The difference in hydrochemical characteristics of geothermal water between the eastern and western parts of the Wugongshan area and its genetic mechanism

The hydrogeochemical signature of the discharged water can reveal significant information on the circulation and evolution of geothermal water, which can further guide the exploration and utilization of geothermal water resources. In this study, the source of major ions, reservoir temperature, and cycle time of geothermal fluids were clarified by the Ion relationship analysis, integrated multicomponent solute geothermometry method, and ¹⁴C isotope analysis, respectively, in the Wugongshan area of South China. Results show that the eastern and western parts of the Wugongshan area have distinct types of geothermal fluids, i.e. HCO₃-Na and SO₄HCO₃-Na, respectively. The major source of HCO₃⁻ and Na⁺ is the hydrolysis of silicate minerals, partially accompanied by cation exchange. While gypsum hydrolysis and sulfide oxidation are the primary producers of SO₄²⁻. Moreover, higher TDS, PH, and degree of cation exchange of geothermal fluids were found in the western part than that in the eastern part. The reservoir temperatures in the eastern and western portions are comparable (115–150 °C). However, the cycle time of the geothermal fluids in the western part (15,743 years on average) is much greater than in the eastern part (2160 years on average), which is considered to be the main reason for the difference in hydrogeochemical characteristics. This study can provide theoretical support for the rational development and usage of geothermal water resources.