In Situ Analyses of Trace Elements, U-Pb and Lu-Hf Isotopes in Zircons from the Tongshankou Granodiorite Porphyry in Southeast Hubei Province, Middle-Lower Yangtze River Metallogenic Belt, China

The Tongshankou Cu-Mo deposit, located in southeast Hubei province, is a typical skarnporphyry type ore deposit closely related to the Tongshankou granodiorite porphyry, characterized by a high Sr/Y ratio. Detailed in situ analyses of the trace elements and U-Pb and Lu-Hf isotopes in zircons from the Tongshankou granodiorite porphyry were performed. Scarcely any inherited zircons were observed, and the analyzed zircons yielded highly concordant results with a weighted mean Pb-206/U-238 age of 143.5 +/- 0.45 Ma (n=20, mean square weighted deviation was 0.75), which was interpreted to represent the crystallization age of the Tongshankou granodiorite porphyry. The chondrite-normalized rare-earth element pattern was characterized by a slope that steeply rises from the light-group rare-earth elements (LREE) to the heavy-group rare-earth elements (HREE) with a positive Ce-anomaly and inconspicuous Eu-anomaly, which was coincident with the pattern of the zircons from the Chuquicamata West porphyry, Chile. The analyzed zircons also had relatively low Hf-176/Hf-77 ratios of 0.282526-0.282604. Assuming t=143 Ma, the corresponding calculated initial Hf isotope compositions (epsilon(Hf)(t)) ranged from -5.6 to -2.9. The results of the in situ analysis of trace elements and U-Pb and Lu-Hf isotopes in zircons from the Tongshankou granodiorite porphyry suggest that a deep-seated process involving a thickened-crust/enriched-mantle interaction may play an important role in the generation of high Sr/Y-ratio magma and potentially in the generation of porphyry Cu-Mo systems.