Hydrogeochemical characteristics and genetic model of Oiga Graben geothermal waters system in Tibet

Based on the study of hot water hydrogeochemical characteristics of the Oiga Graben Geothermal Waters, the authors carried out hot water heat storage temperature and recharge elevation calculation, and established the Oiga Thermal Spring mediumhigh temperature geothermal concept model. The results show that the Oiga hot spring is of medium-alkaline water with low TDS, and the water chemical types are mainly SO₄-Na type, SO₄-Cl-Na type and HCO₃^- SO₄-Na type. The hydrogeochemical characteristics of hot water indicate that the Oiga Springs are characterized by atmospheric rainfall recharge and shallow circulation groundwater in shallow geothermal systems. The hot water is heated by deep melting body and controlled by the Oiga semiinvisible controlled thermal fracture structure. but it is partially balanced or mixed with water in the Na-K-Mg triangle diagram due to the mixing effect by fissure diving or surface cold water. The mixed model is used to estimate the temperature before the influence of hot water and cold water mixing, the temperature range of the heat storage is 120-200℃, and the cold water mixing ratio is 70%-83%.