REVISÃO E RECOMENDAÇÕES PARA O CALCULO E CLASSIFICAÇÃO DE RESERVAS MINERAIS

Abstract

This paper presents a review of ore reserve classification schemes adopted in Brazil, as well as recommendations for computing and classifying ore reserves. Ore reserve classification scheme aims at sorting computed reserves in classes according to the corresponding confidence levels. The mineral reserve is a part of geological resource that can be mined with profit at the time of its determination. The degree of confidence is a function of natural variability of mineral deposits, as measured by the coefficient of variation. However, it is important to observe that for deposits presenting high variability, exploration does not furnish sufficient information for classes of higher confidence. According to modern trends, reserves are estimated from resource models. Resources are classified in decreasing order of confidence as measured, indicated or inferred. Estimated reserves from resources, after considering economical, mining, metallurgical, marketing, legal, environmental, social and political factors, are classified in proved and probable, in decreasing order of confidence, which are derived from measured and indicated resources, respectively. In 1990, the National Department of Mineral Production (DNPM, Brazil) created a work group which has proposed alteration in the Mining Code and Correlated Legislation based on a new model for classification of resources/reserves. This model is up-to-date and adopted worldwide, but the work group also proposed alternative definitions for resources and reserves, which are here considered inadequate for the reasons presented in this paper. Ore reserve estimation follows a logical sequence of steps: geological evaluations, exploration method and sampling evaluations, exploration data evaluation, ore body delineation and selection of an appropriate method for ore reserve estimation. Following these steps, the ore reserve classification of an ore block becomes a natural consequence of the relative density of samples.