Mineralization of MVT Pb-Zn Deposits in the Process of Hydrocarbon Accumulation and Destruction in the Strong Structural Deformation Area of Eastern Sichuan, South China

Abstract

The Mississippi Valley-type (MVT) Pb-Zn deposits and hydrocarbon reservoirs coexist around the margin of the eastern Sichuan basin. This study examined the fluid inclusions, Sr isotope and systematic Rb-Sr, Sm-Nd geochronology for the distinct ore and gangue minerals of four orebodies from two MVT Pb-Zn deposits in the margin of the eastern Sichuan basin, combined with the existing research foundation of oil and gas accumulation and evolution, which was designed to understand the internal relationship between oil and gas accumulation and the involvement of organic matter in metal mineralization. High-density methane, moderate temperature, and salinity inclusions were discovered in the studied MVT Pb-Zn deposits, combined with relatively higher 87Sr/86Sr ratios (0.71088~0.714749), indicating that the ore-forming fluids were derived largely from the hydrocarbon associated basinal brines. Rb-Sr isochron of paragenetic sphalerites and pyrites and Sm-Nd isochron of paragenetic fluorites and calcite from the studied MVT Pb-Zn deposits define isochron ages of 144.5 Ma~138.5 Ma, and 147.6 Ma, respectively, indicating that the Late Jurassic to Early Cretaceous Yanshanian orogeny was an important metallogenic event in the margin of the eastern Sichuan basin. The close temporal and spatial relationship between the MVT mineralization and hydrocarbon accumulation and destruction in the strong structural deformation area of the margin of the eastern Sichuan basin allows us to propose a possible model in which the Yanshanian compressional tectonics drove a large-scale flow of metal- and sulfate- bearing basinal fluids passed under or through methane-bearing carbonate reservoirs, resulting in the MVT mineralization and hydrocarbon accumulation and destruction.