The Origin and Enrichment of Sedimentary Basin Lithium Brines: A Case Study From the Upper Devonian Leduc Formation, Alberta Basin, Canada

Abstract Direct extraction of lithium from oil field brines, herein referred to as “sedimentary basin lithium brines,” is emerging as an economical and environmentally responsible alternative to hard-rock and salar-style brine resources. Relative to the major lithium chemical-producing countries, North America has scarce traditional lithium ore deposits. Sedimentary basin lithium brines present a promising and readily available domestic supply of lithium. Elevated lithium concentrations (>50 mg/L) are known in hydrocarbon fields across North America, but the origin of these brines, the lithium sources, and lithium enrichment mechanisms are largely debated or unknown. Using the Upper Devonian Leduc Formation (Alberta basin, Canada) as a case study, we document the complexity of unraveling brine genesis and evolution. Competing hypotheses regarding Leduc brine origin, postformational brine modification, and lithium sources confound an understanding of the lithium resource homogeneity and longevity. Using brine-dissolved species and isotopic data, we show that the Leduc brines are regionally geochemically distinct across the Devonian Leduc Formation reef complexes. We conclude that these brines originate from both evaporatively concentrated seawater and the dissolution of evaporite sequences and were subsequently modified by local mixing, diagenesis, and rock-water interaction processes. This compositional heterogeneity has implications for lithium resource exploration, production, and valuation of the Leduc Formation and other sedimentary basin lithium brine resources.