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. Rights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 26/09/2021 04:02:54 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 . 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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