An assessment is any effort to express an opinion or make an estimate using sound and reasonable evaluation. Mineral assessments, particularly of undiscovered resources, provide important opportunities and challenges for earth scientists. Assessments create the opportunity to communicate with people outside our area of expertise and to engage in discussions about global issues that affect the future well-being of people around the planet. These studies are challenging because they require us to forecast the future, an uncomfortable task for most scientists. An additional challenge is to report our findings in ways that can be considered in relation to the diverse values, goals, and interests of a large population.
To meet these challenges, resource assessments conducted by the U.S. Geological Survey (USGS) are guided by several principles (Singer, 1993; Charpentier and Klett, 2005): 1) the process must be designed to minimize bias; 2) the degree of uncertainty associated with the assessment should be explicitly expressed; 3) the methodology and course of the assessment should be consistent and documented as transparently as possible, within the limits imposed by the inevitable use of subjective judgment; and 4) the multiple uses for an assessment requires a continuing effort to provide the documentation in such ways as to increase utility to the many types of users.
The USGS currently is conducting a cooperative international study to: (1) outline permissive areas (tracts) and estimate the probable amounts of the world’s undiscovered resources of copper, platinum-group elements (PGE), and potash, and (2) provide a consistent and globally comprehensive analysis of these undiscovered nonfuel mineral resources. Our form of assessment uses deposit models to delineate permissive tracts for undiscovered deposits and grade-tonnage models to describe ore characteristics for each deposit type. Probabilistic estimates of numbers of undiscovered deposits are combined with grade-tonnage models by Monte Carlo simulation to calculate probable amounts of undiscovered resources.
Like most assessments, our study will be incomplete because we are focusing on only a few aspects of mineral resources. However in the process, we are identifying areas where more information is needed and new research is required. Even so, we will provide an assessment with geologically based results in a format that permits economic analysis and integration into decision-support systems.