Abstract:
Precambrian crystalline basement rocks occur extensively in the northern part of South Africa and make up more than 40% of the total bedrock geology of Africa. It is important therefore to understand the aquifer systems associated with these basement rocks since they supply sustainable groundwater to many communities. Most of the water supply in the Limpopo Province, South Africa is groundwater reliant. A Water Research Commission (WRC)-funded research project applied a variety of methodologies to characterize the geochemistry of basement rock aquifers in Limpopo Province. The research outlines principal processes influencing the groundwater chemistry of basement rocks and ultimately influencing sustainable groundwater supply. In particular the research concentrates on groundwater chemistry resulting from sourcerock interaction, and hydrochemical processes including cation exchange, evapotranspiration and dissolution. The methodologies applied in the dissertation include XRD and XRF analysis and ion ratio analysis for water-source deduction and for weathering reactions and factors. The complexity of basement rock aquifers is highlighted if these methodologies are applied to determine the origin of groundwater. The geochemical interactions of these rocks show that a number of factors influence the groundwater composition. Weathering reactions and factors show only a 12% correlation between the minerals, their weathered products and the groundwater cation composition. Furthermore recharge-discharge areas influence most of the anions in the groundwater water. The geochemical characteristics of basement rock aquifers have a dominant Mg-Na-HCO3 water facies overall and don’t show any significant change in chemistry in different host rock types. Copyright
