Behavior of lithium during soil formation: lithium signatures in soil minerals derived from Li–pegmatites

Lithium (Li) is a critical metal for technology development which is driving demand and increasing exploration for new resources. Granite pegmatites represent an important natural source of Li. Soil analysis during geological exploration can provide important insights into the presence of buried pegmatites. Here, we assert that understanding soil and regolith formation and the behavior of Li and associated pathfinder elements can enhance mineral prospecting. This study applies a pedological approach to investigate the physiochemical, mineralogical, and isotopic properties of soil-weathering profiles produced by spodumene-bearing pegmatites and surrounding country rock in the Carolina Tin-Spodumene Belt in south-central North Carolina, USA. Markedly higher Li concentrations are present in soils directly above Li-pegmatite dikes compared to off-dike soils, with > 80 % of the original Li lost during weathering across the above-dike soil profiles. Relic primary Li–rich minerals, spodumene and muscovite, are the main mineral phases responsible for soil Li signatures overlying the dikes. Exchangeable Li represents a negligible fraction of total Li in both above- and off-dike soils. Secondary mineral phases such as Fe, Al, and Mn oxyhydroxides appear to scavenge similar amounts of Li but account for a larger fraction of the total Li pool in off-dike soils. Li-isotope signatures (δ 7 Li) are systematically depleted in off-dike soils, clay fractions, and oxide-associated fractions. Variability of Li within soil-weathering profiles reflects surface mixing, heterogeneity of bedrock lithology, and textural differences caused by eluviation and illuviation. Integrating pedological and geochemical perspectives can, therefore, enhance the value of soil geochemical surveys for Li-pegmatite exploration.