GEOLOGICAL SURVEY CIRCULAR 684 

Mineral Resource Potential of the 

Stillwater Complex and Adiacent Rocks 

in the Northern Part of the Mount Wood 

and Mount Douglas Quadrangles, 

Southwestern Montana 

Mineral Resource Potential of the 

Stillwater Complex and Adiacent Rocks 

in the Northern Part of the Mount Wood 

and Mount Douglas Quadrangles, 

Southwestern Montana 

By Norman J Page and John C. Dohrenwend 

G E 0 l 0 G I C A l S U R V E Y C I R C U l A R 684 

Washington 1973 
United States Department of the Interior 

ROGERS C. B. MORTON, Secretary 

Geological Survey 

V. E. McKelvey, Director 

Free on application to the U.S. Geological Survey, Washington, D.C. 20244 
CONTENTS 

Page 

Abstract -----------------------------------------------------------------------------------------------------------------------------------------· 1 

Introduction ············-··········------------------------------------------------------------------------------------------------------------· 1 

Estimates of potential resources -----------------------------------------------------------------------------------------------· 2 

Nickel-copper potential ------------------------------------------------------------------------------------------------------ 4 

Platinum-group metals potential ---------------------------------------------------------------------------------------- 4 

Chromite -------------------------------------------------------------------------------------------------------------------------------- 4 

Speculative copper-gold potential -------------------------------------------------------------------------------------- 5 

Iron potential --------------------------------------------------·-----------------------------------·----·---------------------------- 5 

Aluminum potential--------------------------------------------------------------------------------------------- ---------------- 6 

Coal potential ------------------------------------------------------------------------------------------------------------------------ 6 

Limestone and dolomite, sand, and gravel ---------------------------------------------------------------------- 7 

Energy requirements ----------------------------------------------------------------------------, ----------------------------------··--- 7 

References cited ---------------------------------------------------------------------------------------------------------------------------- 8 

ILLUSTRATION 

Page 

FIGURE 1. Map of potential resources in the northern parts of the Mount Wood 

and Mount Douglas quadrangles, Montana -------------------------------------------------- 2 

TABLES 

Page 

TABLE 1. Generalized stratigraphic terminology used for the Stillwater area ··-------------- 4 

2. Estimated chi.·omite resource potential for the Stillwater Complex -----------------· 5 

3. Estimated potential aluminum resources for the anorthosites 

of the Stillwater Complex --------------·--------··------·--------------·----·------------------------------ 6 

4. Inferred coal resources of the Stillwater area -------------·-------------------------·----------·--- 7 

III 

Mineral Resource Potential of the Stillwater Complex and 

Adiacent Rocks in the Northern Part of the 

Mount Wood and Mount Douglas Quadrangles, 

Southwestern Montana 

By Norman J Page and John C. Dohrenwend 

ABSTRACT 

The Stillwater Complex contains the largest potential 

chromite and platinum metal resources and second largest 

nickel resources in the United States. The Ultramafic 

zone has produced about 900,000 long tons of chromite 

concentrate and contains unmined reserves equivalent to 

2,520,000 long tons of Cr20a. Nickel and copper sulfide 

minerals that occur in the Basal zone and adjacent hornfelsed metasedimentary rocks represent one of the largest 

nickel potentials in the United States-a known reserve 

of 150 million tons of 0.25 percent nickel and 0.25 percent 

copper. The complex has been estimated to contain the 

largest potential source of platinum metals in the United 

States-possibly over 150 million troy ounces in the 

lower chromite zones and the Basal zone. In addition, the 

anorthosites in the Banded and Upper zones are reported 

to represent a potential alumina resource of almost 2 billion tons. An iron-formation also is present in the adjacent Precambrian metasedimentary rocks, and a coal bed 

is present in the Upper Cretaceous Eagle Sandstone 

nearby. The eventual utilization of these resources 

depends on the availability of large quantities of energy, 

and thus they may not be recovered unless new sources 

of energy or new recovery techniques are developed. 

INTRODUCTION 

Within the last few years, it has become increasingly important to develop quantitative estimates 

of potential mineral resources for the United 

States. Resources were defined by Theobald, 

Schweinfurth, and Duncan ( 1972) as all minerals 

and rocks usable by man now or in the future. 

They included as resources ( 1) currently known 

and recoverable reserves, ( 2) hypothetical and 

speculative undiscovered resources that may be 

recoverable if found, and ( 3) identified and undiscovered resources that require changes in economic conditions or technology to become recoverable. These categories consider both the degree 

1 

of certainty of finding the resource and the feasibility of economically recovering it; diagrams 

embodying these concepts were presented by McKelvey (1973) and Brobst and Pratt (1973). 

Most frequently, this approach results in sizable 

resource estimates, most of which are in thecategory of undiscovered resources requiring changes 

in economics or technology to recover the rna terial. 

(See, for example, Theobald and others, 1972.) 

In addition, these estimates for undiscovered material commonly are pooled, thus applying to a 

large land area with little indication of where to 

search. 

The area covered in this report, approximately 

185 square miles, is in the northern part of the 

Mount Wood and Mount Douglas quadrangles, 

southwestern Montana (fig. 1). The region contains known mineral resources, some of which 

were mined in the past and on which previous investigators (for example, Jackson, 1968; Cornwall, 

1966; Combo and others, 1949; Westgate, 1921) 

based evaluations of reserves of particular commodities. This report defines specific areas of potential resources and evaluates their magnitude. 

Because of the fairly extensive geologic knowledge 

of the area (intensive investigations have been 

carried on since 1916), most of the resources considered here would be categorized as identified 

resources and hypothetical undiscovered resources, but the fact they are not presently being 

mined indicates they have varying degrees of 

economic recovery. As will be shown, relatively 

high estimates of potential resources result from 

considering average grade, either known or reasonably inferred from available data and the area 

or volume of material present for exploitation. 
Yet, even in an area for which the geology is fairly 

well known, the bulk of the potential resources are 

not available, nor will they become available for 

man's use without major economic and technologic changes. 

ESTIMATES OF POTENTIAL RESOURCES 

An evaluation of blocks of ground containing 

potential identified or hypothetical and speculative resources for the northern halves of the Mount 

Wood and Mount Douglas 15-minute quadrangles, 

Very low potential 

LowCu-Au 

-

Coal 

Limestone 

Low Al2 0 3 

Mine 

• 

\@~] High (clos~paced dots) to moderate Ni-Cu-Pt metals 

-

Low to moderate Fe 

Prospect 

• Cr,o, 

Q Pt metals 

,A. Ni·Cu·Pt metals 

• Fe 

~ Limestone quarry 

II Coal 

0 2 MILES 

0 2 KILOMETERS 

/ 

/ 

Montana, is shown in figure 1. This map, containing the Stillwater Complex, delineates areas in 

which the resource potential for a particular commodity is inferred to be high, moderate, low, or 

nonexistent, on the basis of present geologic information. The map is intended to be only a preliminary evaluation of the Stillwater area. Factors 

that have entered into this evaluation are (1) 

known mines, their production, reserves, and 

geologic environment, (2) prospects known before 

1964, their potential production and geologic en110° 

oo' 

/ / / ::::: 

MO~~ 

~~// 

110° 

oo' 

FIGURE 1.-Map of potential resources in the northern parts of 

2 
vironment, (3) areas of mining company exploration since 1964, ( 4) geochemical, mineralogic, and 

petrologic studies, ( 5) geologic mapping and inference, and ( 6) a moderate amount of speculation 

and geologic extension of known occurrences. In 

constructing the map, the geologic maps of the 

Mount Wood and Mount Douglas 15-minute 

quadrangles (Page and others, 1973a, b) were 

used as a base. Data from open-file aeromagnetic 

maps by the U.S. Geological Survey (1971) were 

also incorporated. 

110° 

oo' 

The northern parts of the Mount Wood and 

Mount Douglas 15-minute quadrangles and parts 

of the McLeod Basin and Mount Rae 7 ;2 -minute 

quadrangles in southwestern Montana contain a 

variety of rock types and differ in degree of geologic complexity. The dominant unit is the tabular 

mass of mafic and ultramafic rocks that forms the 

Stillwater Complex; it intrudes Precambrian 

metasedimentary rocks and is overlain by Paleozoic, Mesozoic, and Cenozoic sedimentary rocks. 

Detailed geologic and stratigraphic relations of 

the Mount Wood and Mount Douglas quadrangles, Montana. 

3 
the area were given by Page and N okleberg ( 1970, 

1972) and Page, Simons, and Dohrenwend ( 1973a, 

b). The Stillwater Complex was divided into four 

informal stratigraphic units on the basis of the 

early work of Peoples (1936), Jones, Peoples, and 

Howland ( 1960), Hess ( 1960), and Jackson 

(1961) and the later mapping of Page and Nokleberg ( 1970, 1972). The stratigraphy terminology 

is summarized in table 1. Only those units that are 

pertinent to the resource analysis are included. 

TABLE !.-Generalized stratigraphic terminology used 

for the Stillwater area 

Major units 

Sedimentary and igneous 

rocks of Cenozoic, 

Mesozoic, and 

Paleozic age. 

Stillwater Complex (Precambrian). 

Upper zone } Banded zone 

Ultramafic zone: Bronzitite member 

Peridotite member 

Basal zone. 

Metasedimentary rocks 

(Precambrian) metamorphosed to pyroxene 

hornfels facies rocks. 

Minor units 

Intrusive rocks of intermediate composition (Tertiary). 

Eagle Sandstone (Upper 

Cretaceous) . Madison Limestone 

(Mississippian). 

Anorthosites, gabbros, 

and norites. 

!

Contains about 15 cyclic 

units, 13 of which have a chromitite zone and are labeled A through K 

sequentially from the 

base upward. 

Iron-formation. 

NICKEL-COPPER POTENTIAL 

The major nickel-copper potential of the area is 

from sulfide mineralization associated with the 

Basal zone of the Stillwater Complex (fig. 1). 

Howland (1933) was one of the first to describe 

occurrences of nickel and copper sulfides, and the 

Anaconda Co., the U.S. Geological Survey, and 

the U.S. Bureau of Mines explored the Mouat 

nickel deposit on the west side of the Stillwater 

River between 1937 and 1941 (Cornwall, 1966). 

Nickel and copper prospects known before 1964, 

some of which are shown in figure 1, are abundant 

in and adjacent to the Basal zone. From 1966 to 

1972, five major mining companies (Dayton, 

1971) began exploration programs in the area by 

means of geochemical and geophysical prospecting, trenching, drilling, tunneling, and metallurgical sample testing. Surface exposures of sulfide 

minerals and oxide gossans suggest that most of 

the Basal zone and adjoining metasedimentary 

rocks have a moderate to high resource potential 

4 

for nickel and copper and for byproduct platinum 

metals and possibly cobalt. Reserves of 150 million tons of 0.25 percent nickel and 0.25 percent 

copper ore are known (Dayton, 1971) and are 

present mainly in the area adjacent to the Stillwater River. A more speculative resource estimate 

would be obtained by multiplying the reserves by 

a factor between 2 and 10. 

PLATINUM-GROUP METALS POTENTIAL 

The estimated total platinum metals potential 

of the Stillwater Complex probably exceeds 150 

million troy ounces. Platinum metals have been 

known to occur in the complex since the initial 

work of Howland ( 1933) and Howland, Peoples, 

and Sampson (1936). Studies by Page and Jackson (1967), Leonard, Desborough, and Page 

( 1969), Grimaldi and Schnepfe ( 1969), Greenland, Rowe, and Dinnin (1971, table 2), Page, 

Riley, and Haffty (1969, 1971, 1972), Page 

(1971), and Page, Shimek, and Huffman (1972) 

documented some of the occurrences of platinum 

metal and minerals. On the basis of these studies, 

the A chromitite zone (see table 1) averages about 

0.10 ozjton and attains a maximum known value 

of 0.60 ozjton of platinum, palladium, and rhodium; the B zone contains a slightly smaller 

amount of platinum metals. Therefore, the lower 

two chromitite zones of the Peridotite member, A 

and B, are considered to have a high platinum potential, and the other chromite zones a low to 

moderate potential (fig. 1). The Basal zone thus 

probably contains large tonnages of low-grade material for which Page, Clark, Desborough, and 

Parker ( 1973) estimated the grade to be 0.5 parts 

per million platinum metals with a moderate to 

high potential. Platinum metals are also known 

to be present in sulfide zones in the Banded and 

Upper zones of the complex (Howland, 1933) and 

are suspected to be present in the pegmatitic 

phases of the Bronzitite member of the Ultramafic 

zone. Both of these areas have been assigned a 

low to moderate platinum resource potential 

(fig. 1). 

CHROMITE 

The .total potential chromite resources in the 

Stillwater Complex are estimated to be approximately 7.9 million short tons of Crz03 , all derived 

from the G and H chromitite zones. In addition 

to the potential resources, Jackson (1968) estimated that there are 2.8 million short tons of 

reserves in the Benbow and Mountain View areas. 
Jackson (1968, p. 1509-1510) indicated that the 

thickest chromi te zone is the G zone followed by 

the H zone, and that the highest grade chromite 

is in the H zone followed by the G zone. The maximum Cr/Fe ratio lies between 1.20 and 2.33 as 

determined on purified chromite (Jackson, 1968) , 

and therefore milling techniques would produce 

concentrates of a slightly lower grade. In figure 1, 

the areas where these zones are known to occur 

are considered to be the richest of the potential 

chromite resources and are assigned a high potential. Since other chromite zones occur in the lower 

parts of the cyclic units within the Peridotite 

member, the area encompassed by the Peridotite 

member was assigned a low to moderate chromite 

resource potential. The other rock units do not 

contain significant amounts of Crz03 in any form 

and therefore have no chromite potential. 

The volume of the potential chromite resource 

was then calculated on the basis of the detailed 

mapping by U.S. Geological Survey personnel 

since 1930, summarized on the maps of Page and 

Nokleberg (1970, 1972). The length, average 

thickness, and average Crz03 content of known 

occurrences of the G and H chromite zones were 

compiled and were extrapolated into covered 

areas along the strike of the complex. From the 

estimated volume a recoverable chromite tonnage 

to several depth categories was obtained, which 

includes factors derived from the following 

assumptions: ( 1) Significant concentrations of 

chromite occur only in the G and H chromitites; 

the presence of other, narrower chromite zones 

and widely disseminated chromite was ignored, (2) 

the measured dips of the chromitites range from 

less than 20° to vertical, and the average dip 

throughout the complex approximates 60°, (3) 

the specific gravity of the chromite in G and H 

chromitites is approximately 4.5, (4) the aggregate thickness of the significant chromite zones 

(2 ft or 0.61 m) does not vary by more than 50 

percent from the average measured thickness for 

the western half of the complex, ( 5) the average 

Cr203 content is assumed to be 22 percent for the 

G and H chromitites between Benbow and Moun-

. tain View and 20 percent from Mountain View to 

the western end, on the basis of assays of Wimmler (1948) and others, and (6) the recovery rate 

for normal mining operations would approximate 

50 percent. 

The total potential chromite resources in the 

Stillwater Complex derived from these calcula5 

tions amount to approximately 7.9 million short 

tons of Crz03. A breakdown of this estimate by 

area and depth category is presented in table 2. 

This estimate does not include 2.8 million short 

TABLE 2.-Estimated chromite resource potential for the 

Stillwater Complex 

West of Mountain View 

Cr20a, in thousands of short tons, at depths of- ------ ------- 0-1,000 ft 

(304.8 m) 

1,000-2,000 ft 

(609.6 m) 

(Mouat to Sampson) .......... 2,300 2,300 

Benbow to Mountain View...... 1,500 1,800 

Total .............................. _3'-,8_00 ________ ____,4,'--10_0 

Total, 0-2,000 ft (609.6 m) ........ 7,900 

tons of estimated Cr20 3 reserves and 385,000 

short tons of Cr203 production reported by Jackson ( 1968). Inclusion of the reserves yields a total 

of 10.7 million short tons of Crz03. 

SPECULATIVE COPPER-GOLD POTENTIAL 

Tertiary intrusive rocks of intermediate composition cut the Stillwater Complex on the East 

Boulder Plateau and intrude the Paleozoic and 

Mesozoic sedimentary rocks north of the complex. 

To the south in the headwaters of the Boulder 

River, Tertiary intrusive rocks are associated with 

the alteration and gold deposits of the Independence mining district (Iddings and Weed, 1894; 

Foose and others, 1961). Hess' (1960) descriptions suggested some alteration of the anorthosites 

and gabbros through which the intermediate rocks 

intruded. In view of this, it is possible that some 

hydrothermal activity may have been associated 

with the Tertiary intrusive bodies north of the 

complex and that this activity could have resulted 

in mineralization, such as copper-gold veins, 

disseminated deposits, or replacement deposits. 

On this basis, the area around and over the Tertiary intrusive bodies has been assigned a low 

copper-gold potential (fig. 1). 

IRON POTENTIAL 

The presence of iron-formation in the area extending from the West Fork of the Stillwater River 

to a point west of the Boulder River in the Precambrian metasedimentary rocks implies that 

some iron-resource potential exists. In the late 

1950's, the iron-formation was explored from Iron 

Mountain to Chrome Mountain by U.S. Steel, 

which subsequently dropped its claims (Dayton, 

1971). The most intense exploration appears to 
have been in areas where the iron-formation is 

badly broken by faults and folds and thus where 

it is difficult to delineate continuous areas with 

large tonnages. Because of this intense deformation, most occurrences of iron-formation represent 

only a low to moderate resource potential. In the 

area west of the Boulder River to a point slightly 

east and south of Blakely Creek, however, the 

iron-formation is thicker and more continuous 

than elsewhere, and so it may have a higher potential. 

ALUMINUM POTENTIAL 

The Al20a content of the feldspars of the Upper 

zone is another potential resource in the Stillwater 

Complex. Feldspar is a possible source of aluminum if and when an economic process for the 

extraction of alumina from anorthosite becomes 

available. (See, for example, Ampian, 1967, and 

Leitch and others, 1965.) The Upper zone of the 

complex contains at least three anorthosite zones, 

each about 1,400 feet (426.7 m) thick, but the 

exact position of these zones has not been determined. Therefore, the entire Banded and Upper 

zones have been assigned a low to moderate resource potential for aluminum (fig. 1). The U.S. 

Bureau of Mines (1967) estimated this potential 

at approximately 1.8 billion tons of alumina by 

assuming the existence of a lens of anorthosite 

with a maximum thickness of 4,000 feet ( 1,219.2 

m) and a shape similar to that of the upper part 

of the complex. On the basis of the compiled geologic mapping and stratigraphic information, we 

estimate the resource potential to be nearly 7.7 

billion tons of alumina to a depth of 1,000 feet 

(304.8 m) and 15.4 billion tons to 2,000 feet 

(609.6 m). 

Although the Stillwater Complex is widest 

where Hess (1960) measured a "stratigraphic" 

section and narrows both to the east and to the 

west, field investigations indicate, at least to a 

first approximation, that two of Hess' anorthosite 

zones are virtually continuous and of relatively 

constant thickness throughout the 26-mile ( 41.8 

km) length of the complex. These investigations 

also indicate that the third zone is probably continuous for at least 17 miles (27.4 km). The composition of plagioclase from the anorthosites reported by Hess (1960) and the U.S. Bureau of 

Mines (1967) ranges from An75.5 to An19 and averages approximately An77. Chemical analyses (U.S. 

Bureau of Mines, 1967) indicate an average Al203 

6 

content of approximately 32 weight percent. 

Modal analyses (Hess, 1960) of the anorthosites 

show a range from 85 to 100 percent plagioclase 

and suggest an average of approximately 90 percent plagioclase. Other units appear to have remarkably consistent chemical and modal compositions throughout the length of the complex, and 

these properties are assumed constant for the 

anorthosites. 

The estimate of the potential alumina resources 

(table 3) is also based on the assumption that ( 1) 

TABLE 3.-Estimated potential aluminum resources for 

the anorthosites of the Stillwater Complex, in billions 

of short tons 

Alumina 

Depth (ft) · Anorthosite (AbOa) 

0-1,000 (304.8 m) -------------- 26.6 

0-2,000 (609.6 m) -------------- 53.2 

7.7 

15.4 

AI 

2.7 

5.1 

the average density of the anorthosites is 174lbs/ 

ft3 , (2) the dip of the zone averages 60°, and (3) 

the average recovery rate for mining approximates 

50 percent. 

COAL POTENTIAL 

In the northeastern comer of the Mount Wood 

quadrangle, along the inner valley of the Stillwater River, a coal-rich bed was mined during the 

latter part of the 19th century to serve local demands (Calvert, 1916). Vhay (1934) placed the 

coal stratigraphically at the top of a thick, massively bedded sandstone within the Upper 

Cretaceous Eagle Sandstone. Stratigraphic descriptions of the Eagle Sandstone and of the coal 

beds contained within it were presented for adjacent areas of Montana by Knappen and Moulton 

(1931) and by Roberts (1966, 1972).Asdescribed 

by Calvert (1916), the total thickness of the coal 

in the Stillwater area is approximately 3-5 feet 

(0.9-1.5 m), and his analyses indicate that the 

coal is of high-volatile Band C bituminous ranks 

with a relatively low sulphur content (averaging 

about one-half of 1 percent). Combo, Brown, Pulver, and Taylor (1949) estimated the coal resources in the Stillwater area at approximately 

12.7 million tons. 

The coal resource of the Eagle Sandstone was 

estimated by extrapolations of available geologic 

and stratigraphic data (Calvert, 1916; Vhay, 

1934) in the Stillwater area. Approximate structural contours were estimated for the coal-rich bed 

and were combined with the topographic relief 
to determine the potential area of coal in three 

depth ranges, 0-1,000 feet (304.8 m), 1,000-2,000 

feet (609.6 m), and 2,000-3,000 feet (914.4 m). 

These area estimates were adjusted to resource 

estimates by using an averaged total coal thickness of 3 feet ( 0.91 m), a weight volume factor of 

1,520,000 tons per square mile-foot (equivalent to 

a specific gravity of 1.32), and a 50-percent recovery factor. Assumptions, definitions, and procedures used to prepare this estimate follow the 

conventions established by Averitt (1969). 

The total estimated potential coal resource of 

the Stillwater area is approximately 50 million 

tons. This estimate is broken down by depth and 

local area in table 4, and part of the areal distribuTABLE 4.-lnferred coal resources, in millions of short 

tons, of the Stillwater area 

[Rank, high-volatile B and C bituminous; bed thickness, 28-42 in.] 

Area Overburden (ft) 

Nye area, north of the Stillwater River (Mount Wood quadrangle). 

10-1,000 21,000-2,000 

22,000-3,000 

Hypothetical: South of the Stillwater River, north of Dean Basin, and east of Little Rocky Creek (Beehive quadrangle) . 

Speculative: South of Dean Basin (Beehive and Emerald Lake quadrangles). 

0-1,000 

1,000-2,000 

2,000-3,000 

0-3,000 

Recovery of Recovery of 100 percent 50 percent 

4.8 2.4 7.3 3.7 11.1 5.6 

15.2 

13.7 

9.3 

7.6 

6.6 

4.6 

-26 

Total inferred resource----------------------·------- 112.7 56.4 

1lndicated resource. 2Hypothetical resource. 

tion is shown in figure 1. Because these estimates 

are based on sparse geologic data and only three 

measurements of coal-bed thickness, only the coal 

between 0 and 1,000 feet (304.8 m) in the Nye 

area is considered to be an indicated resource, and 

that between 1,000 and 3,000 feet (914.4 m) a 

hypothetical resource. In the Beehive and Emerald 

Lake quadrangles, the coal is a speculative undiscovered resource because no outcrops of coal 

have been found and large parts of the area are 

covered by Pleistocene and Holocene deposits. 

LIMESTONE AND DOLOMITE, SAND, GRAVEL 

The other commodities present in the Stillwater 

area include limestone and dolomite, sand, and 

gravel. Limestone and dolomite occur in the Paleozoic sedimentary sequence that overlies the 

Stillwater Complex to the north and have been 

quarried from the Madison Limestone south of 

7 

Horseman's Flat for slagging material in the 

manufacture of ferrichrome alloy at the Mountain 

View mill. Therefore, some of the limestone and 

dolomite north of the Stillwater Complex has potential as a slagging material. Extensive glacial 

and alluvial debris cover large areas of the northern part of the Mount Wood quadrangle and have 

some potential for the local production of gravel 

and sand. 

ENERGY REQUIREMENTS 

In addition to the identification of areas where 

potential resources occur and the estimation of 

their magnitude, the energy requirements to extract and refine these resources also must be considered in their evaluation. The amount of energy 

needed to- produce a metal could be a limit to 

identifying usable resources. Unfortunately, only 

a few estimates of energy expenditures as a function of the grade of ore have been made. Bravard, 

Flora, and Portal ( 1972) made such estimates for 

magnesium, aluminum, iron, copper, and titanium; 

their data are used here in examples to demonstrate the value of considering the energy expenditure. 

Production of 1 ton of copper from 1.0 percent 

copper sulfide ore requires about 13,532 kWh 

(kilowatt-hours) of equivalent coal energy, and 

about 24,759 kWh of equivalent coal energy would 

be expended using a 0.3 percent copper sulfide ore 

(Bravard and others, 1972). At the lower grade 

over half of the energy is required for mining and 

milling, and because the amount of ore material 

necessary to produce a ton of copper is exponentially related to the grade of the material, it would 

seem possible that for ores of low grade the energy 

required would also increase exponentially and 

not be inversely proportional to grade, as assumed 

by Bravard, Flora, and Portal (1972). Their basic 

assumptions, however, indicate that copper-nickel 

sulfide ores of the Stillwater area containing 0.5 

percent copper would require about 21,500 kWh 

of equivalent coal energy per ton of copper to 

recover this potential resource. In order to mine 

and refine all the reserves reported in this area, 

5.5 X 1013 Btu (British thermal units) of energy 

would be required, which may be compared with 

the low estimate of 3.27 X 1018 Btu of total cumulative energy demand for the United States from 

the year 1968 to 2000 (U.S. Bureau of Mines, 

1970, p. 15). Because the energy expenditure is 

a small proportion of the energy available, the 
copper-nickel ores are apparently a usable potential resource, but only if technologic and economic 

conditions are satisfactory. 

In contrast, the recovery of the 5.1 X 109 tons of 

aluminum from the anorthosites would require 

about 1.26 X 1018 Btu of energy, using the present 

technology. This is about one twenty-eighth of the 

total energy reserves of the United States (U.S. 

Bureau of Mines, 1970, p. 15), and the aluminum 

recovered would satisfy the contingency forecast 

of demand for aluminum well past the year 2000 

for the world (U.S. Bureau of Mines, 1970, p. 455). 

Such a comparison, however, suggests little feasibility of recovering aluminum from this source, 

and the aluminum would be recoverable only after 

drastic changes in technology or economics. On 

the basis of Calvert's (1916) analyses of the coal, 

·the local coal resource can supply only 2.13 X 1011 

Btu of energy from material between 0 and 1,000 

feet (304.8 m), assuming 100-percent recovery, 

and therefore would not be a large enough energy 

resource to mine and refine either the coppernickel or the aluminum. 

According to Bravard, Flora, and Portal (1972, 

p. 25), between 4,270 and 10,295 kWh of equivalent coal energy is required to produce 1 ton of 

iron, depending on the process and the ore grade. 

This is the lowest amount of energy required for 

production of metals studied by them and indicates that energy usage will not be a limiting 

factor in considering the potential iron resource 

in the Stillwater area. Energy requirements for 

using the chromium and platinum metal resources 

are not known but are believed to be between 

those of iron and aluminum. Therefore these potential resources cannot be evaluated in terms of 

energy requirements without further information. 

REFERENCES CITED 

Ampian, S. C., 1967, Limestone soda process-Correlation of reaction products with extractability of alumina from anorthosite: U.S. Bur. Mines Rept. lnv. 

6933,44 p. 

Averitt, Paul, 1969, Coal resources of the United States, 

January 1967: U.S. Geol. Survey Bull. 1275, 116 p. 

Bravard, J. C., Flora, H. B., 2d, and Portal, Charles, 1972, 

Energy expenditure associated with the production 

and recycle of metals: ORNL-NSF Environmental 

Program Rept. 24, Oak Ridge Natl. Lab., 87 p. 

Brobst, D. A., and Pratt, W. P., 1973, Introduction, in 

United States mineral resources: U.S. Geol. Survey 

Prof. Paper 820, p. 1-8. 

8 

Calvert, W. R., 1916, Geology of the Upper Stillwater 

Basin, Stillwater and Carbon Counties, Montana, 

with special reference to coal and oil: U.S. Geol. Survey Bull. 641-G, p. 199-214. 

Combo, J. X., Brown, D. M., Pulver, H. F., and Taylor, 

D. A., 1949, Coal resources of Montana: U.S. Geol. 

Survey Circ. 53, 28 p. 

Cornwall, H. R., 1966, Nickel deposits of North America: 

U.S. Geol. Survey Bull. 1223,62 p. 

Dayton, Stan, 1971, Hot air over Stillwater, profile of a 

hearing on mineral entry: Eng. and Mining Jour., 

v.172,no.10,p.75-84. 

Foose, R. M., Wise, D. U., and Garbarini, G. S., 1961, 

Structural geology of the Beartooth Mountains, 

Montana and Wyoming: Geol. Soc. America Bull., 

v. 72,p. 1143-1172. 

Greenland, L. P., Rowe, J. J., and Dinnin, J. I., 1971, 

Application of triple coincidence counting and of 

fire-assay separation to the neutron-activation determination of iridium, in Geological Survey research 

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9 

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