Geology of the Globe copper district, Arizona

Ransome, Frederick Leslie · 1903 · Report

The investigation of the Globe district was begun early in the summer of 1901, a month being devoted to preliminary reconnaissances and areal mapping of the

This 1903 document, Geology of the Globe copper district, Arizona, is preserved in the Mountain Man Mining Library for research and reference. Original source: pubs.usgs.gov.

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Professional Paper No. 12 S · {A, Economic Geology, 22 enes B, Descnptive Geology, 25 DEP OF THE INTERIOR UNITED STATES GEOLOGICA'L SURVEY CHARLES D. WALCOTT. DIRECT~)R G E G 'Y~ OJ<' THE GJ_jOBE COPPER .DIS1 1RICrr, ARIZONA BY FREDERICJI<:: LESLIE R~t\...NSOME vV AS .HlNGTON GOVERNMENT PHINTIXG OFFICE

ate Paleozoic Librar .. Washington Du Cu , ,. CONTENTS. Page. Topography of the Globe quadrangle Origin - Lithology, stratigraphical sequence, and local correlation .. Lithology and stratigraphic~! sequence ... ... .. ... · 46 General character, distribution, and stratigraphical position General character, thickness, and stratigraphical position . . ... ... Variations in character connected with distribution .. . . . . . . .

CONTENTS. General geology--Continued. Intrusive eruptive rocks ... Madera diprite (quartz-mica-diorite) . Definition . .. · .· . .. Occurrence and distribution~ . Petrography :. . Solitude granite (granite and muscovite-granite) . Definition ... . . . .. . Occurrence and distribution .. . -; Petrography . Schultze granite (granite or biotite-granite) . Occurrence and distribution . Dikes connected with the intrusion of the Schultze granite . Occurrence and distribution . .. . Petrography . Ruin granite (granitite or biotite-granite) Occurrence and distribution Lost Gulch monzonite (adamellite or quartz-monzonite) : . Occurrence and distribution . Occurrence and distribution . ... . Age and sequence of the granitic rocks · . Contact metamorphism in connection with the granitic intrusions . Occurrence and distribution . Page.

CONTENTS. General geology-Continued. Page. Occurrence and distribution . ..

Importance of faulting in the development of the geological structure of the region. . General classification of the ores . . . .. Genesis of the ores ... ... . Descriptions of mines

CONTENTS. The ore deposits-Continued. Page. Descriptions of mines-Continued. United Globe mines-Continued.

Mines in schist, on the western slope of the Pinal Range. . . . Cole and Goodwin mine . . . . ·'

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Late Paleozoic Library Washington D. C. ILLUSTRATIONS. Page. PLATE I. Geological map of the Globe quadrangle, Arizona ... In pocket. II. Geological sections across the Globe quadrangle . ... III. A; The town of Globe from the north; B, View to the southeast from the north side of Webster Gulch, showing topography characteristic of the Gila conglomerat~- IV. A, Monoclinal structure in the Dripping Spring Range, south of Pioneer; B, View down the dry bed of Pinal Creek from a point about 4 miles north of Globe VI. A, B, Barnes Peak from Scanlan ,Pass; C, View from top of Needle Mountain VII. Generalized columnar sections. .. . . VEL A, A block of Barnes conglomerate, southeast corner of the quadrangle; B, Sheeted Schultze granite on Pinto Creek, west of Schultze ranch. . ... IX. A, Globe limestone containing Devonian fossils, on the road to Tonto Basin, about 4 miles north of Globe; B, Whitetail formation, as exposed by the roadside near the X. Whitetail formation, as exposed three-quarters of a mile northwest of Continental XI. Whitetail formation, as exposed three-quarters of a mile northwest of Continental XII. A, Characteristic bluff of Gila conglomerate as it .occurs in Copper Gulch near the town of Globe; B, Beds of Gila conglomerate on right abutting against steep erosion slope of dacite on left, 1 mile east of the Sixtysix ranch ... . XIII. A, Coarse, crumbling quartz-diorite detritus forming basal portion of Gila. conglomerate near Globe; B, Coarse breccia of dacite and schist forming part of the Gila conglomerate nea the head of Webster Gulch ... ... ... XIV. A, Coarse granitic breccia be ongoing to the Gila conglomerate and forming summit of Needle Mountain; B, T pical surface of Schultze granite showing sheeting or parallel jointing, trail to P nal ranch near Hutton Peak XV. Geological map of a part of lobe Hills in the vicinity of the Old Dominion and United Globe mines. XVI. Geological sections on lines i dicated on Pl. XV .. . XVII. A, Typical weathering of d abase, roadside near Pioneer; B, Characteristic surface of dacite north of the Old Dominion mine. XVIII. A, Outcrop of quartzite fau t breccia on Pinal Creek, about 4 miles north of Globe; B, Outcrop of fault breccia between limestone and diabase on the north

ILLUSTRATIONS. Page. PLATE XIX. Fault plane. developed int9 a scarp by erosion . FIG. XXII. Plan of the principal underground workings of the Old Dominion mine .. XXIV. Geological plan of the secon,d level of the Old Dominion mine . XXV. A, In the open cut of the Old Dominion mine; B, TheGreymine XXVI. Sketch plan of th,e principal underground workings of the Grey mine .. . XXVII. A, The Buffalo mine, from the ridge south of Alice Gulch; B, The Continental mine from the south. . . . . . . 1. Index map, showing position of the Globe quadrangle and the approximate outlines of the three p:iincipal physiographic divisions of Arizona . . . , · 2. Northeast-southwest section through the northern summit of Barnes Peak, showing general stratigraphy and structure . 3. Sketch profile of cuesta fronting the Pinal Range, about 3 miles southwestof Pinal 4. Sketch section from the summit· of the Apache Mountains southwest to Richmond 3 7 · 5. Geological section through Barnes Peak, showing faulted structure . 6. Geological section from Granite Basin to Whitetail Gulch, along northeast-southwest ridge. The line of the section passes half a mile northwest of Webster Mountain.. 7. Diagrammatic cross section through the Old Dominion mine, showing the occurrence of a mass of limestone in the · diabase of the foot wall. . . . . 8. Diagrammatic section through the underground working of the Montgomery claim .of the 'Black ViT arrior group . 10. Diagram showing plan of faulting at the Continental mine " .

Late Paleozoic Library Washington D. C. GEOLOGY OF THE GLOBE COPP~R DISTRICT, ARIZONA. By F. L. RAN1ME. INTRODUCTION AND ACKNOWLEDGlUENTS. The investigation of the Globe district II as begun early in the summer of 1901, a month being devoted to preliminary reconnaissances and areal mapping of the geology. Work was subsequently res med in Octo~er of the same year, with the efficient assistance of Dr. John D. Jlrving, and continued to the 1st of February, 1902. Much time was necessarily consumed in studying and mapping the intricately faulted country in the northwest portion of the . area, and when the season was perforce brought to a close1 it was with the reluctant feeling that the detailed study of the faults of the half of the quadrangle still offered attractive byways of investigation leading beyond the bounds prescribed by economic conditions for the present study. It is hoped that at some future time geological work may be undertaken in adjacent quadrangles and a broader basis provided for a discussion of the structural features of this interesting region. The preparation of this report has been facilitated by various courtesies rendered by the Old Dominion and United Globe companies through their local representatives, Mr. F. W. Hoar and Mr. N. S. Berray, who lent their cordial cooperation to the furfherance of the work. For various chemical analyses and tests I am indebted to Dr. W. F. Hillebrand and Dr. E. T. Allen, of the Chemical Division of t~is Survey, and for paleontological notes embodied in the following pages to Prof. H. S. Williams, of Yale, and Dr. Geo. H. Girty, o:f the Geological Survey. From Mr. S. F. Emmons, geologist in charge of the investigation o:f metalliferous deposits, I have received such general oversight ~nd criticism as gracefully turns ·the performance of his official duties into a source of personal regard and obligation.

GEOLOGY OF THE GLOBE COPPER DISTRICT, .ARIZONA. GEOGRAPHY. For the purposes o£ report the Globe copper district may conveniently · be co1_1sidered as coextensive with the cartographic unit adopted by this survey, FIG. 1.-Index map, showing position of the Globe quadrangle and the approximate outlines of the three principal ,. physiographic divisions of Arizona. the Globe quadrangle, which lies between the · meridians 110° 45' and 111° ·oo' west longitude and the parallels 33° 15' and 33° 30' north latitude. · It is thus a sixteenth o£ a square degree o£ the earth's surface and contains about 250

LITERATURE. square miles. It IS situated in the southeast-central part of the Territory of Arizona, between the Gila River on the south and the Salt River on the north, and includes portions of Gila and Pinal· counties. The. town of Globe, with a population of about 1,500, lies near the eastern edge of the quadrangle and is the terminus of the Gila Valley, Globe and Northern Railway, a branch. line about 130 miles in length, which connects with the Southern Pacific Railroad at . Bowie. The principal drai11age is northward through Pinal and Pinto creeks into the Salt River, but a relatively small area along the southern edge is tributary to the Gila River. The position of the Globe quadrangle and the approximate boundaries of the physiographic divisions of Arizona, presently to be described, are shown in the index map, fig. 1 LITERATURE. The following list Is not intended to be an exhaustive bibliography, even of that part of Arizona included within the Globe quadrangle. It aims merely to enumerate those works which contain some substantial contribution to the geology or to the history of mining development of central Arizona. As in the case of most mining regions, Globe has supplied the theme for much writing of no permanent value. While diligent culling of this evanescent literatur-e may occasionally be rewarded by the discovery of some fact of historical interest, the search has little to enliven its dreariness, and a list of such contribution; can serve no useful purpose. Many general publications on Arizona, containing occasional references to the mines of the Globe region, have also been intentionally omitted. ANTISELL, THOMAS. Explorations and surveys for a railroad route from the Mississippi River to the Pacific Ocean, 1853-1856, Vol. VII, Washington, 1857, Part II, Geological Report, Jpp. 139-166, Plates X-XII. Describes the geology along the ila River from Yuma to the Rio San Pedro, and gives brief notes on the materials and structure of the "Catarina" (Catalina), "Calitro" (Caliuro) Pinaleiio, Chiricahua, Peloncillo, and Mogollon r nges in southeastern Arizona. NEWBERRY, J. S. Report upon the Colorado River of the West, explored in 18571858, by Lieut. J. C. Davi ', Washington, 1~61, Part III. Geological Report, p. 42. First recognition of sandstones res 'ng on granite in the Grand Canyon. Refers them to the Potsdam and reports Silurian, Devonian, and Carboniferous rocks as conformably overlying them. R. Miner~logical fetch of the silver mines of Arizona: Cal. Acad. Sci., Proc., Vol. II, 1863, pp. 12l -139. Notes parallelism of mountain rar ges and extensive development of "Quaternary" gravels in central Arizona. GILBERT, G. K. On the age of lhe Tonto sandstone: Wash. Philos. Soc., Bull., Vol. I, 1874, p. 109. (Brief abstra t.) Considered as probably primordial Silurian.

GEOLOGY OF THE GLOBE COPPER DISTRICT, ARIZONA. MARVINE, A. R. Geology of ro~te ftom St. George, Utah, to the Gila River, Arizona: U.S. Geog. and Geol. Surveys West of the One Hundredth Meridian, Vol. III, Geology, Washington, 1875, pp. 193-225, Plate IV. · Describes boundary region between Colorado Plateau and Basin Range system. Describes and figures geological section from Camp Apache to Florence, across Apache and Pinal ranges. GILBERT, G. K. Report on the geology of portions of Nevada, Utah, California, and Arizona, examined in the years 1871 and. 1872: U. S. Geog. and Geol. Surveys West of the One Hundredth Meridian, Vol. III, Geology, Washington, 1875, pp. 21-187. Describes relation of basin ranges to .the Plateau Region from Nevada and Utah as far as Fort Apache. Characterizes basin range structure. Describes gravels of the valleys. GILBERT, G. K. Report on the geology of portions of New Mexico and Arizona, examined in 1873: U. S. Geog. and Geol. Surveys West of the One Hundredth Meridian, Vol. III, Geology, Washington, 1875, pp. 507'--567. Distinguishes three natural divisions in Arizona-the Range region, the Volcanic region, and the Plateau region. Describes in general the geology and structure of each region in southeastern Arizona. Names; describes, and discusses the Gila conglomerate. PowELL, J. W. Report on the geology of the eastern portion of the Uinta Mountains, etc., Vv-r ashington, 1876. Describes stratigraphy and orography of the Plateau and Basin provinces. HINTON, R. J. The Handbook to Arizona, San Francisco, 1878. Contains historical data in regard to early mines and development .. DuTTON, C. E. Tertiary history of the Grand Canyon district: Monograph U. S. Geol. Survey; Vol. II, Washington, 1882. This work, while not directly touching central Arizona, describes the Great Colorado Plateau, and is invaluable in contributing to that comprehensive view of the geology of the territory which should precede any detailed study of a limited area. BLAKE, W. P. Geology of the Silver King mine: Engineering and Mining Jour., Vol. XXXV, 1883, pp. 238-239, 254-256, 270-271. Historical notes on Globe region. Geological sketch of district in vicinity of the Silver King mine, west of the Globe quadrangle. WALCOTT, C. D. Pre-Carboniferous strata in the Grand Canyon of the Colorado, Arizona: Am. Jour. Sci. (3), Vol. XXVI, 1883, pp. 437~442. Presence of Devonian shown between the Red Wall (Carbonift:;rous) and the Tonto (Cambrian), Chuar and Grand Canyon groups described as unconformably below the Tonto and probably Lower Cambrian. HAMILTON, PATRICK. The Resources of Arizona, 3d ed., San Francisco, 1884, pp . . 143-245. An account of mines and mining, containing much historical information. WENDT, ARTHUR F. The copper ores of the Southwest: Trans. Am. Inst. Min. Eng., Vol. XV, 1886-87, pp. 60-68. Describes the Globe (now the Old Dominion) and the Black Copper mines in the Globe district. Refers the limestone of the former mine to the Carboniferous.

LITERATURE. DouGLAS, JAMES. The copper resources of the United States: Trans. Arri. Inst. Min. Eng., Vol. XIX, 1891 p. 689. Brief reference to the Globe district. WALcoTT; C. D. Correlation papers-Cambrian: Bull. U. S. Geol. Survey No. 81, pp. 220-221. Summarizes and reviews history o ' opinion on the Tonto group of Arizona. Considers the group Cambrian.

VAN RISE, c. R. Correlation papers-Archean 'and Algonkian: Bull. u. s. Geol. Survey No. 86, pp. 326-332J 1892. Summarizes literature of pre-Cambrn in Arizona. GILBERT, G. K. Geological excursion to the Rocky Mountains, .Albuquerque to Flagstaff: Congres Geolqgtque International, Compte Rendu, Fifth Session, · Washington, 1893, pp. 469-4 70. Describes briefly the Colorado Plateau. · · WALCOTT, C. D. Pre-CambriaJ igneous rocks of the Unkar terrane, Grand Canyon of the Colorado, Arizona: fFourteenth Ann. Rept. U. S. Geol. Survey, Pt. li, 1894, pp. 497-519. Reviews literature on the older roc s of the Grand Canyon. Divides them as follows: Unconforilllity · {Grand Canyon Unkar Algonkmn Great unconformity Vishnu Describes the Chuar and Unkar gr@ups. Discusses geological age and correlation. WALCOTT, C. D. Algonkian ro~ks of the Grand Canyon of the Colorado: Jour. Geol., Vol. III, 1895, pp. 3~2-330. Slightly condensed from preceding paper. DouGLAS, JAMES. The copper industry of Arizona: Mineral Industry, 1897, pp. History and general character of ores of the Globe district. BLAKE, W. P. Mining in Arizona: Report of the governor of Arizona to the Seeretary of the Interior, Wasliington, 1899, pp. 43-109. Historical sketch. Notes on the condition of various mines in the year 1899. EMMONS, 8. F. The secondary enrichment of ore deposits: Trans. Am. Inst. Min. · Eng., Vol. XXX, 1901, pp. 192-193. Brief account of the occurrence of the copper ores in the Old Dominion mine. THOMAS, KIRBY. The Globe mining district, Arizona: Mining and Metallurgy, Vol. XXIV,-1901, pp. 231-232. Brief notes on history and production.

GEOLOGY 01!' Ta:E GLOBE OOPPER DISTRICT, .ARIZONA. OUTLINE OF THE PHYSIOGRAPHY OF .ARIZONA. As the detailed investigation of the comparatively small area with which this report is concerned did · not permit of extensive general reconnaissance the foliowing sketch is . necessarily in greater part a compilation, based upon . the · geological literature which has been brought together in the foregoing pages. It is intended to recall to the reader's mind the salient topographic features of a great region and to supply a setting into which to fit the more detailed . characterization of a district that is but a very small part of the whole. The Territory of . Arizona may be ' divided into ·three physiographic regions, which are very rudely outlined in fig. 1, on page 10. The first of these, occupying the northeastern portion of the · Territory, is included within the Colorado Plateau, that wonderful province which the writings of Powell, Gilbert, and Dutton have made c1assic ground in geology. This division, which within the boundaries of Arizona h_as · an area of about 45,000 square miles, drains northward through the Colorado Chiquito (Little Colorado), Rio Puerco, and smaller streams into the Grand Canyon of the Colorado~ Its southwestern limit traverses the Territory in a general southeasterly direction from the Grand Wash, near the eastern border of Nev_ada, to the New Mexico line, a . few miles northeast of Clifton. This limit is not everywhere clearly defined. For about 240 miles, extending from the mouth of Diamond Creek on the Colorado River to the vicinity of Fort Apache, the edge of the plateau is marked, according to Gilbert, a by the continuous . line of the Aubrey cliffs, which divide the waters of the Colorado Chiquito from the Gila. These cliffs are well shown at the southwestern edge of the Mogollon Mesa, where they form an abrupt scarp from 1,000 to 2,000 feet in height,b overlooking Tonto Basin and facing the Mazatzal and Ancha ranges. From Fort Apache eastward to the New Mexico line the. plateau boundary is less distinct. Vast accumulations of volcanic rock have obscured the plateau surface and erosion has partly destroyed its continuity.c The San . Francisco, Mogollon, Blanca (White), and Escudillo mountains are described by Gilbert a as volcanic masses resting upon the general plateau surface. Describing this surface, Dutton e says: '"Its strata are very nearly horizontal, and with the exception of Cataract Canyon and some of its tributaries it is not deeply scored. Low mesas gently rolling and usually clad with an ample growth of pine, pinon, and cedar; broad and shallow valleys, yellow with sand or gray with sage, repeat themselves over the entire area. The altitude is. greater than the plateaus north of the chasm except the Kaibab, being on an average not far from 7,000 to 7,500 .feet. From such commanding points as aWh.e~ler Survey, Vo~. III, 1875, p. 47. bTopographic Atlas U. S., Verde sheet. c Gilbert, Joe. cit., pp. 525-537. dLoc. cit., p. 542. e Tertiary history of the Grand Canyon district: Mon. U.S. Geological Survey Vol. II, 1882, pp. 14-15.

OUTLINE OF THE PHYSIOGRAPHY OF ARIZONA. give an overlook of this region one lonely butt~ is always visible and even conspicuous by reason of its isolation. . It stands about 20 miles south of the Kaibab division of the Grand Canyon, and is named the Red Butte. It consists of . Permian strata lying like a cameo upon the general platform of the Carboniferous beds. The nearest remnant of similar beds is many miles away. The butte owes its preservation to a mantle of basalt which came to the surface near the center of its summit. It is an important factor in the evidence upon which rest the deductions concerning the great erosion of this country. "Fifty or 60 miles south of the river rise the San Francisco Mountains. They are all . volcanoes, and four of them are of large dimensions. The largest, San Francisco Mountain, nearly 13,000 feet high, might be classed among the largest volcanic piles of the west. Around these four masses are scattered many cones, and the lavas which emanated from them have sheeted over a large area. The foundation upon which they are planted is still the same platform of level Carboniferous strata · which stretches calmly and evenly from the base of the Vermilion Cliffs for more than 150 miles southward, patched over here and there with the lingering remnants of lower Permian strata and isolated sheets of basalt. South of the San Francisco M,ountains the level Carboniferous platform extends for 20 or 30 miles, and at last ends abruptly in the· Aubrey Cliffs, which face southward and southwestward, overlooking the sierra country of central Arizona." It is the rolling, partly timbered surface of this great plateau, surmounted by isolated volcanic mountains, which i::>Urrounds the traveler as he journeys across the territory from New Mexico by way of Holbrook and Flagstaff to Ash Fork, on the Santa Fe Pacific Railroad. The second physiogra~hic division, which may be called the Mountain region, adjoins the Plateau region on the southwest, and is essentially a broad zone of short nearly parallel ranges extending diagonally across the territory from the southeast corner northwesterly to the Colorado River. The width of this zone may be taken as from 70 to 150 miles, but as will be later seen its southwestern boundary is not capable of precise demarcation. It is characterized by numerous nearly parallel short ranges separated by valleys often deeply filled with fluviatile and lacustrine deposits. 1lhe individual ranges, such as the Dragoon, Chiricahua, Pinaleno, Caliuro, Santa Catalina, Tortilla, Pinal, Superstition, Aneha, and Mazatzal mountains rarely exceed 50 miles in length or 8,000 feet in altitude. Their general trend 'is nearly and southeast, but near the Mexican border they become. more nearly I north and south, and the mountain zone as a whole coalesces with a belt of north and south ranges which extends northward through New Mexico and borders the Plateau region on the east. The northwesterly belt of Arizona is described by Gilberta as continuous with the Basin Range system of N evacla and Utah, and is considered by him as exhibiting the same prevailing type of orographic structure. He states that his examinations "have a Wheeler Survey, Vol. III, 1875, p. 509.

GEOLOGY OF THE GLOBE COPPER DISTRICT, .ARIZONA. demonstrated no anticlinal structures, except . as minor features. · The usual structure is monoclinal, demonstrably due to faulting in the Chiricahua and Pinal ranges; and presumably so in all the o~hers." a With this conclusion . the observations embodied in the present report accord. As far as can be gathered from existing descriptions the greater number of the ranges consist mainly of Paleozoic sandstones or quartzites and limestones, resting with marked unconformity upon pre-Cambrian schists and granites. The extent to which this ancient basement composes the mass of a given range is dependent upon the elevation of the latter and the amount of subsequent degradation which it has undergone by erosion. The Paleozoic and pre-Cambrian rocks are cut by various eruptives, and partly covered by flows of volcanic rock. Adjoining the mountainous zone on the southwest is the third physiographic division, .also characterized by nu~erous short mountain ranges of prevalent northwest-southeast trend. · But in this region the ranges are separated by broad desert plains underlain by fluviatile and lacustrine · deposits of late geological age, or by undulating granitic lowlands veneered with gravel or _partly covered by flows of lava. 0 This may be termed the deser__!; region of Arizona: It can not be sharply distinguished-at least .without further investigation in the field-from the mountain-ous region, but the boundary between. the two may provisionally be taken as a curved line extending from Nogales, on the Mexican border, past Tucson, Florence, and Phoenix, and thence northwesterly to the Needles, near the California line. The mountain region and the desert region are both included in the Basin Range system of Gilbert. The main drainage of the mountain and desert regions is transverse to the trend of the ranges, through the Gila and Salt rivers and Bill Williams Fork into the Colorado River. ~he minor drainage is by streams, many of them intermittent in character, occupying in general the valleys between the parallel . ranges. TOPOGRAPHY OF THE GLOBE QUADRANGLE. The Globe district lies-in the heart of the mountain region of Arizona. The Pinal Range (including also under that term an irregular group of hills which form a >northwesterly continuation of the Pinal Mountains, as they are locally. designated) extends diagonally across the quadrangle from~ its southeast to it.s northwest corners, and occupies, with its flanking· slopes, about five-sixths of the total area. Five or 6 miles beyond the northeast corner of the quadrangle rise the Apache Mountains, of which only the southwestern foothills appear within the area of the map. (Pl. I.) This range, like the Pinal Range, has a north Wheeler Survey, Vol. III, 1875, p. 517. b Antisell, Pacific Railroad Surveys, Vol. VII, Part II, pp. 130-138.

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Late Paleozoic Library Wa~hington ·D. C. TOPOGRAPHY OF THE GLOBE QUADRANGLE. westerly trend, and lying farther north it occupies a position en echelon with reference to the latter. Between the two ranges lies a broad valley partly filled by a thick fluviatile deposit (Gila formation), which has been dissected by the present streams into a characteristically hilly topography. Practically all of the valley included within the map drains northwestward through Pinal Creek into the Salt River, but close to the eastern border of the quadrangle the railroad crosses through a low pass (3, 750 feet above sea) into the drainage basin of San Carlos Creek, a tributary of the Gila River. (Pl. Ill, .A.) The main Pinal Mountains form a bold serrate range culminating in Pinal Peak, 7,850 feet above sea and about 4,370 feet above the town of Globe, situated on Pinal Creek in the valley just described. From this peak the Mogollon escarpment, forming the southwestern boundary of the plateau region, is clearly visible some 70 miles to th.e north~ while to the southwest the eye sweeps over the Dripping Spring and Tortilla ranges, with many subordinate rocky ridges, nowhere the reservoir at Florence flashes in the afternoon sun, on the border of the desert region. The range itself has been carved by erosion from a mass of nearly vertical schists invaded by extensive batholithic intrusions of granitic rock, and the resultant forms are those usually effected by atmospheric disintegration and running water upon such a mass. The process has been influenced to some extent by the difference in resistance of the various rocks. Those schists which have undergone contact metamorphism about the peripheries of the granitic intrusives are least readily worn down and consequently form most of the ridge crests and sharp summits. The granitic areas as a rule succumb somewhat more readily to erosion and consequently determine the larger canyons and the basin-like hollows such as occur in the vicinity of the Hog ranch and the Pinal and Schultze ranches. Lowest in the scale of resistance are those schists which have not been indurated by proximity to masses of intrusive rock, and which form low foothills or spurs on the flanks of the range, especially on its southwestern side. The northeastern slope of the Pinal Range, abo_ve a line whose average altitude may be roughly placed at 4,200 feet, is abrupt and deeply scored with steep-walled V -canyons. Its spurs preRent the rocky and angular character usually associated with youthful and vigorous erosion of a metamorphic and intrusive complex. But below this line the topography, as is evident from a glance at the map (Pl. I), is of an entire!Y different kind. The general slope, descending to Pinal Creek at the rate of about 290 feet to the mile, is comparatively gentle. The main spurs, although elaborately sculptured (Pl. III, B), show soft, rounded contours, and are separated by long bran·bing arroyos of very even grade. This latter topography, as will later be more fully shown~ is that characteristic of the thick deposits of fluviatile material which in this region fill the valleys between 9651-No. 12-03-2 ·-

GEOLOGY OF THE GLOBE COPPER DISTRI.CT, .ARIZONA. the mountain ranges and lap up over the latter in long gentle slopes intricately dissected by the present streams . Toward the southeast corner · of the quadrangle the Pinal Mountains fall off rapidly to an altitude of a~out 5,000 feet, and are succeeded by several smaller ridges whose forms are evidently conditioned by monoclinal structure with southwesterly dip. South and southwest of Pinal Peak, in the vicinity of the old mining settlement of Pioneer, the ridges (collectively and somewhat vaguely known as the Dripping Spring Range) exhibit a topography which is strikingly controlled by a general monoclinal structure of northwesterly trend and southwesterly dip. (Pl. IV, A.) These ridges, carved from Paleozoic sediments and intrusive sills of diabase, show prevailingly gentle slopes to the southwest, and a series ·of steep slopes, benches, and scarps facing · the crystalline mass of the main Pinal Range. A view over this region, which, unfortunately for the discussion of the interesting structural problems it presents, lies just outside of the Globe quadrangle, gives an impression of regularity and continuity in the several ridges which closer examination dispels. The first impress~n is that produced by 'the regularity in strike and . dip and the repetition of the .same type of profile in the several ridges. The · final conclusion is that derived from a closer study of the underlying geological structure upon which the topography depends, and which is elsewhere discussed in this report. Toward the southwest and west the slopes of the main Pinal Range descend to the Dry Wash of Mineral Creek, showing a similar but scarcely so well marked a change in topography as was described on the northeastern · side of the mountains. The fissile schists, of which the greater part of this slope is composed, are associated with a rather intricately modeled surface of small spurs and ravines, which passes with .no very noticeable change into the topography produced by the erosion of the Gila formation along Mineral Creek. On the west side of the Dry Wash of ~Iineral Creek the older rocks .are buried beneath a great flow of dacite, whose surface, while forming in its larger aspect a gentle slope showing only moderate dissection, is so exceedingly rough and rocky as to be generally impassable for horses and traversable on foot only with much difficulty. Toward the northwest the Pinal . Mountains decrease in altitude to the hilly granitic basin inclosing the Schultze_ ranch. From. this ranch northwestward to the bounds of the quadrangle, between ·the northward-flowing Pinal and Pinto creeks, is an area of crowded hills showing no apparent regularity of form or arrangement. The highest of these is· Webster Mountain, and like Sleeping }3beauty and other prominent knobs in this vicinity it is capped with dacite. To the presence of the same capping is also due the flat mesa-like character of

lJ. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER NO. 12 PL. Ill In the distance is the Graham or Pi naleno Range. The town lies along Pinal Creek, which is entrenched in the Gila conglomerate. Just to the left of the center of the picture is the low pass whence th Ei railroad descends to the Gila Rive r, which flows westward past the no rth ern end of the Pinaleno Range. B . VIEW TO THE SOUTHEAST FROM THE NORTH SIDE OF WEBSTER GULCH, SHOWING TOPOGRAPHY CHARACTERISTIC OF THE GILA CONGLOMERATE. Hills in foreground are composed of Pinal schist and dacite. On the right appear some of H!e northeastern spurs of the Pinal Range. In the distance, r:sing above the dissected deposit of Gila conglomerat, , is the Pinaleno Ra nge.

TOPOGRAPHY OF THE GLOBE QUADRANGLE. some of the higher ridges, ·whose tops are usually exceedingly rugged in detail and are often bounded by precipitous slopes or cliffs, due · to erosional sapping. As a whole the topography of this portion of the quadrangle is rather minutely and irregularly diversified, and as will be later shown this is the direct com~e­ quence of deep erosive etching upon complexly faulted heterogeneous rocks. By this faulting the country has been broken into countless ~mall blocks, and in the subsequent wearing down of the region each block has been to a large extent a · unit, influencing by its position and structure the destroying agencieH at work upon its exposed portion. This complex of hills is und~rlain by granite, of which considerable areas are exposed. The characteristic topographic expression of areas where this rock form~· the surface is that of an undulating or hilly lowland, surrounded by ridges of the other rocks. In the northeastern corner of the quadrangle lies a region of bills,. within which may be distingu~shed two minor topographic divisions. The first of these, in the extreme corner of the quadrangle, consists of .a series of northwest-southeast ridges composed mainly of quartzite, with a prevailing southwest dip. They are essentially strike ridges in which the same beds are partly repeated by faulting. Between these ridges and Pinal Creek is a zone about 3 miles broad within which the valleys and relative lowlands are carved in diabase, while the ridges

and most of the higher hills are composed in their upper portions of quartzite resting with intrusive contact upon the diabase. As in the region north of Schultze ranch, the topography is irregular, and is intimately related to th~ geologica] structure, as will be shown in a succeeding section. · The hills northeast of Globe may all be regarded as the lower southwestern foothills of the Apache Mountains, and may be conveniently called the Globe Hills. The topography characteristic of areas underlain by the Gila formation has already been noted in connection with the description of the northeastern flanks of the Pinal Mountains. Its intricate modeling and yet smooth rounded contours (Pl. III, B) are found, with one or two local exceptions, wherever this formation occurs. They are the notable features in the landscape in the· immediate vicinity ·of Globe, northward along Pinal Creek, about Miami Flat and Russell Gulch,. near the head of Webster Gulch, along portions of Pinto Creek, and elsewhere. No account of the topography can be considered con1plete without some· reference to the stream channels or arroyos. The larger ones, such as Pinal, Pinto, and Mineral creeks, have broad sandy or gravelly beds of very even grade· (Pl. IV, B). This evenness of grade is not as a rule confined to open country, but persists even where the streams, such as Pinto Creek, have cut deep canyons through hard rocks. Rock in place is very rarely exposed in the bottoms of these channels, and being generally for much of the greater pa11t of the

GEOLOGY OF THE GLOBE COPPER DISTRICT, ARIZONA. year, they form the natural roads of the region. Even in the canyons it is usually found that existing obstructions to travel are due to fallen masses ·of rock rather than to falls or inequalities in the stream bed itself. " The tributaries of the main creeks exhibit similar characteristics on a smaller scale, and as a rule it is not until the steeper headwater ramifications of an arroyo are reached that rock in place appears in . its bed, and travel becomes more difficult. This regularity of grade and absence of rocky bottom are particularly noticeable in all the important channels which have trenched the conglomeratic beds of the Gila formation. CLIMATE AS RELATED TO GEOLOGIC~L PROCESSES. The control imposed by climatic conditions upon the geological processes of denudation and degradation which are immediately concerned in sculpturing the hills and in pl'oducing those varied details of form which characterize the scenery of a given district is nowhere more strikingly shown than in those arid countries of which the Globe region furnishes an example. With the exception of the upper slopes of the Pinal Mountains, which from their elevation enjoy a larger share of moisture and more luxuriant vegetation than falls to the lot of the country stretching away from their flanks, the Globe quadrangle is typically arid. Complete meteorological records are not available for any part of the quadrangle. Reports made to the Weather Bureau from Globe for the year 1894 show a mean annual temperature of 64.3°, with an extreme range from 21° in January to 108° in July, and a total precipitation of 12.87 inches. A record of pr.ecipitation has been kept for over ten years at the Pinal ranch, near the western edge of the quadrangle, and shows . an average of about 20 inchesprobable considerably more than falls in the vicinity of the town of Globe. At San Carlos, about 25 miles southeast of Globe, records for a decade past show a mean annual temperature of about 64°, a maximum temperature of 117°, and a minimum of 1°. The average annual precipitation at San Carlos during this period was about 11 inches. At .Florence, about 40 miles southwest of Globe, the mean annual temperature is about 68.5°, the winter8 being apparently somewhat warmer than at San Carlos. As the elevation of Globe is 1,000 feet greater than that of the latter place, its summers are probably somewhat cooler, the maximum at Globe in 1894 being 108° as against 111° at San Carlos. The hottest weather at Globe is usually during June and July. Throughout this part of Arizona a considerable proportion of the scanty annual precipitation falls in the form of rain during the sudden and violent downpours which are common in July and August. The effect of these rains is to wash the loose detritus down the hill slopes and to fill the dry stream beds with

U. S. GEOLOGICAL SUnVEY PROFESSIONAL PAPER NO. 12 PL. IV .A. MONOCLINAL STRUCTURE IN THE DRIPPING SPRING RANGE , SOUTH OF PIONEER. Ridges are capped by quartzite of the Apache group. The other rot ks represented are beds of Globe limestone and sills of diabase. B. VIEW DOWN THE DRY BED OF PINAL CREEK FROM A POINT ABOUT 4 MILES NORTH OF GLOBE. On the left are disturbed beds of Globe limestone containing Devontan fossils and unco nformably overlain by Gila conglomerate.

CLIMATE A.S RELATED TO GEOLOGICAL PROCESSES. transient but turbulent torrents. The erosive work done in a brief time by the more violent of these rains, locally termed '"cloud-bursts," is remarkable, and it is largely through their brief but energetic activity that the process of degradation is carried on. As a result of the prevailing aridity, the Globe quadrangle as a whole supports only the scanty and thorny growth ·characteristic of dry countries. Numerous species of cactus and yucca, with the maguey, paloverde, "hackberry," "cat elaw ," and other thorny shrubs, constitute the common vegetation of the lower slopes. In more favored localities stunted growths of oak and manzanita appear, while larger oaks and sycamores occur along some of the arroyos. In the· Pinal Range small oaks and the western juniper form a transition zone between the typical desert plants ·and the pines and firs which, although much thinned by the sawmills, still flourish in places along the crest and afford striking evidence of the climatic contrasts which, in this region, accompany any notable range in altitude. With the exception of the timbered slopes of the Pinal Mountains, and of a ·few alluvial areas along the main arroyos, the surface of the region· is almost destitute of soil. The scanty shrubbery, and the sparse grass and herbage which spring up wit};l wonderful rapidity after the rains, are insufficient to prevent such soil as may form from being quickly washed away. The humus acids, which in moister climates and beneath a covering of. soil aid in rock decay, have in this region little opportunity to form or to attack the rocks. The latter crumble or flake under the influence of sharp atmospheric changes, and these fragments are rapidly carried into the valleys. The granitic masses crumble into partieles of quartz, flakes of mica, and angular fragments or crystals of comparatively fresh feldspar. The rains acting on this disintegrated material soon wash it down to the larger streams, which carry off the quartz and mica. The larger fragments of feldspar often build up alluvial fans at the mouths of the small ravines heading in a granitic area, and such fans are remarkable for the purity and freshness of the feldspathic material which composes them, the numerous cleavage faces flashing brightly in the sun. Excellent examples of these fans were observed along Pinto Creek, north of Horrell's west ranch. They are evidently transient phenomena, accumulating until an exceptionally wet season causes Pinto Creek to rise and sweep them away. Postponing for the present the special subject of the influence of an arid climate on ore deposition, we may say in general that the dominant geological fact, traceable directly to climatic control, is the overwhelming preponderance of mechanical disintegration over chemical decay and the consequent freshness of the materials transported by the streams.

GEOLOGY 01!' THE GLOBE COPPER DISTRICT, .ARIZONA. GENERAL GEOLOGY. PRELIMINARY OUTLINE. The oldest rocks occurring within the Globe quadrangle are crystalline schists of pre-Cambrian age_. These represent ancient sediments whic~, prior to the deposition of the lowest Cambrian rocks known in this region, were upturned, compressed, intruded by granitic rocks, and metamorphosed to their present crystalline condition. They will be called ~he Pinal schists. It is highly probable that at the close of this pre-Cambrian revolution the region was characterized by a mountainous· topography. But of this no evidence remains to-day, other than can be inferred from the structures al).d textures of the pre-Cambrian rocks. It is certain that a long period of denudation and degradation reduced thi~ crystalline basement to a fairly even surface or peneplain, upon which the next younger rocks . were deposited. These later rocks comprise shales, conglomerates, and quartzites, with a local thickness of ~rom 500 to 800 feet. No fossils have been found in these beds, b~t they are thought to be probably Cambrian irl age, corresponding to the Tonto group ·of the Grand Canyon section. This entire assemblage of shales, eonglomerates, and quartzites wi1l be referred to as the Apache gro~p. Overlying the Apache group is a series of limestones with an observ~d maximum thickness of about . 400 feet. · ThPse limestones are fossiliferous, aqd their age is thereby determined as ranging fro~ Devonian to Upper Carbonifer- But it was found impracticable to consistently divide and map them as two .or more formations, and they will accordingly be treated as a unit and referred to as the Globe limestope. The reasons for this procedure are fully given in tble .sequel. Although no convincing evidence of unconformity was obtained, even 1n ·excellent exposures, it is probable that an erosion . interval separates the Glo~e limestone fr?m the Apache group. The original top of the limestone section is nowhere preserved within the Globe quadrangle. If it was once covered by Mesozoic sediments, all trace of them . bas been removed. The Globe limestone, so far as the Globe quadrangle is concerned,. doses the record of marine sedimentation. During the long geologicaJ interval between the close of the Upper Carboniferous and the extensive effusive eruptions of dacite which are provisionally referred to the early Tertiary, occurred the second great deformation of the region hnposing upon it structures responsible in ·large measure for the features of the present topography. The Paleozoic sediments and their ·underlying crystalline basement were cut by hundreds of faults. Following or accompanying the faulting large masses of diabase were

PINAL SCHISTS. intruded, chiefly in the form of sills between the sedimentary beds of the fault blocks. The intrusion of the diabase was followed by long-continued erosion, during which . the rocks were further faulted and the original sulphide ores deposited. After this period of erosion, which reduced much of the region to very moderate relief, the volcanic energies again manifested themselves through extensive eruptions of dacite, which appears to have covered all of the area with the exception of the higher portions of the Pinal The vents through which the dacite was erupted have not been identified, but the rock is known to . have a distribution far beyond the Globe quadrangle to the north and west. The time of the_ volcanic eruption may be tentatively referred to the. early Tertiary, but the Globe region affords no known facts upon which to base a more precise date. After the dacitic eruption, the region was again deformed by extensive normal faulting. The rocks, traversed br numerous faults, were carved into nearly their pn~sent topography and the waste deposited in the valleys as a v~riable fluviatile ac~umulation ; which has been termed the Gila conglomerate. of this conglomerate can not be exactly determined. It is probably early Pleistocene, or posRibly late Tertiary. During its deposition there was at least one eruption of basalt. The Gila conglomerate has also been faulted, and is generally well dissected by the present arroyos or stream channels, as a result of some regional change, either of elevation or of climate. CRYSTALLINE METAMORPHIC ROCKS. PINAL SCHISTS. Occurrence and distributio/n.-The Pinal schists, broken by granitic intrusions into very irregular masses, are abundantly present and well exposed in the Pinal Mountains, whence their name is derived. a The largest single body of schistose rocks is that underlying the greater part of the western slope of the range, stretching out ragged tongues over its crest and extending down beneath the Gila formation at the northwest foot of the mountains. Another considerable area is found near the southeast corner of the quadrangle, partly bounded on the southeast by a fault. As a rule the schists are separated by intricate boundaries from the granitic rocks .(Madera diorite, Schultze granite, etc.), which have irregul~rly invaded them. Masses of schist, ranging in size from those measurable in inches to those most a The Pinal schists of this report probably correspond to the Arizonian slates of Blake. See Geology of the Silver King mine: Engineering and Mining Journal, Vol. 35, 1883, pp. 238-239.

GEOLOGY OF THE GLOBE COPPER DISTRICT, .ARIZONA. conveniently expressed in miles, are often entirely surrounded by the . eruptive rock, and in the Madera diorite these inclusions are frequently so small and so numerous that it is impracticable to delineate schist and eruptive sep3;rately on a geological map. The practice in such cases has been to map the inclosing granitic rock and to outline only those areas of schist ~hich are of sufficient size and individual importance to appear on a map of the scale used. The great local abundance of schist fragments included in the Madera diorite may be well seen along any of the various roads that ascend the northeastern slope of the mountains. As the schists near the contact with the Madera diorite are usually· highly crystalline resistant rocks, they are less readily degraded than the eruptive rock ·under similar conditions of erosion, and, as a consequence of their greater durability, frequently stand out as ridges and spurs, while the canyons and basins are more comrr~only excavated. in quartz-mica-diorite or granite. This relation is, however, partly due to the fact that the granitic rock as a whole underlies most of the schist, and the exposures of the latter become less extensive as the whole range is degraded. As might be expected in rocks so intricately intruded by batholithic granitic masses, the Pinal schists show variable strikes and dips. They are least disturbed or contorted in the broad belt between the Hog ranch and Hutton Peak and between . Lyons Fork and the main branch of Mineral Cr~ek. In -this area regularly laminated sericite-schists, containing some bands in which the original character of quartzose grits is distinctly recognizable~ predominate, but change to more coarsely crystalline muscovite-schists as the Madera diorite is approached. The prevailing strike of the schistose cleavage in this and in other schist areas of any considerable size is northeasterly and southwesterly. The dip varies from 45° to vertical, and is generally to the northwest. In , smaller masses, included in granite and granitic rocks near the contact of the latter, strike . and dip are often very variable. As a rule the schistosity is roughly parallel with whatever larger banding, due to differences in composition of the schists, may be discernible. This fact is accepted as an indication that the -schistosity is approximately parallel with the original bedding planes of the rocks. It is noteworthy that the strike of the schistose cleavage runs nea·rly at right angles to the dominant trend of the present mountain ranges of the region. The extensive intrusive mass of Schultze granite which stretches from Bloody Tanks Wash southwestward to the Pinal ranch separates the schists of the main Pinal Range from several smaller areas to the north, which together constitute a very irregular and interrupted belt extending from Black Warrior southwestward to Powers Gulch.

PINAL SCHISTS. The schist of these northern areas is lithologically similar to that of the main Pinal Range, but the folia are much more distorted, and the, rock is often so thoroughly shattered as to resemble a fault breccia. With the exception of the area just east of Bloody Tanks and that south of Gold Gulch, it is rarely possible to detect any regular strike and dip of the schistosity. Good exposures of this crumpled, shattered schist may be seen along Webster Gulch, particularly near ~lack Warrior and the Black Copper mine; near the head of Liveoak Canyon and on Pinto Creek. The brecciation of the schist probably dates in part to an early period. At that time the schist laminre were crumpled ·and broken, apparently under slight superincumbent load, and the-open more or less lenticular spaces formed between the contorted lamin::e were filled with quartz. The result was a fragile rock, full of small surfaces of weakness, which was thoroughly shattered by later movements, such as the postdacitic faulting of the region. An isolated mass of Pinal schists occurs 4 miles a little east of north from Globe. This area is surrounded by diabase, from which rock it is very probably separated on all sides by faults. P etrography.-With the exception of occasional bands of greenish amphibolite, later to be described, the Pinal schists are generally rather light gray in color, with frequently a silvery satiny luster. In texture they range from cryptocrystalline slaty sericite-schists, through fine g-ranular fissile rocks of somewhat sugary texture, to imperfectly cleavable, highly · crystalline muscovite-schiRts. The sericite-schists, with their regular cleavage and inconspicuous crystallization, are characteristic of the larger schist areas at some distance from the Madera diorite contact. The coarser, i:nore conspicuously crystalline muscovite-schists are found near the contact, and in masses of schist inclosed by the granitic rock. In ·spite of much variety in coarseness of crystallization, cleavability, arid megascopical appearance, the Pinal schists when studied microscopically show great mineralogical simplicity and uniformity. They are essentially aggregates of quartz and muscovite (including the minutely crystalline variety, sericite), with usually a little microcline or plagioclase, and small amounts of iron ore, zircon (magnetite or specularite), tourmaline, hornblende, biotite, and chlorite. Andalusite and sillimanite are abundant in certain contact facies near the granite, but are not generally present. As a typical example of the sericite-schist there may be described a specimen collected on the trail to Lyons Fork, 2 miles southwest of the Hog ranch. This rock is bright gray, with a beautiful satiny sheen, and is cryptocrystalline in texture. It cleaves readily into thin flakes and shows small greenish knots, or . "knoten," about 2 millimeters jn .size, dotting the lustrous cleavage surfaces.

GEOLOGY OF 'J'HE GLOBE COPPER DISTRICT, ARIZONA. Under the microscope it appears as a clear crystalline aggregate of allotriomorphic quartz grains and small scales of muscovite (sericite), the two minerals being present in nearly equal amount. A thin section cut across the schistose cleavage shows that this structure is due to the concentration of the quartz and muscovite in alternating microscopical bands or layers. Small granules of opaque black iron ore (probably magnetite) are scattered rather abundantly through the principal minerals, while little bunches of green, obscure, :fibrous minerals, either amphibole or chlorite, and occasional minute prisms of tourmaline and rounded crystals of zircon, complete the list of mineral constituents. Microcline, sometimes abundant in the more coarsely crystalline schists, is here absent. Among the sericite-schists on the western slope of the Pinal Range between the Hog . ranch and the Dry Wash of Mineral Creek occur certain bands which, w"Q.ile schistose, preserve in great part the original texture of siliceous ·grits. The small pebbles·, principally quartz, still retain their original _waterworn outlines. while the :finer material of the m~trix has recrystallized as . quartz and sericite. As far as observed these grit bands have ·the . same strike and dip as the schistose cleavage, showing that the secondary structure is here -parallel with the original bedding. A specimen collected 2 miles northeast of Pinal Creek, a few hundred feet from the granite, may be taken as typical of the coarser mica-schist. This is a silvery gray rock of imperfect cleavage, which on fresh fracture flashes with irregularly bounded plates of white mica generally about half a centimeter in diameter. Under the mic~·oscope the principal constituents are see1_1 to be quartz and muscovite, with very irregular allotriomorphic boundaries. The muscovite occurs in large plates, often inclosing the grains of quartz (poikilitic structure), and as the :fine-leaved microcrystalline variety known as sericite. The remaining minerals of the rock are subordinate to the quartz and muscovite. They comprise magnetite in scattered granules, plagioclase in occasional allotriomorphic grains, :fibrolite and rutile ( ?) as acicular or capillary crystals inclosed in quartz, "zircon in short rounded prisms in quartz and muscovite, and chlorite in little interstitial fibrous tufts. Varieties of the Pinal schists · in which biotite predominates over muscovite are not common. Such occur, however, on Pinto Creek, 2 miles southwest of the Schultze ranch. Tourmaline ha'S already been mentioned as a sparing microscopical constituent of · the schists. It is occasionally present, however, in greater abundance, :and in vein quartz is common in certain of the schists near the granite. This occurrence and that of the 9haracteristic contact minerals, andalusite and sillimanite, will be again referred to when the contact phenomena of the granitic rocks are described.

PINAL SOHIS'l'S.

Associated with the prevailing silvery-gray muscovite-or sericite-schists are occasional bands of green schist of fine fibrous texture. A specimen of one of these green schists, taken from a mass of Pin~l schist surrounded by the Madera diorite 2 miles northeast of Pinal Peak, shows upon microscopical examination that its principal mineral constituents are green hornblende, quartz, and epidote, with smaller amounts of biotite, chlorite, and magnetite. The rock' is an amphiboliteschist. Origin.-The preponderance of quartz over all other mineral constituents, the still greater preponderance of quartz and muscovite together, and the general absence of calcic minerals are strongly indicative of the derivation of the Pinal schists from quartzose sediments. That at least a part of the schists are so derived is conclusively shown by the occurrence, at some distance from the intruded granitic rocks, of only partly metamorphosed beds of grit or . coarse sandstone forming an integral part of the schistose series. The presence of muscovite and microcline in the schists renders it probable that these original sediments were of granitic origin-were arkose sandstones or gr~ts similar to those of the Apache group. Their original sedimentary character is also strongly suggested by the regular banding observable in the uncontorted schists on Lyons Fork of Mine'ral Creek, on upper Pinto Creek, and elsewhere. The occasional bands of amphibole-schist, on the other hand, have a mineralogical composition such as results from the metamorphisrp of eruptive rocks. Whether this eruptive material was original1y in the form of dikes cutting the siliceous sediments, or of intercalated tuff beds, can not now be determined. It is impossible to retrace all of the vicissitudes through which rocks so ancient as the Pinal schists have passed or to dete.rmine each step in the probably complex history of their metamorphism. There can be little doubt, how:ever, but that the extensive intrusions of quartz-mica-diorite had much to do with the .transformation f~·om sediments to crystalline schists. The change had been affected at the time of the later intrusion of the Schultze granite ·(granitite), and this rock seems to have produced little if any further metamorphism of the schists. Age.-The Pinal schists have a prevailing nearly vertical schistose structure, probably in the main parallel to original bedding planes. They are intruded by granitic rocks, and both schists and intrusive masses were degraded to a peneplain before the deposition of the Apache group upon the complex basement thus provided. The Pinal schists and the quartzites of the Apache group are thus separated by a profound unconformity, comparable with the break between the Vishnu and Grand Canyon series as described by vV alcott a in the Grand Canyon of the Colorado. In the Grand Canyon, as in the Globe district, this unconformity aJour. Geol., Vol. III, 1895, pp. 312-330.

GEOLOGY OF THE GLOBE COPPER DISTRICT, ARIZONA. separates crystalline schists intruded by granite from the base of the unmetamorphosed sediments. It is -concluded that the Pinal schists and the Vishnu series are assignable with very little doubt to the same geological age. They are both part of the fundamental complex of Arizona. a The Vishnu is doubtfully referred by Walcott, in the latest paper cited, to the Algonkian, while the Grand Canyon series, above the great unconformity and ·below the Cambrian Tonto group, is more certainly assigned to that period. If the Pinal schists are, as supposed, the equivalents of the Vishnu series, they are then much older than the Algonkian rocks represented by the Chuar and Unkar terranes, being separated from the latter by a great unconformity. Furthermore, as described by Powell and Walcott in the Grand Canyon and as shown by study in the Pinal Mountains, the schists of the basal complex are chiefly of sedimentary origin. If the original definition of the Algonkian as including all pre-Cambrian sedimentary roGks b be accepted, then the PinaJ schists belong in the Algonkian, which must be considered as em bracing rocks above and below the most profound unconformity known in Arizona. It seems best therefore to · refer to the Pinal schists simply as pre-Cambrian, leaving it to future investigation to determine· whether the Algonkian is represented in Arizona by the Grand Canyon series, or by the Vishnu series, or by both of these ~:;eries separated by an unconformity apparently as profound as any described in geological literature. SEDIMENTARY ~OCKS. APACHE GROUP. General character and distribution.-The name Apache group rs here applied to a conformable accu_mulation of quartzites, arenaceous shales, grits, and conglomerates, which attain within the quadrangle a maximum thicknes~ of from 800 to a Van Rise, in his correlation paper on the pre-Cambrian rocks of North America (p. 331), has, through an oversight, included the "Grand Canyon schists" within the "Grand Canyon group" of Powell, and has thus been led to the statement that between the Vishnu series and the fundamental complex there is a great unconformity. There is no foundation in the literature of the Grand Canyon for this statement. The Vishnu series with its granitic intrusives is the fundamental complex of the region EO far as known. It is the ''Grand Canyon schists" of Powell, separated by a great unconformity from his overlying" Grand Canyon group," and was considered Archean in the earlier writings of Gilbert and Walcott. b See Van Hise, The iron-ore deposits of the Lake Superior region: Twenty-first Ann. Rept. U. 8. Geol. Survey, Part III, p. 317, footnote. In this, his latest contribution to the geology of the pre-Cambrian rocks, Professor Van Rise has found it necessary to redefine the Algonkian as including "all series which are dominantly of sedimentary origin, or equivalent in age with those which ara dominantly of sedimentary origin," and the Archean as comprising "rocks older than the Algonkian, which are dominantly of igneous origin, but which may· include subordinate amounts of sediments." It is very evident that Professor Van Hise has been driven to this modification by the adoption of a structural rather than a lithological basis upon which to discriminate Algonkian rocks from Archean or Cambrian rocks. The !iCtual divisions are marked by unconformities. The amended definitions thus appear as unsatisfactory makeshifts. They afford really no working basis for determination, and describe rather than define rocks which hav.e really been grouped by other criteria finding no expression in the definitions and having no essential connection with it. In other words, the real definition which Professor VanHise has in his mind and which he makes use of in his work are probably not those which he has published:, but some which very likely have reference to unconformities . . It seems very probable that increasing knowledge will yet demonstrate the futility of attempting to define great geological periods on the basis of an assumption as to the lithological character of their respective systems.

APACHJ!: GROUP. 1,000 feet, and are particularly well exposed on the western face of the Apache .Mountains. The gr.oup rests unconformably on the pre-Cambrian crystalline complex, and is apparently conformably overlain by the Globe limestone. The original continuity of the beds of the Apache group has been greatly impaired by faulting, by intrusions of eruptive rock, and by erosion, so that at the present time the strata occur in relatively small and often isolated blocks or rimsses, which in a general way are peripherally disposed about the main crystalline mass of the ,Pinal Mountains. In the southern half of the quadrangle the Apache group is but scantily represented, strata belonging to it occurring only in the extreme southeast corner and at the northern end of one of the ridges of the Dripping Spring Range, near the Sixtysix i'finch. A short distance to the south of the quadrangle boundary, however, these beds become more prominent, forming numerous short monoclinal ridges and maintaining a general dip of about 20° to the southwest (Pl. IV, A). In the . northern half of the Globe quadrangle the quartzites, shales, and conglomerates of the Apache group occur in numerous small fault blocks and in masses irregularly broken and often inclosed by intrusive bodies of diabase. As a rule only a part of the whole group is represented in any one block of strata, but, as . shown in fig. 2, the full local section, from the bottom of the Globe limestone down to the pre-Cambrian basement, is exposed in Barnes Peak. In the extreme northeast corner of the quadrangle, the quartzites of the Apache group form a series of short generally monoclinal ridges through which the Apache Mountains subside into the lower elevations of the Globe Hills. In the following description and discussion of .the Apache group it is proposed to divide the only complete section found, that of Barnes Peak, which appears to be representative of the greater part of the quadrangle, into four formations. The beds occurring in the numerous fault blocks of the quadrangle will then be correlated as far as possible with the formations of Barnes Peak. In many cases the identification presents no great difficulty, but in others the proper correlation: of the often fragmentary and isolated masses of Apache strata with the type section can not be satisfactorily made. The chief sources of difficulty lie, first, in the considerable lithological variation of the Apache beds within the bounds of the quadrangle, whereby conglomerates and quartzites, not always distinguishable ~rom those in the type section, appear at unexpected places in the stratigraphical column; and, second, in the remarkable manner in which a combination of geological causes has destroyed the original continuity of the beds, producing an effect of shattering and redisposition that may not inaptly be termed kaleidoscopic. No fossils have thus far been found in the Apache group, and all correlation consequently rests upon lithological and

GEOLOGY OF THE GLOBE COPPER DISTRICT, ARIZONA. stratigraphical grounds. It was this group of rocks that Marvine, a in his reconnaissance through this region in the year 1871, appears to have provisionally correlated w"ith the Tonto group of Gilbert. Much 'work remains to be done . before the history of the Apache group shall be fully understood and its formational units receive their final distinction and definition. The field for this investigation, however, lies, not within the greatly faulted area of the Globe quadrangle, but without its borders. Litlwlogy, stratigraphical seq1tence, and local correlation.-ln considering the composition of the Apache group in detail it is necessary to distinguish at the outset the beds lying north of Globe and east of Pinal Creek from those of the rest of the quadrangle. The latter, with some few exceptions, which will later be discussed, are represented by the .typical section of Barnes Peak presently to be described. The former, on the other hand~ appear to correRpond to the Apache VERTICAL AND HORI20NTAL. SCALE o zoo 300 400 soo 600 reet FIG. 2.-Northeast-southwest sectiOn through the northern summit of Barnes Peak, showing general stratigraphy and structure. Mountain section, which differs from that of Barnes Peak, as will be shown in the sequel. Barnes Peak, 5,028 feet in altitude, standing in the northwestern part of . the quadrangle, is .carved from several fault blocks of nearly horizontal strata which rest upon the eroded surface ·.of the Ruin granite. The eastern slope of the hill · is steep and bare and provides a complete exposure of the .Apache · beds from the. base of the Globe limestone, a remnant of which is preserved on the top of the hill, down to the granite (see fig. 2). The lowest bed of the group, resting upon the nearly horizontal eroded surface of the granite, is a conglomerate, varying in thickness from 1 to 6 feet. It is com'posed of imperfectly rounded pebbles of glassy vein quartz with an aReport on the geology of route from St. George, Utah, to Gila River, Arizona: Wheeler Survey, Vol. III, pp. 221-222, 1876.

U. S GEOLOGICAL SURVEY PROFESSIONAL PAPER NO. 12 PL. V A. AN EXPOSURE OF PIONEER SHALE ON THE EAST SIDE OF BARNES PEAK. B . BARNES CONGLOMERATE, ON THE EAST SIDE OF BARNES PEAK. The Barnes conglomerate is shown overlying the shale.

APACHE GROUP. occasional l:imall flake of schist, held together by an abundant pink matrix consisting of cleavage particles of orthoclase or microcline and quartz. The material of this conglomerate appears to have been of local derivation and to represent the surficial detritus of the ancient granitic plain, slightly reworked by the waves of an encroaching sea. It may be conveniently referred to as the Scanlan conglomerate, from Scanlan Pass, through which the trail passes just east of Barnes Peak. Overlying the Scanlan conglomerate are dark reddish-brown arenaceous shales having_ a thickness of about 200 feet. For a distance of about 25 feet above the. Scanlan conglomerate the sandy shales are distinctly arkose, containing abundant fragments of pink feldspar. Toward the top of the formation the shales become more quartzose, but are probably nowhere quite free from particles of granitic feldspar. Intercalated within these fissile shales are occasional beds of quartzite rarely over a foot but occasionally a foot and a half in thickness. This formation of sandy shales with its subordinate thin beds of quartzite will be called the Pioneer shale, from the old mining settlement of that name, just south of the quadrangle, where the shales are well exposed. The Pioneer shale can usually be identified over the western part -of the quadrangle by the thinness of its beds and the dark chocolate or maroon tint of the· hill slopes carved upon them. Very characteristic of the formation are abundant round or . elliptical spots, light buff in color, caused by local removal of the ferruginous coloring matter of the shale. The general appearance of a good exposure of the Pioneer shale is shown in Pl. V, A, from a photograph of a part of the eastern slope of Barnes Peak. Conformably overlying the Pioneer shale, and forming a eonspi0UOUS stratigraphical girdle about Barnes Peak (Pl. VI, A and B), is a conglomerate, from 10 to 15 feet in thickness, which may be named the Barnes conglomerate. This bed is com~osed of well-rounded pebbles of hard, white or pink quartzite, with some · reddish jasper and white vein quartz. The .average diameter of the pebbles is probably 3 or 4 inches. They are embedded in a matrix of arkose grit, which varies greatly in abundance from point to point. In some exposures the pebbles are closely crowded from top to . bottom of the bed. In others they occur in irreg·ular bands or thinly scattered through the feldspathic quartzite. Overlying the Barnes conglomerate are beds of quartzite, with an aggregate thickness of about 400 feet. In a. region singularly lacking in apt names for its topographical features a thoroughly appropriate designation for this quartzite is not available. Distant views indicate that it is prominently developed in the Sierra Ancha, north of the quadrangle, and if this surmise is correct, a formation name derived from these mountains would perhaps be the most s~tisfactory that

GEOLOGY OF THE GLOBE COPPER DISTRICT, ARIZONA. could be chosen. It is safer, however; to adopt provisionally a name less desirable, but .derived £rom a locality where the quartzite is known to occur. For the present, therefore, the quartzites lying between the Barnes conglomerate and the Globe limestone will b.e referred to as the Dripping Spring quartzite, from the Dripping Spring Mountains, a term somewhat vaguely applied but apparently embracing the monoclinal ridges south of Pioneer which owe their boldly scarped outlines to these quartzites and to the underlying Barnes conglomerate (Pl. IV, A). At Barnes Peak the lower 175 feet of the Dripping Spring formation consists of massive beds of streaked buff and pink quartzite, the former being the dominant color. The beds are not sharply defined, the more massive quartzite occurring in bands 10 feet or so in thiekness, which grade one into the other through· rather shaly and laminated varieties. As a rule it is difficult to determine the plane where one beds stops and another begins. These quartzites and the underlying Barnes conglomerate are the most resistant portions of the Apache group, and commonly find prominent topographical expression as cliffs and cuestas. The upper part of the Dripping Spring quartzite iR characterized by thinnerbedded, hard, laminated quartzite, usually streaked with iron oxide and decidedly rusty in general appearance. These beds are apparently conformably overlain at Barnes Peak by the Globe limestone. A graphic summary of the foregoing description of. the type section for this part of the quadrangle is given in Section A, of Pl. VII. No fossils have yet been found In any part of the Apache group. It is now possible to compare with the Barnes Peak section the more fragmentary sections of Apache strata in other parts of the quadrangle. ·In the greatly shattered district lying north and northwest of Webster Mountain and extending beyond the northern edge of the quad.:·angle, little departure is observed from the -Barnes _£.eak section, except in the varying number and thickness of the sills of decomposed diorite-porphyry interealated in the Pioneer shale. As might be inferred from the frequent exposures of the granite basement in this faulted area, the lower beds of the Apache group predominate, although the upper beds are frequentl:r present. The general distribution of the latter is indicated on the geological map by the areas of Globe limestone which, when not bounded by faults or cut off by intrusions of diabase, overlie the Dripping Spring quartzite. The granite in the. northwestern corner of the quadrangle appears to have been worn down to an even plain prior to the deposition of the Apache group. some points the arkose Pioneer shale is found resting directly upon the old . surface with no intervening Scanlan conglomerate. Usually, however, the latter is represented by a . bed, from 1 t? 2 feet in

U. 8. GEOlOGICAl SURVfY PROF£ qo Al PAP£R NO. 12 PL. VI B BARNES PEAK , FROM SCANLAN PASS. The lower slopes, in the ravine are on granite; above this, with no topographic break come the Scanlan con lomerat~ and Pioneer sh le. The Barnes conglomerate and lower division of the Dripping Spring quartzite appear in the cliffs above, wiMie the summit of the peak (on A ) ts composed of the upper Dropptng Sprin quartzot Th. northeast rly ono;~ of the three faults shown on fig. 2 is visible on R. (' ]) VIEW FROM TOP OF NEEDLE MOUNTAIN OVER THE INAL C REEK AREA OF THE GILA CONGLOMERATE. To the right of lJ is seeo the Schultze ranch, surrounded by granit ic hills, behind which rise th high r summits of the PinAl Rang . In the middle-ground, oody T nks Wa h may b d from tho ranch down to Miom1 Fl ts n ar the I ft of(' Surrounding th s flats nd stretching far to th south tnto the drainage bastn of the Gila River, are th low sculptured spurs of Gila conglo rate rtSong st on the rirht ag 1nst th slopes of th Pin I R1nge

APACHE, GROUP. thickness, of quartz pebbles in the usual pink feldspathic matrix. Occasionally th. i: bands of similar pebbles occur in the shale.:::; a foot or more above their base. On the eastern side of Ruin Basin, near the northern edge of the quadrangle; about 200 feet of nearly horizontal Pioneer shale is overlain by the Barnes conglomerate, and the latter by about 50 feet of the Dripping Spring quartzite. A f~ult separat~s the shales from the Ruin granite on the west, so that the base of tfue Apache group has not been exposed. I Between Ruin Basin and Gerald's ranch the Apache be~s, apparently repre-:- sen~ing ehiefly that portion of the group lying· above the Pioneer shale, have beey eonsiderably disturbed by irregular sill-like intrusions of diabase and by faults. Beds having the general character of the upper part of the Dripping Spring quartzite are to all appearances · conformably overlain by the Globe lime- -stone a mile and a quarter northwest of Gerald's house and both north and west of Sleeping Beauty Peak. West of Black Vvarrior, in W ~bster Guleh, the Apaehe group has but fragmentary repr~sentation. Its oecurrence here is of interest, however, as affording the only exposure in the quadrangle illustrating the direct relation of the group to the Pinal schists. The Scanlan conglomerate is here represented by a rather striking breccia eonsisting of more. or less angular fragments of white v~in quartz embedded in a silvery gray matrix of schist particles. This change in the material of the c~mglomerate from point to point shows the very narrowly defined local derivation of its materials. Half a mile north of the Continental mine thin beds of hard red quartzite and of pink grits containing abundant particles of reddish . granitic feldspar rest with ·gentle westerly dip upon an erosion surface of coarse reddish Sehultze granite. The aggregate thiekness of these beds is about 200 feet. A few inches of Scanlan · eonglomerate usually separates the quartzite from the granite, but is not always present. These grits and quartzites thus occupy the usual position of the Pioneer shale, and appear to be a gritty and quartzitic facies of ·that formation. Lithologically, however, they ·might readily be taken for certain of the higher beds of the Dripping Spring quartzite. About 2t miles southwest of the Continental mine, in the gorge of Pinto Creek, are excellent exposures of some of the upper beds of the Apache group and of the overlying Globe limestone, somewhat complicated, however, by the usual faults. The stratigraphical sequence in this locality is shown in Sections D and . E, of Pl. VII. Section D represents the occurrenee of the in the west wall of the canyon haJf a mile upstream from the edge of the quadrangle. Section E corresponds to the east side of the gorge about a quarter of a mile farther downstream. Both sections have at the base thin-bedded 9651-No. 12-03-3

G EO LOGY OF THE GLOBE COPPER DISTRICT, ARIZ ON A. rusty-red quartzites or sandstones, whose weathered surfaces are often dotted with little wart-like excrescences, probably due here, as elsewhere in the quadrangle, to the prese-nce of minute nests of_ sericite dissemi·nated through the mass of the rock. Within' these beds, on the west side of the canyon, occu1s a . stratum of hard siliceous co~glor.O:erate, 6 feet ·in thickness, which is lacking or coneealed on the east side. In both sections there appears a heavy bed, probably from 30 to 50 feet in thic~ness, of a "rather coarse, rusty conglomerate. The pebbles of this conglomerate are p~incipally quartzite, and appear to be lithologically identical with the reddish, warty quartzites which underlie them. No visible unconformity could -be detected, however, in either Section. Overlying tlie conglomerate are thin-bedded dark grits, sandstones, and shales, the latter occasionally showing obscure fucoid markings. On the west side of the canyon (Section D) these beds reach a total thickness of . about 100 feet, and are overlain by a 6-foot bed of ' conglomerate containing some well-rounded quai·tz pebbles, but made up chiefly of rather angular pebbles of quartzite up to ' 8 inches in diameter. Immediately above the conglomerate is an intrusive sheet or sill of decomposed diorite-porphyry abo~t 6 feet in thickness. Apparently the same sill appears in the east wall of the canyon, about 70 feet above the thick brown conglomerate. Above the diorite-porphyry, in both sections, appear hard, yellowish, thin-bedded calcareous .grits, containing scattered pebbles of quartz and quartzites, and immediately underlying gray Globe limest6nes which contain few disti net fossils near their base. From the preceding description it is cleai· that the Pinto Creek sections differ radically from that of Barnes Peak, although the two localities are only a little over 5 miles apart. The_ stratigraphical position of the beds on Pinto Creek, immediately beneath the Globe limestone, into which they apparently grade . through . some calcareous grits, is that of the upper portion of the Dripping Spring quartzite, although there are present two conglomerates not recognized in the Barnes Peak section. Some of the thick, rusty lower conglomerate was recognized on Gold Gulch, 1 mile du~ west of the summit of Porphyry Mountain. But between this point and Barnes Peak the more or less isolated, faulted fragments of the Apache group throw no light upon the lithological relation or gradation between the dissimilar beds underlying the Globe limestone at the two localities. Ft:om -the gorge of Pinto Creek southward the Apache group is unrepresented until ..the s~uthern border of ~be quadrangle is reached. The small area shown on the map (Pl. I), near the Sixtysix ranch, is at the northern end ·of the ridge upon which, some miles to the southwest, is the mining town of Troy. The rocks here are thin-bedded reddish quartzites and red shales showing reticulated mud cracks.

U. GEOLOGICAL URVEY ng quartzite. Apach group Bam B conglom ra ... nglom rat . . . Ruin gran It . (.1) Rt\ H

l"lon r !lbal ·an tan<' n tom r·at Mad ra.dlorl ( 8) PI N~:F:H. SECT10 '. lobe lime tone l'l n r shal Ora nlt .. . ... . ( ') PA rn: )!T. ErT IO,'. (F.) PI ' T CHF.EK , ROF:. GENERALIZED COLUMNAR SECTIONS. (!) PROFE 510 AL PAPER NO. 12 PL. VII lob lim Jo'E't'L

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APACHE GROUP. Their position within the Apache group is as yet unknown, as their study was not carried far beyond the limits of the quadrangle. In the southeastern corner of the quadrangle apparently the entire Barnes Peak section is represented, although the beds are much disturbed by diabase intrusions and by faults. In a general way-the diabase separates the topmost beds of the Dripping Spring quartzite, which immediately underlie the Globe limestone, from the bulk of the · Apache group resting upon the Madera diorite (Pl. I). A generalized columnar section of tlie Apache gr?up as represented in this part of the district is given in Section B, Pl. VII. This section resembles very closely. the typical one of Barnes Peak. The Pioneer shale here has a thickness of about 150 feet. In some places the shales rest directly upon the worn and weathered pre-Cambrian surface of the Madera diorite, and in such cases are very conspicuously feldspathic, being made up largely of particles of pink feldspar derived from the underlying Madera diorite, the coarser particles of feldspar and quartz frequently forming well-defined grit bands near the base of the shales. At other points the Scanlan conglomerate is well developed, reaching a thickness of 5 feet. This conglomerate, however, does not everywhere rest directly upon the Madera diorite, but is occasionally separated from the latter by a coarse arkose containing fairly fresh feldspar fragments over an inch in length. This material, which is not readily disting·uishable from the. massive Madera diorite beneath it, reaches a :r;maximum thickness of about 12 feet and grades insensibly· into the matrix of the Scanlan conglomerate. Above the Pioneer shale comes the Barnes conglomerate, about 15 feet in thickness and crowded with well-rounded pebbles of quartz, jasper, and quartzite (Pl. VIII, A). The Dripping Spring quartzite overlies the Barnes conglomerate and is similar to that at Barnes Peak, although somewhat thinner bedded. (See fig. 3.) Section B, Pl. VII, represents the succession of the Apache beds 2-! miles southwest of Pinal Peak and accordingly just outside of the quadrangle. The correspondence with the Barnes Peak section is close, the most striking difference being in the presence of thick sills of yellowish decomposed diorite-porphyry. The Scanlan conglomerate moreover has here a thickness of from 6 to 10 feet and consists of well-rounded pebbles of quartz and hard compact quartzite up to 8 inches in diameter. The conglomerate rests as a rule upon the ancient reddened ·surface of the Madera diorite, but is locally separated from the latter by a sill of diorite-porphyry. Immediately above the conglome~·ate and · beneath the characteristic dark-red Pioneer shales there intervene from 15 to 30 feet of lightcolored highly feldspathic grits, in fairly thick beds. These grits are not developed in the vicinity of Barnes Peak.

GEOLOGY OF THE GLOBE COPPER DISTRICT, ARIZONA . . It appears from the I :foregoing descriptions that, with the exception of the portion of the group exposed in the gorge of Pinto . Creek, which can not yet be satisfactorily correlated, the Barn.es Peak section is fairly representative of the Apache group as the latter occurs in the western and southern halves of the quadrangle. In the portion of the quadrangle lying north of Globe and east of Pinal Creek the Apache group is very imperfectly represented by fragmentary masses of strata that nowhere afford a complete local section of the whole group. The nearest approach to such a section is found on the western face of the Apache VE:FfTICAL. A"'O HORI'ZONTAL. SCALE s.s.w a:oo:&.:::aa;;csaoS...""""'s'ieoo'===:izo&o...,""""'3;;,;:o:=o 1'eet N.N.E. FIG. 3.-Sketch profile of cuesta fronting the Pinal Range, about 3 miles southwest of Pinal Peak, near Pioneer. Mountains (fig. 4), and is given m conventional columnar forn1 in Pl. VII, 0. The lowest beds rests, as usual, upon a worn granitic surface, in this case apparently a biotite-granite. The Scanlan conglomerate, however, was not rec~ ognized. In its place are beds of hard pinkish quartzites with an aggregate thickness of nearly 200 :feet. The basal bed is a tough, fine-grained, :faintly striped pinkish ·quartzite, speckled with little greenish nests o:f chlorite or sericite, and containing much detrital feldspar. This is succeeded by thick beds of similar character, varying. so~ewhat in texture., which attain a total thickness of 75 feet. Above these thick · beds lie about 125 feet of thinner beds which resemble more and more the Pioneer shale until finally they pass upward with

APACHE GROUP. no well ~defined-plane of separation into beds which have all the characteristics of the latter formation. These transition beds resemble so closely some of ·the upper portions of the Dripping Spring quartzite, as exposed in other parts of the quadrangle, that no certain lithological criteria for their distinction were discoverable. If the quartzite beds just described as underlying the Pioneer shale in the Apache Mountains be really the equivalent of the Scanlan cong-lomerate, they may be called the Scanlan quartzite. But too little work has yet been done beyond the bounds of the quadrangle to render it certain that the Scanl~n conglomerate is everywhere absent beneath these quartzites, and for the present the latter will be referred to merely as '' the lower quartzite." The Pioneer shale reaches a thickness of about 200 feet in the Apache Mountains and exhibits the same lithological character as at Barnes Peak. It is overlain by the Barnes conglomerate, which is locally a bed of hard buff sandstone or quartzite, 15 feet thick and containing subordinate bands of well-rounded quartz pebbles. The Dripping Spring quartzite forms the crest of the Apache Range, and is repre- ~ented by thick beds of buff quartzite, of which about 150 feet remain, the higher beds hav~ng been removed by erosion (fig. 4). The striking change in the Apache group through the addition of 200 feet of quartzite below the Pioneer shale, the absence of a continuous section of the upper beds of the Dripping Spring formation, and the great disturbance due to

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fT1 diabasic intrusions and to faulting, combine to render impossible the satisfactory

GEOLOGY OF THE GLOBE COPPER DISTRICT, ARIZONA. correlation of the various quartzitic masses in the northeastern part of the quadrangle. Near the. northern edge of the area · the '' lower quartzites " are found resting in small remnants upon the Ruin granite . . About the Old Dominion mine the Globe limestone is apparently underlain by rather thin-bedded quartzites of the Dripping Spring formation, while the lower, heavier beds of the same formation determine most of the strike ridges northeast of Ramboz Peak. In the extreme northeast corner 'of the quadrangle a little Globe limestone appears to overlie rusty grits containing ·quartz pebbles up to 5 millimeters in diameter. ·About 2 miles northeast of Ramboz Peak, which is capped by Barnes (?) conglomerate; are cherty · beds, alternating with siliceous conglomerates and grits. The stratigraphical position of these cherts, grits, and conglomerates is not definitely known. It is probable that they either represent the upper part of the Dripping Spring quartzite or - else are the equivalent of a part of the Globe limestone. Future study of the region east of the Globe quadrangle will probably result in finding more satisfactory sections of the Apache group and the Globe limestone, and thereby throw light upon their subdivisions and mutual relationship. A_ge.-As no fossils have been found in the rocks of the Apache group, the precise age of these beds can not be determined until their stratigraphy is studied over a much broader field than that of the Globe quadrangle. There are, however, certain general considerations that indicate, although they do. not fix, the geological period to which the group belongs. As the overlying Globe limestone contains. Devonian fossils, the Apache group can not be younger, and is probably pre-Devonian. As the quartzites rest unconformably upon the Pinal schists and intrusive rocks of the pre-Cambrian crystalline complex, they are evidently much younger than the latter. So far, therefore, its stratigraphical position is concerned, the .Apache group may be ·Algonkian, Cambrian, or Silurian. The apparent absence of fossils, however, · points to the. Cambrian or Algonkian rather than the Silurian, which appears to be well provided with organic remains wherever found in Arizona. At Clifton, about 90 miles easterly from Globe, Mr. Lindgren a has obtained a characteristic .and abundant Lower Silurian fauna. As between Cambrian and Alg·onkian, the former seems to be the more probable. As shown by Powell b and later . ·observers, the Algonkian Grand Canyon group is separated from the Cambrian · ·'Tonto group by a well-marked angular unconformity, the Tonto in places 1:esting upon the Vishnu schists and their associated granitic intrusives. · As no equivalent unc~nformity could be detected between the Apache group and the Globe limestone, it is probable that · the former corresponds to the Tonto group rather than to the Grand Canyon group-a conclusion in general agreement with the aOral communication. bGeology of the Uinta Mountains, etc., Washington, 1876, p. 70.

U. S. GEOLOGICAL SURVEY A. BLOCK OF BARNES CONGLOMERATE, SOUTHEAST CORNER OF THE QUADRANGLE. PROFESSIONAL PAPER NO. 12 PL. VIII B . SHEETED SCHULTZE GRANITE ON PINTO CREEK, WEST OF SCHULTZE RANCH.

GLOBE LIMESTONE. earlier correlation of Marvin e. a The Apache group IS accordingly placed provisionally in the Cambrian. It probably corresponds in part to the Dragoon quartzites of Dumble/ which are reported as underlying limestones containing Devonian and Carboniferous fossils in the Dragoon, Whetstone, Chiricahua, and Mule mountains. GLOBE LIMESTONE. General character and distribu.t·ion.-The name Globe limestone is here applied to a formation consisting almost exclusively of limestone in beds usually ranging from 1 to 6 feet in thicknesR. The formation rests upon the Apache group with no visible angular unconformity and attains a maximum thickness of at least 700 feet, as exposed in the canyon of Pinto Creek. Its upper limit, everywhere within the quadrangle(, is a surface of erosion, the total original thickness being therefore unknown. . Although the Globe limestone apparently rests conformably upon the Dripping Spring quartzite, there are some gTounds, such as the absence of recognizable Silurian beds and the occurrence of the basal quartzitic breccia noted on page 40, for suspecting that the two formations are really separated by an interval of erosion. In the Grand Canyon, according to alcott, c the Devonian strata, with a maximum thickness of 100 feet, rest unconformably upon the Tonto beds, but this unconformity can rarely be detected in actual exposures. As far as could be seen in the Globe district, the limestone beds are themselves conformable throughout. The general distribution of the Globe formation is that of the Apache group, whi~h it overlies. Natural sections, however, are. even more fragmentary than in the case of the latter group, and it was found impracticable to carry over the whole area such lithological and paleontological distinctions as . might occasionally be made in some of ~he more continuous sections. Lithology and stratigraphical sequence.-The basal portion of the Globe limestone is lithologically 1 varied in different parts of the quadrangle. In the canyon of Pinto Creek ·and in the greatly faulted · region between Ruin and Granite basins the base of the formation consists of about 10 feet of calcareous grits, succeeded by gritty fossiliferous limestone which in turn are overlain by. bard gray and buff limestones, with occas~onal bands of calcareous shales, grits, and thiu-bedded quartzite. In other localities, as at Barnes Peak, north of Sleeping Beauty Peak and near the Old Dominion mine, the basal grit::; ar~ absent, and gray limestone, not noticeably fossiliferous, rests directly upon thin-bedded Dripping Spring quartzite. About three-fourths of a mile north of the I · X L mine the base of the Globe limestone is separated from the underlying quartzite by a a Loc. cit., p. 221. bNotes on the Geology of ~southeastern Arizona: Trans. Am. Inst. Min. Eng., Vol. XXXI, pp. 14-19, 1902. c Pre-Carboni'ferous strata in the Grand Canyon of the Colorado, Arizona: Am. Jour. Sci., 3d series. Vol. XXVI, 1883, p. 438.

GEOLOG.Y OF THE GLOBE COPPER DISTRICT, ' ARIZONA. thin bed of siliceous breccia containing angular fragments of quartzite. Wherever thick sections of the Globe limestone are exposed it is found that the alternating buff and gray limestones with subordinate grits are overlain by gray, sometimes slightly pinkish, crinoidal limestones, · usually in rather thick beds, but also some cherty beds and an occasional bed of siliceous eonglomerate. As a rule, however, the limestone occurs in such small faulted masses t~at it is rarely possible to determine the stratigraphical horizon of the beds exposed in a given block. The least fragmentary sections of the Globe. formation found have failed to show· any well:.defined or re?ognizable plane of litholog1cal or structural distinction within the limits of this sequence of beds, among which hard, gray limestones , greatly predominate. Age local correlation.-Fossils were found within the Globe limestone at several points, and their invest'igation by Prof. Henry S. Williams and Dr. G. H. Girty has · shown that they range from the Devonian to the Upper Carboniferous. Unfortunately, however, no single section has been found to clearly embrace the whole formation from its base td the highest fossiliferous Carboniferous strata preserved. Professor Williams has very kindly furnished a brief note on the Devonian fauna, while Dr. Girty has rendered a similar service( in ·regard to the Carboniferous species. These notes are here printed in full. DEVONIAN FOSSILS OF THE GLOBE QUADRANGLE, ARIZONA . By HENRY s. WILLIAMS. Two collections of fossils made by Dr. F: L; ·Ransome 1n the Globe quadrangle, Arizona, were submitted to the writer November 14, 1901, and March 17, 1902, for report upon the age of the horizon represented and the list of the faunas. The collections comprise in all 10 _small lots, which are designated A, B, C, etc., and _labeled as follows: A. Limestone bluff, west side of Pinal Creek, 3! miles northwest of Globe. ·Thin bed of gray limestone about 100 feet above base of exposed limestone section. B. Same locality as A. Band of graylimestone about feet above A. C. Buff limestone about 20 feet thick, immediately overlying bed B. D. Gray limestone, with crinoid stems, overlying C. About 40 ·feet thick to top of section. E. One-quarter mile southwest of Sleeping Beauty· Peak, from near base of limestones which. rest on quartzite. · F. Eastern slope of 5~300-foot limestone h~ll, southeast corner of quadrangle. G. Same locality as F, and probably from· same bed.

U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER NO. 12 PL. IX A. GLOBE LIMESTONE, CONTAINING DEVONIAN FOSSILS; ON THE ROAD TO TONTO BASIN, ABOUT 4 MILES NORTH OF GLOBE. The lower fossiliferous bed is indicated by the letter A. B. WHITETAIL FORMATION, AS EXPOSED BY THE ROADSIDE NEAR THE CONTINENTAL MINE.

DEVONIAN FOSSILS OF THE GLOBE QUADRAN~LE. H. Limestone hill, west side of Gold Gulch. I. Steep slope forming east side of Pinto Creek gorge on western edge of quadrangle. J. Same locality as I. About 40 feet higher in section. List of jaunules. A. B. D. E. F. G. H. J. [ - 1. Atrypa reticularis Linn . X -.. 2. Productella hallana Walcott. X ? 3. Stropheodonta calvini Miller X --- ... - ... -.. i X 4. Cyrtia cyrtiniformis (H. and ,V.) X X 7. Spirifer whitneyi Hall. - . 7 8. Reticularia fimbriata (Conrad) . . . X . 11. - ---: X 1

12. Orthothetes chemungensis (Con.) var.. . X . 13. Dielasma cf. calvini (H. and ,V.) X The accompanying list of species has been identified and their presence in the several faunules a is indicated by the checks in the vertical ~columns opposite the names of the species. The names by which the forms have been recognized by American authors have been used, though in several cases the forms here met with may be regarded as but varieties of species described by European paleontologists. With the exception of the faunule H, the several faunules are probably from the same geological formation, as indicated by th.e species as well as by the similarity of the rock in which they are contained. The fauna represented is the same as that from Rockford and Indepenclence, Iowa, which as a fauna may be appropriately called the Pugnax fauna, on account of the wide distribution of Pugnax pugnus wherever the associated species of the fauna appears. The fauna appears in the New York column after the Tully limestone in the fossiliferous zone preceding the typical Chemung formation, in what has been called the Ithaca formation in: c~ntral New York. a I. e., local faunas.-F. L. R.

GEOLOGY: OF THE GLOBE COPPER DISTRICT, ARIZONA. Taking the first 12 species of the list, it will be noticed that they are all ' brachiopods. In the material examined they are the . only class of organisms recognized, except the crinoid stems; the latter may have supplied the calca,reous material for the limestones in which the species are preserved. The species, or varieties of the same species, are d9minant in a fauna of wide distribution in the Northern Hemisphere. Eight of the 12 species are represented in the Devonian of Nevada a.nd Utah; 9 have been report~d from the Manitoba and Mackenzie River province; all of the 12 from the Lime Creek formation of Iowa; 7 are present in the Lummaton limestone of southern England; 9 of them are reported from Russia; 5 of them are among the limited number of known Chinese Devonian species; and 6 of them have been seen in the Ithaca zone of central New York between the typical Hamilton ' and the typical Chemung formation. They constitute the typical species of . the Lime Creek formation of Iowa, but in New York the species are mostly rare among the species occupying the Ithaca formation. Bo far as at present known, the fauna did not coexist with the typical Spirifer disjunctus fauna of the New York province, but in the eastern part of the State several of the dominant species of the Tropidolep t~ts fauna of the Hamilton appear in the san1e fossiliferous zone· with these species. As measured by the New Y or.k standard geological column, the P~tqnaw fauna -is neo-Devonian in age, and is to be correlated with the epoch of the Ithaca formation. In its general distribution in Europe it is neo-Devonian rather than mesoDevonian, and altho~gh there its · species have a .Carboniferous aspect, they are occasionally represented in faunas classified as of meso-Devonian age. It is the!'efore appropriate on paleontological grounds to classify the formations holding the fauna in Arizona as early neo-Devonian. HENRY s. w NEw HAVEN, CoNN., .March 24, 1902. CARBONIFEROUS FOSSILS FROM THE GLOBE QUADRANGLE, ARIZONA. By GEORGE H. GIRTY. The collections from the Globe quadrangle, Arizona, referred to the writer by Mr. Ransome, contained both Devonian and Carboniferous faunas. The Devonian faunas were sent to Professor Williams, and have already been reported on. The Carboniferous faunas are as follows, the numbers and localities of the different collections being supplied by Mr. Ransome:.

CARBONIFEROUS FOSSILS FROM THE GLOBE QUADRANGLE. No. 337. Gorge of Pinto Creek, east side~ about 300' feet above lowest bed of limestone exposed in creek bed. Gray limestone with some chert. Rhom bop ora lepidodendroides. Seminula subtilita. Eumetria or Hustedia sp. No. 339. Gorge of Pinto Creek, east side. Professor \Villiams's list. Productus cora ( frag. Gray limestone overlying J m No. 340 A. Top of limestone section, with an exposed thickness of about 400 feet, on east side of gorge of Pinto Creek. Gray limestone. Productus ( frag.), semireticulatus type. Productus? similar to Marginifera splendens. Spirifer sp. Reticularia sp. No. 340 B. ,About 20 feet below 340 A. Productus semireticulatus (different from that in 444). No. 340 D. About 250 feet below 340 B. Some shaly and cherty beds m intervening limestones. Fusulina cylindrica. Productus semireticulatus. Squamularia perplexa. No. 444 A. West side of Gorge of Pinto Creek, in little ravine, about 50 feet below dacite cap. · Hard pinkish limestone in beds up to 3 feet in thickness. Productus cora? ( frag.). Productus punctatus. Myalina subquadrata? (frag. ). Aviculopecten sp. (frag. ). No. 444. Same locality as No. 444 A. Archreocidaris sp. Orbiculoidea sp .

Derbya crassa (frag.). Productus semireticulatus. Spirife~ cameratus. Spirifer rockymontanus. ·Myalina subquadrata. Phillipsia sp.

GEOLOGY OE' THE GLOBE COPPER DISTRICT, ARIZONA. No. 444 B. Same locality as No. 444 A, but about 100 feet lower in section. Rhombopora lepidodendroides . . Derbya crassa. Productus, semireticulatus type. Spirifer cameratus? Spirifer boonensis? Seminula subtilita. No. 475: Southeast slope of Sleeping Beauty Peak, close to fault cutting off limestones on the southeast. Yellowish, highly fossiliferous bed in prevailing gray limestone~. Oampophyllum torquium. Crinoid fragments. Productus inflatus. Marginifera? sp . . Spirifer cameratus. Spirifer boonensis. Squamularia perplexa. Seminula · subtilita. All of these faunas · are clearly Carboniferous~ and, on the whole, I am iQ.clined to believe them all Upper Carboniferous, though it may be that 340 A and 337 are of Mississippian age. GEORGE H. GIRTY. WASHINGTON, D. C., April 15, 190tE. The limestone sec~ion on Pinal Creek north of q-lobe, from which were obtained lots A, B, C, and D of Professor Williams's note, is shown in Pl. IX, A, the lower fossil horizon being indicated by the letter A. Below this ho:Hzon the section exposes a thickness of about 100 feet of fairly heavy beds of gray, sometimes slightly buff, limestone, containing as far. as seen no well-preserved fossils. These lower unfossiliferous beds of the Devonian section (which may possibly be preDevonian, although the stratigraphic sequence is apparently unbroken) .are lithologicatly indistinguishable from similar beds occurring elsewhere above Upper Carboniferous fossils, and therein consists one of the obstacles to successfully.cal correlation in . a region of faulted fragmentary stratigraphical masses. Between the fossil horizons A and D there is· exposed a thickness of about 35 feet of gray and yeilow limestones, inclosing characteristic Devonian forms and conformably overlain by about 40 feet of gray limestone containing ' crinoid stems. The upper limit of the section is an eroded surface covered by Gila conglomerate. It is possible, as Professor Williams points out, that the · whole section is Devonian, but it was not found practicable to discover any lithological

GLOBE LIMESTONE. distinction between the gray crinoidal limestone and similar beds known to occur elsewhere in the Carboniferous portion of the Globe formation. Some of the best sections of the limestones are found in the g·orge of Pinto Creek, and three of these are given in columnar form in Pl. VII, D, E, and F. · Section E -is particularly instructive. It shows at the base a considerable developme-nt of the calcareous transitional grits, which here attain a thickness of about 75 feet and are provisionally regarded as a part of the Glo~e formation. Above the grits come about 130 feet of gray limes~ones. apparently corresponding to the similar beds underlying the fossil bed A, on Pinal Creek. Then follow 3' feet of grit and quartzite, and 50 feet of gritty limestone, fossiliferous in part but from which no satisfactory collection was made. Overlying these are about 100 feet of rather rusty lime:::;tones contain.ing the · Devonian forms listed by Professor Williams under I and tT. It thus appears that the Devonian part of the Globe limestone has a probable thickness of nearly 300 feet. Above the fossil horizon J come ·200 feet of gray limestones that are ~ot rwticeably fossiliferous and may be of Carboniferous age. Farther up the slope occur gray limit:!tones carrying Productus cora (No. 339 in Dr. Girty's note) and therefore of Carboniferous age. There is a possibility, however, that the continuity of the section may be broken by a fault, at the point where the column E, (Pl. VII) is terminated, below the knowJl Carboniferous. In section F, Pl. VII, is represented a section also from· the east side of the gorge of Pinto Creek, but taken at a point a little farther north. The upper 500 feet of this section is composed of gray limestones alternating with thin cherty beds and containing Carboniferous fossils. Conformably below are 20 feet of rusty red fossiliferous limestones which are probably Devonian, although no fossils were collected at this point. It appears from the Pinto Creek sections that the Globe formation includes in its lower part at least 300 feet of Devonian st_rata and in ~ts upper part at least 500 feet of Upper Carboniferous beds. No unconformity, however, has been found between the beds belonging to these different periods. \Vhile future work in the broader region about the Globe quadrangle may result in the discovery of such an interruption of sedimentation and in the consequent splitting up of the Globe limestone, it is believed that no such division is at present practicable within the area covered by this report. The case of the Globe limestone recalls that of the Ouray limestone in Colorado, to which Cross a has recently called attention. _The Ouray limestone, an apparent stratigraphical unit containing characteristic Devonian fossils, was at first referred wholly to that period. Lat~r work, however, has 'resulted in the discovery a Geologic formations versus lithologic individuals: Jour. Geol., Vol. X, 1902, pp. 234-235.

GEOLOGY OF THE GLOBE COPPER DISTRICT, .ARIZONA. of Lower Carboniferous fossils in the upper part of this limestone unit. There is nothing: as yet known that precludes the presence of Lower Carbonifero'!s beds in the Globe limestone between th€5 known fossiliferous Upper Carboniferous and the known fossiliferous Devonian. The absence of any recognizable unconformity within the mass of liinestone strata is suggestive of uninterrupted deposition from the Devonian to the Upper Carbo.niferous, and consequently of the . presence of some Lower Carboniferous or Mississippian. The paleontological note furnished by Dr. Girty also intimates that the Lower Carboniferous may be represented. WHITETAIL FORMATION. General character, distribution, and stratigraphic position.-The Whitetail formation (so named from Whitetail Gulch and Spring) is a deposit of rather coarse and often somewhat angular stony detritus that lay in the. hollows of a former Ian~ surface, and . with the . latter was covered by . the dacite eruptions. The deposit varies much both .in thickness and lithological character, and where its relation to the ~acite is not clearly shown can not alw~ys be distinguish~d from certain facies of the younger postdacitic Gila conglomerate. -It appears to have accumulated particularly upon areas of diabase, and in such situations angular or very imperfectly rounded fragments of the underlying eruptive rock with occasional pebbles of limestone make up the . bulk of the deposit, which is usually weathered and partly decomposed. Pl. IX, B, from a photograph of a roadside cutting just southeast of the Continental mine, gives a good idea of the usual appearance of the deposit. The fragments range from a fraction of an inch to a foot or more in size. Material similar to that described and illustrated occurs on Pinto Creek, just above the gorg~, both north and south of Gold Gulch and near the head of Whitetail Gulch. ' ' Three-quarters of a mile northwest of Continental Spring excellent exposures of the Whitetail fo~mation may ·be studied on the south side of a little conical bill capped ~itb dacite. At the lowest point in the section is exposed coarse unstratified diabase detritus, containing fragments of the latter rock up to 3 feet in diameter and an occasimial bowlder limestone in a soft and usually somewhat earthy matrix. (Pl. X.) About 25 feet higher up in the section the coarse material is mingled with some sandy detritus and shows rude stratification. (Pl. X.) Still higher~ the deposit becomes finer ~nd more distinctly bedded (Pl. XI)~ and at the ' top of the 75 feet of the formation here exposed, dark sands, largely of diabasic origin, are overlain by a bed of dacite · tuff. (Pl. XI.) The other areas of the Whitetail formation shown on the geological map (Pl. I) require no special description. The deposit js nearly always found in close

lJ. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER NO. i2 PL. X WHITETAIL FORMATION , AS EXPOSED THREE-QUARTE OF CONTINENTAL SPRING. A, Characte r of deposit 25 fe et stratigraphical ly above B; B , lowe r

U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER NO. 12 PL. XI A B W~ITETAIL FORMATION, AS EXPOSED THREE-QUARTERS OF A MILE NORTHWEST OF CONTINENTAL SPRING. A, Shows character af deposit in rts upper portion; B, top of Whitetail formation overlain by glassy dacite.

GILA . CONGLOMERATE. Late Pa f·eozo ie Libra~y V:' ash ington D. C. · ; proximity to the dacite, for -when the latter is removed by erosion, the soft· "\Whitetail formation can not long remain, . unless, like the area southeast of the Continental mine, it is protected by being faulted in among more durable rockt1. Moreover, with .the removal of th~ dacite, the underlying "\Whitetail formation can not in all cases be certainly distinguished from the Gila conglomerate. Origin.-The Whitetail formation preserves the record of the operation, prior to the dacite eruptions and on a smaller scale, of forces similar to those which afterwards accumulated the sometimes . lithologically indistinguishable Gila conglomerate. Apparently then as at a later date, areas of diabase tended to become lowlands, and were strewn with stony detritus, locally reworked and partly stratified by transient streams. Detrital fans near the mouths of shallow gulches nlerging with the loose stony litter of an arid surface were probably all covered by the tuff and lava of the dacitic eruption and so preserved as the Whitetail forrnation. Age.-In the absence of . fossils, a rough approximation to the age of the Whitetail formation, deduced from the general physical history of the region, is all that can be offered. As it lay upon t?e surface over which the probably early Tertiary dacitic lavas were erupted, it also is referred to the same period. GILA CONGLOMERATE. General character, thickness, and stratigraphical position.-Gilbert, while studying, in 1873, the region drained by the upper Gila and its tributaries~:~, gave the name Gila conglomerate to certain valley deposits which he describe8 as follows: "The bowlders of the conglomerate are of local origin, and their derivation from particular mountain flanks is often indicated by the slopes of the beds. Its cement is calcareous. Interbedded with it are layers of slightly coherent sand, and of trass, and sheets of basalt; the latter, in some cliffs, predominating over the conglomerate. One thousand feet of the beds are frequently exposed, and the maximum exposure on the Prieto is probably 1,500 feet. They have been seen at so many points by Mr. Howell and myself that their distribution can be given in general terms. Beginning at the mouth of the Bonito, below which point their distinctive characters are lost, they follow the Gila for more than 100 miles toward its source, being last seen a little above the mouth of the Gilita. On the San Francisco they extend 80 miles; on the Prieto, 10; and on the Bonito, 15. "\Vhere the Gila intersects the troughs of the Basin Range system, as it does north of Ralston~ the conglomerate is continuous with the gravels which occupy the troughs, and floor the desert plains. Below the Bonito it merges insensibly with the detritus of Pueblo Viejo .Desert. It is, indeed, one of the 'Quaternary gravels' of the desert interior, and is distinguished from its family only by the fact that the water courses which cross it are sinking themselves · into it and destroying it, inst~ad of adding to its depth." a a Wheeler Survey, Vol. III, 1875. Geology, p. 540 .

GEOLOGY OF THE GLOBE COPPER DISTRICT, AR.IZON.A. Deposits identical in character and origin, and in part directly continuous with those noted by Gilbert, occur within the Globe quadrangle, and are in · this report designated by the same name. · The general character of the Gila formation it occurs within the Globe quadrangle is that of a firm but not hard conglomerate, the material of which ranges in coarseness :hom fine sand to bowlders 8 or even 10 feet in diameter. It is nearly always distinctly stratified, but the individual beds show as a rule little persistence, layers conglom~rate passing into sands, or vice versa. (PL XII, A.) The pebbles are sometimes well rounded, most of them having probably bee~ derived , from the erosion of Paleozoic c~nglomerates, but more ofte-n they are subangular or even angular in shape and the formation might appropriately be termed a breccia. The material composing the deposit vari~s greatly in different portions of the area, as will presently be shown. The maximum thickness of the Gila conglomerate within th.e Globe quadrangle is not known. It is certainly more than 700 feet and probably considerably over 1~000 feet. But the bottom of its thickest portions is nowhere exposed. Pinal Creek has not cut down to it, nor has it been reached by any ?f the wells in the vicinity of Globe. The Gila formation is essentially a valley deposit, having usually, in spite of deformation and dissection, a still recognizable relation to the larger features of the existing topography. It lies· ·indifferently upon the eroded Rurfaces of all the other rocks of the quadrangle with the exception of basalt, which occurs as an intercalated flow between the conglomeratic beds, and is therefore of contemporaneous age. The conglomerate is frequentlJ found overlaying dacite, the dacite showing evidence of vigorous erosion prior to the deposition of 'the conglomerate. This relation is well shown on Mineral Creek, about 1 mile east of th~ Sixtysix ranch, the conglomeratic beds here abutting obliquely against a crag of dacite, as shown in ·Pl. XII, B. , Distribution.-The largest area of the Gila conglomerate within the bounds 'of the quadrangle is that which underlies and surrounds the town of Globe, a_nd which 1nay be conveniently referred to as the Pinal Creek area (Pl. VI, 0 and D). It occupies the trough between the Apache and Pinal mountains, lapping far up on the flanks of both ranges. On the northeast. slopes of the Pinal Mountains the conglomerate attains a maximum elevation of 4, 750 feet. On the southwest face of the Apache Mountains it reaches a similar altitude, but being here some miles beyond the quadrangle limits the exact elevation was not a~certained. Near the town of Globe the Gila formation has a widt? of about 6 miles from southwest to northeast. About 4t miles northwest of Globe, at the junction of Pinal Creek and Miami Wash, exposures of underlying rock contract

PROFESSIONAL PAPER N6. 12 I'L. XII A. CHARACTERIST IC BLUFF OF GILA CONGLOMERATE AS IT OCCURS IN COPPER GULCH NEAR THE TOWN OF GLOBE. B. BEDS OF GILA CONGLOMERATE ON RIGHT, ABUTTING AGAINST STEEP EROSION SLOPE OF DACTE ON LEFT, 1 MILE EAST OF THE SI XTY-SIX RANCH. Mi neral Creek flows from right to left t hrough a narrow gorge in the dacit2.

GILA CONGLOMERATE. the actual width of the Gonglomerate to less than a mile, but from this point it again broadens northward beyond the bou~ds of the district here considered. About 2t miles southeast of Globe the Gila conglomerate, preserving its width of about 6 miles, occupies the low divide, which separates the drainage of the Gila from that of the Salt River, and~ broadening out to the southeast, becomes continuous with the deposits originally described by Gilbert, which form so noticeable a· feature of the topography in the basins drained by Alizo, San Carlos and Sycamore creeks, tributary to the upper Gila (Pl. VI, 0 and D). A much smaller area of Gila conglomerate occurs in the southwestern corner of the quadrang-le, lying chiefly on the lower slopes of the Pinal Range, and within the drainage area of Mineral Creek. It will be referred to as the 1\'iineral Creek area. The greater part of this deposit lies in a basin eroded in dacite, but it overlaps directly upon the Pinal schists, up to an elevation of 4,150 feet. Near Hutton Peak small outlying patches of the conglomerate, probably originally part of the larger area to the south, attain a maximum altitude of 5,400 feet-the highest point within the quadrangle at which the Gila formation has been found. An interesting area of the conglomerate lies within the drainage . basin of upper Pinto Creek, and may be referred to as the upper Pinto Creek area. It apparently occupies a shallow structural· trough or syncline of northwest-southeast trend, the structure being brought out on. the geological map (Pl. I) by an intercalated flow of basalt. Another area presenting many features of interest occurs near the head of vVebster Gulch and will be referred to as the Needle Mountain area, from the peak 5,050 feet in altitude, which is capped by the Gila formation . . The Gila conglomerate occurs also on lower Pinto Creek at Horrell's west ranch (lower Pinto Creek area), in several patches in the northeastern corner of the quadrangle, and elsewhere in numerous isolated remnants. _Variations in character connected with distribuiion.-As noted by Gilbert, the pebbles of the conglomerate are derived from the adjacent mountains. _An investigation of the Pinal Creek area shows that most of the pebbles of the conglomerate lying southwest of Pinal Creek are composed of schist or granitic rocks and are derived from the Pinal Mountains, wh~le in the smaller area lying north and east of Globe schist fragments are unknown and pebbles of quartzite limestone and diabase .derived from the Globe Hills predominate. It thus appears that throughout the time occupied by the deposition of the greater part of the conglomerate the axis of the trough of deposition corresponded roughly with the present northwesterly course of Pinal Greek. The lowest bed of the Gila conglomerate exposed near the town of Globe 9651--No. 12--03 4 Late Paleozoic Library Washington D. C.

5o GEOLOGY OF THE GLOBE COPPER DISTRICT, .ARIZONA. deserves some special description and may form an exception to the foregoing statements. This bed, visible in the bluffs along Pinal Creek from 1 to 2 miles northwest of town, in the vicinity of the . Old Dominion mine, and in Copper Gulch and other arroyos trenching the conglomerates in this neighborhood, is locally termed "granite," and several prospecting tunnels have been run into it under . the erroneous impression which such a term implies. · The material indeed much resembles a rather decomposed crumbling granite. But closer · examination shows that it is a detrital deposit, in which bowlders or fragments, up to . 6 feet or more in diameter, of . a gray quartz~ mica-diorite, of the same petrographical character as that intrusive in the schists of the Pinal Mountains, are embedded in finer detritus of the same material. (See Pl. XIII, A.) The general decomposition of the whole and its crumbling character tend to obscure the clastic nature of the deposit; The maximum thickness of this accumulation of dioritie material not known. It grades upward by gradual admixture of quartzites and other pebbles into the usual Gila conglomerate of the Pinal Creek area. Natural sections in the ravine north cf the Old Dominion mine and underground workings show tha·t the bed of quartz-mica-diorite detritu~ rests upon the surface of a flow of dacite, and that this contact dips at a considerable angle toward Pinal Creek. (See Pl. I.) Closely associated with the dioritic conglomerate is a facies (variety) of the Gila eonglomerate made up of fragments of a somewhat decomposed yellowish graq.ite-porphyry, which might also be easily mistaken for a . mass of shattered rock practically in place. Its geological position, however, determines it beyond doubt as a part of the Gila formation. It is best seen where cut by the ·second-level drain tunnel of the Old Dominion mine. No good natural exposures are known, outcrops of the material being concealed by numerous loose frag:- ments of the porphyry, such as cover the ground between the rock breaker and reservoir at the Old Dominion mine. Overlying the basal deposit of dioritic bowlders and fragments in the vicinity of Globe are irregularly bedded conglomerates and sands which form the hills and bluffs immediately about the town. These contain much granitic detritus in the lower beds, which, however, is less abundant in the upper strata. The · generally . shbangular pebbles of schist, quartzite, limestone, diabase; or granite, which make up the coarser part of the deposit, are usually less than 6 · inches in diameter. Excellent exposures of these conglomeratic beds have been provided through the dissection of the present streams, and the deposit can well studied along the bluffs of Pinal Creek, in the lower part of Copper Gulch, in Russell Gulch, and along the eastern border of Miami Flat. As the conglomerates west of Globe are followed toward the Pinal Moun-

lJ. s. GEOLOGICAL suRVEY PROFESSIONAL PAPER NO. 12 PL. XIII A. COARSE CRUMBLING QUARTZ-DIORITE DETR ITUS, FORMI NG BASAL PORTION OF GILA CONGLOM ERATE NEAR GLOBE. Exposure is in Copper Gulch. In the upper -hand corner of the picture the material passes into a more common faci es of th e c'onglomerate, showing imperfect stratification. B. COARSE BRECCIA OF DACITE AND SCHIST, FORMING PART OF THE GILA CONGLOMERATE NEAR THE HEAD OF WEBSTER GULCH .

GILA CONGLOMERATE. tains, whence they were derived, they become notably coarser, and close to the range contain angular blocks of quartz-mica-diorite, granite, and schist up to 5 or 6 feet in diameter. The deposit as a rule is less distinctly bedded near the mountains than at a distance of a few miles away . . The Mineral Creek area of the Gila conglomerate differs rather strikingly in the nature of its materials from the Pinal Creek area. Excellent exposures of the formation are visible on Lyons Fork of Mineral Creek, where the basal bed, resting on dacite, is madp up of angular blocks of the latter rock of all sizes up to 2 or 3 feet in longest dimension, embedded in an abundant pinkish· matrix which is made up of sandy dacitic detritus. A few feet above the base, fragments of schist may be observed mingled with those of dacite, and still higher in the series the schist predominates over the volcanic rock. The whole of this basal portion of the deposit shows so little rounding of the rock fragments as to be, strictly speaking, a breccia -rather than a conglomerate. This breccia is overlain by a series of .locally very regularly stratified, light-colored, tuffaceous beds, alternating with beds of conglomerate. The tuffaceous beds are made up very largely of sherds of vesicular or pumiceous volcanic glass, and some of the nearly white beds contain, except occasional particles of quartz and feldspar, scarcely any other material. Other beds show numerous fragments of dacite, quartzite,' and schist, while still others are composed ·wholly of such subangular rock frag-ments, and resemble the more usual type of the Gila conglomerate found in the Pinal Creek area. On Lyons Fork the tuff and conglomerat~ beds strike north 65° east, and dip southeasterly at a:n angle of about 30° but rather abrupt changes in dip are not uncommon. Between the junction of Lyons Fork with the Dry Wash of Mineral Creek and the Sixtysix ranch the Gila formation is well exposed in the bluffs along the east side of the arroyo. Here it is composed of angular fragments of dacite, schist, diabase, and limestone, the blocks being sometimes 2 or 3 feet across, embedded in a finer conglomeratic or sandy matrix composed of the same materials. The larger angular blocks are not mingled indiscriminately with the finer material, but tend to occur most abundantly along certain rude stratigraphical planes within the mass. Along Mineral Creek east of the Sixtysix ranch and in the arroyos north of Government Spring the Gila conglomerates and intercalated tuffaceous strata occur in thick beds are excellently exposed in the stream bluffs. The fragments of the conglomerate vary greatly in size, ranging from fine sand up to subangular or angular bloc~s 3 feet in diameter, composed of schist, quartzite, limestone, or dacite. About a mile east of Government Spring the tuffaceous beds disappear and the visible nortion of the Gila conglomerat~ is made up 9hiefly of fragments of

GEOLOGY OF THE GLOBE COPPER DISTRICT, .ARIZONA. schist and quartz-mica-diorite from the Pinal Range. The beds here dip gently away from the mountains toward the southwest. The Gila formation of the upper Pinto Creek area is exceedingly variable in character and is noteworthy as containing an intercalated flow of basalt, which · is d~scribed on pages 95 to 97. The southern portion of this area, which, al'3 already indicated, is nearly surrounded by the Schultze granite, is. characterized by a conglomerate composed almost wholly of granite, with a small proportion of schist and quartz fragments. The granitic fragments or bowlders are of all sizes up to 6 or even 10 feet in diameter, and are embedded in a matrix of gra,nitic detritus. The granite of these blocks is identical in character with that which forms the adjacent hills, and one looking over the region from any of the neighboring summits and noting the uniform col~r and obviously granitic character of the rocky surface might readily suppose all to . be granite in place. But on closer scrutiny the eye detects the m,ore rounded contours of the hills carved from the Gila conglomerate and the I absence of the occasional projectmg crags which characterize the true granite topography, while the occurrence of occasional blocks of schist shows that the crumbling granitic detritus which covers the surface has been <l.derived not from an underlying granite in place, but from a remarkably coarse granite conglomerate containing scattered schist bowlders. Toward the northwest the material of the Gila conglomerate changes rather rapidly, the granitic bowlders and matrix giving place to dacitic det:r:itus. Underlying the flow of basalt just north of Cottonwood Canyon and resting upon granite and schists is a soft, well-bedded pinkish depo~it made up of small angular particles of schist and quartz with larger fragments of dacite, all embedded in a dacitic matrix which gives the general color to the deposit. This matrix was at one time a mud or silt made up of fine detritus washed from slopes of dacite in the vicinity. The thickness of the deposit where exposed on Cottonwood Arroyo is about 30 feet, but it is merely the thin edge of a formation elsewhere much thicker. North of the road connecting Pinto Creek with Webster Gulch the Gila formation becomes in places very coarse, bowlders of dacite up to 5 feet in diameter occurring em bedded in a matrix of finer dacitic detritus. These very large bowlders are apparently of local distribution, the bulk of the formation consisting of smaller fragments. In the lower pc:;,rt of Gold Gulch, near the edge of the quadrangle, is a mass of the Gila conglomerate which, while lying in the general line of tte elongated area just described, is not directly connected with the latter. It is nearly surround~d by slopes of dacite, and consists almost exclusively of detritus of this rock. The only foreign material noted was a single bowlder of diabase. The

GILA CONGLOMERATE. fragments of dacite comprising this remarkable deposit range m size from those having a diameter of 10 feet down to particles of microscopical dimensions. The larger fragments are embedded in an ab~ndant matrix of the finer material, the whole having a prevailing pinkish color. The conglomerate is distinctly bedded, the beds dipping toward the axis of the little valley in . which they lie, at angles up to 30°. The deposit rests directly upon massive dacite, and has a maximum thickness of something over 7 5 feet. In the Needle Mountain area the most interesting exposures of the Gila formation are found along the Pinto Creek road a·nd on the summit of Needle Mountain. Along the road just mentioned the deposit is made up of more or less angular fragments of dacite up to 6 feet in greatest diameter em bedded in a firm, tough matrix, consisting chiefly of dacitic particles, but containing also many fragments of schist and some of quartz. This matrix is now sufficiently hard to form waterworn bowlders in the bed of the present arroyo. A typical exposure of this breccia or conglomerate is shown in Pl. XIII, B, from a photograph taken by the roadside about three-quarters of a mile west of the branch to the Continental mme. The fragments over 6 inches in diameter are chiefly dacit~. As snown by the illustration, the material lies in rude nearly horizontal beds. From the Pinto Creek road southward to Needle Mountain there intervenes a distance of about a mile, within which the Gila formation undergoes striking change. The dacitie bowlders disappear to the south and are replaced by fragments of schist and of gianite derived from the Schultze ranch area. The matrix continues to resemble that just described, but the place of the finer schist particles is taken by bits of granitic quartz and feldspar. The craggy summit of Needle Mountain is composed of Gila conglomerate, or breccia, as this facies might more properly be called, which has been carved by erosion into the pinnacles whence the mountain derives its ·name. The general appearance of this breccia is shown in Pl. XIV, A, from a photograph taken on the summit of the peak. The large, more or less angular fragments shown in the illustration are mostly blocks of granite varying in size up to 5 feet, with a gmaller number of schist fragments. The matrix by which these masses are firmly held together is composed of fine granitic detritus, the particles being coated and cemented with oxide of iron, which gives it a pale brick-red color, while the large granite bowlders, deri:ved from the neighboring area of light-colored granite, are nearly white. The result is a rock of unusually striking appearance. · Immediately east of Needle Mountain the Gila formation becomes almost exclusively granitic, although there is occasionally some dacitic material in the matrix. This matrix, however, is rarely seen, as the ridges are covered with the large granitic bowlders which have weathered out from the conglomerate. · The

GEOLOGY OF THE GLOBE COPPER DISTRICT, ARIZONA. result is a surface thickly strewn with masses of fairly fresh granite, and closely resembling that of a moraine. It is moreover sometimes difficult to believe that there is not granite in place immediately beneath so granitic a cover. The bowlders of the Gila formation rapidly diminish~ in size to the east of Needle Mountain. At a distance of a mile they are no larger than is common in the beds between Miami Flat and Globe, and consist chiefly of quartz, quartzite, and schist, pebbles or fragments over 2 inches in diameter being rather rare. Such n1aterial is less resistant than that capping Needle Mountain, and forms the rounded gravel-strewn hills characteristic of the Gila formation. The lower Pinto Creek area of Gila conglomerate extending generally eastward fron1 Horrell's west ranch on Pinto Creek is in part made up of reddish beds composed chiefly of pebbles of dacite with some of quartz, quartzite, and diabase, firmly held in a partly dacitic matrix. These conglomerates are . not conspicuously coarse. Much more might be written descriptive of the Gila formation, so variable is it from point to point. But enough has ~een presented to give some idea of the ·nature and extent of the characteristic changes of material dependent upon very local circumstances. Relation to early topography.-As .pointed out by Gilbert,a the Gila formation is essentially a valley deposit. Although its occurrence is not at the present time ~online.d · to. existing valleys, it is plain tha~ it originally accumulated in d~pressions or lowlands separating mountain ridges, and never formed a continuous deposit over the whole region. Throughout the period of its deposition the Pinal Mountains must have existed as a high range, and the vigorous erosive sculpturing of their slopes contributed a large share of the conglomerate~ mate~ial. The conglomerate and tuff of the Mineral Creek area appear to have been laid down in a valley bounded on the east by the main Pi~al Range and on the west by extensive slopes of dacite, upon which. it undoubtedly overlapped to an unknown distance to the west. The occurrence of patches of the conglomerate at an elevation 1 of 5;400 feet j~st east of Hutton Peak ·indicates that the Mineral Creek deposit was once much more extensive, and that its boundaries could not have been embraced within the limits of the prese-nt . valley, upon the floor of which the remnant of . the . formation lies. The conglomerate originally either swept round to the north pa~t the position of Pinal ranch and joined ·the upper Pinto Creek area, or else there existed in the vicinity of the ranch . a dividing ridge which has since been reduced . by erosion. The latter. hypothesis is considered most probable and most accordant with what has been observed elsewhere in the district. No evidence has been discovered to indicate that the conglom- - erates near Hutton Peak owe their relatively high elevation to faulting. a Wheeler Survey, Vol. III, 1875; Geology, p. 540.

GILA CONGLOMERATE. The Apache Mountains, northeast of the quadrangle, must also have existed although their structure has probably undergone modifications since the conglmi'terate was deposited. In the valley between the Pinal and Apache mountains was laid down the largest single area of conglomerate within the quadrangle. Over most of the northern half of the quadrangle, however, the relation of the Gila formation to an older topography is less clearly read. As the deposit forms tqe summit of Needle Mountain there is at present no topographical barrier between the Needle Mountain and upper Pinto Creek areas. But the coarse nature of the conglomerate on the peak indicates that it was deposited close to a mountain slope, and the character of its materials points plainly to their derivation from the west or southwest. The occurrence of the deposit on the summit of a peak which dominates the surrounding country within a radius of . ·3 miles is alone eloquent of erosion, and taken in connection with the character of the material in the conglomerates of the Needle Mountain and upper Pinto Creek areas, indicates that the two were formerly separated by a northwest-southeast ridge forming a continuation of the Pinal Range. The Needle Mountain area of conglomerate appears to have been deposited on the north against the thick !\ccumulatio~ of dacite which now culminates in Webster Mountain, and which. undoubtedly supplied most of the dacitic detritus to . the younger formation. The lower Pinto Creek area, while obviously modified in outline by deformation and erosion, lies within a valley which in general still persists as part of the drainage basin of Pinto Creek. The presence of several small patches of the Gila conglomerate northeast of Webster Mountain indicates the .former existence of a valley in which the gravels were laid down. But subsequent deformation and erosion have obliterated the boundaries of this hollow. the northeast corner of the quadrangle the deposits of Gila conglomerate are in general related to the present valleys. They consist chiefly of quartzite, and grade without any discoverable break into the modern talus from the quartzite ridges. The relation thus sketched between · the Gila formation and the earlier and the present topographies may be summed up in a general statement. An observer standing on a commanding elevation, such as Pinal Peak, will see below him to the northeast the broad basin in which the town of Globe lies, evidently deeply filled with a relatively soft deposit, intricately carved by the present system of arroyos. (Pl. III, B, and Pl. VI, 0 and D.) He will observe that the deposit is not horizontal, but slopes gently up to the foot of the range upon which he stands, and up to the Apache Mountains to the northeast. He will see that 1t is continuous, with much larger areas to the southwest, apparently filling the

G EO LOGY OF THE GLOBE COPPER DISTRICT, .ARIZ ON .A. basin of the Gila and extending up in long terraced slopes to the Pinaleno and other ranges. The impression made by such a broad view (see Pl. VI, 0 and· D) is that the conglomerate merely fills the existing valleys, and is now being trenched . by the streams as a consequence of Himple regional uplift or climatic ch~mges. But detailed study of the district soon modifies this first impression, and it becomes evident that both deformation and erosion have locally effected topographical transformations whereby valley bottoms of the time of deposition of the Gila ~ormation have in sotne cases become mountain tops of to-day. rapid variation in character, the ·coarseness and angularity of the bowlders. the .distribution of the material with reference to existing mountain ranges, the nature and dip of the stratification, and the :frequent abrupt changes observable in both horizontal and vertical sections, all point decisively to the result of fluviatile action. The bulk of the Gila formation, as it occurs in the Globe quadrangle, was deposited by streams, and resembles the material . :found in the beds of the prevailingly .dry arroyos to-day. The :freshness of the material forming the pebbles and . bowlders, taken in connection with their angular shape, indicates that the detritus supplied to these streams came from slopes where mechanical disintegration strongly preponder:- ated over rock decay-a characteristic of the region at the !?resent time. The occurrence of large angular blocks near the mountains with the rapid gradation into finer materials· toward the· middle of the depositional tract, point to tumultuous transportation-to torrential rushes of water by which large quantities of rock waste were transported in a short time from the moun.tain slopes to the valley with little of that rounding of individual fragments which characterizes the action of streams having a ·more constant flow, and in which the materi~ls as a rule travel more le~surely to greater distances before coming to rest. As already ·pointed out under the heading "Climate," the present erosion in this arid region shows similar characteristics-turbulent floods of water roaring suddenly down channels whose dry beds have been exposed for months to the burning rays of the sun. The transporting power of the streams which deposited the Gila formation diminished very rapidly after they issl!ed from the mountain canyons, and their load was deposited over the valley floors as a series of coalescent detrital fans. That the condition~ of deposition just outlined were not unfavorable to the occurrence of associated lake deposits in the middle of the larger valleys is certain, and it would not be surprising to find in some of the larger basins outside of the Globe quadrangle fluviatile deposits passing into lacustrine sediments. Such a condition seems to have obtained in . the Tonto Basin, north of the region here discussed. But even in s:t;taller valleys it is probable that the

INTRUSIVE ERUPTIVE ROCKS. drainage was at times ponded back by the encroachment of alluvial fans, or by deformation resulting from demonstrable faulting. Moreover, many of these valleys were drained by streams engaged in deepening their outlets throug'h masses of extrusive dacite. Such narrow gorges may have been incapable of discharging the sudden floods poured into the valleys,. and more or less temporary lacustrine conditions have consequently prevailed. The well-bedded tuffs, associated with conglomerates in the Mineral Creek area, were probably deposited in lake waters, and it is interesting to note that the present outlet of this valley is a narrow impassable gorge cut through the dacite; As is shown in pages 97 to 106, the Globe region was extensively faulted after the extrusi'on of the dacite and prior to the deposition of the bulk of the Gila formation. Unless this faulting was extremely slow, it must have modified the drainage, ponding back the streams until they could cut new channels through the blocks of rock which arose athwart their courses. Detailed observations must be c.arried over a much larger area than the Globe quadrangle before the extent to which faulting affected the accumulation of the . Gila formation · can be ascertained. It is noticeable that considerable deposits of Gila conglomerate occur in valleys whose drainage escapes through narrow gorges cut in tilted fault blocks of dacite or older rocks. This. is true of the Mineral Creek, Pinal Creek, and Pinto Creek areas within the quadrangle, and particularly of the Tonto Basin to the north. This relation is suggestive, and deserves further investigation over a broad field. Age.-Gilbert, in his original description of the Gila conglomerate, referred it to the Pleistocene, and there seems to be no good . reason for questioning this conclusion. The deposit has yielded no fossil remains and is known to be the latest extensive detrital accumulation in the :region, antedating the present conditions of drainage but later than the great dacitic eruptions which are tentatively referred to the Tertiary. As it is distinctly older than the insignificant deposits of . the {>resent intermittent streams, it is referred in this report to the early Pl~istocene. INTRUSIVE ERUPTIVE ROCKS. GENERAL STATEMENT. Under the heading "Intrusive eruptive rocks" are included a number of pre-Cambrian eruptives of general granitic appearance, such as granite, granitite, quartz-mica-diorite, granodiorite and monzonite, all of which cut the Pinal schists. Together with these ancient rocks is placed a small mass near Bloody Tanks of somewhat doubtful origin and relationship that has been designated as metadia- Of post-Carboniferous age are the extensive intrusions of . olivine-diabase

GEOLOGY OF THE GLOBE COPPER DISTRICT, ARIZONA. in the form of sills, dikes, and irregular masses. In order to avoid the -reiteration of technical petrographic terms, which mean little to most readers, the various granitic rocks will usually be referred to by lo'cal names~ such as Madera diorite, or Schultze granite, ·consisting of a geographical term denoting a place · of characteristic occurrence and a general rock name as simple and familiar as possible. MADERA DIORITE (QUARTZ-MICA-DIORITE). Dtdinition.-Quartz-mica-diorite is usually a gray rock of granitic texture and habit, consisting essentially of plagioclase feldspar (usually andesine) with quartz arid black mica (bi9tite). There is sometim~s a little orthoclase or micr~­ cline present, in which case the rock approaches granodiorite in composition, while by the addition of hornblende it may grade into tonalite. The local name Madera diorite is derived from Mount Madera, one of the ·peaks of the Pinal Range. Occurrence and distribution.-U nder the name· quartz-mica-diorite may be included a large part of the granular plutonic rocks intrusive as batholiths into the Pinal schists and locality known as · "granite." This rock closely resembles many true granites in its general texture, prevailing gray color, and mode of weathering. Close inspection, however, reveals the fact that the dominant feldspathic constituent is plagioclase and not, as in granite proper, orthoclase. As may be seen from the map, the Madera diorite, with the exception of a single small mas~ in ·schist, north of Black Peak, is limited in its distribution to the southern half of the quadrangle, where it . forms exceedingly irregular bodies which have extensively invaded the schists, dividing the latter into detached masses of widely variant shapes aqd sizes. The relation of the quartz-micadiorite to the schists is often exceedingly intimate. Irregular tongues . of the intrusive rock extend into the schists; and fragments _of the latter are often thickly crowded as inclusions in the former. ' For co11venience of description the Madera diorite may be treated in four areas. · The first. of these, which will be called the Crest area, is the most' northerly. name is suggested by the · fact that it occupies much of the crest of the Pinal Mountains (including Mount Madera), from the Ridge road, in Russell Gulch, northward to the trail between Globe and the Hog ranch. ·On the west it forms the ear-shaped area extending southward from the above named ranch across ~yons ·Fork of Mineral Creek. On the east it is the principal rock of Russell Gulch, up which the Ridge road passes, and extends down beneath the conglomeratic beds of the Gila formation. As far as existing exposures go, the Crest area of quartz-mica-diorite is distinct from other areas of similar rock to the southeast. This isolation, however, is undoubtedly more apparent than real. Connections

MADERA DIORITE. fi9 probably exist beneath the covering of Gila conglomerate and beneath the schist ma;sses at the head of Icehouse Canyon. The second area lies east ·of the Crest area and is of comparatively small extent. , It comprises the rock in which Icehouse Canyon is excavated and extends eastward . across Pinal Creek~ where it is united by a narrow ribbon of the diorite between two schist areas with the third and much larger and very irregular mass forming· Pinal Peak area, so called from the mountain of that name. It is the quartz-mica-diorite of the Pinal Peak area, often thickly crowded with schist inclusions, which is so well exposed along the stage road that, crossing the range at the head of Pinal Canyon, connects Globe with Florence. The last and fourth area lies in the extreme southeastern corner of the quadrangle, and may be conveniently referred to as the Southeastei~n area. It probably connects with the Pinal Peak mass to the northeast, beyond the bounds of the quadrangle. Although all four areas are extremely irregular in outline, they yet, as may be seen on the geological map (Pl. I), show a tendency to elongation parallel with the general strike of the schists, which is northeasterly and southwesterly . . Petrography.-The characteristic rock of the Crest area is granitic in general aspect, usually massive, but it becomes somewhat gneissoidal near the contact with the Pinal schists, particularly to the east of the Hog ranch. Its usual color is bright gray, with none of the flesh-colored tint commonly associated in this region with rocks containing much orthoclase. Epidote is sometimeEJ locally abundant as greenish-yellow flecks, streaks, and veinlets, particularly near the contact with other rocks. The rock is not porphyritic, but has a uniform granular texture, the average size of the component mineral grains being somewhat less than 5 millim((ters. The minerals visible to the unaided eye are milky-white feldspar, usually showing albite striations, quartz, and abundant black mica. The structure as seen under the micrGscope is typically hypidiomorphic granular, the plag~oclase and biotite usually having partial crystallographic outlines. The principal constituents in order of apparent abundance are plagioclase, which optical tests indicate to be_labradorite of the approximate composition Ab 1 An 1a, quartz, biotite, microcline or orthoclase, and muscovite. The accessory constituents are iron ore, apatite, titanite, rutile, and zircon. Epidote and a little sericite and chlorite are always present as secondary minerals. Hornblende is not a constituent of the typical rock of the area, but may occur abundantly in certain contact facies, to be presently described. The amount of orthoclase or microcline present is subject to considerable variation, and, as in the granodiorites and quartz-diorites of the Sierra Nevada, a The method of Michel Levy, in comiection with that of Becke, has been used throughout this investigation for the determination of the feldsparQ.

GEOLOGY OE' THE GLOBE COPPER DISTRICT, ARIZONA. is perfectly allotriomorphic and often incloses the niore nearly idiomorphic plagioclase. The orthoclase is sometimes partly sericitized, but the microcline is fresh and clear. Both forms probably contain a small · proportion of the albite molecule, as indicated by occasional departures froni optical homogeneity. A chemical analysis of au apparently representative specimen collected 2 miles south of the Hog ranch is given under I, while under II is placed an analysis of a typical granodiorite for comparison. Chemical analyses of quartz-mica-diorite and granodiorite. [Dr. W. F. Hillebrand, analyist.] FeO .. MgO .. . Pz05 - Cr20 3 · : NiO . . . · · · BaO . . · . . SrO None. Undet. Undet. Trace. Trace . Undet. Trace. Undet. Undet. a Calculated as FeS2

Trace. Trace.

I. Quartz-mica-diorite, 2 miles south. of the Hog ranch, Globe quadrangle, Arizona. None. Undet. Undet. a(. 06)

Trace(?) Trace. Trace. II. Granodiorite, Grass Valley, Nevada County, Cal. Lindgren, Am. Jour. Sci., 4th series, Vol. IX, 1900, p. 273, analysis III. III. Quartz-mica-diorite, Florence stage road, 2 miles south of Pinal Peak.

MADERA DIORITE. It will be noticed that the Arizona rock is a little lower in silica and alkalies and higher in ferric oxide. Chemically, however, the rock comes within the limits a~s.igned by Lindgren a to granodiorite, although it is evidently not far from the quartz-mica-diorite line. Ignoring the secondary minerals, such as epidote, chlorite~ and sericite, the approximate mineralogical composition of the original fresh rock may be calculated as in I, in . which all the magnesia is calculated as biotite of the same composition as that occurring in a similar quartz-diorite in the Sierra Nevada/ the lime, after subtraction of sufficient for apatite and titanite,. as anorthite, and the soda as albite. The combination of the albite and anorthite molecules affords a labradorite of the approximate composition Ab3An5 , a somewhat more calcic feldspar than was indicated by optical tests in thin section. The potash remaining after the calculation of the biotite was so proportioned between the orthoclase and muscovite molecules as to use up the alumina not required for biotite, anorthite, and albite . . A little of the soda may be combined with potash in the alkali feldspar, but the amount is probably not enough to seriously modify the composition as calculated. Under II is placed the mineralogical composition of the Grass Valley granodiorite as calculated by Lindgren. Mineralogical composition of quartz-mica-diorite and granodiorite. II., Quartz .. Soda feldspar .. . a23. 22 b28. 00 Calcium feldspar ... . .. a20. 45 b 12.10 Potassium feldspar . . .. .. Magnetite Titanite Zircon .. a Labradorite Ab3An5, 43.67 per cent. b Andesine Ab7An3, 40.10 per cent. Comparison of the calculated mineral compositions of two rocks shows that the Arizona . rock is so Mw in potassium feldspar as to place it with the quartz Am. Jour. Sci., 4th series, Vol. IX, 1900, p. 275. b Bull. U. S. Geol. Survey No. 168, p. 218, analysis G.

. G EO LOGY OF THE GLOBE COPPER DISTRICT, ARIZ UN A. diorites rather than with the granodiorites, in which the potassium feldspar should amount to at ·least 8 per cent. ~1icroscopical examination of thin sections shows, . however, that in the particular specimen analyzed the proportion of this feldspar is below the average for the area as a whole. Although the amount of calcium is about the same in the two rocks, in the Grass Valley granodiorite it is partly combined in the hornblende molecule, while in the Madera diorite, where biotite plays the role of constituent, the calc!um, with the exception of a very little in the biotite, titanite, and apatite, is apparently all combined with sodium to form labradorite, an abnorm!1lly calcic feldspar for typical granodiorite, for which the characteristic plagioclase is oligoclase or andesine. The biotite also, by levying on the supply of potassium, reduces the amount available to form potassium feldspar. The comparison of the chemical and mineralogical compositions of the two rocks furnishes an interesting example of the crystallization of chemically similar magmas into mineralogically diverse aggregates.· Although microscopical study shows that orthoclase or microcline 'are sometimes more abundant than in the rock s~lected for analysis, it nevertheless seems advisable to adopt the name quartz-mica-diorite for the mass as a whole, recognizing that it closely approaches the graiJ.odiorites and occasionally shows granodioritic facies. The Crest area of the Madera diorite is not bordered by any persistent peripheral facies, but a well-marked differentiation into local contact modifications occurs at a few points, particularly in the vicinity of the saddle through which the trail from Globe to the Hog ranch passes, and near the contacts with the inclosed masses of schist on the eastern slope of the Pinal Range. These facies a1:e darker in color than the normal rock, and evidently contai~ hornblende as well as biotite, while the quartz becomes very inconspicuous. Under the microscope these darker rocks show a hypidiomorphic granular structure and consist of plagioclase, quartz, hornble~de, and biotite, with accessory iron ore, apatite, titanite, and zircon. The plagioclase is labradorite, ranging from Ab3An4, to somewhat more calcic varieties. The quartz is wholly allotriomorphic, with a tendency to become interstitial. Potassium feldspars were not noted in the thin sections examined, but probably occur in transitional facies. The hornblende is the , common variety, greenish yellow by transmitted light, usually found in dioritic rocks, and the biotite presents no noteworthy features. The secondary minerals are chlorite, largely after biotite, and epidote. The rock is a quartz-hornblende-biotite-diorite, differing from the main rock of the area in the presence of abundant hornblende and in its more calcic feldspars. The · rock .of Icehouse Canyon 1s gray in tint, of rather evenly granular

MADERA DIORITE. texture, and generally shows conspicuous foliation. Its structure is thoroughly gneissic. As already noted on page 59, it is often filled with inclusions of schist. Under the microscope, the ·rock shows a mineralogical composition similar to that of the quartz-mica-diorite of the Crest area. It differs from the latter chiefly in the microscopical evidence of intense squeezing. The original quartz areas, where not completely reduced to aggregates of small granules (cataclastic structure), show shadowy extinctions between crossed nicols, and are granulated on their peripheries. The plagioclase, usually labradorite, is also granulated but to a less extent than the quartz, while the laminre of the biotite and muscovite are bent or contorted. The pot~sh feldspar is a microperthitic microcline which varies in abundance in different specimens. The accessory minerals, spar-:- ingly p~esent, are iron ore, apatite, zircon, and titanite. Epidote occurs as small granular aggregates in close proximity to the biotite. . No chemical analysis bas been made of this rock, but its general petrographical character shows close kinship with the quartz-mica-diorite of the Crest area. It is really a quartz-mica-diorite-gneiss. The quartz-mica-diorite of the Pinal Peak area is -generally more coarsely crystalline than the rocks of Icehouse or Crest areas, the average size of the grains of quartz and feldspar being about one centimeter. The feldspars occasionally show porphyritic development, but as a rule the rock is evenly granular. The minerals visible to the unaided eye are quartz, white striated feldspar, a little orthoclase or microcline, biotite, titanite, and a few specks of chlorite and pyrite. The prevailing tint is gray, but this changes to a decided reddish color near the ba~?e of the Apache group, which is found resting .upon the Madera diorite just south of the quadrangle The rock disintegrates rather easily to a crumbling mass, and in the eastern portion of the area fresh spechnens are obtained with some diffic~ty. Under the microscope the quartz-mica-di-orite of the Pinal Peak mass shows a hypidiomorphic granular aggregate of labradorite, quartz, biotite, microcline, and a little muscovite. The accessory minerals are titanite, which is more abundant than in the other quartz-mica-diorites described, apatite, iron ore, and zircon. In the fresher specimens the secondary minerals are of slight importance and comprise chlorite, epidote, sericite, calcite, and a little fibrous green hornblende. The labradorite has a probable composition of Ab1An1 A chemical analysis of a typical sample of this quartz-mica-diorite coll~cted on the Florence stage road, 2 miles south of Pinal Peak, is given under III in the table of chemical analyses on page 60. It is slightly higher in iron oxides and lime and a little lower in silica than the similar rock of the Crest area, of which an analysis is given in column I. The difference, howev.er, is so small

OF THE GLOBE OOPPER DISTRT.OT, ARIZONA. as to leave no doubt but that both rocks solidified from the same magma, and in all probability they represent one general period of intrusion. Two miles nearly due east of Pinal Peak a specimen was collected from the crest of the ridge lying east of the stage road, which showR abundant small phenocrysts of potassium feldspar. Under the microscope these phenocrysts prove to be microperthitic microcline, which is apparently quite as abundant as the labradorite or andesine plagioclase present. Among the accessory minerals titanite, often in sharply idiomorphic crystals, is more abundant than in the quartz-mica-diorite typical of the area. · This exceptional rock is perhaps a monzonitic facies of the quartz-diorite, as it apparently did not form a distinct area. ·Its relation to the prevalent rock was, however, not clearly established. The red color of the Madera diorite where it is overlain by the Apache group is the result of the pre-Cambrian weathering of the old surface upon which the sediments were laid down.· The immediate cause of the coloration is the decomposition of the feldspars which the microscope shows to consist of fine kaolinitic aggregates containing minute dust-like particles of iron oxide. The granitoid rock of the Southeastern area is probably continuous to the east, beyond the edge of the quadrangle, with the quartz-mica-diorite of the Pinal Peak area. It varies in color from gray near the eastern border of the area to red where it underlies the Apache group to the west. It crumbles readHy when weathered, and exposures of firm fresh rock are not abundant. Specimens of the latter show a handsome greenish-gray rather. coarsely crystalline rock, in which occur scattered and irregular phenocrysts of pink potassium feldspar up to 2 or 3 centimeters in length. The constituents making up the granular groundmass have an average diameter of about 5 millimeters and comprise a rather oily green plagioclase, quartz, and biotite. A thin section under the microscope shows a hypidiomorphic granular aggregate of plagioclase, quartz, microcline, and biotite, named in order of apparent abundance. The plagioclase is principally andesine. The microcline occurs as the porphyritic crystals noticeable in hand specimens and as irregular inclusions in the andesine. The accessory and secondary minerals· are those already noted for the Pinal Peak area. This rock bas not been subjected to chemical analysis, but the microscopical examination indicates that although potassium feldspars are scarcely so abundant as ~be conspicuous phenocrysts might suggest, it is probably more nearly a granodiorite than the quartz-mica-diorites described in the preceding pages. In the absence of chemical investigation, however, and in consideration of its probable continuity with the . plutonJc mass of Pinal Peak, the rock is provisionally included with the Madera diorite.

SOLITUDE GRANITE. The existence of a very small mass of quartz-mica-diorite north of Black Peak was referred to on page 58. This is a dark-gray gneiss, which has apparently been · subjected to some of the same squeezing that has metamorphosed the surrounding schists, into which it was originally intruded. It consists of plagioclase, largely sericitized, quartz, biotite, and a little green hornblende, with the usual accessory and secondary minerals. The quartz is thoroughly granulated and the granules arranged in ·bands. Although more metamorphosed than the quartz-mica-diorite of the larger masses in the Pinal Range, the rock of this little area was probably of the same general type originally and belonged to the same period of intrusion. It is accordingly mapped as l\'Iadera diorite. SOLITUDE GRANITE (GRANITE AND MUSCOVITE-GRANITE) .Definition.-The term granite, used strictly and without modification, stands for a granular plutonic rock, consisting essentially of a potassium feldspar (orthoclase or microcline) quartz, muscovite, and biotite. I£ the black mica is absent entirely, the rock is termed muscovite-granite. There is usually present also a subordinate amount of plagioebse-either albite or oligoclase. Occurrence and distribution.-Granite (using the word in its strict petrographical sense) and muscovite-granite are not abundant rocks in the Globe quadrangle. Their occurrence is limited as far as known to three small areas. One of these lies half-way between Black Warrior aQd the Continental mine, and may be called the vV ill ow Spring area .from the gulch of that name. It will be described later under the heading "The Willow Spring granite." The other two lie southeast of Bloody Tanks, at the head of Solitude Gulch, and together cover about 3 square miles. The latter are masses of very unequal size, separated by a narrow strip of schist. The rocks of these two areas, while in part of similar mineralogical composition, are different in . appearance and texture, and will be separately described. They, like the other granitic rocks of the Pinal Range, are intrusive into the Pinal schists. The smaller of the two southerly masses is cut by porphyry dikes sent out froni the Schultze granite. Petrography.-The principal rock of the southern and largest mass is a light gray, sometimes nearly white muscovite-granite, passing with no recognized break into true granite in the southern portion of the area. It weathers in-yellowish tints, resembling in this respect the granitite of the Schultze area, rather than the grayish-weathering quartz-mica-diorites of the southern part of the Pinal Range. It is mas~:live, and usually of evenly granular texture, the average size of the grains being about 5 millimeters. The minerals visible to the naked eye are quartz, porcelain-white feldspar, silvery white mica (muscovite), and sometimes black mica (biotite). 9651-No. 12-03-5

GEOLOGY OF, THE GLOBE COPPER DISTRICT, ARIZONA._ Under the microscope the rock shows a nearly allotriomorphic aggregate of quartz, microcline, and orthoclase in varying proportions, albite or oligoclase, and muscovite. ·Although the biotite is often entirely lacking, in some facies it is nearly as abundant as muscovite, and the rock becomes granite proper. On the the whole, microcline, quartz, and muscovite are' the most constant and important . constituents, and dark minerals are notably lacking. The feldspars, although somewhat turbid with dust-like particles, are generally fresh. Intergrowths of the various feldspars . are common. The quartz .grains, · as seen in thin section, · usually consist o£ several interlocking granules, but this structure is apparently not of cataclastic origin. Accessory minerals are always very sparingly present. They are titanite! zircon, and tourmaline, the latter in minute prisms. The rock as a whole may be described as ·a muscovite-granite with true granitic facies. The rock .of the neighboring smaller area is darker in color and 'finer grained. In fresh exposures it always shows a peculiar streaky appearance, suggestive of imperfect mixing of a heterogeneous magma. Hand specimens show a uniformly fine granular texture, the muscovite and biotite, the latt~r sometimes aggregated to little dots or bunches, being the only minerals easily recognized by the unaided eye. Under th.e microscope, quartz, muscovite, a little albite or oligoClase, and occasionally andalusite appear as - allvtriomorphic grains, either intricately interlocking or poikilitically inclosed in a somewhat indistinct matrix or mesostasis which is principally if not wholly orthoclase. The andalusite is always allotriomorphic and usually closely associ~ted with the quartz and muscovite. It shows the · Cleavage, faint green and pink pleochroism, index of refraction, double refraction, and other optical properties characteristic of andalusite, but is free from the · black ·carbonaceous inclusions common in this . minerill when a constituent of contact metamorphic rocks. Andalusite bas been described . by Teall a as a constituent of granite in . Cornwall, where it is associated with sillimanite and possibly cordierite, and by Cohen b in granites of the Scbwarzwald and Vosges Mountains. Although in the Arizona occurrences the mineral bas apparently as much title to primary origin as the quartz, muscovite, and feldspar, the general microstructure of the ·rock admits, if it does not suggest, extensive recrystallization ~rought about by metamorphic action, such as might be ascribed to the-intrusion of the later granitite of the Bloody Tanks area. The well-known association of andalusite with contact metamorphism imposes the burden of proof upon any apparent occurrence of it as a primary constituent of an eruptive rock. In the present instance the proof is not at hand~ a :vr'ineralogical Magazine, Vol. VII, 1887, pp. 161-163. b Neues Jahrb. f. Min., 1887, Vol. II, pp. 178-180.

SCHULTZE -GRANITE. The purely accessory minerals of this granite are apatite, titanite, zircon, and iron ore, none of them being abundant. The secondary minerals are a little chlorite and epidote. SCHULTZE GRANITE (GRANITITE. OR BIOTITE-GRANITE). D~nition.-Biotite-granite or granitite is a granular plutonic rock, consisting normally of orthoclase, quartz, and biotite, with usually a little oligoclase. The rocks presently to be ·described depart rather widely from the type and furnish an interesting illustration of the unsatisfactory and transitory character of the general s.theme of rock classification now in use. Occ'ur·rence and distribution.- In contradistinction to the quartz-mica-diorite, which occupies the southern third of the· quadrangle, the characteristic granitoid rocks of the northern two-thirds of the region are granitites. In order to · bring out certain slight mineralogical differences, possibly indicative of difference in age~ these granitites, occur'ring in many separated areas, are mapped and described in two geographical groups, namely, the Schultze granite, so called from the Schultze ranch, and the Ruin granite, from Ruin Basin, a name given to this hollow on account of unusually abundant ruins of prehistoric villages that dot its floor. The largest and most interesting mass of Schultze granite forms what may be termed the Bloody Tanks area: which from the Pinal ranch on the west stretches eastward acrm;s Pinto Creek to Liveoak Gulch. It is this rock which forms the light-colored hills about Schultze's ranch and the rather conspicuous white peaks east of · the Pinal ranch. As a rule its erosion tends toward the development of· broad basins and moderate slopes, which, however, are often hilly and may be exceedingly rough in detail. The surfaces of these hills are but poorly screened by scanty vegetation, so that the rounded outcrops of granitic rock and the · smoother slopes covered by loose particles of feldspar, quartz, and mica impart a pale-yellow tone to the landscape. A rather conspicuous jointing is cha1·acteristic of the mass and is particularly well developed along Pinto Creek (Pl. VIII, Band Pl. XIV, B), where the granite is regularly divided into great 'slabs by joints which strike about north 65° east and dip southeasterly at about Joints having this general trend are abundant over most of the Bloody Tanks area, but they are often associated with northwesterly joints and with still others running in various directions. Marvine, whose route in 1871 evidently led him across the Pinal Range by way of Bloody Tanks and what is now Schultze's ranch, gives a general description of the Schultze granite. · He says: "The granite is a handsome coarse granular aggregate of quartz · grains and · orthoclase, large projecting crystals of the latter, which is mostly white, mottling the weathering rock, while the mica is subordinate, occurring in small black flakes. It is characteristically

GEOLOGY OF THE GLOBE COPPER DISTRICT, . ARIZONA. cut in deep and rugged ravines, and is at first strongly affected with joints havin:g a southern trend and inclined · 65° to 80° eastward,_ with a subordinate system of east and west joints . dipping north, the two together tending to stud . the surface with large tombstone-:like slabs of rock. The first set of joints swings westward as the range is crossed." a The portion of the granitic area lying north of Bloody Tanks and drained through Liveoak Gulch is characterized by a porphyritic facies which has been much fissured and altered, and is often conspicuously stained with salts of copper. The Bloody Tanks mass of . biotite-granite is nowhere in contact with the Paleozoic sediments of the region, so that its age relative to these is not directly determiua ble. Another mass of granitite, ~hich is correlated with the Schultze granite, lies to the west of the Continental mine, and may be conveniently referred to as the Porphyry Mountain area; since it forms the mass of Porphyry Mountain. North of the mine the granitite has the reddish color which is always associated with the pre-Cambrian erosion surface, and is overlain by the basal conglomerate and some of the lower quartzites of the Apache group. P etrography.-The granitoid rock of the Bloody Tanks area is characterized by a prevalent porphyritic structure and a generally light tint. The usual color of slightly weathered surfaces is pale yellow, but fresh specimens are nearly "vhit~, speckled with small flakes of black mica. The constituents visible to the unaided eye are porphyritic crystals of a fresh, white feldspar often as much as 2 inches in length, showing the brilliant cleavage faces and carlsbad twinning characteristic of orthoclase. These phenocrysts lie in a medium granular groundmass whose constituent grains vary from 1 or 2 millimeters up to a centimeter in diameter and co:r:prise quartz, white feldspar, and biotite. Close inspection of cleavage faces shows that the feldspar of the groundmass is predominantly plagioclase. Such is the rock in which the kettle~like holes are eroded at Bloody Tanks, and which is well exposed around the Schultze ranch, on Pinto Creek, and along the tr~il from this creek to the Pinal ranch. Under the microscope thin sections (which as a rule illustrate chiefly the groundmass or granular portion of the rock) show a hypidiomorphic granular aggregate of oligoclase, quartz, orthoclase, and biotite, with accessory · muscovite and a very little iron ore, apatite, and zircon. Small . amounts of epidote and chlorite are occasionally present as alteration products of biotite. The oligoclase, although containing a little brownish microscopic dust, is generally fresh and has a tende:ncy toward idiomorphic form. It is usually polysynthetically twinned according to the albite and pericline laws in rather narrow lamellre, ·and these often combine with carlsbad twinning. The index of refraca Loc. cit., p. 223.

U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER NO. 12 PL. XIV A. COARSE GRANITIC BRECCIA, BELONGING TO THE GI LA CONGLOMERATE AND FORMING SUM MIT OF NEEDLE MOUNTAIN. B. TYPICAL SURFACE OF SCHULTZE GRANITE, SHOWING SHEETING OR PARALLEL JOINTING; ON TRAIL TO PINAL RANCH, NEAR HUTTON PEAK.

r SCHULTZE GRANITE. tion is slightly above 1.54, which, taken in connection with the very small extinction angles observed in sections of albite-carlsbad twins in the zone perpendicular to the brachypinacoid, indicates a calcic oligoclase. The orthoclase occurs as phenocrysts, often irregularly bounded, or peripherally intergrown with oligoclase and quartz, and also allotriomorphically cryf'tallized with quartz between and around the oligoclase in the groundmass. It is fresh and fairly clear and is not noticeably microperthitic, although it contains frequent inclusions of oligoclase, quartz 1 and biotite. The biotite, which is black in hand specimens, shows the usual brownish pleochroism and strong absorption of this mineral in thin sections. Cleavag·e . fl~kes give an axial cross which does not perceptibly open upon rotation_ of the microscopical stage. A chemical analysis of a typical sample of the Schultze granite, collected about a mile west of the Schultze ranch, is given under I in the following table: Chemical analy8e8 of granitite8 and granite-pmphyries. Si 0 Al Fe H20+ s NiO .. Trace. None. Trace. Trace. · Undet. Undet. Trace. None. Undet.

Trace. Undet. Undet. Trace. None.

Trace. Norie. ... Trace.

None. None. None. --- -- ... None. Trace. . 07

GEOLOGY OF THE GLOBE COPPER DISTRICT, .ARIZONA. · I. Granitite, 1 mile west of Schultze's ranch; Dr. Eugene,T . .Allen, analyst. Ii. Granite-porphyry, marginal facies of above; 2 miles south of Schultze's ranch; Dr. Eugene T . .Allen, analyst. III. Granite-porphyry, dike; 1 mile southwest of the Hog ranch; Dr. Eugene T. Allen, analyst. · IV. Granitite; Melibocus, Odenwald. Rosenbusch, Gesteinslehre, second edition, 1901, page 79. Cited for camparison. In its high silica, low iron oxides, magnesia, and lime, and moderately high potash and soda, the analysis corresponds to a granite, while the preponder~nce of soda over potash points to a soda granite, in which might be expected an alkalic feldspar rich in the alQjte molecule. But the optical examination, on the other hand, shows that the chief constituent of the rock is oligoclase. Calculating the magnesia, all of the ~errous oxide, and most of 'the ferric oxide as biotite, and proportioning the remaining potash to the alumina for orthoclase and muscovite after the subtraction of enough of the aJumina to form titanite, albite, and anorthite, the appro:~:imate mineralogical composition of the rock may be given as follows: Mineralogical composition of granitite . SAl 4. 50 · Some of the albite molecule is probably combined with the orthoclase molecule to form alkalic . feldspar. But as the orthoclase is not · microperthitic, and as _the composition of the oligoclase as above calculated agrees well with the optical determinations, this amount is probably not large. It thus appears that about half the rock is composed of oligoclase. It was found in making the foregoing calculation that if all the alumina, after taking out sufficient, for the biotite, anorthite, and albite, were combined with the available potash it would !give nearly as much muscovite as biotite. This result, as microscopical examination shows, is plainly erroneous, and as the alumina in the analy8is rather higher than is common in rocks of this general chemical character half of one per cent of this oxide was assumed as excessive and ·thrown in with the remaining iron oxide as iron ore. This is· in accord with the well-known fact that small and often unavoidable errors in analysis, espea52.24 per cent of oligoclase, of the approximate composition Ab8An3

SCHULTZE GRANITE. cially a.ny occurring in the iron determinations, are cumulatively thrown upon the alumina. Upon consideration of the chemical and mineralogical compositions together it appears that the rock does not fit into existing schemes of classification. It is chemically a sodium-rich granite, but mineralogically it is about half plagioclase. It is conceivable that under slightly different conditions the calcium might have gone into mineralogical combination to form pyroxene or amphibole instead of oligoclase, and the rock would then have been made up chiefly of alkalic feldspar and could be placed without hesitation among the sodium-rich granites. All things con:5idered, it appears to belong-somewhere between the quartz-monzonites and the alkalic granites. · It is placed provisionally with the latter for the reason that chemical composition is considered more important in deciding petrological relationship than the particular m~nner in which the potassium, sodium, and calcium of a given magma enter into mineralogical combination. The foregoing description applies to what may be termed the typical rock of the Bloody Tanks area-the rock characteristic of the mass as a whole, particularly at some distance from its periphery. . Near the latter the typical porphyritic granitoid rock sometimes passes into facies, which, in the absence of a more appropriate name, may be called biotite-granite-porphyry. ·Such porphyry is characteristic of the area north of Bloody Tanks, drained by Liveoak . arroyo, and of the southern border of the granitic area near the schist contact south of the Schultze ranch. The lobe-like projection of the biotite-g-ranite extending northward past Needle Mountain toward . Jewel Hill shows ·much textural variation, passing frequently into facies in which very conspicuous orthoclase phenocryRts lie in a medium granular to. fine granular, rather biotitic groundmass. The orthoclase phenocrysts are occasionally 4 or even 5 inches in length, such large crystals always showing rounded outlines and more or less peripheral poikilitic texture. A typical specimen of the granite~porphyry near the s?hist contact, 2 miles south of the Schultze ranch, shows idiomorphic phenocrysts of orthoclase and quartz in a fine-grained groundmass consisting chiefly of white feldspar, quartz, and biotite. The orthoclase phenocrysts occur in . apparently untwinned individuals of the usual orthoclase habit and have a maximum length of about 2 centimeters. The quartz phenocrysts are o£ slig-htly rounded bipyramidal form, and rarely exceed 5 millimeters in length. Under the microscope the rock shows a typical porphyritic texture. Phenocrysts of orthoclase, quartz, plagioclase (mostly oligoclase), and biotite lie in an extremely fine granular groundma.ss, ~::~uch as is common in "quartz-porphyries," but which was hardly expected in a facies of so crystalline a plutonic rock as the

GEOLOGY OF THE GLOBE OOPPER DISTRICT, ARIZONA. granitite of the Bloody Tanks area. The quartz phenocrysts, too, are embayed as is common in rhyolitic effusive rocks. The is usually untwinned, idiomorphic, and fairly fresh, although all the contain some seriC",ite and indeterminable alteration products. The biotite is almost wholly altered to chlorite, epidote, and iron ore. A chemical analysis of this porphyry is given under II in the table of analyses, on page 69. ·Th_e practical identity of the magma which solidified as porphyritic biotite-granite in the middle of the batholith and as granite-porphyry at the contact with th~ schists is apparent from a comparison of analyses I and II. The modification is textural, and perhaps to some degree mineralogical, but there has been no appreciable magmatic differentiation. The porphyry of Liveoak Gulch has been much shattered, and is often extensively stained with salts of copper. In its petrographic'll char3cter it is similar to that just described, but all gradations may be found along the Western Pass road near Bloody Tanks, from porphyries with microcrystalline groundmass to the typical biotite-granite of the central portion of the batholith. The texturally variable rock which forms the lobe extending across the Pinto Creek road south of J Hill differs microscopically from the typical rock of the Bloody Tanks area in the· presence, with the oligoclase, of a more calcic plagioclase, in part labradtn:ite of the composition Ab1 A n1 Biotite is also a little ·more abundant, and titanite, never more than a very sparing constituent in the normal rock, is here a conspicuous accessory mineral, not only in idiomorphic microscopic crystal.s, but as individuals visible in hand specimens. Iron ore and apatite are also som·ewhat more abundant than in the usual rock of the area . . The small area of granitic rock intrusive in Pinal schist, at the forks of the Gold Gulch and Pinto Creek roads, is probably merely an apophysis (offshoot) of the main Bloody Tanks mass, which it petrographically resembles. The rock of the . Porphyry Mountain area, as exposed in the upper part of Gold Gulch and on Porphyry Mountain, is a light-gray porphyry resembling that of Liveoak Gulch, and .like the latter, it is much fissured and is somewhat generally impregnated with fine pyrite. North of Porphyry Mountain this porphyry grades into a rather coarsely crystalline, crumbling porphyritic granitite which becomes reddish in color as it passes beneath the quartzites of the Apache group. Under the microscope the porphyry and porphyritic granitite of the Continental area closely resemble the corresponding rocks · of the Bloody Tanks area, and both are probably referable to the same magma and to the same period of intrusion.

SCHULTZE GRANITE .AND RUIN GRANITE. · DIKES CONNECTED WITH THE INTRUSION OF THE SCHULTZE GRANITE. Occurrence and distribution.-These dikes, which may be classed generally as granite-porphyries, are confined to the southern half of the quadrangle and cut the Madera diorite and the Pinal schists. Some of them, as for example the dike shown on the map about a mile and a half east of the Pinal ranch and the smaller ones shown about 2 miles southeast of the Schultze ranch, are directly connected with the Bloody Tanks granitite mass. Others, such as the irregular dikes extending southwestward from the Hog ranch and the long one south of Lyons Fork, have no visible connection with any parent granitic body. The dikes, even when occurring in the quartz-mica-diorite, show a marked tendency to conform in trend with the general strike of the schists. The Madera diorite, like most granitic masses of any size, is also cut by lightcolored fine-grained aplitic dikes. These are generally too small to map, and as they present no unusual features their further description may be omited from this paper. Petrography.-The rock forming the middle portions of the ' larger dikes is a granite-porphyry petrographically identical with the marginal_ facies of the . Bloody Tanks mass already described. In order to place this identity beyond question, a chemical analysis was made of a typical specimen from the Hog ranch dike, collected about half a mile southwest of the latter place. This analysis is given in column III on page 69. Comparison with analyses I and II shows not only that all three rocks are formed by the solidification of one magma, but inasmuch as they represent respectively typical specimen.s from the middle and margin of a great batholithic mass and from an outlying dike, they indicate as well remarkable chemical homogeneity of this magma solidifying under conditions geologically diverse. This identity alone is enough to show that· the Bloody Tanks granitite is younger than the quartz-mica-diorite of the Crest area. Near their walls the granite-porphyry dikes often pass into nearly white aphanitic facies in which an occasional minute phenocryst of quartz or may be detected. Under the microscope this marginal variation shows-small phenocrysts of oligoclase and . orthoclase in felsitic ground mass, which extinguishes in shadowy areas between crossed nicols and is a minutely crystalline aggregate of quartz, orthoclase, and probably 9ther feldspars. RUIN GRANITE (GRANITITE OR BIOTITE-GRANITE). Occurreiwe and distribtttion.-Between Pinal and Pinto creeks, near the northern edge of the quadrangle, the exposures of granitite fall into three p~incipal and several smaller areas. It is evident however that all are really part of one great mass which forms a continuous basement beneath the faulted remnants of

GEOLOGY OF THE GLOBE COPPER DISTRICT, ARIZONA. Paleozoic rocks. Thus . the Pinto Creek area in the extreme northwest corner bf the quadrangle is undoubtedly part of the same mass as the granitite forming the broad :floor of Granite Basin northeast of Webster ~fountain; and~ although the connection in this case is less obvious, it is highly probable that the granitite . of Granite Basin is really continuous · with 'the petrographically identical rock of Ruin Basin. The granitite of all these northern areas shows the tendency to form relatively broad basins or valleys of erosion in an even more marked degree tb~n the Schultze granite. It is more generally decomposed than the latter rock, and usually somewhat reddish in color, both of which facts are probably due to less extensive erosion below the old pre-Cambrian surface. The surfaces of the larger areas are only moderately rocky and the generally . gentle slopes are often covered with what might be termed granite crumbs-a coarse angular sand consisting of particles of quartz. crystals, and fragments of pinkish feldspar; and flakes of biotite derived from the crumbling of the rather coarse-grained granitic rock. A little coa1~se reddish granitite correlated with the Ruin granite, is also found about 3 miles east of Gerald's ranch, forming three . small areas near the northern edge of the quadrangle. The Ruin granite is frequently found overlain by the basal conglomerate of the Apache group, resting upon a pre-Cambrian surface of erosion. Petrography.-,--The Ruin granite is uniformly of coa1~se-grained porphyritic texture, with a tendency to crumble into rounded forms from which it is almost impossible to secure fresh hand specimens. Rounded pinkish phenocrysts of ,unstriated feldspar, · often 2 inches in l~, and generally showing carlsbad twinning, are conspicuously scattered throug·h a rather coarsely granular. ground- · mass consisting of preponderating white plagioclase, quartz, black mica, and a , little pink feldspar. In general texture this rock closely resembles the much fresher, coarsely crystalline, and somewhat biotitic facies of the Schultze granite exposed on the Pinto Creek road near the head of Webster Gulch. The resemblance is so close as to suggest in the field that the rocks were originally identical and that the difference in color, largely d"Q.e to the pinkish tint of the phenocrysts in the rock of the northern areas, is merely due to longer exposure to weathering. Under the microscope, however, the large feldspar phenocrysts are found to be a finely microperthitic microcline-a mineral not known in the Bloody Tanks mass. · They are micrqpoikilitic, also, with reference to the other constituents, particularly in their peripheral portions. The groundmass is a hypidiomorphic granular . aggregate of quartz, microcline, oligoclase, and biotite, named in order of apparent abundance, with accessory titanite, apatite, iron ore, and zircon.

RUIN GRANITE AND LOST GULCH MONZONITE. The microcline is .generally fresh, but the oligoclase is more or less altered to turbid aggregates of kaolin and perhaps sericite, while the biotite is partially chloritized. No chemical analysis was made of this rock on account of the absence of perfectly fresh material. Its composition, however, is probably not very different from the normal facies of the Schultze granite, although it is likely to contain a little more iron, magnesium, and titanium, with perhaps a trifle less calcium, the ratio of sodiurr1 to potassium is probably -more nearly ~qual to unity. The chief mineralogical difference in the two rocks appears to be in the behavior of the albite molecule. In the Schultze granite this has united with the anorthite molecule to form abundant oligoclase, while in the -Ruin granite it has in part gone into combination with the orthoclase molecule to form microclinemicroperthite. The smaller amount of oligoclase in the mic~online-bearirig rocl{ is probably somewhat more calcic than in the orthoclase bearing, but this ·tendency has been to some extent counteracted by the formation of titanite. It appears from the · foregoing description that the granitoid rock of the northwestern part of the quadrangle is more nearly a typical biotite-granite than the Bloody Tanks mass of Schultze granite. It differs mineralogically from the latter to a sufficient extent to east some doubt upon the view held in the field that they represented practically simultane~:ms eruptions of the same magma, and they have accordingly been separately mapped and described. The small masses of biotite-granite lying near the northern edge of the quadrangle, about 2t miles east of Gerald's ranch, consists of rather coarsely crystalline . reddish rock, consisting chiefly of microcline, quartz, ·oligoclase, and biotite, and not distinguishable under the microscope from the facies just described. LOST GULCH MONZONITE (ADAMELLITE OR QUARTZ-MONZONITE). Definition.-As defined by Brogger a the monzonites are granular plutonic rocks chemically and mineralogically intermediate . between the syenites and diorites. They are characterized by the pi·esence of nearly equal amounts of orthoclase and plagioclase, together with hornblende, biotite, or augite. . When quartz is present in notable quantities the rock becomes a quartz-monzonite, closely related on the one hand to the granites and on the other to the granodiorites. · Occurrence and distribution.-The Lost Gulch monzonite forms . a roughly quadrangular area about 4 square miles in extent, which occupies the greater part of Lost Gulch, and stretches northeast toward Horrell's ranch, on Pinal a Die Eruptivgesteine des Kristianiagebietes. II, Die Eruptionsfolge der triadischen Eruptivgesteine bei Predazzo, etc., pp. 21-23. Knstiania, 1895.

GEOLOGY OF THE GLOBE COPPER DISTRICT, .ARIZONA. Creek. Like the Madera diorite and Solitude and Schultze granites. the Lost Gulch. monzonite is intrusive into the Pinal schists. Its present boundaries, however, save where overlapped on the east by the Gila formation, are determined chiefly by faults which have dropped the younger rocks so that they abut against the monzonitic fault block (horst). · P etrography.-As it occurs in Lost Gulch, the quartz-monzonite is a finegranular gray rock, containing scattered phenocrysts of potassium feldspar with smaller ones of plagioclase. In megascopical appearance it closely resembles the Willow Spring granite~ Toward the eastern part of the area the rock becomes more closely crystalline and the gray, medium granular groundmass is seen to be made up of potassium feldspar, plagioclase, quar:tz, and biotite. Under the microscope the monzonite shows a hypidiomorphic granular texture. Quartz is apparently the most abundant constituent, followed by plagioclase, microcline, and· biotite. The accessory minerals are iron ore, titanite, apatite, and an occasional zircon. Both the quartz and the microcline show a tendency toward poikilitic structure. The latter mineral is occasionally slightly perthitic. The plagioclase ranges from calcic oligoclase to andesine. A chemical analysis of a fresh medium-grained specimen from Lost Gulch, about 2 miles northwest of ~lack Warrior, is given below under I, while under II is placed for comparison the. analysis of an adamellite from Brixen in the · Tyrol, as cited by Brogger.a Chemical analyses of quartz-monzonites. .69 .01 None. .24 Not det. a Loc. cit., p. 62a.

LOST GULCH MONZONITE. Chemical analyses of quartz-monzonites-Continued. MnO Li20 . :: : . FeS2 a Included with pyrite. Not det. a(.06) None. Trace. Faint trace . I. Quartz-monzonite (adamellite). Lost Gulch, Gila County, Ariz. W. F. Hillebrand, analyst. II. Adamellite. Brixen, .TyroL Rube, analyst. (Bragger, loc. cit., p. 62a.) The mineralogical composition of the Lost Gulch monzonit'e may be calculated from the chemical analyses as follows: 1ffineralogical composition of the Lost Gulch monzonite. Per cent. Quartz . . Orthoclase molecule . .. .. 19. 79 Albite molecule .. a25. 03 Magnetite · . . . . . . . . . . . . . . . . Total . 100. oo In making the foregoing calculation, the albite and anorthite molecules are united to form andesine, for the reason that the microcline is· not noticeably perthitic in the rock analyzed, and the composition of the plagioclase so obtained agrees fairly well with the optical determinations. The Lost Gulch rock is chemically a quartz-monzonite. But in the absence of amphibole or pyroxene, the calcium has all gone into the combination as plagioclase, and consequently this ·mineral predominates over the microcline nearly as two to one. It is conceivable that practically the same magma might crystallize as an aggregate of quartz, . potassium-sodium feldspar, andesine, and diopside, and thus. correspond to Brogger's a Equivalent to 35.74 per cent of andesine of about the composition A b4An3

GEOLOGY OF THE GLOBE COPPER DISTRICT, ARIZONA. mineralogical definition of a quartz-monzonite, as a rock in which the orthoclase (or potassium-sodium feldspar), and plagioclase are present in nearly equal amounts. As it is, the rock lies alnwst exactly on the line between granodiorite and quartzinonzonite according to the distinction made by Lindgren. a WILLOW SPRiNG GRANITE. Occurrence ·and distribution.-This is a small isolated mass lying just north of Webster Gulch ~nd occupying an area of less than a ~quare mile. It is intrusive into the Pinal schists, and, like the Lost Gulch monzonite, is bounded in part by. faults. Petrography.-The Willow Spring granite is gray in color and usually fine grained for a rock of granitic composition, the average size of the grains being less t~an a millimeter. Occasional phenocrysts of orthoclase or microeline occur scattered. through this often nearly aphanitic groundmass. The microscope reveals a hypidiomorphic granular aggregate consisting of abundant ·quartz and microcline with oligoelase, museovhe, and biotite. The exact nature of the oligoclase 'is not readily determinable, owing to the general deeompo~ition of this constituent into nearly cryptocrystalline aggregates, apparently consisting ' principally of kaolin. The accessory minerals are apatite, iron ore, and tourmaline, none of them being abundant; The secondary minerals . are kaolinite, epidote; and chlorite. The exact petrological relationship of the '\\Tillow Spring granite remains somewhat in doubt. It is quite possible that it may be more closely connected with the neighboring quartz-monzonite of Lost Gulch than with the Solitude gr~nite. AGE AND SEQUENCE OF THE GRANITIC ROCKS. All of the graniti(~ rocks of ·the Globe quadrangle are pre-Cambrian, but are yQur~ger · than the Pinal schists into which they are intrusive. The extensive Q.evelopment of gneissic structure in the ~ladera diorite and its absence in the other granitic rocks point to the · earlier age of the former. The Madera diorite is certainly older than the Schultze granite, for it is cut by dikes from the latter. The Solitude granite is also cut by similar dikes and is· accordingly older than 'the Schultze granite, although probably younger than the Madera diorite#· The evidence for the latter relation, . however, is far from conclusive, and depends chiefly upon the more gneissic structure oJ the supposedly older rock. The relative ages of the "'\Villow Spr1.'ngs granite · and Lost Gulch monzonite are unknown. It is almost certain that they are younger than the Madera diorite, but .whether they are younger or older than the Schultze granite has not been a Am. Jour. Sci., 4th series, i/ol. IX, 1900, pp .. 277-281.

METADIABASE. determined. The age of the Ruin granite is also somewhat in doubt, but on account of their close petrographical resemblance the Schu'ltze and Ruin granites are thought to be of practically the same age. CONTACT METAMORPHISM IN CONNECTION WITH THE GRANITIC INTRUSIONS. Distinct contact metamorphism is found only in connection with the Madera diorite. The other granitic rocks were intruded into already metamorphosed and crystalline schists,. and have consequently produced no change that can be clearly distinguished from an earlier and more general metamorphism. While the intrusion of the Madera diorite resulted in undoubted contact phenomena, . it_ is rather difficult to discriminate between these and the broader metaowrphism whereby a series of sedimentary rock~; w:ere transformed into crystalline schists. Andalusite and sillimanite, characteristic contact ~inerals, are frequently prese~t in the coar::5ely crystalline and rather massive muscoviteschists near the quartz-mica-diorite, but are not found the laminated sericitic schists at a distance from the eruptive rock. Black tourmaline, while not uncommon as a microscopical constituent of the schists, is particularly abundant near the eruptive contact associated . with quartz in veins and veinlets. In addition to the development of these minerals, which are characteristic of granitic contact zones, the general crystalline texture of the schists is plainly related to the intrusion of Madera diorite. Near the latter the schists are coarsely crystalline, rather massive, and have lost all traces of original clastic-structure. Away from· the Madera diorit~ they become finely crystalline, fissile, and occasionally retain in part the structure of pebbly grits. It is probabl~ that the 'metamorphic action of the quartz-mica-diorite was not confined to the production. of a welldefined contact zone, but was an important factor in transforming the sedimentary beds as a whole into crystalline schists. That later metamorphic forces have also been effective in imposing its present character upon the pre-Cambrian complex, is shown by the considerable development 'of ~·nei3sic structure in the diorite itself. METADIAHASE . .Definition.-By metadiabase is meant a diabase which has undergone mineralogical change, . although 'its original character is not wholly obliterated. Occurrence and distribution.-The name metadiabase might with justice be applied to certain uralitic facies of the rock described in this report as diabase. For the sake of ·clearness and convenience, however, it is restricted to a small area of more conspicuously altered rock which lies 1! miles east of Schultze's ranch and which is older than the characteristic diabase of the region. Very

GEOLOGY OF THE GLOBE COPPER DISTRICT, ARIZONA. little of this rock is exposed and, as it passes beneath the Gila formation, its . actual extent is not known. Petrography.~The metadiabase is very dark green and rather coarsely the feldspar being so dark in color as to superficially resemble amphibole. A striking peculiarity of the rock is the occurrence of num~rous inclusions of white quartz--apparently vein quartz. These fragments are conspicuously corroded and embayed, and are surrounded by reaction rim~ of amphibole, visible to the unaided eye. The · microscope shows the rock to be a rather coarsely crystalline ophitic aggregate in which the usual place of the augite is taken by nests of lightgreen amphibole with a little biotite, apatite, and iron ore. The feldspar is apparently a calcic labradorite and although fairly fresh, .is brown in transmitted light, the color being due to thiekly crowded minute rods and dark dust-like particles. The amphibole does not merely .occupy the spaces between the feldspars, but prisms <?f the former mineral often project into the latter. Although the general character of the alteration . is similar to ordinary uralitization, yet ' there is a suggestion that the diabase of this mass, like the andalusite-bearing granite adjoining it, has been subjected to contact metamorphism, which appears to have been a local effect of the intrusion of the granitite of the Bloody Tanks area. The quartz inclusions are granular aggregates having the common microscopical character of vein qu~rtz and are enveloped in g-reen amphibole, the small prisms of the latter ·mineral standing generally perpendicular to the surface of th~ quartz. The source of these inclusions is ~ot known. Age.-:-The metadiabase is cut by granite-porphyry dikes from the Bloody Tanks granitite, which is considered as probably of pie-Cambrian age. Tl).e metadiabase is therefore pre-Camb,rian and much older than the diabase next to be described. DIABASE. Dtjin~tion.-Diabase Is an eruptive rock, usually intrusive, and consists essentially of a crystalline aggregate of calcic plagioclase (which may range from labradorite to anorthite) with pyroxene, frequently a little biotite and usually olivine. When the hitter mineral is present, · the rock is commonly termed . an . olivine-diabase. The ordinary accessory constituents are magnetite (usually titaniferous) and apatite. The texture of diabase varies from aphanitic to coarsely crystalline, and as seen under the microscope is ophitic, that is, the .pyroxene (usually augite) fills angular spaces belween the partly idiornorphic crystals of plagioclase. Diabase is usually a heavy rock with dark-gray or greenish color. In the Globe district the diabase, really an olivine-diabase, is commonly called ''diorite" by the miners.

DIABASE. Occurrence distribution.-Diabase occurs intrusive into all the rocks of the Globe region from the pre-Cambrian schists and granitic batholiths up to and including the Globe limestone, as sills (intrusive sheets) ranging f~·om a fraction of an inch to several hundred feet in thickness, as irregular masses cutting across the stratification of the invaded rocks, and as small dikes. Owing to the numerous faults that traverse the region, it. is impossible to determine the number, thickness, and former continuity of the diabase. sills. They appear to have been intruded at different stratigraphical horizons in rocks already much faulted. Thus in one portion of the quadrangle certain beds of the Apache group may be separated by a sill 400 feet thick, while a few miles away the same beds will be found in undisturbed sedimentary contact with smaller sills above or below in the stratigraphical column. One or more sheets varying greatly in thickness are usually found cutting the pre-Cambrian schistose and granitic complex, about 200 feet below the basal conglomerate of the Apache group and lying roughly parallel to the stratification of the latter. Such a sill appears in the ~Southeastern corner of the quadrangle. Another of irregular shape, possibly originally a continuation of the foregoing, is shown near the edge of the map (Pl. I) southwest of Pinal· Peak. North of Webster Mountain there is a relatively thin sill, ,30 or 75 feet in thickness, occurring less than 50 feet below the base of the Apache group, and in the northwestern corner of the quadrangle the granitite is cut by two or more sills at varying distances up to 200 or 300 feet below the old pre-Cambrian erosion surface. These sills are so irregular and have been so faulted as to render their original number, thickness, and position with reference to the Apache sediments which formerly overlaid them rather conjectural. Similar sills occur in the biotite-granite near the edge of the quadrangle north of Globe, and they may generally be found wherever the granitic rocks which underlie the Apache group are extensively exposed. The diabase masses, however, attain their greatest bulk and importance within the stratified rocks of the Apache group and Globe formation. Their intrusion into these quartzites and limestones was accompanied or preceded by extensive faulting which divided the strata into numerous blocks. The molten magma not only forced its way , as sills between the strata of the individual · blocks, but filled the fault fissures and drove the blocks apart. Masses of limestone and quartzite were thus completely enveloped in the invading molten rock and often shifted bodily to an extent which at first view seems scarcely credible. The magma was able . to overcome those forces of gravity or compression tending to hold the . blocks of strata together, and to float them apart. Although tha 9651-No. 12-03-6

GEOLOGY OF THE. GLOBE COPPER DISTRICT, ARIZONA. process can not be exactly paralleled by any familiar simile, it may be partly likened to the break-up and movement of thick ice by a spring :flood. The largest area of diabase within the quadrangle is that extending northward from the Old Dominion mine, and from it may be drawn several illustrations of . the general mechanical effect of the intrusion. Scattered over this· area, particularly west of Ramboz Peak, are little masses of quartzite belonging to the Apache group, and composed of strata dipping generally to the southwest. Some of these masses are bounded in part by faults, but many of them are separated from the diabase by er~ptive contacts. They are not merely remnants of an overlying sedimentary cover, now largely · stripped away from the diabase by erosion, but they are detached, irregular blocks of more or less contorted strata, h;olated in the eruptive rock. Most of them are inclusions, in fact, brought to light by the erosion of the diabase which f'Ormerly completely inclosed them. Such is the mass of quartzite at the. Big Johnnie mine on the western slope of Black Peak. It is made up of beds dipping gently to the south, underlain and overlain by diabase, from which it is separated by intrusive contacts. The sheet of diabase here lying on top of the quartzite and forming the summit of Black Peak has a thickness of at least 300 feet, while it is not known how much more has been removed by erosion. In the workings of the. Grey mine in Copper Gulch masses of quartzite and limestone strata were found irregularly distributed in the diabase down to the sixth level, at a depth of about 300 feet. Below this the shaft is in diabase for 400 feet, although blocks of inclosed strata may possibly be encountered when drifting is begun. About half a mile east of the saddle at the head of Copper Gulch (Pl. XV) a considerable body of limestone strata belonging to the Globe formation it:l inclosed by the diabase, while just south of the limestone, at an elevation of about 300 feet above it, the ·same mass . of diabase passes with an intrusive upper· contact beneath conglomerate, grits and quartzite of the Apache group. Stratigraphically the limestone belongs above the quartzite, but ~ere it lies enveloped in the dia?ase at least' 500 feet below its normal position. A similar condition exists in the Old Dominion mine, as shown in fig. 7, a block of limestone occurring isolated in the diabase that forms the gen-eral foot wall of the Old Dominion fault. Similar examples of the displacement and isolation of blocks of strata at the time of the diabase intrusion might be cited from other parts of the quadrangle. Some of these are evident from an inspection of the general geological map (Pl. I), but the detailed description of all. is not necessary. So far as its upper contact is preserved, the great body of diabase north of Glpbe has the gen~ral character of a thick sill or laccolith. On Buffalo Ridge and elsewhere the intrusive rock passes under the quartzites with a contact which

U . S . Geological Survey Professional Paper No . 12 Pl . Xv I

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.'1 LEG EN 0 ERUPTIVE ROCKS MESOZOIC I J n rtu t sn lter clurr:rps. :woo

DIABASE. in general follows a bedding plane. But even as regards its upper surface, this irregular mass, which forced itself into and around the ·blocks of ·faulted strata, is a. sill only in a very general way. Of its lower surface nothing is known. Although in other parts of the region and in the canyon of the Salt River to the northwest of the quadrangle the diabase forms distinct sills, none of them are demonstrably so thick as this mass, which, if we disregard the bloeks of included strata, is shown by the workings of the Old ·Dominion and Grey mines to reach a thickness of over 800 ieet. Whether it rests upon the lower beds of the . Apache group .or has followed in general the pre-Cambrian surface upon which the sedime~ts were laid down, or whether it extends downward as a batholith to indefinite ~depths, are questions which can not at present be answered. . Petrogl aphy.-When fresh, the diabase typical of all the larger areas in the quadrangle is a · tough,_ heavy, dark-gray holocrystalline rock of medium grain. The minerals readily visible to the unaided eye are plagioclase, augite, and iron ore. The augite is often particularly noticeable on natural surfaces of the rock, as it forms flashing poikilitic blotches, sometimes 2 centimeters in breadth. The weathered rock is usually greenish, and the diabase masses can often be distinguished from a distance by the dark-olive hue of their bare slopes. Hard residual nodules of various sizes and curious nodular surfaces are extremely characteristic of the disintegration of the typical diabase. · The rock crumbles to a greenish sandy soil (saprolite), embedded within which are residual kernels of sound rock ranging in size from that of a pea up to a foot or more in diameter. (Pl. XVII, A.) The larger masses have very characteristic lumpy or warty surfaces, and with the . further progress of disintegration these lumps separate as small nodules. Close examination of these little bodies shows that their form and resistance to disintegration is dependent upon the presence of rounded poikilitic crystals of augite. In addition to the knobs, with which exposed surfaces of the diabase are usually studded, there are sometimes present well-marked projecting ribs or ridges an inch or two in height. These are due to the development of secondary hornblende along minute fissures in the rock and the resistance of this mineral to weathering. Thin sections examined under the J:?microscope .show a perfectly fresh ophitic aggregate of calcic labradorite or bytownite, faintly brownish augite, olivine, and a little biotite, iron ore, apatite, and titanite. In many cases-as, for example, the rock on the summit of Black Peak-the diabase is so fresh that the olivine, which occurs in the usual rounded forms more or less inclosed in the augite, shows scarcely a ·trace of serpentinization. The augite is broadly poikilitic, the apparently isolated angular areas between the partly jdiomorphic crystals of plagioclase showing optical continuity over a large part of the microscopic slide. The angle c: .c is approximately 45°. (

GEOLOGY OF THE GLOBE COPPER DISTRICT~ .ARIZONA. A chemical analysis of a fresh typical specimer: from a hilltop 1 mile northW3St of Black Peak is given below: Chemical analysis of diabase. [Dr. E. T. Allen, analyst.] Zr0 .72" None. None. 02 Without knowledge of the exact composition of the augite, it is impossible to make from the chemical analyses an accurate calculation of the quantitative mineralogical composition of. the rock. Rough calculation, however, checked by optical estimation in thin sections, indicates a composition of about 55 per cent of bytownite, 30 per cent · of augite, 10 per cent of olivine, and 5 per cent of biotite, iron ore, titanite, and apatite. The rock may be considered a typical olivine-diabase. Although the diabase maintains its general character and appearance far beyond the bounds of the Globe quadrangle, it · is subject to certain local variations. In . part these are due merely to alteration, the olivine being serpentinized and the augite wholly or. partly changed to green uralitic amphibole. Every large mass of the diabase is made up in part· of such uralitic facies, and some of the smaller bodies are more less uralitic throughout. Near the intrusive contact of the diabase with other rocks, the former often exhibits well-marked textural variation. It is generally more finely crystalline

te PaleOzoic L.b· W · ' rar . ashington Cil . DIABASE. and may be nearly aphanitic. Vesicular structure is not infrequent and is ticularly characteristic of intrusive contacts of the diabase with the Globe limestone. Such contacts may be well studied east and southeast of Black Peak, near the Murphy ranch, and in the southeastern corner of the quadrangle. In contact with the quartzites of the Apache group, the diabase is usually nearly aphantic and contains small vesicles, filled with chlorite, ealcite, quartz, or specularite. This contact modification, which is usually reddish in color while the typical diabase is dark gray or green, is well exposed south of the saddle at the head of Copper Gulch, a mile and a quarter a little west of south from Barnes Peak, and elsewhere in the quadrangle where the two · rocks are in eruptive contact. The contact facies are, as a r~le, much decomposed. The microscope shows that the augite and olivine have been changed to chlorite, serpentine, calcite, and ferric oxide, while the plagioclases have become obscure aggregates of calcite, quartz, kaolin, and other secondary products. These contact rocks were originally vesicular basalts and some of them appear to have been more or less glassy. Other local facies of the diabase come from variations in the relative amounts of feldspar and ferromagnesian minerals present. Irregular streaks in which the augite and olivine are less abundant than usual are not uncommon, and such local facies are noticeably light colored and feldspathic aB compared with the normal diabase. Within most of the larger diabase areas occur occasional masses of a reddish, usually rather coarsely crystalline rock, consisting of red feldspar, ragged prisms of dark amphibole, and a little iron ore. This rock disintegrates readily, and its field relation to. the normal di:abase is not easily made out, although it seems to occur as segregations from the diabasic magma. under the microscope the rock is rather decomposed, but it is seen that the dominant feldspar is turbid orthoclase or mierocline, associated with a smaller amount of plagioclase, partly chloritized and epidotized amphibole, and a little quartz in micropegmatitic intergrowths with the orthoclase. The rock is in fact a hornblende-syenite, earrying a little quartz, and its composition easts some doubt upon the hypothesis entertained in the field that it Is merely a local facies of the diabase. The diabase occurring as dikes . cutting the pre-Cambrian complex is usually mo're finely erystalline than that of the larger sills, and may be nearly aphanitic. Contact metamorphism.-The metamorphic a~tion of the diabase, even when intruded in great masses into quartzites and limestones, is remarkably slight. The only effect discoverable in the Globe lhu.estone is the development of a little coarser crystalline texture · which may extend for only a few inches from the contact. Even this alteratiOn is not always recognizable. The quartzites often

GEOLOGY OF. THE GLOBE COPPER DISTRICT, ARIZONA. sho~ no preceptible alteration at the diabase contact. In one case, however, for a distance of feet or more from the contact, the quartzite was observed to be thickly speckled with small greenish spots which the microscope showed to be little nests of chlorite. But as these spots are very similar to the little spherical aggregates of _sericite (described on page 36), which are not clearly connected with the intrusion of the diabase, it is by no means certain that they are really a contact phenomenon. Age.-Since the large sills are intrusive into the Globe limestone as well as into the Apache group and older . ro'cks, the main diabasic eruption must have taken place after the close of the Carboniferous. The whole region was afterwards faulted and . greatly eroded before the ·eruption of the dacite, the latter event being assigned with some probability to the Ter~iary. The great diabase intrusions are accordingly referred provisionally to the Mesozoic, although there are no data available to fix within that era the particular period to which they belong. The age of the dark-colored nearly aphanitic dikes and small intrusive masses occurring in the pre-Cambrian complex is not directly determinable. Their geological position leaves it uncertain whether they belong to th,e intrusive period represented by the diabase sills, or to the much later date of the postdacitic eruption of olivine-basalt described · on pages 95 to 97. The distinction has accordingly been made on petrographical grounds, certain fresh, more or less glassy masses, such as that just north of the Pinal ranch, being correlated with the later eruption and colored on the map as olivine-ba.salt, while the more · coarsely crystalline uralitized dikes are considered as probably contemporaneous with the diabase sills. The magmas of the two eruptions were practically identical. DIORITE-PORPHYRY. JJejinition.-By diorite-porphyry is usually meant a holocrystalline intrusive rock having the chemical and mineralogical composition of diorite, but charac- · terized by porphyritic structure, with a well-defined fine-grained gro~ndmass. The rocks here described under this head are generally decomposed, and it is not certain that all of them were originally typical diorite-porphyry. Occurrence and distribution.-The diorite-porphyry occurs most characteristically as sills, ranging in thickness from 1 to 50 feet, in the lower, shaly member of the Apache group, and less frequently as dikes and small irregular · intrusive masses. Small sills are also occasionally found intruded between the beds of the Globe limestone and in the ·granitic rocks just below the base of the sedimentary series. the geological map. On account of their small size, the sills are not shown on They are rarelY absent. however, from the lower part of

DIORITE· PORPHYRY. the Apache group and are well exposed in the southeast and northwest corners of the quadrangle. The relation of the sills to the sedimentary and underlying rocks may be seen in figs. 2, 4, and Pl. VII. Just north of the Old Dominion mine a dike of diorite-porphyry (shown in the geological maps, Pls. I and XV) cuts the diabase and can be traced from the point where it emerges from beneath the dacite flow almost up to the Buffalo mine. A smaller dike of decomposed diorite-porphyry occurs also in diabase ne~r the '96 shaft of the Continental mine. In the Apache Mountains, outside of the quadrangle, occur considerable masses of post-Cambrian diorite-porphyry, which is very much fresher than any of the rock just described. It is not yet known whether the Apache Mountain is contemporaneous with or younger than the decomposed sHls of the Globe quadrangle. Petrography.-The rock of these sills and dikes is always more or less decomposed and its color is usually light yellowish or greenish gray. In the fresher specimens small dull-white phenocrysts of feldspar, and sometimes minute prisms obviously pseudomorphic after hornblende, are recognizable with the unaided eye. Owing to its ready decomposition, the rock easily crumbles, and coherent specimens are obtainable with some difficulty. Microscopical examination of thin sections shows that the rock is generally too · much altered to allow of its precise classification. The plagioclase phenocrysts, apparently for the most part andesine, are partly altered to aggregates of calcite, sericite, and probably kaolin. The original hornblende, and possibly some biotite, are completely changed to chlorite and other secondary products. Small embayed phenocrysts of quartz, while lacking in some facies, are fairly abundant in others, and it is quite possible that these decomposed, greenish-gray sills and dikes embrace rocks of 1nore than type, and were intruded . at different times. The groundmass is usually a finely crystalline aggregate of plagioclase, quartz, and possibly some potassium feldspar, the whole showing the patchy and shadowy extinctions common to many dioritic porphyries when seen between crossed nicols. .The dike north of the Old Dominion mine is a quartz-free dioriteporphyry, with some chlorite which is apparently pseudomorphous after biotite. Age.-As the diorite-porphyry cuts the Globe limestone it is post-Carboniferous. Alongside the county road to Florence, just beyond the southern edge of the quadrangle, dikes of this eruptive, here apparently containing no quartz, cut the diabase and are therefore younger. The same relation obtains in the case of the dikes north of the Old Dominion and near the Continental mines. As a rule, however, the two rocks are rarely found in juxtapositi~n, and this fact, taken in connection with the general decomposition of the diorite~porphyry

GEOLOGY OF THE GLOB:~!.: COPPER DISTRICT, ARIZONA. and its occurrence as regular and often thin sills in blocks of strata which have been faulted and shifted about at the time of the diabasic intrusion, strongly suggests that a part of the porphyry, particularly that which may be provisionally ·termed quartz-diorite-porphyry, represents a period ·of eruptive activity anteriOr to the great in_vasion of diabase, and consequently that the more or less decomposed intrusives here described as diorite-porphyry are not all of the same age. EFFUSIVE ERUPTIVE RO~KS. DACITE. Definition.-The dacites are porphyritic effusive rocks in which crystals of plagioclase, quartz, and hornblende or biotite, as the common essential minerals, are embedded in a more or less glassy groundmass. The biotite-daciteE! are closely related to the rhyolites, which they often much resemble. The relation of the dacites to the rhyolites and andesites among the volcanic rolf:s is similar to that' of the · quartz-diorites to the granites and diorites among the plutonic rocks. Occurrence and distribution.-Owing to its abundance, peculiar weathering, and often striking topographical expression dacite is one of the most conspicuous rocks in the region, familiarly known to ranchman and miner alike as '"trachyte." It form_s one or more effusive sheets or flows, often locally associated with underlying · beds of tuff. The original continuity which this flow probably possessed has been greatly obscured by faulting. The maximum thickness is unknown, but existing remnants show that it must have exceeded 1,000 feet. In spite· of vigorous post-dacitic deformation of the region, it is clear that the flow was poured out over an irregular surface in whose ravines and valleys the Whitetail formation had previously accumulated. As it is one of the y~mngest rocks in the quadrangle and is of fairly resistant nature, the dacite is found capping many of the hills under 6,000 feet in elevation, particularly in the northwestern part of the area. It lies upon various rocks, many of which are soft and easily eroded, and the dacite is consequently a frequent cliff maker and responsible for much of the minor ruggedness of the topography. In natural exposures the dacite varies in color from light pinkish-gray to nearly black. It has a tendency to weather into large, rounded, bowlder-like masses, forming characteristically rocky surfaces, which, as Pl. XVII, .B, shows, are difficult of traverse. These loose masses are frequently over 6 feet in diameter, and, owing to differential weathering of glassy and lithoidal portions of the rock, often show . curiously pitted exteriors. The origin of the bowlders is traceable to a rather irregular division of the rock into rude cuboidal blocks by systems of joints, which are often not visible until brought out by initial disintegration.

DACITE. Such joints can be well seen in the cli:ffR along ~Iineral Creek at the Sixtysix ranch, where various intermediate stages may be observed between angular joint blocks and rounded bowlders. As a rule, the weathering of the dacite is a very superficial process, being confined to the disintegration of exposed surfaces. Decomposition has rarely penetrated the rock for more than a fraction of an inch. By far the most abundant facies is a light pinkish, inconspicuously porphyritic biotite-dacite, which preserves great uniformity of color and texture over the entire region. This is the rock to which the name "trachyte" is erroneously but unanimously applied by the people of Globe. Of far less abundant occurrence is a dark-gray, glassy facies, often showing distinct flow banding, and of typical vitrophyric structure, which is frequently found. at the base of the dacite. It is merely the . quickly cooled glassy bottom of the lava flow. It is not always present, but when it does occur, it invariably intervenes between the pink dacite and the underlying rocks. Beneath this vitrophyre, and not always easily separated from it in the field, are certain local accumulations of bedded dacitic tuffs. These are soft, often plainly detrital rocks, ranging in tint from white to pale lemon yell0w or gray. They were laid down in small local basins, and are often absent, the dacite ,resting directly upon the older rocks. The largest mass of dacite occurring in the Globe quadrangle lies in its southwest corner. This is the rock which forms Hutton Peak and through which Mineral Creek has cut its narrow gorge south of the Sixtysix ranch. It is continuous with the dacite just north of the Pinal ranch and extends for a considerable distance beyond the bounds of the quadrangle to the west. The entire mass is apparently part of a single flow which has undergone deformation and erosiOn. It culminates at 5,608 feet in Hutton Peak and slopes gently southward, with the exceedingly rugged surface characteristic of this rock. Near the Pinal ranch the dacite rests on granite, the surface of the latter having been irregularly eroded before the eruptive rock covered it. Southeast of Hutton Peak it rests upon the Pinal schists. The mass of the flow is composed of the . pink biotite-dacite, but the darker, more glassy, and highly vitrophyric facies described on page 93 is frequently found where the base of the flow is exposed. This variety is usually less than 10 feet in thickness and is apparently an integral part of the main flow. It is not always present, and pink dacite sometimes · rests directly upon the granite or schist. The quartzites occurring south of :Mineral Creek, between the Sixtysix ranch and Government Spring, and forming the northern end of the Dripping Spring Range, appear to have formed an island-like mass around which the dacite flowed and which it possibly formerly buried.

GEOLOGY OF THE GLOBE COPPER DISTRICT, .ARIZONA. In the northwestern part of the quadrangle the principal body of dacite is that culminating in 'V ebster Mountain. This is evidently a very thick portion of the flow as shown by the canyons that have been excavated in it without exposing its base. The area is partly inclosed by peripheral faults whereby this portion of the flow has been relatively dropped with reference to the surrounding older rocks, and its edges in some places brought against the latter. The bounding slopes of this fault block, particularly on the west, north, and east, are often precipitous and good exposures of the bottom of the ~ow are rare. The rock is the prevailing pink daoite, bu~ the dark v~trophyric facies which occurs only at the bottom of the flow is exposed on the east slope of Webster Mountain and at the head of vVillow Spring Gulch. Considerable masses of da~ ite occur ·along Pinto Creek, forming picturesque cliffs south of Horrell's 1:anch, and the same· rock forms the pinnacles and abrupt western wall which look down into the gorge of Pinto Creek south of the mouth of Gold Gulch. Pink biotite-dacite caps most of the higher hills, including Sleeping Beauty Peak, in the much faulted country between Webster Mountain and Pinal Creek. The bluffs overlooking this creek west and south of Horrell's home ranch are, as the map shows, the eroded edge of a much warped and probably faulted fragment of the flow, which rests on diabase and forms an apparent synclinal basin, open to the south and filled with Gila conglom1erate. Half a mile southwest of Black Warrior the tnassive dacite rests upon 40 or 50 feet of tuff containing many fragments of the underlying Pinal schists. The ores of the Geneva, Dadeville, and Montgomery claims occur in this tuff. The area on the south slope of the hill west of Black Warrior, colored the map (Pl. I) as dacite, is composed chiefly of this tuff, most of the overlying massive dacite having been eroded away. North and. east of Globe the dacite flow is represented by an irregular and interrupted remnant which overlies quartzite, limestone, and diabase, and dips gently southwestward· under the Gila conglomerate. This outcrop attains a maximum width of about three-quarters of a mile north of the Old Dominion mine. It lies up?n ·an uneven surface and was considerably eroded before the Gila formation was deposited, since the latter rests directly on limestone and quartzite southeast of the mine. A single tiny remnant of. the dacite, occupying a little saddle in quartzite, 5t miles north of Globe, and at an elevation of 4,500 feet, is the only vestige of the former ext~nsion of the lava flow over the extreme northeastern portion of the quadrangle. In the southeast quarter of the quadrangle the dacite does not occur. Petrography.-The color of the freshly fractured dacite is gray, usually

U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER NO. 12 PL. XVII A . TYPICAL WEATHERING OF D IABASE; O N IWADS ID E N EAR PIONEER. B. CHARACTERISTIC SURFAC F O F DAC ITE, NORTH OF TH E O L D DOMINION MINE.

DACITE. with a decided pinkish tinge. The rock is rough to the touch, and at first glance appears to be more porous than is actually the case. It is firm and tough, rather , than hard and brittle, and is easily quarried ahd shaped. Owing to the small size of the phenocrysts, which rarely exceed 3 milliF eters in length, the porphyritic structure is not conspicuous, and the rock sh ws rather uniform texture. Small included fragments of other rocks are often abundant, and in most cases these are of diabase. · Such inclusions are particularly numerous and well exposed in a little gorge, cut through the eruptive rock, lt miles northeast of Government Spring; but there are few masses of the dacite which do not contain soiiJ.e of these · inclusions. Close examination of a fresh surface of the da~ite shows numerous phenocrysts of feldspar, many of which have the striated cleavage faces of plagioclase, while a few are apparently orthoclase (sanidine). Sparkling hexagonal scales of biotite, rarely over a millimeter or two in diameter, are scattered through the rock, their number varying considerably in different specimens. Phenocrysts of quartz are always present, but are not conspicuous, and occasionally small black phenocrysts of hornblende can be detected. All of the . phenocrysts are embedded i11 a dull pinkish semilithoidal matrix, which gives the general tint to the rock. Seen under the microscope, the prevalent pinkish variety of the dacite shows vitrophyric structure. The phenocrysts of feldspar, quartz, biotite, and occasionally of hornblende, are inclosed in a streaky or ropy, semiopaque, glassy · groundmass, ,showing the beautiful billowy flowage lines characteristic of this structure in andesitic and rhyolitic rocks. The feldspars, which are principally plagioclase, are all more or less rounded - in outline from magmatic corrosion. They are perfectly fresh and clear, and range in composition from labradorite (Ab1An1) to andesine (Ab5An3). Zonal structure is common, the outer shells being less calcic than the inner. The potassic feldspar is much less abundant than the plagioclase, and is the clear, vitreous variety of orthoclase commonly known as -sanidine. It has. been more strongly corroded than the plagioclase and presents rounded or even enlarged outlines. It shows the usual cleavages, optical orientation, index of refraction, and double refraction of orthoclase, but, as far as observed, is not twinned. It is more frequently irregularly cracked than the plagioclase, and fragments of the broken crystal~ have sometimes been displaced by movement of the magma. The ratio of the andesine and labradorite to the orthoclase is probably greater than - 10 to 1. The quartz presents no features of exceptional interest. It is deeply embayed and destitute of all crystal boundaries, as is common in rocks this type. It is perhaps a little more abundant than the orthoclase, but much subordinate to the plagioclase.

GEOLOGY OF THE GLOBE COPPER DISTRICT, ARIZONA. The biotite is the common, conspicuously pleochroic variety, with the strong absorption usual in andesitic rocks. It sometimes shows magmatic alteration, which has involved not only the outer surface of the crystal but its whole mass. This altered mica has lost part its color and pleochroism, the lamellffi have frayed out at the ends and split _apart, and the whole is filled with specks of opaque iron ore. Intergrowths between the different phenocrysts are sometimes met with . . Quartz and andesine rarely form micropegmatite, and andesine or labradorite are occasionally intergrown. The accessory constituents are a green hornblende, occurring in small prismatic crystal fragments, apatite, titanite, zircon, and a little magnetite. The ground mass of the dacite is glassy, and notwithstanding the thickness which the flow must have attained, never exhibits more than incipient crystallization. Globulites, trichites, feldspathic microspherulites, and an indeterminate ferritic dust which renders the groundmass semiopaque and gives the pink tint to the ~ock are common. In some cases the groundmass shows the minutely divided and shadowy double refraction characteristic of the . devitrification of siliceous glasses into obscure aggregates of quartz and feldspar. But distinct well-formed crystals of younger growth than the evidently intratelluric phenocrysts do not occur. The rock is a vitrophyric biotite-dacite, and belongs with the hyalo-daci~es of Rosen busch. a A chemical analysis, made by Dr. E. T. Allen, of a typical specimen of the dacite collected a quarter of a mile north . of the Old Dominion mine is giv~n below under I, while under II is placed an analysis of a biotite-hornblende-dacite from the Washoe district, Nevada, for comparison. Chemical analyses of dacites. Fe Na H 20 - H 20 + ... .. a Massige-Gesteine, 3d ed., pp. 844-848.

DACITE. Chemical analyses of dacites-Continued. 002 F 8 MnO · 0.50 ... None. . 06 None. .03 None. -.. None. None. None. .02 . 08 None. I. Biotite-dacite, one-fourth mile north o£ Old Dominion mine, Globe, Ariz.; E. T. Allen, analyst. II. Dacite, McClellan Peak, Washoe district, Nevada; T. A. Gooch, analyst. Hague and Iddings, Bull. U. 8. Geol. Survey No. 17, p. 33. Cited by Rosenbusch, Gesteinslehre, 2d ed., p. 299' 1901. It has been noted on page 89 that there is frequently found at the bottom of the dacite flow a more glassy :facies, often showing niegascopical flow banding. This rock varies in color from light to dark gray. In many specimens the banding is obviously due to the alternation of streaks of glistening black glass with those of more lithoidal material. Small included rock fragments; particularly o£ diabase~ are perhaps mure numerous in this facies than in the more common pink dacite described in the preceding pages. The phenocrysts recognizable by the unaided eye are of the same kind as those o£ the latter rock. Under the microscope this glassy dacite differs from the pink facies chiefly in the groundmass, which~ being less crowded with incipient crystal growths, is more transparent, and is often a pale-brown, slightly globulitic or trichitic glass. Microscopic flow structures are developed in: great perfection and beauty, and the rock is typically vitrophyric. The phenocrysts are the same as in the more lithoidal dacite, but green hornblende occurs a little more abundantly in those thin sections examined, and is sometimes nearly as abundant as the biotite. A single angular fragment of a diopside-like pyroxene was noted in one thin section~ but this mineral is apparently not a regular constituent of the dacite.

GEOLOGY OF THE GLOBE COPPER DISTRICT, ARIZONA. The other accessory minerals are zircon, apatite, titanite, and iron ore as in the common lithoidal dacite. Occasionally there is found associated with the gray vitrophyre just described a yet more glassy facies. This is a gray brittle volcanic glass of greasy luster in which can be seen small phenocrysts of fresh feldspar, quartz, and biotite. Under the microscope the rock appears as a colorless perlitic glass containing scattered phenocrysts of plagioclase, orthoclase, quartz, and biotite, and minute mierolites of feldspar. The tuffs which have been described as oecurring locally at the base of the massive dacite are nearly white rocks, which are sometimes exceedingly troublesome to separ~te the :field from the overlying massive · dacite. This separation is particularly difficult in the ease of a white or slightly pinkish tuff which immediately underlies th~ gray vitrophyric dacite at several points in the northwestern part of · the quadrangle. · This is a firm rock, showing small cr:rstals or fragments of feldspar, quartz, and biotite in an abundant, uniformly :fine-grained base. It might easily be taken for a massive lithoidal rhyolite. Under the microscope, fractured or corroded crystals of plagioclase, biotite, hornblende, and quartz lie thinly scattered . in a dusty, gray, glassy groundmass which somewhat indistinctly reveals the reentrant curves and sharp points of minute glass sherdsthe characteristic structure of glassy volcanic ash. with nicols crossed, it is seen that very little true glass remains, the groundmass having b.een changed by devitri:fication into a very minute aggregate of indefinite and shadowy crystal forms. Calcite, unknown in the massive dacite, is here abundant, not only throughout the devitri:fied glassy base, but as an alteration product of the plagioclase. In this alteration there is . none of the general clouding and breaking down of the feldspar, as is often seen in · weathered rocks, but the calcite is separated by a sharp boundary from the perfectly clear and fresh plagioclase at the expense of which it is forming .. The tuffs occurring below that just described are usually plainly clastic rocks of light-gray or pale-yellow tints, varying in lithological character from point to point. The microscope shows them to be glassy volcanic ashes, containing fragments of the ·same minerals that occ~r as phenocrysts . in the dacite, . with occasional particles of diabase or other foreign rock, inclosed in a devitri:fied glassy base. .They usually contain abundant calcite. Aqe.-There are no available data for fixing the exact date of the dacitic eruption. It is known to have occurred long after the supposedly Mesozoic · intrusions of diabase, for the latter rock was extensively er9ded before being covered by the dacite. On the other hand, it clearly antedated the development o.f the present topography. The dacite is therefore considered, provisionally, of

B.AS.ALT. Tertia.ry age~ According to an oral communication from Mr. Lindgren, a very similar rock occurs at the base of the extensive volcanic series at Clifton, indicating that it may belong to the earlier part of the Tertiary. BASALT. Dtginition.-Basalt is a dark heavy rock of the same chemical and mineralogical composition as diabase, but usually finely crystalline and often showing vesicular or glassy facies. This rock is of widespread occurrence in the form of effusive~ or surface~ :flows, and as small dikes. Occurrence and distribution.-The largest mass of basalt within the quadrangle occurs near its western border, as a flow, from 50 to 150 feet intercalated in the Gila conglomerate south of Gold Gulch. Other small masses occur between Gold Gulch and Horrell's west ranch. One of the latter is a sheet about 10 feet thick, forming a small area on the crest of a dacite ridge, about 2 miles northwest of the .Continental mine. It rests directly upon the p.ink dacite, and, ar.tho. ugh darker in color~ weathers in similar rounded masses. It may possib r represent a local eruption. . Other bodies occur at lower elevations to the southwest of the ridge. The relation of these to the dacite is not clearly shown. They overlie the Whitetail formation and apparently underlie the dacitel but whether they represent. a thin intrusive sheet or a predacitic surface flow cJ uld not be determined. Inasmuch as the known occurrences of similar basalt are in this region postdacitic, these small masses are provisionally regarded a intrusive, and as contemporaneous with the basalt flow south of Gold Gulch. t is not unlikely, however, that future work to the west of this quadrangle may establish the existence of a predacitic basalt :flow. On Manitou Mountain, overlooking Pinto Creek, small intrusive masses of the basalt have broken thr ugh the granitite and schist, and probably. mark the vents whence the basal ic flow issued. In the southwest portion of the quadrangle are two small intrusive masses . of basalt which are petrographically somewhat different from the !,masses above described, and may possibly belong to a different period of erujion. These form the area just north of Pinal ranch and the tiny body whic 1 cuts the granite-porphyry of the Hog ranch dike. It is possible, too, that so e of the smaller aphanitic dikes oceurring in the schists and granitic rocks of the main Pinal Range, are to be correlated with the basaltic rather than the t iabasic eruption. Petrography.-- -The flow south of Gold Gulch, the small mass on the dacite ridge to the north, and I the intrusive bodies of Manitou Mountain are all composed of typical, dark-gr y olivine-basalt~ showing small phenocrysts of feldspar, augite, and olivine, wit occasional blebs of dark glass, in a dense~ nearly

GEOLOGY OF THE GLOBE COPPER DISTRICT, .ARIZONA. aphanitic, groundmass. The olivine phenocrysts are often partly altered to brown pseudomorphs of iddingsite. The basalt of the main flow is often vesicular, many of the vesicles being filled with calcite. The rock of the doubtful masses occurring between the Whitetail formation and the dacite is a somewhat decomposed grayish basalt in which the olivine phenocrysts have been wholly altered to soft, earthy, ferruginous pseudomorphs; with a frequent bronze luster. The rock is very similar in appearance to the carmeloite of Monterey, Cal. Under the microscope the rock of all the areas, with the exception of those at ·the Pinal ranch and southwest of the Hog ranch, appears as a perfectly normal olivine-basalt, in which phenocrysts of olivine, anorthite, and augite, in varying proportions, lie in a usually holocrystalline, intersertal groundmass, consisting of anorthite laths, augite, and. iron ore. All the minerals are fresh,

with the exception of the olivine, which shows various stages of alteration into the usual reddish-brown iddingsite, fibrous green serpentine, and more obscure . products. The rock of the Pinal ranch area is dark gray, aphanitic, and so traversed by rusty, conchoidal fractures as to render the collection of a sound hand specimen very difficult. The microscope shows a few minute lath-shaped phenocrysts of anorthite lying in a hyalopilitic groundmass made up of microlites of plagioclase, grains of augite and iron ore, and glass. . Olivine was not recognized. The bas::J,lt of the small mass intrusive in the Hog ranch dike is a little more coarsely crystalline than that near the Pinal ranch, and shows small, porphyritic crystals of augite and plagioclase, just visible to the unaided eye. Under the microscope, the thin sections show small rounded phenocrysts of augite and olivine, with laths of anorthite, lying in a very fine holocrystalline groundmass of feldspar micr?lites, with granules of . augite, olivine, and iron ore. Of rare sporadic occurrence are phenoerystiG grains of ~orroded quartz surrounded by reaction rims of augite with intersertal brown mass. Contact metamorphism.-Where . the small dike-like mass of basalt breaks through the Pinal schists on Manitou Mountain, the latter rocks are transformed near the contact into a hard, reddish-brown, partly brecciated · material, which resembles a baked quartzite rather than the usual schist. Under the microscope the metamorphosed rock is seen to be made up of irregular dark bands, consisting of plagioclase and quartz rather obs.curely crystallized and crowded with mi?roscopic particles of some dark pigment, alternating with clear bands consisting chiefly of quartz. The quartz grains, however, are rounded and embayed and are held in a web of brownish microlitic glass. This glass is apparently the result of partial fusion or of the corrosive action of the basaltic magma, acting

FAULTS. along the surfaces where the original allotriomorphic quartz grains came in contact with each other. The process has attacked the grains from their peripheries and has rounded and embayed their outlines. A similar alteration has been effected by the basaltic magma on numerous inclusions of a light gray fine-grained granitic rock. Their sections show that these inclusions are usually enveloped in a film of pale-brown glass, which has also penetrated the inclusion interstitially . for some distance from the actual contact. Age.-North of Gold Gulch the small mass of basalt on the ridge top rests upon dacite, and is therefore younger. The main ~ow , between Gold Gulch and Manitou Mountain, rests upon and is in turn overlain by the Gila cong-lomerate. It is accordingly of the same age as the latter formati~n and may be provisionally referred to the early Pleistocene. Flows of basalt are mentioned by Gilbert, in the citation on page 47 of this report, as occurring in similar positions within the Gila conglomerate in the tributary !'alleys of the upper Gila·. The age of the basalt just north of Gold Gulch, at the edge of the quadrangle is, as previously indi'cated, somewhat doubtful, but is provisionally considered as Pleistocene. Fully as, uncertain is the age of the Pinal ranch mass and of the little body cutting the Hog ranch dike of granite-porphyry. These are included with the Pleistocene basalt merely on the ground of petrographical similarity. They may, · however, be older. FAULTS. IMPORTANCE OF FAULTING IN THE DEVELOPMENT OF THE GEOLOGICAL STRUCTURE OF THE REGION. The preceding pages contain a description of the rocks of the Globe quadrangle-the rough materials from which ·the forces of deformation and erosion have fashioned the existing geological structure and the visible configuration of the region. Before passing, however, to a consideration of the historical sequence and structural results of the geological processes which have wrought upon the rocks, it is desirable to devote some attention to the present expression and significance of that particular form of deformation which is preeminently characteristic of the district. If one will stand upon the top of Webster Mountain and look northward or eastward over the confusedly hilly country ~pread out before him, he will be · struck with the apparent chaotic distribution of the various rocks, as indicated by. their respective and characteristic tints in the landscape. Here and there patches of limestone gleam wh~te through the thin screen of scanty vegetation, while areas of quartzite are indicated· by a reddish color, and masses of diabase by a dull olive tint. The beds show no trace of folding, und the eye seeks in · 9651--'-' No .. 12-03-7

GEOLOGY OF THE GLOBE COPPER Dlt!TRICT, ARIZONA. vain for any persistent or regular structure that may account for this rocky Q) Ql ... 0 ! loJN .IJ9Z09 ·w·a

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patchwork. A similar view is obtained on looking southeast from the steep southeastern slope of the .Pinal Mountains over the region just outside of the bounds of the quadrangle. Here, however, the structure bas more regularity and the manifold repetition of beds of white limestone overlying reddish quartzites, all dipping gently to the southwest, is at once suggestive~ of faulting. That this suggestion is in.fact the clue to the dominant structure of all that part of the quadrangle in which the Apache group and Globe limestone are represented, becomes evident upon closer study. In traversing t~is faulted region one steps with bewildering frequency from quartzite to limestone, granite or diabase, the line of separation being often clearly defined by a fault breccia forming a bold outcrop (Pl. XVIII, A) that may be followed over the country for miles. Probably few equal areas of the earth's surface have been so thoroughly dislocated by an irregular network of normal faults, and at the same tinie exhibit so clearly the details of the fracturing. A rather inadequate conception of the exten~ of this regional shattering may be had from the geological maps (Pis. I and XV), from the generalized geological sections of Pis. · II and XVI and from the more detailed but comparatively simple sections of figs. 5 and 6. The faults there

l.i. S. GEOLOGiCAL SURVEY PROFESSIONAL PAPER NO. 12 PL. XVIil

FAULTS. shown, however, are merely those which attain some structural importance, and the numerous little fault blocks that they

IllY,, Whitet ail Gulch

bound are themselves cut by faults far too many and too closely spaced for representation. For a considerable part of the northwestern portioP of the quadrangle the term regional brecciation perhaps most aptly expresses the actual conditions there found. Probably the majority of the faults have throws of less than 100 feet, and their marked influence upon the general structure of the region is dependent, as a rule, rather upon their enormous number than upon great individual displacement. In spite of much variety in strike and hade, the general result of the faulting has been to drop by successive steps toward th~ northeast, beds having a general southwesterly dip, · the throws of the faults being such as to offset, in the main, the effect of the dip which would otherwise be effective in rapidly car:rying the strata above or below the present erosion .surface of the quadrangle. It is due to these faults of generally moderate displacement that the Globe limestone, for example, retaining in most cases a southwesterly dip of from 20 to 40 degrees, is

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rn "' u; N :. ,-Dripping Sprin~ fjUerl'zlre .. Globe lln?esrone scattered broadcast in small areas over &. (Jiobe /' eslo e § '"' n the quadrangle. -o r;uarrzll'e

:;: --Ba 1rnes conglon?erere Much of the structure of the region ffi

Pioneer shale

--.Ruin }ranile is partly dependent upon faults which no

Y;" 'Diabase longer appear as distinct dislocations, and §. are not represented by fault lines on the

geological maps (Pls. I an~ XV). These - are generally northwesterly or northeast

erly fractures which immediately preceded a [ or accompanied the great diabase intrusion, and which, from I their close con-

. GEOLOGY 0~' THE GLOBE COPPER DISTRICT, ARIZONA. nectioti with this event, may be conveniently distinguished as intrusion faults. They became at the time of eruption channels for dike-like connections between the sills, and were important factors in determining the form of the molten mesh in which the blocks of strata were inclosed. 'Most of the surfaces of dislocation were transformed to er~ptive contacts, with which, however, planes of later faulting frequently in part coincide, as in the case of the Old Dominion fissure described on . pages 136 to 139. In most regions of diversi~ed topography underlain by stratified rocks the dominant structures are due to folding, modified to a greater or less degree by faulting. In the Globe quadrangle, on the other hand, the structure, where not traceable directly to the effect of igneous intrusions, is the result of faulting, while folds are either entirely absent or represented by an occasional gentle and structurally unimportant buckling of the strata occurring in some fault block. DISTRIBUTION OF THE FAULTS. Upon referring to the geological map (Pl. I) it may be seen that the faults are very much more numerous in the northern than the soutqeFn half of the quadrangle. It is further apparent that the crystalline schistose and granitic complex forming the mass of the Pinal Mountains is nearly free from dislocations, while the latter are particularly abundant wherever the Apache group,' Globe limestone and diabase are the prevailing· rocks. To some slight degree this difference is probably exaggerated, as faults in the granitic and schistose terranes are structurally inconspicuous and may be overlooked in mapping, while even small faults may effect striking results in traversing beds of quartzite and lime- . I stone. Such slight exaggerations, however, can hardly detract from the greatactual contrast presented on the one hand by the relatively simple structure of the Pinal Mountains, with their batholithic granitic masses irregularly invading the schists, and on the other by the complex disloc~tion of the no-rthern half of ·the quadrangle. No faults are shown within the large areas of Gila conglomerate, such as the Pinal Creek and Mineral Creek areas. This is chiefly due to the fact that the more important faults antedate the deposition of this formation. It is undoubtedly cut, however, by faults of later age, but it is impossible to trace these for any considerable distance in material of this character. It is almost equally impracticable to detect or follow faults on the surface when dacite forms both walls of the fissure, and this fact is probably in part responsible for the paucity of the faults mapped within dacite areas.

FAULTS. THE EVIDENCE OF FAULTING. 'Vith probabl~ not more than a d~zen exceptions, the several hundred faults shown on the map (Pl. I) were actually traced on the surface, usually by the aid of a fault breccia . . Such a breccia is invariably present where quartzite of the Apache · group forms one or both walls of the fissure. It is commonly made up of angular. fragments of quartzite, with occasionally rounded pebbles dragged in from some conglomerate bed dislocated by the fault, the whole being embedded in a more ·or less . rusty m~trix of siliceous detritus,. and often cemented by oxide of iron. Sometimes fragments of diabase, schist, or other rocks traversed by the fault are mingled with the quartzite, 'and in a few cases, where faults cut Pinal schists, the breccias are composed entirely of fragments of the latter rock. But by far the greater number of the fault breccias in the region consists chiefly of crushed quartzite. These quartzitic breccias are frequently so indurated as to more resistant than the rocks on either side, and they then outcrop boldly as ragged walls stretching across the country. Examples of such indurated breccias are abundant over the northern half of the quadrangle. One forms a conspicuous crag by the I roadside about 4 miles northwest of Globe (Pl. XVIII, ..A). · Another (Pl. XVIII, B) separates limestone from diabase on the northwest side of Big Johnnie Gulch (see Pl. XV). Still others stand out prominently south of the trail from Granite Basin to Horrell's west ranch, and notable breccias of ·schist fragments, showing considerable alteration and mineralization, occur ort Pinto Creek near the mouth ·of Cottonwood Gulch. Frequently the faults bring into juxtaposition rocks unequal in their resistance to disintegration, and a scarp of more or less topographical prominence results from differential erosion. The region affords many examples of such scarps, one of the best being shown in Pl. XIX, where hard quartzites of the Apache group are normally faulted against crumbling Ruin granite. Such scarps are of purely erosional origin depending upon the relative hardness of the rocks and not upon the throw of the fault. Where pronounced topographical expression fails, there is still usually no great difficulty in actually tracing the course of a given fault over a country where the character and attitude of the rock under foot is rarely in doubt~ and where the outcrop of the fault plane is confined within the limits of the single step that usually suffices to pass from one rock to another. Without such clear exposures it would be impossible to express the complex structure other than by the crudest and most inaccurate g:generalizations. The chief embarrassment, as a rule, lies not in :finding the evidence of dislocation, but in determining which one of many faults shall be mapped as structually the most significant where it is

GEOLOGY OF THE GLOBE COPPER DIRTRICT, ARIZONA. impossible to show them all, and, amid the general shattering, in identifying throughout its course the particular fault originally selected. Faults wholly in diabase or limestone are usually not conspicuous. Their courses in the former rock · are often marked by zones of brecciation which are commonly stained black by oxide of manganese and sometimes mineralized with salts _of copper. The passage of a fault through limestone may produce considerable brecciation, which, is likely to be so healed by recrystallization of the calcite as to be detected with some difficulty, as in the case of the Old Dominion fault north of the Hoosier shaft (Pl. XV). While only a very small proportion of the faults are perceptibly mineralized, many of them have been superficially prospected, and the study of some of the more obscure dislocations of the region is indebted to that remarkable instinct which guides the impartial pick of the prospector to ·the discovery of fissures, irrespective of the wealth or poverty of their mineralization. The evidence for the intrusion faults associated with the diabase eruption is of a more general character than that of the later faults directly traceable on the surface. In a few instances the diabase can be observed in undisturbed eruptive contact with a regular surface of -dislocation cutting across the bedding. But in other cases later movement has taken place along this contact, and the original character of the latter is inferred from the petrography of the diabase near the fissure and from the demonstrable inadequacy of the later faulting to . account for all of the contin.uous structures. Taking for example, the Old Dominion fault (fig. 7), we find (p. 136) that the diabase of the foot wall exhibits the texture characteristic of this rock near its original intrusive contacts. Fur~hermore the existence of an included block of limestone in the diabase of the foot wall is unexplainable if the relation of the diabase foot wall to the limestone and quartzite hanging wall be supposed wholly due to faulting of later date than the solidification of the eruptive rock. Lastly, even if the limestone in the foot wall be disregarded, the. general geological evidence indicates that the faulting subsequent to the diabase intrusion has been of too moderate displacement to wholly account for the relative position of diabase · foot wall and limestone hanging wall. Thris the dacite in the upper workings of the Old Dominion mine shows a throw of less than 100 feet, a displacement wholly insufficient to explain the juxtaposition of diabase and limeston~ observed in the lower levels. Still further evidence for these intrusion faults is afforded by the general structure of the region as expressed in the geological maps and sections (Pis. I, II, XV, and XVI). It is apparent from these that extensive dislocation of the beds must have -..precedes or accompanied the diabase intrusion and pr~pared the blocks of strata for their erratic dispersal and rearrangement by the mass of molten magma f~rced into the shattered fabric. ·

U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER NO. 12 PL. XIX FAULT PLANE DEVELOPED INTO A SCARP BY EROSION. Rock on the left (hanging wall) is quartzite , that on the right (foot wal l) is gran1te. The fault 1s normal.

FAULTS. DIRECTIONS . AND CHARACTER OF THE FAULTING. The dominant fault~:! of the Globe quadrangle fall into two groups, (1) those having a generally northeast-southwest trend, and those striking approximately northwest and southeast The dislocations oi the first group dominate the structure of that portion of the Gl~be Hills lying just north of Globe and ·are eonspicuous in the vicinity of Black Warrior and Lost Gulch. These faults have d1ps ranging from 55° to 90°, the greater numb r being inclined about 75° to the horbmntal. Northwesterly dips are about as frequent as southeasterly, and as the throw of the faults is apparently always normal, these dislocations have resulted in dropping downward-pointing wedges of geologically higher rocks between upward-pointing wedges of lower rocks (trough faulting). Thus, on the south slope of Buffalo Ridge (Pl. XV) little areas of !Globe limestone are inlaid, as it were, in the quartzites of the Apache group, [between the two branches of the Buffalo fissure. The Lost Gulch monzonite is I a fault block separated on the northwest and southeast from geologically higher rocks that have been dropped against it by faults of this group. The fissures of the second group dominate the structure northwest of a line passing through Sleeping Beauty Peak and the Uo~tinental mine, and in the e~treme northeast corner of the quadrangle. The usua~ dip of these faults is about 75° and may be either to the northeast or southwest. West of Pinal Creek, the net result of the many displacements has been a general d~popping of the beds toward the northeast (step faulting). In the northeast corner of the quadrangle, however, the faulting already begins to partake of the Jharacter of that along the . western face of the Apache Mountains, resulting in a general elevation of the beds toward the northeast. l · Although faults belonging to the two groups fu t recognized have effected the most conspicuous structural results, they are associated with countless othe1 fissures running in all directions and adding greatly to the complexity of the fault network. It has proved impossible to reduce ~hese generally subordinate fractures to distinct groups or systems, and when is remembered that for every dislocation shown upon the map there are se'j"eral others unrepresented, and that the faults are of different ages, the reason for failure is apparent. The region has not been dissected with mathematical preci~ion along determined lines, but has been shattered by compl~x geological forces to an extent that is only less defiant of analysis than is a pane of shivered gJa~ s. Among the many hundreds of faults occurring within the quadrangle are a number in which the character of the relative movement is not clearly shown, either because the hade of the fault is unknown or tiecause the original geological horizons of the rocks adjacent to the fissure are 'n doubt. The majority of

GEOLOGY OF THE GLOBE COPPER DISTRIC'r, .ARIZONA. the faults, however, are clearly normal, while indubitable cases of reversed or thrust faulting· are unknown. .AGE OF THE FAULTS. The earliest dislocations distinctly recognizable in the structure of the Globe quadrangle are the intrusion faults associated with the post-Carboniferous (Meso- . zoic '4) intrusion of diabase. From the close of this period o:£ revolutionary eruptive activity to the probably Tertiary outbursts of dacitic lava one proces::; onlythat of erosion-has left a fairly legible rec~rd. It is believed, however, that important faulting also took place during this interval, and that. some of the fissures which do not at ,present .cut the dacite, and particularly tl:tose showing mineralization, are actually of predacitic age. The evidence for this · belief is drawn from observations tending to show that the original sulphide ore of the district is older than . the . dacite, as will . be more fully shown in the sequel. The last great faulting of the region, that tremendous shattering which finds its best expression in the . northwestern portion of the ·quadrangle (Pl. I), followed the dacitic . eruptions, and involved their lava in the final structure of the resulting geological mosaic. The date of . this fissuring which blocked out the existing structure of the country is not definitely known. As it occurred after the dacite eruptions and before the accumulation of the Gila conglomerate, it may provisionally and tentatively be referred to the Neocene. Its results. can not always be clearly distinguished from the earlier faulting that followed the diabase intrusions and preceded the eruption of dacite. Faults once initiated have ~sually remained planes of weakness along· which there has been a revival of movement with each successive period of dislocation. Numerous normal faults, usually of small throw (Pl. XX), cut the Gila conglomerate and indicate the continuance of faulting into the Pleistocene, while . the presence o:f soft gouges and unconsolidated breccias in so~e of the N eocene ( ?) faults show that displacement is probably even yet in progress. Although it has been ascertained that the faults of the region are of various ages, it has not been possible to discover that those of any period were distinguished by the. possession of peculiar trends. GEOLOGICAL SIGNIFICANCE .AND ORIGIN . OF THE FAULTING. As the earliest recorded faulting was apparently closely followed by the intrusion of diabase, the circumstan~es under which the fracturing took place and the forces to which it was due are somewhat obscure. It is clear that rather thick and brittle beds were much fissured and that the diabase, instead being confined to regular and persistent sills, filled the. fractures and in many cases greatly

U. S. GEOLOGICAL SURVEY PROFESS IONAL PAPER NO. 12 PL. XX A. B. TYPIC AL FAULTS IN GILA CONGLOMERATE. A , Alice Gul ch near Old Domm ion mine; R , near Bl ac k

J .

GEOLOGICAL SIGNIFICANCE AND ORIGIN OF .f'HE FAULTING. displaced the severed blocks of strata. The number of the dislocations and the comparatively small size of the fault blocks indicate that the beds did not at the time of their rupture lie under great load, and the facility with which the blocks were shifted ·by ·the magma is evidence that the intrusion also took place under no great superincumbent mass. The entire absence from the region of remnants of any rocks that might have overlain the Globe limestone when it and older rocks underwent such extensive deformation affords additional ground for the conclusion that the faulting and intrusion must have taken place within a very moderate distance of the surface· as it was at that time. The present geological structure is such as to suggest that this earlier faulting was generally normal in character, but whether the original dislocation was due directly to the intrusive force of the diabase or to the earlier and perhaps independent stresses has not been determined. The postdiabasic and predacitic faulting, with which is associated the primary mineralization of the quadrangle, can not as a rule be satisfactorily distinguished on structural g-rounds from the postdacitic , faulting-, partly because the ~atter, as in the ,Old Dominion fault, revived older dislocations. In an attempt to deduce from the character of the postdacitic faulting the circumstances under which it took place and the forces to which it was due, the fact that an overwhelming proportion of the faults are demonstrably normal is of prime importance. Normal faulting implies horizontal extension and is incompatible with regional tangential compression, a conclusion which is strongly reenforced by., the absence of folding in the stratified ~ocks. The fact that beds when normally faulted tend to occupy a greater area than before their dislocation can not, however, be taken as evidence that tangential tension has been a [cause of the fracturing-._ The existence of such a stress is geologically improbable, and even if set up it would be relieved by the first fracture formed. The only conceivable i:stresses that can offer any satisfactory explanation of .the faulting of the Globe region are those acting in directions more nearly vertical than horizontal, such as would result from differential elevations or subsidences over the area. The behavior of the rocks may be likened to that of a large and thick sheet of plate glass lying horizontally upon an uneven surface and fissuring under its own weight in consequence of unequal support. The generally rather thick-bedded and brittle rocks of the quadrang-le are, however, far more easily and thoroughly fissured by geolog-ical processes than would be the relatively insignificant mass of glass by the feeble stresses of the suggested experiment. It is certain that the rocks of the quadrangle when broken by the postdacitic faulting were practically free from load other than their own mass. It is inconceivable in the light of the geological history· of the district that any ate Paleozoic Libr"' r fi ashington DQ C~a -·

G EO LOGY O:H' THE GLOBE COPPER DISTRICT, .A.RIZON .A.. · considerable thickness of rock should have accumulated in Tertiary time ·above the dacite and then have been completely removed, leaving no trace of its former presence. "- 7hen the faulting occurred, dacite was probably the surface rock over such considerable portion of the region as did not stand too high to be buried beneath the lava at the time of eruption. It was certainly the youngest rock occurring in any considerable mass within the quadrangle. Erosion s!nce the period of dislocation has undoubtedly reduced the thickness of the dacite. But such reduction does not affect the general force of the statement that when the postdacite faulting occurred, the rocks involved were, with the exception of the Gila conglomerate and Pleistocene basalt, those now exposed, and that the phenomena observed are those associated with rock fracturing taking place close to the surface and therefore under little or no load. The results as described in preceding pages for the northern half of the quadrangle are such as might be expected under the conditions just outlined-a shattered, brecciated region, cut by innumerable small normal faults showing varying local regularity in strike, which is more or less masked by the apparently ·haphazard trend of the countless smaller fractures. It is not known why the main crystalline massif of the Pinal Mountains escaped the minute dissection of the rest of the area. It is possible that its lithological character and the relation of the batholithic masses of granitic rocks to the 'schists presented elements of strength lacking in the surrounding areas where stratified rocks and diabase prevail, and that it . consequently moved as a unit in the general readjustment of the region by faulting. The causes of the postdacite and postdiabase faultings are deep seated and inscrutable. It is suggestive that here, as in the San Juan region of Colorado,a the later fissuring followed an extensive transfer of volcanic material from its subterranean source to the surface. It is probable that there is a more or less direct connection between such volcanic paroxysms and the subsequent fissuring. The earlier, structurally less conspicuous, but economically more important, postdiabase dislocations were also preceded by great eruptive activity, and it is reasonable to regard this faulting also as a phase of regional readjustment after the widespread disturbances efl'ected by the intrusion of the diabase. The latest faulting of the Globe district, . manifested by slips along earlier fault planes and minor dislocations of the Gila conglomerat~, are regarded merely as indications that the shattered rock masses of the region are still approaching by slow steps the elusive goal of final equilibrium, which was not attained by the vigorous movements of the postdacitic fissuring. a see Bull. U. S. Geol. Survey No. 182, 1901, p. 66 .

GEOLOGY OF THE GLOBE COPPER DISTRICT, ARIZONA. GEOLOGICAL HISTORY. Long before Cambrian time the Globe region was part of a sea bottom upon which were accumulating fine grits and siltE}, probably derived from granitic rocks. The source of these sediments is unknown, and no trace of the ancient rocky floor upon which they were laid down .is now visible. In the course of time sedimentation ceased, the beds were folded and compressed by forces acting in a generally northwest-southeast direction, were intruded by. great masses of quartz-mica-diorite (the Madera diorite), and underwent crystalline metamorphism into the Pinal schists. Later intrusions of granite, granitite, and monzonite fJllowed, and at the close of this period of plutonic eruptive activity the region hJd risen above the sea and become mountainous. A new physiographic cycle wrs thus initiated, which wa~ probably well under way, however, before the constructive processes that have just been outlined were concluded. Before the rocks attained their final elevation erosion was vigorously at work, and, upon becoming ascendant, began the actual reduction of the mountainous topography, carrying it successively through the various intermediate stages of the geographical cycle the final one of the nearly featureless worn-down plain of old· agea !peneplain. So much, in brief, of pre-Cambrian history is decipherable from the character, structure, and texture of the older rocks. The cycle was run, and the initiation of Cambrian time was marked by subsidence and a fresh advance of the sea over what had so long been dry land. The sea as it swept over the peneplain found it littered in part with fragments of quartz weathered out from veins in . the schists and granitic rocks, and with smaller particles of feldspar and quartz derived from the disintegration of the granitic masses. The existence of particles of feldspar, which have remained fairly fresh to the present time, appears to afford some indication that the Cambrian climate was not conducive to soil formation or to abundant vegetation. These materials were slightly reworked by the waves into the Scanlan conglomerate, the remnants of which are now · found resting usually upon the weathered and reddened surface of the Madera diorite and the granites, sometimes separated · from the sound rock -by several feet of pre-Cambrian granitic saprolite (disintegrated rock in place). The Scanlan conglomerate, or its equivalent, covered the Pinal schists as well as the plutonic rocks, but the former relationship is visible only in a few fragmentary exposures west of Black Warrior, where ·the Scanlan conglomerate · is represented by a breccia consisting chiefly of glassy quartz fragments embedded in a matrix composed of smaller particles of .schist. It appears that the region was submerged too rapidly to permit any considerable rounding of the pebbles

GEOLOGY OF THE GLOBE COPPER DISTRICT, ARIZONA. by wave a9tion, or to allow much transportation of material. by littoral currents, both of which processes are favored by stability of shore line. The lack of such evidence of long-continued shore action shows that the· floor upon which the Cambrian sediments were deposited was in the main due to subaerial erosion and not to marine planation. Either there were valleys in the old peneplain as much as 200 feet . in depth, or the region subsided unevenly to an equal extent, for in the Apache Mountains the interval between the pre-Cam brian peneplain and the base of the Pioneer shale, elsewhere occupied by from 1 to 6 feet of Scanlan conglomerate, is filled by some 200 feet of hard and varyingly arkose quartzite. ' . Th~ Pioneer shale, overlying the · Scanlan conglomerate and the lower quartzites of the Apache Mountain~, records the accumulation of sandy silt in waters so shallow that the mud sometimes lay bare and was · dried and cracked by the sun. The material o£ these sediments was in part feldspathic and probablJ; derived from an adjacent land mass, composed largely of granitoid rocks similar to those occurring in the Pinal Mountains. While there is no direct proof that the rocks of these mountains themselves were reduced to the general level of the peneplain and covered by the Cambrian sediments, yet it seems most probable that such was the case, and that they owe their present elevation and the stripping of their Paleozoic cover to later movements and to erosion. It is not likely that there existed any such sharp and local exception to the general unevenness of what must have been at one time an extensive peneplain. The deposition of 'the Pioneer shale was succeeded by that of ·the Barnes conglomerate. The origin of this conglomerate, ~hich, with its well..:rounded pebbles · composed largely of quartzite, succeeds so strikingly the reddish sandy shales . and quartzites beneath it, presents questions to which the region investigated returns no answer. Without any apparent unconforniity, the quiet deposition of fine silt was succeeded by the laying down of fairly coarse conglomerate, bearing evidence of continued wave or current action, and plainly derived from earlier · (Algonkian~) sedimentary deposits concerning· which the Globe quadrangle furnishes no k~owledge. The matrix of the Barnes conglomerate, however, still ~bows abundant :feldspathic detritus, such as might hav·e been supplied by a neighboring unsubmerged area of the pre-Camprian granitic rocks. Succeeding the Barnes conglomerate came ·the accumulation of quartzose sands, now represented by the Dripping Spring quartzite. These appear to have been laid down in somewhat deeper water than the preceding beds, although the occurrence of conglomerates and grits in the upper part of the formation suggests a return of littoral conditions at the close of the Cambrian. The geological record of the limited region studied is silent as regards Silu-

GEOLOGICAL HISTORY. rian time. No strata of this age have been identified, nor, on the ot~er hand, has any unconformity been certainly detected between the Cambrian and the Devonian, to acco'urit for their apparent absence. Such field evidence as could be obtained bearing upon this point is inconclusive. Inasmuch as Walcott has shown that an actual unconformity, ·rarely discernible, exists between the Cambrian and Devonian bed·s in the Grand Canyon, it is possible that a similar usually invisible stratigraphical break may be present in the Globe district. .Jf so, the region was elevated with little or no deformation of the be~s, and remained dry land throughout the SiluriaB. It is however, that the absence of the Silurian strata is not due to emergence of the sea bottom, · but to a cutting off of the supply of sedimentary material; either a depression so great as to carry this part of the sea bottom . beyond the reach of land waste, or by a reduction to approximate base-level of the area supplying the sedi~ents. In such an event. the Silurian might be practically unrepresented and yet there would be no real unconformity. Passing to the Devonian, we find some ground for the suggestions last made in the fact that arenaceous deposits are here almost absent and limestones predominate. At the base of the latter are frequently encountered calcareous grits, forming an apparent transition from the underlying quartzit~s to the nearly pure limestones. It has been found impossible to believe these to be other than actual transitional beds in a conformable sequence. Yet they are not always present, and the occurrence of a little quartzitic breccia observed at a single point at the base of the Globe limestone north of Globe (see p. 40) enforces the suggestion of a possible unconformity. From the Devonian to the Upper Carboniferous the region was covered by a sea of some depth abounding in marine life and depositing abundant limestone .. Although no characteristic Lowet~ Carboniferous fauna was found, rocks of that period may be present, and the Globe limestone as a whole contains no visible unconformities. From time to time there were slight incursions of sediment, and in a few instances bands of siliceous conglomerate were intercalated within the limestones. The mass of these is unimportant, but they are significant in showing that this part of the Devonian and Carboniferous sea was probably neither very deep nor far distant from a land mass. The Upper Carboniferous limestone is the latest Paleozoic deposit of which the region preserves any record. If marine conditions continued into the Permian the deposits of that period must have been wholly removed before the strata were broken up · and invaded by diabase. Had Permian or later beds been involved in that structural revolution some traces of them would probably have been "preserved in the resulting intricate lithological mosaic.

GEOLOGY OF THE GLOBE COPPER DISTRICT, .ARIZONA.. There are' no available means of determining whether or not the region became land and was ero~ed before the diabase intrusion. We know only that the latter event with its associated faulting occurred after the accumulation of the Globe limestone, and has left unmistakable record of its structural importance. The region was presumably .elevated above sea level at the close of the Carboniferous and subjected to erosion. It was extensively dissected, probably in Mesozoic time, by numerou::; faults, which appear to have b~en normal in character, -qnusua:lly of moderate throw, and to have had generally northwest-southeast and ·northeast-southwest trends. There is ground for. supposing that the crystalline massif of the Pinal Mountains escaped much of the intensity of this as it did of a later period of -. faulting. Following or accompanying the dislocations an enormous quantity of molten diabase magma was intruded into the rocks of the region, particularly into those most cut by the faults. If present exposures can be taken as generally indicative of the original proportion of the diabas~ · to the stratified rocks, it appears that the intruded . rock fully equaled if it did not considerably exceed in volume the stratified rocks. As the latter were not fused at any point now exposed to observation, room for this great addition of material was effected by mechanical displacement. The dominant form taken by the diabase was that of the intrusive sheet or sill, and had the region not been shattered by faults these sills w.ould probably h~ve been fairly regular, resembling those occurring in the less faulted portions of the country just without the quadrangle, such, for example, as are well exposed in the canyon of Salt River just below its junction with Tonto Creek. As it was, however, the diabase not only forced its way between the beds as sills of varying thickness, but found in the region of greatest faulting the most favorable opportunity for expansion. It o"ccupied the fault fissures and shoved the detached masses of ruptured strata bodily aside, separating them so that they becaJ!le in many cases mere inclusions in a great mass of eruptive rock. All the observed phenomena connected with the faulting and intrusion, as well as the more general geological considerations outlined in preceding pages,. indicate that these events took place comparatively near the surface. The contact metamorphism effected by the diabase is of the most insignificant character, ·while vesicular and aphanitic facies of the intrusive rock are common near original contacts. The. manner in which the blocks of strata were . displaced indicates that they were under no great load, and the great incr~ase of volume resulting from the intrusion of the diabase must have produced considerable actual elevation of the surface over the Globe region. It would seem that with such active deformation and intrusion in progress at so slight a depth, at least some of the magma must have found its way to the surface and been erupted as basalt. Any such manifestation of volcanic activity as ·may have existed has, however, since been removed by erosion. !

GEOLOGICAL HISTORY. With the close of the diabase intrusion the region, having probably gained in elevation, was subjected to subaerial erosion. It is not unlikely that during the Mesozoic it underwent many unrecorded vicissitrldes, and may have been covered by sediments that were afterwards stripped away. It is very p~obable, h~wever, that normal faulting took place during this period, closely followed by ore deposition. At a time which can not be definitely fixed, but which is provisionally considered as coinciding with the earlier part of the Tertiary, the region, characterized by a somewhat diversified topography, was apparently dry land and undergoing erosion. Although the topography was probably less rugged, the general conditions appear not to have been very greatly different from those of the present day. As shown by the accumulation of the Whitetail formation, coarse, rather angular detritus was washed down the slopes and deposited in the more open valleys or gulches. It was this uneven surface that was in greater part buried by the probably early Tert~ary eruptions of dacite. As the Whitetail formation occasionally shows rude stratification in its upper part and the ~assive dacite is frequently underlain by beds of tuff, it is probable that the quadrangle was at this time partly covered by transient bodies of water, possibly due to a disturbance of. the drainage by orogenic movements il1mediately preceding the eruptions. As a result of the latter the whole of the quadrangle, with the possible exception of the Pinal Mountains and some of the foothills of the Apache Mountains, was covered with a flow of dacite, which in its greatest thickness probably exceeded a thousand feet. Following closely after this volcanic activity came the great faulting to which is chiefly due the present structure and less directly the topography of the region. The nature of this faulting has already been described in pages 97 to 106. By it the northern half of the quadrangle was shattered to an· extent but imperfectly shown by the great number of small fault blocks outlined upon the geological map (Pl. I). The southern half .of the quadrangle, however, shows comparatively little dislocation, and it is evident that the crystalline massif of the Pinal Mountains moved as a unit and forms the largest fault block in the area. On the southeast this block is fairly well defined by a strong northe!tst-southwest fault that bas dropped rocks of the Apache group and Globe formation, with intruded masses of diabase against the older Pinal schists and Madera diorite lying to the northwest. Toward the south and southeast the Pinal Mountain block apparently extends beyond the bounds of the On the northwest the passage into the region of Intense faulting is somewhat indefinite, and no single fault was found marking a simple boundary between the Pinal fault block and the shattered

GEOLOGY OF THE GLOBE COPPER DISTRICT, .ARIZONA. rocks to the northwest of it. On the northeast the Pinal Creek area of the Giia conglomerate effectually conceals the structural boundary separating the Pinal . fault block from the minutely dislocated Globe Hills. The strata of these hills dip generally to · the southwest beneath the Gila formation. They reappear again on the back of the Pinal fault block near Pioneer, and here also have a persistent southwesterly dip. If ·the portions of the beds removed from this block by erosion were restored they would lap up over the southwestern slope of the , Pinal Mountains and form a scarp along the crest of that range overlooking the GlobeValley and the very much lower fragments of the same strata in the Globe Hills on the far side of the gravel-filled depression. It is not impossible that the Apache and Globe beds and the overlying dacite formed a complex anticline over the crystalline core of the Pinal Mountains and a sy~cline beneath what is now the Giobe Valley. But as there are here no discoverable traces of structure so wholly lacking in representation in other parts of the region, it is fair to conclude that the observed tectonic relations have resulted either from a single generally northwest-southeast fault of over 6,000 feet maximum throw, or from a zone of faults of like trend. In either ; case the depth of . the Gila conglomerate effectually prevents any study of these faults at the surface. The fissure which cuts . off the Lost Gulch monzonite on the northeast and apparently passes beneath the Gila conglomerate .to the southeast has ·a throw of the kind required in members of the hypothetical fault . zone suggested. The crystalline massif of the Pinal Mountains is thus regarded as an. eroded fault block, uplifted along its northeastern edge, and, consequently, tilted to the southwest. It is possible that the concealed fault or fault zone along the north- . eastern front of the range, of which the maximum throw can scarcely be less than 6,000 feet, is only in part due to postdacitic dislocation, and that the initial displacement dates from the episode of intrusion faulting connected with the .diabase eruption, or that of the postdiabase fissuring. In the absence of any satisfactory evidence for connecting with the recognized geological epochs the events which took place in this district after the close of the Carboniferous, the postdacitic faulting is rather arbitrarily considered. as ending the Tertiary. The provisional nature of this and other post-Carboniferous correlations in this region should not be forgotten. They may be considerably modified when the geological work in the Globe quadrangle is supplemented and extended by the study of a broader area. The divisions recognized appear to be distinct chapters in the local physical history. They may not, however, be correctly inserted in the larger volume of· the geological story of the earth. The Pleistocene was opened by a vigorous erosion of the complex lithological mosaic resulting from the superposition of the postdacitic shattering upon

GEOLOGICAL HISTORY. earlier structures already complex. ·Great quantities of coarse, rocky detritus were washed down the slopes and deposited as the Gila formation in valleys partly, at least, of structural origin. It has already been shown that the conglomeratefilled Globe Valley probably owes its original depression to faulting. The Gila fonnation of the Mineral Creek area fills a hollow eroded in the dacite. The upper Pinto Creek area also occupies a small northwest-southeast valley of erosion, but .there has been some Pleistocene faulting and possibly a very slight synclinal flexure of the deposit along the axis of the trough. The character of the Gila formation indicates that the climatic conditions of the early Pleistocene were not very unlike those of to-day. Prevailing aridity and dominance of mechanical-disintegration over rock decay were prominent features, and the precipitation apparently occurred in violent downpours of short duration. There was at least one er option of basalt during the Pleistocene, as shown by the flow intercalated in the Gila formation south of Gold Gulch, and by the smaller masses in the western part of the quadrangle. The basalt apparently issued from more than one . small vent and its present distribution is not entirely understood. The early Pleistocene erosion that supplied the materials for the Gila formation undoubtedly eff,~cted pronounced changes in the topography, but it usually is difficult or impos~ .ible to distinguish between such changes and those brought about in late Pleistocene time! More or less faulting has continued throughout the Pleistocene, and in the northeastern part of the quadrangle these later dislocations have had a recognizable effect upon the structure, as shown by the shapes and distribution of the areas of Gila conglomerate. In late Pleistocene time erosion has been active over the whole region, reducing the mountains and dissecting the Gila conglomerate. In some parts of the area, as near Hutton Peak and Needle Mountain, this later degradation appears to have been exceptionally active and has left fragments of the Gila formation, originally a valley deposit, upon the summits of ridges and peaks. \Within the large Pinal Creek area of conglomerate, however, the present arroyos have merely effected an intricate dissection and sculpturing, without exposing the base of the formation save near its margins. This trenching was locally accompanied by the cutting of occasional inconspicuous stream terraces, best Reen along

Bloody Tanks Wash. In the present topography of the quadrangle three main features are readily distinguishable-the Pinal Morrntains carved from the uplifted Pinal fault block, the gravel-filled depression of the Globe Valley 9 and the confusedly hilly country 9651-No. 12-03--8

GEOLOGY OF THE GLOBE COPPER DISTRICT, .ARIZONA. in the northern half of the quadrangle. These features depend primarily upon the geological structure whose development bas been traced in the preceding pages, and secondarily upon the erosion of the pre·sent cycle. The elevation of the Pinal block, while it led to the rapid stripping off of the Paleozoic and younger rocks, exposed to the present erosion the little fissured and generally re~:~istant foundation of crystalline schists and granitic batholiths. Thus the Pinal Mountains are the result of an original uplift 'which subsequent erosion bas greatly'_ lowered and sculptured, but, checked by the highly metamorphosed schists, has been unable to degrade to the general level of the surrounding country. The topography of the range is still characterized by the steepness and sharpness of form associated with physiographic youthfulness. The Globe Valley, on the other hand, probably or!ginated as the downthrown region lying northeast of the Pinal uplift, the result of such downthrow being to form a structural depression :floored with shattered Paleozoic sediments, diabase, and dacite. ·How far erosion was able to modify this :floor before it was buried beneath the Gila formation is of course unknown. The existing topography of the valley exhibits a , stage of mature dissection of the fluviatile deposits that fill it. As the· principal intermittent streams issue from the Pinal Range, they tend to retain the axial stream, Pinal Creek, close to the base of the Globe · Hills. Near the northern edge of the quadrangle, however, the conditions are reversed, and the influence of the stronger drainage from the Apache Mountains, with its more extensive deposition of detritus, is · seen in the . crowding of Pinal Creek over toward the hills west Gerald's ranch. The topography of the northern half of the quadrangle is closely related in its irregularity t6 the . rock masses that underlie it. It is such as might . be expected from the erosion of a region having planless heterogeneity of structure. The drainage plan of such a tract records minute adjustments to conditions of great local diversity. Each little fault block by . its materials and position has influenced the topography. Areas of granite or diabase tend to become valleys or basins, while quartzite and limestone form ridges or peaks. THE ORE DEPOSITS. HISTORY OF MINING DEVELOPMENT. Prior to the year 187 4 the desert isolation of the mountains of central Arizona and the predatory Apaches who lurked within these rocky fastnesses appear to have been obstacles from which even the proverbially hardy prospectors shrank. But in that year a . temporary subjection of the Indians opened the way · to the bolder spirits, and a party of prospectors, having crossed. the Pinal Mountains from the west, located the Globe claSm, now part of what is generally

HISTORY OF MINING DEVELOPMENT. · known as the Old Dominion mine. The Silver King mine, lying about 19 miles south-southwest from the present town of Globe, was located by members of this -same party as they were returning to Floren'Ce. Other ·discoveries rapidly followed and small settlements sprang up at various . points. One of the first of these, known · as Ramboz Camp, was founded by Henry Ramboz in 1875. The ruins of this camp and some neglected graves of its pioneers may be seen about 4 miles northeast of Globe, at the foot of Ramboz Peak. It was the base whence active prospecting was carried on in the Globe Hills during the seventies, when some mines, such as the Fame, Centennial, and Rescue, were opened· and produced silver ore in commercial quantities. Although the Globe claim, destined afterwards to become the greatest copper producer in the district, was the earliest location, it attracted but little attention for several years, owing to the greater interest aroused by silver ores and the success which was already attending their exploitation in the Silver King mine. Other settlements or camps sprang into existence about the same time as that .at Ramboz. Among these were Cottonwood Springs, Basin, Watsonville, and McMillanville. Richmond Basin; situated on the southwest slope of the Apache Mountains, first came into notice through the nuggets of native silver which were found in the superficial wash . and decomposed rock forming the floor of the little depression whence the name of the settlement was partly derived. Shafts were sunk, that of the McMorris mine reaching a depth of 800 feet and producing high-grade silver ore up to 1882, when work ceased. Most of this· ore was treated in a mill at Wheatfields, on Pinal Creek, something over 12 miles northwest of Globe, although in 1878 some was apparently worked in the old Miami mill, 4 miles from Globe, at the northern end of ~Iiami Flat. The total yield has been variously reported as from $300,000 to $647,574.85. The Nugget mine, about 2 miles southwest of · Richmond Basin, was also a prominent mine of these early days, and had a small stamp-mill east of Gerald's ranch and 7 miles due north of Globe. McMillanville, in the Apache Mountains, about 20 miles from Globe, was a well-known and active camp during the later seventies, owing largely to the operation of the Stonewall Jackson mine. Rich bunches of ore carrying native silver were found in this mine in 1878 and 1879, and a 5-stamp mill was erected at McMillanville in the latter year. Throughout this period and up to about ·1884 the Silver King continued productive and reache~ a depth of over 700 feet. Like several other of the silver mines mentioned in this historical sketch, it lies outside of the bounds of the Globe quadrangle, although within what mar be broadly considered as the Globe region.

GEOLOGY OF THE GLOBE COPPER · DISTRICT, ARIZONA. Some time prior to 1878 the principal settlement of the district was transferred from Ramboz to Globe, the choice of the latter situation being probably determined by the more plentiful 'water supply afforded by the bed of Pinal Creek and the better position of the latter place as a general distributing point for the whole region. A newspaper, the Arizona Silver Belt, was started about this time, and from its files, extending from May 2, 1878, to January, 1902, many of the facts of the present sketch were gleaned. During 1878 and i879 the raids of the Apaches under Geronimo and Victorio kept the miners in a state of constant anxiety. But, although isolated prospectors sometimes fell ·victims to the savages, the latter never ventured to ·attack the settlement of Globe. In 1880 the Globe region was producing silver from several small . mines within and adjacent to the area embraced by the present quadrangle. The most prominent properties at this time appear to have been the McMorris and Stonewall Jackson, the former being credited with a product of $84,370.58 for six months of the year. The Buffalo and Alice mines were also opened about this time for silver ore, and the Old Dominion was prospected. In May of . this }7ear the Miami, D_uryea, Stone~all, and Isabella mills · were working in all 27 stamps, and the Nugget, Baldwin, Golden Eagle, Irene, Silver Era, and Townsend mills, wit? a total of 65 stamps, were in process of construction. Lost Gulch was at this time coming into notice as a promising :field for gold prospects. It is probably to this . period that the former activity of the abandoned silver mines at Pioneer, . 12 m.iles south-southwest of Globe, is to be referred, but no published record of their operations has been found. In 1883 there were 12 mills reported in the vicinity of Globe working on silver and gold ores and having in all 86 stamps. The Silver King mine had reached a depth of 714 feet on a body of rich silver ore, which, however, gave out near this level. From this . year on silver mining declined, and, although a little desultory prospect_ing and mining continued, and the Fame mine was exploited as late as 1889, the mines were one by one shut down, and the production of silver ores appears to have practically ceased by 1887. The future prominence of copper as the principal product of the ~lobe district appears to have been · at :first unsuspected, in spite of the strong surface indications of the presence of copper ore, and those mines which subsequently became the largest copper producers were at one time worked for ·silver. a The original Old Dominion mine is situated a'bout 4 miles north of Globe, on a vein in quartzite. Its owners, the Old Dominion Company, afterwards purchased the old Globe mine, which is now the principal mine of the region and i:> popularly known as the Old Dominion mine. To avoid as much as possible the confusion which this duplication of names involves, the first mine, to which the name really belongs, will be referred to as the original Old Dominion. It at one time afforded handsome specimens of native silver and free gold from its upper levels, but is no longer worked by the company.

HISTORY O.B' MINING ',rhe first notices of copper, prospecting are in the Arizona S-ilver Belt of July 11, 1878, where reference is made to the abundant copper ore revealed by the very superficial workings on the Globe and Globe Ledge claims. This ore seems, however, to have attracted little serious attention until 1881. About this time the Old Dominion Company erected a small copper furnace on the Western Pass road, about 6 miles nearly due west of Globe and abo~t half a mile northeast of Bloody Tanks. · The ore for this furnace was obtained from a vein the schists near by, but appears to have been only a small pocket and the mine waR soon abandoned. The smelter was moved to Globe and worked for a time on the siliceous copper ore from the original Old Dominion mine; but the company soon purchased the Globe mine, and in May, 1884, this was in full operation and produced 490 tons of copper from two 30-ton furnaces. From this time on the old Globe mine became generally known as the Old Dominion, while the original mine of that name was practically abandoned. In 1886 the property of the Old Dominion Company _was sold at auction to William Keyser, of Baltimore, the reported price being $130,000. The product , at this time is said to have been about 10 tons per day from one furnace, and the total product from 1882 to September 1, 1886, is given as 22,800,000 pounds. There were in all 6 copper furnaces in the district, and mines other than the Old Dominion are credited with a total product of 1,000,000 pounds for the same period. At the end of this year the low price of copper, combined with the necessarily high operating expenses in a region where supplies were hauled by wagon from Wilcox, 120 miles away, compelled the copper mines to close. Early in 1888 the Old Dominion Company was reorganized, work wa$ resumed, and the sixth level opened from the new Interloper shaft. During this and the following year the mine produced 10,515,510 pounds of copper, and is said to have maintained an average annual production of about 8,000,000 pounds up to the close of 1893. The Buffalo mine was producing some copper ore in 1890, but the economic history of these years is largely that of the Old Dominion mine. In 1892 the United Globe Company was organized and the Buffalo, Hoosier, and numerous other claims were consolidated into one group. Three years later the Old Dominion also changed hands. The United Globe mines enlarged their plant in 1895, and began active operations in 1896, directed chiefly to the development of the Hoosier claim, which had produced considerable ore from bodies in limestone near the surface. There was :a general revival of prospecting at this time in Lost Gulch and on Pinto Creek, and development work was in progress at the Continental mine, at the Black Warrior and Black Copper mines, then owned by one company. ln Lost Gulch the Kasser mill of 10 stamps was operating for a time on gold ores.

GEOLOGY OF THE GLOBE COPPER DISTRICT, ARIZONA . . In April, 1897, the Old Dominion mine, which had been producing steadily, with the exception of brief stoppages due to labor difficul~ies, shut down to await the arrival of the railroad, which was completed into Globe on December 1, 1898. The mine then resumed operations and has continued to . produce coppe~ up to the present time. · It continues to be the only large. and steadily productive . mine of the region, although ores in considerable quantity have been shipped from time to . time from the United Globe and smaller properties. The Continental mine, which had . produced some rich copper ore, but not in shipping quantities, was. bought by the Old Dominion Company in 1899, but has not yet been actively worked. PRODUCTION. In the Globe quadrangle the production of coppe1~ far exceeds in importance that of any other metal, and more than three-fourths of the whole output has

come from a single mine, the Old Dominion (formerly k~own as the Globe). The total product of this property and the various mines of the United Globe group at the close of the year 1901 was a , little over 118,000,000 pounds of copper. If an estimated 2,000,000 pound~ additional be added to 'this to cover u-recorded and irregular shipments from smaller mines, there is obtained a total . product for the quadrangle of, in round numbers, 120,000,000 pounds. - Statistics of the outp~t of gold and silver are lacking. The Mc~orris mine, in Richmond Basin, which while not embraced by the Globe quadrangle _comes within what is generally known as the Globe region,- is credited with a production of nearly $150,000 in silver during 1880 and 1881. a The total product of this mine probably exceeded $300,000. Silver was also produced in the early eighties from the surface workings in Richmond Basin, in the form of nuggets, and from several small mines, such as the Fame, Centennial, Nugget, and others, lying north of Globe; but ·the total amount was probably not large. Gold has been mined in. small quantities in Lost aqd Gold gulches, the output from the former being given as $48,000 in 1896. b The production of this metal, however, has been intermittent, and the total is probably inconsiderable. DISTRIBUTION OF THE ORES. The ore bodies which have thus far proved of most importance in the Globe quadrangle occur in the Globe Hills, just north of Globe. The copper ores which have given the district its later prominence are found in the southern part of these hills, within a radius of 3 or 4 miles from Globe, principally in the properties owned by the Old Dominion and the United Globe companies, while the silver a Files of the Arizona Silver Belt for 1881. bG. W. P. Hunt, in the Report of the Governor of Arizona for 1896, p. 108. ,·

' GENERAL CLASSIFICATION OF THE ORES. ores, which :first attracted attention to the region, were formerly mined in the northern portion of the hills and in the adjoining quadrangles to the north and east. Such old silver workings as lie within the Globe quadrangle have. been idle for years. They are none of them extensive and are now of slight importance, and afford in their present condition little opportunity for scientific investigation. Although the same rocks that make up the Globe Hills occur also in the northeastern quadrangle, where they have been :fissured in a remarkable manner, no workable ore and very little mineralization has been found north of a line joining Sleeping Beauty Peak and Webster Mountain. South of this line copper ores occur_ at the Black Warrior and Black Copper mines in Webster and Gold· gulches and at the Geneva and Continental mines, while sufficient gold has been found in Lost and Gold gulches, both in small veins and in superficial gravels, to encourage prospecting and intermittent mining on a small scale since the discovery of the d'istrict. In the -vicinity of Liveoak Gulch the porphyritic facies of the Schultze granite has been much :fissured and shattered, and is often conspicuously stained with carbonates and silicate of copper, while workable deposits of ehrysocolla have been exploited on a small scale in the Liveoak and ~keystone mines. On Pinto Creek, near the mouth of Cottonwood Gulch, the schists are very much brecciated by . numerous fissures, and show conspicuous green stains of copper, but no ore bodies have yet been found. In general it may be said that there is more or less mineralization at several point,s in the Pinal schists close to the contact with the Schultze granite, but ore in workable quantity has not been discovered. In the diabase of Powers Gulch are a few small veins showing, in croppings and shallow prospects, some galena in rusty copperLstained quartz. In the south~rn half of the quadrangle there is comparatively little mineralization, although bodies of ore have been found at the Summit, Cole & Goodwin, and Bobtail mines, in the large irregular area of schist covering much of the western slope of the Pinal Range. Some silver ore has been pioduced by the mines at Pioneer, but they lie just outside of the southern boundary of the quadrangle. On the northeastern slope of the range a little gold has been obtained from the gravels of Pinal Creek, but no workable gold-quartz veins have yet been found. GENERAL CLASSIFICATION OF THE ORES. The o~es of the Globe district may be classed as (1) free gold ores, (2) native silver or silver-lead ores, and (3) eupriferous ores containing varying amounts of the precious metals. ·4-t the present time, . h~wever, ores of the first

GEOLOGY OF THE GLOBE COPPER DISTRICT, ARIZONA. and second classes are mined on so small a scale and so intermittently that it is scarcely necessary to consider them. They play but an insignificant part in the D,lining industry of · the quadrangle, and very little of scientific interest is to be gained from the present underground developments connected with their exploitation. It is to the cupriferous ores that. the district owes its life, and . with them that this report is most concerned. The copper ores may be divided on genetic as well as practical grounds into (1) oxidized ores and (2) sulphide ores. To the former division belongs nearly a1l of the ore produced in the district up to the year 1901, when· some small shipments of sulphide ore w-ere made from the .Summit mine. Sulphide ore, on the other hand, if there be excepted occasional bunches of chalcocite found with oxidized ore, as in the Buffalo mine, is of recent discovery, and a factor of increasing importance in determining the future of mining operations in this quadrangle. · As will be la.ter shown, the sulphide ores are the_oretically capu,ble of further division into primary ores,. or ores of original . deposition, and secondary ores dedved by .subsequent chemical processes from the primary ores. The oxidized ores also may be conveniently distinguished as indigenous and exotic, the former being those produced by the oxidation of sulphides in situ and the latter those deposited after sorrie migration from the place of sulphide oxidation. It is evident t~at this distinction_n can not always be made in practice, and the extent of the migration of the oxidized ores in solution . is rarely determinable. Between the two kinds of ore no hard and fast line can be drawn, but the classification recognizes a factor in ore genesis which both observation and theory agree to. be real, and which in the Globe district has a practical bearing. MINERALOGY . OF THE ORES. The mineralogical character of the Globe ores is simple. The primary sulphide ores and those which in the absence of any evidence of secondary origin may be grouped with them are composed usually of rather crumbling, granular pyrite, with which is 'commonly associated some chalcopyrite. Of less frequent occurT~nce are galena and · sphalerite, with occasionally the tungstate hiibJ?.erite, as in the Bobtail mine. The gangue is altered country rock, or quartz, the latter being rarely abundant, or sometimes calcite, as in the Cole and Goodwin mine .. Loosely coherent pyritic ore, often containing no visible chalcopyrite, is found on · the eleventh and twelfth levels of the Old Dominion mine, between the fifth and sixth levels of the Grey mine, and in the Continental mine. It also occurs, with some finely disseminated through the granite-porphyry (Schultze granite) near the head of Gold Gulch.

Y OF THE ORES. Chalcopyrite is found abt1ndantly in the Summit mine, where it forms the bulk of the ore, m the Cole & Goodwin mine with pyrite, in the Bobtail mine with sphalerite and galena, and 'in a quartz vein in Schultze granite at the Yo Tambien, a prospect on the west side of Pinto Creek, near the mouth of Cottonwood Gulch. Galena occurs very sparingly in the quadrangle, and was seen only at the Bobtail mine, as occasional specks in the Cole & Goodwin ore, and in the partly oxidized ore of some prospects in Powers and Gold gulches. It probably occurs to some extent, however, in the·argentiferous veins in the diabase of the northern Globe Hills, and was seen with sphalerite in the ores of Pioneer and Richmond Basin, which lie outside of the quadrangle. Sphalerite is known only at the Bobtail mine and in minute quantities at ·the Cole & Goodwin ~ine. · Of the foregomg the pynt1c ore of the deeper leyels of the Old Domihwn mine is regarded as most typicalJy primary ore. I It is less certain whether the galena and sphalerite are products of original ore concentration, but there is in this district no known evidence to the contrary. The only secondary sulphide recognized in the quadrangle is chalcocite or copper glance. This occurs as a thin film coating fr~gments of chalcopyrite in the Summit vein, and is here indubitably of later oriJin than the chalcopyrite. The hematite associated with it probably represents part of the iron set free from the chalcopyrite in the change to chalcocite. In the . Buffalo mine massive chalcocite occurs, altering to malachite. As it isl found only in small residual masses and is the only sulphide present, no ·direct light · is thrown on its presumable origin from primary sulphides. In · the Old Dominion mine compact, massive chalcocite oc-curs within the zone of change from oxidized ores to pyritic ore, chiefly on the eleventh and twelfth levels. Some of the chalcocite is free from pyrite, but the latter mineral is often disseminated in small particles through the mass of the gray copper sulphide. When the chalcocite is examined closely, particularly with a lens, it shows an indistinct unevenness of texture suggestive of the obscurer forms of pisolitic structure observed in some bauxites. Critical scrutiny of the inclosed grains of pyrite discovers the fact that their outlines are rounded and that tl~e chalcocite has a more or less distinct, concentric, shelly structure around each grain. These facts at least strongly suggest that the chalcocite has been formed at the expense of the pyrite, and that the minute structure observable in chalcocite now free from pyrite records the . former presence of that mineral and its subsequent replacement by the sulphide of copper. This process will be discussed at greater length, however, in the ·pages devoted to ore genesis.

GEOLOGY OF THE GLOBE COPPER DISTRICT, ARIZONA. As might be expected, the oxidation of sulphides showing so little diversity as those in the Globe· quadrangle, has resulted in mineralogically simple products. Arsenical and antimonial minerals, which in some copper districts accompany the sulphides and give rise, by oxidation, to various mi~eralogically interesting derivatives, are here unknown. Pyrite, chalcopyrite, and chalcocite have their sulphur replaced by oxygen, carbon dioxide, or silica, usually with accompanying hydration, and become hematite, limonite, cuprite, malachite, or chrysocoila. Azurite rarely occurs save as an occasional incrustation on malachite. The hematite when not combined in an aphanitic earthy mixture 'Yith cuprite occurs as specularite, sometimes in a form of a loose powder . of greasy fee.l, but more often in firm aggregates streaked with chrysocolla or malachite .and containing little vugs lined with one of the latter minerals, which in turn is not infrequently covered with drusy quartz. The specularite is found usually in quartzite or limestone, often forming the gangue or matrix of bunches of oxidized ore. The occurrence of limonite is similar to that of hematite, but it never has the unctuous, pulverulent form often taken by the latter. ·It is. found principally in limestone, as a firm, ·aphanitic material, more or less cavernous in texture and passing occasionally into yellow, ocherous varieties. It is usually associated with the oxidized ores of copper, either as a 'casing" between the ore and the limestone, or as a large mass within which the ore, if 'present, ·is found in bunches. It also <:>ecurs intimately mingled with the cuprifer<?us minerals in the ore itself. Limonite is abundant in the Old Dominion mine, and ·appears to be in this district a characteristic accompaniment of oxid1zed copper ores in limestone. Cuprite showing crystalline texture was noted only at the Continental and -'Buffalo mines. Mixed with hematite or limonite, however, it probably makes up a considerable part of the high-grade, aphanitic, brown copper ore found in the Old Dominion and other mines in the Globe Hills. Malachite, or the green carbonate of copper, is very abundant, particularly throughout the Globe Hills, but never, so far as seen, forms large masses. It occurs characteristically as smaH stringers or veinlets, cutting the other oxidized ore minerals or lining small vugs. It is particularly conspicuous in connection with ore bodies in ·quartzite, as the innumerable minute fissures formed in this brittle rock, many of them of microscopical size, are usually filled wi~h malachite, giving a bright-green tint to the whole. In many cases the ·malachite has apparently directly replaced the quartzite, as the microscope showE~ · crystals of the carbonate projecting from the microscopical veinlets into the substance of the rock. Associated with chrysocolla it forms a considerahle proportion of the ore of. the Buffalo, Big Johnnie, Buckeye, and other mines in quartzite. It occurs as veinlets in the chrysocolla of the Keystone mine, and as a conspicuous green stain over much of the granitic porphyry in the vicinity .of Liveoak Gulch.

MINERALOGY OF THE ORES. Azurite, or the blue carbonate of copper, is rarely seen, and only as small druses or incrustations on malachite. Chrysocolla is an abundant and important ore mineral in the Globe quadrangle, although its high contents of silica and water make it relatively low grade as compared with ores containing cuprite or malachite. It varies widely in color from delicate apple-green or turquoise-blue tints to dark green, brown, or black, the darker tints being apparently due in most cases to the presence of oxide of manganese. The green and blue varieties are common in all the oxidized ores of the Old Dominion, Buffalo, and other mines and prospects in the Globe Hills, often occurring as little bunches and veinlets in the cryptocrystalline, impure . cuprite of the high-grade brown ore. A pure, greenish-blue chrysocolla with chalcedonylike banding forms the ore of the Keystone mjne, where it occurs as a vein in granitic porphyry, and is common in neighboring prospects north of Bloody Tanks. · The same mineral constitutes the ores of the Black Warrior, Geneva, and Black Copper mines, occurring chiefly as a replacement and mineralization of dacite tuff. Much of this ore is dark colored, owing to· the presence of manganese oxide, and that of the Geneva especially is of very striking appearance. It consists of kernels of black or dark olive-green chrysocolla of very irregular shape em bedded in lighter-colored varieties of the mineral, ranging in tint from a delicate turquoise blue to a deep bottle green, the whole ore having a resinous luster. These paler-tinted varieties are often arranged in fine concentric bands about the dark kernels; and as they do not always completely fill t4e interstices between the latter, the resulting cavitieR form little vugs, usually lined with pale-blue, botryoidal chrysocolla. Field relations show that this ore occurs as a replacement of dacite tuff, and a study of specimens indicates that the dark kernels, which owe their depth of color to the presence of oxide of manganese, probably represent, original glassy particles of dacite and possibly small schist fragments in the tuff. Traces of flow structure and of original partly crystalline texture can occasionally be detected, and residual flakes of biotite, such as occurs in the dacite, are not uncommon within the dark chrysocolla. The present boundaries of the kernels are not, however, identical with those of the supposed original clastic partiCles. The latter have been rounded and embayed in the process of ore deposition, and in part replaced by the banded chrysocolla, which apparently occupies in the main the place of the former fine interstitial matedal of the tuff. Native gold, silver, and copper were se~n in place only within the zone of oxidation, although the first-named mineral probably occurs to some extent in the district as a primary ore constituent. Gold occurs as thin, hackly plates

GEOLOGY OF THE GLOBE COPPER DISTRICT, AR.IZON,A. and short wires in the massive, impure cuprite of . the ·original Old Dominion mine. More or ~ess native silver has probably been found in many of the oxidized ore deposits in the district, but was seen at the time of visit only in the Continental mine as minute flakes in calcite accompanying cuprite. Native copper in small hackly particles is abundant in certain parts of t4e Old Dominion mine, particularly in mineralized shattered quartzite within the zone of oxidation. PARAGENESIS. By paragenesis is meant the association of the various ore and gangue minerals, with special reference to the order and mode of their formation. As far as known the minerals of the primary sulphide ores were contemporaneously formed and exhibit no regular sequence. Thus, in the Bobtail mine chalcopyrite, sphalerite, galena, pyrite, and hiibnerite occur together in a quartz gangue, none of the minerals named showing evidence of earlier or later origin than the others. The secondary sulphide chalcocite was the latest of the s~lphides to form, as shown by its coating fracture surfaces of chalcopyrite in the Summit mine and its occurrence near the bottom of the zone of oxidation in the Old· Dominion and Grey mines. The oxidized ores are, of course, of generally later date than the sulphides, although it must be borne in mind that the formation of chalcocite is probably still in progress below the zone of complete oxidation. Cuprite, native copper, and hematite appear to be characteristic of the lower portion of the oxidized zone and probably tend in such a position to form first from the sulphides. Occasionally, however, as in the Buffalo mine, chalcocite changes directly into malachite. The-character of the transformation depends upon the nature of the solutions e-ffeCting it, and that in turn upon the ·depth at which the process takes place and the materiais through _which the solutions have previously percolated. As a rule chrysocolla is older than malachite when the two minerals occur together. The silicate, other things being equal, seems to form at a greater depth in the zone of oxidation~ than does the malachite. Azurit~, when it occurs, is of later origin than the malachite. The formation of quartz and calcite is not limited to any single phase or period of ore deposition, but traverses the entire range· of mineralization from th~ primary sulphides to the latest oxidized ores. These gangue minerals are . rarely abundant, however. Exceptions to the usual sequence of the ore minerals as just outlined are by no mean~ difficult to find, and illustrate the variable and complex factors concerned in ore genesis. Thus, a specimen from the Old Dominio-n mine; seen in

FORM AND GEOLOGICAL OCCURRENCE OF THE ORE BODIES. the mine office, showed chalcocite partly altered to malachite and the malachite covered with druses of quartz, upon which were implanted crystals of calcite. Upon the calcite in turn were arborescent crystalline aggregates of native copper. Still another specimen showed copper inclosed in quartz. FORM AND GEOLOGICAL OCCURRENCE OF THE ORE BODIES. The ore bodies of the Globe quadrangle exhibit various forms, and, as is u::mal ·in such cases, these ai·e not sharply distinguishable from 01ie another. Fol-- poses of description, however, they may be classed as (1) lodes, (2) masses in limestone, and (3) irregular mineralizations of shattered or permeable rocks. The lodes, for the most part simple fissure veins, are mineralized postdiabase fault fissures belonging wit~ those already described on pages 97 to 106. Of the hundreds of dislocations dissecting the region, only a very small proportion contain ore~ and these are often structurally unimportant as faults. The cause of the mineralization of certain fissures and its absence from others is unknown. It has been impossible to discover any particular distinction; other than the presence of ore, possessed in common by the mineralized faults and not also found in some of the barren fissures of the region, although the postdacite faults, as far as known, are unmineralized. The greater number of the lodes have approximately northeast-southwest strikes, and dips ranging from 40° to 90q. As examples of lode depos~ts may be cited the Summit, Cole & Goodwin, ' and Bobtail lodes, carrying sulphide ores in Pinal schist, the Keystone vein of chrysocolla in Schultze granite, the Big Johnnie vein carrying cuprite, chrysocolla, and malachite in quartzite, the Josh Billings, containing oxidized ore in diabase, the veins of oxidized ore in the quartzite of Copper Hill, the oxidized North vein in diabase in the Old Dominion mine, the pyritic lodes in diabase.in the lower levels of the same mine, the vein of the original Old Dominion mine in quartzite, and many others, particularly throughout the Globe Hills. Some of these lodes, such as the original Old Dominion, the Keystone, and the Summit, are nearly typical simple fissure veins. The ore fills a formerly nearly empty fissure with little or rio replacement of the original walls. Others, like the Bobtail and Big Johnnie, are mineralized fault breccias. The ore' has filled the interstices between the fragments .of the breccia, and has frequently, to some extent, metasomatically replaced the latter, thus forming a link between the lodes and the other two classes of ore deposits recognized in this. quadrangle. Still other lodes, such as the pyritic deposits in the Old Dominion and Grey mines, might be classed as stringer lodes-that is, they consist of several irregular anastomosing fissures filled ore. Where, as in these cases, the country rock is diabase, the mineralization is not confined with the fissures, but has penetrated

GEOLOGY OF THE GLOBE COPPER DISTRICT, .ARIZONA. into_ the dia~ase by the ,process of metasomatic replacement. Such o:te possesses no regular vein walls, but grades gradually into altered diabase containing dis., seminated pyrite . . ·such a process, while it does not extend to a sufficient lateral distance to .destroy the general lode-like form of . the deposit, nevertheless tends to connect fissure veins through intermediate forms · with the· deposits belonging to the other classes. The pyritic lode of the Continental mine, which . is in a granite-porphyry facies of the Schultze granite, is also a stringer lode and is accompanied by considerable metasomatic . mineralization of the neighboring country rock. When, as is the case in the I X L, Big Johnnie, B1l.:ffalo, and Copper Hill mines, lodes pass upward from diabase into overlying quartzite, the latter rock usually shows the greater mineralization. The only known exception to this is the Josh Billings vein, in which the ore occurs principally in the diabase. Althou,gh the lodes often contain excellent ore, it has . not yet been found in such abundance as in the large masses in limestone, 'Which have supplied most of the copper from the distriCt for the last twenty years . . All of the important ore . bodies thus far discovered in limestone, with the exception of one for~nearly worked in the Buffalo mine, lie on the . southeast sid~ of the Old Dominion fault, and have been worked through the Old Dominion and Hoosier inines. In the former property there is exposed in the hanging wall of the master fissure-the Old Dominion fault-a thickness of from 350 to 550 feet of the Globe limestone resting upon the quartzites of the Apache group. The ore bodies occur rather irregularly throughout this limestone section from the top to the bottom. In general they are rudely lenticu]~u in shape and lie roughly parallel with the nearly horizontal bedding of the limestone. Som~ of them are directly connected with 'the Old Dominion fault, the ore forming the hanging wall and extending irregularly for 20 or 30 feet out into the limestone. Others, although never far from the Old Dominion fault, are completely inclosed within this rock, which, however, always shows more or less fissuring, such as may have given access to the ore-bearing solutions. Some of these ore masses have been of large ·size, one in the Old Dominion mine having been about 200 feet long, 100 feet wide, and 60 feet thick. This, however, was not wholly within the limestone, but was partly in quartzite, and really falls ·also into the third general class of the ore deposits of the district. Other masses ·of ore not coming.' strictly within the definition occur in the Old Do,minion mine at the contact of limestone with overlying dacite. The ore, however, occupies space formerly filled with · limestone and not with dacite, and the . form of such deposits is similar to that occurring wholly in limestone. The ore of these masses in the Globe limestone is always oxidized and often accompanied by large quantities of hematite or limestone. It sometimes rests

Late Paleo oic -vvashJngton ..J

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FORM AND _GEOLOGICAL OCCURRENCE 0]' TH~,!. -B'ODTE~B : dlb-;2~7' snugly against 1h~ limestone, and is sometimes separated 'from the latter by a shell of limonite. The limestone, as a rule, shows very little alteration at a distance of a few inches from the ore or from the iron oxides. Ore occurring in the form of irregular mineralization of shattered or permeable rocks has contributed largely to the total output of the Globe quadrangle. Here belong the masses occurring in brecciated quartzite, always as~ociated with one or more fault fissures, but not confined within their walls. Such bodies have supplied much of the ore of 1 the Old Dominion mine, where a mass of the quartzite lying between th~ Old Dominion and Interloper' faults has been extensively mineralized. Similar conditions exist in the Grey and Buffalo mines, and to some extent in the Buckeye mine. Such ore masses are usually very irregular in form, and often have no sharp boundaries, as workable ore changes gradually into less broken country rock only slightly stained with malachite or chrysocolla. The ore is usually wholly oxidized, and may consist of chrysocolla, cuprite, malachite, specularite, and native copper in varying proportions. Some chalcocite, however, occurs as residual unoxidized kernels in the ore of the Buffalo mine. The microscope shows that the shattering of the brittle quartzite is often exceedingly minute, so that it is not always easy to determine whether there has been any actual metasomatic replacement of the quartzite by ore. As a rule, however, the fact of such replacement can be ascertained, although the bulk of the ore has undoubtedly filled mechanically formed spaces. The conspicuously stained but not hitherto productive schist breccias so noticeable alongside the road from Webster Gulch as it descends into Pinto Creek, and the green-.tinted granitic breccias of Liveoak Gulch are similar in general character to the more richly mineralized deposits in quartzite just described. In this class also come the ore bodies of the BJack Warrior (Montgomery and Dadeville claims), Geneva, and Black Copper mines. In the first two the ore, which is chrysocolla, occurs as a metasomatic replacement of dacite tuff lying between schists below and massive dacite above. All gradations may be traced from the solid chrysocolla resulting from practically complete replacement to tuff showing mere traces of mineralization or none at all. In the Black Warrior and Geneva the ore bodies , re flat, blanket-like masses, passing gradually into tuff on their peripheries. Thry · rest sometimes directly upon the schists, sometimes are separated from the ]atter by a layer of tuff. They are always associated with fault fissures, which arel in part later than the ore. In the Montgomery and Dadeville claims is a strong east-west fault, which was apparently initiated prior to the deposition of the ore. The ore body of the Black Copper mine, also lying between schist and dacite, is of rather irregular shape, and evidently formed at least in part by replacement of dacite or dacite tuff. It has an easterly dip of about 35°, and it is possible that

GEOLOGY OF THE GLOBE COPPER DISTRICT, ARIZONA. it occupies a fault fissure opened prior to ore deposition, and might perhaps be classed with the lodes. ALTERATION OF THE COUNTRY ROCK. Owing to the prevalent oxidation and the absence of extensive mine workings in connection with sulphide ores, the Globe region does not at pl'esent offer favorable opportunities for the study ·of metasomatic alteration of the country rock a~.:; an accompaniment of original ore deposition. Such alteration as was observed was not conspicuous, and was riot particularly studied. In . very few cases have the developments on sulphide ores gone to such a depth as to entirely eliminate the action of descending surface _waters. GENESIS OF THE ORES. The little mining development so far accomplished upon the primary sulphide ore·s has brought to light no evidence against the commonly accepted view that such ores were deposited by ascending solutions of originally meteoric waterwhich had become charged· with ore-forming constituents in the course of a slow and devious underground circulation. Their metalliferous contents were probably deri':"ed from the deep-seated rocks of the region. The diabase, which was so extensively intruded into the Carboniferous and older rocks~ contains abundant augite, olivine, and magnetite, and is obviously a likely source of supply for at least some of ·the ore constituents. In order to test this hypothesis, 10 grams of the fresh diabase, of which a chemical analysis and petrographical description · are given on .'pages 83 to 85, was examined in the Survey laboratory by Dr. E. T. Allen and the presence of a trace of copper determined. As the specimen came from an unfissured mass exhibiting no signs of mineralization, and is shown by the mi?roscoe . to be almost ideally fresh, it is probable that the copper is an original constituent of the rock and a source of at least a part of the copper concentrated by natural processes in the ore bodies. As fissuring, accompanied or followed by the original mineralization of the district, is the important event recorded in the geological history of the region succeeding the intrusion of diabase, it is probable that here, as in other mining districts, there is a close genetic relationship between the manifestations of volcanism and the subsequent ore deposition. The intrusive masses not only supplied ore constituents, but were probably partly responsible for the fissuring, and supplied heat and chemical activity to the underground waters.' In spite of the limited amount of mining work done upon the sulphide ore bodies of the quadrangle, the evidence for the secondary origin the chalcocite is satisfactory. In the Summit mine this mineral occurs probably at less than 200

GENESIS OF THE ORES. feet in depth as a thin, black film coating fracture surfaces of chalcopyrite, and often associated with hematite. The mineral in this case is ·obviously formed subsequently to the fracturing of the chalcopyrite, presumably by descending solutions carrying down copper sulphate from the zone of oxidation. A reaction capable of producing this result may be written thus: Chalcopyrite Cupric sulphate Chalcocite Ferrous sulphate Sulphur dioxide. CuFeS2 + CuS04 Cu2S + FeS04 + The actual reactions, however, are probably more complex, and further chemical study of the action of various solutions upon natural sulphides is required before every step in the pnoeess is known~ Apparently a part of the iron formerly combined with copper and sulphur in chalcopyrite has been redeposited as hematite, by further oxidation of the ferrous sulphate. In the Old Dominion mine the chalcocite, as pointed out by Emmons, a occurs in the transition zone between the · oxidized and pyritic 'ores. According to the observations of Mr. Emmons, chalcocite was first encountered between 400 and 500 feet below the surface, where must have been accompanied by oxidized ore. It is now known to extend downward to the twelfth level, or about 900 feet below the surface, and is here a~sociated with unoxidized pyrite. Its vertical range is thus considerable. At the time of visit no chalcooite was seen in place above the tenth level. The occurrence of the chaleocite as a characteristic mineral of the transitional zone from oxidized to sulphide ore is, alone suggestive of its secondary character. This, however, is still more strongly brought out by the structure of the ore itself, which, as described on page 121, has formed in concentric shells about small residual grains of pyrite. The cupriferous sulphate solutions descending the oxidized zone above have percol~ted through the loosely coherent pyrite and changed it in part to chalcocite. reaction in this case has involved not only the little chalcopyrite in the pyritic ore, but has apparently transformed pyrite to chalcocite without any intermediate stage. That this is possible is shown by the reaction. b Cuprous sulphate Pyrite Chalcocite Ferrous sulphate Cu2SO 4 + FeS Cu2S + FeSO 4 In examining some of the chalcocite from the Old Dominion mine Dr. Hillebrand found that considerable !iron went into ·solution when the mineral, with its inclosed granules of fresh pyrit~, was treated with hydrochloric acid. This suggested that there might be some ferric hydrate present. A section of the. ore, ground as thin as possible, was microscopically examined by transmitted a The secondary enrichment of ore deposits: Trans. Am. Inst. Min. Eng., Vol. XXX, 1901, p. 192. b See VanHise, Some principles controlling the deposition of ores: Trans. Am.Inst. Min. Eng., Vol. XXX, 1901, p.l12. 9651-No. 12-03-

GEOLOGY OF THE GLOBE COPPER DISTRICT; ARIZONA. and reflected light, but nothing accounting for this chemical peculiarity could be detected. The process of sulphide . enrichment . appears to have worked downward, keeping 200 feet or more in advance of distinct oxidation. Chalcocite. thus occurs as residual masses in the oxidized ore, and as bunches in ·pyrite below the limit of oxidation. Below the twelfth level chalcocite will probably be less abundant, and it is rather doubtful whether it will be found in any quantity on the thirteenth level when ~hat depth is reached. The bulk of the oxidized ores are . indigenous, i. e., occupy substantially the places of formerly existent sulphides, the latter having been altered in the usual manner by deRcending solutions, which, starting at the surface with oxygen and carbon dioxide, constantly gathered new materials and effected manifold chemical changes in the ores in their downward progress. Such apparently are the oxidized ores of the Old Dominion, Hoosier, Buffalo, and other mines in ·the Globe Hills. But even in these cases there has evidently been some migration of the ores during the general progress of oxl.dation, although it is difficult to determine how extensive this movement has been. In the Buffalo mine, for example, the occurrence of kernels of chalcocite surrounded by malachite shows that the change has been on. the whole in situ. But microscopical study of the oxidized ore indicates on the other hand, that some of the malachite has directly replaced the quartzite and occupies a position not previously filled by a sulphide. As far as known, no sulphides have been found in the large ore bodies occurring in limestone in the Old Dominion mine, and there is no direct evidence that they were ever present. But reasoning from analogy, with deposit~ of like form and similar geological st;trroundings, known in other districts~ it is fair to suppose that these masses were originally deposited as sulphides, although it is not safe to assume that these sulphides were identical in characte'r with the py-ritic ores now known in the diabase of the lower levels. It is very probable that they were' more cupriferous. with the oxidation these ore bodies much of the iron and copper passed into solution as sulpha~es, carbonates, or silicates, and this change was unavoidably accompanied by _mig-rations of the different ore constituents within the oxidizing mass. That such, indeed, took place is seen by the structure of the oxidized ore, in which stringers or bunches of one ore mineral occur inclosed withi_n another. Moreoyer, these ore solutions can ·scarcely have been confined within the space originally occupied by sulphide ore. They undoubtedly took advantage of . such mechanically formed spaces as may have opened since the sulphides were originally deposited to transport ore into new crevices, and very probably replaced to some extent the in'closing limestone and such of the shattered quartzite as iay within reach of their attack.

GENEStS OF THE ORES. In the case of the chrysocolla deposits of the Black Warrior, Geneva, and Black Copper mines, the or~s occur 'as replacements of dacitic tuff, or possibly dacite in the last-named property, ,and their structure is such as to indicate strongly that they have been deposited directly in the tuff as the hydrous silicate · of copper, and do not represent the alteration in place of former sulphides. Proof of this hypothesis is, perhaps, not to. be had. But the . total absence of sulphides, combined with the lack of iron oxide and the fact tha·jj the ore is practically a single mineral rather than a mixture such as results the oxidation of more or less pyritic ores, are points in its favor. Furthermore, the structure of the ehrysocolla is elosely and minutely related to ·that of the tuff it has replaced, which would probably not be the ease did the ore result .from the alteration of former bodies of sulphides. For, even if the sulphides preserved some vestiges of the original texture of the tuff, the further change into chryso- · co1la could scarcely fail to obliterate them entirely. It is therefore concluded that the chrysocolla ores of these mines are pr<?bably exotic, although it is admitted that actual proof of this is, from the nature of the case, not at hand. The sources of the solutions that .deposited the hydrous silicate of copper are unknown. Although they are always associated with much fissuring, a large part of this is later than the ore, and none of the fissures that have been eut in the underlying schist show such mineralization as would be expected had they served as channels for ore-bearing solutions capable of depositing the overlying ore bodies. The hypothesis that the ores have reached their present position by direct · ' ascent through these fissures m the schists, while attractive at first glance, has insufficient support as far as present developments go. ·A second hypothesis is that they may have come in laterally along the pervious beds of tuff, carrying the copper first as earbonate, afterwards to be transformed to silicate by the abundant silica present in the glassy tuff, the ready solubility of which is shown by the frequent oceurrence of opal and chalcedony in the tufl'aceous and mas~:live dacite. Probably there were seattered over the old surface of shattered schist upon which the tuff was laid down surficial deposits containing carbonate of copper, much as, at the present day, slightly waterworn gravelly detritus cemented by impure malachite may be seen in vVebster, Lm;t, and . Gold gulches, usually just above the level of the existing stream cha~nels. Such deposits show that solution and transportation of ore may be effected by the mere passage of meteoric waters over the surface of a generally mineralized region. The covering of such a surface with a permeable mantle of tuff offers exceptional opportunity for the solution and transport of the scattered, low-grade surficial or~, and its concentration in favorable places at the . base of the tuff through the agency of what are practieally surface waters. The deposition of

GEOLOGY OF THE GLOBE COPPER DISTRICT, A:RIZON.A. this exotic ore would be particularly favored by a fault, such as that at the Montgomery claim, which should _drop the tuff against older, l~ss permeable, and less chemically active rock, thus forming a. depositional trough. It is believed that such an hypothesis best accounts for the chrysocolla ore of the Black Warrior, Geneva, and probably, also, that of the Black Copper, mines. The ore is exotic, and has been derived, not from sulphides in place, but probably from the lateral transport and concentration of scattered surficial deposits of predacitic origin, which were themselves formed by the oxidation and weathering of sulphides. The genesis of the chrysocolla of the Keystone and neighboring veins in granite-porphyry is not cle!l-rlY understood. The purity of the ehrysocolla, its vein structure, and the absence of evidence of sulphide oxidation from the vein and wall rock are Emggestive of an exotic origin of the ore, and its deposit in · the fissure as hydrous copper silicate. The present depth of the Keystone mine; however, is not sufficient to determine_ the real genesis of · the ore body. The occurrence of some unoxidiz~d pyrite in a stringer near the mouth of the lower tunnel indicates that if the chrysocolla is to give place to sulphides in depth, the point of change should not be far off. It is hoped that the mine will be successfully exploited to a sufficient depth to thoroughly expose this i~teresting deposit. IAGE OF THE ORES. As, in this district, prim;ary sulphide ores are found in fissures cutting diabase, they were evidently deposited after the eruption of that rock. Similar original oi·es· also occur in Pinal schist, in which ease there is nothing in their surroundings to show that they are not much older than the ores in diabase. But as they are even less deeply oxidized than the latter, it seems reasonable, in the_ lack of distinct evidence to the contrary, to refer all of the primary sulphide mineralization to one period, subsequent to the great disturbing and mineralizing event in the geological 4evelopment of the region-the' diabase intrusions. Although the fact that the primary ores are later than th~ diabase is readily established, their relation to the dacite is less easily determined. It has been shown that the region was probably faulted after the diabase intrusion and· long before the eruption of the dacite. The results of this faulting were, however, greatly obscured by the postdacite faulting, probably in late Tertiary ti~+Ie. T4ere is some question :whether or no this earlier faulting was important, and whether the original mineralization is related to it or to the postdacite faulting. Owing largely· to the usual oxidation of the ore, no thoroughly conclusive evidence for the decision of . this question could be obtained at any point. That the former of these alternative hypotheses, namely, that the sulphide ores are older

AGE OF THE ORES. than the dacite, is the true one, is, however, strongly indicated by the cumulative weight of several facts, no one of which alone is fully decisive. These may be summarized as follows: The mineralized fault issues north of Globe either pass beneath the dacite :flow without perceptibly faulting it, as may be seen near the I X L mine, and is indicated on the two geological maps, or else they dislocate it to an extent incommensurate with their displacement of the older rockA, as in the case of the Old Dominion fault. It is a dificult matter to trace faults when they enter the dacite, but the total disappearance of the outcrops, several strong fissures where this rock forms the surface, and the striking contrast between the .faulting of the older underlying rocks and the -practical integrity of the dacite :flow as it is exposed just north of G:lobe, admit of but one interpretation. These generally northeast-southwest faults, many of which are more or less mineralized, were originally formed in predacite times. In the nm:thwest corner of the quadrangle, on the other hand, the dacite is conspicuously faulted, but these postdacite faults preponderate, and are not mineralized, or at least have not been shown to contain sulphide ores. This difference in age of the dominant faults thus probably accounts for the notable lack of mineralization in tbe northeastern corner of the quadrangle, in spite of the fact that .the same rocks occur there as notth of Glob~, and are even more thoroughly fissured. · No sulphide ore has yet been found in dacite. In the Old Dominion mine such ore as has been mined near this rock has inyariably been oxidized, even on the lower levels which elsewhere encounter sulphides. The ore bodies never extend irregularly into the dacite, but are separated from it by faults, or else underlie it with every appearance of having been deposited and at least partly oxidized before its eruption. Th~ only bodies of oxidized ore known to occur in dacite or dacite tuff are those of the Black Warrior, Geneva, and Black Copper mines, in which the ore is certainly late~ than the eruptive rock. But it has been shown that these ores consist of chrysocolla and are exotic. Thus their existence in the tuff at the base of the dacite points to the existence of predacite sulphide ores .from which they were originally derived. Their occurrence wou~d be difficult of explanation were it supposed that the original mineralization of the district to_ok place after the eruption of dacite. It is therefore concluded that the hypothesis which assigns the original deposition of the sulphide ores to a period following the intrusion of the diabase and preceding the eruption of the dacite is in harmony with the observed facts as well as with the general theoretical considerations suggestive of a genetic connection between the intruded diabase and the . deposition of ore. The primary mineralization of the Globe district thus probably took place during the later Mesozoic. ·

GEOI.QGY OF THE GLOBE COPPER DISTRICT, ARIZONA. DESCRIPTIONS OF MINES. OLD DOMINION MINE. Situation.-This property, formerly known a.s' the Globe mine, compnsmg a compact group of nine clai:rps, lies on the east side of Pinal Greek, just north of the town of Globe. Of these claims, the Globe and Globe L~dge, located upon a strong fault, -are the most important, and ·have produced the bulk of the ore. Some ore has also been mined from the Alice claim, which ·is on a fissure southeast of the main Old Dominion fault. I£istory ·and product1'on.-The Globe claim was staked in 1875, and was the first mining location in the district. It apparently attracted but little notice for several years, although some superficial work was done in search of silver ore. ·In 1881 the extraction of copper ore began,· and the mine, shortly after purchased by the. original Old Dominion Company, soon became the largest and · steadiest producer of such . ore in the region. In 1886, after yielding between 18,000,000 and 19,000,000 pounds of copper, the mine was sold at auction to William Keyser, of Baltimore. Early in 1888 a new company was organized and the mine was operated almost continuously up to 1895, when it was sold to Lewisohn Brothers, of New York, and ·subsequently transferred to the present owners, the Old Dominion Copper Mining and Smelting Company, of Boston. The mine produced nothing in 1895, butresumed production in 1896 and reaohed .its maximum output in 1901, the latest year for which figures were obtainable for this report. During much of the. time from April, 1897, to the completion of the. railroad, at the close of 1898, the mine was idle. The total production of copper from the Old Dominion mine up to the end of 1901 .is. a little less than 106,500,000 pounds> Up· to the year 1900 no returns of the silver and gold in the copper bullion are obtainable, while the figures for 1900 and 1901 are, by the desire of the company, with~eld from publication. Development.-The underground workings of the Old Dominion mine comprise 12 levels . of generally linear plan (Pl. XXII), extend~ng iwrtheast a~d southwest along a zone of faulting. The main adit is a 3-compartment vertical shaft 827 feet deep, sunk through the hanging wall on the Interloper claiin. with this . shaft all the levels are directly connected except the first level or "mule tunnel," which has its own adits at the lev~l of the shaft collar. There are also several unused shafts and some short tunnels connecting with old workings above the mule tunnel, as well as . some open cuts from which ore is still being mined. From the second and fourth levels drain tunnels have been run out to the surface southwest of the Interloper shaft: The levels from the first to the eighth are from 58 to 72 feet apart, while from the eighth to the twelfth

OLD DOMINION.· MINE. they are separated by intervals of 100 feet. The total length of ground which is more or less explored by these workings is about 3,600 feet and the total depth about 1,000 feet. The largest ore bodies have been found to the northeast of the shaft, and the greatest dev~lopment has consequently been in that portion of the mine. . The principal work on the Alice claim consists of two tunnels, run in from the northeast side of Alice Gulch and connected by raises with each other a1~d with the first level of the main Old Dominion workings. A general plan of the underground workings of the Old Dominion mine is shown in Pl. XXII and an elevation in Pl. XXIII. The ore is carried on an aerial tramway abol,lt 1,200 feet in length down . to the company's smelter on Pinal Creek. (Pl. XXI.) The smelter is equipped with four stacks, of which but one is usually in steady operation, with an average output of about 13 tons of copper per day. As all of the ore thus far mined has been oxidized, it is smelted directly without previous roasting. The country rock.-The rocks met with in the Old Dominion workings are the quartzite of Apache group, the Globe limestone, diabase, and dacite. The quartzite is similar in character to that occurring on top of Buffalo Ridge, but in the Old Dominion mine it is not exposed on the surface except at the northeast end of the Globe claim. It occurs in beds of varymg thickness up to 6 feet, or possibly more, and ranges in texture from pebbly grits to fine-grained vitreous varieties such as form the crest of Buffalo Ridge. The maximum thickness of the quartzite as exposed in the mine workings is about 500 feet, but as part of the quartzite in this section is much crushed and disturbed by faulting, the actual thickness of the bed~ may be considerably less than this. The quartzite beds have a general southerly dip of from 10° to 20°, but, as will be shown, they are locally much disturbed. The Globe limestone overlies the quartzites of Apache group with apparent conformity. The latter relation, however, is difficult of proof owing to slipping and mineralization along the contact between the two rocks. At the surface the limestones are gray in color and thick bedded, as may be well seen in the limestone quarry east of the Interloper shaft. These beds are probably Upper Carboniferous, although no fossils were found at the mine. The beds at the surface are nearly horizontal, but in general throughout the workings they show a southerly dip of ·about 20°. The thickness of the limestone exposed in the Old Dominion mine has not been accurately determined. It is betweei1 350 and 550 feet, and is probably not far from too feet .. It is highly probable that the lowest beds are of Devonian age, but in the absence of fossils in the mine workings or of any wel1-marked stratigraphical plane of division, the beds belonging t? these periods were not discriminated.

GEOLOGY OF THE GLOBE COPPER DISTRICT, ARIZONA. The lithological character of the diabase of the Old Dominion and neighboring mine8 has been fully described on pages 80 to 85 of this report. Here, as else~ where in the Globe region, it is intrusive into the Apache group and Globe formation, chiefly as a sill of unknown thickness which is apparently intruded at the same stratigraphical horizon as that on the northern side of Buffalo Ridge. In the Old Dominion mine, as in that ridge, the Apache group immediately above the diabase is charaCterized by a few feet of rather thin-bedded reddish pebbly grits, but the intrusion of the diabase has not been confined to the injection of ·a single-great sill. It has also cut irregul.:trly across the beds as will later be shown. As a rule, th.e d:iabase seen in the Old Dominion workings is not so · coarsely crystalline as that found in the middle of the large diabase areas of the quadrangle or as the typical and fresh facies forming the top of Black Peak. On the contrary, .· it is frequently almost aphanitic near its contact with the limestone and quartzites. The dacite forms part of an irregular sheet whose geological relationships and petrographical characters have been deBcribed on pages 88 to 94. This rock . is f?und only at the southwest end of the mine, where its relation to the older quartzite, limestone~ and diabase is that of a flow resting upon an old surface of erosion which slopes down toward Pinal Creek. This simple structure bas been modified, however, by a series of faults which will presently be described. Overlying the dacite flow are the conglomeratic beds of the Gila formation. The Gila formation and the dacite are not ore bearing, and the under surface of the latter rock limits the ore-bearing ground of the Old Dominion mine to the southwest (see Pl. XXIII). The fissures.-The most important .fissure in the mine, which wiU be referred to for convenience as the Old Dominion fault, finds prominent expression on the surface. Its general ~trike is about north 55° east, and it dips southeast at an average inclination of 55°, becoming steeper, however, below the ninth level. Passing just JlOrth of the little dacite knob above the mine ·buildings, the outcrop of the fissure crosses diagonally the ridge between Buffalo and Alice gulches, its. course being marked by a line of shafts and open euts·, and descends into Alice Gulch, where for a few hundred feet it is not directly exposed. It is clearly traceable, however, over the southern slope of Buffalo Ridge just north of t.he Globe shaft, crosses Alice Gulch north of the Hoosier shaft, and continues northeastward toward the Grey shaft. The fissure is plainly a norinal fault, as shown by the dropping of the Globe limestone against quartzite of the Apaehe group,, and of dacite against diabase. The throw of the fault as measured by its displacement of the dacite is about 100 feet. But the present r~lative positions of the Pale9zoic beds on each side of the fissure demand the existence of a much

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OI..D DOMINION MINE. greater displacement, probably as much as 1,000 feet. It is thus evident that the Old Dominion fault represents more than a single movement, ab?ut 900 feet of the throw being predacitic and about 100 feet postdacitic. Throughout the greater part of the mine the foot wall of the Old Dominion faul_t is diabase~ usually soft and decomposed for some distance from the fissure. The hanging wall varies, being mainly limestone in the upper levels (see Pl. XXIV), although quartzite, and finally diabase, predominates in the lower levels. Although t~e mine plats show many undulations in the foot wall, its appearance is often strikingly regular, as may be seen in PL XXV, A. · It is usually easily recognized, and is rarely . penetrated for any distance by the workings. The texture of the diabase is somewhat variable, and is frequently fine grained or even aphanitic, resembling facies elsewhere found near intrusive contacts, such as in tlie north crosscut in block vii, a on the tenth level, where the quartzites rest upon what appears to be a sill-like intrusion of diabase. The latter rock is aphanitic at the contact, but shows fine acicular feldspar crystals a few inches away. In block xxix, second level, where quartzite is exposed for a distance of about 40 feet in the bottom of the main drift, and near the line between blocks xxx and xxxi, on the same level (Pl. XXIV), w·here the drift passes from diabase into quartzite, the two rocks are separated by eruptive contacts near to which the diabase is unusually fine in texture. · This quartzite near the northeast end of the second . level is apparently in the foot wall of the Old Dominion fissure and 1closed in diabase, much as is the limestone between , the fifth and seventh levels. There are certain exceptions to the statement that diabase forms the foot wall of the mine, and probably the most remarkable of these is found on the sixth level, where for a distance of over 300 feet along the drift the foot wall is cornposed of limestone in nearly horizontal beds, which in block xi are irregularly intruded by aphanitic diabase. On the southwest the limestone is separated from the usual diabase of the foot wall by a vein of earthy hematite striking northwesterly and dipping southwest at 45°. On the northeast the contact between the limestone_ and diabase is marked by a fault fissure carrying a little crushed rock and traces of ore. A northwest crosscut ha.s been run into this limestone for 300 feet without passing through it. Part of this sam~ mass of limestone appears on the fifth level, in blocks xii, xiii, and xiv, but it is not known on the seventh level, where crosscuts show that it is' underlain by diabase. There is thus inclosed within the diabase of the foot wall a block of limestone strata at least 300 feet square and probably something over 100 feet in thickness. On three sides the beds are cut off sharply by fissures, showing at least some a The convenient notation employed in the mine is retained in Pls. XXII, XXIII, and XXIV, and is self-explanatory.

GEOLOGY OF THE GLOBE COPPER DISTRICT, ARIZONA. movement. The fourth side is as yet unexplored. T~e character of the upper and lower surfaces of this block are unknown, but they are probably intrusive contacts. The general position of th.e block of limestone is shown in fig. 7, which a section across the mine on the line between blocks xi and xii. Faulting _alone, subsequent to the intrusion of the diabase, can not account for the occurrence of the limestone in the foot wall at this place. · It is n.ecesFIG. 7.-Diagrammatic cross section through the Old Dominion mine, showing the occurrence of a mass of limestone in the diabase of the foot wall. Scale: 1 inch 200 feet, approximately. sary to conclude that it is a mass enveloped by the diabase at the time of in.trusion, although some movement has subsequently transfo~med eruptive contacts In part into fault fissures. The occurrence of block in the foot wall, taken in connection with the know? stratigraphical sequence in the hanging wall, shows that· the initial Old

U. 8. GEOLOGICAL SURVEY sw. 0 ° 0 ° " + TENTH L£V£L TWE.LFT V£L ELEVATION OF THE OLD DOMINIO N M I NE SCALE i00e3~=c=OG PROFE&SK>'\AL PAP!A ,.,0, 12 PL XXIII N£.

OLD DOMINION MINE. Dominion fault antedated the intrusion of the diabase, and probably became in greater part a surface of eruptive contact. This conclusion is in harmony with the frequently fine-grained texture of the diabase neat the fissure, a feature known to be characteristic of it in p,roximity to igneous contacts. As will be shown when the ore bodies are described, there is evidence that the original mineralization is older than the dacite. It will also be shown that in the lower levels ore occurs -in the Old Dominion fault in diabase. Consequently a part of the fault"ng· along the Old Dominion fissure, and that part which was followed by mineralization, took place after the. diabase had solidified but before the dacite was erupted. The truth of this is borne out by the following description of the Interloper fault, a branch of the main fissure, showing a displacement that demands in the latter a greater postdiabase throw than the 100 feet of postdacite movement alone would !allow. The preceding discussion ·has related to the main fissure, here called the . Old Dominion. fault, which has been shown to have· been originally an intrusion fault, then in part a plane of eruptive contact, which was afterwards revived as a postdiabase fault of unknown throw and again reopened as a . postdacite normal fault to the extent of a throw of 100 feet. There are, however, several other important fissures encountered in the mine, which are certainly in part and probably wholly later than the diabase intrusion. The most notable of these faults, and olile that bas had m:uch influence upon the genesis of the ore bodies, lies in the hanging wall of ' the Old Dominion fault, and like the latter has a southwesterly dip varying from 50° to 60 ° This fissure, which may conveniently be designated as the Interloper fault, is distinctly recognizable on the second level, where with the Old Dominion fault it incloses a mass of crushed quartzite of lenticular plan (Pl. XXIV) extending southwestward for a distance of 500 feet from the Mooney shaft in block xvii. The banging wall of the Interloper fault on this level is limestone. On the third level the horizontal . section of the lenticular wedge of quartzite lying betwe~n the two faults becomes both longer and broader. · It here· has a length of over 1,100 feet, and the maximum distance separating the two faults, which coalesce at the points of the lens, is about 175 feet. On the fourth, fifth, and sixth levels the Interloper £ault has been less continuously exposed than in the upper workings, but is recognizable at several points as a welt-marked fault, usually having ·quartzite of the Apache group on Its foot and Globe limestone on its hanging walls. Its maximum distance from the Old Dominion fault varies from 100 to 150 feet on these levels. Below the sixth level the Interloper fault can not be identified witl~ certainty among the fault slips of similar trenrl cut at various points in the workings.

GEOLOGY OF THE GLOB~ COPPER DISTRICT, ARIZONA. The throw of the Interloper fault has not been determined. The cross section shown in fig. 7 indicates a displacement of about 400 feet. But the quartzite forming the upper portion of the wedge between the Interloper and Old Dominion faults is so crushed and disturbed that it can not be safely taken as a measure of the throw, which may · be conside1·ably less than 400 feet. This fault was probably formed after the intrusion of diabase and before the eruption of dacite. The Alice vein, as exposed at t. he surface, is approximately . P~rallel with . the Old Dominion fissure, and lies from 300 to 500 feet southeast of the latter. The vein is wholly in limestone as far as e~plored, and has a southeasterly dip ranging from 45° to 609. Between the Alice vein, which as see~ o.n the surface is a mineralized limestone breccia, and the Old Dominion and Interloper · faults the Globe limestone is cut by numerous f3tults, us,ually showing abundant soft gouge, indicating -recent movement. These fissures have not been system- -atically explored, although they are. often associated with bunches of ·ore in the limestone. They have various trends, and although the greater number of them . are approximately parallel .'with the Old Dominion fault, others depart as much as goo from this strike. They sometimes intersect in a perplexing fashion, as may be seen in the Alice workings. The Alice · tunnei (see Pl. XXII) in its curved course from its mouth to its connection with the Alice crosscut makes a turn ·of about goo, and apparently follows more than one of these fissures, which intersect at oblique angles and have various dips. In the first 200 feet the tunnel appears to follow the Alice vein, which, however, shows much recent movement. Ne~r the Alice crosscut the drift follows a strong nearly north-south fissure, exhibiting evidence of considerable recent slipping. This is known in the mine as· the Alice fault, and will be again referred to in, considering those recent faults that have modified the ore bodies. The dislocations occurring between the Old Dominion fault and the Alice vein appear to be for the most part minor faults, which do not c~oss into the foot wall diabase. Although .the diabase of the . f9ot wall is practically unexplored, except on the first level north of the · Globe shaft and on the eleventh and twelfth levels, yet enough has been done to indicate that it is traversed by fissures which, while roughly parallel with the Old Dominion fault, dip steeply in the opposite direction, i. e., to the northwest. Thus the north vein, which has been drifted upon north of the ~ld Globe shaft, dips . northwesterly at angles varying from 50°· to 70°. It approaches the -Old Dominion fault as it is followed upward, and must . meet the .latter just abo,ve the old workings from the Globe sh!Lft. On the eleventh and twelfth levels two distinct veins, diverging northeastward

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OLD DOMINION MINE. from the Interloper shaft, have been drifted on, as shown in Pl. XXII and fig. 7.' It seems likely that the more northerly one, which is nearly vertical, is a fissure in the foot wall similar to the j north vein near the Globe shaft, while the southerly one seems to be the main Dominion fault, although hardly enough work had been done in 1901 to put thi~ beyond question. AJI the fault fissures encountered in the Old Dominion mine show more or less recent movement, and are usually accompanied by soft gouge. Character and occurrence of the m·e.-All of the ore commercially extracted from the Old Dominion mine up to the present time has been oxidized ore, and contained no sulphides. Sulphide ores occur in the lower levels, but no attempt has yet been made to work them on a commercial scale, and they hold a different relation to the country rock from that of the great bulk of the ore which has . given the mine its prosperity. In its commonest form the ore is a dark reddish-brown, compact mixture, showing no crystalline stru~ture, and· composed chiefly of the red oxide of copper with more or less limonite or hematite. The color of this material varies with the proportions of cuprite, limonite, and hematite, being sometimes yellowish, dark brown, or nearly black. The dull tint of the compact earthy oxides is nearly always enlivened by bunches and . veinlets of malachite and of blue or green chrysocolla. Ore of this character is often accompanied by large masses of the specular variety of hematite, usually carrying too little copper to pay for working, or by bodie~ of equally low-grade, cellular limonite. Native copper is sometimes an important ore constituent, and is particularly common in ore occurring in quartzite. Quartz occasionally occurs in beautiful translucent druses coating chrysocolla or malachite, and crystals of calcite are sometimes found in vugs. But aside from such secondary occurrences, the deposit is free from these common gangue

minerals. Azurite is sparingly present in ore bodies near the surface, and native silver has been reported f~'om the old superficial workings. There are frequently. associated with the oxidized ores, _and sometimes filling seams in the neighboring limestone, masses of waxy, clay-like material of . various degrees of firmness and ra ging in color from yellow to pale apple-green. Rough chemical analyses show tha this substance is essentially a hydrous silicate of alumina, or a clay, containing in some cases as much as 7 per cent of magnesia, and in the . green varieties a little copper, which is s·aid to occasionally exceed 6 per cent, thus becoJ?ing low-grade ore. The important ore bodies so far exploited . in the Old Dominion mine lie within the limestones and quartzite forming the hanging wall of the Old Dominion fault. In general these bodies · ar rudely lenticular and lie roughly parallel with Late Pa~eozoic .Library Washington D. C.

GEOLOGY O:B' THE GLOBE COPPER DIS'.rRICT, ARIZONA. the nearly horizontal b~dding of the inclosing rock. They occur particularly along contacts between rocks of .different kinds, as between dacite and limestone, between limestone and quartzite, or between. limestone beds of different lithological character. Some of the ore bodies are directly connected with the Old Dominion fissure, the ore forming the handb:~g wall and extending irregularly for 20 or 30 feet out into the limestone. Such is the ore body still being worked in the principal open cut and shown in Pl. XXV, A. Others are apparently completely inclosed within the limestone, the latter, however, always showing more or less fissuring, s~ch as may have given access to the ore-bearing solutions. As the ore lenses are followed toward the Old Dominion fault it is often found that they turn up at a steeper angle, and either wedge out in the limestone or continue on until they reach the fault. Whether the ore in such cases rises obliquely across the · bedding, or the· beds themselves are flexed upward close to the f~ult, could not 'be made out with certainty. The former, however, seemed · more probable. The lenticular wedge · of quartzite lying between the Old Dominion and Interloper faults is much shattered, particularly above the third level, and has been extensively but irregularly mineralized, the . ore not filling the interstic~s but replacing to some extent the broken quartzite. Of less importance as yet · than the m·es occurring in the hanging-wall limestone and quartzite are certain ore bodies found wholly within the diabase in the form of lodes. These lode ores are of two kinds--the oxidized ore, :mch as has hitherto beel). stoped from the North vein, and the sulphide ore occurring in the lower levels from the ninth down and not yet commercially extracted. It thus appears that the ore of the Old Dominion mine has· been deposited under rather varying conditions, which will be described in a little more detail and illustrated by a few specific examples before passing to considerations of genesis. The occurrence of ore between limestone and dacite may be seen in a little stope from the first level in block xii. The ore is the usual brown, oxidized variety, and is of good quality. It lies upon limestone, which it penetrates . irregularly ·as bunches and stringers, and is overlain by dacite, the contact dipping about 20° to ~he west-northwest. The ore appears to have been deposited. and to have undergone oxidation before the eruption of the dacite, forming, with the eroded · limestone, part of the predacitic surfac.e. The dacite itself h;. unmineralized. The occurrence of ore within the limestone is well illustrated in a small but repres.tentative stope comiecting with the second level in block xv. The ore, which apparently contained a little more chrysocolla than usual, formed an irreg-

U. S. GEOLOGICAL SURVEY I'ROFESSIONAL PAPER NO. 12 PL. XXV A. I N THE 0 PEN CU T 0 F 1 HE 0 L D D 0 M IN I 0 N M IN E. The even foot wall is diabase. The hanging wall is an oxid1zed mass of hematite and ore, extending irregularly into limestone on the left. B. THE GREY M I NE. View is up Copper Gulch along the course of the Old Dominion fau lt. The Grey shaft is in the foreground , while JUSt beyond it is the Grey incline. Behind the latter is the Cuprite shaft and Copper Hi ll. Black Peak lies against the sky to the left.

OLD DOMINION MINE. ular, nearly flat, body 5 or 6 feet in thickness, but gradually thinning out on its periphery, lying generally ·parallel with the bedding planes of the limestone. The workable ore, now mostly removed, was separated from the limestone by a H casing" a few inches in thickness, consisting of cellular limonite containing a little calcite and jasperoid quartz. The open cut (Pl. XXV, A) affords an opportunity for studying on the surfac~ the relation of the ore to the limestone. Here .the flat lenticular form common to many of the ore bodies is not so apparent. 20 or 30 feet from the diabase foot wall of the he mineralization has extended ld Dominion fault into the limestone hanging wall, and the oxidation of this deposit has produced a rusty mass, within which irregular bodies of good ore occur enveloped in worthless specularite and limonite. Some of the largest ore bodies in the min contact between the limestone and the quartzite. have occurred at the bedding Such was the great body stoped above the second level in blocks xxiii and xx' v. This mass of ore is said to have been nearly 100 feet wide, 200 feet long, and about 60 feet thick. It dipped generally a little west of south at a low angle. The occurrence of ore in the shattered quartzite between the Old Dominion . and Interloper faults was studied in 1901 in a stope on the fifth level in block Here good ore, consisting of cuprite, malachite, and thin hackly leaves of native copper, extended very irregularly into th~ quartzite from .the Interloper fault, filling the interstices of the shattered quartzite and partly replacing the fragments. The ore also extends from this stope into the limestone between the fifth and sixth levels as a flat replacement body lying in the bedding, and on the sixth level, lying between massive limestortes, occurs a bed of calcareous shale, which ha-; been mineralized sufficiently to form an important body of ore ranging in tenor from 7 to 13 per cent of copp r. The oxidized ore· of the North vein, while .associated with a distinct fissure, does not, properly speaking, constitute a vein. It is not the filling of a fissure, but occurs in bunches, partly within the fissure, accompanied by soft gouge, · and partly in masses extending irregularly into the diabase walls. The oxidation and recent movement have in t~is case obscured the m;iginal r~lation of ore and country rock. There can be little doubt, however, but that the North · vein originally resembled the lodes next to be described. On the eleventh l~vel northeast of block xi (c bout 800 feet below· the surface), and on the .twelfth level northeast of the shaft (about 900 feet below the surface}, all the workings are in diabase, and the ore occurs as irregular stringers in this rock, forming two well-defined stringer 1 ads or lodes. It consists principally of crumbling pyrite with a friable quartz full of tiny vugs. The

'I GEOLOGY OF THE GLOBE COPPER DISTRICT, ARIZONA. poorest of this pyritic ore contains about -3 per cent of copper, while much of it contains 5 per cent, and some more than this. It is, on the whole, a very lowgrade ore. , The copper is probably combined as chalcopyrite, . but it is usually impossible to detect this mineral by the eye. Closely associated with the pyrite on the eleventh and twelfth levels, and sometimes enveloped in it, are bunches of massive copper glance or chalcocite. The occurrence of this mineral with the pyrite is o:f great interest, but unfortunately the character of the exposures now available is such that the relationship of the chalcocite to the pyrite could no~ be ~atisfactorily studied. Copper glance was first . noted in the mine . on the fifth level in block xxii, or about . 350 feet below the surface, thus making its appearance before the pyrite. The pyrite and chalcocite on the eleventh and twelfth levels form stringers sometimes as much as 5 feet in width. . But the ore is not confined between defini~e walls. As regards the pyrite in particular, all gradations may be observed between solid ore, on the one hand, arid altered diabase speckled .with small crystals of the sulphide, on the other. Grades of ore.-The ores of the Old Dominion mine have a wide range of tenor. That with less than 6 per cent of copper can rarely be profitably · extracted, while .ore containing 20 per cent is regarded as high grade. Most of the ore mined lies between these grades. It is obvious that the .pyritic ore, when unaccompanied by chalcocite, is not at present workable. (]-round-water level.-The level of permanent water in the Old Domimon mine is rather difficult of definition. Oxidized ore prevails down to the tenth level, or to a depth of 600 or 700 feet. The cha:nge to sulphide ores occurs between .the tenth and eleventh levels. and probably marks the original lowest le,rel QI standing water. At the present time great quantities of water find access to the mine through the upper levels southwest of the shaft. This influx, however, is . probably ·almost entirely _due to mining operations, whereby the water saturating the basal portion of the Gila conglomera.te has been tapped and drained into the workings, vvhence it was formerly excluded by the dacite flow (see Pl. XXIII). The influence of recent faulting upon the ore bodies.-Although fault slips later than the ore are of frequent occurrence throughout the mine, they have in most cases resulted merely in minor local complexities, such as have not seriously baffled the search for ore. In those ·portions of the workings lying northeast of the " Alice tunnel and crosscut and southwest of the Interloper shaft different conditions, however, prevail. Inspection of the pl~n ·of the mine shown in Pl. XXII discloses the fact that those workings obviously connected with extensive stoping all lie west of a

OLD DOMINION MINE. north and south line drawn through the Alice crosscu~ about 150 feet from its mouth. East of such an imaginary line is a tract of llpparently barren ground extending nearly to the Globe shaft. This change 's well recognized as a practical factor in mining operations, and is usually ac ounted for by supposing that the ore is cut off by the so-called Alice fault. This explanation is supported by the following. facts: (1) There is a strong fissure striking a little west of north and dipping west about 60° which has been followed for some distance in the Alice tunnel; (2) one of the largest ore bodies in the mine, that over t;Ie second level in blocks xxiii and xxiv, is said to 'have been cut off abruptly on the east by a strong fault .slip dipping to the west; and (3) the nearly north and south drift on the second level extending from block xxiv-6 to blo0k xxv-6 follows this fissure, which is wit~out doubt the same as that already _referred to in the Alice tunnel. The same· fault has been supposed to appear in the er?sscut from the second level in block xx-9; but this is doubtful. If the fault continues so far toward the south, it probably lies farther east. Below the second level the Alice fault has not been recognized. The end of the third-level drift encounter8 a fault slip in block xxiv-6, which is about wh~re the Alice fault should appear. But this fault dips to the east instead of to the west. This, taken in connection with what has already been seen in the Alice tunnel, as well as the presence of several fissures on the first level not previously referred to, suggests that the Alice fault is but one member of a complex zone of intersecting and nonpersistent faults of various strikes and dips, and confined to the hanging-wall side of the Old Dominion fault. It is certain that these faults, whatever their origin, record recent or postmineral movement. It is fairly safe to accept the unanimous testimony of men familiar with the mine that the large body of ore above the second level was cut off abruptly by the Alice fault. Although it is possible that the Alice fault was initiated before the original ore deposition, and that the ore never extended beyond the fracture, yet this seems less .likely than the alternative, that somewhere east of the Alice fault there is a continuation of the ore body. As the ' ' fault is probably normal, the continuation of the ore is likely to be found at a higher level than that already stoped. The occurrence of ore bodies east of the fault zone can not be demonstrated with the data at hand: but there is at least . an inducement for further prospecting. How little exploration in this direction has actually been accomplished is evident from Pl. XXII. The plane of the Alice f~ult and its supposed continuation southward and downward seems to have been accepted on too slight investigation as an absolute barrier, beyond which it was useless to look for ore. 9651-No. 12-03~10

GEOLOGY OF THE GLOBE COPPER DISTRICT, ARIZONA. The development of that part ·of the mine lying southwest of the Interloper shaft (see Pls. XXII and XXIII) has been fraught with many perplexities. These have been due in part to real intricacy of the geological structure, and in part to erroneous interpretations of this structure. Among the · latter may be cite~ the hitherto ~enerally held view that the . flow of dacite, or so-called "trachyte," is a dike, and that the granitic detritus overlying it and forming the base of the Gila · conglomerate is really granite practically in place. Attempts have been made to cut through . the supposed dike and to find some continuation of the Old Dominion fault beyond it. These have not only been futile, but by penetrating the dacite flow and tapping the porous water-bearing Gila formation they have allowed the underground water of the Globe Valley to flow into the mine and to seriously impede f,uture development. . \Vhen it is understood that the supposed trachyte dike is really a superficial lava flow resting upon an old surface of erosion and partly covered by the .. Pleistocene conglomerates that fill the Globe Valley, it becomes clear that attempts to penetrate it in search of ore are worse tl~an usel~ss. On the other hand, the fac~ that it is a flow and not a dike suggests that the lower levels of . the mine when extended northwestwa~d ' may pass entirely beneath the dacite, which will thus no longer cut off the ore-bearing ground in ·that direction. The general relation of the flow to the older rocks and to the overlying Gila formation may be seen from Pl. XXIII, in which an attempt is made. to express, albeit somewhat -diagrammatically, the most probable explanation of the-observed facts in regard· to the ''west end" of the mine. The idea that the dacite was a dike was supposed to receive confirmation from the fact that the second and fourth level drain tunnels both. passed through a few feet of ve.ry much crushed soft "'trachyte" into "granite" (Gila conglomerate). But this hypothesis overlooked a . series of step faults, indicated in Pl. XXIII; which not only explain why the dacite was abnormally thin .where cut by these tunnels, but account also for its crushed condition. As may be seen from Pl. XXIII, the general effect of the fa11lts, which are probably, more numerous than there shown, is to give a deceptive impression that the dacite lies upon a much steeper slope than ·is really the case, and thus to afford fallacious support to the dike hypothesis. The most important of these faults is exposed at several points on or near the , . surface, and is traced on the geological map (Pl. XV). It crosses the Mqle tunnel (Pl. XXII) in block ix, near the junction· of its two adit branches. Here it dips about 40° to the southwest, and drops the granitic Gila conglomerate against the dacite. The fault passes directly beneath the hoist of the Old

OL'D DOMINION MINE. Dominion mine, and is well exposed in the cutting made for the engine house. It is cut by the Interloper shaft between the :first and second levels, the shaft passing gradually from the conglomerate hanging wall into the dacite f~ot wall. Lastly, it is visible in the bluffs of Alice Gulch, southeast of the mine, where it drops higher beds of Gila conglomerate against the lowest granitic bed. The throw of the fault is probably about 75 feet. What appears to be the same fault · was recognized crossing the various· levels below the second, and \is exposed at the southwest face of the eleventh level drift. Other closely spaced faults lie southwest of this one, but are less clearly exposed, and apparently have smaller throws. Several of them are exposed in the conglomerate bluffs of Alice Gulch (Pl. XXI), and are met with in the underground workings. One of the puzzling features encountered in developing the southwest end of the mine was the loss of the diabase foot wall, elsewhere so constant and characteristic. But a moment's consideration shows that this is a necessary and simple consequence of th~ displJcement of a southeasterly-dipping :fissure by a younger normal fault of southwesterly dip. A southwesterly drift along the Old Dominion fault will lose the diabase foot wall as it passes through one of these later faults, as, for example, at the southwest end of the eleventh level, and mu'3t be turned to the right, or northwest, to recover it. While the foregoing facts throw some light upon the general structure of the southwestern portion of the mine, they do not account .for all the complex details there found. In some part these are due to the locally irregular character of the diabase intrusion into the quartzite and limestone. But the disturbance and decomposition of the rocks is very great, and the developments, carried on without a clear conception of the dominant structure, lack the systematic character essential for the attainment of a complete grasp of structural details. The extensive oxidation of ore and country rock in the western end of. the mine is in full accord with the hypothesis that the ore was prm.;ent and partly oxidized at the old surface which the dacite subsequently buried. In weighing the _probabilities of "finding further ore in the southwestern portion of the Old Dominion mine it should be borne in mind that the normal northwes~-southeast step faulting not only offsets the Old Dominion fissure and associated ore bodies to the northwest, but has dropped them to a lower level. Hence oxidized ores may fairly be looked for southwest of this later fault zone at a depth which has brought the rest of the workings into sulphides. Rich oxidized ore occurs in limestone at the southwest end of . the ninth level and may yet be found considerably lower, as the southwest drifts on the te~th level

GEOLOGY . OF THE GLOBE COPPER DISTRICT, AR~ZONA. also show more or less oxidized ore assoc~ated with much limonite. All of the pres~nt workings on the eleventh and tweUth levels are below the zone of odixation, but it is not unlikely that they may encounter oxidized ·ore when pushed ·southwestward under the dacite flow. Inspection of Pl. XXIII shows · that the eleventh level probably has from 400 to 700 feet farther to . go before reaching the dacite, and -if the zone of step faults is not more than 200 feet in width this level may pass entirely beneath the bottom of the lava flow, w liich will thus no .longer cut off the ore to the southwest. Crosscuts to the northwest irom the eleventh and twelfth levels, after they have been extended through the zone of step faults, should :recover the offset portion of the Old Dominion fault~ with a fair probability of finding oxidized ore beneath the dacite in the vicinity of this fault,- and oxidized or sulphide ores in the underlying limestone and quartzite. Such exploration, however, is rendered difficult by the greatly disturbed character of the rocks within the zone of step -faulting and the_ consequent great influx of water from the congloll_lerate-filled basin of the Globe Valley: Moreover, a 1 large element of uncertainty iS' introdu~ed by the possibil~ty that the fault zone is a very wide one, and, by continuing to drop down, portions of the dacitH flow may make it impracticable to extend even the twelfth level beneath the main body of the flow. UNITED GLOBE MINES. General statement.-This company was organized in 1892, and various proper.: ties, among which the most important at that time were the Buffalo and Hoosier mines, were thereby consolidated. At present the ~ompany owns between thirty and forty claims lying north and east of the Old Dominion mine. The more important of their variou~ workings will _be described under the following headings: ''Grey mine," embracing the Hoosier, Grey, Cuprite, Transit, Nevada, Amador, Gladiator, and Centralia claims; "Buffalo mine," ·including · the Buffalo, Mark Twain, and Lizzie claims; "Josh Billings mine," ''Big Johnn~e mine," '' Buckeye mine,'' and '' Stonewall mine." Grey ·mine.-This comprises a series '?f workings which form practically a northeasterly continuation of those belonging to , the Old Dominion mine, and extend for an additional length of. about 3,500 feet along the Old Dominion fault (see Pl. XXVI). The principal adit is the new Grey shaft ~Pl. XXV, B) .in Copper Gulch, about 4,500 feet northeast of the Interloper shaft; but much work was formerly done through · the Hoosier shaft, about 1,400 feet southwest of the Grey. Other adits formerly used are the Transit shaft, about 300 feet west of the Hoosier; the Centralia tunnel, connecting with the second level from Copper Gulch; the Grey incline, a little over 300 feet northeast of the Grey shaft, and the Cuprite shaft, about 400 feet northeast of the Grey incline .

U.S. Geol Ogical Survey

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SKETCH JYtAP OF THE PlUNCIPAL UNEHGROUND WORKINGS OF THE GREY MINE ale lO~ok="""=""""'o '1:JO:;:;o.,..""""""'.,s:o::;o '3"=o~o'" """' .. s~oo feet, ' / ,/' / / ' ' ' / ; ' // / / / I / /

Professi Onal Paper No. 12 Pl. Xxvi

A .MADOR AIM Fifth

LEGEND Seco nd level

fourth level Fifth level , , S1xth lev el --- Boundaries of c lai ms Levels below tlwsi:rth,coTI.lUXled JliJosicr shaft, are n.ot indicated... -: C .LAIM /

Late Paleozoic L ,·b · . rary Washington o. c. UNITED GLOBE MINES. ·-· l4Q Prior to 1892 considerable oxidized ore had beea mined from the open cuts and superficial workings in the limestone, which are noticeable just below the road and about halfway between the Hoosier and Grey shafts. This led to the sinking of the vertical Hoosier shaft through the limestone here for~ing the hanging wall of the Old Dominion fault. The shaft cut the fissure between the eighth and ninth levels, at an approximate depth of 600 feet. Apparently no very large bodies of ore were encountered in the neighborhood of the Hoosier shaft, ~nd the levels' below tlie sixth have 'been allowed to fill with water. The. Grey shaft is sunk in the foot wall chiefly through diabase, but cutting also some masses of quartzite. In January, 1902, it had reached a depth of about 700 feet, the lower 400 feet (below the sixth level) being mainly in diabase. The principal levels are the second and sixth, 86 and 340 feet, respectively' below . the collar of the Grey shaft. Both of these levels connect with the Hoosier shaft through long drifts run on the Old Dominion fissnre, the dip of which varies fro'm 50° to 70°, but is usually steeper. than in the Old Do.minion mine·. Northeast of the Grey shaft the same fissure has been followed to the Cuprite shaft, but . becomes less well defined· beyond that point. As far as it has been followed it shows no perceptible offsetting by later faults. The country rock of the Grey mine is similar to that of the Old Dominion, but is less regular in its distrib_ution. Masses of limestone and quartzite inclosed iu th~ diabase are exceedingly common, and abrupt ch.anges in the lithological character of foot wall or hanging wall are therefore of frequent occurrence, particularly in the lower· levels. In part this irregularity is due to faulting, but the character and structural influence of this faulting is masked by the extensive inclus.ion of masses of strata within the diabase at the time of the latter's eruption. The effect of the intrusion wa~ to produce a s~ructure so erratic in its heterogeneity that it is generally impractica~le to determine to how great an extent later faulting has increased this complexity. It is impossible with the present facilities for observation to satisfactorily reconstruct the intricate fabric that existed prior to the dislocations that followed the diabase intrusion. From the crosscut to the Nevada vein (Pl. XXVI) southwestward to the Transit shaft the main drift of the second ·level follows in general a regular foot wall of diabase. The hanging wall is limestone, but more or less crushed quartzite occurs along the fissure, probably dragged in by faulting. North of the Transit shaft sollle work has been done on the so-called Foot-wall vein, which is identical with the North vein in the Old Dominion ground. As this vein dips to the northwest, while the Old Dominion· fault dips southeast, the · two come together north of the Transit shaft, just above the second level, and a body of ore, now stoped out, occurred at their junction.

. GEOLOGY OF THE GLOBE COPPER DISTRICT,, ARIZONA. The Nevada vein, northwest of the Grey shaft, perhaps a continuation of the Foot-wall vein, is reached by a northerly crosscut . from· the second level drift (see Pl. XXVI). This crosscut follows a fault with a westerly dip of about 80°, and having diabase on the hanging wall and quartzite overlain by limestone on the foot wall. This is probably the· fault shown 300 f~et . west of the Grey shaft on the special geological map (Pl. XV). The Nev.ada vein dips northwest at an angle of about 50c, and has a diabase hanging wall and a quartzite foot wall. Thris within the diabase, which is · the preponderant.' rock on the foot-wall side of the Old Dominion fault, is a mass of quartzite and limestone known to be overlain and underhtin by diabase and limited in its horizontal extent on at least three sides by :faults later than the diabase intrusion. But, although these faults now bound the mass in part, they can not wholly account for its position within the diabase, and this block of quartzite and. limestone illustrates on a considerable scale a featur~ occurring again and again in the deeper workings, partic:ularly those northeast of the Grey shaft, and rendering it impossible to predict what rock the next few feet of drifting n1ay reveaL Most of the faults observed have dips greater than 45° and probably normal throws. A rather :fhit fault was observed, however, in a northwest crosscut on the birth level about 250 feet northeast of the Grey incline. In this case the fault plane dips to the northeast at an angle of about 1!?0 The hanging wall is diabase and the foot wall is shattered quartz1te. The direction of relative motion; however, is unknown. The ore formerly extracted from the superficial workings between the Grey and Hoosier shafte occurred in irregular oxidized mas~es in the hanging-wall limestone, closely resembling those described in the Old Dominion mine. According to Mr. N. S. Berray, a distinction was recognized between the limestones in the Hoosier workings, the large replacement bodies of ore being confined to an upper division of gray, rather thin-bedded limestone, while in a lower massive buff limestone the ore was found only in veins or " -verticals." Thei·e was no opportunity to v~rify this statement at the time of visit, but it is certain that · no such distinction holds in the neighboring Old Dominion mine. The greater part of the workings e6nne.cted with the Grey shaft have been run for prospecting purposes, and the mine is not as yet an extensive producer. Practically all of the ore of late has come from the vicinity of the Cuprite shaft:. One considera~le body occurs in shattered quartzite above the fourth level and just northeast of the Cuprite shaft. It. consists chiefl:y of carbonates and oxide, and resembles the ore occurring in the quartzite of the Old Dominion mine. Much of the shattered quartzite i!l the vicinity of the niain Old Dominion fault is stained green with carbonate · of copper, but the mineralization is not always sufficient-to make ore.

liJNITED GLOBE MINES. Between the fifth and sit th levels near the Cuprite shaft the ore, probably part of the same body noted above, occurs in very irregular stringers in diabase, the ore body being usually hof nded on on~ or more sides ?Y smooth, recent fault surfaces of variable trend. This ore is partly cupriferous pyrite, forming stringers which shade off into pyritib impregnation of the inclosing diabase. These stringers are partly oxidized to· malachite and red oxide, with which there is sometimes associated some c~alcocite. The conditions indicate that such ore as may be found in future below the sixth level, particularly in the diabase, which apparently is the prevailing rock for a considerable depth, will occur as cupriferous pyrite forming irregular stringers and impregnations along the general line of the Old Dominion fissure. The conditions are similar to those in the eleventh and twelfth levels of the Old Dominion mine. B ·buffalo mine.-This is situated at the southwest end of Buffalo Ridge, at the head of the aerial tramway down to the Buffalo smelter. (See Pl. XXVII, A.) This property seems first to have attracted some notice in the year 1879 as a promising silver prospect and was operated on a small scale fur three or four years. But apparently no extensive work was done until about 1890, when it was opened up for copper, and considerable ore was taken out during the next few years, chiefly from a single larg·e ore body extending from 75 to 100 feet downward from the surface. The mine is now idle. The workings . comprise two long adit tunnels connecting through shafts and stopes with the surface on the top of the ridge. The ground explored by these workings has a depth of about 250 feet and a length of 2, 700 feet. They follow in general a strong fault fissure striking with the ridge, or about north 40° east, and having apparently a nearly vertical dip. Associated with this fault is a second fissure dipping to the northwest and uniting with the foriner at an acute angle at the south west end of Buffalo Ridge. These faults are shown on the geological map (Pl. XV), where it may be seen that they have dropped some of the basal beds of the Globe limestone in a trough between the quartzite. The first or lowest level is entirely in diabase and follows an unmineralized fault slip for a distance of about 1,600 feet. The general dip of this fault is to the northwest at an angle of about 75°. Several crosscuts to the northwest fail to reveal a second fissure, and apparently the two faults so noticeable on the surface come together above this level, and are represented below by a single fracture. The northwesterly dip of the latter is rather abnormal, ahd may not represent the average or general inclination. The second level. 162 feet vertically above the first and about 100 feet below the or~ croppings on the top of the hill (see Pl. XXVII, A), is a tu~nel about 2,000 feet in total length, with numerous crosscuts, chiefly to the southeast. It is nearly all in quartzite, including a little conglomerate, and follows a shattered

GEOLOGY OF THE GLOBE COPPER DISTRICT, ARIZONA. mineralized zone to within about 540 feet of the face of the 'main drift. Here . diabase appe~rs and continues for about 20 feet along the drift, being succeeded on the northeast by hard white quartzite, in which no continuation of the mineralized zone has been found. The diabase is apparently brought in by cross faults, which · have offset£ the main fissure zone, followed by the tunnel for the greater part of its length. The ore of the Buffalo mine ·occurred between the second le~el and the surface, m the shattered wedge of quartzite . and limestone lying between the two main faults. That nearest . the surface and first mined occurred as oxidized replacement masses in the limestone, associated with much limonite, as in the Old Dominion mine. But the shattered quartzite underlying the limestone in the fault wedge, as well as the qu~rtzite of the fissure walls, was also mineralized, and was extensively stoped afte:r the or,e in limestone had been exhausted . . The ore, consisting of malachite and cuprite, with occasional residual masses · or kernels · of chalcocite, occurs chiefly as a filling of the interstices and smap fractures in the shattered quartzite. Microscopi~al examination of thin sections of the ore shows that molecular replacement <?f the quartzite . has also. taken place, but . this process appears to have been subordinate to the filling of mechanically formed cavities . . The quartzite ore is destitute of well-defined walls, but grades irregularly into quartzite containing too little copper to pay for working. The most interesting features of the o:r:e occurrence are the presence of chalcocite or copper glance so near to the surface, and the apparent total absence of ore in the diabase beneath the quartzite and limestone. Josh Billings mine._:_The Josh Billings vein outcrops in quartzite along the crest of Buffalo Ridge, with a general strike of north 40° east, and a dip of about · ~l5 ° to, the southeast. It fills a normal fault fissure, the throw of which is about 60 feet. Some prospecting has been done on that portion or the vein in the quartzite, but without .success, the vein apparently· splitting up into small str.ingers in t~is rock and carrying but little ore. All of the present workings are entirely in the diabase beneath the quartzite, and comprise three tunnels that exploit the vein through a vertical distance of . about 400 feet. The lowest, or Maggie, tunnel crosscuts north to the . Maggie, a vein similar in character and parallel to the Josh .Billings, but lying about 300 feet farther northwest. After drifting northeast on this vein for about 650 feet a crosscut was run back south to the Josh Billings. The Josh Billings vein is a fairly regular fissure in the diabase, carrying bunches of high-grade (20 per cent) ore, which is oxidized below the present

li. S. GEOLOGiCAL SURV~V ~ROFESSIONAL PAPER NO. 12 PL. XXVII The black lines In dicate approximately the outcrops of some of the prin 1pal faults. The m1ne buildings and the ~entrance to the main tunnel are behind the diabase spu r skirted by the road in the m idd le-ground of the left of the view. The ore occurs w.th in the gran itic mass which outcrops prominently on the sky line. Th e N1nety Six shaft IS in the little ravine where e two faults bounding the smal ler mass of granite meet at an .acute angle.

UNITED GLOBE MINES. depth of working. There is usually a clay gouge on one side of the ore, showing recent movement. Regular walls are lacking, however, and the ore extends for varying distances into the diabase. The Jo~h Billings and Maggie veins are similar to the North vein in the Old Dominion mine, and with increasing depth will change to sulphide ore and then i·resemble the lodes met with in the eleventh and twelfth levels of that mine. Ore was being shipped from the Josh Billings vein at the time of visit, but although a single body of very good ore ·has been stoped from the neighboring Maggie vein, work on this lode has been for the present abandoned. Big Johnnie mine.-This property is on a mineralized fau1t breccia in Big Johnnie Gulch, on the western slope of Black Peak. The fault strikes about north 40° east, and dips north'west at an angle of 750. or 808 It is exploited . by tunnels and open cuts, and has produced some very good ore. Although wo.rked by lessees in the summer of 1901, the mine was idle at the time of visit. As in the Josh Billings mine, the fissure cuts quartzite underlain by diabase, but, unlike that vein, the ore here occurs in the quartzite, while a lower tunnel run in the diabase failed to find anything of value. The conditions are thus similar . to those met with in the Buffalo mine. The 9-uartzites near the fissure dip sou~heast at about 40°, but flatten toward the southeast to a general dip of 15°, with a strike of north 80° east. The average width of the fault breccia is something less than 2 feet. It consists of fragments of quartzite cemented and partly replaced by cuprite, malachite, chrysocolla, and hematite. Apparently most of the ore has been taken from open cuts along the summit of the lode, which in places split~ into two or more closely parallel veins. Buckeye mine.:-This lies on the southern slope of Copper Gulch, near its head, on a vein in quartzite (Pl. XV). The strike. of the vein ·at the mine is about north 45° east, but, as may be seen from Pl. XV, it has a curved course and soon turns . more easterly. The dip is from 50° to 60° to the northwest. The lode is exploited by a lower tunn~l about 300 feet in length, and numerous shorter tunnels and open cuts extm~ding up to the top of the hill and covering a vertical distance of about 200 feet. Most of the ore has come from the open cuts and superficial upper tunnels. It occurs irregularly in the brecciated quartzite of a :fissure zone as bunches that rarely occupy the full width of the zone. The gr0ater part of the ore, consisting of cuprite, malachite, and chrysocolla, occurs as a filling of the interstices and small fissut·es in the shattered quartzite, but there has also been some replacement of the quartzite fragments themselves. The mine has been worked intermittently for several years, chi~fiy by lessees,

GEOLOGY OF THE GLOBE COPPER DISTRICT, ARlZON .A. and the amount of ore shipped has not been large. Some of it, however, is of high grade. That being shipped in 1901 was said to contain from 20 to 35 per cent of copper, and to carry occasionally as much as 8 ounces of silver and a tenth of an ounce of gold. Stonewall mine.-This ig situated about 1,500 feet south of the Buckeye, and resem"Qles the latter in being wholly in quartzite. The principal fissure strikes north 68° eas~, and dips northwest at an angle of about 75°. Just north of it lies a second fault, which joins ·the first in the ravine west of the mine. A · third fissure, the Arizona, with a nearly east-west course, falls into this second lode from the west. The ore apparently occurs chiefly in the disturbed quartzite between the first and second fissures. ' It is mineralogically similar to that of the Buckeye, but apparently contains much more liematite. The mine has been worked intermittently on a small scale for several years, principally by lessees. OTHER MINES IN THE GLOBE HILLS. Copper Hill mine.-This embraces most of the workings Copper Hill. just northeast of -the Grey mine. The surface rock of the hill is quartzite, dipping generally to the southwest at angle of 20° or 25°. On the northeast these quartzites .are dropped against the diabase of the head of Copper Gulch by the strong, _<;urged Budget · fault (see Pl. XV). On the west they are bounded by another nearly north-south fault, which dips to the west, and has dropped limestone, quartzite, and diabase on that side. Between these two faults the ·quartzite of Copper 'Hill is traversed by numerous closely spaced, approximately parallel fissures, striking about north 50° east. These fissures, which appear to have been formed with very insignificant displacement, are filled with quartzitic breccias from 2 to 4 feet in width, most of which show more or less mineralization, while the intervening quartzite is frequently fissured and stained with carbonate of copper. Most of the breccias . have bee~ explored by open cuts and some malachite ore taken out, but the great bulk of th~ ore · is appar~ntly very low in grade. In 1901 a shaft was being sunk on one of these fissures, in Copper Gulch, at the northwest foot of the hill. About 15 feet below the collar the shaft passed from quartzite into . diabase, which apparently underlies the quartzite of Copper Hill, and was still in the same rock at the time of visit. Original Old Dominion m'l:ne.-This is situated on the east side of Pinal Creek, . about 4 miles north-northeast of Globe, on a clean-c_ut fissure vein in quartzite. It was one of the. earliest mines to be worked in the region, and was . noted in the early eighties for beautiful specimens of free gold with copper carbonates and calcite. It was 4-eveloped through several tunnels, and produced considerable ore, but has been idle for several years, save for the occasional operations of lessees.

MINE8 NORTHWES'.r OF GLOBE. The vein strikes north 30° east, and dips southeast at 75°. It cuts obliquely across the beds of quartzite, which strike about north 80° east, and dip at 45° to the south. · The throw of the fault is unknown. The vein, where $een, is less than a foot in width, ·but fairly regular, and shows no recent movement. The ore is oxidized to an unknown depth. It consists of an ocherous darkred mixture of . cuprite and iron oxide finely streaked with chrysocolla and ·malachite, and sometimes showing native gold in the form-of short wires and thin leaves. The gold is usually embedded in the red oxides. Mallory or I X L mine.-This is situated on the northwest side of Big Johnnie Gulch, the workings comprising several tunnels and a new shaft. There are two principal fissures, one striking about north 35° east, and apparently passing directly through the shaft, and the other striking about north 10° east, and meeting the former about 300 feet southwest of the shaft (see Pl. XV). Between the two faults lies a mass of reddish grit ~nd quartzite, apparently of no great thickness, and evidently overlying diabase. These grits are traversed by several small fractures c~rrying some oxidized copper _ore, and they exhibit considerable diffused mineralization and staining by copper-carbonates. The shaft has penetrated below the quartzite, and gone down for some distance in diabase without finding any pay ore. The conditions appear to be similar to those already described in the Buffalo, Big Johnnie, and Copper Hill mines. MINES NORTHWEST OF GLOBE. Bla,ck Warrior.-This company controls numerous claims in the lower part' of W ebste:c Gulch, none of which have yet been steadily productive. The principal development has been on the Montgomery, a prospect situated nearly a mile southwest of the settlement of Black Warrior and connected by a tramway with the smelter and leaching works. The development consists of three tunnels, of which the middle and lowest are the more important. The country rock includes dacite, dacite tuff, and Pinal schist, and their relations are shown in fig. 8 {p. 156), which is a diagrammatic cross section through the mine. As there indicated, the workings are related to . a fault, of probably less than 50 feet throw, striking nearly east and west and dipping steeply to the south at varying angles. This fault has dropped dacitic tuff and overlying massive dacite on the south, against schist on the north. The ore, which is wholly oxidized, occurs in the dacite tuff on the hangingwall side of the fault. The middle tunnel penetrates this mineralized tuff for a devious westerly course of some 300 feet. The tuff is approximately 50 feet' in thickness, and rests upon an uneven erosion surface of much-shattered schists. It is overlain by massive. vitrophyric dacite. unmineralized the tuff is a

GEOLOGY OF THE GLOBE COPPER DISTRICT, ARIZONA. soft, brownish or grayish material, glistening with flakes of biotite and contain..: ing· small fragments of schist and quartz. As seen in the middle tunnel, the . tuff, as well as the underlying schist, has undergone great disturbance and is traversed by countless small irregular faults in part later than the ore. The latter occurs as irregular streaks of soft chrysocolla, often nearly black, from the :presence of manganese oxide. The chrysocolla seldom forms solid masses, but per~eates the soft, altered tuff, . forming an ore of very low grade, probably rarely carrying over 5 per cent of copper. There are all gradations from this ore to slightly mineralized · tuff merely tinged with the green tint, which shows the presence of a little chrysocolla or malachite. The ore· streaks usually lie nearly . horizontal, or dip gently to the northwest, following the rather indistinct bedding planes of the tuff.

Q APPROXIMATE SCALE IQOF"EET FIG. B.-Diagrammatic section throtigh the unde~ground workings of the Montgomery claim of the Black Warrior group. The lowe! tunnel is wholly in schist, showing no ore ·and scarcely a trace of mineralization, even along the main fault. Raises from this tunnel reach the mineralized tuff above, and connect with the middle tunnel. o work was in progress on the Black Warrior claims at the time of visit, although the company was .erecting· an extensive acid plant for leaching purposes. Black Copper m.ine.-This is situated in Webster Gulch, about 2 miles southwest of Black Warrior. The principal workings <?om prise a vertical 'shaft about 250 feet in depth, with three levels, of which the second, about 80 feet bel'ow the surface, is the most important. There are also some minor superficial workings about '350 feet a little south of west from the main shaft.

MINES NORTHWEST OF GLOBE. The country rock includes Pinal schist and dacite, the ore occurring between · the two, ·as shown in fig. 9. This ore is of the same general mineralogical character as tqat found in the Montgomery and Geneva claims, being a fragile, brittle chrysocolla, often so dark in color as to closely resemble bituminous coal. It is sometimes as much as 12 feet in thickness," resting upon a foot wall of much broken and disturbed schist and overlain by dacite. The dip of the ore body is easterly at an average angle of 35° .

Scale

SCHIST FIG. 9.-Plan and section of the Black Copper mine. According to Dr. Irving, who visited the mine from whose notes this description is ·compiled, the contact between the schist and dacite is primarily normal fault of a rather low angle of dip. The evidence for this, however, is not entirely convincing. The ore is clearly a replacement of dacitic material, as shown by the presence in much of it of little scales of biotite, which is ' usually the last constituent of the dacite tuff to disappear in the process of ore replacement._ This fact, and the similarity of the ore to that of the Geneva and ¥montgomery mines, taken in connection with the low angle of dip, is

G EO LOGY OF THE GLOBE COPPER DISTRICT, ARIZONA. suggestive of. its occurrence· along the contact between an old eroded surface of schist and overlying dacite tuff or dacite. However, it probably is imprac- . ticable to prove from facts observable in the present working~ whether or not there was faulting along the contact prior to mineralization.

Since the ore deposition considerable faulting has evidently tak.en place,· as shown by ·slip planes, polished slickensides, and brecciation of the ore. Below the second level the workings are all in schist, showing the astonish- · ingly minute shattering characteristic of this rock in the lower part of Webster Gulch; and slightly stained with salts of copper. The ore of the Black Copper mine carri~s ·from 10 . to 22 per cent of copper, the green chrysocolla being higher grade than the black ore. Geneva mine.~ This is a small property lying about h!llf a mile southwest of Black Warrior. and belonging to the United Globe Company. In the occurrence of its .ore it shows some resemblance to the Montgomery claim already described. ·The country _rock is dacite tuff, resting upon an uneven, eroded surface of Pi~al schis . The ore is chi·ysocolla, frequently occurring in ~early pure masses, and. Qf y- high grade to . ship, the best of it containing about 20 per oen . of co " Its appearance is very striking, as coal-black, green, and turq~~ise-bluh varieties of the copper silicate occur mingled_ together in a brittle IDaJsshaving t£ highly resinous luster. The black variety, which~ as chemical tests by Dr. Hillebrand show, owes its dark color to the presence of one of the higher oxides of· manganese, · shows · a tendency to· occur in irregul~r blotches or kernels which grade outwardly through, successive concentric shells into green, and finally into pa;le-blue forms of the mineral, the . last sometimes lining· small vugs in botryoidal i~lCrnstations~ · The orH_ is plainly · a replacement of the , and various ·degrees of alteration are exhibited, from tuff slightly flecked with chrysocolla to ore ·such as that d.escribed, in which an occasional flake ·of biotite is the only vestige of its former tuffaceous natui·e. The cause of the striking ·mottled structure is not wholly understood, although it is apparently due to selective and successive· action of the mineralizing solutions upon the constituent particles of the tuff. The dacite tuff in which the ore occurs is 40 or 50 feet in thickness, and rather obscurely bedded or laminated. Particles pf schist are abundant, and they, as well as the eruptive material of the tu.ff, have been locally replaced by ore. The ore occurs as a nearly horizontal blanket-like body 4 feet in maximum thickness, 15 feet wide, and of unkn()wn length, lying near . the base of the tuff. This ribbon of ore trends nearly east a~d west . and dips north at a low angle. In some pl~~es it rests directly upon the schists, in others it separated from · the latter by a layer of altered tuff. It seldom possesses definite boundaries, but

MINES NORTHWEST OF GLOBE. shades off gradually into low-grade ore, and this into kaolinized tuff faintly tinged green by a trace of copper. The tuff and ore is cut off on the east by a normal fault that has dropped them against the Pinal schists, as in the Montgomery claim. The whole deposit, moreover~ is disturbed by small normal faults, most of them showing recent movement. The ore is unsystematically mined by lessees through shallow shafts sunk through the tuff to the ore-bearing horizon, and connecting with drifts and stopes in the ore. Continental mine.-This mine (Pl. XXVII, B) is situated just over the divide from the head of Webster Gulch, within a · rather int-ricately faulted complex of diabase, Schultze *ranite, Globe limestone, and the Whitetail formatiQn. The mine, although located twenty years ago, fi~st began to attract attention about the year 1896, considerable development work then being done and the presence of rich ore ascertained. In 1899 it was purchased by· the Old Dominion Company. No ore has yet been shipped. The workings consist of three tunnel levels with several hundred feet of drifts and crosscuts, two levels, the· fourth and fifth, below the third level tunnel, which is the main adit, and some small shafts. The total depth reached is about 350 feet. As may be seen from the geological map (Pl. I), several structurally important faults converge at the Continental mine, and, as is usually the case, the . rocks in the vicinity of the intersection are not ·only ·disturbed by the main faults, but by many minor dislocations as well. The general · plan of. these faults , is diagrammatically shown in fig. 10. The faults are apparently al1 normal, the diabase having been dropped against the granite. They probably antedate the period of mineralization in the main, but all _show evidence of some recent slipping. The main adit tunnel runs north for about 215 feet in diabase, and then passes through a fault plane into a triangular block of granite-porphyry, within which are situated thB main workings and the ore bodies. So far as known, the ore is confined to this small mass of porphyry and a smaller block lying between it and the Ninety -six shaft (see fig. 10 and Pl. XXVII, B), while the faults bounding these blocks, and the surrounding diabase, limestone, and granite-porphyry, contain, so far as known, no mineralization of economic importance. The ore occurs in connection with minor fissures within these two bodies of porphyry, particularly within the larger one, and not in the stronger faults that inclose . the latter. The main vein, as shown in fig. 10, has a curved course ranging f~om north-

GEOLOGY OF THE GLOBE COPPER DISTRICT, .A.RIZON.A.. east at its eastern end to nearly northwest at its western end. Below a depth of about 100. feet from the surface the ore occurs as a bunchy. vein of quartz, pyrite, and a little chdcopyrite, passing into mineralized porphyry without sharply defined ~alls, and showing considerable recent movement along the fissure. This sulphide ore is low grade, carrying from 2 or 3 per cent up to an occasional terior of 20 per cent of copper. For a distance of about 100 feet down from the surface the vein is oxidized and contains some small bodies of rich ore, consisting of cuprite, . malachite, and azurite, with native silver. The latter occurs chiefly in calcite, tinged green and blue by the carbonates of copper, which often form the gangue of the cuprite. It is not known whether any chalcocite or other cupriferous sulphide occurs between the oxidized zone and the low-grade pyritic ore below. None was seen at the time of visit. ~Wh;detail formation

Scale FIG. 10.-Diagram showing plan of faulting at the Continental mine. The occurrence · of goslarite, or hydrous . sulphate of zinc, as a fluffy efflorescence . of acicular crystals coating some of the drifts, was noted as a rather peculiar feature, as no zinc-hearing minerals were seen in the ore. Keystone mine.-This is situated about a mile and a half north of . Bloody Tanks, in granitic porphyry forming part of the Bloody Tanks area of the Schultze granite. The ore occurs as a fairly regular and persistent vein of chrysocolla striking north 40° west, . and dipping northeast at an angle varying from 40° to. 50°.. The maximum width of the ore is about 18 inches. The developments comprise two tunnels on the vein, about 50 feet apart, the upper or main tunnel being about 350 feet in length. Most 'of the ore has come

MINES IN SC,HIST ON WESTERN SLOPE OF PINAL RANGE. from stopes above the main tunnel. The richest contains about 25 per cent of copper, and the total output of the mine, which has been operated for only two or three years, is given as about $25,000. The ore is bluish-green, brittle chrysocolla, adhering finely to the porphyry walls of the fissure and frequently inclosing fragments of the country rock. For the most part it plainly fills mechanically fori:ned spaces, but there has been some minor replacement of the fractured porphyry by ore. Occasionally a little quartz and malachite occur in the vein, the latter as str~aks in the chrysocolla. At the mouth of the lower tunnel a small stringer was seen carrying pyrite, but no trace of the presence of original sulphides bas yet been found in the Keystone vein. The granite-porphyry in the vicinity of the Keystone mine is much fractured and filled with small stringers of chrysocolla, rarely very persistent, but sometimes large enough to furnish a little marketable ore. Such is a vein lying a few hundred feet west of the Keystone, and approximately parallel to the latter in strike and dip, which has been superficially stoped from the surface. Limeoak mine.-Tbis mine, in Liveoak Gulch, about a third of a mile south of the Keystone, shows similar ore. The main tunnel enters , a bold cliff of porphyry, here vividly stained with copper and affording some ore close to the surface. It is reported that some of the ore in the Liveoak mine occurred alongside schist, probably an included mass in the Schultze granite. No ore was being shipped at the time of visit, and the underground wor): were not examined. MINES IN SCHIST ON THE WES-TERN SLOPE OF THE PINAL RANGE. General character.-These . are small mines or prospects in which the ore occurs,· principally in the form of sulphides, in· fissure veins traversing Pinal schist. The more important properties are the Bobtail, Cole & Goodwin, and Summit mines, all showing ore bodies of considerable promise. Bobtail mine.-This is situated on the north side of Mineral Creek, not far from its bead, and was at the time of . visit in a rather inaccessible position. Improvements in transportation and treatment of the ore were, however, then in contemplation, and have probably since been carried out.

The Bobtail vein strikes north 35° east, and dips 62° to the northwest, thus cutting obliquely across the schistosity of .the Pinal schists (Pl. I). An inclined shaft has been sunk on the vein to a depth of 150 feet, and was being carried down to 200 feet at the time of visit. Connecting with this shaft are short drifts 50 and 100 feet below the surface. 9651-No. 12-03-11

GEOLOGY OF THE GLOBE OOPPER DISTRICT, ARIZONA. The vein is a strong one up to feet in width, the ore minerals occurring as a cement holding together fragments of a schist! fault breccia. . These fragments ·are of somewhat bleached and altered sericite-schi~t of the same character as that forming the walls of the lode and containing a 1ittle finely disseminated pyrite. Soft gouge and slickensides show th~t there has been some slipping along the fissure since the ore was deposited. The ore, practically from the surface down, . consists of chalcopyrite, sphalerite, galena, · and pyrite, named in order of abundance. The sulphides have crystallized, without any recognizable sequence, in the interstices between the schist fragments. They are sometimes a~sociated with a quartz gangue, but this · mineral is not always present in noticeable quantity. The . best of the ore is said to contain 18 per cent of copper, 30 ounces of silver, and an ounce of gold per · ton, but the average is undoubtedly very much lower than this. The tungstate of manganese and iron, hiibnerite, is frequently encountered as small prismatic crystals embedded in the quartz of the more siliceous parts of the vein. It is apparently · of ·the same general age as the associated sulphides. OoZe & Goodwin mine . This is situated on the north side of Lyons Fork of Mineral Creek, about 2! miles southwest of the Hog ranch. The vein strikes north 48° east and dips northwest at anangle of 41°. Like that of the Bobtail, it is a mineralized fault breccia in schist, varying from 2 to 4 feet in width . . It is opened by an inclined . shaft about 200 feet in depth and some short drifts. The ore, almost from the surface down, consists of chalcopyrite and pyrite, with some calcite and occasionally a little quartz. It occurs in bunches, and in part as a replacement of the sericite-schist of the breccia fragments and vein walls. The best ore is said to occur where the schist shows most alteration and mineralization. The richest ore contains ·about 14 per cent of copper and occasionally as much as $3 per ton in gold and silver. A road to the' mine was begun early in the year 1902, with the intention of mining and shipping this ore. Summit mine.-This little mine lies near the head of the Dry Wash of Mineral Creek, on a vein striking with the schistosity of the Pinal schists north 30° east, and dipping northwest, also conformably with the latter, at aQ angle of 45°. The developments consist of a tunnel on the vein about 350 feet long and some small stopes. The ore fills a simple fissure up to 2 feet wide, sometimes accompanied by smaller, nearly parallel, veins or '"streaks" in the foot or hanging wall. No replacement of schist was noted. Much of the ore occurs as a soft, somewhat shattered black mass, and it is only when· the dark fragments are freshly fractured

MINES IN SCHIST ON WESTERN SLOPE OF PINAL RANGE. that it is seen to consist chiefly of massive chalcopyrite, the dark material being merely an external film. A chemical examination of this coating by Dr . . Stokes confirmed the conclusion reached in the field, that it is a sulphide of copper, probably chalcocite. Occasionally the chalcopyrite is honeycombed with an earthy mixture of this amorphous chalcocite and minutely crystalline specular hematite. The ore contains from 1Q to 25 per cent of copper, and small shipments were being made in 1901. There are several other veins in the schists in the of the Summit mine, some of which were being prospected in 1901, but no bodies of workable ore had been uncovered at the time of visit.

INDEX. Adamellite, analysis of , . See also Lost Gulch monzonite. Page. Alice fault, effect on ore bodies Alice vein, description of Allen, E. T., acknowledgments to analyses by 69, 84, 92 Alteration of country rock, discussion of Amador claim. See Grey mine. Analyses, adamellite biotite-hornblende-dacite . . . . . . . . . . . . . . . . . . . . . . . dacite .. .. . diabase , . granite-porphyry . granitite . granodiorite . quartz-mica-diorite . quartz-monzonite . Andalusite, occurrence of . Apache group, age of . character and distribution of. . lithology, stratigraphical sequence, and correla92-93 Area discussed, geographic position of . . . . . . . . . . . . . . geological historyof. 107-114 geological map of In pocket. Arizona, physiography of . . . . . . . . . . . . . . . . . . . . . . . . . . . Arizonian slates, note on Arroyos, character of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Azurite, occurrence of.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Barnes conglomerate, character of . . . . . . . . . . . . . . . . . . deposition of. , 30, 38 Barnes Peak, sections through . . . . . . . . . . . . . . . . . . . . . . 30, 98 views on east side of. . Basalt, age of . definition of . distribution of . . metamorphism caused by . petrography of . Berray, N. S., acknowledgments to . reference to . Big Johnnie Gulch, fault breccia in, plate showing. Big Johnnie mine, description of . Biotite-granite, definition of. : . See also Schultze granite; Ruin granite. Biotite-hornblende-dacite, analysis of. . Black Copper mine, description of . plan and section of . Black Peak, diabase at .. diabase from near, analysis of. .. quartz-mica-diorite near . Black Warrior, Apache group near .. . dacite near . Page. faults near, direction of .. .. .. . .. .. .. .. .. . .. . .. .. Black Warrior mine, description of . 155-156 Bloody Tanks, granite near 67,68-72 Bobtail mine, description of. 161-162 Breccia in Webster Gulch, view of on Needle Mountain, view of .. .. .. .. .. .. .. .. .. . on Pinal Creek, view of .. .. .. .. .. .. .. .. .. . .. . .. . Brogger, W. C., cited on monzonites .. . . .. .. . .. . Buckeye mine, description of ... 153-154 Buffalo claim. See Buffalo mine. · Buffalo mine, description of. 151-152 Carboniferous fossils, report on. . . . . . . . . . . . . . . . . . . . . . 42,.-44 Centralia claim. See Grey mine. Chalcocite, occurrence of. 121,128-129 Chalcopyrite, occurrence of . Chrysocolla, occurrence of. . . Climate, relation of geological processes to . Cohen, E., cited on andalusite . Cole & Goodwin mine, description of . Colorado Plateau, physiographic features of . Conglomerate. See Barnes conglomerate; Gila con~ glomerate; Scanlan conglomerate. Continental mine, Apache group near . description of . faulting at, diagram showing plan of. . view of . Continental Spring, Whitetail formation near . Copper, first notice of. , .. . production of . Copper glance. See Chalcocite. Copper Gulch, diabase in . Gila conglomerate in, view of . Copper Hill mine, description of : . Copper ores, classification oL . Cottonwood Canyon, Gila conglomerate near . Country rock, alteration of . in Old Dominion mine . Crest area, Madera diorite in , . Cross, W., cited on age of Ouray limestone . Crystalline metamorphic rocks, description of . Cuprite, occurrence of . Cuprite claim. See Grey mine. Dacite, age of. .. analysis of . . definition of !?2-93 Late PaleozGic Librar Washington Om CG

INDEX. Dacite, distribution of. ; : . eruptions of. ; . in Old Dominion mine . petrography of surface of, plate showing , . Devonian fossils, report on . Diabase, age of . analysis of · .. · . definition of . distribution of . ~ruption of. .. ." ,, . in Old Dominion mine . metamorphic action of . petrography of. . typical weathering of, plate showing . Dikes connected with Schultze granite, occurrence and petrography of . Diorite, use of term by miners See also Madera diorite. Diorite-porphyry, definition of . distribution of. , . petrography and age of . Dripping Spring quartzite, character of. . deposition of. . Dripping Spring Range, monoclinal structure in, plate showing . topography of. . Dry Wash of Mineral Creek,.topography near . Dumble, E. T., cited on Dragoon quartzites -- Duttcm, C. E., quoted on Colorado Plateau . Emmom, S. F., acknowledgments to . cited on occurrence of chalcocite . . Effusive eruptive rocks, description of. . Erosion, fault plane developed into· scarp by, plate showing . Eruptive rocks, description of. . Fault breccia, character of . Fault plane developed into a scarp by erosion, plate showing . Faulted structure, section showing . Faulting, history of ; ... .. . Faults, age of. . direction and character of . distribution of. . Page. evidence of. 101-102 geological significance an 1 origin of 104-106 importance of, in development of structure 97-100 in Gila conglomerate, plate showing influence upon ore bodies 144-148 See also Fissures. Fissures in Old mine ... . Florence, temperature at . Fossils, reports on · . Galena, occurrence of. . Geneva mine, description of. . Geological processes, relation of climate to Gila conglomerate, age oL : .. character, thickness, and position of . deposition of. . distribution of . faults in, plate showing . origin of . relation to early topography topography characteristic of, plate showing ... . variations in . view over Pinal Creek area of. . views of . 56-()7 48,50 Gilbert, G. K., cited on Colorado Plateau . cited on Gila conglomerate . cited on mountain region of Arizona quoted on Gila conglomerate . Girty, G. H., acknowledgments to determinations of fossils by . Gladiator claim. See Grey mine. Glob Apache group near · ; Page. d ite near · faults near, direction of . . . . . . . . . . . . . . . . . . . . . . . . . Gila conglomerate near . . . . . ... . . . . . . . . . . . . . . . . . . rainfall and temperature at . . . . . . . . . . . . . . . .. . . . . view of Globe claim. See Old Dominion mine. Globe Hills, map of. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . In pocket. Globe limestone, age of character and distribution of. . . . . . . . . . . . . . . . . . . . de'finition of... . .· . in Old Dominion mine ... . lithology and stratigraphical sequence of , . view of . Globe Valley, origin of , . Gold, production of , . Gold Gulch, basalt near . Gila conglomerate near . Schultze granite near . Gooch, T. A., analysis of .. Government Spring, Gila conglomerate near . Granite, definition of . use of terni, for Gila conglomerate . See also Willow Spring granite, Solitude granite, Ruin granite, Schultze granite. Granite Basin, section from Whitetail Gulch to . Granite-porphyry, analysis of. . Granitic breccia on Needle Mountain, view of . Granitic intrusion, metamorphism in connection 'vith . Granitic rocks, age and sequence of. . Granitite, analysis of. ·'· . definition of . ... . mineralogical composition of . See also Ruin granite. Granodiorite, analysis of . mineralogical composition of. . Grass Valley, Cal., granodiorite from, analysis of .. . granodiorite t:rom, mineralogical composition from . Grey claim. See Grey mine. Grey mine, description of . diabase in . 113,114 underground workings of, view of . . . . . . . . . . . . . . view of Ground water, level of, in Old Dominion mine Hillebrand, W. F., acknowledgments to . . . . . . . . . . . . 60, 97 Hoar,F.W., acknowledgmentsto Hog ranch, quartz-mica diorite near, analysis. of quartz-mica diorite from, mineralogical composition of . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . sericite-schist near Hoosier claim. See Grey mine. Hutton Peak, dacite near Schultze granite near, view of I XL mine, description of Icehouse Canyon, quartz-mica-diorite of . . . . . . . . . . . . Interloper fault, description of 139-140 Intrusive eruptive rocks, description of . . . . . . . . . . . .

INDEX. Irving, J.D., reference to . of . Jewel Hill, Schultze granite near . Josh Billings mine, description of . Keyser, W., reference to . Keystone mine, description of . Lewissohn Brothers, reference to . Limestone, ore bodies in . Bee also Globe limestone. Limonite, occurrence of · .. Lindgren, W., cited on fauna at Clifton . cited on granodiorite . Literature on Globe region . Liveoak Gulch, granite-porphyry of . Liveoak mine, description of. . Lizzie claim. See Buffalo mine. Page. 117, 134 12~-127 Lodes, character of. 125-126 Lost Gulch, faults near, direction of . . . ... . . . . . . . . . . . monzonite in . Lost Gulch monzonite, age of . distribution of . . mineralological composition of. . petrography of. . ... . See also Quartz-monzonite. Lyons Fork of Mineral Creek, Gila conglomerate on. sericite-schist near . Madera diorite, age of. . definition of : . distribution of . petrography of. · . . . See also Quartz-mica-diorite. McClellan Peak, Nevada, biotite-b.ornblende-daCite from, analysis of . McMillan ville, mining at. . McMorris mine, production of : . workon . . . .. . . Malachite, occurrence of . Mallory mine, description of . Manitou Mountain, basalt near . Mark Twain claim. See Buffalo mine. Marvine, A. R., cited on Apache group . quoted on chultze granite . Melibocus, granite from, analysis of. . Metadiabase, definition and distribution of . petrography and age of. . Metamorphism by basalt, discussion of . by diabase, discussion of. . by granitic intrusions, discussion of. . Miami Flat, mill at . Mica-schist, description of. . Mineral Creek, dacite near . Gila conglomerate on . See also Dry Wash of Mineral Creek. Mines, descriptions of . . . Mining,·history of . . Monoclinal structure, plate showing . Montgomery claim, section through . See Black Warrior mine. Monzonites, definition of . See also Lost Gulch Monzonite. Mountain region, physiographic features of. . Muscovite-granite. See also Solitude granite. Needle Mountain, Gila conglomerate near : .. Nevada claim. See Grey mine. N evad!! vein, description of . North vein, description of , . 25-21) 30,39 Old Dominion Company, reorganization of property of, sale of -1 · . · · · .. · Old Dominion fault, descriPjtion of. . Old Dominion mine, chalco ite in . country rock in .. . . cross section of .. . . dacite near, analysis of .' . plate showing . . . .. . diabase near . elevation of. . fault in . Page. fissures in , . . . . . . . . . . . . 136-4141 Gila co!lglomerate in . . . . . . . . . . . . . . . . . . . . . . . . . . . ground-water level in. t .. . . . . . . . . . . . ore of, character and oc urrence of .' 141-144 ore bodies in, influence _rf faulting on 144-148 s~con~ leve~ of, geologitl plan of. . . . . . . . . . . . . . . situatiOn, history, and ~evelopment of underground wor) ~f, plan of viewinopencutbf . Old Dominion mine ( origin 1), description of.\ 154-155 Old Dominion mine !lind smelter, view of Ore of Old Dominion minf, character and occurOre ~:f:::::::::::::::::: influence of faulting on .' 144-148 See also Fissures. Ore deposits, history and d scription of. 114-163 classification of 1. . . . . . . . . . . . . . . . . . . . . . . . . distribution of . . 1... . . . . . . . . . . . . . . . . . . . . . . 118-119 Ouray lim~stor:e, ag~ of ... f. . . . . . . . . . . . . . . . . . . . . . . . . Paragenesis, discuss@n of . Pinal Creek, Apache boup near quartzite fault breccia t n, plate showing . . . . . . . view down bed of . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pinal Peak, ~pac~e ?roup ear quartz-mwa-dante nea , analysis of . . . . . . . . . . . . Pinal Peak area, quartz-mi1 a diorite of . . . . . . . . . . . . . Pinal ranch, basalt near... . . . . . . . . . . . . . . . . . . . . . . . . .

mines on western slope of . . . . . . . . . . . . . . . . . .. . . . . 161-163 origin of . .. . . .. ... 113,114 topography of . . . . . . . . . . .. . . .. . . .. . . Pinal schists, age of . . . . . . . . , . . . . . . . . . . . . distribution of . . . . . . . . . . . . . . . . . . . . . . . . . petrography of . Pinto Creek, Apache group on . .. . . . . ... .. .. . ... . . .. Gila conglomerate on . . . Globe limestone on . Schultze granite on, vi1w &f. . . Pioneer, cuesta near, figur~ showing . diabase near, plate sho , 'ng . ... ... .. . monoclinal structure n ar, plate showing . topography near .

Pioneer shale, character of. . deposition of . exposure of, plate showing : · . Pleistocene, erosion during . Porphyry Mountain, Schultze granite near . Powell, J. W., cited on Grand Canyon group · Quartz-diorite at base of Gila conglomerate, view of. Quartz-mica-diorite, analyses of. . definition of . mineralogical composition of. . . See also Madera diorite. Quartz-monzonite, analysis of ... . See also Lost Gulch monzonite. Quartzite in Old Dominion mine . See also Dripping Spring quartzite. Quartzite fault breccia, plate showing . Rainfall, record of. : Ramboz, Henry, reference to . Ramboz Camp, foundation of . Ramboz Peak, rocks exposed near . Ruin Basin, Apache group in . Ruin granite, distribution of . petrography of . San Carlos, rainfall at . Scanlan conglomerate, character of . depositionof. .. . Scanlan Pass, view from ... . Schists. See Pinal schists. Schultze granite, age of ... : . analysis of . dikes connected with : . distribution· of. . petrography of · . views of . Schultze ranch, granite-porphyry from near, analysis of . . . granitite from near, analysis of. . topography near . Sedimentary rocks, occurrence and character of. .. . Sericite-schist, description of . Shale. See Pioneer shale. Silver King mine, discovery of . Sixty six ranch, dacite near . Gila conglomerate near . view of · . Sleeping Beauty Peak, faults near, direction of . INDEX. Page. 30.:31 38,68 Page. Solitude granite, age of Specularite, occurrence of. . Sphalerite, occurrence of Stonewall mine, description of . . . . . . . . . . . . . . . . . . . . . . Stream channels, character of Stringer lodes, occurrence of 125-126 Summit mine, chalcocite in , 128-129 description of 1~2-163 Teall, J. J . H., cited on andalusite . . . . . . . . . . . . . . . . . . Temperature, extremes of 'topography, relation of Gila conglomerate to early. Trachyte, popular use of name Transit claim. See Grey mine. United Globe Company, organization of United Globe mines, description oL 148-154 VanHise, C. R., cited on Grand Canyon schists cited on ore deposition . . . . . . . . . . . . . . . . . . . . . . . . . . definition of Algonkian by . . . . . . . . . . . . . . . . . . . . . . Vegetation, character of Walcott, C. D., cited on Devonian in Grand Canyon. cited on unconformity in the Grand Ganyon.. reference to Washoe, Nev., biotite~hornblende-dacite from,analsis of WebsterGulch, Apache group near .. , dacite and schist breccia near, view of Gila conglomerate near. . . . . . . . . . . . . . . . . . . . . . . . . . view from north side of . . . . . . . . . . . . . . . . . . . . . . . . . Webster Mountain, Apache group near dacite at diabase near section near . Wheatfields, mill at . Whitetail . formation, character, distribution, and position of . origin and age of : . views of ; Whitetail Gulch, section from Granite Basin to . Williams, H. S., acknowledgments to . determination of fossils by . Willow Spring granite, age, distribution, and petrography of · . 40,46

PUBLICATIONS OF UNITED STATES GEOLOGICAL SURVEY. [Professional Paper No.12.] Thf' serial publications of the United States Geological Survey consist of (1) Annual Reports, (2) Monographs, (3) Professional Papers, (4) Bulletins, (5) Mineral Resources, (6) Water-Supply and Irrigation Papers, (7.) Topographic Atlas of the United States-folios and separate sheets thereof, (8) Geologic Atlas of the United States-folios thereof. The classes numbered 2, 7, and 8 are sold at cost of publication; the others are distributed free: A circular giving complete lists niay be had on application. The Bulletins, Professional Papers, and Water-Supply Papers treat of a variety of subjects, and the total number issued is large. They have therefore been classified into the following series: A, Economic geology; B, Descriptive geology; C, Systematic geology and paleontology; D, Petrography and mineralogy; E, Chemistry and physics; F, Geography; G, Miscellaneous; H, Forestry; I, Irrigation; , J, ·water storage; K, Pumping water; L. Quality of water; M, Methods of hydrographic investigations; N, Water power; 0, Underground waters; P, Hydrographic progress reports. This bulletin is. the twenty-second in Series A and the tw.enty-:fifth in Series B, the complete lists of which follow. (B=Bulletin, PP=Professional Paper, WS= Water-Supply Paper.) SERIES A, ECONOMIC GEOLOGY. B 21. Lignites of Great Sioux Reservation: ReportDn region between Grand and Moreau rivers, Dakota, by Bailey Willis, 1885. 16 pp., 5 pls. B 46. Nature and origin of deposits of phosphate of lime, by R. A. F. Penrose, jr., with introduction by N. S. Shaler. 1888. 143 pp. B 65. Str11tigraphy of the bituminous coal field of Pennsylvania, Ohio, and West Virginia, by Israel C; White. 1891. 212 pp., 11 p1s. (Exhausted.) B 111. Geology of Big Stone Gap coal field of Virginia and Kentucky, by Marius R. Campbell. 1893. 106 pp., 6 pls. B 132. The (hsseminated lead ores of southeastern Missouri, by Arthur Winslow. 1896. 31 pp. B 138. Artesian-well prospects m Atlantic Coastal Plain region, by N.H. Darton. 1896. 228 pp., 19 pls. B 139 Geology of Castle Mountain mining district, Montana, by W. H. Weed and L. V. Pirsson. 1896. 164 pp., 17 pls. B 143. Bibliography ot clays and the ceramic arts, by John C. Branner. 1896. 114 pp. B 164. Reconnaissance on the Rio Grande coal fields of Texas, by Thomas Wayland Vaughan, including a report on igneous rocKs from the San Carlos coal field, by E. C. E. Lord. 1900. 100 pp., 11 pls. and maps. B 178. El Paso tin deposits, by Walter Harvey Weed. 1901. 15 pp., 1 pl. B 180. Occurrence ana distribution of corundum in United States, by J. H. Pratt. 1901. 98 pp., 14 pls. B 182. A report on the economic geology of the Silverton quadrangle, Colorado, by F. L. ·Ransome. 1901. 266 pp., 16 pls. E 184. Oil and gas fields of the webtern Interior and northern Texas Coal Measures and of the Upper Cretaceous and Tertiary of the western Gulf coast, by George I. Adams. 1901. 64 pp., 10 pls. B 193. Th~ geological relations and distribution of platinum and associated metals, by J. F. Kemp. 1902. 95 pp., 6 pls. B 198. The Berea grit oil sand in the Uadiz quadrangle, Ohio, by W. T. Griswold. 1902. 43 pp., 1 pl. PP 1. Preliminary report on the Ketchikan mining district, Alaska, with an introductory sketch of the geology of southeastern Alaska, by Alfred Hulse Brooks. 1902. ' 120 pp., 2 pls. ' B 200. Reconnaissance of the borax deposits of Death Valley and Mohave Desert, by M. R. Campbell. 1902. 23 pp., 1 pl. B 202. Tests for gold and silver in s.sales from western Kamas, by Waldemar Lindgren. 1902. 21 pp. PP 2. Reconnaissance of the northwestern portion of Seward Peninsula, Alaska, by A. J. Collier. 1902. 70 pp., 11 pls. PP 10. Reconnaissance from Fort Hamlin to Kotzebue Sound, Alaska, by way of Dail, Kanuti, Allen, and Kowak rivers; by W. C. Mendenhall. 1902. 68 pp., 10 pls. PP 11 Clays of the United States east of the Mississippi River, by Heinrich Ries. 1903. 298 pp., 9 pls. PP 12. Geology of the Globe copper district, Arizona, by F. L. Ransome. 1903. 168 pp., 27 pls. 9651-No. 12-03-12

,II PUBLICATIONS OF UNITED ·STATES GEOLOGICAL SURVEY. SERIES B, DESCRIPTIVE GEOLOGY. B 23. Observations on the junction between the Eastern sandstone and the Keweenaw series on Keweenaw Point, Lake Superior, by R. D. Irving and T. C. Chamberlin. 1885. 124 pp., 17 pls. B 33. Notes on geology of northern California, by J. S. Diller. 1886. 23 pp. B 39. The upper beaches and deltas of Glacial Lake Agassiz, by Warren Upham . . 1887. 84 pp., 1 pl. B 40. Changes in river courses in Washington Territory due to glaciation, by Bailey Willis. 1887. 10pp., 4 pis. B 45. The present condition of knowledge of the geology of Texas, by Robert T. Hill. 1887. 94 pp. B 53. The geology of Nantucket, by Nathaniel Southgate Shaler. 1889. 55 pp., 10 pls. B 57. A geological reconnaissance in southwestern Kansas, by Robert Hay. 1890. 49 pp., 2 pis. B 58. The glacial boundary in western Pennsylvania, . Ohio, Kentucky, Indiana, and Illinois, by George Frederick , Wrignt, with introduction by Thomas Chrowder Chamberlin. 1890. 112 pp., 8 pis. B 67. The relations of the traps of theN ewark system in the New Jersey region, by Nelson Horatio Darton. 1890. 82 pp. B 104. Glaciation of the Yellowstone Valley north of the .Park, by Walter Harvey Weed. 1893. 41 pp., 4 pis. B 108. A geological reeonnaissanc~ in central Washington, by Israel Cook Russell. 1893. 108 pp., 12 pls. B 119. A geological reconnaissance in northwest Wyoming, by George Romans Eldridge. 1894. 72 pp., 4 pis. B 137. The geology of the Fort Riley Military Reservation and vicinity, Kansas, by Robert Hay. 1896. 35 pp., 8 pis. B 144. The moraines of the Missouri Coteau and their attendant deposits, by James Edward Todd. 1896. 71 pp., 21 pls. · B 158. The moraines of southeastern South Dakota and their.attendant deposits, by J. E. Todd. 1899. 171 pp., 27 pls. B 159. The geology of eastern Berkshire County, Massachusetts, by B. K. Emerson. 1899. 139 pp., 9 pis. B 165. Contributions to the geology of Maine', by HenryS. Williams and Herbert E. Gregory. 1900. 212 pp., 14 pls. WS 70. Geology and water resources of the Patrick and Goshen Hole quadrangles in eastern Wyoming and western Nebraska, by George I. Adams. 1902. 50 pp.;n pls. B 199. Geology and water resources of the Snake River Plains of Idaho, by Israel C. Russell. 1902. 192 pp., 25 pis. PP 1. Preliminary report on the Ketchikan mining district, Alaska, with an introductory sketch of the geology of southeastern Alaska, by Alfred Hulse Brooks. 1902. 120 pp., 2 pls. PP 2. Reconnaissance of the northwestern portion of Seward Peninsula, Alaska, by A. J. Collier. 1902. 70 pp., 11 pls. PP 3. Geology and petrography of Crater Lake National Park, by J. S. Diller and H. B. Patton. 1902. 167pp., 19pls. PP 10. Reconnaissance from Fort Hamlin to Kotzebue Sound, Alaska, by way of Dall, Kanuti, Allen, and Kowak rivers, by W. C. Mendenhall. 1902. 68 pp., 10 pis. PP 11. Clays of the United States east of the Mississippi River, by Heinrich Ries. 1903. 298 pp., 9 pls. PP 12. Geology of the Globe copper district, Arizo.na, by F. L. Ransome. 1903. 168 pp., 27 pls. Correspondence should be addressed to

THE DIRECTOR, UNITED STATES GEOLOGICAL SURVEY, WASHINGTON, D. C. FEBRUARY, .1903.

LIBRARY CATALOGUE SLIPS. [Mount each slip upon a separate card, placing the subject at the top of the second slip. The name of the series should not be repeated on the series card, but add. the additional numbers, as received, to the first entry.] Ransome; Frederick Leslie. ... Geology of the Globe copper Arizona ; by Frederick Leslie Ransome. ington, Gov't print. off., 1903. district, Wash168, III p. 27 pl., incl. maps, plans. 10 fig. 29~x23cm . (U.S, Geological survey.- Professional paper no. 12. ) Maps in pocket. "Literature": p. 10-i3. Subject series {A, Econ?m~c geology, 22. B, Descriptive geology, 25. Ransome, Frederick Leslie . . . . Geology of - the Globe Arizona; by Frederick Leslie ington, Gov't print. off., 1903. copper Ransome. district, Wash168, III p. 27 pl., incl. maps, plans. 10 fig. 29~ x 23cm. ( U. S. Geological survey. Professional paper no. 12.) Maps in pocket. . "Literature": p.' 10-13. Subject series {A, Econ?m~c geology, 22. B, Descriptive geology, 25. U. S. Geological survey. Professional papers. no. 12. Ransome, F. L. Geology of the Globe copper district, Arizona . . 1903. U. S. Dept. of the Interior. see also U. S. Geological survey.