The genetic mechanism of Hongjiang geothermal system in Jiangxi, Southeast China: insight from the evidence of hydrochemistry, multiple isotopes, and inverse geochemical models

Investigating the hydrochemical evolution characteristics, circulation processes, and formation mechanisms of geothermal systems provides critical insights for geothermal resources development. This study employs hydrochemistry, multiple isotopes (δ¹⁸O, δ²H, ⁸⁷Sr/⁸⁶Sr), silica-enthalpy mixing model and hydrogeochemical inverse models determine the key hydrogeochemical process. The results demonstrate that all geothermal waters belong to Na-HCO₃ type. Silicate minerals dissolution, cation exchange and mixing take place during the geothermal fluid circulation. The geothermal fluid is originated from precipitation, with a recharge elevation of 813 ~ 1012 m. The reservoir temperature is 111 ~ 121 ℃, determined by SiO₂ geothermometer and multimineral equilibrium method. The geothermal circulation depth with an average of varies from 2641 to 2919 m. Under the effect of hydraulic pressure, the deep geothermal groundwater upwells mixed with shallow cold groundwater with a proportion of 73 ~ 93%. The amount of mineral transfer in the different flow paths is calculated by inverse geochemical simulation. The study indicates that the key reactions in geothermal circulation include albite, quartz and CO₂ (g) dissolution, kaolinite precipitation, and cation exchange interaction. Finally, Conceptual model for genesis of Hongjiang geothermal system has been developed.