Geochemistry and mineralogy behaviour of Llamara Salar (Chile): Origin of solutes and brine evolution.

The Atacama desert in northern Chile, presents a very high dry climate whic h causes a deficit in water resources. This climatic condition, together wi th geological characteristics, volcanic activity, and endorreic depressions , among others, determine the salinity and complexity of the few existing w ater deposits. Therefore, the study of such deposits is of special scientif ic and economic importance. The Llamara Salar's, object of the study proposed in this project, is a sal ine system which maintains its activity due to its geomorphologic location and the climatic characteristic of the region where it is located. Its wate rs have evolved in a complex way through the time to form several saline sy stems. The waters are of neutral type and from the chemical point of view c an be classified as a chloride-sodium system. The mineralogical analysis of the solid faces indicate abundant precipitation of gypsum (CaSO4. 2H(2)O). A systematic study of this system has been done during three years (1994-19 96) which has allowed to interpret the evolution of the characteristics of the systems using the chemical relations(1)), indicating that the saline so lutions remained at equilibrium at every time with calcite and gypsum. Acco rding to Valyashko's Diagram(2)), for solutions of high concentration, the mineral which precipitates after the gypsum is halite, these components rea ch equilibrium with other more soluble sulfates, berates and nitrates when the concentration is very high, close to total desiccation. Also the analys is of the salt crusts and sediments has shown a similar composition, beside s the presence of bloedite, thenardite, mirabilite, glauberite, eugsterite and probertite.