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    东昆仑库德尔特金多金属矿床闪长玢岩年龄、地球化学特征及形成环境

    Age, geochemistry and formation environment of diorite porphyrite in Kudeerte gold-polymetallic deposit, East Kunlun

      摘要
    • 摘要: 为厘定卡尔却卡矿田内的库德尔特金多金属矿床金矿成矿时代及其形成构造环境，对闪长玢岩进行了锆石U−Pb同位素测年和全岩地球化学研究。结果表明，闪长玢岩锆石U−Pb年龄加权平均值为232.6±1.0 Ma（MSWD=0.17），略晚于赋存金矿的花岗闪长岩年龄（244~234.1 Ma）和金矿化绢云母Ar-Ar坪年龄（236.7±4.0 Ma），限定金成矿上限年龄不晚于233 Ma。闪长玢岩SiO2含量为54.96%~55.57%，富Al（Al2O3含量为17.94%~18.07%），高Sr（455×10−6~505×10−6），低Y（19.2×10−6~26.4×10−6）和Yb（2.18×10−6~2.95×10−6），A/CNK值为0.87~0.89，属高钾钙碱性准铝质系列。岩石轻、重稀土元素分馏较明显，轻稀土元素富集，LREE/HREE值为6.24~8.69，（La/Yb）N值为7.25~10.36，Eu中等亏损，富集大离子亲石元素（Rb、Th、U、K等），亏损高场强元素（Nb、Ta、P、Ti等），具有较高Sr/Yb值（154.24~216.74）、Sr/Y值（17.23~24.27）、Nb/Ta值（17.79~20.05）和Mg＃值（49.35~50.18），Rb/Sr值（0.27~0.36）介于0.05~0.5之间。综合区域地质背景与成矿特点认为，闪长玢岩形成于俯冲-碰撞转换构造阶段幔源岩浆底侵中元古代下地壳的局部熔融，中晚三叠世俯冲-碰撞转换时期，东昆仑地区受俯冲板片断离影响处于伸展环境，与典型挤压造山带具有明显差异，强烈壳−幔相互作用促进了区内矿床的集中产出。

       

      Abstract: 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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