新余良山铁矿床磁铁矿原位地球化学特征及其对成矿作用的制约

摘要

"Xinyu" type iron deposit is an important Neoproterozoic formation widely distributed in South China.Ore bodies and wall rocks experienced intensive metamorphism and deformation.Some of the ore districts were influenced by intensive hydrothermal superimposition of late-stage granitic pluton.Based on the field study and lithofacies analysis of the representative "Xinyu" type deposit -Liangshan iron deposit,ore samples far away from and close to the granitic pluton were selected to analyze micro-area and trace elements of magnetite.The research shows that although both types were influenced by metamorphic recrystallization and hydrothermal superimposition in varying degrees,the former sample still preserves hematite from sedimentary metamorphic stage while in the latter sample,hematite has been transformed to magnetite.The distribution features of magnetite in Liangshan ore are consistent with sedimentary metamorphic iron deposit,which is relatively rich in Ti,V,Mn,Co,but poor in Cr,showing medium-high temperature hydrothermal superimposition.We propose a three-stage mineralization model for Liangshan iron deposit,that is,deep-sea ferrosilicon sedimentation,burial metamorphism and deformation,and granitic hydrothermal superimposition.%“新余式”铁矿是广泛分布于华南地区的重要新元古界铁建造,矿体和围岩在形成后经历了强烈变质和变形作用,部分矿区的矿体还受到了后期花岗岩体的强烈热液叠加作用.本文在对“新余式”铁矿的代表性矿床—良山铁矿进行野外考察和岩相分析的基础上,分别选择远离和靠近花岗岩体的矿石样品,开展磁铁矿微区和微量元素分析.研究表明,虽然两种矿石都受到不同程度的变质重结晶和热液叠加作用,但前者仍然保留了大量沉积变质期的赤铁矿,后者中的赤铁矿全部转变为磁铁矿.良山矿石中磁铁矿相对富集Ti、V、Mn、Co,贫Cr,与沉积变质铁矿的分配特征一致,其中靠近花岗岩体的样品相对富集Ti、V、Ni、Zn和Cu,显示中高温热液叠加特征.本文提出了新余良山铁矿的三阶段成矿模型,即深海硅铁质沉积、埋藏变质变形和花岗热液叠加.