Geology of the Mary G Mine area, Pima County, Arizona

Item Type text; Thesis-Reproduction (electronic); maps

Authors Davis, Robert Ellis, 1924-

Publisher The University of Arizona.

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Link to Item http://hdl.handle.net/10150/566661 GEOLOGY OF THE MAHY G MINE AREA PIMA COUNTY, ARIZONA

by Robert E. Davis

A Thesis submitted to the faculty of the Department of Geology in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE in the Graduate College, University of Arizona

1955

Approved^

5 9 7 ?/ / 9SS- £ 4 .

This thesis has been submitted in partial ful­ fillment of requirements for an advanced degree at the University of Arizona and is deposited in the Library to be made available to borrowers under rules of the Library. Brief quotations from this thesis are allowable without special permission, pro­ vided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major depart­ ment or the dean of the Graduate College when in their judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author.

SIGNED: CONTENTS

Section Page INTRODUCTION...... 1 Location and Accessibility ...... 1 Topography and Drainage ...... 4 Previous Investigations ...... • 6 F ie ld W o r k ...... 8 Scope of W ork...... 9 Acknowledgments ...... 10 REGIONAL GEOLOGY...... 11 G e n e ra l...... 11 Cerro Colorado Mountains and Adjacent Ranges . . 13 S ie r r ita Mountains ...... 13 Las Guijas Mountains...... • 14 Cerro Colorado Mountains ...... 14 Limiting Structure of the Cerro Colorado Mountains ...... 15 GEOLOGY...... 16 Igneous Rocks ...... 17 Quartz L a tite Porphyry ...... 17 A ndesite P o r p h y r y ...... 22 Andesite Porphyry D ik e s ...... 27 Sedimentary Rocks...... 29 L a tite Conglomerate ...... 29 S tru ctu re ...... 33 Age of the V olcanics ...... 34 MINERAL DEPOSITS...... 39 General Statement ...... 39

i i Section Page MINERAL DEPOSITS (c o a t.) Mining History in Southern Arizona and the Cerro Colorado D istrict ...... 41 Mary G- M in e ...... 44 Ore D e p o s its ...... • 44 M in in g ...... 45 P ro d u c tio n ...... 47 REFERENCES CITED ...... 48

i i i ILLUSTRATIONS

Figure 1. Index map showing location of Mary G- mine and p rin c ip a l mountain ranges .... Page 3 P late 1. Geologic map and section of the Mary G mine area, Pima County, Arizona . . In Pocket P late 2. Plan map of the Mary G m ine ...... In Pocket INTRODUCTION

Location and Accessibility

The Mary G mine area is located in southeastern Pima County, Arizona, approximately 9 miles north of the small town of Arivaea and about 53 miles south-southwest of Tucson (Fig. 1). The Mary G mine is situated in the NE 1/4 SB l/4 Sec. 21, T. 20 S., R. 10 E., Gila and Salt River Base Line and Meridian, on the west side of a small group of hills that may be considered as part of the Cerro Colorado Mountains. The mining district has been referred to variously as the Arivaea and Cerro Colorado districts. The area can be reached by paved U.S. Highway 89 south from Tucson to Kinsley's Ranch (Arivaea Junction), then by graded dirt road, in a southwesterly direction, for a distance of approximately 17 miles, then by unimproved road north-northwest for about one m ile.

The dirt roads are passable all year long, except for very brief periods during the rainy season when the few nor­ mally dry washes crossed or followed by the road become flooded.

The nearest rail shipping point is Amado, a station on the Southern Pacific Railroad, 3 miles southeast of Kinsley's 2

Ranch. Ore from the mine is trucked to Amado, and from there is shipped by rail to the smelter. - 3 -

TUCSON

Amado

Index mop showing location of Mary G mine and principal mountain ranges.

Fig. I k

Topography and Drainage

The area occupies one of several groups of relatively low hills that lie in a pass between the rounded main mass of the Cerro Colorado Mountains to the northeast and the lower, more serrated Las Guljas Mountains to the southwest. These short, partly detached ranges, together with the more exten­ sive Sierrita Mountains to the north and the San Luis and Oro Blanco Mountains to the south, form the eastern boundary of the Altar Valley, the southward extension of the Avra Valley, west of the Tucson Mountains. The relative positions of these ranges i s shown in Figure 1 .

The groups of hills of which the Mary G- area is a part, although their topographic separation from the main mass of the Cerro Colorado Mountains seems fairly distinct, may be considered as outlying portions of the Cerro Colorados. The elevation of the relatively flat country surrounding the hills is about 3>700 feet, and the hills rise to a maximum elevation of a little more than 4,200 feet.

The topography of the Mary G area generally is typical of that which Bryan (1922, p. 43-46) has described as boul­ der controlled slopes. The hillsides and small drainage cuts usually are covered and filled with a mantle of rook debris that ranges in size from coarse sand to blocks 2 and 3 feet in diameter. Small cliffs of quartz latite porphyry are pres­ ent in places. Soil cover is practically absent over most of 5 the area.

The hills are drained from the south by Cerro Colorado Wash, a trib u ta ry of Sopori Wash. Sopori Wash flows e a s t­ ward to join the Santa Cruz River north of Amado. They are drained from the north and west by the upper reaches of Arroyo Seoo and from the e a s t by Solas Blancas Wash, which join Altar Wash to the northwest and north, respectively. These washes are dry most of the year, as water flows in them only during and immediately following heavy rainstorms. 6

Previous Investigations

No previous geologic study has been undertaken in the area that includes the Mary G mine. The geology of the main part of the Cerro Colorado Mountains is not known in detail, as it has been treated only incidentally to the general re­ connaissance of this desert region. Similarly, the geology of the nearby Las Guijas Mountains is known only in a general way; it has been briefly described in a study of the tungsten resources of the area (Wilson, 1941a). Actually, of the 79 mountain ranges and groups of hills listed by Bryan (1925, p. 74) that are present in the so-called Papago country and the area adjoining it east of the Santa Cruz Valley, the geology of only a small number is well known. Reconnaissance of the re g io n , however, has shown in a general way the rook types present in most of the ranges (Bryan, 1925).

Although some early papers dealing with petrographic, mineralogic, or other special problems of local areas are to be found among the literature, probably the earliest detailed paper is that by Schrader (1915). His investigations, al­ though only a reconnaissance study, presented the general out­ lines of the geology of the Santa Rita and Patagonia Mountains and the Canelo H ills and Empire Mountains.

The reconnaissance studies of Bryan (1922, 1925), Ross (1922, 1923), and Ransoms (1922) made known the g en eral ge­ ologic features of the entire desert region of southcentral 7 and southwestern Arizona. The studies of these early workers and of others, some of whom will he referred to later, have been summarized in their broadest aspects by Barton (1925, 1933).

Later geologic study by Brown (1939), Fowler (1938), Gilluly (1946), Stoyanow (1936, 1942), and Wilson (1933, 1941a) has added greatly to the knowledge of certain areas in the re­ gion and has furnished further data concerning the complexi­ ties of the geology of many of the mountain ranges.

Smaller areas, particularly those within mining districts that are accessible from Tucson, have been the subject of study by graduate students in the Department of Geology of the University of Arizona. Many of the resulting papers will be cited later in the section dealing with the age relation­ ships of the volcanic rocks of southcentral and southwestern A rizona. 8

F ield Work

Field work was accomplished during week-ends and vaca­ tion periods during the school year 1948-49 and the early summer of 1949. The area was revisited briefly in 1953. The geologic map was prepared on a scale of 1:6000 using as a base an enlargement of part of the U.S. Geological Survey 15-minute Arivaca quadrangle.

The map of the underground mine workings (PI. 2) was pre­ pared during evenings, after mining activity had ceased for the day, and several days of inclement weather were spent underground. The mine map is not complete, as some of the workings were not accessible during the period of mapping and some additional underground work has been done since the sum­ mer of 1949. When the area was re v is ite d in 1953, the mine was closed and the equipment partially dismantled.

Petrographic work, consisting of the examination of 12 thin sections, was done during the w riter’s spare time, main­ ly during the summer and fall of 1954. 9

Scope of Work

The Mary G- mine area represents approximately one-half of a larger area examined by the writer and Dan E. Lewis in connection with their graduate studies at the University of Arizona. The area mapped and studied by Lewis adjoins that of the Mary G mine on the east and includes the abandoned Cerro Colorado mine, Cerro Colorado Butte, and the group of hills north of the Butte. The paper describing the geology of that area is in preparation.

The study was originally undertaken to determine the bedrock formations, the structure controlling the emplace­ ment of the ore deposits, and the types of mineralization rep resen ted . As work progressed i t became apparent th a t cer­ tain aspects of the problem were of a much broader nature than had been anticipated. For example, the dating of the volcanics on the basis of evidence found within the area or their correlation with similar rocks of known age in other areas was found to be impossible in the area involved. 10

Acknowledgments

The writer is indebted to the staff of the Department of Geology of the University of Arizona for guidance and sug­ gestions during the field work and the preparation of this re p o rt. To D r..F,W. G alb raith , under whose supervision th e project was done, Dr. B.S. Butler, and the late Dr. M.N. Short, each of whom visited the field, deep appreciation is expressed.

Mr. L.A. R oberts, Mr. H.O. Nygaard, and Mr. Henry G. Worsley, all of the Mary G mine, most generously furnished quarters during the course of the field work, and their gen­ erosity and hearty cooperation are acknowledged. Apprecia­ tion is expressed to Dan E. Lewis and John W. Anthony, then students at the University of Arizona, both of whom spent several days in the field with the writer and assisted in the examination and mapping of the mine workings. 11

REGIONAL GEOLOGY

General

The Cerro Colorado Mountains lie in the eastern portion of the D esert Region of Arizona (Ransome, 1904). This r e ­ gion is characterized by broad alluvium-filled valleys, moun­ tain ranges that rise abruptly from the nearly level desert floor, and mountain pediments that lie unobtrusively between the mountains and valleys. The general trend of the moun­ tain ranges is northwest-southeast and north-south, although some exceptions to the trend are present.

The Papago country, which comprises the southern half of the Desert Region, is that area lying south of the Gila River between Yuma and Tucson. In the Papago country and the area adjoining it east of the Santa Cruz River, Bryan (1925, p. 73-79) lists and classifies geologically 79 mountain ranges and groups of hills. A sumnary of his classification fo llo w s.

Class Ranges 1. Mountains composed largely of alternating beds of acidic and intermediate lava, tuff, volcanic agglomerate and conglomerate, and stream-laid conglomerate ...... 25 2. Mountains composed largely of pre-Tertiary rocks but with some masses of rocks of Tertiary age ...... 22 12

Glass Ranges 3. Mountains composed wholly of pre-Tertiary rooks with no known association of Tertiary l a v a s ...... 17 4. Mountains not well enough known to describe . 15 79

The Cerro Colorado Mountains are included in the group of 15 ranges "not well enough known to describe." If, however, they are composed of Tertiary volcanic rocks, as Bryan sug­ gests (1925, p. 252), the mountains would belong in Class 1.

It can be seen from the above classification that a wide diversity of rocks and structure exists throughout the re­ gion. The rocks in the ranges consist principally of pre- Cambrian gneiss, schist, and intrusives; limestones and quartzites of Paleozoic age; clastic sedimentary rooks and a variety of intrusive and extrusive rocks of Mesozoic age; Tertiary conglomerates, volcanic rocks with associated tuffs and agglomerates, and intrusives; and Quaternary basalt and alluvium (Bryan, 1925, P« 54-70). Occurrences of Paleozoic sedimentary rocks are not common; those that are found are considered to be erosion remnants of larger blocks thrust onto younger rocks or infaulted blocks that have been par­ tially preserved from erosion by the surrounding rocks (Bryan, 1925, p. 55-57).

Each of the rock types listed above is represented in the ranges adjacent to or near the Cerro Colorado Mountains. 13

Gerro Colorado Mountains and Adjacent Ranges

The Gerro Colorado Mountains, and the Sierrita and Las uuijas Mountains adjacent to them on the north and southwest, respectively, constitute a group of ranges in which geologic features representative of the Papago country are found. The distribution of these ranges and of others in the region is shown in Figure 1, Most of the rock types, ranging from the pre-Cambrian intrusives to Tertiary lavas, are in these ranges. The geology of certain parts of the Sierritas and outlying hills is known in seme detail and has been described by Ransome (1922) and others; that of the Cerro Colorado and Las Guijas ranges is known only in a general way. The broader features of the geology have been summarized by Bryan (1925, p. 252), Andrews (1937, p. 171-172), and Wilson (1941a, p. 38).

Sierrita Mountains

The Sierrita Mountains have been described as consist­ ing of "an intrusive granitic core flanked by more or less metamorphosed rocks of sedimentary and eruptive origin" (Ran­ some, 1922, p. 409). The flanking rocks on the east side of the range are faulted and folded limestones, quartzites, shales, and altered andesitic volcanics. The sedimentary rocks are Paleozoic and Mesozoic in age, and they have been intensely metamorphosed locally. Most of the rocks on the 14 west flanks are schistosic and consist of rhyolites and a variety of sedimentary beds. Although metamorphism has been more widespread on the west side, it has not been so intense as on the east; and while most of the original rock types have been changed somewhat texturally, they are still recog­ nizable. Volcanic rocks, perhaps andesites and rhyolites, occur on the south and southwest flanks of the mountains. (Ransome, 1922.)

Las Guijas Mountains

! The main mass of the Las Guijas Mountains consists of fractured granite, the age of which is uncertain, and asso­ ciated dike rocks. The crystalline mass is bounded on the south, in the vicinity of Arivaoa, by shales and sandstones presumably of Cretaceous age. The character of the contact between the sediments and the granite is not known. (Wilson, 1941a, p. 38; personal communication, 1953.)

Cerro Colorado Mountains

The Cerro Colorado Mountains comprise an irregular, rounded group of peaks consisting probably of volcanic flows, with associated tuffs, agglomerates, and conglomerates (An­ drews, 1937> p. 171-172; Bryan, 1925, p. 252). The main mass appears to be bounded on the southwest by normal faults, resulting in steep, rugged cliffs. On the northeast, however, 15 the mass is smoothly rounded to the gently sloping plain that borders the Santa Cruz River Talley. The irregular groups of hills that rise from the low ridge southwest of the faults bounding the main mass probably are chiefly lavas and associated tuffs and conglomerates, and are here considered a part of the Cerro Colorado range.

Limiting Structure of the Cerro Colorado Mountains

The lava complex that constitutes the Cerro Colorado Mountains probably is separated from the crystalline mass of the Las Guijas Mountains by a fault in the vicinity of Las Guijas Wash, which extends along the northeast base of the Guljas range (E.D. Wilson, 1953> personal communication). Immediately north of the Cerro Colorados, the geology is not known. Andrews (1937) shows the area between the Cerro Colo­ rados and the Sierritas as a pediment surface, using the term "pediment" as defined by Bryan (1925, p. 93), broken only by a few isolated hills. Bryan (1925, p. 252) also states that the plains surrounding the Cerro Colorados are presumably pediments. If this interpretation is correct and there is no major structure separating the ranges, the lavas of the Cerro Colorados and the Sierritas may be of the same age. To the east and west of the Cerro Colorado Mountains the gently sloping pediment surfaces merge with the alluvium of the Santa Cruz and Altar Talleys. 16

GEOLOGY

The geology of the Mary G area probably is representa­ tive of a part of the main Cerro Colorado Mountains, which have been briefly described on pages 14-15• For mapping purposes the rocks have been divided into three formations: two units of flow rocks, and an intervening conglomerate.

The earlier of the flows is characterized by the pres­ ence of quartz and a reddish or tan color. On the basis of thin-seotion studies of selected samples, the rock has been designated a quartz latite porphyry. This flow is overlain locally by a conglomerate containing an abundance of quartz latite porphyry fragments. The younger flow rocks consist of highly altered andesite or andesite porphyry characterized by gray to gray-green color and the absence of quartz.

Faulting is predominantly northeast and northwest. Some east-west faulting has occurred, and mineralization is more conspicuous in this set of faults. 17

Igneous Bocks

Volcanic flow rocks comprise most of the igneous rocks in the area. The only intrusive rocks found are the andesite dikes present in the west half of Section 22, about 1,000 feet east of the Mary G mine. The principal types of flow rocks, the quartz latite porphyry and the andesite porphyry, are described in detail below.

Quartz Latite Porphyry

Quartz latite porphyry comprises the earlier of the two principal flows and occupies a considerable part of the area, as shown on Plate 1. The rock is usually some shade of red or ta n , w eathers to bloeky fragm ents, and not uncommonly forms small cliffs, in contrast to andesite porphyry and conglomer­ ate, which tend to weather to more rounded hill slopes.

In the hand specimen the quartz latite porphyry is tan or buff colored, but becomes red to maroon with an increase of iron. The rocks are noticeably porphyritic with an abun­ dance of small (usually less than 0.1 inch in diameter) phenocrysts of quartz and feldspar in an aphanitic matrix that sometimes shows flow banding. The phenocrysts may com­ prise from about 20 to 45 percent of the total volume of the rock.

Quartz occurs as glassy, rounded grains or blebs of 18 anhedral outline; feldspar occurs as white to pink, usually subhedral grains. The feldspar grains are soft, quite altered, and are unidentifiable with the hand lens because twinning has been largely obliterated by alteration. Bio- tite phenocrysts and small grains of hematite occur, but comprise only a few percent of the volume of the rock. On the basis of megascopic examination the rocks, particularly those of the lig h te r c o lo rs, have somewhat th e appearance of rhyolite porphyry.

The aphanitic groundmass may be either dull or slightly glassy in luster, varies from light-tan to brick-red in color, and may be either hard or quite soft. It is of unrecognizable composition in the hand specimen.

Following are descriptions of two thin sections of the quartz latite porphyry that are considered representative of the flow. Specimen #49HED24 was collected from an outcrop on

the east slope of the h ill in the W 1/2 SW l/k Sec. 23. Speci­ men #49HED15 was taken from the northwest-trending ridge in the NE 1/4 ME 1/4 Sec. 21, about one-half mile north of the Mary G mine. The locations of these samples are shown on Plate 1.

Specimen #49RED24:—The section is composed of phenocrysts, mostly less than 2 mm. in longest dimension, set haphazardly, for the most part, in a groundmass of devitrified glass.

Phenocrysts comprise approximately 45 percent of the 19 slide. They consist of plagioclase, about 20 percent of the total; orthoclase, 10 percent; quartz, 10 percent; and minor percentages of biotite, muscovite, epidote, magnetite, hema­ tite, and zircon.

Plagioclase phenocrysts occur as subhedral and euhedral grains and are near albite in composition. They are charac­ terized by their partial alteration to sericite.

Orthoclase occurs as anhedral to euhedral crystals and sometimes shows perthitic intergrowths. They have been al­ tered to a soft, dusty-appearing mineral thought to be one of the clay minerals, perhaps kaolin!te. The perthitic grains show alteration of the potash feldspar to clay minerals and the sodic feldspar to sericite.

Quartz grains are subhedral to anhedral in outline and are commonly corroded and embayed with groundmass.

Biotite phenocrysts are in part fresh, and in part al­ tered to muscovite and hematite aggregates. No magnesium­ bearing minerals are found in association with these aggre­ gates, and the disposition of the magnesium from the original biotite is not in evidence.

The groundmass appears to be almost entirely composed of quartz and feldspar and is stained with iron oxide, presumably limonite. It constitutes about 55 percent of the total volume of the rock, and displays two rather distinct patterns. The 20 first shows a myriad of tiny, incipient crystals, and the second is d is tin c tly fib ro u s, somewhat resembling chalcedony. The fluidal nature of the groundmass is evident from flow banding in much of the slide. Spherulitic structures are present in the groundmass in the form of small rosettes of radiating fibrous quartz masses. The groundmass itself is unaltered, with the exception of devitrification of the glass and the dissemination of iron oxide.

Based on percentage of phenocrysts, the presence of quartz, and the relative amounts of potash and sode-lime feldspars, the rock is classed as quartz latite porphyry.

Specimen #49KED15: —This sectio n also is composed of small phenocrysts contained in a groundmass of devitrified glass. Except for the degree of alteration exhibited and the much more subdued display of flow structure, the slide is very similar to that of Specimen #49HED24.

Phenocrysts comprise perhaps 35 percent of the slide. Their relative proportions are about the same as in Specimen #49RED24. Plagioclase constitutes about 15 percent of the total volume of the rock; orthoclase, 7-8 percent; quartz, 6-7 percent. Accessory minerals include biotite, magnetite, hematite, and zircon.

Plagioclase phenocrysts, less than 2 mm. in long dimen­ sion, are subhedral and euhedral in outline. They have been 21 altered nearly completely to sericite and are unidentifiable as to composition.

Orthoclase phenocrysts are anhedral to euhedral in out­ line, and their alteration to clay(?) minerals has made them nearly translucent. Alteration of orthoclase grains is more nearly complete in this slide than in that of Specimen #49KED24.

Quartz grains, subhedral to anhedral in outline, are somewhat corroded and embayed w ith groundmass.

Biotite grains have been partially altered to muscovite and hem atite aggregates.

The groundmass is similar to that in Specimen #49KED24. It is composed of quartz and feldspar, and displays areas of intergrowths of incipient quartz and feldspar crystals and other areas of the fibrous, chalcedony-like quartz masses. The groundmass appears to contain more feldspar than in Speci­ men #49EED24> but this appearance may be due only to the fact that in this slide the feldspar has been sericitized to a large extent and therefore is more conspicuous. Flow-banding is evident but not nearly so pronounced as in the preceding specimen. The iron oxide that was disseminated throughout Specimen #49RED24 is absent from this specimen.

The slide shows several fractures that are filled with late quartz. 22

On the basis of mineral composition and porphyritic texture, the rock is identified as quartz latite porphyry.

The sim ilarity in composition of Specimens #49KED24 and #49KED15, along with field relationships, indicates that the rocks are parts of the same flow sequence. The more porphy­ ritic texture of Specimen #49HED24, its better development of flow structure, and the lesser degree of alteration indicate that the two specimens are not from the same part of the flow mass.

Andesite Porphyry

The younger of the two principal flow masses of vol­ canic rocks is composed of andesite porphyry. The porphyry occupies the relatively low parts on both the east and west sides of the area and also the higher hills in the central portion (PI. 1). The rocks of this flow are generally gray or gray-green, but may weather to a greenish-tan. The ande­ site porphyry is less resistant to weathering than the quartz latite porphyry, and tends to weather to smoother hill slopes rather than the small cliffs that sometimes mark outcrops of quartz latite porphyry.

Megascopically, the andesite porphyry is some shade of gray or green. It is finely porphyritic and is composed of small (mostly less than $ mm. in long dimension) phenocrysts of altered feldspar and hornblende contained in an aphanatic 23 groundmass. Phenoorysts generally comprise about 45 percent or less of the total volume of the rock. Rather extensive propylitic alteration, evidenced by the green color and prom­ inence of epidote, is characteristic of most hand specimens.

Feldspar occurs as altered, soft, anhedral to euhedral grains that are white to tan or pinkish, and usually less than 2 mm. in diameter. Hornblende occurs as prisms, usually less than 5 mm. in long dimension, and may or may not show some degree of alteration. A few small grains of hematite and biotite occur scattered throughout the rock. Epidote, as an alteration product of both feldspar and hornblende, can also be identified with the hand lens.

The groundmass contains hard and soft areas, is dull in luster, and is gray or green but may be tan on the weathered surface. The composition is indistinguishable in the hand specimen.

Following are descriptions of thin sections of selected samples of andesite or andesite porphyry. Specimen #49EED7 was obtained from an outcrop near the top of the hill in the E 1/2 SE 1/4 Sec. 22, nearly on the section line. Specimen #49HED17 was taken from near the top of the h ill just south of the center of Sec. 22. The exact locations of the samples are shown on P la te 1.

Specimen #49RED?:—The section consists of phenoorysts, 24 mainly of feldspar and hornblende, set in a felty inter- growth of feldspar laths.

The phenocrysts comprise less than 15 percent of the area of the slide and consist of feldspar, about 6-7 percent of the total volume of the rock; hornblende, 5 percent; and perhaps 2-3 percent of accessory minerals, including biotite, pyrite, magnetite, hematite, and apatite.

Feldspar occurs as anhedral to euhedral grains that are mostly less than 2 mm. in long dimension. All gradations in size exist between the phenocrysts and the tiny crystals that comprise the groundmass. The feldspar phenocrysts have been largely altered to aggregates of epidote, clinozoisite, and a little carbonate. Twinning has been destroyed, and their original composition is not known.

Hornblende phenocrysts, ranging in size up to about 5 mm. and slightly greater in long dimension, usually occur as elongate prisms. These prisms have also been altered to ag­ gregates containing epidote, clinozoisite, penninite, car­ bonate, and sometimes quartz. A core of unaltered hornblende not uncommonly rem ains in some of the la rg e r g ra in s.

Magnetite grains scattered throughout the slide are mostly altered to hematite.

The groundmass is composed of altered feldspar laths. Alteration products are the same as those shown in the 25 phenocrystg, and it is difficult to determine the original composition of the feldspar. Refractive indices of unal­ tered remnants of the grains are less than that of the mount­ ing medium of the slide, Canada balsam, indicating a composi­ tion near albite. Small areas with no crystal outline are relatively pure, unaltered albite; and it is thought that these areas might represent secondary albite formed as part of the propylitio alteration that formed epidote, olinozoi- site, chlorite, and carbonate from the pre-existing minerals.

On the basis of texture and mineral composition, Speci­ men #49RED7 is classed as hornblende andesite.

Specimen #49RED7 is representative of the mass of ande­ site from which it was obtained and of the small mass immedi­ ately to the west. It is characterized by its lack of large feldspar phenoorysts and the prominence of hornblende prisms.

Specimen #49EED17:—The slide consists of phenoorysts of altered feldspar and hornblende set in a felty groundmass of small feldspar laths.

Phenoorysts comprise approximately 25 percent of the slide, are always less than 2 mm. in longest dimension, and grade in size into the small crystals of the groundmass. Feldspar phenoorysts comprise about 18 percent of the total volume of the rock; hornblende, about 5 percent; accessory minerals, including biotite, magnetite, hematite, apatite, 26 and quartz, 2-3 percent.

Feldspar phenocrysts are anhedral to euhedral in out­ line and have been highly sericitized and epidotized. A few grains still show faint twinning, tut the grains are uniden­ tifiable as to composition.

Hornblende phenocrysts, mostly elongate prisms, almost without exception show a rim of hematite and limonite sur­ rounding a central core of epidote, clinozoisite(?), and some sericite.

A few phenocrysts, thought to be remnants of biotite, have been altered to sericite and hematite.

The groundmass, consisting of tiny feldspar laths, has been altered largely to sericite and epidote. Remnants of the feldspar show a refractive index close to or less than that of canada balsam, and have been identified as probably albite or oligiclase. In general, the larger grains of feld­ spar have been altered to a greater degree than the smaller ones.

Specimen #49RED17, on the basis of texture and mineral composition, is identified as hornblende andesite porphyry.

Thin sections of several specimens of andesite and an­ desite porphyry were examined, and the relatively high degree of propylitic alteration noted in the sections described 27 above is common to all the sections examined. In some of the specimens, secondary silica occurs as minute veinlets and heals tiny fractures in the rock; some magnetite is present in each of the samples, hut in most instances has been par­ tially or wholly altered to hematite; epidote, chlorite, clinozoisite, and carbonate are found in nearly all the sam­ ples; and the feldspar is mostly near albite or oligoclase in composition.

The main variance in the samples examined is in the size, shape, and abundance of the phenocrysts and not in the min­ eral composition. Specimen #49EED17 is thought to be represen­ ta tiv e of most of the an d esite porphyry in the mapped area. Field relationships between the rocks displaying textural differences are not apparent. It is believed that the rocks probably represent different parts of the same flow, or per­ haps series of flows, of andesite porphyry. It is possible that some dikes of the porphyry cut the flows; but if this is true, they are confined to the general mass of andesite. In only one area were dikes of andesite porphyry found cutting the earlier quartz latite porphyry.

Andesite Porphyry Dikes

Two parallel dikes of andesite porphyry cut quartz la­ tite porphyry in a north-south direction and are well exposed about 1,000 feet east of the Mary G- mine. These dikes can 28 be traced continuously for nearly a mile, and maintain their general northerly trend for their entire length*

The dikes are from 10 to 20 feet in width and, because they are softer than the enclosing quartz latite porphyry, usually are not well exposed. They may be traced fairly easily, however, due to the contrast in color between the two rock types.

Faults offset the dikes to a small degree and show that faulting is later than the emplacement of the dikes (Pi. 1).

South of the fault contact between quartz latite por­ phyry and latite conglomerate in the southwestern part of the area, the dikes can be traced for only a relatively short distance into the latite conglomerate. They are either well covered by conglomerate float or pinch out in this area (P I. 1 ).

In the hand specimen, the rock is a medium-gray color, but weathers to brownish-gray. It is finely porphyritic and contains small phenocrysts of hornblende, about 20 percent of the total volume, and feldspar, about. 10-15 p ercen t. Brief thin-section examination shows the rock to be essenti­ ally the same in mineral composition as other specimens of andesite porphyry and to show the same propylitic alteration. 29

Sedimentary Rocks

Only one sedimentary rook formation was mapped in the Mary G- area. This formation consists of conglomerate that lies in irregular fashion between the two main lava flows and contains principally fragments of quartz latite porphyry. The writer has designated the formation as "latite conglomer­ a te . n

To the east, in the area napped by Lewis, other sedimen­ ta ry rocks have been mapped and include q u a rtz ite and lim e­ stone, the ages of which are uncertain. The limestone appar­ en tly is lo c a l in extent and was mapped in one small a re a . The quartzite, although more extensive,. does not crop out in the Mary G a re a .

Latite Conglomerate

The latite conglomerate is characterized by the prepon­ derance of quartz latite porphyry fragments and the presence of rounded quartzite fragments. Good outcrops are not common, and, with few exceptions, are confined to arroyos. "Where present on higher ground, the outcrops weather to rounded knobs. Areas underlain by the conglomerate are marked by float containing quartz latite porphyry mixed with some dis­ tinctive rounded cobbles and boulders of quartzite. The for­ mation was studied in some detail in the area immediately east of the Mary G mine and in the large area about 2,000 30 feet south-southeast of the mine (PI. l).

The latite conglomerate is not found everywhere between the two main flows, and where present it is of varied thick­ ness. It ranges from a few feet to no more than a few tens of feet thick.

On weathered surfaces the conglomerate ranges in color from gray to tan and light brown. On fresh fracture the matrix is distinctly gray but may be slightly pinkish due to the inclusion of weathered feldspars and of grains of quartz latite porphyry. On weathered surfaces the brownish hues are due in part to oxidation.

The conglomerate consists of fragments of quartz latite porphyry and quartzite cemented in an arkosic matrix. The fragments vary from granules 2 o r 3 mm. in diameter to boul­ ders up to a l i t t l e more than 2 feet in diameter. The smaller sizes generally range from rounded to subangular, and larger sizes from subrounded to angular. The heterogeniety of the formation indicates a nearly complete lack of sorting, and the fragments show practically no lineation. Rudimentary bedding was d etected in a few p laces.

Quartz latite porphyry comprises perhaps 80 to 85 per­ cent of the fragments in the formation, and the remaining 15 to 20 percent consists of quartzite. Careful examination of the conglomerate in two areas revealed no andesite fragments. 31

The quartz latite porphyry fragments are similar to the quartz latite porphyry bedrock in the area, with the excep­ tion of a few large fragments of a definitely banded type, none of which was seen in outcrop. The degree of rounding of the fragments, usually angular to subrounded, indicates that the rocks were transported a short distance and probably were derived from the immediate vicinity.

The quartzite fragments vary from dark gray or black to light gray. They generally are fine grained. The larger boulders are of the light-gray variety, and the smaller sizes consist of both the light and dark types. The degree of rounding, subrounded to rounded, is notably greater than that of the quartz latite porphyry, indicating transportation for greater distances. No quartzites of either type are known in the immediate vicinity. The quartzite in Lewis’ area, to the east, is a coarse-grained, brownish to tan rock that bears no resemblance to the boulders in the conglomerate.

The matrix, under magnification, appears to be distinctly arkosic. It consists of small, partly weathered grains of feldspar and rounded quartz grains, with the quartz predomi­ nating. The matrix shows no reaction to a drop of dilute hydrochloric acid, indicating that the cementing material is not calcite.

The conglomerate is considered post-quartz latite 32 porphyry and pre-andesite porphyry in age, as evidenced by the amount and type of quartz latite porphyry present and the complete absence of andesite porphyry. The inconsistent thickness and content of material from nearby sources indi­ cate that the conglomerate may have been deposited locally in channels and pockets. 33

S tructure

Faulting of the area has taken place in several direc­ tions but, in general, two sets of major faults predominate* The first set is aligned in a roughly northeast-southwest direction, and the second set has an approximate northwest- southeast pattern. A third set of faults, upon which little movement is indicated, are aligned in an east-west direction. Field evidence indicates this group to be later than the other two f a u lt systems.

The east-west faults are characterized by the presence of quartz-carbonate mineralization and by oxidation of the andesite porphyry wall-rook to a brick-red color. Although such mineralization is not confined solely to the latest set of faults, it is more common and more prominent along them than in either of the two earlier sets.

Most of the faults are high-angle normal faults. The amount of displacement along them is not known, because of the lack of information concerning the thickness of the for­ mations involved. Although most of the faulting appears to be post-andesite, the relative ages of the major faults is not clear. Mapping, which shows northeast-southwest faults both offsetting and offset by northwest-southeast faults, indicates that both sets of faults probably belong to the same period of deformation. 34

Age of the Volcanics

The relative ages of the rocks within the restricted area studied and shown on the geologic map (PI. l) seem clear, as shown by the composition of the conglomerate, its d istri­ bution, and the field relations between quartz latite por­ phyry, conglomerate, and andesite porphyry. The actual dat­ ing of the volcanic rocks, however, without the aid of diagnostic fossils in the conglomerate and with no known stratigraphic section from which to determine age relation­ ships, is not clear.

Much of the geologic study in southcentral and south­ western Arizona has been in areas containing igneous rocks, both intrusive and extrusive. Even within a given area, interpretation by individual geologists has led to different age assignments for a given formation. No great discrepan­ cies are involved, however, and the general picture as given by Schrader (1915), Bryan (1925), and later by Brown (1939) and Gilluly (1946) is consistent. Similarities in the Mesozoic-Tertiary sequence of volcanics and elastics have been noted, but there has been little attempt at correlation of the volcanics between the more widely separated mountain ranges. Such correlation would indeed be tenuous on the basis of present knowledge and, in the Mary G- area, would have to be made entirely on the basis of rock types, rather than on the basis of field relations with better-known sedimentary rock 35 formations.

A rather extensive review of the literature bearing on the igneous rocks of southcentral and southwestern Arizona has been made in an attempt to determine if any basis for correlation of the volcanic rocks exists.

In the area east of the Santa Cruz River, intrusive and volcanic rocks have been described by Schrader (1915)» Feiss (1929), Gillingham (1936), Alberding (1938), Mayuga (1940), Sopp (1940), Johnson (1941), Marvin (1942), Kartchner (1944), Feth (1947), Alexis (1949), and Anthony (1951).

The igneous rocks of the Santa Rita and Patagonia Moun­ tains were studied during the reconnaissance work of Schrader (1915) and were placed in two general groups. The earlier group did not include a volcanic sequence. The later group, comprising a sequence of rhyolite, quartz latite porphyry, tuff and agglomerates, andesites, and basalts, rests uncon- formably on pre-Tertiary rocks and was assigned to the Ter­ tiary (Schrader, 1915, P* 57-76). Later work has not brought out any significant changes in this age assignment.

Little information is available regarding the geology of the area south of the Cerro Colorado Mountains. General information has been presented by Barton (1925), Andrews (1937), Fowler (1938), and by Webb and Coryell (1954)• 36

Darton (1925, p. 288) stated that much of the central part of the Tumacacori Mountains consists of a group of Ter­ tiary volcanic rocks similar to those of the Santa Rita Mountains. Webh and Coryell (1953, p. 6- 8 ) briefly describe a Mesozoic series of rhyolite and conglomerate and a late Cenozoic series of acidic to basic lavas, breccias, tuffs, and conglomerates.

North of the Cerro Colorado Mountains, igneous rocks of the Sierrita and Tucson Mountains have been described by Ran­ soms (1922), Gordon (1922), Park (1939), Eckel (1930), Higdon (1933), Brown (1939), Mayuga (1942), Whitcomb (1948), and Houser (1949).

The volcanic rocks of the Tucson Mountains have been de­ scribed in some detail (Brown, 1939). The widespread, struc­ turally complex Cretaceous sequence ranges from 2,000 to 5,000 feet thick and consists principally of andesitic flows but includes dacite, latite, rhyolite, tuffs, and breccias. These rocks are overlain by rhyolites, andesite, tuff, and basalts of Tertiary age. The age of the later sequence has been determined both by stratigraphic relationships and by fossil plant remains in the tuff.

The sequence of andesitic volcanic rocks and associated sediments in the Helmet Peak area of the Sierrita Mountains has been correlated with the Cretaceous sequence of the Tucson Mountains (Mayuga, 1942, p. 39-44). 37

Papers by Bryan (1925), Barton (1925), Wilson (1933), and Gilluly (1946) present the bulk of the geologic informa­ tion available on the region west of the Cerro Colorado Moun­ ta in s .

The volcanic rocks of the Ajo district are known in de­ tail (Gilluly, 1946, p. 25-48). They include andesite, keratophyre, quartz keratophyre, breccias, and tuffs of Cre­ taceous (?) age; and andesite, latite, and basalt, with asso­ ciated tuffs and breccias, of Tertiary(?) age. The Concen­ trator volcanics, those of Cretaceous (?) age, resemble the Cretaceous volcanics of the Tucson Mountains and have been tentatively correlated with them by Gilluly (1946, p. 24-25).

The writer feels that correlation of the volcanic rocks on the basis of lithology alone is, at best, tenuous. The solution to the problem of correlation and age assignments in areas where stratigraphic evidence or fossils are not avail­ able lies perhaps, not in the volcanics themselves, but rather in the associated beds of tuffs and conglomerates. It seems significant, for example, that the Oro Blanco conglomerate of the Ruby area (Fowler, 1938, p. 121) consists principally of igneous rock fragments but also contains quartzite fragments that appear to have been transported a greater distance. This bears some resemblance to the latite conglomerate of the Mary G area. Perhaps detailed studies of the Ainor constitu­ ents of such conglomerates might furnish information useful 38 in correlation, at least between adjacent ranges.

Information gathered in the field work in the Mary G area is not sufficient to establish independently the age of the rocks. Based on the proximity of the area to the Cerro Colorado Mountains and the probable structural rela­ tions between the two areas, the rocks of the Mary G area are here assigned to the Tertiary(?). 39

MINERAL DEPOSITS

General Statement

Mineral deposits in the Mary G area occur in veins that have been deposited along faults by ascending hydrothermal solutions. Economic deposits of sulfide minerals appear to have been localized in the more permeable channels formed by the intersection of faults and fractures, where release of pressure allowed deposition.

Although not confined to the andesite porphyry flow rocks, mineralization is more conspicuous in them, and sur­ face showings of mineralized veins are characterized by a distinct reddening of the normally gray-green andesite. Lo­ cally, quartz and calcite zones can be seen in the red ande­ site wall-rock. The mineralized zones along any given fault are seldom greater than 5 or 6 feet in width, and the quartz and carbonate veins are only a fraction of the total width, in most instances.

Mineralization is more conspicuous along east-west faults (PI. l), but faults in other directions show similar characteristics locally.

The reddening of the andesite is due to the oxidation of 40 iron. It is not known whether sufficient iron is present in the propylitized andesite to supply the seemingly high con­ centration of limonite to the mineralized veins, or whether iron was added from metallizing solutions.

The sulfide deposits in the veins occur in the form of short veinlets and shoots, and nearly always appear to have been concentrated in zones of weakness, formed at the inter­ sections of faults. Economic sulfide deposits were seen only in the Mary G mine, but the depth and direction of many of the deeper prospect pits and adits in the area indicate that shoots similar in shape to those in the Mary G may have been mined from the prospects. 41

Mining History in Southern Arizona and the Cerro Colorado D istrict

Several accounts of the history of southcentral and southwestern Arizona, its exploration, settlement, and the development of mining are to be found in the literature. An interesting sketch of the early history (Bryan, 1925, p. 3- 23) has been briefly summarized by Wilson (1951, P» 2-3).

Early expeditions by the Spanish date prior to the mid­ dle of the 16th century (Bryan, 1925, p. 4-6) and were under­ taken to search for reported great wealth in the unknown Indian country. The first record of actual prospecting dates to 1583, when silver ore reportedly was found near the head­ waters of the Verde River.

L ittle prospecting, and probably no extensive mining, was carried on in the region before the middle of the 18th century. The real development of the mining industry to the point at which it became an economic factor was not begun until 1854, following the Gadsden Purchase and subsequent entry into the region by Americans.

The mining industry has been an active one in Pima County for the past hundred years, in varied degree subject to metal price fluctuations and the stimulus of wartime. Through 1953, the value of metal production in Pima County totalled more than $555,000,000. The principal metals pro­ duced are copper, gold, silver, zinc, and lead, although 42 tungsten, molybdenum, vanadium, and manganese also have been produced (Wilson, 1951, p. 3-4)•

Mining was carried on early in the Cerro Colorado dis­ trict and in the Arivaca district, to the south. Arivaca was mentioned as a mining locality In 1777 (Bryan, 1925, p. 16), and "La Aribae," a land grant dated in 1824, is the oldest mine listed in the Pima County recorder's office (Carpenter, 1927).

According to unpublished notes by J.B. Tenney, in the office of the Arizona Bureau of Mines, the Cerro Colorado mine, about 2.5 miles east-southeast of the Mary G mine, was worked to some extent by the Spaniards prior to 1823. In about 1856 American interests acquired the old mine, renamed it the Heintzelman mine, and started production of silver ore. High-grade ore was produced on a relatively small scale until 1861, when the Civil War brought withdrawal of American troops from the area.

During the late seventies and early eighties the Heint­ zelman and other small mines, including the Liberty, were worked again. Ore was treated in an amalgamation mill at Arivaca. Since 1884, production from the mines in the dis­ trict has been sporadic, and the Mary G mine has been one of the few more successful mines of later years.

Total production of the Cerro Colorado district is 43 s lig h tly more than $300,000, nearly all of which has been silver (Wilson, 1951, p. 14).

The following account of the history of the Mary G- mine is based upon information furnished by Mr. Henry G. Worsley, whose fam ily owns the mine. So f a r as is known, no records of the mine are in existence. All records prior to 1945 were destroyed by fire at the mine camp in that year.

The pro p erty , known o rig in a lly as the Mary E mine, was located in about 1890 by Mr. C lark, who was operating the Liberty mine, 1.5 miles to the north. The claim was relo­ cated in 1912 by Mr. James Guy, who then sold i t to the Worsley family in 1914. The mine has remained in the family since that time, except for a two-year period of litigation that began in 1928. The property is now a patented claim. For the past 20 years the mine has been worked intermittently by Mr. Henry Worsley and by others on a lease basis.

The most recent development apparently was in 1951, when a new shaft was started by the Acme Mining and Development Company. In the fall of 1953, when the mine was revisited by the writer, no activity was in evidence and the equipment was in a state of disrepair. 44

Mary G Mine

Ore D eposits

The ore deposits at the Mary G mine are valued chiefly for their silver content. Some lead and minor quantities of copper and mercury have also been recovered from the ore.

Ore occurs within a mineralized fault or fault zone in andesite porphyry. The main fault, followed by most of the mine workings, trends approximately N. 10° E. and dips 45° W. This south-trending fault zone is intersected at several points by cross faults, or fractures, that vary in strike from N. 40° E. to N. 60° W. and u su ally dip northw ard. The greatest concentration of sulfide mineralization occurs at the intersections of the cross faults with the main fault zone •

Both the hanging wall and foot wall of the mineralized zone are propylitized andesite porphyry that is typical of that found throughout the area. The mineralized zone con­ sists of iron-rich, red andesite porphyry. The fed porphyry varies from hard, competent rock to soft, gougy material.

The silver-bearing sulfide zones occur as small string­ ers, veinlets, and shoots ranging from a few inches to per­ haps 2 feet in width. These stringers seldom can be followed for more than a few feet as they pinch and swell rapidly along their strike. 45

The ore stringers consist chiefly of fine to coarse crystalline masses of galena occurring in a gangue of milky quartz. The stringers have all been partially oxidized. Oxidation products include anglesite as grains and masses surrounding galena, cerrusite as white or slightly grayish crystals and masses, and massicot(?) as yellow, earthy masses and incrustations associated with the other lead m inerals.

Copper occurs as small, earthy masses and crusts of mal­ achite on quartz.

Cinnabar occurs as scales and tiny crystals lining cavi­ ties in quartz.

Mottramite(?), as a coating of drusy crystals on quartz, was identified on one specimen.

Gangue m inerals include milky and grayish, ra th e r fin e ­ grained quartz, some barite, and a little calcite.

Silver occurs with the galena, probably as microscopic inclusions of pyrargyrite or argentiferous tetrahedrite. No silver minerals were identified in the hand specimen.

Mining

The mine is worked through a near-vertical shaft, the depth of which is approximately 135 feet. Early workings were 46 mostly short crosscuts and some raises, now either caved in or lagged off, from the main south-trending drift on the 135- foot level (PI. 2 ). The main drift follows the footwall of the mineralized fault or fault zone, for the most part, for approximately 120 f e e t .

A winze follows the intersection of the main fault and an east-west cross fault. The winze followed an ore shoot consisting of pinching and swelling stringers and pockets of sulfide minerals and, when the mine was visited by the writer, was about 55 feet in vertical depth.

At the 170-foot level, a drift was driven that wandered between the footwall and hanging wall of the mineralized zone, but relatively little sulfide mineralization was encoun­ tered. Mineralization on this level was mainly quartz, with some cinnabar and a little galena.

In general, little difficulty is encountered in mining. The mineralized andesite wall-rock is hard and stands well. Posts, stulls, and loose lagging have been used throughout the mine. Locally, however, the wall-rock is badly broken and, when wet, will run as mud. These local soft zones must be lagged rapidly and tightly.

Water produced through the fractured and faulted andesite usually is not enough to be troublesome in mining. It is pumped to a sump at the bottom of the main shaft and from 47 there is pumped to the surface. Water from the mine is suf­ ficient to supply the needs at the mine and to keep a stock •watering tank filled. Drinking water, however, was hauled from Kinsley’s ranch or from Arivaca.

In 1949 the equipment on the surface consisted of five gasoline engines that operated hoist, compressor, pump, ven­ tilating system, and generator. Four buildings on the property housed the sleeping quarters,"kitchen, and hoisting equipment. A 50-ton ore bin completed the surface equipment.

Production

According to information furnished by Mr. Worsley, pro­ duction from the mine has totalled nearly #100, 000. The values have been mainly from silver, although some lead also has been recovered. Copper and mercury, so far as is known, have not been recovered.

Ore from the mine has been tre a te d a t Hayden and, more recently, at El Paso, Texas. 48

REFERENCES CITED

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Alexis, C.O., 1949, The geology of the northern part of the Huachuoa Mountains, Arizona: Univ. A riz., thesis, 74 P»

Andrews, D.A., 1937, Ground water in the Avra-Altar Valley, Arizona: U.S. Geol. Survey Water-Supply Paper 796-E, p• 163-180.

Anthony, J.W., 1951, Geology of the Montosa-Cottonwood Canyon area, Santa Cruz County, Arizona: Univ. Ariz., thesis, 84 ,p.

Brown, W.H., 1939, Tucson Mountains, an Arizona basin-range type: Geol. Soc. America Bull., v. 50, p. 697-760.

Bryan, Kirk, 1922, Erosion and sedimentation in the Papago country, Arizona, with a sketch of the geology: U.S. Geol. Survey Bull. 730-B, p. 19-90.

, 1925, The Papago Country, Arizona; a geographic, geo­ logic, and hydrologic reconnaissance with a guide to desert watering places: U.S. Geol. Survey Water-Supply Paper 499, 436 p.

Barton, N.H., 1925, A resume of Arizona geology: Univ. Ariz. Ariz. Bur. Mines Bull. 119, 298 p.

, 1933, Guidebook of the western United States, Pt. F, "The Southern Pacific Lines, New Orleans to Los Angeles: U.S. Geol. Survey Bull. 845, p. 145-241.

Eckel, E.B., 1930, Geology and ore deposits of the Mineral Hill area, Pima County, Arizona: Univ. Ariz., thesis, 51 p. 49

Feiss, J.W., 1929, The geology and ore deposits of Hiltano Oamp, Arizona: Univ. Ariz., thesis, 40 p.

Feth, J.H., 1947, The geology of the northern Canelo Hills, Santa Cruz County, Arizona: Univ. Ariz., thesis, 150 p.

Fowler, G.M., 1938, Montana mine, Ruby in Some Arizona ore deposits: Univ. Ariz., Ariz. Bur.Heines Bull. 145, p. 119-124.

Gillingham, T.E., 1936, The geology of the California mine area, Pima County, A rizona: Univ. A r iz ., th e s is , 68 p .

Gilluly, James, 1946, The A jo mining district, Arizona: U.S. Geol. Survey Prof. Paper 209, 112 p.

Gordon, E .R ., 1922, The geology of the Twin B uttes mining district: Univ. Ariz., thesis, 10 p.

Higdon, C.E., 1933, Geology and ore deposits of the Sunshine area, Pima County, Arizona: Univ. A riz., thesis, 25 p.

Houser, F.N., 1949, The geology of the Contention mine area, Twin Buttes, Arizona: Univ. Ariz., thesis, 61 p.

Johnson, V.H., 1941, The geology of the Helvetia mining dis­ trict, Arizona: Univ. Ariz., thesis, 111 p.

Kartchner, W . J t s . , 1944, The geology and ore deposits of a por­ tion of the Harshaw district, Patagonia Mountains, Arizona: Univ. Ariz., thesis, 100 p .

Marvin, T.C., 1942, The geology of the Hilton Ranch area, Pima County, Arizona: Univ. Ariz., thesis, 60 p.

Mayuga, M.N., 1940, The geology of the Empire Peak a re a , Pima County, Arizona: Univ. ariz., thesis, 74 P«

, 1942, The geology and ore deposits of the Helmet Peak area, Pima County, Arizona: Univ. A riz ., th e s is , 126 p .

Univ. of Arizona Library 50

Park, C.F., J r., 1929> Geology of the San Xavier district: Univ. Ariz., thesis, 30 p.

Eansome, F.L., 1904, The geology and ore deposits of the Bisbee quadrangle, Arizona: T7.S. Geol. Survey Prof. Paper 21, 168 p.

, 1922, Ore deposits of the Sierrita Mountains: U.S. 'Geol. Survey Bull. 725, p. 407-428.

Ross, C.P., 1922, Routes to desert watering places in the lower Gila region, Arizona: U.S. Geol. Survey Water- Supply Paper 490-C, p. 1- 4 , 271- 315.

, 1923, The lower Gila region, Arizona; a geographic, geologic, and hydrologic reconnaissance with a guide to desert watering places: U.S. Geol. Survey Water-Supply Paper 498, 237 p.

Schrader, F.C., 1915, Mineral deposits of the Santa Rita and Patagonia Mountains, Arizona, with contributions by J.M. Hill: U.S. Geol. Survey Bull. 582, 373 p.

Sopp, G.P., 1940, Geology of the Montana mine area, Empire Mountains, Arizona: Univ. Ariz., thesis, 63 p*

Stoyanow, A.A., 1936, Correlation of Arizona Paleozoic for­ mations: Geol. Soc. America Bull., v. 47, p. 459-540.

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Webb, B.P. and Coryell, K.C., 1954, Preliminary regional map ping in the Ruby quadrangle, Arizona: U.S. Atomic Energy Comm., R.M.E. 2009, 12 p.

Whitcomb. H .A ., 1948, Geology of the Morgan mine area, Twin Buttes, Arizona: Univ. Ariz., thesis, 82 p. 51

Wilson, E.D., 1933, Geology and mineral deposits of southern Yuma County, Arizona: Univ. Ariz., Ariz. Bur. Mines Bull. 134, 236 p.

_, 1941a, Tungsten deposits of Arizona: Univ. A riz., Ariz. Bur. Mines Bull. 148, 54 P*

, 1941b, Quicksilver (Mercury): Univ. Ariz., Ariz. Bur. Mines Circular no. 9, 13 p.

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PLAN MAP OF THE MARY G MINE

SHOWING FAULTS (IN BLACK) AND SULFIDE ZONES (IN RED)

1949 ' ' fr