Mineral Resources of the Diablo Mountain 

Wilderness Study f Area, Lake County, m Oregon V**^

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Chapter D

Mineral Resources of the Diablo Mountain 

Wilderness Study Area, Lake County, Oregon

By MICHAEL F. DIGGLES, HARLEY D. KING, 

MARK E. GETTINGS, JAMES E. CONRAD, 

DON L. SAWATZKY, and GERILYN S. SOREGHAN 

U.S. Geological Survey

THOMAS J. PETERS and SPENCEE L. WILLETT 

U.S. Bureau of Mines

U.S. GEOLOGICAL SURVEY BULLETIN 1738

MINERAL RESOURCES OF WILDERNESS STUDY AREAS: 

SOUTH-CENTRAL OREGON
U.S. DEPARTMENT OF THE INTERIOR 

MANU EL LUJAN, JR., Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

Any use of trade, product, or firm names

in this publication is for descriptive purposes only

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

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For sale by the

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Library of Congress Cataloging-in-Publication Data

Mineral resources of the Diablo Mountain Wilderness Study Area, Lake County,

Oregon / by Michael F. Diggles...[et al.].

p. cm (Mineral resources of wilderness study areas south-central 

Oregon; ch. D) (U.S. Geological Survey bulletin; 1738-D)

Includes bibliographical references (p. ).

Supt. of Docs, no.: 119.3:1738-D

1. Mines and mineral resources Oregon Diablo Mountain Wilderness. 

2. Diablo Mountian Wilderness (Or.) I. Diggles, M.F. II. Series. III. Series: U.S. 

Geological Survey bulletin; 1738-D.

QE75.B9 no. 1738-D 557 J s dc 20 90-14053 

(TN24.07) [553'.09795'93] CIP
STUDIES RELATED TO WILDERNESS

Bureau of Land Management Wilderness Study Areas

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

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

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

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

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

Diablo Mountain Wilderness Study Area (OR-001-058), Lake County, Oregon.

CONTENTS

Summary Dl

Abstract Dl 

Character and setting Dl 

Identified mineral resources Dl 

Mineral resource potential D3 

Introduction D3

Location and physiography D3 

Procedures D3 

Previous studies D5 

Acknowledgments D5 

Appraisal of identified resources D6

Mining and mineral exploration history D6 

The Oregon claims group D6

Field methods D6

Brine commodity evaluation D7 

The Tenmile and other dolomitic limestone prospects D8 

Geothermal energy D8 

Mineral economics D8

Soda ash D8

Boron compounds D8

Sodium sulfate D9

Byproduct brine commodities D9

Dolomitic limestone D9

Geothermal energy D9

Miscellaneous mineral commodities D10 

Conclusions D10

Recommendations for further work D10 

Assessment of mineral resource potential D10 

Geology D10

Stratigraphy D10

Structure Dll 

Geochemistry Dll

Methods and background Dll

Sample analysis D12

Results and interpretation D12 

Geophysical studies D13

Aeromagnetic survey D13

Gravity survey D14

Remote sensing D15 

Mineral resource assessment D15 

References cited D16 

Appendixes D19

Definition of levels of mineral resource potential and certainty of 

assessment D20

Resource/reserve classification D21 

Geologic time chart D22

Contents
FIGURES

1. Index map showing location of Diablo Mountain Wilderness Study Area, Lake County, 

Oregon D2

2. Map showing mineral resource potential and generalized geology of Diablo Mountain 

Wilderness Study Area, Lake County, Oregon D4

3. Map showing concentrations of chemical components of brine commodities in ground 

water in western part of Diablo Mountain Wilderness Study Area, Oregon D7

4. Aeromagnetic anomaly map of region including Diablo Mountain Wilderness Study Area, 

Oregon D14

5. Bouguer gravity anomaly map of region including Diablo Mountain Wilderness Study 

Area, Oregon D15

VI Contents
Mineral Resources of the Diablo Mountain 

Wilderness Study Area, Lake County, Oregon

By Michael F. Diggles, Harley D. King, Mark E. Gettings, James E. Conrad, Don L. Sawatzky, 

and Gerilyn S. Soreghan 

U.S. Geological Survey

Thomas J. Peters and Spencee L. Willett 

U.S. Bureau of Mines

SUMMARY

Abstract

At the request of the U.S. Bureau of Land Management, 

approximately 85,470 acres of the Diablo Canyon Wilderness 

Study Area was evaluated for identified mineral resources 

(known) and mineral resource potential (undiscovered). In 

this report, the area studied is referred to as the "wilderness 

study area" or "the study area." Any reference to the Diablo 

Mountain Wilderness Study Area refers only to that part of the 

wilderness study area for which a mineral survey was requested 

by the U.S. Bureau of Land Management Fieldwork was 

conducted in 1986, 1988, and 1989 to assess the mineral 

resources and resource potential of the study area.

No energy or mineral resources were identified in the 

study area, but brines within lake and playa sediments contain concentrations of chemical components suitable for the 

production of soda ash, boron compounds, and sodium sulfate. Possible byproducts include potash, salts, bromine, lithium, magnesium compounds, and tungsten. Limestone from 

the study area could be used in the recovery process of brine 

components. The study area includes thermal springs and 

lies within 2 mi of the Summer Lake Known Geothermal 

Resource Area (KGRA). In the western part of the study area, 

the mineral resource potential is moderate for undiscovered 

resources of soda ash, boron compounds, and sodium sulfate 

as well as byproduct magnesium compounds, salts, potash, 

bromine, lithium, and tungsten associated with brines. In a 

small south-central part of the study area, the mineral resource 

potential is low for low-grade high-tonnage epithermal hotspring gold-silver deposits and for magnesium from dolomitic 

limestone. The resource potential of the entire study area is 

moderate for low-temperature geothermal energy useful for 

agricultural and building heating and is low for oil and gas.

Manuscript approved for publication, August 27, 1990

Character and Setting

The Diablo Mountain Wilderness Study Area is just 

east of Summer Lake (fig. 1), about 45 mi north of Lakeview, 

Oreg. It lies on the northwest edge of the Basin and Range 

physiographic province, in the volcanic plateau region lying 

south of the Blue Mountains and east of the Cascade Range. 

The region west of Summer Lake and continuing south of 

the study area is part of the poorly defined Modoc Plateau 

physiographic province that separates the Basin and Range 

and the Cascade Range physiographic provinces. Consolidated rocks within the study area consist mostly of Tertiary 

basalt and tuffaceous sedimentary rocks (see "Appendixes" 

for geologic time chart). The low-lying areas are covered 

by Quaternary alluvial-fan, sand-dune, playa, lacustrine, 

fluvial, and landslide deposits. The principal structural features of the area are normal faults that have large vertical 

offsets. These faults are concentrated at the margins of 

large horst and graben typical of the Basin and Range province.

Identified Mineral Resources

No mineral resources have been identified within or 

adjacent to the study area, but brines within lake and playa 

sediments, sampled from shallow auger holes, contain concentrations of chemical components suitable for the production of soda ash, boron compounds, and sodium sulfate. 

Possible byproducts include potash, salts, bromine, lithium, 

magnesium compounds, and tungsten. Limestone from the 

study area could be used in recovering soda ash, boron 

compounds, sodium sulfate, and magnesium compounds 

from brine. The area includes thermal springs and lies 

within 2 mi of the Summer Lake Known Geothermal Resource Area (KGRA).

Mineral Resources of the Diablo Mountain Wilderness Study Area, Lake County, Oregon D1
AREA OF AAAP

APPROXIMATE BOUNDARY

OF

DIABLO MOUNTAIN

WILDERNESS STUDY AREA

(OR-001-058)

Tenmile 

173 prospect

vf: X Tenmile 

V A Ridge

\

^Summer LakeWm 

" Hot S

j I Summer Lake KGRA

~? (Known Geothermal Resource Area)

10 MILES

Figure 1. Index map showing location of Diablo Mountain Wilderness Study Area, Lake County, Oregon.

D2 Mineral Resources of Wilderness Study Areas: South-Central Oregon
Mineral Resource Potential

The western part of the Diablo Mountain Wilderness 

Study Area has moderate mineral resource potential for 

commodities associated with brines: soda ash, boron compounds, and sodium sulfate as well as byproduct magnesium compounds, salts, potash, bromine, lithium, and tungsten. A low mineral resource potential for low-grade hightonnage epithermal hot-spring gold-silver deposits in the 

area of Tenmile Ridge is suggested by the presence of opal 

in some altered-basalt outcrops and by the presence of mercury in a nearby prospect. The mineral resource potential 

is low for magnesium from dolomitic limestone in the area 

of Tenmile Ridge. The entire study area has moderate 

geothermal energy resource potential for low-temperature 

thermal water useful for agricultural and building heating. 

The Summer Lake KGRA is 2 mi south of the study area. 

Thermal springs at Ana Springs and Summer Lake Hot 

Spring are near the study area, and one known thermalwater spring was observed within the study area. Oil and 

gas resource potential is low throughout the study area.

INTRODUCTION

This mineral survey was requested by the U.S. Bureau of Land Management and is the result of a cooperative 

effort by the U.S. Geological Survey and the U.S. Bureau 

of Mines. An introduction to the wilderness review process, 

mineral survey methods, and agency responsibilities was 

provided by Beikman and others (1983). The U.S. Bureau 

of Mines evaluates identified resources at individual mines 

and known mineralized areas by collecting data on current 

and past mining activities and through field examination of 

mines, prospects, claims, and mineralized areas. Identified 

resources are classified according to a system that is a 

modification of that described by McKelvey (1972) and 

U.S. Bureau of Mines and U.S. Geological Survey (1980). 

U.S. Geological Survey studies are designed to provide a 

scientific basis for assessing the potential for undiscovered 

mineral resources by determining geologic units and structures, possible environments of mineral deposition, presence 

of geochemical and geophysical anomalies, and applicable 

ore-deposit models. Goudarzi (1984) discussed mineral assessment methodology and terminology as they apply to 

these surveys. See "Appendixes" for the definition of levels 

of mineral resource potential and certainty of assessment 

and for the resource/reserve classification.

Location and Physiography

The Diablo Mountain Wilderness Study Area includes 

approximately 85,470 acres and is 45 mi north of Lakeview

and 5 mi north of Paisley, Oreg. (fig. 1). Elevations in the 

area range from 4,300 ft near the shore of Summer Lake to 

6,147 ft at the summit of Diablo Mountain. Access to the 

region is via Oregon State Route 31 connecting U.S. Highways 395 north of Lakeview and 97 south of Bend. Access 

to the area is provided by dirt roads from State Highway 

31. Access within the study area is by four-wheel-drive 

vehicle on jeep trails and by mountain bicycle and by foot. 

The climate is semiarid, and the average annual precipitation 

is about 12 in.; sparse rainfall in the area results in only 

intermittent stream flow. The region contains several lakes, 

of which Summer Lake is one, that occupy closed basins. 

Vegetation consists of low-growing desert shrubs, mostly 

sagebrush, greasewood, creosotebush, burroweed, and 

boxthorn.

Procedures

«

The U.S. Geological Survey conducted detailed field 

investigations of the Diablo Mountain Wilderness Study 

Area in the summers of 1986, 1988, and 1989. This work 

included making a detailed geologic map (Diggles and 

others, 1990), collecting geochemical, petrologic, and geochronologic samples, and examining outcrops for evidence 

of mineralization. Generalized geology is shown in figure 

2.

The U.S. Bureau of Mines work on the Diablo Mountain Wilderness Study Area was done in two phases. The 

central and eastern parts of the area were examined by Willett 

(1987), and the western part of the area was studied by 

Peters and Willett (1989). These studies included library 

search of pertinent geological and mining literature. U.S. 

Bureau of Land Management master tide plats and current 

mining claim recordation data, as well as Lake County mining claim records were examined. Information was also 

obtained from the U.S. Bureau of Land Management 

Lakeview District Office, the Oregon Department of Geology 

and Mineral Industries, Portland, and the U.S. Bureau of 

Mines Mineral Industries Location System and other files 

and records.

U.S. Bureau of Mines fieldwork was done during 

spring 1986 and June 1988. A search was conducted for all 

mines, prospects, and mineralized areas in and within 1 mi 

of the study area. Samples include 45 sediment, 2 brine, 26 

water (predominantly from auger holes), 21 alkali-crust 

(from surfaces of alkali flats adjacent to auger holes), 34 

rock (randomly chipped from homogeneous outcrops), and 

4 sand samples; 1 auger-hole sediment sample was collected for mineral identification by X-ray diffraction (halite). Mineralized sites were examined and sampled. Results of analyses of these samples are on file at the U.S. 

Bureau of Mines, Western Field Operations Center, E. 360 

Third Ave., Spokane, WA 99202.

Mineral Resources of the Diablo Mountain Wilderness Study Area, Lake County, Oregon D3
120°37'30" 120°30'

EXPLANATION

Area having moderate mineral 

resource potential (M) for 

brine compounds

Silver

Gold

Boron

Bromine

Geothermal

energy 

Potash 

Lithium 

Magnesium 

Soda ash 

Table salt

Area having moderate mineral 

resource potential (M) for 

geothermal energy and low 

mineral resource potential 

(L) for other commodities 

where indicated

Levels of certainty of assessment Na2SO4 Sodium sulfate

O/G Oil and gas

W Tungsten Data only suggest level of

potential

C Data give good indication of 

level of potential

APPROXIMATE BOUNDARY

OF 

DIABLO MOUNTAIN

STUDY AREA 

(OR-001-058)

or

M/CGeo 

(entire study area)

M/C Na, B, Na2SO4; 

Mg, NaCl, K, Br, 

Li, W L/B O/G

(entire study area)

Figure 2. Mineral resource potential and generalized geology of Diablo Mountain Wilderness Study Area, Lake 

County, Oregon. Geology generalized from Diggles and others (1990).

D4 Mineral Resources of Wilderness Study Areas: South-Central Oregon
Previous Studies

Waring (1908) discussed the geology and water resources of south-central Oregon. The eastern halves of the 

Klamath Falls and Crescent 1° by 2° quadrangles have been 

mapped by Walker (1963) and Walker and others (1967), 

respectively. Peterson and Mclntyre (1970) presented the 

geology and mineral resources of part of Lake County. An 

assessment of geology, energy, and minerals in the Summer

Qal 

Qsd

Qpl 

Qlf

as

Tbc

Tb

Its

Description of map units

Alluvium (Quaternary) Alluvial fan deposits and 

stream deposits of gravel, sand, and silt

Sand dunes (Quaternary) Large areas of windblown 

sand composed of ash, pumice, and rock-forming 

mineral grains, mostly alkali feldspar and quartz

Playa deposits (Quaternary) Clay, silt, sand, and 

some evaporite deposits. Contains tephra at depth

Lacustrine and fluvial deposits (Quaternary) 

Unconsolidated clay, silt, and gravel

Landslide deposits (Quaternary) Unstratified mixtures of basaltic and tuffaceous sedimentary rocks. 

Includes faulted blocks, rubble, and talus

Claystone (Quaternary) Mostly montmorillonite; 

locally includes marl, micrite, caliche, and opalbearing travertine

Basaltic cinders (Tertiary) Red and reddish black 

cinders and near-vent flows; scoriacious rocks and 

altered basalt

Basalt (Tertiary) Gray to dark-gray plagioclasephyric olivine basalt flows having subophitic to 

diktytaxitic texture. Includes minor basalt-flow 

breccia. Crystals of labradorite are partly to completely enveloped in clinopyroxene. Pyroxene also 

forms interstitial grains. Locally interbedded with 

dolomitic limestone of Pliocene(?) age in vicinity 

of Tenmile Ridge (see fig. 1)

Tuffaceous sedimentary rocks (Tertiary) Semiconsolidated interbedded white, light-yellow, and 

cream-colored lacustrine and fluvial sedimentary 

rocks that consist mostly of tuffaceous sandstone 

and siltstone and locally contain arkosic sandstone 

and pebble conglomerate. Contains alkali feldspar, 

clay minerals, zeolites, and secondary silica 

minerals. Age and correlation uncertain but presumably mostly of middle and late Miocene age 

(Walker, 1977)

Contact

 .. Fault Dashed where approximately located, dotted 

where concealed

X Tenmile prospect 

Figure 2. Continued.

Lake GEM Resources Area (fig. 1) was presented in 

Mathews and others (1983). Geology of the Summer Lake 

area was discussed more extensively in Conrad (1953) and 

Travis (1977). Mineralized waters at Summer Lake were 

discussed by Van Denburgh (1975). Structural geology of 

the Summer Lake area is emphasized in Fuller and Waters 

(1929), Donath (1962), Donath and Kuo (1962), and 

Lawrence (1976).

Acknowledgments

The writers greatly appreciate the cooperation of 

Dennis Simontacchi and Doug Troutman of the U.S. Bureau 

of Land Management in Lakeview, Oreg., for supplying 

information about claim records, geology, history, and 

logistics. Appointment of a field assistant was based on a 

recommendation by the National Association of Geology 

Teachers (NAGT); Gerilyn S. Soreghan was employed 

through the program. The authors are also grateful to Larry 

Hill, Paisley, Oreg., for geographic information about the 

study area and the surrounding region and especially for 

taking them to the thermal springs (fig. 3). John Withers of 

Paisley provided historical background, and John Cremin 

of Lakeview and Harold J. Dyke of Adel, Oreg., provided 

historical and technical information on the Tenmile (Sundown) limestone claim group. Steven Carpenter, Robert 

Deal, and Robert B. Kistlcr of U.S. Borax, Los Angeles, 

Calif., Gail Moulton of Kerr-McGee, Trona, Calif., and 

Dwight Harris of Clayton, Wash., contributed information 

on evaporite mineral commodities. Rex McKee of 

Weyerhaeuser Corp., Longview, Wash., provided 

information on chemicals used in wood processing. Ronald 

Geitgey, Oregon Department of Geology and Mineral 

Industries, Portland, and Dennis Simontacchi and Doug 

Troutman of the U.S. Bureau of Land Management, 

Lakeview, offered important geologic, historical and 

logistical advice. Kent Keller of Washington State University, and Walter Ficklin and Alan Driscoe of the U.S. Geological Survey, Lakewood, Colo., provided information on 

ground-water geochemistry. U.S. Geological Survey personnel A.S. Van Denburgh, Reno, Nev., and G.I. Smith, 

Menlo Park, Calif., provided information on the geology 

and geochemistry of closed-basin lakes. U.S. Bureau of 

Mines personnel, Paulette Atringer, Salt Lake City, Utah, 

and Dennis Kostic, Washington, D.C., provided information on evaporite mineral processing and economics. Field 

assistants in the U.S. Geological Survey geochemical sampling program were Steven Smith and Janet Jones. James 

Canwell, U.S. Bureau of Mines Western Field Operations 

Center, assisted with laboratory studies. U.S. Bureau of 

Mines Western Field Operations Center geologists David 

Benjamin and Terry Neumann assisted in the field during 

the spring of 1986.

Mineral Resources of the Diablo Mountain Wilderness Study Area, Lake County, Oregon D5
APPRAISAL OF IDENTIFIED RESOURCES

By Thomas J. Peters andSpencee L. Willett 

U.S. Bureau of Mines

Mining and Mineral Exploration History

Lake County mining records indicate that the Oregon 

claims group (fig. 3), a large block of 326 placer claims, was 

located in 1901 by an eight-person association and was relocated by the same claimants in 1906. The claims group extended from 2 mi north to 1 mi south of Summer Lake and as 

much as 2 mi east and 1 mi west; it included the entire lake 

and surrounding playa. The discovery, according to Lake 

County mining records, was for "... the valuable metals, sodium and potassium and their compounds of bicarbonate of 

soda, carbonate of soda and potassium sulfate, in paying 

quantities held in solution and in deposit,..." The claimants 

were Charles M. Sain, John T. Reid, Schuyler Duryee, WP. 

Brock, and William, Charles, Canby, and Elwood Balderston. 

The eastern pan of the Oregon Claims group extended into 

the western part of the study area.

With the outbreak of World War I, foreign potash supplies were cut off, and the pice for them increased from 

$0.80 to $8.00 per unit (20 Ib). In 1916, the first successful 

plants to produce potash and other evaporite minerals from 

brine came on line at Searles Lake, Calif. (Teeple, 1929). On 

December 16, 1914, the State of Oregon leased the mineral 

rights to soda salts in Abert and Summer Lake on a royalty 

basis (Hartley, 1915). Ambitious development plans included 

a 270-mi pipeline north to the Columbia River and a large 

hydroelectric plant, an investment of about $7,000,000 (Phaten, 

1916, p. 107-108). Outside but adjacent to the south boundary 

of the study area (fig. 3) are remnants of a water retention 

levee and an evaporation pond. These were apparently developed in 1918; John Withers, a local rancher, recalls that much 

money and effort was spent that year by a crew of men led by 

one Jason Moore. After the armistice, the potash pice dropped 

and by mid-1919 was at $1.75 to $2.00 per 20-lb unit Perhaps 

this was the main reason for not continuing the work at Summer Lake.

In March 1974, a group of claims including the Tenmile 

prospect and six others was located for limestone on the northeast side of Tenmile Ridge. Claimants included Harold J. and 

Marie Dyke of Adel, Oreg., Frances M. Foster, Con O'Keefe, 

Laura Shine, Jerry and Julia Singleton, and Morgan Verling. 

John Cremin (Lakeview, Oreg.) examined the prospect in 1980, 

brought it to the attention of the authors, and reported that 

exposures of the limestone extend into the study area.

The Oregon Claims Group

The Oregon claims group, inactive since 1918, covered 

all of Summer Lake, including the west margin of the Diablo 

Mountain Wilderness Study Area (fig. 3). The prospect was

primarily for brines; no conventionally mineable beds of 

evaporite minerals are known. Summer Lake waters are not 

sufficiently concentrated to be a source of resource-bearing 

bine. In 1969, the lake, with a maximum water depth of 

about 3 ft, contained a calculated total of only 1 million short 

tons of mineral salts; however, the top 5 ft of lake-bottom and 

marginal sediments contained 15 to 20 million short tons of 

evaporite minerals. The greatest quantities of evaporite minerals are under the eastern playa rather than under the lake 

(Van Denburgh, 1975). Seasonal variation of fresh water and 

evaporation renders the solute concentration too inconsistent 

for the lake waters to constitute a bine source for year-round 

processing. Interstitial bines sampled from auger holes (Peters 

and Willett, 1989, tables A-l and A-2) are much higher in 

solutes man the lake-water samples reported by Van Denburgh 

(1975, table 4).

Within the study area, bine-hosting lake and playa 

sediments define a mineral area extending more than 2 mi 

east of the claims group. Much of this area has a veneer of 

windblown sand as much as several tens of feet thick. Several flat-floored topographic depressions, displaying white 

surface efflorescence characteristic of areas underlain by 

evaporative bine, have formed windows through the sand.

Field Methods

Samples from 21 hand-auger holes from within the study 

area east of Summer Lake are described by Peters and Willett 

(1989, plate 1, tables A-l and A-2). Samples consist of alkali 

crust (efflorescence), augered sediment, and, where available, 

auger-hole bine; several springs and seeps were also sampled.

Lake and playa sediments are interbedded. Deeper holes 

typically were collared in brown silt-, clay-, and fine-sandsized playa sediments and extended into black silt- and claysized lake sediments. Only one evaporite bed, 0.4 ft of halite, 

was encountered during augering. Several holes ended in 

coarse, clean, black basaltic beach or stream sand. Permeable 

beds, along with soluble evaporite beds at depth, are essential 

for pumping bine from the sediments and recharging them 

with ground water. Such beds also are needed for recharging 

the ground water with new mineral salts. Clay-dominant 

fades that have high bine content may not yield enough 

bine and contained-evaporite mineral components for commercial exploitation.

Sampling of the mineral area by hand auger yields 

data on the mineral and brine composition of the top few 

feet and allows comparison with chemical data from analogous mineral systems that are better understood. An appropriate place for comparison is Searles Lake, Calif., about 

500 mi to the southeast, where evaporite commodities have 

been extracted from brines and evaporite deposits for more 

than 50 years (Smith, 1979). Meaningful quantitative resource estimation, however, requires drilling and subsurface sampling.

D6 Mineral Resources of Wilderness Study Areas: South-Central Oregon
Brine Commodity Evaluation

Brine samples were analyzed for cation (+) and anion 

(-) components of evaporite commodities that include soda 

ash, boron compounds, sodium sulfate, salts, potash, and 

lithium. Samples were also analyzed for arsenic and antimony, which are not only possible toxic contaminants but 

are also indicators of nearby epithermal mineralization or 

mineralizing processes. The auger-hole sediments and alkali crusts were analyzed for major-element oxides and 36 

trace elements. Possible products, based on component 

concentrations and commodity economics, include soda ash 

(sodium carbonates), boron compounds, and sodium sulfate 

(fig. 3). Possible byproducts include potash, salts, bromine,

lithium, magnesium compounds, and tungsten; their production may be feasible in conjunction with other commodities. Processing of many of the products could be 

facilitated by treating them with dolomitic limestone, which 

is also present in the study area.

Our brine analyses were compared to published 

analyses of brines from Searles Lake, Calif. (Smith, 1979, 

tables 5,16, and 22). Ranges of concentration of possible 

significance now or in the foreseeable future were chosen 

by using the Searles Lake operation as a guide. Our cutoffs 

are lower than those for the Searles Lake brine concentrations because (1) low concentrations in surface samples do 

not preclude higher concentrations at depth, (2) advances in 

extractive technology allow utilization of lower grade brines

120° 45' 120°37'30"

APPROXIMATE BOUNDARY OF

DIABLO MOUNTAIN

WILDERNESS STUDY AREA

(OR-001-058)

\ WEST OF TENMILE RIDGE ROAD

EXPLANATION

Sodium Grade probably 

mineable

Sodium Grade possibly 

mineable west of line; 

>1%Na

Alkalinity Grade probably 

mineable; >5% as CaCOs 

[>0.3%CO3 carbonite]

Alkalinity Grade possibly 

mineable west of line; 

>5% as CaCOs 

[>0.3%CO3]

Boron Grade probably 

mineable; >0.05% B

Boron Grade possibly 

mineable west of line; 

>0.005% B

Sulfate Grade probably 

mineable; >5% 864

Sulfate Grade possibly 

mineable west of line; 

>0.5% SO4

Chlorine Grade probably 

mineable; >5.5% Cl

Chlorine Grade possibly 

mineable west of line;

Figure 3. Concentrations of chemical components of brine commodities in ground water in western part of Diablo Mountain 

Wilderness Study Area, Oregon. Brine concentrations not mapped across all of Oregon claims group.

Mineral Resources of the Diablo Mountain Wilderness Study Area, Lake County, Oregon D7
(Smith, 1979), (3) the advantage of large-scale application 

of such technology is inherent in designing new facilities, 

and (4) possible markets may be closer. Two categories of 

brine commodity occurrence, based on chemical component concentrations, were chosen: a grade probably mineable, and a grade possibly mineable (fig. 3). Occurrences 

of probable economic concentrations are defined as approximately equal to or greater than 50 percent of the grade 

of Searles Lake brines for all products except boron, which 

is of higher unit value. The grades of possibly mineable 

brines in the study area are equal to or greater than 10 

percent of the grade of Searles Lake brines. Boron could 

possibly be mined economically from lower grade brines 

than those at Searles Lake by using advanced technology in 

new plant design (Gail Moulton, oral commun., 1989). 

Grades of brine components at least as good as the possibly 

mineable grade were observed at 12 auger sites and at 

4 seeps.

The areal distributions of brine components in the study 

area were analyzed for possible mining products by plotting 

isocon maps (contour maps of chemical concentrations) of 

the sodium, alkalinity (as CaCO,), boron, sulfate, and chlorine 

concentrations (Peters and Willett, 1989, figs. 3-6). Those 

maps were generalized and combined for this report, and areas 

interpreted to have probably mineable grades are denoted by 

patterns (fig. 3). Isocons were defined by the kriging method 

(Bridges, 1985), and all isocons were smoothed using Golden 

Software's SURFER software on a Microsoft-DOS-based 

desktop computer. Isocons of concentrations within brine or 

in sediment samples were similarly plotted for all byproduct 

components, except tungsten (Peters and Willett, 1989, figs. 

7-11). Fourteen additional isocon, specific conductance, and 

isocon/specific conductance ratio maps were also prepared 

(Peters and Willett, 1989, plate 2). Grades of brine components having possible economic significance extend east of 

the Oregon claims group, but the highest grades are in the 

claim-block vicinity.

The Tenmile and Other Dolomitic Limestone 

Prospects

A dolomitic limestone of Pliocene(?) age is locally 

interbedded with basalt flows at the Tenmile and other dolomitic limestone prospects. It appears to have formed as 

an apron along the east, northeast, and north flanks of 

Tenmile Ridge and may extend for 2 mi to the northwest. 

It crops out discontinuously through a veneer of sand dunes 

and desert pavement. Four samples of the dolomitic limestone were collected (Peters and Willett, 1989). The rock is 

suitable for brine mineral processing and agricultural applications. Usually the thickness could not be determined, but 

Harold Dyke (oral commun., 1988) reports the rock is as 

thick as 30 ft northeast of Tenmile Ridge. No resources 

were estimated because of limited exposure.

Geothermal Energy

One thermal spring was observed in the study area, 

and thermal water was present in one auger hole (Peters 

and Willett, 1989). There are no known geothermal resources in the study area; however, the Summer Late KGRA 

is 2 mi south of the south boundary.

Mineral Economics

Soda Ash

Soda ash (sodium carbonate, N^COj) has been recovered by Kerr-McGee Chemical Corporation from brines at 

Searles Lake by two methods: an older evaporation process, 

and a direct carbonation process. The evaporation process 

involves heating the brines, which causes the double salt 

burkeite (^afO^a^O^) and table salt (NaCl) to precipitate. The remaining liquor is rapidly cooled, and potassium 

chloride is precipitated and filtered out The remaining brine 

is supersaturated with sodium borate, which is precipitated 

after the addition of "seed" crystals (Gail Moulton, oral commun., 1989).

In the direct carbonation process, brine is mixed with 

carbon dioxide (CO2) gas. At Searles Lake (Parkinson, 1977), 

carbon dioxide is produced from powerplant flue gases; but 

traditionally, carbon dioxide has been produced from lime 

kilns.

Uses of soda ash and of a daughter product, caustic 

soda, are undergoing steady growth, especially in the Pacific 

Northwest and in Pacific Rim countries, because of increased 

application in the bleaching of paper pulp. Alkali bleaching 

is ecologically preferable to the current acid process that uses 

chlorine compounds, which produce highly carcinogenic 

dioxine waste products. Soda ash and derivative products are 

widely used in the fluxing of metals and have important applications and markets in the aluminum industry in the northwest 

and in the developing Pacific Rim countries, particularly China.

Soda ash was produced by five companies operating 

five plants in Wyoming and by one company operating two 

plants in California during 1987; total estimated value was 

$600 million. Industrial use of soda ash was in the following proportions: glass, 53 percent; chemicals, 20 percent; 

soap and detergents, 10 percent; flue-gas desulfurization, 4 

percent; pulp, 3 percent; paper, 3 percent; and other uses, 7 

percent (D.S. Kostick, in U.S. Bureau of Mines, 1988, p. 

147). In 1987, the United States exported 2.2 million short 

tons of soda ash; 23 percent went to the largest importer, 

China, and a total of 47 percent went to all Asian countries, 

the largest export market (D.S. Kostick, in Mining Engineering, 1988, p. 416).

Boron Compounds

Generalized boron concentrations of the brines in the 

study area are shown on figure 3. Processing of these

D8 Mineral Resources of Wilderness Study Areas: South-Central Oregon
brines probably would be similar to extraction methods at 

Searles Lake, Calif., where brines containing boron are 

mixed with a liquid extractant that removes boron from the 

brine. Boron is then purged from the extractant with sulfuric acid that produces boric acid [B(OH)3]. Sodium and potassium sulfate remain in the liquor and can be recovered.

Boron, though unfamiliar to most people, has many 

uses. Borates have been used as a flux in metal smithing 

since their introduction into Italy from Mongolia in the 13th 

Century, and they were used to add strength to glass by 

medieval European artisans. Elemental boron was isolated 

in 1808. The boron mineral lineal (Ni^B4Os(OH)4*8 HjO) 

was discovered at Teels Marsh, Nev., in 1872, and ulexite 

(NaCaB3O6(OH)6-5 Eft) was discovered in Death Valley, 

Calif., in 1881. By 1927, underground mining of a massive 

lineal and kemite (Na^O^OH^-S Hp) deposit had begun 

at Boron, Calif. Mining was converted to open-pit methods 

in 1957. U.S. Borax annually produces about one-half of 

the world's boron from these deposits. Kerr-McGee produces boron compounds as a coproduct of solution mining 

of soda ash at Searles Lake (Trona, Calif.). For further 

detail about the boron industry, see P.A. Lyday, in U.S. 

Bureau of Mines (1985, p. 91-102). The United States is 

currently the largest producer of boron compounds at 52 

percent, and Turkey produces 39 percent (P.A. Lyday, in 

U.S. Bureau of Mines, 1988, p. 26-27).

Of the boron compounds produced, 59 percent are 

used in glass making, 7 percent in soaps and detergents, 7 

percent in agriculture, and 27 percent in other uses (Lyday, 

in U.S. Bureau of Mines, 1988, p. 26). Borosilicate glass 

withstands severe temperature changes without cracking. 

Borate compounds are used as metal solvents and fluxes in 

the metals industry, as both herbicides and plant nutrients 

in agriculture, in fire retardants, and in heat-resistant ceramic products such as tiles that protect the Space Shuttle 

from the heat of reentry. Elemental boron fibers are used 

with tungsten-steel alloys for high strength in helicopter 

rotors; boron nitrite approaches the hardness of diamond 

and is more heat resistant. Sodium borohydride is used in 

the bleaching of ground wood (Rex McKee, oral common., 

1989), and there are many additional applications for boron 

compounds.

soap and detergents, 46 percent; pulp and paper, 36 percent; and glass and miscellaneous uses, 18 percent (D.S. 

Kostic, in U.S. Bureau of Mines, 1988, p. 148). The study 

area is closer to pulp and paper markets in the northwestern states than are current sources of sodium sulfate.

Byproduct Brine Commodities

Production of six byproduct commodities from the 

study area may be feasible: table salt (NaCl), potash (K/); or 

muriate of potash, KC1), bromine, lithium, magnesium 

compounds, and tungsten. Byproduct salts are produced at 

Searles Lake, Calif., and two companies in Portland, Oreg., 

currently buy imported Mexican salts for the manufacture 

of caustic soda and chlorine compounds. It may be economical to recover magnesium compounds from the site of 

the Oregon claims group. A local source of dolomitic limestone to be used in processing the brines would make additional magnesium available for byproduct compounds. The 

additional investment needed to extract byproducts from a 

resource-producing tvine, even at low concentration, may 

be somewhat small. Distribution of byproduct concentrations and uses are discussed in more detail by Peters and 

Willett(1989).

Dolomitic Limestone

The dolomitic limestone occurrence along Tenmile 

Ridge may be useful for its possible application in tvine 

commodity processing. Carbon dioxide produced from the 

calcination of limestone or dolomite is used to remove calcium from brines, thus allowing further separation of soda 

ash, boron compounds, and sodium sulfate. A calcination 

byproduct, calcium hydroxide can then be used to convert 

soluble magnesium salts into insoluble magnesium hydroxide, which in turn can be calcined to produce magnesia. 

Another proposed use of the limestone is as a soil conditioner, this may be feasible if there is enough limestone and 

if low-cost rail transportation is available in conjunction 

with development of other mineral commodities.

Sodium Sulfate

Sodium sulfate occurs as two economically important 

minerals: mirabilite or Glauber's salt (NajSO/lO H2O), and 

thenardite (anhydrous Ns^SOJ. Almost all commercial deposits are lacustrine evaporites (W.I. Weisman and C.W. 

Tandy, in Lefond, 1975, p. 1081-1082). Sodium sulfate 

can be extracted from brine as a coproduct of soda ash and 

boron compounds. Only about 48 percent of sodium sulfate 

comes from natural sources; most is manufactured as a byproduct of chemical and rayon factories. End uses are in

Geothermal Energy

Summer Lake Hot Spring (fig. 2) produces 116 °F water 

at a rate of 21 gallons per minute (Peterson and Mclntyre, 

1970) and is developed as a resort. That thermal spring and 

three other geothermally significant wells are included in the 

Summer Lake KGRA (Oregon Department of Geology and 

Mineral Industries, 1982, wells Lk-7,8,9, and 10). Of special 

interest are the Collahan wells Lk-9 and Lk-10, which have 

water temperatures of 212 °F and 231 °F, respectively, but do 

not produce dry steam, the most efficient medium for electric 

power generation. However, water temperature at Summer

Mineral Resources of the Diablo Mountain Wilderness Study Area, Lake County, Oregon D9
Lake KGRA is much higher than the 100 °F minimum needed 

for power production by the binary systems process (Rinehait, 

1980). The bines at these geothermal springs are also possible metal sources (Schultze and Bauer, 1975; Blake, 1974).

Miscellaneous Mineral Commodities

Windblown sand covers most of the surface, perhaps 

20,000 acres, of the western part of the study area but does 

not appear to be a marketable resource because it does not 

contain valuable minerals and is too remote for construction 

purposes. Outcrop areas of basalt (Travis, 1977, plate 1; 

Diggles and others, 1990) total about 1.5 to 2 mi2 near Tenmile 

Ridge. The basalt lacks special chemical characteristics and 

has no special physical characteristics, such as splitting into 

flat plates suitable for facing stone. Basalt is a high-bulk lowvalue material which, in the study area, would only be useful 

as crushed road metal. Ample sources of road metal are 

present outside the study area.

Conclusions

Study-area brines, sampled from shallow auger holes, 

host occurrences of the chemical components of soda ash, 

boron compounds, and sodium sulfate, which may be extracted by solution mining. Byproduct candidates include 

potash, salts, bromine, lithium, magnesium compounds, and 

tungsten. The sample data suggest solution-mineable resources, but drilling will be required for estimates. Limestone 

from the study area could be used in agricultural applications 

or in recovering soda ash, boron, and magnesium compounds 

from brine. Geothermal energy near the study area could be 

used to generate electric power.

Bulk commodity transport by railroad is available from 

Lakeview, Qreg., 45 highway mi to the southeast There are 

no weight restrictions on the 55-mi-long Great Western Railroad shortline from Lakeview to Alturas, Calif.; rail distance 

from Alturas to Portland, Qreg., is 415 mi. Railroad infrastructure could be extended from Lakeview to a new mine 

site for about $200,000 per mi (land not included) (Edward 

Emmel, Oregon Department of Transportation, Salem, oral 

commun., 1989), possibly in conjunction with other bulk 

product development such as perlite from the Tucker Hill 

deposit, 14 mi southeast of the study area (Wilson and 

Emmons, 1985). In this scenario, brine minerals could be 

shipped by rail directly to Portland, a total distance of about 

520 mi; this is a substantially shorter distance than shipment 

from a present producing area, the Green River trona district 

in southwest Wyoming.

Markets for bine-mineral products appear to be undergoing steady growth, especially in the Pacific Northwest and 

in Pacific Rim countries. Soda ash and a daughter product, 

caustic soda, and sodium borohydride have received increased 

use in the bleaching of paper pulp. Alkali bleaching is ecologically preferable to the current acid process that use chlorine 

compounds and produce a carcinogenic dioxin waste product 

Soda ash, soda-ash products, and boric acid are widely used 

in the fluxing of metals and are used in the aluminum industry 

in the Pacific Northwest and in China. Evaporite commodities 

are essential to the backbone industries of many civilizations 

and to many new applications and advanced materials.

Recommendations for Further Work

Due to the possible economic importance of various 

mineral commodity occurrences in the Diablo Mountain Wilderness Study Area, further studies are recommended. More 

detailed mapping and site-specific studies, including drilling, 

should probably be carried out to determine depths and thicknesses of these occurrences. Work should be conducted jointly 

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

ASSESSMENT OF MINERAL RESOURCE

POTENTIAL t

By Michael F. Diggles, Harley D. King, Mark E. 

Gettings, James E. Conrad, Don L. Sawatzky, and 

Gerilyn S. Soreghan 

U.S. Geological Survey

Geology

Stratigraphy

The Diablo Mountain Wilderness Study Area is underlain by sedimentary and volcanic rocks of Tertiary and 

Quaternary age. They are generally flatlying but are broken by normal faults. Tertiary rocks in the study area consist of tuffaceous sedimentary rocks, basalt flows, basaltic 

pyroclastic rocks, tuffaceous sedimentary rocks, rhyolitic 

tuff, and dolomitic limestone.

Tuffaceous sedimentary rocks underlie much of the 

study area. They are semiconsolidated, interbedded white, 

light-yellow, and cream-colored lacustrine and fluvial sedimentary rocks that consist mostly of tuffaceous sandstone 

and siltstone and locally contain arkosic sandstone and 

pebble conglomerate. They contain alkali feldspar, minor 

amounts of clay minerals, zeolites in amygdules, and secondary silica minerals. Their age and correlation are uncertain, but they are presumably mostly of middle and late 

Miocene age (Walker, 1977).

Basalt flows underlie most of the high country in the 

study area. The basalt is medium-gray to dark-gray, is 

plagioclase phyric, contains olivine, and has subophitic to 

diktytaxitic texture. Crystals of labradorite are partly to 

completely enveloped in clinopyroxene. Pyroxene also 

forms interstitial grains. The basalt is olivine-normative 

tholeiite (Irvine and Barager, 1971), rich in aluminum,

D10 Mineral Resources of Wilderness Study Areas: South-Central Oregon
magnesium, and calcium oxides (A12O3, MgO, CaO) and 

depleted in titanium, sodium, and potassium oxides (TiO2, 

Nap, and Kp). A potassium-argon age determination on 

a basalt sample from the Diablo Rim shows an age of 6.3±0.4 

million years (Ma), or latest Miocene (Diggles and others, 

1990). The underlying tuffaceous sedimentary rocks erode 

readily and cause landslides of the basalt

A dolomitic limestone of Pliocene(?) age north and 

east of Tenmile Ridge is locally interbedded with the basalt 

flows. It is present on the flanks of the ridge and crops out 

discontinuously among the dunes to the northwest.

Red and reddish-black basaltic cinders and near-vent 

flows crop out in one area on Tenmile Ridge. These are 

unconsolidated, fine to coarse, scoriaceous oxidized rocks. 

Luedke and Smith (1982) report this volcanic center as a 

basaltic (46-54 percent silica) cinder cone with an age of 

less than 5 Ma. A recently determined potassium-argon age 

of the cinders, however, is 6.6±0.3 Ma (Diggles and others, 

1990). The cinders are quartz-normative alkali-olivine basalt 

(Irvine and Barager, 1971) rich in TiO2, Nap, and K£) and 

depleted in MgO and CaO. Zones of altered basalt flows are 

cut locally by veinlets and dikelets of opal-bearing travertine. 

Vesicular basalt flows are locally altered and amygdaloidal; 

minor amounts of zeolite till some amygdules. There is also 

minor basalt-flow breccia in the study area.

Quaternary sediments consist of alluvium, dune, playa, 

lacustrine, fluvial, landslide, and claystone deposits. The 

alluvium consists of unconsolidated deposits of sand, gravel, 

ash, and pumice that formed in flood plains and fill the 

stream channels. The dune sand is composed of ash, pumice, and mineral grains, mostly alkali feldspar and quartz. 

Playa deposits are made up of clay, silt, sand, and some 

evaporites and contain tephra at depth (Simpson, 1989). 

Lacustrine and fluvial deposits consist of unconsolidated 

clay, silt, and gravel. They are commonly covered by 

meadow or marsh vegetation. Landslide deposits, present 

mostly on the east flank of Diablo Rim, are unstratified 

mixtures of basalt and tuffaceous sedimentary rock. Here, 

as elsewhere, they commonly develop where a basalt rim 

overlies tuffaceous sedimentary rocks. The claystone consists mostly of montmorillonite produced by decomposition 

of volcanic ash. Locally it includes deposits of marl, micrite, 

caliche, and opal-bearing travertine.

The Summer Lake basin was occupied by pluvial Lake 

Chewaucan. Sediments in the basin include tephra from 

several large volcanic eruptions. Between 19 and 12 thousand years ago, landslides from Winter Rim, west of Summer Lake, locally compressed and deformed the sediments 

(Simpson, 1989).

Structure

The study area lies on the northwest edge of the Basin 

and Range physiographic province. Summer Lake occupies a 

closed basin bounded by ridges that have fault-scarp fronts

(Phillips and Van Denburgh, 1971). The structural geology 

of the study area is dominated by high-angle north-northwesttrending normal faults that have cut the range into blocks. J J. 

Rytuba (oral commun., 1987) suggested that the Summer Lake 

area, including the area to the east, now covered with dunes, 

may be a large caldera and may have associated gold resource 

potential. G.W. Walker (oral commun., 1987), however, noted 

that no known ash-flow tuff sheet is correlated with the basin. 

The concurrence of regional north-northwest-trending fault 

zones with older caldera structures and silicic intrusions is 

emerging as one of the most viable means of locating gold 

deposits in this part of the Basin and Range (Rytuba, 1989). 

The Diablo Rim is the most extensive scarp resulting from 

this faulting. A discussion of an inferred intrusion is included 

in the "Geophysics" section. The study area is bounded on 

the northeast by the north-northwest-trending Brothers fault 

zone that has been interpreted as a transcurrent structure that 

bounds the northwest edge of the Basin and Range physiographic province (Lawrence, 1976). The area on the west 

side of Summer Lake and south of the study area is part of the 

poorly defined Modoc Plateau physiographic province that 

separates the Basin and Range and the Cascade Range physiographic provinces (Macdonald, 1966). Vertical offset in the 

study area is apparent at the margins of large fault-bounded 

horst and graben typical of the Basin and Range.

Geochemistry

Methods and Background

A reconnaissance geochemical survey was conducted 

in the Diablo Mountain Wilderness Study Area in the summers of 1986, 1988, and 1989 (Adrian and others, 1990). 

Stream sediments, nonmagnetic heavy-mineral concentrates 

of stream sediments, rocks, and vegetation were used as the 

sample media in this survey. The vegetation samples, along 

with rock samples, were used as sample media in the valley 

area of the western part of the study area where appropriate 

sediment for stream-sediment or heavy-mineral-concentrate 

sampling was not available. Samples were collected from a 

total of 158 sites and included 71 minus-80-mesh stream sediments, 17 plus-80-mesh stream sediments, 70 nonmagnetic 

heavy-mineral concentrates from stream sediments, 61 rocks, 

29 Big Sagebrush (Artemisia tridentata Nuttal), 38 Black 

Greasewood (Sarcobatus vermiculatus [Hooker] Torrey), and 

9 playa deposits.

Stream sediments were selected as a sample medium 

because they represent a composite of the rock and soil 

exposed upstream from the sample site. Nonmagnetic heavymineral-concentrate samples provide information about the 

chemistry of a limited number of minerals in rock material 

eroded from the drainage basin upstream from each sample 

site. Many minerals present in the nonmagnetic fraction of 

heavy-mineral concentrates may be ore forming or ore 

related if mineralization processes have been active in the 

area. The selective concentration of minerals permits

Mineral Resources of the Diablo Mountain Wilderness Study Area, Lake County, Oregon D11
determination of some elements that are not easily detected 

in bulk stream-sediment samples.

The purpose of the vegetation sampling was to look 

for any evidence of mineralized rock in bedrock underlying the clastic surficial deposits in the valley area of the 

western pan of the study area. The predominant large plant 

in that area is greasewood, a halophyte or salt-tolerant plant. 

The literature of biogeochemical exploration for mineral 

deposits contains little information on the use of greasewood as a sample medium. Therefore, a traverse was taken 

along and outside the south boundary of the study area 

where both greasewood and sagebrush grow, and a sample 

of each was collected at each site for comparison of analytical values. The use of the sagebrush in biogeochemical 

exploration for mineral deposits is well established, particularly for gold exploration (Erdman and Olson, 1985; Erdman 

and others, 1988) and also may be useful for base-metal 

exploration (Lovering and Hedal, 1983). Another reason 

for the plant-sampling traverse along and outside the south 

boundary is the presence there of several northwest-trending concealed faults that might be conduits for mineralizing fluids. Mineralized rock, if it formed, also might be 

present along the same faults to the north within the study 

area. Root depths for these plants have been reported as 59 

ft for the greasewood and 33 ft for the sagebrush (Brooks, 

1983). Such depths, if attained by plant specimens used in 

this study, might be sufficient for uptake of elements 

emanating from the substrate and might provide useful 

information.

Mineralized rocks were sought but not observed; most 

rock samples appear fresh and unaltered. Some moderately 

altered rocks were collected near Tenmile Ridge. Some 

rock samples were collected to provide information on geochemical background values; however, most of the rock 

samples were collected to see if analyses might reveal any 

indications of mineralization that were not visually 

recognizable.

Rock samples were crushed and pulverized to less 

than 80-mesh prior to analysis. Stream-sediment samples 

were seived using 80-mesh stainless-steel sieves, and the 

minus-80-mesh fraction was used for analysis. For some 

stream-sediment samples, the fraction greater than 80 mesh 

and less than 18 mesh was obtained by sieving and then 

used for analysis. The heavy-mineral concentrate was produced by panning minus- 10-mesh stream sediment to remove most of the quartz, feldspar, organic materials, and 

clay-sized material. Bromoform (specific gravity 2.86) was 

then used to remove any remaining light mineral grains not 

removed during panning. The resultant heavy-mineral concentrate was separated by use of an electromagnet into three 

fractions: a magnetic fraction chiefly of magnetite, an intermediately magnetic fraction consisting largely of mafic 

rock-forming minerals, and a nonmagnetic fraction composed dominantly of light-colored rock-forming accessory 

minerals and primary and secondary ore-forming and orerelated minerals. The nonmagnetic fraction was split into 

two fractions; one split was used for analysis and the other 

for visual examination with a binocular microscope.

The sagebrush and greasewood samples were collected 

by clipping, with pruning shears, new growth, including 

stems with attached leaves, from three to six of the healthiest and most robust plants within an area as large as about 

50 ft in diameter. Samples were collected in 11-in. by 17- 

in. cloth sample bags that were more than half filled for 

each sample. The plants sampled were generally about 3 ft 

tall but ranged from about 2 ft to 6 ft tall. Plant samples 

were washed in tap water, dried in an oven at 40 °C, and 

then pulverized in a Willey mill. Splits of the dry, pulverized plant material were ashed in a muffle furnace during a 

24-hour period with a maximum temperature of 450 °C.

Sample Analysis

Nonmagnetic heavy-mineral-concentrate, streamsediment (both size fractions), rock, and playa samples were 

analyzed for 31 or 35 elements using a direct-current arc 

emission spectrographic method (Grimes and Marranzino, 

1968). Except for the concentrates, these samples were 

also analyzed for antimony, arsenic, bismuth, cadmium, and 

zinc by inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and for gold and mercury by atomic 

absorption (methods described in Crock and others, 1987). 

The playa-silt and evaporite samples were also analyzed for 

lithium by ICP-AES (Lichte and others, 1987) and for thorium and uranium by delayed neutron counting (McKown 

and Millard, 1987).

All plant-ash samples were analyzed for 40 elements 

by ICP-AES (Lichte and others, 1987). The plant-ash 

samples were also analyzed by another ICP-AES method 

(Motooka, 1988) for nine of the same elements (arsenic, 

gold, silver, bismuth, cadmium, copper, molybdenum, lead, 

and zinc) and for antimony. This method was used to 

obtain lower limits of determination for most of the elements analyzed. Gold was also analyzed in the plant-ash 

samples by flameless atomic absorption spectrophotometry with a graphite furnace atomizer, using a slightly modified version of the method described in O'Leary and Meier 

(1986). This method provides an exceptionally low limit of 

determination, 1 part per billion (ppb). Unashed material 

from 24 of the sagebrush samples and 16 of the greasewood 

samples was also analyzed by hydride generation-atomic 

absorption spectroscopy for arsenic and selenium by modified versions of methods described by Crock and Lichte 

(1982) and Sanzolone and Chao (1987), respectively.

Results and Interpretation

An anomalous silver value of 50 parts per million (ppm) 

was detected in a nonmagnetic heavy-mineral-concentrate 

sample collected in the southern part of the study area, about

D12 Mineral Resources of Wilderness Study Areas: South-Central Oregon
2 mi northeast of Tenmile Ridge. Iron oxide, which can 

become enriched in silver by adsorption (Chao and Theobald, 

1976), was noted in the sample during examination with binocular microscope and may be the source of the silver concentration. Otherwise, a mineral to explain the silver concentration was not identified. A slightly anomalous value of tin 

(500 ppm) was detected in the same concentrate sample and 

in a concentrate from an adjacent stream. A mineral to explain the tin concentrations was not identified in the concentrates. The tin concentrations may be due to the presence of 

cassiterite, variety wood tin, as was found to be the case in 

the Orejana Canyon Wilderness Study Area (Conrad and others, 1988) about 50 mi to the east The tin concentration is 

questionably anomalous; it is the highest tin concentration 

observed in any concentrate from the Diablo Mountain Wilderness Study Area and may be of interest because of its 

occurrence with the silver, although the mutual occurrence 

may be only coincidental and not indicative of any elemental 

association. We conclude that the tin concentrations do not 

suggest the presence of a tin deposit During a follow-up 

study in the drainage areas upstream from these sample-collection sites, rocks that include welded tuff, tuffaceous lacustrine deposits, and plateau-forming basalt flows were examined 

for evidence of alteration or mineralization, but none was 

noted. The anomalous concentrations may be derived from 

mineralization along a northwest-trending fault in the drainage 

areas.

No other notably anomalous concentrations of elements were detected in the concentrate sample discussed 

above or in any other nonmagnetic heavy-mineral-concentrate samples from the Diablo Mountain Wilderness Study 

Area. No anomalous concentrations were determined in 

any of the stream-sediment samples from the study area.

Anomalous gold values were measured in two sagebrush ash samples; one collected at the north boundary of 

the study area (site DM109 in Adrian and others, 1990) has 

32 ppb gold, and one collected about a mile south of the 

study area boundary (site DM105) has 36 ppb gold. An 

anomalous antimony value (16 ppm) was determined in a 

sample of flow basalt (site DM117) collected from an outcrop 1.6 mi northeast of the site that has the 32 ppb gold. 

Anomalous values of arsenic (13-77 ppm) were measured 

in six rock samples from five sites (DM082, DM083, 

DM084, DM093, DM098) just west and southwest of 

Tenmile Ridge. An anomalous arsenic value (18 ppm) was 

also measured in a rock sample from about 3 mi southeast 

of Tenmile Ridge (site DM148). The samples containing 

the anomalous concentrations of arsenic consist of sandand gravel-size grains of reddish scoriaceous pyroclastic 

basalt cemented and (or) permeated with calcium carbonate 

and having disseminated limonite. The arsenic may have 

become enriched in these samples by coprecipitation or absorption with the iron oxide. In this case, the arsenic 

anomaly would be nonsignificant, or not related to mineralized rock. Similar arsenic values (24-83 ppm) were measured in the salty evaporite samples; the highest one is for a 

sample from about a mile north of the study area.

Arsenic and antimony are commonly associated with 

epithermal gold deposits and are used as pathfinder elements 

for those deposits. The anomalous concentrations of these 

elements and of gold in the sagebrush ash samples are considered weak; the arsenic and antimony are not significant 

and are not related to mineralized rock at or near the surface. 

The anomalies may, however, be related to more mineralized 

rock at some unknown depth along one or more of the 

northwest-trending faults.

Geophysical Studies

Aeromagnetic Survey

An aeromagnetic survey including the Diablo Mountain Wilderness Study Area was flown and compiled under 

contract to the U.S. Geological Survey (U.S. Geological 

Survey, 1972). Total-field magnetic data in analog form 

were collected along flightlines in an east-west direction 

spaced at approximately 2-mi intervals at a constant barometric altitude of 9,000 ft. Corrections were applied to the 

data to compensate for diurnal variations of the Earth's 

magnetic field, and a regional field correction of 8 nanoteslas 

(nT) per mi in the direction N. 30° E. was subtracted to 

yield a residual magnetic anomaly dataset. An aeromagnetic map of the study area (fig. 4) was prepared from 

digitized analog data at a contour interval of 50 nT for 

comparison with geologic and topographic maps.

Because of the large terrain clearance (0.75-0.95 mi), 

short-wavelength features such as those due to small-displacement faults are not detected, and only larger features that 

have anomaly wavelengths of several miles or more are represented. The low aeromagnetic anomaly along the west and 

south edges of the study area has relatively little relief and 

reflects the thick, somewhat nonmagnetic sediments and playa 

deposits of Summer Lake. A low anomaly near the north tip 

of the area (F, fig. 4) also correlates with sedimentary rocks 

in that area (Walker and others, 1967). In the south-central 

part of the study area, an east-west-trending positive aeromagnetic anomaly of about 350-nT amplitude (A and D, fig. 

4) is underlain by exposed volcanic rocks in its eastern half 

but extends well out into the sediments and playa deposits of 

Summer Lake to the west The western part of this anomaly 

is very similar to a large anomaly southeast of the study area 

beneath sediments (B, fig. 4) and to a smaller but similar 

anomaly on the same trend just northwest of the study area 

(C, fig. 4). A smaller positive anomaly of about 200-nT 

amplitude lies in the northern part of the study area (E, fig. 4). 

The positive anomalies in the region correlate only in a general way with the mafic volcanic rocks mapped by Walker 

(1963), and the magnetic anomalies are largely inferred to 

reflect deeper structures. Within the study area, the dominant

Mineral Resources of the Diablo Mountain Wilderness Study Area, Lake County, Oregon D13
trends of the gradients defining the anomalies are east-west 

and northwest

Gravity Survey

All available gravity data were obtained from computer 

files from the Defense Mapping Agency (1984). Data from a 

total of 412 stations within the area between lats 42°30' and 

43°15' N. and longs 120°15' and OlW E. were compiled; 76 

of those stations are within or near the borders of the study 

area. The average spacing between stations is approximately 

8 mi. The observed gravity data are on the International 

Gravity Standardization Net datum (Morelli and others, 1974)

120° 45' 120° 30'

10 MILES

Figure 4. Aeromagnetic anomaly map of region including 

Diablo Mountain Wilderness Study Area, Oregon (shaded area). 

Contour interval 50 nanoteslas. H and L denote relative 

maxima and minima, respectively, of magnetic anomaly field. 

Dashed line is outline of inferred buried intrusion. A-F are 

features noted in text.

and were reduced to Bouguer gravity anomaly values using 

standard formula; (Cordell and others, 1982). Terrain corrections were computed to a radius of 167 km around each station. A Bouguer-reduction density of 2,200 kilograms per 

cubic meter (kg nr3) was used in anomaly computation because plots of station altitude versus Bouguer gravity anomaly 

showed the least correlation for this density and because the 

same value has been shown to be the most representative in 

similar volcanic sections (Williams and Finn, 1985). A gravity 

anomaly map of the study area and its surroundings was prepared (fig. 5).

Within and near the study area, the Bouguer gravity 

anomaly field is dominated by the large gravity low beneath 

the Summer Lake sedimentary rocks. Other significant 

anomalies within the study area are lacking, except for a 

single-station low near the east edge of the area (A, fig. 5) and 

a small high (B, fig. 5) near the center of the study area. Hie 

gravity anomaly gradients trend northwest and northeast and 

delineate inferred faults of the Summer Lake graben structure. 

Northeast-trending faults control the northern and southern 

termini of the area of deep sedimentary fill.

The gravity anomaly low over the sedimentary rocks is 

about 24 milligals (mGal) in amplitude, and simple model 

calculations imply a fill depth of about 2 km for density 

contrasts of approximately 300 kg nr3. The locations of some 

boundary and cross faults inferred from the gravity anomaly 

field are shown on figure 5.

The prominent magnetic anomaly high in the southcentral part of the study area (A, fig. 4) has a corresponding 

gravity anomaly high (B, fig. 5) that appears to be displaced 

to the east because of its superposition over the anomaly low 

due to the deep sedimentary fill. The source of both the 

magnetic and gravity anomalies in this area is inferred to be 

an intrusive mass (dashed outline, figs. 4 and 5), probably 

within the upper few kilometers of the crust Outcrops of 

basalt beneath the anomaly extend westward well out into the 

sedimentary rocks (Walker, 1963) and may be evidence of 

uplift from the intrusive body; the young age of the flows and 

pyroclastic rocks suggests that they could be directly related 

to the intrusive mass. About 13 mi southeast of the study 

area, along the same sediment-filled graben structure (Walker, 

1963), dacitic to rhyolitic domes are exposed in an area having 

a similar anomaly pair.

A magnetic anomaly high to the east (D, fig. 4) and a 

smaller one to the north (E, fig. 4) also may be due to intrusions or to extensions of the postulated intrusive mass into the 

sediments, but the gravity anomaly field is less clear. Northeast of the inferred intrusion (A, fig. 5), a gravity anomaly 

low is defined by only one station and therefore is not considered reliable; however, several nearby stations along the east 

boundary of the study area confirm that the gravity field is 

decreasing to some kinds of minima. If this part of the magnetic anomaly field is due to intrusive bodies, the gravity 

anomaly field suggests that the intrusions are less dense than 

the basaltic rocks cropping out in the eastern half of the study

D14 Mineral Resources of Wilderness Study Areas: South-Central Oregon
area and are more dense than the sedimentary rocks. Thus, a 

composition more felsic than basalt is suggested.

Finally, the gravity anomaly field indicates that the 

complex pattern of northwest- and northeast-trending faults 

mapped south of Summer Lake (Walker, 1963) continues 

beneath the sedimentary rocks near the south boundary of the 

study area (fig. 5). The steep gravity gradients in this area 

imply that steeply dipping normal faults bound the fault blocks. 

They also imply that the northeast-trending faults offset the 

axis of the gravity low and presumably the axis of thickest 

sedimentation in a left-lateral sense by about 6 mi.

120°45' 120°30'

10 MILES

Figure 5. Bouguer gravity anomaly map of region including 

Diablo Mountain Wilderness Study Area, Oregon (shaded area). 

Contour interval 2 milligals; Bouguer reduction density used is 

2,200 kilograms per cubic meter; H and L denote relative maxima 

and minima, respectively, in gravity anomaly field. Small squares 

represent gravity station locations. Dashed line shows outline of 

inferred buried intrusion. Heavy lines denote faults inferred 

from gravity anomaly field. A and B are features noted in text

Remote Sensing

Linear features in LANDSAT multispectral scanner 

(MSS) images at a scale of 1:800,000 were mapped by 

photogeologic interpretation for the region of southeastern 

Oregon, and trend concentration maps were made. Linear 

features are the topographic and spectral expression of rock 

fracture patterns and other structural and lithologic lineaments. This expression can be enhanced or subdued by 

scanner resolution, sun orientation, atmospheric phenomena, and vegetation. Analysis of linear features in conjunction with geologic and geophysical maps may reveal new 

relations such as fracture control of mineralization.

Linear features of every orientation are well expressed 

on the surface in southeastern Oregon, except in terrains underlain by volcanic rocks. Locally, areas may show linear 

features related to faults or to rock joint systems. No linear 

features within the study area were discovered by remote 

sensing except along the faults already discussed. Linear 

features in the region surrounding the study area have two 

prominent trends. The dominant trend of N. 20° W. is concentrated northwest of the study area. The second trend, N. 

20° E., consists of three aligned linear features as long as 6 mi 

that lie northeast of the study area.

Mineral Resource Assessment

The mineral resource potential of the Diablo Mountain 

Wilderness Study Area is moderate, certainty level C, for 

commodities associated with bines in the western part of the 

study area. Commodities that may be present beyond known 

occurrences are soda ash, boron compounds, and sodium sulfate; possible byproducts include magnesium compounds, salts, 

potash, bromine, lithium, and tungsten.

The Summer Lake Known Geothermal Resource Area 

(KGRA) is 2 mi south of the study area. There are thermal 

springs (66 °C) at Ana Springs north of the study area 

(Waring, 1908; Brown, 1957) and a thermal spring at Summer Lake Hot Spring west of the study area. A thermal 

spring and thermal water at a sample-collection site are 

present within the study area. The entire study area has 

moderate resource potential, certainty level C, for low-temperature geothermal energy useful for agricultural and 

building heating. Through the use of a low-boiling medium, 

perhaps electricity could be generated as well.

The mineral resource potential is low, certainty level 

B, in the area of Tenmile Ridge for low-grade high-tonnage 

epithermal hot-spring gold-silver deposits of the type defined by Berger (1985; 1986), Berger and Silberman (1985), 

and Berger and Singer (1987). These types of deposits 

have been recognized in the region south of the wilderness 

study area (Rytuba, 1989). The presence of opal among the 

aUered-basalt outcrops in the Tenmile Ridge area and the 

presence of mercury in a prospect 4 mi southwest of the

Mineral Resources of the Diablo Mountain Wilderness Study Area, Lake County, Oregon D15
study area are additional favorable indicators of hot-springtype gold-silver deposits. The presence of a felsic intrusive 

body in this area, inferred from the aeromagnetic and gravity anomaly data, further enhances the favorability of the 

Tenmile Ridge area for hot-spring precious-metal deposits. 

The Slimmer Lake basin may be a caldera-formed feature 

(JJ. Rytuba, oral commun., 1987). The regional northnorthwest-trending fault zones cutting caldera structures and 

silicic volcanic centers are emerging as one of the most 

viable means of locating gold-silver mineral deposits in the 

northern Basin and Range (Rytuba, 1988; 1989).

The mineral resource potential is low, certainty level 

B, for magnesium from dolomitic limestone in the area of 

Tenmile Ridge.

The oil and gas resource potential is low, certainty level 

B, in the entire study area (Fouch, 1982; 1983). Because the 

sedimentary section for oil and gas sources and (or) reservoirs 

is thin and probably all of continental origin, this assessment 

could be too high.

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D18 Mineral Resources of Wilderness Study Areas: South-Central Oregon
APPENDIXES
DEFINITION OF LEVELS OF MINERAL RESOURCE POTENTIAL 

AND CERTAINTY OF ASSESSMENT

LEVELS OF RESOURCE POTENTIAL

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

indicate a high degree of likelihood for resource accumulation, where data support mineral-deposit models 

indicating presence of resources, and where evidence indicates that mineral concentration has taken place. 

Assignment of high resource potential to an area requires some positive knowledge that mineral-forming processes 

have been active in at least part of the area.

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

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

indicate reasonable likelihood for resource accumulation, and (or) where an application of mineral-deposit models 

indicates favorable ground for the specified type(s) of deposits.

L LOW mineral resource potential is assigned to areas where geologic, geochemical, and geophysical characteristics 

define a geologic environment in which the existence of resources is permissive. This broad category embraces 

areas with dispersed but insignificantly mineralized rock, as well as areas with little or no indication of having 

been mineralized.

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

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

moderate, or high level of resource potential.

LEVELS OF CERTAINTY

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

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

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

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

Z

UJ

LU

U

tt

§

A

U/A

UNKNOWN POTENTIAL

B

H/B

HIGH POTENTIAL

M/B

MODERATE POTENTIAL

UB

LOW POTENTIAL

C

H/C

HIGH POTENTIAL

M/C

MODERATE POTENTIAL

L/C

LOW POTENTIAL

D

H/D

HIGH POTENTIAL

M/D

MODERATE POTENTIAL

L/D

LOW POTENTIAL

N/D

NO POTENTIAL

LEVEL OF CERTAINTY

Abstracted with minor modifications from:

Taylor, R.B., and Steven, T.A., 1983, Definition of mineral resource potential: Economic Geology, v. 78, no. 6, p. 1268-1270.

Taylor, R.B., Stoneman, R.J., and Marsh, S.P., 1984, An assessment of the mineral resource potential of the San Isabel National Forest, south-central Colorado: U.S.

Geological Survey Bulletin 1638, p. 40-42. 

Goudarzi, G.H., compiler, 1984, Guide to preparation of mineral survey reports on public lands: U.S. Geological Survey Open-File Report 84-0787, p. 7, 8.

D20 Mineral Resources of Wilderness Study Areas: South-Central Oregon
RESOURCE/RESERVE CLASSIFICATION

ECONOMIC

MARGINALLY 

ECONOMIC

SUBECONOMIC

IDENTIFIED RESOURCES

Demonstrated

Measured

Resc

Indicated

jrves

Marginal 

Reserves

Demonstrated 

Subeconomic

Resources

i

Inferred

Inferred 

Reserves

Inferred 

Marginal 

Reserves

Inferred 

Subeconomic 

Resources

UNDISCOVERED RESOURCES

Probability Range

Hypothetical Speculative

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

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

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

Mineral Resources of the DiaWo Mountain Wilderness Study Area, lake County, Oregon D21
GEOLOGIC TIME CHART

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

EON

Phanerozoic

Proterozoic

Arcnean

pre-Archean2

ERA

Cenozoic

Mesozoic

Paleozoic

Late Proterozoic

Middle Proterozoic

Early Proterozoic

Late Archean

Middle Archean

Early Archean

PERIOD

Quaternary

Neogene

Subperiod

Tertiary _ ,

Paleogene

CnHrw»ruvi

Cretaceous

Jurassic

Triassic

Permian

Pennsylvanian 

Carboniferous

Periods

Mississippian

Devonian

Silurian

Ordovician

Cambrian

(ior\f\j\

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

ACE ESTIMATES OF 

BOUNDARIES IN 

MILLION YEARS (Ma)

 0.010

1.7

 5

 24

 to

 55

 66

96

1 TR

 205

 -240

 290 

~T?O

, .... 1Cf\

 410

AtC

J\JU

~° j/ \j

7UU

IbUU

 2500

 3000

«*~1W

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

'Informal time term without specific rank.

D22 Mineral Resources of Wilderness Study Areas: South-Central Oregon
Mineral Resources of 

Wilderness Study Areas: 

South-Central Oregon

This volume was published as separate chapters A-D

U.S. GEOLOGICAL SURVEY BULLETIN 1738
U.S. DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director
CONTENTS

[Letters designate the separately published chapters]

(A) Mineral Resources of the Devil's Garden Lava Bed, Squaw Ridge Lava Bed, and 

Four Craters Lava Bed Wilderness Study Areas, Lake County, Oregon, by William J. 

Keith, Harley D. King, Mark E. Gettings, and Frederick L. Johnson.

(B) Mineral Resources of the Orejana Canyon Wilderness Study Area, Hamey County, 

Oregon, by James E. Conrad, Harley D. King, Mark E. Gettings, Michael F. Diggles, 

Don L. Sawatzky, and David A. Benjamin.

(C) Mineral Resources of the Abert Rim Wilderness Study Area, Lake County, Oregon, 

by Maureen G. Sherlock, Mark E. Gettings, Harley D. King, and Terry R. Neumann.

(D) Mineral Resources of the Diablo Mountain Wilderness Study Area, Lake County, 

Oregon, by Michael F. Diggles, Harley D. King, Mark E. Gettings, James E. Conrad, 

Don L. Sawatzky, Gerilyn S. Soreghan, Thomas J. Peters, and Spencee L. Willett.

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