UNITED STATES MINERAL RESOURCES 



— Degree of certainty of existence 



EXPLANATION 



Potential resources = Conditional + Hypothetical 

 + Speculative 



Figure 1. — ^Classification of mineral resources used in this 

 volume. 



reserves — 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 technologic- 

 ally minable at present, and to this important cate- 

 gory of identified but subeconomic resources we 

 apply the informal term conditional resources — 

 resources that may eventually become reserves when 

 conditions of economics or technology are met. 

 Conditional resources have an immediate potential, 

 because they are knoion, and their assessment pro- 

 vides 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 cate- 

 gories. Hypothetical resources are here defined as 

 undiscovered resources that we may still reasonably 

 expect to find in knoivn districts; speculative re- 

 sources 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 resources 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 favor- 

 able ground. A different kind of geologic perspec- 

 tive, 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 quan- 

 tify the resource potential of sedimentary basins 

 that are known to exist but have not been suffi- 

 ciently tested for uranium. 



Resources of copper can be used as another ex- 

 ample of the distinction between hypothetical and 

 speculative resources. We are justified in hypothe- 

 sizing, for instance, that porphyry copper deposits 

 are concealed under basin fill in and near the known 

 copper districts of the southwest, whereas the dis- 

 covery in recent years of porphyry-type copper de- 

 posits 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 cur- 

 rently being mined principally in Nevada and Ar- 

 kansas. 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 — specula- 

 tive 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 distinc- 

 tion is that it has forced us to realize that the 

 speculative resources of some commodities are rela- 

 tively low. From a worldwide geologic perspective, 

 we can say that the regions with significant poten- 

 tial for discovery of iron, or phosphorite, or marine 

 evaporites, are largely known; thus, the significant 

 undiscovered resources fall under the heading of 



