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 n (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.%提对滇西九顶山铜钼矿床主要的含矿花岗斑岩开展了系统的年代学、岩石地球化学以及全岩Sr-Nd-Hf同位素的分析工作。LA-ICP-MS锆石U-Pb定年结果表明,九顶山花岗斑岩成岩年龄为34.5~34.9 Ma,与已有的成矿年龄(33.9~35.3 Ma)一致或略早于成矿年龄,处在滇西新生代富碱岩浆活动高峰期内(45~30 Ma),属于青藏高原碰撞造山带的晚碰撞转换成矿作用(40~26 Ma)的产物。详细的岩石地球化学研究表明,研究区花岗斑岩有高硅(SiO2=62.86%~71.57%)、高钾(K2O/Na2O=1.64~2.78)和富碱(K2O+Na2O=8.98%~11.28%)的特点,属于钾玄岩系列岩石。岩体轻稀土元素富集(LREE/HREE=4.84~7.64),具有轻微的负铕异常(δEu=0.82~0.93),富集大离子亲石元素(Rb、Ba、Th、U)和亏损高场强元素(Nb、Ta、Zr、Hf)。Sr-Nd-Hf同位素的研究分析显示岩浆源区起源于“EMII型”富集地幔,“EMII型”富集地幔岩浆在上涌的过程中受到地壳物质的混染,形成壳幔混合源富钾含矿岩浆。
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