【摘要】 毛登-小孤山锡多金属矿田位于大兴安岭南段成矿带。文章通过对该矿田的锆石和锡石进行LA-(MC)-ICP-MS原位U-Pb测年,及对与成矿关系密切的斑状花岗岩主微量元素地球化学特征的研究,揭示了该矿田的成矿时限及成矿地质背景。斑状花岗岩的锆石206Pb/238U加权平均年龄为(132.19±0.77)Ma,锡石207Pb/206Pb-238U/206Pb谐和年龄为(140±20)Ma,表明该矿田的岩浆-成矿作用发生在早白垩世。毛登-小孤山矿田中的斑状花岗岩具有较高的w(SiO2)(70.4%～71.0%),富K2O(4.93%～5.27%),高10 000Ga/Al比值(3.10～4.06),Fe相对Mg较为富集,强烈亏损Sr、Ba、Ti和P元素,稀土元素配分曲线呈右倾,Eu负异常明显,δEu为0.31～0.40,上述特征与A型花岗岩一致。结合区域地质特征、成岩成矿年代学、岩石地球化学结果,表明与大兴安岭南段锡多金属矿相关的花岗岩形成于早白垩世(145～120 Ma)的伸展背景下,为软流圈上涌导致含有大量幔源成分的锡林浩特古陆块部分熔融所形成。更多还原

【Abstract】 The Maodeng-Xiaogushan tin-polymetallic orefield is located along the metallogenic belt of southern Da Hinggan Mountains. In this paper, the authors investigated the geochronology and minerogenic geological setting by using the in situ LA-(MC)-ICP-MS U-Pb method of zircon and cassiterite and geochemistry of porphyritic granite related to mineralization. The weighted mean206 Pb/238 U age of zircon from porphyritic granite is(132.19±0.77)Ma; the207 Pb/206 Pb-238 U/206 Pb concordia age of cassiterite from tin ore is(140 ± 20)Ma. The dating results show that the porphyritic granite related to mineralization and the Maodeng-Xiaogushan tin-polymetallic orefield were formed in the Early Cretaceous. The porphyritic granite is characterized by high SiO2 content(70.4%～71.0%), high K2 O content(4.93%～5.27%) and high ratio of 10 000 Ga/Al(3.10～4.06). Fe is more abundant than Mg. The primitive mantle-normailzed element spider diagrams and chondrite-normalized REE patterns of the porphyritic granite show depletion of Sr, Ba, Ti, P and distinct negative δEu anomalies(δEu=0.31～0.40). These features are coincident with features of A-type granite. The evidence from regional geological characteristics, geochronology and geochemistry supports the argument that the granitoids related to tin-polymetallic mineralization in southern Da Hinggan Mountains were emplaced in an extension setting during the Early Cretaceous. The magma associated with mineralization was formed by the upwelling of the asthenosphere and partial melting of the Xilinhot microcontinent which contained a large number of mantle compositions.更多还原