| Title | Geochemistry of Selected Hot Springs in Jiangxi Province, SE-China |
|---|---|
| Authors | Zhanxue SUN, Zhichao ZHANG, E.V. ZIPPA, Bai GAO and Gongxin CHEN |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | nitric hot springs; carbon dioxide-dominated hot springs; hydrogeochemistry; isotopes; water-rock interaction; China. |
| Abstract | The chemical and isotopic composition of ten selected hot springs in Jiangxi Province, SE-China, are analyzed. Five of them are N2-dominated hot springs. The N2-dominated geothermal waters are characterized by low TDS ranging from 0.135g/L to 0.294g/L, high pH values ( more than 8.5), and nitrogen-predominate ( more than 90%) in dissolved gases. The rest are CO2-dominated hot springs. The CO2-dominated thermal waters are distinguished by higher salinity from 0.245g/L to 1.33g/L but lower pH values (96%) in dissolved gases. Fluid-mineral equilibrium studies suggest that the geothermal water-rock system is an equilibrium -nonequilibrium system in which geothermal waters are close to equilibrium with secondary minerals as carbonates and fluoride, but disequilibrium with endogenous minerals as albite and anorthite. The reasons for extremely low TDS of the nitric hot springs is also discussed based on geochemical modeling using geochemical code PHREEQC. Solute geothermometers and the Log(Q/K) method give subsurface temperatures ranging on average from 80 to 150°C for the nitric geothermal systems. The isotopic studies showed that the nitric hot springs were recharged by local precipitation and have a circulation depth approximately from 1200m to 2700m. Isotopic and gas study showed that the carbon dioxide of the CO2-dominated hot springs are originated from magmatic inorganic sources and the nitrogen of the type is the mixture of mantle derived, crustal and atmospheric N2, and that the CO2 for the N2-dominant type come from crustal organic sources and the 3He/4He ratios represents input of radiogenic 4He in the crust. |