Distal Au deposits associated with Cu-Au skarn mineralization in the Fengshan area, eastern China

Abstract

Carbonate-hosted Au deposits (12 million tonnes at 5.0 g/t Au) are located less than 1.5 km away from Cu-Au skarn deposits in the Fengshan area, Middle-Lower Yangtze River metallogenic belt, eastern China. The skarn deposits occur in the contact zones of late Mesozoic granodiorite porphyry intrusions. Bismuth tellurides and coloradoite (HgTe) occur in Cu-Au skarn and peripheral Au-As ores, respectively, whereas tellurides, including coloradoite, and lorandite (TlAsS2) are present in carbonate-hosted Au ores outside the marble front. New zircon U-Pb ages indicate that the granodiorite porphyry intrusions spatially related to both Cu-Au skarn and carbonate-hosted Au deposits were emplaced between 149.9 ± 1.3 and 145.9 ± 0.7 Ma, which overlaps with molybdenite Re-Os ages of 149.1 ± 2.1 to 145.4 ± 2.9 Ma from the Cu-Au skarn deposits. Sulfur isotope compositions of sulfide minerals from the Cu-Au skarn deposits (δ34S = –2.5 to 6.4‰) are similar to those from carbonate-hosted Au deposits (δ34S = –4.8 to 2.6‰), suggesting a similar magmatic source of sulfur. Geologic, mineralogical, and sulfur isotope evidence collectively indicate that the carbonate-hosted Au deposits are the distal product of Cu-Au skarn mineralization rather than Carlin-type Au deposits, as has been previously suggested. This study proposes a genetic model to illustrate possible linkages between oxidized Cu-Au skarn deposits (associated with oxidized magmas) and carbonate-hosted Au deposits, which may have important implications for Au deposits in the more distal parts of Cu-Au skarn systems in the Middle-Lower Yangtze River metallogenic belt and elsewhere