Genesis of the Yuanlingzhai porphyry molybdenum deposit, Jiangxi province, South China: Constraints from petrochemistry and geochronology

·Granite porphyry and Mo deposit dated at 165.49 ± 0.59 Ma and 160 ± 1–162.7 ± 1.1 Ma.·Western and eastern Keshubei granites mark two discrete magmatic events at ca. 160 Ma and 185–195 Ma.·Ore-forming materials were derived from deep sources and partly from Yuanlingzhai porphyry.

The newly discovered Yuanlingzhai porphyry molybdenum (Mo) deposit in southern Jiangxi province belongs to the group of Mo-only deposits in the Nanling region. The mineralization developed at contact zones between the Yuanlingzhai granite porphyry and Neoproterozoic metamorphic rocks of the Xunwu Formation. Precise LA–MC–ICPMS zircon U–Pb dating of the Yuanlingzhai porphyry, as well as the adjacent western Keshubei and eastern Keshubei granites, yielded ages of 165.49 ± 0.59 Ma, 159.68 ± 0.43 Ma, and 185.13 ± 0.52–195.14 ± 0.63 Ma, respectively. Molybdenite Re–Os isochron ages of the ores are 160 ± 1–162.7 ± 1.1 Ma, which is consistent with the age of large-scale W–Sn deposits in South China. The Yuanlingzhai porphyry is characterized by high K2O, P2O5, and A/CNK (1.33–1.59), and low CaO and Na2O. The rock shows relatively enriched LREE without significant Eu anomalies (Eu/Eu* = 0.80–0.90). Geochemical and mineralogical characteristics indicate that the ore-hosting porphyry is a typical S-type granite generated from the partial melting of crustal material with only minor mantle contribution. Both Harker and evolutionary discrimination diagrams indicate that the Yuanlangzhai and western Keshubei granites are not products of co-magmatic evolution. The Keshubei granites and Xunwu Formation were not significant sources for the components in the porphyry mineralization, but the Yuanlangzhai granite may have supplied some ore-forming material. However, the main ore-forming material was carried by fluids from deep sources, as demonstrated by fluid inclusion and stable isotope data from the molybdenum deposit. The Mo porphyry deposit formed in an extensional setting, and was possibly associated with Jurassic subduction of the Izanagi Plate.