广西罗维钨多金属矿区花岗岩地球化学特征及其与成矿的关系

摘要

罗维钨多金属矿床是近年来广西壮族自治区第四地质队在西大明山地区新发现的一个具大型规模的矽卡岩型矿床,区内的矿床(化)类型主要为矽卡岩型和石英脉型,以前者为主.罗维钨多金属矿区出露2种花岗岩,岩性为似斑状黑云母花岗岩和中细粒花岗岩.笔者对两类花岗岩进行岩相学、主微量和稀土元素含量等测试.二者岩石地球化学特征相似,总体表现为:高硅(SiO2=70.30％～74.78％)、高铝(12.77％～14.12％)、贫钙镁(CaO=1.11％～2.04％,MgO=0.37％～0.71％),∑REE=102.70×10-6～139.69×10-6,LREE/HREE=7.70～15.92,(La/Yb)N=11.15～31.38,轻重稀土分馏明显,轻稀土富集;δEu=0.37～0.62,具有Eu负异常;岩石相对富集Ta、U、Nd,轻度富集K、Th、La、Ce,亏损P、Nb.通过对化学分析结果进行图解说明,得出结论为似斑状黑云母花岗岩和中细粒花岗岩均是以壳源沉积物质为源岩,经过部分熔融、结晶而形成的具演化关系的S型花岗岩,该隐伏岩体可能控制了罗维钨多金属矿的形成,其中偏晚期阶段的中细粒花岗岩更强烈的表现出对W、Mo、Zn、Cu的成矿专属性.%The Luowei tungsten polymetallic deposit is a large scale skarn type deposit,which has been newly found in the west part of Xidamingshan by the No.4 Geological Party of Guangxi.The ore bodies are divided into skarn type and quartz vein type,and the former serves as the main mineralization type.In this paper,two kinds of granites are occurred in the Luowei tungsten polymetallic deposit.They are porphyritic biotite granite and fine-grained granite.The petrographic analyses and the testing of major elements and REE about these two kinds of granites have been carried out in this paper.The results show that these granites have similar geochemical characteristics.These granites have high silicon (SiO2 =70.30％ ～74.78％) and aluminum (12.77％ ～14.12％) contents,but have poor calcium and magnesium (CaO=1.11％ ～2.04％,MgO=0.37％～0.71％).Their ∑REE values range from 102.70 × 10-6 to 139.69 × 10-6,and their LREE/HREE and (La/Yb)N ratios are 7.70 ～ 15.92 and 11.15 ～ 31.38,respectively.These granites have low LREE/HREE ratios,with enriched LREE and Eu depletion (δEu=0.37～0.62).These rocks have clearly enrichment of Ta,U,Nd,mild enrichment of K,Th,La,Ce and depletion of P and Nb.The geochemical diagrams show that porphyritic biotite granite and fine-grained granite belong to S-type granite,and they were formed by the partial melting and crystallization of crust-derived materials.The concealed rock mass might be control the formation of the Luowei tungsten poly metallic deposit.The fine-grained granite in late stage shows more strong mineralization specificity for W,Mo,Zn,Cu deposit.