Mineral Resources of the Cinder Cones

Wilderness Study Area,

San Bernardino County, California

U.S. GEOLOGICAL SURVEY BULLETIN 1712-B

** '-/

Chapter B

Mineral Resources of the Cinder Cones

Wilderness Study Area,

San Bernardino County, California

By HOWARD G. WILSHIRE, JAMES G. FRISKEN, 

ROBERT C. JACHENS, and DOUGLAS V. PROSE 

U.S. Geological Survey

CLAYTON M. RUMSEY and AREL B. McMAHAN 

U.S. Bureau of Mines

U.S. GEOLOGICAL SURVEY BULLETIN 1712-B

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 Cinder Cones Wilderness Study 

Area, San Bernardino County, California.

U.S. Geological Survey Bulletin 1712-B

Bibliography included.

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

1. Mines and mineral resources California Cinder

Cones Wilderness. 2. Geology California Cinder Cones

Wilderness. 3. Cinder Cones Wilderness (Calif.) I.

Wilshire, Howard Gordon, 1926- . II. Series.

QE75.B9 No. 1712-B 557.3 s 86-600395

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

Bureau of Land Management Wilderness Study Areas

The Federal Land Policy and Management Act (Public Law 94-576, October 21, 

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

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

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

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

Cinder Cones Wilderness Study Area (CDCA-239), California Desert Conservation Area, 

San Bernardino County, California.

CONTENTS

Summary Bl 

Abstract 1

Character and setting 1

Identified resources 1

Mineral resource potential 3 

Introduction 3

Area description 3

Previous and present investigations 3 

Appraisal of identified resources 4

History and production 4

Mineral deposits 4 

Assessment of mineral resource potential 5

Geology 5

Geochemical studies 5

Geophysical studies 8

Conclusions 9 

References cited 9 

Appendix 1. Definition of levels of mineral resource potential and certainty of assessment 12

FIGURES

1. Index map showing location of the Cinder Cones Wilderness Study Area,San Bernardino County, 

California B2

2. Map showing the geology and mineral resource potential of the Cinder Cones Wilderness Study Area, 

San Bernardino County, California 6

3. Major elements of mineral resource potential/certainty classification 12

TABLE

1. Prospects in the Cinder Cones Wilderness Study Area Bll

MINERAL RESOURCES OF WILDERNESS STUDY AREAS: 

CENTRAL CALIFORNIA DESERT CONSERVATION AREA

Mineral Resources of the Cinder Cones Wilderness 

Study Area, San Bernardino County, California

By Howard G. Wilshire, James G. Frisken, Robert C. Jachens, and Douglas V. Prose 

U.S. Geological Survey

Clayton M. Rumsey and Arel B. McMahan 

U.S. Bureau of Mines

SUMMARY 

Abstract

At the request of the Bureau of Land 

Management, 44,299 acres of the Cinder Cones 

Wilderness Study Area (CDCA-239) were studied by 

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

Mines. In this report, the area studied is referred to as 

"the wilderness study area", or simply "the study 

area." The study area is located in the Ivanpah upland 

near Baker, Calif. Fieldwork for this report was 

carried out between 1983 and 1985. Two small young 

cinder cones in the wilderness study area contain an 

estimated 30 million tons of cinders; however, there 

are sufficient cinders outside the study area to satisfy 

demand in the foreseeable future. There are no mines 

in the wilderness study area, and of several prospects 

for metallic minerals examined, none contain 

identified resources. Mineralized areas in mines and 

prospects surrounding the study area are associated 

with quartz veins in Cretaceous (see geologic time 

chart on last page of report) granitic intrusions and 

with Proterozoic(?) or Paleozoic rocks near such 

intrusions. Quartz veins are rare in Cretaceous 

granites within the study area, and the limited 

exposures of Proterozoic(?)-Cretaceous rock contacts 

are not strongly altered or mineralized, thus the 

mineral resource potential for gold, silver, lead, and 

zinc is low. Areas underlain by Cretaceous granite, 

Tertiary volcanic and sedimentary rocks, and 

Quaternary alluvium and volcanic rocks have a low 

mineral resource potential for gold, silver, lead, zinc, 

oil, gas, and geothermal energy.

Character and Setting

The Cinder Cones Wilderness Study Area is in 

northeastern San Bernardino County, Calif, and 

includes part of a north-trending assemblage of 

Tertiary and Quaternary basaltic volcanoes. The 

volcanic rocks and underlying granitic rocks form an 

inconspicuous highland called the Ivanpah upland 

(Hewett, 1956) between the Old Dad Mountains to the 

south and the Shadow Mountains to the north (fig. 1).

Older lava flows form an east-sloping mesa within the 

eastern third of the study area, which has about 1,000 

ft of relief on the west side, and 150 ft on the east 

side. Younger lavas and cinder cones lie outside the 

study area to the south, southeast, and southwest of 

the mesa. At least 20 central volcanic vents are 

located in the study area, all but two of which are 

deeply eroded and weathered. West of the mesa is a 

low dome about 5 mi in diameter with a total 

topographic relief of about 1,000 ft, which formed by 

erosion of granitic and Tertiary sedimentary rocks. A 

smaller dome, partially exhumed from beneath 

sedimentary rocks, is located at the south edge of the 

study area.

Rocks of the study area are dominantly granitic 

intrusive rocks, basaltic flows and tephra, and 

sedimentary rocks of various ages. Gneiss crops out in 

small areas, and a variety of dikes unrelated to the 

basaltic volcanism cut the granitic rocks. Apparently 

the basaltic flows are not deformed and retain their 

original depositional attitudes. The volcanic rocks 

overlie Tertiary sedimentary rocks, which are locally 

deformed, and the Proterozoic(?) and Mesozoic 

crystalline rock basement.

Mining activity near the study area has occurred 

intermittently since about 1897 (Hewett, 1956, p. 165), 

but there are no mines within the study area. Gold and 

silver were produced from the Paymaster mine, about 

3 mi south of the study area in the Old Dad mining 

district (Clark, 1970, p. 161), and from the Telegraph 

mine (fig. 1), about 1.5 mi north of the study area 

(Hewett, 1956, p. 120; Wright and others, 1953, p. 

82). Since 1954, cinders have been produced from the 

Cima and Aiken mines (fig. 1) near the southeast 

boundary of the study area (Tognoni, 1983, p. 1).

Identified Resources

Two young cinder cones within the study area 

contain about 30 million tons of volcanic cinders 

similar to those mined at two sites adjacent to the 

southeast border of the study area. Those mines 

contain adequate resources to supply the local market 

demand for the foreseeable future; moreover, many 

other cinder cones in the region have cinders of

Bl
35«30' II6«00' II5«30'

35«00'

To

Death Valley

Junction

Telegraph 

Mine

SHADOW 

MOUNTAINS

Halloran 

Springs

Figure 1. Index map showing location of the Cinder Cones Wilderness Study Area, San 

Bernardino, County, California.

B2
commercial quality. Concentrations of gold and silver 

were found at two prospects in the study area, but no 

gold or silver resources were identified because of the 

limited extent of mineralized rock.

Mineral Resource Potential

Geologic mapping and aero magnetic anomalies 

indicate that contacts between Proterozoic(?) rocks 

and Cretaceous granitic rocks are concealed beneath 

alluvium in the southwestern and extreme northern 

parts of the study area. These concealed contacts are 

believed to have low mineral resource potential for 

gold, silver, lead, and zinc because exposed contacts 

between these rock types in the study area are 

apparently unmineralized. A few isolated rock and 

stream-sediment samples from the study area contain 

anomalous single-element concentrations. The 

geochemistry of these samples is unlike that of nearby 

mining areas, so the remainder of the study area is 

thought to have low potential for gold and silver 

resources.

U.S. Bureau of Mines (Rumsey and McMahan, 

1985) records of proprietary assay results indicate the 

presence of significant concentrations of gold in 

cinders. However, published analyses of cinders from 

these and other sources do not indicate gold anomalies 

in the volcanic rocks. Thorium anomalies in samples 

from the study area are associated with monazite and 

thorite crystals; these minerals are common minor 

accessories in granitic rocks and are not a thorium 

resource.

Geologic and geophysical data indicate that 

relatively thin sections of Tertiary sedimentary and 

volcanic rocks are underlain by granitic and 

metamorphic rocks to depths of at least 2.5 mi; 

therefore, the study area has low potential for oil, gas, 

and geothermal energy resources.

INTRODUCTION 

Area Description

The Cinder Cones Wilderness Study Area (CDCA239) encompasses 44,299 acres in the northeastern 

Mojave Desert. The area is 14 mi nortlmortheast of 

Baker, Calif., and 80 mi southwest of Las Vegas, Nev. 

(fig. 1). All of the study area has low relief; the only 

inaccessible places are west- and east-facing cliffs 

with vertical relief of no more than 200 ft. The lowest 

elevation in the study area is 2,000 ft and the highest 

is 4,955 ft.

The region is arid and experiences moderately 

large seasonal changes in temperature and 

precipitation. Temperatures range from 10°F in 

winter to more than 100°F in the summer. Average 

annual precipitation ranges from about 4 to 6 in. 

(Troxelland Ho fman, 1954).

The density, diversity, and cover of vegetation 

within the wilderness study area are substantially 

greater than in lower-lying areas of the Mojave 

Desert. The dominant plant communities (Vasek and 

Barbour, 1977; Curry, 1983) are Creosote Bush Scrub

and Yucca-Ephedra Scrub. Common representatives in 

the study area of the former community are Larrea 

(creosote), Ambrosia, Krameria, Lycium, Coleogyne, 

Ephedra, Hymenoclea, and various species of Opuntia 

(including barrel, hedgehog, jumping cholla, pencil 

cholla, silver cholla, staghorn cholla, and beavertail 

cactus), perennial and annual grasses, Eriogonum, 

Thamnosoma, Cassia, four-wing saltbush, Haplopappus, 

and Dalea. Plants representing the Yucca-Ephedra 

community include Yucca brevifolia and Y. schidigera, 

Salvia, and Encelia. Some washes contain desert 

willow and catclaw, and most areas of granitic 

alluvium have well-developed lichen and algal crusts. 

Wildlife observed during fieldwork include desert 

tortoises, coyotes, bobcats, rattlesnakes, vultures, 

several kinds of hawks, eagles, owls, ravens, quail, and 

numerous small birds, lizards, rodents, small mammals, 

and insects, in addition to feral burros.

Lava flows in the study area have a noteworthy 

abundance of petroglyphs scribed on outcrop surfaces.

Access to the western, eastern, and northern 

parts of the study area is provided by unimproved 

roads that form part of the study area's boundary (fig. 

1). Access to the southern and southeastern parts is 

provided by unmaintained roads, most of which are 

unsuitable for 4-wheel drive vehicles. A passable trail 

terminates at Indian Spring, 1 mi south of the study 

area boundary.

Previous and Present Investigations

Early geologic mapping by Hewett (1956), which 

included all of the study area, defined the major rock 

units of the area and greatly aided this study. 

Geologic maps of part of the Old Dad Mountains 

include a narrow strip of the southern end of the study 

area (Barca, 1966) and a strip along the eastern side of 

the study area (Evans, 1971). Detailed studies of the 

geomorphology and ages of the Tertiary and 

Quaternary basaltic flows and cinder cones were 

published by Dohrenwend and others (1984). Other 

geologic maps and detailed petrologic studies describe 

the volcanic rocks adjacent to the study area and 

present geochemical data on gold contents of cinders 

from three volcanic cones (Katz, 1981; Breslin, 1982).

The U.S. Geological Survey (USGS) conducted 

field investigations in 1984 and 1985. The work 

included field checking of existing maps, new mapping 

of the entire wilderness study area at a scale of 

1:24,000, geochemical sampling, and gravity surveys. 

Earlier aeromagnetic (U.S. Geological Survey, 1983) 

and gravity (Snyder and others, 1982) surveys are 

reviewed in this report. During 1983, the U.S. Bureau 

of Mines (USBM) conducted a mineral survey of the 

Cinder Cones Wilderness Study Area as part of a joint 

study with the USGS. The USBM investigation 

included a library search for information on mines and 

prospects in and around the study area. These data 

were supplemented by information from claim 

owners. Field investigations conducted in 1983 

examined and sampled known prospects and 

mineralized sites. Unrecorded mineralized sites were 

looked for in reconnaissance surveys.

B3
APPRAISAL OF IDENTIFIED RESOURCES

By Clay ton M. Rumsey and Arel B. McMahan, U.S. 

Bureau of Mines

Introduction

Twenty-six rock samples were collected at 

prospects and mineralized sites in the study area. 

Additionally, 25 rock samples and 58 alluvial samples 

were collected throughout the study area to verify the 

presence or absence of reported gold concentrations. 

Chip samples were collected across mineralized zones 

or other exposures where possible, and grab samples 

were collected from dumps, stockpiles, and float. All 

samples were assayed for gold and silver using a 

combined fire assay-inductively coupled plasma 

method (Rumsey and McMahan, 1985) at detection 

limits of 0.007 and 0.3 parts per million (ppm), 

respectively. Semiquantitative spectrographic 

analyses for 40 elements were performed on selected 

samples to determine if anomalous concentrations of 

other metals were present. Thin sections of seven 

rock samples were examined with a petrographic 

microscope to determine rock type, alteration suites, 

and mineral assemblages. Samples of alluvium were 

either 5-lb grab samples of surficial sand and gravel or 

20-lb channel samples of sediment. Material larger 

than 0.25 in. was screened and visually examined for 

heavy minerals, and the remaining portion was 

concentrated on a Wilfley table. Precious metals in 

the concentrate were recovered by amalgamation.

History and Production

Mining claims on record in the study area in 1981 

included 61 placer and 3 lode claims, none of which are 

currently active. No oil and gas or mineral leases are 

known to exist within the study area. In 1982, the 

nearest mining activity was at the Telegraph mine (fig. 

1), about 1.5 mi north of the study area in the Halloran 

Spring mining district (Clark, 1970, p. 158), and at the 

Cima and Aiken cinder mines within 2 mi of the 

southeast boundary of the study area. Mines and 

prospects examined for this study are shown in figure 2 

and are summarized in table 1.

There has been no recorded mineral production 

from the study area. In prehistoric times, Native 

Americans mined turquoise from deposits 10 mi north 

of the study area, and probably transported it on a 

nearby foot trail that later was named the Mojave trail 

by white settlers (Ver Planck, 1961, p.4). Historical 

mining began around 1897 (Hewett, 1956, p. 165). The 

earliest known production of metallic ore nearby began 

around 1900 at the Paymaster mine (fig. 1), about 3 mi 

southwest of the study area in the Old Dad mining 

district (Clark, 1970, p. 161). From 1932 to 1944, this 

mine produced 316 oz gold and 117 oz silver from 

quartz veins in granite gneiss (Hewett, 1956, p. 120- 

122). The Telegraph mine, discovered in 1930, 

produced 2,560 oz gold, 5,423 oz silver, and 500 Ib 

copper between 1932 and 1948 from quartz veins in 

Cretaceous granitic rocks (Hewett, 1956, p. 120; 

Wright and others, 1953, p. 82).

The Cima and Aiken cinder mines are located in 

the Cima mining district (Tognoni, 1983, p. vi) where 

ten placer claims were located in 1947 (Tognoni, 1983, 

p.8). Production from the Cima cinder mine and from 

what is now the Aiken cinder mine began in 1954 

(Tognoni, 1983, p. 1), and by 1961 total production 

reached at least 1.4 million tons (Tognoni, 1983, p. 26).

Mineral Deposits

Cinder cones in the region are closely associated 

with basalt flows, most of which issued from the same 

vents. Of the 20 central volcanic vents inside the 

study area, 2 cones in the southern part (fig. 2, locality 

6) are young enough to have preserved large amounts 

of slightly weathered cinders suitable for commercial 

use. All of the other vent deposits are substantially 

older so that most of the cinders have been removed 

by erosion and remaining deposits are weathered or 

composed dominantly of lava. The two relatively 

young cinder cones contain about 30 million tons of 

volcanic cinders similar to those at the Cima and 

Aiken deposits. The two mines outside the study area 

have adequate resources to supply local markets for 

the foreseeable future. Also, many other cinder cones 

in the region have commercial-quality cinders.

Proprietary assay results obtained by USBM from 

the owners of the Aiken and Cima cinder mines 

(Rumsey and McMahan, 1985) indicate the presence of 

significant concentrations of gold in cinders and 

possibly in basalt and Cretaceous granite. However, 

neutron-activation analyses of cinders and blocks from 

three cones adjacent to and outside of the study area 

(Breslin, 1982, p.98) revealed gold concentrations of 

less than 0.001 to 0.004 ppm, which are typical of 

basaltic volcanic rocks (Crockett, 1974). Breslin's 

results were confirmed by the USBM sample program 

(Rumsey and McMahan, 1985). Alluvial samples 

collected throughout the study area contain only trace 

amounts of gold.

The levels of gold and silver concentration and 

local alteration of rocks and veins at two prospects 

(fig. 2 and table 1, nos. 2 and 4) in the study area 

indicate the presence of mineralization similar to that 

in Cretaceous granitic rock at the Telegraph mine and 

in Proterozoic(?) gneiss at the Paymaster mine. 

Because of the limited extent of mineralized rock, no 

gold or silver resources were identified at either of the 

two prospects within the study area.

Trace amounts of gold in 51 alluvial samples 

collected throughout the study area suggest that gold 

remained when the parent rock was eroded away, or 

that the trace amounts characterize the parent 

Proterozoic(?) gneiss and (or) Cretaceous granite. 

However, no gold was found in the panned-concentrate 

samples analyzed by the USGS, except at the 

Paymaster mine. Assays show that granitic rocks in 

the study area contain trace amounts of gold. In all 

cases, the gold detected in alluvium and granitic rocks 

is present in amounts too small to be considered a 

resource.

Stone, sand, and gravel deposits within the study 

area are too far from anticipated markets to be 

considered resources. No evidence of oil, gas, 

uranium, or geothermal energy was found in the study

B4
area.

ASSESSMENT OF MINERAL RESOURCE POTENTIAL

By Howard G. Wilshire, James G. Frisken, Robert C. 

Jachens, and Douglas V. Prose, U.S. Geological Survey

Geology

The Cinder Cones Wilderness Study Area is 

underlain mainly by Cretaceous granitic rocks that are 

partly covered by a veneer of Tertiary and Quaternary 

sedimentary and volcanic rocks (fig. 2). Proterozoic(?) 

gneiss, into which the Cretaceous granitic rocks were 

intruded, crops out most extensively on the western 

side of the study area. The Cretaceous rocks are cut 

by northwest-trending dikes of fine-grained porphyritic 

and nonporphyritic hornblende biotite andesite or 

dacite 1 to 15 ft wide. Intrusive contacts between 

Proterozoic(?) rocks and Cretaceous granitic rocks, 

and between Cretaceous granitic rocks and andesite or 

dacite dikes, are locally well exposed. Where exposed, 

these contacts are apparently unaltered.

The Tertiary sedimentary rocks are composed of 

detritus from nearby Cretaceous granitic rocks with 

lesser amounts (generally less than 5 percent) from 

more distant Proterozoic gneiss, dike rocks, and quartz 

veins in the granitic rocks. The moderately to wellbedded, poorly consolidated sedimentary rocks 

composed of boulders, gravel, sand, and silt are 

preserved mainly beneath mesa-capping basalts. At 

the north end of the study area, these rocks dip 25° to 

40° to the southeast and are in angular discordance 

with the overlying basalt flows. To the south, the 

sedimentary rocks appear to be less tilted. Because 

the oldest known basalt flow on the mesa is dated at 

4.8 million years before present (Ma) (Turrin and 

others, 1985), the sedimentary rocks are at least 

Pliocene (2-5 Ma) age. The maximum thickness of 

Tertiary sedimentary rocks is approximately 1,000 ft, 

assuming that the section at the north end of the study 

area is not repeated by faulting. The maximum 

paleotopographic relief on the bedrock surface beneath 

the Tertiary sedimentary rocks is at least 450 ft.

Late Tertiary and early Quaternary basalt flows 

and cinder cones overlie the sedimentary and 

crystalline rocks. Basalt dikes are common in eroded 

cinder cones, but have not been observed in 

Cretaceous granitic rocks. The basalts were erupted 

between about 8 and 0.015 Ma (Turrin and others, 

1985). Younger Quaternary detritus consists of small 

alluvial fans adjacent to bedrock outcrops and more 

extensive unconsolidated alluvium and colluvium on 

gentle slopes.

Geochemical Studies

A reconnaissance geochemical study of the study 

area was undertaken in 1984 by the U.S. Geological 

Survey. Rock samples and the nonmagnetic fraction of 

heavy-mineral concentrates panned from stream 

sediments collected in active streams were analyzed. 

These two sample media were selected because they

are reliable indicators of base- and precious-metal 

anomalies in the arid desert environment of 

southeastern California. Twenty-three rock samples 

of stream cobbles, outcrops, and mine dumps collected 

from sixteen sites adjacent to and within the study 

area are mineralized or altered, and were collected to 

characterize the geochemistry of local ore deposits 

and of mineralized and altered rocks. Thirty-two 

concentrates were prepared from sediment collected 

from 32 washes inside and south of the study area 

representing drainage basins ranging in size from 0.5 

to 5 mi . Two concentrates represent mineralization 

associated with the Paymaster mine, and one is from a 

very small drainage west of the Telegraph mine. The 

other concentrates represent areas without known 

mineralized areas.

Nonmagnetic concentrates usually exclude clays, 

organic material, and common rock-forming minerals 

(some of which contain metal anomalies unrelated to 

ore-forming processes) and concentrate many minerals 

that are commonly related to mineralization and 

alteration, thereby increasing the chances of detecting 

relatively weak geochemical anomalies that may be 

missed by using untreated stream sediments. Also, 

microscopic examination of concentrates allows 

identification of the minerals and man-made 

contaminants that cause the geochemical anomalies.

The rock and nonmagnetic concentrates were 

pulverized, then analyzed for 31 elements by a 

semiquantitative emission spectrographic method 

(Grimes and Marranzino, 1968; Motooka and Grimes, 

1976) and for gold by atomic-absorption methods 

(Thompson and others, 1968). The rocks were also 

analyzed for arsenic, antimony, cadmium, bismuth, and 

zinc by atomic absorption (Viets, 1978), which provides 

lower detection levels for these elements than does 

spectrography.

All the known and potential mineral deposits 

adjacent to the study area and potential mineral 

deposits within it can probably be accounted for by 

Hewett's (1956) model of Laramide ore deposits. 

Hewett considered the Cretaceous intrusive rocks to 

be the dominant element in the mineralizing process 

and pointed out that metallic-mineral deposits were 

concentrated in late-stage dikes, fracture zones, and 

quartz veins emplaced near the contact between the 

plutons and Proterozoic (?) crystalline and Paleozoic 

sedimentary country rocks. The characteristic 

anomalous geochemical suite of these mesothermal 

vein systems consists of antimony, arsenic, bismuth, 

copper, gold, lead, molybdenum, silver, tin, tungsten, 

and vanadium. In some regions, such vein systems may 

be underlain by porphyry copper-molybdenum 

mineralization (Cox and Singer, 1986).

Most important in this area are precious-metal, 

multiple-element, multiple-media, and adjacent-site 

anomalies. Most rock and panned-concentrate samples 

collected for this study do not contain geochemical 

anomalies. Many samples have a restricted suite of 

anomalous elements or are anomalous in only a single 

element. No gold concentrations at the lower 

detection limit of 0.05 ppm were found in 

concentrates. Samples from westward-draining washes 

in the southern part of the study area contain lowlevel lanthanum, lead, molybdenum, thorium, and 

vanadium anomalies, but possess no concentrations of

B5
II5°50' II5°45'

35°20'

35°I5' -

APPROXIMATE BOUNDARY _ 

CINDER CONES WILDERNESS 

STUDY AREA (CDCA-23'"

Figure 2. Map showing the geology and mineral resource potential of the Cinder Cones 

Wilderness Study Area, San Bernardino County, Californina.

B6
EXPLANATION

Area with low mineral resource potential, 

certainly level B (L/B). See appendix 1 and 

figure 3 for definition of levels of mineral 

resource potential and certainty of assessment

COMMODITIES 

Au Gold 

Ag Silver 

Pb Lead 

Zn Zinc

CORRELATION OF MAP UNITS 

"iHolocene and 

-/Pleistocene QUATERNARY

IQTbllQTbcl

TERTIARY

CRETACEOUS 

}PROTEROZOIC(?)

GEOLOGIC MAP UNITS 

Qol Alluvium and colluvium (Holocene and

Pleistocene)

QTbl Basalt lava (Quaternary and Tertiary) 

QTbc Basalt cinders, agglutinate, maar beds

(Quaternary and Tertiary)

Ts Sedimentary rocks (Tertiary)

Kg Granitic rocks (Cretaceous)

Pgn Gneiss (Proterozoic?)

MAP SYMBOLS

 Contact Dashed where approximately

located 

................... Concealed contact Located by

aeromagnetic data

 ^ Tertiary dike rocks Dashed where

approximately located 

4 Prospect Number refers to table 1

Figure 2. Continued.

B7
precious metals. The anomalies may be related to 

contact zones between remnants of the Proterozoic(?) 

rocks and Cretaceous granitic rocks and probably do 

not indicate the presence of a mineral resource.

Mineralized rocks from mines and prospects 

located within 4 mi of the study area mostly contain 

anomalous amounts of antimony, arsenic, bismuth, 

copper, gold, silver, and zinc; some of the samples 

contain low concentrations of molybdenum, tungsten, 

or manganese. The Telegraph mine produced gold and 

silver from quartz veins trending N. 30° E. and dipping 

40° NW. At least 20 such veins occur in intrusive 

rocks southwest of the Telegraph mine. A composite 

sample of quartz-vein material collected from 

outcrops about 1 mi west of the Telegraph mine 

contains 44 ppm gold and 7 ppm silver, demonstrating 

that the ore deposits of the Telegraph mine extend 

along strike to the southwest. A concentrate sample 

from a very small drainage about 1 mi west of the 

Telegraph mine contains anomalous vanadium (500 

ppm). Rock samples collected from mines about 3 mi 

northeast of the Telegraph mine posess relatively 

lower or no concentrations of gold, but are rich in 

silver, copper, lead, and zinc.

Two concentrate samples collected adjacent to 

the Paymaster mine are anomalous in bismuth, copper, 

gold, lead, and silver. Other mines near the Paymaster 

mine have produced precious or base metals from 

quartz veins in the Prospect Mountain Quartzite, a 

formation that is not known to be present in the study 

area.

One concentrate sample from a previous 

geochemical study (Van Trump and Miesch, 1976), 

reportedly collected 2 mi northeast of Granite Spring, 

contained 90 ppm bismuth, 130 ppm copper, 8 ppm 

gold, and 150 ppm lead; a concentrate collected for 

this study 2 mi below this site revealed no anomalous 

concentrations. At a site along the north side of the 

study area, another concentrate collected during 

previous studies (Van Trump and Miesch, 1976) 

reportedly contained 40 ppm bismuth, and a streamsediment sample contained 50 ppm molybdenum. 

These previously determined anomalies in the 

northeast corner of the study area are presumably 

derived from underlying Tertiary sedimentary rocks. 

However, the nine concentrate samples that were 

taken from the same area during our study are not 

anomalous. In that part of the area, the Tertiary 

sedimentary rocks are composed mostly of detritus 

derived from Cretaceous granitic rocks and contain 

less than 5 percent fragments of Proterozoic (?) 

metamorphic rocks and Tertiary andesite or dacite 

dike rocks. No fragments of Paleozoic rocks were 

seen in the Tertiary sedimentary rocks in the northern 

part of the study area. Pebbles of pre-Tertiary 

crystalline rocks were found at seven of our nine 

sample sites, which indicates that these washes drain 

at least limited exposures of pre-Tertiary rocks and 

(or) Tertiary sedimentary rocks derived from preTertiary rocks. The lack of geochemical anomalies in 

our concentrate samples suggests that the existence of 

an extensive mineralized area covered by sedimentary 

rocks and basalt is unlikely.

Anomalous concentrations of lanthanum, 

thorium, and yttrium are present in most of the 

concentrates and seven samples have thorium

concentrations of 5,000 ppm or more. Thorite and 

monazite crystals were identified in some of the 

concentrates and the anomalies are probably derived 

from these accessory minerals in the crystalline 

rocks. It is unlikely that a minable resource occurs 

within the study area. Rare-earth minerals, including 

monazite, are mined at the Mountain Pass mine 11 mi 

northeast of the study area, but that deposit is 

Proterozoic (?) in age and is related to carbonatite and 

syenite-shonkinite intrusions, which are not known to 

occur within the study area. Barite and fluorite are 

also associated with the deposit at Mountain Pass, and 

these minerals were not seen in concentrates.

Geophysical Studies

An aeromagnetic survey of the study area was 

flown in 1981 and compiled under contract to the 

USGS. Total-field magnetic data were obtained from 

east-trending flight lines spaced approximately 0.5 mi 

apart and flown at a height of 1,000 ft above average 

terrain. Because of the topography of the study area, 

actual terrain clearance varied from about 400 to 

1,600 ft. Corrections applied to the data compensate 

for diurnal variations of the Earth's magnetic field, 

and the International Geomagnetic Reference Field 

(updated to December 1981) was subtracted to yield a 

residual magnetic map (U.S. Geological Survey, 1983).

Comparison of anomalies depicted on the 

aeromagnetic map with the exposed rock types 

indicates that, within the study area, rock 

magnetization correlates well with the major rock 

units defined by geologic mapping. Tertiary 

sedimentary rocks and Quaternary alluvium are 

effectively nonmagnetic and cause no magnetic 

anomalies. Tertiary and Quaternary basaltic rocks are 

strongly magnetic and yield high-amplitude, shortwavelength magnetic anomalies, especially over 

volcanic vent deposits. A broad magnetic low over the 

Cretaceous granitic rocks (DeWitt and others, 1984; 

Hewett, 1956) exposed in the central part of the study 

area and a low over similar rocks exposed in the 

southwest corner indicate that these rocks are much 

less magnetic than either the basaltic rocks or the 

Proterozoic (?) gneiss with which they are in contact. 

One exception is the Cretaceous granitic rocks in 

which the Telegraph mine is located; this rock-type 

has a very high proportion of mafic inclusions that 

probably cause the magnetic anomaly. No similar 

rocks are exposed in the study area.

Gravity data near the study area were obtained 

from Snyder and others (1982) and supplemented by 

nine measurements made in 1985. The observed 

gravity data, based on the International Gravity 

Standardization Net datum (Morelli, 1974), were 

reduced to free-air gravity anomalies by using 

standard formulas (Telford and others, 1976). Bouguer, 

curvature, and terrain corrections (out to a distance of 

103.6 mi from each station) at a standard reduction 

density of 2.67 g/cm were added to the free-air 

anomaly at each station to determine complete 

Bouguer gravity anomalies.

The Bouguer gravity field over the study area 

and surrounding regions reflects shallow density 

contrasts and deep-crustal density distributions that

B8
correlate with the topography in a manner consistent 

with the concept of isostasy (Oliver, 1980). To isolate 

that part of the gravity field that arises from nearsurface density distributions, an isostatic residualgravity map was constructed from the Bouguer gravity 

data by removing a regional gravity field computed 

from a model of the crustal-mantle interface, 

assuming Airy-type isostatic compensation (Jachens 

and Griscom, 1985).

The density of some of the major rock units was 

determined by measuring hand samples collected from 

surface exposures near the study area. Thirty-eight 

samples of the Cretaceous granitic rocks averaged 

2.60 + 0.02 g/cm , and six samples of the Proterozoic 

(?) crystalline rocks averaged 2.69 + 0.04 g/cm . 

Although the number of samples of Proterozoic (?) 

crystalline rock is small, their average density agrees 

well with that of 35 other samples of similar rocks 

from the eastern Mojave Desert (2.69 + 0.11 g/cm ). 

Only three samples of basalt were measured and they 

yielded an average density of 2.64 + 0.05 g/cm .

The aeromagnetic data were used as the primary 

means for locating the buried Proterozoic(?) gneissCretaceous granitic rocks contacts (fig. 2). The 

locations of the contacts were inferred from the 

magnetic data using an automated technique for 

locating steeply dipping contrasts in magnetic 

properties (Blakely and Simpson, 1986). The two 

inferred-contact segments in the western part of the 

study area are well defined and agree closely with the 

mapped contact where it is exposed. The easternmost 

of these two segments is also reflected in the gravity 

data by a gradient that separates residual-gravity 

values of about -12 milligal (mGal) over Proterozoic 

(?) rocks to the west from values less than -25 mGal 

over Cretaceous granitic rocks to the east. Gravity 

modeling based on a density contrast of 0.09 g/cm 

between Proterozoic (?) gneiss and Cretaceous granitic 

rocks suggests that the contact is nearly vertical and 

extends to a depth of nearly 2.5 mi.

The inferred-contact segment that lies near the 

north boundary of the study area separates magnetic 

rocks to the north from less magnetic rocks to the 

south. Numerous outcrops of Proterozoic(?) gneiss 

(not shown on fig. 2) are present north of the west half 

of this contact segment and three small exposures 

bracket it in the study area. Cretaceous granitic rocks 

also crop out north of the inferred contact. Thus, the 

area of magnetic rocks north of the contact is not 

underlain completely by Proterozoic (?) gneiss, but 

probably is a mixture of Cretaceous granitic rocks and 

remnants of the magnetic Proterozoic (?) rocks that 

formed the roof of the intrusive rocks. The less 

magnetic rocks to the south probably are Cretaceous 

granitic rocks with or without a cap of Tertiary 

sedimentary rocks largely derived from Cretaceous 

granitic rocks. This interpretation is supported by the 

gravity data, which show low residual gravity values 

north and south of the contact.

Conclusions

Geologic, geophysical, and geochemical studies 

of the Cinder Cones Wilderness Study Area have not 

revealed resources of base- and precious-metals. A

review of mine production and mineral occurrences in 

areas surrounding the study area indicate that 

conditions conducive to base and precious metal 

mineralization are met only locally within the study 

area. Proterozoic (?) and Paleozoic rock surrounding 

Cretaceous granitic intrusions and quartz veins in the 

intrusions are the main hosts of base- and preciousmetal deposits surrounding the study area. Quartz 

veins are rare within the study area, and quartz^vein 

detritus is uncommon in Tertiary and Quaternary 

alluvium. Local exposures of Proterozoic (?)- 

Cretaceous rock contacts in the study area are not 

apparently mineralized; concealed parts of the contact 

zones are revealed by aeromagnetic studies. These 

zones have low potential for precious- and base-metal 

resources, certainty level B (see appendix 1 and figure 

3 for a definition of mineral resource potential and 

levels of certainty). Gold and silver concentrations at 

two prospects in the study area are associated with 

locally altered granitic rock, but no gold or silver 

resources were identified at either locality. Paleozoic 

metasedimentary rocks, which host mineral deposits to 

the south of the study area, are not present within the 

study area.

No hot springs or other indications of geothermal 

activity are associated with the Tertiary and 

Quaternary volcanic rocks, and most of the study area, 

including the area occupied by the volcanic rocks, is 

underlain by Cretaceous granitic rocks and smaller 

areas by Proterozoic (?) metamorphic rocks. 

Geophysical modeling indicates that Cretaceous 

granitic rocks are at least 2.5 mi thick beneath the 

wilderness study area. Hence, the potential for oil, 

gas, and geothermal energy resources is low, certainty 

level C.

Large quantities of sand and gravel are present 

in the northern and south-central parts of the study 

area, but much larger deposits occur outside the study 

area.

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Old Dad Mountain quadrangle, San Bernardino 

County, California: California Division of Mines 

and Geology, Map Sheet 7, scale 1:62,500.

Blakely, R.J., and Simpson, R.W., 1986, Locating edges 

of source bodies from magnetic or gravity 

anomalies: Geophysics, 1986.

Breslin, P.A., 1982, Geology and geochemistry of a 

young cinder cone in the Cima volcanic field, 

eastern Mojave Desert, California: Los Angeles, 

University of California, M.S. thesis, 119 p.

Clark, W.B., 1970, Gold districts of California: 

California Division of Mines and Geology Bulletin 

193, 186 p.

Cox, D.P., and Singer, D.A., 1986, Mineral deposit 

models: U.S. Geological Survey Bulletin 1679, 

378 p.

Crockett, J.H., 1974, Gold, in_ Wedepohl, K.H., ed., 

Handbook of Geochemistry, v. n/4: New York, 

Springer-Verlag Inc., p.79B-l to 79B-10.

Curry, B.B., ed., 1983, Old Dad-Kelso Mountains 

Resource Survey: National Association of 

Geology Teachers, Far Western Section,

B9
Guidebook, 477 p.

DeWitt, E.H., Armstrong, R.L., Sutter, J.F., and 

Zartman, R.E., 1984, U-Th-Pb, Rb-Sr, and Ar-Ar 

mineral and whole-rock isotopic systematics in a 

metamorphosed granitic terrain, southern 

California: Geological Society of America 

Bulletin, v. 95, p. 723-739..

Dohrenwend, J.C., McFadden, L.D., Turrin, B.D., and 

Wells, S.G., 1984, K-Ar dating of the Cima 

volcanic field, eastern Mojave Desert, 

California: Late Cenozoic volcanic history and 

landscape evolution: Geology, v. 12, p. 163-167.

Evans, J.R., 1971, Geology and mineral deposits of the 

Mescal Range quadrangle, San Bernardino County, 

California: California Division of Mines and 

Geology, Map Sheet 17, scale 1:62,500.

Grimes, D.J., and Marranzino, A.P., 1968, Directcurrent arc and alternating-current spark emission 

spectrographic field methods for the 

semiquantitative analysis of geologic materials: 

U.S. Geological Survey Circular 591, 6 p.

Hewett, D.F., 1956, Geology and mineral resources of 

the Ivanpah Quadrangle, California and Nevada: 

U.S. Geological Survey Professional Paper 275, 

172 p.

Jachens, R.C., and Griscom, Andrew, 1985, An 

isostatic residual gravity map of California-A 

residual map for interpretation of anomalies from 

intracrustal sources, in, Hinze, W.J., ed., The 

Utility of Regional Gravity and Magnetic Anomaly 

Maps: Tulsa, Okla., Society of Exploration 

Geophysicists, p. 347-360.

Katz, M.M., 1981, Geology and geochemistry of the 

southern part of the Cima volcanic field: Los 

Angeles, University of California, M.S. thesis, 126

PMorelli, C.E., ed., 1974, The international gravity 

standardization net 1971: International 

Association of Geodesy Special Publication no. 4, 

194 p.

Motooka, J.M., and Grimes, D.J., 1976, Analytical 

precision of one-sixth order semiquantitative 

spectrographic analyses: U.S. Geological Survey 

Circular 738, 25 p.

Oliver, H.W., 1980, General introduction, in, Oliver, 

H.W. ed., Interpretation of the Gravity Map of 

California and its Continental Margin: California 

Division of Mines and Geology Bulletin 205, p. 1-8.

Rumsey, C.M. and McMahan, A.B., 1985, Mineral 

resources of the Cinder Cones Wilderness Study 

Area, San Bernardino County, California: U.S. 

Bureau of Mines Open-File Report MLA 67-85, 12

PSnyder, D.B., Roberts, C.W., Saltus, R.W., and Sikora, 

R.F., 1982, A magnetic tape containing the 

principal facts of 64,026 gravity stations in the 

state of California: available from National 

Technical Information Service, U.S. Department

of Commerce, Springfield, VA 22152, PB 82- 

168287 (description of magnetic tape, PB 82- 

1682791, magnetic tape, 34 p.).

Telford, W.M., Geldart, L.P., Sheriff, R.E., and Keyes, 

D.A., 1976, Applied Geophysics: New York, 

Cambridge University Press, 860 p.

Thompson, C.E., Nakagawa, H.M., and Van Sickle, 

G.H., 1968, Rapid analysis for gold in geologic 

materials, in Geological Survey Research 1968: 

U.S. Geological Survey Professional Paper 600-B, 

p. B130-B132.

Tognoni, H.C., 1983, Market survey of volcanic tephra 

from Red Beauty and Valco cinder cones, San 

Bernardino County, California: Mineral Economics 

Corporation, Phoenix, Ariz., for Denzil Aiken, 

owner, unpublished report, 64 p. Available from 

U.S. Bureau of Mines Western Field Operations 

Center Library, Spokane, Wash.

Troxell, H.C., and Hofmann, W.H., 1954, Hydrology of 

the Mojave Desert, in Geology of Southern 

California: California Division of Mines and 

Geology, Bulletin 170, p. 13-17.

Turrin, B.D., Dohrenwend, J.C., Drake, R.E., and 

Curtis, G.H., 1985, K-Ar ages from the Cima 

volcanic field, eastern Mojave Desert, 

California: Isochron/West, no. 44, p. 9~16.

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

Principles of a re source/re serve classification for 

minerals: U.S. Geological Survey Circular 831, 5

PU.S. Geological Survey, 1983, Aeromagnetic map of 

the Kingman-Trona area, California: U.S. 

Geological Survey Open-File Report 83-663, 2 

sheets, scale 1:250,000.

Van Trump, George, Jr., and Miesch, A.T., 1976, The 

U.S. Geological Survey RASS-STATPAC system 

for management and statistical reduction of 

geochemical data: Computers and Geosciences, v. 

3, p. 475-488.

Vasek, F.C., and Barbour, M.G., 1977, Mojave Desert 

scrub vegetation, in Barbour, M.G., and Major, J. 

eds., Terrestrial Vegetation in California: New 

York, John Wiley and Sons, p. 835-867.

Ver Planck, W.E., 1961, History of mining in 

northeastern San Bernardino County: California 

Division of Mines Mineral Information Service, v. 

14, no. 9, p. 1-8.

Viets, J.G., 1978, Determination of silver, bismuth, 

cadmium, copper, lead, and zinc in geologic 

materials by atomic absorption spectrometry with 

tricaprylmethylammonium chloride: Analytical 

Chemistry, v. 50, p. 1097-1101.

Wright, L.A., Stewart, R.M., Gay, T.E., Jr., and 

Hazenbush, G.C., 1953, Mines and mineral 

deposits of San Bernardino County, California: 

California Journal of Mines and Geology, v. 49> 

nos. 1 and 2, p. 49-192.

BIO
TABLE I Mines and prospects in and adjacent to the Cinder Cones Wilderness Study Area 

[Asterisk indicates location outside of the study area]

Map No. Name Summary Workings and 

production

Sample and 

resource data

1 Unnamed 

prospect

Raw Silver

Cone

prospect

Holladay

Gold

prospect

Little Dove 

prospect

Bronco 

prospect

Cinder 

occurrences

Aiken and 

Cima cinder 

mines

1.5-ft-thick dike strikes N. 30° 

E., 35° SE. in Proterozoic(?) 

gneiss; dike has 4 in. of gouge 

along hanging wall, 2 in. along 

footwall.

Two clayey,brecciated, ironstained shear zones exposed 

for 200 ft in Cretaceous granite; host rock locally altered 

and leached; malachite coats 

10 percent of fractures; one 

zone is 2 ft thick and strikes 

N. 45° W., dips 43° NE.;other 

zone is 3 ft thick, strikes N. 

79° W., and dips 45° SE.; 5 

zones of pink to white altered, 

massive clay-like material are 

as much as 90 ft across.

Northeast-trending contact zone 

between Cretaceous granite and 

Proterozoic schist traced for 

145 ft; rock along the contact 

altered and silicified (5 ft 

thick zone of alteration).

3 brecciated quartz-filled shear 

zones contain gold and silver in 

foliated granite; shear zones 

discontinuously exposed for 130 

ft; quartz is vuggy and ironstained, locally contains limonite and pyrite; zones are about 

1 ft thick, strike N. 80° E., 

N. 70° W., and N. 30° W.; all 

dip 50° N.

A 4-in.-thick quartz-filled shear 

zone is exposed for 30 ft in a 5- 

ft-thick zone of bleached, silicified foliated granite.

Two cinder cones consist of red 

and black, coarse- to moderately 

cellular well-bedded cinders that 

range in grain size from <0.13 to 

6 in. angular block.

Cinder cones at 2 mines consist 

of well-bedded, coarse to 

moderately cellular red to 

black cinders that range in size 

from <0.13 to 6 in. angular 

blocks.

A 20-ft-long adit.

5 trenches totalling 

239 ft and 2 adits 

totalling 101 ft; one 

caved adit and two 

prospect pits.

Three 5-ft-square by 

3-ft-deep prospect 

pits.

One 7-ft-square by 

25-ft-deep shaft; 1 

8-ft-square by 23- 

ft-deep shaft inclined 50° N. Three 5-ftsquare by 3-ft-deep 

pits.

One 50-ft by 100-ft 

bulldozed area.

None.

One sample collected across 

dike and gouge contains no 

gold or silver.

12 samples collected from 

veins and altered zones; 3 

samples contain only traces 

of gold; 5 have 0.05-0.32 oz/ 

ton gold; 3 have only traces 

of silver; 5 have 0.4-1.8 oz/ 

ton silver; 1 select sample 

from 50-lb stockpile contains 

41.3 oz/ton silver; 2 samples 

contain only traces of copper. Mineralized rock of limited extent. No resources 

are apparent.

3 chip samples collected 

across Proterozoic(?) schist, 

silicified schist, and gneiss 

contained no gold or silver.

6 chip samples contain trace 

amounts to 0.15 oz/ton gold; 

1 select grab sample contains 

0.86 oz/ton gold and 1.2 oz/ 

ton silver; 4 chip samples 

contain 0.4 oz/ton silver. 

Mineralized rock of limited 

extent; no resources apparent

One chip sample collected 

across the shear zone contains no gold or silver.

Cinder prospect contains 30 

million tons of volcanic 

cinders.

Cima cinder mine has 

8 cones with excavation pits in 6; recorded production is 

130,000 tons; total 

production much 

greater (Rumsey and 

McMahan, 1985). Aikin 

cinder mine has pits 

in 2 cones; total 

production to 1983 was 

1.28 million tons 

(Rumsey and McMahan, 

1985).

About 8 million tons of 

cinders remained at Aikin 

cinder mine in 1983; cinder 

resources at the Cima 

cinder mine are unknown but 

probably substantial. Both 

mines will supply market 

demand for the forseeable 

future.

Bll
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 by 

letters, A-D (fig. 3).

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

HIGH POTENTIAL

M/B

MODERATE POTENTIAL

L/B

LOW POTENTIAL

H/C

HIGH POTENTIAL

M/C

MODERATE POTENTIAL

L/C

LOW POTENTIAL

H/D

HIGH POTENTIAL

M/D

MODERATE POTENTIAL

L/D

LOW POTENTIAL

N/D

NO POTENTIAL

B C

LEVEL OF CERTAINTY

Figure 3. Major elements of mineral resource potential/certainty classification.

B12
GEOLOGIC TIME CHART 

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

EON

Phanerozoic

Proterozoic

Archean 

pre-Ar

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

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

- 38

- 66

- 96

- 900

OCA

- 410

- 500

- 1600

 4RRD 

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

'Informal time term without specific rank.

B13
GPO 785-048/48025