Mechanisms of lithium enrichment in the aluminum-bearing strata of the late carboniferous benxi formation, Xingxian area, northwestern Shanxi, North China

Rapid growth in lithium (Li) demand has intensified global supply pressure. Although Late Carboniferous aluminum (Al)-bearing Strata in China are known to host significant clay-type Li resources, the modes of occurrence and enrichment mechanisms of Li in the strata remain poorly constrained. This study investigates a typical borehole in Xingxian, northwestern Shanxi Province using correlation analysis, clay separation experiments, and time-of-flight secondary ion mass spectrometry (TOF-SIMS). Results show that Li is predominantly hosted in cookeite within Li-rich horizons, whereas in the remaining horizons, Li is hosted in kaolinite. Provenance discrimination diagrams (Al 2 O 3/ TiO 2 and Nb/Y-Zr/TiO 2 ) indicate that Li was mainly derived from the weathering of intermediate to felsic magmatic rocks along the northern and southern margins of the North China Craton (NCC). Multiple geochemical indicators, including Th/U, V/(V + Ni), La/Y, (La/Yb) N , Rb/K, B/Ga, K 2 O/Li, and Na 2 O/Li, collectively suggest that Li enrichment occurred under suboxic to reducing, alkaline, and low-salinity continental conditions. Thus, a conceptual model is proposed for Li enrichment in the studied Al-bearing strata deposited in the karst cavities of old limestones. In this model, relatively weak weathering (Al/Si < 2.6) of Li-bearing detrital materials during Stage III may have facilitated downward migration of Li from terrigenous claystone, leading to its accumulation at a geochemical barrier between the claystone and bauxite horizons. This process is likely related to a transition from acidic and oxidizing to more alkaline and reducing diagenetic conditions, which favored Li fixation and the development of a Li-rich clay layer upon the bauxite.