Abstract
The southern Great Xing’an Range (SGXR) is located in the eastern Central Asian Orogenic Belt (CAOB), and represents the most important Cu-Mo-Pb-Zn polymetallic mineral province in NE China. The Panjiaduan deposit in the SGXR is characterized by superimposing mineralization: (1) porphyry Mo ore hosted by syenogranite, and (2) superimposing vein-type Cu-Pb-Zn ore, hosted by fracture zones in the Manitu Formation volcanics and granodiorite. Two zircon U-Pb ages of 233.9 ± 2.8 Ma and 236.1 ± 2.8 Ma for the syenogranite (porphyry) ore host indicate that the porphyry Mo mineralization occurred in the Late Triassic, coeval with the adjacent Laojiagou porphyry Mo deposit. Sphalerite from the Cu-Pb-Zn ore veins yielded a Rb-Sr isochron age of 138.5 ± 3.5 Ma, suggesting Early Cretaceous overprinting mineralization. The syenogranite is geochemically similar to the ore-causative monzogranite at Laojiagou. They are unfractionated I-type granites, LILE- and LREE-enriched, and HFSE- and HREE-depleted. In addition, their magma source was likely derived from partial melting of the juvenile lower crust. Major sulfides (pyrite, molybdenite, and galena) from the porphyry ores have slightly lower δ34S values (−2.8 to −0.3 ‰) than the vein-type ore sulfides (pyrite, chalcopyrite, sphalerite, and galena) (1.5 to 5.3 ‰), although they are all close to the mantle δ34S values and thus suggests a magmatic sulfur source. Meanwhile, the Pb isotope compositions of the two ore types suggest that the Pb for the porphyry mineralization was likely derived from an orogenic Pb reservoir, while the latter may have crust-mantle mixed Pb source. We suggested that both mineralization events were formed in an extensional setting, induced by the post-collision tectonics after the Paleo-Asian Ocean closure and the Paleo-Pacific subduction rollback, respectively.
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