川西南喜德热田地下水水文地球化学特征

地下热水的形成和化学组分特征常受断裂构造和热储地层岩性的影响。川西南喜德地热田内出露的冷泉水和地热水严格受断裂控制，前者为主断裂控制的浅循环型碎屑岩或岩溶裂隙孔隙水；后者则为次级断裂所控制的深循环型裂隙水，其热储层为碳酸盐岩。基于喜德热田形成的地质构造背景，通过开展热田内地热水和冷泉水水化学指标的测试和分析及水岩相互作用模拟，对该热田水文地球化学特征进行了研究。结果表明：喜德热田地热水和冷泉水水源均为大气降水，补给高程分别为2 874~3 092 m和2 584~2 818 m。受温度、含水层矿物类型、水岩相互作用的影响，地热水和冷泉水水化学类型和各组分差别较大，前者为HCO3·SO4-Ca·Mg型水，后者为HCO3-Ca·Mg型水。水岩相互作用模拟表明碳酸盐岩矿物、石膏矿物的溶解和沉淀及阳离子交换过程是导致地热水和冷泉水水化学组分差别较大的主要原因。此外，采用二氧化硅类温标计算喜德热田热储温度为56~90 ℃，循环深度为1 422~2 558 m。研究结果对阐明喜德热田的成因模式，地热水的进一步开发和热水资源的可持续利用具有重要意义。

Hydrogeochemical Characteristics of Groundwater in the Xide Geothermal Field,Southwest Sichuan,China

The formation and chemical characteristics of thermal groundwater are commonly influenced by the fault structures and the strata lithology of geothermal reservoirs, such as Xide geothermal field. It is located in north shore of the Sunshui River of Xide town, Liangshan Prefecture, Sichuan Province, and belongs to low medium temperature convective geothermal fluid system in carbonate aquifer. The hydrogeochemical characteristics of cold spring and thermal waters in this area are mainly affected by faults. The cold spring water derived from the shallow circulation clastic rock pore fracture water or karstic fracture water, which was controlled by the main fault. The thermal water originated from deep cycle fissure water, which was significantly influenced by the secondary fault. In addition, the main reservoir of thermal water is carbonate rocks. Based on the local geological structure, hydrochemistry analysis of thermal and cold spring waters were incorporated with water rock interaction simulation to analyze the hydrogeochemical characteristics of groundwater in this area. The results were shown as followings. Thermal and cold spring waters originated from meteoric water and the recharge elevation are of 2,874-3,092 m and 2,584-2,818 m, respectively. The hydrochemical type and chemical components are distinctive between thermal and cold spring waters due to reservoir temperature, aquifer types, and water rock interactions. The thermal waters is of HCO3·SO4-Ca·Mg type, while the cold spring waters is of HCO3-Ca·Mg type. The main cause for those differences is that the dissolution and precipitation of carbonate and gypsum, and cation ion exchange. In addition, the reservoir temperature and circulation depth calculated by silica geothermometer are 56-90 ℃ and 1,422-2,558 m, respectively. The results provide important insights into the genesis of the Xide geothermal field, and are instructive for further management and sustainable utilization of geothermal resource for local government.