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. Spodumene-bearing pegmatite deposits represent an important natural source of Li. Soil analysis during an exploration campaign can provide important insights into the presence of buried pegmatites. Here, we assert that a better understanding of soil and regolith formation and the behavior of Li and associated pathfinder elements can enhance the use of soils in mineral prospecting. This study applies a multifaceted 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 (CTSB) in south-central North Carolina, USA. Markedly higher Li concentrations are present in soils above Li-pegmatite dikes compared to off-dike soils, with over 80% of the original Li lost during weathering. Relic primary Li‑rich minerals, spodumene and muscovite, are the main soil minerals responsible for soil Li signatures overlying Li‑pegmatite dikes, whereas secondary mineral phases such as Fe, Al, and Mn oxides play a role in scavenging Li in off-dike soil profiles. Depth variability of Li in soil profiles reflects surface mixing, heterogeneity of bedrock lithology, and textural differences caused by eluviation and illuviation. The effectiveness of soil prospecting can be influenced by landscape position and soil-sampling depth. Integrating pedological and geochemical perspectives can, therefore, enhance the value of soil geochemical surveys in Li-pegmatite systems like CTSB. A pedogenetic context to mineral prospecting may well be a fruitful approach for critical mineral exploration.