A METHODOLOGICAL PROPOSAL FOR MODELING COPPER WAD DISTRIBUTION IN THE LOMAS BAYAS ORE DEPOSIT, NORTHERN CHILE

The Lomas Bayas ore deposit is located 120 km northeast of Antofagasta city, in the Atacama Desert of northern Chile. The ore body has been defined as a low grade (0.30 % Cu) porphyry type deposit, were hypogene and supergene copper mineralization is hosted by hydrothermal breccias, porphyritic intrusives and quartz veins. Copper oxide mineralization such as antlerite, brochantite, chalcantite, chrysocolle, atacamite and copper wad originated from the oxidation of primary and secondary minerals. Production comes from heap leaching of oxidized ore, being the world lowest grade copper mine in production today.

Copper wad is a generic term in mining for Cu-bearing manganese hydroxide mineral phases. These are resistant to acid leaching and have very slow kinetics of dissolution in the conventional hydrometallurgical processing, consequently is left untreated in the leach pads. These limitations together with operational restrictions led to the fact that the copper wad has not been reported on field mapping and drill core logging, and therefore is not included as part of the total copper resources.

Recent technological innovations in hydrometallurgy for the efficient recovery of metal from copper wad has change the categorization of the wad from waste to an potentially important copper resource, increasing the overall operational grade of the deposits and also extending the life-of-mine operation. This situation creates new challenges in identifying those zones in which the copper wad was present but not previously recorded.

The goal at this project is to investigate geostatistical procedures that could be used to predict the occurrence of copper wad in areas where it was not previously described. The methodology will be focused on finding the best possible correlation between the copper wad and geological features such as mineral associations, petrography, hydrothermal alteration (registered during drill core logging), geochemical data and deterministic modeling. This approach based on geologic control should improve the degree of certainty of finding the copper wad mineralization. Some preliminary results for the application of the methodology to the Lomas Bayas deposit will be shown.