Geochemical characteristics and genetic analysis of PGE in the upper Ordovician-lower Silurian black shale in Southern Sichuan

Through the field geological survey data, X-ray diffraction, the main component and platinum group element test analysis, the mineralogical characteristics, main geochemical characteristics and platinum group element composition characteristics of the Wufeng-Longmaxi Formation shale in the Mabian area of southern Sichuan were studied. The results show that the average content of organic carbon TOC in the Wufeng-Longmaxi shale of the Changheyan Wufeng-Longmaxi Formation in Mabian, southern Sichuan is 2.47%; the mineral composition is mainly composed of quartz minerals and clay minerals. The average content of quartz minerals is 37.95%, and the average content of clay minerals is 40.2%; the average content of shale SiO₂ is 52.90%, the average content of Al₂O₃ is 11.47%; the total amount of platinum group elements is between 1.5-11.9 ng/g, the average value is 5.16 ng/g. The platinum group elements of the Wufeng-Longmaxi shale in the Mabian area of southern Sichuan are characterized by high content of Pt and Pd. The average content of Pd is 3.15 ng/g and the average content of Pt is 1.48 ng/g. The distribution model of platinum group element carbonaceous chondrites is Pt-Pd type, with Pd content about 2.12 times of Pt content. The organic-rich shale in the profile is more enriched in platinum group elements than the lean organic shale. The enrichment of platinum group elements may be related to biological activities; the clay mineral content is negatively correlated with the platinum group element content, and the platinum group elements are not in the adsorbed state Adsorbed on the surface of the particles, the increase of clay minerals actually diluted the content of platinum group elements. The platinum group elements of the Wufeng-Longmaxi Formation in Changheying, Mabian, southern Sichuan are not derived from extraterrestrial materials, but may come from the mantle, and they are obviously differentiated, and their enrichment is within the range of normal marine sediments.