内蒙古毕力赫含金花岗岩类侵入岩锆石U-Pb年龄及地质意义

Zircon U-Pb age of gold-bearing granitic intrusive rocks in Bilihe gold deposit of Inner Mongolia and its geological significance

毕力赫大型斑岩型金矿位于华北克拉通北缘白乃庙-哈达庙铜-钼-金矿化集中区。矿区侵入岩包括以花岗闪长斑岩为主的含金次火山侵入杂岩体和地表广泛出露的钾长花岗斑岩。次火山杂岩体SiO2含量61.5%～71.4%,属亚碱性钙碱性系列,岩石REE配分具LREE富集型,弱Eu负异常,相对富集大离子亲石元素(LILEs)、亏损高场强元素(HFSEs)和Ba,具壳幔混源特征,除亏损Ba之外总体类似陆缘弧花岗岩。LA-ICP-MS锆石U-Pb测年获得含金次火山侵入杂岩体和钾长花岗斑岩成岩年龄分别为283.8±4.2Ma～279.9±6.8Ma和264.2Ma,为早、中二叠世,与野外地质体穿插关系吻合。哈达庙-白乃庙地区晚古生代中-早二叠世的大规模构造-岩浆-成矿作用,与白云鄂博-西拉木伦缝合带两侧大陆对接碰撞的时间一致,受同碰撞构造环境制约。

Bilihe large scale porphyry gold deposit locates in north edge of North China craton,which also in Bainaimiao-Hadamiao Cu-Mo-Au mineralization concentrated area.Intrusive rocks in mining area comprises gold-bearing subvolcanic intrusive complex which mainly are granodiorite porphyry and moyite porphyry that outcropping widely in surface.Content of SiO2 in subvolcanic complex is 61.5%～71.4%,that belongs to sub-alkaline cal-allaline series;REE partition of the rock locates in LREE enrichment,less Eu negative anomaly,enriches relatively large-ion lithophile elements（LILEs）,deficits high field strength elements（HFSEs） and Ba,which are all indicative of mixing of crustal materials with mantle components;except loss Ba,similar to granites from epicontinental arc.LA-ICP-MS zircon U-Pb dating got the lithogenetic age of gold-bearing subvolcanic intrusive complex and moyite porphry.They are 283.8±4.2Ma～279.9±6.8Ma and 264.2Ma separately belong to the Early and Middle Permian.It fits the field geological body interpenetrative relationship.The time of large scale structure-magma-mineralization in Early-Middle Permian of Late Paleozoic of Hadamiao-Bainaimiao area and continental docking collision in both sides of Bayan Obo-Xar Moron suture zone are the same,they all restricted by syn-collision tectonic setting.