Geochemical Evidence for Mixing Between Basin Pore Waters and Evaporated Lake Water, Dasht-e-Nawar, Afghanistan

Abstract

The hydrology of the Dasht-e-Nawar basin in Afghanistan has been largely unstudied, although the basin has been explored in the past for potash and other evaporite resources. Recently there has been a renewed interest in the basin as a possible lithium resource because it fits the conceptual deposit model for lithium brines. The purpose of this study is to evaluate the geochemistry of surface waters and pore waters of the basin to look for evidence of a subsurface lithium brine existing at present or in the geologic past. Interpretation of water geochemical analyses suggests that saline, evaporative lake water infiltrates the subsurface and mixes with fresh local groundwater, thus preventing the formation of a brine at depth. A linear mixing model estimates that while some buried lenses of pore water may contain up to 47% of the saline lake water, most of the basin pore waters are composed of the freshwater endmember. This interpretation suggests that a brine could not form in the basin subsurface because of groundwater mixing and dilution of the shallow, saline pore waters. Hence, while Dasht-e-Nawar appears to be a closed basin with respect to surface water flow, it may not be closed to groundwater flow. Basin boundary faults could provide a pathway for groundwater outflow.