Petrology and geochemistry of Silurian-Triassic sedimentary rocks in the Tongling region of Eastern China: Their roles in the genesis of large stratabound skarn ore deposits

This paper describes the petrology and geochemistry of the Silurian-Triassic sedimentary rocks in the Tongling area in Eastern China, aiming to establish a genetic link between different stratabound skarn deposits and sedimentary lithologies. The results from this study show that some Devonian-Triassic transitional lithological units with compositions varying between siliceous rock and carbonate (especially thinly layered impure carbonate) control the distribution of some large stratabound skarn ore deposits in the Tongling region. Interlayer detachment faults in the transitional lithology rocks are particularly important, controlling the final locations of the deposits. The transitional lithological zones may have also served as source rocks, likely providing some ore-forming metals to the deposits. Gypsum evaporites in rocks from Carboniferous sources may have supplied some sulphur to the hydrothermal systems. Five of such transitional lithological units enriched in organic matter are spatially and closely associated with some large stratabound skarn ore deposits in the Tongling region, suggesting that organic matter may have served as an absorbent or reducing agent during ore formation.