摘要
西坞口矿床是江南隆起带安徽宁国市近年来发现的首个关键金属铷(Rb)矿床,与成矿有关的岩浆岩为花岗斑岩。矿床中发育两类铷矿体:矿体I赋存于花岗斑岩体内,矿体II产于花岗斑岩体顶部。两类矿体的矿物组合均为多硅白云母+石英。矿体I呈透镜体状产于花岗斑岩体顶部,多硅白云母含量可达70%,品位为0.25%;矿体II产于花岗斑岩体和地层接触带,品位为0.21%。前人对西坞口矿床的矿化特征、岩浆岩年代学、岩浆岩成因开展了研究,但关于铷的赋存状态及成矿机制尚不明确。本次工作分别对成矿岩体和两类矿体中的主要矿物开展了电子探针(EPMA)和激光剥蚀电感耦合等离子体质谱仪(LA-ICP-MS)研究,分析结果显示花岗斑岩中斜长石、钾长石和黑云母中Rb的平均含量分别为3.10×10^(-6)、872×10^(-6)和1328×10^(-6),矿体I和II中多硅白云母的Rb平均含量分别为2544×10^(-6)和2686×10^(-6)。多硅白云母晶体化学计算表明,铷以Rb^(+)→K^(+)/Na^(+)置换的方式进入多硅白云母晶格,在多硅白云母中以类质同象的形式赋存。结合矿床地质特征和区域岩浆岩对比分析,本文提出西坞口矿床成矿岩浆具有较高的Rb背景值以及氟(F)含量,矿物结晶作用使得Rb在残余岩浆含量升高,岩浆向热液过渡阶段的富F特征导致原先岩浆体系的架状硅酸盐结构变成层状,进而有利于结晶出大量富Rb的多硅白云母,并富集形成铷矿体。
The Xiwukou rubidium(Rb)deposit—a granite-related ore deposit—is the first discovered Rb deposit in the Jiangnan uplift belt,Ningguo City,Anhui Province.Two spatially distinct orebodies,type-Ⅰand type-Ⅱ,developed in the Xiwukou deposit.The type-Ⅰorebody is hosted in granite porphyry,and the type-Ⅱis at the top of the granite porphyry.The mineral combinations are all phengite+quartz,but ore grade is higher in type-I(0.25%)than in type-Ⅱ(0.21%)orebody.Previous researches had focused on the mineralization characteristics,chronology,petrogenesis,and magmatic source,but the mineral occurrence status of Rb and the metallogenic mechanism in the Xiwukou deposit are still unclear.In this study,we used electron probe analysis and LA-ICP-MS to characterize the granite porphyry-hosted plagioclase,K-feldspar and biotite and phengite in the type-Ⅰ,Ⅱorebodies.We found that the average Rb contents in plagioclase,K-feldspar and biotite,formed in the early stage,were 3.10×10^(-6),872×10^(-6) and 1328×10^(-6),respectively;while in phengite,formed in the late stage,the Rb contents were 2544×10^(-6) and 2686×10^(-6) in type-I and type-II orebodies,respectively.The stoichiometric calculation results show that Rb^(+) is incorporated into phengite through isomorphism replacing K^(+) and Na^(+).Combining the geological characteristics of the deposit with comparative analysis of regional igneous rocks,we propose the following ore-forming mechanism for the Xiwukou Rb deposit:The Rb background value and fluorine content in the ore-forming magmatic fluids was fairly high,and mineral crystallization led to further Rb enrichment in the residual magma.During the transition stage from magma to hydrothermal fluid,the high fluorine condition caused a structural change in silicate,from a framework to layered structure,which facilitated large-scale crystallization of Rb-rich phengnite to form Rb-rich orebody.
作者
陈雪锋
范裕
周涛发
庾江华
钱仕龙
陆中秋
杨张一
洪建民
CHEN Xuefeng;FAN Yu;ZHOU Taofa;YU Jianghua;QIAN Shilong;LU Zhongqiu;YANG Zhangyi;HONG Jianmin(School of Resources and Environmental Engineering,Hefei University of Technology,Hefei 230009,China;Ore Deposit and Exploration Center(ODEC),Hefei University of Technology,Hefei 230009,China;Anhui Province Engineering Research Center for Mineral Resources and Mine Environments,Hefei 230009,China;No.322 Geological Party,Bureau of Geology and Mineral Resources Exploration of Anhui Province,Ma’anshan 243000,China)
出处
《地学前缘》
EI
CAS
CSCD
北大核心
2022年第1期65-80,共16页
Earth Science Frontiers
基金
国家自然科学基金项目(91962218,41872081)
国家重点研发计划项目(2016YFC0600206)
中央高校基本科研业务费专项(PA2019GDZC0093)。
关键词
江南隆起带
西坞口矿床
铷
赋存状态
成矿机制
Jiangnan uplift belt
Xiwukou deposit
rubidium
occurrence status
metallogenic mechanism
