湖南仁里铌钽矿床矿体地球化学特征及其成因意义

Geochemical characteristics and genetic significance of ore bodies in Renli Nb-Ta deposit, Hunan Province

仁里超大型铌钽矿床处于扬子陆块与华夏陆块交汇之江南隆起造山带、幕阜山岩体西南缘,是我国东部近年来新发现的超大型、高品位花岗伟晶岩型铌钽矿。为了查明矿体中伟晶岩地球化学特征,进一步总结区内稀有金属成矿特征,为幕阜山地区乃至华南地区稀有金属找矿与研究提供经验,本次选取5号主矿脉钻孔ZK1616中5-2号矿体的13个矿样进行了主量、微量及稀土元素测试。测试结果:SiO2:70.2%~90.1%, Al2O3:5.23%~16.4%, Na2O+K2O:3.49%~11.5%, A/CNK:1.42~3.28,稀碱总量:202.0×10^-6~1155.9×10^-6,稀土元素含量极低,部分超出了测量精度的下限,A/CNK明显高于花岗岩A/CNK指数,具有较高的分异指数。研究表明矿体中伟晶岩跟其围岩(花岗岩)均属高分异、富硅、过铝质、钙碱性花岗质岩石,稀有金属元素的富集程度与花岗岩分异演化程度有良好的一致性,稀有金属成矿受岩浆的分异演化控制,分异晚期富含F、H2O、CO2的气、热液流体对围岩的稀有金属元素的释出→迁移,对稀有金属成矿产生了叠加作用。多阶段、分带性较复杂的伟晶岩更有利于铌钽等稀有金属成矿。

Renli super-large Nb-Ta deposit is located in the Jiangnan uplift orogenic belt at the intersection of Yangtze block and Cathaysian block and the southwestern margin of Mufushan rock mass, and it is a super-large and high-grade granitic pegmatite-type Nb-Ta deposit newly discovered in eastern China in recent years. In order to ascertain the geochemical characteristics of pegmatite in ore bodies and further summarize the metallogenic characteristics of rare metals in the area, and provide experience for prospecting and research of rare metals in Mufushan area and even in South China. In this paper, 13 ore samples from No. 5-2 ore body of No. 5 main vein borehole ZK1616 were selected for major, trace and rare earth element tests. The test results are as follows: SiO2: 70.2%~90.1%, Al2O3: 5.23%~16.4%, Na2O+K2O: 3.49%~11.5%, A/CNK: 1.42~3.28, total amount of dilute alkali: 202.0×10^-6~1155.9×10^-6, rare earth element content is very low, part of which exceeds the lower limit of measurement accuracy. A/CNK is obviously higher than granite A/CNK index and has higher differentiation index. Studies have shown that the pegmatites in the orebodies and their surrounding rocks(granite) are highly differentiated, silicon-rich, peraluminous, calc-alkaline granitic rocks. The study shows that the pegmatite and its surrounding rock(granite) in the orebody belong to highly differentiated, silica-rich, peraluminous and calc-alkaline granitic rocks, suggesting that the enrichment degree of rare metal elements is well consist with the differentiation and evolution degree of granite. The mineralization of rare metals is controlled by magma differentiation and evolution. In the late stage of differentiation, gaseous and hydrothermal fluids rich in F, H2O and CO2 release and migrate rare metal elements from surrounding rocks. Pegmatites with complex zoning formed through multistage is more favorable for the mineralization of rare metals.