Textures, trace element compositions, and sulfur isotopes of pyrite from the Honghai volcanogenic massive sulfide deposit: Implications for ore genesis and mineral exploration

In this paper, we present textures, trace element compositions, and sulfur isotope data for pyrite from the Honghai volcanogenic massive sulfide deposit to place new constraints on the source and evolution of the ore-forming fluids and provide insights into the ore genesis with implications for future exploration. The Honghai deposit consists of upper lenticular ores comprising massive sulfides that are underlain by stockwork and disseminated sulfides. The textural and isotopic characteristics of the synsedimentary framboidal pyrite (Syn-Py) indicate its formation by biogenetic processes. Coarse-grained pyrite generations (M-Py1, M-Py2, and M-Py3) from the massive sulfides have high Au, Ag, Cu, Zn, Pb, Sb, and Tl concentrations and low Co, Se, Te, Ti, and Sn concentrations, indicating that they precipitated from metal-rich, low- to intermediate-temperature, oxidizing fluids. The high Te, Ti, and Sn concentrations and high Co/Ni ratios in the massive pyrite (M-Py4) associated with magnetite in the massive sulfide lenses, as well as the high Ti, V, Cr, and Ni concentrations and low Al, Mn, and Zn concentrations in the magnetite, suggest that the coexisting M-Py4 and magnetite precipitated under oxidizing and high-temperature (300°C to 500°C) conditions. In contrast, pyrite grains from the underlying stockwork and veins (V-Py1, V-Py2, and V-Py3) are characterized by low Au, Ag, Cu, Zn, Pb, Sb, and Tl concentrations coupled with high Co, Se, Te, and Ti concentrations and high Co/Ni ratios, which are interpreted in terms of reducing and high-temperature ore-forming fluids. The large variations in δ³⁴S values from −6.4‰ to +29.9‰ suggest that the ore-forming fluids were derived from magmatic source that were significantly modified by seawater. The spatial variations of trace element assemblages of pyrite from different levels of the main massive orebodies can be used as an indicator for mineral exploration of Cu-Zn ores in the Honghai deposit. Although no significant difference in δ³⁴S values is observed between the upper massive sulfide lenses and lower stockwork/vein zone, the spiky δ³⁴S pattern noted in the massive pyrite can be used as a marker for the main massive orebodies.