云南祥云县王家庄碱性温泉水化学特征与成因分析

位于云南省祥云县刘厂镇的王家庄温泉水样YMD10-1(王家热水井)与YMD10-2(聚龙温泉宾馆热水井)的矿化度为1.49~1.65 g/L,主要阳离子为Na^+,主要阴离子为HCO3^-,水化学类型均为HCO3-Na型。YMD10-1和YMD10-2的p H值野外测定数据分别为10.8和7,因YMD10-2暴露于空气使其pCO2较高导致其p H野外观测值偏低;实验室p H测定值分别为8和7.6,主要受到pCO2差异影响导致水中碳酸组分发生变化而改变了其p H值。水样的δ^2H-δ^18O数据显示温泉的补给来源为大气降水。利用Si O2温标估算了温泉的地下热储温度为89~92℃。利用226Ra-222Rn法估算出YMD10-1的热水年龄为446.84 a,YMD10-2的热水年龄为319.56 a。估算的地下热水的循环深度为3 808~3 898 m,利用δ^2H和δ^18O估算热水补给高程为2 845~2 865 m,补给区为周边的山区。地下水获得大气降水入渗补给后,经历深循环并获得深部热流加热,沿断裂带上升穿透浅部第四系出露地表。温泉显示碱性是由于长石与水和CO2发生反应,产生大量的HCO3^-,HCO3^-在溶液中有可能水解消耗H^+产生OH^-。王家庄温泉被当地人们用来晒制土碱,与热水Na^+和碳酸的含量高有关。

Characteristics and Formation of the Wangjiazhuang Alkaline Hot Spring in Xiangyun County of Yunnan

The Wangjiazhuang hot spring is located in the Liuchang Township in Xiangyun County of Yunnan, China. The water samples YMD10-1 (from the Wangjia geothermal well) and YMD10-2 (from the Julong hot spring well) range in TDS from 1.49 to 1.65 g/L. The cation and anion are predominated by Na⁺and $HCO_{3}^{-}$ and the hot water is of HCO₃-Na type. The pH values of the water samples are 10.8 and 7, respectively. Because of the high $p_{co_{2}}$ in the YMD10-2 sample, the pH value measured in the field is lower than expected. The pH values measured in laboratory are 8 and 7.6, respectively, which are mainly affected by the diffe-rence in $p_{co_{2}}$, resulting in changes in the carbonate compositions in the water samples. δ ²H and δ ¹⁸O data of the hot water samples indicate that the hot spring is of meteoric origin. The recharge altitude of the hot water is estimated as 2 845-2 865 m, the temperature of the geothermal reservoir as 89-92 ℃, and the depth of the groundwater circulation as approximately 3 808-3 898 m. The age of the hot spring is estimated as 319-447 a with the ²²⁶Ra-²²²Rn method. After receiving recharge from infiltration of precipitation in the surrounding mountain areas, the groundwater undergoes deep circulation and is heated by heat flow, and flows up along the fault zone through the Quaternary sediments and emerges on the lad surface. The alkalinity of the hot spring is attributed to the reaction of feldspar with water and CO₂, resulting in high concentrations of $HCO_{3}^{-}$, and hydro-lysis of $HCO_{3}^{-}$ in solution possibly consumes H⁺ to produce OH^-. The Wangjiazhuang hot spring is used to produce alkali by local people due to high contents of Na⁺, $HCO_{3}^{-}$ and $CO_{3}^{2-}$ in the hot water.