Geochemistry of interstitial brines of Guayatayoc Playa Lake, Northern Argentina Puna Plateau. Preliminary results

LOPEZ STEINMETZ, R.L.; GALLI, C.I.; CHAYLE, W.

Córdoba

Congreso; 11th International Conference on Salt Lake Research; 2011

International Society for Salt Lake Research

The Guayatayoc playa lake is a 200 km² endorheic-evaporitic dry lake located at 3400 meters in the northwestern part of the Argentinean Puna Plateau, between 23°11?S - 23°26?S and 65°57?W - 65°49?W. The region has BSK type weather and rainfalls are generally less than 300 mm per year. The topographic depression of Guayatayoc is bordered by structural ranges which define the well developed shaped alluvial fans in both west and east margins. Playa lake surrounding major lithologies include Ordovician basement marine metasedimentary rocks, Jurassic-Cretaceous dioritic and granitic plutons, Cretaceous-Paleogene sinrift and post-rift marine calcareous sandstones and continental red beds and Miocene dacitic and andesitic volcanic rocks with ignimbrite prevalence. The quaternary filling sediments of the Guayatayoc playa lake are characterized by green clays with ulexite cotton balls at half a meter deep. At the top, the surface holds a thinner than 10 cm halite crust. Interstitial brines were sampled during the last dry season. Preliminary results of chemical analysis are showing Na+ ? (K+) / CI- ? (SO4=) brine types developing in a neutral-sulfated pathway. Its pH is 7.5, then only HCO3= represents alkalinity. Salinities are approximately 117.8 psu (KCl) while maximum analytical content of Na,K,LiCl is 123 g/l. Major ion ratios founded were 1:7.8 for Na+/Cl- and 1:9.4 for Ca2+/SO4=. An Ordovician rocks parental link is assigned to B3+. Based on Guayatayoc brine ion concentration ratios, Li+ and Mg2+ seems to have the same origin (Li/Mg 1:1.07) unlike other cations which appear to be unrelated: Li/K 1:168, Mg/K 1:157, B/K 1:46.7 and Li/B 1:3.6. Aeolian recycling salts seem to have some influence in the Na+ and Cl- ion concentrations for some of input waters coming from west margin.