Great Salt Lake Lithium Sourcing and Groundwater Inflow Investigation

Endorheic basins are chemical repositories for continental brines that evolve from long-term evaporative concentration of surface and groundwaters. Lithium (Li) accumulation in these basins is a product of water-rock interaction, ambient groundwater and hydrothermal input, and mobilization by phyllosilicate ion exchange under certain chemical conditions. The Great Salt Lake (GSL), has sustained average Li concentrations from ~15 to 25 mg/L in the south arm (SA) (Gilbert Bay) and ~45 to 60 mg/L in the north arm (NA) (Gunnison Bay) since 1966. This is despite probable industrial removal of ~200,000 metric tons from 1988 to 2021 via brine extraction for various mineral commodities, implying cryptic Li recharge into the GSL system. Lithium residence time in GSL is estimated to be ~1400 to 1600 years in the NA and 630 to 670 years in the SA. However, this estimate does not account for groundwater seepage contributions along the lake margins, as well as recycled Li that is ionically adsorbed to clay-bearing sediments and occluded within chemical sediments. Climate and lacustrine thermochemical dynamics also play a temporal role in Li concentration in the GSL brine. Spatially, point sources of elevated Li concentrations from modern playa clay-oolitic-bearing sediments and sulfate-rich groundwater spring seeps provide a causal connection for Li sourcing in the lake brine. For example, a single spring in the NA has a Li concentration of 5.86 mg/L with a discharge of 0.0062 m3/s that equates to an input rate of ~1.15 metric tons/yr of Li into the GSL system. Whole rock geochemistry from playa and lake sediments show higher Li concentrations (23–125 ppm) than fringing groundwater (~0.02–30 mg/L) and lake brines (20–80 mg/L). These observations provide unambiguous evidence of localized sourcing of Li that is not accounted for in resource assessments, let alone as solute sources that influence GSL salinity during low lake elevations.