The Jiangnan Mo-W-Pb-Zn metallogenic belt hosts more than fifteen W-Mo and Mo deposits and is located at the margin between the Middle-Lower Yangtze metallogenic belt and the South China Continent. The recently discovered Gaojiabang W-Mo deposit, Chizhou district, Anhui Province, is the one of the largest W-Mo deposits in the belt (25.4 Mt at a grade of 0.28% WO3, 0.11 g/t Mo, with about 10,000 t of that total at an averarge grade of 6.6 g/t Au). The deposit is associated with Jurassic granite and monzonite porphyries that intruded sedimentary rocks of the Cambrian Huangboling Formation. Alteration displays a zonation from granite porphyry to wall rock. Five distinct alteration zones are recognized: deep-seated K-feldspar-biotite-quartz alteration, a quartz-sericite alteration zone, garnet-diopside-epidote alteration zone, calcite-quartz alteration zone, and zone of thermal metamorphism (hornfels). These features are comparable with porphyry Cu-Au-Mo systems. The first three zones of alteration display a close spatial relationship with W-Mo ores. Three distinct styles of W-Mo mineralization are recognized: minor vein-type W-Mo mineralization within sedimentary units; skarn W-Mo mineralization at the contact between sedimentary rocks and granite porphyry; and disseminated Mo(±W) mineralization hosted within both porphyries. The main ore minerals are scheelite, molybdenite, pyrite, pyrrhotite, and minor chalcopyrite, and display a zoned distribution in which most molybdenite occurs inside deep porphyries and the majority of the scheelite is observed inside shallow skarns and hornfels. Based on the presence of redox-indicative mineral assemblages such as pyrrhotite, molybdenite and pyrite in the absence of sulfates, we consider Gaojiabang to be a relatively reduced W-Mo porphyry-skarn system. Our new U-Pb zircon ages confirm Late Jurassic ages for granite (150.4±1.1 Ma) and monzonite porphyries (149.4±1.6 Ma). A molybdenite Re-Os age of 149.5±1.4 Ma indicates that W-Mo mineralization is closely associated with the two porphyries. This new data makes Gaojiabang the oldest deposit recognised so far in the Middle-Lower Yangtze River area, in turn inferring that the westward subduction of the Pacific Plate commenced at âŒ150 Ma. Geochemical data indicate that mineralization in the Gaojiabang deposit derives from multiple sources, dominantly from magmatic rocks and basement strata via mantle-crust interaction, with the single greatest involvment of crustal materials among all deposits in the Middle-Lower Yangtze River area. Sulfides, including pyrite, pyrrhotite and molybdenite, display a wide range of ÎŽ34S between +3.8â° to +12.1â°. The gradual increase of ÎŽ34S from inner porphyry to outer wall rock indicates contamination from crustal marine sedimentary facies as the ore-forming fluids evolved. Following the W-Mo mineralization event at Gaojiabang, emplacement of Qingyang-Jiuhua Complex at 144â127 Ma resulted in a previously unrecognized ductile deformation of porphyries, sedimentary rocks, and ores.