# Hydrogeochemistry of Fault-Related Hot Springs in the Qaidam Basin, China
## 4 Discussion
### Conceptual Model for Fluid Circulation  
Hot springs are mostly exposed at the intersection of branch fractures and main fractures, which is the upper plate of extrusion fractures or deep-cut valleys formed due to fracture action. Geothermal water is recharged by infiltrating precipitation and heated by heat sources in the fracture system during the deep circulation process. Deep faults serve as a conduit not only for additional groundwater infiltration but also for the upward flow of deep geothermal fluids [90]. Understanding the origins and migration paths of springs in active fracture zones is critical for studying hydrogeochemical properties and geothermal resource extraction. Therefore, the present study's findings could be combined with existing geological data to construct a model. The conceptual model of the hydrogeochemical cycle process of hot springs in the study region is illustrated in Figure 9. Hot springs are recharged mainly through atmospheric precipitation and glacial meltwater at 3390-3676 m. The recharge water seeps into the aquifer through hydraulic conductivity fractures between the mountains and the river terraces. The hot springs in the study region differed in spatial distribution, resulting in slight disparity in their recharge sources. The YTBLK and AK springs close to the intersection of the Altun Tagh fault and the East Kunlun fault had an evident recharge from fracture infiltration. In the study region, the Altun Tagh fracture zone and the East Kunlun fracture zone serve as good transport channels for the hot spring water, causing it to be transported downward along the fracture surface. Water-rock interactions with the enriched tuffs in the study regions occur during this transport process, producing small amounts of trace elements and larger macronutrients. Through geothermal heating, a portion of the hot spring water was transported downward to 1.04-2.68 km below the crust, and then, recharged upward to the hot springs around the fracture zone in the study region. The temperature of heat storage ranged from 66.7 to 164.9 \({}^{\circ}\)C. Water-rock interactions occur at various depths under certain temperature and pressure conditions. Spatially, the hot spring thermal storage temperature and circulation depth values were relatively large near the intersection of the Altun Tagh Fault and the East Kunlun fault belt zone, and the fracture intersection area was prone to high-stress-value anomaly zones. This indicated that the fracture controls fluid circulation and transport in this region. In addition, the microseismic activity in this region is relatively frequent, which is probably because the high degree of weakening of the water response here has weakened the fractures and rendered them further prone to earthquakes. Deeper fluid circulation and higher thermal storage temperatures in the hot springs lead to relatively high ambient pressure in the deeper fluids, causing microseismic activity in this region. In the process of a periodic rise, the circulating water may mix with colder surface water or shallow groundwater, eventually becoming hot springs that appear at the surface. In the present study, a water chemistry model was constructed for the hot springs in the study region. This model could serve as a geochemical basis for geothermal resource development. Strong tectonic movements and seismic activities may alter the sub-surface stress-strain state and trigger the fragmentation of aquifers inside the fracture zone, leading to the mixing of deep fluids and shallow cold water; this then affects the degree of water-rock interactions of the underground hot water and changes the hydrochemical components and isotopic characteristics of the hot springs in the study region. This could provide evidence for short-term and upcoming earthquake prediction [91]. The hot spring water in the study region contains huge amounts of fugitive CO\({}_{2}\) gas.