Geochronology and geochemistry of the Wunugetushan porphyry Cu-Mo deposit in NE china, and their geological significance

摘要

The Wunugetushan porphyry Cu-Mo deposit is located in the Manzhouli district of NE China, on the southern margin of the Mesozoic Mongol-Okhotsk Orogenic Belt. Concentric rings of hydrothermal alteration and Cu-Mo mineralization surround an Early-Middle Jurassic monzogranitic porphyry. The Cu-Mo mineralization is clearly related to the quartz-potassic and quartz-sericite alteration. Molybdenite Re-Os and groundmass ~(40)Ar/~(39)Ar of the host porphyry dates indicate that the ore-formation and porphyry-emplacement occurred at 177.6 ± 4.5 Ma and 179.0 ± 1.9 Ma, respectively. Geochemically, the host porphyry of the deposit is characterized by strong LREE/HREE fractionation, enrichment in LILE, Ba, Rb, U, Th and Pb, and depletion of HFSE, Nb, Ta, Ti and HREE. The Sr-Nd-Pb isotopic compositions of the porphyry display an varied initial (~(87)Sr/~(86)Sr)_i ratio, a positive ε_(Nd)(t) values and high ~(206)Pb/~(204)PbIt, ~(207)Pb/~(204)Pb_t and ~(208)Pb/~(204)Pb_t ratios. These data indicate that the magmatic source of the host porphyry comprised two end-members: lithospheric mantle metasomatized by fluids derived from the subducted slab; and continental crust. We infer that the primitive magma of the host porphyry was derived from crust-mantle transition zone. Based on regional geology and geochemistry of the host porphyry, the Wunugetushan deposit is suggested to form in a continental collision environment after closure of the Mongol-Okhotsk Ocean.