Distribution, source, and precipitation mechanism of Sc in the Late Permian claystones in Weining area, SW China

Scandium (Sc) is a critical metal with increasing demand driven by its applications in high-technology industries. The Late Permian claystones in the Sichuan-Yunnan-Guizhou region of southwestern (SW) China represent a potentially new and important Sc resource. This study investigates the distribution, occurrence, and source of Sc in claystones from the Weining area in western Guizhou, and discusses its precipitation mechanism. The sedimentary succession primarily comprises successive layers of ferric, aluminous, carbonaceous, tuffaceous, and silty clastic claystones from bottom to top. Scandium is mainly enriched in ferric claystones, with concentrations reaching up to 56 ppm, while other types contain less than 30 ppm. The principal Sc-hosting minerals include goethite, anatase, brookite, zircon, and xenotime. High-resolution transmission electron microscopy indicates that Sc (~0.9 wt%) is homogeneously distributed within nanometer-scale zircon. The presence of xenotime inclusions within zircon suggests a sedimentary origin. Rare earth element and platinum-group element patterns, together with trace element ratios, indicate that Sc in ferric horizons was derived from intense subaerial weathering of high-Ti basalts and precipitated under oxygenated aquatic conditions. Subsequent multi-stage hydrodynamic processes, including marine transgression-regression and fluvial reworking, facilitated Sc remobilization via mineral dissolution-reprecipitation, ultimately leading to further enrichment within ferric horizons through downward migration.