Mineral Resources of the Million Hills 

Wilderness Study Area, Clark County, Nevada

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Chapter E

Mineral Resources of the

Million Hills Wilderness Study Area,

Clark County, Nevada

By JOEL R. BERGQUIST, GARY A. NOWLAN, and 

H. RICHARD BLANK, JR. 

U.S. Geological Survey

J. DOUGLAS CAUSEY 

U.S. Bureau of Mines

U.S. GEOLOGICAL SURVEY BULLETIN 1730

MINERAL RESOURCES OF WILDERNESS STUDY AREAS: 

SOUTHERN NEVADA
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, 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 : 1994

For sale by

U.S. Geological Survey, Map Distribution 

Box 25286, MS 306, Federal Center 

Denver, CO 80225

Library of Congress Cataloging-in-Publication Data

Mineral resources of the Million Hills Wilderness Study Area, Clark County, 

Nevada /by Joel R. Bergquist... [ et al.]

p. cm. (Mineral resources of wilderness study areas southern 

Nevada ; ch. E) (U.S. Geological Survey bulletin ; 1730-E) 

Includes bibliographical references. 

Supt. of Docs, no.: I 19.3:1730

1. Mines and mineral resources Nevada Million Hills Wilderness. 

2. Million Hills Wilderness (Nev.) I. Bergquist, Joel R. II. Series. III. Series: 

U.S. Geological Survey bulletin ; 1730-E. 

QE75.B9 no. 1730-E 

[TN24.N3] 

557.3 s dc20

[553'.09793'13] 94-12114

CIP
STUDIES RELATED TO WILDERNESS

Bureau of Land Management Wilderness Study Areas

The Federal Land Policy and Management Act (Public Law 94-579, October 21, 1976) 

requires the U.S. Geological Survey and the U.S. Bureau of Mines to conduct mineral surveys 

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 the Million Hills (NV-050-233) Wilderness Study 

Area, Clark County, Nevada.

CONTENTS

Summary El

Abstract El

Character and setting El

Identified resources El

Mineral resource potential E2 

Introduction E4

Location and physiography E4

Previous and present investigations E4

Acknowledgments E5 

Appraisal of identified resources E5

Mining history E5

Mines and prospects E5 

Assessment of resource potential E7

Geology E7

Stratigraphy E8

Geochemical studies E10

Geophysical studies E14

Mineral and energy resource potential E17 

References cited E19 

Appendixes E23

Definition of levels of mineral resource potential and certainty of 

assessment E24

Resource/reserve classification E25

Geologic time chart E26

FIGURES

1. Index map showing location and relations of principal geographic features in and 

near Million Hills Wilderness Study Area, Clark County, Nevada E2

2. Map showing mineral resource potential and generalized geology of Million Hills 

Wilderness Study Area, Clark County, Nevada E3

3. Map showing elements present in anomalous concentrations in samples collected 

from drainage basins in and near Million Hills Wilderness Study Area, Clark 

County, Nevada Ell

4. Residual total-intensity aeromagnetic map of Million Hills Wilderness Study Area 

and vicinity, Clark County, Nevada, and Mohave County, Arizona E16

5. Complete Bouguer gravity anomaly map of Million Hills Wilderness Study Area 

and vicinity, Clark County, Nevada, and Mohave County, Arizona E17

TABLES

1. Mines and prospects in and near Million Hills Wilderness Study Area, Clark 

County, Nevada E6

2. Resource classification of properties and commodities evaluated in Million Hills 

Wilderness Study Area, Clark County, Nevada E7

3. Statistics for selected elements in drainage samples collected in and near Million 

Hills Wilderness Study Area, Clark County, Nevada E13

4. Average of median concentrations of selected elements in bedrock E14

5. Correlation coefficients for analytical data from minus-80-mesh stream-sediment 

samples collected in and near Million Hills Wilderness Study Area, Clark County, 

Nevada E15

Contents

Mineral Resources of the

Million Hills Wilderness Study Area,

Clark County, Nevada

By Joel R. Bergquist, Gary A. Nowlan, anc/H. Richard Blank, Jr. 

U.S. Geological Survey

J. Douglas Causey 

U.S. Bureau of Mines

SUMMARY

Abstract

At the request of the U.S. Bureau of Land Management, 9,599 acres of the Million Hills Wilderness Study 

Area (NV-050-233) in Clark County, southern Nevada, 

were evaluated for identified mineral resources (known) 

and mineral resource potential (undiscovered). Throughout 

this report, "wilderness study area" and "study area" refer 

to those acres for which a mineral survey was requested. 

Fieldwork for this report was carried out in 1987 and 1988.

The study area is at the east edge of the Gold Butte 

mining district. The Quartz claim, in the northwestern part 

of the study area, has inferred subeconomic resources of 

copper, lead, zinc, cobalt, gold, and silver. The Azure Ridge 

mine, located on the northwest boundary of the study area, 

contains inferred subeconomic resources of copper, lead, 

zinc, and lesser amounts of cobalt, gold, silver, gallium, 

and germanium. The study area includes occurrences of 

carbonate rocks, and sand and gravel.

A large part of the study area has high potential for 

undiscovered copper, lead, zinc, cobalt, gold, silver, gallium, and germanium. Most of the study area has low potential for oil and gas. There is no potential for geothermal 

resources.

Character and Setting

The Million Hills Wilderness Study Area is located in 

the eastern Basin and Range physiographic province in

Manuscript approved for publication April 1,1994.

southern Nevada about 60 mi east of Las Vegas (fig. 1). The 

eastern boundary of the study area is the Arizona-Nevada 

bonier, and Lake Mead is about 1.5 mi south of the south 

boundary of the study area. The terrain is characterized by 

rugged hills etched by deeply incised stream drainages. The 

western parts of the hills are in many places faulted and 

eroded to cliffs and ledges. Bedrock in the study area mostly 

consists of layers of Paleozoic (see "Appendixes" for geologic time chart) sedimentary rocks that have been faulted 

and steeply tilted toward the east. The sedimentary rocks 

consist of limestone, dolomite, sandstone, quartzite, and 

shale. Underlying the sedimentary rocks are Precambrian 

gneiss and schist. About 40 percent of the study area is 

covered by alluvium and colluvium. The region has been 

broken by a succession of arcuate faults; the Gold Butte 

fault, a major northeast trending structure, crosses the northern part of the study area.

Identified Resources

Inferred subeconomic resources (see "Appendixes" 

for resource/reserve classification) of copper, lead, zinc, 

cobalt, gold, silver, gallium, and germanium are present in 

the study area. The Quartz claim is in the northern part of 

the study area and has inferred subeconomic resources of 

copper, lead, zinc, cobalt, gold, and silver. The nearby 

Azure Ridge mine, on the northwest boundary of the study 

area, produced minor amounts of copper and zinc in the 

early 1900's and contains inferred subeconomic resources 

of copper, lead, zinc, cobalt, gold, silver, gallium, and germanium along a north-trending fault. The Esperanta group 

of claims, which includes the Azure Ridge mine (formerly 

named Bonelli mine), was actively maintained in 1987.

Carbonate rocks, which in other areas may constitute 

a resource, are here classified as only occurrences. The

Mineral Resources of the Million Hills Wilderness Study Area, Clark County, Nevada El
carbonate strata in the study area are thin bedded, cherty, 

dolomitized, and contain interbeds of sandstone and shale, 

all of which militate against the usefulness of the carbonate rocks for industrial purposes. The sand and gravel in 

the area are also classified as only an occurrence because 

of a near-surface layer of caliche (undesirable in commercial sources) and the distance to current markets. No 

anomalous radioactivity was measured during field studies. 

There were six oil and gas leases as of 1988 in or near 

the study area, although there has been no production from 

these leased areas or from the vicinity of the study area.

Mineral Resource Potential

A large part of the Million Hills Wilderness Study 

Area has high resource potential for copper, lead, zinc, co115°00'

bait, gold, silver, germanium, and gallium in Kipushi-type 

deposits (see fig. 2 for specific location of area). There is 

low resource potential for oil and gas, and no potential for 

geothermal energy in the study area.

Analyses of the stream-sediment samples taken for 

this study revealed strong correlations among the elements 

and provide evidence of carbonate-hosted Kipushi-type 

copper-lead-zinc mineralization. The geochemical signature for Kipushi-type mineralization is a suite of elements 

that consists of copper, lead, zinc, arsenic, cobalt, silver, 

germanium, gallium, molybdenum, tungsten, tin, bismuth, 

uranium, and vanadium (Cox and Bernstein, 1986). The 

geochemical data obtained from sampling the study area 

fit this model quite well. The Apex mine about 50 mi 

northeast of the study area is the nearest known Kipushitype deposit. The Apex mine produced copper, lead, zinc,

114°30' 114°00'

APPROXIMATE BOUNDARY

OF

MILLION HILLS

WILDERNESS STUDY AREA

(NV-050-233)

Figure 1. Index map showing location of principal geographic features near Million Hills Wilderness Study Area, 

Clark County, Nevada.

E2 Mineral Resources of Wilderness Study Areas: Southern Nevada
gold, and silver in the period 1884-1962. The mine was 

closed for a period, then reopened in 1985 for production 

of germanium and gallium (Bernstein, 1986). The Callville

114°05'

36° 

20'

36° 

15'

I

APPROXIMATE BOUNDARY

OF

MILLION HILLS 

WILDERNESS STUDY AREA

(NV-050-233)

Azure Ridge 

mine

H/C Cu, Pb, Zn,

Co, Au, Ag, Ga,

Ge [1,2]

Mrs

X I/

Unnamed 

claim

Limestone hosts the Apex deposit and is also one of the 

bedrock units in the study area. On the basis of (1) the 

Kipushi-type geochemical signature found for this study,

EXPLANATION

| Area having high mineral resource potential (H) 

| Area having low energy resource potential (L)

Levels of certainty of assessment

B Data only suggest the level of mineral resource

potential 

C Data give good indication of the level of mineral

resource potential

Commodities

Ag Silver

Au Gold

Co Cobalt

Cu Copper

Ga Gallium

Ge Germanium

Pb Lead

Zn Zinc

O,G Oil and gas

[ ] Deposit types

1 Kipushi-type copper-lead-zinc

2 Mississippi Valley-type lead-zinc

Geologic map units

Qal Alluvium (Quaternary) Unconsolidated gravel, 

sand, and silt

TV Volcanic rocks (Tertiary) Olivine basalt

Tmc Muddy Creek Formation (Tertiary) Weakly 

indurated gravel, sand, and silt

Pkt Kaibab and Toroweap Formations, undivided

(Permian) Limestone and dolomitic limestone; 

shale, sandstone, and gypsum

Prb Red beds (Permian) Sandstone and shale

PMc Callville Limestone (Permian, Pennsylvanian, and 

Mississippian) Sandy, silty limestone, 

dolomitic limestone, dolomite, shale, and 

siltstone

Mrs Rogers Spring Limestone

(Mississippian) Limestone and dolomitic 

limestone

Dmp Muddy Peak Limestone (Devonian) Limestone 

and dolomitic limestone

Cld Limestone and dolomite (Cambrian)

Cu Quartzite, shale, sandstone, and limestone 

(Cambrian)

pCgs Gneiss and schist (Precambrian)

Contact Dashed where approximately located

Fault, showing dip Dashed where approximately 

located; dotted where concealed

Strike and dip of beds

60

.50

Figure 2. Mineral resource potential and generalized geology of Million Hills Wilderness Study Area, Clark County, Nevada. 

Geology modified from Longwell and others (1965). Arrows along fault show relative direction of movement.

Mineral Resources of the Million Hills Wilderness Study Area, Clark County, Nevada E3
(2) the mineralogy of the mine and claims examined by 

the Bureau of Mines, (3) the proximity and setting of the 

Apex mine, and (4) the similarity of geology at the Apex 

mine and the study area, the Million Hills Wilderness 

Study Area has high resource potential for copper, lead, 

zinc, gold, silver, cobalt, germanium, and gallium.

Most of the study area was determined to have a low 

resource potential for oil and gas by Sandberg (1983a, b). 

This determination was made on the basis of possible 

source rocks and reservoir rocks in the study area and the 

presence of favorable areas to the north and west. Part of 

one oil and gas lease covers about 340 acres in the study 

area, and contiguous lands are covered by additional oil 

and gas leases (Bureau of Land Management, 1988).

The study area is in an area of relatively low heat 

flow, and there are no known warm or hot springs in the 

region surrounding the study area (Muffler, 1979). The 

study area has no potential for geothermal resources.

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). Studies by the U.S. Geological Survey 

are designed to provide a reasonable 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.

Location and Physiography

The Million Hills Wilderness Study Area consists of 

9,599 acres in Clark County, southern Nevada, along the 

Arizona border about 2 mi north of Lake Mead. The regional setting is the eastern margin of the Basin and

Range physiographic province that is characterized by 

elongate, north-trending, fault-bounded ranges separated 

by wide alluviated valleys. The Grand Wash Cliffs, about 

12 mi east of the study area, are considered to be the 

boundary between this province and the Colorado Plateau 

physiographic province. The study area is located along 

the northern part of Azure Ridge, a 12-mi-long, north- to 

northeast-trending ridge. Azure Ridge and two other ridges 

to the northwest, Tramp Ridge and Lime Ridge, are geologically and structurally similar. The Lime Canyon Wilderness Study Area (NV-050-231) includes most of Lime 

Ridge, about 10 mi west of this study area.

The study area is about 16 mi from north to south, 

and ranges in width from about 0.5 mi at the north end to 

5 mi wide on the south boundary. Most of the study area 

is along the rugged bedrock of Azure Ridge, but alluvial 

aprons cover areas of gentler topography along the eastern 

margin and northern parts. Elevations range from about 

3,946 to 1,770 ft. The topography of most of the area is 

exceedingly rugged, with cliffs, ledges, deeply incised 

stream drainages, and broken blocks. The carbonate rocks 

have developed rough weathering surfaces typical of these 

kinds of rock in desert climate. Flora in the area include 

cacti, grasses, yucca, and sagebrush.

Access to the northern and western parts of the study 

area is by dirt road from the north. A road to the Azure 

mine is the only one that enters the study area; and there is 

no road access to the eastern or southern parts of the area.

Previous and Present Investigations

One of the earliest studies of the geology and mineral 

resources of the area is by Longwell (1928). His 1:250,000- 

scale map shows Azure Ridge in a generalized way. Other 

studies of the geology and resources are by the Intermountain Association of Petroleum Geologists (1952) (map scale 

1:380,365); Bowyer and others (1958) (map scale 1:200,000); 

Longwell and others (1965) (geologic map scale 1:250,000); 

Morgan (1968) (map scale 1:31,680), Ledbetter (1970) (no 

map), and Bohannon (1978) (map scale 1:250,000). Volborth 

(1962) studied the Precambrian rocks west of the study area 

and those rocks were dated by Wasserburg and Lanphere 

(1965). Paleozoic stratigraphy of the region is discussed in 

McNair (1951). Tertiary rocks in the region were studied by 

Anderson and others (1972), Brenner and Glanzman (1979), 

and Bohannon (1984). Studies of tectonics and structure in 

the region were done by Anderson (1973), Longwell (1974), 

Bohannon (1979), and Wernicke and others (1982).

Brief discussions of the Gold Butte mining district, 

which includes Azure Ridge, are found in Lincoln (1923), 

Hill (1916), Hewett and others (1936), and Couch and 

Carpenter (1943). Reports on exploration and development 

in the district are given in Yale (1906, 1907, 1908), NarE4 Mineral Resources of Wilderness Study Areas: Southern Nevada
amore and Yale (1909), and Naramore (1911). Production 

of gold from the district is discussed by Heikes (1913, 

1914, 1916, 1917, 1919, 1921a, b), but there is no mention 

of production from the Azure Ridge mine in these reports. 

Production from the mine is reported for the year 1918 by 

Vanderburg (1937, p. 36). Causey (1988) reported on the 

mineral resources of the Million Hills Wilderness Study 

Area.

Results of a sampling program which the Nevada Bureau of Mines and Geology did for the Bureau of Land 

Management were reported by Smith and Tingley (1983a, 

b). Descriptions of wilderness study areas that include geology and mineral resources are given in a publication of 

the Bureau of Land Management (1988). Evaluations of 

the potential for oil and gas in wilderness lands were prepared by Sandberg (1983a, b).

The U.S. Geological Survey visited the study area in 

the 1986 and 1987 field seasons. Fieldwork included geochemical sampling and checking of existing geologic 

maps. Geophysical data covering the area were obtained 

and interpreted. Geochemical samples of stream sediments 

and panned concentrates were taken from the study area 

and analyzed in U.S. Geological Survey laboratories. The 

analytical results are reported in McHugh and Nowlan 

(1989) and McHugh and others (1989).

The mineral investigation of the study area by the 

U.S. Bureau of Mines included collection of information 

related to current and past mining activity. A library search 

was made for information on mines and prospects located 

in and near the study area. This search included checking 

U.S. Bureau of Land Management mining claim recordation indices, Clark County, Nevada, mining claim records, 

and the U.S. Bureau of Mines Mineral Industry Location 

System (MILS). U.S. Bureau of Land Management land 

status and land use records, and U.S. Bureau of Mines 

files were also examined.

The U.S. Bureau of Mines field investigation was 

conducted during March 1987. Active claims in the study 

area were examined, and 48 rock samples were collected 

within and around the claims for geochemical analysis. 

The methods and results of the U.S. Bureau of Mines mineral investigation of the study area were reported by Causey (1988). An investigation of the Quartz claim was done 

by Moyle and Buehler (1990) as a follow up to the work 

by Causey (1988). Additional information is available 

from the U.S. Bureau of Mines, Western Field Operations 

Center, E. 360 Third Ave., Spokane, WA 99202.

Acknowledgments

The authors would like to thank Brent Turrin of the 

U.S. Geological Survey and John Benham and Bill Hale 

of the U.S. Bureau of Mines Western Field Operations 

Center for their assistance in the field.

APPRAISAL OF IDENTIFIED RESOURCES

By}. Douglas Causey 

U.S. Bureau of Mines

Mining History

The study area is on the east edge of the Gold Butte 

mining district south of the Virgin Mountains. Longwell 

and others (1965) described the boundaries of this district 

as bounded on the west and south by Lake Mead, on the 

east by the Colorado River and state boundary, and on the 

north by an east-west line approximately 6 mi north of the 

study area.

Mining activity in the district began in 1873 with the 

discovery of mica. Over 6 short tons of sheet mica (muscovite) were produced before 1900. More recent industrial 

mineral interest has centered on a vermiculite occurrence. 

These minerals are in granitic rocks, which are only exposed west of the study area.

In 1905, gold was discovered in metamorphic and granitic rocks west of the study area. In 1907, argentiferous 

copper and zinc ores were discovered in Paleozoic limestone 

and a limited amount of mining occurred at three mines in the 

district. Total production of gold, silver, copper, and zinc ore 

from the three mines, one of which is in the study area, was 

less than $100,000 (Longwell and others, 1965, p. 126-128).

The Azure Ridge mine was active in 1918; two carloads of hand-sorted zinc ore averaging 40 percent zinc and 

one carload of copper ore averaging 35 percent copper were 

shipped from the mine (Vanderburg, 1937, p. 36). The property is now covered by the Esperanta claims (nos. 1^4), 

which were located November 17, 1934 and are owned by 

Laura Gentry, according to 1987 claim records. No information was found concerning two other claims examined.

Mines and Prospects

Three mineral properties were evaluated in this study 

(table 1). Results of sampling and mapping of the properties, two of which are in the study area and one just outside, 

were reported in Causey (1988). Additional information on 

the Quartz claim, and the Azure Ridge mine including the 

somewhat larger area of the Esperanta claims (nos. 1-4) is 

given in Moyle and Buehler (1990) and in unpublished files 

at the U.S. Bureau of Mines, Western Field Operations 

Center, E. 360 Third Ave., Spokane, WA 99202. Resource 

classifications for all properties and commodities evaluated 

are listed in table 2.

The Azure Ridge mine and an associated group of 

workings, located at the northwest edge of the study area, 

extend south about 1 mi. There are indications of high-grade 

copper-lead-zinc mineralization along Azure Ridge on the 

Esperanta claims (nos. 1-4). Gold, silver, cobalt, gallium,

Mineral Resources of the Million Hills Wilderness Study Area, Clark County, Nevada E5
8

i.

73

Table 1. Mines and prospects in and near Million Hills Wilderness Study Area, Clark County, Nevada 

[pet, percent; ppm, parts per million; cps, counts per second]

Name Description Workings and production Sample 

3 

P*

I?

i

Quartz claim

Azure Ridge mine 

(Bonelli mine, Esperanta 

claims nos. 1-4).

*Unnamed prospect

Alluvium-covered area containing aragonite, 

travertine, and sinter with manganese 

coatings. The manganese-rich crust and veins 

contain high concentrations of cobalt, 

nickel, lead, zinc, barium, and copper. Small 

outcrops of carbonate rock exposed locally.

Cambrian(?) gray dolomite hosts deposit. 

Mineralized rock occurs along bedding-plane 

faults. Ore minerals are mainly base-metal 

carbonates such as malachite, smithsonite, 

and aurichalcite. Cerussite may also be 

present. Mine is near and south of Gold Butte 

fault.

Precambrian locally schistose gneiss, mostly 

granitic with some garnets. Scintillometer 

readings of 75 to 120 cps were obtained.

Two small prospect pits and a 100- 

ft-long trench. No production.

Five adits (180+ ft, 60+ ft, 97 ft, 25 

ft, and 15 ft); one shaft, 11 ft deep; 

two open cuts; and 10 pits. 

Production of two carloads 

averaging 40 pet zinc, and one 

carload averaging 35 pet copper in 

1918 (Vanderburg, 1937, p. 36).

Bulldozed road and a stone 

monument. No production.

Four samples taken. Mangan

9.07 pet manganese, 6,096 p

ppm barium, 107 ppm moly

ppm lead, 80 ppm thallium, a

limited exposure, no resource

elemental and geologic assoc

Kipushi- or Mississippi Vall

as having inferred subeconom

and cobalt.

Forty-three samples taken. S

8.99 pet copper, 33.0 pet lea

3,300 ppm gold, and 142 ppm 

ppm gallium. Mineralized ro

about 5,000 ft long by 1,100 

ft in outcrop. There is an inf

lead- zinc- cobalt- gold- silv

material. The occurrence of 

bodies makes it unrealistic to 

basis of limited sampling.

One sample taken. No econ

detected. There is less than 

thorium in the sample. There 

property.

Outside study area.
Table 2. Resource classification of properties and commodities evaluated in Million Hills Wilderness Study Area, Clark County, Nevada

Property name

Quartz claim

Azure Ridge mine (Bonelli 

mine, Esperanta claims nos. 

1-4).

Unnamed prospect

Alluvial deposits

Carbonate deposits*

Resource 

classification

Inferred subeconomic

resources.

Inferred subeconomic 

resources.

Occurrence

Occurrence

Commodities

Copper, lead, zinc, cobalt.

Copper, lead, zinc, cobalt, gold, silver, 

gallium, germanium.

None.

Sand, gravel.

Limestone, dolomite.

See figure 2 for formations containing these rock and mineral types.

and germanium1 are minor constituents. Mining would 

require underground methods because mineralized rock is in 

a narrow, steeply dipping fault. Because of the podlike nature of the mineralized structure and the lack of data regarding the frequency, size, and distribution of the pods, 

resources were not quantified. However, the mineralized 

rock crops out sporadically over an area about 5,000 ft long 

and as much as 9 ft thick. Within this area there may be other 

high-grade pods. The Esperanta claims were determined to 

contain inferred subeconomic resources of copper, lead, 

zinc, cobalt, gold, silver, gallium, and germanium. The high 

grade reported by Vanderburg (1937, p. 36) is probably not 

continuous along the fault because these analyses were from 

material that was hand sorted from selected mining areas.

Because of limited exposures, no resources could be 

quantified on the Quartz claim. The prospect on the Quartz 

claim probably is about 0.5 mi south of the Gold Butte fault 

(Moyle and Buehler, 1990). The geologic association of 

faults, impure limestone and dolomite, aragonite, travertine, 

and sinter with manganese-rich encrustations, which contain 

unusually high concentrations of cobalt, nickel, lead, zinc, 

barium, molybdenum, thallium, and copper and average to 

low concentrations of gallium and germanium, suggests a 

Mississippi Valley-type lead-zinc deposit or a Kipushi-type 

copper-lead-zinc deposit. Whereas the Azure Ridge mine 

does not have concentrations of cobalt and nickel as high as 

those found on the Quartz claim, many of the high-grade 

samples from the Azure Ridge mine are enriched in most of 

the same elements. This correlation indicates a deposit similar to that at the Azure Ridge mine. The Quartz claim is

'Unpublished analyses of samples from the Azure Ridge mine and 

the Esperanta claims (nos. 1-4) showed concentrations of 4, 6, 25, 120, 

145, and 150 parts per million germanium; and 5, 8, 25, 26, 63, 65, and 

75 parts per million gallium.

2Unpublished analyses of samples from the Quartz claim showed 

three samples with concentrations of <1 part per million and one sample 

with 1 part per million germanium and 2, 2, 3, and 11 parts per million 

gallium.

determined to contain inferred subeconomic resources of 

copper, lead, zinc, cobalt, gold, and silver. No large leadzinc mines have been discovered in the region; however, 

exploration apparently has been limited to digging on surface exposures and little geophysical work and drilling have 

been done. Also, gold and silver seem to have drawn more 

of the mineral industry's attention and exploration money.

Cobalt is of particular interest because it is a strategic 

mineral and is not being produced in the United States. One 

of the last U.S. producers was a lead mine in Missouri 

where cobalt was recovered as a byproduct. Only in the 

Blackbird mining district of Idaho is cobalt a primary commodity the grade there averages 0.6 percent (Kirk, 1985, 

p. 3). All of the United States' cobalt resources (1.4 million 

short tons) are considered subeconomic at $13.00/lb (Engineering and Mining Journal, 1993).

Indications of other mineral resources were not found 

in the study area. Sand and gravel, while widespread, are 

partly cemented with caliche, which lowers the commercial 

value. The study area is also remote from population centers and major transportation systems. The sand and gravel 

are not currently needed for construction, and they have no 

qualities that would make them valuable for any other purpose. There is no indication of uranium or thorium in the 

vicinity. There are no known oil or gas shows, but exploration has been too limited to draw any conclusions at this 

time. As of 1987, there was limited oil and gas leasing 

interest, mostly in the north half of the study area.

ASSESSMENT OF RESOURCE POTENTIAL

By Joel R. Bergquist, Gary A. Nowlan, and 

H. Richard Blank, Jr. 

US. Geological Survey

Geology

The study area is located north of Lake Mead along 

the Arizona border and includes the eastern half of Azure

Mineral Resources of the Million Hills Wilderness Study Area, Clark County, Nevada E7
Ridge. Azure Ridge is separated from geologically and 

structurally similar Tramp Ridge and Lime Ridge to the 

northwest by an alluviated valley. The study area is in the 

eastern margin of the Basin and Range physiographic and 

structural province. The Grand Wash Cliffs, about 12 mi 

to the east, mark the boundary with the Colorado Plateau 

physiographic province. Azure Ridge, Tramp Ridge, and 

Lime Ridge are all predominantly composed of Paleozoic 

sedimentary rocks. The area immediately west and southwest of Azure Ridge is a highland composed almost wholly of Precambrian granite, gneiss, and schist that has been 

deeply dissected. The Paleozoic rocks of Azure Ridge rest 

unconformably on these Precambrian crystalline rocks. 

Jumbo Peak, approximately 5 mi southwest of the study 

area, is composed mainly of Precambrian granite and is 

the highest point in the area with an elevation of 5,763 ft.

Azure Ridge comprises most of the Million Hills Wilderness Study Area and is not a single ridge, but rather a 3- 

mi-wide series of roughly linear, north-trending ridges and 

valleys. These ridges were formed by the uplift, faulting, 

and erosion of the now steeply east-dipping strata. The dips 

of these beds generally range from about 50° to 60° E. The 

ridges reflect the eastward tilting along northeast trending 

faults that have caused repetition of the stratigraphic section in adjacent ridges. Excellent exposures of the strata 

occur along the fault-bounded west sides of the ridges.

Structurally, Azure Ridge is a fault block that has 

been tilted eastward. The ridge is broken by two sets of 

faults: one that trends northeast and a second that trends 

roughly east-west. The Paleozoic section of sedimentary 

rocks is partly in depositional contact and partly in fault 

contact with the underlying Precambrian crystalline rocks 

along the west side of the ridge. The Paleozoic rocks of 

the study area are broken by both normal and beddingplane faults, which partly control the topography and also 

provide pathways for mineralizing fluids. The northern 

part of Azure Ridge is truncated by the northeast-trending 

Gold Butte fault, which is a major structural feature of the 

region. Tramp Ridge and Azure Ridge are lithologically 

and structurally similar, though separated by a distance of 

about 7 mi along the Gold Butte fault. This similarity led 

Longwell and others (1965) to conclude that Tramp Ridge 

and Azure Ridge were previously continuous but were 

separated by a large component of left-lateral strike-slip 

movement along the Gold Butte fault.

Stratigraphy

A Precambrian metamorphic suite of gneiss and schist 

(p gs) forms the basement rocks of the study area and is 

exposed only in the western part of the study area. The 

gneiss and schist are the oldest rocks in the region and 

underlie the Paleozoic strata. This suite comprises quartzmica schist, chlorite schist, amphibolite, and banded gneiss. 

In places, interbedded mica schists and quartzose gneisses 

suggest that they are metamorphosed interbeds of sandstone 

and shale (Longwell and others, 1965). The metamorphic 

rocks are locally strongly deformed by folding and shearing 

that suggest deformation occurred at great depths and pressures. The metamorphic suite was intruded by Precambrian 

granite (not exposed in the study area) and associated dikes 

and stringers, which pervade the metamorphic rocks.

Unconformably overlying the Precambrian basement 

rock is a sequence of Paleozoic stratified sedimentary 

rocks. Many of the Paleozoic rocks in the study area are 

lateral equivalents of strata exposed in the Grand Canyon.

The lowermost Paleozoic unit in the study area ( u) 

comprises undivided Cambrian quartzite, shale, sandstone, 

and limestone. In the Virgin Mountains, laterally equivalent strata consist of the (ascending) Prospect Mountain 

Quartzite, Pioche Shale, Lyndon Limestone, and the Chisholm Shale, all of McNair (1951) (McNair, 1951; Longwell and others (1965). The base of the section, there, is 

the Prospect Mountain Quartzite, which consists of quartzite and sandstone that are light gray to reddish gray, thin 

to thick bedded, locally pebbly, and locally crossbedded 

(McNair, 1951). The Pioche Shale is olive-green or gray 

shale with thin interbeds of sandstone and fossiliferous 

limestone (McNair, 1951). The Lyndon Limestone is a 

gray-weathering, massive bedded, fine- to medium-grained 

limestone that locally has shaly limestone mottling (McNair, 1951). The Chisholm Shale is green to brown, fissile 

to thin-bedded shale that grades upward into a coarsegrained, mottled limestone lying at the base of the Peasley 

Limestone of McNair (1951) (McNair, 1951; Longwell 

and others, 1965).

In the study area, the Cambrian limestone and dolomite, of unit ld, which overlies unit Cu, includes in ascending order, the strata laterally equivalent to Peasley 

Limestone and an unnamed unit composed of limestone and 

dolomitic limestone in the Virgin Mountains. The Peasley 

Limestone there consists of limestone, dolomitic limestone, 

and interbeds of shale. These limestones and dolomitic 

limestones are typically dark gray, brown weathering to 

light gray, fine grained, thin to medium bedded, and mottled 

tan to yellowish-brown (McNair, 1951). The overlying unnamed unit consists of limestone and dolomitic limestone 

that is brown, tan, or gray on fresh and weathered surfaces, 

thin to thick bedded and contains thin beds of oolitic limestone, intraformational conglomerate, and shaly limestone 

(McNair, 1951).

The Devonian Muddy Peak Limestone (Dmp) overlies the Cambrian limestone and dolomite ( ld) in the 

study area and consists of limestone and dolomitic limestone that is light to dark gray or tan to brown, fine to very 

coarse grained, thin to thick bedded or massive, and typically weathering to tan and gray (McNair, 1951). Some of

E8 Mineral Resources of Wilderness Study Areas: Southern Nevada
its beds contain fossils, ripple marks, and sandy horizons. 

The fossil gastropods, brachiopods, Stromatopora, horn 

corals, and fish fragments that occur sparingly in the fossiliferous beds indicate that the rocks are Late Devonian in 

age(McNair, 1951).

The contact between the Mississippian Rogers Spring 

Limestone (Mrs) and the underlying Devonian Muddy Peak 

Limestone in the study area is marked by an erosional unconformity and by a change in the weathering colors of the rocks 

at the contact from brown gray to light gray (McNair, 1951). 

The Rogers Spring Limestone consists of limestone and 

dolomitic limestone that is whitish to dark gray, light to dark 

gray weathering, very fine to coarse grained, and medium to 

thick or massive bedded. Some beds are fossiliferous with 

crinoids, horn corals, brachiopods, gastropods, and Syringopora; and some contain nodules or bands of brown-weathering chert (McNair, 1951).

In the Muddy Mountains, strata laterally equivalent to 

those present in the study area that make up the interval 

between the Mississippian Rogers Spring Limestone and 

the Permian redbeds (unit Prb, discussed below) were 

originally assigned by Long well (1921) to the Callville 

Limestone. Subsequent workers have subdivided the strata 

that constitute Longwell's Callville Limestone into three 

separate formations. Ledbetter (1970), using the terminology of Bissell (1962), mapped and described the Illipah 

Formation below the Callville Limestone as described by 

Welsh (1959) at Azure Ridge. McNair (1951) referred to 

the rocks of the upper part of Longwell's Callville Limestone as the Pakoon Limestone in the Virgin Mountains 

and elsewhere on the basis of their contained Permian fossil fusulinids but not on the basis of lithologies of these 

two units, which are similar. In this part of Arizona, no 

physical boundary has been observed between the Pennsylvanian and Permian beds (Longwell and others, 1965). 

Ledbetter (1970) described the Pakoon Formation of McNair (1951) in the Azure Ridge area. Longwell and others 

(1965) reported that on the basis of a reexamination of 

fusulinids in the section, the lowermost part of the section 

(that is, the rocks which make up the Illipah Formation) 

may actually be Late Mississippian and Early Pennsylvanian in age. The Callville Limestone (PMc) in the study 

area, therefore, consists of (1) the undivided Mississippian 

and Pennsylvanian Illipah Formation of Bissell (1962) and 

Ledbetter (1970), (2) strata laterally equivalent to the 

Pennsylvanian Callville Limestone of McNair (1951), and 

(3) the Permian Pakoon Formation of McNair (1951). 

Herein the rocks of this section at Azure Ridge are called 

the Mississippian to Permian Callville Limestone as used 

by Longwell and others (1965), which follows the original 

definition of the Callville by Longwell (1921).

The Callville Limestone as mapped in the area of this 

report consists of three parts. The lowermost is a 15-ft-thick 

Mississippian and Pennsylvanian section consisting of carbonaceous shale, siltstone, and sandy limestone that constitutes the Illipah Formation of Bissell (1962) and Ledbetter 

(1970). The middle part (wholly Pennsylvanian) of the 

Callville lying above the basal part of the formation consists 

of basal limestones and dolomitic limestones that are typically thick bedded, cliff forming, and oolitic. These rocks 

are generally fine grained but range to coarse grained. They 

are mostly gray where fresh and tan to gray where weathered. There are a few scattered, thin bands of red chert near 

the top of the middle unit of the Callville at Azure Ridge. 

Fossil gastropods occur in the middle part of the sequence 

that consists wholly of Pennsylvanian limestones. The uppermost (Permian) part of the Callville as mapped in this 

report, the Pakoon Formation of McNair (1951), typically is 

silty and, in many places, crossbedded limestone that 

weathers to subdued slopes. The Permian rocks in the 

Callville consist of limestone, dolomitic limestone, and pure 

dolomite all of which are fine grained, gray or tan, fossiliferous, and brown, tan, or pink weathering. Some of the 

Permian strata contain oolites or thin chert beds. The Permian fossils found in these rocks consist mostly of horn 

corals, brachiopods, and fusulinids.

Lying above the Callville Limestone in the study area 

is a sequence of interbedded sandstone and redbeds, here 

termed the redbeds unit (Prb). The contact of this unit with 

the underlying limestones of the Callville is sharp and lithologically distinct. The basal bed of this unit is a sandstone 

whose lateral equivalent in the Virgin Mountains 25 mi 

north of the study area and elsewhere was termed the 

Queantoweap Sandstone by McNair (1951). Ledbetter 

(1970) recognized the Queantoweap at Azure Ridge. The 

sandstone in the study area is pinkish gray, calcareous, 

crossbedded and ledge forming. The Queantoweap is overlain by redbeds, which consist of interbedded reddish sandy 

shale and reddish fine-grained sandstone.

The stratigraphically highest Paleozoic units mapped 

at Azure Ridge are the undivided Permian Kaibab and 

Toroweap Formations (Pkt). The Kaibab is the youngest 

Paleozoic formation in the region. The two units are lithologically similar, although the Kaibab tends to form steeper cliffs than the Toroweap. There is a gypsum bed at the 

top of the Toroweap that marks the boundary between the 

two formations (Longwell and others, 1965).

The Toroweap Formation consists of a basal gypsum 

member, a middle limestone member, and an upper gypsum 

member (Longwell and others, 1965). The gypsum members are generally gray to white or pinkish, slope forming, 

and interbedded with a few thin beds of limestone. The 

upper gypsum member also locally contains some solution 

breccia (Longwell and others, 1965). The middle limestone 

member of the Toroweap consists of limestone and dolomitic limestone that is typically gray to dark gray, fine to 

medium grained, thin to thick bedded, cliff forming, and 

fossiliferous with crinoids and brachiopods (Longwell and 

others, 1965). The limestone of the middle member also 

contains thin bands, lenses, and nodules of chert that in

Mineral Resources of the Million Hills Wilderness Study Area, Clark County, Nevada E9
some beds constitute as much as half the rock. The chert is 

typically gray to pinkish gray on fresh surfaces and weathers brown, giving the rocks a dark color.

The Kaibab Formation consists of limestone and dolomitic limestone, with a solution-collapse breccia at the 

base of the formation. Above the basal part of the unit are 

beds of limestone that are typically, gray, fine to medium 

grained, weathering tan to pinkish gray, and cliff forming. 

Most parts of the formation contain beds, bands, and nodules of chert.

Tertiary sedimentary and volcanic units are exposed 

along the eastern edge of the study area. These are separated from the Paleozoic rocks of Azure Ridge by wide 

expanses of alluvium. The lowermost Tertiary unit is the 

Muddy Creek Formation (Tmc), exposed beneath volcanic 

flow rocks at the north end of the study area. The age of 

the Muddy Creek is constrained by the age of the overlying basalt, which has been radiometrically dated at approximately 2.5 Ma or million years ago (Luedke and 

Smith, 1981). The formation consists of fluvial and lacustrine deposits that were laid down in interior basins. The 

beds consist of gravel, sand, and silt that are weakly indurated, weakly bedded, and relatively flat lying. The color 

of the beds appears generally buff but is varied and not 

distinctive.

Tertiary volcanic flow rocks (Tv) overlie the Muddy 

Creek Formation and are also found as outliers in contact 

with younger Quaternary alluvium. The flows are locally 

vesicular olivine basalt that is blocky or platy weathering, 

and dark brown to black on weathered surfaces.

Quaternary alluvium (Qal) covers about 30 to 40 percent of the study area, mostly in the northern and eastern 

parts. Alluvium in the study area consists of bouldery alluvial fans, coarse gravelly material probably deposited as 

sheetwash, and generally unsorted sand, silt, and clay. 

Along its contact with the Paleozoic rocks of the Million 

Hills, this unit also includes talus deposits.

Geochemical Studies

A reconnaissance geochemical survey of the Million 

Hills Wilderness Study Area was conducted in April 1987. 

Samples of drainage sediment were collected at 28 sites 

on streams draining the wilderness study area and vicinity 

(fig. 3). Stream-sediment samples represent a composite of 

material eroded from the drainage basin of the stream 

sampled. Panned-concentrate samples derived from stream 

sediment contain selectively concentrated minerals that 

may be ore related and may include elements not easily 

detected in stream-sediment samples.

Three samples were collected at each site. One of the 

samples was air dried and then sieved through an 80-mesh 

(0.177-mm) stainless-steel sieve to obtain a stream-sediment sample. The portion that passed through the screen 

was later pulverized to minus-100-mesh (0.149 mm) size 

prior to analysis. For the other two samples at each site, 

enough stream sediment was screened through a 10-mesh 

(2mm) sieve to obtain about 20 Ib. The minus-10-mesh 

samples were panned to remove most of the quartz, feldspar, clay-sized material, and organic matter. One of these 

panned-concentrate samples was further concentrated by a 

series of steps that utilized bromoform (specific gravity 2.8) 

and magnetic separations to produce a nonmagnetic heavymineral-concentrate sample. The nonmagnetic heavy-mineral-concentrate sample includes most nonmagnetic ore 

minerals and accessory minerals such as sphene, zircon, 

apatite, and rutile. Prior to analysis the nonmagnetic heavymineral-concentrate sample was pulverized to minus-100 

mesh size. The raw panned-concentrate samples received 

no further treatment and were analyzed for gold.

The stream-sediment and nonmagnetic heavy-mineralconcentrate samples were analyzed using a six-step semiquantitative emission spectrographic method described by 

Grimes and Marranzino (1968) for calcium (Ca), iron (Fe), 

magnesium (Mg), titanium (Ti), silver (Ag), arsenic (As), 

gold (Au), boron (B), barium (Ba), beryllium (Be), bismuth (Bi), cadmium (Cd), cobalt (Co), chromium (Cr), 

copper (Cu), lanthanum (La), manganese (Mn), molybdenum (Mo), niobium (Nb), nickel (Ni), lead (Pb), antimony 

(Sb), scandium (Sc), tin (Sn), strontium (Sr), thorium (Th), 

vanadium (V), tungsten (W), yttrium (Y), zinc (Zn), and 

zirconium (Zr). In addition, the nonmagnetic heavy-mineral-concentrate samples were analyzed for phosphorus (P), 

sodium (Na), gallium (Ga), germanium (Ge), palladium 

(Pd), and platinum (Pt) by emission spectrography. Also, 

the stream-sediment samples were analyzed for Au by 

graphite-furnace atomic absorption, for uranium (U) by ultraviolet fluorimetry, and for As, Bi, Cd, Sb, and Zn by 

inductively coupled plasma spectroscopy. The raw pannedconcentrate samples were analyzed for Au by flame atomic 

absorption. Analytical data, sampling sites, and references 

to analytical methods are presented in McHugh and others 

(1989).

Selected elements determined in each sample type, 

the lower and upper limits of determination, the range of 

concentrations, the 50th and 90th percentile concentrations, and the threshold (highest background) concentrations are presented in table 3. Threshold concentrations 

were established by visual and statistical examination of 

the data, by comparison of the data from this study with 

data from nearby wilderness study areas (El Dorado, Ireteba Peaks, and Lime Canyon), and by reference to bedrock 

concentrations (table 4) listed by Rose and others (1979).

Correlations for logs of data obtained from the analysis of minus-80-mesh stream-sediment samples are listed 

in table 5. Before the correlation analysis, qualified values 

were replaced by unqualified values. Qualified values are

E10 Mineral Resources of Wilderness Study Areas: Southern Nevada
114°09'30"

36° 

20'

36° 

15'

APPROXIMATE BOUNDARY

OF

MILLION HILLS 

WILDERNESS STUDY AREA

(NV-050-233)

As-i 

Au-a

As-i Cu 

Cr

Be La 

Ni

Zn-i

2 MILES

EXPLANATION 

^~^~ Outline of drainage basin

Sampling site

 Granitic sediment predominant 

A Limestone/dolomite sediment 

predominant

 Sediment is about equal proportions of granitic and limestone/dolomitic material

Elements

Ag Silver

As Arsenic

Au Gold

Ba Barium

Be Beryllium

Cd Cadmium

Co Cobalt

Cr Chromium

Cu Copper

Ga Gallium

La Lanthanum

Mo Molybdenum

Ni Nickel

Pb Lead

Sn Tin

Th Thorium

V Vanadium

W Tungsten

Zn Zinc

Cd-i -i concentration determined by 

inductively coupled plasmaatomic emission spectroscopy; -a, 

concentration determined by 

atomic-absorption spectroscopy

Zn Element anomalous in minus-80- 

mesh stream-sediment sample

Cr Element anomalous in nonmagnetic 

heavy-mineral-concentrate 

sample

lAu-al Gold anomalous in raw pannedconcentrate sample

Figure 3. Elements present in anomalous concentrations in samples collected from drainage basins in and near Million Hills 

Wilderness Study Area, Clark County, Nevada.

Mineral Resources of the Million Hills Wilderness Study Area, Clark County, Nevada E11
those less than the lower limit of determination and greater than the upper limit of determination. Reported concentrations qualified by "N" or "<" were replaced by values 

two emission spectrographic steps below the lower limit 

of determination (table 3). Concentrations qualified by "L" 

were replaced by values one emission spectrographic step 

below the lower limit of determination. No elemental concentrations in minus-80-mesh stream-sediment samples 

were greater than the upper limit of determination. Any 

variable with more than 9 samples containing undetected 

concentrations was omitted from table 5.

Strong correlations among an unusually large group of 

elements that includes Fe, Ti, Be, Co, Cr, Cu, La, Mn, Ni, Pb, 

Sc, V, Y, Cd, Zn, and U are shown in table 5. A number of 

mathematical manipulations and procedures such as r-mode 

factor analysis support this strong correlation. The validity 

of the correlations is also supported by figure 3, which lists 

elements present in anomalous concentrations in each sampled drainage basin. Gold is not included in table 5 because 

half the samples have undetected concentrations. Nevertheless, anomalous concentrations of gold in minus-80-mesh 

stream-sediment samples appear to be closely associated 

with anomalous concentrations of other elements. Sampling 

sites are differentiated on figure 3 on the basis of the rocktype composition of the stream sediment as determined at the 

time of sample collection. The correspondence between sediment composition and anomalous elemental concentrations 

is listed in table 3. Most of the samples containing anomalous concentrations were collected from sites where the sediment was 70 percent or greater granitic composition even 

though, in some cases, bedrock at the sampling site was 

limestone or dolomite.

Correlations among the ferride elements, Fe, Co, Cr, 

Cu, Ni, and V, are very strong (table 5). Correlations of the 

ferride elements with Ti, Mn, and Sc are also very strong. 

The association of Fe, Co, Cr, Cu, Ni, V, Ti, Mn, and Sc is 

fairly common in stream-sediment samples from many geologic and climatic environments and usually reflects the 

presence of common ferromagnesian silicates. However, the 

association of these elements in stream-sediment samples 

from the study area is unusually strong, inclusive, and persistent. In addition, some elements (Be, La, Y, Zr, and U), 

which usually correlate poorly with most of the ferride elements, and elements that are often related to mineralization 

(Cd, Pb, and Zn) also correlate moderately to strongly with 

the ferromagnesian group of elements. Magnesium usually 

correlates positively with the ferromagnesian group, though 

in samples from the study area, the correlation is negative 

and poor. This relationship probably reflects the presence of 

carbonate rocks.

Gneiss and schist underlie parts of the wilderness study 

area (fig. 2) and contribute sediment or have contributed 

sediment in the past to most of the sampled stream channels. 

Material from the gneiss and schist bedrock was probably

recorded as granitic material at the time of sample collection (table 3, fig. 3). Although there is good correspondence 

between granitic sediment and anomalous concentrations of 

many elements, the inclusive and strong correlations in 

table 5 suggest a geochemical signature other than one that 

can be attributed to granitic sediment alone.

The geochemical data from drainage-sediment samples of the wilderness study area and vicinity suggest the 

geochemical signature for a model of carbonate-hosted 

mineral deposits termed Kipushi Cu-Pb-Zn deposits (Cox 

and Bernstein, 1986). The geochemical signature for Kipushi-type mineralization is Cu, Zn, Pb, As, Co, Ag, Ge, 

Ga, Mo, W, Sn, Bi, U, and V (Cox and Bernstein, 1986). 

The nearest known Kipushi-type ore deposit, the Apex 

mine, is about 50 mi northeast of the study area. The Apex 

mine produced Cu, Pb, Ag, and minor amounts of Zn and 

Au from 1884 to 1962 (Bernstein, 1986), operated intermittently thereafter, and was reopened in 1990 (Hecla 

Mining Company, 1990). Apex is the only known mine in 

the world where the primary products are gallium and germanium. Proven and probable reserves at Apex total about 

230,000 short tons with grades of 0.046 percent Ga, 0.105 

percent Ge, and 1.6 percent Cu (Hecla Mining Company, 

1990). The host rock of the deposit is the Callville Limestone. The ore at the Apex mine is associated with zones 

of fault breccia. The limestone has been dolomitized and 

locally silicified within and near the fault zones.

The Azure Ridge mine is a carbonate hosted deposit 

that produced a few carloads of sorted Zn and Cu ore 

(Longwell and others, 1965, p. 130). The ore contained 

minor amounts of Au and Ag. The deposit is associated 

with faults and is in a stratigraphic setting similar to the 

Apex mine. Recent analyses of mineralized samples by the 

U.S. Bureau of Mines reveal Co is present in the deposit 

(Causey, 1988). The Quartz claim (fig. 3), an inactive mining claim, has Mn and Fe oxides in alluvial fill. Samples 

of the oxide contain the following approximate concentrations of elements, in parts per million (ppm): Ni-1,700; 

Mo-110; Pb-1,900; Tl-80; Zn-3,700; Cu-550; Co-6,100; 

Bi-28; As-140; Ba-4900 (Causey, 1988). Manganese-iron 

oxides are effective scavengers of many elements (Chao 

and Theobald, 1976), but a source for the elements must 

exist in order for them to be available for scavenging.

A possible explanation for the geochemical signature 

expressed in the drainage samples from the study area and 

vicinity is that Kipushi-type mineralization is present in 

the subsurface and is the source of anomalous concentrations of a variety of elements in drainage sediment and is 

the source for the Mn-Fe oxides and associated elements 

at the Quartz claim. Mineralogical studies of the nonmagnetic heavy-mineral-concentrate samples might help to establish the residency of many of the elements detected by 

emission spectrography. Selective leaching of minus-80- 

mesh stream-sediment samples might establish whether

E12 Mineral Resources of Wilderness Study Areas: Southern Nevada
Table 3. Statistics for selected elements in drainage samples collected in and near Million Hills Wilderness Study Area, Clark Coun

[Results based on 28 samples. Concentrations determined by emission spectrography except As-i, Cd-i, and Zn-i determined by inductively coupled plas

absorption. N, not detected at lower limit of determination; L, detected below lower limit of determination; G, greater than upper limit of determination; <

limit is open ended, ppm, parts per million; pet, percent]

Number of 

5*

n

i.

90

C

2 nVI

O 

-*>

n

2

5*

3

I

3T

^

ELn

I

ffi V)

?

.< 

>

s

n

w

sQc

^?

Element Limits of determination, ppm

Lower Upper

Range, ppm

Minimum Maximum

Threshold

Percentiles, ppm concentration,

50th 90th ppm

70 pet granitic

sediment, or

greater

Minus-80-mesh stream-sediment samples

As-i

Au-a

Be

Cd-i

Co

Cr

Cu

La

Ni

Sn

V

Zn

Zn-i

Ag

Ba

Be

Bi

Cr

Cu

Ga

Mo

Pb

Th

V

W

Zn

Au-a

5

0.001

1

0.1

5

10

5

20

5

10

10

200

2

1

50

2

20

20

10

10

10

20

200

20

50

500

0.05*

20,000

1,000

1,000

2,000

5,000

20,000

1,000

5,000

1,000

10,000

10,000

18,000

10,000

10,000

2,000

2,000

10,000

50,000

1,000

5,000

50,000

5,000

20,000

20,000

20,000

<

<

N

0.2

N

N

L

N

L

N

15

N

<

N

100

N

N

N

N

N

N

N

N

20

N

N

<

17

0.003

5

5.6

50

1,000

50

500

200

L

500

200

56

5

G

50

20

200

30

L

50

3,000

200

150

1,000

L

0.65

5

0.001

1

1.2

10

85

20

30

20

N

70

N

37

Nonmagnetic

N

1,250

N

N

N

L

N

N

20

N

50

N

N

Raw

<

11

0.001

3

2.6

30

200

40

110

70

L

150

L

48

10

0.001

2

1.9

20

100

30

100

50

N

100

N

49

4

2

7

5

5

8

3

3

7

4

5

8

2

heavy-mineral-concentrate samples

N

10,000

2

N

110

17

N

L

60

N

85

200

N

panned-concentrate

0.05

N

5,000

N

N

70

20

N

N

300

N

100

L

N

samples

<

0

2

4

0

0

1

1

3

1

3

0

3

1

4

*Based on 10-g sample
Table 4. Average of median concentrations of selected elements in bedrock from 

Rose and others, 1979

[Concentrations in parts per million. <, less than value shown; , no value given]

Element

Ag

As

Ai

Ba

Be

Bi

Cd

Co

Cr

Cu

La

Mo

Ni

Sn

Th

V

W

Zn

Granite

0.037

2.1

0.0023

840

3

0.3

0.1

1

4.1

12

55

1.3

4.5

3.0

20

44

1.5

51

Basalt and 

gabbro

0.1

1.5

0.0032

330

1

0.05

0.2

48

170

72

17

1.5

130

1.5

2.7

250

1.0

94

Limestone

0.1

1.1

0.005

92

<1

...

0.035

0.1

11

5

4

0.4

20

<1

1.7

20

0.5

21

Sandstone

0.25

1.2

0.005

170

<1

0.3

<0.1

0.33

35

10

7

0.2

2

0.6

5.5

20

1.6

40

Shale

0.19

12

0.004

550

3

1.0

0.3

19

90

42

39

2.6

68

6

12

130

1.8

100

the elements present in anomalous concentrations are associated with primary minerals, such as sulfides, or secondary Mn-Fe oxides. These additional studies would help 

test the applicability of the Kipushi Cu-Pb-Zn model.

Geophysical Studies

Regional aeromagnetic and gravity data for the Million 

Hills Wilderness Study Area and vicinity assist in establishing the geologic framework essential to evaluation of the 

resource potential. Two aeromagnetic surveys provide data 

at 1-mi spacing: a survey of part of part of the Las Vegas 

I°x2° quadrangle, flown east-west at 1,000 ft above ground 

(U.S. Geological Survey, 1983), and a survey of the Gold 

Butte-Chloride area, flown north-south at 8,000 ft barometric elevation (U.S. Geological Survey, 1972). Gravity data 

are available from the U.S. National Defense Mapping 

Agency (through the National Center for Geophysical and 

Solar-Terrestrial Data, Boulder, Colo.); 16 additional gravity stations were established by the USGS for this project.

A residual total-intensity map was made by merging 

digital data from the two aeromagnetic surveys, after removal of the International Geomagnetic Reference Field (fig. 4). 

The contour intervals are 20 and 100 nanoteslas (nT). The 

area of coverage is much larger than the study area to show 

regional relations. The anomaly field is complex and is dominated by very intense, relatively short wavelength disturbances. Almost all principal anomaly highs are associated 

with exposed metamorphic and granitic rock of the Precambrian crystalline basement complex, the only exception 

being due east of the study area, where the high can be 

attributed to concealed basement rock on the floor of the 

Grand Wash depression (fig. 1). Most of this depression is 

a region of relatively weak anomalies, probably because of 

the increased depth to sources. Strong aeromagnetic anomaly trends in the region are predominantly northwesterly and 

northeasterly. A deep west-northwest-trending low is present 

over the structural depression between the Virgin Mountains 

and the area that includes Lime Ridge, Tramp Ridge, and 

Azure Ridge. A low also is present over Grand Wash, where 

it has an east-northeast trend, possibly reflecting offset on a 

concealed extension of the Gold Butte fault.

The regional Bouguer gravity anomaly field was computed with data from 123 points of gravity observation in the 

area (fig. 5). The standard reduction density, 2.67 g/cm3, was 

used, and terrain corrections were applied for HayfordBowie zones A-O (0-167 km). An explanation of these 

procedures is given in Cordell and others (1982). The principal feature of the gravity field is the down-to-the-east gradient between dense Precambrian crystalline and Paleozoic 

carbonate rocks of the Virgin Mountains and much less dense 

Cenozoic fill of the Grand Wash depression. The basin fill of 

the Grand Wash apparently reaches a maximum thickness in

E14 Mineral Resources of Wilderness Study Areas: Southern Nevada
Table 5. Correlation coefficients for analytical data from minus-80-mesh stream-sediment samples collected in and near Million 

Nevada

[Based on logs of replaced data. Coefficients multiplied by 100. All elements analyzed by enussion spectrography except where suffix denotes other meth

x-ray fluorescence. Results based on analyses of 28 samples]

n 

3_

70

I

3,

3- 

n

^

5*

I

5T

1

i

</> sQ. <

j»

n

wsQ

z

iCL

w

Ca

Fe

Mg 

Ti

B

Ba

Be

Co 

Cr

Cu

La

Mn

Ni

Pb

Sc

Sr

V

Y

Zr

As-i

Cd-i 

Zn-i

Fe Mg Ti B Ba Be Co Cr Cu La Mn

-49 30 -56 -13 -46 -53 -55 -51 -34 -33 -41

-16 89 -9 57 75 91 78 87 84 90

-39 -30 -41 -22 -22 -24 -12 -20 -21 

15 64 69 88 74 75 86 81

10 -4 -14 -2 -21 -23 -26

51 55 51 40 45 49

82 53 69 64 76

67 85 77 85 

63 68 65

73 90

79

Ni

-52

93

-20 

88

-19

54

78

93 

70

90

84

89

Pb

1

66

8 

48

-17

22

52

65

44

82

51

73

68

Sc

-50

93

-27 

87

-13

59

84

91 

65

84

83

91

94

60

Sr

-37

61

-20 

62

-26

70

74

68 

54

62

64

65

73

47

71

V

-38

90

-27 

85

-12

48

64

82 

67

80

88

87

90

56

89

50
the extreme northeast corner of the map area. A deep embay- East-northeast and north to north-northwest aeromagment in the gravity anomaly gradient in the north-central part netic and gravity trends intersect in the vicinity of the

of figure 5 reflects the structural discontinuity in magnetic Azure Ridge mine in the northern part of the study area,

basement evident in the north-central part of figure 4. The east-northeast trends are expressions of the Gold

APPROXIMATE BOUNDARY

OF

MILLION HILLS 

WILDERNESS STUDY AREA

(NV-050-233)

Figure 4. Residual total-intensity aeromagnetic map of Million Hills Wilderness Study Area and vicinity, Clark County, 

Nevada, and Mojave County, Arizona. Contour intervals, 20 and 100 nanoteslas; hachures denote magnetic low.

E16 Mineral Resources of Wilderness Study Areas: Southern Nevada
Butte fault, but the structural discontinuity reflected by the Mineral and Energy Resource Potential 

north to north-northwest trends is concealed. The significance of the structural intersection with regard to possible The Million Hills Wilderness Study Area has high reKipushi-type copper-lead-zinc mineralization is unclear. source potential for copper, lead, zinc, cobalt, gold, silver,

APPROXIMATE BOUNDARY

OF

MILLION HILLS 

WILDERNESS STUDY AREA

(NV-050-233)

Figure 5. Complete Bouguer gravity anomaly map of Million Hills Wilderness Study Area and vicinity, Clark County, 

Nevada, and Mojave County, Arizona. Contour interval, 2 milligals; circles denote gravity stations.

Mineral Resources of the Million Hills Wilderness Study Area, Clark County, Nevada E17
germanium, and gallium in Kipushi-type deposits. There is 

low resource potential for oil and gas, and no potential for 

geothermal energy. There are occurrences of carbonate 

rocks, and sand and gravel.

Evidence of copper-lead-zinc mineralization in the 

study area, which can be interpreted to reflect Kipushi-type 

deposits, was obtained from a geochemical survey that was 

done by the U.S. Geological Survey for this evaluation of 

mineral resources, and from a survey by the U.S. Bureau of 

Mines (Causey, 1988) of the mines, prospects, and mineralized parts of the study area. Kipushi-type deposits are significant because of other metals associated with the copper, 

lead, and zinc. These metals are cobalt, germanium, and 

gallium, all of which are relatively scarce in this country, 

and two of which (cobalt and germanium) are classified as 

strategic and critical minerals. Cobalt is a metal chiefly 

used to make magnetic alloys, and alloys that are heat, 

corrosion, and wear resistant. The end uses are mostly in 

aircraft, jet engines, cutting tools, electrical equipment, 

paints, and chemical products. Germanium is a metalloid 

used chiefly in the electronics and optics industries. It is 

also used in the manufacture of some semiconductor devices, optical lenses with infrared sensing capabilities, fiber 

optics, nuclear radiation detectors, alloys, and as a catalyst. 

Gallium is a metal with a very low melting point (86° F) 

used in the manufacture of electronic components and optical devices, and as an alloying agent in the preparation of 

superconductive devices. The United States is a net importer of all three elements. For additional information on supply, demand, and other facts related to cobalt, germanium, 

and gallium, see Kirk (1985), Plunkert (1985), Petkof 

(1985), and U.S. Bureau of Mines (1993).

Most cobalt is produced as a byproduct from the mining of other metals. The only primary cobalt producing 

district in the United States is the Blackbird district in 

Idaho. The Blackbird district contains relatively high grade 

ore of about 0.6 percent cobalt. Other world cobalt deposits have ore grades of about 0.1 to 2.0 percent (Kirk, 

1985). Data obtained by the U.S. Bureau of Mines in their 

investigation of the study area revealed the presence of as 

much as 0.6 percent cobalt associated with manganese at 

the Quartz claim (Causey, 1988). In their investigation of 

a cobalt-manganese occurrence in the northern part of the 

study area, Moyle and Buehler (1990) found concentrations of cobalt ranging from 0.1 to 0.5 percent. These concentrations were detected in samples from fissures, but the 

volume of cobalt-enriched material at this occurrence is 

very small. The study area thus has samples that contain 

percentages of cobalt as high as those mined in the only 

cobalt producing district in the U.S. This does not necessarily make the cobalt at Azure Ridge mineable, but it 

does raise the possibility of economically significant mineralization in the study area and makes it an area in which 

further exploration may be justified.

The geochemical data from drainage-sediment samples from the study area and immediate vicinity suggest 

the geochemical signature of a carbonate-hosted Kipushitype copper-lead-zinc mineral deposit such as described by 

Cox and Bernstein (1986). The geochemical signature of 

this type of deposit includes the elements: copper, lead, 

zinc, cobalt, germanium, gallium, silver, arsenic, molybdenum, tungsten, tin, bismuth, uranium, and vanadium (Cox 

and Bernstein, 1986). The data obtained from analysis of 

the geochemical samples was compared with a number of 

possible mineral deposit types, including the Mississippi 

Valley type of lead-zinc deposit. However, the correlations 

of the data were by far the strongest for the Kipushi model. The correlations are strong and inclusive with a high 

number of attributes present, and they strongly indicate 

Kipushi-type mineralization as the source of the observed 

geochemical suite of elements. The correlation is empirically observable, but it was also tested and verified by a 

number of statistical procedures including r-mode factor 

analysis. The possibility of the geochemical signature 

coming from underlying Precambrian gneiss and granite 

was rejected because the correlations of elements with the 

Kipushi model are so strong and inclusive. The geochemical signature is stronger than what would appear from the 

Precambrian rocks alone. This then leads to the conclusion 

that the geochemical signature is derived from mineralized 

carbonate rocks. The geochemical signature obtained from 

sampling of the study area can be explained by the presence of subsurface Kipushi-type mineralization, which 

would be the source of the anomalous concentrations of 

the suite of elements found in this study.

The only known Kipushi-type deposit in the conterminous United States is the Apex mine, located about 50 mi 

northeast of the study area and about 12 mi west of St. 

George, Utah. The Apex mine is active, and is the first in 

the world to be mined primarily for germanium and gallium 

(Bernstein, 1986). Between 1884 and 1962 the deposit was 

mined for copper, lead, silver, and minor amounts of zinc 

and gold (Bernstein, 1986). Hecla Mining Co. acquired the 

Apex mine in 1989 and began producing germanium, gallium, and small amounts of byproduct copper in 1990. Proven and probable reserves total 230,200 short tons that grade 

0.105 percent germanium, 0.046 percent gallium, and 1.6 

percent copper (Hecla Mining Co., 1990). The need for 

gallium and germanium decreased with the end of the Cold 

War. The Apex is still active, though now the primary product is cobalt sulfate for the copper industry (Hecla Mining 

Co., 1993). The host rock at the Apex mine is the Callville 

Limestone, a stratigraphic unit that is present in the study 

area. The physical characteristics of the Callville at the 

Apex mine were described by Bernstein (1986) and are 

similar to those of the unit as it crops out in the study area. 

The ore at the Apex mine occurs in breccia, gouge, and 

fissures along steeply dipping (64°-7r W) subparallel

E18 Mineral Resources of Wilderness Study Areas: Southern Nevada
faults in the Apex fault zone that trends north to northeast 

(Bernstein, 1986). The fault zone apparently controlled the 

locus of mineralization at the Apex mine. The Azure Ridge 

mine is in a similar setting of host rocks and structure, and 

the observed mineralization in the study area similarly occurs along steeply dipping faults.

The study area may contain Kipushi-type copper-leadzinc mineralization on the basis of: (1) a geochemical suite 

of anomalous elements from the study area that strongly 

correlates with the geochemistry of known Kipushi-type 

deposits, (2) known mineralization in the study area that 

includes copper, lead, zinc, gold, silver, and cobalt all 

minerals associated with Kipushi-type deposits, (3) the high 

values of cobalt detected in samples from the Azure Ridge 

mine 0.6 percent, (4) the fact that Causey (1988) determined that two mining properties in the study area (the 

Esperanta and Quartz claims) have inferred subeconomic 

resources of copper, lead, zinc, gold, silver, cobalt, gallium, 

and germanium, (5) the existence of permissible, reactive 

host rocks in the study area, (6) the presence of structures 

(primarily high-angle faults) that provide paths for mineralizing fluids and a locus for mineralization, and (7) the similarity of lithology, structure, and mineralization with the 

Apex mine, a known Kipushi-type deposit that is about 50 

mi north northeast of the study area. Therefore, the part of 

the study area underlain by carbonate rocks (see fig. 2 for 

specific location) has high potential, certainty level C, for 

copper, lead, zinc and lesser amounts of cobalt, gold, silver, 

germanium, and gallium in Kipushi-type deposits.

Sandberg (1983a, b) shows a large part of the study 

area as having low potential, certainty level B, for petroleum on the basis of possible presence of source rocks, reservoir rocks, and favorable areas to the north. Harris and 

others (1980) provide evidence from conodont color alteration index measurements that rocks within 40 mi of the 

study area have not been thermally overmatured. Data on 

color alteration of conodonts from Ordovician sedimentary 

rocks about 40 mi west of the study area indicate that area 

is permissible for petroleum. There are no known conodont data from within the study area that would provide 

direct evidence of the degree of thermal maturation. There 

are no known producing wells or shows of oil or gas in 

the region surrounding the study area. However, as of 

1988, there were 6 oil and gas leases in or near the study 

area. One of these leases covers about 340 acres in the 

study area, and contiguous areas are covered by additional 

oil and gas leases (Bureau of Land Management, 1988, p. 

2-35). Because of the permissible geological attributes for 

oil and gas and the known permissible terrane to the north 

and west, a large part of the study area has low potential, 

certainty level B, for oil and gas.

The available data indicate that there is no potential, 

certainty level D, for geothermal resources in the study 

area. The study area lies in an area of relatively low heat 

flow (Muffler, 1979), and there are no known warm or hot

springs in the region surrounding the study area. Therefore, 

the study area has no potential for geothermal resources.

Limestone has a number of industrial uses and crops 

out extensively in the study area, although these rocks are 

considered by Causey (1988) to constitute an occurrence, 

not a resource. This classification is based on the fact that 

carbonate rocks in the study area are generally thin bedded, cherty, and dolomitized; these rocks also contain interbeds of sandstone, shale, and chert, which diminishes 

the value of the carbonate rocks for commercial purposes.

Sand and gravel in the study area likewise constitute 

an occurrence and not a resource (Causey, 1988). This 

classification is based on the presence of a commercially 

undesirable layer of caliche near the ground surface and 

the fact that other sources of sand and gravel are closer to 

existing markets.

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E20 Mineral Resources of Wilderness Study Areas: Southern Nevada
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322.

Rose, A.W., Hawkes, H.E., and Webb, J.S., 1979, Geochemistry 

in mineral exploration, 2nd ed.: London, Academic Press, 

657 p.

Sandberg, Charles A., 1983a, Petroleum potential of wilderness 

lands in Nevada, in Miller, B.M., ed., Petroleum potential of 

wilderness lands in the western United States: U.S. Geological Survey Circular 902-H, 11 p.

 1983b, Petroleum potential of wilderness lands, Nevada: 

U.S. Geological Survey Miscellaneous Investigations Series 

Map 1-1542, 11 p., 1 sheet, scale 1:1,000,000.

Smith, PL., and Tingley, J.V., 1983a, A mineral inventory of the 

Esmeralda-Stateline Resource area, Las Vegas District, Nevada: Nevada Bureau of Mines and Geology Open-File Report 83-11, 176 p.

 1983b, Results of geochemical sampling within EsmeraldaStateline Resource area, Esmeralda, Clark, and southern Nye

Counties, Nevada (portions of Death Valley, Goldfield, Kingman, Las Vegas, Mariposa and Tonopah 2° sheets): Nevada 

Bureau of Mines and Geology Open-File Report 83-12,176 p.

U.S. Bureau of Mines, 1993, Mineral Commodity Summaries: 

U.S. Bureau of Mines, 202 p.

U.S. Bureau of Mines and U.S. Geological Survey, 1980, Principles of a resource/reserve classification for minerals: U.S. 

Geological Survey Circular 831, 5 p.

U.S. Geological Survey, 1972, Aeromagnetic map of the Gold 

Butte-Chloride area, Arizona and Nevada: U.S. Geological 

Survey Geophysical Investigations Map GP-757, scale 

1:62,500.

U.S. Geological Survey, 1983, Aeromagnetic map of part of the 

Las Vegas I°x2° quadrangle, Nevada: U.S. Geological Survey Open-File Report 83-729.

Vanderburg, W.O., 1937, Reconnaissance of mining districts in 

Clark County, Nevada: U.S. Bureau of Mines Information 

Circular 6964, 81 p.

Volborth, Alex, 1962, Rapakivi-type granites in the Precambrian 

complex of Gold Butte, Clark County, Nevada: Geological 

Society of America Bulletin, v. 73, no. 6, p. 813-831.

Wasserburg, G.J., and Lanphere, M.A., 1965, Age determinations 

in the Precambrian of Arizona and Nevada: Geological Society of America Bulletin, v. 76, no. 7, p. 735-758.

Welsh J. E., 1959, Biostratigraphy of the Pennsylvanian and Permian Systems in southern Nevada: Salt Lake City, Utah, 

University of Utah, Ph.D. dissertation, 106 p.

Wernicke, Brian, Spencer, I.E., Burchfiel, B.C., and Guth, PL., 

1982, Magnitude of crustal extension in the southern Great 

Basin: Geology, v. 10, no. 10, p. 499-502.

Yale, C.G., 1906, Nevada, in Mineral resources of the United 

States calendar year 1905: U.S. Geological Survey, p. 259- 

275.

 1907, Nevada, in Mineral resources of the United States, 

calendar year 1906: U.S. Geological Survey, p. 287-300.

 1908, Nevada, in Mineral resources of the United States, 

calendar year 1907, Part 1 Metallic products: U.S. Geological Survey, p. 337-398.

Mineral Resources of the Million Hills Wilderness Study Area, Clark County, Nevada E21

APPENDIXES
DEFINITION OF LEVELS OF MINERAL RESOURCE POTENTIAL 

AND CERTAINTY OF ASSESSMENT

LEVELS OF RESOURCE POTENTIAL

H HIGH mineral resource potential is assigned to areas where geologic, geochemical, and geophysical characteristics indicate a geologic environment favorable for resource occurrence, where interpretations of data 

indicate a high degree of likelihood for resource accumulation, where data support 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 t 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, an (or) where an application of mineraldeposit models indicates favorable ground for the specified type(s) of deposits.

L LOW mineral resource potential is assigned to areas where geologic, geochemical, and geophysical characteristics define a geologic environment in which the existence of resources is permissive. This broad category embraces areas with dispersed but insignificantly mineralized rock, as well as areas with little or not 

indication of having been mineralized.

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

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

low, moderate, or high level of resource potential.

LEVELS OF CERTAINTY

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

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

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

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

B

D_

LLJ

D

o

o

_J

UJ

>

A

U/A

UNKNOWN POTENTIAL

B

H/B

HIGH POTENTIAL

M/B

MODERATE POTENTIAL

L/B

LOW POTENTIAL

C

H/C

HIGH POTENTIAL

M/C

MODERATE POTENTIAL

L/C

LOW POTENTIAL

D

H/D

HIGH POTENTIAL

M/D

MODERATE POTENTIAL

L/D

LOW POTENTIAL

N/D

NO POTENTIAL

LEVEL OF CERTAINTY

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 public lands: U.S. Geological Survey Open-File Report 84-0787, p. 7, 8.

E24 Mineral Resources of Wilderness Study Areas: Southern Nevada
RESOURCE/RESERVE CLASSIFICATION

IDENTIFIED RESOURCES

Demonstrated

Measured Indicated

Inferred

UNDISCOVERED RESOURCES

Probability Range

Hypothetical Speculative

ECONOMIC Reserves Inferred 

Reserves

MARGINALLY 

ECONOMIC

Marginal 

Reserves

Inferred 

Marginal 

Reserves

SUBECONOMIC

Demonstrated

Subeconomic

Resources

Inferred

Subeconomic

Resources

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

resource estimates and public policy: American Scientist, v. 60, p. 32-40; and U.S. Bureau of Mines and U.S. Geological Survey, 1980, Principles 

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

Mineral Resources of the Million Hills Wilderness Study Ai^a, Clark County, Nevada E25
GEOLOGIC TIME CHART

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

EON

Phanerozoic

Proterozoic

Archean

ERA

Cenozoic

Mesozoic

Paleozoic

Late Proterozoic

Middle Proterozoic

Early Proterozoic

Late Archean

Middle Archean

Early Archean

PERIOD

Quaternary

Neogene 

Subperiod

Tertiary 

Paleogene 

Subperiod

Cretaceous

Jurassic

Triassic

Permian

Pennsylvanian 

Carboniferous

Periods 

Mississippian

Devonian

Silurian

Ordovician

Cambrian

ttanr\7\

EPOCH

Holocene

Pleistocene

Pliocene

Miocene

Oligocene

Eocene

Paleocene

Late 

Early

Late 

Middle 

Early

Late 

Middle 

Early

Late 

Early

Late 

Middle 

Early

Late 

Early

Late 

Middle 

Early

Late 

Middle 

Early

Late 

Middle 

Early

Late 

Middle 

Early

pre-Archean2

AGE ESTIMATES OF 

BOUNDARIES IN 

MILLION YEARS (MA)

 0.010

1.7

 5

?a

 55

 66

 96

 205

n .JAO

tan

,_iin

 -360

 410

 135

 500

l^qyn

900

1600

 2500

3000

 3400

 Azzn 

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

2 Informal time term without specific rank.

E26 Mineral Resources of Wilderness Study Areas: Southern Nevada
Mineral Resources of 

Wilderness Study Areas: 

Southern, Nevada

This volume was published as separate chapters A-E

U.S. GEOLOGICAL SURVEY BULLETIN 1730
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director
CONTENTS

[Letters designate the separately published chapters]

(A) Mineral Resources of the La Madre Mountains Wilderness Study Area, Clark 

County, Nevada, by James E. Conrad, Harlan N. Barton, and David A. Lipton.

(B) Mineral Resources of the Mt. Stirling Wilderness Study Area, Clark and Nye 

Counties, Nevada, by Raul J. Madrid, Robert Turner, David W. Brickey, 

H. Richard Blank, and Martin Conyac.

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

Clark County, Nevada, by Ed De Witt, J.L. Anderson, H.N. Barton, R.C. Jachens, 

M.H. Podwysocki, D.W Brickey, and T.J. Close.

(D) Mineral Resources of the Lime Canyon Wilderness Study Area, Clark County, 

Nevada, by James G. Evans, Gary A. Nowlan, Joseph S. Duval, and 

Richard A. Winters.

(E) Mineral Resources of the Million Hills Wilderness Study Area, Clark County, 

Nevada, by Joel R. Bergquist, Gary A. Nowlan, H. Richard Blank, Jr., and 

J. Douglas Causey.

*U.S. GOVEPTWENT PRINTINS OFFICE: 1994-583-048/10003

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i"W\ i'M ^ t$. i"

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