LITHIUM RESOURCES AND BRINE COMPOSITIONS FROM THE SMACKOVER FORMATION IN SOUTHERN ARKANSAS

Southern Arkansas has a long history of oil production from the Jurassic-age Smackover Formation. The Smackover Formation in this region is also the source of brines with anomalously high concentrations of bromide (>6,000 mg/L) and lithium (>1,000 mg/L) and is currently the only source of commercial bromide production in the United States. As the demand for clean energy increases, lithium from these brines is being targeted for commercial production because of the high concentrations and availability of local infrastructure associated with the bromide industry. The U.S. Geological Survey and the Arkansas Department of Energy and Environment—Geological Survey are partnering to assess the potential lithium resources in southern Arkansas. The goals are to identify gaps in historical geochemical datasets with a focus on the Smackover Formation; sample oil and brine production wells to measure lithium concentrations where data gaps exist; map the spatial variability of lithium concentrations in southern Arkansas; and better understand the processes that affect the distribution and geochemical evolution of lithium-containing brines. Previous research found that the high salinity in Smackover brines derived from expulsion of fluids from the underlying Louann Salt. Bromide concentrations in brines from the Smackover Formation are atypically high compared to brines of similar salinities (median chloride to bromide ratio of 40) in the region, as a result of release of bromide during recrystallization of the Louann Salt. Historical datasets show a zone of high lithium brines between faults that bound the area on the southern (Arkansas-Louisiana state-line faults) and northern (South Arkansas fault) extents of the south Arkansas shelf. Contrasting hypotheses identify both fault systems as potential pathways for Smackover fluid migration. Lithium concentrations decrease in brines from units younger than the Smackover Formation. Our study, by building on previous research and filling in important gaps, aims to better understand the source and extent of high lithium brine resources in southern Arkansas.