Geochemical, mineralogical and geostatistical modelling of an IOCG tailings deposit (El Buitre, Chile): implications for environmental safety and economic potential

Abstract

In the mining industry deposits of tailings represent large volumes of the mining wastes, reflecting the mineralogy and chemistry of the ore deposit type of origin. In this paper, we report the results of a mineralogical and geochemical characterization study and geostatistical modelling of an Iron Oxide Copper Gold deposit with neutral pH, in an arid climate. Twenty-eight boreholes allowed recovery of 755 samples for analysis. Modelling by means of co-kriging spatial interpolation allowed determination of the distribution of concentrations for elements of interest in the deposit. Low water flow and near neutral-pH paste restrict the mobility of the chemical elements, limiting the development of an oxidation front and inhibiting the appearance of a secondary mineral enrichment zone and the precipitation of secondary efflorescent salts on the tailings surface. Our observations determine that the composition of the gangue material, and to a lesser extent the effect of the tailings gravitational deposition and the geometry of the deposit, control the geochemical and mineralogical associations and distributions present in this deposit of tailings. The observed low mobility along the tailings profile of some potential pollutants (e.g., As, Mn, Cr and Ni) allows to anticipate a low groundwater pollution risk as long as the current environmental conditions remain. Additionally, the depositional history of the tailings had a great influence on the vertical and horizontal distribution of pyrite. However, the grades of elements economic interest such as Fe, Cu and Co are uniformly distributed, which would facilitate the application of tailings reprocessing technologies. In addition, it would allow maximizing the number of necessary boreholes for its economic evaluation.