【作者】 李林；

【导师】 郑绵平； 倪培；

【作者基本信息】 南京大学 ， 矿物学、岩石学、矿床学， 2016， 硕士

【摘要】 闽西南永梅-拗陷带位于华夏地块东端,是华南重要的铁钼多金属成矿带。龙凤场大型铁矿、洛阳大型铁矿及马坑超大型铁矿均位于该成矿带中。前人对这些矿床进行了地质地球化学方面的研究,但是对成矿流体演化、磁铁矿化机理及矿床成因类型等方面研究极其薄弱,尤其是马坑铁矿。本文选择马坑铁矿作为重点研究对象,在详细的野外地质调查基础上,结合室内对矽卡岩矿物与矿石矿物生成顺序的划分及不同阶段中流体包裹体的岩相学观察,开展流体包裹体地球化学、同位素地球化学及磁铁矿矿物化学的研究,探讨成矿流体来源与演化、磁铁矿化与流体作用的关系及矿床成因类型。马坑铁矿赋存于中石炭统经畲组-下二叠统栖霞组大理岩中,围岩发育大量矽卡岩化。该铁矿矿化过程经历了无水矽卡岩阶段(石榴子石-透辉石)→含水矽卡岩-磁铁矿阶段(角闪石-绿泥石-钙铁辉石-磁铁矿±钙锰辉石±绿帘石)→硫化物阶段(石英-方解石-萤石-方铅矿-闪锌矿±绿泥石)→碳酸盐岩阶段(石英-方解石)。含水矽卡岩-磁铁矿阶段的磁铁矿具有较低Ti+V及较高Ca+Al+Mn。含水矽卡岩-磁铁矿阶段的钙铁辉石中流体包裹体类型主要包括含NaCl子晶三相包裹体和富气相两相包裹体,它们拥有相似的均一温度(分别为458～587℃和451～512℃)和相差很大的盐度(分别为26.5～48.4 wt%NaCl equiv.和2.4～6.9 wt%NaCl equiv.),表明该阶段流体发生沸腾作用。硫化阶段中石英、萤石及方解石包裹体类型主要为富液相两相包裹体,具有明显低的均一温度和盐度,分别变化于182～343℃和1.9～20.1 wt%NaClequiv.之间,表明流体发生混合作用。无水矽卡岩阶段中石榴子石(δ18Ofluid=6.2～8.0‰和δD=-77～-101‰)、含水矽卡岩-磁铁矿阶段中磁铁矿(δ18Ofluid=6.7～9.6‰和δD=-96～-128‰)和硫化物阶段中石英(δ18 Ofluid=-0.85～-1.04‰和δD=-110～-124‰)的氢氧同位素研究结果表明无水矽卡岩阶段和含水矽卡岩-磁铁矿阶段的流体主要来自岩浆流体,而硫化物阶段的流体主要为岩浆水与大气降水的混合。含水矽卡岩-磁铁矿阶段和硫化物阶段中的流体包裹体和氢氧同位素研究结果表明流体沸腾作用导致马坑铁矿磁铁矿化形成,而流体混合导致硫化物的形成。综合以上研究,马坑铁矿早期磁铁矿化流体经历了沸腾作用,晚期硫化物矿化流体经历了岩浆水与大气降水的混合,磁铁矿的形成与流体沸腾作用有关,硫化物形成与流体混合作用有关,该矿的围岩蚀变、矿石成分、成矿流体及磁铁矿化学成分与典型矽卡岩铁矿床有相似之处,明显不同于火山沉积型矿床,应属于矽卡岩型铁矿床。更多还原

【Abstract】 Yong’an-Meizhou depression belt in Southwestern Fujian,geologically located in eastern part of Cathaysia Block,is an important Fe-Mo polymetallic belt in southeastern China.The belt hosts the large scale Longfengchang and Luoyang iron deposit,and the largest scale Makeng iron deposit.Although their geological and geochemical aspects have been investigated by many workers,other aspects such as ore-forming fluid evolution,magnetite mineralization mechanism,and ore deposit genesis have been rarely studied intensively,especially for the Makeng iron deposit.Therefore,on the basis of detailed field investigation,combined with the paragenetic relationship between skarn mineral and ore mineral and fluid inclusions petrographic observation,this paper selected the Makeng iron deposit to carry out on fluid inclusion geochemistry,stable isotope geochemistry,and magnetite mineral chemistry,in order to discuss ore fluid genesis and evolution,magnetite mineralization mechanism,and ore deposit genesis.The Makeng deposit is hosted in marble of Jingshe Formation-Qixia Formation.The host rock develops voluminous skarn mineral alteration.The mineralization process in the Makeng area have undergone anhydrous skarn stage(stage 1)(garnetdiopside)→hydrous skarn-magnetite stage(stage 2)(amphibole-chloritehedenbergite-magnetite±johannsenite±epidote)→sulfide stage(stage 3)(quartzcalcite-fluorite-galena-sphalerite±chlorite)→carbonate stage(stage 4)(quartzcalcite).Magnetite in the hydrous skarn-magnetite stage shows lower contents of Ti+V and higher contents of Ca+Al+Mn.Hedenbergite in the hydrous skarn-magnetite stage consist of halite-bearing three phase inclusions and vapor-rich two phase inclusions,with similar homogenization temperatures(458 to 587℃ and 451 to 512℃,respectively)and contrasted salinities(26.5 to 48.4 wt%NaCl equiv.and 2.4 to 6.9 wt%NaCl equiv.,respectively),indicating fluid boiling took place in this stage,whereas quartz,calcite,and fluorite in the sulfide stage contain liquid-rich aqueous inclusions with a lower temperature and lower salinity of 182 to 343℃ and 1.9 to 20.1 wt%NaCl equiv.,suggesting fluid mixing occurred in this stage.H-O isotopic compositions of garnet(δ18Ofluid=6.2 to 8.0 ‰ and δD=-77 to-101 ‰)in the anhydrous skarn stage,magnetite(δ18Ofluid=6.7 to 9.6 ‰ and δD=-96 to-128 ‰)in the hydrous skarnmagnetite stage,and quartz(δ18Ofluid=-0.85 to-1.04 ‰ and δD=-110 to-124 ‰)in the sulfide stage indicate that ore-forming fluid responsible for the magnetite formation was derived from magmatic water and for the sulfide formation was generated by mixing between magmatic water and meteoric water.Fluid inclusions and H-O isotopic results indicate fluid boiling induced formation of magnetite mineralization,whereas fluid mixing resulted in formation of sulfide mineralization.Over all,ore fluid in the Makeng area experienced fluid boiling in the early magnetite mineralization stage and then fluid mixing between magmatic water and meteoric water in the later sulfide mineralization stage.The former resulted in formation of magnetite and the latter resulted in formation of sulfide.The making iron deposit shares a number of common features with typical skarn deposit,such as wall rock alteration,mineralization process,ore-forming fluid,and magnetite mineral chemistry,marked different from volcanogenic massive deposit,indicating a skarn type iron deposit.更多还原