广西银屏富B花岗岩及其晶洞中电气石的化学组成特征以及对岩浆-热液演化的指示  

CHEMICAL COMPOSITION OF TOURMAILINES FROM THE B-RICH GRANITE AND MIAROLITIC CAVITIES IN YINPING,GUANGXI AND ITS IMPLICATIONS FOR EVOLUTION OF THE MAGMATIC-HYDROTHERMAL SYSTEM

作　　者：黄小勇[1] 张辉[1] 唐勇[1] 管申进[1] 

机构地区：[1]中国科学院地球化学研究所地球深部物质与流体作用地球化学研究室

出　　处：《矿物学报》2008年第1期25-34,共10页Acta Mineralogica Sinica

基　　金：国家自然科学基金(批准号:4027303040673052);国家重点基础研究发展计划“973”项目(2006CB403500-062006CB403500-08)

摘　　要：利用EMPA对广西花山A型花岗岩最晚期岩相-细粒花岗岩及其晶洞中电气石进行矿物学、地球化学研究。结果表明，细粒花岗岩中电气石与晶洞中电气石化学组成非常一致，以高Fe（2．78～3．44apfu）、低的总Al（5．62—6．20apfu）、极低Mg（0．05～0．12apfu）、不含Li、F、Cl等特征。在Fe-Mg图解中，其化学组成近于端元黑电气石。Al^3＋=Fe^3＋和R^＋R^2＋=R^3＋＋□是所研究的电气石中两个主要的置换反应；岩浆电气石和热液成因电气石均位于Al-Fe-Mg三角图解中黑电气石一镁电气石线之下，表明电气石结构中存在明显的Fe^3＋，预示岩浆是在相对高的氧逸度条件下分异演化的。细粒花岗岩中普遍发育几厘米到几十厘米尺度的晶洞以及大量电气石在晶洞中沉淀，暗示A型的花山花岗岩形成演化过程中未发生大规模含水流体相出溶，代之的是蒸汽相分离。由于不存在岩浆．热液体系的演化过程，在银屏细粒花岗岩内及周边地区可能不是寻找锡石-石英脉型矿床的理想靶区。In this paper, mineralogical and geochemical researches on tourmalines from the matrix and miarolitic cavities of the fine granite, which is the latest facies in the Huashan A-type granites, were conducted systematically. The results showed that the tourmalines from the matrix and miarolitic cavities are much similar in chemical composition, characterized by high Fe （2. 78 - 3.44 apfu）, low Al （5.62 - 6.20 apfu）, low Mg （0. 05 -0. 12 apfu） and non-existence of Li, F and Cl. The chemical compositions of tourmalines are very close to those of the end-member of schorl in the Fe-Mg diagram. Al^3＋ = Fe^3＋ and R^＋ ＋ R^2＋ = R^3＋＋□ are the two major substitutions in tourmalines. In Al-Fe-Mg triangle diagram, tourmalines of magmatic origin and hydrothermal origin are under the schorl-dravite line, indicating that high Fe^3＋ contents enter into the structure of tourmalines and magma differentiated under a relatively high oxygen fugacity condition. We deduced that hydrous fluid exsolution from magma didn＇ t occur during the evolution of the Huashan A-type granites for plentiful development of the miarolitic cavities, ranging from several to dozens of centimeters in size and deposition of abundant tourmalines in the miarolitic cavities. Because of the lack of evolution for the magmatic-hydrothermal system, the Yinping granitic pluton and/or nearby areas may not be suitable ideal targets for exploration of cassiterite-quartz ore deposits.

关 键 词：电气石 化学组成 富B花岗岩体系 晶洞 广西银屏 

分 类 号：P574.2[天文地球—矿物学] P578.953[天文地球—地质学]