Mineralization timing and genesis of the Dongxiang stratabound Cu-Mo-W deposit in the Qinhang metallogenic belt (South China): Constraints from U-Pb and Re-Os geochronology and sulfur isotopes

The Qinhang metallogenic belt is one of the important copper polymetallic metallogenic belts in eastern China. In this belt, many ore deposits host high-grade stratabound copper ore bodies. However, there has been considerable controversy over their origins. The key to the dispute over the origin of the deposits is the lack of precise metallogenic age constraints, which seriously restricts our understanding of the metallogenetic regularity of copper polymetallic deposits in the Qinhang metallogenic belt. To address the controversies regarding the genesis of these types of ore deposits in the Qinhang metallogenic belt, this study focuses on Dongxiang, a representative stratabound, copper-rich deposit in South China. Molybdenum mineralization was discovered through detailed field geological surveys and drilling. This paper reports Re-Os dating for molybdenite in different occurrences for the first time. High-precision Re-Os dating of molybdenite in the Dongxiang deposit shows that the weighted ages of molybdenite in different occurrences are relatively consistent, ranging from 160.4 Ma to 158.7 Ma. The isochron age obtained for all samples is 159.6 ± 0.8 Ma, which is consistent with the weighted mean age of 159.6 ± 0.9 Ma. The hydrothermal apatite, closely associated with the chalcopyrite and bornite mineralization in stratabound copper ore bodies, yielded a lower intercept age of 156.4 ± 1.5 Ma. Zircon U-Pb ages of granodiorite porphyry and granite porphyry are 157.5 ± 0.58 Ma and 153.9 ± 0.63 Ma, respectively. Therefore, the Dongxiang deposit’s rock-forming and mineralization age is concentrated between 160 Ma and 154 Ma. Sulfur isotope compositions of sulfides in stratabound copper ore bodies show a narrow range of δ34S values, from 0.1‰ to 1.85‰, which is consistent with a magmatic origin. Combining Cu-Pb-H-O isotope and previous studies, we comprehensively propose that the Dongxiang is a porphyry-distal hydrothermal Cu-Mo-W polymetallic deposit formed in the Late Jurassic and associated with paleo-Pacific plate subduction. The Qinhang metallogenic belt holds significant potential for porphyry-skarn copper polymetallic deposits, rather than sedimentary exhalative deposits.