关键词: 地热田, 水化学特征, 水文地球化学模拟, 成因模式, 青海省互助县, 西宁盆地

Abstract:  The Xining basin is rich in geothermal resources, with geothermal water exhibiting high salinity characteristics. To reveal the formation mechanism and circulation evolution of the high-TDS geothermal water in this area,this study selects a typical geothermal field in Huzhu County, located in the northeastern part of the Xining basin, as the research subject. Through collaborative analysis of multiple methods, including geothermal water sampling and testing, isotope techniques, traditional hydrogeochemical methods, and hydrogeochemical modeling, the hydrochemical characteristics and genetic mechanisms of the geothermal water in the area are systematically investigated. On the basis of determining the hydrochemical characteristics of the Huzhu County geothermal field, the study explores the recharge sources and circulation depth of the geothermal water, quantitatively evaluates the mineral reaction mechanisms responsible for the high salinity during the water cycle, and constructs a genetic model of the geothermal field. The research results indicate: The main hydrochemical components of the geothermal water in the area are Na+, Cl-, and SO42-, with a hydrochemical type of Cl·SO4-Na. The geothermal water in the area is weakly alkaline, with high salinity (TDS) and high fluoride content, where TDS concentrations range from 9 530 to 43 056 mg/L, and fluoride ion concentrations range from 1.26 to 2.31 mg/L. The geothermal water in the area is recharged by atmospheric precipitation infiltration, with a circulation depth of 2 274.9 to 2 635.7 m. During its flow path, it passes through limestone, gneiss, sandstone, and sandy conglomerate strata. The geothermal system in the area is a medium-low temperature conductive type, with the heat source primarily derived from the terrestrial heat flow of the lower crust and upper mantle. The caprock consists of Paleogene mudstone, gypsum rock, and sandy mudstone, while the reservoir is composed of Cretaceous sandstone-sandy conglomerate, with a reservoir temperature of 63.50-72.70  ℃. The high salinity (TDS) of the geothermal water in the area is mainly attributed to the dissolution of gypsum and halite, as well as positive cation exchange. Specifically, the dissolution of halite and positive ion exchange increase the concentrations of Na+ and Cl-, while the dissolution of gypsum from evaporites increases the concentrations of Ca2+ and SO42-. H2SiO3 and F- are derived from the dissolution of quartz and fluorite, respectively. 

Key words: geothermal field, hydrochemistry characteristics, hydrogeochemical simulation, genesis model, Huzhu Country, Qinghai Province, Xining basin