Models for the estimation of world ore reserves

Abstract

Although mineral resources are non-renewable, mineral reserves can be created by new discoveries and from already identified sub-economic resources. A probabilistic model is presented to adjust reserve estimates to changes in minimum workable grade. This model is based upon a rational frequency distribution for the dependence of tonnage on cut-off and average grade. For this purpose the straight lognormal transformation is rejected, and replaced by a logarithmic, three-parameter transformation of wider applicability, including negatively skewed distributions of iron, bauxite, and phosphate deposits. The estimation of ore reserves occasionally serves the restricted purpose of the commercial evaluation of mining property. Yet, more often such estimates have a wider scope: up to forecasts of the adequacy to supply the future needs of a country or the world.