【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， 2011， 硕士

【摘要】 泥河铁矿位于长江中下游成矿带的庐枞矿集区。庐枞地区是我国东部典型的陆相火山-岩浆活动区域,也是国土资源部确定的五个重点矿产勘查区之一。区内与陆相火山-岩浆活动有关的铁矿床是我国铁矿资源中的一种重要成因类型和主要产地。泥河铁矿是安徽省地质调查院在实施2007年度国土资源大调查《安徽庐江盛桥—枞阳横埠地区铁铜矿勘查》项目中的重大新发现。泥河铁矿的发现不仅突破了庐枞地区过去只限于400～500米的勘查深度,也预示了在长江中下游地区进一步开展深部找矿工作具有十分广阔的前景。以泥河铁矿床为对象,进行典型矿床成矿特征和成矿规律总结研究,对推动长江中下游成矿带深部找矿工作具有重要的理论及实践意义。本文以泥河铁矿床为主要解剖对象,罗河铁矿床作为补充研究,以成矿地质作用特征研究、矿田构造研究、成矿作用特征与成矿作用标志研究为重点研究内容,进行系统的矿床成矿地质背景及成矿地质特征,成矿年代学、流体地质学和矿田构造学等研究,从而限定成岩成矿年代,探讨流体的来源、成矿物质的来源、矿化富集规律等,最终厘定泥河铁矿床的成矿地质体,并进行矿床成因探讨。以上述研究为基础,以区域构造-建造-流体-成矿作用作为研究主线,以铁矿床与构造-火山-热事件在时间、空间配置和耦合关系作为研究的主要脉络,探索和总结泥河铁矿床的成矿作用特征、矿化时空结构特征和成矿规律,以进一步深化对陆相次火山热液型铁矿成矿机理和成矿模式的认识。通过室内外综合研究,本文取得了以下主要认识及成果：(1)通过岩石岩相学鉴定、岩石地球化学分析,表明庐枞地区火山岩、次火山岩主要为一套碱性-亚碱性玄武质粗面岩、粗安岩、粗面英安岩、碱玄岩等。岩石地球化学特征表明庐枞火山岩具Si02中等偏高、富碱、富钾、高铝贫钛的特征,且碱性长石化阶段,钾质明显被交代活化迁移出来。火山岩-次火山岩-侵入岩演化从早到晚,Si02与TiO2、Fe2O3、FeO、MgO、CaO、P2O5等呈负相关关系,Si02与A12O3、K2O、Na2O呈一定的正相关关系。庐枞火山岩及侵入岩分异指数表明二者分异趋势相同,为同源产物,与宁芜盆地中生代火山-次火山岩具有相同的岩浆演化特征。(2)庐枞火山岩微量元素相对原始地幔,明显富集Rb、Pb、Hf、Th等大离子亲石元素,Nb、Ti、Y等高场强元素及P元素相对亏损。火山岩及侵入岩微量元素原始地幔标准化蛛网图变化特征相似,说明泥河矿区的次火山岩体及正长-二长岩侵入岩体微量元素具有火山岩继承性结晶分异特征,且晚期岩浆分异程度加强,为一个完整的岩浆演化系列同源异相产物。(3)泥河矿区火山岩→次火山岩→侵入岩稀土元素配分曲线形态较相似,均呈相对平滑的右倾型。且轻重稀土明显分异,轻稀土富集,重稀土相对亏损,均具有轻稀土分馏程度明显高于重稀土分馏程度的特征,稀土元素分布形式可能与富集地幔的部分熔融及地壳物质的不同程度混染有关。(4)火山岩及侵入岩的Sr-Nd同位素和Pb同位素特征表明二者均来源于深部地幔,是岩浆分离结晶演化过程中的同源异相产物。(5)根据野外实地调查,结合室内系统岩相学鉴定,总结了泥河铁矿床围岩蚀变分带特征和相应的蚀变矿物分带特征,自下而上依次为：下部浅色蚀变带(辉石-钾长石-钠长石-磷灰石-硬石膏)→深色蚀变带(辉石-磷灰石-磁铁矿-硬石膏,局部可见石榴子石)→叠加蚀变带(磷灰石-磁铁矿-硬石膏-赤铁矿-黄铁矿)→上部浅色蚀变带(石英-高岭石-绿泥石-碳酸盐-水云母等)。(6)通过对成矿物理化学条件的分析总结,揭示泥河、罗河铁矿床磁铁矿具有多期矿化特征。晚期岩浆结晶分异形成的磁铁矿结晶温度范围(T)为：775～1152℃,氧逸度(f02)为：10-8.89～10-15.27；T=711.04～1114.39℃,ao2=1.86×10-8～3.61xl0-16(据R.Powell和M. Powell,1977),二者获得的温度及氧逸度范围基本一致,明显高于热液作用磁铁矿的形成温度。磁铁矿主成矿阶段为辉石-硬石膏-磁铁矿矿化阶段,成矿温度为350～506℃。氧逸度(f02)、硫逸度(fs2)和酸碱度(pH)等物理化学参数表明膏辉岩与磁铁矿都是在高氧高硫以及酸性环境共同作用下形成的,二者为同期产物,从岩浆作用晚期到热液蚀变作用晚期,成矿环境从高氧高硫弱酸性环境向低氧低硫强酸性环境演化。(7)运用高精度同位素定年技术锆石U-Th-Pb法对成矿岩浆的成岩年龄进行测定初步限定成矿年代为128～134Ma之间,综合国内外成岩成矿理论、庐枞地区各矿化类型的成矿演化序列以及相关年代学数据可合理地进一步约束泥河铁矿的成矿时限为132～131Ma,从而建立起庐枞盆地成岩成矿的时间结构。(8)通过前人资料分析及同位素地球化学分析,铁矿床中的磁铁矿与庐枞盆地火山岩中磁铁矿氧同位素特征表明矿石中的氧化铁和火山岩中的氧化铁可能属同一来源,铁矿质是火山岩经交代作用淬取出来的,铅同位素具深部流体来源特征。泥河-罗河铁矿床成矿热液的硫可能部分来自断陷盆地下伏的地层,特别是三叠纪周冲村组海相硬石膏层,其余为岩浆携带的来自深部的。根据石英-水氧同位素分馏作用与温度的函数关系得出暗色蚀变阶段和磁铁矿生成阶段的水属岩浆水范围,而浅色蚀变黄铁矿化阶段可能有天水参加。(9)根据泥河铁矿床矿体产出特征、矿石组构学特征、围岩蚀变及矿化蚀变特征、成岩成矿时代、成矿物质来源等讨论分析认为泥河-罗河铁矿床为陆相次火山岩浆—热液型矿床成因,闪长玢岩是铁矿床的成矿母岩。(10)根据野外宏观地质调查及室内微观鉴定测试分析,对泥河铁矿床进行矿床地质特征及成矿地质要素总结分析,认为矿体赋存位置明显受地层-构造-岩浆建造的综合控制,成矿作用与构造-岩浆-热事件有关,区内围岩热液蚀变对矿化富集具有重要的促进作用。(11)以上述认识为基础,初步总结了庐枞地区陆相次火山岩型铁矿床的时空分布规律,初步厘清构造-岩浆-流体-成矿关系,建立了庐枞盆地陆相次火山岩型铁矿床综合成矿模式,为研究区找矿提供重要的理论依据。更多还原

【Abstract】 Nihe iron ore deposit is located in the Yangtze River metallogenic belt of Luzong ore district, which is one of five key mineral exploration areas identified by the Ministry of Land and Resources. Luzong region is a typical continental volcanic-igneous activity area in easten China, where continental volcanism-magmatic activity related to iron ore deposits is an important genetic type and the main producer in China’s iron ore resources. Nihe iron is a significant new discovery which is in the implementation of land resources survey project "Sheng Bridge-Zongyang Hengbu area iron-copper exploration in Lujiang, Anhui province."by Geological Survey of Anhui Province in 2007. The discovery of Nihe iron ore deposit not only breakthrough Luzong area past confined to only 400 to 500 meters depth exploration, but also indicates further deep prospecting work has very broad prospects in the Yangtze River. Nihe iron ore deposit as an typical object to do research into metallogenic characteristics and metallogenic regularity summarized, which has important theoretical and practical significance on the promotion of the Yangtze River metallogenic belt deep prospecting work.This paper is targeted on Nihe iron ore deposit as the main anatomical object, Luo River iron ore deposits as a supplementary study, which to focus research on the content of characteristics of geological metallogenesis, structure of ore field, characteristics of mineralization and mineralization signs study. Then having systematic study on metallogenic geological setting and metallogenic geological features, geochronology, fluid geology and tectonics ore field and so forth, which to limit the age of diagenesis and mineralization, and to confer the source of fluid, the source of minerals, enrichment rules of metallogenesis, etc. Ultimately determining the Nihe iron ore deposits geological body and deliberating the genesis. On the basis of the above-mentioned study, dealing the research with the regional structure-construction-fluid-mineralization as the main line, the iron ore deposits and structural-volcano-hot events in time-space configuration and the coupling relationship as the primary context, to explore and summarize characteristics of mineralization, space-time structure of mineralization and metallogenic regularity, and to further deepen knowledge of the continental sub-volcanic hydrothermal iron ore-forming mechanism and mineralization model. Through the comprehensive study of indoor and outdoor, the paper have made made the following main understanding and results: (1) Though rock microphysiography identification, rock geochemical analysis shows that Luzong region volcanic-sub-volcanic rocks are mainly a set of alkaline-sub-alkaline basaltic trachyte, trachyandesite, rough dacite, tephrite and so on. Geochemical features indicate that Luzong volcanic rocks with medium to high SiO2, alkali-rich, potassium-rich, high-aluminum and titanium-poor characteristics. Potassium was significantly to be metasomatism, mobilization and migration out from rock in the mineralization stage of alkali feldspar. Volcanic rock-sub-volcanic-intrusive rock evolution from morning till night, SiO2 and TiO2, Fe2O3, FeO, MgO, CaO,P2O5, etc.was negatively correlated, but SiO2 and A12O3, K2O, Na2O showed a certain positive correlation.In Luzong region, the volcanic and intrusive rocks differentiation index showed both of them have the same differentiation trend, they are the homologous products, and also has the same magma evolution characteristics with mesozoic era volcanic-subvolcanics in Nanjing-Wuhu basin.(2) Luzong volcanic trace elements relatively primitive mantle, significantly enriched in Rb, Pb, Hf, Th and other large ion lithophile elements, but Nb, Ti, Y,et al. high field strength elements and P element are relatively depleted, the variation characteristics between volcanic and intrusive rocks trace elements relatively primitive mantle-normalized spider diagrams is similar,which showed that sub-volcanic body and syenite-monzonite intrusions trace elements in Nihe mining area have characteristics of succession with volcanic features of crystallization differentiation, and the advanced degree of the late magmatic differentiation enhancing. It is the homologous heteropic phases product with a complete magmatic evolution series.(3)The REE curves shape about volcanic,subvolcanic and intrusive rocks in Nihe mining area is similar,which all showed a relatively smooth Right type. LREE and HREE clear differentiation, LREE enriched, HREE loss, and all rocks have the characteristics of light rare earth fractionation significantly higher than the heavy REE fractionation. REE distribution patterns may be related to partial melting of enriched mantle and crustal material of different degree of contamination.(4) the Sr-Nd isotopes and Pb isotopes showed that both volcanic and intrusive rocks are derived from the deep mantle, and both are the homologous heteropic phases product of fractional crystallization of magma evolution.(5) According to field survey, combined with the systematic indoor petrographic identification,summed up the characteristics of rock alteration zoning and the corresponding alteration mineral zoning in Nihe iron ore deposit, bottom-up as follows:the lower light-colored alteration zone (pyroxene-potassium feldspar-albite-apatite-anhydrite)→dark alteration zone (pyroxene- apatite-magnetite- anhydrite,and local shows garnet)→superimposed alteration zone (apatite-magnetite- anhydrite- hematite-pyrite)→upper light-colored alteration zone (quartz- kaolinite- chlorite- carbonate- Hydromica,etc.).(6) Through analyzed and summarized the physical and chemical conditions of mineralization, revealing that the magnetite of Nihe and Luo River iron ore deposits have the features of multi-stage mineralization. The formation of late magmatic fractional crystallization of magnetite crystallization temperature (T) is:775～1152℃, oxygen fugacity (fo2) is: 10-8.96～10-15.27 (according to Buddington and Lindsley,1964); T=711.04～1114.39℃, aO2=1.86×10-8～3.61×10-16(according to R. Powell and M. Powell,1977). Both methods obtained almost the same range of temperature and oxygen fugacity, which significantly higher than the formation temperature of hydrothermal magnetite. The main magnetite mineralization stage is pyroxene-anhydrite-magnetite mineralization stage, forming temperature is 350～506℃. Oxygen fugacity (fo2), sulfur fugacity (fs2) and acidity-basicity (pH) and other physical and chemical parameters indicate that pyroxenite and magnetite are the product for the same period,which formed under the combined action of high sulfur, high oxygen and acid environment. From the late magmatic to late hydrothermal alteration,ore-forming environment evolution from weak acidic environment of high oxygen sulfur into hypoxia-low sulfur and strongly acidic environment.(7) Using high-precision zircon dating technique U-Th-Pb method to determine the diagenetic age of magmatic mineralization, preliminary limit the metallogenic chronology is between 128～134Ma. To synthesize diagenetic mineralization theory at home and abroad and the metallogenic evolution sequence of mineralization types and associated chronology data in Luzong region can be further constrained reasonable time limit for Nihe iron ore deposit mineralization of 132～131Ma. So as to establish the temporal structure of metallogenic Luzong basin.(8) By the previous data analysis and isotope geochemistry, the oxygen isotope characteristics of magnetite in the magnetite ore deposit and magnetite in volcanic rocks of Luzong Basin show that iron oxide in iron ore and iron oxide in volcanic rocks may be of the the same source,the iron mineral were extracted from volcanic rocks by metasomatism. Lead isotope showed a characteristics of deep fluid source. Nihe-Luo River iron ore deposits of ore-forming hydrothermal sulfur may be part from rift basins the underlying strata,especially marine anhydrite layer in Zhou Chong village Triassic, the rest is from the deepen carried by magma. According to quartz-water oxygen isotope fractionation as a function of temperature work out that the water stage in the dark alteration stage and generation phase of magnetite stage is in the range of magmatic water, and the light-colored alteration pyritization stage may have participated in meteoric water.(9) According to the output features of Nihe iron deposit ore body, ore fabric characteristics, wall rock alteration and mineralization alteration features, forming ages, ore resouses,etc., discussion and analysis that Nihe-Luo River iron ore deposits are the continental subvolcanic magmatic-hydrothermal type deposit, the ore host rock of iron ore deposit is diorite porphyry.(10) According to the macro-geological field investigation and indoor micro-identification test and analysis, summarized and analyses the geological features and mineralization geological factors of Nihe iron ore deposits, ore body position significantly integrated control by stratum-tectonic-magmatic construction, mineralization is relevant to construction-magma-hot events, local wall rock hydrothermal alteration plays an important role in promoting mineralization enrichment.(11) Summarized the distribution law of spatial and temporal related to continental sub-volcanic iron deposits in Luzong region, clarify structure-magma-liquid-mineralization relationship, and establishment comprehensive metallogenic model for Luzong Basin continental sub-volcanic-type iron deposits,which provide important theoretical basis for study area prospecting.更多还原