Regularities in the Evolution of Groundwater Quality at Abandoned Copper Sulfide Mines at the Levikha Ore Field, Central Urals, Russia

Аннотация

Over the past decades, dozens of copper sulfide mines in the Urals were decommissioned, abandoned, and flooded. At many of them, acidic mine waters are still generated and poured out on the surface. Concentrations of most components in these waters are several orders of magnitude higher than the maximum permissible concentrations. The chemical composition of the acidic groundwaters is generated in a highly dynamic regime: the concentrations of all components in the water first drastically increase after flooding and then decrease during many years. At the Levikha copper sulfide deposit, Sverdlovsk oblast, the filling of the depression cone in 2007 was followed by the origin of focused groundwater discharge: an anthropogenically produced water body (pond) in a caving within the collapse and subsidence zone. The concentrations of many indicator components were higher ten years after the flooding was terminated than when the mining operations were in progress. The dominant source of the acidic waters with elevated mineralization (total dissolved solids, TDS) is the collapse zone, in which an anthropogenically generated sulfuric-acid weathering crust enriched in secondary minerals developed for tens of years in the process of mine drainage. According to results of numerical geofiltration simulations, the lateral flow makes up 60% of the hydrodynamic balance and dilutes the solution generated in the collapse zone. The movement time of this flow through the collapse zone is six–eight years, and this period of time is marked by extremely high values of practically all indicators in the anthropogenic pond. The composition of rocks whose dissolution–precipitation controls the composition of groundwater in the area of the flooded mine was determined by numerical simulations with the Visual MINTEQ ver.3.0/3.1 software. The duration of the process that forms the composition of the acidic groundwaters is estimated at tens of years.