Hydrogeochemical characteristics of typical mid-temperature hot springs in northern and southern Jiangxi

In order to implement the ″double carbon″ goal and promote the sustainable development and utilization of China′s geothermal resources, the hydrochemical characteristics of Bailing Hot Spring in northern Jiangxi and Tanghu Hot Spring and Baishi Hot Spring in southern Jiangxi were studied by isotopic method and multi-mineral equilibrium simulation. The results showed that Bailing Hot Spring (85℃) is weak alkaline HCO₃-Na type silicon-fluorine water, and its TDS content, H₂SiO₃ content and main ion concentration are lower than those of Tanghu Hot Spring (89℃, weak alkaline HCO₃-Na type silicon-fluorine water) and Baishi Hot Spring (85℃, weak alkaline SO₄-HCO₃-Na type silicon-fluorine water). Although the water of the three hot springs is derived from atmospheric precipitation, the underground retention time is longer in Tanghu Hot Spring and Baishi Hot Spring, while the circulation depth is greater in Bailing Hot Spring. Bailing Hot Spring and Tanghu Hot Spring have strong rock interaction and both show obvious oxygen drift phenomena, but Baishi Hot Spring undergo water-gas isotope exchange, resulting in a decrease in δ¹⁸O in hot water. Dissolution of feldspar, calcite, gypsum, pyrite and oxidation of H₂S provide the source of main ionic constituents in the hot springs. The average reservoir temperatures of Bailing Hot Spring, Tanghu Hot Spring and Baishi Hot Spring are 125, 135 and 149 ℃, respectively, and the corresponding recharge elevations are 1455, 1790 and 1050 m, respectively.