Characteristics and Enrichment Genesis of the Platinum Group Elements (PGEs) in Organic Rich Shale of the Wufeng and Longmaxi Formations of Upper Ordovician and Lower Silurian in the Sichuan Basin

Abstract

The petrology, mineralogy, elemental geochemistry, biology and PGEs characteristics of the black shale of the Wufeng and Longmaxi Formation in the CN outcrop of the Sichuan Basin are studied in this paper. The distribution and change in PGEs at different horizons are summarized, and the reasons for PGEs enrichment are discussed. The results show that the PGEs in the organic-rich shale segment are obviously enriched, which is positively correlated with the Total Organic Carbon (TOC) content and has a Pt–Pd distribution characteristic. δEuN, Pd/Pt, (Pt + Pd)/(Os + Ru + Ir), etc., and SiO2–Al2O3 and It/Pt–Pd/Pt discrimination diagrams, indicate that they are not extraterrestrial sources, nor are they the origins of normal seawater deposition but they are related to hydrothermal deposition. The enrichment process of PGEs is relatively complicated and is controlled by the impact of the sedimentary environment in the restricted basin. The anoxic water environment and organic-rich environment are the main factors of PGEs enrichment. PGEs and TOC have a good positive correlation and can be used as index parameters for sedimentary environments and organic matter enrichment.

Geochemical Characteristics and Geological Significance of Black Shale at the Bottom of the Mufushan Formation in the Lower Cambrian, Lower Yangtze Platform, South China

“…These events had a significant impact on the co-evolution of global geological environments and biota, leading to the widespread distribution of Lower Cambrian black shales. Previous research has indicated that the formation of black shale is facilitated by rapid marine transgressions, oceanic salinity stratification, stagnant water conditions, high biological productivity, extensive organic matter decomposition, and seafloor hydrothermal activity [22,[29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46]. However, the coupling relationship between the genesis of black shales and their depositional environment remains a subject of ongoing debate.…”