## 4 Results and Discussion
### Isotopic Composition
This phenomenon could have been achieved by local processes such as selective infiltration, direct percolation through the faults, degree of differentiation both on land surface and in the unsaturated (vadose) zone, and mixing mechanism from surface water and irrigation processes ([PERSON], 2018). Other samples plotted above the LMWL, which indicated the average isotopic composition of rainwater resulting from the relatively aquifer-mixed system. This was mostly experienced in the winter with low amounts of rainfall, and this was mixed water from rainwater and other water bodies (rivers and lakes) in the aquifer. In aquifer systems that were weathered and fractured, direct infiltration through faults and shearing could have possibly conserved the isotopic composition of the original rain ([PERSON], 2018; [PERSON], 2018; [PERSON] and [PERSON], 2018). Hence, the groundwaters may not have been affected by isotopic differentiation, which made them distinct from rainwater resulting in the depletion of heavy isotopes due to the Rayleigh fractionation processes, which was corroborated with findings from Gat ([PERSON] and [PERSON], 2018). Figure 9: Seasonal variation of \(\delta^{2}\)H and \(\delta^{18}\)O values of the geothermal spring and boreholes. The groundwater was classified into two groups according to the isotopic composition. Sagole and Tshipise had similar signatures (Group 1), and Siloam and Mphephu had similar signatures (Group 2). This could possibly have been due to the closeness in distance above the sea level (altitude) (Siloam-835 m and Mphephu-890 m; Sagole-450 m and Tshipise-520 m) and hydraulic connectivity [53; 54]. Group 1 was recharged at a higher altitude compared to Group 2, and this accounted for the slight enrichment of its isotopic compositions [47]. Also, Figure 1 shows two distinctive geological formations leading to the water chemistry of these geothermal springs, which corroborated the findings from the isotopic signatures. During the infiltration process, the water interacted with the rock minerals with depth and made the water change isotopically from depletion to enrichment (lower altitude to higher altitude). Interestingly, Siloam geothermal water and hot borehole had very similar isotopic compositions, which could be attributed either to the hydraulic connectivity between the deep and shallow aquifer that resulted from a minor fault or the fact that they were from the same aquifer. The study inferred that the geothermal spring waters were from a deep aquifer (thermal gradient) with more depleted isotopic signatures (light isotopic composition). Apparently, the thermal borehole (shallow aquifer) had a similar isotopic signature as the geothermal spring (deep aquifer), and it could be inferred that there was direct interconnectivity between the two aquifer (shallow and deep) systems through the fault at Siloam. This could be attributed to the geological formations and climatic factors of the area. The Pearson correlation showed the relationship among physical, chemical, and isotopic compositions of the geothermal springs/boreholes (Table 3). The temperature showed a positive correlation with pH, alkalinity, K, F, CO\({}_{3}\), and HCO\({}_{3}\), and very weak negative correlation with Ca, Mg, PO\({}_{4}\), \(\delta^{2}\)H, and \(\delta^{18}\)O. This implied that the increase in temperature increased the concentrations of the K, F, CO\({}_{3}\), and HCO\({}_{3}\), and decreased the concentrations of Ca, Mg, and PO\({}_{4}\), thus accounting for the high fluoride concentrations in the groundwater [2; 54]. The high correlation between F\({}^{-}\) and Na\({}^{+}\) was noted because it was an indication of the possible source of F\({}^{-}\). Dissolution of fluoride-bearing minerals, such as cryolite (Na\({}_{3}\)AlF\({}_{6}\)), was depicted as a source of F\({}^{-}\) in hard rock groundwater [55]. However, further investigations are still required to deepen the existing knowledge on this issue in the studied areas.