白云鄂博矿床云母地球化学特征及原位Rb-Sr定年:对稀土-铌成矿作用的指示  

Geochemical characteristics and in-situ Rb-Sr dating of mica in the Bayan Obo deposit:Implications for the controls on REE-Nb ore formation

作　　者：姚璐航 李扬 张文[4] 杨澜 余艳 杨波 李献华[1,2,6] YAO LuHang;LI Yang;ZHANG Wen;YANG Lan;YU Yan;YANG Bo;LI XianHua(State Key Laboratory of Lithospheric and Environmental Coevolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China;Ministry of Education Key Laboratory of Orogenic Belts and Crustal Evolution,School of Earth and Space Sciences,Peking University,Beijing 100871,China;State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Wuhan 430074,China;Mining Research Institute of Baotou Steel(Group)Crop.,Baotou 014010,China;State Key Laboratory of Baiyunobo Rare Earth Resource Research and Comprehensive Utilization,Baotou 014030,China)

机构地区：[1]中国科学院地质与地球物理研究所,岩石圈演化与环境演变全国重点实验室,北京100029 [2]中国科学院大学地球与行星科学学院,北京100049 [3]北京大学地球与空间科学学院,造山带与地壳演化教育部重点实验室,北京100871 [4]中国地质大学地质过程与矿产资源国家重点实验室,武汉430074 [5]包钢集团矿山研究院(有限责任公司),包头014010 [6]白云鄂博稀土资源研究与综合利用全国重点实验室,包头014030

出　　处：《岩石学报》2025年第4期1149-1169,共21页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(92262303);包头钢铁(集团)有限责任公司项目(GZ-2023-1LH-001/002);中国科学院地质与地球物理研究所自主项目(IGGCAS-201901)联合资助.

摘　　要：白云鄂博矿床是世界级的稀土矿床,并蕴含有丰富的铁、氟和铌等资源。云母是该矿床中常见的矿物之一,常与矿石和脉石矿物共生。基于详细的矿床地质和岩相学研究,本文选取了白云鄂博矿床中含云母的代表性矿石类型,包括云母型矿石、萤石条带状矿石、白云石型矿石和霓石型矿石,对其开展了云母原位Rb-Sr定年及地球化学分析,以揭示碳酸岩岩浆-热液演化过程及其对稀土-铌成矿作用的控制。研究结果表明,四类矿石中的云母均为热液成因,结晶温度约为230~480℃。萤石条带状矿石、白云石型矿石和霓石型矿石中的云母主要为富镁金云母,其中,萤石条带状矿石和霓石型矿石中的金云母Rb-Sr反等时线年龄分别为410±14Ma(n=20)和399±12Ma(n=15),而白云石型矿石中的金云母Rb-Sr同位素体系可能被扰动;云母型矿石以镁质黑云母为主,黑云母Rb-Sr反等时线年龄为287±16Ma(n=20)。本文研究揭示,在早古生代,贫稀土的云母主要以脉石矿物的形式从热液流体中结晶,促进了残余流体中稀土含量的升高和之后的矿化;而在二叠纪,部分云母的Rb-Sr体系被矿区大规模的花岗质岩浆活动重置,记录了对早期矿化的改造,可能与高品位的铌矿化相关。The Bayan Obo deposit is a world-class rare earth element(REE)deposit that also hosts significant resources of iron,fluorine and niobium.Mica is a common mineral in the deposit,bearing a close association with ore and gangue minerals.Based on detailed geological and petrographic studies,we use in-situ Rb-Sr isotopic dating and geochemical analyses on mica from representative ore types in the Bayan Obo deposit to reveal how magmatic-hydrothermal evolution of carbonatites have controlled REE-Nb ore formation.Four types of mica-bearing ores are studied,including mica-type ore,fluorite-banded ore,dolomite-type ore and aegirine-type ore.Our results indicate that all micas are of hydrothermal origin with a temperature of 230~480℃.Micas in fluorite-banded ore,dolomite-type ore and aegirine-type ore are predominantly Mg-rich phlogopite,with Rb-Sr isochron ages of 410±14Ma(n=20)and 399±12Ma(n=15)for fluorite-banded ore and aegirine-type ore,respectively.In contrast,the mica Rb-Sr isotopic system in dolomite-type ore may have been disturbed.Mica-type ore consists of magnesian biotite,yielding a Rb-Sr isochron age of 287±16Ma(n=20).These results suggest that during the Early Paleozoic,REE-poor mica crystallized as gangue minerals from hydrothermal fluids,facilitating the enrichment of REE from the residual fluids and subsequent mineralization.During the Permian,large-scale granitic magmatic activity triggered the formation of high-grade Nb mineralization through remobilizing existing low-grade ore,as evidenced by the resetting of the Rb-Sr isotopic system of micas locally.

关 键 词：白云鄂博矿床 云母 地球化学 Rb-Sr同位素定年 

分 类 号：P578.959[天文地球—矿物学] P597.3[天文地球—地质学] P618.7