西藏朗久地热田水文地球化学特征

THE HYDROGEOCHEMICAL FEATURES OF LANGJIU GEOTHERMAL FIELD IN TIBET

朗久热田地下热水为中性－偏碱性低矿化水，富Ｌｉ，Ｂ，Ａｓ；Ｃｌ－ＨＣＯ３－（ＳＯ４）－Ｎａ水是主要水化学类型；Ｃａ２＋，Ｍｇ２＋是钙、镁在水溶液中的主要存在形式，其无机配合物居于次要地位；铀的主要存在形式是〔ＵＯ２（ＣＯ３）３〕４－和〔ＵＯ２（ＣＯ３）２２－〕，铀羟基配合物含量甚微；铀酰配合物计算及氢、氧稳定同位素测试结果表明，朗久地下热水主要是由大气降水起源的渗入水经深循环至还原环境形成，并有部分岩浆水混入；利用地化温标计算的地热系统浅部温度为１５０～２５０℃。

The underground hot water in Langjiu geothermal field is neutral-to-alkalescent, weakly mineralized water and rich in Li, B and As; Cl-HCO3-(SO4)-Na is of its main hydrogeochemical type; Ca2+ and Mg2+ are the main existence form of Ca and Mg and their inorganic complex compounds are inferior; According to the calculation of uranium-acy1 complex compounds and the stable isotopic data of hydrogen and oxygen, Langjiu thermal water is formed from seepage water which originates from meteoric water and deeply circles into crust and maybe is mixed by magmatic water; The calculated temperature of the shallow geothermal reservior ranges from 150℃ to 250℃.