Spatial sampling effect of laboratory practices in a porphyry copper deposit

Serge Antoine Séguret (1)

1 GEOSCIENCES - Centre de Géosciences

Sampling protocols usually concern the way some kilograms of material are reduced to some grams with the same properties, but another protocol has to be considered: the choice of the samples to be used for estimating the resources of the deposit or some of its attributes. An important attribute is the metallurgical recovery, calculated with data sampling the deposit, on which laboratory tests are made to reproduce the metallurgical recovery process at a reduced scale. Such tests are very few because they are expensive; hence, the idea to combine them with exploratory data where the sole in situ grade is known using geostatistical techniques. While trying to put into practice this idea in a porphyry copper deposit located in the Chilean Central Andes, we encountered a surprising situation: laboratory tests and exploration measurements are supposed to use the same material but the total grades they measure do not have the same spatial variability. The paper presents the study and the impact of four causes. Spatial restriction: laboratory samples do not cover the same domain as exploration data. Regularization: laboratory and exploration samples do not have the same size. Sampling density: in the rich unit of the studied area, there are about two hundred laboratory samples and four thousand exploration ones. Grade selection: laboratory practice avoids high and low grades. The study shows that the major cause of the observed differences is the grade selection, but also that the number of laboratory tests is certainly too small with regards to the spatial variability of the grades. The consequence is that the sampling protocol for the metallurgical recovery tests shall be reconsidered if one wants to use them jointly with exploratory data.

Mots clés: Geostatistics; sampling effect; recovery

Domaines: Sciences de l'environnement; Statistiques [math.ST]; Théorie [stat.TH]; Sciences de la Terre

Serge Antoine Séguret. Spatial sampling effect of laboratory practices in a porphyry copper deposit. 5th World Conference on Sampling and Blending, Oct 2011, Santiago, Chile. pp.on CD. ⟨hal-00776905⟩