Petrogenesis and metallogeny of the Dongguashan Cu-Au deposit in the Tongling ore-cluster region,the Lower Yangtze River Metallogenic Belt: Constraints from geochemistry and geochronology

The Dongguashan Cu-Au deposit located in the eastern portion of the Tongling mining district, the Lower Yangtze River Metallogenic Belt (LYRB), Eastern China is a typical one associated with the Qingshanjiao quartz monzodiorite, including porphyry, skarn, and stratabound ores. In order to constrain the petrogenesis of the intrusive rocks and associated Cu-Au mineralization, detailed analyses of the zircon geochronology and geochemistry, whole-rock geochemistry and Sr-Nd-Pb isotopes, and zircon Lu-Hf isotopes were performed. Magmatic zircons from quartz monzodiorite yield U-Pb ages of 136–138 Ma, revealing their formation ages of early Cretaceous. Geochemical characteristics of the quartz monzodiorites (SiO₂ = 63.6–66.2 wt%, high Sr, low Y and Yb concentrations) discriminate their adakitic affinity. They are enriched in LILE and LREE, depleted in HFSE and HREE, and has no or slightly negative Eu anomalies. These geochemical characteristics indicate that the monzodiorites may be primarily derived from the magma mixing of mantle- and LCC-derived melts. The relatively low ε_Nd(t) values (−11.7 to −10.7) and high (⁸⁷Sr/⁸⁶Sr)_i ratios (0.7075 to 0.7078) may be plausibly interpreted by contamination of enriched mantle materials and/or continental crust. The high radiogenic Pb isotopes with (²⁰⁶Pb/²⁰⁴Pb)_i = 17.98–18.09, (²⁰⁷Pb/²⁰⁴Pb)_i = 15.51–15.53, and (²⁰⁸Pb/²⁰⁴Pb)_i = 38.18–38.26 plot in the field of MORB, near the intersection of EM-1 and EM-2, and are considerably different from those of the upper and lower continental crust and the Dabie adakites, which exclude major contamination from the continental crust. Ti-in-zircon temperatures and calculated Ce⁴⁺/Ce³⁺ values fall within the field between MH and FMQ. The results indicate that the intrusive rocks and associated large-scale Cu-Au mineralization in the Dongguashan deposit are resulted from the magma mixing of mantle- and LCC-derived melts. in a lower magma temperature, yet higher fO₂ and water content environment.