Discussion on hydrogeochemical characteristics and genetic model of geothermal waters in Xianshuihe,Anninghe and Longmenshan fault zones in western Sichuan,China
This paper is the result of geothermal geological survey engineering.[Objective]In order to develop and use geothermal water resources in western Sichuan rationally,it is important to study hydrochemical characteristics and genetic models of the geothermal waters spatially linked with the Xianshuihe(XFZ),Anninghe(AFZ),and Longmenshan(LFZ)fault zones.[Methods]The methods of hydrogeochemistry,reservoir temperature calculation,hydrogen and oxygen isotopes were used to estimate hydrochemical types,hydrochemical processes,reservoir temperatures and depths,and recharge sources of 48 typical localities of geothermal waters(or geothermal springs or drilling holes)located around these three fault zones,and reconstruct the mode of their formation.[Results](1)Hydrochemically the geothermal waters are dominated by HCO3-Na type in the XFZ,SO4-Na and Cl-Na types in the LFZ and HCO3·Cl-Na,HCO3·SO4-Ca·Mg and Cl·SO4-Na types in the AFZ.(2)The composition of geothermal waters of the three fault zones are mainly controlled by the dissolution of silicate minerals and ion exchange process.(3)The temperatures of the reservoirs,their depths and the cold water mixing ratio are,respectively,129.6-210.6℃,2532-4184 meters,and 66%-82%for the XFZ,81-121.9℃,2155-3519 meters,and 52%-95%for the AFZ and 108.2-153℃,3573-5654 meters,and 68%-89%for the LFZ.(4)The geothermal waters in the three fault zones are recharged by meteoric waters derived from elevations at 2493 to 5034 meters in the XFZ,3235 to 3839 meters in the AFZ,and 1628 to 4574 meters in the LFZ.(5)The degree of the"δ18O drift"of geothermal waters in the XFZ is higher than that in the AFZ,and the geothermal waters in the LFZ exhibit characteristics of"δ18O drift"and"negative drift".[Conclusions]Our results show that among the three perspective areas of the Sichuan Province,the Xianshuihe Fault Zone possesses a higher commercial potential for the exploration and utilization of medium-high temperature geothermal resources compared to the Anninghe and Longmenshan fault zones.
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