Critical metal enrichment in volcanic-influenced Permian basins: New insights from the Emeishan Large Igneous Province, southwest China

The enrichment of Nb, Zr, Ga, and rare earth elements and yttrium (REY) in sedimentary basins represents a critical, yet poorly constrained component of the global metal cycle. In southwest China, Late Permian coal-bearing strata host Nb-Zr-REY-Ga-rich mudstones, but their metal sources remain debated. Previous studies have primarily attributed this enrichment to either weathered residues of Emeishan Large Igneous Province (ELIP) basalts or alkaline volcaniclastics. Mineralogical and geochemical data from two drill cores of the Longtan Formation in Zhenxiong, eastern Yunnan, China, combined with zircon U-Pb-Hf and whole-rock Sr-Nd isotopic analyses of the mineralized horizons, were used to develop a source-to-sink model for their temporal and spatial evolution. The major- and trace-element characteristics of the mineralized beds (e.g., Al2O3/TiO2, Eu/Eu*, Nb/Yb, and REY distribution patterns) are comparable to ELIP alkaline rocks, whereas non-mineralized beds are closer to ELIP basalts. Zircon U-Pb ages from the mineralized beds cluster at 260.9−257.4 Ma, consistent with late-stage ELIP magmatism, while a small number of older detrital zircons are mainly Neoproterozoic in age. The former records εHf(t) values ranging from −15.71 to +11.37 and TDM1 model ages of 1498−438 Ma, overall showing within-plate affinities, with only a minor arc-related zircon population that may reflect hydrothermal alteration. Whole-rock 87Sr/86Sr(t) values of 0.70259−0.70606 and εNd(t) values of −3.58 to +1.75 show ranges comparable to those of Nb-Ta-mineralized alkaline rocks in the ELIP interior [87Sr/86Sr(t) = 0.70004−0.70424; εNd(t) = 0.4−2.7]. The mineralized mudstones reflect a mixed provenance, dominated by alkaline volcaniclastic input during late-stage ELIP activity, with additional contributions from weathered Precambrian basement rocks beneath ELIP volcanic edifices and, to a lesser extent, Neoproterozoic uplands along the Yangtze Block margins. A minor input also came from contemporaneous arc-related volcanism linked to Paleo-Tethyan subduction, which may have increased upward through the Permian sequence. These results highlight that the enrichment of critical metals in volcanic-influenced sedimentary basins was primarily driven by plume-related alkaline volcaniclastics, with additional contributions from crustal and arc sources.