A combined fluid inclusion and isotopic geochemistry study of the Zhilingtou Mo deposit, South China: Implications for ore genesis and metallogenic setting

Abstract

The Zhilingtou Mo deposit is recently discovered and occurs in the Qin-Hang metallogenic belt, South China. Vein stockworks are hosted in the granite porphyry and the surrounding Paleoproterozoic Badu Group basement. Three stages of mineralization and wallrock alteration were developed: the early stage quartz±K-feldspar veins with potassic alteration, the ore stage quartz–molybdenite veins with strong phyllic alteration overprinting early potassic alteration, and the late stage quartz–pyrite±calcite veins with propylitization. Two-phase liquid-rich aqueous (type I) inclusions in the early stage veins show homogenization temperatures (Th) of 366–442°C, with salinities of 5.3–14.1wt.% NaCl equivalent. Two-phase gas-rich aqueous (type II) and coexisting halite-bearing (type III) inclusions in the ore stage veins display Th of 335–433°C and 329–396°C, and salinities of 0.5–6.2 and 38.6–44.8wt.% NaCl equivalent, respectively. Type I inclusions in the late stage veins yield Th of 187–282°C, with salinities 3.5–7.7wt.% NaCl equivalent. Fluid boiling occurred during the ore stage and probably promoted a rapid precipitation of molybdenite. Laser Raman analysis implies that ore fluids are CO2-poor. Hydrogen and oxygen isotopes indicate that mineralizing fluids are primarily magmatic in origin, with apparently involvement of external meteoric water in the late stage. Lead isotopes suggest that the metals are sourced from the ore-bearing granite porphyry. Trace elements of the ore-bearing granite porphyry display obvious Nb and Ta depletion, indicating arc magma geochemical affinities. Vein stockworks, intensive phyllic alteration, CO2-poor ore fluids, and continental arc setting suggest that the Zhilingtou Mo deposit is likely to be an Endako-type porphyry Mo deposit. It is distinctly different from porphyry Mo deposits in the East Qinling-Dabie metallogenic belt in China, which were formed in a post-collisional setting and characterized by intensive potassic alteration and CO2-rich ore fluids.