Characteristics and resource evaluation of the Jiwa geothemal field in central Qiangtang, northern Tibet, China

The Jiwa hot springs are located north of Jiwa Villiage in Nima Country, Tibet. The occurrence of the hot springs are within a Cenozoic rift basin, controlled by Jiangaizangbu faults. The thermal groundwater has total dissolved solids content of 5.54×103－5.58×103 mg/L, and is hydrochemically of Na-Cl·HCO3 type. The thermal groundwater has high content of H2SiO3、Li+ and F-, and these 3 items meet the requirement of medical use. The fractional melting layers in crust have provided heat energies to the hydrothermal system while the atmospheric precipitation is the major water charging supply, secondly deep area hot fluid. The mixing model study shows that the thermal groundwater is a mixture of hot and cool groundwater, the cool water proportion is between 77% and 95%, and the residence time of mixture is 31a. The temperature of the shallow geothermal reservoir is calculated at 120℃ using SiO2 geothermometer method with a depth of 832 m. The temperature of the hot water before mixing is between 215℃ and 280℃. The corresponding deep geothermal reservoir is estimated at between 1466m and 1900 m. The Jiwa geothemal field has a total area of 6km2. The natural heat discharge amount is more than 7.53×1013 J/a, according to primary evaluation, and the geothermal resource energies in the field is more than 32606×1014 J.