Skarn metallogeny through zircon record: An example from the Daye Cu-Au-Fe-Mo district, eastern China

The Daye district in Eastern China hosts more than 50 Fe-Cu-Au-Mo porphyry-skarn deposits that are associated with intermediate to felsic rocks of Early Cretaceous ages. The origin of these ore-related granitoids has been intensively investigated, but the petrogenetic factors controlling variable metal associations (e.g., Fe, Cu–Mo or Cu-Au-Fe) in different skarn deposits remain not well understood. Here, we present Hf isotope and trace element data of zircons from ore-related intrusions of four representative skarn deposits (i.e., the Lingxiang and Chengchao Fe skarn, the Tonglushan Cu-Au-Fe skarn and the Tongshankou Cu–Mo porphyry-skarn deposits) to better understand controls of the source, oxidation state and fractionation degree of the magmas on the polymetallic metallogeny in the Daye district. Zircons from the ore-related granodiorite at Tongshankou, quartz diorite at Tonglushan and diorite at Lingxiang have comparable εHf(t) values ranging from −11.3 to −1.1, which are similar to values of the Early Cretaceous mafic rocks (εHf (t) = −11.9 to −1.2) in the Daye district and adjacent areas. This similarity suggests that these ore-related intrusions were largely derived from an enriched lithospheric mantle source. In comparison, zircons from the ore-related diorite and quartz monzonite associated with the Chengchao Fe skarn have much lower εHf(t) values (−11.6 to −25.3), indicating larger degrees of crustal contribution. On average, zircons from the Cu-related intrusions at Tongshankou and Tonglushan have higher Ce/Ce* (>1100; method of Zhong et al., 2019) and Ce4+/Ce3+ (>170; method of Ballard et al., 2002) ratios, which are interpreted reflecting higher oxidation state for the magmas. In contrast, zircons from Fe-related intrusions at Chengchao and Lingxiang have much lower average values of Ce/Ce* (