Petrogenesis of the granite porphyry related to the Jiudingshan Cu-Mo deposit in western Yunnan: Constraints from LA-ICP-MS zircon U-Pb chronology, Sr-Nd-Hf isotopes and petrogeochemistry

In this study, the authors carried out a comprehensive research including zircon U-Pb dating, petrogeochemical investigation and Sr-Nd-Hf isotope analysis of the granite porphyry related to the Jiudingshan Cu-Mo deposit in western Yunnan. LA-ICP-MS zircon U-Pb chronology indicates that the porphyry was emplaced at 34.5-34.9 Ma, consistent with or slightly earlier than the formation of the Cu-Mo deposit (33.9-35.3 Ma) and similar in time to the peak of Cenozoic alkali-rich magmatic activity (45-30 Ma) in western Yunnan, indicating that they were formed by the ore-forming process in the period of late-collisional transformation(40-26 Ma). The granite porphyry is silica-rich (SiO₂=62.86%-71.57%), potassium-rich (K₂O/Na₂O=1.64-2.78) and alkali-rich (K₂O + Na₂O = 8.98%-11.28%), belonging to shoshonitic series peraluminous granite, with the characteristics of LREE enrichment, HREE depletion, and weak negative Eu anomaly (δEu=0.82-0.93). The porphyry is enriched in LILEs such as Rb, Ba, Th and U, and depleted in HFSEs such as Nb, Ta, Zr and U. Sr-Nd-Hf isotopes imply that the magma originated from the EMII which was contaminated by crustal materials in the process of magmatic upwelling to form a potassium-rich ore- bearing magma with mixed sources of the crust and the mantle.