Geochemistry of Huasco Salar's, Chile.: Origin of solutes and brine evolution

The Salar of Huasco is a modem saline continental system located in the Andean region of the northeast of Chile. The extremely arid conditions, altitude, volcanity activity to result in a high evaporation rate, yielding brines of high ionic strength. This is of special importance considering that these lakes are located in a desert region rich in minerals with an increasing mining activity. The stratigraphic record of the salar basin shows a central massive saline crust (mirabilite 1 m thick), surrounded by an aureole of fine clay-saline material with a superficial saline crust of a few centimeters composed of chlorides and sulphates. All these deposits were generated in a paleolake developed during the late Tertiary. At present surface waters cover only a minor part of the salar surface. A mineralogic analysis shows that the salar mainly formed by sulphate crusts (mirabilite, tenardite), with a substrate formed by fine saturated sediments with interstitial dissemination of crystals. Chlorides (halite) and sulphates, 20 cm thick form the central part (nucleus). The bottom part of the salar contains hydrated sodium sulphate (mirabilite) with crystals layers up to 1 cm thick The brines of Huasco salar's are Na+>SO4-2>Cl- type. The cationic composition is more homogeneous, with alkaline elements (sodium and potassium) always prevailing over calcium and magnesium. The solutions are in equilibrium with calcite, reaching equilibrium with gypsum and mirabilite when the concentration increases. In the final stages the most concentrated brines are in equilibrium with halite, sylvite and syngenite. The quantities of mirabilite found in these salars is what makes them attractive for commercial exploitation, but the climate conditions are a problem.