Mineral Resources of the Pit River 

Canyon Wilderness Study Area, / i *

Lassen County, California

U.S. GEOLOGICAL SURVEY BULLETIN 1706-E

 *<"£C,- , .^ >~ , £ » ». ,y,~r ***>* 

Chapter E

MINERAL RESOURCES OF WILDERNESS STUDY AREAS: NORTHEASTERN 

CALIFORNIA AND PART OF ADJACENT WASHOE COUNTY, NEVADA

Mineral Resources of the Pit River 

Canyon Wilderness Study Area, 

Lassen County, California

SyMAUREEN G. SHERLOCK 

U.S. Geological Survey

HARRY W. CAMPBELL 

U.S. Bureau of Mines

U.S. GEOLOGICAL SURVEY BULLETIN 1706-E
DEPARTMENT OF THE INTERIOR 

DONALD PAUL MODEL, Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

UNITED STATES GOVERNMENT PRINTING OFFICE 1986

For sale by the

Distribution Branch, Text Products Section

U.S. Geological Survey

604 South Pickett St.

Alexandria, VA 22304

Sherlock, Maureen G.

Mineral resources of the Pit River Canyon 

Wilderness Study Area, Lassen County, California

(U.S. Geological Survey Bulletin; B1706-E

Bibliography: p.

Supt. of Docs, no.: I 19.3:1706-E

1. Mines and mineral resources California Pit

River Canyon Wilderness. 2. Geology California 

Pit River Canyon Wilderness. 3. Pit River Canyon 

Wilderness (Calif.) I. Campbell, Harry W. II. Title. 

III. Series: Geological Survey Bulletin; B1706-E.

QE75.B9 no. B1706-E

[TN24.C2]

557.3 s 

[553'.09794'26]

85-600343
STUDIES RELATED TO WILDERNESS

Bureau of Land Management Wilderness Study Areas

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

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

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

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

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

Canyon Wilderness Study Area (CA-020-103), Lassen County, California.

CONTENTS

Summary El 

Abstract 1 

Character and setting 1 

Mineral resource potential 1 

Introduction 1

Acknowledgments 3 

Appraisal of identified resources 3 

Assessment of potential for undiscovered resources 3 

Geology 3 

Geochemistry 6 

Geophysics 6 

Mineral and energy resources 6

Epithermal precious-metal deposits 6 

Diatomite 6 

Oil and gas resources 6 

Geothermal resources 7 

References cited 7 

Appendix 1. Definition of levels of mineral resource potential and certainty of assessment E8

FIGURES

1. Index map showing the location of the Pit River Canyon Wilderness Study Area, Lassen County, 

California E2

2. Map showing mineral resource potential of the Pit River Canyon Wilderness Study Area, Lassen County, 

California 4

3. Major elements of mineral resource potential/certainty classification. 8

V

MINERAL RESOURCES OF WILDERNESS STUDY AREAS: NORTHEASTERN 

CALIFORNIA AND PART OF ADJACENT WASHOE COUNTY, NEVADA

Mineral Resources of the Pit River Canyon 

Wilderness Study Area, Lassen County, California

SyMaureen G. Sherlock 

U.S. Geological Survey

and Harry W. Campbell 

U.S. Bureau of Mines

SUMMARY 

Abstract

The Pit River Canyon Wilderness Study Area 

(CA-020-103) includes 5,400 acres along the Pit River 

and its tributary Horse Creek in Lassen County, 

northeastern California. The U.S. Geological Survey 

and the U.S. Bureau of Mines examined the area and 

took stream sediment and rock samples during May and 

June 1984. No mines or prospects are located in the 

area; rock types that host metal deposits are absent. 

A cinder cone on which cinders were mined from a pit 

0.3 mi west of the study area does not extend into the 

area. Basalt suitable for aggregate and fill crops out 

in the wilderness study area, but the same kind of rock 

is abundant closer to potential markets. There is a low 

mineral resource potential in the area for gold, silver, 

diatomite, oil and gas, and geothermal energy. The 

certainty level of the mineral resource assessment is 

C.

Character and Setting

The Pit River Canyon Wilderness Study Area is 

about 22 mi east-northeast of Burney, California (fig. 

1), and about 30 mi north-northeast of Lassen Volcanic 

National Park, in the northeastern part of the 

state. Plateau topography characterizes the region, 

although the study area encloses the deep canyons of 

the Pit River and Horse Creek. The Pit River Canyon 

is as deep as 750 ft and Horse Creek Canyon is about 

400 ft deep. The only bedrock unit that crops out in 

the study area is Tertiary basalt (fig. 2).

Mineral Resource Potential

The Pit River Canyon Wilderness Study Area 

contains no identified mineral resources. See figure 2 

for an assessment of mineral resource potential.

Available information from geochemical anaylsis of 

stream-sediment samples does not show anomalous 

concentrations of any element indicative of 

mineralized rock in the drainage area, and existing 

geophysical surveys show anomalies typical of 

continental basaltic terrane. Mineral resources near 

the study area include volcanic cinders, diatomite, 

gold, silver, sand, gravel, and stone. Basalt from the 

study area could be used as aggregate and fill, but 

other suitable rock is available closer to potential 

markets. The sand and gravel deposits in the area are 

small and access to them is generally poor; sand and 

gravel deposits are also plentiful closer to potential 

markets. No metallic or industrial minerals were 

found during this study.

INTRODUCTION

The Pit River Canyon Wilderness Study Area 

(CA-020-103) covers 5,400 acres in Lassen County, 

northeastern California. It includes about 11 linear mi 

of the steep, narrow canyon of the Pit River, where 

elevations range from 3,400 to 4,000 ft at the bottom 

of the canyon and from 3,800 to 4,400 ft along the 

canyon rim. The canyon is 200 to 750 ft deep. The 

highest peak within the study area is 4,539 ft at First 

Butte (fig. 2). Four-wheel drive roads and trails that 

cross the plateau provide access to the canyon rim. 

The canyon bottom in the study area is relatively 

inaccessible. In places it is choked by talus composed 

of large boulders and there are no maintained trails 

into the canyon. Pit River and Horse Creek are 

perennial; North and Spring gulches at the northeast 

boundary and other gulches are intermittent streams. 

All other gulches or canyon entrants are dry.

Dense vegetation along the canyon walls and 

rims consists of ponderosa and Jeffrey pine, juniper, 

oak, mahogany, and numerous shrubs and grasses. 

Grasses, willow, and numerous hydrophilic plants grow 

abundantly along the creek bottoms. Golden eagles 

and prairie falcons nest in the canyon.

El
121°45' 121°30' 121°00' 120°45'

40°45

Figure 1. Index map showing the location of the Pit River Canyon Wilderness 

Study Area, Lassen County, California

E2
The Pit River Canyon Wilderness Study Area is 

about 22 mi east-northeast of Burney, and is about 10 

mi south of State Highway 299 between McArthur and 

Nubieber (fig. 1). Access to Horse Creek and the 

southern rim of the Pit River canyon is by paved road 

from California State Highway 299 from McArthur 

through Pittville to Little Valley. Dirt roads that lead 

north from Little Valley through Clark Valley provide 

access to the south rim of the canyon. Jeep trails that 

lead east from the Pittville-Little Valley road provide 

access to the west canyon rim of Horse Creek. The 

north rim of the Pit River canyon is accessible by dirt 

roads that lead south from California State Highway 

299. The Little Valley 15-minute quadrangle map 

shows some of these roads and trails (fig. 2). Most 

unpaved roads become impassable after rain or snow 

storms. The Western Pacific (now Union Pacific) 

Railroad crosses the plateau south of the Pit River 

canyon and forms a small part of the south boundary of 

the study area; several roads that once crossed the 

railroad tracks are now blocked.

For this study the U.S. Bureau of Mines searched 

the literature for evidence of past or present mining 

activity within and near the study area. Two days of 

field work in May 1984 consisted of visually examining 

the study area.

The U.S. Geological Survey mapped the 

wilderness study area in 1982 at a scale of 1:62,500 by 

photogeologic reconnaissance as part of a study of the 

Neogene volcanic rocks of the Cascade Range (J.G. 

Smith, written commun., 1985) and collected eight 

stream-sediment samples in June 1984. The only prior 

geologic study of the area has been reconnaissance 

mapping (Lydon and others, 1960). The two studies 

assigned different ages to the basalt: Lydon andothers 

(1960) assigned the basalt a Pleistocene age, but Smith 

(J.G. Smith, written commun., 1985) believes they are 

Miocene and Pliocene because of their extension into 

areas where the rocks have been dated at 2 to 7 m.y.

Acknowledgments

The U.S. Bureau of Land Management offices in 

Alturas and Susanville, Calif., generously provided 

information about history, vegetation, and road access 

in the wilderness study area. Land owners in Clark 

Valley and the Pit River valley kindly allowed passage 

through their property to the southeast and northeast 

parts of the study area, respectively. Eugenia Zorich 

was the field assistant for the U.S. Geological 

Survey. Lucia Kuizon, geologist, Western Field 

Operations Center, helped the U.S. Bureau of Mines 

author with the field work.

APPRAISAL OF IDENTIFIED RESOURCES

By Harry W. Campbell, U.S. Bureau of Mines

No mining claims or leases were located within 

the Pit River Canyon Wilderness Study Area in 1984, 

and no evidence of previous mining activity was 

found. Two placer claims, reportedly located north of 

the study area in the NE 1/4 and NW 1/4, sec. 13, T. 36

N., R. 6 E. (U.S. Bureau of Land Management, 1984), 

could not be found. This area is underlain by basalt 

and there is no evidence of valuable minerals.

Cinder pits west and south of the study area 

consist mostly of red, basaltic cinders and minor lapilli 

and bombs; irregular stringers of basalt cut the cinders 

locally. The nearest cinder pit lies 0.3 mi west of the 

study area boundary (fig. 2). The cinders are used as 

highway fill and aggregate, and a small plant at 

Pittville manufactures and sells cinder blocks and 

other cinder products. The cinder deposits do not 

extend into the study area.

Basalt from the study area could be used as 

aggregate and fill, but other suitable rock is available 

closer to potential markets. Sand and gravel deposits 

in the study area are small and access to them is 

generally poor.

ASSESSMENT OF POTENTIAL FOR UNDISCOVERED 

RESOURCES

By Maureen G. Sherlock, U.S. Geological Survey 

Geology

The Pit River Canyon Wilderness Study Area lies 

in the western part of the Modoc Plateau geomorphic 

province, which consists of a series of north-trending, 

block-faulted ranges composed of flood basalt, above 

which rise small shield volcanoes, composite andesitic 

cones, and cinder cones. Volcanic flows, lakebeds, and 

alluvium fill intervening basins. The Modoc Plateau is 

part of the Basin and Range province which was 

flooded by volcanic flows of the Cascade volcanic 

province (Macdonald, 1966).

Late Miocene and Pliocene basalt flows (2 to 7 

m.y., J.G. Smith, written commun., 1985) underlie the 

study area. They are vesicular to nonvesicular black 

flows and are commonly 2 to 50 ft thick (Macdonald, 

1966). A series of northwest-trending, high-angle 

normal faults cut the flows. Red soils, which are 

deepest on flat to gently dipping surfaces, cover much 

of the plateau; these soils are derived from deeply 

weathered basalt and contain subrounded boulders.

Neogene andesite of the same age as the basalt 

formed a shield volcano on Bald Mountain, about 5 mi 

southeast of the study area. Flows originating from 

this volcano extend to within 0.25 mi of the study area 

(fig. 2).

Although basaltic and andesitic flows dominate, 

lake beds and ash-flow tuffs are exposed locally. 

Colluvium, formed from the weathering of lava flows, 

commonly covers these less-resistant rocks. Neither 

lake beds nor ash-flow tuffs extend into the study 

area.

Cinder cones are common in the region, but 

rocks of that age (120,000 to 730,000 B.P.; J.G. Smith, 

written commun., 1985) do not extend into the study 

area.

An 8 m.y.-old Tertiary dacite complex, composed 

of ash-flow tuffs, ash beds, and glassy domes (J.G. 

Smith, written commun., 1985; Finn and Buchanan, 

1984), occurs in the Hayden Hill mining district, 12 mi 

east of the study area. There, argentiferous gold,

E3
i- V28"

UNDARY

RIVER CANYON WILDERNESS

Base from U.S. Geological Survey. 

1:62,500 Little Valley, 1957

Geology by James G. Smith, 1982, 

unpublished photointerpretation

Figure Z. Map showing mineral resource potential of the Pit River Canyon 

Wilderness Study Area, Lassen County, California

E4
EXPLANATION

Area with low mineral or geothermal energy resource potential, 

certainty level C (L/C). Applies to entire wilderness study area. 

See Appendix 1 and Figure 3 for definition of levels of mineral 

resource potential and certainty of assesment

COMMODITIES

Au Gold

Ag Silver

Diat Diatomite

Pet Oil and gas

Geo Geothermal

[ ] TYPES OF DEPOSITS AND OCCURENCES

1 Epithermal precious-metal deposits in 

dacite volcanic rocks

2 Diatomite deposits in lake-bed sediments

CORRELATION OF MAP UNITS 

Quaternary

Tb | Ta | Tertiary

GEOLOGIC MAP UNITS

Qal ALLUVIUM (HOLOCENE AND PLEISTOCENE)

Qb BASALT (QUATERNARY)

Tb BASALT (PLIOCENE AND MIOCENE)

Ta ANDESITE (PLIOCENE AND MIOCENE)

MAP SYMBOLS

 CONTACT- Dashed where approximately located

L NORMAL FAULT-Dashed where approximately located;

dotted where concealed ball and 

bar on downthrown side

® GEOCHEMICAL STREAM-SEDIMENT SITE

H GEOCHEMICAL ROCK SAMPLE SITE

A DIATOMACEOUS (?) LAKE BED DEPOSIT

X CINDER PIT

Figure Z. Continued

E5
minor silver sulfides, and silver-bearing manganese 

oxides are disseminated in sulfide-rich breccias, 

stockworks, and quartz-adularia veins (Finn and 

Buchanan, 1984). This is the closest mining district to 

the study area within the Modoc Plateau (Albers and 

Fraticelli, 1985). No evidence suggests that similar 

mineralized rocks occur in the study area.

Geochemistry

Data from eight stream-sediment samples 

collected in and near the study area (fig. 2) were used 

to assess the geochemical characteristics and potential 

of the area. Sediment in seven of the samples was 

derived totally from basalt. Andesite contributed 

much of the sediment for sample PR-504. Sampling 

sites were selected for the availability of stream 

sediment, potential for panning onsite, and access. 

Stream sediments in basaltic terranes such as that of 

the study area typically consist of coarse pebbles and 

finer material that contains mostly heavy minerals. 

Consequently, the amount of stream sediment 

available at a sampling site is commonly small and 

only a small amount of the light fraction is lost in 

panning.

Stream-sediment samples and panned 

concentrates were analyzed by semiquantitative 

emission spectrography and flame atomic absorption 

(Sherlock and others, 1985). A representative basalt 

sample (fig. 2) was analyzed by fire assay-inductively 

coupled plasma-emission spectrometry methods for 

gold and silver and forty elements. The results of this 

U.S. Bureau of Mines sample analysis are included in 

Sherlock and others (1985). The data indicate an 

unmineralized volcanic terrane (J.G. Frisken, oral 

commun., 1985).

Geophysics

The geophysical evaluation of the study area 

relied on existing gravity surveys (Oliver and others, 

1980). Gravity contours show no anomalous features 

and are consistent with the volcanic nature of the 

region. Airborne Gamma-ray spectrometer and 

magnetometer surveys of the Susanville 1° by 2° 

quadrangle (Western Geophysical Company of 

America, 1981) also show no anomalies in the study 

area. There is a thorium anomaly about 5 mi west of 

the southwest boundary of the study area. This 

represents an irregular increase in thorium over a 

large area due to an elevation of background levels 

rather than to potentially economic deposits (Western 

Geophysical Company of America, 1981).

Mineral and Energy Resources

The Modoc Plateau contains few economic 

mineral deposits. The nearest metallic mineral 

deposits are in dacite at Hayden Hill, 12 mi to the 

east; the nearest non-metallic deposits are cinders in 

Pleistocene basalt 0.3 mi to the west, and diatomite in 

Pliocene lake beds 17 mi to the west.

Epithermal precious-metal deposits

The Hayden Hill mining district was established 

(originally as Providence City) after the 1870 

discovery of gold in the bottom of a spring which 

issued from one of the gold- and silver-bearing veins in 

breccias and silicified felsic tuffs at the base of 

Hayden Hill (Hill, 1915). Soil covering most of the hill 

was panned and sluiced for free gold; the highestgrade lode ore was found in manganese-oxide-rich 

breccias that contain little quartz and sulfides (Hill, 

1915). The small lode deposits produced about $3 

million worth of gold (Clark, 1970). The district is now 

being explored for large, low-grade disseminated-gold 

deposits (Clark, 1985). Recent studies (Finn and 

Buchanan, 1984) indicate three stages of 

mineralization: brecciation, calcite veining, and 

quartz-adularia veining. The volcanic sequence at 

Hayden Hill may be a hot spring vent area (Buchanan, 

1983) or part of a caldera (Hazlett and Grose, 1983). 

Finn and Buchanan (1984) conclude from fluid inclusion 

studies of the vein minerals that the temperature of 

formation of these volcanic rocks was 260° C, 

indicating that they formed at depths greater than 

1,500 ft rather than in hot springs. The dacitic rocks 

are probably restricted to the Hayden Hill area (fig. 1) 

and do not occur in the study area. They are, however, 

older than the basalt in the Pit River canyon (8.3+0.4 

m.y.; Finn and Buchanan, 1984) and could be covered 

by basalts; but nothing suggests that this is likely. 

Therefore, the Pit River Canyon Wilderness Study 

Area has a low potential for epithermal precious-metal 

(Au, Ag) deposits with a C certainty. See Appendix 1 

and figure 3 for definitions of levels of mineral 

resource potential and certainty of assessment.

Diatomite

Pliocene fresh-water lakebed sediments are 

being mined for diatomite near Lake Britton and the 

Hat Creek-Pit River confluence (fig. 1; Oakeshott, 

1957; Lydon and O'Brien, 1974). These deposits may 

have formed in a large lake ponded by lava flows or a 

large landslide about 2 m.y. ago (J.G. Smith, oral 

commun., 1985). Because the elevation of this lake 

was lower than elevations in the Pit River canyon, the 

lake probably never extended into the study area. 

Extensive Pliocene lakebed sediments do not occur 

within the Pit River Canyon Wilderness Study Area. 

White, presumably diatomaceous, lakebed sediments, 

older than those just discussed (J.G. Smith, oral 

commun., 1985), are exposed in one railroad cut (fig. 

2); no interbedded sediments were observed in the 

study area. The Pit River Canyon Wilderness Study 

Area has a low potential for diatomite with a C 

certainty.

Oil and Gas Resources

Scott (1983) qualitatively assessed the Modoc 

Plateau as having a zero to low potential for 

petroleum. He based this assessment on the known 

thickness of Cenozoic volcanic rocks that cover 

marine Cretaceous rocks and scattered Tertiary lake

E6
beds which could be reservoirs for hydrocarbons. The 

Pit River Canyon Wilderness Study Area has a low 

potential for oil and gas resources with a C certainty.

Geothermal Resources

Warm-temperature thermal springs occur 3 mi 

northwest of the study area along a northwest-trending 

fault between basalt and alluvium east of the Pit River 

(Higgins, 1980). They are the only thermal springs 

near the study area, but they are not included in the 

assessment of low-temperature geothermal resources 

of the United States (Reed, ed., 1983; Reed and others, 

1983). The potential for geothermal resources within 

the Pit River Canyon Wilderness Study Area is low 

with a C certainty.

REFERENCES CITED

Albers, J.P., and Fraticelli, L.A., 1985, Preliminary 

mineral resource assessment map of California: 

U.S. Geological Survey Mineral Investigations Map 

MR-88, scale 1:1,000,000.

Buchanan, L.J., 1983, Geology and ore deposits of 

Hayden Hill, Lassen County, California: Geological 

Society of America Abstracts with Programs, v. 15, 

no. 5, p. 326.

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

California Division of Mines and Geology Bulletin 

193, p. 177.

__1985, Gold districts of California an update: 

California Geology, v. 48, no. 1, p. 3-4.

Finn, D.R., and Buchanan, L.J., 1984, Hayden Hill, 

California: Epithermal Au-Ag mineralization 

associated with Cascade volcanism: Geological 

Society of America Abstracts with Programs, v. 16, 

no. 6, p. 509.

Hazlett, D.P., and Grose, T.L.T., 1983, The Hayden 

Hill volcanic center, northeastern California: 

Geological Society of America Abstracts with 

Programs, v. 15, no. 5, p. 330.

Higgins, C.T., 1980, Geothermal resources of 

California: California Division of Mines and 

Geology, California Geologic Data Map Series Map 

4, scale 1:500,000.

Hill, J.M., 1915, Some mining districts in California 

and Nevada: U.S. Geological Survey Bulletin 594,

200 p.

Lydon, P.A., Gay, T.E., Jr., and Jennings, C.W., I960, 

Geologic map of California Westwood (Susanville) 

sheet: California Division of Mines and Geology, 

scale 1:250,000.

Lydon, P.A., and O'Brien, J.C., 1974, Mines and 

Mineral Resources of Shasta County, California: 

California Division of Mines and Geology County 

Report 6, 154 p.

Macdonald, G.A., 1966, Geology of the Cascade Range 

and Modoc Plateau in Bailey, E. H., ed., Geology 

of northern California: California Division of 

Mines and Geology Bulletin 190, p. 65-96.

Oakeshott, G.B., 1957, Diatomite, in_Wright, L.A., ed., 

Mineral Resources of California: California 

Division of Mines and Geology Bulletin 176, 

p. 183-193.

Oliver, H.W., Robins, S.L., and Griscom, Andrew, 1980, 

Bouger gravity map of California, Westwood 

(Susanville) sheet: California Division of Mines and 

Geology, scale 1:250,000.

Reed, M.J., ed., 1983, Assessment of low-temperature 

geothermal resources of the United States 1982: 

U.S. Geological Survey Circular 892, 73 p.

Reed, M.J., Mariner, R.H., Brook, C.A., and Sorey, 

M.L., 1983, Selected data for low-temperature (less 

than 90° C) geothermal systems in the United 

States: Reference data for U.S. Geological Survey 

Circular 892: U.S. Geological Survey Open File 

Report 83-250, 129 p.

Scott, E.W., 1983, Petroleum potential of wilderness 

lands in California: U.S. Geological Survey 

Miscellaneous Geologic Investigations Map 1-538, 

scale 1:1,000,000.

Sherlock, M.G., Frisken, J.G., Adrian Betty, Zorich, 

Eugenia, 1985, Geochemical analyses of streamsediment samples from the Pit River Canyon 

Wilderness Study Area, Lassen County, California: 

U.S. Geological Survey Open-File Report 85-390, 

12 p.

U.S. Bureau of Land Management, 1984, Geographic 

index for California: Mining Claim Recordation 

Index, March 1984.

Western Geophysical Company of America, 1981, 

National Uranium Resource Evaluation Program, 

airborne gamma-ray spectrometer and 

magnetometer survey, Susanville quadrangle, 

California: Grand Junction, Colo., U.S. 

Department of Energy GJBX-410 (81), 2 vol.

E7
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

LEVEL OF CERTAINTY

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

E8

GPO 687-049/45013