Revista Facultad de Ingeniería Universidad de Antioquia (Jul 2012)
Hydrochemical background of the Salar de Aguas Calientes I (Chile)
Abstract
The salar “Aguas Calientes I” is a saline system located in the Chilean altiplane at 4.280 m.a.s.l, and exposed to arid climatic conditions. Chemistry of waters exposed in the salar surface has been studied in this work. During the field survey, several sectors with surficial waters were accurately located by means of GPS, and solutions in springs, wetlands, and saline ponds were sampled. Samples were adequately stored and carried to laboratory for chemical analysis. In several places, saline solid material was also collected for mineralogical analysis. The main water inputs to the salar are situated in the northern and southern areas, this latter being thermal. Other inputs are the scarce precipitations that enter into the salar as surficial and/or subsurficial runoff. All these waters circulate towards the lowest areas of salar, being accu-mulated in several ponds along the western edge as consequence of a light tilting of salar surface. The water chemistry indicate that all of them belong to the same chemical type, Na-Cl, despite the high dispersion in solute content. This is due to the interaction between solutions and underground saline deposits of salar, mainly composed of halite and gypsum. Moreover, concentrations of Li, B, and As were high for all samples, typical of waters related to hydrothermal activity. In the case of As all samples show concentrations above toxicity level, even in the most diluted. The non-thermal fresh spring waters outcropping in the northern margin flow towards the salar, feeding along their course an important wetland (locally named bofedal) and supplying fresh water to herds of camelids. On the contrary, waters present in central and southern areas of salar are highly concentrated in ponds without plants in their margins. Ponds are rimmed by saline minerals, whose mineralogical analysis together with physicochemical calculations on water chemical data indicate an active process of mineral precipitation involving halite and gypsum.
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