Late Oligocene Cu-Mo mineralization at West Zafarghand, Iran: Evidence for a short-lived magmatic-hydrothermal system

This study investigates the magmatic-hydrothermal evolution of the West Zafarghand porphyry Cu-Mo deposit in the central Urumieh-Dokhtar Magmatic Arc (UDMA), Iran using field and petrographic observations, integrated with fluid inclusion microthermometry, TitaniQ thermometry, U-Pb zircon and Re -Os molybdenite geochronology. The deposit is hosted by late Eocene volcanic rocks, intruded by granodiorite and granite porphyries and andesitic dykes swarm. Mineralization includes magnetite-bornite-chalcopyrite and chalcopyrite ± pyrite assemblages, associated with potassic and chlorite-sericite alteration, followed by molybdenite mineralization during transition to phyllic and propylitic, carbonate-bearing alteration. U-Pb zircon geochronology constrains the volcanic host rocks and the granodiorite porphyry to ca. 34–33 Ma, whereas the granite porphyry and the dykes are late Oligocene in age (ca.24–23 Ma). Overlapping late Oligocene Re -Os molybdenite ages indicate a tight genetic link between Cu-Mo mineralization and the emplacement of the younger granitic magmatism. Whole-rock geochemistry indicates derivation from subduction-modified mantle meltsand lower-crust interaction, with the late Oligocene magmatism displaying a weak adakite-like affinity (Sr/Y up to ∼50). Fluid inclusion data define fluid evolution at shallow crustal levels, recording early-stage boiling and phase separation, followed by cooling from ∼570 °C in potassic stage at ∼2.2 km depth to ∼217 °C in propylitic alteration at ∼1.5 km depth. The study highlights: (i) robust geochronology for constraining magmatism and ore formation; (ii) late-stage, highly fractionated, fertile intrusions with weak adakite-like affinity as responsible for mineralization; (iii) fluid boiling promoted Cu-Mo mineralization, and fluid neutralization favored molybdenite–carbonate precipitation.