安徽繁昌地区桃冲铁矿床地球化学特征及矿床成因研究

摘要

The Fanchang District as an important metallogenic cluster district in the Fe-Cu-Au polymetallic metallogenetic belt along the Middle-Lower Yangtze Reaches,develops a series of magnetite deposits represented by Taochong iron deposit.Comparing the REE geochemical characteristics of the magmatic rock,wall rock and ore-bearing skarn in Taochong ore zone,the content and the distribution patterns of REE are significantly different.The skarn has a pattern of LREE enrichment and HREE depletion transitional right-dipping pattern with a positive Eu anomaly.Four types of fluid inclusion： melt inclusion,liquid-gas two-phase inclusion,daughter-minerals bearing polyphase inclusion and liquid phase inclusion,have been found in minerals from Taochong iron deposit on the basis of the petrography,microthermometry and Raman spectrum analyses.Ore-forming fluids are medium-high temperature,high salinity,water-rich,and rich in Na＋,Ca2＋,Mg2＋,K＋,Cl,SO2-4.Ore-forming fluid features and developments are discussed combining with the theory of transmagmatic fluids.It is considered that the origin of iron deposit is Fe-rich skarn ore-magma from the depth.The decoupling of ore-forming fluid and skarn took place in the process of emplacement.The deposit was formed by injection in the weak tectonic belt caused by structural processes.%安徽繁昌地区作为长江中下游Fe、Cu、Au成矿带中的重要矿集区,发育一系列以桃冲铁矿为代表的磁铁矿型铁矿床。对桃冲矿区分布的岩浆岩、围岩与赋矿矽卡岩的稀土元素地球化学特征对比,表明三者稀土含量及其配分模式存在差异,桃冲铁矿夕卡岩稀土总量较低,轻稀土富集重稀土亏损,呈右倾过渡型配分模式,具明显Eu正异常。通过对桃冲铁矿床内包裹体的岩相学、显微测温、激光拉曼光谱探针分析,桃冲铁矿体中发育有熔融包裹体、气液相包裹体、含子晶多相包裹体、纯液相包裹体4种类型。成矿流体具中高温、高盐度、富水特征,富含Na＋、Ca2＋、Mg2＋、K＋、Cl-、SO24-离子。结合透岩浆流体成矿理论探讨成矿流体及演化,认为形成铁矿床的物质来源为深部富铁夕卡岩矿浆,侵位过程中受构造环境影响,因温压条件的迅速改变含矿流体与夕卡岩浆发生解耦作用,于构造薄弱部位贯入形成矿体。