Zircon morphology, geochronology and trace element geochemistry of the granites from the Huangshaping polymetallic deposit, South China: Implications for the magmatic evolution and mineralization processes

摘要

The Huangshaping polymetallic deposit is a large-scale deposit located in the central Nanling region, South China. Different types of mineralization have been classified in the area, which are attributed to three types of granitoids from the composite granitic pluton: quartz porphyry, granophyre and granite porphyry. In order to study the magmatic genesis and evolutionary process, as well as constrain the crystallization and mineralization events, 100 zircon separates from different intrusive stages of the pluton have been analyzed for trace element contents and U-Pb isotopic concentrations. The results show that zircons from the Huangshaping granitoids are enriched in Th, U, Hf, Ti, REE and other trace elements, indicating hydrothermal fluid alteration and transformation. Additionally, there is a large variation between different types of granitoids in terms of trace element concentrations. Compared to the zircons from the quartz porphyry and the granophyre, zircons from the granite porphyry are more enriched in Th, U, Hf, Ti, and P but strongly depleted in Eu. This suggests that the magma that formed the granite porphyry possessed higher temperatures, possibly experienced stronger crystal fractionation and originated from a more evolved, complex magmatic source region with higher degree of crustal maturity. Combined with characteristics of crystal morphology and internal texture, hydrothermal zircons were distinguished from magmatic zircons in each granitoid to reveal mineralization processes. The U-Pb geochronology results show that there are two major stages of mineralization: ~ 190 Ma weak Cu (Pb, Zn) mineralization related to the quartz porphyry and the granophyre, and -155 Ma strong W, Sn (Mo, Pb, Zn) mineralization associated with the granite porphyry. Compositions of these hydrothermal zircons suggest that the earlier stage mineralization could be close to single, relatively cold, reduced and quickly ascended fluids, whereas the later stage might be related to hot, oxidized, strongly fractionated and highly evolved, mixed fluids. This study also indicates that hydrothermal zircons from typical composite granitic plutons could be a good tool to reveal the multi-stage magmatic and mineralization process in middle to late Jurassic South China.