Hydrogeochemical baseline studies prior to gold mining: A case study in Sardinia (Italy)

Waters interacting with the ore deposit are generally non acidic, likely due to the low sulphidation system, the limited extension of the ore veins, the presence of calcite in the hydrothermal alteration assemblage, and the weathering of silicate rocks, which appears to contribute in buffering the acidity produced by the oxidation of sulphide minerals, especially pyrite. The nonacid environment does not favour the mobility of elements associated with the mineralisation, such as Cd, Co, Ni, Pb, Zn, and As. In addition, aqueous transport of these elements seems limited by the precipitation of ferrihydrite, which is able to reduce or remove these elements, particularly As, from solution. However, considering that exploitation will expose large quantities of mineralised materials to weathering, an adequate disposal of waste dumps and tailings needs to be carefully planned to prevent the potential dispersion of contaminants.