Chemical and isotopic features of Li-rich brines from the Salar de Olaroz, Central Andes of NW Argentina

Abstract

The lithium-rich brines of the Salar de Olaroz in the Central Andes of NW Argentina are considered to be of great economic and strategic interest. This study focused on the fluid source(s) and geochemical processes governing the chemical and isotopic characteristics of the surficial waters of Olaroz (residual brines, ephemeral lakes, rivers and tributary streams), aiming to define the mechanisms leading to such a huge Li reservoir. The chemistry of the Rosario River, which is one of the main sources of recharge of the Salar de Olaroz, is mostly controlled by fluid inputs from hydrothermal systems located north of the salar (in the volcanic areas of Rosario de Coyaguayma, Pairique, and Cono Panizo). The hydrothermal fluids are characterized by relatively high Li concentrations, as they interact with Li-rich rocks pertaining to Miocene -Pliocene volcanic formations, Ordovician sedimentary deposits, and, possibly, pre-Ordovician crystalline basement. In the salar, the hyperarid climate regulates the relative proportion between supplied waters and evaporation, inducing deposition/dissolution of salts, which controls the concentrations of main ions in brines and ephemeral lakes. Hence, the peculiar combination of a Lirich primary source, the hydrothermal scavenging by geothermal fluids that feed the Rosario River, and secondary concentration processes affecting the surficial water within the salar leads to the formation of the huge Li reservoir characterizing this area.

Brine grades in Andean salars: When basin size matters A review of the Lithium Triangle

“…A correspondence between Li grades and salar sizes may reflect the importance of basin scale processes such as rock weathering, isolation, evaporation, and time (López Steinmetz et al, 2020b). This would be consistent with the model proposed for the formation of the Atacama's and Olaroz's brines, which took place in a near-surface setting through geochemical processes such as low-temperature weathering, evaporation, formation of transition-zone brines, and ultimately crystallization of halite to increase the concentration of Li in the brines (Munk et al, 2018;Franco et al, 2020). As already mentioned in section 5.1., other studies have reported Li isotopic data showing that volcanic and Paleozoic basement rocks represent the primary source for Li in the Andean plateau (Egenhoff and Lucassen, 2003;Peralta Arnold et al, 2017;García et al, 2019;Meixner et al, 2019).…”