赣东北黄山铌钽矿床成矿岩体地球化学特征及成矿意义

对黄山铌钽矿区含矿岩体(黑云母二长花岗岩、花岗伟晶岩、细粒黑云母花岗岩)的主量元素、微量元素进行地球化学分析,并与成矿带典型A型花岗岩对比,发现它们属于高分异花岗岩,具富硅高碱、贫钙低镁的特征,A/CNK值均>1,属于准铝质—过铝质岩石。岩石富集高场强元素Nb、Th、Ta、Zr、U、Hf及大离子亲石元素Rb,亏损大离子亲石元素Ba、Sr、P及高场强元素Ti。球粒陨石标准化稀土元素配分形式属于"海鸥型",具强烈的Eu负异常。10 000×Ga/Al值均>2.60、Zr+Nb+Ce+Y总量远高于350×10-6,岩石成因类型为板内花岗岩A1亚类,推断岩体是在拉张构造背景下由于地幔物质上涌导致底侵作用,促使下地壳部分熔融形成了初始岩浆,在上侵过程中有地壳物质的混染。岩浆在侵位过程中发生的结晶分异作用,使铌钽等成矿元素与岩浆熔体分离,高分异演化熔体、富挥发份流体(主要是F、Cl)共同作用是铌钽富集的主要因素。

Geochemical characteristics and metallogenic significance of Huangshan Nb-Ta deposit in northeast Jiangxi Province

The main and trace elements of biotite monzogranite, granite pegmatite and fine-grained biotite granite in Huangshan Nb-Ta mining area were analyzed and compared with the typical A-type granites in the metallogenic belt. It shows that they belong to highly differentiated granite, characterized with rich silicon, high alkali, poor calcium and low magnesium, and A/CNK value>1, belonging to quasi aluminous-peraluminous rock. The rocks are enriched with high field strength elements Nb, Th, Ta, Zr, U, Hf and large ion lithophile element Rb, and depleted with large ion lithophile elements Ba, Sr, P and high field strength element Ti. The distribution form of rare earth elements belongs to "Seagull type", with strong Eu negative anomaly. 1 000×Ga/Al values are higher than 2.60, and the total amount of Zr+Nb+Ce+Y is much higher than 350×10-6. The genetic type of the rock is A1 subclass of intraplate granite. It is inferred that the rock mass is underplated due to the upwelling of mantle material under extensional tectonic setting, which promotes the partial melting of the lower crust to form the initial magma, and there is the contamination of crustal material in the upwelling process. The crystallization differentiation of magma in the process of emplacement separates niobium tantalum and other metallogenic elements from magmatic melt. The joint action of highly differentiated evolution melt and volatile rich (mainly F, Cl) fluid is the main factor for the enrichment of niobium tantalum.