https://hal-mines-paristech.archives-ouvertes.fr/hal-00776914Séguret, Serge AntoineSerge AntoineSéguretGEOSCIENCES - Centre de Géosciences - MINES ParisTech - École nationale supérieure des mines de Paris - PSL - Université Paris sciences et lettresBlock model in a multi facies context - Application to a porphyry copper depositHAL CCSD2011[SDE] Environmental Sciences[MATH.MATH-ST] Mathematics [math]/Statistics [math.ST][STAT.TH] Statistics [stat]/Statistics Theory [stat.TH]Séguret, Serge Antoine2013-01-16 14:47:202021-11-17 12:31:182013-01-17 10:51:26enConference papersapplication/pdf1When a mineral deposit is made of geological bodies such as breccias or lenses that concentrate high grades, and when production blocks contain few such bodies, estimating block grades by ordinary kriging may produce unrealistic spatial continuity. To improve the block model, a usual practice consists in (1) estimating spatial proportions of facies (unit), (2) estimating the grades, facies by facies, and (3) combining the results to obtain the block grades. We show that this practice assumes some links between the geological bodies, which will be verified. Then, we try to answer this general question: Given a set of samples where facies and grades are known, what is the best way to build a block model? We propose a methodological work flow which leads to a cokriging system where facies indicators are used, together with their product with the grade, a method that does not require the previous calculation of the facies proportions, at the scale of the blocks, but is implicitly based on them, at the point-support scale. The method is applied to a porphyry copper deposit located in northern Chile. When compared to a usual kriging without any facies consideration, the improvement of the method is slight because the grade follows the contact hierarchy between facies and also an important part of the spatial variability is purely random. When compared to the traditional approach we notice very poor correlation and this makes perhaps questionable some choices made by the geologists.