Mineral Resources of the lower Burro 

Creek Wilderness Study Area, 

Mohave and Yavapai Counties, Arizona 

• ARIZONA 
Chapter B 

Mineral Resources of the 

Lower Burro Creek Wilderness Study Area, 

Mohave and Yavapai Counties, Arizona 

By ROBERT J. MILLER, FLOYD GRAY, JERRY R. HASSEMER, 

WILLIAM F. HANNA and JOHN BRICE Ill 

U.S. Geological Survey 

RUSSELL SCHREINER 

U.S. Bureau of Mines 

U.S. GEOLOGICAL SURVEY BULLETIN 1701 

MINERAL RESOURCES OF WILDERNESSSTUDY AREAS: 

WEST-CENTRAL ARIZONA AND PART OF SAN BERNARDINO COUNTY, CALIFORNIA 
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1987 

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 Lower Burro Creek Wilderness 

Study Area, Mohave and Yavapai counties, Arizona. 

U.S. Geological Survey Bulletin 1701-B (Mineral resources 

of wilderness study areas-west-central Arizona and part 

of San Bernardino County, California; ch. B) 

Bibliography 

Supt. of Docs. No.: I 19.3:1701-B 

1. Mines and mineral resources-Arizona-Lower Burro 

Creek Wilderness. 2. Lower Burro Creek Wilderness (Ariz.) I. 

Miller, Robert J. (Robert Jennings), 1949- . II. Series. 

Ill. Series: Mineral resources of wilderness study areaswest-central Arizona and part of San Bernardino County, 

California; ch. B 

OE75.B9 No. 1701-B 557.3 s 87-600345 

[TN24.A6) (553'.09791 '59] 
STUDIES RELATED TO WfiADERNESS 

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 President 

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

Lower Burro Creek Wilderness Study Area (AZ-020-060), Mohave and Yavapai Counties, 

Arizona. 
CONTENTS 

Summary 81 

Abstract 1 

Character and setting 1 

Identified mineral resources 3 

Mineral resource potential 3 

Introduction 3 

Area description 6 

Previous and present investigations 6 

Acknowledgments 6 

Appraisal of identified resources 6 

Mining history 6 

Appraisal of sites examined 7 

Gold mines and prospects 7 

Bentonite prospects 7 

Magnesite prospects 8 

Agate prospects 8 

Geothermal 8 

Oil and gas 8 

Conclusions 8 

Assessment of mineral resource potential 9 

Geology 9 

Geophysical studies 9 

Geochemical studies 10 

Methods 10 

Results and interpretation 10 

Mineral resource assessment 11 

References cited 12 

Appendixes 

Definitions of levels of mineral resource potential and certainty 

of assessment 17 

Resource/reserve classification 18 

Geologic time chart 19 

FIGURES 

1. Index map showing location of the Lower Burro Creek Wilderness Study Area, 

Mohave and Yavapai Counties, Arizona 82 

2. Map showing mineral resource potential for the Lower Burro Creek Wilderness 

Study Area, Mohave and Yavapai Counties, Arizona 4 

TABLE 

1. Summary of claims and prospects in and adjacent to the Lower Burro Creek 

Wilderness Study Area 820 

v 
MINERAL RESOURCES OF WILDERNESS STUDY AREAS: 

WEST-CENTRAL ARIZONA AND PART OF SAN BERNARDINO COUNTY, CALIFORNIA 

Mineral Resources of the 

Lower Burro Creek Wilderness Study Area, 

Mohave and Yavapai Counties, Arizona 

By Robert J. Miller, Floyd Gray, Jerry R. Hassemer, 

William F. Hanna, and John Brice Ill 

U.S. Geological Survey 

Russell Schreiner 

U.S. Bureau of Mines 

SUMMARY 

Abstract 

The part of the Lower Burro Creek Wilderness 

Study Area (AZ-020-060} on which mineral surveys 

were requested encompasses approximately 21,700 

acres at the south end of the Aquarius Mountains in 

west-central Arizona. In this report, any reference to 

the Lower Burro Wilderness Study Area refers to the 

original 21,660 acres and an additional 10 acres for 

which the Bureau of Land Management requested 

mineral surveys and is referred to as the study area. 

The U.S Bureau of Mines and the U.S. Geological 

Survey conducted geological, geophysical, and 

geochemical surveys during 1984 and 1985 to assess 

the mineral resources (known} and mineral resource 

potential (undiscovered} of the study area. 

Inferred subeconomic mineral gold resources 

were identified. at four mines and prospects in the 

southeastern part of the study area. Sedimentary 

rocks in the eastern part of the study area host 

inferred marginal reserves of bentonite and inferred 

subeconomic resources of magnesite. Undiscovered 

deposits of gold in the study area are likely to be of 

very small tonnage. The mineral resource potential 

for gold is low in three small areas in the eastern part 

of the study area. The mineral resource potential for 

gold, silver, copper, lead, and zinc is low in one area in 

the southern part of the study area. Anomalous 

concentrations of tin in stream sediment samples were 

probably derived from silicic volcanic rocks within the 

study area, therefore two areas are considered to have 

low mineral resource potential for tin. The mineral 

resource potential for magnesite in the area surrounding the inferred subeconomic magnesite resource 

is low. The eastern part of the study area has one area 

each of high, moderate, and low mineral resource 

potential for bentonite. The geothermal resource 

potential is considered to be low for the study area. 

Character and Setting 

The Lower Burro Creek Wilder ness Study Area is 

located approximately 14 mi southeast of Wikieup and 

10 mi west of Bagdad, Ariz. The southwest boundary 

of the study area adjoins Arizona Highway 93. 

Elevations range from 1,920 ft at Burro Creek beneath 

the bridge on Highway 93 to 3,820 ft on an unnamed 

peak in the northern part of the study area. 

The study area lies in the structural transition 

zone between the Colorado Plateau and the Basin and 

Range physiographic province. Proterozoic (see 

appendix for geologic time chart) granitic and 

metamorphic rocks are extensively exposed in the 

region. Within the study area, Middle Proterozoic 

granites intrude schistose rocks of the Early 

Proterozoic Yavapai Series as well as an Early or 

Middle Proterozoic mafic-ultramafic complex. Faultbounded basins within the Proterozoic basement 

locally contain thick accumulations of Tertiary 

volcanic and sedimentary rocks. Laramide (71 Ma) 

plutonic and Laramide(?) volcanic rocks are present 

near Bagdad, 10 mi east of the study area, however 

coeval magmatic activity has not been identified 

within the study area. 

The study area is located near the southwest 

periphery of the Eureka mining district. Much of the 

production from that district has come from a 

Laramide-age porphyry copper deposit. Lesser 

production was from Proterozoic basement-hosted 

volcanogenic massive sulfide deposits, fault-controlled 

81 
i Signal 

Mountain 

Greenwood i Peak 

Eureka mining district 

LOWER BURRO CREEK 

WILDERNESS STUDY AREA 

(AZ-020·060) 

Old Dick ~- 1 and Bruce mine{' ).--/-

// 

-., 

I 

GRAY BACK ~-., 

MOUNTAINS ,-' 

I 

I 

X: Zannaropolis 

I mine 

grave/l 1

1 

-.,_~ I 

\~-J 

,o~ 'Q'----

' Miller 

Mountain 

Arrastra Mountain 

' 

34°15' 

I 

I 

RANGE I 

I 

10 MILES 

AREA OF MAP 

Figure 1. Index map showing location of Lower Burro Creek Wilderness Study Area, Mohave and Yavapai Counties, Arizona. 

·epithermal gold-, silver-, copper-, lead-, and zincbearing veins, and wolframite- and scheelite-bearing 

quartz veins and pegmatites. Tertiary zeolitized tuff 

within the district is mined locally for use as building 

material. 

82 

Gold mining began in the study area in the late 

1800's and has occurred sporadically since. During the 

1960's and 1970's, limited quantities of bentonite and 

magnesite were mined within and adjacent to the east 

boundary of the study area. 
Identified Mineral Resources 

Proterozoic rocks in the south half of the study 

area have been prospected extensively for lode gold 

deposits and the area for placer gold deposits. No 

production records are available for the mines and 

prospects within the area. Inferred subeconomic 

resources of gold were identified at the Golden Key 

mine, Granite State mine, and the Phoebe claims. The 

Golden Key mine has 350 short tons (st) averaging 0.15 

oz gold/st and 5, 700 st averaging 0.06 oz gold/st, the 

Granite State mine has 6,000 st averaging 0.05 oz 

gold/st, and the Phoebe claims have 5,500 st gold 

averaging 0.1 oz gold/st. Samples with similar gold 

values were collected at other prospects within the 

study area, however exposures were not sufficient to 

estimate the tonnage or grade of the deposits. In 

addition to gold, minor amounts of silver, copper, lead, 

zinc, and molybdenum are present in some prospects. 

Bentonite is present in lacustrine sedimentary 

rocks that underlie the eastern part of the study area 

and extend eastward beyond the study area boundary. 

The bentonite having the most favorable chemical and 

physical characteristics and least overburden is found 

within and immediately east of the study area. 

Inferred marginal reserves of 600,000 st of bentonite 

are identified. The deposits of highest grade bentonite 

coincide with deposits of cryptocrystalline 

magnesite. Two million tons of inferred subeconomic 

magnesite resources of variable purity were identified 

within and east of the study area (loc. 14, fig. 2). 

A thermal spring 2 mi southwest of the study 

area has a surface temperature of 37 °C and an 

estimated reservoir temperature of less than 115 °C 

(Goff, 1979). No geothermal activity is present within 

the study area. 

Mineral Resource Potential 

Gold and minor amounts of silver, copper, lead, 

and zinc are present at numerous mines and prospects 

located in the southeastern part of the study area. 

Geology and geochemistry indicate that these 

occurrences are fault-controlled hydrothermal deposits 

hosted by Proterozoic granitic and metamorphic 

rocks. Known deposits in the study area of this type 

have a very small tonnage and low or moderate 

grade. The potential for resources of gold in largetonnage deposits is low in three areas within the study 

area and low for resources of gold, silver, copper, lead, 

and zinc, in one area. 

Tin is present in anomalous concentrations in 

some stream-sediment samples from the study area. 

The tin is probably derived from Miocene fluorineenriched rhyolite domes or associated pyroclastic 

deposits within the study area. The potential for 

resources of tin is considered to be low in two areas 

within the study area. Fluorine-enriched rhyolites may 

be associated with deposits of uranium, beryllium, 

lithium, molybdenum, and tungsten, however no 

evidence was found to indicate the presence of these 

deposits within the study area. Near Bagdad, uranium 

occurs in unusually high concentrations in accessory 

minerals within the Middle Proterozoic Lawler Peak 

Granite (Silver and others, 1984). A general 

aeroradiometric high over the granite in the southeast 

corner of the study area suggests that the same may 

be true there. Anomalous concentrations of uranium 

and thorium in stream-sediment samples from the 

study area are assumed to be the result of this high 

background rather than the result of resource-forming 

processes, therefore there is no potential for 

undiscovered resources of uranium or thorium in the 

study area. 

Bentonite is interbedded with Tertiary 

lacustrine, basin-fill sediments in the eastern part of 

the study area. The thickest exposure of bentonite is 

present along the east boundary of the study area 

where resources of bentonite are identified. The 

potential for resources of bentonite is high in the area 

adjacent to the identified bentonite resource. In this 

area the lacustrine sediments are disrupted and 

repeated by faulting and slumping. Colluvium of 

basalt rubble covers most of the area and prevents the 

determination of the location or thickness of the 

bentonite. The potential for resources of bentonite is 

moderate in one area. Lacustrine rocks present near 

the center of the study area are dominantly composed 

of siltstones and silty mudstones but impure bentonite 

may be present locally. This area has low potential for 

bentonite resources in a deposit of white 

cryptocrystalline magnesite. 

Additional resources of magnesite could be 

present within an area of slumped and colluviumcovered sediments adjacent to the known deposit. The 

potential for resources of magnesite is low in this 

area. 

Zeolites, present as an alteration product of 

siliceous tuffs, are locally interbedded with the 

lacustrine sediments east of the study area. Lithicrich silicic tuff overlies the lacustrine sediments in the 

study area. This tuff may be partially altered to 

zeolite minerals, locally, however ~he study area does 

not have resource potential for zeolites due to the 

high content of lithic detritus present in the tuff. 

The geothermal resource potential is low for the 

study area. There is no potential for oil and gas 

resources in the study area. 

INTRODUCTION 

This mineral survey was requested by the U.S. 

Bureau of Land Managment and is a joint effort by the 

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

The U.S. Bureau of Mines evaluates identified 

resources (known) 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 the 

system described by U.S. Bureau of Mines and U.S. 

Geological Survey (1980). Studies by the U.S. 

Geological Survey are designed to provide a reasonable 

. scientific basis for assessing the potential for mineral 

resources (undiscovered) by determining geologic units 

and structures, possible environments of mineral 

deposition, presence of geochemical and geophysical 

anomalies, and applicable ore-deposit models. Mineral 

assessment methodology and terminology as they apply 

83 
m 

ol::o 

I IJI,!! 

34135' 

Zoid claims 

0 1 2 MILES 

34130' 

113'25' 

APPROXIMATE BOUNDARY OF 

LOWER BURRO CREEK WILDERNESS ...... -...--sTUDY AREA (AZ-020-060) 

AREA 

u ~IMP 

113°20' 

L!C Mag [2] 

L/C Au [3] 

Figure 2. Mineral resource potential for the Lower Burro Creek Wilderness Study Area, Mohave and Yavapai Counties, Arizona. 
aJ 

U1 

• Area with high resource potential 

Area with moderate resource potential 

D Area with low resource potential 

~ Mine with identified resource 

X Prospect with identified resource 

See appendix for definition of levels of mineral resource 

potential and certainty of assessment and description 

of mines and prospects 

Commodities 

Au Gold So Tin 

Ag Silver Ben Bentonite 

Cu Copper Mag Magnesite 

Pb Lead Geo Geothermal 

Zn Zinc 

[] Deposit types 

1 Diagenetic alteration 

2 Hot-spring alteration 

3 Hydrothermal gold-bearing veins and fractures 

4 Tin-bearing rhyolite 

Figure 2. Continued. 

Qs 

Ql 

Trd 

Tb 

Tps 

Tr 

Td 

Pd 

Pg 

Ppg 

Pgc 

Pm 

EXPLANATION 

Description of map units 

Alluvium (Quaternary)- Unconsolidated sand and gravel in 

modem stream channels. Includes talus 

Landslide deposits (Quatemary)--Chaotic assemblages of 

volcanic and sedimentary rocks resulting from 

undercutting of Burro Creek 

Rhyodacite (Miocene)--Variably porphyritic rhyodacite domes 

and associated flows on the west margin of the study area 

Basalt (Miocene)--Mesa-forming basalt flows and minor 

agglomerates and tuffs 

Pyroclastic and sedimentary deposits (Miocene)--Tuffs and 

fluvial and lacustrine tuffaceous sedimentary rocks 

Rhyolite (Miocene)--Coalescing aphyric rhyolite domes 

contemporaneous with and partially overlying 

pyroclastic deposits 

Dolomite (Miocene)--Dolomite and minor interbedded 

lacustrine sediments 

Diabase (Proterozoic)--Dikes and irregular intrusive bodies 

cutting granite 

Granite (Proterozoic)--Weakly foliated to unfoliated, 

medium-grained muscovite-biotite granite. Near contact 

with Pm contains screens of metamorphic rock 

Porphyritic granite (Proterozoic)--Porphyritic medium-grained 

biotite-muscovite granite with orthoclase megacrysts 

.05 to 1 in. in length 

Gabbro complex (Proterozoic)--Gabbro, diorite, and minor 

hornblendite extensively intruded by orthoclaseporphyritic granite and granodiorite 

Metamorphic rocks (Proterozoic)--Biotite and muscovite schist 

and quartz feldspar gniess, possibly correlative in part to 

Yavapai Series rocks near Bagdad. Locally includes 

tongues of granitic intrusive rocks 

Contact--Dashed where approximate 

Normal fault--Dashed where approximate 

Mines and prospects 

1 Golden Key mine 9 Unnamed 

2 Golden Key mine--northern extension 10 Unnamed 

3 Granite State mme 11 Golden Flow claims 

4 Buckhorn and End.log claims 12 Golden Flow claims 

5 Buckhorn and End.log claims 13 Unnamed 

6 Key mine, Leverite claims 14 Jangretta and HMC claims 

7 Leverite claims 15 Bentonia claim 

8 Phoebe claims 

Correlation of map units 

~ 

@] } QUATERNARY 

~ G uanrucy } TERTIARY 

~ DG 

~ 

~ 

~ 

~ 

Unconformity 

I Ppg I 

PROTEROZOIC 
to these surveys were discussed by Goudarzi (1984). 

See appendix for the definition of levels of mineral 

resource potential, certainty of assessment, and 

classification of identified resources. 

Area Description 

The Lower Burro Wilderness Study Area lies 

north of Arizona Highway 93 between Bagdad and 

Wikieup (fig. 1). The part of the area on which mineral 

surveys were requested encompasses approximately 

21,700 acres near Burro Creek (fig. 1). The terrain is 

generally rugged; cliffs and steep canyons are 

common. Arizona Highway 93 bridges a spectacular 

400-ft-deep gorge of Burro Creek west of the study 

area. Relief is moderate and elevation ranges from a 

high of 3,820 ft to a low of 1,960 ft. The climate is 

arid and vegetation consists of a mixture of Sonoran 

desert flora. Yucca, mesquite, and juniper are also 

quite common. Sycamore and cottonwood trees are 

found locally along major washes. 

Access to the area is provided by a dirt road that 

originates from Arizona Highway 93 at Nothing, Ariz., 

follows the east and north boundaries of the study area 

and returns to the highway west of Kaiser Spring 

Canyon. Jeep trails along Bonanza Wash, Kaiser 

Spring Wash, and Haleys Wash provide access to the 

interior of the area. A jeep trail follows parts of the 

powerline transecting the northern part of the area. 

The Golden Key and Granite State mines are also 

reached by jeep trail. 

Previous and Present Investigations 

A geologic map of Mohave County was published 

by Wilson and Moore (1959). Anderson and others 

(1955) describe in detail the geology and. ore deposits 

near Bagdad, Ariz., about 8 mi east of the study area. 

Moyer (1982) concluded that the aphyric rhyolites in 

the area fell into the class of unproductive topaz 

rhyolites (defined by Bikun and others, 1980) after 

completing a detailed study of the Tertiary volcanic 

rocks exposed in the Kaiser Spring quadrangle. 

The U.S. Geological Survey conducted field 

investigations within the study area during 1984 and 

1985. New geologic mapping was completed in areas 

lacking previous mapping and further detail was added 

to areas already mapped. Geochemical samples, 

including stream-sediment, pan-concentrate, 

mineralized and unmineralized rock samples, were 

collected throughout the area (D.E. Detra, unpub. 

data, 1986). 

Investigations by the U.S. Bureau of Mines 

included a search of mining records and field 

examination and sampling of all mines and prospects 

within the area. Based on results of that work, 

mineralized areas were appraised and resources were 

determined when sufficient exposures were present 

(Schreiner, 1985). 

Acknowledgments 

T.H. Eyde of GSA Resources, Cortaro, Ariz., 

provided geologic, historical and other data pertinent 

86 

to the bentonite and magnesite deposits within the 

Lower Burro Creek Wilderness Study Area. C.S. 

Thompson, manager, R.T. Vanderbilt Company, Inc., 

Norwalk, Conn., and M.R. McGath, manager, NL 

Chemicals, Inc., Newberry Springs, Calif., provided 

analyses of a bentonite sample. 

APPRAISAL OF IDENTIFIED RESOURCES 

.!!! Russell Schreiner 

U.S. Bureau of Mines 

Published and unpublished literature relating to 

the Lower Burro Creek Wilderness Study Area was 

searched to obtain pertinent information concerning 

mineral occurrences and mining activity. Mining claim 

information and land status plats were acquired from 

the Bureau of Land Management (BLM) State Office, 

Phoenix, Ariz. Prospects and mineralized areas in and 

within 1 mi of the boundary were mapped by compassand-tape method and sampled. Two hundred and fiftythree channel, chip, and grab samples were taken. 

All samples were fire assayed for gold and 

silver. Inductively coupled plasma-atomic emission 

spectroscopy (ICP-AES) or atomic absorption 

spectrophotometry was used to analyze for copper, 

lead, molybdenum, and zinc. Inductively coupled 

plasma-atomic emission spectroscopy and wet 

chemical methods were used to analyze for elements 

in the bentonite and magnesite samples. Bentonite and 

magnesite samples were analyzed by X-ray diffraction 

to identify and characterize all minerals present. 

At least one sample from each prospect was analyzed 

for 40 elements by semiquantitative optical emission 

spectroscopy to determine the presence of unsuspected 

elements. 

Standard physical property tests used in the oil, 

steel, and foundry industries were performed on 

bentonite samples by the U.S. Bureau of Mines 

Research Center, Tuscaloosa, Ala. Tests included 

viscosity and filtration to determine potential for use 

as drilling mud, plate water absorption to indicate 

potential for pelletizing or agglomeration capacity of. 

fine iron ores to be processed by blast furnaces, and 

compressive tests to indicate potential for use as a 

binder for molding. Additional testing of physical 

properties on a sample of clay was performed by NL 

Chemicals Inc., Newberry Springs, Calif., and R.T. 

Vanderbilt Company Inc., Norwalk, Conn., to 

determine if the clays are suitable for nonconventional uses. 

Tonnage and grade were calculated for deposits 

with adequate exposures and sample data. Sample 

values were averaged and weighted with respect to 

sample length. Projection of the mineralized zone 

beyond the sampling sites was assumed to be one half 

the exposed length when no other data were available. 

All analytical data are available for public 

inspection at the U.S. Bureau of Mines, Intermountain 

Field Operations Center, Denver Federal Center, 

Denver, CO, 80225. 

Mining History 

The Lower Burro Creek Wilderness Study Area is 

located along the southwestern periphery of the 
Eureka mmmg district. Most of the activity in the 

mmmg district has focused on porphyry copper and 

massive sulfide deposits at Bagdad, approximately 8 mi 

east of the study area. In the study· area, intermittent 

mining activity has occurred from the late 1800's to 

the present. No recent gold mining activity has taken 

place and no production records were found. Lode and 

placer claims located for gold are found in the 

southern part of the study area. 

The Jangretta, HMC, and Bentonia claims cover 

bentonite and magnesite deposits in the eastern part of 

the study area. GSA Resources is currently evaluating 

the bentonite deposit and in 1983-1984 parts of the 

deposit were drilled. Bentonite was mined 

(approximately 5,000 to 10,000 st) in the 1960's and 

1970's and used for water impedance in the Patagonia 

Lake dam, Santa Cruz County, Ariz., and as a binder 

for cattle feed. Magnesite was mined on a small scale 

and used as a brightening additive in swimming pool 

plaster (T.H. Eyde, GSA Resources, Cortaro, Ariz., 

oral commun., 1985). 

Concretions containing purple agate are 

collected for lapidary purposes from the bentonite and 

magnesite deposits (John Gutierrez, BLM, Kingman, 

Ariz., oral commun., 1984). 

Five millsite claims, including the remains of a 

small mill, are located at the junction of Burro Creek 

and Bonanza Wash. The mill was built in the 1940's to 

process tungsten ore from the Zannaropolis mine, 4 mi 

east of the study area. 

The Zoid claim block, staked for uranium in 

1980, is located 0.25 to 2 mi south of the study area. 

The claims cover a helium anomaly (a common product 

of the radioactive decay of uranium) in a basin 

containing Tertiary sedimentary and volcanic rocks. 

The basin is adjacent to highly radioactive granitic 

rocks at Greenwood Peak, a few miles to the 

southwest. Two holes were drilled for uranium by 

Union Carbide Corp. approximately 2,400 ft and 2,600 

ft deep in Tertiary sedimentary and volcanic rocks 

(one hole penetrated granitic gneiss basement rocks). 

No mineralized rock was encountered (Ernst Kendall, 

Union Carbide Corp., Grand Junction, Colo., oral 

commun., 1984). 

Oil and gas leases cover the southern part of the 

study area (Schreiner, 1985), but there had been no 

drilling as of August 1984. 

Appraisal of Sites Examined 

Mines and prospects in the study area are located 

on occurrences and deposits of gold, silver, copper, 

lead, and zinc in igneous and metamorphic rocks and 

bentonite, magnesite, and agate in lacustrine rocks. 

Gold Mines and Prospects 

Gold mines and prospects are located on faults in 

granite and gneiss in the southern part of the study 

area. The faults contain gold and minor amounts of 

silver, copper, lead, molybdenum, and zinc (Schreiner, 

1985; table 1). Inferred subeconomic gold resources 

were identified at the Golden Key mine, Granite State 

mine, and Phoebe claims. On the Golden Flow claims, 

sample results suggest that a resource may exist but 

grade and tonnage could not be calculated because of 

insufficient data due to inadequate exposure. Mines 

and prospects are shown on figure 2 and described in 

the appendix. 

Bentonite Prospects 

Deposits of bentonite, magnesite, and 

occurrences of agate are present in a section of 

faulted and slightly folded Tertiary tuffaceous 

lacustrine rocks along Burro Creek in the eastern part 

of the study area. Bentonite and magnesite were 

mined on a small scale along the east boundary of the 

study area. The occurrences and deposits are 

currently covered by the Jangretta and HMC claim 

groups. Additional clay and magnesite deposits are 

exposed along Burro Creek, east of the study area. 

Bentonite is exposed for 60 ft in a partial section 

below a tuff. The bentonite section in descending 

order consists of brown, beige, brown, and green 

beds. The section dips slightly to the southwest. 

Bentonite in the study area was identified by 

chemical and X-ray diffraction analyses as highmagnesium trioctahedral smectites (saponite-type 

clays) containing various types and amounts of 

impurities (Schreiner, 1985, tables 3, 4). The beige 

clay is the purest and has the greatest economic 

potential. Seven sites contained partial exposures of 

the beige clay bed (Schreiner, 1985). The bed is found 

about 25 ft below the tuff and appears to be 

continuous in the area sampled. The beige clay bed is 

white on weathered surfaces, and the top of the bed, 

where exposed, is dolomitic and siliceous, resulting in 

the formation of a boxwork texture. 

Standard physical property tests for bentonite 

used by oil, steel, and foundr:· industries, which 

consumed 70 percent of the domestic output of 

bentonite in 1984 (U.S. Bureau of Mines, 1985, p. 34), 

were performed on four samples of beige clay, one 

sample of brown clay, and one sample of green clay 

(Schreiner, 1985, table 5). The results of these tests 

are compared with runs of commercially acceptable 

clays or standards, a western standard (sodium 

bentonite), and a southern standard (calcium 

bentonite). The physical properties of the clays from 

the study area are far below those of the acceptable 

standards. The one exception is the green clay that 

has a dry-compression strength (70.5 pounds per square 

inch) similar to the western standard and exceeds the 

southern standard, ind_icating that it could possibly be 

used as a binder for molding, but further testing would 

be required by the individual foundry for 

acceptability. Beneficiation to make the clays 

acceptable would incur additional costs, reducing the 

likelihood to producing an economically competitive 

product. 

Though the clays in the study area may not be 

readily suitable for major uses, the crude clays could 

be used locally for water impedance in reservoirs, 

ponds, and ditches. The beige clay, because of its high 

brightness, white color when dry, and purity, has 

potential for use in the higher priced, specialty-clay 

thickener or stabilizer products and in paints, greases, 

cosmetics, and pharmaceuticals. Strict quality 

87 
standards call for beneficiation of clays used as raw 

material for these products. A sample of the beige 

clay was sent to R.T. Vanderbilt Company, Inc., 

Norwalk, Conn., and NL Chemicals, Inc., Newberry 

Springs, Calif., for additional physical property tests 

(Schreiner, 1985, table 4). The companies reported 

that the sample consisted of a low-swelling magnesium 

smectite and minor dolomite having a low viscosity 

and lack of colloidal stability. R.T. Vanderbilt 

Company, Inc., reported that the clay has commercial 

potential as a raw material for making thickener or 

stabilizer products with relatively unsophisticated 

treatment. NL Chemicals reported that because of 

the low swelling property it would be unsuitable for 

their use. 

GSA ·Resources, in a joint venture with an 

undisclosed major clay producer, is currently 

evaluating the beige clay. In 1983 and 1984, GSA 

Resources drilled 22 holes in the deposit within and 

near the east boundary of the study area. Results 

indicate that the beige clay is 3 to 20 ft thick and 

locally contains variable amounts of impurities. The 

clay with the best color, colloidal properties, and 

lowest arsenic levels is present both inside and outside 

the east boundary of the study area. The best clay is 

located adjacent to masses of magnesite, chalcedony, 

and dolomite of varying thickness that appear to be 

located along faults. Alteration of tuffaceous rocks to 

these high magnesium smectites was apparently the 

result of deposition in a lacustrine environment and 

later introduction of hydrothermal solutions from hot 

springs (T.H. Eyde, GSA Resources, oral commun., 

1984). 

Although the beige clay appears to be present 

over a large part of the study area, the least amount 

of overburden is near the east boundary of the study 

area. Considering a 60-ft limit of overburden that 

could be stripped by open-pit mining methods (T.H. 

Eyde, oral commun., 1985), the clay in this locality, 

having a minimum thickness of 5 ft, could be mined 

over an area 3,000 by 500 ft, estimated from outcrop 

locatio~s and topography. Using a tonnage factor of 

13 ft /st, an inferred marginal reserve of 

approximately 600,000 st of clay is identified. 

Magnesite Prospects 

White cryptocrystalline magnesite is present as 

10- to 40-ft-thick mound-like masses within the clays 

near the east boundary of the study area (fig. 2, loc. 

14). Samples contained as much as 90 percent 

magnesite and had chalcedony, dolomite, calcite, and 

saponite-type clay impurities (Schreiner, 1985, table 

6). The amount of impurities present in samples 

appears to be highly variable. An estimated 2 million 

st of inferred subeconomic magnesite resources of 

various grades were identified and could be mined 

using open-pit mining methods. Calculations were 

made assuming that the magnesite is continuous over 

an area of 2,000 by 500 ft, ~verages 20 ft thick, and 

has a tonnage factor of 10 ft /st. Additional deposits 

of magnesite are exposed along Burro Creek east of 

the study area. 

Currently, no market exists for the crude 

magnesite, except for possible local use as an additive 

88 

to increase the brightness of materials, such as 

plaster. The material would have to be processed by 

heavy media separation to remove the impurities and 

dead burned or calcined to produce a commercially 

acceptable product. Basic, Inc., is mining and 

processing ore at Gabbs, Nev., at grades as low as 85 

percent magnesite, which is comparable to some of the 

material in the study area. Basic, Inc., had estimated 

10 million st of magnesite in the Burro Creek area but 

the overall grade was considered too low to warrant 

development (Ty Jepsen, oral commun., 1984). 

Currently, low demand for magnesium compounds 

would make development in the study area unlikely. 

Agate Prospects 

Purple agate is reported (J. Gutierrez, BLM, oral 

commun., April, 1985) to be present in concretions 

within lacustrine rocks in the study area, although 

none was noted by USBM personnel. The agate is used 

in making cabochons for jewelry. Three small pits, 

approximately 1 mi north of the study area, contained 

pockets of black, red, and white chalcedony in a 

siliceous dolomite. Some of the chalcedony contains 

inclusions forming crude dendritic patterns. 

Geothermal 

No geothermal leases were present in or near the 

study area as of March 1984, but a thermal spring 

(surface temperature 37 °C) is located at Warm 

Spring, approximately 2 mi southwest of the study 

area. A geothermal reservoir of moderate 

temperature (estimated at less than 115 °C from 

chemical geothermometry) exists at Warm Spring 

(Goff, 1979). 

Oil and Gas 

Most of the study area acreage has been leased 

for oil and gas but no drilling had occurred as of April 

1984 (John Gutierrez, BLM, Kingman, Ariz., oral 

commun., 1984). 

Conclusions 

Gold and minor amounts of silver and copper, 

lead, zinc, and molybdenum metals are present in 

small deposits along faults in the Proterozoic igneous 

and metamorphic rocks in the Lower Burro Creek 

Wilderness Study Area. Inferred subeconomic gold 

resources are identified at the Golden Key mine (350 

st averaging 0.15 oz gold/st and 5, 700 st averaging 

0.06 oz gold/st), the Granite State mine (6,000 st 

averaging 0.05 oz gold/st), and the Phoebe claims 

(5,500 st averaging 0.1 oz gold/st). Other similar 

deposits within the study area lacked sufficient 

exposures, which prevented detailed mapping and 

sampling and resource calculations. Narrow, 

moderately to steeply dipping fault-controlled deposits 

such as these would be amenable primarily to 

underground mining methods. At an average 1984 gold 
price of $365.00 per oz, these deposits would be 

subeconomic. 

High-magnesium bentonite is present in the 

eastern part of the study area m lacustrine 

sedimentary rocks. The beige clay (inferred marginal 

reserve of approximately 600,000 st) has the greatest 

commercial value and is amenable to open-pit mining 

methods. With beneficiation, this clay could be used 

as a raw material for making thickener or stabilizer 

products. 

White cryptocrystalline magnesite is present in 

the eastern part of the study area also in lacustrine 

sedimentary deposits. An estimated 2 million st of 

inferred subeconomic magnesite resources of various 

grades were identified and are amenable to open-pit 

mining. Some of the magnesite is of similar grade to a 

deposit currently being mined in Nevada. Low demand 

for magnesium compounds makes near-term 

development unlikely. 

Purple agate is present in concretions in the 

lacustrine deposits in the eastern part of the study 

area. The agate is used for lapidary purposes. 

A thermal spring is located approximately 2 mi 

southwest of the study area at Warm Spring. A 

geothermal reservoir of moderate temperature exists 

there which could be used for limited local use. 

No oil and gas resources are known to exist in 

the study area. 

ASSESSMENT OF MINERAL RESOURCE POTENTIAL 

~ Robert J. Miller, Floyd Gray, Jerry R. Hassemer, 

William F. Hanna, and John Brice III 

U.s. Geological Survey 

Geology 

The Lower Burro Creek Wilderness Study Area is 

located in the structural transition zone between the 

Colorado Plateau and the Basin and Range 

physiographic province. Within the study area upper 

Tertiary volcanic and sedimentary rocks lie directly on 

Proterozoic basement rocks that have a complex 

deformational and intrusive history. 

Proterozoic metamorphic rocks on the north side 

of the study area consist of a heterogenous mixture of 

predominantly biotite and quartz-muscovite schist that 

is vertically foliated and extensively intruded by 

equigranular to seriate granite. The schist may be 

correlative with part of the Yavapai Series recognized 

by Anderson and others (1955) near Bagdad, Ariz. 

Metavolcanic rocks comprise much of the Yavapai 

Series at Bagdad and host massive sulfide deposits at 

the Old Dick and Bruce mines. The metavolcanic 

component of the Yavapai present at Bagdad is absent 

in the study area. 

A complex of hornblende gabbro, hornblendite, 

orthoclase augen gneiss, and minor selvages of mica 

schist underlies much of the central and southern parts 

of the study area. The age of the complex is not 

known; however it is intruded by monzogranite 

porphyry assumed to be lithologically correlative with 

the Middle Proterozoic Lawler Peak granite. Ludwig 

and Silver (1977) have determined an age of 1420 Ma 

for the Lawler Peak Granite. (Shafiqullah and others 

(1980) considered a 577 Ma K-Ar age on biotite from 

the granite near Nothing, Ariz., .to be partially reset.) 

Pegmatites that intrude both the gabbro complex and 

the later granite, probably represent the last stage in 

the crystallization of the granite. Numerous generally 

northwest-trending dikes and irregular masses of 

diabase intrude the granite. The diabase has not been 

dated but may be similar in age to Late Proterozoic 

diabase elsewhere in Arizona. 

A Laramide granitic intrusion at Bagdad, Ariz., 

hosts a porphyry copper deposit and may have provided 

the heat source for the redistribution and deposition of 

epithermal gold, silver, copper, lead, and zinc within 

the surrounding Proterozoic basement rocks (Anderson 

and others, 1955). A tuff exposed in the Grayback 

Mountains (fig. 1) was assumed by Anderson and others 

(1955) to represent coeval Laramide volcanic 

activity. No evidence for Laramide magmatic activity 

has been found within the study area. 

The early and middle Tertiary was primarily a 

period of erosion. During the Oligocene and Miocene, 

normal faulting produced extensive basin development 

in the region. Thick accumulations of lacustrine and 

fluvial basin-fill sediments were faulted, tilted, and 

buried by a second period of basin development in the 

late Tertiary. The earlier basin fill hosts a uranium 

deposit at the Anderson mine 20 mi south of the study 

area. These organic-rich sediments were deposited 

under marsh-like conditions and provide a reducing 

environment for the accumulation of uranium. 

The lacustrine sedimentary rocks within the 

study area are generally composed of flat-lying sandy 

mudstone, tuffaceous mudstone, claystone, and tuff 

overlying arkosic sandstone, siltstone, and 

conglomerate. A thin oncolitic dolomite bed is 

extensively silicified and hydrothermally altered to 

magnesite near the east boundary of the study area. 

Tuffs intercalated with the sedimentary rocks are 

altered to bentonite. This unit is lithologicaly similar 

to the Big Sandy Formation exposed near Wikieup. 

Bimodal volcanism occurred within the study 

area between 8 and 12 Ma and has been discussed in 

detail by Moyer (1982). Aphyric rhyolite domes and 

associated tuffs are characterized by a moderately 

enriched fluorine content; lithophysal garnet is present 

locally. A second series of silicic eruptions produced 

domes and flows of biotite-, hornblende-, and feldsparphyric rhyodacite. These eruptions were roughly 

coeval with the eruption of mesa-forming basalt flows 

that covered much of the area. Subsequent faulting 

and erosion has produced the present topography. 

Geophysical Studies 

The Lower Burro Creek Wilderness Study Area is 

covered by regional gravity surveys (Lysonski and 

others, 1980a, b; Aiken and others, 1981) and magnetic 

surveys (Sauck and Sumner, 1970; Western Geophysical 

Company of America, 1979) having sufficient 

resolution to define anomalies of several square 

kilometers in area or larger. Contours of complete 

(terrain corrected) Bouguer gravity anomalies are 

defined by about 15 observation points, most of them 

within a few kilometers of the study area. Contours of 

89 
total-intensity magnetic anomalies are defined by 

three traverses flown 9,000 ft above sea level and 

eight traverses flown 400 ft above the terrain. 

Two gravity features have regional 

significance: (1) a broad 6-mGal low that trends 

southeast over the western two-thirds of the study 

area and is associated with low-density tuffaceous and 

lacustrine sedimentary rocks, rhyolites, and alluvium 

of Tertiary and Quaternary age; and (2) a narrower 4-

mGal high trending northward over the eastern third 

of the study area that is largely associated with higher 

density Precambrian gabbroic rocks. Although the 

mapped gabbroic rocks trend northeastward toward the 

gabbro near Bagdad, Ariz., they are inferred to extend 

in the subsurface on a more northerly trend toward the 

exposed Precambrian terrane north of the study area. 

Magnetic anomalies over the study area are 

generally characterized by low amplitudes and low 

gradients. The trends of three regional highs extend 

into the study area •. At the northwest corner of the 

study area, one magnetic high appears to be associated 

in part with Precambrian intermediate plutpnic rocks; 

however, the main part of this high app.ears to be 

associated with Precambrian gneiss west of the study 

area. Cutting southwestward across part of the 

northwest third of the study area, another high is 

associated with Precambrian intermediate plutonic 

rocks and Tertiary tuffaceous sedimentary rocks and 

rhyolite; it is inferred that the more highly magnetic 

Precambrian rocks underlie the volcanic sequences. 

The main part of this high also appears to be 

associated with Precambrian gneiss north and 

northeast of the study area. At the southeast corner 

of the study area, a north-trending nose is associated 

with Precambrian intermediate plutonic rocks 

immediately southeast of the gabbro complex (fig. 2). 

Precambrian gneiss is not associated with this high. 

The magnetic data, like the gravity data, 

indicate that the body of mapped gabbro within the 

study area does not extend continuously in the 

subsurface to the highly magnetic gabbroic body at the 

west margin of the Bagdad mining district (see 

Vacquier and others, 1963, p. 31-34 and plates 8 and 

9). Instead, the gabbroic rocks within the study area 

are unexpectedly associated with a broad magnetic low 

trending northeastward to a region just west of the 

gabbro near Bagdad, Ariz. This weak magnetic 

depression probably indicates that the gabbro is 

relatively nonmagnetic. However, it is possible that 

the feature is caused by reversed total magnetization 

of the gabbro but only if the body also becomes 

progressively less dense northeast of the study area 

boundary (to accommodate the absence of a continuous 

gravity high). The mesa-forming basalts within and 

outside the study area have little influence on the 

anomaly map, presumably because they are relatively 

thin. 

Because a large number of local occurrences of 

Tertiary intrusive rocks in the Basin and Range 

province of Arizona are associated with the flanks of 

regional magnetic highs, the possibility exists that the 

magnetic highs (noses) in the study area are caused 

primarily by Tertiary intermediate plutonic rocks, 

rather than Precambrian ones. If Tertiary plutonism is 

indicated by the anomaly, this magnetic feature could 

directly or indirectly point to mineralization 

associated with metamorphic core complexes 

810 

(Crittenden and others, 1980; Coney and Reynolds, 

1980) and Tertiary detachment faults (Spencer and 

Welty, 1986). However, apart from this possibility of 

hidden Tertiary intrusive rocks, the available regional 

geophysical data do not delineate terranes of increased 

mineral potential. 

Geochemical Studies 

Methods 

Geochemical sampling was conducted within the 

study area by the U.S. Geological Survey during 1984. 

Stream-sediment, nonmagnetic heavy-mineral 

concentrate, and rock samples were collected at 48, 

48, and 40 sites, respectively. These samples were 

analyzed for 31 elements by a six-step semiquantitative spectrographic method described by 

Grimes and Marranzino (1968). In addition, the 

concentration of uranium and thorium in stream 

sediment samples was determined by delayed neutron 

counting (Millard and Keaton, 1981). Gold was 

analyzed in selected heavy-mineral concentrate 

samples by the atomic absorption method of Thompson 

and others (1968). Rock sample analyses were 

supplemented by the determination of arsenic, 

bismuth, cadmium, antimony, and zinc by an atomic 

absorption method (Viets, 1978). 

The level at which the concentration of an 

element was considered anomalous was determined by 

inspection of histograms, percentiles, and enrichment 

relative to crustal abundance. Frequently, these 

anomalies reflect known mining activity, but in some 

instances may indicate areas of undisclosed or 

previously unrecognized mineralization. 

Results and Interpretation 

Epithermal quartz veins containing variable 

amounts of gold and minor silver were mined or 

prospected in the southeast part of the study area. 

These deposits contain minor or trace amounts of lead, 

zinc, copper, molybdenum, arsenic, antimony, and 

bismuth. The epithermal veins are localized along 

faults cutting Proterozoic granitic and metamorphic 

rocks. Anomalous concentrations of metallic and 

nonmetallic elements in heavy-mineral concentrate 

samples collected within the Proterozoic terrain 

indicate additional epithermal veins may be present. 

In particular, anomalous concentrations of silver, 

barium, bismuth, molybdenum, and tungsten were 

noted in a heavy mineral-concentrate sample collected 

from the drainage north of the Granite State and Key 

mines. 

Anomalous concentrations of tin (greater than 

2,000 ppm) were detected in four concentrate samples 

collected from drainages underlain in part by Miocene 

aphyric rhyolite domes or associated tuffs and 

sedimentary rocks in the northern and central parts of 

the study area. Two of the tin anomalies were not 

associated with anomalies of other elements. A third 

sample contained only minor bismuth and the fourth 

contained anomalous concentrations of barium, zinc, 

and thorium in addition to the tin. 
Anomalous concentrations of uranium and 

thorium are present in most stream sediment and 

heavy mineral concentrates derived from the 

Proterozoic basement rocks within the study area. 

These anomalies may represent elevated background 

values for the Proterozoic granitic rocks. 

Mineral Resource Assessment 

Geologic studies, geochemical sampling, and an 

examination of mines and prospects indicate that 

diverse mineral and energy resources may be present 

within the Lower Burro Creek Wilderness Study Area. 

Gold-, silver-, copper-, lead-, and zinc-bearing 

hydrothermal veins are hosted by Proterozoic granitic 

and metamorphic rocks in the study area. Three areas 

within the eastern part of the study area are assigned 

a low resource potential for gold (certainty level C). 

Gold, silver, copper, lead, and zinc have low resource 

potential in one area (certainty level B). The 

hydrothermal veins are restricted to faults cutting 

Proterozoic rocks however the age of mineralization is 

unknown. Mineralization consists of silica and calcite 

veins and stringers restricted to zones along faults. 

Wallrock alteration is generally minor with argillic 

alteration of feldspar in the host rock limited to within 

a few feet of the fault. Gold and minor silver is 

accompanied by sporadic concentrations of galena, 

anglesi te, malachite, chrysocola, and sphalerite. 

Geochemical analyses indicate minor variable amounts 

of molybdenum, antimony, and arsenic are also present 

locally in the veins, however the study area is not 

considered to have resource potential for these 

commodities. Some aspects of these deposits are 

similar to characteristics of other gold-bearing vein 

systems. Uncertainty as to the age of the deposits or 

probable origin of the mineralizing fluids prevent 

making direct analogies with established deposit 

models. The tonnage of identified gold resources 

within the study area is smaller than the smallest 

tonnages of deposits used in compiling grade/tonnage 

models for typical hydrothermal vein systems (Cox and 

Singer, 1986). 

The flourine-enriched "topaz rhyolites" within 

the study area may host tin mineralization of the type 

described by Huspeni and others (1984), in which 

cassiterite-bearing veins form in the host rhyolite near 

the contact with overlying units. Deposits of this type 

are typically of very low grade and small tonnage. The 

resource potential for tin in two areas within the study 

area is low with certainty of B. 

Uranium and thorium are found in unusually high 

quantities in disseminated trace minerals within the 

Lawler Peak Granite (Silver and others, 1984) near 

Bagdad. Uranium and thorium concentrations in 

sediment samples derived from the Proterozoic 

granitic plutons ·within the study area are consistently 

high. These high uranium and thorium values probably 

indicate background levels for these elements rather 

than the results of ore forming processes. Lacustrine 

sedimentary rocks in the basal part of the Big Sandy 

Formation exposed north of Wikieup may provide a 

favorable environment for uranium mineralization. 

Correlative sedimentary rocks in the study area lack 

evidence of paludal conditions and have a generally 

low-gamma ray signature. There is no resource 

potential for uranium and thorium within the study 

area. 

Bentonite is present within a sequence of 

lacustrine sedimentary rocks underlying the eastern 

part of the study area. Most of the bentonite was 

probably derived by diagenetic alteration from silicic 

tuffs deposited in a saline, alkaline lake environment. 

Dolomite, interbedded with the bentonites, is 

extensively silicified. The silica may have been 

introduced during the alteration of the tuffs or by hot 

spring hydrothermal fluids. The lower part of this 

dolomite bed has been hydrothermally altered to a high 

purity bentonite type clay. Identified resources of this 

clay are located along the eastern boundary of the 

study area. The dolomite horizon extends into the east 

central part of the study area however the distribution 

and intensity of the clay alteration is not well known 

due to extensive colluvial basalt cover, and slumping 

and faulting of sedimentary units. The lacustrine 

sediments thin westward within the study area as a 

result of westward shallowing of the basin in which 

they were deposited. The mineral resource potential 

for bentonite is high (certainty level C) in one area 

adjacent to the area of inferred marginal reserves 

bentonite; and moderate (certainty level C) in one area 

in the east central part of the study area. The 

potential is considered to be moderate due to thinning 

of the host dolomite horizon, increasing distance from 

the probable source of hydrothermal fluids, and 

thinning of bentonite beds derived from the alteration 

of tuffs. 

The mineral resource potential for bentonite is 

low (certainty level C) for one area in the vicinity of 

Haleys Wash. Dolomite, where it is exposed, is thin and 

lacks evidence of clay alteration. The purity of 

bentonite in this area is likely to be low due to detrital 

material washed in from the margin of the basin. 

Also located along the east boundary of the study 

area, and coincident with the bentonite, is a deposit of 

magnesite. This deposit was probably formed by 

hydrothermal replacement of dolomite due to faultcontrolled hot spring activity. Exposures of unaltered 

dolomite west of the known deposit provide evidence 

that the magnesite alteration was not widespread 

within the lacustrine rocks. The mineral resource 

potential for magnesite adjacent to identified 

magnesite resources is low with certainty C. 

Zeolite beds in the Big Sandy Formation near 

Wikieup have been quarried for local use as building 

stone (Janders, 1978). Zeolitized tuff horizons may be 

present within the lacustrine sediments in the eastern 

part of the study area. The purity of known 

occurrences is very low. The study area is not 

considered to have resource potential for zeolites. 

A low-temperature geothermal reservoir exists 

at Warm Springs 2 mi south of the study area. The 

reservoir may be suitable for small scale development 

(Goff, 1979; Witcher and others, 1982). No thermal 

springs are known within the wilderness study area and 

the geothermal resource potential is low with a 

certainty level of C. 

Much of the study area has been leased for oil 

and gas exploration. The Proterozoic granitic and 

metamorphic rocks that underlie most of the 

wilderness study area are unfavorable for oil and gas 

811 
accumulation (Ryder, 1983). Intense Tertiary volcanic 

activity in the study area makes the accumulation of 

oil and gas resources unlikely. There is no oil and gas 

resource potential within the study area. 

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survey of Las Vegas, Kingman, and Prescott 

quadrangles, Nevada, California, and Arizona --

Final Report: U.S. Department of Energy Grand 

Junction Office Report GJBX 59-79, v. 1, 42 p., 

scale 1:500,000. 

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

Mohave County, Arizona: Arizona Bureau of 

Mines, Tucson, Ariz., 1 sheet, scale 1:500,000. 

813 
APPENDIXES 
DEFINITION OF LEVELS OF MINERAL RESOURCE POTENTIAL 

AND CERTAINTY OF ASSESSMENT 

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 

few or no indications of having been mineralized. 

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 of resource accumulation, and (or) where an application of 

mineral-depo~t models indicates favorable ground for the specified type(s) of deposits. 

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

characteristics indicate a geologic environment favorable for resource occurence, where interpretations of 

data indicate a high degree of likelihood for resource accumulation, where data supports 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. 

UNKNOWN mineral resource potential is assigned to areas where information is inadequate to assign low, 

moderate, or high levels of resource potential. 

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

levels of Certainty 

t 

...J 

<{ 

i= 

z 

w 

to 

Q.. 

w 

u 

a: 

::::> 

0 

(/) 

w 

a: 

u.. 

0 

...J 

w 

> w 

...J 

U/A 

UNKNOWN 

POTENTIAL 

A 

H/B 

HIGH POTENTIAL 

M/B 

MODERATE POTENTIAL 

LIB 

LOW 

POTENTIAL 

B 

LEVEL OF 

H/C 

HIGH POTENTIAL 

M/C 

MODERATE POTENTIAL 

LIC 

LOW 

POTENTIAL 

c 

CERTAINTY ~ 

H/D 

HIGH POTENTIAL 

M/D 

MODERATE POTENTIAL 

LID 

LOW POTENTIAL 

N/D 

NO POTENTIAL 

D 

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

B. Available information 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. 

Abstracted with minor modifications from: 

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. 

Goudarzi, G. H., compiler, 1984, Guide to preparation of mineral survey reports on poblic lands: U.S. 

Geological Survey Open-File Report 84-0787, p. 7, 8. 

817 
RESOURCE/RESERVE CLASSIFICATION 

IDENTIFIED RESOURCES UNDISCOVERED RESOURCES 

Demonstrated Inferred Probability Range 

Measured Indicated Hypothetical Speculative 

I I 

ECONOMIC Reserves Inferred 

I Reserves 

I -----r------r------------ -~-

MARGINALLY I Inferred 

ECONOMIC 

Marginal Marginal Reserves Reserves 

I I-- _I_ ---------------------- I I 

SUB- Demonstrated Inferred 

Subeconomic Subeconomic 

ECONOMIC Resources Resources I 

I I 

Major elements of mineral resource classification, excluding reserve base and inferred reserve base. Modified from 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. 

818 
GEOLOGIC TIME CHART 

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

AGE ESTIMATES 

EON ERA PERIOD EPOCH OF BOUNDARIES 

(in Ma) 

Holocene 

Quaternary 0.010 

Pleistocene 

1.7 

Neogene Pliocene 

5 

Cenozoic Subperiod Miocene 

24 

Tertiary Oligocene 

Paleogene 38 

Eocene 

Subperiod 55 

Paleocene 

66 

Late 

Cretaceous - 96 Early 

Late 

Mesozoic Jurassic Middle 

Early 

Late 

Triassic· Middle 

Early 

Phanerozoic 

Permian Late 

Early 

Late 

Pennsylvanian Middle 

Carboniferous Early 

Paleozoic Periods Late Mississippian Early 

Late 

Devonian Middle 

Early 

Late 

Silurian Middle 

Early 

Late 

Ordovician Middle 

Early 

Late 

Cambrian Middle 

Early 

Late Proterozoic 

Proterozoic Middle Proterqzoic 

Early Proterozoic 

Late Archean 

Archean Middle Archean 

Early Archean 

~- ---- - ------(38007)-- ----- pre- Archean 2 

1

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

2

1nformal time term without specific rank. 

138 

205 

-v240 

290 

-330 

360 

410 

435 

500 

,....,5701 

900 

1600 

2500 

3000 

3400 

45 50 1-

819 
820 

TABLE 1. Summary of mines and prospects in and adjacent to the Lower Burro Creek Wilderness Study Area 

Map No. 

(fig. 2) 

Property 

name 

Golden Key mine 

Golden Key minenorthern extension 

Granite State mine 

Buckhorn and Endlog 

claims 

Buckhorn and Endlog 

claims 

Summary 

Mine workings consist of three adits 

(upper, middle, and lower), five shafts, 

and several pits and trenches along a 

fault, striking N. 25° E. and dipping 60° 

NW. in gneiss and granite. The 2.5-ftthick fault is traceable for 2,000 ft. It 

consists of brecciated wallrock, clay 

gouge, sporadic quartz stringers and pods, 

and traces of magnetite and chrysocolla. 

A 180-ft-long ad it, two shafts, and three 

pits are located on a fault striking east, 

dipping 50° N., and traceable for 400 ft 

in gneiss. The fault zone averages 3. 7 ft 

in thickness; consists of brecciated 

wallrock, clay gouge, quartz pods, minor 

white and brown calcite, and ex hi bits 

hematite-limonite staining. 

Consists of three inclined shafts on a 

fault striking N. 30° W., dipping 30° to 

50° NE., and traceable for 220 ft in 

granite. Fault zone averages 2.5 ft 

thick; consists of brecciated wallrock, 

clay gouge, and hematite-limonite 

staining. Brecciated quartz veinlets 

coated by minor amounts of malachite and 

chrysocolla were observed in two areas. 

Three additional small groups of workings 

are within 200 ft of Granite State mine 

(Schreiner, 1985; fig. 5). A shaft, pits, 

and trenches are located on faults 

striking approximately N. 20°-30° E. in 

gneiss. Fault zones consist of sheared 

wallrock, clay gouge, and quartz 

veinlets. Chrysocolla and minor amounts 

of malachite observed with quartz in 

shaft. 

Six prospects consisting of a 22-ft adit, 

two trenches, and three pits are located 

on faults, fractures, and .Pegmatite pods 

in gneiss and granite. 

Caved shaft and seven pits are located on 

faults having quartz veinlets. 

Chalcopyrite, chalcocite, chrysocolla, and 

hematite-limonite staining found in quartz 

at some sampling sites. 

Sample data 

Sixty-eight samples were taken from 

workings. Twenty samples contained 0. 01 

to 1 oz gold/short ton (st) and averaged 

0.12 oz gold/st. An 80-ft-long section in 

the middle adit contains an inferred 

subeconomic resource of 350 st averaging 

0.15 oz gold/st (assuming a width of 20 

ft, an average thickness of 2.6 ft, and a 

tonnage factor of 12 ft 3/st). 

Eleven of 13 chip samples taken along 

fault contained 0. 01 to 0. 28 oz gold/st. 

A select grab sample contained 0. 52 oz 

gold/st. An inferred subeconomic resource 

of 5, 700 st averaging 0.06 oz gold/ st was 

calculated (assuming a width of 94 ft, a 

length of 198 ft, an average thickness of 

3.7 ft, and a tonnage factor of 12 

ft3/st). · 

Eighteen of 19 samples taken along fault 

contained 0.01 to 0.29 oz gold/st. An 

inferred subeconomic resource of 6,000 st 

averaging 0.05 oz gold/st was identified 

and was calculated (assuming a 240 ft 

length, a 120 ft width, an average 

thicknes~ of 2. 5 ft, and a tonnage factor 

of 12 ft /st). 

Five of eight chip samples taken on faults 

contained gold values ranging form 0. 01 to 

0.3 oz/st. A select grab sample from the 

shaft dump contained 0.12 oz gold/st. 

Resources were not calculated because of 

insufficient data due to inadequate 

exposures at these prospects. 

Seven samples were collected. Four chip 

samples contained 0. 04 to 0.17 tr oz 

gold/st. Six chip samples contained 0.1 

to 0.6 tr oz silver/st and base metal 

content less than 0. 01 percent. A select 

grab sample contained 0. 73 tr oz gold/ st, 

0.5 tr oz silver/st, and base metal 

content less than 0.1 percent. 

Eight samples were collected. Two chip 

samples contained 0.01 and 1.19 tr oz 

gold/ st, and base metal content less than 

0. 3 percent. Three select grab samples 

contained as much as 0. 24 tr oz gold/ st, 

2.3 tr oz silver/st, 5.3 percent copper, 

2.5 percent lead, and 0.11 percent 

molybdenum. 
TABLE 1~ Summary of mines and prospects in and adjacent to the Lower Burro Creek Wilderness Study Area--continued 

Map No. 

(fig. 2) 

8 

10 

Property 

name 

Key mine, Lever! te 

claims 

Leverite claims 

Leve rite claims 

Leverite claims 

Lever! te claims 

Phoebe claims 

Unnamed 

Unnamed 

Summary 

Mine consists of a 35-ft-long adit, 15-ftdeep shaft and a 75-ft-deep inclined 

winze. Bot tom of the winze was not 

accessible to USBM personnel. Workings 

follow thin faults and fractures in 

granite; sporadic hematite-stained pods 

and vuggy quartz a few ft in diameter are 

present along fractures; four of these 

pods are located over a distance of SO ft 

in the winze. 

Inclined caved shaft at least 65 ft deep, 

vertical caved shaft at least SO ft deep, 

and three pits are located in granite. No 

mineralized rock found in place but pieces 

of hematite-stained granite and vuggy 

quartz were found on dumps. 

A 40-ft-long adit, and a 20-ft-long adit 

that connects to a caved shaft are present 

along fractures with sporadic limonitestained pods in granite. 

A 7-ft-long adit on a fault and two 

trenches are located on fractures in 

granite. 

A 40-ft-long inclined shaft and a pit are 

located on a fault with quartz veining in 

granite. Galena and chalcopyrite found in 

a select grab sample of quartz pieces from 

dump. 

Prospect consists of an ad it, a tunnel, 

two shafts, trenches, and pits. These 

workings are located on a fault striking 

N. 50° E. and dipping 50° NW. and 

traceable for 240 ft in granite. Fault 

zone averages 2. 3 ft thick and consists of 

brecciated wallrock, clay gouge, and 

sporadic quartz veinlets. Chrysocolla and 

anglesite are present locally. 

A 17-ft-deep inclined shaft, three pits, 

and a trench are located over a distance 

of 100 ft along a fault containing quartz 

veinlets in granite. 

A shaft over SO ft deep that was not 

accessible to U.S. Bureau of Mines USBM 

personnel and a series of pits and 

trenches are located over a distance of 

180 ft on a fault containing quartz 

veinlets. Galena and m~lachite are 

present locally. 

Sample data 

Seven samples were collected. Four chip 

samples contained 0.02 to 0.63 tr oz 

gold/st. Two contained 0.02 tr oz 

silver/st. Two dump samples contained 

0.16 and 0.12 tr oz gold/st. 

Five samples were collected. Dump samples 

contained 0.08 and 0.16 tr oz gold/st in 

random grabs and 0. 20 oz gold/ at in a 

select grab. A chip sample contained 0.1 

tr oz silver/st. 

Six samples were collected. Three chip 

samples contained 0. 01 to 0. 24 tr oz 

gold/st. A select grab sample contained 

0.44 tr oz gold/st, and less than 0.012 

percent base metal content. 

Four samples were collected. Three chip 

samples contained 0.02, 0.16, and 1.01 tr 

oz gold/ st and base metal content less 

than 0.027 percent. A select grab 

contained 0. OS tr oz gold/ at, 0. 4 tr oz 

silver/st, 0.023 percent copper; 2.29 

percent lead, and 0.019 percent zinc. 

Four samples were collected. Three chip 

samples contained 0. 04 to 0. 13 tr oz 

gold/st, 0.1 to 0.2 tr oz silver/at, and 

less than 0.144 percent base metal 

content. A select grab sample contained 

0.13 tr oz gold/st, 0.5 tr oz silver/at, 

and as much as 4.3 percent. 

Seven of 10 samples taken along fault contained 

from 0. 01 to 0. 38 oz gold/ st and averaged 0.1 oz 

gold/st. An inferred subeconomic resource of 

5, 500 at averaging 0.1 oz gold/ st was identified 

and was calculated using a 240 ft length, as 

assumed 120 ft width, a 2.3 ft average 

thickness, and a tonnage factor of 12 ft3/st. 

Four samples were collected. Three 

contained 0. 01 to 0.19 tr oz gold/st. 

Four contained 0,1 to 0.2 tr oz silver/at 

and as much as 1.18 percent base metal 

content. 

Four samples were collected. Three 

contained 0.04 to 0.22 tr oz gold/st and 

0.1 to 0.4 tr oz silver/st. Base metal 

content as much as 1. 45 percent. 

821 
822 

TABLE 1. Summary of mines and prospects in and adjacent to the Lower Burro Creek Wilderness Study Area-Continued 

Map No. 

(fig. 2) 

11 

12 

13 

14 

15 

Property 

name 

Golden Flow claims 

Golden Flow claims 

Unnamed 

Unnamed 

Jangretta and HMC claims 

Bentonia claim 

Summary 

Golden Flow claims are located on east 

boundary of study area in sec. 29, T. 14 

N., R. 10 W. Workings generally are 

located along sheared contacts between 

granite and diabase dikes. Some clay 

gouge and quartz veinlets are present 

along contact. Workings are clustered 

into two groups, a northern and southern. 

Northern group consists of two ad its, 

an inclined shaft, pits and trenches 

(Schreiner, 1985, fig. 7) along the 

granite-diabase contact zone, which 

strikes N. 5° w., dips 30° E., and 

averages I. 6 ft in thickness for a 

distance of 1,000 ft. 

Southern group of workings consists of an 

inclined shaft, an adit, and a series of 

pits and trenches (Schreiner, 1985, fig. 

8) along granite-diabase contact zone, 

which strikes N. 30° W., dips 40° NE., and 

averages 1. 2 ft in thickness over a 

distance of 1,450 ft. 

A trench is located on on fractures and a 

pit is located on a fault in granite. 

A flooded shaft, a 7-ft-long ad it, three 

pits, and a trench are located on a fault 

over a distance of 245 ft in granite. 

Fault zone consists of brecciated wallrock 

and clay gouge. A pit is present 

approximately 200 ft away on a fault 

containing quartz veinlets in granite. 

Deposits of bentonite, magnesite, and 

occurrences of agate are located in a 

section of slightly folded Tertiary 

tuffaceous lacustrine rocks along Burro 

Creek. Bentonite and magnesite have been 

mined on a small scale along east boundary 

of study area 

Deposits of bentonite in Tertiary 

lacustrine rocks near Haleys Wash 

Sample data 

Nine samples contained from 0.01 to 0. 75 

oz gold/st (Schreiner, 1985, table 1). 

Eleven samples taken along contact 

averaged 0. 20 oz gold/ st. Because of 

inadequate exposures, data were not 

sufficient for calculation of resources. 

Fourteen chip samples taken along contact 

contained 0. 03 to 0. 52 oz gold/ st and 

averaged 0.14 oz gold/st (Schreiner, 1985, 

table 1). Eight chip samples were taken 

along other faults and fractures in 

diabase and granite; three contained 0. 01, 

0. 03, and 0. 09 oz gold/st. A. select grab 

sample contained 0.36 oz gold/st. Data 

were not sufficient for resource 

calculation. 

Three samples were collected. One 

contained 0.01 tr oz gold/st. Two 

contained 0.2 and 0.3 tr oz gold/st. 

Eight samples were collected. Three of 

seven samples collected at the main 

prospect contained 0.01 tr oz gold/st. 

Two contained 0.1 tr oz gold/st. One 

contained 0,04 tr oz gold/st, two 

contained 0.1 tr oz silver/st. Base metal 

less than 0,1 percent, One sample 

contained 0.04 tr oz gold/st. 

Considering a 60 ft limit of overburden 

that could be stripped by open pit mining 

methods (Ted Eyde, oral commun., April 

1985), clay in this locality, having a 

minimum thickness of 5 ft, could be mined 

over an area 3,000 by 500 ft, estimated 

from outcrop locations and topo~raphy. 

Using a tonnage factor of 13 ft /st, an 

inferred resource of approximately 600,000 

st of clay was identified. An estimated 2 

million st of magnesite of various grades 

would be amenable ·to open pit mining 

methods, Calculations were made· assuming 

that magnesite is continuous over an area 

of 2,000 by 500 ft, averages 20 ft thick 

and has a tonnage factor of 10 ft3/st. 

GPO 785-048/77409 
Miller and others-MINERAL RESOURCES, LOWER BURRO CREEK WILDERNESS STUDY AREA, ARIZONA-U.~. Geological