赣南富城岩体黑云母及其蚀变产物绿泥石的矿物化学研究--对铀成矿的指示意义  

Mineral chemistry of biotite and chlorite in western part of Fucheng granite,southern Jiangxi Province: Implications for uranium mineralization

作　　者：赵友东[1] 吴俊奇[1] 凌洪飞[1] 王洪作 

机构地区：[1]南京大学内生金属矿床成矿机制研究国家重点实验室,地球科学与工程学院,江苏南京210023

出　　处：《矿床地质》2016年第1期153-168,共16页Mineral Deposits

基　　金：国家重点基础研究发展计划“973”项目(编号:2012CB416703);中国核工业地矿事业部十二五高校基础科研项目的联合资助

摘　　要：富城花岗岩体位于赣南会昌盆地东侧,该岩体西部与橄榄玄粗岩系列火山岩接触,河草坑铀矿田就产于该花岗岩体的内外接触带中。在矿区外围花岗岩中发育大面积的蚀变带,其中的黑云母普遍蚀变为绿泥石。为了深入探讨蚀变与铀矿化的关系,文章运用电子探针技术对该蚀变带的黑云母及其蚀变产物绿泥石进行了矿物化学研究。结果表明,黑云母大部分属铁叶云母,估算出富城花岗岩岩浆的氧逸度lg(f O2)值约为-15.0^-14.3,氧逸度较低,源岩为还原性较强的岩石,有利于铀预富集于源区中;富城产铀花岗岩中黑云母的w(F)高达1.41%~2.01%,表明花岗质岩浆富F,而富F岩浆中U溶解度高,可能是富城岩体富铀的重要原因之一。黑云母被绿泥石交代后呈黑云母假象,绿泥石矿物化学分析结果表明,绿泥石以鲕绿泥石和蠕绿泥石为主,属于富铁的绿泥石,主要形成于还原环境;绿泥石的形成温度介于246~307℃之间,平均276℃。全岩U、Th含量分析结果表明,上部"红化"蚀变层中的w(U)(3.5×10-6~9.4×10-6,平均6.6×10-6)明显低于下部"绿色"蚀变层(7.7×10-6~23.1×10-6,平均13.9×10-6),而"红化"蚀变层与"绿色"蚀变层的Th含量相似,w(Th)平均值分别为35.7×10-6和36.5×10-6。矿前期的带状面型"绿色"蚀变层活化了矿物晶格中的结构铀,后期高氧逸度的流体萃取"绿色"蚀变层中已经活化了的铀而形成含铀热液,经迁移在还原带附近沉淀成矿。Th的价态(正四价)难以随这种氧化还原条件的改变而改变,因此未参与流体成矿过程。The Fucheng granite is located to the east of Huichang basin, southern Jiangxi Province. There are several uranium deposits in the western part of the Fucheng granite which is in contact with shoshonite series volcanic rocks,with the Caotaobei uranium deposit being one of them. Chloritization of biotite in the granite is very common in the western Fucheng granite. Based on electron microprobe analysis data and theoretic calculation results of biotites and chlorites from the western part of the Fucheng granite, the authors studied the mineral chemistry of biotites and chlorites so as to discuss the relationship between chloritization of biotites and uranium mineralization. The results show that most of the biotites belong to siderophyllite. The oxygen fugacity（ lg（ f O2）） of magma of the Fucheng granite is estimated to be relatively low（- 15. 0 -- 14. 3）, which means that the magma was relatively strongly reduced. Its source rock was strongly reduced, which was beneficial to preliminary enrichment of uranium. The F content in biotite is 1. 41% - 2. 01%, showing that granitic magma was rich in F. As U are easy to form complex with F in magma, and this is probably one of the reasons that the Fucheng granite is rich in uranium. Chlorite was mainly derived from biotite by alteration, so it exhibits the shape of biotite. Chemical analysis of chlorite shows that the biotite mostly belongs to chamosite and prochlorite, both of which are rich in Fe element, and were mainly formed in a reductive environment. The formation temperatures of chlorite are between 246 - 307℃（ with an average of 276℃）. The U values of the samples from the upper reddish alteration zone vary from 3. 5 × 10^-6to 9. 4 ×10^-6（ with an average of 6. 6 × 10^-6）, significantly lower than U values of the samples from the lower greenish alteration zone（ 7. 7 × 10^-6- 23. 1 × 10^-6, 13. 9 × 10^-6on average）. The Th values of the samples from the reddish alteration and the greenish alteration zone are basically similar, with

关 键 词：地质学 矿物化学 黑云母与绿泥石 铀成矿 富城岩体 赣南 

分 类 号：P619.14[天文地球—矿床学]