攀枝花铁矿朱家包包矿段层状铁矿体的成因:来自矿物结构定量化分析的证据  

The genesis of layered iron bodies occurring in the middle zone of Panzhihua intrusion,Zhujiabaobao mine:Evidence from quantitative crystal textural analysis

作　　者：李解[1] 罗照华[1] 杨宗锋[1] 李学军[1] 程金华[1] 邱一冉 I.V.Vikentyev 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,北京100083 [2]俄罗斯科学院矿床地质岩石学矿物学地球化学研究所,莫斯科119017

出　　处：《地学前缘》2016年第3期210-220,共11页Earth Science Frontiers

基　　金：国家重点基础研究发展计划"973"项目(2011CB808901);中国地质调查局项目(1212011220921;1212011121266;12120113094100;1212011121075);中俄国际合作项目(RFBR 14-05-91162-NSFC)

摘　　要：岩浆型铁矿床是中国最重要的铁矿类型之一,攀枝花式铁矿赋存于攀枝花大型层状侵入体中,同时是峨眉山地幔柱系统的组成部分。然而此类矿床的成因问题仍未得到有效的解决。文中以攀枝花铁矿朱家包包矿段中部岩相带(MZ)为例,采用定量化结构分析的方法,结合地质学和岩相学观察结果,试图从攀枝花岩体中部岩相带辉长岩中单斜辉石的结构角度解释攀枝花式铁矿层状矿体的成因。岩相学观察可见部分样品中单斜辉石和斜长石具有明显的溶蚀结构以及角闪石、蛇纹石的增生边,被溶蚀的部分由铁钛氧化物填充,而铁钛氧化物之间发育共结结构。晶体粒度分布(CSD)显示,被溶蚀的单斜辉石较未溶蚀样品具有更陡的CSD曲线斜率,CSD曲线小颗粒处弯曲程度更大,以及更高的铁矿含量,说明溶蚀作用导致了CSD曲线变得更陡,产生了类似于粗化作用的CSD曲线。晶体空间分布(SDP)显示中部岩相带岩体上部有分选的趋势,而岩体下部则表现出挤压的趋势,说明了岩体上部保留了岩浆结晶过程中的矿物颗粒分选的趋势,而下部由于普遍的溶蚀导致了矿物粒间空隙增大,难以支撑上部的荷载,表现出挤压趋势。造岩矿物溶蚀、富水的角闪石、蛇纹石生长边以及填隙的铁钛氧化物说明有流体存在。在攀枝花岩体中段结晶晚期,富铁流体加入半固结的岩体使得造岩矿物溶蚀,而后填充于空隙,流体逃逸后铁矿物富集沉淀成矿。岩体下部具普遍的溶蚀作用,受荷载富铁流体被挤压逃逸,形成了块状的贫铁岩体;上部流体水平运移,没有受到挤压作用,流体逃逸后保留了铁矿的含量,形成了富集的层状铁矿体。这种层状矿体的成因模型类似于透岩浆流体模型。Magmatic iron deposit, occurring in Panzhihua layered intrusion, is one of the most important iron resources in China and builds up Emeishan mantle plume. However, the metallogenic mechanism is still left controversial. In this article, the middle zone of Panzhihua intrusion in Zhuiiabaobao mine is investigated. With the analysis of quantitative clinopyroxene texture, the genesis of layered iron bodies has been put forward based on field and microscopic observation. In the aspect of petrography, the textures of clinopyroxene and plagioclase in dissolved samples have been obviously changed by dissolution and the dissolved parts were occupied by oxide. Crystal Size Distribution diagrams show that dissolved samples have steeper CSD slopes and are more curved at small granularity with higher oxide than those of the original. It is explained that the dissolution results in a more steep CSD slope and a coarsening-like CSD diagram. Spatial Distribution Pattern shows that crystals in the upper part are better sorted, however the lower underwent compaction from the former. Sorting in magmatic processes have been recorded in the upper part and the lower are suffered from dissolution which results in bigger pore space. Rocks with larger space can not hold up the weight from the lower part so compaction trend is shown up. It is shown that fluid exists during oxide forming processes revealed by dissolution of rock-forming minerals and fluid-rich amphibole together with serpentine around the dissolved minerals and interstitial oxide. During the late magmatic stage of Panzhihua intrusion. Fluid rich in iron injected into the unsolidificated body, resulting in the dissolution, then filled the pore space. Iron formed when fluid escaped. Pervasive dissolution occurred in the lower part and iron-rich fluid escaped by compaction, so poor bulk ore body came into being. In the upper part, fluid moved horizontally without compaction, so rich layered iron body formed. This ore-forming pattern is similar to transmagmatic fuild metallogen

关 键 词：攀枝花式铁矿 结构定量化分析 溶蚀作用 透岩浆流体 成矿模型 

分 类 号：P588.12[天文地球—岩石学] P618.31[天文地球—地质学]