新疆磁海铁矿床地球化学特征

【作者】 唐萍芝；

【导师】 王京彬； 王玉往；

【作者基本信息】 昆明理工大学 ， 矿产普查与勘探， 2010， 硕士

【摘要】 本文是在北京矿产地质研究院承担的国家重点基础研究发展规划项目(973项目)“中亚造山带大陆动力学过程与成矿作用”项目之“后碰撞过程壳幔物质交换与成矿”课题(2007CB411304)资助下完成。本文主要以新疆磁海铁矿床为研究对象,在综合分析前人研究成果基础上,通过野外实地考察和室内显微镜观察,系统开展岩石、矿石、矿物的地球化学研究,探讨磁海铁矿的矿床地球化学特征,并结合矿床对比研究,进一步揭示磁海矿床的成因特征和形成机制。主要取得以下认识：(1)磁海矿区与成矿有关的镁铁-超镁铁岩,由橄榄辉长岩、橄长岩、辉长岩、辉绿岩、玄武岩等组成,为富铁质钙碱玄武岩系列,形成于后碰撞拉张阶段。辉绿岩具多期侵入特点,属原始岩浆经分离结晶后残余熔体结晶的产物,其全铁含量高于橄长岩和橄榄辉长岩,说明铁在岩浆分离结晶晚期有富集作用。(2)磁铁矿矿石中P2O5、SiO2和指示深部物质来源的Co、Ni、Cu含量较高；磁铁矿稀土元素特征与辉绿岩相近,表明磁海铁矿的形成与矿区辉绿岩关系密切,磁铁矿主要来源于辉绿岩体；矿石中V、Ti、Cr含量甚微,与岩浆分异磁铁矿有区别。(3)矿石的稀土元素特征与矿区蚀变岩石相似；黄铁矿以相对亏损S、富集Fe和含Co为特点,Co/Ni比值大于1,表明矿床的形成与岩浆期后热液活动有关。(4)在磁海矿区首次发现黑柱石,其成分特征显示与富铁质岩浆活动有关,为基性岩浆与地层接触交代的产物,为次火山热液成矿提供了佐证；黑柱石形成于成矿作用晚期,对早期形成的磁铁矿起贫化作用。(5)磁铁矿矿石中普遍含钴较高,个别富硫化物矿石中钴可达0.16%,具有综合利用价值；Co主要产于黄铁矿、磁黄铁矿等硫化物中,并有钴的独立矿物辉砷钴矿和斜方砷钴矿,一方面反映成矿物质来源较深,另一方面说明铁和钴在岩浆-热液演化过程中属于不同阶段的产物,钴的形成趋于在热液晚期阶段富集。(6)磁海矿床与长江中下游典型夕卡岩型铁矿和玢岩型铁矿在成矿机制等方面,存在一定的相似性,但与磁海矿床有关的成矿岩体更偏基性,代表该类型铁矿床中偏基性的端元。更多还原

【Abstract】 This thesis is supported by the Major State Basic Research Program of People’s Republic of China:Mantle-Crust Interaction and Mineralization in Post-collisional Stage (No.2007CB411304) of’Geodynamic Process and Metallogeny of the Central Asian Orogenic Belt’project, undertaked by Beijing Institute of Geology for Mineral Resources.Based on field investigation and microscope observation, this work focuses on the geochemistry of the Cihai iron deposit in Xinjiang, including geochemistry of mafic-ultramafic rocks, magnetite and sulfide ores, magnetite and sulfide minerals; ilvaite and cobalt. By comparative study with related iron deposits, the author discussed the metallogensis type and ore-forming mechanism of Cihai deposit. The main achieved advancements from this thesis are as follows:(1) Mafic-ultramafic rocks are composed by olivine gabbro, troctolite, gabbro, gabbro-diabase, and diabase in the Cihai ore district, which belongs to iron-rich and calc-alkaline rock series formed in post-collisional extension phase. The diabase in Cihai area characterized by multi-phase intrusion is the crystallizing product of residual melt derived from magmatic crystallization differentiation. The FeO content in diabase is higher than in troctolite and olivine gabbro, which may suggest that there exist Fe enrichment in the late stage of magmatic differentiation crystallization.(2) Magnetite ore contains high P2O5 and SiO2 component, and the deep-source elements like Co, Ni and Cu are high in ore as well. The magnetite composition shows that it has typomorphic charactersitics of magmatic magnetite. Accordant REE geochemistry between the magnetite and diabase may imply that the ore mineral is mainly derived from diabase. Noticeably, the lower V, Ti and Cr contents in magnetite ore suggest that the Cihai deposit is distinctly different from the magmatic differentiation deposit.(3) The REE pattern of magnetite ore is in accord with that of alterated rocks of the ore deposit area. Pyrite composition of Cihai is characterized by lower S content, higher Fe and Co content with higher Co/Ni ratio (>1). These characteristics indicate that the mineralization of Cihai deposit may attribute to postmagmatic hydrothermalism.(4) Ilvaite was first found in the Cihai deposit. The composition characteristics indicate that the ilvaite has relationship with iron magmatic activity. It is considered that the formation of ilvaite is related to mafic subvolcanic rocks and to the hydrothermal metallogeny, which provided a circumstantial evidence for hydrothermal metasomatism. The ilvaite formed in later mineralization stage and played a dilution effect to the early magnetite.(5) Cobalt partially enriches in Cihai iron ore and can be comprehensive utilized, in particularly in sulfide-rich ore that cobalt reachs to 0.16%. The cobalt mostly disperses in pyrite and pyrrhotite, but Co minerals like cobaltite and safflorite can be observed in ore. Geochemistry and occurrence of cobalt reveal that the ore-forming metals may come from the deep, and that the iron and cobalt formed in different mineralization stage of the magmatic-hydrothermal evolution process, or cobalt tends to enrich in the late hydrothermal stage.(6) Cihai deposit is similar to typical skarn type deposit and porphyrite iron deposit in metallogenic mechanism, but with distinct mafic-ultramafic hosting igneous rocks. It is suggestion that the Cihai iron deposit is the basic end member of these deposit types.更多还原