【摘要】 塔东铁矿体主要呈层状、似层状或透镜状赋存于塔东群拉拉沟组,矿石类型以磁铁角闪岩为主,具典型条带状构造。通过对拉拉沟组赋矿岩石-黑云钾长片麻岩进行岩石地球化学和锆石U-Pb年代学研究,确定该矿床的形成时代、构造背景以及成因类型。显微岩相学及全岩主微量元素研究结果表明,黑云钾长片麻岩的原岩为流纹质-英安质火山凝灰岩,形成于板块俯冲背景下的大洋岛弧构造环境。黑云钾长片麻岩的锆石CL图像和U-Pb定年结果显示,19个岩浆锆石测点加权平均年龄为(725.6±7.4) Ma,代表其原岩形成时限,间接指示了塔东铁矿赋矿地层的沉积时代为新元古代中期。通过与邻区铁矿的对比研究表明,塔东铁矿的成矿时代较晚、矿石类型特殊,与典型BIF铁矿相差较大。综上所述,塔东铁矿矿床成因类型应为火山沉积变质型。更多还原

【Abstract】 The stratiform,stratoid and lenticular iron orebodies of the Tadong iron deposit are mainly hosted within the metamorphic rocks of the Lalagou Formation,Tadong Group. The ore-rock type is mainly magnetite amphibolite with typical banded structures. To determine the forming age,tectonic setting and genetic type of the Tadong iron deposit,the whole-rock geochemistry analysis and zircon U-Pb dating for the ore-hosting biotite k-feldspar gneiss of the Lalagou Formation were conducted. The results of microscopic petrography and whole rock major and trace elements indicate that the protolith of the biotite k-feldspar gneiss is rhyolitic-dacitic volcanic tuff which was formed under an oceanic arc setting related to plate subduction. Zircon CL images and U-Pb dating results of the biotite k-feldspar gneiss show that the weighted mean age of nineteen magmatic zircons is( 725. 6 ± 7. 4) Ma,which represents the age of the protolith and indirectly indicates that the sedimentary age of the ore-hosting strata in the Tadong iron deposit is the Middle Neoproterozoic. By comparing characteristics of the Tadong iron deposit and others in adjacent areas,the authors conclude that the formation time and the ore type of the Tadong iron deposit are different from those of other typical BIFs,which suggests that the genetic type of the Tadong iron deposit should be volcanic-sedimentary metamorphic type.更多还原