MINERAL RESERVES, RESOURCES, RESOURCE POTENTIAL, 

AND CERTAINTY 

D EFINITIONS OF MINERAL RESERVES, 

resources, resource potential, and certainty of 

assessment have been adopted by the Geological 

Survey and U.S. Bureau of Mines to foster more 

uniform terminology and more accurate communication. The exact nomenclature used depends on the 

commodity being described, but the unified terminology can be applied to all commodities. 

The terminology of McKelvey (1972) for both 

discovered and undiscovered mineral resources, 

modified by Brobst and Pratt (1973, p. 1-8), has been 

adopted with minor changes for joint use by the U.S. 

Bureau of Mines and U.S. Geological Survey (1976a, 

b, 1980). This terminology applies to the description 

of the mineral endowment of an area. Resource 

assessment studies evaluate the likelihood of the 

occurrence of mineral deposits (resources) in terms of 

levels of mineral resource potential and the certainty 

of the assessment (Goudarzi, 1984). The likelihood of 

occurrence is not a measure of the resources themselves; consequently, the McKelvey classification 

should not be used in assessment studies except for 

descriptions of identified resources. 

RESERVES AND RESOURCES 

The total mineral endowment of an area is divided 

into two major parts: identified resources and undiscovered resources. These, in turn, are subdivided 

on the basis of the adequacy of knowledge about the 

deposits and current economic factors (fig. 21). The 

definitions of reserve and resource terms as follows 

are quoted or paraphrased from Geological Survey 

Circular 831 (U.S. Bureau of Mines and U.S. 

Geological Survey, 1980). 

Resource. A concentration of naturally occurring 

solid, liquid, or gaseous materials in or on the 

Earth's crust in such form that economic extraction 

of a commodity is regarded as feasible, either currently or at some future time. 

Identified resource. A resource whose location, 

grade, quality, and quantity are known or can be 

estimated from specific geologic evidence. Identified 

resources include economic, marginally economic, 

and subeconomic resources. 

Undiscovered resources. Undiscovered bodies of 

mineral-bearing material whose existence is surmised from broad (regional) knowledge and theory. 

Reserve. That portion of an identified resource from 

which a usable mineral or energy commodity can be 

economically and legally extracted at the time of 

determination. The term "ore" applies to reserves 

of some kinds of mineral commodities, generally 

metallic, but for want of another term it is sometimes applied to nonmetallic commodities. 

Definitions given here for "measured," "indicated," 

and "inferred" resources may be applied to both identified economic resources (reserves) and identified 

subeconomic resources. 

Measured. Materials whose quality and quantity 

have been determined, within a margin of error of 

less than 20 percent, by quantitative data, including 

appropriate analyses, from closely spaced and 

geologically well-known sample sites. 

Indicated. Materials whose quality and quantity 

have been estimated partly from analyses and 

measurements and partly from reasonable geologic 

inferences. 

Demonstrated. A collective term for the sum of 

materials in both measured and indicated resources. 

Inferred. Materials in identified but unexplored 

deposits whose quality and quantity have been 

estimated from geologic projections. 

The terms "hypothetical resource" and "speculative 

resource" apply to undiscovered resources and are 

useful when estimating resource endowment. 

Hypothetical resources. Undiscovered materials 

that may reasonably be expected to exist in known 

mining districts under known geologic conditions. 

Speculative resources. Undiscovered materials that 

may occur in known types of deposits in geologic 

settings where no previous discoveries have been 

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

remain to be recognized. 

The terms "proved," "probable," and "possible" 

are commonly used by industry for economic evaluations of ore in specific deposits or districts. "Proved" 

Mineral reserves, resources, resource potential, and certainty 95 
Ll Cumulative 

.. IDENTIFIED RESOURCES - - - UNDISCOVERED RESOURCES 

I I 

n! 43 

$ 

E 

1 Indicated hfwd l*;-I 

MARGINALLY 

ECONOMlC 

1 Inferred reserves 

- Increasing degree of 

geologic assurance 

Marginal reserves 

I 

Demonstrated 

subeconomic resources 

Figure 21. Classification of mineral resources (from U.S. Bureau of Mines and U.S. Geological Survey, 1980, p. 5) 

corresponds closely to "measured." "Probable" and 

"possible" usually describe estimates of partly sampled deposits; both fall within the meaning of the 

term "indicated" as here defined. 

The Survey author's estimate of reserves and 

resources for a district or area should nearly always 

be presented in such a way as to conceal figures for 

individual properties. Quotation of published estimates 

is permissible so long as they are properly ascribed. 

Inferred 

marginal reserves 

Inferred 

subeconomic 

resources 

MINERAL RESOURCE POTENTIAL AND 

+ - 

I 

Mineral-assessment reports use a dual scheme based 

on two ratings, "resource potential" and "certainty" 

(fig. 22). The general format for the scheme was suggested by Voelker and others (1979). As shown by 

figure 22, the level of resource potential expresses the 

favorability of the area for a given resource; the level 

of certainty indicates the confidence with which the 

level of resource potential was assigned (Goudarzi, 

1984). 

The definition of mineral resource potential and of 

the several levels of resource potential follow the suggestions of Taylor and Steven (1983) for use in joint 

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

assessment reports (Goudarzi, 1984). 

Mineral resource potential is the likelihood for the 

occurrence of undiscovered mineral resources in 

a defined area; it is closely related to mineralresource favorability. The term "resource potential" 

is preferred for the description of an area; 

"resource favorability" is preferred for description 

of a specific rock mass or geologic environment. 

Low potential is assigned to areas where geologic, 

geochemical, and geophysical characteristics define 

environments in which the existence of resources is 

unlikely. This broad category embraces areas that 

have dispersed but insignificantly mineralized rock, 

as well as areas that have few or no indications of 

having been mineralized. 

Moderate potential is assigned to areas (1) where 

geologic, geochemical, and geophysical characteristics indicate environments favorable for resource 

occurrence, (2) where interpretations of data indicate a reasonable likelihood of resource accumulation, and (3) where application of knowledge of 

types of mineral deposits indicates favorable ground 

for specific types of deposits. 

High potential is assigned to areas (1) where geologic, geochemical, and geophysical characteristics 

indicate environments favorable for resource occurrence, (2) where interpretations of data indicate a 

96 Mineral resource potential and certainty 
high degree of likelihood for resource accumulation, 

(3) where knowledge of types of mineral deposits 

supports determinations of the presence of 

resources, and (4) where data indicate that minerals 

have concentrated in at least a part of the area. 

Resources or deposits need not be identified for an 

area to have high resource potential. 

Unknown potential is assigned to areas where information is inadequate to assign low, moderate, or 

high levels of potential; this category is generally 

used for areas that have covering rock units and 

have inadequate geophysical and geochemical data. 

The phrase "no potential" should be applied only to 

a specific kind of resource in a carefully defined 

area; it should not be used as a summary rating for 

all commodities in any area. 

The level of certainty applied to a rating of 

resource potential indicates the degree of confidence 

with which the rating was assigned. The level of certainty should reflect (1) the adequacy of the geologic, 

geochemical, and geophysical data available at the 

time of evaluation, and (2) how well the specific 

deposit type being evaluated is understood. Generally, 

the attributes of a mineral-deposit type are determined first, specific requirements for assignment of 

high, moderate, and low potential are determined 

next, and the nature and amount of data required for 

assignment of level of certainty are determined last. 

Level A. Available information is not adequate to 

determine the level of mineral resource potential; 

this level of certainty is assigned when the area is 

assigned unknown resource potential for a specific 

commodity. 

Level B. Available information suggests the level of 

resource potential; level B is assigned where the 

general geologic environment is known but key 

evidence is lacking on such aspects as rock units, 

structure, activity of resource-forming processes, or 

expectable types of mineral deposits. 

Level C. Available information gives a good indication 

of the level of mineral resource potential; level C 

is used where geologic environments are clearly 

defined but where specific evidence is inadequate to 

evaluate past activity of resource-forming processes 

(mineralization). 

Level D. Available information clearly defines the 

level of mineral resource potential; generally level D 

is used where geologic environments are clearly 

defined, activity or lack of activity of resourceforming processes can be ascertained, and data 

on expectable mineral-deposit types are well 

understood. 

B 

LEVEL OF CERTAINTY 

Figure 22. Mineral-assessment classification based on 

level of resource potential versus level of certainty 

(based on Voelker and others, 1979). 

UIA 

UNKNOWN 

POTENTIAL 

The approach to resource evaluation should be 

aggressive and basically optimistic-even imaginative 

and daring. Undiscovered resources will remain undiscovered as long as investigations are limited to 

an inventory of known deposits or as long as investigators fail to use carefully reasoned geologic 

predictions to suggest the likelihood of resource 

occurrences. Conclusions must be based solidly on 

evidence, the criteria for conclusions must be stated 

clearly, and an account of the logic used in the analysis must be provided. The assessment should state the 

date of the assessment: although the rocks change 

very slowly, our understanding of them may change 

rapidly. 

HIC 

HYiH POTENTIAL 

MIC 

MODERATE POTENTIAL 

UC 

LOW 

POTENTIAL 

HIB 

HIGH POTENTIAL 

MIB 

WOOERATE POTENTUL 

UB 

LOW 

POTENTIAL 

Levels of certainty 97 

HID 

HIGH POTENTIAL 

MID 

WOOERATE POTENTIAL 

UD 

LOW POTENTIAL 

NID 

No POTENTIAL