FIGURE 12.3 Mineral resources are either known or undiscovered. Those that have been identified and are profitable to mine are called reserves. Those believed to exist in areas of know deposits but have yet to be located are considered hypothetical resources; all other mineral resources are speculative.
In order to quantify the value of their mineral resources, mining companies and governments will typically classify their holdings based on economic status. For example, the U.S. Geological Survey uses the term mineral resource to describe those deposits that are feasible to mine using existing technology. This definition simply means the technical ability to extract the minerals exists, but says nothing about its profitability. A mineral reserve, on the other hand, is a deposit that is economical to extract under current conditions. As shown in Figure 12.3, this classification makes it possible for geologists to quantify what is referred to as total mineral reserves, which represents all the known deposits currently economical to mine. The remaining know deposits are then combined with some estimate of deposits yet to be found, providing what is called the total mineral resource. This concept is important because it allows economists to estimate how much of a particular resource is available to the global marketplace at any given time. The ratio of reserves to resources, of course, will vary as supply and demand affects the market price for a particular resource. Should demand decrease or supply increase, prices will fall and many marginally economical mining operations will shut down, causing the total reserves to decrease. The opposite will occur when demand goes up or supply goes down. Oftentimes the driving force behind these changes are updated or new technologies that allow lower-grade deposits to be mined.
Geology of mineral Resources
In this section we will explore some of the more common geologic processes that result in crustal elements becoming concentrated, thereby forming enriched mineral deposits. These enrichment processes operating within the Earth system will be broken down into igneous, metamorphic, sedimentary, and weathering processes.