DOES THE HYDROLOGIC BUDGET OF THE SALAR DE ATACAMA CLOSE? IMPLICATIONS FOR REGIONAL GROUNDWATER FLOW

The Salar de Atacama is a hyper-arid endorheic basin in northern Chile that has accumulated approximately 1500 cubic kilometers of halite since the Miocene. Fresher groundwater entering the basin is evaporated and concentrated into high-density, lithium-rich brine in saturation with halite that is an important global lithium resource. To date, the regional hydrologic budget and watershed boundaries of the Salar de Atacama are not well constrained. Understanding this budget and quantifying best estimates of recharge and discharge for the basin has implications for resource management and development, lithium weathering and deposition processes and paleoclimate studies. We evaluate whether the fluid budget of the basin is closed within the topographic watershed divide and assess the implications of these estimates for deeper regional groundwater flow paths and a potential magmatic source of brine to the basin.

Here we present a synthesis of existing precipitation and evaporation data combined with new physical hydrologic data, fluid and salt budget calculations and geochemical data to evaluate the potential for deep regional flow paths and additional fluid sources into the basin. Precipitation and evaporation values are estimated for the watershed from existing satellite and field based studies. We compile these estimates into a hydrologic budget calculation, which is evaluated alongside physical hydrologic field measurements of hydraulic gradients and freshwater and brine geochemistry analyses. Initial results suggest that the hydrology of the topographic watershed cannot fully explain groundwater discharge amounts and that there is evidence for deep regional flow paths into the basin. These results have applications for groundwater modeling efforts, paleoclimate studies and lithium resource evaluations in the Salar de Atacama and similar basinal brine lithium resources globally.