TRACKING RESOURCES AND ESTIMATING FUTURE SUPPLIES

Mineral resources are the building blocks of civilization and understanding their distribution, production, and future supplies is necessary for decision making on many different levels. The U.S. Geological Survey supports data collection (e.g., annual Mineral Commodity Summaries) and research on a wide variety of nonfuel mineral resources (e.g., SIR-5220: The Principal Rare Earth Elements Deposits of the United States—A Summary of Domestic Deposits and a Global Perspective). Research is conducted to understand the geologic processes that control how and where ore deposits form and to probabilistically estimate (or assess) quantities, qualities, and areas of undiscovered mineral resources that can serve as potential future supply.

Estimating future supplies of mineral resources can be done in several different ways including extrapolating from detailed compilations of known deposits (e.g., Jowitt et al., 2013), theoretical models such as the Kesler and Wilkinson (2008) tectonic diffusion model, and the USGS 3-part assessment protocol (Singer and Menzie, 2010). The first step is the creation of global grade and tonnage models to establish frequency distributions of tonnages and average grades of well-explored deposits of the type being assessed. The second step is delineation of permissive tracts for each deposit type under consideration. The third step is estimation of the number of undiscovered deposits in each tract based upon known geology and deposit models outlining the essential characteristics of that deposit type. These can then be aggregated for an overall estimate of the undiscovered resource in a given region.

All of these methods are constrained by historical trends of price and technology. Radical changes in prices such as in 1971 when the US dollar was no longer pegged to gold at $35/oz or in technology such as the advent of open pit mining or the use of heap-leaching have enabled mining of rock that was previously considered “worthless”. Future developments such as direct extraction of elements from sea water (Cathles, 2010) also have been proposed as game changers. Thus, estimates of future supplies of mineral resources should be viewed as a snapshot of a moving target rather than of a fixed quantity.