A Geochemical And Geophysical Characterization Of Acid Mine Drainage And Sulfide Tailings At Karabash Mine Site (South Ural, Russia)
The Karabash mine area was chosen as the research site for its potential hazardous influence on the environment of Chelyabinsk region. This work presents the results of a geochemical and geophysical characterization of an old tailing containing high contents of sulfide minerals, primarily pyrite (up to 25 wt%), chalcopyrite (3 wt%) and up to 1 wt% of sphalerite and galena. In order to obtain a representative characterization of the study area, geochemical analysis of surface water samples, groundwater composition, bottom sediments analysis and thermodynamic modelling were selected. In all compounds, high levels of trace elements (including Pb, Zn, Cu, Cd, Co, Ni, Fe, Mn) were observed. A thermodynamic modelling study (WATEQ4f) revealed the mobilization of heavy metals mostly through the aqueous and sulfate complexes. Due to the large amounts of dispersed sulfide minerals, the pyrite-rich tailing characterized by an electrically conductive geophysical signature in comparison to the surrounding resistive bedrock. Meteoric water, getting on a tailings surface, gradually penetrates, on the way dissolving secondary minerals and metal salts, being saturated with them. Poorly permeable grounds are capable to accumulate waters, forming underground reservoirs. The distribution of layers with low resitivities suggests that the infiltration of highly mineralized solutions spreads in a direction transverse to the river flow zone. These layers extend to depths of 1–15 m, indicating the penetration of toxicants into the groundwater horizon. The pollution of groundwater confirmed by chemical analysis, according to which the concentrations of Zn, Pb, Ni, Cu and Cd in groundwater samples are two to three orders of magnitude higher than the maximum permissible concentrations (MPC). ERT technique combined with 3D models suggests along with the vertical penetration into groundwater, there is a lateral spread of low resistivity within water-saturated layers, which in this case may be termed an "acid wave".
Keywords- Acid mine drainage, pollution, heavy metals, electrical resistivity tomography, WATEQ4f.