Re–Os isotopes and geochemistry of pyrite from the Dongguashan Cu(-Au) deposit, Eastern China: Implications for porphyry-skarn-stratabound mineralization systems

Abstract

Stratabound deposits are widely distributed along the Middle-Lower Yangtze River metallogenic belt (Eastern China). The stratabound mineralization system in these stratabound deposits remains enigmatic as to whether it is associated with late Mesozoic intrusions or late Carboniferous sedimentary exhalative processes. Dongguashan is a typical stratabound deposit and is characterized by pyrite that formed in porphyry-skarn-stratabound orebodies, which makes it ideal for comparing porphyry, skarn, and stratabound mineralization systems by pyrite study. We classify pyrite types according to occurrence and generation. Specifically, the pyrite in the porphyry orebodies is composed of Py-p1 (potassic zone) and Py-p2 (propylitic and phyllic zone). Py-s, among garnet grains, occurs in the skarn orebodies. From top to bottom, the pyrite in the stratabound orebodies is composed of macrocrystalline pyrite (Py-m) in the massive mineralization zone, Py-l in the laminated mineralization zone, and coarse-grained pyrite (Py-v1) and microcrystalline pyrite (Py-v2) in the vein-like mineralization zone. Co, Ni, Se, As, and Au are most likely to occur as solid solutions in the Dongguashan pyrite. Pb and Bi are likely distributed in Dongguashan pyrite homogeneously as nanoinclusions. The Zn, Cu, and Mo in Dongguashan pyrite indicate that these elements occur as micromineral inclusions. The positive correlation between S and Fe, high Co/Ni ratios (mostly > 2), and coexistence with hydrothermal minerals imply a magmatic-hydrothermal origin for the Dongguashan pyrite. Py-m yields a Re–Os isochron age of 135.8 ± 2.8 Ma (MSWD = 1.8), which is interpreted as the stratabound ore-forming age. Combined with previous results, the porphyry-skarn-stratabound mineralization is the product of the same hydrothermal fluid system related to Early Cretaceous magmatic activity.