Additivity, Metallurgical Recovery, and Grade

Proper estimation of the metallurgical recovery is very important for the assessment of the economical value of a mining business. As this quantity is nonadditive, it is not possible to model its spatial variability or to perform its estimation directly. In the present work, we first recall that additivity can concern the intrinsic nature of point-support quantities, and not only the usual support effect encountered in data sets mixing samples with different sizes. Then, on a practical study based on sulphide copper data, we show when non-additive practices have an impact on the results and when they do not. Finally, we open a discussion where we explain how to proceed to assess metallurgical recovery. INTRODUCTION Since the early 90’s Codelco has been preoccupied making efforts to understand the spatial variability of some relevant metallurgical variables such as recovery, Bond Index, and Starkey Index. The consideration of the spatial variability of those variables has very important economical implications for the mining business (Carrasco and Tapia, 1998; Pease et al., 1998; Caceres et al., 2006). Some practical problems arise when assessing the local variability of metallurgical variables: Generally the samples are not at constant support. Sometimes, in order to get enough weight to perform several tests, several increments coming from very different locations are combined in a composite sample, so that the spatial location is lost. Metallurgical recovery is not additive, therefore the assessment of its spatial variability is not direct. Generally, the available number of samples is not sufficient to do a proper assessment. The spatial models of the geological variables which control the metallurgical behaviour such as lithology, alteration, texture, liberation factor, surface properties and ore zones are not available or are not taken into account. ha l-0 07 76 94 3, v er si on 1 16 J an 2 01 3 Author manuscript, published in "8th international Geostatistics Congress, Santiago : Chili (2008)"