内蒙古白音诺尔锌铅矿床中侏罗世成矿事件:来自闪锌矿Rb-Sr等时线年龄的证据

Middle Jurassic mineralization event in theBaiyinnuoer deposit:Evidence from the sphalerite Rb-Sr isochron age

白音诺尔矽卡岩型锌铅矿床位于大兴安岭南段成矿带内,是我国东北最大的锌铅矿床之一。矽卡岩及矿体主要产在黄岗梁组不同岩性段内或者酸性侵入体与二叠纪大理岩的接触部位。此次研究对矿区内与凝灰熔岩关系密切的主矿体中闪锌矿开展了Rb-Sr等时线定年,并获得了等时线年龄为(167.6±4.9)Ma (MSWD=1.3),指示出白音诺尔矿床存在中侏罗世的成矿事件。结合前人报道的矿区成岩成矿年龄,文章认为白音诺尔矿床存在多期锌铅矿化事件,包括早三叠世(~240Ma)、中侏罗世(~167 Ma)和早白垩世(~140 Ma)。闪锌矿锶同位素组成显示其初始87Sr/86Sr比值为0.710702~0.719997,平均值为0.715380,略低于大陆地壳的平均值,高于地幔值,暗示白音诺尔矿床中侏罗世成矿物质可能主要来源于大陆地壳并伴随有少量地幔组分加入。结合前人的研究成果,文章认为白音诺尔矿床与凝灰熔岩相关的中侏罗世成矿事件是大兴安岭南段一次区域性构造热事件的产物,并且可能与蒙古—鄂霍茨克洋的闭合有关。因此,建议在以后整个大兴安岭南段的找矿工作中,应该更加注意对侏罗纪岩浆热液锌铅矿床的寻找。

The Baiyinnuoer Zn-Pb deposit,located in the Southern Great Xing’an Range,is one of the largest Zn-Pb deposits in northeastern China.Skarn and orebodies mainly occur between different units of the Huanggangliang Formation,or within the contact zone between the intrusions and Permian marble.In this study,we report the results of Rb-Sr isotopic dating for sphalerite from the Baiyinnuoer major orebody closely associated with the tuff lava,which yield an isochron age of 167.6±4.9 Ma(MSWD=1.3),constraining the timing of mineralization as the Middle Jurassic.Combined with previous studies,we propose that multiple mineralization events occurred in the Baiyinnuoer deposit during the Early Triassic(~240 Ma),Middle Jurassic(~167 Ma)and Early Cretaceous(~140 Ma).The initial 87Sr/86Sr ratios of the sphalerites are between 0.710702 and 0.719997,with a mean value of 0.715380,which is slightly lower than that of the continental crust mean value and higher than that of mantle,suggesting that the metallogenic components in the Baiyinnuoer may have been mainly derived from the continental crust and accompanied by minor input of mantle components.Combining the results of this study with those from previous work,we propose that the Baiyinnuoer Jurassic mineralization event associated with the tuff lava is considered to be the product of regional tectono-magmatic event(the closure of the Mongol-Okhotsk Ocean)in the Southern Great Xing’an Range,and more attention must be paid to the potential scope for prospecting the Jurassic magmatic-hydrothermal Zn-Pb ore deposits in the entire Great Xing’an Range.