Geochronology, geochemistry, and Hf isotopic compositions of the Jintonghu porphyry Cu-Mo deposit in the Zijinshan ore district, SE China: Insights into the controlling factors on magma fertility

Abstract

The Jintonghu porphyry Cu-Mo deposit is located in the Zijinshan ore district within the southeastern coastal volcanic belt, China. Copper mineralization is predominantly restricted to the granodiorite porphyry, whereas the other intrusions remain barren. This disparity highlights the need for deeper insights into the controlling factors on magma fertility and its contribution to copper mineralization. There are four intrusive phases at Jintonghu, including the Early Cretaceous pre-mineralization Sifang granodiorite (109.2 ± 0.6 Ma), syn-mineralization diorite porphyry (105.4 ± 0.4 Ma), dacite porphyry (105.5 ± 0.5 Ma), and granodiorite porphyry (105.5 ± 0.5 Ma and 105.6 ± 0.5 Ma), late-mineralization porphyritic granodiorite (103.4 ± 0.6 Ma), and Late Cretaceous post-mineralization quartz syenite porphyry (99.1 ± 1.0 Ma). Zircon Hf isotopic compositions demonstrate that the Early Cretaceous intrusions share a similar source. The granodiorite porphyry and porphyritic granodiorite present higher zircon ε_Hf(t) values (−2.49 to 1.43), suggesting an increasing contribution from the mantle-derived materials or juvenile crust. The estimated oxygen fugacity based on zircon trace elements shows no clear differences among the pre-, syn-, and late-mineralization phases, suggesting that oxygen fugacity is not the first-order factor controlling magma fertility at Jintonghu. Instead, the granodiorite porphyry and porphyritic granodiorite are inferred to be more hydrous, as evidenced by distinctly elevated zircon Eu/Eu* (0.42–0.91), 10,000 × (Eu/Eu*)/Y (4.61–17.5), and (Ce/Nd)/Y (0.01–0.19) ratios, along with low zircon Dy/Yb (0.11–0.17) ratios and amphibole-dominated fractionation. Therefore, high magmatic water content is the dominant factor controlling magma fertility in the Jintonghu deposit. Furthermore, the porphyritic granodiorite shares coincident geochemical proxies with those of the ore-hosting granodiorite porphyry, combined with their comparable alteration patterns, indicating its copper mineralization potential.