湖南桂东小江花岗岩体:一个潜在Rb-Nb-Y矿床的岩石化学特征及其成矿远景

铷是一种具有广泛用途的稀有金属。湖南桂东县小江地区曾于1958年地质预查确定为砂锡矿,但未见进一步工作的报道。本次工作系统采集了矿区的细粒二云母花岗岩、黑云母斑状花岗岩、粗粒黑云母花岗岩的岩石样品。精细测试表明,三者是同期花岗岩浆多阶段演化的产物,随着演化程度的增高,岩体内的稀有金属含量逐渐增高。细粒二云母花岗岩属于重稀土富集型花岗岩,稀土配分模式表现出岩浆晚期富挥发份组成而造成的四分组效应,其基岩中的Rb2O含量超过0.1%,达到花岗岩型铷矿床的工业品位;Nb的含量达到伴生矿的要求,具有全岩矿化的特征;风化壳中Y的含量达到许多离子吸附型矿床的钇含量。Rb元素主要赋存在二云母花岗岩的钾长石和黑云母中,Y主要赋存在萤石中。按照二云母花岗岩的厚度50m计算,Rb2O储量约为16万吨。除此之外,矿区还应该注意寻找伟晶岩型稀有金属矿脉,并重视矿区风化壳发生离子吸附型重稀土矿化的可能性。

The Petrochemical Feactures and Rb-Nb-Y Potential of the Xiaojiang Granitic Intrusion, Guidong, Hunan

Rb is an important rare metal element used widely in industry.Placer Sn was explored in the Xiaojiang region in Guidong,Hunan in 1958,but no follow-up work has been reported.Samples were collected from the fine-grained two-mica granite,the biotite porphyritic granite,and the coarse grained biotite granite in the Xiaojiang ore field.The petrochemical features of the samples show that the three types of granites were likely originated from the same granitic magma.Due to fractional crystallization of the granitic magma,the latest fine-grained two-mica granite is enriched in rare metals and Y with tetrad REE pattern.For example,in the two-mica granite,Rb2O(>0.10%),Nb2O5(>0.005%),and Y2O3(>0.01%) contents are beyond or around the cutoff grades.The EMPA analysis shows that Rb is enriched in K-feldspar and biotite,while Y is enriched in fluorite.In the end,the reserves of Rb2O is estimated to be about 320,000 tons assuming the Rb mineralization depth of the Xiaojiang granite is 50 m,and granite has a promising perspective for pegmatite type rare metal deposit and ion adsorption type REE deposit as well.