内蒙古苏右旗毕力赫金矿区安山岩LA-ICP-MS锆石U-Pb年龄、元素地球化学特征及其形成的构造环境

LA-ICP-MS zircon U-Pb age,geochemistry of andesite in Bilihe goldfield,Suniteyouqi,Inner Mongolia and its tectonic significance

毕力赫大型斑岩型金矿位于华北克拉通北缘早古生代增生造山带。矿区出露一套岩性为安山岩-英安岩-流纹岩的火山岩组合,安山岩属于亚碱性、高钾钙碱性系列,具有较高的MgO含量(2.05%～10.29%),低的FeOT/MgO比值和TiO2含量(0.21%～0.85%);Cr(44×10-6～473×10-6)、Ni(19.3×10-6～249.4×10-6)含量高,亏损Nb、Ta、Ti、P,无或弱的Eu/Eu*异常,具有安底斯型活动大陆边缘火山岩特征。LA-ICP-MS锆石U-Pb测年获得安山岩和安山质凝灰岩成岩年龄分别为281±4.3Ma和281±12Ma,为早二叠世,这与毕力赫金矿成矿年代以及与成矿有关的花岗闪长斑岩结晶年龄一致,表明了矿区成岩-成矿作用与晚古生代华北板块与西伯利亚板块之间俯冲-造山作用有关,指示华北克拉通北缘寻找晚古生代浅成低温-斑岩型金(铜)矿具有巨大潜力。火山岩以及与成矿相关侵入岩出现U-Pb年龄为1.8Ga、2.0Ga和2.4Ga的古老继承性锆石,暗示矿区存在华北克拉通基底,古老变质基底岩石可能是制约本区金矿成矿主要因素之一。

The Bilihe large-scale porphyry gold deposit locates in the Early Paleozoic accretionary orogenic belt of the northern margin of North China Craton.The lithology in Bilihe goldfield was the set of volcanic rocks which include andesite,dacite and rhyolite.The andesite belongs to sub-alkaline,high-K calc-alkaline series,with higher content of MgO（2.05%～10.29%） ,low FeOT/MgO ratio and the content of TiO2（0.21%～0.85%） and with high content of Cr（44×10-6～473×10-6） ,Ni（19.3×10-6～249.4×10-6） ,depleted Nb,Ta,Ti,P,absence or minor of Eu/Eu anomalies,which collectively indicated the andesite with the characteristics of volcanic rocks of typical Andean-type active continental margin.The weighted average 206Pb/238U ages of andesite and andesitic tuff were 281±4.3Ma and 281±12Ma（the Early Permian） ,by LA-ICP-MS zircon U-Pb dating respectively,and consistent with the crystallization age（279Ma） of granodiorite porphyry that related to gold mineralization and ore-forming age（272Ma） ,which indicated that diagenesis-metallogenesis of mining area was associated with collisional orogeny between the North China plate and the Siberian plate in the Late Paleozoic,and suggesting that it had the great potential to find Late Paleozoic epithermal-porphyry type gold（copper） deposits in northern margin of the North China Craton.U-Pb ages of the ancient inherited zircons presents in the volcanic rocks and intrusive rocks associated with mineralization were 1.8Ga,2.0Ga and 2.4Ga,implying that the mining area was presence of ancient basement of the North China Craton,and as a major factor in generating gold mineralization.