The oldest Mo porphyry mineralization in the Yangtze Valley Metallogenic Belt of eastern China: Constraints on its origin from geochemistry, geochronology and fluid inclusion studies at Matou
Abstract The Matou Mo(-Cu) deposit, located in the Yangtze Valley Metallogenic Belt of central-eastern China, is a typical porphyry-type Mo deposit. The orebodies at the deposit are hosted by Matou porphyritic granodiorite, which is the largest intrusive in the area. Quartz vein-type and disseminated sulfide mineralization are well developed in the porphyry and near its contact with Silurian sandstone. Crosscutting relationships indicate that porphyritic granodiorite is the oldest phase in the pluton, which is crosscut by a porphyritic diorite containing traces of chalcopyrite, and later dolerite dykes. These phases have U-Pb zircon dates of 147 ± 3, 140 ± 1 and 135 ± 1 Ma, which confirms the cross-cutting relationships observed in the field. A Re-Os molybdenite isochron age of 147 ± 4 Ma indicates that the porphyritic granodiorite is the source of the oldest Mo mineralization in the metallogenic belt and was formed during a change of the tectonic setting in the area, from an intracontinental orogeny to extensional tectonics. From 147 to 135 Ma, crust-mantle interaction played an important role in the formation of magmatic rocks at Matou. Systematic petrological and geochemistry investigations reveal that the three phases have a crust source with minor input from the mantle. Investigation of ore-forming fluid, H-O isotopes, S isotopes, and the Re content of molybdenite indicate that the ore-forming fluid and metals were derived from the lower crust. During the evolution of fluid from initial magmatic fluids (stage I) to ore-forming fluids (stage II), fluid boiling accompanied by the input of relatively cooler meteoric water led to the deposition of the Mo mineralization.