湖南尖峰岭稀有金属花岗岩地球化学特征及成矿作用

湖南尖峰岭矿床是一个典型的花岗岩型Li、Nb和Ta稀有金属矿床,为研究花岗岩成矿作用以及指导湘南地区稀有金属找矿工作,采用XRF、ICP-MS和ISE法分析了与成矿有关的黑云母花岗岩、钠长石花岗岩及云英岩的中主量、微量元素和挥发分。结果表明:钠长石花岗岩和云英岩中的SiO_2(70.6%~84.85%)和挥发分F(2.43%~3.74%)质量分数高,富Al_2O_3(9.36%~22.99%),且A/CNK1.0,为过铝质岩石,全碱(w(Na_2O+K_2O)=1.51%~7.52%)和w(CaO)(0.1%~3.44%)变化大,w(Fe_2O_3)、w(MgO)、w(TiO_2)、w(MnO)、w(P_2O_5)较低;稀土元素组成具显著的Eu负异常和"M"型四分组效应,强烈富集Rb、Th、U、Nb、Ta元素,亏损Ba、Sr、Ti元素。花岗岩地球化学特征显示在演化过程中经历了高程度分异演化作用和岩浆不混溶作用,其挥发分F对稀有元素有明显的富集作用,并制约着熔体/流体体系的地球化学行为及其成矿效应。钠长石花岗岩和云英岩的稀有金属富集成矿受到岩浆不混溶作用、水岩反应、风化淋滤作用的共同控制。

Geochemical features and mineralization of Jianfengling rare metal granite in Hunan Province

The Jianfengling deposit, which is located in Linwu County of Hunan Province, is a typical granite-type Nb-Ta-Li ore deposit. Analysis of major elements, trace elements and volatiles of albite granite and greisens was carried out by using XRF, ICP-MS and ISE methods in order to investigate granite metallogenesis and further to give assistance for exploring rare metal ore prospective areas in southeastern Hunan Province. The results show that the albite granites and greisens are characterized by high values of SiO₂(70.6%~84.85%), Al₂O₃(9.36%~22.99%), A/CNK>1.0 and F (2.43%~3.74%), large range content of Na₂O+K₂O (1.51%~7.52%) and CaO 0.1%~3.44%), and extremely low content of Fe₂O₃, MgO, TiO₂, MnO and P₂O₅, with significant Eu anomalies and m-type tetrad effects. They are strongly enriched in Rb, Th, U, Nb and Ta, but depleted in Ba, Sr and Ti elements. All these characteristics show that these granites were formed through high differentiation of magma and magma immiscibility. It is believed that rare metals enrichment and melt-fluid geochemical behavior and ore-forming effect were attributed to such restrictive functions as volatile F, the unmixing of magma, water-rock reaction and weathering leaching process, which led to rare metals enrichment in albite granites and greisens to form ore deposit.