Weathering, provenance, and tectonic setting of lithium-bearing clay deposits in the Guide area, China: constraints from major-trace elements and lithium isotopes

The claystone in the Guide area of the Qaidam Basin on the northeastern margin of the Qinghai-Xizang Plateau contains lithium resources. This paper adopts geochemical and isotopic geochemical approaches to analyze the paleoenvironment, tectonic setting, sediment provenance, weathering processes, and lithium sources of the lithium-bearing claystones in the study area, and summarizes the genetic mechanisms of the lithium-bearing claystones. The results indicate that the claystone is dominated by illite and chlorite in mineral composition, with lithium primarily hosted in illite and kaolinite. The paleo-sedimentary aqueous conditions of the claystone correspond to a weakly oxidizing-weakly reducing, brackish water environment, under a semi-arid to semi-humid paleoclimate. Meanwhile, weakly oxidizing-weakly reducing, freshwater, and humid sedimentary environments are more favorable for the formation of lithium-bearing minerals, as evidenced by the highest lithium content in the clay. The source rocks of lithium-bearing clays in the study area were subject to the tectonic setting of the island arc-continental margin transition. Their provenance is dominated by felsic igneous rocks, with minor contributions from intermediate igneous rocks and recycled sedimentary materials. Weathering conditions of the lithium-bearing claystones in the study area indicate that their source rocks experienced weak to moderate weathering, and a certain degree of potassium metasomatism may have occurred during diagenesis. Lithium isotope analyses reveal that lithium in the clays is primarily derived from lithium supplied by sedimentary-stage water bodies and deep-seated hydrothermal fluids. Lithium isotope analysis shows that the δ 7 Li values of lithium in the clay range from 3.67‰ to 8.27‰, with an average of 5.7‰, it indicates that the lithium in the clay of the study area may originate from deep hydrothermal fluids and sedimentary detrital materials.