96. The origin and mode of occurrence of the Lake Superior copper deposits: Am. Inst. Min. Eng. Trans., vol. 27, pp.669- 696, 189. 'VEED, WALTER HARVEY. The copper mines of the United States in 1905: U. · Geol. Survey BuiJ. 2 5, pp. 93- 124, 1906. The Copper Handbook, vol. 11, 1912-13. The Mines Handbook and Copper Handbook, vols. 12-15, 1916-1922. WHITNEY, JOSIAH DWIGHT. Report of work in the Upper Peninsula of Michigan: Gen. Land Office Rept. for 1847 (30th Cong., 1st sess., S. Ex. Doc. 2), pp. 221- 230, 1847. Description and analysis of three minerals from Lake Superior: Boston Jour. Nat. Hist., vol. 5, pp. 486-489,
B1BLIOGH.APHY \VEIITNEY, JosiAH DwiGHT- ontinued. [On jack onite, a n w mineral from the L!~k e Superior region]: Boston Soc. at. Hist. Proc., vol. 3, pp. 5- [On the compo ition of chloritoid or chlorite spar and masonite; and on oxide of copper from Copper Harbor, Lake uperior]: Boston Soc. rat. Hist. Proc., vol. 3, pp. 10D-103, 1 49. [Report of field work in the Lake Superior land district]: 30th Cong., 2d ess., . Ex. Doc. 2, pp. 154-159, 1 49. Notes on the topography, soil, geolOgy, etc., of the district between Portage Lake and the Ontonagon: 31st Cong., 1st ess., . Ex. Doc. 1, pt. 3, and H. Ex. Doc. 5, pt. 3, pp. 649-701, 1 49. Field notes for 1 47 [in the Lake uperior region] : Idem, pp. 713- 75 . [On the mineral lands of the Lake uperior region]: Boston Soc. at. Hist. Proc., vol. 3, pp. 21D-212, 1850. atalog of the rocks, mineral , tc., collected on the di trict between Portage and Montreal River during the years 1847 and 1 4 : rnithsonian In t . Ann. Rept., vol. 9, for 1 54, pp. 3 7- 392, 1 55. Remarks on some points connected with the geology of the north shore of Lake Superior: Am. Assoc. Adv. ci. Proc. for 1 55, pp. 202-209, 1 56. otes on the geological position of tbe Lake uperior sandstone: Min. Mag., 2d er., vol. l, _pp. 435-446, 1 60. (See also Foster, John Wells.) \YELLs, RoGER C. Chemistry of deposition of native copper from ascending solutions: . S. Geol. urvey Bull. 77 , 1925. WHITTLESEY, CHARLES. Copper regions of Lake uperior, 64 pp., 1 46. Description of part of Wisconsin south of Lake Superior, with map , in Owen, D. D., Report of a geological urvey of Wisconsin, Iowa, and Minnesota, pp. 42 470, 1 52. Drift tching , Lak up rior: noal ci., vol. 2, pp. 57- 59, l Ycla nd, 1 54. On the origin of t h zoic rock of Michigan and 'Yi on in: Am. A soc. Ad . i. Proc., v I. 13, pp. 301- 30 , 1 60. Ancient mining on th hor of Lake up ri r: mitbonia I n t . ontr. Know! dge, vol. 13, art. 4 (155) 29 pp., 1 63. Th Penoki mineral rang , 'I is. : Bo ton oc. at. Hi t . Proc., vol. 9, pp. 235-244, 1 63. Physical g ology of Lake uperior : . m. A oc. dv. Proc., vol. 24, pp. 60-72, 1 76. n the origin of min raJ vein : Am. A soc. Adv. ci. Proc., vol. 25, pp. 213- 216, 1 77. nth Iron Riv r silver di trict: Eng. and Min. Jour., vol. 23, pp. 254-255, 27 - 279, 1 77. Pr glacial channel of Eagle River, Mich. [abstract]: Am. A soc. Adv. ci. Proc., vol. 31, p. 352, 1 The preglacial channel of Eagle River, K eweenaw Point, Lake Superior : Am. Jour. ci., 3d ser., vol. 29, pp. 392397, 1 WILLIAMS, CHARLE P. (and Blandy, J. F.) ... the Copper Range of Lake uperior: Am. Jour. ci., 2d ser., vol. 34, pp. 112-120, 1 62. WINCHELL, ALEXA DER. Notice of a small collection of fossils from the Potsdam sandstone of Wiscon in and the Lake Superior sandstone of Michigan: Am. Jour. Sci., 2d ser., vol. 37, pp. 226- 232, The soils and subsoils of Michigan, 30 pp., Lansing, 1 65. Map of the State of Michigan colored to show the geological formations, 15 by 18 inches, l 64(?); notice, Neues Jahrb.1 186 , pp. 99-101. Wr CHELL, ALEXA DER-Continucd. otes on some post-Tertiary phenom na in 1i ·h.igan [abstract]: Am. aturali t, vol. 4, pp. 504-505, 1 70. Report on the progre of the tate Geological urvey of Michigan, 64 pp., Lan ing, 1 71. Michigan; being condensed popular ketche of the topography, climate, and geology of the 'tate [ xtracted from 'Valling's Atla of Michigan], 121 pp., map , larcmoni, r. H., 1 73. The diagonal sy tem in the phy ical f aturr of l\1 ichiga n: Am. Jour. ci., 3d ser., vol. 6, pp. 36 40, 1 73. yllabu of a course of lectur on g olo '.1" to h deli,·ercd in the Syracu e Univcr ity during the winter term f 1 74-75, 32 pp., yracu e, 1 75. WINCHELL, ALEXA DER U e of "oph.iiic " and r lated term in petrography: Gcol. Soc. Ameri ca Bull., vol. 20, pp. 661- 667, 190 . (and others) . H andbook of mining in the Lake upcrior region, prepared for Lake Superior meeting of Am. I n t. :\'lin. and Met. Eng., August, 1920, 260 pp., illu . (incl. map ) , Minneapoli , 1920. "' 1 'CHELL, HoRAcE VA oeAN. Hi torical ketch of the discovery of mineral depo it in the Lake uperior region: Lake uperior Min. Proc. vol. 2, pp. 33- 7 , 1 94; Minnesota G ol. urvey Ann. R ept., vol. 23, pp. 116- 155, 1 95. \¥INCHELL, EWTON HORACE. ketch of the work of the sea on of 1 7 : Minnc ota Geol. urvey eventh Ann. Rept., pp. 9-25, 1 79. The cuprifer us erie at Duluth : Mione ota Geol. urvey E ighth nn. Rept., pp. 22- 26, 1 Preliminary Jist of rocks: i[inoesota Geol. urvey 1 ioth no. Rept. , pp. 1 114, 1 T pica! thin sections of the rocks of the cupriferous eries in Minnesota: Am. soc. Adv. ci. Proc., vol. 30, pp. 16D-166, 1 2; Minnesota Geol. urvey Tenth nn. Rept., pp. 137- 143, 1 2; abstract, cience, vol. 2, p. 441, 1 In·ing and ham berlin andstone : .\..m . G ologi t, '" I. 1 pp. 44-57, 1 't 'P · of progressiYc re carch in the g ology of the Lake uperior region prior to the late Wiscon in un ·ey: Am. Geologist, vol. 16, pp. 12- 20, 1 95. The Keweenawan according to the Wis onsin geologists: Idem, pp. 7 A rationa l ,riew of the Keweenawan: Idem, pp. 15 The late t eruptive of the Lake uperior region: Idem, pp. 26 omparative taxonomy of the rocks of the Lake upcrior region: Idem, pp. 331- 337. (and Grant, . .) Volcanic ash from the north h re of Lake uperior: Am. Geologist, vol. 1 , pp. 211- 213, 1 96. Thomsonite and lintonite from the north shore of Lake uperior: Am. Geologi t, vol. 22, pp. 347- 349, 1 9 . Common zeolites of the Minnesota shore of Lake up rior : Am. Geologist, vol. 23, pp. 17 177, 1 99. Adularia and other secondary minerals of copper-bearing ro ks: Idem, pp. 317-31 . General index of the annual report of the Minne ota urvey: Minnesota Geol. urvey Twenty-fourth Ann. Rept., pp. 179-284, 1 99. The Keweenawan at Lake of the Woods in Minnesota [abstract]: cience, new ser., vol. 23, p. 2 9, 1906; Am. Assoc. dv. Sci. Proc., vol. 55, p. 37 , 1906. Woons, THOMAS The porphyry intrusions of the iichigau c pper di tri ·t: Eng. and Min. Jour. vol. 1071 pp. 29 302, 3 figs., 1919,
THE COP PER DEPOSITS OF MICHIGAN WRIGHT, CHARLES E. First annual report of the commissioner of mmera.l statistics of the State of Michigan, for 1877- 7 and prev1ous years, 229 pp., Marquette, 1 79. Report of the State geologist from May 1, 1 5, to January 1, 1 : Michigan Geol. urvey Rept. for 1 91- 92, PP· 33- 37, 1 93.
RIGHT, FRED EuGE E. Report of progress in the Porcupmes: M1ch1gan GeoJ. urvey Rept. for 1903, pp. 33- 44, 1905. Notes on the rocks and minerals of Michigan, to accompany the loan collection issued by the Michigan Colleg~ of Mines, prepared by the department of geology, 10o pp., map, Houghton, 1905. The intrusive rocks of Mount Bohemia, Mich.: Michigan Geol. Survey Rept. for 190 , pp. 355- 402, map, 1909; abstract, Science, new ser., vol. 27, p. 76 , 1907. (a nd Lane, A. .) Preliminary geological map of the Porcupine Mountains and vicinity: iichigan Geol. Survey Rept. for 190 , pl. 1, 1909. WRIGHT, JAMES EY. The development of the copper indu try of northern Michigan: Michigan Polit. ci. Assoc. Pubs., vol. 3, No. 5, Ann Arbor, 1899. GEOGRAPHY Location.- The copper district of iichigan i in the extreme northern part of the northern peninsula, in Keweenaw, Houghton, and Ontonagon Countie . It mine all }je within a narrow belt from 2 to 4 mile wide and more than 100 miles long. Topography.- Tho mo t prominent topographic feature of the copper country i a broa.d flat-topped ridge or narrow plateau extending in a northea terly direction through the district and falling off to a. lowland both to th nor.th and to the south. The northern po ·tion projects into Lake uperior as Keweenaw Point. Thi plateau rises to a general level of 500 to 600 f et above Lake up rior, wiLh ridges such as the Greenstone and Bohemia Range , in Keweenaw oun y, ri ing still higher. In the outh end of th di trict the Porcupine Mountain form a prominent feature north of the main ridge. The main ridge or plat au 1 u t through by everal low transverse gap or alley . Th deepest are the Porta()'e Lake and Ontonago n River vall ys, but there are m~y other of similar pe. The drainage is mainly outward from the central ridge, and mo t of the stream ar mall. The.large t is Ontonagon Riv r, which ri es south of the main ridO'e and flows northward through the Ontonagon Gn~. A mo t of th tr am have mall ba in , they are ubject to marked variation in flow. In dry summers and continuou ly cold wint rs the flow in nuu1v of the tr am i v ry mall, but while the now i rapidly melting in tho pring th re is a large flow. Olimate.-The followin()' tatemenlis of tho climatic condition are taken fr m the u:rnma.ry for 1924 prepared by Howard B. owdri k, melieorologi t o! the Houghton tation of theW ather Bureau, United tates Department of O'ri ultur . The Hotwhton ·tation is in the Portage Lake valley, 2 feet above lake level, and the average onditi ns n the Copper Range Plateau both north and outh of it are somewhat more evere. Th water f Lake uperior on thr e ide of h region greatly t mp r the climate. Killing frost in the autumn i, later than at many tation much f rther outh and although the piing open late, there are almo n ver p ri d of high temperature followed b. injuriou fre zing weather. For the la t 23 year th averng date of the Ia t killing fro t, in pring hA. fall n in Ylay and that of the first in autumn ha fallen in October, and the avera()'e interval between them ha b n 149 day . The summer clima e, with it long unn clay and cool nights, i almo t perf ct. The wint r aro cold but not unpleasant. O'l'eat amount f now fall, but it is u ually dry, and becau e of exp rtne s developed through many y nr of experien in handling it, the railroad and electric line are not seriously inconvenienced. 1 et i almo L unknown. Weather conditions at Houghton, Mich., 1901- 1924 Temperature (°F .) Relative humidCloudiness (tenths of sky) Precipitation (I uch s) ity (per cent) g Means Extremes Greatest io24 hours
;., ij :s Highest Lowest
,. "' E !(! "' g .§ "' e e ""
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!:1
g .s s "§ .; g
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E-< ct A is 1906 ' - 31 1906 I - 19 1910 I - 22 19o1 I - 1o 1901 I 34 66;
July,
Jan., --s11 n-
GEOGRAPHY Weather conditions at Houghton, Mich., 1901- 19f4-Continued -umber of days lor conditions specified Wind ;; ., "' " I Maximum velocity for
Temperature
e e .e
5 minutes
'00 0:: '0
:::l'S
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Maximum Minimum 0.> o o ->o so bD .c·g
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s ., E ., ., 9: OtQ
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,-- Januar.v February- ApriL - - - - - - - July October_ - - - - - I 1· 5 "· 169-1-5- !Zl--1-,~ -, 25 1 E. 1 63 : w. Total for period. Indu.strie .- The chief industry of Keweenaw Point is copper mining and smelting; of far less importance are lumbering and agriculture. In addition to the e there i some fishing and a little mauufa turing. Copper mining bas been the most important industry for many years, and until the end of th World War, when copp r mining nearly e erywhere wa em-tailed, it had made a pretty steady growth. Lumbering i of course deer a ing in importance as the original timb r i remoY d, but th re i till much original hardwood timb r tanding and lumbering will continu f r orne time. the timber bas been cut some of tb land ba b en lear d for farming and agrieul ture hn been t adily Arpanding. Much of the soil i good, nnd although the sea on are short, pecially n the higher land of the Copper Range, the region i uit d to certain types of agri ulture, especially the growing of potatoe and root crop aenerally. Dairy product ar also more than u.ffici nt to upply local demand . Transportation.- The di trict borders on Lake uperior, and Portage and Torch Lake and the Portage Lake anal bring lake transportation into its heart. Mo t of the heavy freight, ucb a. fuel and much of the copper, therefore has the advantage of lake freight rate . Lak transportation u ually open by May 1 and clo e in D ember. The district i al o connected with outside points by the hicago, Milwaukee & St. Paul Railway and the Duluth, outh bore & Atlantic Railroad. It i also erved by th Mineral Range Railroad and the Copper Range Railroad. The Keweenaw entral Railroad has served the northern part of the district in the past and would undoubtedly resume operation if conditions should justify. wi tb the mill railr9ad . everal of the mines are connected and melters by privat ly owned An improYed highway extend from opper Harbor, near the end of Keweenaw Point, to Rockland, on Ontonagon River. Tbi road, together with numerou branches, bring practically all part of t.he distri t within a few miles of good highway , which are op n to automobile traffic for about ight month of the year. The north end of the Porcupine fountain ection a.l o ha improved highway , and th hicngo, Milwaukee & ... t. Paul Railway ha a branch to the White Pine mine. Power.- Practically all power for the district i aenerat d from coal brought in by Lake teamer . M ucb of the power is used directly as steam power or a compre sed air produced by steam power, but there i a steadily increasing use of electric power generated at central plants. The only water-power plant in the district is that of the Victoria Copper Co. on the West Branch of Ontonagon River. A fall of 71 feet was utilized to produce compressed air directly, which operated all the machinery of the mine and mill. A dam to store water in Lake Gogebic helps to equalize the flow of the riYer, and the power available could be considerably increased by rai ing the dam. There i a fall on the Ea t Branch of Ontonagon River that has not yet been utilized for developing power, and some power could al o be generated on other mall stream in the di trict. The irregular ea. onal flow of the stream , howeYer, would make storage dam nece ary to develop power continuously.
'HIE .PPEH DEPOSITS F M[ HWA PHY IOGRAPHY An a count of the development of tho ph io- (7raphic featur of tho opper di trict require~ c~nideration of a much wider area than the dt i elf. Such descriptions hA.ve been prepared by Martin 7 for the Lake uperior region, by Leverett for the northern peninsula, and by Lane 9 for the copper di trict, and only a brief outline will b'e preanted here. The ridge or plateau known as the opper Range ropre ents an old mature erosion urfaco with monadnook ri ing above it general level and al o valley below that level. With the elevation of thi old urface the softer rock on each ide of the pre ent range were eroded to form th pre eut lowland , while the ry talline rock were but little affected. (See pl. 53.) This was the condition of the region before the glacial epoch. The glaciation had little to do in forming the major phy iographic features, but it affected the minor features profoundly. When the ice swept over the region it scoured off the soil and the weathered outcrops of the rocks. It smoothed the outline and probably widened and deepened the valley somewhat, but it did not change the major rock features. In local protected areas the effect of preglacial weathering i preserved-for example, it can be well een in a shaft on the Petherick vein, near Copper , Keweenaw County. The deposits laid down by the ice and the accompanying tream are prominent feature of the d tail of the phy iography and are economically important both from the iewpoint of the farmer, becau e th y form the oil, and from that of the miner, bccau e they on tituto ft rock cover which affec tho ea. e of both exploration and development. There are four principal type. of glacial depo it on the Copper Range-the general till beet or ground moraine; moraine formed around the margin of the ice tongues; depo it formed in glacial lakes; and depo its laid down by treams flowing from the ice. The mo t extensive of the e depo its is the ground moraine, which was left in greater or less amount everywhere a the ice melted. It covers practically all the range except a few steep ridges from w. it ha. been removed or on which it could not accumulate. Over much of the area it form a rather shallow · mantle, which i not continuous but fi]Js minor depres ions and covers the outcrop of the weaker rocks uch as the amygdaloids. The marginal moraines cover a much smaller area. The most prominent one, which outlines the ice lobe that moved do' n Keweenaw Bay, touches the Copper Range at Wheal Kate Mountain, near South Range, 1 Martin, Lawrence, . S. Oeol. Survey Moo. 52, p. 85, 1911. Lever tt, Frank, Michigan Geol. Survey Pub. 7, Ocol. scr. 5, 1911. 'Lnno, A. 0., Michigan Goo!. Survoy Pub. 6, Oeol. ser. 4, p. 4 , 1011. nndfollowsitsouthw' Lward Lo apoiuLb yond Win na, whore it tums southward a L' und Keweenaw Bay. This moraine buries tho rock deeply and i a impediment to prosp cting. The lake d posit w r formed m th lake along the south mn,rgin f the i c. In their early tagc these lake drained into th bn in f Missi ippi RivN. Lat r as the ice melt d, low r outlet were opened w the ~st and tho lake dropp d to u c ively lower ' levels. The mo t oxten tv of th e lakes m the opper Range wa Lake Duluth, whi h ov red mo t of the area. At alumet it high t bore line urround entennial Heigh , about 70 f t above the level of Lake up rior, and in the south end of the district only the higher ummit proj ct d a i land . This highest tag a I How d by u ces ively lower tagwho e po itio.ns ·are mnrkod by old beach line . ince these were form d th ha been tilted o that there is a light ri e in altitude of each beach line from outh to north, th nmount of whi h has not been deter· mined for th opper Rang . In these lake were f rmed xt nsiv depo its of clay mix d with boulder , specially in th outhern part of the range. The e d po it hav not buried the rock as deepl as the marginal moraine, but ill place they con titute a decided handicap to prospecting. Since the glacial epo h ro ion ha modified the depo its som hat, e pecially n ar treams, but in the main ther ha been little han(7 . ( ee pl. 54.) BEDRO K GEOLOGY BROADER RELATIONS Location and extent.- Tho nati" opp r dep ·it· of Lake upcrior Ill' inclo'ed in rock. of r owc(llH\WIIll age. The ar a in whi h th . c ro ks ar expo cd li ' in the outh rn pA.rt of th pr - amhrinn hicld of orth America and form a part of the Lake uporior basin. Along the outh shore of the lake it extend from Keweenaw Point southwe tward thr ugh north· ern Wiscon in into Minnesota. ( ce pl. 2.) The Keweenawan rocks border the north h re of tho lake in Minnesota to the anaclian boundry, cr p out ou I le Royal, and in anada appear in the Black Bay and Thunder Bay eli tricts and extend northward around Lake ipigon. To the ea. t of thi almo t continuou area they o cur in scattered outcrop olong the shore and on islands of Lake Superior. Character of the rocks.- The Keweenawan eri comprise coarse clastic sediment and intru iva and extrusive igneous rocks. Both the base and the upper part of the series were formed during periods sedimentation. The igneous activity became dom.J· nant after a maximum of 1,500 feet of edim nts bad been deposited, when basaltic flows were poured o.ut, one after another, with occasional short intervemng periods of sedimentation. More rar ly a idic erup· tions occurred. The flows were probably fi stl.l'e
Stratigraphic position of lite subdivisions of the Keweenawan series of Jfichigan to which names have been applied !Compiled by M. Ornee Wilmarth (se('retary or I be l'OlllWltlee on geologic uumes, U. S. Oeologlcal Sun·ey), under the supen·islon of B. 8. Butler, May, 1926. Asterisks ( iudicnte inten·eniog rocks] ICewceua\,~a.n series: J:l""rcda sandstone Nonesuch shu.lc: 1. Sha1c and thin sandstones 2. 1 oncsuch lode (sandstone, some thin shale, and congloulcratc) 3. Shalc 1 thin Copper Harbor group: Outer conglomerate, 1,000-3,500 feet .Lake Shore trap, 0--1,800 feet: J . Trap (upper) 2. Conglomerate (middle) 3. Trap (lower) Great conglomerate (No. 22), 340--2,200 feet Eagle Ril,er group ( ~lan·iue's group C), 1,-!1 i - 2,300 feet Trap !,land ~line conglomerate of I.Je Royal Conglomerate o. 21 Trap, etc. Conglomerate No. 20 Trap Conglomerate No. 19
Ash bed group, 1, I;)() 2, :on fert Conglomerate Xu. Ib Diabase tmd nmygdaloid HAncoC'k C'ouglomeratc (~o. 1 7) Hancock \rest conglorners.f.c of .\Iarviuc
_\ am.1·gdaloid (.\shbed lode) =.\tlantic amygdaloid C\tlnntic lodc)=South Pewabic amyrrdaloid (South At·nold amygdaloid (Arnold lode) Trap
Trap
Pewu.bic " "est conglOJncrate (No. Hi) Trap
Ashb1'd now Pcwabic lode) A Uurd ic now J-\ mold now 'outh Pcwabic ftow Quincy amygdaloid Pcwabic amygdaloid (.bic lode)} Quirrcr Pcw.nbic amygdaloid PewabiC flow Tmp
Old Pewabic amygdaloid (Old Pmmbic lode)}= Oid Pewabic Trap flow
Pcwabic Far \Vest lodes\ \\rest lodc= ' 1 .\la.in" lode Pewabic East lode PcwabJC nmygdaiOLd lodes Quincy :unygd:1loid lodes Quincy lode= Old Quinc-y
:flr~~ny & Boston am)·gdaloid (Albany & lloston lode)}= Albany & J3oston flow Duluth gnl>bro (intrusive) Lodes or Hancock mine l:' l11an <·onglomcratc No. i 7) Include: [~~ancock am~·gdalllid tH~uu:uc-k lode)} Hancock flow rap 1\1:s~:rd" epidote='' St. tvr fl.ry" epidote= tt I\1esnard bed., I ' ' Chippewa ' 1 felsite Chippewa 11 porphyry Central Mmc group, 3 823- 25,000± feet (different facies or same form:.niou) Greenstone fiow c''crystu.llinc trap,'' ,.diorite," the ((slide") Allouez conglomerate (i\ o. 15) (Allouez lode) 11 Albany & Boston 11 conglomerate
Medora amygdaloid lcdora lode)} M d f! Trap r e ora ow
illaoitou amvgdaloid (Manitou lode)} 'I "to fl Trap u ow
l\Iandan amygdaloid (l\landan lode)}= Mandan fioll" I' Trap (ophitc) Mandan ophite of Lane
Houghton conglomerate ( ro . 14) ="Central Minc 11 conglomerate 900--1,460± feet "Calumet & Hecla conglomerate (.'\o. 13) ="Calumet conglomerate
f~!~met amygdaloid (Calumet lode)}=Calurnet flow
Osceola amygdaloid (Osceola lode)} -O· 1 n Ophitc sceo a
-450± feet Xorth amygdaloid (.'\orth lode)}- N tl ft
Trap l. or 1
~,Iontreal amygdaloid P1ontrc"l lode)}= Montreal flow 1rap
'¥est ~linesota conglomerate, 150 feet West ~Jin esota trap, 2,160 feet 11 Oneida" conglom.ernle (probably= Allouez conglomerate) T oltec trap, 1,i10 feet Xationnl sond::;tone, 50 feet (Probai)Jy :'\o. 12 congl merate) South end of Keweenaw Point: Shawmut amygdaloid} ( hawmut lode) Sha,nuut flow Trap .. Calico amygdaloid (Calico lode)}- C l" fl Trap a 1co
Korth am)·gdnloid} (North lode) 'orth flow Trap l Minc,o!a , 570 feet
(short distance) 'hawmut conglomerate (Probably=No. 11 or l\o. 12. Is the J ohnson Creek oonglom<:>rnte of Lane)
l>:enrsargc t·onglomerate (probably conglomerate No. 12, according to Butler) =conglomerate Xo. 11 of ,\larvine Xorth l::itar conglomerate .\linong breccia of Isle Royal =(probably) Mine ota conglomerate =(probably) Kingston conglomerate= l\o. 10 of .\Iardne
:llinong porphyritc}o. !\Iinong trap ccur Oil Isle Ro) al
H uginnin porphyrite o! Isle Royal
Kearsarge West amygdaloid (Kearsarge \Vest lode)}!" 11. t fl Trap \.C3.rsargc cs ow
Kearsarge amygdaloid (Kearsarge lode)} '· 'Volverine" amygdaloid =Kearsarge fiow Kearsarge trap
Wolverine sandstone (conglomerate l\o. 9) Old Colony amvgdaloid (Old Colony lode)} Old C 1 n Trap "
o ony
Old Colony sandstone
Torch Lake or Tomahawk amygdaloid (Torch L~k e lode)} 'f 1 l , fl Trap
ore 1 ..~a'-".e ow
!)ld ~layflower amygdo.loid (Old May(Jower lode) . (Position qneslionable)}-Oid ~Iayflowcr flow
Isle Royale amygdaloid (Isle Royale lode) ) ='·Grand Portage" amygdaloid (Grand Portage lode) Isle Royale now =(probably) Arcadian amygdaloid (Arcadian lode) "Grand Portage" flow =(probably) 'Yinona amygdaloid (Winona lode) =Arcadian flow West lode Winona flow Isle Ro;alc trap
Dought.'l amygdaloid Trap =Douglas flow Oneco amygdnloid 1 Oue-c·o tlow (probably ncar horizon or Isle ·r (Oneco lode) l\o,·nll' tmn·gdaloicl) rap f:~:; ~lay flower amygdaloid (i\ew Mayflower lode)} :-lew Mayflower flow (may belong here, Butler Rays)
·"r·cw Arcadian amygdaloid (~ew Arcadian lode)}- New Arcadian flow ·
:~r!P Louis" amygdaloid (St. Louis lode) a St. Louis n flow " Big" trap 0--400± feet
"J3oheruitPI Range gr up. 9,500 ± feet: Bohemia conglomerate ( No. R) '' ~1ount Bohemia. conglomei aLe Forest conglomerate f"uledonia conglomerate - Winona con?lomcrate
1 ' :s-cbraska' conglomerate - Colcdoniu. couglomerute ::\lay= ~1ichigan conglomerate Proba.bly=''St Louis' conglolUerate ( f · f r tion) (If intrusive, is probably middle or upper 1\:('WPC') :'\lo:IJlt Houghton f~lsite )1ount Houghton quartz porphyn- different a.c1cs o same orrna ·
Hohcmia porphyrite PnL.ysville porphyry
Conglomerate No. 7
Couglomeratc N"o. G
Conglomerate No.5 (probably= Baltic suudstoM)
Conglomerate No. 4
~labb amygdaloid (ophj tc) ( ::llabb lode)}= J\-labb flow Trap
Baltic West amygdaloid ( Baltic West lode)}= Baltic \\.est flow Trap, 40--GO feet Baltic nmygdnloid (Baltic lode)
Probably=Superior amygdalocl Bal t>c fl ' Trap (oph ite)
J3altic conglomerate o. 3) Gabbro of i\lount Bohemia (Is in trusi vc and ma.y be upper Keweenawan) Lac Ia Belle conglomerate (::IIay be conglomemtc Ko. 3 or younge r)
Conglomerate No. 6
Felsite of Indiana mine (Ts intrusive and regarded by A. C . Lane as possi· blv equivalent to the l,J:aysviJ le porphyry) Conglomerate ~o.
Conglomerate
Wyandot !"\o. 8 am;·gcJaloid} Wyandot i\o. 8 Oow Trap ·
Superior " "est nm .. '·gduloidl (Superior \re-t lode) I Superior West now
Superior amygdnloid} (~upcrior lode) 8upcrior flow Trap
'alico amYgdaloid (Colil'o lode nt Trap
:'\1Jnesota. mane)}= Calico flow linesota ronglonwr!lte \Vyandot am_,·grlalnid l (Wyandot lode) (Probably= Winona Wyandot llow an ,ygrlaloirl ) Trap )J"onl'it"'h trap ~orwich conglomera.te n Bad River u gttbbro 3,0Q0-4,500 fret
Conglomerate (ununmed) Knowlton nm~·gdaloid) (Knowlton lode) J\:n011"!ton tlow Tmp
~lerchants amYgd:lloid) (::IIcrchnnis lode) :\Jorchanls tlow Trap Piscab.q ua lode
Masa amygdaloid} Trap(Mass lode) ::lh\,, II ow
:-<orth Butler amygdaloid} . , (North Butler lode) Xorth Butler flow I rap
Butlm· amygdaloid} (J3utlcr lode) =Buller tlow Trap
Nebraska lode l:louth llutlcr am,·gdaloid} , (.' uth llutlcr lode) =South Butler tlow frap
Ogima amygdaloid} , (Ogitna lode) =Ogimn now l'rap
Evergreen aruvad loid 1 (EYer green lo~P) J Evergreen flow Trap
Xew Mass amYgTi!lll)id} Xew :\[ass now Trap ;\a. 8 conglomer!ltC Forest amygdaloid} (Forest lode) =Forest flow Trap .
Luke am,·gdaloid) (Lake lode) =Lake flow Trap
. conglomerate Conglomerate )!o. 2 Basal sandstone, 200--460 feet l,L40± reet Conglomerate No. 1 Amygdaloid '' Viet orin.'' nmr~rl.aloid} (VictoriA. lode) =Forest ("Victorin.") flow Trap
.\lgomah n mygdaloid1 . (Algomalt lode) J Algomah flow lrap
rt!orrnit~· 1 w l)!C to call Lwo dlslintl unfls sueb 85 rhe Kenr~3r).:e on~~;lomemte and tho Kenrsnrge nmygdalohl or n l!'lrl!or unit nnd one of Its parts, such as tbe A~ gr(lnp and tho Ashbod .amygdaloid, by the same n.nue. 'UnlJO f).lan ser1es derivod from a localitY\ nud it J:; ndoi ",~o ~pea ted use of quotaticm mark! iS ob}tetioo:Lblo, the- Oeolol(ie:a\ ~un·ey's rnles hove suspended, and with ro-w tnceptlous the uarneg lu currtlnt use tu the nreo hsvo boon nooepted without quolatlon monks. lu lhe are;~ co~·ered by this. 1·eport bowev ted ' er, o. local uomouclature hns become llrwly established u
"' roed unit must ba.re a separtate uame h tl. lo<:a U"-M:.o nn as lC r lJ.U ,:oE.-Ucder the current rules Of Str~tlgraphi o nc lotl.lfe :~.-t.:i~ rna rJlO.DY duplication!. As It is impractlcob!e to C nnge us
' .;.0 ~oclnted conglomerates, am~gdaioLdS_,. and ot ' .. ocks, ,
n~.~er wh 1ch tbe ua.m .1r es or \·arious lUloes hnve heeti 8r !ll'ce p. 16.)
§ :.:
'· t.. "' ..J '·' "' :;5 '-' t
(f)
:z
..J c:: "'
t.. ..J c:: :z
c:: v
U. S. GEOLOGICAl SURVEY One-of the falls of Lhc KrwCCili\W fault fnlllin<·. Pholograpl( hy C. · Ha,,lillgS Costly and valuable information going to wn' l Inclusion zone in
STRATIGRAPHY eruptions; how many the~e were i not· known, but they are to be numbered m the hundreds. Igneous activity gradually cea ed, the intervening periods of ed.imentation becoming more frequent and longer. The upper part of the eries i made up largely of a conglomerate overlain by a thick sandstone. Intru ion probably though not certainly occurred during the Keweenawan epoch. On the north bore the great Duluth gabbro laccolith of Minnesota was intruded e entially along the unconformity at the base 'of the Kewee~awan. Similar intru ive rock occur south of the lake in Wisconsin, and it is thought that the e are outcrop of the arne great body extending b neath the lal e, from one side of the Lake uperior ynclinal ba in to the other. mailer intru ive bodie occur toward the base of the Keweenawan at interval along Keweenaw Point. Both their petrographic character and their po ition in the erie ugge t that the ar contemporaneou with and derived from the arne magma a the Duluth gabbro. Other example of intru ive rock that are probably of Keweenawan age are the dikes in th Gogebic iron country and the Logan ill in Minne ota and Ontario. STRATIGRAPHY MAPS AND SECTIONS The detailed geologic map and section (pls. 2-32) are based largely on data from diamond drilling and underground opening . Outcrops have of cour e been u ed as far a possible. As the region is largely covered with drift and th depth to beclJ:ock i unknown except at the location of drill hole or other opening , it wa d cided to how the rock b d on the urfa e map a pr ject d on their dip thr uah the drift to th urfa . Wher th r i no drift cover th -outcrop a hown coincide with th actual bedrock outcrop. Where ther is a drift cov ring a given contact in we tward-dipping bed is shown farther ea t than its po ition on the bedro k urface b II di tance that varie with the thiclmes of the drift and tho dip of th bed . The dip i indicated on the map and hown on the e tion , Md the thickne of drift at tho drill hole is hown on the section , and it i al o indica d on the map by a gap between the location of the hole and th po ition of the b drock. tho K w enaw fault, wher th bed· are in general con id rabl brok n and in many place have low dip , the urfa e outcrop ha not been hown. The tructure so far a it is known is indicated in the sections. On both maps and section th character of the traps is hown by l tters, as 0 for ophite , M form laphyres. Th character of amygrlaloids, a fragm ntal, scoriaceou , or cellular, is shown by yrnbols. AGE AND RELATIONS The rocks of Keweenaw Point are of Keweenawan and Cambrian age. On the Gog bic Iron Range, ncar by, the Keweenawan rests unconformably upon the upper Huronian, and Keweenawan dik cut the earlier rocks. Overlying the upper K weena> an, without apparent unconformity or abrupt chang of character, is ft sandstone which ha been con ider d to be Upper Cambrian. This relation does not exist on Keweenaw Point, where the upper Keweena\ an sand tone (called the Freda) is eparated from the Upper Carnbrian:sandston (the Jacobsville, "Ea tern," or Lake Superior sandstone) by a gr at overthrust fault. In the valley of St. roix River, in western Wisconsin, fossiliferou pper am brian sand tone lies unconformably on middle Keweenawan b d . The Jacob ville sand tone may be likewise unconformable on the Keweenawan in the South Trap Range of Michigan, but there the relations are ob cured by faulting, and the problem is complicat d further by the doubt that exists regarding the equivalence of the Jacobsville ("Eastern") and tone to the pper Cambrian of the St. Croix Valley. Thi relation may mean simply that the Lake Superior ba in wft forming during Keweenawan time and in place the late t member was laid down unconformably on the earlier members, which had been already tilted, though there wa no break in the general serie . In northern Wi cousin the Freda and tone is overlain conformably by other sand tones of Keweenawan age, into which, indeed, it eerns to grade imperceptibly. It would appear from this relation that the formation were laid down in one period of continuou deposition without interruption by diastrophic movements. Although the accepted usage of the United tate Geological Survey is to group the Keweenawan with the pre- arnbrian, the fact that the apparently major unconformity lies below the Keweenawan series rath r than above it ha led orne geologist to the view that the major division between the Cambrian · and pre- ambrian should be placed at the ba e of the Keweenawan. Thu , Lane groups the rocks of the Keweenawan a. ambrian. 10 The present work hu contributed nothing of significance toward determining th r lation , and it seem to be still .an open question with good arguments on both ide .103 GENERAL CHARACTER AND DISTRIBUTION The Keweenawan eries i divided in a general way into upper, middle, and lower Keweenawan, which are further ubdivided into groups and formation Y Th eral workers in the di trict have cla ed the ubdivi ion omewhat differently, a indi ated in the following table : to For n discussion or tho age nod relations or the Keweenawan soo Van llise, C. R., and Leith, C. K., 'l'he geology or the Lake Superior region: U. . Oeol. Survey !.<Ion. 52, pp. 384, 389, 415, 416, 616, 620, 625, 1911; Laue, A. C., 'l'be Keweeuaw>ln series or Michigan: Michigan Oeol. Survey Pub. 6 (Oool. ser. 4), pp. 41, 629, 630, 911-942, 1909. toa ince this report was prepared C. R. StauJier (Ago or the red clastic seri or 1inn ota: Oeol oc. America Dull., vol. 38, pp. 469-47 , 1927) bas reported the Ooding or Middle Cambrian fossils near the top or the rod sediments below the t. roixan series in Minnesota. These rocks have in the past been correlated, some· what uncertainly, with the Keweenawan. 11 Lane, A. ., op. cit., p. 20.
THE COPPER DEPOSITS OF MICHIGAN Classification of subdivisions of Keweenawan series lassi!lcation a me
Tbicknass (feet) Irving Van Hlse and Leith Lane and Gordon (?) pper Keweenawan. 400- 1, 00 340- 2, 200 Middle I eweenawan Low r 1 ewcenawan. Central (?) - 9, 500 The rock consist of acidic and basic intrusive and extrusive rocks, hale, and tone, conglomerate, ash, and tuff. The same rock types, both igneous and sedimentary, are characteristic of th Keweenawan of the entire Lake Superior region. The Keweenaw Point belt extends southwestward into northern Wi - cousin and dip northwestward under Lake Superior. Rocks of the arne types emerge on the north side of the Lake Superior yncljne in Minnesota, Isle Royal, and Ontario. Lane believes that some of the specific horizons identified in the Michigan copper district can be recognized on Isle Royal. 12 SEDIMENTS DISTRIBUTION The sediments are decidedly subordinate in the lower groups on Keweenaw Point. They become increasingly abundant in the upper groups, however, con tituting practically the entire thickness of the series above the Eagle River group. GE ERAL CHARACTER The sediments are predominantly red in color, feldspathic, and poorly sorted; they show horseshoe-shaped ripple marks, cross-bedding, and mud cracks, and so far asknown they havenofossils. Their characteristics indicate that they were deposited largely or entirely under terre trial conditions. 13 extensive. The two types are distinct in composition and in source of material, and it seem de irable for certain purpo es to regard them a eparate units, though from pur ly tratigraphic on iderations they might well be grouped together, a th y ommonly have been. FELSITE CONGLOMERATE Extent and thickness of beds.- onglomerate of tbe felsitic type i the principal edirnentary rock in the copper district. Beds of it range in thickne s from a few inches to 3,500 feet. orne have been traced for many miles along the strike; the Allouez conglomerate, for in ta.nce, i recognized for over 50 miles along the strike and has been identified by Lane acros the lake on Isle Royal, though nowhere is it known to be more than 50 feet in thickness. The recognition and enumeration by Marvine 14 of 22 conglomerates numbered from the base of the series upward to the Great onglomerate constitutes the chief basi of correlation u d in all the later geologic work in the di trict. Vertical distribution.- The conglomerate form a relatively mall proportion of the lower part of the eries and a large proportion of the upper part. In the lower part many of the :flows have no fel ·itic sediment between them, indicating that edimentation at a given place, at least, was intermittent. Character of material.-The fel itic conglomerates are iliceous in general compo ition, the mo t abunco GLOMERATE dant rocks in them being felsite and quartz porphyry. nder conglomerate, as here considered, are inIn the north end of 'the district every bed contains eluded rocks of two types-those that are composed many varieties of such rocks, from the den est fel ite predominantly of felsitic material anu those that are to very coarse quartz and feldspar porphyries and composed of fragments of amygdaloid in a basic sand from highly siliceous rocks to rocks that are strongly and have heretofore been called either amygdaloid feldspathic and rich in iron. In the south end of conglomerate or scoriaceous amygdaloid. A bed of the di trict felsitic pebbles predominate and those of the second type immediately underlies or forms the quartz porphyry are practically ab ent so far ns lower part of the felsitic Calumet & Hecla conglomobserved. Amygdaloid pebbles are present in most erate but is distinct from it in character and is far more of the felsite conglomerates, and locally such basic --- · material may become plentiful, but fragments of trap u IJaoe, A. C., Geological report on Isle Royale, Mich.: Michigan Oeol. Survey, · d' vol. o, pt. 1, 1898. are decidedly unusual. In the south end of the 1S- " Van Rise, C. R., and Leith, C. K., op. cit., p. 417. Lane, A. C., 'l'he Keweenawan series or Michigan: Michigan Oeol. Survey Pub. 8, Oeol. scr. 4, p. 32, 1909. ,. Mnrvine, A. R., Michigan Oeol. Survey, vol. 1, pt. 2, 1 73.
STRATIGRAPHY trict pebble of iron formation have been ob erved, and in the Calumet & Hecla conglomerate there are a few pebble of hard white quartzite, which is not known elsewhere in the Keweenawan series. Except for the amygdaloid pebble , which are of local derivation, all the con tituents are physically and chemically resi tant. Most of the pebbles are fairly well rounded; some, however, are subangular and might be regarded as having been tran ported no great distance were it not that imilar angularity i to be found among hard mat rial on beache subject to strong wave action and can not be taken to indicate feeble abrasion. (Jharacter of bed .-The beds, as is true of conglomerate in general, are lenticular, thinning or thickening rather rapidly along the trike. Where thin they are u ually of rather fine texture, con i ting of sand ton or grit; the coar er material, the large t boulder in which are rarely o er a foot in diameter, i u ually pres nt in rather thick beds, though the thick bed nre not at all place compo ed of coar e ma.terial. The Wolverine and tone included in the conglomerate of Marvine, for example, in place attain a con iderable thickne , though u ually retaining the texture of a and tone or shale. Len e of sandstone are pre ent in much of the conglomerate. Cro -bedding, mud crack and ripple marks are common features. ( ee pl. 55.) (Jharacte1· of underlying bed.- Commonly the felsitic conalom ra i und rlain by a oft red or browni h ba ic and tone, locally ripple-marked, and contains pebbles f am gdaloid that bee me in reasingly abundant toward the ba o and wer e id ntly derived from the underlyinO" am O"daloid. Thi i hat Lane ha designat d amygdaloidal conglomerate. Where the fel ito conglom rate i underlain by the mor ba ic fragmental mat rial, am gdaloid p bble are likely to be pre en t in th f l i tic la er and mor noticeably toward its ba but rarely in abundance. Much le common! a fel ite p bbl may be found in the basic layer. On the whol th re hn be n little commingling of th two kind of mat rial, and a a rule the b undary betwe n th fol ·ite and the ba ic lnyers i pretty di - tinct. I arely doe either the fel iti ro k or the underlying basi onO"lom rate re t directly on trap without the intervention of a band of amygdaloid, though there i ·in many place evidence that orne of the tltnygdal id ha b en eroded. ource of material.- Tb principal material of the fel ite congl m~l·ate i imilar to that ompo in()" everal e off 1 ite and acidic porphyry, in part at least mtru iva, that are exposed in the district. Lane has called attention to the irnilarity between certain pehbles in the alumet & Hecla conglomerate n.nd an intru ive rocl near the Ke> eenaw fault ea t of Calumet. There ar conglomerate of like character, however, that are older than any of the expo ed masses of similar igneous rock , and the exposed rna ses seem much too small to have furnished the large amount of material that the conglomerate contain. The variety of acidic igneous types is greater in the conglomerate beds than ' ould be expected if they were derived wholly or mainly from the breakdown of any single igneous body. Furthermore, as already mentioned pebbles of iron formation and of foreign quartzite are present sparingly in the conglomerate beds, and on Michipicoten I land imilar conglomerates carry pebbles of granite and gneis . Lane 15 and other have sugge ted that certain exten ive flows of felsite, poured out on top of the basalt flows, immediately succumbed to ero ion, thus forming a nearly contemporaneou conglomerate. orne of the pebbles of felsitic texture how flow structure which may be a result of surface flow; but it i not nece arily o, for imilar structure i present in fel ite that i known to be intru i e, and the e pebbles howinO" flow structuTe are mingled with an abundance of others of uch coar e porphyritic and holocry talline texture a to make their derivation from effusive rock unlikely. AldTich, 16 of the Wi con in Geological urvey, believes that much of the material in the conglomerates of Wisconsin is derived from rhyolite flows. He describe conglomerates re ting on rhyolite flows and made up in part of pebbles that are similar to the flows and are thought to have come from. them. Nowhere in the Michigan copper region, however, is a conglomerate known to rest upon or be in contact with a fel itic rna s that can be regarded as effusive. It seem probable that the conglomerate pebbles were not of immedin.te local derivation but came from long-lived upland ompo ed mainly of felsite and quartz porphyry, and that the debris from these upland , together with a small proportion of other material from different sources, was spread intermittently on the adjacent piedmont plains occupied mainly by the ba ic flows. Wher uoh upland were located is not !mown, for no remnants of formations that seem adequate to hnv furni hed the material for the conglomerates have been found. Th y may have been outside the pr nt limits of the Keweenawan and in the area now coveTed by the Jacobsville ("Ea tern" or ambrian) sand tone, or they may ha e been inside the e limits and in the area now occupied by the Freda sandstone (upper Keweenawan). It eems probable that they came from the same direction a the flow and were spread over and carried do' n the gently sloping surfaces of the flow . ldrich 17 and Hotchkiss 18 believe that the source of the similar acidic and ba.sic rocks in Wisconsin was in the interior of the Lake Superior " Laue, A. C., 'l'he Kewoooawoo series of Michigan: Michigan Oeol. Sur vey Pub. 6 (Oeol. ser. 4), p. 753, 1908. " Aldrich, H. R., Magnetic surveying ou the copper·beariog rocks of Wisconsin: Ecoo. Geology, vol. 1 , p. 500, 1923. " Idem, p. 571. u Hotchkiss, W. 0., Lake Superior geosyuclloe: Oeol. Soc. America Bull., vol. 34 pp. 669-67 ' 1923.
'l'IU1 COPPER DEPOSI'l' OF' MICHIGA basin, and there are reasons for supposing a similar source for the rocks in Michigan, as is pointed out in ' the di cu ion of igneous rocks on page 26. Manner of deposition.- Tbe upper surfaces of many of the lava flow are not eroded and are immediately overlain by other flows without the intervention of any sediment. edimentation therefore must have been intermittent. Two contrasting ways in which the intermittent deposition of the felsite conglomerate might have been accomplished have been imaginedthat the conglomerates are marine deposits and were accumulated in a body of water that alternately advA.nced and retreated from the area during the period. of lava · accumulation; or that they are dominantly terre trial deposits and were accumulated intermittently on a plain that was being flooded by lava. The second hypothesis appears the more probable. There has been an increasing tendency among geologi ts, including workers in the Michigan region, to regard sediments of this general type a having accumulated on land or in very shallow water. Within the stratigraphic limits that embrace the ono-lomerate no sediments of undoubted marine origin are known, nor any that are more probably marine than the conglomerates themselves. The presence of ripple mark and mud cracks is strongly indicative of depo ition in streams, puddles, or shallow sheets of water. Perhaps these Michigan conglomerates find their closest analogy in point of origin with the extensive Gila conglomerate of Arizona and western ew Mexico and similar deposits of who e terrestrial origin there can be little doubt. Empha i should be placed on the fact that the red olor of the cono-lomerates is not due mainly to weathering and oxidation, the causes most commonly assigned in explaining red sediments. The conglomerates are red because the pebbles in them are red. Compari on shows that the felsite and porphyry are but little redder than the red fel ite and quartz porphyry masses, such as Mount Houghton, the Bare Hill , and the body ea t of alumet. The pebble in these conglomerates are almo t as free from weathering as the fre best similar massive rock in glaciated outcrops. The color in both is due to minute plates of primary hematite. The cementmg material of the conglomerates contains much iron oxide in grain not inclosed in rock. In the Great conglomerate the oxide is magnetite partly altered to hematite and limonite. In the Calumet & Hecla conglomerate little unaltered magnetite remains. It is probable that some of the limonite resulted from surface oxidation. AMYGDALOIDAL CONGLOMERATE Relation to f elsite conglomerate.- The Calumet & Hecla felsite conglomerate is immediately underlain by a fragmental layer consisting chiefly of basaltic material- in part basic sand, in part pebbles 01 bould r of amygdaloid- re ting upon the amygda. loidal upper part of a ba altic flow. To material of this type Lane ha applied the name 11 amygdaloidai conglomerate." imilar material underlies most of the fel ite conglom rate and i pr ent on numerous flow without accompanying fel itic material. Ap. parently Lane and other have r garded such ba ic fragmental stuff as a part of a ingle conglomera~ formation, of which the overlying felsite portion is perhap tho more conspicuou and certainly the more important economically. For purposes of strati· graphic correlation this view leads to no difficulty, but as the acidic and ba ic portion are derived from different sources and a they al o differ in di tribution and per i tence, it eem advi able, e pecially for the copper-bearing conglomerate , to make a eparation between the amygdaloidal c nglomerate and the fel ite conglomerate. For example, the copper of the aluroet & Hecla conglomerate lode i confined nlmo t exclu ively to the upper, fel ite portion, th underlying basic portion being now here an ore; the fel i te portion i of slight lateral extent, thinning out to and tone and tben pinching almost entirely, but the basic edimentary portion continues on regardle s of whether or not the felsite conglomerate i pre ent. To designate the amygdaloidal conglomerate the Calumet & Hecla conglomerate without qualification at places where the fel ite portion is ab ent might lead to a mi understanding as to the pos ibility of finding ore at such place . In the sections and map this and imilar beds ha e been classed under the term " coriaceous amygdaloids," a term well e tabli bed in the records of the district, though it i · recognized that "amygdaloidal conglomerate" convey a bett r idea of their probable mode of formation. Origin.- The e coriaceous amygdaloid or a.mygdaloidal conglomerate have often been con idered true "ash beds" or the accumulation of explo iva volcanic material-bombs and volcanic a h. That some explosive material was produced in c nnection with the basic flows is entirely po ible, but the evidence that it was of noteworthy amount is not clear, and the sedimentary origin seem adequate to account for the deposit a they are. The fel ite ediments are characteristically underlain by amygdaloidal con· glomerate. It i not uncommon to find orne fel itic sediment resting on the ·amygdaloidal conglomerate where no well-defined and persistent fel ite con· glomerate is present. There are, however, many beds of amygdaloidal conglomerate with which no felsite is associated. Very commonly the amygdaloid of the underlying flow has been partly eroded, and in places it has been entirely removed so that the dark conglomerate rests directly on trap. I t is clear, therefore, that the amygdaloidal conglomerates have been
STRATIGRAPHY formed repeatedly at horizons where both erosion and sedimentation have taken place, and that they are products of erosion rather than of e}.-plosive eruption. The amygdaloidal conglomerates with which no felsite sediment is associated are similar to those that are accompanied by felsitic rock and doubtless are of similar origin. It eems mo t likely that the amygdaloidal conglomera.te repre en t the early tages of a period of erosion and edimentation, hen the sedimentary material wa mainly deri ed near at hand from the readily eroded amygdaloid . Where the edimen tation persisted a long time, so that the ba ic lava were exten ively mantled with gravel and sand, felsitic debri from more di tant source mingled with that from the ba ic lava and became the dominant material of the ediment. Where the period was short only the ba ic material accumulated. SAND TO E A D HALE At the top of the Keweenawan eries occur the None uch hale and the Freda sand tone. The on - uch formation con i ts of black and red hales intertratified with layer of and tone. The Freda andtone i the uppermo t formation of the Keweenawan eries in Michigan. Its material indicate that it was derived mainly from basic igneous rock , and Lane regards its source as having been predominantly in pre-Keweenawan rock .19 A H A D TUFF Material may be a h, though not abundant, i widely di tribut d. 1any of the flow ' ith brecciated top con nin mall quantitie of fin ly granulated material mingled with the coar e that may be ash, though it may be mer ly small fra(l"ment of th arne origin a th lar(l"er. Th hb d and similar bed are con idcred on paO' 33, und r typ of amygdaloid , but th ir probabl mode of rigin i outlined abov , under amygdaloidal onglomernte. One iliceou layer, called the "Me nard" epidote, i aid to ontain quantities of acidi a h 20 and is a cribed to a period of rhyolite ruption. IGNEOUS ROCKS 'l'he major part of the igneou rock xpos d on Keweenaw Point arc ba ic lava flow , which make up mo t of th central portion of the Keweenawan series and whose outer p f rms the higher portion or backbone of Keweenaw Poi,nt. Intru ive ro k of the gabbro and "red rock" typ , similar to the Duluth gabbro and "red rock," and f 1 ite and quartz porphyry intru ·ive , are pre ent at several localities near the ba e of the seri , and intru ive ar al o pre ent. 11 Van Rise, C. R., nnd Leith, 0 . K., op cit., p. 414. Lane, A. 0., Jour. Geology ol. 15, p, 690, 1907. p Lane, A. 0., The Keweenaw series of Michigan: Michigan Oeol. Survey ub. 6 (Oool. ser. 4), pp. 409, 665, 1909. 5 54Q-29--3 high in the serie in the Porcupine Mountain . It is possible that orne of the fel ite bodie are surfa e flow. EXTRUSIVE ROCKS DISTRIBUTION The ba ic lava flow in the central portion of the Keweenawan erie extend n a b It 1 to 3 miles wide from the end of Ke\ eenaw Point into Wi con in. ( ee pl. 2.) A outhern b lt of flo, , th outh Trap Range, diverges from the main rang n ar the MichiO"an-Wi con in boundary and extends ea tward toward Keweenaw Bay. In addition to the e main belts there are a few small flow , the Lake hore trap, in the prevailingly edimentary ro k of he upper part of the Keweenawan serie . EXTENT OF BEDS e eral of the flows ha e b en traced for 40 or 50 miles along the outcrop. The Green tone flo, , for example, which form Gre n tone Cliff, in Keweenaw County, i known from the end of Keweena' Point to a locality outh of Portage La.k ; the "Big" trap, immediately above the " t. Loui " conglom rate, extends from a point con iderably outh of Calum t well toward the end of Ke' eenaw Point; the Kear arge flow has been traced for 40 miles. Doubtle there are l}umerou flow not so ea. ily recognized and followed that persi t for mile . At everal horizon there are serie of relatively thin flow which can be traced, collectively, for long distance , thou(l"h it i rarely po ible to correlate the indi idua.l flo, between di tant outcrop . The Pewabic flo\ , in the northern pa.rt of the di trict, nnd the Ever(l"reen and su ceedin(l" flovv , in the southern part, are of thi character. Lane believe that he can recogniz om of the individual flow of Keweenaw Point in the utcrop on I le Royal, which li 50 mil di tant, near the north ide of the Lake upcrior ba in. THICKNESS There is a notable variation in t.he thickne s of the portion of the Keweenawan eries compo ed predominantly of lava flows at different points along the range. The total thickne of the series i nowhere known, as it everywhere abut again t the Keweenaw fault. In Kew enaw County the thicknes between the Great conglomerate and the Keweenaw fault is about 15,000 feet. t Calumet about 11,000 feet is exposed between the Great conglomerate and the fault, but the fault apparently cuts the serie at a much higher horizon here than in Keweenaw County. ear outh Range about 11,000 feet is expo ed, but here the fault cuts the series much lower than at alumet. At Victoria probably not more than ,000 feet i expo ed
/ THE COPPER DEPOSITS OF MICHIGAN between the Great conglomerate and the Keweenaw fault. The beds that have been most definitely correlated through the di trict are the Great conglomerate "St. Louis" conO'lomerate near alumet and with tb Bohemia conglomerate in eweenaw ounty. Th~ correlations are probable but not certain. Lik. wise No. ~~nglomerate in Ontonagon County i u:t pos1tivel known to be the extension of No. at Portage Lake but is thought to be. ' ' f E>-1--+--'-'CIIark O.D.H.4 --4+--MandBn D. D. H. 6 ' ., oo Mt:~ndou·l'l-onten8c Sec. 7 + + ,A.<wLI,anifov-Frontenoc Sec .J f f f f f f f f f 'Central O.D.H. 2 /;r ' ' ' . ,' . ' f . ' ' ' ., ""
'"'
~;::t t=;J=:=8r:tJiff D.O. H. 3 tiff' " e=>i~A::=:::::::j:==?ci:-iliff " lil'f' " :.e 1--0.iibwtJy No.I ' 1',';-~;:g: IY,o.j : + +-.JVJMohtJwk 21st crosscut : at Ahmeek No.2 shaft
u.D.H. " " " I shaft r==;a.o.H. af N. Ke8rsarge No.4 shaft It i d: P,, + 1--+-IWo/veri ne lith level crosscut + 4---L Centennial DD.H. 12th level e--t-~, ! 1--'C&H. D.O.H C Bnd A at No 20 shaft
r--C&H 8/st crosscut ', aunum " ,, -7-aurium "
:a Salle D.D.H 12 8 Salle " " a aile " a aile " 6-9-IO Franklin Jr. 32crosscut , ' ,' . ' ' . ' f ' ' . ' . '. ,, ~;=:=l=::/~ D. D. H. J EXPLANATION Arrzygd(J/otd j Trap FIGURE I.-Variation in thickness or Kearsarge flow If these correlations are correct it is apparent from an examination of Lhe plate showing correlation of sections that the greatest thickness between conglomerates o. and No. 15 is at alumet, where it i about ,000 feet; at Franklin it is about 6,000 feet; at South Range it is little over 5,000 feet; and at Winona and farther south it is little more than 4,000 fe t. The greater thick ning in the vicinity of Calumet seem to b due, in la.rge part at least, to th pre ence of the "Big" trap above o. conglomerate and to 1,000 to 1,500 feet of thin flow that seem to be largely ab ent at Portage Lake and farther south. omewhat imilar thinning seem to occur northward into Keweenaw County. Th~re is a tendency to thinning outhward higher in the serie , as can be seen by inspection of the plate, but it is much le s marked. Between th Allouez conglomerate (No. 15) and the Great conglomerate ( o. 22) the greate t recorded thickne s is about 4,000 feet at Eagle Ri er. At alumet the interval is about 3,000 feet. outh of Calumet it i about 2,700 feet at Franklin Junior and about 2,400 feet at outh Range. The greatest cau e for variation in tbi part of the action is the difference in thick· ne s of the Green tone flow. The individual flow vary greatly in thickness from place to place. In general the more extensive flows are thick; the Greentone flow has a maximum thickne of 1,300 feet in Keweenaw ounty; the "Big" trap exceed 400 feet, and the Kear arge flow (fig. 1) exceeds 200 feet. The e great flow commonly thin rather gradually from their thicker portions, as is well shown by the Greenstone flow, which thins southward from Keweenaw County, where it forms the great Greenstone Cliff, to only moderate thickne at Calumet, and which can not be positively identified south of Portage Lake except by its relations to other beds. An inspection of Plate 2 will show the rather gradual thin· ning of other flows thouO'h some thin rather ' o ( o. 22), the Allouez conglomerate (No. 15), and the No. c~nglomerate. The correlation of .r o. 8 is not as certam as that of the other two. The No 8 abruptly, as the Mandan flo north of De a· ware, in Keweenaw County and the thick flow above No. 8 conglomerate near S~uth Range. cong omerate at Portage Lake is correlated with the Although certain flows can be traced for long di .· tances, and in certain places and horizons all the indi·
STRATIGRAPHY 'dual flows throughout a considerable thickness can closely correlated, at other places and horizons ~ere is little certainty in the correlation of individual beds even in sections but a short di tance apart, thou~h there m~y be an.d frequently is a good correlation of the general senes of flow . In certain portions of the series the flows over long distances are prevailingly much thinner or thicker than the general average. One persistent belt of thin flows lies above the "St. Louis" and No.8 conglomerates; with the exception of the heavy trap that is immediately above the conglomerate in places the flows in this belt, for several hundred feet statigraphically, are thin, many being only 5 or 10 feet thick. To ales pronounced degree this is true of the belt above the "Mesnard" epidote. The flows for several hundred feet below the Allouez conglomerate or between the Allouez and Kearsarge conglomerates, on the other hand, average unu ually thick, many of them reaching 100 to 200 feet or even more. In addition to the broader variation in thickness of the flow over long distance di cu ed above and shown on the geologic maps and sections, there are local variation due largely to irregularities in the top of a flow or of the ·urface on which it re ts. The urfaces of some of the flows are irregular and hummocky, bowing diff r nces in altitude of a much a 20 feet or even more. It i vident that the thickne s of a flo, measured from the top of the hummocks would differ mat rially from the thicknes measured from the bottom of the depr ion , e p cially if the How hould r ton one with equall iiTegular top and a depre ion in the upper flow lay over a hummock in the lower. In the flow with fragmental tops, in which mo t of the copper depo its occur, marked variation in thickne s are the rule and make a clo e determination of the thickne of a flow from place to place impo ible. In general it may be aid that the fiow having cellular or smooth tops are th roo t uniform in thickne and those having fragmental or rough top the lea t uniform. edimentary deposits commonly approach a pl!ille. The base of a flow that re t on a conglomerate, and- ~ne, "scoriae ou ' amygdaloid, or cellular amygdalotd will therefore be a nearly plane urface; a flow that rests on a fragmental amygdaloid will have an uneven ba e, and it thi kness will vary accordingly. COMPOSITION OF FLOWS 'rhe great bulk of the flows of the Keweenawan series are ba altic, rather simple mineralogically, and monotonou ly similar in appearance. The di trict cont · f ams, however, numerous typ s of lava grading rom typical olivine ba alt through ande ite to rhyolite. 'rhe more basic flow are typical olivine basalts co.md P0 ed e entially of feld par, pyroxene, olivine, an m th a~net1te, the last two now largely altered to 0 er lnllleral In the flow of more andesitic composition olivine decrea e and di appears and the proportion of feld par to pyroxen increa es. Biotite has been noted in the feld pathic flow but i not common or abundant. Toward the 1i higan tat line, north of Lake Gogebic, are feld pathic flow , with a very low proportion of dark mineral but without visible quartz phenocry t , ' hich approach rhyolite, and farther outh, in Wi cousin, Aldri h 21 noted rhyolite porphyry flow , which al o occur in the eries north of L ake uperior. The Keweenawan flow are of the "plateau" type. ( ee p. 25.) In the following tabulation of analyse two of the typical K eweenawan flow are compared in compo ition 'vith plateau ba a1ts from other localities a given by Wa hington 1! and 'ith Daly s average basalt. Average composition of plateau basalts 5o. 61 4 7. 46 I 5o. o1 9. 3 : 6. 55 otdet. H20± fl20+ -- - --- - - 2. 04 -- Ti02- 39 t[n 100. 03 100. 29 1. Deccan basalts; 11 analyses. 2. Oregonian basalt ; 6 analyses. 3. 1'bu.lcan basalts· 33 analyses. 4. Bed o. 6.'i, En~le River, Keweenaw Point, Mich.; Lane, A. ., The Keweenaw series or Michigan: Michigan Geol. Survey Pub. 6 (Geol. ser. 4), p. 110. 5. Greenstone Oow, Keweenaw Point, Mich.; idem, p. 112. 6. Dnly's average basalt. The Greenstone flow ( o. 5) i an olivine ba alt; th Eagle River rock ( o. 4) is mor feldspathic but clearly of ba altic type. TEXTURAL TYPES The one out tanding chBJ·acteri tic of tho flows that is mo t u eful in their cla ification i th ir texture, which erves a one of the major base of correlation from s ction to s ction. Textural classification may be made in hand pecimen, drill core, or outcrop and gives to some extent an indication of the variation in chemical composition. Lane has di tingui bed four gen ral types-ophite, melaphyre, porphyrite, and glomeroporphyrite. The many variation of these type , which, ind d, grade into one another, are de ignated by modifying adjectives, uch a feldspathic. Lane al o recognize dolerites, which are a coar e or pogmatitic faci s of an of th other . 11 Aldrich, H. R., Econ. Geology, vol. I , p. 570, Ul'tl. " Washington, n. ., Deccan traps and other plateau basalts: Ocol. 'oc. America Bull., vol. 33, pp. 774, 779, 789, 1922.
THE COPPER DEPOSITS OF MICHIGA There may be differences of opinion as to the appropriat ness of th names u ed in thi classification, but to anyone who has examined drill cores from thi serie of rocks there can be no doubt as to the u efulne s of the di tinction . The textural features that have been empha ized come out very strongly on the ground urface of drill cores, a can be een by reference to Plate 56. Lane's classification has therefore been us d in the maps and sections accompanying tl:)is report. Ophite.- Ophitic texture is the roughly circular mottling of the rock produced by crystals of pyroxene that urround and inclose the feldspar crystals (pl . 56, 57). The ophitic lava arc the "luster-mottled melaphyres" of the earlier publications on the di - trict. The size of the pyroxene cry tals varies with their di tancc from the contact of cooling and somewhat with the composition of the lava. Lane 23 has given an exhaustive di cussion of this subject and its application, which need not be repeated here. Rouo-hly he finds that the size of the pyroxene increases 1 millimeter for each to 10 feet of di tance from the upper or lower contact of the flow. It i needle s to say that this fact i of great value in studying the flows having ophitic texture. In some of the thick flows, like the Greenstone flow, the crystal are 2 inches and more in .diameter, and their outlines are not readily traced in the ordinary sized drill core, but they are con picuous on a weathered surface, where the center stand up as knob , and in fre hly broken rock they can be seen by the fla hing of cleavage faces. Where inclusions have been dragged into a flow the mottling around them is finer than elsewhere at a corre ponding distance from the surfaces of the flow. Thi may account for some of the ophites of varying or banded mottling. Porphyrites.- The porphyrites are rock that contain well-defined cry tals, usually of feldspar, of an older generation than the same mineral in the groundrna . Glomeroporphyrites.- In the glomeroporphyrites the feld pars show a con iderable variation in size, though not so definite a difforen e in size and time of formation a is shown between the feldspar phenocry ts and the groundmas feld pars in the porphyTites. The larger fold pars are collected into bunche or clots. Melaphy1·e.- Melaphyre is a term appli d to rocks that . how none of the distinctive textures indicated above. Many bed that show a distinctive texture near the center lose it near the margins, and many thin flow do not how a distinctive texture in any part. There are also orne flows 100 feet or more " Laoe, A. C., Michigao Oeol. Survey Pub. 6 (Oeol. ser. 4) , vol. 1, p. 145, 1911. in th.ickne that how no distinctiv texture and cla sed as melaphyre. Dolerite.- Th term dol rite i u ed to de i t · · · h l f · gnae p~1 twn , ill t . e a vas o certaill typo , in which lhe mm rals, e pemally the f ld~~ars, are unusually cos~ and the rock. ha . a p ~mat1tic texture. Rock of th~ type. occm· ill the th~cker beds and i regarded as portwn. that. cry talhz d late. It is allied to the pegm.n.tlte fame of om intru iv rock . The term d?lente has been u ed by some petrographers in 8 different ense. RELATION OF TEXTURE TO COMPOSITION The oph.itic texture is b t developed in the more basic la a , wh re it i conspicuous even in the thin flows and v ry near to th margin of the thick flows. In thC' m~ro feld pathic lavas th ophiti texture may be con p1cuou near the center of thick flow but 11b en t from th thinner flow nnd n ar the margin of the thicker flows. The porphyritic and glomeroporphyritic textures are characteristic of the more f ldspathic bed or tho e approachino- andesite, though ph nocrysts are pre e~t in orne oph.itic flow , a the K arsarge flow, LU which they are e pecially abundant just below the amygdaloidal top. The melaphyre texture, as alr ady indicated found in the less basic bed . The feldspathic bed' in the south end of the district show no definite texture and are of the melaphyre type. DISTRIBUTION OF THE DIFFERENT ROCKS Most parts of the ection are characterized by the predominance of one or another of the e textural types, which were produced by recurrenc of different phases of the eruption of lava. Below Io. 6 conglomerate (see pl. 15) the flow are prevailingly ophite , commonly of the banded type. For a few hundred feet below and everal hundred feet above o. 8 conglomerate, glomeroporphyrites and melaphyres predominate, especially from Portage Lake north to Keweenaw County. The eries of thin beds above No. 8 conglomerate are typically glomero· porphyrite . Between the Kear arge conglomerate and the "Mesnard" epidote the flows are typically ophites, and above the "Mesnard" gloroeropor· phyrite and melaphyres prevail. The flows above the Great conglomerate and below the Outer con· glomerate-the Lake Shore trap- are melaphyres. Commonly there is a transition zone of varying width between the flows of different types, in which the rock is intermediate and more variable in composition. In the south end of the district the "Chippewa" felsite, a siliceous rock of rhyolitic composition, forms a continuous belt in the upper part of the lava series and also crops out in the central area of the Por· cupine Mountains. This ro~k is similar in com·
STRATIGRAPHY po ition and character to some of the felsite intrusives, and its pre ence in the center of the Porcupine dome therefore natuTally suggested, to Irving and tho e who have studied it since, the possibility that it is intrusive and that the dome is of laccolithic origin. That there are intru ive rocks in this area is known, but those who have studied the felsite have regarded it as an elfu ive which has been domed with the other rock and have correlated it with the "Chippewa" felsite belt to the outh. CHARACTER OF ERUPTIVE ROCKS The Keweenawan flow clearly belong to the type of volcanic accwnulation known a plateau or fi sure flow , which are recognized in many part of the world. Washington 24 ha recently summarized the characteri tic of this type of flow in a paper from which the followin()' pa age i quoted: In various part of the earth and nt different geological horizons are large area covered by very ext nsive, generally horizontal series of sheets of basaltic lavas, the series of overlying flow often attaining thicknes es of thousands of meters. In some cases they are accompanied by flows of rhyolite. These basalts have poured out in an evidently very fluid condition, a they occupy preexisting valleys and cover the lower topogr~phic feature much like flood of water, the separate flowbemg very long-many of them measured by miles. It is generally a umed by volcanologist that these xtensive, horizontal, very fluid flows ha e i ued quietly from fi - sures-an idea first suggc ted by ir Archibald Geikie.z6 Volcanic cones, formed of Java , ashes, or both, are present in pl~c~, but these are inconspicuous, being low because of the fimd1ty of the lavas, and they always form a very minor feature of the complex. uch lavas are called variously "fi ure" or ' plateau" flows. The term "plateau" is u ed here b cause the word "fis ure" co~notes the mod of origin, which is still omewhat uncertam.
It is well known that the lavas of these plateau eruptions are mostly basalt, and this petrographical character is the u ually accepted explanation of the great extension and horizontality of ~he sheets, since basalts generally are known to be notably fusible at a lower temperature and more fluid when fu ed than are m il' · ores ICIC lavas. But ba alts vary much both chemically and modally, and many of them a.r evidently on extrusion less fi ·d
· , Ul than are those of the plateaus. This is e pecially true of the basalts of many volcanoes of the xplo ive type the flowsohl'hd ' I'd ;v He o not extend very far and are oft n found conso 1 a ted on steep slopes, as was pointed out nearly 100 years ago by Lyell. Aft d' er 1scu IDO' the Deccan, Oregonian, Thul an or ~~rthern Atlantic, Siberian, Patagonian, Algonkian ew~enawnn ) , and Palisade ( ew Jer ey) r gion , a hmgton r ache th following conclusion : We may n basalt ow summanze the general characters of the plateau fiss s. Structurally, they have characteristically issued from by ur7s, although this quiet extrusion is sometimes accompanied ffilnor expl . t' . T ver ostve ac tvtty. hey form horizontal flows of limy great extent, indicating a high degree of fluidity at the
e:-.1.rusion. The flows are individually of considerable 11 Wash! gto Bull., vol n, 1:!. S., Deccan traps and oth01 plateau basalts: Qeol. Soc, meriCll u Nat · PP. 765-804, 1022. urc, November 4, 1 o. thickness, and the total thickness of the series of uperimpo ed flows !s very great. Ash bed and layer of scoria are not abundant. In several regions the ba alts are a sociated with flows of rhyolite or toscanite, while accompanying andesite and t rachyte are rarely met with, and lenadic lava , such as phonolite or tephrite, seldom or never occur. They have been extruded at very different geological epochs, from the pre-Co.mbrian to recent times. Megascopically, they are very dark, black or occasionally brownish black, rarely dark gray. In granularity they may vary from rather coar ely doleritic to densely aphanitic, some few being evidently highly vitreou . Ve icular forms seem to be rare as compared with ordinary basalts of volcanic cones The great majority are aphyric, but there is some tendency to a porphyritic development of the feldspar, especially in the Thulean region, forming a special textural type. Augite seldom forms megaphenocrysts, and these small and sparse, whi le olivine phenocryst are very rarely present, except in some of the Algonkian and Palisadan [Trias ic] diabases. Chemically, the plateau basalts differ materially from other basalts in one or two features. In the table are given the averages of analyses of basalts of various regions, with the average basalt as computed by Daly from 161 analyses of basalts so named by the authors.26 [ ee p. 23.} The averages of the three most typical plateau basalt regions-the Deccan, Oregonian, and Thulean-are closely alike. The chief difference is seen in the much higher amount of iron oxides, with ferrous oxide greatly preponde.rating over ferric oxide. In the typical plateau basalts the combined iron oxides would amount to about 14 per cent or more, and this is the more marked if only the most abundant group of the more fernie basalts are considered. I am inclined to think that the comparatively high ferric oxide shown in Daly's average is due in part to oxidation of ferrous oxide through slight alteration and in part to defective determination of the ferrous oxide-a not unusual analytical error. The percentage of titanium dioxide is appreciably high in the plateau basalts. It would thus appear that the plateau basalts differ from what might be called the cone basalts essentially in the higher iron and titanium content of the former and possibly in the relatively less oxidized condition of the iron. This must be considered as a broad general distinction. Examples may be found among typical plateau basalts in which the iron oxides are not specially high, just as examples may be found among cone basalts in which the iron oxides are much higher than the average. Mineralogically, as we have seen, this chemical difference is expressed in the presence of highly ferromagnesian hedenbergitic enstatite-augite in the plateau basalts, in contrast to that of highly calcic or diopsidic augite in the cone basalts. It may also find expression in the striking tendency of the augit-e and magnetite to be among the last minerals to crystallize; so that the glass present in the not wholly crystallized plateau basalts would have a. composition corresponding to a mixture of augite and magnetite, examples of which we have seen on the island of Skye, in Colorado, and possibly elsewhere. The preceding descriptions of the plateau basalts, showing that one of their main chemical characteristics is the high percentage of iron oxides, and especially of ferrous oxide, furnish an explanation of their great fluidity at the time of extrusion. It is a matter of common observation that basalts generally are fusible at a lower temperature and are more fluid when molten than are more feldspathic or more silicic rocks. It is also well known that ferrous silicates are more readily fusible than are magnesium or calcium silicates. The experience of iron and steel workers and smelters bears testimony to the lower fusibility and greater fluidity of slags containing considerable iron.
te Dilly, R. ..\m. Acnd. Proc., vol. 46, p. 224, 1910.
THE COPPER DEPOSITS OF MICIDGAN Inasmuch as the fissure eruptions which furnished t~e plateau basalts show light explosive acti vi~y, it to j)e mferred that the magma contained comparatively little gas,. so that the effect of this class of components in lowering the fusmg point or increasing the fluidity hould be less than in ordinary basalts of the explosive cone type. We seem, ther fore, o be justified in ascribing the peculiar phy. ica~ co~di~ion of the e basalt during their extrusion chiefly to thetr tron content. It is clear that the Keweenawan flows belong with the plateau type, that they \ver probab~y crup~ed from fissures, and that they were highly , formmg sheet of nearly uniform thickness over large area , a feature in which they approach sedimentary formations. Whether their great fluidity was due primarily to the p.igh iron content, to a high initial temperature, to high gas content, or to a combination of the e conditions is not so clearly established. LOCATION OF VOLCA.NIC VENTS Although it seems likely that the flows issued from fissures, there is no positive evidence to indicate where these fi.ssmes were located. It has been suggested that the Keweenawan dikes, which, as Van Rise and Leith 27 point out, practically surround Lake uperior, fill the fissures through which the lava..s issued. The same authors consider it possible that similar vents may underlie Lake Superior. The presence of d epseated intrusive rocks near the Keweenaw fault has led Lane 28 to believe that the fault is possibly the fissure through which the lavas poured. Hotchki believes that fis ures centralized within the Lake Superior basin were of chief importance as lava vents and cites evidence to support this view. The work on which this report is based has added little positive evidence of the direction of flow of the lavas. The "pipe" amygdules, however, which have been formed at the base of some of the flows, are in places bent away from the basin, or up the present dip, suggesting a flow from the north or from some locality within the basin. The Calumet & Hecla conglomerate also thickens down the dip, and the cross-bedding in places suggests currents from down the present dip. Both these facts seem to indicate that the lavas came from the north. As i pointed out in the discussion of structme (p. 50), there is reason to believe that the Lake uperior basin was being formed while the lava series was being built up. The filling of the basin could have been accomplished either by lava flowing into the basin from the rim or by lava issuing from fissures within the basin. If Lane is correct in correlating beds on opposite sides of the basin, it would perhaps be more likely that the lava flowed outward both north and south from vents withi.il. the basin than that it originated on one side, filled the basin, and then extended completely across. 11 Van Uisc, C. R., and Leith, . K., U.S. Oeol. urvey Mon. 52, p. 411, 1911. II Lone, A. ., Unexplored parts of Keweenaw Point: Lake Superior Min. lust. Proc., vol. 17, p. 135, 1912. "notobkiss; W. 0., Tb,e Lake !lperior geosyncline: Ocol. Soc, America Bull., vol. 34, pp. 669-6781 1923, A 1YGDALO!O Ea. h flow is m~tde up of two major part , which grade into e~tch other. The larg r part in mot flows, especially in the thick nos, i a rna ive rock, varying, principally in textur , from enter to bot~m and top. This is the trap portion. The top of the flow, usually to a depth o£ er~tl feet, is porous and cellular. Tbis is the amygdaloid portion. u uall an amygdaloid porti u n t the base also, but as a rule it is only a few inches in tbicknes . TRAP The trap makes up 80 to 90 p r cent of the ~tal thickne s of the thicker flows but constitutes a smaller proportion of th thinner flow . It is a dark-gray or greeni h-gray rock, ordinarily of rather uniform app arance except for grain. It is commonly much cut by joints of varying directi ns, which cause it in mining to pre ent blocky, angular surf es that serve to distinguish it, even on dust- overed faces, from the "shorter" or more granular fracture of the amygdaloid. Only in the Greenstone and a f w other flows, and there crudely, has the columnar jointing so common in basalts been observed. As has been noted generally in other regions and emphasized particularly by Lane for this region, the top and bottom portions of the trap are likely be of finer grain than the middle portion. Thi variation in size of grain, especially in the ophites, may be constant that it is possible to determine approximately the distance of a pecimen from the margin of the flow by determining its average size of grain. As a rule, the thicker the flow the coarser the texture of it middle portion; in the Greens tone flow, for in tance, the coarsest material is composed of grains 2 inches or more in diameter. In many of the coarser-grained flows, the presence of large crystals of pyroxene with included feldspar crystals gives the peculiar spotted ~q>pearance that characteriz s Pumpelly "lu ter· mottled melaphyre" and Lane's "ophite." A notable variation within some of the thicker flows is afforded by lenses of coarse pegmatitic material rich in feldspar and frequently in iron oxide which Lane has called "doleri tic" bands. These are present in the Green· stone flow and other large· "ophites" but are more abundant in the more highly feldspathic flows. The trap of certain flows, notably those in the Asbbcd group, contains small laths or plates of lighter-colored feldspar scattered more or less sparingly through the fine-grained groundmass. In some flows and possibly in all there is a slig~t tendency toward the concentration of more basiC material near the bottom by settling. At the base of the amygdaloid of the Kearsarge flow there is a .z~ne from a few inches to several feet thick contaJDJDg abundant feldspar phenocrysts that collected by ri in~ from the underlying lava. But such evidences 0 gravitative segregation are relatively inconspicuous.
STRATIGRAPHY The most noteworthy chemical variation in the flows is an increase in ratio of ferric to ferrous iron from bottom to top. This feature is discussed on page 34. In the early days, before the true character of the rocks had been ascertained, the "amygdaloid" and the "trap" were not recognized as parts of a single geologic unit but were regarded as independent bodies, and a more definite distinction was accordingly made between them than would be made now. The commercial importance of the amygdaloid as contrasted 11~th the trap has, however, caused this distinction to survive long after the geologic relation of the two had been recognized, and even now there are many who do not clearly realize that a given layer of amygdaloid is any more closely connected to the underlyillg tr"ap than to the overlying one. The trap represents that portion of the flow from which the gas had escaped before consolidation and crystallization of the rock took place; the amygdaloid repreents the upper bubbly or frothy crust in which the ri ing gas bubbles were frozen before they could escape because the top of the flow consolidated more quickly than the main portion underneath. The thin amygdaloid layer at the base of a flow was likewise produced by the freezing-in of gas bubbles. BOTTOM AMYGDALOID LAYER Many descriptions of flowing lava refer to the continual falling down of solidified lava blocks and fragments over the advancing front of the flow, which overrides and buries them. This would imply that at the bottom of the flow there should be found an accumulation of fragmental material of the same nature as that which makes up the brecciated tops; indeed, some descriptions mention the frAgmental layers at both top and bottom of flows. In the Michigan lavas no such fragmental material is consi tently pres nt at the bottoms of the flows. ExarrUnation has been made of the bottoms of many flows, including some of both the smooth-top and the brecciated or rough-top types, without revealing fragmental material that has been dearly rolled under. At the bases of some flows that rest on sedimentary rocks, however, a few feet of amygdaloid is found in some places. As this basal amygdaloid is particularly well developed in flows resting on sediments in its stronger development has not been noted ~flows resting directly on other flows, it seems more likely that it has resulted from some characteristic of the underlying bed- water content, for examplethan from material rolled under the advancing flow. 0 evidence has been seen to indicate that fragmental material that may have been rolled under the flow was either remelted or was floated up into the flow. The same statement applies to the material of the underlying bed. All the evidence indicates that the bottom froze very quickly, though where a flow covered very open-textured material th la,va, filled. the spaces between the fragments for a short di tance below the surface. This is especially noticeable where a flow covered coarse trappy fragmental amygdaloid. Characteristically the basal amygdaloid con ists of a lower layer of finely amygdular rock, u ually not more than an inch in thiclme s, and an overlying layer containing larger amygdules, which in some places are elongated upward and are then called " pipe" amygdules. This second layer i commonly onl or 3 inches thick but may be a foot or mor , and the pipe amygdules range from a fraction of an inch to more than 6 inches in length. The pipe amygdules are not strongly developed in all :flow . They are well shown at some places in the flows that overlie the Kearsarge flow, the Calumet & Hecla conglomerate, and the Pewabic lode and in certain flows in the Mayflower-Old Colony mine. Other flows, a those above the 0 ceola, I le Royale, and Baltic lodes, how very little ba al amygdaloid. Usually the pipes extend upward perpendicular to the underlying urface, but at orne plac s in the flow above the Calumet & He la conglomerate and in the Mayflower-Old Colony mine the upper parts of the pipes are bent over in a common direction which is believed to be the direction of flow. The basal amygdaloid above some sedimentary beds may reach a few feet in thickness and be distinctly fragmental. The evidence seems to indicate that the basal amygdaloid was formed by the rapid cooling of the lava in contact with the underlying rock. The thin layer immediately above the cooler rock solidified very quickly, and the ga liberated from the lava was ntrapped small bubbles. hove this bottom layer there was more time for the gas bubbles to collect and coalesce, and much larg r on were formed. Under certain condition these bubbles expanded upward into the le vi cous lava, forming the pipe-shaped cells which, when later fill d with minerals, became pipe amygdul . The fact that the ba~al amygdaloid i more strongly developed above sedimentary beds than above other flows suggests that the gas that filled the caviti may have been in part d rived from the underlying material and also that th edimentary beds contain d more water than the flows. Such water -wa converted to steam and ab orlted by the overflowing lava and wa thus a factor in the formation of the ba al amygdaloid. The thinness or ab ence of basal amygdaloid in :;ome flow may mean that the lava flowed over a. 6Urface not yet cooled and that solidification wa slow enough to permit the gas to escape before the lava became sufficiently viscous to retain it a bubbles. TH.E LAVA TOPS VARIETIES The copper derived from the amygdaloidal tops of the lava flows has amounted to nearly half the total prod,uction from the region and now exceeds that
THE COPPER DEPOSITS OF MICHIGAN from conglomerate lodes and fi sure combined. The greatest part of thi production from amygdaloids has come from only six flows of the scores that are present. It is essential, therefore, that the character and method of origin of these upper parts of the flows b under tood if a clear idea i to be gained of the condition that determined the deposition in them of commercial ore. The tops of lava flows have long been divided by geologi ts into two general types- smooth tops and rough tops-to which the native Hawaiian names, respectively "pahoehoe" and "aa," are commonly applied. The smooth tops are highly vesicular or c liular; the rough tops less so. Both types are plentifully represented by the Keweenawan flows, and the differences between them are such as to affect materially the ease of copper deposition in them. The smooth tops may be further divided into normal vesicular tops and coalescing ve icular tops; the rouO'h tops are separable into fragmental or brecciated tops and scoriaceous tops. (See pls. 58-61.) In their typical development the different types of tops are perfectly distinct in character, but th re are all gradations between the different types in different I flows and between most of the types in some single flows. Thus the Kearsarge lode has in some places a 1 typical cellular top, in others a well-developed fragmental top. The same is true of some of the Pewabic flows. The Ashbed flow is typically scoriaceous but locally fragmental. Many flows, however, have a tendency to be either cellular or fragmental over long stretches. The tops of the thin series of flows above o. 8 conglomerate are rather typically cellular. The Osceola flow and other flows have fragmental tops for many miles. The thickness of the flow does not seem to control the character of the top. Many of the thin flows have cellular tops, but the tops of thick flows may be either cellular or fragmental. More of the fragmental tops occur, however, on thick flows, though there are numerous examples of fragmental tops on relatively thin The differences between the rough and the smooth tops go far beyond mere difference in texture of surface; the smooth 1!s>PS approach much more nearly a. plane surface, but the rough tops were hummocky u.nd irregular, with differences in altitude of probably 30 feet. This difference is brought out strilringly in the drifts that follow the tops of the flows. In the 'Pewabic lode, a smooth-top flow, the drifts are essentially straight for hundreds of feet, but in the Osceola lode, a rough-top flow, they are exceedingly irregular. SMOOTH TOPS The most notable differences in the smooth tops arise from the size and distribution of the gas bubbles or vesicles, now chiefly filled with minerals to form amygdul~l? t Jn ~he prevajlin~ class of smooth tops the vesicles are abundant, of mod ro.t size, and arranged more or less d finit ly in la er parallel to the mface of the flow, so that the rock commonly has a banded appearance. Generally the amygdules are small and abundant near the top and increase in iz and decrease in number de per in the flow. The layers may be closely spaced or may b separated by layers of rock containing relativ ly few amygdules, several times as thick as the diameter of an averag amygdule. Irregular spacing of the layer is the rule, though in plnces in the P wabic lode (see pl. 56) there is an approach to regular spacing. The individual vesi les are for the most part not spherical but flattened in the plane of the flow, orne being d cidedly clon()'ated and a few showing a tendency to be flatter on their upper ide. The distribution of the v sicles in layers and the elongation of the icles in the plane of the lode have commonly been ascribed to flow movement in the lavas. It seem likely that the banding in the Michigan flows may be el\.'Plained a follows: A period in which many rising gas bubbles collected under a solidified surface was followed by a period of relatively rapid consolidation when few bubbles collected, and this in turn by another period when many bubbles collected, and so on till a depth was attained where the gas was not present in sufficient quantity to form vesicles. The amygdules are fewer and the banding less di tinct near the base of an amygdaloid. simi· Jar grouping of vesicles is present in slags olidified in pots where there is no flow movement of th liquid. The individual bubble in a layer may b eparated by rock tuff exceeding th ir own diameter, or they may be so closely spaced that two or mor adjacent one may coalesce into a unit that is of irregular hap because the lava had become too viscous to pennit the enlarged bubble to a sume the usual rounded fonn. In this way some extremely irregular amygdule may result, and those that are large and conspicuou , a in places near the bottom of th vesicular zone, con titute what Pumpelly and Marvine called "p eudo-aroyg· dule ," on the assumption that they were formed chiefly by replacement of rock rather than by filling of gas cavities. Some amygdules were lightly en· larged by replacement, but there is little to uggest that this process took place generally or on a large scale. Rarely if at all in this or in any of the oth r types of tops is the degree of vesiculation such as to justify the term pumice. A structure more like that of Swis cheese is the common one. Permeability is the quality of the amygdaloid tops that makes them more receptive to copper depo ition than the traps. The cellular or banded vesicular rock of the smooth-top flows is more permeable than non· vesicular rock, such as the underlying trap, for t~e reason that in a given volume of it only part is solid rock. A rock iP. which the vesicles make up 50 per
STRATIGRAPHY cent by volume would have twice tb perm ability of otherwi e imilar but nonve icular rock. But this cellular rock has no thTOUO'h-going and continuous opening , ·uch a would f~vorable to high p erme~ bility; instead, each openmg 1 of small extent and 1 walled off from other openings by olid rock. The difference in permeability b tween the cellular tops and the brecciated top i therefore very great, and for this rea on the mooth top of the normal sort contain little copper as comp.red to the rough top . A subdivision of the cellular type of smooth lava top is recognized in hich the individual vesicl are much larger, reaching an inch or mor in diameter, at least in certain layer . Many of these e icle in the arne layer coalesce into a thin, jagged gash that may attain a lateral extent of as much as 10 or 12 feet in a ingle cro section and perhaps form a connected opening for cores of feet in the plane of the flow. Rock containing the e openings may be called a coale cing top, or "lode." A series of uch openings with little rock material between may con titute almo t unbroken opening for long stretches along the plane of the flow. avera! such open layers may occur in the ame flow top. Where the degree of coal cing of the ve icles isle than that ju t described, the large ve icle , now filled with min ral , may be lo ely enced lilce beads on A. tring. The cau e of thi oalescing of the ' i les is probably to be found in the diD' ring t mp rature and gas content of the lavas. Th b st-lmown xamples of the conle ing cellular top ar th Pewabic lodes. These flows are thin and hav ropy surfa s in places. They are o sm oth and ven that the Quincy mine ' orki.ng , whi h follow them, are e s ntially strai()'ht for hundr ds f feet. The top or e icular portion of the flo, s are only a f w f et tlli 1- but v ry regular, and the banding au d by th larger and the s~1aller ve i ular openings is strikin()'ly· even and perSistent. ( ee pl. 5 .) All th relati ns su()'gest thn,t thee flows were v ry fluid and relati ely full of gas when the ' er poured out. Th y prelid \Vith tops almost a flat and smooth as that of a lak . Po ibly flow had a ed befor a crust had form d, but if not, the flow of lava und r the crust di turb d it v ry little. In the highly liquid lava, the rising ga bubbles were able to com bin int much larger ones that, on r aching the ?ottom of the crust at any given sta<Ye of its for- ~A.tJOn, oal seed commonly into th exten ive flat aye1 alr n,dy de ribed. In other parts f th se flows, howov r, the top are broken into n, typi aJ breccia or "fra )"mental " am gdaloid. The economic significan e of thi modification of the smooth-top flow is that the r ulting ro k is of lnuch higher p rm n.bility and th rcfor much more . usceptible to replacem nt than the normal typ , with ~ts small and more evenly distributed vesi le . The road, flat op nings in this conJe cing facies are separated by only short distances from other similar openings, so that lu tions could move for a long distance parallel to the {low surfa e without having to penetrate solid rock for more than a small fra ti n of that distance. It is a striking and significant fact that of the six amygdaloid lodes that ha e been larO' produ ers of copper, only one is of th smooth-top type, and that one, the Pewabic lode or series of lodes, is of this relatively more permeable coal scing variety. Other flows lower in th s ries show a similar structure but not in so marked a degre a the Pewabic lod s; no ore has yet been found in them. FRAGMENTAL OR BRECCIATED TOPS Character.- The rough-top flows, as ahead indicated, are much less numerous than those of smoo h top, but they are of e pecial interest because four of the six profitable amygdaloid depo its are predominantly of this type and the other two are in part of this type. Mo t of the other amygdaloid d posits that have yielded con iderable copper are al o of this type. The br cciated top consi t of fragments of lava ranging in size from minute grain to rna ive block everal feet in dimen ion. Ordinarily the individual fragments are under 6 or inches in diameter, and the average size i les than half that. In consequence only rarely doe one of the larger blocks or slabs project noti eably above the general level of the flow urfa e. These flows, therefore, though classed in the rough-top type, ha e a surface le s rough and blocky than that of th modern flow to which the name "aa i commonly applied, and the general smoothne and regularity of the bottom of the overlyin()' flow how that the e brec ia tops have not been chang d from a rou()'h, blocky condition to their pres nt state by cru hi.ng and packin<Y due to the w ight of rock above. In hape the frn,gment range from labs or irregularly angular piece through subangular to rounded. In ()'en ral the lar<Yer piece are the more angular and tho sma.ller ones more rounded, though many smn,ll piece are angular. Large and mall fmgmouts are pronli uou ly jumbled together, though in some flow the mailer fragment predominate near the top and the lar()'er one nen,r the bottom of the fragmental layer. The general accumulation of materin,l give an appearance not unlike a conglomerate, and probably for this reason it has ometim s been called "amygdnloidal conglomerate," though that term a used by Lane appar ntly does not include these brecciated tops. There is considern.ble variation in the textw·e of different fragment , ven of those that are contiguou . A rounded piece entirely urround d by a fine-O'rained margin but of coarser center may lie again t one that is rath r uniformly amy()'dular and anoth r of
THE OPPER DEPOSIT OF MI HIGA fine even grilin · or a p1 o may be fine grained oo one id and gradu ally become coar er toward the other . ide. maller pieces ma be uniformly fine or com e, though ev n those not more than an inch aero s may >;how marked difference in textm . The greater number of the e fragments ' ere vo icular and are now amygdular thr ugh filling of the ve icle . ome of the fragment how th band d arrangement of y icles a in the tops and undou htedly were broken from a larger structure of that kind ; others may exhibit, pA.rticularly near their margins, an arrang ment of icle more or le s parallel to the outline of th fragmen t. In many fragments the vesicle near the urfacc are mailer than tho e farth r in. Very commonly an outer shell a fraction of an inch thick i of den c material containing coun tle minute, even mi roscopic vesicle ; it clo ely re embles the thin lay r at the very top of the mooth fl ow and i clearl the result of quick chilling. orne fragment howing thi chilled margin around part of their periphery may be coarser grained for the remainder of their ircumferen e, a if broken awn,y from a large rna aft r the chilled urfac had formed and after the in terior part had olidifi d. till other fragment have a fin ly granular, almo t trappy texture, but fine grain may al o b pre ent throughout a fragment in conequen e of rapid cooling. o t of the maHer fragment con ist of the mor finely ve icular material, and mo t of the larger one of the more coar ely ve icular, hut many xception are to be een. Th - space between the larger fragment are filled with finer ma terial of the arne general haracter grading down to fine par ticl s. In mo t of the fl ow tudied that po e the brecciated typ . of top thi mixture of fragmental material give pla e downward in the flow rather abruptly to the cry tallio trap. The contact between the two i 1ik ly to b irregul ar on a mall cale but appear mooth and rather regular when viewed broadly. The trap for a few feet und r the fragmental layer may contain included fragment of amyo-dular ro k similar to that in th fragmen tal zone but generall.v mor rounded, a if partly remelted or re orbed. The lay r of trap containing the e inclusion de ignated the "A.mygdaloid inclu ion 7.one." It i present in th traps not only under the hr cciated tops but at o und er ome <'Oriac ou top or o- alled amygdaloidal conglom erate , bu t it ha. not been een under th nonbroc iatcd mooth top . . In the top of the I le Royal and Osceola flow , which arc exc llont exampl s of tho brecciated type, th re may oc ur in the midst of the breccia layer lab of trap a f w feet in thicl ne and as much a 20 f t or even more in length. Thi material, called by th miner "vein Lrap, ' i likely to ontain partly r ·orbed nmygdul ar patche like tho e of the amygdaloid in lu ion z ne. The lab ar commonly para\. lel to the plane of th lod , but om may be tipped at an angl to it. Th fragm n n.l material undern ath the e lab i f the am character a that above them. In place the e lab how feeble pipe amygdule n th ir und r ide in ontnct with the lower IA.yer of fmgmeotal tuff. WI or thi developm nt of vein rap i ·on id rabl , th . eparation of th fragm ntal mnt rinl produc s a .ort of doubl1 lode. \modifies. ion of th a,n approach oward th hown in the K ar arol de. In th productive portion of thi lode a la r of ty pical frao-mental material ordinarily oc upie the upp r f w f t · the fragments are notabl. mall n nr th top and coa1 er below. ithou abrupt han e th fragmen t become larger downward, the frn.gm ntal ·hara t r b come le and Ie evideo , th v i I in r a age iz , and tho band d truc.ture a umes promin nee. In hort, the hi f haracteri tic of the mooth top are a aio d. But thi cellular rock underl ing fmgmeotal ro k i not e (lrywhere continuou over large ar a but i mpo d of blocks or fragment , a if h ru L had b n b1·ol en up while it wa till in a mipla tic conditi n. T h block may be tilted at an angl wi h the plan of th lod and how a tend en y to hill -d maro--i..n and coar er interior, ugge ting that the final cry taJlization occurred after the breaking, a ind ed i true of th mall fra · ment in the brecciated portion of the lod . I n place lava ha filled the pace between the blo k a s cement. Where he bre cia ted p rti n of the lode is ab ent or lightly developed, a ou t ide th productin area of the K ear arge lode and over c n iderable tract within the main productive area, the t ndcncy for the cellular portion to be broken into larg block · i much le on picuou or i ab ent. The c llular portion is in place compo d of everal mall flow or gu hes howing banded amygdaloid and chi.ll margin. The intermediate zone of the K ar arg top ha been called "cellular middle lode," to di tingui hit from the "fragmental lode" abov . I t i not pre ent . in all part of he lode and no t equally con picuou at all places where pre ent. A very little of the nmc sort of thing i een here and th r in the mid t of the I le Royale lode, which for the mo t part i of the brecciated type, and it i pre nt in part of th_e Baltic lode, e p cially m area where the lode 1 relatively thin. Still farth er down in tho K ear arg top below tl~e " middle lode" horizon the rock become coa1 er Ill texture, and the vesicle become le numerous and larger and how little tendency to gather in bands. This lower, chloritic zone of the K ear arge top
called "foot lode." Material of tbi character 1 common on the under ide of many of tho lod s, uch
TRATIGRAPHY a the Baltic, I le Royale, Evergreen, and uc ceding lode of that eries. till deeper in the K ar arge the amygdaloid inclu ion zone occurs locally, though it i nowhere conspicuou and in mo t pla e i ab en t, and thi pa e , a u ual, into the main trap of Lhc flow. The Pewabi eric of flow lik wi illustrate cbnracteri tic of bo h the cellular and the fragmental . top . The top of the e· flow are chietl of . Lhc cellular and cellular oal cing type. In many plaee , however, the uppermo t foot or l of he lode coni t of breccia, which giYe pla downward to th rock with coa1e cing iclc . In uch place th breccia i ommonly made up of fragment of [e~cing lode mor r le w ll developed and obviou lyre u1tcd from the breaking up fa ale cing top that continued to form beneath it. In other place over large area the lode i t pically fragmental but of more uniform thicknc than i characteri tic of "fragm n al lode." Of uch character i part of the Ea. t lode in th lower level in the outh nd of th Quin y mine. Her the lod ehano-e within a f w fe t from typi ally oale cino- to typically utal. The fragmental portion ccm to b cUipticalin outline and to pitch rathedlatly ou thward; its lower portion xt nd below he min workirw and ba- n t b en tra cd. In th upp r 1 ,. l f th Quincy min the Main ' lod<' o\·er laro-c ar a i typi ally fragm n tal i much thicker Lh11n th co ale 'i ng portion of the l de and , hu;; th · irregularitic in tbi kne haracteri tic f fragm nLal lode . In th low r le,- l of he mine his lode i of Lh oalc ino1 Th z no f charwe wa· not en, a it lie in a worked out and caved porti n f th min . The top of th br c ia , thouo-h not coar ly jaga d, unduln.tc more mark dly han the nonfraamcntal top . Th fragmental material i pil d up in hummock or ridge , paratcd by ba in or valley . Tbc thicker br 'Cia natw'ally how o-r nt'r irrcaulariti b of urfa than thin fragmenLal la. ers like th I enr- . argo lod , but alt mati n of cl Yation fl nd d - pre ion are g nerally haracteri tic of the type. 1'he rnn.ximum rang from to1 of humm ck to bo torn of ao- i perhap 30 feet, and in place the lop from hummock t ba in may be t ep. Where thi undulating urfa of th brec in. tops, c?vered and pr rved by u ·e ding flo~ and later trlted, i f llow cl by the mine working , the hummock bulge up into th oYorlying flow, wh rea in the ba in ?r cl pre ion the ov rlying tro.p m to hula down ~nto the lode. The irr gulariti s ar economicall L~portant, not only becau e Lhey ne e ' iLato crooked '1Hne working but b cau e thi .k fl, ·cumulaLi n of breccia are found a a rul to be b tt r mineralized than thin one n ar b . It i not w rth that whore the frn.gm nta.l mo.t rial ha pi! up Rb . th g n rul urface of the flow it ha al o unk deeper into th underlying t rap, and onv rsely, wher depre ion occur on the breccia urface, the top of the trap i higher than el~ cwh re; thi produ e a podlike thi kenina and thinning of the breccia la e1 . Whether r not the e variation in tlu kne of the br ccia haYe any definite relation to th dire tion of lava flow ha not been determin d, but a om what y tematic repetition of ariation in ertain flow ugge t that there may be uch a relation. It i evident that the e layer of fragmental material mu t be mu h more permeable than the mooth top , even though the e ar highly and coar el ve icular. In part a a con eq u nee of thi gr at r permeability, the brecciated top , though probably not more than one-tenth a numerou a the mooth top , include the four great produc iv lod -the K ar ara , Baltic, 0 eola, and I le Royale; moreO>er the Pewabi only in part repre ent the mo h top , there b ing large area of fragmental material .in thi lode. Origin.- The origin of thi fraamental textur in Kew enawan lava ha been variou ly xplained. It ha been argued by Hubbnrd and ther that part of the material, at l a t, i cro ion d bri . Hubbard and Lane hav al o explained mu b of it a n, on equ nee of brecciation due to lidina along the flow contact at the time of uptilting f the bed , and Hubbard ha pr di ted that th thicker the flow the more br ciation will it· top how. rant, who tudied the flow in Wi con in, attributed h brec iated top to flow· movement modified in om place b ero ion and depo itiou. The h po hesi that th typical fragmental top are of dimenta.ry origin em to be ntirely lacking in upport, though many of them have been rework d by rosi nal and d po itional agen ie , which have produc d th "am gdaloidal couglomernte "or" coriac ou am gdaloid .' Th hypothe is hat they ar primarily due o lipping n b d cern al o without suppor . Th irregular 'dovetailing " of tb contact with the over! iog flow, due to the hummocky nature of rouab top , did not make u h contnct favorable to lipping. 1\1oreover, the br cia a coar and open, the top part of it wa. ftlled with the la a from th o,·erl ino- flow, bowing clearly that the brec ia wa present b for tho overlying flow <'OV red it and of cour before tilting of th bed . . Th in lu, ion of amygdaloid fragments partly r - orbed in th trap under the amygdaloid eems to indica t.e learly that the frugm ntal top wer form d while tho inLeriOI' portion of the flows wer till fluid and pre umably till mo ing. Th irregular piling up of tho fraamcnt on the :flow can probably b be t explained by flow f rec imilar to tho in a moving ·lloatin oj fi ld . u h mo\ t ·would r . ult in
THE COPPER DEPO ITS OF MICIDGAN much abra ion of the fragment The fact that wh r the fragment are piled above the general level they also sink deeper into the flow indicate that they were piled up while the underlying lava wa still fluid enough to permit the inking of the material, as i ink deeper where it is piled high r above th wa ·er surface. It eems likely, therefore, that flow mo ement wn a factor in producing the rough top as we now c them, but it evidently was not the ole factor, bccau o all the flows mu t have been moving and in general over smface of the arne type with the arne gradient, some olidifying as smooth top , some as rough. There must, therefore, have been orne difference in the lava it elf. That the difference wa not n cc - sarily very great is indicated by the fact that a top may pass from one type to another within a very hort distance. That the composition as we DO\ find it was not the cau e is indicated by the clo e similarity in composition of flow with tops of different type and the pre ence of top of different type on part of the same flow. The influence of the O'a eous con titu nts of la' as that e cape during solidification i a factor not ea ily studied in these old flo\v , but it has been given much study in recent and active flows. Washington 30 has recently ummarized the e idence and the view of variou writers on th.i ubject, a well a contributing the conclusions from hi own tudy, and as hi ummary has so direct a bearing on the formation of the tops of different type in thi di trict, it i in large part quoted below. The cau e of the differences between the two form has been the ubject of much di cussion and i still an unsolved problem, the chief difficultie centering about the formation of aa or block lava. According to Dutton "pahoehoe i formed by small offshoots of very bot and highly liquid lava from the main stream driven out laterally or in advance of it in a succe ion of smail belches. The e spread out very t hin and are quickly cooled." On the other hand, "the . fields of 'aa' are formed by the .flowing of large mass of Java while in a condition approaching that of olidification ." Dutton lays stres on the mu h greater thickne of the " aa" flow and r gards this and the consequent difference in cooling a the cau es of the diver e character . Dana thinks that " in an 'aa' flow the lava must have been subj cted to some deeply acLing cooEng a gency," and that "the cooling was not from above downward, as in pahoehoe, ,but largely fr m below upward." He conclude. that this cooling agency is subterranean waL r in the region pa. ed over, an explanation which is combated by Hitchcock and which do s not ccm to be supported by field evidence. Daly attri bute· the difference to "gas control," which he thinks is shown by the different vc iculation of the two forms. The vesicl s in pahoehoe are relatively more numerous, more regular in form, being mo tly pherical, smaller in size, and more evenly eli tributed than in "aa," in which they are irregularly cattercd through the ma.· , mo. t of t hem of very much greater " Wushi ugton, ll. ., T he forma lion of aa and pahoehoe: Am. Jour. ci., 5th · r., vol. 6, pp. 409-423, 1923. ize, relatively fewer, and of irr gu lar hap , many being mucn longated. Their toLal volume is gon rally 1 ss per unit volume of rock than in pahoehoe, and "Lhe 'aa' ve iclc ha undoubtedlv grown through the c ale · of many bubble · f ga . The difference in fi ld habit i thu xplaincd by the relatire abundanc of volatile maLtcr and, still mor , by the evenne of its di tribution." Day and h 31 call aLL n Li n to 'Lh' rapid ex pan ion of the ga c with th rei a.· f pre' ·ur (a. 'aa' lava reach the urface) which i a cooling phono m 'non, and which, if the xpa.n ion t~k place ·uddenly from a high pre urc into the· air, might be extr mcly mpid. u ·h rapid expan ion and con cquent co ling, when occurring . udd nly at the surface, may very well be the ufTici nL au ·c of t h 'n11.' lava formation. ,reat block appear to ha,·e cool d in thi way o rapidly that no pportunity wa given forth udd nly projected and rapidly expanding lava t 'h al' and rc um liquid flow. The projected ma c arc cooled almo ·t in tantl,v throughout their ma and remain di cret block . " D ctor Day' b lief i · that pahoehoe lava. i t he high-tempera.Lu ·c form, containing relatively little f!,2 , wherea the "aa" i ue at a I wer temperature, contains much ga , an l cools quickly th.roughout it ma. becau e of the rapid xpan ion and Limination of the ga . Jaggar thinks it " probable that the quantity of confined ga , in solution or in bubble form, control the method of freezing. Pos ibly the ga es ar near r equilibrium in pahoehoe than in 'aa.' The heat equation plays an important role, and this involves reaction between tb ga cs as well as their oxidation in air. Ga expansion may be more rapid in 'aa ' and so induce internal solidification. Furthermore, here arc enormous differences in the Late or oxidation or the iron at the moment of internal solidification, and as yet we know nothing of the progress of crystallization in the field." At Ve uviu , according to Mercalli,s2 the m t rapid flow and those which contain mo t gas take the " aa" form, wheress the slower and more viscous lavas generally are of the pahoehoe type. He thinks that the difference between the two depeud on " different conditions of cooling," but that difference in the angle of slope has a marked effect. imilar views are cxpre ed by Von Walter bausenas in describing t he lavas of Etna. There seems to be general agreement in the belief Lhat the "aa" form is produced from a highly gas-charged lava by rapid cooling due to the escape of gas, but the que tion a a whole must still be considered unsettled. There are, howercr, two or th.ree differential features of the two forms of lava which do not seem to have as yet b en studied in connecti n with this problem but which may throw some light on it. The are the relative amounts of the iron oxides, the di!T r nt degree~ of crystallinity of the two forms, and the different size of the respective flows. After showing that there i no e ential dillercncc in chemical compo ition but that t.he smooth top are distinctly less cry talline than tho rough, W a hington continue : Inasmuch as the chemical compositions of the "aa" and the pahoehoe forms of these lavas are identical som other factor or factors, physical or physico-chemical must be sought to explain these differences in the crystar'linity, which appear to be connected wi.th the structural and field difl'ercnccs of the lavas. Any difference in the initial temperature aL the time of extrusion does not seem to be adequate in itself, as Lhis difference would not be very great and would be eliminated soou after extrusion. :: Geol. Soc. America Bull., vol. 24, p. 598, 1913. 33 Mercalli, G., Vulcani atlivi delia terra, p. 179, 1907. Von Wnitcrshausen, S., Dcr Eloa, vol. 2, pp. 393 ct seq., 1 0.
STRATIGRAPHY t he only factor that appears to be competent to serve as an adequate cause is the gas content of t he magma. That the magma wh ich solidifies as " aa" has a ,·ery high gas content is commonly recognized. It is shown by the loud roaring and hissing noises of a moving "aa" flow, the nu merous flames on the front and over the surface of " aa '1 flows, and by the abundance of noxious gases, which often make near approach difficult. T he lesser gas content of pahoehoe is evident from the much quieter, almost noiseless flow and the absence of flames. Indeed, so qu iet and so free from gas are most pahoehoe flows that one can easily (apart from the beat) study them from their brinks. Although pahoehoe flows are fairh· fluent on their extrusion their viscosity increases very rapidly. An excellent illustration of _!;his is given by Brigham 3 in his description of a pahoehoe flow issuing from a dome. " It was white-bot cream when it came out from under the cru t, but in the distance of perhaps a foot had changed to a cherryred molasses, while a few feet more t ransformed t he tream into full-red tar." The formation of the two forms of lava takes place about a follows, according to my conception of it . Pahoehoe Ja, a come out highly heated, probably in large par t by internal ga reaction , but not highly charged with gas, m uch of thi ha,·ing 1 been lost by immering in the throat n ar the urface or el ewhere in the cour e of flow. Becau. e of t he high temp rature the greater part of the comparatively small amount. of gas that remain after· efTu ion i . oon lost, whereby the ftu i lity of the lava rapidly di mi ni he and with it the po ibility of internal mol cular motion, o that an early stop i put to cry ·tallization, although the emimolten, high ly vi cou gla ti ll capable of low continuous motion. s the tC'mperature fall.· and ih viscosity incrca e , the comparatively 'mall amount of ga till pre ent in the magma i gradually cxp lied fr m olut.ion and there being few olid point to erve a. nucl i and th material ' being very vi cou , the ga i lib rat d quite un iformly throughout t.hc rna and form mall, pheroidal, rath r un iformly distributed bubble . lab of pahoehoe gen rally how an incre e in izc and number of ve icl toward the bottom an effect probably caus c1 by th quick r cooling and olidiiication of the upper part, which radiate its h at into he air. "Aa" i. u at a low r temperatur than paho ho c rtainly more highly charged with v latile matt r, o that t he ga pre ent r the "aa" magma, in pite of it loll' r temperatur , initially much more fluid than i the pabo hoe. nder these condition of great fl uidity and lower temperature the crystallization of labradorite and augite begins early and proceeds with rapidity. The fluidity f t he liquid port ion and the con equent rapidity of crystallization ar maintained and, indeed, nhanced by evcral circumsta nce . I n the fir t place, the eparation of ~he cry tals, in which t he gase are not appreciably soluble, rnorcases the gas concentration (and t he pressure) within the remaining liquid, t hus maintaining a high degree of fluidity and con equent po ibility of internal molecular movement, so that c_rystallization is facilitated. This increa c in ga concentrat_,on rapidly r aches or exceeds the point of ·atur.ation, the hberation or desolution (if I may be permitted to coin a word) of the ga being greatly facilitated by the pre ence of innumerable crystals whose angles and edges serve as nu,clei and give abundant Op]~ortur~ity forth cape of gas, in virtue of the action of s~ch ohd pomts as centers of the liberation of ga-s. The gas ten'd_ to coalesce into large bubbles and so pa out of 10 liq\.Hd, remains constantly saturated with gas throughout the continuous crystallization and hence r~main s very fluid and favorable to crystallization. Two other factors also tend to preserve the fluidity of the grad_ually dimini hing liquid portion of the lava. The one 18 connected wit h what has been call d the "second boiliug ~:·B righam, W. T., 'rhe volcanoes of Kil nuea and Mauna Lon: Bisbop Museum em., vol. 2, No.1, p. 141, 1909 point " 35- that is, the increased gas pre ure re. ul ting from the formation of crystals in a cooling liquid. The formation of cry tal in a liquid lava give out latent heat,36 a ilicate minerals appear to be normal in tbi re p ct, so that t he crystallization itself will tend to maintain t he temp rature of the still molten portion or diminish the slope of t he cooling gradient. It follow that, in so far as we now know the therma l behavior of silicate , t he crystallization or partial solidification of the lava may have a very appreciable effect in maintaining the fluidity of the remaining liquid portion by retarding the increase in viscosity. The other po ible factor is indicated by study of the thin ections of the cry tallin basaltic la a of H awaii and of other localities. This shows t hat feld par begin to cry tallize fi r t, augite and magnetite belong:ng to the later stage of cry tallization. Becau e of t hi early cry tallizat ion of feld pars the port ion of t he lava that remain liquid becomes increa ingly fernie and therefore m re and more fluid, so that the flow of the lava stream i maintained, in spite of t he abundant cry tallization, and with it cont inued liquidity also the facility for crystallization. The liberation of ga from the rna s of "aa" will thu be increasingly rapid, po ibly violent toward the end, and the cry tallization of the lava which form " aa" i con eq ucntly very rapid after a certain degree of fluidity has been reached, t he great flu idity of the . teadily dimini hing liquid p rtion of t he flow being 111:1-intained rp to t he point of complete lidificat.ion, a i demandcci by th microtcxtu ral feature of the "aa" lava. Thi ' :1.cc unt · well for the fan ta. tic, rough urface forms and for t.h large, elongated, random bubbl s, both of which arc eharacteri tic of t he "aa" form. The cone] u ion reached by W a hington from the tudy of re nt and active flow rongly suggest that varyino- gas cont nt a a controlling factor in forming the different type of tops in the Kew nawan lava. . 11 SCORIA CE O US TOPS" Tb misnamed type of ro k known locally a " s oriaceou top " ha already been described in the ction on amygdaloidal conglomerate (p. 20). Briefly, it consi ts of amygdaloidal fragments in a matrix of fine ba i.e and which grades downward into normal amygdaloidal rock and in many places upward into fine basic sediment and at numerou horizons finally into fel itic andstone or conglomerate. As the name implie , lodes of this type have been regarded a the re ult of explosive volcanic action, the sediment being considered volca.nic a h. The Ashbed is the type example. The "scoriaceou amygdaloids " are more permeable than the smooth cellular top but 1 ss permeable than tbe brecciated tops, because the interstices between the fragments are filled with a fine sandy to clayey sediment. Of the numerous examples of this type the Asbbed lode, on which the Atlantic, Copper Fall , and other mines are located, i the only one from which ore bas been produced. " Morey, 0. W ., The devolopmentor pro ·ure in magmns ns a result or cry ·t.allization: Wnsbington cad. ci. Jour., '' 01. 12, p. 219, 1922. 3a Mercalli (Vulcani attivi della torra, p . . I 0, 1907) attributes the long-continued prosorvntion or heat by lava flow , orton amounting to several year , to this devolopment or latent heat or crystallization. In July, 1914, Doctor Day and I could scorch papor in crevices or the flow of 1910 at Etna.
THE COPPER DEPO IT OF Ml HIG r ALTERA'l'ION ALTERATION OF TRAPS Except for the alteration efl'ected by the r?~per depo. iting olution , the basaltic rock nrc urpn mgly fro. h in view of their ba ic compo ition and their gr at fiO'e. the ore-rlopo itinO' olution · moved in qunntity only nlong the more permeable pathw~ys, th dense traps have e capod mo t of the chcnucal nnd mineralogical chan <Yc that accompanied the d po ition of copper. Glaciation lnr"'elY removed whatever weatherin"' product had been formed earlier, and since glaciation only incipient kaolinizRtion and limonitization and li<Yht pby ical de ompo ition of the traps hav oc urrcd, eYen wher the rocks w r not covered by CY]acial deposit . ca us - the devel pment f pl 'ntiful hematite nnd 1 thr fllling of the' e i u_lar and other opening , together \\'ith morr or le s r placement f tlw roek I y lode minernl. The formation of hcmntitc C1tused or a,ccompanied in. ome of the top an incrrn c iri ir n ontcnt, notabl· 11 bove that in th parts f the flow . hither this inrrrn c is A.n al tcn'ltion or an original magmatic cfl'c t i llO nltogc clenr; thr q urstion is di. cus. ed n pagr 3G. The aYitic or \·r~ir lr s of tl' r lnY11 top. , in the main, long r maincd empty, tho1!0'h probnhly some chlorite and perhap f lcL pnr fl depo. ited in them durina the oling of the laYa. Thor . e ms no rca on to bcli y that th w iclc f ne flow wer filled before The principal alteration , a ide from ore depo iti n and urfac weathering, occurr d in the oliYine and the ma()'netite; the pyroxen and the fold par of th trap are u ually unaffected. Th olivine, which at the time of crystallization wa common in man of th traps, i now pro Ol'\Ted in relatively few. It form er pnce i filled with orp ntine and hematit hRYe replaced it. This breakdown appeal'S to hR \·e caused no mnrked
in chemical compo ition within the limit of the oli ine individual but to have b en, rather, a rearrangement of the elements into minoral of greater tabili ty under the condition exi ting. 1 the next flO\\" nppean'd, nor that during th genrral period of lavn cxtru. ion there were , uc e. L\·e period of ve. i lc frlling. The vcsirl . appear to have been fill dafter all th . flow had bren . preacl , the ov rlying thi k eclimentary formnti n d po. itcd, and th ro k tilt d to their pre ~ent attitud . Practically all the fracture , and mall, tha wcr proclu ed by cl formation of tho rock . any th , ame mineral n tho e hich form the am)mclulc . The min ral of th amygdule of th fracture ar , in fact, iden· tical with the gaoguo min ral accompanying thr cop- They are therefor further di cu d under tho 1 heading " Ore cl po it " (p. 1 07). The magnetite wa al tercd more or le s completely to hematite. The hematite e m to have worked in from the urface, but it al o p rmeated all tbrou"'h the magn tite individual , which therefore pre ent a pitted appearance uncl r tbe micro cope. In place magnetite i completely altered to hematite minute irregular tringer and tendril of hcmntite extend out from the magnetite grain among the urrounding mineral , . ugge ting that in the alteration of the iron mineral an increa e in volume fore cl some of the hom a tit to lodge out ide tb original boundary of the mago tite. orne of the magnetite was evidently titaniferou , for it alteration ha produced numcrou granular particle of a nonmetallic mineral, probably titanite, in the midst of the mor abundant hematite. Th alteration of the e two minm als, . o far as h a be n a c rtainecl, wa almo t magmatic- that is, it too place very hortly after the ro k had oliclifi d, unle s, indeed, these early iron-b arin()' mincraJs were already altered by the tim tho pyroxene and the feldspar had cry tallizecl m·ouncl them, a i di cu cd later (p. 53). Th dominant tendency in the alterntion of both th se mineral wa. · the convcr ion of fen u to f rric iron. Thi oxidation of iron ugge t a . o ·iation in origin ' ith th hematite in th top of many of tho flow and i a"'a,in referred to in that connection (p. 35). ALTERATION OF THE LAVA TOPS Alt ration of the top of the lava flow· is of two type , produ ed at difl'crent time and by differli)nt RED COLOR OF AMYGDALOID TOPS STATEMENT OF TBE PROBLEM Th oxidation and concentration of the iron in the top of the flow app ar to hav r ceiv cl littl in\'e ligation; the e proces e , therefor , will b eli u. ed in con iclerable cl tail, and evernl po ible method · by which they might hav b en effected will 1 c con- "idered. Tho onclu ion reach cl ma b at tho out et; it i that bo h the oxid tion and the concentration of iron w r ac mpli heel b gn c escaping from. the oliclifying and cry tallizing lavn. The inclo ed ga e were eith r neutral or rcdu inu toward iron at th t mperature at whi h the lavn merged but b cam . tron"'lY oxidizing a the temp ratur de rea Pel, w:ith the re ult that much of the ferrou iron wa converted to the ferric tate, th conver ion being mor and mo re complete a the upper y>a.1:t of the flow wa approached. A triking feature of the tops of many of the fi hogan flow is th eir reel color, which range in inten ily from bright brick; through darker and dnller shades to fa.int browns but alway. contra ts with th gray or greeni h gr~ty of the deep r por ion of Lhc flow. Thi red hue may di n,ppe~tr before the botLorn of the amygdular zon is reached or it may extend for a hort eli tance into the trap. It is u eful in tho recognition of amygdaloid bed on outcrop , in cross· cut , or in drill cores. It i pre ent in many of the cellular smooth-topped amygclaloicls and iE! trqngly
TRATIGRAPHY de1,eloped in ~he brec ia~ed top . In he "scoriaceou top " or amygdaloid conglomerate the r d color may be rather faint or altogether wantinO', although the fine mud i u ually brown. Thi red color, which i due to the pr ence of ferric oxid , i pre ent in all the amygdaloid lode (and in the fel ite conglomerate a well) from which noteworthy quantitie of copper have be n produced, and om explanation of it i involved with almo t every theory of the origin of ~he copper depo it that ha been ad van ed. It t.herefore merits careful inve tigation . The enrichment of th lava top in f rric oxide h a been a cribed by orne ob erver to weatherin()', a proce which wa uppo ed to be facilitated by the brec iation that c rtain top hav undergone. Other inYestigator , laying tre on the fact that all the red top are mineralized in one way or another, have inferred that ferric oxide wa a by-product of Yariou kind of mineralization. Th pr ent di cu ion ma} well beo-i.n by putting the e hypothe o to the test. The probl m is pr ent d in implifiecl form h:v tho red top which ha,7 e b n de cri bed a occurring in many part of the world on la a that have be 'n erupted in comparati v ly re en t tim and 11 pp a r to be Yirtually unaltered. u h la a were tudi cl bv T. . Broderi k in the n ake River and Colum bi·~ River n'gion for th purp of btaining ligh ou the hi t ry of th Mi higan ft w .. mA.ny lumbi a urfa e haYe uffered in con - na ke Ri r flow are imply and dire tly the of ' hich th Iron cont nt of lava top at 1' win Fall , Idaho [tl . C. Kenny, ona ly ·tJ Dista nce I ron (per cent) from top of flow (foot) ~'crric Ferrous Totnl The e r ult how a v.irLually ·on ca nt. iron l'Ontcn from the urfacc down , but a marked A.nd progr JYC chau ()'e in th tate of oxidation of the iron. t th e surfac 70 per cent of th tr n .i ferric; th.i. percentage gradually dimini he , o tha in the lowe t ample, from about th middle of the flow, le than 12 per cent of the iron i ferri c. Examination of poli bed and thin c tion of th minerals in these flow bow tha t the chi f ironbearing mineral in th deep part f the flow ore magnetite, olivine, and p rox n . In the upp r, red portion, hematite account for mo of th iron . orne of th hematit wa form d by alteration from maCYnetite or, together with erpentine, fr m olivine; but ome how no .ign of Yer haYin()' been anythinO' el e, and th:i oc u1'S ill platy or bla l d ta l , generally of minut iz , f uncl charA..ct ri tica.lly in the gla y mA.trix . urroundin()' the plngioclA. c cr taL. The plagiocla e i prncticnlly unal cr d. othing in th hemical re ult, or in Lh minr rals pre nt in t hcs l clA.ho flow ttg?;r. t. t hA.t. iron ha CELLU LAR TOP PER CENT ' Ferr ic tron ferrous iron FtOURE 2.- hange in iron in lava top at T win Fall , Idaho been added to he top . o Ye i le filling or vf'in of I at r min ral are to be e n. partialr arrangem nt of the iron and an in reA. e in th degree of it oxidation n ar t he tops of the flow em to be all that ha happened. The e change an not b a cribcd to any later alteration but appear to ha e be n accompli. h d by the time the lava had Edified or very shortly arterwA.rd. OXIDATION IN SMOOTH-TOP FLOWS OF KEWEENAWAN SERIES Many of the I wcenawan :flo, ho' the same kind of tran ition from uno:\idized trap to oxidized top a th mor recent we tern la a . The following analy e of ampl from a mooth-top flow, the econd flow below the olvm·ine sand tone at the Wolverine mine (fiO'. 3), inclicA.t that th changes invol ed are clo ely . imilar to tho e repre ented in the analy es of the Idaho flow. The ample group d int ompo ite ench of whi h ropr nt a horizon tal di tan of 50 f t in a cro s ·u t which trav r e th e flow at right an()'le t from top to bottom, The dip of the flow i · ttJJ.proximately 40°.
THE COPPER DEPOSITS OF MICHIGA Iron content of typical smooth-top K eweenawan flow H C. Kenny, analyst] Distance from top of Oow (feet) 1 Iron (per cent) Along crosscut Normal to top I Ferric I Ferrous Total (opproximnte)1 Q-50 Q-30 5Q-100 15Q-200 9Q-120 I Here, a in the nake River lava , the total iron is essentially con tant, but the ferric iron increa e teadily toward the top and the ferrous iron de_cre_a c almost as steadily. Both the Idaho fi.Dd the M1ehwnn analyse how that the red top are the extr me expresion of a change which has taken place tbrou()'hout Ferrc iron Ferrous 1ron FIG o RE 3.-Iron content or smooth-top Oow (second flow below Wolverine sand· stone, Wolverine mine) the flow. Two causes have produced the reddeningnamely, the greater abundance of hematite and the decreasing ize of it particles toward the top of the flow. The effect of fineness of division of A. mall amount of hematite in giving a brilliant red color to agates and ja pers is well kno·wn, and A. irnilar effect is clearly revealed by micro copic , tudy of the e Michigan lavas. OXIDATION AND CONCENTRATION IN BRECCIATED-TOP FLOWS Although the red fiow top. of the cellular, smoothtop type contain o far as determined about the same proportion of total iron as the body of the fiow orne of the fragmental tops contain a con iderably higher percentage of total iron than there t of the flow, but, ju t as in the nonfragmental tops, most of the iron i in the ferric state and occurs a hematite. ( ee pls. 62, 63.) The Kearsarge lode is a conspicuous example of concentration of iron in the top and is the one that has been most studied. The following table shows the iron content at varying distances from th top of th Kear arrre fl ' in a single ection. Di tanc ar horizontal; the dip of the bed i 35' to 40°. !Ton content of Kem·sa1·ge flow, Wolverine mine rr. . Kenny, analyst Nonnnl to top v rric Along crm eu~ prox i m a l ) l4"rrrous 'l'otal Q-50 100- 1 -o 9Q-120 Thi series of specimen , which r pre ents a section of the entire fiow from t p to bottom, bows a concentration of iron in both top and bot. om as compared A FRAGMENTAL TOP PER CENT Ferric iron Ferrous iron FIOURE 4.- Iron content or Kearsarge flow. A, Calumet & Uecln mine tsl level; B, Wolverine mine with the middle portion, the greater on enLra~ion being at the top. ( ee ftg. 4, B.) The ferric uon content increase steadily and the ferr us iron decreases steadily from the bottom upward. The upper part of the K ar arge flow has been sampled at shorter intervals to how-still more closely where the notable changes in proportion of ferrous to f rric iron and the most marked increase of ferric iron are to be found (fig. 4, A), and the results are as follows:
U . S . GEO LOG ICAL S URVEY PROFESSIO!\ATJ PAPE R 144 PLATE 55 TEXTURE OF SEDIMENTAHY HOCKS AS SII OW N l N DIA,\ IONO-DJULL COHES a, Felsite conglomerate (Keweenawan) ; b, Jftcobsvillc ('' EasLcrn ") so .one, showing bleached areas; c, Jacobsv ille( .. Eastern ") sa ndstone, show log ··mud flakes''
U. S. OEOLOGlCAL SORVEY TE T H.E OF LAVAS A SIIOW1 I N DIAMO 0 -DIHLL CO HES .a , Ophitic texture as soon oo wouthcrcd surface; b, porphyri te; c, rnclaphyre; d, " dol rite,'' pegmatitic facies of traps; e, finer glomcroporphyrite; f, course glomeroporphyriLo; g. band L'<I ophite: h. Lypicnl ophi Lc
. S. GEQT,OG lCAL S RVEY PROFE T N AL PAPER 144 PLATE 57 a b d f TEXT 11 EOFLAVA A II OWN 11 M IC HOS OPJ SE T IO S n, Typical ophi tc from Lh Grc nst.ono: b, dinbnsic structure in flow hclow th nlumcL lloolo conglomcrat.c: c, tro.p just. above t.hc CuJumel H ecla conglomerule ; d , fuirl y fresh ophi t from Osceola flow; c, foot lrop from Kcar fl o"' ; f, typical " foot lode" from Ke>.Lrsa.rge Oow. All X about 30
P it F'£8, I XAL PAI'Elt 144 PLATE 58 U . B. GEOLOGICAL RVEY n b d g TEXT fiE OF FLOW TOP ' A EEN IN LODES u, Cellular lode. l nd ing lown.rd coolescing; b. c ·llulur lode. somewhat coulcscing; c. coalescing lode; d, banded coalescing lode; C, strong band in coalc· ing lode; r. g. frugmcntal lode. All from Quincy lllinc
0 . S. GEOLOG ICAL SURVE\' f>ROFESS IO:-.IAL PAPEn 144 PLATE 59 TEXTUHE Of FLOW TOPS AS SEEN I N SPECINI ENS a, Two uL , ccllulor lode; third from , coalcscillg lode; righl, frogmentullodc. h, Frugr.ncn Lollode, Isle Royale mine. c, Portly resorbed am ygdaloid inclusion in Isle Royale Oow; block circle indiculescnd of drill core
PROI' RLONAL PAPER 144 PLATE 00 U. S . CEOLOCI CAT RVEY T EXT URE OF FLOW TOP A . EEN IN D IAMO D-DRI LL CO RE n b Cellular amygdaloid, upper part; c, amygdaloid of glomcroporphyri tc flow; d. ccllulur amygdaloid deep in amygdaloid · c, frugmcntul a rn ygdnloid; ' ' C. scorinccous amygdaloid or amygdaloidaJ conglom ruLe '
U. S. GEOLOGI CA L SURVEY PRO.FESSI ON AL PAPER 144 PLATE 61 a b d e TEXTUI11.': 0~" FLOW TOP A EEN IN 'l'lil t ECT!O o, Vesicular top of Kco"orgc lode, rich in hcrnoli tc, X32; b. typical chilled K corsorgo am ygdaloid , X32 ; c, Lhiu Lroppy lode f,·om l ·lc l\oyolo mine, X32; d, top of Quincy lode showing fresh feldspar, with amygdu le of quart?. and cpidolo, X21 ; , calcite-cement ed breccia, Jslo Hoyalo amygd ttloid, X 32: f, fresh feldspar in hcmnli tc-rich top, Kcnrsurgo led , X298. All onhugcments ttpproxill'lole
U. S. GEOLO .ICAL SUHVEY a ; 1 ( i .f' 4f- v i ,. 0 I J J.''.J.l t.·: ' .. ·
. .
IRQ OXIDES l FLOW TOPS AS SEE PROFEJ S IONAl, PAPE R 144 PLATE 62 b d POLlSHED SECTIO S n, D endrites of magnetite altered c_ompletely to h emawtc, Hnwflii, 1 5; c, same, X 640; b, magne tite ni ter d to hematite, with ioLCrscrtal ureas full of finely divided hcmat.1Lc, X215; d, dassemmat.cd hcmntato surrow1d 10g feldspar, Kearsarge am ygdaloid, X338 ; c, d issemina ted hematite, Kearsarge a mygdalo1d, X 338; f, dis·emina ted hematite, Kearsarge lode, X l 03. All colorgc, meols approximate
U. S. GrJO I. OG !C:If. U RVEY PROFE TOl\AL PAPE R IH PLATE 03 b !HON OX m E· I 1 HOC S AS EEN IN I'O LI S II EI) SECTI Ol\S n, lJ 11 n l tert~d "'"J!'"'' i t_o fro m t he rcf' lo n C'. o li vi!'O pa rtl y rcd . X 82: h , f , IHmn 1 i t in l ·ilc pe bbles fro 111 t_hr Cn lun~ t'l I h·clu co ry~ l o nwn~ te, X 11 5; c, 'ly nltorcd to ilclll n lr t.c . tra p nbo vo lslo lloyul lode (no te s tnn of P. cc··· h(' IIIOirlt) . X II d . lllHl!:ll<"l tto 111 to hcmutil rnid d lo of SC<lond fl ow lw low ulurnoL Jl conglom o.rn to, X 158; c. litunifcrous m ugnctit a lt rin to hcrnutit c, X :!28. A II (nlurgcmrnl s upproxi rnut
. S. GEOLOG ICA!, RVEY PROF'ESS IONA!. PAPEH !14 P T.ATE 64 b d ALTEHAT LO A D El'LA EME 'T OF M l EllA LS u, ficU feldspar (dark orcas) replacing nmygdaloid , light orcas quartz and carboout.e, Ma. s nliuo; b, prchnitizo liou of feldspar, X60; c, p11111· pellyite in qua rlz a!Lercd Lo sericite, X200; d , quartz a nd calcite along Ahmeek mass fissure (note zonal gro wth of quartz) , x:IO; c, upid to in calcite alter d Lo chlorit e (cent ers of cryU>.Is alter rnosL r ad ily), X76. All cnlargemcnl!l opproximale
STRATIGRAPHY {ron content of top of Kearsarge flow, Red Jacket crosscut, Calumet & Hecla mine Analyzed at mill laboratory, Calumet & Hecla Consolidated Copper Co.] !Iorizontal disIron (per cent) tance from top -- of lode (feet) Ferric Ferrous Total There ult of the two group of analy es are repr - ented graphically in Figw·e 4. The noteworthy features are (1) the higher percentages of total iron both at the top and toward the bottom of the flow, that at the top being the highest; (2) the teady increa e in ferric iron from bottom to top, with a sudden increa e in rate in the upper 20 feet-that i , in the brecciated amygdular top; (3) the increa e of total iron at the top as ociated with an increa e in fenic iron, but the in rease in total iron in the bottom third of the flow as ociated with a slight decrea rn ferric iron. Five pairs of complete ro k analy e are available for a contra t between the oxidized tops and th deeper uno~'idized parts of the corre ponding flow of Keweenawan lava . The e analyses are father di - cu ed under "Weathering" (p. 40), e peciallv Sa and 5b, which are th only ones that have been tudied by the writers. A nalyses of upper and lo wer parts of K eweenawan flows Ja lb 2a 2b 3a 3b 5b 4n I 4b J J i02 -- --- AJ203- -- ] . 92 - - 9. 50 ,, 9. 37 I 11. 40 I I ?2. 7 ?3. 9 . o ' ln. Specimen 47600, country rock 70 feet from thr lode, S(,· lr,·el, inoua mine, Michigan. lb. preimPn 47499, c nt r of lode, same locnlily as 1~. Annlys · Ju and Jb by R. D. !Inll, ni\·. Wisconsi n. 2n. lli'Citn n 47506, 12 feet from footw,lll of 63d lov I of Quincy mine, Michigan. 2b. pcclmen 47605, foo~wall o r lode, same locality as 2b. Analyses 2a and 2b by R. D. linll, niv. Wisconsin. 3a. Melaphyre, lower zone of bed 64, Eaglo River section, !icbigan. 3b. Prehnltized upper zono of bed 64, same locality as 3a. Pumpelly, Raphael, Meta omatic development of the copper-bearing rocks of Lake uperior: Am. Acad. Arts and Sol. Proc., vol. 13, p. 293, 1 78. 4a. Fresh bllSOitic rock from center of Oow, 15 r t from lod , Dingle Creek mine, Douglas County, Wis. 4b. SuperJacent nmygdaloidnl lode, same Oow as 4a. Aualyscs 4a and olb by W. 0. Wilcox, Uuiv. Wisconsin. 5:1. Kearsarg amygdaloid lode, 1st level, nlumct !Iecla mine. 5b. Samr, specimrn from top 4 loch of lode. Antllyses Sa and 5b made aL m ill laboratory, Calumet & H ecla Consolidated opper o. Analyses Ia Lo 4b ar quoted frOID an llis . . R., and Leith, . K., U. c. Oeol. nrvey M on. 62, p. , 1911. From th pail' of anal c , an incr n e f f rric ir n and a d cr a of ferrou iron toward the top and all but one of' hi h show an in r a e in total iron upward, ertnin inf r nee ma be drawn in r gard to oth r hano- s that accompany the e increases in ir n and oxygen. Fr quent r f ren e will be made to these analy es in the en uing discussion. It must b borne in mind that the analyses repr sent the compo ition of the ro ks after they have b en affected by many kinds of alteration in the period that has elap ed from he tin1 of la a outflow to the present day, and that in the top or amygdaloidal portion of the flows the ombined ffect of alteration has be n, o.s a rule and p rhaps without exception, much greater than in the trap. Only the specimens represented by Sa and 5b have been studied by th writers, and the dis u sion are based primarily on the e, but the application to the other analy es is pointed out. ample Sa and 5b were elected from ro k that bowed the lea t effect of the mineralizing solutions. Explanation of some of the features of the other analy es could be ventured only if the nature of the material w re known. MINERALOGIC FEATURES The mineralogic expre sions of these variations in oxygen and iron content are mentioned, so far as the trap are concerned, in the section dealing with alteration (p. 34), as the changes vid ntly affect rock m..illeral previously cry tallized. But beyond the partial or complete conver ion of olivine and magnetite to hematite, the trap seems to be in the same state
THE OPPER DEPO I'r OF MI HIG a when fit cr tallir.ed, and there i n thinO' in th l'O k it elf o uggcst tha it cry. al lir.crl. under nbnormal condit.i n . 'l'h i?"nificant mineralogic fcntu res a ttendinO' iron oxidation and concen trn tion in th lava top are al o outlined abO\' (p. 35), but ome further detnils mn~T p rtin ntly be gi n before rli cu. ion of the cause of th bchnvior of oxyg n and Iron. The textur of the upper vc ·iculnr of a flow alway. finer than that of the trap in the same now. The fine r.-grainerl, dcn:;e t porti0n arc At the vc1· top of the mooth flow. nnd around· the margin f fraement of the breccinted top.. In th eden e t part ve icl e:- are plentiful but e x ceeding]~ mall; deep r in the mooth flow. or to war I thr c n ter in the fraO' the YC iclc. incrca e in ir. ·, but the tex ure ·Of the rock it elf, hough coarsening ,:ome- ·what, remain. comparatively fine o long ns vc. iclc are plentiful. All thi fine-grained mntcrial i . ccn in thin . retion to compri e on titucnt oft\\' kind - minute ct·y ·tnl· or microlitcs and a compa t matrix which, dr. pitc e pecial 0fforts to obtai11 ections of unusual thinne. , remain nontran parent. \.monO' th tran pnr nt cry tal par predominn.tc. ; it i. pre mt in dclicntc microlitcs of fairly perfect lath- hapcd outlin<' except for f~ttcnuatcd clongati n of th . ide' of thr. crystal be on l the middle to O'ive the chara tcri tie pit fork termination . ( <'pl. 61.) Thi hapc f th feld par impli an increa in"' \'i·cosit. of the orrounding mediu~1 /; whi h wa to be cxp cted in th c quickly chillinO' lava top . Commonly th feldspa.r i trikinO'l. clear and fre h, with pla<riocla e twinning a ily ecn. ( " pl. 61.) It ranges from oligo la cand ine to an de ine · the f ld ·par of the trap portion i. lnbrndorite, in part high.ly cal i ·. Here and there arc p eudomOrJ h who ·c outline di tinctly or va"'Ltcly uggest oli inc but whose transparent part i n w ~·p ontine. Hematite i the only oLb r recognizable mmernl pr cot (except for the ve icl filling , which aTe of later introduction and are con ider d farther on). In the c lava , as in the lava of Idaho, the hematite is partly in mall ragged lump or irregular pongy pat he deriv d from magnetite or olivine, but it mainly o cur a minute short crystalline plate ditributed thro ugh the opaque matrix. For tbe mo t part thi distribu ion of the hcmatit plate i even and y tcmatic, uggestive of the inter ertal pattern, but a,round the f ld par crystal and the ve icle the hcmatit particle app<>ar crowded and piled up, a if eith r pu hed aside by or a ttractcd to the expanding gns bubble or the growin()' feld par microlite, neither of which ontai n hematite. Th groundma s o1· matrix of the c variou ry tals i opaque, proba.b~y because the h matite ,plates are o abundant a everywh re to overlap, even in a thin " Day, A. L., Allen, E. '1'., and Iddings, J . P., 'l'he isomorphism and therm~l propert1es of the feldspars: C~ i e lost, ·w a hiogton Pub. 31, p. 91, 19Q5, ection. 1·ial , contn iH ent in thC' trap lo. t il oriO'inal h . at a,nd p rhap ha.. solidifi d. CAUSE OF IRON OXIDATION AND CONCENTRATION c eral po. ibl co.u c of th in r a ·e off rri iron and of Lo al iron toward the Lop f the flow merit coosicl ration- (a) pr n -day w nth ring; (b) action of oluLion indcpcndrnL in rigin from the lavas; (c) normal weatherinO' f Lh 0 w ' hi! :-.:po ed at tho urface prior to cov ring b th nc ·t f1 w; (d) alteration by ater r gn.. c. O'i vcn off from I at r flo, ; (e) rapid atm phcrie oxidation while the t p of the now wn hot; (f) pn umatol ti alteration by a cs O'iven off th . la a of th fl w it lf b f r , during, and aft r olidifiration; (g) dir ct maO'matic grcO'ation. MODERN WEA'l'HERING Modern weathcrin"' may be liminat d b th following coo idemtion and di mi ed without furth r argum nt: Th oxidation .i 1 arly earli r than the copper, whi h. a hown in the di cu i o of ore deposition (p. 53) i not of r cont formation; and the oxidation of a giv n flow i the am at a depth of 5,000 feet, where the rock are tiO'ht and dry, a .it is in the zone of actively cir ulating ground v at,er~ . INDEPENDENT QJ, TIO S Under the action of indep ndent olution may be c.on ·.idered two unrelated influencesthe a tion of circulating oxygenated ground water after a flow has been overed by others and thu protected from direct atmospheric oxidation, and the a, tion of oxidizinO' mineralizing solution such as those beli ved by Pm~pelly to have both depo ited the copper and oxidized the ferrous iron mineral . The activity of oxygcnat d waters i so losely related to ordinary weathering that it must be, in large mea ure, credited or di red ited on th evidence regarding that process, which i · di cu ed below and rejected. · Pumpelly's ideas of the nature and som e of tho solutions that earried tl)e copper aud of the react . .ion
TRATIGRAPHY by which the m tal' a d po it d are discu sed fully und r " Ore d po it ' (p. 120) and are regarded rtf:' not in accord wi th the fact now a,·ai lable. T hat argument need not b an ticipated here, but th following geneml con. idera tions may be mrn tioncd a controverting the cl e relation a . umed by Pumpelly to exi t between o:\.ridntion of iron nnd depo ition of copper. 1. Tho oxidation is n m re marked :in on part of the erie than in an thor. flow in the upper part of the eric , thou and of fpet tra tigmphically aboYe the flow. carrying cop[ er in c mmercial quantitie , i a well oxidit~ed a one of imilar textnre carr.) ing minable copper. 2. In a gi,-en lava top- for xample, that "·hich contain he 0 eola lod the de<>'ree of oxidation i the arne where it i minahl a i i mile distant where it is barren. 3. Thu west rn lava , which -how no oYid nc of tho action of min ralizin<>' olution , uch il. n icle fillin<Y, di play the am feature of oxidation a the Oow in the Michigan opper di ri t. URFA E W E ATHER I NG IMMEDIATE J, Y AF"'I'ER E XTH U TO X welland xhibited to a ater or le s degree by the op of ba i flo w if their color an d their in rea d iron 1md oxy<>' n onten t were occa ion d b normal wea hering. It can r adily be hown that the K eweenawan f:low do not exhibit the e change . o t of th fl ow- of th mooth cellul ar typ how no eviden e of d i in to<>'ration. R op top ar preen·cd inta t, a well as all th · minute origin al textural detail of the rock, ,·en o the very urfa e. There ha b en n rumbling, oft nin or d v lopmcn t of pace; there ha been no lu mping and th ref re no on iderable lateriti concentra ion; th r i no Yi ible relation between amount of oxidation and proximity to joint , and th refore no con id ruble moYemen of iron or oxyo-en by olution can ha,Te oc urrcd after th rock were fo rm d. In the ,olumbia. River flo ,,·s, where tho ro k ha clearly weath red to form a. r [dual oil tho trap und th oil ha crumb! d nnd rotted to a gr at depth along tho joint plane. , bu t t he o-r a r part of any thi k flow at h top of whi h th oil mA.y lie i lef inta t. Limonitic alt rati n tain the r k alon<>' all joint and fra ures, both on a large ale and mi ro. copicall. . Y t in the e ~1i ch igan flow tha have the red top th increa in fe rri oxid , thOLJO'h at it maximum in th upper 10 to 20 ( t, , tarts practically at h ba. e of the flow and i nowh rc cen to be related to j int' and fra ture . I t i difficult, therefore to a' ribe th tate of oxidation of th iron t.o weathe rin<>'. till mor difficult i it to explain the a tual increa e in t tal iron a a con equ nc of weatherin<>'. If in1ply th oxidation of the iron normally contain d in he ro k w re involved, it would perhap uffi e to ay that tho gla · y portion are highe t in ferri iron be au they ar roo t u eptible to alteration. But the ar a tunlly higher not only in ferri bu in total u·on. Yid nc of iron nrichm nt after olidification hn b en recognized, ex ept uch a i r lated to the copp r mineralization, whi h occur-r d much later, and xc pt for rare and minor coating of pe ularite. o concentration of ferric iron ha been fo und to hav aken place by the fillin of opening . The h matite i uniformly di tribu ted throughout th devitrified <>'roundma , in " hi h the most minute texture have been pre er d. The downwnrd deer fise of the ferric oxide i not obviou ly in ompatible with weatherin(Y, but th e di tribu tion f total iron is not to be explain d by weatberino-. It in .r a c. toward th top and to a sli<>'ht extent toward the bott m of the fl w. D etailed tudy f the eli tribu tion of the ferri ir n r cal other f 11 t.uro diffi ult of explanation by w ath ring. For exn.mpl , n the Osc oln a.nd I le Royale lode ther - are not uo ommonly tretche of den trappy mat rial in th mid, t of the frngmental mat rial divide it in to an upper a.ud a lower portion. It would
THE COPPER DEPOSITS OF MICHIG; be natural to expect that weath ring would b somewhat les inten e below thi relatively imp rmeable trap than abo e it, but no differe~ce c~n be dete~ted; both upper and lower layer a,re 1ron-nch and h1ghly OA-idized. Large areas of the Kear a,rge lode are covered by one or more nonfragmental ~o': of lo?al extent which are pos e eel of cha,ra.cten t1c so hke th Kearsarge they are regarded a proba.bly Si02 Q Fe FeO Mgo CaO NazO KzO HzO- "' ., 'I . -·
0 g co "' 1{"'
./ ; /, / / /
:-- Ll'l - / "' · i- -
, :
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. " V{ti 0 -
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- f , --Analyses IA-IB - -- Analyses 2A-2 B -- -A naly ses 3A -3B Analyses4A-4B A naly ses 5A-5B FtGURE 5.-Gains and losses in constituents in oxidized tops as compared with trap portions o! flows. ( ee analyses, p. 37.) Points on the diagram are obtained by dividing the percentage o! each constituent in the trap by tho percentage o! the sam constituent in tbe amygdaloid a! top o! that trap, and multiplying the quotient by 100. The points then indicate lor ach constituent the number of grams of amygdaloid required to furnish the amount of that constituent present in 100 grams of lhc equivalent trap. 'fhus the diagram shows that there is as much Fe,o, io 35 to 85 grams of amygdaloid (aecording lo which pair of analyses is chosen) as there is io 100 grams of the corresponding lrap. Assuming any constitu nt as constant, all points lor other constituents to the right indicate a loss, and to the left a gain. Thus assuming i01 or Ah 1 to have remained constant in the change !rom trap material to amygdaloid, Fe,01 and CaO have been added and F'eO and MgO have been lost. (Leith and Mend, Metamorphic geology, p. 288, New York, 1915)
mall urface gu hes from the Kearsa,rge flow itself. The Kearsarge lode i as well oxidized below these gu he as el ewhere. A similar condition is present on the Baltic flow. If weathering has been effective in producing ferric oxide, it either mu t have worked with surprising rapidity before the gu hes covered the main flow , or el e it ha shown a surpri ing preference for action on the main flows. Especially difficult is it to explain the increa e in total iron content in the Kearsarge amygdaloid where covered by these gushes. The extra iron can not have come from lateritic concentration of the Kea arge flow, for tha,t is precluded by the evidence already adduced, an~ moreover none Michigan flows after they hav unci rgono ovcrnl · periods of alteration and mineralization and the changes due to each period are not readily separated. Two of the changes found to b charaoteri tic in the weathering of basic igneous rocks have been pointed out. In the five pair of analyses (see p. 37 and fig. 5) available for the compari on of oxidized top · and deeper trap ilica i con tant or has ga,in d rela,tivo to alumina. In four out of the five total iron has gained relative to alumina; in the fifth pa,ir the iron-alumina ratio is about constant, in pite of the fact that tl~e specimen that represents the top of the flow in thiS
TRATlGRAPIIY pair wa tal en f~·om. the lower part of. a ~onfragmental amygdaloid, wh1ch 1 alway · low r m u·on than th upper part. The later min ralizing pro e e have appar ntly exerted little etrect on th ilica-alumina ratio . The traps them elve contain about 46 per c nt i02 and 17 per cent Al20 3. The chief minerals added to the top of the flow that would affect the i02- Al20a rntio are epidote, pumpellyite, chlorite, and quartz. The fii::;t three of the e have le ilica and more alumina than the trap ratio; the quartz, of course, would increa e the ilica, but it is probably not pre ent in a proportion ufficient to exceed th ilica deficienc of the oth r three. The introduction of epidote, pumpellyite, and hlorite would cau e a lo of iron in the top of flows relati e to alumina and hence would a cen tua any effect of w atbering. The fact, th n, that the red top , a compared with their corre ponding trap , E e how a gain of both ilica and total iron relative to alumina, in pite of oppo ing tendenci s introduced by the later mineralization, argu '::: 100 again t weathering. By the evidence of tructure, texture, and di tribution of ferric oxid , ther fore, th weathering hypoth i app a1 to be liminated. The min ralogic evid nc point to the am c n lu i n. W athering of ba alt ,
n in tho lumbia Ri er lava fi ld, ha yi ld d
" u c
kaolinic and limonitic oil but ha left much of Lhe ma()'n tite un xidized. In th r d top E of tho 1ichigan and Idaho flow there i ;:; neither ka lin n r limonit · th I ld par , not- .s with tanding tl1 ir rninu ize and intimate ! conta t with h matit , ar rilcingly Ire h, but the marrn tit i alt r d almo t ompl tel . In Mi higan Lh magnetite ha in man place. been hang d to hemaLit Throu()'hout th zoo flow beneath it would, moroo r, be greatly impeded by the thin hilled lcin which, as alt·ead hown, wa usually roll d under the advancinO' il w or quicldy formed at the bottom. modification of thi idea i that the altering olution did not come entirely from the overlying flow but was afford d by moi ture and air pres nt in the permeable top of the underlying flow and ntrapp d there by the ou tpow·ing of the next flo, . The re ul ing team and ho air might au e orne oxidation, but it eem unlikely that the permeable top ' ould originall hold cnou()'h oxygen a air to equal the amount pre ent in exce f rric iron; and a for iron concentration, it i evident that nothing could be /
Per cent ) v
A J Per cent , k=' r
v
B
I) / 1(
thickn , of the flow. In the bn al of I ] aho FtG RE 6.- hang iu chamctcr and content of iron in di iTetent parts of lava Oows. A, moothand in tb f Wa bing n that. hn 0 not top Oow; B,brcccia-lop (low been afl'ected by recent w a therin th alt rat.ion of th magn tite i mor lo 1. onfincd to th upper part of the fl ' , ' -h re the conL n t of ferric ir n i highe t. flYDHOTHERMA L AT,Tf,) RATIO Alooration of rock by hot oluLion ema.oating from a.u igneou rna i a rnmon phon m non· a la a How, therefor , mjO'ht oncei vably be aJ tered by elution d riv d from a lat r flow ' ith which it i iJl intimat onta t.. pr f ha b n found, however, that uch action ha occurred to an appreciable degree in th Michigan lava , and this agone could not pos ibly xplain the ditrerencc whi h Lhe top and the bottom of a giv n flow xhibit. Downward p - sage of olutions from a liquid flo, t.o th cooled a compli bed by uch a proce , unles it left a orre pondinO'ly iron-1 ached rna or unl the irour bb d material wa removed by olution- neither of which ha happ ned. nder either form of the hypo the i , it would eem that a ba aJ t flo, which was able to for e ox.-yg n do' m ard for core of fe t into the amygdaloid, and e en into the trap, of th underlying flow, ought to produ Oin perceptible effe ton the top of an underlying f l ite onO'lom rate, ev n though the fel ite wa aheady almo t compl tcly oxidized and th ugh f l it is a more table ro k than ba alt. Yet tho tops of fel it conglomerate that are directly o erlain by ba alt nowhere how any p cial oxidation or any other chanO'e that can b a cribed to the action of tho lava. or ar the amygdaloidal conglomerate more
THE COPPER DEPO l'l'S OF MICIIIG; t~oroughly oxidized .where they are in. d.irect ontact I the nAxt OVCJ"l mg fiow than whet e th Y are para to l from it by a bed of fel itic conglomerate. Th.i hypoth i , ther fore, com to re cive no upport I from fi ld ob enat.ion . ATMOSPRE RJC OXIDATIO OF HOT TOP There is much to comm nd th id a that the la a top helve uuderaone ver rapid urface oxidati n while they were expo eel to he atmo phere in a highly heat d condition.3P This proce might ac ounL for the produ tion of h matite in toad of limonit , and for the fre hne s of th fold par m.icrolite and the sur ival of the delicat testur of th rock. tudy of the cold and the hot part of dump f ba ic lag how that a thin film of hematit -red i produced on the very urfa · of the slag, mainly b fore it ool below red hent; but fracture tha.t have open d in the solidified but till ery ho black lag aft r orne apparently ritical temperatur ha be n pa ed remain bla ·k and unoxidiz d; also where dr p nnd thin hee of the molten lag are form d by the ·pla he or patt r and ch.ill uddenly they olidify jet-black without und ergoing perceptibl oxidation. The c dark lags, xpo cd to weath rina in both northern and ou hern climate , undergo l change durina many years than they experienced .in fiv e or t n minut s h n at or ju t below r d heat. Many lag , however, do not become oxidized and r elden d at the urface, even while ho . The rea on for thi difference in beha ior i not apparent. If on a hallow layer of lag olidifying a a compa t gla and lo ing it heat '" r quickly a tliin red film will form in a f w minute , it i po ible that a thick lava fJow, ·which would remain hot for a much long r time, might ab tract o much ox:ygen from the air a to b come con iderably oxidiz d w ll down into it vesicular top; and the depth of oxidation would be till greater if th top wcr brec iated. Jnggar, indeed, I eli ve that air i carri d down by conve tion from the urfac to the d per portion of the flow, wh r it combine rapidly with the ferrou iron of the lavn. But uch actwn, while it may and probably do a c unt f r ome of the oxidation of the top and per hap might causc a little O:'l:yge11 to penctratc d ply into the lava that solidified as trap, could not aid in the oncentration of iron toward the Bow urfac s. This hot oxidation might hav helped ·to rai the oxyg n content of the fl w tops, but some other proce . rn u t have produced the main feature of iron nnd oxygen di tribution. JI1AGMA'rlC PROCES 'r:S Th remaining po ible ea,u ·es of tho e lded on page 3 relat to the b havior of molten magma and 19 Husscll, I. ., A rcconnnlssnncc In southeast.crn Washington: u. . Ocol. Survey Water- uppl y Paper 4, p. 13, I 07. , 1'. A., , ei mol. Soc. America Hull., vol. 10, p. 155, 1920. · arc o loscly a Hied 11 hoi b en them is neither ca y nor p it i . Mctgmatic gregation.- Tbc quickly hill d top and b ttom of Oow nr supp cd o hn e . olidificd before difl' r ntiati n hud made pr noun hang and th reforc tor present clo. cl th mp ition of the oriainal maama. ithin th flow, wh r . olidificntion by cry talli ~ing pro ·ceded m r 1 wl. , inkina of heav ery tal ha , in num r u cxRmpl , produced n concentration of the f 'rromn<m ian n titucnl· owRrd the ba~ e, ll'fl. ing tn. upp r potti n l ba ic, and floating of liahLcr 'l" tal ha incren d thi' .40 That graYitatiYe cliff r ntiaLi n ha op rated i indicated by o CUlT nee lik h zon fill d with fold par ry tnl j u t u nd r the am o-daloid portion of the Keal argc flow, in hi h th cr) ta l hnve e\·idontly mo,·cd upwnrd from d ep r in the flow; and he in in total and in I ITOU iron which orne of the flow h w in th ir lo\ r third, a compared with th middle, i on · t nt ' ith light incr a in magnetite, liYin , and pyroxcn toward Lbc ba c. Ri ing and inkin()" of cr tal however, doe no accoun L for d p oxidation and dor not e>.."Plain th con en tion of ith r iron or o.~ in th flow top . Fumarolic alteration.- It i cry talli~ing magma o-iv ' hi b mny attack not only older ndja ent r k bu als the earlier olidifi d portion of the maama it elf. In a ti,· volcanic region the la a b rd ring fumarolic ent i con picuou ly alt r d by he heat d g that emanate from the und rlyiog, till fiuid mn.<rma. It i known, in parti ular, that f rrou ir n may b oxidized by fumarolic a tionY e exampl that ha been de crib d by Diller <l2 and ob erved by .Mr. Broderick occur in the flow of the inder on , ncar Mount La en, alif. A ho n by Diller, the ind r Cone itself was formed abo~t 200 years ago, but the near-by fiow of blacl~ quartz ba alt wa poured out som what lat r. The flow came out inlo a small lake and i of the aa typo, exec dingly rough and difficult to ' alk upon. It ontains many great blocks of bla k lava that are reddened on some portion of their urface, which may be the top, the b ttom, or any ide; and it i trewn with many littl bcap of loosely cementcd brilliant-red ve icular fragm nts. Along part of the rim of the deep rat r at the top of the Cinder Cone th expo d urfaces of lava frag· ments are olor d briaht orange and red. Tbe di · tribution of all the c oloration of th rock bows clearly that they are related to fumarolic action. ' 0 Daly, H. A., Igneous rocks an~heirorigin, p. 450, 1914. Dowen, K. I.., 'I'M late stages or the evolut.ion or Igneous rocks· Jour Oeology vol 2J No. , suppl.,
"OauL!er, Armand, ompl Rend vol 132 pp 61 1 9 932 1001· vo!.l36, P· 16 1903, '
' f ' , t "Diller, J . S., A late volcanic eruption in northern alirornla: U.S. Oeol. SurreY nun. 79, 1891.
STRATIGRAPHY Thin and poli bed e tion of thi n d basalt grea.tly re em.bl ome that w~r . cut from the fineo-ra.ined iron-ncb part of br c01as ill the I cw enawan "erie. In th r cent a in the an i nt lava fre h microlites of feld and cry tal of olivine partly or wholly altered h matite are emb dd d in a gla y · matrix rov.·ded with minute particle of hematite, the abundan of ' hi h ac ount for the red color and for th high proportion of ferri · iron found by chemical analy i . The black Ye i ular ba alt oi inder on contain 4.30 per nt of iron in tbe f rrou tat and 1.51 per cent of iron in the ferric tate, a total of 5. 1 nt. Th redden d equivalent, altered by hot tbe arne amount f total onJy 0.79 per cent of thi i in he f rrou per cent being in th ferric tate. Tb.i , then, i a ca e of impl oxidation by fumar li a tion of iron already pre ent in the rock. What the xidizin a.gent wa i not known· it may ha. e b n team or ome more vigorou ly o:-.:idizin()' ga or i may have been atmo ph ric oxy()'en aff tin()' th rock where hot ga e kept it heat d for a lon()'er tim than el ew·herc. Thu , at ind r one fu.maroli a tion i a factor, direct or indirect, in locally oxidizing the iron of ba alt with ut a.H rin()' i am unt, and th rc ulting rock i mu h like that in man. f th r d t p f th Mi hiaan ba al . It may nC'xt be inquir d wh thC'r or not fumarolic a ion r any n Li n f Y 1 ani a e can a for h oxida i n of ir n but for that incr a in quantity f ir n which ha occurred in fl w top lik thC' K ar ar()'c amy()'daloid. Thi incr a. i n t m r 1 n r lativ ne, u h a wouJd b a. ompli hed h a partial r moYal of m other on titu nt , for, a alr·cad. mph iz d th r i n vid nc tha.t u h rC'm val ha occulT d. Th r h be n au a tual ndditi n f iron, and thi ir n hn been intr due d into th . olid O'}a without filii ng th , e ic ulfll' ca i tic . Th d po iLion f ferric compound , including h matit and f rri chloride around fumar le ha often been ob rv d.43 \Yh th r or n t uch addi i n of f rri i.r n cou ld be in orponitcd into tho rock matter iLself i a que tion on whi ch thor i no e idenc availabl . E en if it is granted, h , ever, that typical fumarole ould produ a thorough pcrmeati n of h rock by f !Tic oxid around local \'On t , it i n t ea y to under tand how th y r.ould aft' .t t, a. 'ked nnd fa.irly uniform the top of ore of superpo od flow . In th br ciatcd top. that wor ontinuou ly brok n a th flow was in pr gre ga e migh t ri. c at all point through th top from th und rly ing lava. In the smooth top it w uld be xpectcd that the ()'a would e cap throu()'h mor lo ali1.ed v nt. , but n uch v n ha c h on r ocrniz d. An uch a tion "Clarke, F. w., Tho <Iota r g ocbcmistry, 5th cd.: . s. Ocol. urv y Dull. iiO, llP. 261 ct seq., 192<1. Allen, E. 1'., ('hemical !lSI ct · of volcanism: Frnnklin In~t. Jour., voi. 103, p. 34, 1922. i clo ely akin to the a. tion from the O'fl e of the flow before olidifi ation that di m the followin()' tion. · Fumarolic a tion in the tri t en c ben, although it may a. compli h both the oxidation and he dcpo ition of iron around local v nt~ , could not afl' ct the wide pr ad, continuous, and deeply penetra in()' oxida.- tion C'cn in the :Yfichigan flow . 1ction of ga e from the flow ·.- Ther remain to be con idcr d the a ti n of ga e gi v n off from the fl ,,. i elf befor olidifi ation and a tincr on the melt and on th gath rin()' ru t a they a ended. Tha ga ri ing from the lower part of the ).:[i higan fl w wa abundant in th upper part while they were fluid i ho\m by the profu i n of ve icJe . How much more ga wa liberated befor the vi o ity became ufficicnt to impri on it a bubble i- not known, but it may ll be that in both th m oth-top and the iat d-top flow the ga repr ented by v icle i the mallcr of the to al. N arly all ob erver- of flowing lava r fer to th - great 'olumc of team and oth r ()'a c O'iven ofl'from it top. ih . tri 44 for example, who inv tigated volcanic o·a e at Etna a : ' Th fre h, till flowin()' la,·a a t like one O'J' at fumarole and mit- from i urfa c white fume .' ther example of the high era ont nt are cited in the eli u ion of th la '' a flow on 1 a()' · 32. The effect of the e O'fl c , if th y produ d any cfl'ect , mu t have been imilar in di tribution to the ob oxidation and iron nrichm nt.
the chief direc ion of e cap - of th ga e i upward toward the urface, the lo' er part of the fl w will come into ontact wi th only th ga that it held, but th uppermo part, o long a it remain liquid, will b tra er d not onl~ by it ga but by n arly all that ilib rated from th park of the melt low r do·wn. Furtherm re, th upper part a it become vi ou and tend to lacken it ra.t of flow compar d with the mor fluid material deep r down, will r ceive the ga not onl fr m the portion- ori()'i nally below it but nl o fr m Lho en ' portions tha flow underneath it. If, then, a given porion of la,va i chancrcd ch mically in proportion to the quanti y of ga that pa e through it th chemical efl'ect f th ga hould be lea n ar the bottom of t.he flo,v and greate t ncar he top. The di tribu tion of h ma.titC' i bus in trikin()' harmony with the h pothe i that it wa form d t,Ju ugh the agency of ga liberated from the. flo, fl it O'radually cooled. Th hypoth i recci,·e further upport from h di ·tribuLion of the hemat.it a con uudcr the mi roopc. The particle f hem a tit f rm a pa tem that m chara. tori ti ally ign ou . The are no t depo - itcd in the vc i le nor included in tb fold par micr - lite but aTe rowdcd around both, a if pu, hed a ide by or a trncted to he growing ry tal and cxpnnding " ('ite.d b~·
THE COPPER DEPOSITS OF MICHIGAN bubbles. All this suggests that the hematite was formed before the olidification of the ro k and i not a product of later alteration by fumarole or othenvi e. The chemical composition of the ga e who e action on the Keweenawan flow i so trongly sugge ted can only be conjectured. Information regarding the ga es even of modern la> as i not abundant, but there is evidence that they may contain both a volatile compound of iron and an oxidizing agent. The emanations from some of the lavas of Etna ontained ferric chloride, though those from others did not. Iron oxide was depo ited by fumarole in the Valley of Ten Thousand Smokes, Alaska, 45 and many other instances could be cited. Emanations from intrusive magmas, again, have in many places depo - ited not only magnetite but hematite in large quantity. The iron is supposed by some to have been expelled in 5 .B QJ
70 Q) 0. The t mp ratur of basaltic la o on i uing 1s probably abov 1,000° . We 1 rna con idor, th n, tho probabl reaction of the tw~ mo t abundant ga s during th cooling of the flo> s. For the q u ation Ea tman and E van 47 have ho> n from 675° to 1,000° . th hydr g n in the mixture ranae from 46 to 9.9 per c nt by volum - that i , at th hicrher tempcrfttme th ro wu little t nd ncy to th oxidation of ferrou iron, bu t at the low r temperature uch oxidation v a pronounc d. Day and hepherd 4 have hown that nt 1,100° . water i sen tiully n utral to powd r d ba ultic rock. Th re uro no publi hed dnta on the r a tion of water and ferrou iron below 675° ., but h pherd 49 tat Ox'"Jgen, and iron , which ha be n di cu ed by that at and b low 600° . t am ha a trongly oxidizing effect upon ferrou iron. Uuch i known of the ch mica] t m arbon, Findla .50 Tho tability r lation of mo t intere t in the pr n t di u ion nr th e of 0 2, CO, FeO, and F .03. Figur 7 giv the tabilit relation for the equatlon F o3 . + 0 4 3F eO + COz. The temperatm e mo t fav rabl for th movem nt of the reaction to t he 1 ft i 490° ; nt 1,000° the ten laney i trongly to movemen t to the right. It would appear, then, that wh n th loxn i. ued and until th y had r a h d a temperature 33o'35o' 40o' 450' soo· sso' 6oo' 6so' 1oo· 1so' 800 850 900 950 990.. below 1,000° the tendency for H20 or z to Degrees Centigrade oxidize FeO would not b mark d. the tem· FJGUR~; i.- tabi litpclation for the equation Fc,O,+COp3FeO+C02. (After Findlay) perature decrea ed, however, this tendency uJd the form of ferric chloride. It is therefore reasonable to uppose that the gases of the lavas contained some volatile compound of ferric iron, together with agents capable of oxidizing the iron already in the flow. If the iron was conveyed upward as volatilized ferric chloride, it fixation as hematite may have been aided, if not mainly accomplished, by atmospheric oxygen. which would doubtless be very active at certain temperatures. Jaggar 16 believes that its action may penetrate deeply under certain conditions. F ew data are available regarding the ga es given off from the e old s. It is of intere t, neverthelcs , to con id r some po sible or probable reaction , though it must be recognized that the actual reaction were much more complex. The following i po ibly the simple t condition. team or water vapor is the most abundant ga given off by cooling lavn , and next in amoun t is caJ·bon dioxide. ay and Shepherd found the aa e from Kilauea to con i t largely of water andb the dri d ga cs to contn.in from about 24 to 74 per cent of 0 2, mo t of them 60 per cent. or more, and 3.5 "Zies, E. 0 ., The fwn arolic incrustations in the Valley or 'l'eo 'l'housantl mokes: at. Oeog. Soc. Contr. 'l'echnical Papers, vol. I, 1 o. 3, 1924. "Jaggar, '1' . A., jr., Seismol. Soc. America Bull., vol. 10, p. 155, 1920. increa e to a ma."\.'irn.um at 490° for 0 2 and 11 maximum at some undetermined temperature, pr b· ably below 600°, for H 20, or a point at which the tops would have been solidified or very vi cou . The top of the flows would reach the oxidizing tom· perature for FeO oone t and would doubtle be held at a favorable temperature a long a large volume of gas were po. i.p.g through them, so that in re p ct to t micro.ture nnd quantity of gas pa - ing through th m the top arc mo. t fo.vorably ituatcd for a relatively long period and consequently high 1 degree of oxidation. Any rainfall on th urface of the flow while they were still hot would act a an oxidizing agent, so that this may have been an addi1 tional factor in the high oxidation of the top, a well as contact with the oxygen of the air. As et forth in the section on formation of lava tops the mooth tops occur on flows that i sued with a low gas content and the rough fragmental tops on flows that i sued with a high ga · content. It i a "Eastman, E. D ., and Evans, Jl. M., Equili bria Involving the oxides of iron: Am. Chem., oc. Jour., vol. 46 p. 41 Day, A· L., and Sbcpbe;d, E . S., .\Vater and volcanic acti vity: Oeol. Soc A mcnca Bull., vol. 24, p. 603, 1913. '' Shcpberd, E . S., oral communication '° Findlay, Aloxander, The phase rule ~od its applications ,5th ed., p. 248, J923
STRATIGRAPHY reasonable as umption that the high oxidation of the breccia tops is due to their relatively high gas content and that the relatively slight oxidation of the smooth-top flows is due to low ga cont nt. This long discu ion, then, leads to the general conclusion that, although the oxidation of the iron in the flows may have b en due to everal agencies, it wa effected in dominant part by the action of the o-a es given off by the la a it elf ; and it i regarded as probable that the gase mo t active in the process w re HzO and COPPER CONTE T OF 'l'HE BAoALT The literature hold many ref r nee to the pre ence of copper in fresh ba. ic ro k , both intru i' and xtru ive. The analy e of ba alt , dia.ba e , and gabbros compiled by Wa hington 61 hO\ that copper was determined in few, but in th eleven analy e in which copper was determined it wa r ported in q uantities ranging from a trace to 0.94 per cent of CuO. The average of the e i 0.27 per cent of uO, or 0.22 per cent of Cu. A hown beyond, thi amount i five or six time that of the copper found in fre h traps from the Keweenawan eri . Lane 62 and Grout 53 have a et"ted that the fr h Keweenawan ba alt. contain mall quantitie of copper a an orio-inal r pyrogcneti on tituent. If the ba alt contained unu ual amount for ro k of thi type, that fact mio-ht have, a the author mphaize, a signifi nn t b aring o the origin of th omm r ial con entration f pp r. Lane 54 oncluded that the whol ba alti ri s in it pr ondition contain about 0.02 p r nt f opp r. rout found from 0.012 to 0.029 p r ent f copper in enral ampies of ba alt that he regard d a fr h, tak n from the [ewe nawan f Minne otn. Ue al o found that the fre he t p imon contain d the mo t copp r and the mo t altered p cimen (charact r of alterati n no given) the l a t opp r, and he inf rred that copper wa remoYed b th al_t ration . Fr m ro copi work and from finding that in a partly altered roc.k co?taining 0.02 p r cent of coppoT only one-tenth of tht amount wa olubl in ni ric acid, Grout c ncluded that mo t of th copp r i pr s n t, in the fre h rock, not M metalli copp r or a. sulphide bu t in the form of an in oluble ilicate, probably as o int d , ith the abundant ba ic ilicates of the ro k . Morozewicz/ 6 on the other hand, timated that th ?asalt dik of the Command r I land carry opper m the fr sh rock to the extent f 0.04 p r ent. Fr m te ts mad on ev r~tl min ral con tituent h c ncluded that the magnetite contain tho pp r ; no II Wash! gt 11 La 0 on, H . . , U.S. Gool. Survey Prof. Paper 99, pp. 1049-l!OO, 1917. 110 no, A. C., Miebigon Goo!. urv y Pub. 6, vo!. 1, pp. 175 t seq., t91l. 11 0rout, li'. F ., Econ. Geology, vo!. 6, pp. 473-476, 1910. P. Cit., vo!. 2 p 778 llM , .. lDSGI ~rozewicz, J., Das Vorkonunon von gediogeuom Kupfer au[ q n Komandor· 0 Com. g6ol. M6m., new ser., Jivr. 721 pp. 45-88, 1912. copper wa found in the pyroxene, and no sulphm was found in the rock. In the course of the present examination, an independent estimate of the copper present in the Michigan basalts was made. About 20 pieces of drill core, each repre enting the freshest-appearing trap obtainable, were taken from drill holes on the Cliff La aile ' ' eneca, Ahmeek, and Osceola properties. All of them were combined into a composite sample, which was analyzed for copper soluble in nitric acid, for total copper by fu ion, and for ulphur. The purpose of determining copper after fusion and sulphur was to ascertain the total copper present and gain an idea of its tate of combination. If more copper were obtained by fusion than by olution in nitric acid, the fact would lend support to the commonly held views that copper was pre ent in the silicate as copper silicate, or in magnetite as an oxide. Similarly, a composite sample was made, from the arne drill core , of tra.p that looked altered or was fissured and chloritized but that contained no copper isible to the naked eye, and a third sample consisting of nmygdaloids, which likewi e held no vi ible copper. The rea on for making the e two composites was that Lane had included materials of these kinds in the samples from which he estimated the average copper content of the trap , and it was thought that his inclu ion of amygdaloid and of altered and fissured trap probably gave him a higher average copper content than would have been obtained from the freshest trap alone. The composite samples were assayed by W. J. Hillenbrand, of the alumet & Hecla Co., with the following result , hich are subject to an error of about 0.02 per ent. Copper and sulphur in composite samples o.f trap and amygdaloid coprer Copper by o!ub e in fusion ulpbur nitric ncid Thus, the freshe t obtainable traps of the district ontain a f w hundredth of 1 per cent of copper. The quantity is greater than that found by Lane and by Grout in the Keweenawan of Minnesota, but it is much less than that hown in analyse of similar rocks from some other loca.litie . It was expected that the altered trap and the amygdaloids would run higher in copp r, but the results show that tb y have about the same amount as the freshest trap. The copper obtained by fusion i the same, within the limit of error, as the opp r soluble in nitric acid, so that little, probably none of the copper is contained in insoluble silicates. Olivine is soluble in nitric acid, tmd if olivine were present in the rocks any copper
THE COPPER DEPOSITS OF MICHIGAN that it contained would be.soluble in acid. However, the olivine is practically all altered, and whether or not its alteration product, serpentine, ' ould yield any copper it might contain to a nitric acid solution is not known. Sulphur is present in small amounts, more than enough to combine with all the copper as chalcocite but not so much as would be pre ent if the copper occurred in chalcopyrite alone. The analy es uggest, therefore, that the copper is probably not pre ent as silicate but that it may be pre nt in part as sulphide and in part in ome other ta!ie of ombination or a native copper, or 'wholly as chalcocite, or as chalcocite and chalcopyrite together. Poli h d section of the duplicates of the trap ampies included in the composite sample how under the microscope that copp r is pre ent in tiny rounded speck of native metal and chalcopyrite. J ative copper is more abundant than the sulphide. In ome sections both are pre ent, but mo t contain only the one or the other. Specimens of the Green ton flow (none of which wa included in the compo ite ample) show native copper, chalcopyrite, and probably chalEXPLANATION
Senostone Flows and sed1ments (Cambnan a nd Keweenawan) FIGUR E .-Geologic section rrom Vermilion Lake, Minn., to Calumet, ll!ich., showIng probable extent or Duluth laccolith b~nea th Lake uperior basin. ( ec pls.l and 3 ror areal geology.) cocite. Although micro copic e timation of amount so minute can not be quantitative, the definite copper minerals seen appear to be present in the proper order of abundance to account for all the copper indicated by the analyses, and it is probable that all or very nearly all of the copper is pre ent a nativ metal or sulphides. . Is the copper in the basalts primary, or has it been introduced after the rocks were formed? If the Keweenawan lava came from the arne general magmatic ource a that from which the copper of the ore depo its wa sub equently drawn, it would seem reasonable to suppose that they would contain a little primary copper; on the other band, all the rocks have suffered more or less alteration, and some copper may have been introduced into even the lea t altered. The facts from which conclusions are to be drawn are the e: (a) The fresbe t traps that can be obtained contain only minute quantitie of copper. The available analyses of rocks of the same family from other localities on the average six times as much copp r a the l\1gan ba alt ; (b) these freshest traps, however, have been somewhat altered; (c) the fre he t trap , the fi.s ured and altered traps, and the amygdaloid , when all are carefully elected to holf no copper to the e, contain ub tantially equ~ quantiti of opp r, within the limit of analytic~ error; (d) a.naly e how th pr en e of ulpbur and ugge t but do not po iti ly prove that the copper~ not pr ent as ilicate or oxide; (e) micr copic exam. ination of poli hed e tion taken from th ame mall piec a w re analyzed ch mi ally rev al Lhe pr ence of minute particl of nati copper and copper ulphicle throughout v n the fr he t trap. From th e fact the foll wing mor or l tentative deduction may be mad : (a) Th pre umption trong that th e d fmit opper min ral contain all the copper which the analy es h w; (b) the pre umption i al o trono- that part at 1 a t of these copper mineral are primar. c n tituent of th trap; (c) it is po ible r v n probabl that om of the copper wa introduced by mineralizino- olutiou . In the oa1 e pegmatitic or dol ritic 1 n that are common in . om of the thi k flow both native copper a.nd c pper ulphid occur in intimate a o iation with the rock mineral a w 11 a with alcite and locally with prehnit . It m. mo t lik ly that all these mineral are prim ry lio the p gmatit , ' hich evi· dently re ulted from a differ ntiation of th lava during cooling. 1 TRUSIVE ROCKS GENERAL FEATURES Throughout the di trict intru iv ro k occur in the lower part of the eri , n ar the Keweenaw fault. ( ee fig. 8.) To the outh, at P rcupine Mountain, and north of Lake Goo- bic they are pre ent in the middle and upper part of the erie al o. These intru ive rock compri gabbr and "gabbro aplite" imilar to the gabbro and red rock of th Duluth lacco· lith or lopolith; quartz porphyry and felsite, which are regarded as probably the fine-grained equivalent of the Duluth red rock; and dark chloritized ba ic dikes, which 1are pre ent north of Lake Gogebic. The e rocks have been intruded in mas e of variou form; a stock occur at Mount Bohemia and proba.bly ome of the bodies near the Wisconsin boundary also are stocks; the Mount Houghton intru ive body and ome bodies north of Lake Gogebic appear to be sills or laccoliths; and dikes occur at many place toward the Wisconsin boundary and very rarely in the northern portion of the di trict. The similarity of the rocks to the Duluth gabbro and red rock serie and their occurrence near the ba e of the Keweenawan and along the great Keweenaw fault has led to the belief that they are a part of ~he Duluth laccolith, which crops out in a imilar relatiOn on the north side of the basin and probably extends beneath the basin as is more fu:liy di cu ed under " tructure" (p. 50).56 16 Vau Rise, C. R., nod Leith, C. K ., op. cit., pp. 377-37 . Grout, F. F., 'l'h~ lopohth, au Igneous. rorm exemplified by the Dwutb gabbro: Am. Jour. Sci., lt ser., Vol. 46, pp. 516-522, 1918.
STRATIGRAPHY Rocks of the gabbro and red rock type occur at Mount Bohemia and near the Michigan-Wi con in bow1dary, where relatively large bodie are surrounded by zones showing pronou~ced k alteration. Diamond drilling at the Indiana mme also encountered gabbro. siliceous and fine textured as these. The ''Chippewa" felsite and the felsite of Porcupine Mountain are similar to those just described but have been regarded by geologists who have given most study to them as flows. There is also a similar rock at the Bear Lake prospect, west of Calumet, which has the appearance of a rhyolite flow but may be intrusive. This is in the Freda sandstone and is stratigraphically the highest known occurrence of felsite. The gabbro of Mount Bohemia i a dark gray-red granitoid rock of variable though typically medium grain. Its es ential mineral ar plagiocla e, pyroxene, and magnetite in rou()'hly equal amount . c es ory ' The rocks vary considerably in texture in different bodies and also in a single body. In the coarser varieties phenocryst of quartz and feld par 2 or 3 millimeters in diameter are present rather abundantly. These are inclo ed in a felsitic groundmass of quartz and feldspar. The finer varieties are typical felsites, in which phenocry ts are either small and scarce or altogether ab ent. D ark minerals are characteri tically absent from these rocks, but practically all have a reddish color due to the pre ence of countless dustlike particles of hematite, which appears to be an original con tituent. All th se rocks, as well a the pebbles of irnilar fel ites and quartz porphyries in the conglomerates, are rich in ferric iron. The chemical minerals are horn blend , apatit , quartz, titanite, and ulphide . The pyroxene i partly altered to hornblende and chlorite, and th feld par to ericit and chlorite. Leucoxene occur as an alteration product of tita.niferou magnetite. 1 hi rock has been d cribed by Wright 57 and called oligocla e gabbro. The a sociated red rock or gabbro aplite i a coar ertextw·ed rock composed e entinlly of oligocla -albit and quartz with ubordinate ortho lase, magnetite, apatite, titanite and zir on. It occur a dike and a a tock in the gabbro and adj acent ro k . The following analy e , taken from Lane' report/ show the chemical compo ition of the e and alli d iutru ive rocks : Analyses of intrusive rocks from Keweenaw Point
:
2. OJ .J. 43 21. 00l!goclasegabbrof Mount Bohemia. L. irschbraum, analyst. · abbro aplite, ount B hemin. L . Kirsrhhroum. analyst. 3. Mount fl oughton Quortz porphyry. Micblgnn Oeot. Surv )', vol. ", pt. 2, p. 1 I . F. P. Durrall, analyst. 4. ~'!ouu t liough ton quartz porphyry. Idem, p. 42. F . . P. Burrall, an ysl. QUA.RTZ PORPHYRY AND FELSITE Bodie of quartz porphyry and felsite are pres nt at several pla es n ar the K we naw fault. The larger known bodies near the fault from north to south are at Fi h ov , Bare Hills, and Mount Houghton, south of liff, south of Ahmeek, ea t of alumet, and at th Indiana min . orth of La1 e Go()'ebic are some large mas es of quartz porphyry that are pTobably intrusive. At se eral of th localitie tb r is no clear evidence of the relation of the e rna es to the flows and sediment , but wher the relation is obvious they are intrusive into these ro ks. Th fine felsite may show di tinct fl w structure in bodi s that are known to be intrusive, as is common for ro ks as 11 Wright, 1<'. E., Tho tr~ ro~s o~Motmt Bohemia, Mich.: Michigan Oeol. Ropt. for 190 , pp. 363-370, 1909. )QII. ane, A. C., Michtsau Oeo). S11rv y Pub. 6 (Oool. seJ'. 4), vol. 1, pp. 106-109, omposition of the Mount Houghton mas is hown in the analyses given above. The other bodies are apparently of similar compo ition. BASIC DIKES ery few basic dikes have been noted in the part of the district that has been most studied. A few 1 examples of probable dikes were seen in the drill ore from the north end of the district. In the Onondaga drill section, north of Lake Gogebic, numerous small fine-grained green, highly chloritized dikes cut both the quartz porphyry and the lava flows. The intruded rocks for a few inches from the dike contact are considerably chloritized. AGE OF INTRUSIVE ROCKS There is no basis for determining the age of the intrusive rocks more definitely than as Keweenawan or post-Keweenawan. The felsite fragments in the conglomerates closely resemble those found in place and are generally believed to have been derived from similar masses, as they are unlike any earlier rocks known in the region. If this belief is correct, felsitic intrusion, extrusion, or both must have begun early in Keweenawan time to have formed the source of the early conglomerates, and the igneous activity probably continued into late Keweenawan time, at }east in the Porcupine Mountain area, where the latest known Keweenawan rocks are involved in the domical tructure thA.t is attributed to intrusion. Similar evid nee of late igneous activity is afforded by the presence of A. fine-grained acidic rock well up in the Freda sa.nd tone (upper KeweenA.wan) near Bear Lake. Whether the intrusive rocks near the base of the series, as represented alon<>' 1\:eween&w Point1 are early or late is not known.
THE COPPER DEPOSITS OF MITCHlGA STRUCTURE The broader structural features of the Lake uperior region have been summarized by Van Rise and Leith/ and only such features need be set forth here as bear directly on the rocks of the copper district. FOLDS The dominating structural fenture of the region is the Lake uperior syncline. This tructural ba in is roughly outlined by the present area of Lake uperior with a southwestern extension into Minnesota. We t of Keweenaw Point the general strike of the axi of the basin is about . 30° E., extending into i[innesota. Ea~t of Keweenaw Point the strike i ea t of south. In thi direction the syncline extend to the east end of Lake uperior. Keweenaw Point is on the south limb of thi syncline. The north limb is eArposed on the north shore of Lake Superior and on Isle Royal. Bed that are thought to be at essentially the same horizons crop out on Keweenaw Point and on Isle Royal, about 50 miles apart across the general strike of the ba in. The syncline is asymmetrical, the beds on the outh limb dipping notably more steeply than tho e on the north. There is a teady flattening in the dip of the beds from the base of the Keweenawan series toward the top. On Keweenaw Point the dip ranges from 80° in the lower beds to 10° at ome points where the upper Keweenawan sandstone dip under the lake. The south limb of the Lake Superior yncline is irregular in detail, being made up of a series of tran - verse anticline and synclines that pitch down the dip of the main trough. ( ee pl. 3.) Keweenaw Point is near the crest of a northward-pitching anticline that causes the strike of the beds to change between the south and north ends from north of east, through eust, to south of east. To the southwest the Keweenaw anticline merges into the Ontonagon syncline. West of the Ontonagon syncline is another anticline with its crest about at Bessemer and Ironwood. These are very broad, open folds, the distance between the adjacent crests of the Be semer and Keweenaw anticlines being approximately 110 miles. On these large cross folds are nwnerous subordinate anticline and synclines. of similar character and trend as the Allouez anticline, the Isle Royale (mine) synclille, the Balti<· anticline, the Winona anticline, the Firesteel River yncline, and the Ma s anticline. These also are broad, open folds but are only 5 to 10 miles across, as contrasted with 100 miles for the major cross folds. Some of the folds, such as the Allouez anticline and the I le Royale syncline, show a rather uniform bending of the beds, with some faulting near the crest. In other , such as the Baltic and Mass anticline , the b ds are b nt harply at.the crests and at the margins of the folds, but the lunbs of the folds are fairly traight. oo Van Btse, C. R., and Leith, 0. K., U. S. Geol. Survey Moo. 52, p. 620, 1911. The domical uplift at Porcupine Mountain, al 0 a minor fold on the outh limb of the Lake uperior syncline, is 12 to 15 m.il 1 ng and 4 to 6 mile wide. It has the ame g nora} trend a the Lake uperior syncline. J umerou faults nre associated with this dome. FAULTS The Kewe naw fault, the major fault of the region, trike in a gen ral northeasterly dir ction, parallel w:i th the Lak upcrior yn line in this area. It varies in trike, however, and in general bends with the tmn. . v r e northward-pitching anticline and ynclines on j the ou th limb of th Lak uperior Basin. The fault i known from B te Gris a , near th end of I eweenaw Point, where it i cov r cl by the wat rs of Lake U· perior, to Lake Gogebic, a distance of about 100 miles. It doubtle s extend farth r cast under Lake uperior and may be repre nt d to th west by faults that have been found in Wi con in.60 The fault is r verse or overthrust and ha for eel th Kew enawan rocks up and over the Jacob ville ("Ea t rn " or ambrian) , and tone and thus duplicated the Keweenawan and the overlying so.ncl tone. The rock of the main Cop· per Range and the outh T rap Range are believed to have been once ontinuou and are now eparo.ted by the Keweenaw fault. The fault dip northwe t. The angle of dip is known in few place but where known ranges from 20° to 70° and in the main steepen or flattens with the dip of the overlying lava . The rocks adjacent to the fault are much broken and di · placed. In general the normal northward-dipping lava flow on the hanging-wall ide of the fault are bent downward so that in pla e the clip is reversed, and the flat-lying sand ones on th footwall side are turned up rather abruptly. ssociated with the main fault o.re numerou branch faults, some of which are known to diverge half a mile from the main fault, as that at the Mayflower-Old olony mine. The flows in the block between the main fault and the branch are nearly flat-lying or have a southerly dip. The rocks of the lava flows for several hundred feet from the fault are in most places greatly broken and brecciated. This condition has rendered diamond drilling near the fault difficult and expensive and is the main reason why so little definite information re· garding the attitude of the fault is available. The sand tone is less brecciated. In the following para· graphs are recorded the definite facts concerning the fault that are available : At Bete Gri the fault can be seen under the shallow waters of the bay, but little is known of its attitude. outheast of Cliff a diamond-drill section shows two faults over half a mile apart, ·with a block of nearly horizontal flows betw on them. At the Mayflower-Old Colony mine diamond drilling has shown a branch diverging from the main fault to oo Aldrich, H. R., op. cit., p. 569.
STRUCTURE a maximum di tance of about half a mile. Between the main fault and the branch the bed are nearly horizontal or have a slight southerly dip opposite to the normal dip. The branch fault was evidently formed after there had been some movement on the main fault, as it reache the "Ea tern" sandstone in depth. The dip of the branch fault is omewhat steeper than the normal dip of the trap bed at thi locality. The dip of the main fault is not 1 nown but i vidently le . At Wall Ravine the fault i poorly eA.rpo ed but seem to dip about 20°. The "Ea tern" and tone beneath and adjacent to the fault is sharply upturned, and a vertical "wall" formed by a re i taut layer of the upturned "Ea tern" and tone has given the name to the ravine. The t. Louis diamond-drill ections how the fault to dip almost parallel with the normal dip of the trap bed,· about 3 °, and there seem to be little disturbance of the rock near the fault. Where expo ed 11t Dougla s Houghton Fall the fault dips 30°-32°, a flatter angle than the normal dip of the bed . The bed near the fault, however, dip only 15°-20°. In the Torch Lake diamond-drill ection the relation are complicated by intru ion, so that the dip of the fault is uncertain. The bed , however, fiatten very much a the approa h th fault. Where· expo ed at Hungarian Fall tb fault dip 30°-32°. The bed abo,~e th fault are r latively flat and are evidently draaa d down by the fault. At Oneco two diamond-drill hol cu the fault a depth, and it outcrop ha b en l ated fairly lo ely near by. The a rag dip of the f au 1 t i 17° between the out rop and th near r hole and 22° bet' en the outcrop and the more di tant hole. Th b d flatten in dip to' ard the f.ault and are po ibl overturned near it. Accordina to H. W. Fe iocr th trap bed xpo ed by the oxplorati n n ar th fault along the 'WPO eci Baltic horizon in th land f tho Ar 'ad ian ,on olidated opper tely overturned and dip to the east. Where xpo ed in a ravin outh of I le Ro al the fault dip 56°, n arly p!U·all l to th b d above it. There are other fault , probably r lat d to the eweenaw fault, within the trap eries near by. the Atlantic prosp ct the fault wa lo ate~ at Pomts 1,200 feet apart v rti ally and 300 feet liorizontally; t.he dip, a indi ated by the e point , i 50°, which is somewhat flatter than the dip of the tra1 beds immediately above. In the vicinity of the Indiana mine the b d near the fault are much brok n and contain intrusi e rock . At the Lake and South Lake mine there i a broad, gentle syncline and 11 narrow, st -ep anticline between the fault and the point where the rock ha the normal Westerly dip. The folding produced the e features Was a part of th fault movement. The fault has been exposed at the Victoria mine, where a section of the adit shows that it dip about 70°, a little more teeply than the bed . In addition to the Keweenaw fault and those closely a ociated with it already mentioned, there are many fi ure near the Keweenaw fault that dip nearly parallel with or omewhat steeper than the bed . These are particularly con picuou in the mine opened near the Keweenaw fault. On these trike fis ure the movement may be carcely noticeable or may be a few feet but is rarely large. There are also a few reverse faults which cut the beds transversely at a somewhat higher angle, such as the Ha.ncock nnd Isle Royale faults, with apparent horizontal di placements of about 600 and 175 feet, re pectively, but in which the actual displacement along the direction of movement was doubtless several times a. much. The Branch fi sure of the Michigan (Mine ota mine) may be of this cla but has a relatively small displacement. Another group that may be put in this class are fault or lips that parallel the beds. These are difficult to recognize, and it i usually impossible to determine the amount of movement on them, but there can be no doubt that faulting has occurred between the beds, 'B pecially on the conglomerate beds, which rather characteri tically ha e on the hanging-wall side a heavy gouge that ha resulted from movement. Evidently the plane surface of the conglomerates as ontrasted with the rough urface of most of the flows made the top of the conglomerate a zone of easy lipping, and much of the movement during the tilting of the bed appears to have occurr d on the conglomerate . L. L. Hubbard 61 has particularly emphasized faulting of this type. There are large reverse fault around the Porcupine Mountain dome. Wright and Lane 62 how a fault extendina along the ntire south margin of the dome, and th re i a trong reverse fault in the workings of th bite Pine mine. nr the ere ts of the anticline there are numeron tran v rse :fi sure that apparently have resulted from the bending of the rocks when the anticlines were forrned. The e are particularly noticeable on the Kew enaw antic.line, from the orth An1erican mine to Copper Harbor, where the fi ures cut the Greentone ridge. In the traight stretch between the Allouez anticline nnd the beginning of the harp urving of the Kewe naw anticline at the North Ameri a.n mine the Green tone flow is massive and almo t free from fi me , but it is strongly fis ured around the anti line. Man of the fissure ai·e mineralized- the li:ff, Phoenix, opper Falls, Central, Dela' are, and many other . Mo t of the low gaps tlu·ough the Gr en tone flow have also evidently been clotermin d by fissure . Along many of the ten ion " MlcWgau Oeol. Survey, vol. 6, p. 91, l 98. "Wright, F. E., and Lane, A. C., MicWgao Oeol. Survoy Ropt. for 1908, pl. 1, 1909.
THE COPPER DEPOSITS OF MICHIGAN breaks there has been some movement, and along some it may reach ten and po sibly hundreds of feet, though there are no great fault . Fis ure and faults of the same character are present on some of the smaller folds, as the Allouez, Baltic, and Mass anticlines. Where · there is much displacement on the faults associated with the anticlines, it i commonly in a wide zone of shattering, in some extending over a hundred or even several hundred feet, as in the Allouez shatter zone, on the .Allouez anticline, and the zone between the Baltic and Trimountain mines, on the Baltic anticline. Commonly where there ha.s been much movement one or more planes in the zone show strong gouges. The fissures and faults on the smaller anticlines are mineralized- for example, the Mass fissure and Arsenide fissure, on the Allouez anticline, and similar though less highly mineralized eros fissures on the Baltic and other anticlines. AGE AND CAUSE OF FOLDING AND FAULTING There is a very close relation between folding, faulting, and igneous activity in the region, and all three processes are probably different expression resulting from a common cause. Two general ideas have been advanced rega.rding 1 the relations of folding to igneous activity. One as wnes that the synclinal tructure of the Lake Superior basin is the re ult of some phase of igneous activity. Thus Lane 63 has thought that the material of the lavas came from beneath the Lake uperior basin and that the pace thus vacated was filled by the settling or slumping of the crust above. Grout 64 considers the sub idence of the roof of the Duluth gabbro laccolith or lopoli th a factor in the formation of the Lake Superior syncline. Hotchkiss 65 likewi e considers the origin of the yncline to be a sociated with the igneous activity. He pictures a great body of igneous material rising slowly through the earth's crust beneath the present Lake Superior basin. For a long period before Keweenawan time thi rising igneous mass elevR.ted the smface above it and tilted the rock away from the present basin. The rising surface wa eroded, and the material thus derived was deposited around the margin. In Keweenawan time the magma broke through to the surface as ba altic and felsitic flows. This release of pressme and transfer of material to the mface caused the crust to s~ttle. The process of transfer and settling contm~ through the Keweenawan epoch, resulting in a tiltmg of the beds toward the axis of the basin the earlier beds being most affected and the late; ones progressi ely less, as outlined below. ::Laue C., Michigan <;Jeol. Su~vey Pub. 6 (Oeol. ser. 4), vol. 1, p. 22, 1911. Grout, .E. F., '_!'he lopohtb-an 1gneous Corm exomplifled by tho Dulutb gab· bro: Am. Jour. c1., 4tb ser., vol. 46, pp. 516-522, 1918. "Hotchkiss, W. 0., The Lake Superior geosyncline: Oeol. Soc. America Bull vol. 34, pp. 667-G78, 1923. ., According to the se ond onception, orogenic mov&- ment, one pha e of which was the folding of the Lake up rior yncline, is regard d a the cau e rather than the effect of the igneou activity. Van Hi e and Leith,66 though not denying the pos ible dependence of the foldinO' upon the extru ion of the Keweenawan basalts, believe i.t r asonable to a sume that the dominant trend of the fold of the pre- am brian hield was probably e tablish d b for K woenawa.n time and that a thru t from th south again t a continental area to the north was ffe tive in the folding of the Lake uperior yncl in . Whiche r ause was ff cti e or predominant, the folding took place during Keweenawan time. However, it took place lowly. If Lane's correlation of flows and ediment from one ide of tho lake to the other is corT t, ro ion and deposition must have kept pace with the formation of the syncl:ine, sv that there was no con id rabl phy i graphic basin at any period, and if the material moved from the enter of the ba in outward, the center mu t have been a physiographic ele ation. In both explanations the folding is pre umod to ha been in progres during Keweenawan time and to have been e ntially completed at its end, so that late K eweena' an beds were little affected. The domical character of the Porcupine Mountain uplift and the known pre once of intru ive rocks within it strongly ugge t that thi fold has resulted from the intru ion of ign ou material, po ibly in laccolithic form. There are also outcrop of intru ive bodies near the ere t of the K weenaw anticline and the Bes emer-I.ronwood anticline, and an intrusive body underlies the Allouez anticline. orne small intru ive bodies, however, such a that east of alumet and that at the Indiana mine, are not a ociated with notable anticlines. On the whole ther eem to be orne . ugge tion that the tran ver e fold nre as ociated with intrusive bodies, but it is not clear whether the intrusion was the cause or the effect of the folding. The transverse folds involve rocks of late Keweenawan age and were evidently formed during or after Keweenawan time. 1 he cau e and time of formation of the Keweenaw fault are not usceptible of rigid proof with the evidence now available, a is indicated by the difference of opinion concerning it. Van Hise and Leith regard the faulting as post-Cambrian, possibly post-Cretace· ous. Lane believes that it started in Keweenawan time and continued " ag s later. " It i of course clear that there ha. been movement since the depo ition of the J acobsville ("Eastern ") sandstone. The reverse or overthrust character of the fault a.nd the attitude of the adjacent rocks :indicat~ that thi , like many such faults, started as a fold, whiCh broke when the elastic limit of the rocks wa If Van Rise, C. R., and Leltb, C. K., op. cit., pp. 411, 622, 623.
STRUCTURE exceeded. The fault clo ely parallels the Lake ' uperior yncline, and the block to the north, toward the center of the synclin , wa thrust upward and outward relative to the block to the outh. If it is assumed that the entire Keweenawan series was laid down before the formation of the Lake Superior basin Oneco sec:t.\on mation during Keweenawan time and the fold that preceded the fault was also being formed then, the Jacobsville sandstone wa laid down unconformably on the upturned edges of the earlier Keweenawan beds and a movement on the fault of only a few thousand feet would account for the known di placeSt.Louis section extended / / EX P LANATION ).finor fauiU tnd· fiSSu re s auoc.1eled ""tlh ke'weenw fult FIGURE 9.-Possible de,eloprnenL or tho Kow ouaw fault and relations to beds on the assumption that the foldiug ! faulting were both later than the deposition or tho JncohsvUlo S!llldstonc :~s begun, the di placem nt on the fault ne es ary to rmg the Cambrian Ja ob ville and tone into contact with middl Keweena\ an b ds would bo about 3 1 miles, and the r lation a th y exi t might hav b en ~roduced by combined folding and faulting, as hown 1 ~?thoaccompanyinadiagram. ( eefig.9.) If,a eems Jkely, the Lake Superior ba in wa in proc f forment of the Jacob ville and tone and produce the attitude of the beds adjac nt to the fault as they are lmown and as is hown in Fiaure 10. Under this econd as umption the movem nt on th fold and subsequent fault began in Kew enawan tin1 and ontinued aft r the Jacob ville ("Ea tern") and tone wa laid down, po ibly for a long time aft r.
The Copper Deposits Of Micwgan - ..
/
Lower Keweenawan Lower Keweenawan
Lower Keweenawan
Lower Keweenawan ... r ' /
Jacobsville "Eastern" sandstone Lower Keweenawan
Jacobsville "E.aste rn" sandst one Lower Keweenawan
IOMiles FIGURE 10.-Possible development or the Keweenaw fault on tbe asswnptlon that the folding was earlier than the deposition or the Jacobsville sandstone )
U. S. GEOLO GI CAL S HVEY PROFE SIOl\AL PAPEH 144 PLATE 65 a b d ALTE HATIO A D REPLA EME T OF M l 1 E HALS n, Cornplol.o sil iciflcn lion of foldspnr, Qu incy mine. X:l2; b, feldspur cornplotely ull.orcd to sori ite. lslo Royale lodo nenr vein lot of dornoykitc, X I66; c, foldspnr complolcly nltcred lo snponil.e, Osccoln lode, X77; d. shells of pidoto in cnlciLc, x:12; o, pumpellyite in scri ito, X205; f, pumpellyi te in qunrlz, X:-32. All cn lorgcmcnts ooproximat
S. OEOLOGI AL PR FE S lO ' AI, PAl' E ll 144 PORCELA l C DATOLlTE n, Porcclanic daLoliLc inclosing copper (dark spots); b, mammillary surface of porcclanic dntoliLe
. S. GEOLO .! CAL S H \'lo Eulargcd about 69 diameters l A PARTLY R EPLA ED HY DATOLITE ()"I C r~c k fissu re, OPJ>Cr Falls min P HOF£S,' I0:\A I. PAPJ::H 1~4 P LATE 67 AT I VE SI L VER (LI GHT 11Y TAL ) 0 AT I E COPPER orlh Kcarsnrgc mine. Photograph by F. T. Reeder from specimen in llis collcclioo
U. . GEOLOGICAL URVEY PROFES 10:-IAL PAPEll 144 PLATE 68 d e RELATIO OF SULPI:UDES A D OTHER MI ERALS a, J3orni t.c and chn l~opyri.Lc from Wolverine s.andsLone, X ; b, chalcocit.c in~rgro~n with calcit.c, X85; c, chalcocit:e (~ark) and rsc uicn l copper (light.), Chump1on n11nc, X 32; d, chnlcoclt.c nnd. arson iCt~l copper, Chnoop1on m 1nc, etched, X 85; e, copper nrsclllde 10 chalcocll .. e , BuiLc m1nc, X43; f, etched cholcocilc surrounding spcculantc, IJuJt-ac mmc, X ll9. All enlargements approx·imat.e
MI ERALOGY The thru t movement from the interior of the ba in ugge t that the cau e of the Keweenaw fault was probably clo ely allied to the formation of th Lake uperior yncline and the intru ion of the laccolith. It seem po ible that succe ive upward thru ts nltcrnatin<Y with outpouring of lava and ettling during the igneou a ti vity produced the folding and finnlly the faulting along the margin of the area. The fault and fi ure on th anticline and yncline nre pretty clearly ten ion era k produced during the folding of he rock . MINERALOGY Th follo\,~ing di ·u ion of the mineralogy i ba ed largely on the note of harle Palache and Alfred Wandke. D o ·tor Palach made a stud of th general mineralo<Yy of th di trict, and Do tor Wandke did much of the micro copic work on ro k and minerals. In addition Dr. T. M. Broderi k made a pe ial tudy of the arsenide . Th work f the e men wa carried on for the alumet - H ecla on olidated Copper o. and ha been uppl ment d by ob ervation made throughout th inve tigation. The minerals of the di. trict r adily fall into three main o-roups, ba ed upon t heir p riod of formationthose of the rocl -forming period, those of the oreforming period, and tho e of th p riod f weathering. ( e fio-.11. ) ROCK-FORMING P ERIOD Tho coolincr of th ba alti la a flow cry tallization of oli.vin magnetite or ilm nitc, of more or le gla . a bubble in the viscous lava I ft op n ca itic or v Inter~ ti e in th ophitc may al o haY been ga fill d and lat r left op n or fill d "·ith Ia . A tho roc! c ol d and r allized, it ' a permeated ll'l~h g ou manation , which rna hav b n the ch_Iof ng nt in pr du ino- th fir.' t a.l tcration f the mmeral or gla · alr Rely form d. The o hano-
II"CI" principally th br akiug do' n of o-la with olf r b ' Ing r c of d1 lv d minNnl - h matitc, py r xene, and l par (in phcruliti ·form) · th erpC'ntinization of ?iivm , with or wiLhout C't ing fr of iron oxide, ;nnmly homaLite; probably th formation f hlorite rom ~Ia of int r iLia! pa o or m icrration o fill u h area If op n; and th oxidation of fen ·ou iron th ~In , magn tit , and ili at to h matite. It wa IQ th" f 1 POrJod that Lho r d top of th la a.s w ro ormed. COlT Sl ondincr p riod in t he formation . ttc , quartz, f ld par, and h matit were the I rmcipal min raJ to b f rm d. me of the f l it wore later br ken up and depo it d t form the conglomerate with liLtlo mineral hang . ORE-FORMING PERIOD The main ore-f rming period occurred aJt r thr rock b~td been ilted to es entially th ir pre n po ition and brol en by many fra ture . Th y w ' r then perm ated by hot, chemically active olu tion ' bich tended to rearrange the ons i tuen t of the rock into new mineral ombination and al o to introduce ome additional con tituent . ithin thi period there wa a broad general sequence of mineral formation but thi quonce wa ubj ct o many variation and i likely to b ob cur d by it own complexity. The early part of th p riod wa chara'terized by th format-ion of the anh drou or le hydrous min ral , uch a feld par, hloriL, and epidote; the later part by the formation of tbe mor h drou mineral , . uch a laumontite anal ite and aponit . ( ee fi.cr. 11.) opp r " form d mainly in tho intermediate part of the period. 11a.uy of the mineral w r formed alono- a path leading awa. from a our e of olution , a b utward from a. fi ure or channel way, and mineral of one t pe would be forming at the advancing front of the repla ment wav while min ra.l of another type ' er replacing the e earlier mineral n arer the our at th am time and perhap only a few incho away. Thu th fron t of the replacem nt wa e in amycrdaloid b 1 marked by the de tru tion of hematite and the formation of pidote and pumpellyite, but the e ame mineral nearer the ourc of th solution ' ere beincr b r pia ed bv copper. In th iron-rich boulder in tho alume c" Hecla con<Ylomerate th ro k wa chloritiz d at th front of th replacement wave and replaced by copper a littl n ar r the ource, both pro es e o id ntl. having b n in proo-re at the arne tim and, in pl~tce , bu t a fraction of an inch apart. Th compl xity of thi period i illustrated b the relation of mineral in tb Allou z hatter r.oue, where mov mont '"a in progre during mineralization and th r r peated opening of fi ur and h a.lin()" r min raJ . ( ee pls. 64, 65.) The neral f event in th is zon i belie ed to ha e b el\ 1. Fi ' uring occurred, and quartz and epidote were f rmed. 2. During th ilicifi ation of the fi. ure walls a. little of th hematite, whi h ant dated the fi urmcr, wa r moYed. 3. A pidote develop d, hematit derrea ed in amount, owing in par · to th rocombinati n of h matito into epidot . ilicification pro eedcd, a little of th pulverulent f rric ox--ide may ha,· r ery tallized into the pe - ular black Yari t . 5. A little pump llyite wa. formed.
a: u 0 a: 0:: w a. w 0:: cr w
z cr w :z:: 5
AMYGDALOID LODES AND FISSURES CONGLOM ERATE LODES -£:A R L Y ROCK- FORMING PERIOD Olivin~ Pl~l!ioclose Pyroxene Ma()nefte Seroenh ne (bowlineite) Chl~nte Hemat1te Orthoclose Chlorite Eo1dacite Pumoellvite Prehnite Coooer Dotolite Silver A:nkerite Ouortz Sericite Col cite Arsenides 5 lofHdes Albite Aduloria Ch lorite ( saoonitel Anolcite Su l gh<~tes (barite, anh.drite, gvosum) LATE: +- ORE PERIOD
Cupnte WEATHERING PERIOD ' Orthnd""" l.hlor it" Pumnellvte Connf'r Ou,.rtz Colc1te Sulnh1de Borite Tenonte (mei&Onrte
Mal~ch 1 te Ch rysocoll~
Explanation
Abunda nt Not a b unda nt ROCK- FORMING PERIOD Felsite conglomerate Felsite composed of qul:, feldspar, and hematite Much 1ron o.xde also in 1nterstit1al sand F lOUR I'. 11. Pa.rngencsts of mml' or :"1-llcbigun copper d eposi ts £A RL Y LA T£ ORE PERIOD l 1ttle L"1tle
WEATHERING PERIOD S imilar to amygdaloid lodes c.n
'"d '"d t;l ::0 tl t;l '"d rFJ
i:l::
Q
MI ERALOGY 6. The early q uartz-epi~ote rillxture w~s shattered, ' and quartz, epidote, cal 1te, and prehmte were depo ited in the fractures. 7. Prebnite partly replaced p1dote, quartz, and calcite, and copper wa deposited. The min ral already formed were agam shatter~d , and more alcite and quartz were .deposited, toaether with copper. 9. battering was ren wed, and q nartz and calcite, with orne laumontite, entered. Tho mineral of this p riod both filled open cavities and replac d mineral of the rock-forrillng period and the earlier part of the ore-forming period. The replacement generally occurred volume for volume, but in pla e the altering olution removed more than they depo ited and form d cavitie near the main channel , which may hav be orne place of depo it for later minerals. The veins wer formed mainly by replacement, though there wa doubtle orne filling of open pace . PERIOD OF WEATHERING The glaciation of the region ha removed roo t of the product of preglacial weathering. It is only in area protected from glacial action or area of battering where weathering wa probably unu ually deep or in a "Ociation with min ral that were readily u ceptible to oxidation that any notable amount of ' eather d material i pre cnt. In w ath rino- nati e opper ha generally, a i u ual in oth r r gion be n altered first to oxide Rnd later to arbonat or ili at . MINERALS OF THE KEWEENAWAN COPPER-BEARING ROCKS In the following alphabetic li t ar includ d th principal known mineral of th di trict, and following that i a hort d ription of th oc urr n e of each. ln the d h min mJ are group d according to Dana' .\dularin. Dat. Iii . Pow llit,c. Algod ni le. l omcykilc. Pr hnit . Anakil('. Epidote. Purnpell .l·itc. Anhydrite. Fauja it. . Py rite. Ankerite. F ld par. Pyrolu ilc. Apatil . l!luorit . . Pyroxen Apophyllitc. alcna. Quartz. Arsenides. yp·um. Rutile. Atacamite. H matite. aponite. Barite. H ulandite. , erieite. Biotite. Hornblende. crp ntine. Bornite. Hyd rocarb n. ' ilver. Bowlingitc. Ilm nite. peculari ie. 13ruci le. J aolin. , phalerit.e. Calcite. Laumontite. 'til bite. Chalcedony. Limonite. Tenorite. Chalcocit . Magnetite. Thomsonite. Chalcopyrite. falachit . Titanite. Chiora trolite. Manganite. Tourmaline. Chlorite. atrolite. Whitneyite. CbrysocoiJa. livine. Zircon. Copper. Plagioclase. Zoi ite. Cuprite. ATIVE METAL Silver (Ag) occurs in arying amount in all the lodes and .fissure . Among the .fi mes the Cliff has probably been most productive of ilver and among the lode the Pewabic. ilv r occur in the ulphide and arsenide .fi sures as well a in the native opper .fi mes. orne of it was formed at the arne time as the associated copper, though in it mo t conspicuous occmrences in vugs it wa apparently formed lightly later than roo t of the copper. ( ee pl. 67.) ative opper ( u) occur in amygdaloid , onglomerate , and fi sures throughout the district. It form rna e ranging from those of micro copic size to orne weighing 600 ton . ommonly it i without definite crystal outline, but in vugs it occur in cry tal and cry tal aggregates, u ually with rather imperfect crystal form. This cry talliz d copper ha apparently been depo ited in open spaces, without replacing other minerals. orne crystallized opper ha form d in fault o-ouo-e. In the main the metal has been form d by repla ment of the earlier minerals of the ore period, uch a chlorite, epidote, a.nd zoi ite, a well a of the rock-forming minerals. It i very commonly intergrown with prehnite and datolite and le s commonly with quartz and calcite. Mo t of the copper i earli r than the zeolites laumontite and analcite and earlier than aponite, adularia, barite, anhydrite, and gyp- . urn, though a little copper ha been depo ited as late a any of the e mineral . Where copper i a ociated with chalcocite in .fi me either min ral may be the earlier, or the t o may be contemporaneous. In the lode the ulphide-bearing .fis ure are at lea t in part lat r than the copper of the lode . The lode ro k adjacent to copper is characteri tically bleached by the r moval and alteration of hematite, a i di cus ed in the section on ore depo it (p. 133). LPHIDE Galena (Pb ) i rare, but minut rystal of it have been not d at the Mendota diamond-drill hole o. 40 with chalcopyrite and at outh liff with pyrite and phalerite. halcocite ( u2 ), though formed b for copper in me place , i one of the later mineral' of the oreforming period. It i of wide pread occurrence in .fi sme cuttino- rock of all kind . It i e'pecially condi uou in fis ures in the Bn.ltic lode, where it occurs with ankerite, and it i al o pr ent locally in the lode it elf. It i rather common in .fi ure in the Isle Royale lode, where it occurs with ankerit and a little pecularite and where it i later than the pecularite. The rock adjacent to the vein in thi lode is trongly bl ached. Finely divided chalcocit darken the mall calcite vein that o CJU" in the Uouez conglomerate wherev r it h been open d, and the min rnl occur imilarly in everal other conglomerate . In the Calumet & Hecla conglom rate it i mo t abundant
THE COPPER DEPOSITS OF MICIDGAN at the entennial hafts, north of the main ore hoot. It i pre ent in vein and vug at Mount Bohemia. Cal ite-chalcocite eins are plentiful in the White Pine and Carp Lake mine , and chalcocite i di eminated in part of the sand tone. In short, chalcocite is wid pread but now~ere abundant, though the Baltic lode contain vein of nearly olid chalcocite everal inche wide. ( ee pl . 6 , 69.) phalerite (Zn ) i rare but i reported from a £i sure at outh Oliff with pyrite and galena. Bornite ( u5FeS4) in mall amount accompanie the chalcocite in orne of the sulphide fi sure . The fi - ure in the Baltic lode contain bornite roo t abundantly,butitispre ental oinfis ure in th I leRoyale lode. It in a common mineral in the vein and vug in the gabbro and gabbro aplite of Mount Bohemia. Ohalcopy1·ite (OuFe 2) i of rather rare occurrence. It i pre ent in the veins of Mount Bohemia and was een in drill cores near a felsite intru ive at Mendota. It occurs sparingly in vein with chalcocite in the Isle Royale and Baltic lodes and wa observed in vein in quartz porphyry in the Onondaga drill cores. It is visible in orne of the pegmatitic len e in the thicker flows and is present a micro copic crystal in some of the fre he t normal trap. It occurs al o in the Wolverine sandstone in the Ahmeek mine. Pyrite (FeS2) is reported in a small fi sure with phalerite and galena at outh Oliff. Pyrite is' notable for its practical ab ence. ARSE IDES Arsenic, in the form of copper arsenides (pl. 71), occurs in Michigan as ociated with the copper in depo its of all type - amygdaloid and conglomerate lode and fi sures- but is mo t abundant in certain of the fissure depo its, and in the lode it i especially localized near the ar enide fissures. The lode copper of the Baltic and Isle Royale _lodes, howe er, is arsenical throughou and distinctly lighter in color than the arsenic-free copper. On etched surface the "arsenical" copper approache in appearance orne of the ar enic compounds. Compounds of copper and aT enic.-As they occur in Michigan, the ar enides form mixtures so intimate and complex that the early investigators 67 mi took different combination of minerals for new pecies. Examination in polished ection shows at least seven ' recognizable varietie , not including thre that con- ' tain nickel and cobalt. It has not been po ible to eparat thes varieties and determine their chemical ' compo ition by analy es, and the composition asi()'ned to them i that given in the textbooks. It is -" Koenig, 0 . A., Ou a:ti.ficial production of crystallized domeykite, algodonito , I argcntodomcykitc, nnd st1b1 domoykite: Am . Philos. Soc. Proc., vol. 42 pp. 2!9mJ~ . entirely po ible that som of them, sp ially those high in copper and low in arseni , may b solid olu. tion or alloy and not deft.nite min ral . Domeykite ( u3As) i high st in arsenic, and it wa the arlie tto form, being pr c d d only by magn t..ite and th uickcl. cobalt ars nid . Dome kit i ein d and replaced by algodonite, who e formula ha b n gi en a, CuJs. Etching poli h d urf a r f ~go doni to how that it is not a simple substar, out an inter rowth of two minerals, which ar herod ignated a and a.lgodonite. Algodonito i in turn uc coded and in part replaced by ub tan e still higher in oppor; se oral f these are now recognized, thou()'h all w re form rly called whitneyito and a ign d th formula ugAs. These are h re de igoat d a, {3, -y, and o whitoeyite. They may well be olid olu tion r alloy ratb r than defi· nite compound . Etching ests show that th se ulr stance are veined by nati e copp r. Thu ltere is a definite order of dopo iti n in the rie . This order is invariably domeykite, algodonit , whitne "te, and native copp r. Each mineml partl replace its im· mediate predece or; domeyki.te, o far a observed, has not b n replaced by whitneyite or nati e copper, nor algodonite by native copper. Each ars 'de was followed by the on next higher in copper eontent, until finally native copper was precipitated. The order of depo ition of the individual members of the general algodonite and whitneyite group can not be o definitely stated. Even this, however, eem to be consistent with the general rule of elimination of arsenic. For example, where whitneyite was replaced or followed b:v copper, the whitneyite is of the 'Y or! variety, but the whitneyite that replaced algodonite is in most place the lighter, more ar enical a or P whitneyite. In ome specimens two members of the whitneyite group seem to grade into each other, in· stead of ha vi.ng sharply defined contacts. Every pecimen of algodonite so far examined is an intimate intergrowth of the two constituent a and algodonite. Where a predominates over the color of the mixture is tin white, but with a predominance of the speci· men ha a di tinct pinkish tone, as if had a higher copper content. The algodonite that ha r placed domeykite generally has a predominance of the a variety, but where algodonite is replaced by whit· neyite the variety is predominant. Although the phy ical and chemical propertie a de cribed erve in general to determine roughly the ar enides pre ent in a given specimen, examination in poli bed ection makes it po ible to differentiate varieties that are not di tingui hable in the band pecimen and to determine their paragenesi . Below i a list of the copper arsenide arranged in the order of their known or inferred copper content, together with their diagnostic properties in polished section.
MI ERALOGY Diagnostic properties of copper ar Name ComposiColor of polished surface in tioo oblique light Hemurks NH,OH 1 r--- Domeykite - - 'u3A White - E f fer v e ce n ce blacken . olor unc.banged, de- !!. cleavage pattern . Turn yellowAfter rubbing on plate brown. fine abr iv dull gray compared with algodonite under imilar condition . A.lgodonite:
Whitneyite: I deep purple. Bring ou faint difuaAs__ fere.nce between a }Blacken P i n k i b c.reJUDy E f fer e c en c e white. dark brown. ! After etching "itb H::\03, poll h gently and a mooth blue-gray,
white. In general the erie ! Deep creamy white E f fer v e c en c e bro~ - --- hauptite?). chocola e-brO\\·n. Fain brown rub off_ Little effect , rub off. how colors grading from algodonite to that of pure copper. "Y i decidedly pinker than other . li L decidedly lighter than copper. All characterized by immediate browning with H I. brown. The color and lack of browning b H I u ed to di tingui b from the whi ne:rite group. "Y whitneyite?). The everal group f arsenide are not difficult o recognize in hand pecim n . The colot range fr m the white of d meykite and alg donit through the pale copp r-r d of th whitn ite o-r up to the c pperred of pure c pper. One p r c nt of ar enic in ar ni al copper cau e a per eptible lightening of the olor. The malleability of the min ral al o varie . Domeykite i decidedly brittle, algodonite i mu h 1 and the wbitneyite group i decidedly malleable but 1 o than pur copp r. ( ec pl. 70.) Heating in gla ube driv off th from dome kite and alg d nit , but difficulty from whitneyite the l w r ar nic om pound . The alt ration of the n.r enide are haracteri tic. Domeykite rapidly tarni he to a halcopyriteyellow. orne ha weathered to cuprite. The brightgreen coloration that bas developed along the ar enide fissures underground since they were opened by mining is probably due to the formation of an arsenate and seems to be chiefly connected with algodonite. Whitneyite tarni he brown rather quickly. Ori.gin.- It is pointed out in the ection on ore deposits (p. 132) that in general, although there are some notable exceptions, the high r the lode is in the eries the lower its arsenic content. This i also true of the occurrence of sulphides of copper, and what i said of the distribution of ar enic may be aid of the distribution of sulphur. The explanation of this relation, which seems to be consistent with the ch mical theory favored by the writei , is that the olutions which traversed the lower beds had not be n in intimate contact with the oxidizing environment of the dull but no color change. lod for a loner a time a tho e which d po it d copp r in th high r bed , and for that r ason their ar enic and ulphur failed to become compl tcly oxidized into a mor olubl tate. Th r ar three po ible rea on why tho olution hould have had le s opportunity f r oxidation: (1) Th ro k toward the ba e of th eri ar more fi med than tho e high r up, hence olution could find in th fi ure a more p rmenble pathway than th oxidized amygdaloids. The a1 nid and. ulphid o cur by far the mo t ubundantl in fi ur . (2) The o currence of e.veral intru iv bod ie townrd he ba e of th , eric mn.y m~a.n that n macrmati urc for the c pp r lie· mu ·h near r th pro ont urface iu thi part of th erie than cl ' here. Thu th failure of complete oxidation of th olution may be due to the fact that in that general ar a they ere too clo e to the magmatic ource. (3) Similarly, if the battered zone a ociated with the Keweenaw fault i regarded as the main trunk channel for solutions emanating from a deep magmatic source, uch olution had not been in contact with an oxidizing environment sufficiently long when they tra er ed the rocks adjacent to that trunk channel. The presence of sulphides in the one uch lode n ar the Porcupin Mountain does not help in deciding which of the e po sible cau e had the greate t effect, for major faulting, fi uring, and intrusive rocks ar all pr ent near by. Another po sibility which merit consideration i that the depo ition of ar enide and ulphide in th fissure occUlT d ub equent to the main period of mineralization and was due to a change in the character
THE COPPER DEPOSITS OF MI HIGA of the elutions, th later ones being high r in . ulphur and ar eni . It i certain that in hi in e tigation of the e copp r arsenide Koenig 6 had very complex m:Lxtmes to deal with. His mohawkite and keweenawit and other new pecie were undoubtedly such mixture . Modern ·metallographic methods were not available at th time he did hi work. It i to be hoped that the problems of the ear enide , the elution of which have ju t been tarted in thi work, will be furthers udied by other . The present writer haxe pecialized on the material found in th Michigan copper di trict. It will be intere ting to learn what pecimen from other di trict reveal. It would seem that chemical analy es and metallographic work upon synthetic compound of copper and ar enic, if cooling curv are taken and the con titution diagram of tho e metals i kept in mind, would throw some light on the nature of the mineral . Cobalt and nickel mineral have been recognized in a fissure in the eneca mine, on the third level, 2,100 feet north of No. 2 shaft. The mineral present in the other ar enide fi sure cro ing the Kearsarge are pre ent in tb.is fissme- that is, domeykite, algodonite, and whitneyite. The microscope reveals in addition at least three other ar enides, one a white mineral, another a pinki h white, and the third a brownish pink, like niccolite. Chemical te ts by Mr. Hillenbrand at the Calumet & Hecla melter show abundant nickel. Borax bead te t show cobalt. The late George Heath, of th Calumet & Hecla melter, tated that in the ar enide of the Ahmeek fi ures there i but a trace of nickel. Therefore the nickel and cobalt are probably accounted for by the new mineral . The equence in a()'e eem to be, fu· t, the wb.ite mineral, next the pinki h wb.ite, then the domeykite, followed by the other copper arsenides in their usual order. The brownish-pink mineral is present in very minor amounts in the sections seen, and its relations were not deterunined. The magnetite was formed early in the nickel-cobalt stage. The tests on the white and pinkish-white minerals so far have not corresponded to those of any described mineral. The pinkish-white mineral shows the following properties in polished section: Hardness, that of magnetite; effect of HNOa, effervesces, fumes s~igbtly brown, no coating or etching; of HCl, negative; of HgCl2, brown, rubs clean; of KCN, negative· of Fe la, negative. The white mineral is hard and ne()'ative to H I Q 3, HCl, and FeCl3. If ful'tber investigation of these nickel-cobalt arsenides hould e tabli h them as new species, it would be de irable to retain the name mohawkite and keweenav.rite which Koenig gave to certain intimate mixtme of ar en.ide from these :fi ures. es Koenig, Q. A., op. cit. HALOID ' Fluorite ( 'aF2) i r port d from th Indiana mine by Hore and from EAPlo Riv r by ' cama n. It wa; a.l o noted in diamond-drill c r from th nonda~1 exploration north of Lake og bi , ' here it occursin fi ure in quartr. porphyry. OXIDE Qw1.rtz ( i0 2) occm s a an o rigi1lal mi.nernl in th1 felsite and quartz porphyries. It i present i11 · tically all lodes and fi ur , throughout the d' trirt a a vein filling, a. a filJinO' of ''e. irlc and replacinv other mineral and rock. It i perhap mo t abundant in th Evergreen lode. and th I le R oya.l lode but it i plentiful in other , a. th Baltic and Pewabic and loca.ll. in th eol and Kea1. arge. In th1 :fi ure it i parti ula.rly abundant' ith the at "enid . Quartz wa fo11ned through th 0'1' a tcr part of the ore period but most abundantly in the middl portion. It replac d the ro k min ral and om of the earlier ore mineral and wa in turn r pla ed by ome of the lat r min ral . ha.lcetiony o u a linin()' of \"ltus in the P wabic lod and in a,mygd ul in the Kear· arge lode. It ha replaced zoi ite and ma.ny place . Cuprit ( u 20 ) oc ur in w ll-form d ry Lnl at the Indiana mine a an oxidation product of opper: it occurs imilarly at the Algomah mine, wh r it larg ly alter d to tenorite. The opp r in many of the mine opening i colored with a film of cuprite. In pla e thi film ha cl arly formed aft r the mille were opened. In other pla e , e pe iallv in tJ,c higher level , it probably formed bcfor the mine were op ned. Tenorite (melaconite, uO), th black oxide of copper, is e pe ially abundant at the ]O'omah mine and at Copper Harbor and doubtl s oc ut ' el C· where, It is a product of oxidation of ot:her m,i.neral · Atacamite (Cu2Cl(OH3)) occurs in well-formed radiating crystals as an oxidation product at the Algomah mine. Hematite (Fe20 3) is apparently a primary mineral in the felsite and in the felsite pebbles of the con· glomerates. The abundant hematite in the red top of the lava flows i believed to have been formed from magnetite and the iron silicates or from the glu Y portion of the top of flow , or possibly in part crys· tallized directly during the olidification and cooling of the flow . Deeper in the flow the hematite ha formed from magnetite and olivine, likewise probably during · olidifica.tion. Thi proc i fully di. cp ed in the ection on oxidation of lava top (p. 3 ). Hematite occurs in small amolmt in some of tho vein' that contain sulphide and ar enide. In the e it is usually as ociated with ank rite. In th conglomerate
MI ERALOGY peculnr hematite i present in some of the iron-rich porphyTy boulders. Specular hematite al o occurs sparingly in fractures _both the. conglomerate and amygdaloid lod s. It 1 mcluded m the r d feld par of the lode . Characteri tically hematite ha been de troyed near copper, and the iron has been eith r recombined or removed. The formation of hematite mainly prec ded the ore-forming period. During that period a little was formed, probably by the recry talliza tion £ earlier hematite. ilmenite (FeTiOa) occur as a primary min ral in traps. It ha been altered in place to hematite and titanite. Brucite ( g02H2) occurs in vug in the I l ""Royal and Kear arge lod s. It i a late mineral of th ore period. In the one pecimen from th Kear arge loci it ha r plac d laumontite. In th 1 le Royale mine it was replaced by ericite :VIagnetite (Fe30 4) wa originally an abundant primary mineral in nearly all the flow , but it has been entirely altered to hematite in the top of the flow a.nd throughout ome flow . Thi alteration i discu sed in connection with O}..idation of lava top (p. 34). J1agnetite i pre ent a o-rain in ome of the conglomerates, a the Great conglomerate and the Houghton cono-lomcrate, but in most of them it has been altered to hematite r limonite. It i rarely pre nt in the fi ur v in . Th magn tit of th flow i titnnif rou , and h matite, titanite, and rutile were formed from it on alt ra ion. Rutil (Ti02) o curs in ba al a an alteration product of titaniferou iron or , and it oc ur al o in th fehtcs, wh r it was po ibl d rived from bioti . Man()'anit (~ln203 .H20) occm as mall cr tal in vugs in the alumet Ho la conglomerat . t th Mangan c min , n ar oppor Harbor, it o ur ' ith other mano-an e mineral as a "v in," ntially coin iding with an amygdaloid a hort eli tance below the Gr at nglomerate. Th " ein" wa opened for a few hundred feet along the trike, and some ore wa hipped from the mine. Pyrolu ite (Mn02) occms at the Manganese mine, near Copper Harbor. Limonite· (2Fe20 3.3H20) occurs sparingly on weathered urface of trap. It i pre ent in the conglomer- ~tes, probably a alteration produ<?,t of magnetite. It 1s rar ly n in the amygdaloid lode . ARBO ATE Calcite ( a 0 8) j perhaps the most widespread mineral of tho ore-forming period. I t occur as crystal in open caviti and replace oth r mineral nnd i everywhere pre ent in veins, amygdaloids, and conglomorat . It wa form d from about the middle to the end of th ore-forming period, and therefore it hn repla od many mineral and has it elf been replaced b everal. It occurs in the pegmatitic lenses in orne of the thick trap It i al o being formed in , the pre ent mine working where water i dripping in the upper levels and around rna e of opp r in the walls of opening in the deep level . In many pla e cry tal of calcite inclo e mall cry tal of copp r. Ankerite ((Ca,Mg,Fe,Mn)C03, compo ition ariable) i common in the ulphide and a enide vein and is al o abtmdant in parts of the Baltic lode as a lode mineral. In sulphide veins it commonly o cu next to the wall , with sulphides in the center. The arne relation i hown in the Baltic lod , where the carbonate line cavitie and inclo e ulphide. It ha also replaced the lode rock. Wber it i a ociated with calcite the calcite is later. The mineral apparently wa formed at intermediate to late tag in the ore period and is lo ely a ociated with ulphid and ar enide . Malachite ( u2(0HhC03) was noted particularly at the Algomah mine as an oxidation product. It i doubtle pre ent in mall amount at oth r pla e . ILICATE The plagiocla e erie of feld par , con i ting of i. omorphou mL'\ture of albite (I aAl iaO ) and anorthite (Ca 2 i20 8), is repr ented by plagiocla e of interm diate compo ition, which forms an abundant orio-inal on tituent of all th flow . !bite i pr ent in the f l ites. The feld par of the flow unden ent littl alteration durino- the oxidation of the flow top , the microlit of plao-io la e b ing till remarkably fre h. Plagiocla e wa , how v r one of the earlie t mineral to b atta ked by the ore olution , though locally i remain remarkably fresh in oth rwise n.ltered ro k. The f ld par wa commonly replac d by hlorite, epidote, zoi ite, ericite, or alcit , but prehnite or IUlY of the later min ral have r pla ed plagio la e. lbito in r latively mall amount i pre nt in many plac a one of the later minerals of the ore-forming period. Orthoclase (KA1Si80 8) occurs in three distinct ways-as an original mineral of the felsite, as an early mineral of the ore period (red feldspar), and as adularia, a late mineral of the ore period. The original orthocla e of the felsites occurs both as phenocryst and in the groundma s. Red feld par, probably of variabl compo ition, i abundant in several of the lodes and i al o pre ent in many fi ure . It i especially abundant in th Butler lode and adja ent lod , in the uperior lod , and in part of the Keararge and 0 ceola amygdaloid . It is pre ent but not abundant in the conglomerates. It occurs in fis ure and amygdul s, and it replaces the rock, e pecially in the Ev rgreen and ucceeding lodes but to orne extent in mo t of the other lodes. It wa one of the earlie t mineral of th or period and wa replaced by chlorite, epidote, and later minerals.
THE COPPER DEPOSI'fS OF MICHIG Copp r occurs with red f ld par, but the a sociation i not notably clo e. Th f ldspar, lik man mineral of the ore period, i far mor wide pread than copper. ularia occur to a minor extent in lode and fi - sur a well-for111ed \'hi te to pinki b crystal , u ua.lly in open · space . I t wa' apparently a relntivel late mineral of th ore period . Pyroxene ( a(Mg,Fe) i20 6) i fin ahundant primary mineral of all the basic flows. 1ts u ual alteration i to hematite and erpentine. In place it i stained with limonite. It was rather resi tant. to alteration by the ore olution , but where the altera1 tion wa. i.nten it wa replaced, like the other rock mineral . Hornblende wa no ted in the Green tone flow a. :ociated with biotite. Oli ine (Mg,Fc)z i0 4) wa. an early mineral to cry tallize in mo t of the lfwa flow . It i now mo. tl altered, characteristically to serpentine or bowlingite and hematite. The. e mineral were in places further altered to others. Frc h olivine wa ob erved only in the coar e pha e of the Green tone flow. Zircon (Zr, i04) occur as a primary mineral of the felsites. · Pumpellyite (6Ca0.3Al20 3.7 i02AH20), provisionally called zoisite, occur in bluish-green lath-shaped crystals or needles, in mo t places in radiating group . It i thi. mineral that give the chnracteri tic blui green color to much of the lode material in the mines in the outh end of the district. It is near zoisite in compo ition but differ from zoisite cry tallographically . Doctor Palache 69 ha de cribed this mineral in detfiil. Analysis of pumpellyite [Helen E. Yassnr, analyst) Analysis I ::llolecular ratio
. i 02--- --- 0. 616=7 K20 . 293=3 mgl . 524=6 H20 + . 349=4 The mineral i abundant in all the amygdaloid lodes and in all the fi sure . It is present but not usually abundant in the conglomerates. It is especially conspir.uous in the Isle Royale lode and in the Ev.ergreen and succee~ing lodes, but hardly more so than 10 parts of the Baltic and Pewabic lodes. It occur in open cavities and replaces the rock. In "P~acbe, barles, and ~r, H. E., Some minerals of tbe Keweenaw copper d POSit ; pumpellyite, a new mmerai; seric1tc; sapooite: Am. Mineralogist vol 10 pp. 412-41 1925.
mn,ny places pumpellyite with quartz ha partly replaced large olum of roc] . It ommonly fo~ lowed epidote in formation but pre edcd copper. 1t replac d the earlier min rals of the or period, .uch a chlorite nnd epidote, and in turn Wll replaced b1 the later mineral , including opp r. It i not u uall~ abundant in highly oxidized rock, u h a th the Kear arge amygdaloid. It i clo. ely a . ociat~ with copper in many place , but appar ntly, likemam of the gangue mineral , i far mor wide pread occurrence than copper. The lodes of the Pe~vabic rie. in particular in n umerou pla e are rather highl purupellyitized wh re th y ar not known to contain abunda.n t copp r. Epidote (romp ition varinble, appr ximRtel)- HC~ (Al,F )3 i3013), yf:'llow-gr n minernl , i e1ery· wh r abundnnt in both vein and lode , beina per· hap e p iall abundanl in thP Ev rgr on and uc· ceeding lode of tho erir. and in th I lo Royalr lode. I i aLo abundant locnll. in the nlurnet & He la on<>'lomeratc. Epiclotc rharart ri. Li ally hR£ repla eel th ro 1- mineral though it ho al o been formed in openin()' ·. comrn nl. .fl1 t replaced plagio la e but even ually replaced much of the rock in ma . In th lum & Jlerla on!?:lom rate i replfl eel andstonc l n 1 n lhc 1\:ea.rst\rge lode il relatiYely abundant in tho upper, highly oxidized portion a ontra. ted with th lower, l oxidizrd portion. The il'on ent ring the pidotc wtt apparently derived from the hematit of th ro k . Epidote~ one of the earl min rals of the ore-forming period. in th main preceding copper, bu it al o appNll to ha e b en f rmed to a li<Yht extent !at r than copper. a i ut anhydrite and . ericit in th I lc Royalr min , f r in tance. Epiclot i in mnny place clo.el)· a. ociated with opper, but like rbl rit ancl ·alcite, it i far mor wide pread Lhe co tnmercinlly valuable copper minerals . Tourmaline occur in felsite fra<Ym nt in the conglomerates. It is unrelated t the opper mineralization . Laumontite (CaAbSi.10 12.4H20 ) is usually pink or salmon-colored, but in places, especially in some vugs, it is white. It occurs in practically all the fissures and a.mygdaloids. It is abundant in many fissures and locally in the amygdaloids but is practically absent from the conglomerate . It is one of th lat r minerals of the ore period and ha replac d th earlier minerals but was in tum replaced by some of the later minerals. It wa mainly later than copp r, but a little copper was formed after the laumontit . It i not closely associated with copper and i far more widespread than copper in occurrence. Wh re !au· montite is abundant the lodes are usually relatively poor in copper. atrolite (N ~Al2Si30 10.2H20) occurs with analcite and adularia at Copper Falls.
MI ERALOGY Analcite (N aAl izOu.HzO) occur commonly as a vein mineral, more rarely in vugs in the lodes. It occurs in vug a white, well-formed cry tal , in many of which the centers are partly di olved. ln veins it rarely shows cry tal form and is pinkish in color. It is one of the late minerals of the ore-forming period but in places wa followed by aponite and calcite. It is a common mineral but nowh re abundant. Mo t occurrence were noted in the Kearsarge lode. tilbite (CaAlz i60 ,6.6Hz0 ) occur in the 0 ceola amy(1daloid and at Copp r Fall . Heulandite ( aAlz io0 ,6.5H z0) is one of the rare t zeolite of the di trict. Thoro onite ( a lz izO .2 zO ) occurs mainly a a filling of amygdule but al. o in veins. It is usually not clo ely as ociatHd with copper. Apophyllite was ob erved in the t. lair, Robbins, Cliff, and orth American fi ure . It i one of the late. t minerals. Chlora.strolite occur a amygdule fill.i.llg in flows on I leRoyal. It i worn from the matrix by wave action, and the stones are gathered on th beac.he . Fauja.site (Hz(Ca a2)Alz(Si0 3) 5.9Hz0) from opper Fall i in the Whitney collection. Datolite (H 2Ca2B 2 i20 10) occur. in hoth fi s me and . It is probably pre en t in mo t of the amygdaloid lode , but it i relatively abundant in the Evergreen and . u ceeding lode , pcciall at the Ma s Mine, in part of the K ar arge and 0 enola lod , in par of the PewA.bic lode , and in th hbed lode in Keweenaw ouut . It ha not been noted in the conglomerate lode . It o ur in fi ure at many places and is abundant at the opp r Fall (Owl reek) and Petheri k fi nr , ' h re locally at 1 a tit formed the main gauO'ue min ral. Datolite form both welldeveloped ry tal and cl n e pore lani rna e . The cry. talline dntolite occur, in both fi. urc. and lode . It may be pink from in luded copper, and wh re the cry tal are mall they oc ur a a loo. e, rumbly granular aggr o-at . Th por lanic ari t characteri tically a irr gular , pheroidal rna. , with a botryoidal urface. ( e pl. 56.) These rna. e of datolite ommonly ontain ma,n mall pecks of copper, which ar u ually con ~ntrated ncar the urface of the rna s, though le commonly th concentrn.tion is toward the center. Tbi v-ari ty ha been found mo. t abundantlv in t.h hiO'her le el of the Pewabi lode but i pr e~t in oth r lode . Datolit apparently wa. one of the intermediate to later mineral of th or period. Prehnite ( Al2( i04 ) 3 a2H 2) commonly occur. in radiating cry tal aggregate but in tb v in p cially may appear ma. ivo. Much of it has a light appler~en tint, but it varie greatly in color, . orne of it emg nearly black. It i abundant in veins through5 540- 29--G out the district. It i pre ent in roo t of the amygdaloid , where it ha filled e icle or replaced arlier minerals or rock. Locally it i abundant in the am 0'- daJoid , a in the 0 ceola lode, where it largely replaced ba ie edin1ent. It i rare in the conO'lomerates. Prehnite wa formed mainly a an intermediate mineral of the ore period , but orne\ as later. In the v in it i very commonly as ociated with copper, which in many place i di . eminated through it in minute grain . The highly prehnitized a,myO'daloid, however, is not u ually high in copper. Prehnite has been replaced by the later mineral . ericite (mu covite, lai H2~ i30 ,z) ha mainly replaced rock and earlier ore mineral but al o filled open pace . It i mo t abundant a a r placement mineral in the wall of the arsenide and ulphide fi sures and in orne of the lodes, a the I le Royale and locally in the Baltic. In the I le Ro ale lode it i rather abundant a a oft talco e min ral replacing fragmental amygdaloid. ericite eem to have been formed from a moderately early tage in the oreforming period to a rather late stage. Analysis of sericite j1·om I sle Royale amygdaloid [llelon E . Vassar, analyst] 2 Fc2 a20 - Ti02- -- --- -- - - Trace. Biotite (Al2Mg2KH i30 12, with variable proportion of ferric and ferrous iron) i a rare primary on tituent of orne of th basic lava flows, such a.s the hbed group and the Green tone flow. hloritc (dele ite, H 10(Mg,Fe).Al4 i4022, varia,ble) occur abundantly as a ' e icle filling and a a vein mineral, and it ha also replaced rock minerals. It i parti ularly abundant in . ome of the v in and has r plac d tb adjacent all ro k . In the amygdaloids it. is pe ially on pi ·uou in the le . oxidized part , uch a the lov; er portion. In the Calumet & Hecla c.onglomera.t it. ha repla ed orne of the iron-rich p bble , wh re it i a o iated with copper. At White Pine it urround hydro arbon and ha be n replaced by opp r. orne chlorite wa probabl formed during th cooling a,nd olidification of the lnva . It wa an abundant early mineral of the ore-forminO' period but a.pparently ontinued to form till late in that period. It replaced many mineral a.nd wa. repla ed by evral, being very commonly replaced by copper. erpentine (Mg3H 4 iz0 9) i a common alteration produ t of olivine in the tmp , and it a.lso occur in cavitie in the amyo-daloid lodes. The serpentine of
THE COPPER DEPOSITS OF MICHIGAN the former type wa earlier than the ore p riod; that of the latter type was formed late in the ore period. . Bowlingite is the common alteration product. of olivine in many of the flow . It i resi. t~~,nt to ~~,Iter ation but has been replaced in place by prebnite and ca.lcite.. aponite (Al20 3.Mg0.10 i02.15 or l6H20 ) occurs in eve.ral of the lodes, where it has filled vesicle , replaced other minerals, and formed as a crust on other mineral . It was noted mo t abundantly in the K arsarge lode. It is apparently a late mineral of the ore period. Analyses of saponite from the K ea1·sa1·ge lode [llelen E. Vassar, analyst] South Jt~~rsarge Ahmeek mine Si02 Ah03 Trace. Trace. H20 + H20- Kaolin (H4Al2Si20g) occurs in the Isle Royale mine on laumontite and in the KeMsarge lode as a crust on red feldspM. It is probably a late mineral of the oreforming period. A little occurs clouding plagioclase that is believed to have been formed when the lavas were exposed at the time of extrusion. Chry ocolla (CuSi03.2H20 ) occurs as an oxidation product at the Algomah mine and the Allouez conglomerate mine and at Copper Harbor. Titanite (CaTiSiOs) is rather abundant in all the flows as an alteration product of olivine, pyroxene, or titaniferous magnetite. In highly altered lode rock it is common as a residual mineral. PHOSPHATES Apatite (Ca5(P0 .)3F or Cas(P04)a l) occurs rather sparingly a needles or pri m in the felsit pebble;~ of the conglomerates and in the lava flows. It is an early original mineral of the rock . ULPHATE Barite (Ba 0 4) occUI·s most ·ommonly in vein, in many place with ulpbide. It al o occw· in everal of the amygdaloid and in the iron-rich p bble of the Calumet & Hecla conglomerate. t the White Pine min it i a v in mineral and a cement in the and. tone. It wa among the late min ral , though fol· lowed in pla e by aponite, adularia, and datolite. It i wide pread but nowhere abundant. Anhydrite ( a 0 4) occw·s in vug and ha replaced rock in the I le Royal mine. It wa al o co !lee~ from the dump of the 1a s mine. It eem to beof the late ore-forming tage but is veined in the I le Royale mine by laumontite and epidote. Gyp urn (Ca 0 4.2H20 ) o ur paringly at numer· ou place , both in fi.s ure and in the lodes. It nowhere abundant. It appear to be a late miner~ . In the I le Royale mine it seem to have beeu formed from anhydrite. In the Victoria mine it ha formed in puddle of salt water that stand in a cro cut. MOLYBDATES A D TU GSTATES Powellite (Ca(Mo,W)0 4) ha been reported from the Isle Royale mine, and a few well-formed cry tal· have been found in the Calumet & Hecla conO'lom· erate. The mineral is said to contain both molyb· denum and tungsten. HYDROCARRO r A dark hydrocarbon is rather plentiful in the one· such lode at the White Pine mine, where it occurs in fi.ssme and as a cement in the sandstone. In places it is urrounded by and wa evidently earlier than copper. The hydrocMbon in the fi ure contains abundant copper.
PART 2. ORE DEPOSITS HISTORY That the existence of native copper in the Lake uperior district was known to early Indians and that copper was mined by them is shown by numerous ancient pits containing masses of native copper in Yarious stages of removal, together with the crude tone tools used in mining, and by the implements made from copper that are found in the region. (See pl. 1.) The earliest visits to the district by white men were made about the middle of the event enth centmy. In 1672 two Jesuit priest publi bed a map of Lake uperior, and from time to time the Jesuit mi ionaries and other brought accounts of copper found along its hores. The nam s of these early explorers-La aile, Allouez, Mesnard, Marquette, and Du Luthha>e been pre erved in the geographic nomenclature of the region. In 1771 Alexander H enry, an Engli hman, began the first mining operation on the banks of Ontonagon River near the pres nt ictoria mine, where a great boulder of copper bad b n found. This boulder attracted mu h att ntion and was v ntually ent to Wa hington where it is till on exhibition at the National 1us urn. This work ' a soon abandoned however, for the country ro k wa the unproductiv~ Jacobsville ("Ea tern") and tone, the boulder a it later app ared b ing a gla ial erratic derived from lodes that crop out farther north. The Lake uperior copper industry bad its real beginning in 1 30, tb ear in which Dr. Douglass ~?~ght~n.' Michigan s fir t tat g ologist, made his ID1t1al VlSlt to the r gion. His report, publi bed in 1 41, aroused a general int rest in the di trict. In 1 44 th~ Fed ral o rnment beO'an a land urvey at the mstance and under the dire tion of Doctor Roughton, w~ch was combined with the geologic and topograph1c urv y he wa th n making for ~he tate f Michigan. The e surveys, though ~nLerrupted by the d ath of Doctor Houghton late m 1 45, w re pu h d to rapid completion and rved ~oth to increase intere tin th di trict and to facilitate It ~arly expl ration and d velopment. Mining perm1ts w r i u d by the Fed ral Government the fi t . ' a1? . 1 44, but they were aboli bed in 1 46, and ~~ lands wer placed on sale. . 1he P1ttsburgh & Boston Mining o., organiz d 1 44, began operations at opper Harbor, wh re a th v tons .of black. oxide of copper was min d. In e followmg year 1t opened the fir t successful mine, the Cliff mine, on a cross fissure vein in the north end of the district; the first dividend was paid in 1 49. The Minesota mine ;va opened on a strike fi ure towa.rd the southwe t end of the di trict in 1 49 and paid its first dividend in 1 54, followed by the neighbor.ing T ational mine with a dividend in 1 61. The entral mine, op rating on the entral fi ur , northea t of the Cliff mine, made its first hipment in 1 56 and began to pay dividends in 1864. The fi sur mines were noted for the enormous piece of "rna " copper encountered in them. Several of th se rna es were estimated to w igh about 500 ton each. The Pewabic and Quincy mines were the fir t succe sful mines on an amygdaloid lode. They ' ere opened on the Pewabic amygdaJoid, in the PortagE~ Lake region, in the central part of the district, in 1 56 ; both mines began paying dividends in 1 62. The Isle Royale lode, 1 also in the Portage Lake region, had been opened as early as 1 52 by the Isle Royale Mining Co., incorporated origina!Jy to mine on Isle Royal, in Lake uperior. ltbough worked intermittently by a number of ompani , this lode ielded no dividends until 1913. · The Atlantic lode was di covered in 1 64 and explored by the outh Pewabic Mining Co. Inten ive development was begun by the Atlantic Mining Co. in 1 72. The famou Calumet & Hecla conglomerate was opened in 1 64, and the company paid its initial dividend in 1869. Ten years later the Kear arge and Osceola lodes ·were opened. The Baltic lode wa discovered in 18 2 but remained unexplored until 15 years later. This was the la t important lode to be opened. , Most of the fis me depo its have long since cea ed tu be productive. Of the lode depo its, all that have been largely productive are still producing or may be expected to produce under favorable condition , though some of the mines on the lode have been worked out or consolidated with others. ' The terms "lode" and "fissure deposit" are here applied in accordance with local usage. Strictly speaking, the "fissure deposits" are lodes, aud the so-called "lodes" are not so, being rather in the nature or bed·replacement deposits. The latter, however, will consistently be called lodes in the present report; lor the word is convenient and readily understood, and its use in this sense is perhaps not posi· tlvely incorrect. As much can hardly be said or other applications or the term that are current In the district, where the word is used to designate (1) Java tops or conglomerates, or parts or them, which, though susceptible or mineralization, are not actually mineralized; (2) rock substance that hns been mineralized; and (3) rock substance that is susceptible or mineralization. In general the use or the word in any or these senses will be avoided in this report, as being not ooly illogical bot likely to cause confusion where the word is nsed in two or more senses in the same sentence.
THE COPPER DEPOSITS OF MICHIGAN PRODUCTION The fir t production of copper in the Lake Superior district marked the real beginning of copper mining a a great industry in the nited tate . In it fir t ix years of activity- from 1 44 to 1 50-the di tri t !-- NOlllJd SON nOd '01JIA gz61
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Z9Bl l 9Bl 6. !lSI S!lSt -!lSI lml L SONnOd JO SN01l11 V'I produced more than 4,000,000 po~ds, while all the rest of the country produced less than one-fourth as muc~. Yearly production steadily increased to a max"llllum of 269,700,000 pounds in 1916. The total production from 1 45 to the end of 1925 has been 7,500,000,000 pounds. Among the copper district of the United States the Lake Superior di trict ranks second in total production. As a State Michigan ranks third, having produced 21 per cen~ of all the copper produced in the United tat to the end of 1925, while rizona had produced 31 per cent and Montana 25 per cent. 2 Dw·ing the 1 year 1906- 1923, for which definite figme are available, an a rage of 9,240,000 hortt{)ru of ore wa mined annuall , whi h yi ld d an avera e of 200,000,000 pound o£ copper, or 21.56 pound to the ton. Th yield wa 25.2 pounds to the ton for 1906, but dropped to 17.7 pound for 1914. For 191 ' 1919, 1920, and 1921 there pective yield were 19.2, 22.1, 23.7, and 24 pound to the ton. The following tn.ble ho' the produ tion of the di trict by year , by mine , and by lode from the beginning of operation to the end of 1925. ( ee al fig . 12- 14.) Refined copper produced in Michigan copper [ om piled from U. . Oeol. uney M in raJ Resources; figures for !924 and 111> furnished by Bureau of Mines. Smelter production] Pounds 11032,640 11 5051 2 0 11 2 11 2 0 11 7441 960 11 7441 0 0 21 9051 2 0 41 074, 560 5, 0 I 320 '211, 40 91 531, 200 91 157, 120 '926, 400 121 0691 120 15, 037, 120 13, 5 5, 600 12, 9 5, 2 0 12, 490, 240 14, 35 ' 400 13, 749, 120 17, 525, 760 20, 935, 040 26, 624, 640 24, 622, 0 0 26, 750, 0 0 24, 552, 640 30,0 9,920 34,332,4 0 36, 039, 360 3 '270,400 39,025, 2 0 39, 690, 560 42, 4 , 960 49, 736, 960 54, 573, 120 56, 982, 765 59, 702, 404 69,353,202 72, 14 '172 79,890,798 1 Figures furnished by Bureau of Mines. 1 93 - - - 1 95 - - 1 9 Pounds 75 471, 90 6 472, 034 1 17 5, 6ij 101, 410, 2ii 114 222, 709 123 19 ' 460 112 605, Oi 114, 30 , iO 129, 330, 749 143, 524, 069 145, 2 2, 059 15 ' 491, 703 147, 400, 33 145, 461, 49 156, 2 9, 4 I 170, 609,22 192, 400, 5ii 20 ' 309, 130 230, 2 7, 992 229, 695, 7:W 219, 131,503 222, 2 9, 584 227, 005, 923 221, 462,9 4 21 ' 1 5, 236 231, 112, 2 155, 715, 6 15 ' 009, 74 23 ' 956, 411 269, 794, 531 26 ' 50 ' 09 231, 096, !50 177, 594, !35 153, 4 3, 952 100, 91 ' 001 122,545, 126 137, 691, 306 145, 333, 22i 13 ' 029, 764 7, 504, 265, 441
Production
ALL UE-Z C NGLO MERA E 21 253 L B EVERGREEN SERI ES 125,960,4S2 L B S. ATLANTIC AMYGDALOID 142,840,8 04 LBS. ALL FISSU RES 199,853,000 LBS. ISLE ROYALE AMYGDALOID 210,839,585 LBS. OSCEOLA-AMYGDALOID 416,398,662 LBS. PEWABIC AMYGDALOID 8 73,734,108 LBS. BALTIC AMYGDALOI D 872,98~860 LBS. KEARSARG.E AMYGDALOID 1, 176.87 1,725 I..BS. CALUM ET CONGLOMERATE 3,375,353,670 L.BS. PRODUCTION BY LODES OSCEOLA AMYGDALOID $ 14,789,825 PEWABIC AMYGDALOID $29.24 2 ,500 BALTIC AMYGDALOI D $43,004,033 KEARSARGE AMYGDALOID S50,882.000 CALUMET CONGLOMERATE $148.726,051 DIVIDENDS BY LODES Total for district to 19?-5 ineh.Jain.- Total for district to 19?...5 incluaive 7.51&,526, 121 pounds of topper $297,2211.466 FIGURE 13.-Productlon and dividends of Mlcblgan copper mines to end o! 1926! br lodlll) I 1· .r· o· .,
ALL OTHER MINES (LODE AND FISSUR~ 509,983, 366 LBS ALLOUEZ 108,009,6 0 LBS. ATlANTIC 118,282.028 LBS. FRANKLIN 154,316,551 LBS. ISLE ROYALE t80,S37, 157 LBS. WOLVERINE 188,797,107 LBS. MOHAWK 259,34 5,245 LBS. AHMEEK 267,726,374 LBS. TAMARACK 389,215,899 LBS. OSCEOLA 477,371 ,115 LBS. TRIMOUNTAIN 141,040,592 LBS. BALTIC 263,523,7 11 LBS. CHAMPION 438,403,286 LBS. Q UINCY 726.022,243 LBS. CALUM ET & HECLA 3,242,016,280 LBS. PRODUCTION BY COMPANIES OR MINES THE COPPER DEPOSIT OF MICHIGA TAMARACK $9,420,000 WOLVERINE '$.10,350,000 MOHAWK $1 0,750,000 AHM EEK $1 3.?50,000 OSCEOLA $18.044,825 TRIMOUNTAI H S3.28J.OOO BALTIC $10,001,772 CHAMPION S29,070,26 1 QUINCY $27,002,500 CALUMET & HECLA $148,413,051 DIVIDENDS BY COMPANIES OR MINES Total Cor district to 1925 inclusive Total for district to 1925 inelusi v(: 7,516,520,121 pounds of copper $297.226,466 FIGURE lt.-Prodnction and dividends of Michigan copper mines to end of 1925, by companies or mines
Company PRODUCTION tatistics of copper production in Michigan copper district, 184E-1926, by companies Lode Period opper (pounds) Rock treated (tons) Yield per ton (pounds) Dividend Total Per pound (cents) 1 1 1 1 10, 71403 , · {Kearsarge amygdalOid_}
249 915 343 Ahmeek -- -- 17; 11; 031 10, 53,819 14,050, 000
85~ Algomah -- 12,467 - - -- -4; 9i -,-·43- -i6.-72- -z:-56; 666- --3.-47 1 62-1 7 -- -- --
a 7 I 957 a 20, 000 ' 11 , 2 2, 02 ;714;452- -ii-57- 996;666-1 4 Aztec 1 52-1 200, 5 4, 164 , 672, 553 7, 950, 000 Assumed. 1 61- 191 - - - - -- Prior to 475, 747 2, 31, 092, 153 127,6 6, 924 213, 17, 5 4 67, 351,569 2, 12 1 050 33,935 3, 554 2, 449, 106, 01 33,033, 675 2, 901, 635 47, 219, 399 1, 754, 493 43 ,403, 2 6 1 7, 915 4,606,690 1, 595, 003 06, 633 1, 770, 570 116, 00 17, 706 352 e 1 633, 603 4, 2 2, 50 1, 576, 2, 934 169, 502 143, 217 49, 67 2, 915, 730 332, 000 69, 164 669, 9 1 14,329, 231 24, 656, 624 e 80, 1 6, 631 e 34, 473, 9 4 1, 255 75,397 3, 529, 822 313, 848 17, 559, 557 123, 724 540,052 25, 309, 270 213, 245 57, 229, 052 49. 47 ) 12, 374, 23 14, 59 I 914 b 160, 963, 755 2, 331, 524
360, ooo 1 1. 01 2, 130, 000 14, 156, 309 29, 070, 260. 96 100, 000 1, 64, 236 d 2 I 576, 646 -- 1, 240, 000 e 3, 053, 240 30, 315 Based portly on estimates. Includes $12,660,704 received from other companies. lnclud $26,401, 74 timoted dividends received ({Om othQr companies.
THE COPPER DEPO ITS OF MICHIGA d t . · 'lichigan cop11er district, 1845- 1925, by com7Janicsontinu d tati tic of co7Jper pro uc tOn " Company Lode - IPeriod lotd.
Keweenaw Copper_ - 1 62- 1 9L - d I "d 1 56- 1 L - and Perkins fi sure .
1 59, 1 64 -- 1 53, 1 5 - - 1 74-1 80, 1 971903. Copp\'r (pounds) I 1 1 194 171, 71,963 21, 237 14, 490, 36 179, 565 992, 757 3,499 6, 60 1 24 717, 403 14, 21 7, 14, 730 72, 091 Hock lr ntod (tons) Yield por tou (pounds) -J 10, 469, 751 16. a9 I 521 ; 767- -15.-55-} Dividends Total Per po! (ceol!) $2:556,-6661. 4 100, 000
320, 409
-- 10,000 , - --- --- 6, 222, 0 15 - - - - - - - - -- - 4.4, 394, 62 2, 9 6, 136 4, 095 - - - - --- a 9 174, 10 a 1 006, 420 4, 0 5, 175 -- 34, 706, 66 1, 20, 000 11, 612, 952 1, 00 3 9, 556 4.44, 640 1, 509, 163 5, 657 313, 005 993, 360 1, 13 ' 97 41, 440 49, 662 a 25, 056, 02 3, 034, 311 556, 424 130, 000 27, 23,416 a16, 632, 536 a 357, 032 449, 416 33, 600, 216 24, 730 6, 60 4, 505, 266 367, 124, 14 5, 425,417 26 ' 945, 4 31,000 5,443,195 5, 21, 136 14, 014, 050 10, 136 10, 750, 000 320, 000 7, 4 977, 92 16, 250, 345 9, 513, 943 25. 62 ) 1 ' 044, 25
27, 002, 500 14, 371, 072 I 1 . 11 --- io6, ooo 1, 011, 071 . - -- -- - - - - - 1,8 2, 529 17, 222 3, 46, 163 1,463, 336 --- 165, 843 Based partly on estimates. Pounds of mohawkJte. Assumed.
C{)mpauy PRODUCTIO tatistics of copper production in Michigan copper district, 1845- 1925, by companies- Continued Lode Period Copper (pounds) Rock treated (tons) Yield per too (pounds) Dividends, Total Per pound (cents) uth Lake 7 - -- 190, 736 1, 042, 211 3, 562, 967 17, 93 30, 01 ' 271 0, 07 5 Fr u r:es - - - - - 55-1 uperior (Houghton upcnor arnygdalord 190 County). uperior (Ontonagon -- --- - -- - -- --- - - - - - -- County).
Calumet&Heclacon- glomerate. · glom rate. - 525, 7, 79 0 379, 971, 101 d 9, 237, 000 9,462, 191 1, 550, 474 13, 591, 141 6, 703, 079 $649,000 9, 420,000 3, 250, 000 59, 74 379, 153 139, 697, 2 9 124, 721 19, 567, 792 1 ' 233, 169 6 ' 000 16, 497, 396 1, 1 6, 3 1, 979, 37 1, 700, 51 11. 51 -- - White Pine - 7, 654 33, 437.50
u· 1, 207,471 1 6, 17 729 39, 973 :46--263- -22.-66- 10, 350, 000 2, 927 7, 516, 504, 197 251, 320, 142 - - -- --- 335, 969,044. 46 Total production, omitting figur s for which no con·e pa neling tonnage are given : Including copper reclaimed from and - -- - - - - - 7, 031, 64 , 114 251, 320, 142 Not including copper reclaimed from sand --- - -- - - - -- 6, 903, 961, 190 251, 320, 142 from oth r compa ni · ') . E timatcd divid nd paid fr m a tual miniu.g p rati n - - - 1- -- --- - 1297 , 266,466.46 T ributa copper for 101 . alurnet & Hecla, 12,550,70-l; Copper Range (estimated), $26,491, 74. Production and divid nds from 7Jrincipallode , 1 45-1925 Lod Atf Evcr~reen and u c di -JOd--: Estimated. Refined copper (pounds) Total P r ton 3, 375, 300, 000 Q 51. 26 1, 176,900, 000 73 700,000 73 000, 000 416, 400, 000 210, 00, 000 ' 16. 39 142, 00, 000 69, 500,000 d 11. 29 66,500,000 10 to 20 30, 500, 000 20, 000, 000 1 ' 200, 000 7, 300, 000 A,·eragc 1001- 1925 onl y. b Dividends Total 14 '726, 051 b 50, 2, 000 29, 242, 500 43, 004,032 b 14, 7 9, 25 2, 550,000 990, 000 one. rone. 649,000 None. 33, 437 None. Per pound or copper( cents)
--- d l'rank lin Jr. mine only.
THE COPPER DEPOSITS OF MICHIGA . · · M . h" pper district 1845-19f5, by lodes and ntines Production and dwtdends tn tc tgan co ' Calumet & Hecla conilomerate Mine . Conglomerate Branch. Com pany Calumet & Hecla: Conglome r ate Branch. T amarack J umor OsceolaConsolidatedMining. Period 1 66-1925 1915-1925 1 73- 1 0 1 92- 1 96 1 97- 1902 T otal production, omitting figures for which no corresponding tonnages are given: I ncluding copper reclaimed from sands Rock treated (tons) 57, 229, 052 12, 374, 23 35 ,450 5 I 213, 265 5 I 213, 265 Kearsarge amygdaloid I -io;-oi;252-j 91 ' 43 & t 2, 261, 90 K earsarge Branch_ ' ec a, en enma' j 2, 331, 524 Kearsarge, and Osceola.
-io;344;447outh K earsarge___ 6, 427, 605 30, 315 739,624 19214, 014,050 7, 44 eneca Copper Corporation_ 1920- 1924 14 , 530 eneca. 17,313 f-:i9 46--263- ' ' Production Refined copper (pounds) Total Per too I , 966, 0 3 119, 190 379, 971, 101 2, 31 092, 153 127, G 6, 024 12, 52, 02 2, 56,267,371 2, 9 3, 954, 295 6 1 241, 492, 1 6 2, 222, 9 9 Dividends To tel Per O 14 I 726, 051 33, 033, 675 14. GO o 29, 7 2, 000 67, 351, 569 21,237 160, 62, 279 115 156, 251 313, 4 7 l 14, 730 259, 114, 34 1 . 49 --- -1o;75o;ooo 49, 62 !3, 5 1, 922 1, 979, 37 1 10 350 000 1 6, 171 729
Total production, omitting figures for which no corre pending tonnages are given. 1, 176, 71, 725 50, 2, 000 60,511, 104 1 1, 15 , 075,429 -- Pe wablc amygdaloid Albany & Boston Albany & Boston Mining 1862-1864 - --- 14,9 2
1857- 1860 --- - 669, 9 1 457, 450 14, 329, 231 1871- 1 3 24, 656, 624 d 1o83 1919 0 - , o 3, 888,462 o 80, 1 6, 631 27, 23,416 ii.= =ll [ 1' 240, 000 1 I 000, 000 ! 1856-1861 - - 4, 505, 266 27,002, 500 1 3. 74 1911- 1925 14, 371, 072 26 I 9451 4 8
T otal production omitting figures for which no corresponding 31,614,410 - tonnages are given. Bailie amygdaloid 8, 672, 553 200, 584, 164 $7, 950, 000 1, 820, 612 62, 939, 547 2, 0 4, 772 43, 624 1,343,303 6, 703, 079 139, 697,2 9 3, 250, 000 14, 156, 309 43 ,403, 2 6 29 070, 261 1, 550, 474. 30, 018, 271 '649, 000 4.9,729 540,052 10. 86 - 32, 996,380 873, 525, 912 43, 004, 033 Estimated .
PRODUCTION Production and dividends in Michigan copper district, 1845-1925, by lodes and mines-Continued Osceola amygdaloid Mine Company Period Rock treated (tons) Osceola Branch 14, 59 '914 2 '531 0 ceola Branch - -- - Centennial Copper Mining
153, 662 Osceola_- --- -- 9, 513, 943 -- - Total production. omitting figures for which no corresponding 24, 295, 050 t{)nnages are g1ven. Isle Royale amygdaloid Is] R
10, 469, 751 Production Dividends Refined copper (pounds) Per Total roound Total Per ton cents) 213,817, 5 4 531, 9 3 106, 01 -- -- --- 9, 825 1, 917, 90) 190, 7 7, 3"93 0 9, 237, 000 -- -- -- --- --- 416, 398, 662 -- 0 14, 789, 25 407, 054, 61 16. 75 -- 3, 529, 22 25, 309,270 1- --- - - - -- - --- ' 81 ' 194 heiden & Columheiden & olumbian Copbian. per. 171, 71 , 963 I 16. 39 $2, 550, 000 $2, 550, ooo 1 1. 21 Ash bed Atlantic) amygdaloid 1, 772, 231 '- - ' -- - --- - - - 7 -i3.-57-! $99o,-ooo- --o.- -4 0 17, 706, 352 - : ~H; 449,416
3, 562, 967 1 Garden Garden ! Ph nix Ph on olidatcd opp r. outh P ewabic 4 ' 063 Total production omitting figur for which no corr ponding tonnages ar given. ' 762, 515 11 '731, 444 Allouez conalomerate Albany & Boston Albany & Bo ton Mining Allouez Mining 0 3, 053, 240 oncs uch lode Nonesuch 1 6 - 1 85 7.-654 -I White White Pine Estimated . 61, 057 25, 7 6, 651 1, 770, 570 0 34, 473, 9 4 6, 624, 991 69,521,253 one. 389, 556 1 - -- 1 ' 233, 169 20. 54 1 33, 437. 50 1 622, 725 1 20. 54 33, 437. 50 1 0. 18 Assum d.
THE COPPER DEPOSIT OF MICHIGAN Production and dividends from fissttres in Michigan copper districts, 181,5- 1925 F'issure Mioo ! Rock Ia nd - - - - - - - - - - --- Cliff North Period Prior to 1 55- 1 1 53-1 95 1 55- 1 9 --- - - nofluod copper (pounds) Dividends
'l'olai Per ilOUnd () 34, 707,000 1, 20, 000 ] l , 6131 000 320, 000 9, 1741 000 --- --- 51, 75, 000 2, 130, 000 4.lt 3 1 2071 000 2, 51 1620 1, 509, 000 - , 39, 722, 000
9 , 20, 000 Ma Estimated.
ot separated !rom Kearsarge lode. 17, 032, 00 0 11, 567, 000 (b) O I 634, 000 100, 000 5,41 , 000 - -- 1, 5411000 -- , 1, 011, 000 445, 000 313, 000 - - , c 230, 000 ' -- 1 1 000 1 141, 000 -i d 130, 000 --- 72, 000 - 50, 000 - d 20, 000
10, 000 --· --- 11 000 - - - - - - - - -- 199, Pounds or mohawkite. A urned. Dividends paid in Michigan copper district, 1845- 1925 Company Period 1911- 1923 CentraL 1 64-1905 Copper Fall - 1 64-1 71 opper Range.-- 1905- 1925 Dividends $14, 0501000 2, 50, 000 990, 000 7, 950, 000 0 160, 963, 755 360, 000 2, 1301 000 29, 070, 260. 96 100, 000 b 2 1 5761 646 1, 240, 000 2, 550, 000 160, 000 1, 820, 000 10, 750, 000 320, 000 181 0441825 Includes $12,550,704 rcce;ved from other companies. Includes $26,491,874 estimated dJvideuds received Cr01n other companJes. Com pany Period uperi -- - Duplication (e timated dividends paid from di viclends received from other companies - Estimated dividends paid from actual mining operations - -- -- Dividends 1 0001 000 I 201 000 2 51 1 620 27: 0021 500 91 420. 000 3 2501 000 I 331 437. 50 101 350, 000 335, 9691 044. 46 391 0421 57 . 00 2971 2261 466. 46 'Calumet & Hecla, $121550,704; Copper Range (estimated), $2614911874·
PRODUCTION Dividends paid in Michigan copper district, 1845-1925, by companies and year Year I umber/ Amount Ahmeek (All from workings on Kearsarge lode] J91L $100, 000. 00 !912 --- 900, 000.00 !913 -- 1, 100, 000. 00 J91L 300, 000. 00 1915 1, 150, 000. 00 1916 2, 500, 000. 00 1917--- -- -- 3, 200, 000. 00 191 - --- 2, 000, 000. 00 1919 .. 600, 000. 00 300, 000. 00 1922 .. 400, 000. 00
500, 000. 00 1, 000, 000. 00 14, 050 000. 00 Allouez (All from workings on Kearsarge lode] 191 -- - --- 100, 000. 00 700, 000. 00 1, 200, 000. 00 750, 000. 00 100, 000. 00 2, 50, 000. 00 Allan lie 990, 000. 00 Baltic (A ll from workings on Baltic lode) 1907 -- - -- 1908 - -- 1909 --- 1910 -- - - -- 1, 250, 000. 00 1, 400, 000. 00 1, 000, 000. 00 900 000. 00 1, 000, 000. 00 1, 000, 000. 00 500, 000. 00 700, 000. 00 200, 000. 00 7, 950, 000. 00 Liquidating. 0 16 dividends to 189 . Year I umber/ Calumet & Hecla CALUMET MINING I!ECLA MINIKG Amount 200, 000. 00 100, 000. 00 300, 000. 00 ' 100 000.00 300 000. 00 250, 000. 00 650, 000. 00 CAL UMET .t. II ECLA ll1NfNG , -- - I 191 --- - c 194 155, 000, 000. 00 Includes 117 to 1000. Year Tumber/ Amount CAL MET .t. H"ECLA CONSOLrDAT'ED COPP ER 1, 002, 751. 00 1, 002, 751. 00 3, 00 ' 253. 00 5 1 5, 013,. 755. 00 SUMMARY 300, 000 650, 000 Calumet & Hecla :\lining 5, 013, 755 Paid by Calumet & 12, 550, 704 Paid from it own mining operations_ 14 , 413, 051 Centennial [All from workings on Kearsarge lode] Year urnAmount ber 90, 000. 00 90, 000. 00 191 --- - 1 0, 000. 00 360 000. 00 Central [All from tLsurc workings] 50, 000. 00 50, 000. 00 50, 000. 00 50, 000. 00 40, 000. 00 70, 000. 00 0, 000. 00 50, 000. 00 0, 000. 00 160, 000. 00 160, 000. 00 0, 000. 00 100, 000. 00 140, 000. 00 100, 000.00 0, 000. 00 100, 000. 00 120, 000. 00 50, 000. 00 60, 000. 00 40, 000. 00 30 000. 00 40, 000. 00 40,000.00 70, 000.00 40, 000. 00 20, 000. 00 20,000.00 160, 000. 00
THE COPPER DEPOSITS OF MICHIGAN Dividends paid in Michigan copper district, 1 45- 1925, by companies and years-Continued Year I umber! Amount Amount Year Champion Franklin Mohawk [All from workings on Baltic lode] [All from workings on Pewabic lode] [A II from workings on Kearsarge lode] - 60, 0000 00 ' 500, 0000 00 100, 000° 00 900, 000. 00 60, 0000 00 190 250, 000.00 20, 0000 00 300, 000. 00 40, 000° 00 200,0000 00 0, 0000 00 175,000.00 40,0000 00 350, 0000 00 0, 0000 00 500, 0000 00 40, 0000 00 100, 000. 00 120, 0000 00 600, 0000 00 0, 0000 00 1' 700, 0000 00 0, 0000 00 2, 050, 000. 00 0, 0000 00 1' 000, 000. 00 160, oooo oo I 1919 500, 000.00 120, 0000 0 550, 0000 00 0, 0000 00 I 300, 0000 00 1923 - - - - - - -- a 315,000000 1, 240, 0000 00 460, 000.00 10, 750,000000 300,000° 00 1, ~88; 888:88 I i 1, 200, 000° 00 1, 000, 000° 00 190 - - - -- 500, 000° 00 1 4 - 1909- - - - - 00, 000° 00 1910- - - - 900, 000° 00 500, 0000 00 1, 100,0000 00 - 1916 6, 014, 540° 96 1, 975, noo oo I
. 9 - I 1, 2 0, 0000 00 1 93 - - 191 600, 0000 00 i 1922 - 600, 000° 00 i 7 00, 0000 00 I 7 0, 0000 00 1 140, 0000 00 Isle Hoyalc aUonnl 1 29,070,2600 96 I All frorn fissure workiDb'S] 1so, oooo oo I Copper Falls [A II from fissure workings] $60, 0000 oo 40, 0000 00 1oo, oooo oo Copper Range 1906 --- - -- 190 -- - -- 191 1919 - 1922 - --- --- ] 923_-- 1924 - 1925 - Estimated divid e nd s received from other com- $1, 536, 0 60 00 2, 304, 100 00 2, 304, 100 00 1, 536, 7400 00 1, 536, 9300 00 1, 537, 3400 00 1, 357, 104. 00 7 ' 42 1, 0 4, 49 0 00 1, 1 2, 0030 00 3, 941, 64 0 00 3, 943, 9120 50 2, 366, 3940 00 9 6, 0150 50 591, 6250 50 394,4220 00 394, 4250 00 394, 7270 00 394, 7270 00 2 ' 576, 6460 00 E t1mated dividends paid from its own 2, 084, 7720 00 1 1916 -- 450, 000° 00 1917 --- 900, 0000 00
' 3175o5, ooooooo oooo IJ 1
- 40 000 00 150, o oo oo · 1 11-- --- - 20' oooooo 225 ooo oo 20' ooO: oo
2, 550, 0000 00 320, 000. 00 Osceola Kearsarge [All from workings on Kearsarge lode] 0, 0000 00 !8; 888: gg I i 160, 0000 00 '' i Minesota fAll from fi ure workings] i 90, oooo oo I 90, 0000 00 I 1 200, 0000 00 1 7 300, 0000 00 --- 300, 000° 00 1 9o9 - -, 1 o ooo o I 9 0 , 120, 0000 00
100, 0000 00 , 16~ oon oo 985 160,0000 00 19 6-- - - - 60, 0000 00 1 7 - 50, 0000 00 10, 0000 00 119 1, 820, 0000 00
0, 000. 00 60, 000. 00 210, 0000 00 225, 000. 00 200, 000.00 150, 000° 00 7, 500° 00 50, 000° 00 150, 000. 00 50, 000° ()() 225, 000.00 150, 000° 00 150, 000° ()() 100, 000° 00 100, 000.00 125, 000. 00 191, 000°00 277, 250° ()() 55 ' 450° 00 571, 200° 00 576, 900° 00 192, 300° 00 3 4, 600° 00 961, 500. ()() 1, 249, 950. 0000 192, 300. 769, 200° ()() 961, 500° 00 721 125° 00 75° 00 1; 009; 575° ()()
PRODUCTIO Dividends paid in Michigan copper distr·ict, 1845-1925, by companies and yearsContinued Year - Amount Osceola-Continued !91L-- i91L -- !91L i917 ... 191 1919 1920 1lol1 Pewabic I 63 .. I 93 4 - - Phoenix $2 8,450. 00 769, 200. 00 1, 53 ' 400. 00 1, 923, 000. 00 961, 500. 00 '450. 00 96, 150. 00
192, 300. 00 i 96, 150. 00 . 60, 000. 00 120, 000. 00 200, 000. 00 20, 000. 00 40, 000. 00 20, 000. 00 400, 000. 00 140, 000. 00 1, 000,000.00 $20, 000. 00 Pittsburgh & Bos ton lA II !rom workings on ClifT ll urc] I 63 -- - 1 64 165 I 6 169 1872- -- - - -- Quincy 1874 1 4 ln liquidation. 6o, o o. oo I 4, 000. 00 o, ono. o : 0, 000. 00 I 90, 000. 00 7 '00 . 00 1 0, 000. 00 1 0, 000. 00 160, 000. 00 1 0, 0 . 00 0, 000. 00 0, 000. 00 1 0, 000. 00 320, 0 0. 00 200, 000.00 120, 000. 00 60 000. 00 100, 000. 00 100, 000. 00 3, 6'W. 0 2, 51 $60, 000. 00 200, 000. 00 2 0, 000. 00 160, 000. 00 60, 000. 00 40, 000. 00 120, 000. 00 140, 000. 00 350, 000. 00 100, 000. 00 160, 000. 00 Year Amount Year Amount I umber! 11
Quincy-Continued Tamarnck $440, 000. 00 640, 000. 00 590, 000. 00 00, 000. 00 600, 000. 00 600, 000. 00 400, 000. 00 400, 000. 00 360, 000. 00 360, 000. 00 4 0, 000. 00 600, 000. 00 1, 020, 000. 00 1, 200, 000. 00 90, 000. 00 120, 000. 00 300, 000. 00 420, 000. 00 $220,000.00 160,000.00 1 77- - - - - 0, 000. 00 i 100, 000. 00 I 1 9 L - - - - - 220, 000. 00 320, 000. 00 I 1 94- - - - - 520, 000. 00 I 1 95. - - - . -- . - 3 0, 000. 00 2 0, 000. 00 1 0, 000. 00 1 1 9 - - - - - - -- - - - 240, 000. 00 200, 000. 00 1900- - - - - - 360, 000. 00 2 0, 000. 00 1904_-- - --- 320,000. 00 450, 000. 00 1 92 - - 350, 000. 00 1907- - 300, 000. 00 400, 000. 00 400, 000. 00 9, 420, 000. 00 1 96 - 1, 200, 000. 00 'l'rinaountain 00, 000. 00 650, 000. 00 [A II !rom workings on Baltic lode) 950, 000. 00 900,000.00 900,000.00 7 00, 000. 00 1903- - - - - - - I 550, 000. 00 1904-- - - - - - 500, 000. 00 600,000.00 1906- - - - - - 1' 250, 000. 00 1907-- - - - - - 1, 4 5, 000. 00 190 - - - - - 495, 000. 00 1909- - - - - 440, 000. 00 550, 000. 00 440, 000. 00 4r I 550, ooo. oo 412, 50Q 00 55, 000.00 0, 000. 00 1, 760, 000.00 1917-- - -- - 1, 9 0, 000. 00 4t I 935, 000. oo 1919- - -- 440, 000. 00 OT&. opper Handbook, 1922, says: "Year 191 marked Quincy's seventieth annh·ersary. During this Lim it paid its stockhold $26,452,500 in dividends and still had $21, ,124 C!lsh surplus: this is equivalent to a profit or 4n cents on each ol 613,596,622 pounds copper prodnc d, nod sold at an nvcrag price lor the entire 70 years ol 16.13 cents, equal to 9 ,9i3,400." Ridge 50, 000. 00 20, 000. 00 20, 000. 00 10, 000. 00 1 00, 000. 00 uperior 100, 000. 00 100, 000. 00 200, 000. 00 I 249, 000. 00 649, 000. 00 First liquidating. I Second liquidating. 1903- -- - - 1912 191 - $300, 000. 00 500, 000. 00 150, 000. 00 300, 000. 00 200, 000. 00 500, 000. 00 1, 300, 000. 00 3 250, 000. 00
While Pine 1917 1 $29, 062. 50 191 4, 375. 00 ~--3-3-.-4-37-. -5-0 Wolveri.ne 1 9 1915 191 - $60, 000. 00 210, 000. 00 240, 000. 00 240, 000. 00 240, 000. 00 330, 000. 00 450, 000. 00 660, 000. 00 1, 020, 000. 00 1, 050, 000. 00 600, 000. 00 600, 000. 00 600, 000. 00 540, 000. 00 600, 000. 00 300, 000. 00 120, 000. 00 540, 000. 00 720, 000. 00 10, 000. 00 240, 000. 00 150 000. 00 30, 000. 00 10,350, 000. 00
THE COPPER DEPO ITS OF MICHIG Detailed statistics of production in i\1 ichigan copper district, 184<5-19£5, by companies [Definite information as to no prod~ctiou is iudiC!Ited in tho tables by the word " 'one." Years lor which no information is available are omitted] Ad ven t ure.- I n Ontonagon County. rganized in 1 50 a Adventur Mining Co.; 1,000 shares, 200,000. Fir t company to introduce tribute sy tern about 1 55; prov d p rofitabl~ . I n 1 5 purcha ed pr pert:v of the Merchant Co. old 111 1 70 and new company organized. o work done by company sin e 1 77, although ome work wa done by tributer after that date. Adventure on olidated Copper o. orgauized in October, 1 9 ; 100,000 hares at 25. l ade up of Adventur , Hilton, and I nowlton mine .
rked Knowlton, Ogima, Ierchant, Evergreen, la s, and Butler lode . Hilton, formerly Ohio, was open d 1 63. Knowlton opened 1 60, worked intermittently 1 65-1900 by tributers. Refined copper (pounds) Year Rock treated (tons) 1 Total Per ton 1 5 1 1 5 t f: t t 42,904 97, 036 136: 094
o Estimated. ' D~ring Orst 4 months 00,4 10 tons stamped yielded 975 944 pounds refined coppe M10e closed October, 1917. ilver sold in 191 , 1,283.59. r. Aetn a.- In Kew enaw ount . 20,000 har , $500,000. rganized January, 1 &!· Year 1 64 1 66 Refined copper ' (pounds) 4: 131 62, 5 Year 1 6 otlnty. I ncorporate KEARSARGE AMYGDALOID larch :n, Relined cop)le:' (pounds) Year Rock treated (tons) 1 , j Per!ou 190 -- 191 16, 400 7 ,360 166, 960 320, 733 404, 3 5 650, 600 5 ·, 331 937, 54 1, 151, 002 1,267, 592 1, 195, 15 750, 750 212, 170 439, 769 10, 01, 252 MA 1'1 lTRE Total !i.l 1909 1, 660 223, 525 1, 660 223,525 1, 660 223,525 1, 660 223,525 2, 290 30 I 660 I 134.79 4,1 563, 050 11, 326 1, 465, 774 13,00 1, 221, 45 17!. 31. 3, 6 3 631, 155 191 169, 752 6, 120 664, 065 !0 5! 3, 929 !49. 5 513, 000
1922- - - - -- -- 1, 403, 000
1 1 o' o rock from fissure stamped; entire production from masses. Percentage of copper, 1921, 7.5; 1922, 76.75. ·
Productio Total
Refined copper (pounds) Silver sold Rock stamped (tons) Total Per too 1903-- -- -- -- 190L 16, 400 190.L 7 ' 360 1goL 166, 960 320, 733 !90 -- 29 ' 17 !909 406, 045 1910 530, 365 !91L 59 , 549 652, 260 !91L 3 3, 749 590, 519 !91L 94 , 74 !91L-- -- 1, 164, 010 1, 271, 275 191 1, 196, 541 !91L 756, 70 1920 22, 192 !92L-- -- 212, 170 !922 439, 769 1923 - --- - one. 376, 6 7 1, 552, 957 3, 077, 507 5, 510, 9 5 6, 2 0, 241 9, 19 ' 110 11, 44,954 15, 196, 127 16, 455, 769 9, 220, 74 13, 634, 605 21, 00, 492 24, 142, 15 27, 919, 12 24, 51, 235 17, 223, 111 20, 4 9, 43 6, 255, 200 14, 5, 0 1 17, 11, 031 267, 726, 374
' 22. 97 19. 2 1 . 43 --- -- 22. 33
25. 2 24. 0 --- $4, 025. 54 14, 026. 50 16, 503. 60 16, 171. 37 --
- 29. 4 33. 5
Albany & Bo ton.- I n H ought n County. Organized June, 1 60; 20,000 s hares , ·soo,ooo. I n pring of 1 62 roo t of the work u. p nd d in t hi.· location. Resumed late in 1 62 and continu a ii v I.v in 1 63. W rked Pewabic amygdaloid. bout I 64 worked ". lban_v & Bo i n" (Allouez) onglomeratc. old o Penin ula opper Mining o. in 1 2, and to Franklin ~li ni ng o. in 1 95; mine now kn wn a Franklin Jr. Ye r Refined copper (pounds) 7 !),2 1 <ia, ! o6 Ci2, 493 2:3-l, fi~6 1 n 1, 7G Year Refl,ocd copper (pounds) G, 200 G, 01 1, 74(i Durin year ~nding larrh, 1 , produrod :md sold 271,200 pounds of ingoL copper. Albion.- e 1anha tan. Algomab.- In ut nng n uni . lgomah iining o. organized Jun 4, 1910. ork d 1 52- 1 54 by tl. com pan of the _same name with n gaiiv r ult . o rock milled. I n 1914, 12,467 pound of refin d copper from hand-picked ore. Allouez.- In I we naw ounty. rganized eptember, I 59. Little work done to 1 69, when work began on Allouez conglomerate. Temporary suspension, and in 1 71 work re- ;med to 1 77. Leased to Allouez Tribute Co. for three year , 1 ovember, 1 77-_1 Company r umed control ovember · 1 0, and at one began activ op ration . Reorganized 00,000 bar s at 25 and work d to June 1, 1 5, when it was I a ed to Wat on & Wall f r t rm of three Year ' but in 1 7 pr perty attach d by r ditor and work mpany re LJm d control in 1 9, and a r organiza- I orb d by alumet & H ecla on olidated PPCr o. ptemb r 1, 1923. ALLOUEZ CONGLO~fERATE I Refined copper (pounds) Year Rock treated (tons) I 'l'otal I Per to:- 3, 57 5 21, 163 1, 00 ' 134 1, 3 5, 574 0 1,561, 7 5 1 77 - - - - 1' 300, 279 1 7 --- 1, 131, 146 - 1, 431,452 --- - 1, 31 '471 63, 362 1, 204, 224 97,232 1, 6 3, 557 1 102,3 1, 751,377 1 4- , 119,630 1, 932,170 b 2, 170,476 l, ' 314, 19 116,60 1, 762, 16 97, o2o I 1, 407, 2 14 s 1 93 --- - -- Nona 25,7 6, 651 1 During year ending July 1, I 76, 51,135 tons stamped yielded 1,433,833 pound refined copper. 62,500 tons stamped by company produced 1,050,546 pound ingot, or 16. pounds per too; tributers produced 1,119,930 pounds ingot. KEAR ,,ROE AMYGDALOID Year RO<'k lre ted (tons) 1905 0 41, 120 b17 190 -- 247, 119 ' 610 333,61 354:457 1 534, 7 05 566,960 1917 -- 191 51~ 131,643 4, 91 Ioaludes 4, 95 tons !rom stock pile. Includes 108 tons !rom stock pile. ilver old, $22, 9.24. Total production, 1 ,009,640 pounds. A m erican.- e North American. ltefined copper (pounds) 'l'otal Per ton 1, 167, 957 3,4 6, 900 2, 934, 116 3, 047 051 -t, oo1, 532 I 1s. 93 4 655, 702 t . 4 4, 7 0, 494 I H). 56 5, 525, 45 - 1 4 091, 129 6, 056, 54 I 10, 043,459 10; 219 290 . , 92, 915 I 7, 071, 21 3, 749, 9 4 1 2, 222, 989 1 A m ygdaloid.- In Keweenaw Couuty. rganized July, 1 60; 20,000 ha.res, $500,000. ompany operation u pended in 1 66 and min worked on tribute.
THE COPPER DEPOSITS OF MICHIGAN Year Refined copper (pounds) 97, 591 .50). 13 ' 124 135, 795 41 ' 964 340, 66 161, 375 122, 694 33, 010 47, 610 2 ' 250 15, 40 1, 259 1, 541, 1 0 Arcadlan.--In H ughton ounty. Organized July, 1 64; 20,000 har , 500,000. Mining operation were not commenc d until after eptember 1, 1 64. Arcadian Copper o. incon ora.ted under laws of Michigan, June, 1 9 , with apital of 2 500 000; reincorporated under law of ew Jer ey, 1 99. Reorganized a ew Arcadian Copper Co. April 27, 1909. Arcadian Conoliclatcd form ed January 1, 1920, taking over all property and effects of the ow Arcadian and the Jew Baltic opp r companic ; 250,000 hares, 6,250,000. Mineral land compri e ix old mine - the Arcadian, Edward·, Dougla s, ncorcl, Highland, and t. Mary's. Yetlr / Year ARCADIAN LODE Refined copper (pounds) 4, 593 5, 16 24, 760 34, 037 500, 000 Year NE\V AIICAD!AN LODE Refined copper (pound ) 1, 350, 000 500, 000 600, 000 3, 019, 206 .Rock treated (tons) Refined copper (pound ) 'rota I I Per ton 3, 45 1 391 --- 79, 209 53; 27 .None. -- -- 10, 136 164, 794 Total production, 3,1 ,000 pounds. Arnold.- I n Keweenaw County. Arnold operated in small way in 1 60. Arnold mine proper, developed on Ashbed amygdaloid, was opened in 1863. Incorporated in April, 1864; 100,000 shares at $25. Two holdings, Copper Falls mine and Arnold; Copper Falls, absorbed 1898. Operated 1863 to about 1869; closed 1869- 1892; active 1892-1894; idle 1894 to February, 1 97, when work wa.s resumed. Worked mostly on Asbbed. Year
Refined copper (pounds) 152, 320 763, 911 56, 000 1, 772, 231 As bed.-I.n I ewecnaw., ounty. Petherick Mining o. organized Aprrl, 1 61, by Copper Fall Mining Worked .1 61- 1 .65 .and pended operations; re umed in 1872; became rdle agau1 rn 1 71. I n 1 73 Indiana mill purcba ed. In 1 77 pr per y ~lo ed out at heriff ' sale. In 1 0 A hbed Mining o. organ r z~d; !O,?OO hares at $25. Work resumed in 1 1 and dr contrnued 111 1 2, producing a few ton of copper. Between 1 9 and 1900 exploratory work carried on; idle in I n June, 1905, resumed activity. , Relln d copper (Peuncb) Year Rock trented (tons) 'l'otal Per ton 133, 1 3 1 64_- --- - 51, 22 one. 1 6 - 12, 000 one. one. 10, 570 13, 34. 5, 115 172,291 4, 449 152,94.6 1 76- 5, 563 5, 224
1 Atlantlc.- In Houghton oun y. tlantic ~lining C'o. organized Decemb r 31, 1 72, by con lidation of oulh Pewabic and Adam mining companie ; 4.0,000 share at 25. ( outh Pcwabic organized 1 65; capital xhau t d nnd sold to Atlantic. iarted work 1 65; b an proclu tion I. 66.) Mine cl crl by caving in lay, 1906. I Rock lreatecl (tons) Refined copper (pounds) Year '!'oral Per ron 13,475 1, 760 1 6 11 52 I 25 1' 646, 57 51,04 63:36 69, 72 I 372, 4.06 0, 000 1:567,036 1 76- - - 96, 696 1' 35, 04.1 1 05, 7 0 2, 054, 304 111,709 2 006 075 1 122,66 2:339:073 169, 25 2,423,225 176, 555 2, 52 , 009 1 9, 00 2, 631,70 195,669 2, 6 2,197 209,510 3, 163,5 5 241,010 3, 5 2, 256 247,035 3, 503,670 255,750 3, 641,865 298, 055 3, 974,972 1889- - --- 278, 680 3, 69 I 837 1890_-- -- 278, 300 3, 619, 972 297, 030 3, 653, 671 1892_-- 300, 900 34,, 722031,, 97353 315,670 315,626 4,437, 609 331, 05 4, 32, 497 I 14. 6 371,12 45. ,, 19049', 26263 394,296 370, 767 4 377 399 380,7 1 4:675: 410,674 4, 930,149 409, 124 4, 6 '6, 446,09 4, 949,366 431,397 5, 505,59 390,526 5, 321, 59 295,220 4, 049,731 11 000 I 1 ' 121, 44, 995 1 Estimated.
PRODUCTIO \ztec.- In nionagon . ounty. F ir t known a Aztec \llning Co. Reorga1_1iz d ugupt, 'l'1 R63; 20,0b00 1hare_t' ·00 000. In 1 71 mtne boug
og r., y w 10m 1 . ' Id to Doctor Hu.· e:v and a n w company organized in 1,000,000. All work discontinued . 1 '2 Reincorporated in 1909 a. outh Lake Mining lD 11,1, Co. Refined copper Year (pound ) Refined copper (pounds) 3, 3 1 1 70--- -- 10, 05 2, 321 3, 467 51, 139 6, 251 1 1 77 , 1 ' 493 6, 203 1 79 - --- - ' 700 32, 000 0, 000 2 - 25, 2 13, 153 11,550 13, 412 16, 252 27, 378 29, 934 23, 392 16, 737 5, 757 1, 734 3, 129 72, 000 : 175, 267 Baltlc.- In Houghton County. Exploratory work wa fir t done on the Baltic property in 1 2, when the lode 1\'a expo ed by test pit . Property wa pureha d from t. Mary' Canal Mineral Land o. in ,· ember 1 97, and Baltic ?\lining Co. organized December, 1 97; 100,000 hares, 2,.500,000. hsorbed hy Copper Range o. in 1917. Rock Lr at d (tons) ; 2, 400 199. - 35,411 '59, 114, 703 -190, 2 7 535, 624 1905 -- 604' 70!l 1906 6~9. 932 7 6 I 2, 764, 117 14, 260 7 1, 419 9 ' 795 1912 652, 433 I :m 333, 2 9 324, 433 37 '443 191 369, 2 7 191 - --- 325, 342 1919::: 293, 601 1920 ... -- -- -- 217355', 35372 195, 16 165, 04 1924·- 137, 01 150, 101 - 140, 95 Ro.fined copper (pounds) Total
Per ton 42, 766 1 603, 570 1, 735, 060 2, ·II , 432 6, 2 5, 19 10, 5 0, 9 7 I:., 177. 72. 14, :3 .J, ' 4 1-1. 397, 557 16, 70-1,, 1R 17, 72..J, 854 17, 17, 36 17 549, 762 15, 370,449 13, 373, 961 7, 736, 124 7, 001, 945 12, 02 '947 12, 425, 04 11, 214, 61 10, 406, 097 7, 64, 653 6, 613, 91 7, 60 ' 47 5, 329, 56 4, 77, 24 4, 769, 2 6 4 255 069 2:3. 7,' rganized May, Year R fined copper 1- (pou nds) 1 6' 1866
75, 000
399, 115 Belt (Boh e mian) .- I n Ontonagon ounty. The original company wa organized l\larch 27, 1 4 , and about that time II'Ork wa. begun. Location was early knoll'n Pi catauqua and wa old to Bohemian in 1, 53. Bohemian commenced mining operation late in 1 50 (probably on another tract) ; u pended in December, 1 51; r umed June, 1 52. R eorganized 1 62. I or ked until I 66, clo · d to 1, 70; re umed for short time after 1 70. Bohemian a nd Gr at We tern pa. ed into hand of Belt Minin" Co. by purcha e in 1 2 and worked until 1 ·w ork re urn d on mall cale in pring of 1 Company wound up it organization, and prop rty wa turned over to bondhold r , who foreclo ed mortgage and old. In 1900 a nell' organization was formed and property acquired by Arcti opper :\1ini ng Co. ption taken on Belt in 1901 and haft unwatered in J un of that .1·ear, but work wa u pended. Became Lake Copper o. in Xovember, 100,000 har , 2,500,000. Year 1 63 : . 1 65 - Estimnt d. Refined copper I (pounds) 12, 000 3, 903 0 33, 945 1 32, 563 22, 069 63, 502 69, 23 '630 65, 100 100, 45 7, 535 Boh e mian.- , 'ee Belt. Year Refined copper (pounds) ' 762 10, 653 17, 703 1, 4 5, 625 130, 51 7, 300 666, 031 Caledonia (Nebraska).- In Ontonagon ounLy. Organized March, 1 63; 20,000 hare , 500,000. Prop rty form rly ebra ka. b. orbed by Flint tee! opper o. in Year Relined copper Sil ,·er old (pounds) 54, 000 5, 500 17, 000 -- - 40, 400
1 64 .. - - 23,4 4 104,652 1 6 -- 26, 243 1 69 1 70 ... - -- ~50 1 71 3, 377 475, 747 Calumet & Hecla.- I o Houghton County. Calumet Mining Co. organized 1 65. Hecla Mining Co. organized 1 66. Portland Copper Co. and cott Copper Co. were purcha ed and on May 1, 1 71, were con olidated with the Calumet Mining o. and the H ecla M ining o. forming the Calumet & H cia 'lining o. Allouez, hmc k, nt nnial, alumet I H cia and reola w re eo n l i dated eptemb r 1, 1923, forming the alumct <J' H ecla on olidated opp r o. The land of the company include the following t ra ·t hmeek. Allou z. m gdaloid. aluroct. ent nnial. central. onglomerate. Dana. D lawar . ' agl Harbor. Eagle River. Florida. Frontenac. H cla. Iroquoi . Lac La Belle. Laurium. Madi on. Man ice I and . Manitou. Mendotn.. Montreal. orth Kear arge. Northwest . orth II'C tern. p ch sceoln.. Pawnee. Porljland. c tt. t. Loui. outh K ear arge. T amarack. T amarack Jr.
THE COPPER DEPOSIT OF MICHIGAN Production from all lodes [Docs not include copper roolairood from sands] r Refinod copper (pounds) Year o 187 --- - 1 0- - 18 2 1 5-
190 Rock treated (tons) Total 1 1, 116, 601 1 194, 770 23 ' 709 249, 5 3 259,971 I 249, 164 276, 123 2 4, 026 325, 074 334, 911 341, 905 396, 37 437, 76 567, 129 633, 5 5 605, 239 14, 213 52, 03 936, 465 1, 00 '249 1, 00 '4 1 1, 114, 133 1, 212, 335 1, 24 ' 051 1, 271, 334 1, 276, 66 1, 404, 506 1, 621, 416 1, 454, 694 1, 625, 634 1, 697, 010 1, 673, 221 1, 717, 645 1. 939, 5 2, 253, 672 2, 503, 111 1 2, 699, 919 1, 927, 00 2, 79.5, 514 2, 909, 972 2, 06, 610 2, 035, 625 2, 592, 462 3, 1 '5 3 3, 160, 274 3, 159, 570 2, 76, 392 1, 30, 760 1, 560, 240 261,320 620, 160 1, 073, 014 1, 463,245 2, 047, 661 01, 6 3, 174 1 ' 53, 736 20, 147, 040 21, 364,305 21, 577, 593 22, 574, 25 25,237, 642 26, 300, 0 31, 272, 119 31, 347, 670 32, 070, 6 9 34, 1, 264 40, 449, 763 50, 020, 77 51, 700, 536 43, 940, 351 53, 73 , 05 51 33 741 60, 495, 639 66,746, 0 4 1 71, 03, 47 77, 320, 30 7 559, 30 I 2, 620, 976 6, 704, 979 5, 039,276 9, 045, 6 0 9, 097,026 75, 65, 202 4,!l24, 642 4, 432 491 3, 224, 042 ' 6, 1 0, 541 7, 304, 6 9 92, 594, 167 1 6, 52 ' 009 1, 17 ,326 I 53, 252, 402 72, 059 545 74, 130, 977 67, 56, 429 45, 016, 921 53, 691, 562 71, 030, 51 71, 349, 591 6 1419, 26 5 ' 722, 969 43, 776, 194 43, 4 9, 643 9, 65, 400 29, 130, 500 45,672,600 54,510, 000 64,250,000 Per too 66:0 ·H. 09 74, 159, 490 3, 114, 389, 356 Fiscal years beginning Apr. 1[ 1873-1908; Apr. 1 to Dec. 31, 1909· calendar years 1910-1925 Includes production or consol dated mines beginning Sept. 1. ' · Remarks Min fire. Mine fire in July and ovcmbcr 1in fire Nov. 30. tatted exploratory work on 0 c ollt. onglom rate min fir Ma.v 27. 'topp d work on ' olA. Joel . \rork on 0 >'ecola rrsuntrrl in .Jut~·. ilver ·old, . 1 l,·H.i0.36. 'ilver sold, . 23 ,36 .06. ' ilver old, . 294,065.12. , ilver old, '140,323.5 .
PRODUCTIO nefined copper per ton of rock treated (pounds) Reclamation from old tailings (Calumet & Hecla conglomerate) Calumet & Hecla Osceola Year )'a1r I conglomamygdaloid ernte 55.24
4. 4 5. 6 --- 3. 0 90. 6
93. 6 --- ,
92. 4 - 1 1.6 72. 6 , 64. 6 66. 2 71. 2 69. 4
66. 2 6 .2 - 66. 6 Calumet lloela Osceola conglornamygdaloid crate 63.4 --- 54. 95 --- 52. 24 49. 75 49. 74 37. 75 - CA LU>J ET .i llECLA RECLAldATION PLANT Refined copper (pounds) 191 ' 1924 - - -, Rock treated (tons) 1 1, 732 545, 727 715: 007 915, 659 1, 37 ' 500 367, 000 1, 37 ' 250 1, 743, 100 1, 6 7, 700 2, 125, 000 ,-- 'l'otal 1, 5 2, 02 5, 412, 649 9 075, 457 9, 2-±5, 3 9, 0 2, 952 141 13 I 240 5, 301, 736 11, 362, 500 16 901, 200 1 1 627, 000 121, 007, 924 1 TAY ARACK RECLAMATION PLANT Per ton 7)-i months. Summary Refl ned copper (pound ) Period Rock treated (tons) 1 Total
Per ton , 1 65- 1925 57, 229, 052 a 2, 95 1 779, 077 I 2, 331, 524 67, 351, 569
2 12 I 050 14, 59 I 914 213, 17, 5 "" I 74, 159, 490 3, 242, 076, 2 o I lorludes L27, ,924 pounds reel imed from tailings. Carp Lake.- In ntonngon ounty. rgn.nizt:!d in 1 5 . ~lining begun in 1 59 a nd ·u 1 nd d in 1 62. R umed eptember 25, 1 97, and work d a f w months. ork r umcd for a hort period in umm r of 1 9 . In 1901 th pr p rty was owned by th Porcupine opp r o. ; 500,000 shar at 5. Yaar
Refined copper (pounds) 6, 42 2, 00 10, 546 13, 1 5 33, 935 . Ccntcnnlai.- In H ughton unt . ' hoolcraft organized In 1 63. Work common cd in mali way in 1 66. Worked ~thout profit 1 6 - 1 75 and :~.band ned. L a d about 1 73. mpnny went into bankruptcy and ~bout 1 7 ; 40,000 har · at 25. In 1 1l;,new company on ceola amygdaloid. Work usp nd d in t of 1 3 ~ccau c of lack of funds. R sumcd D ecember, . 1 · Very little work don to 1 97. R rgauiz d a ent u- ~18 1 Copper Mining o. in 1 96. bsorb d by alum t & ec 11 Consolidated opper o. Septemb r 1, 1923. Refined copper (pounds) Year Rock treated (tons) Total Per ton '290 -- / 426,366 743, 22 1 72_ - - - -- 3 4, 242 - 309, 7 5 -- -- - --- 10,61 3, 554 531; 9 3 01 - - 1 9 L - 1 92 one. - - -- 127, 202 71,403 722, 4 6 1, 012, 314 921, 070 76, 4 0 641, 294 1,446, 54 2, 253, 015 2, 373, 572 2, 196, 377 2, 5 3, 793 1, 572, 566 1, 493, 34 1 9 --- 56, 032 77, 903 64, 9 2 5, 939 b 69, 453 90 166j 000 190 - 169, 693 No production !lfter January. July 4 to Doc. 31. Includes 9,043 tons from stock pile.
THE COPPER DEPOSITS OF MICHIG Reflood copper (pounds) Rock treated (tons) / , Year Total Per ton 5, 443 1914 - --- - -- 14 '332 191 - - 159,040 6 1920 41,41 1, 742, 33 1, 612, 262 z, 2 1, 5130o0 I 2, 347, 2 367, 400 2 002, 57 z' 492 1 365: 14 37, 675, 633 1 ' January to July. The figures given above for 1 69- 1 74 and 1 2 repre ent production from the Calumet & Hecla conglomerate; the estimated quantity derived from the conglomerate in 1 97 (1,2 5 tons) was 35,440 pounds (27.5 pounds per ton) and in 1 9 (5,000 tons) 3,750 pound (16.75 pound · per ton), making a total from the conglomerate of 2,0 5,273 pound . The production from the 0 ceola lode was a follows: Reflood copper (pounds) Year Rock treated (tons) 2, 531 a 3 a 51,032 n, 903 1 a 21, 400 Total Per lou a 27. 5 a 15. 43 ! 1 Estimated. The figures given in the first table above for 1901- 1920 rep- . resent production from the Kear arge lode; the e tima.ted output from this lode in 1900 (43,5 2 tons of rock treated) was 696,314 pounds or 15.93 pou nds per ton, making the total output from the Kearsarge lode (2,261, 90 tons treated) 33,033,675 pounds, or 14.60 pounds per ton. Cen traL- I n Keweenaw County. Organized November 15 During 1 55 net earning 7,000; fir t mine in M ichiga~ di ·tri t to produce and ell during its fir t year enough copper to more than pay expense for the year. Cost to stockholders for entral $100,000. tarted stamping in March 1 65 · closed J uly, 1 9 . old to Frontenac Copper Co. i 1905? and !at r ab orbed by Calumet & Hecla Mining Co. Year Rock treated (tons) 1 5 Roflued copper (pounds) 'ilver sold Per ton 3, 36 --- 64, 903 143, 011 241, 622 114, 197 4 4, 764 619, 26 901, 292 Includes tons st~wpod plus hea':'y copper. Smelter production 1 55-1 6; mtne production 1 7- 1 g . Refined coppor (pounds) Ycnr Rock treated (tons) 'l'otnl Per too C 1, J3J, 99 20, 141 d 1, 393, 036 17,526 1, 244,441 15, 1, 00, 943 07, 01 1, 327, 156 1,432,662 19,353 1 246,061 16, 537 1, 503, 117 16, 456 1, 740, 603 17, 66 1, 466, 952 13, 6 1 2, 161, 400 ) 51 1 7 ) 1 995, 609 15, 030 1, 91, 013 13,452 1,799,495 15,535 21, 259 1: -11 ; 465 1 353 5 7 1 26 I 556 ) I 446: 74 7 2, 157 40 21, 106 2, 512, 21, 737 1 92~279 1, 17, 023 21: 527 1, 270, 592 23, 536 1, 413, 391 24, 316 1, 313, 197 21, 931 1, 625, 9 2 22, 750 1, 1 0 040 15,710 549, 71 379, 020
I " I 1:h 9 2 59 60 52 35 ilv~rsotd - 1, 22i."06 J' l '4i 1, 142. 1 l, 109.62 I, 126.02 l, 023. li 390. !)() 469,243 1 51, 75, 527 r - :-- ' loclu lcs 32,756 pounds of iogOL lost in lake. 4 Includes 60,000 pounds of ingoL (esti mated) lost in lake. Estimate. Champlon.- In Houghton ounty. Organized December, 1 99. One-half of capital toek owned b,v opp r Range Co. and other half by t. Mary' ifineral Land nder Copper Range Co. management. Refined copper (pounds) Year Rock treated (tons) --- 190 - - --- - ../ 121,47 3 9, 0 2 442, 061 604, 4 3 671, 7 5 794, 703 753, 90 722, 051 734,392 765, 306 421, 49 614, 54 923, 743 936, 656 776,036 594, 235 503, 030 321, 664 531, 7 0 503, 593 449, 130 457, 160 414, 645 14, 156, 309 Total Per too 4, 165, 7 -1 10, 564, 147 12, 212, 954 1s, -o7, 4 26 2s. o. 16, 954, 9 61 25.21 16, 4 9, 436 17, 7 6, 7 63 1 I 005, 071 ° 19,224, 174 15, 639, 426 17, 225, 50 12,0 0, 594 15, 807, 206 25. 7! 33, 407, 599 33, 601, 136 27, 550, 343 I 211 74 I 514 19, 6, 917 13, 610, 324 20 719, 307 3 ' 9 11; 957: 6os 1 438,403,2 6
PRODUCTIO Clark.- In Keweenaw ounty. Mine wa opened in 1 5 F ch Copper itntng o. and pas ed through variou
d · I 1 1900 after 15 year of tdlene s, work wa re ume . hand · ' & H 1 M" · · d Option to alum t ee a mmg o. In o anc wss un er to G . . melting, Refining & M11111·Ig o. 111 1910. d n u~stue- ~ful attempt was al o made to mnte a mangane e epo 1 on thi property. Year Refined copper (pounds) Year Hefined copper (POU11ds) 17,749 1 7 21,520 7, 244 67, 475 3 ' 774 1 7, 915 34, 13 cutr.- In Keweenaw ounty. Pittsburgh & Bo ton opper Harbor Wning o. organized in 1 44. Pitt burgh & Bo ton ~lining Co. organized J\lareh 1 , 1 4 , and worked the !iff 6 ·nre to its clo ing in June, 1 70. Paid it first dividend in 1 19. Fir t dividend-paying property in di trict. Paid regular miannual dividend 1 50 to 1 57. The property wa sold to Cliff Copper Co. in 1 71, and operation were re umed in April, 1 72. Affair of Pittsburgh & Bo ton 1ining o. wound up and corporation eli olved in 1 79. Property later old to Tamarack Mining Co. liff 1ining Co. organized in 1910. Year Rock treated (tons) Ooncts 14, 276 20: 730 16, 329 13, 730 11, 336
Refined copper (pounds) 19, 91 37, 609 410, 771 996,464 1, 2 2, 131 714, 650 46,474 29, 360 1, 071, 2 1,315,30 1, 74, 197 2, 220, 934 b 2, 435, 2, 260,433 1, 415 007 l, 43, 393 1, 92 ' 011 2, 004,960 2, 100, 354 1 351, 334 1, 494, 626 1, 642, 42 1, 121, 725 1, 227, 746 711, "61 444, 3 1 141, 23 c 401, 606 c 1, 009, 21 0 1, 3 9, 190 0 751, 552 ) 61, 319 c 206, 000 134,336 7 ,962 79, 3 2 66, 053 10,374 2 ' 255 '332 22,342 3 ' 206, 906 'Include8 71 ' Rsthnat00.'630 pounds [rom accumulated slags. Silver sold 41 5,040. 4 6, 751. 07 2,405.17 1, 196. 37 7, 265. 26 2, 921. 69 1, 771. 19 2, 127. 55 5, 270. 17 4, 033. 0 3, 327. 6 2, 33 . 00 1, 032. 43 1, 396. 46 Concord.- I n Houghton County. Organized May, 1 64. In 1 6 Concord and P ewabic consolidated. oncord et off as separate organizution in 1 79. Ab ·orbed by Arcadian in 1 9 . Year Refined cop]X'r (pounds) Yoar Refined copper (pounds) 22, 51 900, 146 10, 464 2 ' 49 1, 595, 003 Con.,.lomerate.- ee Delaware; Pennsylvania. Connecticut.- In Keweenaw County. Operated on a fis ure we ·t of D elaware. Ab orbed by Amygdaloid o. Produced prior to 1 60 116, 00 pounds of refined copper, including 29,000 pound in the year ending eptember 1, 1 56, and 37,000 pound in the year ending eptember 1, 1 57. Copper Fall .- I n Keweenaw County. Copper Fall Co. organized October 16, 1 45. In 1 4 reorganized a Copper Falls Mining Co. In 1 55 a reorganization with capital toek increa eel to 500,000 divided into 20,000 hare . I n 1 61 the company set off and organized the Petherick. In 1 76 a reorganization with capital tock increa eel to 1,000 000 divided into 20,000 share . tamp mill burned iu 1 7 . 'i orked Ashbed and five fi ures. AU operation u pended in 1 93. Year 1 6 ALL LODE Refined copper (pound) 44, 00 22, 400 22, 400 4, 4 0 None. 12, 651 91, 737 144, 269 200,000 20 ' 010 307, 305 444, 661 576, 7 510, 1 560, 011 45 ,299 319, 34 35 ' 0 470, 000 1 1, 137, 169 1,594, 604 479,3 4 691,400 Year Hefined copper (pounds) 520, 62 1, 2 6, 540 1, 070, 359 407, 5 7 17,4 11, 790 one. 6, 615 669, 121 5 7, 500 04, 000 91, 16 1, 150, 53 1, 37 '679 736, 477 1, 199, 950 69, 136 1, 330, 000 1, 427, 000 1, 1 1, 975 70, 005 26, 339, 955 772, 990 II 47 ' b 50,000 6, 615 649, 121 5 6, 000 04, 000 91, 16 1, 150, 53 1, 37 '679 1 7 736, 4 77 -- 1, 199,950 69, 136 1 90 1, 330, 000 1, 427,000 1, 1 1, 97 5 : 1 93_ --- 70,005 17, 706, 352 Estimatod. & Assumed.
THE COPPER DEPO ITS OF MICHIGAr FISSURES Refined copper (pounds) Yenr \Old Copper! Child Owl reek Copper :Falls Hill Falls
;. -l-L~2oo - 1 Sw - -- ° 45, 69 i 2-ooo- 11: 134 11, 135
1956---1- - -- -- -- 1Q4, OQQ 153' 650 1 ·-7 1o3 6oo 1 ,
': --T 210' 230 5, 620 -.- --ooo 6, 720 i --- ;7-277 25 9, 694 1 60 --- 15:000 0 116,000 -- --- 761,000 1 67_ -- 1, 356, 000 399, 3 4 b591,400 b 672, 990 b 37 I b 420, 62 b 1, 1 6, 540 b 970,359 b 357,5 1 --- -- b 17,4 1 77 - -- b 11,950 --- -- -- b 11,790 --- -- - -- --- 0 20, OQQ -- -- --- - -- - 1, 500 - -- -- 7, 2 3, 010 731, 212 500, 7 1 86, 400 32, 094 Estimated . SUMMARY Lode Child fissure - --- Bill fissure Old Assumed. Period Refined copper (pounds) 32, 094 731, 212 500, 6,400 7, 2 3, 010 1 ! 1 5 - 1893 8, 633, 603 17, 706, 352 26, 339, 955 Delaware (see also Penn ylvanla).- I n Keweenaw County. In 1 47 orthwest Copper Mining As ociation formed. In 1 49 reorganized a orthwe t Mining Co. with increased capital stock. About 1 50-1 60, 939,000 expended, exhausting capital. Reorganized in 1 61 as Penn ylvania Mining Co. In June, 1 63, estate divided and Delaware Mining Co. organized. Idle 1 65- 1 72. I n 186 67 property in hands of bondholders for two years, when bonds were 'chased by E. Davis, of Philadelphia, who perfected a fourth organization in J 7 the Delaware opper Mining Co. In January, 1 1, onglomerate .1ining Co. took po session; articles of as ociation dated January 5, 1 0; 50,000 shares of 25 each; included rortbwe t, Delaware, Pennsylvania, Maryland, and Wyoming propertie. . In 1 property reorganized a Lac La Belle Mining Co. but no effort made to re ume operation . On ida Copper o. incorporated in ovember, 1 99, and did some exploratory work. Operation were on fis ures, Allouez conglomerate, and various amygdaloids. Later acquired by Calumet & Hecla Mining Co. Hcfinod COiliJCr (pounlJ) Year Hock trent (t ns) 'Po tal 1 72 !L :33, 4 L 7 1 7 - - -- 2 '0, 34 5 J.!O, 012 233, l.J 3 6, 091 ' 734, 249 1 3 20, 2915 tl 222, 11 7 120, 6 d 1, 140, 173 - dH , 155 ' H , 505 '', 913 4, 154, 0 For production prior to organizution or Dolawure Pennsylvania. .Min rnl tetistics, 1 2, gives 310,743 pound . 'One-baH from Allouez conglomerate; one- from fi. ·ure; 41,104 tons s1ampol yi !dod 671, 1 pound refined copper. From Allouez conglomerate. From Korthwest vein; no work on conglom rate, J Derby.--In Ontonagon ouniy. 20,000 hare of 5 each. Work wa begun in 1 52 and continued for thre yruw. In 53 produc d 2,934 pound · of r fin d copper. Dougla .--In Houghton ounty. Organized January, 63, and worked uniil 1 6 . , unk four haft ·, probably on Arcadian amygdaloid. Lat er acqui red b~- rcadian. Year Refined copper (pounds) 27, 240? 6, 09 16, 209 65, 77 Yenr oopper (pounds) 50, 109 3, 25 169, 50'! Douglass Hou hton.--In ntonagon County. peration· commenced on mall cal in 1 46, but work not vigorous!) pu bed until 1 50. old out in February 1 64, to He!1woo_d Mines Corporation which recommenced mining operatiOns 111
3 'lay, 1 65. To the end of 1 56 the mine had produced 14 1 pounds of refined copper. Eagle Rlver.--In Keweenaw ouniy. rganized February, 1 53; 20,000 hares, 500,000. Did con idera.L>Ie work 011 Babbitt vein . In 1 55 mall tamp mill pui up. Year 1 5 - Refined copper (pou nds) 1, 500 2, 611 2, 000 6, 637 12, 000 Year Refined coppei (pounds) 5:652 n ,3 9 L 9,67 . d pEvergreen Bluff.--In Ontonagon ounty. Organize d ·n tember, 1 53; 20,000 hare of 25 each . Mining suspende
fall of 1857; resumed Juu , 1 5 until 1 63. In March, 1 ' new directors, continued to 1 7o; after 1 78 little work on tribute.
PRODUCTION -Year Refined copper (pounds) Year 1 Refined copper (peuods) 2, 599 14, 007 25, 110 46,942 6, 665 3 ' 11 63,817 99, 187 119, 257 141, 446 413, 765 I b 2 1, 142 c 413, 100 c 435, 700 322, 609 I 147,662 oJsn. l, 1864, to May 1, 1865, estimated. May 1 to Doc. 3I, 1865, estimated. 'Eslim.ted. 111, 420 45, 048 71, 73 30, 405 10, 651 6, 736 1, 006 1, 077 26, 21, 5 0 15, 304 2, 915, 730 Flint Steel Rlver.- In Ontonagon County. Organized April, 1 53, but property had been worked in 1 50. uspended rork in summer of 1 5 , and from that time until middle of July, ! 63, nothlng was done on the property, except some mall eiplorations made in 1 60 and 1 61. Worked Caledonia al O· Csledonia formerly known as ebraska; changed to Caledonia in I 63. Consolidated in 1 71 a Flint tcel Copper Co. In I i3 mines shut down and lea ed for eight year . Refined copper (peuods) Year Refined copper (peunds) 8, 651 4, 000 2, 106 29, 657 216, 959 0 110, 054 30, 92,500 45, 74 76, 69 i · ~des the product of 40,506 peunds or mineral !rom 1 Forest. ee Victoria. 4 ' 772 33, 054 30, 115 26, 067 3 ' 356 43, 192 2 ,0 0 4, 140 69, 164 Franklln.- In Houghton County. Organiz d April, 1 57. Clmmenced work in July, 1 57, on P wabic am gdaloid. tamp mill completed in 1 61. Leased 1 7 Franklin Cl. resumed work in July, 1 74. In 1 94 purchas d Franklin 1r. mine. In 190 Franklin mine old to Quincy. In 1909 ~ouez conglomerate abandoned. I n eptembcr 1915 Frankon ~ade profits for fir t time in 20 car . p ration di - conhn d · K ue In May,. 1919. n exploratory haft begun on . earsarge amygdaloid at Franklin Jr. in 1923 and discontinued ;:ring of 1926. Franklin Jr. mine once known a Albany ' on, and next as Peninsula. Rock treat d (tons)
42, 434 40,474 36, 610 2 ' 134 40, 136 57., 196 51, 356 43, 02 67, 154 50,92 I Refined copper (pounds) 'l'ota I Per ton 6, 699 113, 211 234, 211 315, 60 1, 566, 043 1,466, 645 1, 27 , 6 4 1, 211, 335 1, 559, 4 1 1, 63 '994 1,402, 455 1, 467, 476 1, 559, 940 1, 178, 178 ilvcr sold
$610. 71
1, 065. 12
Refloed copper (pounds) Year Rock treated (tons) 1873 I 96,35 112, 590 113, 32 1 82- - - - - - 11 ' 370 1 83 125, 775 12 '878 137, 276 13,385 137, 137 18 9- 141, 579 144,393 135, 57 123,236 124, 90 13 ' 163 126,990 122,079 132,026 116,696 7 9 26 '571 ilv r sold Total I Per too 673, 678 1 --- --- 417, 59 366, 000 1' 567,790 1, 167, 633 1, 926, 641
2, 339, 17 - -- - -- - 2, 599, 073 2, 29, 703 2, 336, 466 '- - -- - - 2, 67 ' 797 --- 3, 264, 120 I 27. 7 o. 04 3, 4 9, 3o 3, 74 ,652 2,399.83 3, 999, 172 29. 2 I 1, 511. 1 4,264,297 2, 001.20 3, 915, 3 I 2 . 55 4, 046. 59 3,655,751 2, 727.2 4 346, 062 3, 143. 10 5,63 ' 112 3,700.34 4, 319, 840 2, 371. 34 3, 769, 605 1, 592. 55 3, 504, 244 3, 556, 4 7 25. 81 --- -- 3, 0 6, 933 24. 31 2, 746, 076 22. 49 2, 623, 702 - 2, 90 ' 3 4 1 22. 03 - - - -- - - - - - 1, 230, 000 13. 70 - --- - 3, 663, 710 13. 64 -- - -- - 313,552 315, 6 7 3, 757, 419 b 5, 259, 140 c 5, 309, 030 3 9, 470 374, 130 372,378 3 3,290 190 -- - -- - 342, 596 170,546 113, 59 6, 300 176, 462 123, 179 7, 324 122,01 267,2 6 303,625 191 --- -- - 273, 964 109,565 4,771, 050 4, 206, 0 5 1 11. 25 -- -- 4, 571, 570 12. 28 4,401,248 11. 48 3,703, 421 10. 82 966, 353 . 49 1 710, 651 9. 0 -- 1, 021, 440 . 30 - - - 93, 2 3 1, 314, 969 10. 0 3, 116, 566 3, 155, 574 I 1, 062 9. 70 - -- 192()-1925_ -- - --- - -- --- 154, 316, 451 Includes 1, peuods from sands . lucludos 21, pounds !rom sands. ' locludes 3, 79 peuods from sands. Fulton.- In Keweenaw County. Fulton Mining Co. began work in 1 53, on Forsyth mine. In 1 53 produced 1,255 pounds of refined copper. Total production probably larger, but no definite data available. Garden City.- In I eweena.w County. Organized October 24, 1 55; 20,000 shares, 500,000. Two shaft unk in Ashbed in 1 56, and large tamp mill built. Work ceased 1 5 , resumed 1 59. o work done since 1 66. In 1 79 reorganized a aton Mining Co. but no work done on property. roar Rotloed copper Year Refined copper (pounds) (pounds) y 4,000 11,397 14, 000 36,000 75,397 10,000
THE COPPER DEPOSITS OF MICHIGA Grand Portage.- In Houghton ounty. Portage Mining Co. organized 1 52. Reorganized in i\Ia.r, 1 60, a· Grand Portage tlfining o. nnd ·orne work done. ol~ in 1 79 and organized anew in 1 0; capital 500,000. OperatiOn in 1 In 1 97 sold to Isle Royale Con. olidated iVhmng o. Year
Refined copper (pounds) 403, 321 4 9, 104 4 3, 592 159, 2 2 Year 1 3 72, 314 34, 124 35, 423 Hoflned copper (pounds) 26, 264 757, 0 0 I 735, 59 255, 60 3, 529, 22 Mineral Stati ties, 1 , gives product for the year (all tribute work) a ,326 pounds refined copper. Year ltO!'k tr utcd (tons) 1 73-- - - 1 75.-- - 1 79 --- - - - 0. ] --- 1911 - - - - b 4 1' ':199 1913 12,612 203, 112 l!oflncd copp~r (i><JUnd! 'l'otnl 9, 132 61, 365 2 ' 229 7, 294 3, 032 571, 97 540, 575 4 4, 906 562, 636 203, 037 150, 000 754, 74.9 I 212, 0 9 4 ,67 Per 1oa Hock treated, 18,959 tons; yield, 39.03 pound per ton. 302, 725 71, 124 2, 21, 934 4, 005, 3, 041,514 13. 2? 13.41) Gratlot.- In Keweenaw ounty. rganized Februar_,., Lately operated by. n ca. In 1923 22,051 tons hoist d to tock pile. Year 1920·- - - - Rock treated (tons) 2 ' 522 1, 347 b 446 30, 315 Refined copper (pounds) Total 265, 69 14, 275 33, 704 313, 4 Per ton 13,158 tons hoisted, 35 per cent of which was placed on stock oile. Mill test (taken !rom stock pile). Great Western.- ee Belt. Hancock (Sumner).- In Houghton County. Organized in April, 1 59, as Hancock :\lining Co. Company continued work until capital wa exhau ted and then lea ed the mine on tribute until 1 72, when it wa sold; in 1 73 name changed to umner .\1inin r Co., but little work wa. done; in \\'inter of l 79 or 1 0 it wa old and Hancock Copper :\fining o. organized; 40,000 hare of 25 each. Work tarted July, 0, and di continued in urnmer of 1 5. Hancock ousolidated !fining Co. organized June, 1906. Idle in 1922- 1925. ( umner organized ovember, 1 67.) year Rook treated 186! -1,
--- April to December. Refined copper (pounds) Total 9 ' 662 111,432 103, 22 61,044 75,000 596, 717 854, 000 160, 000 76,000 107, 731 59, 710 54, 366 Per tou 191 227, 04.9 17, 559, 557 ' Operations suspend d from Jul)' 13, 1913, to Jun. 2, 101 t Hilton (Ohio).- In ntonagon ounty. Fir t mining opcrati n on thi prop rty in 1 50. Location abandoned from 1 53 until l\Iay, 1, 63, wh n Hilton !\lining Co. wa organized. unk a f w trial haft . f ,,. tributer ,,. rked ,inre I 65. Year ,, H fined copper (pounds) J 11, 179 6, 411 5, 757 3, 345 3, 555 6, 07 Year Houghton.- . ee Huron. Jlough.ton Copper.- I n Houghton rated January, 1910. Year Rock treated (tons) 14,657 1916. - - 19,444 15,62 49, 729 llofine<l OOJ!JIOI (pounds) 2 oro 10: 342 19, 135 li. 1.\.i 14,631 123, i2l ount.v. IncorpoHeft ned COJJper (J)Olilldsl To till i'tr!oD 156, 766 204, 274 10 . .\.i 179, 012 !1.45 None. - 5.JO, 052 Huron.- I n Houghton ounty. Organized Dercmbcr. I 53 Huron mine opened in 1 55 on I le Royale lode. nlled Ags· wam from 1 6 to 1 71, when name was changed to Houghton_I n 18 0 reorganized as Huron opper ining Co. In 1 9' included in I le Royale onsolidated Mining o.
PRODUCTION Rock treated (tons) Rellned copper (pou nds) Silver sold Total Per ton I 55 1 10, ooo gob 162 ' 139, 305 --- - 163 a 13 1 206 164 101, 745 165 476,011 - - 167 --- --- 1, 367, 169 --- --- -- - - 1 1, 4 0, 0 0 --- -- -- 1, 6 2, 63 --- 4, 1 3 --- 553, 6 9 - --- 475, 3 - 251,005 - -- - - 1 75 --- 63, 2 9 - - - - - -- 63, 57 - - 1 ii - - - 2 161 29,760 1 70, 2 5 -- 254, 515 - --- 364, 037 --- 1 720, 213 -- 66, 313 1, 927, 660 95, 476 2, 25 , 90, 130 1, 992, 695 1, 4 4, 103 2, 375, 147 - - 112, 723 2, 219, 473 101,3 4 1, 736, 777 17.2 - 1 257 059 562,776 From Feb. I to Oct. 31, ,34b pounds of refined COJ>per prodm-ed. 1 \nnual report dated I says, '"l'he year 1866 Is o!nJtted bocaus an accurate ent of amount mined ct\n not be obtained from any record in possession of lt!ienleompany." lndlann.- In Ontonag n Indiana opp r o. organized in I 62 and work d st adil v for three year,;, then stopped; r com mon ·eel in jul ' , tamp mill , ld to Petherick o. Indiana Minin<r o. organiz d in 1909. No rock milled. "' I land.- n Isle Royal. rgani z d 1 74 a I land :\lining CAl.; 40,000 hare of 25 ach. Operated years. Stamp mill huilt in 1 75 and burn d in 1 76. L a. don tribute. Year
'BYL!Iand 'rrlbute Co. Refined copper (pounds) 67 a 76, 03 213, 2'15 Isle Royale.- In Tl oughton ounh. Old I lc Rovalc mine opened ·
111 May, 1 52. The work on thi · property the fir, t mm ng done in tho Portage Lake di trict. ompany stopped ' work in 1857, and the mine wa lea ed on tribute to 1abb Brothers. In 1 62 purchased what was known a. the Web ter Miniug o. prop rty. Company worked again 1 63- 1 70, leasing the mine once more to lVIabbs Brother , who worked it for some years. Isle Royale opper Co. incorporated 1 99 and in April of that year took ov r I le Royale Con olidated Mining Co., organized in 1 97, and Iiner ' Copper o., organized in 1 9 . Present I le Royale includes old I lc Royale, Grand Portage, Huron, which compri ed original I lc Royale con olidation in 1 97, and a! o Frue and Dorlge, which were taken into Miner con olidation in 1 9 . Year ReOned copper (pounds) Year -, Reflood copper (pounds) ,-- 1 53 -- 1 , 73 1 1, 217 a 97,262 250, 164 1 6, 000 240, 100 b 323,510 1 0, 76 1 5 96,6 2 31,9 5 336, 19 1 7 31, 933 c 96, 139 1 79 26, c 26,770 77,469 5 , 130 47, 30 1 65d - 5 2, 3 6 35,447 16, 74 532,793 I 1 ao, 164 762, 52 295, 033 ' 1 1 -g-4 150, 672 Estimated. Includes 11,125 pounds or relined copper estimated in mineral lost in lake. ' Smel tar productian. "14,000tonsstampod rrom ~1abbs vein, yielding about 2.6 per cent. Year Rock treated (tons)
1901 --- -- 1 5, 175 1902 --- 263, 672 1903 199, 493 1904 -- 154, 30 195, FO 192, 210 1907--- - -- 175,450 190 401,2 0 520, 1911 - 457, HO 531, 105 1913 314, 679 474,349 6 0, 270 925, 419 922, 160 191 - 974, 50 724,667 591, 971 116,576 1922 30 '940 315,507 1925- 37 ' 459 J ,523 ounces. Relined copper (pounds) iJver sold Total Per ton ' 1 194 '-- - - 2, 171,955
3, 569, 74 3, 134, 601
2, 442, 905 15. , 2, 973, 7 1
2, 937, 09 -- 2, 66 7. 60 3,011,664
5, 719, 056 12, 073. I 7, 567, 399 23, 215. 99 7,490,120 20,336.55 1 6, 957 3 126. 16 4, 15 , M 14, 7 . 01 6 601 235 17, 477. 9 9: 342: 106 3 ' 973. 56 12, 412, 111 53, 0 6. 76 13, 4 0, 921 4, 962. 44 15, 442, 50 0, 743. 43 13,007, 647 94, 144. 01 10,621, 01 75,075.53 2, 491,000 21. 37 6, 639,970 26. 92 --- -- - ' 002, 244 25. 90 --- , 1 03, 000 I 25. 6 9, 543, 000 25. 22 0, 537, 157 1
THE COPPER DEPOSITS OF :MICHIGAN t Organized as Kear arge Kearsarge.- In Houghton oun y. Ab bed by 0 ceola Mining Co.; 50,000 shares of $25 each. sor Consolidated Mining Co. in December, 1897. Year Refined copper (pounds) Rock treated ,-:::--:-:-1 Sil ver sold (tons) 1 Per ton 24, 250 56, 104 60, 619 I 1,424 60,9 6 64, 2 7 I 64, 000 34,5 7 1 829 1 5 1 33. 95 1 59 ' 525 1' 727 1 390 1 21. 21 1' 99 ' 710 1 31. 09 -$466.-77 1:377:226 I 39. 2 - 14, 512, 07 3 -- -- I Keweenaw Copper.- In Keweenaw County. Organized March 13, 1905. Work was started in su mmer of .1905 by diamond drilling on Medora and Mandan properties. I ncludes Aetna, Empire, Girard, Hanover, Copper Harbor, ' as hington, I. eweenaw, Mandan, Medora, Vulcan, Resolut , Boston and P hoenix (Penn?). Resolute was old to Keweenaw C~pper Co. late in 1905 or early in 1906. 7,500 tons of stamp rock on tock pile in 1906. Year 1 Refined e<>pper (pounds)
179, 565
K ing Phllip.- See Winona. Knowlton.- I n Ontonagon County. Organized August 6, Mine opened in 1 62; di continued on company account 1 66-1 67 then worked on tribute. Ab orbed by Adventme Consolidated Copper Co. 0 . A hley says (Copper mi nes of Lake uperior, 1 73): " 1,0 6,000 pounds ingot copper taken out from 1 63 to 1 69." Yoar 1862 1 6 -- - 1 69 - -- - - Refined copper (pounds) Year Refined copper (pounds) 5, 975 5, 451 8, 629 122, 77 21, 36 196, 724 ?.1, 976 1 , 06 106, 977 38, 70 23, 145 7, 120 6, 215 ! 6, 562 1 992, 757 Lac La Belle.- In Keweenaw County. Prior to 1 50 the Lac La Belle Co. had driven a tunnel into the hiU 400 feet and found a vein 1 inches wide. No further work was done until 1 66. The following statement is taken from Eng. and Min. Jour., October 1 , 1 90, p. 448: "Mendota Mining Co. commenced operations in 1866 on property formerly worked by the Lac La Belle Mining Co., sees. 29 and 32, T. 5 , R. 29, Keweenaw County. Three hundred feet of sinking and 700 feet of drifting were done and operations were suspended. Later the land of the company were sold for taxes. Company owned 4,320 acres surrounding Lac La Belle. In fall of 1 66 t his company completed a canal from Lac La Belle to Bete Gri at co t of $100,000, receiving from the Government in consideration therefor 100,000 acres of land in Fichoolcrnft County, Mich. About the time of the completion of thi canal mining operations in the vicinity of Lac k Belle were su pended, and the canal was allowed to U! up." The production wns 3,499 pound of r fi ned copper prior 1o 1 .. Lake.- In Ontonagon ounty.. Organized in No 11!m~r, 19o5. Property formerly Belt . F 1rst work on Rnowltoo lode. Shut down from July 1, 1913, to April, 1915. Work Slllpcnded January 31, 1919. Year 1909 ·- 1913 · - Hock (tons) 10, 125 14,4 5 I b 3 109 19: 211 1 59, 4 70, 440 63, 191 Fiscal year Ar ril, 1909, to A pril, 1910. t2 141 ton from stock p1le. ' l\f ay 1 to July 1. . N ine month Apr. 30, 1916. Refined copper (Pund!) - 1'otnl Jer loa 170, 01 31 , 050 1, 300, 562 2 7, 200 1, 5 1, 071 1, 4 9, 247 1, 46 1, 93 one. 7, 32G, 227 15. &I Lake Superior.- I n ntonagon ounty. Lake 'uperior Copper Co. organized in 1 59 by M ine ta Co. to vork a portion of it e tate. Worked by tributer from time time after 1 74. Year R efi ned copper (pounds) 2, 432 1, 951 2, 01 5, 22 Year Refined '( (powds) 2, 106 1, OS6 Lake uperlor Copper.- I n K ewe naw County. P hoenix. D be La Salle.- I n Houghton ounty . Organized ecem r, Includes Caldwell and other la nd . Pu rchas~ Tecum eh in May 1910. Mined on Kear arge am gdalold and drove cro cut from Osceola amygdaloid to Allou?z con lorn· erate. All production is from Kear arge amygdaloid. R efined copper (pounds) Rock treated / Year (tons) T otal I r er ton I ilver JOid
1 , 970 2, 221 45, 509 0, 959 144, 29 1 5,014 191 176, 423 32,995 3, 430 633, 77 one. 43, 906 540, 731 7 2,493 1, 3 0, 352 1, 919, 775 1, 32, 665 340, 719 59, 71 3 one. 7, 14, 730 . 12. 6 14. 79 10. 57 1 t Summit Madison (Sum )lJit) .- In K eweenaw Coun Y· t " d uotil 1 56. organized 1852-53. Mining work con mue. . August, 1859, reorganized as Madison Mlm ng shares of $25 each. Work resumed in 1863. Some herif!'s to 1 76, when company bega n again. ; 9, and sale in 187 but redeemed by compa ny 1n Septcmbe ' ed in h Work resum reorganized with 40,000 shares of $25 eac · gh' by 1880 and continued until May, 1882. Property JOU Central about 1885.
PRODUC'.riON Year I Relined copper (pounds) 4,000 16,000 14,8 1 34,000 Year Refined copper (pounds) 1, 676 1, 534 72, 091 Manhattan (Old Albion).- In Keweenaw County. Albion commenced operations in 1 4 ; suspended 1 57- 1 62; resumed operations as Manhattan Mining Co. in January, 1 63; 20,000 hare· of $25 each . Abandoned in 1 65. 5 tons of copper taken out in inking haft (about 1 63). ~Ia s.- In Ontonagon ounty. Mass Mining o. organited in 1ay, 1 56, worked until 1 60, idle 1 60-1 64, when work was begun on Evergreen lode; totally suspended again in 1 6 . A little work on tribute. Company resumed in 1 74 and continued to 1 4, when property was leased to Mass Tribute Co., which worked it until 1 , when operations ceased. Mass Consolidated Mining Co. organized February, 1 99; made up of Ridge, Ma s, Ogima, Merrimac, and Hazard mines; capital 2,500,000. Ridge began 1 50. Ogima opened 1 60; closed 1 6 . Merrimac organized in 1 63. Hazard did little work on orth Range , or Mine ota Belt. A few old test pits and shafts. Purch ed Evergreen Bluff Mining Co. in 19ll (?). Year Refined copper (pounds) Rock treated !-: (tons) Silver sold Totnl Per ton ·1 - 16,22
1 12,000 --- 52,6 2 12,936 10, 112 1 1 '939 --- 3, 213 ! :: , 265 : 74 11' 925 --- --- 10i: ni 1 4 412, 339 18( 7, 779 517, 159 - 1 7, 761 467, 6 4 1 3 15,472 737, 440 1 4 - --
1 16,000 --- 70,944 5 '349 1 - 1 91 .. 62, 187 - 30, 114 --- --- 17,450 19 41,805 ,' 18,372 53, 507
:190090991 : 122, 239 73,297 152,562 2, 345, 05
122,611 2,576,447 $1,303. 9 105,614 2,1 2, 931 20. 67 1906 -- -- 143' 430 2, 007' 950 1 5, 7 9 2, 106,739 11.34 es, mated (rom nnnual report. Year Rock treated (tons) v / 1907 --- 204, 599 171, 268 139,404 90,747 73,475 132, 91 1913- -- - 7 ' 250 1914_ --- 209, 354 323, 335 2 7, 900 1917- 244, 671 191 --- 196,456 123,780 Refined copper (pouodg) Total 2,07 '677 1, 766, 930 1, 723, 436 1, 321, 1, 326, 9 2, 045, 006 1, 213, 545 2, 955, 952 4, 638, 452 4, 752, 5 8 3, 9 4, 616 3, 403, 27 1, 963, 178 Per too Silver sold <1, 359. 37 d 1, 290. 95 1, 655. 40 None. 1 1 50, 616, 77
--J 1,813 ounces. d 1,i72 ounces. Sale or silver from date or organization to end or 1917, $15,280.37. 1,264 ounces. 1\fe nard.- In Houghton County. Organized in May, 1 59; 20,000 shares of 25 each. Tributer worked after company ceased. I n 1876 taken over by Pewabic interest . Sold to Quincy in 1 97. Year Relined copper Year Relined copper (pounds) (pounds) 43, 127 9, 269 4,000 6, 589 15, 600 5, 510 84,095 Mlchigan.- In ntonagon County. Organized June, 1 9 , and began work in eptember. Reorganized January, 1 99. wns properties formerly known as Minesota, Rockland, and uperior. Rockland set off from 1inesota in 1 53 and closed in 1 70. Little work on tribute. Min ota mine di covered 1 47, opened 1 4 , clo ed 1 70. Little work on tribute after Michigan discontinued work on company account at end of 1910 and mine let on tribute until May, 1913, when all work topped and mine was idle until July, 1915. Work was again su p nded October 1, 1920. Con olidated with Mohawk Mining Co. in 1923. ilver old, $294 (in 1921). Year
Rock treated ) (tons) Total Per ton 1902---J 125, 055 152, 200 140,225 150,407 190, 331 I 1909- - 14 ' 172
1913- - - -- --- I 1916 - -- -1 2,091 191 -- 40, 65 1919 62,373 46, 2 9 1921-1925 - 33, 601 166, 9 275, 07 2, 746, 127 2, 91, 796 2, 75, 341 2, 665,404 3,000, 206 1, 979, 305 36, 6 2 327, 773 162, 590 19, 727 b 0, 000 35, 400 1, 177, 176 1, 697, 107 1, 075, 492 r one. - - --- 1 21,245,703 Mill test or 1,100 tons or rock treated yielded 14,670 pounds or refined copper, or 13.33 pounds per too. Estimated from 90,000 pounds or mass copper shipped.
THE COPPER DEPOSITS OF MICHIGAN rRODUCTION 8 Y LODE Refined copper (pounds) Yeor vein alico lode Evergreen and succeeding lodes 33,601 ° 50,000 0 75,000 ° ' 0 1,373,000 ° 1,373,127 1905- - - 0 1, 445, 000 ° 1, 446, 796 - -- -- ° 1,000,000 0 1,500,000 °1,500,206 0 700, QQQ 0 1,279,305 -- -- 36,6 2 327, 773 -- - 162,590 -- -- - 19, 727 0-000 as' 400
1, 177:176 1, 075,4 9, 174, 10 '006, 420 4, 065, 175 Mine ota.- I n Ontonagon ounty. Incorporated in 1 4 , 3,000 shares; reorganized in 1 55, 20,000 hare of 50 each. Mine worked by tributers after 1 70. Later became part of !Vlichigan, which wa consolidated with Mohawk in 1923. Year 185 --- 1 6 - 1 7 - -- Refined copper (pounds) 3, 020, 000 2, 0 0, 000 3,490, 714 3,952, 000 3, 02, 914 3,344, 57 '2, 6 0, 500 ilver sold 9 6.95 (112 pounds). SG54.44 (7 pounds) . · 606. 3 (70 pounds). , 644.61 ( pounds) . 3, 016, 24 . ] ,039.92 (l d 2, 520, QQQ I $912.71. 5 pounds). 1, 677, 500 1, 446, 000 403, 000 391, 500 376, 500 230, 900 227, 500 401, 500 36 QQQ I 252, 000 14 ' 171 1 6, 33 133, 419 '954 113, 14 175, 027 92, 762 32, 033 24, 227 1 10, 672 6, 226 1, 144 12, 60 34, 706, 66 S~elter pr~duction 184 - 1 6 , 27,307, V3 pounds. river sold 1n I 52 amounted to 261.69, and in 18M to 1 6.46. molter production given as 3,212,426 pounds. Smelter production given as 2,135,936 pouods. m Iter production given as 1,634, r. pounds. ~finong .- n Isle Royal. Minong Mining Co. organized December 16, 1 74; 40,000 hares of 25 each. Built tamp mill in 1 76. Reorganized in 1 79 a.s Minong Copper 20,000 shares of $25 each. Company . topped work in 1 1 but tributers worked for two seasons. ince the faLl of 1 3 no work has been done. Year Rotlned COJ?pe'-1 (pounds) 4 ' 344 114, 537 104, 92 90, 596 72, 515 27,407 Year Refined !Xlp~r (pennd) l\fohawk.- I n Keweenaw County. Mohawk Mining Co. organized rovcmbcr, 1 9 , and took vcr par of land of Fulton Mining o. tarted stamping in D ccmber, 1902. Wolv rinc and Michigan con olidated with Mohawk on Augu l 15, 1923. In 1900 produced 70,000 pounds mohawkilc; in 1901, 1GO, 97 pou nds. Year Rock treated (tons) 190 1910 1 191 - -- --- 2 ' 441 459, 162 5 6, 305 61 ' 543 640, 777 6 5, 23 19,019 02, 537 802,54 7 7, 941 366,45 649,649 29, 7 9 664, 547 605, 202 454, 293 560, 734 434, 9 6 ,273 512, 393 405, 412 702, 534 640, 069 14, 014, 050 Stamp mill idle July 14 to Dec. I . I eOnO<l copper (pennd ) Totnl 226, 24 G, 2 4., 327 ' 149, 515 9, 3 7, 614 9, 352, 252 10, 107, 266 10, 295, 11, 24 '474 11, 412,066 12, 091, 056 11, 995, 59 5, 77 ' 235 11, 094, 59 15, 2, 914 13, 34, 034 1 12 ::113 ' 7 w: 7 1: 04.1 12, 57,392 10, 269, 24 14, 054,235 11, 209,396 9, 452, 539 15, 215, 197 15, 19, 922 Per ton 15. OJ Natlonai.- I n Ontonagon County. Chartered April, l 4 · Worked until 1 71. Remained idle except for tribute work until May, 1 0. Rechartered in 1 78 and in 190 . Active mining ceased August, 1 93; since then a little tributing bas been done. Year ., Refined copper Silver sold (pouods) 57,631 - - 0 1 00, 000 - - - - - - - - - 49, 302 - 176,4 3 - -- --- -- 316,957 264, 04 - - - - - - - - - 4 8, 176 1, 078, 609 1,383, 760 865, 752 561, 179 6 '516 -- 695, 027 1, 011. 41 647, 371 b 916. 71 475, 633 178. 74 256, 947 260, 659 -- 411,086 336, 770 1 167, 70 - -- I y Refloed copper Silver sold ear (pounds) 11, 612, 952 Estimated. 679 ounces. , 1 o ounces. 8,750 tons or rock treated
PRODUCTION ·cw Arcadian.- ee Arcadian . ;ew York and Michigan.- In Keweenaw ounty. Opened 46. clo ed in 1 47; reopened 1 52--53. Four mall 10 1 'eighing about 1, 00 pounds were ·hipped in 1 52. J118SSCSIV t . d . J Xonesuch.- ln Ont nagon oun y. rgantze tn une, \l"orked at interval fo1· ev ral years. In 1 75 tock .1 '· d to 40 000 hare ·. Idle 1 75- 1 77, and ·tamp mill mrrease ' burned oon afterward . Leased for even years by Capt. Thomas Hooper. Over $500,000 pent. , Hefined copper ' Year Hefined copper Year (pounds) (pounds)
3, 502 119, 061 3, 261 46, 450 23, 67 27,450 2 ' 4 4 49, 667 31, 973
3 9, 556 55, 5 4 Xorth Amerlcan.- I n I<:.weenaw ounty. Organized in IS4 ; 6,000 hare., 3 0,000. hare incr a. ed to 10,000 with ;arne capital about 1 51. Opened old orth mcri an mine in Il6 and worked uniil 1 '53. In 1 -2 OJ ened outh Cliff mine. In I 60 old eniir property to Pitt burgh & Bo ton Mining Co. ltw then let on tribute for three year. In 1 64 North Ameri1'80 mine eta ide by the Pitt burgh & Bo ton to be operated by newly organized American lining o. The orth American ure, during the four years it wa worked, yielded 445,000 pound of copper. Remainder of producti n by North merican Mining Co. came from !iff fi ure. Year 1 9.. r·? "'· 1853 ! l lmated. Refined copper (pounds) 51, 296 170,6 17f, 360 51,296 251,597 203, 763 307, 22 I Year Ret! ned copper (pounds) 40 ' 252 275, 95 3 ,919 22, 52 1, 953, 03 North Clitr. In I ewe naw ounty. Organiz d cptcmber 20, 1 5 , by Wng off 1,002.25 acr s from lands of Pitt burgh Boston ~lining . Reorganiz d larch 22, 1 59 und r special rhar~er which hac! originally been grant d to th " warns ott li~Iung o. of :\1 ichigan" and th nam changed to orth ~lining o. f Michigan. p rati n · suspended at end of IllO; rc umcd in 1 63. In 1 59 produced 2,435 pound of ~fined copper (from op nings); in 1 64, 3,222 pound ; total, ~,657 pounds. Xorth Lake.- In Ontonag n rganized Augu t, !901 · No rock milled. ~orth we t.- e P nn ylvania. :lorthwe tern.- In 1 ew enaw unty. 1 5, ns Northwestern Mining o. R organized tcr ilr · 11 '. uung o. of D trait, Marrh 16, 1 4. ; capital 300,000. : amp mill erected in 1 52. Work u in 1 57, r umed '~ring of 1 63, again suspend d in January 1 65. Later
08 by entral. In 1 63 ilv r solei am unting to Year Retlnod copper - - (pounds) l I 155 1856"" 44, 166 154, 900 I 0, 30 16, 75 Year Rotlu d copper (pounds) 313, 005 Norwich.- In Ontonagon County. ein discovered on Norwich and Wind or propcrtie in Jul perations at orwich mine began 1lay, 1 50, but not worked with any con- ·iderable force until 1 52. In February, 1 55, American 'lining Co. of Vermont organized ~orwich lining Co.; 20,000 har of 25 each. Operation u. pended in 1 5 becau of financial difficulties. om work done on tribute 1 5 1 63. In :May, 1 63, orwich reorganized and for·med a con olidation with Windsor m.ine, and work recomm need immediately. Con alidation with Hamilton o. wa decided on, April 14, 1 64, followed immediately by a divi ion of the proper y, exchange of stock and the formation of two companies, the Norwich ceding the property known a the Wind or mine and receiving the north part of the Ham.ilton. l\fine wa hut down in 1 65. orne work was done in 1 99--1900 u ncler the name of E ex Copper Co. Year Estimated. Refined copper (pound ) Year Refined copper (pounds) ,-- 6, 339 11 5 1 39, 000 34,451 9, 730 293, 210 216,000 ,300 220, 000 116, 000 993, 360 Ogima .- In Ontonagon ounty. Proper y worked under tribute 1 57- 1 60. Purcha ed in fall of 1 60 and Ogima Mining o. organized in Deccmb r of that year; 20,000 hare of 25 each. topped work in 1 6 . Ground above adit level worked at interval by tributers. In 1 lea cd for three year to ;\leads. Later ab orbed by Mass. Year R fined COJ?per / Year Refined copper (pounds) (pounds) 7 00 14, 166 17,937 40,957 b 2 ' 700 16: 776 b 35, 000 1 1 2 4, 207 277,310 1, 106 16 I 4 0 I 1 5- -, 12, 291 1 I 045 I 39 1, 13 ' 97 ummcr of I Eslimntcd. Ohio.- ec Hilton. Ohio Trap R ock.- In ountv. Special charier granted 1 49; 6,000 har , ompany commencccl operation in 1 46 and up to eptember, 1 53, had expended about 90,000 with but !itt! return f copper. apital exhau ted in 1 55, and company reorganized with capital tock 300,000. o work done ince 1 57. In 1 53 produc d 2,755 pound of refined copper; in 1 5 , 3 ,6 5 pound ; total, 41,440 p unds. Ojibway.- In I eweenaw ounty. rganized June, 1907; 100,000 shares of 25 each. orked I ear argc amygdaloid. In 1911 treated 7,44 ton of rock and produced 49,6G2 pound · f refined copper, or 6.65 pounds per ton. Ma copper r - tnin d at mine amount d to 0.7 pound p r ton stamped bringing total product up to 7.35 pounds per ton, with tanings lo c of nbout 3 pounds. 0 ceola.- In Houghton ouuty. Organized ' 25 I n 1 79 con olidated with Opechce, f nning 0 c ola on olidated Mining o. Reincorporated 1903. Fir t work d on alumet & Hecla conglom rate. In 1 77 Osceola amygdaloid located. l ar nrge and outlt Kear arg mine operat d on I car arge amygdaloid, and Tamarack J r. on Calum t & Hecla c nglomeratc. R organized including thr e
THE COPPER DEPOSITS OF MICHIGAN mines- Osceola Tamarack Jr., and Kearsarge. Tamarack Jrd. ' · peoe set off from Tamarack about 1 90. South I earsargemme 0 by Osceola Consolidated Mining Co. in 1 99. Absorbed by Calumet & Hecla Consolidated Copper Co. September I, 1923. Year f Rock treated (tons) ALL LODES Refined copper (pounds) Sill'er sold ·rota! - 1 - Per ton 25,763 936,002 36.33 33, 4 1, 330, 313 39.30 43, 075 1, 693,737 39. 32 1 77 - 7 ' 339 2, 77 4, 777 35. 42 79, 439 ° 2, 705, 99 $5, 525. 61 95,055 b3,197,387 4,898.36 107,3 6 3,31,061 31.4 , 1,294. 07 160,8 0 4, 176, 976 2, 694. 25 172, 529 4, 179,7 2 3, 476. 91 175,320 4, 256,409 3, 757.7
181, 60 4, 247, 630 2, 3 3. 99 72,923 1, 939, 169
137,725 3, 560,7 6 1,30.93 1 87 145, 200 3, 5 3, 723 24. 68 1 3, 036 4, 134, 320 22. 59 - 17 5, 5 7 4, 534, 127 1 3, 25 5, 294,792 1, 23 . 74 234, 325 6, 543, 358 1, 249. 10 247, 575 7, 098, 656 236, 75 6, 715,870 1894 264, 050 6, 91 ' 502 26. 20 233,238 6, 270,373 26.88 1 96- 24 ' 062 6, 251, 304 -- 443,086 11,201, 103 -- 5o5; oo8 12, 6 2, 297 546,326 11, 258, 049
6 3, 066 12, 566,471
793,207 13,723,4 7 836,400 13,416,396
924,400 16,059,636
1, 095,520 20, 472,429 1, 007,200 18,93 '965
1, 016, 240 18,5 '451
1907- 11, 603 1 14, 134,753
1, 241,400 21,250,794 -- - 1, 494,845 25,296,657 16.9 -- - 1, 217,720 19,346,566
1, 246, 596 18,38 '193
1, 246, 557 18,413,387
735,044 11,325,010 - -- 1914. 1, 10 '447 14,970,737
1, 361,0 9 19, 731,472
1, 2 4, 6 1 19,5 6, 501 15.25 1917 1, 237, 05 16,0 4, 958
1, 194,967 15,919,647 739,364 10, 824,331 14.64 ' I 26,742,216 I 477,371, 115 17. 5 1- -- tncludes 79, 78 pounds from sands. includes ,555 pounds from sands. ' o. 6 Osceola closed in August. OSCEOLA MINE CCALUMET .t HECLA CONOLOl!ERATE) Year Rock treated (tons) 33:848 43,075 1 11- - - - - - 78, 339 I 79 - - -- 5 : 600 Refined copper (pounds) Total Per ton one. 936, 002 1,330, 313 1, 693,737 2, 774, 777 0 2, 705, 998 b 1, 971, 140 1, 240 061 one. 12,652,028 358, 450 ,; + Includes 79,878 pounds from S~ll<ls, ~ncludas 68,565 pounds from sands. TAMARACK JUNIOR MINE (CALU M ET '' ll ECLA CONOLO~IERATE) [Sec Tamarack Jr. Min lug Co. for production 1 92-t 961 Year 1 9 Estimated. I Rock treated (tons) 64, 57 100, 764 1 105, 742 121, 744 121, 652 100, 959 3, 760 619, 47 Refined copper (peunds) -- Total 0 1, 655, 000 0 2, 620, 000 0 2, 511, 000 0 2, 276, 000 0 1, 79, 000 0 1, 413, 000 "14.0 0 50, 000 "13. 3 12,404, 000 NORTH KEARSARGE MINE (KEARSAilGE AMYGO.UOID) 1 97 - - 0 6 ' 194 70, 534 77,3 1900 - - '57 104,162 197' 60 1 34 7' 600 456,960 1905 - 3 1, 520 1906-- - 345, 200 1907_ - - -- 256, 314 465, 70 605,055 701,315 767, 272 672,24 300,903 45 '609 612, 31 651,079 691,263 "I 5 q 1 3 191 745, 722 I 1919 465,034 291,50 1 9, 22, 740 146, 371, 443 Estimated. SOUTH KEARSARGE M.INE (KEARSARGE AMYODALOID) ·5, 670 °93,000 1901 -- --- - 59, 979 ° 995, 000 160,320 a 2, 39,000 275,440 ° 4, 840,000 34 '440 ° 6, 737,000 350, 560 a 6, 9 6, 000 392,520 ° 7, 7 9, 000 1907_ - -- -- --- 310, 925 ° 5, 969, 000 190 392,627 ° 7 273,000 1909- - - 456, 3 0 ; 609, 666 450,103 '16 '794 479,324 ' 734, 140 45 '745 '322, 025 256,233 5, 004,000 '402 6, 303,000 476, 1 5 7, 962,824 40 '572 6, 96 '749 343,254 4, 900,7 1 21 '72 3, 271,446 124, 1 07 2, 07 ' 445 71,091 1, 311,3 1 1921- 1923 17· 91 6,427, 605 Estimated.
PRODUCTION Estimated. OSCEOLA MINE (OSCEOLA AMYGDALOID) Rock treated I (tons) -, 36, 455 6 '000 160, 172, 529 175, 320 I 1 1, 60 72, 923 ' 137, 725 I 145, 200 1 3, 036 175, 5 7 1 3, 25 234, 325 247, 575 236, 75 264, 050 233, 23 24 ' 062 310, 035 333, 710 363, 216 467, 074 507,414 Refined copper (pounds) 'I'otal 1, 226, 247 2, 141, 000 4, 176, 976 4, 179, 7 2 4, 256, 409 4, 247, 630 1, 939, 169 3, 560, 7 6 3, 5 3, 723 4, 134, 320 4, 534, 127 5, 294, 792 6, 543, 35 7, 09 ' 656 6, 715, 70 6, 91 '502 6, 270, 373 6, 251,304 ' 241, 103 7, 76, 297 7, 203, 049 '55 '471 9, 049, 4 7 Per too OSCEOLA MINE (OSCEOLA AMYODALOID)-()Ontinued Year Rock treated (tons) 377,520 297,600 290,120 1905- - - - --- 27 5, 120 21, 52o 1 244,364 3 2, 903 1909--- - -- 433, 410 66, 302 Refined eopper (pounds) Total Per too 6, 015, 396 5, 123, 636 5, 2 9, 429 4, 959, 965 4, 776, 451 3 s' 22' 794 6: 474: 363 1, 022, 9 2 ' one. 1912 - · - 115, 564 177,90 261,436 272,073 225,030 191 7_- -- 203, 2 191 - - - 230,517 150,223 1920- - - - - 93, 3 3 1,479,642 1, 952, 010 2,972, 000 .3, 2,069 3,350, 014 2, 516, 736 3, 252, 233 2,365,226 1, 671, 263 9, 513, 943 Estimated. SOMMARY Period Refined eopper (pounds) Rock treated (tons) , Total Per ton 977, 92 16, 250, 345 9, 513, 943 25, 056, 02 261,527,694 Penln ula.-In Houghton ounty. Wa Albany & Bo ton np to I 2, wh n it becam P oin · ula. Mine lo ed in 1 92. Purchased by Franklin Mining o. in 1 94, after "hich known 1.1 Franklin Jr. min . Output all deri\·ed from AJlouez onomerate. Year Reflod copper j (pounds) , Year R~fioed opper (pounds) 49,400 1, 10 ' 660 1,225,91 191 1,599,670 736,507 6,624,9 1 131,o5n5fi 1 1 92-- - - - -. !/9,39! tons stamped, ylcldio; 10.00 pounds to the ton. Penln ula.- In Ontonagon ount . Organiz d July 30, 1 0. A v in wa worked to orne xt nt in 1 51. bnndoned by 1 54, a ther wa · littl ncouragcm nt to go on. I roduced 44 0 pounds of refin d copp r in 1 51. P.eun ~ylvanla (Northwest).- In K w naw ountv. gazed in 1 61; 20,000 hare of 25 each. Or- Year Reftnedcoppt·r I (pounds) Yeor Refined copper (pounds) 34, 322 195, 020 29.,199 269, 174 229, 077 19 : 0 0 242, 097 109,920 Hi3, 960 379, 369 12 , 090 I 326,660 3, 34 5 ' 543 166, 100 Pethcrlck.-See Ashbed. 3, Q3 '311 ·~t;:blc.:-In Houghton ounty. Organized ~tel om work b ginning 1 55. In 1 on or l cwabtc were con olidaicd. M in lea ed from Jun , 1 70, 190, 7 7, 393 26, 742, 216 477, 371, 115 to July, 1 74. Concord set ofi a a separate organization in Purcha ·ed by Quincy in 1 91. Year Rock treated (tons) Retl.oed copper (pounds) Silver sold Total Per too 1 - 22, 179 ° 129, 546 236, 254 1 5 -- 416, 603 1 59 -- - - - --- b 1, 032, 0 7
1, 917, 426 1 6L . 3 , 724 1, 49, 192 1, 571, 2 1 1,691,724 1' 429, 57 1 65_39, 64 1, 731, 394 51, 913 1, 346, 140 46, 000 1, 646, 45 42, 494 1, 043, 523 43, 199 9 0, 409 1 70-- - --- 546, 616 444, 600 467,000 572, 400 294, 607 625,271 56 '995 693, 777 1 7 -- - "23, 26 7, 299 336, 519 970, 509 60, 427 1, 72, 7 1, 4 2, 664 1, 171, 47 227, 34 Includes 21,879 pounds lost by shipwreck. 1 406. 6 (1,3 2 ounces). 1,032.93 (919 ounce ). $593.35 (42 ounces). 397.10 (270 ounce). 195. 2 (116 ounces). Includes 2,13 pounds lost by ship7treck. tamped 23,912 tons during 7 months and 22 days
THE COPPER DEPOSITS OF MICHIGAN Pboenlx.- In Keweenaw County. Phoenix Consolidated Copper Co., organized April, 1 99; 100,000 shares of 25 each. Comprised old Phoenix, Bay tate, t. Clair, Garden ity, and 0 acre of the old Atlas purcha ed in 1900. ucce or of Lake Superior Copper Co., which was organized February 22, 1 44; 1,200 shares of $100. Mining commenced October 22, 1 44; abandoned in 1 47; recommenced in 1 50 and continued to February, 1 53. A stamp mill was built in 1 45, the first in the di trict, but proved a failure. In August, 1 49, reorganiz d and Phoenix Copper Co. took over as ets. tarted work on Ashbed in 1 55. In 1 63 worked Phoenix and Robbins fi - ures. In 1 71 Bay State property acquired. Worked n company account to 1 3 and on tribute July, 1 3, to 1 6 Garden City worked 1 59-1 6 . St. Clair operated 1 6" 1 74 and 1 80- 1 5. Work discontinued June 15, 1905. Hcsumed work on Ashbed October, 1913, and continued to December, 1917. Property sold to Keweenaw Copper o. in 1923 and Phoenix Co. dissolved. Year 185 186 1917 - Refined copper (pounds) 8, 960 11, 200 15, 6 0 3, 427 6, 000 16, 000 34,000 0 45, 000 56, 590 40,062 63, 590 144, 118 332, 775 Silver sold b 244, 15 202, 000 196,000 260, 000 796,630 999, ooo 1 1, 219, 62 $1,147.08 (87 ounces)
521, 0 1 $89 .09 (6 1 ounces). 1, 39 , 440 $2,950.49 (2,250 ounces). 1, 404, 276 $6,204.69 ( 4,732 ounces). 1, 396, 530 2,120.42 (1, 41 ounces) 1, 022, 493 $1,267.03 (1,100 ounces)· 301, 172 $777.12 (727 ounces) · 543,426 436, 010 409, 357 537, 177 512, 291 621, 004 361, 108 101, o4 I 11,000 93, 643 ' 100,000 202, 23 1, 162, 201 7,42 .60 (13,375 ounces). 273,214 1 one. Estimated t·:o-;;O:cto:b;::e~r :29: Includes 33,000 pounds r;om Ash bed ' 15,200 tons on stock pile · October to December ·Rock treated 6 915 to · Rock treated, 41,14 tons; yield, 9.25 pounds P~~;J;~e.ld, 9.96 pounds per ton. Pittsburgh & Boston.- See !iff. Pittsburgh & Isle Royale.- On !Rl' Royal.
R fined COp)llt (JlOunds)
i 3,360 ,960 12,410 24, 730 Pot·tagc.- In Houghton ou nty. Organized in 1 52 d mining commene d in November of that y ar. Por tage. Produced 6,60 pounds of r fined copper in 1 3 Quincy.- In H oughton Cou nty. I ncorporated -larch .30 1 4 . In 1 56 Pewabic de d i, c vered. ew compan1: formed under sam name 1n 1 7 . Reincorporated in 190. Ab orb d Pewabic in 1 91. In 1 97 purcha ed Mesnnrd and Pontiac proper tie and incrca cd their capital tock to 100 000 har . Purchased old Franklin mine December 1, 190 . ' Yenr Rock treated (tons) Refined copper (pounds) Total 13,462 122, 762 306, 772 357, 114 1, 140, 304 2, 564, 52 0 2, 125, 000 0 2, 420, 000 0 2, 400, 000 0 2, 200, 000 0 2, 300, 000 a 1, 00, 000 0 1, 500, 000 2, 460, 635 2, 572,9 0 2, 33 ' 2, 276, 30 2, 00, 005 3, 046, 69 2, 92, 617 2, 949, 63 2, 720,55 0 2, 900, 000 0 2, 00, 000 0 4, 000, ~00 5, 702, 606 5, 6 2, 663 5, 549, 0 7 5, 6 0, 0 7 5, 4 ,530 5, 923, 519 5, 609, 762 6, 367, 09 6, 405, 6 6 1 064, 253 10, 542, 519 11, 103, 926 14,39 ,477 15,4 4, 014 16, 304, 721 16, 63, 477 16, 924, 61 16, 354, 061 14, 301, 1 2 14, 116, 551 20, 540, 720 1 ' 498, 2 Silver sold Per too -.-49.-9 5i7.-i6
a 41. 0 0 47. 19 o 46. 6 1 2, 263. 35 r-Tosi . -6 3, 745. 53 22, 080. 42 31. 19 1 1 1 024. 95 29, 405. 60 24, 490. 64 25. 26 I 25, 474. oo 17, 170. 5 16, 300. ()() 19. 29 I 21, 000. 00
PRODUCTION r ock treated (tons) Refined copp r (pounds) Silver sold Total ton -· (J.j 1, 01 ' 73 1 135, 162 1905 1 1 ' 343, 160 $25, 75 . 9 1 ' 27, 557 27, 077. 20 !900 ' ' 16, 194, 3 25, 35 . 00 1907. - - - -- - - 1909 --, 19!0 -. - 1911 1, 3 2, 524 1912 1, 309, 253 1913 -- 04, 645 1, 016, 666 1, 269, 000 19,796, 05
20, 600, 361 -- 30, 227. 51 12, 1 4, 12 20, 32. 79 1916 1, 204, 026 15, 356, 3 o I 15. 1 12, 630. oo 22, 054, 13 11, 29. 0 21, 065, 612 26, 159. 19 1917 1, 277, 73 1, 174, 147 22, 195, 577 - 960, 393 1920 -- 09, 263 1921.. .. -- 767, 100 1922 67 4, 499 1923 546, 670 192-L 5 ' 100 1925. .. . . . 5 6, 913 133,050 ounces. 'I.W,7i4 ounces. 19,94 , 965 19,476, 320 19, 216, 070 16, 960, 265 15, 402, 726 13, 000, 733 14, 3 ,633 14,357,523 726, 000, 319 d 150,139 ounces. 115,137 ounces. Rhode I laud.- In Houghton ouuty. Rhode Island 'Jining Co. organized about 1 60 and worked Allouez conglomerate. Rhod I land Copper Co. organiz 1 9 . Fir t exploratory work done by Rhode I land Mining o. 1 64-65 ~dending a trench from a point we t of highway ea t to Allouez ronglomerate, which expo ed all the lode for that distance. Xo. 1 haft started on Pewabic lode in 1 9 . Year Refined copper (pounds) 1903 a 24, 000 b 7, 000 31,000 Estimated from 31,611 pounds mass and barrel for tbc year. 1E..<Iimated from 9, 92 pounds mass and barrel for tbc year. .- In Ontonagon Worked five year ; lea d 1 company organized. Tille lot in 1 96 by fn.ilu r rganiz d pril, 1 50. In October, 1 63, new int rval by tribut rsowner to pay tax. Lat r became part of 'Ia on lid at d 1ining o. ilver amountiog to 254.55 sold in 1 76. Y1ar Hock Refined copper 1 Rock He fined copper treated Year treat d (tons) (pounds) (tons) (pounds) 22,400 2, 17 290, 01 a 37, 600 2, 017 296, 15 70, 631 251, 37 73, 74 215,469 5 ' 790 3, 925 223, 353 7 , 690 2, 300 235, 606 a 40, 000 1, 44 102, 936 0 60, 000 60, 155 16, 917 4 , 74, 030 170, 433 1 1 63, 390 142, 411 15 ' 272 1 4, 037 18 7 4, 902 162, 037
50,924 253, 40
2 ' 000 245,400 17, 645 350, 150 43, 049 257, 910 23, 611 231, 140 64, 363 374, 113 32 ,447 5,443,195 'i!.~lmatcd. Rockland.- In Ontonagon ounty. rganized eptemhrr 27, 1 53; 20,000 shares of 25 each. tamp mill ererted 1 55- 56. In 1 70 company hut down. Pa d into hand ational intere ts. Worked by tributers more or le Year Refined copper Sil ''er sold (pounds) 34, 554 - -- 139, 01 -- 2 2, 06 7 - - - - - - - - 56 ' 264 372, 647 515, 7 51, 945 , 446 455, 5 2 -- --- --- 269, 043 -- 23 2, 173 - - - - - - - - 116, 077 - , 119, 634 1 9 '500 1854-1863 and 1 65-1 67 are smelter returns. 1, 700 tons of rock treated. I pounds. d 16 pounds. 7 pounds. 110 pounds. Yenr Refined copper s· (pounds) lnr solrl ll9, 000 95, 000 - -- --- . - 60 000 - . 51, 000 1 23, -1.00 -15, 260 - 11,440 57 600 -- -- 3 '700 , 17, 77 -- 1' 92-l 1- - - - - - - 33, 00 1 15, 21, 136 1 -- Saginaw.- On Isle Royal. Worked from 1 75 to 1 79. I n 1 77 produced 1, 00 pounds of refined copper; in 1 79, 49,464 pound ; total, 51,264 pounds. Schoolcmft.- ee Centennial. St. Clair.- In Keweenaw County. Organized in 1863 and operated on fi sure. Stamp mill erected in 1 72 but not used, as work was su pended during panic of 1 73, and property w·ent into hands of creditors until 1 79, when company was reorganized. Later became part of Phoenix Consolidated Copper o. Year 1 65-- - - 1 6 - 1 73 Refined col) per (pounds) ' 15 62, 200 7, 723 130, 665 46, 197 1 '072 1, 67 5,400 Year 5 I Refined coJ?per (pounds) 13, 195 125,493 7, 126 125, 225 139, 407 79,6 6 1, 011, 071 eneca.- In I eweeuaw County. eneca Mining Co., organized 1ar h, 1 60; di ol ed 0 tober 10, 191 . all of it tock being conveyed to the eneca opp r orporaiion, which wa incorporn.t d in 1916 in New York. line clo ed in pril, n ca opper Mining o. incorporatecl Fehruary 27, 1. 25, and work re umecl in ovrmb r of that year. I -Hcf\ncd copper (pound I ock treated
(tons) Per ton 1 77 7, 10 1 7 - 7, 09 -- - 21,395 497,6 o I 1921. 14,397 1 466,323 '617 272,1 2 1 21, 644 529,1 9 2, 477 1 1, 796,54 1925-- 17, 313 2 4, 241 Year
THE COPPER DEPOSITS OF MICHIGAN belden & Columblan.- In Houghton County. Shelden Mining Co., organized in 1 53. Albion Mining Co. conducted operations on this property in 1 53. 'V ork uspended in 1 57. In 1 60 the property was sold and the olumbian wa organized; began work in June of that year; operations su pended in January, 1 61, and resumed in November, 1 62. In Jun , 1 64, changed name to Shelden & Columbian Copper Co. Idle since 1 70 except for some tributing. Year . Refined : pper II (pounds) Year Refined copper (pounds) Slskowit.- On Isle Royal. Work began on this location a early as 1 45. Siskowit Mining As ociation commenced opera tions in summer of 1 47. i kowit Mining Co. of Michigan organized May, 1 49, and resumed the mining operations which had been suspended by the a sociation. Mine clo ed in 1 55. Refined copper Year (pouuns) 190, 736 South Lake.- In Ontonagon County. Formerly known a Aztec; reorganized in August, 1909, as South Lake Mining Co. and capital stock increased to $2,500,000. Production cea cd in July, 1918. Year Rock treated (ODS) 3, 993 I 6 ' 3 191 7,694 Refined copper (pounds) Total Per too 61, 637 754, 433 rone. r o. 075 1, 042, 211 I 13. 02 Star.- In Keweenaw County. Began work in 1 51 and worked until 1 57. Resumed in 1 64. Refined copperpoun (rounds)
1, 000 1857 4, 77 185 - 1, 760 Summit .- ee Madi on. Stunner.- ee Hancock. 8 uperlor.- In Houghton ounty. Organized July 23 1904· 100,000 shares of $25 each. Min closed November,' 1920: Property purcha cd by alumet & Hecla and company di solved in 1925. Year Rook treated (tons) Refined copper (rounds) Total V' 962 ,-- 21, 24.4 1, 641 I 1, 7 1, 315 140, 514 3, 1 1, 041 191L 162, 599 3, 236,233 172,322 1 3, 921,974 130, 26 2, 992, 765 1 191, 62 3 217, 635 212,051 3, 66, 4 4 1 5, 315 3, 034, 656 129, 5 7 2, 201,672 191 106, 213 1, 676,446 27,267 563, 935 9, 549 322, 71 liver sold - 1921- 1925 - 1 one. ll 1, 550, 474 I Superior.- In Ontonagon ounty. 1 55; 20,000 har of 25 each. ber 1 99. Year 1 5 1 64 -- --- - Refined copper (rounds) 1, 740 10, 000 54,642 70, 000 66, 500 56, 522 9, 673 66,000 1 19. 36 Year Refined ooppe~ (pounds) 36, 400 56,000 4, 521 3, 936 5, 70 1: 476 525, Tamarack.- Io Houghton County. Organized January, Declared first dividend in 1 Property old to Calumet & Hecla Mining Co. on April 1, 1917, and company dissolved. Rock treated (tons) Refined copper (pounds) Total Per ton b 363 b 7, 435 ---54.'76 1, 979,400 90,5 7 4, 636,521 144,412 10,3 9, 67
169, 250 11,036, 469 155,250 I 92 I 249 2 2, 9 7 14,076,957 !U~ 393, 62 15,5 0, 214 1 94 -- - 410,250 13,472,81
229, 174 8, 022,213 490,625 16,045, 039 1897- - -- 611, 539 20, 222, 559 1 9 --- 670, 32 19,662,545 631, 090 1 I 565, 602 19,1 1, 605 1,000, 52 1902 15, 961152 657:920 15,2 6, 093 2h 642, 320 14,961, 750,120 15, 24,008 3 9, 6 0 9, 832,644 2~. 533,600 11,07 1604 2 '6 654, 97 12, 06, 127 6 9, 099 13,533, 207
· 1 1 525, 554 11, 063,606 Calendar year , 1 2-1 S3 and 1896-1916· fiscal years (July 1 to June 30), 1 1 94; July 1 to Dec. 31, 1 95· Jan. 1 to June :io 1917. ' From short sinking. ' '
PRODUCTION Rock treated
Refined copper (pounds)
19IL - -- 392, 33 7, 494,077 1 1912 - - 421, 3 5 7, 90 '745 1913 -- 227, 563 4, 16 '743 1914 - 57, 410 1, 074, 80 1915 - - - 217, 027 1 3, '150 1916 --- -- - -- 363,649 6, 61 '505 1917 - - - -- - 5, 039, 995 99 Tamarack J'unlor.- In Houghton County . Organi zed in 1 . Ab orbed by Osceola Con olidated Mining Year I Refined copper (pounds) I 92 -- - - - - 796, 769 1, 610, 259 2,372,302 2,547,861 2,135,000 9,462,191 Tecumseb.- In Houghton ounty. T cumseh Copper Co. organized in March, 18 0. on olidat d with La aile Copper Co. the later part of 1906. Produced 59, 74 pound of refined ropper in 1906. Toltec.-In Ontonagon ounty. Organized iu 1 50. Began mining in July, 1 51. In 1 55 consolidated with Farm lfining Co. and became Toltec Con olidated Mining Co. Year tlmated. Refined copper (pounds) '720 13,000 106, 000 11 ' 401 3, 036 379, 153 Trlmountaln.- In Houghton ount rganiz d .January, I 99. Di olved in 1923, mine being acquired by opp r Range Co. Year 191 L .. -- 1912 -. -- - - - - - 1913. --- - - 1914--- 1915 1916-- 1917 .. --- - 191 · · · -- 1919· -- -- - 192o:::::
1922 192c -- 1924 102s:::::: Rock treated (tons) 207, 956 507, 377 534, 640 70, 43 506, 924 4 4,35 334, 929 323, 40 317, 299 347, 366, 663 229, 149 277, 251 34 ,6 4 34\J, 504 264,655 201,433 171, 995 116, 76 143, 172 130, 913 6, 273 ' 159 35,465 6, 746, 703 R fined copper (pounds) 'f otal Per'ton 141, 040, 592 h . 20 17. 9" 21. 7, 34:. 10 Vlctorla.- I n Ontonagon County. Mine first opened in 1 49 as Cushin. Forest Mining Co. organized 1 50. Glenn set off from Forest in 1 52. Reorganized April, 1 5 , as Victoria Minjng Co. Operated regularly 1 50- 1 55, then at intervals until pre ent compat~y assumed control. Victoria Copper Mining o. organized January, 1 99, and work commenced in March of that year. I ncludes old ictoria, Glenn, Shirley, Sylvan, Oneida, and Arctic properties. Operations suspended July, 1904; re umed early in 1906. Idle ince end of April, 1921. Year Rock treated (tons) 1854 1 6 - - - 39, 1 5 95, 035 11 ,605 122,497 126, 94 131, 955 1913.- 137, 163 124, 42 133,9 4 146,690 137,2 6 191 - 106,730 1919 . . .. --L 9,206 1921 1922- 1925 ... r one. Rufined copper (pounds) Total Per ton 6, 720 3, 360 '960 41, 354 93,000 "17 '606 7, 490 ' 360 9, 20 3,570 3,903 1, 90 4, 052 b 3, 442 546, 334 1, 207, 337 1, 290, 040 1,062, 21 1, 164, 564 1,303, 331 1, 224, 911 1,42 , 693 1,4 6,242 1,499, 695 1, 661, 32 1, 612, 64_0 1, 533, 536 1, 245, 590 1, 060, 29 240,000 one. 20, 024,513 Estimated. old In June. Represents mass and barrel taken out in running th drifts. Vulcan.- In Keweenaw County. Op ration commenced in 1 64; 613 pounds of refined copper taken from openings. ' White Plne.- In Ontonagon County. Organized in 1909; 150,000 common and 50,000 preferred shares; capital 5,000,000. p ration cea d in rovember, 1920. -- Refined copper (pounds) Year Rock treated 1 1 (tons) Silver sold (ounces) 1915 114,039 1 ' 90 212, 194, 56 1919. - --- 84,00 1920 - 93, 260 None. 887, 654 Total Per ton 2, 24, 145 4,207,449 4,067, 529 3,273, 680 1,979, 268 1,850, 787 one. 18, 233, 169 d $39,856.16. --- b73, 66 e 66, 933 46, 1 30, 77 "38, 107 4, 710
260, 6 1 95 per cent or production. $62,181.83. Smelt.er cJean-up . $28,937.46.
THE COPPER DEPOSITS OF MI HIGA Windsor.- In Ontonagon ounty. Worked in I 54- "5 as a epnrate and distinct intere t of the merican .Mining
of Vermont. Absorbed by 'orwich in 1 63. Pnor to 1 ali produced 6 ,000 pounds of refined copper. Winona.- In Houghton ounty. Organized in April, 1 64. Few hipments. In 1 70 mine wa let to tributer . Reorganized as Winona opper o. ovember 3, 1 9 . In 1911 ab orbed King Philip opper _o. Closed in May, 1920. Year Rook treated (Ions) 3, 772 1903 51, 435 34,030 19,399 102,100 97,445 181,148 120, 06 123,339 102,594 161,829 1917 112, 0 3 39: 654 I one. Refined cop!)& (pounds) 'l'otnl Per ton 101, 1 1, 036, 944 1 646, 025 27 ' 1 2 1, 2 5, 63 Jone. 1, 275, 675 2, 307, 237 1, 448, 737 1,352,085 1, 722, 63 2, 167, 255 1, 494, 472 4 756, 26 819, 57 561, 23 430,012 , 17, 684, 234 1 Produced by lessees. Wolverine.- In Houghton County. Operated from January, 1 2, to November, 1 4. Reorganized as Woh·erine Copper Mining Co. in August, 1 90. Con olidated with Mohawk Mining Co. Augu t 16, 1923. Mine clo ed April, Rock treated (tons) Refined copper (pound ) 'l'otal Per ton 25, 623 - - - - - - - - 699,622 -- - 18 4 - -- 00, 000 j 370, 925 --- 18 6 - 3, 208 -- 31,524 500,074 I 10,491 21 , 55 I 76,440 1,611,857 1 94 90,195 1, 744,070 I 85, 155 2, 011,638 ,. 82,270 2, 237,698 130,0 9 3,470,927 1 9 - 1 4, 799 4, 700, 373 1 99 1 4, 594 4, 7 56, 646 1900- - 190, 104 I 4, 907, 646 1 7, 4 2 4, 9 4, 367 279 011 1 260,3 6 29. 6o 314; 091 9, 300,695 1904- -- 321, 13 1 9, 729, 971 341, 20 9, 681, 706 1906- - - -- - 344, 062 9, 372, 982 34 '860 9, 356,123 190 -- - 373, 694 9, 995, 7 48 390, 37 1 9, 757,101 3 '476 9, 617,16 1911. 401,308 I 9, 40 3 '502 8, 350,312 1 2,127 3,435,459 397,614 7, 250, 66 a 8, 9 6, 641,492 Calendar years, I 2-1 6 and 1924; 1891 includes Sept 1 1891 t A · o12 incluDdes May JO to June 30, 1893; tl~cal Years (July i to June 3CJ) .u Y 1 eo. 31, 1923; Jao"tlary to AprU, 19211. '
1916 191 -- - Hock troJ.Pfl (tnn) 352, 45 :)03, 49 29 'o, 9 257, 294 263, 053 290, 411:) 244, 310 95,40 205,42 43, 663 R en ned COPJ>Cr (JJOundl) 'l'01nl 5, .56, 4, 60 ' 65 4, 562, 617 3, 032, 225 3, 640,303 3, 924, 270 3, 544, 79 1, 605, 121 3, 265, 356 574,0 1 I Wyandot.- In Houghton ount.v. rganized February2~ 99; 100,000 hare of 25 each. Idle fr m eptember, 1914, to April, 1915. lo ed !at in 1917 or early in 191 . Refined copper (pounds) Year Rock tr ted (tons) rer(OO 1, 605 19, 973 1, 322 b20, 000 one. 1 one. 2,927 39, 973 Tailings assay 5.26 pounds. E timntcd. OPERATING PRA TICE An adequate discu sion of the pr ailing minin and metallurgical practic in the di tri t at the pre ent time by competent authority would make a very considerable report. Here it i intended only to give the reader a general idea of the methods u ed. MINING DEVELOP 1E 'T The ore bodies are tabular in form, average from 5 to 30 feet or more in thiclme s, and dip at angles of 30° to 72°. All the lodes have be n opened from the outcrop by inclined shaft unk in or lose under the lode and spaced, in modern operations, at intervals of 2~500 feet or more along the trike. In early operatiOn the spacing was clo er. The deepe t of these haft', which is on the Calumet & Hecla conglomerate, 8 length along the incline of 9,065 feet and attru.ns a vertical depth of 5,459 feet-that is, 4,815 feet below Lake uperior, or 4,213 feet below sea level. !he Michigan copper properties arc bounded on all ~~dedcs by vertical planes. This has undoubtedly avoJd many of the legal diffi ulties that have plagued wes~rn mining operations, but it has in places been a handJC&P to the most effective development. To open the deeper portion of the Cal urn t & Hec conglomerate ore body the old Tamarack Co. sun d live vertical shafts to depths of 3,409 to 5,308 feet
connected them on several levels by crosscuts. the meantime the Calumet & Hecla Co. put down r.
OPERATING PRACTICE deep vertical shaft, the Red Jacket, to serve its deeper levels. The vertical shafts are connected by crosscuts ~th the driits on the lo~e . To reach deep parts of the Kearsarge amygdaloid, where the outcrop was wned by others, the Allouez and Ahmeek companie ;unk four shafts at an angle of 10° from the vertical, curving the shafts into or parallel to the lode where this was reached. Th Seneca Co. unk a vertical shaft to th Kear arge lode and urved it parallel to the lode. On account of low capacity and expensive maintenance the inclined shafts are 1 s effective for very deep mining, and the Calumet & Hecla Consolidated Copper Co. is abandoning one after another of its deep inclined shafts on the conglomerate lode a.nd is preparing to work at greater depth bysubinclines from a main haulageway on the eightyfirst level, which is tributary to the Red Jacket vertical shaft. In the early days the di tance between levels, measured down the dip, wa usually 60 feet (10 fathoms); now the interval is 100 to 150 or even 200 feet. An effective method of sampling the native copper deposits has not been devel p d. The choice of ground to be mined i made by the mining captains on the basis of visual inspection, aided by feeling, for the mall rough particle of metal may be felt where they are not easily seen. The standard for judgment are empirical, ubject to u h check a are afforded by tho weekly or mon thl mill r urn on the or fr m all top of n. given haft or of tha en tir mine. In general, any rock in which pp r is det cted by ight or touch goe a or , and that in whi h none i o detected is noli intenti nail min d. TOPI Open stope.-Wh r the dip i b tw n 35° and 45°, as it i in the mine n ar alumct, th p n top is commonly used. A rai e is put up to th l vel abov , after which stoping pr eed , I aving a floor pillar under the level above and a ufficient number of round pillars in the tope to upport the hanging wall. Th commone t practice ha b en t ad ance the tope outward from the haft pillar to th limit of !ih o-round t'b 1:> n utary to the haft, and before abandoning the 1 vel ~~recover as many of the pillnrs as an be tal en out With. afe!iy; later still the floor pillars are r mov d provided they are rich enough to ju tify this ind pendent · opera~Ion. The more re ent practi ·e how ver carries the drifts to th limit farthe t fro~ th haft a~t stopes on the retreat. In this way only nough ars are left to give temporary prote tion to the ·~~ast of the tope, nnd as the stope r tr at , nll pos1 6 stope pillars and the floor pilla1 al are mined out. In either ca e no timber is used exc pt in the construction of loading hutes. In mining the deeper parts of the Calumet & Hecla conglomerate lode stope pillars are not used. Instead, timber stulls are used in sufficient number to afford a zone of protection near the breast of the stope, but as this zone moves along with the progress of the stope the timbers are removed, and caving of the hanging wall follows. Room and pillar.-In the deeper levels of the Quincy mine, where the dip i less than 40° and the lode narrow, a modification of the open-stope method has been adopted to meet the condition of great rock pressure. The interval between levels is 200 feet; stopes 100 feet long are supported temporarily by short stulls and later are partly or completely filled with wa-ste rock from development operations. Between the stopes pillars 100 feet wide are left extending through from level to level, as round stope pillar have been found inadequate. On the advance, therefore, something over 50 per cent of the lode i mined, the remainder being left for support to be recovered so far as may be possible on the retreat. hrinkage stope.- At the Isle Royale mine the dip ranges from 50° to 56° and is thu too steep to permit work in an open stope without tirnber. A timber bulkhead with numerous loading chutes i erected to separate the drift from the stope. Extraction i accomplished by inclined cuts; usually poor ore left unbroken affords sufficient support. The ore is allowed to accumulate to a conv nient height, a.nd th urplu is drawn off through the chutes. pon completion f the stope all or is drawn off and the stope is abandoned, beginning at the limits farthe t from the shaft. Horizontal cut and fill.- At the Baltic, Champion, and Trimountain mines the dip approximat 70° and the lode is unusually wide. Two dry walls with opening for loading chutes are constructed of waste rock and covered \vith timber, forming a haulage way nlong the center of the lode on the level. As waste from mining operations accumulates behind and above these haulage wa s cir ular dry-walled mill hole are extended upward from the loading chute and kept ev n with the top of the fill. toping i carried on by horizontal cuts worked from the top of the fill. s each round is bla ted down the broken rock is sorted by handling and vi ual inspection, the ore is thrown into the mill holes, and the reject is left to constitute the filling. Where the lode is rich and the amount of reject therefore inadequate to maintain the fill at a proper height additional filling material is obtained by exploratory stoping along the footwall and by blowing in wet mill tailings shot down from the surface. Floor pillars below the fill of .the overlymg l.3vel are supported by large timber cribs and are then stoped by inclined cuts from under the pillar. The size of shaft pillars varies with the depth. In some of the old inclined shafts no shaft pillars were left
THE COPPER DEPOSITS OF MICHIGAN in the upper levels of the early days. As the ~hafts were deepened pillars were loft, say, 50 feet wide r sometimes less, on each side. At still greater depLh the shaft pillars were made 100 feet wide on each sid and now, in certain shafts at the deepest level , 200 feet is left for each pillar, or a total block of 400 f et for the shaft. vVbere the shafts are canied in the footwall of the lode shaft pillars are not neces ary, and by some it is regarded as better not to len ,·e pillars in the lode over the shaft. TRANSPORTATION The ore is drawn from the stopes through hute of varying design and construction into cars, which are commonly of several ton capacity. In the flatter stopes drag-line scrapers are used for moving the ore down the footwall. By the use of long platforms erected over the track scrapers are also used to some extent for loading cars where no chutes are provided, as in the deep levels of the Calumet & Hecla conglomerate, and for mucking. in drifts. The so-called mucking machines and other forms of mechanical shovels have gained little foothold in this district. Power has largely displaced handwork for tramming. At most mines the cars are dumped directly into the skip, but at the Quincy and Seneca mines skip pocket are used. Hoisting is, of course, in balance, except in some of the old inclines. Each shaft is equipped with a rock house containing grizzlie!'l and crusher, o that about 4 inches is the maximum size of material delivered to the railway cars for transportation to the stamp mills. U DERGROUND CONDITIO S The mine of the district are notably clean and comfortable. atural ventilation commonly suffices, even in the deepest workings, to maintain the air c;lear, fre h, and cooler than the adjacent rocks. The rock temperatme is low. A compilation of existing data on rock temperature by C. E. Van trand, of t~e United States Geological Survey, gives the followmg gradients of increase with depth: From 60 to 1,0 0 feet 1° F. to every 99.1 feet. From 60 to 1,915 feet 1° F. to every 105.6 feet. From 60 to 3,090 feet 1° F. to every 119.3 feet. From 60 to 5,367 feet 1° F. to every 117.4 feet. The rock temperature on the eighty-first level of the Red J~cket shaft in the Kearsarge lode, at a depth of approxnnately 4,900 feet, a.s determined by Mr. Van Orstrand, is 86-!~ F. It seem evident that, far as temperatme 1s concerned, mining may be extended much deeper without any such serious ~convenience a has ~een encountered, for example, m the deep t. John del Rey mine, in Brazil. Except in the upper 1 vels, where water is plentiful th mines are striltingly dry. o far as possible wate; i caught apd pumped froPl sh~llow depths, but sorne scapes and flows down th shnJt and a count for the gr ater part of th wn,t r en ou n tor d at depth. Away from the shafL th workings are du ty, and water has to b pip d from th urfa e for u e in the Leyner drill ; othorwi th air f the tope would be filled with du t. 0 casi nnl dr-op accumulate on the roof of drift , but rar ly i ther enough water to drip. E n in newly opened ground only a little ater is en ountered, and that qui kly drain out. The expen e of pumping, th n, i r latively low. In the a1umet H cla min , ·· with over 200 miles of ' drifts and shafts nnd pra tically ontinuous stope covering b tween 2 and 3 quare mile on the plane of the lode, Lhe total pumping duty amount to only 1,200 gallon a minute, n twith tanding the fact that. removal of so much or during 60 y ar of operation has caused much fra turing, cru bing, and caving of 'the hanging wall and thus ha made th rocks much more permeable than th y were bef re mining began. The drift over of th di tri t may ontain much water, and if the mine working break through to the drift a con iderable flow of water may result, a occurred in tb hampion mine in 1924. MILLING 1 arly all the ore mined from the di trict i ent to the stamp mill . The ex ·eption nre th "rna e "1 encountered in the 1 de and commonly in the cro.11 fis ure ; the ear ent dire t to th sm lter. In all the mill the ore is first ru bed by team tamps of large capacity. Then follow succ ive concentrations and cru hings, involving ball mill, rod mills, and jigs and tables. Flotation follow gravity concentration in the alumet & Hecla and Quincy mill , and ammonia leaching i the final in the former. By the be t practice a recovery of 95 per cent is obtained. The copper content of the mill concentrate or "mineral" range from 50 to 75 per cent and average about 60 per c. ot. A recent development of technical and economtc intere t is the reworking of the great tonnage of old conglomerate mill tailings accumulated in Torch L.ake near the Calumet & Hecla and Tamarack mill · The mill records of tonnage and copper content of the tailings produced yearly for over half a century gave a basis for computing the copper ontained in the entire mas . Both tonnage and metal content were checked by elaborate sampling, and the figures ~bus obtained were in striking agreement with those denved from the mill records. 'I he winning of copper fro~ 1 Several types o~nterial prorluced mines nod mills ~re ~wn bY local terms. "Mass" copper consists of the large bodies of copper round In the fisSUrtlir and in some or tbe lodes ranging lo weight from JOO pounds or 1 ss to hundredS~ tons. Smaller bodies of copper that were separated from the rock were follllcr stored and shipped in barrels and wer consequently known as "barrel" work,
this term is still used. Rock containing small bodies or copper scot to the mills or separation is kuown as "mill" rock. 'l'be concentrate froro the uJill rock Is tmo: as "mineral." "Ore" as used locally in tbc district refers to the sulpbide&n arsenide mjoerals, b11t tbis use or the term is not foUQ"~JrQd. il;l tile Ji'(esqo.\ paper.
CO GLOMERATE LODES the 0 tailings will require years at the present rate of production. The taihngs are elevated b tion dredge and pumped to a plant on shore, where sue fl · d 1 h. hing concentration, otatwn, an eac mg are cru ' · f Th employed, with a very .ati ·actory recovery. . e ost per pound of producmg copper from the e tail- ~ogs i the lowe t in the district. A the copp r i coa.r er and the rock ofter in the amygdaloid than in the conglomerate lode , the former have alway yielded a larger proportion of their copper to initial treatment. Re-treatment of amygdaloid tailing i therefore not yet fca ible. SMELTING The copper in the product delivered to the smelters is already almost wholly in the metallic state and forms from 50 to nearly 100 per cent of the product, the proportion depending on whether it is mill concentrate or mas copper of th low r o-rades. The melting process is therefor imple in principle, but, a most of the product is furnace-refin d, and the tandard of quality for Lake copper i high, much are 1s exerci ed in the m ltino- op ration . opper hat carrie a u1Iicient amount of silv r to make the separation and recovery of thi metal profitable i refined electrolytically. Electrolyti refining has been used a! o in order to purify some of the copper containing mall amounts of arsenic, but in recent years nearly all of the arsenical copp r i furna e-r fined and old for opp r h tl lono- b n r o-ard d b ome con urn rs a X' lling in rtain qualiti and ba commanded a r l clrolytic r pp r. The PPER DEP IT PRINCIPAL TYPES depo i are thu of tabular f rm. There are no irregular bodi , larg in all dim n ion , like tho c of th well-lmown 1 w-grado di ominated deposits of copper in other r gion . In the lode depo it and mo t of the larg r fi sure d~posits the copp r i in the m tallic state, om of it shghtly arsenical. A f w of the larger fi ure d po its r ':he torrn "lode" :S thu; usod in tho region denotes no oro zouo-;:nr;;;el t-;;-t~ bedding nod mado np largely ·or tho rock Itself- a restriction or tho general uot4ra) ~)J!uitlcanco or tbo term as appli~CI to oro doposlt or talltllnr rorrq. carry c.opper-rich arsenides, and many of the smaller ones carry the copper-rich sulphide chalcocite. Copper arsenides and sulphide are rarely and sparingly pre ent in the lodes independent of fi sure . Although o-reat ma es of metallic copper, as much as hundred of tons in weight, have been encountered in some of the fi sure and in certain of the amygdaloid lode , the depo its as a whole are of low grade; the highest average yield for a year ever attained by the district as a whole was about 4Yz per cent; for the last 10 or 15 y ars the average recovery for all the mine has been about 20 pounds to the ton, or 1 per cent, and that for certain individual mines as low as 11 to 15 pounds. DISTRIBUTION IN THE KEWEENAWAN SERIES The economically important kno;vn deposits with a single exception are confined to the portion of the Keweenawan serie that is composed predominantly of lava flows, but they have a wide tratigraphic range within that portion. The principal productive lodes from the base upward are the Baltic amygdaloid, Isle Royale amygdaloid, Kearsarge amygdaloid, Osceola amygdaloid, Calumet & Hecla conglomerate, Allouez conglomerate, Pewabic amygdaloid, and A hbed amygdaloid. The fissure depo its are confined to the arne stratigraphic portion of the eries, though in the main the valuable fis ure deposit and the lode depo its occur in diff rent area along the strike of the formation. The ex ption to the di tribution indicated above h one u h lode, in the formation of that name, ' 11 up in th edimentar portion of the erie . The mineralization at this horizon occurred mainly in andston , and to a le extent in hale. The abnormally high po ition of th lode in the Keweenawan ro k i probably due to the pre en e of intrusive rock in the n ar-by Porcupine Mountain CONGLOMERATE LODES PHYSICAL CHARACTER Much of what i aid below regarding the conglomerate lode is ba d on ob ervation of the alurnet c· H cla ongl merate, which ha been the mo t clo ely t.udied. Mo t of the oth r cono-lomerate , thouo-h th y ha e been less thoroughly explored, app tu· to re embl it in th ir e ential haracter . The conglomerate are compo d mainly of ili eous material, chiefly fel ite and quartz porphyry. They contain few b ulder mor than a foot in diameter, and for roo t of the Calumet & He la conglom rate the large t pebble are con iderably 1 than a foot in diameter. The matrix consi t of fine material of the ame general compo ition as th pebble . here the Calumet & Hecla congl merate thins to 5 feet or 1 it is not a true conglomerate but a ro k of finer texture
THE COPPER DEPOSITS OF MICHIGAN Jranging from coarse grit to and ton . The horizon of thi conglomerate, r cognized for many mile along the : Lri.ke, i marked chiefly by red or brown basic shaly to and r ediment with ome felsitic and. ear alumet it op~n out rather abruptly into a len of typi al f 1 ite cono-lomerate pitching to the north at an angle of about h ' 35° and broadening and thickening down the dip. Where trun ated by the ero ion surface the len ha a hm:izontal extent of about 10,000 feet. On the even ty-fifth level a similar section measures 17,000 feet, and it apparently continues to broaden as it ~es deeper; the lowe t working , at the ninety- ·third level, have not yet been extended to it lateral limits. Within the limits of exploration the thickness 'Of the conglomerate ranges from 5 feet or le s near the margins and 10 or 15 feet where the axis reaches the surface to 30 feet and more along the axis of the lens on the lower levels. In other words, the area of a given cction of the lode increa e from the urface downward to the present depth of development. Explorations along the horizon of the alumet & Hecla conglomerate both north and south of the lens at Calumet have failed to disclose either another thick body of fel ito conglomerate or any encouraging evidence of mineralization. The Allouez conglomerate is very imilar in character to the fcl itic portion of the Calumet & Hecla conglomerate, though much more per i tent and over considerable aTea much thicker. It i lenticular, however, in places pinching out completely or repre- ~ented only by a thin clay seam. uch clay earns have been called " lides' and interpreted as faults, paralJel or nearly paralJ l to the bedding, which locally have cut out the conglomerate. imilar clay seams are found wher the conglom rate is pre ent, and although they undoubtedly repre ent slipping, there seem to be no reason for believing that they have faulted out the conglomerate. It seems more likely, unle other evidence of important faulting is found, that the so-called "slides" repre ent areas where the conglomerate was not deposited. The Kearsarge conglomerate in places closely resemble the alumet & Hecla, but at several points where it has been opened, even though much thicker than the Calumet & Hecla, it i composed mainly of relatively fine material and ranges from a fine conglomerate to grit and sand tone. o. 8 conglomerate i in general similar to the others. Where cut in the Arcadian workings it is somewhat mineralized. The great conglomerate formations in the upper part of the Keweenawan series are in general similar in charnctcr to the lower beds, though in places at least, they contain a larg r proportion of basic materiaL IRO CONTENT The felsite conglomerates thToughout the series are of strong dark-red color. This redness is a property both of the pebbles and of the fm r matrix in which th y are inclo ed. Th red olor of the felsite and porphyry p bbl s, lib o that of the massiv bodie o! felsite and porphyry in th district, is due to the pr sence of small r stal f h matite, which micro. scopic study of thin and P li hed sections shows to be an original constitu nt of the rocks. The available data indicate that these silic ous rocl s of the Kewee. nawan series are relatively rich in f rric compared with f rrous iron, as is shown by th following determina. tions: Iron in Mo1tnt lloughton fel ite and in a f elsite pebble from th1 Allouez conglomerate Felsite pebble from Allouez ('Onglomerate Fe.Oa FeO The iron oxide in the finer part of the conglomerate and in the sandy band i of two kinds- included plate of hematite iu th grain of f lsit , a ju t de cribed, and irregular lastic grains of iron oxide that once w re titaniferou mao-neti.te. In the sand· stone lenses the grains of oxide nre in large part con· centrated in layers of ' black sand," giving the rock a banded appearance; some of the e grains, as seen under the micro cope, ar made up of limonite eros ed by bar of ilmenite. In the thin conglomerate bed that mark the lower part of the s ries the e grain consist mainly of hematite with similar ilmenite bara; very few of the grain are attracted by an ordinary magnet. orne of the iron o:-..ide grains in the Great conglomerate, however, are distinctly magnetic and under the microscope are found to con ist mainly of magnetite with bars of ilmenite; the magnetite is partly oxidized, but the ilmenite is unattacked. These facts suggest that the clastic grains of iron oxide were derived from the erosion of areas of basalt and that although the amygdaloid and trap were largely destroyed and dissipated (though perhap represented in part by the red basic mud rock under· neath the fel ite conglomerates) the compact iron oxide grains, because heavy and chemically stable, were preserved and were accumulated with the fel· sitic debri . . Hematite, the pr vailing oxide in the conglomer~t~, JS not a by-product of copper mineralization; Jt 15 pre ent in all the beds whether mineralized or not, and mineralization in t ad of producing it has ~estroyed it. ( ee p. 103.) The conglomerates, mdeed, though not as rich in hematite as the amygda· loids, contained before mineralization a notable a~ount of ferric iron but, except for a few an1ygda· l01d pebbles, very little ferrous iron.
CONGLOMERATE LODES The average amount of iron in the conglomerate has not been closely determined. A fel ite pebble from the Allouez conglomerate was found to contain 4. per cent of FezOa and 0.6 per cent of FeO. The iron content of the conglomerate i probably very close to 5 per cent of F ez0 3 and 0.6 per cent of FeO. Certain porphyry pebble and boulder much higher in ferric oxide are of interest because of their e pecial usceptibility to copper replacement; those that have been peripherally or entirely replaced by copper form, resp ctively, the copper "skulls" and " boulders" so often described. One of these iron-rich pebbles gave 12.6 per cent of FezOa and 1.30 per cent of FeO. ?111NERALIZA TIO MINERALOGY The minerals that have been introduced into the conglomerate since its consolidation are fev.r and of simple character as compared wi h the c rre pondinomineral of the amygdaloid . Th y all belong to the same general period of min ralization a th cop.per. The more abundant mineral , named in the order of their depo ition, are red alkali feld par early; epidote and pumpellyite, mainly earlier than copper; al ite and quartz, throughout; copper; chlorit , a sociated 1 with the alteration accompanying opper, especially in the iron-rich p b ble . The zeolites and the allied mineral like pr hnit are trikingly ab ent from th conglom rate· laumontite, though pre nt in fr ur in th n.dja ut trap, almo t n vcr p r i t wh re th s fi . ur - conti nue into th onglom rat . It i. ,·id nt therefor that the zeolit wer n t a hara t ri tic and n · nr product of the min rn.lizing lution but tbot th ir formati n wa, primaril. d p 11elen n th natur of the rock through whi h the lution pa. d. ROCK ALTERATION The pper o ur hi ft in th finer c mcntin" material of the medium erat . ndoubtedl in in the andy matri;{ of replaced th ment. Th pebble , especially tho of den fel ite, are ~enerally unrepla ed, thotwh h r and ther bl a hmg may offect their bord rs r xtend throuo-h them along planes of p rmeability. A few p bble of quartz porphyr were attacked by copper, but even where advon d replacement has occurred the phenocry t of quartz and of feld par r main. In some pebbles the f ld par cry tnJs contain minute opper Bakes, and the feld pars may have b n attacked ~hus before the groundmass was replaced. Wh re Irou.-rich pebbles were partly r plac d by copper, the ferne oxide was in part r mo ed and in part r duced and recombined into chloriL , which i a con picuous alteration product of such pebbles, as described by Pumpelly and Lane. In these pebbles, chloritized and partly converted to copper, crystal of barite may be pre en t. The most conspicuou alteration a so iated with the copper wa a pronounced bleaching of the conglomerate from n. rich browni h red to a light pink or almon color. Thi change is recognized by all tho e working on the lode as an accompaniment of good ore and is so intimately and faithfully a sociated with copper from the largest rna e down to microscopic particle as to leave no doubt that an intimate ' causal relation eA'i t between the two. It re ulted from the removal of a part, commonly a large part, of the hematite of the conglomerate with no very pronounced change in the other mineral . In the mineralized portion of the rock the fine material and the small pebbles are generally bleached entirely, but the larger pebbles may be bleached only at their margins, the centers remaining dark. This bleaching, as exemplified in the alumet & Hecla lode, is . omewhat more conspicuous in the lower part of the mine than in the upper part but is to be een practically everywhere. Alteration of another type, whose effect are most conspicuou in certain lenses of sand tone, converted a large part of the rock into pale yellowi h-green epidote. This chano-e re ulted from a recombination of the materials originally pre ent, together with a coniderable addition of ferric iron. Eviden e of alteration of thi kind i to be een specially in the andy mara-ins of the alumet o- Hecla onglomerate where it i thinning down. DI .TR IB TIO OF COPPER IN THE LODE GENERAL CONTROLS f llowing di u sion applie directly to the Calurn t - H la onglomerate, but in it general featme it relate to th other conglomerate lodes in so far a they ar known. The opper o cur chiefly in the andy matri.~ of the medium and coar er cono-Iomerat . It may be pre ent a mall isolated grain , but more commonly it form a pongy rna s throuo-h the matrix; and in e pecially rich places the matrix ha b en largely r placed, o that the ore con i ts of abundant felsite pebbles in a cement of metallic copp r. D po ition of t:;b.e opper in the matrix, more than in the pebbles, probably wa due to physical cau es rather than to differences in compo ition. The contacts between the sand grain of th matrix and the smooth mfa e of the pebble ar much more p rm able than the pebbles them elv and notably more so than th ma es of clo ely pa ked grain in the mid t of the andy matrix or in the larger andy I n es. Higher p rmeability means greater fa ility for the pa age of olution , and all the evidence indicate that the inten ity of mineralization varied in proportion to the quantity of solution that passed through a given volume of rock. The rate at which copper was deposited by replace-
THE COPPER DEPOSITS OF MICHIGAN ment of rock was proportionate to the rock UTface expo cd to replacement, and the ratio of surface to mas i higher in the andy matrix than in the peb?~es. The two controls, then, were favorable to depos1t10n of copper in the sand mixed with abundant pebbles but unfavomble to deposition where sand occurred alone. Not only in detail but in a larger way the copper IS distributed irregularly through the lode. The conSurface O JO (D
w
w --'s 0 POUNDS OF COPPER 400,000
!
FIOVRt; 15.- Variatioo in copper content per loot or dcpih, Calumet & Hecla mine glomerate is distinctly a banded rock, made up of layers or thin lenses that differ in texture. Certain of these bands are well charged with copper; others near by and apparently similar may contain little. This difference in intensity of mineralizatior.. from place to place is again not due to variation in composition but is an evident consequence of difference in permeability; the more permeable layers were channelways for the solutions, and in these channelway more copper was precipitated. larg ly replaced. This may be the re ult of local cau e . For example, solution that has ntered a fairly permeable layer lying n ar the middle of the lode and bounded on ea h ide by 1 permeable band may continue al no- thi hannelway for ome di tan e to a place wh r oth r layer are more permeable but ar dammed off by les P rmeable bands. Farther along the e more p nneable bed may be reached by the olution and may eventually become the principal chann lway in a giv n stretch of the lode. The on q u n that the copper is found in ov rlapping streak or l n. through the conglomerate bed. The well-mineraliz d treak may occupy any po ition in the lode from footwall to hanging wall, and at places two or more good streak may be pre~ent lean conglomerate between. These well-mmerahzed layer may persi t for long di tance or they may be of relatively short extent. RlCHNESS IN RELATION TO DEPTH In the de per part of Lhe alumeL ' Hecla mine, where th alumet He la conglomerate len i broad and thi k, the min ralized treak ond len e con titut a mailer proportion of th onglomerate and the poor len es a larg r proportion. lligher up, whore the congl merato body is mall r ancj. thinn r, the richer streaks predominate ov r the p or one . In cone1 quen e, the conglom rate a a whol is di tin~tly ri h r in the upper than in th l w r par of the mme. The difference in grad , howev r, i duo mainly to the fact that in the lower part a mailer portion of the lode has been mineralized rather than to any material difference in inten ity of mineralization or abundance of copper in the part that ha been mineralized. That i if the mineralized len es of the lower le el could be ' 1 mined without inclu ion of mat rial from the urumner· alized parts of the lode, the ore so obtained would com· ' pare favorably in copper content with that from higher levels, where the lode as a whole is much richer. The riche t rock in the alumet & Hecla conglom· erate, averaging about 0 pounds to the ton for yearly yield, wa e entially at the present surface (see pl. 3 ), and there has been a fairly steady decrea e in richness of the rock mined till at the present depth of oper~· tions the yield i 35 to 40 pounds. The axi of ma.XI· mum mineralization occupi s a position about ~arallel with and a little above the axis of greatest thickness of the conglomerate lens. ( ee pl. 38.) f In a given cro . section of the lode, however, the most permeable layer may not always be the one most There is no con iderable hange in total quant1ty 0 copper at any given horizontal section from tho top to the bottom of the mine-that is, horizontal sheets of unit thickne s at the tw nty-fifth, fiftieth, and sev· enty-fifth levels would each contain about the sa~e quantity of copper. (See fig. 15.) But as dept~ 18 attained and the conglomerate lens increases size, essentially the same quantity of copper is distnbuted
THE COPPER DEPOSITS OF MICHIGAN through a greater volume of rock, with resulting lower grade for the lode as a whole at the deeper levels. In the upper level , where the lode was relatively thin and the ore rich, the entire width of the lode was stoped, and all the copper that it contained was recovered, even though part of the thickness of the lode was too lean to pay provided it could conveniently have been left unmined. As the lode thickened and decrea ed in average grade lower down, streaks that were barren or too poor in copper to pay for handling were left unmined wherever they were thick enough or o related to the good ore as to make thi pos ible. Becau e of the copper thu left the recovery from the lode at depth has been less than the recovery at higher levels, where all the lode wa mined. The actual decline in riclmess from top to bottom, viewed geologically, result apparently from the fact that as the solution rose tlu·ough the conglomerate mass that contracted upward it encounter d a constantly decrea ing volume of conglomerate and consequently traveled through and mineralized a larger and larger proportion of it, until, near the present surface, the cro s ection wa o reduced that nearly all the conglomerate wa traver ed and converted into ore. The inferen e is that had the Calumet & Hecla conglomerate maintained to the surface the same cro s section as it has at depth, the ore near the surface would be of essentially the same grade as that at the deep levels. The inverted-funnel tructure afforded b the onglomerat len i a pecial ca e of the barri r ondition, will h i con idcr d in more detail on page 115. The Allouez is th only o h r onglom rat that ha been explor d to any great ext nt. It ha been opened and mined at three 1 calitie - at the Franklin Jr., Allouez, and lawar mine . Th minerali~ation i very im.ilar to that of th alum t & Hecla ~onglomerate, but in all thre pla th nglomerate L rather thick, and only porti n of it are mineralized. It ha yield d on th whol a l w-o-rad or thouo-h ' b 1t contains len of o-o d grade. notable feature of the Allou z ·onglomerat i th unu ual amount of chalco ite in it wherever it has b en opened. This u!p_hid 9ccur chara teri tically intergrown with caLcite in veinlet along joint ; the al ite i dark because of it chalcocite on en , and th me allic lu t~r and treak of th . ulphidc 11rc ob cured b the calcite. 'hn,l O<'ite o cur similnrl though in le er amount in the Kearsaro-e conglom rat and, indeed m all oth rs examined, in luding the alumet & Hecla. In tbe latter it i appar ntly mo t abundant near tho margin of th or hoot, for it, i relatively ~bundant on the dumps of the entenninJ shafts and, 0 ale s extent, on thos of the Osceola shafts, at the north and south end of the shoot, r spe .tiv ly. SANDSTONE AND SHALE LODES GE ERAL RELATIO S Sandstone and shale become inereasingly abundant in the upper part of the Keweenawan sediments. They are plentiful in the Copper Harbor group and become dominant in the overlying Nonesuch, Freda, and Jacobsville format.ions. The only formation that needs special consideration as a copper bearer i the onesuch. It consists prevailingly of red sandstone and shale, but in the Porcupine Mountain region it includes a con iderable thickness of black, fine-textured shale that covers a considerable area. Immediately beneath this black shale the sandstone, in everal localities at least, is gray instead of red. This gray sand tone and the black shale are the principal copper-bearing rocks of the Porcupine fountain region. The old Carp Lake mine is high up on the north ide of the uplift and at a lower horizon-namely, in red sandstone just below the Lake hore trap. Most of the explorat.ion at the Nonesuch horizon has been done at the White Pine, J one uch, and White Pine Extension mines. These mine are several miles apart, south and outheast of the Porcupine Mountain uplift. The tlu·ee depo its are near pronounced faults, and the ore bodies at White Pine, at least, are associated with minor cro s faults and fissures. The Porcupine Mountain uplift i probably due to a laccolithic intrusion either of the fel ite that forms most of the range, which, however, is commonly regarded as a lava flow, or of coarser porphyry, of ' hich small exposures are known. The fracturing and faulting in the surrounding rocks was, like the doming, a result of this intru ive action. Along the openings so produced the ore solutions probably a cended, and they may be regarded as having come from the same source as the igneous rock. U ERALIZATION A D ROCK ALTERATION In the sandstone, which i arkosic, copper occurs in the more permeable laye1 , pecially those immediately under impermeable covers of shale. It has filled the pore spaces and partly replaced the less resi ta,nt grains and is present also along joints a.nd fractures. The proportion of silver to copper is rugher than in mo t oth r depo it of the di trict, and, in xceptional patches n few inches aero s, ilver may quite di place copper and make up a considerable fraction of the r k. Part of th gra and tone of the Ione uch formation has cl nrly been derived from the red by bleaching, as it repeatedly grades into the red. It is not o clear that the lay r immediately under the shale
THE COPPER DEPOSITS OF MICIDGAN was once red and has been bleached. This alteration can not be as definite! a cribed to copper mineralization a the bleaching in the conglomerates and amygdaloid lower in tb serie . It is b lieved, however, that the bleaching of the sand tone has been accomplished by ulpbur-bearing solutions that deposited the copper. The sandstone that lies immediately belo> the shale is pe1 istently gray wherever exposed, whether mineralized or not, though sandstones at other horizon are characteristically red except near mineralized ro k, where they are bleached gray. The cause for tbi change of color can not be definitely as igncd, but three po sible cause have been recognized- namely, the action of bituminou matter from the overlying hales, of hydrocarbon entering the sandstone through the fault fi sures, and of the solutions that depo ited copper and chalcocite. In the White Pine mine, where the gray rocks were most thoroughly examined, they contain a considerable amount of black asphaltic hydrocarbon, as well as of copper and of chalcocite. The hydrocarbon or the agencies that deposited it may have exerted a bleaching effect on the rocks. The d.i tribution of both hydrocarbon and copper seems to be controlled by fissuring and by the permeability of the beds, so lihat in this small area wherever copper is present hydrocarbon is present also, and the influence of each on the iron oxide has not been clearly d.i tinguished. The hydroca~bon appears to be earlier than the copper, , for ome of 1t has been partly replaced by chlorite, and ome of the chlorite has been in turn replaced by copper. There · is al o the possibility that the black shale itself, which at the White Pine mine is bituminous, reduced the iron of the sandstone immed.iately underneath it and thus accounted for the bleaching in that layer. Hydrocarbon in the shale so far as known is confined to the White Pine area, where the fracture extend into the shale. It is possible that the hydrocarbon may have been distilled from the hale by the igneous intrusion, but it may have 1 been introduced into both shale and sandstone from some outside source. . I~ving 5 speaks of having observed cores of magnetIte m the copper of the onesuch formation, and this statement bas been frequently repeated. ishio s examined specimens from this formation and failed , to fmd 1?-agnetite. did, however, find hydrocarbon w1th the relat10ns that Irving had attributed to magnetite. Observations of the present writers confu·m those of ishio as to both the absence of· magnetite and the presence of hydrocarbon. Anothe~ erroneo~s impression that may be gained I from t~e literature IS that the copper in the onesuch format10n occurs mainly as chalcocite; this belief prob- · 1 Irving, R. D., Coppor-bearingrocksofLakeSuperior: u.s. Oeol s M 5, p. 132, 1 . urvey on. e ishio, Keijiro, Native copper and silver in the onesucb formation, Michigan: Econ. Geology, vol. 14, pp. 124--134, 1919. ably r suited from mistaking hydrocarbon for chal. cocit . amples f all grades of oncentrates from the White Pine mill in ~e. mber, 191 , as r ported hi Mr. Geor<Ye L. H ath, mdwate that about 9 per ce;1 of the copper i native and about 2 per cent occurs as sulphide. Thi proportion of sulphid , however much more than is shown in th onglomcrate ~nd amygdaloid lodes. t the Carp Lal e mine the red sandstone immediately below the Lake bore trap has been mineralized locally from a few inch to a few feet below the base of the trap, and in these places it ha been bleached to a gray color. Tho copper in th bleached andstone is metallic copper, at lea t in larg part. The bleaching of the red andslion m !early r lated to the Copper. On the dump of th tunnel is fi ure material consisting of ankerite or om mixed arbonate con· taining plentiful chalcocite. In the arp Lake occurrence no hydrocarbon " as noted. AMYGDALOID LODES TYPES OF A lYGDALOID Three types of amygdaloidal top of flow have been recognized- banded c llular; brecciated, including some that combine both br cciated and nonbrecciated amygdaloid; and coriac ous amygdaloid. The e types differ from one another in those phy icnl and chemical character , e pe ially in d gree of permea· bility and hematite content, that det rmine the extent to which they are likely to be impregnated with copper. The banded cellular amygdaloid is common in the .flows of the district, but it is not important a a copper producer except in the coalescing type. coriaceous amygdaloids have been till le productive. The brecciated amygdaloid i the dominating type a regards copper production, and it will be de cribed first; the other type will then b contra ted witb it. BRECCIATED AMYGDALOID LODES PHYSICAL CHARACTER The tructural and textural haracteristic of the lava tops that were brecciated during olidificatiou are de cribed on pa()'e 29. Their chi I feature that concern ore depo ition are variation from place to place in d gree of fragmentation- they range from layer of nearly rna sive material 3 or 4 feet thick to thoroughly brecciated layer 6 10 20 and even 50 ' ' ' or 60 feet th.ick; chilled or finer-grained. borders for many of the fragm nt , especially near tho top of the flow; and a high degree of ve iculation of most of the fragment . a rule, tho thicl parts of the tops are w .11 brccciat d and th refor highly p rro able; the thm parts are relatively den e and impermeable; the change from one to the o thor type may be gradual or ~brupt. Commonly the thick breccia tops bulge mto the overlying trap and down into the und e~ lymg flow; J;he thin lode br ccia on the contrary, 18 '
AMYGDALOID LODES inched between a sag of th overlying trap and an ppward bulg of the und rlying trap. The pr ·ence btu·s or slabs of trappy rock in the mid t of the breccia gives in places the effect of a double lode. The brecciated amygdaloid type is well repro ented by the 0 ceola, I l Royale, and Baltic lode . The Kearsarge lode, which repre a transition to the banded cellular type (sec p. 30), has been ubdivided into br cciated amygdaloid, intermediate omewbat broken cellular amygdaloid, and unbroken cellular foot amygdaloid. ffiON CONTENT The red color hown by the top of all the Bow i e pecially con picuou in tho c of the brecciated type. It is believed (sec p. 34) that the countlc tiny plate of hematite to which thi red color i due were formed before the copper mineralization, ha'{ing been produced while each flow wa solidifying wherea the copper was introduced after all the flow and ediment of the erios had accumulated and had been tilted. In the amygdaloid , a in the conglomerate , the red color i present throughout the known extent of the lodes, continuing far beyond those relatively small parts of the lode here copper ha been dopo ited in important amount. The percen tago of ferric iron as hom a tit in these brecciated amygdaloid oxc eels the total p rcentage of iron in deeper parts of the colT sponding flow - in some places by as much a 40 p r cent. MINERALIZATION .Jfineralogy.- Th min ral ompo iti n f the top rock before it n acted on b th or ol n tio n wa imple. Feldspar, h matit and gla or it d itrified equivalent w r the chief on tituent..
the action b th or luti n however, the mineralogy wa varied nnd compl x. B far th ()'r ator number of th long li t of mineral sp ci found in thi di trict were produ d in th , perm abl lava. top by heated olu Lion . Mo t f th e min oral ar either pr ent in mall amount r are n t intima t ly and ignificantl a ociat d ' i h th pp r. om characteristically fill i I , other cur chi fty in crack and fi ur , till oth r, have replac d the rock material, and mo t vari tic ccur in all th way . The mineral mo t intimntel a o iatcd with th copper ar · quartz, al ite, epidote, pump lJ itc (a gr~~ni h fibrous or pri mati min ral ' hich ro. emblo ZOJStte and which wa called zoi it in making th recor~s of drill c r ), chlorite, r d feld par, and prehntte. Datolito ac ompanies tho copp r in parts the Pewabic, 0 ceolo, I 1. Royal , and Ev rgr en ericite i. pro ent plentifully in tho I le oyalo lode but is not intimtLLcly a ociat d with th ~P~er. It i locally abundant in the Baltic lode with tnular relation . Ani rit i n.b undant in part of the Baltic lode. T he hydrous magne ium-aluminum silicate, saponit , i ommon in ome of the rich ground, e pecially in the KoarRarge lode. nalcitc i rath r wide prcad but ra.rrly plentiful and as a rule not closely connected with the opp r. Apophyllite is found paringly with copp r in the Phoenix mine on the A hbed lode. Lawnontite i' tho mo t abundant of the zeolite . It occur::; mainly in fi sw'e \Vith little or no copp r, and where it i locally abundant in amy()'dules tho lode i g n rally poor· th mineral is re()'ard d b tho miners a a bad i()'n and apparently ju tl:r so. ~ill told, th zeolite play a eli tinctly ubordinate and incon equontial part in tho mineralogy of the depo it . Pr hnite and datolit , hydrous silica tc tran itional in chara tor toward the zeolite , arc far mor intima tel connected "·ith t.ho copper. ulphides and arsenides of opp r are pre ent in veins that cut the lod at variou angle . o al o i native copper. The copper of orne of the lodes i somewhat arsenical, but in a lode of low ar enic content the proportion of ar enic may ri e perceptibly in the lode copper clo e to nn ar onide vciH. Native il er i pre ent along with the opper in all the lode , a nerally in amount too mall to pay for , paration but in some of the lodes or part of them, e p ially the P wabic, it adds in appre iablo degree t the value of the product. Rock alteration.- Alteration of the lava top , the filling of the e icle to form amygdul , and the em ntation of th br ia were effected at the same time 1md by the ame olution . The v i le "- re till unfilled when mineralization beaan, for pebbles of am gdaloid included in th f l ite conglom rate contain la tic sand arain in their peripheral ve icle , and thi and ha b en partl replaced b. the arne min ral that fill d the int rior ve icl . Each of the mineral in the amyadule i pr ent between fraament and repla c rock material; conv I all the min ral that r plac d the rock after th magmatic tag arc found al o a breccia cement and a am gdul fillina ; and all the min ral of th · fi. ure have al o r pla,ced rock, emented brec ia, and filled e i le . r commonly the mat rial of the amygdule continue beyond the original vo icle b undar , havin()' partly or ompl t ly r placed portion of the rock. Th c menting of the breccia hu nl o be n necomplished lal'D' ly by replacement of mueh of th finer material en tho lara r fraO'tnents, thou()'h there ha be n ome fill in~ of open pace . The mo t common and abw1dant mineral of the amygdule nrc calcite, quartz, epidote, pump llvite, chlorit , and opp r. Epidote n.nd copper fHor the upp r part f th l de, or tho e which wer riche tin f rric iron; hlorit and pumpell, ito are more abundant in the lower part of tho lode, near the horizon where it grades into trap. Tho same min rals, with the addition of ericit in the Isle Royal lod , nrc th
THE COPPER DEPOSITS OF MICHIGAN Chl.ef t d f the or less commonly in the other lodes. In the rock thu constituents of the breccia cemen an o replacement products. Thus it is evident that the altered chlorite i abundant and intimately a ocialed three processes of vesicle filling, brMcia cementation, with the copper, which 0 curs mainly in amygdull'.l and rock replacement were in eparable and interproducing " shot copper," but also forms filn1 o; related and were a ociated with . the depo ition of plate along joints. Red feld par may be plentiful in copper. places. There ha been no on picu u bleaching, In all the amygdaloid lodes, as in the conglomerate mainly because the r ck n a.r the foot of the lode was lode , the most conspicuous alteration of the country never very red, and be ause hlOI·ite, the predominant rock accompanying the depo ition of copper was a alteration product, is dar1 lik the trap, and epidote pronounced bleaching of the red color. Along with is far less common than in the upp r r d part of the this destruction of the red color, which was due to lodes, wh re it seems to have been formed t ough removal of hematite, the rock suffered an even more a recombination of part of the ferri iron. The lower profound alteration. Thi occurred around the copfew inches of the overlying trap gen rally how s.lteraper in all the amygdaloid lodes, and in general the tion of this chloritic type, and in places a very little same minerals have re ulted in all, though there is a copper is present. marked difference in the proportion of the several alteration minernls in the different lodes aqd even in different parts of the same lode. Two general types of bleaching are recognized and have been called, from lodes in which each is characteristically shown, the Kearsarge · type and the Isle Royale type, or, in descriptive terms, the iron-removal type and the quartz-pumpellyite type. Only here and there was copper deposited in red rock without attendant alteration and bleaching of one or the other of the e types, but the deposition of copper occurred at places in the dark part of the lode near the underlying trap without bleaching, though accompanied by rock alteration. The alteration typical of the red, brecciated upper portion of the Kearsarge and other highly oxidized lode effected a destruction of hematite and the formation of epidote, calcite, pumpellyite, chlorite, and quartz. The rock around the copper was bleached to a light-gray color of greenish or pinkish ca.st and commonly somewhat oftened ; areas rich in copper are thus con picuou . The copper ha been formed largely by replacement of the rock, and apparently having once tarted to form at a given place, it continued growing till con iderable lumps were accumulated . The copper has clearly replaced the altered r~ck in the bleached zone a.round it. Roughly, the d1ameter of a bl ached zone 1s three to four time the diameter of the copp r which it surrounds, but both . the opper and the bleached zone are very irregular. In the I le Royale lode and in many of the lode in the south end of the district the alteration has resulted in a characteri tic grayish-green rock of hard, compa t text~e compo ed mainly of pumpellyite, epidote, cal01te, and quartz. The pumpellyite is the mo t abundant mineral and gives the color to the rock. The copp r occurs in the midst of the bleached rock into which it grew, a in the Kearsarge type. Bleached rock of this type is conspicudus in the Baltic lode and with more q uartm and less pumpellyite, in the Pewabi~ lode. Alteration of a third type occurred in the darkolored basal portion of the Kearsarge lode and more CELLULAR AMYGDALOID LODE The only lode of the cellular type that havo been extensively mined are the Pe' abic amygdaloid lodes. These lodes belong to the " oalescing " variety of the cellular type; they are composed of layers in which amygdule are relatively carce, alternating with layers in which the ga.s bubbles were o abundant that they coalesced so a..s to form irregular flat cavities. The e cavities are filled with vein minerals, and the lode has the appearan e of a banded vein. In places these cavities extend continuou ly in a cro rection of the lode for as much a 10 to 15 feet, though their average extent is much less. ( ee pl. 5 .) In th plane of the lode some of the e openinO' must have been continuous for tens and perhaps for hundreds of feet. The Pewabic lodes are characterized by this type of top, but they contain large areas of fragmental top and orne of the more ordinary type of cellular top. This "coalescing" type of flow i commonly flatsurfaced. The drifts in the Quincy mine that follow the narrow lodes are e entially traight for hundreds of feet and contrast strikingly with drifts following the tops of fragmental lodes. It is evident that the coalescing top, with it long continuous openings, would be relatively permeable and permit the passage of large quantities of mineral· izing solutions. The coalescing Pewabic lodes are of a browni h color where least mineralized bnt distinctly I s red than most of t!he fragmental lode , including the fragmental areas of the Pewabic lode . They are probably 1 s completely oxidized than the e other lode , though some of the difference in the color maY be due to the coar er grain of the hematite. In the coalescing Pewabic lodes quartz and pump.el· lyite are the characteristic minerals, though calcite and epidote are not rare. The rock alteration is of the · quartz-pumpellyite type, and the lode is consequently hard. Bleaching is not as pronounced as in most of the other lodes. An unusual amount of the copper occurs in masses, some weighing many ton ' that characteristically lie parallel with the lode and are
AMYGDALOID LODES Cl·ated with strongly developed amygdular bands. asso M t of the copper, however, occurs m sma grams sc:ttered throughout the amygdaloid, much of it having replaced the rock. The fine copper is also mmonly associated with strong amygdular bands. coin the fragmental Pewabic lodes bleaching is more pronounced and is in part of the iron-removal type. In the upper levels of the Quincy mine, probably in the fragmental lode, nodular masses of porcelanic datolite were present. No datolite was noted in the deeper levels. SCORIACEOUS AMYGDALOID LODES The Ashbed lode, which has been most productive in the Atlantic mine but has also yielded copper in the Phoenix mine, near Eagle River, and in the Copper Falls mine, farther north, is the principal representative of the amygdaloid lodes of scoriaceous type. Other examples of this type are numerous but so far as known contain little copper. As none of the mines on the Ashbed lode are active there has been but meager opportunity to examine the lode. Apparently it varies much from place to place. In the Atlantic mine its character is apparently rather typically "scoriaceou ,"as described on page 176. His composed of amygdular fragments cemented with brown to red sediment and is distinctly soft. The copper was distributed rather uniformly through the rock, and its deposition wa accompanied by rather feeble bleaching. In the Phoenix mine th u pp r or ' gray' lode appears to be similar in haracter but the lower or "red" lode is possibly le s s oriaceous. At Copper Falls mu h of the amygdaloid is apparently rather typically fragm ntal, though containing some ediment. It is well oxidized, and bleach d rock of the iron-removal type is conspicuous in a sociation with the copper. D!STRIBUTIO OF COPPER I AMYGDALOID LODES DISTRIBUTION OF SHOOTS IN THE LODES r one of the important amygdaloid lodes are mineralized over more than a small part of their known ex.tent. The Kearsarge lode has b en traced. for 40 ~es or more but is known to be commercially mineralized for only about 5 miles, though it contains notable amounts of copper for double that distance. The Osceola lode has been developed for but little ~ore than 3 miles along the outcrop, although its ength is known to be several times 3 miles. imilar ~nd.itions exist in the other lodes. The copper, then, IS concentrated in shoots within the lodes. 1 With the possible exception of the Allouez congo~erate and the Ashbed amygdaloid, n ither of ~hich has been shown to be rich at any point, no lode \known to be commercially mineralized in two IV! ely separated parts. This probably does not result from any fundamental cause but is the outcome of generalization from a small number of cases. It is frequently stated in the district that but one mineralized lode is to be found in any one section across the series. This statement, however, is by no means true, as is indicated by the overlapping of the Calumet & Hecla conglomerate and Osceola ore shoots. Moreover, in the closely spaced series of lodes, like the Pewabic amygdaloid lodes and the Evergreen and succeeding lodes, several ore shoots have been developed in the same cross section. Immediately above the main Baltic lode is an ore shoot in the Baltic West lode, and above the main uperior lode is an ore shoot in the uperior West lode. The distribution of ore bodies in each lode appears to be independent of the adjacent lodes and to be governed by local causes, which are discussed under "Causes of ore shoots" (p. 115). DISTRIBUTION OF COPPER IN THE SHOOTS Within the mineralized portion of a lode or what may be regarded a a major ore shoot, the copper shows con iderable inequality of di tribution, both in the plane of the lode and acros the lode. In drifting along the lode through a major ore hoot patches or zone of lean ground, in part too lean to be worked, are generally encountered. ome of these are areas in which the lode is thin; some occur along fractmes or shatter zones. The area of profitabl ground between uch lean area may be regarded as ho'ot of a second order. An example is afforded by the rich outh K arsaro-e-Wol rine hoot, which li s within the main hoot that extends from entennial to Gratiot on the Kear arge lode. The e better shoots differ greatly in ize, but all are large a measmed by the standard of the u ual mining di trict. Their sizo, indeed, is gen rally so gr at that, although they have been developed to depth and length of everal thou and feet, n ither their shape nor the pattern of their distribution is satisfactorily known. There is strong indication, however, that many of the better shoot are of elono-ated hape and that orne of them pitch rather teeply within the plane of th lode. ariation aero the plane of the lode permit clo er inve tigation. The amygdaloid lode are generally rich t near the hanging wall and deer ase in value toward the footwall. Thi i notably true of the K ar arge lodo. It i al o tru of. the Osceola lode, though in the 0 c ola and Baltic lodes ther are w llmineralized ar as near the footwall. The Pewabic amygdaloid lode are narrow, and the variation in di tribution of copper within them is not o noticeable. o defmite information i available for the A hbed lode. In the I le Royale lode, in contrast to the other , the riche t o-round is pretty conistently along the footwall. Permeability ems to have been a controlling factor in determining the placo of depo ition of copper in the
THE COPPER DEPOSITS OF MICHIGAN lode. In CTenoral the top of an amygdaloid was the more permeable, and the greate t volume of olution pas ed through that part of the lode. In highly fragmental lode. orne of the deeper parts are loo e and permeable and therefore wer well mineralized. The rea on for the re er al of the u ual rela.tiou in the I le Royale lode is not entirely clear. The cau e ~hat cern mo t likely is the pre ence of joints or hearing plane parallel to the lode near its ba e. Th o joints did not develop in the frinble mo t ~horouCThly brecciated por~ion of the lod , and the pre once of the minemlized zone in and near ~he join along the footwall uggests that the e fractures, which are con~in uous for long dis~ances, made tills the most perm able portion of the lode. RICHNESS IN RELATION TO DEPTH everal ore bodie in the di trict have given indication of decreasing copper content with incr a e in the depth to which they ha e been mined. The main Superior lode and the up rior We t lode were ' found too poor in depth to justify continued operation , and the Calumet & Hecla conglomerate i known to have decreased rather teadily downward in grade of rock. The Baltic mine i of low grade in 1 the bottom levels, though the hampion mine, on the same lode, ba rich ground in its lower level ; the orth Winona shafts went into poorer ground in the lowe t levels, though there is indication that the southern shafts encountered the ore hoot pitching downward. Are uch changes in grade due to increa e in depth, or are they due to local condition peculiar to each case? Thi subject i more fully di cu ed under "Cause of ore shoot," but it may be aid here that where the ore bodies are be t known the decrea e can be accounted for by condition peculiar to the particular deposit. Thus the alumet & Hecla conglomerate shoot pre nt depth. In the deep levels, a in the upp level , favorable lod r ck is usually well minerauz:~ and unfavorabl ro I is poorly min ralized. In the K ar arge lod , wlu h ha. been opened con. tinuou ly for 4 to 5 mile along the trike, ome stretche in the top levels were poor, such as par of the Jorth Kear arg and Wolverine ground, but other tretche were ri h, u h the outh Kear arge part of Wolverine, th hm k, and the outh Mohawk. The e difference are pretty clearly due to differences in chara ter of the amygdaloid. imilar differences occw· in th lower working on the lode and are apparently due to the am ·n.u e, and not to change in depth. o change in the chnracter of mineral or the type of rock alteration ha been noted even in the deepest working , such a tho e of tho Quin y mine. There i little doubt that for n lode of uniform ize and charact r a depth xist at which tho dearee of minerabation would chang probably for the worseb au e of factor correlat d with increase in depth; if, for example, the lode were feel b:v fi ure , it might be expected a change would occw· \here uch feedin(T fi ure were p!l ed. Th fi ure depo its, with the ingle xc ption of tha.t on the Ahmeek Ma fi sure, have decrea ed in richne downward to such an extent that th have been abandoned, and in this fact there is certainly a ugge tion hat depth i influ· en tial. There i no clrar videnc , however, that the chnnge of grade oh er ed in the lode mine up to the pro ent time are prim!lrily due to increa. e in depth. FISSURE DEPOSITS GENERAL FEAT RID ~ncrease in size down the dip and decrea e in grade m about the same ratio. The amygdaloid in the lower level of the Baltic i relatively thin, cellular, and unfavorable and has the arne effe t on copper content that similar rock does higher in the hoot, even where surrounded .by rich ore .. The bottom of the uperior We t lode IS also relatively thin and cellular. The condition of the bottom of the main uperior shoot is not l~own . It thus appears that in the amygdaloid depo 1ts . the decrea e in tenor with depth is due to changes m r~ck texture that result in imilar changes along the stnke a well:a in~depth. Fis ur depo it or vein have been of relatircly .light importance in the Michigan copper di trict as compared with the lode deposit , though n nwnber of mine , notably the liff, the entral, and the Mine, ota, were operated profitably on fis ur , and the Ahmeek Ma fi ur is being worked by the alu· met & Hecla Co. in conjunction with it. amygdaloid mine. Many other fi ures have been developed nod 1 have yielded considerable copper. But the combined production from fi ure mines has been less than 3 per cent of the total production of the di trict, and the dividends from the e mine have been only about 2.5 per cent of the total dividend . The Qu.U:cy mine has been opened for 8,000 feet down the dip. In this mine one lode was found most productive in t?e upper level , another in the deeper levels, also one m the north end of the mine, another in the so~ th end. On the whole ther is no evidence that there IS a notable decrease in the grade of rock to the The fis ure in the north end of the district trike aero s the beds and dip teeply. They are apparently ten ion cracks that developed during the folding of the hed transverse to the Lake Superior . yncline. The fi sure in the south end of the district strike nearlY parallel with the bed nnd dip somewhat more teeply. They may po sibly be related in origin to the Keweenaw fault. The principal fissures in the miner's sense, are notf ' es o smg e breaks through the rock but rather zon
FISSURE DEPOSITS aile! or interbranching fracture . The width of r:~ fissures or fissure zones ranges from that of a tig~t ack up to 10 feet or more. At many places there 1s c:me bre ciation of the rock within the fissure walls, but little gouge is present. In respect to mineral content, the fissures may be separated into thr~e types-~hose in which copp~r is predominantly nat1ve, to whiCh all the commercially important fissures belong; those that carry copper arsenides; and those that contain copper sulphides. There is no sharp line between the types, but commonly the copper in a singl fissure occurs chiefly in one of these conditions. The gangue minerals of the fissures are the same as tho e a ociated with the copper in the amygadaloid lodes. In some, like the Mass fissure, the mineralogy is simple, the copper being accompanied chiefly by calcite, quartz, epidote, and chlorite, with only minor quantities of other minerals. In other fissures, like the Copper Falls (Owl reek), prehn;.te, datolite, analcite, and some rarer zeolites are plentifully ass - ciated with th comm ner minerals. Apophyllite is present in some, A.nd laumontite i common in many. Certain fi sure arry opper that is distinctly arsenical. ome of the arsenide fi ure depo it are es entially quartz-arsenide vein , though mo t of them contain carbonate, which i in part iron bearing. ~lany of the sulphide veins ontain dolomite and siderite or ankerite, together with a littl pecularite. The mineral of th fissur v in ar similar to those o( the lodes, though th r p rhap rn ro xtreme miati n amonO' th -than among tho lode deposit . Rock alteration along th is not xton i e where they cut through th d n e traps. hlorite i the most abundant altcr~ttion product in these rock, but pumpellyite, opidot , laumontit , and aleite are comm n, and eri ite i form d plentifully along orne of the ulphide and ar enid v in . Alteration of th amygdal id wh re they ar cut by the fi uresis more dilli ult of re ognition b au e of their ~om plex mineralogy. The mo t no teworthy hange 1 a darkening of the red amygdaloid lode for di - t~nce in som places as mu h a 100 fe t on each Ic~e of the fissures. Thi darkening i oc a ion d chiefly by the development of chlorite but in part from removal of hematite, peciall of fin st ()'rain. DIS'l'RIDUTIO OF COPPER I VEIN The distribution of copper in the fis ure vein i ~veu more irregular than that in tho amygdnloid ro~es. In some of the fissur v in mo t of the opper ~Imed large ma e weighing a ton or more, finely dJ eminated copper occurring in but r latively mall quantity. In others small mas es wor commone t · and in a few "stamp copper" (COl per disseminated through the vein material in small grains) predominated. everal masses estimated at nearly 500 tons each have been encountered in fissure vein . It is now impos ible to study the underground relations in the more exten ively developed old fissure mines, which have been closed for some years, but certain deduction may be drawn from the description and report concerning them and from examination of the fissures that cross the Kearsarge lode. In the fi sures that ros the KearsarO'e lode, both those that contain native copper and tho e that ontain arsenides, the copper was deposited in greater part at and near, mainly above, the crossing of the lode. Few if any rna ses worth the cost of getting them have been found more than 400 feet from the lode. D e cription of the old mine trongly uggo t that the fi m in them lil ewi e were more productiv where they cro sed a erie of thick, well-oxidized amygdaloid below the Groen tone flow and at the horizon, above th Green tone flow. A imilar relation i ugge ted in t.he ).ifine ota fi ur , at the outh nd of the di trict. Thi fi ur and the have been found to b but not below their int rection with the ).!(inc otn. onO'lomerato. Likewi e, in the fi ure arrying chalco ite, whi<'h are rather abundant in tho Baltic lode and le o in the I 1 Royal lode, the chalcocite em to be mo t abundant wher r near the points wher th y cut the lode. Thu tho ()'en rule for oppor o currence in fi - sur of all type s m to b that it i. mo t abundant at aud ncar the int r ction of the fi ure with thick, w ll-oxidiz d amygdaloid . This one ntration of copper nt uch int r oction ugge ts that hematite i no ded for precipitation of copper in fi ur a well a in conglom rat and amyO'daloid . cording to de criptions of old fi ure min , the amyO'daloid and conglom rate wer commonl mineralized for a hort distance from the fi sures. In a few place tlli lode mineralization formed commercial ore. What happened to the Kea1 arge lode n ar the intOI ctinO' fi w· s i not o clear, becau e of the min ralization f the entire lode for eral mile along th trike by olution that n cond d along the lod apparent} indep nd ntly of tl,}e fi ure . The net re ult of the min ralization of fi ure and lode is that th lode i darkened ncar th fi ure becau e of chloritization and the removal of hematit and its opper cont nt i omowhut low r thHn away from tho fi sure . Tho rea on for th abttndant pr cipitation of copper at th int r ection of orne of tho fi ur , ith th lode and the impovcri hment of lod n ar int 1 ction of other fi ures ar di cu ed in tho s ction on gene is (p. 135).
THE COPPER DEPOSITS OF MICIDGAN HAS THERE BEEN ENRICHMENT OF -THE DEPOSITS? In either pro pecting for or developing ~re bodies it is important to know the general be?avwr of the type that is under consideration. It IS well e. ta~ li hed that the richne of some types of depo 1ts 1 greatc t near the urface and decreases downward. orne types have a barr n zon at the urface followed by a rich zone, which in turn gives place to ore of lower grade. Many copper depo it ar of the latter type, and it has been clearly hown t~at the n zone near the urface and the underlymg rich zone have resulted from .a leaching of metal from the former and its deposition in the latter-a proce lmown as enrichment. In the following paragraphs the data r lative to the behavior of the Lake Superior copper depo its with increase in distance from the outcrop are set forth, and the conclu ion i reached that in these depo its enrichment h~s been unimportant. NO EVIDENCE THAT THE LODES ARE POOR AT THE SURFACE AND RICHER BELOW In either prospecting or developing sulphide deposits, it is of fundamental importance to recognize that an outcrop that is nearly barren of copper may give place at depth to a zone of rich ore, which may grade off into material of lower grade. In the Lake Superior district there seems to be a general though far from definite feeling that the best ore is some hundreds of feet below the outcrop-that is, that there is a gradual increase of copper for some distance below the outcrop to a maximum depth, below which there is a decrease. Lane 7 has implied his acceptance of this idea by suggesting the explanation that copper is leached in the fresh-water zone and that it attains its maximum richness at about the boundary between the fresh-water and salt-water zones or at the calcium chloride zone, below which it gradually falls off. This influence of water is -liscussed on page 122. If it is true that there is comn.Jilly a leached zone near the surface, prospecting of a lode should be carried on at considerable depth, despite the heavy e}rpense entailed by so doing; if it is not true, a given sum of money may be better expended in examining a greater stretch of lode near the outcrop. The location of property boundaries of course must affect any scheme that calls for extended explorati.on of a lode along the strike, but even so the pr~sence or absence of surface leaching and downward enrichment will materially affect the planning of explorations. Kearsarge lode.- At the outh Kearsarge mine good ore was present practically at the outcrop, and although the ground varied in grade in different parts of the mine, there is no record of a consistent change 'Lane, A. C., Lake Superior Min. . Proc., vol. 17, p. 1~4. 1912. from the surface downward. In the Wolverine and North Kearsarge mines and at least a part of the Ahmeek mine the upper levels were relatively poor and the intermediate and low r levels decidedly richer. In the south end of the Mohawk mine there was very good ground in the upper lev ls, notably south of No. 5 shaft, and apparently the rock in the upper levels of this part of the mine was as good a deeper in the mine or as in the orth Ahmeek mine, which is opened below it. In the north end of the Mohawk mine surface pits encountered good rock, and so far as known the upper levels of that part of the mine averaged as good as the deeper le els, though this end averages poorer than the south end. It appears, then, that a part of the productive portion of the Kearsarge lode was as rich at or ry near the outcrop as at greater depth, but that the remainder of the lode was relatively poor near the surface. A study of all available facts regarding the character of rock in relation to tenor of ore has hown, however, that the areas of low-grade ore near the surface ru:e coincident with areas of relatively thin or cellular, rmpermeable lode rock. Areas of rock of similar character deeper in the mines are similarly low in copp r, a fact which, together with the lack of evidenc that the e portions ever contained more copper, bas led to the belief that the lower copp r content is due to the character of the rock, and that depth below the pre ent outcrop of the lode iB not causally related to it. Osceola lode.- The ouwrop of the 0 ceola lode was richest at the north end of the 0 ceola mine, where, to judge from report '· the rock ' as as good a any found at depth on the lode. Throuo-hout the alumet & Hecla workings on the 0 ceola lode the top level average as rich a at any greater depth. outh of o. 3 shaft, in the Osceola mine, the top level were poor. The ground was also poor in o. 6 haft to the twenty-fifth level and farther south to greater depth. It is thus apparent that for the 0 ceola lode, a well as for the Kear arge, the upper portion wa good ov~r part of the area and poor over the remainder. There 15 a bar of thin lode rock. along the south boundary of the shoot and this rather than any leaching of the lode, is tho'ugbt to b e the cause for the poor ground south. This relation is discus ed under "ConditiOn determining position of ore shoots" (p. 115) · & Calumet & Hecla conglomerate.- The Calumet ' Hecla conglomerate lode was rich at the between o. 3 Calumet and o. 5 Hecla, and aga~ from a point 400 feet south of No. 10 Hecla to beyond o. 1 0 . ceola. In the Osceola mine aod o. 12 haft of the Hecla the shafts went from g~o ore into poor ground with depth. Nos. 6, 7, nn ? Hecla went through poor ground into rich ore. .0·t" Hecla to No. 3 Calumet went f~om rich ore 10 lower-grade ground with increase m depth. 1·. th t ur· and 6 Calumet went tb.rough poor ground to e tieth level before they entered good ore. The outcrop
HAS THERE BEEN ENRICHMENT OF THE DEPOSITS? h Calumet & Hecla conglomerate lode was, in of t e · h A t d · h in some places and poor mot ers. ..rl. s u y short, nc h h h h baracter of the lode rock has s own t at t e of t e c d · l d iff differences in copper content are corrc ate w1t 1 er- . the original character of the rock; where the ences JD h" Poor the felsite conglomerate was very t m ore was ' represented bv a thm bed of sandstone; where or wns
"d lomerate was present at the outcrop m cons1 ercong · 1· d Th · bl thickne s it was wel mmera 1ze . ere 1s no a c l" d · d" ation that the poor areas were ever mmera 1ze mro " h h d ubsequently leached or that the nc areas ave an · f · l been subsequently enriched. It 1s there ore ogwa to conclude that the variation in richne s i on the character of the rock rather than on po 1tlon relative to the outcrop. Pewabic amygdaloid lodes.-. orne of the Pewabw amygdaloid lode were richest near the urface, and som; at greater depth. In general, it may be said that commercial ore was found in the upper level in the centml and southern parts of t.he Quincy property, whereas to the north, in o. shaft, a long stretch of lode was pa ed through before commercial ore wa encountered, and farther north the profitable ore is till deeper. It appears, then, that the condition in the Pewabic lodes are similar to those in the other lodes discu sed. Atlantic lode.-The maps of the Atlantic mine indiCflte that in places stoping was carried close to the outcrop. The grade of the ore in these places is not known, but a the or in the d eper part of the lode wa of low grnde it is rea onable to uppo e that the ore near the urface wa no much poorer, eL e it would not ha e b en mined. necessarily or usually throughout their productive extent. For example, the Cliff fissure was apparently rich in copper at the outcrop east of the Greenstone flow, but No. 4 shaft, which was sunk through the Greenstone flow, did not encounter ore till it had pll.Ssed through that bed. It is evident that the rich and poor parts of the vein are related to the character of the fissure and of the adjacent rocks rather than to position relative to the present surface. imilar .. relations might be cited for many of the veins through the district. NO EVIDENCE OF LEACHING AND REMOVAL OF COPPER NEAR THE SURFACE Isle Royale lode. toping ' a carried close to the I Statistics of production indi ate that the lodes at the outcrop have beeri as rich as at greater depths. The question may be asked, however, if there is physical evidence of leaching of copper near the surface or precipitation at depth. The first point to determine in answering this question is, What constitutes evidence of leaching of copper? At fir t sight the alterations of the rock associated with the copper might be taken for such evidence. The most striking of these alterations is the bleachinO' of the rock around the copper. In places there has been considerable bleaching of the pumpellyitization t pe, with which little deposition of copper was a sociated, and it might be inferred that this bleaching is of the same origin as that seen in rich copper ore and has persisted after the copper was removed. This barren bleached rock, however, seems as abundant on the deeper as on the higher levels. In rock affected by bleaching of the iron-removal type, copper seem always to be present. In the conglomerate there has been some bleaching associated with epidotization and accompanied by little deposition of copper, but this again seems to be no more abundant near the surface than deep in the mine. The amount of bleached rock associated with copp r seem , inde d, to be rather less in the upper than in the d eper parts of the lodes. owhere has bleach d barren lode ro k that sugO'ested that it had once been ri h in copper been seen near the surface. outcrop in th I le Ro ale lod , and although a larger percentag of the lode hilS probably been mined at the lower than at the higher level , thi fact is apparently more tho result f hange of mining method than of difference in chara ter of th lode. Baltic lode.-At all three mines on the Baltic lod the grollDd appears t hav be n good at the outcrop and to have hown no zone of decided nri hment at lower levels. Evergreen and succeeding lodes.- The mine on the Evergreen and ucceeding lodes in the outh end of the di trict have practically all stoped close to th surface with apparently as good ground as Itt any greater depth. Nonesuch lode.- In the onesuch lode llS developed at the White Pine mine there seems to be no evidence to connect grn.de of the rock with it po ition relati e to the outcrop of the l de. . Veins.-Without following out each important vein In _detail, it may be said that in a general way the vemsshow the same relation as the lodes. Most of the Productive v ins that have been developed have had good copper near the surface in places, though not nother evid nee of leaching might be the pa age from rich ore at depth to lean rock near the surface without chang in the character of the lode-forming rock. In the mine tudied no example of such a cb.nnO'e ha be n found . On the other hand, in the conO'lomerate lod there is a rn,th r st n.dy increa e in ~·nd of rock· from the deeper level to the surface. In the amygdaloid lodes change in grade in the mine studi d ha been much more clo ely llS ociated with change in charncter of lode than with increa m distance from the outcrop . It i to be xpected that the ordinary surface water will di olve some metallic copp r, but the metal has not been o di olved in ufficient amount to leav evidence that has been recognized. The deep salt waters a.re also known to contain copper, which will
THE COPPER DEPOSITS OF MICHIGAN be deposited on iron, as ha occurred in the water from deep drill hole in the Baltic mine. ( ee d · · " 121 ) In a few " hemistry of ore epo , p. · places, a at Copper Harbol' and the Algomah mtne, oxidized copper mineral have been forn:ed, but the e are near the surface and afford no eVIden e of movement of the copper. NO EVIDENCE OF ENRICHMENT AT THE SALT-WATER HORIZON In the mines studied no evidence ha been recognized of enrichment at the horizon of the change from fr h to alt water or to calcium chloride water. Lane point out that leaching ha probably occurT d in some hatter zone and cite particuliuly th on in . ection 16, Atlanti . The main evidenc of leftChinO' however seems to be the lack of copper. bl ' If such negative evidence is accepted as valid, the Allouez shatter zone al o must be regarded a leached near the urface; yet this zone ha been opened well below the top of the alt water without encountering evidence of enrichment. The shatter :r.ones are pretty clearly poor in copper, but, all evidence considered, it seem mor likely that copper wa not depo ited abundantly than that it wa deposited and later removed. SUMMARY AND CONCLUSIONS The foregoing detail regarding leaching and en- :·ichmon t may be ummarized a follow : Virtually every lode has been as rich at some place near the urface as in any of it deeper portion . Where the lode i leM near the urface no evidence is afforded by the way in which tho rock ha been altered to indicate that thi portion of the lod was ever rich in copper. In every lode examin d, where lean ore near the urface gives place to rich ore at depth, it has been found that the change coincide with a change in tho original character of the lode rock that eems ad - quate to account for the change in copper content. o evidence of enrichment at the zone of change from fresh to salt water or to calcium chloride water has been found in any of the mines. PERSISTENCE WITH DEPTH All ore deposits must sooner or later show a decrease in metal content with increa o in depth; there is however, a great difference in th depth at which such decrease becomes important in different types of depo it , a.ncl it i desirable to have some basis for judging what may be expected for a given type, ·with due allowance for the fact that each deposit has its own peculiaritie . For example, in the well-known type of disseminated copper deposit which owes its better portions to downward enrichment, it is reasonably certain that the enri h d zone will be but f w hun~ed feet thick. It is al o pretty ' ell tabli hed Lhat m the Tertiary type of gold- il or deposits the bulk of th recio!ll metal i likely to be f und within 1,000 to 2, 00 fee of the sw·face and that many depo it fail before a depth of 1,000 feet is r ached. On th other and in certain gold-quartz dopo it , as tho e of the ~Iother Lode of California, the metal content of the veins peri ts at lea t to 3,000 f et and probably to con. iderably greater depth. In planning the develop. ment of mines to work depo it o extensive those of the Lake uperior c pper di tri t, some ba is ol judgment a to what i to be exp cted at de th i ol prime importan e. In apprai ing the effe t of depth, it i nee · ary to con ider geologic units and noli pr perty unit . Thu· a tudy of the min ralizati n of the alumet , Hecla conglomerate based on the r ult, attained in depth in the property of the 0 ceola Mining Co. wo..tld lead to conclu ions quit differ nt from tho e reached by con idering the ore ho t a a unit. Developm nt ha v b n arri d to o great a depth in certain depo it that th re is a very con 'derable body of fact on' hi h to ba e judgm nt a to what~ likely to be found in dopo it that have not been · deeply developed, a well to what may be expected at till greater depth. ev lopment ha been carried to a v rti al depth of ab u t a mile in the C umet & H cia con()'lomerat and th P ' abic aroygd oid and to more than half that depth in other amygdaloids. To thi depth there has b en recognized no significan' chan()'e in the typ of min ral in the lode. In the conglomerate lode there eom to be le bleachin or removal of the iron in the higher level ; locally at least thi lack of bleaching i rather pronounced. The arne seems to be true for the Osceola lode. That it holds for the other lode i less ertain. Lane tat tha sodium minerals, like analcite and natrolite, are cofi· fined to the upper level . This statement i not u~· ported by the present investigation of the amygdaloid lodes, for analcite has been found on the deeper levels of the 0 ceola mine. In the alumet & Hecla con· glomerate lode zeolites are haracteri tically ab ent. The literature contams num rous statement that silver is more abundant on the upper level . Thee tatemonts have not been verified. o far a regards the recovery of silver from th electrolytic tr 11tlllent of copp r, there seems to be no ba~s for the belief thai the ratio of silv r to copper decreases with depOt. Shoots relatively rich in silver, for the conglomera~~ lode, are present in tho lower level at the outh end the Calumet & HeclEL conglomerate body. It . eo;n, pretty c rtain that ugs rich in silver, which d!SP n) the metal conspicuously, were more abund~t nt the higher levels, but it is not certain that silver wa actually more abundant at these levels than 1 Michigan Oeol. Survey Pub. 6, p. 871, tOll
CONDITIONS DETERMINING POSITION OF ORE SHOOTS It ha al o been st·ated that ulphides are less abundant in depth, but this also has not b en verified. In 0 e I le Royale min it doe not seem to be true, and \phides appear to be as abundant in the lower levels ~the Baltic lode a at higher levels. ome of the lodes lying near th base of the Keweenawan eries were rela.tively high in ar enic, and it has been ugge ted that this may be so b cau e the olution that mineralized the e lode had flowed for a relatively hort distance in them and therefore had been le completely oxidized than the olution that mineralized the higher lode . If thi i true, it would be expected that there would be, in general, an incr a in the arsenic content of a given lod with incr a e in depth. uch an incr a e, however, ha not been defmitely ob erved to the pr sent depth of mining. Mineralogically, therefor , th re i no con picuou change reco"'nized to the pre nt d pth. The available evidence indica te that the native copper of the Lake uperior region wa deposited through a wide vertical ran"'e. As the content of orne of th great lode ha failed to how an stematic decrea e with depth after having been followed down for thou and of feet, opper or may be expect d to persi t to great depth-even greater than i now known. It i not to be expected, however, that all depo it. of the type will attain the same d pth, and the ugge tion some have been comm rcia.lly bottom d i at lea. t warmnted b the rather g neral failure of the fi sure depo i \\-ith in r a d d pth. It i al po ibl that ome lode hn,t ho' ron"' a.lt ration' ith little copper may r pre ent th r t of dopo it richer in their high r ptut', ' hich hav b n 0 DTTIO DETERMINI G PO ITION OF ORE HOOT In genernl th r ar two main factor that ha e influenced th formation of the re hoot -(a) permeability, which ip.ftu nc d th flow of solution , and (b) the character f the r ck , ' hich may have had a ch mical influ nee in pr cipitating mineral . addition tru tural r lation may hav had an tmportant eff ct. The gr at or shoots are r lated . tr·uctural features and p culiarities of th indiVidual lod s. hief amon"' the e ar , on the one hand!. the occurr n e of imperm able or barri r conditiOn in an oth rwi open-t xtur d lode, and, the other hand, the lo al opening up of a prevailtngly tight, impermeable lod . The form r t pe i ~amplified by the 0 ceola lode; the latt r by the alumct & Hecla con"'lomerate and. the Kear arO'e lode. PERMEABILITY OF ROCK The lode depo its are formed only in the more Permeable beds, such as the conglom rates, fragrne;tal amygdaloid , and coale cing amygdaloid , an are con istently lacking in the more abundant but less permeable cellular amygdaloids. The continuous breaks in which the fissure deposits occur also permit the ready flow of solution. Permeable rock, then, is es ential to the formation of such ore deposit as these copper lodes. Roughly, the rocks of the district may be grouped in the following order of permeability: Fi sured rock, fragmental amygdaloid, felsite conglomerate, coalescing amygdaloid, sandstone, "scoriaceo us amygdaloid," ordinary cellular amygdaloid, trappy fragmental amygdaloid more or less lavacemented, trap, shale, fault gouge. BARRIERS OF RELATIVELY IMPERMEABLE ROCK The more permeable rocks are a po itive factor in the formation of ore bodies, but the les permeable rocks may be an important negative factor in directing the movement of ore solutions. This is well hown in some of the ore shoots of the district. The Calumet & Hecla conglomerate shoot i a relatively small len of felsite conglomerate which thin in each direction along the strike. The sandy and shaly bed underlying the fel ite conglom rate ontinue along the trike in both direction . The conglomerate body is thinne t and shortest near the outcrop and thickens and len{)'thens with increased depth, thus giving the effect of an inverted funnel. olutions rising along the lode are converged by the less permeable rocks at the marO'ins of the fel ite conglomerate and by the relatively impermeable hanging,-wall and footwall rock into a teadily contracting channel of permeabl rock, o that mor solution pa e through each unit volume of con"'lomerate in the upper part than in th lo' er part. ( ee fig. 16.) The richness of the ore at any depth i about in inverse ratio to the thickness and extent of the lode at that depth, a fact which indicates that copper was deposited in proportion to the amount of solution pas ing through the rock. The funn ling effect illustrated in the alumet & H cla conO'lomerate p rhaps gives the most favorable onditions for the convergence of olution and the formation of ore shoot ·the Calumet & Hecla shoot, at any rate, i the riche t yet opened. A concentrating eff ct may, however, result if a barrier of relatively impermeable rock interrupt a permeable lode. uch damming may re ult ither from a change in character of th lod its If, a from fragmental to cellular, or fr m th off etting of the lode by a fault. In Rll the amygdaloid lodes th re are repeated examples of c llular imperm able lava in th fragmental p rmeable lava, a.nd con i tently the cellular lode is poor, apparently be ause it ha n.ot permitted the ready passage of olution but has diverted them to the more open rock. The outh boundary of the Osceola shoot is formed by a southward-pitching inclined bar of cellular amygdaloid in the prevailingly fragmental amygdaloid. ( e pl. 39.) The Osceola shoot is richest close under this impermeable bar, and.
THE COPPER DEPOSITS OF MICIDGAN it gradually decreases in richness northward and away from the bar. Above the bar the amygdaloid is fragmental and favorable in character but contains little copper. This relation suggests that solutions rising along the lode were diverted by and concentrated under the bar and that the most copper was deposited where the flow was greatest:r-that is, close lmder the bar. The examples cited above illustrate two general conditions favorable to concentration of solutions and the formation of ore bodies-(a), a lode that is generally impermeable but has areas of permeable rock (see fig. 16); (b), a lode that i prevailingly permeable but has bars or areas of impermeable material so placed as to cause a diversion and concentration of solutions rising along the lode. PERMEABLE t FIGU RE 16.-lnfiuence of varying permeability of rock on flow of solu· Lions and formation of ore shoots In the first class are the Calumet & Hecla conglomerate and the Kearsarge lode. The rocks at the Calumet & Hecla conglomerate horizon have been examined for many miles along the strike, but only at Calumet has a well-developed felsite conglomerate ?een ~oW:d·. The Kearsarge lode for the 4 to 5 miles m which 1t 1s commercially mineralized is in the main a well-developed fragmental lode, but for miles to the north and_ south, so far as lmown, it is prevailin 1 cellular. This class perhaps includes other lo~: about which less is lmown. s In the second class are the Osceola lode and the ~llouez conglomerate. The Osceola lode i prevailillgly fr~gmen~al and permeable for miles and is somewhat mmeralized at many places but it is 1m , own to contam a commercial ore shoot only at 0 where it interr-upted by an inclined bar of c:~~l:; amygdalOid. The Allouez conglomerate is a thick, well-developed conglomerat over long stretches b t locally i repro en ted by a clay "seam" or " lid u, This conglomerate has been found to be so ,:~n mineralized as. to en ourage exten ive de elopment at the Franklin Jr., Allouez, and Delaware mines The Arcadian lode hould probably be assigned this class and perhaps the Winona, of whose character less is known. The shb dis a lode that is permeable o er long stretches and min ralized at several places a at the Atlantic, Phoenix, Arnold, and Copper Fafu mines. The details of the character of rock at these places are not well known. orne of the southern lodes may also be in this lass, but too little was een of them to warrant a cla sifi ation. The rock at the general horizon of tho Baltic lode northeast and southwest of the develop d area is fragmental lava, but the correlation is somewhat un rtain. The principal developed area of th Baltic lode in the opper Range mines is bounded in both dire tions by strong zones of fi suring and shattering. FAULT BARRIER A fault off etting a lode and so situated that the intersection with the lod mak s an angle with the dip of the lode would con titute a barrier similar to an inclined bar within the l de itself. o exampl of an ore shoot under such a fault barr-ier has been clearly established; but the Hanco k fault forms such an intersection with the lodes it crosses, and practically all the ore from the lodes of the Hancock mine and the Pewabic amygdaloid lode in the vicinity of the fault ha come from the north or lower side of the fault. The productive portion of the Baltic lode is bounded by faulted zones with heavy gouges, but their attitude, so far as known, doe not seem particularly favorable to the converging of solutions. The fissures in the north end of the district have been most productive for a short distance under the . Greenstone flow, which has been regarded by myth, Lane, and others as a barrier to rising solution , but there has been slipping or faulting between the Green· stone flow and the Allouez conglomerate, which has produced fault gouge or " lide," and this gouge i probably the true barrier so far as one ex:i t · There can be no doubt that the fissures are relatively rich under the Greenstone flow or "slide," but the cause may be a combination of barrier and chemical effect, as is shown on page 118. In some of the fissures the copper is said to spread out under the " !ide.~' At the White Pine mine the J onesuch shale thought to have acted as a barrier. Solutions rising along fissures have spread out when they reached the shale, forming an ore shoot in the sandstone under the Lane, who favors the hypothesis of downward· moVlllg solutions, regards the White Pine fault n s barrier, with the ore shoot above it.
CO DITIO S DETERMINI G POSITIO r OF ORE SHOOTS FOLDS The broad pitching anticlines, like the Allouez, Baltic, Winona, and Mass. ~nticlines,. might have a nverging influence on olutwn and thus ~~duce ore shoots. If solutions were rising along a lode they would have a tendency to concentrate toward the crests of uch anticline . everal important ore shoots, including the Kear arge, Baltic, Winona, and Mass, are situated on such anti lines, though their riche t portion are not con istently near the crest , and in detail the di tribution of rich and poor ground is far more dElpendent on character of rock than on structural position. The Isle Royale hoot, indeed, hn its riche t portion near the trough of a syncline, and here too the charact r of the lode rock seem to have a more effective control than po ition on the syncline. The effect of the anticline i therefore omewhat uncertain. STRIKE FISSURES Both Hubbard and Lane have uggested a relationship between mineralization and fi sures parallel to the lodes, and they have cited the Baltic lode particularly as an example. Most of the numerous trike fissures in the Baltic lode are slightly teeper than the dip of the lode and cro s it at a low angle, o that it seems unlikely that they were produced by simple slipping between beds of trap, as sugge ted by Hubbard. They may, rather, have been formed by the forces that produced the K ' nnw fault. Regardle of how the fi ur w r form d, h w ver, the kind and relation of th min ral in th fi ure and in the lode indicat that the min ralization in the lode and that in the .fi ur had a omewhat similar relation b t' n trike vein and lode mineral- ~ation exi ts in the I l Ro al min . The Branch fi ur , in the 1in ota mine, cro ed lbe nlico lod at a low angle. The ali o lod was mined profitabl abov th int 1 e tion but' a found 1 striking generally aero the lode are numerou on all the anticline , and practically all the lodes in the district are cro sed by uch fi sur s. They are abundant in the Kearsarge lode north of the orth Kearsarge mine, in the I le Royale mine, in the mines on the Baltic lode, and in the Evergreen and ucceeding lodes on the Mass anticline; they are present but not abundant in the Quincy mine, the Osceola lode, and the Calumet & Hecla conglomerate. Cro s fi ures are especially a bun dan t in the north end of the di trict on the Keweenaw anticline. The available descriptions of the fissure deposits in this end of the di trict indicate that in many places the lodes were mineralized near the fis ures and that some were mined for a short di tance from the intersections but were soon abandoned becau e of marked falling off in richne . This relation suagests that th lode rock was mineralized by solution leaking from the fissures, and so does the fact that in the Kear arge lode the ore near the arsenic fis ures is distinctly arsenical. Here, however, the lode i consi tently poorer near the fi sures than a,: ay from them, and the general relation do not indicate that the e fi sures erved as feeders for the main mineralization. One prominent fi sure eros es the Calumet & Hecla conglomerate, but the mineralization do not eem to have been related to it; in general, the lode is perhaps poorer near the fis ure. There is al o a prominent fissure eros ing the Pewabic lodes, and the lodes were di - tinctly poor r near it in the upper levels and apparently al o, though to a le marked degree, in the lower levels. prominent fi ure i also pre ent in the tlantic mine, but its relation to mineralization is not lmown. On the whole there seems to be no close r la tion b tween the mineralization and the cro s fi ure. It is, th n, fairly clear that there wa ome mineralpoor below. In th P , abic, 0 c ola, alum t " J Rc.cla conglom rate, and earsarge lod , however, l~ke fi ure n.re not on pi uou , and there i no endenco to sugge t that the mineralization of the e lodes i dependent on strike fi ur s. It eems, on the whole, that trike fi sure may well be a cau e for ore ~hoo t in lodes, but they d not appear to b pr ent m. all the lodes nor to be a nece ary condition of mtneralization. ization of lod where cro ed by well-mineralized fis ure ; and it i hown on page 110 that the lodes also affected mineralization in the fis ure. It does not eem likely, however, that th main mineralization of the larger lode depo its extended outward from CROSS FISSURES b Fi ure ro ing the strike of the lodes have al o een regard d for a long time a a po ible cause of ~re hoot , and such fissures and their relation to ~tru ive fel ite b die ha e be n empha ized parhcularly by T. . Woods. 9 teeply dipping fissures ' WOOds~: acd Min j T. ., Tho porphyry iutrusivos or tho M·~~iyan copper district: Eng. · our., vol. 107, pp. 2W-302, 1919. 5 540---29-9 cro fis ure . In sugg sting a relation to fel ite intrusives, Woods ha called attention to the felsite bodie , including that of Mount Bohemia, under the Keweenaw anticline; that under the Kearsarge mines, below the Allouez anticline; tha~ east of Calumet; and that at the Indiana mine. He belie e that the cro .fi sur s reached the intru ive bodie and that the ore solution pas ed outward from these bodie along the fissure . . The pre ence of fel ite under orne of the antiCline and the sugge tion that intrusive bodies may underlie other anticlines, where not expo ed, is discussed under" tructure" (p. 50). On page 124 it is shown to be po sible that the ore solutions originated from the same soul'Ce as the small intrusive bodies and that
THE COPPER DEPOSITS OF MICHIGAN some of the sulphide veins may bear a clo e relation to certain exposed intru ive bodies such as the one at Mount Bohemia. With due con ideration of all th se suggestive relations, the evidence does not s~em cient to prove that the main lode were mmerahzed by solutions conducted into them, by wa of cross fi sures, from the small expo ed intru ive bodie , or from unexposed bodies of the arne type. The most serious objection seems to be the lack of mineralization in many favorable lodes crossed by the fi ure . If the olution passed along such fi sures and from them into the permeable lodes, it would be expected that every lode that was physically and chemically favorable would be mineralized, at least to some extent, where crossed by a mineralized fissure. For insta.nce, two fragmental well-oAidized amygdaloid have been opened in many places between the mineralized portions of the Calumet & Hecla conglomerate and the Osceola amygdaloid, but nowhere have they been found to contain much copper. This fact is difficult to reconcile with the hypothesis of mineralization by cro s fissures, but it may be explained if the elutions found en trance deeper in the lode. It seems clear that the lodes have influenced the mineralization in cross fi sures and that there has been some mineralization of the lode outward from cross fissures, but it also seems unlikely that the chief mineralization of the great lodes has been eff cted through the cro s fissure . The helpfulness for prospecting in recognizing a relation of ore hoot to cross fi sure , to anticlines, or to fel ite bodies is apparent, but this fact makes it all the more necessary to beware of exaggerating the closeness of such relation . INFLUENCE OF THICK FLOWS Lane ha pointed out that some of the ore shoots may lie below unusually thick flows. This relation has long been recognized for the fissure deposits ?eneath the Greenstone flow, but, as already suggested, Its real cause may be the "slide" at the Allouez conglomerate. An examination of the geologic map does not seem to give strong support to this idea ior other known deposits. The Kearsarge lode is a long distance below the Greenstone flow, which, moreover, is not very thick over the southern part of the productive area of the Kearsarge lode, and the "Big" trap above conglomerate is a heavy flow below this lode. There are no particularly thick beds above the Calumet & Hecla and Osceola lodes at Calumet. The beds above the Pewabic amygdaloid lodes at Quincy are rather thin.. The flow above the Isle Royale lode is thick but not exceptionally so; the thickest and most massive flow in the section at the Isle Royale mine is the Mabb ophite, which lies below the Isle Royale lode but above the Baltic lode. Farther south at the Copper Range mines on the Baltic lode, the thickness of the Mabb ophite has decreased to ordinary size and the thickest bed lies near o. 8 conglomerate at a considerable distance above the Baltic. gether, ther"t.for , thor of a relation bet' en ov rlyin()' b d . eem to b no I a.r indication }mown or dopo its and thick CHEMICAL COMPOSITION The ferric iron of the rock i believed to be a controlling factor in the pr ipitntion of m ta.lli copper. Ferric iron i abundant in all tho amygdaloirl nnd con. glomerate that have fl. ph ical character favorable to ore d po ition and wa ther for pre ent in nil the bed through whi h larg olume of . olution pa ed and becau e of thi wide distribution i may not hav~ gr atly in.fluenc d th localization of the ore hoots in the lode . Ferric iron may, howcv r, hnve hnd a much more activo part. in forming the ore hoot. in t.hc fi ure depo its. Development how that in the Arsenide fi . ures and in the 'i:a. fi ure, cro ing the Krarsarge lod , mo t of th copper and ar. enido wa precipitated nea,r the lode, hiefl abo e it. De ription of the fi ure dcpo it in the north end of the di trict indicate that a in1ilar relation betw en opper and a group of well-oxidized fragmen tnl amy gel aloid wn rc ognized by tho. e who explored th fi . ure . In the . outh end of the di trict the fi ur worked by the 1Iinesota and a,djoining mine cmTi -d their opper at and above their inter ertion with the Mine ota conglomerate, a typical fel ite conglomerat . A imila,r relation is shown in orne of the fi. ure cro. ing the Baltic lode. Ore hoots in :fi ure , then, nppenr to occur mo tcommonly at the inter ection of the :fi ure with a thick, well-oxidized bed. The foregoing statement regarding the conditioru favorable to the formation of ore . hoots imply, of course, that mineralizing solution ro e along the lode and :fi sure . That even under the most favorable condition solutions in ufficient volume to form ore bodies traver ed all the favorable lode nnd all the fi · sures is not probable. How the elutions may have gained acces. to the lodes and fi sures i discus ed on page 125. It mAy be stated here that the answer to this que tion would be very helpful in the earch for ore bodie , but at present the problem is ob cure, little recognized evjdence being available on \Vhich to base conclusion · It ~eems certain, however, that many favorable lodesm fa,ct, most favorable lode over long tretches-werc not traversed by ore-bearing solution in large volume and therefore do not have ore shoots. GENESIS OF THE DEPOSITS SIMILAR ORIGIN OF ALL TYPES The outstanding trait that is common to the copper deposits of Michiganto fissure depos1t
well as to lode deposits in widely differing rocks-:-! the fact that the copper is mainly present a natJVC metal. In copper deposits the world over the occur· renee of native copper, except as an alteratio~ prot· uct of other minerals, is unusual and has eV1dent Y
GE E IS OF THE DEPOSITS It d from conditions that are not wide pread. re u e · h d ·t · opper is abundant, however, ill t e epo 1 s Native c f 1 · h · t of all types in th1s d1 -a act w uc. ~ou:t . o Condition or at least a clo e rmilanty ill common conditions of deposition for all the depos1ts. FEATURES COMMON TO ALL TYPES A common re ult in the d.eP? its of d.ifferent types · ht come either from a unilar olutwn regardle s nug · h' h · d f of the kind of rock ill w 1c 1t acte or rom some f ture common to all the rock that produc d the eault. The idea of the copper being carri d in solu- ~on 8 native metal and precipitated a uch is regarded a unlikely. ( ee p. 129.) If the features common to all the type can be eparated from the numerou feature that ar not common to all, the cause of copper precipitation and the nature of the mineraliziAg olutions are more likely to appear. uch a com pari on may · be fir t made between the conglomerate and amygdaloid lode and extended to the other~. All the rock th'at have been mineralized to form lodes were oriainally relatively permeable. The lode depo it are in the conglomerate , in fragmental and coale cing amygdaloids, and in sandstone, which, however carrie ore only near fi. sure . They are con istently lacking in the relatively impermeable hale , trap , and cellular amygdaloid . The fi. ure were of course permeable regard! of the type of rock through which th pa d. In original min ral mpo ition th onalom rate are much impl r than h am gdal id , yet a the copper in the lod f both typ i native, all the condition e entia.l to th d po ition f nativ copper mu t have be n pr nt in b th. The out tandin()' f atur that e m to have been common to th tv.- typ of ro k b fore th copper mineralization wa the pre en e of abundant f rric oxide in the form of h matite. Th and tone lod al o are red and h rnatite bearing, and the fi ur seem to be produ tiv only ncar the point where they cro r d con l rneratc or amygdaloid. The mineral of the re-d po iting period that ar common to the onglomerate and the amygdaloid lodes are omparativ ly f w. red pota h- oda feldspar was form d early in lode o£ both type . fold par i n t on pi uou in all th amygdalotd , but in om of those in which it i lacking a Potash mica, eri it , is pre nt, though in the I le Royale lode, wh re the ericite is particularly A.bundant, it eems to hav been formed, in part at lea t, late the mineralizing period. Epidote and pumpcll~tte are pre ent in both conglomerates and amygdalotd . hlorite is abundant in the amygdaloid and much le s pl ntiful in the conglom rate . Calctto and quartz are abundant in both. These compri e the mineral that are at all common in the two types of lodes. The whole series of zeolites and allied mineral , which range from rare to abundant in the amygdaloids and the fi sure deposits, are practically absent from the conglomerates. There can be little doubt that they have resulted mainly from a recombination of elements in the amygdaloid lodes, which, in contrast with the conglomerates, were chemically unstable in ontact with the ore-forming solution . The boron of datolite, the fluorine of apophyllite, the pota h of feld par and sericite, and perhap other element be ide the copper doubtle s came from the solution and not from the rock. Mo t of the mineral introduced into th amygdaloids and the fi ures, whether filling ve icle or fracture or replacing the rock , an not b reaarded a e ential to the formation of the native copper, but a ornething is known of their conditions of occurrence el ewhere and, from experim ntal work, omething of their range of tability, th e mineral indicate th phy ical condition under which the native copper was formed. The triking alteration that is common to the lode in conglomerate, in sandstone, and in amygdaloid is the bleaching of the red rock in the immediate vicinity of copper and a a rule nowhere el e. Thi bleaching has resulted in different minerals in different lode , but the chemical change in all lodes i in the same direction- namely, toward a removal or r cOlllbination of the ferric iron. In the fi ure depo it a similar tend ncy i hown by the alteration of part of the hematite and th formation of chlorite in the red lode n ar the fi ure intere tion . The e ential feature hQwn by all the types of d po it are therefore perm ability and pre ence of f rri iron originally and removal or recombination of the iron clo to the introduced opper. SINGLE PERIOD OF MINERALIZATION The mineralization ha been a igned by various writer to different time according to their conception of the oriain of the ore . Pump lly, believing that the copper wa leached from the and tone overlying the trap serie , upposed , that th oro wa depo ited later than the trap and the o rl ing andstone. The general abandonment of the idea of d rivation of the copper from the upper and tone r mov that ba i for the dating of the ore . Van Rise and Leith 10 rega.rded the main mineralization a confined to middle Keweenawan time and therefor as of essentially the arne age a the mineraliz d rock . They state, how Y r, that mineralized boulde1 deriv d from underlying bed are present in some barren conglomerate and thus indicate an earlier period of mineralization, before the conglomerate were laid down. They do not mention where or by whom thi ob ervation wa made. In the work
THE COPPER DEPO ITS OF MICHIG on which the present report is based no p~bb~es or boulder that had been mineralized before be~g m?orporated in a conglomerate were seen. ifmeralized amygdaloid boulders in congl.omerate were f~un~, ~ut there wa good reason to behave that the mmeralization occurred long after the conglomerate was ~epos ited. The hypothe is of a preconglomer~te. peno.d of minera.lization needs verification before It 1s ent1tled to credit. Lane believe that the ores were deposited while the basalts were till hot and therefore, presumably, fairly soon after theu· formation, but his conception of imbibition of surface waters and of the dependence of copper deposition on the present position of water zones appear to imply mineralization after tilting had be n accomplished. He regards the arsenide and sulphide veins as possibly of la.ter and independent origin. The conclusion reached in this work is that the major mineralization was effected during a ingle period of somewhat complex activities that followed the completion of all the e ential deformation that the rocks reveal. This deformation, it is thought, began during the outpouring of the Keweenawan lava and the deposition of the associated sedilnents and was completed shortly after theil· accumulation wa finished; the mineralization prouably followed lin media tel afterward, perhaps overlapping the last structural adjustments. The evidence upon which this conclusion is based is summarized below. The Keweenaw fault bends with he cro fold , such as the Keweenaw anticline, the Allouez anticline, and the Isle Royale syncline, and its change in direction are too great to be rea onably explained in any other way than to as ume that the fault itself was folded. It is therefore probably older than at least the last of this folding. The cross fissures from Allouez narthward are tension crack radial to the cross folds and produced at the same time. The countless minor fractUTes that cut the rocks are also most plau ibly ascribed to the stresses that produced the faulting and cross folding, because these minor breaks are more con picuou and numerous near the places of major deformation and are di posed conformably to them. Copper mineralization did not occur in the Keweenaw fault itself, so far as known, but it affected the highly fractured zone adjacent to the fault and there- ·fore was undoubtedly later than the fault and this attendant shattering. The mineralization in the of all types from a single ource o.nd dUTing a single period. The sulphide. v ins co?-tain intergrown metal. lie copper or ro rge mto native copper voins. The same is true of the arsenide veins, with the modifies· tion that the copper is ar nical, as are some of the copper fi sures them clvo , and t~e arsenide veins carry some chalcocite. The sulph1de and arsenide fissures are thus appar ntly of the same source and of the arne age as the d posits of metallic copper. The domical uplift of the Porcupine Mountains is not closely conn cted with the other structur~ ol Kew enaw Point and i probably due to intrusion. Faults of varying magnitude are a sociated with the uplift. The age relation of the dome to the other structural features of Keweenaw Point is not known, though the latest rocks of the region are involved in all of them. The precipitation of native copper and subordinate chalcocite along and near the faults ol the Porcupine Mountain region may therefore hare occulTed in a different period from that of the main mineralization far.ther northea t, though there is no evidence that it did. imilarly the sulphide fis ures that extend out from the intrusive rna s of Mount Bohemia may belong to an ind pend nt period, but it seems more reasonable and in accord with the known facts to assume that all the mineralization was accomplished in a single period. Such a period doubtless was of considerable length. Some of the minerals wore formed eo.rlier nnd some later in the period, and the same minerals were deposited at different times in different place. . me veins apparently were lightly earlier than themmeral· ization of the lodes they cut, and some were. la~er . There was, however, no cessation of mineraltzallon from the beginning to the end. As all the rocks of Keweenawan age known on Keweenaw Point were affected by the structural deformation already described, it is evident that the mineralization was later than the Keweenawan rocks of the district. It is believed, however, from evidence given on page 124, to have been accomplished within the limits of Keweenawan time. HYPOTHESES OF ORIGIN cross fissures was of cour e later than the fissures. The mineralization of the lodes was similar in character to that of the fi sures, and the presence of arsenides and sulphides in the lodes adjacent to fissures containing these minerals is a further indication of their close relation. It is clear that the copper is later than the roc~ in which it is found and was therefore introduced mto them. The important elements of genesis of such epigenetic deposits are the source of the coppe~, ~be method of transportation, and the cause of prccipi~· tion. Two contrasting views of the origin of t Michigan deposits are presented in the litera~u.re and may be designated as that of descending ongl.ll that of ascending origin. DEPOSITION BY DESCENDING SOLUTIONS SOURCE OF COPPER h thesis of Pumpelly, who first formulated the YP0 b 0 Tho same minera~ association in all these types and the interrelation of the types indicate mineralization descending origin, supposed the copper to have ~ey derived from the sandstones that originally over
GENESIS OF THE DEPOSITS the traps. The failure to find copper in the sandstone b ds where they are still present has led to the a:andonroent of the idea that they were a source of ~he copper. Lane, whose views are presented in detail in his report on the Keweenawan series, suggests different sources, all directly connected with the basic lava flows. He suggests that the copper was dissolved in the waters of desert lakes or playas that collected on the surface of the lavas. The copper in the waters was either derived from the weathering of the lavas or was contained in volcanic emanations given off by the lavas and collected in the surface waters. Lane further suggests that the copper may have been derived from the solution of the copper that is disseminated in the freshest traps. !ODE OF TRA SPORTATION Pumpelly suppo ed the copper to have been leached from the sand tones by surface waters and to have been carried into the underlying rocks by gravity. At the time of Pumpelly's study the depo its had been developed only to shallow depth, and the assumption of uch a movement of the solutions seemed to offer no difficulties. Since then the deposits have been developed to a vertical depth of more than a mile or a distance down the dip of the lodes of more than 9,000 feet. The presence of strong mineralization far below present sea level can hardly be attributed to the action of ordinary gravit irculation under pre ent condition . Moreov r, the d per lev ls of all the mines are e entially dry. Pocket of water encountered on thee levels quickly drain off and remain dry. mo deep drill hoi , however, maintain a small flow of water for considerabl periods at least, and in the Baltic and oth r mines the water i under some pre ure. The region i one of moderate precipitation, and the upper lev Is of the mines contain abundanti water. The failure of the mfa e water to ink through the lodes to the deep openings indicates that t~e ordinary gravity circulation to gr at depth is very slight. Thi conclu ion, of cours , coiT sponds with the general experience in other di tri t . . The position of the ore shoot beneath relatively unpermeable barriers, such as that of the 0 ceola lode, the White Pine d posits, and the fis ure deposit below the Allouez "slide " is also hard to reconcile with gravity circulation but suggests solutions rising from depth under pressure. The fact should be kept in mind concentration of the ores of iron in the neighboring iron country, where the depo it have been opened to con iderable depths, is attributed to circulation of urface water , but where the iron is concentrated near impermeable rocks it is above rather than below them. .The difficulties of atliributing the movement of the llllneralizing solutions to ordinary gravity cir ulation ~ave bee~ recognized by Lane, who ha suggested the YPotheslS of 11 im bi bi tion ." This hypothesi app ar1 enlily suppose that the flows remained hot and the ve ides were filled with hot ga es or liquids till the rocks were tilted to their present po ition and were, in places at I a t, covered by desert lakes or playas containing opper in olution. As the rocks cooled the gases and liquids in the openings contracted and thus made room for the solutions that covered the outcrops to pass down the lode . This hypothe is ha the advantage over that of ordinary gravity circulation in that it accounts for the space necessary for the solution to enter at areat depth. It only allows, however, for sufficient solution to fill the cavities and necessitates more highly concentrated solutions than are known as smface solutions in order to produce the deep ore shoots. Moreover, it encounter::s most of the difficulties of ordinary gravity circulation as to position of ore shoots under barriers and slight circulation at depth. Lane point out that the tend ncy to form a vacuum as the gase contract would produ e a 11suckina" or 11in1bibition" effect. Thi , however, could help but little in overcoming the friction of deep circulation, a at be t it could amount to only one atmospher-e, or the pre ure of a 33-foot column of water. Lane ha al o applied the idea of concentration by diffu ion to the Michigan depo its. Thi id a apparently a sume that the rocks are saturated with e entially stagnant water or olution. This solution would dis olve some of the copper that is di seminated through the flows, and the copper so dissolved would tend to become uniformly diffu ed through the solution. It is suppo ed that certain of the rocks had a precipitating effect on the copper in solution. Where the copp r wa being precipitated, the olution would contain le than el ewhere, but the diffu ion force would can e more to come in to equalize the concentration. This in tmn would be precipitated. By this proce the copper di aminated through the traps would be concentrated in certain parts of the serie . This idea of concentration doe not encounter the di:fficultie in olved in that of deep gravity circulation. That the pre ent-day deep water contain copper i indicated by analyses. Water from a deep drill hole in the Baltic mine precipitates copper on crap tin, and Mr. W. H. Schacht, general manaaer of the Copper Range Co., tates that the same water di olved the copper from fuse caps that chanced to fall into it. The hypothe is of diffusion certainly has attractions in expl!l.ining the filling of amygdular cavities with copper and other mineral . It is difficult, however, to reconcile this hypothesis with some of the broader features of copper occurrence. If the hypothesis is valid, it i not easy to understand why a generally fragmental well-oxidized lode like the 0 ceola is not uniformly mineralized throughout its extent. Under this hypothesis there would seem to be nothing except the character of the lode rock that wo11ld tend to cause ore shoots, and there seems to be nothing in the proc-
THE COPPER DEPOSITS OF MICHIGA e s that would cause the precipitation to occur under impermeable barriers. In fact, it would be natunl to expect that precipitation would occur throughout all amygdaloids and conglomerates, though varying in amount according to th character of the rock. The diffusion hypothesis fails to eA.-plain why the Calumet & Hecla conglomerate is rich while, so far as known, most of the other conglomerates are lean or barren. The same difference in richness is shown by amygdaloids that appear equally well adapted for mineralization. It is difficult to explain the concentration in sandstone adjacent to fissures under the onesuch shale at a con iderable di tauce from lava flow . It seem , then, that although the hypothe i of diffusion avoids some of the difficulties presented by that of gravity crrculation or that of "imbibition" it encounters others that make it equally hard to accept. CAU E OF PRECIPITATIOI Pumpelly considered that the copper was taken into solution in the oxidized form as sulphate or carbonate, as would be expected and is known to occur in the action of smface water. He further supposed that the e solution in pa sing into the trap bed encountered abundant ferrou minerals and that the copper solution were reduced and the ferrous iron oxidized to ferric iron, re ulting in native copper and . the ferric mineral hematite, epidote, and chlori te. The abundance of hematite and other ferric mineral in the lodes evidently sugge ted this explanation. The modifications of Pumpelly's idea likewise assume th~t the_ copper i in the oxidized state, though Lane con tder 1t to have been carried as chloride in the waters of desert lakes that were sucked into the lodes; he supposes the copper to have been reduced and the iron oxidized e sentially as outlined by Pumpelly. CHLORIDE WATER CONCEPTION At Lane' suggestion, G. Fernekes undertook what amounted to a laboratory demonstration of Pumpelly's method of copper precipitation. He found u that und~r certai_n co~di tions. f~1-rou s chloride acting on cup~lC c?Jonde will pre01p1tate metallic copper and ferne oxide! one _of the conditions being the presence of. an alkahn~ mmeral to neutralize the hydrochloric aCid formed m the reaction. Prehnite and datolite were foun~ to work atisfactorily as neutralizers, whereas ·with labradorite and laumontite no native copp~r was produced. Fernekes expre sed these reactwn by the following equations: 2Fe012 + 20u012 20uCl+ 2FeCl3 2FeCl2 + 2CuCl 2Cu + 2FeCl3 FeCl3 + 2H20 Fe(OH)2Cl + 2HCl. These experiments, together with some mad b H. ~oke 12 _slightly earlier, which showed tha: thy tron mm~rals, siderite and hornblende, p_reclpltate metallic copper from cupric sulphate solutiOns, cau ed Lane to adopt the hypothesis that the " Econ. Geology, vol. 2, pp. 580-584, 1007. "Econ. Oeolo~:y, vol. 1, pp. 648-649, 1006. precipitation of he metallic opp r was brought ab h d t' ·f f OUt by t e r ucmg ac ton ? . err u tron. He concluded that the c_ommon o01atwn of _opper with prehnite and datohte and 1ts rarer a . o 1at10n with feld and laumontit are explained by F rnekes's find;~r and he empha ize the conn ction b tween the chlor·~' wa.t~rs of th. mine.' parti ularl;v tho e containi~; calc1um chlonde, wh1ch, a h pomts out, carry small quantitie of copper, and the solution from which the copper wa precipitated. Lane rearranged and expanded Ferneke 's equations into a single one which he give a follow : ' 2F 12 +2 u l +3Ca i02 2 u + Fe20 a+ 3 i02+3CaCl1. MINE WATERS Further di cu ion of Laue' idea nece itate some specific con ideration of th concentrated brines present in all the mines xc pt near the urface. As Lane has di cu ed the matter fully/3 a brief summary will suffice. The character of the water hows progressire changes from the surface downward. Lane make the following clas es: (a) At and near the surface, soft and fresh, with sodium in quantities more than sufficient to combine with the chlorine present . (b) At some di tance (g nerally 500 to 2,000 feet before ii attract attention unle especially sought) the chlorine is higher and the water is charged with common salt. (c) At great depth a strong s lution of calcium chloride containing some copper. The following analyses illu trate the composition of each of the three cla es: Analyses of mine waters [Grams per liter] urfaco Intermediate I Deep s 1 7. 0 0. 357 3. 172 1176. 027 175.4 2. 200 1 1.5 4 0 . . 010 I Fe.OOI . 004 . 006 ; Tr. Tr. Tr. 2. 3 ione. Tr. Tone. 1: 1 . 700 J 5. 079 2 0. 489 1279.3 I. Allouez mine pond. Lane A. C., Lake Superior Min. lost. Proe., vol.l3, p.9l. Dca~boro.e Chemical \Yorks, analyst. 2· Moha" k mtne, o. I shAft, tenth level, dripping. Idem, p. 121. 3· Mohawk mine, No. I shaft twelfth level dripping Idem p. 121. ~ulncy mine, dripping on 'nrty-!Hth level north or" o. 2 shaft. Id~m,t p. col: lccted ~rsarge looe, Hed Jacket crosscu~ , eighty- level~ depth 4,oop f · ugust, 1921, from drip. R. c. \veils, u.s. Oeol. ::survey, ana ys · 11 Lane, A. C., Michigan Oeol. Survey Pub. 6, vol. 2, pp. 774- 846, !9ll.
GENESIS OF THE DEPOSITS The explanation proposed by Lane for the different t pes of waters is that the deep water wa.s connatet~at is inclosed in the rocks when they were buried; that the water near the surface is water that was "sucked" into the beds and dissolved carbonates as it pa ed through the rock; and that the intermediate water resulted from reaction b tween the other two, the e sential reaction b ing between r azC03 of the upper water and CaCl2 of the lower to produce NaCI and CaCOa. He believe that when the concentration of sodium chloride became sufficient in the middle water zone, sodium zeolites, like analcite, were precipitated. Lane xplain the strongest brines as probably the residue left after most of the water had been ab orbed in hydration of the rock. Van Hi e and Leith 14 regard similar solutions encountered at depth in the iron region, as resulting from a condition of "deep stagnancy" in which the waters became progres ively richer in the mo t soluble alt, and they do not believe that the e olution are related to any particular type of rock or to iron depo ition in the region. In con idering the solutions in t.he copper eli trict, however, they uggest 15 that these waters may repre ent th "re iduum or brine" of the ore-depo itina olution , but why they are so regarded in the copper di trict and not in the iron di trict is not stated. The following point rna be regarded as facts or well-founded deduction : l. Th hallow wat 1 urface origin and have derived th ir from materials taken up from the air, th oil, and th r k . 2. As greater depth i attain d the ' aters become progressiv ly le in amoun . 3. The relative pr portion of hloride to sodium hlorid in rea with th downward decrea e in the amount of wat r and in r a e in concentration. 4. It i probabl that in the opp r country a very con iderable amount of r ion ha taken place, so that the rocks now in the zone of fr h water were at one time much farther from the urface and po ibly were in a zone that bore the arne relation to the surface then exi ting that th pre nt d ep "dry zone bears to the surfa e of to-day. 5. From the for going conclu i ns it i probably t~e that there has been a progres ive downward I.!Ugration of the upper zone . The evidence seem indecisive a to whether the e strong chloride waters are "connate " waters still further concentrated, a Lane uppo e ; "deep stagnant" portion of the general ground water; or the residual part of asc nding magmatic wate1 . trong brines are found at depth in many parts of the world. Concentration ha be n explained as due to hydration, as Lane suggests, and to evaporation 11 U 8 u ld' · Ocol. Survey Mon. 52, p. 544, 191.1. em, p. by expanding gases in oil and gas regions. 16 Their particular composition has been explained by reduced solubility of certain salts in presence of a common ion, 17 which might cause sodium chloride to precipitate while calcium chloride remains in solution. As a matter of fact, stalactites of sodium chloride have been observed in the Quincy mine and have been reported to occur in other places where the waters are mainly calcic. There is, moreover, good re!lson to believe that in th~ deep levels, where the rocks are essentially dry, both calcium and sodium chlorides are present as solids. After a specimen of such rock ha.s been wetted it will on drying accumulate a considerable crust of salts that have been dissolved and brought to the surface of the specimen. pecimens from deep levels, essentially dry when collected, become wet and even drip during damp or rainy weather, owing to their absorption of water from the air. Of more concern in the present study than the origin and relations of the waters of the eli trict is their possible connection with copper deposition. Lane's ideas in this regard have already been outlined. In the investigation here recorded no evidence indicating a close genetic connection between the salt waters and the deposition of copper has been recognized. In general, the salt waters are as abundant and a concentrated in unmineralized as in mineralized portions of the lodes. There is practically no evidence that the mineralizing solutions were acid; a little calcite ha been di solved, but this re ult could have been ac omplished as well by alkaline as by acid olutions, and the whole character of the mineralogy indicate that the olutions were not acid. o evidence of sodium zeolite deposition or copper depo ition in zone that correspond to the present ' ater zone has been found. Zeolites, except laumontite, whi h in places i abundant, are scantily pre ent in both hallow and deep zones of the amygdaloid lode but ab ent from the conglomerate lodes, ·and copper depo ition how no recognizable dependence on depth. The pre ence of traces of copper in the strong brines is not surprising when it is realized that these liquors ha e clige ted the copper-bearing rock for untold years. Wells found that an artificial copper-free brine of otherwise the same composition as the deep waters ( ample 5, p. 122), when put in contact with metallic copper, quickly dissolved copper in an amount comparable to that contained in the mine waters. Pumpelly suppo ed that the oxidized copper solution entered rocks rich in ferrous iron and were redu ed, at the same time oxidizing the iron. But it i now established, as di cussed in the oxidation of "Mills, R. V. A., and Wells, R. C., U.S. Ocol. Survey Bull. 693, pp. 4-86, 1919. " Idem, p. 73.
THE COPPER DEPOSITS OF MICHIGAN lava tops and ferric iron content of conglomerates, that the mineralized amygda.loids and the conglomerates were especially rich in ferric iron and in f~r rou iron before they were acted on by the mmerallzing solutions. Furthermore, the ferric iron of the lodes in the vicinity of copper has been removed or chemically reduced to ferrous iron. This removal or change of iron is pretty clearly connected with the deposition of the copper. These facts not only cast grave doubt on any idea of origin that suppose the copper to have resulted from the reduction of oxidized copper solutions, as solutions of surface origin probably would be. and were a. sumed to be, but they strongly suggest that the direct oppo ite was true-namely, that the copper solutions were reducing in character. The minerals, moreover, that accompany the copper and were formed at the same time are of a class that are believed to originate at moderately high temperature and certainly are not such as are formed by cool surface solutions. Altogether both the chemical changes and the character of the minerals seem opposed to the idea of formation from surface solutions. There appears, however, no such chemical objection to the idea of concentration by diffu ion. A part at least of the copper in the traps is in the form of sulphide, and it might be taken into solution and transported as such. When it entered the highly oxidized amygdaloids and conglomerates it might react with the ferric oxide, reducing that to ferrous oxide and in turn having its sulphur oxidized and the copper precipitated as metal, essentially in the manner set forth in the following section for ascending solutions. However, it is difficult to explain why so many amygdaloids, all rich in ferric iron and favorable physically and chemically to the proce s of diffusion, are barren. From the foregoing discussion it appears that there are seriou phy ical and chemical objections to the idea that the depo its were formed by de cending s~fa~e water~. The hypothesis of concentration by cliffu wn avOids some of these difficulties but encounters others equally serious in regard to the di tribution of the copper. DEPOSITION BY ASCENDING SOLUTIONS To show that the copper was depo ited by ascending solution would by no means fully account for the deposit . The hypothesis now to be discussed goes further and a. sumes that the copper-bearing solutions were expelled forcibly, at high temperature, from a magma chamber in which they originated. The probability of this as ~mption must depend largely upon the degree to which the chemical character of the solutions, as judged by the work they have done re embles that of ore-forming olutions that have bee~ act~ ve in o~her re~ions where there is virtual proof of the1r genet1c relatwnship to igneous magmas. A magmatic origin for th Michigan. copper depo its as fir t propo d by H. L. myth 1ll 1 96. F. E right, an Hi , L ith, and teidtman, R. E. Bore. T. . Wood , and J. E. purr have ince implied 0; a erted a similar origin. The oro oro depo it , in Bolivia, which how many points of re emblance to the Michigan depo it wer ascribed to de p-seated au e n early a 1846 by . A. de la Ribette and definitely Lo a magmatic origin in 1906 by G. teinmann, and still later by ingewald and Miller and ingewald and Berry. For somewhat imilar d p its in ew J r ey J. olney Lewi in 1907 propo ed a magmatic source. 0 RCE OF THE COPPER There i no dir t conn tion b tw en the main ore deposits of the di trict and the e)..'])O ed intrusire rock . However, ertnin a o iations of small copper deposit with the kn wn intru i e rocks indicate what is thought to be true of the large ore bodie . Copper sulphide veinlets cut the intru ive mass of !fount Bohemia 18 and adjacent rock and apparenUy terminate outward from the intrusive body; copper sulphides are concentrated al o in the miarolitic cari· ties of the aplitic phase of the intrusive gabbro. Wright appears to regard the intrusive mas as de· rived from the magmatic re ervoir that furnished the somewhat older basalts and fel ites and to consider the copper sulphides inclo ed in it as related in source to the native copper and the copper sulphides and arsenides of the larger deposits of the region. uJ. phide veins are likewi e as ociated with the intrusire gabbro near the Michigan-Wiscon in boundary and the quartz porphyry bodies north of Lake Gogcbir. Native copper, with some sulphide, occurs near tho Porcupine Mountains, where intru ive rocks that are probably of late Keweenawan age are thought to account for the uplift and faulting. Arsenical copper with some sulphide occurs at the Indiana mine in felsite, which Lane 19 regard as intrusive. Chalcocite is present also in probably intrusive felsite east of Allouez. The Duluth gabbro, thought by most who have studied it to be of late Keweenawan age, may well be a part of the same intrusive mass with Mount Bohemia, the Porcupine Mountains, and the bodies of intrusive felsite and quartz porphyry known at many places throughout the di trict; this mass would thus underlie the whole lava series. Small copper sulphide deposits/0 with or without nickel, are found in the gabbro or just outside its contact. Pegmatitic knots or lenses occur in some of the traps of the district, especially those of grea~r thickd ness, and some of these contain copp r sulphides native copper. These pegmatitic lens.es are present 11 Wright, F. E., Michigan Oeol. Survey R pt. !or 1908, pp. 302-394, !900· 11 Private report to the company. 20 Nebel, M. L., Ecoo. Geology, vol. 14, p. 399, 1010.
GE ESIS OF THE DEPOSITS nly well within the thicker :flows. They seem to ~ave re ulted from .a ~ifferentiation d~ring the process of crystallization s1mil~r to ~hat wb~ch produces the pe!!lllatitic portion of mtrus1ve bodies, though they ar: of small extent, and the differentiation has not progres ed far. They do, however, show a differentiation towA.rd increasing copper content that in a great intrusive body might well result in abundant copper-bearing solutions. In nearly all these examples of close association of copper with intru ive bodies copper sulphides are present, fi.Dd in most of them, except where the inclo ing rock is red, sulphide predominates over native copper. Where the veins are within the intru ive rocks, only sulphides are usually present, though copper occurs in felsite at ~he Indiana mine. DIRECTIO OF MOVEME T OF THE SOLUTIONS The concentration of copper on the under sides of relatively impermeable barriers is perhaps the most direct indication that the solutions came from below after the rocks had assumed t4eir present attitude, but it is not the mo t convincing evidence of ascending flow. II, as most student of the problem now agree, the ore were deposited from hot solutions, they must have been hot either because they :flowed through hot rocks or because they came from a heated source; the first a umption would imply precipitation within o hort a p riod that the lava had not cooled; th econd, indicative al o of rapid action, would probably require fl. magmatic ource for both the solution and the heat. From" hat ha b n aid in connection with gravity circulation (p. 121) it i clear that the penneability of the rock wa low when the driving force on the olution wa only gravity, or gravity plus one atmo phere. Gr ater :fluidity and greater driving force would help to overcome low perm ability, and both the e advantage would exi t if the olutions came from a mngmatic ource. Marked decrea in vi co ity of olution att nd ri ing temperature and undoubt dly continu s as solution pass from the liquid to the ga ous tate. Ths olutions coming from a maama r ervoir may be a um d to b under pr ure sufficient to lift column of molten rock thou ands of f t to the surface. Tho more mobile con tituent , the ore-forming solutions, hould tA.rt out from the magma chamber, therefore, with pr ssure at lea t equal to that on a column of molten ror.k from the arne ource and should be able to maintain that pres ure to higher l~vels in the cru t becau e of their les er weight and Vl cosity and their lower solidifying point. Recent work at the Carnegie Geophysical Laboratory 21 uggest that great pressure may be developed just at the u:o~!~ey, 0. W., Tho dov lopmoot or prossuro in magmas as a result or crystalliza· · 8Shlngtoo Acad. Sci. Jour., vol. 12, p. 219, 1922. 58540---29-10 time the volatile constituents are liberated and made available for migration. Altogether, the evidences of enormous forces associated with igneous activity, such as volcanic explo ions, elevation of vast quantities of magma, and penetration of emanations into dense rocks, as in contact metamorphi m, show that solutions from magmatic source have a much greater ability to move through difficultly permeable rocks than waters imp lied only by their own head. Ascending solutions are never in want of an outlet, provided their pressure is great enough. The farther descending solutions penetrate the tighter they find the rocks; but rising solutions, which are 1 ast viscous and under greatest pressure at depth, where the difficulty of ascent is greatest, are continually reaching more permeable material above as their ability to flow become diminished through lo of temperature and pre ure, and at the surface there is always a free outlet. With great volumes of solution pa ing any given point on the upward journey there would tend to ari e a uniformity of temperature for long distances along the channel way. Hot water tarting through a long cold pipe would warm the near end of the pipe and emerge cold at the far end, whereas much hot water flowing continuously through the pipe would in due time warm it from end to end to about the arne temperature. Where the rate of beat conduction i o low a it i in rock , thi tendency could doubtles afford e entially uniform temperatmes throughout as great a v rtical range a that repre en ted by the mine working and thus give the ob erved constancy to the character of mineral depo ition throughout that range. MEA OF ACCESS OF THE OLUTTO If th olution a ended from some deep- eated sour e they mu t have had mean of reaching the horizons where th y are known to have precipitated copper. Two po ible mean of acce may be conidered- inter ection of the productive beds by the underlying intru ive rna from which the ore solutio,n came; or a cent along fra ture that cut the e bed . More spe ifically, these hypothe es are that the olution reached their horizons of pr cipitation from cro cutting contact of the Duluth gabbro; or that they were brought to the e horizon by the deep exten ion of the K weenaw fault. third means would be utilization of whatever avenues presented them elve in the regions lyina near the magmatic our e and the gradual and progre ive collection of the olution into the more permeable channelways at the higher 1 vel . ASCENT FROM CONTACTS OF THE DULUTH GABBRO There i r a on to suppo e that the Duluth laccolith extend beneath thi region at or near the contact of the Keweenawan and the underlying rocks.
THE COPPER DEPOSITS OF MICHIG Grout and Hotchki have suggested, fW'ther, that the Lake uperior basin has re ulted from slumping of the essentially horizontal crustal strata into an underlying magmatic basin, and that dming tllis lumping the magma pu hed into lllgher parts of the crust. Whether this or orne other idea as to the cau e of the ba in i correct, it is to be expected that a rna s of magma of the size of the Duluth or Lake uperior laccolith would send offshoots into the overlying rocks and show an irregular upper surface. That there are such off hoots may be inferred from the presence of intrusive rocks suggestive of Duluth gabbro parentage well above the ba e of the Keweena' an. That the main gabbro would actually inject its more mobile constituents into adjacent opening i indicated by the analogous occmrence of copper mineral in fractmes near these minor intru ive rna se . If the main intrusive body, in working its way upward, intersected a permeable amygdaloid or conglomerate bed, the mobile con tituents given off by the magma would pass upward along such a channelway, and where they encountered favorable physical and chemical conditions they would deposit certain of their constituents. Tells inference suppose that the bed now mineralized extend for long di tances down the dip-a supposition that seem probable from the known extent along the outcrop of mo t of the productive beds and also from the less positive correlation of certain beds or groups of beds on Keweenaw Point and Isle Royal. It i perhap al o worthy of note that the productive parts of the Kear a1·o-e Baltic, and Osceola lodes coincide with the :St portions of the flows as shown along the outcrop. It is not likely, however, that all bed that extend to great depth will be equally favorable as solution channels. It is known that an amygdaloid or a conglomer~te may change within a short di tance along ~he ·trike from a relatively permeable to a relatively Impermeable bed. To be favorable it mu t not only have been permeable at its intersection with the our e of solutions but must have continued as a permeable channel to the level of the present smface at lea t, and doubtless to the original smface, in order to ha.ve an outlet that. would ~ermit the pa sage of a la1g volume of solutwn. It IS obvious that not every b d that is f~vorable where cut by the present erosion urface ?r mm~ workings would be equally favorable for an mdefinite distance down the dip any more than alon~ the. strilce. Some bed ' therefore, might be well mme.rahzed while others that are of apparently equal pr~llli e . w~ere now eA.'J)osed received only nough mmeralizatwn. of the feebler kind to fill vesicles or cause cementatwn. Beyond ~he a~alogy. with the deposits adjacent to the su~ordmate mtrusive bodies like that of Mount Bohen:la and the intrusive mass which probably underhes the Porcupine uplift and WJ.·th or d · e epOSitS on the margin of in~ru . ive b~dies in :nany other parts of the worl.d, th r I dn t v1denc in upport of tbi partwular pathway of tran f r for the maumat· n solutwns to the. plac whei:o they act d. Perhw the most sugg tiv fact relative to dir ct a cent alonP the perm able lode from th ir int r oction with th, Dul~th gabbr? is th pr s nee of the chief copper~ beanng beds m the low r part of th K weenawan series. But even thi may b due to the influence of the Keweenaw fault. · ASCENT FROM THE KEWEENAW FAULT The Keweena\v fault ha long b en on idered by Lane and other a po sible channel for oruptiv rock. Attention ba b n called by Lan to the , vera! bodie of intrusi e rock clo to th fault, with the implication that the in tru ive material may hm ri en along it. Tbi implication ugg th fault a a po ible charm lway for the or olutioo . That the copper min ralization followed the main fault movement e m to b indicated by the mineral· ization of tho br aks in tho lllghly batt r d area near the fault. o far a known, howe or, no evidence of mineralization ba b en found on tho fftult it elf; tbi would indicate that it was not particularly permeable as compared with fra tur le s filled by gouge or with open-textured amygdaloid or conglomerate b d . The great horizontal xtent of th fault nnd the magnitude of its throw indicate that it prr i t down· ward for a gr at di Laue -far nough, it i ea y to believe, to tap the magmatic re ervoir in which the mineralizing olution originated. AlthouO'h endcntly le s permeabl than open fracture and porou bed, it greater acce ibility and continuity may have made it the chief channelway by which the olution pa d upward in a direction tran ver e to th rock tructure. The Keweenaw fault i a rever e fault, dipping with or slightly flatter than the bed , and th re are mnller nearly parallel fault above it which probably branch from it. If the main fault and it branches truncate the higher bed down the dip, becau e tho bed dip more steeply than the fault, olutions ri ing along the fault would tend to enter any porous bed and continue along it a affording a shorter and probably an ea ier channel way to the surface than the upper part of the fault fissure. Essentially the arne conditions would control the beds selected and mineralized in this ascent of the solutions in the beds from the Keweenaw fault as would control the beds entered directly from inter· section with the Duluth gabbro. It may be supposed that the fractures occupied by the fissure deposits reached down to the fault and thus furnished easy channelways f~r the upward movement of solutions. Where fissure deposits are ab~dant, as along the crest of the Keweenaw anticline m the north. end of the district, no largely productive lode deposits have been developed, but in the central area,
GE 'ESIS OF THE DEPOSITS here fi sures are less numerou , the copper occurs w ainlY in the lodes. This difference sugge ts that Inhere plentiful fi suring furni hed easy channels of w cape for the olutions they did not traverse the lodes sufficient quantity to form large depo its. Many of the smaller fi sures, however, were fed locally from tho lode they cut, and the ame thing may be true of some of the larger ones. The pre ence of the copper in the one uch lode at White Pine in close association with faults and fractures branching from a pronounced reverse fault which itself i not lmown to be mineraliz d, i ugge tive of similar relations between the main copper deposits of Keweenaw Point and the Keweenaw fault. If the Keneenaw fault down the dip cut into higher bed than those which lie against it at the surface, there probably is some horizon in the folded bed to which it becomes tangent and below which it cut back again to older b d . ( ee fig. 10.) If this is o, any of the favorable bed near the bottom of the series might rec i e olution direct from the fault and become mineralized, but beds above the horizon of tangency would not be cut and so would rec ive only uch solution a wer able to leak out from the major channelways and therefore would be only feebly mineralized. everal bed of the lower part of the eries ss high a the A hbed lode carry con iderable quantitie of copper, but abo e that horizon there is nothing of known value e in the Por upine re()'ion, wher local condition account for the ex ption. ulphide are mor abundant in fra ture that cut amygdaloid lod n ar th fault han in tho o that cut lode high r in th be explained if, a ugoitation" (p. 130), th lution w re oriO'inall ulphide 1 solution and w re oxidized b long contact with th hematite of th lod . At horizon n ar th fault th olution may ha e f llo' ed th lode f r h01'tor di - lances and thu hav b n 1 compl t 1 oxidized, "'iih more abundant a a r ul . But th ,Uiouez conglomerat well above the fault known, may indicate that the generalization is unfounded. It must be recognized, rnoreo er, that there is much more fi suring of the rock near the base of the series and that ar enical copper in fis ures may, in part at least, account for the higher arseni al content of the lower lodes. There is reason to believe that some of the lodes are fed by fissures that enter or cro s them within the pre ent range of observation. Thi eern especially evident in the Calico lode of the Michigan mine, which was largely mined above the inter ection of the Branch fissure but i poor below the intersection. The similarit,y of the minerals in orne of the strike fissures that cross the Baltic lode to the minerals in the lode and the local m'erging of fissure mineralization into lode mineralization are hio-hly sugge tive that the lodes were at least in part fed by the fissures. GRADUAL ACCUMULATION IN PERMEABLE CHANNELWAYS If olutions are fore d again t a body of rock varying in permeability from place to place, they will enter uch opening a are fir t pre ented but will seek the avenues ea ie t to follow and eventually will flow in greate t volume throu()'h the rno t permeable portions of the rock. Thi principle may have gov rn d the upward movement of the mineralizing olutions in Michigan. A id from its piau ibility and the certainty that it works on an important cale in movement of the hallow ground water, there i only one reason for thinking that it may apply here. It po ibly e:-..'plain more readily than the other suggestion the fact that the mineralizing solutions appear to have reached e entially all part of the rocks of the lava er1e . CA E A TD COr DITIO OF PRECIPI'l'ATIOr Three contra ting views may be con ider d as to th nature of th copper-bearing olution from which the or were d po ited-(1) that the opper was tran ported in an oxidized condition a sulphate, chloride, arbonate, or ili ate and wa depo it d by ch -mical r duction of uch compounds; (2) that the opper wa tran ported actually or potentially in the that no great signifi an e occurrence of ulphid . The lodes farth t from the fault, the hbed, Pewabic, alumet Iocla onglomerate, and 0 ceola, carry high-grad copp r, x eedingly low in ar eni . The Kear arge and I le Royale lode , n arer to the fault, and especially the Baltic, which i clo e t to it, CO~tain more ar nic. This may likewi b an indicatton that the solutions became more highly o:x'idized as they travel farther from the Keweenaw fault. The 1 Lake lode, which lie relatively low in the eri and near the fault, contain nonarsenical copper, and thi occurrence, although it may be an exception to the general rule through some special condition not ' rn tn.lli tate and o d · po ited; (3) that the copper , a tran ported actually or potentially a ulphide and ar enide and wa d po itcd mainly a native metal as a re ult of the r mo al of the sulphur or arsenic by oxidation. The e i w may be called re pectively th redu tion hypothesi , the saturation hypothesis, and the xidation hypothe i . PRECIPITATION BY REDUCING ACTION OF FERROUS lRON To myth 22 belong the credit of recognizing that the mineralogy of the depo its and certain tructural features, such a the occurrence of copper in the fissure depo it on the under side of the Green tone
THE COPPER DEPOSITS OF MI lUG flow are not in accord with the view that the olutions cam~ from above, as Pumpelly had proposed, but indicated instead that they came from a deep-seated source, of which boron and fluorine are especially suggestive. myth concluded that ea~h of the amygdaloid lodes had been weathered while expo. ed at the surface and so had acquired the ferromagnestan alteration products which Pumpelly had a cribed to the breakdown of the pyroxene and olivine of the basalts. The calcium and sodium minerals, however, 'which Pumpelly thought were similarly derived from the feldspar, myth said had been introduced, along with the copper that is found a ociated with them, from below, after the rocks had been tilted to their present attitude. Smyth accepted Pumpelly's explanation of the cause of precipitation as the one best in accord with known facts- namely, reduction of oxidized copper compounds by the ferrous iron minerals of the lodes. It is to be regretted that these ideas were recorded only in the most summarized form and therefore failed to receive the recognition that they deserved. Smyth's account of the mineralogy, structure, and age of the deposits still seems correct. Since that account was published, however, it has been shown that chlorite, epidote, pumpellyite, and allied minerals are hydrothermal minerals rather than products of weathering, and, as set forth on page 3 , weathering is thought to have been of minor importance in producing red lava top . The mineralization and rock alteration, therefore, represent ·a single period and a single cau e rather than two widely separated period and different causes. Again, Pumpelly' idea, accepted by myth, of copper precipitation by reduction is contradicted by the fact that copper is not closely accompanied by hematite but is intimately a ociated with bleached rock. It also fails to account for the copper in the conglomerates, particularly in the rich Calumet & Hecla conglomerate. It is subject, in short, to exactly the same objections a the hypothe is that the solutions were descending. It postulates, moreover, the pre ence in a cending solutions of o.xidized copper compounds, whereas ascending solutwn , the world over, are now known to deposit copper in combination with sulphur or some similar element of antioxidizing character. In describing the nativo copper and chalcocite deposits of ew Jersey, Lewis 23 noted the tendency toward concentration under barriers of low permeability, the bleaching of the red rock around the copper, which had also been noted by Weed, 24 and the close a sociation of the copper with igneous masses. Lewis concluded that the copper had been deposited from a cending hot solution , probably derived from the underlying source of the basic rocks of the region. II Lewis, J . V., Econ. Geology, vol. 2, pp. 242-257, 1907. " Weed, W. 11., ow Jersey Geol. urvey A.nn. Rept. lor 1902 ,p. 135, 1903. For the formation of nativ copp r, L wis cited experi. ments by toke 25 and sugge ted that cupric sulpha! contained in the ascending soluti~ns had been reduce: to cuprou ul~h~te by the ~ct10n of min rals and solution contammg ferrous 1ron, and that native copper had been depo ited from the cuprou sulphate where the solutions had be om sufficiently cooled. The bleaching he explained a r ulting from leaching of the hematite by acid ulphat olution . In a later pap r, r ad at the meeting of the ciety of Economic Geologi t in De mber, 1922, ~wis further empha ized the structural relations outlined above and the relation of the copper depo its to intru. sive bodie . In thi paper he recognized the proba. bility that the solutions as they came from the ma. matic source were reducing rather than oxidizing. In general, L wi ' idea of th ew Jersey occurrence will appl qually well to tho e of Michigan. Wat on 26 regard the nativ opper depo it of the outh Atlantic tate a derived from sulphides di seminated in the basic la as. The copper was collected by circulating hot olution and precipitated as meta.lli copper in area ri h in ferric iron by the oxidation of the olution . 'i a.t on re ognize the possibility that the olution may have been deriYed from deep- eated intru ive magma . Wright' refer nee to the pre ence of sulphides near intrusives and in the lower b d of the eries and of native copper with little ulphide higher up 27 indi· cates relations i.rnilar to tho e in ew Jersey. He asserted that any theory of origin would have to explain the e relations. Beyond implying that the copper near the intrusives is magmatic and that · therefore all of it throughout the di trict may be magmatic, Wright did not go. \an Rise 2 cited the Michigan copper ores as examples of depo its formed by meteoric ' ·aters that had first de cended, then moved laterally, dis olving copper as they went, and finally ascended and precipi tated the copper as now seen. He adopted the Pumpelly idea of precipitation by ferrous iron. Van Hise, Leith, and teidtmann 29 concluded that the ores were formed by hot olution and that the type of rock alteration is unlike that accompli bed by meteoric waters. As to the source of the water, they said: "On the whole the evidence is taken to point to a probable original concentration of copper by hot solutions, largely of juvenile contribution .but more or less mixed, necessarily, with meteoric waters, and a later working over of the deposits by waters dominantly of meteoric source." As to whether the juvenile (that is, magmatic) waters were derived from the intrusive rocks or from the lava flows they were "Stokes, H. N., Econ. Geology, vol. 1, p. 645, 1906. dWiib "Watson, T. L., Native copper deposits of South Atlantic States compare those of Michigan: Econ. Geology, vol. 1 , pp. 732-751, 1923. " Wright, F. E., Michigan Geol. Survey Rept. for 190 , pp. 392-394, 1009· 11 Van Hlse, C. R., Am. Inst. Mln. Eng. Trans., vol. 30, pp.f 9-98, !90011 U.S. Geol. Survey Moo. 52, pp. 68G-591, 1911. j
GENESIS OF THE DEPOSITS ·tnm· but they somewhat favored the origin uncer .. , from the flows. The heat they thought was partly supplied by the hot magmatic wathers and J?dartlyd the still bot flows. The copper t ey cons1 ere m art to have come as chloride from the same magmatic ~ource as the hot juvenile solutions, along w_ith boron, fluorine, C02, and perhaps other .magmatic ema~a tions but in part to have been denved from leaching of th~ basic wall rocks by the mingled hot solutions. The precipitation of the copper, they concluded, was accomplished through reduction of the copper solut.ion by ferrous iron minerals and by ferrous solutions derived from them, in essentially the way Pumpelly had proposed. Finally, they concluded that the brines of the deep levels are probably the residues of the ancient ore-forming solutions, possibly mixed with meteoric water. The part of th se views of Van Hi e, Leith, and toidtmann that have to do with meteoric water are discu sed on page 120. The parts that deal with magmatic waters follow myth in large mea urc but go fw'ther in recognizing that the type of rock alteration contra ts entir ly with that produced by weathering or by meteoric water . If the magmatic waters came from the lava flow , there w re presumably several period. of mineralization, as succes iv flows were in the proper condition to yield emanations. The pre ence of mineralized boulder of amygdaloid in what was considered unmineraliz d conglomerate wa thought to m an min ralization b for con- ~omerate d po ition and apparent! trengthened he belief that th lava rather than the intru ives ~·ere the ource of th min ralizing olutions. Horo 30 appended to a.n excellent summary of previou literature on th di trict his own idea a to tho origin of the d po it . H con lud d that tho copper and tho Kew onawan ign ou rock had a common ourc ; that the copper i ntially a primary depo it from a ending olution ' hich follow d the oxtru ion of la a o closely that the rocks were till hot, although they had already be n fractured; that tilting and faulting followed copper d position; that the copper r pla d tho rocks and wa pr cipitaLed from ch.lorid solution by th reducing Rction of ferrous iron. Th se conclu ions were ' ll presented and accompani d by shrewd and pertinent ob ervations on other features of the copper deposits. The conception introduced are discu sed above. Woods 31 ompha iz d the po sibility that the f lsite and quartz porphyry intru i e rna es may have been the sources of the copper, which he thought may have been firt deposited by a cending m~tematic solutions and then enriched by downward-moving water in t the same way that the porphyry deposits of the 0 t have been originally formed and later enriched. : ~?re, R. E., Michigan Gaol. Survey Pub. 19, pp. 157- 161, 191 5. OOds, T. S., Eng. nnd Min. Jour., vol. 107, p . 300, 1919. PRECIPITATION IN CONSEQUENCE OF SATURATION It may be supposed that metallic copper was deposited, because that was what the solutions carried, and that it was precipitated by cooling· of the solution or by some other cause, in the same way that calcium carbonate solutions precipitate calcite. Perhaps Spurr had some such idea in mind when, in hi short article 32 arguing for the magmatic origin of these deposits, he asked if the intercrystallization of copper with chalcocite does not indicate a deficiency of sulphur in the solutions. The chief objection to this idea of precipitation by saturation is that in all but a few of the thousands of copper depo its that have been studied throughout the world it is apparent that the copper has be n transported either as a sulphur, arsenic, or allied compound, as in mo t primary deposits, or as an oxidized compound, as in the econdary depo it . The native copper in many secondary deposit has cl arly resulted from the oxidation of sulphide in place. On the other hand, the conception has certain attractions. I ative gold may possibly be carried a such in solution and perhaps native silver also. In general, precipitation that take place without evident attack of the solutions on the wall rocks may be thought to re ult from the fact that the solutions had reached the aturation point through decreas of temperature or other physical cau es rat;her than from orne chemical reaction that rendered the ubstances they carried le oluble. In the Michigan depo it there is characteri tically a pronotmced chemical change in the inclosir~g, rock, but locally copper is pre ent in rock that shows little change, as in part of the upper levels of the Calumet & Hecla conglomerat , locally in the Kearsarge and Pewabic lodes, and in fissure . Doubtless the chemical reaction that cau ed the precipitation of native copper did not all take place j u t where the copper wa precipitated. It is entirely probable that the reactions began a oon as the temperature and other phy ical conditions permitted, and they may have gone on for orne time before any copper was precipitated. Once copper tarted to form, it would act as nuclei for further precipitat;ion from solution that had been und rgoin()' chemical reaction some distance away. In con id ring the immen e mas es of copper, hundred of tons in weight, it is not reasonable to uppo e that the entir·c chemical reaction wa confined to th rock replaced by the copper or to that immediately urrounding it;, and the supposition would be no more rea onable for the smaller masses. PRECIPITATION BY OXIDATION Mo t of the copper deposits of the world con i t of ulphide 33 or have been derived directly from sul- " purr, J . E., The copper ores of Lake Superior: Eng. and 1in. Jour., vol. 110, pp. 35$-357, 1920. n For brevity in expression the su1phide group is hero used to include also the related compounds with arsonic, antimony, etc.
THE COPPER DEPOSITS OF MICHIG N phide by uperficial oxidation. The relatively ~all cla of primary depo its of nati e copper, of wluch the Michicran deposit afford the chief example, constitute the only exception to the rule. Although the tra.n portation of copper in solution that dcpo it it as sulphide or allied mineral is not yet well under tood, the fact that it is o tran ported and deposit d in by far the gr ater number of depo it mu t be accepted. It i advisable, therefore, to inquire whether the Michigan and similar depo it repre ent not an entirely different and independent scheme of copper transportation and depo ition but rather a modification of the ordinary method through the influence of special conditions. What kind of pecial modifying conditions would erve to preclpita te native copper from solutions that normally would deposit copper ulphide? The metallurgi t, who tran form copper sulphide into metallic copper, would an wer that if the copp r sulphide solutions could be oxidized under the right conditions llJld to the proper degree, metallic copper would be formed. Twenty years ago, G. Steinmann 34 advanced the idea that the native copper and chalcocite depo it of Coro Coro, Bolivia, originated from ascending magmatic solution that would normally have deposited only copper sulphides, but because the solutions entered hematite-bearing rock , part of the sulphur was ox-idized by the oxygen of the hematite and therefore part of the copper was precipitated as native metal in the midst of bleached areas of the rock, and the re t of the copper united with the remaining sulphur to form chalcocite. How doe thi idea of precipitation by oxidation apply to the Michigan depo its? everal conditions mu t be met to make it seem applicable. 1. There should be definite evidence that sulphides had been present in the ore-forming solutions. 2. If oxidation wa the cau e of the conversion of copper sulphide into native copper, the rock in which the metallic copper was deposited mu t have been oxidizing in their nature. 3. At the places where copper was deposited the oxidizing power of the rock should have been les ened if not de troyed. 4. Oxidized compounds of sulphur might be expected. The extent to which these requirements are met by the Michigan deposit is discussed below. PRESE NCE OF SULPHIDES Sulphide and arsenides of copper in the Michigan district are subordinate in quantity but are of widespread occurrence. Copper sulphides occur in pegmatitic kn?t or len es in c~rtain of the thicker traps, and there IS a close connectiOn between sulphides and intrusive mas es. Copper ulphide has been found in several of the lodes, especially in the Baltic and " F t.schrift llarry Rosonbuscb, p. 360, 1006. I 1 Royale, and in count! fi uro , large and small in and n ar the lode . opper ar enide have bee~ ob rv d paringly in th I le Royal lodo and are plentiful in evoral largo cro fl uros. opper ul· phide and mctollic copp r ( e pl. 6 ) or copper ar ld and 111 toliic copp.er ar in many places intimately intergrown. Th r thus proof that practically tbroucrhout th di trict at lea t a part of the copper wa tron port d in the manner common to mot pri· mary copper d po its l ewher , an d that the depo ilion of sulphid and ar:sonid of copp r w nt on at the ame time a the d position of metallic opper. If the ulphide and ar~ nid compounds of copper repre ent the minor re idue of ulphur and ar enic that e cap d oxidation, it might be xpected that the copper ulphide and ar nide formed would be tho t lowe t in sulphur and ar nic and highe t in copper, and uch i th ca e. The prevailing copper ulphide i chalcocite, with a mol cular ratio of copper to sulphur of 2: 1, th highe t among all known copper· ulphur minerals. Borni te, with a ratio of 5:4, is far los ommon; chalcop ri te, with a ratio of 1:2, l common till ; and pyrite, the ommone t ulphide in nature and the one that ugge t an abundance of sulphur, i in the Michigan d po it practically absent. The ai enides show a iroilar tend ncy. In other recrion the conunon unoxidized copp r-al enic miner· al are enargite and tennantite, with proportion of copper, ar enic, and ulphur of 3: i :4 and :2:7, repectiYely. In Michigan th mineral or nb cnt and in tead the ar enic i ombin din the uncommon mineral domeykite, algodonite, and whltnoyite, all high in copper, low in ars nic, and devoid of ulphur, with copp r a1 enic ratio of 3:1, 6 :1, and 9:1 , ro pee· tively.35 Mor over, certain of the lode , notably the Baltic and I le Royale and in 1 degree the Kearsarge, carry "ar enical copper"-that is, metal con· taining small amount of ai enic but enough to modify the mechanical and electrical properties of the copper. Although sulphur doubtle exec d arsenic in total amount in the di trict, there are no such mn sivc and exten ive occurrences of chalcocite as the o· call d "mohawkite" ar nide vein of the Ahmeek and Mohawk mine and ar enic i more abundant in proportion to uiphur than in other copper d' · tricts. The idea uggests it. elf that ulphur "'.8 oxidized with relatively greater ease than arsomc, and this idea accord with the behavior of the e elements in copper smelting. Finally, the oxidation hypo the is would sug~e .t that the olutions that had traveled in the mo t ll_ltt· mate contact with the oxidizincr agent would prectpt· tate the least sulphide and ars nide, and vice versa. This suggestion likewise is borne out by the fact ' as discussed below. 11 The exact composition o! these arsenides bas not been worked out, becaus;i~ tbe intlmate intergrowths that prevent isolation o! any single variety. There 1 given are those recorded in tho textbooks.
GE ESIS OF THE DEPOSITS PRESE "CE OF A OXIDIZING AGEN'r The conglomerate layer and the lava tops contained a noteworthy proportion of ferric iron, chi fly as hematite. Thi hematit wa pre ent in the rocks from the time of their formation and therefore long antedated the depo ition of copper, which came only after the entire erie had been accumulated and the i.Jt.ing and faulting had be n accomplished. Ferric compounds can part with one-third of th ir oxygen in the pr sence of a reducing agent. H ematite, therefore, may be regarded as a potential oxidizing aJTent toward a solution of r ducing nature. The que tion then ari es, Did hematite actually oxidize ore solution bearing copper sulphide and thus cau e the precipitation of m tallic copper? That rock of normal composition contain copper sulphide ore , wherea red rocks rich in ferric oxide are likely to contain nativ copper, i shown by the following figure : Ferric and ferrous iron content of inclosing rock of some copper deposits I Fas 1 FetO, ulpbide: Fe as FeO Bingham, Bisbee, Ariz., limestone (Fe20 a+ FeO)I Xative copper: andstone, Iron-rich boulder, Calumet c 11 Ia I Allouez conglomerate, felsite p bbl Michigan - --- - --- - - -- - Puca sandstone, oro oro, Bolivia andstone .r ew Jersey: Total Fe . ot only is the ferri iron higher in the rocks that mclo e nn.tive copper but it i pre ent as the oxide, whorea mo t of the iron in the rock that contain ulphid i combined a ilicate and thu probably is les available for rea tion. ative copper is common in the upper levels of deposit that have undergone sulphide enrichment. The condition of occurren e and method of formation of thi_ native copper are well under tood; it i plainly an OXIdation produ t of chalcocite. The oxidation i Probably accompli h d by atmo pheric oxyo-en, but many believ 36 that it i ac omplished also by ferric sulphate, well known as an oxidizing agent. In the production of native copper by the action of ferric ~ulphate on chalcocite, the iron compound would be m solution and the copper compound solid, whereas the Michigan native copp r is inferred to have been Ltndgrco, W"nldcmar, formed by reaction between copper sulphide in solution and ferric iron in the solid state. Inasmuch as the first reaction certainly takes place, it would seem that the second might do so under the proper conditions; and it has actually been produced experimentally.36" The results of experiments relating to this problem and conclusions drawn from them are presented by R. C. Wells on pages 137- 141. .Another indication that hematite acted as an oxidizing agent to precipitate metallic copper i een in the field relation . The field evid nee may be considered urider two head -the relation of native copper and copper sulphide to the proxirriity of hematitebearing rocks, and the effect upon hematite where metallic copper has been precipitated. The first of the e topics is considered here; the second in the succeedino- section on bleaching. Where the ore olution evidently traveled in mo t intimate contact with the oxidizing agent, the largest proportion of metallic copper and the smalle t proportion of ulphide or ar enide are found; and conversely where the solutions appear to have moved mainly through rock of nonoxidizing charact r, the proportion of sulphide or ar enide to m tallic copper i highe t. The fir t requirement for ore formation on a commercial scale was the presence of extensive through-going channel of relatively high permeability throuo-h which the ore solutions could pa s. The e permeable hannel were of thr e orts-the conglomerate layers; the ve icular lava top , especially the brecciated tops; and large fractmes relatively free from gouge, uch a th cro s fractures due to the tension on the anticline , a the Allouez and Keweenaw anticlin , a.nd trike fi me near the base of the serie , as n ar the Baltic lode. Innumerable smaller fractures pre ent throughout the district but e pecially abundant in the region of major disturbances also acted as minor channel for the ore-forming solution. The channel afforded by the conglomerate layer and the lava tops were relatively rich in hematite. If hematite exerted an oxidizing effect on the solution that came into ontact with it, then those that moved for the longe t di tances through the small openings of these hematite-bearing lodes had the greatest opportunity to become oxidized. The channels of the third type-the major cross fissmes-cut mainly through the dark, unoxidized trap ; only small parts of their walls consist of the hematite-bearing conglomerates or amygdaloids. 1oreover, the e fis ures probably afforded readier and more direct passageway for the solutions than the more interrupted, more circuitous,:and probably maHer openings of the lodes. The olutions in the fi ure were therefore not in uch Ir it is !ISSUmod that the copper was carried in solution ns some compoundsulphide, for example-n condition in which it must have been carried in nature, then tho action of ferric oxide wns to prevent its depo ition ns sult hide through selective oxidation of the sulphur. 'l'be copper under these conditions could still deposit as native metal, whereas the more common process in the formation of ores IS the change of native metal to sulphide.
THE COPPER DEPOSITS OF MICHIGAN close contact with the adjacent rock as the solution in the conglomerates and the lava tops, and c~nsequently it might be expected that the solutions movmg through the cono-lomerate and amygdaloid lodes would be more thoroughly oxidized than the solutions pas ing along the fi sures. This in general is true; very little sulphide occms in the amygdaloid lodes independent of fi sures. In the conglomerate lode practically no sulphide occurs in the cement in the way common for the metallic copper. The Allouez conglomerate in particular and some of the other conglomerates in less deo-ree contain widespread chalcocite ill notable th~ugh noncommercial amount. But this chalcocite is not chiefly within the conglomerate rock it elf, like the metallic copper, but is intergrown with calcite (see pl. 68) in fractures that cut the conglomerate at close intervals in all directions. The abundance of sulphide veins in the conglomerates may be due to the greater brittleness of the conglomerate, which made small-scale fracturing more easy, the lower hematite content of the conglomerate, and the greater chemical stability of the rock, which rendered its hematite less available. ery little sulphide is present in the main ore shoot of the Calumet & Hecla conglomerate, but sulphide is relatively abundant along the margins of the main ore shoot at Centennial and Osceola. In the sandstone lodes of the onesuch formation and in the overlying shale a little chalcocite is present. Here the ore solutions probably did not move for long di tances in the red andstones but gained access to the beds from the White Pine fault and the related minor fractures, and so opportunity wa not afforded for complete oxidation of the solutions by the hematite of the red rocks. The ratio of chalcocite to metallic copper, in the shales, which appears to be higher than in the sandstones, would be due to lack of hematite in the black shales. The amount of copper occUlTing as sulphide is relatively small: Samples in the White Pine mine indicated that only 2 per cent of the total copper is combined as sulphide, and by far the largest part of this is present in fissures and minor faults, where the opportunity for oxidation by the rocks was low. Some of the amygdaloid lodes contain "arsenical copper," but in this the ratio of arsenic to copper is exceedingly low-a small fraction of 1 per cent. Definite copper-arsenide minerals are practically unknown as constituents of any of the lodes except in the immediate vicinity of some of the arsenide fissures. Many fi sures contain pure metallic copper, but many also carry arsenical copper, and the fissures are the chief source of the sulphides and almost the sole source of the arsenides of the district. Moreover, the cro s fissures of the Cliff-Central type ·have been found to carry notable quantities of copper only near th ir int 1 ctions with hematite-rich amygdaloid or conglomerat lod s. For the old fis. ure vein of Kewe naw ounty, on uch horizon occurs und r th Gre n ton flow and another in the icinity of the A hb d amygdnloid. The relation of copper in the eros fi ur to th intersection of a hematite-rich lode is w 11 hown by the Ma fi ure and the Kearsarg lode in the h:m ek mine: The cop. p r in th fi ur i ry di tinctly concentrated in the neighborhood of its int r ction with the lode, e pe. cially on the hanging-' nil ide of the lode; at many levels the Kearsarge lod is cut aero s by a olid wall of copper in the fi ur . Thi sugg t that the olution that moved along th .fi ure would not have d posited copper in abW1dan in o.ny form at this point had it not b en for th ff t f the amygdaloid. Th many small earn of opper that extend from the Kear aro-e lod into th trap of the footwall or hanging wall as a rule contain opper for only short di tnnces away from th main lod . It app ars en· d nt that they w re f d by the olution that flowed along the lode and that the r action that cau ed the precipitation of copp r oc urr d in the lode rather than in the fi ur . One further relation ugge ts th influence of long contact with red rocl on th condition in which the copper was depo it d. Th copp r of th lode high· e t in the erie , the hb d, Pewabic, alumet & Hecla copglomerate, and 0 ola, i notably pure. In the Kearsarge, I 1 Royale, and Baltic lode , which are low in the serie , the copp r become increa ingly arsenical. The two lowe t lod , the I le Royale and particularly the Baltic, contain more sulphide-bearing fi ures than any other lode. If the solutions gained acces to the bed that are now the lodes from the Keweenaw fault as th main feeding channel, it would follow that the lodes highe t in the series are at the pre ent smface farther from their intersection with the Keweenaw fault than the lodes that lie deeper in the series and crop out clo er to the fault. On the assumption that the fault con· tinues downward at a dip 5° flatter than that of the bed , it is found that the distance down the lode from the present surface to the int rsection with the Keweenaw fault is about six times as great for the Ashbcd, five times for the Pewabic, fom times for the Calumet ' Hecla conglomerate and between four and three ' 't times for the Osceola, Kearsarge, and Isle Royale 1 is for the Baltic. This would mean that the solutwn traveled six times as far from the connection with tho fault in the oxidizing environment of the red lode of the Ashbed (and corresponding distances in tho other lodes) as they did in the Baltic. The result might be that in lodes in which the olu· tions traveled long distances nearly all the sulphur and arsenic was oxidized but where the distance was '
O, S. GEOLO olCA I, llVEY PROFE J ONAL PAPEll 144 PLATE 69 a LPH I DE VEl t n, cin of nnli vo copper (ligh L) nnd chol<:oci l (dork), BuiLic mine: h. chalcocilo (ligh L) und hornil c (du rk) . gunguo qunrt.z nnd onkcri t.c, Bollic min ·ocilo (durkc.st ) in urn ygduloid , lighl urcus iron-bmwing · lrbonnlo, Trimountuin min
U. , GEOLOGICAL a b e AH EN IOES OF OPPEH 250 . c olgodonite a, Oomcyki tc etched with 11,0 11 , at least four comnoocn ts t>, X242: b, the two va rieties of olgodonitc in tcrgrowk, X · '·r~y mincml, etched with r H40 11 . whitncyite between groins of ulgodonitc, X250; d, olgotloni LC (two constitucut8) a un nown g ct.ch ·d with N I I.O H , X250; c, cuprite ultcring to tcnoritc, Algoma mine, X l 20. AU cnlurgemcnts approxtmu1c
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U. S. GEO LOGICAL S n E Y TEXTUHE AND ALTEHATLO OF CAL MET H ECLA CO G LOMERATE LODE . . d h copper; d, und~\; a, Olcuclung or 0 11 SldC Lowurd copper, scale nbouL 10 long; h, blcuchmg or pehhlc, X J !1; c, conglomcrolc portl y replacer rork nssocmtcd ground view or lode; c, couglomeratc pebble partly rct>lnced by copper (dark bonds); r underground view or lode show.ng blcuchmg copper, light. bunds copper bearing '
U. s. QEOLOGTCAL S RV8Y PROFE. IOXAT, PAPER 144 PLATE 73 :1b IJLI~ A IJI NG OF !VIY GOALOJ O LOD" n, Bl hing of mny ~tl ttl o iu uS!<ocioLd wi Lh 'Oppor. Osceola lode; b. blenching uf rock ti<liu ·cnL In !<tdphido vein, Bui LJc lode; c, bleaching of umyguuloid ussociuLCd wi Lh copper, K cursurgo lode
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GE~ESIS OF THE DEPOSITS shorter ome of the sulphur and arsenic rem~in xidized. It might be expected that w1th mcreasmg uno. l d h · d h · d th down a given o e-t at 1s, towar t e mtere~ion with the Keweenaw fault-the proportion of secenic and of sulphur would increase. There is a sugars d · f · estion that this is true as re ate to arsemc, or 1t ~liS long been believed that the ar enic content increases with depth; this relation, however, has not been proved. The Keweenaw fault is of course not proved to be the channelway for the ore solutions, but the relations outlined suggest that it was the channelway quite as much as they explain the distribution of sulphur and arsenic. They support thegeneral hypothesis but without proving any part of it. The copper contained in the pegmatitic streak in trap occurs partly as sulphide; is this · becau e the liquors that depo ited it were never in contact with the oxidizing influence of red rock? H ematite is abundant in the pecrmatite lenses, and it seems probable that a the rocks cool d these lense went through much the ame history as the copper depo it . At the proper temperature this h matite tended to oxidize the sulphur of the solution but evidently wa not ufficicntly active to cau e all of the copp r to deposit a metal Why the sulphur was not all oxidized i not clear. The copper occurring in fis ures clo ely associated with intru ive rna es, as at Mount Bohemia, and therefore depo ited before having mimted far from its point of i ue, i lik wi e chi fly or 11·holly in th form of ulphid , and th amc lack of opportunity for oxidation rna b the r a on why it is not nativ . Taken a a whole, the field vid nc m t indicate that metallic copp r wa d po ited in abundance only in homatit -rich rock or in clo proximity to uch rock . Mo t of th ulphide and ar nidc compound of copper are confined to fractur that allow d the olutions to a cend either for long di tan cs through rap or at any rate with l in tim ate contact with the hematite of the lodes. Further evidence of oxida ion of tho copper-b arinO' olution is record d in the follo11'ing ection. b DESTRUCTIO OF OXIOIZI G AGE T-BLE ACUI G Tho amygdaloid and conglomerate layer have a r d color becau e of their cont nt of minute cry talline fiake of hematite that was formed before the d po if ton of copper . When copper was d po ited the hematite was in part de troycd. r T.he following et of analy es how th content of aud ferrous iron in the unaltered red rock and in the adjacent bleached equivalent clo e to metallic copper and the chemical change that has taken place in the rock during mineralization. Thi change shown diagrammatically in Figures 17 and 1 . 10 Per cent Ke al"s 6 r ge b77r-rYz'T77nrn7Ti>'7;'7?-:;!r~ n bleached omygdoloid 0 see ola 7 ~''~"lf.Lf-<...<...<:..L..L.f.L..<'""'-''+' Unbleached amygda loid Average of Unbleached analyses Fe I" Fe Total Fe FIGURE 17.-Change in iron content of bleached rock associated "·ith copper Numbers at left refer to table below. Change in iron content produced by bleaching of rock associated with copper [Specimens in collection of Calumet & Hecla Consolidated Copper Co.] Original rock r· AI tered rock pecim n o. Fo as Fe.Os I Fe as FeO Fe as FesOa Fe as FeO
7. 14 - - - 12 1 1. Pebble from Allouez conglomerate, Allouez mine, T. ll:f. Broderick, analyst. 2. Iron-rich pebble, Catwn t · Hecla conglomemte, T. M. Broderick, analyst. 3. Amygdaloidat boulder in Calumet & Hecla conglomerate, 0. L. Heath, analyst. 4. Top ol K arsargo lode, Ahmeek mine, 0 . L. ITeath, analyst. 5. Top of Koarsarge lode, outh Kearsarge anne, 0 . L. Heath, analnt. 6. Kearsarg lode, Ahmeek mine, A, B, 0, progressive stages of bleaclting, 0 . L. lleath, analyst. 7. Osceola lode, Centennial mine, 0 . L. Heath, analyst. 8. Isle Royale, Isle Royale mine, IT. C. Kenny, analyst. . 9. Composite sample of Isle Royale lodu and bleached eqmvalcnt, 0 . L. Heath, analyst. andston from Ieos parUy mineralized, Calumet & llecla conglom mte, IT. C. Kenny, analyst. 11 . Iron-rich boulder, alumet & llecla conglomerate, H . 0 . Kenny, analyst. 12. A ''erage of 10 specimens representing lodes of d!!Terent typos.
THE COPPER DEPOSITS OF MICHIGA F' gure 17 illu trates tho chang in iron a.ccompanying ~ineralization for a munber of typica.l example · 'The principal constituents of the . una.ltered and bleached rock are hown in the followmg nnaly e Analyses of unaltered and bleached rock [Specimens in coliection of Calumet & Hecla Consolidated Copper Co. H. C Kenny, analyst) Ia lb 2a 2b 3a 3b i 02 63. 1 153. 1
Al203- I' · · Fc20a - - - · 5 I 6 4 13 4 1. 7 I . 6 · 6 · · 5 1. 55 1" 9.75 · 4 · 1--9-2. 5--:,-9--5. 4--
15 0 per cent of copper removed before analysis. Ja, Dark, bard, oxid ized rock from Kearsarge lode, Ahmeek rome; lb, blenched -equivalent associated with copper. 2a, Red sandstone, Calumet & Uecla conglomerate; 2b, mmerahzed portton or -same stratum. 3a, lron-rich boulder, Calumet & Hecla conglomerate; 3b, bleached eqmvalent associated with copper. It is apparent from the e chemical re ults, a well as from the microscopic study of the rock , that the ·copper-depositing solutions first attacked the hematite .and that the iron was largely removed or recombined a somewhat le s marked con ersion of I rric to ferrous iron. Tho fact that th re bas been ome reduction of ferric to ferrou iron points to the probability that the iron that has been r moved WtlS also fir t reduet!d to the ferrou state, b cause under the condition that probably exi Led ferrous ompound arc more oluble than ferric. If ferric iron wa reduc d to feuous iron, there mu t have been an oxidation of the agent that accompli bed the reduction, and it is of inter st to know what thRt agent wa . Among the r clueing agent that mighL have been pre ent are carbon, carbon mono ·ide, hydrocarbon, hydrogen, and ulphur or some incompletely oxidized form of ulphur. As calcit is plentiful, it is po ible that some le oxidized carbon-b aring material acted as the reduciuO' agent and wa it elf oxidized to the carbonate condition. Lane has, indeed, suO'ge ted that the hydmcarbon which R. T. hamberlin found in ro k of thi di Lrict act d as a reducing agent, thouO'h Lane a ume that it acted on oxidized copp r compounds. Hydrocarbon are, however, no more plentiful in the ro 1 her than in many other regions where no u h peculinr re ult a depo i· tion of native copp r and de truction of hcmaLite are found ; there is no significant connection between ~he occurrence of calcite and eith r depo ition of nat1ve opper r bl aching, and a o 8 8 gg- §8§ the White Pine mine, where 1--'L()T--NT--T"'-<tr.or95@rn_ a lid h dro arbon mo t probably d rived from the J adJ. acen t carbonaccou shale 2:-.!.::-: t--t-t-t+-t-H
i pro ent in fair abundance, the amount of bleaching is t / not on picuou Y grea er than where hydrocarbon occur only in mere traces or not at all, but sulphide are more plentiful there in proportion to copper: at any other place Lll red rocks in the di trict. ! It has been sugge ted that the bleaching around cop?er resulted from the reactwn between the ferric oxide and the metallic copper ,and therefore occurred after the vv ·t d uch Samples Ia, 1 b Samples 2a, 2b Samples 3a, 3b FJGURE 18.-Composition of bleached and unbleached r0ck. (For explanation of manner of constructing the diagram see fig. 5, p. 40.) copper was deposr e · . . a reduction of ferric oXlde.IB readily accomplished and IS, before there was any conspicuous change in the other ·Constituents. The copper replaced the rock substance as a whole, but in advance of this replacement the hematite was destroyed and the iron removed either .entirely or in part, and whatever remained was combined into other minerals. (See pls. 72, 73.) The general tendency in the alteration that produces . bleaching is a removal of considerable ferric iron and indeed a difficulty in chemical analyses when ferne oxide determined in the presence of metallic copper. Moreover some of the copper ore when brought to · the surfa;e shows a thin film of green copper carb~nj ate or of red mcide of copper surrounding the roe 11er' ·d· d copp and this has been suggested as the oxr rze E · · · 'ted ixanu· compound produced m the reactiOn cr · er nation and inquiry show, however, that the copp
GENESIS OF THE DEPO ITS when the rock is :first broken is not green but bright d metallic or at roo t covered by a mere film of :~prite. Moreover, the removal of hematite is not the only effect in ~he bleached areas .. In the amyg~a loid lodes in particular, t~e destru~twn of. hemat1~e wa accompanied by an mtense mrneralogiC, chemial and textural breakdown of the rock surrounding ~h: copper-an alteration that would not be likely to re ult from the mere action of the metallic copper on the rock. There is no doubt that the metallic copper was replacing the bleached rock-that i., that the removal of iron, although everywhere going on at the same time as the depo ition of copper near by, wa accomplished at any given point in advance of the precipitation of copper; bleaching wa the fr nt of the alteration wave; replacement by copper wa the nd. The practi al absence of bleached pots without accompanying copper further indicate that depo ition of copper and bleaching of ro k were intimately a ociated and that copper has not been removed ince its depo ition. The exceedingly low copper and iron content of the mine waters likewi e proves that reaction between iron and copper i not now in progre , or, if at all, to only a very slight extent. The hypo the i that copper ulphide olutions acted a the reducing agent that de troyed the hematite appears to fit the fact in a sati factory way and at once explain both the bleaching of the rock and thA deposition of opper in the native tat . The power of the metallic ulphid a · r du ing aO'ent i hown by the ea e with whi h th y take up ox gen to form ulphate - fnr more r adily, for in tan , than the ferrou iron mineral uccumb to o::-..'i.dation. In the oxidation of the " ulphide solu tion th pro ha, gone o fat· a t oxidize th ulphur, but the c pper wa deposited as m tal. 'l.'he copper occur generally in irr gular ma e rather than uniformly di tribut d thr urrh the lod . It is impo ible to as urn that the r plA.c d ro kit elf could supply enough r activ ag nt of an kind t cau e the precipitati n of thr tim it n weight of copper, either in the small particle or in the gr at ma ton and ev n hundr d of tons in weiO'ht. It i more likely, a uggest d in conn tion with the at~tration hypothesis (p. 129), that tho reaction was takmg pia e A. tho olu tion pa d t.hrotwh th lode until uch a degree of concentration wa r ached that copper pre ipitati n had to begin. ln places opper is accompanied by only sliO'ht if any immediat ly local blea bing. This is the ca e, for example, in parts of the Pewabi lode, in the upper eve! of the alum t & Hecla conglomerate mine, and in the copper-bearing fissu res that cut the Keararge lode. Wells has found in his experim nt that the metallic copper commonly does not replace the solid reagent that cau es the precipitation but rather grows out into the free olution, often not in contact at all with the precipitant. Th laboratory experiments thus appear to be in harmony with the natural occurrence. Copper was depo ited in the cross fi ures chiefly at and near their intersection with thick hematite-rich lode . Where in the Ahmeek and Mohawk mines some of the e fissures, notably the Ma fi ure, cro s the K earsarge lode, the destruction of hematite is of a different t pe from that seen in the blea hed rock that so commonly surrounds the copper. Along the e copper-bearinO' cro fi sure for a width of 10 to several ten of feet the Kear arge lode i darker and leaner than u unl. Along the Ma fi ure in the Ahmeek mine the dark lean zone extends for 0 to 100 feet on each side of tbe fis ure. D etermination of iron OAides show the following contra t between the dark material and the normal red material near by: Alteration of Kearsarge lode near Mass fissure Fe as FesOs Fens FeO 1 The changes indicated by these analyse suO'gest that the solution moving generally along the fi ure but oaking into the Kearsarge lode were at that time and place able to de troy but little of the ferric iron but were, on the contrary, relatively highly charged with ferrou iron, which they precipitated. Mi roopic examination of the dark material reveal a differenc in t' o re pe t from the normal rock of the Kear arO' lod -(a) much chlorite ha been intro-
due d throughout and account for about all the added ferrou iron· (b) all the fin r flake and particles of hematite have been removed and with them the r d color, but the larger grain of hematite, whi h make up the greate t part, by weight, are still present and account for the mall decline in ferric iron content notwith tanding the marked chang in color. It eem probable that the solution moved along the inter ection of the fi sure with the Kearsarge lode; the main avenue of flow was throuO'h the fi ure, but there wa alwa local p netration into the perm able lode, and in con equence the olutions, before reachin()' the level now expo ed in the mine, were oxidized at the exp n e of the hematite of the lode and became charged with ferrous iron and uncombined copper. Having undergone the e reaction , the olutions depo ited the constituents with which they had become saturated, but the copper wa depo ited mainly in the fis ure it elf as masse of native metal while the ferrous iron, which could not be precipitated alone, wa depo ited a chlorite partly along the fi sur and partly in the lode. The lod rock, because of it gla s condition, wa.s probably more su ceptible to
THE COPPER DEPO IT OF MICHIGAN reaction than the trap that in the main bounds the fissure. The channel afforded by the fi ure and the immediately adjacent parts of the lode probably constituted an easier avenue for a cent than that offered by the lode alone. The solutions flowing along the fis ure, therefore, should have reached the altitude of the present mine workino-s before those which moved up the lode and accomplished the normnl mineralization characteristic of the Kea1 arge. If o, the alteration ju t described had been accompli bed, in part at lea t, near the fissure by the time the normal lode olutions reached that point. With tho most finely divided and hence the most reactive of the hematite already gone, the lode near the fi sure wa less favorable for precipitating copper from the later solutions than the lode away from the fis ure. It is not definitely known whether uch copper as occurs in the darkened zone along the fi sure wa deposited by the fissure olutions, by the lode solutions, or by both. The de criptions of certain of the fissure veins of Keweenaw ounty mined in earlier days, notably the Cliff and the Central, indicate that some lode contained sufficient copper to warrant e;>.'])]oration of them out ide the limits of the fi ure or fissure zone; and as a rule the exploration of the e "floors," as they were called, was abandoned not far from tho fissures. The natural inference is that certain of the lodes clo e to the cross fissures had been mineralized by the solution , which in the main were traveling along the fis ures themselve . The arsenide fissures that cross the Kearsarge lode carry iron carbonate in considerable abundance, and an iron carbonate is characteristically pre ent in the sulphide fissmes in alfd near the Baltic lode. It is evident, therefore, that the solutions that traversed the fi ures were also relatively rich in ferrous 1ron. PHESE.' CE O:P SULPHATES If copp r ulphide were oxidized and in consequence precipitated native copper, the oxidation would obviously affect the sulphur. What condition or combination of sulphur might actua.lly be expected? Elemental sulphur is known to be formed from the oxidation of sulphide and from the oxidation of certain sulphur-bearing hot-spring waters, but these occurrences do not justify the inference that sulphur shoul~ have been formed · in the Michigan copper deposits. ulphur dioxide, which .is present in volca~c ~anations, .may produced in part by oXIdatwn of sulphides, directly or indirectly, and 1t IS lmown to be formed in small quantity from the artificial oxidation of pyrite under certain conditions. The sulphite salts derived from it (or from sulphurous acid-H20 + 0 2) are either easily soluble or unstable and so it could not be expected that any of thes~ sulphur compounds would now be pre ent, no matter how much 0 2 may have formed. In nature oxidiz d ulphur occur by far the mot commonly as sulphat , and wh n olid ulphide oxidize, sulphate and ulphuric acid are formed from all or nearly all tho ulphur of th ulphide ; moreover, as has been indicat d cl wh re,37 the ulphate pre ent a gangue mineral in primary ore dopo·it have probably been d rived b hypogene oxidation of sulphur-b aring olution . ulphatc are the only oxidiz d compounds of ulphur that are likely to form mineral and be found in tho deposit , but, a only 8 few of the ulphate arc notably in oluble, it i not to be e;>.'])ected that even th sui ph ate will be found in abundance. Sulphuric acid, if formed, would undoubtedly unite with one or more ba c ; o only sulphate salt would be expected. If copp r sulphide were oxidized by hematite, one probable product of the reaction would be ferrous ulphate. I t i certain, however, that if the solution contained base that form rclatil'ely in oluble ulphate uch sulphate would form and be precipitated in a cordance with their abundance and solubility. Th sulphate of mo t of the common element in the Mi higan rocl are highly soluble. This i true of odium, pota ium, magnesium, and aluminum, and it i true of ferrou iron except when . jn contact with an oxidizing agent of stronger powrr than hematite. The pre nt mine water contain only slight and occa ·i nal Lrace of sulphate , thou17h gypsum i being precipitated from mine waters in the Victoria mine; but unless it i hown that the pre nt mine water are part of tho e that d po ited the ore , the pre ence or absence of ulphates in the e waters i of no particular significance. The barium and calcium ulphates barite, anhy· drite, and gypsum occur in the Michigan depo. it and are the only sulphates sufficiently insoluble to be expected. Barite account for all of the barium o far as known, but the two calcium sulphates account for only a very small fraction of the total calcium present in the lodes. The total quantity of sulphate repre entcd by the e three min rals is far too little to account for all the sulphur of the solutions the native copper came from sulphide. In explanatiOn of this discrepancy, reference may be made to the behavior of the sulphate radicle in regions where sulphide ores undergo superficial oxidation. In.c~mp like Bibee and Globe, in Arizona, great quant1t1
sulphide ore contained in lime ton have been oxt· dized near the surface, with the production of corrc· spondingly great quantities of soluble sulphates and s~phuric acid; these have plainly enough re~cte~ the adjacent limestone and must have forme calcium sulphate on an enormous scale, yet the " BuLler, B. 8., Primary (hypogene) sulphate minerals In ore deposits: Econ. Geology, vol. 14, p. 681, 1919.
GE ESIS OF THE DEPOSITS inentl gypsum is present only sparsely in and near ~ese oxidized ore bodies. This is due in part to the rather ready solubility of calcium ulphate in water. A compari on with other di tricts where sulphate solution are known to have formed in large quantity i doubtle the mo t reliable omce of an explanation of the conditions in tho Michigan di trict. Sufficient fact and experimental data are not available to afford 8 reliable interpretation of conditions o complex a tho e that affected the ore solutions in this di trict, though certain xperimental fact may be pointed out. Thee are taken mainly from a paper by tieglitz.38 In a saturated water olution of calcium carbonate and calciwn ulphate, at 1 ° ., the concentration of ulphate ion is five thousand times greater than that of carbonate ion . C02 increa s the solubility of calcittm carbonate in olution a bicarbonate, and thi eff ct continues with increase in pr ur of C02. The pre ence of other sulphate decrea es the solubility of calcium sulphates. The solubility of calcium sulphate and calcium carbonate is increa ed by the presence of sodium chloride up to a certain concentration, above which that of both decreases. Increase in temperature reduce the solubility of calcium sulphate, which is but slightly soluble at 200° C.39 Incr a e in temperature al o reduces the olubility of C02 and in consequence probably that of calcium carbonate. Too little is known of the infiuence of these several factors to warrant any definite conclu ion , but perhap the relativ ly high temperature of formation account for th fa t that an alcium ulphat wa precipitated. Th argum nt with r p ct to oxidation product of ulphid may b ummarized a foll~w. uch OAidation product w r probably earned away for th roo t part in th form of ga or of solubl alt, ither of which would b di ipated with relative a oon after th min ralizing proce had cea ed. Th onl ulphate produced by ulphid oxidation that ould be expect d to r main are the ulphatc of barium and calcium. Barit in fact i present perhap a plentifully a th g n ral carcit of the cl m nt barium would permit, and anhydrite gyp um are pre nt a pl ntifully a th olubility of calcium ulphate would p rmit and a plentifully as th yare found in other r gion where calcium sulphate mu t have b n produced in gr at quantity. All ~roe sulphate min ral have be n found only in the 1mmediato vi inity of copp r-a fact whi h rna well be regard d a eviden that they ar product of the reaction by which the metallic copp r wa formed. .The gyp urn which is abundantly pre ent, togeth r ~me barite and celestite, in and near the Coro q II U tz, Julius, Tbo relations of cqullibrlum botwecn Cllrbon dioxldo of tbe ere and t~1e calcium sulphat , calcium cerbonnt , and calcium biCIIrbonato "Mel ~Iutton to contact with it: Cam gio Inst. Washington Pub. 107, 1009. c er, A. F., Am. Chem. Soc. Jour., vol. 32, pp. 50-66, 1910. Coro depo its of Bolivia wa likewi e e::-.-plained by Steinmann as formed from the sulphate radicle produced by the oxidation of the sulphur of the copper ulphide olution . Carbonates are not abundantly associated with the Coro Coro depo its. CHE:\:U TRY OF THE DEPOSITION OF ATIVE COPPER FR0:\1 ASCENDING OLUTIO S By R. C. WELLS As a very con iderable weight of evidence indicates that the native copper in the Lake Superior di trict was deposited from olutions that may be characterized in a broad way as a cending, the chemical problem of accounting for the depo ition of the copper as native metal i th reby delimited to a certain extent. Many of the condition attendant on it deposition are tmknown, a the olvent with all their more soluble di olved matter have pre umably di - appeared, and the solid remaining are relatively few in number and simple in chemical character. But, on the other hand, the idea of a cending solutions, e pecially on the large cale exemplified in the Michigan district, impli certain general condition , partly phy ical, partly chemical, which sugge t a imple cla sification of the po ibilities. The condition , or rather the changes in condition , that w.ould naturally be expected to exi t in association with a cendinO' olution , ar , in the order of their probable importance, cooling, relief of pre ure, oxidation, dilution, and reduction of acidity. Chemical UO'ge tions based on old or new e21.-perimental evidence are offered herewith under each of the e head . The details of roo t of the new experiment are given in a eparate publication,40 and what i pre ented here i largely a urnmary unencumbered with the chemical detail . Need1 to ay, the experimental field i till far from cover d, a neither melt , vapor , alkaline olutions, nor olution above 300° C. have been tudied to any great xtent. The re ult are uch as could be obtained 'vith workable solution and the apparatus available. They are ufficient, however, both to supplement and to modify previou knowledge. DEPOSITION BY COOLING ot solutions carrying cuprou ulphate depo it metallic copper on cooling. Thi action i believed to occur as th r ult of the change u2 04 Cu + Cu 04 so that only part of the copper can be thu removed from olution. uprous sulphate may be formed in a number of way -for in tance, by the action of copper on cupric sulphate, by the action of variou ulphides on cupric ulphate, or by partial oxidation of opper sulphid . Wells, R. C., Chemistry of the depo ition of native copper from ascending solutions: U. S. Oeol. Survey Bull. 77 , 1925.
THE COPPER DEPOSIT OF MICHIGA A metallic il er accompanie copper in a few depo it it is of intore t to note that metallic ilver likewi e depo ited when certain olution are cooled, as indicated by t)B two following reaction g2 0 4 + u2 0 4 2 g + 2 u 0 4 Ag2 0 4 + 2Fe 0 4 2 g + Fe2( 0 4)3 Gold behaves similarly, as shown by Stokes : AuCl3+3CuCl Au+3Cu lz All these equation represent reversible reaction that proceed toward the right with falling temperature and in the opposite direction with rising temperature. Vapors and melts would become more or le s fixed by cooling al o, but they can not be adequately discussed at present. or is it purposed to eli cuss in this place whether the theory here et forth or any of the other theories proposed would apply to a relatively local movement of the fluids from the interior of a lava flow to its cool top as well as to movement on a much larger scale. DEPOSITION BY RELIEF OF PRESSURE _The solubility of most salts changes very slightly pres ure. For example, that of copper ulphate is known to increase with pressure some 3.2 per cent for 60 atmospheres, but that such a chano-e could be significant· in the problem under discu ~ion eems ?oub~ful. The solubility of ga es, on the other hand, 1s affected to an enormous extent by changes in pre sure, and, as ga e like C02 and H2 increa e the solubility of the carbonates and ulphides to a marked ex~ent, it i evident that relief of pressure would favor the deposition of such compound - that i , if the ?as s escape from solu tion. Carbonates are pre ent m the copper lodes- in fact, copper and calcite are beautifully .in t~rgrown in some specimen . Thee cape of carbo~ dwXIde through relief of pre ure is a possible ~xplanatwn for the form~tion of the calcite. othing known as to the solutwn or precipitation of copper rt~elf through changes in pre ure, except that ind~re~tly the reducing action of hydrogen and sulphur ?!OXIde copper compounds is increa ed by moderate mcrease m ~ressure, as much more of these gases is thereby .h~ld I? solution. This fact would not account for precipitatiOn through relief of pres ure ho d · b , wever, an 1t pr~ .ably has no application to the problem of the depos1t10n of copper. DEPOSITION BY FRACTIONAL OXIDATION OF COPPER SULPHIDE !he. theory that native copper wa formed by the OXIdatwn of copper sulphide in solution b f . · 'd . h Y ell'lC OXI em t e rocks of the lodes has been advocated with eon~dence by the. authors of this report, lnrgely on the bas1s of field evrdence. The formation of t 11. b .d . me o 1c Y. OXI a t~on of the sulphide is a familiar opma wn m sme tmg practice. Analogous react· based on th · wns, e OXI Izmg actwn of cupric salts and ferric salts, ore cited in the literatur . The action of ·d ified ferric salts on the sulphides of opper uacd
din eli . nu or ary con appear to result in the formation of ferrous and cupri salts, o that the problem re ol it elf in part into a stud of the oxidation of CO!>ve "d b · per u phi e y cupnc sa t . onsid rable study ha been giv n to the e varia po ibilities. The theory here pr po ed implies che~. ical reaction. There ar oth r ground in the field relfttions for thinking that the solution wero a cending, and such solution 'i ould be loo-ical ource of copper ulphide. In the experim nta.l work, however it ha not yet be~n pos ib~e to produ e metallic coppe; merely by ch m1eal r a tion unaccompanied by cool. ina-. In o far a cooling ha be n an e entia! part of the verifi ation of th th or , the idea of ascending olution receive upport. The exp rimental evidence indicate , however, that at a till high r temperature than could be conv niently attain d with the apparatu available, copper might b depo itod by reaction alone and thus the th ory render d independent of the feature of cooling. The tep by which f rric xide may act on a olution of opper ulphide are a follow : Hot acid solution containing copp r and ulphur, a umed for the a1 e of implicit to be qui valent in th ir chemical pot ntialitie to a id olution carryino- cuprou ulphide, meet f rric oxide. The acid i decrea ed by olution of orne ferric oxide. The ferric alt thu 1 formed ex rt an oxidizing influ n e, whi h is, however, at once balanc d by the reducing action o cuprou ulpbide, wit.h the production of ferrou ulphate and cupric ulphate, a indicated by the following reaction: Cuz + 5Fez03 + 11Hz 0 4 lOFe 0 4 + 2 u o. + uH,O The oxidizing action of the ferric alt eems to carry the opper to the cupric tage at fi1 t and rather rapidly. Further work i needed to ee if the reaction can be uffici ntly lov ed down through the u of le acid to yield chiefly cuprou ulphate. However, experiment shows that when further cuprou ulphide i available, its pre ence, a well as the decrea e of acidity and the formation of water and cupric sulpha to, favors the reactions CuzS + Cu 0 4 + 4H20 5Cu2 0 4 + 4H2 04 CuzS + 3 uS04 + 4H20 5Cu + 4H2 0 4 The second of thi pair of 1:eactions may po ibly occur at a very high temperature but has not yet been realized experimentally. However, the reaction yield cuprous sulphate, which depo It copper on cooling. The consumption of cuprouv sulphide in these way would obviously leave le 9 of it to be deposited as the solutions cooled, where~ c?pper would still be deposited on cooling. Condttwns favoring the depo ition of copper would be an
GENESIS OF THE DEPOSITS 139' · itial high temperature; the reduction of acidity to point where no more ferric oxide would be attacked r the local exhaustion of the ferric oxide by the lut.ion and reduction a outlined; and, lastly, cooling snd dilution of the initially heated solutions. In !hi way the ulphur would make its exit as ferrous sulphate. A reaction that embraces all the steps mentioned would be Cu2 + 3Fez0a + 5H2 04 2Cu + 6FeS04 + 5H20 Metallic copper has been obtained experimentally from the sub tances indicated in this equation after heating them with water in sealed tubes to 300° and cooling. It would be highly de irable to how that olution ofle acidity, such a tho e containing carbon dioxide under high pressure, would yield similar results, but the writer has not yet been able to do so. orne acid seem nece sary to give the ferric iron ufficient activity to initiate the action, and the proper range appears to be one in which some ferric oxide di solves to give a definite oxidizing action, likewi e in uring !hat a large excess of ferrou salt will not precipitate copper, o that only the ulphur and neither the ferrous iron nor the copper shall be oxidized. Experiments at ordinary temperature , at which the activitie of the >ereral reagents could be better regulated, would also be de irable, but the reactions involved occur too slowly at uch temperature for ob ervation within the ime aYailable. ln view of the diffi.culti of reproducing the natural tondition exa tl the writ r feel that the exp rimental evidence mak thi th or of th origin of the Lake uperi r copper a tenable on a ide from the strong field evid nee in it favor. DEPOSITION BY DILUTION . lution arrying on iderable cuprou chloride, wh1eh i larg ly soluble in ertain brine and other concentrated olutions, depo it copper on being radually diluted. Thi mod of orio'in may a count fo: some of th "ma " copp r in the Lak uperior mme where ro fi sure have permitted the intermmgli.ng of the concentrnt d brine with more dilute lution , although it i evid nt that uch a view ren~ers the d p ition of th rna opper not n sar~y contcmpornn ou ith the d po ition malll lodc . The reaction for this chang is 2 llz u 13 4 a+ + u + u ++ + 6 IThat i , a complex or double salt that exi ts in the ~n~ntrate.d solutions br13aks up into single alt on utton, With accompanying precipitation of some of 1116 copper. DEPOSITION BY REDUCTION OF ACIDITY ~Joderate changes in acidity or alkalinity are genera Y characterized by the chemist as changes in the Sorensen number or pH value, which defines the hydrogen-ion concentration of the solution by the equation pH= -log [H+] in which [H+] represents the concentration of the hydrogen ion in gram-equivalent per liter. The pH number of ore-forming olutions is of coniderable importance and has not been studied as much as it de erve to be. It i obvious that as olutions pas from an acid to an alkalin reaction the olubility product of the oxide will be reachedfor example, those of ferric oxide, copper oxide, and ferrous oxide-in the order of re pective increa ing olubility. The pH number likewise determines to n large extent the solubility of other ore and gangue mineral , such as the sulphide and carbonates. But the oncentration of the valuable metal in aqueous solution that "Tould be furnished by uch compound under ordinary condition are extremely smallo small, in fact, that they are not within the range of ordinary analytical determination. It eems hi()'hly .improbable, likewi e, that uch small concentrations have played any part in the tran portation of ore ; for if they had, ore depo it could not be formed at all. It i the ta k of the chemi t who i eekin()' to explain the gene i of ore to point out pecial in tance of olubility and the condition that effect change of olubility and to earch for uch ondition if they are not known. In thi inve tigation alkaline olution with pH value much O'reater than 5.5 eemed to offer little aid toward olving the problem, inasmuch as ferrous alt , ' hich w re almost certainly pre ent in abundan in th or -forming olution , would cause depo ition of both copper and f rric oxide. In experim nt with olution aturated with ferric oxide at ordinary temperatme, the writer has found that the pH number mu t be a low a 5.5 before a te t for f rri.c iron can be obtained with pota ium ulphocyanate. olution of even o low an acidity a thi would therefor have geolo()'ic i()'nificance. Precipitation of copper b ferrou alt , the agency long held to account for th fonnation of native copper in the Lake Superior d.i trict, can occur only if hydroly i of the ferric alt to in oluble ferric oxide is brought about through continuou n utralization or continuou ly increa ing heat-that i , by an increa e of the pH numb r. The writer's recent experin1ents on this method of deposition show that when ferrous hydroxide is used as the reducing and neutralizing agent, acting on cuprous chloride solutions, both of the following reactions occur: 3Fe0 + 2 u 2 u + Fe20 3 + Fe lz 4Fe0 + 2 uCl 2 u + Fe30 4 + FeC12
THE COPPER DEPOSIT OF MICHIGA Deposition of copper from cuprous chloride s~l utions may be brought about even by ferrous chlonde, ever, when the pH number is carefully regul.atedas, for instance, by means of defmite proportions of acetic acid and sodium acetate. When ferrous chloride and cuprous chloride are introduced into such solutions, boiling in an atmosphere of nitrogen, no copper is precipitated if the pH value is initially less than about 5.0. In one experiment with a pH value of 5.2 a sli()'ht film probably containing some copper, formed b ' ' on the walls of the flask in the course of two hour boiling. With a pH value of 5.3 the depo it sho~ed some small particles of ferric oxide, each surrounding a nucleus of minute crystals of copper visible with a lens. Repetition of the experiment with more ferrou chloride and less cuprous chloride, in a flask with a slight film remaining from the previous experiment, gave a deposit showing under a len or a microscope numerous crystals of copper, some spicules, and some thick crystals showing triangular faces, most of them largely covered with iron oxide, which also adhered to the glass in the form of minute lumps and floes without definite form. This iron oxide was not magnetic. The reaction occurring in this case may be written 2FeC}z + 2CuCl + 6N aCOOCH3 + 3H20 2Cu + Fe203 + 6HCOOCH3 + 6 aCl These experiments show that the use of ferrous hydroxide is not absolutely nece sary for the deposition of metallic copper but that more soluble ferrous compounds suffice; that copper is a recognizable product when the reaction is made to occur very slowly; and that the deposition of copper is not dependent on cooling, a point previously unsettled. This mode of forming native copper can obviously not be left out of consideration entirely, because of the common association of ferrous and copper compounds, and it might be viewed as an adjunct to any theory in which mixtures of ferrous and cuprous salts are involved. On it myth based his theory of the deposition of copper from ascending solutions, which the writer has ventured to supplement with the process of neutralization. Neutralization is suggested in order that the initial solutions can be assumed to have been not very alkaline, so that appreciable concentrations of copper salts and ferrous salts could be present in them. If the initial solutions were alkaline in the presence of ferrous compounds it is difficult to see how significant quantities of copper could have been transported. Bu-t cooling must also usually occur in a cending solutions, and, as has been shown above cooling alone will deposit copper from slightly acid solutions containing cuprous and ferrous sulphates so that reduction by ferrous compounds is not abso1 utely needed as an explanation of the deposition of the nopper. The th or of r duction by fen·ou compound h been ad ocated b ev ral geologist without re~a:d to whether th cupriferou solutions were ascending or descending, and ome study has been given to the neutralizing action of th lode minerals. For example Lane and Fern k s found that prehnite and datolit~ , ere more active than labradorite and laumontit~. Lane' equation for this action is 2Fc b + 2Cu l + 3 a iOJ 2 u + F 0 3 + 3 i01 + 3 a b Thi equation is al o an attempt to explain the calcium chloride' ater now found in the de per levels of the mine . Be ond ailing attention to the mall quantity of such wat rs in the mines, relative to the copper, the writer will only refer to the di cus ion of this feature of the probl m in another section. All the r action elucidat d by Biddle, toke , Fernekes, and Lane, however, involve d po ition of Fez01, whereas the pr ent tudy has been devoted largely to the attempt to explain the dis olving of F~Oa in connection with the d po ition of copper, which field evidence so strongly indicate . In the light of present knowledge it appears difficult to decide whether a cending olutions would in general tend to become more acid or 1 s acid in their reaction. In so far as they undergo oxidation they would probably become more acid, but the loss of uch go es as H2 , C02, and 0 2 would have the oppo ite effect, so that it is difficult to be certain of the final r ult. number of compound , e pecially tho e of a altlike character, are decompo ed by heat into free a~ids and bases, and such decomposition would certamly tend to occur to a greater or less extent at depth If such compounds are pre ent. The acids, being volatile, could move into cooler regions, where they would recombine with any bases available, but the bases wouJd be left at the point of decomposition. A somewhat similar result might be brought about through the action of ilica as an "acid" in displ~c ing the more volatile acids from their salts at high temperatures, but at low temperatures in aqueou solutions silica is an extremely weak acid in com~ar~ son with the strength of the bases with which It 1 generally associated. In other words, there see~ to be several reasons for supposing that hot solutw~s R.nd gases at depth would tend to be acid, wherea Ill cooler regions, except for the oxidation of sulphur compounds, alkalinity would become more pronounced. This line of speculation favors the theory that ~op· per might be deposited from ascending acid solutJO~S through the agency of neutralization, but, if so, fem~ oxide should accompany the copper, which does generally appear to be the case in the Lake uperi~r ores. Moreover, this theory leaves sulphur coropoun and the oxidizing action of ferric oxide out of ~on sideration, and for that reason it can not be given
GE ESIS OF THE DEPOSITS first place a an explanation of the formation of the Lake uperior copper. CONCLUSIONS To recapitulate, five agen ies that might effect the deposition of copper fron: ascending. solutions have been considered-(!) coolmg, (2) relief of pressure, (3} oxidation, (4) dilution, (5) reduction of acidity. Three of these agencie require specific constituents in the solution-the first, cuprous sulphate; the third, potential cuprous sulphide; the fourth, cuprous chloride. The third also demand an oxidizing environment for the incoming solutions, and the fifth is baed on an environment that will neutralize acidity. Two of the agencie , however, may probably be excluded from consideration at once on account of the difficulty of defining the conditions with the nece ary degree of certainty. These are the second and fifth. The only application of the second agency that appears of importance as a po sible cau e ·of the deposition of native copper is the escape of certain acid gases, part icularly carbon dioxide, which would leave the solutions more Alkaline. This would tend to assist the deposition of copper by ferrous compounds, but other factors, such as oxidation, might tend to make the solutions more acid. It i extremely difficult to feel sure of the direction of the variation of acidity, so that it seems best to dismiss the fifth agency and with it the second from consideration. Another rea on for doing o i the field evid nee that the precipitating olutions eem to have di solved lerricoxide rather than to hav depo ited it as required by the fifth agen y for the depo ition of native copper, and still a third reason · that ulphur compound are not con idered or their gen ral absen e xplained by either the econd or th fifth ag n ie . The first and fourth agencies are so general that they might apply almo . t anywhere. They al o require the pre ence of pe ific om pounds, cuprou ulphate and cuprous chloride, re pectively, and to call on them as explanations of a rath r unu ual type of ore, that of native copper, obviou ly r quire orne addit.ional feature, su h as, po sibly the large scale of the field. But this is as unwarrant d as it is unnece ary. Thus t?e third agency is 1 ft a the only alternative ex1)lanation. The third agency of depo ition seems to fit the Lake up.erior district best becau e the speeific inftuen e of ~errtc oxide in the gangue ro ks i taken into account m determining the character of the copper mineral depo ited, and it is probably. unnecessary to delimit the character of the olutions further than to . ay that they were a potential source of cuprous sulphide and, 80 far as the nece sities of the chemical ex"})eriments sugg.est, somewhat acid. The last statem nt might . 1bly imply nothing further than solutions conanung large quantities of carbon dioxide. The general absence of sulphides is explained by the oxidizing action of ferric. oxide, and the deposition of copper i explained by cooling of the resulting solutions at least, if not by a direct chemical reaction, which appears probable at moderately high temperature . SUMMARY OF GENESIS In the preceding page the everal views regarding the origin of the native copper deposits of fichigan that have been advanced by previou investigators have been outlined, and the view held by the present writers have been elaborated in d tail. A brief general summary of the argument may help the reader to judge the relative merits of all the e propo ed explanations. It will be empha ized in this review that the theory arrived at by the writer differs outstandingly from tho e of orne others in po tulating that the copper was depo ited from a cending rather than descending solutions and was precipitated by oxidation of the ore solutions rather than by reduction. As in the fuller statement, origin, transportation, and depo ition will be con idered in turn. SOURCE OF COPPER If the depo its were formed by de cending olutions the copper mu t have been derived from the general mas of the Keweenawan lava , which are known to contain mall amounts of copper- amotmts omparable to tho e contained in imilar rocks at many place . o far a lmown, thi copper is pretty uniformly di tributed. It i regarded by those who favor the view of de cending water a an ample ource for the copp r depo it . Tho e who favor the view of ascending olutions mu t al o recognize this minutely di eminated copper a quantitatively sufficient, but they ee no evidence that it ha been concentrated. It i till contained in the trap to the extent of a few hundredth of 1 per cent. I it rea onable to suppo e hat olution would di olve out a constituent pre, ent in minu e quantity and concenlirate it to the amount of 50 to 100 time without having a notable effe t in di olving the mineral that are pre ent in much larger quantity? Tho e , ho favor the view of an a cending origin con ider the Duluth· gabbro, which is believed to underlie the whole region, as the source of the copper. Copper in mall amotmt i as ociated with the mall off hoot of thi igneous body, and to tho e who e experience ha led them to look upon intru ive bodies a a ource of ore depo it thi ource com adequate, favorably loco,ted, and probable. TRANSPORTATION Gravity circulation of solution i regarded a the tran porting agent in the theory of descending origin. Doubt is thrown on the sufficiency of that method by the very slow rate of gravity circulation a indicated by the dryne s of the deep le l of the mine and by
THE COPPER DEPOSITS OF MICHIGA the difficulty of conce1vmg a gravity circulation as operative far below ea level, a it mu t have been under conditions at all like the pre ent. Moreover, the po ition of many of the ore shoots beneath relatively impermeable rock eems io.con i teut with deposition by descending solution . The view of concentration by diffu ion a oid orne of the difficultie of gravity circulation but meet others in explaining why copp r wa not concentrated equally in all lodes of imilar phy ical character and chemical compo ition and why the ore occurs o definitely in boots. In the theory of a cending origin the medium of tran portation i regarded a the olution given off by the crystallizing magma of the Duluth gabbro. These were heated liquid or O'a es and therefore very mobile and w re under high pre ure, which ould force them in quantity through rock where gravity circulation would be practically nil. The olu ion either entered the lode bY' the direct connection of the downward exten ion of the lodes with the igneou mass or were led into the lodes through faults or fissure that extended to the igneous ma . Thi explanation eem to fmni h an entirely adequate means of tran portation and one entirely imilar to that believed to have been active in the formation of most primary copper depo its. CAUSE OF DEPOSITION The theory of de cending origin a umes that the copper wa carried a an oxidized compound and wa deposited through reduction by ferrous iron. The conglomerate and amygdaloid were very rich in ferric iron and poor in ferron iron long before the copper was introduced. Moreover, the alteration of the rock a ociated with the copper indicate that when the copper wa depo ited the ferric oxide was actually reduced and ferrou oxide added-a fact which hows pretty clearly that reduction by ferrous oxide wa not the proce s that formed the copper. The theory of a cending origin as umes that the solution were uch a ordinarily depo it sulphide and were e entially reducing and that if they had encountered rocks of the ordinary compo ition they would have d posited sulphides. But because these olutions encountered rock with a high content of f~r~1.c ~ron there. w~re chemical changes before preClpltatwn. Ferne 1ron was reduced, sulphur wa oxidized, and native copper was formed. The lode rich in ferric iron would be the places mo t favorable for the pre ipitation of copper. OTHER RELATED DEPOSI TS rr:here are t~rough?ut the world other deposits of nat1ve copper m the copper appears to have been deposited as nau1ve metal and not to have been formed by surface oxidation of some other mineral ' such as chalco ite. The chief examples of such d. posits o cur in oro Coro, Bolivia; the Tria sic are e of ew Jer ey ~nd Connecticut; ape d'Or, No~ Ob rstem, Germany; ommander I land the Faroe I lands; ao ~aulo, _Brazil; Uppe; the opper and h1te R1ver di trict omobabi Mountain , rizona; Nov~ Zembla, Rus ia; and opp rmine Ri,7er, Canada. The condi t.ion of occurren e at the e localitie are et forth below: Ooro Ooro, Bolivia. t Coro oro occur thelnrf!est of a series of similar copper d po its that lie in a z~ne that extends acros the B livian high plateau. The copper i found in the Pu a r d and tone, of Cretaceou age, in both vein and beddc L depo its. Minernlization ha occurred at a number of clo ely paced horizon . The do min ant copp r min ral i the native metal, althouO'h the ulphide chal ocite and the arsenide dom ykite are sparingly dev loped. ative ilver i al o found a o iat d with the copper. Oxides of copper occur at the surface but gi e way to the native metal, which per i ts at lea t to 3 0 meters, the greate t d pth attained b the pr ent workin!!S. The sand tone, which away from tho ore ha a di · tinctly r d color tone due to iron oxide or hydroxide, i bleached in the vicinity of the ore. The copper is thus usually surrounded by a halo of whiti h or green· ish rock that grades into the r d which is the prevalent color of the formation away from ore. A.t oro oro we idently hM·e the e ential con· dition to produce native copper from a cending ulphide solution . None of the c mplication of lm flow a po ible ource of copper, of ferrou mineral" as po ible reducer of oxidized copper olution , nor of zeolite , prehnite, datolite, feld par, or other n O· ciated mineral , that have erved to cloud the ituation in Michigan, are pre en t. The evidence indicate that the solutions were a cending and that they were of the type that ordinarily would depo it ulphide · They encountered a highly oxidizing environment (red sand tone) and deposit d native copper and native ilver with con id~rable copper sulphide (chal· cocite) and some ar enide . The rock swTounding the metals was bleached, and sulphates wore depo itcd. The conditions are e entially those that are found 10 the conglomerate and sand tone lode of Michigan. Triassic of New JerseyY-The Tria ic of cw Jersey consists mainly of characteristic red shale and sandstone but comprises also coar e conglomerate, black argillite, and gray or green flag tone. Both · · · h Lnke 1ntn1s1ve and extrusive rock re embling t e Superior basalts in composition are al o pre:'c~L The main intrusive ma sis that forming the Pa~ a e diabase. The ore occurs in veins, which cut bot~ 1gne· ous and sedimentary rocks and disseminated 111 the
" Sing~wald, J. T., Johns Hopkins Univ. Studies in Geology "Lew1s, J. V., State Geologist New Jersey Ann. Rept. Cor 1900, PP·
OTHER RELATED DEPOSITS sediments either just below the base of the effusive 1 rocks or close to the dikes. . The dominant copper mmeral of the vems m the Pali flde diabase i halcopyri te. In the s diments dose to intrusive rocks the copper occurs chiefly in chalcopyrite, bornite, and chalcocite, the native metal being absent. Away from the intrusive rocks native copper is the dominant ore mineral, although a little chalcocite is u ually pre ent. ~1o t of the native copper occurs in the red shale and sandstone just beneath the effu ive rocks that constitute First Mountain. The deposit in the American mine, near Somerville, . .T., is typical of thee occurrences. The ore bed is a purple rock with a texture between that of a fine-grained sandstone and a hale. This bed, which has been explored for a depth of 1,300 feet down the dip, is sparingly mineralir.ed over a maximum thickness of 2Yz feet.. Whererer the copper occur in this bed t.he rock has lost its purple color and is blanched to a pale gray or greenish white. Cha1cocite is invariably as ociated with the native copper, which it apparently follows in age. Triassic of Oonnecticut. 43- In the central part of Connecticut basaltic flows, some of which show red amygdaloidal top , are interbedded with the red Triic and tone and hale. At the ewgate pri on, im bury, dis eminated bornite occur in the sandlone, wherea the near-by trap carries native copper. At Yferiden a core of native copper i inclo ed by a hell of chalco it , thu indicating the chalcocite to be the young r min ral. Cap d Or, cotia.44,_Th native copper at Cap d'Or, o a otia, a c.ording to ir William Daw on, form rna ranging from orne e eral pound in weight d wn to the m t minute grain in the vein and 1i ur s that trav r e the trap, interbedded with the r d Tria i dim nts. The trap i amygdnloidal and carrie variou zeolit , uch a analcite, natrolite, and habazit . The depo it w re examined by A. . Lan , who f und h m trik.ingly like tho o at Lake up rior. Lftne notes that the copper i found in v in that cut tho la a .. Oberstein, Germany.- t Ob r tein, Germany, amygdaloidal ba alt ar int rbedd d with r d and tones and hale f P rmian and Tria ic ao-e. In the amygdaloidal caviti of the ba alt and in the red sediments a little di minatod native copper occurs. Fi ure cutting the trap al contain narrow vein o_r chalcopyrite, with which ar a so iated pyrite, calClle, prehnite, a boron min ral (datolite?), and analcite. Commander I land, Russia!5- The depo its of ommander Island, Ru ia, are d cribed at leno-th by ~1orozewicz. The i land con i t of Tertiary effu ive rocks belonging to tho oda rhyolite family, overlain :~oye, W. G., personal communication, 1922. awson, William, Arcadian geology, 1 7 . . forotewicz, J ., Com. g6ol. [Om., new ser., livr. 72, p. 44, 1012. by andesitic and ba altic tuff and breccia . The effu ive and cla tic rocks are cut by ba altic and ande - itic dikes. The basaltic tuffs are de cribed as being of a gray-green color and are cut by ba altic dike . The copper occw·s in both the tuff and the dike and i as ociated with zeolite . The order of min ral formation i given a iron oxide, calcite, anal it , and w1re copper. Faroe llands.~ 6-The Faroe I land con i t of late T ertiary ba alts with which are a ociated red tuff and volcanic breccias. Betw en orne of the flows are red shaly layers carrying plant r main . Dik and ills are rare, and marked fa.ult are rru mg. The effu ive rock are typical amygdaloidal ba alt , in which the amygdul are rich in zeoli o . ative opper appears spar ely di eminated in the tops of the youngest a well a in the oldest of the e flow . The copper-bearino- amygdaloidal portion of the flow is of a violet-aray color. A ociated with and apparently later than the copper are the zeoli , tilbite, and heulandite. The copper al o occur in the intertice of the breccia intimately as o iated with the cementing zeolite . At uderoe the copper occur in the amygdaloidal portion of a d n e black trap. The amygdaloidal cavities carry tilbite, m ol.ite, heulandite, and a fluorine-bearing apophyllite, as well as copper; the copper eem to be the olde t of the e 'mineral and i found upon the wall of the cavities. At Vaag the copper occur a thin plate in a dark-brown tuff. ao Paulo, Brazil.41- In the tate of ao Paulo, Brazil, diabasic rocks occur a dikes and stocks and a flow interbedded with Pe,rrnian sa.nd tone and hale. The flows are amygdaloidal, their ve icles ha ing been filled with zeolite , chalcedony, and calcite. .A.t orocabana the browni h-black diaba e shows flattened open spaces that are now lined with chalcedony and filled with a hydrou iron silicate. Native copper occurs at the boundary between these two min ral . pper erbia. 4 - The native copper of pper erbia occurs in the vuggy O'pe.nino-s of a hornblende ande ite., which bows dacitic pha es, toaether with chabazite, heulandite, stilbite, apoph llite, and calcite. The copper i incrusted with the zeolites. It i of the leaf variety, although cry tal are al o found. The copper occurs also in rtain highly propylitized portion of the an de ite ; it is here a ociated with chabazite, heulandite, tilbite, opal, halcedony, and calcite, which are younaer than the copp r. White River, Alaska.49- The copper minerals on White River, Alaska, occur in interb dd d effu ive and pyroclastic r ck of arbon.iferou age. Both sulphides and native copp r are present. The lava "Cornu, F ., Zeitschr. prakt. Geologie, 1907, p. 321. n ITussak, E., Ueber das Vorkommeu von gediegnn Kupfer in den Diabaseu von Sno P aulo: centralbl. Mineralogic, 1906, pp. 333-335. 11 Lazarcvic, M ., . prakt. Geologic, vol. I , pp. 81- 2, 1010 . Knopr, Adolph, Econ. Geology, vol. 5, p. 247, 1910.
THE COPPER DEPOSITS OF MICHIG are slightly altered basalt of dark-brown, reddi tized rock. opp r. al 0 ° CUI U: a ~re n augite por. and green colors. The contact between two flo, s lS ph rite. T)le rock 1 as a rule easily determined because of a marked color along' ith th copper .thl pldottzatwn l marked, al. difference. The copper minerals include both suithough abundant ptdot d es not always signify phi de (usually chalcocite) and native copper; t~1ey copper. are generally confined to the upper or amygdalotd~l Zwickau, axony.s
ative copp r occurs in the red portions of the flows, althou()'h they al 0 occur ill beds at Zwickau, axony. On both side of minute veins and stringers. A sociated with the copper copper einlets tho r d rock i bleached yellowish minerals are zeolites, prehnite, quartz, and calcite. owing to the r duction f the ferri hydroxide that At the head of the Middle Fork of White Ri r the color tho rock · country rock con i ts of stratiform ba alts intercalated Algodones, (Jhile. 63-ln th M rc de mine, Algawith beds of breccia and brick-red tuff. The native done , hile, a M ozoic gray sand tone is cut by a copper which occurs here is apparently limited to a diabase porphyry dike. In fracture in the dike there certain definite volcanic sheet- a reddi h lava, which is a little nati o copper, with which a little native is in places highly amygdaloidal. For 200 feet along ilver is associated. · ative copper and cuprite iu as the outcrop of the amygdaloidal rock metallic copsociation with alcit and quar z replace propylitized per intergrown with prehnite, calcite, and zeolite portions of the rock, whi h i trongly impregnated can be found here and there in encouraging amounts. with native copper. J o ore appeal to make iu the The copper occms as irregular reticulating ma ses of and tone. The amygdul s of this dike rock contain metal several inches long and as small lumps and calcite and dele site (?), and the mineral algodonite minute particles embedded in the minerals that line al o occms at this locality. or fill vesicles in the lava flow. Oomobabi Mountains, Arizona.64-In the ea tern Oopper River district, Alaska.50-In the opper portion of the omobabi Mountain , rizona, there River district of Ala ka the copper occurs in the prear len e of altered gr enish lava a much a 100 Triassic basaltic and ande itic rock , which attain a feet long, l ing irr gularly on lava. In this greenish thickness of more than 3,000 feet. The native metal lava quartz occurs as an alteration product of a red occurs at different horizons in different parts of the amygdaloidal ba alt, and with the quartz in places district, but nowhere in encouraging amounts. there is native copper and cuprite. The altered rock On Glacier Creek, a tributary to Chitistone River, that carries the copper is thoroughly epidotized and the native metal, associated with chalcocite, occurs silicified. The amygdules usually show chlorite, epi· in a green tone filled with black amygdules. Masses dote, quartz, and copper. The epidotized rock is cut of native copper weighing several pounds are found, by minute veinlets of quartz, epidote, and albite. but the metal is present chiefly as small specks in the Permian "Red B eds" of the Southwe t. 65-ln tho green tone and the black amygdules and as paper- "Red Beds " of the outhwest copper ore occurs in thin sheets or leaves. bituminous clay slate and marl in nuggets, nodules, On Fall Creek native copper occurs in a shattered or groups of irregular pockets, as carbonate , silicates, grayish amygdaloidal greenstone. It forms small and siliceous carbonate . At Judge Kerr's farm, near particles in both the altered and the seemingly unArcher City, Tex., the green copper ore occurs in altered greenstone and also in small veinlets of calcite whitish-blue to dark-gray clay . At the Ball mine, and quartz. about 7 miles northwest of Archer ity, the ore con· On ugget Creek a very little native copper occurs sists of nodule and nuggets in a tiff white to gray in the reddi h, highly epidotized amygdaloidal portion bituminous clay slate or marl. This clay slate is inter· of a basaltic flow. The copper is intimately as ociated bedded with iron-rich clay ·and conglomerate. At the with calcite and appears to be later than the chlorite Isbell lead, half to three-quarters of a mile outhea t flpidote, qu)1rtz, and prehnite. ' of the Ball mine, the ore occur as p eudomorphs after Nova Zembla, Russia. 61- The rocks of the ova wood or as irregular lumps of black and green ilicates Zembla islands are interbedded lime tones, conglomerin a slightly bituminous clay slate and marl. at~s, a?d basaltic_lavas. The basalt is in part intensely In Oklahoma 66 the ore occurs as sulphide and as the ep1dot1Zed and lS also cut by calcite and epidote native metal in the "Red Beds," consisting of sand· veins. Both sulphides and native copper are dissenn· The sand· stone and shale of a prevailingly red co or. nated in the amygdaloidal portions of the basalt and through stone is fine grained and ranges in co or in veins. The native copper occurs in a red-bro'"" d b locallY white and yellow to red. T he sulphi e as brecciated top of gray-green or black basalt, which :nay locally be bright red owing to the presence of 1ron hydrate. The copper is depo ited in the epido- "Mofllt,, F. IJ., U. . Geol. Survey JJull. 345, pp. 143, 168, 1908. "Volt, W., 7.ettschr. prakt. Geologic, vol. 21, p. 42, 1913. " eucs Jahrb., I 73, p. 64. d iblt 41 Moricke, W ., Die Gold· Silber- und Kupfcr-Enlagerstlltten lD Chile uo Ber Abhllngigkeit von Eruptivgesteinen: aturf. Gesell. Freiburg im Drolsgau ., Band 10, p. 1 0, 1 97. "Joralemon, I. B., report to Calumet & Arizona Copper Co. "Schmitz, E. J., Am. Inst. Min. Eng. Trans., vol. 26, pp. 97-10 1 96· " T'&~ J J,W . A .,Econ. Geology, vol. 6,pp. 221-226,1910.
OTHER RELATED DEPOSITS placed the woody material at a definite horizon. Znong the sulphides observed were chalcocite and chalcopyrite. \zurite, malachite, and chalcanthite areal o present. At oldwater, Okla. ,S 7 the copper occurs as very thin sheet in a bed of red shale. In ew Mexico 6 the ores occur not necessarily in the red beds that give rise to the name, but in the liuhtrcolored sandstones which are interbedded with them. The mo t con picuous ores are malachite and azurite, but these are merely o:x.i.dation products of chalcocite. With the chalcocite are small quantities of bornite, pyrite, and chalcopyrite. ear Estey the chalcocite ore replaces the calcite cement of a 500-foot bed of red sandstone. The Copper Glance mine has sulphides, silicates, and carbonates of copper in a Jhitish, yellowish, or reddi h sandstone. With the chalcocite a little hematite is a sociated. Of the copper minerals in the ore worked, about 60 per cent n chalcocite and about 40 per cent carbonate. About 5 per cent of the total copper content in most of the ore is present as native copper. Jlontana.-Billingsley and Grimes 69 describe an occurrence of native opper at opp r Hill on Baggs Creek, ea t of Deer Lodge, Mont. Copper Hill consi Is of a series of lava flows, basaltic at the ba e but andesitic toward the top. " ative copper in appreciable amount is restricted to limited len es within these flows. The m tal occur in the groundmass, in the augite phenocry ts, and in the amygdaloidal caviti , in tb latt r as with quartz cal ite, and zeolite (rar ).' Th author on ider the depo it due to a concen trati n by comparativ Jy cool waters of copper originally ide pread a a on titu nt (0.02 I per cent or le s) of the original rock. Arctic anada.-It bas long been lmov n that native copper occur on the mainland and i lands of northern anada over a wid area. The e depo it have been vi ited by a number of men, but the be t accotmts of them are on by Dr. Jame ougla ,60 based on an examination and reports by G orge M. Douglas, Lionel Douglas, and Augu t Sandberg, who examined the oppermine Riv r region in 1911, and one by J. J. ' eill,61 on the rctic coa t we t of Kent Penin ula. The r port by 0' r eill review ~revious literature and contains maps showing what IS known of the geology and geography of the region. The native copper occurs in a serie of ba altic lavas mterbedded with ba ic or amygdaloidal conglomerate. The regions about whi h mo t i known ar those ~ear Coppermine River and Bathur t Inlet. In the opperrnme River r gion, a cording to Sandberg, red ~ortb, Erasmus, and DonnelL, John, Oeol. Soc. America Bull., vol. 12, pp. WLindgr W our en, aldemar, and others, U.S. Oeol. Survoy Prof. Paper , 1910.
0 t· tng1lley, Paul, and Orlmas, J. A., Ore deposits or the Boulder batholith, , 0 0" Am. Inst. Min. Eng. ., vol. 5 , p. 293, 191 . anadlan Min In t T 83 4'
· s . raos.,vo. ,pp. ,. IAanadlon Arctic expedition, 1913- 191 , Rapt., vol. Ll, Geology and g ogrnpby, ''· -107A, 1924. rock occurs, and the rock a sociatcd with the copper is much altered. These conditions re emble tho e found in ilichigan. In bed No. 2 the rock, where exposed, has been very much altered in some places to epidote and a crumbling mas of lightcolored rock, in which nearly all the amygdules contain copper carbonate . 1 ative copper in the form of chips and flakes is fairly abundant in thi altered rock. In the Bathurst Inlet region the copper occurs dis eminated in the traps, in the amygda.loids, and in fissures. Copper sulphide, principally cbalcoci te, has replaced dolomite underlying basalt, and cha.lcopyri te and chalcocite are di eminated in some of the sills or dikes of the region. Chalcocite al o occur in fissures in both regions. 0' r eill ums up the evidence on the origin of the deposits as follows: FACTS FA VORI ' 0 A SYNGENETIC ORIGIN 1. The apparently uniform di tribution of native copper in , individual flows of lava of large extent, and the occurrence of such flows throughout so exten ive a di trict. 2. The copper is abundant in some flows and apparently absent from others. 3. The copper occur minutely di eminated throughout the den e, rna ive part of the flows, as well as in the upper amygdaloidal part . 4. In many places the rocks containing the copper are appar ntly fresh and unfissured. 5. In many instances copper occurs in the dense groundmass of a flow, while apparently none occurs in the amygdaloidal portion of the same flow. opper sulphides occur disseminated through massive sills of diaba e, which probably came from the same magma as did the surface flows. :ro enrichment of native copper ha occurred in flows cut by sill of diabase, although the flows contain native copper and the ills sulphides of c pper. .n On the Coppermine River conglomerate interbedded with copper-bearing lava flows carry native copper in the contained pebbles, but copper was not observed in the matrix by the Douglas party. The copper therefore mu t have been in the amygdaloid before the immediately overlying conglomerat were deposited. FACTS FAVORI G A EPI GE ' ETIC ORIGI pecimens of the copper-bearing flows examined under the microscope show that minute grains of native copper replace the matrL" or some of the minerals of the rock. ative copper forms the outer edge and in some ca ·es the c nter of amygdule , and in ome instances replaces other minerals of the amygdaloid filling. 3. In places native copper occurs in thin fissu1·es and in veins in the flow , and at some places the copper was found to be more abundant nearer minute fissures than through the re t of the rock. halcocite occurs in some of the vein in the flows. 5. Dolomites immediately underlying the copper-bearing ba alts in many places have been partly replaced by chalcocite. The chalcocite is intimately mixed with covellite, so that it i probable that secondary enrichment has taken place to some extent. tone place, on Iglor-u-allik I land, copper occurs about the contact of two of the flows of basalt. The lower foot of the " Sec also No. 7 under "Facts favoring an epigenetic origin."
THE COPPER DEPOSIT OF MICHIGAN upper flow contains considerable native copper, but no copper was seen throughout the re t of it. 7. A specimen of native copper in conglomerate was brought from the Coppermine River district to Dr. J. A. Allen, of the niversity of Alberta. The writer was shown this specimen and was immediately struck with the fact that the native copper in this case bad replaced most of the matrLx around the pebbles of amygdaloid. APPLICATION OF GEOLOGY TO MINI G In the preceding pages and on the accompanying maps are presented in con iderable detail the fac so far a they have been ascertained regarding the rocks of the district and the occurrence of the ore . The different theories of the way in which the ore were deposited have also been discu sed. It ha been hoped that both fact and theories would be of a i tance in the search for new ore deposits. This geologic report might perhaps wi ely stop here and leave the practical application of its contents to be made by the mine operator of the district. Certain feature that bear on the search for new ore, however, will be pointed out, but reader may draw their own conclusions, which may differ more or less from those presented in the following page . LIKELIHOOD OF FINDING NEW ORE BODIES The ad vi ability of searching for new ore bodies in the lodes i to be measured by the economic record of the ore bodies already mined and by the probability that similar bodies remain which can be found at rea onable cost. To the end of 1925 the mine of the district bad paid in dividends about $290,000,000. It i safe to say that before the present known ore bodies are mined out and the companies liquidated the dividends will be at least $400,000,000. There no _close record of capit_al expenditures, but from av~ilable data they are estimated at $150,000,000. It 1s. apparent, therefore, that the district bas yielded a pr_ofit_, probably better than the average for d1. A large part of the dividends have come from operations on a few ore shoots and the capital expenditures in developing these b~ots have ually been s~all, o that the profits on these partiCular operatiOn have been large. Most of the capital expenditures, however, have been made in development . th_at have paid nothing. In this respect the Michigan copper di trict does not differ from most other district . Granted tb~t sev:r~l ore boot have yielded large ~rofit , b?w _likely lS 1t that there are similar shoots m the d~s y:t undiscovered? Most of the bedrock m the d1 is covered with glacial drift and tberefo_re not open to inspection, yet although some depo 1ts have been found by accident, roo t of the ore shoot . have be_en di covered on the outcrops or by old Indian working that doubtless tarted on outcrops. Once a shoot bas been located, extensions have been traced. An in pection of the geologic map will give an idea of the amount of devel pmeut , k done out ide the ore bodies ~nd make it clear thoroughly pro p cted area I but a small part or th total. There seem no doubt that undi covered or: hoots eA.':i t. That the e ·hoot are no ea. y to di over i indicated by pa t exp rience. t best a r~tth or lnrge expenditure must b made b fore the u cc s or an enterpri e can be e tablish d. This, how ' or, should not di courao-e tho e in a po ition to und rtnke uch operation , a it i a condition that now prevail in prac ically all mining di tri t ·. In other di trict a truly as in thi , roo t depo it as of di cove~ have already be n found. CONDITIONS OF EXPLORATION DRIFT COVERING Much of the di trict i overed by glacial drift, which add greatly t th expen e of exploration everywhere and whi h ov r on idorable area , where it is everal hundred f et thick, has to the pre enL laro-ely prohibited exton iv exploration. Only Lhe mas ive or otberwi e r i tant bed , uch a the Green ton flow, crop out prominently. The amygdaloids are relatively weak rock and arc ordinarily eroded omewhat below the trap and covered oven where the trap are expo ed. Though the lodes are rarely expo ed, it ba b en mainly by expo ure that the ore shoots have been found. DISTRIB TIO OF DEPOSITS The copper depo it are di tributed stratio-raphically through several thou and feet of rock, and geographically the main productive portion occupies a belt 2 to 4 miles wide extending from entral to ictoria, a distance of about 75 miles, though the l11 part of the production to date has come from the central portion of thi belt, about 40 miles in length. Thi belt is among the largest mineralized areas in the world. The production since 1845 has been comparnble to that from the Butte district since 1 0, which ha come from a few square miles. Mo t of the copper produced in the Michigan di trict ba come a few large depo its, but the e are widely cattered, and the ore form but a very mall part of the rock within the mineralized area. The location of the ore bodies, even though large, in so extensive an area is, of cour e, relatively difficult. GRADE OF ORE All the lode depo its are of relatively low grade. The average yield fOl' 11ll lode deposits from the Champion mine north has been about 26.9 pounds to the ton, and from 1906 to 1923 the average for nJI mines of the district was about 21.5 pounds to the ton. If the Calumet & Hecla conglomerate is excluded, the average yield from the northern amygdaloid lode
CO DITIONS OF EXPLORATION ha been 20. pound to the ton from the beginning and 19.6 pounds from 1906 to 1923. Although the re hoot are unusually large and regular as compared :ith tho e in other di trict , neverthele it is evident that in some the grade is not far above the economic limit, and a light change in grade or in operating condition uffice to put it below that limit. After an ore hoot has been fotmd, it i nece ary to open a large mas of the lode to det rmine the size of the shoot and arade of the ore before it can be kno1111 whether or not a mine can be developed. T o determine the e question i more diffi cult and co tly in this di tri t than in mo t other . Th lode must be opened by und rground working ext nding for thou and of feet, and mill te t mu t be made on the rock. Owing to the irregular di tribution of the copper, no method of ampling that ha been dereloped give even a afe appr ximation of the grade of the ore. 'When the lode has been opened, tho e familiar with th ore can make a rough e timate of the copper content. If it i rich, the operator are warranted in goina forward, but if it approaches the lower limit, only extensive mill t t will determine whether it i commercial or not. In the pa t large urns have been expended in the development of hoot that proved to be below commercial grade, and it seem inevitable that this experience will be repeated in the future. It i not necessary, howe.ver, to erect an expensive mill in advance of proving a depo. it a has been clone in some places in the past, for it is u nally pos ible to make te ts in existing mills, and in recent year till ha been the custom. SIZE OF DEPO IT AND GRADE OF ORE The belief is ometim s expres ed that if ore of somewhat lower grade could be succe sfully mined, imrnen e deposits would be asailabl , but the in rease would probably not be as great a is thought by orne. orne ore shoots grade at the margin rather gradually in to leaner and leaner or but it i far more common to go within a relatively hort di tance from profitable to hopele sly unprofitable ground. Within an ore hoot considembly more ground could be taken if the commercial grade were lowered. It is perhaps c.ommon to think of high-grade depo its as necessarily small and of low-grade depo it a likely to be large. Whether or not there is any j u tifi ation for uch an idea a a general prineiple, it doc not seem to hold good for the Michigan lode depo. its. one of the great ore shoot have been mined out, nor are different shoot mined to the arne extent, and therefore no final compari on i pos ible. evertheles there i a strong indication, a is ugge ted by the following table, that the larger shoot as measured by their content of copper, are con istently of the higher grade. The richer hoots have heen mn::"f profitable and therefore most dev loped; if the lcA nt>r shoots had had the same amount of d lopment th y would probably how better than they do. Yield from lode ore shoots through 1925 Copper (pounds) hoot Total Per too Di,idends Total Per pound ol copper (cents) - 3, 375, 000. 000 14 ' 700, 000 1, 177, 000, 000 50, 0, 000 B~tic --- - 73, 700, 000 29, 242, 500 73, 000. 000 43, 004 000 416,400, 000 14, 700, 000 210, 00, 000 2 550, 000 - -- 142, 00, 000 990, 000 50, 000, 000 b 15
l'ictoria - - 31, 000, 000 b 19 c 649, 000 20, 000, 000 bJ2 'The bigb grade ol tbe Baltic lode is du in part to sorting. It · 18 apparent that the relation between grade nnd depos~t as indicated by mining to dnte i not ;rc Y con 1stent, and of conr e the actual ize i 1_'IDined . everth le there is an unmi takable 0 Icat10n that the larger depo it are th higher in grade. If, then, a low-e:rade ore i encount red in pro p t" " tb ec ~ng, it should be develop d to make ure that ofe o~enmg are not in a poor spot in or on the margin tb a ~lche~· hoot, but when it i once cstabli h d that tb e:. oot_1s oflow grade, there is little rea. on to beli v a lt will make up in ize what it lacks in ri hne .
1 ' 000 000 33, 337. 50 17, 000, 000 b 14 -- Approximate. Includes final liquidation dividend, 192.5. SIZE A D GRADE NECES ARY FOR S CCESS The size and amde of a. lode d po it nece ary for uccess in op ration will of our e vary with condition . An inspection of the precedina table will how that in the past the profit have been roughly in proportion to the amount of or mined and the grade of the d - posit . As a rule, th lode depo it that bav produced more than 100,000 000 pound have been consi tently profitabl and tho e that have produced le have be n rather con i t ntly unprofitable, though
THE COPPER DEPO ITS OF MI HIG the Superior and White Pine deposit , because of rather rich ore and other fa 01·able conditions, have made earnings from a much smaller production. The lowest grade of ore that has generally been profitable in the pa t eems to be about 15 pounds to the ton, though the Atlantic hoot, which yielded a profit, averaged somewhat below that. It hardly need be said that relatively mall mines located in rich parts of the large shoot , such as the outh Kear arge and Wolverine mines in the Kearsarge shoot, have been very profitable. The profits from operations depend on many factors that will not be di cus ed here. The mo t detailed publi hed di cu sion of the subject i one by Denton,63 who reache the following conclusion: It seems likely therefore that the minimum requirements for a profitable mine in one of our amygdaloids are, approximately, that 50 per cent of the lode must produce around 20 pounds per square foot of lode mined, concentrated into 1 ton of stamp rock. The mine one hopes for mu t show at least 60 per cent of the lode area producing 30 pounds of copper and 1 ton of stamp rock per square foot. In other words, the minimum requirements where the rock is not sorted are that in one-half of the developed ground the lode must be 11 feet thick and yield 20 pounds of copper to the ton, and in the "mine one hopes for" 60 per cent of the developed ground must have a lode thiclme of 11 feet and yield 30 pounds to to the ton. Where the rock is sorted the lode might be thicker and corre pondingly leaner. It i hardly neces ary to say that an ore shoot must be considerably developed before any clear idea of the size and grade can be gathered. Where exten ive development ha been made on reasonably encomaging ground but failed to develop a mine, the resulting loss may be diminished by mining some of the be t ground opened. Fi.s mes have yielded a comparatively small proportJOn of the copper and of the dividends for the district. In dividends per pound of copper, however, they compare favorably with lode deposits. The fissmes that have proved profitable have been those t~at yielded mainly rna s copper. and, with the exceptwn of the Mass :fi sure of the Ahmeek mine were ri~h and ~rofitable from the smface. In depo' its of this class It was not necessary to open extensively in advance of profitable extraction, and the fi sures that prove~ profitable were so almost from the start of operatiOns. The fissmes commonly contain a considerable amount of stamp rock, but tho e in which the copper was mainly in stamp rock have not been profitable. There are numerous fissures on the K weenaw anticline that have been prospected but litt~e .., Denton, F. W., ~evelopment and extraction methods Cor Lake Superior deposits: Lake Superior Min. Inst. Bull., August, J922. copper or not at a.ll, and the in ntive for fi m e>..'J)loration much t,he arne as that for lod exploration. EXPLORATION OF LODES ertain geologic condition that ha e proved faro_ able to the formation of deposits may be briefir r:. viewed here in their b aring on xplorat,ion. · CHARACTER OF AMYGDALOID LODES Amygdaloid lodes hav been epamted into four cla ses- cellular, cellular-coalescing, fragmental, and scoriaceous. The characteristics of the e cln e hare been fully di cu ed in preceding section and need not be re tated here. o mine or encouraging pro pect have been developed in typical c llular amygdaloids, which appear unqualifiedly unfavorabl . This applies equally to all celluln,r rock, whether the top of the flow i of that character throughout its extent or wh ther it is !ragmental in places and cellular in place . The fact that the lode is fragmental in one place increa e the probability that it may be fragmental in other places. All but two of the largely productive amygdaloids of the di trict and most of tho e that have given some encouragement are of the fragmental type. There seems no doubt that this is the most favorable type. The fragme.ntal amygdaloid form not more than 10 to 15 per cent of the total, and cellular amygdaloids make up most of the remainder. It is evident, therefore, that the phy ical character of the amygdaloids affords criteria by which a large proportion can be eliminated. A con iderable propor ion of the copper from the Pewabic amygdaloid lodes of the Quincy mine h11 come from cellular-coalescing rock, though the lode are in part fragmental. There is no doubt that valuable depo its can and do occur in the cellular-coalescing lodes. The Ashbed is the only scoriaceou lode in which shoots have been opened. The Atlantic mine i the only depo it in the Ashbed that has been profitable, and that not largely so. It is evidently po iblo for 1 the lodes of the scoriaceous type to be minm:alized to the extent of containing profitable shoot , but they are pretty clearly on the border line between favorable and unfavorable. The influence of hematite in causing the precipitation of metallic copper indicates that highly oxidized lodes are the roo t favorable for ore depo ition. The same influences that tend to form fra()'mental lodes seem to cau e high oxid'ation, so that in° the mni.n the lodes that are physically favorable are also ch mtealiY favorable. It may be pointed out, therefore, that cellular amygdaloid that is highly oxidized may be more likely to pass into fragmental amygdaloid than that which is poorly oxidized.
EXPLORATION OF LODES CO GLOMERATES Only two of the several conglomerates of the district have been shown to be extensively mineralized, ly the Calumet & Hecla, and the Allouez. Both, name , h e mineralized, are moderately coarse, and the wer h hi d C Juroet & Hecla conglomerate, w ere It t ns an c:anges to sandstone, quickly decreases in copper ntent. It appears that a moderately coarse c~n ;romerate has the permeability requisite for formmg ore deposit. It seems probable that a moderately :m conglomerate that pinches out in pl.ace.s along the trike but is continuous down the di~ IS more favorable than a thick conglomerate contmuous for long stretches that gives no opportunity for conl'ergence of rising solutions .. All .the conglo~erat~s have relatively abundant ferne oXIde and are m this re pect apparently chemically favorable to copper depo ition. The sand tone of the onesuch formation at the White Pine mine and neighboring prospects is the only sand tone known to be strongly mineralized and that is mineralized only relatively near to fissures. andstone therefore doe not seem to be favorable to mineralization, though it is of course more favorable than shale. MI ERALOGY AS A GUIDE I EXPLORATION A D DEVELOPMENT A detailed study of the mineralogy and paragenesis of minerals has been a feature of all the more comprehen ivll geologic studies of the district, starting with Pumpelly s work and continuing through the present investigation. One of the obje ts of the e mineralogic ludic has been to find, if possible, minerals that would erve a indications of either the presence or the ab ence of copper in their neighborhood. It may be aid at the start that th e studies have not developed &IIJ very po itive aids in either the general exploration tage or the later development and mining tage . 1lincralogic features, like textural featmes, are largely of local occwTence, and the best of ore shoots are known to contain patch s of minerals that are regarded as unfavorable indications of copper; likewise many amygdaloids which so far as kno"rn contain no ore shoots may for long di tan e carry mineral combinations that are characteristic of some of the big ore shoots in the district. In the later .tagc of development ob ervation of the copper It elf is a b tter indication of the grade of the ground than a study of the gangue mineral . Mli'I'ERALOGIC GUIDES IN AMYGDALOIDS The principal minerals that are regarded favorably a indications of copper in amygdaloids are the q.uartz-pumpellyite-epidote combination which is assoCiated with copper, e pecially in the Isle Royale, 5 540-29--11 Baltic, Pewabic, and Evergreen lodes. However, many impermeable cellular amygdaloids that show alteration of this type are encountered in diamond drilling and crosscutting. The pre ence of these minerals should not lead to more extensive examination by underground openings unless other features, such as favorable physical character of rock or pre ence of copper, give additional cau e for encouragement. The rock bleached through the removal of iron, on the other hand, is much more rare and, so far as known, is invariably accompanied by copper. Furthermore, there is a di tinct feeling that this bleached rock is indicative of a rather intense degree of mineralization, so that if a drill hole or a crosscut encounters a little copper surrounded by bleached rock, it is regarded more favorably than a similar quantity of copper without the bleached rock. Red feldspar, prehnite, and datolite are to be regarded as more favorable than otherwise. The prehni te usually has some fine copper associated with it though prebnitized areas in the Osceola lode are rather poor. In general a fragmental lode showing these minerals, with perhaps some epidote and 1 pumpellyite, is to be regarded more favorably than a lode of the same type with nothing but calcite in the interfragmental spaces. What probably amounts to the same thing is that the greater the variety of minerals the more favorable the appearance of the lode. Most of the commercial lodes have a greater variety of mineral than the average amygdaloid. Calcite and chlorite are rather indeci ive indicators. The intense chloritization in orne places, such as adjacent to fi sures in the Kearsarge lode and in the shattered areas near the Keweenaw fault, would seem to be an unfavorable sign. Laumontite is generally regarded unfavorably. However, there are local patches of lean laumontitized rock in the best ore shoots. The value of copper it elf as an indication of an ore shoot needs some discussion. If copper is present in a drill core from an amygdaloid, it is of course always encouraging, but it is more encouraging under certain conditions than under others. The most favorable mode of occurrence i in a sociation with rock bleached by the removal of iron in a fragmenta! amygdaloi~. opper a ociated with the pumpellyite~quar.tz~epi dote combination is al o favorable, espeCially If ill a fragmentallode. Copper in a fragmental lode leads to illterest ill ~he lode at that point, whereas copper in some quantity in a cellular lode encourages examination of that lode elsewhere to ee if it changes into one of more favorable character such as a coalescing cellulnr lode or a fragment~! lode. Very fine copper in prehnite. or calcite is pretty common and not very encouragillg. opper in small seams in amygdaloids of any type is in general of little intere t.
THE COPPER DEPOSITS OF MICHIGAN MINERALOGIC GUIDES IN CONGLOMERATES the ba in, _any that reach th_e pre ent OUtcrop may be a sumed to extend a long d.i tance down the dip. It The variety of introduced minerals in conglomer1·s qtlestionable, ther for , whether thickne s of flow · dal "d b t in general ates is much les than ill amyg · 01 s, u should be given any w ight in the matter of favorthe same principles apply to the use of mineralogy ill ability. exploring and developing rock of both type · Man! of the conglomerates seen in drill cores hav~ practically none of these minerals, with the exceptwn of a little calcite. As in the amygdaloids, the occurrence of rock bleached by iron removal as a rule proba.bly indicates copper mineralization. Likewi e,_ it i p~ob able that a greater variety of secondary millerals ill a conglomerate is a better indication than calcite alone. MINERALOGIC GUIDES IN FISSURES Little if any choice between two fi ure can be made on the basi of mineralogy. The chief gangue mineral in the Mas fissure at the Ahmeek mine is calcite. The Owl Creek fi sure at the Copper Falls mine in places had an abundance of datolite. Prehnite is common in many of the fissures of Keweenaw County. Some of the barren "cro sing " in the lode of the district are said to be mainly calcite. In many places the Mass fissure at the Ahmeek mine is mer ly a chlorite seam. In general, other thing being equal, a fissure with a variety of gangue mineral i more encouraging than one with only a few. In summary, although mineralogy is of value in exploration, its use mu t be accompanied by an understanding of its limitations. Some of the limitations are indicated. The best ign of copper is copper itself and the occurrence of copper in favorable lode rock is a much better ign than all the gangue minerals without copper in unfavorable rock. In development and mining mineralogy is of less use. In these operations the copper itself as seen in the opening is the best guide. ORE SHOOTS EXTENT OF LODES In several of the lodes it is pretty clear that the ore-forming solutions have traveled upward for long distances in the lodes themselves. It may thus be assumed that a long downward extension of permeable lode is essential to the formation of an ore shoot. It might be supposed that long downward extension would accompany long lateral extension of flows and that therefore the relatively thick flows extending for long distances along the strike would be most favorable. There is some support for this idea in the fact that the Kear arge, Osceola, and Baltic are all relatively thi k flows and that the first two are known for long distances along the strike. The individual · flow of the Pewabic amygdaloid are relatively thin and apparently not continuous for long distances. However, if the flows came from the central part of BARRIER The con entrating eff ct of barrier i fully di. cu ed on paa 115. Barrier in the lode it elf . Ther ar two general condition in the lode them el e fa orable to concentration of solution -(a) a lode that i 1 reYailingly impermeable but contain p rm able ar fl. haYing 11 long downward ex ten ion; (b) a lode that i prevailingly permeable but contain bar of impermeable rock so pla ed a to cause a concentration of ri ing olution . The alumet & He la conglomemte and the Kear arge amygdaloid are xampl of the first type, and the 0 eola lode of th cond. Recognition of the fir t type should be of help in pro pecting. , In the second type, where the barrier in the lode i relatively mall, it i probably quite a ea y to find the ore hoot it elf a it i to find th barrier. In the development of an ore boot once found, ho' ver, the recognition of the barrier hould be of decided help. Folds.- It would be eJ~.'"Pected that olutions ri ing along a lode would tend to concentrate near the crest of the anticlinal folds that extend down the dip tran verse to the g neral trike of the rock . The pre ence of ore boot on th Allouez, Baltic, Winona, Mass, and Michigan anti line l nd upport to thi idea. On the other hand, there are everal depo it , such a the Calumet & Hecla cono-lomerate, 0 ceola, and Quincy, that are not on folds, and the I le Royale and Fore t ("Victoria") are on ynclines. In the shoots studied in detail that are on anticline the distribution of copper is more clo ely related to the character of the lode rock than to the ere t of the anticline. The position of the anticlines are well known, and if the idea proves to have any merit it can be easily applied. Favlts.-A fault off etting a lode and making an angle with the dip of the lode would be a barrier that would tend to concentrate ri ing olutions the arne a impermeable rock. [any faults are known that have sufficient throw to produce this effect, and there are doubtless many mall unknown fault that might have this influence. FISSURE DEPOSITS The ore shoots in everal fis ures are at or near the intersection with thick well-oxidized amygdaloids or conglomerates and ar~und the Keweenaw anticline they occur ~der the Allouez "slide, " which prob· ably acted as a barrier. These relations should be kept in mind in the prospecting of fissures.
EXPLORATIO EOLOGIC DlS'I':JUR TIO The ore depo it in general are di tributed geologicslly from a horizon near the lowe t exposed part of the series to one well toward the top of the portion where flows predominate. The deposits in the Noneuch formation are much higher but so far as known are present only near the Porcupine Mountain dome. There seems to be no very systematic arrangem nt in the geologic horizon at which the depo it occur. ~ear the central portion of the di trict, in a relatively short tretch from Quincy to Baltic, lodes occur from the higbe t to the lowe t and at intermediate horizons. To the north the largely productive lode are at intermediate horizons, though the Ashbed high in the serie ba been productive well to the north, at Copper Fall . In the south end of the di trict the productive lode have been mainly near o. conglomerate, at an intermediate horizon. From the di"tribution of the known deposits there seem little reason for favoring one horizon in the ene over another. GEOGRAPHIC DISTRIB TION Geographically the most productive part of the district, from Champion to Mohawk, is centrally located. Lode production greatly predominates in this central portion. North of the more highly producti>e area there has been considera-ble output from fissures, and south of it from both lod13s and fi sures. There is ome rea on to think that mineralization decrease in amount north and south of the central area, but it is not to b upposed that th commercial limit ar tho indicated b the pre ent profitable lode mine . The a ertion fr qt.i. ntly made that only one depo it occurs in an s ction across the mineralized belt is not wholly upported by the fa t . The Calumet & Hecla couglom rat and ceola shoot in part o erlap. The llouez cono-lomerate i min raliz d and ~as mined abo e th Kearsarge shoot. The tlantic m part overlies th I lo Ro al and uperior. The Quincy ha min d veral lodes in the arne ection, and in the south nd of the di trict the same is true of operation. on the Ev rgreen and succeeding lod . There eems no good rea on for con idering that an area is di tin tly les promi ing becau e an ore shoot has already been dev lop d in the cro s ection of the belt in which the area lies or that a section in which boot has been develop d i parti ularly prom- ·mg for that r a on alone. In no lode, up to the pre ent time, have two wid ly separated profitabl or shoots been developed fd 1 ely separat d hoot have been developed in the Ashbed, in the Allou z conglom rate, and in the Ever- ~eu and ucc d~g lod~ of that eri , but not more T~n one of those m a g1ven lode ha been profitable. ere com , th n, to be no basi for suppo ing that a horizon at which productive depo it have been found in one part of the di trict i a particularly favorable horizon for prospecting in another part far distant, nor for pro pecting a well-known and productive lode at a place far from an area where it is known to be productive, unless at thi place it shows favorable character and signs of mineralization. Prospecting of well-known lodes at a distance from areas where they are known to be productive has been pretty thoroughly tried, and to the pre ent time it has consistently re ulted in failure. There eems no rea on, however, why a lode hould not contain more than one ore shoot, and if it is favorable in character at a distance from the known hoot, it should be considered as attentively as other equally favorable lodes. If it is phy ically unfavorable, on the other hand, it deserve no more attention than other unfavorable lodes. In hort, a given lode at a given place should be treated according to the local indications, and no money and effort hould be expended on the ba i of what the arne lode may contain 20 mile away. RELATIO TO PRESE T RFACE Ali known important depo it appear to have r ached the urface and to hav been as rich at orne place along the outcrop a at any greater d pth. ( ee p. 112.) It would seem, therefore, that in prospecting the chance of striking a hoot at the richest point i probably as good at one depth a at another within practical limit . The depth at which general xplora tion hould be carried on hould be governed by th co t at the particular place con idered. In new territory relatively shallow depth will u ually be cheape t. ear old mines deeper exploration from exi ting openings may be ju t a cheap, and the deep opening may develop much le water and tllU cause les future expen e in pumping in ca e the pro pect is abandoned. It i of cour e to be recognized that exploration for known or uppo ed hoot entering a prop rty at depth con titute a pecial ca e. EXPLORATION STAGES Exploration in the Copp r Rano-e ha now been in progre for more than 75 years and in different places ha reach d very different stages in it progr toward what may be regarded as complete exploration. For the portion of the range in Wi con in the Wiscon in G ological urvey has now in progre s the outlining of the broader geologic relations. For mall area in Michigan very detailed information is available. All tag between those extremes are to be found. The problem to be olved in any given area and the method of attacking it depend on the information already in hand. In an area of which little i known the effective method i to proceed from the more
THE COPPER DEPOSITS OF NITCHIGA general type of information to the more detailed. Lode exploration may be efficiently conducted in the following general order: (1) Geologic reconnaissance; (2) location of favorable lodes; (3) search for ore hoots; (4) development of prospects; (5) development of known ore bodies. Geologic reconnaissance.-For most of the copper belt of Michigan the early stage has been passed, and the general distribution and relations of the rock are known. ear the end of Keweenaw Point and toward the Wi consin boundary there i till something to he gained from work of this type. Location of favorable lodes.-With the genernllocation and geologic relations determined, the next tep is to find what are regarded a favorable lode and conver ely to determine unfavorable lodes. For the area between Victoria and Breakfast Lake the accompanying geolo5ic maps and section give the character of the lodes and theirpo ition o far as known. For some areas this information i rather detailed but ' for others it is very slight. It is evident that much remains to be done in this stage of e:\.-ploration. Search for ore shoots.-As i well known, no lode is mineralized to a commercial degree over more than a small part of its extent. Moreover, numerous beds that have all the properties that are regarded a favorable to mineralization are not known to contain minable ore at any place, though no lode bas been thoroughly tested throughout. It is clear that the copper occms in distinct hoot , only the laro-er and richer of which are of commercial importance~ It is always pos ible that a hoot may be discovered at any stage of exploration, and as a matter of fact most of those now known have been located in the early st~ges or e_n~irely by chance. The probability of lo~a.tmg additwnal shoot by finding outcrops c~nt.amm~ copper or by following up old Indian diggm~s 1s not great. Ore shoots are likely to be found m the ~uture only by systematic search, implying an exploratiOn program and the u e of methods ma~rially different from those that .were cheapest in earlier stages. Developm_ent of prospects .- Once a stretch of lode that con.tams an encouraging amount of copper is located, 1t must be developed to determine whether or. not it is of a size and grade to make a mine. At this s.tage in partic~ar an un~erstanding of the behavwr of the shoots m the developed mines is lik 1 to be of assistance. e Y Expl~rati?n. oj ore shoots.-The milling of the great ore bodies, if 1t 1s to be carried out efficiently, must be pl~nn~d far ahead of actual operation. The determmatwn of the probable position and extent of a known ore s~oot in undeveloped ground is an important functwn of exploration. IE'l'HODS OF EXPLORATIO The several methods of exploration that have b li d . h een common y app e m t e r gwn, usually in tho d d ( ) r er name , are 1 exammat10n and mapping of surf exposures; trenching or ~igging test pits where:~ overburden 1s shallow; (3) dHtmond drillino-· (4) und "'' er. ground openmg . Other method have been trie on a far le s extensive scale. E~mina~ion of surface.- To get all th information that 1s pos 1ble from an examination of the surface is of course the first ste~ in exploration work at any tage. It ' as early appli d and re ulted in outlinin~ the broader features of the geology which have long been known. This method i particularly useful in the reconnaissance stao-e of eA-ploration but may also be u eful in later stage . on iderable dmailed information may hu b ob ained for mall ~rea e. pecially along tret he of lake hore and lo~ 1wer cha.nnels. El ewhere only the more re ·,tant be~s are common! expo ed, and the amygdaloids, whiCh are weak and en ily eroded, u ually oroupy relatively depre ed areas and ar therefore com· monly covered. Trenches and pits.- Th r ults ob ained by digging trenche and pits in exploration are of course dependent on depth and haracter of overburden and on conditions. In general this method is practicable only in areas covered by a few feet of overburden and is not applicable to swampy ar as even where the overburden is thin. v herever it can be effectively applied, this method is u eful in all the earlier stage of exploration-namely, geologic reconnaissance, loca· tion of favorable lodes, and search for ore hootl . Diamond drilling.-Diamond drilling bas been em· ployed in exploration in the copper country since 1 2 and has probably furnished more detailed geologic information than all other methods combined. It is highly effective in determining the character of flows ~or general correlation, and where killfully conducted 1t has proved very useful in determining the character of lodes. The medium-sized 1 >1!-inch core from the "A" bit is much more informing than the J1-inch core from the "E" bit and i well worth the difference in cost. Although diamond drilling is the mot efficient method of getting information as to the kind of rocks and the character and position of lode wbe~e 1 ?utcrops or surface trenching will not furni h th1 mformation, the diamond drill has proved of rather doubtful service in the search for ore shoots. Owing to the very irregular distribution of copper in the average amygdaloid lode, a drill-core sample is likely to be equally misleading whether it contains copper or not, though the presence of copper should, of c?urse, always be regarded as encouraging. Cores sufficwntly encouraging to cause the sinking of exploratory
EXPLORATIO h vo been obtained at several places, as Mandan, OJibway, Mayflower-Old Colony, and St. Louis, where disappointing results were encountered when the lodes were opened. The Lake lode, on the other band was located by diamond drilling and proved sufficiently mineralized to lead to rather extensive development. At the ew Arcadian mine the lode that showed best in the drilling proved disappointing, butanear-by lode that was opened in the underground e.~loration has been extensively developed. Diamond drilling is thus a far less reliable guide in the search for ore shoots than trenching or underground openings, methods by .which it is advisable, where indications warrant the expense, to expose considerable portions of the potential lode. Obviously, however, the information as to copper content obtained by diamond drilling is not to be neglected. Drill-core samples are more nearly representative of conglomerates than of amygdaloids, because the copper is more evenly disributed in the former rock than in the latter. The uniformity of distribution and the consequent reliability of drill-core samples is naturally ev n greater for finer sediments; the cores have been shown to ~ve the copper content of the onesuch sandstone and shale, for example, with a fair degree of accuracy. The diamond drill has been used rather exten ivcly in some mines to locate copper ground in known lodes. It bas been us d most in the Quincy mine, where the lode is of the coalescing type, and for that type it i said to be effective. It was also used in the Osceola mine to locat "foot lode 'c pper, but here it produced rather indifferent re ults and was given up. In the arerage amygdaloid lode the o.d 'risability of its u e fortbi purpo e ~cems open to que"tion. Foot for foot, diamond drilling i , of cour. e, much cheaper than un.dergrow1d opening. Probablv at lea.~t4 fE:'et of drilling can be done at the cost of 1 foot ofunderground opening. In cross- ectioning inclined bed· the ratio i o en more favorable to the drill, ~·hich can cut the bod at right angles and traverse 1 given tratigraphie thickness with a minimum footage, as a cro scut can rarely do. It may thus bo Wsible to ection a lode or seri of lodes s veral times with the diamond drill at the same co t as a single section with an underground opening. Ohurn drilling.- Churn drilling, so far as known ha been n cd only at tho Laurium property. ~ecord . of this work do not indicate thA.t it is effective : .giving ~ny type of information in this district, and ill cuttmgs mu t obviously be far less informing !han a core. The churn drill might be effective in d 'lli n ug through overburden to bedrock. Underground opening.- Underground opening, of ~~rse, gives, foot for foot, the most ntisfactorv mo:mntion of all kinds. For general geologic infOI:- :bon or the location of fav-orable lodes it is ordinarily t ex~ensiv . In the search for ore shoots where renchmg is not practicable it is probably the most effective method. In the development of prospects it is the only effective means of determining the position of the ore shoot and the copper content of the ground. Other methods.-The dip needle has been employed by the Wisconsin Geological Survey in working out the general distribution and structure of the copperbearing rocks. This method has been but relatively little employed in the Michigan copper district, and for much of the area more detailed data are already a.vailable than are likely to result from dip-needle work alone. For certain problems, even in the more intensively developed areas, thA dip needle will furnish geologic data at a lower cost than most other methods. In the :ess developed areas it has a larger field of u efulness. The po sibilities of the use of the dip needle are discussed in the section on geophysical methods (pp . 156168). Oth<'r geophysical methods have been but little used in the Copper Range. Electrical methods have been tried as outlined on pages 158- 160 but have given ns yet no very encouraging results. APPLICA'riON OF METHODS The results a tt.air.ed with a given amount of money vary considerably with the skill used in choosing and applying the different means of exploration, even when the simple t methods are employed. SURFACE EXAMINATION A careful determination of the type and gr11.in of the traps may giv-e considerable information on the thickness and correlation of beds that are only slightly expo ed and thus save more expensive work by restricting trenching and drilling to the vicinity of flow tops. TRENCHING In trenching acros the stril{e of flows, if the grain of the rock i determined, it is po sible to judge the approximate thich.rness of many flows and to avoid continuous trenching over the central portion of such flow. DIAMOND DRII.LING Diamond drilling has been pretty thoroughly developed and sy tematiz d in the district, but there are certain features that may well be emphasized. In making cross ections it is the general practice to di·jH the ection across the suppo ed strike and, unle s there are p cial reasons for doing otherwise, at nearly right a.ngles to the .mppo ed dip of the beds. This of course gives the mn.xirnum section for a. given footage. It is worth going to considerable trouble, if necessary, to determine the strike of the beds before starting an extensive eros ection. The purpose of a eros section is to determine not only the character of the beds but their attitude, and for this purpo e a correlation between two holes is necessary. It is desirable, therefore, to find a characteristic bed that will permit correlation near the bottom of the hole farthest down the dip and to cut this a me bed near the
THE COPPER DEPOSIT OF MICHIGAN top of the next hole up the dip. It is well worth while to carry a hole some distance beyond what would otherwi e be the roo t economical limi t m length or to stop it short of that limit if uch a correlation can be effected. A sedimentary bed i usually the be t for correlation, but certain characteristic flows are ntisfactory. If beds of ftworable character are encountered n ar the bottom of a hole, it is worth while to cut tho e in the next hole to determine their character at another point. To accomplish this, a hole may be stopped short of the most economic length after pas ing through favorable amygdaloid in order to stil.rt th P. next hole near the outcrop of tho e beds and cuL Ll1em again. Both the "A 11 bit, with 1 Ys-inch core, and the "E bit, with Ys-inch c.ore, have been u ed in the di trict. The "A" bit has given a far better core recovery, e pecially of the amygdaloids, and therefore a better idea of the beds, and this advA.ntage is well worth the difference in co t of operation. Larger bits have been used, but except under special conditions they are probably not ju tified by the additional information obtained. A careful record should bo made of every hole at the time of drilling, but in addition the core should be preserved, so. that it can be reexamined when desired. A core may be stored at a cost of but a few cents a foot, and there is no justification for not pre erving it. A few suggestions resulting from the examination of mnny thousand feet of core may not be out of place. ore are usu~lly stored in wooden boxe ranging from 5 to 9 feet m length and containinO' from five to eight or nine rows of core each. The of core are commonly separated by wooden dividers. The size of b?x is .not material, but pine lumber, even of poor quality, IS preferable to even high-grade hemlock. Sheet zinc may be used for divider in place of wood strip . This save orne space, and the cost per foo t of core i about the same. Marking of t~e de~th within the box and marking of. the box are highly rmportant. For marking depth , 1-mch wooden blocks the width of the core should be used. The depth should be clearly marked in pencil on the top and one side of the block. A block should be plac~d the end of each pull. It is convenient if the begmrung of the box is marked with an arrow and _it is advisable to follow the general custom of placmg ~he cores so that they are to be read from Red marks on the ?-iVIding opposite places where copper is found m the core are helpful.. ':l'he box, not the cover, should be marked both ms1de a.nd outside with the name of the property, the number of the hole and th depth. Metal tags with the numbers and letter: stamped. on ar~ .durable, but the box itself should be marked m add1t10n. Cores should be stored in' a dry place and piled well above t.he ground. Tf 011t of doors or in a leaky building, they might a well be thrown out at 0 as the boxes will soon be ~oc~yed . ( e pl. 54, B~ce, Some years ago tho Mwhigan Geological urve recognizing that the matter wa one of public e t, undertook to preserve su h core ns were not b e~ng cared for by the. compRnio . nfortunately this effort was not ontmu d, and those already co]. lected were not giv n prop r car . · UNDERGROUND EXPLORATION Depth.-The fiTst que tion to d termine in exploration is the most favorable depth. A an ore hoot is as likely to be found at one d pth as .another ( ee p. 11 2), the depth of xploration depends on the cost ' and in roo t place the mo t economical depth would probably be hallow. Ho1·izontal ver u verNcal exploration.- In many of the e::\"Ploration in th di tri t, haft ha\'e been sunk toad pth of 1,000 to 2,000 feet, and the vertical element of exploration ha been mpha ized, a con· trasted with exploration along the lode . vYhether the chance of en ountering an ore shoot will be greate t b-y opening down the dip of a lode or along the strike will depend on th attitude of the ore hoot. If the hoot extend directly down the dip, exploration in that dire tion will be l ea~t effective and drifting along the lode mo t effectiv , but if the hoot i horizontal the reverse will be tru . Mo t of the known hoot trend mor n arly with the dip of the lode than with th trik , and therefore, in general, drifting should be preferable to inking. Drifting, moreover, ha the advantage of being cheaper; it also affords the ea ier method of following an irregular lode and of te ting an lod by eros cuts. If encouraging re~ ult are not encountered at one level, it i very que tionable wh ther drifting at another level is j u tified in 0' neral pro pecting, but if the exten ion of a known hoot i being ought, drifting at another lev l may b de irable. Example are cited in the di u ion of ore hoots where a lode i poor in tretche near the surface and richer at depth, but as a rule drifting along the lode would have encountered the rich hoot with lc effort than opening down th lode. If an encouraging amount of copper i encountered, it i of course worth while to open the hoot down the dip as well as along the trike, but it i' de irable to follow the shoot along the trike to it limits on each level opened in order to get the horizontal extent sn.d probable attitude as early as po ible. If a lod~ IS rich, it is common practice to run level in it dunng development, at the regular op rating intervals of 1_25 to 150 feet. If the depo it i of doubtful gra?e Size perhaps the more common and better practice 15 to open it only at considerably greater intervals; the probable extent and gmd are thus determined at 8 lower co t.
SUGGESTIOr S FOR FUTURE GEOLOGIC WORK IN THE COPPER RA GE Transver e versus longitudinal explm·ation.-In past xploration two practice have been more or le s con- ~tently followed-the examination of a lode or lode known to be mineralized el where in the di trict, to the exclusion of the other lode ; and a preliminary cro sectioning of all the lode in an area by diamond drill, trench, or crosscut and the further examination of any encomaging lodes that may be found. The information already available for much of the di trict uives a general idea of the character of the bed , from which it can be judged what method is likely to give the be-t re ults. Cro cutting would usually be employed where it is de ired to inve tigate several adjacent lodes that are known to be of favorable character. If, on the oth r hand, diamond drilling ba shown a promising lode in a eries of unfavorable lodes the promi ing lode would of com· e be best examined by it elf. Prospecting fissures.-It ha been pointed out that many of the known :fis ure deposits occur at the intersection of :fissU!l'e with trong lodes and also that they may be under barriers like the Allouez "lide." These, then, are the place to be specially examined by the method that local conditions render ea ie t. Where fis ures are closely paced it may be advantageou to drift on a strong amygdaloid aero a number of such fi sure , further developing any that how promise. Where they are widely spaced it will probably be ad,ranta.geou to examine each fi ure separa.t ly. Equipment for pro pecting.- I i obviou that no pro pectin it earli t tage of dev lopment ju tifie thea" tuuption that it will be amine. Therefore, until s pro pect i pretty well pro d the equipment and the openings should b the cheaper~ t that can be effectively employed. ertainl the buildina of a mill hould wait till the ore for it i fully a ur d. uch a policy may lead to light lo e in the rela.tiv l few pro p ct that develop into mine , but th own r of u h properti can stand th lo s. SUGGESTIONS FOR FUTURE GEOLOGIC WORK IN THE COPPER RANGE The present report i but one of a erie that have been made dming the last 75 year~ . Each of the reports re orded the available fa ts concerning the geology of the di trict and xpre sed the opinion of th~ author r garding the occurrence of the ore . II'Itb each ucceeding report there ha been a arowing body of facts and a changing iew regarding the occurrence of the ores.. The hange in view bas been influenced by the accumulating facts, by the general increa e in knowledge of or depo it , and of course by the views of the different individuals who have been engaD'ed in the several i::J.vestigations. d Each of the previous report ha been helpful in the evelopment of the di trict, and it is hoped that thi one will al o be helpful. The authors of the report probably realize more keenly than others its shortcomings, and they are well aware how much remains to be done and how important the continuance of geologic work in the district is likely to be. Many of the problems can be solved only by a teady, per istent collection and correlation of data from year to year, and the necessity for this work will not cea e till mining in the district i definitely abandoned. One of the first neces itie for a geologic study is an accurate base map. A modern topographic map ha been prepared for the central part of the copper district in 1ichigan, but this should be extended over the di trict a a base for accurately recording geologic data. The di trict pre ent numerou geologic problems that are still un olved or only partly olved. Among the e are the probl m of the Keweenaw fault and the a so cia ted problem , such as the depth and attitude of the Keweenawan lava beneath the "Eastern" andtone, and whether or not they contain valuable copper depo its ea t of the Keweenaw fault. olution of the e problems will involve the study of the South Trap Range and its relation to the Copper Range. The Porcupine 1ountain area, the portion of the Copper Ra.nge we tward from the Victoria mine to the Wiscon in boundary, and the ar a near the end of Keweenaw Point, in Keweenaw Cotmty, are but little known. Throughout the di trict, in fact, there are rath r large area of which little is known, a can be een b in p ction of the map . Much can doubtle be done toward filling these gaps by magnetic urv and other relati ely cheap methods. This work should be done on a scale and with an accuracy uitable to u e in mining de elopment. Much trenching and other exploration was carried on in the early day , e pecially in Keweenaw County, of which there i no record. The loca.tion of the e openings on an accurat ba e map would give considerable information a to what has ah·eady been done and as to localitie where additional exploration i mo t promismg. In thi ame area there i considerable to be done in mapping outcrops when a uitable base map is available. It i::s already demon trated that dip-needle mapping of th formation can be carried on to advantage, and there i a considerable field for thi work in further mapping of the aeneral geology. The po ibility of the development and application of a ophy ical methods to the search for ore in the di trict hould be kept con tautly in mind. The fact that they hav not been notably helpful to the present time hould not di courage the tudy of uch methods. Likewi e there should be a continuing study of the ore oc urrence with the purpo of di covering additional guide to the search for or . Progre has been made in thi direction ov r a period of 75 years, and it i clear that the end ha not yet been reached.
THE COPPER DEPOSITS OF MICHIGAN To summarize, it may be stated that what is ~eeded in this as in every other mining di trict is contmu~us geologic work with an accurate record and correlatiOn of all data relating to the occurrence of ores and the steady and persi tent attempt to apply new kno:ledge and new methods to the finding of new ore bodies and the exploration of those already known. GEOPHYSICAL METHODS APPLIED TO EXPLORATION AND GEOLOGIC MAPPING By T. M. BRODERICK and C. D. HoHL INTRODUCTION USE OF GEOPHYSICAL METHODS During the last few years considerable interest has been aroused in the application of geophysical methods to the search for economic minerals. Well-authenticated cases of the discovery of deposits so diverse as iron ore, copper sulphide deposits, gold veins, and oil pools either directly or indirectly as a result of the use of th~se methods, are on record. The recent widespread interest in this subject is the outcome of the rapid development of the methods in the last decade, particularly in Germany, Sweden, and France. One type of geophysical observation has long been known and used in the Lake Superior region. Every geologist in the iron districts regards the magnetic dip needle as an essential part of his equipment, and a "magnetic survey" is in by far the greater number of explorations one of the first steps. Curiously enough, however, the possibilities of magnetic observations, regarded as essential in geologic mapping in the iron districts of the adjacent counties, were practically ignored in the copper country. It is safe to say that the present high degree of completeness of knowledge of the stratigraphy in this district could have been obtained at an enormous saving had magnetic surveying been used in the explorations of the old type. Thousands of ·feet of diamond drilling and trenching could have been dispensed with, preliminary shafts and crosscuts, poking around to "find the lode," would have been unnecessary, many miles of e;wensive transit work on the surface could have been saved, and mines such as the Ahmeek and Mohawk, long undiscovered because of a simple curvature in the strike of the lode, would have been found as soon as anyone with a dip needle had taken the trouble to work along the strike from the original discovery. However, the results we~·e obtained, even though at unnecessary expense; but it is to be hoped that the futile "cut and try" exploration will be indulged in less and le s as time goes on and scientific principles of exploration are followed. The present problem is to decide what use to make of geophysical methods, in the light of present knowledge of the geology of the district. o very positive statements can be made in the following discussion of this subject. However ' some experimental work has been done and considerable study has been given to the use of these methods by the geological department of the Calumet & Hecla Consolidated Copper Co., and we feel that we are ina position to say what there is to b said on the present status of geophysical methods as aid to geologic work in this di trict. PRlr C.IPLES OF GEOPHYSICAL METHODS All geophy ical method depend upon a contra tin the physical properti s of the mineral depo it it elf with tho e of the surrounding rock, or upon the di. covery or delineation by means of such contra t of some geologic feature to which mineral depo it are related. Thu , magnetic d po it are more ma.gnetic, ma ive chalcopyrite depo it are better conductors, and alt domes have a mailer gravitative attraction than the surrounding rock. Or a mineral body which of itself may have no out tandinO' physical property amenable to inve tigation by geophy ical method may be related to certain geologic features which could be outlined by such methods. Thu , oil pools are di covered by outlining salt domes, hematite bodie by their relation to magnetic dike , or chalcopyrite depo it by their relation to a certain con· tact. The essential condition in all geophysical work is that there be a. detectable contra t in certain physical properties of the feature that is being sought, be it the mineral deposit its lf or some geologic true· ture or condition to which the depo it is related. The phy ical property upon which the method de· pend may be magnetic polarity, magnetic perme· ability, electrical polarity or conductivity, density, elastici y, or one of certain oth r properties that used more rarely. The manner and degree in this e ential condition of contra t in physical prop· erties is met by the rock and ore bodies of thi dis· trict will be brought out in the following paragraphs. THE THREE FU DAME TALLY DIFFERENT APPLICATIONS OF GEOPHYSICS There are three radically different methods of co~· ducting geophy ical inves igations. (I) If the phy. t· cal properties of certain ore bodie or mineral depostts themselves have the nece sary contrast with tho e. of the country rock, that method can be selected which takes advantaO'e of thi contrast and the work can be carried on ~ith the direct object of locating the mineral deposits themselve~ . (2) It may be po ible to take advantage of the physical properties of rocks a sociated with the mineral deposits, enabling true· h · aide· tural features known to be related to t e rower posits to be determined. (3) Geophysical methods may be used in general geologic mapping whe~e th~ immediate objective is not so directly the locatiOn~ mineral deposits as it is to build up a general geolog.te map which it is hoped will ultimately be of u e exploration. The following discu sion will take up tn order these three methods.
DIRECT APPLICATIO OF GEOPHYSICS TO COPPER FINDING DIRECT APPLICATION OF GEOPHYSICS TO COPPER FINDING EXIST! TG CONDITIONS There are two general types of copper deposits in the Lake Superior district-the so-called lode deposits, which are in amygdaloid or more rarely in conglomerate, and the fissure deposit . The fissure deposits are unimportant as producers, having furnished less than 3 per cent of the copper of the district. A satisfactory geophy ical method should be able to detect an amygdaloidal ore body having as little as 1 per cent of copper with a much as 30 feet of overburden I and it is therefore apparent at the start that the exi t.in<Y conditions are on the whole unfavorable. In the first place, the desirable degree of contrast between the ore bodies and the unmineralized lodes is not present. The sole difference, so far as we have been able to ob erve, between a mineralized lode and many unminerali.zed lodes is that the former has 1 per. cent of its weight in native copper, which is -rt-oof 1ts volume, whereas the latter have less copper. Othen1ri e the mineralized lode is apparently the same in texture, mineralogy, porosity, permeability, water content, and chemical composition a dozens of ~eralized lo.des, and for that matter many a lode 1 the same out 1de the boundaries of the ore shoot as it is within these boundaries, except for the small copper content. The overburden of glacial drift, which covers almost the entire di trict, ranges from some hundreds of feet in thickness down to the vanishing point. Inasmuch a the pro pecting in the la t 0 years ha involved a very. thor?ugh e.·amination of the outcrop and the glace1 drift, it folio' s that most of the undi covered bodies are probably under rather d ep overburden. here are probably none hat cr p out or are covered for any extent by l s than 5 feet of overburden, and there. are probably more co er d by at lea t 20 fe t of drift than b less than that amount. BtLt with geophy ical a with other m thod applied on the surf~ce , the thicker th overburd n the les the chance of discovery. The ore bodie are tabular and dip rather steeply 50 that the outcrop , although of great lenO'th ar~ narr f b ' ow, s~y rom 10 o 20 feet on th a rage. The a~ygdalo1d lod s are highly variable in \Vidth some them. '~dcni.ng out from a few feet to 40 feet or t~re a distan e of 50 or 60 f et along the srike. The e conditions reduce the chan es of dis- ~very by a g ophysical method, because they introuce the possibility that the lines of observation may cro· the lodes ov r the narrow spots. The conditions are very different from tho e in a district where the ore dep 't . os1 s are arge, homog neous, and equidilllens10nal. . mo~t of the dopo its the copper is very irregular Ill oth stze and distribution. Some of it is microscopic, being so fine that it gives a uniform pink tone to the including mineral, such as datolite or quartz. From these there are intermediate particles, nuggets, sheets, and masses weighing hundreds of pounds and even thousands of ~ounds. No physical continuity between the part1cles and masses exi ts to any degree except possibly in the conglomerate ore, where th~ copper forms an interlacing cement in certain beds and is probably physically continuous over areas of some hundreds of square feet. A very serious handicap to geophysical work in this dist~·ic~ is the impossibility of making any exhaustive preliminary tests over known ore bodies. All such bodies have been worked from the surface downward and very little "back" or un toped ground was left at the surface. Furthermore, in most places there is a maze of power lines, pipe lines, tracks and other artificial structures both on the surface ~nd underground in the vicinity of the outcrops of the lodes which would give much stronger "geophy ical ,; effects than the modest copper content of the lodes themselves. In one or two places in the district it ha.s been possible to make rather dubiou test over shaft pillars and old backs or roofs of ore bodie but the e have not been at all sati factory nor convin' inO'. The condition outlined above make it seem unlikei; that geophysical methods can be of direct use in the ~xploration for copper deposits of the lode type. It IS true that the fissure deposits pre ent much more favorable conditions for geophysical work, but the history of the production of the di trict does not ~courage the belief that fi ure deposits of any great 1ze could be found. Therefore exploration for fissures la k the incentive that i offered by exploration for lod The one out tanding feature that compels consideration of the po ibilitie of geophysics in this district is the fact that the ore mineral is native copper, which occupies a position in the series of natural electrical conductors far above that of the common sulphide minerals, such as chalcopyrite, which lend themselves so w ll to pro pecting by electrical methods. It is possible that under certain conditions ore carrying 1 per c nt of native copper would be a.s easily detected by electrical methods a ore carrym· 0' say b) ' 30 per cent of chalcopyrite. Because of the high condu~tivity of metallic copper, no such encourageill nt 1 offered to any other known method of geophy ical exploration as there is to electrical methods. Of the other common methods the gravitometric and seismic have not been tried in lode exploration, simply be au e the conditions in the district seem to offer no hope for succes . The possibilities of the use of magnetic methods in the search for copper deposits have been considered in conjunction with magnetic observations made for various purposes, and this work is de cribed in succeeding paragraphs.
THE OPPER DEPOSIT OF MICHIGA same potential b t' een and urrounding the electrodes ELECTRICAL METHOD t . 1 e f a b t are reo-ular geome n ca curv , o c arac er pre. Direct conductivity and resi tance methods.-Long deten:inable by the th or tical con ideration inbefore the development of the technique of the modern volved. II, howe er, a b dy ~·ock .or ore having electrical prospecting methods, tests were made of the either higher or lo' er onduct1v1ty hes within the conductivity of the copper-bearing lodes. In 1 93 fi ld b tween the ele trod s, th points of equal Prof. James Fisher, now of the physics departn:ent of potential do not lie along th regular th~oretical the Michigan College of Mines, measured the :esista~ce curve of the homo a- neou fi ld, but the lme are of stretches of copper-bearing lode in the Qumcy rome found to be di torted in th icinity of the body of and of the "Eastern" and Freda sand tones. Contact different conductivity. If it i of lower condu tivity with the lode wa made often by attaching t~e terthan the urrounding ro k, th equipotential line are minals to copper masses in the rock. The resistance crowded together n ar it. If it i of higher conwas thus determined between point · About 1900 ductivity, a mo t ore bodi ar , the quipotential N. . Osborne, at present with the nited line are pr ad apart o' r it and in it immediate Bureau of tandards, did ome work along e~mpovicinity. tential lines for the E. J. Longyear Co., both m the A brief te t of thi m thocl wa made o er the I le Lake Superior copper district and on the Mesabi iron Royale lode at a point where it wa a sumed to be range. Variable and apparently inconsistent m~a uremineralized. I though th lod it lf appears to have ments were obtained, and nothing of theoret1cal or di torted the equipotential line , imilar di tortion practical importance resulted. Mr. F. · Bo on, were made b adjacent amygdaloid not known to chief electrical engineer of the Calumet & Hecla Conbe mineralized. It i f lt that both the theoretical solidated Copper Co., has found that it is pos ible con id ration and the e xperim nt throw doubt on in the deep salt-water zones in one of the mines to the po ibilitie of the u ce ful u e f thi method in operate electric trolley locomotives without the regular it pre ent tag of clev lopment in the M.ic~gau cop· metallic ground return, the conductivity of the waterper di trict. It i apparently able to mdJCate the soaked lode providing an adequate return circuit. locations of amyo-claloid and would therefore be of Spontaneous polarization.- The method of ponu~e in general ma~ping of tructure and tratigr~phy. taneous polarization depends upon the electrical curHowever, magnetic 111 thod are 0 much more qmckly, rents set up at the outcrop of an ore body because simply, and economically u ed for the ame purp.o e of its chemical alteration in the zone of oxidation. that there would be n xcu e for u ing the lcctncal Observations were taken aero s the I le Royale lode method for general geologic work where magnetic and across the Kearsarge amygdaloid and Kear arge method apply. conglomerate lodes at Ahmeek by mean of two Jnd1u;tive methods.-In the inductive method a loop movable electrodes, at a fixed distance apart, in conof in ulated wire i laid out on the ground, u ually in a tact with the ground. Traverse were made by rectangular form. n alternating current prorid.ed shifting the electrodes along lines at right angles to by a generator or by an induction coil operated w1th the ore bodie . The potential difference between the a torage batery is sent through the loop .. ~hus a electrodes was determined at the different tations by primary alternating magnetic field i et up w1 th.e means of a potentiometer in circuit with the elecloop of an ideal predeterminable shape if the ground IS trodes. Absolutely no electrical effects were observed h e body of homogeneous. If a conductor uc a an or other than those due to the ordinary weak and irregcertain types i in the field, however,. a econdary fiel dd ular ground current . This test wa by no means, is set up about the conductor. Thi secondary fie however, a conclu ive elimination of this method as i opposed to the primary field and therefore cause of po sible u e in the di trict. The rate of oxidation a distortion of the ideal primary field above and .near of native copper, on which this method depends, is h d f plificathe conductor. By ingeniou met o s o am . . very slow compared with the rate of oxidation of ' · fi ld VIthm tion and observation of the electromagnetic e ' sulphide mineral and would therefore offer less the loop, the secondary currents clue to certain types chances for the method here. Equipotential lines.- The method of equipotential of ore bodies can be recognized. "th After some preliminary laboratory tests WJ lines depend upon the fact that if a direct current is b. h ,.,ere . pecimens of rock and ore, the re ult o w IC ' sent through homogeneous ground between two de to of an indifferent character, attempts wer~ rna electrodes the lines connecting the points having the known lodes.
carry out practJCa vest1gatwns o er "Wo wish to acknowledge the assistance and cooperation or the experts in elecThese included test: over the Kearsarge, PewabJlC, trloal prospecting who worked with us in what we regard as a piece or economic d B h t & Hec 8 research. Without their technical skill and apparatus we could not have carried an altic amygdaloids and t e a ume on tho work. 'l'he e;q> who were in the district were Sherwin F. Kelly and conglomerate. All these trials showed the copper· Ingomar 'l'ennborg with his assistant Mr. Roxtrom. In fairness to these gentleb · l d h h d t table eff . men it should be stated that they regard the possibilities of their respective methods earmg 0 cs to give we a t oug e ec et & somewhat mora optimistically than wo state thorn in the following discus ion. The strongest effects were hown over the Calum ·
DIRECT APPLICATIO OF GEOPHYSICS TO COPPER FINDI G Hecla conglomerate_ and the Pewabic amygdaloid. Hter critical analys1 , however, these te ts were not ' ati factory as appeared at fir t sight. Dip- :eedle reading ' ere taken along the sA.me ections 0 which the electrical trA.verses were run. The ~oorsarge and Pewabic amygdaloids A.nd the Calumet & Hecla conglomerate showed varyin()' degrees of magnetic disturbance in the vicinity of the lodes, and the electrical effects aboYe the Kearsarge lode were definitely related to the magnetic anomalies rather than to the copper of the lode. The results of the te ts at the Baltic and Champion mines, over the Baltic lode, were 1msati factory for everal reasons, among which were great thickne s of overhurden, exceptionAlly rough topography, wire fence , and the fact that where the conditions were most favorA.ble and weak el ctriCA.l effect were obtained over the lode ci.milar effects were obtained away from the lode. The td ov r the Pewabic lode, which may or ma.y not b<' ignificant, indicated three minemlized lod s . It i. po ible that there are three mineralized lodes where the te ts were made, inasmuch a mineralization in adjacent amygdaloid is a characteri tic of the Pewabicore body. H ere again, however, there were complications ctue to magnetiom of the and the possible pre. ence of underground pipes, rail , wires, and cable . The conditions over the Pewahic lode were not. uch a to give a atisfactory te t of thi method. The mo t sati factorv te t wa the on over the Calumet & Hecla congiomerA.te. Fortunately there ~·a a haft pillar 200 ft>et wid Itt No. 12 haft, alumet · H cla. Th haft it elf wa not in operation, there bein()' no haft hou e nor machincr at th .urface. Th o erburdrn is about 20 feet cle p, tb ooppPr content of th rock i about 2 p r c n t, and the copper hA.s tbe ramifying and conn cted form more common to onglomerA.te than to amygdaloid mineralizA.tion. Th condition for fa orable re ult were the be t to be expected in lode mineralization in thi· district. Furthermore, althou()'h tho adjA.c n t lrap howod som magnetic di~turbanc , the effect were not t.I·ong nor sudden, the magn ti CUI'Ye baring long, slop . The ro ults of the elec- ~rics l test , though weak, were the trongest obtained the di~trict and were app~trently dne to the copper 10 the lode. The e test over known lod indicated that under the mo t favorable condition of copper content, copper di tribution, la k of complictting factors such as trong magnoti m in the trap , and thinnc s of orerburdcn the inductive method might detect an onknowu copper-bearing lod . Furth rmore, it was noped that with additional work in the di trict the Plectrical prospecting xperts might develop their methods to the great r degree of r fin em en t nee sary f~r sca~ch for the 1ichigan type of copper deposit. i CCordiugly, the lectrical pro pee tor were engaged or further field work. Exploratory cro cuts at shallow depths were being driven at the time on the lands of the La Salle Copper Co. and the Cliff Mining Co. On the La Salle ground 772 miles of double traverse was run, and on the Cliff ground 4 mile . The traverse lines were run at right angles to the strike and ranged in length from a few thou and of feet up to 3 miles. Two parallel lines of observation 200 feet apart were run in each test. This was thought to be safer than a single line of observation, becau e of the many variable conditions which might allm an ore shoot to give no effect in one spot but a detectable effect not far distant. orne of these lines were run over the ground to be explored by the cro cut . Dip-needle reading were taken wherever electrical ob ervations were made, and in many places electrical effects were obtained, only to be eliminated from further con ideration by finding that they were due to the local magneti m of the rocks. This ability to eliminate electrical effects due to the magnetite in the rocks by a method so simple and economical is a decided advantage. In order to make doubly ure that certain electrical eff cts were act,ually due to magnetite, the te timony of the dip needl was ch eked by digging a 170-foot trench in one place where the electrical and clip-needle caves both bowed eli turbance . As wa expected, no copper wa found in the amygdaloids thu exposed. Certain electrical effects were apparently related to the water content of the overbmden, weak distmbances being obtained where the traver e line. cro sed from dry sand to wet wampy oil. I o electrical indications wer obtained which w re u pected of being related to a copper d po it. However, no copper depo its were found in the cro cut through a part of the t-erritory covered by t.he electrical work. Oondusions.-The condition existing in this district eem to be di tinctly unfavorable to the successful application of geophysical methods to the direct search for copper depo its. The electrical methods would seem to have the be t chance of success, and several of the e have been given brief and inconclusive trials. The inductive method gave mo t encouragement. The present ituation may be summarized as follows : 1. Low-grade d po its, erratic di tribution of copper, erratic variations in thicknes of the lodes, which on the average are thin, lack of contrast between conductivity of the mineralized and the unmineralized rock, thi k and irregular overburden, the chances that the greater number of undiscovered lodes are in the regions of thicker overburden, the interference of magnetite in the traps, and the high water content of the permeable amygdaloid , unmineralized as well as mineralized, are all featmes that tend to make electrical pro pecting difficult. 2. There are practically no pla.ces in the district where conclusive tests of geophy ica.l methods can be made ov r known ore bodies.
THE COPPER DEPOSIT OF MICHIGAN 3. Present electrical methods were developed chiefly to explore for massive sulphide deposits, which appar- -ently give very much stronger and more definite results than the disseminated native copper deposits. Much greater refinement in technique seems to be necessary before these methods can be used with confidence in this district. 4. Those who are expert in these method feel that they have passed the experimental stage, and this feeling is doubtless justified as regards ma sive sulphide deposits; but considerably more experimenting must be done before these methods can be applied in the Michigan copper country with the same degree of confidence. It is felt that there is enough of a chance of successful adaptation of these methods to the conditions of the district to warrant further research. The research should be carried on by men who are not intere ted in the commercialization of any particular method, and it should be financed as experimental work rather than as a method which has been demonstrated to be successful with ore bodies of this type. A Federal Government or State organization could undoubtedly handle the experimental work. .At any rate, as experience is gained in the practice of the methods elsewhere, the tendency will undoubtedly be to become more and more expert in the detection and interpretation of the weaker effects due to lean disseminated deposits, thus approaching a solution of the problem of thi district. 5. Because of the weakness of the electrical effects which these copper deposits produce, other weak effects due to such features as topographic rouD"hness small quantiti~s m_agnetit~, and irregulariti;s in g~ound water distnbutwn, which are in districts of massive sulphide deposits of a small order of magnitude compared. with · th~ e~ectrical effects of the ore body, become m the Michigan district of about the same order of magnitude as the effects due to the copper and therefore lead to confusion. 6. Too great a coincidence of favorable conditions see:ns to be required for positive results. The most satisfactory of the tests over known lodes was that over the Calumet & Hecla conglomerate, where the 1 coppe~· content >:as exceptionally high, the copper distnbutwn exceptwnally favorable, and the overburden pro~ably rather less than the average of that coverin und1Scovered deposits. g 7. If it is true that such a coincidence of several favorable factors is required for a deposi't t · · · ff o give a positive e ect where the line of observati'on h t · h appens . o cross It, en negative results do not go very far m condemnmg the ground explored by ele t · 1 methods. c nca : The encomaging fea~mes are that the ore mined is native copper; that despite the fact that the methods have not been devel~ped for the pmpose of detectin such weak effects, tnals over known ore where condt tions are most favorable give detectable though min t effects; and th_at the dip ne dle. o~ers a rapid, pensive, and stmple ~cans _of elrmmating one of the causes of uncertamty m the mterpretation of electrical effects. No attempt ha:s be~n made in this discussion to present the techni~al Ide of g ophysical prospecting. Some of the more Important p aper on the subject in the English language are listed in an article by Hans Lundberg.64 INDIRECT APPLICATION OF GEOPHYSICS TO COPPER FINDING If there were surrounding the copper depo it a wide pread zone of alteration characterized by excessive development of magnetite or the destruction of the magnetite alr ady present in the trap , or if the copper depo its were related to certain structural features uch as fold , fi ures, faults, unconformities, or contacts, geophysical methods that could detect such featmes would be of indirect use in the search for the deposits. The copper-bearing series is by no means homogeneous magnetically. Different ·flows and different parts of the same flow vary in magnetite content. Furthermore, there are erratic concentrations of magnetite all over the district, some of them in the bedrock, others in glacial boulders. It would therefore be expected that irregularities in compa or dip-needle readings would be obtained omewhere in the vicinity of the copper depo it a well a el e\there. uch erratic readings near the copper dcpo it naturally attracted attention, and it ha even been a erted that " There i certainly a deflection in the vicinity of the richer copper belt . " 65 Work thu far accomplished, however, indicates that the maunetic deflections in the vicinity of the copper depo it are simply those due to the primary magnetite concentration in the original rock , unchanged by sub equent mineralization, and therefore in no way related to the copper deposits. imilarly, no structural relation, such as those suggested above, are known to cxi t. Some ore bodies are on synclinal and ome on anticlinal cross fold ; others occur where the strike i essentially a straiD"ht line for mile . ome have thousand of cro s faults, strike fault , and .fi urcs; knowledge indicates that there i no pre ent posibility of applying geophysics in thi indirect manner. So far as now known, the only such application of geophysics likely to be feasible would be to determine th~ lateral extensions of a new deposit by tracing the strike of the lode in which it lies with the dip needle or by some similar muans. " Practical Points on electrical prosiJ()cting for loca-;ion or mineral deposits: Min.
ng. Jour., vol. 12, pp. 737-738, October, 1926. d . Mench?, A. H., The development or the copper mines or Lake Supenor sn geologtcal relations: Michigan Geol. Survey Pub. 6 (Geol. soc. 4) vol. PP· 7-931, 1911.
APPLICATIO OF GEOPHYSICAL METHODS TO GEOLOGIC MAPPI @ APPLICATION OF GEOPHYSICAL METHODS TO GEOLOGIC MAPPING EARLY GEOLOGIC WORK 'cry early in the history of the district fair geologic ps wore made by following trap/ and conglomerate ~:ges thus making general_ correlations of beds at rJ
h certain horizons and determmmg t e genera structure. Thus it was a simple matter, for instance, to trace the Greenstone for many miles in Keweenaw County and the Evergreen flow in Ontonagon County becau o of the almost continuous outcrops along prominent bluffs. .As one after another of the lode deposits were discovered, the idea that these few "master lodes" extend throughout the di trict took hold, and it persists to the present d . .ay. The great object of the axplorers was to locate these "master lodes "-the Isle Royale, the Pewabic, the Calumet & Hecla conglomerate, and the others- on their particular properties. This was a matter of stratigraphic mapping, and therefore infinite pains were taken to ascertain the tratigraphic relation of these beds to the more easily traceable key beds. Thus there followed a period of trenching ba ed upon accurate surveying, in the attempt to follow from one end of the district to the other the lodes that were lmown to be mineralized at some point. The introduction of the diamond drill opened up great pos ibilities in the determination of stratigraphy, and extensive campaigns of drilling followed. It would be safe to estimate that a million feet of diamond drilling ha b en done in th district, a large share of it b ing chargeable to pur ly tratigraphic purpo , b au o f w of tho explor r were 'atisfied with th diam nd-drill core a e idonce of the pre once or nonpr en o of ommercial depo its. The net rc ult of all this drilling was a very detailed knowledge of tho stratigraphy but no discovery of new ore bodies, with tho po sible exception of th Lake lode, which produced about 7,000,000 pounds of c pper before it was fore d to hut do' n. While all thi drilling, urv ying, trenching, and haft inking was going on in search of the "master lode " in the copp r di trict, magnetic in trument were being u ed ju t a f w mil to the outh, in the iron di tricts, not only in locating iron depo its but in tracing horizons of magnetic beds. Magnetism in the rocks of tho copper di trict was noted on the plats of the original land survey, and in 1 73 Brook pub- !~hed an account of the use of magnetic observations m the MichiO'an iron districts. 66 It is certain that the same knowledge of the structure and stratigraphy of the di trict could have been obtained much more economically had the dip n edle been used in conjunction with th other methods, or, to put it another way, the same amount of money would have furnished much more structural and strati- ~Brooks,'!'. D., Michignn Ocol. Survey, pt. 1, vol. 1, pp. 20!;-243, 1873. graphic information had the dip needle been used in each locality before trenching, drilling, or shaft sinking. Many of the holes and shafts would never have been put down, and those that were sunk would have been more accurately located and directed. The present problem, however, is concerned with whs.t. 'should be done in the way of mapping geology by applied geophysics now and in the near future. IDEAL CO DITIONS FOR MAGNETIC WORK Magnetic contrasts in roclcs.-.Although gravitative, seismic, and electrical methods would undoubtedly serve to determine the geologic structw·e, the conditions for mapping by means of magnetic ob ervations are so much more favorable that the other methods are not to be con idered. The interbedded flow and conglomerates, many of them extending along the strike for ten of miles, carry magnetite in varying quantities. Thu there are the contmsts in adjacent rock bodies which form the indi pensable conditions for any successful geophysical work. The variation in the magnetite content of adjacent beds causes distortions in the earth's magnetic field, and there are several types of instruments which can detect these distortions, Simplicity of geologic structure.-The fact that the magnetite content and concentration is a property of many beds in which it occurs and that a a rule wherever one of these beds is eros ed it can be depended upon to give a magnetic effect peculiar to itself makes it po ible to trace certain beds for miles by the simple ob ervation of this effect. Furthermore, the beds areparallel to a remarkable degree, so that once a po itive correlation is e tabli bed rather vague features in thenear-by parts of the section, if they conform with the established correlation, can be related to other features at definite horizons with much more certainty than would be pos ible where the structw·e i more complex. These conditions make the interpretation of mo t of the magnetic data very imple. umerous geologic checks available.- One who undertake to do magnetic work of the general reconnaissance type, cro ing the mineral belt at regular interval , hould not, over the greater part of the district at, lea t, be at a lo to know where he i geologically. It i po ible in most place to tie in to known geologic feature , becau 'e of the many diamond-drill section and the extensive exploration . The question immediately arises why, if the geology i so well known, hould any exten ive magnetic mapping be undertaken? This is indeed a debatable question, and it will be con idered throughout this discussion. The point to be made here is that if it hould be decided to carry on fl.ny magnetic surveying, the exi ting knowledge of the district is sufficient to enable a close coordination between magnetic effect and known geology to be maintfl.ined during the work.
THE COPPER DEPO ITS OF 11 RIGA Favorable geographic and topographic condition .- The country is very well adapted to the rapid methods of maO'netic surveying. The copper-bearing formation a: a whole occupies a long, narrow belt, in which the longer dimension is parallel to the trike. Roads and railroads extending along the belt within the limits of the series provide easy access to the belt almost from end to end. Over the greater part of the district a complete dip-needle traver e of the formation can be laid out at any place and omplated with a few days. umerous ection corners, roads, diamond-drill hole , and mine shaft , abandoned and operating, provide convenient geographic tie points. United States Geological urvey topographic maps covering that portion of the di trict extending from Cliff to Globe are available. 'l'HEORY A D PRACTICE OF MAGNETIC S RVEYI G Fundamental 1Jrinciples.-Over areas underlain by magnetically homogeneous rock material the earth's magnetic field is essentially uniform, the lines of magnetic force having a uniform inclination a.nd spacing; or, expre ed in another way, the magnetic field is uniform in direction and intensity. If a rock formation of different magnetic permeability lies within the otherwi e magnetically homogeneou rock formation , the ideal or normal earth's field is distorted in the vicinity of the magnetically different formation. The line of force are steepened or flattened and they are crowded together in orne place and spread out in other ; or, to put it more properly, there are local variations in the direction and inten ity of the earth's field. Mapping geology by mean of magnetic instrument , herein referred to a "magnetic urveying," simply involve the detection, tracing, and geologic interpretation of these local variations or anomalie in the earth's magnetic field. Instruments.-A variety of in truments have been de igned for thi purpose. ighting on a distant object and walking directly toward it, taking the magnetic bea~ing of the line traversed at intervals with an ordinary compa s, may serve to detect variations in the direction of the horizontal component of the earth' field. Com pas es equipped with sundials are u ed to determine the true meridian at a given station, and the deviation of the horizontal component of the earth's field, or the declination, is observed by reading the angle between the meridian and the position of the compa needle. The period of vibration of the needle from place to place can be determined, and a mea ure of the variations in the horizontal intensity of the earth' field thereby obtained. Th roo t useful all-round in trument for magnetic urveying, in its simplicity, easy repair and adjustment, lightne in weight, sen itiveness, rapidity in takinO' observation , and ati factory re ult , i the dip ne dl . E entinlly it i a magnetized needle which wing in a ,. rtical plan about a horizontal axi. In~ ad of winging out it nt r of grarity, like th dtp n dl u d 1ll the tudy of torrc·trial magn ti m, it ha a ount rw ight which i ad. j u ted that th needl a ume a po iti n mo emitive to magn tic variation of the normal fi ld. Thu in the Lake uperior di trict the n dlc ore adju d to come tor st in a nearly horizontal po ition in th normal field. In making an b er atiou, the magnetic meridian i fir t d t rmin l by u ing th dip ne dle in the horizontal po i ion, a with an ordinary compa '. It i then tilted up into a v rti al plan of the meridian and leveled b m an of a I eling bubble, and the deflection of the needle from h horizon tal i r din d gr es. B tandardizing thi pro cdur , which i almo t e ential if r ading that ,..,-ill b truly omparable ar to be obtained, it i p ibl to mak and r~cord a dip-needle ob ern1tion in 30 cond . More omplicated and mor en iti;·e in tnutent· for making magnetic ob ervation ore 1wnilable. There are, for in tance, arious type of mao-netometers which determine all the element of dir 'tion and int nsity. The additional d licacy and refinement of the result yi lded by uch in trument in ordinary work, howev r, do not compen ate for the clum ine s, need of tran i ur ey for locations of observation tation , liability to dama<Ye, difficulty in repairing, and time con um d in pr paring for and making ob rvation . Plotting of re ult .-Th r ar v r'al methol of plotting dip-needle r adinO' . magnetic contour map may b made by onne tin()' point which ~ire the ame dip-needle ariation . \.nother method i to lay out the line of tra er e on the map and plot a profile of the dip-needle readings from it a a ba e. Thi i the method u ed in bowing the magnetic data on the accompanying map (pl . 6- 9). The traight line repre en t the line of traver e, which may be either a tran it line or a road. From it a a ba e the dip-needle readin<Ys in degrees are plotted. Where the north end of the needle i below the horizontal, the reading is plus, and the point i plotted at a di tance above the traver e line proportionate to the number of degree of deflection. Where the outh en? of the needle is belo' the horizon tal the reading 15 minus, and the point i plotted below th traver e line. Where several men with differ nt dip needle have taken observation in the arne ar a, it is de irable to reduce all the ob erva tion to a common ba i in order that they may be ati factorily compared. In o~der to do this the needle are all read at a single tatiOn, preferably one where the earth's field is normal and thu for each in trument a "normal " reading i o?· tain d, and in plotting on the map all the reading Jfi degrees above and below th horizontal are recalc~· lated to degrees above and below the "norn1al." T_h1 has not been done in the profiles on th accompanyJDg
APPLICATION OF GEOPHYSICAL METHOD TO GEOLOGIC MAPPI TG 018p, be ause the r ading were all taken with one in trument, so adjusted that the "normal" position of the needle was about horizontal, or approximately 0°. The curves are so plotted that they are correctly read by one facing north or ea t. HI TORY OF WORK IN THE LAKE SUPERIOR KEWEE 1AWA ROCKS Early observations.-The earliest records of the observation of magnetic variation are those made at the time of the original land surveys. orne of these are noted on the town hip plat . While the land survey was still in progre s geologic work by Jackson and his assistants was being carried on, and some attempt was· made to find out whether there was any relation between the copper deposits and the magnetic anomalie .67 Thi work was not brought to a stage where any definite r ult one way or another ould be announced. Recent work.-During the many years in which y tematic magnetic surveying has been carried on in the iron districts occa ional traver es were made, intentionally or unintentionally, in areas underlain by Keweenawan traps. Magnetic lines of attraction, uppo edly due to iron-bearing formation, after inve tigation by diamond drilling or otherwise have been found to be related to lava flows. In recent year the tate geological surveys of ~finne ota and Wi cousin have conducted y tematic inve tigation of the Keweenawan igneou rock , using ma.gn tic ob rvati n a on of the mean of mapping th g Logy. o far neith r organization ha publi hed a formal rep rt f th work, although brief preliminar pap r hav been written pre enting some of th r ult . 68 Th maan tic work in the .Minne ta K w nawan wa don larg 1 in the area of the great K e nn,.;an intru i , the Duluth gabbro. Enough w rk wa don ov r the trap to the outh of the gabbro to how trong magnetic attraction at rtain horizon in tho b d . In mor recent year the Minne ta ological ur ey ha done ome magn tic work in th Keweenawan lava , but it was more or le incidental to other proj t and ha. not be n mad th obj t of eriou in e tiaation. . By far the mo t compr hen i e magnetic w·veying m the Keweenawan ha be n done by field parti of the Wiscon in eological and atural Hi tory Ul'vey T un~er the immediate uper i ion of H . R. Aldrich. In work wa tart d by W. 0. Hotchki , at that time Dir ctor of the urv y, in 1922 and ha. b:~ackson, C. T., R port on the geological and mineralogical urvcy or the mineral Doc ,or tho United tatcs In the State or Michigan: 31st Coug., Jst ., S. Ex. 11 U' pt, _3, and H. Ex. Doc. 5, pt. 3, pp. 586-605, 1849. Itt rOdertck, T. 1., 'l' hc relation or the titanirerous magnetite or northeastern ;13~nesota to tho Duluth gabbro: Econ. Geology, vol. 12, pp. 663-!396, 1917; ome rol.~r;so r magnettcsurveys or the magneti te deposits or tho Duluth gablJro: I dow, rockJ dr fi1Pv· 36-<19, 191 . Aldrich. n. n., Magnetic surveying on the copper-bearing i<cou in: Idem, vol. 1 , pp. 562-574, 1923. been carried on by Mr. Aldrich from the beginning to the pre ent time. Many hlmdreds of square mile of drift-covered Keweenawan rock are being mapped tructurally and stratigraphi ally by magnetic m thod . The cattered outcrop are thus pla ed in their true relation to one another, and fault , fold , formation boundaries, unconformities, and indiviClual beds are being mapped largely by magnetic method . few diamond-drill ections are available, and the e, together with orne good expo ure of the ection along tream , enable the ob erv r to tie in the magnetic features to the geoloay from place to place. Except perhap the land-clas ification work over po ible iron-bearing lands, done by the same organization, 69 thi is, so far as we are aware, the mo t comprehensive magnetic urvey ver made with no immediate application to ore finding as a direct objective. However, there are no known theoretical ground which in any way di courage the idea that the po ibilities of valuable copper depo it existing in Wi cousin are not as good a in Michigan, and the fact that. they have been found in Michigan and not in Wisconsin i not conclu ive. The members of the Wi con in Geological urvey believe that The areas away from Keweenaw Point may perhaps at once come in for new examination, but we feel that if not at present .the attention will come within a very few years. Then the que tion comes, if the expo ures are so meager and if the drift cover i so deep that geologists in the past have not been able to obtain the data necessary for a final conclusive opinion, what can a geologist do in such an area? o far as a 1 thorough examination and te ting of the rock is concerned, we of the ur ey fully agree that ordinary methods hold out little hope for an immediate solution of the problem. But we believe that there is much that may be done on the surface by means of a magnetic survey that will aid campaigns for the y tema.tic disclosure of what lies below the drift. 70 Be ide this magnetic work on the Keweenawan formation out ide of the Michigan copper district, magnetic ob ervations have been made in recent years within the di trict itself, th r ults of which are di u ed below. RECE ' T WORK WITHIN 'l'HE COPPER DISTRICT We have no knowledge of any attempt at systematic magn tic work in the Michigan copper district betwe n that at the time of Jack on and the pre ent work by the geological department of the Calumet & Hecla Con olidated Copper Co. This department has carried on om magnetic work at three different period , with as many different purpo es in view. The purpo e and general re ults of the work in these period are briefl as follows : 1Vorlc prior to 192/J.- Wh n the pecial geologic surv y of the alumet & Hecla Mining o. was 69 Hotchkiss, W. 0., and others, Mineral land classification showing indications or iron formation: Wisconsin Oeol. Survey Bull. 44, 1915. "Aldrich, op. cit., p. 574.
THE COPPER DEPOSITS OF MICHIGAN started on the ground in 1920, it was necessary to make tentative decisions as to the lines of re earch to be taken up first. The statements found in t~e literature that copper-bearing lodes caused magnetAc di turbances were of com· e a challenge, and some observations were made with the dip needle in 1920 to check this statement. As a result of these observations and those made at a later date for the same purpose, it was decided that there were no obvious magnetic peculiarities in the vicinity of the copper depo its which could be detected by ordinary dipReedle practice in the light of present knowledge. Magnetic traverses have been run across the Calumet & Hecla conglomerate and the Kearsarge, Pewabic, and Baltic amygdaloid ore bodies. On the other hand, we do not presume to state positively that a campaign of magnetic work carried out over a period of perhaps several years by competent geologi ts would not reveal magnetic pecwiarities by which ore bodies might be detected. Our present position is just as it was after the tests in 1920-that there are more promising lines of research, which therefore demand first attention. The brief magnetic work of the first summer likewise demonstrated the possibility of tracing the strike of certain beds by their magnetic characteristics. Work in 1925.-The magnetic work done in 1925 was ill.tended for the specific purpose of eliminating effects that were due to magnetite of the traps and sediments from further consideration in the study of the reswts of electrical pro pecting. The locations of the magnetic traverses thus were coincident with those of the electrical traver e . Eight sections, with a total length of 15 miles, were made on the lands of the La Salle Copper Co., and two sections, with a total length of 8 miles, on the lands of the Cliff Mining Co. All this work was in what may be termed the productive mineral belt. Magnetic observations were taken at all tlie stations where electrical observations were made. These were spaced 30 feet apart along surveyed lines at right angles to the strike. The magnetic traverses at La alle are shown as dipneedle profiles on Plate . Tho e at Cliff, made in connection with electrical prospecting, are the straightline traverses shown on Plate 7. There wts of this dip-needle work in eliminating electrical effects due to the magnetite of the rocks were most satisfactory. The observations mA.de at this time also furnish data of use in the study of the possibilities of maanetic work in structural and stratigraphic geology. b Work in 1926.-As A. preliminary to exploratory work about to be started in Keweenaw County it was dec~ded fo1: variou rea o~s carry on som~ magnetlc work m 1926. At this trme 38 miles of traverses were run, and magnebic observations were made at 25-foot interval . This work wa done in the autmnn and as it was desirable to get as many data as possibl~ before, inter topped the work, it was d cided to take the observations along the e eral road cro ing the formation, carrying location by pa ing and Brunton compas . The numerou po ible tie-ins to welllocated f atures, both g agraphic and geologic, made this a sati factory method, although, of cow e, the plotting of re tilt~ wa more difficwt than it would have been if section line had been followed. The data so obtained, added to tho e of previous years form the basis of the following di cus ion of the appli: cation of magnetic method to structural and tratigraphic mapping in this di trict. We have made a totttl of over 60 mil s of traver e and over 12,000 ob ervations. The e fiaure are by no mean impresi e when compared with similar figure of the larger State surveys or tho e of many iron companie . They become impressive, however, when it is realized how high a proportion of them can be tied up closely to the local stratigraphy because of the numerous diamond-drill exploration and outcrops. RESULTS Determination of strike.-One of the imple t and most easily obtainable deductions by means of mag· netic work is the local strike. A magnetic bed is picked up and crossed at suitable intervals, and the line connecting that particular feature from section to section is the strike of the bed. It is desirable to know the strike in diamond drilling and in sinking inclined shafts. Example of diam nd-drill bole that wowd have been pointed differently and would have yielded more sati factory information may be seen on the map showing the Cliff Mining Co.'s lands. Exam· ples of shafts that would have been sunk differently had the strike been known are the Lake No. 1 and the ew Baltic shaft, near the Keweenaw fawt. rumerous examples of strike lines determined magnetically may be seen by reference to the magnetic section on the maps. Tho eon the La Salle lauds are e pecially good. Tracing beds at specific horizons.- In earlier days, when certain lodes were known to be mineralized in different places, it was de irable to find the lateral extensions of the ore bodies, not only on the pro~erties where development was going en but on adJacent properties. This work involved first tracing the stril;:e of the lode itself, by trenching, survey~g, diamond drilling, pit or shaft sinking, and crosscuttmg or by a combination of these methods. In manY places the desired information could have been obtained at an insignificant fraction of the expense and time by dip-needle work. Such a problem would be solved by getting the horizontal distance from ~he lode to one or more near-by maanetic beds, tracwg b t these beds with the dip needle onto the adJacon lands, and then measuring back to the position of t~e lode. Every engineer who has worked in the distnct
APPLICATION OF GEOPHYSICAL METHODS TO GEOLOGIC MAPPI1 G n cite instS:Uces where time and mon y could have ~aved bad the location of some particular lode been ]mown to the explorers. There are part of the ;ection where magnetic work of this type would be 1. successful than in other parts. For instance, the magnetic deviations are much weaker in some places toward the Keweenaw fault than higher in the section. ot enough magnetic data are available to reveal whether this is a secondary characteri tic of s11 rocks near the fault or a primary characteri tic of that part of the section. At any rate, it would be much more difficult to trace lodes by dip-needle de1·ia.tions of only 1° or 2° than it would by deviations of6°or7°. Location of faults, folds, and fissures.-Folds in the formation can be easily determined by magnetic methods, the magnetic lines following the curvature of the bedding. Similarly faults can be located by offsets in the magnetic lines, although in some locali- ·es the magnetic lines do not extend right up to the fault plane, which probably means that the magnetite has been altered in the zones of crushing adjacent to the faults. Thi apparent destruction of magnetite near faults suggests the possibility of locating fi sures to be explored for copper deposits. Magnetic methods tould probably have been of great aid in solving the s ructural problems where there are loca1 complication , especially near the Keweenaw fault. Such areas are present at the Mayflower-Old Colony, ew Arcadian, Lake, and elsewhere. The po sibility that these area are too close to the Kew enaw fault to yield traceable lin of magnetic attraction would make magnetic work of no avail, but o far a we are aware magnetic method hn.v not b en tried in any of the e places, and the explorers have had to feel their way along by means of expensive diamond drilling and underground work. Other relations of magnetic features to geologic features.-The dip-needle profiles on the accompanyina map show certain recurring features, the recognition of which is of importance because they arc the bases of correlation from one section to another. There are long stretches where the curve is essentially flat and lithout character; other stretches where the cmve is rough, duo to clos ly spaced areas of high, low, and nonnal attraction; other stretches where the cmve is abroad sag or an arch; and still others where the curve, though rouo-h in detail, is in a broad way a succession oThfsharp ri os, falling back to normal more gradually. e latter feature Aldrich 71 likens to the teeth of a rip aw. These peculiarities are the resultants of ieveral factors, of which some are r lated to primary features of the rocks and others are not. The underlying cause of the variations in the magnetic field at the present surface is the unequal primary distribu1Atdncb, H. R., op. cit., p. 666. tion of magnetite in the inclined succession of traps and sediments. To some extent this unequal distribution is related to differences in the magnetite content of succes ive flows. There are several types of extrusive rocks, varying chemically, mineralogically, and texturally. They range in composition from rather acidic felsites to the more basic members of the basalt group, and they vary widely in their magnetite content. Unequal distribution of magnetite is also the re ult of the unequal thickness of the flows. In general, the thicker flows give the stronger magnetic effects, probably in part becau e the slower cooling of the thick flows allows a more complete segregation of the magnetite to occur, and therefore a flow, say, 200 feet thick would have a greater magnetite concentration than five 40-foot flows of the same compo ition as the 200-foot flow. In general, the thicker ophites seem to cause the stronger magnetic effects. The La alle profiles show this feature, the irregular curve from the neighborhood of the Calumet & Hecla conglomerate to the Kearsarge conglomerate being due to a series of rather thick ophites. On the other hand, the more acidic glomeroporphyrites between the ''Mesnard bed" and o. 17 conglomerate do not give much magnetic variation, nor do the thin feldspathic melaphyres and ophites ju t above and below the Kearsarge amygdaloid. Local alteration , none of th m so far recognized as being related to copper mineralization, have detroyed some of the primary magnetite o that its pre ent di tribution i probably more erratic than it wa originally. The most notable of th e alterations i the one which oxidized the ferrou iron of each flow while it was till hot, starting, perhap , as soon a the flow reached the surface and continuing th1·oughout the period of cry talliza.tion and even later. Thu there is very little magnetite left in the amygdaloidal tops of the flow , and the crystals of magnetite and other ferr us iron mineral deep within the flows are replaced to arying degree by hematite. Ev n more erratic i the alteration of the magnetite in the vicinity of the faults and fi ure . Little is kno'ivn about this alteration at pre ent, but there are strono- indications that it exists. For in tance, the traver es which crossed the thick Greens tone flow in K weenaw ounty along the roads through the big gap caused by fis ure zones show.flat magnetic curves, wherea those that eros ed at the Ojibway and orth American, away from any known fault or fi ure zone , show violent magnetic effect in the Greenstone area. Finally, there is the masking effect of the overburden and to orne extent of the topography. In general, th thinner the overburden the more ragged the dip-needle curve, the effect of the overburden being to smooth out and gen ralize the curve, elimi-
THE COPPER DEPOSITS OF MICHIG r nating orne of th minor variation and comb~g erie of lo ely spaced magnetic highs and !ows mto broad areas of normal deflections or of uplift or depre ion. What is taken to be an effect of thick overburden is displayed by the northern part of the traverse runnina from Lac La B lie to Mandan. In the lower part ;f the section, just north of the point where it diverges from the section extending northwestward toward Delaware, the curve is rough and the overburden is thin, with many outcrops. umerou correlations on the basi of magnetic observations can be made between the two profiles in their southern part , but in their northern parts the two section are very different. The western one, through the Delaware area, shows the magnetic characteri - tics of that part of the section as displayed in profile run aero it elsewhere. The ea. tern one, through the Mandan area, is much more mooth, and in part of the section where the rocks in mo t places causn great magnetic contrasts the resultant curve is without marked characteristics. The sharp, strong magnetic effect e pecially characteri tic of the thick ophites in the vicinity of the Calumet & Hecla conglomerate are entirely lacking in the Mandan profile. Diamond-drill holes in both of the e areas show that at Delaware the drift i much thinner than at Mandan, and it is thought that the thicker drift at Mandan is largely responsible for the lack of the u ual strong magn tic contrasts in that section. Abrupt changes in topography modify the magnetic curves to ome degree, and the varying thickne of drift, together with abrupt topographic changes, may tend to make the correlation of geologic horizons with the.ir related mngnetic effects somewhat difficult. Persistence of magnetic features.- The value of magnetic work in mapping tratigraphy is dependent upon the persistency of the magnetic properties of the beds at different horizons, which is pictured by a similarity in the dip-needle curves for different sections across the strike. If the concentrations of magnetite were haphazard and not characteristic of any particular geologic horizons, the magnetic lines would not be parallel to the strike or to any other feature, and therefore the magnetic observations would be of no use in geologic mapping. Such is not the case. The magnetite concentrations are characteristic of certain geologic horizons. Some of them are much more persistent than others, however, like the flows themselves. Some magnetic effects can be followed for many miles; other effeets are difftcult to find in a parallel section but a few hundred feet distant. The magnetic attraction at about the horizon of the Ashbed lode is well marked in five out of the six sections that cross it in Keweenaw County. It is also pre ent many miles to the south ' in the La alle area. This is an example of a very persistent and reliable magnetic line. Another persistent magnetic line i found about 1,300 feet horizontally above the Ash bed lod in Keweenaw County. In general, the closer the traverses the greater the number of possible magnetic correlations. The double traverse lines 200 feet apart in the La alle area show in most places practically parallel magnetic urves, and correlations between them can be drawn at 100-foot intervals or in place even less. The distance between pairs is about half a mil , and the number of possible correlations betwe n pair i much le than that between th two curve making each pair. In Keweenaw County, where the di tance between traven is still greater, the number o( rea onable magnetic correlation i corre pondingly les . The experience in correlating between diamond-drill ection i the arne. In pection of the map ho\ that where the drill ections ar clo e tog th r many more correlation can be made from hol to h l than wh re they are paced. The flow thin ut and di app ar, and 8 8 r ult the con·e pondina magnetic lines become weaker and di appear. vVher one flow wedge ·out and i replaced along the trik by another flow, the two are generally of th am p trographic type. For instanc , where one of th more basic flow , uch a an ophite, wedae out, it pla e alona the trike i not as' umed by one of the mor acidic flows, uch a a glomeroporphyrite, but ommonly by another ophite or a flow of similar ompo ition. This mean that the flows poured out during the arne stages of the igneous activity w re of a imilar haracter. Thus there are portions ( the s ti n charact rized by glomeroporphyrite othe1 characterized by ophit , and till other by interm diate type . The change from a part of the ection haracterized by one rock type to a part characteriz d by another rock type are not abrupt, for there are in mo t places everal flow of an intermediate type b twe n the two extremes. Thu between a group of ophites and a group of feld· pathic melaphyres there are likely to be a few feldspathic ophites and ome feld pathic melaphyre with a faintly developed ophitic texture. Most of the accompanying maps and e ti n how this grouping of the various type of flow , and it i di cus ed el ewhere. The point to be con id red here is to what extent thi per i ten e of th belt of flows, in spi_te ?f the lack of persistence of the individual flows w1tlun the belts, is reflected in the magnetic profiles. An inspection of the magnetic profiles shows that the belt of glomeroporphyrites between the top of the Green· stone (or the ba e of the "Mesnard bed") and tl~e Ashbed lode (or the overlying o. 17 conglomerate) 1 relatively homogeneous magnetically but that the ophites between the Calumet & Hecla and Kear·arge conglomerate are not magnetically homogeneou as belt. This difference cau es smooth curves in the one case and rough curve in the other. Other belt hav~ their characteristic magnetic effects. In genern the persistence of magnetic effects bears a close rein.·
APPLICATIO OF GEOPHY !CAL METHODS TO GEOLOGIC MAPPING tion to the persi tence of the beds which ause them. ! 11jven magnetic line probably weaken and distp;ears as the flow which causes it thin and wedges out. A broad general feature of the magnetic profiles related to a group of flows of a given type i more persi tent, just as the group i more per i tent than the individual flows of which it con i ts. Aldrich 72 inferred this wedging out of individual flows and th exi tence and per i tence of the belts of flows of "iroilar composition in the Wisconsin Keweenawan alroo t solely from the detail and broad features of hi marnetic profiles. Jfagnetic correlation .-The foregoing di cus ion will enable the reader to appreciate the many variable conditions which mu t be taken into account in the interpretation of magnetic observations in term of tratigraphy and structure. The first step in thi interprel3tion is to correlate the magnetic feature of two or more a:l.jacent cro s traver e . The next step i to correlate the magnetic f ature with the local geology-to tie up certain maO'netic line with the formations which cau them, and to relate broad magnetic features to similarly broad O'eologic features. Finally, by working from areas where the geology is well known to area where the O'eology i les c rtain, the determination of the geology from the mA.gnetic features becomes po ible. orne interpretation of the e featur 11.re indicated on the map . The mo t reliable magnetic correlations from ection to section are shown. The e ar more numerou in the mo~e clo ely ·paced tra er e . th r po ible corr lation ar apparent, but mo t of th s ha\'e not b n indicated becau e they ar I ertain. Further data would of c~ur'e allow mor accurate int rpretation to be made. It is thought that even the fe\ tra er e hat are at present availabl are worth pre enting, a erve to how the po ibilitie of the method in a di trict where they form a imple, rapid, and economical means of obtaining valuabl geologic informa.tion. PRESENT ATTITUDE TOWARD MAGNETIC SURVEYING As a result of this tudy of the application of magnetic methods to g ologic problems in this di trict the conclu ion et forth below have be n reached. Thee conclusion are, of cour~ e, not to be r O'arded as final. Further data , undoubtedly streno-then or modify them or set up orne others in their ~laces, if any of them should pro e to be un ound. I. There is no rea on to hope that the copper ore bodies in amygdaloids and onglomerate an be detected by magnetic m thod . o feature of mabO'netite d' . 1Slr1bution is known to be in an way related to the P.rc ence of the opper. There may be zone of alterat;on adjacent to fissures and fault , in whi h some of lte magnetite has been destroyed. orne of the e zone may be mio ralized, and it is onceivable that
11 Aldrich, U. R., op. cit., p. 508. a earch for fis ure depo its in drift-covered ountry might be aided by magnetic urveying. 2. Magnetic method are of u e in th preliminary stage of the exploration of pecific area . ip-needle traver e across the formation at clo el pa d int rval give a great amount of detailed information oncerning the geology, such as the trike, the pre ence of faults with amount of off et, a general idea of the thicknes and character of the trap , and om id a of the thickne s of overburden. For thi purpo e th traverse hould be made at interval of not more than a quarter of a mile, and they hould b e>en more clo ely paced where any tructural complications are found. Reading should be taken at about 25-foot interval along the traver e . 3. Where it i de irable to trace the trike of a specific lode, magnetic method will ordinarily rve. A traver~ e hould be run aero s the formation where the po ition of the lode i known, thu determining it' relation to th near-by magn tic beds. Then parallel traverse are made at interval into th area where the po ition of the lode i to be traced, the lode being located by it determined po ition with re pe t to the magnetic bed . 4. Magnetic m thod hould help in olvinO' local tructural problem such a tho e pertaining to faulting or to pitching yncline and anti line like tho e that occur at the Lake and ew Arcadian mine . ince the beginning of geologic work in the di' - trict empha. i ha been placed upon detailed tratiO'- raphy. A are ult the tratigra.phy i e pecially well known. Individual conglomerates and trap ha>e been 1 trac d for more than 50 miles along the trike. The character of the bed in the different parts of th ection i known from one end of the di tri t to the oth r. All thi detailed information ha been obtained by urfa e mapping, diamond drilling, and underground opening . Th re are orne place in the di trict, of cour e, where the tructure and tratigraphy are not o well known a in other place . uch area occur south of Victoria and e t of Mandan, and the next tep in ratiO'raphic and tructural mapping in the di tri t might well be accompli bed by a magnetic ur ey of these ar a . Anyone who would enter into uch a project hould be convinced of it ju tification on the ba i of it scientific or economic importance. It would be of con iderable cientific , intere t to map the geoloo-y from the Victoria mine to the i cousin line, thu onuecting in greater detail th geology of the copper di trict with that of the \"Vi con in Kewe nawan, now b in()' mapped by the Wi con in GeoloO'i al urvey. u h a project would be e peciall valua.ble to the tat of Wi onin, becau e it would enable an interpretation of the 1 Wiscon in O'Cology to be made more clo ely in term of the geology of the opp r-producing portion of the Kew enawan eri .
THE COPPER DEPOSI'l'S OF MICHIGA One of the roo t intere ting tudie yet to be made in the Michigan Keweenawan is along the southern and eastern edges of the "Ea tern" sandstone. The so-called South Range branche off from the main Keweenawan belt in the vicinity of Be emer and Wakefield and extend southea tward for over 50 miles. It con ists of northward-dipping Keweenawan traps and ediments, overlain by the "Eastern " sandstone. Al o within the and tone area are scattered outcrops of trap, as at Silver Mountain and in the Sturgeon River valley. A thoi'ough study of the stratigraphy, petrography, and structural relations in this area would undoubtedly throw some light on the relations of the "Ea tern" and "We tern" sandstones and of the traps and the "Eastern" sandstone, and on some of the little understood feature of the Keweenaw fault problem, such as amount of movement, thickness of sandstone, and rocks that underlie the sandstone. We have more than once heard practical men in the district seriously raise a que tion as to the economic pos ibilitie of the Keweenawan formation southea t of the Keweenaw fault, beneath the "Ea tern" sandstone. It is our opinion that a study of the South Range and the sandstone area to the north and ea t of it offers an almost certain chance of making important scientific contributions to some of the fundamental structural problem of the district, and that some of these contributions might have an economic bearing. Magnetic methods would be of use in this project, inasmuch as it is probable that the "Eastern" sandstone overlying the trap i very thin for some di tance from the contact ' therefore making it possible to trace the structure of the underlying trap by their magnetic effects. So far as the part of the district between Victoria and Mandan is concerned, a project of general magnetic mapping i les attractive. The geologic maps accompanying this report furnish for that part of the district a degree of detail and accuracy far beyond the most extravagant ideas of successful outcome of a magnetic survey in a region such as that of the Wiscousin Keweenawan. In other word , the magnet· surveyor would start in this ar a with a map of mo~: detail and greater acc_uracy t~an h ev~r could hope to make at the end of his work m the Wisconsin Kewee. nawan area. A certain amount of magnetic work in such well-mapped area would be of use, however in gaining an understanding of the way in which 'the various magnetic effects should be interpreted. Then when magnetic data from large unexplored drift. covered areas, such as those in Wisconsin, are studied a much greater degree or' certainty in their geologi~ interpr tation would b po sible. The method of magnetic surveying for general stratigraphy are fairly well standardized. Traverses acros the formation, u ually following land lines, are run at interval , and the dip-needle reading are taken at equal interval along the traverse . The di tance between traver es should vary with the degree of detail of the information de ired and the degree of detail already known. The interval between ob ervations should var in the same way. In order to make a contribution to the geology of the clo ely drilled areas, uch a La alle or Delaware-Mandan, maanetic traverse should be run at interval of, say, one-eighth of a mile or le s with reading taken every 25 feet. In the relatively unmapped country, such a that outhwe t of Victoria, traver es every half mile with readings every 50 feet would probably furni h a degree of detail which would serve as a basis for a fairly good contribution to the local geology. 6. Many problems of a topical rather than an areal nature pre ent themselves a p ible subject of re· search in which magnetic method could be u ed. Among tho e that have occurred to u are the mapping of the Lake hore trap, a study of the fel ite (pre ent information not being sufficient to determine the intrusive or extrusive character of some of them), the relation of magnetic effects to character and thickn "S of trap, the di tribution of magnetite in the flows, and the relation of magnetic effects to tho tops and bottom of flows.
PART 3. DETAILED DESCRIPTION OF LODES A D FI SURE In the following pages the ore deposits are described by lodes and fissures. A description by properties would in some ca es cover depo its on several lodes and fissmes, and a description by mines would in 581eral cases cover but a part of a lode. The descriptions of lodes are arranged in order of stratigraphic position from higher to lower. NONESUCH LODE The onesuch lode is present throughout the Copper Range of Michigan, but prospecting and mining in it have been confined to the vicinity of the Porcupine ~fountains, mainly around their ea t end. The White Pine mine is the only one that ha made a notable production of copper from the Nonesuch lode. It was the only mine on the lode that was acce·sible at the time that this study was made, and therefore most of the statements regarding mineralization on the lode are ba ed on observations made in that mine. STRATIGRAPHIC OCCURREN CE The I onesuch lode i near the base of the T onesuch hale, which lies between the Copper Harbor group and the Freda sandstone and is the highe t formation known to be mineraliz d in the di trict. The Tonesuch formation is made up predominantly of red and black hale and red sand ton . ear its ba e is a persistent gray and tono about 7 feet thick overlain by a thick black hale. Below th sand tone is about 4 to 6 feet of black shale followed by red sand tone and len es of con{)'lomerate. The gray sandstone underlying the thick bla k hal , the thin bed of shale below, and a fe, fe t of andstone b low the shale are the mo t p r i tontly mineralized strata in the formation, but wh r mineralization ha been greate t it ha extend d to a maximum di tance of 75 or 0 f et below the ba e of tho black shale. maline, apatite, iron oxides, chlorite, micas, jasper, and fragments of felsite, trap, and volcanic glass in a matrix of finer grains of the same kinds, with calcite, silica, and iron oxides in considerable amount as cementing materials. Changes in the sand tone due to mineralization are mentioned on page 171. STRUCTURE Structurally the Porcupine Mountain area is a domical uplift that constitutes a conspicuous irregularity on the south limb of the Lake uperior syncline. Felsite and coarser porphyry occupy the center of this uplift. Around and dipping away from them are the Eagle River group and younger formations, including the formation of particular economic interest, the onesuch. The uplift has not merely domed the beds upward but some of the beds have been broken across, so that although the felsite is in contact with the traps of the Eagle River group on the north and northwest sides of the mountains, it is brought against very teeply inclined younger rocks, including Nonesuch beds, on the southeast side. Irving and later Wright and Lane explained the absence of the older rocks (like the Eagle River traps) on the southea.st side of the fel ite as due to a fault, called the "mftin Porcupine fault," along the margin of the fel ite. Where the eastern end of this suppo ed fault is indicated on the original map of Wright and Lane, exploration between the Wh.ite Pine and Nonesuch mines hows no fault to be present. If the felsite rna is an intrusive, this cutting out of certain bed along it border might be explained n a cro scutting intrusive contact. The deformation in the Porcupine region may be are ult of the injection of nn igneous mass from below. Tho shape and nature of the uplift suggest that the intrusive body assumed the toad tool shape of the 1 forms known as laccoliths. Over 40 years ago Irving recognized this structural similarity, but he concluded that "the e mountains owe their existence in all probability to a fold," and thus he was left with the presumption that the fel ite is a sul'face flow. Lane The black shale is a rather finely laminated, somewhat chloritic rock. pecimens of the hale from the \White Pine min , whon hoated in a clo d tub , give off the tarry odor of hydrocarbons. The sandstone layer , which are predominantly red, rang from medium-grained andstone through grit to conglomerate, with p bbl several inches in diameter. The 1 conglomerate consi ts mainly of pebbles of fol ite and quartz porphyry and thus resembles the conglomerates of the principal copper district to the northeast. !he andstone of the b ds in which the copper occurs tssoen under the microscope to be made up of medium coarse grained fragments, largely subangular. he constitu nts are quartz, feldspar, epidote, toural o concluded that both the narrow east-west belt of felsite south of the mountain and the larger body of felsite in the Porcupine Mountain region are effusive. Lane, however, mentions several small intrusive es just beyond the northwestern margin of the main felsite area (sees. 3 and 4, T. 50 N., R. 44 W.), also intrusive rock , including felsites similar in appearan e to th~tt in the Porcupine Mountain mass, a fow
THE COPPER DEPO IT OF MICHIGA miles to the outhea t; and these fel itic ma ses may be offshoot from a common sour e. The tru ture of the region is probably due to the intrusion of an igneou mass of later a.ge tl:an any of the rock in which deposit of copper and silver ~re found. The indications of intrusive force actmg upward and outward are not confined to the ~eneral doming of t,he overlying rock and to th? cuttmg out of certain bed we t of the I one uch rrune. In pection of Wright and Lane's geologic map of the Porcupine region (see pl. 14) shows the presen~e of numerous fault dispo ed radially across the fel1te co~tact on both the north and outh sides of the mountams, and al 0 the pu hing outward from the ea t en~ of ~be felsite ma s of a fan-shaped block some 3 rrules w1de from north to outb, at the horizon of the ba e of the onesuch formation, and a mile ' ide at the top of the Lake bore trap, outh of the old Halliwell mine. A marked by the offset in the ba e of the I onesuch bale, this block bas been shoved ea tward for nearly 2 miles. The geologic detail regarding this di placed block are known only along its southern edge, where the exploration of the White Pine mine have revealed certain feature clearly. It seem evident that the outtbru ting of the block was accompli bed by a combination of faulting and of buckling or folding of the beds. Its south or southwest ide i bounded by a nearly vertical fault, the White Pine fault, and as indicated on the map and bown by certain drilling exploration , it north side i likewi e marked by a fault, which extend ea tward from the old Halliwell mine. But on the .outh side, at least, the e faults were developed only after the rock had been folded o harply that they broke aero s, and further dislocation wa effected by faulting. There i a sugge tion from the map that farther north similar blocks between fault radially arranged with re pect to the ea t end of the main fel ite ma have imilarly been shoved out away from the motmtain, though to a somewhat shorter di tance. Branching from the reverse White Pine fault as hown in the White Pine mine are numerous minor faults that break the beds in the vicinity of the major fault . The detail of these faults are given in the d cription of the White Pine mine (p. 172). All the known features connected with thi particular part of the region point to the production of the tru tural features by the intru ion of the igneous core of the Porcupine Mountains and the doming up and outward thrusting of the rocks that were invaded. This general etting helps to an understanding of the d tails of structure that have exerted a control on the ore deposition in the White Pine mine. MINERALIZATION ORE MI ERALS The ore mineral are native opper, native ilver and chalcocite. Th native m tal o cur chiefly a' cementina material in the and tone lode and as di emin:ted grain or as flake lying along jointing plane in the hale . ubordinatel they are pre ent in fi ur and fault gouge hnJcocite occur mot con picuou ly in mall fi ur vein , with calcite gangue. It i al o parsely di eminated in the and tones and in the shale . FAVORABLE CONDITIONS The condition that have be n effective in localizing the ore minerals arc th confining effect of relati'lely impermeabl hale , proximity to fracture that acted as hannels for the introdu tion of ore-carrying solution , and favorabl mineral aic or t xtural condition of certain bed in the and tone . Influence of hale bed .- The lode are in the andstone clo e und rn ath th thick capping of hale, which a ted a a barrier t tho ri ing solution that depo ited the ore. The wo bed mo t widely min ralized arc immediately b low the shale, oparated from ea h other by a few feet of mineralized shale. At the vVhite Pine min , where mineralization ha been mo t intense near fissure , c rtain bed hare been mineralized for 70 to 0 feet below the heary overlying hale, but each of th low r bed ha for it hanging wall or roof a bed of sand tone omewhat more shaly than normal, which seems to have acted as a barrier to the rising elution . Influence of fis ures .-The deposit at th~ nTJ1.1te Pine mine are clo ely connected with the Wh1te Pme fault and the a ociated bran h fault , as i di cu sed in detail on page 173. Fault occur also in. the ''!cinity of the Nonesuch and White Pine Extenswn ~me though there is no definite record of their relat10n to mineralization. Longyear, 1 who wa in charge of an exploration in T. 51 ., R . 41 and 42 W., north of the White Pine mine, ay : "The drilling he~ ha shown the principal mineralized area to be m the immediate vicinity of the three northeast and south- . ted out west faults." Lane 2 al o orne year ago pom the importa.nce of prospecting along fault in th.e Porcupine Mountain di trict. Altogether the ~VI dence seem to point very definitely to the as ocintwn ·of mineralization with fault . · alona The ore-bearing elution appear to ha en en d the faults from a deep- eated source till they reache the heavy shale bed in which the fault fis ure were ' 1 Lougyear, C. S., Michigan Oeol. urvey Pub. 21, ser. 20, P· 20, 191 . 1. we 'Lane, A. C., Unexplored part.s of the Copper flange of Keweenaw 010 · uperior Mining lost. Bull., vol. 17, p. 133, 1912.
NONE UCH LODE iJnpem1eable owing to the formation of gouge in the e . It rock . Below thi imp rm able bed the olutions ~read out into the more permeable rock and deposited t,he ore minerals. JJineralogic and textural influences.- The third factor in controlling the di tribu tion of the copper i the physical and mineralogic character of the beds imp~nated . In so far as thi factor may relate to difference between the parti ular bed mineralized and other near-by layers of the and ton , it i beliered to be of omewhat le importance than the two factor ju t di cu s d- namely, proximity to one of the l!n·ger cro s fault and an impervious cap rock. Xear one of these fault at the \Vhite Pine mine the mineralized layer is thicker than it i farther away. Within the lode the copper is in many places confined to certain beds. Thu a 1 de 6 f t thick may have mo t of it copper in two or more layer~ that together make up not more th.an on -third of the total. In mo t hand pecimen , and in thin ection a well, the copper is een to follow ertain b dding planes. Th' habit is undoubtedly du to ome favorable textural or mineralogic f ature of th b d , but the e hare not been recognized ex ept by the pre ence of topper a ociated with them. The and tone at the ba e of the one uch hale, like mo t sand tone of the Kewe nawan erie of the Lak uperior region, are predominantly red. Th red color i due to the rath r plentiful f rric oxide with which the fel itic a rain are impregnated and also ferric oxide, which, t g th r ' ith calcit , f rm ilie chief cem nting material of th rock . The and tone lay that arr copper have b n bleached to a gra or gr eni -gra olor. Thin ection from th lod at th ho\ that ther i not mu h cal ito r maining, but in it place a a c ment i a pitchy black h dro arbon in an amount r aching a ma:\:imum of probably 2 per cent. Th greeni h tinge in this blea h d ro k i due t{) chlorite, which o cur larg 1 a fringe about the and grain and e p iall around th edg of the patche of hydro arbon. Th forri oxide oriainally pre cnt in the unbleach d r ck ha id ntly b n ~uccd to ferrou oxid and in part gon into combmation a chlorite, but mo t of it app ar to have been removed. Thi bl aching ha o curred wh ther or not impregnation with opper ha taken pla e ju t at that point. 1any drill r ord how "aray andlone" at the horizon of th lode , but it 01 p r content may b v ry lo' . . The impres ion gain d from tudy of the andstone Ill the White Pine mine i that th hydrocarbon, like the copper, ha been introduced along the :fi ures and that it abundance has been det 1mi:ned by the same factor -nam ly the pr ence of an imperviou ca · ' PP~g, proximity to a pronounc d cro fault, and certam textural and mineralogic f ature of tho b d . The hydro arbon, liko the copp r, occm b low the shale and shaly and tone and i di tributed through a greater thickne of beds and in gr ater amount near the cro s faults. It is more abundant in certain layers at the e horizon , perhaps in tho e which were rich in replaceable calcite. The hydrocarbon occur in the eros faults and :fis ure to an even greater proportionate extent than the copper; good- ized pieces of 10 to 20 pound in weight mad up laraely of hydrocarbon have be n obtained from uch fault . The hydrocarbon i thought to hav a greater horizontal di tribution along the lode than th copper, however, a it i found extending out along the beds farther than copper in commercial quantity. The ource of the hydrocarbon i not known with certainty, but ina mu h a th overlyina black hale is bituminou , yielding a tarry di tillate when heated in a gla tube, it eem probable that the hydrocarbon ha been derived either from this hale or from orne imilar rock that may lie deeper in the eries, by di tillation under the heat and pre ure attendant upon the intru ion and metamorphi m of the region, or perhap it wa r mo ed by the heated waters that carried the copper, although none of the shale een in the mine appear to be leached or to have lo t any of it black piament. The genetic relation of thi carbonaceou ub tance and the copper ar not entirely clear. Ina much a the arne general conditions controlled the distribution of each, they are clo ely a ociated. The copper ocelli in man place a a hell about the hydrocarbon, repla ing the hlorite fringe. The period of depo ition of hydrocarbon th ref ore wa fini hed before that of the copp r. Fmthermore, the ma ive hydrocarbon of the fault zone i well impregnated with copp r; wheth r thi means replacement of the hydrocarbon by copper or imultaneou d po ition of the two i not clear. The e relation might be thought to ugge t that the hydrocarbon wa active a a precipitant of the copper. In all the mine of the main productive region to tho northea t, however, copper has been precipitated in the lode that are high in ferric iron, and the precipitation ha been attended by bleaching of the rock occa ion d by reduction and removal of the iron but without the sliahte t evid nee tha.t any hydrocarbon ha b en involv d. This i as true of the conglomerate lode (parts of which are made up of andtone like the lode at the White Pine mine) as it i of the amygdaloid lode . Bleaching of the rock through reduction and removal of the iron i lil ewi e characteri tic of the White Pine lode . It i evident that the copper of the White Pine di trict entered an environment that would ha.v be n fa 01·able for copper pr - cipitation had there b n no hydrocarbon pre ent. The facts that copper occur clo e to bituminous shale only in the Porcupine region and that o far as known
THE COPPER DEPOSITS OF MICHIGAN hydrocarbon is a ocia ted with copper only that region, and everywhere close to the shale, len.d we1ght to the view that the hydrocarbon bas been denved locally from the shale and at be t exerted but a subordinate and modifying influence on the deposition of the copper, if indeed it had any influence at all. In summary it may be repeated that the textul'al and mineraloO'ic factors in the localization of the copper are of minorb importance. The following generalizations may be made regarding the color of the sandstone and the presence of hydrocarbon and of copper: o copper was seen in red sand tone, although copper occurs in gray bands in red sandstone. . o gray sandstone was seen at the Wh1te Pme mine without some hydrocarbon. 3. Little if any hydrocarbon was noted in red sandstone. 4. Gray sandstone without copper was noted. 5. The sandstone of the lodes may have been in part rendered gray by the hydrocarbon before the copper had all been deposited. 6. Although there eems to be a close connection between the hydrocarbon and the copper, it may be purely fortuitous; in any case the indications are that the copper solutions entered what would have been a favorable environment for copper precipitation had there been no hydrocarbon present. 7. Here, as in the larger deposits farther northeast, the deposition of copper is believed to have been accomplished by the oxidizing effect of ferric oxide in the rocks upon the copper sulphide solutions. In the fractures them elves, where the contact of the solutions with the rock was le s intimate, part of the copper was deposited as native metal and part as the sulphide chalcocite. WHITE PINE MINE Location and topography.- The White Pine mine (pl. 33) is in sees. 4, 5, , and 9, T. 50 N ., R. 42 W., Ontonagon County, a few miles east of the Porcupine Mountain , and is the mo t southwesterly producer among the mine of the copper district. In the immediate vicinity of the mine the country, which stand about 200 feet above Lake uperior, i flat and monotonou . The bedrock is buried by glacial drift a much as 160 feet in thickness. The northward-flowing streams have cut rather shallow 1 va.lleys into the drift and in places have exposed bedrock. These exvo ure and the drill records show that the rock surface also is one of little relief. Production.- The White Pine Copper Co. was organized in 1909. Its production and dividends to the end of 1923 were as follow : Refined copper produced: Dividends paid: 887, 654 1 '233, 169 260, 681 $33, 43 Rock .-Th following ection i compiled from the notes of drill hole o. 162, 1, 00 f et south of o. 3 haft, upplementcd by the data obtained in the mine con crning the ro ks b low th econd lode. The members of particulM c onomic importance are indicated by ind ntion. Section at White Pine mine
Feet Red shale - 300t Red sandstone and shal Black shale Black shale --- - - 70-110 Gray sandstone (First lode) Red sandstone Gray to red sand tone 8 (lower Red sandstone - Felsite conglomerate - - Gray to red sand tone 3 (Third lode)_ Red sand tone --- 600t Structure.-The relation of th structure of the White Pine area to the g neral structmal features of the region i shown on the map of the Porcupine 1ountains and vicinity (pl. 14). In greater detail, the structure near the mine is shown in the mall map of Plate 33, which shows the contour plan of the first lode, compiled from diamond-drill records and mine workings. In the neighborhood of the White Pine mine the rocks have been dislocated along a outMea t line so that tho e on the northea t side have been moed outheastward about 2 miles (as marked by the poi· tion of the fir t lode at the level of Lak uperior) and upward J.Jrobably more than 1,500 feet. Thi diago· nal upward di placement has been accompli hod partly by a buckling fold, which accounts for the strong curvature of the lode a it approaches the fault, and partly by faulting, which produces perhaps half of the total horizontal displacement and likewi o a~o.u half of tbe total vertical di placement. Tho Mite Pine fault is of revere throw; it dips steeply north· east, and its northea t side, containing most of the mine workings, i the upthrown side. As this di location forms t.he outhwestcrn boundary of the outthru t block it is evident that the block on
I k the northeast side of the fault-that 1s, the b oc that contains tho principal mine workings-moved, · to and that on the southwest was stationary, rolative the country rock in general. It is probable that the block that moved would suffer greater stressc than the one that remain d at re t, and it seems likely tb~t the region of the ].)resent mine workings (1, pl. 33) a place of greater di tUTbance than the region on\: opposite side of the fault (II I). Faulting of the roch.) · t tS appears favorable for the occurrence of ore 10 locality, as is shown below. Gray where mineralized; etsewbere red.
NONESUCH LODE The nlinor fault that are numerou in the dev loped portion of the mine ar irregular in trike, dip, and throw, but certain generalizations concerning their behavior can be made. Two principal ones (Nand K. pl. 33), from which many of the others arc subordinate branche , are well expo ed underground. The existence of another fault of apparently similar direction of strike and throw is ugge t d by the drill records in he neighborhood of , ome 1,500 feet ea t of o. 5 shaft. The known faults, like N and K, decrea e in amount of throw as distance from the White Pine fault increases. The place at which the uaae ted di locationS i revealed i distinctly farther from the supposed continuation of the White Pine fault than the farthest known exten ions of T and K, yet the eli placement at is greater than the maximum at and K. There is apo ibility, therefore, that S i a larger fault than the others and that nearer to the White Pine fault along there may exi t either a ingle trong fault or a region of disturbance imilar to that in the N-K block and of eren greater in ten ity. The known cro s fault , with the exception of K and &few mailer one , have their downthrown side to the southea t. As the fault K ha its downthrown ide to the northwest, the greater part of the block of mJund between o. 3 and o. 4 shaft has been dropped with re pect to the blo ks on th northwe t. and outhea t. The faults and K have cau ed a greater di placement of the lodes than any of the others that w re tra eable for any con iderable di - lance through the min . Th ir di pla ement i miablo, but in gen ral they bring the Fir t lode on one ide w U down toward the Third lod on the other side; thi implie orne 40 to 50 f et of vertical di placement. Mo t of he ro fault cau a di pla ment ofles than 10 feet. The e cro fault a a rul are curved rather than s raight, and many of them twi t urpri ingly. Th y are probably contemporaneou with th major di locat.ion repre entcd by the folding and by the White ~ine fault. Th curvature i conv x in dip a well a 10 triko toward the outhea t until the faults finally become tangent to the White Pine fault. They branch, horsetail fa hion, on the convex ide a they swing ~way from tbe White Pine fault, and they de rease 10 amount of throw outward from it. All th e facts sugge t that the e minor cro fault are due to drag dong the major White Pine fault in or ncar a emipla tic material such as the thick overl ing hale. .Mineralization.-Tb general featur s f the mtneralization of the onesuch lode are describ d on :ages ~69-171, but the special relation of the faults ranching from the Whit Pine fault mny be pointed out. The evidence of the premineral age of th cro s f~ults lies in the facts that the lodes ar thickest and nche tin the immediate vicinity of the larger cro s faults, and that the cross faults themselves are well mineralized, even the smalle t joint and fi sures in the sandstone and adjacent shale carrying copper. The riche t ground in the mine is in and immediately adjacent to the block between the principal cross faults, N and K . Here the lodes are both thickest and riche t. The records of the diamond drilling from the surface give the copper percentage for the everal mineralized beds. Multiplying each of the e percentag s by the number of feet of rock which it repre ents and adding together the e products give a percentage-foot figure for each hole that repre ent what may be termed the "intensity of mineralization" of the ground penetrated. To obtain these figure , only the footage~ of ground that assayed 0.5 per cent or more of copper were con idered. For example, the intensity of mineralization of a given hole i computed thus: Material Black shale - -- Feet Copper I amputation (per cent) Trace. 5 X l.6 r. 35 7X 1. 35= 9. 45 Plate 33 sho"·s the po ition of ea h drill hole together with the inten ity of mineralization as thus obtained for it also contours drawn at 25-unit intervals over the entire area drilled. It is apparent that the block between faults and K and the immediate vicinity is by far the riche t ground drilled, copper contents and thickne s of lodes both beina cousider d. The evidence of the drill records was confirmed by sampling in the workings of the mine at different intervals, chiefly east of the fault K. Over 50 samples were taken, a ay for which were furnished by Mr. . H . Ben diet. The places for sampling the several lodes were selected a nearly along the same vertical line as the e}..l)O ure in the workinas allowed. Thus the same method of rnultiplyina percentage of copper by thicl n ss of lode and addina the products gives fiaures ' hich repres nt "intensity of mineralization" at different plac . The e figures likewise show that mineraliza.tion is mo t intense near the fault K, grading outward from it toward Io. 5 shaft. Minor deviations from the general rule are probably due to the enriching eff ct of subordinate fractures near point wh re the a ay samples were taken. Plate 33 sho" s that shafts r os. 3 and 4 are in the heart of the only noteworthy ore body penetrated by the drillina. The hol s to the' northea t and northwe t along the outcrop of the lode indicate that the mineralization i slight there as compared with that in the present workinas.
THE COPPER DEPOSITS OF Ml HIGA Other evidence indicating that faults N and K were channels for the mineralizing solutions is afforded by a serie of small but very rich ore bodies, including all the rich silver bodies seen, which cling very close to these faults. They are in the nature of thickenings of the normal lodes, and mineralization of two lodes that are not mineralized generally through the mine- namely, the Lower econd lode and the Third lode. The mineralization of the Third lode, so far a now known, i on.fined to the highly mineralized part of the area, centering about Nand K. Plate 33 shows that in places outside of the present mine workings where there are break in the structural contours, indicating cross faulting, there are in reases in the mineralization. uch place are found in the ' E. 34 sec. 6 and the E . 34 sec. 9 (fault ). To summarize: In the White Pine mine the copper was probably brought in by olutions ascending along the White Pine fault. As these olutions leaked out into the somewhat permeable and tone, they continued to ascend in the sand tone until they were diverted slantingly upward by the hale barriers. But the movement of solutions was al o facilitated by the cross faults, and especially by the tronger ones. By this combination of conditions the favorable portions of the rock were afforded a sufficient volume of solution to become commercial lodes, whereas farther away from the faults the richnes falls below the economic limit. Copper or chalcocite wa al o deposited in the faults and fracture themselves. This relation between faults and the be t mineralization is in accord ·with the experience of those who have worked elsewhere in the Porcupine Mountain di trict. F..J-tensions of ore bodies.-Development of the lodes at the White Pine mine bas been carried from the outcrop down to the White Pine fault. The lode has been located on the downthrown side of the fault, but development of it has been very light, and principally at No. 2 shaft. As indicated in the di cussion of structure there are some reasons for suppo ing that the downthrown block may be less broken by branch faults than the upthrown block and therefore less favorable to mineralization. If the solutions were rising along the White Pine fault it also seems probable that the beds on the upthrown side were more favorably situated to receive them. Diamond drilling shows that the beds associated with the branch fault east of the White Pine mine workings are mineralized at some distance from thEI main fault, and it seems.possible that this mineralization may be more inten e nearer the main fault. WHITE PINE EXTENSION MINE The following statements regarding the White Pine Extension mine are largely compiled from the records of the company. The mine i in T. 50 N., R. 44 W., about miles we t of the V hite Pine mine. The working are in the on such formation south of the Porcupine Mountain uplift. The property has been developed by diamond drilling across sees. 7, 12, 13 and 14, with a total of 45 hol s ranging in depth fro~ 80 to 1,400 feet. haft ha b en sunk to a depth on the inclin of 43 feet, and drift have been opened on the ro. 2 hale on the second and fourth levels for a maximum di tanco of 3,3 0 f et. The rock b long to th onesuch formation which, a ho>m in the drill core from the Fred~ and tone dowm ard, include the following beds: Feet Upper gri L- Lower grit_ . -- --- - 10± 15 ± 6±
o. 2 sandstone. Red and tone. The bed dip away from the Porcupine Mountain uplift at an angle of 3° in the mine working . They appear to be regular in the main, t.hough there is minor faulting aero s the lod . Mineralization ha occurred mainly in o. 1 hale, o. 2 shale, and a b d in th sand tone about 9 feet below o. 2 hale, known a o. 3 andstone. At 33 feet from J o. 2 hale a cro cut on th fourth evel encountered " quartz-banded hale " with di - seminated ulpbide which a ayed 20 pound of copper to the ton for a thickness of 3 feet. The copper occurs in the shale mainly a thin heet and flakes in the bed parting and joint . Drifts hav.e been opened on ro. 2 hale with cro - cuts at 100-foot interval to o. 1 hale and at 200foot interval to o. 3 sand tone. When operations ceased in May, 1918, the following work had been accomplished: Feet haft, incline depth -- - Drifts: First level, 14 feet north, 11 feet south Second level, 1,542 feet north, 1,83 feet south - 3,3 0 Fourth level, 1,13 feet north, 1,0 0 feet south 2,21 No. 2 shale for a width of 4.8 feet, including ome barren shale that breaks with the ore, has an average copper content of 21 pound to the ton. orth of the shaft there is some relatively poor ground aver· aging about 13 pounds to the ton. If this is eliminatedd the south ends of the drifts average between 23 nn 24 pounds to the ton.
ASHBED AMYGDALOID A total of 23 samples of o. 1 shale assaying from 6to20pound to the ton gave an average of 12 pounds for 11 thickne s of 5.7 feet. A total of 10 ob ervations on o. 3 and tone on the econd level showed a width of 1.6 to 3 feet and 3 copper content of 0 to 2 pound . On the fourth ere! the sand tone howed no mineralization and in some cro scuts could not be identified. When the mine was clo ed water wa being p~ped st the rate of 92 gallons a minute. NONESUCH MINE The None uch mine, about 3 miles west of the White Pine, wa productive intermittently from 1 68 to 1 5, and it recorded production i 3 9,556 pounds of copper. The mine is developed by four shafts. 4 Xo. 3, the deepe t, went to the fifth level, a depth of 460 feet. The occurrence of the ore, apparently, is :imilar to that of the neighboring White Pine mine. ONONDAGA EXPLORATION The one uch formation was examined by diamond drilling by the Onondaga Copper Co. in Tp . 49 and 50 T., R . 42 and 43 W., on the outh side of the structural basin south of the Porcupine Mountains. The formation. is similar to that on the north ide of !he ba in, but the copper content a revealed by the drilling did not warrant development. OTHER PROPERTIES orth and northea t f the White Pine mine pit hare been unk in da pa t on bunch of opper or ilrer ore in the sand tone, apparently a ociated with faults. orne of the e fault may b of a magnitude corre ponding to tbat of the White Pine fault. ee pl. 14.) Tho rocks at the Non such horizon were xamined by diamond drilling in T. 51 ., R . 41 and 42 W. orne copper wa found, and the be t ground wa reported to be near the fault ,5 but it was not further developed. LAKE SHORE TRAP HORIZON The sandstone immediately under the Lake hore trap is mineralized at several points on the north ide of the Porcupine Mountains and was developed years ago in the Carp Lake mine. From 1860 to 1 65 there wa a recorded production of 33,935 pounds of copper. The copper of this mine ha replaced red sand tone immediately below the Lake hore trap. The and tone is mineralized from a fev inche to a few feet from the trap. Where mineraliz d, the red and tone i bleached to gray. o hydrocarbon wa noted in thi andstone. On the dump of the Carp Lake tunnel i vein material con i ting mainly of calcite and in part an iron-bearing carbonate with included chalcocite. The sand tone has been shown to be mineraliz d over a di tance of everal thou and feet near the arp Lake mine and i reported to be mineralized at s veral other point along the north lope of the Porcupine Mountain . ASHBED AMYGDALOID The A hbed amygdaloid (pl. 34) has been pro - pected from the Atlantic mine, outh of Portage Lake, nearly to the end of Keweenaw Point. Whether the developm nts on this tretch are on the arne bed i not known, but they are at the same general horizon, a little below ro. 17 conglomerate. The mo t exten ive developm nt have been made at the Copper Falls, Arnold, and Phoenix mine , in Keweenaw ounty, and the Atlantic mine, outh of Portage Lake. PRODUCTION The following table shows the production from the A hbed amygdaloid to the end of 1925: Production and dividends from Ashbed lode to end of 19135 Mine Period Rock treated (tons) I 714, 452 Arnold C ty 1 59 1 66_- - D Ashbed: 'E II mated. Comm. Minerai Statistics Ann. . for I opper produced (pounds) Per ton Dividends Per pound (cent) 11 , 2 21 o2 13. 57 I $99ol ooo o. 4 11 171 706, 352 5561 424 --- -- --- 3571 032 '- - 9. 35 - 1421 401 04 1- - - - - ---1 9901 000
THE COPPER DEPOSITS OF MICHIGA CHARACTER OF ROCK The Ash bed flows are toward the andesitic end of the basaltic series and are everywhere porphyritic, containing rather abundant small feldspar phenocryst , which are u ually collected in ne ts. The amygdaloid is prevailingly of the sconaceous type and is ordinarily cited as the typical example of scoriaceou amygdaloid. There is, however, n~table variation in the amount of the clastic matenal m the Ashbed at different place . At the Atlantic mine, so far as indicated by the dump material, it is distinctly of the scoriaceous type with pebbles and boulders of amygdaloid in a sandy matrix. At the Phoenix mine the upper part, or "gray" bed, is of the same character, but tho lower part, or "red" bed, is ~ot described as scoriaceous. At the Copper Falls mme the bed is locally sandy and approaches the scoriaceous type, but for the most part it is rather typically fragmental. At mo t of the places in Keweenaw County where it has been cut by the diamond drill the lode is scoriaceou . At the Copper Falls mine it is well oxidized, and at the Atlantic it is said to be chocolate-colored. The Ashbed seems, therefore, to be a fairly well oxidized amygdaloid. MINERALIZATION The mineralization of the Ashbed does not seem to differ materially from that of other lodes. The more abundant minerals at the Copper Falls mine are calcite, quartz, epidote, and pumpellyite. ear the fissure datolite i apparently abundant, and in Keweenaw County it appears to be generally more abundant on the Ashbed than on the other lodes. At the Phoeni,"" mine the basal portion of the lode is chloritized. ot enough of the Atlantic lode has been seen to give a very clear idea of the mineralization. At the Copper Falls mine much of tho bleaching associated with c·opper is of the iron-removal type. At the Copper Falls mine the upper part of the lode seems to contain more copper than the deeper part, and there is some copper in the basal amygdaloid of the overlying flow. At the Phoeni,"" mine the copper seems to occur throughout the "gray" lode, but the top of the "red" lode is richest. At several places in Keweenaw Cotmty where the lode has been cut by the diamond drill the copper seems to be in amygdules in the lower trappy part of the lode. DEVELOPMENTS COPPER FALLS MI E At the Copp r Falls mine of the Arnold Mining Co. the Ashbed had been opened in 1891 to a depth of about 1,500 feet and had been opened and stoped for about 2,400 feet along the strike. The workings extend about 1,000 feet ea t and 1,400 feet west of the Owl Creek fi sure. Work continued for a year or so after 1 91, but the extent of the late t opening is unknown. The hbed was al o opened adjacent to the Pethorick fi Ul'e but to what extent i not known. The A hb d lode as on in tho upper level of the Copper Fall mine is of the fragmental type of amygdaloid with ome andy material and is well oxidized. The width stoped varies greatly but probably averages 6 to feet. The lode oem riche t near the top. A report by Wadsworth state that the lode averaged 10 to 12 feet in thickne s and yi lded about 1 per cent of copper. The yield in 1 59 i given as 22. pounds to the ton. There i no record of the output from the hbed eparate from the output from the Owl Creek fi sure, whi h was operated at the same time, but the production from the A hbed wa certainly con iderable. The r lation between the Owl reek and other fi sures and the mineralization of the i not very clear, but the min ralization s ems to have been stronge t near this fi ure. Allr OLD MI E At the Arnold mine the lode has been op ned by o. 1 shaft to the eighth level. On the fifth level a drift has been carried 210 fc t to a fi sure, which was opened for a short di tan e. The drift ha been extended also about 300 f t south, to a fi W'e which wa opened for about 400 feet. The level above the fifth were not carried far from th haft. PHOE ' IX l\U E The Phoenix mine of the Keweenaw opper Co., on the Ashbed lode, was not operating when thi report was in preparation. The following note taken from the company records and statements by Mr. C. A. Wright, superintendent. The hanging wall i marked by a clay slip that dips and strikes with the formation. This pos ibly repro· sents o. 17 conglomerate. Below the clay lip i t~e amygdaloid of a trap averaging about 15 fe~t lll thickness. ext is the "gray" lode, with a lip at the top. The "gray" lode is described as an amygda· loidal trap that grade downward into den e trap. In places there is sandstone at the top of the "gray" lode, ranging from a fraction of an inch to several feet in thickness; the lode averages 6 to 7 feet. The trap of the "gray" lode is at some place 15 feet thick, but at other places it appears to be ab Next is the "red" lode described as amygdalolda ' conglomerate with no mention of sandy matena · The thickness of the "red" lode averages 15 to 20 feet but is variable. This suggests that the "red" lode here, as at the Copper Falls mine, may. be a fragmental than a scoriaceous amygdalotd. '1 h trap of the "red" lode is about 60 feet thick. e next amygdaloid i described as narrow, and reddi b gray; it is mineralized in spots but seems very ''bunchy.''
LODES OF THE HANCOCK MINE The Ashbed is crossed in the Phoenix workings by the Phoenix and Armstrong fi smes, and near the :urface a third fissme was opened. A fault we t of we Phoenix fi sme offs ts the beds to the ea t of the --ure about 60 feet to the north. The Ashbed has been opened at the Phoenix mine 0 a depth on the dip of 1,600 feet and along the strike for about 2,500 feet. Mo t of the development na been on the "gray" lode, and most of the proauction has apparently been from this lode. The copper in the "gray " lode i said to be fine. From October 13, 1916, to December 31, 1917, oi,215 tons of rock was hoi ted, of which 1 ,993 tons ra· discarded; 4 ,063 tons tamped yielded 449,416 pounds of copper, a recovery of 9.35 pounds to the ron, with a lo in tailings of 5.65 pounds to the ton. This can probably be taken a representing the grade of the "gray" lode. The "red" lode has al o been opened in everal ~lace , at most of which it i reported to show an encouraging amount of copper near the top of the lode, in a zone a much a 4 feet in thicknes . It ·. said that the copper is coarser than that in the ·'gray" lode. orne mineralization i reported to hm oecurred al o near the base of the lode. Apparently not enough stoping ha been done on the "red ' lode to give a clear idea of the copper content. The lode clo e to the fi m e i aid to be poor, but there .,some uggestion that it may be better in the general ricinity of the fi mes than it is away from them. The A hbed wa al o opened at Garden Cit , ea t of the Phoenix working . ld report indicate that amygdaloid similar to tho e at the Phoenix were pr ent and that the opper content was encouraging. The produ tion, howe er, ' a mall. The "red' lode appear to have been the one mo t worked at Garden ity. HAr COCK l\II E The Ashbed ha been op ned at the Han o~k mine but is de cribed with the other lode of that min on pages 1 77- 17 . ATLA TIC MI E At the Atlantic mine the A hbed lode has been opened for about 5, 00 feet along the trike and down to the thirty-fifth level. ( ee pl. 34.) H ere the lode wa of the coriaceou typ , wa oft, averag d !2 feet or more in thi ]mess, and eem to have been rather uniform in character and in mineralization in the central part of the mine but b came poorer both to the north and to the south. The copper is aid to have been rather uniformly di tribut d through the lode, and the developed ground has been nearly all toped. .The only structural feature of importance at this mme is a strong fissure or "cro ing" with a teep northerly dip extending through the mine just north of o. 2 shaft. The filling of this fi me, as judged by descriptions and some material on the dump, was a coarsely crystalline calcite, in places at lea t with a pinki h tinO'e. It i said that in the upper levels the lode near the fi sure was poor, and a rather wide pillar was left. In the lower levels the pillar left wa much narrower. In the early years of operation of the tlantic Mining Co. the rock averaged 18 to 20 pounds of copper to the ton, but for much of the productive period it did not exceed 15 pounds and dropped almost to 11 pounds. For the last year., of operation it wa as follows: 1902, 11.09 pound ; 1903, 12.7 ; 1904, 13.63; 1905, 13.72; 1906, 14.69. When the mine was clo ed by caving in 1906 it was reported that the central portion in the deeper level bows no indication of a decrease in the grade of ore. The profitable operation of the Atlantic mine on a lode that averaged so low was due partly to the rather uniform mineralization, which made mining cheap, and partly to the softne of the lode, which was favorable to cheap mining and milling. LODES OF THE HANCOCK MINE Production from the lodes of the Hancock mine (pl. 35) began in 1 61 and continued with interruptions till 191 . The total production from the e lode , together with a con iderable production from the Pewabic lodes by the Hancock on olidated Mining Co. that has not been separated i 17,559,557 pounds. The earlier production, from 1 61 to 1 6, 5,360,000 pound , was derived from lode o. 1; and the later production, from 1911 to 191 , 12,199,000 pound , mainly from lodes o . 3 and 4 and the Pewabic lode . In the later years the yield averaged about 13.5 pounds copper to the ton. The writer ha,d no opportunity for an examination of the Hancock mine, and the followinO' tatements and the accompanying maps and sections are based on data furni hed by the Hancock Con olidated Mining o. The lode of the Hancock mine lie between r o. 17 conglomerate and the Pewabic lode . The old o. 1 lode i , to judO'e from the de cription and from the cour e of the drift along it, apparently on the Hancock fault, a rever e fault which strike at the surface about . 54 ° E. and dip at a considerably steeper angle than th bed . The fault fi ure evidently curves very irreO'ularly, both the dip and strike varyinO' greatly from place to place, and it doubtless has numerous branches. The apparent displacement of the bed , m a ur d horizontally at right anO'les to the strilce, i about 600 feet but differs con iderably at different points. The actual movement on the fault to produce this apparent di placement was certainly much 0'1' ater. o. 1lode ha been opened along the trike for about 1,200 feet and to the fourteenth level. Most of the
THE COPPER DEPOSITS OF MICHIGAN toping wa done betwe n the urface and the teuth level. There i a strong ugge tion of a outherly pitch to the ore hoot. o. 3 lode i the amygdaloid of the third flow b low o. 17 conglomerate and is th ref ore at the general horizon of the A hbed amygdaloid. It i , in places at lea t, scoriaceous and in this respect re emble the A hbed. The o. 3 lode ha been opened for about 1,500 feet along the stJrik and ha been toped mainly between t.he tenth and eighteenth level . o. 2 lode i the amygdaloid next below o. 3 lod . The lode called Io. 9, above the eighteenth level i probably I o. 2 repeated below the Hancock fault. o. 2 lode has been opened for about 1 000 feet along the strike and toped mainly betwe n the sixth and eleventh level . The toping on the part known a o. 9 is mainly between the twelfth and eio-hteenth level . The true o. 9 lode, a it may be called, below the eighte nth level i above the fault and below o. 16 conglomerate. o. 4 lode i a little belo' thi No. 9 lode and probably a little above the P wabic Far Wet lodes. There are, then, two general horizon of mineralization-one represented by lode o. 2 and o. 3, 1 ing near th . horizon f the A hb d amygdaloid, and the other repr nt d by o. 4 and the true o. 9 which lie below . o. 16 no-lorn rate. In addition 0 . 1 lode i appar ntly on the IIanco k fault. Mot of the ore thus far d veloped occurred above the Hancock fault. P EWABIC AMYGDALOID LODES LOCATION AND PRODUCTION The P wabic amygdaloid lode (pl. 36) have been mined mainly in the properties that now form the Quincy mine. Th pre ent Quincy mine (see pl. 74, .A) include the Old Quincy, Pewabic, Franklin, Mesnard, Pontiac, and others. Out ide the Quincy mine the lode have been mined in the Han ock mine, adjoining the Quincy on the outh and in th Franklin Junior mine to th north. To the south the rocks at this horizon wero ox ten i vely explored by the aumkeag opper o. and to the north they were opened at the Rhode I land mine and have been cut by the vertical shafts at alumet but only lightly explored. The following table show the production of the Pewabic amygdaloid lode from the beginning of operation to 1925: Production and dividends from Pewabic amygdaloid lode, 1855- 1925 Refined COPI r (pounds) Dividends Mine Period Rock treated (tons) Per pound of copper (\ Total P r ton Total 1 29, 242, 500 Estimated. Much of tho production from tho Hancock mine for 1911 to 191 , amounting to 12,199,000 pounds of copp r, was derived !rom the Pewabic lodes. CHARACTER OF FLOWS The Pewabic amygdaloid lodes at the Quincy mine consi t of a group of relatively thin flows. These overlap so that it is possible to follow amygdaloid continuously and still pass from the amygdaloid of one flow to that of another. It is difficult to correlate the flows certainly from one point to another unles the top of the flow has been actuaUy followed as one flow may give place to another within a hundreds or, in the thinner flows, a few tens of feet. In composition the Pewabic Bows fall toward the ande itic end of the basaltic Keweenawan series. Textmally they are glomeroporphyrites and feldspathic melaphyres, with ophitic textme in some of the thicker beds, such as the one below the Pewabic Far West lodes in the lower 50 levels at o. 2 shaft. All or nearly all the beds are porphyritic, containing well-developed feldspar phenocrysts. CHARA"CTER OF AMYGDALOIDS The amygdaloids of all the flows of the Pewabic lodes are characteri tically of the coalescing typ~, though different lodes vary in the degree to which.tlus c~aracter is developed, and there may al o be a decided d.ifference in its development in different parts of 8 smgle flow. Where it is well developed there are from 2 or 3 to as many as or 10 cavernous bands or layers
PEW ABIC AMYGDALOID LODES · a lode from 3 to 5 feet thick. It i not uncommon ~see these ba.nds continuous along a cro section of t~e lode for 10 to 15 feet or even more, and in the plane r the lode such layers mu t form conn cted openings ~or tens and probably for hundred of feet. There is every gradation from the .well-banded or layered lode to that in which the vesiCles show only a moderate tendency to collect in layer and do not form continuou openings. Fragmental tops are not chara teri tic of the Pewabic lode a a whole. A little fragmental rock occm at the top of the amygdaloid in many places, and over con iderable area the lode i typically fragmental, though more uniform in thickne than most of the fragmental lode . A large area of this character is present in the outh nd of the mine, extending from the seventy- ixth to the eighty-first level and covering an area of 400,000 to 500,000 square feet. A smaller area, o far a opened, i pre - ent in the bottom (eighty-fir t to eighty-fifth level) near Io. 2 haft. o far a ob erved in the lower level , the Ea t branches of the eri show more fragmental amygdaloid than the We t branche . The upper and intermediate level wer een in only a few place , but it is tated in old de cription and by those familiar with the upper levels that the "main ' lode wa a thick, soft, chocolate-colored lode. orne of it wa seen on the twenty-second level between o. 2 and Io. 6 hafts, where for the mo t part it i a typical fragmental lode, bowing all the characteri tic of that type. The lod thin and thi ken from pla e to place with bulge into the hanaina wall and th footwall. Where the lod i thin it tend to b orne ellular and coale cing. On the ntyv nth l v 1 b tw n o. 2 and o. 1 haft the character f the lod alt mate between rather tight c llular, t nding to oa.l cing, broken in place into large block , and fairl w ll developed fragm ntal. The fragmental por i n have been -loped and doubtl were con iderabl mineralized. From ob ervation in and de cription of the lode in the upper level it seem probabl that large area of the 11main" lode above, a , the thirty-fifth le el were fragmental. om of the oth r lodes wh re een in the upp r 1 vel are a eli tin tly oal cing a any on the low r l vel . The oxidation of th c ale in()' lodes i l than that of the fragmentallod s though th top ar distinctly reddened. The fragm~ntal portion of the lodes are moderately well oxidized, though not o highly a many fragm ntallode el ewhere. MINERALIZATION The mineralization as ociated with the deposition of ! copper in these lodes was simple. ilicifi.cation of the od · 0 18 pronounced, and quartz is abundant, commonly as well-formed crystals in the open cavities. Calcite is al o nearly everywhere pre ent and rather abundant. Pumpellyite is pre ent as a product of rock alteration and also in open cavitie , and epidote i common but le s abundant than pumpellyite. Chlorite is abundant in amygdules in the base of the flows and throughout the trap part of some of the flows. Near fis ures the chlorite may be replaced by the light-colored mineral , quartz or calcite, which gives the rock adjacent to the fi ure a much more amygdular app aranc . Zeolite are par ely represented. Laumontite i pre ent in the Main par crossing and · was noted in oth r mall fi ure . In the lode it is rarely een on the lower levels but i rather abundant for a con iderable di tanc from the par eros ing on the upper level . I o oth r zeolites were noted. Prehnite is pr sent but not common. odular rna es of porcelanic datolite are aid to have been of common occurrence in the upper le el of the min , but no datolite was seen in the lower lev ls. ROCK ALTERATION The bleaching and alt ration of the rock is characteri tically of the quartz-pumpellyite type common in the coalescing lode . In the well-oxidized fragmental portions, especially where een in the upper 1 vels, the quartz-pumpellyite alteration i l s conspicuou and the bleaching i due more to the removal of iron, as in the Kear age and 0 c ola lode . Before th mineralization, when the cavitie were empty, the w ll-developed coale cing amygdaloid wa much mor p rmeable than the c llular amygdaloid a.nd would permit the pa age of much more of the min ralizing olu tion than the cellular type. It is evidently for thi rea on that the richer copper ground i in the well-d veloped coale cing lodes, and although the e are not everywhere rich, the poorly develop d coale cing and cellular lodes are pretty con i ten tly poor. Con id red in more detail, the coar e copper and rna s very commonly are a ociated with strongly developed band in an amygdaloid, though the copper and a ociat d mineral g nerally replaced the rock adj aeon t to the opening . The finer copper also is as a rule clo ly a ociated with well-developed band , thouah it may extend ome di tance from them; and some copper i of cour e found in cellular amygdaloid and even in amygdules in the trappy portion of the lode. Fragmental lode rock i of coUI'se distinctly permeable and readily replaceable and therefore favorable to mineralization. The rna es of such rock expo ed in the bottom of No.2 haft ar pretty con istently rich. The fragm n tal amygdaloid in the "main" lode in the upper level of the mine wa evidently w 11 mineralized, and in plac sit was rich. maller areas of fragmental lode and areas where a foot or so of the top of the lode is fragmental are commonly good to rich ground.
THE COPPER DEPOSITS OF MI HIGAN It is pretty clear, therefore, that a fragmental lode in this series can be as favorable and possibly more favorable than a well-developed coalescing lode. There is some minor fissuring both parallel to and across the lodes. The fissures IU'e commonly mineralized and evidently were favorable to the movement of solution. MINERALIZATION IN DIFFERENT LODES The Pewabic lodes are separated into three groups by the Quincy Mining Co. for the purpose of the underground mapping. The grouping is based on position, and the three groups :1re called the Ea t lodes, the West lodes (includin& the "main" lode), and the Far West lodes. The East lodes are east of o. 2 shaft in the upper levels. The shaft was in the "main" lode, which apparently corresponds to the West lodes in the lower levels. The Far We t lodes are tratigraphically above or west of the West lodes. The East lodes are the most persi tent and regular in the lower and middle levels. They consist of a lower or foot branch and an upper or west branch. The flow who e top forms the lower branch lode re t on the Old Pewabic flow. It is usually not more than 30 to 40 feet thick. It consists in places of one flow, and in places apparently of more than one. The upper flow is even thinner; in places only 10 feet of trap, or even le s, separates the two branches, and it is possible that the upper flow is not everywhere pre ent. In the outh end of the mine the upper branch of the lode has been most extensively opened. toping on this branch extended from the tenth level, between No. 7 and Io. 2 shafts, to the bottom of the mine. To the north there is little work on this hranch to the twenty-seventh level in o. 6 shaft, and somewhat lower in o. 8. Below this to about the sixty-fifth level in o. 8 and o. 6 shafts not more than 50 per cent of the lode has been taken. From about the sixty-fifth level to the bottom in the north end more of the upper branch has been taken, and in the south end it has been very largely stoped. The lower branch was mined but little to about the fortieth level. From the fortieth to about the sixtyfifth level it wa extensively mined north of o. 6 shaft, and considerable was taken in the south end of the mine. Below the sixty-fifth level this branch bas been mined very little in the south end but some has been taken between No. 6 and o. 8 and considerable north of No. 8. Above the si-xty-third level both branches have in places been mined in the same area, though not as a rule. Below this level in the north end of the mine both have been mined. This difference apparently is due in part to a change in mining method rather than to a udden change in the character of the lodes. "MAIN" BRANCH Down to about the thirtieth level the "main" brn.nch was the one most extensively mined. Thi i above the East lodes and apparently correspond to the West lodes in the lower level . In the lower level it has been but lightly developed to the north of o. shaft and to the south of o. 7 but has been rather extensively mined from o. 6 and o. 2 in the central part. There is more than one lode in thi West group. What is known as the hanging-wall branch ha been most exten ively min d. Th e branches in the lower level do not seem to have the long strctche of continuous favorable rock that are pre ent in the East lodes, but where favorable rock is pre ent it is very well mineralized. PEWABIC FAR WEST LODES The Pewabic Far West lod s have been developed principally below the fiftieth level near ro. 2 and o. 6 shafts. In the upper part of the developed area at o. 2 haft they are separated from the We t lodes by an ophitic trap, which is as much a 130 feet thick in this part of the mine, but apparently thins very much down the dip, up the dip, and toward No. 6 shaft. The Far West lodes are above this trap, in the coale cing amygdaloidal tops of severnl mall flows. o far as open d, these tops appear to have shorter stretches of favorable amygdaloid than the Ea t or We t lode , but where their character is favorable they are well mineralized. In the preceding paragraphs the changes in the lode. in different parts of the mine have been noted in some detail to bring out the idea that in a erie of lodes like the Pewabic too much emphasis should not be placed on local changes in character of amygdllloid and copper content of individual lodes in their effect on the favorability of the series a a whole. It i apparent, so far as the present extensive development show, that some of the lodes were richer in the upper levels, some in the intermediate levels, and some in the lower levels. Some were most extensively mined in the north end of the developed area and some in the outh end. The series as a whole appears to have been about equally productive in the upper and in the lower levels of the mine. FISSURES OR "CROSSINGS " A strong cross fissure extends through the mi~e , dipping north at a high angle (se pl. 36) and cro 111g No. 6 shaft at the fifty-fifth level. The strike of the fissure, as indicated in the fifty-first level foot'':aU crosscut, is about 10° from right angles with the tnke of the lode. This eros cut intersects the Allouez conglomerate and in fact all the lodes cut by it onlY~ short distance from the fissure. Where it erose
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PEW ABIC AMYGDALOID LODES dw "main' lode in he upper lev I little toping was doue adjacent to thi fi ure, and the lode was evidently poor. Thi. condition continued to about the fiftieth level. Below that toping wa carried close to the fi ure, which is aid to have had little effect on the copper content of the lode for more than a few feet on each ide and in place good ore i pre ent again t the fi w· . Whe~·e een in the lower levels the fi ure ha di placed the lode very little, though the rock is brok n for everal i et. Th fi ure filling con ist mainly of calcite, laumontite, and quartz. Chloritization and pump llyiti;.;ation of the wall ro k are con picuou in and n ar the fi -ure but xtend only a hort di tance. 'Vherc the " par cro ing" wa een on the upper level , laumontite i abundant in the lode for a con iderable di tance from . the fi sure. Pinkcalcitei the mo abundant min ral in the fi ure; quartz and epidote are pre ent locally. opper i pre ent in the fi ure wh rever examined, and at one place a good- ized rna wa en. The copper content of the fi w· ha not been uffi ient to en ourage work on it. Two other cro ings are noted on th mine map ; one of these passes between o. 6 and o. haft and i about parallel to the main cro ing ; another cro e No. haft at the twelfth level and d,ip about ll'ith the north boundary of th ore shoot. ither 1 copper. During this period the ield wa ab:mt 9 to 12 pound of copper to the ton of ro k. The writers have had no opportunity to examine the lode in the mine. The lode has been op ned by four hafts, but mo-t of the operation have b n conducted from the K o. 1 shaft, which exte d to the thirty- ev nth level. No. 3 shaft goes to the fifteenth level. The lode ha been opened for about 3, 0 fe t along the strik , but mo t of the d velopm nt ha b 3n within 1,500 feet north and 1,000 feet outh of o. 1 haft. In the upper level mo t of th ground toped wnnorthof o.1 haft;inthelow rl v l thepr d.u ti,·e ground extended uth of the haft, ugcrestin()' a south,vard pitch of the outh boundary of the ore shoot. The ground wa toped over a long r tr tch in the lower level than in the upper, and betw en the upper and lower le el there wa an area in whi h compar tively little of the lode wa toped. RHODE ISLAND MINE The Pewabic amygdaloid ha been opened at tbe Rhode I land mine by two shaft - )l o. 1 to the fourt.h level, No. 2 to the tenth level. The openincr::; extend about 2,700 f et along the trike for about equal d.i tance north and outh of To. 2 haft. few tons of ma and barrel copper has been hipped from the Rhod Island mine. Th re ha been no of the e were e n. Th fir t e m to hax had no notable cff t on th grade f Lhe lode adj ac nt to it. The econd i mainl. out.ide th top d ar a. 1 oppor unit. for th writm to examine the lode in the FAULTS The only fault f n te that a:IT cts th P wa hi l des ·. the linn co k fault, whi h cut the lod in the , ou Lh end of the Quin y mine and in the Hanco k min . Thi fault i rrpre nted in the ro~s ecti n of. o. 7 ·hafL a cro . ing th haft at the fi(t enth lev-el and ~aching the ur·fa in the h n()'inrr-wall id f the 'haft. The e two point give th fault a dip of about 75°. At th fifteenth 1 1 it i marked on the 018P a ha\·ing a dip of 76° 30' and a trike of . 17° 4 ' W. for n hort di tan . Th fault i m r fully described in onnecti n with th lode of the Han ock mine {p. 177) and hown in th cro ection of that mine. Th rlilouez ('Albany Bo ton") onglomerate, 88 repre en ted in th old adit, i ff et approximately 600 feet on the l v 1. Th P wabi lode n the ixteenth lev l i indic ted a. having a imilar off et. FRANKLIN JR. MINE r The production from the P wabic lode and that rorn Lhe conglom rato lode in the Franklin Jr. mine ~·ere not oparately r cord d fo r part of th time. ~fter t.he clo ·ing of th conglom rate lode in 1909 the cwah1c lode produc d about 16,000,000 pound of 58540-29--13 . ALLO EZ ONGLOMERATE ("ALBANY & BOSTO, " ) The .~Wouez conglomerate (pl. 37) ha been op ned and mined at thr e widely epara ted localitie ~-a t Delawlll' , at Allouez, and at Fraoklin. P ROD UCTION The fi1 t product.ion from thi conglomerate wa ' made by the .Albany - Bo"ton o. in 1 62 at the prc' - ent Franklin Jr. mine. In 1 82 th mine old· to tlie Peninsula Copp r o., which operated it till In 1 95 it wa old to the Franklin ~1ining Co. The Pewabic lode wa being mined for part of the period, and there i no accurate record of the total production from the l o u ez conglomerate, but it wa about 34,500,000 pound . The a.verage grade of the rock in th later p riod a between 11 and 12 pound of copper to the ton. Work wa begun on the onglomerate by the llou z Mining o. in 1 69. From that in1e there was alt rn ation of company operation nnd work by tributer till 1 92, wh n production cea ed. The total r corded production from the Allou z mine wa 25,7 6,000 pound . During the later part of th p riod the vield ranged from 13 to 19 pound of copper to the ton of rock.
THE COPPER DEPO IT From 1 47 for many year the fi. sure and th conalomerate lode wer worked at D laware by differ nt companie , u ually in the mo t in ffici nt manner . -\ltogether a larae amount of mon y wa exp nded to little purpo~e . fill were built ncar Delaware, and later a railroad wa extended to Lac La Boll , where a mill wa built. There is no accurate record of th production from the conglomerate eparate from the fi sures, but it i e timated at about 1,770 000 pound . The large t output was made in 1 3 and 1 4, wh n the rock yielded from about to 11 pound of copper to the ton of rock. The recovery ''a poor, howe,·er, and the tailing probably contain a much or more than wa recovered. Prnduclion from A.llouez conglomerate )line Period Refined copper (I>onud) --1 Franklin Jr.: Franklin - 1901-1919 llouez ... - -- - - 1 69- 1 92 CHARACTER OF CONGLOMERATE 65, 057 6, 624, 991 34 473, 9 4 25, 7 6, 6 1 1, 770. 570 69, 521, 253 There has been no opportunity for the \\'Titer- to examine the Allouez conglomerate a expo ed in the mine working . A seen on the dump at all thre localities it is a moderately coarse fel ite conglomerate similar to the Calumet & Hecla conglomerate. From 1 cription- it appears that len es of the Allouez conglOinerate were well mineralized and some were rich but that much of it wa poorly mineralized or barren. The character of the mineralization and of the rock alteration e ms to be similar to that of the alumet & Hecla conglomerate. feature that i pr nounced in the Allouez conglomerate at all thre localitie is the presence along joints and earns of many dark 'ein of calcite containing finely divided halcocite. imilar ein are pre ent on the margin~ of the alumet & Hecla conglomerate ore hoot as at ent nnial, but are not ommon in the main sh~ot. FRANKLIN JR. MINE Th .\.llouez conglomerate ha been opened at the F_ranklin Jr. mine by two hafts from the outcrop-in o. 1 t the twenty-fourth level and in To. 2 to the nineteenth level. 'rhe openings extend for about 2 500 feet along the strike, and v .. -ithin this area most of the ground ha been toped. The conglomerate has al o b en opened below the shaft working by eros fr m the ~ewabic o. 1 shaft from the twentyJxth to the thn·ty-sev nth levels and here also for a maximum eli lance along the strike of about 2 500 feet, .but the proporti n of the ground toped in 'thi area 1 not o great. The stope map . uaae t that the main ore hoot in this area pitche outh. RHODE ISLAND MINE A little hallow work wa done on the Allouez conglomerate by the Rhode Lland o. LODE IN LIFF Ml E In the early operation in the liif mine con iderabl1 attention wa given to the ninth amygdaloid or "floor," which w opened to the 90-fathom level sod followed by drift for hort di tnnce on roo t of the level ; on the 0-fathom level a drift wa extended we t about 500 feet and ea t about 400 feet. The earlv report poke faYorably of the howing in thN drift , but in 1 64 a te t run bowed the rock to arer· age le than 15 pound to the ton, and work wa: abandoned. In the report for 1 64 it i tated that the copper ontent decrease ay from the fi ;ure. The thirteenth "floor ' is al o pok n of in the early report a well mineralized, but very little worbecm, to have been done nit. When the mine wa reopen d in 1906 short ~ift; were run on am gdaloid in the outh end of the nune Whether all looked favorable or not is not el'ident. It is tated that ome fair ro k wa taken, but the average wa evidently poor. Later some work wa don on amygdaloid in the north nd without encom·aaina re ult . no work was done at this time on the 1th thirteenth "floors," which w re regarded a ill0' favorable in the early day . ALUMET & HECLA CONGLOMERATE LODE LOCATION AND EXTENT The Calumet & Hecla conglornentte (pl. 3 k. been opened at numerous places from Portage La·~ t laCt'· nearly to the end of Keweenaw Point. In mo P : it i a coriaceou amygdaloid with a few inche" to
CALUMET & HECLA COr GLOMERATE LODE few feet of o erl ing fel itic and or grit. Only in the nlumet area has it been hown to be a welldeveloped fel ite conglomerate. The lode ha been developed in th 0 ceola, Calumet & Hecla, Tamarack, Tamarack Junior, and entennial mine , now all owned by the Calumet & Hecla Con olidated opper o., for a distance of about 1 ,000 feet along the strike and to a maximum depth of 9,300 feet down the dip. ( ee pl. 75 , D.) P RODUCTION The Calumet & Hecla cono-lomerate wa di covered in 1 64, and production from it began in 1 65. The foUowing table shows the production from the lode to the end of 1925: Production and div-idends from the Calumet & Hecla conglomerate, 1865-1925 Refined copper (pound ) Dividends Iine Period Rock treated (tons) Total Per ton Total Per pound of copper (ceo l 1 CentenniaL - -- DO Tamarack- -- - 5-1917 - 379, 971, 101 ) Calumet & Hecla:
57,229,052 2, 31,092,153 14 ,726,051 12,374, 23 I 127, 6 6, 924 35,450 12,652,02 j Tamarack Junior: l : 1~; !8;; 656 26.-62- Total production omitting figures for which no corresponding tonnage is given: 3, 375, 353, 670 14 ,726,051 5 ' 213, 265 2, 56, 267, 371 2, 9 3, 95'*, 295 1 Including copper reclaimed from 5 ,213, 265 Estimated. COMPOSITION The conglomeratic portion of the Calumet & Hecla conglom rat is mad~ up of eral kind of ro k varyis e pecially abundant. Thi rock re embles in color the fel ite intru ive outh of hme k, although it i not thought to have furni hed material for the Calumet e la cono-lomerate. f w quartzite boulder were noted in the r o-ion of the lope haft and in orth Tamaraolc uch a local variation in the compo ition ugo-e t rath r near-by our e for the material. ing om what in pr p rtion fr m place to pla . Th common ,-arieti nr fel ite, f ld par porphyr , quartzfeld par p rph 'ry, am gd loid, and trap, with other type of ro k u h a quar zitc in mall amount. The iliceou r k mal- up probably more than 95 per cent of the lod . Ill !!daloid bould rs, whi h 8.1' IDO t ' IROX OXIDE OF THE FEL ITE A)lD QUARTZ PORPHYRIES " OF KEWEE A W POINT plentiful n at· th ba of th lode, npp ar to ha been derived from the amygdaloid immediately b n ath the The followino- note relate to the ource of the conglomerate and to hn,v m cd but a v r h rt di 1 rath r abundant f rric oxide in the lode. The chief lance. few bould I' of m r highl oxidiz d amygdaloid nnd of trap ar pr cnt that mny have me from other our , . indication ha. been f und that th iliceou. p bble w re doriv d from carli r c nglompurpo e of th examination here summarized were to d tennin wh ther the bulk of the iron oxide in erat . This and Lh ab enc r basi p bbl ex ept of the amygdaloid imm dia ely b low mak it eem th onglom mt mu t hav b n derived from SOU!' c utsido th ric of flow and cono-lomera te th~t make up the immediate! undorl ing part of th .ene . early all tho material of th onglomcrate IS red to bro"ll in col r, o that the cneral olor fiect of the unmin raliz d lode i dark r d to brownish red. 1 the alumet - Hecla conglomerate were there when the mineralizino- olution entered, or were introduced at an earl tage of the mineralization, and to determin what oxide the are. It i b lieved that the type of iron oxide and it ' abundan e in the several f 1 ites in place along Keweenaw Point throw con id rable light on these que - tion . P li h d urface of the e fel ite show that the r all contain hematite to a greater or le extent. In s veral pc imen wh re the reticulate structure 1'her on idcrabl variation th qunntity of the diO'crC'nt typ of rock in difl'cr nt part of th lode. ~or cxnmple, fcl iLc and feld par porphyria. ar relatively nbundant outh of the bar en o. 6 and N'o. 10 II ccla wh rea north of that bar quartz Porphyry is r Lativcly abundant. In th lo~ or part or th min , to the outh, the quartz porph ry also abundant. In th upper le l in o. 5 nlumct a light-c lor d vari t of fel it porphyry hara teri ti of the mao-netit -ilmenite int rgro> th ugge t 'd tha magnetite might be pre ent, it absence was d finit ly e tabli hcd by uch te ts as treatino- the poli hcd urface with hot concentrated hydr - hloric a id and po' dering the ro k and testing with a magnet. It wa hown that be ond a reasonable doubt the hief iron oxide of the f l ite from the end of r weenaw P int to th Porcupine M untain is h matite.
THE COPPER DEPO IT OF MICHIGA - There i viden e that thi hematite i a primary mineral of the fel ite . It app a1 homoO'eneous under the hiO'be t magnification avRilable both before and after tr atment with hot concentrated h. drochloric acid, bowing no i land of unreplaced maO'nctite uch a are common where hematite ha r plac d magnetite. The rock contain int rgrowth that reemble those of magnetite and ilmenite, but such forms are al o as umed by hematite and ilmenite. :tvlany examples of hematite with lathlike form were noted, sugge ting cro s se tion of tabular hematite crystal ; the e are probably identical with the elongated opaque reddi h form in the fcl ite and acidi porphyries de cribed by Irving under th name "ferrit . ' Hematite a a primary mineral oc UJ at many localitie in ilic ous and feldspathic ro k , where ferrou iron is absent or pre ent in mall amount . That the ferrous iron in some of the Keweenaw Poin felsite i low a compar d with the ferri Iron shown by the following analy e . I>o FcO tatement f n of thee mpan. 's chemist who ana. 1 z d th darl mnt rial of tho floLtttion lim . of the conCYlomerRtc, ha it i a ' dark-r d powd r nnd but slightly magn tic." His lliHily i i. R.S foll w : i 2 1& 22 Total iron 11 F -- 4.5. 4l U -- Ti 2- - G. -16 took place. of the rock un· unding pp r, both in conglom· rate and amygdaloid , i reduction and removal of ferri ir n. Ther f r , if xidati n f maanetitc took pla e during the min ralizntion it is a r ,-m al of the commonl ob r d r action. To te t thi point the iron oxid in om of the ediment , uch IRQ:-< OXIDES IN THE CALU)JET & HECLA COXGLOMERATE a the r at ngl merate at a<Yle Harb r, far !\WRY The chief modes of 0 cmTence of iron oxide in the from opper depo i , wa tudied, and the maQ'Detite 1 wa f und to how the arne oxidation to a varying alumet & Hecla conglomerate may be cla ified as in he alumet H cia con· follow : (1) Di seminated in rather fine particle in 1 hanO'e i ind pendent of cop· the fel ite and quartz porphyry fragment and boulder ; (2) in round d grains in be andy matrix of the , per mineralization and pr bably took e in part conglomerate and particularly in black band in the oon af er the cry tallization f th maO'netitc in it' and tone; (3) a hematite in oft, con iderably altered 1 par nt lava flow ( ee p. 42) and in part during the boulder , many of which are iron-rich and form the time it wa expo ed to weath ring. familiar copper kulls when replaced; (4) as pecular 3. Many pebble and boulder , oft and much h matite in -v--ug and along plane of weakne . altered1 are red with ferric oxide. orne of them con· The available information on the e mode of o curtain feldspar and quartz phenocry ts. Thi he:nntite r nc may b ummarized a follows: eems different, on the one hand, from the fincl.v di·· 1. All the poli hed ection show that th comparaerninated primary hematite f the hard f l itc and, on ti,cly unaltered fragm nt of felsite and quartz porthe other hand, from tho hiny black sp cular hematite phyry- that is, tho c that are not oftened or 1 which i to be a ociated with the recrystallizinO' effect bleached- contain hematite in varying am unt , a 1 of th mineralizing solution actincr on the ro k. The catter d fine grain . In thi re pect they are the explanation of the occurrence of the e oft oxidized same, a clo ely as could be determined, a the fel ite boulders i not clear. That there were pha e of the in place. The arne te t to e tabli h the ab ence of 1 porphyrie with more abundant iron-bearing iJicnte mngnetite were made on such material with negative than the prevailinO' type i probable. Irving de c_ri?e To ults. 1 many Keweenawan quartz porphyries as contnmJng 2. Rounded grains :1f iron oxid occur plentifully altered augite and ays that there are gradation from throughout the finer material of the onglomerate. the highly siliceous pha es to the diaba e porphyne_. A very litt] or no magnetic material was found in Hence, a possible source of the e iron-rich boulder ~e~eatedly te ting the powdered ro k with a magnet, not hard to imagine. The hief difficulty orne tO 1t 1s concluded that the e grain con ist of limonite explaining their pre ence in such a soft oxidize::l tote hematite, and ilmenite. Thi conclusion accords with in the conglomerate. If they were oxidized before Pnla he 1s determination on the black table concendeposition, how could th y tand up under the rather trates of he conglomerate. It al. o agree with the severe mechanical abra ion to whi h they would be
CALUMET & HECLA 0 GLOMERATE LODE subjected'? If they came to rest as hard unaltered pebble but wer~ later oftene~ and would mean more mten e weathe·rmg than IS md1cated for most of the onglomerate material, though such pebbles would be presumed to b relatively usceptible to oxidation. 4. pecular hematite is not uncommon in open spaces of various sorts in the conglomerate. It is regarded a a re ult of the rearrangement of. ferric oxide, shown to have been pre ent in abundance before the ore-b aring olu tions en terecl. CHA~GE IN THE IRON OXIDE D "RING MI TERALIZATION The effect of the ore-bearing solutions upon the iron oxides i notable. Chemical aualy es of bleached and unaltered fel ite, study of polished ections of pebbles IYith bl ached portions, examination of hand pecimens and the interiors of copper 'skulls," and obser1 vation of the bleaching on a large scale underground all point to the same conclu ion-that the introduction of copper has been accomparued by the removal of ferric iron. Polished section show that the bleached portions of pebbles, whose unaltered parts have swarms of tiny hematite crystals, are entirely lacking in ferric oxide. Hand specimens show that black iron oxide bands in the unbleached sand largely di appear on passing in to a mineralized portion. imilarly, the soft iron-ri,ch boulders, which analy es how may run over 12 p r cent of ferric oxide, are bleache<l and cont in practicall no ferric oxid where the c pper ha been introduc d. The effe t upon th ilmenite ha n t been ob erved in p li hed ec ion, but the petrographic xamination of thin ti n indicate that much of it chang · to titanite. In an epidotized sand nothing i left of man iron ox.id grains but the kel ton of r ticulate ilmerute surround d by a trans par n t mineral, ugg tino- that ' the hematit or limonite went to build the epidote, leaving the ilmen.i te. Therefor , while it com clear that t,he oro olution had the power of rearranging the iron oxide, the evidence indicate that the bulk of th iron oxide came in at the tirno of edim ntation as ferric oxide, mu h of it n primary h matite from and in the fel ite and quartz porphyry. It wa remov d by th ore-b aring olution , and thi r mo a.l bleached the ro k and wns clo ely a o iated with the pr cipitati n of copper. THICKNESS The conglomeratic portion of the Calum t c· Hecla c?nglomerate, o far a dev loped, i di tin tly lenticular. The lono-itudinal axis of groate t thicl ne extend almost due north from about the collar of No. 1 conglom rat haft, 0 c ola mine. Both ea t and we t of thi m dial lin the lode thin but not uniformly. Ther ar s y ral minor axes t the east comin"' to the urface at ro. 5 He la, o. 1 H cla, and ~o. 2 alumet. ( ee pl. 3 .) The len thins not only to the ea t and we t but to the ou h or toward the out rop. A far outh a o. Hecla the lode ha nearly feathered out to the ea t, and at mo t but a few hundred feet appears to have been eroded. outh from No. 10 much more of it has b en eroded. Alono- the main axi the conglomerate thickens toward the north, or down the dip, the thicker portion being found around o. 5 Tamarack and in orth Tamarack. In pa. ing from outh to north the thicker part of the conglomerate len widens notably, o that a eros section through o. 5 Tamarack would include a width of conglomerate having a thickne s of 10 feet or more, at lea t four or five times a great as a imilar ection pa mg through the collar of o. 10 Hecla. It is apparent that in passing downward from the urface succes ive ection aero the entire lode would contain an increa. ing amount of rock. Thi i equally true whether the ection i taken parallel to the pre ent urface or at right ano-le with the major axis of the lode. rough estimate of the relative amount of lode exceeding 5 feet in thickne at the urface and at the twenty-fifth, fiftieth, and seventy-fifth level gives the approximate ratio 3:4: 7: 10. ection at right angle to the axis of the lode at equal interval pa sing about throuo-h o. 10 He la and o. 1 Hecla and near Red Ja k t haft crive a ratio of about 4: :11. TEXTURE The texture of the lode, like the thickne , >arie from place to place, and in a broad way there i a rather clo e correspondence between thickn , s of lode and texture. Wher the lode is thick coar e mat rial relativ ly abundant, and where it i thin fine mat rial i relntively abundant. Thu , wh re the lode i le than 5 f et thick it i composed larg ly of coar e to fine and; where it i more than 10 fe t thi k it is prevailingly a pebble to boulder conglomerate. The portion of intermediate thickne , oYer con iderable area at lea t, a i e n in the upper lev I of the Calumet and of Hecla shafts o . 1 to 5, i intermediat al o in texture, the prevailing rock being a coarse grit to fme pebble conglomerate. In the coa er part of the cono-lomerate there is a varying but u ually rather large p rcentage of coarse to fine o-rit that f rm the matr.L\: for the pebble . The coar e and fine pha e of the conglomerate, in luding and ton , do not differ crreatly in ompo ition except that the finer portions contain considerable ferric oxid and ilmenite in grains. In the and tone the e form definite band that are practi ally ver wher no tic able, but the grains are al o pr en t in the fin matrix of th coar e type of the conglomerate. The finer part of th conglomerat,e are therefore ri her in ferric oxide and in ilmenite than the coarser part.
THE COPPER DEPO ITS OF MICHIGA Th re ar oarser and finer pha e of the conglon:- erate pre ent in practically ever ection. Thu , _1t would be hard to find a ection that did not ontam some band of and tone, and in th fin r b d there are len es of coarser material. There i no very clearly recognized regularity a to the strati~raphic po ition in the lode of the fine and coar e matenal. It is common to find sand tone on the footwall, on th hanging wall, or in in term diate po ition , and, on the other hand, the coar er pha e may occupy all the e po ition . The general impre ion gained fr m lo~km~ at th lode as expo ed in drift iM that the b IS e ntially parall 1 to the wa 11 . \There min rali~ation. ha followed the bedding, however, o that the mmerahzed rock i prominent for r lati ely lono- di tances, there is a distinct appearance of cro -bedding of large pattem. vYhere be t seen the diYergence of beddinoplane is to the north, parall l to the axis of the conglom rate. Cro -bedding of mall pattern i e n here and there but j not common. HANGING WALL The hanging wall of the conglomerate oYer a large part of the developed area i a den trap with a rather pronounced ba al amygdaloid, from 2 to 6 ·nche in thickness, and with pipe amygdule extend- ! ng upward from the contact of the conglom rate. The ba al amygdaloid is commonly lightly oxidized for 1 inch to 6 inche from the contact. The actual contact i lightly irr gular, the laYa being molded around boulder in the conglomerate. In the northea ern part of th mine there are frequent! 1, 2, or pos ibly 3 small flows above the main onglomerate lode. In places fel itic and or conglomerate oYerlie the mall flow . On the twentyninth leYel, outh of o. 5 alumet, the drift follow a 3 to 4 foot b d of fel itic s!lnd re ting on a 3 to 4 foot lava flow that in turn re t on the main conglomerate lode. In To. 4 Calumet the hano-ing-wall flow was recognized a low as the forty-ninth le,el. The flow ha e been r coo-nized to the outh a far a o. 2 shaft. A mall hanging-·wall flow (about 15 fe t thick) i al o pre ent on the i ;:ty- ixth level of the slope haft where th eros ut extend to o. 3 T amarack. It would appear that mall flow are present, locally at lea t, over a con iderable part of the area north of alumet and aboYe the L'\ty- i..."Xth lev l. The mall flows commonly ho'v ome oxidation and in place are rather well o.-idized. FOOTWALL The footwall of th onglomerate i everywhere a scoria eou amygdaloid, but it differs notably in diff rent place . Over con iderable area there may be from 6 inche to 4 feet of oft reel basic and tone or hale immediately beneath the f lsitic conglomerate. Jearer it ba this sand t n or hal begin to ontain p bble or bould r of amygdaloid, whi h gradually be ome more nb1., and within 3 or 4 feet it pa e into scoria,ccou am gdaloid fill d wiLh nndtone and hale; thi in tum o-ivc pla to amygdaloid with decrea ing nmounL of la tic material, nnd the amygdaloid pn e into the footwall trap. 'l'he f l ito conglom rat mn, r t on rock of any one of the c lower t p , uggc ting that ' her th upper member are la kino- th hav be n r m ,-ed by ero ion. The data a ailabl do not indi aLe any very d finite di tribution of the difl" typ wh re they form th imm din te fo twall. The t ne and hale ar , h wever, r abundant wh re the 1 de thin out to the north a t and al. o to the outh where the lode has be n ob cured-namely, on the fortyninth and fifti th level outh of o. L Hecla; likewi c wh re the lode i thin n the cv nth lev l en t and w st of o. 6 II la. The o cut- ugge t that in a broad way r ion ha b en r lati,- ly lilrht where the conglom rat. lode i thi.nn t. The fo twall alono- th mnin a.xi of the conglomen1te u ero ~ion, a Th re eem, ' inde d, to be little vidcn e f vigorou ero ion at the ba e of the con glom ra to, although the oriaceou amygdaloid i it elf id n e of oro io and depo ition at thi horizon. The lin of parati n between tho fel itic diment and th u d rl i.Tlg amyo-daloid i· u ually harp. Pebbl and bould of th tmderlyino- amygdaloid arc pr nt in th lower part of th conglomerate, but rarely i fel iti material minuled abundantly with th ba ic and of th footwall. The pre once of the boulder of am o-daloid in the ba of the conglom rate ugo-e t that ther has been orne ero ion and that the fin r portion. h1n·c b en carried away or o di cmi.nated throuo-h the conglomerate that th y arc not recognized. Benea~h the thicker part of the onglomerate the itmyo-daloJd i u ually dark and how littl oxidation. Whore the conglomerate i thin, the amygdaloid i- commonly di tinctly reddened by oxidation. STRUCTURE Faults.- But one pronounc d fault zone cro ing th_e conglomerate lode has been recognized. Thi zone 18 at the surface between Nos. 3 and 4 Hecla and cro e the seventy-ninth level abovt 400 feet north of ro. 6 shaft. The fault has not been cut out i~e the lod~t and the strik.e can not be closely det rmmed, but 1 seems to be es entially at right angle to the str~ke of the lode. The dip i everywhere steep but not untform. If the strike is at right angles to the lode the a vern~e dip is about 82° . The horizontal offs t on fault on the upper and lower level is about The ame is reported for the upper level of Tamara o. 1. The block south 0f the fault moved to t~e west. There is a rather trong gouge on the fault 10
CAL MET & HECLA CO TGLOMERATE LODE the hanging-wall trap, which ha been mineralized with calcite, laumontite, and copper. Over a zone of 100 feet on each side of this fault there are minor faults with a throw of not more than a few inches IYhere ob erTed. Another fault, which has been raced for everal hundred feet, cro e thelodeat the cro scut from No. 5 Tamanwk on the eighty-first lerel. Thi ffiUlt strik , at a low angle with the lode, about);!. 45°E., anddipsnorthwe~t. Where ob er-ved, the dip i irregular, ranging from 60° to 90°. The hanuing wall i up about 6 feet; therefore the fault i rerer·e. Xot uncommonly there i a li ken id d zone on the footwall or hanging wall of the conglomerate. Thi indicate orne m ,. ment, but nowhere i the amount kno1m. Fi ure and joints.- Fi sure and joint are abundant throughout the conglomerate lode . .:.fany of them ran be traced into the footwall or hanging "-all, but show no displacement. They are commonly nearly rertical and at right angle to the lode. They are more abundant in ertain area , but clo e insp ction orer a few feet of lode almo t anywhere will di clo e fis ure or joints. ).ifany of them contain copper and calcite, and the adjacent rock i bleach d, indicating that they are earli r than the mineralization. On a few of the e joint a little chalcocite occurs, clo ely a ·ociated with the cal ite, and where the lode wa opened at Centennial mall calcite-chalcocite Yem were raLh r abundant. ALTERATION The conalomerat , wh r unmincraliz d, i dark reddi b brown, th prcvnilin()' color b inO' due to the pre n c of I rric O:\-id b th in th p hbl and a mall grain in th fin r matrix and in the sand. \\'here copp r i n t pre <'nt the lod ha a rather uniform appcaranc and m o haYe suff r d little lliteration in it burial by the hanging-' all 0 w. The pidoLizati n of som of the 1 an O'round., e p - cially alona th border of th hoot lion which i m OFT BO LDER In part, of the con()'lomera t oft boulders are rather numerou . Tb e u ually contain phenocr or red fe.ld par and quartz and app ar to have be n similar to th quartz-feld par porph ry that i abundnnt in the onO'lomerate, a p inted out by P.umpclly and other . At pre nt they ho1 ra,ther diverse charact ristic . In ma,ny of them a oft reddi h-brown to darl greeni h-bro> n material incl e the phenocryst . Th s app ar to be rich in iron tnuch richer than any of the fresh quartz-feld par porphyry pebble . In oth r pebble a oft O'f en chl~ritic mat rial inclo e the ph no ryst . :\early nil the p bles are often d and altered to the center and gi1·e no vidence of the originnl character of the rock except for the phenocry-ts. A few have relati,Tely bard centers. ln ome of the e epidote i a btmdant, sugge ting that the original rock ,,-as fir t hlghly epidotized and later altered to it present condition. In others there appears to be little or no epidote. .:.1aO'netite, barite, and secondary pecularite have been noted in these bard center . A the soft pebbles appear to be as abundant in the rock that contains no copper as in that which is well mineralized with eopper, there seem no reason to connect this alteration of the pebbles intimately with copper mineralization. The oft pebble are u ually in clo e proximit to other pebbles of quartz porphyry that show no similar alteration. Thi mu t mean either that there ''as some tron()' electi ,-e action or that the oft pebbl - were altered in whole or in part before hey ". re incorporated in the conglomerate. That they were incorporated in their pre ent soft eondition seem hardly po sible. It may be that they had und rgone some alteration and were in a condition to be further altered readily when they were incorporated, and that they were oftened and oxidized before the conglomerate wa buried. o ati factory e:\-plunation of the e pebbles ha. yet been uggested.
~IINERALI ZATIO . CHARACTER The mo t triking and characteri t.ic fea.tur of the min ralization i the pronounced bleaching of the ro k that accompanied tho depo ition of copper. At nearl)7 e,·ery pla re the lode i expo ed the presence' of opJ er i indi ated by th pale brick-r d or almon color of the mineralized porti n a contra ted ' ith the dark browni h r d of the unmineralized lode. In th finer material the mall pieces of rock may be largel ' bl ach d to the center, so that he lod ha a rath r uniform color. In the coarser material the pebbl hav been bl a bed for a short distance from the urfacc,butth innrpartretain its r.i()'inal olor. The oarser copper is commonly in the cement 1 here it ha partly replac d the rock rna t riul. \There the ro k i bl ached, an examination of the I oli h d surface g nerall di clo e the pre ence f opper. Bleaching not plainly connected with copper ha been noted only in len e of epidotized and tone. In such len es pebble may how a bleaching imilar to that a ociat d 1dth copper, and u h l n es are commonly surrounded by a nauow zone, rarely more than 1 in h wide, of bleached ro k. Th bl aching a o iated with the depo ition f opper ha r ult d from a removal of f rric oxid ommonly there i no evidence of the f rri oxide hn.vi~g b n onY rted to another mineral that ha remnined. There are, howe' r, ex cpti ns. nnd tone len ::; haYe b en nlmo t omplet ly changed to pidote, Apparently from a c mbitHttion of the f rri oxid \\·ith other consti uent of th '!lnd n
THE OPPER DEPO. ITS OF MI HIGAX to form epidote, though orne of th epido t-iz d nndton i higher in iron than the orre ponding unepid - tized Andstone. opper i commonly pr ent in the e len e , but it i rarely abundant. The econd excep ion i po ibly th alLerution of th iron-rich boulders to form " kull ' f opper. In this r placement the portion of the bould rs rich in f rric oxide clo o to !,he copper hu b on nl ter d to It oft gray t green material that appear" chloritic. There has been a larg rem ''al of ir n, but ome remains a ferric or ferr u ilicate. MISERAL5 There are few minerals in the conglomerate hat an be regnrded a gangue mineral · in the en e that they \\·ere deposited with the copp r. Calcite i · abundant in the lode, but its di tribntion doe not seem to be lo ely onnected with the di - tribution of copper. Epidote, like alcite, i rather abundan , though usually not in the rich ()'round. It is in pla e. plentiful near the margins of ore hoot , and it occurs around many area of calcite, ug()'e tin()' that tho lim was obtained from the alcite and the ferric oxide from the onglomerate. It i perhap mo t con picuous where it has replaced len e of and tone. uch len es are pre cut in many part of the mine, thouO'h they nre decidedly more num rous where the ()'round b 1 poor. In the onglomerate lode there i no indication of clo e as ociation of epidote with rich copper ground. R ed feldspar i pre ent throughout the mine in .,.arinbl amount . Like calcite and epidote, ho\\·cver, it ho,\· no clo e a ociation th rich ()'round, though c pper i commonly pre nt with feld par. It em rA.ther more abundant on the lower le,·el . Barit oc ur haracteri tically in the oft iron-rich pebble ·. locally in their bleached portion , a ociated with copper. Barite in u h pebble i" common in ~he l levels of the Hecla, but it wa rarely een m the north end of the mine. h~orite .i rare in the conglomerate except in the oft 1ron-nch pebble , where chloritic minerals of undet rmined compo ition ar common; also in the altered amyg laloid pebble . Zeolitic mineral are characteristically ab ent from th con()'lomerate lode. Fi ures pa sing from the la ,-a to the conglomerate lo o their zeolites at the c n tact. DISTRIBUTION OF THE COPPER T.he characteristic occurrence of the copper is in len t1 u~ar sh.oot flattened in the plane of the lode. The mmcrahzed beds may occur in any part of the !od~ , as nea~- the hn.n~n()' wall, near the foot wall, or m. mtermedtate po 1t10n . In the upper part of the nun~, where he lode i relatively thin, the mineraliz d portwn may form a large percentage of the lode. In the l wer I >vel , whor Lh lod i · Lhi k, tho miner 1. iz d portion may b' onl. Rr lAtively mall pnrtoft~e tot.al thickne ". There ar no b:ious . difl' r n s in th l'iginal chara ters of tho nnn ruhz d nnd the unmin ralized parts of the lod , and it roms proball that liht cliff renee in perm abilit may hn v I cen th chiel determinin()' fa tor in producing th d 'PO it . eralization rna b influ n d, how r, by variation in compo ition, th eA' et of which may connict in place with that of p rmeabilit . For example, it has b n point d out that the liner mat rial contain. more ferric xide and ilm nite a ()'rain the oar cr material. In the al tera ion of th lode' the smaller purti lc ar ompl t l bl ach d, while th pebble ar bu partly bl a h d. It,,. uld folloll' that th fin r s dim nt ontain mor fenic oxide available for rea tion und if thi i a fa. tor in the pre ipitati n of copper, it would ecm that, other thin()' being equal, the fin r-O'rain d part of the lode would be more favorable. n the other band, the andy portions are pre umabl not favorable to free circulation of olution . There i th n probably orne combination of uffi i n t p rm ability and abundant iron oxide that is mo t fa v rable to precipitation ol opper. INFLUENCE OF FAULTS AND FISSURES Th lod i cr ed by n rath r trong persi tent fault and b a great number of joint and fi ure ths1 how little or no di pla emcnt. 'I'h larg fault and many of the joint and fi ure arc min ralized. me >ery hand ome pecimen of arbor ent copper hare been taken from the lar()' fault. Ther i no good evidence, however, that any of the e were channels that admitted the ore-forming oluti n to the lode. A zone of poor ground 1i immediately north of the large fault through part of the min at l a t, but the ground to the outh of it i generally good. Thi difl.' renee ug()' ts that th gou()' may have acted a a dam against ore olu tion moving from the south through the onglomorate and thu cau ed a lean ar a north of the fault. There i littl recognized evidence that the ground i particularly rich where the joint and fi ure arc abundant or particularly 1 lean where they are few. :Inn of the ure howov r, are b rdered by a zone of bleaching and were evidently chann l for mineralizing olutionf within the lode. The cro cut di clo e many strike fi sure outs.ide the onglomeratc that contain alcite, quar z, chlonte, laumontite, red feld par, prehnite, and opper. A few cro s fi ure imilarly min ralized have been noted .. The po ition f th len of min ralized ground 10 th lode i di tinctly sugge tive of elution m ring upward through th onglomemt .
CALUMET & HECLA CO GLOMERATE LODE MINERALIZATION OF WALLS The basal amygdaloid of the hanging-wall trap locally contains orne copper. It is aid th~tt in the northeo tern part of the mine the thin amyadaloida bed were in places sufficiently mineralized to have been taken for ore. Certain joints in the hanging wall contain sheet copper. Ordinarily there is no copper in the footwall immediately below the conglomerate. Where mineralized conglomerate rests on the ba ic sand or on the coriaceou amygdaloid the mineralized rock cuts off sharply at the contact. In the lower part of the amygdaloid, however, here is in many places a little copper. This is A. sociated with chlorit , and the occurrence is imilar to that near the ba e of the Keararge amygdaloid. \\here the conglomerate i very thin or lacking and the amygdaloid i moderately oxidized, a on the forty-ninth level outh of o. 12 H cla, the amygdaloid may contain more copper. Here it i a ociated with bleached area , and the occurrence, in general, i imilar to that of the amygdaloid lode . CHANGE IN GRADE OF ORE From the urfa e to the lower level th re has been a very pronoun d decrea e in the grade of the ro k. veral possibl cau e for thi decrea e are uge ted-that the precipitation of opper was controlled by di tanc below the urfa tha exi t d wh n the depo it wer formed; that th d crea i du to a chang in hara ter of th conalomerate; or hat d po ilion wa influ n ed b h contraction of the onglomerat bod upward. It, i po ible that all th e cau e and pcrhap oth r hav be n operative. There i Jj ttle d u bt that di tan e b low the u.r- !ace exi ting at the im f min ralization was a fa tor in dctcrminina wh r d po ition of copper b gan. Doubtlc there wn a rang of depth in each lode that furni hed th conditi n f heat and pre ur mo t favorable to d po iti n, and probably h depo ition wa le both abo e and below t,hat r gion. Parts of th 1 de are ph i ally and chemi all ~ore fnvorabl than oLh r . Th finer rock, provid d ltpermitted fr pa age of the olution , would m to be more favorable than conr e onglomera te. This may, in part, a ount for th very ri h ground in the upper level of th alumet mine, ' here the conglomerate i fine, and it may lik wi ac ount for th low grade in ome of he thi k part of the lod . . 'l'he conglom rate a developed i a tapering body, lncrea ing h th in thi kne s and in width, and consequently in volume, down the u.: i . It i rotwhly .ted thn.t the relative amount of th onglomeratc at the urface and the tw nty-fifth, fiftieth, and eventy-fifth l vel ,q,re in the rn.tio 3 :4:7: 10. Thi upward contraction of the body A.nd ons quent decrease in th olume of conglomerat ugg st that -29--H the change in grade may be due in part to the converging of the ore-depo iting solution through a steadily decreasing volume of rock. It has been found that ections a ro s the shoot at different level , as the twenty-fifth, fifti th, and seventy-fifth contain approJ~.-imately the same amolillt of copp r, but that in the lower lev 1 the ore, beina distributed through more rock, is of lower arade. The grade map (pl. 3 ) shows very leady that there i a teady decrea e in the grade of the ro k from the surface downward and that in general the uccessive belts of different grade lie roughly parallel to the pre ent surface. By far the richest rock in the mine i in the " pocket ' lying between the north boundary of the ore body and the bar of thin conglomerate bet' een o. 5 and o. 10 Hecla shaft . From thi bar north rich shoots come to the surface betwe n the mall bar of thin conglomerate. This r lation suggests that there were minor outlets through these channels. Below the bar of thin conglomerate-that i , below the twenty-fifth level-the grad belt are n arly horizontal except in the outh Hecla, where good ground extends up along the main a..u of the conglomerate body. In the lower levels of th mine a bar of poor ground with a gen ral north rly trend lie ju t south of :X o. 5 Tamarack haft. Thi broadens to the north. Likewi e, a bar of poor ground seems to come in at the north rn xten ion of the orth Tamarack workings, though the fact nece ary to outline thi ground are not a ailable. MAP SHOWING " COPPER PER UNIT AREA OF LODE" The data on which the map howing grade of rock and thi kn of lode are ba ed have been combined on Plate 3 by multipl ing pound of copp r to the ton of rock at each point by the thickne of lode at th arne point and dividing the produ t by the number of cubic feet of rock to the ton, thu obtainino· fiaure that r present the amount of copper per quare foot of lod at the different point . An examination of tlu map indicate that th' nr a of ma2':imum mineralization do not oincide with the area of riche t rock. The area of maximum mineralization trend north' ard and down th lode, rouahly parall 1 to the main axi of the onglomerate body but somewhat abov it, and the mineralization de r a e in intensity northward and down the axi . There are some ex epti n to these a neral endenr.i .. Th mo t pronounced are a tenden y for th inten it to increase in the pocket toward th outcrop of th He la, a.nd the pre ence of a rather large ar a of relatively low min ralization in the icinity of the lower workings of the Tamn.rack. att mpt ha b en mad to det nmne the relati\-e amount of copper in difrerent horizontal cro s sc tion
THE COPPER DEPO IT OF MI HI AX of the 1 de. Thi ha been done by mulliplyino- the "foot-pound '' figure (obtained by multiplying pound per ton b thickne of lod ) by the length of loci on the ection n,t the different leYcl . One e timate took th gen ral a,· rage for the le cl a the ' footpound" fio-ure · ano here timat calculated ach line in everal ection , which were combin d to obtain the "foot-pound ' figure. The gr atest dillerenc , on th -e,·enty-fifth level, resulted from difl'erence- in e timate on the undevelop d ar a at the north end of that leYel and may be taken a- repre enting th uncertainty a to that area. The ayeracre of the two e imate crives the following r lative amount of copper on the different level , in a unit ection: Twenty-fifth, 133; fiftieth, 133 ; eventyfifth, 115; average, 127. The eventy-fifth lcYel thus hows 10 per cent below the averao-e. It i apparent, then, that o far a the e data are trustworthy they indicate a decrease in mineralization "·ith increa e in depth, thouo-h the de rea hown i certainly not beyond the limits of error in th data u d. What they eem to how with con iderable certainty i that tho tendency toward a deer a e in total mineralization with increa e in depth i not m rked, but that the large decrea e in grad i due mn.inly o the dissemination of appro~imately the same amount of copper through a larger volume of rock. A calculati n of th amount of copper in the lode from the data indicated on the map~ , with the a umption that 7 5 per cent of the lode ha been toped, give approxirnately the amount that ha been actually recovered and thu tends to corroborate the approximate accuracy of the data u eel on the map . If it is a umed that tho ame amount of copper i eli- eminated through the lode at ach level and fur her that the grade at the e'enty-fifth level i 30 pound to the ton, then at the fiftieth level it hould be 43 pound , at the twenty-fifth 75 pounds, and near the urface 100 pound . The recorded o-racles how a rath r urpri ing approach to these figure . There eem no rea on to expect a change in the e general relations with increa eel depth. Th lode appear~ to be increa ing both in extent and width, and it \\·ould follow that there hould be a decrea e in grade of ore. There doe , however, appear to be some tendency to break up more with d pth into poor and rich hoots. The appearance of the lode underground ugge t thi rather more strongly than the data brought out on the map. CAUSE OF CONVERGENCE OF SOLUTIO NS AND INFLUENCE OF BARRIERS _point~d out on page 101 and indicated on the map ho\\·mo- thiClme s of lode (pl. 3 ) the part developed j a projection from a much larger body of conglomemte. A no triking r lation has been found betw en fi ures and mineralization, it is believed that the . olution gained entrance at ome point below the r a de,· loped nne! ro. along Lh loci . Tf mo,·cment unimpeded tho olution ' ould probably rise dire tly along th loci toward th ut rop. If, how. e,- r, th ' mot a barri r h y w uld b defl eted and move up' ard below th bani I'. Iti ofint re t,th n,tonotewlwLsu hbaniersmay be. A i well known, h finer a diment the le · readily olution mo,Te · through it. Townrd the edge of the ono-lomerato 1 n s Lh material b come finer, and wh re tho lod i le than 5 f Lin thicknc · it i mainly and. Th ro appear. to hav b on little movement of th olu ion through the andy part, and they may be r garcl d n under the ircum, tance effective barrier to th movem n t of h olutiw. Th fa orabl influenc of th onvero-ing barriers on th grade of oro i eli us eel under ' re shoot " (p. 115). COPPER BOULDERS AND SKULLS 1fany of the pebble of porphyry r.i h in iron and other largely alt r d. to a hloriti material that lie in the ore hootn haY be n Ycry fa,·orabl tor placement by copp r. Purnp lly long ago de crib d the char· acteri ti of the p b ble thu. rep lac d. The inner part of the p bble and pr umabl th part lea t aff by the copp r olution i a r d porphyry. The material varie on id rably but i commonly rather oft and friable, dark red-brown to gr enish black, and evidently ri h in f ni iron. xt to the copper of the " kull ," which arc onl thin enYelope · of copper urrounding the p bble , i a zon of gray· green oft chloritic rock, which grad in to the red central part. There i mu h lc iron in the chloritic part of the pebble , and much of that pre en t · ferrou lron. In other pebble the eopp r pen trate to the center and only a mall proportion of the rock material remain . Thi consi,t of phenocry t of fold par nnd quartz and ome gre n chloritic material imilar to that de cribed abo,Te. The f ld par i omewhat altered, but the nature of thi alt ration ha not been determined. SILVER Very little ilver wa een in the conglom rate iode. That ob erved, principall in th outhern tope· on the lower leYel of r o. 10 Hecla, i imila.r in moda of occurrence to the amygdaloid. It seem to be lightly . later than the copper. It is aid that ilver wa much more abundant in the upper level of the Hecla haft . OSCEOLA LODE HISTORY .\ND PROD UCTION Impor ant production from the 0 ceola lode in the Osceola mine began in 1 79 and continued without interruption for any whol year till 1920. Explora· tion on the Os eola lode by the ,alumet · H eclA 0· began in 1 95 and steady production in 1904. The following table how th pr duction from the lod_o from the b ginning of operation till the end of 19Za.
0 CEOLA LODE P1·oduction and dividends from Osceola lode, 1 79-1925 Company Period DiYiaonuo Copper produced (pounds) l Rock treated (tons) -- --; Total Per ton of Per pound of copper (cents) rock Total / 9, 513,943 14,59 , 914 213, 17, 5 4 190, 7 7, 393 Centennial 2, 531 531, 9 3 · 14,7 9, 25 106, 01 -- 1 97- 1900 153, 662 Production omitting fi ures for which no 24,295,050 24, 295, 050 416, 39 ' 662 407, 054, 61 14,7 9. 25 OSCEOLA FLOW The 0 eola fiow (pl. 39), which i a well-marked ophite, ha been tr ced with a rea onable degree of certainty from the Arcadian to th liff mine. Outide thi. tretch th re i doubt of the accuracy of ted colT lation . At the liff miue the flow i 35 feet thick; at the Ahmeek, 130 feet; at the Red Jacket haft, e>entyei"hth level, 210 feet; at the La all , 1 0 f et· at the Franklin Jr., 9 fe t; and at the rcadian, 129 fe t. I is tJ10 thicke. t part of the flow, near Calumet, that thu far ha been productiv . In thi re pect the 0 ceola i. like tho Kea1 arge flow. picuous feature of the footwall a th y t rc of the I le Royale lode. THICKNESS The lode rano-e in thi knc from as little a 1 foot to a much a 60 feet· perhap in a few pla e it i even thicker. In gen ral, the lod i thicker in the hummocks, on i tino- mainly of fragmental rock, that ri e above the average lev l of the top of the flow, and i thinn r in the depr ion b low the general level, a the fragmental material commonly xtend deeper und r the hummock than i doc under th depre ions. This i what ,,-ould b expect d if th £ragmen al mat rial float din irregular rna e on the htva- thehigher th loo olidifi d mil terial wa piled above the gencnll l >el th deep r it would ink into he liquid or pla tic part of the flow and it would remain there wh n the whole cam to r t and olidifi d. It i the lower portion of the e downward bulge that conti ut tb o- alled ' foot lode. In plac the lode contain a bar of "vein trap" with frao-mental rock above and b low. Thi , howv r, has rar ly been een to be continuou over very la,roar a . Ordinarily the fragmental material und rl ing the hin trap layer i co nne ted near by with that on th top of the fiow, and in mo t places the lod i imply a con inuou thick ma of fragm ntal ro k. The lode al o how ariation tha are on a laro-er cale than tho e mention d abo e. Band of relati ely tbi k and thin breccia pit h in a outhwe terly dir tion, in general, parflll l to the southern bounda.ry of th 0 ceola ore hoot. u h a thin band i rather con i tently pr ent a.lono- the outh b undary of the Os eola hoo , and imilar band are pre ent in both the 0 ceola and th alum t & He la portion of the lode. Within the e thin and thick belt the minor variation f hummo k and dcpre ions ar pre ent. HANGING WALL The hanging \\-all of the 0 eola lode is a heavy trap with a rath r indi tinct conta t b tween its hin ba al amygdaloid and the upper urface of the 0 ola lode. In many pla e the hll.nging wall i jointed
THE COPPER DEPOSIT OF MI HIGA and heet copper i pr ent on the joints. In both of the e features-namely, th lack of a clear- ut upper boundary and the pre en e of opper in the I hanging wall-the 0 ceoln, differs from he Ke r argo lode. STRUCTURE Except for the feature of he lod it elf, the tructure in the 0 ceola mine i imple. There i no noteworthy folding or faulting, and only relatively few mall fis ures cro the lode. ALTERATION AND MINERALIZATION OF THE LODE Oxidation.-In it general character the oxidati n of the 0 ceola lode does not differ from that f other fragmental lodes. A in the other lod , it i earlier than and independ n t of the copp r mineralization and vari s with the character of the rock. The highly fragmental lava i con i tently well oxidized · be ellular and trappy rock i much les oxidized. There is not the same change in degree f oxidation from the banging wall toward the footwall in the Osceola that there i in the Kearsar()'e lode. The Kearsarge lode is most highly oxidized near the trap, but the Osceola lode i highly oxidized throu()'houtrsome of its fragmental " foot lode " is apparently oxidized as much as any other rock in the lode. Oxidation h.a extended rather deeply into the "foot trap," which for orne distance from the lode is distinctly redder than the "hanging trap. ' In thi re p ct, as in some othe1 , this lode re emble the Isle Royale lode. Alteration and mineralization later than oxidation.- The result of the alteration and mineralization of the lode that were !ater than the oxidation do not differ in general from those of the Kearsarge lode. Prehnite and datolite are more abundant than in the Kearsarge. Epidote is di. tributed throughout the 0 ceola lode, whereas in the K ear~ar()'e it is largely confined to the upper part. This i apparently a result of the deep oxidation of the 0 ceola lode. Ble.ached r~ck ver~ similar to that of the Kearsarge lode IS a oCiated w1th the copper and differ from that found in the Pewabic, I le Royale, and Baltic lodes in containing a relatively mall amount of pumpellyite. The more abundant minerals are feldspar (rather irreg~ arly dis~ributed), calcite, quartz, epidote, pumpellyite, chlonte, and prehnite. Prehnite i most abundant in the andy area . The le. s abundant mineral , which are rather unevenly di tributed are datolite, mo t plentiful toward the ou th bounda~y of the ore body; laumontite, mainly in fi ure ; analcite, al o larg ly in fi . ures; and a little aponi te in the lode. DISTRIBUTION OF COPPER IN THE LODE Distribution through thickness of the lode.- In the 0 ceola lode, as in the Kearsarge, by far the richest and mo t uniformly mineralized portion lie. against the h~tnging w~tll. Th min rnliz d rock, howorer extend irregularly do> nward, in place 50 f ot 0; more from the hanO'il10' ' all. o quantitati''O data ar a ailable a to tho rolati v amount of copp r at differon t depth. in th lod , but th general impresion i. th11t the top 4 to 5 f et contains fully 75 to o per ent of the opp r that is pre ent in the upp r tO feet of lode and that th 1 foot ju t b lo, the hanging wall i by f1u· the rich t part of th lod . Th opper that lie d ep in the lode i i rr O'LJlarl di tributed. It i confin d to th ar a wh r th fragmental rock extend to on id rable d pth , but ther i too little information n to th grade of ro k fr m Lhe foot ' orking to d termin ' heth r r not coppor 11h ay or u ually pr nt in omm r ial q uantitie in tho area . Fiv ampl s of red lod rock that how d no cop· per on ordioar in p ction were tak n to determine if copp r i present in rock in which it i no r ndily een, and, if o, in what amount. ay of these ample ranged from 2. to 4. pound to the ton, with an !1\'erage of 3.76 pound . s a general rul , "thick lod " and "deep foot lode" occur where the lode bulg up into the hanging wall and, conver ely, are not to be exp cted wher the hanging wall bulg down into th lode. If experience how that opp r in comm rcial quantity is present in a ufficient numb r of place where 'deep foot lode" occur to warrant pro p cting for it, then thi relation to the hanging wall would eem to offer a very economical method for locating th area of thick lode. Distribution in the plane of the lode·.-It hn already been noted that there ar bar of thin amygdaloid pitching outhwe tin the lod . The. e bar are u ually poor in copper, though their thicker portion contain ome commer ial ground. long the outh boundary of the ore hoot, where it ha b n examined the lode eem to be rather uniformly bin and tight. This thin trea.k i regarded a an inclined barrier that has prevented the direct upward mov mont of the ore solutions along the lode and cau ed a concentration b neath it. This belief i supported by the fa t that south of thi barrier the lode i lean, even though it is moderately or even in place de idedly thick and has the other physical charact rs that ar regarded as favorable. The best ground in the shoot ha in general been fo.und clo e to the barrier, and the grade has decreo .ed With increasing distance from it; but the grade vanes notably with the chara--ter of the lode, and too little d~finite information is available to give a very clear Picture of the variations and their cau s. The following facts, however, have a bearing on the matter. In the lower levels there is a notable change in the grade of rock northward from the south bou11dory. The area south of Osceola o. 6 shaft is of decidedly better grade than that of o. 5 shaft. In the acces· sible levels near the bottom of o. 5 the lode is of
OSCEOLA LODE only roeclium thickne , a condition which ' a prob- ' ably a factor in producing the lower grade, but regardJe of the differen in character of lode, there seems to be a decrea e toward the north in general, which is ob erved in the alumet & Hecla o.' 0 ceola ground a well a in the 0 ceola mine. Takeri as a who! , there is a dee1·ea e in the grade northward, till in o. 1 haft there i 3: much lower proportion of pay rock than in the south ide of the hoot, and in the entennial it apparently was not sufficient to encourage de>elopment below "the twelfth level. A haft farther north in Wolverine ground i apparently out of th hoot · and encounter d no encouraging copper content to the fifth level. Tamarack o. 1 in it upper le el encountered some commercial rock, but thi continued for only a few level , when the rock became of too low grade to pay. The available facts thus suggest that the commercial rock will be found to fail toward the north along a line roughly paralleling the outhern boundary of the ore hoot. Thi~ mean , of cour e, that the shafts from the north to outh will reach unprofitable ground at progre ivel greater depth . o. 1 even at the outcrop i at about the margin of pay ground. o. 17 arerngecl poor below the tenth level. o. 16 seem to be getting leaner in the lower level . If thi trend continues, o. 15 will soon be getting into poorer ground, though the Tamarack found orne good ground betwe n 1 o . 15 and 14 at n iderably gr at r depth. No . 14 and 13 ' ould e m to hav a good distance to go befor the encounter poor ground. Xo. 5 ola i bottom d in rath r p or ground, and th que Lion nn.turall ari hether thi i the bottom of th hoot. Th gon ral trend would sugge t that it i not. Fmthermore, there is a rather wide bar of thin lode in alumet r H la ground that, if proj ct d, would about int r ect the bottom of o. 5 haft, and it i po ible that th po r grade in th bottom of o. 5 i in part du to thi bar of poor, thin lod ro k, and that the bottom of th shoot i at very con id rabl gr ater d pth. VARIATION IN COPPER CONTENT WITH DEPTH In any di ·cu ion of th variation of the opp r content, of th 0 ceola lode with d pth, it i nece ar to con idor th or shoot a a whole and not a ection as repre ent d by any ingl shaft. on id ring individual hafts, there i littl doubt that all th a1umet & Hecla haft and o . 1, 2, and cola ' ould ~rentually how a decrea in copper ont nt ' ith a · in d pth. os. 5 and 6 0 ceola, on the oth r hand pu through 1 an or nearl barr n grouud for everal hundred fe t b fore ent ring th ore hoot, nud ther nr indication that th O" t"Ound al nO" o. 5 haft i growing l an r in the low r 1 v l . If, however, an inclined bel · parall l to th tr nd of the ore hoot is examin d- for exampl , a belt 1,000, 2,000, or 3,000 feet north of and parallel to th outh boundary of the ore hoot-no cl ar eYid nee i found of a decrea e in copper content with in rea e in depth down the hoot. The grade of th ore recently min d in the l wer level of the 0 ceola mine i lower than that of the ore formerly mined in the upper level , but this is, in part at least, a· matter of changes in mining method and policy, a is di cu sed below, rather than a real change in the copper content of the lode. There are no exact data available to check the grade of the ore in different part of the mine, but the impre ion gained from in pection of the lode i that the copper content of the rock in the ore hoot in the lower level outh of o. 6 shaft ompare fayorably with that in the higher level of the mine. CHANGES IN METHOD OF MINI NG There have been decided chang in the method of mining lode of this typ in the di tri t and in the 0 ceola mine itself, a i very e id nt to one going through th workings of different period and of different d pth of . In the arly day of mining on the 0 ceola lode the method e m to have been to make the highe t po ible recovery from the hanging ide of the lod ; the hanging wall wa tripp d clean, and the pillar ,., rc mall. o great ffort wa made at that im to get a high recovery of the copper deep in the lode. r latively narrow tope an·ied again t the hanging wall, and wh re copper wa xpo ed near the footwall it wa apparently follow d; but where it wa not expo d li tle if any effort wa xpended in earch for it. Thu ther wa a hi()"h p rc nta()"e of recovery from the hanging ide of the lod and a low recover from the f t ide. Mor over, in the early mining a much larg r proportion of the thin and poor portion of the lode wa left untou hed than in the lat r operation . The r und r thi early typ of mining ov r a distan e of 2,000 to 3,000 feet north of the outh boundary of the hoot yield d 22 to 29 pounds of copper to he ton. In the low r level of the min outh of o. 6 haft, for example-the ' idth top d average di - tinctly gr ater than in the upper l Yel , and mor of th 1 de ha been mined, de pite the fact that th re ha not be n th former hi()"h r covery of th rock just b low th hanging wall, a few inche to a foot of lode bcin()" commonly left on the ha.nging wall, and that the pilla.r ar more num · rous and larger than in the upp r working , a i r quir d by th gr at r depth. 1 he re ult f thi change from the earlier me hod ar not v ry c rtain, but the impre ion i that onidern.bly more lod rock has been mined per unit area, with p rhap little if an greater r co ery of opper p r unit area. For xampl , ay he averug thi lm mined in 1920 wa 12 f t, in luding foot work, with n r covery of 1 pound to the ton, or
THE COPPER DEPO IT OF Ml HIG r about 1 pound to ncb quare foot o.f lod ; in the early mining feet of lode wa mined w1th a rec very of 27 pound to the ton, or 1 pound to the quare foot. KEARSARGE LODE HISTORY AND PRODUCTION The earlie t notable production from the Koar argo lode wa made in the Kear-arge mine; now the orth Ke1warge, in 1 7, though developm en~ ba~ begun some years before. Produ tion from th1 mme wa foll0 ,,- d by of n io-hborinO' mtn - namely, the olverin in 1 95, th outh h .. ar a.rge in 1900, and the entennial and alum t a II ln in 1904 . .lt 1 th north en l of tho lode tho 1 hn,wl b O'!Hl production in 1903, follow d b th hm ek in 1904, the .Allouez in 1905, th Gra iot in 1910, and th eneca in 1921. Pro pectin()' ho, be n xt nd d to Lhe north by the Ojibwn , lifr, Mi .kownbi , Manitou-Frontena and K w na' opp r (Mandan) mpanie and to the outh by tho Laurium, La all , nnd Franklin Jr. Product1·0n and dividend from K ear arge lode to end of J9?5 :lline Rock treated (tons) j Refined copper (poun~ Total Per ton 'l'otnl Per POUnd or N]'r(~nts) All 4-, 91 1 '13 Calumet c' Hecla, Kearsarge branch j 1 -io:344:4471601 62,279 hIT 6, 4271 605 115, 156,251 out. ,_ear a rge .. 1910-1920 313, 4 10.35 -- 739,624 -- ?
14, Ol4, 050 259; 114; 34 1 :49 --- 10, 750, 000 1 90~- 192 0 O" b '
.. 9?0-1924 H ; 530 3 561, 922 - --
17, 313 2 4, 241 50, 2, 000 Pr duciion omitting figure for ''.·hich no corresponding tonnages are g"·en -- -- 601 511, 10,1 11 15 I 075, 429 19. 14 - )fines now belonging to the Calumet & Hecla Consolidated Copper Co. Estimated. KEARSARGE FLOW EXTEKT A).' D RITE RIA FOR RECOG .. ITION Th Kear arge flow (pl. 40) ha been recoo-nized from Atlantic to Mandan, in Keweenaw County, a di tance of about 35 mile . The rock i a well-developed ophit . The identifi ation of thi flow i commonly based on the porphyritic character of its upper portion and on its po ition immediat ly above the Wolverine sand tone. With the e aid it can be recognized more ea. ily and certainly than roo t of the other flow . The plagio lase phenocry t are u ua.lly mo t abundant in the trap just below the amygdaloid, thou()'h they are pre ent in the amygdaloid. They vary con id rably from place to place, both in ize ·and in abundance. ually the tabular cry tnl do n t exceed half an inch in length and make up but a small part of the rock. Locally, how ver, they reach an inch in length and over short stretche may form a con iderable percentage of the rock. In the "west flow ' they are le s abundant than in the main flow. Tho cone en tra tion of phenocry ts at the base of the amygdaloid appears to have [re ulted from the ri ing of the cry tal through the molten lava till they reached the olid or vi cou portion near the top, where they were topped. The le er number· in the thin " we t flo,.,·" may be du to th fact that they collected from a maHer volume of lava. "What i cla sed a the K ear arge flow does not ever wher con i t of a ingle flow; in many pl~ce tb re are wo or more flows at th K ar arge honzon that contain feld par phenocry t and are grouped 8 Kea1 arge. In the principo,l producti v area, from. the entennial mine to the Gratiot mine, the a.mygdalord of the lowe t flow of the eri s ha been mined, and oaly locally have the amygdaloids of the "w t lode " bee.n shown to contain copper in paying quantity. In. thJ area the hi()'her flow are r latively thin, phenocryst o h ll lar are few, and the amygda.loidal top are of t cc u typn and usually but little oxidized. THICKNE S At o. 2 haft Ahmeek the basal Kear::;arge flow ' ' 'all the is 200 feet thick at the surface and ha e · Y . same thickne s in the cro cut on the Ma. fi w·e1 JD . l t 10 the lower level .. On the tw~ l~v 1, Centennra ~da· Kearsarge trap 1 179 feet thiCk, w1th 6 feet of amy, 1 loid a total of 1 5 feet. At the urface the .tots . ' ton I tluckne s of the fiow a cnled from a cro ec 1 · · how 170 feet. The eros cut in the lvenne mllle
KEARSARGE LODE the Kear arg bed about 200 feet thick. Between No. 1 n,nd o. 2 haft , Mohawk, on the twenty-fir t lerol, the flow is 1 5 feeli lihick. IIi lihu cern that in the main produclii e area thi ba al flow has a thickne of 170 to 200 feet. Lo ally overlying the basal flow are thin flows of the Kear arge type. How much of the lod cov red by uch flow is not known, but there are c rliainly place wh re none ar pr en , and in other plac a many a half a dozen flow ar pre cut below en the ba al Kear-arge and the next hea y trap. The e flow arc u ually thin, but a flow 5 f et thick, with phenocry t , lies on the main K ar arge flow at o. 4 haft, orth Kear aro-c, and a flow of imilar thickne· ha been noted in a cro scut on the 11a fi ure in the Ahmeek mine. It app ar , fore, that in the produc iv area the Kearsarg flow may reach a total thickne of 300 fe t. The followino- ob rvation were mad nor h of the more developed area: Gratiot: :;-Jo. 2 shaft, amygdaloid 20 feet, trap 169 feet, total 19 feet; ~o. 1 shaft, amygdaloid 9 feet, trap 193 fe t, total 202 feet. eneca No. 1 shaft: Diamond-drill hole No. 6, more than 127 feet in five flows; ba al trap 63 feet. Diamond-drill hole o. 3, 74 feet from top cut, five amygdaloids and ba e of serie not reached. Diamond-drill hole o. 1, ba al trap more than 4 feet, sandstone not reached. Diamond-drill hole :;-Jo. 5, 950 feet north of ro. 1 shaft, 113 feet of Kear arge flo\Ys with four amygdaloid , ba al trap 24 feet. The old eneca No. 1 shaft is sunk near he Wolverine and tone, and cro scuts were extended from it into the hanging wall. Fir t level, cro cut 150 feet; econd le\el, cro cut 50 feet drift on an amygdaloid; third lerel, cro cut about 350 f et apparently cutting the entire series of .f ea.r a.rg flow , drift about 700 f t, apparently on top amygdaloid; fifth lev 1, cro scut about 230 f et, drift on an amygdaloid, po ibly the top amygdaloid. Ojibway: Kearsarge apparently con i t of two or more flows. Basal flow at o. 1 shaft reported 35 to 5 feet, at No. 2 haft 260 to 360 feet. Cliff: Diamond-drill hoi 1 o. 1 at shaft, olverine sandstone 33 feet, trap 93 fe t, amygdaloid 6 feet, trap 2 feet, amygdaloid 7 feet (we t lode?). Diamond-drill hole J:\o. 11, 1,900 feet along strike from south boundary, Wolverine andstone 2 feet, ba al trap 107 feet, amygdaloid 22 f et, second trap 7 feet, econd amygdaloid 10 feet, follo\Y d by a eries of small flows. Diamond-drill hole ro. 12, Wolverine a.ndstone 3 feet, basal trap 46 feet, amygdaloid 5 feet, econd trap 12 fe t, amygdaloid (Kearsarge) 14 feet, third trap 7 feet, amygdaloid (Kear arge) feet. Diamond-drill hole 1 o. 3, 5,200 fe t north of south boundary, Wolverine sandstone 19 feet, ba al trap 174 feet, amygdaloid (I ea.rsarge) 24 feet, second trap 1 feet, amygdaloid 11 f t. Diamond-drill hole o. 4, 5,600 feet north of south boundary, Wolv rine sand tone 5 fe t, ba al trap 113 feet, amygdaloid 1 f et, second trap 77 feet, amygdaloid 13 feet. Central mine: Kearsarge as scaled from a cro section, 235 feet in three flows. Diamond-drill hole o. 2, olverine sandstone thin, basal trap 70 fe t, amygdaloid 5 feet, ecood t rap 57 feet, 1\mygdaloid (Kear arge) 33 feet. Manitou-Frontenac: Diamond-drill hole No. 7- , Wolverine sandstone 6 feet, basal t.rap 2 feet, amygdaloid 4 feet. Diamond-drill hole o. 3- 5- , Wolverine sand tone thin, hA.snl trap 19 feet, amygdaloid 5 feet, econd trap 63 feet, amygdaloid 3 feet, third trap 39 feet, am;.·gdaloid 5 feet, fourth trap 21 feet, amygdaloid 14 feet, total Kearsarge flow 169 feet. Mandan: Diamond-drill hole :;-Jo. 9, Wolverine and tone thin, basal trap 55 feet, amygdaloid 6 feet; appears to be one flow. From the records given above it i apparent tlut north of the Gratiot mine the ba al Kearsarge flow become decidedly variable in thickne , ranging from 24 feet in diamond-drill hole o. 5, encca, to -60 feet or more in Jo. 2 haft, Ojibway, 19 fe li in th Frontenac, and 27 and 45 feet at Mandan. In contra t with the main producti e itrea, the basal flow i in mo t place thin, nnd the whol erie d cs n t maintain the thickne of the ba al flow in th ar a from the Gratiot to the entennial mine. The following ob ervation were mad outh of th productive area: Laurium: Diamond-drill hole_ o. 3, 1,700 feet south of north boundary, Wolverine sand tone 10 inche , ba al trap llO f t, amygdaloid 10 feet, econd trap 4 feet, amygdaloid 2 feet. Diamond-drill hole :;-Jo. 2, 00 feet north of shaft, Wolverine saud tone 3 feet, basal trap 141 feet, amygdaloid 71! feet. Diamond-drill hole ro. 4, 900 f et from extreme outh boundary, Wolverine sands one 10 feet, ba al trap 144 feet, amygdaloid 11 feet, econd trap 4 feet, amygdaloid 7 feet. Calumet & Hecla: Eighty-first level eros cut, Red Jacket shaft, two small flows over the main Kearsarge lode; ba a! flow 1 1 feet. La aile: Diamond-drill hole :;-Jo. 12, oppo ite :;-Jo. 2 haft, Wolverine sandstone 2 feet, ba a! trap 131 feet, I ear arge amygdaloid 9 feet, trap 75 feet. o. 2 La aile shaft i on fir t amygdaloid. Diamond-drill hole No. 13, 1,700 feet outh of No. 2 shaft, from top down, hanging-wall t rap 60 feet, top Kear arge amygdaloid 4 feet, trap 15 feet, amygdaloid 4 feet, trap 20 feet, amygdaloid 14 feet, trap 20+ fee'-; Wolverine sand - tone not noted. Diamond-drill hole o. 14, 250 feet do~m dip from ro. 13, hanging-wall trap 65 feet, Kea arge amygdaloid 4 feet, Kear arge trap 33 + feet. Diamond-drill hole ro. 1, 5,200 fe t outh of o. 2 haft, at No.5 La Salle,\\ olverine and tone 7 feet, ba a! trap 2 feet, amygdaloid 4 feet, econd trap 2 feet, amygdaloid 6 feet, third trap 10 feet, amygdaloid 12 fe t, fourth trap 29 feet, amygdaloid 171! feet, fifth trap 271! feet, amygdaloid 6 inche , ixth Kearsarge trap 471! feet, amygdaloid 7 f et. Diamond-drill hole ro. 4, at No. 6 LA. aile, Wolverin and tone, fit'"t flow, lowe t Kear arge trap 42 feet, amygdaloid 3 feet; econd flow, trap feet, amygdaloid 7 feet; bird flow, trap 14 feet, amygdaloid 4 f et; fourth Kear arg trap 14 feet, amygdaloid 7 feet; hanging-wall trap 14 feet. Diamond-drill hole os. 6, 9, 10, 1,500 feet south of o. 6 La. alle; diamond-drill hole 1 o. 9, Wolverine andstone 1 foot, I a a! t rap 96 feet, amygdaloid 2 fe t, econd trap 37 fe t, amygdaloid 4 feet, hanging-wall trap 62 feet. Franklin Jr. mine, thit·ty- econd level cro scut: Wolverine and tone 10 f t, ba al t rap (broken) 10 fe t, amygdaloid 16 feet; econd fl w, t rap 22 feet, amygdaloid 30 feet. Franklin Jr. new haft: Fir t Kear arge amygdaloid 7 f et, trap 2 feet; second Kear arge amygdaloid 6 f et, trap 33 feet; third Kear arge amygdaloid 9 feet, trap 2 feet; Wolverine sandston (?) 4 inches. Arcadian o. 1: Total flow 109 feet; No. 2, total flow 101 feet. 1 aumkeag: Diamond-drill hole J, Wolverine sa.ndstone 1 fnot, trap 57 feet, amygdaloid 17 f et. Isle R yale mine: Wolverine andstone 1 foot, t rap 49 feet, amygdaloid 5 feet. tlantic: Woh·erine and tone 6 feet, trap 40 feet, amygdaloid 17 feet.
19G 'l'HE COPPER DEPO IT:S OF 1LCHlGA::\ From the e ob crvation 1L 1 apparent outh of the entennial min there i tt thinning of the Kear- -argc flow , and that outh of No . 1 and La the bn. al flow i thin and the erie genern.lly con L t of a . ucce ion of bin flo\ . CHARACTER OF KEAR ARG E A~IYGDALOID GENERAL FEATURES ~ext to the Pewabic, the K ar arae lode i the mo-t regular of the large productive lode of tho ditrict, yet it vari. notably in character from plac to place. In tho main producti'e ar a the amygdaloid can be roughly eparatod into material of three type. - namely " fragmental lode," band d amygdaloid, and "foot lode. The "fraomcn tal l de ' on ist of irregular angular to ubangular fragment of amygdaloid. Th amygdaloid fraamen t are predominantly fine and contain very n·um rous but small amygdule , indicating relatinly rapid olidification; but n1.i:x:ed ' ith the fine fragments are orne of coar r texture. In the Kear arge lode a a whole individual frag~ ment rather rarely exceed a foo t in ar ate t dimenion, and mo t of the fragments range from 6 inche to a fraction of an inch. In the top portion the fragment a\erage smaller than toward the ba e. In po ition "fragmental lode, if pre ent, i alway a th top, inunediately beneath the hanging-wall trap. I t giYe plac downward either to cellular band d amygdaloid or to "foot lode;" if the former, the tran ition is likely to be gradual ; if the latter, i i more likely to be abrupt. Tho thickne s of the "fragmental lode " probably a,-erage 5 to 6 feet but range from 20 feet down to the vani hina point. Very ommonly, where the ' fraamen tal lode" i thicke t it bulge into the hanging wall, indicating that it form d light elevation on he urfa e that wa buried by the overlying flow, and it al o ext nd deeper into the underlying material at uch place . The band d amygdaloid, a antra ted with the "fragmental lode, ' i an unbroken ro k body O\er on iderable area . The amygdule are commonly more abundant a cer ain horizon , giving the ro k a banded appearance in cro s ection. In texture it aries i.th dist.an e from tho surface of the lode. 'Yherc it form th top of th lode the upper portion fine t,extured and it in r a es in coarsones with i.ncrea e in di ·tan e from the urface. Where it i. c Creel b "fraam n tal lode the finer-textured part no t pre ent. Evidently the " fragmental lode" offered the arne prote tion from rapid cooling a the chill d upper portion of the banded amyadaloid. The banded amygdaloid may lie immediately below the hanging-wall trap or it may grade upward into "fraamental lode." D ownward it grade into "foot lode." In m t pla e it i l 3- th!ln 6 feet thick ' but it may e.·ceed that tbickn lo ally, a. in orne part of th upp r lev l of th Wolverine, Xorth K arsara , 1 hawk, and her .min . Th rock in the z n botw en th bA. am)gda. loid and th fo twall trap i eall d "foo 1 d ." It dill' r from th band d amyadaloid in having a oar er textur , with lar r and f wer amygdule" and le
for the amygdul to form in band . It grade upward into llular amygdaloid or under· lie "fragm ntal lode." In a r. fow p]a c it imm diately underl i the hanging-wall Lrap. Down· ward i grade into th f otwall trap. Locally it contaitr a few fragm nt. of cellular amygdaloid. It rar 1 xco cl G fe t in thickn s . From tho foreaoina tat mont it is a.ppar nt that the lod may on i t of " fragmental lode," banded amygdaloid, and " f ot lod ' ; of "fragmental lode" and " foot lode '; of band d n mygdaloid and "foot lode · or rar ly of ' foot lode" alon . The tbicke t part of the lod alway ompri e a fragmental layer and in many plac all thr type . The thin parts probably con i t mo t commonl of banded amygdn· 1 id and "foot· lode," though a lav ' mentod · mental thin lode i a common ty[ e. The avemge thi kne - f ground somewhat in th dill' rent min of Kear·arge lode. In everal of th min th lod ha b en o largely remov d from th pa rt d velop d that it i po ible to o timate r ughly th av rag thi kne stoped from the quantity of rock produced and the area mined. uch timatc are hown on pag 199. The amount of around left in toping diff r" considerably in different min ; it probabl rang from 10 to 35 per cent. The outh Kear ara ha one of the highe t recoverie , and it ar ator Loping width as alculatecl is probably due in part to that fact. For tho 11ohawk the actual t pin a width i aid to be about 12 feet, wherea the calculat d width is 9.5 feet, indicating that about 20 p r c nt of the lode i left. It appear from the calculation that the a,·cra.(7e thickne of lod toped cl crease fr m the uth Kear arge northward. That thi difference can not be attributed to toping wid r than i warranted in the outh Kcar arge and part of the Woh-eri.nc i indicated by the average high yi ld in c pper per ton of rock from the e mine . It mu t of our c be recognized that there is a decided V'ariation in the thickne of lode in different part of indi,·idunl mine . In th Mohawk, for example, th" lode average distinctly thicker at the outh than at the north end. Tho large t area of thin and cellular amygdaloid in the producti,·e part of the K ar argo lode extend along the outcrop from about the north boundary of the outh Kear arge to the Mohawk mine. For much , of the eli tan e it extend but a few hundred feet
KEARSARGE LODE bclo11 the out rop, but in the orth Kear,arge and \Yolrerine mine it r ache a. deep a the twentieth lerel. ( ee pl. 40.) Another large body of ellular rock i pre ent in the north end of the :\1oha.wk mine. At the urface it extend from about T 4 haft to the north boundary, nod in the bottom l v-el from about o. 2 shaft to the boundnry. Inter p r ed with fragmental rock the lode rock of thi type apparently extend beyond :\o. 1 Gratio haft, though th lode in that ~trea :1a.s been le deY loped. It i al o predo min ant north of the new ene a haft in the deeper lev-el . Fragmental lode ro k oc u1·~ along the ::\1oha\\'k-Gra.tiot boundary in th upp r le' l of o. 2 Gratiot, and mallcr nrea in t;he upp r and intermedin.te Je,- l of Xo. 1 Gratiot and in the lo..,.· r lc,· 1 of the new eneca haft. A third body of cllu lar lode i found in the low r lev l north and outh of A.lloucz o. 1 ·haft, and a maller body i pre ent north of No. 2 . \llouez. Another retch of thin lode i pr ent in the Xorth Ahme k, xtendin()' from ro. 4 haft north, alonO' the :-.1ohawk boundary b yond o. 4 ~lohn11·k. The bodie f thin lode includ d in the encral area of thick lo e thu far outlined ha'e heir ~rea test extent along the trike of the lode and relatirel,l mall extent on th dip. If thi pattern prove to be typical, it rna be pos ible t 0' t s m idea of !Je di tanc through a thin bar from it extent nlong the trike. LOCAL OBSERVATIONS .\t jibwn.y accord ing to Hubbard 6 thN' i n.n eat lod and a w t I d thn.t are copp r bearing. Both cern to b irr gular in thickne n.nd t be cut out in pia ·e~. Hubbard UO'g t that th been eroded and that th old reco(l'nizabl . i prcsen t in th ing ridO'e . T copper." and ontn.ins LitUe information i avail~tbl a to +he chara ter of tho lode at the lif[ haft. Fr m an in pection of the. dump th irnpr ion wa gained thu t the lode is mamly of the cellul1u· t p , though ome bre in i. ~re ont. Th diamond-drill hole nt the shn ft hows
1 ~l:way Mining o., Repts., 1909- 1912. e up rior Mining [nst. Proc., vol. 17, p. 234. 1912. two flow , the bottom one 134 f t thick with a 6-foot amygdaloid, and the top one 30 fe t thick, with a 7-foot amygdaloid. In the main the lode eem d rather poorly oxidized. Feld par ph no ry t are pre ent but r ather sparingly. Most of the wor!" wa done on the lower amygdaloid, from which mo t of the material on the dump wa probably dori.v- d. At the Rhode Island mine 10 f et of br ccia lod , almo t a "conglomerate," wa noted by Lane. The thickne of the ba al bed i 19 f et; the we flo,\· i:=; 6 feet thick, w·ith 11 feet of r d amygdaloid. At the Franklin Jr. mine the K ar arge amygdaloid wa located, and the core how a little copper. 9 The hirty- econd level cro scut howed enough copper on the footwall ide of the lode to warrant further exploration, according to the report of the company. The explorations in the n w Kear arae haft three Kear arge flow with cellular top . In the D elawnre drill cLion the Kear arge amygdaloid h a been cut in everal diamond-drill hol . In n.ll it i a thin (3 to 4 feet), nonfragmental, poorly oxidiz d amygdaloid. orne of the hole cut "w t" lodes al o with thin, nonfragmental, poorly o:.'i.idiz d nmyadaloid . outh of the main productiv area the 1 de, o far a known, eem to be tltinn r nnd le fraamental than in tb product.iv ar a. Thi chang i apparent in the outh nd of tho entennial min . Little i known of the charact r f the lode in the alum t · Hecla, but farther outh, in th La alle min , it i only lo ally fragmental and in gen ral only moderately oxidized. Th diamond-drill re ord how that the ar arac flow in La all ground con i ted of three to five thin flow with am gdaloid_. In the outb haft the dev lopment eem to have b en on the upper amyadaloid of thi erie . The north shafts n.re ev:id ntly on the fu· t am. gdaloid above the olerin and tone. In th Laurium ground the diamond-dTill record indicate but on thick £1 w. In tbe productive ar a of the Kear~arg lod the copp r ha practical! all como from th fu· A.m gdaloid abov th Wolverine and tone. I'r m the e note it appear that nowher out iuf' of the main productiv ar aha,· large ar a of thick "fragmentn.llod been di co er d. STRUCTURE ALLO EZ ANTI LINE Th maJor true ural feature of the produ tiY par of th lod i the \llou z anticline. The A.xi of thi ar h pa o nonr I o. 1 hmeek haft; th bed fiatt n out at tho outh n ar the nt nnial haft: nnd ~tt the north b twe n o . 3 and 4 Mohawk. Within tb e limits the n.veragc di,·erO'once from a
THE COPPER DEPO IT' OF A1ICHIGA. plan in the po ition of the Kearsarge bed out ide thi fold is about 5° for both limbs, or about 9 feet in 100 f ct. The stcepe t dips are at the cr t of the anticline, and if the dips con tinuc down the lod at the ame angle as at the surface, the anticline mu t gradually flatten, and at 10,000 feet down the dip it mu t nearly disappear. The anticline i much le pronounced in the high r beds of the erie than it is to,Yard the base. FAULTS AND FI URES ALTERATION AND MINERALIZATION X I DA TI , Oxidation wa the alLorfttion f the lode. Th oxidaticm of ih K ar aron.nd other Joel · fully dis ·w cl in tho r:r n raJ , o Li n of Lhc r po;t (p. 34). Tho fril.r:rmental p rtion of tlt " ar~ lode ar highly oxidized and nm1 u ally high in f rrie oxide. Th oxidation i boliev d to haY takcu plac~ during th oolino- of the h1.Yn, arli r than nnd quite inclepend 1tly of t h dcpositi n of copper. AL'rERATIOK A OMPA ryr ' G M I ERALTZATIO:\ By far the most prominent erie of fi ure trike a little we t of north and as a rule dip steeply ea tward. Among those are the shatter zone, the Y!oThe alteration that took pla ub quent to the oxihawkite, Mass, and Fulton fissure , and half a dozen dation may not ali ha 0 ° CUlT d at the sam time but fis ures in the Mohawk mine. Fi ur of thi s ri to epara tc it cl arly i n t a Y· 1\Iu h of it ee~ to are les abundant to the south but are pre ent tlu·oughhav been clo ely o. o iat d "·ith the depo ition of copout the developed area. per, but certain pha of the o.lt ration e m to hare There has been om movement on many of tho been mor wide pr ad than th c PP r depo ition and fis ures. The hatter zone pa sing through Ahmeek not ne e arily 1 ely tied to i . For xo., reel feldand Allouez has the greatest displacement. It i a par, though pre ent nearly Y rywh re in the Kearbelt 200 to 400 feet wide that contain many fi sm . sarge lode,i di tin tly ,~ariabl in amount. lnLa alle It ha been traced through the Ahmeek and Allouez orth Kear argc, orth hmeek, and 1ohawk ground workings, and its persistence to the north and outh it i rather abundant, but in outh Ahmeek ground i indicated by the low Allouez Gap, which doubtles ther i le . Epidot i al o far m r widely di trib· has re ulted from ero ion of thew akened rocks of this uted in the lod than imp rtant c depo it . It zone. The displacement is about 100 feet, the lode may b added that what i true of th Kea1 arge to the north of the zone being that distance to the lode i al o tru of oth r lode . ome that ha'c \Cry west of the portion to the south. Both the north and little copper how a more or le pronounced cpidoti· outh boundaries of the zone are marked by trong zation. Thi uo-gc t that orne of th change may red clay gouge ; that to the north i the thicker not have be n due primarily to th copper-bearing mea uring from 6 inches to everal feet. A sociated elution but probabl to the general temperature with the north gouge is a. strong prehnite-epidotecondition that accompani d the mineralization. copper vein that ha been greatly shattered, eemThe mineralization that followed th oxidation of ingly by the movement that produced the fi ure. the lode bore a di tinct relat.ion to the ompo ition The hatter zone that pa es along the boundary of the lode after oxidation. Thu pidote a ferric between the orth Ahmeek and Mohawk mine offsilicate, i abundant in the more highly oxidized porsets the lode in the upper workings of the Moh awk tion of the lode but i mu h lc abundant in the but this offset d crea e with depth till in the orth 'foot lo~e" that wa le highly oxi.diz d. Chlorite Ahmeek it is little more than the width of the lode. and pumpellyite, ferrou -ferric ilicate , are charncThis shatter zone is narrower than the Ahmeek1 teri tic of the le oxidized " foot lode " and al o of the All?uez zo.ne but re e.mble it closely in other ro pect . ' ba al amygdaloid of the hanging-wall trap, though I t 1 con Iderably Wider in the Mohawk than in the they are al o present in the more highly oxidized orth hme k. The fault south of o. 1 Gratiot portion of the lode. ofl' cts the lode about 50 feet to the we t on the north The change from pidote to hlorite in pa ing from ide. the Kearsarge lod to the basal amyo-daloid of the The other prominent fis ure commonly how 9 overlying trap is very sharp. Areas of the e rock litt.le go ug , and in places there i some brecciation of but a fraction of an inch apart how the characteri t1c t~e adjacent rock. ot un ommonly the fi ure zone mineralization of each. In the we t 1 d , which are widen out to 2 to 3 f et. muc~ les oxidized than the main lode, pumpellyite.i Another et. of fis ure trikes approximately ea t, relatively abundant. Minerals that do not contaJO r nearly at right angles to the north- outh fi ·sure iron show no such control a indicated above. Thus, and toeply outh. X one of tho 0 ar~ , quartz and feldspar are distributed throughout the promment, and f w can be traced for more than a lode, and so is laumontite where pr sen t; in fact. f '.v hundred f et. TlJCr arc numerou fi. ure 1.n the fa~· as recognized, the control is onfined to the Iron mmeral. mm.e: that do noL s em to fall into any well-dcYeloped 'I' · he most conspicuou and striking change thn.t 1 rcr:r1ona sy. tom, but they are commonJy mall and h traceabl for only short di ances. ose Y as ociated with copper is a pronounced bl~ac: mg of the rock around the copper in the upper lughl)
KEARSARGE LODE oxidized portion of the lode. In this portion the copper hn replac d the ro k in rna es of diver e ize , the large t w ighing everal hundred pound . urrounding the copper is an area of light-gray rock in 1rbich the hematite of the r d lode ha largely disappeared. Quartz, pumpellyite, epidote, calcite, and ome of the feld par of the rock are the mo t abundant minerals. The relation of the copper to these minerals indicates that it i later and that it continued to replace these minerals after they were formed. In the lower part of the lode, e pecially in the "foot lode," where the rock i much less oxidized, bleaching i l ss pronounced, epidote decrea~es in amount, and chlorite becom s abundant. Th copper ha replaced the rock to a le s ext nt and i more abundant as an amygdule fillincr. YIELD In general, the Kearsarge lode i riche t near he hanging wall; the richest ore is not alway , perhap not u ually, at the v ry top, but the fir t 3 to 5 feet i the richest part of the lode and grade do,inward into leaner rock. In the 'IT' olverine mine the "foot lode" wa not ext n ively mined in the earlier year , but it i aid to have been in the la t few years a rather large factor in the production. In the earlier years the rock mined averaged 25 to 30 pound to the ton; in the la t few year it ha averaged 15 to 16 pound , indi a ting that th "foot lod " i much lower in opp r han th upp r part, though some low-grade material from th t p par ha been mined at the am tim . imilar but mu h le s marked change CUlT d in th uth K ar arg ' h n the "foot lode" b gan t be mor ext n i>ely min d. The copper d rived from a giv n ar a f lod varie to a con iderabl ext nt with the thi kn of the lod , though th r nr notnble ox ption . For the larger mines on the Kear aro- a to whi h data are available, the following tabl how the averacre cal ulnted thickne of lod top d the average quantity of rock mined per squar fo t of lod ar a and th average yield of opper. Rock mind and copper produced per quare foot of K ear arge lod opper (pounds) 'Phickn s Hock (tons of lod per square I (feet) foot) Per sq uar Per too foot or rock !l!ino uth Kearsarge J 2. 6 Allouez Ahmeek--;;;~ -1- a~d-2 10. 1 4 17. 26 Ahmeek o . 3 and 4 Mohawk Wolverin 7. 64 The relatively large amount of unprofitable around in the Wolverine, Centennial, and orth Kear~ arge make the figure for the e mines le accurate. There i a rather regular decrea e in the a v:erage toping width from the South Kear arge mine northward to the Mohawk, the averag in the latter mine being fully 3 feet le s than that in the former. Except in the outh hmeek ( o . 1 and 2) there is al o a decrease in the copper per square foot of lode. The Wolverine has the highest-grade rock, and in part of the mine the lode i a thick as in the outh Kearsarge, so that thi part probably ha the highest yield 1 per square foot of lode. Th grade of rock in the Ahmeek has averacred d.istinctly hicrher than that in the outh Kearsarge, but the averag thickne s ~toped i 2 feet le , o that the average per quare foot of lode is slicrhtly les . It appear that although the lode is mineralized from the entennial to the :Mohawk, two Area richer than the average have been developed. One in lude the outh Kearsarge and Wolverine with adjacent part of the Centennial and orth Kear argo; the other includes the outh Ahmeek, outh Mohawk, and par of the Allou z. There are al o certain poor area that in general corre pond to the areas of thin and cellular lode already outlined and a sociated with the strong fi uros and fi. ure zon . ( ee pl. 40.) PROBABLE CAUSES OF RICH AND POOR GROUND Three principal cause seem to have been operative in determining the richn of the ground-character of rock, tructural relations, and relation to strong fi m· s. Of tho e the charact r of rock and relation to trong fi urc are the more conspicuou CHARACTER OF ROCK Within he productiv·e portion of the Kear arge lod th thin parts of the lode and those consisting of den e, trappy am gdaloid are consistently poor. In the larger areas where the lode is poor it i thin or tight and relati ely imp rm able. The riche t ore ha been formed in thick rna es of strongly dev loped fragmental top. The thick parts of the lode are not all rich, nor are part of apparently equal thickne s imilarly rich, but rich part of the lode are always thick or loo e and £ragmen tal in te."Xture. Out ide of the main productive area there are, so far a availabl data indicate, no lnrgo areas of thick fragm ntal top, mo t of the out ide exploration having di clo ed only thin or cellular amygdaloid. Th parts of th l de that are above the average grnde in the Ahm ek mine and the south end of the Mohawk are d cidedly of the fragmental and welloxidized type. The snme i apparently true of the Wolverine- outh Kear arge hoot. In the orth
THE COPPER DEPOSIT OF MICHI Kearsarge rome and in the upper level of Gratiot o. 2 shaft th re i some good-looking rock that carries only a fair quantity of copp r. Th lode in tho north end of th ~1ohawk mine is prevailingly cellular to trappy, moderately thick, and moderately oxidized. It contain some very good ground but much of it i only fair, and a consid rabl amount i poor. The same i true of the thin and trappy portion of the lode in the Torth rear arge, Wolverin J Allouez, and eneca mine . !NFL ENCE OF STRUCTURE A D 'l'EXT RE The tructural and textural features that had an influence on the movement of solution may al o have been an important factor in directing solutions to or from certain parts of the lode. The tructural f atures are independent of the lode; tho textural .feature form a part of the lode. St1·uctu1·e.-The structural features that have affected the movement of olution in the lode a.re folds, fault , and fissures. The Allouez anticline is the most pronoun ed fold in the productive area of the lode. If the solutions were trav ling upward through the lode, they would have a tendency to move toward and cone ntrate along the ere t of the anticline and, other thinobeing equal, this should be relatively rich ground. o . 1 and 2 shafts in the hmeek mine are e entially on tho cre~ t of the anticline, and although the toping width here i le than in some of the mine farther outh, the grade of the rock average higher than in any other mine except the Wolverine. Faults that offset the lode by more than its thickness and that intersect it in a line who e cour e i not directly down the dip con titutc barrier beneath which the olution may be concentrated and tbu produce rich hoot of ore. The hatter zone is the only fault on the Kear arge lode that seems likely to have had uch an influence, and the extent of it influence i not very clear. orne rich ground wa found close under it in the Allouez mine, but to what extent thi· ground wa due to the shatter zone can hardly be stated. The rich ground of os. 1 and 2 Ahme k haft i in an area of trong fi. ures, including the hatter zone and the 'fohawkite and 'fa fi ure , but convincing evidence that these fis urc w re a fa tor in the enrichment of the lode in thi area ha not be n found. ulphide are pre cnt in Rmall amount in numerou place in the lode but ar~ mo t abundant near the shatter zone. The lode is cro sed by many fi sure , the mo t promin nt of ' hich strike we t of north and dip st eply ea t. Many of the e fi ure contain copper a native metal, as ar enide , or a ulphide . The fi ure ha been by far the most extensively d veloped, but copper i present at the cro ino- of the lode in many_p f -the fis. ur . . Th fi ure nry on id rn bl in th r of their mineralization. In th fa. . fl ur calcite is the mo t abundant gnno-u min0ral, thoua-h quartz and epidote ar lo all abundant. In th Mohawkite fi ure quartz i r lati ly pl ntiful. 1 n th !U cnide fi ures in he north nd of th 11ohn\ k mine ankerite (iron-calcium-mno-ne ium carbonat ) i a nry abundant constituent, and p cularit wa not d in mall mnount at on point. Ev n h re Lh ank rite i tho pr dominant gangue mineral in tho ar enide fi ures, the min ral mo t intimaL ly n ociated with the ar enid i quartz. In the Ma. s fi ur th r i a de ided onccutration of the copper at th r s ing of the Kenrsarg lode and for a few hundred f et abov th ro ino-, beyond which it fall off rapidly, thouo-h copp r i. pr ent a mu h a 1,100 f et from ho lod . F of the other fi ures have been followed far enouo-h away from the lode to how the r lation l arl , but o far a the evidonc goo it indicate a tr not nd ncy for copper to be precipitated in and n ar th Kearsarge lode. Thi is hown in many of tho mall fi ure, which contain rna e of copp r in the lod but little or no copper even a few feet away. drift ha broo ext nded into the hanging wall on aft ur (~fohnwk o. 4 haft, 22d I vel outh, n ar o. 5) for ewral hundred feet. For a hort di tanc in th hanaing wall there wa con idcrabl mn copp r, but it seemed to decrea e with di tanc from th K a1 arae lode, though the drift ha not be n extended far enouo-h to demon trate this conclu ively. The ar enide fi ure , uch a the Mohawkite, hare been pro pected but a f w feet from he lode in the Ahmeek mine, and he influenc of th lod on the precipitation of the ar enid s i n t known. The ar enide fi ure near th north nd of the Mohawk mine has been followed by drift in th upper 1 vel · The mineral eemed to occur at the cro ing and for a short distance in the hanging ... vall, a on the :\ln fi ure. numb r of the le prominent fi ure such a the Fulton and som unnamed fi ure in the Ahme k and Allouez mine , contain ar enicn.l copper, and tho e seem to corr pond in habit to tho e that carry copper, o that there app ar to be a very clo 8 relation between the copper fis ures a,nd the arsenide fi ure . A relation b tween copper in th fi urc and in the lode is indicat d by the pre ence of ome arsenical copper in th 1 de near the arsenide fi ure · The fis ure that contain ar enide arc either trong them elves or are lo ely a ociated with strong fi ure . Texture.-The textural features within the lode that have been effective in diverting and con verging th mineralizing olution ar th areas of relatively impermeable amygdaloid. The rock in the e areas i by no mean absolutely impermeable, but it per· meabilit,y i sufficiently low to cause some of the olu·
KEARSARGE LODE tion that ' ould naturally pa through it to move by ea ier channel through the areas of thicker and more rermeable rock. \.long bar of thin r cellular lode extend from the Ahmeek to the ou th Kear arge in the upper level of the mine . In t.he lower level of the Allouez there i another bar of thin lode that reach the bottom of the mine and has not been completely outlined, but there is a suggestion that at deeper level it may extend pretty nearly across the Allouez and into the 1 orth Keni arge. Between these bars of thin lode i an area of fair to thick lode in the orth Kear arge that is partly pocketed by the thin lode. t the south end of the barrier i the thick lode of the outh Kearsarge, which reaches the pre ent surface. trong fi suro zone· are mo t abundant in the Ahmeek and 1ohawk mine . In both the change in appearance of the rock near the fis ures is well recognized. In the 1ohawk two general type of lode rock are recognized- " gray lode ' and "brown lode." The "gray lod " i mo t exten ive in th north ond of the mine and the "brown lode" in the outh end, though "gray lode ' is present near the fi ures in the south nd. In the Ahmeek mine dark or chloritic lode rock is pre ent along the ?v!ohawkite, Ma , and Fulton fissures. The change in the lod along the e fissure i due to a chloritization and to orne extent a serici ization of the lode rock. Alteration of the arne type has resulted in the "gray lode" near the fi sure in lihe Mohawk mine. It eem to be a general rule that the portion of the lode adjacent to the trong fi ures in the Ahmeek and Mohawk mines are relatively poor. What seems to be an exception wa seen south of Mohawk o. 4 shaft, on the twenty- econd level near o. 5 shaft, where a "mass" fi sure cut exceptionally thick and highly oxidized lode. Here the lode is aid to be well ' mineralized and carried con iderable rna copper. It seems pos ible that these two bars of thin lode ' have together tended to divert the solutions that were rising along the anticline southward through the thick lode of the Wolverine and outh Kearsarge and that uch a convergence of the olutions has re ulted in the Wolverine- outh Kearsarge shoot. Much of the lode that lie between these two bars in the North Kea1 arge mine is of good thickne and looks favorable, and copper i well di tributed through it, but the masse are mall, and little of the lode rock i above a>erage tenor and a con iderable part i below arerage. It seem pos ible that owing to the barrier above, which prevented free pa age out, and to some extent to the barrier belo, , which di rted tho solution outhward, th r ' a not a normal fl w of mineralizina olution throuah thi part of the lode and fore, thouah fa rabl in barn t r, it wa not heavily min raHz d. The \Yolverine- outh K arsarge area i fav rable 1 because it eontain the hick t part of the lode, and probably aJ 0 b CaU tb bar Of thin lode ba 6 I diYerled oluti n through it that w uld oth rwi e have pa ::l toward th outcrop through gr und farther north. A ome' hat imilar ndition i pr ent in ratiot Xo. 2 haft. Th upper 1 f that shaft are in a moderately thi k, favorabl lode but how little opper. From the t nlh to the fifteenth l ol n ar the Mohawk boundary the lode is of good hara ter and from fair to rich in copper. Betwe n th e area of favorabl rock i a bar of thin lode sho\vinO' in the haft from the eighth to the tw lo This bar ha apparently diverted the solution that mineralized the favorable r ck b low it; and th favorabl r ck above the bar, o far a dev loped, i poor in copper. lNFLUE CE OF FISSURES 0 THE LODE 'l'h~ inOuence of fi sure on adj acent part of the odo I triking and v ry gen rally r cognized by the oper.ator . Except in a very few place th lode in ~he u~mediate vicinity of trong fi ure is d cidedly ower 111. copper than the av ragfl at greater distance. Apparently rna copper .was not encountered in notable quantity on this fi sure in the higher levels. The shatter zone seem to be imilar to the fi ure , except that in thi zone there ha been more mov - ment of the rock and thick gouge has re ulted. The rocks of the shatt r zone seem to have been altered like tho e near tho :fi ure , but in addition there is strong laumontitization. The gouge, however, is decidedly red, and the rock near the gouge is commonly r d al o, giving to the shatter zone a di tinctly red tone. This zone is everywhere poor in copper. In the Ahmeek and Mohawk mines the copper in th lode n ar the ar enide fi ure i arsenical. In the Moha\ k nr enical copper wa found in the "gray lode" 35 feet from an ar enide vein. CONDITIONS FAVORABLE TO MINERALIZATION IN THE KNOWN PRODUCTIVE PORTION OF THE KEARSARGE LODE Several conditions that are r garded as having been favorable to mineralization ar pre ent in the productive part of the lode that are not kno'vn to be pre ent outside of the productive area, and there are oth r that Muld be con idered po ibly favorable. The lode i of the fragm ntal type throughout tho productive area. Outside of the productive area, so far as indicated by data now available, there are no large bodio of thick fragmental lode. Tho lod ha uffer d an unu ually high degree of o, idation throughout the productive area. The productiv area i on the Allouez anticline, which may have been a factor in the convergence of the mineralizing solution . Tho north end of the productiv area is cro sed by a eri f trong fissure . Thi is not regarded a among the favorable ondition , but it ma be so.
THE COPPER DEPOSIT OF IICHIG ' In the arne cro c tion a· the c ntral portion o( th productive part of the lod but at a lower graphic horizon i fl. body of intru ive fel it .
i anoth r factor whi h i not regarded a. c sent1al but whi h may be fa,-orable. EFFECT OF DEPTH ON THE COPPER CONTENT OF THE LODE The study of the Y fl.r ara lode ha show·n no evidence of leaching of opper near the urfa e and r precipitation at greater depth. Where the lode i poor at the surface, a in part of the W olv·e1·i n and fault. and ground. f th alnme · lie la ( ' nt nnial 11nd 1 [o hawk (\Y h·crinc) STRUCTURE Th r ck nf rm to th general trike and dip of th bed in tbi part of the rang down l about the horizon f tho 1 t. LouiM ' cono-lomerate, where the normal tructur i interrupted b. th ).[ayflower fault. Thi fault i appftr ntly n bran h of th~ Keweenaw fault, which i eem to join a hort di. tan e outh of th Old olony tunn I. Tho Keweenaw and Mo, fl wer fault diY rg from a point outh of the Old Colony tunn l ( e pl. ) to 11 maximum known paration of ftbout half fl milo in th nor h end of the 1via flower- ld olony prop rty. t the Old olony tunnel th .:-.ra. flow r fault is r orth K a1 arge mine,, the rock i imperYiou and unfavorable, and th rei no indication that it wa ever well mineralized. ViThere imilar ro k en ountered in the deeper working , a in the lower part of the Allouez and in part of the Korth }..bmcek, he low copper content i encountered. about 700 feet ea t of and voral hundr d f et trati. \iVhere favorable lod rock reaches the outcrop, a in the outh end of the ~Iohawk mine, it i well minerl:\-lized, and th sfl.me i true of favorable rock at greater dep h. If the mineralizing olution in the main were traveling up the lode, the lode in general mu t continue permeable down to the connection with the source of the solutions, otherwi e they would not have found their way to the level now developed. That mining will disclo e area of unfavorable rock and varin.tion in the copp r ontent at greater depth i to be expe ted from the known condition in the developed areas. The encountering of an area of unfavorable rock should not be regarded a di couraging for the lode as a whole, though it may be o for an individual property. Poor ground, due both to character of rock and to the influence of fissure , i likely to be foUlld here o,nd ther at greater depth as it ha been to the pre out depth. It is not intended to imply that a g neral decrea e in the copper cont nt of the Kearsarge lode will not be found at depth, but there i no rea on to think that it will be other than a gradual falling off for the lode a a whole. o far a known, the cau e that re ulted in a decrease in the o-racle of the rock on the Calumet & Hecla conglom rate lode- namely, an increa e in th thickne and extent of the lode with increased dep hwill probably not aff ct the Kearsarge lode. The condition are more lil\:ely to approach tho e of , th Quincy lode, where a depth nearly a.s great a on th Calum t & Hecla conglomerate ha been attained with no notable deer a e in copper content. M AYFLOWER- OLD COLONY MINE graphi ally below the onglomerate. To the north th faul approache be t. Loui " onglomerate, and in the north end of th property near the urface it cut out that ono-lom rate and so me of the OYerlying " Big" trap. Th dip of the fo,ult i ligh ly teeper than that of the b d , and at depth th " t. Loui ono-lom rat is pre ent in the north end of the pr p rty, a indi at d by diamond drilling. The continuati n of hi faul north of the ar a drilled an onl_ b inferr d. Tho " t. Loui ' cono-lomorate crop out about half a milo n rth of the northern drill hol , and it i. pr ty certain that the fault lie ea t of the congl m rat and very probably connects with the area of fel ite in that region ( ce pl. ), with which, indeed, it ma b a sociatcd in ongill. In the block between the Keweenaw and ,:..Io,flower faults the rock are brok n and di placed by minor fault of diverse attitud , but in general the beds are horizontal or have a gentle ea tward dipthe reverse of that normal for the formation we t of the fault". The block contains many bed of melaphyre nod glomeroporphyrite, with ome rather thi k ophitic beds and two pe1 istent bed of conglomerat . It i not posi ively known where the e rock belong in the general erie , but there can be little doubt that the~· ar higher in the erie than the rock adja ent on the opposite ide of the Mayflower fault. Similar trn~ are pre ent in the erie above th "Big ' trap, but ID the neare t ection observed there are no conglomerates above the "Big" trap that cot-re pond with tho e below the fault. There ~re, however, odimcn· tary bed in the erie both to the ou h and north that might have developed into conglomerate· Rock imilar to the series of melaphyro and glom· The tlayflower-Old olony Co. wa form d by a eroporphyrite immediately above the "Bio-" trap do con olidation of tho two properties indicated in the not again appear till the Green tone flo, ba name. The prop rty ov rs the portion of the opperpa ed, and it seems more probable that the roc b aring eric extending from a horizon a hort di~ - 1 the fault block correspond to the eries ab v the' B1g tan o below th \Yoh-erine and tone to the Ke\\-eenaw 1 trap than to the erie o,bove the Green tone flow.
I LE ROYALE LODE DEVELOPMENTS The earlier d vclopmcnt of th Old olony or ou thern portion of th proper y on i ted of ev ral haft and n tunnel. 'l'hc Old Colony tunnel start ncar th Keweenaw fault and wa driv n aero the a di tancc of about 2,500 f' t, or to the fourth flow abore tho " Big ' trap. The No. 1 and o. 2 haft wcr on amygdaloid about midway b twe n the Kenrsar"e amyo-daloid and th "Big" trap. No. 2 wn on a bed a little higher in tho eri s than o. 1. Xo ,-cry 1 ar record i available of the re ult of the o arlirr operation , though o far a knov,rn no copper wa produced. On th dump of K o. 1 and Xo. 2 haft there i some fragm ntallodc rock with a little copper. Th pump haft i on an amygdaloid a few hundred feet lower than No. 1 haft. The North haft in the north rn part of the Old olony property, wa in the area between th K weenaw and ayflower fault . Th IIaddy shaft opened two amygdaloid. a little higher in the erie than the o. 2 Old Colony haft. The everal operation apparently failed to open a lode that gave much encourao-emont. About 1910 an exten ive drillinoampaign undertaken by both the l-1ayflower and Old Colony compame to pro poet the low r porti n f tho copperbearing erie on th ir proporti s. After thi tra t had been mor int n iv ly drilled han any other area in he opper Range, the two compani ', were merged, and the pro cnt ~To. 1 haft wa unk to 11 d pth of 1, 760 f et to pro pe t th 1Ia flo\\·er lode. The haft tart in the "Bio-' trap, but the prop cting has been in the r ck below the ).hv.Oowcr fault, on the 1,450 and 1,700 foot l vels. Th Mayflow r amygdaloid occur above t\vo well-d. fined cono-Jomerate , which have been a great help in working out the structure of thi much-faulted block of ground. At the end of 1924 a cro cut was being run 1 . 70° n T. from the eventeenth level, No. 1 shaft, to pro poet above the "Bio- ' trap at the horizon of th t. Loui " amygdaloid. ISLE ROYALE LODE HISTORY AND PRODUCTION Production from the I le Royale lode (pl. 41) began in 1 55. The present I 1 Royale Copper o. i a con olidation of enral companie, , including the old I le Royale, Huron, Grand Portag , and l.Iiners. Production and dividend from I sle Royale and Arcadian lodes, 1 .-5-1925 -- 1 opper pro<!uccd (pounds) Rock trealed (ton ) Toto! PerI OD of Mine Period T otal Per pouno of copper ( nt ·) rock I.le Rm·al lode: Portage lie Royal heiden - Arcadian lode: 1, 60?- 1 u 25, 309,270 '-- -- - 17f ~l3; Hi 169, 502 3, 019, 206 1, 595, 003 2, 550, 000
EXTENT AND CORRELATION Whn.t i now r d. a th I lc Royalo amygJaloid ha b en lmown under Y ral nn.m . In th I I Royal min , from n. point outh of o. 7 haft toa pointnorthof o.1,iti Jm wn a th I le Ro al lode. From a p int north f o. 1 haft to PortaoLak i what , n. known a rand Portaol de. Until recent y ar th identity of th I le R )-ale and t.h " rand Portao-o:>, ' lode wa not tabli hed. In th I lo Royn.lo min th' part north of th fault Ira known a th \Vest lod , but it i now evidcn t that tho two n.r faulted portion of th sam b d, th Grand Portn.g or northern tion bein di pla d we about 175 feet, a i learly hown in th mille working . or h of Portage Ln.k th _\.rcA.clian lode, from its po ition relative to o. conglomerate which lies below it, ha be n .rded a equivalent to the I l Royale lode. The chanwter of the lode material a e n on tho \.rcadian dump ho,,· a clo sumlarity to the I 'le Royal lode; the Arcadian, lik th I lc Royale, i hio-hly and coarsely breeeiat d and carric numerou inclusions in the lower part; it oxidation i comparable to that of th I le Royale; and both scri i ir.ation and pumpellyitization arc factor in it alteration. It long uppo ed that the b d on oppo it id of Portage Lake wero off ct by a fault concealed b th lak . Iarvine 10 a umcd a horizontal thro\\- of 720 f t, th north id being di placed · un·~ y . ,·ol. I. pt. 2. p. 61, I 73.
THE COPPER DEPO ITS OF MI HIGA we tward. Hubbard/ 1 however, hR shown by the po ition and strike of No. conglomerate at two points 15,000 feet apart on oppo ite ide of Portage Lake, that the horizontal di placement on this supposed fault could not exceed 275 feet. Furthermore, it i now known that the fault already mentioned as occurring north of the I le Royale o. 1 shaft intervene between the two position u ed by Hubbard and accounts for 175 feet of the total, thus reducing to a maximum of 100 feet the displacement of a fault under Portage Lake. o small a displacement over o gr at a distance may be due imply to a slight bend in the strike of the formations. Farther north the " t. Loui " lode is at about the same horizon, but neither thi nor any other known lode north of the Arcadian bears close re emblance to the I le Royale. To the ou th a lode in the tratigraphic po ition of the Isle Royale ha been open din the Elm River (Contact) property near Twin Lakes, and al o in the Winona mine, where it is known a the Winona lode and ha a thick breccia top with pumpellyitic alteration like that of the Isle Royale. Identification till farther south i le s certain; the Evergreen and ucceeding lodes and the Forest (" Victoria") lod are at about the same distance above the uppo ed o. 8 conglomerate as the Isle Royale lode. The e lode are con idered separately. 'l'hickness of I sle Royale flow Arcadian : Feet Isle Royale: Diamond-drill hole CHARACTER OF LODE The I le Royale flow as repre en ted at the I le Royale mine is of the fragmental-top type o well illu trated el ewhere in the Baltic, Kearsarge, and 0 ceola lode . The lode or top portion of the flow may in turn be separated into everal phases or types that are easily re ognized but that show gradation from one to another. These may be designated, from the top down, fmCYmental zone, banded amygdaloid, "vein trap," and foot-inclusion zone. The la t forms the tran ition to th main trap portion of the flow. In addition, irregular mall tongues or stringers from the overlying flow extend down in many places from a few inche to a few f et into the upper portion of the lode and are di tingui habl only with some are from the lode proper. FRAGMEN'l'AL ZO E The fragmental portion of the lode consi ts of irr gular fragments of amygdaloid and fine-grained 11 Hubbard. L. J-., Michigan Geol. urvcy, vol. 6, pt. 2, p. 108, 1 98. trap ronCYing from mall CYrain to tabular blo k ereral f et in gr ate t dim n ion. In form the fraa. m nt rang from hnrply angular thr ugh ubnngulnr to fairly well rounded. In gen rnl, the lar er fragm nt ar mor ano-ulnr than a larCYe proportion of the maller fragm ent . Th top portion of the fragmental zon i ompo eel f fra.CYmenL of a little mailer av rage iz than he bottom portion. In any given ec ion of h lod , h wev-er, there i a mingling of fragment of 1z . In texture the fragment rna b r fin 1. am rgdular, r more coal ely amyCYdular with eli tin t " hilled" r finergrain d margin , or trapp and virtually unif rm in haract r. The more traplike frao-m nt ar in general common r near tho ba than n nr the top of the fraa. mental part of th lode. s a rule th ve icle a.r fill d ' ith minerAl , though they may be only partly fill d, p cially if epidot i the filling material. The pa b tw en the fragments likewi contain mineral . In general, the color of thi mineral filling, wh ther in th int r tice or a amyo-dule , contra t plainly "ith the u ual r d color of the rock fragment them lv ; but in man 1 place nenr the ov rlying rap, e p cinll. wher the lode i thin, the r ck, although 1 arly br cciated, contain little mineral filling of ontra ting olor, and th lode has in con equen e a dead, " burn d' appearance, mottled with alt mating mall pat h of bri k-red and darker brown, dark gra , or dark gre n. BA DE D AMYGDALOID Relatively hort tretche of the lode contain banded amygdaloid similar in general to what ha been called "intermediate lode ' in the Kcar arge but le s abundant and per i tent. Thi material may be overlain b: the hanging-wall trap and grade below into the foot inclu ion zone, or el ewhere banded amygdaloid a few feet thick may p r i t over con iderable area immediately below the fragmental zone. In other place large slabs of banded or cellular am_ gdaloid lie in the midst of the fragmental material. Most commonly the fragmental zone gives place to the foot inclusion zone without a di tinct intervening layer of cellular rock. FOOT I CLUSIO ZONE Directly below the fragmental zone, or the banded amygdaloid, is a brownish-gray rock 6f rather fino trappy texture, known in them ine as "foot trap." It commonly contains somewhat indefinite patches or illelusions of amygdaloidal rock; the amygdule in the e fragment consist usually of chlorite, though les commonly of calcite or orne other light-colored mineral, with or without chloritic nmygdules near the outer margins of the inclu ion. orne inclu ion are harply angular, e entially like the amygdular fragment of
ISLE ROYALE LODE the brecciated- portion of tho flow, but far more are rounded, in con equence of partial melting by the indo ing material, and in extreme ca e of melting or ro orption tho po ition of the original inclu ion is marked by an ar a containing amygdular cavities but po se ing no recognizable boundaries. The inclusion rang , in gen ra.l, from an inch or le to 6 or iuche in diameter; a few reach 2 or 3 feet. They ar mo t abundant and most conspicuou in the upper part of tbi zone and decrease in number and become more completely resorbed and smaller farther do;vn. They coa e to be abundant 10 to 12 feet below the upper limit of th zone. The e amygdular inclu ion are regarded a piece from the fragmental zone sunk or dragged into the lower, till molten, and moving portion of tho flow and partly remelted by it. In contra t with the amygdules of inclusion , the trappy rock of this zone contain amygdule of its oiVn, but the e are commonly spar ely distributed and noticeably large, a i usual in 'tho lower portions of the lode tlu·oughou t the district: VEIN TRAP lab of trappy rock included in the fragmental zone are known a "vein trap." In general thi material how no notable differences from that of the foot inclu ion zone, though in places it exhibits a slightly chilled border. Some slabs have an under margin marked by notably elongated or "pipe" arnygdules, and a a rule, tho large amygdul that occur par ely in the f ot inclu ion zon ar lacking. Th o lab range from 1 foot to 4 or 5 fe tin thiclme and from a fe, I et to cY ra.l or . of f t in extent. The smaliPr lab. mn li parall l to tho wall of the lode orb tilt d at any angl to th m; th larg r rna es of necc it · are n tiall par all l to th wall . Fragmental mat rial lie both above and below the lab . Thee lab ' of v in trap probably r pre ent part of the flow that olidifi d without br ciation ju t under tho fraomental la er but w r th n brok n by the continu d moY ment of the flo, and had frs.gm ntal material draog d or f rmed undern ath them. MAl< TRAP The foot pa gradually into a moncton u trap r k, pra tically d void of amygdule and of Alll gdular in lu ions, which con titu t s the main lower part f th I l Royal flow; thi trap i gr encr and 1 s bro>vn than th of the fo t inclu. ion zone. HA GI G-WALL TRAP by no m an o common or o characteri tic a in the corre ponding position above the KearsarO'e lode. The banging-wall flow abov the I le Royale lode range in thicknes from 195 to 225 feet. At Winona. th flow abov the "Winona lode i 310 f t thick. The trap has invaded the top portion of the frao-- menta.l zone a small tongu and irregular tringer that ranO'e from le s than an inch to a few in he or even a foot or more in width. The e tongues and stringer~ ar distinctly reddish, and in tbi re pect as well a in their finer grain they diller notably from he main mas from which they bran h ; they are thu more like the I le Royal trap, from which, however, they may be di tingui b d by their den er texture, their amygdules, and their red rather than brov.lli h color. These invadin()" tongu s are not everywhere readily di tingui habl from the fragmental material that they penetrate, for the two are not unlike in textur and are clo ely imilar in color. Ordinarily, however, the tongu are lightly redder near their margin , and at their very edge th y may be marked by a faint lighter-colored line appar ntly du to incipient bleaching or el e to the depo ition of a colorl min ral. The e inva ion are rarely of such regularity a to b mi taken for dike ; they penetrate irregularly into and ramify through th fragmental material part of which the may urround. Although irregular and variable in direction, Their averao-e attitude i likely to approximate right angle to the hanging-wall contact, and th y gradually fork and pinch, so that mo t of tb m terminate le than 4 or 5 feet below the ontac . Th y probably r pre ent place where the r latiYely Huid melt of th o,-erlyino- flow has locally brok n through the chilled lo\ r contact of that flow and thus found a.cce s into the loo e and jumbled material of the fragmental zone. DI TRIBUTIO OF TYPES The distribution of the veral pha e of the lode eem mo t unsy tematic. Throughout the mine area of thick fragmental ro k ar inter per ed with ar a of thin, den er fragmental rock, of band d amygdaloid, or of vein trap. The foot inclu ion zone verywher pre n t, though its thickne and the number of it inclu ions may vary. The ar a of thick fragmental rock are very irregularly distributed; at many place where the fragm ntal material wa piled above th general level of the flow surface it no' 1 ulge into the o erlying trap. Wher these bulges are pronounced ther may be an ' apr arent local chan()"e in the dip of th lode, the dip seeming to flatten on the up-dip side of the..,e bulge and to steep n on the down-dip ide. imilar local modification of the footwall dip i effected by abrupt re ntrant of the thick fragmental rock into the ba al The trap immediately o erlying tho I l Royal flow i a dark greeni h-gray and di tin tly ry talline rock tlutt ommonl may be di tinguished r adil fro1n th more browni h and fmer-grnin d trap of the ~ow it elf. Pip amygdule in the trap ju t abov he l le Ro al lode are pre ent in pla e , but they are 1 trap, the footwall dip b ing t eper on the up-dip ido and flatter on the down-dip side of the e reen-
THE COPPER DEPO IT OF MI RIGA r trants. On the other hand, wh re the fragmental ' material i notably thin, the hanging wall appear to bend in toward the footwall and tb'e footwall to ri from it normal po ition.' In the e thin place the fragm ntal rock commonly lo e something of it brecciated appearance, becoming more den e nnd rna sive, but it retain it red color, which chiefly ser ve to distingui h it from the rock of the footwall. Th rei thu a tendency toward alternate divergence and convergence of hanging wall and footwall- i , toward alternnte thickening and thinning of tho lod · But not v ry swing in one wall i accompanied by an oppo ite swing in the other wall. ~Ioreovcr, the bulges into the hanging wall, ' hich may mea ure a much a 10 or oven 20 feet, nr more extreme than the bulges into the footwall, which ordinarily do not e xcced 5 to feet. The bulac of fragmental material 1 into tho lower part of the lode may be more abrupt, so that locally th boundary bo tween the fragmental zone and th foot inclu ion zone may be almost at riaht angles to the plane of tho lode. The bulges into the hanging wall are mark d by lopes which appear to ha\e been, when the flow wa in it original horizontal attitude, of less than 40° and ' hich thus may have been limited to the angl of repo e of loo e fragment . Vein trap is naturally commone t whore tho fragmental layer is thick but is not present in all thick place . The various kinds of lode rock are not only irregularly intermingled but occur in decidedly different proportion in different part of the mine. In the working of Xo. 4 and Ko. 5 shaft the fragmental zone i relatively thick and the area of thin lode and banded lode are comparati\ely small. In the o. 7 haft reaion ' down to the 7th or bottom level, the lode i relatively thin, and areas of thick fragmental rock are mall. The O'l' und outh of o. 6 shaft is intermediate in character en that of Io. 5 and that of o. 7. In the old Huron working , e pecially about No. 6 and J o. Huron shafts, the lode average thinner than in the neighborhood of I le Royale haft o . 4 and 5, and th alternation between thick and thin lode are numerou and abrup t, e pecially in the upper lev 1 . At rtain of the thicker pla o , pecially south of K o. old Huron shaft, the lode i double through the pre enee f a relatively large ma of "vein trap" betw n two lavers of fraam ntal rock. Here both the upp r And the low r fragm ntallayer were ore-bearing, but as a rule only the upp r layer was thoroughly explor d by the Huron management. outh f o. 2 haft, in he upper level , the lode i of good thi lm and grade, but in depth, clown to the rAnd Portage fault and e pecially northward to the limit of the workings beyond o. 1 haft, thin lode pr dominate , thouah with numerou local exception . Th rand Portage or fault d portion of the lode ha ntiAlly the same haract r as the main ection outh of the fault, but the ay rag thi lm c of the fragmcntnl zone m t b a li Lie ar ater than m·ouncl r o. l and . 2 haft. , on the main ection of the lode. The eli tributi n through u t th mine f ar a of thi k and hin fragmoninl ma tcrinl int r-pcl with cellular rock and of nr a of tra pp motorial ,·crlain nnd underlain b ntal rock thouah ug()'c ting complicat d and vnri cl m d of oriain, i bcli ,. d to re ult from comparaiiv ly imple ndiiiou of lllovement and olidifi ntion whil the flow wa in progrc , a i eli cu eel in c un ti n with hnracter of top on paa 31. STRUCTURE ISLE HO "ALE A id entire rie , the lnr~c - t struetural featur r Y alcd in th min i- th I le Ro al yn line. Thi i a g ntle f ld "·hich account for th UlTature of th lod . 1t axi i at about :t\o. 4 haft. Th fa t that lhe be t ground ccntCI' about th axi ugg t that tho pre on of th fold had omethina to do with th localization of th copp r. The clip of the lode at the north and ou th, a near ~o. 2 and o. G haft , r p tiv ly, i t eper, about 56° than near No. 4 and Io. 5 haft , 'her the dip i about 51°. If a imilar difl' r nee in dip wcr maintained d wnward th fold would b me lc and lc marked, and at a dep h f ab ut 10,000 f t down the lode from the outcrop i would eli appear. Indc d, at the pre ent deepe t level th urvatur of the lode i notably le than at the urface, that i , the level are traighter than tho e abov . On the other hand, the bed higher in the eri , xpo eel to the we t n far a the hbed or tlan i lod , retain the ynclinnl tructure. A the e higher bed where they r ach the urface overlie ( tratigraphi ally, or perpendi ·ular to the bedding) deeper parts f the I le Royal lode and therefore are likely to reflect th tructure xi·ting nt cl pth on that lode, it would em probable that the l le Royale yncline per i t downward for a long di tanc . FA LT The only large fault recognized in the mine i the Grand Portage fault, en ountered in the north end. · It strike . 35°-60° E . and dips 60°- 0° JW. The section north of the fault i the " West lode," known as the "Grand Portage lode" before it identity with the I le Royale was e tablished. Where each ection of the lode meets the fault, it is bent or drn.gged around so a to point somewhat in the direction of the other ection. This attitude confirms the con lusion n to the direction of eli placement caused by the fault and trengthens the correlation of the two ection a parts of the arne lode. The fault off et the northern cc· tion of the lode about 175 feet toward the west, as mea ur d on the lev l. Thi is the eli tance nt. right
I LE ROYALE LODE angles to h lod , but the actuRl amount of di placement mu t ha e be n greater, ranoing from om 300 feet to ,-cry much more, depending on the direction of the movement. On the as ump ion that the fault i an o1erthru t the Grand Portage ection moved relatil'cly upward and li.o-htly to the outhw t. If hat i as umed a the true direction of eli pla ement, then any point in th lode outh of the fault would find it equivalent in the Grand Portage block orne four or fiv leYel higher up. But in Rny ase, x ept that pecial one in which th eli placement had b en entirely in a horizontal direction, equivalent portion of the lod on oppo ite side of the fault would not be at the ame le el. Thi r lation may explain difference in the lode on the two ide of the fault on any ~l'en level. The character f th Grand Portage fault varies from plac to place. In the upper levels north of Xo. 1 haft it i a clean-cut break, carrying from a few inche 'up to 2 feet of gouge and brecciated ro k, with pronounced drao-o-ino- of the lode but only minor fracturing parallel to the fault. T ward the boLtom of ~o. 1 haft, however, and in th workingn north of Xo. 2 the fault i le s d finite and implo; it tend to fray into a eries of fracture of omewhat variable dip and strike but conforming on the whole to the general direction of the fault· the e fra.cture are more likely to carry vein of either light or dark colored calcite than to on ain a notable amount f g uge. .\uoth r fnul of approximat ly lh am trik end dip and with th am dir tion of di pla em nt wa ob J'\' d fr m th io-hth l 1 of T clo e to th old Huron ' orkin(l' t th south of . 4 r b nd. It h rizontnl di pla emcnl i n t ov r 30 feet a m a ured on th l vel . In charnct r it r embl he rand P rtagc fl:wlt, b ing well defined and nl a f w inch to a foot in width in the upper I v I but breaking into brancbe that form a fr~t tur d z ne in th d ep r workinO's. It carrio quartz, cal it , pump llyit , copper, and chalcocite. In contra t with th se two fault , which appear to belon<> to the am erie , ther nre other fault and fracture that tril n arl. par all 1 to th lod but uenerally a littl mor to th n rth. ~1lor half of these dip ao-ain t the lode· th other dip with it all at s steeper han th ' inclination f th lod : The mall divergence in tril bet~' c n the e frn tures and the lode might p rmit n icl ra,ble di plac men t alon" th m to e ap r c gnition, but o far a can be ccn ther i only light di placement along any of thee br ak and none whatever along many. Th y are render d con picu u hi fly by tho vein min ral depo itcd in them, which con i t mainly of laumontite, calcite, and quartz, in place with a littl chalcoci e or copper. All the e fault for which the direction of di plac - m nt i evident appear to be rever e faults-that is, the hanging-wall ide of the fault ha been rai ed relative to the foo wall ide. This i, the a me type of faultino- a that shown by the Keweenaw fault. Diamond drilling ba di do ed, according to Lane, several oth r fault between the I le Royale lode and the Keweenaw fault and parallel to the Keweena·w; the e he ha interpreted a probably rever e fault al-o. It thu eem rea onable to a wne that the hanging-wall block of the Keweenaw fault, up to and beyond the I le Royale lode, uffcred di tort-ion at the time of the main faulting and had relativ ly subordi- ' nate sympath tic fault and fracture developed in it. The fault carry mineral of th general period of copper depo ition and thu 111· believed to have b n formed before the mineralization. F I . RE Fi ·ure ar abundant in the mine and vary o-r atly in their a titude. orne of the larger one arc di - cus ed aboYe in onnection with fnultinO'. Mo t of the fi urc an be grouped into a few ystem . Tho e of one y tern trike . 50°- 65° E., and mo t of them dip outhea tat rather teep angle , although ome of them dip northwe t. Tbi y tem i be t de elop rl in the outh end of the mine and i more par ely repre nted in the north end. Another . toms rik s . 2 - 0- 45° W. and ha tecp dip. It i repre entcd in both tb north and t.he outh end of the mine. A third erie trik nem·ly parallel to the lode and dips in the . ame dir ction a the loci but perhaps on the average a little more teeply. Tbi y tern apparntly clumge trike with the main cur'a ure of the lode and . o k cp entially parallel with the lode thr ughout the mine. A slight amount of d:i pla ement of rever -fault direction can be een along orne of the e fi ur . The e fi sure are pre cnt in the main trap under th lode, and orne of them pa throuo-h into t.he hnnging-\\·all trap where this i expo ed by the workina . A a rule only the tronger fractur per i t from be trap of the footwall into the fragmental zone and many of the e ar defie ted upon entering the lode to a om e approximately parallel or more nearly parallel with it. In general, then, fissme are mo t common in n zone a few feet thi k that occupies th ba al portion of the lode and con titu te the main copp r zon . In place tbi concentration of fi uro n ar the ba e of th lod gives to it a di tin t a.ppearance of heeting approximately parallel to the wall , as i well shown in many of th old stop , where in the bla ting the rock ha brok n lean nlong th e joint . On thi ac ount, and becau e of the position of the be t copper along the ba e of the lode, in contrn t with mo t of the other amyo-da.loicl in which the
THE COPPER DEPO IT OF MICHIGAN be t ground is near the hanging wall, it i desirable to ascertain the nature and cause of thi fractming and it.s effect on copper localization. Copper mineraliza.tion is often found to have terminated downwR.rd at a. fractw·e plane essentially parallel to the lode, known by the miner a the "foot slip" and regarded as the boundary between the lode and the underlying "foot trap." The readine s with which the bla ting breaks to uch a fractw·e plane would seem to indicate that sheeting nearly parallel to the lode is indeed a characteristic of the zone just at the bottom of thP fragmental layer. The assumption of this condition of sheeting along the foot of the lode must not be carried too far, however. For example, where the fissuring essentially parallel to the lode is best shown, two or three other systems of joints are likely to be well developed al o, and the que tion arises whether, if there were occasion to carry the mining in a different direction, one of these other joint ystem might not seem the prominent one to the miners and be a conspicuous after bla ting as the "foot slip" is now. In the cro scuts from shaft to lode it can not be seen that fracture or joints parallel to the lode are notably more common or stronger than those in other planes, and when the lode is reached it is not commonly marked by a conspicuous concentration of fracture planes parallel to it. Where the lode pinches and the footwall rise perceptibly from it normal position the "foot lip" tend to swing with the footwall, but it i les conspicuou where the footwall i high and the lode is thin t.han it is where it lies farther down from the hanging wall under a thick fragmental zone. The 1 change in direction of the slip i also le extreme than that of the bottom of the fragmental lode. The slip i therefore deeper in the foot inclusion zone where pa sing over the upward bulges of the footwall than where the lode is thick, for there it i either close to or actually \Vithin the fragmental part of the lode. The relative importance of the fractw·e that are approximately parallel to the lode n contrasted with frn.cture of other direction is not verv definitely ' known . Their effect, however, in guiding and limiting the flow of mineralizing solution to the horizon close to the footwall can not be overlooked. It is not umeasonable to . uppose that fis nring along the ba e of the lode and especially in a plane about parallel to the lode may be noticeable in the .Isle Royale mine becau e of proximity to the Keweenaw ' fault to which tbi fissuring may be related. Another po sible cause of the frocturing parallel to the lode is lipping of th beds when the I le Royale syncline was formed. Altogether, the origin and the importance of the foot slip at the Isle Royale mine n.re not at all clearly under tood. Many of the fi ure are min ralized; tho detai~ are given und r the next heading. ROCK ALTERATION AND ORE DEPOSITION The effect of two di tinct peri d. of alteraLion can be recognized in the lod - one earlier than copper deposition and iudep ndent of it, th other belieYed to be clo ely as ciated with the form~ttion of the ore. FIR T Oxidation was the earli t alteration to afi'ect the lode. Thi chan()' probably took pla e b fore the lode wa bw·ied by the overlying flow. All of the fragmental part of the lode was decidedly oxidized and reddened, n.pparently about the arne degree throughout it thickne . Thi porou material wa· apparently rather trongl affect d by oxidation, eYen where overlain by a lay r of" vein" trn.p. The cellular amygdaloid and the den er material that characteriz · place where the lod i thin w re also oxidized and reddened though to a le inten e degTee, and the oxidation and reddening extend d with father decrea e of in ten ity into the trap of the foot inclu ion zone. In general, the fragmental portion of the lode ha been more highly oll..'idized than the nonfragment~ portion, but the fragment in the foot inclu ion zone rarely how more oxidation than the urrounding trap. The tongue of overlying trap that extend into the lode, a well as the bottom porti n of the main hanging· wall flow for a few ince above the lode nre red and oxidized, in di tinct ontra t to the main portion of the rna., . Thi oxidation may have been accom· plished at the time of or shor ly after the outpouring of the hangin<Y-wall trap by means of the oxygen included in th porous lode on which it was sprend. Although the oxidation of the main lode undoubtedly produced a notable change in color of the rock, through the development of hematite, the textme of the rock was unaffected, and feld par, the chief con· tituent, was not altered. ECO. D PERIOD The econd period of alteration cam long after the , urrounding rock had been formed, and probably after the lode had been tilted into approximately it present position. In contrast with the early alters· tion, a main fe~tturc of which was the conversion of ferrous iron to fer:ric, the Alteration of the econd period wa complex and more inten e, causing in many plac.es a profound change in both appearance nnd character of the rock. Embraced in this com· posite alteration were t.he successive but somewhat overlapping development of epidote, pumpellyite, quartz, sericite, calcite, metallic copper, and copper sulphides and arsenide a well a several other ' mineral of less common or less abundant occurrence.
ISLE ROYALE LODE Thi. ccond period it elf ecm divi ible into at lea t two and po ibl_ thr tage -an early tage intimately connected with the depo i tion of mo t of the metallic copper and pr ducing epidote, pumpellyite, quartz, and calcite; a later tage sub equent to t.he depo ition of mo t of the copper and characterized by the deYelopment of ericite with quartz, calcite, anhydrite, gyp um, and a little barite· and a final tage or else th con luding pha e of the econd, in which the mineral of the ericite sta(}'e o cnr along with copper ulpbidc and ars nide or ar,enicnl copper, chiefly in yeinlet through the lod . The tage of copp r depo ition is marl ed by the production of a greeni h or grayi h rock, a re ult of the quartz-pump llyite typ of blea hing, in which pumpellyite i the most prominent mineral produced, with le abundant quartz, calcite, and epidote. A little prehni te, alkali feld par, or laumontite may be pre ent here and there. This gr eni h rock, den e and u ually hard r than the unbleached red breccia, i the chara teri tic a sociate of mo t of the m tallic copper of the lode. It may occur in patche and treaks or may persi t in long stretches of the lode, but it i generally confined to a layer embracing the lower part of the fragmental zone and the uppermo t part of the foot inclu ion zone; and it i from tbi layer that most of the copp r i obtained in the mine. Little copper o curs in this layer that is not inclosed in the gre n, pumpellyitiz d ro k, but th re may b con·idera.bl ma e of th gre n r k that ontain little or no copp r. A a rule, how or, opper and the bleach d rock ar clo e ompanion . Thi gr n opper-bearin(}' la rcr oin ide lo ely with tho zone of fracturing along the footwall deribE>d abo o under "Fi ure ." Many of the fisure either carry copper or are marked b especially pronouncod pumpcllyitic alteration A-loner thorn. It may be that the con entration of copp r and th accompanying bleaching wa lo aliz d near the base of the lod by r on of thi b l t of fra turing, which added to th normal perm ability of the fragmental part of the lode. In pla e in tbi pump llyitic zon th min rals and lhe texture of the original ro k ~tre en tir ly destroyed. uch alteration with att ndant copper deposition is scanty in the thin parts of th lod , ' her there i little breccia, and is stroncrest ' here well-marked littlealtered fragmental rock li s above the pumpellyite zone. On Lh und r ide ' h r the min ralized zone is ' In conta t with th trap f the foot inclusion zone, lhe bleach d rock i likely to terminate abruptl and in places is bounded by a br ak or fracture that ep.arate it sharply from th dar! er rock und rneath. It 1 probable that thi gr en rock is formed mainly by alterati n of the breccia nnd to a les ext n t by alteration of non fragm n tal amygdaloid or of trap. At many place re idual of the fragmental tru ture can be seen in t!le gr en rock and it fad out gntdually upward t'J typical red fragmental amygdaloid; in the main tb alteration ha obliterated the breccia tru ture, o that the part derived from breccia and that dcri \'ed from the underlying trap are indi tingui hable. In place this purnpellyitic zone and the accompan - ing copper extend above their usual upper limit int the main fragmental portion of the lode, ven to the hangincr wall and rarely for a few inche into the overlying trap. In such place the alter tion is le , the bleaching or removal of the red color and replacement by green not so marked, the destru tion of the brecciated tructure le s thorough, and the amount of copper mailer than in the principal zone. The e upward extensions of the copper-pumpellyite zone ar generally iti place where the lode i wide t and the fragmental layer thicl est-in short probably place of greater than average permeability. In orne of the old Huron workings, wher a tendency t ward double lode i to be een, this bleaching i pre cut in both hanging-wall and footwall portions, though it is not very inten e in either. Sericite is the mo t characteristic or di tinctive mineral of the later tage of rock alteration. It is very abundant in ome of the red fragmental parts of the lode, but it di tribution i irregular, contra ting in thi re pect with the perva i ve di tribu tion of the pulverulent. hemA-tite that gives the red color to the breccia. In parts of the I le Royale mine the breccia i well ericitized, as in the upper and interm diate level of o. 6 haft and in part of Jo. 7 haft and of the Grand Portage lode. In other part of the mine, as in ro. 2, o. 4, and o. 5 haft , the ericiti11ation wa much le s inten e. The mineral o cur hie.fiy a a cement to the fragment , formed in part b filling of interfragment paces and in part by replac ment of the mailer fracrment that lay between the larger ones. In many place where sericite wa · depo ited, rocl olution went on more rapidly t,han mineral deposition, the result being to produce a vugcry t xtur in the brecciated material. This i hown particularly well in the lower le el of o. 2 haft, wh re pumpellyite and later ericite have replRced the breccia; leaving vug that arc now lined with ~ry - tal of calcite and quartz. Where pre ent abundantly th ericite may be identified by it oftne and rather o-re.as feel, al o by its ligh olor, ranging from white to pinki h or pale green, which contra t with the trong red color of the brec ia fragment' cern en ted by it. In smaller quantity al o it has partly replaced th lA.rger fragments, but gon rully tbi replacement wa not so xten iv a to de troy either the textuTe or th red color of the fragments. By depo ition chi fly in t.he paces between the fragm nt , the eri ite ~tppear to have luted or
THE COPPER DEPO IT OF }II HIOAX plugged up the brec ia and thus to have decrea e.d t~e perm ability of tho e portion of the lode in which is plentiful. Because of it oft and omewhat pla t1 character, the sericite would probably be more efi'ectual in this re pect than quartz, calcite, or the other brittle minerals that were dopo ited in imilar relation to the breccia fragments. It wa at first thought that the depo ition of the sericite , its plugging effect bad taken place in the highly brecciated portion of the lode because that was the most permeable, before the pmnpellyite-quartzcopper mineralization. ub equent tudy, e pecially with the micro cope, hows that thi conclusion wa ill founded. early or quite all the sericite i found to be younger than the pumpellyite and to have replaced it in part. It i thus neces ary to conclude that the solutions from which pumpellyite and metallic copper (and accompanying mineru.ls) were depo ited entered the lode before the fragmental portion wa ealed up by sericite, that they therefore cho e the zone near the ba e not by neces ity but by preference, and con equently that thi zone, becau e a site of fracturing, wa actually more permeable at the out et than the highly fragmental but les fi urecl material overlying it. At places where the fragmental tuff wa e pecially permeable, however- and apparently tbi is where it was thicke t-some copper and zoi ite did find their way up into it toward the hanging wall. Later, when the sericite-forming solution came along, they had to content them eh·es with the main.ma of the breccia, which was then the mo-t permeable material available; they were excluded from the fractured zone near the ba e, which had aheady been occupied by copper and pumpellyite; they attacked the margin of the pump llyite zone but were unable to penetrate far into it; and they gained little access to those thick place in the fragmental lode where copper and pumpellyite had been formed. In much of the be t ground in the mine, e pecially nenr the o. 4 and o. 5 haft , calcite, accompanied by more or les quartz and by smaller amount of prehnite, strongly predominates over sericite as the cemonLing material of the fragmental zone. In certain areas, moreover, notably on the fourteenth level south and nineteenth level north of o. 5 haft, on the twenty- ix:th and twenty-seventh levels of o. 2 shaft, and on the fifteenth level at the south end of the Grand Portage section of the lode, anhydrite, with or without gypsum, occurs in a similar cementing relation to the breccia, locally forming patches several in h a ro . cattered here and there through the lode al o is a very little barite. The possible signifi.- ance of these sulphate mineral is considered on pa()'e 136 in connection with the general hypothe i that the metallic copper was depo ited as a re ult of the oxidation of copper sulphide olutions by hematite. opper ulphid sand ar conical oppor, accompanied by cal ite, cricite, quartz, chlorite, and specular h mn.tiL , o ·cur in num r U ' Y inl ts that cut the lode. Po ibly contcmporaneou with th . c nt·e the copper ar eniclcn that hin· be n found on the twelfth level 8 tho very north end of tho rand Portage ection. Th e occur in fragmental material near but not a tually in vcinlet . Th ar ·enid patch arc bor. dred b rock that shows bl a hing o[ the iron-rcm018j type and that und r them icr cope in found to contain oricite in addition to the u ual quartz, pidote, calcite, and laumontite. In O'eneral the ulphid voinl t are narrow, bein~ rarely more than 3 inche in width and commonly much le . In om , a on n th fourte nth level north of o. 5 shaft, th chal o ite occur in hort lenticular rna se from ' hich pe imen weighing a pound or two may be llect d. The gangue con· stitute the chief filling or replacing material of the vein, o that it is frequ ntly nece ary to earch carefully before finding tho ulphide which the gangue mineral ugge t i pre en t. The wall rock of these veinlet chloritized, ericitiz d, and calcitized. For a width of an in h or two the red wall rock may bo bleached by the bodily removal of the iron and r placement by ericite and calcite; or tho immediate wall may be dark green, owing to the removal of the ferric iron and the developm n t of chlorite. In the vein proper calcite and quartz ar the chief minerals, although ankerite, a carbonate of lin1e, magne ium, and ferrou iron, i al o common. Where ankerite forms the O'angue, both bornite and chalcopyrite may be very sparingly developed and pecular hematite, magnetite, and metallic copper are al o to be found. The central part of the vein may carry rna ivc ul· phide, which ha replaced the carbonate. A a rule the chalcocite i confined to the vern·, but in the Grand Portage ection a well a on the econd and third levels north of o. 7 haft it hn been found sparingly developed within the sericitized lode. The di tribution of ar enide and arsenical copper ha not been studied in detail. At one place arsenical copper, domeykite, and whitneyite are a sociated wit~ chalcocite· the a()'e relation are not clear, but there I.S a suggesti~n tha~ the ar enides preceded the ul~~de. Arsenical copper ha been found in highly sericttt~ed fragmental rock; there may be in this mine n relatiOn between arsenic and sericite, uch a is shown by the sericitic alteration along th Mohawkite fis ure in the Ahmeek mine, but the Isle Royale ericite is by.n~ means invariably a ·ociated with ar enide or ar enica copper. CHE:~!I TRY OF ORE DEPOSITIO::\ The chemical chango that accompanied the dcpo:l· t. f 1 d . to hare 10n o copper m the I le Royale o e appeal t d d · h · ;,., tile other . n e m t e same g neral dn· . a . lode 1mportant amygdaloid . In the mam, the Ied t bv ro k cern to have been favored for replacom or~ . · copper. The rock alt ration attending the preclplta·
WI~OXA LODE Lion of copper ha been relatively profound. Ther ha b en a notabl decrea e in total iron and a reduction of ferric to ferron iron. A. compared with tho rock alteration accompanying tho d po ition of copper in tho Kear arge lode, there ha boon le remo,al of the iron, and more of what r main ha been converted from tho ferri to the ferron ondition; there ha a! o been more dep ition of quartz. The phy ical re ult j- seen in the difference between the Isle Ro ale type and the Kear ar()' typ of bleaching. Potash wa a notable con tituent of he olutions, as indicated by the abundant ericite and th smaller amount of orthocla e feldspar, the former more and the latt r le~' plentiful than in the Kear arge and 0 ceola lod . ulphide ar more abundant in this lode than in the Kear arge and 0 eola lode and indi ate that in the later tage of the ore-depo iting period, when ubordinate open fracture ' re followed by the olution , ulphur compound wer the table form for copp r depo ition. IL i not clear why hematite wa destroyed on a larg ale at the time when mo t of the copper was d po itcd and wa later precipitated in minor amount along with chalcocite. Arsenic a arsenical copper and ar euide rna , like the ulphide , be produ t of the later ta()'e of the peri d of mineralization, but the evidence on thi point is meager and inconclu iYe. Through u t. th de cribed ab v , variou ro k lcm nL. w rc taken into oluti n n Lh ro k wn atta kd. The dcpo iti n of opper bodily r plac d th ro k would al o naturally for into oluti n nch ro k con titnent as calcium, dium aluminum, and ili a. It em altog thor probabl that th ()'angue min m! formed b~r the mineralizati u, u h. n qunrtz epidot , pumpellyit , cricitc ealcite, and laum ntiL , repro out. in th main r ombination of th rock con tituent in form hat wor stable at the tage of the min rali~in(l' p riod. AR ADIA LODE Th .\..r ad ian lod ·(pl. 42) was fit nt op n d by the Ar o.dian and ncord mpnni , ' hi h produced a small amount of opp r. Th m st c:xL n ivc developmont r made by tho Arcadian Copper . within n period of a f w ycnrs, b ginning nbout 1 !) . Th louo wo. op nod for about 000 fc t al nO' th trike ' "' by five haft·. .North and south of thi dcv loped urea arc hallow hafts. Th principal hafts fr m north to uth are o 4, opened to tho sixth l vel; Jo. 3, t tho seventh lev l· .r o. 2, to tho eighth l v l; No. l, Lo the leYcl; and shaft A, to he ninth level. Th mo t exton iv Loping wa done from o. 2 haft, ncar the cent r of he clev loped area, and from shaft A, at th ou Lh end of he dcvclu1 -d n rea. From l 90 to 1902 t,he Arcadian ppor o. prod u d 2,950,000 pound of copp r. There in no available record of the grade of the ore, but it not uffiricntly high to ju tify continued mining of tho lod . The r adian lode is a few hundred feet above . ·o. conglomerate and i beUev d to be the northward exten ion of the I le Royale ( 'Grand Portag '') lode. It wa aid t a\erage about 13 f tin thi lme s. Th material on the dump indi ate that the lode i ' ·ell oxidized, and that, like he I le Royal , it i tr ugly fragm ntal. The mineralization appear~ to b in general imilar to that of th I le Royale, th ugh there i considerable feld par in the Arcadian lode anc! littl of the sericite that i l cally abundant in th I lc Royale lod . NEW AR ADIA LODE The I e,,. Arcadian lode i a hort di tance abo,·e o. 8 conglomerate and below the Arcadian lode. It ha been developed by the Arcadian Con olidated Copper Co. through the ew Arcadian and Tew Baltic shafts. From th New Arcadian haft the lode has been opened along the strike for a minimum di - tance of about 2,500 feet on the 600-foot level, and the haft goes down to th 1, 50-foot level. From the ew Baleic shaft it ha been opened for about 1,500 feet along the· strike and down to the 1 250-foot level; the mo t work ha been done on the 950-foot, 1,100foot, and 1,250-foot level . The ew Arcadian lode i in ()'eneral of the fraO'- mental type, but stretche of fragmental rock alternate with tretche of cellular rock. The fragmental area show encouraging mineralization, which is mainly of the quartz-pumpellyite-epidote type with orne fairly coar e copper. .Ar a of cellular amygdaloid in thi a in other lode , are characteri tically poor. No heavy faulting of the lode ha been recognized, but there are ome fault of small throw that offset the lode and have cau ed some difficulty in following it. To the pre ent time (1925) there ha been only a little tc t toping and no production on a commercial cale. In 1915 a cording to the annual report of the compan , 3, 45 ton of rock icldcd 79,209 pounds of copper, or an a\' rage of 20.62 pound to the ton. In 1916, 1,391 tons of rock yi 32,307 pound or 23.2 p und to the ton. In 1917, 4,900 ton of rock yi ld d 53,27 pound , or 10. 7 pound to the ton. Th av ra()'e for th thr e :rears was 16.3 pound to the ton. WINONA LODE PRODUCTION AND CHARACTER The main output fr m the Winona lode (pl. -12) ha been d rived from the ·winona mine, which in ludc the King Philip mine. The lode wa opened by old Indian pit and thor fore di co,·cred earl . Operation by whit m n b gan about 1 64, and a little copp r wa produced in ucceoding ycnrs. In the arli01· part of the produ ti,·c period th r O\·er.'r wa not very hi()'h,
THE COPPER DEPOSIT OF ~ICHI 'AN because mu h of the copper i in rather fine parti l · From 1902 to 1907 about 3,350,000 pound of copper ' a produ ed. The mine was then idle till 1911, when the company was reorganized a the Winona opper o., and it wa then actie till 1920, when operation ' re uspended ex ept for a little development work. It total recorded production, from 1902 to 1920 is 1,262,67 tons of rock, yielding 17,6 4,234 pound of copper- a.n aver~tge of 14 pound to the ton. The inona lode i about 400 feet aboYe o. conglomerate, at the general horizon of the Isle Royale lode. On the Vlinonn p1·operLy the inona lode i developed by six shaft. - from north to outh No . 1 to 4 \Yinona and o . 1 and 2 King Philip. Development ha been carried for about 9,000 f et along the lode. The northern part of the developed portion of the lode crops out ju t ftt the ba e of n prominent bluff. On thi outcrop the Indian. dug shallow pit , and it was eventually opened by the northern inona haft . The outhern part of the developed portion of the lode, which i open d by the southern Winona haft and
th King Philip shaft , wa covered by gla ial drift .. The \VTit~rs did not examine the mine. T.he following descript.ion i · made up from the mi'\}e map , from examination of the dump, and from descript.ion by :\fe. srs. T . S. Woods and R. R. Seeber. The lode, which'is of the fragmental type a.nd fairly well oxidized, appears to be very irregular, changing from thick t.o thin within hort di tance . There i a ' per is tent " .lide" or gouge zone a few feet above the lode 1r. eeber say about 14 feet. In places th lode extend to this " lid e." The mineralization wa of the ame general type a that of the other lode . P,umpellyit. , quartz, epidote, and calcite are plentiful. Prehnite, lamnontite, and probably other mineral are pre. ent. The copper i a. sociated with quartz and pumpellyite. A indicated by pre ent development , the ore lies in a flat outhward-dipping hoot ( ee pl. 42) that crop out near Winona o. 2 shaft. The northern Winona . hafts seem to pa s through the shoot, but-I iu the King Philip hafts it i ral hundred feet below the urface. The ore-bearing grotmd i appar- ' en tly made up of a series of mall nearly parallel shoot , inter. per ed with poor treak . Even the . maHer hoots contain area in which the lode i thick and rclati vely high in copper and nre&. in which the lode. L thin and poOl'. Where the lode extend to the banging-wall lip it is said to be thick and rich. The Winona lode in man. ways re embles th I 1 Royale lode wiLh which it is commonly correlated. WYANDOT MINE The \Yinona lode wn op ned Itt the Wyandot mine b a haft to the 1,000-f t 1 v l, fr m ' hi h ·hort drift were rnn. The lode wa reported a carrying ome copp r but op rations in tbi mine were 0011 di continu d. ELM RIVER MINE The Elm River opp r o. op ned a lode at the gen ral horizon of the inona b a haft. to the .500foot level, wh r drifts wer ext nd d for about 1,000 fe t,. The lode ' n.s nl o opened n tho firt le'l'cl for a f w hundred fe t. Th r ults ,,. re appn.rently not very encouraging. t o. 6 th lode ''a entered by a ro cut n a depth or about ~50 f et and wa follow d for about 700 feet. CHEROKEE MINE The berokee opp r o. opened a lode that i. farther from I o. ODCYlomerate n.nd pos ibly tratigraphicall high r than th Winona lode. A haft was uok to the fourth le 1 and short drift carried on each level. It wa r ported that . ome tretche· of commercial grounrl were op ned. There i a fault outh of the haft ( ee pl. l 2) that di place the rocks on the outh about 500 feet to the east. WYANDOT NO. LODE The \Vyandot opper o. opened a lod in a cro cut from the 700-foot level To. 11 haft about 1 100 feet horizontally (950 f et ·tratigraphi ally) below the hnnging wall of o. conglomerate. The lode wa opened on thi 1 \el and b a winze to the 00, 900, and 1,000 foot leY l on each of ' hich drift were carried. The lode i fragmental in haractcr, and the result were reported a . omewhat ncouraging. test hipment of 1,605 ton of rock made in 191 i yielded 12.54 pound of copper to the ton. EVERGREEN AND SUC EEDING LODE All the mine" on the E,· rgreen and uccecding lode were idle at the time the re()'ion "·a. examined, and only very meager o b rvA tion o underground ":er made a.t the Ma s and '\.dYenture mine . OCCURRENCE o far a learned; howe\' r, it doe~ not show the tendency for the ore t.o f rm near the footwall, which j sop rsi tent and unu, ual a feature of the Isle Royale lod From the Lake mine at the north to the Victoria mine at the south there have been rather exten ive developments on a serie of lodes whos ba e i about 400 to 500 feet above o. conglomerate and which extend through a thicknes of about 500 feet of flow · Thi series i at th general horizon of the Winona and Isle Royale bed , to Ute north, and of the Fore t ("Victoria") lode, to the outh. The correlation of , individual flow from one d velopment to another i probably om what uncertain but in each of the opening in the Lake, outh Lak' Adventure, Ma s, and Michigan mines there are se~eral lodes that carry
EVERGREEN AND SUCCEEDING LODES sufficient copper to have encouraged exten ive development, and a substantial amount of copper has been produced from the series as a_wholo. From higher to lower honzons the lodes are the Knowlton, Merchant, Mass, North Butler, Butler, outh Butler, Ogima, and Evergreen, with other amygdaloid present in places. ( ee pls. 43-46.) The position of these lodes is shown in Plate 13. The lodes that have been roo t de eloped and most productive are the Butler, Evergreen, and Knowlton. The Butler lode has yielded the large t amount, but the Evergreen and Knowlton lodes have made a con iderable output. PRODUCTION The records of production from the several lodes of the series have not u ually been kept separate by the mining companie , but the total for the series is es entially the production of the companies mentioned below, with the exception of the production from the Mine ota fi sure and the Calico lode by mines that have become a part of the present Mohawk Mining Co. (Michigan mine) and from the Lake lode by the Lake Mining Co., which is not here included with the group. Production from E vergreen and succeeding lodes to end of 19£fi Rock Copper produced (pounds) Mine Period treated
1915-1923 0, 075 1 51-1923 1920 - F mall. 1, 0-±2, 211 10, 7 3, 9 50, 616, 77 - - - - - - - - b 4, 065, 17 5 -- - - - --- 66, 50 1 152 1 'Does not Include production from the Lnke lode.
~~ted; doas not include production !rom tho Min ots fissure nnd Calico CHARACTER OF FLOWS The flow of the Evergreen and ucceeding lodes are intermodiat in compo ition, falling toward the ande ite end of the ba altic series. Texturally they aro chiefly mclaphyre and glomeroporphyrite , but oph.itic texture occur in some of the thicker flows. STRUCTURE ext to the general tilting of the bed and the Kew~enaw fault the large t structural feature affecting ~h1s series of beds is the pronounced o.nticliuc with Its crest at Mass. This fold ext nds southward nearly to Flintsteel River and northward to the Lake mine. Like the Baltic anticline, it does not show a gradual change in stril{e around the fold but a very sho.rp change at Mass City of about 35°. · The Lake mine syncline extends into this region, and this series of beds are involved in that fold, but the correlation of the individual beds in the Lake 58540- 29--15 mine bauin with the normally d'ipping bcd,r to the north is somewhat uncertain, and the lodes have therefore been considered separately. There are many fis ures and faults with small throw on the Mass anticline, a is u ual where the rocks have been folded to that extent. The opportunity for observing these fissures has been too meager to warrant any generalizations regarding them. It may be noted, however, that many of them are pTobably tension fis ures re ulting from the folding, though some are essentially trike fissure that dip in an opposite direction to the lode. All the fissures noted are mineralized and were e idently formed before the period of mineralization, though there has been movement on some of them ince mineralization. CHARACTER OF AMYGDALOIDS Wherever een the . amygdaloids of this series of flows are fragmental to some degree. Very commonly the fragmental material is rather coarse and trappy. Like all other fragmental amygdaloid these diff r greatly in different places, but characteristically areas in which the lode is moderately thick and fragmental alternate with areas in which it is thin and cellular or trappy and fragmental. The relative extent of these areas varies from place to place. Some of the lodes, e pecially parts of the Evergreen lode opened in the Mass mine, show locally a distinct tendency to pas into amygdaloid of the coalescing type, thouo-h this tendency was not seen to persi t over very large area . MINERALIZATION The result of mineralization in all the lode of the series i similar. The abundant mineral are quartz, f ld par, pumpellyite, chlorite, calcite, and epidote. Red f ld par i u ually abundant in all the lodes. The le abundant minerals are prehnite, datolite, and laumontite. Zeolite other than laumontite were not noted though pos ibly present. Anhydrite was found on the dump at the Mass mine, but thi mineral eems to be relatively rare in the e as in other lodes. Copper in small. and large rna e is irregularly distributed through the lode. In the Evergreen lode, in the .fa s mine at least, much of the copper is pre ent in mas es-in fact a rather large percentage of the copper in all the lodes i coarse. ROCK ALTERATION The quartz-pumpellyite rock i the characteri tic product of rock alteration associated with the copper, though there ha been much replacement of rock by red par and le by chlorite and epidote. RELATION OF MINERALIZATION TO CHARACTER OF LODE A close relation between character of lode and mineralization is evident wherever the lodes have been examined. Rich ground is wholly confined to frag-
THE COPPER DEPO ITS OF MI RIGA mental parts of the lode, and tho ar n of good ~round u ually coincide with area in which the lode 1 al o relatively thick. The thin, cellular, and .trappy parts of the lode arc con i tently poor. There IS apparently mine production. In th pr m nt, no d finite trend of or niz d on n. large seal . Min r ()'round n.rc re ognized. nt tage of develop. hoots ha b en recog. h ot of good and poor orne tendency for the favorable rock form belts or 11 shoots," but ob ervn.tion in the mm s ha been too scanty to make this certain. BUTLER LODE l\IASS MI ' E The Butler lode (pl. 45) bas been themostprodu~tive of the lodes of this series and bas been mo t extensively developed in the Ma s mine, where it ha been opened for about 5,000 feet along the strike and rather extensively to the thirteenth level. Large area have be n stoped in the ground adjacent to shaft . e~.r shaft B and more e pecially, near shaft the topmg has not be~n as continuous, and presumably the ground is le s regularly mineralized. Lithologic chamcter.-Wbere (:'xamined, as it has been over small areas only, the lode i generally fragmental but largely of rather coarse trappy character. As in most other fragmental lode , areas of definitely fragmental rock are inter per ed with areas of thin trappy or cellular rock. Mr. E. W. Walker, the superintendent, states that in places the lode was unusun.lly wide and was mineralized near the footwall and hanging wall but barren in the middle. In uch places two topes were calTied. tructure.- Tbe main tructural f nture of the lode in thi mine i a eries of mineralized fi ure . Locally the e may how light di placement, but they rarely offset the lode as much as it width. A "cro ing" I near shaft A is said to displace the lode along a brecciated zone. o mapping of the fi ure ha been carried over the area, but there i one sm·jcs striking northea t and one northwe t. There are al o fissures striking approximately with the lod , orne of which dip with the lode and other aero the lode at a high angle. ll the fis ure contain e entially the same minerals as the lode and were evidently formed before the mineralization, though there has been movement on some of them since mineralization. According to Mr. Walk r, no close relation betw en fissurin()' and mineralization of the lode has been recognized, though the fissures have evidently rendered the lode more permeable. Mineralization.-Tbe mo t abundant minerals of the lode are quartz, calcite, pumpellyite, epidote, and feldspar. Datolite is not uncommon but apparently not abundant. The pumpellyite type of bleaching was the characteristic alteration a sociated with the depo .itio~ of copper. The fine copper of the stamp rock 1s said to be more evenly di tributed in this lode than in the Evergreen lode. That there is considerable coar e copper, however, is indicated by the fact that mass copper constituted about 26 per cent of the total Yield.- During th lat f mining by the1Ia-- on olidn.tcd Mining th yi ld ' about hal! 8 ton of tamp ro k p r quare foot of lode. about 50 per cut of the rocl· wa discarded underground, about a ton of ro k p r quare foot of lode wa broken or an n.vertwe hi kn of around 12 I et. The rock milled yi 15 to 17 p und. I c pper to the ton. AD E ' '1' RE i\JI E In th d ntur min th BuLler lod ha been op n d for about 2,500 f ot along Lhe trike and down to the igh h lev 1, but nl r lativ ly mall area hav be n top d. Wh r seen in the upper levcl' fragmental rock eem to form a relaLively mall proportion of th lod , and the ar n. b twe n the fragmental portion ar "tight" and poor. The mineral· ization wa imilar to thn.t in the Ma mine.
record of he grad of ro k or production are available. TR LAKE MI E The Butler lod ha b n op n d to a mall extent in the outh Lake mine from the urface to the 600· foot level. It i tated in th company report" that the opening made on th lode b for operation were su pended were en om·aging and that it gave the most promise of all th 1 d in the min . Rock milled in 191 amounted to 7,694 ton and averaged 2 pound of copper to th ton. It is not tated what extent thi rock wa ole ted. LAKE MI E Development work on the Butler lode wa done in tho Lake mine from 1917 to 1919 through a cro cut on the 600-foot level of the Knowlton shaft. The lode was open d for about 1,400 fe t along the strike and was reported to contain stretches of fair copper ground. The lode had b en earlier opened by the No. 1 and o. 2 Butler haft from the surface to third level and for about 1,000 feet along the tr ·e. orne stoping was done on the fir t and second level, but no record of the results is available. ORTH LAKE ll E The North Lake o.'s report for 1918 state that the Butler lode was cut in the 00-foot crosscut a~d followed by a drift for 30 feet. It was said to contaiD an encouraging amount of copper. EVERGREEN LODE MASS MI E ( I 46) ha In the Mass mine the Evergreen lode P · . It been opened for about 3,500 feet along the stnke. the has been rather extensively opened down eleventh level from shaft B and to a lesser dept 1 a
KNOWLTO LODE lateral extent from shaft A. There was no good opportunity to examine this lode in it best-mineralized portions. It is evidently fragmental, though not o highly fragmental a the Butler lode, and in places is coale cing. The fragmental part of the lode is of the rather coarse trappy typ . Its mineralization was similar to that of the other lodes of the series. Quartz, calcite, pumpellyite, epidote, and feldspar are the common minerals. Like the adjoining lode , this lode is cut in the Mas mine by numerous fi sures. All are mineralized, and some contain con iderable copper. The copper is coar er than in the Butle.r lode, yielding a larger proportion of mas -in fact, stamp rock is relatively unimportant. The copper is said by Mr. Walker to show a slight tendency to occur in shoots with a outhwe terly pitch. The production from this lode, in recent year at lea t, ha b en much less than that from the Butler lode. ADVE1 TURE MINE In the Adventure mine the Evergre n lode has been opened for a few hundred feet on the adit level and to a slight extent on the sixth level. Little stoping has been done in thi mine. The lode where een in the adit level is fragmental but relatively thin. It contained copper rather per i tently for a foot or so near the hanging wall. TH LAKE MINE The Evergr n lod ' a cut m the outh Lake workings, but no r rd of it haractor a there hown ha b on found. LAKE Ml E In th Lake min the Evor5reen lod wa cut on the 600-foot level from th Kno; lton haft and open d for about 700 feet along the strike. The r port of the company for 1919 tate that th lode a opened is very encouraging and is con ider d the be t of the cries a op n d in the Lak Jnine. stope ov r 200 f~et long wa tarted. mall te t hipment , rouo-hly ptcked at the surface, yielded from 1 to 34 pounds to the ton. ORTH LAKE MI E The Ev rgreen horizon wa reach d in the orth Lake workings, but no description of the character of the lode is availabl . KNOWLTON LODE . The l nowlton lod (pl. 43) bas been most extenst:ely open d in tho Ma , AdYenture, and Lake ~nes. It wa s en in only a few place in the Mass mtne, where it i of th fragm ntal type. A judged from the material on the dumps it i fragmental in ' c other place wher it has b en opened. MASS MI E In the Mas mine the Knowlton lode has been rno t extensiYely opened from shaft On the third level a drift has been carried on the lode for about 2,000 feet. The lode ha been largely toped for 200 to 300 feet each side of haft C to the eighth level. In shaft B the lode ha been opened on the fourth, eventh, tenth, and elennth levels, but littl ground has been toped. From haft it ha been opened on the tenth l vel only. N ar haft , according to Mr. Walker, it wa of good grade. ADVE TT RE Ml:\'E The main operation of the .Adv nture min were on the Knowlton lode. In o . 1, 2, and 3 hafts the lode was open d for about 2,000 feet along the trike, and in o. 3 haft it was opened to the thirteenth level. Only a relatively mall proportion of tho ground opened was stoped. The large t area stoped were near o. 2 haft to the tenth lev I and midway between o . 3 and 4 haft on level 7 to 10. o. 4 shaft wa uppo ed to b · located on the Knowlton lode, but later a lode wa found about 60 feet from the hanging wall of the one on which the haft wa sunk, and it wa thought that this might b the Knowlton. The lode a open din the Adven1 tur mine ha averaged rather low in copper. Prior to 1906, according to the corn pany' report of 1907, all rock tamped averaged 12.29 pound to the ton; in th fir t half of 1907 it fell to .7 pound , but it improved during the econd half of that year, when the mine ' a clo d. The mine wa operated for a short tim in 1916- 17 but wa oon clo ed again. LAKE MI E The Knowlton lode ha been opened at the Lake mine for about 1,200 feet along the strike and a deep a th ixth level in th main Knowlton haft. topino- ha been done near this haft from the fir t to the si xth level . orne areas of fair ground wer sajd to have b en op ned. MICHIGA MINE A l de that i locally known a the Butler lode but appear to be higher, po ibly at the Knowlton horizon, has been opened by E of the Michigan mine to the eighth level and for a maximum di tance along the trike of about 1,400 f et. The mo t exten ive stoping has been done in what appear to be· a we tward-pitching hoot that cro the shaft below the fifth level. ( ee pl. 43.) A indicated by material on the dump the lode i fragm ntal, and the character of mineralizn.tion is imilar to that at other plac wh re the lode ha been opened.
THE COPPER DEP OSITS OF MI HIG OGIMA LODE The Ogirna lode (pl. 44) has been ope~ed to a .slight extent in haft C and B of the Mass rome and m th~ Adventw-e mine. It contains patches of f~·agm~nt rock and some of these are fairly well rrunerahzed. The 'openings the whole have apparently not been en cow-aging. OTHER LODES There has been light development of the Merchant and orth Butler lodes in the Mass and Ad enture mines and of a lode in the foot of the Evergreen at the Lake mine. These lode are somewhat fragmental and in plnces carry copper, but as yet they have offered little encouragement to ext.en i e development. FOREST ("VICTORIA") LODE The statements regarding the Forest lode (pl. 47) are ba ed on a brief visit to the Victoria mine in A ugu t, 1923 on the mine maps and record , and on tatements by the late George Hooper, superintendent during the later operations, and by Charles Hooper. PRODUCTION The Victoria mine, on the Fore. t lode Ontonagon River, is the westernmost mine on the main mno-e that has made a notable production. It wa also"' one of the earliest producers in that part of the district. Production of Forest lode in Victoria mine to end of 1988 Period Rock treated (tons) Copper produced (pounds) Total Per ton of rork 1 55--1 7 ---+ 1, 700,518 GEOLOGIC HORIZON The Fore t lode is one of the series a short distance above o. 8 conglomerate, but with which one, if any, of tho e developed to the east it is to be correlated is not certain, and it is therefore considered separately. It i low in the series and probably near the Evergreen horizon. This lode has been slightly prospected for sever!l-1 miles to the south on the Tremont-Devon, Cass, and other properties but not extensively developed. CHARACTER OF AMYGDALOID Where seen in the Victoria mine the lode shows alternations of areas of rather thin cellular to coalescing amygdaloid with smaller areas of fragmental rock. The areas of fragmental rock seemed to bulge rather deeply into the underlying material, but Mr. Hooper stated that there were bulges of this character into the hanging wall also. The fragmental parts of the lode are 50 feet thick in places. The thicker masses of frngmental rock are irr gularly di tributed in the d veloped area, though th Y how some tendency to form hoot . MINERALIZATION Quftrtz, pumpell ito, epid t , nnd calcite are the roost abundant minorn.l a so iated with the copper. Pr ]m ite is fairly abundant. The rock alteration· mainly of the quartz-pumpellyite typo. Much of the copper occur ll r latively large rna e.. Mr. Hoop r tated that in th later operation m, copper had run a much a 50 por cent of the t11tal production and that th stamp rock wa low grade, carrying le than 10 pound of copper to the ton. The thick bulge of fragmen tnl rock are by far he rice t port.ion of th min , th ugh 1r. Hooper tated that uch rich ar n have not yielded a very large proportion of the total output. Th richne of the o-round ems to how a lo r lation to the degree to which the lode i fragmental. EXTENT 'OF DEVELOPMENT The lode ha been opened in the ictoria mine for about 00 feet along th strike nnd to the twen~y· ighth level. The ar a in whi h exton ive t<>pmo ha been don i con id rabl · 1 , a can be een by reference to Plate 4 7. orne work wa dono in the early day' on the Tremontevon property, we t of the icto~ia, and more recenLly diam nd drilling ha been done m ord~r to locate the Fore t amygdaloid. n amygdalotd that was thought to be the Forest was encountered and wa. reported' to contain orne copper. LAKE LODE PRODUCTION The Lake lode (pl. 4 ) was located by diamond drilling in 1907. Development began in 190 , and the fir tproduct.ion was made in 1909. From1909lol91, when production wa u pended, the Lake lode~;~ vielded 7 326 227 pound of copper. The yte J. ' ' t or ore ranged from about 16.0 to 26.5 pounds per on d Th ock was milled and avera.o-ed about 23 poun s. e r Orted to a varyino- deo-ree The company repobr b o · d · t e for 1918 state that " 11 n0w stope opene Lake shaft showed a steadily decreasing copper con6 b · stapes 5 or tent of rock. "' ln t e newel " tons had to be di carded for every ton shtpped. LOCATION d d d first opcne The Lake lode was d1 covere an th lode near the Keweena\7 fault. D evelopments 00 in the Lake and South L ake mines show 1:clinal portion of the lode is on the north end of a Y basin pitching southwest. 'ble when The openings on the lode were not access~ tentcnt· the wri~ers visited the region, and ~be :h: records concermng the lode are taken largely from
BALTIC LODE and report of the Lake and South Lake companies and from descriptions by Mr. C. J. McKie, manager of the Lake mine when operations on the lode were uspended. STRUCTURE The general structure of the area is that of a broad syncline lying between the northward-dipping series of the Evergreen Bluff, to the north, and the Keweenaw fault, to the south. The main workings of the Lake mine are around the north end of thi basin, and tho e of the South Lake mine are on the north ide of the basin, where the bed dip to the northwe t and southeast from the a);.is of an anticline that trikes about with the general trend of the range. CORRELATION In the present stage of development there is posibly some uncertainty as to the exact correlation of the Lake lode with the lode north of the anticline, which have the normal northerly dip of the range. It seems clear, however, that the Lake lode is one of the serie of lodes above No. 8 conglomerate, and probably it is near the Ever<Yreen lode of that series. A lode which may or may not be the Lake lode ha been opened at the Algomah mine, west of the Lake mine, on the south ide of the Lake mine ba in, at the general horizon of the Lake lode. CHARACTER The Lake lode is distinctly of the fraO'mental type, and, like tho EYergreen and most of the succeeding lode , here they have b en open d, it how great variation in thickne from place to place. In some place it i apparently thick and fragmental; in others the amygdaloid ha nearly disappeared. The lode hn been developed in the Lake mine for a di tance of about 3,500 fe t along the trike and down to the eleventh level. orne copper is said to be present throughout the e opening , but the copper content wa highe t for a distance of 500 to 600 feet north and outh of the main shaft, where 25 to 30 per cent of the rock has been stoped. It i reported that orne copper wa found in the drift on the Lake lode in the outh Lake mine, but no stoping was done. The fragmental amygdaloid of the Lake lode wa brown and well oxidized. The principal mineral associated with the copper are quartz, pumpellyite, and calcite, which are accompanied by om epidote and a little red feldspar. The alteration of the lode rock was typically of the quartz-pumpellyite type. ALGOMAH LODE Operations on the Algomah lode began in 1910, but the only production has con isted of te t shipments. A shipment of 74,560 pounds of ore made in 1914 yielded 18 per cent of copper, according to the company s report for that year. The shaft on the lgomah lode is on the south ide of the Lake mine ba in, at the general horizon of the Lake lode and only 60 feet from the K weenaw fault. Whether or not this lode i the ame as the Lake lode has not yet been determined. Near the surface the lode dips 60° N. The shaft was not accessible at the time of the writer ' vi it to the district. In a hort level about 30 feet below the collar of the haft the lode is mainly cellular, with small area of fragmental amygdaloid. The rock showed the pumpellyite rock alteration characteri tic of many of the lod in this part of the di trict. The company s report , howe er, state that little native metal wa found but that the copper was nearly all combined as bla k oxide, melaconite, green arbonate, malachite, and ilicate. The ore ·een on the dump corroborates this statement. The lode has been developed for about 2,000 feet along the strike on the fir t level. About 1,000 fe t north of the haft the drift on the amyO'daloid entered the Keweenaw fault, which wa followed for ome distance. The shaft wa sunk to a depth of 55 feet, and a cro cut wa driven north from the econd level for about 950 feet to explore for other lodes. BALTIC LODE HISTORY AND PRODUCTION Important development of the Baltic lode (pl. 49) began at the Baltic mine about 1 9 . The Trimountain mine and the Champion mine began production in 1902. Originally the three mine were operated under separate organization , but at pr ent the Copp r Range Co. o'vn the Baltic and Trin1ountain and one-half of the Champion; the other half of the Champion i owned by the St. iary' Mineral Land Co. The Copper Range Co. also owns the Atlantic mine. Th followinO' tabl bows .the production from tho mine and dividends from the beginnin<Y of operation to tho end of 1925. A more detailed tatement of production i given in the stati tical ection. Production and dividends from the Baltic lode, 1 98-1925 Rock treated (tons) I Baltii>-- --- - - - - - - - - - - -' 1 "9=.1916 . , 672, 553 T. 0 1917- 1925 1, 20, 612 43, 625 1902::: 19~3 ,, 7 o ,, o 1902 19~5 Mino Period 31,396,177 Does not Include production from Superior Iodo. Refill d copper (pounds) - Dividends Total Per ton Total 200, 5 4, 164 7, 950, 000 62, 939, 547 34. 57 b 2 084 772 1, 343, 303 ' ' 139, 697, 2 9 3,'250, 000 43 , 403, 286 3o. 97 29, o1o, 26o. 96 1 842, 967, 5 9 1-uT! 42, 355, o32. !l~ 1 Copper Range Co. Estimated. Per pound of copper (cents)
THE COPPER DEPO ITS OF U HIG1 The relatively high copp r content of the rock treated from the Baltic lode as compared with that from the other amygdaloid lodes of the di trict is due mainly to the present method of mining, which permits discarding underground a relatively large P rcentage of poor rock. The table of production b years (pp. 79, 2) show the change in copper content of rock treated re ultino- from the development of this method of mining. The method ha been de crib d and the re ult di cu ed by Denton and cbacht, of the Copper Range o., \Vho show that for the period 1915- 1921 as compared with 190 - 1914 the yield per ton of ro k treated increa ed from 24.8 to 37.2 potmd , or 50 per cent. The rock recovered per quare foot of lode decreased from 1.54 to 1.40 tons. The lode ha been developed in the three mines for about 20,000 feet along the trike and in depth to the twenty- eventh level in the Champion mine, the thirtysixth level in the Trimountain mine, and the thirtyninth level in the Baltic mine. EXTENT AND CORRELATION The Baltic lode ha been opened throuo-h the three mine of the Copper R ange Co.- the Baltic, hampion, and Trimountain. orth of these the Atlantic Mining Co.'s ection 16 explorations were presumably at this horizon, and farther north the uperior and Houghton Copper mines are at the general horizon of the Baltic lode and probably on that lode. till farther north an amyo-daloid at thi horizon ha been prospected by the I le Royale Copper o., and north of Portage Lake b the rcadian on olidated opper o. The identification and correlation of the Baltic l~de becomes increa ingly uncertain with increa ing d1 tance from the principal mines on the lode. outhof the Copper Range Co.'smines an amyo-daloid at the Baltic horizon ha been prospected at th; Globe and Challenge mine . The No. 3 conglomerate is not developed at the e localitie , and the correlation is somewhat doubtful, but the horizon ha certainly been reached at the Globe, not o certainly at the Challenge. BALTI C FLOW The .Baltic flow at the Copper Range Co.'s mine is o~h1te 150 to 200 feet thick. It varie considerably m thlCkne s from pla e to place. Re ting on the Baltic flow in the developed area are a number ?f thin di connected flows. orne of these seem to. thm out both up and down the dip and along the stnke; oth r are as yet only partly outlined. Exampl s of tho e that seem to thin out are found in the upper le els of the Trimountain min d example of both kind in the south end of thee, h:~ pion mine. "D.canton, F. W., Development and extraction methods f depostts: Lake uperior Min. rest Bull 1922 , or Lake Supenor copper 'h ds ·
PP . , 2. Schacht w rr M' ln me, o of the Copper Range Co : Am M' d ' ·
g · · · m. an Met Eng T ' pp. 46- 310, 1925; I,akc uperior Min lost B 11 """ ., vol. · u lu, PP. 56-79. The o mall flows apparently cupy and ted t · · h f f n ° fill dopr m t ur n th main flow. Th'· ig indi A. ted by the fa· t that Lh di tanc from the o. 3 conglom rate, ben ath Lh Baltic Uow to th top of the high t of th o flow and t th to~ of the Baltic flow wher th Y ar ab nt, i far more unilo e t,han the .di tan o fr m th on glom rate to the topr~ t.he Balt1c flow m a ur d b h wh r tho overlying r th y ar ab ent. The small no, may be u hes from th main flo\ ' r for ed out after a consid rable cru thad form don it but' bile mo tolthe interior a till fluid . Th o-u h t in part to fill hollow in the or.iO'inal urfa of th flow, and in part the po ibly au d th ru t on which ther flowed to ettl into tho fluid p rtion beneath, th~ lo' erinO' the top f th main flow at the pine . Abov the main Balti flow and the "gu h" flow· r tina- on it i a flow that has a thickne of 40 to 60 f t wh r it ha be n u t in the developed area. The Baltic v e t 1 d i at th t p of thi flow. STRUCTURE FOLD The roo t pr nounced tructural f ature in the opp r Ranoo. mine i a br ad anticline whose ere t pa e b tween the Baltic and Trimountain rnine . Thi fold cau a very harp change in trike, amounting to about 30°, botw en the e two min and in the outh end of the Baltic workino- . In thi area the grotmd is much broken by fault and lip , and the e probably di pla the lode con iderably, thouah pre ent development d not make this certain. In the outh end of the Baltic mine the lode swing> around in a zone of con iderable fi uring and a umes the general trike that it ha in the Trirnountain mine, but if continued on thi trike it would not meet the lode in the Trimountain mine. Thi ugge ts an off· set bet\ een the Baltic and Trimountain mine. ( ee pl. 10.) CRO S FA ·LT A ' D LIP In all the mine there are fault or lip with trong clay gouges striking nearly aero the lode; mo t the e have teep dip , though a few dip a low a 30 · The smaller lip have aused but little di placem~nt of the lode, and a drift carried on the general tnke u ually reenters the lode a short di tan e beyond such a slip, or the displacement may be so slight that the lode is not lost. On some of the slips ho'\\oever there is a displace- ' ' · the ment of as much as 60 to 70 feet- for example, ID lower levels of the Baltic mine between I o. 4 and Nt' 5 shafts and ih the south end south of No.2 sha t. The faults do not show a uniform direction of di pla~ ment. In many of the smaller faults the block nortlt of the break is offset to the west, but a trong fau
BALTIC LODE south of Baltic o. 2 shaft has moved the south block relatively westward. Examples of the cro s breaks with heavy clay gouges, together with vein minerals, are to be seen at the south limit of developments in the Champion mine and the north end of the Baltic mine. ome of the fissures in the Trimountain mine also have strong gouges, and, as already noted, there is apparently much fissuring with goug s in the u ea between the Baltic and Trimountain mines, where the lode makes a sharp change in strike, and the area of the tlantic Co.'s ection 16 exploration north of Baltic is said to be much broken and fissured. STRIKE FlSS RES Throughout the mines there are numerous fi sure that strike with the lode or nearly so and dip more teeply than the lode, or from 75° to 90° where the lode dips 70°. These fissures are seen in the openings in the lode and in the crosscuts on both sides of the lode. In the long hanging-\ all crosscut on the even th level of the hampion mine such fissures are numerous near the lode but become less numerous with increa - ing di tance from it. They are numerous and strong in the crosscut back of o. 4 shaft in the Baltic mine, but less numerous and weaker above the Baltic lode. This increase in abundance of stril e fi ure toward the Keweenaw fault, whi h i a f w hundr d fe t outhwe t of th Baltic lode, ugge ts that th fi sur may have been form d at the arne time and b the arne forces that produ d the fault. CHARACTER OF BALTIC AMYGDALOID Although th writer wer not able to xamin the Baltic lode over large area in th older work d-out portion of the mine , it i fairly clear from th examination made and from de rip ion by tho e familiar ' ith the old r , orl ing that the lode i of the fragm ntal type. Like all th oth r fraO'm ntal amygdaloid , th Baltic l de how notable va.riati n in the quantity of fragmental material from plac to pla e. In many place the lode i 50 feet or ev n more in thickne and i compo ed of fragmental am gdaloid throuO'hout; in other place it i but a few fe t thi k and i Compo d of rather coarse trapp fraO'm nt . Locall the space b tween the larg fragm nt are fill d with t~ngue from tb hancing flow that ext nd for ome dt tan e below the top of the amyO'da.loid. In still other places the lod i cellular, with sliO'ht tendency to fragmental character. A in th oth r fra!mlental amygdaloids, unu ually thi k pA.rt f th lode tend to bu.lg both to the banging wall and the foot' all. variation appear in both A. small and a large rattern. In an area of pr vailingl thick, notably ragmcntal amygdaloid, t.here ar area of thin and trappy or cellular amygdaloid. and in an area of prevailingly thin trappy amygdaloid there are areas of fairly typical fragmental amygdaloid. In the larger pattern the largest areas of thick fragmental amyO'- daloid occur in the Champion mine and in the upper level of the Baltic mine. In the lower level of the Baltic, in the Trim.ountain, and in the lower level of the northern part of the Champion mine the lode contain on the averaO'e le s fra!mlental material, though there ar area of markedly fragmental amygdaloid. In the mailer pattern there is a distinct tendency for the areas of abundant and le abundant fragmental material to form "belts ' or " hoot " with a rather low outherly pitch. Thi tenden y i particularly apparent in the Trim.ountain mine but is al o evident in the Baltic and Champion mine . Whether or not this tenden y i al o pre ent in the larO'er pattern is not clear in the pre ent state of development. There i , however, a sugge tion of it in the lower le>el of the Baltic mine, where the lode contain a rela ti' ly mall proportion of fragm n tal rock. Where the mall overlying flow or ' gu he " ar pr ent, the lode beneath them em to a erage thinner than where they are lacking. In place , at lea t, there eem to be e pecia.Uy thick fragm ntal amygdaloid ar und th margin of uch flow , a if they bad :filled in depre ion underlain by relatively thin amyO'daloid urrounded by ridge of thick amygdaloid. The amygdaloid of the e "gu h" flow averfi.O'e thinn r .and i more cellular than that of the main flow, whi h i probably to be expected from their origin. The lode varie greatly in thickne . In the Champion mine in numerou place it is 50 feet thick and in ome place even more; the average topin()' width i about 26 fe t. 13 In the Trimountain mine the average i about 16 feet. In the upper level of the Baltic mine the lode averaged 20 to 23 f et, but in the bottom of the mine it i relatively thin and cellular. OXIDATION The Baltic lode is well oxidized though di tinctly le o than th Kear arge lod . The markedly fragm ntal rock, where not bleached by mineralizing olution , is bro·wn to reddi h and well oxidized throughout. Trappy fragmental rock and cellular rock are u ually le oxidized, though the tongues from the overlyinO' flow that fill the paces between coarse, trappy fragmental rock are commonly di - tinctly oxidized and give the lode a reddish appearance. MINERALIZATION H ERALS The minerals of the Baltic lode are few. The abundant mineral a ociated with copper are quartz, pumpellyite, epidote, and carbona both calcite 11 Schacht, W. IT., op. cit., p. 5
THE COPPER DEPO ITS OF MI HIGA and an iron-bearing carbonate. Locally_ seri~ite i plentiful a in the south end of the ChamplOn rome on the ninth and tenth lev ls. It is pre ont but_ not abundant in many other place in all the mme · Laumontite is pre ent in many fissures and locally in the lode. Other zeolites wore not noted and ce~ tainly are relatively rare. Prehnite is pre ent but I not abundant except in soll').e fissures. Orth~clase, which i abundant in many other lode and m the Superior mine, to the north, is almo t entu:ely lacking in the Copper Range Co.'s mines. Datohte wa not noted. Sulphides of copper are unu ually abundant in all three mines. Theil· characteristic occurrence is in the fissures that dip 75° to 90° and trike n arly parallel with the lode, and they are like' i o present in cross fis ures. They also occur in tho lode in the same manner as the copper, but tbi type of occurrence is rare. It was seen best in the Trilnountain mine, on the twelfth level, in the stope south of o. 4 shaft from the end of the stope to o. 2 mill, where most of the copper in the lode is chalcocite a ociated with u·on carbonate of the same type as occurs in the fis ures. Chalcocite i by far the most abundant sulphide in the fissures, but bornite i not rare. Chalcopyrite is reported to occur in a few places. The mineral most characteristically associated with the sulphides, both in lode and in fi ures, is an ironbearing carbonate. This mineral usually forms on tho walls of tho fi sures, with the sulphide in the center. A sllnilar relation exists where sulphide forms in the lode; the sulphide is surrounded by the iron ' carbonate. The iron carbonate is far more widespread than the sulphide. Over large areas it has permeated and replaced the amygdaloid, so that the rock, when expo ed on the dumps, quickly tums brown from oxidation of the iron in the carbonate, as can be readily seen on the dumps of the Baltic mine. In many places copper is associated with the sulphides. Usually it occurs at the margins of the sulphide veins, but it may occur with quartz in the center of a vein. Where a vein branches and dies out in fragmental lode rock, chalcocite may give place to copper in the extreme ends. In the mass copper fissure in Trimountain No. 2 shaft, twenty-fifth level outh, the mass copper was found near the intersection with the lode; where the fissure was followed into the footwall trap chalacocite appeared, though copper was still present. Only a relatively small amount of copper wa pre ent in both forms away from the lode. Barite has been found in the Baltic lode but here as elsewhere is rare except in some of the fissures. The prii1cipal commercial occurrence of copper is in the lode, whe~e _it is ~regularly distributed through the amygdaloid m bod1es ranging from minute specks to ~as sever_al_ tons in weight. Mo t of the copper m this lode 1s m relatively small rna ses . . Schacht 14 u Op. cit., p. 5. gives the p rc ntngo of the various sizes of copper produced a follo\ s: Percent Less than 20 pounds but over Y2 inch 9
Largo rna c of copp r have been found in two fi urc at and n A.r thou· inters ction with tho lode. ear Trin1otm tain r o. 2 shaft a mass fi ure W!.i mined {rom above the twenty-fifth level to the twentr. eventh. It i aid that most of the copper was fo~d jut below tho Baltic lode. Ma 's copper ha also been mined from a fi sure in the We t lode of tho B~tit mine, above the twentieth 1 vel. The fi. ure trikfi nearly parall l with the lode but dip more teeply. The copper wa in the banging wall of the \lest lode. The fi ure i of the same y tem as those that carry chalcocite, but it carried no ulphide o far R wa; noted. tfass copp r in con iderable quantity i said to have been r covered from strike fi. ures in the hampion I o. 2 haft. The copper is said to hm occurred mainly in the trap b low the lode. ROCK ALTERA TIO The characteristic rock alt ration i of the quartz· pumpellyite typo, with varying amounts of epidote. Wherever copper is pre ent tho lode is bleached. usually to tho -gr en color characteristic of .ab~ · dant pumpellyite. This type of rock alteratton h more fully di cus ed on page 107. Alteration of the same type occurs along the fis ures both in ti1e lode and in the adj acen I; trap rock. RELATIO OF MI ERALIZATION TO CHARACTER OF LODE In a broad way there is a close relation between character of amygdaloid and degree of minernlizati~n. Rich ground is formed in thick fragme~tal amygd~:~ Thin trappy fragmental amygdaloid and_ ce amygdaloid are commonly poor. The thtek frs~· mental amyo-daloid is not invariably rich, but thin "' "h rmore or cellular lode is nowhere known to be nc ove than small areas. The largest areas of thick fragmental amyg 8 · d in the upper opened are m the Champ10n mme an . h t part of the Baltic mine. These are also the nctlin areas developed on the lode. mine and in the lower part of the B_alt1c ~he 0 £ragmen tal and i3 not so well mme:altzed.om other respect the B altic lode does not differ fr mineralized fragmen liallodes. RESULTS OF OPERATION . th thickness o The variation of copper content WI to 11 sno lode is shown by the data published by~ u Denton, F. w., op. cit., p. 42.
SUPERIOR LODES chacht 16 on the results of operations to 1921 on the richest and poorest units of operation on the Baltic lode. Results of operation of mines on Baltic lode 1 Productive lode area per cent Champion l Trim.ountam It is readily seen that the thicker parts of the lode have been the more productive. The Baltic mine is intermediate in character and productivity between the other two. BALTI C WEST LODE The Baltic West lode is the first amygdaloid above the Baltic lode. The underlying trap i from 40 to 60 feet thick, fine grained, and brownish_ The amygdaloid of the portion opened, mainly in the Baltic mine, i of the fraomental type and is similar in character to the thinner parts of the fragmental amygdaloid on the main Baltic lode. There have been no large areas developed on this lode comparing in thickne s with the thick fragmental Baltic lode of the Champion and upper level of the Baltic mine. There is some suggestion in this lode, a in the main lode, that the amygdaloid i in areas or belt of moderately fragment 1 and lightly fragmental or Uular lode. The pre ent developments do not give much id a of the trend of such belt , but apparently if pre nt they do not pitch very teeply. The r ult of mineralization and rock alteration are entirely similar to tho e sho\vn in the main lode, and there i the arne general relation between mineralization and character of rock. RELATION OF FISSURE MINERALIZATION AND LODE MINERALIZATION Hubbard 17 long ago uggested that the stril e fi sw·e in the Baltic lode were the main channels through which the minerulizing solutio s pas ed. He regarded the d po it as a true lode in the ense that it is a zone of clo ely paced mineralized fi ures rather than a mineralized amygdaloid. The close similarity of the mineral of the fis ur of the amygdaloid-the pre ence of abundant lron carbonate and quartz in both, and the arne type of rock alteration in both-cert inly give good reason for suppo ing that the solution that produced the fis ure mineralization and the amygdaloid mineralization were very similar. The main dill reneenamely,· the relative abundance of sulphide in the 11 Schacht, W. II., op. cit., p. 5. u llubbard, L. L., J,ake Superior Min. Inst. Proc., vol. 17, p. 229, 1912. 58540-2916 fi sures and their relative scarcity in the amygdaloidmay be due to the oxidizing effect of the ferric iron of the amygdaloid, a has been di cussed on page 129. This is particularly indicated where fi ures finger out and are lo t in fragmental amygdaloid_ The mineral in some uch fi sures changes near the ends from chalcocite to nati e copper. It is al o sugge ted by the presence in the amygdaloid over small area of chalcocite in tead of native copper, as ha been noted especially in the Trimountain mine. The e relation also sugge t that the mineral in the veins and in the amygdaloids were formed during the arne general period of mineralization, but there can be no doubt that orne of the mineral in the fi ures were deposited later than some of the minerals in the amygdaloid, and the mineral that now fill the fi ure may have been deposited largely after the mineralization of the amygdaloid. Indeed, this must have been the ca e if the fi. sures were realLy the channel through which the mineralizing solution entered the amygdaloid. The general subject of lode mineralization i discus ed on page 124, where it is pointed out that in some of the lode of the di trict there is no evidence to the pre ent depth of development as to how the mineralizing solution entered the lode , but the mineralization seem to have been effected by olution ri ing along the lode . It i entirely pos ible that solutions may have entered the Baltic and other amygdaloid with which mineralized fi. ures are as ociated, in part throuO'h the fi. ure that are now expo ed and in part through fi.s ures that entered the lode below the pre ent depth of the mine . SUPERIOR LODES OCCURRENCE The main uperior lode (pl. 4 ) i approximately at t.he same horizon as the Baltic lode and may be identical with it. It ha been developed by the uperior Copper Co. and the Houghton Copper Co. Between th uperior mine and the opper Range Co.' mine , to the outh, on the Baltic lod , are the Copper Ra.nge Co.' ction 16 explorations, which are in a zone of con iderable faulting, and no po itive correlation of the bed ha been carried across this zone. Here as on the Baltic lode, both a main lode, called the uperior lode, a.nd a we t lode, calLed the uperior W st lode, have been worked. The main lode has b en opened in the two mine for a horizontal distance of about 6,000 feet and down to the thirty-fir t level in the uperior mine and about the fow'teenth leve1 in the Houghton Copper mine. PRODUCTION The following table gives the result of operations on the lodes to the end of 1925.
THE COPPER DEPOSIT OF fi RIGA Production and dividends from the Superior lodes, 1906- 1923 Mine Period CHARACTER The main uperior lode, as indicated by the material on the dumps of the two mines and from de criptions, is a fragmental lode of di tinctly scoriaceous character, with orne shaly to andy rock a.bove tb lode in th Superior mine. The uperior West lode where mined i prevailingly fragmental but contain area of cellular top. Outside of the main ore hoot the fragmental are~ appear to be small a compared with the cellular. MINERALIZATION The roo t abundant mineral a ociated with copper in the uperior West lode are quartz, pumpellyite, epidote, calcite, and feldspar. Feld par is unu ually abundant in this lode, as contra ted with it carcity on the Baltic lode. Laumontite i pre ent in fi ures and locally in the lode. Chalcocite and barite are present in mall amount in fi ure cro ing the lode. The writers had no opportunity to examine the main uperior lode. ORE SHOOTS The ore shoot in the main uperior lode was developed in the uperior mine from the surface to the nineteenth level, but little of it wa mined below the seventeenth level. The productive around extended for 1,200 to 1,500 feet along the strike, but le s than 50 per cent of the lode within the hoot was mined for ore. The general pitch of the hoot in the lode wa to the north. In the uperior We t lode a hoot pitching south at. a low angle was opened from the tw to the thirt!-first level, but most of the ore ~ined was obtamed between the twelfth and twenty-third level · Thi hoot wa developed along the trike for 1,000 to 1,500 feet, and in the mo t producti e part b~tween the twelfth and eighteenth lev Is a rather high percentage of the lode was mined. In the lower level the shoot wa mall and "b~mchy." In 1920 the mine wa clo ed, and the manao-em nt stated t~at ore re erves had been exhau ted a~d that prospect~g for new ore had not been sufficient! encouragmg to warrant further expenditure. y _The Hough ton Copper mine is north of the uperior mu:e, and t~e main openings are thought to be on the mam upenor lode. The shaft is in the foot of th "Ea t l d " h' h · e o e, w lC lS probably the main lode. There Rook treated (tons) ha been lod Rollned copper produced (pounds) Total Per ton Total uperior min . nly relati el mall ar a of the lode w re toped. The discard of r k brok n in 1912 wa 41 per cent and the opp r ield wa I w. ' I LE ROYALE On the I le R oyal pr p rt an amyo-daloid at the horizon of h Balti lode ha been opened by the! and ection 12 haft , but without encouragin re ult . FEL ITE OF I DIAN A MI E DEVELOPMENT The o. 1 Indiana haft wa begun in 1910 to explor an ar a of fel it which had been cut in diamond-drill hol o. 2 and from which a very rich core had b n taken at a d pth of about 1,400 feet. Thi exploration wa arri d on till 1916. The haft " a unk below the fourt enth level, and openin · were made at the 600-foot, 1,150-foot, and 1,400-foot le el . The re ult of thi work indicated that the frl ite is an irregular body intruded in to tb trap . The fel ite on the dun1p i a reddish fin -grainedro kwith cattered phenocry t of quartz and feld par. It i all much battered, and ther i al o mu h f I ite breccia, which probably came from the vicinity of the contact with the trap, where a con iderable part of the e:;,.--ploration wa carried on. MINERALIZATION Calci to is everywhere pre en t along earn in the rock, and the fel ite i bleached to a light gray. In omeof the rock this bleaching has included the whole ares between fi ure . Oxidized copper mineral , carbonate (malachite), and ilicat occur along many of the fi. ure . Where the oxidized minerals are pre eot the original mineral ha e u ually been entirely altered, but in some of the lea t alter d portions chalcocite and "brittle'' ar enical copper are present. It i probable that the oxidized minerals have been derived from both of these. In the larger fissure rather mas ivc coppe: wa found. There are mas e several hundred pound in weight on the dump.
FISSURE DEPOSITS 0 . 2 drill hole, from which the rich core was taken, wa not identified underground, but the management believed when operation were uspended in 1916 that the core had come from a mineralized fi ure or vein, like those encountered in the working , and that th vein wa probably. not of great extent. FI SURE DEPOSITS HISTORY Apart from the in idental extraction of copper from fi ure in mine that exploit the amygdaloid and conglomerate lodes, there are S'ome mining operations devoted primarily to fi me deposit . The fir t copper produced in the di trict wa taken from the fi ure depo it of Keweenaw and Ontonagon ounties. ( ee pl . 50- 52.) Production began in 1 45, and fi w·e mine were operating till about 1 90. Except for the production from the Ma s fi sme by the Ahmeek Mining Co., beginning in 1909, there ha been little operation on fi sure depo it ince that time. PRODUCTION The total recorded production of copper from fi me to the end of 1925 amounted to 199, 53,000 pound ; of this total 61,315,000 pound came from the Minesota fi ure, of Ontonagon County, l~aving a total of 13 ,53 ,000 pound from the fi me of Keweenaw County. (For the production of individual fis ure ee p. 72 and the r port on mining ompani in th stati tical ection, pp. 76- 9 .) Of all th fi m tha hav be n wor1 d indep ndently of th lode in he di trict, only t!U"ee ha e yielded a profi th liff, ntral, and 1ine o a. Tho Cliff paid 2,51 ,620 in dividends; tho entral 2,130,000; and th Min ota 1, 20,000, plu ationa! 320,000, Ol' , 2, 140,000. Th opp r Falls paid 100,000 in dividend , but that wa le than the a e m n coll t d. The Phoenix paid 20,000. The Ma fi me in Lh hm k mine ha undoubtedly been profitabl and probably would have b n profitable if worked alone. DISTRIBUTION Plate 50 h w the relati n of the Green tone flow and th Allou z conglomerate to th principal fi ure worked in Keweenaw ounty from hm k to Delaware. The fi ure in the north end of the di trict are ten ion cracl on th fold . Thu there i a serie of fi ure n ar th cre£t of th Allouez anticlin ·. From the Gratiot River gap nearly to the Jorth mericau ~ap th Gr en ton flow, which i perfect! expo ed, 1 ma ive and almo t without .fi ming. ear the ot:th Am rican gap th great K w naw anticline begm , and fi uring of varying degrees of inteu it i pre ent from that locality to the end of Keweenaw Poiut. DISTRIBUTION OF COPPER IN THE FISSURES The only .fi ure that the writers have been able to study in any detail ru·e those that cro the Kear ru·ae lode in the Ahmeek and Mohawk mine . orne of these contain native copper, others ru· enides. On the Ma s fi me only ha drifting been cruTied far from the Kearsarge lode, though on a few others drifts have been extended a much a 200 or 300 feet from the lode. Ther i trong evidence that the Kearsarge lode ha been a large factor in cau ing the precipitation of the copper in the Mass fi sme. Thi evidence consi ts fir t in the di tribution of the copper in the fi me. The copper i mo t abundant at the interection of the amygdaloid and the fi me aud decrea e with increa ed di tance from the amygdaloid. On the footwall ide it extend but a hort distance, but on the hanging-wall ide it extend much farther. Between the Kear 111·ge amygdaloid and the Kearsarge conglomerate there are no thick amygdaloid lodes, and no relation between copper and any amyadaloid but the Kear 111·ge ha been noted. The econd evidenc of relation hip i the alteration of the lode adjacent to the .6. w·e. In gen ral the lode nea.r th fi me i chloritized and ericitiz d and contain le copper. o far a can be determined from the m ager amount of development, the arne conditions hold true for the other fi ure that ro the Kearsarge lode, both copper and ar enide .6. ure . The parts of the lode adja ent to the ar enide fi me contain orne ar enide , and there can be little doubt that the copper aJ·nenic olutions were traYeling alona the e fis ure and precipitated th ir burden at the cro ing of the Kearsarge lode. The gradation from fts mes hiah in arsenic to tho e low in ai\ enic, like the Fulton and other fi me , strongly uage ts a common age and origin for all the fi w·e depo it . The Ma fi ure i cro ed by a bedding fault about 200 feet stratiaraphicaily above the Kear ru·ae amygdaloid. Mo t of he copper i found b low thi fault, but no harp chanae in th amount of copper in the fi me after pa · ing the fault ha been recognized. The mo t productive fi me depo. it in the north end of the di trict have been found beneath the Greentone flow, though ome copper ha been produced from fi ure above the Green tone flow. There ha been no opportunity for direct tud of these depo it , and the de criptions in the literature are far from complete. From uch information a available, however, there eem to be at left t two po ible cau e for the special richne s of the fi me beneath the Green tone flow. The fir t i · the pre ence of a fault or "slide," immediately beneath the Greenstone flo, , at the horizon of ·the Allouez conglomerate, whether the conglomerate i present or not. Thi movement has produced a rather thick gouge, which may have
THE COPPER DEPOSITS OF MlCHIGA acted a a dam to rising olution and cau ed them to concentrate ju t beneath the Green tone flow. _Locally there i a di placement of the fi sures along this fault, which cau es the fis ures to end again t the gouge and would favor concentration of olutions. The second po ible cau e is the same a already di cu sed for the fi sures cro ing the Kearsarge lodenamely, that the amygdaloid lodes ~ter ec_ted by the fi ure were an influential factor m cau mg the precipitation of the copper. From drill-core records at the Delaware, liff, and ont:ral mines and description of the Cliff mine, a well a from material on the mine dumps, it appears that there arc favorable amygdaloids in the belt under the Green tone flow. In some reports mention i made of the favorable influence of amygdaloids on the vein, which seems to have been pretty clearly recognized by the early op rators. Furthermore, some of the veins above the Green tone flow are correlated, though not certainly, with tho e below, as the Petherick and the orthwe tern, the Cliff and the orth !iii; and doubtle s others have continuation above the Greenstone flow. Above the Allouez conglomerate horizon the veins eom to be poor or barren until they reach the amygdaloid at the horizon of the Ashbed lode, which are the next higher thick amygdaloid . The fi sure depo it a ociated with the shbed are not a large as those below the Greenstone flow, but it seems likely that the solutions pa ed through the Green tone :flow and overlying beds but did not depo it much copper till they reached the favorable environment of the amygdaJoids at the horizon of the A hbed lode. If this i true, it would seem that neither the Green tone flow nor the '' lide" beneath it wa everywhere a very efi'ective barrier to the passage of ore solutions along the e fi sme . It may be noted, however, that apparently in neither the Cliff nor the Central mine has a largely productive deposit been found on the extension above the Greenstone :flow. The extension of the entral fissure above the Green tone flow ha not been identified, but the supposed exten 'ion of the Cliff has been prospected without finding valuable depo i~s, though the fissure contains some copper where 1t crosses the Ashbed. The Cliff fissure is offset by a fault at the horizon of the Allouez concrlomerate and the same may be true of the Central. would doubtless tend to limit the mineralization to the sections below the faults. From the detailed descriptions of the different fi sure deposits beneath the Green tone flow it appear that the fissures are not ever! where and probably not generally mineralized to th}-s fl?w or to the ((slide" but have the maximum ~nerahzati?n a s~ort distance below the slide. The diamond-drill sectwns at the J orth American Cliff and entral mines show that the amygd·aloids 'imme~ diately beneath the r n ton !low are not y thick or favorable 11s compar d with those below:~ flought n cong ~om rat . Th fi ure , however, pro~ ably averaged rwher above tho Houghton conglomera~ than below it, so that ' hil th r i a general relation between thick am gdal id and pp r in the fi 'Ures this relation i not close. ' t several localiti s a slide has been reported at the horizon of o. 17 conO'lom rate and may have been a fa tor in tho f rmation I fi sure depo it in the hbed amygd l id flow . It appear that th r is a ry notable difference in the effect of the fi ur on the amygdaloids near the cro ing in the K ar arg and on the amygdaloid to th n rt h, under the r n tone :flow. The Kearsarge lode · relative! poor in opp r near the fi ure intersections, wher a both tho hbed and the amygdaloid below the Groen tone flow ar aid to be be t near the intersections of fi ure . Thi dificr nco i not nee ·· saril in con · tent ' i th th operation of the arne cau e . pparen tl both tho K ar arge lode and the amyo-dnloid to the north were mildly mineralized near the cro ino- by the olution that traveled alona tho fi me . To judg from what an be ob erved in the mines on the Kear ~arg lode, the e early olutions al o altered the lode wh r th y mineralized them, de troying much of th ir favor ble chemical character, so that when the ~ater mineralizing olution came up n.long tho Kearsarg lode they encountered unfaorable ground near the fi ure and hence did not depo-it much additional copper in tho c pal't of the lode. In the Ontonagon di tl'i t tho fi ures are nearly parallel with the trike of the bed . In the main Minesota or T orth branch mineralization occurs in the fis ure at and above the' uppo ed intersection with the Mine ota conglomerate, ugge ting that in th' deposit the character of the bod cro ed by the fi ure is the controlling factor. The position of the down· ward extension of the fi ure i not certain. If the dip and strilce of it known portion are maintained it cuts aero the bed ; but there i a po ibility that it curve into the conglomerate bed and becomes a bed fi me. From the foregoincr statement it is apparent t~at 1 li tiOD a clear understanding of tho cau e of the oca za . of the copper in the fissures i of great iroportauce_w pro pecting for this type of deposit. In the depo.Its hi h th mo·t at the Kearsarge lode cro sings, for w c h definite information is available, the character lode seems to be the controlling factor. The depo 1 of which le s is known such as those under the Green· ' h th character stone flow afford reason to behave t at e f h ' . h the presence o t e lode 1s an mfluentlal factor, thoug of the "slides" and the offsetting of the fissure onn·r · · the flow o mg barners, have aided in concentratwg the solutions.
FISSURE DEPOSITS STATE OF DIVISION OF COPPER The Mass fissure of the Ahmeek mine (pl. 51) differs from mo t of the other known fissures in the eli trict in that it contains practically no stamp rock, whereas from the others the recovery from stamp rock was large. The approximate percentages which the several kinds of copper made of the total production from the different fissures are a follows: Cliff, 70 per cent mass, 15 per cent barrel, 15 per cent stamp Phoenix, 50 per cent mass and barrel, 50 per cent stamp. Central, 50 per cent mass, 50 per cent barrel and stamp. orthwestern (1 54), about 30 per cent stamp. iioesota (1 66), 30 per cent mass, 43 per cent stamp. Copper Falls, a large amount of stamp copper. Robbins, mainly stamp rock. At nearly all the mines stamp mills were regarded as e ential parts of the plant . Rock was stamped from the Stoutenberg, Clark, Eagle River, Madison, Amygdaloid Mining Co., t. Clair, and other fi ures, in addition to those mentioned above. In the early day rock was calcined in stone kilns before being tamped. EXPLORATION OF FISSURES I CENTIVE TO EXPLORATIO The total production of copper from fissures ha been small as compared with_ that from lodes. Each of the principal lode of the district has produced nearly as much as all the fi sure together, and mo t of them much more. Th total amount of th di idend from fi ure depo it ha al o been mode t a compar d with those re ul ing from lode minincr. The dividend per pound of copper, however- about 3.5 cent - i about the same a that of the lode mines. It is ' orth whil , th refore, to con ider whether any onsid rable veins remain unopened or but partly developed. Examination of the records and of the field indicates that by no means all th wide fi ures that are expo ed in the reenston bluff have been exten i ely explored; that almost nothincr is known of the exten ive area compri cd in the "gaps" in the Green tone flow; that the experienc gained in the en tral exploration indicates that valuable deposit may be found in fis ure that make little show where they cro the Green tone bluff; and that a s cond favorable belt for fi ure xploration may po sibly be pre ent ea t of the one und r the Gr enstone flow. di tin t advantage in fi sure exploration is that the promi ing zone b n ath tho Green tone flow is very definitely outlined, and other area of po sible promise might be outlined with equal d finitenes . The co t of exploration would be much lc than in the early days, when much money ' as expended in promotion, in many separate organization , and in road, mill , and other features that could now be partly eliminated. Altocr th r there s ms good rcason to expect that a comprehensive campaign of fissure exploration would re ult in the development of mine that would give a moderate reliurn for the effort. It is hardly to be expected that any great mines would be developed on fis ures. GE ER.A.L FEATURES OF EXPLORATIO In any general plan of exploration of the fissures of Keweenaw County, there are cerliain fealiures that; should be considered. Among the more important are (1) significance of the gaps in the Greenstone flow; (2) significance to be attached to the character of the fi sures as they are exposed in the Greenstone flow; (3) influence of thick, fragmental, well-oxidized amygdaloids on the precipitation of copper in the fissures; (4) influence of faults or barriers on the localization of copper. 1. There is little doubt that the gaps in the Greenstone flow have re ulted from weakne s of the rock due to fault or fi ures. Definite indication of thi is seen in the di placement of the rocks and in the shearing of the rock bordering some of these gap , as the Eagle River gap and the Central gap. T, o of the gaps have been prospected, the Madison and the Amygdaloid. In the Madi on a fi sure was e>.:po ed, but little was done on it, owing to the difficulty of drainage. In the Amygdaloid the Drexel fi ure was developed by the .Amycrdaloid l 1ining Co. and yielded considerable copper. Diamond drilling a ro the Iorth American, Arnold, and entral gaps has shown fi ures pre ent in each. Therefore, so far as de elopment have been carried in the north end of the di tri t, there is reason to suppo e lihat the gaps may mark the location of fis ures. On the Allouez anticline the slirongest shatter zones, where they cro s the Kearsarge lode, do not contain productive fissures. There are fissures in these zones, and what they contain in the belt under the Greenstone flow has not been determined. The drilling of three of the gaps, the North American, Arnold, and Central, indicates that the gaps ar9 due to fi uring and faulting, a.lthough in none is a wide shatter zone pre ent. In the "road gap" at the entral mine there i a mineralized fi sure; in the main gap, a fault with only a narrow fracture zone about feet wide. 2. The Greenstone bluff and some of the ridges north of it are practically lihe only places where the fissmes arc naturally exposed, and it is important to know " hether the character of the fissures as shown in the bluff is any indication of what is to be expected of them in the favorable zone b low the Greenstone flow. J aturally the fi sures that appear largest in the Greenstone flow are the ones that have been chosen for pro pecting. This pro pecting has led to the development of one paying fissure 1nine, the Cliff; a second that would doubt! shave paid under modern
THE COPPER DEPO IT OF MI HIGA r 1: Ph · .. and everal other efficient manauement, t Je oenL'::' that might ba;e nearly or quite paid the co t t leJr development, a the t. Clair, the fis ure :rrune A.t Delaware, and the Drexel. On the other hand, man_Y of the other fi _ure prospected becau of t_hell' G t fl ..,. ha e melded httle prommence m the reen one o'y J or no copper. The mo t productive fi ure, the entral, wa not recognized where it cro ed the Green tone flow but was discovered in an outcrop about 600 fe t outh of thi flow and in ancient pit which pre umably were sunk on the outcrop of the vein. It therefore appears that too mu h reliance hould not be placed on the appearance of a fi ure in the Green tone flow, but a more certain method and perhaps a cheap would be to drift on a favorable amygdaloid along c~o. en stretches of fi smed uround with the idea of exannrung all the fi ures of the ar a where they ros ed the favorable zone. 3. There i rea on to believe that the thick fragGGE TED EXPLORAT£0 In the following paragraph ar sugge ted exploration which might d t rmine the point outlined above and th re ult of which would f om e influence ant furth r con id ration of th g neral problem. · At pre ent all that i known about Lhe influence of thick amyo-daloids a ide from that b low the Greenstone flo, i that the 0 eola horizon where the Ctmtral fi uro cro ed it at d pth was w ll mineralized and that the aughn illo Ii ur bowed best in what wa thought to be the 0 eola amygdaloid. It j of cour e po ibl to proj ct any of tho known min ralized fi. ure to th ro ing of belt lower in the eric and pro p t at that point, but it would eem advantageou t u e h information gained in pro pecting the known favorabl horizon in deciding h w to pro pect one that i little known. FISSURE MINES AND PROSPECTS OF KEWEENAW AND ONTONAGON COUNTmS mental, well-oxidized amygdaloid had a favorable tar.- T, 0 mil outh of opper Harbor, in the effect on the precipitation of copper in the fi ure · E. 72 ec. 9, T. 5 N ., R. 2 ., u h of the GreenSuch amygdaloids are pre ent in the belt under the tone flow. Two haf , r unk on the principal Green tone flow and may or may not have been the vein 300 and 90 f t de p. Th w r connected by controlling factor in making thi a favorable b It. drift and by an adit 1 v 1 f r drainau . Little topThat it is a favorable belt has been well demon trated. ing has b en done (1 64). n am. udal id belt 13 feet The practical que tion is therefore not o much whether wide, aiT ing copper, wa op n d 150 f et east of t~e theamygdaloidsunder theGreenstonefiowhaveexerted transvors in. \.noth 'r in 1.> ing prospected m a favorable influence a whether imilar amygdaloids 1 64 carried rich barrel r k n ar th urfa.ce. D. · el ewhere that have not been explor d have exerted hild , the agent, report opening two vein , one 700 such an influence. There are thick amygdaloid below 1 fe t to the we t of the tar in and one 600 feet to the thi belt at about the horizon of the 0 ceola lode, in ea t. The one to the w t wa op n d 100 feet from which fis mes have been prospected but little. The the Gr en tone flow, wh r it wa 5 fe t wide and well Central fi me wa mineralized at thi general horizon, charged with copper. It wa opened al o 1,000 feet but other fi ure have not been examined where they from the Green tone flo> , where it carried le s coppe:- cross thi belt. ( ee accompanying ections.) The recorded production of th tar Mining Co. 1 4. A fault at the ba e of the Greenstone flow offsets 17 93 pound . orne of the :ein~. Any interruption of the vein Ozark. outh of Copp r Harbor and north and wet along such an mclmed plane would tend to produce a of the tar property. Th veins b ar . 10° IV. and barrier and concentration of solution beneath it. uch 1 have been mined on both ide of the Green tone flow. a b~rrier condition wo~d favor the formation of deTwo veins were opened by adit and three haft· po 1ts, although the eVIdence from the fis ures that I mall rna e of c,opper were frequently found, enough cro s favorable part the Kearsarge, the A~hb~d, to give encouragement but not enough to pay co · and the conglomerate m the outh end of the d1 Th d d d t' · 1 7 915 pound . suuge ts that barrier may not bee ential. Je recoOii:t e pro tuhc wtn 1£ Mos'quito Lake, in ec. 14, METHOD OF EX'PtLORATIOr elected areas along a thick amygdaloid could be pro pected either by sinking a haft and drifting, or in pla es by driving an adit that would permit explora1 tion near the surface. The latter method would eliminate both pumping and hoi ting and would erve in the examination of long stretche of territory, but 1 probably sufficient d pth to explore under the deeper gaps could not be obtained in this way, and it would give only v~ry shallow exploration of the promising fi ures, wh1ch would then have to be examined further by shaft. ron y.- ou eas o 0 feet T. 58, ., R. 29 W. Two hafts were unk 3t d by apart, No. 1 to a depth of 300 fee~, and epper. levels. The vein was wide but fa1led to Y1e Lcok in f M quito a e, Medora.-One nule southwe to I di tely the E . Y2 sec. 17, T. 5 ., R. 29 W., Jmroe /wa outh of the Greenstone ftow. The com~u e but organized in 1851. Con iderable work was onf;und. a relatively small amount of copper wa in the Amygdaloid "floor " were said to be pre ent a other mines. 10 T. Native Oopper.-N orth of Delaware_, lll se:ing 'the ., R. 30 W. Worked on a velll cro~ Ashbed horizon but found nothing encouragJOg.
FISSURE DEPOSITS Conglomerate.- nder the names N orthwe t Copper Co., Pennsylvania Mining Co., Delaware Mining Co., and onglomerate Mining Co. the veins and the Allouez conglomerate at Delaware were worked at different time . The orthwe t opper Co. began operation in 1 47 and developed three fi sure . To the end of 1 59 it had eA'])ended 611,000, and its copper ale had amounted to 32 ,000. In 1 61 the Penn ylvania -Mining o. wa organized to take over the property. Thi company opened three additional vein and undertook exten ive urface improvements, expending 126,000, but produced no copper. In 1 63 part of the territory wa sold to the Delaware ~fining o., under the arne management. The two companie are said to have pent nearly 2,000,000 in the next few years but produced little copper. In 1 66 the property wa taken over by the bondholders. The two propertie were in 1 76 united a the D laware Copper Mining o. This ompany operated with little production till 1 1, when it wa reorganized as the Conglomerate Mining Co. The new company i aid to have expended 1,300,000 in making urface improvement and opening th Conglomerate min . The mine at pre ent belong to the alumet & Hecla Con olidated C pper o. Altogether more than 4,000,000 wa pent, and to 1 6 a total of 7,1 ,000 pound of copper wa produced. t no p riod in it hi tory wa the mine operated at a profit. Three fi ure- w r deY l pcd to a con id rable extent- the tout nb rcr, D la\ ar , and Hocran. The toutenberg wa- op ned to the eicrh h 1 vel, the Delaware to the ninth lev- l, and the Hogan to the fourth l v l. The geologi relation in all the fi urc cern to have been entially th am . Th produ ti e part of each wa clo und r th llouez onglomerate, though the fi ure do not app ar to hav b en :rllined into the Allouez concrlom rat . The report tate that veral amygdaloid 'floor w r pre nt in the mine and that the amygdaloid had a, marked influ n e on the , vein. Tho "floor " w re al o mined and appar ntly furni hed a con id rabl pn,rt of the production. The map how that th toping on the amygdaloid deer a ed away from th fi ure indicatincr that the richne of th ground decrea ed in the ame direction. Conn cticut.-We t of th Delawar . Owned by .\mygdaloid Mining o. Op n d by thr e hafts1 °· 1, near r en tone flow, 60 fathom ; o. 2, 20 fathom ; . 3, 6 to 7 fathoms-and an adit. Adit level r;lriven 551 feet; 10 fathom below adit, drifted 1 1 feet; 20 fath ms b low adit, 514 feet; 30 fathoms below adit, 147 foot. Total r corded yield 116,800 Pound of copper. . Amygdaloid.-Ju t west f th Delawflr . Open d 111 1 60 and op rated throucrh 1 7 . o tatemcot or Ina o P nowing th am unt of de elopment ha been fou~d. R corded pr du tion 1,541,1 0 pound . Eagle llarbor.- Explored a. vein cro ing th Greenlone flow, midway b tw en the Madi on And Amygdaloid gap . It wa reported to carry good copp r a hove the A hbed horizon in ec. . I t eros ed the Gre n tone flow in low, poorly exposed ground, and the e:>..'])loration (1 66) failed to locate the fi W'e. A vein through iadi on gap wa opened in the lo\ ground. It arried orne opper but wa not further explored (1 65) on account of the difficulty of working. A vein we t of the gap was opened by a haft and adit to a depth of 72 feet. The vein wa found 3 Yz feet wide but wa aid to be in "hard rock" and unproftta,ble. The E ex fi ure, whi h pa se through a gap, ' a explored in ec. 16 by an adit. t 500 feet from the Green tone flow a haft 100 feet deep wa unk and a drift tar ted north (1 65 ?) . The vein, where followed by tho adit, wa reported to be rich in stamp copper, but appar ntly further development did not reveal a valuabl depo it. Anoth r ein farther ast, r ported a 3 feet wide and yielding good tamp opper, wa open d in 1 66. No produ tion i recorded from the e explora ion . Madi on.- The Madi on 1ining Co. operated on thr e fi ure - the Perkin , 2,000 feet we t of 1adi on gap, and the Ea t and We. t vein , 4,000 feet we t of adi on gap. The Ea t or main lode ha three haft and an adit le el. No. 3 ha,ft i opened to the 20fathom level, o. 2 to the 30-fathom, and o. 1 only to the adit leyel. haft were connected on the adit, 10-fathom a,nd 20-fathom level , and ome toping wa don . The We t lode was opened by haft a,nd winze to the 20-fathom lev 1 with some toping. It i reported th11t about 250,000 wa expended. The r corded production ' a 72,000 pound . The 1ladi on gap wa not xplored except for a pit that lo a ted a fi ure. Dana.- The Dana fi sure, about 4,000 feet en t; of th ntral mine, wa opened by an adit 7 0 feet lona and b. three haft. , bu it prov d unproductive. opper Fall .-The opper Fall Mining Co. wa one of the earlie t in the eli trict. It conducted operation on v ral fi ure and on the A hbed lode. At difl'crent tim tract have b en et a ide from the oricrinal grant and recombination made. At pr ent the ground belong to the Arnold Mining o. Altocreth r the opp r Fall Co. olle ted · 1,000,000 from a e m nts and paid "' 100,000 in dividend . It ha the di tinction of being th only mine in the north end of the di trict above the Green tone flow that has paid dividend , but it evicl ntly wa not a profitable undertaking. Th mo t pro perous period wa in the late ixties, when a mall but ri ·h area in the Owl reck vein wa being mined. This vein was develop d hy an adit that tart near he ba e of the Great c nglomerat and ext nels through the trap serie , probably into th Green tone flow. There i om unc rtainty fr m the old r ords a to th relation of the oro to the differ nt t pe of rock. In gen ral it ma be aid that th fis ure wa pr due ive only in tlt vicinity of the hbed l cle. pparentl nothincr
THE COPPER DEPOSIT OF MICHIGAN encouraging was found from the Greenstone flow to a short distance below the Ashbed and from a short di tance above the Ashbed to the Great conglomerate. According to Marvine's Eagle River section, there were no truck amygdaloids between the Greenstone flow and the Ashbed amygdaloid. Abo e the A hbed are some amy<Ydaloids but apparently none a thick as that flow. It seems logical to conclude that tho Ashbed amygdaloid was a factor in the enrichment of the vein at tills point. The Ashbed amy()'daloid it lf is mineralized and was mined for 1,000 feet or more on both ide of the fi sure. o statement ha been found to indicate whether it was notably richer or poorer near the fissure, though the old stope map UO'O'ests better ground near the fissure than at a disoo tance. Datolite is abundant in the Owl reek fi sure and in the Ashbed amygdaloid. As the A hbed wa mined for part of the time the production from the fis uresis not known accurately, but it is e timn ted a follows : Owl Creek fis ure, 7,2 3,000 pounds; Copper Falls :fi ure, 731,000 pound ; Old Copper Fall fissure, 6,000 pounds; Hill fissure, 501,000 pound ; Childs fi sure, 32,000 pounds. It i e timated that the A hbed amygdaloid yielded 17,706,000 pounds of copper. Petherick.-Tho Petherick fissure is about 2,000 feet west of the Owl Creek fissure and has been developed in the same general stratigraphic horizon. It has been opened, so far as known, continuously by adit and shaft for about 2,300 feet along the trike and to a ma.'rimum depth from the outcrop at o. 6 shaft to the adit level of about 225 feet. ( ee pl. 50.) To accurate record is available of the stoping on this fissure. There was some stoping on the Ashbed amygdaloid adjacent to the fissure working , of which, too, there is no record. It i therefore not known how much of the production of the Petherick Mining Co. came from the :fissme and how much from the A . As indicated by the material on the dump, datolite was abundant in the fissure and in the A hbed adjacent to the fissure. In this respect the Petherick resembles the neighboring Owl Creek fi sure. Old Copper Falls.-The Copper Falls Co. began work in 1 45 on the Old Copper Falls fissure. The outcrop was exposed in the falls of the strE--am. The worl- was continued till 1850, and a depth of 267 feet was attained. Some good ground was developed, but the production was small and the operations were unprofitable. o1·thwestern.- The Northwestern Minin()' Co. beo-an
b t::l operatiOns m 1845 on a fi sure below the Greenstone flow and worked rather continuously till 1857; some was also done later by this company on the ongmal fi Ul'e and on the southward extension of the entral fi sure. A sessments to the amount of $22 ,000 w re collected, and copper to the value of about $75,000 wa produced. The workings compri~ four shaft , 109, 201, 215, and 225 feet deop, anailit 1,226 feet long, and 1 vols os. 10, 20, and 30, re'pec. ti ely 944, 1,057, and 124 feet long. Tho recordoo produ tion i 313,000 pound . Oentml.-Tho de cription of tho Central vein il compil d from the mine maps and from Hubbard'· account. The entral mine was opened in 1 · and clo ed in 1 9 . During th.is period it yirldel 51, 75,527 pounds of copper, and tho compltllypaid about , 2,130,000 in divid nd . Tho mine i opened on a fi ure vein striking nearly nt right angl , to the bed and dipping very tee ply to the en. t iu the upper level and liO'htly le steeply in the lower level . There i no pronounced gap or outcrop of v in in the face of tho r enstono bluff to indicate where the :fi urc cro e . It rna be off et by n trike fault at or near the ba e of the Green t{)ne fiow. The :fi ure wa di overed by outcrops and in ancien pit about 600 f et outh of the Greenstone bluff. The productive part near tho urface was clo e under the Gre n ton flow, though the minable portion nowhere cems Lo have extended to or into the Allouez conglomerate. ith in rea ed depth the mineralized portion gets farther and farther from tho Green tone flow. The ore sho t has it gr ate t extent along the strike of the fi ure at about the 100-fathom level. Below that it narrow to about the 200-fathom lml, where it a()'ain expand ; it ontinues to the Kearsal'it conglomerate at about the twenty-ninth level, where the :fi ure is di pla eel by a fault. The principal structural feature are the main :fi ure and the trike fault at the Kearsarge conglomerate. The fault cu!' out the Kearsar()'e con()'lomerate and offset the rem b b below the fault 2 4 feet to the we t. Tho r~ct that the thick conglomerate is completely cut out by the strike fault sugge ts a large movement of which the horizontal off et of the fissure i a mall component. Below the fault what is regarded as the continuation of the fissure was found to contain but little copper, d' I though the fissure appears to be wide. o
statement is made in Hubbard's description regarding · d f liner~· the age of the fault relative to the peno o 0 . ed ization. As the breccia along the fault is mincrnhz however, it is probable that minerEtlization follow the faulting. . f the No detailed de cription of the charactel 0 d amygdaloids intersected by the fis~ure has beonf~~:of Pumpelly briefly described those m the uppor P da· the mine. He mentioned three soft brown amyg d 1 · 1 merate an 01ds between the Calumet & Hec a cong 0 t the the Houghton conglomerate. These are A.t abou
'd out upWSlll· honzon where the lode begins to Wl en C lumel The character of the amygdaloids below the 1 dis· & Hecla conglomerate is not know~. Ce~tr;heone mond-drill hole No. 9, west of the rome, an ental at Arnold Gap (No. 11) show thick fra,UJll
FISSURE DEPOSITS aroygdaloids above and below the Houghton conglomerate. The cause for the concentration at thi point is su ceptible of several explanations. If the faulting preceded the mineralization, it is hardly reasonable 00 uppose that tlle mineralizing solutions rose along the fissmc below the fault and then jumped across to the portion above the fault. If mineralization preceded faulting and the movement was of great magnitude, a barren part of the fissme might be brought into contact with a mineralized part. The mineralized portion of the fi sure is inunediately above the point 1rhere the conglomerate is cut out. Thi , together with the fact that the crushed portion of the Kearsarge conglomerate is mineralized, has led to the suggestion that the solutions ro e along the conglomerate and escaped into the fissure where the conglomerate was cut out. The rea on for the variation in mineralization along the fissme is not clear, and little information · available concerning the character either of the fissme or of the inclosing bed to give a basis for an interpretation. The map show , however, a di tinct tendency for the expansion in the hoot to extend along the bedding rather than aero s it. This suggests an influence of the beds in precipitating copper. The soft brown bed noted by Pumpelly at about the horizon where the upper expansion occurs may have influenced the precipitation. Whether similar beds are conn ted with the lower expan ion is not known. Tho mincrnlization did not extend to the Greenstone flow, and o far a can be judged from the map there i little C\"idenc of the d fleeting ot· rlamming influence of tlu flow. There appear to haYe be n orne min ralizotion of ev-eral of the amygdaloid near the fis urr, and the Calumet & Hecla conglomerate wa well mineralized adjncent to th fi sur at about the eiO'hte nth level. ~owhere wa commercial rock found to extend far from the fi ure. In the alumet & Hecla conglomerate ore extended about 40 feet on each ide of the fi ure. The Houghton eonglomerate wa reported a well mineralized, but no stop.ing wns done on it. Winthrop.-The Winthrop Mining o. worked several years on a fi sure in the W. 34 ec. 23, T. 5 ., 31 W., west of the entral min . 1 o production I reported. Eagle River.- The Babbitt vein, l ,000 feet cast of the t. Clair, was open d in 1 0 by the EaO'le River
o., which put down two shaft , 275 feet apart, one close to the Green tone flow. The recorded production is 49,67 pounds. St. 07,air (acquired by the Phoenix Consolidated ~?PPer Co.).- The t. Clair vein is east of the Eagle GIVer gap, and the mine is immediately under the Hoenstone flow. A fault or 11 slide" branches from the Greenstone flow contact about 150 feet below the outcrop. It dips more steeply than the contact and thu diverO'es from it wit~ increasing depth. At the lOth level the stratigraphic distance between the Green tone flow and the fault i about 350 feet. Practically all the stoping has been done between the Greenstone flow and the fault. The stopes eem to extend up to the flow and in places cross the fau:t but have extended only a short distance below it. The mine was opened to the twelfth level. The vein is said to have been rich, carrying 2 to 3 per cent of copper, but it wa narrow, and the mineralized area wa relatively small. Under the conditions of operation it evidently did not pay. Bay tate.-The Bay State Co. operated on the Phoenix or Bay tate fi sure, south of the Phoenix mine, and was later absorbed by the Phocni~ o. Phoenix.-The Phoenix Copper Co., now absorbed by the Keweenaw Copper Co., was organized in 1 44 and was one of the earliest companies in the district. It operated on numerous veins and on the Ashbed amygdaloid. The total a se ment by the old Phoenix and the Phoenix Con olidated are given by tevens as 2,3 5,500, and the dividends as $20,000. The only really profitable operations seem to have been conducted for a few year in the early seventies on the Phoeni~ fi sure. Phoenixfissut·e.-The only description found of the rocks under the Green tone flow in the Phoeni."X mine i that by Marvine. Thi description doc not give the impr sion of any particularly thick amygdaloids in the mine. There i a belt of thin flow , but the amygdaloid are apparently small. The Allouez conglomerate i repre ented by a 11 lide." Exten ive toping has nowhere been carried more t.han 1,400 feet from the Green tone flow along the level, or about 700 feet aero s the bed . J othing has been seen in the report to indicate where the riche t ground was found. The vein evidently varied in grade from place to place, but ther i no tatement of the conditions a companying thi variation. either is it stated whether or not there wa a notable change in grade f1·om the urface downward. The deepest workings on the inclined haft are at a vertical depth of about 1,000 feet. tevens tates that the yield from 1 72 to 1 5 wa 473 pounds per fathom, or about 1.5 per cent. o m ntion is made of operations on amygdaloid . Robbins or 1Vest.-The Robbins or West vein was developed by the Phoenix Co. a short di tance west of the Phoenix or Bay tate vein. It ha a more easterly trike than the Phoenix and cuts the beds at an acute angle. The mineralized belt, as indicated by the stope map, is 100 to 250 feet wide and 50 to 75 feet below the Allouez slide. The maps indicate but one amygdaloid belt, 300 to 350 feet below the stopes, but other amygdaloids are undoubtedly present. The mine has been opened to a vertical dl:'pth of about 600 feet.
THE OPPER DEPO IT OF MI HIG ome good ground wa found, but n a w?ole it did not pay. The vein i aid to ha e contamed no rna copper, producing stamp rock only. Old Phoenix.-A vein was encountered under the bed of Eao-le River near tho A hbed cro sing and followed for ~everal hundred feet. One account of this vein describe the copper and ilver a occurring wi_th waterworn pebbles, ugg ting a plao~r depo 1t. Other indicate that it is a vein that ha b en followed by the river. A few thou and pound of copper and ome silver was t 1ken from thi vein. It apparently was never developed at depth except where the A hbed drift cro ed its downward exten ion. There it i a thick calcite vein with orne copper but not in <'Ommercial quantitie . Vaughnsville.- The Cliff Copper o. opened the Vaughnsville fissw·e, nearly a mile outh of the Greentone flow. The stronge t mineralization wa found at the intersection of an amygdaloid suppo ed to be the Osceola. Oliff.- The Cliff mine, on the I iff fi ure, ' a the fir t laro-e copper producer of the Lake uperior region. Production began in 1 45, when it yielded about 20,000 pound of copper. The mine wa operated, with the exception of an interval from 1 70 to 1 72, until1 3. It wa idle from 1 3 until1906, when it wa reopened and some amygdaloid in the upper level were explored adjacent to the fi sure. total of 3 ,207,000 pound of copp r wru pr due d, and the company paid 2,51 ,620 in dividend . The productive portion of the liff fi ure lie under the Green tone flow. At the mine the Allouez conglomerate i repre ented by the " lide," a few inche of clny gouo-e. Immedintoly under the lide i a eric of :nail flows numbered in the Cliff mine upward from 1 to 13. The e have an average thiclme of about 50 feet, and o far as can be judged from the old map , from one-third to one-half of the rock in this belt is amygdaloid. The five bed next to the Calumet & Hecla conglomerate average about 90 feet in thickne . The series of thin bed beneath the Green tone flow form a relatively weak zone, a i indicated by the pronounced depr ion in the bedrock urface just south of the Greenstone bluff. The thicke t amygdaloid, as indicated on the map , is o. 13, the one immediately beneath the " lido." ?· 9 is al o indicated on the maps as a thick amygdaiold. o detailed de ription of the amygdaloid has been found, and it i therefore not known whether they are fragmental or how well they are oxidized. Examination of the dump indicates that there i at least one fragmental, well-oxidized amygdaloid. The diamond1 drill section west of the fis ure show some thick fragmental amygdaloid below the Houghton conglomerate. The developments have been confined to beds above the alumct & Hecla conglomerate. cuts n arly at right aug! , to tht pl to th a t, with local reversal of dip. It i w 11 exp d a a ' ide veined an~ battered zone in th fac of th rccu ton bluff and ha b en follow d from a point south of the tiff mine worl ings o th lake hor . In plac in the mine working it bran h s. Th r are two " lidc "noted in the mine worl ings- on at the horizon of the Allou z onglom rat and on that r ache the urface at about o. 2 haft, uth liff. Both arc c ·entially parallel to the b d , and both have di placed thefi urt but lightly. The cond lido has two branche for the first f w hundr d f t. Ju t north of o. 3 haft, liff, the lode i r d by a trong zone ol fi urino-, which i r pr ut d on the map as verti· al. Littl dev lop mont work ha be n done south ol tbi zon . The min ralizn.tion wa in tho main confined to the fi ure, though th r wa om min ralizatiou of the amygdaloid . II r , a in th mor productive part of th mine, the amygdaloid fn· clo ely paced, and the old map how no 1 r lation b tween rna of copp r and am gdaloid . Old r port peak of rich copper in th ein a ociat d with tho ninth and thirteenth floor , and n on of th old map. pecial rn ntion i made of ri b ground in the fi ure where it int r ect th thirteenth floor (ju t b low the lide) from the 30-fathom t th 60-fathom level. In the low r l v ls, how v r, min ra.lization docs not eem to have been trono- in the hirt enth floor. Mention i al o made of ri b o-round whrre the fi;. ~ure plit and includ a hor e of the country rock. To the north the mineralization was limited by the lide. The vein p os through the Green tone flow but ha not been found to contain commercial copper there. The orth liff working are at the intcrsec· tion of the fi ure with the hbed amygdaloid. Here the vein i said to b a zone of fis uring 10 feet wide, but it contained relatively little copper. h d. ·b t. oft e o very clear de cription of the 1 tn u wn rd ha copper in the fi ure south from the llouez been found. The general impre ion gain d from t~e old report i that the v in wa riche t clo e to t; Greenstone flow and grew lean r toward tho outh, that the di tribution wa irregular, the rice t P being associated with the inter cction of amygda 01 d. nt is mae In some of the old report the statcmc h that the mineralization wa cut off on tho
g · . 1· ttle stoplll " lide " and the maps show that very 1 , ' · ay ha1e was done outh of that lide. The em beJore about reached the limit of profitable working! t the pa ing the lido, and therefore it is not cl~ar_ 1a the slide it elf was an important factor in ~un _tulgl'erl · 1· · d · eraltzatJOn · mmera 1zatwn. The ft uro an mm f 0 al evidently extended south of the slide. Expl~rAtn ol o. 5 shaft, which is on the southern proW
FISSURE DEPO ITS the Cliff vein, has failed to di clo e a strongly mineralized fis ure. Two pos ible causes for the richn of the fis ure benea.th the Greenstone flow have been suggested: 1. The fissure has been off et at the slide about 20 feet. If this offset occurred before mineralization, the interruption of the fi sure and the pre ence of the gouge of the slide would form a barrier that might result in A. concentration of olutions ri ing along it. 2. The area of greate t productivity is in a belt in which amygdaloid are very abundant, and there evidently was a relation between richness of the vein and some of the amygdaloid . Th available description of the amygdaloids is too meager to judge of their character, but if there are everal well-oxidized amygdaloid they might be an influential or even a controlling factor in the mineralization. orth Oli.ff.- Tbe orth li.ff Mining Co. wa organized in 1 5 to work the exten ion of the Cliff fi sure above the Green tone flow on larid et apart by the Pitt burgh & Boston Mining Co. The Cliff fi ure had previously been traced by pit every few hundr d feet from the mo t northerly liff haft to th ba e of the Great conglomerate, a di tance of 9,000 feet. [n the Green tone flow th fi sure wa found to be not more than 14 inches wide and contain only a little copper. In the A hb d lode the vein wa found broken into numerou brancbe for a width of 10 feet or more, and the branch were well filled with barrel and stamp copp r. Tbre vertical haft w re unk on the fi w· n ar th A hb d lod , one to the 30fathom le 1, and an adit wa dri en outh for mor than 1,700 fc t, cutting the A hb d. The production to March 21, 1 64, was 5,657 pound of r ·fined opper tak n from tho fi ur a mo. n inclin d haft wa a o unl on th hbed in or n ar th liff fi ure, and om drifting ' a don on that lode, but there i no r cord a to th r ult obtained. orth Am rican.- The orth Am rican Mining Co. worked for fom year on a fi ure under th r on ton flow in th E. Y2 ec. 2, T. 57 ., R. 32 . The workings aro on th north ido of the orth American gap, and the bearing of th fi ur , . 5 ° W., i such that it oon enter th !Yap. It wa worl d to a depth of 415 f et. The total yield was 445,000 pound of :efin d copper. Th fi ur i split into thro part m the upper lev I . There appear to b a difference of about 30° in th trend of the fi ure and that of the gap. Albion-Manhattan.- Th. lbion-Manhatta.n o. in unk a shaft 115 f et through the Gr en tone flow, drove an adit to connect with it and unk 200 feet below the adit level. The vein 2 Y2 feet wide but barren. Later a haft unk to a d pth of 70 feet near the Green tone flow yielded 5 ton of copper. - Mohawk. overal a1 enide fi ure have been pro - Pected in the north end of the Mohawk min . The main mineralized area i at the cro ing of the Kearsarge lode and extend for a short di tance into the hanging wall of the Kear arge. A fi ure opened south of o. 6 Mohawk haft contained orne copper near the inter ection with the lode. The lode i al o reported a rich near the fi ure. Fulton.-The Fulton fis ure was opened in 1 53 in the W . e . 33, T. 57 N., R. 32 W. The vein was 1 inche wide. The arne fi ure ha been opened in the ort;h Ahmeek mine, where orne mas e of copper have been found, but a it i ar enical litt,le has been mined. What, eem to be the ame fi ure ha been opened und r the Gre n tone flow. The vein material on the dump contain opper, but no record of the work ha been found. The recorded production from this fi ure by the For ythe Mining o. ' a 1,255 pound , and ome opper ha al o been produced by the Mohawk and Ahmeek minin(Y companie . Mas .-Th Ma fi ure of the Ahmeek mine' here it ro e the Kear arge lode trike about . 20° W. and dip teeply to the ea t. The fi ure ha b en opened to the twenty- ixth level. Along the trike it ha been developed to maximum di tance of about 1,100 feet to the northwe t from the Kear arg lode and about 600 feet to the outhea t. lido fault inter e t th fi ure about 200 feet tratigraphically and 300 f et horizontally above the Kear ar(Ye lode. The fi ure, however, i not di placed. The fi ure \arie con iderably in character from place to place. ommonly the fi ure zone ha a width of 2 to 4 feet, but it rna pinch to a few inche or may spr ad to con id rably more than the avera!Ye width. Where the fi ure zone i broad the rock within i sheared and brecciated. al ito i th roo t abundant vein mineral. Locally a foot or mor of calcite occur~ in the fi ure. Quartz, epidote, prehnite, and laumontite are locally pre ent. Copp r occur typically in larg irre!Yular more or le s lenticular rna e . In place there i a olid rna of opper a foot or e en more in thickne in the vein. om rna e containing more than 200 ton of copper have been min d. Where th ma ive copper occurs theotherveinmineral areu ually par elyrepre nted. Chloritization i the roo t characteri tic alteration of the wall rock and the breccia within the fi ure, though th re i some ericitization. Mo t of the copper has been mined within 400 feet horizontally above and 200 feet horizontally below the Kear arge lode. Copper is known to occur 1,000 feet from the Kearsarge lode, but the rna e beyond 400 feet are mall and scattering. Little copper has been mined above the ninth level. The general di - tribution of copper is shown in Plate 51. The Mass fissme to the end of 1925 is estimated to have yielded 11,567,000 pounds of copper. Arsenide.-The Arsenide fissures in the Ahmeek, Mohawk, and eneca mines have the same general dip
THE COPPER DEPOSITS OF HCHIGAN and strike as the Mass fissure. They hn.ve been developed but a short distance away from the Kearsarge lode. The principal vein minernl are quartz, calcite, ankerite, and the copper ar enide . Albite, prehnite, and laumontite are present in variable amounts. The typical rock al!ieration a ociated with the Arsenide fi sures is chloritization and ericitization. In places the veins contain a foot or even more. of nearly olid copper a1 enides at their intersection with the Kear arge lode, but there ha b en little production from these veins. The Mine ota conglom rate is a few hundred f above the Ever~r .n and su ceeding lodes, and~~! alico amygdaloid 1 about 125 f aoove the '1' ,1 me. sota conglomerate. ext above tho 0 alico lodo i th orth lode, on which some d velopmont work, he b en done. The b ds dip 47°-50° ., steepenin~ slightly with in rea d d pth and toward the south. west. triking approximately with the bed but dipping at a steep r anglo i the Bran h v in or fi ure. The outcrop is mainly in the hanging wall of the ali co lode except b tw on haft A and B. At shaft B th Branch v in i repr en ted a diverging from the Calico lod abovo the fifth level and entering the conglomeril.te b n th thirteenth and fourteenth , level . The dip varies con iderably from place to Minesota and Branch fissures and Oalico lod .- The occurrence of the ore in the Calico lode of the Mine- I sota mine i closely associated with that in the fissures, and they are therefore de cribed together. The statements here given are based on old de criptions and company maps and records, a there wa no opportunity for underground examination. The copper occurs mainly in o northward-clipping beds and in strike fissures that parallel the beds or dip more steeply than the beds and cut them. The lower bed, the Mine ota conglomerate ( outh Branch)1S about 125 feet below the Calico amygdaloid (North Branch). Striking nearly parallel with the bed is the Branch fi sure (Middle Branch), which cuts both t~e Minesota conglomerate and the Calico amygdalOid. The Minesota fissure is represented as diverging from the Branch fissure where the latter cuts the Minesota conglomerate and as following the top of the conglomerate to the outcrop. The operations on the Minesota fi ure (pl. 52) were nmong the earliest and have been the most profitable in Ontonagon C~unty. o separate record of the copper from the Mrnesota and Branch fi sures and Calico lode is available, but mo t of the output came from the Mine ota and Branch fi ure . Production began in 1 4 . To 1 0 a total of 53,000,000 pounds of copper wa pr_oduced from the 1inesota, ational, and Rockland mrnes, and dividends of 2,140,000 were paid. . 'l'he Michigan Copper Mining Co., began operations m 1899. From 1899 to 1912 the Calico lode and the B~anch vein were rather extensively opened and mmed. . The Branch vein was apparently the most productive. A total of 17,180,000 pounds of copper was pr?duced. The yield from the stamp rock probably did not exceed 12 pounds to tho ton, but there was much mass copper, especially on the Branch vein. Production and dillidends from .Minesota and Branch fissures and Caluo lode Dividends Mine Period Copper produced (pounds) Total Per pound of copper (cents) 34, 707, 000 $1,820,000 11, 613,000 320, 000 1854-1880 5,821,000 0 9, 174,000 Calico lode 1900- 1913 as, 006, 000
69, 321, 000 2, 140, 000 Estlmated . plac . At the ontact with th conglomerate the Branch fi sure i r pro ent d a splitting off from the outh or Mine ota fi ure, which i hown a following the hanging wall of th conglomerate to the outcrop. There was apparently little di placement of theheds on the Branch fi ure, though in places at least there seem to have been much battering of the rock. Other fi ure are mention d in the record but do not seem to have been of gr at importance. The Mine ota conglom rate where seen on the ou~ crop i a pebble to boulder conglomerate composed mainly of fel itic material and imilar to the other fel itic conglom rate of the area. In some action' it is repros nted as 25 f ot thick and underlain by nearly as much sand ton , though it doubtle rarif· in thickne and average less than 25 feet. The Calico lode is apparently a fragmental lode varying in thickne s and in character from place to place, as i characteri tic of the fragmentallod in general. The Mine ota fis ur follows the hanging wall of the Mine ota conglomerate from the outcrop to its intersection with the Branch fissure. The copper occuned characteristically in masse , some of great ize. One rna s of 527 tons, the large t over found . was taken out in 1 56. The masses arc s~tid to have occurred both in the fissure and in the underlying conglomerates. Apparently much of the replaced conglomerate but was clo ely n ociatcd with the fissure. Where seen on the dump the copper bearing conglomerate shows the bleaching by remova of iron characteristic of conglomerate mineraliznt~on el ewhere. The Minesota fissure WitS producti~t from the surface to about the 140-fn.thom !eve: Beyond the junction of the Branch fissure it app~a~ to have been poor, this junction and those of mmo fissures it was apparently rich. . b the The developments on the Calico amygdaloid Y d Michigan Copper Mining Co. showed the best grounh b · · · th the Drt!DC to e at and above the mtersectwn Wl fi · · The-- ssure, especially m shafts A and B. . shaft fair ground reported below the intersectiOn l1l
FISSURE DEPOSITS C, but not much was stoped. The Calico lode yielded little mass copper, the output being mainly stamp rock. The Branch fissure was mined by the tfichigan Copper Mining Co. nearly to the intersection of the Minesota conglomerate between shafts B and C, but at the intersection it was said to be lean. It is not clear from the descriptions whether the fissure continued on its normal dip through the conglomerate or flattened into the dip of the conglomerate. The copper occmred mainly as mass copper, but there was considerable production from stamp rock. LARGE-SCALE MAPS AND GEOLOGIC SECTIONS The surface map of the di trict were prepared on a scale of 1 inch 500 feet. A small e-dition of the e maps was published in 1925. The cro s ection were prepared on a scale of 1 inch 200 feet. Part of them were prepared on tracing cloth and can be reproduced by blue printing. It wa not found feasible to publi h the detailed descriptions of section , but two copie of such records have been prepared. The ori<Yinal plate of the large-scale surface maps and of the cro s ection have been deposited with the 1ichigan chool of Mines and Technology at Hou<Yhton, together with one copy of the de cription of g ologic section . A cond copy of the de cription of g ologic ction has be n d po ited in the Alumet H cia library at alum t. A f w copie of the large- cale map ar · a ailable for di tribution by the United tate Geolo<Yical urvoy. ADDENDA TO BIBLIOGRAPHY The following entries wore obtain d after thi report was in page proof: BALDWIN, c. KEMBLE. Tailings di po a] plant at the Wolverine mill: Eng. and 1in. Jour., vol. , pp. 71- 73, 1909. BLAKE, WILLIAM P. The rna s copper of Lake uperior mine and the method 1 of mining it: Am. Inst. Min. Eng. Tran ., vol. 4, p. 110, 1 76. BnoDEntCK, THOMAS MoNTEITH, and HoHL, . D. Geophysical methods applied to xploration and geologic mapping: E on. Geology, vol. 23, pp. 4 9-514, 192 . CAMPBELL, A. c. The copper and iron bearing rocks of Lake uperior: Eng. and in. Jour., vol. 31, pp. 20- 21, 1 CooPER, JAMEs B. The history of copper smelting in the Lake uperior region: Eng. and Min. Jour., vol. 71, pp. 529-530, 1901. CRANE, w. R. Drilling practice in the Lake Superior copper mines· Drifting and stoping at Lake Superior; Underground or~ handling at Lake Superior; haft sinking at the Wolverine mine; Ore breaking at Lake Superior; Mine timbering at Lake uperior: Eng. and Min. Jour., vol. 2, 1906. Norwich.-The Norwich mine, to 10 miles southwest of the Victoria mine, wa productive intermittently from about 1852 to about 1870. The records show an output of 993,360 pounds of copper. The operations were mainly on fissures eros ing the beds. The fissures contained some large masses of copper, but considerable rock was also milled. The fissures are described as quartz-epidote veins. The Norwich property was later e:A"J)lored by the Ca s Copper Co., mainly by diamond drilling. Northeast of the Norwich mine there were some early operations on fissures, but apparently little copper was produced. Enw ARDS, G. E. The Quincy mine, Michigan, from stope to smelter: Min. and Eng. World, Apr. 20, 1912. FRASER, LEE. Practice at the Osceola. mill, Lake uperior: Eng. and Min. Jour., vol. 83, pp. 11 0- 11 3, 1907. HODGE, WALTER R. The Ahmeek mill, Hubbell, Mich.: Eng. and Min. Jour., vol. 94, pp. 749-571, 1912. HonE, REar ALD EDWIN. Methods of prospecting and developing deposits in Michigan: Canadian Min. Jour., Jan. 1, 1913. HouGHTON, JACOB, Jr. Early hi tory of the mineral region of Lake uperior: m. Min. Jour. and Railroad Gazette, vol. 1, pp. 57-59, 1 47. LowE, FRANCIS A. The ilver Islet mine and its present developments: Eng. and 1in. Jour., vol. 34, pp. 320- 323, 1 MoFFETT, . E. Romances of the world's great mines, III, Calumet & Hecla: Co mopolitan, April, 1903. p All'fE, RALPH D. The story of a copper mine: Outing, June, 1907. RICE, CLAUDE T. Baltic method of mining: Eng. and Min. Jour., vol. 93, pp. 43- 47, 1912; Sinking the Hancock o. 2 shaft: Eng. and Min. Jour., vol. 95, pp. 7 7-791, 1913. ROLKER, CHARLES - 1. The Allouez mine and ore dre ing, as practiced in the Lake Superior copper district: Eng. and Min. Jour., vol. 23, pp. 274-275, 294-296, 314-315, 335- 336, 1 77. INGEWALD 1 JOSEPH T ., Jr. Genetic compari on of Michigan and Bolivian copper depo its: Econ . Geology, vol. 23, o. 1, pp. 55-61, 192 ; Review of "Beitriige zur Fra.ge der Entstehung der Balima.nischen Kupferzlagerstiitten vom Tyrus Carico," by Bruno Geier (1 eue Jahrb., Bcilage-Ba.nd 5 , pp. 1- 42, 1927): Econ. Geology, vol. 23, pp. 5 3- 5 4, 192 . KEWES 1 EDWARD. Electric ore-finding y tern: Eng. and iin. Jour., vol. 75, pp. 780-7 2, 1903. TO E1 CHARLES J. Lode copper mining on Keweenaw Point, Michigan: Min. World, October, 190 . WINCHELL, rEwTON HoRACE. Ancient copper mines of Isle Royal: Eng. and Min. Jour., vol. 32, pp. 184-186,· 201- 202, 1 81.
INDEX Page A Acknowledgments for aid Adventure company, production bY Aetna company, production bY Age of the rocks -- Ahmeek company, dividends paid by production by -- 76--77 Alaska, copper deposit-S in 143-144 Albany & Boston company, production bY Albion-Manhattan prospect, opening of A!godonitc, formation and properties oL 56--57 Algomah company, production bY Algomah lode, features oL --- Allouez company, dividends paid by .IJiouez conglomerate, development on 1 1-1 2 longitudinal sections oL Plate 37, in pocket .IJJouez mine, features oL of rocks, causes and effects oL 34-45 Amygdaloid company, production by -- --- 77-7 Amygdaloid mine, working oL - Amygdaloidal conglomerate, origin oL 20-21 W Amygdaloids, bottom layer oL Amygdular Inclusions, glaciated surface showing resistance or, plate showing Arcadian company, production by Arcadian lode, features of. Arnold company, production by Arsenides, occurrence or. 56-- dirccllon or movement oL Ash, occurrenco or._ Ash bed amygdaloid, deYclopmcnts on J76--J7i nature and min ralization oL--- Ashbed company, production bY Ashbed lode, longitudinal sections oL Plate 34, in pocket Atlantic company, dividends pald by Atlantic mine, features and production oL 1tmospbere, possibility or oxidation or iron in Java tops bY B Raltlccompany, dividend~ pale! bY D 1 Production bY 0 \1C lode, extent and correlation or ongitudln<ti S'lCtlon~ oL- - Plato 49, in pocket mineralitlltlon or 21~220. 221 structure or DaiJ 21 -219 D est lodo, features or 0 niT crs, effect or '
D ate company, production by ay tate prospect work on m D~It_company, production b;:: ::::: Dbhography on the copper de sits addenda to po
3-!4
Page Bleaching, oxidation indicated bY 133-136 Branch fissure, operation on 232,233 Broderick, T. 1:., and IIohl, C. D., Geophysical methods applied toe~plora - Butler lode, description of Caledonia company, production by Calico lode, operation on 232-233 Calkins, F. C., acknowledgment to nlumet, view oL alteration in, plate showing longitudinal section or- Plate 3 , in pocket thick:n Calumet dividends paid by Canada, copper deposits in 14&---146 Carbonates, occurrence oL. Carp Lake company, production bY entennial company, dividends paid by Central company, dh-idends paid bY hampion company, di,·idends paid bY berokoo mine, opening oL- -- Clark company, production bY --- -- Clark prospect, opening oL lifT compen_y, production by !iff mine, lodes in Composition, chemieal, of the rooks, influence of, on the p sition or ore shoots. Concord company, production bY Conglomerate, nature and source of. . 1 21 Conglomerate mine, development oL onnecticut company, production by Contact opper opper, content or, in the basalts 4&---46 deposition or, cau e oL. --- by reduction or arid itY 139-141 depo~ its or, principal types oL 101, 157 intergrowth or, with sih·er, plate showing Copper Falls company, dividend paid hY Copper Falls mine, description or. development oL. 227-228 opper Range, geologic map or, from Adventure to Victoria Plate 13, in pocket geologic map or, from Atlantic to from Grat iot to La aile ... Plate , in pocket
I DEX Page Copper Range, geologic map of, from Keweenaw Point to Mount from La Salle to Atlantlc --- -- Plate 9, Ln pocket map oL.- Plate 3, in pocket stratigraphic sections oL ... Plato 15, in pocket topographic map of, from Painesdale to Cliff, Mich Plato 4, in pockot Copper Range company, dividends paid bY -- Coro Coro, Bolivia, copper deposit at. D Dana prospect, opening oL --- - Delaware, development at. .. - Delaware company, production bY --- Deuton, F. W., quoted --- --- Depth, persistence of metals with 114- 115 richness in relation to Derby company, production by Descending solutions, precipitation from 122-124 source of copper in ... --- --- 120--121 Development, methods of.. -- 9 gg Diamond drill, use or, in exploration 152-153,153- 154 Douglass company, production bY Douglass Houghton company, production bY--- E Eagle II arbor prospect, opening of Eagle River company, production·;; - - - - opcnmg oL Enrichment, downward, evidence on. ::::::::::::::::::::-il2-114 Evergreen Bluff company, production bY --- Evergreen lode, development on --- ZJ<I-215 !48-150 F Faults of tho district.. influence of, on tho position of oro shoots Felsite conglomerate, bod underlying · -· nature and distribution or.
F lng, !Jerman, acknowledgmon-tt~:::: :: ·- -- -- 13H36 Field work record of
F lssur , influence or, on the position of ore shoots.
mioornlized, distribution of --- · llt- 118
production and "ci[~jd~;d;·f~~;,;-- m-226 sections showing development ~i; pj - 72, 2Zl Flint Stool River company, production by ate 50, in pocket Flows, thick, influence of, on the position ;(~;;~i_;;;t; -- -· Fluorite occurrence of
llS ---
Pagt u lnfluonco of, on the position of oro shoots~::::::::::: :::·:·:::::::·
Forest lode, d ription oL -- ·· ,16 longitud inal sections oL PI te 4i Franklin compauy, divldouds paid bY '
!.1 Freda sandstone, occurrence of. : - lSI Fulton company, production bY Fulton mine, work on :::::: a Garden City company, production bY a f
Oeolog1c work, suggestions for --- IM-ll6 Geophysi_cs, electrical methods of oxploratiou bY 1 !CO Grand Portage company, production bY Gratiot company, production bY :::::::::::::::: llancock company, production bY · Hancock lode, longitudinal sections of Plato 35,1o pocket ·:: Hematite. Ste Ferric iron. llillonbrand, W. F., acknowledgment tO · Hilton company, production bY Hob!, C. D., with Broderick, T. M., Geophysical methods applied to exploration and geologic m ppin&-- 1:.6-llS Houghton Copper company, production by Huron company, production bY --- --- Hydrocarbon, occurrence oL Hydrothermal action, possibility of oxidation of iron in Java tops by lHZ Igneous rocks. See Extrusive rocks and Intrusive rocks. Indiana company, production bY lndiaua mine, felsite oL -- zr.-2:?3 Intrusive rocks, nature and kinds oL· -- Investigations, earlier lron City prospect, opening oL Iron or.ldes as seen in polished sections, plates showing._- -- Island company, production by Isle Royale company, dividends paid by .. -- --· --- -- production by Isle RoYale lode, deposition of ore on.- 2<&-211 extent and correlation oL -- 203--:'01 longitudinal sections of -- Plate41, in pocket nature of rocks of. 20HI :!13 structure oL 200-~ Isle Royale mine, view north from, plato showing._ Isle Royale property, openings on m K Kearsarge company, dividends paid bY Kearsarge flow, description oL ... 191-116 Kearsarge lode, causes of rich and PQor ground on .. -- 11/H'II'l content of ore at and below the surface in --- II! longitudinal section of Plate 40, in pocket mineralization of J9S-IS'l Kenney, H. C., acknowledgment tO Keweenaw Copper rompany, production bY -- Keweonaw fault, age and cause oL 5or63 Keweenaw mine, longit_udinal sectio~:s of Plato37,1n pocke: Keweenawan and assoCiated rocks, geologic map and sections oL Plate 2,1n poc:n ~oweenawan series, subdivisions oL 11· Knowlton company, production bY
I NDEX Page La Salle comP!\JlY, production by-- -- -- --- !Ale LaBelle company, production by- - - longitudinal section oL-- Plate 4, 10 poe ct Lake mino, opening --- 214, 21: J7.1 !AlkeSuperior company, productiOn bY--- -- L.ke Superior syncline, features oL-- : . --- e ' Leaching near surface, evidence on-- --- -- --- Lode, use or term --- Lodes, amygdaloid, distribution or copper rn_-- 109--~ 10 brecciated amygdaloid, character oL -- 10&- 07 mineralization oL 107- 10 cellular amygdaloid, nature and mineralization oL 108-109 1:onglomorate, distribution or copper in - --- 103-105 mineralization oL -- --- sandstone and shale, mineralization oL 105-106 scoriaeeous amygdaloid, featoTcs oL M Madison company, production by Madison prospect, opening oL Manhattan company, production bY ~!anitou , goologic section on. -- Plate 17, in pocket )!ass company, production by --- --- -- Mass fissure, mining on --- sections showing development along Plate 51, in pocket MayOower-Oid Colony mine, description oL 202-203 )fedora prospect, opening oL Merchant lode, opening on Meuche, A. IT., acknowl<ldgment to )!ichlgan company, production by -- Michigan mine, development on lod oL- Plate 52, in po<lket Minesota company, di.-Jdends paid by - - Minong company, production by_. Mohawk company, dividends pa id bY Mohawk mine, work on--- - N National company, dividends paid bY-- New Arcadian lode, features oL New York and Michigan company, production bY ~onnsuch company, production by Nonesuch lode, content of ore in American company, production bY ~Ortb American mine, work OD ~ Butler lode, opening on Page ZH North Lake mine, opening oL 2H, 215 orthwestern company, production bY- - -- -- --- orthwestern mine, development oL orw!ch company, production bY --- orwich mine, operation oL Ogima company, production bY Ohio Trap Rock company, produclion bY Ojibway company, production by Old Colony mine. See Mayflower-Old Colony mine. Old Phoenix vein, work on--- O'Neill, J. J., quoted -- 145-146 Onondaga exploration, result oL--- Ore-forming period, formation of minerals io-- -- 53-55 Osceola company, dividends paid bY 74--75 Osceola lode, content or ore in - 1!2 longitudinal sections oL --- -- Plate 39, in pocket methods or mining on -- 19~-194 Outline or the report Xl-XII Oxides, occurrence oL 58---59 Oxidizing agent, destruction oL -- --- 133- 136 presence or, in tbe rocks. 131- 13-1 p Peninsula company, production bY Pennsylvania company, production bY Petherick prospect, opening oL - --- --- - Powabic amygdaloid lodes, content or ore in description oL - --- 178-1 1 longitudinal sections oL - Plate ~6. in pocket Pewabic company, dividends paid bY Phoenix company, dividends paid bY PhoenL< fissure, features oL --- Phoenix mine, description oL 176-177 Phosphates, occurrence oL -- Physiography or the district Pittsburgh & Boston company, dividends paid bY- - - 7 See also CliiT company. Pittsburgh & Isle Royale company, production bY-- Porphyritos, texture oL- Portage company, production by Powellite, occurrence oL - - -- Presque Isle River, geologic map from, to Victoria mine, Mich Plate 14, in pocket Production or copper, 1 45--1925 - 64-0 . Prospecting, conditions oL 14&-14 See also ExplorPtion. Q Quincy company, d ividends paid bY- Quincy mine, geologic sections in -- Plate 23, in pocket o. ~shalt bouse, or plnte showing -- R Rhode Island"1lompaoy, production by Rhode Island mine, features oL- Richness in relation to depth-- -- -- Ridge company, dividends paid bY production by- JJO
I DEX Page Robbins mine, development oL_ Rockland company, production bY s aginew companY, production bY t. Clair company, product.ion by St. Clair mine, development oL !14 Salt-water horizon, evidence on enrichment at
Scope of the report ections, method of showing rocks ln eeber, R. R., acknowledgment tO enecn company, production bY -- --- --- --- - - - -- --- - - - Shelden & Columbian company, productiOn bY hoots conditions determining position oL 115- 11 iii cat~, occurrence oL 69-02 Silver, lntergrowth of, with copper, plate showln& Siskowit company, production bY Smelting, practice in Solutions action of on iron ln toPS 38-39 South Lake compa~Y. production by- SJuth Lake mlne, features oL 214,215 Star company, production bY
Sulphates, occurrence oL 62, 136-137 ulpbide veins, plate showing Sulphides, distribution oL 55-56,130 Superior company (in Houghton County), dividends paid bY- production bY Superior company (in Ontonagon County), production b~· nature and production oL 221-222 Surveying, magnetic, results obtainable bY 164-168 magnetic, theory and practice oL !62-163 T T. 50 Tps. 50 and 51 N., R. 38 W., geologic sections ln Plates 30 and 31, in pocket T . 52 ., R. 36 W., geologic sections in Plates 27, 28, and 29, in pocket T. 55 T. 56 Tps. 57 and 58 ., Rs. 31 and 32 W., geologic sections in Plate 18, in pocket ramarack compauy, dividends paid bY- Pag! Tamarac junior company, production bY ·- r. 'l'ecumsbh company, production bY r, Tempenture in the mines Texture or sedimentary rocks, as it appears in drill cores, plato showing_ To! teo company, production by 1; Tops, l av~, alteration oL -- -' 3HJ fr!l!;me.ntal or brecciated, character oL 29-3! Iron oxidation in, cause oL- 38-41 oxidation in, mineralogic features OL--- -- 37~ red color oL 34-31 &3 ·mooth, oxidation in ~'>-36 structure of rough variety oL 29-33 ?J lEI\ture of, as see.n in lodes, plato showlng '!'rap, ai1 eration oL nature oL 'IS·T. Trimountnin company, dividends paid bY i! r. Vaughnsville pro peel, opening oL Zll Veins, content of ore in -- Victoria comp ny, production I - - - · r. Victor!.>. mine, description oL --- 21! Volcani vents, location oL 2! Vulcan .:ompany, production bY--- r. w Weath~ring , formntion of minerals durin&-- !.1 pos., ibiiity of oxidation of iron in i!lva tops bY 3H1 Wells, ll. C., Chemistry of the deposition of ·e copper from ascending White Plne company, di,-ideods paid bY ;; production by g; \)bite Pine Extension mine, d cription oL li+-m White Plne mlne, d cription oL -- Ii2-li4 maps oL Plate 33. in pockel Whitneyite, formation and properti oL -- 56-0i W~odsor com pan~· . produc~ion by gs Wmona company, production by -- ;ll_ Winona lode, descnption oL kel longitudinal sections oL Plate 42, in Win Wolverine company, dividends paid bY Wyandot company, production bY Wyandot mine, opening oL IVyandot No.8 lode, features oL --- ---