湖南仁里-传梓源伟晶岩型稀有金属矿床云母地球化学特征及其指示意义

Geochemical characteristics and indication of mica in Renli-Chuanziyuan pegmatite type rare metal deposit in Hunan Province

仁里—传梓源稀有金属矿床是新近发现的大型伟晶岩型稀有金属成矿区,为揭示伟晶岩演化过程及稀有金属富集矿化机制,对仁里—传梓源矿区各类伟晶岩和花岗岩中云母进行岩矿鉴定、电子探针分析(EPMA)和激光剥蚀电感耦合等离子质谱分析(LA−ICP−MS)。研究结果表明:伟晶岩中云母具有白云母−多硅白云母(MS1)→富锂白云母−富锂多硅白云母(MS2)→富氟铯锂云母(MS3)→白云母(MS4)的演化趋势,在演化过程中发生Mg和Ti与Mn,Al,Si,Fe,Li,F,OH等元素置换;含MS1和MS2类型的伟晶岩产生于单一岩浆演化阶段,富氟铯锂云母(MS3)的出现指示体系产生超临界流体,伟晶岩转变为岩浆−热液演化,含MS4类型的伟晶岩产生于体系演化最后阶段,富F流体出溶,Li大量结晶产生锂辉石;流体的产生有利于体系富集的铌钽沉淀矿化,使钠长石伟晶岩和锂辉石−钠长石伟晶岩成为主要的成矿阶段;矿区幕阜山岩体两类花岗岩中,白云母二长花岗岩中云母在成分上与稀有金属伟晶岩的云母更接近,结合时空耦合关系,认为其应是成矿母岩。

Renli-Chuanziyuan rare metal deposit is a newly discovered large pegmatite rare metal deposit.In order to explore the evolution process of pegmatite and enrichment and mineralization mechanism of rare metals,rock and mineral identification,electron probe microanalysis(EPMA)and laser ablation inductively coupled plasma mass spectrometry(LA−ICP−MS)analysis of mica in various pegmatites and granites in Renli-Chuanziyuan mining area were carried out.The results show that mica in pegmatite has the evolution trend of muscovite-polysilicon muscovite(MS1)→lithium−rich muscovite−lithium−rich polysilicon muscovite(MS2)→fluorine−rich cesium−lithium muscovite(MS3)→muscovite(MS4),and the replacement of Mg,Ti and Mn,Al,Si,Fe,Li,F and OH occurs during the evolution process.The pegmatite in the MS1 and MS2 stages was generated from a single magmatic evolution.The emergence of fluorine−rich cesium lithium mica(MS3)indicates that the system generates supercritical fluid,and the pegmatite transformes into magmatic−hydrothermal evolution.The pegmatite in the MS4 stage is generated in the final stage of the system evolution.The F−rich fluid dissolves,and a large number of Li crystals generates spodumene.The generation of fluid is conducive to the precipitation and mineralization of Nb and Ta enriched in the system,making albite pegmatite and spodumene−albite pegmatite become the main metallogenic stages.Among the two types of granites of Mufushan rock mass in the mining area,the composition of muscovite in muscovite monzonitic granite is closer to that of rare metal pegmatite.Combined with the time−space coupling relationship,it is considered that muscovite monzonitic granite should be the metallogenic parent rock.