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

FRANCO M.G.; BORDA L.G.; GARCÍA M.G; LOPEZ STEINMETZ R.; FLORES P.; CORDOBA, F.E.

San Salvador de Jujuy

Workshop; 3rd International Workshop on Lithium, Industrial Minerals and Energy; 2016

UNJU

TheSalar de Olaroz is part of the Olaroz-Cauchari closed-basin, set in asubmeridional-enlogated tectonic depression in northern Argentinean Puna. Itconstitutes a saline system of great economic interest due to the highconcentrations of Li, B and K of its brines. The sub-basin of the Salar deOlaroz (24º05´S - 66º40´W; 3950 m a.s.l.) occupies an area of 3219 km2and it is limited to the south by the Archibarca alluvial fan, that acts as anatural barrier between Olaroz and Cauchari salt pans. The salar is fed by anumber of temporary fluvial courses that reach the salar with NW-SE direction. TheRosario river which its regime is permanent, reaches the salar from the northernpart of the basin and generates an extensive fan. In the distal part of thefan, spots of thermal springs have been observed. The geomorphologicalenvironment of the region corresponds to a typical playa-lake landscape with associationsof characteristic geoforms. In order to generate an actualistic model of thephysical-chemical function of the salar, the characterization of the currentdepositional environment of this evaporitic system was performed on the basisof a geomorphological, sedimentological and hydrogeochemical analysis. Characterizationof current subenvironments of the salt complex was performed on the basis ofthe satellite images analysis, aerial photographs and field observations. Surfacewater 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 andtrace ions were determined by ICP-MS and anions by ion chromatography. For the analysisand characterization of sedimentary facies and evapofacies, efflorescences andsalt crusts were sampled from the different salar´s sub-environments. This setof data was integrated in order to define different sub-environments ofevaporite system: alluvial fans, sandflat, dry mudflat, saline mudflat, dunesand palaeo-dune fields, ephemeral lakes, springs and salt pan. The first results indicate that theshallowest brines of saline core show neutral pH, high concentrations of totaldissolved solids (TDS ˃ 300 g L-1) and are of the Cl- /Na + type. Meanwhile, river and lake waters are alkaline (pH between8.03 and 8.98), and they have TDS concentrations below 3.6 g L-1 andare Na +/Cl- type, except for the waters of theArchibarca stream that are Na + / Cl- (SO42-) type. The hot springs located northern of the salar are ofthe 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, withconcentrations that vary between 1454 and 3345 mg L-1, 200 and 3000mg L-1 and 2164 and 47103 mg L-1, respectively. Thesevalues decrease significantly to the margins of the salar. By contrast, theriver waters that discharge into the salt pan present lower concentrations ofMg2 + (between 25 and 33 mg L-1), Li +(between 3 and 8 mg L-1) and K + (between 13.5 and 27 mgL-1) while the lake located in the north of the salar haveconcentrations of Mg2 +, Li + and K +ranging between 21-177 mg L-1, 9.9 -19 mg L-1 and 36-71mg L- 1, respectively. In particular, the thermal waters have valuesof 4064 mg L-1 of Mg +, 156.6 mg L-1 Li +and 1755 mg L-1 of K +. These preliminary results suggestthat the observed spatial chemical variability identified in water reservoirsof the different sub-environments of the salar could be linked not only toclimatic factors (aridity and elevated rates of evaporation) but also tothermal activity. Contributions of Li from rock weathering and the incorporationof solutes during mixing of meteoric and thermal waters need to be analyzed inorder to better understand the dynamics of Li and its spatial distribution inthe salar.