Age,geochemistry and formation environment of diorite porphyrite in Kudeerte gold-polymetallic deposit,East Kunlun
In order to determine the metallogenic age and tectonic environment of the Kudeerte gold-polymetallic deposit in Kaerqueka ore field,this work studies on zircon U-Pb isotopic dating and whole rock geochemical analysis of diorite porphyrite.The results indicated that the zircon U-Pb weighted average age of diorite porphyrite is 232.6±1 Ma(MSWD=0.17),which is slightly later than the granodiorite age(244～234.1 Ma)and Ar-Ar plateau age(236.7±4.0 Ma)of gold mineralization sericite,limiting the upper age of gold mineralization to no later than 233 Ma.The dioritie porphyrite has SiO2 ranges from 54.96%to 55.57%,rich in Al(17.94%to 18.07%,Al2O3),and high in Sr(455×10-6～505×10-6),low Y(19.2×10-6～26.4×10-6)and Yb(2.18×10-6～2.95×10-6).A/CNK ratios range from 0.87 to 0.89,and belong to high potassium calc-alkaline sub-aluminum series.The fractionation of light and high rare earth elements(LREEs and HREEs)is obvious,and the LREEs are enriched.The LREE/HREE ratios range from 6.24 to 8.69,and the(La/Yb)N ratios from 7.25 to 10.36,and the Eu is medium deficit.Enrichment of large-ion lithophile elements(LILEs),such as Rb,Th,U,K,etc.,and depletion of high-field strength elements(HFSEs),such as Nb,Ta,P and Ti.It has high Sr/Yb ratios of 154.24 to 216.74,Sr/Y ratios of 17.23 to 24.27,Nb/Ta ratios of 17.79 to 20.05,Mg#values of 49.35 to 50.18,and Rb/Sr ratios of 0.27 to 0.3,in the range of 0.05 to 0.5.Based on the regional geological background and metallogenic characteristics,it is believed that the diorite porphyrite was formed in the partial melting of the mesoproterozoic lower crust during the subduction-collision transition tectonic stage of mantle source magma,and the East Kunlun area was in an extended environment influenced by subduction plate fragmentation during the Middle-Late Triassic subduction-collision transition,which is obviously different from the typical compressional orogenic belt.The strong crust-mantle interaction promotes the concentrated production of deposits in the area.
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