Evolution of Karst Geothermal Hydrochemical Characteristics and Genesis Mechanism in Northern Jinan, Shandong, Eastern China

The study of geothermal water hydrochemical characteristics and solute transport evolution can provide a reliable hydrogeochemical basis for the development and protection of geothermal resources. Currently, there is a lack of systematic research on the hydrochemical evolution mechanism of geothermal fields in northern Jinan, which limits the development and use of geothermal fields. In this study, the hydrochemical properties of groundwater in northern Jinan were described by analyzing the hydrochemical characteristics of 16 geothermal water samples and 3 cold water samples. The results show that during the transformation from cold water in the south to geothermal water in the north, the contents of major ions all show an increasing trend and the hydrochemical characteristics show obvious zoning characteristics. The hydrochemical type evolved from HCO₃-Ca to HCO₃-Ca·Mg type, and then further evolved SO₄-Ca and SO₄-Ca·Na type water. Dissolution-precipitation of carbonate, sulfate, halite, and silicate minerals is one of the important processes that controls the chemical characteristics of geothermal water. The water source is mainly from the atmospheric precipitation in the Taiyi Mountain, with an altitude of 698.99-1464.91 m.s.a.l. The thermal reservoir temperature in the study area is estimated to be 55.62-98.16 °C. This paper proposes a conceptual model of the karst geothermal water flow system in northern Jinan, which provides a new idea for exploring the geothermal water genesis mechanism under similar geological conditions.