Investigation of hydrogeochemical processes of groundwater at royal Bafokeng platinum mine in the Bushveld Igneous Complex, South Africa

Abstract

This study was conducted in a platinum mining area to investigate the hydrogeochemical processes that influence groundwater chemistry. Information on the physicochemical properties of the groundwater was obtained from the mine’s database. The data were collected quarterly from monitoring boreholes for eight years (from 2007 to 2014). Furthermore, six underground workplaces that experienced water challenges were investigated to identify the source of water and come up with suitable solutions to deal with water challenges. For this part of the investigation, water samples were collected in March 2019 and were used to measure the physicochemical and chemical parameters. Water-rock interaction, bivariate plot analysis and water type classification were used in the study. The study revealed that the magnesium bicarbonate water type is the most dominant, followed by the magnesium sulphate water type and then mixed water type. The dissolution of fluorite was confirmed from saturation index results and this was supported by the trends in bivariate plots, as well as stoichiometric ratios. Dissolution, mixing and silicate weathering were recognised as processes, which take place in the groundwater system around RBplat and this was confirmed by a Durov plot. Saturation index results indicated precipitation of calcite, owing to its oversaturation. Silicate and carbonate weathering were also identified as processes contributing to the high concentrations of ions in the groundwater system. Based on the stable isotopes (deuterium and oxygen 18) results, the source of water in the underground workings originates from moisture that circulates regionally and recharged with minimal evaporation effects. This water shows a similar isotopic composition to the local precipitation. The municipal water supply from the underground tap deviates from the other samples and the PMWL, this confirms that there is no leak of the pipes and the other samples are of direct recharge from precipitation.