Stochastic rock type modeling in a porphyry copper deposit and its application to copper grade evaluation

Abstract

An accurate definition of geological domains that differentiate the types of mineralogy, alteration and lithology is a critical step in mineral resources and ore reserves evaluation. Deterministic models define just one interpretation of the layout of these domains, based on drill hole data and mining geologist point of view, but do not take into account the uncertainty in areas with fewer data and do not offer any measure of the uncertainty in the domain boundaries. Instead, stochastic models based on geostatistical simulation allow assessing the uncertainty in the spatial layout of the domains. This study addresses the application of plurigaussian simulation in order to simulate the layout of porphyry, skarn and non-mineralized dykes in Sungun porphyry copper deposit (Iran) and to map their probabilities of occurrence over the region of interest. These probabilities are then used for weighting the copper grade prediction associated with each domain so as to obtain the final grade model. Results show the continuity of the grades proper to each domain and across domain boundaries, and compare favorably with respect to the approach based on deterministic geological modeling.