Mineral Resources of the Newberry 

Mountains and Rod man Mountains 

Wilderness Study / Areas, f San Bernardino

County, California

U.S. GEOLOGICAL SURVEY BULLETIN 1712-A

Chapter A

Mineral Resources of the Newberry Mountains 

and Rodman Mountains Wilderness Study Areas, 

San Bernardino County, California

By BRETT F. COX, ANDREW GRISCOM, JAMES E. KILBURN, 

GARY L. RAINES, and DANIEL H. KNEPPER, Jr. 

U.S. Geological Survey

CHARLES SABINE and LUCIA KUIZON 

U.S. Bureau of Mines

U.S. GEOLOGICAL SURVEY BULLETIN 1712

MINERAL RESOURCES OF WILDERNESS STUDY AREAS: 

CENTRAL CALIFORNIA DESERT CONSERVATION AREA
DEPARTMENT OF THE INTERIOR 

DONALD PAUL MODEL, 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 Newberry Mountains and 

Rodman Mountains Wilderness Study Areas, San 

Bernardino County, California.

U.S. Geological Survey Bulletin B-1712-A

Bibliography

Supt. of Docs. No.: I 19.3:1712-A

1. Mines and mineral resources California Newberry

Mountains Wilderness. 2. Mines and mineral resources 

California Rodman Mountains Wilderness. 3. Geology 

California Newberry Mountains Wilderness. 4. Geology 

California Rodman Mountains Wilderness. 5. Newberry

Mountains Wilderness (Calif.) 6. Rodman Mountains

Wilderness (Calif.) I. Cox, Brett F. II. Series.

QE75.B9 No. 1712-A 557.3 s 87-600015

[TN24.C2] [553'.09794'95]
STUDIES RELATED TO WILDERNESS

Bureau of Land Managment Wilderness Study Areas

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

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

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

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

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

Newberry Mountains (CDCA-206) and Rodman Mountains (CDCA-207) Wilderness Study 

Areas, California Desert Conservation Area, San Bernardino County, California.

CONTENTS

Summary Al

Abstract 1

Character and setting 1

Mineral resources and potential for undiscovered resources 3

Newberry Mountains Wilderness Study Area 3

Rodman Mountains Wilderness Study Area 3 

Introduction 3

Location and physiography 3 

Previous studies 6 

Procedures and sources of data 6 

Acknowledgments 6 

Appraisal of identified resources 8

Field work and analytical methods 8

Regional history of mining and mineral exploration 8

Sites examined for this study 8

Newberry Mountains Wilderness Study Area 8

Rodman Mountains Wilderness Study Area 11 

Conclusions 11

Assessment of mineral resource potential 11 

Geology 11

Rock units 11

Geologic structure 13

Rock alteration and veins 14 

Geochemical studies 17

Methods 17

Summary of results 17

Newberry Mountains Wilderness Study Area 17

Rodman Mountains Wilderness Study Area 18 

Geophysical studies 19

Gravity survey 19

Aeromagnetic survey 19 

Conclusions 22

General summary 22

Mineral resource potential of the Newberry Mountains Wilderness Study Area 23

Mineral resource potential of the Rodman Mountains Wilderness Study Area 23 

References cited 24

Appendix 1. Definition of levels of mineral resource potential and certainty of assessment 27 

Geologic Time Chart 28

FIGURES

1. Index map showing location of the Newberry Mountains and Rodman Mountains Wilderness Study Areas A2

2. Map showing geology and mineral resource potential of the Newberry Mountains and Rodman Mountains 

Wilderness Study Areas 4

3. Map showing areas of altered rocks in the Newberry Mountains and Rodman Mountains Wilderness Study 

Areas 7

4. Map showing geochemical sample sites and geochemical anomalies in the Newberry Mountains and Rodman 

Mountains Wilderness Study Areas 15

5. Isostatic residual gravity map of the Newberry Mountains and Rodman Mountains Wilderness Study Areas 20

6. Map showing aeromagnetic interpretation of the Newberry Mountains and Rodman Mountains Wilderness 

Study Areas 21

7. Major elements of mineral resource potential/certainty classification 27

TABLES

1. Mines and prospects in and adjacent to the Newberry Mountains Wilderness Study Area 9

2. Mines, prospects, and mineralized sites in and adjacent to the Rodman Mountains 

Wilderness Study Area 10

MINERAL RESOURCES OF WILDERNESS STUDY AREAS: 

CENTRAL CALIFORNIA DESERT CONSERVATION AREA

Mineral Resources of the Newberry Mountains 

and Rodman Mountains Wilderness Study Areas, 

San Bernardino County, California

By Brett F. Cox, Andrew Griscom, James E. Kilburn,Gary L. Raines, and Daniel H.Knepper, Jr 

U.S. Geological Survey

and Charles Sabine and Lucia Kuizon 

U.S. Bureau of Mines

SUMMARY 

Abstract

The Newberry Mountains (CDCA-206) and 

Rodman Mountains (CDCA-207) Wilderness Study 

Areas occupy adjacent mountain ranges in the central 

Mojave Desert, 10 to 30 mi southeast of Barstow, 

Calif. The parts of the two study areas on which 

mineral surveys were requested encompass 

approximately 27,964 acres and 16,900 acres, 

respectively. Fieldwork conducted between 1983 and 

1985 included geologic, geochemical, and geophysical 

studies by the U.S. Geological Survey and a survey of 

mines, prospects, and mineralized areas by the U.S. 

Bureau of Mines. There are no currently or formerly 

productive mineral deposits inside either study area. 

However, despite the lack of identified mineral 

resources, both study areas have localized potential 

for undiscovered resources, as discussed below.

The Newberry Mountains Wilderness Study Area 

contains two areas with mineral resource potential. 

(See appendix 1 for definitions of levels of mineral 

resource potential.) There is moderate potential for 

undiscovered epithermal gold and silver deposits in a 

zone crossing the west margin of the study area, and 

there is moderate potential for undiscovered 

epithermal silver deposits at the east end of the study 

area.

The Rodman Mountains Wilderness Study Area 

contains three areas with mineral resource potential. 

There is moderate potential for undiscovered smallscale vein deposits of gold, silver, and copper in two 

areas in the southwestern and north-central parts of 

the study area, and there is low potential for 

undiscovered placer gold in a small area near the 

northeast corner of the study area.

In this report, any references to the "wilderness 

study area" or the "study area" refe* only to that part 

of the wilderness study area designated by the U.S. 

Bureau of Land Management as suitable for mineral 

surveys.

Character and Setting

The Newberry Mountains and Rodman Mountains 

Wilderness Study Areas lie adjacent to one another in 

the Mojave Desert of southeastern California (fig. 1). 

Both study areas are rugged and dry, consisting of 

sparsely vegetated ridges and steep-walled canyons 

occupied by sandy washes. The canyons open onto 

large alluvial fans along the northern margins of the 

study areas. The 1-mi gap between the study areas is 

occupied by the large northeast-trending canyon of 

Kane Wash.

Both study areas are underlain by Mesozoic ( 240 

to 63 million years before present, or Ma; see Geologic 

Time Chart, last page of this report) plutonic rocks, by 

a diverse assemblage of earliest Miocene 

(approximately 24 to 20 Ma) intrusive, extrusive, and 

sedimentary rocks, and by Quaternary alluvium. The 

Newberry Mountains Wilderness Study Area is 

underlain predominantly by Miocene volcanic and 

sedimentary strata, which surround several hills of 

Mesozoic plutonic rocks. The plutonic rocks locally 

contain small pendants of Mesozoifc metavolcanic 

rocks. The plutonic rocks and the Miocene strata are 

intruded by volcanic dikes of rhyolitic to intermediate 

composition, located mostly in the eastern part of the 

Newberry Mountains Wilderness Study Area.

The belt of Miocene strata and associated 

intrusive rocks continues east of Kane Wash where it 

underlies the northern and northeastern parts of the 

Rodman Mountains Wilderness Study Area. The 

southern two-thirds of the study area is underlain 

primarily by Mesozoic plutonic rocks. Miocene 

conglomerate and Pleistocene (approximately 0.6 Ma) 

basalt depositionally overlie the plutonic rocks in the 

central and northwestern parts of the study area.

The Miocene rocks in both study areas were 

strongly faulted and tilted moderately toward the 

southwest during intense regional northeast extension 

that was contemporaneous with early Miocene 

volcanism and sedimentation. Granitic rocks exposed 

along the north flank of the Newberry Mountains were

Al
Daggett

NEWBERRY MOUNTAINS

WILDERNESS STUDY

AREA (CDCA-206)

RODMAN MOUNTAINS ,, WILDERNESS STUDY/u^-H 

AREA (CDCA-207) \^ )

Lavic Dry

SIDEWINDER 

MOUNTAIN

/ \ Emerson 

k VDry Lake 

\^ ^

MelvilleX ) 

Dry Lake K

1. Index map showing location of the Newberry Mountains and Rodman Mountains 

Wilderness Study Areas.

A2
strongly crushed and sheared during this extensional 

episode. Subsequent deformation of the region after 

early Miocene time has resulted from right-lateral 

movements along the Camp Rock and Calico faults 

(fig. 2).

Mining and prospecting within the central Mojave 

Desert region have occurred intermittently since the 

1860's. There is no record of mineral production from 

either the Newberry Mountains or Rodman Mountains 

Wilderness Study Areas, but numerous prospects within 

and near these areas have revealed occurrences of 

gold, silver, copper, iron, barium, and manganese. All 

of these commodities have been mined in nearby 

ranges that are geologically similar to the Newberry 

and Rodman Mountains. In particular, silver has been 

produced in the Calico Mountains approximately 10 to 

15 mi northwest of the Newberry Mountains; gold, 

silver, and copper have been mined in the Ord and Fry 

Mountains southwest of the Newberry and Rodman 

Mountains; and iron ore has been mined at Iron Ridge 

and on adjacent hills southeast of the Rodman 

Mountains (fig. 1). Nonmetallic materials, including 

clays, gravel, volcanic cinders, and boron- and 

strontium-bearing minerals, also have been produced 

from the surrounding region.

Mineral Resources and Potential for Undiscovered 

Resources

There are no identified mineral resources within 

either the Newberry Mountains or Rodman Mountains 

Wilderness Study Areas. However, on the basis of 

geologic and geochemical evidence and the distribution 

of known mineral occurrences, there is moderate 

potential for undiscovered gold and silver resources in 

the Newberry Mountains Wilderness Study Area; and 

there is moderate potential for undiscovered lode 

copper, gold, and silver resources and low potential for 

undiscovered placer gold resources in the Rodman 

Mountains Wilderness Study Area (fig. 2).

Newberry Mountains Wilderness Study Area

An east-trending zone crossing the west margin 

of the Newberry Mountains Wilderness Study Area 

(zone A on fig. 2) has a moderate potential for 

undiscovered gold and silver resources. This zone 

contains intersecting east- and north-trending faults 

that cut Miocene strata and locally juxtapose them 

against Mesozoic plutonic rocks. The combined 

presence of altered rocks, veins, geochemical 

anomalies for gold and silver, and a mine with a 

history of minor gold production (Azucar mine, 0.7 mi 

west of the study area) supports a moderate potential 

for undiscovered mineral resources; the zone also 

coincides with a linear aeromagnetic anomaly.

A broad zone of altered rocks that straddles the 

east margin of the study area has a moderate potential 

for undiscovered silver resources (zone B on fig. 2). 

This area consists mostly of Miocene extrusive and 

intrusive rocks of rhyolitic to andesitic composition 

that are locally enriched in secondary potassium 

feldspar. The combined presence of abundant Tertiary 

intrusions, potassium-feldspar alteration, and barium 

and silver geochemical anomalies supports a moderate

potential for undiscovered mineral resources. In terms 

of geologic setting, rock alteration, and geochemical 

anomalies, this area is similar to mineralized areas of 

the Calico Mountains to the northwest, where silver is 

found in barite-rich veins associated with Miocene 

intrusive rocks and potassium-feldspar alteration.

Rodman Mountains Wilderness Study Area

Moderate potential for undiscovered gold, silver, 

and copper resources is ascribed to a zone at the 

southwest corner of the Rodman Mountains Wilderness 

Study Area (zone C on fig. 2). An examination of 

several prospects in this zone indicates potentially 

significant occurrences of copper, gold, and silver 

within veins and shear zones cutting plutonic rocks. 

Moderate potential for undiscovered gold, silver, and 

copper resources is also assigned to a second area in 

the north-central part of the study area (zone D on fig. 

2) where anomalous geochemical abundances of copper 

and silver in a quartz vein and stream-sediment 

concentrates suggest that significant mineral 

concentrations might be present. Low potential for 

undiscovered placer gold resources is assigned to a 

small area near the northeast corner of the study area 

(zone E on fig. 2), where terrace gravels locally 

contain an anomalous amount of gold.

INTRODUCTION 

Location and Physiography

The Newberry Mountains (CDCA-206) and 

Rodman Mountains (CDCA-207) Wilderness Study 

Areas occupy neighboring mountain ranges in the 

central Mojave Desert region 10 to 30 mi southeast of 

Barstow, Calif, (fig. 1). The study areas lie 1 to 5 mi 

south of Interstate Highway 40 and the Atchison, 

Topeka, and Santa Fe Railroad, and are directly east 

of a well-maintained unpaved county route, Camp 

Rock Road. Both study areas are located in dry, 

sparsely vegetated mountainous terrane.

The mineral survey of the Newberry Mountains 

Wilderness Study Area encompassed 27,964 acres of 

very rugged terrain with a total relief of about 3,000 

ft. The sinuous crest of the Newberry Mountains, with 

summit elevations ranging from 3,300 to 5,100 ft, 

passes northeastward through the center of the study 

area. Several deep canyons are incised into the 

northern flank and eastern end of the range. These 

canyons emerge onto alluvial fans near the margins of 

the study area. The relatively gently sloping south 

flank of the Newberry Mountains contains several 

smaller canyons that are tributaries of Kane Wash, a 

northeast-flowing ephemeral stream that separates the 

Newberry Mountains from the Rodman Mountains to 

the southeast.

The Rodman Mountains Wilderness Study Area 

contains about 16,900 acres of moderately rugged 

terrane on the northern flank of the Rodman 

Mountains. Relief is slightly less than in the Newberry 

Mountains, totalling about 2,600 ft. Elevations 

increase southward from approximately 2,400 ft at the 

north margin of the study area to 5,000 ft near the 

south margin. Steep slopes and badlands topography

A3
116°50' 116°45' 116°40'

34° 50'

34045- _ NEWBERRY MOUNTAINS WILDERNESS STUDY AREA (CDCA-206) \ RODMAN MOUNTAINS .WILDERNESS STUDY -> AREA (CDCA-207)

& M/C Au,Ag,Cu s

ZONE E 

placer

34°40

4 MILES

Figure 2. Map showing geology and mineral resource potential of the Newberry Mountains and Rodman Mountains 

Wilderness Study Areas.
EXPLANATION

Area with moderate mineral resource potentialArea with low mineral resource potential but with some indication 

of resource-forming processes

See Appendix 1 for definition of levels of mineral resource potential and certainty of assessment

X^g Mine with identified resources of volcanic cinders 

Commodities

Ag Silver 

Au Gold 

Cu Copper

Volcanic cinders

Geologic map units

Qa Alluvium (Holocene and Pleistocene)

Qb Basalt (Pleistocene)

Qbc Basalt cinders (Pleistocene)

Ti Fine-grained intrusive rocks (Miocene)

TVS Volcanic and sedimentary rocks (Miocene)

Kmg Monzogranite (Cretaceous)

Jsg Syenogranite (Jurassic?)Jqm Quartz monzonite (Jurassic)

Jd Diorite (Jurassic)J"E mv Metavolcanic rocks (Jurassic or Triassic)MzPzms Metasedimentary rocks (Mesozoic or Paleozoic)pCgn Gneiss (Precambrian)

Contact

Fault-Dotted where concealed; arrows indicate sense of

lateral slip; bar and ball on downthrown side 

Newberry Mountains detachment fault (Dokka, 1980, 1986)--

Dotted where concealed; sawteeth on upper plate

Mine or prospect without identified resources-Numbers refer to tables 1 and 2 Placer gold occurrence indicated by stream-sediment geochemistry-Number

refers to table 2

Figure 2. Continued.
dominate the northern part of the study area, but 

relatively gentle slopes prevail in the southern half of 

the area. One large area of gentle slopes is underlain 

by Pleistocene basalt flows that erupted near the south 

edge of the study area and flowed northwest to Kane 

Wash.

Access within the Newberry Mountains and 

Rodman Mountains Wilderness Study Areas is largely 

limited to foot travel. The margins of the areas can 

be reached by several dirt roads and jeep trails that 

originate from Camp Rock Road and from a paved 

road adjacent to Interstate Highway 40 east of 

Newberry Springs. Chief among these are a gas 

pipeline service road following Kane Wash and other 

dirt roads along the south and east margins of the 

Rodman Mountains Wilderness Study Area. 

Unimproved jeep trails extend up several canyons in 

the western and eastern parts of the Newberry 

Mountains Wilderness Study Area.

Previous Studies

Gardner (1940) and Tucker and Sampson (1940) 

were the first to map and describe the geology and 

mineral resources of the region in detail. The mines 

and mineral deposits of the region later were described 

by Wright and others (1953). A series of unpublished 

reports prepared for the Southern Pacific Railroad 

presented additional geologic mapping and mineralresource evaluations (Anctil, 1956; Dorsey, 1956a, 

1956b; Kojan, 1956; Stejer and Olcott, 1956). The U.S. 

Geological Survey mapped the geology of several 15- 

minute quadrangles that include the Newberry and 

Rodman Mountains (Dibblee, 1964a, 1964b, 1970; 

Dibblee and Bassett, 1966). Hawkins (1976) mapped an 

area astride the Camp Rock fault that extends into the 

west end of the Newberry Mountains Wilderness Study 

Area. Nason and others (1979) described Miocene 

volcanic rocks in the Newberry Mountains. Dokka 

(1980, 1983, 1986), Dokka and Glazner (1982), and 

Dokka and Woodburne (1986) described the Cenozoic 

tectonic history of the region and presented geologic 

maps of the Newberry Mountains area. Sanner (1985) 

mapped Miocene volcanic and sedimentary rocks in the 

northeastern Rodman Mountains. Both wilderness 

study areas are included in regional National Uranium 

Resource Evaluation studies conducted for the U.S. 

Department of Energy (Leedom and Kiloh, 1978; High 

Life Helicopters, Inc., 1980). Vredenburgh (1980) 

summarized the geology and mineral resources of both 

study areas and surrounding areas in an unpublished 

U.S. Bureau of Land Management report.

Procedures and Sources of Data

Field and laboratory studies conducted between 

1983 and 1985, as well as previous reports and public 

documents, provided data for the conclusions of this 

report. General format and terminology follow the 

guidelines of Goudarzi (1984).

The U.S. Bureau of Mines reviewed literature, 

mining-claim records, and production records, and 

inspected mines, prospects, claims, and mineralized 

areas in and near the study areas. Rock samples 

collected from prospects and mineralized areas and 

alluvium collected from selected drainages were 

analyzed for elements of possible economic 

significance. These data were used to determine past 

and present mining and mineral exploration activities 

and to characterize mineral occurrences within and 

immediately adjacent to the study areas (Sabine, 1985; 

Kuizon, 1985).

The U.S. Geological Survey compiled a 1:48,000- 

scale geologic map covering both study areas, largely 

on the basis of detailed (l:24,000-scale) mapping 

conducted during the present investigation (B.F. Cox, 

unpub. data, 1986). A generalized version of this 

geologic map is shown on figure 2. Geologic 

quadrangle maps (Dibblee, 1964a, b, 1970; Dibblee and 

Bassett, 1966) were used as general references during 

field work and compilation of the map. Previous 

mapping southwest of the Camp Rock fault (Weber, 

1963; Hawkins, 1976; and Karish, 1983) and northeast 

of the Calico fault (Sanner, 1985) is incorporated in 

simplified form. Many of the major structural 

features on the map, particularly the Kane Springs 

fault and Newberry Mountains detachment fault, were 

previously identified by Dokka (1980, 1986). Altered 

rocks potentially related to hydrothermal alteration or 

mineralization were identified from field observations 

and by inspection of Landsat multispectral-scanner 

images (fig. 3). Veins, altered rocks, and heavymineral concentrate samples from active stream 

channels were analyzed so that chemical variations 

reflecting concentrations of ore minerals could be 

identified (fig 4; Detra and Kilburn, 1985; B.F. Cox, 

unpub. data, 1986). The geophysical survey of the 

study areas involved compilation and interpretation of 

gravity and aeromagnetic maps based on both previous 

and new field measurements (figs. 5 and 6). The 

geologic, geochemical, and geophysical data were 

evaluated along with the information obtained by the 

U.S. Bureau of Mines to assess the potential for 

undiscovered mineral resources in the two study areas.

Acknowledgments

E.A. Rodriguez and R.L. Morin of the U.S. 

Geological Survey assisted with the geological and 

geophysical field studies. Geochemical analyses of 

rock samples collected by the U.S. Geological Survey 

were performed by J.G. Crock, L. Bradley, P.H. 

Briggs, T.L. Fries, T.P. Frost, and B. Libby. Personnel 

of the U.S. Bureau of Land Management Barstow 

Resource Area Office provided much helpful 

information, aerial photographs, and logistical support; 

special thanks to Daryl Albiston, Chris Rush, Ken 

Schulte, and Tim Smith. Thanks also to Don and Ruth 

Mulligan for information about the Flying M 

Association property (table 2).

A6
116°50' 116°45 116°40'

34°50

34°45' -

Boundary of Wilderness 

Study Area; NM is 

Newberry Mountains; RM 

is Rodman Mountains

Area of limonitic minerals

Figure 3. Map showing areas of altered rocks in the Newberry Mountains and Rodman 

Mountains Wilderness Study Areas.

A7
APPRAISAL OF IDENTIFIED RESOURCES

by Charles Sabine and Lucia Kuizon, 

U.S. Bureau of Mines

Field Work and Analytical Methods

In 1983, U.S. Bureau of Mines personnel 

examined and evaluated mines and prospects in and 

adjacent to the Newberry Mountains and Rodman 

Mountains Wilderness Study Areas (Sabine, 1985; 

Kuizon, 1985). Twenty mines and prospects were 

examined (tables 1 and 2) and 51 rock samples and 5 

alluvial samples were collected. The alluvial samples 

were panned, concentrated on a Wilfley table 1 , and 

checked microscopically for gold and other heavy 

minerals. Samples were analyzed for copper, gold, 

lead, silver, tungsten, and zinc by various quantitative 

methods, including fire assay, inductively coupled 

plasma, and x-ray fluorescence. At least one sample 

from each prospect was analyzed for 40 elements by 

semiquantitative emission-spectrographic analysis.

Regional History of Mining and Mineral Exploration

Mineral exploration began over 100 years ago in 

the central Mojave Desert region. No mines with 

recorded production are located within either of the 

study areas, but there has been significant mineral 

production in neighboring ranges where geologic 

conditions are similar in some respects to those in the 

study areas. Iron, silver, gold, and copper have been 

the most noteworthy metallic mineral products of the 

surrounding region.

Iron deposits at Iron Ridge and west of Galway 

Dry Lake (fig. 1) were mined during the 1940's and 

early 1950's (Wright and others, 1953; Dibblee, 

1964b ). The iron ore consists of metasomatic bodies 

of magnetite and hematite situated along contacts 

between granitic rocks and metamorphosed limestone 

and dolomite pendants. Reserves at Iron Ridge have 

been estimated at 1.8 million tons of ore containing 

30-65 percent iron (Lamey, 1948). Two other iron 

prospects are located at the north end of the Fry 

Mountains (Dibblee, 1964b, site N) and at the north end 

of Ord Mountain (Weber, 1963). A contactmetasomatic tungsten occurrence also is present on 

the north flank of Ord Mountain (Weber, 1963).

In the Ord Mountains and Fry Mountains to the 

west and southwest of the Rodman Mountains, gold, 

silver, and copper minerals are associated with quartz 

veins and sheared rocks along north-trending faults and 

fissures that cut Mesozoic metavolcanic and plutonic 

rocks. Common gangue minerals are quartz, barite,

epidote, fluorite, and hydrous iron oxides. 

Approximately 2,000 tons of ore mined primarily for 

copper and gold were produced from the Ord Mountain 

area between 1917 and 1942 (Weber, 1963). Veins and 

shear zones in the Fry Mountains produced ore valued 

mainly for its gold content (Dibblee, 1964b, sites FK). Metavolcanic rocks similar to those that underlie 

much of the Ord Mountains are exposed between the 

two study areas in the southeastern Newberry 

Mountains and westernmost Rodman Mountains. These 

rocks have been explored at over 200 mining claims, 

including the Lucky Don Juan prospect and the former 

L & L mine, but no significant production has been 

recorded.

An historically important silver-mining district is 

located in the Calico Mountains region, 10 to 15 mi 

northwest of the Newberry Mountains (Weber, 1967). 

Silver occurs primarily in veins in Miocene extrusive 

and intrusive rocks; locally they form disseminated 

deposits in sedimentary rocks. Gangue minerals 

consist mostly of barite and jasper. Between 1892 and 

1896, 15 to 20 million ounces of silver were extracted 

from mines in the Calico Mountains (Harthrong, 

1983). Minor amounts of gold, copper, lead, and barite 

have been produced from the region.

The Calico Mountains lie within a southeasttrending belt of Tertiary precious-metal occurrences 

that extends from ranges near the Gar lock fault 

southeast to the Bullion Mountains (Gardner, 1980). 

The study areas lie along this trend, and several mines 

and prospects in the northeastern Rodman Mountains 

have been developed in search of silver and other 

minerals (Dibblee, 1964b, site L; 1966, site D). These 

include the Silver Bell mine, about 2 mi east of the 

Rodman Mountains Wilderness Study Area (fig. 1). 

However, there has been no recorded production of 

gold, silver, and base metals from Tertiary rocks in 

either the Newberry and Rodman Mountains.

Sites Examined for this Study

Twenty mines and prospects in and adjacent to 

the study areas were examined for this study (fig. 2). 

Information concerning these properties is given in 

tables 1 and 2.

Newberry Mountains Wilderness Study Area

Eleven mines and prospects in and near the 

Newberry Mountains Wilderness Study Area were 

examined for this study (table 1); seven are located 

within the study area. Only two properties, the 

Azucar mine (fig. 2, no. 2) and the Northrup prospect 

(fig. 2, no. 10), had mineral occurrences.

The Azucar mine, located about 0.7 mi west of 

the study area, explores a gold-bearing quartz vein

Any use of trade names is for descriptive purposes 

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

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

A8
Table I Mines and prospects in and adjacent to the Newberry Mountains Wilderness Study Area (CDCA-206) 

[Asterisk (*) indicates location outside study area]

Map no.

1

Name

Prospect

Summary

Gray andesite. No evidence of mineralization

Workings 

and production

Twenty-ft-deep vertical

Sample and resource data

One sample; no significant mineral values.

Azucar mine

10

Prospect 

Prospect

Prospect

Copenhagen 

West prospect

Prospect

Prospect

Prospect

Northrup 

prospect

Prospect

or alteration.

Milky quartz vein, 1 ft thick, along fault in 

quartz monzonite and diorite. Vein strikes 

north, curving to northeast, dips 50° to 55° 

E.

Fanglomerate composed of andesite and other 

volcanic rock fragments. No evidence of 

mineral ization.

Two vertical veins of brecciated calcite 

within andesite. One body 300 ft long, 

10-40 ft thick, relief 80 ft; other body 

150 ft long, 5-35 ft thick, relief 50 ft.

Dark gray diorite cut by thin dikes of 

iron-oxide-stained granite with segregations 

of white quartz. No evidence of mineralization.

White to gray lapilli tuff. No evidence of 

mineral ization.

Colluvium composed of volcanic rock fragments. 

No evidence of mineralization.

Iron-oxide-stained light-gray felsite. No 

evidence of mineralization.

Contact, iron-oxide-stained light-gray to 

pale-reddish-purple felsite on west and 

dark brown metamorphosed volcanic breccia 

on east. No evidence of mineralization.

Northwest-trending vein of psilomelane, pyrolusite, and calcite, 1 in. to 1 ft thick and 

6 ft long, in volcanic breccia. Outcrops 

are obscured by colluvium. Locality is 

adjacent to a northwest-trending fault.

White lapilli tuff. No evidence of 

mineralization.

shaft.

Vein explored by two trenches 

and an inclined shaft said to 

be 135 ft deep with 120 ft of 

drifts (Wright and others, 

1953), an adit that is caved 

55 ft from the portal, two 

pits, and a trench. U.S. 

Bureau of Mines files indicate 

6 oz of gold were recovered 

from 20 tons of ore in 1941.

Twenty-ft-long adit.

One cut at end of larger 

vei n.

Two trenches, 20 and 14 

ft long.

One pit.

Eleven samples; three samples from the vein 

contain 0.017-0.082 oz/ton gold and 

0.046-0.151 oz/ton silver. Samples from 

other workings contain no significant 

mineral values.

One sample; no significant mineral values.

Four samples; no significant mineral values 

Occurrence is too small to be considered a 

source of lime or decorative stone.

Two samples; no significant mineral values.

One sample; no significant mineral values.

One 20-ft-long adit, ruin One sample; no significant mineral values.

of a dwelling. Adit may 

have been driven to 

develop a small spring.

Two cuts, 55 and 15 ft long. Three samples; no significant mineral 

Several hundred tons removed values, 

for road fill during the 

1950's (Dibblee and Bassett, 

1966).

Two small pits.

One bulldozer scraping, 45 by 

20 ft.

One pit.

One sample; no significant mineral values.

One sample from the vein contained 

49 percent MnO, 2.4 percent Fe^, 

3.0 percent Si02 , 1.3 percent A1 2 0 3 , 

and 0.56 percent I^O. A spectrographic 

analysis indicates more than 10 percent 

barium. The occurrence is too small to be 

a manganese resource.

One sample; no significant mineral values.

A9
Table 2--Mines, prospects, and mineralized sites in and adjacent to the Rodman Mountains Wilderness Study Area (CDCA-207) 

[Asterisk (*) indicates location outside study area; underlining indicates property containing resources or possible resources]

Map no. Name Summa ry

Workings 

and production Sample and resource data

12* Kane Wash Pendant of metasedimentary rocks including 

prospect marble and tactite in quartz monzonite. 

Area has been sheared and intruded by 

dikes. No metallic minerals were observed. 

Similar geology does not occur within the 

study area.

13 Fort Cady Road Shear zone in andesite breccia containing 

No. 1 prospect calcite, chalcedony, copper minerals, and 

stilbite, a zeolite mineral. The shear 

zone is 5 ft wide, strikes N. 35° E., 

and dips 73° NW. The andesite breccia 

zone is over 500 ft wide and 1,500 ft long. 

It is truncated to the south and east by 

the Calico fault.

14 Fort Cady Road Quartz vein in shear zone in granitic rock 

No. 2 prospect strikes N. 10° W. and dips 50° NE.; ranges 

from 0.2 to 0.5 ft thick, and is exposed 

for 25 ft.

15 Alluvial sample Stream terrace deposit overlying basalt and

site andesite. Gravel deposit ranges to 4 ft thick 

and contains about 80 percent granitic clasts.

16 Box Canyon Monzogranite near Calico Fault. Prospect 

prospect was noted by Kojan (1956), but not found 

during the U.S. Bureau of Mines field 

examination. Area was sampled as part of 

a uranium survey (Leedom and Kiloh, 1978).

17 Maralin No. 5 Altered siliceous andesite dike 2.8 to 4.0 ft 

prospect thick in granitic rock contains chrysocolla, 

limonite, quartz, chlorite, epidote, and 

magnetite. The dike is sheared along contact, strikes N. 5° W., dips 75° SW., and 

can be traced by float for about 1,000 ft.

18* Red Top Flat Cinder cone is composed of red and black 

mine scoria and basalt fragments, and is

partially breached. The cone is 300 ft high 

and covers 80 acres.

19 Valley prospect Quartz vein as thick as 0.9 ft strikes north

and dips 70° W. along contact between granitic 

country rock and porphyritic dike. Vein 

contains limonite pseudomorphs and boxwork, 

chalcopyrite, chrysocolla, and manganese 

dendrites. It can be traced by float for 

125 ft between two pits. The granite contains 

sericite veinlets, brecciated feldspar, and 

minor magnetite and apatite.

20* Flying M Gold occurs in Quaternary alluvial fan 

Association deposits ranging from 2 to 33 ft thick 

claim group above granitic bedrock (Latker, 1979). These 

(formerly known deposits do not extend into the study area, 

as Camp Rock Two shear zones occur in an adit. One shear 

Mine) zone composed of limonite, gouge, and altered 

granitic rock is 0.15 to 0.5 ft thick, 35 ft 

long, strikes N. 15°-30° E., and dips 70° 

SE. The other is composed of white clay 

gouge 0.4 to 0.9 ft thick, 50 ft long, 

strikes N. 80° E. and dips 58° NW.

21 Moonlight Barite vein as thick as 1.0 ft strikes

prospect N. 45° E., dips 90° , and contains quartz

with liroonite, chrysocolla, and other copper 

minerals. Vein not observed beyond shaft. 

Altered quartz monzonite country rock 

shows albitization and minor sericitization 

and kaolinization. Hornblende and biotite 

have been altered to epidote and chlorite. 

Minor amounts of magnetite, apatite, and 

sphene were also found.

One 22-ft-long adit, one 25- 

ft-deep inclined shaft, two 

pits, one open cut, and 

numerous trenches.

One 12-ft-long adit.

One 23-ft-long adit, two 

open cuts.

Nofle.

None.

Seven-ft-deep pit.

Twelve samples of marble, tacite, gneiss, 

and dike rock were collected. One sample 

contains 0.01 oz/ton gold; three samples 

contain 0.2-0.3 oz/ton silver. Four 

samples of tactite contain 0.03 percent 

W03 . Samples taken by Dorsey (1956b) 

contained minor gold, silver, and tungsten.

One chip sample has no significant mineral 

values.

One chip and one select sample of the 

quartz vein contain trace and 0.3 oz/ton 

silver and 0.011 percent and 0.60 percent 

copper. Two chip samples of altered 

granitic rock in shear zone have no 

significant mineral values. A sample 

taken by Dorsey (1956b) contained trace 

gold and 0.1 oz/ton silver.

One reconnaissance pan sample of alluvium 

contains 0.0165 or/yd j gold. Total 

alluvium volume probably is about 

300,000 yd 3 . Exploration may reveal 

gold resources.

One chip sample contained 1 ppm U-jOg, 

and 12.7 ppm, 1.4 ppm, and 3.3 ppm of 

equivalent thorium, uranium and potassium 

(Leedom and Kiloh, 1978).

Two chip samples of the dike contain 

0.5 oz/ton silver and 0.56 percent 

copper, and 0.024 percent copper.

A quarry on the south face 

have been mined since the 

1950's. An unknown amount 

of volcanic cinder was 

produced. About 12,000 tons 

have been produced since 1982 

by current operators; future 

production is estimated at 

12,000 tons/year.

Two pits 6 ft and 4 ft deep.

Trenches, test pits, and 

one 295-ft-long adit in 

bedrock with 15-ft-deep 

winze and two small stopes 

10 ft and 12 ft high.

A vertical shaft 22 ft deep.

Estimated reserves are 12 million tons of 

volcanic cinder suitable for lightweight 

aggregate and soil conditioner.

Two select samples; one contains 0.3 oz/ 

ton gold and 0.95 percent copper, the 

the other contains 0.04 oz/ton gold, 

0.8 oz/ton silver, and 0.40 percent 

copper.

One pan sample of alluvium on granitic 

bedrock contains 0.0026 or/yd3 gold 

and trace garnet. Two chip samples 

of shear zones in adit contain 

1.96 oz/ton gold, 0.1 oz/ton silver, 

0.1 percent copper; and 0.01 oz/ton gold, 

1.3 oz/ton silver, and 0.1 percent copper. 

Owners reported 26.5 ft averaging 0.0203 

oz/yd3 gold in one drill hole. Additional 

exploration may reveal gold resources.

One select vein sample contains 0.04 oz/ 

ton gold, 0.1 oz/ton silver, 0.74 percent 

copper, and 26.7 percent barium.

A10
within granitic rocks. U.S. Bureau of Mines files indicate 6 oz of gold were recovered from 20 tons of ore 

in 1941. Sample data from surface exposures (table 1) 

and the lack of significant recorded production suggest 

that mineral resources of economic grade are not 

likely to exist at the Azucar mine. However, the 

property could not be fully evaluated because 

underground workings were inaccessible.

The Northrup prospect is the only property 

located within the study area that contains a mineral 

occurrence. A 6-in-wide vein of manganese-oxide 

minerals (psilomelane and pyrolusite) and calcite lies 

within volcanic breccia and trends northwest parallel 

to a nearby fault (fig. 2, no 10). Other manganiferous 

veins within and near the study area have been 

described previously. At the Black Raven prospect, 

outside the study area about 1 mi north-northeast of 

the Northrup prospect, veins containing manganeseoxide minerals and black calcite occupy a fault zone in 

volcanic rocks (Trask, 1950, p. 193). Manganese-oxidebearing veins have also been reported within 

brecciated granite near the northwest corner of the 

study area (SW^ sec. 7, T. 8 N., R. 1 E.,) (Dorsey, 

1956a). Additional veins containing manganese-oxide 

minerals were observed during this study. None of the 

manganiferous veins within and near the study area are 

large enough to contain resources of manganese under 

present or foreseeable future market conditions.

Three alluvial samples collected from drainages 

with placer claims in the northwestern and 

southwestern parts of the study area contained only 

traces of gold.

Sand and gravel is plentiful in and near the study 

area and has been extracted mainly for use in highway 

construction from numerous pits north and east of the 

study area. Sources outside the study area should 

satisfy local and regional demand in the foreseeable 

future.

Stone has been produced from four quarries 

outside the northeast end of the study area. During 

the 1950's, light-gray felsite was quarried for road 

metal from two pits 1.5 mi southwest of Newberry 

Springs (fig. 2, no. 8). Outcrops of similar rock extend 

southward into the study area. Two active quarries 1.7 

and 2.0 mi southeast of Newberry Springs exploit a 

body of bright red porphyritic dacite or quartz latite. 

This type of rock is not found in the study area. 

During August, 1986, the Santa Fe Railroad began site 

development for a ballast quarry to be located 0.4 mi 

north of the study area in NW^s SWV sec. 5, T.8N., 

R.3E. Rocks at the quarry site consist mostly of 

extrusive andesite and dacite; similar rocks are 

widespread in the study area.

Rodman Mountains Wilderness Study Area

Nine mines and prospects and one placer gold 

occurrence in and near the Rodman Mountains 

Wilderness Study Area were examined for this study 

(table 2). There are no active mines within the study 

area. However, the Red Top Flat mine (fig. 2, no. 18) 

was producing volcanic cinder in 1984 and contains 

approximately 12 million tons of reserves that lie 

entirely outside the study area. The Flying M Association claim group (fig. 2, no. 20) was being explored for

placer and lode gold in 1984; the mineral occurrences 

at this property do not extend into the study area.

Three prospects in the southwestern part of the 

study area expose gold-bearing quartz and barite veins, 

and a siliceous dike (fig. 2, nos. 17, 19, and 21). The 

veins are discontinuous and the dike is poorly 

exposed. Resources were not identified due to the 

limited surface exposures, but further study of these 

prospects is warranted.

An alluvial sample from a stream-terrace deposit 

near the east margin of the study area (fig. 2, no. 15) 

contams an anomalous gold concentration of 0.0165 

oz/yd . Placer gold has not previously been 

recognized in this area. The total volume of alluvium 

within this deposit probably is about 300,000 yd3 , and 

additional terrace gravels are present nearby. 

Sampling was not adequate to determine average gold 

values, but the high concentration of gold in the single 

reconnaissance sample suggests that more detailed 

sampling might delineate placer resources at this site.

Conclusions

No mineral resources were identified within 

either of the study areas. Manganiferous veins within 

the Newberry Mountains Wilderness Study Area are too 

small to constitute mineral resources under present or 

foreseeable future market conditions. Occurrences of 

lode gold, silver, and copper in the southwestern part 

of the Rodman Mountains Wilderness Study Area, and 

of placer gold near the east margin of the study area, 

warrant further study.

ASSESSMENT OF MINERAL RESOURCE POTENTIAL

By Brett F. Cox, Andrew Griscom, James E. Kilburn, 

Gary L. Raines, and Daniel H. Knepper, Jr., 

U.S. Geological Survey

Geology

The Newberry and Rodman Mountains are 

underlain chiefly by Jurassic and Cretaceous plutonic 

rocks and by Miocene volcanic and sedimentary rocks 

(fig. 2). The plutonic rocks locally contain pendants of 

gneiss, metasedimentary rocks, and metavolcanic 

rocks. The region was disrupted by normal faulting in 

middle Cenozoic time and by strike-slip faulting in 

late Cenozoic time.

Rock Units

Outcrops of prebatholithic rocks are relatively 

sparse in the region, and none were mapped in the 

Rodman Mountains Wilderness Study Area. A small 

pendant of Precambrian gneiss lies astride the west 

margin of the Newberry Mountains Wilderness Study 

Area. Metasedimentary rocks of Paleozoic or early 

Mesozoic age apparently are absent from both study 

areas, but a small body of marble crops out in Kane 

Wash between the study areas. Mesozoic metavolcanic 

rocks, termed the Ord Mountain Group by Gardner

All
(1940), form small bodies in the southwestern and 

northeastern parts of the Newberry Mountains 

Wilderness Study Area and a large pendant exposed 

north and south of Kane Wash between the two study 

areas. These metavolcanic rocks consist 

predominantly of silicic to intermediate flows and 

shallow intrusive bodies. Recent geochronologic and 

regional stratigraphic studies suggest that the 

metavolcanic rocks are mostly Triassic but locally 

include Jurassic rocks (Karish, 1983; Walker, 1985).

Mesozoic plutonic rocks in the region represent a 

southward continuation of the Sierra Nevada 

batholith. The plutonic rocks underlie most of the 

Rodman Mountains Wilderness Study Area and form 

several isolated outcrops surrounded by Miocene rocks 

and Quaternary alluvium in the Newberry Mountains 

Wilderness Study Area. Four main plutonic lithologies 

are present (fig. 2; plutonic rock nomenclature after 

Streckeisen, 1976). First, dark-gray diorite, including 

minor quartz diorite, forms numerous small bodies that 

locally intrude gneiss and metavolcanic rocks and that 

are in turn intruded by younger plutons. Several 

masses of diorite are present in the northwestern part 

of the Newberry Mountains Wilderness Study Area. 

Second, medium-gray coarse-grained quartz monzonite 

underlies a large area including the western third of 

the Rodman Mountains Wilderness Study Area. The 

quartz monzonite is also abundant in the Ord 

Mountains and Fry Mountains southwest of the Camp 

Rock fault. Locally, the quartz monzonite is intruded 

by north-trending dikes composed of weakly 

metamorphosed fine-grained mafic rocks (not shown on 

fig. 2). The third type of plutonic rock consists of 

leucocratic syenogranite, which is particularly 

abundant in the Newberry Mountains Wilderness Study 

Area. Along the north flank of the Newberry 

Mountains, this rock unit consists of colorful, pink, 

coarse-grained rocks that are strongly fractured and 

brecciated; by contrast, the two outcrops on the south 

flank of the range are generally finer grained, drab 

gray or tan, and relatively unfractured. Finally, lightgray, medium-grained monzogranite forms an 

extensive north-trending belt that includes the eastern 

third of the Rodman Mountains Wilderness Study 

Area. Similar rocks are locally exposed along Kane 

Wash south of the Newberry Mountains Wilderness 

Study Area.

Dating by the Ar40/Ar39 method in the Fry 

Mountains (Karish, 1983) indicates that the quartz 

monzonite unit and rocks resembling those in the 

diorite unit are Jurassic in age and that the monzonite 

unit is Late Cretaceous in age. The age of the 

syenogranite in the Newberry Mountains is uncertain, 

but similar rocks in the east-central Mojave Desert 

have yielded Jurassic ages.

Miocene volcanic and sedimentary rocks overlie 

the batholithic and prebatholithic rocks throughout 

most of the Newberry Mountains Wilderness Study 

Area and extend eastward across the northern end of 

the Rodman Mountains Wilderness Study Area. A lobe 

of Miocene strata that is largely hidden beneath flows 

of Pleistocene basalt extends southward across the 

central part of the Rodman Mountains Wilderness 

Study Area. The volcanic and sedimentary rocks are 

lithologically diverse (Dibblee, 1964a, b, 1970; Dibblee 

and Bassett, 1966; Cox, 1986), but in this report they

are consolidated into a single map unit (fig. 2). They 

consist of a lower stratigraphic sequence rich in 

volcanic rocks and an upper sequence composed mostly 

of sedimentary rocks.

The lower, volcanogenic, sequence forms most of 

the crest and north flank of the Newberry Mountains 

and also crops out in the northeastern part of the 

Rodman Mountains Wilderness Study Area. The lower 

part of this sequence consists mostly of extrusive 

rhyolite and volcanic debris-flow breccia and locally 

contains dikes and flows of andesite and dacite. These 

rocks are unconformably overlain by extrusive basalt, 

andesite, dacite, and rhyolite, with interlayered 

conglomerate, sedimentary breccia, and minor lapilli 

tuff. A basalt flow yielded an early Miocene (23.1±2.3 

Ma) potassium-argon age (Nason and others, 1979).

The upper sequence of volcanic and sedimentary 

rocks is largely restricted to the southern fringe of the 

Miocene outcrop belt, and its youngest parts lap 

depositionally onto pre-Cenozoic rocks along the 

northern edge of the Ord and Rodman Mountains. 

Unconformities are present within it and locally at its 

base. The sequence consists predominantly of 

conglomerate, sedimentary breccia, and pebbly 

sandstone, and it also contains minor amounts of 

pumiceous air-fall tuff, as well as a distinctive layer 

of ash-flow tuff near Kane Wash, which Glazner and 

others (1986) have correlated with the Peach Springs 

Tuff of Young and Brennan (1974). The ash-flow tuff 

near Kane Wash has been dated at 21+1.0 Ma by the 

fission-track method (Dokka, 1980). Radiometric ages 

for the Peach Springs Tuff and correlative units in 

other ranges seem to indicate an age of 19 Ma 

(Glazner and others, 1986).

Dikes of aphanitic to fine-grained porphyritic 

rocks intrude the lower sequence of volcanic and 

sedimentary rocks in the eastern part of the Newberry 

Mountains Wilderness Study Area and near the mouth 

of Box Canyon immediately northeast of the Rodman 

Mountains Wilderness Study Area. Most of these 

intrusions are rhyolitic to dacitic in composition, but 

dikes of andesite and basalt are also present in smaller 

amounts. In addition, geophysical studies (this report) 

suggest that a large Tertiary stock or plug is concealed 

beneath surficial rocks and sediments at the east end 

of the Newberry Mountains Wilderness Study Area and 

northwest end of the Rodman Mountains Wilderness 

Study Area. None of the Tertiary intrusive rocks 

within the Newberry Mountains have been dated 

radiometrically, but intrusive relations and 

compositional similarities with extrusive volcanic 

rocks in the range suggest that they are early Miocene 

in age. A large felsic intrusion at the southeast corner 

of the map area (fig. 2) yielded a potassium-argon age 

of approximately 24 Ma (R.K. Dokka, oral commun., 

1986).

Quaternary basalt flows and alluvium underlie a 

relatively small part of the two study areas. The 

basalt erupted from vents near the south boundary of 

the Rodman Mountains Wilderness Study Area and 

flowed northwest to Kane Wash. A cinder cone that 

formed in the vent area is the site of an active mining 

operation; however, this cinder cone lies outside the 

study area. Previous studies have shown that the 

basalt is alkalic (Wise, 1969, table 1, sample 6) and was 

erupted during the Pleistocene, approximately 0.6 Ma

A12
(W. B. Bull, oral commun., 1986). A northwesttrending fault that cuts the basalt near the cinder cone 

(fig. 2) may have served as a conduit for the eruptions. 

Quaternary alluvium in the two study areas 

consists of sand and gravel deposited in stream 

canyons and on alluvial fans. The deposits range 

widely in age, but only one generalized unit is shown 

on the map.

Geologic Structure

In common with adjacent areas of the Mojave 

Desert to the north and east, the Newberry and 

Rodman Mountains were subjected to an intense 

episode of northeast crustal extension 

contemporaneous with early Miocene volcanism and 

sedimentation between about 23 and 21 Ma (Dokka, 

1986; Dokka and Woodburne, 1986). The main 

structural features of this deformational event have 

been established by previous work (Dokka, 1980, 1983, 

1986; Dokka and Glazner, 1982). Geologic mapping 

conducted during the present study confirms the main 

structural interpretations of this previous work, while 

clarifying stratigraphic relations within the Miocene 

section and providing more detailed information on the 

nature of Miocene and younger faulting. The main 

structural features produced by early Miocene crustal 

extension are (1) the Newberry Mountains detachment 

fault (Dokka, 1980, 1986; Dokka and Glazner, 1982) 

separating Miocene strata from underlying plutonic 

rocks, (2) the Kane Springs fault (Dokka, 1980, 1986; 

Dokka and Glazner, 1982), which forms the abrupt 

southern boundary of the extensional complex, and (3) 

abundant north- and northwest-trending faults that cut 

Miocene strata and that locally cut pre-Cenozoic 

basement rocks.

The basal contact of the Miocene rocks was 

originally interpreted to be a major buttress 

unconformity with many thousands of feet of 

paleorelief (Dibblee, 1970, 1971), but more recently it 

has been shown to be a detachment fault that 

separates highly extended Miocene rocks in the upper 

plate from relatively unextended pre-Cenozoic rocks 

of the lower plate (Dokka, 1980; Dokka and Glazner, 

1982). Syenogranite on the footwall of the Newberry 

Mountains detachment fault is shattered in a zone of 

indurated, hematite-stained breccia and cataclasite 

several hundred feet thick. Cataclasis of the 

syenogranite is especially pronounced in the 

northwestern part of the Newberry Mountains 

Wilderness Study Area. By contrast, the two outcrops 

of syenogranite on the south flank of the Newberry 

Mountains are not cataclastically deformed, and the 

westernmost of these two outcrops locally is 

depositionally overlain by the lower unit of Miocene 

volcanic and sedimentary rocks. Therefore, these 

southern two outcrops of plutonic rocks apparently lie 

within the upper plate of the detachment fault, as 

implied by Dokka and Glazner (1982, fig. 3). 

Hematite that coats fractures in the breccia and 

cataclasite probably was introduced by hydrothermal 

fluids; however, no other evidence of alteration or 

mineralization was observed in association with the 

detachment fault.

The extended terrane is bounded on the south by

the east-trending Kane Springs fault, which has been 

interpreted as a right-lateral strike-slip or oblique-slip 

transform fault that marks an abrupt transition to a 

region of no extension south of the fault (Dokka, 1980, 

1983, 1986; Dokka and Glazner, 1982). The Kane 

Springs fault is well exposed in the northern and 

northeastern parts of the Rodman Mountains, where it 

appears from the map pattern to dip gently to steeply 

northward. The fault is largely concealed along the 

north side of Kane Wash, where it is overlain by gently 

dipping, relatively unfaulted conglomerate, sandstone, 

and ash-flow tuff that form the largely post-kinematic 

upper sequence of Miocene volcanic and sedimentary 

rocks (Dokka, 1980; Dokka and Glazner, 1982). 

Geologic mapping for the present study revealed that 

the segment of the fault along Kane Wash locally has 

been reactivated as a south-vergent thrust or reverse 

fault, possibly related to late Cenozoic development of 

the Camp Rock and Calico fault systems. No evidence 

of mineralization was observed in association with the 

Kane Springs fault.

The Miocene volcanic and sedimentary rocks are 

tilted and extended along many north- and northwesttrending, moderately to steeply dipping, normal and 

oblique-slip faults that have their east sides displaced 

relatively downward. Mapping for this study revealed 

that these faults are particularly abundant in the 

north-central and northeastern parts of the Newberry 

Mountains. Some of the faults are restricted to the 

upper plate of the Newberry Mountains detachment 

fault, whereas others cut and offset the detachment 

fault (Dokka and Glazner, 1982). In the central and 

northern parts of the Newberry Mountains Wilderness 

Study Area, arcuate northwest-trending faults 

systematically truncate and offset north-trending 

faults (fig. 2). These arcuate faults terminate 

southeastward against a north-trending fault that is 

antithetic, that is, its east side is displaced relatively 

upward rather than downward, causing the 

reappearance of pre-Cenozoic rocks and the Newberry 

Mountains detachment fault in the northeastern part 

of the study area. Both this antithetic fault and the 

Newberry Mountains detachment fault are intruded by 

silicic dikes, indicating that intrusive activity 

continued after movement on the detachment fault 

and high-angle faults had ended. Many of the northand northwest-trending faults are lined with veins 

composed of calcite and manganese-oxide minerals; 

these veins are discussed in the following section on 

rock alteration and veining.

The late Cenozoic tectonic development of the 

Newberry and Rodman Mountains region has been 

dominated by right-lateral displacements on the Camp 

Rock and Calico faults. These two structures belong 

to a larger family of northwest-trending wrench faults 

that traverse the Mojave Desert region (Jennings, 

1975). The Camp Rock and Calico faults offset the 

Kane Springs fault and other structures related to 

early Miocene extensional deformation. Based on this, 

and on observed offsets of pre-Cenozoic rock units, 

previous workers have proposed that the total 

displacements on the Camp Rock and Calico faults 

near the Newberry and Rodman Mountains are 

approximately 1 to 2.5 mi and 5 to 6 mi, respectively 

(Hawkins, 1976; Miller, 1980; Dokka, 1983). These 

estimates are generally confirmed by geologic and

A13
geophysical evidence from this study. Although the 

faults are post-early Miocene, the more precise onset 

of faulting is uncertain (Dokka, 1983). The Camp Rock 

and Calico faults have both been active during 

Quaternary time, and the Calico fault has been active 

recently, as indicated by scarps in Holocene alluvium 

east of the Newberry Mountains.

Rock Alteration and Veins

Pre-Cenozoic and Cenozoic hydrothermal 

activity potentially related to mineralizing systems 

has locally involved the following processes in and near 

the Newberry and Rodman Mountains Wilderness Study 

Areas: (1) albitization of plutonic rocks, (2) potassium 

metasomatism of Miocene volcanic rocks, (3) argillic 

alteration of Miocene basalt, (4) concentrations of 

limonitic minerals, and (5) formation of veins. 

Propylitic alteration of Miocene andesite and basalt is 

present locally, but it is generally minor and is not 

included in the following discussion.

Jurassic quartz monzonite is pervasively 

albitized to grayish-white rock within a large irregular 

zone that includes the southwest corner of the Rodman 

Mountains Wilderness Study Area (fig. 3). The 

affected rocks are strongly jointed and form angular 

outcrop surfaces. Primary potassium feldspar is 

almost totally replaced and primary plagioclase 

(andesine to sodic labradorite) is partly replaced by 

albite or sodic oligoclase in as much as 75 percent of 

the quartz monzonite in this zone. Associated 

mineralogical effects include partial to complete 

alteration of hornblende and biotite to actinolite, 

epidote, and sphene. Small areas of albitized quartz 

monzonite are common north of the zone mapped on 

figure 3, but these are largely restricted to the 

immediate vicinity of joints and fractures.

Similar albitization affected Jurassic plutonic 

rocks over a broad region of the central and eastern 

Mojave Desert (Alien and others, 1983; Karish, 1983; 

Miller and others, 1985; Fox, 1985). The albitization 

may have been caused by a late Mesozoic episode of 

hydrothermal activity that has been identified in part 

of this region on the basis of anomalous oxygen-isotope 

ratios in Jurassic and older rocks (Solomon and Taylor, 

1981). The possible relation between albitization and 

regional patterns of mineralization is uncertain and 

warrants future study.

Several mineral occurrences near the southwest 

corner of the Rodman Mountains Wilderness Study 

Area lie near the margins of the zone of albitized 

quartz monzonite and may be genetically related to 

it. Four prospects (fig. 2 and table 2, nos. 17, 19, 20, 

and 21) expose veins and altered rocks containing 

copper minerals and anomalous concentrations of gold 

and silver. Albitized quartz monzonite sampled 

farther east and about 0.5 mi south of the study area 

contains anomalous concentrations of copper, lead, and 

molybdenum (fig. 4). Similar albitized plutonic rocks 

are present in the deep root zone of the Yerington 

porphyry-copper deposit in western Nevada (Carten, 

1981). The albitized quartz monzonite and associated 

mineral occurrences near the southwest corner of the 

Rodman Mountains Wilderness Study Area may 

likewise have formed deep within a hydrothermal

circulation system.

Potassium metasomatism of variable intensity 

affects many volcanic rocks in a large area that is 

approximately coextensive with the belt of Miocene 

intrusions near the east end of the Newberry 

Mountains Wilderness Study Area (fig. 3). Field 

observations suggest that alteration is most abundant 

and intense in the northeastern half of this area. 

Similar alteration is associated with intrusive rocks in 

a smaller area directly northeast of the Rodman 

Mountains Wilderness Study Area (Sanner, 1985, p. 

20). The rocks most affected consist of intrusive 

rhyolite to dacite; however, extrusive basalt, andesite, 

and dacite located near the intrusive bodies also are 

similarly altered to varying degrees. Typically, the 

altered intrusive rocks are grayish red with light-gray 

mottles and are strongly enriched in potassium, 

containing I^O concentrations ranging from 7.6 to 

11.6 percent. By comparison, unaltered intrusive rocks 

within the altered zone are light to medium brown, 

gray, or pinkish gray and contain less than 5 percent 

K2O. The excess potassium in the altered rocks 

resides in secondary potassium feldspar that replaces 

both phenocrystic and ground mass plagioclase. The 

groundmass commonly also contains abundant 

secondary quartz and fine-grained opaque material. 

Some of the altered intrusive rocks are strongly 

brecciated, possibly in part owing to hydrothermal 

processes.

Similar potassium metasomatism affects 

Miocene volcanic and sedimentary rocks in the 

southeastern Cady Mountains 15 to 20 mi east of the 

Newberry Mountains (Hewett, 1964; Glazner, 1980; 

Chapin and Glazner, 1983; Bartley and Glazner, 1985) 

and in the southwestern Calico Mountains about 15 mi 

to the northwest (Darby Fletcher, oral commun., 

1986). Two aerial gamma-ray spectrometer surveys 

(U.S. Bureau of Land Management, unpub. data, 1978; 

High Life Helicopters, Inc., 1980) indicate potassium 

concentrations 2 to 3 times higher than regional 

background values in each of these areas in the 

Newberry, Cady, and Calico Mountains, and also in a 

fourth area near Mt. General about 6 mi northwest of 

Barstow. Data from these surveys were used to help 

define the limits of the altered zone in the Newberry 

Mountains, as mapped on figure 3.

The strongest aerial potassium anomaly in the 

central Mojave Desert region is centered on the area 

of historical silver mining in the Calico Mountains 

(Weber, 1967; Dibblee, 1970). Similarly, the potassium 

anomaly near Mt. General is located near a prospect 

containing a silver occurrence (Bowen, 1954, pi. 2). 

Broad zones of potassium metasomatism are spatially 

associated with epithermal ore deposits in other 

regions, such as those surrounding the silver-base 

metal deposits in the Creede mining district of 

southwest Colorado (Bethke and others, 1976; P.B. 

Barton, Jr., oral commun., 1986). These comparisons 

suggest that potassium metasomatism may be a useful 

guide when prospecting for epithermal mineral 

deposits in the central Mojave Desert region. Areas 

that contain extensive potassium-feldspar alteration 

but that have little or no mining history, such as the 

northeastern Newberry Mountains and southeastern 

Cady Mountains, may warrant further investigation 

for evidence of mineralization. Evidence of possible

A14
34° 50' 

EX

Materia

o Non

Con

or 

EXPLANATION

Element Symbols

a Alte

A Vein

RODMAN MO

WILDERNESS 

ARFA (CDC

La Lanthanum

Mo Molybdenum

Pb Lead

Sb Antimony

Sn Tin

Ag Silver

As Arsenic

Au Gold

* Ba Barium

Bi Bismuth

Cd Cadmium *Sr Strontium

Cu Copper W Tungsten

Hg Mercury Zn Zinc

* Barium and strontium anomalies shown only for concentrate samples, 

but are also common in manganese-bearing veinsFigure 4. Map showing geochemical sample sites and geochemical anomalies in the N

Mountains and Rodman Mountains Wilderness Study Areas,
epithermal silver mineralization at the east end of the 

Newberry Mountains Wilderness Study Area is 

discussed in the geochemistry section of this report.

A zone of argillic alteration within basalt lies 

along a large northwest-trending fault in the 

southwestern part of the Newberry Mountains 

Wilderness Study Area (fig. 3). The altered basalt 

within this zone consists of friable light-gray rock that 

contrasts sharply with indurated dark-gray basalt 

exposed immediately outside the zone. The zone of 

alteration cuts sharply across layering in a thick 

sequence of basalt flows. An unidentified clay mineral 

has replaced plagioclase crystals and lines vesicles in 

the rock. The altered basalt is a possible target for 

future mineral exploration because it lies at the 

southeast end of a belt of mineralized rocks defined by 

quartz and calcite veins, geochemical anomalies, and a 

gold-silver prospect at the Azucar mine (zone A on fig.

2).

Bedrock outcrops containing anomalous 

concentrations of limonitic minerals (ferric-oxide, 

ferric-sulfate, and ferric-carbonate minerals) were 

identified on Landsat multispectral-scanner images 

using a color-ratio compositing technique described by 

Rowan and others (1974). These areas were field 

checked, and four areas within or near the two study 

areas showed evidence of hydrothermal alteration (fig.

3). The boundaries of the areas containing limonite 

are only approximately located because of the small 

scale (1:800,000) of the original Landsat images. A 

fifth area containing limonite was identified during 

geologic mapping for this report.

One area of limonitic alteration straddles the 

western border of the Newberry Mountains Wilderness 

Study Area, directly east of the Azucar mine, and 

coincides with part of mineral resource zone A. Rocks 

near the center of this area contain calcite veins in 

propylitically altered andesite and basalt. A second 

area lies within metavolcanic rocks west of the 

Rodman Mountains Wilderness Study Area and directly 

south of the former L & L mine. A third area lies 

within quartz monzonite in the southwestern part of 

the Rodman Mountains Wilderness Study Area and is 

included within mineral resource potential zone C. 

Chloritization of mafic minerals and albitization and 

weak sericitization of feldspar were observed in this 

area. A fourth area lies directly east of the Rodman 

Mountains Wilderness Study Area. This area was field 

checked in its eastward extension, outside the mapped 

area of figure 2 and directly south of Silver Bell 

mine. There, andesitic and basaltic rocks show signs 

of weak propylitic alteration and contain veins of 

black calcite. The fifth area of limonitic alteration 

forms a narrow northwest-trending band within quartz 

monzonite in the north-central part of the Rodman 

Mountains Wilderness Study Area, and lies within the 

northwestern part of mineral resource potential zone 

D.

Several types of veins are present in rocks of the 

study areas. Pre-Cenozoic rocks locally contain 

monomineralic veins of white or colorless quartz. 

Such veins were observed in plutonic rocks located at 

the Azucar mine and in the southwestern and northcentral parts of the Rodman Mountains Wilderness 

Study Area (zones A, C, and D on fig. 2). Quartz veins 

in these areas and in neighboring ranges to the south

and west locally contain anomalous amounts of gold, 

silver, and copper.

The Miocene rocks exposed throughout the 

Newberry Mountains Wilderness Study Area and in the 

northern part of the Rodman Mountains Wilderness 

Study Area contain veins of calcite, manganese-oxide 

minerals, chalcedony, and opal. Some of these veins 

contain minor amounts of quartz, which typically 

originated by recrystallization of fibrous chalcedony. 

Most abundant are manganiferous veins composed 

mostly of calcite and manganese-oxide minerals 

including pyrolusite and psilomelane. Locally, these 

veins contain anomalous concentrations of silver and 

several other metals (see geochemistry section). 

Manganiferous veins are most abundant along northand northwest-trending faults and fractures that cut 

moderately tilted Miocene strata in the central and 

northeastern Newberry Mountains and northeastern 

Rodman Mountains. The richest concentrations of 

manganese-oxide minerals were observed adjacent to a 

northwest-trending fault in the general vicinity of the 

Northrup prospect (fig. 2, no. 10). Manganiferous veins 

were not seen in the relatively undisturbed flat-lying 

strata that form the upper sequence of volcanic and 

sedimentary rocks along Kane Wash and in the 

northeastern Rodman Mountains. Sparse veinlets of 

manganese-oxide minerals are also present in 

brecciated pink syenogranite in the northwestern 

Newberry Mountains.

Manganiferous veins in the upper-plate rocks 

typically consist of "black calcite" (Hewett and 

Radtke, 1967) darkened by disseminated fine-grained 

inclusions of manganese-oxide minerals (1 to 10 

percent by volume). Layers of black calcite commonly 

alternate with layers of either white calcite or 

relatively pure manganese-oxide minerals, resulting in 

prominent banding parallel to vein margins. 

Chalcedony and quartz are present in some of the 

veins, where they commonly have formed interstitial 

to, or as replacements of, black calcite that 

crystallized earlier. Barite crystals locally are 

associated with the chalcedony and quartz and rarely 

form thin monomineralic barite veins. The largest 

manganiferous veins are several fee.t thick and several 

hundred feet long.

The manganiferous veins probably were 

precipitated by ascending low-temperature 

hydrothermal fluids. Episodes of vein brecciation and 

shearing commonly alternated with episodes of vein 

growth; this, together with apparent restriction of the 

veins to the older tilted rock sequences, suggests that 

the veins developed synchronously with faulting of the 

upper-plate rocks. Thus, the episode of hydrothermal 

activity that produced the manganiferous veins may 

have been coeval with the brief period of early 

Miocene crustal extension that occurred between 

about 23 and 21 Ma.

Grayish-white aphanitic veins consisting of opal 

or chalcedony and variable amounts of fine-grained 

calcite and other carbonate minerals were observed 

along several faults near the south and west margins of 

the Newberry Mountains Wilderness Study Area. These 

veins contain little or no field or geochemical evidence 

of metallic mineralization. They apparently are quite 

young, as some of them cut older Quaternary alluvium 

at the northwest corner of the Newberry Mountains

A16
Wilderness Study Area.

Geochemical Studies

Methods

Reconnaissance geochemical studies were 

conducted to help determine the nature, location, and 

intensity of ore-forming processes in the study areas. 

Samples included altered rocks, veins, and heavymineral concentrates from stream sediments. Sandy 

alluvium was reduced to a nonmagnetic heavy-mineral 

concentrate by hand panning, heavy-liquid immersion, 

and electromagnetic separation. Each concentrate 

sample was split into two parts: one for 

spectrographic analysis and the other for mineralogical 

studies. All rock and concentrate samples were 

analyzed for 30 elements using a semiquantitative 

emission-spectrographic method (Grimes and 

Marranzino, 1968). Vein samples rich in carbonate and 

manganese-oxide minerals were diluted with a mixture 

of aluminum oxide, potassium carbonate, and silica 

prior to spectrographic analysis. Some samples 

collected from veins and altered rocks were also 

analyzed for gold by an atomic absorption method 

(Ward and others, 1969) and for tungsten by an 

induction-coupled plasma method. The analytical 

results obtained for the stream-sediment concentrate 

samples were presented by Detra and Kilburn (1985). 

The locations of all vein, rock, and concentrate 

geochemical samples are shown on figure 4; anomalous 

concentrations of ore-forming and pathfinder elements 

are indicated by element symbols adjacent to the 

sample sites.

Summary of Results

Anomalous concentrations of metallic and 

nonmetallic elements in altered rocks, veins, and 

stream-sediment concentrate samples confirm that 

both study areas contain mineralized rocks. Arsenic, 

barium, gold, molybdenum, and silver geochemical 

anomalies are clustered within two zones near the 

west and east ends of the Newberry Mountains Wilderness Study Area; in addition, widespread 

manganiferous veins in the western and central parts 

of the study area contain anomalous concentrations of 

copper, lead, molybdenum, silver, tungsten, and zinc. 

The data indicate that epithermal mineralization of 

variable intensity has occurred in much of the 

Newberry Mountains Wilderness Study Area. Barium 

and tungsten anomalies are widespread in the Rod man 

Mountains Wilderness Study Area and are locally 

accompanied by bismuth, copper, lanthanum, lead, 

molybdenum, and silver anomalies. These geochemical 

anomalies are attributed to widespread quartz veins, 

to minor small bodies of mineralized skarn, and to 

lanthanum-bear ing heavy minerals disseminated in 

quartz monzonite.

Newberry Mountains Wilderness Study Area

An east-trending arcuate zone astride the west

margin of the Newberry Mountains Wilderness Study 

Area contains arsenic, cadmium, gold, mercury, 

molybdenum, silver, and tungsten geochemical 

anomalies (zone A on fig. 2; fig. 4). The most intense 

anomalies are in stream-sediment concentrates, 

including a silver anomaly of 1,000 parts per million 

(ppm) near the Azucar mine and a 700-ppm gold 

anomaly in the central part of the zone. An anomalous 

concentration of arsenic (22 ppm) was detected in 

argillically altered basaltic rocks near the east end of 

the zone. Concentrations of 500 ppm arsenic, 650 ppm 

molybdenum, and 25 ppm tungsten were measured in 

veinlets of manganese-oxide minerals within dacite 

flow-breccia directly north of the area of argillized 

basalt. A concentration of limonitic minerals was 

identified from Landsat images where zone A crosses 

the western boundary of the study area (fig. 3). Two 

samples of black calcite were collected from veins in 

this limonitic area: one sample contains 20 ppm 

tungsten; the other contains 37 ppm arsenic, 1.9 ppm 

cadmium, 1.2 ppm mercury, and 7 ppm molybdenum. 

Directly west of the limonitic area, U.S. Bureau of 

Mines personnel found small amounts of gold and silver 

in a quartz vein at the Azucar mine (table 1).

Although the geochemical anomalies detected in 

veins and altered rocks provide clear indications of 

hydrothermal activity and localized mineralization 

within zone A, the type and intensity of mineralization 

is uncertain because of ambiguities in the 

interpretation of the stream-sediment-concentrate 

geochemistry. The concentrate samples that contain 

gold and silver anomalies were collected in small 

drainage basins underlain largely by coarse-grained 

Miocene conglomerate. The rock detritus in the 

conglomerate was derived from pre-Cenozoic plutonic 

and metavolcanic rocks located near Ord Mountain, 

where there are abundant veins containing gold, silver, 

and copper minerals in a gangue of quartz and barite 

(Weber, 1963). Veins and metasomatic replacement 

bodies containing scheelite are also located near Ord 

Mountain. The age of mineralization in the Ord 

Mountain area has not been determined, but it may be 

Mesozoic and therefore older than the Miocene 

conglomerate in the Newberry Mountains. For these 

reasons, all of the anomalous concentrations of 

barium, bismuth, copper, gold, lead, silver, tin, and 

tungsten found in concentrates near the south and west 

margins of the Newberry Mountains Wilderness Study 

Area are suspect, and may merely reflect the detrital 

mineralogy of conglomeratic rocks derived from 

mineralized rocks near Ord Mountain.

As an additional complication, the geochemical 

anomalies in rocks and veins within zone A may reflect 

the combined effects of two unrelated episodes of 

mineralization. At the Azucar mine, monomineralic 

quartz veins are present in Mesozoic plutonic rocks, 

whereas the eastern two-thirds of the zone contains 

veins of calcite and manganese-oxide minerals in 

argillically and propylitically altered Miocene volcanic 

rocks. Quartz veins similar to those at the Azucar 

mine are common in pre-Cenozoic rocks over a broad 

region south of the Newberry Mountains, and they may 

be Mesozoic, rather than Tertiary, in age. Because 

vein occurrences of gold and silver in zone A have 

been found only at the Azucar mine, and because the 

gold and silver detected in stream-sediment

A17
concentrates may be recycled from Miocene conglomerate, the existence of epithermal gold or silver 

occurrences in Miocene rocks in the eastern part of 

zone A remains in doubt.

A cluster of geochemical anomalies found in 

stream-sediment concentrates at the east end of the 

Newberry Mountains Wilderness Study Area includes 

numerous barium anomalies (10,000 ppm or greater) 

accompanied in many drainages by lead (3,000 to 

30,000 ppm) and strontium (1,500 to 7,000 ppm) 

anomalies, and in three drainages by silver anomalies 

(1, 20, and 50 ppm). Microscopic examination of 

concentrate samples showed abundant barite as the 

source of the barium anomalies; the strontium 

anomalies probably reflect impurities contained within 

barite. The barite may be derived from abundant 

manganese-oxide-bearing veins and sparse, narrow, 

monomineralic barite veins that are present in this 

part of the Newberry Mountains. Conglomerate 

containing detritus of pre-Cenozoic rocks is absent 

from this area, so most of the stream-sediment 

anomalies probably can be attributed to in situ 

mineralization. The distribution of the anomalies 

correlates generally with the outcrop area of Miocene 

intrusive rocks (fig. 2) and with the zone of widespread 

potassium metasomatism (fig. 3) near the northeast 

end of the Newberry Mountains. Several samples 

collected from veins and altered rocks in this area 

contain anomalous concentrations of arsenic, 

cadmium, copper, lead, molybdenum, silver, and zinc.

The spatial association of barium, lead, and 

silver geochemical anomalies, silicic intrusive rocks, 

and potassium metasomatism also occurs in 

mineralized parts of the Calico Mountains about 15 mi 

to the northwest. However, in the Calico district, 

veins and disseminated deposits contain silver minerals 

in a gangue of abundant jasper and barite and minor 

amounts of manganese-oxide minerals (Weber, 1967). 

Veins in the Newberry Mountains consist mostly of 

calcite and manganese-oxide minerals; thick veins of 

barite and jasper containing silver minerals have not 

been observed. Therefore, the analogy with the Calico 

district is limited to gross similarities of geochemistry 

and rock alteration and is not reinforced by more 

direct evidence of mineralization.

Veins composed of manganese-oxide minerals and 

manganiferous black calcite were sampled in the 

western, central, and northern parts of the Newberry 

Mountains Wilderness Study Area. These veins locally 

contain anomalous amounts of various elements, with 

the maximum concentrations as follows: arsenic, 500 

ppm; barium, greater than 10,000 ppm; copper, 210 

ppm; lead, 250 ppm; manganese, greater than 10,000 

ppm; molybdenum, 650 ppm; silver, 39 ppm; strontium, 

3,200 ppm; tungsten, 210 ppm; and zinc, greater than 

2,000 ppm. Atomic-absorption analyses did not detect 

gold in any of the vein samples. Anomalous 

concentrations of silver and other metals in epithermal 

veins of manganese-oxide minerals and black calcite 

have been noted in numerous mining districts in the 

western United States (Hewett, 1964; Hewett and 

Radtke, 1967), and in some cases the manganese-oxide 

minerals have actually been mined as silver ore 

(Cousins, 1984; Heyl and others, 1973, p. 593-594). 

None of the vein-related geochemical anomalies in the 

Newberry Mountains Wilderness Study Area are large

enough to imply mineral-resource potential. However, 

the anomalies indicate widespread low-grade 

epithermal mineralization that previously was not 

recognized in the study area.

Rod man Mountains Wilderness Study Area

The stream-sediment-concentrate geochemical 

data for the Rodman Mountains Wilderness Study Area 

indicate anomalous concentrations of several 

elements, with the maximum concentrations as 

follows: barium, greater than 10,000 ppm; bismuth, 

1,000 ppm; copper, 200 ppm; lanthanum, 2,000 ppm; 

lead, 10,000 ppm; molybdenum, 30 ppm; silver, 10 ppm; 

and tungsten, 7,000 ppm. The barium and tungsten 

anomalies are abundant and widespread, whereas 

anomalous concentrations of other elements are more 

localized. Optical examination of the concentrate 

samples revealed that barite and scheelite are the 

sources of the barium and tungsten anomalies, 

respectively. Other common heavy minerals in the 

samples include rutile, sphene, anatase, apatite, 

andalusite, and zircon. Heavy minerals present in 

minor amounts include monazite, fluorite, tourmaline, 

and hematite. In addition, lead shot was identified as 

a contaminant in two of the three samples having 

anomalous lead concentrations.

By analogy with known occurrences of 

mineralized rocks within and near the study area (for 

example, see Weber, 1963), the minerals barite and 

scheelite, and the isolated bismuth, copper, 

molybdenum, and silver anomalies, probably are 

derived largely from widespread quartz veins in the 

quartz monzonite and monzogranite units. Skarn 

associated with small isolated masses of calcareous 

metasedimentary rocks engulfed by the plutonic rocks 

probably is the source of some of the tungsten, 

bismuth, and molybdenum anomalies; small inclusions 

of metasedimentary rock were observed at several 

locations, and the identification of the contactmetamorphic mineral andalusite in the heavy-mineral 

concentrates suggests that such inclusions may be 

fairly common.

A cluster of geochemical anomalies is associated 

with zone D in the north-central part of the study area 

(figs. 2 and 4). Sheared and mineralized quartz 

monzonite at a prospect near the northwest margin of 

the zone contains anomalous amounts of arsenic (24 

ppm), bismuth (182 ppm), copper (greater than 20,000 

ppm), lead (7,000 ppm), molybdenum (1,000 ppm) and 

silver (100 ppm). U.S. Bureau of Mines personnel found 

concentrations of copper and silver in a quartz vein at 

this same prospect (table 2, no. 14). A narrow 

northwest-trending band of limonite-stained quartz 

monzonite about 0.4 mi southwest of this prospect (fig. 

3) is slightly enriched in antimony (7 ppm) and 

molybdenum (10 ppm). Two stream-sediment 

concentrates collected near the center of zone D 

contained anomalous concentrations of bismuth (150 

ppm), lead (5,000 and 10,000 ppm), and copper (150 

ppm), in addition to barium (greater than 10,000 ppm) 

and tungsten (1,000 and 2,000 ppm). The bismuth, 

lead, and copper anomalies are suspect, however, 

because lead shot was identified in one of the two 

concentrate samples. Finally, a stream-sediment

A18
concentrate collected about 0.8 mi downstream and to 

the northeast of the zone contains an anomalous 

concentration of silver (10 ppm). This cluster of 

geochemical anomalies in rocks and stream-sediment 

concentrates indicates that hydrothermal processes 

locally caused some accumulation of silver, copper and 

other metals in zone D, although it is not clear from 

the geochemical data whether resources have 

accumulated anywhere in the zone. Several streamsediment concentrates collected within and near zone 

C at the southwest corner of the study area contain 

little evidence of mineralization, despite the presence 

of several prospects within the zone (table Ib, nos. 17, 

19, 20, 21).

Lanthanum anomalies are spatially associated 

with the quartz monzonite unit in the western part of 

the study area. Outcrops of Miocene conglomerate in 

the southeastern part of the study area are composed 

almost exclusively of detritus from the quartz 

monzonite unit. This may explain the two isolated 

lanthanum anomalies to the east of and downstream 

from the conglomerate outcrops. The lanthanum 

anomalies are attributed to monazite, a rare-earth 

phosphate mineral that was identified in the 

concentrate samples. In addition to lanthanum and 

other rare-earth elements, monazite typically contains 

substantial amounts of thorium (Clark and others, 

1966, table 24-5). Therefore, monazite may also be 

responsible for elevated thorium values (as much as 2 

to 3 times regional background) measured over the 

quartz monzonite unit by an aerial gamma-ray survey 

(High Life Helicopters, Inc., 1980, flight lines 16 and 

17). The monazite may be disseminated as an 

accessory mineral within the quartz monzonite, or it 

may occur in sparse pegmatitic lenses that were 

observed within the quartz monzonite. Although 

monazite can be an important ore mineral in certain 

geologic settings, occurrences in normal granitic rocks 

and pegmatite bodies are rarely concentrated enough 

to be viable sources of either rare-earth minerals or 

thorium. Therefore, no mineral-resource significance 

is inferred for monazite in the Rodman Mountains 

Wilderness Study Area.

Geophysical Studies

Gravity Survey

Gravity data for the vicinity of the Newberry 

and Rodman Mountains were obtained from published 

sources (Oliver and others, 1980; Roberts and others, 

1981) and were supplemented by 37 new measurements 

(Andrew Griscom, unpub. data, 1984). The combined 

data were converted to Bouguer gravity values, and 

then an isostatic residual gravity map was constructed 

to isolate that part of the gravitational field that 

arises from near-surface density distributions (fig. 5). 

Sources of gravity anomalies were evaluated by 

comparing the gravity map with the distribution of 

major rock units.

Local gravity highs of 5-8 milligals (mGals) 

amplitude are associated with dense Mesozoic 

metavolcanic rocks (fig. 5, anomalies I and II) and 

diorite (fig. 5, southwest part of anomaly III). The 

felsic Mesozoic granitic rocks, including the quartz

monzonite, monzogranite, and syenogranite units, have 

a low average density of 2.63 g/cm^ (14 samples) and 

produce gravity levels of about -22 to -28 mGals. The 

densities of the superimposed Miocene volcanic and 

sedimentary rocks must be lower than that of the 

granitic rocks by at least 0.2 and 0.3 g/cm , 

respectively. However, local gravity lows produced by 

the Miocene volcanic and sedimentary rocks amount to 

amplitudes of no more than -3 and -5 mGals, 

respectively, implying that the depth to pre-Cenozoic 

basement is everywhere less than 1,000 ft. Thus, the 

gravity data do not support major vertical offsets on 

normal faults bordering the tilted sections of Miocene 

rocks.

A gravity high (fig. 5, anomaly III) that extends 

northeastward across the northern boundary of the 

Newberry Mountains Wilderness Study Area is caused 

by a concealed body of relatively dense pre-Cenozoic 

rocks, probably either metavolcanic rocks or diorite. 

This gravity high is cut off to the northeast by the 

Calico fault at point D; a similar linear high at point 

D' (approximately 6 mi to the southeast along the 

fault) may be the offset extension of this gravity 

high. If so, this confirms the right-lateral strike-slip 

offset deduced for this fault from geology (Dokka, 

1983, table 1). Similar analysis of offset gravity 

patterns on each side of the Camp Rock fault suggests 

right-lateral offset of about 2.5 mi, also in 

approximate agreement with the geologically deduced 

offset (Dokka, 1983, table 1).

Aeromagnetic Survey

Contoured aeromagnetic maps are available for 

all of the Newberry Mountains Wilderness Study Area 

and for about 20 percent of the Rodman Mountains 

Wilderness Study Area and extend to the southwest and 

northwest of both areas (U.S. Geological Survey, in 

press). The data were collected in 1957 and 1958 along 

parallel flight lines trending northeast and spaced 0.25 

mi apart with a nominal altitude of 500 ft above 

ground. Contouring was done by hand and the Earth's 

main field was not removed. The main magnetic 

anomalies in and near the study areas are delineated 

on figure 6.

Comparison of the aeromagnetic map with the 

geologic map (fig. 2) indicates that large areas of 

Mesozoic metavolcanic rocks are moderately magnetic 

and produce anomalies of about 500 gammas (fig. 6, 

anomalies I and II), whereas the granitic rocks are at 

most weakly magnetic and rarely produce magnetic 

anomalies in excess of 100 gammas amplitude. In the 

Newberry Mountains Wilderness Study Area, Miocene 

intermediate and mafic volcanic rocks are relatively 

magnetic by comparison with interbedded sedimentary 

rocks and produce narrow linear magnetic highs, 

commonly less than 2,000 ft wide and 500 gammas in 

amplitude, that trend generally north or northwest 

parallel to the local structural trends in this region. 

These linear magnetic highs are terminated to the 

south by a steep south-sloping magnetic gradient (fig. 

6, anomaly IV) that reflects a boundary with less 

magnetic strata of the upper unit of volcanic and 

sedimentary rocks, which consist of conglomerate and 

silicic tuff without any mafic or intermediate volcanic

A19
116°55' 116°35' 116°25'

34°40

34°35

EXPLANATION

Gravity contours Hachured for closed lows; Roman numerals refer to 

gravity highs discussed in text; contour interval is 2 mGal

Fault Arrows show direction of relative movement

Gravity-anomaly axis offset by fault; letters A, B, C, and D refer to 

axes that correspond to axes A 1 , B 1 , C 1 , and D 1 on opposite side of 

fault

Boundary of Wilderness Study Area; NM is Newberry Mountains; RM is Rodman 

Mountains

Gravity station

Figure 5. feostatic residual gravity map of the Newberry Mountains and Rodman 

Mountains Wilderness Study Areas.

A20
116°50' 116°45' 116°40'

34°50 -

34°45' U

116°30'

10 MILES

EXPLANATION

Boundary of magnetic high or low Hachures point in direction of lower 

Jl / intensity of magnetic field; Roman numerals refer to anomalies discussed 

in text

Fault Arrows show direction of relative movement 

Discontinuity in magnetic contour pattern

__«._«, Axis of magnetic anomaly offset by fault; letters A, B, and C refer to 

axes that correspond to axes A 1 , B 1 , and C 1 on opposite side of fault

 ^ Boundary of Wilderness Study Area; NM is Newberry Mountains; RM is Rodman 

Mountains

2X X Mine or prospect; numbers refer to properties described in tables 1 and 2 

-$- Drill hole

Figure 6. Map showing aeromagnetic interpretation of the Newberry Mountains and Rodman 

Mountains Wilderness Study Areas.

A21
rocks. This steep magnetic gradient trends 

approximately east along the north side of Kane Wash 

and appears to be truncated against the Camp Rock 

fault. The apparent westward extension of the 

magnetic gradient (fig. 6, anomaly IV) is offset about

2.4 mi northwestward along the Camp Rock fault, in 

close agreement with the right-lateral displacement of

2.5 mi inferred from the gravity map. In addition, the 

correlation of linear magnetic highs on each side of 

this fault (fig. 6: anomaly axes A and B correspond to 

axes A' and B', respectively) suggests right-lateral 

offsets of approximately 2.8 mi each.

Two major magnetic features on the map appear 

to have their source rocks concealed by a thin cover of 

Miocene sedimentary and volcanic rocks. The first 

feature, a magnetic high that overlaps the north 

border of the Newberry Mountains Wilderness Study 

Area, is about 300 gammas in amplitude and 2 mi in 

source width (fig. 6, anomaly III). This anomaly 

correlates with the eastern part of the gravity high 

(fig. 5, anomaly III) described previously and is 

tentatively interpreted as a concealed mass of 

Mesozoic metavolcanic rocks because this unit appears 

to be the only one that produces both gravity and 

magnetic highs. The second feature is a major 

magnetic low (fig. 6, anomaly V) about -700 gammas in 

amplitude and 2-3 mi wide. The west border of this 

feature is located within the Newberry Mountains 

Wilderness Study Area and its eastern part is located 

within the Rodman Mountains Wilderness Study Area. 

The approximate outline of the source mass is shown 

on figure 6. The anomaly is caused by a relatively 

thick mass of reversely magnetized rock buried no 

more than 1,000 ft below the surface. Because of its 

reverse magnetization, the source mass is interpreted 

to be a Tertiary stock or plug. Since there is no 

accompanying gravity anomaly, the intrusion 

apparently is composed of silicic or intermediate 

rock. Geometric relations between the magnetic low 

and an associated polarization high on its north side 

indicate that the intrusion has a vertical extent of at 

least 1.5 mi.

Several mines and prospects near the two study 

areas are associated with geophysical anomalies; 

therefore, similar geophysical anomalies might serve 

as guides to other mineral occurrences. The former L 

& L mine and the Lucky Don Juan prospect (fig. 6) are 

both near the crests of gravity and magnetic highs 

(anomalies I and II of figs. 5 and 6) associated with 

metavolcanic rocks. Accordingly, the gravity and 

magnetic highs (anomaly III of figs. 5 and 6) at the 

northern border of the Newberry Mountains Wilderness 

Study Area may be similarly associated with mineral 

occurrences concealed beneath the Miocene volcanic 

and sedimentary rocks. The gravity and magnetic data 

indicate that the Tertiary and Quaternary units within 

the Newberry and Rodman Mountains Wilderness Study 

Areas are relatively thin, overlying pre-Cenozoic 

basement rocks at depths of less than 1,000 ft. Thus, 

any concealed mineral deposits in the basement rocks 

should be at sufficiently shallow depths to be of 

economic interest. A small magnetic low (fig. 6, 

anomaly VI) that occurs over the Camp Rock mine may 

be caused by local hydrothermal alteration that 

destroyed magnetite. Similar magnetic features have 

not been identified within that part of the Rodman

Mountains Wilderness Study Area covered by 

aeromagnetic data. A large magnetic high (fig. 6, 

anomaly VII) of 1,500 gammas amplitude is located 

over an alluviated valley at the southern border of the 

map area. This anomaly is associated with an outcrop 

of marble and a small body of magnetite-hematite 

scarn (Dibblee, 1964b). According to a U.S. Bureau of 

Land Management report (Vredenburgh, 1980), drilling 

near this magnetic high has delineated two large 

bodies of iron ore. No similar magnetic feature was 

identified within either study area. An east-trending 

discontinuity in the aeromagnetic contours that 

crosses the western border of the Newberry Mountains 

Wilderness Study Area (fig. 6, anomaly VIII) coincides 

with a zone of altered rocks, geochemical anomalies, 

and east-trending faults (zone A on fig. 2). The 

Azucar mine lies near the west end of this 

discontinuity.

Another feature of possible economic interest is 

the large reversed magnetic anomaly (fig. 6, anomaly 

V) that is interpreted to be a Tertiary intrusion. This 

intrusion, though concealed, could be a source of 

Tertiary epithermal mineralization.

Conclusions

General Summary

A review of regional mineral resource patterns 

indicates that the general vicinity of the Newberry and 

Rodman Mountains is characterized by three main 

types of mineral deposits. First, Tertiary rock 

sequences in the region locally contain epithermal vein 

and disseminated deposits of gold and silver, as 

exemplified by the Calico mining district northwest of 

the Newberry Mountains. These epithermal deposits 

typically contain only small amounts of copper and 

sulfide minerals and contain a high ratio of silver to 

gold. Second, the pre-Cenozoic rocks in ranges south 

and west of the Newberry and Rodman Mountains 

contain low-tonnage but locally rich vein deposits of 

gold, silver, and copper. Third, skarn deposits 

containing tungsten and iron minerals are present in 

several nearby ranges where plutonic rocks have 

intruded calcareous inetasedimentary rocks.

Despite the existence of these mineral deposits 

in nearby areas, there are no known deposits of gold, 

silver, copper, iron, or tungsten in either wilderness 

study area. In this final section, the mineral resource 

potential of the study areas, that is, the likelihood that 

undiscovered mineral resources are present, is assessed 

by integrating the pertinent evidence from geologic, 

geochemical, and geophysical studies and the local 

prospecting history. Areas having mineral resource 

potential are shown on figure 2. Definitions of levels 

of mineral resource potential and certainty of 

assessment are provided in appendix 1.

Two areas in the Newberry Mountains Wilderness 

Study Area have moderate potential, certainty level B, 

for epithermal precious-metal deposits: an area at the 

east end of the study area has potential for silver, and 

an area at the west end of the study area has potential 

for both gold and silver. Two areas in the Rodman 

Mountains Wilderness Study Area contain vein 

occurrences of precious and base metals, and both of

A22
these areas are assigned a moderate mineral resource 

potential, certainty level C, for gold, silver, and 

copper. Gold-bearing terrace gravels that occur 

locally in the Rodman Mountains Wilderness Study 

Area are assigned a low potential, certainty level B, 

for placer gold resources.

Large mappable bodies of metasedimentary rocks 

were not observed in either study area, and skarnrelated resources of iron or tungsten consequently are 

unlikely to be found in either area. Because the 

Miocene rock sequences in both areas lack fine-grained 

sedimentary rocks, sediment-hosted accumulations of 

boron, strontium, uranium, and bentonitic clay similar 

to those found in neighboring mountain ranges to the 

north and east are unlikely to be present in either 

study area. Leedom and Kiloh (1978) sampled 

Mesozoic plutonic rocks and Miocene volcanic and 

sedimentary rocks from the vicinity of the Newberry 

Mountains and Rodman Mountains Wilderness Study 

Areas and obtained uranium values that fall within 

normal background levels for the Mojave Desert 

region. No evidence of oil, gas, or geothermal energy 

resources was found in either wilderness study area.

Mineral Resource Potential of the Newberry Mountains 

Wilderness Study Area

An arcuate zone of altered, veined, and faulted 

rocks that crosses the west margin of the Newberry 

Mountains Wilderness Study Area (zone A on fig. 2) has 

a moderate resource potential, certainty level B, for 

epithermal deposits of gold and silver. This 

assessment is based on the following evidence: (1) 

geochemical anomalies in veins, altered rocks, and 

stream-sediment concentrates; (2) a local 

concentration of limonitic minerals astride the 

western border of the study area; (3) an aeromagnetic 

discontinuity that approximately coincides with zone 

A; and (4) minor recorded production of gold at the 

Azucar mine, which lies outside the study area near 

the west end of the zone. The supporting evidence is 

ambiguous, particularly regarding the eastern part of 

zone A, which lies within the study area. Several 

prominent anomalies for gold and silver were detected 

in heavy-mineral concentrates, but these anomalies 

may represent detrital material recycled from 

Miocene conglomerate, rather than epithermal 

mineralization within zone A. The gold-bearing quartz 

veins at the Azucar mine are located in plutonic rocks 

and may be Mesozoic in age. There is no direct 

evidence indicating that gold and silver have been 

introduced into the Miocene rocks that underlie the 

eastern part of zone A. Nevertheless, veins and 

altered volcanic rocks in the eastern part of the zone 

contain anomalous concentrations of arsenic and 

mercury, and this is a favorable indication that 

epithermal veins containing gold and silver could be 

present in the study area.

Zone B at the east end of the Newberry 

Mountains Wilderness Study Area has a moderate 

resource potential, certainty level B, for epithermal 

silver. Supporting evidence includes the following: (1) 

locally intense potassium metasomatism of Miocene 

volcanic rocks; (2) anomalous concentrations of 

barium, lead, and silver in stream-sediment

concentrates and anomalous concentrations of arsenic 

and silver in veins and altered rocks; (3) abundant 

exposed Miocene intrusions; and (4) an aeromagnetic 

anomaly indicating a large concealed Tertiary 

intrusive body that could have supplied heat for 

prolonged hydrothermal circulation, rock alteration, 

and epithermal mineralization. However, direct 

evidence of mineralization in the form of veins or 

disseminated occurrences containing silver minerals 

have not been found in the Newberry Mountains either 

by this study or by historical prospecting. 

Furthermore, large veins of barite and jasper such as 

those that host silver deposits in the Calico Mountains 

have not been observed in the Newberry Mountains 

region. Therefore, if epithermal silver deposits are 

present in zone B, they probably are comparatively 

small, low-grade, or are concealed at depth.

There also is evidence for widespread low-grade 

epithermal mineralization throughout much of the 

northern half of the Newberry Mountains Wilderness 

Study Area. This evidence consists of numerous veins 

of manganese-oxide minerals and manganiferous black 

calcite, some containing low concentrations of silver, 

copper, lead, molybdenum, zinc, and tungsten. 

However, these veins invariably are too small to be 

considered manganese resources, and the metal 

concentrations are too low to indicate any resource 

potential for silver or other metals.

Mineral Resource Potential of the Rodman Mountains 

Wilderness Study Area

Zones C and D in the southwestern and northern 

parts of the Rodman Mountains Wilderness Study Area 

have a moderate resource potential, certainty level C, 

for gold, silver, and copper. These zones contain 

prospects that expose quartz and barite veins and 

altered rocks, all of which contain copper minerals and 

anomalous concentrations of silver and, in some 

places, gold (zone C, table 2, sites 17, 19, 20, and 21; 

zone D, table 2, site 14). Zone C straddles an area of 

albitized plutonic rocks that may represent deepseated hydrothermal alteration contemporaneous with 

mineralization. Both zones contain areas with 

anomalous concentrations of limonitic minerals. Zone 

D is further delineated by anomalous concentrations of 

bismuth, copper, lead, and silver in stream-sediment 

concentrates collected within and downstream from 

the zone. However, the mineral occurrences in zones 

C and D are low grade and sparse, and no resources 

were identified. Stream-sediment geochemistry does 

not provide strong evidence of significant mineral 

concentrations in either zone. Any mineral resources 

that might exist within zones C and D probably would 

be limited to small deposits of gold, silver, and copper 

similar to those previously mined in the Fry and Ord 

Mountains areas to the south and west of the study 

area.

Zone E near the east margin of the study area 

has a low resource potential, certainty level B, for 

placer gold. A single panned sample of terrace 

alluvium (table 2, site 15) from the zone contained 

0.0165 oz/yd gold. The boundary of zone E is drawn 

to include both the sajnpled terrace deposit and 

neighboring terrace deposits of similar age. The

A23
anomalous concentration of gold in the reconnaissance 

sample may warrant additional geochemical studies of 

the terrace gravels in this area. However, the 

combined geologic and geochemical data for adjacent 

parts of the study area suggest that placer gold 

resources are unlikely to exist in zone E. The goldbearing stream terrace overlies Miocene volcanic and 

sedimentary rocks, but the gold probably was derived 

from plutonic rocks upstream on the southwest side of 

the Calico fault system. The plutonic rocks apparently 

are only weakly mineralized and probably do not 

contain sufficient amounts of gold to generate placer 

gold resources downstream in zone E. The anomalous 

placer gold concentration measured in zone E may 

have come from quartz veins in zone D, where some 

evidence of mineralization has been observed. If so, 

then zone D probably was subsequently displaced at 

least 0.5 mi from the gold-bearing terrace gravels by 

right-lateral displacement on the Calico fault, 

probably during late Pleistocene and Holocene time.

There is no potential for radioactive-mineral 

resources in the Rodman Mountains Wilderness Study 

Area based on currently available information. An 

aerial gamma-ray spectroscopy survey (High Life 

Helicopters, Inc., 1980) indicates anomalous 

concentrations of thorium and slightly anomalous 

concentrations of uranium over the outcrop belt of 

quartz monzonite in the western part of the study 

area. These anomalies probably are attributable to the 

rare-earth phosphate mineral monazite, which was 

identified in the stream-sediment concentrates from 

this area. The monazite probably is disseminated in 

the quartz monzonite or within pegmatitic bodies 

within the quartz monzonite. In either case, it is 

unlikely to be concentrated enough to constitute a 

resource for thorium, uranium, or rare-earth elements.

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A26
APPENDIX 1. Definition of levels of mineral resource 

potential and certainty of assessment

Mineral resource potential is defined as the 

likelihood of the presence of mineral resources in a 

defined area; it is not a measure of the amount of 

resources or their profitability.

Mineral resources are concentrations of naturally 

occurring solid, liquid, or gaseous materials in such 

form and amount that economic extraction of a commodity from the concentration is currently or potentially feasible.

Low mineral resource potential is assigned to 

areas where geologic, geochemical, and geophysical 

characteristics indicate a geologic environment where 

the existence of resources is unlikely. This level of 

potential embraces areas of dispersed mineralized rock 

as well as areas having few or no indications of 

mineralization. Assignment of low potential requires 

specific positive knowledge; it is not used as a catchall 

for areas where adequate data are lacking.

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 a reasonable chance for resource 

accumulation, and where an application of genetic and 

(or) occurrence models indicates favorable ground.

High mineral resource potential is assigned to 

areas where geologic, geochemical, and geophysical 

characteristics indicate a geologic environment 

favorable for resources, where interpretations of data 

indicate a high likelihood for resource accumulation, 

where data support occurrence and (or) genetic models 

indicating presence of resources, and where evidence 

indicates that mineral concentration has taken place. 

Assignment of high resource potential requires positive 

knowledge that resource-forming processes have been 

active in at least part of the area; it does not require 

that occurrences or deposits be identified.

Unknown mineral resource potential is assigned 

to areas where the level of knowledge is so inadequate 

that classification of the area as high, moderate, or

low would be misleading. The phrase "no mineral 

resource potential" applies only to a specific resource 

type in a well-defined area. This phrase is not used if 

there is the slightest possibility of resource 

occurrence; it is not appropriate as the summary 

rating for any area.

Expression of the certainty of the mineral 

resource assessment incorporates a consideration of (1) 

the adequacy of the geologic, geochemical, geophysical, and resource data base available at the time of 

the assessment, (2) the adequacy of the occurrence or 

the genetic model used as the basis for a specific 

evaluation, and (3) an evaluation of the likelihood that 

the expected mineral endowment of the area is, or 

could be, economically extractable.

Levels of certainty of assessment are denoted oy 

letters, A-D(fig.T).

A. The available data are not adequate to 

determine the level of mineral resource potential. 

Level A is used with an assignment of unknown mineral 

resource potential.

B. The available data are adequate to suggest 

the geologic environment and the level of mineral 

resource potential, but either evidence is insufficient 

to establish precisely the likelihood of resource occurrence, or occurrence and (or) genetic models are not 

known well enough for predictive resource assessment.

C. The available data give a good indication of 

the geologic environment and the level of mineral 

resource potential, but additional evidence is needed 

to establish precisely the likelihood of resource occurrence, the activity of resource-forming processes, or 

available occurrence and (or) genetic models are 

minimal for predictive applications.

D. The available data clearly define the geologic 

environment and the level of mineral resource 

potential, and indicate the activity of resourceforming processes. Key evidence to interpret the 

presence or absence of specified types of resources is 

available, and occurrence and (or) genetic models are 

adequate for predictive resource assessment.

U/A

UNKNOWN 

POTENTIAL

H/B

HlbH POTENTIAL

M/B

MODERATE POTENTIAL

L/B

LOW POTENTIAL

H/C

HIGH POTENTIAL

M/C

MODERATE POTENTIAL

L/C 1

LOW POTENTIAL

H/D

HIGH POTENTIAL

M/D

MODERATE POTENTIAL

L/D

LOW POTENTIAL

N/D

NO POTENTIAL

LEVEL OF CERTAINTY

Figure 7. Major elements of mineral resource potential/certainty classification.

A27
GEOLOGIC TIME CHART 

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

EON

Phanerozoic

Proterozoic

Archean

pre -Arc

ERA

Cenozoic

Mesozoic

Paleozoic

Late Proterozoic

Middle Proterozoic

Early Proterozoic

Late Archean

Middle Archean

Early Archean 

hean 2

PERIOD

Quaternary

Neogene 

Subperiod

Tertiary 

Paleogene 

Subperiod

Cretaceous

Jurassic

Triassic

Permian

Pennsylvanian 

Carboniferous

Periods 

Mississippian

Devonian

Silurian

Ordovician

Cambrian

 -(3800?)- -

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

_ _

AGE ESTIMATES 

OF BOUNDARIES 

(in Ma)

- 0.010 

- 1.7

- 24

oo

*J*J

_ fi£

- 96

_ 1"SQ

one

- 290

_ sen

- 410

^ 500

*jr \J

onn

- 1600

- 2500

oUUU

\j^\j\j

 dKKn 

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

informal time term without specific rank.

A28

GPO 785-048/48030