Petroleum evolution and its genetic relationship with the associated Jinding Pb-Zn deposit in Lanping Basin, Southwest China

The spatial association of hydrocarbons with metalliferous ore deposits is found worldwide and is particularly common to MVT Pb-Zn deposits. Heavy oil and bitumen are found in the Jinding Pb-Zn deposit within the Lanping Basin, South China. However, the temporal and genetic associations between hydrocarbons and the deposit are still controversial. To this end, integrating Raman analysis, Re-Os geochronology and transmission electron microscopy analysis of the bitumen and in situ S isotope analyses of the sulfide, the petroleum evolution of the Jinding reservoir and its genetic relationship with the Pb-Zn deposits were discussed. Bitumen Re-Os data from this study and published works indicate that the late Triassic shales underwent two distinct oilgeneration events before mineralisation (similar to 25 Ma), with initial oil generation occurring during the early Cretaceous (similar to 116 Ma) and the second during the early Paleogene (ca. 68-59 Ma). These two ages agree with the modelled thermal history of the Jinding reservoir. Combining the oil-before-ore timing sequence, high metal abundance of the bitumen, two negative sulfur isotope peaks of the sulfide and high S/C atomic ratio of the bitumen from the Jinding deposit, the oil-containing aqueous solutions were considered as one metal carrier during the hydrocarbon migration and accumulation; further, bacterial sulfate reduction and thermo-chemically induced sulfate reduction processes could have participated in the supply of reduced sulfur for the Pb-Zn deposit precipitation.