GEOLOGICAL SURVEY CIRCULAR 682 

;:.-:·:.:::.,.:,.;_.,._::.:;;: 

Summary of United States 

:Mineral Resources 

Summary of United States 

Mineral Resources 

By Donald A. Brobst, Walden P. Pratt, and V. E. McKelvey 

GEOLOGICAL SURVEY CIRCULAR 682 

This circular is an excerpt from Professional Paper 820, United 

States Mineral Resources, and consists of its first two chapters. 

These chapters summarize our resources and provide the basic 

guidelines under which the individual commo.dities were 

evaluated in greater detail in that report. 

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 
SUMMARY OF UNITED STATES MINERAL RESOURCES 

INTRODUCTION 

By DoNALD A. BROBST and WALDEN P. PRATT 

CONTENTS 

Page 

The purpose of this book ------------------------- 1 

Resources or reserves? --------------------------- 1 

J\ vvarning -------------------------------------- 2 

Our dependence on minerals ---------------------- 3 

Classification of resources ------------------------ 3 

Public avvareness, resource estimates, and geologic 

availability ------------------------------------ 5 

General conclusions ------------------------------ 6 

Mineral potential: vvhere do vve stand? --------- 6 

Lovv-grade ores and the environment ---------- 7 

Economics and waste ------------------------- 7 

The energy factor -----------------------~--- 8 

The need for research ---------------------------- 8 

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

FIGURE 

Page 

1. Classification of mineral resources used in this 

volume 4 

TABLE 

Page 

1. Potential U.S. resources of some important mineral commodities ------------------------- 7 

THE PURPOSE OF THIS BOOK 

Our civilization is dependent on minerals. Few 

people living in the United States and other developed nations pass through a single day without using 

raw or manufactured materials· that have been 

made from, processed by, fertilized with, or in some 

other way affected by minerals or mineral products. 

Without a steady supply of minerals our civilization could not survive. 

Unlike most other natural resources, minerals 

are not renewable. They are formed in the earth's 

crust by infinitesimally slow natural geologic processes acting for thousands or millions of years. 

Once removed and used, they cannot be grown again. 

The vital question, then, is this: Is our supply of 

minerals running out? 

To answer this question, as it applies to nearly 

all the mineral commodities in use today, is the 

general aim of this book. More specifically, the book 

attempts to provide answers to three basic questions 

about each mineral commodity: (1) How important 

is it to our present industrial civilization and standard of living? (2) how much of it do we have and 

to what extent is it economically and technologically 

available? and (3) how and where can we firid more? 

The emphasis here is on domestic resources, but 

many chapters include information on foreign resources, generally most complete for those commodities for which we are most dependent upon sources 

abroad. 

The answers to the above questions are matters 

that should be of concern not only to geologists 

(both professional and student), but also to exploration managers, research administrators, economists 

and economic analysts, legislators, lawyers, planners, magazine and newspaper editors, and indeed 

many segments of the public at large. The book has 

been written with this varied audience in mind. 

The descriptions of the geology and origin of mineral deposits in each chapter necessarily involve 

some scientific jargon, but discussions of the uses, 

importance, history of exploitation, resources, and 

problems needing research are cast largely in nontechnical language so that they may be of use to 

scientist and nonscientist alike. 

RESOURCES OR RESERVES? 

A fundamental concept in the evaluation of mineral resources is the distinction between resources 

and reserves. Detailed definitions vary (the entire 

problem of resource terminology is currently being 

1 
2 UNITED STATES MINERAL RESOURCES 

studied by the National Commission on Materials 

Policy), but the principal distinction is based on 

current economic availability: reserves are known, 

identified deposits of mineral-bearing rock from 

which the mineral or minerals can be extracted 

profitably with existing technology and under present economic conditions; whereas resources include 

not only reserves but also other mineral deposits 

that may eventually become available--either known 

deposits that are not economically or technologically 

recoverable at present, or unknown deposits, rich or 

lean, that may be inferred to exist but have not yet 

been discovered. A simple analogy from the field of 

personal finance, suggested by our colleague J. E. 

Gair, may be helpful in clarifying this important 

distinction: Reserves are represented by the funds 

in one's bank account and by other liquid assets; 

resources then include, in addition, all other assets 

and, more importantly, all income one may expect 

to receive, from whatever source, through the duration of one's lifetime. We will discuss various categories of resources and their relation to reserves 

later in this introduction, but for the present we 

would emphasize that because reserves are the only 

part of the total resource that is immediately available, they are of paramount concern to the mineral 

industry, and reserve estimates for most mineral 

commodities are generally available and are undergoing constant revision. For most minerals, however, current reserves are only a small part of the 

total resource. The remainder of the total-the potential resources-are by far the most important 

for the long term, and they receive major emphasis 

in this book. Mineral resources, whether real or 

potential, are geologic entities-concentrations of 

one or more elements in the earth's crust. Because 

such concentrations occur as the result of geologic 

processes, the question of how and where to find 

more of them can ultimately be resolved only 

through the understanding of geologic principles and 

the application of geologic insight; accordingly, the 

chapters of this volume deal with predictions based 

on geologic reasoning, and have been written by 

geologists. 

A WARNING 

Implicit in the distinction between reserves and 

resources is a serious danger, which we state now 

and will reiterate throughout this volume: Potential resources are not reserves; they are "birds in 

the bush," or to return to the analogy already used, 

they are frozen assets and next year's income, and 

cannot be used to pay this month's bills. No matter 

how optimistic an outlook is engendered by estimates 

of vast resources, such resources cannot be mined, 

much less used, until they have been converted into 

the category of reserves, whether by discovery (of 

undiscovered resources of minable quality), or by 

improvements in technology (for recovering identified subeconomic resources), or by both. For nearly 

all minerals, the estimates of potential resources 

indicate quantities that may become available only 

if we vigorously pursue geologic and technologic 

research to discover new mineral deposits in regions and geologic environments that are known to 

be favorable, to discover new favorable regions and 

environments, to discover new kinds of mineral 

deposits not previously recognized, to improve existing exploration techniques and develop new ones, 

and to improve extractive technology for processing 

low-grade ores that are not now economically recoverable. Readers of this volume must therefore 

be cautioned that the resource estimates contained 

herein are indeed estimates, not measurements ; and 

they present an optimistic outlook for many commodities only in the context that they represent a 

potential, not a reality. Using these estimates in 

any effort to optimize our domestic resource outlook may only defeat the purpose if they are removed from this context or are quoted without 

adequate qualification. We have attempted to insure 

against such misinterpretation by repeating definitions of the appropriate resource terminology on 

all tables of resource estimates in this volume. 

Even with these qualifiers, some may criticize this 

volume for its articulation of a philosophy that they 

may consider to be unrealistic. We can only offer 

the response that in the fairly recent past, each of 

the kinds of geologic and technologic research enumerated in the preceding paragraph has in fact 

resulted in the conversion of potential resources 

into minable reserves-"rock in the box," in mining 

parlance; a few examples are the discoveries of the 

huge Kidd Creek zinc-copper-silver ore deposit in 

Ontario and the disseminated gold deposits of Carlin 

and Cortez in Nevada, and the development of technology for processing taconite iron ores. 

Indeed the events of the last 20 years are the best 

reason for optimism. In 1952, the recoverable reserves of lead were estimated to be 7.1 million tons, 

of which only about 1 million tons was called proved 

reserve. These figures were quoted on page 41 of 

volume 2 of "Resources for Freedom" (President's 

Materials Policy Commission, 1952), better known 

as the Paley report. Farther down on that page we 

find the following statement, "The poor discovery 

record of the past few decades provides little basis 

for optimism that the equivalent of the southeast 
INTRODUCTION 3 

Missouri district can be expected to turn up in the 

future ; the major hope lies in the development of 

some new methods of prospecting, as, for example, 

methods that would indicate the probability of deposits in the absence of surface ontcrops." Drilling 

in the mid-1950's on the west side of the Southeast 

Missouri district resulted in the discovery of the 

large unexposed deposits of lead ore known as the 

Viburnum Trend. By 1970, half a dozen mines were 

operating, and the reserves of lead in Missouri alone 

had increased to 30 million tons. (See the chapter 

on "Lead" in this volume.) The Viburnum Trend 

will yield more lead than the total production of the 

old part of the district. With the phoenixlike rejuvenation of the Southeast Missouri district, the 

Viburnum Trend becomes the perfect example of a 

potential resource converted to a reserve. 

We see no reason why such discoveries and developments cannot be expected to continue in the 

future. To point the direction to potential resources 

and to attempt to evaluate them are the objectives 

of this book. 

OUR DEPENDENCE ON MINERALS 

Few people are fully aware of their daily dependence upon minerals. An awareness is growing as 

the fragilities of modern civilization, stemming 

from population growth and economic expansion, 

become recognizable not only as world and national 

problems, but also as personal problems. The availability of mineral resources to meet the projected 

demands will critically affect future events. 

It is important, therefore, to be able to predict the 

occurrence of minerals, with some degree of realism, 

on several different scales of both time and space; 

we must know not only in which direction a particular mine opening should be extended to continue in 

an ore body, but over a longer time period, we must 

know where prospecting and exploration should be 

concentrated to discover new deposits of each kind 

of mineral-and the likelihood of success. In other 

words, where are our potential mineral resources 

and how large are they? How long will they last? 

For which minerals, if any, are we "in good shape"? 

Is our supply of any minerals unlimited? Of which 

ones. do we have very little, or are we li! .. ely to run 

out in the near future? For these, is there a geologic 

probability that more can be discovered in the 

United States ?-that is, are there geologic environments in which such minerals are likely to occur? 

If so, where? And what problems are likely to be 

encountered in finding and extracting them? If 

domestic resources are not likely to be sufficient, 

then to which parts of the globe must we look for 

adequate resources in the future? These are the 

questions to which the authors of this volume have 

addressed themselves. 

CLASSIFICATION OF RESOURCES 

What, then, is a mineral resource? To begin with, 

we may define a mineral resource as a concentration 

of elements in a particular location in or on the 

earth's crust (or, now, also in the oceans), in such 

a form that a usable mineral commodity-whether 

it be an element (such as iron or aluminum), a 

chemical compound (such as salt or borax), a mineral (such as emerald or asbestos), or a rock (such 

as marble, coal, or gypsum)-can be extracted from 

it. The perceptive reader will recognize that such a 

definition has little practical value if the particular 

mineral commodity cannot be extracted at a profit. 

As already suggested, this feasibility of profitable 

extraction, or economic availability, is one of two 

parameters that distinguish between resources and 

reserves ; the other parameter is the degree of certainty of existence. These two parameters were 

origin~lly formulated into a classification of resources by V. E. McKelvey ( 1972), whose presentation of these conc~pts is so vital to the philosophy 

of resources, and whose classification is so important as the cornerstone of the present volume, that 

we have included his article as the second chapter 

of this volume. We will summarize McKelvey's resource classification by stating merely that he defines reserves as economically recoverable material 

in identified deposits, and applies the term resources 

to include "deposits not yet discovered as well as 

identified deposits that cannot be recovered now." 

The terms recoverable, paramarginal, and submarginal designate successively lower degrees of economic recoverability; paramarginal resources are 

defined as low-grade resources that are recoverable 

at prices as much as 1.5 times those prevailing now, 

and submarginal resources are those of still lower 

grade. (See fig. 4, p. 12.) 

In this volume we use a similar classification of 

resources; but because of our conviction that the 

long-range potential lies in resources that have not 

yet been discovered, our classification places less 

emphasis on the definition of various levels of economic recoverability, and more emphasis on evaluating the undiscovered-defining the various degrees 

of certainty. For the purpose of this volume, we 

distinguish three different such degrees (fig. 1). 

Identified resources are specific bodies of mineralbearing rock whose existence and location are 

known. They may or may not be evaluated as to 

extent and grade. Identified resources include 
4 UNITED STATES MINERAL RESOURCES 

Undiscovered resoutces 

Identified resources In known 

EXPLANATION 

VI Potential resources= Conditional + Hypothetical 

L.Lj + Speculative 

FIGURE 1.-Classification of mineral resources used in this 

volume. 

Teserves-masses of rock whose extent and grade 

are known to a greater or lesser degree and whose 

grade and physical nature are such that they may 

be extracted at a profit with existing technology and 

at present price levels. These last constraints of 

technology and economics exclude from the category 

of reserves many mineral deposits that are known 

and evaluated but are not profitably or technologically minable at present, and to this important -category of identified but subeconomic resources we 

apply the informal term conditional 'resourcesresources that may eventually become reserves when 

conditions of economics or technology are met. 

Conditional resources have an immediate potential, 

because they are known, and their assessment provides a target for technologic research. This term 

is used in the volume primarily as a convenience, 

because most authors were unable to distinguish 

the paramarginal and submarginal categories in 

McKelvey's classification. 

We divide the remaining potential resources, all 

undiscovered, into two informally designated categories. Hypothetical resouTces are here defined as 

undiscovered resources that we may still reasonably 

expect to find in known distTiCtS ,' speculative reSOUrCeS are defined as undiscovered resources that 

may exist elsewhere-either conventional types of 

deposits in broad geologic terranes in which as yet 

there are no discoveries, or else unconventional 

types of resources that have only recently been 

recognized (or are yet to be recognized) as having 

some potential. 

The utility of this distinction can be demonstrated 

by a few examples. In evaluating sandstone-type 

uranium deposits, for instance, we would consider 

as hypothetical resouTces the deposits that have so 

far eluded discovery in the known districts of New 

Mexico or Wyoming; our geologic knowledge tells 

us that there is good reason to expect we will find 

more deposits in those areas similar to the deposits 

already known, and our estimate of hypothetical 

resources is, in this case, an attempt to quantify 

the potential of these undiscovered resources, mainly 

on the basis of the extent of unexplored but favorable ground. A different kind of geologic perspective, on the other hand, suggests that there is still 

some likelihood of finding not just new deposits, 

but new major uranium districts. Our estimate of 

these speculative resources, even though it may be 

only an order of magnitude, is an attempt to quantify the resource potential of sedimentary basins 

that are known to exist but have not been sufficiently tested for uranium. 

Resources of copper can be used as another example of the distinction between hypothetical and 

speculative resources. We are justified in hypothesizing, for instance, that porphyry copper deposits 

are concealed under basin fill in and near the known 

copper districts of the southwest, whereas the discovery in recent years of porphyry-type copper deposits of Paleozoic and Precambrian age in Eastern 

North America permits us to speculate that whole 

new regions have some potential for new discoveries. 

Yet another example of the distinction between 

hypothetical and speculative resources involves the 

black bedded deposits of barite such as those currently being mined principally in Nevada and Arkansas. The known deposits are scattered over wide 

areas of both States, and chances are excellent that 

new deposits - hypothetical resources - will be 

found. But recent geologic studies of these deposits 

suggest that they are related more to sedimentary 

processes than was formerly believed. If this is true, 

then the potential for the discovery of new deposits 

and districts in other sedimentary basins-speculative resources-is likewise excellent. This example 

is an indication of how the reexamination and study 

of basic geologic principles can help to open new 

areas and environments favorable for exploration. 

One further aspect of the value of such a distinction is that it has forced us to realize that the 

speculative resources of some commodities are relatively low. From a worldwide geologic perspective, 

we can say that the regions with significant potential for discovery of iron, or phosphorite, or marine 

evaporites, are largely known; thus, the significant 

undiscovered resources fall under the heading of 
INTRODUCTION 5 

"hypothetical," rather than "speculative." F'or some 

commodities, this may simply reflect insufficient 

knowledge of regional geology to identifiy other 

promising areas, but for others it is an expression 

of confidence that the favorable terranes have all 

been identified. 

The entire field in the diagram of figure 1 represents our total primary resources (as distinct from 

secondary resources, such as recycled scrap, which 

are not considered in this volume) -identified reserves, plus potential resources, which consist of 

conditional, hypothetical, and speculative resources. 

Conversions of potential resources into reserves are 

made by discovery, technologic advance, or changes 

in economic conditions. The same processes may 

lead to similar conversions from outside the fieldto make potential resources from materials at present inconceivable as resources. 

A corollary of the emphasis of this volume on 

geologic rather than economic factors is that our 

classification is less concerned with the degrees of 

feasibility of recovery defined by McKelvey. We 

recognize that the concepts of paramarginal and 

submarginal resources are valid, but because of the 

broader objectives of this volume, nearly all our 

authors found that a single degree of distinction 

based on economic recoverability was difficult 

enough to obtain for identified resources, let alone 

for undiscovered resources, without the further 

complication of another degree defined by a specific 

price factor. Thus, nearly all the chapters of this 

volume differentiate three major categories of resources-identified, hypothetical, and speculative; 

within the first category, most chapters differentiate 

between recoverable identified resources (reserves), 

and subeconomic identified resources (conditional 

resources). In only a· few chapters have the authors 

attempted to extend the levels of economic recoverability into the hypothetical and speculative fields, 

and where this has been done, it is generally in 

terms of "recoverable" versus "subeconomic"-for 

example, "subeconomic hypothetical resources." 

Special problems are posed in classifying the 

resources found in sea-floor manganese nodules, in 

metal-bearing muds of the Red Sea, and in the 

recently discovered metal-bearing sedimentary rocks 

of the Belt Supergroup in Idaho and Montana. Some 

authors were reluctant to characterize the deposits 

in these three environments as identified resources. 

We see no question that they are identified, in that 

they broadly fit the criteria of being known as to 

existence and location; but we well realize that they 

are not fully evaluated. Our decision to classify 

these resources as "identified," for consistency of 

treatment within this volume, may therefore be regarded as arbitrary and is in no way binding on 

our authors or on our readers. We note, however, 

that officials of two major U.S. mining companies 

were recently reported to have said they "expect to 

be selling metal made from the [sea-floor] nodules 

by the end of the decade" (Faltermayer, 1972, p. 

170). Such expectations, in our view, are not likely 

to have been predicated on resources that are undiscovered. 

PUBLIC AWARENESS, RESOURCE ESTIMATES, 

AND GEOLOGIC AVAILABILITY 

Public awareness of our dependence on mineral 

resources appears to be growing. With this growth 

in awareness-and indeed responsible for some of 

it--is a growth in the number of magazine and 

newspaper articles, and even books, that attempt 

to evaluate our supply of mineral resources and in 

some cases to forecast economic or cultural trends 

that are dependent on this supply. (See, for example, 

Faltermayer, 1972; Meadows and others, 1972; U.S. 

News and World Report, 1972.) The almost universal tendency of such articles is to discuss mineral 

resources principally from the perspective of economic availability under a given set of conditions, 

thereby overlooking the vital fact that reserves are 

but a part of resources. The results are, we feel, 

disturbing. Evaluations predicated only on knowledge (or estimates) of current reserves can easily 

lead to forecasts of the death of the industrial society in a short time. On the other hand, evaluations based on another kind of assumption suggest 

that a rise in prices will increase the reserves and 

bring much more material to market economically 

from lower and lower grade material in larger and 

larger deposits. This reasoning too is fallacious because elements are available in the earth's crust in 

very finite amounts. But in both instances, the 

reasoning leads to serious misinterpretations because it does not give adequate consideration to the 

single factor that ultimately determines all levels 

and degrees of mineral potential: geologic availability. Geologic availability concerns the existence 

and concentration of certain elements or combinations of elements and is the most fundamental characteristic of a mineral commodity that governs its 

commercial use. 

Assessment of geologic availability of a commodity requires basic knowledge of the geology, 

mineralogy, and geochemistry of that material, the 

geologic environments in which it occurs, and its 

concentration in those environments. The technology of exploration, mining, beneficiation, recov-
6 UNITED STATES MINERAL RESOURCES 

ery, and use is founded upon this information. 

Studies of geologic availability are indispensableat all levels of commerce, industry, and government-for any economic planning that considers 

the available supply or use of primary mineral commodities and their byproducts. 

Generally, however, public concepts of the magnitude of mineral resources are based on evaluations 

of economic rather than geologic availability, and 

even these are subject to numerous problems. Sound, 

accurate estimates of reserves for large regions are 

highly difficult to compile, for many reasons. Reserve data from industrial deposits may not be 

available because of the problems of competition 

and taxes. Managements of many companies believe 

that in the competitive atmosphere of business they 

should not release information about their reserves. 

Some States tax the reserves in the ground held by 

mining companies, making it economically advantageous, and in some cases necessary, to produce at 

capacity for years from deposits that are continually 

reported to be nearly exhausted. Definition of tonnages of mineral resources of sufficiently high grade 

to be minable at current prices is difficult enough 

without trying to distinguish grades minable at 1.5 

or more times greater than the current price. Economic evaluations of a specific mineral deposit have 

become a complex task for a team of specialists, 

including not only geologists but also mining engineers, ore dressers, metallurgists, and economists. 

So many complex factors govern price at any given 

time that it would seem foolhardy to estimate resources in each of the economic categories and 

expect the results to be meaningful for very long. 

At some time, however, the pressures of both 

economic and geologic factors will meet in crisis. 

Economic factors may be altered rapidly. Changes 

in demand and use alter patterns of production and 

consumption; new deposits are sought elsewhere; 

substitutes will be sought; and new technology will 

be developed as the ingenuity of man is focused on 

solving the problems. But there is no economic 

availability if there is no geologic availability. Of 

the two factors, geologic availability is the more 

fundamental because without it economic availability is not pertinent. Just as no biological miracle 

can make it possible to extract blood from a turnip, 

neither technological magic nor astronomic dollar 

value can make it possible to extract gold or aluminum or borax or mica from rocks in which they are 

not present. Geologic availability, therefore, is the 

ultimate determinant of mineral potential, and it 

is geologic availability that is stressed in the evaluations of potential mineral resources in this volume. 

Few chapters in the volume attempt to distinguish 

between tonnages now recoverable and those available only at subeconomic levels of the three 

"certainty-of-existence" categories shown in figure 

1, but virtually every chapter offers a quantitative 

evaluation in numbers or words for the resources 

in each of the three categories, and the use of the 

threefold terminology has been applied as rigorously 

and uniformly as practical in each chapter. 

GENERAL CONCLUSIONS 

We realize that this book lacks a plot sufficient to 

induce its readers into proceeding through it from 

cover to cover. Therefore, we offer here some general conclusions on several aspects of the Nation's 

mineral-resource position, which have emerged 

from our editorial overview of the chapters as 

a whole. Of first importance is a summary answer 

to the principal question to which the volume is 

directed : Where do we stand with regard to resources of each commodity? Other conclusions pertain to the increasing importance, as resources, of 

large volumes of low-grade rocks, and attendant 

environmental problems; the problem of enormous 

quantities of potential mineral byproducts that are 

now literally being wasted ; the factor of energy in 

the extraction of minerals; and finally, the pressing 

need for vigorous research along many lines. 

MINERAL POTENTIAL: WHERE DO WE STAND? 

Each chapter of the volume has its own calculation or other evaluation of resources governed by 

those factors deemed by the authors to be important 

to the respective commodity. There is no way to 

make the data in each chapter absolutely comparable. We would prefer that users of the volume read 

the chapters of interest to them in order to obtain 

the best possible understanding of the authors' presentation of resource data, and then formulate their 

own conclusions. We have, however, compiled a 

table that shows resource appraisals on a numerical 

scale, for commodities of major importance, put 

into perspective in terms of the minimum anticipated cumulative demand 1 for the period 1968-2000 

as compiled by the U.S. Bureau of Mines (1970). 

Once again we emphasize that the resources indicated here are for the most part potential, and that 

their eventual availability as reserves is entirely 

dependent on continued geologic and technologic 

research as well as economic factors. 

1 In using "demand" values for purposes of ·comparison we do not 

represent them as being specific goals to be reached. This volume presents 

no social or political judgments; its sole purpose is to make available 

reliab!e geologic resource facts and assessments for public policy decision as 

well as for use by the minerals industry. 
INTRODUCTION 7 

TABLE 1.-Potential U.S. resources of some important mineral commodities, in relation to minimum anticipated cumulative demand to year 2000 A.D. 

ST=short tons. lb=pounds. 

LT=long tons. Tr oz=troy ounces. Identified resources: Includes reserves, and materials other than re- serves that are r~onably. well known as to location, extent, and grade, that may be explOitable m the future under more favorable economic conditi~ns or with improvements in technology. 

Hypothetical resources: Undiscovered but geo!ogically predictable deposits of materials similar to present identified resources I. Do~estic resources (of the category shown) a~e greater than 10 times· the minimum anticipated cumulative demand 1968-2000 II. Domestic resources are 2 to 10 times the MACD · 

III. Do:~~. resources are approximately 75 p~rcent to 2 times the 

IV. Domest!c resources are approximately 35-75 percent the MACD. V. Domest!c resources are approximately 1o-35 percent the MACD. VI. Domestic resources are less than 10 percent of the MACD. 

Commodity 

Aluminum ------ Asbestos -------- Barite ---------- Chromium -------

Clay ------------ Copper ---------- Fluorine -------- Gold ------------ Gypsum --------- Iron ------------

Lead ------------ Manganese ------ Mercury -------- Mica, scrap ------ Molybdenum ____ _ 

Nickel ---------- Phosphate ------- Sand and gravel _ 

Silver ---------- Sulfur ---------- Thorium -------- Titanium ( Ti02) _ 

Tungsten -------- Uranium -------- Vanadium ------- Zinc ------------

Identi- Minimum anticipated fied Hypothetical cumulative demand, re- resources 1968-2000 1 sources 

290,000,000 ST 

32,700,000 ST 

25,300,000 ST 

20,100,000 ST 

2,81:3,500,000 ST 

96,400,000 ST 

37,600,000 ST 

372,000,000 Tr oz 719,800,000 ST 

3,280,000,000 ST 

37,000,000 ST 

47,000,000 ST 

2,600,000 flasks 

13,000,000 ST 

3,100,000,000 lbs 

16,200,000,000 lbs 

190,000,000 ST 

56,800,000,000 ST 

3,700,000,000 Tr oz 47:J,OOO,OOO LT 

27,500 ST 2 

38,000,000 ST 

1,100,000,000 lbs 

1,190,000 ST 

420,000 ST 

57,000,000 ST 

II Not estimated. 

V VI 

II II 

VI VI 

III II 

III III 

v v 

HI Not estimated. 

I I 

II I 

III IV 

III Not estimated. 

V Not estimated. 

II I 

I 1 

HI Not estimated. 

II I 

III Not estimated. 

III III 

I I 

II Not estimated. 

II II 

IV IV 

II III 

II Not estimated. 

II II 

1 As estimated by U.S. Bureau of Mines, 1970. 2

• For thorium, maximu1r. anticipated cumulative demand 1968-2000, whtch assumes commercial development of economically attractive thorium reactors by 1980. 

Careful study of both this table and the volume 

in its entirety leads to the conclusion that only a 

few commodities are readily available to the United 

States in quantities adequate to last for hundreds 

of years. By no means is it too early to become 

concerned about future mineral supplies-and to 

start planning. Charles F. Park (1968) wrote of 

the decrease in mineral supplies that is placing 

modern American affluence in jeopardy. The real 

extent of our dependence on mineral resources places 

in jeopardy not merely affluence, but world civilization. 

LOW -GRADE ORES AND THE ENVIRONMENT 

The impelling need for minerals poses environmental problems of· concern to all. Probably foremost among these is the fact that for many minerals future production will depend on mining enormous volumes of low-grade ores, with necessarily 

strong environmental impact. The problem can be 

temporary, and can be solved, as witness the utilization of the manganese deposits in the Nikopol 

region, U.S.S.R., described in the chapter on "Manganese." But in most areas the opposing factions of 

industry and environmentalist are still just facing 

off. We believe the problem must be met squarely, 

realistically, and soon, by frank and objective exchange-not merely between small groups representing the mining industry on the one hand and 

outdoor enthusiasts on the other but between 

indus try and the public at large. The environment 

is far bigger then any small interest group. Ultimately, a concerned public must decide in which 

order to place its priorities, and each faction of that 

public is entitled to basic information on the need 

for and availability of mineral resources as a foundation on which to base its decisions. Thus, as only 

two examples of such factions, the enthusiastic 

hiker-whether fisherman, Scout leader, or vacationing city dweller-must realize that his dacroncovered aluminum-frame backpack, his nylon fishing line, his polyurethane foam pad, and even his 

dehydrated foods are either made of or processed 

by mineral products, which continue to be used up 

and must continue to be made available. Conversely, 

the miner must realize that his assertion of need to 

develop a new copper deposit, when the technology 

of extraction may leave not only important potential byproducts but half the copper itself in the 

ground, may sound more like expediency than need. 

It is beyond the scope of this volume to attempt 

a comprehensive review or evaluation of the mineral-environmental problem in general. Our purpose here is simply to indicate that the chapters of 

this volume provide some of the basic information 

on which such reviews or evaluations should be 

based. 

ECONOMICS AND WASTE 

A major aspect of resources that appears in many 

of these chapters is the extent to which many potential byproducts or coproducts are literally being 

wasted-lost forever-because there is no apparent 

economic incentive for recovering them. Some minerals go into slurry ponds, some into slags, some up 

the flue. Examples of such commodities are the 

vanadium in magnetite deposits; selenium, tellurium, and gold lost through in-place leaching of 

porphyry copper deposits; fluorine, vanadium, urani urn, scandi urn, and rare earths in marine phosphorites; cadmium, bismuth, and cobalt in lead 

ores ; and several metals in coal ash. Strictly speak-
8 UNIT'ED S:TATES MINERAL· RESOURCES 

ing, these resources belong in the category of conditional resources, but we believe there is a significant 

distinction between resources that are not economically minable under present conditions and those 

that either are not recovered because of selective 

mining, or are discarded because of selective processing. In many cases the perspective of geologic 

availability makes possible the view that what may 

seem economical for the short term is not necessarily so for the long term, and these potential 

resources should not be overlooked or misused. 

THE ENERGY FACTOR 

Extraction and processing of all minerals requires 

some form of energy, and it is a safe generalization 

to say that to produce a fixed amount.of any given 

commodity, the lower the grade of ore, the greater 

is the quantity of energy required. Although this 

volume contains individual chapters on mineral 

energy resources, a comprehensive evaluation of 

energy resources in the context of their specific 

relation to extract~on of minerals is far beyond the 

scope of the book. The reader should bear in mind 

that as the mining industry turns to lower and lower 

grades of many ores, the cost and availability of the 

required energy are probably the single most important factors that will ultimately determine 

whether or not a particular mineral deposit can be 

worked economically. 

THE NEED FOR RESEARCH 

Potential resources are transformed into reserves 

not by moving rock, but by expanding the artificial 

boundaries of geologic knowledge and economic 

availability that delimit "reserves" from "resources" ; hence, the potential of most of the resources discussed in this volume can be realized 

only as a result of applied research. Development 

of new technologies will make economic extraction 

of conditional resources feasible; innovative application of old geologic theory and the creation of new 

concepts of ore formation can be expected to lead 

to the discovery of conventional mineral deposits in 

favorable regions (hypothetical resources) ; research 

and exploration can be counted on to discover some 

new types of deposits and some new ore environments and regions that we do not know about now 

(speculative resources). 

Clearly, to these factors of geologic and economic 

availability we must also add the factor of human 

ingenuity. W. E. Pratt (1943), vice president of 

Standard Oil Co., in speaking some years ago of 

petroleum exploration, cogently expressed a viewpoint that is equally pertinent for mineral exploration: "* * * physical conditions in the earth's crust 

impose fewer and less formidable obstacles to the 

development of commercial oil fields over the earth 

than do some of our mental and social habits * * * . 

Whatever the geological conditions may be and 

whatever technique we employ, we find oil in the 

earth very rarely unless we have first acquired an 

appropriate mental attitude * * *. Where oil really 

is, then, in the final analysis, is in our own heads !" 

Tile chapters of this volume constitute a beginning 

effort to cultivate the "appropriate mental attitude" 

and to articulate the resulting ideas in terms of 

where and in what magnitudes our future mineral 

resources might be found. Only by continuing this 

effort, through vigorous pursuit of exploration, research, and technologic development, can we confidently expect to locate these potential resources and 

convert them into usable reserves. 

REFERENCES CITED 

Faltermayer, Edmund, 1972, Metals: the warning signals 

are up: Fortune, October 1972, p. 109-112, 164, 169-

170, 174-176. 

McKelvey, V. E., 1972, Mineral resource estimates and public policy: American Scientist, v. 60, no. 1, p. 32-40; 

reprinted in this book. 

Meadows, D. H., Meadows, D. L., Randers, JS!frgen, and 

Behrens, W. W. III, 1972, The limits to growth: New 

York, Universe Books, 205 p. 

Park, C. F., Jr., 1968, Affluence in jeopardy: San Francisco, 

Freeman, Cooper & Co., 368 p. 

Pratt, W. E., 1943, Oil in the Earth: Lawrence, Kansas 

Univ. Press, 110 p. 

President's Materials Policy Commi55ion, W. S. Paley, chm., 

1952, Resources for freedom: Washington, U.S. Govt. 

Printing Office, 818 p., 5 vols. 

U.S. Bureau of Mines, 1970, Mineral facts and problems: 

U.S. Bur. Mines Bull. 650, 1291 p. 

U.S. News and World Report, 1972, U.S. becoming a "have 

not" in raw materials-what to do?: U.S. News and 

World Report, v. 73, no. 23, p. 81-84. 
MINERAL RESOURCE ESTIMATES AND PUBLIC POLICY 

By V. E. McKELVEY 

CONTENTS 

Introduction 

Concepts of reserves and resources ----------------

Examples of estimates of potential resources -------

Quantifying the undiscovered ---------------------

Need for review of resource adequacy -------------

Selected bibliography -----------------------------

FIGURES 

2. Graph showing per capita energy consumption 

Page 

9 

11 

13 

14 

17 

18 

Page 

compared to per capita Gross National Product 10 

3. Graph showing per capita steel consumption compared to per capita Gross National Product ___ 10 

4. Diagram showing classification of mineral reserves and resources ----------------------- 12 

5. Graph showing domestic reserves of elements 

compared to their abundance in the earth's 

crust -------------------------------------- 16 

TABLE 

Page 

2. Some estimates of U.S. crude-oil reserves and resources ------------------------------------ 14 

INTRODUCTION 

Not many people, I have found, realize the extent 

of our dependence on minerals. It was both a surprise and a pleasure, therefore, to come across the 

observations of George Orwell in his book "The Road 

to Wigan Pier." When describing the working conditions of English miners in the 1930's, he evidently was led to reflect on the significance of coal: · Our civilization ... is founded on coal, more completely 

than one realizes until one stops to think about it. The 

machines that keep us alive, and the machines that make 

the machines are all directly or indirectly dependent upon 

coal . . . . Practically everything we do, from eating an ice 

to crossing the Atlantic, and from baking a loaf to writing 

a novel, involves the use of coal, directly or indirectly. For 

all the arts of peace coal is needed ; if war breaks out it is 

needed all the more. In time of revolution the miner must go 

on working or the revolution must stop, for revolution as 

much as reaction needs coal . . . In order that Hitler may 

march the goosestep, that the Pope may denounce Bolshevism, 

that the cricket crowds may assemble at Lords, that the 

Nancy poets may scratch one another's backs, coal has ·got 

to be forthcoming. 

To make Orwell's statement entirely accurateand ruin its force with complications-we should 

speak of mineral fuels, instead of coal, and of other 

minerals also, for it is true that minerals and mineral fuels are the resources that make the industrial 

society possible. The essential role of minerals and 

mineral fuels in human life may be illustrated by a 

simple equation 

L 

p 

in which the society's average level of living (L), 

measured in its useful consumption of goods and 

services, is seen to be a function of its useful consumption of all kinds of raw materials (R), including metals, nonmetals, water, soil minerals, biologic 

produce, and so on; times its useful consumption of 

all forms of energy (E) ; times its useful consumption of all forms of ingenuity (I), including political 

and socio-economic as well as technologic ingenuity; 

divided by the number of people (P) who share in 

the total product. 

This is a restatement of the classical economists' 

equation in which national output is considered to 

be a function of its use of capital and labor, but it 

shows what capital and labor really are. Far from 

being mere money, which is what it is popularly 

thought to mean, capital represents accumulated 

usable raw materials and things made from them, 

usable energy, and especially accumulated knowl9 
10 UNIT'ED STATES MINERAL RESOURCES 

edge. And the muscle power expended in mere physical toil, which is what labor is often thought to 

mean, is a trivial contribution to national output 

compared to that supplied by people in the form of 

skills and ingenuity. 

This is only a conceptual equation, of course, for 

numerical values cannot be assigned to some of its 

components, and no doubt some of them-ingenuity 

in particular-should receive far more weight than 

others. Moreover, its components are highly interrelated and interdependent. It is the development 

and use of a high degree of ingenuity that makes 

possible the high consumption of minerals and fuels, 

and the use of minerals and fuels are each essential 

to the availability and use of the other. Nevertheless, the expression serves to emphasize that level 

of living is a function of our intelligent use of 

natural resources, and it brings out the importance 

of the use of energy and minerals in the industrial 

society. As shown in figure 2, per capital Gross Na-

• 1- z z 

0 w 8000 -.J 

1-c( 

ll.> 

~­;::);::) 

(1)0 

Zw 

0 .... 6000 

(Jc( 

>o 

(!J(J 

a:u. 

~0 

w (I) 4000 

c(~ 

1-c( 

-a: 

ll.(!J 

c(o 

(J..J 

ffi ~ 2000 

ll.! 

. . 

. . 

$1 000 $3000 $4000 $5000 

PER CAPITA GNP IN 1967 

FIGURE 2.-Per capita energy consumption compared to per 

capita Gross National Product (GNP) in countries for 

which statistics are available in the United Nations "Statistical Yearbook" for 1967. 

tional Product among the countries of the world is, 

in fact, closely related to their per capita consumption of energy. Steel consumption also shows a close 

relation to per capita GNP (fig. 3), as does the consumption of many other minerals. 

Because of the key role that minerals and fuels 

play in economic growth and in economic and military security, the extent of their resources is a 

(I) 600~­

~ 

c( 

a: 

" 0 

::!500fLJ ll. 

~ 

;::) 

(I) 

z 

0 

(J 300f- .J I 

~ I 

t 200~ ll. 

c( 

(J 

a: 

w 

ll. 

100,- • 

. ~ 

.. . . 

.. 

$5000 

PER CAPITA GNP IN 1967 

FIGURE 3.-Per capita steel consumption compared to per 

capita Gross National Product (GNP) in countries for 

which statistics are available in the United Nations "Statistical Yearbook" for 1967. 

matter of great importance to government, and 

questions concerning the magnitude of resources 

arise in conjunction with many public problems . 

To cite some recent examples, the magnitude of 

low-cost coal and uranium reserves has been at the 

heart of the question as to when to press the development of the breeder reactor-which requires 

a research-and-development program involving such 

an enormous outlay of public capital that it would 

be unwise to make the investment until absolutely 

necessary. 

Similarly, estimates of potential oil and gas resources are needed for policy decisions related to 

the development of oil shale and coal as commercial 

sources of hydrocarbons, and estimates are needed 

also as the basis for decisions concerning prices and 

import controls. 

Faced with a developing shortage of natural gas, 

the Federal Power Commission is presently much 

interested in knowing whether or not reserves reported by industry are an accurate indication of the 
MINERAL RESOURCE ESTIMATES AND PUBLIC POLICY 11 

amount of natural gas actually on hand ; it also 

wants to know the extent of potential resources and 

the effect of price on their exploration and development. At the regional or local level, decisions with 

respect to the designation of wilderness areas and 

parks, the construction of dams, and other matters 

related to land use involve appraisal of the distribution and amount of the resources in the area. 

The questions of the need for an international 

regime governing the development of seabed resources, the character such arrangement should 

have, the definition of the area to which it should 

apply also involve, among other considerations, 

analysis of the probable character, distribtuion, and 

magnitude of subsea mineral resources. 

And coming to the forefront is the most serious 

question of all-namely, whether or not resources 

are adequate to support the continued existence of 

the world's population and indeed our own. The possibility to consider here goes much beyond Malthus' 

gloomy observations concerning the propensity of 

a population to grow to the limit of its food supply, 

for both population and level of living have grown 

as the result of the consumption of nonrenewable 

resources, and both are already far too high to 

maintain without industrialized, high-energy, and 

high mineral-consuming agriculture, transportation, 

and manufacturing. I will say more about this question later, but to indicate something of the magnitude of the problem let me point out that, in attaining our high level of living in the United States, we 

have used more minerals and mineral fuels during 

the last 30 years than all the people of the world 

used previously. This enormous consumption will 

have to be doubled just to meet the needs of the 

people now living in the United States through the 

remainder of their lifetimes, to say nothing about 

the needs of succeeding generations, or the increased 

consumption that will have to take place in the 

lesser developed countries if they are to attain a 

similar level of living. 

CONCEPTS OF RESERVES AND RESOURCES 

The focus of most of industry's concern over the 

extent of mineral resources is on the magnitude of 

the supplies that exist now or that can be developed 

in the near term, and this is of public interest also. 

Many other policy decisions, however, relate to the 

much more difficult question of potential supplies, 

a question that to be answered properly must take 

account both of the extent of undiscovered deposits 

as well as deposits that cannot be produced profitably now but may become workable in the future. 

Unfortunately, the need to take account of such 

deposits is often overlooked, and there is a widespread tendency to think of potential resources as 

consisting merely of materials in known deposits 

producible under present economic and technologic 

conditions. 

In connection with my own involvement in resource appraisal, I have been developing over the 

last several years a system of resource classification 

and terminology that brings out the classes of resources that need to be taken into account in appraising future supplies, which I believe helps to 

put the supply problem into a useful perspective. 

Before describing it, however, I want to emphasize 

that the problem of estimating potential resources 

has several built-in uncertainties that make an accurate and complete resource inventory impossible, 

no matter how comprehensive its scope. 

One such uncertainty results from the nature of 

the occurrence of mineral deposits, for most of them 

lie hidden beneath the earth's surface and are. difficult to locate and to examine in a way that yields 

accurate knowledge of their extent and quality. 

Another source of uncertainty is that the specifications of recoverable materials are constantly changing as the advance of technology permits us to mine 

or process minerals that were once too low in grade, 

too inaccessible, or too refractory to recovery profitably. Still another results from advances that make 

it possible to utilize materials not previously visualized as usable at all. 

For these reasons the quantity of usable resources 

is not fixed but changes with progress in science, 

technology, and exploration and with shifts in economic conditions. We must expect to revise our 

estimates periodically to take account of new developments. Even incomplete and provisional estimates are better than none at all, and if they 

differentiate known, undiscovered, and presently 

uneconomic resources they will help to define the 

supply problem and provide a basis for policy decisions relating to it. 

The need to differentiate the known and the recoverable from the undiscovered and the uneconomic 

requires that a resource classification system convey two prime elements of information: the degree 

of certainty about the existence of the materials 

and the economic feasibility of recovering them. 

These two elements have been recognized in existing terminology, but only incompletely. Thus as 

used by both the mining and the petroleum industries, the term reserves generally refers to economically recoverable material in identified deposits, 

and the term resources includes in addition deposits 

not yet discovered as well as identified deposits that 
12 UNITED STATES MINERAL RESOURCES 

cannot be recovered now (for example, Blondel and 

Lasky, 1956). 

The degree of certainty about the existence of 

the materials is described by terms such as proved, 

probable, and possible, the terms traditionally used 

by industry, and measured, indicated, and inferred, 

the terms devised during World War II by the Geological Survey and the Bureau of Mines to serve 

better the broader purpose of national resource 

appraisal. Usage of these degree-of-certainty terms 

is by no means standard, but all their definitions 

show that they refer only to deposits or structures 

known to exist. 

Thus, one of the generally accepted definitions of 

possible ore· states that it is to apply to deposits 

whose existence is known from at least one exposure, and another definition refers to an ore body 

sampled only on one side. The definition of inferred 

reserves agreed to by the Survey and the Bureau 

of Mines permits inclusion of completely concealed 

deposits for which there is specific geologic evidence and for which the specific location can be 

described, but it makes no allowance for ore in unknown structures of undiscovered districts. The 

previous definitions of both sets of terms also link 

them to deposits minable at a profit; the classification system comprised of these terms has thus 

neglected deposits that might become minable as 

the result of technologic or economic developments. 

To remedy these defects, I have suggested that 

existing terminology be expanded into the broader 

framework shown in figure 4, in which degree of 

certainty increases from right to left and feasibility of economic recovery increases from bottom 

to top. Either of the series of terms already used 

to describe degree of certainty may be used with 

reference to identified deposits and applied not only 

to presently minable deposits but to others that 

have been identified with the same degree of certainty. Feasibility-of-recovery categories are designated by the terms recoverable, paramarginal, and 

submarginal. 

Paramarginal resources are defined here as those 

that are recoverable at prices as much as 1.5 times 

those prevailing now. (I am indebted to S. P. 

Schweinfurth for suggesting the prefix para to indicate that the materials described are not only those 

just on the margin of economic recoverability, the 

common economic meaning of the term marginal.) 

At first thought this price factor may seem to be 

unrealistic. The fact is, however, that prices of many 

mineral commodities vary within such a range from 

place to place at any given time, and a price elasIdentified Undiscovered 

Proved l Probable I Possible 

I I 

Q 

«< 

t Reserves > 0 

u 

Q 

I I - I I «< 

c: 

~ «< Resources e 

~ «< 

-- + + + - «< 

c: 

60 

:; 

e 

= I I I 

Degree of certainty 

FIGURE 4.-Classification of mineral reserves and resources. 

Degree of certainty increases from right to left, and 

feasibility of economic recovery increases from bottom to 

top. 

ticity of this order of magnitude is not uncommon 

for many commodities over a space of a few years 

or even months, as shown by recent variations in 

prices of copper, mercury, silver, sulfur, and coal. 

Deposits in this category thus become commercially 

available at price increases that can be borne without serious economic effects, and chances are that 

improvements in existing technology will make them 

available at prices little or no higher than those 

prevailing now. 

Over the longer period, we can expect that technologic advances will make it profitable to mine 

resources that would be much too costly to produce 

now, and, of course, that is the reason for trying to 

take account of submarginal resources. Again, it 

might seem ridiculous to consider resources that 

cost two or three times more than those produced 

now as having any future value at all. But keep in 

mind, as one of many examples, that the cutoff 

grade' for copper has been reduced progressively not 

just by a factor of two or three but by a factor of 

10 since the turn of the century and by a factor of 

about 250 over the history of mining. Many of the 

fuels and minerals being produced today would once 

have been classed as submarginal under this definition, and it is reasonable to believe that continued 

technologic progress will create recoverable reserves 

from this category. 
MINERAL RESOURCE ESTIMATES AND PUBLIC POLICY 13 

EXAMPLES OF FSTIMATES OF POTENTIAL 

RESOURCES 

For most minerals, the chief value of this classification at present is to call attention to the information needed for a comprehensive appraisal of their 

potential, for we haven't developed the knowledge 

and the methods necessary to make meaningful 

estimates of the magnitude of undiscovered deposits, 

and we don't know enough about the cost of producing most presently noncommercial deposits to 

separate paramarginal from submarginal resources. 

Enough information is available for the mineral 

fuels, however, to see their potential in such a 

framework. 

The fuel for which the most complete information 

is available is the newest one-uranium. As a result 

of extensive research sponsored by the Atomic Energy Commission, uranium reserves and resources 

are reported in several cost-of-recovery categories, 

from less than $8 to more than $100 per. pound of 

UaOs. For the lower cost ores, the AEC .. makes periodic estimates in two degree-of-certainty categories, 

one that it calls reasonably assured reserves and the 

other it calls additional resources, defined as uranium surmised to occur in unexplored extensions of 

known deposits or in undiscovered deposits in known 

J]ranium districts. Both the AEC and the Geological 

Survey have made estimates from time to time· of 

resources in other degree-of-certainty and cost-ofrecovery categories. 

Ore in the less-than-$8-per-pound class is minable 

now, and the AEC estimates reasonably assured 

reserves to be 143,000 tons and additional resources 

to be 167,000 tons of UaOs-just about enough to 

supply the lifetime needs of reactors in use or 

ordered in 1968 and only half that required for 

reactors expected to be in use by 1980. The Geological Survey, however, estimates that undiscovered resources of presently minable quality may 

amount to 750,000 tons, or about 2.5 times that in 

identified deposits and districts. Resources in the 

$8- to $30-a-pound category in identified and undiscovered deposits add only about 600,000 tons of 

U30 8 and thus do not significantly increase potential 

reserves. 

But tens of millions of tons come into prospect 

in the price range of $30 to $100 per pound. Uranium at such prices would be usable in the breeder 

reactor. The breeder, of course, would utilize not 

only U235 but also U238, which is 140 times more 

abundant than U235• Plainly the significance of uranium as a commercial fuel lies in its use in the 

breeder reactor, and one may question, as a number 

of critics have (for example, Inglis, 1971), the 

advisability of enlarging nuclear generating capacity 

until the breeder is ready for commercial use. 

Until recently the only information available about 

petroleum resources consisted of estimates of proved 

reserves prepared annually by the American Petroleum Institute and the American Gas Association, 

plus a few estimates of what has been called ultimate production, that is, the total likely to be 

eventually recovered. A few years ago, however, the 

API began to report estimates of total oil in place 

in proved acreage, and the Potential Gas Committee 

began to estimate possible and probable reserves of 

natural gas, defining them as consisting of gas 

expected to be found in extensions of identified fields 

and in new discoveries in presently productive strata 

in producing provinces. It also introduced another 

category, speculative resources-equivalent to what 

I have called "undiscovered" -to represent gas to 

be found in nonproducing provinces and in presently 

unproductive strata in producing provinces. 

In 1970 the National Petroleum Council released 

a summary of a report on "Future Petroleum Provinces of the United States," prepared at the request 

of the Department of the Interior, in which it reported estimates of crude oil in the combined 

probable-possible class and in the speculative category. In addition, NPC estimated the amounts that 

would be available under two assumptions as to the 

percent of the oil originally in place that might be 

recovered in the future (table 2). NPC did not assess 

the cost of such recovery, but the average recovery 

is now about 30 percent of the oil in place, and NPC 

expects it to increase gradually to about 42 percent 

in the year 2000 and to 60 percent eventually. The 

NPC estimates do not cover all potentially favorable 

areas either on land or offshore but, even so, in the 

sum of these various categories NPC sees about 12 

times as much oil remaining to be discovered and 

produced as exists in proved reserves alone. 

The Potential Gas Committee's estimates of potential gas resources similarly do not cover all 

favorable areas, but they indicate that resources in 

the probable, possible, and speculative categories 

are about twice that of proved reserves and past 

production. Because about 80 percent of the gas 

originally in place is now recovered, paramarginal 

and submarginal resources in ordinary gas reservoirs 

are not as large as for crude oil. Paramarginal and 

submarginal gas resources may be significant, however, in kinds of rocks from which gas is not now 

recovered, namely impermeable strata and coal. In 

the Rocky Mountain province, for instance, Haun, 

Barlow, and Hallinger (1970) recently estimated 
14 UNITED STATES MINERAL RESOURCES 

TABLE 2.-Some estimates of U.S. crude-oil reserves and resources, in billion barrels 

[API, American Petroleum Institute; NPC, National Petroleum Council] 

In identified fields or stuctures In undiscovered fields and structures 

Proved Probable-possible (speculative) 

Recoverable at present rate 1 ---------------

Additional at 42 percent recovery ---------- Additional at 60 percent recovery -----------

Oil originally in place ----------------------

31 (API) 

47 (NPC) 

69 (NPC) 

74 (NPC) 

22 (NPC) 

40 (NPC) 

227 (NPC) 

67 (NPC) 

21 (NPC) 

37 (NPC) 

388 (API) 209 (NPC) 2 

Total oil originally in place ----------------- Ultimate production 2 

---------------------

2200 (Hendricks and Schweinfurth, 1968). 

190 (Hubber.t, 19·69); 353 (Moore, 1966); 433 (Weeks) 3

; 450 (Elliott 

and Linden; 1968); 432-495 (NPC); 550 (Hendricks and Schweinfurth, 1968) . 

1 Average recovery is 30 percent of oil in place. 2 Includes past production of 86 billion barrels. 8 See McKelvey (1968, Table II, p. 18). 

potential gas resources in ordinary reservoirs to be 

in the range of 100 to 200 trillion cubic feet, but 

pointed out that gas in impermeable strata which 

might be released by nuclear stimulation would be 

several times that amount. Gas occluded in coalnow only a menace in this country as a cause of 

explosions-is already recovered in some European 

mines and is also a potentially large resource. 

The uncertainties concerning potential coal resources center not on their total magnitude, as they 

do for oil and gas, but on the amounts available at 

present prices. Because coal beds have great lateral 

continuity, geologie mapping and stratigraphic studies make it possible to project them long distances 

from their outcrops and to categorize them in terms 

of thickness of beds, thickness of overburden, rank 

of coal, and other features that affect cost. The Geological Survey has prepared such estimates, but the 

cost of recovering coal in the various categories has 

yet to be determined. Coal in beds more than 14 

inches thick totals at least 3.3 trillion tons in the 

United States, but estimates of the amounts minable at present prices have ranged from 20 to 220 

billion tons. (See U.S. Office of Science and Technology, "Energy R and D and National Progress.") 

Because 20 billion tons represents nearly a 40-year 

supply at present rates of consumption, it is easy 

to see why the studies needed to determine how 

much would be available at various costs have not 

been undertaken. The question is by no means only 

of academic interest, for the nuclear power development program was justified in part in its early years 

on the assumption that reserves of low-cost coal 

were extremely limited, and part qf the continued 

growth of the nuclear power industry is said to be 

the result of the difficulty power companies are 

having in acquiring low-cost reserves. 

QUANTIFYING THE UNDISCOVERED 

Considering potential resources in the degree-ofcertainty, cost-of-recovery framework brings out 

the joint role that geologists, engineers, mineral 

technologists, and economists must play in estimating their magnitude. Having emphasized the importance of the economic and technologic side of 

the problem, I want now to turn to the geological 

side and consider the problem of how to appraise 

the extent of undiscovered reserves and resources. 

It is difficult enough to estimate the extent of unexplored resources of the inferred or possible class. 

In fact, it is even difficult to estimate measured or 

proved reserves with a high degree of accuracy until 

they have been largely mined out. Thus, estimates 

of proved reserves prepared in advance of appreciable production commonly have an error of about 

25 percent, and the error in estimates of incompletely explored deposits is usually much larger. 

Generally the combination of the geologist's inherent 

conservatism and the lack of information on the 

geology of concealed areas leads to estimates that 

err in being too low rather than too high. 

One eminent mining geologist reported that, having recognized these effects, he once arbitrarily 

tripled his calculations to arrive at an estimate of 

the ore remaining in a producing district; twice the 

amount of his inflated estimate, however, was found 

and mined over the next 2{) years, and more was in 

prospect. To match many such stories are at least 

a few prematurely deserted mills and mine installations built on the expectation of finding ore that 

did not materialize. Both kinds of experiences emphasize the difficulty of appraising the extent of 

mineral deposits even in partly explored areas. In 

the light of such experiences one is justified in asking-as many well-informed people have--whether 

estimates of the magnitude of undiscovered deposits 

can have enough reliability to make them worthwhile. 

The fact that new districts are still being discovered for nearly every commodity and that large 

areas favorable for the occurrence of minerals of 

all kinds are covered by alluvium, volcanics, glacial 
MINERAL RESOURCE ESTIMATES AND PUBLIC POLICY 15 

drift, seawater, or other materials that conceal possible mineral-bearing rocks or structures assures us 

that undiscovered deposits are still to be found. 

Qualitatively, at least, we know something about 

the distribution of minerals with respect to other 

geologic phenomena and, if this is so, we have a 

chance of developing quantitative relations that will 

give us at least a start. 

Two principal approaches to the problem have 

been taken thus far. One is to extrapolate observations related to rate of industrial activity, such as 

annual production of the commodity; the other is to 

extrapolate observations that relate to the abundance of the mineral in the geologic environment 

in which it is found, 

The first of these methods has been utilized by 

M. K. Hubbert (1969), C. L. Moore (1966), and 

M. A. Elliott and H. R. Linden (1968) in estimating ultimate reserves of petroleum. The essential 

ff'.atures of this approach are to analyze the growth 

in production, proved reserves, and discovery per 

foot of drilling over time and to project these rate 

phenomena to terminal values in order to predict 

ultimate production. Hubbert has used the logistic 

curve for his projections, and Moore has utilized the 

Gompertz curve, with results more than twice as 

high as those of Hubbert. As Hubbert has pointed 

out, these methods utilize the most reliable information collected on the petroleum industry; modern 

records on production, proved reserves, number of 

wells drilled, and similar activities are both relatively complete and accurate, at least as compared 

with quantitative knowledge about geologic features 

that affect the distribution of petroleum. 

The rate methods, however, have an inherent 

weakness in that the phenomena they analyze reflect 

human activities that are strongly influenced by 

economic, political, and other factors that bear no 

relation to the amount of oil or other material that 

lies in the ground. Moreover, they make no allowance for major breakthroughs that might transform 

extensive paramarginal or submarginal resources 

into recoverable reserves, nor do they provide a 

means of estimating the potential resources of unexplored regions. Such projections have some value 

in indicating what will happen over the short term 

if recent trends continue, but they can have only 

limited success in appraising potential resources. 

Even the goal of such projections, namely the 

prediction of ultimate production, is not a useful 

one. Not only is it impossible to predict the quantitative effects of man's future activities but the concept implies that the activities of the past are a 

part of an inexorable process with only one possible outcome. Far more useful, in my opinion, are 

estimates of the amounts of various kinds of materials that are in the ground in various environments ; such estimates establish targets for both the 

explorer and the technologist, and they give us a 

basis for choosing among alternative ways of meeting our needs for mineral supplies. 

The second principal approach taken thus far to 

the estimation of undiscovered resources involves 

the extrapolation of data on the abundance of mineral deposits from explored to unexplored ground 

on the basis of either the area or the volume of 

broadly favorable rocks. In the field of metalliferous 

deposits, Nolan (1950) pioneered in extrapolation 

on the basis of area in his study of the spatial and 

size distribution of mineral deposits in the Boulder 

Dam region and in his conclusion that a similar 

distribution should prevail in adjacent concealed 

and unexplored areas. Weeks (1958, 1965) and Pratt 

(1950) played similar roles with respect to the estimation of petroleum resources-Weeks extrapolating on the basis of oil per unit volume of sediment 

and Pratt on the basis of oil per unit area. Many 

of the estimates of crude oil that went into the 

NPC study were made by the volumetric method, 

utilizing locally appropriate factors on the amount 

of oil expected per cubic mile of sediment. Olson and 

Overstreet (1964) have since used the area method 

to estimate the magnitude of world thorium resources as a function of the size of areas of igneous 

and metamorphic rocks as compared with India and 

the United States, and A. P. Butler (written commun., 1958) used the magnitude of sandstone uranium ore reserves exposed in outcrop as a basis for 

estimating the area in back of the outcrop that is 

similarly mineralized. 

Several years ago, Zapp (1962) and Hendricks 

(1965) introduced another approach, based on the 

amount of drilling required to explore adequately 

the ground favorable for exploration and the reserves discovered by the footage already drilleda procedure usable in combination with either the 

volumetric or areal approach. Recently J. B. Zimmerman and F. L. Long (cited in "Oil and Gas 

Journal, 1969") applied this approach to the estimation of gas resources in the Delaware-Val Verde 

basins of west Texas and southeastern New Mexico; 

and Haun, Barlow, and Hallinger (1970) used it to 

estimate potential natural gas resources in the 

Rocky Mountain region. In the field of metals, 

Lowell (1970) has estimated the number of undiscovered porphyry copper deposits in the southwestern United States, Chile and Peru, and British Columbia as a function of the proportion of the 
16 UNITED STATES MINERAL RESOURCES 

favorable pre-ore surface adequately explored by 

drilling, and Armstrong (1970) has similarly estimated undiscovered uranium reserves in the Gas 

Hills area of Wyoming on the basis of the ratios 

between explored and unexplored favorable areas. 

I have suggested another variant of the areal 

method for estimating reserves of nonfuel minerals 

which is based on the fact that the tonnage of 

minable reserves of the well-explored elements in 

the United States is roughly equal to their crustal 

abundance in percent times a billion or 10 billion 

(fig. 5). Obviously this relation is influenced by the 

If) 

z 

g 109 

1-

a: 

0 

I: 

If) 

z 

....:107 

~ 

If) 

w 

> 

a: 

w 

If) 

w 

a: 105 

~ 

II/) 

w 

::?; 

0 

c 

103~~~~~~=w~~~~WL~~~u=~~w 

10-6 10-4 H)-2 1 

ABUNDANCE (A) IN EARTH'S CRUST, IN PERCENT 

FIGURE 5.-Domestic reserves of elements compared to their 

abundance in the earth's crust. Tonnage of ore minable 

now is shown by a dot; tonnage of lowergrade ores whose 

exploitation depends upon future technological advances 

or higher prices is shown by a bar. 

extent of exploration, for it is only reserves of the 

long-sought and well-explored minerals that display 

the relation to abundance. But it is this feature 

that gives the method its greatest usefulness, for 

it makes it possible to estimate potential resources 

of elements, such as uranium and thorium, that 

have been prospected for only a short period. Sekine 

(1963) tested this method for Japan and found it 

applicable there, which surprised me a little, for I 

would not have thought Japan to be a large enough 

sample of the continental crust to bring out this 

relationship. 

The relation between reserves and abundance, of 

course, can at best be only an approximate one, useful mainly in order-of-magnitude estimates, for 

obviously crustal abundance of an element is only 

one of its properties that lead to its concentration. 

That it is an important factor, however, may be 

seen not only in its influence on the magnitude of 

reserves but also in other expressions of its influence 

on the concentrations of the elements. For example, 

of the 18 or so elements with crustal abundances 

greater than about 200 parts per million, all but 

fluorine and strontium are rock forming in the 

sense that some extensive rocks are composed chiefly 

of minerals of which each of these elements is a 

major constituent. Of the less abundant elements, 

only chromium, nitrogen, and boron have this distinction. Only a few other elements, such as copper, 

lead, and zinc, even form ore bodies composed 

mainly of minerals of which the valuable element 

is a major constituent, and in a general way the 

grade of minable ores decreases with decreasing 

crustal abundance. A similar gross correlation exists 

between abundance of the elements and the number 

of minerals in which they are a significant constituent . 

Members of a committee of the Geology and the 

Conservation of Mineral Resources Board of the 

Soviet Union have described a somewhat similar 

method for the quantitative evaluation of what they 

call predicted reserves of oil and gas, based on estimates of the total amount of hydrocarbons in the 

source rock and of the fraction that has migrated 

into commercial reservoirs--estimates that would 

be much more difficult to obtain for petroleum than 

for the elements. Probably for this reason not much 

use has been made of this method, but it seems 

likely that quantitative studies of the effects of the 

natural fractionation of the elements might be of 

some value in estimating total resources in various 

size and grade categories. 

Some studies of the grade-frequency distribution 

of the elements have, in fact, been undertaken by 

geochemists in the last couple of decades, and, 

taking off from Nolan's work, several investigators 

have studied the areal and size-frequency distribution of mineral deposits in conjunction with attempts to apply the methods of operations research 

to exploration (for example, Allais, 1957; Slichter, 

1960; Griffiths, 1964; DeGeoffroy and Wu, 1970, 

and Harris and Euresty, 1969). None of these studies has been concerned . with the estimation of undiscovered reserves, but they have identified two 

features about the distribution of mineral deposits 

that may be applicable to the problem. 

One is that the size distribution of both metalliferous deposits, expressed in dollar value of production, and of oil and gas, expressed in volumetric 

units, has been found to be log normal, which means 
MINERAL RESOURCE ESTIMATES AND PUBLIC POLICY 17 

that of a large population of deposits, a few contain 

most of the ore (for example, Slichter, 1960; Kaufman, 1963) . In the Boulder Dam area, for example, 

4 percent of the districts produced 80 percent of the 

total value of recorded production. The petroleum 

industry in the United States has a rule of thumb 

that 5 percent of the fields account for 50 percent 

of the reserves and 50 percent of fields, for 95 percent. And in the USSR, about 5 percent of the oil 

fields contain about 75 percent of the oil, and 10 

percent of the gas fields have 85 percent of the 

gas reserves. 

The other feature of interest is that in many deposits the grade-tonnage distribution is also log 

normal, and the geochemists have found this to be 

the case also with the frequency distribution of 

minor elements. 

These patterns of size- and grade-frequency distribution will not in themselves provide information 

on the magnitude of potential resources, for they 

describe only how minerals are distributed and not 

how much is present. But if these patterns are combined with quantitative data on the incidence of 

congeneric deposits in various kinds of environments, the volume or area of favorable ground, and 

the extent to which it has been explored, they might 

yield more useful estimates of potential resources 

than are obtainable by any of the procedures so far 

applied. Thus, estimates of total resources described 

in terms of their size- and grade-frequency distributions could be further analyzed in the light of 

economic criteria defining the size, grade, and accessibility of deposits workable at various costs, 

and then partitioned into feasibility-of-recovery and 

degree-of-certainty categories to provide targets for 

exploration and technologic development as well as 

guidance for policy decisions. 

Essential for such estimates, of course, is better 

knowledge than is now in hand for many minerals 

on the volume of ore per unit of favorable ground 

and on the characteristics of favorable ground itself. 

For petroleum the development of such knowledge 

is already well advanced. For example, whereas most 

estimates of resources have been based on an assumed average petroleum content of about 50,000 

barrels per cubic mile of sediment, varied a little 

perhaps to reflect judgments of favorability, the 

range in various basins is from 10,000 to more than 

2,000,000 barrels per cubic mile. As shown by the 

recent analysis by Halbouty and his colleagues 

(1970) of the factors affecting the formation of 

giant fields, the geologic criteria are developing that 

make it possible to classify sedimentary basins in 

terms of their petroleum potential. Knowledge of 

the mode of occurrence and genesis of many metalliferous minerals and of the geology of the terranes 

in which they occur is not sufficient to support comprehensive estimates prepared in this way. But for 

many kinds of deposits enough is known to utilize 

this kind of approach on a district or regional basis, 

and I hope a start can soon be made in this direction. 

NEED FOR REVIEW OF RESOURCE 

ADEQUACY 

Let me return now to the question of whether or 

not resources are adequate to maintain our present 

level of living. This is not a new question by any 

means. In 1908 it was raised as a national policy 

issue at the famous Governors' Conference on Resources, and it has been the subject of rather extensive inquiry by several national and international 

bodies since then. In spite of some of the dire predictions about the future made by various people 

in the course of these inquiries, they did not lead 

to any major change in our full-speed-ahead policy 

of economic development. Some of these inquiries, 

in fact, led to immediate investigations that revealed a greater resource potential for certain 

minerals than had been thought to exist, and the 

net effect was to alleviate rather than heighten 

concern. 

Now, however, concern about resource adequacy 

is mounting again. The overall tone of the recent 

National Academy of Sciences' report on "Resources 

and Man" was cautionary if not pessimistic about 

continued expansion in the production and use of 

mineral resources, and many scientists, including 

some eminent geologists, have expressed grave 

doubts about our ability to continue on our present 

course. The question is also being raised internationally, particularly in developing countries where 

concern is being expressed that our disproportionate 

use of minerals to support our high level of living 

may be depriving them of their own future. 

Personally, I am confident that for millennia to 

come we can· continue to develop the mineral supplies needed to maintain a high level of living for 

those who now enjoy it and raise it for the impoverished people of our own country and the world. 

My reasons for thinking so are that there is a 

visible undeveloped potential of substantial proportions in each of the processes by which we create 

resources and that our experience justifies the belief that these processes have dimensions beyond 

our knowledge and even beyond our imagination at 

any given time. 

Setting aside the unimaginable, I will mention 

some examples of the. believable. I am sure all geolo-
18 UNITED STATES MINERAL RESOURCES 

gists would agree that minable undiscovered deposits remain in explored as well as unexplored areas 

and that progress in our knowledge of regional 

geology and in exploration will lead to the discovery of many of them. With respect to unexplored 

areas, the mineral potential of the continental margins and ocean basins deserves particular emphasis, 

for the technology that will give us access to it is 

clearly now in sight. For many critical minerals, 

we already know of substantial paramarginal and 

submarginal resources that experience tells us 

should be brought within economic reach by technological advance. The process of substituting an 

abundant for a scarce material has also been pursued successfully, thus far not out of need but out 

of economic opportunity, and plainly has much potential as a means of enlarging usable resources. 

Extending our supplies by increasing the efficiency of recovery and use of raw materials has 

also been significant. For example, a unit weight 

of today's steel provides 43 percent more structurai 

support than it did only 10 years ago, reducing proportionately the amount required for a given purpose. Similarly, we make as much electric power 

from 1 ton of coal now as we were able to make 

from 7 tons around the turn of the century. Our 

rising awareness of pollution and its effects surely 

will force us to pay even more attention to increasing the efficiency of mineral recovery and use as a 

means of reducing the release of contaminants to 

the environment. For similar reasons, we are likely 

to pursue more diligently processes of recovery, reuse, and recycling of mineral materials than we 

have in the past. 

Most important to secure our future is an abundant and cheap supply of energy, for if that is 

available we can obtain materials from low-quality 

sources, perhaps even country rocks, as Harrison 

Brown (1954, p. 174--175) has suggested. Again. I 

am personally optimistic on this matter, with respect to the fossil fuels and particularly to the 

nuclear fuels. Not only does the breeder reactor 

appear to be near enough to practical reality to 

justify the belief that it will permit the use of 

extremely low-grade sources of uranium and thorium that will carry us far into the future, but during the last couple of years there have been exciting 

new developments in the prospects for commercial 

energy from fusion. Gothermal energy has a large 

unexploited potential, and new concepts are also 

being developed to permit the commercial use of 

solar energy. 

But many others do not share these views, and it 

seems likely that soon there will be a demand for a 

confrontation with the full-speed-ahead philosophy 

that will have to be answered by a deep review of 

resource adequacy. I myself think that such a review is necessary, simply because the stakes have 

become so high. Our own population, to say nothing 

of the world's, is already too large to exist without 

industrialized, high energy- and mineral-consuming 

agriculture, transportation, and manufacturing. If 

our supply of critical materials is enough to meet 

our needs for only a few decades, a mere tapering 

off in the rate of increase of their use, or even a 

modest cutback, would stretch out these supplies 

for only a trivial period. If resource adequacy cannot be assured into the far-distant future, a major 

reorientation of our philosophy, goals, and way of 

life will be necessary. And if we do need to revert 

to a low resource-consuming economy, we will have 

to begin the process as quickly as possible in order 

to avoid chaos and catastrophe. 

Comprehensive resource estimates will be essential for this critical examination of resource adequacy, and they will have to be made by techniques 

of accepted reliability. The techniques I have described for making such estimates have thus far 

been applied to only a few minerals, and none of 

them have been developed to the point of general 

acceptance. Better methods need to be devised and 

applied more widely, and I hope that others can be 

enlisted in the effort necessary to do both. 

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Buyalov, N. I., Erofeev, N. S., Kalinen, N. A., Kleschev, 

A. I., Kudryashova, N. M., L'vov, M. S., Simakov, S. N., 

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DeGeoffroy, J., and Wu, S. M., 1970, A statistical study of 

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Elliott, M. A., and Lind'=:n, H. R., 1968, A new analysis of 

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v. 20, p. 135-141. 
MINERAL RESOURCE ESTIMATES AND PUBLIC POLICY 19 

Griffiths, J. C., 1962, Frequency distributions of some natural 

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198. 

--- 1964, Exploration for natural resources: Operations 

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Sr., Klemme, H. D., and Shabad, Theodore, 1970; Giant 

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Harris, D. P., and Euresty, D., 1969, A preliminary model 

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--- 1950, How tonnage and grade relations help predict 

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GPO 865·199