Investigation of the acid mine drainage potential of the Kopanang rock dump, Vaal Reefs

Abstract

The Kopanang rock dump is one of several rock dumps in the Vaal Reefs gold mining area that may have an impact on the surface and groundwater quality. Few Acid Mine Drainage (AMD) studies exist on rock dumps in the South African gold industry due to the overwhelming acid generation from slime dams. Due to the existence of sulfide minerals in the Kopanang rock dump, there is a possibility that acid generation can occur, depending on the mineralogical composition of the rocks. If the rock dump generates acid it will increase the possibility of heavy metal leaching and pollute the underlying aquifers. The aim of this study was to determine whether the dump generates acid and if so to quantify the acid generation and the impact it has on the surface and groundwater. From this study it was concluded that the rock dump has a potential to produce acid resulting in AMD. However, the inherent minerals in the rock dump (calcite, dolomite, mica and chlorite) have a neutralising effect on the produced acid that may form. Furthermore, the underlying dolomite acts as a buffer for any residual acid. There is, however, evidence of water pollution around the waste rock dump and in the groundwater adjacent to the rock dump. This polluted water has a neutral pH with elevated uranium and sulfate concentrations. The final conclusion was that the waste rock dump produces neutral mine drainage (NMD). An additional finding was that high run-off water from the rock dump infiltrates through the prevailing bedding planes and joints in the underlying dolomites. This, together with the weight of the rock dump, contributed to the formation of small sinkholes.