| Elucidating the hydrochemical characteristics and genetic mechanisms of geothermal water provides a vital scientific basis for the sustainable exploitation of geothermal resources. Sulfate-type geothermal water, which is very special, was found from the confined limestone aquifer in Xiwenzhuang Uplift, Taiyuan. The genetic mechanism and principal controlling factors of the geothermal water was studied in the paper by means of hydrogeochemical methods. The results shows that the hydrogeochemical types of the geothermal water are predominantly SO4-Ca, SO4-Ca·Mg, and SO4-Ca·Na. Ion content correlation analysis reveals that the hydrochemical composition is governed by the dissolution of both carbonate and sulfate minerals, with the dissolution of sulfate minerals being dominant. The excess Ca2+ is primarily derived from gypsum (CaSO4·2H2O) dissolution and cation exchange processes. The geothermal reservoir temperature estimated by Na-K-Ca-Mg geothermometer ranges from 101.3 ℃ to 141.1 ℃, with the average circulation depth of approximately 3.47 km. Although the hydrochemical composition suggests a primarily mineral dissolution origin, the Na-K-Mg triangle diagram and PHREEQC simulation results indicates that the groundwater has not reached to water-rock equilibrium. The Chloro-Alkaline Indices (CAI) confirmed that positive cation exchange occurs during groundwater circulation. It is concluded that groundwater dissolves gypsum from the strata along with the flow process. With the elevation of geothermal reservoir temperatures, the dissolution of sulfate minerals is enhanced, ultimately leading to the formation of the distinct sulfate-type geothermal water. |