内蒙古道伦达坝铜钨锡矿床LA-ICP-MS锆石和锡石U-Pb年龄及其地质意义

摘要

道伦达坝矿床位于大兴安岭南段,是一个铜钨锡矿床,其铜、钨、锡储量均达中型.矿体呈脉状,主要产于二叠系砂板岩中的断裂破碎带中,华力西期黑云母花岗岩中的断裂破碎带中亦赋存有矿体.文章选取2件石英-萤石-白云母-电气石-锡石-黑钨矿阶段的矿石样品对其中的进行了LA-ICP-MS U-Pb定年,获得2件样品的207Pb/206Pb-238U/206Pb谐和年龄分别为(134.7±6.6) Ma(MSWD=1.4)和(136.8±7.4) Ma(MSWD=1.7),206Pb/207Pb-238U/207Pb等时线年龄分别为(132±12) Ma(MSWD=0.76)和(135±13) Ma(MSWD =0.9).锡石定年结果表明,道伦达坝矿床形成于早白垩世.对矿区外围张家营子岩体中的斑状细粒花岗岩进行了LA-ICP-MS锆石U-Pb测年,获得的206Pb/238U加权平均年龄为(135±1) Ma(MSWD=1.3),该岩体的形成年龄与道伦达坝矿床的成矿年龄在误差范围内一致.本次定年结果表明道伦达坝矿床形成于早白垩世,与同期的花岗质岩浆活动有密切的成因联系,该矿床属于与花岗岩有关的岩浆热液脉型矿床.%The Daolundaba deposit,located in the southern Da Hinggan Mountains,is a medium-sized copper-tungstentin deposit.The orebodies in the deposit occur as veins in fractured zones mainly in the Permian sandy slate and subordinately in the Variscan biotite granite.Two cassiterite samples from the quartz-fluorite-muscovite-tourmaline-cassiterite-woframite stage of the Daolundaba deposit were selected for LA-ICP-MS cassiterite U-Pb dating,which yielded 207Pb/206Pb-238U/206Pb concordia ages of (134.7 ± 6.6) Ma (MSWD =1.4) and (136.8 ± 7.4) Ma (MSWD =1.7) as well as 206Pb/207Pb-238U/207Pb isochron ages of (132 ± 12) Ma (MSWD =0.76) and (135 ± 13) Ma (MSWD =0.9),respectively,indicating that the mineralization of the Daoluntangba Cu-W-Sn deposit took place in the Early Cretaceous.A zircon sample from the Zhangjiayingzi porphyritic fine-grained granite outside the mining area was selected for LA-ICP-MS zircon U-Pb dating,which yielded a weighted mean 206Pb/238U age of (135 ± 1) Ma (MSWD =1.3),indicating that the crystallization age of this granite is consistent with the metallogenic age of the Daolundaba deposit within the error.The dating results in this study show that the Daolundaba deposit was formed in the Early Cretaceous and was closely related to the granitic magmatism in the same period.The Daolundaba deposit belongs to the magmatic hydrothermal vein type deposit related to granite.