k?:Ji!!{KW{ffi):ii=J.El~'i:~~; The Con term 1 no us U n 1ted States M 1 neral 

Assessment Program: Background 

Information to Accompany Folio of 

Geologic, Geochemical, Geophysical, 

and Mineral Resource Maps of the Ajo 

and Lukeville 1 o by 2° Quadrangles, 

Arizona 
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The Conterminous United States Mineral 

Assessment Program: Background 

Information to Accompany Folio of 

Geologic, Geochemical, Geophysical, 

and Mineral Resource Maps of the Ajo 

and Lukeville 1 o by 2° Quadrangles, 

Arizona 

By FLOYD GRAY, RICHARD M. TOSDAL, 

JOCELYN A. PETERSON, DENNIS P. COX, 

ROBERT J. MILLER, DOUGLAS P. KLEIN, 

PAUL K. THEOBALD, GORDON B. HAXEL, 

MICHAEL GRUBENSKY, GARY RAINES, 

HARLAN N. BARTON, DONALD A. SINGER, 

and ROBERT EPPINGER 

U.S. GEOLOGICAL SURVEY CIRCULAR 1082 
U.S. DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, Jr., Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

Any use of trade, product, or firm names 

in this publication is for descriptive purposes only 

and does not imply endorsement by the U.S. Government 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1992 

Free on application to 

Book and Open-File Report Sales 

U.S. Geological Survey 

Box 25286 

Denver, CO 80225 

Library of Congress Cataloging in Publication Data 

The Conterminous United States Mineral Assessment Program : background 

information to accompany folio of geologic, geochemical, geophysical, and 

mineral resource maps of the Ajo and Lukeville 1 o by 2° quadrangles, 

Arizona I by Floyd Gray ... [et al.]. 

p. em. -- (U.S. Geological Survey circular ; 1 082) 

Includes bibliographical references. 

Supt. of Docs. no.: I 19.4/2:1082 

1. Geology--Arizona--Ajo Region. 2. Mines and mineral resources--

Arizona--Ajo Region. I. Gray, Floyd. II. Series. 

QE89.A9C66 1992 92-33599 

553'.09791'7--dc20 CIP 
CONTENTS 

Abstract 1 

Introduction 1 

Purpose and scope 1 

Location and geography 1 

Land status 2 

Access restrictions 2 

Acknowledgments 3 

Geologic investigations 4 

Previous work 4 

Present study 4 

Description of component maps and studies 

of the Ajo and Lukeville quadrangles folio 5 

Geology 5 

Proterozoic rocks 5 

Paleozoic rocks 7 

Mesozoic rocks 7 

Jurassic rocks 7 

Upper Jurassic(?) and Cretaceous rocks 7 

Late Mesozoic and early Cenozoic rocks 9 

Cenozoic rocks 10 

Paleogene rocks 10 

Tertiary volcanic rocks 10 

Geochemical studies 11 

Geophysical studies 12 

Gravity maps 12 

Aeromagnetic map 14 

Landsat imagery 14 

Geologic studies in the Ajo Mining District 15 

Mineral occurrence map (MF-1834-A) 17 

Technique used in mineral assessment 18 

Introduction 18 

Information needs for resource assessments 18 

Mineral resource assessment maps (OF-85-527, MF-1834-B) 19 

Selected references 21 

FIGURES 

1--6. Maps showing: 

1. Location of Ajo and Lukeville 1 o by 2° quadrangles . 2 

2. Status of land within Ajo and Lukeville 1° by 2° quadrangles 3 

3. Location of approximate boundary between northern and southern Papago 

terranes and physiography of Ajo and Lukeville 1 o by 2° quadrangles 6 

4. Generalized geology of Ajo and Lukeville 1 o by 2° quadrangles 8 

5. Areas of significant regional aeromagnetic and gravity features and locations of 

selected studies in Ajo and Lukeville 1 o by 2° quadrangles 13 

6. Geology of Ajo Mining District 16 

7. Flow diagram showing how information from field studies is applied to selection of deposit 

models and delineation of tracts in mineral resource map 19 

Contents Ill 
8. Flow diagram showing how resource assessment is derived from mineral resource 

map, estimates of number of undiscovered deposits, and worldwide grade-tonnage 

data 20 

9. Inverse cumulative distribution of copper tonnage and grade in porphyry copper 

deposits in Arizona, in and near Ajo and Lukeville 1 o by 2° quadrangles 20 

TABLES 

1. Component maps of the Ajo and Lukeville 1 o by 2° quadrangles assessment 5 

2. Geochemically anomalous areas in parts of the Ajo and Lukeville 1 o by 2° 

quadrangles 12 

IV Contents 
The Conterminous United States Mineral Assessment 

Program: Background Information to Accompany Folio 

of Geologic, Geochemical, Geophysical, and Mineral 

Resource Maps of the Ajo and Lukeville 1 o by 2° 

Quadrangles, Arizona 

By Floyd Gray, Richard M. Tosdal, jocelyn A. Peterson, Dennis P. Cox, Robert j. Miller, 

Douglas P. Klein, Paul K. Theobald, Gordon B. Haxel, Michael Grubensky, Gary Raines, 

Harlan N. Barton, Donald A. Singer, and Robert Eppinger 

ABSTRACT 

Encompassing about 21,000 km2 in southwestern Arizona, the Ajo and Lukeville 1 o by 2° quadrangles have 

been the subject of mineral resource investigations utilizing field and laboratory studies in the disciplines of geology, geochemistry, geophysics, and Landsat imagery. The 

results of these studies are published as a folio of maps, 

figures, and tables, with accompanying discussions. Past 

mineral production has been limited to copper from the 

Ajo Mining District. In addition to copper, the quadrangles contain potentially significant resources of gold 

and silver; a few other commodities, including molybdenum and evaporites, may also exist in the area as appreciable resources. This circular provides background 

information on the mineral deposits and on the investigations and integrates the information presented in the folio. 

The bibliography cites references to the geology, 

geochemistry, geophysics, and mineral deposits of the two 

quadrangles. 

INTRODUCTION 

Purpose and Scope 

This circular and the folio of maps published for the 

Ajo and Lukeville 1 o by 2° quadrangles are part of a 

series of reports by the U.S. Geological Survey on the 

mineral resource potential of the conterminous United 

States. These studies are conducted under the Conterminous United States Mineral Assessment Program 

(CUSMAP), which provides regional mineral appraisal 

information to assist in the formulation of a long-range 

Manuscript approved for publication March 2, 1992. 

national minerals policy and to provide Federal, State, 

and local governments with information for land-use 

planning. CUSMAP studies include (1) compilations of 

published geoscience and mineral resource data; (2) regional geologic, geophysical, geochemical, and remotesensing field investigations to obtain new data; and (3) 

interpretations and syntheses of data to produce systematic assessments of the mineral resource potential of selected areas. CUSMAP investigations also provide 

regional geological, geochemical, and geophysical information that is useful in a broad range of earth science 

studies of the conterminous United States; such information can be used in developing a framework for mineral 

exploration and in specific studies, such as the mineral 

resource assessment of wilderness areas. 

Location and Geography 

The Ajo and Lukeville 1 o by 2° quadrangles cover 

approximately 21,000 km2 in southwestern Arizona (fig. 

1 ). The eastern, northern, and western boundaries of 

these quadrangles lie, respectively, approximately 100 

km west of Tucson, 50 km south of Phoenix, and 60 km 

east of Yuma, Arizona. The Ajo 1 o by 2° quadrangle is 

located between latitude 32° and 33° N. and between longitude 112° and 114° W.; its southwest comer lies in 

Mexico. The Lukeville 1 o by 2° quadrangle lies mostly in 

Mexico; only the triangular part of the northeast comer, 

from latitude 31 °37' to 32° N. and from longitude 112° to 

113°15' W., lies within Arizona, south of the Ajo quadrangle. Mexican lands were not evaluated (fig. 1 ). 

The only major highways in the area are U.S. Interstate Highway 8, which crosses east-west along the entire 

northern part of the Ajo 1 o by 2° quadrangle; Arizona 

Introduction 
State Highway 85, from north of Gila Bend to Lukeville 

on the Mexican border; and Arizona State Highway 86, 

from Why east to the Santa Rosa Valley in the eastern part 

of the Ajo quadrangle. Major towns located within the 

study area are Ajo, Gila Bend, and Lukeville (fig. 1 ). 

The quadrangles contain a system of northwesttrending mountains and valleys that are part of the Basin 

and Range physiographic province. The vegetation is 

part of the Sonoran Desertscrub biotic community, consisting of the Lower Colorado River and Arizona Upland 

subdivisions. The common vegetation consists of shrubs 

(dominantly creosote bush) and cacti, including saguaro, 

organ pipe, and cholla. Near washes, shrubs and trees 

such as acacia, mesquite, ironwood, and palo verde are 

common (Brown, 1982). 

Land status 

Most of the area within the Ajo and Lukeville 1 o by 

2° quadrangles is Federal and Indian Reservation land in 

which access has been limited for several decades (see fig. 

0 10 20 30 40 MILES 

AREA OF MAP 0 10 20 30 40 50 KILOMETERS 

2). The Barry M Goldwater Air Force Range covers the 

western, central, and southwestern parts of the Ajo quadrangle, and the southwestern part of the quadrangle also 

includes the Cabeza Prieta National Wildlife Refuge. The 

U.S. Army Yuma Proving Ground and the Kofa National 

Wildlife Refuge extend into the northwestern corner of the 

Ajo quadrangle. Also present in the quadrangle are the 

Organ Pipe Cactus National Monument, the western part 

of the Tohono O'odham (formerly Papago) Indian Reservation, and the southern part of the Ak Chin and Gila 

Bend Indian Reservations. Private- and State-owned land 

is in a strip along the north edge of the Ajo quadrangle 

and the area surrounding Ajo. Because of the many years 

of restricted access to much of the Ajo quadrangle, new 

exploration techniques and new deposit models have not 

been tested in the quadrangle. 

Access Restrictions 

At the time of this investigation, access to the great 

majority of the study area was restricted and required 

Figure 1. Location of Ajo and Lukeville 1 o by 2° quadrangles and surrounding area in southwestern Arizona. 

2 The Conterminous United States Mineral Assessment Program: Ajo and Lukeville 1 o by r Quadrangles, Arizona 
both approval several months in advance and day-to-day 

coordination with military authorities. The U.S. Air 

Force controls the Barry M. Goldwater Air Force Range 

(fig. 2), but operational control of the western part of the 

military range is by the U.S. Marine Corps based at 

Yuma. The U.S. Army restricts access to the Yuma 

Proving Ground in the northwest portion of the quadrangle. Access was also limited to the Kofa and Cabeza 

Prieta Game Ranges because both of these areas are 

within larger areas restricted by the military. Coordination with the U.S. Border Patrol offices in Yuma and Gila 

Bend was maintained for work near the international border. Access to most restricted areas was by helicopter. 

Permission to sample within the Organ Pipe Cactus 

National Monument was obtained for the March and 

April 1979 and 1980 field seasons. Most site access was 

by helicopter based at Ajo. Sites closer than 2 km to 

roads were visited on foot. 

Acknowledgments 

Compilation of the Ajo and Lukeville CUSMAP reports would not have been possible without the contributions of many colleagues in the U.S. Geological Survey. 

We especially appreciate the consultation by A.K. 

Armstrong and the field assistance of Michael Cosca, 

Lottie Soli, Thomas Young, Richard L. LeVeque, and 

Katherine Kahle. John Rozelle, Jim Frisken, and Robert 

Turner facilitated much of the geochemical work. Competent commercial helicopter crews were essential in 

carrying out the geologic mapping, geochemical sampling, and geophysical observations. M.F. Hornberger, 

R.L. Ray, and K.A. Johnson helped with office compilation of the field data. E.H. McKee provided potassiumargon ages of rock samples collected in the initial phase of 

our study. W.D. Menzie discussed with us many aspects 

of the technique used in mineral resource assessment. 

Gila Bend Indian 

Reservation 

•Gila Bend AkChin 

Indian 

Reservation 

112° 

Barry M. Goldwater Air Force Range 

Cabeza Prieta National Wildlife Refuge 

and 

Barry M. Goldwater Air Force Range 

AREA OF MAP 

0 

0 

Cabeza Prieta 

National 

Wildlife 

Refuge 

eAjo 

Organ Pipe Cactus 

National Monument 

5 10 15 MILES 

10 20 30 KILOMETERS 

Tohono O'odham 

Indian 

Reservation 

Figure 2. Status of land within Ajo and Lukeville 1 o by 2° quadrangles. Undesignated areas are under State or private ownership. 

Introduction 3 
A large part of the quadrangles is managed by the 

Luke Air Force Base. We wish to thank the commanding officer and other personnel for the help and courtesies they gave us during our study. Many thanks also go 

to the numerous dispatchers on duty, who maintained 

daily contacts with us regarding the scheduling of military exercises in the study area. 

GEOLOGIC INVESTIGATIONS 

Previous Work 

Prior to the 1900's little was known about the geology of the Ajo and Lukeville 1 o by 2° quadrangles, and 

most of the investigations were topical studies focused 

on specific mineralized areas, Paleozoic or Mesozoic 

stratigraphic sequences, water resources, or areas of special petrologic interest. The first published regional geologic studies conducted in the quadrangles were 

associated with water resource investigations by Bryan 

(1925), Heindl (1960), and Heindl and others (1962) of 

the U.S. Geological Survey. Proterozoic, Paleozoic, and 

Mesozoic stratigraphy in the northeastern part of the 

study area was studied by Carpenter ( 194 7), 

McClymonds (1959), Hammer (1961), Heindl (1965a), 

and Chaffee (1974). The geology of the Ajo Mining 

District was detailed by Gilluly (1937, 1946). Neogene 

volcanic rocks in parts of the Ajo Range and Aguila 

Mountains were mapped, respectively, by Jones (1974) 

and Tucker (1980). Potassium-argon geochronology of 

southwestern Arizona is presented in Shafiqullah and 

others ( 1980). The status of mineral information for the 

Tohono O'odham Indian Reservation in the eastern part 

of the quadrangle is described by Johnson and others 

(1975). Summaries of geology, mineral deposits, and 

production for most mining properties in Pima County 

are given by Keith (1974). 

Present Study 

This study of the Ajo and Lukeville 1 o by 2° quadrangles was conducted mostly between 1978 and 1983. 

An interdisciplinary team of earth scientists and technicians undertook systematic geologic mapping and made 

studies of the geochemistry, geophysics, Landsat imagery, and mineral deposits to produce a mineral assessment of the study area. These collateral field and 

laboratory studies were completed early in 1984. Specific topical and regional geologic and mineral resource 

investigations by team members during the CUSMAP 

study have been completed, and the results have been 

published in several reports (see table 1 ). The study 

originated as an outgrowth of investigations of the 

Tohono 0' odham Indian Reservation and combines new 

geologic mapping with existing mapping to relate mineral 

resources, regional structure, and tectonostratigraphic units 

with ore deposit models. The project was incorporated 

into the CUSMAP program in 1980. 

Extensive new geologic mapping, facilitated by helicopter support, of Tertiary volcanic sequences was done 

in the central and southern parts of the study area and in 

the metamorphic rocks of the Mohawk Mountains. Detailed studies of the Jurassic and older granitoids in the 

southeastern part of the study area, begun earlier, were 

continued during this project. 

The geochemical survey consisted of ( 1) the collection and analysis of samples of stream sediment and of 

the nonmagnetic fractions of heavy-mineral concentrates 

from stream sediment, and (2) the identification of heavy 

minerals found in the nonmagnetic concentrates. 

Semiquantitative spectrographic analyses provided data 

on the abundance of 31 trace elements in each sample. 

Anomalously high concentrations of certain trace elements helped to identify mineralized areas. A review 

was made of available information on mines, quarries, 

and abandoned prospects. The existence and locations 

of many of the mines and prospects entered previously 

in the Mineral Resource Data System (MRDS) of the 

U.S. Geological Survey (Peterson, 1984) were confirmed 

during the field studies. 

Maps showing mineral occurrences, geophysical information, areas of alteration (determined by Landsat 

imagery), and locations of geochemical samples containing anomalous concentrations of trace elements, 

were generated and used in conjunction with maps of favorable geologic units to infer the potential for various 

metallic commodities. Similar methods of combining 

data are also used to determine the potential for several 

nonmetallic commodities, except that geochemical data 

for such commodities are generally lacking, insufficient, 

or inappropriate. As a result, the inferred potential for 

these commodities is based largely on the combined information about mineral occurrences and the distribution 

of favorable geologic units. The potential for some industrial minerals is assessed only in broad terms. Such materials are available essentially throughout the area, and their 

usefulness may be as much a function of proximity to 

markets and variations in weathering as of bedrock geology. Geologic units from which resources of these construction materials have been obtained are accorded a 

somewhat greater potential for additional resources than 

are units that have not been exploited in the past. 

The results of this study are presented in a series of U.S. 

Geological Survey Miscellaneous Field Studies Maps and 

Open-File Reports (table 1) and in the abstracts volume of a 

USGS-sponsored conference on the quadrangles (Gray, 1988). 

Other maps and reports related to the program are included in 

the bibliography at the end of this report. 

4 The Conterminous United States Mineral Assessment Program: Ajo and Lukeville 1 o by r Quadrangles, Arizona 
Table 1. Component maps of the Ajo and Lukeville 1 o by 2° quadrangle assessment 

U.S. Geological 

Survey map 

Author Subject 

MF-1834-A (Peterson and Tosdal, 1987) Mineral occurrences and tabulation of geologic, commodity, and 

production data 

MF-1834-B 

MF-1834-C 

(Peterson and others, 1987) 

(Theobald and Barton, 

1987a) 

Mineral resource assessment 

Geochemical distribution and abundance of copper in geochemical 

samples 

MF-1834-D (Theobald and Barton, 

1987b) 

Geochemical distribution and abundance of lead, molybdenum, 

bismuth, and tungsten in geochemical samples 

MF-1834-E (Theobald and Barton, 1988) Geochemical distribution and abundance of zinc, silver, antimony, 

manganese, barium, and strontium in geochemical samples 

I-2139 (Klein and Kucks, 1990) 

Open-File Report (Gray and others, 1987) 

Gravity and aeromagnetic anomalies 

Geology 

87-217 

DESCRIPTION OF COMPONENT MAPS AND 

STUDIES OF THE AJO AND LUKEVILLE 

QUADRANGLES FOLIO 

Geology 

The bedrock geology of the Ajo and Lukeville 1 o by 

2° quadrangles can be divided into four broad terranes. 

The first, in the western part of the study area, consists 

of Proterozoic gneiss intruded by Late Cretaceous and 

(or) early Tertiary granite. The gneissic rocks have had 

a geologic history unlike similar-age rocks to the east, 

from which they are separated by a possible major tectonic break in the Growler and San Cristobal Valleys. 

This second terrane consists of Proterozoic, Paleozoic, 

and Mesozoic rocks and has a geologic history like that 

of much of southern and southeastern Arizona. This terrane has been referred to previously as the northern 

Papago terrane (Haxel and others, 1984 ). The third terrane, or southern Papago terrane of Haxel and others 

(1984 ), underlies the southeast one-third of the quadrangles and constitutes a region where Proterozoic and 

Paleozoic rocks are sparse to absent and, where exposed, 

are demonstrably allochthonous. The geology of this 

terrane is characterized by Late Cretaceous and (or) 

early Tertiary compressional deformation and early Tertiary plutonism. Rocks of the Jurassic magmatic arc are 

the oldest autochthonous rocks in this terrane. The 

boundary between the northern and southern Papago terranes is arcuate and gradational and passes through the 

southern Growler Mountains, the northern Gunsight Hills, 

and the Cimarron-Sheridan Mountains (fig. 3). The fourth 

terrane consists of Oligocene and younger volcanic rocks 

that unconformably overlie the early Tertiary and older 

metamorphic and plutonic rocks. A generalized geologic 

map of the quadrangles is shown in figure 4. 

Proterozoic Rocks 

The western Proterozoic terrane consists of gneissic 

rocks that crop out in the ranges to the west of the 

Growler Valley and the Agua Dulce Mountains. The 

gneisses can be subdivided into three facies. The most 

widespread facies consists of biotite-bearing 

quartzofeldspathic gneiss, orthogneiss, and amphibolite. 

These rocks are separated from the second gneiss facies 

by Tertiary detachment faults on the eastern side of the 

Mohawk Mountains (Mueller and others, 1982). The 

second gneiss facies of the western terrane consists of 

Early Proterozoic orthogneiss that is overlain by quartzite, quartz calcsilicate, and quartzofeldspathic 

metasedimentary rocks (L.T. Silver, oral commun., 

1982). A sillimanite orthogneiss, interpreted to be a 

metamorphosed paleosol, separates the orthogneiss from 

the metasedimentary rocks. The second facies is found 

only on the east side of the Mohawk Mountains. The 

metamorphic grade and uranium-lead isotopic ages of 

the two gneiss facies are different from those of Proterozoic rocks in the northeast one-third of the Ajo quadrangle (L.T. Silver, oral commun., 1982). Postkinematic 

K-feldspar megacryst granites intrude the first gneiss facies in the southern Sierra Pinta Mountains and northern 

Agua Dulce Mountains. The third gneiss facies is found 

near Buck Peak in the northern Cabeza Prieta Mountains. These rocks contain a significant component of 

calcsilicate gneiss in addition to biotite and 

quartzofeldspathic gneiss. The age of this facies is uncertain and is constrained only as older than Late Cretaceous. 

Description of Component Maps and Studies of the Ajo and Lukeville Quadrangles Folio 5 
Proterozoic rocks in the northeast one-third of the 

Ajo quadrangle have had a geologic history similar to 

that of Proterozoic rocks elsewhere in southern Arizona. 

They consist of muscovite-biotite or muscovite-quartz 

feldspar schist and gneiss derived from supracrustal 

lithologies and are the oldest rocks in this terrane. These 

metamorphic rocks consist primarily of the unit known rec 

gionally as the Pinal Schist, but they also include a part of 

the Cardigan gneiss (Gilluly, 1946) near Ajo. 

Several generations of Proterozoic granitoid rocks 

have intruded the supracrustal rocks. The older 

granitoids are deformed and crop out in the Maricopa 

and Little Ajo Mountains. Uranium-lead ages for these 

rocks indicate late Early Proterozoic emplacement ages 

(L.T. Silver, oral commun., 1982; J.L. Wooden and J.S. 

Stacey, oral commun., 1986). In several ranges, Middle 

Proterozoic K-feldspar megacryst granites intruded the 

deformed rocks. These granitoids are undeformed ana 

0 5 10 15 MILES 

0 10 20 30 KILOMETERS 

are generally referred to as anorogenic granites (Silver, 

1978). Limited uranium-lead and K-Ar dating indicates 

that these rocks have ages of about I ,400 Ma (Balla, 

1972). Included in this suite are the Oracle Granite of 

Peterson (1938) and the Chico Shunie Quartz Monzonite 

(Gilluly, 1946). In the northern Vekol Mountains and at 

Table Top Mountain, sedimentary rocks of the Middle 

Proterozoic Apache Group (Carpenter, 1947; Shride, 

1967) unconformably overlie the older granitoids and 

gneissic rocks (Dockter and Keith, 1978; Peterson and 

others, 1987). The youngest Proterozoic rock in this terrane is diabase that occurs as sills and dikes. The diabase is considered correlative with the 1,100 Ma diabase 

that intruded the Apache Group in central and southeastern Arizona (Shride, 1967; Silver, 1978). 

The boundary between the two Proterozoic terranes 

lies in the Growler and San Cristobal Valleys and corresponds approximately to the inferred trace of the 

112' 

Gila Bend o 

Figure 3. Location of approximate boundary (heavy line) between northern and southern Papago terranes and physiography of Ajo 

and Lukeville 1' by 2" quadrangles. Shaded areas indicate highlands. 

& The Conterminous United States Mineral Assessment Program: Ajo and lukeville 1' by 2' Quadrangles, Arizona 
Mojave-Sonora megashear of Silver and Anderson 

(1974, 1983; Anderson and Silver, 1979), a Late Jurassic 

sinistral strike-slip fault with as much as 800 km of displacement. If the boundary is the megashear, the two 

terranes could have been tectonically juxtaposed in the 

Mesozoic. However, Shafiqullah and others (1980) suggest that the juxtaposition of the Proterozoic terranes, 

which forms a part of the basis for the megashear, occurred during the Proterozoic. 

Paleozoic Rocks 

During the Paleozoic, at least the northeastern part 

of the area was part of a stable cratonic platform that 

was buried beneath about 2 km of carbonate and clastic 

sedimentary rocks (Wilson, 1962; Chaffee, 1974; Peirce, 

1976). Stratigraphic sections that contain many of the 

Paleozoic formations known in southwestern Arizona 

crop out in the Vekol Mountains and near Lime Hill in 

the southeasternmost Growler Mountains. Smaller outcrops are scattered between these ranges, and many of 

them occur as roof pendants in Mesozoic granitoids. 

Rocks of Paleozoic age include the Cambrian Bolsa 

Quartzite, the Cambrian Abrigo Formation, the Devonian 

Martin Formation, and the Mississippian Escabrosa 

Limestone. The Pennsylvanian and Permian Naco 

Group, the uppermost unit of the southern Arizona 

cratonal sequence, does not outcrop within the quadrangles because it was removed by erosion prior to the 

deposition of Mesozoic volcanic and sedimentary rocks 

(Titley, 1976). 

Mesozoic Rocks 

The oldest Mesozoic rocks in the area are Jurassic in 

age and once were part of a through-going continentalmargin magmatic arc. Cessation of arc magmatism was 

followed by uplift and erosion of the arc in the Cretaceous; magmatism during this time was sparse. In the 

Late Cretaceous, magmatism resumed as the arc swept 

eastward across southern Arizona. Near the end of the 

Cretaceous and continuing into the early Cenozoic, compressional deformation and intrusion of postkinematic, 

crustally derived plutons affected the rocks of the southem Papago terrane. 

Jurassic Rocks 

Most of the volcanic activity of the Jurassic magmatic arc was centered around dominantly explosive silicic and locally intermediate volcanic centers (Tosdal 

and others, 1989). Thick sections of locally derived 

clastic rocks filled intra-arc basins (Haxel and others, 

1980). The silicic volcanic and associated sedimentary 

rocks of the intra-arc basins are known as the Lower and 

Middle Jurassic Fresnal Canyon sequence of Tosdal and 

others (1989), which includes rocks of the La Abra Plain 

in Organ Pipe Cactus National Monument. The principal rock type is rhyolitic metaporphyry that has conspicuous quartz phenocrysts and, locally, a relict 

volcanic texture. Quartzite, feldspathic phyllite, and 

semischist with subordinate arenaceous marble are minor 

supracrustal lithologies. Metagranite porphyry associated with quartz porphyry metarhyolite intrusive rocks of 

the intra-arc basins in the Quitobaquito Hills has a uranium-lead age of 175 Ma (Anderson and RoldanQuintana, 1979). 

In the Kupk Hills in the southeastern part of the 

area, a Middle Jurassic(?) granodiorite orthogneiss crops 

out. This pluton is lithologically correlated with the 

Middle Jurassic (informal) Kitt Peak-Trigo Peaks 

superunit (Tosdal and others, 1989) and is the only 

known exposure of these areally widespread plutonic 

rocks in the Ajo and Lukeville quadrangles. Haxel and 

others ( 1984) previously considered the granodiorite 

orthogneiss to be of Late Cretaceous or early Tertiary 

age. The regional significance of this isolated exposure 

is unknown, but its correlative granitoids are part of a 

compositionally expanded superunit of batholithic proportions that intruded the upper crust in Middle and Late 

Jurassic time. 

The youngest supracrustal rocks of the magmatic arc 

are known regionally as the Middle(?) and Upper Jurassic Artesa sequence of Tosdal and others ( 1989). These 

rocks crop out in the Agua Dulce Mountains and the 

Quijotoa Mountains; in the latter range they were locally 

assigned to the Tertiary by Rytuba and others (1978). 

Volcanic rocks in the magmatic arc consist of approximately subequal amounts of trachyitic and rhyolitic 

rocks. Immature clastic rocks, many of which are reworked volcanic rocks, are also found. Late Jurassic 

subvolcanic granitoids called the (informal) Ko Vaya 

superunit (Tosdal and others, 1989) intrude the 

supracrustal rocks in the Quijotoa and Agua Dulce 

Mountains (Rytuba and others, 1978; Tosdal and others, 

1989). Other outcrops of these granitoids are in the La 

Lesna Mountains, in the hills south of Cimarron Peak, 

and in the Puerto Blanco Mountains. In the latter range, 

the granites have intruded the silicic volcanic rocks of 

the Fresnal Canyon sequence. Detailed mapping in 

ranges to the east has shown the volcanic rocks of the 

Artesa sequence and the granitoids of the Ko Vaya 

superunit to be essentially comagmatic units that formed 

volcano-plutonic centers (Briskey and others, 1978; 

Haxel, 1978). 

Upper Jurassic(?) and Cretaceous Rocks 

Locally derived Upper Jurassic(?) and Cretaceous 

immature clastic rocks overlie Jurassic and older rocks 

Description of Component Maps and Studies of the Ajo and Lukeville Quadrangles Folio 7 
= 

-4 

=- I'D 

n 

;-

= = 

3 

:r 

c = 

Ill 

c: 

= 

~· Q. 

VI 

Ill 

~ 

~ :;· 

I'D 

i. 

> Ill 

~ Ill 

Ill 

~ a 

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a 

OQ 

.. 

"' ?. 

> 

=· "' = Q. 

rc 

rr 

~ 

ii" 

... 0 

c:r 

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c 

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.. 

OQ "' = 

ii" 

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= = 

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114° 113° 

33° ---,=g 

Qa 

Tcs 

0 10 20 30 MILES 

I I I I I I I I 

0 10 20 30 40 50 KILOMETERS 

• 

Gila Bend 

Qa 

Tc~ 

Trr -\,\/ (!9 

.,a 

Tb 

Qa 

\~5~ \~~ ~ '?~ 

Tb '-t.. ~\ - \o~ ~TKgh 

Ta Trr 

Figure 4. Generalized geologic map of Ajo and Lukeville 1 o by 2° quadrangles, (modified from Gray and others, 1987). 

112° 
and include unnamed strata in the Vekol Mountains 

(Hayes, 1970), Sheridan Mountains, and Cimarron 

Mountains; thermally metamorphosed rocks in the 

southeasternmost Growler Mountains (Gray and others, 

1987); and scattered outcrops in the low hills northwest 

of the Bates Mountains. Consisting of various combina-

~ .9 

tions of arkosic and arenitic sandstone, conglomerate, 

'0 '0 u 0 and siltstone, and rare andesitic to rhyolitic volcanic and c c ·a as as "(ij N hypabyssal rocks, these Upper Jurassic(?) and Creta- ~ en en 0 :::l ~ Q) ceous sedimentary rocks record the unroofing and ero- as 0 :e Q) 3 

:::l Cii ~ Q) 0 ~ as sion of the Jurassic magmatic arc (Haxel and others, 

!:::. s u en Q) u :e 1980; Tosdal and others, 1989). The conglomerate-rich Q) "(ij u .ll! en "5 Q) en ~ en 0 as 1- '0 ~ "(ij e .c N ch outcrops in the northeastern part of the Ajo quadrangle g en as e :::l ~ ~ .9: en ~ =o Q) '0 ·c: have been tentatively correlated with the Lower Creta- .ll! :::l as e Q) 0 0 0 as e 3 "E '0 Cii 0, Q) c a.. Q) Q) en ceous Glance Conglomerate that forms the basal forma- en ·e :§" 0 '0 :::l E ~ 0 en ·c: .ll! 0 ·s; c tion of the Bisbee Group (Hayes, 1970). Q) 0 0 =o (ii as Q) e -oO ·a =o 0 -~ 0 0 Q) C N w N c 0 

en 0 as ~ en as e e :::l ~ chen > (i) 0 enG> '0 

c .! ci Q) -~ :::l '0 ~ ·c: c ~e as .c. (5o c- Q) ·e e ::c 3: Late Mesozoic and Early Cenozoic Rocks >. ea.. Q) ·- Q) as.2 en en =o a.. 0 .co ~~ .ll! '0 ~~ ~ en '0 

'as 0 '0 c '0 Q) Q)- s~ c as'O In the Late Cretaceous, magmatism in south-central ~ (ii 'OQ) e '0 g as as --o c c ... c :::l 0 lii~ ~ as 0 Arizona resumed as the continental-margin magmatic arc Q)(.) Q)~ 0 0 ·c: .! en t5 l ::0 E :;:::; :;:::; ·c: ·c: as E Ui ·c: en as c =o 0 =o ::c "Q) "E :; swept eastward in response to events at the plate margin 

en 0 Q) ~ ~ 0 Q) ~ 0 c: 0 as 1- ::I: CJ) (!) (!) > CJ) (!) CJ) (!) (.) u. (Coney and Reynolds, 1977). In several ranges in the 

z northern Papago terrane (fig. 3), andesitic to rhyolitic ::::» .c. > en volcanic rocks were erupted. The best known of these is a. C) en C) en >- C) C) 

cC ~ ;;2 ~ C) > If X en 1- the Concentrator Volcanics (Gilluly, 1946) near Ajo. :E 1- ~ ~ ~ >- X a. 

u.. Compositionally expanded metaluminous granitoids in0 truded the upper crust and, locally, the Late Cretaceous 

z 

0 volcanic rocks. The granitoids include the New Cornelia 

j::: en pluton of Gilluly (1946) (see also Cox and Ohta, 1984; a. C) 

a: '0 :::l Hag strum and others, 1987), the granodiorite of 

0 ~ c. 0 '0 '0 "(ij c: Gunsight Hills (Tosdal and others, 1986), granite of en 0 c: 0 as w as ~ .ll! 

~ ·c: Q (ii ~ Bandeja Well in the southeasternmost Growler Moun- as ui as as as 0 ~ ~ :e Q) c: :e tains (Gray and others, 1985), and unnamed granite bod-

(i) 0 as Q) ~ Q) > :e !:::. as a; Q) ui ~ !:::. ies in the Cimarron Mountains (Briskey and others, ~ 0 :::l a; Q) 3: Q) 0 as .! !:::. as Q. 0 0 1978) and the Vekol Mountains. Porphyry copper de- :e c: 0 :e ·c: as ;;;:: 0 

.s~ en Q) Ui c Q) ~ c ~ posits at Ajo and in the Vekol Mountains are associated .! !:::. ·e !:::. "(ij a.. as ·a; ·c::; '0 ~ C) 

"E c: 0 en with these granitoids. Uranium-lead ages and K-Ar mini- -g:e as .! as as a. :::l '0 en '0 

c- '0 ~ Q) as~ 0 '0 "(ij :e as~ ".§ 0 mum ages for these bodies range between about 68 and 64 '0 :E c Q) 0 Q) - as ·c: :0 .S-o ~ "'0 Q) c: !:::. Q)·- as ~ c -t:: ~ Ma, confirming the Late Cretaceous ages for the granitoids :2 asc Q) as as ·e ~~ '0 a:: as 0 i en C) c (ij as :e ~ .ll! as- -~ E (McDowell, 1971; J.E. Wright in Tosdal, 1979; Tosdal and :e '0 0 Q)- '0 ·c::; Q) E Q) Q) Q)en c :gc:u as Q) Cii as_ c: e "'0 !:::. as .2c -:::l 

~ a; others, 1986; Hagstrom and others, 1987). !:::. c: ·- 0 ·.o: E "'0~ en 0 t»O Q) c: Q) '0 C:Q) m g__~ .! as .! ·c: c- Q)- ::0 ~~ -c .& .c ~ c as en West of Ajo, several granitoid plutons have intruded cnas 0 .Ct:: ·::; as c (]) 

as :; '0 0 --o C)- :::l ... Q) en Q) :::1 - c: 0 asG> 

E oQ. .! ~!:::. c E 0 G> as 0 ... c the western Proterozoic terrane. Most of these plutons ...J 

-~ as .c. :::l - "(ij - 0 > -~en 

~ .Eu ·.;:::; en en c: ·s; Cii Q) 0 are petrologically different from the Late Cretaceous 32 0 Cii c, Cii Q) b 0 ..2 en '0 >. ::c >. en c: en '0 s u as c .c. .c. as 0 as c <( m ~ plutons of the northern Papago terrane in that they are <( a: (.) a: m (.) m <( m I 

-o:i compositionally restricted to rocks of monzogranitic and ~ granitic compositions; parts of the largest pluton contain, 0, ... .c as > ::II as 1- as ... en a; ~ ~ in addition to biotitite, the accessory minerals muscovite .= 0 .= .c 0 .c C) 0 0 1- 1- 1- 1- 1- 1- 1- 1- i.i: 

and garnet. The largest pluton outcrops in some five 

ranges from the Granite Mountains westward and was 

informally called the "Gunnery Range granite" by 

Shaffiqullah and others (1980). Other plutons compose 

much of the Copper Mountains and the northernmost 

Mohawk Mountains; a small part of a much larger 

Description of Component Maps and Studies of the Ajo and Lukeville Quadrangles Folio 9 
granodiorite body south of the international boundary in 

northern Sonora crops out in the Tule Mountains. The 

granodiorite in the Tule Mountains is dated as Late Cretaceous (Anderson and Roldan-Quintana, 1979; R.M. 

Tosdal and R.J. Miller, 1982-86, unpub. data). Potassium-argon biotite and muscovite minimum ages from 

the other granitoids are early Tertiary and range from 

about 53 Ma on the west to about 40 Ma in the Granite 

Mountains (Shafiqullah and others, 1980; Tosdal and 

Miller, 1988). Arnold (1986) reported 53.40 ± 0.30 and 

53.70 ± 0.20 Rb-Sr whole-rock isochron minimum ages 

for the "Gunnery Range granite." Late Cretaceous and 

(or) early Tertiary ages are presently tentatively assigned 

to these granitoids. 

Mesozoic and early Tertiary orogenesis in the southern Papago terrane has involved a complex interplay between thrust faulting, regional metamorphism, and 

plutonism (Haxel and others, 1984). In the Quitobaquito 

Hills and adjacent Puerto Blanco Mountains, the Jurassic 

rocks are deformed in an imbricate stack of syn-metamorphic thrust faults. In the Gunsight Hills, a now-vertical ductile shear zone cuts one of the Late Cretaceous 

granitoids (Tosdal and others, 1986). The core of the 

Sierra Blanca is a window into the regionally 

subhorizontal Baboquivari-Window Mountain Well 

thrust of Haxel and others (1984). The Mesozoic rocks 

in the Copperosity Hills at the north end of the Cimarron 

Mountains are also folded and cut by south-dipping 

thrust faults (Dockter and Keith, 1978). Metamorphism 

in these ranges took place dominantly under greenschistfacies conditions, but mineral assemblages indicative of 

the lower amphibolite facies are found locally (Haxel 

and others, 1984; Tosdal and others, 1986; Reynolds and 

others, 1988). Late- to postkinematic peraluminous 

granites intruded the shortened terrane. In the quadrangles, the granite of Senita Basin exposed south of the 

Puerto Blanco Mountains and the granite of Sierra 

Blanca in the Sierra Blanca represent this suite of plutons. These garnet-bearing two-mica granites are 

crustally derived and are inferred to be of early Tertiary 

age based on correlation with similar granites of known 

age (Keith and others, 1980; Wright and Haxel, 1982; 

Farmer and DePaolo, 1983). 

Cenozoic Rocks 

Paleogene Rocks 

After the cessation of magmatism and compressional 

deformation, the rocks of the Ajo and Lukeville quadrangles underwent a period of tectonic and magmatic 

quiescence. In general, K-Ar mica ages from west to 

east across the quadrangles become progressively 

younger; this age pattern does not apply to the northern 

Papago terrane, where the high-level granitoids cooled 

soon after they were intruded. Biotite and white mica 

minimum ages in the Cabeza Prieta Mountains are about 

53 to 50 Ma (Shafiqullah and others, 1980; Tosdal and 

Miller, 1988) and decrease to between 40 and 30 Ma 

and, locally, between 30 and 20 Main the eastern part of 

the quadrangles. The general pattern of minimum ages 

decreasing from west to east is interpreted to result from 

the uplift and cooling of the terrane in the early Cenozoic. The pattern of K-Ar mica ages across the Gunsight 

Hills is a good example of the regional pattern. There, a 

Late Cretaceous and (or) earliest Tertiary (pre-59 Ma on 

hornblende) ductile shear zone has been tilted from an 

inferred originally subhorizontal attitude to its current 

near-vertical attitude in the latest Oligocene. From high 

structural levels to low levels, as inferred by the metamorphic mineral assemblages (Tosdal and others, 1986), 

the minimum ages of igneous and metamorphic biotite 

and vein alteration white mica decrease from between 47 

and 40 Ma to 32 Ma (Shafiqullah and others, 1980; 

Tosdal and Miller, 1988). Latest Oligocene and early 

Miocene large-scale crustal extension, observed in the 

easternmost part of the quadrangles in the Sierra Blanca 

(Davis, 1980), disrupted and locally overprinted the 

cooling pattern. 

Tertiary Volcanic Rocks 

Tertiary volcanic rocks within the Ajo and Lukeville 

1 o by 2 o quadrangles form a volcanic field composed of 

flows that comprise the entire compositional range from 

basalt to rhyolite. Parts of this field have been informally called the Ajo volcanic field. (May and others, 

1981; Gray and others, 1983; Gray and Miller, 1984a, b; 

Gray and others, 1985; Tosdal and others, 1986). Tertiary volcanic rocks crop out over approximately 5,000 

km2, extending from the Mexican border on the south to 

just north of U.S. Interstate Highway 8 on the north, and 

from the Growler and Aguila Mountains on the west to 

the Vekol and Quijotoa Valleys on the east. Scattered 

Tertiary volcanic rocks in the Vekol Mountains and in 

the Palomas Mountains (Dockter and Keith, 1978; 

Rytuba and others, 1978; Briskey and others, 1978) are 

probably older than, but not related to, the Miocene 

rocks in the central part of the study area. 

Conventional K-Ar geochronology has been used 

extensively in the Ajo and Lukeville quadrangles to establish the age of Tertiary volcanism and broadly contemporaneous tectonic activity. Sixty new K-Ar ages for 

volcanic rocks were produced during this study. Age 

data available prior to the inception of this study have 

been compiled by Tosdal ( 1979). 

The Tertiary volcanic rocks in the central part of the 

study area are divided into three sequences that are each 

separated by angular unconformities: (1) the oldest sequence, of late Oligocene and early Miocene age, consists of red fanglomerate and coarse arkosic sandstone 

10 The Conterminous United States Mineral Assessment Program: Ajo and Lukeville 1 o by r Quadrangles, Arizona 
intercalated with andesite, rhyolite, rhyodacite, and local 

pyroclastic rocks; (2) the complex middle sequence consists of early and middle Miocene basalt, latite, silicic 

flows, and associated pyroclastic rocks; and (3) the 

youngest sequence, of middle Miocene age, is composed 

of basaltic andesite and andesite (Gray and Miller, 1984a, 

b). The angular discordance between the middle and 

youngest sequence is typically minor (less than 10°-15°). 

The oldest sequence is exposed in scattered areas 

along the north and west edges of the field in the northwestern Sauceda, Little Ajo, and Growler Mountains. It 

is characterized by steeply tilted volcanic rocks intercalated with coarse clastic sedimentary strata. Initiation of 

volcanism coincided with local uplift and unroofing of 

crystalline basement rocks. In the Ajo area (Gilluly, 

1946), the Growler Mountains (Gray and others, 1983), 

and the northwestern Sauceda Mountains, massively bedded coarse fanglomerate and coarse arkosic pebbly sandstone were locally derived from Proterozoic granite and 

gneiss. The coarse fanglomerate grades upward into 

coarse arkosic sandstone. Interbedded flows increase in 

abundance upward. An age of 23.8 ± 0.8 Ma was obtained from one of these flows near North Ajo Peak in 

the Little Ajo Mountains. Because this flow is near the 

top of the sequence, it provides a minimum age for the 

accumulation of the fanglomerates. A tuff lying 

nonconformably above the tilted andesite-fanglomerate 

sequence yielded an age of 22.0 ± 0.7 Ma (Gray and 

Miller, 1984a). 

The middle sequence, the most widespread of the 

three, forms a heterogeneous assemblage of basaltic, 

andesitic, and rhyolitic rocks. The oldest rocks in the 

sequence are rhyolitic to rhyodacitic flows and tuffs. Silicic volcanism migrated southward from the Sand Tank 

Mountains into the Sikort Chuapo Mountains and the 

Ajo Range, eventually resulting in the eruption of rhyolitic flows and tuffs in the Ajo Range at approximately 

17-16 Ma (R.M. Tosdal, unpub. data; R.J. Miller, 

unpub. data; Jones, 1974; May and others, 1981; Gray 

and others, 1985). Contemporaneous with silicic volcanism at approximately 21 Ma, basalt and basaltic andesite 

were erupted in the region extending from the northern 

Sauceda Mountains to the southern Sand Tank Mountains. The most distinctive rock type of the middle sequence is the coarsely porphyritic Childs Latite in the 

Ajo area (Gilluly, 1946; Gray and others, 1985). 

Basaltic andesite was erupted between 16 and 14 

Ma. The major source for flows in the western part of 

the Ajo volcanic field was Batamote Mountain, a dissected shield volcano. Minor vents and oxidized cinder 

cones are present in the Cipriano Hills and the Growler 

and Bates Mountains farther north. 

The Sentinel and Pinacate basalt flows, adjacent to 

the northern and southwestern parts of the volcanic field, 

respectively, postdate most Basin and Range style block 

faulting. These basalts range in age from 5 to 1 Ma and 

are not considered part of the Tertiary volcanic field 

(Eberly and Stanley, 1978, Nos. 1-6; Gutmann, 1976). 

Geochemical Studies 

Geochemical maps included in the folio of the Ajo 

and Lukeville 1 o by 2° quadrangles display the distribution and abundance of selected elements and delineate 

areas with anomalous concentrations of these elements. 

The reconnaissance geochemical sampling was done 

during 1979 and 1980. The area covered includes all of 

the Ajo I o by 2° quadrangle in the U.S., except the 

Tohono O'odham Indian Reservation, and includes part 

of the Lukeville 1 o by 2° quadrangle, west of the Indian 

Reservation and north of the Mexican border. A total of 

971 sample localities yielded 971 samples of stream 

sediment finer than 30 mesh and 952 samples of the 

nonmagnetic fraction of heavy-mineral concentrates from 

stream sediments. Sample localities were selected on 

first-order drainage channels, generally reflecting a 

drainage basin of less than 1 km2. These localities represent the mountain ranges and their immediate flanks 

and disregard the 80 percent of the quadrangles underlain by a thick fill of young sediments in the basins. 

The average sampling density for the mountain ranges 

was one sample locality per 3.1 km2. All samples were 

analyzed by optical emission spectroscopy for 31 elements (Ag, As, Au, B, Ba, Be, Bi, Ca, Cd, Co, Cr, Cu, 

Fe, La, Mg, Mn, Mo, Nb, Ni, Pb, Sb, Sc, Sn, Sr, Th, Ti, 

V, W, Y, Zn, and Zr) using a six-step semiquantitative 

emission spectrographic method (Grimes and 

Marranzino, 1968). 

Geochemical data sets were merged and manipulated 

by computers located at the U.S. Geological Survey's 

computer center in Denver, Colorado. Collection, preparation, and analytical procedures are presented in Barton and 

others (1982); initial interpretations and statistical parameters for resource evaluation of geochemical data are given 

in Theobald and Barton (1983). Parts of the data have 

been used to produce the geochemical distribution and 

abundance plots incorporated into the geochemical maps. 

The elements shown on these maps were selected for their 

pertinence to the delineation of areas favorable for the occurrence of metalliferous mineral deposits. 

Analyses of the distribution of eleven of these elements-considered singularly, in element groups, or in 

comparison with the other elements-are used to define 

16 anomalous areas favorable for the occurrence of metalliferous deposits. The geochemical characteristics of 

each of these anomalous areas are summarized in table 2. 

Copper is considered both as a single element and as part 

of a suite of elements common in rock-forming minerals 

(Theobald and Barton, 1983, 1987a). Lead, molybdenum, 

Description of Component Maps and Studies of the Ajo and Lukeville Quadrangles Folio 11 
Table 2. Geochemically anomalous areas in parts of the Ajo and 

Lukeville 1 o by--2° quadrangles 

[Anomalous elements are listed by their chemical symbol; Ba+Sr, anomalous joint score 

for the two elements in heavy-mineral concentrates; -Sr, anomalously low strontium 

content in stream sediment] 

Anomalous areas 

1. 

2. 

3. 

4. 

Highway 84 ------------

Booth Hills -------------

Maricopa ---------------

Painted Rock -----------

5. Sauceda -----------------

6. Batamote ---------------

7. A jo ----------------------

8. Ajo Range--------------

9. Growler Pass-----------

10. Sonoyta -----------------

11. La Abra Plain ----------

12. Agua Dulce ------------

13. Mohawk ----------------

14. Mohawk Pass ----------

15. Copper Mountains ----

16. Cabeza Prieta ----------

Anomalous elements 

Pb, W, Bi, Mn, -Sr 

Pb,Mo, W,Bi 

Pb, W,Bi,Mn 

Pb, Mo, Mn, Ba+Sr 

Cu, Sb, Mn, Ba+Sr 

Cu, Sb, Mn, Ba+Sr 

Cu 

Cu, Pb, Mo, W, Bi, Ba, -Sr 

Cu, Pb, Mo, W, Bi, Sb, -Sr 

Cu, Pb, Mo, W, Ag, Sb, Zn, -Sr 

Pb,Mo, W 

Pb,Mo, W,Bi 

Pb,Mo, W,Bi 

Pb, Mo, W, Bi, Ba+Sr 

Cu 

Ag, Ba+Sr 

tungsten, and bismuth are mutually sympathetic, and 

these four elements are interpreted singularly and as a 

group (Theobald and Barton, 1983, 1987b ). Silver, antimony, and zinc were only occasionally detected, and 

their presence in measurable amounts is considered 

anomalous (Theobald and Barton, 1983, 1988). 

Manganese, barium, and strontium provide both direct and indirect evidence of mineral potential. Manganese oxides, barite, and celestite have been produced 

from occurrences in the study area. These same minerals are often associated with the other metallic elements 

and can provide a larger geochemical halo than is seen 

for the metallic elements. Manganese oxides are the 

host for a variety of elements in the supergene environment; these elements, when hosted in this way, can be 

indicative of remobilized metal. This seems to be the 

situation for anomalies 5, 6, and 8. Strontium is often 

depleted in hydrothermally altered rocks surrounding a 

mineral deposit; thus, although high barium and (or) 

strontium in heavy-mineral concentrates indicates the 

presence of barite or celestite, abnormally low strontium 

in the stream sediments may also indicate areas of hydrothermal alteration. 

The 16 anomalous areas all contain several anomalous sites. Most are complex, exhibiting anomalous 

characteristics for a variety of elements. The scale of 

the regional reconnaissance sampling is such that small, 

but significant, anomalies could easily be reflected by 

only a single site or even be missed. Any detailed 

evaluation of the area should consider individual anomalous sites as well as these anomalous areas. Furthermore, the scale of the reconnaissance leads to regional 

simplification of the anomalous patterns. Anomaly 13 

(the Mohawk anomaly) consists in detail of three or four 

discrete anomalies that are merged in the regional synthesis (Eppinger and others, 1988). Similarly, anomalies 

10 and 11 (the Sonoyta and La Abra Plain anomalies) 

overlap, yielding a complex assemblage of elements that 

is difficult to resolve at the regional scale. 

Some of the anomalous areas reflect exposed mineralization; anomaly 7, at Ajo, is an obvious example. 

Other anomalous areas most likely reflect chemical leakage from concealed metal sources. Huston (Huston and 

Theobald, 1990) has demonstrated that anomaly 6, in the 

Batamote Mountains, is derived from metal incorporated 

in secondary iron and manganese oxides coating fractures adjacent to young faults cutting the Batamote 

andesite. Thus, the presence of an older metal source 

concealed beneath the andesite is a distinct possibility. 

Similar relations may be inferred for anomaly 5, in the 

Sauceda Mountains, where the surface chemical characteristics may reflect mineralization concealed at deeper 

levels of the rhyolitic volcanic sequence; for anomaly 8, 

in the Ajo Range, where the surface chemistry may reflect 

leakage along faults in the volcanic rocks from a concealed metal source beneath these rocks; and for anomaly 

13, in the Mohawk Mountains, where at least one of the 

anomalies found by more detailed examination seems to 

reflect mineralization peripheral to a primary source concealed beneath the pediment gravels to the east of the 

Mohawk Mountains (Eppinger and others, 1988). 

Geophysical Studies 

Geophysical data acquired for the mineral resource assessment of the Ajo and Lukeville 1 o by 2° quadrangles 

include quadrangle-wide gravity and aeromagnetic surveys 

and rock sampling to determine densities and magnetizations of rocks encountered in the survey area (Klein and 

Johnson, 1983). The latter provides information that aids 

in interpreting the origins of the anomalies. 

Regional aeromagnetic and gravity maps in the quadrangles form the fundamental geophysical data. These 

maps are supplemented by more detailed aeromagnetic 

studies in the Ajo, Cimarron Mountains, Sauceda Mountains, and Crater Range areas, and by geoelectric studies in 

the Mohawk Mountains and Table Top Mountain areas. 

Synthesis of these data relates the geophysics to the geology and mineralization of the quadrangles. The locations 

of the detailed studies and of the regional anomalies mentioned below are shown in figure 5. 

Gravity Maps 

The regional gravity data consist of two maps: a 

complete Bouguer gravity anomaly map and a residual 

Bouguer gravity anomaly map. These maps are compiled 

12 The Conterminous United States Mineral Assessment Program: Ajo and Lukeville 1 o by r Quadrangles, Arizona 
0 

"' "' Q 

-s· 

6' 

= 

s. 

("\ 

Q 

3 

~ 

= 

a "' 

~ .. 

"C 

.. "' 

= 

~ 

~ c 

~ 

· 

s. 

:r 

> "' 

'0' 

.. 

= 

~ 

,.... 

c 

[ 

ii' 

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c 

~ 

iil 

CJQ = 

ii' 

.., "' 

~ 

6' 

.... 

"' 

114° ..------------., 

0 5 

-...\~~":! 

+'"'t, 

10 15 MILES 

0 10 20 30 KILOMETERS 

EXPLANATION 

c~cD 

<;? 

1 1 I I 1.,. 

II I I I" 

Areas of outcrop 

Areas of detailed aeromagnetic study 

(E) indicates detailed geoelectric study 

Selected gravity highs or lows (ticks on side of lower gravity) 

Selected aeromagnetic highs 

Regional aeromagnetic high 

112° 

Gila Bendo 

t 

Figure 5. Areas of significant regional aeromagnetic and gravity features and locations of selected studies in Ajo and Lukeville 1 o by 2° quadrangles. 
from 4,157 gravity observations. Complete Bouguer 

anomalies contain information on the deep crust and 

mantle, which is not of critical importance to mineral investigations, whereas residual Bouguer anomalies are filtered to emphasize information in the mid- and 

upper-crust regions, which are important to the origin 

and mining of mineral resources. 

The residual gravity anomaly map reflects lateral 

variations in the density of the crust from the surface to 

depths of a few tens of kilometers. Information on buried geological structures is the primary contribution of 

gravity interpretation. Mineral deposits are commonly 

associated with faults and intrusions that have a density 

contrast with their surrounding rocks; thus, gravity 

anomalies provide a means either to identify buried environments favorable to mineralization or to estimate the 

subsurface extent of mapped geologic features. Examples of gravity anomalies that are likely caused by 

crustal intrusion are the lows associated with the 

Batamote Mountains, the Sauceda Mountains, and the 

Cabeza Prieta Mountains (fig. 5). In these cases, plutonic intrusions of siliceous composition and (or) crustal 

brecciation associated with intrusion are probable causes 

of the low densities reflected in the gravity data. 

A further result from the study of gravity maps is 

the distribution of deep basins, as opposed to areas that 

may have bedrock at relatively shallow depth and thus 

are amenable to mining. The Quijotoa Valley, particularly its more southern reaches, is an area where the lack 

of an intense gravity low suggests that a deep basin, 

which is typical in valleys of the southwest, either has 

not developed or has been modified by subsequent geologic events. The deepest basins are apparently restricted to the west half of the quadrangles, as indicated 

by the major gravity lows over the Growler, San 

Cristobal, and Mohawk Valleys. A few moderate gravity lows exist over valleys to the east, but the only major 

basin inferred east of Ajo is on the east boundary of the 

quadrangles beneath the Santa Rosa Valley. The depths 

of the basins in the Ajo and Lukeville 1 o by 2° quadrangles have been previously studied by Oppenheimer 

and Sumner (1980). 

Aeromagnetic Map 

The aeromagnetic map was compiled from four surveys flown at 1.2 km above sea level along east-west 

lines at 1.6-km intervals. The map presents anomalies 

that reflect the lateral variations in the magnetic structure of the crust, which are due to the varying content of 

magnetized minerals in different rock types. These data 

are used in identifying geologic contrasts from the surface to depths of a few tens of kilometers. As with 

gravity anomalies, the main contribution of aeromagnetic 

interpretation is the identification of buried contrasts 

related to faulting and intrusion, both of which have a 

bearing on the distribution of mineralization. Inasmuch 

as the physical properties involved are different, the 

gravity and aeromagnetic anomalies show complementary but different aspects of crustal structure. 

One result of the study of aeromagnetic anomalies is 

the delineation of geologic contrasts that are covered by 

alluvium or volcanic rocks. In addition to providing a 

degree of geologic mapping beyond outcrops, these contrasts may become targets for future exploration by other 

geophysical, geochemical, or drill-hole techniques that 

will aid in identifying the geologic source of the 

anomaly and ·in estimating its potential for mineralization. In the quadrangles, 102 aeromagnetic anomalies 

are identified that have the correct dimensions for nearsurface (few hundred meters depth) intrusion or faulting. 

Although many of these anomalies are discarded as being insignificant to mineralization based on their association with identified or extrapolated geologic relations, 

others remain viable targets for future study. Several of 

the aeromagnetic anomalies that are under relatively 

shallow cover, or that are deeper but transverse to 

mapped geologic structure and thus indicative of anomalous conditions at depth, are indicated on figure 5. 

Study of the aeromagnetic data has also identified a 

regional aeromagnetic high that extends from the 

Sentinal Plain to Cimarron Peak (fig. 5). This anomaly 

is not entirely explained by surface exposures of magnetized volcanic rocks, such as the outcrops of the Sentinel 

Plain. It probably represents a zone of crustal· intrusion. 

This anomaly has importance in characterizing the tectonic setting of the area and may be significant in indicating a source of mineralizing magma (Klein, 1982a). 

Landsat Imagery 

As a part of this study, two types of analyses of 

Landsat Multispectral Scanner data were used to define 

mineralized areas. These two analyses are limonite mapping as a guide to hydrothermal alteration and lineament 

analysis as a guide to regional structural controls of mineralization. Digitally processed Multispectral Scanner 

data were used for all analyses. 

Limonitic materials were identified using the colorratio composite method (Rowan and others, 1974). This 

technique was used to map areas of hydrothermal alteration associated with limonitic materials and to help define mineralized areas. The term limonite is used as 

defined by Blanchard ( 1968)-that is, as a general term 

for iron oxides-but modified to include any material 

with the unique spectral reflectance properties of ferric 

oxide minerals such as hematite and goethite as defined 

by Hunt (1980). The minerals pyrite and (or) hematite 

are commonly associated with hydrothermal alteration 

14 The Conterminous United States Mineral Assessment Program: Ajo and Lukeville 1° by r Quadrangles, Arizona 
that is possibly related to mineralization; these minerals 

weather to produce limonite, which is detected by this 

color-ratio composite technique. Areas of hydrothermal 

alteration that lack limonitic materials will not be detected by this technique; however, areas of this type are 

believed to be insignificant in the study area. Most areas defined as limonitic from the satellite analysis were 

visited briefly in 1979 and 1980 to determine if the limonite was associated with hydrothermal alteration. 

A lineament analysis of southwestern Arizona was 

performed to define regional structural controls of mineralization. The techniques and philosophy of interpretation used for the lineament analysis are fully described 

in Sawatzsky and Raines (1981) and are a continuation 

of studies in Sonora, Mexico (Raines, 1978; Turner and 

others, 1982). Basically this lineament analysis identified regional lineaments and correlated these lineaments 

with known occurrences of mineralization in southwestern Arizona. This correlation was then used to identify 

areas with similar characteristics in the Ajo and 

Lukeville quadrangles. 

Geologic Studies in the Ajo Mining District 

As part of this resource assessment, a detailed study 

was made of the Ajo Mining District that resulted in a 

reevaluation of the geologic history and structure. The 

Ajo Mining District comprises the Ajo porphyry copper 

deposit and various small vein deposits in the Little Ajo 

Mountains of western Pima County. The New Cornelia 

Mine, developed on the Ajo deposit by Phelps Dodge 

Corporation, has produced 2.5 million tonnes of copper 

since it was opened in 1917. Ajo is the westernmost deposit of a large cluster of porphyry copper-molybdenum 

deposits in southeastern Arizona, and although molybdenum is recovered from parts of the deposit, it most closely 

matches the porphyry copper-gold model of Cox (1986a). 

The geology of the Ajo 15' quadrangle and the New 

Cornelia Mine was described by Gilluly (1946). A geologic map of the Ajo Mining District, modified from 

Gilluly's work, is shown in figure 6. Proterozoic gneiss 

and granite and possible Mesozoic volcanic rocks of intermediate composition are intruded by quartz dioritic to 

monzogranitic rocks, which Gilluly named the Cornelia 

Quartz Monzonite. Copper mineralization is related to 

granodiorite porphyry phases of this latter unit in the 

eastern part of the district, and similar granitoid rocks 

are also exposed in a large pluton in the Cardigan Peak 

area. Gilluly mapped a major normal fault in Gibson 

Arroyo west of the mine and concluded that the copper 

deposit represented the down-faulted apex of the pluton 

of Cardigan Peak west of this fault. The Locomotive 

Fanglomerate lies unconformably on the Precambrian 

and Mesozoic(?) rocks and on the granodiorite porphyry 

in the mine area. No evidence indicates that the 

fanglomerate was cut by the Gibson Arroyo fault. 

Andesitic rocks referred to as the Ajo Volcanics lie 

within and at the top of the fanglomerate and form the 

oldest unit of the Ajo volcanic field of Miocene age. 

Wadsworth (1968) subdivided intrusive phases in 

the Cornelia pluton and described textural features in 

support of Gilluly's idea that the Ajo deposit was the 

apex of the pluton. McDowell (1971) published K-Ar 

ages of 65-63 Ma for mineralized rocks in the New 

Cornelia Mine, and of 20 Ma for a sample from the pluton 

west of the Gibson Arroyo fault. He ascribed this difference in ages to a younger episode of hydrothermal alteration that influenced only the rocks west of the fault. 

As a part of the Ajo and Lukeville 1° by 2° quadrangles mineral resource assessment, a study of the district was made to determine the relation between the 

pluton of Cardigan Peak and the Ajo deposit (fig. 6). 

Cox and others (1981) described fluid inclusions in igneous quartz from widely separated samples in the pluton 

that contain daughter minerals of Na, K, and Fe chlorides and Cu-Fe sulfides. These inclusions suggested 

that highly saline, metal-rich solutions were evolving 

from the pluton at the time of crystallization, consistent 

with the idea that the pluton was the root zone of the 

deposit. Cox and Ohta (1984) mapped the pluton at a 

scale of 1:25,000 and outlined areas of hydrothermal alteration that are cut by the Gibson Arroyo fault. This 

alteration, in which biotite and K-feldspar are replaced 

by actinolite and oligoclase, respectively, was also noted 

by Carten ( 1979) in the root zone of the Yerington porphyry copper deposit in Nevada. 

The root-zone theory, however, has not survived the 

continuing work of geochronologists. Lee Silver (oral 

common., 1985), R.M. Tosdal (written common., 1987), 

and J.S. Stacey and J.L. Wooden (written common., 

1986) have reported incomplete uranium-lead ages that 

corroborate McDowell's (1971) middle Tertiary age for 

the pluton. Hagstrom and others (1987) reported K-Ar 

ages for the pluton ranging from 23.0 to 21.6 Ma and 

25.3 to 23.8 Ma for the Ajo Volcanics. These ages confirm that the pluton is roughly 40 m.y. younger than the 

porphyry copper deposit and similar in age to the Ajo 

Volcanics interlayered with the upper part of the Locomotive Fanglomerate. Aside from the fluid inclusions 

and the alteration in the pluton, the only other hydrothermal features related to the middle Tertiary intrusion are 

small hematite-chalcopyrite veins with chloritic alteration that are distributed around the southwest margin of 

the pluton. Hagstrom and others (1987) geographically 

restricted the Cornelia Quartz Monzonite (informally 

called the Cornelia pluton) to intrusive rocks of 

Laramide age exposed in the New Cornelia Mine and on 

the ridge immediately northwest of the mine; they reassigned the intrusive rocks of middle Tertiary age west of 

Description of Component Maps and Studies of the Ajo and Lukeville Quadrangles Folio 15 
0'\ '"" 

-1 

I'D =-

n 

Q 

;-= 

3 

:r 

Q 

c 

Ill 

c: 

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e!.. 

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3 

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AJO-LUKEVILLE 

QUADRANGLES 

~ AREA OF MAP 

112°55' 

Qal 

. '''','''' .~~"t!t.~ 

:rctg ····.:J~o41o 

Teqm ···.,,ul\tl': 

'•·,,-Jq, ~ 

'•,,,~(j(.)-

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I 1,... ... ,----------------------.:''---~-

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0 0.5 MILE 

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Figure 6. Geologic map of Ajo Mining District, southwestern Arizona. 

112°53' 

Qal 

Mountain 

Qal 

Tl 
Cl) the Gibson Arroyo fault to the informally designated Q) Ci) J:: ·- Cardigan Peak pluton. -

0 c: Cl) Hagstrom and others ( 1987), with the cooperation of Eo - 0 "C Q)_.:. Q) Ron Gibbs of Phelps Dodge Corporation, collected ~ro "C 

·s: samples from the New Cornelia Mine area and from the ·- en :c ::I..-

tffur c: 

:::1 Cardigan Peak pluton. Paleomagnetic analyses of these "C I Cii ~ Q) samples revealed that the Ajo deposit has been rotated - J:: ·c: (ti Cl)- Q) :::1 0 0 0 0-c N approximately 120°, so that its apex plunges 30° to the c: Q) c: c: 0 south and its root zone is exposed near the town of Ajo. ~ ~ ~ 0 0 

~ ~ .... :::1 ·g N Q) According toR. Gibbs (oral commun., 1986), drill holes 

(.).!:; :c t: J:: 

Q) Cl) N :::1 

cu ~ that pass through the deposit encounter Proterozoic 

ca ~ t: c;::- 0 "C 

.....IJ: cu Cl) Q) :::1 gneiss at depth. In the Cardigan Peak area, the only :::1 Q) 

"C Q) 0" 0 ·c: "C = 0 samples that gave reliable paleomagnetic orientations c: Q) "C Q) :::1 Q) "C cu Cl) c: 0 J:: (ti 

~-; ~ cu cu en Q) -o were from steeply dipping dikes cutting the pluton. >- ~ e 0 

.5!1 :g J:: 0 c: ~ e- ·g ~ 0 0 t: 0 ~ These show consistent middle Tertiary poles, indicating :c 0 

~ ~ 0 :c Cl) (.) ~ .5 a. 0 that these rocks have not been rotated after their intrusion. >-0 ~ ~ "C ·c: "C Q) ~ ~~ Q) cu c: J:: Q) These new data on the Ajo district raise as many Q) N ·g ·g c: 0 cu ~ J:: 

-t: :c :c -~ 0 Cl) "C ~ 

c: cu C) new questions as they answer. The similarity of ages > Cl)- Q) 0 0 "C ·a; .2 = 0 :::1 c: c: cb .... c: 0 0 Q) 

"SO ~ ~ between the Cardigan Peak pluton and the overlying Ajo ~ J:: c: (!)~ Cl Cl) C.cu (!) (!) u: ! cu the cooling, fracturing, and hy- . 5!1 i c: .... E cu~ Cl Volcanics requires that - c: Q) .!21 e l Q) .... 

c: 0 .;...; 0 s drothermal alteration of the pluton, the movement on the 

(5(.)0 c: ~e:. c: "3 0 0 cu Gibson Arroyo Fault, and the deposition of most of the (.) (.) (.) (.) LL 

Locomotive Fanglomerate took place within a time span 

0000000[!] of about 4 m.y. (25.3 to 21.6 Ma). Although no major 

z 

mineral deposits are known to be related to the Cardigan 

0 Peak pluton, its fluid inclusions and hydrothermal alteri= ation suggest that hydrothermal processes were related to 

<C 

z its crystallization. Plutons of middle Tertiary age should 

<C be considered prospective for hydrothermal deposits of ..J 

0.. unknown type in the Ajo region. >< w 

~ Mineral Occurrence Map (MF-1834-A) a. 

Cl) c;::- "C ~ ~ cu Ore has been produced in the Ajo and Lukeville 1 o ~ :e 

~ "C Q) by 2° quadrangles from the following types of mineral c: c cu '5 cu ~ deposits: pegmatite, placer gold, porphyry copper (Cu- E N 

Q) ~ t: ·g Au), manganese and polymetallic replacement, Cu-skam, ca cu ·u; :::1 :c :::1 c: 0" N and various types of vein deposits. Additionally, one lo- Q_ ~ 0 0 t: 

_fg 1 ti cu cality of chemically precipitated celestite and one gossan cu :::1 

·u; :e ~ 0" 

0 ~ 0 Q) "C that contains base and precious metals have been discov- a. ~ 0 c cu ~ c: Q) :e >- ·a ~ cu "C ered. The mineral occurrence map shows the locations Q) J:: ~ ~ * ~ ~ Q) e- ·c: £ ·g cu ~ c 0 ~ "§ ·g of known mines and prospects with symbols representa- cu :e Q) c: a. :c :c ~ cu E 0 ~ C) 

~ ~ 0 Q) tive of their deposit type. Small dots indicate prospects :e 0 "S "C N "C Q) c ·c: Q) ·c: ·c: c: Q) 

c: Q) en a. ~ c: ~ ~ 0 c: about which little is known. They are probably small ·e Q) c c: -~ E -~ 

~ cu ~ C) C) C) veins, except for several possible placer-gold prospects "C Q) 0 

Cl) LL cu 

Q) 0 

N C) 0 0 N C) -o N N t: c: "C ·c: Q) 0.. c: cb c: c: cu cb (l) 

cu c: in Growler Valley. A table that accompanies the map cu > 0 c: 0 0 :::1 c: :::1 

E <( 0 :s c: :::! u: ~ ~ 0 u: c: cu ·.;::; :::1 "C 0 E C) summarizes available published and unpublished data c: ·s: Q) > 0 'E 0 ~ about location, geology, and resources at each deposit. Q) 0 0 c: 0 cu u <( en < ....J (.) I Entries in the minerals column give representative min- ~ 000[;] [!][i]0000[1]~ QJ erals at the property, but they are not complete lists. A .. 

:I reference indicating where further information can be l:lO 

~ found is also given for each deposit. Generally, the unpublished reference materials of the Arizona Department 

of Mineral Resources are available in the U.S. Geological 

Description of Component Maps and Studies of the Ajo and Lukeville Quadrangles Folio 17 
Survey's Mineral Resource Data System (MRDS) file 

records. The table is arranged by 15' (or 7~') quadrangles from the northwest corner to the southeast corner 

of the 1 o by 2° quadrangles to facilitate easy transition 

between the table and map. 

The MRDS contains entries for most of the deposits 

listed in the table (Peterson, 1984). Inquiries about information stored in MRDS may be obtained from the 

Regional MRDS Representative at the U.S. Geological 

Survey, 12201 Sunrise Valley Drive, Reston, VA 22092, 

or at the U.S. Geological Survey, 345 Middlefield Road, 

Menlo Park, CA 94025. 

Vein deposits are widely scattered throughout the 

mountain ranges of the quadrangles. Other deposit types 

are more restricted geographically owing to geologic 

constraints. Skarn and replacement deposits are restricted to areas of Paleozoic carbonate rocks, which 

crop out primarily in the Vekol Mountains in the northeastern part of the quadrangles. Several Laramide-age 

hornblende-biotite granitoid plutons occur in the eastern 

half of the quadrangles, but only two areas are known to 

contain porphyry copper deposits. Two areas have confirmed accumulations of placer gold, and several 

propsects in Growler Valley are probably also placer 

prospects. Of numerous small pegmatite bodies in the 

metamorphic terranes in the western half of the quadrangles, only two have been prospected specifically for 

pegmatite minerals. Some of the pegmatites are spatially related to vein deposits that have been prospected 

for base and precious metals, but these pegmatites were 

neither the source of the mineralized rock nor the object 

of the prospecting. Except for the porphyry copper deposit at Ajo, the manganese replacement deposits in the 

Cimarron Mountains, and the placer-gold deposits in the 

Quijotoa Mountains, the known deposits in the quadrangles are small or nonproductive, although the Vekol 

Hills porphyry copper deposit in the V ekol Mountains 

could potentially yield significant amounts of copper. 

Technique Used In Mineral Assessment 

Introduction 

Quadrangles that are 1 o by 2° and other similarly 

large regions are assessed with the purpose of supplying 

information on mineral resources for use in making decisions on public land that will effect exploration and development and for decisions relating to national or 

regional resource planning. These decisions require consideration of undiscovered deposits (Richter and others, 

1975; Singer, 1975; Hodges and others, 1984). The basic parts of the assessments are ( 1) the construction of 

grade/tonnage, or contained metal, models and the description of types of deposits that are known or suspected; (2) the delineation of tracts within which the 

occurrence of various types of deposits is geologically 

plausible; and (3) the estimation of the number of undiscovered deposits of each type that are likely to occur 

within the delineated tracts. 

Information Needs for Resource Assessments 

Requirements for the multistage assessment process 

can be divided into two broad categories: ( 1) information within the region being assessed; and (2) procedures 

to integrate this information in the assessment. The 

within-region information should include a buffer zone 

around the region to allow for interpolation. 

The first requirement for information in the region is 

a geologic map at the same or a more detailed scale as 

that of the assessment. The map should emphasize lithologic units and ages rather than broadly grouped units. 

The geologic map is the primary basis for delineating 

tracts and identifying which are permissive for different 

deposit types. 

The second requirement for information is an inventory of known deposits and prospects in and near the region being assessed. Because of incomplete deposit 

descriptions, it will not be possible to identify the deposit types for most prospects and some deposits, but 

those that can be identified will increase confidence in 

tracts delineated for the deposit type. Prospects may indicate possible deposit types and place limits on what is 

possible elsewhere. Because much of the older literature 

is based on rock and mineral deposit terminologies and 

genetic concepts not used today, older literature may require reinterpretation for proper deposit-type identification. Thus, field examination of at least some deposits 

in the assessment region is required. 

Geophysics, particularly aeromagnetics, has in some 

cases indicated anomalous or mineralized areas, but its 

greatest contributions to assessing large regions have been 

in extending permissive rock units under covered areas 

and in identifying rock units in poorly mapped areas. 

Both stream-sediment and rock geochemistry have provided similar benefits to large regional assessments, providing direct evidence for the presence of elements or 

suites of elements associated with the processes of mineralization. 

Another kind of information that can be useful is 

knowledge of the extent and efficiency of past exploration 

in the region. Where exploration has not taken place, 

large variability in the estimated number of deposits might 

be expected, but where there has been extensive and efficient exploration, there should be little uncertainty in the 

estimated number of deposits. Exploration information is 

often difficult to obtain and to evaluate. 

The second stage in assessment is integration of all 

this information, diagrammed in the flow chart in figure 

7. In Alaska, assessments have been performed mentally 

18 The Conterminous United States Mineral Assessment Program: Ajo and Lukeville 1 o by 2° Quadrangles, Arizona 
by several economic geologists (Richter and others, 

1975). The key to this approach is a requirement that 

the geologist have many years of experience with a variety of deposit types and geologic settings. In the assessment of Colombia (Hodges and others, 1984) the large 

number of descriptive (Cox, 1983a, b) and associated 

grade-tonnage (Singer and Mosier, 1983a, b) models 

provided both guidance in the integration of information 

and a common set of standards. Although the process of 

delineating tracts by deposit type still requires mental integration of many variables, documentation of the characteristics of various types of deposits broadens the 

scope of the integration. Thus, deposit models, whether 

in the minds of experienced geologists, written on paper, 

or perhaps in a computer, provide a format for the integration of the information in the assessed region. After 

selecting the appropriate deposit models and delineating 

permissive tracts for them, an estimate of the number of 

undiscovered deposits was made (fig. 8). In the Ajo and 

Lukeville quadrangles, estimates were made for porphyry copper, skarn and polymetallic replacement, porphyry molybdenum, and evaporite deposits by a group of 

five geoscientists with diverse backgrounds who participated in the study. Estimates were made individually, 

but a Kendall rank correlation analysis showed that these 

estimates reached a consensus in most cases. Undiscovered deposits estimated for each deposit type have the 

same grade-tonnage distribution as the world-wide distribution for that deposit type. That is, half of the undiscovered deposits would be larger and half smaller than 

the median for that type. 

The form of presentation of the assessment is critical. A map or maps showing the location of tracts with 

mineral potential is required and must be keyed to 

tables, organized by tract, in which deposit types, known 

deposits, geologic environment, and comments particular 

to each tract are presented. A short summary of the deposit types, exploration guides, and recommendations is 

useful. Graphical presentation of grade-tonnage models 

(fig. 9A, B) and of descriptive models has achieved wide 

acceptance. These descriptive and grade-tonnage models 

have been enlarged and republished as U.S. Geological 

Survey Bulletin 1693 (Cox and Singer, 1986). 

Mineral Resource Assessment Maps (OF-85-527, 

MF-1834-8) 

The mineral resource assessment for the Ajo and 

Lukeville 1 o by 2° quadrangles consists of three maps 

that outl~ne permissive tracts for 16 deposit types and a 

text that discusses the mineral resource assessment. The 

assessment, which follows the method of Singer (1975) 

wherever possible, estimates the number of undiscovered 

deposits of a given type that might occur within the 

tracts. This method was applied for several deposit 

types. Lacking good deposit models or adequate information on the tracts, some deposit types were discussed 

qualitatively. We delineated tracts within the quadrangles and organized the text according to deposit type, 

primarily using available deposit models (Cox and 

Singer, 1986). Each section of the text provides an inGeologic map 

Known deposits 

and occurrences 1---

~ 

..... 

Geochemistry ..... Mineral ...... Mineral resource ..... 

..... deposit Ill"' map 

..... models ...... 

~ 

Geophysics 1---

Exploration 

history 

Figure 7. Diagram showing how flow of information from field studies is applied to selection of 

deposit models and delineation of tracts in mineral resource map. 

Description of Component Maps and Studies of the Ajo and Lukeville Quadrangles Folio 19 
troductory statement about the deposit type and explains 

why it was included. Criteria favorable for the presence 

of such a deposit are listed and are used to delineate the 

tracts. A brief description of known deposits in or near 

the quadrangle is given. The final section discusses the 

mineral resource assessment and includes probabilistic 

estimates for the number of undiscovered deposits, 

where appropriate. 

Porphyry copper, skarn, and polymetallic replacement deposits are known in the quadrangles, and there is 

potential for additional discoveries elsewhere. Twelve 

tracts for porphyry copper are delineated in and near exposed, or possibly buried, Laramide-age plutons. Not 

enough information was available to delineate separately 

for the types (Mo- or Au-rich) of porphyry copper deposits. Ten tracts for porphyry copper-related skarn, 

skarn, and polymetallic replacement deposits are shown 

where Paleozoic limestone is known or likely to be 

present. There is a 50 percent chance of one or more 

undiscovered porphyry copper-molybdenum or porphyry 

copper-related skarn deposits and a 10 percent chance of 

Mineral resource 

map 

Estimated number 

of undiscovered 

deposits 

-

Worldwide data on ~ 

grade and tonnage 

of deposits 

Step 1 IIIIo.. 

Step 2 ~ 1111"" 

Step 3 1111o.. 

Ill"' 

/ 

• 

Mineral 

resource 

assessment 

Land use Guidelines for 

decisions new research 

Exploration and 

development 

strategy 

Figure 8. Diagram showing how resource assessment is derived 

from mineral resource map, estimates of number of undiscovered deposits, and worldwide grade-tonnage data. Applications 

of resource assessment are shown on lower right side. 

Figure 9. Inverse cumulative distribution of copper tonnage (A) 

and grade (B) in porphyry copper deposits in Arizona, showing 

tonnages and grades for deposits in and near Ajo and Lukeville 

1 o by r quadrangles. Tonnages and grades for these deposits 

are not significantly correlated. 

0.9 

0.8 

(/) 0.7 ~ 

en 

0 

ll. 0.6 w 

Cl 

~ 

0 z 0.5 

0 

i= 

c: 

0 

ll. 

0 

c: 

ll. 

0.4 

0.3 

0.2 

0.1 

0.0 

6.3 

0.9 

0.8 

(/) 0.7 

~ 

en 

~ 0.6 w 

Cl 

~ 

0 0.5 

z 

0 

i= 

c: 0 0.4 

ll. 

0 

c: 

ll. 0.3 

0.2 

0.1 

0.0 

A 

25 

B 

Sacaton 

-0---------------------- Silver Bell I 0 

jo 

~~----------------

1 Lakeshore 

100 400 1600 6300 25000 100000 

METRIC TONS, IN MILLIONS 

0.18 0.32 0.56 1.0 1.8 3.2 5.6 10.0 

COPPER GRADE, IN PERCENT 

20 The Conterminous United States Mineral Assessment Program: Ajo and Lukeville 1 o by r Quadrangles, Arizona 
four or more. There is also a 50 percent chance of one 

or more undiscovered Cu-skarn deposits and a 10 percent chance of four or more. There is a smaller probability that the quadrangles contain undiscovered 

replacement deposits. 

Porphyry molybdenum deposits (low-fluorine type) 

have not previously been discovered in the quadrangles, 

but data suggest that 10 tracts contain some characteristics favorable for such deposits. There is a 50 percent 

chance of one or more undiscovered porphyry molybdenum deposits and a 10 percent chance of two or more. 

Known vein deposits in the quadrangles include 

gold-silver-quartz veins that include low-sulfide goldquartz veins, epithermal veins, vein-type iron deposits, 

and tungsten-bearing veins. Seven tracts with known 

gold-silver-quartz veins may contain additional deposits. 

Eight tracts show evidence for the existence of undiscovered epithermal vein deposits, and three tracts may have 

vein-type iron deposits. The undiscovered gold-silverquartz veins and iron-bearing veins could contain uranium. Nine tracts show evidence for tungsten-bearing 

veins. If the known veins of these types in the quadrangles are representative, additional new deposits would 

likely be small. 

There are numerous pegmatites, particularly in the 

western part of the quadrangles, but most are small and 

of simple mineralogy. Four tracts have potential for productive pegmatites based on known occurrences and 

geochemical data. 

Undiscovered manganese replacement deposits would 

most likely be near the known deposits in the three designated tracts. Although limestone provides evidence for 

these deposits, there is no direct evidence for manganese 

in limestones outside the Cimarron Mountains. 

Four tracts delineated for placer gold include known 

placer-gold localities and suspected placer localities 

based on evidence on the pediments or on the presence 

of suitable source terranes in the adjacent mountains. 

Geological, geochemical, and (or) geophysical data 

suggest the possibility of several other deposit types. 

These include gneiss-hosted and volcanic-hosted disseminated gold mineralization, rhyolite-hosted tin deposits, 

evaporite deposits, various types of basin-hosted uranium 

deposits, perlite, and zeolites. In addition, warm-water 

wells suggest the possibility of geothermal resources. 

SELECTED REFERENCES 

The asterisks (*) denote references cited in this report. 

Plus signs (+) indicate uncited references that mainly or entirely pertain to the Ajo and Lukeville quadrangles or are 

especially significant for regional relations of the quadrangle. Unmarked references are uncited general, regional, or topical in scope but contain material relevant to 

the Ajo and Lukeville quadrangles. Additional references 

to many mining properties are contained in the MRDS 

computer file (an acronym for the U.S. Geological Survey's 

Mineral Resource Data System available from: U.S. Geological Survey, 920 National Center, 12201 Sunrise Valley 

Drive, Reston, VA 22092). 

* Anderson, T.H., and Roldan-Quintana, J., eds., 1979, Geology of northern Sonora: Instituto de Geologia U .N .A.M., 

Hermosillo, Sonora, Mexico, and the University of Pittsburgh, Penn., GSA Guidebook Field Trip #27, 1979, 

Geological Society of America Annual Meeting, San Diego. 

* Anderson, T.H., and Silver, L.T., 1979, The role of the 

Mohave-Sonora Megashear in the tectonic evolution of 

Northern Sonora, in Geology of Northern Sonora, Field 

trip Guidebook #27: Geological Society of America Annual Meeting, p. 1. 

* Arnold, A. H., 1986, Geologic implications of a geochemical 

study of three two-mica granites in southern Arizona: 

Tucson, University of Arizona, M.S. thesis, 155 p. 

* Balla, J.C., 1972, The relationship of Laramide stocks to regional structure in central Arizona: Tucson, University of 

Arizona, Ph.D. dissertation, 184 p. 

* Barton, H.N., Theobald, P.K., Turner, R.L., Eppinger, R.G., 

and Frisken, J.G., 1982, Geochemical data for the Ajo 

two-degree quadrangle, Arizona: U.S. Geological Survey 

Open-File Report 82-419, 116 p. 

Beikman, H.M., Haxel, G.B., and Miller, R.J., in press, Geologic map of the Tohono 0' odham Indian Reservation, 

southern Arizona: U.S. Geological Survey Miscellaneous 

Geologic Investigations Map I-2017, scale 1:125,000 

* Blanchard, Roland, 1968, Interpretation of leached outcrops: 

Nevada Bureau of Mines Bulletin 66, p. 7. 

+Boler, F.M., and Baer, M.J., 1981, Principal facts for gravity 

stations in the Ajo 1 o by 2° quadrangle and Papago Indian 

Reservation, southwest Arizona: U.S. Geological Survey 

Open-File Report 81-993, 8 p. 

* Briskey, J.A., Haxel, Gordon, Peterson, J.A., and Theodore, 

T.G., 1978, Reconnaissance geologic map of the Gu Achi 

15-minute quadrangle, Pima County, Arizona: U.S. Geological Survey Miscellaneous Field Studies Map MF-965, 

scale 1:62,500. 

* Brown, D.E., ed., 1982, Biotic communities of the American 

Southwest United States and Mexico: Desert Plants, v. 4, 

n. 14, 342 p. 

* Bryan, Kirk, 1925, The Papago country, Arizona: U.S. Geological Survey Water Supply Paper 499, 436 p. 

* Carpenter, R.H., 1947, The geology and ore deposits of the 

Vekol Mountains, Pinal County, Arizona: Stanford, Calif., Stanford University, Ph.D. dissertation, 110 p. 

* Carten, R.B., 1979, Na-(Ca) metasomatism and its timespace relationship to K-metasomatism at the Yerington, 

Nevada porphyry copper deposit [abs.]: Geological Society of America Abstracts with Programs, v. 11, no. 7, p. 

399. 

* Chaffee, M.A., 1974, Stratigraphic relations of the Bolsa 

Quartzite, Vekol Mountains, Pinal County, Arizona: U.S. 

Geological Survey Journal of Research, v. 2, no. 2, p. 143, 

146. 

Selected References 21 
Cohen, K.K., Anderson, T.H., Schmidt, V.A., and Haxel, 

G.B., 1981, Paleomagnetic results from Early Jurassic 

units from the Sil Nakya Hills and the Baboqufvari Mountains, south-central Arizona [abs.]: Geological Society of 

America Abstracts with Programs, v. 13, p. 428. 

Coney, P.J., 1978, The plate tectonic setting of southeastern 

Arizona, in Callender, J.F., Wilt, J.C., and Clemons, R.E., 

eds., Land of Cochise: Socorro, New Mexico Geological 

Society Guidebook, 29th Field Conference, p. 285-290. 

* Coney, P.J., and Reynolds, S.J., 1977, Cordilleran Benioff 

zones: Nature, v. 270, p. 403-406. 

* Cox, D.P., 1986a, Descriptive model for porphyry Cu-Au, in 

Cox, D.P., and Singer, D.A., eds., Mineral deposit models: 

U.S. Geological Survey Bulletin 1693, p. 110. 

*---1986b, Geochemistry of Laramide and middle Tertiary 

plutons in the Ajo Mining District, Pima Co., Ariz: U.S. 

Geological Survey Open-File Report 88-672, 13 p. 

* Cox, D.P., Czamanske, G.K., and Bain, J.H.C., 1981, Mineral-rich fluid inclusions in the root zone of a porphyry 

copper system, Ajo, Arizona [abs.]: Geological Society of 

America Abstracts with Programs, v. 13, no. 7, p. 433. 

* Cox, D.P., and Ohta, Eijun, 1984, Maps showing rock types, 

hydrothermal alteration, and distribution of fluid inclusions in the Cornelia pluton, Ajo Mining District, Pima 

County, Arizona: U.S. Geological Survey Open-File Report 84-388, scale 1:25,000. 

*Cox, D.P., ed., 1983a, U.S. Geological Survey -

INGEOMINAS mineral resource assessment of Colombia: 

Ore deposit models: U.S. Geological Survey Open-File 

Report 83-423, 64 p. 

*---P.ed., 1983b, U.S. Geological Survey-INGEOMINAS 

mineral resource assessment of Colombia: Additional ore 

deposit models: U.S. Geological Survey Open-File Report 

83-901, 37 p. 

* Cox, D.P., and Singer, D.A., eds., 1986, Mineral deposit 

models: U.S. Geological Survey Bulletin 1693, 379 p. 

* Davis, G.H., 1980, Structural characteristics of metamorphic 

core complexes, southern Arizona, in Crittenden, M.D., 

Jr., Coney, P.J., and Davis, G.H., eds., Cordilleran metamorphic core complexes: Geological Society of America 

Memoir 153, p. 217-267. 

Dillon, J.D., Haxel, G.B., and Tosdal, R.M., 1990, Structural 

evidence for northeastward movement on the Chocolate 

Mountains thrust, southeasternmost California: Journal of 

Geophysical Research, v. 95, no. B12, p. 19, 953-19,971. 

+Dixon, D.W., 1966, Geology of the New Cornelia Mine, Ajo, 

Arizona, in Titley, S.R., and Hicks, C.L., eds., Geology of 

the porphyry copper deposits of southwestern North 

America: Tucson, The University of Arizona Press, 

p.123-132. 

* Dockter, R.D., and Keith, W.J., 1978, Reconnaissance geologic map of the Vekol Mountains quadrangle, Arizona: 

U.S. Geological Survey Miscellaneous Field Studies Map 

MF-931, scale 1:62,500. 

*Eberly, L.D., and Stanley, T.B., Jr., 1978, Cenozoic stratigraphy and geologic history of southwestern Arizona: 

Geological Society of America Bulletin, v. 89, p. 921-940. 

* Eppinger, R.G., Theobald, P.K., Klein, D.P., and Raines, 

G.L., 1988, Geological, geochemical, and geophysical 

studies in the central portion of the Mohawk Mountains, 

southwestern Arizona USA, in Gray, Floyd (compiler), 

Abstracts of the symposium of the geology and mineral 

deposits of the Ajo and Lukeville 1° x 2° quadrangle, Arizona: U.S. Geological Survey Open-File Report 88-217, 

p. 10-13. 

* Farmer, G.L., and DePaolo, D.J., 1983, Origin of Mesozoic 

and Tertiary granite in the western U.S. and implications 

for pre-Mesozoic crustal structure. I. Nd and Sr isotopic 

studies in the geocline of the northern Great Basin: Journal of Geophysical Research, v. 88, p. 3379-3401. 

Ficklin, W.H., Preston, D.J., Stanley, A.R., and Nowlan, 

G.A., 1980, Analytical results for 127 water samples from 

the Papago Indian Reservation and vicinity, Arizona: U.S. 

Geological Survey Open-File Report 80-310, 22 p. 

Galbraith, F.W., Heindl, L.A., and Sykes, G.G., 1959, Volcanic craters of the Pinacate Mountains, Sonora, Mexico, 

Trip 6, Road log, Arizona Geological Society, Southern 

Arizona Guidebook II: Geological Society of America, 

Cordilleran Section, April 2-6, 1959, Tucson, p. 253-270. 

Gilluly, James, 1935, Ajo district (Arizona), in Copper resources of the world: 16th International Geological 

Congress, v. 1, p. 228-233. 

*---1937, Geology and ore deposits of the Ajo quadrangle, 

Arizona: Arizona Bureau of Mines Bulletin 141, 83 p. 

+---1942, The mineralization of the Ajo copper district, 

Arizona: Economic Geology, v. 37, p. 247-309. 

*---1946, The Ajo Mining District, Arizona: U.S. Geological Survey Professional Paper 209, 112 p. 

* Gray, Floyd (compiler), 1988, Abstracts of the symposium of 

the geology and mineral deposits of the Ajo and Lukeville 

1 o X 2° quadrangle, Arizona: U.S. Geological Survey 

Open-File Report 88-217, p. 10-13. 

* Gray, Floyd, and Miller, R.J., 1984a, New K-Ar age of volcanic rocks near Ajo, Pima and Maricopa Counties, 

southwestern Arizona: Isochron/West, no. 41, p. 3-6. 

*---1984b, Stratigraphy, geochronology and geochemistry 

of a calc-alkaline volcanic field near Ajo, southwestern 

Arizona [abs.]: Geological Society of America Abstracts 

with Programs, v. 16, no. 6, p. 526. 

* Gray, Floyd, Miller, R.J., Grubensky, M.J., Haxel, Gordon, 

Tosdal, R.M., Peterson, D.W., May, D.J., and Silver, L.T., 

1987 [1988], Preliminary geologic map of the Ajo and 

Lukeville 1 o by 2° quadrangles, southwestern Arizona: 

U.S. Geological Survey Open-File Report 87-217, scale 

1:250,000 .. 

* Gray, Floyd, Miller, R.J., Peterson, D.W., May, D.J., Tosdal, 

R.M., and Kahle, Katherine, 1983, Geology of the 

Growler Mountains, Pima and Maricopa Counties, Arizona: U.S. Geological Survey Miscellaneous Field 

Studies Map MF-1681, scale 1:62,500. 

* Gray, Floyd, Miller, R.J., and Soli, Lottie, 1985, Reconnaissance geologic map and aeromagnetic map of the Hat 

Mountain quadrangle, Maricopa County, Arizona: U.S. 

Geological Survey Open-File Report 85-138, scale 

1:62,500. 

* Grimes, D.J., and Marranzino, A.P., 1968, Direct-current 

spark emission spectrographic field for the 

semiquantitative analysis of geologic materials: U.S. Geological Survey Circular 591, 6 p. 

Grubensky, M.J., Haxel, G.B., and Koch, R.D., in press, Geo22 The Conterminous United States Mineral Assessment Program: Ajo and Lukeville 1 o by 2° Quadrangles, Arizona 
logic map of the Castle Dome Mountains, southwestern 

Arizona: U.S. Geological Survey Miscellaneous Geologic 

Investigations Map 1-2138, scale 1:62,500. 

* Gutmann, J.T., 1976, Geology of Crater Elegante, Sonora, 

Mexico: Geological Society of America Bulletin, v. 87, p. 

1718-1729. 

* Hagstrom, J.T., Cox, D.P., and Miller, R.J., 1987, Structural 

reinterpretation of the Ajo Mining District, Pima County, 

Arizona, based on paleomagnetic and geochronologic 

studies: Economic Geology, v. 82, p. 1348-1361. 

Hamilton, Warren, Tosdal, R.M., Stone, Paul, and Haxel, 

G.B., 1987, Mesozoic tectonics of southeastern California, 

in Davis, G.H., and VandenDolder, E.M., eds., Geologic 

diversity of Arizona and its margins: Excursions to 

choice areas: Arizona Bureau of Geology and Mineral 

Technology, Geological Survey Branch, Special Paper 5, 

p. 337-350. 

* Hammer, D.F., 1961, Geology and ore deposits of the Jackrabbit area, Pinal County, Arizona: Tucson, University of 

Arizona, M.S. thesis, 156 p. 

Hargan, B.A., 1978, Regional gravity data analysis of the 

Papago Indian Reservation, Pima County, Arizona: Tucson, University of Arizona, M.S. thesis, 105 p. 

* Haxel, Gordon, 1978, Reconnaissance geologic map of the 

Comobabi quadrangle, Pima County, Arizona: U.S. Geological Survey Miscellar.eous Field Studies Map MF-964, 

scale 1:62,500. 

---1981, Late Cretaceous and early Tertiary orogenesis, 

south-central Arizona [abs.]: Geological Society of 

America Abstracts with Programs, v. 13, no. 2, p. 60. 

---1987, Trace-element systematics of peraluminous 

leucogranites, Baboqufvari Mountains chain, south-central 

Arizona [abs.]: Geological Society of America Abstracts 

with Programs, v. 19, p. 388. 

---1989, Geochemistry of peraluminous leucogranites, 

south-central Arizona [abs.], in Continental magmatism 

abstracts, International Association of Volcanology and 

Chemistry of the Earth's Interior, General Assembly, 

Santa Fe: New Mexico Bureau of Mines and Mineral Resources Bulletin 131, p. 124. 

Haxel, G.B., Anderson, T.H., Riggs, N.R., and Goodwin, 

L.G., 1988, The Papago terrane: A crustal anomaly in 

south-central Arizona and north-central Sonora [abs.]: 

Geological Society of America Abstracts with Programs, 

v. 20, p. 168. 

Haxel, G.B., Bagby, W.C., and Tosdal, R.M., 1987, Uppercrustal section through a Middle to Late Jurassic regional 

metamorphic and plutonic terrane, Kofa Mountains, southwestern Arizona [abs.]: Geological Society of America 

Abstracts with Programs, v. 19, p. 697. 

Haxel, G.B., Budahn, J.R., Fries, T.L., King, B.W., White, 

L.D., and Aruscavage, P.J., 1987, Geochemistry of the 

Orocopia Schist, southeastern California: Summary, in 

Dickinson, W .R., and Klute, M.A., eds., Mesozoic rocks 

of southern Arizona and adjacent areas: Arizona Geological Society Digest, v. 18, p. 49-64. 

Haxel, G.B., Briskey, J.A., May, D.J., Tosdal, R.M., and 

Wright, J.E., 1985, Reconnaissance petrochemistry of Jurassic igneous rocks, Baboqufvari and Comobabi 

Mountains area, southern Arizona [abs.]: Geological Society of America Abstracts with Programs, v. 17, p. 361. 

Haxel, G.B., and Grubensky, M.J., 1984, Tectonic significance of localization of middle Tertiary detachment faults 

along Mesozoic and early Tertiary thrust faults, southern 

Arizona region [abs.]: Geological Society of America Abstracts with Programs, v. 16, no. 6, p. 533. 

Haxel, Gordon, Gray, Floyd, Briskey, J.A., Tosdal, R.M., and 

Wright, J.E., 1983, 'Two contrasting suites of Late Cretaceous and early Tertiary granitoids, south-central Arizona 

[abs.]: Geological Society of America Abstracts with Programs, v. 15, p. 410. 

Haxel, G.B., Jacobson, C.E., and Tosdal, R.M., 1988, Multiple low-angle faults atop the Orocopia Schist, 

southwestern Arizona and southeastern California [abs.]: 

Geological Society of America Abstracts with Programs, 

v. 20, p. A383. 

+ Haxel, Gordon, Mueller, Karl, Frost, Eric, and Silver, L.T., 

1982, Mid-Tertiary detachment faulting in the northernmost Mohawk Mountains, southwestern Arizona [abs.]: 

Geological Society of America Abstracts with Programs, 

v. 14, no. 4, p. 171. 

Haxel, G.B., Simmons, A.M., and McCarthy, J., 1990, 

Synextensional dioritic magmatism within and beneath 

metamorphic core complexes, southern Arizona and southeastern California: integration of structural, petrologic, and 

PACE seismic refraction data [abs.]: Geological Society 

of America Abstracts with Programs, v. 22, p. 28-29. 

Haxel, G.B., and Tosdal, R.M., 1986, Significance of the 

Orocopia Schist and Chocolate Mountains thrust in the 

late Mesozoic tectonic evolution of the southeastern California-southwestern Arizona region: Extended abstract, in 

Beatty, Barbara, and Wilkinson, P.A.K., eds., Frontiers in 

geology and ore deposits of Arizona and the Southwest: 

Arizona Geological Society Digest, v. 16, p. 52-61. 

Haxel, G.B., Tosdal, R.M., and Dillon, J.T., 1985, Tectonic 

setting and lithology of the Winterhaven Formation, a new 

Mesozoic stratigraphic unit in southeasternmost California 

and southwestern Arizona: U.S. Geological Survey Bulletin 1599, 19 p. 

Haxel, G.B., Tosdal, R.M., and Dillon, J.T., 1986, Field guide 

to the Chocolate Mountains thrust and Orocopia Schist, 

Gavilan Wash area, southeasternmost California, in 

Beatty, Barbara, and Wilkinson, P.A.K., eds., Frontiers in 

geology and ore deposits of Arizona and the Southwest: 

Arizona Geological Society Digest, v. 16, p. 282-293. 

* Haxel, Gordon, Tosdal, R.M., May, D.J., and Wright, J.E., 

1981, Latest Cretaceous and early Tertiary thrust faulting, 

regional metamorphism, and granitic plutonism, southcentral Arizona [abs.], in Howard, K.A., Carr, M.D., and 

Miller, D.M., eds., Tectonic framework of the Mojave and 

Sonoran Deserts, California and Arizona:~ U.S. Geological 

Survey Open-File Report 81-503, p. 42-44. 

* Haxel, Gordon, Tosdal, R.M., May, D.J., and Wright, J.E., 

1984, Latest Cretaceous and early Tertiary orogenesis in 

south-central Arizona: Thrust faulting, regional metamorphism, and granitic plutonism: Geological Society of 

America Bulletin, v. 95, p. 631-653. 

* Haxel, Gordon, Wright, J.E., May, D.J., Tosdal, R.M., 1980, 

Reconnaissance geology of the Mesozoic and lower Cenozoic rocks of the southern Papago Indian Reservation, 

Selected References 23 
Arizona: a preliminary report, in Jenny, J.P., and Stone, 

Claudia, eds., A preliminary report on studies in western 

Arizona: Arizona Geological Society Digest, v. 12, p. 17-

29. 

* Hayes, P.T., 1970, Cretaceous paleogeography of southeastern Arizona and adjacent areas: U.S. Geological Survey 

Professional Paper 658-B, 42 p. 

* Heindl, L.A., 1960, Cenozoic geology of the Papago Indian 

Reservation, Pima, Maricopa, and Pinal Counties, Arizona: Arizona Geological Society Digest, v. 3, p. 31-34. 

* ---1965a, Mesozoic formations in the Vekol Mountains, 

Papago Indian Reservation, Arizona: U.S. Geological 

Survey Bulletin 1194-G, 9 p. 

---1965b, Mesozoic formations in the Comobabi and 

Roskruge Mountains, Papago Indian Reservation, Arizona, 

in Contributions to stratigraphy: U.S. Geological Survey 

Bulletin 1194-H, 15 p. 

*Heindl, L.A., Cosner, O.J., Page, H.G., Armstrong, C.A., and 

Kister, L.R., 1962, Summary of occurrence of ground water on the Papago Indian Reservation: U.S. Geological 

Survey Hydrologic Investigations Atlas HA-55, scale 

1:250,000. 

* Hodges, C.A., Cox, D.P., Singer, D.A., Case, J.E., Berger, 

B.R., and Albers, J.P., 1984, U.S. Geological SurveyINGEOMINAS mineral resource assessment of Colombia: 

U.S. Geological Survey Open-File Report 84-345, 2 

sheets, scale 1: 1 ,000,000, 193 p. 

Hollett, K.J., 1981, Maps showing ground-water conditions in 

the San Simon Wash area, Papago Indian Reservation, 

Arizona-1979: U.S. Geological Survey Water-Resources 

Investigations Open-File Report 81-530. 

Howell, D.G., Puis, G.S., and Haxel, G.B, 1982, Terrane accretion and dispersion, southern Cordilleran [abs.]: 

Geological Society of America Abstracts with Programs, 

v. 14, p. 519. 

Howell, D.G., Gibson, J.D., Puis, G.S., Knapp, J.H., Haxel, 

G.B., Keller, B.R., Silver, L.T., and Vedder, J.G., 1985, 

Ocean-Continent Transect C-3: Southern California borderland to Rio Grande rift: Geological Society of 

America Transect Program, 3 sheets, 23 p. 

*Hunt, G.R., 1980, Electromagnetic radiation-The communication link in remote sensing, in Siegal, B.S., and 

Gillespie, A.R., Remote sensing in geology: New York, 

John Wiley and Sons, p. 5-45. 

+ Huston, D.L., 1984, The significance of a widespread stream 

sediment anomaly in the Batamote Mountains, Pima 

County, Arizona: Tucson, University of Arizona, M.S. 

thesis, 163 p. 

* Huston, D.L., and Theobald, P.K., 1990, The nature and possible significance of the Batamote copper-bismuth-silver 

anomaly, Pima County, Arizona: U.S. Geological Survey 

Bulletin 1907, 19 p. 

* Johnson, M.G., Bergquist, Joel, and Lindquist, A.E., 1975, 

Status of mineral resource information for the Gila Bend, 

Papago, and San Xavier Indian Reservations, Arizona: 

U.S. Geological Survey and U.S. Bureau of Mines for 

U.S. Bureau of Indian Affairs, Administrative Report No. 

BIA-9, 82 p. 

Johnston, W.P., 1972, K-Ar dates on intrusive rocks and alteration associated with the Lakeshore porphyry copper 

deposit, Pinal County, Arizona: Isochron/W est, no. 4, p. 

29-30. 

Jones, E.L., Jr., and Ransome, F.L., 1920, Deposits of manganese ore in Arizona: U.S. Geological Survey Bulletin 

710-D, p. 93-184. 

* Jones, W.C., 1974, General geology of the northern portion 

of the Ajo Range, Pima County, Arizona: Tucson, University of Arizona, M.S. thesis, 77 p. 

+Kahle, K.M., Conway, D.R., and Haxel, Gordon, 1978, Preliminary geologic map of the Ajo 1 o by 2o quadrangle, 

Arizona: U.S. Geological Survey Open-File Report 78-

1096, 2 sheets, scale 1 :250,000. 

* Keith, S.B ., 1974, Index of mining properties in Pima 

County, Arizona: Arizona Bureau of Mines Bulletin 189, 

156 p. 

---1978a, Index of mining properties in Yuma County, 

Arizona: Arizona Bureau of Geology and Mineral Technology Bulletin 192, 185 p. 

---1978b, Origins of Arizona copper deposits: hypotheses: Fieldnotes, v. 8, nos. 1-2, p. 8-9, 12, 17. 

* Keith, S.B., Reynolds, S.J., Damon, P.E., Shafiqullah, 

Muhammad, Livingston, D.E. and Pushkar, P.D.,1980, 

Evidence for multiple intrusion and deformation within 

the Santa Catalina-Rincon-Tortolita crystalline complex, 

southeastern Arizona, in Crittenden, M.D., Jr., Coney, 

P.J., and Davis, G.H., eds., Cordilleran metamorphic core 

complexes: Geological Society of America Memoir 153, 

p. 217-267. 

* Klein, D.P., 1982a, Regional gravity and magnetic evidence 

for a tectonic weakness across southwestern Arizona, in 

Frost, E.G., and Martin, D.L., eds., Mesozoic-Cenozoic 

tectonic evolution of the Colorado River Region: San Diego, Calif., Cordilleran Publishers, p. 61-67. 

+ ---1982b, Residual aeromagnetic map of the Ajo and 

Lukeville 1 o by 2° quadrangles, southwestern Arizona: 

U.S. Geological Survey Open-File Report 82-599, scale 

1:250,000. 

+ ---1983, Residual aeromagnetic map of the Hat Mountain quadrangle, Arizona: U.S. Geological Survey 

Open-File Report 83-292, scale 1:62,500. 

+Klein, D.P., and Baer, M.J., 1983, Audio-magnetotelluric and 

telluric profile data near the Mohawk Mountains and the 

Table Top Mountains, southwestern Arizona: U.S. Geological Survey Open-File Report 83-238, 7 p. 

* Klein, D.P., and Johnson, G.R., 1983, Density, porosity, and 

magnetic properties of rock specimens from southwestern 

Arizona: U.S. Geological Survey Open-File Report 83-

808, 10 p. 

* Klein, D.P., and Kucks, R.P., 1990, Gravity and aeromagnetic anomaly maps of the Ajo and Lukeville 1° X 2° 

quadrangles, southwestern Arizona, U.S. Geological Survey Miscellaneous Investigations Map I-2139, 2 sheets, 

scale 1:250,000. 

Luck, J.M., Haxel, G.B., and Theodore, T.G., 1983, Study of 

molybdenites from western North America using rhenium 

( 187Re)-osmium (1870s) geochronometer: unexpected old 

ages [abs.]: Eos (American Geophysical Union, Transactions), v. 64, no. 18, p. 334. 

* May, D.J., Peterson, D.W., Tosdal, R.M., LeVeque, R.A., 

and Miller, R.J., 1981, Miocene volcanic rocks of the Ajo 

24 The Conterminous United States Mineral Assessment Program: Ajo and Lukeville 1 o by r Quadrangles, Arizona 
Range, south-central Arizona [abs.], in Howard, K.A., 

Carr, M.D., and Miller, D.M., eds., Tectonic framework 

of the Mojave and Sonoran Deserts, California and Arizona: U.S. Geological Survey Open-File Report 81-503, 

p. 65-66. 

+ May, D.J., Tosdal, R.M., and Haxel, Gordon, 1981, Imbricate thrust faulting of Late Cretaceous or early Tertiary 

age, Organ Pipe Cactus National Monument, southwestern 

Arizona [abs.]: Geological Society of America Abstracts 

with Programs, v. 13, p. 95. 

* McClymonds, N.E., 1959, Precambrian and Paleozoic sedimentary rocks on the Papago Indian Reservation, Arizona: 

Arizona Geological Society Guidebook II, p. 77-84. 

*McDowell, F.W., 1971, K-Ar ages of igneous rocks from the 

western United States: Isochron/W est, no. 2, p. 1-17. 

Mosier, E.L., and Allcott, G.H., 1979, Geochemical evidence 

for thorium and associated elements in northern Sonora, 

Mexico, in Watterson, J.R., and Theobald, P.K., eds., 

Geochemical exploration 1978: Rexdale, Ontario Association of Exploration Geochemists, p. 129-137. 

* Mueller, K.J., Frost, E.G., and Haxel, Gordon, 1982, MidTertiary detachment faulting in the Mohawk Mountains of 

southwestern Arizona, in Frost, E.G., and Martin, D.L., 

eds., Mesozoic-Cenozoic tectonic evolution of the Colorado River region, California, Arizona, and Nevada: San 

Diego, Cslif., Cordilleran Publishers, p. 448-457. 

* Oppenheimer, J.M., and Sumner, J.S., 1980, Depth to bedrock in the basins of southern Arizona: Ajo and 

Lukeville, 2 sheets: Tucson, Laboratory of Geophysics, 

Department of Geosciences, University of Arizona, scale 

1:250,000. 

* Peirce, H.W., 1976, Elements of Paleozoic tectonics in Arizona: Arizona Geological Society Digest, v. 10, p. 37-57. 

* Peterson, J .A., 1984, Arizona mineral resource data: Information available through the U.S. Geological Survey 

Mineral Resource Data System: U.S. Geological Survey 

Circular 931, 31 p. 

+ Peterson, J.A., Cox, D.P., and Gray, Floyd, 1985, Mineral 

resource assessment of the Ajo and Lukeville 1 o by 2° 

quadrangles, Arizona: U.S. Geological Survey Open-File 

Report 85-0527, 77 p., 3 sheets, scale 1:250,000. 

* ---1987, Mineral resource .assessment maps of the Ajo 

and Lukeville 1 o by 2° quadrangles, Arizona: U.S. Geological Survey Miscellaneous Field Studies Map 

MF-1834-B, scale 1:250,000. 

* Peterson, J.A., and Tosdal, R.M., 1987, Mineral occurrence 

map and tabulation of geologic, commodity, and production data, Ajo and Lukeville quadrangles, southwestern 

Arizona: U.S. Geological Survey Miscellaneous Field 

Studies Map MF-1834-A, scale 1:250,000. 

* Peterson, N.P., 1938, Geology and ore deposits of the Mammoth mining camp area, Pinal County, Arizona: Arizona 

Bureau of Mines Bulletin 155, Geology Serial 11, 63 p. 

* Raines, G.L., 1978, A porphyry copper exploration model 

for northern Sonora, Mexico: U.S. Geological Survey 

Journal of Research, v. 6, no. 1, p. 51-78. 

* Reynolds, S.J., Richard, S.M., Haxel, G.B., Tosdal, R.M., 

and Laubach, S.E., 1988, Geologic setting of Mesozoic 

and Cenozoic metamorphism in Arizona, in Ernst, W .G., 

ed., Metamorphism and crustal evolution of the western 

United States, Rubey Volume 7: Englewood Cliffs, N.J., 

Prentice-Hall, p. 466-501. 

* Richter, D.H., Singer, D.A., and Cox, D.P., 1975, Mineral 

resources map of the Nabesna quadrangle, Alaska: U.S. 

Geological Survey Miscellaneous Field Studies Map MF655, 1 sheet, scale 1:250,000. 

Riggs, N.R., Haxel, G.B., and Busby-Spera, C.J., 1990, Paleogeography and tectonic setting of the Jurassic magmatic 

arc in southern Arizona: progress and problems [abs.]: 

Geological Society of America Abstracts with Programs, 

v. 22, p. 78. 

Rose, A.W., Hawkes, H.E., and Webb, J.S., 1979, Geochemistry in mineral exploration (2d ed.): London, Academic 

Press, 657 p. 

* Rowan, L.C., Wetlaufer, P.H., Goetz, A.F.H., Billingsley, 

F.C., and Stewart, J.H., 1974, Discrimination of rock types 

and detection of hydrothermally altered areas in south-central Nevada by the use of computer enhanced ERTS 

images: U.S. Geological Survey Professional Paper 883, 

35 p. 

* Rytuba, J.J., Till, A.B., Blair, W.N., and Haxel, Gordon, 

1978, Reconnaissance geologic map of the Quijotoa 

Mountains quadrangle, Pima County, Arizona: U.S. Geological Survey Miscellaneous Field Studies Map MF-937, 

scale 1:62,500. 

* Sawatzsky, D.L., and Raines, G.L., 1981, Geologic uses of 

linear features maps from small scale images, in O'Leary, 

D.W., and Earl, J.L., eds., Third International Conference 

on Basement Tectonics, Denver, Colo., Basement Tectonics Committee, Proceedings, p. 91-100. 

* Shafiqullah, M., Damon, P.E., Lynch, D.J., Reynolds, S.J., 

Rehrig, W.A., and Raymond, R.H., 1980, K-Ar geochronology and geologic history of southwestern Arizona and 

adjacent areas: Arizona Geological Society Digest, v. 12, 

p. 201-260. 

*Shride, A.F., 1967, Younger Precambrian geology in southern 

Arizona: U.S. Geological Survey Professional Paper 566, 

89 p. 

* Silver, L.T., 1978, Precambian formations and Precambrian 

history in Cochise County, southeastern Arizona, in 

Callender, J.F., Wilt, J.C., and Clemons, R.E., eds., Land 

of Cochise: Socorro, New Mexico Geological Society, 

Guidebook, 29th Field Conference, p. 157-163. 

* Silver, L.T., and Anderson, T.H., 1974, Possible left-lateral 

early to middle Mesozoic disruption of the southwestem 

North American craton margin [abs.]: Geological Society 

of America Abstracts with Programs, v. 6, no. 7, p. 955-

956. 

* ---1983, Further evidence and analysis of the role of the 

Mojave-Sonora megashear(s) in Mesozoic Cordilleran tectonics [abs.]: Geological Society of America Abstracts 

with Programs, v. 15, p. 273. 

* Singer, D.A., 1975, Mineral resource models and the Alaska 

Mineral Resource Assessment Program, in Vogely, W.A., 

ed., Mineral materials modeling: A state-of-the-art review: Baltimore, Md., Johns Hopkins University Press, p. 

370-382. 

* Singer, D.A., and Mosier, D.L., eds., 1983a, Mineral deposit 

grade-tonnage models: U.S. Geological Survey Open-File 

Report 83-623, 100 p. 

Selected References 25 
* ---1983b, Mineral deposit grade-tonnage models II: 

U.S. Geological Survey Open-File Report 83-902, 101 p. 

+Steele, H.J., 1978, Vekol Hills copper deposit, Pinal County, 

Arizona [abs.], in Jenny, J.P., and Hauch, H.R., eds., Porphyry Copper Symposium, Proceedings: Arizona 

Geological Society Digest, v. 11, p. 36. 

Stewart, J.H., Anderson, T.H., Haxel, G.B., Silver, L.T., and 

Wright, J.E., 1986, Late Triassic paleogeography of the 

southern Cordillera: The problem of a source for voluminous volcanic detritus in the Chinle Formation of the 

Colorado Plateau region: Geology, v. 14, p. 567-570. 

---1987, Late Triassic paleogeography of the southern 

Cordillera: The problem of a source for voluminous volcanic detritus in the Chinle Formation of the Colorado 

Plateau region: Discussion and Reply: Geology, v. 15, p. 

578-579. 

* Theobald, P.K., and Barton, H.N., 1983, Statistical parameters for resource evaluation of geochemical data for the 

Ajo 1 o by 2° quadrangle, Arizona: U.S. Geological Survey Open-File Report 83-734, 44 p. 

* ---1987a, Map showing anomalous copper concentrations in stream sediments and heavy-mineral concentrates 

from the Ajo and Lukeville 1 o by 2° quadrangles, Arizona: U.S. Geological Survey Miscellaneous Field 

Studies Map MF-1834-C, scale 1 :500,000. 

* ---1987b, Maps showing anomalous concentrations of 

lead, molybdenum, bismuth, and tungsten in stream sediments and heavy-mineral concentrates from parts of the 

Ajo and Lukeville 1 o by 2° quadrangles, Arizona: U.S. 

Geological Survey Miscellaneous Field Studies Map MF1834-D, scale 1:500,000. 

* ---1988, Maps showing anomalous concentrations of the 

zinc, silver, antimony, manganese, barium, and strontium 

in stream sediment and heavy-mineral concentrates from 

parts of the Ajo and Lukeville 1 o X 2° quadrangles, Arizona: U.S. Geological Survey Miscellaneous Field 

Studies Map MF-1834-E, scale 1:500,000. 

* Titley, S.R., 1976, Evidence for Mesozoic linear tectonic pattern in southeastern Arizona: Arizona Geological Society 

Digest, v. 10, p. 71-101. 

* Tosdal, R.M., 1979, Preliminary compilation of isotopic ages 

within the Ajo 1 o by 2° quadrangle, Arizona: U.S. Geological Survey Open-File Report 79-399, 7 p. 

Tosdal, R.M., and Haxel, Gordon, 1982, Two belts of Late 

Cretaceous to early Tertiary crystalline thrust faults in 

southwestern Arizona and southeastern California [abs.]: 

Geological Society of America Abstracts with Programs, 

v. 14, no. 4, p. 240. 

Tosdal, R.M., Haxel, G.B., Anderson, T.H., Connors, C.D., 

May, D.J ., and Wright, J .E., 1990, Highlights of Jurassic, 

Late Cretaceous to early Tertiary, and middle Tertiary tectonics, south-central Arizona and north-central Sonora, in 

Gehrels, G.E., and Spencer, J.E., eds., Geologic excursions through the Sonoran Desert region, Arizona and 

Sonora: Arizona Geological Survey Special Paper 7, p. 

76-88. 

Tosdal, R.M., Haxel, G.B., and Dillon, J.T., 1985, Lithologic 

associations of gold deposits, southeastern California and 

southwestern Arizona [abs.]: Geological Society of 

America Abstracts with Programs, v. 17, p. 414. 

* Tosdal, R. M., Haxel, G.B., and Wright, J.W., 1989, Jurassic 

geology of the Sonoran Desert region, southern Arizona, 

southeastern California, and northernmost Sonora: Construction of a continental-margin magmatic arc, in Jenny, 

J.P. and Reynolds, S.J., 1989, Geologic evolution of Arizona: Arizona Geological Society Digest, v. 17, p. 

397-434. 

'* Tosdal, R.M., and Miller, R.J., 1988, Thermo-tectonic terranes of the Ajo and Lukeville 1° X 2° quadrangles: 

K-Ar geochronology of early Tertiary and older rock, in 

Gray, Floyd (compiler), Abstracts of the symposium of the 

geology and mineral deposits of the Ajo and Lukeville 1° 

X 2° quadrangle, Arizona: U.S. Geological Survey 

Open-File Report 88-217, p. 10-13. 

* Tosdal, R.M., Peterson, D.W., May, D.J., LeVeque, R.A., 

and Miller, R.J., 1986, Reconnaissance geologic map of 

the Mount Ajo and part of the Pisinimo quadrangle, Pima 

County, Arizona: U.S. Geological Survey Miscellaneous 

Field Studies Map MF-1820, scale 1:62,500. 

* Tucker, W .C., 1980, The geology of the Aguila Mountains 

quadrangle, Yuma, Maricopa, and Pima Counties, Arizona: Arizona Geological Society Digest, v. 12, p. 

111-122. 

* Turner, R.L., Raines, G.L., Kleinkopf, M.D., and LeeMoreno, J.L., 1982, Regional northeast-trending structural 

control of mineralization, northern Sonora, Mexico: Economic Geology, v. 77, p. 25-37. 

+ U.S. Department of the Interior, Bureau of Indian Affairs, 

1977, Draft environmental impact statement, Vekol Hills 

project, Papago Indian Reservation, Pinal County, Arizona: 251 p. 

+ U.S. Geological Survey, 1979, Aeromagnetic map of the 

Aguila Mountains, and vicinity, Arizona: U.S. Geological 

Survey Open-File Report 79-1446, scale 1:250,000. 

---1980, Composite aeromagnetic map of the Papago 

area, Arizona: U.S. Geological Survey Open-File Report 

80-56, scale 1:250,000. 

+ ---1980, Aeromagnetic map of Cabeza Prieta area, 

southern Arizona: U.S. Geological Survey Open-File Report 80-97, scale 1:250,000. 

+ ---1980, Aeromagnetic map of the northern part of the 

Ajo 1 o by r quadrangle: U.S. Geological Survey OpenFile Report 80-1126, scale 1:250,000. 

+ ---1982, Aeromagnetic map of the Ajo area, Arizona: 

U.S. Geological Survey Open-File Report 82-665, scale 

1:62,500. 

* Wadsworth, W.B., 1968, The Cornelia pluton, Ajo, Arizona: 

Economic Geology, v. 63, p. 101-115. 

Ward, F.N., Nakagawa, H.M., Harms, T.F., and Van Sickle, 

G .H., 1969, Atomic absorption methods useful in 

geochemical exploration: U.S. Geological Survey Bulletin 

1289, 45 p. 

Wilson, B.D., 1933, Geology and mineral deposits of southern Yuma County, Arizona: Arizona Bureau of Mines 

Bulletin 134, 223 p. 

* ---1962, A resume of the geology of Arizona: Arizona 

Bureau of Mines Bulletin 171, 140 p. 

Wilson, B.D., Moore, R.T., and Cooper, J.R., 1969, Geologic 

map of Arizona: Arizona Bureau of Mines and U.S. Geological Survey, scale 1:500,000. 

26 The Conterminous United States Mineral Assessment Program: Ajo and Lukeville 1 o by 2° Quadrangles, Arizona 
Wilson, W.E., and Miller, D.K., 1974, Minerals of the 

Rowley Mine: The Mineralogical Record, v. 5, no. 1, p. 

10-30. 

* Wright, J.E., and Haxel, Gordon, 1982, A garnet-two-mica 

granite, Coyote Mountains, southern Arizona: Geologic 

setting, uranium-lead isotopic systematics of zircons, and 

nature of the granite source region: Geological Society of 

America Bulletin, v. 93, p. 1176-1188. 

Wright, J.E., Haxel, G.B., and May, D.J., 1981, Early Jurassic 

uranium-lead isotopic ages for Mesozoic supracrustal sequences, Papago Indian Reservation, southern Arizona 

[abs.]: Geological Society of America Abstracts with Programs, v. 13, p. 115. 

Zemann, J., and Wedepohl, K.H., 1972, Copper, in 

Wedepohl, K.H., ed., Handbook of geochemistry: Berlin, 

Springer-Verlag, p. 29-A-1 to 29-A-13. 

Selected References 27 

SELECTED SERIES OF U.S. GEOLOGICAL SURVEY PUBUCATIONS 

Periodicals 

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prices charged may differ from the prices in catalogs* annou~ments, 

and publications. · 
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