Geochemical constraints on the origin of Li-rich claystones in a carbonate weathering environment: Insights from the Jiujialu Formation, central Guizhou

• Lithium originated from nearby Loushanguan Group argillaceous dolomite. • Lithium is mainly structural in smectite; exchangeable lithium is minimal. • Alkaline, reducing karst settings favored smectite and lithium enrichment. • A selective lithium enrichment mechanism is inferred but remains unclear. Lithium is recognized as a critical element with widespread applications in emerging industries. In recent years, the unusual enrichment of lithium in claystones from southwestern China has attracted significant attention. However, the sources, host minerals, and enrichment mechanisms of lithium remain poorly understood. This study investigates the major and trace element compositions and mineral assemblages of co-deposited detrital materials in argillaceous dolomite, and claystones from four sections of the Lower Carboniferous Jiujialu Formation (C 1 jj) in central Guizhou Province, South China. The results show that detrital materials in the argillaceous dolomite with an average lithium content of approximately 46.17 ppm are primarily composed of quartz, muscovite, and microcline. A positive correlation between the δ 7 Li values of Li-rich claystones and their host dolomites suggests that lithium released during the weathering of argillaceous carbonate rocks became enriched in the overlying weathering crust, forming the Li-rich claystones. The lithium content and δ 7 Li values in the claystones correlate with the Chemical Index of Alteration (CIA), showing enrichment at the intermediate weathering stage (CIA = 75–90) and depletion during intense weathering (CIA > 90). Moreover, when the MgO content of the bulk claystone is below 0.25 wt%, lithium content increases sharply with MgO, accompanied by high δ 7 Li values, indicating Mg-poor smectite phase as the Li host. High-lithium claystones exhibit broader smectite peaks in X-ray diffraction (XRD) compared to their low-lithium counterparts, indicating that smectite plays a key role in lithium enrichment. Given the sensitivity of lithium isotopes to clay mineral formation—which is closely influenced to environmental conditions—this study proposes that intermediate weathering (CIA = 75–90) and an alkaline, poorly drained, reducing, and low-salinity depositional environment are favorable for the formation of Li-rich smectite during the weathering of argillaceous carbonate rocks. Notably, although carbonate rocks are typically poor in lithium, the widespread occurrence of Li-rich claystones in carbonate weathering–sedimentary systems suggest a possible mechanism of selective lithium enrichment during clay mineral formation under such conditions. This mechanism warrants further investigation.