Petrogenesis and mineralization of the Fenghuangshan skarn Cu–Au deposit, Tongling ore cluster field, Lower Yangtze metallogenic belt

Abstract

The Fenghuangshan copper–gold deposit, located in the Tongling ore cluster field along the Lower Yangtze metallogenic belt (LYRB) in eastern China, mainly consist of skarn ores hosted in granodiorite. U–Pb dating of magmatic zircons from Fenghuangshan granodiorite yields a weighted mean 206Pb/238U age of 143.1±1.6Ma. Five molybdenite samples collected in the Fenghuangshan deposit yield a Re–Os isochron age of 141.7±0.8Ma, demonstrating that the ore formation event is coeval with the Fenghuangshan granodiorite intrusion. The magmatic zircon ƐHf(T) values vary from −12.0 to −28.3, corresponding two-stage Hf model ages between 1.6Ga to 2.4Ga. Geochemical and isotopic signatures suggest that the Fenghuangshan granodiorite resembles adakite, which was derived from partial melting of the subducted oceanic crust towards LYRB during the early Cretaceous. The occurrence of inherited zircons shows the intrusive granodiorite was assimilated by old crustal materials during its emplacement. The biotite thermobarometry, zircon Ce(IV)/Ce(III) ratios and Eu anomalies coincidently demonstrate that the magma source of granodiorite was under high to moderate oxidized condition, conducive to Cu–Au mineralization. The sulfide ores in Fenghuangshan deposit are enriched in Pd and Pt, which could also be a consequence of the high oxidized magma source. The high Re abundance in molybdenite and platinum group element (PGE) contents of sulfide ores suggest that the ore-forming materials are characterized by mixed sources from the mantle and crust, and were slightly affected by hydrothermal alteration.