Post-mining groundwater geochemistry evolution in on the Levikha sulfide deposits of the Middle Urals (Russia)

Abstract

Mining of volcanogenic copper pyrite deposits of the Middle Urals leads to the rock disintegration, their grinding, increasing the interaction surface. Sulfide minerals are oxidized by interaction with oxygen-enriched meteoric water and secondary minerals are formed (crystallo-hydrates of sulphates, hydroxides). Here technogenic zone hypergene (sulfuric acid weathering crust) is being formed. Once the water pumping activities are finished, the piezometric level recovers its position decreasing the unsaturated zone created during the mining activity, this increases the water-rock ratio increasing the amount of suppliers of sulphates, iron, non-ferrous metals and other elements to groundwater. It defines a low rate of rehabilitation of mining areas after the completion of mining and cessation of dewatering. The regularities of acidic water formation after filling the depression cone are investigated on the abandoned copper mines of the Middle Urals (Russia). The longevity of formation of extremely acidic and polluted waters is determined by the degree of saturation of the supergene zone with secondary minerals and the intensity of water exchange. Seasonal decrease in the component’s concentrations t in the period of winter and summer low water was recorded. The unstable character of groundwater components changes with a half-life of more than 5 thousand days is established. The duration of rehabilitation and restoration of groundwater quality will be at least a hundred years.