内蒙古白音诺尔铅锌矿床成矿时代及其地质意义——来自侵入岩地球化学及年代学的制约

Geological Significance and Metallogenic Epoch of the Baiyinnuoer Pb-Zn Deposit in Inner Mongolia:Constraints from Geochemistry and Chronology of Intrusive Rocks

内蒙古白音诺尔铅锌矿床位于大兴安岭成矿带南段,是一个典型的矽卡岩型矿床。为了精确厘定该矿床的成矿时代,对区内与成矿关系密切的花岗闪长斑岩及流纹斑岩中的锆石进行了LA-ICP-MS定年,获得花岗闪长斑岩与流纹斑岩的形成年龄分别为(253.4±0.9)Ma和(133.6±0.7)Ma。岩石地球化学研究表明,花岗闪长斑岩为准铝质岩石,流纹斑岩为过铝质岩石,两者均具有轻重稀土分异明显、富集大离子亲石元素(LILE)、相对亏损高场强元素(HFSE)的特点。结合矿床地质特征及前人在区域上的研究成果,认为白音诺尔铅锌矿床存在两期明显的矿化事件,早期矿化发生在253.4 Ma左右,晚期矿化发生在133.6Ma左右。白音诺尔铅锌矿床早期矿化很可能与古亚洲洋闭合碰撞后伸展有关,晚期矿化受蒙古—鄂霍茨克洋俯冲的影响。

Located in the south section of the Daxing’anling metallogenic belt,the Baiyinnuoer Pb Zn deposit is a typical skarn deposit.In order to determine the mineralization age of the deposit,LA ICP MS U Pb dating of zircons in the granodiorite porphyry and rhyolite porphyry associated with the mineralization was studied.The results suggest that the granodiorite and rhyolite porphyry were crystallized in(253.4±0.9)Ma and(133.6±0.7)Ma.The rock geochemistry indicates that the granodiorite is quasi-aluminous,and the rhyolite porphyry is excessive-aluminous.Both of them are characterized by fractionation of HREE and LREE,enrichment of large ion lithophile elements(LILE)and relative depletion of high field strength elements(HFSE).Combined with the geological characteristics and the previous research in this region,we conclude that two mineralization events occurred in the deposit with the early mineralization at about 253.4 Ma and the late one at about 133.6 Ma.The early mineralization may be related to the closure of the Paleo-Asian Ocean and the late mineralization was influenced by the subduction of the Mongolia-Okhotsk Ocean.The Baiyinnuoer Pb-Zn deposit was formed in the post-collisional extension.