Abstract
The Central Andes of South America host the largest known lithium resources in a confined area, but the primary lithium sources of the salar deposits and the mobilisation process of lithium are still a matter of speculation. Chemical weathering at or near the surface and leaching in hydrothermal systems of the active magmatic arc are considered the two main mechanisms of Li extraction from the source rock. The lithium and strontium isotope composition of typical salar deposits offer insights into the processes on how Li brine deposits in Andean evaporites are formed. Data from the Salar de Pozuelos indicate near-surface chemical weathering in a cold and dry climate as the dominant mobilisation process of Li, with evaporation being responsible for the enrichment. The Cenozoic ignimbrites are the favoured source rock for the Li, with subordinate additions from the Palaeozoic basement. The identification of the source rocks is supported by radiogenic Nd and Pb and stable B isotope data from salar deposits. A comparison with other Li brine and salt deposits in the Altiplano-Puna Plateau and its western foothills places the Salar de Pozuelos as an endmember of Li solubilisation by chemical weathering with only minor hydrothermal mobilisation of Li.
Highlights
The arid climate and active tectonics formed and sustain numerous Cenozoic endorheic basins on the Altiplano-Puna Plateau of the Central Andes in NW Argentina, in southern Bolivia, and in the western slope of the Plateau in northern Chile between 20 and 27°S (e.g. Hartley and Chong 2002; Strecker et al 2007; Quade et al 2015)
The occurrence of lithium enrichment in the Central Andes is geographically confined to the ‘Lithium Triangle’, an informal term used by the mining industry, which refers to the area between southern Bolivia, NW Argentina and NE Chile
Salar surface basin, and drill core samples from Salar de Pozuelos were analysed for Li and Sr isotope composition and Li contents (Tables 2, 3, and 4)
Summary
The arid climate and active tectonics formed and sustain numerous Cenozoic endorheic basins on the Altiplano-Puna Plateau of the Central Andes in NW Argentina, in southern Bolivia, and in the western slope of the Plateau in northern Chile between 20 and 27°S (e.g. Hartley and Chong 2002; Strecker et al 2007; Quade et al 2015). The occurrence of lithium enrichment in the Central Andes is geographically confined to the ‘Lithium Triangle’, an informal term used by the mining industry, which refers to the area between southern Bolivia, NW Argentina and NE Chile. Boron forms a number of borate minerals within the Andean evaporite deposits and received considerable interest of the mining industry.
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