Numerous low-temperature geothermal waters are distributed extensively in Mangbang-Longling of western Yunnan in China, whose formation mechanism has not been completely investigated yet. This study focused on the hydrogeochemical evolution, reservoir temperature, and recharge origin of geothermal waters using hydrogeochemical and deuterium-oxygen (D-O) isotopic studies. The low-temperature geothermal waters were characterized by HCO₃-Na type, while shallow cold spring was of the hydrochemical type of HCO₃-Ca. The hydrogeochemical characteristics of low-temperature geothermal waters were mainly determined by the dissolution of silicate minerals based on the geological condition and correlations of major and minor ions. The reservoir temperatures of low-temperature geothermal waters ranged from 111°C to 126°C estimated by silica geothermometry and the silicon-enthalpy graphic method. Low-temperature geothermal waters circulated at the largest depth of 1794–2077 m where deep high-temperature geothermal waters were involved. The data points of δD and δ¹⁸O of the hot spring water samples in the study area show a linear right-up trend, indicating the δ¹⁸O reaction between the water and rock and a possible mixture of magmatic water from below. The low-temperature thermal waters were recharged by meteoric water at the elevation of 2362–3653 m calculated by δD values. Upwelling by heating energy, low-temperature geothermal waters were exposed as geothermal springs in the fault and fracture intersection and mixed by up to 72% shallow cold waters at surface. Based on acquired data, a conceptual model of the low-temperature geothermal waters in the Mangbang-Longling area was proposed for future exploitation.

中文翻译：

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滇西芒帮-龙岭地区低温地热水水文地球化学特征及形成

云南西部芒浜—龙岭地区广泛分布着大量的低温地热水，其形成机制尚未完全研究。本研究利用水文地球化学和氘-氧 (DO) 同位素研究，重点研究地热水的水文地球化学演化、储层温度和补给来源。低温地热水以HCO ₃ -Na型为特征，浅层冷泉为HCO ₃水化学型-Ca。低温地热水的水文地球化学特征主要是由硅酸盐矿物的溶解作用决定的，根据地质条件和主次离子的相互关系。低温地热水储层温度范围为 111°C 至 126°C，通过二氧化硅地球测温法和硅焓图法估计。低温地热水循环最大深度为1 794～2 077 m，涉及深部高温地热水。研究区温泉水样的δ D 和δ ¹⁸ O数据点呈线性右上趋势，表明δ ¹⁸O 水和岩石之间的反应以及可能来自下方的岩浆水混合物。低温热水域通过大气水以2362-3653米由计算出的海拔充电δ d的值。在热能的作用下，低温地热水在断层和裂缝交叉处以地热泉的形式暴露出来，并在地表与高达 72% 的浅冷水混合。根据获取的数据，提出了芒浜-龙岭地区低温地热水概念模型，以供未来开发利用。