Strauch Gerhard, Oyarzun Jorge, Fiebig-Wittmaack Melitta, González Edmundo, Weise Stephan M
Department of Hydrogeology, UFZ Centre for Environmental Research Leipzig-Halle GmbH, Germany.
Isotopes Environ Health Stud. 2006 Sep;42(3):303-22. doi: 10.1080/10256010600839707.
We present the results of an isotope (2H and 18O) and hydrogeochemical study in order to constrain the origin, recharge, and evolution of the surface and groundwater in the arid Andean realm of the Elqui watershed. The results of 2H and18O analyses of water samples obtained during our summer and winter campaigns indicate a generally meteoric origin of the river and spring waters of the watershed. The isotope signature of water of the Elqui river and its tributaries as well as that of groundwater in the coastal region fits the 2H-18O relation of delta2H =7.61delta18O+6.1. A relatively fast discharge and a quasi-closed catchment area can be asserted for water along the river flow path. The tributaries from the more arid coastal area, north of the Elqui river, differ in their isotopic signature due to evaporation and hydrochemically due to interactions with the strongly altered and fractured volcanic rocks of the basement. In the Andean zone, the18O-enriched hydrothermal spring of Baños del Toro exhibits the influence of water-rock interaction processes. The chemistry of the river water changes from sulphate- to chloride-rich along the river course from the high Andean mountains to the coast. The sulphate-rich character of these Andean waters reflects their passage through sulphide-rich rock massifs that were subjected to strong oxidation processes in the near superficial environment. This sulphate signature is enforced by past and present mining of precious metal epithermal deposits (e.g. those of El Indio-Tambo Au-Cu-As district), in which mineralised zones were developed during a series of Miocene magmatic-hydrothermal episodes in the Andean realm. Owing to the proximity of the lower Elqui river waters and its tributaries to the Pacific coast, the chloride character may be induced by agricultural and marine (sea spray, fog) sources. Generally, the main source of the Elqui river water is mainly attributed to surface runoff and less to contributions from the basement fractured aquifer.
我们展示了一项同位素（氘和氧-18）及水文地球化学研究的结果，以确定埃尔基河流域干旱安第斯地区地表水和地下水的来源、补给及演化情况。在夏季和冬季考察期间采集的水样的氘和氧-18分析结果表明，该流域的河水和泉水总体上源自大气降水。埃尔基河及其支流的水以及沿海地区地下水的同位素特征符合δ2H = 7.61δ18O + 6.1的氘-氧-18关系。沿河流流动路径的水具有相对较快的流量和近乎封闭的集水区域。埃尔基河北部较为干旱的沿海地区的支流，其同位素特征因蒸发而有所不同，在水化学方面则因与基底强烈蚀变和断裂的火山岩相互作用而不同。在安第斯地区，托罗温泉富含氧-18的热液泉显示出水-岩相互作用过程的影响。从安第斯山脉高处到海岸，河水的化学性质沿河道从富含硫酸盐变为富含氯化物。这些安第斯水域富含硫酸盐的特征反映了它们流经富含硫化物的岩体，这些岩体在近地表环境中经历了强烈的氧化过程。这种硫酸盐特征因过去和现在对贵金属浅成热液矿床（如埃尔印第奥-坦波金-铜-砷矿区）的开采而增强，在安第斯地区的一系列中新世岩浆-热液活动期间形成了矿化带。由于埃尔基河下游及其支流靠近太平洋海岸，氯化物特征可能由农业和海洋（海浪喷雾、雾气）来源引起。一般来说，埃尔基河流水的主要来源主要归因于地表径流，而较少来自基底裂隙含水层的补给。
