Abstract

The modelling of lithological domains is a critical step in mineral resource and reserve evaluation. Deterministic models rely on an interpretation of the available drill hole data and expert knowledge, but do not account for the uncertainty in the spatial extent of the lithological domains. Instead, probabilistic models based on conditional simulation can be used to map the probabilities of occurrence of the domains within the deposit, which reflect the uncertainty in their presence or absence at unsampled locations. The mineral grade model is then obtained by weighting the predicted grades associated with each lithological domain by the probability of occurrence of this doman. Such an approach accounts for the continuity of the grades proper to each lithological domam and for the uncertainty in the spatial extent of these domains within the deposit. An application to a porphyry copper deposit is presented. © The Southern African Institute of Mining and Metallurgy, 2007.