Mineral Resources of the 

Aubrey Peak Wilderness Study Area, 

Mohave CC?unty, Arizona 

, .. u.s. cE0L10GICAL sURvEY suCL~Ti~ 1.701-D· 

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Chapter D 

Mineral Resources of the 

Aubrey Peak Wilderness Study Area, 

Mohave County, Arizona 

By JAMES G. EVANS, RANDALL H. HILL, 

WILLIAM. F. HANNA, and DANIEL H. KNEPPER 

U.S. Geological Survey 

MICHAEL E. LANE 

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 : 1989 

For sale by the 

Books and Open-File Reports Section 

U.s.· Geological Survey 

Federal Center, Box 25425 

Denver, CO 80225 

Library of Congress Cataloging-in-Publication Data 

Mineral resources of the Aubrey Peak Wilderness Study Area, Mohave 

County, Arizona I james G. Evans . . . [et al.] 

p. em. -(Mineral resources of wilderness study areas-westcentral Arizona and part of San Bernardino County, California; ch. D)(U.S. 

Geological Survey bulletin ; 1701-D) 

Bibliography: p. 

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

1". Mines and mineral resources-Arizona-Aubrey Peak Wilderness. 

2. Aubrey Peak Wilderness (Ariz.) I. Evans, james George, 1938-

11. Series: U.S. Geological Survey bu lleti~ ; 1701-D. 

QE75.B9 no. 1701-D 557.3s-dc20 89-600143 

[TN24.A6] [553'.09791'59] CIP 
STUDIES RELATED TO WILDERNESS 

Bureau of Land Management Wilderness Study Area 

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

present. Results must be made available to the public and be submitted to the P.r~~ident 

and the Congress. This report presents the results of a mineral survey of the Aubrey 

Peak Wilderness Study Area (AZ-020-{)54), Mohave County, Arizona. 
CONTENTS 

Summary Dl 

Abstract Dl 

Character and setting Dl 

Identified resources Dl 

Mineral resource potential Dl 

Introduction D2 

Area description D2 

Previous and present investigations D3 

Appraisal of identified resources D3 

Methods D3 

Mining history D3 

Appraisal of sites examined DS 

Assessment of mineral resource potential D6 

Geology D6 

Geochemical studies D7 

Geophysical studies DS 

Mineral and energy resource potential D9 

References cited DU 

Appendixes 

Definition of levels of mineral resource potential and certainty of 

assessment D14 

Resource/reserve classification DlS 

Geologic time chart D16 

FIGURES 

1. Index map showing location of Aubrey Peak Wilderness Study Area, Mohave 

County, Arizona D2 

2. Map showing mineral resource potential, identified resources, and generalized 

geology of Aubrey Peak Wilderness Study Area, Mohave County, 

Arizona D4 

3. Aeromagnetic anomaly map of Aubrey Peak Wilderness Study Area, Mohave 

County, Arizona DlO 

Contents V 
Mineral Resources of the 

Aubrey Peak Wilderness Study Area, 

Mohave County, Arizona 

By James G. Evans, Randall H. Hill, William F. Hanna, and Daniel H. Knepper 

U.S. Geological Survey 

Michael E. Lane 

U.S. Bureau of Mines 

SUMMARY 

Abstract 

At the request of the Bureau of Land Management, the 

Aubrey Peak Wilderness Study Area, comprising approximately 16,550 acres, was evaluated for mineral resources. 

and mineral resource potential. Throughout this report, "wilderness study area" and "study area" refer to the 16,550 

acres for which a mineral survey was requested. The U.S. 

Geological Survey and the U.S. Bureau of Mines conducted 

geologic, geochemical, and geophysical surveys to assess 

the identified mineral resources (known) and mineral 

resource potential (undiscovered) of the study area. Fieldwork for this report was carried out in 1987 and 1988. 

Prospecting has occurred in and near the study area, and 

several adits and a mine shaft are present; there was no 

mining activity at the time of this investigation. Inferred 

subeconomic silver resources of 14,000 short tons (st), 

averaging 6.38 oz (troy)/st, and inferred subeconomic gold 

resources of 400 st, averaging 0.075 oz/st, exist in the study 

area. A low-grade perlite demonstrated subeconomic 

resource of 15 million st is present in the study area. Three 

areas in the northwestern, northeastern, and southeastern 

parts of the study area have low resource potential for silver 

and barium; a small part of the southeastern area with low 

potential for silver and barium also has low potential for 

undiscovered gold resources. Areas in the southwestern, 

southestern, and north-central parts of the study area and an 

area along the eastern boundary have low mineral resource 

potential for undiscovered barium. The study area contains 

sand and gravel deposits that are not economic, largely 

because of distance from markets. The entire study area has 

low resource potential for oil and gas. The study area has no 

potential for geothermal resources. 

Character and Setting 

The Aubrey Peak Wilderness Study Area is located 

near Lake Havasu and is 27 mi east of Lake Havasu City, 

Manuscript approved for publication, May 10, 1989. 

Arizona (fig. 1). The study area has a total relief of 1,500 

ft and consists mostly of hills and washes; it contains a 

few steep ridges and canyons that are cut to depths of as 

much as 500ft. The study area is underlain by a Precambrian granite and gneiss rock unit that is partly covered 

by volcanic, volcaniclastic, and sedimentary rocks of 

Miocene and early Pliocene age and by Holocene sand 

and gravel deposits (fig. 2) (see "appendixes" for geologic time chart). Numerous minor faults cut the rocks of 

the study area. The entire study ar~a is in the upper plate 

of the regional Rawhide detachment fault of Miocene 

age. 

Identified Resources 

Approximately 14,000 st of inferred subeconomic 

silver resources was identified in the study area. Of this 

amount, 4,000 st averages 10.03 oz/st, 7,000 st averages 

4.44 oz/st, and 3,000 st averages 6.02 oz/st. An inferred 

subeconomic gold resource of about 400 st averages 

0.075 oz/st. A low-grade demonstrated subeconomit 

perlite resource of about 15 million st was identified. 

About one-third of the study area is covered by oil and 

gas leases, but no drilling has been done. 

Mineral Resource Potential 

Three areas in the northwestern, northeastern, and 

southeastern parts of the Aubrey Peak Wilderness Study 

Area have low resource potential for silver and barium; 

these commodities are associated with weak hydrothermal alteration of Precambrian granite and Miocene 

arkose, conglomerate, and sedimentary breccia. A 

smaller area within the southeastern part of the study 

area with low potential for silver and barium also has low 

potential for gold in Precambrian rocks. There are four 

areas of low resource potential for barium in the study 

area; three of them are adjacent to areas of low silver and 

Mineral Resources of the Aubrey Peak Wilderness Study Area, Arizona 01 
barium resource potential. Barium may also be present 

in unaltered Miocene clastic rocks that may contain 

authigenic barite, although no such barite was observed 

during this study. The entire study area has low energy 

resource potential for oil and gas. There is no resource 

potential for geothermal energy. 

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). 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 and structures, 

possible environments of mineral deposition, presence of 

geochemical and geophysical anomalies, and applicable 

ore-deposit models. Goudarzi (1984) discussed mineral 

assessment methodology and terminology as they apply 

to these surveys. See "appendixes" for the definition of 

levels of mineral resource potential and certainty of 

assessment and for the resource/reserve classification. 

Area Description 

The Aubrey Peak Wilderness Study Area 

(AZ-020-054) covers approximately 16,550 acres in the 

desert highlands east of Lake Havasu City, Arizona (fig. 

1). The terrain of the study area is rugged, rising from 

about 1,600 ft at the south end to 3,132 ft at an unnamed 

peak in the west-central part. The hills and sharp ridges 

APPROXIMATE BOUNDARY 

OF 

34° 

30' 

AUBREY PEAK 

WILDERNESS STUDY AREA 

(AZ-020-054) 

0 5 MILES l...---.....J 

AREA OF MAP 

34° 

00'~---------L~------------~----------------------~----~~ 

Figure 1. Index map showing location of Aubrey Peak Wilderness Study Area, 

Mohave County, Arizona. 

02 Mineral Resources of Wilderness Study Areas: West-Central Arizona 
are cut by broad sandy washes and steep rocky canyons as 

much as 500 ft deep. Although arid, the study area 

supports a variety of desert plants including native 

grasses, creosotebush, ocotillo, cactuses (several varieties 

ranging in size from small barrel cactus to saguaro as tall 

as 20ft), and desert trees (ironwood, smoketree, cat-claw 

acacia, mesquite, and paloverde ). Numerous species of 

birds, small mammals, and reptiles including several 

species of lizards, desert tortoises, and four species of 

rattlesnakes inhabit the study area. 

The study area is accessible from a gravel road 

along Castaneda Wash (fig. 1). This road connects with 

Arizona Highway 95 by way of Planet Ranch road 

(gravel) on the south, and it connects with Interstate 40 

by way of a gravel road across Dutch ~lat on the north. 

Dirt roads and jeep trails follow the boundary of the 

study area. 

Previous and Present Investigations 

Bancroft (1911), in his report on. ore deposits in 

northern Yuma County (now called La Paz County), 

included the McCracken mine about 1 mi north of the 

study area in southern Mohave County. The study area is 

included in the geologic map of Mohave County by 

Wilson and Moore (1959) and in the geologic map of the 

Castaneda Hills 15-minute quadrangle by. N.H. Suneson 

and Ivo Lucchitta (unpub. data, 1980). Suneson and 

Lucchitta also studied the volcanism and tectonism of the 

region (Lucchitta and Suneson, 1977a, b; 1979; Suneson, 

1980; Suneson and Lucchitta, 19_78, 1979, 1983). 

The U.S. Geological Survey conducted field investigations in the study area during 1987. This work 

included geological reconnaissance and geochemical. 

sampling. Samples of the Precambrian rocks were collected for petrographic analysis. Geochemical data were 

obtained from 40 stream-sediment samples, 40 heavymineral-concentrate samples, and 59 rock samples (R.H. 

Hill, unpub. data, 1988). 

The U.S. Bureau of Mines spent 10 days in 1987 

examining surface and accessible underground workings 

(Lane, 1988). Seventy-seven rock samples were collected; 62 of these samples were from within the study 

area and 15 samples were from sites less than 0.5 mi 

outside the study area. 

APPRAISAL OF IDENTIFIED RESOURCES 

By Michael E. Lane 

U.S. Bureau of Mines 

Methods 

Prior to the field investigation, U.S. Bure~u of 

Mines' geologists reviewed literature on mining and 

geology of the region. In addition, Bureau of Land 

Management records were reviewed for mining-claim 

information and oil and gas leases and lease applications. 

Surface and accessible underground workings were surveyed by compass and tape, mapped, and sampled. A 

total of 77 samples was taken; 62 were from within the 

study area. Chip samples were taken at workings and 

perlite outcrops, and grab samples were taken of dump 

material. All but the perlite samples were analyzed by 

neutron activation for 34 elements including gold and 

silver. In addition, 6 samples were analyzed for gold by 

fire assay, 6 samples were analyzed for zinc by atomic 

absorption, 1 sample was analyzed for manganese by 

atomic abso~ption, 35 samples were analyzed for barium 

by X-ray diffraction and gravimetric methods, and 7 

samples were analyzed for fluorine by distillation. These 

analyses were done by Bondar-Clegg and Company, Ltd., 

Denver, Colo. Perlite samples were analyzed by the 

Perlite Corp., Chester, Penn. Complete analytical data 

for all samples are available for public inspection at the 

U.S. Bureau of Mines, Intermountain Field Operations 

Center, Building 20, Denver Federal Center, Denver, CO 

80225. 

Mining History 

No production records for the study area were 

found. There are no patented claims in the study area; 

however, three blocks of unpatented claims are located in 

the study area near and along the southeast boundary. 

Approximately one-third of the wilderness study area is 

covered by oil and gas leases, but no drilling for oil or gas 

has taken place in the study area. 

The McCracken mine, about 1 mi north of the 

study area, is a lead-silver mine that was discovered in 

1874 (Arizona Bureau of Geology and Mineral Technology, unpub. data, 1987). The ore at the mine occurs in 

four prominent north-striking veins 6 to 30 ft wide and at 

least 750 ft deep. One vein was reported by Bancrq_ft 

(1911, p. 125) to extend 2 mi south of McCracken 

Mountain, but no structure could be traced beyond the 

mine area during the present study because the rocks are 

covered ·by alluvium. No veins or mineralized fault zones 

were seen at the surface during an aerial reconnaissance. 

Production in the McCracken district was intermittent from 1875 until1985 when the mine was shut down 

due to low silver prices. Between 1911 and 1981, 10,000 

pounds (lbs) of copper, 3,031,000 lbs of lead, 43,000 lbs 

of zinc, 100 lbs of molybdenum, 100 troy ounces (oz) of 

gold, and 699,000 oz of silver were produced at the 

McCracken mine (Keith and others, 1983, p. 36--37). In 

1980 alone, about 60,000 st of ore averaging 3.5 oz/st of 

silver was produced at the McCracken mi~e. In 1984, 

about 30,000 st of ore averaging 12 oz/st of silver was 

produced (Corwin Coe, Arizona Silver Corp., oral commun., 1987). 

Mineral Resources of the Aubrey Peak Wilderness Study Area, Arizona 03 
The mining districts near the study area are 

described by Farnham and Stewart (1958, p. 52, 53). 

Production data are from Keith and others (1983, p. 

36-40). The Castaneda mining district is adjacent to the 

west boundary of the study area and was established 

by claims located in 1953; no workings of that district 

were found to extend into or near the study area. Only a 

L/B O,G 

(entire study area) 

LIB Ag, Ba 

0 

L/C Ba 

1 MILE 

small quantity of manganese that was hand-picked from 

float was produced in this district. The Owens and Mesa 

mining districts are about 6 mi south of the wilderness 

study area. Production in the Owens district between 

1921 and 1956 was 63,000 lbs of lead, 100 oz of gold, 

10,000 oz of silver, and 3,000 lbs of copper from veins in 

schistose diorite and pegmatite. Production in the Mesa 

)<: McCracken mine 

L/C Ba 

L!C Ag, Ba 

Keenans Camp 

L!C Ag, Ba, Au 

Centennial Wash 

Figure 2. Mineral resource potential, identified resources, and generalized geology of Aubrey Peak Wilderness Study Area, 

Mohave County, Arizona. Geology modified from N.H. Suneson and lvo Lucchitta (unpub. data, 1980). 

04 Mineral Resources of Wilderness Study Areas: West-Central Arizona 
district in 1954 was between 40,000 and 80,000 st of 

manganese ore from fractures in Paleozoic limestone 

and bedded manganese deposits in Tertiary sandstone. 

Appraisal of Sites Examined 

Thirty-three pits, 4 short adits, and 1 shallow shaft 

inside the study area were sampled (Lane, 1988). Most of 

the workings are concentrated near Keenans Camp and 

along Centennial Wash near the southeast boundary of 

the area; three are near the northeast boundary. No 

information was found to indicate when the pits, adits, 

and shaft were worked. 

The veins sampled in the study area are similar in 

· composition to those at the McCracken mine; they 

contain quartz, barite, calcite, and minor amounts of 

fluorite. These veins are not traceable beyond the vicinity 

of the workings, and it is not known if the veins in the 

study area are related to the veins at the McCracken 

mme. 

D 

B 

c 

Ag 

Au 

Ba 

O,G 

Qa 

Tf 

Tb 

Tvs 

Ts 

p-eg 

EXPLANATION 

Area of low mineral resource potential (L) 

Levels of certainty of assessment 

Data only suggest level of potential 

Data give good indication of level of 

potential 

Commodities 

Silver 

Gold 

Barium 

Oil and gas 

Identified resources 

Workings having inferred subeconomic gold 

or silver resources-See text for amount 

and grade 

Outcrops of perlite-See text for amount and 

grade 

Geologic map units 

Alluvium (Quaternary) 

Fanglomerate (Pliocene or upper Miocene) 

Basalt (upper Miocene) 

Volcanic, volcaniclastic, and sedimentary 

rocks (middle Miocene) 

Sedimentary rocks (middle to lower 

Miocene)-Arkose, conglomerate, and 

sedimentary breccia 

Granite and gneiss (Precambrian) 

Contact 

Fault-Dotted where concealed 

Figure 2. Continued. 

Gold concentrations in excess of 0.01 oz/st were 

found in 13 of the 20 samples taken at a cluster of 

workings along Centennial Wash within the study area 

(fig. 2). The samples are from fracture zones and veins in 

volcanic breccia, conglomerate, schist, diorite, and 

altered granite; their gold content ranges from 16 parts 

per billion (ppb) to 12 parts per million (ppm). 

An inferred subeconomic gold resource of about 

400 st of material averaging 0.075 oz/st was estimated for 

rock in two short adits (Lane, 1988). The estimate was 

based on an assumed length of 47 ft, width of 25 ft, 

average sample width of 3.74 ft, and a tonnage factor of 

12 cubic feet per short ton (fe /st). Trace amounts of gold 

(3.13 ppm or 0.1 oz/st) were found in two samples in the 

study area southwest of Centennial Wash, but no 

resources could be estimated at this site because of the 

limited exposure of mineralized rock. Subsurface sampiing is necessary to determine if gold continues at depth 

(Lane, 1988, p. 7). 

Silver is contained in 23 of the 25 samples taken at 

workings near Keenans Camp (fig. 2). The samples are 

from veins of calcite and barite containing minor 

amounts of quartz and hematite in arkose. The silver 

content of the samples ranges from 0.8 to 636 ppm (0.026 

to 18.6 oz/st). Fifteen samples contain silver in excess of 

2 oz/st. Inferred subeconomic silver resources were estimated using a tonnage factor of 12 fe /stand a width of 50 

ft. Different lengths and average sample widths were 

used for each of three areas. One area contains 4,000 st 

averaging 10.03 oz/st (length of 265 ft, average sample 

width of 3.65 ft). Another area contains about 7,000 st 

averaging 4.44 oz/st (length of 347 ft, average sample 

width of 4.67 ft). Another area contains about 3,000 st 

averaging 6.02 oz/st (length of 24 7 ft, average sample 

width of 3.30 ft). Silver occurs in two other samples (5.3 

and 18.6 oz/st), but no resources could be estimated 

because a continuous ore-be~ing structure was not 

found. 

Five perlite samples were taken in the wilderness 

study area at two perlite outcrops (fig. 2). The larger 

outcrop is traceable for about 8,500 ft and is estimated to 

be about 700 ft wide. The smaller outcrop is estimated to 

be 4,700 ft long and about 200ft wide. Both perlite beds 

are about 30 ft thick. A tonnage factor of 13.0 fe /st was 

used in estimating the amount of resources in the two 

outcrops. The perlite has expansion densities of 5.25 to 

16.00 pounds per cubic foot (lbs/ft3), which covers the 

most widely used bulk-density range (7 to 15 lbs/fe), and 

could be used for filter aids, horticultural applications, 

lightweight concrete aggregate, loose-fill applications, 

abrasive in soaps and cleansers, a curing agent in caulking compounds, and in castings in foundries. However, 

the perlite generally expands poorly, has a gray color, 

contains much unexpandable material, and is, therefore, 

not of desirable commercial quality. Therefore, the perlite in the study area would not compete favorably with 

Mineral Resources of the Aubrey Peak Wilderness Study Area, Arizona 05 
other perlite being commercially exploited at this time. A 

low-grade demonstrated sub economic perlite resource of 

approximately 15 million st was estimated for the two 

large outcrops within the study area (Lane, 1988, p. 

8-10). 

Sand and gravel deposits occur in the study area, 

but their properties are not unique and other deposits 

closer to markets are abundant in the region. For these 

reasons, the sand and gravel are unlikely to have economic value in the foreseeable future. 

About one-third of the study area is covered by oil 

and gas leases, but no drilling for oil and gas has been 

done in the study area. There are no geothermal leases in 

or near the study area. There are no thermal springs, 

wells, or known geothermal resource areas in or near the 

study area (Muffler, 1979; Witcher and others, 1982). 

ASSESSMENT OF MINERAL RESOURCE 

POTENTIAL 

By James G. Evans, Randall H. Hill, William F. Hanna, and 

Daniel H. Knepper 

U.S. Geological Survey 

Geology 

The Aubrey Peak Wilderness Study Area is underlain by Precambrian gneiss and granite and by Miocene 

to Quaternary sedimentary, volcanic, and volcaniclastic 

rocks and alluvium. Geology shown in figure 2 is simplified from mapping by N.H. Suncson and Ivo Lucchitta 

(unpub. data, 1980). 

The oldest rock unit (pGg) in the study area 

contains medium- to coarse-grained, commonly porphyritic granitic rocks containing potassium feldspar phenocrysts as much as 2 in. long, weakly foliated gneiss, augen 

gneiss containing potassium feldspar augen as much as 1 

in. long, and minor amounts of recrystallized cataclasite 

and schist. The unit is cut by vertical dikes of very coarse 

grained granite pegmatite as much as 3 ft wide and by 

veins of quartz and calcite as much as 0.5 ft wide. 

Compositions range from quartz monzonite to granite in 

the grani.tic rocks and from quartz diorite to granite in 

the gneiss, which is probably foliated plutonic rock. Most 

of the unit consists of plagioclase, potassium feldspar 

(perthite, antiperthite, and microcline ), and quartz. The 

chief mafic minerals are biotite (1 to 7 percent) and 

hornblende (0 to 4 percent). Some gneiss contains aggregates of epidote, biotite, ilmenite, and sphene. Magnetite, 

garnet, pyrite, zircon, and quartz-feldspar symplectite are 

also present. 

The granite and gneiss have undergone several 

kinds of alteration. The potassium feldspar phenocrysts 

and augen appear to have replaced plagioclase and 

quartz. This relation suggests that the present granitic 

composition of some of the rocks is a result of metasomatism of a less potassic protolith, possibly granodiorite 

or quartz diorite. Plagioclase is commonly slightly altered 

to sericite and is locally saussuritized. Mafic minerals are 

slightly altered to chlorite. Magnetite is partly altered to 

hematite, and this alteration is locally abundant. Ilmenite 

is altered to sphene and leucoxene. Microscopic quartz 

veins cut potassium feldspar phenocrysts. As much as 15 

percent of some sheared rocks are replaced by calcite. 

Much of the unit east of approximately 113°50' W. 

long. in the study area is composed of the Signal Granite 

(Lucchitta and Suneson, 1982), a granitic batholith at 

least 20 mi in diameter and well exposed near the ghost 

town of Signal, 13 mi northeast of the study area. The age 

of the Signal Granite is Middle Proterozoic on the basis 

of a U-Pb (uranium-lead) age of 1410±3 million years 

before present (Ma) (Gray and others, 1989). Rocks west 

of 113°50' W.long. are also likely Precambrian, but they 

may be older than the Signal Granite. 

Tertiary arkose, conglomerate, and coarse sedimentary breccia overlie the Precambrian rocks (fig. 2). 

The description of these rocks is taken from N.H. Suneson and Ivo Lucchitta (unpub. data, 1980). The base of 

the section is pale red arkosic sandstone and granule to 

pebble conglomerate that are generally poorly consolidated and sorted and are moderately stratified; clasts are 

coarse-grained, locally derived granite. These basal beds 

are overlain by poorly to well-consolidated, wellstratified arkose, limestone, and tuffaceous sedimentary 

rock; clasts include several kinds of plutonic and metamorphic rock. These beds are overlain by the breccia of 

Ester Basin, which has a breccia facies and an alluvial 

facies. The breccia facies is a widespread, chaotic, primarily monolithologic sedimentary unit that consists mostly 

of angular meta-andesite clasts as much as several feet 

across. The breccia facies is unstratified, unsorted, and 

moderately to poorly indurated; this facies also includes 

minor amounts of poorly foliated metasedimentary 

rocks, white quartzite, and gray limestone. The alluvial 

facies comprises a well-stratified, well-consolidated arkosic sandstone and a granule-to-cobble conglomerate containing abundant subrounded clasts of meta-andesite. In 

places, a poorly consolidated sedimentary breccia of 

angular blocks of foliated, sheared coarse-grained granite overlies the breccia of Ester Basin. A heterogeneous 

sedimentary unit consisting of limestone, chert, gypsiferous beds, siltstone, sandstone, and tuff overlies the 

breccia units. 

The age of these sedimentary rocks (Ts) is not 

clearly understood. Seven miles west of the study area, 

they underlie a basalt unit that has been dated at early to 

middle Miocene (K-Ar (potassium-argon) ages, 

18.7±0.3 Ma and 16.5±0.2 Ma, Suneso:c, 1980, p. 185). 

Included in these sedimentary rocks is the arkose 

of Keenans Camp, a widespread arkosic conglomerate 

that overlies the sedimentary rocks described above and 

is partly contemporaneous with the basalt mentioned 

06 Mineral Resources of Wilderness Study Areas: West-Central Arizona 
above and the overlying volcanic rocks described below. 

The lower part of this arkosic conglomerate is a reddishbrown, well-consolidated, well-stratified, locally tuffaceous coarse sandstone and pebble and cobble conglomerate that grades upward to sandstone and siltstone. The 

upper part is a poorly stratified, poorly consolidated 

sandstone and boulder conglomerate; clasts consist of 

granitic rock, gneiss, basalt, metavolcanic rock, quartzite, 

and diabase. The arkose of Keenans Camp is early to 

middle Miocene, based on its relations with dated volcanic rocks. 

Overlying the sedimentary rocks is a unit of volcanic, volcaniclastic, and sedimentary rocks that consists 

mostly of rhyolite flows, small rhyolite intrusions that fed 

the flows, and volcaniclastic rocks of rhyolitic composition. A few dikes of quartz-bearing basalt are included in 

this unit. The rhyolite flows and intrusions are aphyric or 

porphyritic, glassy to devitrified, locally brecciated, and 

flow banded. Phenocrysts include sanidine, quartz, plagioclase, biotite, and minor amounts of hornblende. The 

groundmass is granophyric, cryptocrystalline, or glassy. 

Contemporaneous volcaniclastic rocks include ash-flow 

and air-fall tuff and tuffaceous sandstone and conglomerate. The tuff is well-stratified and locally lapilli rich. 

The sandstone is distinctly bedded and contains some 

crossbedding and siltstone beds. The quartz-bearing 

basalt included in the unit is light to dark gray and 

contains from 4 to 12 percent phenocrysts of quartz, very 

corroded plagioclase, and minor amounts of olivine and 

clinopyroxene. The quartz phenocrysts are embayed and 

have pyroxene reaction rims. 

The volcanic, volcaniclastic, and sedimentary rocks 

unit is assigned a middle Miocene age; K-Ar ages of 

rhyolites in and near the study area range from 15.1 ±0.1 

to 10.3±0.1 Ma, and most are between 12 and 13 Ma 

(Suneson, 1980, p. 185). Two samples from the Aubrey 

Peak Wilderness Study Area were dated at 12.4±0.1 Ma 

and 12.4±0.2 Ma (Suneson and Lucchitta, 1979) or 

middle Miocene. Potassium-argon ages of quartzbearing basalts are similar (13.7±0.3 and 12.4±0.1 Ma, 

Suneson, 1980, p. 186); the older age is for a sample from 

the study area. 

Several small exposures of megacryst-bearing 

basalt crop out in the study area. These basalt flows 

contain abundant phenocrysts of plagioclase and clinopyroxene but include minor amounts of olivine, spinel, and 

magnetite that are as much as 3 in. long and typically 0.13 

to 0.5 in. long. Potassium-argon ages on samples of this 

basalt near the Aubrey Peak Wilderness Study Area 

range from 6.8±0.2 to 8.6±0.3 Ma (Suneson, 1980, p. 

187-188), which indicates a late Miocene age. 

The Precambrian and Tertiary rocks described 

above are overlain in the southern end of the study area 

by a sequence of heterogeneous, coarse clastic strata. 

The lower part of this sequence is well-stratified, consolidated, coarse sandstone and pebble-to-boulder conglomerate containing thin local tuff beds. The upper part 

of this sequence is poorly consolidated, stratified, and 

sorted fanglomerate with abundant angular clasts. The 

age of these deposits is late Miocene or Pliocene. 

Quaternary alluvium includes unconsolidated 

channel fill (silt, sand, gravel, and boulders), undissected 

pediment gravel, desert pavement with desert varnish, 

and locally derived slope wash, talus, and landslides. 

The entire study area is in the upper plate of the 

Rawhide low-angle detachment fault that is exposed in 

the Rawhide Mountains 5 mi south of the study area. 

Movement of the upper plate was northeastward (Shackelford, 1980). The study area is in the 60-mi-wide Colorado River extensional corridor, across which slip on all 

faults is estimated to total about 30 mi (Howard and 

John, 1987). Age of inception of the extensional movement is not known. Suneson and Lucchitta (1983), however, suggest that most movement on the Rawhide 

detachment fault and related listric faults occurred after 

eruption of the oldest basalts in the region (18.7 and 16.5 

Ma) and ceased by 14 million years ago. The period of 

detachment faulting was succeeded by development of 

steep normal faults, most of which strike northwesterly. 

The normal faults may have been active until about 7 

million years ago, as suggested by the mostly unfaulted 

porphyritic basalts of that age 7 mi west of the study area. 

Several steep northeast-striking faults offset the 

northwest-striking normal faults. 

Geochemical Studies 

A reconnaissance geochemical survey was conducted in the Aubrey Peak Wilderness Study Area. 

Minus-60-mesh stream-sediment samples, nonmagnetic 

heavy-mineral concentrates derived from stream sediment, and rocks were selected as the sample media in this 

study. Stream sediments and heavy-mineral concentrates 

were collected at 40 sites. Twenty-eight fresh and unaltered rock samples were collected near these sample 

sites. In addition, 1 rock sample was taken from a mine 

dump, and 30 rock samples, mostly of altered Precambrian rock, were taken elsewhere in the study area. 

Stream-sediment samples were collected from 

active alluvium in stream channels. Stream sediments 

represent a composite of rock and soil exposed upstream 

from the sample site. Heavy-mineral concentrates represent a concentration of ore-forming and ore-related 

minerals and permit determination of some elements 

that are not easily detected in bulk stream sediments. 

Heavy-mineral concentrates derived from stream 

sedime1its are a useful sample medium . in arid and 

semiarid environments or in areas of rugged topography 

where mechanical erosion is greater than chemical erosion (Bugrov and Shalabey, 1975; Overstreet and Marsh, 

1981). 

Mineral Resources of the Aubrey Peak Wilderness Study Area, Arizona 07 
Rocks were taken from mineralized and unminer-· 

alized outcrops and one mine dump. Samples that 

appeared fresh and unaltered were collected to determine geochemical background values. Altered or mineralized samples were collected to determine the suite of 

elements associated with the observed altered or mineralized rock. 

Samples of the stream sediments, nonmagnetic 

heavy-mineral concentrates, and rocks were analyzed for 

31 elements using a semiquantitative direct-current arc 

emission spectrographic method (Grimes and Marranzino, 1968). In addition, rock and stream-sediment samples were analyzed for certain elements by more sensitive 

methods. These elements and methods are as follows: 

arsenic, antimony, bismuth, cadmium, and zinc by inductively coupled plasma-atomic emission spectrometry 

(Crock and others, 1987); gold, tellurium, and thallium 

by electrothermal atomic-absorption spectroscopy 

(Hubert and Chao, 1985); and uranium by a fluorometric 

method (O'Leary and Meier, 1984). These analyses were 

used to identify drainages with anomalous concentrations 

of minor elements. Anomalous concentrations in the 

stream-sediment, heavy-mineral-concentrate, and rock 

samples were determined for each element by inspecting 

histograms for each of the sample media. 

Samples from the study area contain anomalous 

concentrations of several elements, of which barium, 

gold, lead, molybdenum, silver, tin, tungsten, and zinc are 

possibly related to mineralization. Areas in the eastern, 

northeastern, southeastern, and southwestern parts of 

the study area have anomalous values of barium in 

nonmagnetic heavy-mineral concentrates. Drainages in 

the northeastern part of the study area are downstream 

from the McCracken mine. They are characterized by 

anomalous concentrations of barium (greater than 

10,000 ppm), lead (300 to 1,000 ppm), silver (20 to 200 

ppm), tungsten (100 ppm), and zinc (700 to 1,500 ppm) 

in the heavy-mineral-concentrate samples and by weakly 

anomalous concentrations of lead and zinc in the minus60-mesh stream-sediment samples. These values are 

partly a result of contamination from mine dumps in the 

McCracken mine area. Some rock samples from the 

northeastern part of the study area contain anomalous 

concentrations of barium, copper, molybdenum, silver, 

and zinc, and they indicate that some mineralized ground 

also occurs in the study area. Anomalous concentrations 

of barium in heavy-mineral concentrates collected in 

drainages along the east side of the study area that lie 

partly outside the study area may also be attributable to 

contamination from mine dumps. One of these drainages 

also carries anomalous concentrations of silver (10 ppm), 

lead (2,000 ppm), and zinc (1,500 ppm) that may be 

partly derived from the mine workings outside the study 

area near Keenans Camp. Mine workings within the 

study area along this drainage also contain high concentrations of lead, silver, and zinc. 

In the northwestern corner of the study area is a 

small drainage that contains high concentrations of barium (greater than10,000 ppm), lead (15,000 ppm), silver 

(150 ppm), and zinc (15,000 ppm) in the heavy-mineral 

concentrates and high values of lead (1,000 ppm), silver 

(7 ppm), and zinc (2,000 ppm) in minus-60-mesh streamsediment samples. The source of the small isolated 

anomaly is not known. It may be due to mineralization in 

the study area or to contamination from alluvium 

brought in from the McCracken mine area during a 

previous episode of alluvial fan formation. 

Low concentrations of gold (16 ppb to 12 ppm) 

were found by the U.S. Bureau of Mines in volcanic 

breccia, conglomerate, schist, diorite, and altered granite 

near the eastern edge of the study area. These concentrations of gold are greater than crustal abundance (3 to 

4 ppb, Simons and Prinz, 1973) and are considered 

anomalous. Gold was not detected in rock samples 

collected by the U.S. Geological Survey in that area or in 

stream sediments and heavy-mineral concentrates collected in nearby drainages. 

Much of the mineralized area characterized by 

anomalous concentrations of barium, gold, lead, molybdenum, silver, tin, tungsten, and zinc is underlain by the 

Signal Granite (mapped as part of unit pGg, fig. 2). The 

age of mineralization is not known, but it may be 

Miocene or younger because there is evidence of silver, 

lead, and zinc mineralization in the Miocene arkose of 

Keenans Camp. The· mineralization may have been 

related to the Miocene volcanism, as suggested by a 

sample of rhyolite containing 5 ppm silver. The possibility 

exists, however, that the Miocene mineralization may 

have involved a partial redistribution of elements from 

older, possibly Precambrian, mineralized rocks. Anomalous concentrations of barium in stream sediments and 

heavy-mineral concentrates may be due in part to authigenic barite in sedimentary rocks (unit Ts, fig. 2) of the 

study area, although such barite was not observed during 

this study. 

Geophysical Studies 

A digitally processed Landsat Thematic Mapper 

color-ratio composite image was used to interpret the 

location and distribution of spectral-reflectance characteristics in the Aubrey Peak Wilderness Study Area that 

suggest the presence of selected minerals commonly 

associated with hydrothermally altered rocks. No field 

studies were made to confirm the inferences of the 

reflectance studies. The anomalous areas of most interest 

are associated with outcrops of Tertiary volcanic and 

volcaniclastic rocks in a zone trending northwestward 

across the study area. Other clusters of anomalies are 

associated with Tertiary volcanic and volcaniclastic rocks 

in the southwestern part of the study area and with 

Precambrian crystalline rocks and Tertiary sedimentary 

08 Mineral Resources of Wilderness Study Areas: West-Central Arizona 
rocks in the northern and southeastern parts of the study 

area. 

Areas of possible ferric oxide minerals (particularly hematite, goethite, and jarosite) coincide with areas 

having barium, barium and silver, and barium, gold, and 

silver anomalies in the northern and eastern parts of the 

study area. In the southern part of the study area, areas 

possibly containing ferric oxide minerals and hydroxylbearing, hydrated sulfate and carbonate minerals (clay 

minerals, micas, gypsum, alunite, jarosite, calcite, and 

dolomite) overlap areas of anomalous barium. The 

prominent northwest-trending zone that shows reflectance values characteristic of hydrothermal alteration is 

coincident with Tertiary volcanic rocks across the central 

part of the study area and is not associated with any 

geochemical anomalies; it does include most of the 

perlite resources and coincides with a zone of aeromagnetic lows. The suggestion of widespread hydrothermal 

alteration in the study area is consistent with the geological observations, although the actual areas of hydrothermal alteration observed in the field and inferred by the 

geochemical data do not closely coincide with the areas 

of possible hydrothermal alteration inferred from the 

reflectance studies. 

The Aubrey Peak Wilderness Study Area is covered by regional gravity (Aiken and others, 1981; 

Defense Mapping Agency Aerospace Center, 1974, 

1975) and aeromagnetic surveys (Western Geophysical 

Company of America, Aero Service Division, 1979); 

aeromagnetic surveys have sufficient resolution to define 

anomalies of about 2 mi2 or larger. Contours of complete 

(terrain-corrected) Bouguer gravity anomalies are 

defined by 25 gravity stations surrounding the study area. 

Contours of total-field magnetic anomalies are defined 

by measurements made along nine east-west flightlines 

spaced 1 mi apart and one north-south tieline at a 

nominal height of 400 ft above the terrain. 

The study area is transected by a smooth gravity 

gradient defined by values increasing southwestward 

from a low northeast of the study area to a high southwest of the study area. The lows and the highs do not 

closely correspond to the pattern of late Tertiary sedimentary rock and exposures of crystalline basement rock; 

therefore, they probably reflect subsurface rock density 

contrasts. 

Of several large-amplitude aeromagnetic anomalies in this region, five are within the study area, labeled 

A through E in figure 3. These five anomalies have 

amplitudes and wavelengths characteristic of highly 

mafic igneous rocks, such as gabbro and diorite, that 

occur in core complexes of Arizona but are not exposed 

in the Aubrey Peak Wilderness Study Area. 

Highs A and D overlap small mapped areas of 

basalt, which suggests that the mafic intrusive rocks 

causing these highs may be part of a feeder system for the 

basalt. Highs B and E, not associated with mapped basalt, 

are also inferred to be caused by mafic intrusive rocks 

having strong total magnetization of normal polarity. 

Low C, nested between highs A and B, is probably a 

polarization feature coupled to high A. Hypothetically, 

low C could be caused partly by a mafic pipe having a 

total magnetization of reversed polarity, but there is no 

other evidence for such a feature. Most of the highamplitude anomalies border the northwest-trending zone 

of small-amplitude lows in figure 3, which coincides with 

a fairly nonmagnetic northwest-trending zone of rhyolitic 

volcanic rocks. 

Several high-amplitude aeromagnetic anomalies 

overlap areas having geochemical anomalies. For exalllple, high A overlaps the small barium, gold, and silver 

anomaly and a barium and silver anomaly; high B overlaps two barium anomalies; and high E flanks a small 

barium and silver anomaly, although this geochemical 

anomaly may be associated with fossil placers from 

outside the study area. Because many barite vein deposits 

in the western United States are associated with igneous 

rocks of Tertiary age (Brobst, 1973), the spatial association of aeromagnetic anomalies to barium anomalies in 

the study area suggests that the barium may have been 

derived from hydrothermal activity near the margins of 

the inferred subsurface mafic intrusions. 

Mineral and Energy Resource Potential 

Geologic and geochemical data indicate that zones 

within the Aubrey Peak Wilderness Study Area have low 

resource potential for silver, barium, and gold, for silver 

and barium, and for barium alone with a C certainty level 

and for silver and barium with a B certainty level. The 

resource potential for petroleum and natural gas for the 

entire study area is low with a B certainty level. 

Geologic, geochemical, and geophysical data suggest that there is low resource potential for silver and 

barium in the northwestern, northeastern, and southeastern parts of the study area (fig. 2). This potential is 

indicated by anomalous concentrations of barium and 

silver in heavy-mineral-concentrate samples, which also 

contain anomalous concentrations of lead, molybdenum, 

tin, tungsten, and zinc that may indicate hydrothermal 

alteration. The potential is low because the rocks that 

look most altered and mineralized have fairly low concentrations of barium and silver, and no large deposits 

enriched in either element were found. A certainty level 

C is assigned to the areas in the northeastern and 

southeastern parts of the study area because the rocks 

there are generally well exposed, and the geochemical 

data do not suggest the possibility of large, undiscovered 

near-surface silver and barium resources. The higher 

concentrations of silver in some heavy-mineral concentrates are partly due to contamination from mine workings outside the study area. The small area of low 

Mineral Resources of the Aubrey Peak Wilderness Study Area, Arizona 09 
potential for silver and barium in the northwestern part 

of the study area is assigned a certainty level B because 

the source of the barium and silver is unknown and may 

not be in the study area. 

There is low resource potential for barium in the 

northeastern (two areas, one of which lies along the east 

boundary), southeastern, and southwestern parts of the 

study area (fig. 2). The potential is suggested by the 

anomalous concentrations of barium in heavy-mineral 

concentrates and is low because of the absence of large 

occurrences in the region; the barite occurs as thin, 

discontinuous veins. The barium is associated with anomalous concentrations of one or more of the following 

elements that may indicate hydrothermal alteration: lead, 

tin, and tungsten. The barium anomalies may be partly 

due to contamination from outside the eastern part of the 

·study area. Elsewhere, the barium may have been 

derived from barite veins or possible authigenic barite in 

Miocene sedimentary rocks. A certainty level C is 

assigned because no large deposits were found in the 

generally well exposed rocks. 

A small area having low resource potential for 

silver, barium, and gold occurs in the southeastern part of 

the study area (fig. 2). This potential is indicated by 

Figure 3. Aeromagnetic anomaly map of Aubrey Peak Wilderness Study Area, Mohave County, Arlzona. Contour intervals 20 

and 100 nanoteslas. Hachures indicate closed areas of lower values. See text for discussion of anomalies labeled A through 

E. Crosshatched lines denote flightline traces. 

010 Mineral Resources of Wilderness Study Areas: West-Central Arizona 
anomalous concentrations of gold in rock samples ncar 

pits and tunnels. The potential is considered Jow because 

of the low concentrations of gold and the small areal 

extent over which gold-bearing structures can be traced. 

A certainty level of C is assigned because the area of the 

anomaly is well exposed, and the geochemical data do not 

suggest the possibility of large amounts of undiscovered 

resources. 

Anomalous concentrations of lead, molybdenum, 

tin, tungsten, and zinc in stream-sediment, pannedconcentrate, and rock samples in the study area may 

indicate hydrothermal alteration and possible mineral-

·ization. These elements, however, do not occur in concentrations suggesting that they form deposits in the 

study area. 

Ryder (1983) assessed the oil and gas potential of 

the study area as zero to low, on the basis of the extensive 

occurrences of Precambrian granite and gneiss constituting the basement rocks of the wilderness study area and 

of the overlying Tertiary volcanic rocks. Such rocks are 

not conducive to the accumulation of hydrocarbons. If 

present, hydrocarbons would be associated with deposits 

on the flanks of the Tertiary basins. The resource potential for oil and gas is low, certainty level B, for the entire 

study area. 

No geothermal resources were found in or adjacent 

to the study area (Witcher and others, 1982; Muffler, 

1979). Although the study area contains numerous rhyolite and basalt intrusions and the study area is in a 

region that probably underwent greater than normal heat 

flow during the Miocene and early Pliocene, the Miocene 

intrusions in the study area are small, and the entire 

region has most likely cooled to near ambient temperatures since the early Pliocene. Therefore, there is no 

potential for geothermal resources, certainty level D. 

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Suneson, N.H., and Lucchitta, Ivo, 1978, Bimodal volcanism 

along the eastern margin of the Basin and Range province, western Arizona: Geological Society of America 

Abstracts with Programs, v. 10, p. 149. 

---1979, K/Ar ages of Cenozoic volcanic rocks, west-central 

Arizona: Isochron/West, no. 24, p. 25-29. 

---1983, Origin of bimodal volcanism, southern Basin and 

Range province, west-central Arizona: Geological Society of America Bulletin, v. 94, no. 8, p. 1005-1019. 

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. 

U.S. Defense Mapping Agency Aerospace Center, 1974, World 

relative gravity reference network, North America, pt. 2: 

Defense Mapping Agency Aerospace Center Reference 

Publication 25, with supplement updating gravity values 

to the International Gravity Standardization Net 1971, 

1,635 p. 

---1975, Holding, storage, and retrieval of gravity data: 

Defense Mapping Agency Aerospace Center, Reference 

Publication RP-75-003, 33 p. 

Western Geophysical Company of America, Aero Space Division, 1979, Airborne gamma-ray spectrometer and magnetometer survey of Las Vegas quadrangle (Arizona, 

California, Nevada), Williams quadrangle (Arizona), 

Prescott quadrangle (Arizona), and Kingman quadrangle (Arizona, California, Nevada), final report: Grand 

Junction, Colo., U.S. Department of Energy Report 

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

Wilson, E.D., and Moore, R.T., 1959, Geologic map of Mohave 

County, Arizona: Arizona Bureau of Mines County Map, 

scale 1:375,000. 

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

Geothermal resources of Arizona: Arizona Bureau of 

Geology and Mineral Technology Map 15-2, scale 

1:500,000. 

012 Mineral Resources of Wilderness Study Areas: West-Central Arizona 
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 char7 

actcristics indicate a geologic environment favorable for resource occurrence, where interpretations of data 

indicate a high degree of likelihood for resource accumulation, where data support mineral-deposit 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 likelihood for resource accumulation, and (or) where an application of mineral-deposit models 

indicates favorable ground for the specified typc(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. 

8 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. 

i 

_, 

< 

~ 

z 

UJ 

.,_ 

2 

w 

~ :::> 

0 

c.n 

UJ 

0:: 

u.. 

0 

...J 

w 

> w 

_, 

A 

U/A 

UNKNOWN POTENTIAL 

Abstracted with minor modiOcatlons from: 

B c 

H/8 H/C 

HIGH POTENTIAL HIGH POTENTIAL 

M/B M/C 

MODERATE POTENTIAL MODERATE POTENTIAL 

l/B L/C 

LOW POTENTIAL LOW POTENTIAL 

LEVEl OF CERTAINTY 

D 

H/D 

HIGH POTENTIAL 

MID 

MODERATE POTENTIAL 

LID 

LOW POTENTIAL 

N/D 

NO POTENTIAL 

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

Taylor, R.B., Stoneman, R.J., and Marsh, S.P., 1984, An assessment of the mineral 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. 

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

IDENTIFIED RESOURCES UNDISCOVERED RESOURCES 

Demonstrated Probability Range 

Inferred 

Measured I Indicated Hypothetical I Speculative 

I I 

I Inferred I 

ECONOMIC Reserves Reserves 

I ----------- ____ T ____ I 

Inferred -~-

MARGINALLY Marginal Marginal ECONOMIC Reserves Reserves 

I --·--------- I 

----.----- -,-

SUB- Demonstrated Inferred 

Subeconomi c Subeconomic 

ECONOMIC Resources Resources I 1 l 

Major clements 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 Resources of the Aubrey Peak Wilderness Study Area, Arizona 015 
GEOLOGIC TIME CHART 

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

EON ERA PERIOD EPOCH 

Quaternary Holocene 

Pleistocene 

Neogene Pliocene 

Cenozoic Subperiod Miocene 

Tertiary Paleogene Oligocene 

Subperiod Eocene 

Paleocene 

Cretaceous late 

Early 

late 

Mesozoic jurassic Middle 

Early 

late 

Triassic Middle 

Early 

Penn ian late 

Phanerozoic Early 

late 

Pennsylvanian Middle 

Carboniferous Early Periods 

Mississippian late 

Early 

late 

Devonian Middle 

Paleozoic Early 

late 

Silurian Middle 

Early 

late 

Ordovician Middle 

Early 

late 

Cambrian Middle 

Early 

late Proterozoic 

Proterozoic Middle Proterozoic 

Early Proterozoic 

late Archean 

Archean Middle Archean 

Early Archean 

--------------- - - - - - - - - - - -.- - - - - - - - - - - - - - - (3800?)- - - - - - - - - -.- - • - - - - -

pre-Archean2 

1Rocks older than 570 Ma also called Precambrian, a time term without specific rank. 2Jnformal time term without specific rank. 

016 Mineral Resources of Wilderness Study Areas: West-Central Arizona 

AGE ESTIMATES OF 

BOUNDARIES IN 

MILLION YEARS (Ma} 

0.010 

1.7 

5 

24 

38 

55 

66 

- 96 

138 

205 

-240 

290 

-330 

360 

410 

435 

500 

1-570 

900 

1600 

2500 

3000 

3400 

4550 
l?~rr~@<dJ~~ta1~~ 

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evans and others-MINERAL RESOURCES, AUBREY PEAK WILDERNESS STUDY AREA, ARIZONA-U.S. Geological 

---~--------------~ - . - - - "' - "+! ,;