Lithium in the Brines Under Southern Arkansas: 5.1 to 19 Million Metric Tons

Lithium, the lightest metal, is on the U.S. Geological Survey's list of critical elements because of its role in renewable energy. It is also used in ceramics, glassmaking and other industries, and demand is expected to grow as the world shifts from combustion engines to electric vehicles, whose rechargeable batteries use it.

Where it is found

Lithium occurs in some igneous rocks and clays, and dissolved in underground brines — very salty water. Lithium-rich brines are found across the United States, including in the Smackover Formation, a Jurassic rock unit stretching along the Gulf Coast from Texas to Florida. The formation lies about 2,000 feet down at its northern edge and more than 22,000 feet further south. The brine fills the pore spaces between its mineral grains; its upper, more porous part is informally called the Reynolds oolite.

USGS scientists and staff of the Arkansas Office of the State Geologist collect brine samples at an oil well with its operator. Photograph by Katherine Knierim, USGS

How much is in the brine

Historical data (1965–2018) and new samples (2022) show lithium concentrations across the Gulf Coast Smackover from about 1 to 477 milligrams per liter. Many wells above 100 mg/L are in southwestern Arkansas, especially Lafayette, Columbia and Union Counties. Samples from the 1960s in southern Arkansas reported more than 500 mg/L, but those figures could not be verified, and recent sampling nearby found nothing as high.

Andrew Masterson, Colin Doolan and Katherine Knierim hold a tailgate safety meeting before sampling brines. Photograph by Amanda Herzberg, USGS

Observed and model-predicted lithium concentrations in Smackover Formation brines in southern Arkansas (A), and observed concentrations across the Gulf Coast region (B). U.S. Geological Survey

Measuring it

Brine comes up as a waste product of oil and gas production. Samples are taken from oil, gas or brine wells, filtered, and analyzed in the lab for dissolved lithium and many other substances. In 2022, USGS and the Arkansas Department of Energy and Environment's Office of the State Geologist sampled brines in southern Arkansas for the USGS Brine Research Instrumentation and Experimental Laboratory (BRInE) in Reston, Virginia. Lithium is measured in its dissolved ionic form.

Amanda Herzberg analyzes brine samples on the inductively coupled plasma optical emission spectrometer in the BRInE laboratory. Photograph by Amanda Herzberg, USGS

The estimate

The total depends on how much brine there is — the volume of rock and its porosity — and how much lithium it carries.

• The Reynolds oolite ranges from 0 feet (where it pinches out) to more than 400 feet thick in southern Arkansas. Its porosity ranges from 0.5 to 31 percent, averaging 10 to 31 percent in the region's oil reservoirs, so the team calculated brine volume at 10, 20 and 30 percent.
• A machine-learning model, trained on concentration data and geology, predicted lithium across the region where no samples exist, in low, median and high versions to show the uncertainty. At a resolution of about 1.5 square miles, it shows regional patterns, not amounts at particular sites.

A "box model" of the Reynolds oolite: the lithium present depends on the brine in its pore space and on predicted concentrations. U.S. Geological Survey

Calculated lithium, million metric tons; concentrations are model averages.

Result: between 5.1 and 19.0 million metric tons of lithium in the Smackover brines of southern Arkansas. This is lithium in place — it says nothing about whether extracting it is technically or economically feasible. And in 2022 alone, about 5,000 metric tons of dissolved lithium came to the surface in the waste brine of southern Arkansas's oil, gas and brine industries.

Bonnie McDevitt, Amanda Herzberg, Madalyn Blondes and Colin Doolan process brine samples at a mobile field station. Photograph by Katherine Knierim, USGS

Sources

Based on Lithium Resource in the Smackover Formation Brines of Southern Arkansas, U.S. Geological Survey Fact Sheet 2024–3052, USGS Publications Warehouse, drawing on Knierim and others (2024), Blondes and others (2023) and Bradley and others (2017); a work of the United States government in the public domain.