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Molybdenite Re–Os and zircon U–Pb isotopic data are first obtained from the stockwork and disseminated-style gold-bearing ores and the fine-grained granite hosting these ores in the Xiawolong gold mine, respectively, which is located within the Muping–Rushan gold metallogenic belt, eastern Jiaodong Peninsula, so as to illustrate the genesis of gold mineralization and its implication for exploration. Four molybdenite samples yield a well-defined Re–Os isochron age of 118.4 ± 2.5 Ma (2σ), which is identical to the weighted average Re–Os model age of 118 ± 1.7 Ma (2σ). Integration of the new geochronologic data with those reported recently from the other gold mines in the Muping–Rushan gold metallogenic belt suggests that a discrete gold event occurred in Xiawolong ca. 4 m.y. older than that for the other gold mineralization at ca. 114 Ma in eastern Jiaodong. In addition, two fine-grained granite samples, measured using the LA-ICP-MS zircon U–Pb method, produce the first precise ages of 118 ± 2 to 117 ± 2 Ma (2σ), identical to the molybdenite Re–Os ages, within the margin of error and obtained in this study. The fine-grained granite has a similar lithology and emplacement age as those of the medium-grained monzogranite consisting of the marginal facies of the Sanfoshan batholith, and is considered to be the crystallization products of Sanfoshan granitic magma in the late stage. Combined with the previous S-Pb-D-O isotope, fluid inclusion and geological studies, which suggest that the ore-forming fluid of Xiawolong gold mineralization is from magmatic water, and the identification that the magnetite coexists with the gold-bearing pyrite and molybdenite in the gold ores, which indicates a high oxygen fugacity (fO₂) of both the magma and resultant hydrothermal fluids, it is logical to infer that the Xiawolong gold deposit is genetically in relation to the Sanfoshan granitic magmatism, which is high in fO₂ and rich in Au at the magmatic–hydrothermal transition stage, and the change in fO₂ mostly likely makes a significant contribution to the precipitation of Au. This result reveals that the late-stage granitic magma with high fO₂, which is crystallized into the fine-grained granite, probably is also rich in Au, except the W–Mo–Cu–Zn–U–Be–Li–Nb–Ta–Sn–Bi-elements. Therefore, based on the extensional tectonic regime for the early Cretaceous Jiaodong gold deposits, we propose that gold exploration in the Jiaodong should not only focus on the fault-hosted Au but also on the fine-grained granite-hosted Au around the apical portions of the late Early Cretaceous small-granitic intrusions with high fO₂. This model could also be important for prospecting in other gold ore districts, which have a similar tectonic setting. Full article

The Xiawolong gold deposit, located in the Muping–Rushan gold metallogenic belt (eastern Jiaodong Peninsula), is a newly discovered deposit that developed in the late Early Cretaceous as fine-grained granite. Gold mineralization, which mainly occurs in the middle of fresh fine-grained granite dikes, consists of stockwork-style and disseminated ores. They are characterized by middle-high-temperature mineral assemblages, such as molybdenite and magnetite, associated with gold-bearing pyrite. Four types of primary fluid inclusions, contained within the quartz grains from the gold-bearing disseminated and stockwork-style fine-grained granitic ores, were identified based on microthermometry and Raman spectroscopy. The types identified were type 1 aqueous inclusions with middle-high temperature (201 to 480 °C) and middle-low salinity of 0.18 to 17.00 wt.% NaCl equiv.; type 2 H₂O–CO₂ inclusions, which show middle-high temperatures (218 to 385 °C), middle-low salinities (1.23 to 13.26 wt.% equiv. NaCl), and variable XCO₂ (0.031 to 0.044); type 3 daughter mineral-bearing inclusions with high temperature (416 to 446 °C) and relatively constant and high salinity (28.59 to 32.87 wt.% NaCl equiv.); and type 4 CO₂ fluid inclusions, which possess a bulk density of 0.405 to 0.758 g/cm³ and a constant XCO₂ (0.952 to 0.990) (according to the decreasing abundance of fluid inclusions). The δ¹⁸O_water range is between 3.4 and 5.9‰, and the range of the δD is from −97.1 to −77.4‰, which indicates that the ore-forming process is of a magmatic water origin. The δ³⁴S values possess a narrow range between 4.5 and 9.3‰, indicating the source of the Mesozoic Kunyushan granitoids. The Pb isotopic compositions of pyrite show that the Mesozoic Kunyushan granitoids are the main lead source for pyrites. Types 1, 2, and 3 fluid inclusions coexist in the same view field of the quartz grain, which are suggested to occur as the result of fluid immiscibility because of the boiling of a single homogeneous NaCl-CaCl₂-KCl-CO₂-H₂O system. The fluid immiscibility, rather the fluid mixing and wall-rock sulfidation, is the mechanism of gold precipitation in the Xiawolong deposit. Compared with both the “Linglong-type” and “Jiaojia-type” gold deposits in the Jiaodong Peninsula in terms of geological–petrographic evidence and all of the available geochemical data, it can be concluded the Xiawolong gold deposit is of magmatic hydrothermal origin, having a genetic relation to the fine-grained granite. Full article