【作者】 张成；

【导师】 毛景文； 李延河；

【作者基本信息】 中国地质大学(北京) ， 矿物学、岩石学、矿床学， 2012， 硕士

【摘要】 宁芜盆地地处扬子板块北缘，西临郯庐断裂带，属长江中下游成矿带中发育的继承性火山岩断陷盆地。梅山铁矿床是宁芜盆地中典型的大型铁矿床，具有品位高、储量大等特点。目前关于矿床成因仍存在争议，主要成矿观点包括火山期后气、液交代矿床（张荣华等，1977），矿浆热液矿床（陈毓川，1981；袁家铮等，1997），类矽卡岩型矿床（毛景文等，2012），对该矿床的地质地球化学特征及矿床成因的研究具有科研及生产的双重价值。本文在前人研究基础上，对梅山铁矿进行了细致野外地质调查，开展了岩相学、矿相学、元素地球化学、同位素地球化学等工作，研究了梅山铁矿床地质地球化学特征及成因，并得到以下新认识：矿床主矿体内含大量矽卡岩型矿物，具有类矽卡岩成因成矿特点；边部网脉浸染状矿石具有热液交代特征。该矿床成矿经历了类矽卡岩阶段、网脉浸染状磁铁矿阶段、石英硫化物阶段及碳酸盐阶段。类矽卡岩成矿阶段是主成矿阶段，主要形成块状和斑点状磁铁矿矿石。矿床中磁铁矿稀土元素Eu为负异常，与辉长闪长玢岩稀土元素特征相似，表明梅山铁矿床磁铁矿与辉长闪长玢岩可能同源，为同一火山旋回之产物。矿床中黄铁矿的δ34S范围分布在8.9‰-14.3‰，平均值为11.9‰，较典型岩浆硫的值明显偏高；石膏的δ34S值为18.5‰-23.3‰，平均值为21.43‰，具海相硫酸盐的典型特征。表明矿床中硫化物及硫酸盐的S均来自于三叠纪膏岩层，硫化物由SO2-4还原形成，不排除少量硫来自岩浆热液的可能性。矿床中菱铁矿δ13CV-PDB值为0.1‰-0.9‰，平均0.5‰，方解石δ13CV-PDB值为-5.3‰-1.6‰，平均为-1.12‰，具海相碳酸盐的典型特征，表明成矿后期形成的菱铁矿及方解石中碳主要来自下部地层中的海相碳酸盐，少部分可能来自于热液，这与硫同位素研究结果完全一致。岩浆/热液在上升侵位过程中同化混染了膏盐层中的硫酸盐、碳酸盐和石盐；硫酸盐与岩浆和热液中的Fe2+反应形成磁铁矿/赤铁矿富集成矿，硫酸盐自身则被还原形成硫化物；碳酸盐与硅酸盐岩浆反应则形成矽卡岩；石榴石等矽卡岩矿物普遍发生了强烈的菱铁矿化，产出位置远离碳酸盐地层，与典型矽卡岩型矿床存在明显差异。综上所述，梅山铁矿床应属于类矽卡岩型-热液交代型铁矿。更多还原

【Abstract】 ^Located in the north margin of Yangtze plate and west of the Tan-Lu fault zone,Ningwu basin is the succession volcanic rift basin in middle-lower Yangtze RiverValley metallogenic belt. Meishan iron deposit is a typical large iron ore deposit inNingwu basin with the characteristics of high grade and large reserves. Its ore genesisremains controversial, the main metallogenic point of view including the post-volcanic gas, liquid metasomatic deposit（Zhang et al.，1977）pulp hydrothermaldeposits（Chen，1981；Yuan et al.，1997）skarn-like deposit（Mao et al.，2012）the research on geological, geochemical characteristics and genesis of this deposithave the double value both of research and production.On the basis of previous studies, this paper conducted a detailed fieldgeological survey and mineral petrography, geochemistry, isotope geochemistry onMeishan iron deposit, researched on its geological, geochemical characteristics andore-forming process, and achieved new understandings as follows:The main ore body of the deposit contained a large number of skarn mineralswith skarn-like metallogenic characteristics；its edge net-vein disseminated ores havethe hydrothermal feature. This deposit experienced a skarn-like stage, net-veindisseminated magnetite stage, quartz sulfide stage and carbonate stage. In which thestage of forming the massive and spotted structure magnetite ore skarn-like stage isthe main mineralization stage.The rare earth elements of magnetite in this deposit showing a Eu negativeanomaly, compared with the previous measure of rare earth elements characteristics ingabbro-diorite porphyry indicating that Meishan iron deposit magnetite andgabbro-diorite porphyry are homologous as the product of the same volcanic cycle.Theδ34S value of pyrite in the deposit range from8.9‰to-14.3‰, with anaverage of11.9‰; theδ³⁴S of pyrite in the deposit range from18.5‰to23.3‰,with an average of21.43‰. The sulfur isotope geochemistry studies have shown thatsulfide and δ³⁴S of sulfates in the deposit are both from the Triassic gypsolyte, sulfurcompounds formed by the reduction of SO₄^2-,and it may include the possibility of asmall amount of sulfur from magmatic hydrothermal. Theδ¹³CV-PDBvalue of siderite in the deposit varies form0.1‰to0.9‰,withan average of0.5‰; δ18OV-SMOWvalue range from15.3‰to17.7‰, with anaverage of16.8‰. Theδ13CV-PDBvalue of calcite in the deposit varies form-5.3‰to-1.6‰, with an average of-1.12‰; δ¹⁸OV-SMOWvalue range from16.7‰to18.9‰, with an average of17.86‰. The carbon and oxygen isotope geochemistry studieshave shown that the carbon in formation of siderite and calcite in the late stagemineralization is mainly the marine carbonate source， and experienced thehydrothermal water-rock reactions，is the superimposition of late hydrothermalformation and a small portion of which may come from the hydrothermal.In summary and by comparing Meishan iron ore deposit with typical skarndeposits we can come to the conclusion that the formation of main ore body inMeishan iron ore deposits and general skarn-type deposits are quite different andshould be classified as skarn-like hydrothermal metasomatic mineralization.更多还原