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内蒙古火龙沟铅锌矿床是近期勘查发现、预期可达中型规模以上的铅锌矿床之一,笔者对该矿区的侵入岩——正长花岗岩进行了LA-MC-ICP-MS锆石U_Pb定年和主量、微量元素分析,锆石U_Pb定年结果为(224.0±2.5)Ma,表明,该岩体侵位于晚三叠世。岩石地球化学研究结果显示火龙沟正长花岗岩体具有明显富Si O2和ALK、贫Mg O和TFe的特点,A/NK-A/CNK图解显示正长花岗岩属于准铝质花岗岩。微量元素蛛网图显示富集大离子亲石元素Rb、Th、U、K,亏损高场强元素Nb、Ta、Ti。稀土元素配分模式表现出富集LREE,亏损HREE的右倾型,LREE/HREE=8.04~10.40,具有明显Eu的负异常。花岗岩锆饱和温度计算结果表明该花岗岩岩浆形成温度为820℃,属于高温花岗岩,以上地球化学特征和高温的特点表明该花岗岩为A型花岗岩。结合区域构造演化历史,笔者认为该花岗岩体形成于古亚洲洋闭合后的造山后垮塌岩石圈伸展构造环境。
The HuoGongGou lead-zinc deposit in Inner Mongolia is one of the lead-zinc deposits discovered recently and expected to reach above the medium-scale scale. The author has conducted LA-MC-ICP-MS zircon U_Pb dating of the intrusive rock- According to the analysis of major and trace elements, the zircon U_Pb dating results are (224.0 ± 2.5) Ma, indicating that the intrusive body is located in the Late Triassic. The results of rock geochemistry show that the Huo Long Gouzheng granite body has the characteristics of rich Si O2 and ALK, poor Mg O and TFe. The A / NK-A / CNK diagram shows that the orthogranite belongs to the quasi-aluminous granite. Trace elemental cobweb maps show enrichment of large ion lithophile elements Rb, Th, U, K, depleted high field strength elements Nb, Ta, Ti. The REE pattern shows a right-leaning type enriched in LREE and a depleted HREE with a LREE / HREE of 8.04-10.40 and a distinct Eu anomaly. The calculation results of the zirconium saturation temperature show that the magmatic formation temperature of the granite is 820 ℃ and belongs to the high-temperature granite. The above geochemical characteristics and high temperature indicate that the granite is A-type granite. Combined with the history of regional tectonic evolution, the authors believe that the granite body formed after the closure of the Paleo-Asian Ocean collapsed lithospheric extension tectonic environment.