Hydrogeochemical Characteristics And Genetic Model Of Geothermal Water In Ganzi-Litang Fault Zone

Located in the west of Sichuan Province and the southeast margin of Qinghai Tibet Plateau,Ganzi Litang fault zone is an important geothermal resource exploration area with strong hydrothermal activity.In this paper,the geothermal system of ganzi-Litang fault zone is studied based on regional geological background,detailed field geological survey,geothermal water and geochemical data of rock samples.The distribution characteristics of geothermal resources are summarized.The distribution of geothermal resources in the study area is affected by deep structures and controlled by active strike-slip faults.The fault basin formed by strike-slip faults and the intersection of faults are favorable locations for geothermal water enrichment and exposure.The hydrogeochemical characteristics and water-rock interaction of geothermal water were analyzed.The geothermal water in the study area is mainly HCO₃-Na water,with a small amount of HCO₃-Na·Ca water and HCO₃·SO₄-Na water.The hydrochemical type of the thermal water is mainly controlled by aquifer lithology and runoff path.The recharge source and recharge elevation of geothermal water were analyzed by hydrogen and oxygen isotope.It was found that atmospheric precipitation was the main recharge source of geothermal water in the study area,and the recharge altitude was3825m～5076m.The reservoir temperature of each hydrothermal activity area were calculated by using a variety of geothermometer,among which the reservoir temperature of Ganzi hydrothermal activity area have a range of 170℃～180℃,the reservoir temperature of Xinlong hydrothermal activity area have a range of155℃～160℃,the reservoir temperature of Litang hydrothermal activity area have a range of 200℃～210℃,the reservoir temperature of jiawa hydrothermal activity area have a range of 160℃～175℃.The geothermal water circulation depth was estimated,and the circulation depth of geothermal water in Ganzi,Xinlong and Jiawa hydrothermal activity areas have a range of 3100m～3400m.The circulation depth of Litang hydrothermal area is 3956m,mixed with 48%～82%cold water in the process of migration.The reservoir in the study area is mainly fractured thermal reservoir,which is composed of fractured carbonate rock,granite and slate.The elements of the geothermal system were comprehensively analyzed,and the genetic model of geothermal water of deep fault zones type was proposed to provide reference for the rational development and utilization of geothermal resources in western Sichuan.