江西黄山铌(钽)矿床中铌钽矿物的矿物学特征及地质意义

Mineralogy and Geological Significance of Niobium and Tantalum Minerals in the Huangshan Niobium (Tantalum) Deposit,Jiangxi Province,South China

江西葛源黄山铌(钽)矿位于赣杭构造带灵山花岗岩体的西侧,矿区内发育黑云母花岗岩、钠长石化花岗岩、萤石石英脉、伟晶岩4种岩性。通过详细的岩相学观察、铌钽矿物的电子探针化学组成、元素面扫描分析,揭示了黄山铌(钽)矿中铌钽的赋存状态及灵山岩体演化与铌钽富集过程的关系。研究结果表明,黄山铌(钽)矿中铌钽矿物主要为铌铁矿和铌铁金红石,铌铁矿交代了早期形成的铌铁金红石,期间发生了如下置换关系:3Ti^(4+)→2(Nb^(5+)+Ta^(5+))+Fe^(2+)。黄山铌(钽)矿主要富Nb,与松树岗铌钽矿相比,含矿岩体中F、Li的质量分数较低。F可以降低固相线温度,延长岩浆结晶分异的时间,增加岩浆的结晶分异程度。Li会增加Nb、Ta的溶解度,但是对Ta的效果更明显。因此,黄山铌(钽)矿的岩浆演化程度低于松树岗铌钽矿,后期岩浆—热液演化阶段的流体作用较弱,导致黄山铌(钽)矿以富Nb为主。

The Huangshan niobium(tantalum) deposit in Geyuan County, Jiangxi Province is located in the west side of Lingshan granite pluton, Gan-Hang Belt. This paper studies the occurrence of niobium and tantalum minerals in biotite granite, albite granite,fluorite-quartz vein, and pegmatite by petrographical observation, and mineral chemical and elemental mapping analysis with EPMA. The paper also discusses the relationship between the magma evolution of Lingshan granite and the niobium tantalum mineralization. The results indicate that the niobium and tantalum minerals in the Huangshan niobium(tantalum) deposit are columbite and niobium rutile. The columbite replaced the early formed niobium rutile with the exchange reaction of 3 Ti^4+→2(Nb^5++Ta^5+)+Fe^2+. Huangshan niobium(tantalum) deposit is mainly rich in Nb. Compared with Songshugang niobium tantalum deposit, Huangshan niobium(tantalum) deposit contains lower F and Li in the whole rock. Fluorine can reduce the temperature of solidus line and extend the duration of magmatic crystallization, and increase the degree of magma evolution. The higher Li content increases the solubility of Nb and Ta, but the effect on Ta is more obvious. Accordingly, it is speculated that the magma evolution of Huangshan niobium(tantalum) deposit is lower than that of Songshugang, and the fluid interaction in the magma-hydrothermal transitional stage is weaker than that of Songshugang. However, the Songshugang niobium tantalum deposit underwent strong magmatic evolution, and the fluid reaction in the magma-hydrothermal transition stage promoted the enrichment and precipitation of Ta.