Silver Lead Deposits of Eureka, NV

1884 · Historical

Monograph Vol 7 of the USGS, this 1884 publication describes the silver-lead deposits of Eureka, NV and discusses ore deposition theories prevalent at the

This 1884 document, Silver Lead Deposits of Eureka, NV, is preserved in the Mountain Man Mining Library for research and reference. Original source: archive.org.

Vii.

Department Of The Intericir

UNITED STATES GEOLOGICAL SUi¥EY

Washington D. C. ..

SIIiVBB-IiEAD DEPOSITS OF BURBKA, NEVADA: BY JOSEPH S. CURTIS.

tJ3^ mis mmme mnnd /e iiansmiWm ^ mm4 i^ is seni idi^mam ide ^mimsmmkn tfmsiiimiimt ^s ikMnaimmm e^tdamm. tfi mam Mfi 4mm m^m, mM^ie^ ^4 seme time adei me ie^iim ^id^ m/ei,

^dase dm ^m/ me ikewsea iei^Mi a ma ieiain i/^ d^si dm}/, if ide ^^i^M ^ide M. cVf ^^^mim/ ^^if^, Wmsdin§iim, ^. ^

Chief Clerk.

o

Depaetmekt Of The Interiob

Monographs

Of The

United States Geological Survey

Volume Vii

Washington Oovebnhent Pbintino Office

18S4

United States Geological Survey

J. W. Powell Dekectoe

Silvee-Lead Deposits

Of

Eureka Nevada

By JOSEPH STORY CURTIS

Washington Goveenment Feinting Office

Letter Of Tiansmittal.

• ' Sam Fkamcisco, Cm*., /nimiify 1, 1884.

Sii: I lia¥e the hoBCir to transmit herewith a memciir on the Eiireim Miaes by Mr. J. S. Cartis- I Yisited the mme important mines with Mr. Cmrtis at the' conclmaion of his field work, and have ^careftily scmtiiiiiei the conclttsions drawn from it So far as I am able to judge, the olbser- ¥atioiii are correct and the inferences from them sonnd. ¥©ry respectfttlly, yoar obedient serraat,

G, E BECKER, Ge§kffist in cMrge^ P^fic ^mw^ Hon. J. W. Powell,

Contents.

I-tttur of T»wiinllital,...., ,.,,,.,.,.,, ...,....,,,.,...,,,,.,..,....,.«,.,,.,,.,,,,«.,,,,,,,.. ¥

Conliiiilii.. ........................................'.... ........ ............................... vii

Mwilwitloiii ................................................................................. m

Tm^m ......................................... ........................................... xi

Brief OrntMii© ©flminlto ......-.................—.-. .................................. ...... xiii

Cliiflw I.— |]teii«r»l Dmwrif tfom ©f Enwilii DlnMnt...... ............ .... .... . ...... ...... 1

H.— flmflm© Gl«il<^gf ............ ................................................. &

r? .— fitrnotnwi of Mmhj HM ...... .... .... .... .... ........ .... .... .... .... .... .... W

Y.-^i}^ of Fm^mtMmmmMM^i.Mmhj MM.. ,,..,.,,,.......,,.,,.,..,,. ,..,,. 51

¥1.— The Oki Bnpoiilii ........-..............-............—.......,.....-....... 64

fH.— Til© SiMiWMi of tlio Oni ...................................................... 80

▼HL— Tli« Maniiar of D©p«iltioii of «» Oni-... .... ............. .... .... ........ .... 93

Ii:.—Wiitor. ........ :..........-.....-....-......................... .............. 107

3L— D© tlm Mttlij Hil Dupiilto-lbiHi m Loiiif ...... ...... ...... .... .... ........ .... Ill

XI.— AniMlfiBf ................................................................... 1»

1[IL—Pttii|»ctiiif ......................................................... ......... 1»

Xin.— Tiilinto Syitoiii .............................................................. 150

JM.—'Rm^^gMA^Mm^kMWMm. •.,••.. ^.»,....,,*..,,,..,,,,..,„....,,,..^^. 158

X¥.--Motaliiiio^ .................................................................. 158

XYI.— Aiimii Him ............................................ ...i.. ..--.. .......... 165

XVH.— Fmtnwi of Eiwilji DMricit ...... ...... .... .... ...... •..•.. .... .... .... ........ 1»

X¥IIL—8iiBiiiiiy >,..>...,,.,,....,,..,,.,...,,,,,,,.,..,.,...,,.,...............-... ITU

liii« ................................... ......................................... .......... 1S5

Illustrations.

Plabi I.---Siiriiio« geological niiif .......-..............--.—...-....-—..—... -i>li>wi.... 4

n._ir«rtii»l-«niiiiHieoMom of Ftit^ M

m.— Eteviittoii Mii plum «f o©iitiiol» if Emlij HiM iiiiB«i ...... ....... ......f©l#wi.... 22

IV.— Maul section of Bnlij Hil .........-..,-.............-.--.....-.— .-. -fiws.... »

v.— Vcirtiijal owmwuiisticiiMi Mos. 1,X 3, iini 4 .—.. ...... ...... ..--.-- ......fmnii.-. «

VI.— Viitiimlciwis-iiMjtionKo. 6** .......... ^ 3lf

YII.— Vertaiml ciwiiHiiiictioM N »

IX.— Vortiod ciwiiMWlionMo.8 -..-......,.... ....^ »

• X.—Vfi*iciilcKiii8-iiiM5tiom Mo. ».......„ 32

XL— Verliciil CKMUHWJtioii No. 1§. .................................... -.-..IbHowi..-. 32

XIL— Vortioiil aMWHicttoii Mo. 11.... ............................... ......fcHows.-.. 32

XIIL— Horiiontiil socti#iis Mos. 1, 8, Mii 3.—... ...... -.....--.......-.. ----.foHows.*^. 31

XI¥.— HoiiJwmM iwctioiM Mot. 4,6, ant 6. ............................... ...follows... . »

XV.— Meal fimllimg of the two sialo Imllii .......... .......... .... ........ ....inciii.... W

X VI.— Frojeotion of the liuijciag wiill of tlio Bmb j Hil fimlt ................... fiioos .... 411

Wm* L— SelAtiom of tbefoniifttions to the nuiiiiiHiiife. ....•..•••.••........•.•..... .•••...... 31

2.— Plan of nmiii drill mni oroiii-4rifl 6IMI-foot Itvel, Mclmioiiiiiiiao.... ...... .... .... .... 82

3.— Poiiitwii Off cupola in mmflo...... .... .......... .... .... .............. ...... ...... .... 127

4.— Potttion of cufoli in mmlle ............ .... .......... ...... .... .... ..-..---...--. .... 128

5.— Electric i«ir¥0. ..-......................-........-....---.-...---..— ................ 144

6.— Assiij cmrro .....-................-..........-..-.............-......—. ............ 144

7.— Ilnst»tloii of olooMoiiliiotivilj .................................................... 116

8.— Set of timtiam ...................................................................... 154

9.— Bidnnomift-amiiif ........................................................ .......... 156

li.— EiiMikiifriiiiiing...... ....................... ^•..— ...................... ........... 161

Pieface.

The ield work upon wMch the following report is based was beguB in JeIj, 1881, and concluded late in 1882, the assays and many of the chemical eMminations being made during the progress of the ield work, as occa- " sion required, in a temporary laboratory arranged for the purpose.

In 1879 Mr. George F. Becker made a preliminary examination of the more important mines. My report was prepared under his superTision, and I am indebted to him for much valuable advice and assistance. In 1880 Mr. Arnold Hague mad© a detailed survey-of the general geology of the district an abstract of the results of which appeared in the Third Annual Meport of the Director. Upon this abstract I ha¥e relied for the determination of the stratigraphy and the relations of the district at large to the ore-bearing formations, I also had the advantage of spending some days in observations on the surface geology with Mr. Hague in 1881. The surface geological map published with this report is taken from Mr. Hague's atlas, which will be published with his memoir.

Mr. C- R Brown was my assistant during- a great portion of the time occupied by the field work and rendered important services in collecting specimens and in the laboratory. Mr. N. Wescoatt, formerly surveyor for the Richmond company, gave me much information in regard to the workings of the Richmond mine, furnishing maps upon which the drawings of that mine are based, as well as drawing Plate III. To Mr. E. Probert, manager, and Mr. R. Rickard, superintendent, of this company, I am also indebted for many facilities, as well as -to Messrs. Bryan, Longley, Morrison, and Davis, employes. . Mr. T. X Read, superintendent of the Emreka Consolidated, not only fnmished me important maps and information, but gave me every

3m MUlFAOll.

assistance in Ma power in visiting the mines in Ms chmip L Mr. Bye©, foreman of the iam© nmn©, rendered me man j facilities, as did also Mr. Stewami, of the company's reduction works. Mr. E. N. MoMnson, superintendent, and Mr. John N. Williams, foreman, of the Albion, showed me e¥ery courtesy possible, and gave me free access to the mine. Mr. Kermeen, of the Rmby-Diinderbttrg, ga¥e me every attention.

To siiperiEteiideEts and mine-owners too numerous to mention I have to return thanks for the universally courteous treatment that I received at their hands.

X S. C.

Sam Fbaicisco, Meeker 31, 1883.

Brief Outline Of Results.

Ryni tlw yew IMt wp to the f nMenl IIiim (188S) Xamkii Dlttriet biM f iviiiiMd ailNnit |iO,Mi,iMI gold mcl •ilTiir, mi ■Iwiil 22ll,Mli ton* nf 1«*1. Owtng to tbe iMSI tlwt tbe iepMits of tMii diatriol hme Immb inon} eomf lately doTolopid ttum any ©tlitr ©f » iliiiltor climiBCtor on tli« Ftclflc slop*, ttmj offer ¥«ry comf l«tii opportmiitiM for th© •eliiiitll« iiiTiiitifiitloa of tbe pliciMiiiipiia ■Itatdlng tlifi cImm of dopotlte. In MYonl nspects Ihey nmiiiiilili} tliOM of ]L««ii¥lle, Colomdo.

Tlie •tmctiini of Praiifcwit Moiuitiiiii md Xmliy HiB, tltie jirtiieipil ptiiiBg iMmllMMi In the iistiict, it ezpkliMid Ib dutefl in Cliapten lH. and IT. of Ihfai TOporl. Tlie invottiiptioii hmm doiMrlliMl hM nsnltod in Aowlng that tbe doniiiaiit fuctor of the stnetmni of Bmliy Hill it ihi extcmiiiTO fiMtlt wMcli biui iotomitiifliil the pnMMait nliitioiit of titio fonDAtionii, the aptitedii of tlie grotui for om iepotllioii, tlie ingrMt of ore-lieariBf eoliitlonii, auid llie iiMiiiii systoni liy wbicli tbe on iMMiies ani omniietei. Tlio piweiioA of Mm fault, wMcli Ins Imwii oaUed the Bmby Hill fkidt, !• markoi liy m iMimi IUImI in places with rbyolito.

Tlie Mdliiieiititry teds of tlie dteMet vn of ibq Cainliriiiii, Sflvriiiii, BuTonkn, CiirlioiilfeiDai, and Qoatonmry ^riodji. BItlierte do depoalto of Tulno, witti ohq oiiiatptift* In tlie tnaitite of the Sttmiiiii, Iuito Immb imiid #iitiiidii of tlio lineiitoiMe of tlio CmMiiii and Silmiaa, mii tliey have Immib noatly eoniiiei to tlie limeatonea of Ibe fonner «g«, Ihovgli tbe depMllioB of tie or© took ptoo© withoiit ionit ia Tortlafy or pott-Tertiatj timeii. The igiii»m» woke of Ui© itotfict occurrfng meiir tlie miiioi awi gmilto, qnarta-fotf 1 jiy, tiomMimcleani •uglto-^ndmiltoi, AyoMto. aaii liiiiiilt. Gnuiito-pirf hyiy mm! incilii occur, howoTor, la thto wfion. •

The on above the WAto^lf!TeI ia principilly coiiiiMitc4 of the mlnenlt n^enftr anglcMiito, cwniMiitot nliiietito, ad •rmlfenitfi, witli totj little qwtrtB and cmlcito; the gaiigae 1>«Ib|| foi tho^iiMNit pmt liydnt«d oxide of iron. The ore alao aariiea ounaidenMe gold snd allTeTr and sine i« pnemt f mlmMy as osrlioiiiite and alliiiiite. Below the water-level the ore la ohleiy onniiioiiei of pyrite, afwniof jrlte, galeiui, Monde, tiid a fuw otilur anlphidiMi, •• well as »lver and gold.

The ore depoeite ttieiniielTeo an very IrrefpilaT Is fonn, MHetlmea RMwniMiiig lodes, immetiiiiee "•took*/* and tonetiinee lieda. Ore hodiea of an j lisf are always capped liy cairea or In aoine way oonneeled with smeh openimga li th# tmk and with teaoima. Thli conneolloii of oro ■ liodlee with iamnnia ia anivetiia! in the diatriol The cavea were p wlrnMy fonnei ainc* tho dcpnaitiiia of the om, pirtly hf the action of water oarryliif cmrlionio aoli, and partly liy the ArlDkage of the ore canaiid hy deooapNiltloB. Slnoe thia last action took plaoo the ore has In many laatanoee Imwd reiistrlhatad hj the iow of mndergwuind watom. The fonner pwieiioo of tlimie waters ia iliowii li j the itwtiioatlon of pirtloni of the ort liodiea, and hy tnecs of aqasotia aolion ezMMted hy the tnmmiidinf Hiiieat4nie.

It It likely that the oonatitiieiits of the ore were dertvei firatii tome aiiiiitiYit riMik by molntioii, the aolntiont heinf due to the tolfatarie aotion Incidoiil to the enptlon of Mrge inaaaca of rhyollte. They entered the Umeatone from Imloir thnmgh inninie, and the greater pari, at least, of the or« was depositeil by direot smhstltnllon for that rock. The Inn-atone wae istnwid and cniehed in many dimotioiia hy the varloiis iwltiiif moveineiita and gave fi»e imgness to the orshearisK aoliiilcMia, which foHoiipd the idisinMils of least iniiistaiifNi and depoaitsd the om in miaiHiiii of ¥ory Imijpiljir foni.

The aasayii of country rock ahoir cmictaaiTely that the malatiala for the ore oould wit have Hieem doilTed fWin any of the andlmentary fomiatlone. The tuarte^perphyry Is the only Igneona mok of the diatriol in wMeh aajrttiliif bat trace of the preolourMietala hat hmn found, and atthnngh It doet not eovor nmch ground on the amfaoo II nay he of nmoh mom oonsldemMe extent hollow. The naalts obtained frmn Iti owMninaHon poini to it mi the soiUDe of the on in Its netgUwrhood, at leaat The gnmlte which prohaMy nnierliMi the fonaattoini of Prospect Mountain and Bohy Hll may also have been a noiiiwi of the ore, lint if tneh la the caae the eztraetion of the heavy metala ftuin It haa heen very eonf lete, at when found op the imrfaoe it contains ioaiwily a trsoo of allver, gold, or lesl.

The prooeaa of determining the preaeaoe of an on body by nieaiia of exaet aaiays of the annvvadinf Mnettone hat ■a yet led to no praetleal application, allhoiigh the retnltt obtained ky thia method of praipieting oolnolde In a remarkable manner with the deotrloal experlmentt made by Dr. Biniii with a irlew to the tame object. The methods naod In assaying are Italy enplainod in the ohapter on that snliJoet.

The chanoea of inding ore In the deeper workfagi of Knby Hll are ounillortd to be faTomblo, though the q nalltf Hid aise of on Mies oanmot be predloted with certainty.

: f f ' I- •

Silver-Lead Deposits Of Eureka,

BY J. S, CWBTIfl.

OHAPTll I. '-^ ''" ^'■'''-

©BMlSIlAIi »158CBIPTIOM OF KWBBKA DISTIHCfr.

; I "■..■■Jill :

p#.iti#ii.^Eiireka Mining District is sitttated on the westefn inde,ci|^|^e Diamoni Mange in the ematem part of the State of Nevada ai^d f oafh.fif the Central Paciic Railroad. The town of Eureka, which forms ,tl|e. -Ijfiiiiieas center of this region, is about 90 miles south of Palisade, a stalipE ip the above-mentioned railroad. Enreka is connected with Palisade, hj, % par-row-gauge road. The town lies at an aMtiide of about 6,500 feet ,abo.¥© sea-level, in a calion, which, foEowing a northarlj, course, enlep .DiamcMid Valley. Bmby Hill, distant about two miles west of Eiireka,^ is the ,ii|ii|iing center of the district On the Mil which gives its name to the ti?.wn ^rfi.the mines which, through their large production of lead, silver, a^d jgQl^r \^^^ given Eureka District a world-wide notoriety. The Buby Hill m^m ir^by no means the only productive mines of the district, but they are those which up to the present time have been most extensively worked and have a|fo|rded the best returns for invested capital. On account of the facilitiep pifered for the study of mining geology, these mines are also the most interesting from a scientific point of view. They have been examined by miiiy fible geologists and mining engineers, among whom there has been gr«|a| diversity of opinion in regard to the nature of the deposit • 'f : / ,_ ,.|

T0iMif«piij.— The surface of the country in which Eureka, Seprf t Cipon,

and Silverado Districts are situated is broken up, by a series of c^iioiis, into 26&4 L— 1

2 ^ Sil¥Eb»Leab Bep08It8 Of Eukeka, Hbyada.

narrow ridges or spurs which join either the Prospect Mountain ridge on the-west or the main Diamond Eange on the east These spurs are separated from each other by a main callon running from Diamond Valley on the-north to Fish Lake Valley on the south. One of the principal of them, extending a little south of east from Prospect Peak, the central and highest-elevation of the Prospect Mountain ridge, divides the watershed of the east side of that rid^e so that the regions lying to the north and south of the-crest of the spur are drained respectively by Diamond and Fish Creek Valleys. At the • northern end of this callon, near its entrance into Diamond Valley, is situated the town of Eureka. Silverado District lies a few miles-east of the main cafion, in the hills south of the divide, and Secret Caflon District on the southern portion of Prospect Mountain, and its spurs west of the before-mentioned main cafion. The mines which will be described in. this memoir are confined to Eureka District, which includes the northerly portion of Prospect Mountain and its spurs. Of these spurs Ruby Hill is^ the most important, and Adams Hill, though detached, is also to be regarded, as a member of the system.

promineBt eiemtton..— Prospect Mountain is a narrow and steep ridge, some-seven miles in length, extending from Diamond Valley to Fish Creek Valley. The mountain itself consists of an anticlinal fold which at its greatest elevation, Prospect Peak, is 9,600 feet above sea-level, and, with the exception, of Diamond Peak, is the highest point in the neighborhood. From this-point it descends gradually, forming in-egular and rugged peaks, and is lost in the valleys on the north and south. The width of the uplift varies from- a mile to a mile and a half, and is greatest in the neighborhood of Prospect Peak. The northern watershed is cut up by three long and deep cafions, Goodwin, New York, and the cafion which connects with Secret on the-empty

into Fish Creek Valley. The western slope of Prospect Mountain is^ very much steeper than the eastern, and is divided into abrupt and rough ridges by short cailons which open into Spring Valley.

^ Ruby Hill forms the northern spur of Prospect Mountain, but the axis, of its fold has a northwest direction from its junction with the main mountain. At -its highest point it reaches an altitude of 7,300 feet above sea-

GEMBilAL DlSCRBPTIOlf OF EUEEKA DISTEIOT. , 3

le¥el, or about 700 feet al)0¥e Spring Vallej, which divides the Prospect Mountain ridge from the next succeeding one on the west. Although the-hill has a "rather steep ascent it is by no means as rugged as many parts of the mountain of which it forms a spur.

Adams Hill is a low hill, about 6,950 feet above sea-level, and is situated about half a mile north of Ruby Hill, from which it is separated by a narrow ravine leading into Spring Valley. It is somewhat lower than Mnby Hill, and presents no particular feature of topographical interest It may be regarded as the north end of the Prospect Mountain anticlinal, and slopes oif gradually toward Spring and Diamond Valleys.

Hoosac Mountain, somewhat noteworthy on account of a mine in the quartzite, lies just north of the divide between Secret Cafion and the main cafion. It« altitude above sea-level is about 8,500 feet

History.— Ore was first discovered in this district in 1864, in Mew York Gallon, near the present "76" mine, and a company was organized in New York to work the mines, under the direction of Major McCoy, one of the pioneers of this region. These discovery claims, although producing some rich ore, were shortly abandoned, and the district remained uninhabited until the latter part of 1868 or the beginning of 1869, at which time Major McCoy recommenced mining operations on what is called Mineral Hill, an elevation situated a short distance south of Ruby Hill Subsequently, in the same year, some men in his employ located the Champion and Buckeye claims on the southwest side of Muby Hill, and shortly afterwards the Richmond and Tip-Top ground was taken up.

In Nevada in those days silver-bearing lead ores unless very rich were considered of little value, and although the outcrops of these locations exposed large quantities of such ore, little interest was taken in them until,

early part of 1870 succeeded in smelting ores from the Champion and Buckeye, if not with profit, at any rate with satisfactory metallurgical results. This induced Messrs. Buel & Bateman to bond these mines and organize the Eureka Consolidated Mining Company of San Francisco. Furnaces were then built near what now forms the north end of the town-of Eureka, and active operations began upon the claims of the company.

4 SIIi¥EB.ljEAD BEPOSIT8 OF EUBEKA, 1E¥ABA.

Still later tt© Tip-Top and Eichmoml claims were soM by Meisrs. BttBE & English to a company in London, and smelting works were erected, under tlie supenrision of Mr. English, at the south end of the town. Th# Jackson and Phoenix companies were also inoorporated in San Francisco about this time, and the explorations, which have since resulted in the production of such large amounts of lead, silver, and gold from these properties, were begin in earnest The Maryland and other mines in Silverado ■ District, 16 miles southeast of Eureka, were being opened during this period by an English company, and a large mill was being built at Pinto The Page & Corwin and the Geddes & Bertrand mines in Secret Cafion, south of Eureka, had been producing rich ore since 1869, and a mill was also built on the spot where the present leaching works stand. Secret Cafion at this time formed part of Eui'eka District, but has since been severed from it. Mr. Bobbins was also developing the Kentuck and Mountain Boy claims in a range of mountains about fifteen miles west of Eureka.

It is not necessary to foHow the history of Eureka throttgh all the vicissitudes which are incident to the growth of such towns, nor to describe the different enterprises which have been undertaken and abandoneSi; suffice it to say, that* in the course of twelve years this mining camp has been twice partiaHy washed away by foods, once ravaged by the small-pox, and twice almost completely destroyed by fire, but remains to-day, after thirteen years of prosperity, one of the most productive mining towns on the Pacific Slope.

The number of inhabitants of the district is at present in the neighborhood of 6,000, but, as in other mining camps, a close estimate is very difficult owing to the fioating character of the population.

p»i„cti«n.^A8 nearly as can be estimated the production of the precious jji0talg lip |0 the end of 1882 has been about sixty millions ©f dollars. Probably about one-third of this amount, or twenty millions of dollars, was gold. It is difficult to ascertain the quantity of lead produced, but this is approximately 225,000 tons.

United States Geological Survey

Convenlional Si^iis Showing Strike anU approximate anf|le of Dips

Al/ap ejclnicted from the Heport on Uie

" 0" — 10- 1_ 30'- 46"

_ lO* — 20-t 45* - 70*

Camukian

Mountajn Lower I.ont' Ml Kurrka Pogonip HaiTibiirf^ HamburgJ Secret (." t

Qu&ternar\- CoalMrusur«s T imestcm*- (,>uarl vi i It* I,i rTiosio nr SHtI*- Liinoatone Shul^

Q

Lc

Silver-Lead Deposits Pl I

Hi1.L And Adjacent Country

v' ^^^itidoyyofEtirekxhDUtrict by Arnold Hague

-| indicates thw principal locjJllK'S where Ibssils wcrr obtained

Igneous

.fault lines

jv.oeclMt. Prospect Mt. Pumice Augite Hornblende Quaj-tz

V-rsione Quartxite Basalt and Tufa Khyolite Andesite Andesite Pori)hyry Grajiiie

Grade Curves 5»0 fret Wrlical Interval

otntnii gi»i«unr.^lf r. AmoM Ha^e has descrilbed the general geology of this mining district,* as well as that of the whole region lying within a radius of ten miles from Prospect Peak, and little more is therefore necessary here than a reference to his results. The Cambrian, Silurian, Be¥onian, and CarboEiferons are all represented in the formations of this district, though it is only in the rocks of the first two that metalliferous deposits of any kind ha¥e been fottnd, and excepting the Hoosac mine, in the Eureka qnartzite of the Silurian, it is only in the rocks of the Cambrian period that deposits of any great value have been discovered.

Formatton..— Mr. Hagut distiflguishes the following beds in the Cambrian, beginning with the oldest: Prospect Mountain quartzite, Prospect Mountain limestone, Secret Cafion shale, Hamburg limestone, Hamburg shale. These fi¥e formations have all been laid down conformably. The rocks of the Silurian in the order of succession are Pogonip limestone. Eureka quartzite, and Lone Mountain limestone. According to Mr. Hague, the first two of these beds have been laid down conformably with the formations which represent-the Cambrian, but there appears to be a non-conformity between the Lone Mountain limestone and the overlying quartzite. The rocks of the Devonian in this neighborhood are the White Pine shale and Nevada limestone, in the latter of which the mines of Alhambra Hill, in Silverado District, are situated.

Eetotionsof tiieiiiiiie«tothef©nii«tioM.— With th© ©xcoption of the Hoosac mine in the Eureka quartzite, and the Bullwhacker and other mines in the Pogonip

• Abetm-ct of Keport om tk© Gte©l0gy of th© Emrekn Diita-iot, Wevmclfi, by AraoM Hmgne ; TMri Anniial Beport of the Director of tli© U, S. Geological Siirvej, 1882. Mr. Hague's full report ia not yet in print.

5

6 silVeb-IiBab bbposits of bubeka, nevaba.

Hmestone on the slope north of Adams Hill, all the miEes which will be discussed in this report are found either ia the Prospect Mountain or Hamburg limestones. Mo deposits whatever have been found in the Secret Gafion shale which separates these two beds, and although it is true that pyrite, both as impregnatioos and in masses, as well as distinctly defined veins of quartz accompanied by calcite, has been found in the Prospect Mountain quartzite, the lowest of the sedimentary beds of the district, it has had no economic value. These occurrences moreover do not seem to be in any way connected with the deposits in limestone. As far as is known, there is no ore in the Hamburg shale.

Qnarteite.— The Prospcct Mountain quartzite occurs on Prospect Peak, and extends northerly, southerly, and westerly from this point, covering an area of about a square mile. It is also found in the shape of a horseshoe at the northern end of Prospect Mountain, where it divides Ruby Hill, of which it forms the lower western portion, from the main mountain. There is a third small outcrop of this rock on the west slope of Prospect Mountain, between the two above-mentioned localties. These three places are the only ones where this quartzite is found in the district. On the surface it is of a reddish color, which is no doubt due to the oxidation of pyrite, but at a depth of a thousand feet, or at a point where oxidation has not set in, it is of a grayish-white color. It is brittle, particularly near the Imestone, where it is often possible to crush it in the hand. It breaks in sharp angular pieces, of which the faces of fracture have a somewhat vitreous appearance. Aboveground it is usually harder and more compact. It is evidently not even approximately pure silica, and is more or less associated with clayey material.

pro.pect Mcmntoin Hiii««toiie.— The Prospect Mountftin limestone composes the - bulk of Prospect Mountain and Ruby Hill. It was laid down conformably on the quartzite, and to subsequent upheaval and the erosion of overlying formations owes its present prominence on the hill and mountain. Its strike is northerly, following the ridge cf Prospect Mountain until it reaches Ruby Hill, where it bends round to the west, following the quartzite horseshoe. Its dip as exposed by the workings of the Ruby Hill mines is certainly much less than 40°, but owing to the absence in most places of all signs of stratifi-

Spefacb Geology. 7

•cation, and to the occurrence of several fawlts, an exact statement of its mean dip is impossible. This dip is, however, much less than it would at first appear to be on an examination of its contact with the quartzite, as that has apparently been moved upward along the plane of its contact with the limastonfe, thereby crowding that rock outward. This is the case on the northern portion of Prospect Mottntain, as well as on Ruby Hill On the .surface this limestonfe usually has a bluish-gray color. It weathers to a ■chalky white, and is corrugated and roughened by the mechanical and •chemical action of water. In texture it is granular-crystalline, and it is frequently hard and tough. Underground it exhibits numerous varieties •of habitus and color. It appears as calcite, coarae marble, hard white and black limestone, and in the neighborhood of ore bodies is usually stained from a light and dirty yellow to a deep reddish brown by oxides of iron. CJonsiderable masses are often met with which have been crushed to a mere powder, and in the neighborhood of ore bodies it is generally more or less broken up. Numerous caves and vuggs occur in it, and it everywhere shows the action of water. Breccias of different kinds of limestone, cemented to- .gether by calcite, are quite common, and occurrences of that mineral and of aragonite are frequently met with in the openings in the rock. This limestone is sometimes found distinctly stratified, and is then usually of a •dark bluish-gray color. It everywhere gives evidences of having been subjected to immense pressure. *

Secret ciiioii«ii*ie.— The Secret Cafion shale overlies the Prospect Mountain limestone, and forms a narrow belt wMch folows the course of the ridge of Prospect Mountain, and, like the above-mentioned limestone, bends round to the west on reaching Muby Hill This shale is of a dull bluish color, ■except where exposed to the atmosphere it has weathered to a dirty yellow, •or where it has been subjected to the action of surface waters through fissures underground. It is often disintegrated to a mere clay. It is usualy Argillaceous, though sometimes it alternates with thin layers of stratified limestone, and the strata are much bent and twisted.

H«iiiinifiiiiii««t©iic.— The Hamburg limestone does not. differ so materially from the Prospect Mountain limestone underground as it does on the surface. As far as its physical properties are concerned, the limestone in the

8 Sil¥Bm-Lbad Bbposits Of Eukeka, Nb¥Aba.

Bttbjr-^DliiliiM'lmrg mine, which is in th© Hamburg limestoii©, might b© mis-takei' ^^f thAt of Prospect M ountaiii. It is only through its connection with-lill%ell-©8tabli8hed belt of Hamburg limestone that its relatiTe ag© cftri bfl'dMifei. It is hard to say what the properties of the limestone in th©-'H6toilliil*g mine are which make it easy to recognize the difference between! it »ii# the Prospect M onntain limeitone, but they are characteristic eiioi%h^tcJ 'fieiider it evident even to the casual obseiirer that it is a different limest6tie. •' It breaks with a sharper fracture, which is probably due to the larger ^quantity of silica that it contains; and one or two Tarieties resemble quarMlfef iti 'texture. The Hamburg shale diffeni in no essential respects frcml thd-SeHfet Cafion shale.

■ ■ ■•t%#iii^iiiii*4toini.. — The Pogonip limestone forms a nearly continuous belt on* thb eaitrt* slope of Prospect Mountain, and on the north and east sides of •Alatris^Sill where that eleration merges in the valley. In this Hniestotafe 'tfe#*fe«l discoveries in the district were made in New York Gallon. In itai%*%lBtf 'iittfated the Bullwhacker, Williamsburg, and other mines. In coMr^liii-'^flttiestone does not differ much from the two limestones before desi^rillei^'%ife%t' that it is of a brownish tinge, but it is softer, shows fewer si^fis of ^ili*tfemorphic action, and is almost everywhere distinctly stratified. ttiiliiiyif4ir4nii».^^The Eureka quartzite conaposes Hoosac Peak and the entire *^ill^ Mlf of the mountain of that name. It also occurs as a naixow band on the west side of New York Cafion and east of the main cailon where'it Irilfers Fish Creek Valley. Its color is white, reddish, or bluish, and4fe1s^iMi^ hard and compact In texture it is granular, and it is rarely fonrid itiritifiild. ' It is apparently nearly pure silica.

?liJ«iiiiiif(»i:ki.-^The only massive rocks which make their appearance in the nllettllitefous zone which is occupied by Prospect Mountain and ita off- 8hb^fcb"«#ll'gfa!llte, quartz-porphyry, and rhy elite, but homblende-andesite is fotit^'iri its neighborhood, and basalt within three miles.

' • .'irtiiAte-— JTb© granite crops out at Mineral Hill at the north end of Prospect Mountain, covering an area of but a few acres; and this is its only occti^Sgrifeein'the district. It appears between the limestone and the quartzite? ''^R-il ^eiafl'se-grained, grayish in color, and very much weathered at the

surfiice. What its unilergroiind climrmcter may lie is not known, m there have been no explorations maie in, it.

QiMirt»-|iiifpiijrfy.-— QMartz-poi^phyr appears in two places north of Adams Hill Mr. Hague assigns no definite age to this rock, but states that it is post-Cambrian. From the manner of its occurrence in the Bnllwhacker mine it would appear to be of earlier origin than the ore. This rock has a reddish color on the surface and a granular texture. Where exposed underground it is white, shows considerable quartz, and contains cubes of pyrite. Neither variety is hard.

Ri,y«,iite._Ilhyolite is abundant in the neighborhood of the mines as well as in immediate proximity to the ore. In some portions of the district it covers large areas, but in the mines it is only found in the form of dikes, which, so far as is known, have never exceeded 20 feet in width. There are particularly large outbursts of this rock at Purple Mountain near Ruby Hill and at Pinto Peak. It is of a nearly white color, sometimes with a pinkish tinge, and of various degrees of hardness.

H©niiii«iMi«-«ini«itc.— Homblende-andesite occurs near Hoosac Mountain, where it covers a considerable territory. It is of a crystalline texture, dark color, and is considerably weathered. The last two rocks are assigned by Mr. Hague to the Tertiary age.

pwBiiiiiiriiriii«ti©iiiiitii«pii«iiixniiiie.-— In tho PhoBnix mine there 18 anoccuiTence of a peculiar rock, the exact nature of which has not been determined. The position which it occupies can be seen on referring to vertical section No. 3, Plate ¥. As far as known it lies wholly in the qiiartzite. It is usually of a black color and contains large quantities of magnetite and pyrite. It is everywhere penetrated by small seams of calcite, and some specimens are composed almost entirely of that mineral and clay, which latter substance often fills cracks and fissures in the mass of the rock. Some pieces showing the least decomposition when treated with boiling chlor-hydric acid give oiFa great deal of carbonic acid, and the iron and other soluble substances are completely dissolved, while a white skeleton of some siliceous material is left which exhibits a cellular structure. The mass shows no signs of any stratification, and everywhere exhibits evidence of the extended metamorphism to which it has been subjected. The form in

10 SIIiYBfrLBAD DEPOSITS OF BPEBKA, METABA.

-ivliicli it occurs would! indicate tliat it was an intriideii mass of igBeotti rock, •and this theory is in a measure sustained by the fact that specimeiii closely resembling rhyolite ha¥e been found in the mass. Other specimeiM are composed almost entirely of calcium carbonate and have unquestionably the structure of limestone. In the upper levels of the mine this rock is so much •decomposed and mixed with quartzit© that its boundaries are not distinct It is very possible that it was originally an intercalated bed of limestone and 'has been metamorphosed by an intruded mass of rhyolite and the attending •solfataric action.

Chaptee Iii.

rofuphciiirai.— Prospect MoEtttaiH and its adjacent spurs form an anti- -clinal fold of which the axial plan© is usually somewhat west of the crest of the principal ridge. The course of fhis plane is nearly due north and south, •except at Eiibj Hill, where it turns toward the west. At those places on •the western side of the mountain where the strata ha¥© been laid bare by mining explorations, the traces of bedding are so rare that it is impossible to form an accurate idea of the prevailing angle of dip.

When the alternating beds of shale and limestone, which at present form the mountain, were folded and uplifted an enormous crushing and .grinding force was exerted upon the different members of the series. Those rocks, such as the shales, which were flexible and would give, stood the •test of this great pressure with the least injury to their physical structure, and, although they were much disturbed and flattened out, retained their -original character. With the limestones it was otherwise. Their hard and •compact nature and their tendency to break instead of bend when subjected to great pressure caused the formation of numerous fissures and faults. Most of these fissures were formed parallel to the axis of fold, though many •faults also occurred in every direction. As this uplifting and crushing continued great zones in the fold were ground almost to powder. Where the limestone was the weakest or the pressure the greatest the first shattering began, and as these breaks weakened the mass of the rock where they took place, the grinding went on indefinitely until the uplifting force had spent itself.

ininciico of ©mptivii rocta.— Subsequently to the primal folding by which Prosjiect Mountain was formed eruptions of rhyolite occurred, which had a fur-

11

12 Silteb-Liab. D1P08Its Of Eureka, Nbtada,

ther disturbing effect mpoii th© stractmro of the comitrj. There me n© large omtbiirats of this rock on Prospect Moantain itiolf, but it app©m» as dikes in several places, and largo masses of it, and homblende-andeiite, occmr in the immediate neighborhood. Many issmres and faults ha¥e umqaestionably been caused by the eruption of rhyolte, and as it is among the latest distttrbing agents which have entered into the formation of the country, it is worthy of attention. It is also extremely probable that the eruption of rhyolite and the solfataric action consequent upon it had an intimate connection with, if they did not actually cause, the deposition of th© ore. Although the evidence found in the mines that the rhyolite preceded the deposition of ore is not absolutely conclusive, it is strong enough to make this order of succession almost certain. Where found in the mines the rhyolite is very much decomposed, being in places wholly changed to clay, but still retaining enough of its original characteristics to permit of its determination with certainty. At a distance from the or© bodies this rock, although somewhat weathered, is much fresher.

Retotiona of tiie gimiiito to tii© otii«r fonnattoiia.^It is not likely that the granite of Mineral HiU, which is the only known occurrence of granite in the district, broke through the quartzite and limestone, but that it originaly formed a submarine hill in the bed of the ocean upon which the quartzite, limestone, etc., were laid down, and that its exposure in its present position is due to erosion. Quartzite containing bowlders of a rock which was probably granite hai been taken from the bottom of the Michmond shaft, which has attained a depth of 1,230 feet, and is the deepest in the district These bowlders consist of granular quartz, mica, and a substance that appears to be decomposed feldspar. It has not been possible to determine the nature of this rock with certainty, but it is very probable that it is an altered granite. Such being the case, jt would indicate that the body of that rock was at no great distance.

Dif«ctioiioftiie«upoftiicw«rio««fiinii*ttoii..— The stratft of the formmtions which compose Prospect Mountain do not always dip away from the axial plane of the fold. There is a notable example of this occurrence in the Ruby- Dunderburg mine, which is situated at the head of Goodwin Gallon. The principal shaft is sunk in the Hamburg limestone, but at a depth of 450

2

United States Geological Survey

Julius Bi«n * Co Uth

Verticai. Section Of Prospect Mountain, T

Prospect Mt LimrBtonc

Stratififfd Secret Cf

Limestone Limestone Shale Shale

r

a» 100 9 too

teo «iu

140 tfO IDO «> eo M> K» O

Silver- Lead Deposits Pl. 11

u ndTpfliurg

J SX!.'urii«.t>oli.>K>»t

; Through Prospect Mt. And Eureka Tunnels

Cn Hamburg Hamburg

STRUCTURE OF PEO8PB0T MOUHTAOf. 13

feet it intersects the Hamburg shale, whicli in this part of the mountain dips west instemd' of east, as it sliOttM if it followed its normal pitch. At m depth of 800 feet it stil dips n'est, and at an angle much lees than it did above, showing that this irregularit j, which may be only local how©¥er, is more oonsiderable than was to be expected from the nature of the ground, for the reason that the Secret Galon shale which underlies the Hamburg limestone dips to the east, and if the Hamburg ^ shale should continue its present pitch for some distance further it would com© in contact with the Secret Gallon shale and shut out the Hamburg limestone altogether. There is a strong rhyoHte dike which cuts through the Imestone and shale, pitching to the east, and it is very probable that it is not only connected with the distortion of the strata, but also with the formation of the ore deposits in this mine. Dikes of rhyolite, such as occur in the Ruby-Dunderburg mine, will no doubt be found to exist in many places as mining explorations lay bare the undergronnd formations. As they are rarely but a few feet wide, they may easily lie concealed' in the surface debris in those places where there has not been a large o¥eriow of the la¥a. •

ii«ctt©ii ©f wtmp^ ii©iiiitiiiii thrcmf ii Buriita TuiiiiisL— The undergTOttud workings of Prospect Mountain and its. spurs, although they have now reached a considerable extent, give by no means a perfect idea of the internal structure of that region, as they expose but a relati¥ely small portion of its rocks. On the east side exposures ha¥e been made by the Eureka Tunnel, which has been dri¥en from a point near the head of the west branch of Goodwin Galon in a nearly doe west direction into Prospect Mountain. It is now over 2,000 feet in length, and has passed several hundred feet beyond the ridge of that mountain, below which it attains a depth of about 800 feet The following are the different formations encountered, in the order of their

85 feet mineral limestone* (Hamburg Imestone). 290 feet shale (Secret Gallon shale).

•Tl© nmn© " miniiml liiiiii8l»ii©" Iimi Ii«©b gi¥Oii by tl© iiiiii©» of th© diatoiot to tluit liminitoiiii in wMeli Uie on iepiMiita cNsonr. AHhonf li llie tonn " metiillifoniiis ^ woiild Im mon Miootiioiily cwmiot as iipfil«d to tliit rook, tho word *' mlnemF' it Qftiid not only tiy minen, Mt liy wriiws on mining law, imi liiis im fnictio© com© to b© synonymom wltk "om-lmaiiiif *'; tMr© it almiiiiiiit fmooieiit, tlioniferfi, for tho iumi of tb© tmm in this iifiittoiilioii.

14 -SIIiTBE^LEAB BBPOSITS OF EUREKA, ¥E¥ADA.

51 feet mineral limestone (Prospect Mottntain limestone). 460 feet shale (Prospect Mountain limestone).

50 feet mineral limestone (Prospect Mountain limestone). The tnnnel section, Plate II., gi¥es an excellent ide« of the formations-which compose the east slope of Prospect Mountain and its spurs. It is-true that in all probability no other section parallel to this one, and taken at a considerable distance either north or south of it, would closely correspond, yet it is safe -to assume that there would be enough resemblance between them to permit of this particular one being taken as a type. Mr. Hague, in his geological map of the district, has placed the mouth of this-tunnel in the Hamburg limestone. The first bdt of shale encountered is-therefore the Secret Gallon shale.

The second belt of shale is probably nothing more than a fragment of the third and widest, and has been brought into its present position in the-tunnel by movements of upheaval. If Plate II. is examined it will be seen that the numerous faults which have occurred along the line of the Eureka Tunnel have so displaced the shale beds that it is not possible to determine with any certainty what was their original position. In drawing this -section it has been necessary to depend very much on probabilities in placing-the di¥iding lines between the different formations. The mass of shale marked B, Plate II., does not appear in the tunnel, but it is exposed in the-incline winzes of the workings below the tunnel level from a distance 50-feet below that level down to the deepest excavations. As these iEclinewinzes are several hundred feet south of the tunnel, and as the sti-ike of the gfiale 18 east of north, it would appear in the tunnel section in the position shown in the plate. There is only one boundary of this shale which has been exposed, namely, that which is laid bare in the winzes, and the other-boundaries given it in the section must be necessarily of a very indefinite-

"The tarin "Frospect Mountain limestone" of coara© refers to a group ©f Wis charncterkecl by the prc»nce of cartain foMili. Thoagli limestone predomiimtes, the inlerealiitocl ihales whicM are characteiiitio of this fomiatioa, according t© Mr. Hague, are necessarily classiied as members of the samiigronp of Imdi.

8Tbuctube Of Pbospbcit Moumtaim. . 15-

nature. On Ruby Hil there are at least two beds of shale, on© of which . is intercalated in the Prospect Mountain limestone, and it is certain that at ■ least that number can be found on Prospect Mountain.

Whether the third and widest belt of shale encowntered in this tunnel actually comes to the surface or not cannot be deteiinined at present witk absolute certainty, but shale rock is found above the Industry mine, and it ' is probable that it is a part of the third body of shale encountered in the • tunnel.

This third belt of shale is also somewhat different in character from the-irst, which seems closely allied to that found on the surface at Muby Hill. It consists of alternate strata of argillaceous shale and thin bands of stratiied limestone, and, although considerably thicker than the lower shale of Rubjr Hill, is lithologically almost identical with it The width of this shale in, the tunnel may be owing to the iatter position which it occupies or to local expansion. The irst zone of limestone has the usual appearance of the • mineral limestone of the district. It is crushed and broken, and all signs-of stimtification have been obliterated. It is usually gray in color and sometimes stained yellowish by iron oxide. It contains vnggs and numerous ■ seams. Where not too much crushed, it is crystalline in texture and sometimes brecciated, the different fragments being cemented together by calcite. One of its peculiarities is the difference of the varieties which it presents • within a few feet. The foregoing will apply to all the metalliferous limestones of 'the district It is difficult to state what the precise differences - are which distinguish the mineral limestone from the other limestones. • It is not the difference in geological age which distinguishes it, but rather-differences which are diie to dynamical and chemical action. It is never • continuously stratiied, and it is never found for any considerable distance • without a change in its physical characteristics. It always bears strong • evidences of metamorphism. The next ssone of limestone is the largest, extending 935 feet from the irst to the second belt of shale. It presents - the usual characteristics of the mineral limestone, and owing to its great extent offers almost all the varieties of that rock to be seen on any part of ' the mountain. The narrow belt of mineral limestone found further on is ■ similar to the main mass, from which it is separated by a thin belt of shale. .

16 SILTEB-IiBAD DJEPOSIT8 OF BWBBKA, NEVADA.

This thin band of shal© most likely was at some tim© part of the third and widest mass of shale, which lies to the west, and was separated from it by a series of famlts; at any rate fattlts are apparent along its contact with the limestone. Alternating beds of ihatterod limestone and shale seem to be characteristic of this portion of Prospect Mountain.

At ¥arioiis points along its course the tnnnel cwts through seams and fissures which generaly cross it at right angles. Their usual pitch is easterly, though there are many exceptions to this rale. The most prominent on© of these fissures is at a point 840 feet from the month of the tannel.

Its dip is nearly Yertical, perhaps a little inclned to the east It is open in places and filled with sediment, bowlders, etc., which ha¥e been washed in from above. At the point where it is encountered it is about 350 feet below the surface, and it is a characteristic example of nranerons occurrences of the same Mnd, both in the mountain and in Bnby Hill. Like many others, it has been accompanied by ore, which waa found on the north side of the tunnel The principal ore body yet discovered was found about 1 ,200 feet from the mouth of the tunnel, and was also connected with a fissure which runs a little west of south, but pitches westerly. It did not extend any distance above the tunnel level, but it was followed down about 100 feet, when a ¥ery considerable pipe of ore was encountered running under the tunnel in a northerly direction. Most of these fissures and seams are faults produced by the folding and upheaval of Prospect Mountain.

Although there have been local subsidences, it is safe to say that the portions of country which lie west of the fissures upon the foot-wall side have as a rule been raised the highest. The strata have reached their greatest relative height just over the axis of fold. The third belt of shale is 0¥er-lain by black stratified limestone, which, at its contact with the shale, pitches west at a steep angle until a Ittle distance beyond the summit its stratification is nearly horizontal. West of the stratified limestone the tunnel is in mineral limestone.

The following is a list of specimens from -the tunnel, and the points at which they were taken:

43i feet from entrsnM ...... Blmsk cmshcid limcistiine cemented by calcite, Mable.

4l5i feet from entrance ...... Orayiali crualied limestun©, oeiipiot gminilar.

STBUCf PEE OF PKOSPECT MOUFTAIM. 17

iSi feet from entrtnc©, ..... Blniskblack limestoi©,- compict gnnmlar.

1,§1§ feet from ©iita»iic€i. . . . . .White limestcm©, compact crystalMiie.

1,1IMI ieet ipom entrance. . . . . .White limestiiii©, compact crystalline, partly caMle.

1,2<M) feet from entrance .,.--. Grmj strmtiied llmeetoiie, compact franElar. 1,8511 feet from entrance. . . . . .Black llmeitoii©, compact granular.

l,ilM) feet from entrance ..... Gray stratiied limestone, compact gmnElar.

( First west cross-cut cast side, Mniah-graj limestone, oom- 84© feet from entrance. .... I pact, brecciated.

I Sediment from issare. 1,2IMI feet from entrance at discovery winze near ore ..... . Yellowish-gray crashed Mme-sf

one, friable, crystalline. 1,2©© feet from entrance. - - . . .Calcite, stained with manganese.

Secti©ii of Pr©»i>ect MountMii thnrngli Prospect Moniitiiiii Tunnel.— Tho PrOSpGCt * MoilHtllin

Tunnel, starting at a point abeiit 2,700 feet west of the summit, nearly opposite the Eureka Tunnel and s©¥eral hundred feet below it, has been driven 2,350 feet into the mottntain. For the first 1,400 feet it passes through a hard compact white limestone, which in places resembles marble. This limestone is not often fissured, but contains some cayities washed out by water. There is nothing about it to indicate that it is mineral limestone. At a distance of 1,400 feet from the entrance a issnre is encountered at nearly right angles, which dips 80^ to the west From this point tho character of the limestone changes; it is much more broken, and many of the ordinary varieties of mineral limestone are found, as well as seams crossing the course of the tunnel. At 1,835-feet ore was discovered, bat as yet the deposit has not proved valmable. At a little over 2,100 feet stratified limestone wiw encountered along a fault seam, which dips to the west (see Plat© II.). 4t 2,250 feet shale makes its appearance along a similar seam. The twisting of the stratification of both the stratified Imestone and shale indicates that the portions of country east of these two seams were raised relatively to the portion on the west Although not absolutely cer- ^jj^^ ll jg pj.^|^^|j|^ ii^^i ii^^ gijj^i^ ^^g glj^ljg^^ ll^j^gl^^^ encountered in the

end of the Prospect Mountain Tunnel is the same body as that encountered in the end of the Eureka Tunnel.

Oeiieml interniil •tmctmM ©f Pr©«|iecf MiniBtMa.— It Will be noticod that the WCSt sido

of the mountain diflfers greatly in the formations that compose it from the

eastern. This in some measure is owing to the fact that a larger portion of

the overlying rocks have been eroded, and that there has not been the same mm h—2

18 SILTEM-IiBAD DBPOSHS OF EUREKA, MEtADA.

amomit of faulting mo¥eiii©iitf It is passible also tliat tb© western side of this portion of the ridge has not been tilted to the extent that the eastern has, thereby leaving a broader mass of limestone along the line of the tunnel. The qnartzite must lie at a ¥ery considerable distance below the tunnel bwt it is possible that the tunnel will strike it as it is driven to the east

Dtatribtttion of om In Frospect Monntaia.— The largcst portion of Pfospect M ottntaiii and its adjacent spurs is composed of mineral limestone, and evidence of the number of metalliferous deposits contained in it is offered by the numerous outcrops of gossan, which occur along its whole extent, but which are particularly numerous from Euby Hill to the Secret Gallon divide. The mines on both sides of the mountain have produced considerable quantities of ore, and there is every reason to believe that this region, when properly explored will produce important quantities for years to come. With the exception of some few mines the properties of Prospect- Mountain have been but slightly developed. Those, however, that have been opened to any great extent show that there are numerous masses of ore contained in the Hamburg as weH as in the Prospect Mountain limestones, and that although no such large bodies as existed in Muby Hill have-been discovered there are many of them. The ore, too, in general is perhaps of a better quality.

Chapter Iv.

THK STBIJCTIIBIB OF MUBY HHiIj. Iiiliieiic* of fniiilte oa tlie mnhj Hill fonaatioiis.— Th© ftxis of fold of Mmby HM, if

such a confttsedly uplifted mass can he said to lia¥e an axii of fold, has a northwest direction from its pciint of junction with Mineral Hil, as the northern end of Prospect Mountain is caled. Mineral Hill is composed in part of an outcrop of granite. The quartzite overles the granite on its northern side and bends around it to the east and west in the shape of a horseshoe. The Imestone touches the granite on the south and overlies the quartzite, separating it on the surface on the east and west sides from the granite. Although the granite does not seem to have broken through the overlying formations, its presence may have had some iniuence in determining the present position of the quartzite and Hmestone on this part of the mountain, and from indications observed in the Richmond shaft (see page 12), it is possible that it underlies the quartzite at no very great depth in the Muby Hill mines. Ruby Hill is separated from Mineral Hil by a narrow divide and a deep ravine which has been eroded in the quartzite. This quartzite is found extending along the southwestern base of the former Mil and dips under it to the northeast; that is to say, it pitches northeast at this point On the east iank of Mineral Hill, on the other hand, the quartzite dips to the east and on the western slope the quartzite also has a westerly pitch. The Imestone of Ruby Hill formed one and the same body with that of Mineral Hill before erosion, and it is merely the continuation of the long belt of limestone of which the greater part of Prospect Mountain is composed. The bulk of Ruby Hil is made up of this rock, tiie shale only maHng its appearance on the northeastern slope.

20 Silver-Lead Deposits Op Eubeka, Nevada.

Q«iitt«-piifiiiijry«riipttoii.— About » mil© and a quarter to the north of Eaby Hill, and beyond Adams Hill proper, there has been an eruption of qmartzporphyry wMch covers many acres. If this eruption took place at the time of the folding and upheaval to which Prospect Mountain and Enby Hill owe their origin, it would account for the defection to the northwest of the different formations found on Enby Hill. Whether the eruption of this volcanic mags actually caused the bending and twisting before mentioned or not, the fact remains that these formations were so deflected during the upheaval, or subsequent to it, that they lie nearly at right angles to the position they would ha¥e occupied had they not been subjected to some other ^ force than that of simple iiphea¥al along their axis of fold. That pressure was exerted from some point, to the north of Euby Hill is clearly pro¥ed by the marks of striation observable at various points on the walls of the cross-faults, or those faults which in many places trmvers© the Imestone of Euby Hill in a northerly or northeasterly direction. These striation marks usually dip to 'the northeast, which would indicate that the lateral force had been appMed from that direction.

F«iiit«.^It cannot be said that all the fault-fissures occurring on Euby Hill have one general course, but they can be divided into two general systems; the first consisting of those which are approximately parallel to the strike of the formations and which were produced entirely by the folding and upheaval, and the second made up of those which were cmused by the same forces supplemented by a strong lateral pressure. These two systems of fissures are mostly to be found in the limestone. To what extent they occur in the qnartzite cannot be determined, m the workings in that rock are not very extensive, but it is probable from the nature of that formation that they are not so frequent There are numerous instances, however, of cross-fissures faulting the quartzite, and this is particularly the case in the Eichmond, and will be more fuly discussed when the quartzite in that mine is examined. Cross-faults have been noticed in the shale, but they are not so easily detected there, owing to its tendency to bend rather than to break. There are several examples of fissures of the first kind which fault both limestone and shale.

STKUCTUilB OF KWBY HILIi. 21

Rhjoiiteemptioii.— There has been another erttption of igneous rock in the neighborhood of Emby Hill, namely, the rhyolite of Purple Mountain, which is situated about a mile and a half east of the mines, but this eruption could not have caused the defection of the Ruby Hill formations to the northwest, as it occurred subsequent to the original uphea¥al, although it was no doubt intimately connected with the subsequent phenomena which accompanied the deposition of the ore.

Emtent of tie limestone on tfcemrfkce.^The fftCC of thc quartzitC maSS wMch 0¥er-lies

the granite dips at an angle of about 40° northeasterly under the limestone of Kuby Hill. The exposure of this belt of limestone on the surface extends over 4,000 feet from the northwest to the southeast. On the northwest end it is covered by the d^bris^of Spring Valley, and on the southeast is cut oflf by a fault which Mr. Hague has called the "Jackson faulf (Plate I.). This brings it in contact with the Pogonip limestone lying to the east of the Jackson hoisting works. Its width on the surface is from 800 to 2,000 feet It shows few signs of stratiication on the hill itself, and is usually a compact highly crystalline limestone, gray in color and much weathered.

Extent of the .imie on till! •nrikce.— Beginning »t the Dorthwest, the shale irst makes its appearance at the Albion mine, follows round a promontory of - limestone, which extends nearly 1,000 feet to the north, and narrows down to a point in the lower part, of the town of Muby Hill before reaching the fault to the east The shape of this shale body is very irregular; it is widest to the north of the Richmond hoisting works, where it attains a width of 2,400 feet, and narrowest, except where it comes to a point, north of the above-mentioned promontory. Its course is nearly east and west, and its dip northerly. The angle of dip of its stratification varies greatly. It sometimes reaches 45°, but is frequently as small as 25®.

Dipof iiietiifeeforiiiaticiii..^It-may be as well to state here that nowhere on Ruby Hill does the dip of the stratification of any of the three formations, quartisite, limestone, and shale, correspond with the dip of their planes of coBtact In other words, the strata of these three formations do not conform to each other in their present position in the mines, though no doubt they were originally laid down conformably. This lack of parallelism is

22 SniTEB-IilAD DIPOBITB OF BIIBIKA, MBVADA.

pecoiar to tli© region of Mmb j Hil* and f rospect M onntMn, and is dn© to faults wMch in many places have followed the contact of the different formations. The local noM-confonnity boars upon the or© bodies only as an indication of stmctiire-

R«i«ti©ii«of tfciitiiw«fonii«tioii«iiii<iefifiimiid.-—Tlio sttbteiTanain stractur© of Ruby Hill presents features of unusual interest to the geologist and miner. The underground explorations ha¥0 been ¥ery extensiYO, but they ha¥0 not been so complete that it has been possible to trace the contacts of the different rocks in every instance, and in making the maps wMch accompany this memoir it has often been necessary to calculate the position of points not actually exposed. These calculations have been made with car© and dme reference to the position which the different formations bear to each other at all exposed points. The main beds of Ruby Hil are an underlying mass of quartzite, a broad zone of mineral Imestone, and an overlying belt of shale, all of which have been tilted so that they stand at an angle of about 40° ; this angle being somewhat greater in the upper than in the lower workings of the mines. That these strata should piteh at a smaller angle as they approach the Valley is naturally to be expected. Beginning at the Jackson mine, the most southerly location on the mineral zone, the strike of these formations is to the north, bnt their course is soon delected toward the west, antil, in the Albion mine, the most northerly, they strike nearly east and west Their course nndergronnd resembles in its general outlines that on the surface, though there are many irregularities and frequent breaks caused by faults. As far as the deepest workings have penetrated (namely, to a depth of 1,230 feet in the Richmond shaft), the average dip of the contact of the quartzite and limestone has been found to be about 40^. Mear the surface the angle of dip is much less, as the highest point of the quartzite seems to be at the crest of an anticlinal fold. The line of contact between quartzite and limestone on the southwest slope of

Ruby Hil wonld be very near the top of this anticlinal, which can be ob-

•It.ilioiili "b© mcmtiiMiecl tlmt Kmliy Hil proper stops -»t tlic iivM© nootli of the Bnimkii lioistiiig works, Mii tlmt the JmjkiioB mii Pkaniijc mines ar© ©n ^nrs ©f Proafeot MoiuiMii, Tli© tanm " Bnby Hill miiiei/' liiiir©¥©r, wffl b© ni©d In tiia i«p©rt m inolmding th© Jiickiion, Pli»nij:, K, K. (now balonglng to llie Snrelcii Coiiipftny)| Ennlcii, Siolmiondi tmi Albion, Iho sii: minet tiwl an attnmtiid on tliiili ImII of limestone inolnded lietiriMm the f awtzito and sbiile.

UNfTLD STATES GEOLOGICAL SURVEY

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STIIIJCTIJRE OF BUBY HIUi. 23

served in a tmniiel wMch is ran into the southwest side of Ruby Hill some few hundred feet to the northeast of the Isandula shaft, a shaft sunk in the debris of Spring Valley. In this tunnel the quai'tzite is cut thromgh, and there are ligiis of a iat nndidation; the strata dipping to the northeast in the face of the tunnel and to the southwest at its entmnce. There is said to he another locality where this can be observed, bit it was not possible to examine it, as the drift in which it occurs was inaccessible. It is in a drift run to the west from the Buckeye shaft, and 30 feet below the irst level (Lawton tnnnel) of the Eureka mine. The position of the qnartiite can be seen on vertical cross-section No. 6, Plate VII.

Tit fuarteite null iiiiie«t©ii««iiit»ct.— There is HO regularity about the dip of the quartzite and limestone contact, and there are but few places along its surface where a cross-section would show that the dip remained constant for mny considerable distance. A glance at the various vertical fjross-sections and the plan of underground contacts (Plate III.) will show that both the dip and the strike of the quartssite contact are verylrregular. In some places, though these are not frequent, this contact pitches back. This can be obseinred on the plan of contacts (Plate III.), where the quartzite on the fourth level of the Eureka projects out over that found below on the ifth.. It also pitches back at the end of a drift from the big cave situated nearly on a level with the little tenth level of the same mine. This cave, which will afterwards be described, lies west of the main incline from the ninth level. Besides smaller irregularities in the quartzite, there are three large _ protrusions along the course of this contact, which occur, respectively, in the PhcBnix, K. K., and Richmond mines. The first of these occurs in the Phoenix and K. K. ground and extends from above the fourth level down to the seventh of the latter mine with a northerly trend. The second begins about 300 feet southwest of the Lawton or Eureka shaft on the third level and extends with a northeasterly trend down to the tenth level. The third begins on the surface near the "compromise line^** and trends in a northerly direction down to the ninth level of the Eichmond, where it disappears. Along the line of dip of this same contact there is a great depression sev-

•TIm " compromiia Mm©" m tie Mutt di¥idiiig ti© respective cluiiiii ©f tlio BioliiiMiiid luid Bmwkii coiif miiin, mii wiw ostiiMliliei ioring tli© ©inly lilig atton iotwten tlmii© mines.

24 Siltem-Lbab Deposits Of Ewbeka, Mevada.

©ml Imndred feet in vertical extent, whicli occurs at about the same depth in all the mines, and which, combined with the undulations along the line of strike, forms large basins of an oval shape. These basins are intimately connected with the ore bodies and will be referred to later.

Tfctmrfnfimit.^The contact surface between the limestone and the shale, like that between the qnartzit© and limestone, is very irregnlar, but there seems to be little similarity between them, owing to the presence of a fault This fault, to which the name Ruby Hill fault has been given, has had a very important bearing iipon_ the structure of the mineral zone as well as upon the ore deposits themsel¥es. Beginning at the southeast, it is first to be observed at the American shaft, which is about 25 feet deep, and is sit- -nated a few hundred feet south of the Jackgon hoisting works. The course of the fault from this point is a little west of north, and, although not perceptible on the surface, passes west of the Jackson hoisting works, and can be seen in the workings of that mine as well as in a tunnel near the Phoenix line. From this shaft it changes its course to the northwest, and were it not for the debris could no doubt be seen northeast of the Phoenix shaft It passes northeast of the Eureka and K. K. shafts, but must be very close to the latter, and is plainly visible near the mouth of a tunnel run southwesterly to connect with the Bell shaft. The last place where it can be observed <p the surface is near the Richmond office. Although this fault is not continuously traceable above ground, owing to the debris, its existence is fully established by the fact that it is encountered at numerous points in the underground workings of all the mines of Ruby Hill.

wp null •trike of the mmin finiit.^The average dip of the plane of this fault is about 70° northeasterly, and it is of remarkable uniformity, scarcely ever varying 5^ one way or the other. Its course also is extremely direct, with the exception of the bend between the Phoenix and Jackson. This fault is marked by the presence of a fissure filled with clay, which is widest in the Jackson and Phoenix mines, where in places it measures as much as 15 feet

The iuinii of the iwrnrc^Tho filling or material contained in this fissure is very different at different points along its course, although there is not much change in it where it is followed along its line of dip.

Stmuctuke Of Euby Hill. 25

In the Jackson and PhcBnix mines it is rhyolite, which is usually much decomposed, but owing to the njica and smoky qnartz which it contains is still easily recognizable. At a place somewhere between the last point at which it is seen in the Phoenix, and the first where it is encountered in the K. K., positive evidences of its rhyolitic character are lost It is likely that the change is gradual, as there is something over a hundred feet of unexplored ground between where the rhyolite is last seen on the sixth level of the Phoenix aiid the first place where it is encountered on the sixth level of the K. K. It is possible, however, that this change may take place suddenly. Where the fissure is found in the K. K. and Eureka mines, the filling is of a dull yellow, bluish, or occasionally white color, whereas in the before-mentioned localities it was uniformly white, except where stained by its contact with ore. In following the fissure northwest it becomes narrower, until in the Richmond mine it is only a few inches wide, although it is a distinct and well-defined seam, with a different character of limestone on either side of it The clay has here lost its plastic nature and is a calcareous product of the attrition of the two walls. Underground, as well as on the surface, this fissure takes a northwest course, after leaving the Jackson, which it retains until it is last seen in the Albion ground.

. ocneriii femture* of the main i»»iire.— Tliis fissuro will hercaftcr be Cftllcd the Ruby Hill fault or main fissure, as to its formation are due the most important features ■■ of the present structure of Euby Hill, as well as the relations of the ore bodies to each other. A careful description of its manner of occurrence and of the phenomena attending it is necessary for a complete understanding, of the deposits of Ruby Hill; and although when examined in one particular locality it does not seem to be of remarkable importance, taken throughout its entire course it is found to be the key to the solution of the glj^^^l^yg^l pj.^|j|^,jj ^f iIj^ jniu^pa^i 2^jfj^^^ ^ ^Yoof of its comparatively recent formation is the fact that it faults all the formations with which it comes in contact, but is itself nowhere faulted or dislocated. At various points in the lower levels of all the mines southeast of the compromise line shale is encountered on the northeast or hanging wall side of this fissure. This body of shale, however, nowhere reaches the surface^ as it is cut off by the fault As the workings in this shale are inconsiderable, it is impossible to tell what

26 . SILTBB-IiEAB DEPOSITS OF EUEEKA, NET ABA.

may be its angle of dip, liEt it is apparently less than 45°, and the shale pitches to the northeast away from the fissura As this formation will be described -at len^h hereafter, it is only necessary to mention it here in reference to the fault It is evident that the country southwest or on the foot-wall side of this fissnre has been raised many hundred feet relatively to the hanging wall. Whether the former was raised or the latter snbsided is immaterial, as the same effect wonld be produced in either case. It is probable, how- ■e¥er, that there was both iubsidence and upheaval, but that the latter exceeded the former. In the Eureka mine the distance to which the southwest wall has been raised relatively to the northeast wall is over 1,400 feet The faulting action is represented in Plate IV. Fig. 1 is an ideal section of the country through the junction of theLocan shaft cross-cut and the twelfth level -of the Eureka mine, on a line at right angles to the strike of the fault which is represented by the line X Y. The order of succession of the formations, beginning at the lowest, is : Prospect Mountain quartzite; Prospect Mountain limestone, consisting of two beds of limestone, with an intercalated bed of ahale; Secret Cafion shale; Hamburg limestone; Hamburg shale; Pogonip limestone. Fig. 2 represents the position of the different formations after the faulting and uplifting of the foot wall, and after the erosion of the overlying formations had given the country its present configuration. It will be noticed that the intercalated belt of shale to the southwest of the fissure has been eroded as well as the upper stratum of Prospect Mountain limestone. In the Eureka mine the lower shale is not found much above the little tenth level (830 feet below the top of the Lawton shaft), but in the Jack-aon it appears above the third level (315 feet below the top of the Jackson shaft). In the Richmond mine it is exposed from the surface down to nearly the deepest workings, but as the shale in the Richmond is of a complicated structure its discussion will be postponed until the shale itself is examined. One of the remarkiable features of this widely extended Ruby Hill fault, which runs in an unbroken line from beyond the Jackson to the Albion, is its extreme regularity when compared with the contact planes of the three formations, qpartzite, limestone, and shale. In breaking through •these formations it seems to have been but little infiuenced by the difference in their cohesion. In the Richmond mine, crushed limestone occupies the

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STBUCTUEB OF BIJBT HILIi. 27

footwall side of the issnr© a-nd shale the hanging wall above the fifth le¥el. Below that l0¥el stratified limestone lEtervenes between the fissure and the «hal©. In this mine the fissure is generally filled with a hard black clay, and is often not more than an inch wide. It might be mistaken for an wdinary slip, were it not for the differences in character everywhere exhib^ ited by the rocks on each side of it Splices or small slips are of frequent occurrence in connection with it, as is often the case with such fissures. In this mine it appears at first sight to be of little importance, and has been overlooked almost entirely by the engineers who have examined the iindergronnd workings. When, however, it is taken in connection with its ©xten^ sion through all the mines to the southeast, and with the fact that it is a fault plane along which the whole southwestern country has been raised from 500 to 2,000 feet, it becomes of great importance as regards the structure of Ruby Hill.

DettiiiiMideacriptioiiof tii«iiiiiiiii««iire.— It will besGon ott examining the plan of contacts (Plate III.) and the various horizontal sections (Plates XIII. and XI¥.) of the different mines that there are a number of places on the various levels where the distance between the points at which the fissure has been laid bare is very considerable. The nsnal method of prospecting in the mines southeast of the Richmond has been to run a main level along the line of contact between quartzite and limestone, sometimes cutting through the •qnartzite where its projections into the limestone are so great that the length of the drift would be materially increased if this contact were followed; and then if ore was not encountered along this line, to seek for it by driving nnmeronp cross-cuts towards what was supposed to be the shale, but was in reality the Ruby Hill fault. Sometimes it was found to be more convenient to keep the principal drift entirely in limestone and cross-cut in opposite ilirections from it. Often these cross-drifts did not reach either the qnartzite or main fissure, though the mine superintendents were usually more particular about a thorough exploration of the quartzite contact than they were •about the fissure. Drifts along this fissure were uncommon, except in the lower levels,' where the quartzite and fissure came together. Owing to this method of prospecting, the plane of the fissure was not as well explored as was that of the contact of quartzite and limestone. There can be no rea-

28 SIIiVEK-IiEAD DEPOSITS OF BUKBKA, NBTABA.

gonabl© doubt, however, that the fissmre, which in the Jackson and Phoenix carries rhyolite, is identical with that which in the K. K. and the Eureka carries calcareous clay. The fissure is intersected by drifts in over twenty places, all of which correspond in position with that which the fissure would be sEpposed to occupy from an examination of the exposures taken singly. Better proof than this of the identity of a surface is rarely met with in mines. When there are many fissures or slips it is not always an easy matter to distinguish one from the other, for one may have given out and another one taken its place, or faults might have occurred which would bring another fissure into the place where the first was to have been expected. This could not be the case in the present instance, as there is no strong fissure within several hundred feet at any rate of the one in question. This is shown by the explorations which have been carried on in the "front limestone*' on the sixth level of the K. K. and in the cross-cut to the Locan shaft in the Eureka mieed. So, too, the contact of an irregular surface, like the contact of quartzite and limestone, requires more proof than that of a regular one. In the present case the evidence is amply suMcient not only to prove the continuity of the fissure, but its unusual regularity. If the change in the material composing the filling of the fissure had occurred at the single bend of any importance in this fissure, which appears in the Jackson, a drift along its course might have been necessary to establish the identity of the two branches. The rhyolite, however, gives out between the workings of the PhcBnix and K. K., and to the northwest of this point is replaced by clay identical with that -which fills the fissure in the Eureka and K. K., so that the disappearance of the rhyolite forms no argument against the continuity of the fissure. This clay also, as found in the Eureka and K. K., is partly derived from the rhyolite, and is merely the decomposed feldspar of that rock mixed with crushed limestone.

Tiie BMiii i»»iire at the Amtrimn •ii»fi.-^The first point where the main fissure is noticeable at the southeast end of the Ruby Hill fault is at the American shaft, wliicli is situated over 400 feet south of the Jackson hoisting works. The s'jaft, which is 25 feet deep, is sunk in Pogonip limestone. From near the bottom of this shaft a cross-cut has been driven to the quartzite in a southwesterly direction. In this cross-cut, 16 feet from the shaft, the main

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Structure Of Ruby Hill. 29

fisiure, containing decomposed rtyolte, is ©nconntered. On the west side of the fiwttre, which pitches easterlj, interstratified limestone and shale are found, the strata of limestone hecomiag less nnineroiis as the qnartzite is approached. These beds continue for a distance of 184 feet and to within 10 feet of the qnartzite, this inter¥al being occupied by crushed Prospect Mountain limestone. • .

The main iwiire in tie j«ckiKiii.— The fissiire containiDg rhyolite is also found in the Jackson tunnel. In proceeding downward it is next to be found on the third le¥el of the Jackson mine, though it may possibly make its appearance in some of the abandoned workings which are now inaccessible. It crosses the new Jackson shaft somewhere abo¥e the third level and continues with its msnal dip and strike down to the fourth and ifth. It appears at numerous points on all these levels and is invariably filled with rhyolite, which is more or less decomposed. It is 150 feet from tihe qnartzite on the third level in the cross-cnt to the old Jackson shaft, is about 15 feet from it on the fourth, and comes in contact with it somewhere between the fourth and fifth. It is 60 feet west of the shale on the third, and lies on the footwall side of it on the fourth, in the before-mentioned cross-cut

me inaiii ittiire In tim phomiji.— In the PhcBnix the main fissure, still filled with rhyolite, is first noticed on the fonrth level and continues with its accustomed pitch and strike down to the deepest workings on the seventh level. It is over 200 feet removed from the qnartzite on the fourth, bnt comes in contact with it about 40 feet below the fifth near the Jackson line. On the sixth level, farther to the northwest, it is but a few feet from the qnartzite at the end of the cross-cut from the main incline. It may be as well to state here that the depth at which the main fissure comes in contact with the qnartzite increases as the fissure is followed westward. Three hundred feet farther to the northwest, on this same level, it is 60 feet southwest of a body of shale, probably the same which is encountered in the Jackson. On the seventh level it is almost everywhere in contact with the qnartzite, and is also in all likelihood in close proximity to the shale.

mmm Mmmm la tiie-K. K.— The fissure is first encountered in the K. K. mine on the third level and dips at its usual angle down to the deepest workings on the ninth level. On the third it lies over 250 feet northeast of the quartz-

30 SHiTEB-LBAD DBPOSITB OF BUIIBKA, ¥B¥ADA.

ite, and on tli© sixth it comes in contact with it In the sontheastem part of the K. K. ground the qiiartiit© face foHows the course of the fiisure, hnt as the Eureka line is approached the quartiite bends westward. In the lower liYels the qmartzite and the fissiire are together for nearly the whole of their extent, and the limestone is shut out from between them.

Unto iMiire In the Eureka.— In the Eureka mine the Mnby Hill fault can be-noticed near the surface in the Bel shaft tunnel Thii tnnnel has been dri¥en in a southwesterly direction from a point 300 feet distant from the " compromise line to connect with the Bell shall, and cuts through the fissure about 50 feet from the month. The fissnr© can also be found in the Utah-tunnel near by, and is encomntered in one or two other places, but it is not an easy matter to trace it on the surface, as the seam is small and usually covered with debris. At the surface it is about 100 feet from the qnartzite^ It is not again met with in the workings of the Eureka mine until it is encountered in se¥eral cross-cuts on the fifth level. Its dip and strike between-these levels seem to be normal and to conform with the dip and strike in all other parts of the mine. It is first found in contact with the quartzite on the twelfth level, 1,030 feet below the top of the Lawton shaft Near the K. K, line the junction takes place somewhat above the twelfth level. In the cross-cut to the Locan shaft, 12 feet above the twelfth level, the fissure which les between quartzite and shale is very narrow, but contains a foot or so of ore. As this level is followed toward the compromise Ine the quartzite bends-around towards the west, a block of limestone intervening between it and the fissure. The fissure comes in contact with the shale nearly as high up-as the ninth level, but the developments made at this point are not suMcient to determine at exactly what point the junction takes place. On the little-tenth (60 feet above the tenth), tenth, and eleventh levels the main fissure Ij^g ijjul^j. ii^Q f|)0|.,|^g^|i ^j. g0utliffestem side of the shale as the compromise line is approached. At or near this line on all these levels the shale bends-to the northeast, but the fissure continues its usual course. Its character in this region can be best observed on the tenth level of the Eureka and the seventh of the Richmond two corresponding levels. While in contact with the shale the usual clay filling of the fissure is much thicker and stained:

United States Geological Survey

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STBUCTUKB OF BUBY HILIi.

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sligMy yellow. M Ech of this clay is deri¥0cl from the shale by attritiott and the decomposing action o£ waters passing along the issiire.

ii*iiii«ii«iiitiniEiciiiiioiii.— The fissure leaves the shale at a short cross-ciit in the Michmoed ground just after the compromise line is passed, and is her© ¥ery narrow, although it is plainly defined, and contains from a few inches to a foot of clay. It continues its normal course, and is distinctly visible, with its filling of clay, along the northwest drift in the southeastern portion of the Richmond seventh level. After leaving the shale the space between the latter and the fault is occupied by stratified limestone, while the rock lying on the southwest of it consists of the usual broken and highly metamorphosed limestone. On the surface this fissure can be seen near the Richmond oflSce. On 'the first level of this mine it is in contact with the shale, 94 feet west of the Richmond shaft On the second level it is 35 feet west of the shaft, and is also in contact with the shale, and remains so down to the fourth, where it is somewhat split up, and exhibits a tendency to^ leave the shale. On the fifth level the fissure is found

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ail

Wm. l.—SfMion of fotnmtloiii to

A. crovMI limeitoiir. B. niaiii ltiHi>an>. C. atnliifMl liiinnitMic.

D, miitiiict of lilnitii^ii E. aliiilp. limMMtoae lUMi tluil*.

in the first north cross-cut 182 feet from the main drift. Between it and the shale the stratified limestone, which is here 30 feet wide, can be first definitely distinguished. This band of limestone, which increases in width as depth is attained, is always found on the hanging-wall side of the fissure,

32 SIIjVBI-IjEAD deposits of EUEBKA, NEVADA.

between it and the' shale below the fifth le¥el On the ninth it has been eross-cut for over 100 feet without the shale being encomitered. The diagram, Fig. 1, represents the relati¥e positions of the mineral-beaiing limestone, fissure, stratified limestone, and shale, as they are developed by a cross-cut The fissure is not often wide, but it exhibits unmistakable signs of a great upward movement of the country to the southwest of it. In places there are vertical striations, and the hard stratified limestone which fonns its hanging waU is often polished as smooth as ^lass. The Strata immediately adjoining the fissure are nearly parallel with it, but as they approach the shale their angle of dip becomes less until it is frequently as small as 20°. The contact of the stratified limestone mnd shale is very irregular, the strata of the two formations being intermingled, so that there . is no wel-defined line of demarkation between the two. This contact, as far as can be determined by the examination of the limited portion exposed in a drift, has less dip than the main fissure, but the dip of the bedding-planes of the shale conform very nearly to those of the limestone. The curvature of the planes of bedding in Imestone and shale shows the upward motion of the southwest country. The upper portion of the Prospect Mountain limestone which underlay the shale retained its stratification, and is now found to the northeast of the fissure, while the lower portion was forced upward to the southwest of the fissure, its stratification being for the most part obliterated by the crashing accompanying its translocation. This stratified limestone is of dai'k color, and is similar in character to that composing a large block which at the uplifting of the southwest country was left in a comparatively undisturbed condition. This rock can be observed on the sixth level of the Richmond, near the A. C. line (the dividing line between the Richmond and Albion mines), in the widest part of the mineral belt.

The places where cross-cuts have been driven up to the shale are not as numerous as could be wished, but there are enough of them to establish the general relative position of the fissure and shale, and it cannot be reasonably doubted that the fault is continuous between the points where it has been laid bare. This fissure, has very nearly the same dip and stiike that it had in the mines to the southeast. It extends through the Richmond

UNiTfn STATES GEOLOGICAL SURVEY

jjbixiu;

VTJRTirAI. CROSS SECTION N«B. RICHMOND MINE. I'HROrOII O P.

Prospect Mt Limestone.

Prospect Mt. Cnish<>d StraUfied Secret CA

Quartzite Limestone Limestone Shale Ore

Cd

Woriiinga projected on the Section

Scale 200 ft - I Inch

igj»jy 9o sp

United States Geological Survey.

Silver -Lead Deposits Pl.Xi

Vertical Cross Section N^ 10. Richmond Mine. Through S.T.

Prospc ct Mt Lime stone .

Prospect Mt Quartzite

Limestone

Crushed SlraUfied Limestone Limestone

Hi

Ih

Secret Cn Shale

Workings prqfected on the Section.

no

T

I

Scale 200 ft -I Inch

•P

f

•i»

Jt

'LfJlP f

•P 7 .?

T t

?

»

Pket •

r

_i?

United States Geological Survey.

Silver -Lead Deposits Pl.Xi

Jitliii* Elt«n * Co I.iuT

VERTI(L\L CROSS SKCTION N" 10. RICHMOTs^D MINE. THROUGH S.T.

Pro»pcct Mt Limestone.

Prospect Ml Quartzite

Cniahed Limestone Limestone

Strauned Limeatone

Secret Cn Shale

"Workmjs prqiected on the Section.

r

Mw

-f

Scale 200 ft - 1 Inch

•P

T

-r»

T

U.T f

T

Jl

Y

T

20

Id

Feet

T

-J?

• Stkucture Of Eijby Hill. 33

into the Albion, where it is smaller and less distinct and probably disappears altogether.

TheEttiij Hill fmiit mii tii« qnartsitc— Where¥er th© main fissure comes in contact with the quartzite the dip of the face of the latter corresponds with the dip of the fissure. The reason for this coincidence of dip is obvious. The face of the quartzite when in contact with the fissure is no longer the orig^ inal contact of quartzite and limestone, but is the fault face of the southwestern uplifted country. The manner of this uphea¥al is explained in Fig. 2, Plate IV. The change of dip of the face of the quartzite when it comes in contact with the fissure can be noticed on the vertical cross sections (Plates V. to XII.}. Up to the present time no signs of the fissure entering the quartzite have been observed, and it is not to be expected that it will do so until a much greater depth is obtained. Mevertheless, as all the shale and limestone beds and the quartzite pitch off latter as the valley is approached, it is but reasonable to suppose that the fissure will eventually enter the quartzite unless the dip of the fissure also should decrease very materially. From the fact that an important fault has taken place on the fissure, it is not likely that depth will effect its dip in any marked degree. Neither is it probable that it will disappear at any depth to which explorations can be carried, as the fault which produced it is so widely extended.

Mr. Hague says that the thickness of the Prospect Mountain limestone can be taken at 3,050 feet As close a calculation as it has been possible to make of the thickness of the bed of limestone between the lower or intercalated bed of shale and the Secret Cafion shale gives this bed a thickness of about 1,300 feet Allowing 100 feet for the thickness of the lower shale, there remain 1,650 feet of Prospect Mountain limestone. This calculation is based upon the measurements that have been made near the Eureka main incline and the Locan shaft, and presupposes that the dip of the strata is 40°. If there were no other factors to be regarded, the distance at which the Euby Hill fault could be expected to enter the quartzite would be about 2,200 feet below the twelfth level of the Eureka, or 3,230 below the top of the Lawton shaft It is almost ceiiain, however, that this distance will be very much decreased, owing to the fact that this lower bed of limestone has been very much crushed and pressed together by the 2i54

S4 ' SIIiTlK-LEAB BBPOS1T8 OF EUEBKA, NIYADA.

quartzite moving upward along the Ruby Hill fault It is rerj likely that", this distance will be considerably less, though there is not much probability that the fault will enter the limestone within 1,500 feet below the Eureka twelfth level. These calculations are made for the portion of country from which the ideal section, Plate I¥., has been made.

secondiiry i««iire.— At the time of the disturbance which produced the main, fault another and secondary issure was formed along the contact of tho-quartzite and limestone, and the quartzite was raised higher than the lime- Btoee, giving rise to the formation of a limestone wedge between the quartzsite on the one hand and the main fissure on the other. The dip of the-quartzite contact does not greatly exceed 40°, while the dip of the main issure is about 70°. The two surfaces of motion therefore approach each other and must eventually meet. In some mines this has already been shown to be the case, and the line of junction is exposed at various depths-in the lower workings of those southeast of the compromise line. To the-northwest of this line the lowest workings have not reached the junction.

The crashed condition of the limestone wedge is due to the upward movement of the southwestern country against the hanging wall of the main fissure. This upward movement also accounts in some measure for the disturbed nature of the contact between the quartzite and limestone, though there is no doubt but that there were many irregularities in this contact, before the faulting took place. This is shown by the contact between shale and limestone, which is also very irregular, but it could not have been produced by the fault, as it lies in an undisturbed region. The undulations-and protuberances in both quartzite and limestone were probably in the main produced by the primary folding which formed the hill.

Up to the present time all the ore of any impoitance taken from Ruby Hill has been extracted from the country southwest of the Ruby Hill fault,, between it and the quartzite. The limestone northeast of the fissure, or the- " front limestone," as it has been called, although it has been considerably prospected, has yielded no remuneration. An examination of the vertical cross-sections of the Ruby Hill mines (Plates V. to XII.) will explain the-relative positions of the two fissures and of the limestone and ore between, them, and the elevation (Plate III.) exhibits the line of their junction. Im

13

UNITED STATES GEClCOiCAL SURVEY

Silver- Lead Deposits P&#x27;. .Xib

J SCuraa.OeoktfUt .

STBUCTUEll OF EUBY HILL. 35

some places the cross-sections show that liie dip has again become slightly latter in the deepest workings, but this is probabl j not a permanent change.

Two iHiit. of .tale exist.— It has ftlreadj been mentioned that two belts of shale, only one of which appears at the surface, exist on Enby Hill. If the geological map of the district (Plate I.) is examined, it will be noticed that the shale and limestone contact on the surface lies at a considerable distance northeast from the Jackson, Phcjenix, K, K., and Eureka mines. Taking into account the general dip of the Secret Cafion shale on the surface and that of the shale where it ia encountered below, it is at one© apparent that the two must be distinct masses. On the third and fourth IcTels of the Jackson mine, in the cross-cut to the old shaft, a body of shale upwards of 100 feet thick is encountered, which lies on the east side of the main fissure and dips away from it

Lower iieit of »ii«ie in tiiii Annsriam imd jiicki©ii.^This lower shale has been faulted by the fissure, and the western portion has been raised up and can be seen in the American shaft cross-cut, described on page 28. Here it occupies the position where it was to be expected, namely, on the west side of the Euby Hill fault This is the only known place where this underground or lower> belt of shale is to be found on the surface, the faulted portion having been removed by erosion at all other points aboTCground.

In the cross-cut on the third level of the Jackson it is about fiO feet east of the main fissure and on the fourth it is in contact with it It is upwards of 100 feet thick on the third level and widens out somewhat as depth is attained, so that in the cross-cut on the fourth it is 145 feet wide. The dip of the contact of the shale with the limestone on the third and the rhyolite on the fourth is 70° toward the northeast The dip of the stratification, at its contact with the limestone or rhyolite, is ¥ery nearly the same

planes of bedding of the shale become latter, though-they again dip off more sharply as a fault plane is approached, which separates the shale from the black stratified limestone in which the old shaft was sunk. The stratified limestone northeast of this fault plane exhibits the same phenomena as regards dip as did the shale at its contact with the limestone or the rhyolite. The dip of this fault plane is about 70° northeasterly, and it

36 Silvkk-Lbab Beposits Of Eureka, Bevaba.

has a northwesteiiy and southeasterly course. Mo rhyolit© accompanies it, but between it and the succeeding stratified limestone there is the ordinary clay produced by attrition. The phenomena just described conclusively prove the uplifting of this country in benches.

The quartzite was most raised, sliding along its contact with the Prospect Mountain limestone; this limestone also being uplifted along the fiasmre while the shale was raised along the fault between it and the stratified Ime-stone. During the upward motion of these different benches each rising portion drew along with it more or less that which next succeeded. This is Visible in the present arrangement of the strata. In ascending it will be obserFed that the main fissure, which faults or cuts oif the shale, is no longer in contact with this rock on the third level of the Jackson, Fig. 2, Plate V. This is probably owing to the irregular form of the shale mass.

Tiie lower .Min In the Pi,«iai«._The next plac© where the shale is encountered is on the sixth level of the PhcEuix. It is laid bar© by a northeastern crosscut 50 feet long 31 lO feet northwest of the northeastern cross-cut from the main incline. At the point where it is to be seen it is but 50 feet from the main fissure, but as the drift does not pane through it it is not possible to determine whether the same fault exists that is to be found on the northeastern side of the shale in the Jackson. It is altogether probable that it does, however, and that this is the same body of shale that is exposed in that mine, as its position is that which would be occupied by the Jackson shale did it follow the course and dip which has been exposed in the cross-cuts to the old Jackson shaft Moreover it occurs on a In© between the next shale encountered in the Eureka and that found in the Jackson. The PlicBttix shale also does not appear on the surface.

i-iiwer stale In the E. K.— There is pFobably shale to be seen in the lower workings of the K. K., but as everything in that mine has been fiooded below the sixth level for several years, it was not possible to examine the ground, and information in regard to it was not reliable, as the clay in the main fissure haa often been described as shale. Still as shale is encountered in the lower levels of the Eureka and Phoenix mines, it is likely that it is to be found in those of the K. K.

Sc«l# 400 ft- 1 toGh.

MilipO 100 «0O lOO Mo IMO

Tt i i tTi i i t T I . I I I I I I I I I I

me 100 no

United States Geological Survey

Silver -Lead Deposits Pl Xiv

Julius Bl«n & Co LlOt

Prospect Mt Limestone

Prospect Mt Quarlztte

Cnifcht?*! Sti'atifird

• tone LinirHtonc Liinc«ton« Shale

Secret Cn Shale

J 9.Curtls.0«olofi»t

CnMS Fi«»<ireft

a Ihnr "i miij

U I I U I I I I?

«0D 000

E3 □

Scale 400 f t • 1 Inch.

1 I i 1 1 I I 1 L.

SfBUCTURE OF BUSY HILIi. • • ' 37"

i.onrer.iiiii«intii«Eiiwikii.— This niiidergroiiini shal© is exposed in the cross-cut from the twelfth level of the Eureka mine to the Locan shaft. Vertical cross-section No 7, Plate VIII., shows the position of this ehale. At this point it is ¥ery narrow, mot exceeding 20 feet, and is more or less mixed with stratiied limestone. In this region it probably extends up m high as the little tenth, and it forms the hanging wall of the main fissure, which takes up the space between it and the quartzite. During the process ot upheaTftl which formed the main fissure and the secondary fissure at the contact of the quartzite and limestone, there was considerable motion along the face of the quartzite, and the shale which lay northeast of the fissure was dragged upward, so that where it forms the hanging wall the dip of its stratification is nearly parallel with that of the fissure. This can be noticed in the cross-cut The natural dip of the shale, howe¥er, is less than 40^, so that as depth is attained it will gradually pitch off Matter and the limestone will again make its appearance in the form of a wedge between the fissure and the shale. This occurrence is already indicated on the thirteenth and fourteenth levels, where the limestone appears to be growing wider. This limestone, having been subjected to a pressure similar to that exerted in the upper wedge between the hanging wall of the main fissure and the quartzite, will be found to be in a like crushed and broken state. At a point on the tenth level just over the main incline, 140 feet above the twelfth, the sliale is found in contact with the main fissure, which is here some distance from the quartzite. In going southeast from this point the shale gives out, but in going northwest it is found in contact with the fissure. Further along toward the compromise line the cross-cut passes through it for 120 feet before reaching the limestone. Above this point the shale reaches as high as the little tenth, always forming the hanging wall of the ggg^jj,^^ Ij^I ^j^g ^^1 £q^jj^ ^i^^j,^ ii^^ ggg^^^ ij^g 1^^^^ ^^^ above it on the

ninth. Below the twelfth level it was not possible to inspect it, as the thirteenth and fourteenth levels have been under water for several years, but from information obtained it must occupy about the position laid down on the map.

This shale may or may not be the same as that which is found in the PhcBBix and Jackson, but the fact before mentioned, that it lies in a line

38 8iIi¥BB-IilAB BEPOS1T8 OF EUKEKA, MITABA.

with those two belts and also that it is accompaaied by a issmre 011 its hanging-wmll side similar to the one which occurs in a similar position with it in the Jackson mine, would tend to pro¥e that these three bodies of shsde were parts of a continEoiis belt Thej are moreover identical in their physical character.

dmnectioiioftiiiitwoiMiitiof ■imie.^If the shftle 18 twiced from the point where it is found over the main incline on the tenth le¥el of the Eureka past Ihe compromise line into the Richmond 8©¥enth, and from the seventh up to the sixth, and so on up to the fourth, and thence through the shaft to the surface, the continuity of shale from the lowest workings of the Eureka up to the spot where it comes to the surface back of the Richmond hoisting works is established. But, on the other hand, if it is followed upward from the place where it is exposed in the cross-cut to the Locan shaft on the twelfth level of the Eureka along the line of its contact with the main is-sure, it is lost sight of above the little tenth level of that mine. If it followed the issure, it would be found on the surface about 800 feet southwest of the Locan shaft, and in the Bell shaft tunnel But the shale on the surface lies over 300 feet northeast of that shaft There is no other shale on the surface between the Locan and Lawton shafts, and none is found in the former shaft until a depth of 1,020 feet is attained. The shale on the surface, however, northeast of this shaft can be followed around to the southwest of the Richmond hoisting works, so that the two masses of shale, the upper and lower, must be connected somewhere below, the Locan shaft being sunk in the limestone between them. (See Plate L).

Causes whlcli produced tlie junction of the two »liiile liclt».^— ThrOUgh the faulting incident

to the upheaval the lower belt of shale has been brought into contact with the upper or surface shale somewhere near the compromise line. At exactly what point this junction takes place, it is a difficult matter to determine, except on the tenth level of the Eureka and the seventh and eighth of the Richmond, owing to the insufficiency of the explorationp and the broken character of the ground; but it is evident that there is a junction as will be seen if the surface map is compared with the underground sections.

There is a sharp bend in the shale contact on the surface along the compromise line. From observations made below on the sixth, seventh,

United States Geological Survey

Silver-Lead Deposits Pl. Xv

Ideal Faulting Of The Two Shale Belts.

Stkuctuee Of Busy Hill. 39

and eighth levels oi th© Michmani, it is almost certain that this bend in the .shal© is not due to twisting and distortion, but was caused by a vertical fault which followed very nearly the course of the compromise line. When the couBtry was raised up, th© portion of it lying northwest of the compro- 'mise line fault was not raised to th© same height as th© portion of country lying on th© southeast side of it. In other words, the block of ground just •described subsided either absolutely or i-relatively. It is almost certain that in this manner the northwest end of the underground or lower body of shale was brought in contact with the surface or upper belt of shale along this •compromise line fault The position of the two bodies of shale southeast •of the compromise line favors this belief. Similar cross-faults noticed in the quartzite in the Eichmond mine also tend to prove the fact of a frequent cross-faulting of the formations in this part of the hill This being the case, the lower belt of shale must underlie the stratified limestone in th© Richmond mine, and it will be encountered at greater depth. At this lower level the ground must have very much the same appearance as the country •on the northeast side of the main fissure in the cross-cut to the Locao shaft The fissure, however, at the point where it cuts this lower belt of shal© might or might not be in contact with the quart-zite. A calculation made •on the basis of th© displacement of the shale on the surface would bring the lower belt of shale in contact with the fissure at a point about 1,700 feet below the top of the Richmond shaft, or about 500 feet below the present lowest workings. Another proof that th© lower belt of shale has been brought into contact with the surface shal© near the compromise line is furnished by the fact that the surface or upper bed of shale is always underlain by distinctly stratified limestone whereas th© lower shale is not This stratified limestone is not to be seen southeast of the compromise line or fault, where the lower shale makes its appearance. It will be noticed that this cross-fault does not in any way affect the course of the Ruby Hill fault; it was, therefore, formed at the same time or prior to it

iiitt«triiti«iiiftiiiiiii«iiiief of fcttitini.— Figures 1, 2, and 3, Plate XV., represent the manner in which the two belts of shale were dislocated by the cross-fault .and the main fault A B, Fig. 1, represents the upper or larger belt of •shale, and a b the lower, there being limestone between and on either side

40 Silvbe-Liad Deposits Of Bueika, 11¥Ada.

of them, which, how6¥er, for sake of clearness, is omitteii in the diagrams. The point of view is in the Eichmoud gi'ound looking towards the Eiirekfii| and the two bodies of shale dip easterly at an angle of 40®. The plane M N O P, Fig. 1, represents the direction of the cross-fault, which was the first on© to occur. This fault takes place nearly on the compromise line, and has a nearly ¥ertical dip. When the faulting occurred the Mocks B and fe, representing portions of the two shale belts, slipped down until they occupied the positions relative to the blocks A and a shown in Fig. 2. The plane Q E S T shows the direction of the main fault, and after it occurred the pieces a' ¥ and B' were raised above the present surface of the ground, and have been removed by erosion. The piece a' con^esponds to the shale which was cut off from below the ninth level of the Eureka; the piece ¥ is the con-responding portion of the lower belt of shale, supposed to exist below the present workings of the Eichmond, and B' is the part of the larger mass of shale, which was removed by the main fault. The face n, Fig. 3, represents, the shale as it now exists in the Eureka, and the face B represents the shale in the Eichmond. The irregular lines on the tops of blocks A and B represent the surfaces of erosion as nearly as possible as they exist at present. If the line efg km taken as representing the Eich-mond seventh and the Eureka tenth levels, it will be seen that conditions exist in these ideal beds of shale similar to those which actually occur in the two mines. In the Eichmond the contact between shale and limestone is continuous to the surface, and it can also be traced in to the Eureka ground along the tenth level of that mine, but cannot there be followed to the surface.

Plate X¥I. represents a projection of the different formations that are found on the hanging wall of the main fissure upon a vertical plane parallel to its course. The point of view is from the mineral zone. The various beds of shale are lettered to correspond with those in Fig. 3, Plate XV. As the strata of shale and limestone were not only very much crumpled and disturbed before the faulting took place, but during that dislocation as well, the structure of this country is very complicated, and it is a matter of great difficulty to trace the movements that have taken place.

United States Geological Survey

Silver- Lead Deposits Pl Xvi

VERTICAL PROJIlLTION- HANGING WALL OF THE MAIN FISSURE IN THE RICHMOND AND EUREKA MINES

Prospect Mt Limestone.

Crushed StraUTied

Limestone Limestone Limestone .

Secret Cn Shale

E

I i 1 jT I I I M

40O Sou

Scale 'lOO ft - I Inch.

lOOD ISOO

Iboo 700O

SIOWB IS0IS0 1«0U0K»af> som> to o

Stmuctumb Of Buby Hill. 41

simieiiitinsiiJMoa,— A large part of the work which has been done in the lower l©¥els northwest of the A C* line has been performed by the Richmond company.

On this end of the hill the shale does not present any remarkable features. Its contact with the limestone is irregular, as usual, but its position underground conforms very nearly with that which it occupies on the surface, always allowing for the dip of the formations. There are occasionally masses of it intruded in the limestone. South of the Albion shaft it is in close proximity to the quartzite, touching it in places. The quartzite referred to is a nan'ow belt of quartzite, which will be described hereafter. The shale is shown in the various horizontal sections, and it retains its general relations to the limestone down to the deepest point west of the A C line, namely, at the end of the ninth level of the Michmond.

Front limestone.— The time and manner of formation of the Muby Hill fault, and its subsequent illing either with rhyolite or clay, are matters of very great importance as regards the history of the mineralization of the limestone between the quartzite and the fault-fissure and the prospects of finding ore either at a greater depth or by prosecuting developments in the so-called front limestone. This body of rock lies northeast of the main fissure, and although it has in many places the appearance of the ore-bearing ground has hitherto been found unproductive, all the ore having been obtained from the limestone wedge between the main fissure and the quartzite. It is true that the prospecting done in the front limestone has not been sulficient to prove that it contains no ore bodies, but it has been sufiicient to discourage search in that direction. It shows at any rate no such outcrops as were apparent in the Champion, Buckeye, and Tip-Top claims (the original locations of the Eureka Consolidated and Richmond companies), situated lj^ ll^^ g^^ll^^j^gl^j^ gl^p^ ^£ £^|jy giii^ j^gi ^1^^^^ ii^^ qjjj^j,|.2j|.^ ^^^ limestone contact If the theory, which will be discussed hereafter, is correct, namely, that the ore was brought up in solutions from below through the main fissure, the barrenness of the front limestone is easily accounted for

•Tie A C line is parallel to the compromis© line, and is tlie diYiding line between fclie Kichinond and Albion ground, which wae established by the courts in the suits between the two companies. Prior to the ixing of this lino the Richmond company had explored a large portion of the ground which is now held by the Albion.

42 SILFER-LIAB B1POSIT8 OF EtIRElIA, METADA.

"by the presence of the lower belt of shale. The shale in general is mnlavorjible to the passage of solutions of an j M nd, as well m to the deposition of ore, and in this particular instance (see Plate ¥111.) it meted as a barrier to confine the metalliferous solutions to the wedge of crushed limestone abo¥e it, between the main and secondary fissures.

Front limctonii in tic Eurcta.— The explorations in the front limestone consist of a few cross-cuts from the different levels of the K. K. and Eureka mines. The principal of these cross-cuts is the one connecting the twelfth level of the Eureka with the Locan shaft This cross-cut is 508 feet long and is •driven from its junction with the twelfth level, near the station of the main incline, in a northeasterly direction, through the upper belt of Prospect Mountain limestone lying between the upper and lower belts of shale. The rock through which it passes does not differ in any material respect from the limestone which is found above between the quartzite and main fissure; but it is harder and more compact, and does not show evidences of having been crushed and disturbed to the same extent as the latter, except in the immediate neighborhood of the fissure. It is dark colored, and shows some ■slight signs of stratification.

Front limeitone in the K. K.— The cross-cut ott the sixth Icvcl of the K. K. (see horizontal section No. 2, Plate XIII.) lays bare another portion of the froot limestone. This drift is over 300 feet long, and although the limestone is •different in color and texture from that in the cross-cut just described, there IS no greater difference than can be observed in varieties of limestone in the mass between the quartzite and fissure. Samples for assay were taken •every 30 feet in this drift, and the results obtained will be discussed in the •chapter on assays. No signs of stratification were observed in this limestone, and it was of a grayish-white color. It is harder and more compact the farther it is removed from th"e contact with the fissure, and it is highly •crystalline in texture. It is considerably broken near this contact, and portions of it are crushed and mixed with the clay. The limestone between the fissure and this quartzite is crushed to a powder in many places, and forms a narrow belt scarcely a foot wide, which is often stained with iron. In another cross-cut, some 30 feet long, farther to the southeast, the limestone is of a blackish color, and breaks in sharp angular pieces. Similar

STRUOTUKl OF BIJBY HHjIi, ' 43

material, however, can he found in many places in the mineral belt, and this dark rock exhibits no characteristic features that would distinguish it as coming from the fi'ont limestone.

cii*«icteri«ti« of tiM front limestoiie.— It has not been possible to find any charac- ■teristic features in either of these two" limestones which would distinguish them from each other; and although the littiestone southwest of the fissure -certainly belongs to the lower belt of limestone and that northeast of it to the upper, yet there is nothing in the appearance of either that would indi- •cate that they belonged to different masses unless it is that the front lime- .stone is less disturbed and that its stratification is more fi-equently perceptible.

Tlie qiimrteitc •oiitlieaat of the oomprointee line.— The qUftrtZlte in the foUF minCS SOUth-east

of the Richmond shaft appears to be substantially a solid mass many hundred feet in thickness. Its contact with the limestone is very irregular, •and the rock near the surface is often displaced to a greater or less extent by faults, but it is comparatively easy to explain these irregularities and to account for the phenomena exhibited. Not so, however, with the quartzite in the Richmond and Albion gi-ound northwest of the working shaft of the former mine.

TiieiiiiarteiteiiitteEiciiiiiciiiiiaiiiiAiwoii.— The explanation of the occurrence of this quartzite and of the manner in which it was brought into its present position in this part of the hill is a matter of great diiSculty, partly owing to the absence of sufficient explorations in the neighborhood of the Eichniond shaft and partly on account of the complex character of the movements which have taken place. The quartzite (see Plate III.) on entering the Richmond ground from the Eureka bends toward the west, as has -already been stated, and forms a promontory which pitches to the north. This rock is first encountered in the Richmond shaft at a point about 30 feet above the seventh level and the shaft continues in quartzite down to the deepest point reached, namely, a perpendicular distance from the surface of 1,230 feet, which would give the quartzite a vertical thickness of at least 580 feet. A cross-cut on the twelfth level, driven a little east of north, passes through 360 feet of this rock before reaching the limestone. A cross- •cut on the 1,050-foot level driven a little west of north strikes the limestone

44 Silybe-Liad Deposits Of Btjbika, Metaba,

160 feet froiii_ tlie shaft. It will be seen that hotli of these cross-cttts are mil through the a1bo¥©-meiitioiied promontory, and that they ^v© some idea of its shape at the depth at which they were run. These cross-cmts and other workings in. the Michmond ground . near the compromise line prove that the qnartzite in which the shaft is sunk is the main body of quartzite which nnderlies the limestone of Ruby Hill. (See Plate XIV.)

ThemirrciwiiiiartMtii.— At Variable distftnces, according to the depth attained, northwest of the Richmond shaft, the secondary fissure, as the contact fissure between quartzite and limestcine hag been called, leaves the main body of quartzite and passes off into the limestone. It can be seen on all the levels of the Richmond and Albion mines where the workings have been pushed sufficiently to the south and west, bnt it is particularly well developed on the second and fourth levels of the former, where its course has been followed by drifts until it disappears in the northwest "portion of the Albion ground. The most remarkable feature connected with this fissure is the fact that it is accompanied by quartzite. In the upper levels this quartzite is a very thin band, seldom exceeding 10 feet, and often much less, but in the lower levels it is much wider, reaching a breadth of 80 feet on the Richmond ninth level. Its junction with the main body of the quartzite is not clearly shown on any of the levels, but it is considerably northwest of the shaft in the upper levels, and gradually approaches the shaft, as depth is reached, until on the ninth level it is at about the point shown on the horizontal section No. 6, Plate XIV. The fissure is plainest on the upper side of this narrow belt of quartzite, but a parting is nevertheless distinguishable in many places on the under side". There are several cross-faults and undulations in this quartzite, which were probably produced by the primal upheaval. As the problem of the occurrence of the quartzite in this portion of Ruby Hill is as complicated as that of the shale near the compromise line, a detailed examination of its appearance is necessary to a full comprehension of the phenomena attending the formation of the mineral zone.

Dctcription of the quartiiite in ietaii.^In the Richmoud the quartzitc is first encountered on the second level, but it has not been as thoroughly explored on that level as it has been on the fourth, 200 feet below it. It is not certain at

Struct0B1 Of Ruby Hill. 45

exactly what paint oe this latter level the quartzit© begins to thin out, but an alteration in its width is irst noticeable about 800 feet westerly from the shaft. (See Plate XIII.). Here the qeartzite is but a few feet thick, and a short distaiMje farther to the west it is but a few inches, being scarcely more than a seam illed with qiiartzite, limestone, and clay. This character it retains in the continuation of this level, varying in thickness from a few inches np to 20 feet or more until the extreme northwest workings in the Albion ground are reached. Near the point where this thinning ont of the qnartzite is noticed there are nnmistakable signs of a fault This fault is of no great lateral extent, and forms one of a series of similar faults which are found in this narrow strip of qnartzite at various points on the different levels. These faults have a general northerly comrse, and dip sometimes easteriy and sometimes westerly. What has been the extent of the faulting in a vertical direction cannot be determined with any certainty, but in some cases it has been considerable. At the point mentioned above, there are two slips; bnt it is the one which has a westerly dip of 85^ that seems to displace the qnartzite. One hundred feet beyond this point a drift has been ran into the " back lime,*' as the limestone is called which lies on the southwestern side of this narrow strip of qnartzite.

In proceeding along the fourth level from the shaft, the main body of qnartzite is l^ft at some unknown point, the explorations that have been made in the back lime not having been smiScient to discover it, and the narrow band that is followed is but a splinter from the main mass. On the Richmond fifth level the qnartzite is to be found at two points. The first is about 200 feet south of the shaft, and the second is at the end of the first southwest cross-cut In both places it appears to be the main solid body. Still it is possible that at the last point it may be only 50 feet thick, for it is found no wider than that on the sixth level 100 feet below and some little farther west The explorations on the sixth level (Plate XIII.) lay bare the contact of the quartzite and limestone for a long distance. The end of the long southwest cross-cut, which is called the fissure drift, reveals the same fault in the quartzite that is exposed on the fourth. In the southeasterly branch of this southwesterly fissure drift the quartzite is found to be 50 feet thick. It is faulted and brought down to a seam by the fissure which

48 SILTEE-LBAB DEPOSITS OF lURlKA, MIVABA.

followed the southwestern _ "brancli of this drift, bet in all probability it widens out again in the manner shown on the map, as it is found at the southeast onthe first level of the Albion 30 feet above the Richmond sixth. It there follows a course almost identical with that exposed above it on the fourth. It seems to have the same bends and twists exhibited on that level, and it is likely that its position at any intermediate point between the two^ levels could be calculated within a few feet. Both in the Albion first and in the Richmond fourth, 170 feet above it, the quartzite also comes in contact with shale bodies, and the manner of occurrence in the two cases is-very similar. The quartzite on the Albion first is very narrow, and although it lies along a well-defined fissure it is not an easy matter to obtain characteristic specimens, as it is much mixed with limestone and clay- On the seventh level of the Richmond there is a fault 190 feet from the-shaft, but it lies over 200 feet to the southwest of the point at which ita position above would indicate its reappearance. The quartzite and lU accompanying fissure is found at the southeast end of the Albion second or intermediate level At this point it has been cross-cut ten feet and the-back limestone has not been encountered. In following along this level, the fissure, which is here nearly perpendicular, leaves the quartzite. It is-true that this fissure contains more or less clay and , quartzite for a considerable distance, but the limestone on the southwest side of it does not seem to have the usual characteristics of the back limestone. In passing along the eighth level a fault is again noticeable, at a point where there is a sharp bend in the drift 390 feet west of the shaft. The point is nearly direciy below the fault on the sixth.

As the seventh level does not extend far enough south to expose thia fault, were it in the position on that level indicated by its occurrence on the-sixth and eighth, it is impossible to tell whether the fault which is exposed on the seventh, 1 90 feet from the shaft, is the same as the one on the sixth and eighth. It possibly is another fault, but those exposed on the sixth and eighth must be identical Shortly after leaving this point nothing more isto be seen of this quartzite on the eighth level until it is laid bare in the south cross-cut west of this fault. It is here about 30 feet wide, and i» somewhat different in character from the ordinary quartzite. It is grayish

STEUOTUBl OF KUBY HILL. 4T

in color, rather slaty m kminatei in texture, and sandj to the tcmcli. A close examination, however, shows that it is quartzite. This cross-eiit is ran? some distance into the back lime, which has its usual hahitus. The quartz-it© is again laid bare on the third le¥el of the Albion, which coiTesponds with the Michmond eighth, in two westerly cross-cuts from the Albion shaft The qiiartzite has been faulted by a issure near the winze which descends-from the Albion second, and is not visible along the southeasterly drift.

On the ninth level of the Michmond (Plate Xl¥.), which is run almost entirely in back limestone, the qnartzite, except near the shaft, is of the same character as that which appears in the south cross-cut on the eighth. Near the station, another fault is discovered. Again the question arises,. Can this fault be in any way connected with the others above it f It is-most likely a separate fault which here shows itself for the first time. Southeast of the shaft, toward the compromise line, the quart-zit© retains its normal character and apparently its normal thickness.

On the ninth le¥el the narrow belt of quarfczite must join the main mass somewhere between the north cross-cut from the water drift and the shaft What the position of this dismembered mass may be on the l,CI50-foot and lower levels future developments alone will show. In descending, this belt of qnartzite widens until on the ninth level it reaches a width of over 80 feet in places. On both its hanging and foot wall sides, but especially on its hanging, it exhibits signs of considerable motion, and it is more or less mixed up with limestone at the planes of contact, and occasionally contains fragments of the latter rock even at a considerable distance from the limestone. Its lamination seems to be due rather to the effect of movement under immense pressure than to the manner of deposition. Where the quartzite is found unbroken and of the normal character it shows no such indications of stratification.

Dip«ini«trik«iif thetiiininnirteite.— The dip of thjB contacts of this belt of quartzite is much greater in many places than that of the main mass, although its irregularities are such that it is impossible to make an exact determination. The average dip in the levels above the Richmond ninth is about 45", but in the lower levels it would correspond more nearly with that of the main fissure. The course of this qnartzite is very tortuous, as a reference to th#

48 Sil¥1M»Lbab Diposits Of Bueeka, Nevada.

various hoiizoetal sectioBs will show; but it is remarkable in this respect, the irregularities nearl j coiTespoad on all the levels.

ReiatioMof tiieqttmrt«it«Miii«iicoiiiiiryiMii«i.— The motioii of tMs quftrtzit© upward along the plane of its contact with the limestone has already been mentioned. It is a difficult matter to. tell what has been the extent of the upward motion, but that it has been verj considerable is shown by the comminutioE of the qeartzite and limestone at their contact, and the nrnmerous striation marks where either of these rocks have remained in a solid condition. When the main fissure was made and the faulting took place which raised that portion of country lying southwest of the fissure, the qnartzito was moved up, not only along the fissure, but also along the plane of its contact with the limestcine, and the limestone wedge between the qnartzite and the fissure slid back against the limestone hanging wall. The upward motion of the qmartzite crushed and otherwise dismembered the limestone lying between it and the solid northeastern wall. When the fissure between the quartzit© and limestone reached a point southwest of the present Richmond hoisting works, it shot off into the limestone instead of following around the contact plane of these two rocks, which turns towards the south. The continuation of this quartzite fissure is the fissure which is found in the Richmond and Albion mines accompanying the narrow band of quartzite, and which has been descrirbed in detail. The Ruby Hill fault fissure lies much farther to the northeast, near the shale, and has also been described in detail. The positions of these two fissures and their relations to each other can be observed in the different maps and diagrams. They are designated by heavy black lines.

The manner in which the narrow band of quartzite found its way into its present position seems to admit of but one solution, namely, that its occurrence is due to a succession of faulting movements which followed the line of the accompanying fissure, and that it originally formed part of the main body of quartzite which must here underlie the limestone. It is altogether improbable that it constituted a distinct bed of quartzite laid down upon the back limestone. In this case some indications of its existence would have been noticed in other parts of Ruby Hill It is not possible

STSUCTUEl Of BUBY HILL. 49

either ttat it is quartz, and was deposited after the fonnation of the issmre, as under the microscope it exhibits the structure of quartzite.

Relation of the twiilMiife* to the cmitttry rock.— The tWO fisSEFeS, the SeCOIldarj ftlld

main fissmres, do not exhibit a width which is in any way proportional to the amount of movement which has taken place along their planes. The main issnre in the Eureka, and other southeastern mines, is very strong, often having a width of 12 feet or more, but in the Eichmond and Albion it is scarcely more than a seam, and woald naturally not be considered of much importance if the great difference in the country rock on each side of it was not taken into account The secondary issnre, although it is always accompanied by more or less clay, does not always exhibit absolute proof of its nature, and in some places might be mistaken for the ordinary contact of two dissimilar rocks, but when considered as a whole and in conjunction with the narrow strip of quartzite in the Eichmond mine the fact that it is a distinct rent in the earth's crust can hardly be disputed. Back iiBiMtoiie.— This term is used in reference to the limestone which is found on the footwall side of the narrow band of quartzite, which in the Eichmond and Albion ground accompanies the secondary issure. In the cross-cut run into the limestone at the point on the fourth level already mentioned (page 45), the quartzite appears in the roof of the main drift, and is scarcely more than a foot wide. Except that it is mixed more than usual with clay and limestone, it differs in no w«y from the ordinary quartzite. It has the same pinkish color and friable nature. The back Imestone is pulverized almost to a powder at the contact, but becomes more compact as the drift penetrates farther from the issure. This limestone differs in a great many respects fipom the limestone which is encountered between the quartzite and shale. It is blackish, breaks with an angular fracture, has a somewhat glassy appearance, and its planes of fracture are lined with quartz or calcite. It is a highly metamorphosed and somewhat siliciied limestone, and contains some bituminous matter. At yet no ore of any kind has ever been found in it. Its peculiarities are very characteristic, and it is easily recognizable wherever found. Specimens taken at a depth of 900 feet are not distinguishable from those that have been taken at four. 2664 L— 4

so SILTEM^LBAD DEPOSITS OF ItJElKA, MBTADA,

Relatioii of the Ruby Hill fimlt to the Jackson finilt.^lf th© 81lrfaC6-IIiap, Plate I., iff

examined an ©xtensi¥e fault will be noticed just east of the Jackson hoisting works. This fault extends a considerable distance to the north and south, and has been called by Mr. Hague the Jackson fault The maia fissure of Ruby Hill, the one containing rhyolite, joins the Jackson fault Bomewhere south of the Anaerican shaft, but at exactly what point has not yet been determined, the surface of the ground being covered by debris, while the underground developments are inconsiderable. It has baen stated that the limestone in which the American shaft is sunk is the Pogonip limestone. It is therefore possible that the main fissure of Ruby Hill is identical with the Jackson fault at this point, though the fault laid down by Mr. Hague runs nearly due north from the American shaft That there is another fault parallel to the main Ruby Hill fissure is clearly shown on th© cross-cuts to the old Jackson shaft, and it is probable that this other fissure is no other than the one which Mr. Hague has called the "Jackson fault ''^ There seems to be ¥ery little doubt that the eruptioiifl of rhyolite which occur in this neighborhood, of which Purple Mountain is a prominent example, are intimately connected with all these faults.

OHAPf EE ¥.

OBKS OF PBOSFKCT MOHNTAJOf AHH BTIBY HJCLIi. C3a»«llmtioii of til© I%«ipect Miiiiiitaln ani Eiiliir Hill ii«s«.^Tll© OTBB of Ruliy Hill MB tO

he classed under the head of argentiferotts-aiuiferoiis lead ores. They are 0f two classes, oxidized and mnoxidized, thoegli np to the present tim© almost all the ores produced by the mines of Ruby Hill have been of the former character, snlphnrets being only found in a very few places in a region two or three hundred feet above the water level and in some localities below it. As might naturally be expected, the line which divides the ojddized from the mnoxidized ores is not sharply denied, and the transition is a gradual one.

Inlnencaof tlieiif«ter-IeircliiiioKii«tloii.— In 801316 plaCCS whorO OF© is foUnd ftt ft

considerable distance below the water-level, it is in an altered condition, which would seem to point to the fact that the present water-level is somewhat higher than it has been at some previous time. This is probably the case, as it is not possible that oxidation could have taken place at any considerable depth below the surface of the water. The workings of the mines of Euby Hill have at present reached a depth of over 1,"20§ feet, the deepest point being the bottom of the Richmond shaft. The greatest depth at- . tained in the old workings of the Eureka is 200 feet higher than the bottom of this shaft. From the lower workings of the Eureka up 200 feet the ground has been iooded for several years. The water rises 150 feet in the Richmond shaft, but remains at that point. From this it will be seen that there is a difference in water-level of 250 feet between the two mines.- The surplus water from the twelfth level of the Eureka lows down a wime to the Richmond ninth level, 70 feet below, and inally reaches a permanent level in another winze 180 feet deeper. In the Richmond mine no ore has been found below the ninth level, 900 feet from the surface, so that it cannot be determined with certainty what its mineralogical character may be below the water-level.

52 Siltee^Liab Beposits Of Bueeka, Nevada.

It will be noticed from a referenc© to the actual w ater-le¥el line marked on the eleTation (Plate III.) that it is verj irregular, showing that there is not everywhere a free circulation of water between the extreme workings on the mineral zone, as well as that the water-level at the northwest end is verj much below that at the southeast The irregularity in the character of the ore in the neighborhood of the present water-level is no doubt due to the rise and fall of the water at different periods, and to the nature of the ground, which in some places is more accessible to the action of the air.

Local iiiie»iicii« in the Rnhj Hill oim.— Although there me some slight local differences in the ores produced by the mines of Ruby Hill, they are so inconsiderable that it is not necessary to describe them by localties, and although their variety is very great, yet the different oxidized ores do not seem to be confined to any one level or any particular chute 4)f ore, but occur indiscriminately at all depths. Snlphnrets, particularly galena, are found to some extent intermingled with the oxidized ores, but those represent mere remnants which have ©scared oxidation and are nsnaly insignificant in qnantity. Masses of snlphnrets occur only below or near the water-lne.

iitoef«ii©coifriiiiiiiiiiiiqrHitt.^B©fore dsscriMng the different varieties of or© found in the mines of Mmby Hill, it may be wel to mention the minerals of which thoy are composed. It is very possible that other minerals than those which are given in the following list occur, bnt as their presence has not been detected in the careful examinations wMch have been made" of the ores, it is not likely that they exist in any great quantity, or that they are very nnmeroms.

The galena is msnally of a medinm grain, and more or less mixed with sulphate of lead. It occurs in the form of nodules, which are changed at the mrface into snlphate and carbonate of lead, and in irregnowing

to the admixture of sulphate, and contains small quantities of arsenic and antimony, and in some cases molybdenum, which is probably in the state of sulphide. It usually carries from $100 to $150 per ton in silver and from $1 to $10 in gold. It is richer in silver and poorer in gold than the average ores. Psendomorphs of galena after other minerals, although they may exist, have not been noticed. This fact renders it improbable that any sulphide 'Of lead has been deposited since the period of oxidation.

The Oris. , 53

Anglesite (sulpliate of lead) is an important mineral in the composition of the Eareka ores. It forms a large portion of the "yellow carbonate '^ of the miner, and is present to some extent in all the lead-hearing ores of the hill It is the product of the decompositioii of the galena, and occurs in three forms: as colorless crystals in geodes in the galena and other ores in a manner that shows that it was deposited from a solution of the sulphate; in compact masses of a dull black color, usually containing undecom posed sulphide and a kernel of galena; and in finely divided particles disseminated throughout the ore. In the latter case it is not distinguishable by the eye, and its presence can only be detected by the usual tests for sulphuric acid and lead.

Cerussite (carbonate of lead) almost always occurs crystallized, sometimes in acicular crystals mixed with other minerals throughout the ore ; sometimes in geodes and surrounding nodules of galena and anglesite, and in massive aggregations -of small crystals of a dark color. In this latter instance it is called "sulphuret ore" by the miners, and probably contains an admixture of mimetite, as arsenic acid can often be detected by means of the blow-pipe. The dark color is due to the presence of manganese. It is evidently the ultimate product resulting from the decompositioii of the galena after that mineral had been changed into sulphate. It seems also to exist disseminated in a finely divided state throughout the so-caled "red carbonate," a mixture of different lead minerals and hydrated oxide of iron, for this ore gives a reaction for carbonic acid whl© it contains scarcely any lime.

Mimetite* (chloro-arsenate of lead) is found in colorless crystals

•Anffcljsis of colorless mimetite from the Bidnnoncl min©, Eorekii, Wevudii, bj F. A. Massie, of tie University of Virgiaia :

Til© sf ecimcii con silted of slender, almost acicnliir, lexagonal prising, aggregated into m friaW© jjjj^gg^ ^IIIj ji fy^ gniaii crygiaii, ©f imifcnit© gcattened fclrongloiit it. Th© IndiTiiiial crystals wer© color- IMS and transpaieiit, with ftdamantiii© luster imi wMtm stiemk, tlio generiil aspect of tlio mass Tiny mmcli like that of cariiasit©. Hardness = about 3 ; sp. gr. = 6.92 ; very ©asilj fusible. Analysis g»¥© :

PbiOi t»c«

PbO 68.21

PbCli BM

100.31 In aecurdimoe wltli tli© wofl-known fommlm :

64- SIIiTEB^IjEAB BEFOSIIS OF EUEEKA, ¥B¥ADA,

and in yellow masses more or less mixed witli Bttlphate. The occmrrence of crystals is rare, but the "yellow carbonate^* oi»u contaies considerable quantities of tliis mineral. As the galena which has bean focmd in the mines of Emby Hill rarely contains much arsenic, it is not likely that mimetite was formed through the oxidation of galena alone, bEt that it resulted from the simultaneous decomposition of that mineral and arsenopyrite. This is made probable by the fact that the "yellow carbonate/' a widely distributed ore, although it is sometimes composed of sulphate of lead and hydrated oxide of iron alone, is usually a mixture of sulphate of lead, cMoro-arsenate of lead, and hydrated oxide of iron. If the "yellow carbonate*' resulted from the decomposition of araenical galena alone it would not contain the hydrated oxide of iron except as an admixture. That the iron is not always an ingredient resulting from a subsequent mixture of the products of oxidation is shown by fragments here and there in the mass wMch retain the original structure of the minerals which composed them.

This mimetite has been found in the form of stalactites, stalagmites, and in columns in vuggs in some of the ore bodies. It occurs as minute hexagonal crystals surrounding a core of some brown mineral, wMch is probably limonite. The vugg in which the specimen belonging to the collection was found occurred in the upper part of an ore body, which was distinctly stratiied, indicating that the material composing it had been re-arranged since it was oxidized. The minerals in tha interior of the vugg had evidently been -crystallized from solutions since the rearrangement of the ore. The manner of formation of these stalactites, etc., seems to be plain. The araenopyrite, pyrite, and galena, which formed the original ore, were oxidized, sulphate of iron being irst formed. This sulphate of iron tricMed down, forming numerous columns, upon which the later product of decomposition, mimetite, was afterwards deposited. In time the sulphate of iron lost its sulphuric acid and became limonite, which remained as a core.

Wulfenite (molybdate of lead) is of frequent occurrence in the ores of Euby Hill It is found as aggregates of ine tabular crystals • coating nodules of galena changed into sulphate and carbonate, and frequently mixed with crystals of the latter as well as in minute crystals disseminated

throughoEt the ore. Some of tbe galena coetains considerable molybdejmin, but whether the quantity contained in it will account for the presence of the considerable amount of wnlfenite in some of the ore is a matter of ■dottbi From the manner in which some of it is found surrounding nodules of galena caeying molybdenum, and from its occurrence mixed with the -other products of decomposition of that mineral,, it is e¥ident that a portion -of it at least was formed by the decomposition of the molybdeEnm-bearing .galena. Thus far the existence of molybdenite (sulphide of molybdenum) has not been detected in the oxidized or nnoxidizjed ore. It exists, how- ^•ever, in the underlying qnartzite. Seireral Bpecimens of this mineral were found in sinking the Richmond shaft from the 900 to the 1,200-foot le¥el, .also in the cross-cut from the 1 ,200-foot station through the qnartzite to the limestone. As it is usually found in the qnartzite, it is in a ¥ery inely divided state, and were it not for the few exceptional specimens that ha¥© been found, its presence would ha¥e been overlooked. It is probable that its occurrence in the quartzite is due to secondary causes, and that, like the pyrite, it was not an original constituent of that rock. It is not improbable that it will be found in considerable quantity in the uooxidized ore below 'the water level.

Pyrite and arsenopyiite both occur in the unoxidizsed ores, and the former is found in the quartzite and in some of the other rocks of Ruby Hill Arsenopyrite is not as plentiful in the unoxidized ores as the amount of arsenic in combination with lead in the oxidized ores would lead one to expect, if the theory that arsenopyrite was the original source of the arsenic is correct; but the bodies of sulphurets hitherto discovered have been so few and small that they cannot be taken as representing quantitatively the minerals which originally composed the oxidized ore bodies. M arcasite has been observed in the shale.

Limonite (hydrated sesquioxide of iron) is the principal component ^of the Euby Hill ores. It stains the ore from a light brown to a deep reddish-brown according to the quantity present and the extent of its hydration, and together with mimetite forms the coloring matter of the "yellow carbonate.^' It is sometimes found _ compact, but is usually ue- . evenly distributed throughout the mass of the ore. Pseudomorphs of this

56 Silvbk-Lbad Biposits Of Eubika, Mevada,

mineral after pyrite have occasioeally been obserred. Hematite (sesquioxide of iron) is also present in the ore, but it in not as often met with m the hydrate.

Blende (sulpliide of zinc) is found to some extent in the upper portions of the mines, and is of frequent occurrence in the lower workings in connection with pyrite and galena. It is nsnally a dull black cryptocrystalline substance, but is sometimes crystalline. In the latter form it is found in the "black" chamber between the eighth and ninth levels of the Eureka mines.

Calamine (silicate of ssinc) is often met with in ine characteristic crystals in connection with earthy limonite.' It usually occnra at the junction of ore bodies with the limestone, and in many instances is psendomorphons after that rock.

Smithsonite (carbonate of zjiec) is no doubt present in the ore and is the product of the decomposition of blende, but no characteristic specimens have been noticed. Zincite Xoxide of zinc) is probably present, but its detection is difficult on account of the admixture of iron in al the ores.

Calcite (carbonate of lime) is everywhere found in the Eureka mines. It occurs transparent, but is usually of an opaque milky color, cementing together the crushed mass of the rock and in clumps of crystals in vuggs and other ca¥ities. Calcite is of rare occurrence in the ore itself. The calcite, as well as the limestone, carries more or less carbonate of magnesia, but none has as yet been found which contains sufficient of that substance to entitle it to the name dolomite.

Aragonite (orthorhombic carbonate of lime) is of frequent occurrence. It is particularly plentiful in the caves and smaller cavities of the limestone, where it often covers the entire roof and walls. In many places it is constantly forming from the water which is oozing from the limestone. It occurs in the form of radiating groups of acicular crystals and as fibrous • crusts and nodules covering the debris on the floors, as well as on the sides and roofs of the caves.

Meiimreineiit of tiie g rowtii of «Mf onite cryitmia.— Somc observations Were made iu a large cave between the ninth and tenth levels of the Eureka mine in regard to the growth of these crystals, which were measured as follows: 'A co-

IHl OSES, 57

ordinate scale pasted on a board was liiiEg directly beMnd the group of crystals, the growtli of which was to he measured, and a trsHsit instrument was placed at a coE¥lenient spot at from 10 to 15 feet in front of the scale. It was found con¥©ment to use a transit, as the construction of this instrament permitted the removal of the telescope without the derangement of the tripod, and as the moisture collected so fast on the lenses within the telescope that it was impossible to observe the crystals if it was left underground over night When the telescope was replaced it could be put exactly in its former position, thus preventiug any inaccuracies which might arise from the removal of the point of obser¥atioE from the original line of sight The temperature in this case remained at nearly 54|^ F. (30.1 C), the Yariation not being 1|^ F. during the whole time (some six weeks) over which the observations extended. The moisture in the atmosphere was very near the dew-point, as was shown by a very slight decrease in the temperature upon moistening the bulb of the thermometer. The water was dripping from many points in the roof of the cave, and the sides were wet with it

Buring the irst period of observation the maximum growth of any of the crystals observed was five-sixteenths of an inch in three weeks. This particular crystal began its growth in a large drop of water, which gradually diminished in size until at the end of three weeks it had totally disappeared. Buring the first part of this time the crystal formed most rapidly, and seemed to shoot out of the drop of water. Its increase was then perceptible from day to day. The growth of this crystal, as well as others in the group, was evidently dependent upon the size of the drop of water surrounding it, for although the whole of the group of crystals was wet increase was only perceptible in those crystals surrounded by a drop of water. Mo definite growth within a given time could be fixed upon as normal

The maximum growth in another aggregation of crystals observed for a like period, of three weeks was found to be three-eighths of an inch, and the general conditions and results were similar to those noticed in the first instance. It will be noticed that the evaporation of the drops of water was comparatively rapid, notwithstanding the fact that the temperature was close to the dew-point. This is explained by the character of the ventilation of

M SIIiTBB-IilAD -DEPOSITS OF BGBBKA, NEVADA.

the cave, wMcli at its lowest point was connected with the main incline and Mt its highest by means of a winze with the ninth level above. Although the atmosphere remained near the dew-point, it was constantlj renewed. The observations were conducted verj near the center of the cave.

Roth* says that spathic and fibrous calcium carbonate (calcite or arm- .gonite, or both together) are common in the form of stalactites and stalagmites in the cavities and fissures of limestone, and in the tunnels, shafts, .and drifts of the mines. Dana* mentions that it is forming in an old mine in Monte Vasa," Italy, at a temperature below the boiling-point of water. The conditions which govern the formation of aragonlte and calcite, respectively, ai'e not understood. In Ruby Hill, however, aragonite is forming under ordinary pressure at a low temperature.

Siderite (carbonate of iron and lime) has been frequently noticed.

Quartz is found in crystals in cavities and mixed through the ore at rare intervals. It is not an important mineral in the ore, except that it is neces- .jiary to its reduction by smelting.

A silicate of iron has been noticed, but it is not of common occurrence.

Clays which are more or less mixtures of silicate of alumina, carbonate of lime, oxide of iron, and other substances, are to be found at the contacts of the different formations, and at numerous places in the ore-chambers. These clays are sometimes merely the products of attrition of the two walk of a fissure, and again have been produced by the decompo- .sition of igneous rocks or an infiltration from above. Steatite and talc ai-e occasionally met with, but are unimportant

Rarer minermit.— Molybdenite htts bccn detected in the quartzite from the bottom of the Richmond shaft, and both carbonates of copper (malachite and azurite) have been met with in small quantities. As phosphorus has been found in some of the ores it is highly probable that pyromorphite is present. It is also likely that leadhillite (sulphate and carbonate of lead) •as a distinct mineral may occur here (if anywhere), as admixtures of sul- .phate and carbonate of lead are very common. Oxide of lead as a mineral has not been found io the ores in the course of the present examination,

•Motli: Algurneino Geologie. I., p. &34. Berlin, 1879. •Dana: Sjitem of Mineralogy, p. 696. Mojr York, 1874.

The Obes. 59

though it may exist It ' is not likel j, however, that if it formed at any time it could remaiii long in quantity mncjomliiiied with carhcwiic acid in the presence of waters cajrying so mmch of that compound. Wad has been observed in the PhcBnii: mine and in some other localities; also other forms of manganese in different places, and nickel is said to have been found, though no specimens have been obtained.

iiiiim*ciMrfiam*inifiiiii.^Th© ores of the district are not accurately classified by the mineii, but receive names indicative of their most striMng charmcteristics and the popular idea of the corresponding composition. It may be well to describe some of the more important varieties. Most of the or© has a reddish or yellowish color, due to the presence of oxide of iron, chloro-arsenate, or molybdate of lead. The shades of color vary according to the ' predominance of one or the other of these minerals and the quantity of -earthy material mixed with them. 'On© of the principal kinds of or© is composed of a hydrated oxide of iron mixed with some sulphate and carbonate of lead and containing intermingled grains and lumps of nndecomposed galena. This ore is often called "red carbonate/* It usually carries about equal values of gold and silver, from $25 to $50 of each per ton,^ though sometimes the gold is considerably in excess. Another variety is the "yellow carbonate." This term is applied in general by the miners to any ore of a yellow color which contains lead. It belongs particularly, however, to a very characteristic ore, which is a mixture of the hydrated oxide of iron with the sulphate and chloro-arsenate of lead in varying proportions. The ratio of the silver to the gold in this ore is not at all uniform; sometimes one metal, sometimes the other, being in excess. The value of both metals does not usually exceed $100 per ton. Another variety of "yellow carbonate" is that which owes its color to the molybdate of lead mixed through it. As the molybdate of lead usually carries but little silver and less gold, this ore is not very rich unless it contains other minerals bearing the precious metals. The so-called "sulphuret ore" of the miners is an almost pure crystalized carbonate of lead. It is grayish in color, and consists of aggregated crystals of cerussite. It is sometimes quite rich in silver, assaying as high as $125, but like all the lead ores proper is poor in gold. There are several varieties of red ore, consisting principally of the hydrated oxide

60 SILYEB-LEAD DEPOSITS OF EUEEKjI, METABA.

uf iron, witli a little lead and silver, wMch are tolerably rich in gold. Tlier© is waually nothing in their appearance to indicate their value, and it ii only by constant assaying that it is possible to determine what they are worth. ' Qnarti ores, especially those carrying qaartz in visible crystals, are uncommon, except in the Eureka Tunnel and some parts of Prospect M ommtain, but when found they are nsnally rich in gold and poor in silver and lead. There is a morons crystalline quartz ore found in some places in the Richmond mine, from which assays of over $300 per ton (i)4!lf 7 per cent) in gold, with but a few dollars in siker, have been obtained. The snlphmret ores usually consist of a compact mass, composed of pyrite, arsenopyrite, galena, and blende, and vary very considerably in the amounts of silver and gold that they contain. The minera do not as yet distinguish different varieties by name.

Aamiyito of Ricimioiiii ore.— The follo wing anftlysis of ore from the Richmond mine for the year 1878 will serve as an example of the ores from all the mines of Ruby Hill, which greatly resemble each other both as regards qmaMty and the minerals which compose them. The sample analyzed was an average of all the Richmond ore worked at the fttraacesof that company during the previous year, and the analysis was made by Fred. Clandet, of London.*

Per cant. Pur mmi.

Lead oxM© ......-,-.... 36.66 laad .... .... 33,12

Copper oxide- ........... ,16 Copper ...... .12

Iron protoxide* ......... 34.3§ Iron ......... MJ7

iZincoiid© ....... ...... 2.37 Zinc......... IJf

Mangaaese oxide .-....- .13

Arsenic acid ..... ...... 6.34 Arseiiio ...... 4.13

Antimony ........ ..... .26 Antimony .... .25

Snlplmric acid .......... 4.18 Selplmr ..... 1J7

Silica...... ........... 2Ji

Almnina ............... .64

ft

Mme .................. 1.14

•Ccipici, by permissiim, from tli© recoris of tl© company.

*Iii this aniiljsiB tli© iron is represented in th© form of protoxide, wliercai it oconri m iciqiil- ©xidc. Tliat it was intended t© glT© it in the form of eesqiiioxid© is Blown hf the peroeiitiift of iron (24.07) given would correspond with 34.39 of sosquioxid©.

The Oris. 61

Magnesia ............... .41

Water anicarlwiiic acid. WM Siver and g©ld. . ....... .1§

1CMIJ2 27.55 Ttgj ounces* 8U¥©r per ton of 2,0<MI pwiBds. 13§ Tmj ounces* guld psr toB of 2,00© pianis.

Althottgh this analysis does not show all the smbstanceB that are present in the ores of the Eichmond mine, jet it r©pi©Bent» the most imiiortaiit and principal ones. One of the remarkable features of this ore is its freedom from earth material, the total amount of silica, alumina, Ime, and magneiia that it contains being but 5.14 per cent That it should contain but a small quantity of silica is bnt natural, as there are no highly silicious rocks immediately connected with it, but that it should carry such a small percentage of lime and magnesia, occurring as it does almost wholy in a limestone formation, is a fact that it is somewhat difficult to account for. Whatever the source of the or© may ha¥e been, it is evident that it was deposited almost entirely free from earthy material. The hydrated oxide of iron may be regarded as the gangne of this ore.

iM«cii.«i0ii of till! «ii«iF»i».— Upon examining this analysis it will be noticed that the lead haa been estimated in the form of oxide. The lead, howe¥er, is present in the form of galena, carbonate, sulphate, molybdate, arsenate, and chloride, the chloride being combined with the arsenate in the mineral mimetite, which is of frequent occurrence in the ore. The mineral pyromorphite may be present in the ore, but it has not been detected, although there is a trace of phosphoric acid present ^ Lead is also present in other forms, but as they represent in the aggregate but a small proportion of that metal they may be regarded as merely accessory It is difficult to estimate lli^ py^pQrtion of the different lead minerals contained in this ore, but it is probable that galena (sulphide), cerussite (carbonate), and anglesite (sulphate) are present in about equal quantities, and the next most important combinations are mimetite (arsenate and chloride) and wnlfenite (molybdate).

When copper has been detected in the ore it has been in the form of carbonate. Zinc has been estimated entirely in the state of oxide, but it

•Psji. *P2.87.

62 Silyie-Lbad Biposits Of Eubeka, ¥E¥Ada.

accura in the form of blend© (sttlpMde), calamine* (silicate), and probably as smithsoaite (carbonate). It is most common in the form of calamine. Manganese occurs mostly as wad. Arsenic is almost entirely combined with lead as arsenic acid, and the same is most likely the case with the small percentage of antimony which the ore contains.

In the abo¥e analysis it will be seen that the snlphur has been estimated almost entirely as sulphuric acid, although it is partly combined with lead in the form of galena. Most of the sulphuric acid is combined with lead, though to some extent it is no doubt combined with calcium. Silica is present in the form of quartz principally and combined with iron and aluminium. The calcium and magnesium are present, combined for the most part with carbonic acid.

The silver is found in the form of chloride and sulphide, and the gold exists in all probability in a inely di¥ided metallc state. In this analysis no account has been taken of the chlorine, and for some unaccountable reason molybdic acid has been omitted. It must have been present in the ore analyzed, as wulfenite is a common mineral in the Muby Hill ores. The footing of the different elements in this analysis amounts to 100.52, but it would be considembly less if a portion of the sulphuric acid had been estimated as sulphur, which would leave room for several substances which are unquestionably present

In a qualitative analysis of the Ruby Hill ores, Dr, MelviHe, of th# United States Geological Survey, detected the following elements:

Gold.

Chlerin©.

Silirer.

Magnesimn.

Saidnm.

Copper.

Arsenic.

Oarbcm,

Zinc.

Antimony.

Iron.

Mfimganese.

Rulntlvii vmlnii of the ©tm ©f I»ni«pect Mcmiitaiii and Rolqr HiU.^The OrCS of PrOSpCCt Mountain are very similar to those of Euby Hill, though perhaps there is a greater

•Im tMs report tli© wort calimiiiie will he need t© icrignat© tie ailicato of line, and imitliioiiit© for ciirlionato of zinc, tMs lieing ih© nomonclatiiKi adof tci hj Buna. Ties© tomi liii¥© ljo«a used hj Tsurioiiswriten Inii pmiiiisoiioiis manner, iome^siDg smithfioiiitoto issipuile IM silicsliiy and eiiliiiBiiie> tbe oartioiuito. Brogniart naed calfmiiiie for silicate and nnilliKintle for oartionate. Brooks and MiMer in 18&8 fUTuned tliwe nAmM. Qaenatodl cmled tlie rarlionfite oalmniDe aid lli« BiMeatfi wiUemite.

The 0E18. B$

variety of them. ' As a ml© they contain more silcioms material, and as a. class are probably richer than those of the hill. The difference in valtte isin part owing to the fact that the deposits are smaller, and although it cannot be said in reference to this district that small deposits in general ai ©• , richer than large ones, yet it is true that the ores brought to market from Prospect Mountain are more ¥aluable than those from Enby Hill, inasmuch, as a body of ore of considerable size can be made to pay even when the ore-is of a low grade, whereas a small one containing the same grade of ore would not yield sufficient metal to defray the expense of mining. A large-number of the mines of Prospect Mountain, however, actually contain higher-grade ores than those of Ruby Hill.

vmrietiea ©f Proapect Monntmiii ore«.— The OFcs of the Ruby-Bundorburg min0-closely resemble those of Ruby Hill. The ores of the Eureka Tunnel, on the other hand, which is at present the principal producing mine on Prospect Mountain, differ in several respects from those of Ruby Hil. They are-more silicious, an ore occurring frequently which is composed in great part of quartz ; a great deal of the arsenic acid in the yellow carbonate is replaced byantimonic acid; massive blocks of so-called "black metal/' a mixture of sulphide and sulphate of lead carrying considerable silver (sometimes as high as $1,000 to the ton), are often met with; carbonate of copper and oxide of" manganese are not uncommon, and quartz crystals are frequently found scattered through the ore.

The ores of the mines on the west slope of the mountain are noted forthe relatively larger proportion of gold to silver that they contain. Among-the richest of these are the ores of the Silver Connor and Williams mines. The ore from the former of these mines contains but little lead. The ore-of the Banner mine is noted for the large amount of silica it contains. It ^ji j^lmQgl Ijq q^Hq^ ^ qnjijig ore. The Dead Broke ore contains considerable argentiferous galena and " black metal/'

OHAPTll ¥1.

Tmk Omk Bbfosits.

cinMiicaiioii of tii« ©miitfHisits.— The ow deposits of Emreka District, thoiigli they contain gold, can be classed under the head of silver-lead deposits in limestone The tjrpe of deposits to which those of Eureka belong is on© often met with in the older limestones of the Great Basin, and although these particular deposits have been of more value, and are more widely known than any of the others, and exhibit some very interesting stnictttral features, yet they cannot be said to" form an isolated class. An extended comparison of these deposits either with similar ones in the Great Basin or with others of the same general character elsewhere, does liot come within the scope of this report, but it may be well to present some points, both of resemblance and difference between them and the best known examples of similar types in other mining regions. Although the gold and silver in the Eureka ores are the metals which render their mining possible, yet the quantity of them present in these ores, measured by weight, is so small, in comparison with the lead, that a classification based upon these metals alone would be misleading. As in many of their features they resemble other lead deposits in limestone, it seems best to regard them simply as lead deposits, in which the gold and silver are merely accessory, though very important ingredients. All lead ores carry some silver, and with it some gold, though in many of them it is only possible to obtain traces of these metals.

L«ii i«iiii«it« In itoertone of tiie Qremt BMin.— Throughout the 'Q-rcat Basiu' there are a large number of lead deposits, all of which exhibit many features of similarity. They occur in limestones and dolomitic limestones of Paleeozoic age, and are mostly of very irregular form. Their ores consist principally

The Oee Deposits. 65

of argentiferous galena with antimonial and arsenieal comlbiiiatioiis and pjrit© and the decomposition products derived from these miiieimls. CompoEiids of eopper, zinc, and other metals occasionally accompany these ores. In by far the greater nEmber of instances the dxidatioii has been carried to a great depth, sometimes reaching or exceeding 1,000 feet. The extent of this oxidation is in a great measmr© due to the absence of any large quantity of water until considerable depth is reached. The characteristic gangne of these ores is the hydrated oxide of iron with more or less calcite. Quarti is rarely found in any great quantity, except where the deposits occur in the form of contact lodes between limestone and porphyry, the quartz being probably derived from the decomposition of the porphyry. An example of such lodes is oifered by the 2 G, mine in Tybo District, Nye County, Nevada. It is found to be more proitable to reduce all these ores by smelting than by any other process. Among the principal districts where such ores are found may be mentioned Eureka, White Pine, and Bristol, in Nevada; Cerro Gordo, in CaMfomia, and OpMr, Big Cottonwood, and Litie Cottonwood, in Utah— al of which occur in Palaeozoic rocks, though in some cases, at all events, the deposition of ore is referable to a much more recent era.

Deposits ©f the Upper iii««totiiipL— The lead deposits of the Upper Mississippi* occur in dolomites of the Lower Silurian. The ore is found in caves, in openings between the strata, and in so-caEed gash Yeins. The stratiication of the country rock is iat, and it shows scarcely any signs of dynamic disturbance or alteration through chemical causes even in the neighborhood of the ore. The lead is found almost always in the form of galena, accompanied by limonite and occasionally smithsonite (zinc carbonate) and blende, rarely by pyrite. Calcite and barite occur, but quartz and combinations of lead with arsenic are not met with. The galena contains but traces of sil- ¥er and gold. There are no signs of issure veins and the ore is not found at any great depth below the surface. From the occurrence of the galena in the forms of stalactites and stalagmites in the caves, and the absence of decomposition in the country rock near the deposits, it is evident that the openings were irst formed and the ore was deposited in them firom solu-

• J. D. Wliltiiej. Metallic weallli of tk© Unitoi Stiitoi.

66 SILVERXEAB DEPOSITS OF EUEEKA, HfiYABA.

tioHs or otlierwise, and tliat substitution of minerals for country rock playeil ao important part. With regard to the age of the country rock and the occurrence of limonite with the galena, these deposits resemble those of Eureka District, but in other respects, such as structure and manner of ore deposition, they diflfer widely.

Deporitm of MiwowL^The lead deposits of Missouri and Arkansas also occur in the dolomites of the Lower Silurian. The or© is galena, with but traces of silTer and gold. It is often accompanied by calamine (zinc silicate) and limonite. It is found in nests in clay, also in beds as fine impregnations in the calciferous limestone, as well as in fiat masses between the strata. In the flat veins cerussite occurs. Gralena is also found in impregnations in dolomite and in cavities and caves mixed with gravel, zinc ore, clay, and barite. Calamine and some blende, as well as barite, almost always accompany the galena. Quartz crystals are also found. The occur^enc© of these deposits is very similar to those of the Upper Mississippi, but very dissimilar to those of Eureka.

DeiMMit«ofL««iiiriii«.^Th© doposits of Loadvilk, Colorado, resemble those of Eureka in a great many respects, as can be seen upon reference to an "Abstract of a Report upon the Geology and Mining Industry of Lead-vile, Colorado, by S. F. Emmons/'* Mr. Emmons states that the investigations mad© in Leadville have proved the following facts:

"As regards their origin—

"I. That they have been derived from aqueous solutions.

*'II. That these solutions came from above.

"III. That they derive their metallic contents from the neighboring eruptive rocks.

"IV. That in their original form they were deposited not later than the Cretaceous period.

"As regai'ds their mode of formation—

"I. That the metals were deposited from their solutions mainly as sul- -phides.

"II. That the process of deposition of the vein-material was a chemi-

• Second Annaiil Report of the Director of the U. 8. Geological SnrYey, 1881.

The Oee D1Posit8. ■ 67

cal interchange or an actual replacement of the rock-mass in which thej were deposited.

"III. That the mineral solmtioiis or ore-curreHts concentrated aloag natural water channels and followed by preference the bedding planes at a certain geological horizon; but that thej also penetrated the mass of the adjoining rocks through cross-joints and cleavage planes.

"And with regard to distribution—

"I. That the main mass of argentiferous lead ores is found In calcareomagnesian rocks.

"II. That the siMcions rocks, porphyries, and erystallin© rocks contain proportionately more gold and copper."

As regards origin, the Eureka and Leadfille deposits do not diifer, except that in Eureka District the metal-bearing solutions came from below, and their connection with eruptive rocks is not as plain in Eureka as in Leadville.

As regards their mode of formation, the deposits of the two regions differ only in respect to the manner in which the solutions of minerals were distributed. In Eureka, also, the lead is found only in the limestone, and the most silicionsrocks carry the most gold.

The varieties of minerals found in the two districts are similar, but the galena in Eureka seems to have been more completely oxidized than that in Leadville.

D«p©«it« of cuBiiieriiiiii Mill Dtrtifiiiiw.^The lead deposits of Cumberland and Derbyshire in England are found in the Carbomferons limestone, between the strata of which there are masses of porphyry,* which in that country are called "toadstone." The ore is found in fissures which cut the strata. With these fissures pipes, caves, and other irregular openings containing ore are more or less closely connected. Flat bodies or beds are also found between the strata. The fissnres are mostly occupied by true lodes, which, however, do not contain ore where they traverse the porphyry, and are not

AccorcUng to y. Grodieck (LugcrstStton dm Erz©, p. 245) it is donlitfiil whetlior %Ma porphyry i» intriiaiv© or wlietlier tli© limcaton© overlying it was i©pisit©i after it« ©wption. Investigation mad© by Mr. Emmons of the deposits Ie Leadville, wWcli occur in liinestoiics of tli© CftrboniforonB, seem to prove that tho porphyry, wWoli in that i»gloa la also imiid li©twa©ii llo stimta, w intrasiv©. And aWiongli IliiB fact does not absolutely warmnt tli© lieMcf that snoli is th© omi© with th© deposits in England, if. heigh tene the probability of such m maimer of ocoiirreiic». *

68 Sil¥Ee»]Lbab Deposits Of Bctbeka, Nevada.

productiYe in the 0¥erljing millstone grit and slate. With the exception that the fissures themselTes are not often ore-bearing and that almost all signs of stratification ha¥e been obliterated in Eureka, there are strong points of resemblance between the Nevada deposits and those of Cumberland and Berby shire. The galena in the English ores* never contains over $37.70 (0.1 per cent) of silver to the ton of 2,000 pounds, and it is usually poorer. It is not often accompanied by blend© or pyrite. Fluorite and barite, as well as calcite, are common; but quartz is seldom found.

Depii«it« of we«tph«ii*.— The Ore deposits of Eureka resemble those of West- ■ phalia^ in a few respects. The or© in the latter locality is found in irregular masses, which are all more or less connected with fissures or breaks associated with slates and limestone. It occurs only in the limestone and never in the slate, and it is evident that ^ in_ both regions the nature of the country rock has had an immediate effect upon the deposition of the ore.

Depoiiteof Upper siiciii,— The dcposits of UppcF Silcsia/ in which calaminn is the prevailing ore, although they have some points in common with those of Eureka, are, 'on account of difference in structure and variety of minerals, more widely removed from them than most of the lead deposits.

i>epi«it«of Raibi.— The deposits of Raibl, in Carinthia, so fully described by Posepny,* have considerable similarity to those of Eureka, and although they are principally interesting on account of the bearing they have upon the theory of substitution of ore for limestone, yet a general description of them may be found useful here, as showing some physical characteristics which they have in common with those of Eureka. According to this author the deposits are found in a thick belt of ore-bearing limestone (erzfiihrender Kalkstein), which overlies a calcareous tufa and underles slate on the southern slope of the Alps. The strata pitch gently to the south. The upper portion of this ore-bearing limestone is more or less magnesian, and' contains here and there layers of dolomite slate. The ore deposits are found concentrated on the hanging-wall side of these

•Hcmwood oa Metalliferoiis Beposits and SmbterraneaE Temperatares, Part I., pp. 108 ani lOi, *▼, Cotta: Erilii||©rstitteii, II., p. 133.

•Fieteli, Zeitoclur. fltr Burg , Htttten m. Saliiieiiwes©!!, B.21, 1873, p.2».

*F. Pofcif nf : Di© Bleimmi Galinel-EnlagciMtiltoii worn HaiM in Kiniten. Jalirli. i©r k. k. g«olog. • E©loli»-AiMii»II,Wi©ii,1873, B. XHII.

The Oee Deposits. . 69

layers. They lia¥e sometimes the form of lodes, sometimes of beds, and are often ¥ery irregElar. The galena deposits are found principally IE the dolomite and the calamine* deposits in the limestone. This for-_ mation is cut up by numerous fault-issues (Blatte) which ha¥e a northerly course. These correspond exactly with those found in the ^ureka mines, and are scarcely more than seams in the rock. The ore deposits are found along them, sometimes on one side and sometimes on the other, the enriching of the ore-bearing limestone seeming to depend upon the presence of fissures and the dolomite slate. Occasionally the ore deposits take on the character of lodes along these, fissures, and sometimes they are connected deposits of very irregular shape. The stratification of the ore-bearing limestone is indistinct and in.the neighborhood of the fissures it is crushed and broken. The lead ores are poor in silTer. Further reference to these deposits will be made when the theory of substitution is examined.

Afeof tliedepo«lt«liirel«tloiitotlieftinii«tioa.— The dopOSltS of Eurcka, aS Wcll M

all those which have been mentioned, are unquestionably of later formation than the limestone or dolomite which contained them, and though but few of them can be reckoned among the lodes in the narrower sense of the word, yet they are all so intimately connected with fissures, creTices, and seams that they unquestionably owe their existence to the presence of fissures.

The discovery of a prototype for the deposits of any particular district is hardly possible,' as no two portions of the earth's crust present exactly the same geological features, and if any two such existed there is no probability that they would both be ore-bearing, or, if they were, that they should have been supplied with ore by precisely the same agencies. The occurrence of silver in paying quantities with lead ores is very common, particularly west of the Eocky Mountains, but the presence of gold also in paying quantities, which forms so marked a characteristic of the Eureka ores, is exceptional.

cimsiiic«tioii«cc©riiiii|itofona.^A classificfttion of the ore deposits of Eureka Bistrict as regards their form is a matter of considerable difficulty. There

•Poiepnf nmd the wowl fjalamiiie to imclai© Imtli calwniiie and smitlisoiiilii.

70 Siltee-Lead Deposits Of Euieka, Nevada.

are some of them whicli can be termed fissure or contact veins, bet in most cases thej are ver}^ irregular in foi-m, and are better described by the German word "Stock" than by any mining term nsed in English. The word "pipe'' can be applied to many of them, but in its ordinary use a "pipe" implies a "rake/* while the ramified strwcture of the Cumberland deposits is rarely well marked at Eureka. They are often lenticular. This term, however, cannot always be used to describe their form, as they have offblioots in all directions. Any classification, however, which is dependent on mere differences of form must be more or less imperfect

sii«?e of tint iepoiit..— The dcposits sometimes spread out inta immense chambers that measure more than fifty feet in each direction, and which are completely filled with ore, with the -exception of an occasional ca¥e or limestone pillar. From the sides of these chambers, which scarcely ever present smooth walk, there are branches, and auxiliary pipes lead up or down, or in a horizontal direction, to other bodies. The ore bodies do not seem to follow any particular direction, either as regards dip or strike, and at first Bight they appear to be distributed throughout the ore^bearing fonnation without any regularity. This is not wholly the case, and although no well-defined law can be found governing their occurrence, this is connected with that of certain phenomena in the country rock, such as fissures, caves, and broken limestone.

R«iatiiin of ill* inporfta to tim unmmtona.— The distribution of the Ore lias been determined almost entirely by the physical character of the limestone in which it is found, and not by any chemical or mineralogical differences in the rock. In other words, whether the limestone was dolomitic or not, and whether it was nearly pure or somewhat argillaceous, it was always a rock which would fulfill the chemical conditions necessary to the deposition of ore. Even supposing that dolomitic limestone is generally better adapted to induce deposition—and this is something which has never been proved— the greater facilities offered by a crashed and broken limestone, no matter what its character, to the percolation of the metal-bearing solutions, would more than compensate for anj chemical advantages which a particular kind of limestone offered. Although the typical fissure vein is found in limestone in many parts of the world, its occurrence in that rock in the Great Basin

THE OKB DlPOSITa 71

18 rax0. The rarity of tMs type of regular deposits at Eureka can be accounted for in a great measure if the extremely crashed character of the country surrounding them is taken into account. When the upheaval of the mountain ranges began, the rock was cracked and fissured in many directions, the fissures no doubt extending to great depths and having considerable lateral extent; but as the uplifting and grinding process was prolonged, these fissures themselves were in a great measure* obliterated and faulted, new ones of less magnitude taking their place. This operation seems to have been carried on until the mountain was no longer a solid mass penetrated by great cracks, but was composed of shattered zones of limestone separated here and there by bodies of unbroken rock. The ore-bearing solutions entered the rock through the channels of least resistance, the crushed limestone offering less resistance in many places than the main fissures themselves, and deposition followed in forms of a degree of iwegularity corresponding to the complexity of the preceding dynamical effects.

Di«iMi«itioii of the ofc in tii« dmmbera.^The Ore itt the Upper part of larger chambers is mostly in a loose state, sometimes in layers; and is usually covered by beds of sand, gravel, and bowlders of variable thickness. It is difficult to believe that this mass owes its structure to any other cause than rearrangement by subterranean water cnrrents, though it is not likely that the original position of the material was remote from that which it now occupies. There is of course every reason to suppose that waters either from the surface or from below have flowed through these rocks in notable quantities ever since they were interacted by fissures, but the floods which have left the traces just described in the upper portions of the chambers must be comparatively recent, since the stratified ore has been rearranged since its oxidation. In the lower part of the chambers, on the other hand, the ore is more compact and usually appears as if it occupied its original position.

Connection of om boiiie* with tiit inmrMte.— On Muby Hill, in the mines lying southeast of the "compromise line," the ore is usually found in the limestone at or near its contact with the quartzite, except close to the surface, where it is generally at some distance from that formation. Although a complete connection has not been established between all these ore bodies and the quartzite, or between all the ore bodies themselves, yet their location and

72 Sultee-Lead Deposits Of Eueeka, Netada.

tlie relation tliat they bear to tte secondary or contact issur© between quartzite and limestone indicate that that fissure has often ser¥ed as an ore channel This is more apparent as the ore is followed downward to the level at which it takes up the whole of the space between the quartzite and the main northeast fissure. (See cross-cut to Locae shaft, Plat© VIII.) It has been mentioned that most of the ore bodies in the Eureka lay along the quartzite and limestone contact; but there has been one notable exception, namely, the seventh and eighth level ore body. This, with its ramifications, reached to the northeast clay in places and extended from a short distance below the fifth down to nearly the ninth level. It was the largest single mass of ore ever found on the hill, and firom it were extracted over two million dollars. There have been several large bodies of ore near the quartzite in the K. K. mine, but, with the exception of a mass near the sur- ' face in the Jackson ground, the ore bodies in the portion of the mineral zones lying southeast of the Eureka have not been very large.

Northwest of the "compromise line" the ore haa been found on the quartzite in only one place, viz., above the fourth level of the Eiclimond mine near that Hne. A reference to the various horizontal sectipns (Plates XIII. and XIV.) will also show that the mineral zone or the wedge of Ime- Btone between the two fissures is small in this part of the hill. The surface ore bodies at the Champion, Buckeye, and Richmond claims of the Eureka and Michmond companies were of very considerable extent, but at the present time it is difficult to say how much ore was extracted from them, as the workings have caved in many places and are inaccessible. In fact, exact data in regard to the quantity of ore extracted from any of the or© bodies, except those of the Richmond, are wanting; but as they are not necessary to a geological discussion of the Ruby Hill deposits, they can be dispensed with.

occurwiieea of tiie mm iioiie* In Fiwi|iect Mimiitaiii.— TheF© is vcry little difference in the manner of occurrenc© of ore bodies in Prospect Mountain and Ruby Hill On the mountain there are no workings in the neighborhood of the quartzite, and thus far the metalliferous zones have been separated by belts of undisturbed limestone and shale. The size of the ore bodies in the.

Thb Obe Deposits. 73

mountain lias been mucli less than those in the hill, mud the ca¥e» have been smaller and less Emnerous.

FiMnresMiiiniiti.— Both Prospect Mountaiii and Eiibj Hill are traversed b J muneroEs fissures or faults. The more important and persistent of these follow the course of the axial plane of the anticlinal fold, which, in the case of Prospect Mountain, has a north and south course, and in the case of Ruby Hill, a northwest by southeast course, and dip away from it There are, however, a great number of cross-fissures. The former seem to have been faults accompanied by upward movements, while the latter show that there has been lateral as well as vertical pressure exerted during their formation. . As a rule these fault-fissures are mere seams, although they may extend several hundred feet in every direction. Sometimes, however, they are of considerable width, and have been partially filled with bowlders broken from the walls and debris washed in from above. They occasionally contain ore and in several cases assume the appearance of fissure veins. Where fissures containing lead ore occur in limestone in Cumberland, Derbyshire, and in many parts of Europe, the country is very much less disturbed than it is in Eureka, and the mountain folds are much less sharp. Examples of fissure veins are not absolutely wanting at Eureka. There is one in the Banner mine which crosses the axis of fold of Prospect Mountain, and is remarkably regular for a lode in limestone. The east ore body of the Eichmond mine begins in the Tip Top claim, on© of the location claims of the Eichmond Company, and extends down to the Potts chamber on the "compromise line." A fissure seems to exist through the entire area thus indicated, and though the ore does not always fill the fissure and though the fissure itself often shrinks to a mere seam, the whole occurrence can properly be regar4ed as a fissure vein. In the Euby-Bunderburg there is an instructive deposit which in some portions fills a clean-cut fissure a foot or more in width, and in which at some points the ore penetrates the hanging wall in large irregular outgrowths from the vein, which have supplied most of the ore.

c«ire«ineoiinecttoiiwitiior«iMiii««.^Caves are found in many places in the limestone and are of frequent occurrence in connection with ore bodies; in fact, no large ore bodies have been found which had no caves over them; but

74 ■ SILVEE-LBAD DEPOSITS OF lUBlKA, IT lYADA.

caves are lij no means always accompanied by ore bodies. They resemble all caves found in limestoE©, and have been produced, ia part at any rate, by the solvent action of water carrying carbonic acid. These waters passed through issues and cracks, enlarging them, and dissolved the limestone, especially where it was crushed and broken. The finely crushed limestone was dissolved first, and the large fragments and bowldere settled down and were finally either completely dissolved or remained in the bottom of the caves. This action was naturally most considerable at those points where the best opportunity was aiforded for the free ofrculation of the water, and as the limestone was not uniformly shattered, and as the different varieties of rock did not ofier equal resistance, the openings formed were of a very irregular character. * The roof and sides of the. caves are sometimes entirely bare and only show the characteristic surface which results from the action of a solvent Deposition of calcium carbonate, however, as well as its solution, has taken place on a large scale and is still going on. The roof and sides of most of these caves are covered by aragonite crystals, and in some of them crystals of this mineral are still forming.

Connection of or«iiiMite« •ml i»Mr«.-^In the ncighborhood of seams the limestone i8 often crushed to a powder or is broken into fragments, which are occasionally cemented together by calcite, forming a breccia. This fissured and crushed country gave ingress to waters both from above and below. The surface waters, owing to the carbonic acid which they contained, had a solvent action upon the limestone, and those from below carried ores in solution, which were, at least in part, substituted for the limestone. The waters from both these sources removed limestone, which was again deposited when the solutions became supersaturated. The question whether the caves were partially formed before the deposition of the ore, during its deposition, or after it, will be discussed hereafter; but it may be stated here that a great portion of the ore in these ore bodies was directly substituted for the limestone. The irregularity of the course of the dissolving waters is everywhere perceptible in the ore bodies and caves. They have every possible form and vary greatly in size, sometimes being but small stringers and occasionally measuring upwards of a hundred feet in all di-

The Oke Deposits. 75

rectiom They are sometimes round, and agaiE tabmlar, and are found with and without ramifications. There are pear-shaped deposits and pipes round and fiat, irregular and symmetriaiL A common form is that of a bent sausage somewhat fiattened, and both ends downward. In fact, the form of the deposit has been go¥erned by the permeability of the rock. Although these deposits are of all shapes and sizes, taken as a whole they have a downward trend; that is to say, they extend farther in depth than they do laterally. Some are found lying nearly fiat, like bed veins, but this manner of occurrence can usually be accounted for by the hardness and insolubility of the underlying rock. The ore bodies at first sight often seem to hare no connection with any fissure or channel through "which they could ha¥e been filled, but such a connection has been demonstrated in so great a number of cases that it may be presumed to have existed in all.

In by far the greater number of instances this fissure has led to the discovery of the ore body, or its existence has been shown in the workings subsequent to the discovery. In some it has been closed by pressure, in others it has not been revealed by the explorations of the miner, who naturally does not think it necessary to follow every small crevice or opening which he may encounter. This connection of ore bodies with fissures is a very important one, as it throws a great deal of light upon the nature of the deposits, and although the fissure may apparently be very insignificant and nothing more than a seam in the rock, the crushing and rending of the limestone in its neighborhood attendant upon its formation have given the metal-bearing solution an opportunity of penetrating the rock, and although the fissure itself may not have been the ore channel, the formation of the ore bodies has been dependent upon it.

KmrnrnpU of conmictioii* lietween mm hoMm Mii ft»«ar«m.. NumerOUS exaUipleS of aU

evident connection between ore bodies and fissures are to be found in this district Besides the east and west ore bodies of the Michmond mine, which will be more fully described hereafter, the Euby-Dunderburg and Williams mines, on Prospect Mountain, are among the best instances of this occurrence; but examples of fissures connected with ore bodies have been found in almost all of the mines of the district Mo doubt many of the deposits in limestone which occur at numerous points in the Great Basin would

76 SIIi¥EB»IiEAD DEPOSITS OF EUREKA, 1B¥ADA.

exhibit similar features as regards fissures and ore bodies if they were more carefully examined.

The main fissures which follow the axial plane of the fold show that there wm a zone of crushed rock produced in the country parallel to them. The dissolving waters followed this zone and often penetrated to a considerable distance laterally. When there is more than one fissure in such a zone it is a matter of great diMciilty to decide which one ought to be considered the true ore earner or decisive factor in determining the present arrangement of the deposits. Several fissures may ha¥e been instrumental in determining the or© channels.

Belative »ge« of iMnres Mill ore boiliem.— Although mOSt of the fisSUrCS with wMch

ore bodies are connected were unquestionably formed before the deposition of the ore, yet there are some few which may possibly have been made since its deposition. It is a very difiicult matter, where^ there are no signs of stratification in the country rock, to tell whether a fissure has faulted an ore body or not When two ore bodies are found at some distance from one another and on opposite sides of a fissure, it by no means follows that they were originally portions of a mass which has been faulted by the ^ fissure. The two ore bodies may always have been distinct. There cannot have been much faulting since the deposition of the ore, for fissures, the existence of irhich prior to the deposition of ore cannot be disputed, show very few signs of any displacement

The partial falling in of caves and the mixing of bowlders of limestone and ore near open fissures does not prove that there was any considerable motion of the country. The roof of the big cave between the ninth and tenth levels of the Eureka is falling in from time to time, but this is probably due to the chemical action of water loosening blocks of limestone, and the mixing up of ore and limestone in the northwestern portion of the Richmond mine below the seventh level can be attributed to the mechanical action of the same agent

Sediment.— In connectiott with fissures it may be well to describe the transported material or sediment which is often an accompaniment of fissures and ore bodies. It consists of loose bowlders of gravel more or less connected together, of large and small brecciated fragments of limestone,

Tme Ore Diposits. 77

or of loose sand. Ita natere, tte position it occupies and its stmctur© show that it cottld only lia¥e been brought into its present place by the aid of water. It is to be looked upon, therefore, as simply a wash from higher points which has filed the ca¥ities and interstices of the rock formed by dynamic and chemical causes. This wash frequently accompanies large ore bodies, and is nsnally found adjoining or overlying the ore, and although it is not an infallible indication of its presence, it is one which is not to be overlooked. The two-million-dollar ore chamber on the eighth level of. the Eureka mine was discovered by following such a wash. This body extended up above the seventh level and down nearly to the ninth, and covered a great deal of ground with ils ramifications and pipes. On the other hand, there is a very large mass of material of a similar origin, in the form of fine sand, on the fifth level of the Phoenix, which, although pretty well prospected, has not led to any discoveries. These washes are more frequent at or near the surface, but are found down almost to the water level.

Demcriptioa of emt ore boiiy.—- It has already bceu remarked that the quartzife and limestone contact in the Richmond ground bends to the west, and the fissure that accompanies it continues with the narrow band of quartzite on its normal northwest course. Parallel with this fissure there is a system of fissures which extend from near the surface at the Tip Top incline down to the tenth level of the Richmond mine. These were accompanied by ore chambers which form an almost >|Bontinuou8 body down to a point a little below the seventh level of the Richmond. Below this point no ore has been found in the Richmond in this part of the mine, although there is a well-defined fissure extending to the tenth level. From the position which this fissure occupies, however, it is almost certain that it is the Ruby Hill fault, and it is very probable that the system of fissures mentioned above joins the main one somewhere below the seventh level From this it will be seen that the Tip Top fissure, or the "east ore body," is an offshoot of the main fissure which is shown at the winze on the ninth level on the horizontal section, Mo. 6, Plate XIV. One of the most famous of this series of ore bodies is the Potts chamber, most of which in the Richmond mine lies between the fifth and sixth levels. It is also connected with the series

78 Silvee-Lbad Deposits Of Bubeka, Etetada.

of ore bodies whicli are found at the contact of quartzite and liniestoiie in tlie Eureka ground.

Dccription of we.t ore body.— Th© w©st OFO bodj, Es th© sGcond System of cliambers' in the Riclimond mine is called, begins near the surface in the Eureka ground in the neighborhood of the "compromise line." These chambers are all connected with one another in some manner, and most of them are connected with a system of fissures. It pitches north, and as depth is obtained passes through the Richmond and enters the Albion ground. It lies under and northwest of the east ore body, and does not in any place connect with it or directly with the Potts chamber. Mevertheless, as the upper part of the west ore body lies on or near the quartzite in the Eureka mine, and as in this mine ore is traceable along the quartzite to the Potts chamber, the two or© bodies are indirectly connected. The positions of these ore chutes can be seen in the vertical cross-sections, Plates IX. to XII , and in the elevation, Plate III. From them has been taken very nearly one-half of the or© extracted from Rnby Hill.

Connection of ore lMiili«« with depressloiii In tie fwrtelte.— As hftS bcCn Stated in Chapter

IV., many of the ore bodies in the Ruby Hill mines are intimately connected with sags or depressions in the quartzite; and the manner of formation of these basins was there described. That large ore bodies should be of frequent occurrence in these depressions is not strange when it is remembered that the limestone in them was in a shattered and crushed condition, and that the quartzite, with its casing of clay, served to a certain extent to confine the metal-bearing solutions to this limestone mass, where large quantities of those solutions were probably allowed to settle quietly and deposit ore. It was in these basins that the conditions most favorable to ore deposition were found.

In tii0 Riutjnaond ground, although such depressions in the quartzite occurred in the upper as well as in the lower levels of the mine, they do not seem to have been accompanied by or© bodies, in spite of the fact that the character of the limestone was favorable to ore deposition. This can be accounted for by several facts. The two main ore channels in the Richmond mine, the east and west ore bodies, did not approach the quartzite, owing to the fact that the fissures with which they were connected did not

The Oee Beposiis. 79

lie near that rock in the portion of the mine above the water level There is, moreover, a large block of imdistiirbed gi'OEiid, which has already been described, page 32, and which in a measure separates the west ore body from the crushed limestone near the qiiartzite. It is difficult to tell exactly how this undisturbed ground defected the ore solutions, but it is likely that it was on© of the principal causes of the arrangement of the ore bodies. There are large blocks of ground in the upper levels of the Richmond mine, near the quartzite, which have been incompletely explored, and it is by no means improbaHe that new ore channels may be revealed and important ore bodies may be discovered by careful prospecting in that direction.

Chapter Vii.

Thk Sowbcib Of Ticb Owe,

Tin»ft«i la fugarii to tii« f©nii«ttoii of om iieiMiiitt.-^Oii© of the iiiost impor tftiit inquMes connected with the geology of the Eureka Bistrict relates to the source of the ore, for a SECcessful solution of this problem would afford information YftluaMe in the search for further deposits, besides possessing great scientific interest A discussion of the ¥arioiis theories which have been held in regard to the formation of ore deposits in general, some of which might be found applicable to the Eureka deposits, cannot find a place in this report, but it may be well to mention the only solutions of this problem which are in any way warranted by the facts which have been observed. These are: First, a' deposition of the ore in smaE particles simnltaneonsly with the Imestone, the ore being afterward segregatei into nearly isolated bodies, either by chemical or mechanical action; second, a segregation of the ore in the limestone from the country rock on either side of it; and, third, a deposition from solutions which came from below.

Melatlir* tiiii« at wMcli tli« mlaenil* we» i«fo«lte«!L^Althoilgh the pcriods ftt which th©

different minerals which compose the or© bodies were brought into their present position may have been separate and distinct, it is highly improbable that such has been the case, and it is not likely that some of them should have been segregated from the country rock, and others either have been washed in from above or brought up in solutions from below. Evidence against this last smpppsition is not plentiful in the ojddized ore masses, where the original position of the or© has often been changed by the low of underground streams, although it can still be found in the least disturbed portions of them. But in the mndecomposed sulphuret ores there is clear proof that the various minerals were deposited^simultaneously. Thgy occur irregularly, but in about the same relative proportions throughout the mass; they show no signs of concentric structure or of successive deposition, and although this is not positive evidence that their sources were the same, yet

SOUECB OF IHl OBE. 81

it is difficult tci cxmcaive of a deriTatioa from different Bources without a difference in the time of deposition, which would necessarily result in a ¥variation in the character of the ore.

m^mm cotttrfnci in tim country rock.— There is » sharp distinction between the composition of the ore and that of the inclosing rock. Iron oxide forms the gangue of the ore bodies, and about one-half of the ore is composed of that mineral, the other portion being made up of lead, arsenic, sulphur, zinc, silver, carbonic acid, etc. The first four of theiie substances do not seem to occur in the least metamorphosed limestone, and only appear in the more altered limestone in small bunches and seams in the neighborhood of ore bodies. There is a large block of stratified limestone on the sixth level of the Richmond, which is ¥ery little altered, and it shows no evidence of ever having contained any quantity of the metals enumerated above. It is hard, compact, and crystalline-granular. It is distinctly stratified, and has been comparatively little disturbed The highly-altered Imestone, on the other hand, contains notable quantities of some of these metals.

Ratio ©f til. mm t© the limctoii..— As close a calculatioH as possible has been made of the relative proportion of or© to limestone, in order that some idea may be formed of what percentage of the metals that rock must have originally contained if the ore had been uniformly distributed in small particles throughout its mass. The ratio of the limestone to the ore extracted from that portion of the mineral zone situated between the main fissure (the Muby Hill fault) and the contact fissure, between the quartzite and limestone in the ground southeast of the Richmond shaft, is about 100 to 1. In the mineral zone northwest of this shaft the ratio of limestone to ore is somewhat greater. If a reduction of one-half is made for large bodies of low-grade ore which up to the present time would not warrant extraction,, and for yet undiscovered masses, of which it is but reasonable to suppose

the Richmond shaft, the ratio of the limestone to the ore would be 50 to 1. Putting the assay value of the ore at $40 in gold and silver to the ton of 2,000 pounds, and the percentage of lead at 10 per cent, which cannot be regarded as too high when all the ore which has been removed from the mines is taken into account, then each ton of limestone must originaly have contained 80 cents in value of the precious metals and 0.2 per cent lead, 2Si4

82

Sil¥Ee&quot;Lead Bep08Its Of Eueeka, Nevada.

Amoimtofiiiireriiitiiecoiiiitrf rock.— Among aU tlio assajs of coEiitry rock made only one over 50 cents was obtained, and that was in the immediate ¥iciiiity of a large ore body, near the sixth level of the Richmond mine. The farther from an ore body a sample is taken the poorer as a rale is the limestone, as will be shown hereafter when the assays are examined in detail Fifteen cents in silver is a remarkably high assay to be got from stratified limestone. That rock lying near the shale outside of the main fissure contains scarcely more than a trace of the precious metals. Suppose the

Fig. 2.— Plan of main drift and crow-drift, 6CX)-foot le¥©l, Miclmioiii miae. Scale, 400 feet=l incli.

calculation made above to be incorrect, and let the possible value of the limestone be reduced to one-half, or 40 cents, this amount would still be ¥ery considerably in excess of the average value of even the crushed and most altered rock, and very much greater than the highest assays obtained from unchanged limestone.

mmjm of country rock.^With a view to determining, if possible, whether the ore was derived from the surrounding limestone, or whether the^ limestone was impregnated with ore from the ore bodies or the solutions to which they owe their origin, careful assays were made of the limestone on two lines leading up to a large ore body, the lowest portion of which was about 30 feet above the sixth level of the Richmond mine. Since these assays

SOUKOl OF THE ORE.

8S

were mad© the contiiniity of tliis ore chute with hut a few breaks has been established aearly dowa to the ninth level The preceding diagram, Fig, 2, explains the positions of the ore bodies and their relations to the country rock.

Fi»t •eriei of aiiaFi.— The ArftWc miiiierals on the main drift refer to the numbers of the first series of samples which were taken for assay. The positions on the drift from which the samples were taken are marked by black dots. The samples were taken e¥ery 25 feet, and the subjoined list describes the character of the rock and its assay value in silver. •

Mo.

M I

15

18

Is &#x27;

»

21

22

23

28

2f

3©

Ii

Dencription.

Tilnie.

A¥«ragei.

Blue mliiild .

Black 8Tiiat1Fied Limistok*.

¥elow toll broken limetton© .............

.....do..................................

......in..................................

Bluok, haail, ooiuf set , stained Imwtiiiie .

Saoio blacker ......... ... ...........

Smo© »oni«w li»l foMmtod .................

......do...... ............. ...............

Broken frijilil© white limeeton© ....... ........

Broken f rinlile Mack llmcitoiie ...............

......do .............. .. ......................

Broken fiialjl© y ellowiali-bkcli Miii©itoii© ......

Broken frl»M© wilt© llmeitoiie ................

Same darker.. ......................... ........

Broken friaMe browniali Hinestim©. ............

Broken friable blacklili Miiac»t©ini .............

Sam© more cumpict.... .......................

FriaMe w i ite 1 ini««toiie .....'..........,........

Compiet w li It© 1 Iniestiiae ...................... .

Broken fiiaMa wMto Mmeiitoii*. ............... ,

.... do ...... .................................

.....io... .............................. ........

Saul© more compMit. ............. ..............

. .. d©.. ........................... ...........

Broken frialil© wMto Miiitttoini ............... ,

Sam© comiiaot ............... ............*..,..

......do.......... .............................

WMlii aad blank llineiitene witli j«llowapolt« SlIllllillKTf ...................................

......do........................................

Cmm.

12

25

15

14

13J

W

m

14

li

2i. 13 W

li| 12 9 11 11, 21 12 13 10 MJ

Ii J

m

>12|

m

m

m

•SMpipii&

84

SILYIR-LIAD DIPOSITS OF EUEEKA, NIVADA. Msi Jf#. 1— Comtiaiioi.

Vo.

Bwcriptloii.

BLACK STEAHFUUI IJMBJTOia.

I .

€4 ComiMict cry ■tellia© liliick HnniBtiiii© .........

35 CoBipftct cryitnllln© wiitu •tiiiiiei liiii«»ti»e . . Si ' Compict crjitaUin© btaclf limeiten*. .........

37 1...... do... ........ .................. ..........

38 ......do ......................................

▼liva

ATtnfei.

Ill 8>

li

BLACK »BOI»X OJttSfOMl,

Broken Mmk MiiicBtoii*-.. . ............

Broken yeUowMi stiiiadl UniestoiU} ... Broken ndiitli •talnei Imeiioiie ^ . . . .

......do................................

m

secoini«erieeofii«i«3».^The RoDiaa niniierals on the northeast side of the main drift coiTespond to another set of samples which were taken in the same drift at the designated spots. This second set of samples was taken in order that a comparison might he made between the assay values of the limestone and the electrical phenomena observed by Dr. Bams at the same points. They are only given here that m many assays as possible may be brought to bear on the qnesion of the impregnation of the limestone, and will be referred to in more detail when the results of Dr. Barus's work are examined.

I

n

■ ni

w

V Vi

vn vra

Ix

X

Xi

xn xm xrr

Xv X¥I

xvn arriii

I>w«rlfllo&.

Blue iluil*!.. ...................... .........

SMglitly •talBei black ttntlifli liiiiittaiio . Sune lots stftlaei, willi onloito. ............

Broken frlAble white Itmestono ............

......do....................................

......io ....................................

Smuii ilglitlf stoiiied .....................

......io ........................ ............

Same brocciiitod and tliglitly stall^i .......

Broken MaM© wWt© Mineetoiie ............

Broken Imediited Umetloiie •tMiied black. Beidiali •Imtiled liinestaBe .............. .

Black broken tMnedlliiiectoad............

WMte broken alAined Mmcetene ...........

......do ....................................

Saw dtgiitlyttrfiied. ............. ........

Black iMneil Maii»tiiiiii ....................

AiMiy ▼alve.

7 li 12 li

t li 12 12 15 li 65 » 2f li 17

ATungw.

m

lil

li

«i

Soue€B Of The Ore.

85

ThwwriMof wiimyt.— A iMfd set of samples marked with dots and numbers on the diagram was taken from the cross-drift, and the result of the assays with a description of the samples is annexed.

IjIST Mo. 3.

V9.

Bint •Imle .......-..,..-..-. .....................

Oimyiili lliii«it©ii© ...............................

Hari black liim««tmie, wWi ciJcit© luii »i ipnti. ..... do...........................................

Crmlied litocls lliii«itoii©, witli caloit© ...........

Sim© »#» brolieii ini •tallied .................. .

WMto biiiceiiilei Mmeitomi ilglitlf itMawi . . . . .

^8iiimii«¥a 8......... ............ ............. .

CoBipict calclto illglitly ttaiiied ............. ...

Wliltii ornsliei llinestoiiii ....................... ,

......io.......... ...................... ...........

Blniiili broken limestoiie, wllli cdolto ............

Sunt} ni©Pilii»k©n..... ................. .........

......io.. ....................................... -.

Omjlili, ▼©ry miicli brotoa lintttoini ...........

Slmitor, Imt fiilTfiiiiiei ...........................

Similar, Imt Wiifali.. ............ ................

Yolow mnil wddfali wfl linil«ii limtitMie .......

Blntoh, iomewliatlirotoii.. ............ ..........

^memomhmkem. .............. ................

......do...........................................

fcliiiali •tiiiii«ii limeiton© ............. ............

SMI© mow liKilieii mii •toined ................... .

HMi wMto ipariystafaiini Umtttenii... ..........

Soft jciUovlsh broken liBiiiploiie .................

Soft, taken near ¥o. 14 of LM ITaS .............

▼tine.

Clifili.

Awiigtt.

m

m

m

m

It

Ml

iptociiMtoii ©f «««yt.— None of the specimens of limestone assayed contained any ore, at least none that was perceptible to the eye, and they had the appearance of the ordinary limestone found in the mineral belt The assays, which were made with great care in the manner described in Chapter XI., proTe: First, that the country rock near the ore bodies is richer in silver than that at some distance from themj second, that the least changed and metamorphosed limestone is the poorest; and, last, that the most crushed and broken limestone, and that which is somewhat stained with

86 Sil¥Ee»Lead Beposits Of Eubeka, ¥B¥Ada.

ferric oxide, is usually the richest There are several exceptions to b© noticed in these specimens, but they do not seem to be sufficient to affect these general results. Although it has not been possible to fix with certainty on any particular variety of limestone which is to be regarded as the poorest, or richest, its contents in the precious metals bearing no very definite relations to its physical properties, yet it is usEally possible to form some idea of the ¥alive of a piece of rock from its appearance, the crushed and stained varieties being usually the richest It will be noticed that the specimens taken on either of the lines leading up to their junction below the large ore bodies do not show a gradual increase in value as the ore is approached. The want of" regularity in this increase is owing to the facts that there is no uniformity in the character of the limestone, and that there appear to be zones of rich and poor rock crossing the course of the main drift and cross-drift. The existence of snch zones cannot be fully established by the number of assays that were made, as the limestone is constantly changing, and a rich piece and a poor piece are often found side by side; still the variations of certain groups of assays from the general average indicate that such zones exist.

Sample Mo. 3, in the first list of assays on the main drift, shows 34 cents in silver. This is an extraordioary amount to be obtained from limestone within the stratified zone, but although other samples were taken from the same spot no second such assay was obtained. It is abnormal, and it wonld have been struck from the list had it not been deemed proper to give the assays exactly as they were taken, although in reckoning the average assay value of the stratified limestone (Nos. 2, 4, 5, 6, 7, and 8) it has been omitted, as the other samples which were taken afterwards in the same spot were less than the average (121 cents).

The average of the next five samples, from 9 to 13 inclusive, which were taken from the crushed limestone, is 151 cents. The stratified and crushed limestones are separated by a fissure which may have been the source of impregnation of the zones on each side of it. At any rate the averages of five samples decrease down to the fourth lot assaying 101, when they begin to increase again up to No. 34, which is in the next zone of stratified limestone. The average value of this zone of stratified limestone

SOUBCl OF THl ORE. 87

is only 9t cents. The four samples, 39 to 42, inclusive, are in the broken limestone just below a large ore body, ami their average is 19i cents. The samples which are markedr on the map with Roman numerals do not show any remarkable changes until No. 13 is reached, which was taken from near No. 42 of the other list It assayed 65 cents, and an average of nine other samples taken in the drift southeast of this point showed 17f cents. These samples were not far removed from ore bodies. Although the samples in list No. 3, taken in the cross-drift, do not show a uniform increase in metallic contents m the ore is approached, yet they indicate that the rock in the neighborhood of the ore is the richest on the average. The stratified limestone which lies outside the main fissnre in this drift averages but 9 cents. The shale is invariably of low grade, the highest assay obtained being only 6 cents.

Result..— From the foregoing facts it will be seen that it is scai'cely possible that the ore bodies could have been formed by segregation from the surrounding limestone. Had such been the case all the metals composing the ore bodies would have been found in appreciable quantities in the least changed limestone. The assays prove moreover that the silver in this rock was in all probability an impregnation accompanying the deposition of the ore bodies and was not an original constituent of the limestone.

8eirf«f«ti©iif«iiiitiieiiiii««toiie.— If the orc had been collected in its present position by segregation of any kind, there would have been innumerable places in which minute clusters and bunches would have been formed, and the limestone, instead of being perfectly barren or practically so for great distances in all directions, would have exhibited here and there at least signs of ore. The large caves and pipes are not the only openings to be found in the mass of limestone. There are openings of every size and

frequent occurrence throughout the ore-bearing zone as well as in the limestone which has not been found to be productive, though the last has not been snfficiendy explored to prove that these openings are as common as in the above-mentioned zone. That some of the cavities referred to may have been formed since the deposition of the ore is very possible, bnt it has been shown already that most of the fissures and cracks were produced

88 SIL¥BB»IiEAD DIPOSITS OF EWRIKA, MBVADA.

before tli© formatiott of the ore bodies. Had segregation taken place at all, it must lia¥e taken place throiigkoiit the mass of limestone; and it is very difficult to conceive of metal-bearing solmtioiis or ore m any otlier form traversing tmndreds of feet of limestone, offering every opportmnity for the deposition of ore, and passing* across fissures in such a manner as to leave no trace of their passage in many of the openings which nmst necessarily have been in their course, if they were derived from the country rock; yet this is what must have occurred, if the theory of segregatioii were applicable. Had the ore been segregated, it is probable, too, that there would have been no well-defined boundary between the country rock and the ore. Such is not the case, however. The ore is as definitely cut off when it comes in contact with the limestone as if it had been shoveled or rammed into the caves and openings. The limestone is often impregnated with ferric oxide in the neighborhood of ore chamben, but the dividing-ln© between the ferruginous limestone and the ore is very plain. The limestone at a distance of 6 inches from very rich ore often shows no signs of iron or of anything else that would indicate tlie proximity of ore.

sef«f«tiim from the ■•iiiii«.— The shall Bowher© carries more than a trace of silver and gold, and what has been said in regard to a segregation from the limestone apples also to the shale. Indeed, it is still more improbable that metal-bearing solutions should have been mnintemipted in their passage through the clay of the Rnby Hill fault and should not have been concentrated on its hanging-wall side. A derivation of the ore from the shale is, therefore, inadmissible.

8eff«i»ti©iifKiiiitii«n»rt«itii.— SEver, gold, lead, and some other minerals have been found in small quantities in the quartzite, but ores were never obtained from the latter rock in paying quantities, and occurred chiefiy in small seams and fissures. It has been explained that there has been considerable motion of the quartzite upward against the limestone along a fissure, and that this fissure contains a great deal of clay and was of prior origin to the ore bodies. What has been said in regard to mineral solutions traversing the clay of the main fissure is equally true in this case. A segregation of or© from the quartzite is, therefore, hardly among the possibilities. Neither is it possible to suppose that the or© was introduced from above, for none

Source Of The Orb, 89

of the rocks wMcli may have covered .the present surface contain any heavy metals.

The maniitr in which the om entereil the llmeitont.— Tho ©vidcilCe ill regard tO the ftCtUftl

source of the ore is rather of a negative than of a positive character. The theory of segregation is untenahle; and other theories, such as that of a deposition in beds simnltaneoEsly with the country rock or of an iniltration from above, are not to be 'thought of. The only reasonable explanation which can be given of the source of the ore, and the only on© which is not contradicted by the observed facts, is that the ore bodies were formed by infiltration from below. It has already been shown that the ore chambers are intimately connected with fissures. Some of these— for instance, the main fissure, as exposed on the-twelfth level of the Eureka, in the crosscut to the Locan shaft— evidently served as channels for ore-bearing solutions, and it is extremely probable that most of them at one time or other have carried mineral solutions to the ore bodies. iJl fissures are more or less connected with the two principal ones, and many of the ore bodies are also connected together, and they have in general a downward trend. All the facts point to an ascension of the solutions, and these solutions were in all likelihood a result of the solfataric action consequent upon the efuptioE of rhvolite.

cameof tii««©if«t«iriciictioii.— It has already been stated that there is a strong probability, if it is not absolutely certain, that the eruption of rhyolite preceded the deposition of ore. Extensive eruptions of this rock took place at no great distance from the mines, and, as has been described, a dike of it follows one of the chief fissures of the mineral zone. The decomposition of this dike and of other rocks accompanying it, especially the quartz-porphyry, is such as is characteristic of volcanic regions, and its occurrence must almost inevitably be ascribed either to the rhyolite eruption or to the still more recent outburst of basalt There is no basalt, however, either in or near the mines, and therefore nothing to indicate a connection between its ejection and the deposition of ore. The solfataric action traceable in the mines is therefore most naturally referred to the rhyolite eruption. It is of course no objection to this hypothesis that the rhyolite is itself decomposed, since the -decomposition of lavas within a few days of their ejection, by the gases and solutions of the same eruption, has frequently been observed; while

90 SlLVEK-LlAB DEPOSITS OF EUREKA, NEVADA.

the period of the rhyolite eruptions near Eureka may have covered centuries. The character of the decompositioii of the rhyolite is familiar, and consists largely in the extraction of the heavy bases and alkalies, leaving siliceous clay as a residue. Snlphureted hydrogen is almost invariably an accompaniment of volcanic action, and the alkalies in solution were in part converted thereby into sulphides. As most of the sulphides of the metals are soluble in solutions of the alkaline sulphides, a vehicle was thus formed for the transportation of any of those metallic sulphides which might be present^ Those sulphides, or compounds which would yield them, might have formed constituents of the rhyolite.

Rhyolite «« a .otirce of the ore.— As a matter of fact there is no rhyolite in the immediate vicinity of the ore which contains sufficient gold, silver, or lead to admit of its' being regarded as the source of these minerals in the ore. It is barely possible, though not likely, that the rhyolite body of which the dikes in the mines are the upward continuation, may have carried a notably larger percentage of heavy metals than that now to be found in a fresh state on the surface. In fact, near the min€?8, it is almost completely decomposed, and it cannot be obtained in a tolerably fresh state above ground at considerable distances from the workings.

Q««rt»-pofpiiyryai«ioiirc«oftiieom^The rhyolto is iiot tho ouly eruptivc rock met with in the mines. Quartz-porphyry also occurs, but only in the neighborhood of Adams Hill. This rock, however, contains considerable quantities, relatively speaking, of gold and silver, particularly of the former. The explorations in the mines in which it is found are not sufficient to give any deinite idea of its extent, bet it is possible that it is much more extensive than its croppitigs suggest The result of the assays made of this porphyry, which are described in the chapter on assays, indicates that this rock contained silver and gold, and perhaps lead, after it solidiied and before any solfataric action could have affected it. Though the age of the quartz-porphyry cannot be proved from this district, there can be no doubt, from its lithological character and its mode of occurrence in innumerable other localities, that it is pre-Tertiary and far older than the rhyolite. That the solfataric action incident to this eruption had an effect upon this porphyry is extremely probable; at any rate, changes of a solfataric character were

SOUEOl OP THE OEE. 91

brought about in it, such as the fonnation of iron pyritt and the concentration of gold and silver in "that mineral from the porphyiitic mass. Moreover, although it is not certain that the gold, silver, and lead in the mines in its immediate neighborhood were derived from this rock, yet the amount of gold, silver, and lead it contains, and the transformatioii it has undergone, render it a possible source of these metals in the ore of the mines of Adams Hill. The mines of Adams Hill, which are mentioned in another portion of this memoir, are many of them noted for the large proportion of gold to silver found in their ores. As regards the mines of Ruby Hill, which are separated from those of Adams Hill by an intervening belt of shale, it cannot be stated as anything more than a possibility that their ore was derived from the decomposition of the quartz-porphyry.

Qr«iiite«i«poitiMe«oiirccof theore.— It hfts already boen mentioned (page 12) that gimnite probably underlies the sedimentar}" rocks of Ruby Hill, and perhaps those of the whole district This rock has but on© small outcrop. It has been carefully assayed, but only a trace of silver and no gold has been discovered in it The only place where specimens could be obtained was on Mineral Hill, and they were all much decomposed. It is nowhere exposed in the underground workings, although bowlders resembling granite have been found in the quartzite near the bottom of the Richmond shaft. It is only natural to expect that this decomposed granite should show very little of the precious metals even if the undecomposed rock originally contained perceptible quantities. Investigations which have been made of massive rocks carrying gold and silver have always shown that the decomposed varieties were invariably poorer in these metals than the unaltered rock, except where enriched by infiltration.

Source of the ore in Proipect Mouiitiiiii.— With reforencc to the deposits of Prospect Mountain, which are almost identical with those of Ruby Hill, it can be stated that although there is no quartz-porphyry or any other massive rock caiTying perceptible quantities of gold and silver in its immediate vicinity, yet there is no proof that such rocks do not exist in depth in or near the ore-bearing formation, and that, as such rocks have been found on Adams Hill in connection with ore deposits, it is possible that they may have been the source of the ore in that region as well.

92 SILTllE-IiEAD DEPOSITS OF IWItlKA, iTBVABA.

cimciiMioa..— The results of tie chemical and physical examinations wMch have been made of the rocks of Eureka have been rather -negative than positive as regards the source of the silver. They have shown what rocks have not been the source of the ore more conclusively than they have proved its origin. They seem, however, to point in but one direction, namely, to some massive rock which has been decomposed by the soMktaric action attending the eruption of rhyolite. Through the decomposition of this rock metal-bearing solutions were formed which afterward penetrated the limestone and deposited the ore

OHAPfll ¥111.

MAinnEII OF THE BBPOSITIOIT OF THE OBK. Derivatiiiii m4 ciwiilatloii of the metallifewni* •©liiti©ii«.— In th© foregOlllg chftpteF it 1m»

been stated that the or© was probably derivei from some ma88i¥e rock by solfataric action. Th© solutions containing th© ore penetrated the limestone,, passing through issnres and interstices in the broken rock, and deposited the or© where conditions of temperature, pressnre, and chemical acti¥ity were favorable to its precipitation. The irregularity of th© deposits and their connection with fissares and other phenomena ha¥e already been described and accounted for, but as yet no attempt has been made to* explain th© canses which led to th© release of the minerals from the solutions which contained them and their aggregation in immense chambers. It is impossible to determine what may have been the chemical composition of these solutions, but it is not improbable that they consisted in great part of sulphides of the heavy metals dissolved in alkalne sulphides. These solutions were necessarily formed under the ininence of heat and pressure- Rising into th© shattered limestone at a diminishing pressure and temperature, th© liquids lost much of their solvent power and many of the metals-that they contained were precipitated.

Mmaerin wiiiciitfc«©f«wii«i«ii«iitei.----As to th© manner of this precipitation, two theories only are admissible, either that the or© was precipitated from the-solutions in pro-existing large openings, or that it was substituted directly for the limestone, that rock being dissolved and metallic minerals being left-in its place. In other words, the or© was either deposited in caYes and other openings, or th© caves found above the ore bodies were caused by a- shrinkage of the ore and the action of dissolving waters.

iniiHiftMiceof tii«iiiiuiiierof deiMisitioii.— At fiiBt sight tMs quostioii do©8 not se©ni of great practical importance, for if the mineral-bearing solmtioTas came-

94 SILYlB-LEAlf BEPOSITS OF BUMIKA, FBTADA.

from a considerable distance below, and it is Mg M j probable that they did, it would be reasonable to suppose that the deposition would continue as far as it would be possible to follow it. An investigation of the phenomena attending the formation of these deposits will show, however, that the manner in which the ore was deposited has a very important bearing upon the probabilities of inding ore at any considerable distance below the water level.

Theory of the formaticm of mire..— The formfttion of cftves in Hmestoue ia Esnally attributable to the action of waters percolating from the surface and canning carbonic acid in solution. As is well known, even rain-water contains carbonic acid in solution, though in small quantities corresponding to the traces of carbonic anhydride always present in the atmosphere. The air occupying the pores of the soil for a considerable distance from the surface is much more highly charged with carbonic anhydride than the free atmosphere, a fact no doubt due to the oxidation of organic matter, and the percolating waters are correspondingly charged with carbonic acid. Below the permanent water-level of a limestone country ^ the water is nearly saturated with calcium carbonate, and though there is a slow circulation of subterranean currents beneath this level no strong local action can be expected. To form a cave at a given spot, water containing free carbonic acid must be supplied in sufficient quantities, and an escape must be provided for the more or less saturated solution of calcium carbonate which results from the corrosion of the rock. Caves cannot, therefore, form at an indefinite 'depth from the smface of the limestone under any circumstances, for, after passing a certain distance through limestone, the percolating waters would be nearly or quite saturated. Caves, too, can only be found in a country with deep drainage, since otherwise the saturated solvent could not be removed.

The rate of cave formation is dependent upon the quantity of water, the amount of carbonic acid that it contains, and the velocity with which it flows. Climatic changes and changes in the formation from dynamic causes accelerate or retard the action of these waters as the case may be, but a tendency to the formation of caves exists wherever water percolates through limestone. The solution of limestone ordinarily appears to be accompanied by the deposition of more or less calcium carbonate in the

MAIOflM OF D1P08ITI0N. 95

sadie iieighborhood. When the processes of solution and deposition go oa simiiltaiieomsly their coexistence is no doubt due to local differences of temperature aad pressure. Changes in the amount of percolating water and other circumstances may also bring about deposition where solvent action once prevailed, or mm f er#if. As before stated, the dissolving of the limestone in particular directions has been owing in great measure to the antecedent crushing of the limestone.

Cottncctlon of cave* with i»iiire», ore bodies, ami each other In Eureka.— Thc CaVOB in Eureka

District are of more frequent occurrence near the surface than they are in depth, no caves of any importance having been found below 1,000 feet They are almost invariably connected with some fissure, and are also often connected with one another by fissures and open pipes. Mo oxidized ore body of any great magnitude is found without a cave above it, which is usually proportionate in siise to the ore body, but all caves are by no means accompanied by masses of ore. Though the caves are very irregular, having ramifications in all directions, they form a system or systems which have a downward trend approaching the foot wall of the formation in which they are found. As the ore bodies are associated with caves their deposition is, of course, similar.

Action of water In the cava*.— The Foof and sides of the caves sometimes present the appearance of a chamber blasted out of the solid rock, and do not show any signs of the action of water. This, however, is rarely the case, and is a result of the faHing in of the roof and sides as theywere originally formed. The action of the water can often be observed upon some of the sides of the bowlders, which in such instances always cover the bottom of the caves. Usually the surfaces of the caves show the effect of the corroding action to which they have been subjected; the rock is hollowed out in cup-like forms, which are roughened and indented with lines caused by the difference in solubility of the various parts of the rock These surfaces have a light-grayish color streaked with white, and in the neighborhood of ore are more or less stained with ferric oxide.

Formation of arag onlte and cal Ite in tite cave*.— CJlttSterS Of aragOnite and Calcite

crystals are frequently found covering large areas on the roof and sides. ' Although water is found dripping from the roof of some of these caves it

96 8Ilyee-Leab Biposits Of Bueeka, Nb¥Ada.

never aceiimttlates in any consideraH© quantity on the doors, but the atmosphere is always damp. The growth of aragonite crystals-is not confined to the roofs and sides of the caves, howldera which have fallen from the roof often being covered with them. Whether these crystals are of , stalagmitic origin or whether they owe their formation to exudations from the floor is uncertain, but the latter supposition ieems the more likely, for although drops of water were seen falling from clmsters of aragonite crystals in the roof no corresponding aggregations were noticed where the drops struck below. The caves above ore bodies do not differ in any respect from those in which no ore is found, and although they may have been formed at a different period there is no reason to suppose that they owe their origin to a different cause.

Comnsction of emwm with the outer air.— That SOM© of theS© CftVeS ftT© COnneCtcd

together by openings, and that they have connection with the outer air, is proved by the fact that in many of them there is a very decided draught of air, although they may be several hundred feet below the surface. In some instances this draught is so strong that a lighted candle held near contracted openings leading to the caves is extinguished.

Deptii to whicii the cave fonnaniiii eitteiid..— From the foregolug, it appears that the cave formation in general does not extend to any very considerable depth and that its limit in Eureka is probably reached within a thousand feet. -If the theory of a simple crystallization of minerals fix)m solutions in pre-existing caves Irere correct, it is evident that the practical limit of ore deposition would be reached at the point where cave formation was no longer possible. This would naturally be the point where the carbonie acid solution, being saturated, ceased to dissolve limestone. In Eureka,, the limit of the cave formation is probably reached in less than a thousand feet, or before the water level* is attained, as in the Richmond ground between the 7th and 9th levels there are several partially open fissures-which, although they show that considerable water has passed through them, nevertheless do not exhibit anything like the same amount of corrosive action which is everywhere apparent in the upper caves. The struct-

« In speaMng of it© wmter i©¥©l, i»fci»iMS« i» tad to tie miiiei ©f Bmlij ffiU, tlioi© ©f Prosptct Monntaiii not yet liaviiig wiieliei tMt cl©f tl.

lire of the issues is plainly visifele, and tlie bowlders in these are angular, showing that they have not been much attacked by water.

Asxmnfiiiiieiit of the ore In the chamber*.— During the inVCStigatiOE of the Eureka

deposits, upon which this report is based, several fa¥orable opportunities were oiered for examining freshly-discovered ore bodies of considerable size. In two of these cases the ore was discovered by following seams stained with ferric oxide. The two places mentioned were above the ninth level of the Eureka and below the sixth level of the Eichmond. The ore was struck in both instances considerably below the caves which formed the apices of the chambers. The ore in the lower part of the chambers, if not in what could be called a solid state, was at least in a much more compact form than it was in their upper portions. It had the appearance of being in place, that is to say, that of being in the position which it originally occupied when deposited from solutions. With the ore composing the upper portion of these ore bodies it was otherwise; this was in a loose state and often distinctly stratiied, the strata being composed of different varieties of ore. There was frequently a layer of gray carbonate of lead, followed by a yellow on© composed of a mixture of ferric oxide and plumbic sul- • phate, with here and there, through the whole, bunches of galena surrounded by its products of decomposition.

In the Eichmond ore body a small cavity in the ore-mass was observed containing stalactitic columns of minerals, which were evidently formed by crystallization from solutions. The layers of ore were covered by layers of sand and gravel and bowlders which formed the bottom of the caves. The whole upper portion of this mass showed clearly that it was brought into its present position by water, and the stratification of the ore proved that it was deposited in its present position since oxidation took place. There ^^Ye layers of the miners' yellow carbonate, composed of every shade of yellow and brown, which, although some of them were not a sixteenth of an inch thick, were as distinctly defined and as clearly visible to the eye as any layers .would be in a piece of shale of unquestioned sedimentary origin. The planes of stratification were rarely horizontal, and this was not remarkable, .as a large mass of loose ore in a cave of irregular slmpe

and with inclined sides would not settle in a uniform manner, and the strata 2CM I,— 7

§8 SILVlfi-LEAB DEPOSITS OF EUKEKA, irETABA,

would be more or less bent Moreover, water carrying ine particles of ore in SEspension, trickling slowly down over an irregiilarly^nclined snr-face, would not deposit tlie particles in horizontal layers, but in layers conforming more or less to tlie inclination of the bed in m'liich it lowed. This stratification is common enough in the upper part of ore bodies, and is occasionally met with in the lower portion, though it is, of course, most apparent when the strata have been least disturbed by pressure. It is not meant that the ore throngliont these chambers had a stratified appearance; on the contrary, the different ore-minerals seemed to be mixed throughout the mass without reference to any law of distribution. It sometimes appears as if there were more unaltered galena in the lower portions of ore bodies than in the upper, but the difference, if any exists, is so slight that it is not of much importance. In large ore bodies the ore is much more compact at the bottom than at the top, which may be accounted for by the difference of pressure. The limestone surrounding ore chambers is frequently stained with iron. This seems to be less common in the upper part of the caves than it is lower down. The staining of the limestone is often observed where seams are found leading to ore bodies or where separate masses are connected together, as is often the case, by small pipes.

Evidence* in the ore of |i«etiil©nnirplitoiii after llmcitonc^In manyof th© OrO bodieS wllich

have been discovered strong evidence has been found that a portion of the ore is pseudomorphous after limestone, or, in other words, that it has been substituted for that rock. A mass of ore sometimes contains a rounded bowlder of limestone as a nucleus; a great deal of the ore, when it has not been stratified or pressed into a compact mass, exhibits the form of crushed and brecciated limestone. Small masses of ore sometimes completely fill the spaces between the limestone walls; are perfectly solid, and show clearly that they have not been disturbed since they were deposited. If these deposits had been formed by the crystallization of minerals from solution they would have exhibited, notwithstanding their oxidation, the banded structure which is everywhere supposed to be an accompaniment of this manner of deposition. Although the deposits first described are oxidized to a great extent, the change in their chemical nature would not have been sufficient to obliterate all traces of structure from their mass. Pseudoiulucbb

of Diposiiioir. 99

morplis of galena after calcit© have been observed at Anireasberg and in other miaes. Had they been found at Eureka, it is scarcely probable that they would have remaiiied recognizable, in view of the smbseqiieiit oxidation of the ore. It is probable, however, that calcite crystals were not formed until after the period of ore deposition, and it is, therefore, in no way remarkable that the search for psendomorphs after calcite was unsuccessful

Edmtioii of tli« rliyolltc «nnHloii miiil tlie caire« to the formatioii of or«.— The disturbance incident to the rhyolite ernption caused the fanlting and crashing which prepared the limestone for the circulation of the metal-bearing fluids. It is not likely that the waters carrying carbonic a«d had effected any material dissolution of the limestone before an opportunity was given for their free circulation by the shattered condition of the country. If the deposition of ore is correctly referred to soMataric action consequent upon the rhyolte eruption, the precipitation of the sulphurets may have begun immediately after the outburst of volcanic rock and before a sufficient period had elapsed to allow of the formation of caves. Besides the caves above ore bodies, there are many cavernous openings in the limestone in wMch no ore occurs; but some of these empty caves, as has been mentioned, are connected by open Assures or pipes with ore bodies. Had these caves existed at the time of the deposition of ore, it is difficult to see why they failed to receive » share of the deposits. Although this is not absolute proof that these caves were made after the ore was deposited, it is entirely consistent with such a theory.

If the caves had been formed first, they certainly would have contained gravel, bowlders, etc., washed in by water or representing insoluble residues, and this mmterial would have been found underlying the ore. This, however, is not the case; the ore is very free from admixtures of foreign sub-staMces, and wherever tins detritus is found, it either overles the ore or occupies a position adjacent to it, consistent with the hypothesis of subse- i|u©nt placement If the caves were not formed after the deposition of tho ore, they must necessarily have been enlarged during the oxidation of the sulphurets, for this can have been sustained only by supplies of oxygen carried by water from the surface. This water must Imve held carbonic aeid in

100 Sil¥Ee»Lbad Deposits Of Itoeka, ¥E¥Aba.

solmtion and must lia¥e attacked the limestone. It is true that in manj c&Tes the ore has the appearance of having been placed in the cmp-shaped cavities which are so common and which were evidently formed before the ore came into them; hut it must be remembered that much of the ore, especially in the upper part of the caves, has been brought into its present position by water.

Pmitimlly formeil cmvea imii ore cliainbii».^][ll ft pOrtiOB of th© gTOUIld already described, between the seventh and ninth levels of the Richmond mine, there is a great deal of open country; there fure no caves, however, and it does not often show signs of the action of surface waters. The ground is shattered and there are large issues which are filled for the most part with bowlders and fragments which have fallen into them. Around some of these bowlders ferric oxide and ore are found, but these masses are not of any great size. Some of the fragments are rounded off as if ore had been substituted for 'their exterior parts, and the whole mass presents the appearance of an ore chamber, the formation of which had been interrupted. From the seventh level a distinct ore channel can be traced up to the west ore body as well as downward to the ninth level.

Eiriictoofojtiitattonoiitii«biiikoftiiccireiMMiii».--T^ chemical reactions wMch took place when the ore was substituted for the limestone are unknown, but from observations made in small masses of oaddized ore resulting from th© decomposition of sulphnrets, that were evidently formed by substitution, it would seem that the ore replaced the limestone very nearly bulk for bulk; that is to sayj very nearly though not quite filled the space originally occupied by the limestone. In the masses referred to there were no signs of the vigorous action of water carrying carbonic acid, and the walls were compact; therefore it is not likely that these bodies had been disturbed since the ore was

was due to oxidation. In the large chambers, where there is a cave directly over the ore body, the size of this cave has usually, but not invariably, borne a direct relation to the size of the ore body, a large cave being followed by a large mass of ore. This would indicate that the cave owed its origin in a measure to the shrinkage of the ore. Whether the ore shrinks or expands in oxidizing is a point wMch depends upon its composition.

Were the ore composed entirelj of pyrite it would shrink on oxidizing. Although the hydrated oxide of iron occupies molecule for molecule more space than the pyrite, yet the quantity of iron left in place after th© oxidation of » mass of pyrite is not equal to the amount of that metal that the pyrite originally contained, owing to the fact that in the process of oxidation soliiHo salts are formed which are carried off. To the action of such soluble salts is no doubt due the staining of the limestone with ferric oxide in the neighborhood of ore bodies. On the other hand, if the ore were composed entirely of galena it would increase in bulk when changed into carbonate, though the carbonate of lead is to some extent soluble in waters carrying cai'bonic acid.

ob««nrmtioii« mmiic In « mil** of pjrite.— FroiB what has bcon obserYod of a mass of pyrite containing but a little blende and galena on the eleventh level of the Eureka mine, it would appear that oxidation is followed by a slight shrinkage of the ore body. This body of mineral is a compact mass which seems, as far as explorations have developed it, to touch the limestone everywhere throughout its surface. The pyrite, however, is separated from the limestone by a coating of ferric oxide nearly m foot thick. The ferric oxide contains grains and rounded fragments of limestone, and by its structure shows that the pyrite from which it was derived was brought into place by substitution. Pseudomorphs of pyrite after calcite are well known, although no specimens have been observed in Eureka; pseudomorphs of pyrite after fragments of limestone, however, are often found on Ruby Hill. The ferric oxide is also much more porous and less compact than the pyrite. A shrinkage of the mass took place upon the leaching which followed oxidation.

EirWciic€« of the contraction of ore bodies •Incti oxMmtlon.— As pyrite Originally COmpOSed

more than half the volume of the ore bodies, it is highly probable that m considerable contraction has taken place in their mass since oxidation began. Supposing such a decrease of volume to have been brought about by oxidation, an opening would be produced above the ore body proportioned to its size, as the ore becoming porous would naturally settle by its own weight Add to this the action of surface waters carrying carbonic acid, which would enlarge these cavities and to some extent redistribute the ore, and a condition of things is brought about precisely similar to that which at

1§2 " ■ SHiVEII-IilAD DIPOSITS OF BIJBEKA, HETADA.

present exists in the large ore chainlbera. In the uncliaEgei me bdiies, wMcli are encountered occasionally near the water, Iter© is nowhere any ©¥id©nce of the banded stractnre characteristic of the simple crystalization of minerals from solution. The galena, blende, and pyrite of wMch these ore masses are principally composed are distributed in bunches and compact masses, and nowhere is there any evidence of paragenetic order. It is true that a paragenesis of minerals is traceable in many places 'in the oxidized ore, but this is due to successive stages of decomposition.

©••cription ©f the EmiM ii«in»it«.^Attention has been already called (Chapter VI.) to Eaibl, in Carinthia, where galena and zinc deposits occiir in a Imestone formation. Poiepnj^/ who very fttlly describes these deposits, mentions the folowing facts: The galena deposits occur principally in the dolomite, and the zinc deposits in the underlying limestone. They are to be classed neither as beds nor as lodes. As to the genesis of the ore, they differ very widely; the galena deposits were made in pre-existing cavities in the dolomite, while the zinc ore is psendomorphons after limestone, or, im other words, was brought into its present position by substitution for country rock. The proofs this author gives of the manner of formation of the lead deposits are very conclusive. The ore, which consists principaly of galena, blende, pyrite, and dolomite (cenissite, smithsonite, calcite, and barite being comparatively nncommon), is deposited in concentric layers, the cavities being sometimes completely filled, though often an empty space is found at the center, and hardly admit of a doubt in regard to their being formed by crystallization from solutions. The occarrence of a peculiar tubular galena ore (Rohrenerz), which was formed around pre-existing stalactites of dolomite, effectually establishes the fact that the cavities existed before the ore-bearing solutions made their appearance. As regards the manner of their formation, the «nc deposits are widely different from those of lead. The ores composing them are zinc bloom, smithsonite, calamine, and mixtures of these minerals with manganese and iron oxides, different kinds of iron ores, and peculiar clays. The calamine is seldom found

•F. Poiepnf. Bi© BM-mni Gmlmci-Efilagenitittcii Ton Bailil in Kimton. Jiilnrli. der k. k. g«iilo||iBoli«ii, MeioliMHiitalt. Wi«if 1W3| B. niriM.

#i:cept in the dolomite, and the smithsoeite is the principal zinc ore in the limestone.

¥m^ur» «iiiciii«toii«.— It is not necessar j to give ii detailed description of the specimens of zinc ore from which Posepn^y^ concludes that these deposits axe pseudormorphs after limestone. Suffice it to say that the zinc minerals have very often precisely the same structure as the original lime-atone, and that many pieces have been found in which the thin veins of calcite in that rock are continued in the form of smithsonite in the adjoining zinc ore. In some few places in 'the mineral zone the galena-hlende deposits have undergone decomposition, and galena, blende, and calamine are found together. Poiepnlgives the priority of formation to the galena-blende deposits, as at some points where ■ decomposition has taken place and a portion of the ore has been removed part of the space has been illed with calamine. He further says that the calamine is probably the product of the decomposition of the blende, and that the zinc deposits themselves were formed^ by the substitution of zinc carbonate for calcium carbonate. From the fact that the galena-blende and the zinc deposits in Raibl are formed each in a different manner, this author regards it as probable that in the regions of Upper Silesia, Belgium, and Sardinia, where these two kinds of ore occur in the same deposits, they owe their origin to the same different causes which brought about their deposition in Raibl

c©iiiiiMi»oa of RaiM and Eii«kJi.^Although iho Eurekft ores do not contain a very large amount of zinc, either as blende, calamine, or smithsonite, yet numerous specimens of calamine have been found in the oxidized ores which exactly correspond with the pseudomorphs after limestone which Poiepnydescribes, and which were evidently formed directly or indirectly by substitution for limestone. Whether the zinc was originally substituted for

was oxidized irst and in the form of a solution attacked the limestone, is uncertain, but it is probable that it was deposited as silicate from a solution, as examples of other secondary minerals in the form of stalactites and stalagmites are not uncommon in druses in the oxidized ore bodies. The inferences which Posepn^ draws regarding the deposits of Upper Silesia, etc., from those of Eaibl, are certainly not applicable to the Eureka ores.

104 Silverliad Deposits Of Eureka, ¥E¥Ad4.

The internal structure of the ore masses in no waj resemMeB those of RaibL Where the ore is not oxidized there are no signs of a banded or concentric structure, and the phenomena ob8er¥ed point entirely to substitution of the sulphurets for country rock.

Sonie of the ore ^iMiiliei formed by iiilirtitiitloii.^The UnOXidizcd Ore bodieS hSYO UOt

yet been sufficiently explored to establish the fact that they were formed in toto by substitution, but sufficient e¥idence has been obtained to prove that a considerable portion of the ore at least was deposited in this mannaf. In the cases of the Upper Mississippi, and those of" Missouri, the galena is found in the form of stalactites and stalagmites, which proves the pre-existence of the openings, but in Eureka no puch case has been noted.

«:viiience agmfaat the •oil.titiitioii theory .^There is ottc argumcut to hfi advanccd against the theory that the ore bodies were formed exclusively by substitution, namely, that some of the ore chambers are far removed from what seems to have been their most natural course. It has been remarked that in the mines southeast of the "compromise line" the ore bodies are of rare occurrence near the Ruby Hill fault-fissure, except when the two fissures approach in the deeper workings. The ground in the neighborhood of this fault presents all the conditions necessary to the fulfillment of the phenomena of substitution; it is crushed, shattered, and broken in various ways, and is traversed by cross-fissures. The lines^ on which ore is found gradually approach the quartzite foot wall, and correspond almost exactly with what would have been the natural channels of surface-waters descending through fissures. If the caves were not formed before the ore, why did the ore solutions not follow other channels apparently offering equal facilities for the substitution of ore! No satisfactory answer has been found for this question, but it is manifest that mine-workings, however extensive,, ji0i|T0r fully exp0g0 the system of umierground fissures, and it is entirely possible that a barrier to the passage of solutions in this direction existed which has not been brought to light Even had ore been deposited only in pre-existing openings, traces of lead minerals should have b?en precipitated in the interstices of this broken ground if it was accessible to metalliferous solutions, but none such could be discovered.

FrcfOBilcrifflce of evi«l«ac« In favor of the iiitatitiitiiiii theory .^WeigMng tll6 ©VldeilCe OH

both sides of the question, it appears that a large part of the ore was brought into its present position by substitution, while it seems impossible* to demonstrate that any part of it was deposited in pre-existing caves. It is highly probable that all the ore was deposited by substitution, and that future developments will effectually establish the fact. There is no reason for believing that, if the physical conditions favorable to the deposition continue below the water level, deposits of ore will cease to be found below that point

Age of the ore.— In the Ruby-Dunderburg mine, on Prospect Mountain, there is a rhyolite dike similar to that of the Jackson and Phoenix. In all of these mines ore has been found in contact with and below the rhytilite in the limestone, but has never been found on the opposite side of it. This fact alone would not necessarily prove that the dike is older than the ore bodies, for these might occupy their present relation to it in consequence of a fault; but the manner in which the ore is deposited on the rhyolite, showing no signs of having been disturbed, and the fact that the rhyolite does not in any place contain inclosed fragments of ore, though it often contains country rock, go to prove that the eruption occurred before the deposition of the ore and that it did not fault the ore bodies. Another fact tending to prove the subsequent formation of the ore is the extreme decomposition of the rhyolite' through the ore-bearing region, which was no doubt brought about by chemical action attending the deposition of ore.

Although it has not been established beyond doubt that the rhyolite eruption caused the upheaval which made the main fault on Muby Hill, yet it is extremely probable that such was the case. It has been shown that this fault was the last dynamic disturbance of any importance that occurred in this region, and nothing is more natural than to connect it with the latest volcanic outburst in its neighborhood. If the Ruby Hill fault was formed by the rhyolite eruption it is likely that the rhyolite was injected into it at the time of its occurrence. The ore solutions seem to have entered the limestone through the main issure after its formation and not simultaneously with It And it may be inferred that the ore solutions owe their genesis to the solfataric action following the ejection of that eruptive rock As the

1§6 SIL¥EB.LEAD DEPOSITS OF BITBIKA, IflTABA.

rhyolite emptioii covered a considerable period it is not improbable tbat there have been overiows of that rock since the beginning of the ore deposition at some point in the district. As the rhyolite eruption occurred in the Tertiary it follows that the ore formation was not of an earlier date. The soMktaric action to which this region was once subjected has long jsince spent itself, and there is nothing to indicate that the increment of heat is abnormal.

Chapter Ix.

Water In Pr©«|i«* Motiateia.— The d©©pest sbaft OH Prosptct Moiiiilmiii, the Adas, the working shaft of the Muby-Bunderbiirg Company, has attainei M depth 0f over 800 feet, and up to that depth but little water has been •encomitered. In the other mines in this part of the district no water of jtny consequence has been met with, and from the great altitude of many of them above the valley no trouble on account of water need be expected for some time to come.

watur la mmhj HiL- — Qu Muhj Hil, th© wfttoF question is becoming a very important one, and in the future the difficulty of draining the mines may prove a serious impediment to exploration. The water now stands just below the 1,050-foot level in the Richmond shaft, bat in the old workings of th© Eureka it rose to the twelfth level, 220 feet above this point, before the cross-cut from the 1,200-foot level of the Locan shaft cnt the Ruby Hill fissure. The surplus water from the twelfth level of the Eureka flowed down a winise to the Richmond ninth, and finally reached a permanent level Mt about 1,050 feet A reference to the water line on Plate III. shows that the water level in the mines on Ruby Hill is highest at the southeast end ■or where the limestone wedge is the smallest, and that it gradually declines until, In the Richmond ground, where the limestone is the widest, it stands in the Richmond shaft at a point 650 feet below the water level in the Incline of the PhcBuix. It will thus be seen that the water from the south- -east end of the mineral belt gradually finds its way into the Richmond; that is to say, that it has a tendency to low in that direction, though owing to the fact that the workings of the mines are mot everywhere connected in th© lower levels the water does not folow an uninterrupted course.

108 SllLVEM.IiBAD DEPOSITS OF EUEIKA, ITEYADJu

This is not surprisiiig when the nature of the ground is taken into account. The two fissures, which are everywhere accompanied by a thick easing of clay, meet at a point much nearer the surface in the Phcjenix, the line of junction gradually descending as the Albion is approached. This line of junction corresponds very nearly with the water level, showing that the closing in of the two fissures forms a Bort of fiat funnel which debouchea in the Michmond mine. The water level in this mine is something below the level of Biamond Valley, where the Eureka Caflon enters it It has already been mentioned that there is a considerable zone of fissured ground in the lower levels of the Richmond. This broken ground naturally permits a tolerably free circulation of the water, and as the water level in this mine is about what it would be in the upper part of Biamond Valley it is reasonable to suppose that a permanent water level has been reached in the Richmond. Irregularities in the distribution of water are often brought about by the intervention of" blocks of unfissured ground, or by the presence of clay seams. An illustration of this was given by the occurrences observed in a drift from the 1,200-foot level of the Michmond shaft This shaft was comparatively dry down to a depth of 1,230 feet The last 500 feet were sunk in quartzite. At 1,200 feet a cross-cut was started through this rock to the north. No water that could not be easily handled with bailing tanks was encountered, and whaa the limestone was penetrated it was found to be nearly diy, the water -from the quartzite being excluded by the clay. In driving a short drift to the northeast from the main crosscut, however, a stream of water was struck which became unmanageable without the aid of pumps, and it rose to near the 1,050-foot level, and at this point it has remained, notwithstanding the large flow of water that there has been from the Eureka mine. This Eureka water, however, did not §Q^ down the shaft, but into a winze which was sunk on what appears to be the fissure of the Ruby Hill fault The ground near this fissure is much shattered, and the disappearance of the water goes to prove that this condition continues to some depth.

wmter In the Locan .haft.^Io the Locan shaft, wMch hfts now attained a depth of over 1 ,200 feet, it had always been possible to control the water, which was first encountered at a depth of 100 feet, with the hoisting

Watie. 109

maeMaery with wMch the shaft was eqEippei even while sinking to the 84f?-foot level When this level was reached a cross-cut was driven to the old workings with which connection was made just above the twelfth level, a little over 1,000 feet below the top of the Lawton shaft The water from the Locan shaft was allowed to iow along this cross-cnt and enter the twelfth level, where, joining with the other water on that level, it was conducted to the "water winze" on the Richmond ninth.

Shortly before this report was finished, pumping machinery having a capacity of 600 gallons per minute was completed at the Locan shaft and sinking was continued. Stratified limestone and shale were struck at a depth of 1,020 feet The stratification of this bed -was nearly horizontal, and at a depth of over 1,200 feet the shaft had not penetrated it A sonthwest cross-cut was run from the 1,200-foot station to the main fissure, a distance of 800 feet The first 60 feet were in shale and the rest in a mass of limestone mixed with clay, which is the product of the Rnby Hill fault The fault fissure contained ore, and when it was cut by the drift a body of water was developed which soon filled the cross-cut in spite of the pump. The flow of water was so sudden that the men had barely time to escape from the drift. It^ose to a height of 1,035 feet in the shaft (about 50 feet above the water level in the Richmond), and up to the present time (December, 1883) it has not been possible to materially lower it

The low of water from the shale was not as great as from the limestone above it, the shale acting as a barrier. It will be observed that before the large body of water was struck in the end of the cross-cut from the 1,200-foot level of the -Locan shaft, the water rose in the shaft to the 840-foot level, and ran into the twelfth level of the old workings, but after the fissure was cut it only rose to 1,035 feet, or about the upper surface of the shale. The fact that the tapping of the main fissure partially drained the twelfth and thirteenth levels, shows that there was a water channel between these levels and the point at which the vein was cut on the 1 ,200-foot level of the Locan shaft, and as this water, as well as that which drained into the shaft from the limestone overlying the shale, would not rise higlier than 1,035 feet, a level which is but a few feet higher than the water level in the Richmond, it would appear that there was a water channel also along

11§ SlIi¥Eil.LEAI> BlPOSIfS OF lUIlBKA, NETADJu

the main issure between the place where the vein wan struck in the 1,200-foot Locaii cross-cut and the Eichmond ground. This is made all the moro probable by the fact that although the Eichmond received the water of the Eureka in the manner mentioned on page 51, yet the water level in the "water winze" of the former mine was not materially altered.

pro«pect« of water in tiiii future.— Although this flow of Water has not been controlled by the present pnmping machinery, it is unlikely that it is of SEcli an extent that more powerful pumps would liOt exhaust it. It must be borne in mind that the lower belt of shale cannot but act, partially at any rate, as a barrier to the low of water from the upper limestone, and, therefore, it is but reasonable to expect that the iow of water in "the lower Mm©- stone will not be uncontrollable. This haa been indicated in a measure by the fact that the limestone encountered in the cross-cut on the 1,200-fool level of the Eichmond wan at first nearly dry, and the water that was afterwards struck on the same level was not present in such quantity that a pump like the one at the Locan shaft would not easily have managed it. It is very likely that the contact of ^the quartiite and limestone will be the principal source of the water, and for that reason it is to be avoided a» much as possible.

CHAPTEl X.

BO THE BUBY HBLIi BBFOSITS FOBM A LOBE ? mfference of tclentiic opinions on tlii« •uljiect.^Oll this SUbjCCt there ftppeaXS tO llftTe

been a great difference of opinion. In the celebrated lawsuit between the Eureka and Richmond mining companies, which was argued before Justice Field, of the United StatcB Supreme Court, Judge Sawyer, of the ninth United States circuit, and Judge Hilljer, for the district of Ne¥ada, ia Jnly, 1877, a large amount of expert testimony was offered by both parties. Messrs, T. SteiTy Hunt, W. S. Keyes, R W. Raymond, T. J. Reid, and 1. E. James testified in fa¥or of the Eureka that in their opinion the zone of limestone inckded between the qnartzite and the shale* was a lode in the miner's sense of the term; whereas Messrs. Clarence King, J. D. Hague, J. D. Whitney, William Ashbumer, and N, Wescoatt declared it as their opinion that neither from a practical nor a scientific point of ¥iew could the above mentioned belt of limestone be regarded as a lode, and denied the existence of a stratum of shale in the position mentioned by the other experts.

cii«.tiiic»iiiiigtotii««iiit.— The Richmond company had been following down a body of ore which had been de¥©loped in the Richmond and Tip-Top inclines and terminated in the Potts chamber, which lay partly in the ground claimed by both companies. The so-called "compromise line'* had been established, after a former trial, as a boundary between tlie properties of the two companies, and it was the prolongation of this line, or rather of a

•TM» shale was variooslj referred to hj the Enrela experts as ol»y and tlml©. In tl© Eureka gioniid the claj wai supposed to l>« a fcWn belt of sliale whicli Imd lieen iattencd crnt hj presinr© ani iecomposei. Bj some it was believed to be a contumation of the Mime body of tliiil© whicli ©Jdaioi on the surface and below in tbe Kioliinond mine. It Is, in nmlity, m rbyolit© ilk© In tlie Jnckwii mii Plmniit.

112 SILTlR-IiEAB BIPOSITS OF EUEEKA, ]fl¥ABA.

perpendiciikr plane passing through this line, that the Eureka cximpmny claimed as the limit of their ground. In order to establish their claim it was necessary that the Eurekm should prove that they possessed a lode, or, at any rate, a mineralized zone within the meaning of the United States mining laws. The Richmond company, on the other hand, claimed the whole of the Potts chamber, inasmiicli as they had a right to follow their body of ore, as developed ia the Richmond, m it passed into the Eureka claim beyond the extreme northeasterly point of the compromise line as it was originally established. This body of ore, which was continuous, or very nearly so, from the surface down to the deepest workings of the mine (at that time about the ninth level), followed a fissure or system of fissurei for nearly the whole distance. Sometimes the ore was found on the lower side of the fissure planes, sometimes on the upper, the fissures frequently expanding into an ore body. The course of the fissures was about N. 45° W. On the other hand, the Eureka company followed an ore body Ijmg on the quartzite firom some distance above the end of the fifth level down to below the seventh. From this point ore was traced to the body at the end of the ninth level which connected with the Potts chamber.

There was considerable difference of testimony in regard to the continuity of the ore-connection between the Eureka seventh and ninth levels. In some places it consisted of iron oxide carrying but a small amount of gold and silver, which was found along the quartzite.

In view of the existence of a secondary fissure between the quaiiiite and limestone, which the investigations forming the subject of this report have proved, this ore-connection was a valid one. The Eureka and Richmond, therefore, each established the existence of a lode leading into the Potts chamber from their respective claims. The former claimed that their lode extended from the quartzite to what they called the shale (the clay of the Ruby Hill fault or main fissure), and the latter that their lode wai wholly in limestone and had no connection with either quartzite or shale.

Decteionof jaignFicM.^The court dccidcd that the belt of limestone between the quartzite and shale (as understood by the Eureka people) constituted a lode in the sense of the law of 1872 and the usage of miners, and that, therefore, the portion of the Potts chamber situated southeast of the ©xten-

^ion of the compromise Ine belonged to the Eureka compan j, as a vertical plane passing through the compromise Hue, and its extension was, by Yirtme • of the agreement between the two parties, the boundary of their indi¥id«al rights; moreo¥er,r that the Richmond company cx)ttld not follow the ore ■outside of a vertical plane passing through their end line.

Ded«i#ii of the unittti 8tat©« Supreme cmift.^The case was Carried to the United -States Supreme Court, on appeal, and the decision of the lower court was •sustained by Chief Justice Wait©, upon the ground that the agreement ■^ifected between the two parties in 1873 gave all ground situated on the "northwest side of a vertical plane passing through the compromise line to 4he Richmond company and all that lying to the southeast of this plane to •the Eureka company, and that the conditions under which this compromise ■was made necessitated the prolongation of this plane across ihe mineral zone. Chief Justice Waite did not state whether, in his opinion, this min- ^eral zone between the quartzite and shale or clay constituted a lode or not

SttBiiiiafy oftli«phy»li»lchanict»rtotlw©ftli«iiiln«fml«» at the eXtTOnie

-southeastern corner of the plan of contacts (Plat© III.), a belt of Imestone

is visible which Mr. Arnold Hague has determined as Cambrian, and to

which he has given the name of Prospect Mountain limestone. This lime-

•stone extends in a northwesterly direction nearly to the Albion Bhaft; is

bounded on the southwest by a mass of quartaite, also Cambrian, and on

the northeast by a belt of stratiied limestone and shale belonging to the

risame period. These three formations, which al dip to the northeast, were

•originally laid down one upon the other at ihe bottom of the sea and

.afterwards raised above water at the close of the Carboniferous. At some

period subsequent to their uphea¥al and prior to the deposition of ore, a

•deep and extensiYe isiure and fault cut through these formations. Its

•course was about northwest and its dip about 70® to the northeast For

the present purpose, it can be taken as extending from one end of the plan

*of contacts to the other. It can be seen near the surface southwest of

■the American shaft, in the Jackson, Bell-shaft and Utah tunnels, and in

-a short incline beyond the Richmond mine office, and may be visible in

•other places. It no doubt could be traced for the whole distance exposed

•on the map if trouble were taken to remove the debris from the rock in

place. This issure is exposed in numerous places underground and its inter- 2§m 1^—8

114 SILVER-IiEAD BIPOSITS OF lUBBKA, IBVADA.

section witli the qEartiite is Md bare in the deeper workiagti of all the miaes except the Richmend and Albion. It is accompanied b j an aiudliary fissure between quartzite and limestone which joins it below.

coniitionibeiowtiiejiinctioiiof the two i«»ii»«.—-- Where the two fissEres conie together IE all the mines southeast of the comproniise line the ore has been found filling the fissure between the quartaite and the limestone, or between the quartzite and the lower belt of shale. Whether this will continue to be the case as the fissure is followed downward is a naatter of speculation. It is likely, howe%'er, that when the lower wedge of limestone widens out the ore bodies will take on their usual irregular character, although they will be no doubt in some way connected with Ihe fissure to which they owe their origin.

Condition* nortliwoit of the compwinwe line.— The chailgC which tftkoS place itt the

Richmond ground soon after the compromise line is passed has been fully explained. The two ore chutes, called, respectiYely, the west ore body and the east ore body, have the complexion of two distinct lodes in limestone. Whether the Potts chamber, which forms a part of the east ore body, actually touched the quartzite or not is uncertain, but, at any rate, it was within a few feet of it This ore body, howe¥er, does not approach the quartzite in any other place. The west ore body touches the quartzite in the Eureka ground near the compromise line, but in all other parts of the mine occupies a position about midway between the secondary fissure on the quartzite, and the m-ain Ruby Hill fault to the northeast As these two fissures are gradually coming together, and, no doubt, meet at greater depth, it is e¥ident that if these two ore chutes continue down they will eventually form the filling between the two fissures. From the present appearance of the ground it wonld seem as if the ore-channel which fed the east or© body was near the compromise line, and that it was on the main fissure which is exposed in the winzes from the seventh, eighth, and ninth levels of the Richmond near that line ; and that the source of the ore of the west ore body was the system of fissures which branch out from small ore bodies, extending from the sixth to the ninth levels near the A G line. The fact must not be overlooked that there is a connection between these two ore chutes along the quartzite in the Eureka ground; that is to say, there is a fissure with ore in it here and there. It is, however, impos-

The Lobe Question. 115

sible to state wifli certainty what the original ore channels may ha¥e been. N0 doubt many cracks, fissures, and vents through which the ore-bearieg sokitions passed have been completely closed since the ore was deposited, and it is Mkely that in many such openings the ore has left very little trace of its passage. When the openings were small, these solutions would naturally pass with considerable velocity, and little or no ore would be precipitated: The immense pressure of the surrounding rock would be sufficient to completely close many ore channels. The ore that has been exposed in the Albion mine is a continuation of the Richmond west ore body, and nearly the same conditions prevail in this part of the hill as in the Eichmond. ,

Diicmslon of the meminf of the word* "lode," "home," etc.— In a WOrd, th© main fisSUl'e

and the secondary fissure branching from it inclose between them a mass of limestone whicli is penetrated in many places Iby crevices. The ore bodies occur within the limestone mass and are all connected with the fissure system just described. The ore bodies are usually lenticular or irregular in form, but sometimes follow the fissures as tabular masses. What name is to be given to this occurrence, though no doubt important from a legal point of view, is a verbal rather than a scientific question. There are portions of it to which no one has hesitated to apply the name of lode or vein. In the usage of English-speaking miners the tei-ms vein and lode are nearly but not quite synonymous. A vein may or may not carry ore, for it is perfectly correct and entirely usual to speak of a vein of calcite or other barren mineral, a connection in which the word lode could not be applied. In reference to ore deposits, lode is not used to denote the filling of ve'ry small fissures, for a stringer might be called a vein of small size, but scarcely a lode. It is most often used to indicate the contents of more complex fissures, or as synonymous with composite vein, system of veins, etc., while the term vein, with qualification, usually refers to the filling of fissures of a simpler character. Thus in the early days of the Comstock the two main branches of the deposit were known as the "east vein" and the "west vein," while the whole system was called the Comstock lode. So, too, Henwood says:" "The wider parts of hdes rarely consist of veinstone only, but inclose also blocks of the adjoining {commtry)^ and thus assume a brecciated structure. Their widest portions often {Mm Jmrse) split, but such separate veins are seldom rich."

« Metallifepciiis Beposits, p. 84.

116 SIL¥ER»IiEAB DEPOSITS OF BIJBBKA, IfBTADA.

As there is an unqEestionaM© connecticm in depth between the ¥iirioiii ore-bearing regions of the Ruby Hill deposits, if this Bomendatttre is correct the ore bodies are to be regarded m branches of a single lode. Nevertheless, the fact is that these deposits diiPer essential from those which yielded the usually accepted definition of the words vein and lode, and the analogies between the two ¥arieties are so distant that an attempt to apply the terminology of typical veins to the Eiiby Hill deposits as a whole leads immediately to misunderstandings. In ordinary veins ore is deposited in pre-existing openings, while the bodies of Mnby Hill were mainly deposited by substitution. In ordinary veins nearly all the space not occupied by fragments of rock is filled with ore and other minerals. In the Eureka occurrence many of the fissures have served merely as channels for the solutions, and space for deposition has been provided mainly by chemical means. The bearing of those differences is readily made apparent. In typical lodes a fragment of country rock entirely inclosed within the fissure, and hence completely and substantially snrronnded by ore and gangee minerals, is called a "horse," but a mass of rock divided from the surronnding country by mere cracks not filled with vein matter is not called a horse.

The term "horse" is usually nnequivocal and signifies a mass of country rock of considerable size entirely inclosed in ore or vein matter. One can always conceive, however, of the croppings of a vein being eroded to the level of the center of a horse, one surface of which would then be exposed to the air, and the horse would not be entirely inclosed by ore and gangue. Masses of rock in the croppings of a lode when they resemble horses in other respects are therefore known by the same name. No definite limits can be assigned to the size of a true horse, which certainly depends upon the size of the lode as well as upon individual opinion. Nevertheless, although there are horses in the Comstock lode a few hundred feet wide, it would be a most extraordinary lode 'that would contain a horse exceeding 1,000 feet in width, and the limestone wedge of Mnby Hill is much wider than that on the surface. All miners will probably agree that a horse must be a portion of the contents of a vein or lode.

In the mineral zone of Muby Hill many masses of rock are surrounded by fissures, most of which are mere fault seams, though some of them have

been no doubt the cbaanels of dre-bearing solutions. These masses in ordinary Yeins miglit hmvo been smrouiided bj vein matter, hu% owing to the peculiar manner in which ore was deposited in this locality, the surrounding fissures do not often show ore. These masses of rock then take the place of horses firom a structural point of view, bnt do not answer the cnn-ent definition of the term, and a misunderstanding or an error is involved either in calling them horses or in denying their structural analogy to horses. If it were once admitted, however, that a mass of rock not substantially inclosed in ore or secreted gangne minerals may be called a horse whenever the fissures by which it is divided from the solid country belong to an ore-bearing system the consequences would be serious, for a horse is always regarded as a part of the fissure filling, as a portion of the vein or lode, and the lode would then necessarily be coextensive with the fissure system. In that case the term lode would be synonymous with mining region. The quicksilver belt of California would be a single lode, as, too, the California gold belt, and the great Arizona and Utah mineral zones would each represent a single complex vein.

ci«««iiciitioii of mm deposits •ccorcung to iiifcrtat autiiow.— Such an extended Signification of the words lode and horse would also be wholly at variance with any system of the classification of ore deposits which has hitherto been adopted, for these depend to a very great extent upon the external form of ore bodies. Ton Gotta says:* "I divide all ore deposits primarily according to their form into regular and irregular. The former fall into two groups, beds and veins; the latter into stocks and impregnations/' In the next paragraph he sajs: "A single aggregation of ore may consist of several separate deposits of different forms.'' These passages make it as clear as possible that von Cotta regarded a substantially regular tabular form as essential to a vein, anil i||rh0ii 01-0 masses of different shapes are so associated as to imply a simultaneous and common origin he would relegate them to'different classes without regard to the community of origin. Since von Cotta, two eminent mining geologists, Grimm and von Groddeck, have written important monographs dealing with the classification of ore deposits. Each has endeavored to give greater weight to genesis in classification than von Cotta did. The folowing table explains the classification of each of these authors:

•Bntliifiiittitttii, JL, f . t.

J .

118 8IIi¥E!B-TiFiAP DIPOSITS OF BIJBBKA, lIllTADJu

▼JJIIOUS CTiAMIFICATIOllS OF OIB BEFOfllTS.

I.— Bepusits of regular

I.— Primary deposits:

form:

poeits in wMcli th© or©

is an esiseiilM cwnstit-

a. MsteUiffiroiia vtiste

ment of ill© oomntry

ft. fliittiui Willi iiMmi.

mi eoal. h. Tlmmm,

a. Orilmiiy ■▼©Ilia CQii«r.

-tioni.

iDftl portions of mm-ft

. Bid TiiliMi flJigfirfilling

of «i¥iti«».

h Oni-lMiiHiiiglMwMiiin.

fr. €mw illnip. 4, Deposito formed liy miitiiiiiorpli ism or SMlMtitotion.

II.— Separat© deposits of

form:

deposits.

ti© ore is distinct fmm

m. Betiovliited Teliis

a. B«da.

<I. Bntum.f

form.

m. Baddtti tnuMiii.

of ■trntlication. •

•The Crcrmiiii word Qiing compriins the Englieli wordii lode, ¥©iii, and dike.

*Voin8 whicli cut the strati iciitioii of formations if tlic^country rock is stratiied.

« Veins between the itmt» of a fommtioii wMch lav© lion foimod sine© tlie rook wmii iopotitad.

*• Similar to gasli Tcina, only not coming to th© surface.

•Von Cottm miikes a tluirp division between op© mid country rock m part of the dttnition of stock. Grimm calls bodio* witch pass o¥©r gmdiimEj into tb© country WMJk, as woU as tboio wMck are sliarply defined, stocks (Sfcocko). Von Cotta iilso iiwidos stocks into two classes— tbos© tbat conform t# tb© strati icntion of the oooiitry rock and tkoii© that do mot.

/Von Cottii rommrks tli»t, strictly apoaking, roticolmtod ▼•!»« should not lio olmiiiied aa do-posit* of irrognlftr form, bot as the nnion of a great nnmbcr of small veins; in otbor worda, tko imcliiiod ang olar fragments ar© so largo, compiinii witli tlii width of iho fissures, that tbey oiimiot be considered m liorsos.

'Von Cotta nseii those terms to doscribo the local ooomwinco of Tariona irregular or© boiiim

An examination of this table will show that the term lode m iinderstooi hj these attth^rs cmmcit be applied to the wedge of limestone betweea

The M&gt;Bb Qubsiion. 119

the qmtrtaiite and th© Ruby HiE ftmli Prof. IL Pimipellj also Imi published, in Johnson^B Encyclopadia, a classification of ore deposits according to which, how©¥©r, the or© deposits of Ruby Hill as a whole would be as far removed ifroiii typical veins as in the other systems. Some of the or© bodies in the limestone wedge are well-defined veins, and when they connect with each other they can he considered as parts of the same lode.

iiiii*»*<ieiiiiti©iiofiiMie.^No¥erth0l©s8, it will be conceded that the miners' definition of the word lode, however indefinite it may be, has a much more comprehensive meaning. Dr. Raymond, in his testimony in the Richmond and Eureka lawsuit/ says: "The whole subject of the classification of mineral deposits is one in which the interests "of the miner have entirely overridden the reasonings of the chemists and geologists. The miners made the definition first As used by miners before being defined by any authority it [lode] simply meant that formation by which the miner could be led or gEided. It is an alteration of the word load; and whatever the miner could follow, expecting to find ore, was his lode. Some formation, within which he could find ore and out of which he could not expect to find ore, was his lode/' The mining law of the United States as interpreted by the courts also gives a broader signification to the word lode

Pccewityof miiettcf ciii««iiciitioii0f0r«iepo»it«.^The different definitions of the word lode have given rise to a great deal of discussion in the courts, and a classification of or© deposits which would reconcile the adverse views would tend to simplify the question for the miner, the lawyer, and the geologist. Mr. S. F. Emmons,* while introducing the classifications of Messrs. von Gotta, Grimm, von Grroddeck, and -Pumpelly, in his abstract of a report upon Leadville, Colorado, recognizes the necessity of a more satisfactory classification. Ho says: "That the difference of origin and manner of formation should be a more important factor in the classification of ore deposits than has been the case hitherto is generally admitted, but, owing to the fact that the definite determination of such origin requires more laborious and expensive investigations, especially from a chemical point of view, than geologists are in general able or willing to make, trustworthy data are as yet too meager to form a basis for a general classification from this standpoint"

•8iifraiii« Coiirt of tli« Unitod StiitM, Mm. 1056 mni li60, p. 810.

^S«M>iii AnniiAl Bnport of Iho Binolor of tlitt Unitoi Sliitofl Gtoologlosl Bmrw^j, f • 833.

CHAPTEl XI. ASSAYING.

Otiect ©f 9mmyim mmmtrj rock.— With S ¥i©W tO disC€l¥erillg, if pOMlH©, the^

source of the ore in the miees of Eureka District, attmeroiis and careful assays of all the different kinds of country rock in the neighborhood of the-ore bodies were made by the author. As the quantity of the precious-metals contained in any of these rocks is extremely small, it waa necessary to take unusual precautions in order to determine with any degree of exactitude the amounts of gold and siker present Assayers do not ordinarily attempt to estimate with accuracy any Talues of either gold or siker less-than one dollar to the ton (0.0001659 gold or 0.0026518 per cent silver), and m the country rock of this district never contains so much as this, particularly delicate methods were required in the determination of the-actual quantities of these metals.

DMcuitj of obtainiiif pure i«mi.— Oue of th© principal obstaclcs to be overcome-in obtaining satisfactory results in the assaying of all rocks containing very small percentages of the precious metals, is the difficulty of obtaining a lead iiix which does not contain very appreciable amounts of gold and silver. The purest litharge which it was possible to obtain from dealers contained from 10 to 50 cents of silver to the ton of 2,000 pounds (0.00026d2 to 0.0013259 per cent), and as it was necessary to use from twice to three-times as much litharge as the weight of the material assayed almost all the silver obtained from assays of country rock made with such litharge came-from the litharge itself.

AppTOximiiteijr puns iitii«ff« reqnireiL— At fiiTst sight it might 8©om possibl© to Obtain correct results by assaying the litharge separately and deducting its-value in silver from the value of the assayed rock. This is not practicable,, however, for the litharge of commerce is not only argenttferoiis but of vei-jr

- Assaukg. : ■ 121

variable compoaitioE, and no mecliaiiical method of mixiiig is sufficient to bring about the degree of homogeEeitj required. The smaller the relation of the silver in the rock under assay to the silver in the litharge the gi'eater is the uncertainty arising from the argentiferous character of the flux, and

unless the litharge is nearly pure it is impossible to discriminate between errors arising from this cause and those due to insufficiency in the time of melting, imperfect iuidity-of the slag, and the like.

Qnmtiiy of reindnif nMteriri n«ceii«i«y.^The Weight of the Icftd button is dependent upon the amount of reducing material used in the flux and the amount of sesqnioxides present in the rock, ■ which it is necessary to reduce to protoxides, provided reducing gases be excluded. Ai there were no other sesquioxides than that of iron present, and this only in very small quantities, the weight of the lead button was not materially altered in that way. For reasons which will be given hereafter, it was found advisable not to use sufficient reducing matter to exclude all the oxide of lead from the slag.

E«i«ttoii ©f tii« wMwm to tiic aiaoiiiit of lea* r«iii«ii.^Experiments made with diiSerent quantities of reducing material upon the same iux showed that part of the silver in the litharge went into the button of metallic lead, while a part of it remained in the unreduced litharge in the slag. As might naturally be supposed, the proportion of silver to lead in the reduced button was always greater than in the litharge employed. The proportion of silver to lead also increased with the time during which the flux was kept melted and varied with the temperature and perhaps with other circumstances in such a manner that no law governing the proportions in which the two metals-were reduced could be detected. When rich litharge, or litharge containing very appreciable amounts of silver, was used, it was therefore impossible to estimate with any sufficient degree of accuracy the amount of silver from the litharge which is united with that of the rock in the lead button* Even when the whole of the litharge is reduced, or as nearly as possible reduced, it is not likely that^all the silver it contained is concentrated in the lead button, and it is only by using litharge (or any suitable form of lead), which contains little or no silver that it is possible to render the resulting-error smal enough to permit of estimating the probable amount of silver wMch the litharge gives up to the lead button

122 SILVBl-LBAB DEPOSITS OF BUMIKA, HKVAIIA.

Diniiiciit Mudtoariiin i WMto Icfti (carbonat© of lead), sugar of lead (acetate

of lead), and the best granulated lead ordinarily contain upwards of ten cents to the ton (0.000265 per cent), and although any of them may be used-in assaying rocks containing less than 50 cents to the ton (0.001325 per cent), yet 4he results obtained are more or less uncertain, and are not at all to be relied upon in ¥ery poor rocks, such, for instance, as carry below 10 cents to the ton (0.000265 per cent). Moreover, the carbonate of lead, owing to the carbonic acid it contains, is liable to boil over in the crucible, though this can be obYiated by a previous calcining. A like objection can be made to the acetate, the acetic acid of which contains more carbon than is needed to reduce the oxide of lead. If it is used in its natural state it swells up, and after the acetic acid is decomposed the reside ual carbon thickens the slag and prevents the proper settling of the globules of lead which everywhere permeate the mass. This diiSculty, however, can also be remedied by a previous calcining. Granulated metallic lead, though otherwise unobjectionable, melts too quickly and unites at once in a mass at the bottom of the crucible, thereby preventing every particle of the powdered rock from coming in direct contact with it; and although such an intimate contact is unnecessary in assaying ordinary ores, it is found indispensable where the material to be assayed contains such extremely small quantities of the precious metals as do the ordinary country rocks of a mining region.

ojiMc of lead r«iiiit«ii in the .laii.— It has becu remarked that the slag is the better for the presence of oxide of lead. This is notably the case when the rock treated is silicious, as in combination with other bases it renders the silicate formed more fusible and liquid. Litharge seems also to attack quartz more energetically than even soda or potash. Even in those rocks which contain scarcely anything but carbonate of lime it is found to assist in the formation of a proper slag.

Tiiiiprecei«iiiopteiforiiiiikiiiiriith»rfe.^The KthaTge uscd itt assaying all the Eureka rocks, as well as those of the Comstock, was made at the reining works of the Richmond Company in Eureka. The following process was adopted in manufacturing this litharge. One thousand pounds of market lead the refined lead obtained from the parting of silver and lead by the Luce &

Assahmg. 123

Moam method, contaiiiiiif mboiit $1 to the torn ((U0265 per cent), wm cupelled on a frmk bone-aili test in an English refining fkmaco. The first 300 pounds of Itharge reittlting from this CEpellation-ran ¥ery poor, containing icarcelj 2 cento to tha ton (0.000053 per cent ). The litharge which followed gradually increased in ¥alEe until toward the last it contained nearly as much as the original lead. This laat litharge was reduced by charcoal in a black-lead crucible, and the resulting lead was again cupelled, yielding an excellent quality of litharge. Upon reducing and recupelling the best litharge it was found that the percentage of silTer was but little reduced, showing that a point cmn be reached in the process of desilverization at which it is not practicable to separate the silver from the lead bj cnpellation. The refined litharge also contained a trace of gold, but the quantity was so exceedingly small that it was neglected in the ©stimatioE of gold values in assays of single samples.

mmjimt^.mu^..—In assaying the litharge itself an interesting phenomenon was observed. If the litharge was mixed with suiScient charcoal to effect its reduction and the resulting lead was cupelled, it wa« found that a very much smaller quantity of silver was obtained than if the usual lux, consisting of bicarbonate of soda and bitartrate of potash, was used. To what imperfection in the-process this is due is not clear. The proportional loss with ordinaiy litharge is much smaller than with that which contains extraordinarily little silver.

Ejiperiment..— The following experiments illustimting the fact were made in dephcate, in order that the results might bo conclusive: (a) 8CiO grains litharge were reduced with 600 grains bicarbonate of soda, 200 grains bitartrate of potash, and 200 grains borax. Silver resulting from cupellation, 6 cents per ton (0.000159 per cent). (6) 800 gi'ains litharge were reduced with 61 HI grains bicarbonate of soda and 200 grains tartrate of potash. Silver resulting from cupellation, 5 cents (0.0001325 per cent), (c) 800 grains litharge were reduced with 30 grains powdered charcoal and 200 grains borax. Silver resulting from cupellation, trace, (d) 800 grains litharge were reduced with 30 grains powdered charcoal. Silver resultiiig from cupellation, trace.

124 SILTJBB-IiBAB DEPOSITS OF BUKIKA, NBYABA.

Eoiiito.— From these experimente it will b© seea that th© larg ©it mmottnt of silYcr was obtained fronoi the method employed ia («), mud thmt the Edition of borax iacreaaed the qeantitj of silver where charcoal was not used as the reducing agent It Ib probable that the eifeet of the borax was merely a mechanical one, facilitating tli© settling of the miimte particles of lead by rendering the slag more liquid, and that it had no reducing power on the silver in whatever form that metal may have been. In all these assays two hours were occupied in melting, and the lead buttons were cupelled at the lowest possible tamperatnre.

Emiieriiiieiito ia redttdng agent..— Scverftl ©experiments wcre made to determine the beet reducing agents, and bitartrate of potash was found to give better results than any other. Upon the application of heat this substance is decomposed into carbonate of potash and carbon, both of which act energetically upon the substances to b© reduced. Borax in the presence of strong reducing agents never takes up silver, even when it is used in considerable quantity.

Composition 0ffl«i.— The following is the composition of the flux used with 377.09 grains of the limestones of Eureka District:

Oniiiis. Litharge ........................ ................. 77©

Bicarbonate of soda ...................... ....... §81)

Bitartrate of potaah .............................. 165

Bormx.. .......... .................. ............. 4CM)

With but iHght modifications this flux answers for almost any country rock.

weif hi. ii.ei.^The weight adopted for the assays of the Eureka rocks, a& well as those of the Comstock made for Mr. Gr. F. Becker, was 371.09 grains. Grains were employed instead of grams, as they correspond with the Oertling assay weights used with the latest improved Becker balance, and 377.09 of them were taken, as the .Ii2-grain rider then represented 10 cents, to the ton (0.00026S) for o¥ery diYision of the balance beam. The values-were calculated in cents to the ton of 2,000 pounds, as is usualy the case-on the Pacific slojic, but they are also given in percentages.

Tiiii«iiiiiiii«i«er0f Bieitiiit.— In Order to obtain the maximum results it was-necessary to melt the assays for nearly two hounsi This was accomplished

ill a charcoal draft furnace, wMck would admit four No. 10 Frencli crucibles at once. The fnel employed was charcoal made fifom the pifion pine, mnd it was scarcely inferior in heating power to coke. The heat was kept as nearly as possible at a point a little below the melting point of cast iron, and experience showed that after two hours the silver obtained no longer increased nor yet perceptibly diminiBhed. With a higher temperature it may be that the time might be shortened, bat taking into consideration the volatility of silver at high temperatEres this expedient cannot be considered advisable. When the melting was less prolonged the maximnm amount of silver was never obtained; indeed, in a series of careful experiments made " to determine the best time of melting, it was found that some assays which had been-kept at a melting heat too short a time, though thoroughly melted, yielded less silver than the litharge alone was known to contain.

Ctt|i«iiiiti©iniai ciipsi..— The lead buttons were cupelled in a small muffle furnace, the heat of which could be easily regulated, the fnel employed being also charcoal Usually but two cupeHations wBre carried on at one time and great care was taken to reduce the loss by cnpellation to a mini-nmm by keeping the heat at the lowest temperature consistent with the oxidation of the lead. In order that the heat should be maintained at the lowest possible point, the cupels used were mad© from one part of fine leached wood ashes and two parts of bone ashes. The ashes were those resulting from the burning of cedar wood, the most available wood containing little silica. The cupels were prepared in the following manner: The mold was filled with the requisite amount of the moistened mixture of the two ashes and the maas was pressed into shape by the punch. Then a coating of dry elutriated bone ash was spresid over the top of the cupel, the punch again inserted and driven home. In this way a cupel was obtained which had great absorbing power, allowed the lead to be cupelled at an exceedingly low temperature, and because of its smooth surface prevented the small silver button from being engulfed in the coarse material of which the cupel was composed. The button, too, could easily be removed by the point of a knife without retaining any of -the bone ashes.

L«i«iijciipei«ttoii.^Many experiments with a view to determining the loss by cupellation have been made by Hambly, Klasek, Plattner, and others;

126 SILVEB-IiEAD DEPOSITS OF BPBEKA, ¥BVABA.

but as the conditions atteniing this loss are iepenient upon tbe quality of tlie cupel and the character of the furnace and fire, it 'm Bot possible to accept the results obtained by them, as applicable in all cases. Some experiments upon the loss by cupellation were made for this iii¥estimation, as nearly as' possible under the 'same conditions as those existing in the assays for the determination of small amounts of silver. It was found that m^hen the temperature was not too high for feather litharge to form and when the draught was not too great, there was no perceptible loss of silver under .01 grain, which ■represents $1 to the ton of 2,000 pounds, notwithstanding that this .01 grain was cupelled with 400 grains of lead. In fact, in most instances, the button resulting from the cmpellation of .01 grain or less of silver with 400 grains of lead weighed from 0.5 to 10 per cent more than the actual amount of chemically pure silver cupelled with the lead. This excess is owing to the fact that the silver button obtained by cupellation is never absolutely pure, but always contains from 0.2 to 5 per cent, lead, as well as fine particles of the cupel. There is always a loss of silver in cupellation, but as this loss rarely exceeds 1 per cent, of the amount of silver present it can be entirely neglected in rocks containing less than $1 to the ton (0.00265 per cent). This loss does not begin to be important until a value of over $10 to the ton (0 0265 per cent) is reached- When the contents in silver is less than .01 grain, or less than $1 to the ton of 2,000 pounds, and the amount of lead alloyed with it 400 grains or less, the button resulting from the cupellation is invariably slightly in excess of the actual quantity of silver contained in the alloy. With amounts of silver exceeding .01 grain and lead exceeding 400 grains, up to a point where the quantity of silver does not exceed .1 grain, the weight of the button does not vary perceptibly,- no matter what may be the quantity of lead (within

that the quantity of lead did not to a greater extent affect the quantity of silver obtained, but it must be remembered that the greater part of the loss by cupellation takes place at the moment of "brightening," and that this loss is directly proportional to the quantity of silver present. It is also true that the gi'eater the quantity of lead to be oxidized the greater is the loss of silver. But this latter loss is so small in comparison with the former

ASSATmro.

that it makes no perceptible diierenc© whether 10§ or 1,00§ grains of lead ax© ttsed with .1 gndn of 8il¥er. It has been pointed out that the loss of sil¥er is compensated for in small buttons by the lead retained and it would seem that this ought to be equally tree of large ones, but as a matter of fact it is not, probably because large buttons remain for a longer time melted, thereby being more completely cupelled. As the silFer contained in any of the country rocks of Eureka District scarcely ever reached 50 cents to the ton (0.001325 per cent) the assays can be regarded as unaffected by any loss in cupellation. An experiment was made to test this inference, and it was found that there was no perceptible loss in cupelling 60 cents (.005 grain) of sil¥er with 400 grains of lead at a temperature considerably abo¥e that required for proper cupellation.

EjtFerimeiitii.— In regard to the joss by cupellation in general the following experiments may be of interest is showing the differences in loss at various points in the muffle.

Nine assays, each containing 5 grains silver and 30 grains lead, were cupelled and the losses expressed in thousandths of the unit of 5 gimins attending each, with the number of the assay, are shown in the diagram of the muffle in the position occupied by the corresponding cupel:

• Biicili of maffle.

Fig. 3.— Position of cupels im muffle.

The order 9, 6, 3, 2, 8, 5, 7, 4, 1 represents the order in which the cupels were withdrawn from the muffle, and therefore the speed at which the cupellation took place. Nos. 7, 8, and 9 were cupelled at the proper temperature, but those in the back part of the muffle were too hot It will

SIIi¥BiHilJJI DlPOSrrS' OF IWEEKA, NEVADA.

he obser¥ed that Mm. 9, 6, and 3 were fiaishei first, showiiif thmt the dntft on that side of the muffl© was the strongest The assaj which showed the least loss was No. 7, which was in a poBition where the draft was the least and the temperature the loirest and where the cepellation occupied nearly the maxinmin time. The quantity of lead used with these assays was considerably more than was necessary for a proper cupelation. It was used in order to render the differences in loss as palpable as possible.

Six assays of 5 grains sil¥er with 25 grains lead ga¥e the following result:

Back of muffle.

Fio. 4.— Position of ompiils ia mnfl©, •

The order in which they were remo¥ed was 6-3-2-5-1-4; 5-1-4 being finished at about the same moment Here, also, the draft was greatest on the right side of the muffle, and No. 4, which occupied the position of No. 7 in the former experiment, exhibited the least loss. The quantity of lead was still too great for perfect cnpellatioii.

Two assays of 6 grains silver with 15 grains lead, cupelled side by side, ga¥e a loss of 3.5 and 3.8 thousandths of the unit of 6 grains. This loss

small as it is possible to rendeif it

Manner of fWBoviiifbiittoM from cupeto.^ As many of the silvcr buttoBS obtained from the assays mad© of the Eureka rocks were so small that they could scarcely be di8eo¥ered by the naked ©ye, it was-found next to impossible to remo¥© them from the cupel by raising them in pincera. Another method

• Brano Eerl, Httttemkimde, I¥., f . K. Leif idg , IMS.

was therefore resorted to. After they were loosened -froin the hone ash, Ihe cttpel was tipped up and the buttons were allowed to fall upon a polished steel aii¥iL When struck hy a polished steel hammer any adhering impmities were removed and the fattened button was found sticking to the face of the hammer, from which it could be easily brushed into the scale-pan.

MiuMierof wnifiiiiif.^Iii th© Beck©r balance, used in weighing the silver buttons, the right arm of the beam is divided into twenty parts. If a rider weighing .005 grain is used each one of these spaces will represent .001 grain, and if a weight of rock equal to 377.01 grains is used in making the assays each one of these parts will represent 10 cents to the ton, or 0.0002652 per cent. By placing a card-board scale, on which each on© of these parts is divided into ten, behind the beam and using a magnifying glass in front of it the position of the rider between any two of the pointa marked on the beam can be determined with accuracy up to one-tenth of the space, which would represent a value of one cent to the ton (0.0000265 per cent). When new and in good order the Becker balance is sensitive up to .0001 grain, which represents a value of one cent to the ton. Alowing a difference of one cent (0.0000265 per cent) one way or the other, it is safe to say that buttons can be weighed with almost absolute accuracy up to within two cents to the ton, or plus or minus one cent As is 4el known, Haxkort and afterward Plattner,* instead of attempting to weigh extremely small bet-tons, measured their diameters between two fin© lines converging at a smal angle, which were engraved on an ivory scale. Very smal silver buttons are almost exactly spherical, and the method is therefore not only rational but calculated to give more exact results than weighing, but it requires very delicate manipulation to place the button so that both lines are exactly tangent to it A common microscope with a micrometer eye-piece may be used instead of Plattner^s scale, and the measurement naade both more rapidly and more accurately. This method also obviates the necessity of removing the buttons from the cupel.

iii»cciinici«i©ftii«««iiiti.— Admitting that the loss by cmpellation is so smal that it can be neglected, and that the method of weighing is correct within two cents, the other sources of inaccuracy attending the assaying of rock-containing but minute quantities of silver are reduced to two, the imperfect

•Plattniir's FrolbiikiiBit Tli«0iiir Molitiir, f. 35; Ii6if lig, 188B. 2664 I^— f

130 SIL¥BE»LBAD DEPOSITS OF EIJEBKA, JfETADA.

redEction of the "pulp*' and imperfect detennination of the cxintents of the litharge. If proper care ie taken in melting, most of the sil¥er contained in the rock can be collected in the lead button. It caeeot be expected that all the silver will be obtained, but what remains in the slag can be reduced to an almost constant quantity by reproducing in all assays nearly thesame conditions, such as fineness of "pulp," length of time of melting, quantity of finx, etc. Assays of the same rock have been repeated several times with identically the same results. The quantity of silver produced after a certain point does not seem to vary perceptibly with the time during which the assay is kept melted. The second source of inaccuracy is the more difficult to control, namely, the impossibility of obtaining a finx absolutely free from silver, or of correctly determining the amount of silver in the button which is derived from that source.

iictio»i,fMt«rt«tei,fp«t-ii«iiti.«w«.— The quantity of litharge used in assays ing Eureka rocks was about 770 grains. To reduce this litharge 165 grains of bitartrate of potash were added, and the resulting button of lead, when reducing gases from the fire had been excluded as far as possible, usually weighed in the neighborhood of 425 grains. Almost all the limestones in Eureka district carry more or less" free carbon.* The quantity of sesquioxide of iron present was so slight that only a very small portion of the carbon was absorbed in reducing it to the protoxide (FeO.). Where there was any quantity of that mineral present in the rock it was necessary to increase the amount of bitartrate used in order to obtain a lead button of about 425-grains in weight.

Bciiriiif ©f the rfiirtir In Ik* litiMff • on tii« reittiti.— The silver Contained in the 425-grains of lead reduced from the 770 grains of litharge was ft cents per torn (0.0001511 per cent.) when the flux itself was assayed. " This amount scarcely over varied, but frequent check assays were made. When peroxide of iron, or other substances requiring reduction were present the weight of the lead button was less and the amount of silver it contained was also less. When other reducing substances were present, such as organic matter in the limestone, the weight of the lead was greater as well as the amount of the silver resulting from cupellation. This increase or decrease in the amount of silver

•Tliis is piirticoliirij the oas© with the no-called **biiok limiiitoii©,"

ASSA¥rNG. 131

WM, howeTer, not proportional to the weight of the lead, m has 1}ci©e ©xpMned "before. The differeac©, howe¥er, between buttoiiB weighing 3§0 grains and those weighing ,500 grains never exceeded 2 cents (0.000053 per cent), and it is therefore safo to say that when the lead button did not ¥ar j more than 25 grains either way from 425 grains the possible difierenc© could not exceed one cent (0.0000266 per cent). Allowing 2 cents (0.000053 per cent), or plus or minES one cent for inaccuracies in weighing, the total amount of all the possible inaccnracies can be reckoned at 3 cents (0.0000715 per cent), or pins or minus If cents.

ncmiit ©f ef«ini.^The possiWo errors in the silver assay as it has been described are the following: Inaccuracies in weighing the "pulp"; imperfect flnxing; insufficiency of the time of melting; impurity of the Itharge; loss by cnpellation; mechanical losses; and inaccuracies in weighing the silver button. All these errors, with the exception of those caused by silver in the litharge and the inaccuracies in weighing the silver button, are so infinitesimal, when the assay Jias been properly conducted, that they may be neglected altogether. The other two sources of error, the litharge and the balance together, cannot change the results more than three cents, and the influence of the latter of these can be very much reduced by the iubstitutiott of a microscope with a micrometer eye-piece for the balance.

■rtiiiMtiim of ii<iii._The determination of the amount of gold in any country rock where it is-present in extremely small quantities is attended with great, difficulties. It is scarcely ever as much in value aa the silver and is always-very much less in quantity. It is only by the concentration of a large number of assays that it can be determined at all, and the results even of this method are not always reliable. It is impossible to obtain Itharge freefitim gold as wel as silver, and it is much more difficult to determine itsqnjyritily 0|. t|j0 ^fjaui that it has upon the assay. As nearly as could b# determined, the amount of gold in the Htharge used wai about one cent to the ton of 2,000 pounds (0.0000016 per cent.). This result was obtained in the following manner: Twenty assays of the ordinary fiux were reduced in the usual way, and the resulting lead buttons were separately cupeled until the lead remaining would weigh about twenty grains. The cupels were then removed from the fire and allowed to cool. The twenty lead buttons, which

colectively would weigh about 400 grains, wer© reiiiO¥©d from the cupels and placed in a scorifier in the muffle with 5 grains of borax glass. When tha mass wa« thoroMghl j melted it was poured into a mold and the lead was again cupelled. The gold in the rock was all determined bj concentrated assajs in this manner, except when a series of assays were made fifom samples taken near together. In this latter case the 'average ¥alive in gold was determined by dissolYing the whole number of the silver buttons. u«« of iMmyfc— While various purposes may be subserved by assays of country rocks the main objects of those here described were first to ascertain in which of the rocks the preciona metals could be detected, and second to trace the variations of tenor in diiferent occmrences of the same rock. As a qualitative method exception can scarcely be taken to the dry assay, while even if the degree of accuracy reached in determining the absolute contents in precious metals of the Enreka rocks has been overestimated, the value of the results would scarcely be impaired; for it will hardly be denied that the results form a smfficient basis f^r a comparison of different samples of the same rock all containing very smaE quantities of silver and gold. For the purposes of this report it makes very little difference whether a certain mass of limestone realy contains 10 cents or 20 cents, if it can be proved that a second body of Imestone contains twice as much, or it may be hatf as mnch. In other words liie main purpose was to ascertain the relative contents, not the absolute contents, of the samples assayed. Even if the methods employed were ideally exact it would be impossible to calculate the metallic contents of. any large blocks of ground with precision, since it would be impossible to obtain samples which should correc€y represent the average of the mass. The following pages contain al the assays of Eureka rocks, except those wMch were given in the chapter on the source of the ore, as wel as some special determinations which were made of several minerali.

13S

lAlIPLBS TlXiai E¥1E¥ EIGHT FEET IJf THE SBCOMI CE08»-CUT OM THE FOUBTM JLEVBI* OF THE EUKEKA MHIE, BEOmimO AT THE JUMCTIOM.

U©.

Bfnoriflioii.

Brow nisli cmslied limisitoiMi ............ .

Oimyiali Imiiato&ii, hMier ...............

GimjMi llmisitoii© .......................

GrayUi Hmeitaifi, Bore teokini...... ...

WMtii liinttit©!!©, not Teij Iwit..........

......i© ..................... ............

CnwlMiit brokciit, spitloi HidmIiiim. .....

Brokfia, grsyltlilliiififltonii...............

,.....Aii. ............... .................

S«m«, "but moiii ooiii»ot. .«.....-.. .....

Mnifili liniiMitonfi, miihiii laxii... . ......

......ii>. ...................... ..........

Skih^ Mtaolter........ ....... ...-....-.

,.....do..... ...................... ..-...,

Mwtiiiiii lutfd, ■tafmed tliiiii«taii«.........

Cnulied, stitiiied Mniwteoii ..............

Sum©, mvm oonipiol...... ...... .........

Cmstie^ Irokei HniMitopo ..............

......do..................................

......i©. ........................ .........

n

M

w m m w

m

18

m m m m m u m m

Is

• Tim nvenipi vuliiii In geM ww t MMito to flui Imi. i Bntton lotl t& mmiYlag froia cnpi.

SAMPIiES TAKEM E¥EKY FI¥E FEET IN SIMUMCI THE EICHMOMB SHAFT FEOII THE

him TO THE 1,200-FOOT IMYMs.

Qmtrtsite. ......in...

It

m m m li

Is

li

li li li

It

Is Is

ss

Is Is

• Bnttoii ImI in nniyiriiii from oiif«l.

SILTEB-IilAB D1POBIT8 OF EUBEKA, ]fl¥ABA.

TMs f martiita contained iron p jrites ani some moljMenite. AM llit silver buttons were dis«ol¥ed together, and th© resuMng gold gav© an average of 4 cents to each example. The usual ittx was employed ia assaying this rock, except that liO grains Mtartmte of potash and 350 grains of borax were used.

ckiortniitfiiiite* ©f EicAiaoni "rwi" mi ««y«tt<p^ — ^The finely pnlveriied sample was leached for one week with hypoanlphite of soda, and the difference between the assay value of the nnleached samples and that of the leached sample showed that 36.1 per cent of the silver contained in the ore was in the foiiii of chloride.

ASSAYS OF VAMOUS B0CiD8.

Va

It

Oiwito teM MliMinl Bil BiMsli iefMniipiMi....^

Siii pnonji f wMto fknii Mliitml BiB oaciyiiif bimsIi

funie ©idiii. ...................... ...-^-.. ...... ........

W«itlif}i»i ]|iiM»toB« from top of Kmlij MM, nir ¥. 8.

Ckxitogloiil ittrraj iiiimiiiiitiil .......................... .

XimkA tniitsilA ftm Carilios Mil, mramip of four mhi-flu

..... .......................................... .......

QnAirtslto teni iHii of onuHnit mi fhM Ivml of tti« M-

SbjoHto tali fruni fiuiRy iMok of Mob Mil, Samkii .....

"Bank " lliiMMtiNif} fkwn «iii nf cwmi-cnt m, ••▼milli toriil

«ftli©Mcliiiniiid....... -....-.-..........-. .............

Mnmiitaiio froni Jmaotifiii of ini cnw^wt and iiW-iiMil

lir¥«l©ftll«Illotalllllli ..................................

IiiiM»tm« fboBi Ite ooiitMt with f mftstto fttni inl

BOitii umw-oiit on Hit XioliiiMMid aintliteTiiI............

IteiiUi **1»i>]i" IniMtoiiii frwii and of inl Mmtliifiiil

iiUt oppMito mnmimI nortli omai-ciil iiiiitli l«¥el of th»

|tt ft |i mf mii| ..............................................

WMto qiuiiliBitfi miMir wntMi with Inicttoiiii, l.tet-iml

Dtoniapmdl rlijiililt ffcuiii "rlij#llii wiimi," mii UwA

iif tilt Flmiiilii: ..........................................

* * l*™! " Mimcitiinii IktM —to plMM........ ....... ...I...

"Aoal** BniMtaiie froni ttm teeoai cRMt-enl mi tii« I

■ixlii lurriil of IheK K,a8fiiiililrimiiiidiiilrtft........l

XnM.

Tumi.

Omit. 2

•M

Tumi.

li •it

Taut.

Timcii.

• tnitM two WIllflM I

I I ftmi BMr low-grain on.

Assayiko.

SAMPLES TAKEN 30 FEET APABT, BEOINNINO AT THE END OF THE FIB8T CB0S84!UT IN THE '< FRONT" LIMESTONE ON THE SIXTH LEVEL OF THE K. K.

Viib

1!i««i.

li 4

S

•

li

.

11

l%iiii fliiitiifili witli inf ■111 iiiipiii|.]wi , ,

D«i«iita«tfiin«f cMiMiiiiaviiriiwi»iiBiii«oii«».---Tlie ietemiiiiatioiis were naai© in the foUowiEg manner: One liuadred grains of finely pulTerizei rock were dis-solTed in hot chlorhjiric acid, filtered, and the residue was dried at above 100^ mnd weighed. This insolable part was ignited and the carbon determined by difference.

ITo.

1 S

©f tliii EluliBitiid. ^JnMlnWii iwittiir IM pur «ait ......

A great deal of the limestone between the main and secondary fissures carries free carbon, the amount sometimes reacMag 1 per cent

An examination was made of the clay from the main fissure from al the points where it is exposed in the Etireka mine, for the purpose of determining the quantity of the carbonates of lime, etc., which it contained. The largest percentage of carbonates obtained was 85 per cent and the lowest 15 per cent As a rale the clay was most calcareous near the surface and the most silicious below, though there were local exceptions. As it was in part the product of attrition and decomposition of walls of qnartzite, limestone, and shale, and no doubt in part also a product of the decomposition of rliyolitej its Tariable composition is accounted for.

136 SILTEE^liEAB BEPOSITS OF 1¥BEKA, ITBVADA,

fcimiliiatloii ©f iiiMutj-inwiiliyfy faun tli« BhIIwImicIiw mint-^TlliB pOFptiy rjT OCCUrS IH til©

form of a dike in the above-mentioiiecl mine. It cuntaiiis nttineroiis cubes of pyrite distributed throeghoet its mMs, which Bometiiiies measure as much as one-eighth of an inch. The pyrite is bright, and shows no signs of weathering except where it has been exposed for some time to the action of the air. Clean crystals of this pyrite were picked from the matrix and were assayed for gold and silver, 377.09 grains being pulverized and roasted sweet in the muffle. The roasted mass was mixed with 770 grains litharge, 580 grains bicarbonate of soda, 270 grains bitartrate of potash, and 700 grains borax. The whole mass was melted two and one-half hours and the resulting lead button cupelled.

Per cent. ¥»lEeiii8ilv©r,6§ cents .......... ............ i.©§lf23S

VaM© in foli, 8© cents ........................ i.iCMI1327

The amount of silver and gold contained in this porphyry when it was assayed without separating the pyrite was:

P§r cent.

Silver.icents. ............ .................... f.WWlSil

GkiM, 12 cents...... i.OCMMIlti

From this it will be seen that the ratio of the gold to the silver was greater in the porphyry than it was in the pyrite itself, and that either the coarse crystals of pyrite (those that were selected for assay) were purer than the fine crystals, which is highly improbable, or that the porphyry carried gold and silver independently of the pyrite. Usually pyrite is found to be the matrix of gold and not of silver, but in this instance these relations seem to have been reversed.

A sample of porphyry from the surface, in which the pyrite had been completely decomposed by the continued action of the atmosphere, gave very nearly the same amounts of gold and silver as that which contained mndecomposed pyrite. The results were:

P«r cent. Silver, 7 cents ................................ §.§001856

Geli, 13 cents ................................ §.§§0§21§

The amount of pyrite contained in the porphyry was 1.89 per cent This was determined by 'Br. Melville, assistiint chemist of the Greological Survey, by calculation from the amount of sulphur in the rock.

Assa¥Ing. 137

That the iron pjrite did not carry all the gold and silver in this porphjry 18 shown hj the fact that it contmined^when assayed sepaimtely only 80 'cents (0.0001327 per cent) gold and 65 cents (0.0017236 per cent) siker, whereas it should have assayed §6.34 (0.0010518 per cent) gold and $3.17 (0.0085062 per cent) silver, there being 1.89 per cent of it in the porphyry, had it contained all the precions metals present in that rock. There seems to be no doubt that, the iron pyrite present in this porphyry is a secondary product; that is to say, that it wan not crystallissed oat of the melted mass when it cooled, but that it was formed later either through the action of snlphnreted hydrogen or snlphnr in ^ some other form upon the iron contained in the rock. It is diiScalt to conceive of the formation of pyrite from a melted mass under conditions which would permit of the iron retaining the extra atom of snlphnr necessary to its composition. As it is evident that this porphyry contains silver and gold independent of that in the pyrite, it is highly probable that these metals were present in that rock before the formation of the pyrite, and that the same causes, probably those of solfataric action, which brought about the formation of the pyrite, effected a partial concentration of the silver and gold in this mineral.

■ This porphyry was also examined for lead. The ordinary methodB of analysis failed to reveal its presence, although it was thought highly probable that it entered" into combination with the rock in very minute quantities. I adopted the following method, founded on the well-known tendency of gold to retain small quantities of lead even when in m melted state and exposed to the air. Forty grammes of the inely-pulverized porphyry were mixed with 150 grammes of carbonate -of potash in a porcelain dish, and the whole was moistened with an acid solution of terchloride of gold which contained 10 grammes of gold. The mass was dried and fused for four hours in a French clay crucible in a coke fire. The resulting gold button was then analyzed by Dr. Melville in the folowing manner: The gold was dissolved in aqua regia and filtered hot to remove traces of slag. The gold was precipitated with oxalic acid, the solution filtered, and the filter washed with hot water to remove chloride of lead. The filtrate was evaporated to dryness and ignited at the lowest practicable temperature to decompose the oxalate, and also to remove the excess of oxalic acid used in precipitating

138 SILTEB-IiBAB BBPOSITS OF E¥»BKA, ITBTADA.

^di. The residue was dissolved in nitric acid andfiltercid. Th© gold pre- •cipitated was treated with hot aitric acid to remoTe anj oxalate of Itad present; filtered, and tliis nitric acid soltttion was added "to the fimt nitric acid soltttion obtained, and the whole evaporated to a small bulk, aboiit 1 €. c. This was divided into two portions. One was tested with diluted .sulphuric acid and the insoluble sulphate of lead was obtained ; the second portion was tested with pota88ie45hromate,-when chromale of lead was pre- •cipitated and crystallized by boilng. The whole of the lead was then converted into sulphate and weighed. The weight waa 0.0033 grammes. That there might be no question as to the character of the compomnd, the sulphate was finally reduced to metallic lead. The 0.0033 granimes (0 J0825 -per cent) do not represent all the lead that was probably contained in the porphyry, as there was no doubt some loss, but the result is suiSciently accE- Tate to establish the fact that . this rock, although considerably metamor- -phosed, contained appreciable amomnts of lead as well as gold and silver. As the assay value of the porphyry in silver waa 6 cents (0.00015S1 per -cent), there was about 52 times as much lead present as silver.

OHAPfll XII. FmospucfriirG.

livtliMls ©f pwwptctliif III mlnta •©ntlitiMt of tht cmaf miiils* Ila«.-^Tll© lEOtllod of prCISp^Ct-

ing adopted by the superintendeEts of the mines oe Ruby Hill has been iwniewhat different in th© two regions which mre separated by the compromise line. This line, which was adopted by the Richmond and Eureka companies m a boundary Ine between their respectiY© claims, seems also to have been a natural division, as the ground on either side of it in the belt •of mineral limestone exhibits somewhat different stmctnml features. This difference has been fully explained in the chapter on the structure of Ruby Hil, The fact that most of the bodies of ore found during the earlier . workings lay near the qnartiite in the mines southeast of the cotipromise line, caused the adoption of a method of prospecting which consisted in •fiinking perpendicular shafts in the Imestone, driving cross-cute to the ^quartzito, which was called the foot wall, and running levels along the contact of that rock and the limestone. When this contact W8te not so irregular that the drifts became longer and more expensive than the advantages •of a clay seam warranted, the levels were kept close along the quartzite, and cross drift were run off into the limestone where indications were favorable for finding ore. Where the course of the quartzite face was too irregular the levels were driven near it parallel to its general direction. To •define exactly what the Eureka miner considers to be "indications^* is a difficult task Mssures and seams, crushed, broken, and brecciated lime- •stone, limestone stained with ferric oxide, and caves are considered to be good indications for ore— though drift in which the country rock has shown .aU these phenomena have often developed nothing. On the other hand, no •ore bodies have been found which, on one side or another, do not exhibit

140 Siltek-Lbab Deposits Of Eubeka, Neyada.

mme of these "iniications." Ore bodies lia¥© sometiiiies been fottnd after driftinf hundreds oi feet through the hardest and most mnfavormble looHng gromid. This was the case on the seventh le¥el of the Richmond (see Plate XIV.), where a drift had been ran to make a connection. Where the ore was first found there was no indication w hate¥er of its proximit j until the ore body itself was encountered. The limestone was of a hard, compact nature and grayish color, and was not considered particularly favorable for ore. On the eighth and ninth levels some notice of the near approach to ore was given by stained limestone through which the drifts passed before it was reached, and by a fissnre. Since the discovery these ore bodies on the different levels have been connected by npraises and winzes, and a well-defined ore channel has been established from the seventh to the ninth levels, even connecting with the west ore body above the sixth. Tme, the ore was not entirely continuous, but fissures, seams, and stained limestone extended over the whole distance, forming a connection between the ore bodies such that all of the latter would have been discovered if the indications had been followed downward from the large ore body on the fifth level.

MetiicKiofproiipectiif In tii«Eiciiiii©iii.— Owing to the nature of the Richmond ground it is doubtful if the method of folowing the quartzite and limestone contact adopted in the Eureka and other southeastern mines would have been productive! of good results. The or© bodies in the Richmond, with one exception near the compromise line, do not touch the quartzite, but are invariably connected with some fissure. In the deeper workings of this mine it has been customary to drive straight levels in the limestone, independently of the quartzite, and to follow the fissures which may be encountered in all directions. Brifts are also run where other indications point to a possible ore body,

it may not be thought particularly favorable for ore, must not remain un-prospected. This last method is made necessary in this mine by the fact that the ground which lies between the quartzite and the Ruby Hill fault is very extensive and ore bodies might easily exist in it without indicating their presence in any manner. Although ore has not been found near the quartzite in this mine, except in one instance, there is a possibility that it

may exist in that neighborhood in the upper levels, as ther6 are no drifts for any distance along the qumrtzit© except on the fourth and sixth levels. The company is now prosecuting a search in this direction with reasonable hopes of success. In fiict there is a great deal of ground in all the upper levels of the Eichmond mine which warrants systematic prospecting. In the mines southeast of it, however, the limestone has been very thoroughly prospected down to the point where the two fissures come together, and it is not likely that any very extensive ore bodies will ever be discovered in it, although it will probably be worked for a long time to come, for the sake of the small masses of ore that have been overlooked or neglected.

The structure of the country in these mines has been fully explained and the existence of a second limestone wedge, below the lower belt of shale, has been pointed out The obvious method of prospecting this ground is to sink shafts ^ through the lower belt of shale northeast of the present workings and to drift in the underlying limestone. Such a system of prospecting is at present being carried on in the Eureka, and if successful 'the example of this company no doubt will be followed by the others.- A cross-section of the old and new workings of the Eureka is given in Plate ¥111. As the two fissures in the Richmond mine are stil very far apart, the same methods of prospecting which were followed in the upper levels are continued below.

M«tii«i«©fpf«i«f«:tiaf onPwi«ii«*M©i» mcthods of prospecting followed

in the large mines of Prospect Mountain do not differ much from those in vogue on Ruby Hil. In the small mines the ore is usually followed from the surface down, either by vertical or inclined shafts, and the ore is ex- " tracted as the conditions of the ground permit. The Rnby-Dunderburg and Hamburg mines, as well as several others, are worked systematically with perpendicular shafts and levels run at stated intervals.

A portion of Prospect Mountain is being prospected by driving tunnels from both sides of the mountain at those points where the nature of the ground permits of obtaining a great depth with a comparatively smal length of adit As a means of opening mines tunnels are in general expensive and unsatisfactory. Usually the distance to be driven in order to attain any considerable deplh is very great; the tunnel is nearly useless in ©xplor---

142 8Ilveb»Lbad Bbposit8 Of Eureka, ¥E¥Aba.

ing the ground belaw its level, and is onlj advaEtageaiis as a meims of Yeetilation and as an exit for the water. Grround -below the tunnel level can be worked and drained to advantage only bj the help of a verticf 1 sliaft from the surface, and such a shaft costs m much as if there was-no tunnel. The advantages of the tunnel system in Prospect Mountain, however, as a means of prospecting are numerous. In the irst place, owing to the topography of the country, it is possible in many places to gain a foot or more in depth with every two feet of tunnel. Again, the deposits are found throughout a belt of limestone over a mile in width, and are as likely to be discovered by a tunnel as a shaft. Moreover, many of the claims on the surface are owned by small companies, which cannot afford expensive hoisting machinery, but which could pay their proportion of the outlay necessary for the part of the tunnel developing their ground.

The presence of ore cannot be predicted with certainty, but this much at least can be said, that all the indications, and the results so far obtained, poiiit to the existence of numerous ore bodies in the heart of Prospect Mountain, and although mining for the precious metals has not been reduced to anything like as great a certainty as is the case with coal and iron mining, a skillful use of the knowledge already obtainable wil in some measure reduce risks which invariably attend mining operations. The air and ventilation are good in all the mines of the district where proper connections have been made, even in the lower levels.

Mectricni ©teenmticiii lUMi ii»*y«.^In dcscribing the second list of assays, page- Si, reference was made to some observations by Br. Baras in the Richmond mine in regard to the electrical activity of ore bodies. Mr. Becker, in summarizing this investigation,* says: "Of the different surveys made^ the-one on the 600-foot level of the Richmond mine, west drift, presents the greatest interest, because it was here that all the precautions necessary could be satisfactorily applied. The line of survey, moreover, lay completely outside of the ore body, and all the points tapped were in rock„ essentially of the same kind. The measurements were made in various-gal vanometric ways, and the results were subsequently checked by a *zero'

•Tko metlioii employed and tie resnltB obtained iir© fully expliiiiiiid % Br. Carl Bariis im tli# Clfi©l©gy ©f tie ComstDck Lode, Clmf . X.

Pkospectiiig. * . Ms

method. It was found tliat tie distribEtion of potentiml along th© lengtkof the drift, even after an inter¥al of four months, has riot materialy changed, and that on passing from barren rock toward and across th© or© body, small, thottgh decided, variatimis of potential were encountered in ita- ¥icinity.

"-Rftjiilfe.— The electrical effects observed were too distinctly pronounced to be referable to an aggregate of incidental errors, and they were of the character which must have been produced had th© ore bodies been the seat of an electrooaotiTe force. The experiments made cannot be said to have settled the question as to whether lode currentu will or will not be of practical assistance to the prospector. Indeed, as yet it cannot even be asserted with fnll assurance that the currents obtained are due to the ore bodies. What has been observed is simply a local electrical effect sufficiently coincident with the ore body to afford in itself fair grounds for the assumption that these contained the canse. Giving the investigations of Fox and Eeich proper weight, however, the supposition that the currents in the Richmond mine were not due to the ore bodies is exceedingly improbable. But unfortunately they are so m'oak as to require an almost impracticable delicacy in the researches designed to detect and estimate them. It is highly probable that under certain circumstances more powerful cun-enta are generated than those found in Eureka It is not unlikely, for example, that galena, cinnabar, and the copper sulphosalts produce electrical effects of far greater magnitude, and that the .method might be readily available for the discovery of such ores. The results thus give much encouragement to further investigations in this direction "

Fig. 5, page 144, represents the plotted curve resulting from Dr. Bams's determination of potentials, and Fig. 6, same page, represents the curve resulting from the plotting of the assay values of the samples taken from the points L, II., up to X¥III. In plotting the electric as well as the assay curve, the linear distances between the points I. and II., I. and III., etc.^ are taken as the abscissas, the values of the potentials being the ordinates in the electric curve, and the assay values being the ordinates in the assay curve. Beyond the point XVIII. no samples were taken, as it was not possible to find Br. Barus's points. The assays were made some

Silver-Lead Deposits Op Eureka, Nevada.

time after Dr. Barus's electrical experiments, but before his results were known to me. Fig. 2, page 82, represents the position of the points L, II., III., etc., as well as the relations of the ore bodies to the formations. Mr. Becker, in his summary, states that the question of the practical value of lode currents to the prospector has not yet been settled.

The same may be said to be true of the value of the assays of country rock as a means of determining the positions of ore bodies. Nevertheless the coincidence of the two curves just mentioned, although by no means complete, is yet too remarkable to be overlooked. The assays taken at points

m'

Fig. 5.— Electric curve.

Begion of ore bodies.

Beglozi of ore bodies.

XIII. and XIV. are abnormal. Although other assays were taken afterwards at these two points, no assays as low as XIII. nor anything as high as XIV. were obtained. If, therefore, the assays XIII. and XIV. were left out, and the points XII. and XV. joined by a straight line, a curve almost identical with that of Dr. Barus would result.

practicid use of assaying in prospecting for ore. — Thcrc are many things that rcudcr it a very difficult matter to make practical use of the assay value of the country rock in prospecting for ore bodies. The maximum diflferences between the various specimens are in any case small; ordinarily the country

rock is not of. a sufficiently homogeneous climracter to ©xMMt a uniforai increaa© in vain© m an or© bodj is approached. Usually when there is • marked increase in this yeIu© there are other indicatioiis of the presence of ore bodies, SEch as stained and broken rock, fissEres, and Ike phenomena, which lead the miner in the proper direction; and the determination of the direction in which an or© body los from a point in a drift where good aways have been obtained is a very difficult matter, while prospecting in a wrong direction is always a very expensive affair. At a remote point, where data indicating the direction of an ore body wonld be of exceeding utility, the relative differences in the assays are so smal that no marked advantage can • be obtained from them and they would be very liable to mislead the prospector. Motwithstanding these drawbacks, it is possible to render the assaying of country rock of practical advantage, especially when the diamond drill is nsed as a means of prospecting. Smbseqnent to the electrical experiments and to the determination of the values of the country rock on the 600-foot level of the Richmond, a considerable body of ore was discovered just a few feet below this level near the point XV., where the electrical phenomena and the assays indicated the presence of ore. The discovery was made, however, by following a stratum of ferric oiade in a cross-drift a short distance from the main level, and was not dne either to Dr. Barns's experiments or the assays of country rock, as before the discovery of this ore body it was snpposed that the phenomena observed were referable to the large body of ore which existed above this level. This body of ore, however, was further removed from point XV. than the ore 8iilisei|iienliy discovered.

The correspondence between the assay values of the rock and tiie valnei of electrical potentials found by Dr. Bams is clearly not accidental If it is possible that the phenomena are connected as canse and effect, or that the differences of potential are due to the traces of ore in the rock, then both methods only lead to the detection of local differences in composition, which may indeed be referred with some probability to the presence of ore bodies in the neighborhood, but which might also be dne to an accidental diaaemination of metallic compounds and be independent of the

existence of ore in considerable quantities. On the other hand, if the two 2654 1.^—1©

146 Siltim-Lbad Beposits Of Eubeka, Itevaba.

Beries of phenomena me to be regarded as two effects of one cause, and are not immediately dependent upon one another, each affords a remarkable confirmation of the inferences which would be most naturally drawn from the other. The facts were submitted to Br. Barus for his opinion, which is as folows:

"It is entirely impossible that there should be any direct connection between the assay value of the rock at a given point and the value of earth potential for the same point The nature of the distribution of electrical potential can be made clear to those unfamiliar with the subject by the aid of an analogy. Instead of drawing inferences with reference to an ore body considered as a source of electrical activity, I will suppose that we have to do with a hot body, that is, one whose temperature is decidedly above that of the surronnd-

F». 7.— Illiisteiti©!! ©f ©loctrtoal mstlvltj.

ing rocL Let c I, Mg. 7, represent the surface of the earth. Let A be an area (in section) of constant high temperature beneath it. Suppose the body has been in place for an indefinite length of time, so that the thermal distribution has become stationary. Let the problem be that of finding the body A from observations made on the surface of the earth. The first step would be to take earth temperatures at con¥lenient number of points intermediate between c and some remote point, 1. If the distances were then plotted as abscissas and the earth temperatures as ordinates, a curve would be obtained which in the simplest case would be charactenzed for an abscissa corresponding to a point nearest the hot body j1 by a maximiim.

■ • "By an exteaiiom of the same rcMoning, it is clear that if th© smrfacci were le¥©l and horizontal, and if a complete thermal sttrrey of the surface were to b© made, the result might be expressed by a series of isothermal contours analogous to those by wMch topographical features are ordinarily presented, and that the summit of an elevation on the thermal map would lie ¥erticaly abo¥© the hot body.

" Similar methods of procedure and expression are applicable to a center of electrical excitation. If the body were electricaly active, an electrical survey would result in the determination of a series of eqni-potential oontottrs Beparated by a fixed diiference of potential, and these would cnlminate above the ore body. In short, replace temperatnre by potential, isothermal by eqni-potential, and the consideration made in reference to the hot body wil apply to an ore body, only that in the case of electrical excitation wo have to do with circumstances vastly more complex, with a body, as it wer©,^ in part hot, in part cold, or one over which heat is irregularly distributed.

**The remarks mad© on the surface manifestations of a subterranean hot body apply readily to any imaginary Ine or any imaginary plane lying beneath th© surface and sufficiently near the hot body. To make the case perfectly general, however, we should have to consider the isothermal surfaces themselves in their actual position and contour. The first of these would completely envelop the hot body; whereaa, subsequent ones intersect the iiirface of the eajfth until finally they would become indistinguishable fi*oni the normal terrestrial isotheimal, as shown by th© dotted lines in the figure* Similarly, in th© case of a detailed electrical investigation, it would bo necoisary to trace the eqni-potentials as surfaces surrounding and intoniectiiig the electricaly active ore body. The presence of an or© body is ovidentiy manifosted throughout the whole superficial and subterranean rogion in which the equi-potential surfaces are trmceable or in which an electrical disturbance due to the presence of an ore body ©xistii, and the applcabilty of the electrical method of prospecting consists in the fact that lii© indications of the existence of an ore body occupy a space greatly in excess of the siae of th© body itself, ninioly, the whole region of sensible electrical excitation.

148 Silvek-Lead- Deposits Of Eueeka, Metaba.

"The analogj between the electrical method and the metliod of assay 18 clear, for in the Imtter advantage is also taken of the fact that the indications of ore occupy a greater space than the ore bodj itself. The differences are also clear, for while the assa j method depends upon the soliiMHt j of the ore, the permeaMlit j of the rock, the distribution of fisanres, and the like, the electrical method depends upon the distribution of electrical acti¥ity in the body producing the effect, and upon the electrical conductivity of the smromnding rock. The two methods are, therefore, entirely independent, and it is a particularly interesting fact that the results obtained in the Richmond mine were accordant Mr. Curtis and I have met irith a coincidence of two independent effects of the same cause, both of which indicate in different ways the presence of ore im the vicinity of point XT. of the 600-foot level of the Richmond mine. It is gratifying to find tiiat an ore body was actualy discovered, subsequently to our experiments and independently of them, precisely where we had most reason to look for it I greatly regret not to have been able to be present to study the distribution of potential relative to the new body in detail.

"There is one more remark with a bearing on these inferences wMch I desire to make. The relation of the earth-potential encountered aloag any line of electrical survey to distance, when expressed graphicaly, appears as a broken line possessing certain distinct characteristics. I proved, however, that the progress in the values of earth-potential, observed on payssing from one point of a drift to another, is continuous, and -imt therefore the potential line in our diagram, however sinuous, never suffers a break of continuity; whence it follows tiiat we may regard the curves obtained as containing unknown disturbing effects superimposed on the decidedly larger electrical effect attributable to the ore bodies. I infer that in any extended line of electrical survey, besides the large field of electrical excitation due to the or© bodies, very many smaller fields, distributed throughout the mine, are constantly encountered and intersected."

p«ii©ftiiiimiitii«i€ifpfwiiitctiii|fiiy«^ method of prospecting by assays

has onejmportant advantage over the electrical meliiod; it can be carried out with_ comparatively Ittie expense and with Ittle loss of time. It must be remembered, however, that the assays will be useless unless mad© with

Peospeoteig. 149

the greatest cure. And as man j assays as cciii¥©iii©iit should Ibe* made in order that local differoEces in the rock should he rendered as smal m poisiHa. In mnning a drift, it would be wel to take four assays per day, which might be used separately or a¥ermged. • Care should be taken to elclmde aU seams containing traces of ore, wMch can be assayed separately if demrod, as it is the enricMng of the country rock itself that it is necessary to obsenre.*

Great cantion should be employed in making nse of these assays and tike results should be carefklly compared with other indications im" the country rock and the general structure of the ground. With proper precautions the assaying of the oonntry rock will in many instances become an important aid to the miner. The method *is better adapted to the discovery of large and irregular bodies of ore in a formation similar to that in Eureka than it is to the search for small, though rich veins.

•Tli« iii©tlioii mioi im iwsmying th© Emskii mm luni Mlj ©xplnlnai in CiMiflar XL

Chapter Xiii.

TBIBlJTli STSTlili:.

• wm«.— The wages paid to miners in Eureka Bistiict, m w©1 as in most mimng camps of Nevada, are $4* per shift of ten hemri. In mmt of the mines on Ruhj Hil the shafts are sunk and levek opened b j contract, as are Mkewise drifts, crose-cnta, winzes, and npraiseB when driven in the country rock. The companies furnish timber, lumber, and tools, and the contractors candles, powder, fmse, etc. The waste is usually remoTed by men paid by the company. The contract price varies with the Mnd and size of the excavation and the hardness of the rock. For drifts mn by the Burleigh dril, the minimmm price paid the miner is $5 per running foot, and the maximum $12. The latter price is only paid in extraordinarily compact and "short-breaking** ground; $9 per foot wonld be about the average for hard ground. The cost per foot for blasting material is from f 1.25 to $1.80. For drifts ran by hand-drills the cost is from $6 to $14, bnt the cost of blasting material is only about one-ifth of what it is when Burleigh drills are used. In sinking shafts and winzes the cost is somewhat greater. Where blasting is not necessary drifts are ran for less than $3 per foot At these rates it is supposed that the miner will earn something over $4 per shift, as contractors nsnaUy work harder than miners paid by the day. As a matter of fact, however, contractors often make less than $4, as work by the shift at those wages is nsnally scarce, and they prefer earning less to remaining idle, while the rules of the Miners* Union prohibit them from taking smaler wages.

Ore is generally extracted from the chambers by miners on da/s pay, except where it ii removed under " tribute '*^a pr0 riila method of paying

•In fKune flMiM wben tlm work is purtioiiliirlj bftri or diuiferoiiii, as ie tiui oiwe in nonici minos om tl© Comstook, tl© lengtli of bMM m redoosd to ©iglit horns, ani ©vem low.

Tmbute System. 151

mineni wHct lias been im «m for man j years in Comwal and olsewhero. A general iescriptioa of this iystem m it has been applied in th© miaes of Eureka District will perhap be of interest

Tiw»trfinit«if«teiii.— In the year 1878, in the older workings of the Eureka mine, there was a ¥ery considerable amount of ore which had not been extracted from the ore chambers, either through oversight or improper mining^ Many small ore bodies also had been passed over as too poor or insigmficant to be worth removing, and there was reason to believe that undiscovered ore bodies of small size existed, as turned out to be the case.

In the year mentioned, Mr. T. J. Read, superintendent of the mine, introduced the method of taking out or© on tribute, in order to utilize the large quantities of it known to eidst in the earlier workings. The ground which was to be worked in this manner was divided up into blocks or "^'pitches," as they are called by the Cornish miner. These pitches were allotted to individuals or companies (which usually consisted of two men), and 10 per cent of the assay value in gold and silver of all ore above $40 ' was paid to tributers. This rate was paid for about one year when it was increased to IS per cent Then a new schedule of prices was arranged, based upon the assay value of the ore: $6 per ton of 2,000 pounds was paid for $40 ore and $30 for 8100 ore, with proportional prices for the intervening grades. Finally, in 188 1 , still another schedule of prices was adopted : $2.50 was paid for ore assaying $30 per ton, and 50 per cent of all that it assayed above $30. Thus $65 ore brought the tributer $2.50 plus $17.60, •or $20. The company furnishes tools, hoists the ore, and transports it to the smelting works. The tributer supplies his own candles, fuse, powder, •etc., as well as timber, buying them from the company at or near cost, handles his own waste, and delivers his ore at the shaft. When a tributer runs a prospecting drift and does not succeed in inding ore, it is not customary to charge him with powder, etc. .In those cases where a tributer strikes a very large body of ore requiring timbering in square sets, the ground is taken away from him after he has been allowed to make remunerative wages. Such a fortunate strike both for the tributer and the company has only occurred in one instance since the tribute system was introduced.

152 ^ILTEK^LBAB DEPOSITS OF lUKEKA, FBVABA. ^

Extracting ore under th© tribute system has also bieii intrcidttcei in the Kidnnond as well as in many other mines of the district, and it has been found to work very well.

Adirmtaf e« md ifa«i!v«iitiif •• of til© triiiiite Bfrteni.— The tribiiters sometiiaies fill up drifts and other workings which ought to be kept open, and injure the mine generally, but this is the case only when they are not properly restricted and the foreman of the mine does not attend to his duty. Qronnd worked under the tribute system soon acquires an ill-kept, disorderly appearance not calculated to impress visitors favorably. The approbation wMch orderly galleries excites in the mind of a mining man is not founded on love of neatness, however, but on the fact that it facilitftt# th% operation of the mine. It must be remembered that the ground is not given over to tribnters until it has been practically abandoned by the company, and that the ore which is obtained in this manner is nearly clear gain; and since the ground left by the tributers is entirely valueless, there is no object in maintaining it in working order. In fact^ extraction under the tribute system is analogous to cutting away the pillars of a coal seam rather than to more regular mining operations.

Although some tributers are fortunate and discover valuable deposits of ore, by far the greater number do not make miners' wages; but men generally, and miners in particular, prefer to run the risk of making nothing if at the same time they have the chance of getting extraordinary remunera- - tion for their labor. The difficulty of obtaining continuous employment at day's pay also acts as an inducement to tributers. As the large ore bodies are worked out, the demand for such labor decreases and many miners are thrown out of employment who prefer to work on tribute to seeking their fortunes in new camps. As adopted in Eureka Biitrict the tribute system has been very successful

OHAPTll XIV. TniBiattiirG iir thk kubbka muces.

•ni«iii«iinidoftfiiiiiefiiif.— The methods employed in timbering shafts and drtfte in the mines of the Eureka Bistrict do not differ in mny material respect from those employed in other regions of the Pacific slope, while the system adopted for preventing the caving of excavated ore chambers originated on the Comstock, and has been described by Mr J. B. Hague,* It is now in nse in all districts of the West where the size of the ore bodies has made it necessary to depart from the methods nsualy employed in smaE lodes. The framing of the timbers at Eureka, however, presents some par^ ticnlarities to which it is desirable to call attention.

FiijwieiiiMtiiwiiftiitdiii^ a rale, the limestone composing the

ore-bearing isone refnires bnt little timbering where it is penetrated by drifts and winieg, and it is only where it has been crushed 'to a powder that workings of this character need to be kept open by timbers. Where drifts have been mn along the line of the qaartzite and limeitone contact, timbering is almost always necessary, as the qnartzite and accompanying clay scale off and in the coarse of time fill mp the drift. Briifls in the qmartasite itaelf stand better, but, nevertheless, often require timbers, especially where there is mnch water. There are bat few workings in the shale, bmt if there were, mnch timbering would no doubt be required to keep the ground open for any considerable length of time, as is shown by the cross-cnt through the lower belt of shale on the "1,200-foot level of the Locan shaft The "crawlng"'* of the shale in this instance is mnch increased by the water present in it at this level, and it has been necessary to retimber the crosscut several times witHn a few months. Shafts and winzes in the Imestone

•Exf l©»ti©ii of till Fortitili Piiriil©!. V©L HL

Silvbblbad Dbposit8 Op Eureka, Nevada.

of course require some timbers, but usually no more than are necessary for the support of ladder-ways, etc. The Richmond shaft, over 1,200 feet deep, which passes through shale, limestone, and quartzite, is only **cribbed^^ for the entire distance with two-inch plank, except at the stations, where timbers are used. Timbering, however, will eventually be necessary in this shaft, not only below the water level but above as well. Below the water level the limestone stands very well, owing partly to its nature and partly to the more compact character of the rock as depth is attained. The quartzite ought always to be timbered below the water level, and it would be found more economical in the long run to timber all working shafts carefully.

Method of timberinc. — Fig. 8 represents a complete set of rectangular timbers, as they are used in carrying up a stope in an ore body. These tim-

Timbering.

Iten are similar in their general features to those in use on the Comstook. It is only as regards the manner in which they are framed that they di£fer,,

jind ©▼©!! in tHs roipect the differences are but sight

When an ore body is encountered in driving a drift, it is nwial to place ■the int sil across the drift, laying the ties parallel to the drift. This is' 4oii© to retain as wide a space as possible for the passage of the car, the «ili being longer than the ties. In carrying up the timbering the timber which forms the cap of a lower set becomes the sil of the set above it 'The same is the case with the ties. In beginning a stope the sils often •consist of a long piece of timber in which the posts are mortised at their usual distance apart As each set is raised the caps are covered with two-inch plank,. and in this way doors are constructed. The spaces between the doors and timbers are filled with waste, and thus a compact mass is formed from one side of the ore chamber to the other and from the bottom to the top, which takes the place of the ore removed, and which is capable of sustaining the enormoiii pressure exerted by the surrounding rock The ■timbers are wedged and braced against the limestone walls of the cham-

f0f

Fill. 9.— Mclmioni fimmiiig.

bers, so that the whole stands sold. It is customary to fill in with waste, -as opportunity offers, the absence of that peculiar "crawling" ground so •common on the Comstock obviating the necessity for immediate filling.

156 Siltbb-Leab Beposits Of Buebka, Nbyada.

Sometiiiits the icMiiiiig is r©iiio¥©d before the spaces between llie tunbtni arofiied.

M«tiici«iofffiMiiiaf latiiiEidiiiiiiiMi^— Fig. § TOpreseiits the posts, caps, mnl ties ai framed in th© Miclmioad mine. The tenon of the post is 9 by S b j If inches; that of the tie, SI bj 6 bj II inches. The tenon proper of the imp is I by 71 by 3 inches, but there are several shoulders on the cap mado to fit the spaces left between the post and tie. The dimensiona of al these different parts can be seen in Fig. 9, and the manner in which they come together in Fig. 8.

This method of framing is compHcated, and therefoie expensiTO, bnt it is claimed that it gives great strength to the joint Upon an examination of Fig. 9 it will be observed that the tenons of the posts, and also some of the shonlders of the caps, are cut somewhat short of what would be their proper length if they were frmmed to meet exactly. TMa is to alow the timbers to come together easily, aa aej irregularities in the joints caused either by imperfect cutting or smbsequent warping would interfere witii their proper fitting were not some space allowed. This is the more necessary on accomnt • of the complicated system of joining. Pressiue soon causes any imperfect parts to meet

ii«tiioiiorft«iiiiiif intiiaBiif**.— Pig. 10 represents the timbers as they are framed at tiie Eureka mine. The tenon of the post is 8 by 8 by 2 inches, that of the cap 6 by 8 by 4 inches, and that of the tie 12 by 8 by 2 inches. The tenons of al these are also cut somewhat scant, but as there are not so many shoulders as in the Richmond timbers tiiey do not need as mnch play and are easily fitted together. Timber men iisttally prefer the Eureka to the Mchmond method, contending that the timbers are equally strong and more easily framed. The Eureka timbers seem best calculated to resist pressure from al sides, while those of the Richmond offer the greatest resistance parallel with the caps. This wonld be what was required in timbering an ore body the greatest dimension of which was along tiie course of the lode, as is the case with Comstook bonanzas. . In this case the ties womld be placed parallel to the walls and the caps at right angles. In Emreka, however, the ore bodies are very irregular and the pressure is usnaly about the same from all sides. On the first discovery of an ore chamber, too, it

Ml impossiMe to dttermiii© witli an j certainly what maj lb© its mltiniat© course, ani coasequeiitly how the timhers shcmld be placed. It is, therefore, wel to ha¥t a system of timbering wMch wil be ©f maly effectiTe im

t*'

Fin. 10.— Enrotai frumiiif .

Ill directioiii. When all the pressure comes from above, which, howe¥er,

11 rarely the case, it would be weH to have the emdi of the posts rest directly om each other, not alowing the tenon of the caps to intervene.

ii«i«M«iii till, ©f tilt tiiiiii«fc-—The msiial length of the posts is 6 feet between shoulders; that of the cap and ties 5 and 4 feet, respectively. The timber used is pine from the Siena Nevada. It is hewn 12 by 12, 10 by 12, or 10 by 10 inches square, and is of excelent material. The ties used in the Eichmond are 10 by 10 or 10 by 12 inches, as the case may require. Im the Eureka they are msmally 12 by 12, though occasionally they are but 10 by 12 inches. Sets of timbers 10 by 10 inches are sometimes used when the ground will permit of it and the ore bodies are small, but 12 by

12 inches for the posts and caps at least is the rule.

The timbers are cut into the required lengths by circular saws, and framed by hand. Spit lagging and sometimes poles are used in the drifts and smal ore bodies where the heaviest timber and planking are not required.

Chapter Ty.

MBTAiliUKGY OF THE BlJBllKA OWMB.

R«iiictiiiaofoft».— Almost all the mm of Eureka Bistrict are reduced either • at the Richmend or Eureka smelting works, which are situated, respectively, at the seuth and north ends of the town of Eureka. At different periods other companies ha¥e smelted their own and custom ores, Imt it has usiialy been found most adTantageons to ha¥e ores reduced at one or the other of the above-mentioned works, as the large scale on which their operations are conducted enables them to smelt at a less cost

¥o exhaustive investigation of the metallurgical processes curried on in Eureka is intended in this report, and only such a general description wil be given as will enable the reader to compare the general methods and apparatus with those employed in other districts. The ores have already been described in a separate chapter, and an analysis of those of the Richmond mine, which closely resemble al others in Rnby Hil, has been added, so that a further description of them wil be mmnecessary here.

BMcriftiiHi m MdmnMii nwta.— The wofks of the Richmond company, which are the largest aad in some respects the most complete, are situated in the sonthem part of the town of Eureka, and are connected with the company's- mine on Ruby Hill by a narrow-gauge railroad, about three miles in length. The distance to the mine by wagon road is somewhat shorter, as, on account of the difference in elevation between the town and the hill, the railroad could not be built in a straight Ine. These works have a capacity of from. 250 to 300 toes per day, according to the nature of the or© to be reduced. A reinery is connected with these smelling works, in which the furnace-lead is calcined and the silver and gold are separated from it

Pa t f i p ti im of fimiacf .— In the Smelting department there are four shaft fkrnaces with an individual capacity of from 50 to 100 tons of raw or© per day. •(iw)

METALLUBGT. 15t'

These ftiniaces, altlioiigli thej differ sligMlj in size, are all constractei in nearly the same maimer. The portioa of the stack abo¥e the smelting • zone is constmctei of ordinary brick and is cylindrical in form. It is supported by cast-iron pillars, which rest on a solid fonndation. The smelting-zone itself is composed of a water jacket, or rather seTeral water jackets, called "baches/' and is oblong in shape. The "baches" are hollow boxes-of boiler plate 30 inches high, 20 inches broad, and 6 inches deep at the top and 4 inches at the bottom. In the center of each is an opening for a - tnyere, which may be a water tuyere or merely a pipe to con¥ey the blast . The water tuyeres are long, and are used at those points where It is necessary to convey the blast for some distance into the charge. The baches - are inclined a little outward at the top on the upper edge of the crucible or ■ lead well They are joined to the stack above by a course or two of ire-brick luted with clay. They are fastened to each other on the sides by key-bolts, which can be easily removed in case of an accident, such as the^ burning through of the iron of the bache. This arrangement allows the removal of one of these waterjackets and of its replacement by a new one • without interference with the working of the furnace. The baches are open at the top and continually receive a stream of cold water which keeps them-cool. The iron comes in direct cont«ict with the charge as in all water-jacket furnaces. The furnace has an open hearth at one end with a slag ■ sppnt as well as one for speiss. The latter is placed one and one-half inches below the former. The lead is allowed to ran ont of an opening on the^ side of the lead well, which is a very short distance below the speiss spout When one of the-large furnaces is working properly there is a continuous-iow of all the three smelting products, slag, speiss, and lead, from the crucible. The furnaces are barred out re|fiilarly once every twelve hours, the - front bache being removed for that purpose* It is said to have been proved by repeated experiments that the nature of the Eureka ores renders - their advantageous smelting in a furnace with a closed hearth impossible, as the large quantity of iron in the ore makes a continual baping out necessary in order to. prevent the formation of "sows." The separation of thediffereiit smeMng products, slag, speiss, and lead, is tolerably complete.

16§ SILTBR-IiBAD DIPOSITS OF lUBBKA, NITADA.

ccMiiffirftiiMfifciMfivMiiiiiiiii^^ tu mlygj i of the fficlmioiid

ore shows less than 3 per cent of silica and mlioiit 30 per cent of iron s«ii|iiioxida In order to make a slag witli sufficitiit silica for good smtltiBg, qmartios© ores are added, or qmrtiit© wion iacli-ores ire not to Ibe obtained. The slag and speiss, analyses of wMcli by Mr. F. Clamdet are annexed, resulted from smelting the ore, an analysis of which by the same chemist is given on page 60, The material famished Mr. Clandet is stated to ha¥e been the regular daily samples taken throughout an entire year.

Speiss.

Fumtiit, Arsenio .................................. ............ 32.18

Antimony ........................ .................... .13

MolyMtnimi ...................... ........ .......... 2 Jl

Sttlphir. ........... ............................ ..... 3J4

Iniid. .................................... ............ 2.18

Oufpor....... .............................. .......... IM

Iron...... ...... ................................... .. Sl.il

Zimii.... .......... ...... .................... ........ M

Mm© ................................................. J4

SMcii ............. .................................. M

Sflver ani goM ....................................... .i2t

Siver, per turn ©f !,§©§ pmuids, Ml iws.} guli, i.43 m.

Wm unlit. SHica ................................................ 23.S1

Iron pTOtmriie ........................................ S8Ja

Alimina .......................... ................... 1.S4 •

Ijead oxide ........................................... 3.S1

MelalMe lead.... ............................... ....... 8.2i

Coppfiroxids ......*....-......... ....... ............. Li8

Zinc ©lid©............ .................. ............. ^M

Miiiigiiiiciii© oMd© .................. ................... J3

MoljMeniini ........................ ................. M

Arsenic .. ^... ...................................... .. Ji

SttlpMr . . . . . . ...... .................................. Mt

Mm©...... ................. . ...................... 4.78

Magnesia ............................................. Ul

Slver, OM m. t© ik% torn ©f 2,iOi pmndsj fold,-tiiiciib

This speiss containg an miiisiially small atomic pr<^ortioii of araenic, for if the smlplmr is supposed to b© combinoi with the metals and arsenic an arsenide of iroa corresponding to the formula F©iAii remaiiis, whereas in man J speisses the arsenide of iron is either FegAsj or FeiAsf.

The analysis of slag shows that it is werj basic and the foramla dadnced from it is that of a subsilicate. Although this slag is verj much more basic than is ordinarily the case where lead ores are profitably smelted, yet the Eureka smelters claim that they obtain better results than they would if the percentage of silica was much increased. The amount of arsenic in the ore, wMch causes the formation of speiss, without doubt renders the smelting of such a basic mixture possible. The ine dust, which is colected in long canals connected with a Mgh stack on the hillside, is mixed to a thick paste with clay and water in the proportion of one part clay and two parts of dust, is somewhat dried, and added to the charge.

■jnmipiinif acfcaiifc— The folowiog is BM eximpl© of a charge of on© of tiit

furnaces:

Oianxisl ............................... ......sciMipi.-.. 4§

Mchmoni ©r© ............................... 8lMi¥els .... 5§

Eiiliy-Diiiid«rbiirg(siHiiioii» ©»).... . ...•...-....€©..•,... li

Hooeaci di^ (gilMoiiii and riidi) . ^ . . - . ...... ......do...... Hi

Slver Mck (rilMois oie) ...,-..... ............ -d© ..... . i

Adobe ime dmsl ... . ........................ ....do ...... 4

Sp©t«... --...-- ................ .............. :do...... 1

Qmartai «».-.... .......................... ....do...... 2

The Eichmond ore contained tibree to four per cent silca. The rest of the ftilcii required for smelting is mpplied by the Mmby-Bnnderburg, SilTer Lick, and other more or leis quartiost ores, and by the Hoosac slag. The Hoosac slag was a rich slag from the imperfect smelting of lead ore with a quartz gangue. The charge is supposed to contain about the foHowing percentages:

PmriMiil Ferriecjdde...... .......-.-., ......................... 40

SMca........... ............-.".-......•.......... ...... M

Otler miiiciriils ......................................... 18

Iw 26M

162 Silybb^Lbad Deposits Of Eumeka, ¥B¥Ada.

wmA' — ^The fiiel used in smelting is charcoal nMide from the pilioa pine. The ooal prodttced from this wood is ugmally werj good, and in this district it is of an exceptionally fin© quality, th© method by which it is mamifactured having been brought nearly to perfection. Nearly all the coal-burners are Italans who have been attracted to this country by the opportunities offered for this particular class of labor. About 30 bushels of coal are required per ton of ore smelted, and the present cost is 30 cents per bushel

RBiaiini.— The lead from the smelting of Michmond ore does not usually require calcining. Hard lead is refined in large rectangular cast-iron pans, which will hold about 14 tons. The time required for softening is from two to four days, according to the quality of the lead.

pmttinKiiiMiig.— The process used in concentrating the silver in the lead is the Luce & Mozan process, a modification of the Pattinson method, and is carried on as follows: The principal portions of the apparatus employed are two melting pots, one comparatively large crystalHzing pot on a lower level, two receivers or molds below the crystallizing pot, and a crane to handle the cakes of lead after they ha¥e solidified in the molds. The upper pots are provided with covers and the lower one with a hood and pipe to carry off the steam and times. There is a pipe by which waterls let into the crystaUiier above, and one for admitting steam into it below. The steam valve consists of a horizontal pipe which penetrates to the center of the pot, and within this pipe there is a rod with a button on the end which enters the pot. On screwing the rod in, the button is removed from the end of the pipe and steam is forced into the melted load through which it is distributed, by moans of a perforated i&ils© bottom, throughout the whole mass. The receiver or molds on each side of the crystallizer hold 7,400 pounds of lead. When the lead is drawn off into these molds an "eye'' is introduced into tiie melted mass before it coola In removing these cakes the hook of the crane chain is inserted in the eye, and by moans of the steam hoist attached to the crane 'they are removed from the molds. When either market or rich lead is drawn from the crystal-liver, molds on two wheels and a peg are placed in a semi-circle around the discharge pipe and filled by a movable spout. The cakes are hoisted and placed in the melting pots by the crane. It is unmecessafy to enter into a

fkrtlier iescriptiom of the mechanical details of 111© apparmtiM and process, wMch Imve teen repeatedly described in the technicsal jommala.

The first operatioii consists in melting down 50 long of lead in one of the pofe. This is then drawn oflF into the crystalKzer, and water is turned

on to chill the lead, because much time would be required to cool it by radiation. Then steam is admitted, which thoroughly stirs and at the same time completely refines the melted mass. When liie crystaMization is completed, which takes place in about one hour from* the time the lead is drawn off from the melting pot, about two-thirds of the mass is in the form of crystak assaying 100 onnces to the ton and one-third is still melted, containing about 460 ounces. This rich lead is drawn off into molds and taken to the cupel furnaces. In the mean time enough lead of the ¥alue of 100 ounces to the ton has been melted in the second pot, and is alowed to flow into the crystaUizer, where it immediately dissolYOS the crystals of 100-omnoe lea4 This is now crystallized, giving 75-ounce poor lead and ISO-ounce rich lead, which is drawn off as before. The lead is thus crystaiized until market lead of about the ¥alue of one ounce to the ton is obtained. This refiiirea nine crystallizations, which give lead of approximately the subjoined valmes:

fiKAP FKOM THE CEYSTAMJZAIlOy OF tSi OUWCllS TiKAB.

OmiMMi to tlif} ton. Mwfc igyatiilll«ition .................................. lOi

Second cry stalliiiitioii ................................ 7i

Third ©lystalliiJiiMon..... ............................ m

Sixtli caystaUiaitiom ................................. S

Se¥ciith igysliil1igali<Mi ............................... fi

MfhtiiiajstiUimliciii.. ...................... ........ 2.S

iriitiiciyBliillimticn.......-..........^ 1.2S

II ig found that there is no nensible ©nrichment of the lead after it haa reached 550 ounces (leaB than 2 per cent). The ratio of the gold to the iil¥er in the lead from the smelting fiimaces is about 1 to 32 by weight, or in value about f 1 gold to $2 siver.

The use of steam in this process appears MgMy adTantageous. Th# stiiriiig produced is probably more thorough than that accomplihed by

164 SILTER-IiMAD DEPOSIfS OF EUREKA, lOSTADA.

m machinery, wMcli as hitherto designed is somewhat complex mud subject to

frequent stoppages for repairs. The steam is alsD in part decdinposed at the temperature maiiitaiiied, and thus accomplishes a ¥erj consideraMe reine-ment of the lead during the process of csoncentralioii, producing an excellent market lead from comparati¥ely hard Imllion.

ciiii«ii«tioii.— The rich lead is cupelled in furnaces of the English mode! with hone-ash tests. The test holds from a ton upwards. It is filled with lead which is brought to a cupeling heat and an air-Mast is turned on. This Mast is preferred to steam, as the latter becomes moist and also increases the loss in silver, although the loss in any case is sight The test is kept full of lead by adding bars one by one at the back of the furnace and alowing them to gradualy melt down. It is tapped every twenty-four hours, when from six to eight bars containing two-thirds silver are obtained. Sixty such bars, on a second cmpelation, give in about sixteen hours 16,000 ounces of dor^ silver, J65 fine in silver and .030 fine in gold. A test lasts about ten days. In refining, concentrating, and cupeling mountain mahogany wood ii use4 It is a very smperiw fkel, mi costs from $10 to $12 per cord.

The poor Itharge, containing about an ounct to the ton, Is reduced to market lead in reverbermtory ftumaces, with refuie charcoal from the bins. The rich Itharge, containing as high as 75 onnces, is resmelted with a furnace charge, as there is almost always a dearth of lead in the ores.

iijirMti««MiiiiMi4irMit«fii»iiff«iiii^ jM B, question whcther Eureka is an

advantageous localty for refining bullon, fuel being high and labor $4 per day.^ Kefimng on the spot obviates the necessity of paying interest upon the money required to freight llie unparted lead to a refinery in San Francisco or the East, and the market is frequency so overstocked with lead that it is better to wait for a rise before shipping. On the other hand, high charges are incurred in exprossiiig iie iortf iilveri which would be avoided if the buUion were transported by freight an it comes from th© fomaces.

Chapter Xvi.

% ABiUlf S HTTili.

Tdpufiiipiij iunifiifiiMitioii..— The smnniit of Adami HM is situated mlmmt 8,400 feet nearly in© north from the top of Mmhj Hill The Ml is a gentle elevation which rises to a height of 6,940 feet above sea-level and slopes with a gradual descent toward the valleys on the west and north. It is divided from Mnby Hill by a moderately deep ravine which enters Spring Valley.

The principal part of the hill is composed of Hamburg Mmestone, tiie Secret Cation shale forming a band running east and west along its southern iank, and the Hamburg shale making its appearance in a Ike naanner on the northern slope. To the north of the Hamburg shale and to the east of the Hamburg limestone the Pogonip Mmestone ii exposed. The non-appearance of the Hamburg 'shale between the Hamburg and Pogonip limestones at the. latter place is dtt© to the continuation of the Jackson fault described by Mr. Hague. North of the Hamburg shale, in the Pogonip Imestone, there is a large ontcrop of quartz-porphyry, and still farther on in the same rock a smaller overiow which is visible mndergronnd in the workings of the Bnllwhacker mine. The dip of all the formations of Adams Hill, including the Secret Cafion shale, is apparently to the north.

strtietei*.— Although the mining explorations which have been made on Adams Hill are not sufficient to give a complete idea of its internal structure, they are, nevertheless, extensive enough to show that it is composed of a bed of limestone underlain and overlain by distinct beds of shale, al of which have a variable dip to the north. There is much less evidence of faulting and crushing in Adams Hill than there is in either Mnby Hill or Prospect Mountain. The rock does not seem to have been subjected to the enormous pressure that has caused the grinding up of the Imestone in

X

166 SILYBil-IilAII DEPOSITS OP BUBIKA, IflTABA.

those last-mentioned localities. On Adams Hill that rock is harder, more compact, and lees smbject to sudden changes in its physical characteristics. In many places the Hambiirg limestone is capped by a conglomermte consisting of bowlders of limestone cemented together by a tough calcareous material. In this conglomerate fragments and even bowlders of ore are often found. This ore does not resemble in any respect the ores of Ruby Hill, and it is likely that it, as well as the accompanying limestone, are the products of the erosion of the immediate neighborhood, which have been cemented together by calcareous waters.

om ii«iMiiit«.— The deposits of this portion of Eureka District are as varied in regard to form as those of Rmby Hill, but in many other respects they differ from them. There is very little resemblance between them and true lodes, though they are all more or less connected with fissures and slips, and some of them which occur in the limestone near the shale seem to have a general course parallel to the contact of those formations. An instance of this occurrence can be observed in the Bowman mine, which lies near the Secret Cafion shale. Caves, which are so characteristic of Prospect Mountain and Ruby Hill, are rare; and although it is possible that such openings may exist in numbers, the explorations have not yet revealed them. It is true that the deepest mine workings have as yet attained but a moderate depth, not much exceeding 200 feet, although the explorations have been quite numerous. Nevertheless it is probable that if caves were numerous they would have been revealed before now, for it can be safely said they are of more frequent occurrence and usually of greater extent near the surface than at great depth. This is easily explained by the fact that the waters carrying carbonic acid, to which they owe their origin, becomes saturated with calcium carbonate as it descends, thereby losing its solvent power. The absence of caves, which in other portions of the district are so intimately connected witii ore bodies, would seem to indicate that the genesis of these deposits was somewhat different from that of the ordinary class. This theory is also sustained by the fact that the ores are of a different character from those of Ruby Hill. The most noticeable difference is the prevalence of quartz ores. This can be said to be the distinguishing feature of the ores of Adams Hill, as well as those occurring in the Pogonip limestone on

the iat to tlb© north, which i» designated on the map as Mineral Point The ores do not occur in compact form as the illing of chambers, but are found in bunches in. cracks and seiiins in the limestone, and although maases of ore of considerable size are not unknown, the j exist in the form of silicified limestone more 'or less impregnated with silver and lead minerals.

Tim ©re..— -The Ettrekft quartiite, which Mr. Hagme has placed just above the Pogonip limestone, at one time co¥ered the whole of Adams Hill, and there is still a small area of this rock to be seen on the northwestern slope of the hill near the road to the Wide West mine. It is not impossible that the qnartz in the ore was derived from this qnartzite. Still it is not likel j, however, as it would be necessary for the iilicions solutions, which were formed from this qnartzite, to traverse the underlying Hamburg shale as well as the Pogonip Imestone. Also, if the qnartz in the ore was derived from the qnartzite, it is likely that the ore was as well, as the two seem to have been deposited simnltaneonsly, though this might possibly have occurred-where the components of the ore were derived from different sources. The Enreka qeartzite also carries small amounts of the precious metals; but the same objection to the secretion of the ore from this rock can be advanced that was offered in regard to the secretion of the ore in Ruby Hill from the outside country rock. It could hardly have passed through the Hamburg shale. It js possible, however, that the ore in the Pogonip limestone was derived from this source, though, as has been explained in Chapter VII., it is more justly referable to another source.

Another noteworthy fact in regard to the ores of Adams Hill is that they carry as a rule a high percentage of gold, although there are some that carry no gold whatever. The contents in gold is a distinctive feature of this region. Lead in the form of carbonate and sttlphide is common, and both the Bnllwhacker and Williamsburg mines have produced large quantities of this metal.

Qinirte-ii0rpiijfyi»ai0iirc«of tilt ore.— The quartz-porphyry which occurs in the Bullwhacker mine has already been mentioned (Chapter VII.) as the probable source of the ore in its immediate neighborhood. This porphyry stil contains considerable quantities, relatively speaking, of gold, silver, and lead (see Chapter XI.), and although it does not cover a very extensive

168 • SHiTBR^IiBAD DIPOSITS OF BUKEKA, ITBVABA.

area 011 the surface it is very Ikely that it may extend underground into AdiuiiB Hili If this is the case, it has vary Iktly been the source of the ore in the mines of that region. If it has been the source of the ore it is probaHe that the quarti has also beta derived from it through the decomposition of its silcatom

-..u^^The ore of this region is uauaUy of very good quality, but the rock is frequently hard and it is extracted with some difficulty. The mines have been opened by individttals and small companies, and they have not been sufficiently explored to determine either their permanency or their future value. Just at present there is not very mnch mining going on in this part of the district, but there seems to be no reason for believing that the deposits do not extend to considerable -depth, and it is to be hoped that the decreased cost of mining and of reduction which inevitably follows the increasing age of a mining camp wfll cause the revival of this industl-j.

Chapter Xvii.

Futijiik Of Bwkbka Bistbict.

Eiit«iitoftiiiiPirii«f«*M©iiiitiiiiiii»^ mining region of Prospect Momntein,

compriged between Spring Valley on the west and the Secret Cafion road om - the east, will no doubt prodece large quantitiefi of ore for yea» to come.. As yet a begimiiiig only has been made in the development of the deposits in this portion of the district. It ie tme that there are several mines, the Hamburg, Bnby-Bunderbttrg, and one or two others, which have been pretty well opened, though in all of these there is a great deal of ground which remains as yet in a virgin state, bat in by far the majority of instances the claims of Prospect Mountain and vicinity have not been explored to any great extent If the surface geological map is examined it will be seen that the two belte of limestone, which Mr. Hagne has named, respectively, the Prospect Mountain and Hamburg limestone, are very wide; and although they cannot be regarded as ore-bearing thronghont their whole extent,- yet surface explorations have shown that the deposits contained in them are very numerous. Undergronnd developments, as far as they have extended, have also proved that these deposits are continnons to a considerable depth. It is therefore very probable that nnmerons unexpected ore bodies will be discovered throughout this region in the course of fnture deep-prospecting operations.

E«liitlir« mlm ©f the Ww^p^ Moiuitalii aai Enliy HIM iliipi»lti.^At filBt sight BO reaSOn

appears why m extensive ore bodies should not be encountered in Prospect Mountain m have been found hitherto in Rnby Hill, bnt a carefal examination of the strttctnral features of the two regions leads to the belief that the ore bodies of the former locality will never reach the size of those of the latter.

170 &quot; Silyee^Lbad Bep08Its Of Eubeka, ¥E¥Aba.

It has been stated before that the opportmiities for the iepoaitioii of ore 'have depended in a great measure upon the extent to wMch the limestone •has been crushed and thus prepared for its reception and deposition. It ^cannot be said that such a shattering of formations has not taken place to a .great extent on Prospect Mountain. It has, and its results are shown by the numerous fissures and zones of pulverized rock which are encountered in this region; nevertheless, the upheaval and faulting did not take place under conditions that were in every way as favorable as those which resulted in the present structure of Ruby Hill The imulu which brought about the .present an-angement of the formations in the latter locality were accompanied by the formation of a fault-fissure which acted as a channel through which the metalliferous solutions entered the wedge-shaped mass of lime- -stone lying between this main fissure and the quartzite. Whatever other part this quartzite may have played in the formation of the mineral zone of Ruby Hill, it certainly had the effect of confining the ore-bearing solutions to the crushed limestone bounded by the clay of the Ruby Hill fault •. Had these solutions entered a mass of limestone of unlimited extent, although -the amount of ore deposits might have been as great in the aggregate, it is not likely that ore bodies of a size equal to that for which this mineral belt has been noted would have been deposited. It cannot be denied that certain ore channels exist in _ Prospect Mountain, and that they are also confined in some instances between belts of shale, or between walls of limestone; yet, as far as present developments have shown, there has been no such limitation of the ore to a well-defined region.

Eesimrcei of Prospect Monntmiii.^These facts, however, need not prove a drawback to a careful exploration of the resources of Prospect Mountain. The •Ruby Hill deposits were worked to a large extent when the cost of mining and reducing ores was far greater than it is at present, in spite of which they paid large profits; and a reduction in the cost of working-ores, coupled with the increased facilities offered by the tunnels amd more systematic methods of mining, will compensate in a very great degree for any difference in the size of the ore bodies which may exist in the two regions.

Ilel«tlir« richncM of the depositi of Proipect Momitaitt mii Ettby Hlll.^— It ig Said that tho

-ore of Prospect Mountain, as a rule, is richer than that of Ruby Hill. This

Futuee Of The District. 171

may m may not be th© case. The only present means of ietermining the facts me by judging of tb© ore that is brought to the smelting works for reduction. The returns show that the ore of Prospect Mountain aTerages richer than that of Ruby Hill, but this is ¥ery likely owiiig to the fact that -only ore of a high grade will pay for mining when the deposits are small, and cannot be taken, therefore, as a criterion of the value of all the ore in these mines.

Diiiciiitjof makiiif pwiiiiction..— What will be the fntnre of the mines of Rnby HiU is ¥ery uncertain, and any predictions in regard to it must necessarily be inferences from the results of the explorations which have been made in the present lower workings. These explorations have not been carried sufficiently far to give indisputable indications as to the changes which may be expected in regard to the ore below the water-level Moreover, the structural features in the lower levels of these mines have undergone a change, and it is impossible to tell with any certainty what effect they may have upon the general worth of these ore deposits.

probawiMiii of initof or« In the lower workinpi.^The stmctEre of the orc-bearing zone and the relation of the ore bodies to it have been fully described in the preceding pages of this report, down to a level, in the mines southeast 4)f the -compromise line, where the two fissures come together, and in the Richmond and Albion mines to a depth at which it is clear that they are -approaching and will probably meet below. It has been stated that the bodies of ore in the MichmiJnd mine have decreased in size as well as number below the sixth level The ground, however, below this level, although it has been prospected to some extent, has not been Sufficiently cut up to prove the absence of large ore bodies, and it is possible that the failure of ore is only apparent^ and that future developments may expose large bodies, l^er© is nothing in the nature of the limestone inconsistent with such a belief. The same may be said of that poTtion of the Albion ground which lies immediately northwest of the "AC" Ine. The ground in which the Albion shaft is sunk and that which lies west of it is unfavorable for ore, the limestone not resembling that which contains ore in other parts of Ruby Hill, while the faulting motion has not been great, and the limestone is therefore less disturbed. Even if ore should not be found in any quantities in these

172 BIIiTEB^LEAD BEPOSIT8 OF EIJEEEA, NETABA.

two mines in the lower l©¥els before tie two fissures emu© together, iMs wiH not pro¥e that mo or© bodies are to be expected im the Imeatoii© wMch iiiiderlies the lower belt of shale. It will "only pro¥e that the limestone or the fissure system in this part of the hill was for some unknown reason unfavorable to the deposition of ore. It will be a ¥ery discoEraging circttmstanee to the companies interested, but it may be expected. Large lones of barren ground have been known in the upper le¥el8 as wel.

ConiMoM of oni de|Miiitli>ii In tlm lower wedge of limertciiio.— If Plftt© VIII. ii referred tO,

it will be seen that the lower mass of limestone is gradually widening out, as would ine¥itably be the case if the ideal section of Rttby Hill (Plate IV.) be true. The main fissure below the great limestone wedge has a hanging wall of crushed limestone which is overlain by a belt of shale. If the theory of the source of the ore stated in Chapter VII. is correct, the .ore solutions passed upward through this fissure along the contact with ilie Imestone, which offered all the conditions necessary to a deposition of the ore, provided the ore substituted itse¥ for limestoiie. If such was not the case, and the ore was deposited in ca¥e8 pre¥iou8ly formed, there is litie likelihood that this ca¥e formation coeM have taken place in the lower bed of Imestone, for the folowing reasons: It is certain that the caves in the upper Ime-stone were formed after the faulting occurred which broke up this mass of rock and formed the main fissure. This main fissure with its wall of clay and the lower belt of shale effectually excluded any great flow of surface water into the lower belt of limestone, nor does the cave formation even in the upper limestone seem to have extended to the lowest points of this wedge of rock, probably because percolating surface waters became saturated with calcium carbonate upon reaching this depth. It is therefore improbable that caves of any great extent could have been formed at the depth at which this limestone lies. It will be seen, therefore, that the chances of finding any considerable bodies of ore in the lower limestone, if the ore deposition was dependent upon the prior formation of caves, are very few. But the evidence that the ore bodies were formed, at least in part, by substitution is very conclusive. There seems to be no probability that such a manner of deposition should be limited to a few hundred feet or to the upper mass of limestone.

Future Of The Bistbiot. 173

Th© lower bed of linieston© lying between the fissure on the qmarijate and the lower stratmin of shale affords almost ©qeal strttctEral fmcilities to the upper. It has been rent and crttshed by the upward movement of the quartzite in a similar manner for a considerable distance, at least below the region where the lower Btratmn of shale was cut off by the fault It would, therefore, offer every possible opportunity for the circulation of metalliferoiis ^ fluids. Ore has also been found in the Mmby Hill famlt-fissEre at the place where it was cut by the drift from the 1,200-foot station of the Locan shaft. The flow of water was unfortunately so great, however, that it was not posable to determine the extent of this body. There thus seems to be no well-founded reason for beHeving that masses of ore do not exist in the lower stratum of limestone.

Whether the ore bodies will prove as large and as numerous as they have been above is a matter which cannot be decided from the limited number of facts wMch have been observed in the lower worMegs. Whether the extraction of this ore will be profitable will depend upon the flow of water, siie of ore bodies, value of ore, and facilities with which it can be redttced. As to the size of the ore bodies, no satisfactory predictions caa be made. No very great change in the value of the ore as regards silver need be feared. There will be poor ore bodies m well as rich ones, no doubt, but the ore is more likely to be somewhat richer in silver than the reverse, if there is any analogy between the ores of this district and those of a similar character in others where oxidation has taken place. With regard to the value in gold it is otherwise. The contents of the Eureka ores in gold has on the average been gradually decreasing as depth was attained, and-it is but reasonable to suppose that this wEl be the case below the water-level. No entirely satisfactory reason can be given for this decrease in gold, but it is of very frequent occurrence in auriferous silver ores in many parts of the Great Basin. It was, however, not the case on the Comstock, and the change noticed in the ores of Eureka may be only a local one.

This fact need not necessarily be a cause of uneasiness, aa there is no likelihood that the gold wil give out altogether, and a sight reduction in the quantity of this metal present would not materially reduce the value of

J 74 SILYERLEAB DEPOSITS OF EUKEKA, IfBTADA.

the ores. WMle many geologists ani many ©engineers believe that ore deposition is not limited to any depth within human reach, others are of the opinion that ore in considerable quantity usually occurs only within a moderate distance of the surface. This question, however, cannot he satisfactorily discussed from a theoretical point of view until much more is known of the chemical and physical conditions of ore deposition, nor as a matter of observation until far more thorough explorations have been carried on at great depths in mining regions. Some deposits have been followed to an immense depth (over 3,000 feet) without any diminution in yield; and if it were possible to gauge the erosion to which their croppings have been subjected since their formation, these and others would very Ikely yield more striking data. On the other hand, in many cases the search for ore below a certain depth has proved futile, but such cases afford purely negative evidence. Explorations at considerable depths are extremely expense-ive, and -are rarely made on a large scale. It is .consequently as yet impossible to say even of any single district that ore in paying quantities does not exist below a certain level, though it is certainly true of some that no indications of its existence have been found which would warrant the continuance of the search for it

That the various companies owning these mines are ftily justified in view of the former enormous production and the probabilities of finding ore in prosecnting a diHgent though expensive search below the levels as yet reached seems to be beyond question.

As regards the future of Adams HiH and adjacent country, not much cam be mid; the mines have not been worked to any great depth or extent^ and but few predictions can therefor© be made in regard to them.

CHAPTEl XYIII.

Summaby.

The following summary itates in a condensed form the nator© of theiavestigations described in the foregoing chapters and the conclusions to which they haYe led.

Dcucfiiitiiiii of Bowioi Mstrict.— Eureka Mining District is situated on the western side of the Biamond Eange, in the eastern part of the State of Ne¥ada . and south of the Central Paciic Railroad.

The district was discovered in 1864, bnt it was afterwards abandoned until the latter part of 1 868, when mining operations were again begun.

The most important town in the district is Eureka, sitaated about 2 miles distant from the principal mines which are on Ruby Hill.

This Mil forms the northern spur of Prospect Mountain, a ridge seYeiml. mEes long, which reaches an altitmd© of over 9,000 feet, and itself forms a spur of the Diamond Range. North of Ruby Hill lies Adams Hill, a low-elevation distant something less than a mile. On these hills and on the : mountain and its spurs ai-e situated all the mines of any importance in the district

As nearly as can be estimated the production of the precious metals^ up to the end of 1882 hms been about sixty millions of dolars. It is diiSciilt to ascertain the quantity of lead produced, but this is approximately- 225,000 tona.

Sukface Oboloqt.

Mr. Arnold Hague has described the general geology of this district,*"

•▲IwtaMt of Boforl on Hm Qeoliigy of IImi Ennilcii BMrioly ggrniii, % AmoM Higno. TMiC ImiiMBfiporl of Hit Blmstor of tiw W. & Ocologioal Bmrwrnj. mi '

176 siltee-IjEad bepositi of eureka, itetaba.

Ibttt a reference to his results is necessmry to a clear coneeptioiir of the reliitions of the mines to the different formations.

The Cambrian, Silurian, BeTonian, and Carboniferous are al represented in this district, though it is only in the rocks of the first two that metalliferoTis deposits of any kind ha¥e been found.

Funmnioim.— Mr. Hague distinguishes the following beds in the Cambrian, beginning with the oldest : Prospect Mountain quartzite. Prospect Mountain Hmestone, Secret Callon shale, Hamburg limestone, Hamburg shale. ' Those five formations have all been Md down conformably. The rocks of the Silurian in the order of succession are Pogonip limestone, Eureka qmartiite, and Lone Mountain limestone. The rocks of the Devonian in this neighborhood are the White Pine shale and Nevada Imestone.

Erfiitf©iMiiftii«iiiiiie«totiiiiroriiuitioiifc-— With th© ©exception of the Hoosac mine in the Eureka .quartiite, and the Bulwhacker and other mines in the Pogo-nip limestone on the slope north of Adams HUl, all the mines which have been discussed in this memoir are found in the Prospect Mountain and Hamburg limestones. Mo deposits whatever have been found in the Secret Caflon shale wMch separates these two beds, and although it is true that pyrite, both as impregnations and in masses, as wel as distinctly-defined veins of quarti accompanied by calcite, have been found in the Prospect Mountain quartzite, the lowest of the sedimentary beds *of the district, it has had no economic value. These occurrences, moreover, do not seem to be in any way connected with th© deposits in Imestone, and, as far as is known, there is no ore in the Hamburg shale.

M— iyt f a,c fc i . The only mmssive rocks which make their appearance in the metaiiferouB aone which is occupied by Prospect Mountain and its offshoots are grmnite, quarti-porphyry, and rhyolite, but homblende-andesite is found in its neighborhood. Quarta-porphyry, probably Mesozoic, appears in two places north of Adams HEl, and^ seems to be of earlier origin than the ore. Mhyolite is abundant in the neighborhood of the mines, as well as in immediate proximity to the ore. In some portions of th© district it covers large areas, but in the mines it is only found in the form of dikes. Homblende-andesite occurs near Hoosac Mountain, where it covers considerable territory, and basalt is found within three miles.

Summaey. 177

The Stbuctuee Of Pb08Fect Moumtaiw.

iiMiiiwofiipiniiiinii.— Prospect Mountaiii and its adjacent spurs form an anticlinal fold, of which the axial plane is somewhat west of the crest of the principal ridge. The course of this plane is nearly due north and south except at Ruby Hill, where it turns towards the west Evidences of bedding are so rare that it is often impossible to form an accurate idea of the prevailing angle of dip. When the formations which at present compos© the mountain were folded and uplifted, an enormous crushing and grinding force was exerted upon the different members of the series. Those rocks, such aa the shales, which were flexible were much twisted and distorted, but retained their original character. The limestones, on the other hand, were much crushed and fissured, and faulted in many directions. Most of the fissures were found parallel to the axis of fold, and as the uplifting and crashing continued great zones of limestone were ground almost to powder.

iiiiii«i«iof««iptiirefii€to.^Sub8equently to the primal folding liie Tarious eruptions, especially that of rhyolite, had a further disturbing effect upon the structure of the country. Many fissures md faults have unquestionably been caused by the eruption of the rhyolite, and, as will appear later, it had a direct influence upon the deposition of ore.

The only known occurrence of granite in the district is on Mineral Hill at the north end of Prospect Mountain. It is probable that this mass formed a submarine Ml! upon which the quaitzite, limestone, etc., were Md down, and that its exposure in its present position is due to erosion after upheaval had taken place.

Bowlders resembling this granite have been taken from the quartzite in the Richmond shaft. The strata of the formations which compose Prospect Mountain usually dip away from the axial plane of the fold, though there are notable exceptions to this rule.

scctfon of pkiiiii«* Mmiiitnia tiifoiif ii Burekm tniiiici.— The bost Opportunity for Studying the formations on the eastern slope of Prospect Mountain is given by the Eureka tunnel, which has been driven from a point near the head of the west branch of Goodwin ,Cafion in a nearly due weit direction into the heart of the mountain. 2iMi.— 12

178 Siltem-Lead Deposits Of Eueeka, ¥E¥Ada.

The following are the different formations encountered, in the order of their succession from the mottth of the tunnel:

8fi feet mineral limesfcoa©* ...... Hamburg limeston©.

2i§ feet shale .................. Secret Oaion sliale.

' 935 feet mineral limestone ........ Prospect lIoEntain limestone.

311 feet shale *..... ............ Prospect MoEiitaiii limestoii©.

51 feet mineral limestoii©. . - . . . . .Prospect Mottntain limestoiie.

46CI feet shale ....... ....-..-.-. Prospect Mouetaia limestone.

90 feet straliied limestone ..... .Prospect Momitain limestone.

§0 feet mineral limestone. . . . , . . .Prospect Monntmin limestone.

At various points along its course the tunnel cuts through seams and. fissures, which generally cross it at right angles. Their usual pitch is easterlj, though there are many exceptions to the rule. The msot prominent one of these fissures is at a point 840 feet from the mouth of the tunnel. It dips nearly ¥vertically, perhaps a little inclined to the east It. is open in places and filled with sediment, bowlders, etc., which have been washed in firom above. At the point where it is encountered it is about 350 feet below the surface, and it is a characteristic example of numerous occurrences of the same kind both in the mountain and in Ruby Hill. Like many others, it has been accompanied by ore which was formed on the west side of the-tunnel. Faulting has occurred on most of these fissures, and it is safe to say that the portions of country which lie west of the fissures or upon the foot-wall side have as a rule been relatively raised, and the strata have reached their greatest relative elevation just over the axis of fold.

The stratified limestone in the end of the tunnel pitches west at a steep angle where first encountered, but gradually becomes latter until a little distance west of the summit its stratification is nearly horizontal,

Bectioii of Pmepcct Mewntiiin thimifli Pr«»p©ct Mottntmiii tnmiel.— — The PrOSpCCt Mountftill.

tunnel, starting at a point about 2,700 feet west of the summit, nearly op- pQgil0 the Eureka tunnel and several hundred feet below it, has been driven over 2,350 feet into the mountain. For the first 1,400 feet it passes through a hard, compact, wMte limestone, which in places reiembles marble. This-

•**Min©ral llmeBtiiii©" is tli© torm employed in tli© district to iciignat© th© lii»k©ii ani metiimorplioicd rock iiliiiost iii¥iiri»lily ooaaectcd with ore.

•The tmrm •• Proipecfc Monntiiiii limoston©," of conn©, refers to a group of licdi cliJinicl»rii5«i %■ the proaenoe of Mrtiuii fomlls. Thomgli limestone predominiitei the iiitiireiilatcid dialet we nMeaeiiril j olmasified m memliors of the samo group of lieds.

limeston© is not often fissured, but contains some ca¥iti©8 excavated by water. , There is nothing about it to' indicate that it ii mineral Imeatone. At a distance of 1,400 feet from the entrance a fissure is encountered nearly at right angles, which dips 80® to the west -From this point the character of the limestone changes; it is much more broken, and many of the ordinary varieties of mineral limestone are found, as well as seams, crossing the course of the tunnel. At 1,835 feet ore was discovered, but as yet the deposit has not proved valuable. At about 2,100 feet stratified limestone was encountered along a fault-seam which dips to the west, and at" 2,250 feet shale makes its appearance along a similar seam (see Plate EL). It is probable that this shale is the same body as that encountered toward the end of the Eureka tunnel. All of the rock encountered in this tunnel belongs to the Prospect Mountain limestone.

Qeneriil Internal »triiclM« of Pwjipcct MomitMii.^It wiU b© llOtlCed (PlfttC II.) that

the west side of the mountain difiers greatiy from the eastern. This in some measure is owing to the fact that a larger portion of the overlying rocks have been eroded, and that the axis of fold les somewhat west of the ridge.

DiBtritmiioo of ore in i%«infect ii©iiiit«iii.— The IfUTger portiott of th© mountnitt and . Its adjacent spurs is composed of mineral limestone, and evidence of the number of metalliferous deposits contained in it is offered by the numerous outcrops of gossan which occur along its whole extent, but which are particularly numerous fi*om Ruby Hill to the Secret Galon divide. With the exception of some few mines, the properties of Prospect Mountain have been but slightly developed. Those, however, that have been opened to any great extent show that there are numerous masses of ore contained in the Hamburg m_ wel as the Prospect Mountain Imestones, although ne bodies of such a sii© as those discovered in Euby Hill have been found.

The Stbuctokb Of Euby Hill.

Tim fmiiiatiiiii. of Ruiif HIM.— Thc positioM of th© different formations on the surface of- Ruby Hill, and the relations that they bear to the granite of Mineral Hill, can be observed by a reference to the geological map of the district The limestone of these two hills formed one and the same body

180 Silybe-Lead Beposits Of Bueeka, ¥B¥Ada.

before erosion, and it is merely the continuation of the long belt of limestone of wMch the greater part of Prospect M ottntmin is composed.

The main beds of Ruby Hill are a mass of quartzite, which is probably underlain by the granite of Mineral Hill; a broad zone of mineral limestone and an 0¥erlying belt of shale. Al of these beds ha¥e been tilted so that they stand at an angle of about 40°, though nowhere on Ruby Hill does the dip of the stratification of any of the beds conform to the dip of ^ their planes of contact This lack of parallelism is characteristic of the region of Ruby Hill, and is due to a succession of faulting movements. There are two systems of fault-fissures on Ruby Hill. The first consists of those which are approximately parallel to the strike of the formations, and which were produced entirely by the main folding and upheaval, and the second made up of those which were caused by the same forces supplemented by strong lateral pressure.

That there has been lateral pressure exerted from a northeasterly direction at some time is shown by the direction of the striation marks observable on tbes© latter faults, which have been caled cross-faults. Beginning at the Jackson mine at the southeast, the strike of the formations is to the north, but it is soon delected to the west until in the Albion mine it is nearly due west

Tim qtmitiitii anil iiniestoiie cmitiicL— The Ino of the coiitact of the quartzsite and limestone on the surface of Ruby Hill represents very nearly the crest of the anticlinal' fold. Underground, this contact is extremely irregular. Besides smaller irregularities in the quartzite there are three large protrusions along the course of this contact, wMch occur respectively in the Phoenix, K. K., and Richmond mines. Along the line of dip of the quartzite and limestone contact there is a great depression several hundred feet in vertical extent, which occurs at about the same depth in all the mines, and which combined with undulations along the line of strike forms large basins. These basins are intimately connected with the ore bodies and will be referred to later.

Til. iiMta fii«it.— The most important structural feature of Ruby Hill is a fault which at the southeastern end of the mineral zone is first to be seen at the American shaft. (See Plate IH.) From this point, this fault, which

Summabt. 181

• has been called the Rub j Hill faalti though Bot perceptible in many places on the surface, passes west of the Jackson hoisting works, its coerse veering toward the west, and is visible in a tunnel near the PhcBnix line. It passes northeast of the PhcBnix, Lawton, and K. K. shafts, but must be very close to the latter. It can next be seen near the mouth of a tunnel ran to connect with the Bell shaft The last place where it can be observed on the surface is near the Bichmond office. Although this fault is not continuously traceable above ground owing to the debris^ its existence is fully established by the fact that it is encountered at numerous points in the underground workings of all the mines of Buby Hill. The average dip of the plane of this fault is about 70° northeasterly, and it is of remarkable uniformity, scarcely ever varying 5° one way or the other. Its course, also, is extremely direct, with the exception of the bend between the Phoenix and Jackson. This Ruby Hill fault is marked by the presence of a fissure filled with rhyolite and clay which is widest in the Jackson and Phoenix, where in places it measures as much as 15 feet In these two mines it is filled with rhyolite, which, although much decomposed, is still easily recognizable. In following the fissure west the clay is found to be more calcareous, and in the K. K. and Eureka positive proofs of rhyolitic character are lost In the Richmond mine the fissure is narrow, and although a distinct and wel-defined seam is only a few inches wide.

Tbe nmiii i-nrc^This fault fissuTe hfts bccn called the main fissure, as to its formation are due the most important features of the present structure of Ruby Hill A proof of its comparative recent formation is the fact that it faults all the formations with which it comes in contact, but is itself nowhere faulted. It is evident that the country southwest or on the footwall side of this fault has been raised many hundred feet above its hanging wall. The distance has apparently been greatest in the Eureka, where it has certainly exceeded 1,400 feet (See Plate VIII.)

The dip of the qmartzite and limestone contact does not greatly exceed 40^, while the dip of the main fissure is about 70°. The two surfaces of motion therefore approach each other, and the line of junction is exposed at various depths in the lower workings of all the mines except the Richmond and Albion. In these mines the lowest workings have not yet reached

182 SILTIK^LEAB BEPOSITS OF BUBBKA, lOEVAJCIJu

th© jttnctioii. The face of the qeartzite when in contact with the fiflsur© is no longer the original contact of quartzit© and limestone, bat is the fmiilt Ikce of the southwestern uplifted country. (See Plat© IV.) It is eYident that if the fissm-e continnes downward with its present dip, at some depth it niEst enter the qiiartzite,

TiieiiecoiiiimryfiMtifi*.— At th© time of th© disturbance which produced the Euby Hill fault, another and secondary fissure was formed along the contact of th© qnartzite and limestone, and the quartzite was raised higher than the limestone, giving rise to the formation of a wedge of limestone between the quartzite and the main fissure. Up to the present time all the ore of any importance taken from Ruby Hill has been extracted from this we%e of limestone, the crushed condition of which is due to the upward movement of the southwestern country against th© hanging wall of the main fissure. Section 7, Plate VIII., is typical of the relations of th© two fissures to each other and to the quartzite, limestone, and shale in the mines southeast of the "compromise line.^

The two belt, of iiimie.— Two belts of 8hale,-only one of which appears on the surface, are known to exist in Ruby Hill. The upper or surface shale can be observed on the map, Plate I. Taking into account the general dip of th© surface shale and that of the shale where it is encountered below, it is at once apparent that the two must be distinct masses in al the mines southeast of the compromise line. In the Richmond mine, however, it is different Th© shale on the surface in which the shaft is sunk is the same body of shale that is encountered below. The manner in which the Richmond shale and the lower belt of shale have been brought together in the lower workings of the Richmond and Eureka, and the manner in which this lower shale has been faulted, have been fully explained in the body of this report.

Inlueace of the maitt iwnre oa the ore formmtion.— The time aud manner of tho formation of the Ruby Hill fault and its subsequent filling either with rhyolite or clay are matters of very great importance as regards th© mineraliaation of the limestone between the qnartzite and this fissure, and the prospects of finding ore either at a greater depth or by prosecuting developments in the so-called "front limestone." This body of rock lies northeast of the

Summaey. 183

tnaiii fissttre, and althoiigli it has in many places the appearance of ore- Ibearing ground lias hitherto been fomid unproductive, all the ore having been obtained from th© wedge of limestone between the main fissure and the qEartzite. It is true that the prospecting done in the front Imestone has not been siifficient to prove that it contains no ore bodies, but it has been sufficient to discourage search in that direction.

As far as prospected, the front limestone does not exhibit the crushed condition that is so apparent in the wedge of limestone between the qmartzite and the main fissure.

TiiecitMftMteiiitiieEiciiiiioBi.^ — The qiiartzite soutlieast of the Richmond shaft mppears to be a sold mass many hundred feet thick Its contact with the limestone is very irregular, and the rock near the surface is often displaced to a greater or less extent by faults, but it is comparatively easy to explain tliese irregularities and to account for the phenomena exhibited. Mot so, however, with the quartzite in the Richmond and Albion ground northwest of the working shaft of the former mine. The quartzite in these two mines consists of a narrow baud from a few inches to 90 feet wide, which bends mnd twists in many directions. It accompanies the secondary fissure which leaves the face of the main body of quartzite somewhere near the Richmond shaft

FonMtioiioftiieii«ffowini«ft«it«.^The manner in which the narrow band of ijuartzite found it« way into its present position seems to admit of but one solution, namely, that its occuiTonce is due to a fault or a succession of faulting movements which followed the line of the accompanying fissure, and that it originally formed part of the main body of quartzite, which must here underlie the limestone. It is altogether improbable that it constituted a distinct bed of quartzite laid down upon the back limestone. In this case

Ruby Hill. It is not possible that it is quartz, and was deposited after the formation of the fissure, as under the microscope it exhibits the stmcture of iquartzite.

Back limestone. — ^The tcrm "back Imestone" is given to the limestone which is found on the footwall side of the naiTow band of quartzite. This rock differs in many respects from the limestone which is encountered between

184 Silvbe^Lbab Deposits Of E¥Ebka, Mbyaba.

the quartzit© and shale. As yet no ore of any kind has been found in it. Its peculiarities are ¥ery characteristic, and it is easily recogniiaMe wherever found.

Tiiejiick«<»&mit.^The main fissure joins a fault which Mr. Hague ha« called the Jackson fault, somewhere near the American shaft

Oees Of Eukeka Bi8Tbict.

iiinenii«.^The following minerals have been noticed in the ores of Eureka Bistrict: Galena, anglesite, cerussite, mimetite, wulfenite, limonite, calamine, smithsooite, calcite, siderite, aragonite, quartz, steatite, blende, pyrite, ai-senopyrite, molybdenite, malachite, azurite, and wad. The lead minerals are well represented, and it is highly probable that most of the known varieties exist in greater or less quantities in the ores, although the presence of all of tliem has not been detected. Antimony is present in many ores, but in what form has not been determined. Silver and gold are present; silver in the form of chloride and sulphide, and gold probably in the metallic state. Down to the somewhat irregular water-line the ores are substantially oxidized, and consist mainly of lead carbonate and sulphate carrying precious metals, and accompanied by ferric hydrate. The average tenor is 15 per cent, lead, 0.079 per cent silver, 0.00248 per cent gold. Quartzose ores are rare, but when found are important as a fiux for the ordinary baaic variety. The various classes of ores recognized by the miners are described in Chapter V., but may be omitted here.

ciiiiMiificiitioiniftiieoredeiKirit«.^The orc dcposits of Eureka District, though they contain gold, can be classed under the head of silver-lead deposits in limestone. The type of deposits to which those of Eureka belong is one often met with in the older limestones of the Great Basin, and although lljgg^ pg^j^l^ji^lgj. ii^pQgjig i^^^Q 1)^^11 0f ijjQ,.0 ybIub and are more widely

known than any of the others, and exhibit some very interesting structural ^ features, they cannot be said to form an isolated class.

The lead deposits of the Great Basin in general, and those of Eureka in particular, have-some points in common with all the known varieties of lead deposits in the world, but the resemblance is not sufficient to allow any one of these to be taken as a prototype of those of Eureka. As regards

the ores and their manner of ibrmation, the Lead vile deposits of Col- ©rado, described by Mr. EmmoES," resemble those of Eureka most, but the t#o regions differ widely in respect to the structure of the country and the relations of the deposits to the different formfttions. A classification of the ore deposits of this district, as regards their form, is a matter of considerable difficulty. Some of them may be termed fissure or contact veini, but in most cases they are very irregular in forai and are better described by the Grerman word "Stock" than by any mining term used in English. They are often lenticular, but this word cannot always be used to describe them, as they oft-en ha¥e offshoots in all directions. Any classification, however, that is dependent on mere differences of form must be more or less unsatisfactory.

iMiitfiiniti«i©ftiiii ©»!!©«••.— The ore bodies do not seem to follow any particular direction either as regards dip or strike, and at first sight they appear to be distributed throughout the ore-bearing formation without any regularity. This is not wholly the case; and although no well-defined law can be found governing their occurrence, this is connected with that of certain phenomena in the country rock, such as fissures, caves, and broken limestone.

Fiifiamtioiioftii«©wii«ii#fc — ^The distribution of the ore has been determined almost entirely by the physical character of the limestone in which it is ftund, and not by any chemical or mineralogical differences in the rock. The greater facilities offered by a crushed and broken limestone, no matter what its character, to the percolation of metal-bearing solutions would more than compensate for any chemical advantages which a particular kind of limestone might offer. During the process of upheaval to which Prospect Mountain and Ruby Hill were subjected, the limestone was fissured and crushed, great zones of shattered rock being formed, which are separated here and there by unbroken belts. The ore-bearing solutions entered the rock through the channels of least resistance, the crushed limestone offering fewer obstructions than the fissures themselves, and deposition followed in forms of a degree of irregularity corresponding to the complexity of the preceding dynamical effects.

•Second Annaal Report of th© Director, of tlie U, S, Qcologiciil Snrvej, 1881.

188 Silter-Lbab-Beposits Of Bijeeka, Nevada.

Ee«rr»iif emcnt of tli« om hj water.— FfOIH th© dispOSitlOIl of th© Ore ill ft Stmtified

form in the upper part of many of the large ore chambers it is evident that it owes its present position to rearrangement by subterranean water currents. This occurrene.© has been of comparatively recent date, as th© ore has been thus deposited since its oxidation.

c«iaectioiioforeiK>iii«iwitiifi«nirc»,ete,^Ore bodics ftr© intimately connected with the oQcmrrence of fissures, ca¥es, sediment, and on Ruby Hill with depressions in the quartzite. The ore bodies at first sight often seem to have no connection with any fissure or channel through which they could have been filled, but such a connection has been demonstrated in so great a number of cases that it may be presumed to have existed in all In by far the greater number of instances the fissure has led to the discovery of the body, or the existence of the fissure has been shown in the workings subsequent to the discovery of ore. Sometimes it has been almost obliterated by pressure, and in others it has not been 'revealed by th© explorations of th© miner.

cmw..— Caves are found in many places in th© limestone, and no large ore body has been found which had no cave over it, but caves are by no means always accompanied by ore bodies.

Depr««iioii« in tiic miirteite imii ore.— Th© manner in which the depressions in the quartzite on Ruby Hill occur has been already explained. That large or© bodies should b© of frequent occurrence in these depressions is not strange, when it is remembered that th© limestone in them was in a shattered and crushed condition, and that the quartiit© with its casing of clay served to a certain extent to confine the metal-bearing solutions to the limestone mass, where large quantities of these solutions were probably allowed to «ettl© quietly and deposit ore.

Rel«tioii»oftlieorel>©die«totliefoniiiitioii«.— On Pfogpect ]|f0||i||||i|| ilj^j.^ ^.^ jj^

workings in th© neighborhood of th© quartzite, and thus far th© metalliferous zones have been separated by belts of undisturbed limestone and ahale. The size of the ore bodies in th© mountain has been much smaller than those on Ruby Hill, and the. caves have been smaller and less numerous.

Summary. 187

In th© mines on Ruby Hill, southeagt of the "compromise line," the ore hoiiies asualy occur comnected with the quaxtzite, but in the Richmond and Albion they fure almost always far removed from it

Souice Of The Obe.

F«i«»iM«iinifcc«©ftiiiiof«.— Th© possible sources of the or© are a deposition in small particles with the Imestono, the ore being afbrwards segregated into nearly isolated bodies either by chemical or mechanical action; a segregation of tiie ore in the limestone from th© country rock on either -side of it; mnd a deposition from solutions which came from below.

Ff«d©iMiii«t«toi«tii«<iiifcfeatKici»..^Se series of assays mad© with ©xtraor-

'dinary precautions show that the stratified limestone contains only the mi-cutest traces of sil¥©r, while the mineral limestone, especially where it is iron-stained, contains a number of cents per ton. Th© silver contents, how- •ever, on the whole, diminishes as the distance from the ore bodies increases, and nowhere answers to the composition which th© rock must have possessed had the ore bodies been derived from it Th© trace of silver in th© limestone is an impregnation from the ore* bodies. Th© shale never ■carries more than a trace of silver and gold, and th© quartzite conld not hav© ftimished the material of th© ore bodies. There are also good structural reasons for believing that the ore cannot have been formed by segregation from the surrounding rocks. Meither do the examinations furnish any reasons for believing that either th© granite or th© rhyoMt© yielded th© metallic compounds of th© or© bodies.

Qu*rti-pofpiiyfy ii« « mmm ©f the ore.— On th© oth©r hand, th© qttartz-porphy ry proves to contain silver, gold, and lead in no inconsiderable quantities, and has manifestly been subjected to chemical action involving the solution of -a portion of its metallic contents. Of this th© decomposition of th© rock, combined with a notable© concentration of sEver and gold in the pyrit© (which is of secondary origin), are evidences. While the quartz-porphyry -appears on th© surface only in a small area, it is entirely possible that the mass underlies a great part of the district, and that it may hav© yielded the •or© which was deposited in the limestone. This, however, is uncertain, while it is tolerably safe to say that of all the rocks which appear at the

188 Siltee-Lbab Deposits Of Eueeka, Metaba.

surface the quartz-porphyry is the only one which can ha¥e furnished the metals of the ore bodies.

The solfiitiiric action mii the or« toniiatl©ii-— Th© Ill»EEer of OCCEll'©BC© of th© OF©

and its connection with the fissure system are consistent only with the snp-position that whatever the source of the ore may have been, it reached its present position in ascending solutions. The formation of the ore-bearing solutions is almost certainly due to the soMataric action arising from the eruption of the rhyoHte. The intrusion of this rock was the last dynamical disturbance on Muby Hill, for the main fissure with the rhyolite dike faults all formations with which it comes in contact, except the ore bodies, and is itself nowhere faulted. The rhyolte dike also shows every evidence of sotfataric decomposition. There is no evidence of two distinct periods of soMatarism, and unless the ore formation and the alteration of the lava are due to comparatively late volcanic agencies, which have left no other trace of their existence, the ore deposition and the eruption of rhyolite must have been related phenomena.

• Ma»Meb Of The Depositiom Of The Obe.

The i«iMi.itioii of tii« ore..— The solutions containing the or© penetrated the Imestone, passing through fissures and interstices in the broken rock, and deposited the ore where conditions of temperature and chemical activity were favorable to its precipitation. It is impossible to determine what may have been the chemical composition of the solutions which carried the ore, but it is not improbable that they consisted in great part of metallic sulphides dissolved in alkaline sulphides. These solutions were necessarily formed under the influence of heat and pressure. Rising into the shattered limestone at a diminishing pressure and temperature, the liquids lost much of their solvent power and many of the metals that they contained were precipitated. This precipitation could have occurred in only two ways: either through deposition in pre-existing large cavities or through a substitution of ore for country rock. The manner in which the deposition took place has a very important bearing upon the probabilities ot finding ore at any considerable distance below the water level

8Wmmary. 189

me foniMtioii of ttiir««.— The formfttioii of ai¥es in limestoii© is usually attrilbmtalble to the action of waters percolating from the surface and carrying carbonic acid in soluticwi. To form a cave at a giTen spot, water containing free carbonic acid must be supplied in sufficient quantities, and an escape must be provided for the more or less saturated solution of calcium carbonate. Gaves cannot, therefore, form at .an indefinite depth from the surface, and their practical limit is reached at the water level. The caYes in Eureka are of more frequent occurrence near the surface than in depth, and they are not found at all below the water level If the theory of a simple deposition of minerals from solutions in pre-existing caves were correct, it is evident that the limit of the ore would be reached at the point where cave formation was no longer possible.

The .niMtitiitioii tii«iry.— -In the JBurcka deposits nothing has been observed which would indicate that the ore had been crystallzed from solutions im pre-existing cavities. The banded and concentric structure, characteristic of that manner of deposition, is nowhere visible, and although it is conceivable that it might have been obliterated in the oxidized ore bodies, it is impossible that such should have been the case in the unchanged masses of sulphurets. The masses of sulphurets on the other hand offer strong evidence in 'favor of the theory of substitution. The minerals have replaced the Ime-stone in such a manner that they have often retained the structural form of that rock. Rounded bowlders of Imestone have also been found as the nucleus of masses of ore.

The sulphttret ore shrinks to some extent owing to the leaching which follows oxidation, and this accounts for the apparent relative size of many of the caves over ore bodies. These caves were no doubt subsequently con- _ siderably enlarged by the waters bearing carbonic acid. If the deposition of ore is correctly referred to the solfataric action consequent upon the rhyolite eruption, it is likely that the precipitation of the sulphurets began soon after the outburst of volcanic rock, and before there could have been much cave formation.

That the lead deposits of Maibl (see Chapter ¥111.) and of other places should not have been formed by substitution is not an argument which would prove that the same was the case in Eureka. In the Leadville de-

190 Siii¥Jt!lB»LBAD DEPOSITS OF BUEEKA, MET ABA.

posits, wMch in many respects resemble those of Eureka, the ore has been substituted for limestone, according to Mr. EmmoBS.*

Frepomleimiice of evidence In fmror of tlie •utatitntioii theory.— Wcigllillg thc CYideilCe OH

both sides of the question, it appears that a large part of the ore was brought into its present position by substitution, while it seems impossible to demonstrate that any part of it was deposited in pre-existing ca¥itie& It is highly probable that all the ore was deposited by substittttion, and that, future developments will effectually establish the fact. ^

Assaymg.

Object of imiiiyinir country rock.^ With a view to discoverfng, if posslMe, the source of the ore in the mines of Eureka Bietrict, numerous and careful assays of all the different kinds of country rock in the neighborhood of the ore bodies were made. As the quantity of the precious metals contained in any of these rocks is extremely small, it was necessary to take unusual precautions in order to determine with any degree of exactitude the amounts of gold and silver present Assayers do not ordinarily attempt to estimate with accuracy any ¥alue of either gold or silver less than one dollar to the ton (0.0026518 per cent), and as the country rock of this district never contains so much as this, particularly delicate methods were required in the determination of the actual quantities of these metals.

iii»iifwyoftiiiipfiicei«0fiiMiifiiiir.— -The process by which the results given in this report were obtained have been folly explained in the chapter on assaying, and it is only necessary to state that it was found possible to determine the value of silver in any country rock within a cent and a half- It was not possible, however, to determine the gold value with equal accumcy, as the quantity of it was^extremely small; and it was neglected in most cases.

Ui« of iwiiv*.— While various purposes maybe subserved by assays of country rocks, the main objects of those described in this report were, irst„ to ascertain in which of the rocks the precious metals could be detected,, and, secoAd, to trace the variations of tenor in different occurrences of the same rock. As a qualtative method, exception can scarcely be taken to the

•Suconi Anmml Beport of tli© Dirontof of ilii P. 8. Cteologiail Smrref .

Swmmaey. 191

drj assay, w Mle ©Ten if th© degree of accuracy reached in determining tli# absolttt© contents in precious metals of the Eureka rocks haa been overestimated, the ¥alee of the results would scarcely be impaired, for it will hardly be denied that the resttlts form a sufficient basis for a comparison of 'different samples of the same rock, all containing very small quantities of silver and gold. For the purposes of this report it makes little difference whether a certain mass of limestone really contains 10 cents or 20 cents, if it can be proved that a second body of limestone contains twice as much, or, it may be, half as much. In other words, the main purpose was to ascertain the relative contents, not the absolute contents, of the samples-assayed. Even if the methods employed were ideally exact, it would be-impossible to calculate the metallic contents of large blocks of ground with precision, since it would be impossible to obtain samples which-should correctly represent the average of the mass,

Peospectimq.

iietii«i« of pr<i.i>ectiiif.— There is nothing remarkable about the methods of prospecting in the Eureka Bistrict On Prospect Mountain it' consists in following seams or fissures in the limestone which show indications of ore,, or in sinking shafts and driving levels in different directions in that rock^ At present Prospect Mountain is being explored by a system of tunnels, which method, owing tothe natuip of the ground and the relation of thcr claims to each other, offers some advantages. On Ruby Hill the shafts are-sunk in the zone of mineral limestone between the quartzite and shale, and prospecting is carried on by cross-cutting between the two last formations, particular attention being paid to the following of fissures and broken ground. Caves, as well as stained limestone, are usually considered an indication of ore.

Earth cufwnt* mmi a^vt la Mmom to pii«ii«!tiiit.^It cannot be Said that the electrical experiments made by Br. Barus in the Eureka mines have as yet led to-any decisive results as regards the indication of the presence of ore bodies. There is, however, a remarkable coincidence in the results obtained by Br. Baxus with those obtained from assays of country rock along a line leading* up to an ore body. In both cases the presence of the same body was indi-

192 Siltib-Lbad Deposits Of Bpeeka, Mbtada.

cated as it was approached, altlioiigli the indications were not so pronoiiiicel that they might not ha¥e been caused hj qualities of the rock independent of the or© body itself.

As yet no practical benefit has been derived either from the electrical experiments or from the assays of country rock. This is partially dee to the fact that neither of those methods of search have been sufficiently developed to give definite results. As regards assaying, it may be said that although the indications are often indefinite, this method can be carried out with comparatively little expense and with little loss of time, though great care must always be used in making the assays and in employing the resulting values.

Fiitiitti of Fiti«pect iiiomit*to.^The mining region of Prospect Mountain comprised between Spring Valley on the west and the Secret Calion road on the east will no doubt produce large quantities of ore for years to come. Though several of the mines of this portion of the district have been developed to a considerable extent, there remain a great many claims which are still in a virgin state. Underground explorations have proved that many of the deposits are continuous to a considerable depth. It is therefore very probable that numerous unexpected ore bodies will be discovered throughout this region in the course of future deep prospecting operations. The ore bodies of Prospect Mountain, however, are not likely to be as large as those of Enby Hill, owing to the structure of the country. Taking into consideration the height of the mountain and the fact that no quantity of water has been encountered even at a depth of over 800 feet, no trouble need be anticipated from that source for some time to come.

Fiituni ©f tie mine, of Ruby Hiii.^What will bc the future of the mines of Euby Hill is very uncertain, and any predictions in regard to it must necessarily be inferred from the results of the explorations which have been made in the present lower workings. These workings have not as yet given any certain indications of the future. The probability of finding ore in the lower wedge of limestone depends in a great measure upon the validity of the theory of substitution. If this theory is the true one^and the proofs

Summaby. 193

favoring of it are strong— there seems to be no reason for doiiMiig the presenc© of ore below, provided that the limestone was in a it state to admit the ore-bearing solutions during the period of deposition. That this was the case is indicated by what has been thus far observed in the lower limestone and by the fact that ore was found in the Enby Hill fault-issnre when it was laid bare by the cross-cut from the 1,200-foot level of the Locan shaft. On the other hand, if the ore bodies were dependent npon the prior formation of caves they will not be found below the water-level, m cave formation could not take place much below that plane.

Whether the extraction of the ore in the deeper workings wiU prove profitable will depend upon the iow of water, size of ore bodies, value of ore, and facilities Mth which it can be reduced. Water may prove a serious impediment,- but it is not necessarily on© which should be fatal to the exploration of these mines. As to the size of the ore bodies no satisfactory predictions can be made. No great change in the value of the ore as regards silver need be feared, though it is possible that the contents in gold

may decrease.

2S54 t— .13

A JlNi ■ J , H-Ji JaL. •

A. C.lliiii.B«wlFti»ii of »••-•••--••••-•••---■••"-•-• *<*

,Strstii«41iiiiiMitoiMiBMa' Iii0 ................ 83

Aoid, Carbonloi inlneiimlii Minfoiiialloii............ M

AiiHiiiHiUJJtltiiieof.. ........................ ....... B

, PoMtloii nf .............................. 3

Aftofopt. -.......-•-..-... -...-• ..-....-...-...—..--. 105

, ilelfttivt, of onilMidiMitiiiiaiiiiiiM................ 76

Alfs, XnAliniidsr KaUutoiii In fte ................... 68

Aiii«iioiiii«liiifl,Biilijmilfkiilt lit tli«.. ...... ....M,M,1M

.M«iiiiMmni»ttJiii. ............. «,mil3

ABglmlto.. ................................... .......... »

Angcmito, FoRDiitioiiof; Xotli mdBaiiA. ....... ...... S8

, MuMRiniiiieiilof eiyiitels of ............. Sib B7, 58

Arkimaa, Bcpwlteof-. .................... .......---. ii

JLiBKiiilo, Soiiroo©!. im tlmow... ................. .--.--- 85

Aumyi, Diaciisiiioii of.. --...-....-...-.--..--...•. ..---. 85

tn oomiiictlon witli diietrioal ozpriniiiiito . .... 143

©I ComntiiokHiclai in- O.F.Bucknr ............ 124

gnmlt©.. ........ ..................... ....... m

of Imaitiiii©, lit Mat ...................... ...H^ii

,ilidli»t. ......... ............... iS

.▼iirioiM... .......... ......Ml, 114, 135

of fiwrMto . — ....-...... ................113,114

of qmirte-iKirplijiy ............. ............lli,137

of Ayolt©.-... ....... ........................ 134

,Uii© of ........................................ Mt

AAlminior, W. T.j Taittnioiij of ........ . ............. ill

Ammjing ; action of bitartwte of potmili ©n Uiuirgt .... 130

oottntry rook m » nmiiiii of pfwipiotliif . .... 144

■ , Objoctof ............. ......12i,1ii

jcnpelljitloii.... ................ .............. 12S

; Hitiiiiation of foM. ...... ........ ........... 131

. nnxtimsdia.......... ....................... 124

, Innccnimcics of rosnlto !a ................... 12f

Mtluirf ©-...-................................ 123

, Lou b J cnpiUatloa In.... ......... ...131^127,128

, Moiiftiirliiglmttoniiii...... ........ .......... 12i

• . ¥i» of....................................... 112

, WoighliigbiittoiM In ........................ 12i

, Wolglitoiiioilii. ....... ...... ............... IM

ABiirit© ................................................ m

Back llmoitoii©, Bencription of.... .............. ......4i-183

, Oreaoftio.... ...................... ...... i3

Bmui, Br. Ciirli olectiiciil tzfuriiiifinte In tho Mdimond

..........................142; Ml

Pup. BitTOi Dr. Cmtli on llio olMtzlnl aotlYltf of oni

lioilai ................. ....MHM7,14S

B— ilt» noar tlio mtimt, Abtcnooof..... ................ 8t

Beokcr, G-. F. 5 Amiiyi of Conaatock mmhm for .......... 121

I on tlio elecMctil oxpirimoiite of Dr. JBwnii ................................. 143

Bif oavo. Bow poll in tlio ............................. if

, IxfUiiMicmto in tko....... ............ ....56, §7,61

, Koofof the... ...................... .......... fi

, Tompomtttwilntlio..... .......... ...... ...... m

BlgCott©nwo#d District................................ m

Bltertnitoofpotiiiili, Action iif, on MtlTpi ............. no

Blitto in tlio ieponito of EMM.. .................. ....... 68

Hondo........ ............................ r............. m

BriotolDkMct... ............... ........................ m

Biiokoyo ©Mm . ........................................ t

Ombodloiof ill©........................ W

Bud A Batomaa oifuiiiio K«i»l»Con. Co ............. S

Bnlwliaokor mim© In lli« Popiiilp Mmeotono.. .......... S

,lj«id in Hi©. ............... .......... Iff

, Qiwrts-porpliyrj in tlio . .ISH, IW, IM, Mi Cal—lfio ............................................. St

Cidolto........ ........................... ............... it

OamlirlMi, Oro ioponito rfmoot oxcliiaivol j ia tlio ...... . i

rof niientod ftl Smmkii ...................... s

Carbon ia iock% Botiimiiiiiitioii of...................... 115

CirlMimito of coppsr .................................... IS8

lead....................................... m

llm©.... ....-...........*....... ............. fit

sine ....................................... M

Cwlwiiio Aoidin cuTO forauillon, Inincnoo of ........... M

Ciirl»nlf©KiiM, Orodopoiifslntli©. ............... ...... f?

roproaentud Hi Ennek*... ....... ........ S

C»v©% Acttonof wiitorim .............................. tn

ii»iiiiioatioii»of or©............................. isi

, CllMAtic chiinf ©9 in rogard to fonmstlon of ..... . It

, Connnctlon of, idtli iasiins© and oro liodlo* ...... iS

, Doftli of fonnatioii of....... .............. ...... tt

, Formiitlon of .................................... lii

inAiaiii«HiH ................................... im

In conneotion with oPt ....................... ..7*. Mi

, Purtiiil J formed, and ore cluiniliiiw ............. lOi

iBektfonof, tothoformmtionof or© .............. 99

, Tlieorjof tli«forni»tloii of.. ....... ............. M

ChmnlMg, Potto..... ................................ ..71^111

duunlioiitArfiiiigoiiiont of oro ia.. ..................... if

Siltek-Lbad Deposits Of Eureka, ¥B¥Aba.

Fug©. ChMnlmm, Steitllcmtlciiiof or© la. ..................... flitS

CliaiiiiiitoiicWin .......... .............................. S

Clmrfo for •furniio©... ................... .............. Ml

CtiloK)-»ni«ii»t6ofl«iiii ................................. 53

Cliiiid©!, F.J imiilyifa of miclmaoiid OKI li J .............. «

; imilyaii of Ili«lim«iiitoflif ..-.-..-.--.. IW i ittiiljitoof Mclmioiidipiiiiliy............ IW

Cliiji.. ......................................... ........ 5S

CMiiimtlo clmiigwi iifr©ctlnf fonnatioii ©f emrm .......--. M

C©inproiiii««liiiii«imiatiir*lMMiiiiary........... ..... 18t

,BoiicrlptioBof the. ....... ............ 23

fault. Effect of llio, on the two ilmlo Wto ............................... M

C©iiiil»cli Lode ........................................ 115

CttHtiict ©f lIii«itofiiJ imd sluil© ......................... M

Contact of qumTttlto and liineiitoiio ..................... 23

C©iinlry»6k.Aiii»yi©f.........82,83,8l,85.1SI,lM.18^1B«

, Mattlscoiitiilneiia. .............. ....... M

CrmiiiuMti in MclmioiidworlM.... ........ ............. It2

CnmlMirliind, Or© dopoaiti of ....... . . . ................ f7

Capoliitioii ; deaorlptioii of tlio proociu ml tlii} MiiiiiiaMl . IM .Lo»»lij.... ..................... ........... 12i

.TompumtnM mad in.. ............... ...... 12S

Cupul*, Frupamtioii of ................................. 125

Basil, J.D.; oBfomuitfonof fmffiiiiito.................. 5S

Bead Biott mill©, Onii of Hi© .......................... IB

ItolKNiilicm ©f iniiionils, Seliitiiri} tine of tJiii ............ St

Dcrbjsliliii, Or« iopoaitii of . . . . ........................ i7

Diifto, CiMit of mnmiiig.. ........ ....................... 15i

,TliiilMirliig of.......... .................... ...188, 151

Eiirft imiiwite in Ml*ti©n to f Kiiiiiictliii ............... Ml

Bast on lioi j, Connection of tbn, wilb Imiitiw ......... 75

, Dnicriptioii of til© ....................... T7

in Mclinioiii mlno .................. — ... 7S

, Ow cluiiiiicl of tlio. ................ ...... 114

E—t ▼tin on thsComttook.................... .......... 115

EtooMmlMitiTtt J of o» boiici in connectfon witli ^mf . Ml EnmnHiii, 8. F.j doicriptioii ©f twiivlflii itfuniti. .ill, W, 185 ; on nwewlty for the el —ticintlon of on dcpoiiito. ................... ............ Hi

I on porpliyfj Hi LendviHt.. -.-......-... W

Eruptive rofilui, Doscriptloii of.......................... 8,9

.Ininonoeof ......................... ..li,tl

EwflUmniderEjiltotoiii in BMW.......... .............. S8

Emrtikii, Altltnieof thetowBof......................... 1

Emrota DiitrictcompMiii Willi KiiiM........ ........... IW

,Fiw»»t.. ....................... ....... 4

jGenenilfeoliifj of...... ....... ........ S

.Htotorjef .. ..—..................... i

,Mll«li¥OTOCll« of. ......-.--.... ........ i,t

, Mlnemls in . . . . . IS, 53, M, 5S, Of , 17, 5% Hi, 1S4

,Fopnl«tlonof ........... ............... 4

,Poiilti©iiof. ........ .......... ......... I

.Production of... ............... ........ i

, Sedinmntiiry formiitions of ..........-.•» 7, 8

,ToiMignipliy of......................... 1

■iiniltt nine ; l»w snit wltb tlhe Molmiiiiid..... ........ Ill

, Main iwiEWJ in tlie -........-.-.-.....-.. ii

, Metliod of prospoctlng In tlie. ....... .13i, 14i

. Method oftimlMsriiig in tie.............. lit

, Ckder of IbeformationiiiBtlie........... 11

, Organlaitlonoftlic-. ............. ....... S

Sniiilcii mine, TrtbntosystAniiBtlie. .......... ......... IM

Tunnel, Fonnmtioni in tlie ...................... IIS

.Ore* of tic... ...... —--................ •

Bxiieriinentii, Electrical................................. 143

Experimonti on ImM by ciifiill»tion .. ........ ..-.ISi, W, MS

r»nlt, The Jiiclion. ........................ ..........tl, 184

, The nmln. ......".. .............................. M

Fiinltinf In Fronpaci M«nnt*in. .. .- . ................... Iff

. Mjmncrof, neiir Ccnifiwiiiiiiilln*......,...... W

movementi fa Adams Hill .................... IIKI

Fault* In the Eiinska Timnel ........................... ITS

111 til© quarliit©. ...........................44,41^47

In KutiyHiU........ ................... ........m^ll

, Mftnner of occorrencc of . . ...................... Tl

Meli.J'nitlct.IlocMon of ................ ............. HI

; trios micliniond and BmMk» anil ......... Ill

MMum in Biuinor mine. ......................... ....... ft

, Tlioimln... .......... .................... ....M,ai

.Mijolltoillinf of............... .... 15

Meanw, Tlie •ooond»ry, iMilween fmirtrfto mi Imiiaton© ....... ....................................1111,182

Hmnwiaainilcatloni of or©.. ............ ............. iti

between t lie Itli and itk loTela of tie Mclmioncl ••

, Connection of, witli oni Iwilei vid aiToe . f 4,7 S,llli, IW

fa Adiuns Hill....... .................. ........ lii

la CnmlwrliuidiiiidBerliyiWni ................ »

in PHmpect Monmtiiln ......................... !•

.Jnnction of tlie two priBclfal.. ....... ......... 114

, Mimnorofoccorninc© of ...................... W

Fonmitlons of AiiuniHEL.. ................... ........ MS

of Knwlr* Metricl.. ........... !!,•» 7, §.•.!•, 17*

, Balitlons of, to ore liodiea .................. IW

Fkmt Imoitone, Burwnnota of, ■43coiiiitiid for. ...--..-.. II

, Cliiuiiwterlaticaof....... ....... ............ 43

in the Kn»li».... .......................... 41

intli©E:.X... ...................... ....... 41

EnelforiBielting ....................................... lH

Fniiiacoii, DuscrlpMon of til© Mclmioiii...... ........... lli

FntuifioflJiireks, The frolniM©.. ............. ......... Ifl

of Prospect Monntiiln........................... IM

of EnljyHlll...... ..................... ......... IM

CMemi in CamlMrliiod md BerbytMnii Tslme of ...... . 6t

iatlioBnwiltmonj*. ...................... ....... B

Gang, Delnltlon of ..................................... US

Qcdiee Ufc Burtniiid milao ............................... i

CkiM Mmnmfcnl...— .......... ........................ Iff

, DiiCMiiio of aninnnt ia III© Mmhj Hil om......... 17i

.Katlmmtten of ................ ............ ....iai,lll

im til© iJlfcwint WMska .............................. 117

lnllie«roiof Aiama Hil......................... Iff

,Ilatiooi; tosttTerbiMeluiOBdlMii............... IIS

0fmiilt© ssmsonrwi of tlieow...... ............ ......... SI

, Aamyvjilne of ................................ IM

inMiiby Hill. ....................... .......... li

, Occnrrencniof...... ...... ..................... 8

Owitt Biwbi, Oocnnrencii of itmro Tefas in. ........... . 7©

OriBun, J. I on olwialiQAtloii of or« depMltt...... . ...... US

Hkfme, AmoM ; ieeoriptloii of fonaatloiii ........... Ill, 17f

I ietennliiiitlonof fomiitiiinaliy........ IIS

, Binwlion of Jmskaom fknlt aeeiirdinf to................. .................. m

, Tliickne« of tli© formatioiM acooidlng to.................................... 11

Index.

HagE© AmoM, BtrmtigfmpMoiil ctai«lfl«itliii lij...-., § Hague, J. D., Tttitimony of..................--."---... HI

; tlmberiiif on th© Comstook dnicifliiii hj.. 118 Hmiilnirir mill© ......................................... lit

HLarlort; on iniiMiiirDmeiit of Imttmit .-.-......---..--. 12i

Hematif o .............................................. W

Hcnwooi, Description of lodctby. ........-..---. --..-. 116

; on value of galonifc in Bngllili mm....... ... W

Hillyer, Jnig© ; in Micliinond aai Enrelm liiwKiit. ..... Ill

Hooaac mino. ......... .................................. 5

MooMio Moantoin, P©i!tioii©f .......................... S

ilag.. ............................... ........... Ml

Hornlilende-iMideiilt©, Oociiimjnciii of .................. . •

Ilorsc, Deinltion of...... ..................... .......... IM

Hunt, T, Stcny ; Teitlmonj of ......................... Ill

IndiciitioMof or©.....................................-. 13i

Iniliiitry mio© .......................................... 15

Ii-andnliialMft. .............................. ........... 21

Jackson fault In AdMns Hil....... ..................... 1115

named liy Mr. Hupi© ............ ........ 11

. Kelatlon of the. to Enliy Hfll fkolt. ...... m

Jackion Company, organlxntlon ©f tli©. ................. 4

Jackson mlno, Mtln iiwiiiwi In tli©. ........... .......... 2i

Jmckson tunnel, Main finlt In th*... ........ ............ 118

Jamoii,!. E. ; Toitlmonjof ............................ Ill

l[©ntiiclt mine .......................................... 4

Korl, B. ; on lo«i hj cmpollatioii ........................ 128

Kejm, W. S., Tottimony of........ ............. ........ HI

King, Clareno**, Testimony of........ ....... ............ HI

K. K-mln©, Mninisiiiroln tli©.....................-.... M

owned liy th© IttPiks Co ................... 22

Ijiwinlt li©two©n tie Biclnnonl mi EnwkJi compimioii........ ..................................... Ill, 112

L©iii depjulta of Miniioiiri...................... -.......- ••

tmid, II©t«nnln*tion of, in q mite-porpliyry ........ .137, 1S8

, Biffonmt kind© of, aa Inx ......................... 122

.Mttcnltf of obtainingpttw ....................... Mi

In ofiMi of JLdimis HiU. ............. ........... ... If?

oxii© repaired if th© almg ......................... 122

fWMlmiit....... -.....-...-..-......-••.-•.•.. -..-.. i

mininii: .................................. ....---. 118

LwidliiMto.............. ................. ............... IS

I.«idviU«, Ore icponilaiof ................. ...-.........••,•1

Jitter of InHUBnlttal ................................... ▼

Ijliiciitmfi, Amoanl of allTtr in tho........... .......... 88

, Aniiiys of.. .............. i2,8S. 84. 81,111, 114 mi

.iMlCll.AlMJiOf...... ....................Hll.llli

, Dowriptton of ................ .,...114 1»

, Broken Mid stiitned, mi an Indication of #n. . IW , Dolomitlo, whfitlMir f»v©nil>lit fur mm. ....... Ti

fmm 4t]i le¥«l ©f lit© Xnniltii, AuMiyi #f . . . . . Ul

ftwin Wohinoni mimic, ¥iiln©of .............. UM

ftum tof of KEby Hill. ¥iiln©of ............. 114

, I^ont, miMiyiof....... ...................... lli

,Cli»iiict©ri»ti«iof.................... 4t

, I)©icrlptlon©f ....................... 41

, In th© Enwito ....................... il

, Impwgnatifna of, wltt ore....... ........... tS

, "Mlaenil".... ................... ........... 11

, FlijilciilnMmifioftli© ...................... lli

,Fi©niioiBOrplisofoiiiiill©r.................. M

Puf©. IJiPiiiton©, Pnoniomorplii of pyrttii «ftiir. .............. lil

, Kiitioof.toor©. ............... .......... ... SI

, Sufwigiitloii of omftonilJi©..... ............ 8f

w©ilf©, Ore taken fifom tli©.......-..-........ M

Mmoiiit©.. ................ ............................. S5

Lltlmrf©, Action of Mtartmt© of p>tiiili©n............. IM

, ApppoEimiitely pnni, required................ 121

; lM»ring of silver in it on resnlta .............. lli

, Bust r©daclngiif©nt for.... ........ ........... 121

J conttntninstliror ............................. 12S

, Poor, how »dnc©4 at tli© Kiclmioni mlii© .... M4

J proc©«i by wMoliniailo.. ...... ............... IB

.Fmilty of ....... .................... .......... 1»

tlttl© Cottonwood Bistrict........... ............. ...... «

Lodo; apf Mod to llo Knby Hill dofoiits...... .......... lit

,MIn©ni*d6inItlon of ...................... ....115. lli

f nostlon, Biiferonc«i of opinion In T©f»ri to ...... . ill

LiM5©AEo«inpr©cei» ............. .................... 162

»t til© American sliiift .................... fS

, ©©tailed dtscription of tlio ............... fl

.FUUiigof tli6,intli©Kicliiionl........... W

, InlEono© of th©, on tie fomuitioMi ....... 181

in th© Eureka........ ........... .......... St

intli© Jackmn ............................ 27

in tlioKi:........ .............. .......... »

to tli©Pli»nlx. .................... ........ 2i

intlio Mclinionl .......................... II

MoC#y, M^oTi emrlj mintog op«nitiona liy ............ S

Molting. 1!ini«ittid Milliner of. in fUNiiyinf .............. 124

MangiiiieM go

lI©l¥lM% Pr., Ailyali of Rnliy Hfll oroa by ........... «

. IMormlnation of pyrit© In tonrte-iwrfkyFj %............................... iM

, 8©p«»tion of load from gold li j ...... . IW. UM

M©tliiidof pWMpiotliigln Piwip»tMoiiiit«ia........... 141

in th© niin©a wntlnMit of tk© oompromli* Ma©, ...... ....... lli

in ti© Mclmiond ...---......... l<li

lliiliirinf intli© Ennik*.................... im

Elcliniond. ......... ....... iM

, MiiiiMroffoniiatlon of ...................... M

Mlniifd Hill, MmtworMngart... ............... ....... m

MliitiililiiBnlijHIi; amgonito ...................... SS

i anglaalta.... ....... ............ 61

J MMinopjiits..... .............. m

I ii«uit©...... ............ ....... 68

f Wand©......................... lit

I cri-imiin©. ............. ......... M

I oiiMt© .................. ....... m

I onrmalt©...... .................. if

I galoiiii... ............. ......... 88

I foM ......................... §2

I Iwinatitii.... ........ ........... §5

I loidMllto.. ............. ...... m

I Mmonit© ....................... 55

I iiiiiljicMto.... ......... ......... m

I inaiiinMio©© .................... 6t

I mifoiiait©..... ..„•-.. ......... 55

I nilni©tlt©...... .................. 54

I iiiolyM«iiilt8 ................. ii,iS

I iilol©!. ................. ........ it

I ©xM©«f taii...... ...... ......lllLii

Sil¥Be»Lbad Deposits Of Eureka, Met Aba.

M lntiilB JB Hull J Hfll } ffritii. ......................... iS

J pjwmorpliito .-..-..-......---. US

I qnmrti. ........... .............. S8

; •ilT«r .......................... M

i unitliioiitta .................... Hi

I •Iwitlte ........................ S8

i talo ............................ US

I wRd....... ............. ........ m

in the on ieposito of llie Upfur MiHlitipf 1 . . iS •*Mlii«iiil"linia«teii©... .............. .................. 13

Minonil Point.. ............................ ............. Ii7

MMnr^mm, Clianictoriitlc* of the. ....... ........... Ill

Mia© worMngi In Adams Hill. ,...-...-.-..... ......... HW

Mimonri, Fonnntion of or© in.... .............. ......... 1©4

, Lend lepD«lti of ...-..-..-.......-.---."--... <•

MolyMiitoof loud................-............. — ..... M

MolyMennni, Soure* of, Intlmoni ..................... US

Momntaiii Boy oWm.......... .-....-.-..... ...-...-.--. i

MonntJiiii maliof Miy «• ftiel ............................ lii

OpMrlMiiWct ....... ................ ................. I»

0»,Agiiof th©. .................................. ...... lis

, Ajmlf ail of Molmiond.... ........ ................ Hi, §1

,Ai!i*iig«aeiitoftlie»iii til© clMUiiliiiiB .............. OT

dMmiel of the oiMit ©re liodj-.. ...—.-... ..---...-.. IM

ohiimiicl of tlioweiiiMnilMiiy ..-.........-..--..-.. 114

c#iM«icti©ii..... .-...........-.-...-....-- ---...--• HI

depiMtitioiai, Coniitioiui of, in lower linioiiloBt. ...... m

, Dopoiitioii of, 111 th© oliaiiitMiri. ................ ..II, 1S8

, Ptotrilmtloii of, In Pnwfiicl Moiimt»iii...........lS,17i

, B¥ideiioM in, of pneudomorpliliiii ftftar HnoitMiA. 98 , Ex tmctioii of, on triliiito ................... IIW, 151, 1112

, Granite iiaaiioiiico of th©......... ....... -....-.... tl

, Importanoo of nnumarofdopnilttoa of ............ it

In tlio lowor worliingi of Mnby Hil.-. ...... ....... 171

in til© BiiliyHllfimll.... .............. ........... M

,Maiuiier of ieiwiiitioii of tli« ....................... t3

in wMchilontenedtlMiliiiietlai©.......... St

, Fotmllil© iOiiWMi© of the ............................ IW

.Qmiirte.. .................................... ..-.-. •§

, Cjuiirts-porf kyrj m » i©iii«© of llm. .......... ...M, Mf

.Eiitiooftli©, to tliolliaeiteiMi.... ....... ........... 81

, Bod oarlMJiMito................ ......... ...--..--.-. ii

,B©liilloAof oikTfii to tit© fonnillin irf W

,EliyolitoiMi»i»aro©oftli©.... ............ ......... ii

jMchiBoni, cMorimitloiitoit of...... ............... 1S4

, S©gT«ffilioii of, Ikni tlioliinettxnu}. ...... .......... S?

, from thaqiiiirMto. .......... ....... 88

item thoitmlo...... ....... ........ 88

, SkriiiliJig© of tho .................................. 101

, Source of the, in ProspoctMotmtiiiii......... ...... tl

, Stntiflciatioii of, in itie diUMlMn .................97,98

.Siilplmrot.. ........................... — -....-... »,!»

, Yellow caAonat©... . .............................. I©

Or© bodies ; connected witli issnroa in tlio Euliy-Diindcr-

, Connootion of, with Isaiirea imd emrm . . 74, 75, 95 ©f th© Iticlmioni cMm..... ...... ........... 72

, KolMlom of, to tlio formatloii* .............. 18i

, Sistoof, in Prospect Moiintftin .............. TO

, Stiiliiiotito© in til© ........................... 97

, Tiiiil>©ring of tlio ........................... 153

, Connoistion of, with th© qniirtalto. ........... 731

, Contimiit J of; in the Eurokii. ....... ........ ua

Ofolwiiti, Contfamltyot la lii© mtolmoiii ............. lit

, Cimlracttoii of ............................... Ml

, Mbcto of oxliMion Oft... ......... ........... M©

, Kloetriciiliictliitjof ................ 141,147.148

I ,Fomimtton of..-.. ............... --..---...-.. 185

In mmnMitioii w itk drpniMteit in tlie nimrtglla 78 iMnuMi in til© WilaiBi »lno .................... Ii

in FrospoctMoonteiii. ............. .......... 71

of tMm Bnckoyo mill Cfcanif ion ..^.. ......... 71

Oni dupnitii. Agoof tlio................................ ii

, ClMuiiflofttioii of, ncooidiitf to dilienal m-

thow. ........ .......IIMM

tli©EttHik».............. m

, ComfftTlKiii of riolmesf of Praapiel Moiuitain, withBmlijHil..... ...... ......... ITU

i loptli to wMcli tliof oxtend .............. 114

, ypooiiiity of ol>iiM.ontion of ............. . lli

«f AiamiHil ............................ lii

of XnnkA ixmpfmd witli otben. . . . .M, M, iS|

•7.i8,ii oftiiiidfill6,B«iioriptlon of ............. 9^m

of Miimonii ............................... ©

ofFfoepiiOtMoiiiitiJii-.. ............ ...... 18i

of BMM. ........................... ....... Ml

of Hi© QimtBMiii ........................ ii

of tho Upper MiiMiiiippi.................. i5

of UppirSfleilJi......... ....... ........... 68

of Woitpliillii.. ............... ............ 08

I Stoofci.... .......................... ...... 185

, Thoiirloo in wpiri to tli© fonnnttai of . . . . 8i

, Tli©sli»tooftli©... ...-..-.-... ........... 7i

Oiini,Cliiiiiiloiition of ................................... 51

, CoMpodtf OB of; in tlio ©iii«t Btala .-....,....-... €5

of Aimii* Hfll......... ............... ......... imiW

of PnMipMOt MoimtJiiii ............................ iS

ofmElijHiE.LoaililIiar«no©« In ................. M

,Bi>iiictlon of ...................................... 158

, Tiilno oi; in BiilM............. .................... iO

CWiiition, Iniuenoo of tlio wmtiirloToliifoa. ..-.-...-.. il of onw In UioQiiHitBiiiils..... .............. fS

OxMa of Ipon......... ............... .................... »

loud............................— .*.-....-..... 68

I*ii|lp&CorwMiiiino.. ........................... .••.... 4

Paljiotok i»ek% Omdoponltolii. ---—...... ........... «

Piittlniioii proc«ii ..... ...-.....-.......---........-..- im

PhfliiiixCo., Organimtioii of tlio... .-.....-.. -.—..—.— 4

Mia©, MMn tatmo in th©. ...................... M

, Poooliwfoniiiition in th© '....'...... ...... t

Fhosfhoms, FiwMmoo of, in tlio or©©.. ........ ..-....-.- 58

Molaoli, on iopulti of UppirSllodi............ ........ i8

PMlDor, on nemnmnont of iwiHiy tmttont ............. 129

Fogoniflimeaton©.... -............-...-...--..--. ...... 8

Porphyry in Cmnliorliind iind BorbyiMMi. .............. 17

LoadTitto.... ........................ -..-.. W

Poiopnj, F., Conclmiions of...... ............ ........... 103

; on dopiaitaofKiillil.. ....... ........... •8,192

Poti, CrystnUlMng ..................................... 182

Pottiohamlw............. .................. .....71, 112, 114

Profac©............. --........-....-.-..,..-..--.. -...-- xl

Proipictiiig liy miMiys, Uso of tli© mollioi of ....... . l#l, 1^49

, Mottiods of. ........... .....»!«, 141,112. Ifl

RroipiMJtMciiiitiilii. AMtaimif ..........---.— — -" «

, Dip of til© fommtloii In. --..---•--• M , Btotriliiitl©!! of tli« ©win- --••-•-■ H , BmptlTiiriicki in.. ....... .-•••--•- H

, Eartmit of tli© ora dniiositloii la. ... . IW

. ]r»iiltiii|£ in. ............... .-....- Wi

.Fntnr© of..-.. ...... ........... - IW

.Gnuiltolii...... ............. ..-••- 12

, Ocoiinr«iiC€ii of ......-.--. i

, Mmniier of upliwivalof... ........... 177

, CkxJiuTiinoeof oi»Tlxidl€»in..... 72

oro iep«it«, Extent of the ......... 1«

.Section of................. ..-11,17,1W

,Sluilel»ltoof ...................... M

, SlM of or© Iwdlmi in.. ...... ........ 72

, SoETOo of the ore in. ....... .---...- tl

, Stani«tiir«of.-. ...... ......--.--.-•• 11

tuiiii©!, ronnftttojia in tlio .......... 17f

.Water in til©. ..-...— ...... IW

Pioiiioiiiorplui of jpilaim after oilcitt....... ..--•. .----• W

©»»ftisrlini«it»B©...... ....... --.... W

pjritc after ailcito.. ......... ........ lil

limiiiton*. ...... ......... Ml

I»niiipillj, Frof. m, i on cliMisiiiJiitioii of orn infoilte. ... lit

Pyrito ••» matrix of gold imdtiviir.................... IW

minoml .................................... »

, Effect of oriinlioii on .......................... Ml

, Gold and uliwrliiliMi. ....... .................. IW

, ObmirTfttloni of » miiiis of .. .................. lil

Pyromorpliito......... -.-•••••---•--- ••---•-""•-••--•• *

QmrMto md ttmoatoim ooatiiot in Knby Hil. .......... 18©

.AniMijirf......-....-...--.--. — — •••— IW-IM

Comootion of ore IwdiMi witfa. iepimiiiloiii in

• tiio.. ....-...............—....-"."... miw

.Ikiilto in tlio.................. ........ ---44,45, 47

in tho Molmond imi AlMon ......-..-..-.. 43, 183

,Mliioriil»iiitlio. ............ — .".....-.--.- W

.Kiitaitloiiof iiiiCOiidiBylliitiinitotlio.......... 48

,8©grfi|j»tioiiof orofroin tli« .................. 8S

■oiitli«i»t of ilmooBipwuiiiiwiMiMi.... -.-...-.- 42

,Tk© narrow; 4i»criptiott of.. ............... 43. 44

i dipiiiidiMkoof ............... 47

; mimiier of formation of..... --.. 4B

,IJpw»riinotloaoflii©. ................. ...... 47

|Jni»tii-i»rpliyTj, Age of tl© ........................... W

lumaoiircoof ttiooro ...........IW, 1117,187

, Baconipoiition of tlio ................. 8i

. Dotormlniitioii of loiii im tho. ...... .17, 13«

.OcctnTcncea of.................. ...... 9

EMM comparmlwitliEiirokii -..-........---. ........... IW

, Or© clopoalt« of .................... . ........--- iS, 1©2

, Thoory of tnlistitiitioii applied to ............. 1©3» IW

Make, Use of tliu word ........ ......................... 70

Bmjmond, E. W. ; on minsni' ieinition of lodo. . ......... Hi

, Tesilmou}- of ......................... Ill

Build. T. J,. Teatimony €»f .............................. Ill

lUidiiciBig mgoiite, Experimcnta on. ..................... . 124

litlnirgo,Eiip«rimeiition .... ................ 123

mmtorial; quantity rfiqiiijwid. ................. 121

B«iniiig, AtvamtJigwi fttti di»iidviiniiig«iof-....-..— ... If*

B«iiltii,Briofoiitliao of...... .................. ........ »»

, Tmocmmoitia of, in ■•••jiiig.-... ----.. .-•--... 12i

Eh joMtii »• • nonrcooftlioor©-.. ............ .....--...- ^

, Aimajiof...... .......-.-....-.-. —-.-.-.-- - 184

, Docompoiition of ...-....... — ---.--.-.--•--•. 8*

ilk© in tlio Miilif-Diiiiiorbiirg, Jnoluioii, und PhcBEii:....... ....... ...................... • Its

•mpMonintlieTortiary. ............ .......... IM

tiling of th© mi^n insiiro. ..................... 25

from quarry.................................. m

, Occurrcno© of. .... . ........................... •

of Purple Momntiiln..-. ................. ...... 21

EelJition of, to tb© fornmtion of or©. .......... - Si

Mohmoiii oWm, Orabodioiof tho...... ................ W

, Location of the ....................... 3

Coinpniy, Orgsnlsation of the. ...... ........ 4

; lawsnit with tJi© Eorokii Con. Co. . Ill fnrniioet, Botoription of tlio ................. IW

ineline... ....... .. ......................... Ill

mla©, CMorinatioii toat of op© of th.©. ........ 114

, CroMisamres in tie... ....... ......... 20

, MainfliMinrointli©......... ........... Ill

, Metliod of tiinberiaig in tho. ........... IM

of pHMipootliig in tho. -.-.-.... 14©

, Potta cliiinil»r of th©. .............. .71, 112

, Ffwpootinji li J iii«iyi in ttio .....----. 114

, Qumrtadt© in th© ....................... 1S3

■Imft, Gmnita in th©. ................. ....... 177

, Bopthoftlio. .............. ........... 12

•lug and ipelM, Analyiwi of ................. . IfW

imoltiJig work% Bosoriptioii of tko. ......... 158

Eoblilni, B. Colior, Emrl j smoMng opomtiomi hj ...... 3

Boelai,lliiiisiv©-. .................................. ...... 17i

Bocky Mountiilii©, Load ores wait of tko.......... ..... it

Both; on fonmition of •ragonito ....................... 68

Buliy-IMndoTtinrg »Ib©, Bip in tho. ............ ....... 12

In tlio Hmmbmi IJiiiottoiMi. . . .% Mi

, Or© dopoiltiin tho............ TS

.Ownof tlio ................... tS

Hnliy mm. Altitnd© of........................ .......... 2

jCiunbriiui in.-... ............................ 118

, Contact of quiirtilto imi limiMitoii© In ....... . 211

, Bip of tlm fornurtaoniof..--.-. .............. 21

.Extent of tholimoitoneof...... ....... ...... 21

•hiiloof... ............. ........ a

, Funltii Mil fault moTementi In ......... . . .2©, 2i

.Fmturo of.... .......................... ...... ll»

,Gninlt©iii. ........ ........ ................ li

nilnoii,LMof th©.... .................. ...... M

, Poaition of .................................. . 1

, Qnarti-porphyry eruption neiir . ............. »

, Kelations of tho formations of ,.-..-........ . 21

. Ehyolitoiioar... ..................... ........ 21

, Kocka of.--.. . .-.....-.-... .................. li

, SncoeiiiiloEof thofonnstiomln.............. 2i

, Tho main fault in ........................... 24

fa.iiilt, AhiMinc© of om "bodieii noiii' th© ........ HM

and tho quartait© ...................... 32

, Camii© of tho. .......................... 1©$

, Description of tho ............ .113, IW, 181

, Eictont of tho, in Euroka mince ........ 2§

, Ore in tho...... ......... ............... 173

, B«hitaon of the, to the JackiKni fault .. 6i SawyoT, Jiidg© ; ia tho Ricliiiiond-Enrekft suit .......... ill

S«iin» aa indiciitlons of ore............................. Mi

SILVBB-LMAB DEPOSITS OF EUBBKA, IfEYABA.

Piig&

fiiic©iid»ry itsniii, Cuimiictioa of or© ^Mm Willi tie. - . 72 , WpMidfoniiatlciiiof til©............ SS

, Selaticiiii of tlo, to tbo qvartsito .... 4S

S«diiiii©iit in ooiiiftctloii wllli or© ......................... 78

SovMitj-iilx miim ....................................... 8

SlmlHTiiiilieriiig of.. ........................... ....IM, 154

ShaKConaootioiiof tli©twoli©ltoof............. .....17,18

» Dip of th©, In til© Eureka ........................ 3«

Jiio]ki!»ii ....................... 18

ImtlieAlWoii..................................... 4S

in til© Blolmioiii imd Bmrekii .................... HI

Lower tell of, ia tlio Ajuericiui md Jmikiioii. .... M

Buwikii. ...... ..-.,-.-...... M

Kk. .............. ........ 3S

PluBnii:. ...... ...... ....... m

,Plif»lciiliiiitm»of til©......-..-................. lO

. Two belts of.... ........................ .......M, 182

Slioatoof iron.......................................... S8

lino ......................................... Hi

fflmriiMa irepretiinteid at Eurekii ......................... 5

.Lower, ]IL«ii iopiilta in tlie . ......,.........•!,••

SilTor, Estliiiation of, In country rock..... .............. 12©

InorwofAdiiiiiiHill ........................... IW

in tlioiillureiitroclcB.... .,...-.-...-. ........... 181

,RiitiooC to RoM In Rlcliinoiiilwii... ........... lil

, £eMtoB uf tho, to the amount of loud TOdmood. . 121 SUtct Cimiior min©, Ores of tie ....................... €8

Slaf , Anidjiils ©f McliiDond ............................ ll»

Smiiltliig, Hmtiittoiiipta at........ .................... 1

SoMktaiioiiotloinind or© fonnatioii............... ....... 188

,Cmi«iii of ............................. 8t

Solotionii, Bertimtioii ©f....... ............ .............. m

Spoolmcmi from the Emwikatniiiinil...................... If

Spoiiia, Aimljii* of.... .......................... ........ Mi

StaliMStitoi in or© liodiiia................. ...... .......... if

Btofuo, UiMof, IntliiiliiioiiftBosiiiifnwin............ Its

Stock. Us© of tho word... ....................... .....fi, la

.Boijiitloii of.... ......................... ........ 118

Bttliitltatioii, KnHikii or© ImkIIos formed hj. ...... ....... 1114

in Ikvorof tti© . . . lilS» 18i. ll» SnlplMitoofliiiid... ......................... ...,..—.-. 58

Solf Mi© of molf Menmin ............................. i8|i8

■tiio ........................................ M

Snlpliimt OTOi Biii«iioi» of wmmnir of dufiMtttoii of tin! 8i

SupwiBio Ckwrt of the ITaltiid Slat—, Bgclil.oii of this. . . . US

Tulileof Cknitoiiti...... ...... .......................... ▼!

T©rtiiirf,miijoMtii«niptioii in IJmi......... -......— -. lif

Theory of •abstltntiom.... .................... .......... lit

TlmlMifiiiftGfiiiofiiliiiotlioiiif....... ...... --......•...- Mi

Timlieni, Material and •i»o of. ...... .................... Ml

BpTopcMm .......................................... i

incline......................................... Ill

Tribiit* iystom, Beiicriptioii of th© ................... Mi, IM

TniutiileatBiiiiMiiiaofpnMpiotiBf ................. .141, Itt

TylM), 2 G min© at ...................................... m

IJppiir Mli!»l««lppl mgioa, Formatloa of #wi ia !!». ...... lit

Lead depMlta of lli« ........ US

lJpp«r8i«ii»,0iii deposit* ©f.. ................... ...... §8

Utiiliiiiiiiermlaoini ...................................... Uf

tmniiol, Malmimlt In tlie. ............-.-.— .-.-...- Hi

¥oiii,Minens* Hi© of the wort. ......... ................. 115

▼onCottii; OAoUiMiflcftlloiiof ore d«po«tto .............. lli

{ OB depotiti of WMtfhatai. ...... ........... «

▼oa Ofodleck ; on claaalioitlon ©f owi dopotlto ......... 118

I on porphyry In Cmmlifirliiiii ...... ...... if

Wad ................................................... ••

Wupjoof minori ....................................... 1S§

Wiiltii,ClilefJn«tieo,Be©iii«iof ...........-.-..-...--. Ill

Wiitiir, Extentoflow of ............................... Mi

in Pwiipect Moimliilii :............--.....-.... HIT

the Atta« shaft... .................... ........ Iff

Kolij Hill worklnpi...... ......... ....... Iff

lobelia ©imiondViiaof ........................ liB

,PKMip<»to©Ci!ilili©fiitai«i ...................... lli

,Boiri»ng©m«iitofoniliy ....................... Ml

wins© In the McluBiiiid .............-..-.— ..... lli

Weighing anaay hnttoni ................................ Mi

Wolflitamied in HMmyfaf. .............................. IM

Womsoati% ¥., Tuittmcaiy of ............................ Ill

W«i!t©rol>ody, ]Oeiicrlptlon©ftli« ................:..... IS

.Coimeotloiiof lJi©,wiliitii»iii«a......... fi

,Cli©cliiiian«l©f til©.........-............ 114

Weaipttiilia, On iepofiit« of.. .................... ....... it

WftitToln on theComttook. ..................... ....... lli

WMI»PiB©IM«triot .................................... 65

WMtnejt J. B.,To©lliioiiy of ........................... Ill

Widii Weatnilniioa AinmiHil ....................... Iff

WiHiiiiM iiilii%Oi«a of tM... -....-. ........... ....... 61

WiHIitmalnirg mtno ..................................... Iff

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