Geochemical and sedimentological characterization of the Salar de Olaroz, northern Argentinean Puna, Central Andes.

BORDA, L.; FLORES, P. ; FRANCO, G.; LÓPEZ STEINMETZ, R.; GARCÍA, G.; CÓRDOBA, F.

San Salvador de Jujuy

Workshop; Proceedings 3rd International Workshop on Lithium, Industrial Minerals and Energy (IWLiME 2016); 2016

Universidad de Jujuy

The Salar de Olaroz is part of the Olaroz-Cauchari closed-basin, set in a submeridional-enlogated tectonic depression in northern Argentinean Puna. It constitutes a saline system of great economic interest due to the high concentrations of Li, B and K of its brines. The sub-basin of the Salar de Olaroz (24º05´S - 66º40´W; 3950 m a.s.l.) occupies an area of 3219 km2 and it is limited to the south by the Archibarca alluvial fan, that acts as a natural barrier between Olaroz and Cauchari salt pans. The salar is fed by a number of temporary fluvial courses that reach the salar with NW-SE direction. The Rosario river which its regime is permanent, reaches the salar from the northern part of the basin and generates an extensive fan. In the distal part of the fan, spots of thermal springs have been observed. The geomorphological environment of the region corresponds to a typical playa-lake landscape with associations of characteristic geoforms. In order to generate an actualistic model of the physical-chemical function of the salar, the characterization of the current depositional environment of this evaporitic system was performed on the basis of a geomorphological, sedimentological and hydrogeochemical analysis.Characterization of current subenvironments of the salt complex was performed on the basis of the satellite images analysis, aerial photographs and field observations. Surface water samples were collected from different sub-environments of the salar and in-situ measurements of pH, temperature, conductivity, TDS and alkalinity were performed. In the laboratory, major and trace ions were determined by ICP-MS and anions by ion chromatography. For the analysis and characterization of sedimentary facies and evapofacies, efflorescences and salt crusts were sampled from the different salar´s sub-environments. This set of data was integrated in order to define different sub-environments of evaporite system: alluvial fans, sandflat, dry mudflat, saline mudflat, dunes and palaeo-dune fields, ephemeral lakes, springs and salt pan.The first results indicate that the shallowest brines of saline core show neutral pH, high concentrations of total dissolved solids (TDS ˃ 300 g L-1) and are of the Cl- / Na + type. Meanwhile, river and lake waters are alkaline (pH between 8.03 and 8.98), and they have TDS concentrations below 3.6 g L-1 and are Na +/Cl- type, except for the waters of the Archibarca stream that are Na + / Cl- (SO4 2-) type. The hot springs located northern of the salar are of the Cl- / Na + type and they show neutral pHs, temperatures ranging between 19 and 28 ° C and TDS concentrations > 30 g L- 1.The highest concentration of Mg2+, Li + and K + were recorded in the salt pan, with concentrations that vary between 1454 and 3345 mg L-1, 200 and 3000 mg L-1 and 2164 and 47103 mg L-1, respectively. These values decrease significantly to the margins of the salar. By contrast, the river waters that discharge into the salt pan present lower concentrations of Mg2 + (between 25 and 33 mg L-1), Li + (between 3 and 8 mg L-1) and K + (between 13.5 and 27 mg L-1) while the lake located in the north of the salar have concentrations of Mg2 +, Li + and K + ranging between 21-177 mg L-1, 9.9 -19 mg L-1 and 36-71 mg L- 1, respectively. In particular, the thermal waters have values of 4064 mg L-1 of Mg +, 156.6 mg L-1 Li + and 1755 mg L-1 of K +.These preliminary results suggest that the observed spatial chemical variability identified in water reservoirs of the different sub-environments of the salar could be linked not only to climatic factors (aridity and elevated rates of evaporation) but also to thermal activity. Contributions of Li from rock weathering and the incorporation of solutes during mixing of meteoric and thermal waters need to be analyzed in order to better understand the dynamics of Li and its spatial distribution in the salar.