河北武安玉石洼铁矿中磁铁矿特征及其对铁矿床成因指示意义  

Magnetite characteristics of the Yushiwa iron deposit in Wu’an,Hebei Province and its indication significance to the genesis of iron deposit

作　　者：侯晓阳 苏尚国[1] 杨跃跃 HOU Xiaoyang;SU Shangguo;YANG Yueyue(School of Earth Sciences and Resources,China University of Geosciences(Beijing),Beijing 100083,China)

机构地区：[1]中国地质大学(北京)地球科学与资源学院

出　　处：《地学前缘》2019年第6期244-256,共13页Earth Science Frontiers

基　　金：中国地质调查局项目(12120115069701);国家自然科学基金项目(41272105)

摘　　要：夕卡岩铁矿床的成因一直以来备受争议,主要有接触交代和矿浆成因等模型。河北武安玉石洼铁矿是邯邢地区主要的夕卡岩铁矿之一,对矿区尖山剖面中的三类磁铁矿成分进行详细研究有助于解决此问题。产于剖面下部玉石洼铁矿主矿体中的磁铁矿以高Ti为特征,而在上部结晶灰岩中矿脉状中磁铁矿以高Si(w(SiO2)>1%)为特点,赋存于中部二长岩矿脉中的磁铁矿具有过渡的成分特征。通过对此三类磁铁矿中主量元素、微量元素研究发现,从下部玉石洼主矿体向上部结晶灰岩中的磁铁矿脉,磁铁矿具有Ti含量逐渐减少而Si、Mg含量逐渐增加的特征。高硅磁铁矿呈自形晶,与方解石平衡共生,其形成与流体有关,很可能是流体晶矿物。磁铁矿Fe-V/Ti判别图解显示下部玉石洼主矿体中部分磁铁矿具有岩浆成因,二长岩和结晶灰岩中的脉状矿石中磁铁矿具有热液成因,磁铁矿由下部到上部具有岩浆成因过渡为热液成因的连续过程。根据玉石洼矿区磁铁矿的这些特征,我们认为铁矿浆中含有大量流体,应该为"含铁熔体-流体",由于流体超压使"含铁熔体-流体流"在岩浆通道中快速上升,至地壳浅部空间就位,在空间上由下部形成高温高Ti磁铁矿过渡为上部形成具有流体晶特征的高Si磁铁矿的岩浆通道成矿系统模型。The genesis of skarn iron deposit has long been controversial involving mainly the contact metasomatism and ore magma genetic models.The Yushiwa iron deposit is one of the major skarn iron deposits in the Handan-Xingtai area,Hebei Province.It contains three types of magnetite ores in the Jianshan section,on which a detailed study should help to resolve the genetic controversy.Magnetite in the main ore body of the Yushiwa iron deposit in the lower part of the profile is characterized by high Ti content.However,magnetite veins in the upper crystalline limestone have high Si(w(SiO2)>1%)content.And magnetite in monzonite has a transitional composition.Through major and trace elemental analysis of the three types of magnetite,we found gradual decreasing Ti and increasing Si and Mg contents in magnetite in the main ore body in the lower Yushiwa iron deposit to magnetite veins in the upper crystalline limestone.High silicon magnetite forms euhedral crystal and coexists with calcite in equilibrium.Its formation has fluid involvement,making it possible a fluid crystal mineral.The magnetite Fe-V/Ti discrimination diagram shows a magmatic genesis of the iron ore body of the lower Yushiwa iron deposit,and a hydrothermal genesis of magnetite veins in monzonite and crystalline limestone.The iron deposit experienced a continuous transition from magma genesis of the lower part to hydrothermal genesis of the upper part.According to these characteristics,we believe that the iron ore slurry contains a large amount of fluid to form the"iron bearing melt-fluid".Under fluid overpressure,the"iron bearing melt-fluid"rises rapidly from the magmatic conduit to arrive at the shallow part of the crust,forming high-temperature high-Ti magnetite in the lower part and transitioning to high-Si magnetite of fluid crystal in the upper part of the deposit.We call this metallogenic model a magmatic conduit metallogenic system.

关 键 词：邯邢铁矿 高钛磁铁矿 高硅磁铁矿 含矿熔体-流体流 岩浆通道成矿系统 

分 类 号：P618.31[天文地球—矿床学] P578.46[天文地球—地质学]