Geochemistry of Siloam and Tshipise Geothermal Springs, Limpopo Province, South Africa

Abstract

Geothermal springs are natural geological phenomena that occur throughout the world, and South Africa (SA) is endowed with several springs of this nature. Most of the geothermal springs in SA (31%) are found in Limpopo Province. Assessment of geochemistry of Siloam and Tshipise geothermal springs were undertaken during 2014 winter (May – July) and summer (October – December) seasons. Water samples were collected from the springs and stored at low temperatures (+/- 4°C) for analysis of hydrochemical parameters and acidification was carried out before trace metals analyses. The results show that Siloam and Tshipise geothermal springs water are not suitable for drinking due to high pH, high fluoride concentrations and some metals such as Hg, Ni and Pb. Various index methods such as Sodium Percentage (SP), Sodium Absorption Ration (SAR), Residual Sodium Carbonate (RSC), Permeability Index (PI), Kelly’s index (KR) and Electrical Conductivity (EC) were used to evaluate groundwater quality for irrigation and most of the index has a similar result. Hence, the spring water is suitable for irrigation purposes. The water type is Na-Cl in both seasons for both site except for Siloam in winter having Na-HCO₃. There were slight variations in the hydrochemical compositions of geothermal spring water, although they were not significant (p>0.05). However, there were significant differences in mean trace elements concentrations in geothermal spring water in summer compared to winter season (p<0.1) for both Siloam and Tshipise springs. This can be attributed to the rainfall in summer which aids in more dissociation of rock particles and the release of more trace elements. Variations in mean trace elements concentrations could also be linked to the differences in fundamental changes in water chemistry from deep sources of the geothermal springs. It has thus been established and/or inferred that the dominant processes controlling the geothermal water are geothermal gradient, silicate weathering, mineral dissolution, cation exchange and inverse cation exchange.