| 其他摘要 | The Sanjiang Tethyan Metallogenic Domain (STMD) is an important part of the Tethyan giant metallogenic belt. Porphyry Cu ± Mo ± Au mineralization events in the STMD occurred in the Indosinian and Himalayan periods, and extensive documentation. Yanshanian porphyry Mo ± Cu mineralization in the STMD is known in the literature, but it remains poorly studied. The Yidun Arc is a part of the STMD in the eastern Tibetan Plateau. Recently, four newly discovered Mo-Cu-(W) ore deposits related to granitic intrusions were found distributed along the north-south strike in the southern Yidun Arc, which are identified as the Xiuwacu, Relin, Hongshan, and Tongchanggou deposits herein. These four deposits formed along high-angle north-northwest or north-west strike-slip faults, with vein-type and porphyry-type Mo-Cu mineralization developed in the intrusions. Molybdenite Re-Os and zircon U-Pb dating together with zircon Hf-Oisotopes and whole-rock geochemistry and Sr-Nd isotopes of the intrusions were studied to discern the relationship between mineralization and magmatism, metallogenesis, and tectonic settings. Molybdenite from skarn-type mineralization at the Hongshan deposit has a Re-Os isochron age of 81.2 ± 2.6 Ma (MSWD = 1.3, n = 5) consistent with previously published zircon U-Pb ages and Re-Os ages of porphyry-type Mo mineralization. These results indicate that the Hongshan is a Late Cretaceous porphyry-skarn Cu-Mo deposit. Zircon U-Pb ages of the granitic intrusions in the Xiuwacu, Relin, and Tongchanggou deposits varying from ~87.4 Ma to ~82.7 Ma. Combined with published molybdenite Re-Os age spectrum (~85 Ma to ~81.2 Ma), it is proposed that the Mo-Cu-(W) mineralization in the Shangri-La region is spatially and temporally related to the Late Cretaceous granitic intrusions. The four intrusions are relatively high in Si, K, and low in Mg, Ca, and P, and they are moderately to highly fractional metaluminous and slightly peraluminous (A/CNK = 0.96 – 1.07) I-type granites. Amphibole, feldspars, biotite, Fe-Ti oxides (titanite, ilmenite et al.), and apatite were probably involved during the fractionation process. They have relatively high (87Sr/86Sr)i (0.7069 to 0.7098) and δ18O (5.9‰ to 8.4‰), and negative εNd (-5.3 to -8.5) and εHf (-8.6 to -2.3) values, and ancient Nd and Hf model ages (1.3-1.7 Ga), which indicates that they were derived from similar sources predominately through partial melting of ancient mafic-intermediate lower continental crust, probably with a component of mantle contribution. In additon, the Relin, Hongshan, and Tongchanggou intrusions have high Sr/Y and La/Yb ratios, it indicates that they were derived from thickened lower crust. Combined with the distribution of the Late Mesozoic ignous intrusions and the cooling history of the eastern Tibetan Plateau, we propose that four intrusions in the southern Yidun Terrane were generated under a late- or post-collision environment related to the Lhasa-Qiangtang collision during the Late Cretaceous. Furthermore, the occurrence of these late- or post-collision magmas probably indicates that the timing of the Lhasa-Qiangtang collision and the uplifting of the eastern Tibetan Plateau was probably earlier than the Late Cretaceous, and the Lhasa-Qiangtang collision did not cease until ca. 80 Ma at least. Fluid inclusion studies indicate that the ore-forming fluids are moderate-high tempature and moderate-low salinity (T：146.6~550.0 ℃，S：4.18~18.63 wt% NaCl eq.) or moderate-high tempature and moderate-high salinity (T：125.2~393.7 ℃，S：4.45~47.4 wt% NaCl eq.) H2O-NaCl±CO2 fluids. The fluids inclusions in the quartz-vein from the ores in the Hongshan deposits are dominated by two-phase liquid-rich aqueous inclusions, while CO2-rich and daughter-bearing fluid inclusions are also common. The vapor phase are composed of CO2, CH4, and H2O, and daughter minerals include NaCl, KCl, CaCO3 and molybdenite. Generally, the ore-forming fluids in Hongshan deposits show the characteristics of |
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