243 Critical Mineral Resources and Recovery in the Americas: Emerging Methods in Exploration and Sustainable Extraction, Part I

This session explores the role of critical minerals in technology and the low-carbon economy, focusing on geological discoveries, sustainable extraction methods, and recycling to support secure, environmentally responsible mineral supply chains in the Americas.

Wednesday, 22 October 2025
8:00 AM - 12:00 PM
HBGCC, 217A

Pedology for Geological Exploration: Lithium Signatures in Soils over Li-Pegmatites in the Carolina Piedmont

Paper number: 243-9
Program: Technical Sessions
Time: 10:10 AM – 10:25 AM

Authors

  • Peizhou Lu Presenting Author
    Duke University, Nicholas School of the Environment, Durham, NC
  • Russell Harmon
    North Carolina State University, Department of Marine, Earth, & Atmospheric Sciences, Raleigh, NC
  • Lamont Leatherman
    Formerly at Piedmont Lithium Inc., Belmont, NC
  • Mike Mason
    Formerly at Piedmont Lithium Inc., Belmont, NC
  • Gordon Williams
    Duke University, Nicholas School of the Environment, Durham, NC
  • Adam Curry
    North Carolina Department of Environmental Quality, Division of Energy, Mineral, and Land Resources, Raleigh, NC
  • Leon Kelly
    Duke University, Nicholas School of the Environment, Durham, NC
  • Anselme Dossou
    Duke University, Nicholas School of the Environment, Durham, NC
  • Daniel Richter
    Duke University, Nicholas School of the Environment, Durham, NC

Abstract

The Carolina Tin-Spodumene Belt (CTSB) bears one of the largest pegmatite-lithium (Li) deposits in North America. Li concentrations in soils throughout the CTSB exceed that in regional and national soils by up to two to three orders of magnitude (~100 to ~2500 mg/kg vs < 30 mg/kg, respectively), underscoring the value of soil geochemistry as a prospecting tool for Li-pegmatites. However, prospecting studies often rely on soil samples collected from a single, surficial depth per site, limiting our understanding of the origin of soil Li signatures and their variability with soil depth and lateral distance from Li-pegmatite dikes—particularly in regions like the CTSB, where pegmatite intrusions into a diverse suite of metamorphic country rocks have produced heterogeneous soil parent materials. 

 

In this study, we adopt a pedological approach to characterizing Li signatures of the soil and weathering profiles (Kanhapludults) developed directly above pegmatite dikes and at nearby off-dike locations. Results highlight the markedly higher Li concentrations in soils above the dike (up to 3700 mg/kg) compared to off-dike soils (~100–400 mg/kg), with depth-related variations largely explained by differences in soil texture within individual profiles. Strong correlations (R² > 0.7) between Li concentrations and the fractions (wt%) of sand particles (> 50-µm) are observed across all profiles, with the sand fraction retaining the highest Li concentration, ranging from ~2.6 to ~7.2 times those of the finer silt (> 2-µm) and clay (< 2-µm) fractions. Isotope analysis suggests that the soil sand fraction closely resembles the primary Li-pegmatite rock (δ⁷Li ≈ -0.6 ‰), and we infer from the X-ray diffraction that primary muscovite grains are the most significant Li-bearing minerals in these soils. 

 

Our findings locate the soil Li within sand-sized primary minerals, likely muscovite grains inherited from the Li-pegmatite, advancing our understanding of how soil Li signatures develop under differential weathering conditions. Integrating pedological and geochemical perspectives in exploratory geology will potentially improve the interpretation of soil geochemical anomalies and the effectiveness of exploration strategies in Li-pegmatite systems such as the CTSB.

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

doi: 10.1130/abs/2025AM-414221

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