Two-stage Cu-Pb-Zn mineralization of the Baoshan deposit in southern Hunan, South China: Constraints from zircon and pyrite geochronology and geochemistry

The Baoshan Cu-Pb-Zn deposit is one of the representative polymetallic deposits in the middle of the Nanling Range, the western part of the Qin-Hang ore belt. In order to better understand the magmatic activity (granodiorite porphyry and porphyritic granodiorite) and mineralization in the Baoshan deposit, in situ U-Pb and Lu-Hf isotope studies of zircons and trace element compositions of two generations of pyrite (ore stage: Py I and post-ore stage: Py II) have been carried out. This constrains the geochronology, magma source, fluid composition, and the origin of the ore-forming materials. The zircon U-Pb dating results from two types of intrusions show two geochronological populations: (i) similar to 180 Ma for the Cu (Pb-Zn) mineralization that is related to the porphyritic granodiorite, and (ii) similar to 160 Ma for the Cu-Pb-Zn mineralization which is associated with the granodiorite porphyry. The similar REE patterns, Hf/U, Nb/Ta, and Y/Ho ratios along with Hf isotopic characteristics of both granite types indicate that these rocks were sourced from the partial melting of lithospheric mantle and lower crust. Zircons from the granodiorite porphyry have higher Nb, Ta, Lu, and Hf contents, but lower Ti contents and Th/U ratios than those from the porphyritic granodiorite, suggesting that the magma -forming granodiorite porphyry had lower temperature, higher oxygen fugacity, and probably experienced strong crystal fractionation. Py I and Py II are associated with the porphyritic granodiorite and are related to the mineralization that occurred at similar to 180 Ma. The composition of pyrite in the two stages indicates the contribution of granite and limestone to mineralization. The higher contents of metals (Cu, Pb, Zn, Bi, Ag, except Co and Ni) in Py I than in Py II indicate the cooling and mixing process of ore-forming fluid with meteoric water. The geochemical characteristics of the pyrite generations and U-Pb dating of zircons suggest that the small-scale mineralization occurred at similar to 180 Ma under a relatively high-temperature and lower oxidized magmatic environment, whereas the major metallogenic event occurred at similar to 160 Ma under a low-temperature, medium oxidized, and strongly fractionated magmatic environment. This study reveals that the multi-stage magmatic and mineralization processes mainly occurred during the Early to Late Jurassic in South China.

Automated summary

This study reveals the magmatic activity and mineralization process of the Baoshan Cu-Pb-Zn deposit through in situ U-Pb and Lu-Hf isotope studies of zircons and trace element compositions of two generations of pyrite. The results provide insights into the geochronology, magma source, fluid composition, and origin of the ore-forming materials. Furthermore, the study highlights the multi-stage magmatic and mineralization processes in the Early to Late Jurassic in South China.