## 3 Materials and Methods
### Analytical Methods  
Samples were analysed for hydrochemical parameters in the laboratory using the standard recommended methods [31]. The sample pH, sodium absorption ratio (SAR), alkalinity, and temporary hardness were determined using ManTech Titrasity Autotitrator (Guelph, Ontario NIH6J2, Canada). The samples for anions (F-, Cl-, NO3-, SO4-, PO4-, HCO3-) and major cations (Na+, K+, Ca2+, and Mg2+) analyses were filtered and analysed using the ion chromatography method (Dionex Model DX 500) (1228 Titan way, Sunnyvale, CA 94088-3603). Quality assurance/quality control (QA/QC) was  
Figure 3: Geology map showing the geothermal springs within the Soutpansberg Group.  
incorporated into geothermal spring water sampling and analyses to enhance sample integrity, increase the confidence of analytical data as reliable analytical information, and prevent reporting wrong positive values caused by contamination. Field blank and splits were ensured for the water samples. The instruments used were calibrated with a standard solution to avoid analytical errors. The method detection limit (MDL) for each cation was obtained by US EPA method 200.8 [32]. The MDLs for each cation were 0.03 ug/L (Na+), 0.07 ug/L (Mg2+), 0.4 ug/L (K+), and 0.03 ug/L (Ca2+). The MDLs for each anion were determined according to US EPA method 300.0, rev 2.1 [33] accuracy measurements methodology. The MDLs for each anion were 25 ug/L (F-), 12.5 ug/L (NO3-), 500 ug/L (Cl-), 125 ug/L (SO4-), and 150 ug/L (PO4-). The samples were analysed in triplicate to obtain the mean values of the concentrations  
Stable isotopes analyses of the samples were performed using Thermo Delta V mass spectrometer connected to a Gasbench at Environmental Isotope Laboratory (EIL) iThemba LABS Johannesburg, South Africa. Samples were flushed using a mixture of either H2 or CO2 in He, which was also used as the equilibration gas. The water samples were equilibrated along with platinum (Pt) catalyst in preparation for deuterium measurements [34]. The equilibration time of the water samples with hydrogen gas was 40 mins, whereas carbon dioxide gas was equilibrated with water samples in about 20 h. Laboratory standards calibrated against international reference materials were analysed with each batch of the samples.  
Conventionally, the isotope ratios of \({}^{2}\)H/\({}^{1}\)H and \({}^{18}\)O/\({}^{16}\)O in the water samples were expressed as per mil (%00) deviation relative to the Standard Mean Ocean Water (SMOW) as follows:  
\[\delta\ (\%0)\ =\ \frac{R_{sample}-R_{smow}}{R_{smow}}\times 1000 \tag{1}\]  
where R represents the ratio of heavy to light isotopes (D/H or \({}^{18}\)O/\({}^{16}\)O) in the sample and standard, respectively. The oxygen and hydrogen isotopic ratios were henceforth expressed individually as \(\delta^{18}\)O and \(\delta^{2}\)H, respectively, or collectively as \(\delta\) values. Total analytical precisions were estimated at 0.2%0 for \(\delta^{18}\)O and 0.8%0 for \(\delta^{2}\)H. The generated Thohoyandou local meteoric water line (TLMWL) [35] was used for the interpretation of the isotopic composition of the geothermal springs.  
The chloro-alkaline indices CAI 1, 2 indicate the possible ion exchange reaction between groundwater and the host environment, as suggested by [PERSON] [44]. Chloro-alkaline indices used in the evaluation of base exchange were calculated using Equations (2) and (3):  
\[\text{CAI-1}=\text{Cl}-(\text{Na}+\text{K})/\text{Cl} \tag{2}\]  
\[\text{CAI-2}=\text{Cl}-(\text{Na}+\text{K})/(\text{SO}_{4}+\text{HCO}_{3}+ \text{NO}_{3}) \tag{3}\]  
All values from chemical analyses were presented as mean values and standard deviation using Microsoft Office Excel 2018. Data presentations were made using tables and graphs. [PERSON]'s correlation coefficient was used to test the relationship between hydrochemical parameters and isotopic compositions at \(\alpha\) = 0.05 level of significance.