【作者】 江满容；

【导师】 张均；

【作者基本信息】 中国地质大学 ， 矿产普查与勘探， 2014， 博士

【摘要】 宁芜盆地、庐枞盆地及攀西地区是我国陆相火山岩型铁矿研究的重要基地,而此类矿床中的矿石是在特定的地质条件下经过漫长的成矿过程演化而形成的,记录着成矿作用的相关信息。宁芜-庐枞地区铁矿床的赋矿岩体为一套晚侏罗世-早白垩世的中酸性次火山岩,其中以出露于地表-30m以下的宁芜梅山铁矿和地表-600m以下庐枞泥河铁矿为典型代表；而攀西地区平川铁矿的赋矿岩体为一套晚二叠世-早三叠世基性-超基性的次火山岩,矿体出露地表。泥河→梅山→平川铁矿的赋矿次火山岩体依次为偏酸性→中性→基性-超基性。三个矿床虽然都是陆相火山岩型铁矿,但是产出的地质背景、赋矿岩体、控矿构造、成矿作用、成矿流体及矿石组构等方面都有所差异。本次研究,以宁芜盆地梅山铁矿床、庐枞地区泥河铁矿床以及攀西地区平川铁矿床为研究对象,在矿相学理论指导基础上,进行系统的矿石组构学研究,并结合矿床地球化学和流体地质学等理论知识,选择具代表性的标型矿物组合通过探寻其物理性质、化学成分、流体性质及同位素组成在不同成矿环境的指纹信息,反馈不同成矿地质作用对标型矿物形成的制约作用,旨在揭示不同陆相火山岩系列的铁矿床在成矿作用过程中的共性及差异性。本次研究对深入认识陆相火山岩铁矿成矿作用,总结完善该类型铁矿床的成矿规律研究及推动深部找矿具有重要的意义。本次研究成果如下：(1)矿石组构学梅山铁矿早阶段伴随有网脉浸染状磁铁矿矿化,形成浸染状、网脉状贫矿体,晚阶段发生富矿流体的充填,形成块状富矿体；中期蚀变作用阶段磁铁矿发生赤铁矿化等,形成假象-半假象赤铁矿。典型矿石结构主要有自形-半自形粒状结构、它形粒状结构、交代结构、脉状-网脉状结构、格状结构、共结边结构、生长环边结构等。泥河铁矿矿石构造主要有浸染状构造、块状构造、斑杂状构造、细脉浸染状构造、网脉状构造,矿石结构主要有自形-半自形粒状结构、它形粒状结构、交代结构、格状结构、脉状-网脉状结构等。平川铁矿矿山梁子矿段和道坪子矿段的矿石构造主要有致密块状构造、浸染状构造、角砾状构造、脉状-网脉状构造,矿石结构主要有自形-半自形粒状结构、似海绵陨铁结构、交代结构、包含结构、碎裂结构。总体来说,陆相火山岩型铁矿床金属矿物主要为磁铁矿,其次赤铁矿、黄铁矿及菱铁矿。泥河铁矿床以次火山热液交代作用为主；梅山铁矿床以次火山热液交代作用为主,充填作用为辅；平川地区道坪子-矿段梁子矿段以充填成矿为主,交代作用为辅；平川烂纸厂矿段为火山沉积-变质成矿。(2)成矿期及成矿阶段的划分泥河铁矿和梅山铁矿都经历了三个成矿期,包括晚期岩浆结晶分异期,气水-热液成矿期和表生氧化期。泥河铁矿床的气水-热液成矿期可分为碱交代作用阶段、硬石膏-透辉石-磁铁矿化阶段、铁硫-钙充填交代阶段及硅化-泥化水热交代阶段。梅山铁矿在岩浆成矿期已经开始富集成矿物质,可进一步划分为岩浆结晶分异阶段、碱性长石化阶段及硬石膏-(磷灰石)-磁铁矿-透辉石／石榴石阶段；气水-热液成矿期划分为硬石膏-(磷灰石)-黄铁矿-磁铁矿阶段、石英-黄铁矿-磁铁矿阶段、含水硅酸盐矿物叠加作用阶段、硬石膏-黄铁矿化阶段及硅化-泥化-碳酸盐化阶段。平川铁矿在不同矿段表现出不同的成矿类型。基本上,成矿期可划分为岩浆分异期(大杉树矿段)、火山喷发-沉积期(烂纸厂)、次火山热液期(矿山梁子、道坪子矿段)和后生改造期。(3)磁铁矿的成因特征①磁铁矿至少可分为三个世代：早期为细粒它形磁铁矿,呈稀疏浸染状分布于赋矿次火山岩体中；中期为硬石膏-透辉石-磷灰石-磁铁矿化阶段(梅山、泥河)或(金云母)(蛇纹石)-磷灰石-磁铁矿化阶段(平川)以浸染状-块状构造产出的磁铁矿石,磁铁矿呈细粒它形粒状结构：晚期为以硬石膏-石英/碳酸盐-磷灰石-磁铁矿阶段脉状-网脉状构造产出的粗粒-伟晶状磁铁矿(泥河)、致密块状磁铁矿(梅山)或细粒碳酸盐-(硫化物)-磁铁矿阶段以梳状构造(矿山梁子)产出的中粗粒磁铁矿。根据其产出组构特征,一般早期为岩浆结晶分异的产物；中期为次火山岩热液交代作用的产物,为主矿体的主要组成部分;晚期为热液充填成矿。②磁铁矿晶胞参数：梅山及泥河铁矿床的晶胞参数(ao为8.38892-8.39057nm和8.38630-8.38965nm)分布在接触交代和热液交代型磁铁矿范围内,应为热液交代成因。而平川铁矿(包括矿山梁子和道坪子)磁铁矿的晶格常数ao分别为8.392-8.395nm和8.391-8.398nm,显示磁铁矿主体为热液交代成因,部分可能为岩浆作用形成。③梅山铁矿早期深部辉长闪长玢岩中的磁铁矿属于富钛低镁型-富钛富钒型；而后期接触交代作用下形成的磁铁矿属于低钛富镁型-低钛富钒型。泥河铁矿早期磁铁矿颗粒为富钛低镁型-富钛富钒型；泥河铁矿中期浸染状磁铁矿为低钛低镁型-低钛富钒型；晚期粗粒脉状磁铁矿Ti02含量在1%左右波动,比较偏过渡类型。矿山梁子及道坪子主矿体磁铁矿石矿山梁子以低钛、低铝、高镁含量为特征。电子探针数据显示由泥河→梅山→平川,磁铁矿的TFeO、Fe2O3含量及Fe2O3/FeO值明显增加,FeO含量明显降低,这可能与成矿溶液中铁质含量、成矿作用形式及矿质沉淀的空间位置有关。④梅山铁矿磁铁矿TiO2、Al2O3、MgO和MnO的对数分布图显示,A1203略负向偏倚分布,MgO、TiO2和MnO均呈较明显的负向偏倚特征,与岩浆型磁铁矿相似,可能为该区后期磁铁矿继承了部分岩浆结晶分异期的元素。泥河铁矿磁铁矿MnO、MgO略具对数负向偏倚分布,整体与火山岩型磁铁矿较为相似。平川铁矿道坪子矿段整体与矽卡岩型磁铁矿较为相似,可能与成矿期后大量的碳酸盐交代作用有关。⑤磁铁矿TiO2-Al2O3-MgO, TiO2-Al2O3-(MgO+MnO)成因图解显示,平川矿山梁子及道坪子主矿体磁铁矿具明显的热液交代和接触交代作用特征,而烂纸厂为沉积变质作用而成；泥河铁矿特征值分布集中,为与中性岩浆有关的火山岩型-热液型过渡类型；梅山铁矿特征值分布非常分散,为明显的过渡性成矿。⑥不同类型矿床、不同矿石结构和构造产出的磁铁矿TiO2-Al2O3-(MgO+MnO)成因图解也具有一定规律性。梅山铁矿磁铁矿为与火山岩有关的岩浆期后热液作用成矿,脉状矿石为岩浆期后矿质充填形成,以它形细粒结构集合体为特征；角砾状矿石及块状矿石则是早期热液交代萃取围岩中的铁质,晚期矿质大规模沉淀而成,该作用过程中发育区内最广泛的浸染状磁铁矿化,磁铁矿受后期热液作用的影响而被交代溶蚀呈残余结构。泥河铁矿磁铁矿主要分布于Ⅱ、Ⅲ、Ⅳ区的过渡区间,角砾状构造→浸染状构造→斑杂状构造→伟晶状构造→致密块状构造→网脉浸染状磁铁矿石中磁铁矿由火山岩型→岩浆型→热液型逐渐过渡,但浸染状磁铁矿石、伟晶状磁铁矿石及块状磁铁矿石受热液交代混染分布略分散。从磁铁矿产出结构特征来看,细粒它形结构与交代残余结构磁铁矿主要为火山岩型,粗粒自形-它形粒状结构磁铁矿偏向于热液成因,与区内以次火山岩-热液成矿特征较为一致。平川矿山梁子及道坪子矿段磁铁矿几乎都分布于矽卡岩型区域内,仅道坪子矿段发育的浸染状、细脉状磁铁矿石受地层混染而有向热液型过渡的趋势,矿山梁子矿段应该为富铁质矿浆沿本区火山机构及区内构造薄弱面充填成矿,受区内碳酸盐围岩影响。烂纸厂矿段磁铁矿为典型的沉积变质成因类型。⑦磁铁矿H-O稳定同位素：梅山磁铁矿H-O同位素特征显示成矿热液总体显示岩浆水(5DH2O=-73-84%o,δ18OH2O=6.68-8.9‰)的特征,大气降水混入不明显。泥河磁铁矿H-O同位素特征表明主成矿阶段的流体主要为岩浆水,成矿晚阶段则主要为天水。平川磁铁矿δ18OMt介于5.6-10.3‰之间,明显区别于岩浆型磁铁矿和沉积变质型磁铁矿,与辉长质岩浆(δ180=5.5～7.4‰)相近,说明形成磁铁矿的氧与深部岩浆源具有亲缘关系。成矿热液中的水主要来源于岩浆体系,和区内岩浆活动密切相关,但因碳酸盐脱碳作用而具有低δD和高δ180特征。(4)蚀变-矿化分带规律梅山铁矿围岩蚀变空间上,自下而上,分为岩体深部浅色蚀变带、接触带附近深色蚀变带和上部安山质火山岩中浅色蚀变带,磁铁矿化开始于岩体深部浅色蚀变带,在接触带附近深色蚀变带富集。泥河铁矿床矿体,自下而上分为①下部浅色蚀变带、②深色蚀变带、③叠加蚀变带及④上部浅色蚀变带。分别对应钠长石化、紫色硬石膏-透辉石-(磷灰石)-磁铁矿化、含石英-赤铁矿-(菱铁矿)-浅色硬石膏-黄铁矿化及硅化-泥化。次生石英岩化是磁铁矿化的远程指示性蚀变,膏辉岩化出现在近矿和容矿蚀变带,钠长石化大规模发育标志铁矿化作用的开始,亦即深部找矿勘探的终止。平川铁矿的道坪子矿段V号矿体产于辉长岩体与碳酸盐岩接触带,具充填交代成因,围岩蚀变相对较为发育,可划分为4个蚀变带：①蛇纹石化大理岩带、②金云母-蛇纹石-磁铁矿化带、③金云母-透闪石化带、及④绿帘石-阳起石-透辉石化带。各蚀变带渐变过渡,向接触带两侧蚀变程度逐渐减弱。金云母-蛇纹石-磁铁矿带是主要赋矿部位,主要发育在细粒辉绿辉长岩中,金云母和蛇纹石是近矿围岩蚀变标志。(5)蚀变-矿化作用过程中的元素迁移本次研究的陆相火山岩型铁矿中泥河铁矿具有保存最完整及最典型的蚀变分带特征,因此选取其作为研究对象,对蚀变-矿化作用过程进行探讨,分析元素迁移规律。针对泥河铁矿床蚀变矿化带对蚀变岩主量元素分析,以早期蚀变岩石为原岩与稍晚期蚀变岩石的不活动元素拟合最佳等浓度方程,采用改良后的等浓度图法(The Isocon Diagram)来定量探讨蚀变过程中元素迁移特征。早期碱交代作用阶段以Na质富集为主,代表着铁矿化作用的开始。Fe质迁移与Na质富集为负相关,与P富集呈正相关关系。深色蚀变带以铁、镁、钙交代作用为主,膏辉岩以强烈富集Ca、Mg,弱富集Fe、Si为特征,为磁铁矿化过程富集Fe、P提供物质基础。叠加蚀变带以铁、硫、钙充填交代作用为主,早期赤铁矿-(菱铁矿)-硬石膏-黄铁矿化过程伴随强烈的硅酸盐矿物绿泥石化、绿帘石化水解,富集Fe、P、S和LOI,强烈亏损Ca、Mg；黄铁矿-硬石膏化蚀变岩以强烈富集Ca、Sr和Ba,强烈亏损Al、Si、K、Mg和Na,较亏损P为特征,Ba、Sr等大离子亲石元素富集可能与硬石膏大规模沉淀有关。上部浅色蚀变带以硅、钾、铝水热交代作用为主,水云母-高岭土带富集K、Al,而早期蚀变迁移出的Si质则在次生石英岩化带沉淀形成硅质岩壳,磁铁矿化强度与硅化强度呈正相关关系,区内硅质的大规模沉淀标志着铁矿成矿作用过程全部结束。在整个矿化作用过程中Ti仅在磁铁矿大规模沉淀时发生类质同象置换而迁移,在其它蚀变过程中均以不活动组分存在。钠长石化的大量出现标志着铁矿化的开始；膏辉岩化是近矿和容矿蚀变；次生石英岩化是远程指示性蚀变。泥河铁矿床早期发育于辉石粗安玢岩体中的蚀变矿化过程微量稀土元素未发生明显的迁移。由辉石粗安玢岩内带至砖桥组粗安岩,微量-稀土元素逐渐降低,指示着稀土元素由内带向外带运移,亦指明了热液流体的运移方向。综上所述,陆相火山岩型铁矿床矿石组构学特征、磁铁矿成因标型特征及蚀变-矿化分带特征显示,铁质来源与岩浆岩密切相关。中性和基性-超基性火山岩系列铁矿床产出于火山岩体内部或接触带部位,铁矿体以交代充填成矿为主,均发育浸染状矿化、块状矿化及脉状-网脉状矿化,局部发育角砾状矿化。由于矿体产出位置及成矿环境差异导致产出不同类型矿石组构特征及磁铁矿类型。磁铁矿化学成分特征表明浸染状细粒它形磁铁矿颗粒具有火山岩型或岩浆型-热液型过渡特征,说明其对火山岩中的铁质具有继承性特征。通过研究泥河铁矿各蚀变矿化带的元素迁移规律结合区内成矿流体特征,探讨了陆相火山岩型铁矿床成矿作用过程及矿床形成机制,并建立了蚀变-矿化模型。更多还原

【Abstract】 The Ningwu Mesozoic volcanic basin, Luzong Mesozoic volcanic basin, and Pan-Xi region widely developed continental volcanic rock-hosted iron deposit.This type of iron deposit suffered a long metallogenic evolution under multiple specific geological conditions. Study its metallogenesis can provide information that is helpful for us better understandind the mechanism of continental volcanic rock-hosted iron deposit.The host rocks in Ningwu-Luzong basin are a group of intermediate to acid subvolcanic rocks formed in late Jurassic to early Cretaceous, of which are well outcropped in Meishan deposit and Nihe deposit. By contrast, the host rocks of Pingchuan deposit in Pan-Xi region are a group of basic-ultrabasic subvolcanic rocks which formed in late Permian to early Triassic. The lithology of ore host subvolcanic rock in Nihe, Meishan and Pingchuan ranges from acidic to ultrabasic type. The three deposits differences in geological setting, host rocks, ore-controlling structures, mineralization, ore-forming fluids and ore structures.This paper takes Meishan iron deposit in Ningwu basin, Nihe Fe deposit in Luzong basin, Pingchuan Fe deposit in Pan-Xi region as the main research targets. Base on the mineralogy, geochemistry, ore-forming fluids, and typomorphic mineral assembles, this paper focus in the different metallogenic environment, including chemical compositions, physical and chemical properties, fluids features and isotopic compositions, which constrain from typomorphic minerals. Studies of continental volcanic rock-hosted iron deposit and explore their metallogenic commonness and differences_are vital to conclude the metallogenic regularities. It is also valuable in promoting the mineral prediction and deep mineral exploration. Major achievements are as follows:(1) Ore fabricIn the early stage, the Meishan Fe deposit is accompanied by disseminated magnetite stockwork mineralization and forming disseminated, stockwork lean ore; in the late stage, ore-forming fluids filling and massive ores; during interim alteration stage, hematitization happened and produce martite. The typical ore textures mainly consist of euhedral-subhedral grain, anhedral grain, metasomatic texture, vein-stockwork texture, trellis texture, growth rim texture and so on.The structure of Nihe Fe deposit mainly includes disseminated, massive, mottled, veinlet and stockwork. Textures mainly consist of euhedral-subhedral grain, anhedral grain, metasomatic texture, trellis texture, vein-stockwork texture and so on.There are several ore blocks in the Hirakawa Fe deposit, including the kuangshanliangzi, the daopingzi and so on. Ore structures in this deposit mainly include dense massive, disseminated, brecciated, and vein-stockwork structures. Ore textures mainly consist of euhedral-subhedral grain, sponge iron meteorite-like, metasomatic, containing and fragmentation textures.Overall, the metallic minerals of continental volcanic-type iron deposits include magnetite, hematite, pyrite and siderite. The Nihe Fe deposit is mainly related to subvolcanic hydrothermal metasomatism; the Meishan Fe deposit is mainly related to subvolcanic metasomatism with cavity filling; the daopingzi-kuangshanliangzi ore block in Hirakawa area is mainly related to cavity filling with metasomatism.(2) Division of mineralization period and mineralization stageThe Nihe and Meishan Fe deposits have experienced three mineralization periods:The late magmatic period, gas-water hydrothermal period and epigenetic oxidation period. The gas-water hydrothermal period occurs in Nihe Fe ore deposit can be divided into alkali metasomatism stage, anhydrite-diopside-magnetite stage, Fe-sulfur-calcium filling-metasomatic stage and silicification-argillization hydrothermal stage. During magmatic period, Meishan Fe deposit begun to have enrichment of metallogenic materials, and it can be divided into magmatic crystallization differentiation stage, alkaline feldspathization stage and anhydrite-(apatite)-magnetite-diopside±garnet) stage. Gas-water hydrothermal period can be divided into anhydrite-(apatite)-pyrite-magnetite stage, quartz-pyrite-magnetite stage, hydrous silicate minerals stage, anhydrite-pyritization stage and silicification-argillization-carbonation stage.The Pingchuan Fe deposit in different ore block showed different mineralization types. The mineralization period can be divided into magmatic differentiation stage (Dashanshu ore block), volcanic eruption-depositional stage (Lanzhichang ore block) and subvolcanic hydrothermal stage (Kuangshanliangzi and Daopingzi ore block) and epigenetic transformation stage.(3) Genetic features of magnetite①At least three stages of magnetite have been recognized:Anhedral fine-granular magnetite at Stage1was formed during the magmatic crystallization differentiation period, and mainly occur as sparsely disseminated in subvolcanic host rocks; disseminated and massive magnetite at Stage2was formed during the anhydrite-diopside-apatite-magnetite stage (e.g. the Meishan deposit and Nihe deposit) or (flogopite)-(serpentine)-apatite-magnetite stage (e.g. the Pingchuan deposit); course-granular vein-stockwork magnetite at Stage3was formed during the anhydrite-quartz (or carbonate)-apatite-magnetite stage (e.g. the Nihe deposit), dense blocky magnetite (e.g. the Meishan deposit) or medium-coarse granular pectinate structure were formed at fine-granular carbonate-(sulphide)-magnetite stage. Generally, according to the fabrics, Stage1was formed during magmatic crystallization differentiation period, Stage2was formed during the subvolcanic metasomatism and occupy the majority of the ore body; and Stage3was formed by hydrothermal filling.②Crystal cell parameters of magnetite:Crystal cell parameters of magnetite from the Meishan deposit (a0ranges from8.38892to8.39057nm) and the Nihe deposit (a0ranges from8.38630to8.38965nm) fall into the field of hydrothermal metasomatic type magnetite, which indicate its hydrothermal metasomatic genesis. By contrast, crystal cell parameters of magnetite from the Pingchuan Fe deposit (including Kuangshanliangzi and Daopingzi) ranges from8.392to8.395nm and from8.391to8.398nm, which suggest that the magnetite manily belong to hydrothermal metasomatic genesis, with a lesser amount of magmatic genesis.③Magnetite in diorite porphyry at deep depth of the Meishan Fe deposit at the early stage exhibit the high-Ti,-V and low-K characters, but magnetites which were formed during the contact metasomatism are characterized by high-Mg,-V and low-Ti characters. In the Nihe Fe deposit, magnetite at Stage1exhibits high-Ti,-V and low Mg characters; and high-V and low-Ti and-Mg at Stage2. But TiO2in course-granular magnetite fluctuated around1%, which is typical of the transitional type.④In the TiO2, A12O3, MgO and MnO logarithmic distribution diagram showing spot analyses of magnetite from the Meishan Fe deposit, A12O3compositions exhibit a slightly negative biased distribution, while TiO2, MgO and MnO compositions are negative biased distributed apparently, which are similar to the magmatic type magnetite. By contrast, the diagram of magnetite from the Nihe Fe deposit illustrate that MnO and MgO are negative biased distribution, which are similar to volcanic type magnetite in general. The distribution patterns in Daopingzi Fe deposit are similar to skarn type magnetite, which indicate the association between quantities carbonated metasomatism at late stage.⑤In the ternary plot of TiO2-Al2O3-MgO and TiO2-Al2O3-(MgO+MnO) discriminant diagram of magnetite, data from Kuangshanliangzi and Daopingzi tend to fall in the hydrothermal metasomatic and contact metasomatic region. Data from the Nihe Fe deposit are intensive, while those from the Meishan Fe deposit are dispersion.⑥Different types of ore deposits, ore texture and structure output of magnetite has a certain regularity in the ternary plot of TiO2-Al2O3-(MgO+MnO) discriminant diagram. The magnetite from the Meishan Fe deposit was magmatic hydrothermalism subsequently after the subvolcanic activity. Vein-stockwork structure ores were mineral filling during postmagmatic stage, which characterized by anhedral fine-granular aggregation; hydrothermal fluid in the early stage went through a composition exchange with the wall rock, which led to the precipitation of large quantities of iron and formed brecciated and massive ore, this stage is characterized by ubiquitous disseminated magnetite, most of the magnetite were residual dissolution as the consequence of late-stage hydrothermal metasomatism.Magnetite are mainly distributed in the transition zone of Ⅱ, Ⅲ, Ⅳ area in the Nihe Fe deposit. The genetic type of the magnetic gradually transform from volcanic type→magmatic type→hydrothermal type in breccia structure, disseminated structure, taxitic structure, pegmatitic structure, dense block structure and net vein disseminated iron ore. Disseminated, pegmatitic and dense block structure iron ore is heated fluid metasomatism contamination, and the distribution of the data is slightly scattered. From output texture characteristics, anhedral fine-granular and metasomatic relict texture magnetites were volcanic type. Genetic type of coarse grain structure magnetite towards hydrothermal origin, which was successively appear in the volcanic rock-hydrothermal ore-forming features. Magnetite in the ternary plot of TiO2-Al2O3-(MgO+MnO) discriminant diagram almost all distributed in the skarn type areac in Pingchuan Kuangshanliangzi and Daopingzi ore block. Kuangshanliangzi should be for the rich iron ore pulp filling mineralization along the volcanic mechanism and regional tectonic weak surface, which is affected by the carbonate rock in the area. Magnetite is a typical sedimentary metamorphism type in Lanzhichang ore block.⑦Stable isotope of Magnetite:Oxygen and hydrogen isotope analyses of magnetite from Meishan Fe deposit show the charecteristic of primary magmatic waters with little evolving of meteoric waters. The oxygen and hydrogen isotope results from the Nihe Fe deposit imply that primary magmatic waters contribute to the the hydrothermal fluid at the main metallogenic stage, while meteoric waters play an important role at the late stage. The δ18OMt values fall between5.6%o and10.3%o, which differ from magmatic type magnetite and sedimentary metamorphogenic type magnetite but similar to that of gabbroic magma (δ180=5.5-7.4%o). These results suggest that magnetite and deep magma chamber have similar source origin. Waters in metallogenic hydrothermal fluids are mainly from magmatic system, probably related to magmatic activity in the area. In addition, the metallogenic hydrothermal fluids tend to be low δD and high δ18O, due to decarbonization process.(4) Regularity of alteration-ore tumble beltThe wall rock alteration of Meishan Fe deposit can be divided into three parts from the bottom up, including light colored alteration belt at the deep of the rock, dark alteration belt near the contact zone, and light colored alteration belt in the andesitic volcano rock spatially. The magnetite begins in the light colored alteration belt at the deep of the rock, enriched in the dark alteration zone near the contact belt.The ore bodies of Nihe Fe deposit fall into lower light colored alteration belt, dark alteration belt, superimposed alteration belt and upper light colored alteration belt, from the bottom up, corresponding to albitization, purple anhydritization-diopsidization-(apatitization)--magnetite, quartz-hematitization-(sideritization)-light anhydritization-pyritization and silicide-argillization. Secondary quartzite is an indicative alteration of magnetite. Anhydrite pyroxenitization in the alteration zone is close to or contain the ore body. Large-scaled development of albitization marks the beginning of the iron ore mineralization, which implies the termination of deep ore exploration.The V ore body of Daopingzi ore block from the Pingchuan Fe deposit is located in the contact zone between gabbro and carbonatite, which is filling metasomatic genesis. The wall rock alteration is well developed, which can be divided into four alteration belts:serpentinization marble belt, phlogopite-serpentinization-magnetite belt, phlogopite-tremolitization belt, and epidotization-actinolitization-diopsidization belt. The four alteration belts change gradually, and the alteration degree show much weak on the marginal area of contact zone. The main ore-bearing are is the phlogopite-erpentinization-magnetite belt, which is situated in fine grained diabase-gabbro and is marked by phlogopite and serpentine alteration.(5) Elements migration in the process of alteration and mineralizationThe Nihe Fe deposit, as one of the research objects of this thesis and showing the well preserved wall rock alteration with clear and typical zoning, was selected for further study on the main and trace elements migration during the mineralization and alteration process. Based on the major elements analysis of alteration rocks, this study employed the alteration rocks in earlier stage as original rocks and then fitted the best concentration equation between slightly late alteration rock with immobile elements by Isocon Diagram method, to quantitatively reveal the main and trace elements migration in the process of hydrothermal alteration.The earlier alkali metasomatism stage was characterized by the enrichment of Na and represented the start of iron mineralization. The migration of Fe shows negative correlation with the enrichment of Na and positive correlation with enrichment of P. The dark color alteration zoning mainly includes the metasomatism of Fe, Mg, and Ca. The anhydrite-diopside alteration zone is characterized by strong enrichment of Ca and Mg, and slight enrichment of Fe and Si, which supply the material for the enrichment of Fe and P in the iron mineralization stage. The superimposed alteration zone mainly includes the filling and metasomatism of Fe, S, and Ca. The earlier mineralization stage of hematite-(siderite)-anhydrite-pyrite of the superimposed alteration accompanied strong hydrolysis alteration with chlorite and epidote of the silicate minerals, and showed enrichment of Fe, P, S, and LOI, and strong loss of Ca and Mg. The pyrite-anhydrite alteration rocks show strong enrichment of Ca, Sr, and Ba, and strong loss of Al, Si, K, Mg, and Na, and slight loss of P. The loss of Ba and Sr which are the large ion lithophile elements was probably caused by the formation of abundant anhydrite. The top light color alteration belt mainly consists of metasomatism of Si, K, Al, in which the hydromica-kaolin zone is characterized by the enrichment of K and Al. The abundant Si as the migration of earlier alteration formed the secondary quartzite shell. Fe mineralization shows positive correlation with the secondary quartzite. The formation of the abundant secondary quartzite indicates the finish of the Fe mineralization. In the whole hydrothermal alteration process, the Ti just migrated in the form of isomorphous substitution during the formation of abundant magnetite, and kept as immobile components in the other alteration processes.The formation of abundant albite indicates the beginning of Fe mineralization; the anhydrite-diopside alteration exists near the Fe orebodies, and the secondary quartzite alteration is the indicative alteration of long-distance.The trace and rare earth elements in the earlier alteration zones hosted in the trachyandesite porphyrite did not show apparent migration. However from the trachyandesite porphyrite to the trachyandesite of Zhuanqiao volcanic cycle, the trace and rare earth elements decreased gradually, indicating the migration of the hydrothermal fluid from inner to outer.In summary, the ore fabric, the magnetite typomorphic characteristics, and the alteration mineralization assemblage of the continental volcanic type iron ore deposit show that the source of iron is closely related to magmatic rocks. Neutral and basic-ultrabasic volcanic rock series iron ore deposits occur within the volcanic rock mass or contact with iron ore body, which is given priority to with metasomatic filling mineralization. They are dominated by magnetic iron ore with disseminated mineralization, block mineralization, vein-net mineralization, and locally breccia mineralization. Different occurence location and ore-forming environment resulted in different types of ore fabrics and magnetite ores. The chemical compositions characteristics of magnetite show that disseminated fine-grained granular magnetite has characteristics of volcanic type, or magma-hydrothermal type. The iron of the disseminated fine-grained magnetite in the volcanic rocks has characteristics of inheritance. Based on the iron ore element migration rule in the altered mineralization belt, in combination with characteristics of ore-forming fluid in the mineralization process, the alteration and mineralization model is set up. By studying element migration regularity of the altered mineralization belt, in combination with characteristics of ore-forming fluid of Nihe Fe ore deposit, and exploring the metallogenic process and formation mechanism of continental volcanic type iron ore deposit, the altered mineralization model is established.更多还原