沉积铁矿形成过程中的生物作用

    沉积赤铁矿和层控黄铁矿、菱铁矿的成矿过程中都离不开生物的作用。不同情况下，其表现形式不尽相同。生物的活动形成赤铁矿受层石、毒球状黄铁矿以及有机质的还原作用由赤铁矿转变为菱铁矿。
    冀西北宣龙地区铁质叠层石和铁质核形石同心纹层中普遍含有微体古植物化石，属于低等蓝藻类，形态以丝状体为主，部分为羽状体，它们直接地参与了铁的成矿作用。
        

宣龙铁矿铁质鲕粒的显微结构及成因

宣龙铁矿的铁质鲕粒由各种不同的核心和微层状外壳组成。核心的组分主要是石英砂粒、赤铁矿内碎屑和凝块以及粒状菱铁矿等。外壳的纹层分别由显微结构不同的板状、片状、均匀和不均匀粒状泥晶赤铁矿以及少量菱铁矿组成。其中板伏、片状、均匀粒状赤铁矿和菱铁矿主要是以化学或生物化学方式在核心表层逐层沉积结果;不等粒状赤铁矿微层则是鲕粒滚动中对铁质颗粒粘附而成。菌藻类生长繁殖改变沉积环境的物化性质,对铁质沉积起着重要作用。     

河北省宣龙式铁矿的地球化学特征及其地质意义

本文报道了宣龙式铁矿的主量元素、微量元素、稀土元素、Fe同位素和Nd同位素的分析结果。结果显示:主量元素的化学成分中Fe2O3T的含量最高,并且具有较高的Al2O3、TiO2和P2O5含量;微量元素含量总体与平均地壳相似,并显示氧化-还原敏感元素V、U、Mo的相对富集;稀土总量高、轻稀土元素亏损重稀土元素富集、无Ce、Eu正异常、Y/Ho比值与地壳平均值相似;同时,铁矿具有较低的εNd值,这些特征表明宣龙式铁矿的成矿物质来源为陆源。相对于标准物质IRMM-014,宣龙式铁矿中赤铁矿的Fe同位素组成均为正值,这与由现代蓝细菌氧化而成的赤铁矿Fe同位素组成应小于或等于0不同,因此,宣龙铁矿是由铁细菌氧化为主的生物粘结矿床。此外,铁矿无Ce的负异常;V、U、Mo的相对富集;Fe同位素比值为正值的这些特征均说明当时铁矿沉淀的环境为低氧状态。     

中国铁矿成矿地质特征和资源潜力

中国铁矿主要分为七大类型时常同积变质型磁铁－赤铁矿床，基性侵入体岩型钡钛磁铁矿床，矽卡岩型磁铁矿床，火山岩型磁铁－赤铁矿床，沉积型赤铁－菱铁矿床，多因复合－迭加型磁铁－赤铁矿床，风化淋滤褐铁－赤铁矿床。     

基于航空高光谱遥感的沉积变质型铁矿找矿预测—以北祁连镜铁山地区为例

沉积变质型铁矿是北祁连山西段重要的矿床类型,一直以来都是该地区矿产勘查的重要对象,区内产有知名的镜铁山铁矿床。由于北祁连山地区山势陡峻、交通不便,地质工作程度相对较低,开展传统的地质调查工作难度较大。航空高光谱遥感具有高空间分辨率和高光谱分辨率特点,其在矿物信息识别上较多光谱遥感有了质的提升,同时在该地区开展航空高光谱遥感调查是发挥遥感技术的高效性和先行性优势所在。本文基于调查区内沉积变质型铁矿床地质特征,利用航空高光谱遥感数据提取的赤铁矿、菱铁矿信息开展针对沉积变质型铁矿找矿预测。结果表明,提取的赤铁矿信息或直接指示铁（化）体产出位置,或指示含赤铁矿地层产出信息,这为直接或间接寻找铁矿床提供了重要信息;菱铁矿信息同样可作为寻找铁矿床的重要依据,分布范围较大的菱铁矿信息可直接指示富菱铁矿的铁（化）体产出位置。     

冀西北宣龙地区菱铁矿的成因

本文以中晚元古代宣龙式铁岩中的菱铁矿为例,讨论碎屑岩中菱铁矿的成因。 宣龙式铁岩产于中晚元古代串岭沟组。成层状,层位稳定,分布较广,西起怀安龙泉寺,东至承德小平台一线均有出露,其中尤以宣龙地区发育最好。 宣龙地区的菱铁矿矿层薄,数量少,往往与赤铁矿构成混合矿体。该区菱铁矿分布规律性明显。横向上,由西往东逐渐增多;纵向上,由下至上由分散状变成层状,与赤铁矿间互产出。     

国外菱铁矿床概述

菱铁矿矿床,大部分是由菱铁矿与赤铁矿(镜铁矿)——褐铁矿及磁铁矿组成的混合型铁矿床,有少部分为由菱铁矿或以菱铁矿为主的单一型铁矿床。其地表部分极易氧化成褐铁矿。长期以来,这一类型铁矿,在世界铁矿类型中只占次要地位。一般认为沉积菱铁矿在世界上分布广泛,但矿层很薄,稳定性较差,品位很低,不具工业价值,只有在铁矿资源贫乏的德国、英国才进行开采;在内生作用过程中,菱铁矿主要产于岩浆期后低温热液及火山作用后期,其储量和开采量多不被人们重视。事实上世界许多重要铁矿如北美上湖铁矿及仅次于上湖的中欧侏罗系而状铁矿,其矿物成分除赤铁矿、磁铁矿与褐铁矿外,菱铁矿也占一定比例,部分地区则以菱铁矿为主。在碳酸盐岩中的菱铁矿矿床,多属单一型菱铁矿,其成因有沉积与热液两种不同的看法。下面介绍几个规模     

冀东司家营铁矿尾矿特征及综合利用建议

通过对冀东司家营铁矿尾矿的化学成分、矿物组成、矿物粒度、解离度以及矿物连生关系等测定,分析了该尾矿综合利用的途径,为同类型沉积变质型铁矿(BIF型铁矿)尾矿综合利用提供参考.分析结果表明,司家营铁尾矿属高硅高铁低铝尾矿;矿物组成以石英、阳起石、透辉石和长石为主,含少量赤铁矿、铁白云石、大隅石及云母等矿物;尾矿粒度以细砂...     

式可布台铁矿地质特征及成矿模式

式可布台铁矿床是西天山阿吾拉勒铁铜成矿带上发现较早、规模较大的赤铁矿矿床,是我国著名富铁矿床。该矿床矿石类型主要为赤铁矿,次为褐铁矿、镜铁矿及菱铁矿和磁铁矿。经矿床特征分析认为,成矿主要物质来源于上石炭统依什基里克组,构造活动为重要的控矿因素,结合成矿地质背景与控矿因素总结成矿模式,指出了找矿标志。     

山东省济宁强磁异常区深部铁矿初步验证及其意义

山东省济宁磁异常是一个重、磁同源体,面积大于100 km2,磁异常峰值为3800nT。钻探验证在孔深1041.57～1796.54m位置发现铁矿体,矿体总厚度74.04～220m,磁性铁平均品位15.89～25.19%。矿石类型有条带状方解磁铁石英岩和条带状磁铁石英大理岩,矿石的主要组成矿物为石英、方解石、磁铁矿、磁赤铁矿、菱铁矿。矿体产于济宁岩群浅变质岩系中,矿床特征与条带状铁建造（BIF）铁矿或鞍山式铁矿有明显区别,铁矿成因类型属与千枚岩、变质中酸性火山岩、大理岩有关的沉积变质型铁矿床。该区铁矿资源潜力巨大。     

The Role of Organic Matter in the Formation of Siderite from Xuanlong Area,Hebei Province

Based on the analysis of siderite distribution,occurrence,chemical compositionk,structureal characteristics,carbon-oxygen isotopic characteristics and relationship between siderite and hematite,this paper presents a systematic study of siderite in the region studied.suggesting that the siderite in the Xuanlong area genetically resulted from organically reduced primary hematite during the diagenesis.The ferric and ferrous relations directly depend on organic contents.In the presence of organic matter ferrous iron can be converted to ferric iron through or ganic reduction.The above conclusion has also been proved by organic geochemistry.data.     

Diagenetic crystallization and oxidation of siderite in red bed (Buntsandstein) sediments from the Central Iberian Chain,Spain

Compactional deformation facilitated replacement of dolomite and calcite by siderite and its subsequent oxidation in carbonate cemented red beds of the Triassic Buntsandstein in the Iberian Chain. Locally, the sedimentary clasts were cemented by carbonate that was derived from dissolution of locally exposed dolomite in the basement. Microstructures indicate that during sedimentation of the rocks, oxidizing conditions prevailed in the sediments and the basement was reddened by impregnation of hematite. Reducing conditions prevailed during deformation of the sediments. Ferric iron was reduced to Fe²⁺, that reacted with deformed dolomite and calcite cement to produce fine grained siderite. At a later stage, siderite crystallites were (partly) oxidized to form a secondary phase of brown ferric oxide (goethite). Locally, goethite transformed to fine grained hematite that caused secondary reddening of the sediments. The reactions are associated with a combined volume loss of the solid phases of c. 50% per reaction mol; this was accommodated by the formation of pores. Oxidation of siderite was associated with release of CO₂; localized dissolution took place of feldspar and concurrently growth of kaolinite occurred by acidifying condition during release of CO₂. The relation of redox reactions and deformation is comparable to those in red bed conglomerates in the region. Reductive dissolution occurred at sites of stress concentration, particularly at contact points of pebbles. Late stage precipitation of ferric oxides and pyrolusite took place at oxidizing conditions in association with uplift.     

Characteristics of arsenic adsorption from aqueous solution: Effect of arsenic species and natural adsorbents

Batch and column experiments were conducted on As adsorption from aqueous solution by natural solids to test the feasibility of these materials to act as adsorbents for As removal from groundwater and drinking water. The solids considered are natural hematite and natural siderite. The As species studied are As(V), As(III) and dimethylarsinic acid (DMA). Arsenic(III), As(V) and DMA were removed to different extents by the solids studied from water solutions containing these three As species, with the highest efficiency for As(V). In aqueous solutions with a mixture of As species, adsorption kinetics depend on the species. On both materials, As(V) was preferentially adsorbed in the batches and first reached equilibrium, followed by DMA and As(III). The As adsorption took place more slowly on natural hematite and natural siderite compared with ferrihydrite. The results demonstrate that the amount of As removed from As(III) batches was greater than that from As(V) batches due to a surface alteration of the solids caused by As(III) oxidation. Although the highest efficiency for As retention was observed on hematite HIO1 in the batch experiments, siderite used as column filling was more efficient in removing As from water containing the As species studied in comparison with hematite. The coating of fresh Fe(III)-oxides was much more intensive in the siderite-packed column than in the hematite-packed column. The combination of siderite and hematite would promote the column filling performance in removing As from aqueous solution.     

Trace and rare-earth element behaviors during alteration and mineralization in the Attepe iron deposits (Feke-Adana,southern Turkey)

Hydrothermal-metasomatic iron ores consisting mainly of siderite, ankerite and hematite are located in the Lower–Middle Cambrian limestone marbles of the Eastern Taurus Belt. The siderite, ankerite, hematite and host rock samples from the deposits have been investigated for major, trace, and rare-earth elements (REE) to evaluate the element mobility and mass transfer during fluid–rock interactions.     

Selective flocculation of hematite in the hematite-quartz-ferric ion-polyacrylic acid system. Part 1, activation and deactivation of quartz

This investigation has shown that quartz can be activated for polyacrylic acid adsorption by hydrolyzing metal cations, similar to activation in flotation. Detailed experiments on activation phenomena with ferric ions have been performed. The flocculation of activated quartz can be prevented by suitable additions of disodium EDTA, sodium hexametaphosphate or potassium fluoride. Selective flocculation of hematite with polyacrylic acid from a hematite/quartz mixture can be achieved in the pH range 3 to 9, but the process is not selective in the presence of ferric ions. Suitable additions of EDTA or KF are particularly successful in preventing quartz activation by ferric ions and the facilitating selective flocculation of hematite in artificial mixtures of quartz and hematite.     

Les minerais de fer de l'Ordovicien inférieur du bassin de Bretagne-Anjou,France*

The iron resources of the ‘Bretagne-Anjou’ basin proceed essentially from four layers of sedimentary ore in the lower gres armoricain (Arenig). The more frequent paragenesis combine quartz, magnetite, siderite and silicates (bavalite, stilpnomelane). The hematite and pyrite parageneses are rarer. Two ore types were distinguished petrographically: one type with allochems and one without allochems. The study of both paragenesis and thickness variations of the ore layers enables one to reconstitute the sedimentation history: iron is dissolved on the emerged cadomian reliefs and transported to the sedimentary basin, which was shallow and strewn with islands and shoals. Then, according to local conditions, iron precipitated either under its oxydized forms (hematite, magnetite) or under its reduced forms (silicates, pyrite, siderite). The essential factors of parageneses differentiation were the depth of the basin, the water agitation and the organic matter content of the sediment. In some cases little concretions were formed in the sediment and gave rise to allochems which can be moved away later and deposited elsewhere.     

山西袁家村矿区前寒武纪铁矿的形成条件

山西省吕梁山地区早元古宙袁家村铁矿以变质程度浅、地层剖面完整和地质构造简单为特征。厚约1200m 的袁家村组含铁岩系可以分成三个段,它们分别代表了三个沉积-成矿旋回。其中每一个旋回都是以粗碎屑岩开始,经过粉砂岩和泥质岩逐渐过渡为较纯的胶体化学沉积物即硅质岩。矿区出现的铁矿物相沿剖面自下而上依次为黄铁矿、菱铁矿、铁硅酸盐(包括铁绿泥石、铁滑石和黑硬绿泥石)、磁铁矿和赤铁矿。这些铁矿物相是沉积阶段、成岩阶段至初级变质阶段的产物。它们在地层剖面上的空间分布,反映各旋回铁矿物相的形成环境,在时间上自早至晚,空间上自下而上,其氧逸度逐渐增高。控制铁矿物相类型和其中铁价态形式的主要因素,是沉积时泥砂质碎屑组分和铁硅质胶体化学组分的性质和相对比例,以及其中有机质的存在与否及其多寡。