湖南省地热水水文地球化学特征

为了查明湖南省地热水的赋存状况、估算研究区热储的温度、冷热水的混合比值及热水循环深度等信息，文章利用离子比值法、phreeqc计算矿物饱和指数法以及硅—焓模型等方法，对研究区69处地热水进行水文地球化学分析。结果表明:研究区地热水主要的水化学类型为HCO3-Ca和HCO3-Ca·Mg，其次为SO4·HCO3-Ca·Mg和SO4-Ca；77%地热水中钙镁离子的比值大于3，表明地热水的封存时间久；利用phreeqc计算出多矿物饱和指数，表明二氧化硅矿物最接近饱和状态；使用硅—焓混合模型估算研究区热储温度和冷水混入比例，表明热储温度范围为32~226 ℃，均值为140 ℃，冷水混入比例平均为85%，占比较大；利用地温梯度计算地热水循环深度范围为5~6 km，平均深度5.34 km。总之，湖南省地热水演化时间长，径流时间比较久，区域循环深度大，热液经热储增温后，经过长时间的径流、水岩作用等，地热水在高压以及热动力驱动下向地表循环，在地表附近与冷水混合后形成以低温为主的“未成熟”中低温热水。 

Hydrogeochemical characteristics of geothermal water in Hunan Province

Hunan Province hosts abundant geothermal water resources，while little research of hydrochemistry on them has been made. research is not thorough. The purpose of this work is to analyze the occurrence of geothermal water in Hunan Province，estimate the temperature of the heat storage in the study area，the mixing ratio of cold and hot water，and the depth of hot water circulation. Using the ion ratio method，phreeqc calculation of mineral saturation and the silicon enthalpy model， we analyze hydro-geochemestry of geothermal water at 69 sites in the study area. The results indicate that the main hydrochemical types of geothermal water are HCO3-Ca and HCO3-Ca.Mg， followed by SO4.HCO3-Ca.Mg and SO4-Ca； The ratio of calcium to magnesium ions in 77% of all geothermal water in the study area is greater than 3，reflecting the long storage time of geothermal water in Hunan Province. Using phreeqc to calculate the multi-mineral saturation index finds that the silica mineral is closest to the saturated state. Using the silicon-enthal pymixing model to estimate the heat storage temperature and the mixing ratio of cold water in the study area，the results show that the thermal storage temperature ranges 32 ℃~226 ℃，140 ℃ on average，and the average cold water mixing ratio is 85%，which is relatively large. The geothermal gradient is used to calculate the geothermal water circulation depth， yielding of 5-6 km， 5.34 km on average. In general，the geothermal water in Hunan Province has a long evolution time，a relatively long runoff time，and a large regional circulation depth. After the hydrothermal fluid is warmed by the thermal storage a long period of runoff and water-rock interaction，the geothermal water is driven by high pressure and thermodynamics. The geothermal water circulates to the surface of the ground，where it is mixed with cold water near the surface to form "immature" medium-low temperature hot water， dominated by low temperature.