The Zhangsanying alkali granite is located in the northern margin of the North China Craton.The whole rock is Nb-enriched and has a highly fractionated feature,showing a great rare metal metallogenetic potential.In this paper,we aim at identifying the species of Nb-bearing minerals and understanding the magma evolution process.We carry out a whole range of research on microstructure and mineral chemistry of columbite group minerals.The results illustrate that the columbite group minerals are the main Nb-bearing minerals,which have high contents of Nb and low contents of Ta and most are columbites-(Fe)with a small amount of columbites-(Mn).Geneses of the minerals are divided into magmatic and magmatic-hydrothermal types.The magmatic type of the columbite group minerals,numerous in quantity,is euhedral and has oscillatory zonation structures,indicating that they crystallize during magmatic process.Their BSE images show bright rim and reverse oscillatory zonation structures,implying melt metasomatism.The magmatic-hydrothermal type is fewer.They have homogenous chemical compositions,with higher Mn# and Ta#,and they rapidly deposit from melt.The magma evolution of the Zhangsanying alkali granite involves magma cooling,magmatic-hydrothermal transition,and hydrothermal periods.The magmatism is crucial for Nb enrichment.The melt partly contributes to Nb and Ta enrichment during magmatic-hydrothermal transition period.Fluid metasomatism is weak during hydrothermal period and has few impacts on rare metal enrichment.
关键词
铌铁矿族矿物/岩浆演化/张三营/华北克拉通北缘/稀有金属
Key words
Columbite group mineral/Magma evolution/Zhangsanying/Northern margin of the North China Craton/Rare metals
维普
万方数据