Hydrochemical Processes and Isotopic Study of Geothermal Springs within Soutpansberg, Limpopo Province, South Africa

Abstract

Geothermal springs and boreholes within the Soutpansberg Group were sampled and analysed for their major ion chemistry and stable isotope compositions in order to ascertain the possible sources and geochemical processes of the waters. The temperature of the geothermal springs ranges from 41 °C to 49 °C (thermal/hot waters) and 53 °C to 69 °C (scalding/hyperthermal waters). The major water types are Na-Cl and Na-HCO3, which are typical of marine and deep groundwaters influenced by ion-exchange processes. The hydrochemical parameters suggest that thermal gradient, carbonate weathering, mineral dissolution, ion exchange, and evaporation are the main geochemical processes controlling the geothermal springs. The δ18O and δ2H values vary from −5.82‰ to −4.82‰ for δ18O and −33.5‰ to −24.6‰ for δ2H for all the geothermal spring water. The isotopic ranges of the groundwater are relatively smaller and more depleted than those of rainwater (δ2H = −9.8‰ and δ18O = −2.7‰). The δ2H and δ18O signatures reveal a significant infiltration before evaporation. The δ2H and δ18O values further confirm that the waters are of meteoric origin, which implies that modern rainfall is the fundamental component of recharge derived from the infiltration of local precipitation with significant contribution of another type of water in the deeper part of the aquifer. These results provide further insight into this basement aquifer, which is a vital resource for the region.

Keywords

• geochemical process
• geothermal springs
• meteoric origin
• Soutpansberg
• stable isotopes
• water type