# Hydrogeochemistry of Fault-Related Hot Springs in the Qaidam Basin, China
## 4 Discussion
### Hydrochemical Characteristics of the Hot Springs
#### 4.1.1 Major Components in the Spring Water
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline
**Sampling Springs** & **He** & **H\({}_{2}\)** & **CO\({}_{2}\)** & **CH\({}_{4}\)** & **N\({}_{2}\)** & **O\({}_{2}\)** & **Ar** & **\({}^{3}\)He/\({}^{4}\)He** & **\({}_{4}\)He/\({}_{20}\)Ne** & **CO\({}_{2}\)/\({}_{3}\)He** & **\({}^{813}\)CCO\({}_{2}\)** \\  & **(ppm)** & **(ppm)** & **(\%)** & **(\%)** & **(\%)** & **(\%)** & **(\%)** & **(10\({}^{-7}\))** & **\({}_{4}\)He/\({}_{20}\)Ne** & **CO\({}_{2}\)/\({}_{3}\)He** & **(10\({}^{9}\))** & **(\%, vs. PDB)** \\ \hline YTBLK & 153 & 3.2 & 95.43 & 0.5185 & 5.02 & 0.49 & 0.026 & 2.085 & 768 & 29.56 & \(-\)3.4 \\ AK & 36 & 5 & 99.58 & 0.0024 & 1.25 & 0.25 & 0.03 & 6.116 & 164 & 44.98 & \(-\)6.4 \\ \hline \end{tabular}
\end{table} 
Table 2: Gas composition of the samples in the hot spring gases. increased gradually from the east to the west direction in the hot springs in the study region. HCO\({}_{3}\)\({}^{-}\) is formed primarily through the dissolution of carbonates in sedimentary rocks and the weathering dissolution of aluminosilicate minerals (sodium feldspar and calcium feldspar) in magmatic and metamorphic rocks. The presence of SO\({}_{4}\)\({}^{2-}\) indicates the presence of gypsum (CaSO\({}_{4}\)\({}^{-}\)H\({}_{2}\)O) in sedimentary rocks or that the environment in which underground hot water appears and migrates is an oxidizing environment. A high CI\({}^{-}\) concentration indicates that water is discharged directly from a deep thermal reservoir with minimal mixing or conduction cooling and that water is supplied from the deep-water reservoir. When analyzed from a spatial perspective, the type of water chemistry in the study region was demonstrated to be relatively complex. The hot spring ion content was relatively higher spatially on the west side of the region compared to the east side. This could be attributed to the different surrounding rocks distributed along the fracture zone and the different activities of the surrounding fractures. To a certain extent, trace elements in hot springs reflect the degree of water-rock interaction in the groundwater. The presence of 24 trace elements, including Ag, Al, Ba, Be, Cd, Co, Cr, Cu, Fe, Li, Mn, Mo, Ni, Pb, Sb, Se, Sn, Sr, Th, Ti, U, V, Zn, and B, was observed at the four hot spring sampling sites. Table 1 shows the trace element concentrations. The magnitude of trace element enrichment coefficients can be used to determine the source of trace elements in hot spring water, which is calculated as follows:  
\[\mathrm{EF_{i}=(C_{i}/C_{R})w/(C_{i}/C_{R})r} \tag{1}\]  
Figure 2: Ion concentration diagrams. (**a**) Percentage of major cations. (**b**) Percentage of major anions. (**c**) Piper diagram of sampling sites in study area. In Equation (1), \(\mathrm{C_{i}}\) denotes the elemental content in the sample, \(\mathrm{C_{R}}\) denotes the content of the selected reference element, \(\mathrm{W}\) denotes the elemental concentration in the water sample, and \(\mathrm{r}\) denotes the elemental concentration in the rock. The enrichment coefficients reflect the degree of enrichment of a certain element in the region; the larger the enrichment coefficients, the more concentrated the element. The smaller the enrichment coefficients, the more dispersed the element. Considering the information on the location and lithology of the study region, along with the findings of recent research, the regional average value of trace elements in the Upper Ganjigou Formation at the northwestern margin of the Qaidam Basin was selected as the standard value. The contents of Ba, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sr, Th, Ti, U, V, and Zn in the rocks were 387.62, 13.92, 111.65, 31.88, 32600.42, 643.31, 36.46, 25.40, 289.77, 10.50, 147.00, 2.77, 93.08, and 103.40 ug/g, respectively [43]. Ti was selected as the reference element owing to its greater stability. The trace element data were normalized to calculate the enrichment factors of trace elements (EFs) in the study region. The enrichment factor of Sr in the hot spring water in the study region was the strongest (Figure 3).