A mineral resource is “a concentration of naturally occurring solid, liquid, or gaseous ma- terial,inorontheearth’scrust,insuchform and amount that economic extraction of a com- modity from the concentration is currently or potentially feasible” (Craig et al., 1998:20). The size and nature of many mineral resources are well known, whereas others are undiscovered and totally unknown. Figure 3–1 shows a spectrum of resources that diVer in their degree of certainty, commonly described as measured, indicated, in- ferred, hypothetical, and speculative. Another important dimension is the economic feasibil- ity or cost of extracting and using the resources. Some resources are currently profitable to exploit; others may be economical in the future, but cur- rently are not. Along this dimension,.
