Geological characteristics, fluid inclusions and H-O-C-S isotopes of the Zaopa Ag-Mo prospect in the Suizao area, Hubei Province: Implications for ore genesis

Abstract

The Zaopa Ag-Mo prospect is located in the Tongbai-Dabie orogenic belt in central China. The orebodies occur as quartz veins and are controlled by secondary faults of the Wushan fault zone in the Suizao area, and hosted by the Zhoulou granite. We document three hydrothermal stages, characterized by albite-quartz-sulfide veins (stage I), quartz-sulfide (stage II) and quartz-fluorite assemblages (stage III), respectively. Silver is mainly found in hessite and galena. There are three types of fluid inclusions in quartz and fluorite including: (1) liquid-rich aqueous fluid inclusions (L + V); (2) aqueous-carbonic fluid inclusions (L + V + CO2); (3) pure carbonic fluid inclusions (pure CO2). Laser Raman spectroscopic analyses indicate the existence of carbon dioxide in the fluid inclusions. The fluid system of the Zaopa Ag-Mo prospect is composed of CO2-NaCl-H2O. The homogenization temperatures of the three stages are 380 to 495 °C, 337 to 404 °C and 246 to 336 °C, respectively. The salinities of the three stages are 11.1–17.5 wt% NaCl eq., 6.7–12.7 wt% NaCl eq. and 1.6–9.9 wt% NaCl eq., respectively. The stage I sulfides (molybdenite, chalcopyrite, pyrite) show a δ34S value around 0‰ (−3.1 to +1.0‰), indicating a magmatic origin. The stage II sulfides (galena, sphalerite, pyrite) also show a δ34S value around 0‰ (−5.7 to +1.6‰), again indicating a magmatic origin. The C-H-O isotope data shows that the fluids of the early stage were derived from a magmatic source, but the fluids of the late stage mixed with meteoric waters. By comparing the characteristics of the Mo deposits in China and those from other countries, we conclude that the Zaopa Ag-Mo prospect is a structurally-controlled magmatic-hydrothermal vein type deposit.