西藏萨迦冲曲流域地下热水成因及工程效应分析

Geothermal Water Genesis and Engineering Effect in Saga Chongqu Basin, Tibet

拟建中尼铁路途经西藏萨迦县和拉孜县,地热灾害是拟建中尼铁路工程建设过程中可能遇到的地质工程问题之一。通过计算离子比例系数,绘制Gibbs图、Na-K-Mg三角图和SiO_(2)溶解度曲线,分析了研究区地下热水的水化学特征及其水文地球化学演化过程的主要控制因素,并根据氢氧同位素数据分析了研究区地下热水的补给来源,基于此对拟建中尼铁路工程建设提出了合理的热害防治措施。结果表明:卡乌地下热水的水化学类型为Cl-Na型,曲参岗地下热水为Cl·HCO_(3)-Na型,锡钦地下热水为HCO_(3)-Na·Ca型;研究区地下热水水化学组分的形成普遍受到硅酸盐矿物溶解的影响,其中卡乌、曲参岗地下热水的水化学组成主要受蒸发/沉淀作用的影响,锡钦地下热水的优势离子受蒸发/沉淀作用和水-岩相互作用共同的影响;卡乌地下热水为40年以前的"古水"占优势的水,锡钦地下热水为新近入渗水和古水的混合水;萨迦县卡乌地热水具有腐蚀性,且卡乌泉口出露温度达到当地沸点,为高温地热资源,隧道工程必须绕避卡乌温泉区。

Geothermal damage is the main geological engineering problem of the proposed China-Nepal Cross-border railway through Saga and Lazi.On the basis of analyzing the hydrochemical characteristics of geothermal water and its genesis,and comprehensively using the ion ratio coefficient,Gibbs,Na-K-Mg giggenbach plot,SiO_(2) solubility curve,hydrogen and oxygen stable isotopic method to analyze the geothermal water genesis in the study area,this paper puts forward reasonable suggestions specific to the geothermal damage in China-Nepal Cross-border railway construction.The result shows that Kawu hydrochemistry type is Cl-Na,Qucangang is Cl·HCO_(3)-Na type,and Xiqin belongs to HCO_(3)-Na·Ca.The hydrochemical composition is affected by the dissolution of silicateminerals in the study area.The hydrochemical composition of the geothermal water in Kawu and Qucangang are mainly affected by evaporation,and the dominant ions of Xiqin geothermal water are affected by evaporation/precipitation and water-rock interaction.Kawu spring is dominated by"ancient water"40 years ago,and Xiqin spring is a mixture of recent infiltration water and ancient water.The geothermal water in Sakya County is corrosive,and the outlet temperature of Kawu spring as a high-temperature geothermal resource reaches the local boiling point.The tunnel project must circumvent the Kawu spring area.