Origin of Salts and Brine Evolution of Bolivian and Chilean Salars

Abstract

Central Andes in Bolivia and northern Chile contain numerous internal drainage basins occupied by saline lakes and salt crusts (salars). Salts in inflow waters stem from two origins: alteration of volcanic rocks, which produces dilute waters, and brine recycling, which leads to brackish waters. Chilean alteration waters are three times more concentrated in average than Bolivian waters, which is related to a higher sulfur content in Chilean volcanoes. Brackish inflows stem from brines which leak out from present salars and mix with dilute groundwater. Most of the incoming salts are recycled salts. The cycling process is likely to have begun when ancient salars were buried by volcanic eruptions. Three major brine groups are found in Andean salars: alkaline, sulfate-rich, and calciumrich brines. Evaporation modeling of inflows shows good agreement between predicted and observed brines in Chile. Alkaline salars are completely lacking in Chile, which is accounted for by higher sulfate and lower alkalinity of inflow waters, in turn related to the suspected higher sulfur content in Chilean volcanic rocks. Six Bolivian salars are alkaline, a lower number than that predicted by evaporative modeling. Deposition on the drainage basin of eolian sulfur eroded from native deposits shifts the initial alkaline evolution to sulfate brines. The occurrence of calcium-rich brines in Andean salars is not compatible with volcanic drainage basins, which can only produce alkaline or sulfate-rich weathering waters. The discrepancy is likely due to recycled calcic brines from ancient salars in sedimentary basins, now buried below volcanic formations. Calcic salars are not in equilibrium with their volcanic environment and may slowly change with time to sulfate-rich salars.

Sources of surface water for the Soncor ecosystem, Salar de Atacama basin, northern Chile

“…The peripheral zone, located east and north of the nucleus (Fig. 1(c)), is composed of alluvial mud deposits, and sulphate and calcium carbonate salts (Risacher and Fritz 2009). In this zone, the groundwater reaches the surface, flooding large parts of the periphery (Muñoz-Pardo et al 2004).…”

Uses of the reject brine from inland desalination for fish farming, Spirulina cultivation, and irrigation of forage shrub and crops

“…The Central Andes contain one of the most spectacular set of saline lakes and salt crusts in the world, with three major brine groups: alkaline, sulfate-rich, and calcium-rich brines [47].…”

Enrichment of arsenic transforming and resistant heterotrophic bacteria from sediments of two salt lakes in Northern Chile

“…It is worth considering that no alkaline brines are known in Chilean salt flats because of the higher sulfate and the lower alkalinity of inflow waters, as a consequence of the suspected higher sulfur content in Chilean volcanic rocks (Risacher and Fritz 2009).…”