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.

Occurrence and Health-Risk Assessment of Trace Metals in Geothermal Springs within Soutpansberg, Limpopo Province, South Africa

“…The five factors are interrelated and are indicative of rock-water interactions, such as thermal gradient, mineral dissolution and ion exchange, as the major geochemical processes governing the groundwater chemistry. This supports the previous findings in water types [43], and confirms that the rock-water interaction is one of the major processes controlling the chemistry of the geothermal springs and boreholes. The PCA/FA loading factors for the trace metals in the geothermal spring and borehole samples, taken within Soutpansberg, are shown in Table 6.…”

“…pH values ranged from 7.17 to 9.39, which implies that the waters are alkaline in nature. This could be a result of the water types' Na-HCO 3 and NaCl from the studied geothermal springs, as reported by Durowoju et al [43]. The water temperature of springs ranges between 41.3 • C and 68.9 • C (Table 4), and are classified as: Mphephu (MPS and MPW) and Sagole (SGS and SGW) springs, and Siloam (SH1 and SH2) boreholes, are thermal (hot) water with temperatures ranging between 41 • C to 49 • C; Siloam (SAW) and Tshipise (TSS and TSW) geothermal springs can be classified as scalding (hyperthermal) with temperature ranging between 53 • C and 69 • C. The seasonal variation leads to the fluctuation of the thermal property of the springs.…”

“…For instance, two homesteads where the borehole water was sampled are next to one another, and their water characteristics are different (one is hot and the other is cold). The chemical and isotopic parameters of these boreholes differ, as reported by Durowoju et al [43]. Hence, there is a possibility of common host rock and minor faults connecting the aquifer of geothermal spring and boreholes, thus there is aquifer interconnectivity [43].…”

“…The chemical and isotopic parameters of these boreholes differ, as reported by Durowoju et al [43]. Hence, there is a possibility of common host rock and minor faults connecting the aquifer of geothermal spring and boreholes, thus there is aquifer interconnectivity [43].…”

National Stable Isotope Baseline for Precipitation in Malawi to Underpin Integrated Water Resources Management

“…The LMWL's intercept (13.0 (±2.0)‰) representing the deuterium excess value, greater than the GMWL intercept of 10‰, is probably due to the influence of the Salima and Central Water Laboratory station samples in Central Malawi and Chinyonga station samples in southern Malawi which recorded higher d-excess values. The LMWL's slope of 8.0 (±0.3) is comparable with 8.0 for the GMWL, from which it is reasonably inferred that a condensation process leading to local precipitation formation occurred under equilibrium conditions and without significant evaporation phenomena [18,62].…”