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Chapter G 

Mineral Resources of the 

Rawhide Mountains Wilderness Study Area, 

La Paz and Mohave Counties, Arizona 

By RICHARD M. TOSDAL, BRUCE BRYANT, 

RANDALL H. HILL, WILLIAM F. HANNA, 

DANIEL H. KNEPPER, JR., STEPHANIE L. JONES, and 

K.S. OLIVER 

U.S. Geological Survey 

STEVEN E. TUFTIN 

U.S. Bureau of Mines 

U.S. GEOLOGICAL SURVEY BULLETIN 1701 

MINERAL RESOURCES OF WILDERNESS STUDY AREAS: 

WEST-CENTRAL ARIZONA 
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 1990 

For sale by the Books and 

Open-File Reports Section, 

U.S. Geological Survey 

Federal Center, Box 25425 

Denver, CO 80225 

Ubrary of Congress Cataloging-In-Publication Data 

Mineral resources of the Rawhide Mountains wilderness study area, La Paz 

and Mohave counties, Ariz./ by R.M. Tosdal ... [et al.]. 

p. cm.-(U.S. Geological Survey bulletin; 1701-G) 

Includes bibliographical references. 

Supt. of Docs. no.: I 19.3:1701-G 

1. Mines and mineral resources-Arizona-Rawhide Mountains Wilderness. 2. Rawhide Mountains Wilderness (Ariz.) I. Tosdal, R.M. II. Series 

QE75.B9 no. 1701-G 557.3 s-dc 20 89-600375 

[TN24.A6] [553'.09791'72) CIP 
STUDIES RELATED TO WILDERNESS 

Bureau of Land Management Wilderness Study Areas 

The Federal Land Policy and Management Act (Public Law 94-579, October 21, 

1976) requires the U.S. Geological Survey and the U.S. Bureau of Mines to conduct 

mineral surveys of certain areas to determine the mineral values, if any, that may be 

present. Results must be made available to the public and submitted to the President and 

the Congress. This report presents the results of a mineral survey of part of the Rawhide 

Mountains Wilderness Study Area (A2rl>20-058A), La Paz and Mohave Counties, 

Arizona. 
CONTENTS 

Summary 

Abstract 

Gl 

Gl 

Character and setting Gl 

Identified resources G3 

Mineral resource potential 

Introduction G3 

Location and Physiography 

Previous work G4 

Methods of study G4 

Acknowledgments G4 

G3 

G4 

Appraisal of identified resources and known mineralized areas 

Summary G4 

Methods of investigation GS 

Mining history GS 

Appraisal of identified resources G6 

G4 

Mineralization associated with northwest -striking faults G6 

Mineralization associated with the Buckskin-Rawhide detachment 

fault G7 

Conclusions G8 

Assessment of mineral resource potential 

Geology G8 

Geologic setting G8 

Lower-plate terrane 

Upper-plate terrane 

Post-detachment rocks 

Structure GlO 

Geochemistry GlO 

G9 

G9 

G9 

Methods of study GlO 

Geochemical results GlO 

Geophysical studies GU 

Gravity and magnetic data 

Remote sensing G14 

Mineral resource assessment 

Base and precious metals 

Manganese G16 

Uranium and vanadium 

Oil and gas G17 

Geothermal water 

Sand and gravel 

References cited G17 

Appendixes 

G17 

G17 

GU 

G16 

G16 

G17 

GS 

Definition of levels of mineral resource potential and certainty of 

assessment G22 

Resource/reserve classification G23 

Geologic time chart G24 

Contents V 
VI Contents 

FIGURES 

1. Index map showing location of the Rawhide Mountains Wilderness Study Area, 

La Paz and Mohave Counties, Arizona G2 

2. Map showing mineral resource potential and generalized geology of the Rawhide 

Mountains Wilderness Study Area, La Paz and Mohave Counties, 

Arizona Gl2 

3. Bouger gravity anomaly map of the Rawhide Mountains Wilderness Study Area, 

La Paz and Mohave Counties, Arizona G14 

4. Aeromagnetic anomaly map of the Rawhide Mountains Wilderness Study Area, 

La Paz and Mohave Counties, Arizona GlS ~ 
Mineral Resources of the 

Rawhide Mountains Wilderness Study Area, 

La Paz and Mohave Counties, Arizona 

By Richard M. Tosdal, Bruce Bryant, Randall H. Hill, William F. Hanna, 

Daniel H. Knepper, Jr., Stephanie L. Jones, and K.S. Ofiver 

U.S. Geological Survey 

Steven E. Tuftin 

U.S. Bureau of Mines 

SUMMARY 

Abstract 

The Rawhide Mountains Wilderness Study area 

(AZ-Q2Q-058A} lies in the Rawhide Mountains and eastern 

Buckskin Mountains, west-central Arizona, some 40 mi east 

of Parker, Ariz. At the request of the U.S. Bureau of Land 

Management, mineral surveys of approximately 40,025 acres 

were done by the U.S. Geological Survey and U.S. Bureau of 

Mines to assess the mineral resources (known} and mineral resource potential (undiscovered) of the area. In this 

report, the study area refers to only that part of the wilderness 

study area for which a mineral survey was requested by the 

U.S. Bureau of land Management. 

Mining and prospecting activity has occurred in, or 

adjacent to, the Rawhide Mountains Wilderness Study Area 

in the northwest at the Big Kimble mine area, in the northcentral part of the study area, in the area immediately west of 

Alamo Lake on the east side of the study area, in the Alamo 

and Lincoln Ranch mineral districts in the west-central part of 

the area, and in the southern part of the study area. In most 

areas, gold, silver, and copper occur in mylonitic gneiss and 

schist along north~est-striking high-angle faults or along the 

Buckskin-Rawhide detachment fault and its subsidiary highand low-angle normal faults. Inferred gold, silver, and copper 

resources in these areas are subeconomic. Copper prospects in Tertiary conglomerates and mudstones west of 

Alamo Lake contain zones of hematite and thin seams of 

chrysocolla and malachite along shear zones related to the 

Buckskin-Rawhide detachment fault. Manganese occurs in 

Tertiary conglomerates along the southwest border of the 

study area on the fringe of the Lincoln Ranch mineral district. 

The deposits in both areas are too thin and too low grade. to 

be economic. . · 

Manuscript approved for publication, October 16, 1989. 

The mineral resource potential for precious and base 

metals (gold, silver, copper} is moderate and locally high in 

several areas. These areas are structurally controlled by 

northwest-striking high-angle faults in the western and southwestern parts of the study area, by high- and low-angle faults 

in the lower-plate terrane north of and immediately south of 

the Bill Williams River in the center of the study area, and by 

the Buckskin-Rawhide detachment fault and its upper-plate 

faults on the north-central and northwest parts of the area. A 

low mineral resource potential for precious and base metals 

is assigned to the southern part of the study area. Areas of 

moderate potential for manganese and low potential for 

uranium and vanadium resources occur in the limited Tertiary 

sedimentary and volcanic rocks in the northwestern, northeastern, southwestern, and east-central parts of the study 

area. There is low potential for low-temperature geothermal 

water in the northeasternmost part of the study area. The 

entire Rawhide Mountains Wilderness Study Area has low 

resource potential for sand and gravel in the sparse alluvial 

deposits and low resource potential for oil and gas. 

Character and Setting 

The Rawhide Mountains Wilderness Study area 

(AZ-020-058A) covers approximately 40,025 acres in 

west-central Arizona, (fig. 1) some 40 mi east of Parker . ' Anz. The study area lies astride the Bill Williams River ' which divides the Rawhide Mountains on the north from 

the Buckskin Mountains on the south. Elevations in the 

study area range from about 800 ft along the Bill 

Williams River to 3,927 ft at the Buckskin benchmark, at 

the crest of the Buckskin Mountains. 

The study area lies in the northwest-trending belt 

of metamorphic core complexes in west-central Arizona. 

(Rehrig and Reynolds, 1980). ~n these complexes, midcrustal and deeper rocks were tectonically transported to 

Mineral Resources of the Rawhide Mountains Wilderness Study Area, Arizona G1 
the surface along shallow-dipping normal faults or detachment faults during a period of extensional tectonism 

in the late Oligocene and Miocene (Davis and others, 

1980; Spencer and Reynolds, 1986a; Davis, 1988) (see 

"Appendixes" for geologic time chart). The BuckskinRawhide detachment fault of Spencer and Reynolds 

(1986b) crops out discontinuously along the west, north, 

and east borders of the study area (fig. 2). The detachment fault divides the bedrock geology of the area into 

two parts: an extended upper plate of Proterozoic, Paleozoic, Mesozoic, and Tertiary metamorphic, igneous, and 

sedimentary rocks, and a lower plate of Tertiary plutons 

and mylonite and mylonitic gneiss that were derived from 

Proterozoic, Paleozoic, Mesozoic, and Tertiary metamorphic, igneous, and sedimentary protoliths. Mylonitic 

deformation in the lower plate is considered to be a 

deeper level expression of, and slightly older than, brittle 

extensional faulting along the detachment fault and its 

upper plate (Davis, 1983; Spencer and Reynolds, 1986a; 

Howard and John, 1987; Davis and Lister, 1988). Syntectonic sedimentation and volcanism accompanied extension, and these rocks now crop out in the highly 

faulted upper-plate terrane (Davis and others, 1980; 

Otton, 1982; Spencer and.Reynolds, 1986b). 

During the last stages or after the end of the 

extensional deformation, high-angle faults cut the detachment terrane. The Lincoln Ranch reverse fault is the 

largest of these faults in the study area. 

\ I \.- /' -..,.. 

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8 

AREA OF MAP 

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I '- _,r \ / "'!ine.ral '~, ~ 1 \ / dtstnct ._.L----__.,:._ __ __. 

( \ / 7 ~~\ \ . 

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/ \ district, 

\ / APPROXIMATE BOUNDARY \~~~di;~t 1/ ~ \ 

. x RAWHIDE MOUNTAINS \ 

Mtdway I' ' , , WILDERNESS STUDY AREA \ 

/I ....... -...... (AZ-020-058A) \ I ~ \ 

/ " 1To ' Bouse .... i/ .... ._ ....... ._ ._ ...... 

To 

end en 

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i .. 

HARCUVAR 

MOUNTAINS 

5 MILES 

Figure 1. Index map showing location of the Rawhide Mountains Wilderness Study Area, La Paz and Mohave Counties, 

Arizona. Dashed hachured lines outline approximate boundaries of mineral districts adjoining the study area, as defined 

by Keith and others (1983a, b) and Spencer and Welty (1985, 1989). Dashed lines indicate unimproved roads. 

G2 Mineral Resources of Wilderness Study Areas: West-Central Arizona 
The extensional fault system, its associated syntectonic basins, and the younger high-angle faults are important controls on the distribution of mineral resources 

in the study area (Spencer and Welty, 1985, 1989). 

Mineral exploration in western Arizona and southeastern 

California has focused on these geologic terranes, and 

some metallic deposits and prospects are known (Sherbourne and others, 1979; Wilkins and Heidrick, 1982; 

Lehman and others, 1987; Wilkinson and others, 1988; 

Spencer and others, 1988). 

Identified Resources 

Mining and prospecting activity has occurred in the 

northern, central, and southern parts of the Rawhide 

Mountains Wilderness Study Area (fig. 2). Low gold, 

silver, and copper concentrations occur in northweststriking fault zones in mylonitic gneiss and metasedimentary rocks. Inferred subeconomic resources of 200,000 

tons of 0.02 troy ounces of gold per short ton of ore (troy 

oz gold/st), 0.04 troy oz silver/st, and 0.2 weight-percent 

copper are calculated for a mineralized fault zone in the 

Big Kimble mine area (fig. 2, No.3). In the north-central 

part of the study area, inferred subeconomic resources of 

20,000 tons of 0.05 troy oz gold/st, 0.01 troy oz silver/st, 

and 0.4 weight-percent copper are calculated for one of 

the faults in the area. The southeastern part of the 

Bluebell subdistrict of the Alamo mineral district has an 

adit with inferred subeconomic resources of 20,000 tons 

of 0.02 troy oz gold/st, 0.05 troy oz silver/st, and 0.15 

weight-percent copper (fig. 2, No.9). A nearby fault has 

inferred subeconomic resources of 90,000 tons of 0.05 

troy oz gold/st, 0.2 troy oz silver/st, and 0.7 weightpercent copper. The Bernard mine area (fig. 2, No.6) has 

an inferred subeconomic resource of 400,000 tons of 0.07 

troy oz gold/st, 0.2 troy oz silver/st, and 0.4 weightpercent copper. 

Prospects in and near the study area along the 

southwest edge of Alamo Lake are in Tertiary sedimentary rocks that contain zones of hematite and thin seams 

of chrysocolla and malachite in shear zones along the 

Buckskin-Rawhide detachment fault. Manganese concentrations related to shear zones in the BuckskinRawhide detachment fault are found in Tertiary 

sedimentary rocks along the west border of the study 

area. Resources were not determined for these areas 

because the occurrences are small. 

Mineral Resource Potential 

There is moderate and locally high mineral resource potential for precious and base metals (gold, 

silver, and copper) in the Rawhide Mountains Wilderness Study Area (fig. 2). These areas are located along 

high-angle faults in the western part of the study area, 

along high- and low-angle faults in the lower-plate terrane north of and immediately south of the Bill Williams 

River, and along the Buckskin-Rawhide detachment fault 

and related upper-plate faults in the northeastern, northwestern, and southwestern parts of the study area. Areas 

of high resource potential for these elements are defined 

by favorable geologic, geochemical, and geophysical data 

and by the presence of identified mineral resources 

inside and immediately adjacent to the study area. The 

southern part of the study area has a low resource 

potential for precious and base-metal. Areas of moderate 

potential for manganese and low potential for uranium 

and vanadium resources occur in the limited outcrops of 

Tertiary sedimentary and volcanic rocks in the northwestern, southwestern, northeastern, and east-central parts of 

the study area. 

The resource potential for oil and gas throughout 

the entire Rawhide Mountains Wilderness Study Area is 

low because of the sparsity of appropriate hydrocarbonbearing rocks. A low potential for low-temperature geothermal waters in the northeast corner of the study area 

is based on (1) the presence of a buried high-angle fault 

that in nearby areas is the locus of low-temperature 

geothermal springs and (2) the lack of any known occurrence of geothermal springs in the immediately adjacent 

area. The potential for sand and gravel resources is low 

and restricted to regions throughout the study area 

where alluvial fans and washes are present. 

INTRODUCTION 

This mineral survey was requested by the U.S. 

Bureau of Land Management and is the result of a 

cooperative effort by the U.S. Geological Survey and the 

U.S. Bureau of Mines. An introduction to the wilderness 

review process, mineral survey methods, and agency 

responsibilities was provided by Beikman and others 

(1983). Goudarzi (1984) discussed mineral assessment 

methodology and terminology as they apply to these 

surveys. The U.S. Bureau of Mines evaluates identified 

resources at individual mines and known mineralized 

areas by collecting data on current and past mining 

activities and through field examination of mines, prospects, claims, and mineralized areas. Identified resources 

are classified according to a system that is a modification 

of that described by McKelvey (1972) and U.S. Bureau of 

Mines and U.S. Geological Survey (1980). U.S. Geological Survey studies are designed to provide a scientific 

basis for assessing the potential for undiscovered mineral 

resources by determining geologic units a~d structures, 

possible environments of mineral deposition, presence of 

geochemical and geophysical anomalies, and applicable 

ore-deposit models. See "Appendixes" for the definition 

of levels of mineral resource potential and certainty of 

assessment and for. the resource/reserve classification. 

Mineral Resource• of the Rawhide Mountains Wilderness Study Area, Arizona G3 
Location and Physiography 

The Rawhide Mountains Wilderness Study Area 

(~20-{)58A) covers approximately 40,025 acres in 

west-central Arizona (fig. 1), some 40 mi east of Parker, 

Ariz. The study area lies astride the Bill Williams River, 

which divides the southeastern Rawhide Mountains on 

the north from the Buckskin Mountains on the south. 

Alamo Lake on the Bill Williams River lies just east of 

the study area. Elevations in the study area range from 

about 800 ft along the Bill Williams River to 3,927 ft at 

the Buckskin benchmark, the crest of the Buckskin 

Mountains (fig. 2). - -

Access to the Buckskin Mountains south of the Bill 

Williams River is provided by a paved road between 

Wenden and the Alamo Dam. A gravel gasline road 

leaves the paved road and crosses the Buckskin Mountains into the Reid Valley where Lincoln Ranch is 

located. Access to the Rawhide Mountains north of the 

river is provided by dirt roads heading south from Yucca, 

Ariz. 

The vegetation of the study areas is classified as 

Sonoran Desert scrub, and the main subdivision found in 

the study areas is the Arizona Upland subdivision 

(Brown, 1982). The Arizona Upland subdivision is a 

shrubland or low woodland of leguminous trees with 

open areas of shrubs and cacti. Cacti are important in this 

subdivision, and 20 species of cacti are largely confined 

to, or best represented in, the Arizona Upl~nd subd~v~­

sion. Major areas of the Lower Colorado Rtver subdtvt_-

sion are also found in the study area, especially in the 

Buckskin Mountains. Locally common riparian areas and 

wetland meadows are found around seeps, streams, and 

washes. The dominant shrubs and cacti include many 

species of cholla ( Opuntia spp. ), saguaro (Carnegie a 

gigantea), creosotebush (Larrea tridentata), and littleleaf 

paloverde ( Cercidium microphylum ). 

Previous work 

Early descriptions of the rock types and various 

mineral deposits in the Rawhide and Buckskin Mountains are found in Lee (1908), Bancroft (1911), and Jones 

and Ransome (1920). Lasky and Webber (1949) described the manganese deposits in the adjacent Artillery 

Mountains. The Rawhide Mountains were mapped by 

Shackelford (1976, 1980). Geologists from the Arizona 

Burea~ of Geology and Mineral Technology have studied 

the geologic setting of the mineral occurrences within the 

region (Keith and others, 1983a, b; Spencer and Welty, 

1985, 1986, 1989; Welty and others, 1985; Spencer and 

Reynolds, 1986a, b), and their work has been invaluable 

during the course of this mineral resource investigation. 

Spencer and Welty (1985) defined mineral districts 

throughout the region, including the study area, and 

these district names are used in this report. Spencer and 

Welty (1989) subsequently subdivided the mineral districts into subdistricts, and these subdivisions are used 

where appropriate. Areas outside of the study area have 

been actively explored for precious-metal and uraniumvanadium deposits (Sherbourne and others, 1979; Otton, 

1981, 1982; Wilkins and Heidrick, 1982; Mueller and 

Halbach, 1983; Wilkins and others, 1986; Lehman and 

others, 1987; Spencer and others, 1988), and the results 

of this work are applicable to the mineral resource 

potential of the study area. 

Methods of Study 

The U.S. Geological Survey conducted detailed 

field investigations of the Rawhide Mountains Wilderness Study Area in the winters of 1986 and 1987. This 

work included geologic mapping at scales of 1:24,000 and 

1:62,500, geochemical sampling, and the examination of 

outcrops for evidence of mineralization. The geochemical survey sampled rocks and stream sediments, which 

were analyzed for 33 elements by semiquantitative emission spectrography and for arsenic, antimony, bismuth, 

cadmium, gold, mercury, and zinc by atomic absorption. 

Regional gravity and aeromagnetic surveys were used in 

the assessment. Landsat thematic mapper images were 

interpreted for evidence of potential hydrothermal alte~­

ation in the study area. Further details on each analytical 

procedure undertaken for this resource assessment are 

given in a following section. 

Acknowledgments 

This work was supported by the Mineral Resource 

Appraisal and the National Geologic Mapping Programs 

of the U.S. Geological Survey. Discussions with J.E. 

Spencer and SJ. Reynolds of the Arizona Geological 

Survey improved our understanding of the geology of the 

area. A special thanks is extended to Diana Mangan for 

preparation of the figures and to Julia Thomas for 

patiently overseeing the final publication of the bulletin. 

APPRAISAL OF IDENTIFIED RESOURCES 

AND KNOWN MINERALIZED AREAS 

By Steven E. Tuftin 

U. S. Bureau of Mines 

Summary 

Most rocks in the study area are Tertiary mylonite, 

gneiss, and schist that were derived from Proterozoic, 

Paleozoic, Mesozoic, and Tertiary metamorphic, igneous, and sedimentary protoliths. These mylonitic rocks 

are part of a Tertiary metamorphic core complex and 

form the lower plate of the Buckskin-Rawhide detachG4 Mineral Resources of Wilderness Study Areas: West-Central Arizona 
ment fault of middle Tertiary age. Rocks in the upper 

plate of the detachment fault include granite, schist, and 

gneiss of Proterozoic, Paleozoic, and Mesozoic age and 

sedimentary and volcanic rocks of Tertiary age; these 

rocks are sparse within the study area. Northweststriking, northeast-dipping faults cut all the rocks and the 

detachment fault. 

Mines and prospects occur in or near the northern, 

west-central, east-central, and southwestern parts of the 

Rawhide Mountains Wilderness Study Area (fig. 2). 

Mineralized zones in three areas in the study area were 

of sufficient size to determine available resources. These 

areas are (1) a fault zone in the north-central part of the 

study area (fig. 2, No.4), (2) parts of the Alamo mineral 

district inside the study ar·ea, and (3) the Big Kimble 

mine area (fig. 2, No.3), just outside the north boundary 

of the study area. In all these areas, the mineralization in 

exposed parts of fault zones is oxidized. Under these 

conditions silver and copper are commonly depleted in 

the oxidized parts of the fault zones and concentrated in 

a lower sulfide zone. Drilling and geophysical work are 

needed to determine if additional resources are present 

at depth. 

Copper prospects along the west edge of Alamo 

Lake are in Tertiary conglomerates and siltstones that 

contain zones of hematite and thin seams of chrysocolla 

and malachite. These mineralized zones are adjacent to 

the Buckskin-Rawhide detachment fault. Copper concentrations in excess of 1 weight-percent were found in 

six samples from this area; however, the limited thickness 

and extent of the Tertiary strata in this area do not favor 

economic development of the minerals. 

Manganese oxides coat the surfaces of clasts and 

form part of the matrix of Tertiary conglomerate along 

the west border of the study area. Only small outcrops of 

conglomerate extend into the study area. The 

manganese-bearing zones here are too thin and low 

grade to be economic. 

Methods of Investigation 

A literature search was made for minerals information pertinent to the study area. Bureau of Land 

Management records were checked for current mining 

claims and oil and gas leases. A total of 32 field days was 

spent in the field examination of this study area in March, 

April, and May 1987. 

Two hundred and sixteen rock samples were collected from mines, prospects, and outcrops in and near 

the study area. Gold content was determined by fire assay 

with an atomic absorption spectrometry finish; silver and 

copper were determined by atomic absorption spectrometry. Of these samples, 22 were selected for multielement analyses by inductively coupled plasma-atomic 

emission spectrometry. Sample analyses were conducted 

I 

by Chemex Labs Inc., Sparks, Nev. Assay data and 

analytical results are summarized by Tuftin (1989) and 

are available for public inspection at the U.S. Bureau of 

Mines, Intermountain Field Operations Center, Building 

20, Denver Federal Center, Denver, Co. 

Mining History 

The study area includes most of the Bluebell 

subdistrict of the Alamo mineral district and lies adjacent 

to the Lincoln Ranch mineral district, the Black Burro 

mineral district, the Cleopatra mineral district, and the 

Artillery mineral district (fig. 1). Spencer and Welty 

(1985, 1989) outlined the extent of these districts and 

briefly described the individual workings within them. 

The Bluebell subdistrict of the Alamo mineral 

district lies in the west-central part of the study area (figs. 

1, 2). It includes nine patented claims (the ArizonaMontana mines (fig. 2, No.7)) outside the study area, the 

Mystery Hill group (fig. 2, No. 8) with workings extending into the study area, and the Bernard mine area (fig. 2, 

No. 6) in the southwestern part of the district (Tuftin, 

1989) The district is a past producer of copper, silver, 

gold, and minor lead. 

The claims forming the Arizona-Montana mines 

were located in July 1906. Mines and prospects in this 

group were worked intermittently until 1937 and produced approximately 170 tons of ore averaging 6 weightpercent copper, 0.8 troy oz silver/st, and 0.1 troy oz 

gold/st (Keith, 1978, p. 114). 

The Mystery Hill group includes numerous small 

workings that lie east of the Arizona-Montana mines and 

extend inside the study area. Keith (1978, p. 115) reports 

that the Mystery Hill group was first worked in the late 

1800's and worked sporadically through 1945, producing 

more than 500 tons of ore averaging about 3 weightpercent copper, 2 troy oz silver/st, 0.1 troy oz gold/st, and 

0.5 weight-percent lead. 

The Bernard mine area includes several prospect 

pits and small adits on a northwest -striking fault zone in 

the study area. This area was worked intermittently from 

1912-1936, producing 138 tons of ore averaging about 1 

weight-percent copper, 0.1 troy oz silver/st, and 0.1 

gold/st (Keith, 1978, p. 114). 

The Kimble subdistrict of the Cleopatra mineral 

district extends into the northwestern part of the study 

area (fig. 1 ). The Big Kimble mine is in the southeastern 

part of the Kimble subdistrict, along the north boundary 

of the study area. The Kimble subdistrict has produced 

50 tons of ore averaging 0.412 troy oz gold/st, 0.373 troy 

oz silver/st, and 0.14 weight-percent copper (Spencer and 

Welty, 1985, p. 4). 

The Lincoln Ranch mineral district is centered 

about 1.5 mi west of the study area (fig. 1). Almost all of 

the production in this district was from the Doyle mine 

(fig. 2, No. 11), an open-pit operation that was worked in 

Mineral Resources of the Rawhide Mountains Wilderness Study Area, Arizona G5 
the middle to late 1950's. The Doyle mine produced 

approximately 70,000 long tons of ore averaging 15-16 

weight-percent manganese (Keith 1978, p. 114). 

About 80 percent of the study area is covered by oil 

and gas leases and lease applications; however, there has 

been no drilling in or near the study area. 

]Low-temperature (less than 50 °C) geothermal 

waters are reported from wells and springs about 12 mi 

northeast of the study area along the Big Sandy River 

(fig. 1; Witcher and others, 1982; Stone and Witcher, 

1982). There are, however, no surface indications of 

hot-water spring activity in the study area. 

Gold, silver, copper, and manganese occur in the 

Rawhide Mountains Wilderness Study Area. Gold, silver, 

and copper occur in northwest -striking, northeastdipping fault zones in mylonitic rocks throughout the 

study area. Some of these occurrences are of sufficient 

size to calculate subeconomic resources. Hematite with 

copper minerals occur in upper-plate rocks adjacent to 

the Buckskin-Rawhide detachment fault west of Alamo 

lLake. Manganese oxides occur in the matrix in upperplate Tertiary conglomerate adjacent to the detachment 

fault along the west border of the study area. Resources 

were not determined for the latter two areas because the 

occurrences are smalL 

li\lili~(Sii'SJ~o~~oo~ 12\$$0CDSJ~sdl wo~~ 

INioDiihlw(S$~o$~1i'D~D~~ !FSJlUJ~~~ 

Gold, silver, and copper are found in oxidized 

portions of northwest-striking, northeast-dipping fault 

zones in lower-plate rocks in the Rawhide Mountains 

Study Area. Fault zones in the study area are oxidized 

where exposed. Silver and copper may have been depleted in the oxidized parts of the fault zones and concentrated! at a previous water table (zone of secondary 

sulfide enrichment). Drilling and geophysical! work would 

be needed to determine the presence of enriched zones at 

depth. A totan of 730,000 tons of resources was determined! for (1) selected strlllctures in the north-central pad 

of the study area, (2) parts of the Alamo mineral district 

in the west-centrall part of the study area, and (3) the Big 

Kimb!e mine area just outside the lllodlht boundary of the 

study area (Tuftin, 1989). ][n this repod, resollllrces are 

classified llllsing tlhte methods outRined by U.S. Bureau of 

Mines and U.S. GeoUogicaU SlUlnvey (1980). 

][n tlhte north-centraD part of the study area (fig. 2, 

No. 4), a smalU grollllp of workings, consistilllg of allll 

18-ft-deep shaft, a 9-ft-long adit, and several pits alllldl 

trenches, Dies alollllg five northwest-trending fauRt zollles in 

gneiss (Tllllftin, 1989). Twenty-six samples were takellll 

from these workings mull from Olllltcrops in the area. ][l!ll a!U 

but one of the fault zones, gold concentrations are very 

low to absent. The exception is from the eastern fault 

zone which contains gold concentrations ranging from 

0.002 troy oz/st to 0.205 troy oz/st. Silver and copper are 

associated with the gold but they typically occur in very 

low concentrations (Tuftin, 1989). An inferred subeconomic resource of 20,000 tons of 0.05 troy oz gold/st, 0.01 

troy oz silver/st, and 0.4 weight-percent copper was 

calculated for the eastern fault zone. This estimate 

assumes an average thickness of 1.3 ft, a depth of 225 ft, 

and a length of 450 ft for the fault zone. Metal concentrations in the other fault zones in this vicinity are very 

low and do not constitute a resource. 

Spencer and Welty (1985, p. 5-7) define the 

Bluebell subdistrict of the Alamo mineral district to 

include the mineralized area in the west-central part of 

the study area (figs. 1, 2). Workings in these sections can 

be subdivided into smaller groups. One group lies around 

the Bernard mine area, which includes numerous small 

workings lying in the western and southern parts of the 

mineral district (fig. 2, Nos. 6, 9). A second group of 

workings, in the eastern part of the mineral district, form 

the Mystery Hill group of unpatented claims (fig. 2, No. 

8). A third group, which includes the patented ArizonaMontana mines (fig. 2, No. 7), is outside the study area. 

The workings in the Alamo mineral district follow several 

northwest-striking, northeast-dipping fault zones in mylonitic gneiss with scattered lenses of metasedimentary 

rocks. Chrysocolla commonly coats fracture surfaces in 

the fault zones. 

The Bernard mine workings (fig. 2, No. 6) include 

10 prospect pits and 6 small adits on a northwest -striking, 

northeast-dipping fault zone in gneiss. Twenty-eight samples were collected from the mines and prospects in this 

area (Tuftin, 1989). The highest gold concentration 

found in the Rawhide Mountains Wilderness Study Area 

is from a 1.3-ft chip sample taken across a silicified 

breccia zone with gouge in a 22-ft-long adit. This sample 

contained a concentration of 0.3 troy oz gold/st. Seven 

samples from this fault zone have concentrations of 0.1 

troy oz gold/st or greater, and one contains 2.05 troy oz/st 

silver (Tuftin, 1989). Two samples had copper in excess 

of 1 weight-percent (Tuftin, 1989). The copper is present 

in the mineral chrysocoila, which forms thin seams and 

streaks in a breccia zone. An inferred! subeconomic 

resource of 400,000 tons of 0.07 troy oz gold/st, 0.2 troy 

oz sHver/st, alllld 0.4 weight-percent copper is estimated 

for the fauUt zone in the Bernard mine area using an 

estimated! Uength of 1,700 ft, a depth of 850 ft, and an 

average thickness of 2.5 ft for the fault zone. 

Unnamed workings southeast of the Bernard mine 

occlUlr alollllg a llllorthwest -striking, northeast -dipping fault 

zone (fig. 2, No. 9). One adit was driven along a horizontall siincified zone in gneiss that contains lenses of fluorite 

and callcite crystals. The silicified zone ranges from 1 to 4 

ft thiclk. Of 25 samples taken from this adit, 21 contained 
gold, with concentrations ranging from 0.003 to 0.072 

troy oz/st. Silver concentrations were detected in 22 

samples, with concentrations ranging from 0.01 to 0.69 

troy oz/st. One sample contained copper in excess of 1 

weight-percent. An inferred subeconomic resource of 

20,000 tons of 0.02 troy oz gold/st, 0.05 troy oz silver/st, 

and 0.15 weight-percent copper are estimated for this 

ad it, based on an estimated strike length of 345 ft, a width 

of 310 ft, and an average thickness of 2.1 ft (Tuftin, 

1989). Six samples collected from prospects in another 

northwest-striking fault zone contained gold, with concentrations ranging from 0.018 troy oz/st to 0.097 troy 

oz/st. An inferred subeconomic resource of 90,000 tons 

of 0.05 troy oz gold/st, 0.2 troy oz silver/st, and 0.7 

weight-percent copper estimated for this structure is 

based on an estimated strike length of 800 ft, a depth of 

400ft, and an average thickness of 2.3 ft (Tuftin, 1989). 

Workings in the Mystery Hill group (fig. 2, No. 8) 

are both inside and outside the study area east of the 

Arizona-Montana mines. They include numerous pits, 

short adits, and shafts on predominantly northwesttrending, northeast-dipping fault zones in gneiss with 

scattered lenses of metasedimentary rock. All 53 samples 

from workings and outcrops along the fault zones in the 

area typically contain very low gold and silver concentrations; 4 samples contain at least 0.03 troy oz gold/st, 2 

samples contain more than 0.5 troy oz silver/st, and 13 

samples contain copper in excess of 1 weight-percent 

(Tuftin, 1989). The highest gold concentration found in 

the Mystery Hill group, 0.086 troy oz gold/st, was collected from an outcrop of silicified gneiss in the far northern 

part of section 20. Samples having high gold concentrations are randomly distributed in parts of the fault zones 

that are not noticeably different from those which have 

little or no gold. Because the metal concentrations in 

fault zones in the Mystery Hill group are low and 

mineralization is discontinuous, these occurrences do not 

constitute a resource. 

Mines and prospects in the Arizona-Montana 

mines (fig. 2, No. 7) are privately owned. At the request 

of owner, analytical information relating to this area is 

proprietary and cannot be published. 

Numerous prospect pits and several small adits and 

shafts are in and near the southern part of the study area, 

about 1 mi southwest of the Buckskin benchmark (fig. 2, 

No. 12). These working form the Ives Peak subdistrict of 

the Alamo mineral district of Spencer and Welty (1989). 

The workings in the area are in seven 4- to 5-ft-wide fault 

zones in gneiss. The fault zones have a predominantly 

northwest strike and dip to the northeast; however, one 

fault zone about 250ft south of the study area strikes east 

and dips to the north. Twenty-nine samples were taken 

from the mines and prospects in this area. Gold was 

detected in 3 of these samples, and silver was detected in 

16; 3 samples show more than 1 weight-percent copper 

(Tuftin, 1989). Although three samples contain more 

than 1 weight-percent copper, surface samples indicate 

that the average metal concentrations are too low and 

mineralization too discontinuous to constitute a resource. 

Workings at the Big Kimble mine just outside the 

northwest boundary of the study area (fig. 2, No. 3) 

follow a northwest-trending, northeast-dipping fault zone 

in gneiss that was traced for about 1,000 ft. The fault 

zone is characterized by fractured and silicified gneiss, 

veins and lenses of quartz, breccia, and gouge. Limonite 

and chrysocolla typically coat fracture surfaces in the 

fault zone. Twenty-nine samples were taken from a part 

of the fault zone exposed by bulldozer cuts, a trench, a 

shaft, and three adits in the area. A sample collected 

from the footwall of a fault zone at the collar of an 

inaccessible shaft contained 0.086 troy oz/st gold (Tuftin, 

1989), the highest gold concentration measured for the 

Big Kimble workings. Six samples from the area have 

gold in excess of 0.02 troy oz/st; most samples contain 

less than 0.01 troy oz gold/st. Silver and copper are 

associated with the gold, but both are of less importance. 

An inferred subeconomic resource of 200,000 tons of 

0.02 troy oz gold/st, 0.04 troy oz silver/st, and 0.2 weightpercent copper was calculated for the fault zone in the 

Big Kimble mine area. This resource assumes an average 

thickness of 3.3 ft, a width of 500 ft, and a strike length of 

1,500 ft for the fault zone. This resource is outside of the 

study area, but extensions of the resource project toward, 

and may be present in, the study area. 

Mineralization Associated with the 

Buckskin-Rawhide Detachment Fault 

Copper occurs in mid-Tertiary dark-reddish-brown 

conglomerates and siltstones in the upper plate of the 

Buckskin-Rawhide detachment fault in the northeastern 

part of the study area near Alamo Lake (figs. 1, 2). These 

sedimentary rocks occur as small and discontinuous 

outcrops with discontinuous zones of mineralization 

along bedding planes or shear zones that are typically 3 to 

5 ft thick and contain abundant hematite and thin seams 

of chrysocolla and malachite. Eleven samples were taken 

from prospects in this area (Tuftin, 1989). Gold was 

detected in four of these samples, although the concentrations are at or near the detection limit in three of 

them. Silver was detected in six samples, but only in trace 

amounts. Six samples contained copper in excess of 1 

weight-percent. Thin seams and coatings of chrysocolla 

occur along fracture surfaces at these sample sites, and, 

although some of copper concentrations are more than 1 

weight-percent, the limited thickness and extent of the 

Tertiary strata in this area do not favor min~ral concentration in economic amounts. The mineralized zones in 

the Alamo Lake area are of limited extent, and the gold 

and silver concentrations are low. A mineral resource is 

not identified in this area. 

Mineral Resources of the Rawhide Mountains Wilderness Study Area, Arizona G7 
Manganese occurs in middle Tertiary conglomerates adjacent to the Buckskin-Rawhide detachment fault 

along the southwest border of the study area. These 

manganese occurrences are on the fringe of the lLincoln 

Ranch mineral district, which is centered about 1 mi west 

of the study area (figs. 1, 2): Manganese was mined by 

open-pit operations in this district, and most of the 

production was from the Doyle mine (fig. 2, No. 11; 

Keith, 1978, p. 114). The best grade mined (averaging 

15-16 weight-percent manganese) was closely associated 

with shear zones along the Buckskin-Rawhide detachment fault. Keith (1978, p. 19) t?Stimates that 200,000 

tons or more of manganese-bearing material averaging 3 

to 10 weight-percent manganese may remain around the 

previously operated mines. Several prospects expose 

Tertiary conglomerate with manganiferous lenses that 

range from 3 to 7 ft thick (Tuftin, 1989). The conglomerate consists of quartz and granite boulders between 2 

and 8 in. in diameter. Manganese oxides coat the surface 

of the boulders and form part of the conglomerate 

matrix. Three chip samples taken from prospects near 

the study area boundary contain more than 1 weightpercent manganese (Tuftin, 1989). These occurrences 

could not exceed 3 weight-percent manganese because 

there is a high ratio of gangue to manganese-oxides. At 

least 35 weight-percent manganese is required to be 

ore-grade (Jones, 1985, p. 485). H is unlikely that any 

development of the manganese-bearing strata would 

occur in the study area because the manganese-bearing 

strata are thin, the Tertiary strata in this area are of 

limited extent, and there is a high ratio of gangue 

minerals to manganese. 

Gold, silver, and copper concentrations occur in 

northwest-striking northeast-dipping fault zones in 

lower-plate gneiss and metasedimentary rocks in portions of the northern, central, and southern parts of the 

Rawhide Mountains Wilderness Study Area. An estimatedl total of 730,000 tons of inferred subeconomic resources was determined for several of the northwest-trending 

structures in the study area, from the Alamo mineral 

district in the west-central part, through the north-central 

part, to the Big Kimble mine area north of the study area. 

Resources of the Big Kimble mine project toward! the 

study area and may be present in it. ][n all these areas, the 

exposed parts of the veins are too thin and low grade to 

be economically mined on a large scale at the present 

time or in the foreseeable future. Drilling and geophysical work would be n,eeded to determine if additional 

resources are present at depth. 

Along the nodheast border of the study area, 

Tertiary sedimentary rocks adjacent to shear zones of the 

Buckskin-Rawhide detachment fault contain copper concentrations; however, th~ limited thickness and extent of 

the mineralized strata in this area do not favor economic 

development. 

Manganese concentrations along the west border 

of the study area are in conglomerates adjacent to shear 

zones of the detachment fault. Economic development of 

manganese in the study area is not likely because only 

small outcrops of Tertiary strata extend into the study 

area and the manganese-bearing zones are thin, low 

grade, and of limited strike extent. 

.til\~~!E~~~!EN!f COfF ~~N!E!PJ.til\l !PJ!E~COl!J!PJ(Cle 

[p)(Q)lf!EN!f~.til\l 

By Richard M. Tosdal, Bruce Bryant, Randall H. Hill, 

William F. Hanna, Daniel H. Knepper, Jr., 

Stephanie l. Jones, and K.S. Oliver 

U. S. Geological Survey 

The Rawhide Mountains Wilderness Study Area 

lies in the northwest-trending belt of metamorphic core 

complexes in the Basin and Range province of westcentral Arizona. (Rehrig and Reynolds, 1980). ][n these 

complexes, midcrustal and deeper rocks were tectonically transported to the surface along shallow-dipping 

normal faults or detachment faults during a period of 

extensional tectonism in the late Oligocene and Miocene 

(Spencer and Reynolds, 1986a). The detachment fault in 

the map area is known as the Buckskin-Rawhide detachment fault of Spencer and Reynolds (1986b ), and it crops 

out discontinuously around the borders of the study area 

(fig. 2). 

The Buckskin-Rawhide detachment fault divides 

the bedrock geology of the map area into two parts: an 

extended upper plate of Proterozoic, Paleozoic, and 

Mesozoic igneous and sedimentary rocks and Tertiary 

volcanic and sedimentary rocks, and a lower plate of 

Tertiary plutons and mylonitic rocks derived from Proterozoic, Paleozoic, Mesozoic, and Tertiary igneous, metamorphic, and sedimentary protoliths (fig. 2). Mylonitic 

deformation in the lower plate is considered to be a 

deeper level expression of, and slightly older than, brittle 

extensional ,faulting along the detachment fault and its 

upper plate (Davis, 1983; Spencer and Reynolds, 1986a; 

Howard and John, 1987; Davis and lLister, 1988). Syntectonic sedimentation and volcanism accompanied extension, and these rocks now crop out in the highly 

faulted upper-plate terrane (Davis and oth~rs, 1980; 

Spencer and Reynolds, 1986b). K-Ar, 40Arl9 Ar, and 

fnssion-track geochronologic data indicate that deformation ceased! by the middle Miocene (Otton, 1982; Spencer 

and! Reynolds, 1986a; lBryant and Naessar, 1987). 
During the last stages or after the end of the 

extensional deformation, high-angle faults cut the detachment terrane. The lLincoln Ranch reverse fault is the 

best known of these faults. Post-detachment rocks include sandstones, conglomerates, and unconsolidated 

sediments that have accumulated in scattered areas 

throughout the region. 

The rocks units of the lower-plate terrane are 

characterized by a subhorizontal mylonitic foliation and 

an accompanying northwest-trending elongation lineation. This fabric was superposed on all the lower-plate 

rock units during Tertiary extensional deformation, and 

it overprints any older metamorphic fabric. The following 

description of these rocks deals only with the protoliths of 

the Tertiary mylonites. 

The oldest protolith in the lower-plate terrane is a 

heterogeneous Proterozoic gneissic terrane consisting of 

augen gneiss, layered hornblende-bearing mafic gneiss, 

metagranite, quartzofeldspathic migmatites, and pegmatites. Most of these rocks have been deformed several 

times. 

Marbles, quartzites, calc-silicate rocks, phyllites, 

and schist are interleaved with the Proterozoic gneissic 

rocks. These rocks are considered equivalent to Paleozoic and lower Mesozoic cratonal sedimentary rocks and 

Jurassic volcanic rocks that crop out in the upper plate of 

the Buckskin-Rawhide detachment fault and also on the 

Colorado Plateau, about 80 mi to the northeast (Shackelford, 1976; Reynolds and others, 1987). The tectonic 

interleaving of the Proterozoic, Paleozoic, and Mesozoic 

rocks probably occurred in the late Mesozoic during 

contractional deformation similar to that documented in 

the upper plates of the detachment faults in the region 

and in adjacent ranges to the southeast (Reynolds and 

others, 1986; Spencer and Reynolds, 1987; Bryant and 

Wooden, ·1989). 

lLeucocratic garnet-bearing mylonitic granite 

gneiss and associated aplite and pegmatite gneiss intruded the older terrane prior to the mylonitic deformation. 

These granitic gneiss occur as sills, dikes, and small 

plutons. The rocks are lithologically similar to the granite 

of Tank Pass of Rehrig and Reynolds (1980) in the 

Harcuvar Mountains, some 20 mi to the southeast 

There, the granite is assigned a lLate Cretaceous age, on 

the basis of an unpublished Rb-Sr isochron (Reynolds 

and others, 1983). 

A heterogeneous assemblage of medium- to 

coarse-grained igneous rocks of the Swansea plutonic 

suite (Bryant and Wooden, 1989) is the youngest rock 

unit in the lower-plate terrane. Rock types include gabbro, diorite, porphyritic granodiorite, and Reucocratic 

granodiorite. Parts of this suite have been previously 

mapped! as Mesozoic diorite and quartz monzoll1lite lby 

Shackelford (1976). Most of the rocks are variably mylonitized and metamorphosed, but some rocks of the 

plutonic suite are interpreted to have intruded the lowerplate terrane synkinematically with the myUonitic deformation (Shackelford, 1976; Bryant and Wooden, 1989). 

A U-Pb zircon age of 21.6±1.5 Ma from a granodiorite 

outside of the map area (Bryant and Wooden, 1989) 

indicates an early Miocene age for the younger part of 

the suite. Kn the study area, the Swansea plutonic suite 

underlies much of the Rawhide Mountains. 

lUJppS!r·I?~Sl~~ 'iJSfrfrSlii'DS 

Upper-plate rock units are typically fault bounded 

and commonly intensely brecciated and fractured. :For 

the most part, upper-plate rocks lie outside the study 

area. The following description includes rock units outside of the study area but within the map area shown on 

figure 2. 

Xntensely brecciated granite, layered gneiss, and 

minor diorite dikes that occur west of the study area in 

the Reid Valley (lLincoln Ranch area) may be the oldest 

rocks in the upper plate. According to Spencer and 

Reynolds (1986a), these rocks could be either Proterozoic or Mesozoic. 

Weakly to moderately metamorphosed marble, 

schist, phyllite, and quartzite occur in Reid Valley and in 

the Rawhide Mountains. Shackelford (1976) and Spencer and! Reynolds (1986a) correlate these rocks with 

other cratonal! Paleozoic rocks found in the region and on 

the nearby Colorado Plateau. The relation of these rocks 

to the Proterozoic or Mesozoic grai1litic rocks is unknown, as they occur in separate fault blocks. 

Tertiary sedimentary and volcanic rocks unconformably overlie the crystalline and metasedimentary 

rocks. The sedimentary rocks consist of reddish sandstone, conglomerate, breccia, siltstone, mudstone, and 

grey limestone. The volcanic rocks consist of basaltic, 

andesitic, and latitic flows, flow breccias, and! agglomerates; silicic tuffs are minor. All the rocks dip moderately 

to steeply. Previous workers in the region (Shackelford!, 

1976; Spencer and Reynolds, 1986a) correlated these 

rocks to the Chapin Wash and Artillery :Formations and 

to the Sandtrap conglomerate of lLasky and! Webber 

(1949). K-Ar dates from the interbedded! volcanic rocks 

in the region indicate that tlhese rocks are of Miocene age 

(Otton, 1982). 

!?1o~~a[Q)®~~clhlm~II'D~ !ffic~~~ 

lPost-dletachment rocks are sparse in the map area. 

The rocks are divided into three broad! units. The oYdest 

unit COJrnsists of subhorizontal conglomerate alllldl sMdlstone that filled structural depressions in the dldaclhment 

terrane after dne cessation of extensionaU deformation. 

Detritus in these rocks is llocaHy dlerivedl. CDasts of 
upper-plate rocks are more abundant than are those of 

mylonitic rocks of the lower-plate terrane. 

The younger units consist of unconsolidated to 

poorly consolidated sandstone and conglomerate and 

alluvium that unconformably overlies all older rock units. 

Mylonitic rocks of the lower plate are a major detrital 

component. The sandstone and conglomerate occur in 

moderate dissected alluvial fans and as terrace gravels 

above the modern washes. Alluvium occurs in the modern washes and fills larger valleys such as Reid Valley 

near Lincoln Ranch. 

Structure 

The major structure within the study area is the 

Buckskin-Rawhide detachment fault. The regionally subhorizontal normal fault superposes high-crustal-level 

rocks, including syntectonic sedimentary rocks, onto 

rocks that were at mid-crustal depths prior to extension. 

Presently the detachment dips off the edges of the 

mylonitic rocks in its lower plate. Other low-angle normal faults structurally below the detachment fault are 

abundant in the Rawhide Mountains. All of the lowangle faults cut the regionally shallow dipping and undulating mylonitic fabrics. 

Brittle high- and low-angle faults in the upper-plate 

rocks formed contemporaneously with the detachment 

fault. Intense brecciation and fracturing along these 

faults are important to the deposition of metallic minerals by hydrothermal fluids circulating along the structures (Wilkins and Heidrick, 1982; Spencer and Welty, 

1986; Beane and others, 1986). Many small mines in and 

adjoining the study area are located along the faults in 

the upper-plate terrane. 

The Lincoln Ranch reverse fault cuts the mylonitic 

lower plate and the Buckskin-Rawhide detachment fault. 

The Lincoln Ranch fault dips steeply northeast in the 

center of the map area but dips shallowly northeast in the 

Rawhide Mountains (Shackelford, 1976). Other subparallel high-angle faults cut the lower-plate mylonitic rocks. 

Numerous base- and precious-metal mines are located 

along the smaller high-angle faults (fig. 2). 

Geochemistry 

Methods of Study 

A total of 73 minus-60-mesh stream-sediment 

samples collected from active stream alluvium and 73 

heavy-mineral, panned concentrates derived from stream 

sediment were selected as primary sample media. These 

sediments are thought to represent a composite of the 

chemistry of rock and soil exposed in the drainage basin 

upstream from the sample site. Chemical analysis of 

these stream-sediment samples provides data useful in 

identifying those drainages which contain unusually high 

concentrations of elements that may be related to mineral occurrences. In addition, studies have show:n that 

heavy-mineral panned concentrations derived from 

stream sediments are a useful sample medium in arid 

and semiarid environments or in areas of rugged topography, where mechanical erosion dominates over chemical erosion (Bugrov and Shalaby, 1975; Overstreet and 

Marsh, 1981). The heavy-mineral-concentrate samples 

provide information about the chemistry of a limited 

number of minerals present in the rock material eroded 

from the drainage basin upstream from each sample site. 

This selective concentration of ore-related minerals permits determination of some elements that are not easily 

detected in bulk stream-sediment samples. 

To represent the rocks exposed in the vicinity of the 

sample sites, 65 fresh and unaltered rock samples were 

collected. In addition, seven composite mine-dump samples were collected to provide some general information 

on the mineralization present in the area. All samples 

were analyzed for 31 elements using a semiquantitative 

direct-current arc emission spectrographic method 

(Grimes and Marranzino, 1968). In addition, the rock 

and stream-sediment samples were analyzed for arsenic, 

antimony, bismuth, cadmium, zinc, gold, tellurium, and 

thallium by wet chemical and atomic absorption techniques. 

Geochemical Results 

Of the elements analyzed by emission spectrography and wet chemical analysis, barium, copper, lead, 

molybdenum, tellurium, tungsten, and zinc were deemed 

to be related to possible mineralization. Threshold values, defined as the upper limit of normal background 

values, were determined for each element by inspection 

of frequency distribution histograms for all sample media. The composite mine-dump rock samples were not 

included in construction of the histograms. A geochemical value higher than the threshold value is considered 

anomalous and worthy of scrutiny as a possible indicator 

of mineralization. 

Three anomalous areas were identified in the study 

area on the basis of the presence of multi-element 

anomalies clustered within a restricted geographic region. Several other isolated sites contained single or 

multi-element anomalies. Future follow-up studies in the 

area should re-examine all anomalies, particularly since 

the scale of sampling for this compilation would allow a 

moderate-sized deposit to be identified by only one 

sample locality. 

An area on the west-central boundary of the study 

area exhibits strongly anomalous values of barium, copper, lead, molybdenum, tungsten, and zinc in heavymineral-concentrate samples and copper, cobalt, nickel, 

tellurium, and zinc in the minus-60-mesh streamsediment samples. The source of these anomalies is the 

G10 Mineral Resources of Wilderness Study Areas: West-Central Arizona 
epithermal quartz veins and mine dumps at the ArizonaMontana mines, Bluebell mine, and other mines and 

prospects in the area. The mineralization here is localized along high-angle faults that cut the mylonitic rocks 

of the lower plate of the Buckskin-Rawhide detachment 

fault. The faults are parallel to, and probably related to, 

the high-angle Lincoln Ranch fault, located about a mile 

to the west. 

In the western part of the study area along the 

north side of the Bill Williams River, five drainage basins 

are all characterized by anomalous concentrations of 

barium, copper, lead, vanadium, and zinc in the heavymineral concentrat~s; one drainage basin also has anomalous concentrations of tungsten. Scattered, weakly 

anomalous concentrations of copper,cobalt, lead, molybdenum, and zinc are identified in the minus-60-mesh 

stream-sediment samples. These anomalies are probably 

related to hydrothermal alteration along the BuckskinRawhide detachment fault or to unidentified epithermal 

mineralization along the Lincoln Ranch fault. 

In the northwest part of the study area, strongly 

anomalous concentrations of barium in heavy-mineralconcentrate samples and moderately anomalous concentrations of arsenic, copper, lead, and zinc in the minus60-mesh stream-sediment samples have been identified 

in five drainage areas. Two sources for these anomalies 

are suggested. One source is contamination from a 

stratiform manganese prospect north of the study area in 

combination with the fault-controlled epithermal veins at 

the Big Kimble mine. A second source is the hydrothermal alteration along the detachment fault in the immediate area. 

Scattered throughout the study area are sites 

whose heavy-mineral-concentrate samples contain only a 

few anomalous elements. Barium or barium and lead 

anomalies occur downstream from the Swansea plutonic 

suite in the Rawhide Mountains. Isolated sites containing 

only anomalous concentrations of barium in the heavymineral concentrates are found in the southern Buckskin 

Mountains and may be related to contact zones between 

Late Cretaceous mylonitic granite gneiss and the Proterozoic country rocks. The lack of other anomalous elements in these samples suggests that these anomalies 

might not be related to hydrothermal mineralization. 

Just north of the Bill Williams River in the central 

part of the study area, a drainage basin contains strongly 

anomalous concentrations of barium, lead, and molybdenum in a heavy-mineral-concentrate sample. Weakly 

anomalous concentrations of copper in the minus-60-

mesh stream-sediment sample are found at the same site. 

Epithermal veins and mine dumps upstream from the 

sample site in the north-central area are considered to be 

the source of the anomaly. 

Two areas show anomalous concentrations of molybdenum in minus-60-mesh stream-sediment samples. 

One site in the extreme sout~-central part of the study 

area is also associated with moderately anomalous concentrations of copper. The other molybdenum anomaly 

occurs in the southeast part of the study area. 

Three other sites are immediately south of the Bill 

Williams River in the Buckskin Mountains. One streamsediment sample site from Ives Wash contains anomalous concentrations of copper. Less than 1 mi to the west, 

anomalous concentrations of gold were detected in a 

single stream-sediment sample. A stream-sediment sample from near Alamo Dam contains high concentrations 

of tungsten. All locations are close to faults and may 

reflect local epithermal mineralization. 

Geophysical studies 

Gravity and Magnetic Data 

The study area is covered by regional gravity (Aiken and others, 1981; Defense Mapping Agency Aerospace Center, 1974, 1975) and aeromagnetic (Western 

Geophysical Company of America, Aero Service Division, 1979) surveys having sufficient resolution to define 

anomalies of about 2 me in area or larger. Contours of 

complete (terrain-corrected) Bouguer gravity anomalies· 

are defined by 13 gravity stations within or near the study 

area. Contours of total-field magnetic anomalies are 

defined by measurements made along 11 east-west flightlines spaced 1 mi apart at a nominal height of 400 ft 

above terrain. 

The gravity anomaly map (fig. 3) shows that the 

study area and surrounding region are transected by a 

uniform gradient which is steep north of the area and 

gentle over the area, with anomaly values increasing 

toward the south. The steep part of the gradient appears 

to be caused by the strong density contrast and nearly 

vertical edge of a block of mylonitic Proterozoic, Paleozoic, Mesozoic, and Tertiary rocks which underlies the 

Rawhide Mountains and the Buckskin Mountains immediately to the south. A northwest-trending fault in 

Sandtrap Wash along the northeast boundary of the 

study area probably forms the edge of the the mylonitic 

rocks. Superposed on the gentle part of the gradient are 

a small-amplitude high, in the form of a north-facing 

nose over the western part of the area, and a smallamplitude low in the form of a southwest-facing nose 

over the eastern part of the area. The high is mainly 

associated with the Tertiary Swansea plutonic suite which 

contains diorite of high density. The influence of the 

diorite on the high is inferred to be small, however, 

because the magnetic anomaly data do not indicate a 

subsurface abundance of this mafic rock. The low is not 

associated with specific terranes of mapped rocks, and its 

source is unknown. Possible sources of the low are a 

low-density quartzofeldspathic or granitic mylonite or a 

nonmagnetic low-density felsic body intruding the mylonite at shallow depth. 

Mineral Resources of the Rawhide Mountains Wilderness Study Area, Arizona G11 
Base from USGS 1:62,500 

Ives Peak, Artillery Peak 

EXPLANATION 

---Contact 

---Fault-Dashed where inferred; dotted 

where concealed 

..... _ _. • .___ Reverse fault-Dotted where concealed; 

sawteeth on upper plate 

.11...-LL......I.&...-UII Buckskin-Rawhide detachment faultDotted where concealed; ticks on the 

upper plate 

X' a Mine-Number refers to iist of mines and 

prospects. Red overprint indicates 

identified resource. 

Prospect-Number refers to list of mines 

and prospects 

• 

.. 

~ 

D 

B 

c 

D 

Ag 

Au 

Cu 

Mn 

u 

v 

Geo 

OG 

SG 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

Qal 

OTs 

Tc 

Tvs 

msg 

Ts 

Km 

mgn 

EXPLANATION 

Area having high mineral resource potential (H) for gold, · 

silver, and copper 

Area having moderate mineral resource potential (M) for 

gold, silver, and copper 

Area having moderate mineral resource potential (M) for 

manganese and low mineral resource potential (L) for 

uranium and vanadium 

Area having low resource potential (L) for commodities as 

indicated 

Level of certainty of assessment 

Data only suggest level of potential 

Data give good indication of level of potential 

Data clearly defme level of potential 

Commodities 

Silver 

Gold 

Copper 

Manganese 

Uranium 

Vanadium 

Geothermal 

Oil and gas 

Sand and gravel 

Mines and prospects 

Bonanza mine 

McGuffie mine 

Big Kimble mine 

Unnamed mines and prospects in north-central area 

Unnamed prospects by Alamo Lake 

Bernard mine 

Arizona-Montana mines 

Mystery Hill group 

Unnamed mines in sections 19 and 20 

Bluebell mine 

Doyle mine 

Unnamed mines and prospects southwest of Buckskin 

benchmark 

Geologic map units 

Post-detachment rocks 

Alluvial deposits (Quaternary) 

Sandstone and conglomerate (Quaternary and Late 

Tertiary) 

Conglomerate and sandstone (Late Tertiary) 

Upper-plate rocks 

Sedimentary and volcanic rocks (Miocene and 

Oligocene?) 

Metasedimentary and granitic rocks (Mesozoic, 

Paleozoic, and Proterozoic) 

Lower-plate rocks 

Swansea plutonic suite (Miocene) 

Mylonitic granite (Late Cretaceous) \ 

Mylonitic gneiss (Tertiary, Mesozoic, Paleozoic, and 

Proterozoic) 

Figure 2. Mineral resource potential and generalized geology of the Rawhide Mountains Wilderness Study Area, La Paz and Mohave Counties, Arizona. Geology of Reid Valley and Lincoln Ranch area modified from Spencer and Reynolds (1986a). Geology of Rawhide 

Mountains modified from Shackelford (1976) and modified by Bruce Bryant (1986 to 1987). Geology of Buckskin Mountains by Bruce Bryant (1986 to 1987) and R.M. Tosdal (1987). 

G12 Mineral Resources of Wilderness Study Areas: West-Central Arizona Mineral Resources of the Rawhide Mountains Wilderness Study Area, Arizona G13 
The aeromagnetic anomaly map (fig. 4) is dominated by a northwest-trending region of highs, marked by 

nonhachured contours above 200 nanoteslas (nT). An 

isolated east-west trending high above the 200 nT contour occurs over the western part of the area. Most of the 

large region of highs in the Rawhide and Buckskin 

Mountains correlates with the exposures of the Swansea 

plutonic suite (fig. 2) and in the southeast part of the 

study area with outcrops of mafic gneisses in the lowerplate terrane. In the absence of further subsurface information, it is inferred that much of the region of the high 

is underlain by the Swansea pl~tonic complex. The 

isolated east -west high has an unknown source, but it also 

correlates with outcrops of the Swansea plutonic suite 

(fig. 2). This latter high clearly is not associated with the 

exposed magnetic diorite phase of the plutonic suite to 

the south because, in agreement with gravity anomaly 

data, this diorite is insufficient in vertical extent to 

generate a significant anomaly. 

The most significant conclusion drawn from the 

combined gravity and magnetic anomaly data is that 

normal-density, magnetic, felsic intrusive rocks underlie 

significant parts of the study area. High-density, magnetic 

diorite in the western part of the area is thin and limited 

areally. 

Remote Sensing 

Digital image data acquired by the Thematic Mapper (TM) system on the Landsat-4 satellite (image No. 

40174-17383) were analyzed to detect and map areas 

Figure 3. Bouguer gravity anomaly map of the Rawhide Mountains Wilderness Study Area (shaded), La Paz and Mohave 

Counties, Arizona. Contour interval 1 milligal; gravity stations denoted by x. 

G14 Mineral Resource• of Wlldemeu Study Areaa: Weat-Central Arizona 
that may contain hydrothermally altered rocks. The six 

visible and near-infrared bands of image data were 

digitally processed to enhance spectral characteristics of 

minerals that often accompany alteration or are derived 

from the weathering of altered rocks. Visual interpretation of a vegetation-masked TM color-ratio composite 

consists of identifying areas having concentrations of 

limonite (group 1 ), areas of hydroxl-bearing and/or hydrated minerals (group 2), and areas where both groups 

of minerals occur together (group 3). Identification of 

the different groups is based on the spectral responses of 

the different limonitic minerals in the TM bands (Hunt 

and Salisbury, 1971, Raines, 1977; Hunt and Ashley, 

1977). 

On the basis of the TM images, areas of the 

different limonite-group minerals occur in the Rawhide 

Mountains Wilderness Study Area. Areas of ,alluvial 

deposits and Tertiary sedimentary rocks were excluded 

from this analysis. Moderate to dense vegetation obscures the rocks and soils of much of the study area and 

hinders the interpretation of the TM images. Furthermore, the rugged topography in the study area, combined 

with the relatively low solar-elevation angle at the time 

the TM data were acquired, results in a significant part of 

the study area being in deep to moderate shadow on the 

TM data. Vegetation and shadows have, therefore, greatIy limited the area of surface rocks and soils that could be 

spectrally analyzed for evidence of possible alteration 

Figure 4. Aeromagnetic anomaly map of the Rawhide Mountains Wilderness Study Area (shaded), La Paz and Mohave 

Counties, Arizona. Contour interval 20 nanoteslas; hachures indicate closed areas of lower values. Dotted lines show 

flightlines. 

Mineral Resources of the Rawhide Mountains Wilderness Study Area, Arizona G15 
minerals. Because of these masking effects, the areas of 

identified anomalies may represent only portions of more 

extensive areas. 

A fairly uniform distribution of group-1 (limonite) 

minerals occurs over the southern, western, central!, and 

northwestern parts of the study area. Because of the size 

of these areas, it is believed that they are probably related! 

to the distribution and weathering of one or more 

prominent rock units and do not suggest that large scale 

hydrothermal alteration has occurred in the area. Within 

the study area, other potential-alteration anomalies of 

groups 1 and 3 are moderately abundant. Concentrations 

of group-2 minerals only are rare within the study area. 

Concentrations of group-3 minerals are spatially associated with clusters of shafts and adits at the known 

mineral occurrences in the Alamo mineral district (figs. 

1, 2, Nos. 6, 7, 8, 9, 10) and around the Bonanza, 

McGuffie, and Big Kimble mines (fig. 2, Nos. 1, 2, 3) 

north of the study area. Other concentrations of groups 1 

and 3 are scattered throughout the study area and! are ll1lOt 

clearly related to areas of known altered rocks or mineralization. Several areas of minerals of groups 1 and! 3 nne 

in the southern Buckskin Mountains where the lLate 

Cretaceous mylonitic granite crops out. No known mineral occurrence is known withill the area, although 

anomalous barium concentration was detected in one 

stream-sediment sample from the area. 

'fhe assessment of the mineral resource potential 

of the Rawhide Mountains Wilderness Study Area draws 

upon different and! diverse sets of geoUogic data. Jindudledl 

lin these data are the regional! geoHogy, geoclhtemistry, 

geophysics, mi:neraU occunellce maps, minillg drum 

records, and! the available ore deposit models tlhtat are 

appljcable to the geologic terrane ill1l the study area. 

'fhese data were used! to deiineate favorabUe tracts witlhtin 

the study area, and! an estimate of the leveU of resource 

potential and! degree of certainty for each tract well"e 

made by using the criteria outlined ilDl the "Appendixes." 

'fhrough.out thns dnscussnolDl, mil!1lerall resource potelDltiall 

refers only to undiscovell"ed minell"alill"esotuces. 

Areas of resource poteJrntnall foll" gold, sinvell", copper, 

manganese, uranium, and! vanadium minerals are JPll"eselDlt 

in the study area. 'fhese Me ouHilDled on ft'igune 2 and! Me 

discussed lbeUow. AppHcalble metallic ore dleposnt mooeUs 

for tlhe study area indudle detachmelrllt-fault-ll"eUated baseand! pll"ecious-metan deposits (WiUcil!1ls and! lHieidlll"nclk, 

1982; Wilkins and! others, 1986; Spencell" and! WeUty, 

1986; SpelDlcell" and! others, 1988), stll"ataboundl allhdl faulltcontrolledl manganese deposits (Cox allhdl SiJrngell", 1986; 

Spencer and! Welty, 1985}, and! strataboulDldl ullll"mium and! 

vanadium dlepnsits (Sherbourne and! others, 1979; OUolDl, 

1981; Spencer and Welty, 1985). One smalll area lhtas 

resource potential for low-temperature geothermal waters. 'fhe entire study area has a low potential for oil and 

gas and deposits of sand and gravel. 

Base- and precious-metal mines and prospects in 

and! adjacent to the Rawhide Mountains Wilderness 

Study Area have been worked intermittently since the 

late 1800's and have produced approximately 2,000 tons 

of ore containing 34 tons of copper, 157 tons of lead, 11.5 

tons of zinc, about 10,000 oz of silver, and less than 200 

oz of gold (Keith, 1978; Keith and others, 1983a, b). 'fhe 

mineral occurrences are epithermal in character. 'fhe 

mines are developed in the high-angle faults cutting the 

mylonitic lower-plate rocks (Alamo mineral district), in 

ll"eplacement deposits in carbonate rocks, in epithermal 

veins il!11 faults, and as veins and replacement minerals in 

How-angle structures in and! above the Buckskin-Rawhide 

detachment fault (Welty and others, 1985). lLow-angle 

ll1lormal fault systems in adjoining ranges are also sites of 

these types of epithermal deposits (Wilkins and Heidrick, 

1982; Spencer and other~, 1988). 

On the basis of !mowll mineral occurrences within 

alhe entire region, alK areas along the high- and low-angle 

faults, particularly where reactive (carbonate) rocks are 

present, are assigned. a moderate mineraR resource potential with a cell"tainty level of C for gold, silver, and 

copper. These areas are in the north half and part of the 

southwest corner of the study area (fig. 2). Geochemical 

and! thematic mapping data support this assignment. 

Areas of high. resource potential with a certainty level of 

C foll" gold!, silver, and! copper are assigned to areas 

adjoining llmoWll1l minerall occurrellllces and! nlDlduding 

those areas where sulbecolDlomic ll"esoull"ces have been 

ndlelDltifned. 'fhese areas nJrndudle those parts of the Alamo 

mnllerall district within due west-centra! part of the study 

area, tlhle area immediately south of the lBig JIGmble mine 

ill1l the lDlorthwestern part of dne study Mea, and m area in 

the lDlorth-centrallpart of the study area (fig. 2). Most of 

the southell"lrll part of the srudy all"ea is assigned a low 

ll"esource potential! with a certainty leven of lB for gold, 

sinvell", and! coppell". 

MilDles nll1l the lLinoollDl RalDlch mi1!1lell"ali district to the 

·west and! the ArtilRery mnlDlell"ali distll"ict to the lrllodheast of 

tlhle Rawhide MoulDltailDls Wilderness Study Area, have 

sigllllifncant pll"oouctiolDl of mMgalDlese (Keith, 1978; Keith 

and! othell"s, 1983a, 10 ). 'fhe deposits are allol!Jlg high .. MgUe 

faiUllts cuUillllg the ulDlmetamolrJPhosed uppell"-plate ll"ocks 

or are stll"atalOOulrlldl ilDl 'fertiary sedimentary ll"OCb (JLasky 

Mdl Webbell", 1949; Spellllcell" allhdi Welty, 1985). Uppell"-

plate 'fell"tiacy sedimelDl~aJrY rrocb occull" on]y m smaU! 

areas illll the study arrea. Alreas located nlDl the southwest-
ern, east-central, northwestern, and northeastern parts of 

the study area are assigned a moderate resource potential for manganese with a certainty level of C (fig. 2). 

Uranium and Vanadium 

The Anderson uranium-vanadium mine is located 

in the Date Creek Basin 15 mi east of the Rawhide 

Mountains Wilderness Study Area. The deposit occurs in 

fine-grained sedimentary and volcanic rocks assigned to 

the middle Tertiary Chapin Wash Formation (Sherbourne and others, 1979; Otton, 1981; Spencer and 

Welty, 1985). These rocks extend in the subsurface to the 

northeast edge of the study area and crop out locally 

there. Volcanic and sedimentary rocks that crop out in 

the northwestern and southwestern parts of the study 

area are also broadly correlative with the Chapin Wash 

Formation. Although there is no known evidence to 

indicate any uranium or vanadium mineralization, the 

presence of the appropriate rock units and structures 

requires that these areas be assigned a low resource 

potential for uranium and vanadium with a certainty level 

of B (fig. 2). 

Oil and Gas 

Despite the presence of a significant number of oil 

and gas leases or lease applications, the entire Rawhide 

Mountains Wilderness Study Area is assigned a low 

resource potential with a certainty level of D for oil and 

gas. This resource potential level is justified because of 

the general lack of the usual hydrocarbon-bearing rocks, 

because the generally thin sections of unmetamorphosed 

rock are structurally bounded at shallow depths and are 

underlain by mid-crustal mylonitic rocks, and because 

much of the exposed terrane is underlain at the surface 

by the mid-crustal mylonitic rocks. 

Geothermal Water 

A low resource potential with a certainty level of B 

is assigned for low-temperature (less than 50 °C) geothermal waters in the northeast corner of the Rawhide 

Mountains Wilderness Study Area. This designation is 

based on the presence of geothermal wells and springs 

about 12 mi northeast of the study area along the Big 

Sandy River (fig. 1; Witcher and others, 1982; Stone and 

Witcher, 1982). These springs occur along high-angle 

faults where waters that have circulated to depths in the 

crust and were warmed by the normal geothermal gradients come back to the surface under normal hydrologic 

circumstances (Stone and Witcher, 1982, p. 368). Similar 

geothermal springs could occur adjacent to the northeast 

corner of the study area where a buried fault occurs 

along Sandtrap Wash. There are, however, no surface 

indications of hot water spring activity in the study area. 

Sand and gravel 

No known commercial sand and gravel deposits are 

located near the Rawhide Mountains Wilderness Study 

Area. In addition, areas of unconsolidated to poorly 

consolidated alluvial deposits are relatively scarce within 

the study area. However, a low resource potential with a 

certainty level of B is assigned to the entire area for sand 

and gravel. 

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in geology and ore deposits of Arizona and the southwest: Tucson, Arizona Geological Society Digest, v. 16, 

p. 35-51. 

Reynolds, SJ., Spencer, J.E., and DeWitt, Ed, 1987, Stratigraphy and U-Th-lPb geochronology of Triassic and Jurassic 

rocks in west-central Arizona, in Dickinson, W.R., and 

Klute, M.A., eds., Mesozoic rocks of southern Arizona 

and adjacent areas: Tucson, Arizona Geological Society 

Digest, v. 18, p. 65-80. 

Shackelford, T J., 1976, Structural geology of the Rawhide 

Mountains, Mohave County, Arizona: Los Angeles, University of Southern California, Ph.D. dissertation, 176 p. 

---1980, Tertiary tectonic denudation of a Mesozoic-early 

Tertiary(?) gneiss complex, Rawhide Mountains, western 

Arizona: Geology, v. 8, p. 190--194. 

Sherbourne, J.E., Jr., Buckovic, W.A., DeWitt, lE.B., Hellinger, 

T.S., and Pavlak, SJ., 1979, Major uranium discovery in 

volcaniclastic sediments, Basin and Range Province: 

American Association of l?etroleum Geologists Bulletin, 

v. 63, p. 621--646. 

Spencer, J .lE., and Reynolds, SJ ., 1986a, Geologic map of the 

Lincoln Ranch basin, eastern Buckskin Mountains, westem Arizona: Arizona Bureau of Geology and Mineral 

Technology Open-File Report 86-2, scale 1.24,000. 

--1986b, Some aspects of the middle Tertiary tectonics of 

Arizona and southeastern California, in Beatty, Barbara, 
and Wilkinson, P.A.K., eds., Frontiers in geology and ore 

deposits of Arizona and the southwest: Tucson, Arizona 

Geological Society Digest, v. 16, p. 102-107. 

---1987, Interaction between Mesozoic and Cenozoic tectonic features in the Buckskin Mountains and adjacent 

areas, west-central Arizona and southeastern California 

[abs.]: Geological Society of America Abstracts with 

Programs, v. 19, p. 852-853. 

Spencer, J.E., and Welty, J.W., 1985, Reconnaissance geology 

of mineralized areas in parts of the Buckskin, Rawhide, 

McCracken, and northeast Harcuvar Mountains, western 

Arizona: Arizona Bureau of Geology and Mineral Technology Open-File Report 85-6, 31 p. 

---1986, Possible controls of base- and precious metal 

mineralization associated with Tertiary detachment 

faulting in the lower Colorado River trough, Arizona and 

California: Geology, v. 14, p. 195-198. 

---1989, Geology of mineral deposits in the Buckskin and 

Rawhide Mountains: Arizona Geological Survey Dunetin 198, p. 215-254. 

Spencer, J.E., Duncan, J.T., and Burton, W.O., 1988, The 

Copperstone mine-Arizona's new gold producer: Arizona Bureau of Geology and Mineral Technology Fieldnotes, v. 18, no. 2, p. 1-3. 

Stone, Claudia, and Witcher, J.C., 1982, Final contract report: 

Geothermal energy in Arizona: Arizona Bureau of Geology and Mineral Technology Open-File Report 83-12, 

395 p. 

Tuftin, S.E., 1989, Mineral resources of a part of the Rawhide 

Mountains Wilderness Study Area (AZ-020-058A, La 

Paz and Mojave Counties, Arizona: U.S. Bureau of 

Mines Open-file Report, MLA 13-89, 50 p. 

U.S. Bureau of Mines and U.S. Geological Survey, 1980, 

Principles of a resource/reserve classification for minerals: U.S. Geological Survey Circular 831, 5 p. 

Welty, J.W., Spencer, J..E., Allen, G.B., Reynolds, S.J., and 

Trapp, R.A., 1985, Geology and production of Middle 

Tertiary mineral districts in Arizona: Arizona Bureau of 

Geology and Mineral Technology Open-File Report 

85-1, 88 p. 

Western Geophysical Company of America, Aero Service 

Division, 1979, Airborne gamma-ray spectrometer and 

magnetometer surveys of Las Vegas quadrangle (Arizona, California, Nevada), Williams quadrangle (Arizona), 

Prescott quadrangle (Arizona), and Kingman quadrangle (Arizona, California, Nevada), final report: U.S. 

Department of Energy, Grand Junction Office [Report] 

GJBX 59-79, v. 1 and 2, n.p., scale 1:500,000. 

Wilkins, Joe, Jr., and Heidrick, T.L., 1982, Base and precious 

metal mineralization related to low-angle tectonic features in the Whipple Mountains, California, and Buckskin Mountains, 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, Calif., Cordilleran Publishers, p. 182-203. 

Wilkins, Joe, Jr., Beane, R.E., and Heidrick, T.L., 1986, Mineralization related to detachment faults-a model, 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. 

108-117. 

Wilkinson, W.H., Wendt, C.J.,and Dennis, M.D., 1988, Gold 

mineralization along the Riverside detachment fault, 

Riverside County, California, in Schafer, R.W., Cooper, 

J.J., Vikre, P.G., eds., Bulk mineable precious metal 

deposits of the western United States: Reno, Nev., 

Geological Society of Nevada, p. 487-503. 

Witcher, J.C., Stone, Claudia, and Hahman, W.R., Sr., 1982, 

Geothermal resources of Arizona: Arizona Bureau of 

Geology and Mineral Technology map, scale 1:500,000. 

Mineral Resources of the Rawhide Mountains Wilderness Study Area, Arizona G19 
APPENDIXES 
DEFINITION OF LEVELS OF MINERAL RESOURCE POTENTIAL 

AND CERTAINTY OF ASSESSMENT 

LEVELS OF RESOURCE POTENTIAL 

H HIGH mineral resource potential is assigned to areas where geologic, geochemical, and geophysical 

characteristics indicate a geologic environment favorable for resource occurrence, where interpretations 

of data indicate a high degree of likelihood for resource accumulation, where data support mineraldeposit models indicating presence of resources, and where evidence indicates that mineral concentration has taken place. Assignment of high resource potential to an area requires some positive knowledge 

that mineral-forming processes have been active in at least part of the area. 

M MODERATE mineral resource potential is assigned to areas where geologic, geochemical, and 

geophysical characteristics indicate a geologic environment favorable for resource occurrence, where 

interpretations of data indicate reasonable likelihoo.d for resource accumulation, and (or) where an 

application of mineral-deposit models indicates favorable ground for the specified type(s) of deposits. 

L LOW mineral resource potential is assigned to areas where geologic, geochemical, and geophysical 

characteristics define a geologic environment in which the existence of resources is permissive. This 

broad category embraces areas with dispersed but insignificantly mineralized rock, as well as areas with 

little or no indication of having been mineralized. 

N NO mineral resource potential is a category reserved for a specific type of resource in a well-defined area. 

U UNKNOWN mineral resource potential is assigned to areas where information is inadequate to assign a 

low, moderate, or high level of resource potential. 

LEVELS OF CERTAINTY 

A Available information is not adequate for determination of the level of mineral resource potential. 

B Available information only suggests the level of mineral resource potential. 

C Available information gives a good indication of the level of mineral resource potential. 

D Available information clearly defines the level of mineral resource potential. 

1 

~ i= 

z 

w 

b 

0. 

w 

0 

a: 

:::> 

0 

f3 

a: 

u. 

0 

_. 

w 

~ 

A 

U/A 

UNKNOWN POTENTIAL 

Abstracted wnh minor modifications from: 

8 c D 

H/8 H/C H/0 

HIGH POTENTIAL HIGH POTENTIAL HIGH POTENTIAL 

M/8 M/C M/0 

MODERATE POTENTIAL MODERATE POTENTIAL MODERATE POTENTIAL 

LID 

LIB LIC LOW POTENTIAL 

LOW POTENTIAL LOW POTENTIAL N/D 

NO POTENTIAL 

LEVEL OF CERTAINTY 

Taylor, A.B., and Steven, T.A, 1983, Deflnllon of mineral resource potential: Economic Geology, v. 78, no. 6, p. 1268-1270. 

Taylor, A.B., Stoneman, R.J., and Marsh, S.P., 1984, An assessment of the mileral resource potential of the San Isabel National Forest, south-central Colorado: 

u.s. Geological Survey Bulletin 1638, p. 40-42. 

Goudarzl, G.H., complier, 1984, Guide to preparation of mineral survey reports on public lands: U.S. Geological Survey Open-File Report 84-0787, p. 7, 8. 

G22 Mineral Resources of Wilderness Study Areas: West-Central Arizona 
RESOURCE/RESERVE CLASSIFICATION 

IDENTIFIED RESOURCES UNDISCOVERED RESOURCES 

Demonstrated Probability Range 

Inferred 

Measured Indicated Hypothetical Speculative 

ECONOMIC Reserves Inferred 

Reserves I ----1- --------- - - -

MARGINALLY Marginal Inferred I 

ECONOMIC Reserves Marginal 

Reserves I ----1- --------- - - -

SUB- Demonstrated Inferred I 

Subeconomic Subeconomic 

ECONOMIC Resources Resources 

I I 

Major elements of mineral resource classification, excluding reserve base and inferred reserve base. Modified from McKelvey, V.E., 1972, 

Mineral resource estimates and public policy: American Scientist, v. 60, p. 32-40; and U.S. Bureau of Mines and U.S. Geological Survey, 

1980, Principles of a resource/reserve classification for minerals: U.S. Geological Survey Circular 831, p. 5. 

Mineral Reaourcea of the Rawhide Mountain• Wllderneaa Study Are•, Arlzon• G23 
GEOLOGIC TIME CHART 

Terms and boundary ages used by the U.S. Geological Survey in this report 

EON ERA PERIOD 

Quaternary 

Neogene 

Cenozoic Subperlod 

Tertiary 

Paleogene 

Subperlod 

Cretaceous 

Mesozoic 

Jurassic 

Triassic 

Phanerozoic Permian 

Pennsylvanian 

Carboniferous 

Periods 

Mississippian 

Paleozoic 

Devonian 

Silurian 

Ordovician 

Cambrian 

Late Proterozoic 

Proterozoic Middle Proterozoic 

Early Proterozoic 

Late Archean 

Archean Middle Archean 

Early Archean 

- - - - - - - - - - -(3800?) 

pre-Archean2 

1 Rocka older than 570 Ma also called Precambrian, a time term without specific rank. 

2 Informal time term without apeclflc rank. 

G24 Mineral Resource• of Wlldemeaa Study Areaa: Weat.C.ntral Arizona 

-

AGE ESTIMATES OF 

EPOCH BOUNDARIES IN 

MILUON YEARS (Ma) 

Holocene 0.010 

Pleistocene 1.7 

Pliocene 5 

Miocene 

Oligocene 

24 

38 Eocene 

Paleocene 

55 

66 

Late 

~ 96 

Early 

Late 

138 

Middle 

Early 

205 Late 

Middle 

Early -240 

Late 

Early 290 

Late 

Middle 

Early -330 

Late 

Early 

Late 360 

Middle 

Early 41.0 

Late 

Middle 

Early 435 

Late 

Middle 

Early 500 

Late 

Middle 

Early 1 -570 

900 

1600 

2500 

3000 

3400 

- - -

4550 
Mineral Resources of 

Wilderness St~dy Areas: 

West-Central Arizona 

This volume was published as separate chapters A-G 

U.S. GEOLOGICAL SURVEY BULLETIN 1701 
DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 
·coNTENTS 

{Letters designate the separately published chapters] 

(A) Mineral Resources of the Big Horn Mountains Wilderness Study Area, 

Maricopa County, Arizona, by Floyd Gray, RJ. Miller, J.R. Hassemer, 

William F. Hanna, John C. Brice III, and Russell A. Schreiner. 

(B) Mineral Resources of the Lower Burro Creek Wilderenss Study Area, 

Mohave and Yavapai Counties, Arizona, by Rober J. Miller, Floyd Gray, 

Jerry R. Hassemer, William F. Hanna, John Brice III, and Russell Schreiner. 

(C) Mineral Resources of the Harquahala Mountains Wilderness Study Area, 

La Paz and Maricopa Counties, Arizona, by E. De Witt, S.M. Richard, 

J.R. Hassemer, W.F. Hanna, and J.R. Thompson. 

(D) Mineral Resources of the Aubrey Peak Wilderness Study Area, Mohave 

County, Arizona, by James G. Evans, Randall H. Hill, William F. Hanna, 

Daniel H. Knepper, and Michael E. Lane. 

(E) Mineral Resources of the Arrastra Mountain/Peoples Canyon Wilderness 

Study Area, La Paz, Mohave, and Yavapai Counties, Arizona, by Floyd Gray, 

Robert J. Miller, James A. Pitkin, William C. Bagby, Jerry R. Hassemer, 

J. Howard McCarthy, William F. Hanna, Mary Lou Conant Callas, and 

Michael E. Lane. 

(F) Mineral Resources of the Harcuvar Mountains Wilderness Study Area, La Paz 

County, Arizona, by Harald Drewes, Ed Dewitt, Randall H. Hill, William F. 

Hanna, Daniel H. Knepper, Jr., Steven E. Tuftin, Stephen J. Reynolds, 

Jon E. Spencer, and Sarwar Azam. 

(G) Mineral Resources of the Rawhide Mountains Wilderness Study Area, La Paz 

and Mohave Counties, Arizona, by Richard M. Tosdal, Bruce Bryant, Randall 

H. Hill, William F. Hanna, Daniel H. Knepper, Jr., Stephanie L. Jones, 

K.S. Oliver, and Steven E. Tuftin. 
SlEl!E<C"frElD SrEAHES Of U.S. GlEOlOG~CAl SURVIEV PUIBl~CAT~ONS 

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