Mesozoic magmatism and metallogeny in the Chizhou area, Middle-Lower Yangtze Valley, SE China: Constrained by petrochemistry, geochemistry and geochronology

摘要

The Chizhou area, southeast China, hosts extensive W-Mo-Pb-Zn and Cu-Au deposits but remains relatively unstudied. A wide range of Mesozoic magmatic intrusives were analyzed (whole-rock geochemistry, Sr-Nd isotopes, zircon U-Pb dating, and zircon Lu-Hf isotopes) in order to elucidate their genesis, relationship to W-Mo-Pb-Zn-Cu-Au mineralization, and the tectonic setting of emplacement. Zircon U-Pb geochronology yielded a range of ages (147-110 Ma) encompassing three magmatic episodes; 147-135 Ma, 130-120 Ma, and 115-110 Ma. This work marks the first time the youngest episode has been identified. The oldest episode resulted in the formation of small granite porphyries, always associated with skarn-porphyry type W-Mo-Pb-Zn-Cu-Au deposits under an extensional setting. The 130-120 Ma and 115-110 Ma intrusives were the products of enhanced N-S extension with no associated mineralization. A comparative study reveals two types of magmatism-mineralization systems: acid magmatic rocks in the Chizhou area related to skarn-porphyry type W-Mo-Pb-Zn-Cu-Au deposits and intermediate-acid magmatic rocks in the Tongling area related to skarn-porphyry type Cu-Au-Fe-S deposits. Whole-rock Sr-Nd isotopes, zircon Lu-Hf isotopes, and inherited zircon U-Pb ages suggest that the lower crust and meso-neoproterozoic Shangxi group rocks were the main sources of magmatic rocks and related W-Mo-Pb-Zn-Cu-Au deposits. A genetic model for Mesozoic magmatism-skarn-porphyry type W-Mo-Pb-Zn-Cu-Au mineralization involves partial melting of the lower crust, mixing with the re-melted products of Meso-neoproterozoic Shangxi group rocks, and assimilation/fractional crystallization process. Results from this study suggest that there is great potential for the discovery of more and larger skarn-porphyry type W-Mo deposits in the transitional W-Mo-Pb-Zn metallogenic belt.