## 5 Discussion
### Hydrochemical Characteristics and Evolution of Spring Water
#### 5.1.4 Reservoir Temperature and Circulation Depth Estimates  
Cation geothermometers require chemical equilibrium for reliable deep reservoir temperature estimates. As shown in Figure 4, none of the samples exhibit full equilibrium, due to dilution or mixing between deep thermal fluids and shallow cold waters. Therefore, cation geothermometers may over- or under-estimate true reservoir temperatures in such settings. In immature systems, silica-based geothermometers are more suitable [71], although their accuracy depends on silica phase equilibrium (e.g., quartz vs. chalcedony vs. amorphous silica). To improve estimation, a multi-mineral equilibrium method is used to determine the temperature at which all selected minerals (e.g., quartz, chalcedony, calcite) reach saturation (SI = 0), representing the deep reservoir temperature (Figure 5). The depth of sub-thermal water circulation is estimated using  
\[\mathrm{H}\;=\;\frac{\mathrm{T}-\mathrm{T}_{0}}{\mathrm{g}}+\mathrm{h}\]  
The average temperature in the study area is taken as 3 \({}^{\circ}\)C, the geothermal temperature gradient is 2.5 \({}^{\circ}\)C/100 m, and the depth of the normothermic zone is 30 m [57]. As seen in Table 2, the study area's hot springs have reservoir temperatures of 18-90 \({}^{\circ}\)C and circulation depths of 621-3492 m. Most of the hot springs are classified as medium-low temperature geothermal resources, with only S13 classified as a medium-high temperature geothermal resource. The remaining hot springs have shallow circulation depths and are characterized by immature water, likely mixed with shallow cold water.  
Figure 4: Na-K-Mg ternary diagrams.  
\begin{table}
\begin{tabular}{l c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **Quartz, No** & **Quartz, Maximum** & **Multicomponent** & **Average Reservoir** & **Average Reservoir** \\  & **Steam Loss (\({}^{\circ}\)C)** & **Steam Loss (\({}^{\circ}\)C)** & **Chancelon (\({}^{\circ}\)C)** & **Chemical Equbra (\({}^{\circ}\)C)** & **Temperature (\({}^{\circ}\)C)** & **Deepth (m)** \\ \hline S1 & 36.19 & 3.40 & 44.49 & 19.00 & 26 & 941 \\ S2 & 6.15 & - & 16.94 & 48.00 & 18 & 621 \\ S3 & 32.95 & 0.13 & 41.55 & 42.00 & 29 & 1076 \\ S4 & 16.82 & - & 26.79 & 51.00 & 24 & 856 \\ S5 & 23.05 & - & 32.51 & 48.00 & 26 & 946 \\ S6 & 24.04 & - & 33.42 & 58.00 & 29 & 1065 \\ S7 & 50.23 & 17.72 & 57.15 & 22.00 & 37 & 1381 \\ S8 & 26.02 & - & 35.23 & 19.00 & 20 & 712 \\ S9 & 14.35 & - & 24.52 & 66.00 & 26 & 959 \\ S10 & 14.92 & - & 25.04 & 62.00 & 25 & 930 \\ S11 & 23.75 & - & 33.15 & 72.00 & 32 & 1199 \\ S12 & 22.38 & - & 31.91 & 61.00 & 29 & 1063 \\ S13 & 99.06 & 68.93 & 100.18 & 90.00 & 90 & 3492 \\ S14 & 53.52 & 21.11 & 60.10 & 81.00 & 54 & 2067 \\ S15 & 55.00 & 22.63 & 61.42 & 42.00 & 45 & 1720 \\ S16 & 41.06 & 8.35 & 48.90 & 66.00 & 41 & 1553 \\ S17 & 21.60 & - & 31.19 & 38.00 & 23 & 818 \\ S18 & 31.14 & - & 39.90 & 10.00 & 20 & 720 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Multi-method reservoir temperature estimation.  
Figure 5: Variation pattern of reservoir mineral saturation index (log (Q/K)) with temperature.