231-2 Insights from a high lithium basinal brine source: A geochemical comparison of Smackover and Cotton Valley formation waters of southern Arkansas and northern Louisiana

Session: Critical Mineral Resources and Recovery in the Americas: Emerging Methods in Exploration and Sustainable Extraction (Posters)

Poster Booth No.: 272

Presenting Author:

Andrew Masterson

Authors:

Masterson, Andrew L.¹, Knierim, Katherine J.², McDevitt, Bonnie³, Herzberg, Amanda S.⁴, Doolan, Colin A.⁵, Chenault, Jessica M.⁶, Ausbrooks, Scott M.⁷

Abstract:

The Jurassic Smackover and Cotton Valley Formations are two prolific petroleum producing units within a thick and laterally extensive Mesozoic sedimentary sequence of the Gulf Coast region. Substantial attention has focused on the high lithium (>100 mg/L) concentrations of Smackover Formation brines, which in southern Arkansas may contain between 5 and 19 million tons of dissolved lithium. These brines are being explored by industry to determine their commodity potential via scalable direct lithium extraction technologies. Despite a half century of brine geochemical observations, many outstanding questions exist regarding the behavior of lithium in Smackover and overlying Cotton Valley brines across the region including its geological controls, relationship with produced water formation brine salinity and major dissolved species, and an understanding potential solid silicate sources.

To address some of these knowledge gaps and build upon historical brine geochemical archival records, the U.S. Geological Survey sampled 27 oil, gas, and brine wells across southern Arkansas in 2022, and 26 wells in northern Louisiana in 2024 with the majority producing from the Smackover and Cotton Valley Formations at depths ranging from 5,000-13,000 feet. Brines were analyzed for a suite of geochemical and physical parameters including total dissolved solids (TDS), major cations and anions, and isotopic measurements including d⁷Li, ⁸⁷Sr/⁸⁶Sr, and d²H-H₂O/d¹⁸O-H₂O.

Lithium concentrations from the recently collected samples ranged from 1-250 mg/L across northern Louisiana and southern Arkansas and scale with TDS, with the highest concentrations occurring where TDS exceeds 250 g/L. Dissolved lithium concentrations scale with other alkali elements suggesting sourcing from high temperature alteration of silicate minerals. Stable lithium isotope values from high salinity (>250 g/L) Smackover brine samples in southern Arkansas (d⁷Li = +14.0±1.2‰) are substantially heavier compared with high salinity samples from northern Louisiana (d⁷Li = +9.4±1.2‰) where the Smackover Formation is 3,000-4,000 ft deeper. Isotope mixing models suggest a greater contribution of lithium from the evaporation of paleoseawater in the shallower southern Arkansas brine samples while deeper sections in Louisiana exhibit significant water-rock interaction and early loss of lithium from evaporated seawater. We evaluate these data from Smackover and Cotton Valley brines in a regional context and demonstrate the utility of isotope tools for understanding the complexity of lithium sources in northern Gulf Coast basinal brines.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7542

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