Genesis of the Maogongdong deposit in the Dahutang W-Cu-(Mo) ore field of northern Jiangxi Province, South China: constraints from mineralogy, fluid inclusions, and H-O-C-S isotopes

The Maogongdong deposit is located in the giant Dahutang W-Cu-(Mo) ore field, northern Jiangxi Province, South China. It is mainly a vein-type deposit, characterized by early W and late Cu-Mo mineralization, and temporally and spatially associated with Late Mesozoic S-type muscovite granites emplaced into a Neoproterozoic granodiorite batholith and the Shuangqiaoshan Group metasedimentary rocks. Fluid inclusions and H-O isotopes suggest that the early ore-forming fluids of the Maogongdong deposit are mainly magmatic water with relatively high temperature (270-410 degrees C) and moderate-to-low salinity, while the late ore-forming fluids are mixed with meteoric water, with medium-to-low temperature (160-270 degrees C) and low salinity. Infrared and conventional microthermometric studies of fluid inclusions of the main tungsten mineralization stage show that the homogenization temperatures of primary fluid inclusion assemblages in wolframite (325 to 355 degrees C) are about 20 degrees C higher than those of coexisting scheelite and generally 40 degrees C higher than those in quartz. The delta S-34 values of sulfides (- 5.2 to - 1.3 parts per thousand) in the sulfide stage are slightly lower than the magmatic sulfur (- 1.7 to 0.6 parts per thousand) in the pre-ore stage, most likely due to an increase in oxygen fugacity. The low carbon isotope values (- 26.2 to - 15.5 parts per thousand) of fluid inclusions in the tungsten mineralization stage show that a large amount of organic carbon was added before mineralization. Fluid cooling and pressure decrease are the main factors of tungsten ore precipitation, while local boiling may also make a contribution. Mixing of the different fluids led to the formation of copper and molybdenum ores.