摘要
别也萨麻斯矿床是目前新发现的分布在新疆北阿尔泰以Li矿化为主的花岗伟晶岩型稀有金属矿床,具有独特性和代表性。矿区发育Li-Nb-Ta矿化和Nb-Ta矿化两类伟晶岩,二云母二长花岗岩是含矿伟晶岩脉群的直接围岩。在系统的野外地质特征调查(包括野外露头和钻孔岩芯赋矿岩系、矿化特征、蚀变类型等的详细观察)基础上,对含矿伟晶岩和二云母二长花岗岩开展了LA-ICP-MS锆石U-Pb定年和原位Hf同位素研究。获得锆石206Pb/238U加权平均年龄分别为(151.0±1.8)Ma和(449.0±4.2)Ma,含矿伟晶岩形成于晚侏罗世,二云母二长花岗岩则形成于晚奥陶世。含矿伟晶岩和二云母二长花岗岩的εHf(t)值分别为0.62~1.30和1.35~6.07,二阶段Hf模式年龄为1161~1118 Ma和1345~1037 Ma。含矿伟晶岩的εHf(t)值较花岗岩小得多,二阶段Hf模式年龄与形成年龄的差值较花岗岩大得多,表明两者是阿尔泰造山带在不同演化阶段下的产物。悬殊的年龄差、不同的大地构造背景与不同的形成物源表明别也萨麻斯稀有金属矿床含矿伟晶岩与二云母二长花岗岩在成因上并无联系,近矿花岗岩围岩并非含矿伟晶岩脉的真正母体。
The newly discovered Bieyesamasi rare metal deposit, which is distributed in North Altay of Xinjiang and characterized by Li-dominated mineralization, is distinctive and representative. Li-Nb-Ta and Nb-Ta mineralized pegmatites are both developed in the mining area, and two-mica monzogranite is the direct surrounding rock of ore-bearing pegmatite veins. Based on the systematic field geological investigation(including detailed observations of field outcrops, drill holes, mineralization characteristics and alteration types, etc.), LA-ICP-MS zircon U-Pb dating and in-situ Hf isotope were carried out on ore-bearing pegmatite and two-mica monzogranite. The weighted mean 206Pb/238U ages are(151.0±1.8)Ma and(449.0±4.2)Ma, respectively. Ore-bearing pegmatite is formed in Late Jurassic, but two-mica monzogranite is formed in Late Ordovician. Ore-bearing pegmatite and two-mica monzogranite have εHf(t) values of 0.62-1.30 and 1.35-6.07, respectively, and have the two-stage mode ages of Hf isotope varying from 1 161 to 1 118 Ma and from 1 345 to 1 037 Ma, respectively. The εHf(t) values of ore-bearing pegmatite are much smaller than those of granite, and the gaps between the two-stage model age of Hf isotope and the formation age are much larger than those of granite, indicating that they are the products of Altay orogenic belt at different evolution stages. The large gaps in formation ages, different geotectonic backgrounds and different formation sources together show that there is no genetic relationship between ore-bearing pegmatite and two-mica monzogranite of Bieyesamasi rare metal deposit. The surrounding granite near the orebodies is not the true parent rock of ore-bearing pegmatite veins.
作者
丁建刚
杨成栋
杨富全
李强
DING Jian-gang;YANG Cheng-dong;YANG Fu-quan;LI Qiang(No.701 Geological Team,Xinjiang Nonferrous Geoexploration Bureau,Changji 831100,Xinjiang,China;MNR Key Laboratory of Metallogeny and Mineral Assessment,Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing 100037,China)
出处
《地球科学与环境学报》
CAS
北大核心
2020年第1期71-85,共15页
Journal of Earth Sciences and Environment
基金
国家重点研发计划项目(2017YFC0602703)
