HYDROGEOCHEMICAL CHARACTERISTICS AND GENESIS MECHANISM OF GEOTHERMAL WATER IN AWANG, EASTERN TIBET

Based on the geothermal setting of the Awang Township of Tibet, we analyzed the characteristics and genetic mechanism of geothermal water with the aid of field investigation, hydrogeochemistry, and environmental isotopes. The hydrochemical types of geothermal water belong to HCO₃-Na type, resulting from leaching and cation interaction between geothermal water and surrounding rocks. The composition of hydrogen and oxygen isotope indicates an origin of meteoric water. The slight oxygen drift is produced by water-rock interaction and high temperature of geothermal reservoir. The recharge area with estimated altitude of 4600~4800 m is located in northwest mountain areas. The analyses of Na-K-Mg triangle graph and saturation index collectively show the geothermal water is mixed by shallow cold water with the proportion of 60% to 70%. The temperatures of deep geothermal reservoirs are 170~200 ℃ suggesting by quartz and Na-K geothermometers. The circulation depth of geothermal water is 4500~5300 m. The genetic mechanism of geothermal water in Awang Township can be concluded as follows: the thermal water recharged from precipitation is heated by terrestrial heat flow, arises and exposes as geothermal springs along the fault zone.