Southern Sichuan is located in the middle-outer zone of the Permian Emeishan Large Igneous Province, extensively distributed with claystones of the Lower Permian Longtan Formation related to igneous rock eathering-deposition , with geological background and metallogenic conditions for forming lithium and other critical metal resources.In this paper, a systematic geological survey of the lower part of the Upper Permian Longtan Formation in Xingwen area of southern Sichuan has been carried out, and the chemical analysis of samples from the study area and drill cores has been carried out to determine the distribution and enrichment of lithium in the claystones. On this basis, the mineral composition of the lithium-rich claystones was analyzed by powder crystal X-ray diffraction (XRD), and the distribution characteristics of the elements on the micrometer scale were analyzed by focused-ion-beam and time-of-flight secondary ion mass spectrometer (FIB-TOF-SIMS). The results show that the claystones in the lower part of Longtan Formation are rich in Li, Ga, Nb and other elements, which is a rich layer of several critical metals, and has good ore-forming potential and prospecting prospect.These claystones originate from weathering processes of volcanic rocks within the Emeishan Large Igneous Province. The lithium-rich rocks are mainly pyrite-bearing kaolinite claystones, and their sedimentary environment is the saline environment of lagoons in the transition area of sea and land. The Li content is closely related to the chemical weathering intensity (CIA index), which shows the characteristics of weathering-sedimentary deposits. In addition to a small amount of in lepidolite,lithium is mainly adsorbed in the montmorillonite phase of claystones, some of it enters the montmorillonite mineral structure, and some of it occurs in illite. Besides weathering release from volcanic rocks, a portion of lithium potentially originates directly from coastal shallow groundwater, contributing to the formation of high-grade lithium-bearing mica within lithium-rich claystones.