Reserve Estimation at Porphyry Copper Deposits Using Uncertainty Models in Geologic Unit Boundaries

Summary: Simulation method give use most probable models that could be to obtain the best and worst case of a resource. So, average of these models is similar to estimated model but will not have estimated model problems. In the introduced new method after determining the rock type probability models the grade distribution is evaluated using geostatistical simulations. This method in addition to containing the probability models use from simulated grades that case be most authentic. Performance of method presented using a case study of a porphyry copper mine in Chile. Geological modeling is one of essential processes in ore reserves and resources evaluation that is precedence over the grade estimate. It is containing the deterministic division of deposit into smaller subdomains that called geological units. Although it cased to present the better treatment from the spatial grade variability, but it is not possible to present the uncertainty models in the boundaries of geological units that are need to classify the ore reserves and resources according to international standards such as JORC. This article presents an approach that uses geological uncertainty that could be incorporate in the evaluation of mineral resources. Introduced method applied on the rihoblanco deposit case study in chile. Methodology and Approaches: At first to obtain probabilistic descriptions of three different lithological units the geostatistical simulation have been used in this deposit (granodiorit, tourmaline breccia and another breccias). Then to determine the grade uncertainty of the deposit the conditional simulations have been applied. Finally, mineral resource model presented using weighting the copper grade realizations by occurrence probability of deferent geological units. Presented model able to produce a grade model that contain the geologic models uncertainty with avoidance of artificial models that caused by deterministic boundary hypotheses between high grade and low grade areas of ore in near the geologic boundaries. Results and Conclusions: Introduced method presented better results compared to the kriging method. Results shown that evaluation of the deposit geological uncertainty prevented from creates the unrealistic models of kriging method. Reliability of model is evaluated which less standard deviation of weighted realizations conditional variance show that reliability of them are suitable. Also, coefficient of variation in domains boundary was low which shows the method is suitable and uncertainty in boundaries is low. Also, presented new method compared with general simulation of grade distribution that new method represented higher tonnage percentage in grade-tonnage curves.