GEOLOGICAL SURVEY CIRCULAR 698

Mineral Resources: 

Potentials and Problems

Mineral Resources: 

Potentials and Problems

By Walden P. Pratt and Donald A. Brobst

GEOLOGICAL SURVEY CIRCULAR 698

A summary of United States resources of 27 ma/or 

mineral commodities, and the problems 

involved in their utilization

1974
United States Department of the Interior

ROGERS C. B. MORION, Secretory

Geological Survey

V. E. McKelvey, Director

First printing 1974 

Second printing 1974

Free on application to the U.S. Geological Survey, National Center, Reston, Va. 22092
CONTENTS

Abstract ______________

Introduction __________

Resources and reserves _________

Focus of this report _______

Resource summaries ___________

Principal nonferrous metals 

Aluminum _____________

Copper _ ____. 

Titanium ________. 

Zinc ___________. 

Gold ___________. 

Lead ____________

Platinum _________ 

Tin ____________. 

Silver __________.

Page 

1 

1

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2

3

3

3

5

5

6

6

7

8

8

8

Resource summaries Continued 

Principal ferrous 

Iron __ .

Silicon ____ 

Molybdenum 

Manganese _ 

Tungsten __ 

Cobalt _____ 

Chromium __ 

Vanadium _ 

Tantalum 

Niobium ___ 

Mineral fuels __ 

Oil and gas 

Coal _____ 

Uranium _ 

Thorium ___

Magnesium 9 References cited

Page

9

9

10

10

11

11

12

12

13

13

13

14

14

15

16

17

17

18

19

ILLUSTRATION

FIGURE 1. Classification of mineral resources 

Page

2

TABLES

TABLE 1. Principal nonferrous metals

2. Principal ferrous metals .

3. Mineral fuels .

Page 

4

10

14

III

Mineral Resources: Potentials and Problems

By Walden P. Pratt and Donald A. Brobst

ABSTRACT

The encyclopedic nature of "United States Mineral 

Resources" (U.S. Geological Survey Professional Paper 

820) seems to have inhibited its widespread use by 

people other than professional geologists. A summary 

of the principal findings and conclusions of Professional Paper 820 is presented with special regard to 

the resources of 27 mineral commodities of major importance to our industrial civilization (based on dollar value) and the problems involved in the utilization of these resources of the 10 most important nonferrous metals, the 11 principal ferrous metals, and 

the 6 principal fossil and nuclear fuels.

INTRODUCTION

"United States Mineral Resources" (Brobst 

and Pratt, 1973) reviewed the long-term 

United States position for potential resources 

of 65 mineral commodities or commodity 

groups. One of the main purposes of the report 

was to provide people other than geologists 

with easily understandable factual data on the 

resources of the many mineral commodities 

that are important to our daily lives. However, 

the comprehensive encyclopedic nature of the 

volume seriously inhibits its effective use for 

this purpose; the 722 pages of scientific and 

technical prose does not make for great popular 

consumption.

We have, therefore, condensed a great mass 

of information into a form more readily usable 

by other writers and the general public. The 

present report summarizes the principal findings and conclusions of the larger report with 

regard to 27 mineral commodities of major importance to our industrial civilization: the 10 

most important nonferrous metals, the 11 principal ferrous metals, and the principal fossil 

and nuclear fuels petroleum and natural gas, 

coal, uranium, thorium, and oil shales. A separate companion article (W. P. Pratt and D. A. 

Brobst, written commun., 1974) has emphasized the importance of undiscovered highgrade resources in contrast to known resources 

that are not recoverable because of economic or 

technologic factors. The lesson to be drawn 

from both articles is the same. Our large resources of many minerals are at this point only 

a potential, not a reality. To bring them into 

the category of available reserves is not a simple matter of raising the price; it will require 

enormous research efforts, with long lead times. 

Crash programs responding to the shortage of 

the moment will not suffice. We hope that these 

two articles together may enlighten a larger 

segment of the American public to the problems that confront us if we are to overcome 

our present complacency and avert many future crises of mineral supply.

We acknowledge once again the efforts of our 

many colleagues without whose experience and 

continuing cooperation neither the large report 

nor the present one would have been possible.

RESOURCES AND RESERVES

Mineral reserves are materials from which a 

usable mineral or energy commodity can be 

extracted profitably by using existing technology and under present economic and legal 

conditions. They represent only a part of the 

broad field of mineral resources. In a longrange assessment of resources, reserves must 

be distinguished from other mineral deposits 

that may eventually become available: (1) 

Known deposits that cannot be profitably mined 

at present because of economics, technology, or 

legal restraints and (2) unknown deposits, 

rich or lean, that may be inferred to exist on 

the basis of geological reasoning but that have
not yet been discovered. In order to make this 

distinction useful for all the commodities discussed in "United States Mineral Resources" 

we adapted a classification of mineral resources 

previously suggested by McKelvey (1972), 

which differentiated reserves and other resources on the basis of two factors: feasibility 

of economic recovery and geologic assurance or 

certainty of existence. This classification, with 

minor changes, has been accepted for formal 

use by the U.S. Geological Survey and U.S. 

Bureau of Mines, and is shown in figure 1.

Economic

Subeconomic

IDENTIFIED

RESERVES

IDENTIFIED 

SUBECONOMIC 

RESOURCES

UNDISCOVERED

In known 

districts

HYPOTHETICAL

RESOURCES

In undiscovered 

districts or forms

SPECULATIVE

-

RESOURCES

Increosing degree of 

~ geologic ossuronce

Reserves: Identified resources from which a usable 

mineral or energy commodity can be economically 

and legally extracted at the time of determination.

Identified-subeconomic resources: Materials that are 

not reserves, but that may become reserves as a result of changes in economic and legal conditions. 

(Referred to as "conditional resources" in Brobst 

and Pratt, 1973.)

Hypothetical resources: Undiscovered materials that 

may reasonably be expected to exist in a known mining district under known geologic conditions.

Speculative resources: Undiscovered materials that may 

occur either in known types of deposits in a favorable geologic setting where no discoveries have been 

made, or in as-yet-unknown types of deposits that 

remain to be recognized. 

FIGURE 1. Classification of mineral resources.

FOCUS OF THIS REPORT

Our known reserves of most minerals are 

relatively small in relation to long-term demand, and the deficit can be made up only 

through a combination of four actions:

1. Reducing the demand, through substitution 

of other minerals, reduction of waste, or 

elimination of some uses.

2. Supplementing the raw (primary) mineral 

supply, through recovery and recycling of 

scrap and used materials.

3. Importing raw or refined minerals from 

foreign sources.

4. Increasing our reserves, through discovery 

of new mineral deposits (hypothetical 

and speculative resources) and through 

development of technology for the feasible recovery of low-grade deposits (identified subeconomic resources). 

Probably no one of these actions alone will be 

enough to solve our long-range supply problems, but each one is important. The first two, 

which deal with processing of minerals and use 

of the products, are beyond the scope of this 

report, and the third is an increasingly sensitive question of international economics and 

politics. This report deals with the potential 

impact of the fourth action, by attempting to 

evaluate our resources that may eventually be 

converted into reserves.

We emphasize that the resource figures presented here are estimates, and obviously those 

that relate to undiscovered resources must be 

very rough estimates indeed. They will undergo 

constant revision in future years, probably for 

both better and worse, as new deposits are 

found, new theories are evolved, and old ideas 

discarded. However, they have been made by 

geologists who have spent a significant part of 

their careers studying the geology of their respective commodities, and they may probably 

be regarded as the most reliable resource estimates now publicly available. (Readers who 

have questions may refer to Brobst and Pratt 

(1973) or directly to the authors for more details.) We hope that a continuing resource appraisal program now being implemented in the 

Geological Survey may make possible the periodic refinement of these estimates and also may 

eventually be extended to include appraisal of 

the impact of the first three actions listed above 

on our domestic mineral supply.

Estimates of reserves are made by the U.S. 

Bureau of Mines, largely on the basis of data 

supplied annually by the mineral industries. 

Because of the competitive nature of the free 

enterprise system, and further because some 

States levy taxes on mineral reserves in the 

ground, mining companies, understandably, 

may be less than candid in reporting known 

reserves long in advance of their exploitation. 

We believe that many such known but unre-
ported reserves are accounted for in our estimates of undiscovered (hypothetical and speculative) resources; they are still "undiscovered" 

from the standpoint of being public information. Although reserve data are reported to the 

Bureau of Mines in strict confidence, it seems 

likely that modification of the tax laws in some 

States would increase the reliability of total 

reserve estimates.

RESOURCE SUMMARIES

The rest of this report consists of summary 

information on the resources of three groups of 

minerals: nonferrous metals, ferrous metals, 

and mineral fuels. The text summarizes for 

each commodity the principal uses; the extent 

to which the United States depended on imports in 1972 (see below), and the principal 

sources of these imports; the extent of domestic reserves; the resource potential (identified 

subeconomic, hypothetical, and speculative resources) ; and the particular problems of discovery or technology that hamper our ability to 

convert the potential resources into reserves. 

Tables 1-3 summarize three factors for each 

mineral: (1) The dollar value of U.S. primary 

demand for 1968 (the latest year for which 

these data are readily available), as a means of 

ranking the minerals in relative importance, 

(2) the approximate 1972 U.S. consumption, 

and (3) the minimum projected cumulative 

U.S. demand to the year 2000.

The nonmetallic mineral commodities are not 

included in this review because the most important ones, in terms of the criterion used to 

rank the metallic minerals, are nearly all in 

long supply, and their reserves are adequate 

for the long term.

Data on imports in 1972, as reported here, 

may be misleading for several minerals of 

which we have little or no reserves. For example, the statement that we imported 67 percent 

of our 1972 consumption of niobium seems to 

imply that the remaining 33 percent came from 

domestic production yet domestic reserves are 

reported to be nil. In this and similar cases, the 

difference between imparts and consumption is 

accounted for by supply from domestic stocks 

(inventories) already on hand, including Government stockpile release not by domestic production from very small or nonexistent reserves.

Future demand is difficult to evaluate. To assume continued use at present rates, and no 

growth in either population or per capita use, 

would give a minimum figure that would be 

easy to project indefinitely; but the resulting 

projections would be unrealistically small, except for a few commodities whose consumption 

may be cut back drastically because of substitutes or environmental concerns. As an alternative, we use here figures estimated by the U.S. 

Bureau of Mines for the minimum anticipated 

cumulative demand (MACD) for the period 

1968 to 2000 the total amount of each commodity we are expected to need, at the very 

least, from 1968 until the end of the century. 

(No attempt has been made to reduce the 

MACD to allow for the part already used from 

1968 to 1973, but because demand for most 

commodities is projected to increase annually, 

this difference would amount to no more than 

a few percent of the total MACD.) These estimates are based on extrapolation of recent 

trends, modified by a number of contingencies 

assumed for technological, economic, social, environmental, and other relevant influences 

(U.S. Bureau of Mines, 1970). We believe these 

are the most reasonable projections available of 

probable minimum demand for each commodity 

over the next 26 years a convenient minimum 

time span for assessment of "long-term" demand. The MACD for each commodity is shown 

in tables 1-3 and is used in the text.

Statistical data relating to production, consumption, imports, and reserves are taken from 

published reports of the U.S. Bureau of Mines 

(U.S. Bureau of Mines, 1970; U.S. Department 

of Interior, 1973, 1974). The estimates of identified subeconomic, hypothetical, and speculative resources, and discussions of their problems, are based on the commodity chapters of 

Brobst and Pratt (1973).

PRINCIPAL NONFERROUS METALS 

ALUMINUM

Aluminum (S. H. Patterson and J. R. Dyni, 

in Brobst and Pratt, 1973, p. 35-43) is widely 

used in construction materials, aircraft and 

autos, electrical equipment, containers, and 

home consumer products. We import approximately 96 percent of our aluminum as bauxite, 

alumina (aluminum oxide derived from baux-
ite), and the metal, mainly from Jamaica, Surinam, and Australia. Virtually the only aluminum ore from which aluminum can be profitably recovered at present is bauxite, a complex 

impure mixture of aluminum hydroxides. Domestic bauxite reserves contain 13 million short 

tons of aluminum, less than 5 percent MACD. 

Identified subeconomic resources of bauxite in 

Hawaii, Washington, and Oregon amount to 

about 20 percent MACD, but for much of this 

material, a process of profitable extraction has 

not been devised. Hypothetical and speculative 

resources of bauxite in the United States are 

considered to be small, because the areas that 

have geologic environments in which bauxite 

commonly occurs are relatively small in extent 

and have been explored.

Potential resources of aluminum other than 

bauxite include a variety of minerals and rocks. 

An enormous amount of aluminum is involved, 

but few of these resources can be exploited 

without major technological or economic breakthroughs. High-alumina clays seem to be the 

most favorable of these potential sources because of their high aluminum content (25-35 

percent alumina) and their widespread occurrence; the chief factors prohibiting their use at 

present are the lack of a method for profitable 

extraction of the alumina, and the greater value 

of the deposits for kaolin and for refractory and 

ceramic clays. Another major subeconomic resource of aluminum is dawsonite, a basic sodium-aluminum carbonate, soluble in acid. It occurs as crystals in the rich oil shales of the 

Green River Formation in northwestern Colorado, where one area of 250 square miles contains an estimated resource of some 3.5 billion 

tons of aluminum more than 12 X MACD. In 

addition, the rock contains an average of about 

30 gallons of shale oil per ton; costs of mining 

and processing the rock would therefore be

partly offset by coproduction of shale oil and 

nahcolite (soda ash) from the same rock. Processes for extraction of the aluminum are known, 

but utilization of this vast resource is largely 

dependent on solution of the technological, legal, 

and environmental problems of the oil shale.

Alunite (hydrous potassium aluminum sulfate) deposits near Cedar City, Utah, reportedly contain about 31 million tons of aluminum, 

or 11 percent MACD. Recovery of alumina 

from these deposits is now being tested by industry in a pilot plant at Golden, Colo. Alunite 

is a present source of aluminum in the 

U.S.S.R., and a plant for the recovery of alumina and fertilizers from alunite is planned in 

Mexico. Alumina and potassium sulfate were 

recovered experimentally from alunite in Utah 

during World War II (Parker, 1969).

Anorthosite, an igneous rock containing 23- 

28 percent alumina, occurs in large masses in 

Wyoming, California, New York, and elsewhere 

in the United States. A pilot plant operated by 

the U.S. Bureau of Mines in the early 1950's 

proved that alumina can be recovered from 

anorthosite, but not at currently competitive 

costs. Although United States anorthosite is not 

likely to become a source of aluminum in the 

near future, it constitutes an enormous lowgrade resource.

In view of our present dependence on imports of bauxite and bauxite-derived alumina, 

it would appear that exploration for new bauxite deposits, especially in tropical areas, should 

be supplemented by research on methods for 

economical recovery of alumina from domestic 

nonbauxite resources. Any such methods, however, must deal with the large energy demands 

of conventional aluminum-reduction processes, 

a factor which a prominent consumer advocate 

recently highlighted by characterizing aluminum beverage cans as "congealed electricity."

TABLE 1. Principal nonferrous metals

Commodity

Aluminum __________________

Copper _ _ _ _ _ ______

Titanium _ _ _ __ _

Zinc _ _ _ __ _ ______________

Gold _____ _____ ___

Lead

Platinum group _____________

Tin ________ ___________

Silver _ ____________________

Magnesium _ _ _ ____ _ _ _

Value ( millions ) of 

U.S. primary demand 

1968

q»1 QQQ

1,300

____ 414

OQA

OKQ

943

____ 202

1Qfi

____ 193

___ 144

Approximate 1972 con- 

, sumption (short tons 

except as noted)

4,707,000

2,351,000

440,000 {

1,535,000

9,400,000 troy oz

1,435,000

1,430,000 troy oz

67,000 long tons

137,000,000 troy oz

1,100,000

Minimum anticipated cumulative demand, 1968-2000 (short 

tons, except as noted)

290,000,000

96,400,000

21,100,000 (nonmetal)

1,000,000 (metal) 

57,000,000

372,000,000 troy oz

37,000,000

43,600,000 troy oz

6,200,000 long tons

3,700,000,000 troy oz

40,900,000
COPPER

Copper (D. P. Cox and others, in Brobst and 

Pratt, 1973, p. 163-190) is used for electrical 

applications (53 percent of U.S. consumption 

in 1970), and in construction, industrial machinery, transportation, ordnance, and many 

other uses. Foreign sources, mainly Canada, 

Peru, and Chile, supplied about 18 percent of 

our needs in 1972. Most of current U.S. production comes from the porphyry copper deposits of the West large bodies of igneous rock 

(typically porphyries) through which copper 

minerals are disseminated in such small 

amounts that they can be recovered only by 

mass-mining techniques. The cutoff grade, or 

minimum copper content for which these ores 

can be processed economically, is currently 

0.2 to 0.4 percent.

The U.S. Bureau of Mines (Bennett and 

others, 1973) estimates domestic copper reserves on the basis of three different price 

levels, as follows: at 50 cents per pound, reserves are 83 million tons; at 75 cents, 114 million tons, and at $2.00 per pound, 180 million 

tons. Of this total, the strict definition of reserves limits us to a range of about 100-110 million tons (about l.lX MACD) for reserves at 

the recent price range of 65-70 cents. The remaining 70 million to 80 million tons at prices 

as much as $2.00 is then, by definition, part of 

the identified subeconomic resources category; it 

includes deep deposits not now workable and 

known porphyry deposits averaging as little as 

0.25 percent copper. It also includes an estimated 11 million tons in low-grade beds in 

Michigan. It does not, however, include an additional estimated 60 million tons in low-grade 

copper-nickel sulfide deposits in the Duluth 

Gabbro Complex of Minnesota, on which further research is needed on geology, mining 

methods, and technology of extracting the ore 

minerals, before mining will become economically and technologically feasible. It also does 

not include low-grade copper deposits in Precambrian sedimentary rocks in western Montana and adjacent parts of Idaho, which are 

currently being explored and evaluated; it 

seems clear that these deposits will eventually 

constitute a very large resource. Estimated 

hypothetical resources of as much as 150 million tons of copper (about 1.5x MACD) include resources in several areas but chiefly.' 

those in undiscovered deposits concealed under 

basin fill in the major porphyry copper regions 

of the Southwest. Whereas southeastern Arizona is the most favorable general target for 

discovery of hypothetical resources, most of the 

western Basin and Range province should be 

considered pristine exploration ground for 

speculative resources because of the generally 

favorable regional geology. In both places, even 

though these undiscovered resources are probably very large, discovering them will require 

an enormous amount of geologic and geophysical mapping, imaginative analysis of geologic 

data, and continued improvement of exploration techniques.

TITANIUM

Titanium (Harry Klemic and others, in 

Brobst and Pratt, 1973, p. 653-665; J. W. 

Stamper, in U.S. Bureau of Mines, 1970, p. 

773-794) is useful principally in the modern 

industrial technology of affluent societies. Only 

about 5 percent of titanium raw materials is 

used to produce titanium metal; the remaining 

95 percent is used to make titania (titanium 

dioxide), which because of its whiteness, opacity, and chemical inertness, is especially suitable for use as a pigment in paints and other 

surface coatings and in plastics. Titanium metal 

and its alloys are used in the aerospace industry because of their favorable strength: weight 

ratio, and in the chemical industry because of 

their resistance to corrosion. The two principal 

mineral resources of titanium are ilmenite 

(FeTiOs) and rutile (Ti02 ). Metallic titanium 

is made from rutile and accounts for about 27 

percent of the rutile used; the rest of the rutile 

and nearly all the ilmenite are used in making 

pigments. Although rutile is preferred as a 

source of titanium metal because the cost of 

processing ilmenite is so much higher, rutile is 

available in the United States only in deposits 

which at present are economically marginal or 

submarginal. Conversely, ilmenite is more 

abundant than rutile and is produced in many 

countries, including the United States. The 

United States in 1972 imported 86 percent of 

the rutile it consumed, mostly from Australia 

and Sierra Leone, but only 18 percent of its ilmenite needs, mainly from Canada and Aus-
tralia; the ratio of ilmenite to rutile consumed 

was about 7:1.

Ilmenite is an accessory mineral in certain 

types of iron ores, and its greatest resources 

are in such iron ores, and in some modern or 

fossil beach sands. U.S. reserves of ilmenite are 

equivalent to about 1.4 X MACD. Rutile reserves are here considered to be nil because of 

virtual cessation of rutile production. Identified 

sub economic resources of titanium are estimated to be on the order of 147 million short 

tons, or 6.7X MACD. Nearly half this resource 

is in subeconomic titanif erous iron-ore deposits 

in Alaska, from which ilmenite would be produced as a byproduct. Other large identified 

subeconomic resources are in Hawaiian laterites; marginal resources are in both bedrock 

and sand deposits in the producing areas of the 

east coast of the United States (mostly ilmenite, minor rutile) and in magnetite-ilmenite 

deposits in the Duluth Gabbro Complex of 

Minnesota; all these resources are at present 

subeconomic because of economics or beneficiation problems or both. Identified subeconomic 

resources of rutile are estimated at 2.7-3.4 

million short tons; this amount is only a fraction of MACD for titanium oxide, but as rutile 

is the preferred source material for metallic titanium, it is equivalent to about 1.6-2.0 X the 

MACD of 1 million tons for titanium metal. Inasmuch as rutile has been produced in the past 

from most of the deposits that constitute the 

identified subeconomic resources, resumption of 

production will be largely a matter of economics. Estimated hypothetical resources are about 

4x MACD, mostly in bedrock ilmenite deposits. 

Speculative resources are probably great in geologic environments common in regions such as 

Canada and South Africa but not in the United 

States.

ZINC

Zinc (Helmuth Wedow, Jr., and others, in 

Brobst and Pratt 1973, p. 697-711) is used 

chiefly in the automobile, household appliance, 

and hardware industries, for zinc-base alloy 

die castings, for galvanizing iron and steel 

products, and in the manufacture of brass. 

About 52 percent of domestic consumption in 

1972 was imported from foreign sources, 

chiefly Canada, Mexico, Peru, and Australia.

U.S. reserves amount to about 30 million short 

tons, or about 53 percent of MACD. Identified 

subeconomic resources estimated at more than 

80 million tons (more than 1.4X MACD) occur 

chiefly in low-grade deposits in sedimentary 

carbonate rocks in the Mississippi Valley and 

Appalachian regions and in deep-lying deposits 

in Washington State. Some of these resources 

are in old mines that have been closed within 

the past few years because of short-term low 

metal prices. Such resources formerly reserves until the price dropped below a certain 

level now will require an even higher price to 

become enonomically recoverable because of the 

added cost of reopening mines that have filled 

up with water. Hypothetical and speculative 

resources of the same geologic type, elsewhere 

in North America, including both recoverable 

and subeconomic deposits, constitute a resource potential estimated at several hundred 

million tons of zinc, awaiting discovery 

through effective exploration techniques.

GOLD

Gold (F. S. Simons and W. C. Prinz, in 

Brobst and Pratt, 1973, p. 263-275) is used 

mainly in jewelry and the arts (60 percent of 

consumption in 1971), in electronic components 

(29 percent), and in dentistry (11 percent). 

Gold imports in 1972 were 61 percent of consumption, mostly from Canada and, through 

Switzerland, from South Africa. Although more 

excitement is popularly attached to gold mines 

proper, byproduct gold currently accounts for 

40 percent of the total U.S. gold output, most 

of it from copper mines. Differentiation between gold reserves and resources is particularly sensitive to price fluctuations, which in 

the past 2 years (1972-73) have been extremely volatile; estimates given here are based 

on the price of $35 per troy ounce that obtained 

in 1968 when most of the detailed reserve estimates were made; consequently, some of the 

material considered identified subeconomic resources on that basis has now been moved into 

the reserve category, either theoretically or 

actually (Loehwing, 1973). With this in mind, 

estimated reserves as of 1970, including both 

primary and byproduct gold, were about 82 

million troy ounces, or 22 percent MACD. 

Identified subeconomic resources estimated by
the U.S. Bureau of Mines (1967) as potentially 

recoverable at prices up to $145 per oz were 244 

million oz (66 percent MACD), including 30 

million oz of byproduct gold. This does not include two other significant resources: an estimated several hundred million ounces dispersed 

in a volume of some 50 cubic miles of goldbearing conglomerates (consolidated gravels) 

in northwestern Wyoming, and another estimated several hundred million ounces of potential byproduct gold in identified subeconomic 

resources of porphyry copper ores. Either of 

these identified subeconomic resources by itself 

is of the same order of magnitude as the MACD 

of 372 million oz. However, formidable technologic and legal problems militate against 

utilization of the resources in the Wyoming 

conglomerates, and the recovery of the gold in 

the identified subeconomic copper resources, as 

well as from copper reserves, will depend not 

only on conditions that govern the eventual 

mining of the copper, but also on the method 

used. In-place leaching methods recently introduced in Arizona, although they decrease the 

adverse impact of copper mining on the environment, leave all the byproduct metals (notably gold, silver, molybdenum, and selenium) 

behind. Recovery of gold from abundant materials in which it occurs in extremely low concentrations, such as sea-floor sediments in the 

Bering Sea and along parts of the Pacific 

Coast (concentrations of 10-390 parts per billion (ppb), or seawater itself (0.01-0.05 ppb), 

presents a potentially rewarding challenge to 

technology. (A median concentration of 0.03 

ppb would be about 1 oz of gold per million cu 

m of seawater enough water to flood two football fields to a depth of 100 m3

The principal hypothetical and speculative 

resource's of primary gold are probably to be 

found in deposits of the so-called Carlin type, 

in which the gold occurs as grains of submicroscopic size (less than 10 /*,,, or a hundredth of 

a millimeter, across), disseminated in darkgray limestone beds rocks so nondescript that 

neither gold nor anything else was normally 

sought in them 30 years ago. Two deposits of 

this type in Nevada together accounted for 

more than 20 percent of domestic gold production in 1969. Very likely, other deposits of this 

type have been overlooked. Large areas in the

West are underlain by rocks now recognized as 

favorable hosts for this new type of gold deposit; these areas should be geologically 

mapped to outline the most favorable targets 

for exploration.

Another area that has strong possibilities for 

discovery of hypothetical resources is the northern Black Hills of South Dakota, site of the 

Homestake gold deposit, which is currently the 

most productive in the United States. The 

Homestake mine is in Precambrian rocks, less 

than 2 miles distant from the edge of an extensive cover of younger sedimentary rocks. 

This cover once extended over the area of the 

mine, but was eroded away in fairly recent 

geologic time. The same rocks and structures 

that contain the Homestake deposit continue 

underneath the younger rocks, and J. J. Norton 

(1974) has recently proposed testing of the 

hypothesis that another Homestake-type deposit might be discovered by carefully planned 

exploration of the buried Precambrian rocks. 

Total recorded production of the Homestake 

mine to date is more than 35 million oz.

LEAD

Lead (H. T. Morris and others, in Brobst 

and Pratt, 1973, p. 313-332) is used primarily 

in storage batteries (42 percent), from which 

it is recoverable, and in leaded gasoline (20 

percent), from which it is not; other important 

uses are in the construction industry and in 

pigments, cable sheathing, type metal, and ammunition. About 26 percent of the lead used in 

the United States in 1972 came from foreign 

countries, principally Canada, Peru, Australia, 

and Mexico. Lead reserves are estimated at 56 

million short tons, about 1.5x MACD. Identified subeconomic resources in low-grade deposits of conventional types in the United States 

have not been estimated quantitatively but may 

be of the same order of magnitude as the reserves ; recovery of these resources is as much a 

matter of economics as of technology. As with 

zinc, however, some of these resources are in old 

mines that have been closed; their recovery now, 

even though metal prices have risen considerably, will be very costly and impractical because 

the mines have been allowed to fill with water. 

Quantitative estimates have not been made for 

hypothetical and speculative resources either;
the outlook for continuing discovery of additional resources at a rate that exceeds consumption will depend largely on continued research 

on regional geology and new methods of exploration to apply in geologically favorable areas.

PLATINUM

Platinum (N. J Page and others, in Brobst 

and Pratt, 1973, p. 537-545) and the related 

metals, ruthenium, rhodium, palladium, osmium, and iridium, which occur with platinum 

in nature, are used now much less in jewelry 

than in a variety of industrial applications, including production of high-octane fuels, vitamins and drugs, synthetic fibers, fertilizers, 

and manufacture of electrical components. Future demand could be greatly increased by the 

use of platinum in automotive emission-control 

mufflers. U.S. production is only about 1 percent of consumption; principal U.S. imports are 

from the U.S.S.R., the Republic of South Africa, and Canada. Domestic reserves of 3 million 

troy oz, almost entirely in copper ores, represent only 7 percent of MACD. Identified subeconomic resources are estimated at about 20.6 

million oz, or 47 percent MACD. About a third 

of this is in low-grade placer and vein deposits 

in the Goodnews Bay area, Alaska, about half 

is in two titanium-bearing iron-ore deposits in 

Alaska, and about one-fifth is in currently unrecoverable chromite deposits in the Stillwater 

Complex, Montana. Hypothetical resources are 

very large, more than 4x MACD, but almost 

entirely subeconomic. Speculative resources are 

thought to be large, especially in the large 

areas of Alaska that have not yet been mapped 

geologically. Discovery of these resources 

would be aided by detailed mapping of geologically favorable belts that are known to exist 

and by improvement of analytical techniques 

for the platinum-group metals at very low concentrations.

TIN

Tin (C. L. Sainsbury and B. L. Reed, in 

Brobst and Pratt, 1973, p. 637-651; Sainsbury, 

1969) is used in making tinplate (principally 

for "tin" cans), solders, bearing alloys, and 

bronze and brass. The United States imports 

virtually 100 percent of its primary tin requirements, of which about 90 percent comes from 

Malaysia and Thailand. In 1972, about 23 percent of its tin demand was met by secondary 

sources (reclaimed tin). A negligible amount of 

tin is recovered as a byproduct from the molybdenum mine at Climax, Colo. Reserves are estimated by the Geological Survey at about 38,000 

long tons, or a scant 0.61 percent of MACD. 

Most of this is in fluorspar deposits on the 

Seward Peninsula, from which tin will be one 

of several byproducts. Figures on the production and reserves of tin in the Climax molybdenum mine are not available. Identified subeconomic resources are estimated to be just slightly 

greater than reserves; together with the reserves, they would provide only about 1*4 

years' supply at the 1971 rate of consumption. 

Hypothetical and speculative resources in conventional types of deposits are each estimated 

to be of the same order of magnitude as the 

reserves.

Tin shows a well-marked geologic association 

with silicic granitic or volcanic rocks. Although 

most geologic environments of these types in 

the United States Lave been prospected, many 

have not been examined with their tin potential 

as a primary objective. Furthermore, the large 

gap between known tin resources and the resource potential suggested by the crustal abundance of tin (R. L. Erickson, in Brobst and 

Pratt, 1973, p. 21-25) at least suggests that 

additional promise for finding undiscovered resources may lie in Unconventional speculative 

resources that is, the possibility of a new 

geologic environment for tin concentrations.

SILVER

Silver (A. V. Heyl and others, in Brobst and 

Pratt, 1973, p. 581-603) has its greatest current use in photographic materials; this use 

alone accounts for nearly all our annual production of newly mined silver. Other important 

uses are in electrical and electronic products, 

sterling and plated ware, and brazing alloys. 

Imported silver supplied 44 percent of domestic 

needs in 1972, most of it coming from Canada, 

Peru, and Mexico. Byproduct silver from basemetal and gold ores accounts for roughly twothirds of U.S. production and resources, the remainder being from ores in which silver is the 

principal metal. Reserves in currently operating mines are estimated to be about 1,300 million troy oz, or 35 percent MACD. Identified

8
subeconomic resources that might become recoverable with a threefold to fourfold increase 

in the price of silver (over the October 1972 

price of $1.80 per oz) are roughly estimated to 

be of the same order of magnitude as the reserves. Recovery of these subeconomic resources, however, is not entirely dependent on 

price increases; porphyry copper deposits supply about 20 percent of domestic silver production, which, like byproduct gold, is recoverable 

by mass (open-pit) mining but not by the new 

in-place copper-leaching techniques. A significant identified subeconomic resource is in the 

copper deposits disseminated in Precambrian 

sedimentary rocks of Idaho and Montana, 

which are still being evaluated. Estimated hypothetical resources, about 92 percent MACD, 

are largely potential byproduct resources in 

undiscovered but predicted sedimentary copper 

deposits (Precambrian) and porphyry copper 

deposits. Possibilities for discovery of speculative resources are highly favorable, in both primary and byproduct silver deposits.

Two recent developments are tending to increase U.S. dependence on foreign silver 

sources. First, increasing amounts of silver are 

being used in photography and other industrial 

applications from which it cannot be recovered 

and recycled. Second, as a byproduct or coproduct of copper, lead, zinc, and gold ores, the 

production of silver depends largely on the production of these other metals; therefore, because of the closure of one-third of our domestic lead and zinc smelters, domestic silver 

production has declined. As the consumption of 

silver is not likely to decrease in the foreseeable 

future, our growing dependence on foreign 

sources can be decreased only by the discovery 

of new domestic deposits and by more efficient 

mining methods and environmentally clean recovery methods.

MAGNESIUM

Magnesium (G. I. Smith and others, in 

Brobst and Pratt, 1973, p. 210) is the tenth 

most important nonferrous metal by virtue of 

its use as the metal, and as the oxide in preparing refractories and chemicals. Magnesium 

resources in brines, in widespread sedimentary 

rocks, and in seawater assure the United States 

a virtually inexhaustible supply.

PRINCIPAL FERROUS METALS 

IRON

Iron (Harry Klemic and others, in Brobst 

and Pratt, 1973, p. 291-306) is the principal 

metal used in modern industrial civilization and 

is indispensable to everyday living. Iron and 

iron alloys (steel) are essential to the construction of buildings, bridges, and railroads, and 

the manufacture of industrial machinery, 

transportation equipment, pipelines, tools, containers, fasteners, pigments, and countless 

other items. Although other materials such as 

wood, aluminum, and plastics are used as substitutes for steel in some items of manufacture, 

there are no practical substitutes for iron and 

steel for a broad spectrum of purposes. The 

United States imported 28 percent of its iron 

ore in 1972, most of it from Canada and Venezuela. Domestic reserves are estimated at 2 

billion short tons, or abouo equal to 60 percent 

MACD. Identified subezonoiric resources of 

iron ore contain about 22,3 billion metric tons 

of iron, equal to about 7x iviACD, but the bulk 

of these resources are of a mineralogical nature 

different from cu^re.itly usable low grade deposits, and they will require development of a 

different technology. Ear j:ous hypothetical 

resources of iron ore are predicated on the expectation that many identified iron-ore resources within half a mile of the surface are 

underlain by similar resources proportional in 

amount to the near-surface identified quantities. At present, however, physical limitations 

upon depths to which mining activities can be 

carried on in various types of rock impose limitations on not only the evaluation of hypothetical resources at great depths, but also the 

expectation of their recovery. Speculative resources in the United States are relatively low 

because the most promising regions for ironore discovery have largely been identified and 

at least part explored. The principal need is to 

obtain mora detailed information concerning the 

geology of these regions. Because most of the 

major iron deposits or iron-bearing formations 

have associated magnetic anomalies, major programs of aeromagnetic surveying to delineate 

the zones of magnetic rocks and potential ore 

bodies should be continued. In some places, further geologic studies and interpretation of the 

magnetic and geologic data are needed.
TABLE 2. Principal ferrous metals

Commodity Value (millions) of 

U.S. primary demand, 

1968

Approximate 1972 consumption (short tons)

Minimum anticipated cumulative demand, 1968-2000 (short 

tons)

Iron ___________________

Nickel ____ ___________

Silicon ___ _ _ _ _ _ ____ _

Molybdenum __ _ _ ___ _ _ _

Manganese _ _ __ _ _ __ _ _ _,

Tungsten ____ _ ______ _

Cobalt ______ ________ _

Chromium ______ ___________

Vanadium __ _ _ _ _ ______

Tantalum _ _ _ __ _______

Niobium (Columbium) _________

$1,294

300

148

90

64

43

26

24

20

11

6

86,000,000

230,000

470,000

23,400

1,260,000

6,600

7,000

420,000

7,200

564

2,135

3,280,000,000

8,100,000

22,900,000

1,550,000

47,000,000

550,000

260,000

20,100,000

420,000

31,000

138,000

NICKEL

Nickel (H. R. Cornwall, in Brobst and Pratt, 

1973, p. 437-442) not only strengthens steel but 

also imparts corrosion resistance over a wide 

range of temperatures; hence, nickel steel is 

used widely in the chemical industries as well 

as in aircraft, motor vehicles, and electrical 

machinery. In 1972, the United States imported 

74 percent of its nickel needs, principally from 

Canada and Norway (where some nickel ores 

of Canadian origin are refined). Reserves are 

about 200,000 short tons, a scant 2.5 percent of 

MACD. Identified subeconomic resources are 

estimated at 15.2 million tons (nearly 1.9X 

MACD) ; 90 percent of this resource is in lowgrade copper-nickel sulfide deposits in the Duluth Gabbro Complex of Minnesota (see under 

Copper). Another 5 percent is in laterites, residual soils formed during long periods of intensive weathering and erosion over sparsely 

nickel-bearing rocks in the Pacific Northwest; 

these deposits are too small and remote to be 

mined profitably under current economic conditions. Deep-sea manganese oxide nodules 

could eventually contribute to U.S. nickel production, but technologic and legal problems preclude an estimate of this potential resource at 

present. Additional large identified subeconomic 

resources would be made available by the development of new metallurgical techniques to 

produce nickel from peridotite and serpentinite, rocks that occur in many areas of the 

United States and universally contain 0.2-0.4 

percent nickel. Extraction of nickel from these 

resources, however, is likely to require so much 

energy that the process will not be feasible. 

Hypothetical and speculative resurccs are not 

estimated, but discovery of a new type of 

nickel-sulfide deposit in the Thompson district,

Manitoba, Canada, suggests a new type of geologic mechanism for the formation of nickel 

deposits. The greatest need therefore is for 

detailed geologic and geophysical mapping of 

geologic environments in the United States that 

are potentially favorable for either Thompsonor Duluth-type nickel deposits.

SILICON *

Silicon (K. B. Ketner, in Brobst and Pratt, 

1973, p. 577-580; F. E. Brantley, in U.S. Bureau of Mines, 1970, p. 369-384), in the form 

of high-purity silica (quartz) sand or its consolidated equivalents (sandstone and quartzite), is important not only for steelmaking and 

other metallurgical uses, but also in the manufacture of glass, ceramic ware, and chemicals. 

A possible future application of potentially 

great importance is the use of silica fibers in 

the manufacture of flywheels for energy-storage units, which could be used not only for 

large installations but for such small-scale 

items as automobile power sources (Post and 

Post, 1973).

Silica sand and sandstone are among the 

more common sedimentary formations cropping 

out in the United States, and, in general, their 

stratigraphic positions, extent, thicknesses, and 

the areas of outcrop are rather well known. It 

is unlikely that important units of high-purity 

silica sand and sandstone remain to be discovered. Therefore, almost all silica sand and sandstone units can be regarded as identified rather 

than undiscovered resources. Parts of these 

identified resources can be classed as reserves: 

such parts are where certain favorable geologic 

features are combined with favorable geographic circumstances so that the deposits are 

workable under present economic conditions.

10
Favorable geologic features include chemical 

purity, uniform grain size, friability (ease of 

crumbling), amenability to beneficiation, and 

proximity to the surface. The favorable geographic circumstances are proximity to markets and to transportation facilities.

Although U.S. silica-sand resources are so 

large that they are unlikely to be depleted by 

normal use, a large proportion of the most 

favorably located deposits may be precluded 

from exploitation by shortsighted public policies either unconscious, as when residential 

developments are allowed to spread over valuable sand deposits, or deliberate, as when landuse laws are invoked to prohibit exploitation of 

known deposits in urban areas. The result is 

not that we will run out of silica sand, but that 

costs will increase because mining will be confined to areas remote from industrial users and 

the ultimate consumers. Sand and sandstone 

deposits capable of yielding high-quality silica 

sand should be identified and precisely delineated on geologic maps, especially on large-scale 

maps of urban regions. Geologic maps exist for 

many urban areas, but workable silica-sand deposits are specially designated on only a few of 

these. Precise location of all deposits in urban 

regions would permit orderly planning for the 

most beneficial use of land underlain by silicasand deposits.

MOLYBDENUM

Molybdenum (R. U. King and others, in 

Brobst and Pratt, 1973, p. 425-435) is used 

principally in alloy, stainless, and tool steels. 

Other importance uses are in lubricants, agriculture, chemicals, and pigments. The element 

also has an assured future use as a principal 

material in nuclear and space applications. The 

United States is a net exporter of molybdenum, 

having reserves of approximately 3.15 million 

short tons (2x MACD) and estimated identified subeconomic resources of about 14.4 million 

short tons (more than 9x MACD) ; the subeconomic resources are in deposits having 

grades lower than the present cutoff, and the 

problem here is largely-one of economics. Hypothetical resources in the United States are estimated to be on the order of half a billion tons 

(several hundred times MACD).

MANGANESE

Manganese (J. V. N. Dorr, II, and others, in 

Brobst and Pratt, 1973, p. 385-399) is essential 

in two ways to the manufacture of steel: (1) 

Used as a scavenger in the molten metal, it 

combines with sulfur and oxygen, which make 

steel brittle, and removes them as part of the 

slag; (2) used as an alloy, it makes steel more 

resistant to shock or abrasion. Manganese oxide 

is used in the chemical industry and in dry 

batteries. More than 90 percent of manganese 

consumption in the United States is by the steel 

industry, and no substitute has yet been found, 

despite much effort. About 13-20 pounds of 

manganese (as alloy or metal) is consumed per 

ton of steel manufactured in the United States; 

elsewhere in the world the amount of manganese needed per ton of steel may range from 

13 to 50 pounds, owing to the wide range of 

efficiencies in its use. Clearly, the element is 

essential to the whole industrial capacity of the 

world. When we can do without steel, we can 

do without manganese. The United States in 

1972 imported 95 percent of its manganese, 

mainly from Gabon, Brazil, the Republic of 

South Africa, and Zaire. Although the United 

States has many small deposits of high-grade 

material, they cannot be considered reserves 

under present economic conditions, nor would 

they constitute significant reserves even at 

much higher prices (Brooks, 1966, p. 70-72).

Identified subeconomic resources contain an 

estimated 73 million short tons of manganese, 

or nearly 1.6x MACD. More than 80 percent 

of this resource is in deposits in Maine, Minnesota, and Arizona. Technologically feasible 

processes of extraction have been developed for 

much of this material, but they could be used 

only at 2-5 x the present world price for manganese and would require great energy input. 

Of the remaining estimated identified subeconomic resources, about 16 percent (nearly 12 

million short tons of manganese), plus an additional unmeasured but much larger resource in 

similar rocks at somewhat deeper levels, is contained in carbonate nodules and enclosing manganiferous shales of the Pierre Shale in South 

Dakota. This resource is essentially unworkable at present because of mining, ore-dressing, 

metallurgical, and pollution problems. Manganese oxide nodules known to occur over large

11
areas of the sea floor at many localities have 

not been included in estimates of U.S. resources, but if the legal status of deep-sea mining can be favorably resolved, it appears likely 

that the nodules will eventually contribute to 

U.S. production. Hypothetical resources in the 

United States are nil, because the known districts are in general well enough known for 

most possibilities to have been identified. Speculative resources cannot be estimated, but geologic theory suggests several broad targets for 

research and exploration.

TUNGSTEN

Tungsten (S. W. Hobbs and J. E. Elliott, in 

Brobst and Pratt, 1973, p. 667-678) imparts to 

its compounds and alloys the properties of extreme hardness, ability to retain hardness and 

strength at high temperatures, high tensile 

strength, adequate electrical conductivity, and 

high wear resistance. Its principal uses, as 

tungsten carbide and in a variety of steels and 

nonferrous alloys, are in metalworking machinery, tool steel, construction and mining 

machinery, drill bits, turbines, rocket nozzles, 

structural material in nuclear and space applications, transportation equipment, electrical 

equipment, and many other items. Imports in 

1971, mainly from Canada, Bolivia, Peru, and 

Australia, supplied 44 percent of domestic consumption. Domestic reserves are estimated by 

the Geological Survey at about 119,000 short 

tons, or about 22 percent MACD. Identified 

subeconomic resources of approximately 305,- 

000 short tons (56 percent MACD) are mostly 

in deposits like those currently being mined, 

but of lower grade. The parts of the western 

United States from which most of our tungsten 

has been produced include vast areas, covered 

by surficial debris and by sedimentary or volcanic rocks geologically younger than those in 

which the tungsten is found, that undoubtedly 

conceal hypothetical resources of recoverable 

grade, at least equal in volume to, if not greatly 

exceeding, known deposits. Discovery of such 

deposits will require continued geologic mapping of exposed areas and imaginative and intensive application of various geophysical and 

other methods to identify favorable geologic 

situations in the intervening covered areas. An 

additional hypothetical resource lies in the possibility of byproduct recovery of tungsten from 

molybdenum deposits like the one at Climax, 

Colo., which is a significant source of our current domestic supply; as new molybdenum deposits of this type are discovered and developed, they will probably provide new tungsten 

reserves. Speculative resources may very likely 

be discovered in new districts in the known 

circum-Pacific tungsten belt, and a better understanding of small tungsten deposits in the 

Rocky Mountains might lead to the discovery 

of major new resources in that region.

COBALT

Cobalt (J. S. Vhay and others, in Brobst and 

Pratt, 1973, p. 143-155) is used in high-temperature alloys (the "superalloys"), permanentmagnet alloys, cutting and wear-resistant alloys, tool steels, miscellaneous other alloys, and 

for a variety of other industrial and chemical 

purposes. The United States imported 98 percent of its apparent consumption in 1972, the 

major sources being Zaire, Canada, Morocco, 

and Zambia. Most of the world's supply of cobalt reaches the market as a byproduct of mining copper, nickel, and silver ores; smaller 

amounts are byproducts of iron, chromium, 

lead, zinc, uranium, and manganese. U.S. reserves are estimated at 28,000 short tons, or 11 

percent MACD. Identified subeconomic resources, most of which are available only as 

byproducts, are estimated at more than 800,000 

short tons, or more than 3x MACD. About 60 

percent of this estimated resource is in the 

copper-nickel sulfide ores of the Duluth Gabbro 

Complex in Minnesota, which are not yet economically or technologically minable (,«ee under 

Copper). Probably the next largest single resource is in the lead ores of the Southeast 

Missouri district, where recovery of cobalt (as 

well as nickel) is more a problem of technology 

and economics than of geologic availability. 

Hypothetical resources are directly related to 

those of the major metals with whose ores cobalt is associated, most notably nickel, copper, 

iron, and lead. Possibilities seem favorable for 

the discovery of new cobalt-bearing ores of 

nickel and iron in eastern Pennsylvania, copper 

in Minnesota, Alaska, and the Appalachian region, and lead in the Mississippi Valley. As 

with the major metals, discovery of such re12
sources depends on delineation of favorable exploration ground through careful geologic 

analysis and on the refinement of ore-finding 

techniques. A particular need in the case of 

cobalt is new and better technology for the recovery of cobalt (currently selling for about 

$3.15 per pound) from ores containing less 

valuable lead, zinc, and copper; loss of such 

valuable byproducts in mining, beneficiating, 

and smelting is not only a financial loss to the 

producer, but may be an irretrievable loss of 

the material itself.

CHROMIUM

Chromium (T. P. Thayer, in Brobst and 

Pratt, 1973, p. 111-121) is used to make stainless steel, tool steel, and various alloys and 

superalloys which are used mainly in construction, transportation, and machinery and equipment. The United States in 1972 imported 100 

percent of its chromium consumption, mainly 

from the U.S.S.R., the Republic of South Africa, and Turkey. We have no reserves of chromium. Identified subeconomic resources amount 

to only about 1.67 million short tons, or 8 percent MACD; they would be difficult to mine 

and expensive to use. Hypothetical and speculative resources are even less, mainly because 

the geologic environments in which chromium 

occurs are of limited occurrence in the United 

States; moreover, the few postulated relatively 

large deposits could mitigate the national supply problem only temporarily and at very high 

cost. The nearest potential resources of significant size, both identified subeconomic and undiscovered, are in a deposit in Manitoba similar 

to the principal large U.S. resource (in the 

Stillwater Complex of Montana), and in very 

large low-grade deposits in Greenland; both 

metallurgical research and, ,for the Greenland 

deposits, more detailed geologic information, 

are needed.

VANADIUM

Vanadium (R. P. Fischer, in Brobst and 

Pratt, 1973, p. 679-688) is added to steel to 

toughen and strengthen it and to control its 

grain size; vanadium steels are used for construction, high-pressure pipelines, transportation equipment, and metal-working machinery. 

Vanadium-titanium alloys are used in the aerospace field, and vanadium alloyed with several

other metals is a candidate for use in the nuclear industry as a fuel-cladding material for 

advanced fast-breeder reactors. In 1972, the 

United States imported 32 percent of its vanadium, mainly from the Republic of South Africa, Chile, and the U.S.S.R. U.S. reserves are 

115,000 short tons, about 27 percent MACD; 

most of this quantity is contained in uranium 

and phosphate deposits from which vanadium 

would be recovered as a byproduct. Identified 

subeconomic resources are very large probably on the order of a few million tons, or several times MACD; to extract the vanadium 

from some of these deposits would require 

modified metallurgical practices, and some deposits are in rocks such as carbonaceous shale 

that have not l^een mined previously and would 

require new technology altogether. Potentially 

recoverable vanadium is currently being lost 

from some operations that mine magnetite iron 

ores, others than mine phosphate rock, and 

others that burn or refine crude oil. Hypothetical and speculative resources have not been 

evaluated because the greatest potential for 

vanadium resources appears to be in byproduct 

recovery rather than in discovery of new deposits that would be mined primarily for vanadium.

TANTALUM

Tantalum (R. L. Parker and J. W. Adams, 

in Brobst and Pratt, 1973, p. 443-454) is still 

classed as a ferrous metal because of its earlier 

predominant use as an alloying element in steel, 

but its principal use now is in the electronics 

industry, largely in the manufacture of capacitors and rectifiers. The remainder goes into the 

production of superalloys for high-temperature 

corrosion-resistant applications, into tantalum 

carbide for high-temperature cutting tools, and 

into tantalum metal for a variety of corrosionresistant uses. Imports in 1972 accounted for 

97 percent of U.S. consumption; the principal 

sources were Nigeria, Malaysia, Australia, and 

Thailand.

The United States has no reserves of tantalum. Identified subeconomic resources are estimated at a scant 1,720 tons, less than 6 percent 

of MACD; recovery of the tantalum minerals 

in these resources, though technically feasible, 

is not profitable at present prices. The likeli13
hood of discovering large new deposits of tantalum, of the type now exploitable commercially, is small. As is true of tin, the large gap 

between known tantalum resources and the resource potential suggested by the crustal abundance of tantalum (R. L. Erickson, in Brobst 

and Pratt, 1973, p. 21-25) indicates the need 

for geologic research on the possible existence 

of new types of deposits unconventional 

speculative resources.

NIOBIUM

Niobium (R. L. Parker and J. W. Adams, in 

Brobst and Pratt, 1973, p. 443-454) still referred to as columbium to some extent in 

metallurgy and mineral trades is used chiefly 

in the form of ferrocolumbium as an alloying 

element in carbon and alloy steel, stainless 

steel, and superalloys. High-strength low-alloy 

niobium steels are used in the construction of 

large buildings, pipelines, and machinery and 

structures where savings in weight and increased durability and strength are important. 

Niobium alloys are used in aircraft and rocket 

engines, and unalloyed niobium is an important 

construction material in nuclear reactors. The 

United States in 1972 imported 67 percent of 

its consumption, principally from Brazil, Nigeria, Malaysia, and Thailand.

Domestic reserves at current prices are nil. 

Identified subeconomic resources total an estimated 121,000 tons of niobium, or about 88 percent MACD. More than half this resource is 

contained in a single body of carbonatite (an 

unusual igneous rock) near Powderhorn, Colo.; 

another third of the resource is a potential byproduct of bauxite (aluminum) deposits in

Arkansas, from which recovery of the niobium 

is unprofitable under present market conditions. Improvements in technology could bring 

both these resources into the reserve category.

Hypothetical resources no doubt occur as 

blind ore bodies in known carbonatite masses, 

or as ore bodies in undiscovered carbonatites 

in known carbonatite provinces. These resources constitute probably several times the 

amount of currently known resources; their 

discovery will depend on continuing geologic 

and exploration activities. The outlook for 

speculative resources seems good, because of 

the probability that other carbonatite deposits, 

now concealed beneath younger rocks, remain 

to be discovered somewhere in the Rocky Mountains and the Midwest. Continued geologic mapping and development of new exploration methods will aid in the discovery of these resources.

MINERAL FUELS

A national energy crisis is now generally 

recognized, although there is still some debate 

whether it is temporary or long lived. Individual facets of the problem, and possible solutions, have become a matter of daily news. It 

would be presumptuous for us to attempt any 

kind of comprehensive statement on a problem 

of such magnitude and diversity, except to 

point out that to whatever extent any of the 

solutions involve mineral fuel resources, they 

are subject to the law of geologic availability. 

Thus, summaries are presented here to provide 

a brief appraisal of the geologic availability of 

the mineral fuels, rather than to offer an instant solution to the energy crisis.

TABLE 3. Mineral fuels

Commodity

Petroleum "1 Shale oil ] 

Natural gas _ _ __ _

Coal _

Uranium pentoxide _ _

Thorium _ _ _ _ _ _ _

Value ( millions ) of 

U.S. primary demand, 

1968

__ _ $13,769

_ __ 3,109

_____ 2,147

60

_ ___ 1.5

Approximate 1972 

consumption

1 5.96 billion bbls

22.6 trillion cu ft

13,300 short tons

Minimum anticipated cumulative 

demand, 1968-2000

2 195 billion bbls

860 trillion cu ft

27 billion short tons

3 2,400,000 short tons

27,500 short tons (maximum)

1 One bbl (barrel) equals 42 gallons.

2 This MACD, etsimated in 1968 for petroleum, can theoretically be satisfied equally well by shale oil. However, shale oil is not 

now being produced commercially and probably will not be produced in significant quantities before about 1978, so the extent 

to which MACD can be met by shale oil will depend on the speed with which, and the capacity to which, commercial production can 

be developed. It is estimated that a maximum production rate of 1 million bbls per day (0.3 billion bbls per year) is not likely to 

be reached before about 1985 at the earliest, so that total cumulative production by the year 2000 probably will not exceed 5 billion 

bbls.

3 Revised estimate by the U.S. Atomic Energy Commission for approximate period 1972-2000.

14
OIL AND GAS

Oil and gas (T. H. McCulloh, in Brobst and 

Pratt, 1973, p. 477-496) are at once the most 

crucial and yet among the most difficult to 

evaluate of our energy resources. Estimates of 

oil and gas reserves ("proved reserves" in the 

parlance of the petroleum industry) are made 

periodically by the industry; the most recent 

estimates published are recoverable reserves of 

36.3 billion barrels of oil (about 7 years' production at the present rate, or 19 percent 

MACD) and 266 trillion cubic feet of gas 

(about 13 years' production at the present rate, 

or 31 percent MACD) (U.S. Department of the 

Interior, 1974). Estimates of resources, however, are subject to the condition that no matter how they are made, they ultimately involve 

projections from the results of oil and gas exploration to date. Because very large areas of 

the earth have yet to be adequately explored 

geologically (especially parts of the seabed), 

and because our techniques for identifying oil 

and gas traps are very imperfect, the results 

of oil and gas exploration to date are an inadequate base on which to project results of future 

exploration. Thus, recent estimates of ultimate 

producible oil in the United States have ranged 

from 165 billion barrels (Arps and others, 

1970) to 550 billion barrels (Schweinfurth, in 

McKelvey and others, 1973), and estimates of 

ultimate oil in place have ranged from 587 

billion (Moore, 1970) to 2,900 billion barrels 

(Schweinfurth, in McKelvey and others, 1973). 

Perhaps more significant than the magnitudes of 

these estimates of resources (the most conservative of which is equivalent to 85 percent MACD) 

is their demonstration of the low recovery factor, the difference between producible oil and oil 

in place. When present techniques are used, for 

every gallon of oil pumped out of the ground, 2 

gallons are left behind, locked in the poor 

spaces of the rocks by surface tension.

What are the principal problems to be solved 

in the effort to convert these potential resources of oil and gas into reserves? The distribution of fluid hydrocarbons in sedimentary 

rocks and basins is extremely uneven (although 

subject to certain broad general patterns), and 

a substantial understanding of the underlying 

physical and chemical reasons for their distribution is needed, particularly (1) the nature of

the processes by which organic remains interred in sediment are transformed to protopetroleum and thence to fluid hydrocarbons capable of migration, and (2) the chemical and 

physical processes by which such mobilized hydrocarbons are expelled from source rocks and 

trapped during their migrations to form commercial accumulations. In general, the oil and 

gas fields that have been discovered are conspicuous (from the viewpoint of exploration 

techniques), very large, or in regions that have 

undergone thorough prospecting. Remaining to 

be discovered are innumerable small reservoirs, 

large reservoirs that are inconspicuous (again, 

from the viewpoint of the exploration techniques available), and traps of all sizes in regions that have not yet been prospected thoroughly or at all. Not all subsurface hydrocarbon 

accumulations are worth finding, however. For 

every accumulation that can be found and produced economically, doubtless many accumulations are so small that the volumes of hydrocarbons producible would be insufficient to 

repay the costs of finding them. Moreover, a 

very large percentage of the total oil (and gas) 

occurs in a very small percentage of all known 

accumulations. More than 85 percent of the 

world's hydrocarbon production plus reserves 

occurs in less than 5 percent (238 fields) of all 

producing accumulations. Even more remarkable, 65 percent occurs in slightly more than 1 

percent of all fields the 55 "supergiants" (a 

billion barrels of oil or a trillion cubic feet of 

gas, or more) (Halbouty and others, 1970; 

Klemme, 1971) and an astounding 15 percent 

occurs in only two immense accumulations in 

the Middle East, the Ghawar field in Saudi 

Arabia and the Burgan field in Kuwait. In 

smaller areas, similar relations exist.

New oil-producing regions and areas have 

been discovered through combinations of business enterprise, economic pressures of many 

sorts, technologic advances, and exploitation 

effectiveness. There is considerable room for 

continuation of this evolutionary achievement. 

Much of the United States Continental Shelf is 

unexplored. The onshore-offshore region south 

of Cape Hatteras has much in common geologically with the onshore-offshore region of 

Saudi Arabia, including a very thick section of 

structurally simple sedimentary rocks of the

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same ages and similar compositions beneath a 

very large area. Prior to discovery by the drill, 

and subsequent development, the Ghawar field 

(the largest single oilfield known in the world) 

was not a particularly conspicuous prospect or 

structure, either from surface geologic mapping 

or from geophysical interpretation (Arabian 

American Oil Co., 1959). Another such inconspicuous "supergiant" might lie beneath the 

Blake Plateau, or somewhere else within the 

territorial limits of the United States. Discovery of new oil and gas fields and new provinces 

will require (1) research on the process of formation, migration, and entrapment, (2) detailed geologic mapping to outline potentially 

favorable geologic formations and structures, 

and (3) development and application of new 

and better geophysical exploration techniques. 

Last but far from least, although only the drill 

bit can finally prove the presence of oil, "oil 

must be sought first of all in our minds!" 

(Pratt, 1942, p. 49).

COAL

Of coal consumed in the United States (Paul 

Averitt, in Brobst and Pratt, 1973, p. 133-142), 

about 62 percent is used in the production of 

electric power, 20 percent is used by the steel 

industry, 16 percent in manufacturing, and 2 

percent for all other purposes. Coal is also of 

great future value and importance as a subsidiary source of synthetic gas, liquid fuels, and 

lubricants.

Coal is widespread and abundant in the 

United States. Coal-bearing rocks underlie 

about 13 percent of the land area of the 50 

States and are present in parts of 37 States. 

On any basis of analysis, U.S. resources of coal 

are larger than the combined resources of 

petroleum, natural gas, oil shale, and bituminous sandstone, but use of coal lags behind use 

of both petroleum and natural gas because they 

are cleaner and easier to handle. Recoverable 

coal reserves are estimated at 197 billion short 

tons, or about 7 MACD. Total identified resources in the ground, including reserves in 

thick accessible beds and subeconomic resources 

in thinner or less accessible beds, are estimated 

at 1,581 billion tons, or 58x MACD. Recoverability ranges from 40 to 90 percent, depending 

largely on the method of mining, but it is influenced by many other diverse factors such as 

the nature of the roof rock, joints, faults, and 

the need to protect oil and gas wells and fields. 

Average long-term recoverability, nationwide, 

is probably about 50 percent. Unmapped and 

unexplored areas in known coal fields contain 

substantial additional resources of an estimated 

1,643 billion tons that must be classed as hypothetical. Although large, the hypothetical resources are, for the most part, relatively inaccessible for mining at present, and a more 

exact delineation of the magnitude, distribution, and future utility of such resources will 

require a .substantial amount of detailed geologic mapping, exploration, and study over a 

long period. The major geologic features of the 

United States are known well enough to justify 

the statement that in all probability, no major 

coal fields remain to be discovered; hence there 

are no speculative resources.

Sulfur in coal is an undesirable element; it 

lowers the quality of coke and of the resulting 

iron and steel products; it contributes to corrosion, to the formation of boiler deposits, and 

to air pollution; its presence in spoil banks inhibits the growth of vegetation; and as sulf uric 

acid, it is the main deleterious compound in 

acid mine waters, which contribute to stream 

pollution. The sulfur content of coal in the 

United States ranges from 0.2 to about 7.0 percent; the average is 1.0-2.0 percent. Sulfur content is highest in bituminous coals of Pennsylvanian age in the Appalachian and Interior coal 

basins, which account for about 34 percent of 

the identified coal resources; it is low, generally 

less than 1 percent, in subbituminous coal and 

lignite of the Rocky Mountain and Northern 

Great Plains regions, which account for 56 percent of the identified resources.

Coal contains small but significant quantities 

of 25 metallic and nonmetallic elements, which 

are of considerable interest because some may 

become of future resource importance, and 

others may be pollutants. Five elements uranium, germanium, arsenic, boron, and beryllium occur locally in vastly greater concentrations than their estimated concentration in the 

earth's crust; others, including barium, bismuth, cobalt, copper, gallium, lanthanum, lead, 

lithium, mercury, molybdenum, nickel, scandium, selenium, silver, strontium, tin, vanadium,

16
yttrium, zinc, and zirconium, occur locally in 

appreciably greater concentrations. When coal 

is burned, most of these elements are concentrated in the coal ash, but a few of the more 

volatile elements are emitted into the atmosphere.

URANIUM

Uranium (W. I. Finch and others, in Brobst 

and Pratt, 1973, p. 456-468) is well known as 

an important energy source. The readily fissionable isotope, U235 , constitutes only about 0.7 

percent of natural uranium; U238, which constitutes most of the remainder, is not readily fissionable, but under neutron bombardment converts to fissionable plutonium-239. Although 

the demand for electricity generated by nuclear 

energy is expected to increase significantly for 

many years, technological developments may 

ultimately permit a decrease in the amount of 

uranium required to generate the needed electricity. If fast breeder reactors are developed 

by the mid-1980's, annual domestic uranium 

requirements are expected to peak in about the 

year 2000 at about 150,000 short tons of U3 08 , 

about 10 times the 1972 requirement, after 

which they will decline gradually to about the 

same level as in 1972, as the currently used 

nonbreeder reactors are phased out. If, on the 

other hand, fast breeder reactors are not successfully developed, uranium requirements will 

continue to increase. In this regard it is appropriate to quote from a 1969 report to the National Academy of Sciences by M. King Hubbert (1969, p. 227-228) :

The energy potentially obtainable by breeder reactors 

from rocks occurring at minable depths in the United 

States and containing 50 grams or more of uranium 

and thorium combined per metric ton is hundreds of 

thousands of times larger than that of all of the 

fossil fuels combined. It is clear, therefore, that by 

the transition to a complete breeder-reactor program 

before the initial supply of uranium-235 is exhausted, 

very much larger supplies of energy can be made 

available than now exist. Failure to make this transition would constitute one of the major disasters in 

human history.

Domestic reserves of uranium, about 273,000 

short tons of U3O8 (at $8 per Ib), can supply 

domestic requirements into the early 1980's. 

For identified subeconomic resources, the greatest promise is in low-grade resources in marine 

phosphate rocks in Idaho and adjacent States, 

in Florida, and in North Carolina. These deposits contain an estimated 6 million tons of U3 08 , 

more than 20 times the uranium in present reserves, or more than 2x MACD, but to obtain 

significant supplies of uranium from them 

would require major technological changes. A 

very small amount of the total identified subeconomic resources in phosphate rock can be 

obtained at moderate cost as a byproduct of 

making fertilizer, but at present, most of the 

uranium in phosphorite that is used to make 

fertilizer by the wet process phosphoric acid 

method stays in the fertilizer and is lost as a 

resource when the fertilizer is used. (On April 

10, 1974, a Florida subsidiary of Gulf Oil Corp. 

announced construction of a pilot plant to test 

a new process for extracting uranium from 

phosphate rock being converted to phosphoric 

acid.) To obtain more of this uranium would 

require mining and treating the rock principally for uranium; unit costs would be high, 

and vast quantities of rock would have to be 

moved somewhat more than 25 billion tons of 

rock, or nearly a third of the total identified 

phosphorite resources, to obtain enough uranium to fulfill the MACD. Uranium in phosphate rock that is used to make elemental phosphorus by the electric furnace method goes 

mostly into the silicate slag. A process for recovering uranium from the slag has not been 

devised. Marine black shales, especially in Tennessee and adjacent States, also contain large 

identified subeconomic resources of uranium, 

but recovery would require mining vast areas 

by open-cut and underground methods, as well 

as development of an economic technology of 

extraction. Recoverable hypothetical resources, 

that is, new rich ore bodies in the known mining districts, are estimated at 500,000 tons 

U3 O8 ; these resources, if discovered and mined, 

would satisfy estimated domestic requirements 

only until the early 1990's. Subeconomic hypothetical resources amount to somewhat less. 

The pressing need is for discovery of speculative resources in new districts; therefore, research on geologic guides to new districts is 

urgently needed.

THORIUM

Thorium (M. H. Staatz and J. C. Olson, in 

Brobst and Pratt, 1973, p. 468-476)) has a 

small current demand, mostly for use in mak17
ing incandescent gas mantles and magnesium 

alloys, but it has considerable potential as a 

fuel for nuclear reactors, of which the farthest 

advanced at present is the high-temperature 

gas-cooled reactor. Because of this potential, we 

will here compare thorium reserves and resources to the maximum anticipated cumulative 

demand 1968-2000, which assumes commercial 

development of economically attractive thorium reactors by 1980. In that context, domestic 

reserves, producible as byproducts of titanium 

mining from Atlantic Coast beach placers, are 

equivalent to only 50 percent of the maximum 

anticipated cumulative demand. Identified subeconomic resources are substantial; the amount 

of thorium contained in relatively rich vein deposits, from which it would be the principal 

product, is more than 3x maximum anticipated 

cumulative demand and an even greater amount 

is contained in lower grade veins, in stream 

placer deposits, and in deposits from which it 

would be a byproduct. Still another resource is 

the Oonway Granite of New Hampshire, a body 

of granite exposed over an area of 300 square 

miles and probably several miles deep. The Conway Granite contains an average of 2 ounces of 

thorium per short ton of rock. The energy released by nuclear fission of the thorium contained in just 1 cubic yard of this rock would 

be equivalent in fuel energy to about 300 short 

tons of coal, or 1,500 barrels of crude oil. If the 

entire area of 300 square miles were quarried 

to a depth of only 110 yards and the thorium 

used in nuclear reactors, the fuel equivalent of 

the energy produced would be about 30 trillion 

tons of coal, or 150 trillion barrels of crude oil 

(Hubbert, 1969, p. 227), about 165 times the 

coal reserves of the United States, or more than 

3,900 times the proved recoverable reserves of 

crude oil! Utilization would, of course, depend 

on development of a technology for extracting 

the thorium and on minimizing the environmental impact. Nevertheless, the amount of 

available energy would be enormous. The outlook for discovery of hypothetical and speculative resources is good. Systematic geologic 

analysis should be made of known thorium regions to select favorable areas for prospecting, 

and geologic criteria should be applied to search 

for potentially favorable environments in less 

explored regions.

OIL SHALE

Oil shale (W. C. Culbertson and J. K Pitman, in Brobst and Pratt, 1973, p. 497-503) is 

a fine-grained sedimentary rock containing organic matter that has the property of yielding 

substantial amounts of oil when heated in a 

closed retort (destructive distillation) but is 

mostly insoluble in ordinary petroleum solvents. The United States contains immense 

amounts of oil shale, but no oil-shale venture 

has been a commercial success in the last 100 

years, principally because of the abundant supplies of lower cost oil, gas, and coal. The rising 

demand for energy, however, requires consideration of this abundant energy resource as a 

long-range supplement to the dwindling supplies of other fossil fuels. (See footnote 2 on 

table 3.)

In classifying -public lands as valuable for 

oil shale, the U.S. Geological Survey specifies 

the minimum thickness and grade of oil shale 

as 15 feet of shale yielding an average of 15 

gallons of oil per ton. On this basis, the identified subeconomic resources in the Green River 

Formation in Colorado, Utah, and Wyoming 

are estimated to total 1.8 trillion barrels of oil 

(one barrel contains 42 gallons). Nearly onequarter of this amount (418 billion barrels, or 

about 2.1x MACD) is in oil shale yielding 30 

or more gallons per ton. The recent increases 

in the price of oil mean that the more accessible of these higher grade deposits may soon be 

economically recoverable. Further increases in 

the price of crude oil, or major developments in 

the technology of recovering shale oil, or the 

value of coproducts such as aluminum or nahcolite (soda ash), locally present in the shale, 

may make less accessible or lower grade deposits economically recoverable in the near future. 

The hypothetical resources in the Green River 

Formation are estimated to total about 650 

billion barrels, of which perhaps 50 billion barrels are in oil shale yielding 30 or more gallons 

per ton.

The possibility of heating the oil shale underground and pumping the oil to the surface has 

been investigated by private industry in western Colorado and by the U.S. Bureau of Mines 

in southwest Wyoming (L. W. Schramm, in 

U.S. Bureau of Mines, 1970, p. 188). Many 

technical problems remain to be solved, but

18
this method holds promise as a way to obtain 

the oil with little harm to the environment.

The synthetic-gas potential of oil shale of the 

Green River Formation has been investigated 

by the Institute of Gas Technology. Their data 

indicate that high-quality synthetic gas could 

be produced at the rate of 100 cubic feet of gas 

for each gallon of shale oil that could be produced by a conventional retort, or 4,200 cubic 

feet for each barrel of shale oil. Thus the Green 

River Formation could be the source of an 

enormous amount of gas instead of oil, but at 

a relatively high price compared with present 

natural-gas prices.

Further identified subeconomic resources of 

an estimated 200 billion barrels of shale oil 

(using a minimum thickness and grade of 5 

feet of shale yielding an average of 10 gallons 

of oil per ton) occur in marine black shales of 

the central and eastern United States. Oil 

shales in Alaska (not to be confused with the 

crude oil of the Prudhoe Bay fields) are incompletely known but are estimated to contain 

hypothetical resources of about 450 billion barrels of oil.

For speculative resources, it is unlikely that 

any other deposit of the magnitude of the Green 

River Formation exists in the United States; 

however, small high-grade deposits may be 

present in the many unexplored lacustrine deposits of Tertiary age in the western United 

States (Feth, 1963), particularly in Montana, 

Nevada, and Wyoming (Duncan and Swanson, 

1965, p. 16).

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Bennett, H. J., Moore, Lyman, Welborn, L. E., and 

Toland, J. E., 1973, An economic appraisal of the 

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Brooks, D. B., 1966, Low-grade and nonconventional 

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Halbouty, M. T., Meyerhoff, A. A., King, R. E., Dott, 

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1970, World's giant oil and gas fields; geologic 

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McKelvey, V. E., Wang, F. H., Schweinfurth, S. P., 

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