The genesis of typical geothermal water in Shigatse based on hydrochemical characteristics and isotopes

• Based on the comprehensive analysis of water chemistry , hydrogen and oxygen isotope (δ 2 H-δ 18 O), strontium isotope ( 87 Sr/ 86 Sr) and sulfur isotope (δ 34 S), the hydrogeochemical evolution path of geothermal water in the study area was revealed, and the thermal reservoir temperature was estimated by silicon-enthalpy model and geothermal temperature scale. • Through hydrogen and oxygen isotope end-member analysis, it is determined that the geothermal water recharge elevation is 2541-5971 meters, mainly from atmospheric precipitation , and its δ 18 O drift degree indicates the characteristics of deep circulation and high temperature water-rock interaction. • Combined with Piper trilinear diagram, ion proportional coefficient and saturation index (SI), it is clarified that the dominant hydrochemical type of geothermal water is HCO 3 -Na type, which is controlled by silicate weathering and evaporation concentration. Based on this, a conceptual model of ' supply-circulation-discharge ' is constructed to provide a basis for resource evaluation for sustainable development of geothermal fields. Shigatse City, located in the tectonically active Qinghai-Tibet Plateau, possesses abundant geothermal resources with complex formation mechanisms. This study systematically examines the characteristics of water-rock interactions within the geothermal system using an integrated approach that combines hydrogeochemical analysis and multiple isotope tracers. The key findings are as follows: (1) The geothermal system is classified as a thermal convection type within tectonic uplift zones. Geothermal water undergoes extensive water-rock interactions during migration, exhibiting deep circulation characteristics; (2) Hydrochemical analysis identifies the geothermal water was predominantly HCO 3 -Na type, with notably high Na + and TDS concentrations compared to typical geothermal fluids. Sulfur isotope analysis indicates that sulfate mineral dissolution is the primary sulfur source; (3) Geothermometric calculations estimate reservoir temperatures between 118 and 275°C, while mixing model analysis suggests that shallow cold water contributes 67−88% of the geothermal water composition; (4) Stable isotope studies reveal that the primary recharge sources are high-altitude snowmelt water and atmospheric precipitation, with recharge elevations ranging from 2541 to 5971 m. Strontium isotope analysis further establishes a genetic relationship between geothermal water and regional marine sedimentary formations. This study innovatively introduces a "deep water-rock interaction-shallow mixing" genetic model and develops a comprehensive conceptual model of the geothermal system. The findings enhance understanding of geothermal formation mechanisms in tectonically active plateau regions and provide a theoretical foundation for exploration, development, and sustainable utilization of geothermal resources.