Provenance of early Permian Li-rich claystone from Central Yunnan, South China: Constrained by Sr-Nd-Pb isotopes, geochemistry, and zircon U–Pb ages

Abstract

A new lithium-rich claystone from the Lower Permian has been detected in Central Yunnan, Southwestern China that could be great potential for Lithium (Li) exploration, yet the origin of the claystone is still being debated. To study it further, new geochronological, geochemical, and Sr–Nd–Pb isotopic analyses were systematically conducted on the Daoshitou Formation (P1d) claystone, as well as on the underlying strata. Through detrital zircon U–Pb dating of the claystone in the Daoshitou Formation, three major age peaks were revealed, at ∼960 Ma, ∼790 Ma, ∼550 Ma, respectively, along with three minor peaks of ∼2500 Ma, ∼1500 Ma, and ∼1200 Ma. Detrital zircons in the claystone have age spectra that closely match those of the Lower Ordovician sedimentary rocks in Central Yunnan, indicating these rocks are the major contributor of detrital zircons. However, the rock source determined by geochemical features decouples with the zircon source determined by detrital zircon data. The A–CN–K ternary diagram obviously reveals analogous predicted weathering trends between the Weining Formation (C2w) and Daoshitou Formation, suggesting a potential provenance link. Furthermore, the weathering trends of samples from three drill cores indicate that the transformation of clay mineral (smectite–illite–chlorite/kaolinite) may facilitate Li enrichment. Smectite, as the precursor mineral for Li enrichment, typically forms and preserves in a slightly alkaline environment, which suggests that the Li-rich claystone is likely to formed in this environment. Low Na/Li and K/Li ratios indicate low cation exchange selectivity in sedimentary environments, which promote the proliferation of adsorption sites for Li on smectite. The weathering products from the Weining Formation, composed of impure carbonates, could provide a slightly alkaline environment with low ion strength for the adsorption of Li. In addition, Sr–Nd–Pb isotopic compositions also reveal the significant similarity between the Daoshitou Formation and Weining Formation. Therefore, we suggest that the weathering of the Weining Formation provided the primary material to Daoshitou Formation claystone.