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.
Highlights
Geothermal springs are geological phenomena that occur in all parts of the world
This study showed that the molar ratios of geothermal spring samples generally ranged from 0.4–3.11 compared to the seawater ratio of 0.86, Na/Cl for the geothermal spring samples generally ranged from 0.4–3.11 compared to the seawater which implied that 67% of the water had a Na/Cl ration higher than that of the seawater, while 33%
Results of hydrochemical parameters of geothermal springs within Soutpansberg Group suggest that the thermal gradient, carbonate weathering, mineral dissolution, ion exchange, and evaporation are the main controlling geochemical processes in the variation of groundwater quality
Summary
Geothermal springs are geological phenomena that occur in all parts of the world. They could be of volcanic or meteoric origin [1,2] with uses ranging from power generation, industrial processing, agriculture, aquaculture, bottled water, the extraction of rare elements, and the use of thermophilic bacteria for industrial purposes, among others [1]. The socio-economic importance of geothermal springs has fluctuated over time, but over the past few decades, there has been an unprecedented resurgence of interest in this resource mainly due to a diversification in the application of the waters [1,2,3]. The geothermal springs in the Province were classified according to the residing mountain—Waterberg Group, Soutpansberg Group, and Drakensberg Group [2].
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