Jurassic magmatism and metallogeny in the eastern Qin-Hang Metallogenic Belt, SE China: An example from the Yongping Cu deposit

Abstract

The large Yongping Cu deposit is situated in the eastern Qin-Hang Metallogenic Belt (SE China) and close to the Jiang-Shao suture zone. Igneous rocks at Yongping occur as granitoids, including the porphyritic biotite granite stock of Shizitou and quartz porphyry and granite porphyry dykes, which recorded the Jurassic – Cretaceous magmatic evolution and tectonic setting at Yongping.This integrated study comprises whole-rock analysis, U–Pb zircon dating and Hf isotope analyses of the Yongping granitoids in order to better understand the genesis of the Yongping Cu deposit. The Yongping granitoids show typical I-type affinity with P2O5 decreasing with fractionation, and yielded ages of 160.2 ± 1.6 Ma (the porphyritic biotite granite), 158.7 ± 1.5 Ma (the quartz porphyry) and 152.7 ± 1.7 Ma (the granite porphyry), indicating their formation in the Late Jurassic. The Nb/Ta, Mg#, εHf(t) and TDM2 of porphyritic biotite granite, quartz porphyry and granite porphyry suggests that they are the partial melting product of Precambrian metamorphosed crustal basement with contribution of mantle material and that the porphyritic biotite granite and the granite porphyry contain more mantle-derived material than the quartz porphyry. In addition to the close temporal and spatial relationship between the Shizitou stock and the Yongping stratiform orebody, the magma of the porphyritic biotite granite has higher oxygen fugacity (avg. zircon Ce4+ / Ce3+ = 303) and is more hydrous also indicate quite a good potential for Cu mineralization, in contrast to the late quartz and granite porphyries. Overall, the Yongping stratiform mineralization may have been a skarn-type mineralization associated with the porphyritic biotite granite stock of Shizitou. The Shizitou stock as well as the quartz porphyry and granite porphyry dykes are products of the lithospheric extension and asthenospheric upwelling related to the Paleo-Pacific plate subduction.