The mechanism of high salinity geothermal water formed in karst low-temperature hydrothermal system

The formation mechanism of high salinity geothermal water is significant for utilizing geothermal resources and mineral resources. The high salinity in geothermal water may be derived from the geothermal mother fluid or from the evaporite dissolution. It is difficult to distinguish between these two sources because they may have similar hydrochemistry. In this paper, water chemistry and stable isotopes were used to explore the high salinity geothermal water in Yanchanghe geothermal field, central China. It is a low-temperature hydrothermal system in the inland karst area. The thermal water is Cl-Na type with high salinity (TDS > 8,400 mg/L). The modified silicon thermometer is more suitable and the reasonable result is about 58.8 degree celsius. The maximum circulation depth is 1.9 km. Using the temperature of hot and cold water to estimate the mixing ratio is 58%-81%. Saturation index (SI), Na/1000-K/100-Mg-1/2 and Gibbs diagram suggest that the main source of salt in geothermal water is derived from the evaporite dissolution, which provides Cl- of 11,264-31,279 mg/L and Na+ of 9,272-21,236 mg/L. We found the combination of temperature and hydrogeochemistry can be used to investigate the formation mechanism and mixing process of high-salinity geothermal water formed in a karst low-temperature hydrothermal system.