A spatial association between hydrocarbon reservoirs and metalliferous deposits is found worldwide. However, the genetic relationship between them is unclear. The associated fluids record information related to petroleum evolution and mineralization. Integrating UPb dating and geochemical analysis on calcite associated with either bitumen or cinnabar and transmission electron microscopy analysis of the bitumen along the mercury belt of the Xuefeng Uplift, South China, this work provides evidence supporting that hydrocarbons are critical in mercury mineralization. The UPb age for the calcite associated with either bitumen (395–402 Ma) or cinnabar (389–391 Ma) indicates that oil migration/accumulation and mercury mineralization were broadly coeval. The similar geochemical data (δ13C–δ18O and REE) on bitumen- and cinnabar-associated calcite indicate that they are cogenetic and derived from the dissolution of the limestone under low temperatures. High mercury abundance (0.20% to 0.36%) and the nanoscale mercury-bearing isolated aggregates within the solid bitumen indicate that the hydrocarbons could have functioned as a mercury carrier before mineralization. Furthermore, the similar evolution trend of the sulfur isotope composition among cinnabar, the contemporaneous seawater sulfate and gypsum, and the higher S/C atomic ratio (>0.03) of the bitumen indicate that petroleum participated in thermochemical sulfate reduction and could be a vital mechanism for mercury precipitation. After generating from the organic-rich shale, the hydrocarbons and ore-forming fluids migrated, and the hydrocarbons might have functioned as a carrier and reducing agent during mercury mineralization.

Genetic relationship between petroleum evolution and mercury mineralization: Insights from calcite U Pb dating, geochemical characterization, and solid bitumen TEM analysis