Abstract: The Zhefang Basin in Mang City of Yunnan Province is located in the middle-south section of the Sanjiang orogenic belt. There are many faults, strong magmatism and abundant geothermal resources in this area, but research on these different aspects of this area is low at present. In this study, a geological, geophysical, hydrogeological and hydrogeochemical investigation was carried out in the sedimentary rock area on the eastern side of the Longling-Ruili Fault. Water samples were collected and subjected to hydrochemical analysis, stable isotope measurements, and quantitative calculations. The silicon-enthalpy equation method and the silicon-enthalpy diagram method were used to quantitatively evaluate the cold-water mixing ratio in hot spring water, and to estimate hot water recharge elevation, recharge zone temperature, thermal storage temperature, cycle depth, and natural heat release of the hot spring. The calculated δ13CCO2 value of CO2 is -16.56‰. The sources of CO₂ involved in water-rock reaction are a mixture of both mantle and soil. Moreover, the water-rock reaction is mainly reflected as CO₂ entering the reservoir and the surrounding rock to produce HCO₃-. The genetic type of groundwater hydrochemical components is mainly constrained by rock weathering type. The chemical characteristics of geothermal fluid, the state of occurrence of geothermal resources, the mechanism of thermal cycle and the source of heat source in Zhefang jade pool were further identified. The formation and evolution of geothermal water in the study area were analyzed. The research results provide new support for geothermal research in Zhefang area and important guidance for the sustainable development and protection of tourism resources in the jade pool.

Key words: Zhefang basin, hotspring, hydrogeochemical characteristics, stable isotopes, water-rock interaction