Zircon U-Pb-Hf isotopes and mineral chemistry of Early Cretaceous granodiorite in the Lunggar iron deposit in central Lhasa, Tibet Y, China

Abstract

The Lunggar iron deposit belongs to the Bangong-Nujiang metallogenic belt and is located in central Lhasa on the Tibetan Plateau. In the Lunggar deposit, iron mineralization formed in the skarnization contact zone between the Early Cretaceous granodiorite and the late Permian Xiala Formation limestone. In this study, we achieved detailed zircon U-Pb-Hf isotopes and mineral chemistry for the Early Cretaceous granodiorite. Zircon U-Pb dating results indicate that the Early Cretaceous granodiorite emplaced at ca. 119 Ma. Based on the trace elements in zircons and the mineral chemical composition of amphibole and biotite, the Early Cretaceous granodiorite was believed to form under condition of high temperature (>700 °C), low pressure (100–400 MPa), and relatively high oxygen fugacity (lg/O₂)(−13.6 to −13.9) and H₂O content (4%–8%). Zircon trace elements, Hf isotope and biotite chemistry collectively reveal that significant juvenile mantle-derived magmas contributed to the source of the granodiorite. The relatively high log/O₂ and shallow magma chamber are beneficial for skarn iron mineralization, implying remarkable potential for further prospecting in the Lunggar iron deposit.

Keywords

zircon U-Pb-Hf isotope / mineral chemistry / crystallization condition / Lunggar iron deposit / central Lhasa

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