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1.
铁建造和鲕铁岩是地史上两类主要的富铁沉积,不仅记录了地球大气与海洋氧化还原状态和化学条件演变,而且也反
应了构造运动、岩浆活动和生物的相互作用过程.过去对铁建造已有深入研究,而有关前寒武纪铁岩成因与古海洋和构造背景
研究甚少.运用扫描电镜(scanningelectronicmicroscopy,简称SEM)、X射线衍射(X-raydiffraction,简称XRD)、能谱(energy
dispersive spectroscopy,简称EDS)技术分析铁鲕的微组构、矿物成分和化学组成,讨论华北串岭沟组(1.65~1.64Ga)鲕铁岩
的成因环境及其与Columbia超大陆裂解的关系.研究表明,铁鲕主要由赤铁矿和少量高岭石组成,贫陆源碎屑和Al2O3;鲕包
壳由微片状赤铁矿构成的致密和疏松纹层交互组成;Fe-Al呈明显的负相关性,表明铁主要源于缺氧富铁深海水体而非陆源
风化.鲕铁岩集中在快速海进和低陆源输入引起的沉积饥饿期,发育于氧化还原界面附近的潮下贫氧环境.与超大陆裂解伴生
的岩浆活动、基底沉降和快速海侵是促进鲕铁岩形成的重要因素.串岭沟组底部铁岩是华北地台响应Columbia超大陆裂解而
发生构造与环境转化的重要沉积记录. 相似文献
2.
《矿产与地质》2019,(5)
以偃(师)龙(门)地区上石炭统本溪组铝土矿豆鲕结构为研究对象,通过岩石薄片观察、扫描电镜和能谱分析等手段,对铝土矿豆鲕结构的宏观沉积特征、岩石学特征进行了分析,在其分析基础上,结合豆鲕状铝土矿的结构特征,对豫西偃龙地区本溪组铝土矿豆鲕结构成因机制进行了研究。认为:豆鲕结构是伴随着铝成矿过程的化学成因构造,豆鲕核心往往是在富铁铝化作用的早期局部形成的铁铝化程度较高的物质,也可以是在铁铝化作用的过程中,早期铁铝化程度较高的破碎的碎屑物质;豆鲕的圈层是一种加铁和脱铁的交替过程,最有可能是在潜育化作用下形成的漂白层和淀积层,是富铁铝化作用形成的包裹核心的、相对均一的圈层改造的结果。 相似文献
3.
鲕状铁建造(Ooidal Ironstones,OIS)是一种独特的含砂质、泥质、硅质或硅质碳酸盐,且铁质鲕粒含量超过50％,铁含量超过15％的沉积铁矿床.上扬子地区中—上泥盆统OIS广泛发育,被称之为"宁乡式铁矿",是我国南方重要的铁矿资源.本文选取鄂西地区的火烧坪铁矿床作为研究对象,通过对沉积相的识别与划分、矿石组构的鉴定与统计、鲕粒的显微形貌和成分分析,试图精确厘定铁质鲕粒的形成环境以及形成过程,建立和完善火烧坪乃至"宁乡式铁矿"的成矿模式.研究表明,火烧坪铁质鲕粒主要产于以含泥砂质碳酸盐为主的滨-浅海带,特别是滨-浅海转换带远端和浅海带近端,而具有工业意义的矿层均产于海侵旋回中海进—海退—海进的快速转换带.结合火烧坪铁矿沉积环境,本文为鲕粒的胶体化学成因模型提供了新证据,并完善了 OIS成矿模型:①海进过程中,风化作用加剧所导致的海水富营养化促使海水深部呈缺氧的还原环境,Fe2+得以局部富集;②短时期的海退给鲕粒的形成提供了核心物质的来源的同时,还使得水体动力环境和氧化还原环境发生改变,促进了鲕粒的沉积和生长;③又一次的海进使OIS得以沉积埋藏和保存. 相似文献
4.
术语本文所采用的"铁岩(ironstone)"这一术语是指含铁15%以上的化学沉积岩."含铁建造(iron formation)"是指主要由铁质岩组成的、最上层和最底层均为铁质岩的可在地质图上标示出的岩石单元.化学沉积岩限于其体积占50%以上的无机和(或)有机化学沉淀物,这些沉淀物来自地表水体和(或)那些沉淀物的成岩交代产物.铁质岩可由主要的富铁和贫铁矿物来修饰,如:条带状菱铁矿-燧石铁岩和鲕状赤铁矿-石英铁质岩,其中"燧石"包括重结晶燧石, 相似文献
5.
玉石沟铬铁矿床的成因 总被引：2，自引：0，他引：2
玉石沟铬铁矿床产于北祁连蛇绿岩型超镁铁岩中，可分为产于堆积超镁铁岩中的堆积铬铁矿床和产于地幔橄榄岩中的豆荚状铬铁矿床两种类型。堆积铬铁矿床由玄武岩浆分离结晶作用形成，位于辉长岩下约２０ｍ处的纯橄岩或辉石岩中；豆荚状铬铁矿床由地幔岩部分熔融作用形成，产于地幔橄榄岩上部或顶部基性程度最高的纯橄岩或纯橄岩－斜辉辉橄岩杂岩带，位于堆积杂岩下约２００～１７００ｍ范围内。 相似文献
6.
冀西北铁岩的结构和构造类似于碳酸盐岩,因此,借鉴于现代碳酸盐相模式与沉积环境,有可能恢复古代铁岩的沉积环境。本文对铁岩分类及其沉积环境进行了探讨。 相似文献
7.
8.
通过对黔北务正道地区安场向斜东南翼ZK288-16井中大竹园组铝土矿含矿岩系的沉积学分析,辨别出该口钻井记录下的包括两次准同生淋滤作用及一次后生淋滤作用在内的3次淋滤作用。土状-半土状铝土矿层是记录淋滤作用发生的标志性层位,与下伏岩(矿)层呈现渐变关系,说明土状-半土状铝土矿是由碎屑状或豆鲕状铝土岩(矿)经过淋滤作用转化而来,在此过程中,杂质元素被移除,铝元素相对富集而形成富矿,而碎屑状与豆鲕状铝土矿也经过不同程度的淋滤作用。区域上的钻孔对比表明,区域内这种多期淋滤作用对于提升矿石品质、控制矿层厚度具有重要意义。 相似文献
9.
铝土矿床中豆鲕粒结构的形成,直接与红土化作用有关.本文试以黔北铝土矿床为例,论述了古代喀斯特型铝土矿床中豆鲕结构的成因机理。其豆鲕粒结构存在的本身便标志着经历了红土化阶段或直接源出于红土物质。当化学风化作用进入到酸性淋溶阶段时,大量的有机酸胶、铝、硅、铁胶,经过复杂的分凝、软胶化、扩散、间歇反应、陈化等胶体化学作用,直接孕育成了豆鲕粒结构.豆鲕粒的形状、大小、密度、分布等特征,则取决于原始溶胶的数量、浓度,浓度梯度和相对稳定度。与豆鲕粒结构密切伴生的复胶状结构,其成因也是胶体作用所致.属风化作用或与风化作用密切有关的矿床类型. 相似文献
10.
朱伟鹏 《沉积与特提斯地质》2023,43(1):87-100
宁乡式铁矿是我国南方最具代表性的沉积型铁矿,为了探讨其沉积特征与成矿机制,本文借助偏光显微镜、扫描电子显微镜和TESCAN综合矿物分析仪,选取采自桂东北、鄂西成矿区的若干矿石样品进行岩石学和沉积学研究,深入剖析铁质鲕粒的显微组构和地球化学特征。结果显示宁乡式铁矿为混积岩,具有典型的鲕状结构,可划分为砂岩型、灰岩型和混合型等三种类型,赋存于中泥盆统信都组、上泥盆统黄家磴组和写经寺组地层中,含矿岩系总体为一套砂岩、泥页岩和泥灰岩组合,形成于区域海侵背景下的滨海、滨–浅海转换带;矿石中铁质鲕粒形态多样,粒径多集中于0.2～0.5 mm,少数铁质鲕粒的矿物相和主量元素呈圈层状分布,核心可为石英或生物碎屑充填,外部为赤铁矿、鲕绿泥石及胶磷矿环带互层。研究表明矿石的形成可划分为成矿物质准备期、铁质鲕粒形成期和铁矿沉积期三个阶段,强烈的古陆风化作用提供了成矿物质来源,成矿物质在机械沉积作用、胶体化学沉积作用和生物沉积作用下富集并沉淀,期间经历了复杂的氧化还原过程,最终压实固结为宁乡式铁矿。 相似文献
11.
T. P. Young 《Geological Journal》1991,26(4):317-327
Pendent didymograptid graptolites are described from mudstones immediately overlying the Hen-dy-capel ironstone (St. Tudwal's Peninsula, Lly̌n, North Wales). The graptolites indicate a Llanvirn age for these beds, implying a Llanvirn or Arenig age for the ironstone, in contrast with the previous interpretation of a gracilis Biozone age. The redating of the ironstone horizon suggests that the Pen-y-gaer mudstones may be at the base of the local Nant Ffrancon Formation, rather than being equivalent to the lower Caradoc Tyddyn Dicwm beds above the Tremadog ironstone as widely supposed. The ironstones at Trefor, Betws Garmon, and Llandegai, which have been correlated with the Hen-dy-capel ironstone on the basis of acritarch assemblages, may also have a similar age. A reinterpretation of the age of these localities as Llanvirn would remove the stratigraphic problems introduced by their previously suggested early gracilis Biozone age. The Hen-dy-capel ironstone forms one of a large number of ironstones recorded from close to the Arenig-Llanvirn boundary in N. Wales, and elsewhere at high southern palaeolatitudes. 相似文献
12.
廖士范 《沉积与特提斯地质》1993,(3):1-8
我国显生宙鲕铁石主要分布在我国中南、西南,其次为华东地区,主要产于中奥陶世,中、晚泥盆世,早、中侏罗世地层中,以晚泥盆世最为重要,其矿石储量占70.5％,沉积条件最好,为接近封闭的浅海泻湖中。奥陶纪及泥盆纪海水中沉积的鲕粒直径分别为0.7—2mm,0.2—0.8mm。侏罗纪湖水沉积的鲕铁石直径为0.15—0.66mm。鲕粒环带的形成,与水体波动能量使铁质围绕碎屑矿物,或围绕先已形成的自形晶微粒铁矿物旋转有关。静水沉积时能量小,无环带形成,多为无核心的铁质团粒。鲕粒环带,杂基多为自形晶铁矿物或碳酸盐物,鲕核有的为石英碎屑,右的为自形晶铁矿物或碎屑铁矿物。 相似文献
13.
The Late Coniacian, shallow-marine Bad Heart Formation of the Western Canada foreland basin is very unusual in that it contains economically significant ooidal ironstone. Deposition of shallow-water and iron-rich facies appears to have been localized over the crest and flanks of a subtle intrabasinal arch, in part interpreted as a forebulge and partly attributed to reactivation of the long-lived Peace River Arch. The formation comprises two upward-shoaling allomembers, typically 5–10 m thick, that are bounded by regionally mappable ravinement surfaces. The lower unit, allomember 1, grades up from laminated mudstone to bioturbated silty sandstone, which is abruptly overlain by bioturbated ooidal silty sandstone grading into an almost clastic-free ooidal ironstone up to 7 m thick. Ooidal ironstone was concentrated into NW- to SE-trending ridges, kilometres wide and tens of kilometres long. Ironstone formation appears to have been promoted by: (a) drowning of the arch, which progressively curtailed sediment supply; and (b) enhanced reworking over the shallowly submerged arch and over a fault-bounded block that underwent episodic vertical movement of 10–20 m during Bad Heart deposition. Allomember 2 also shoals upwards from mudstone to bioturbated and laminated silty sandstone but lacks ooids, apparently reflecting a rejuvenated supply of detrital sediment from the arch. The marine ravinement surface above allomember 2 is a Skolithos firmground, above which is developed a regional blanket of ooidal sediment. In the east, ooids are dispersed in a bioturbated silty sandstone with abundant evidence of repeated reworking and early siderite and phosphate cements. Westwards, this facies grades, over about 40 km, into almost clastic-free ooidal ironstone about 5 m thick; the lateral facies change may reflect progressive clastic starvation distal to a low-relief source area. The two allomembers are interpreted to reflect eustatic oscillations of about 10 m, superimposed on episodic tectonic warping and block-faulting events. The development of ooidal ironstone immediately above initial marine flooding surfaces indicates a close relationship to marine transgression, reflecting sediment-starved conditions. Ironstone does not appear to be related to either sequence boundaries or maximum flooding surfaces. The Bad Heart Formation is blanketed by marine mudstone deposited in response to major flexural subsidence and rejuvenation of clastic sources in the Cordillera to the SW. 相似文献
14.
Eric Gloaguen Yannick Branquet Philippe Boulvais Yves Moëlo Jean-Jacques Chauvel Pierre-Jacques Chiappero Eric Marcoux 《Mineralium Deposita》2007,42(4):399-422
In the Saint-Aubin-des-Chateaux quarry (Armorican Hercynian belt, western France), an epigenetic hydrothermal alteration affects
an oolitic ironstone layer intercalated within the Lower Ordovician Grès armoricain Formation. The hydrothermal overprint
produced pervasive and massive sulphidation with stratoid pyritised lenticular bodies within the oolitic ironstone layer.
These sulphide lenses are spatially associated with strike-slip faults and extend laterally from them. After the massive sulphidation
stage (Fe–As, stage 1), subsequent fracturing allowed the deposition of base metals (stage 2) and Pb–Sb–Au (stage 3) parageneses
in veins. The dominant brittle structures are vertical extension veins, conjugate shear veins and strike-slip faults of various
orders. All these structures are filled with the same paragenetic sequence. Deformation analysis allows the identification
of structures that developed incrementally via right-lateral simple shear compatible with bulk strain affecting the Central
Armorican Domain. Each increment corresponds to a fracture set filled with specific parageneses. Successive hydrothermal pulses
reflect clockwise rotation of the horizontal shortening direction. Geothermometry on chlorite and arsenopyrite shows an input
of hot hydrothermal fluids (maximum of 390–350°C) during the main sulphide stage 1. The subsequent stages present a marked
temperature drop (300–275°C). Lead isotopes suggest that the lead source is similar for all hydrothermal stages and corresponds
to the underlying Neo-Proterozoic basement. Lead isotope data, relative ages of deformation and comparison with neighbouring
deposits suggest that large-scale fluid pulses occurred during the whole Hercynian orogeny rather than pulses restricted to
the late Hercynian period. The vicinity of the Hercynian internal domain appears as a key control for deformation and fluid
flow in the oolitic ironstones, which acted as a chemical and structural trap for the hydrothermal fluids. The epigenetic
mineralisation of Saint-Aubin-des-Chateaux appears to be very similar to epigenetic sulphidation described in banded iron
formation-hosted gold deposits. 相似文献
15.
The oolitic ironstones ore deposit of Jebel Ank (central Tunisia), is a simply folded stratiform ore body of about 2.5–8 m thickness located in the upper part of the epicontinental Souar Formation (Late Eocene) and is covered by the continental Segui Formation (Mio-Pliocene). The deposit contains about 20 Mt of ore with an average grade of 50% Fe. Generally, oolitic iron deposition occurs in shallow water lagoonal environments. The Jebel Ank deposit lies between two regional disconformities (Late Eocene and Miocene), and is evidence of a transitional stage at the end of regional regression before renewed transgression. The footwall of the oolitic iron ore-bearing bed consists of a fine-grained sandstone bed (10–20 cm-thick) pinching out laterally westward into green clays. The hanging wall is composed of thin-bedded limestone and clay alternations (2–3.5 m-thick).Iron occurs in the form of cryptocrystalline goethite with limited Al-Fe substitution. The goethite contains around 48% Fe, 5% Al and up to 1.5% P. Jarosite, alunite and manganese minerals (cryptomelane, psilomelane and manjiorite) are supergene secondary minerals, probably related to descending surface fluids. These manganese minerals occur as accessory minerals with the goethite and are most abundant at the lowermost part of the succession showing varied morphologies (local cement, space filling and free centimeter sized nodules). Fe-oolites in the deposit are similar to those documented in many other oolitic ironstone deposits. The dominant Fe-oolite type (>90%) has a concentrically laminated cortex with no nucleus. The nuclei of the oolites that do have a nucleus are most commonly detrital quartz grains.Major elements in high grade samples (Fe2O3 > 65%) vary within a limited range and show higher concentrations of SiO2 (average 7.85%) and Al2O3 (average 5.1%), with minor TiO2, MnO, MgO, Na2O, K2O, and SO3 (less than 1%). PAAS-normalized trace elements of bulk samples and Fe-oolite generally show similar behavior, both are enriched in V, Co, Ni, Mo, As, Zn, and Y and are depleted in Cu, Rb, Zr, Nb, Ba, and Hf. Anomalous V, Cr, Ni, Zn, and REE-Y are correlated with goethite. PAAS-normalized REE-Y patterns of both bulk samples and Fe-oolite show slight HREE enrichment, positive Ce with negative Y anomalies.The mineralogy (goethite and cryptomelane) along with the geochemistry (Si vs. Al; As + Cu + Mo + Pb + V + Zn vs. Ni + Co binary plots; Zn–Ni–Co triangular diagram, REE-Y content and patterns and Ce/Ce1 vs. Nd and Ce/Ce1 vs. YN/HoN binary plots) of the studied oolitic ironstone are congruent with a hydrogenetic type. While two possible sources of iron for Jebel Ank ironstone can be proposed: (i) submarine weathering of glauconite-rich sandstone and (ii) detrital iron from adjacent continental hinterland, the later is the more plausible source of iron, based on paleogeographic setting, the occurrence of fine sandstone underlying the iron level, occurrence of Mn-ores in the lower part of the Fe-ores succession, high phosphorous, zinc, ∑REE-Y concentrations and Y/Ho ratios, and low La/Ce ratios. 相似文献
16.
The contact between the Silurian black phyllite and the Cambro–Ordovician underlying rocks has been investigated over different tectonic units, affected by green-schist facies metamorphism, in the inner nappe zone of the Sardinia Variscides. In spite of strain and metamorphism, the field work highlighted the occurrence of diamictic sediments. In the Canaglia Tectonic Unit the diamictite consists of dark, massive metamorphic claystone bearing chamositic ooliths, chamositic nodules and millimetre to centimetre sized clasts, dispersed, or gathered in clusters, within the muddy matrix. In the Argentiera Tectonic Unit the diamictite consists of angular clasts, ranging in size from few millimetres to several decimetres, scattered within a finely laminated black sericitic meta-argillite. Field data, textural and compositional analyses suggest a glacio-marine environment for the formation of the diamictites.
The Canaglia diamictite deposited in a protected, glacial-influenced, shore. Compositionally it can be defined as ironstone; in the Upper part it hosts a horizon of clast-supported conglomeratic hard ironstone, mostly made of magnetite, which testifies for sub-aerial reworking. The source of the iron is to be related to local, glacio-eustatic driven, emergence of Upper Ordovician alkaline mafic volcanics. These are widespread in the uppermost Ordovician of the Canaglia Unit, possibly linked to the rifting stage that invested the north Gondwana margin, before the uppermost Ordovician–early Silurian sea level rise.
The Argentiera diamictite deposited beyond the iron-rich diamictite in the outer euxinic shelf that was reached by rain out of rafted debris. 相似文献
17.
澳大利亚Cloncurry地区大部分被元古宙地层所覆盖,其中赋存有大量世界级的成矿热液系统。大型热液系统大都与含磁铁矿或赤铁矿等铁氧化物的铁矿化岩石密切相关。铁氧化物和铜金矿化的矿物学、地球化学及年代学特征反映出成矿过程可能涉及到多种流体间的作用和水岩反应。对Cloncurry地区典型矿床和区域Na-Ca热液系统的研究表明,含铁氧化物的铁矿化岩石与铜金矿化之间的关系可分为4类:①贫磁铁矿或赤铁矿的"Kiruna-型"铁矿化岩石;②铜金矿化赋存于含铁氧化物的铁矿化岩石中;③与铁氧化物有关的铜金矿化;④少量或者不含铁氧化物的铜金矿化。该分类提供了一些与铁氧化物有关的铜金矿化成因联系、矿物学和矿化类型信息。 相似文献
18.
Sideritic ironstones in Tertiary lacustrine oil shale from the Lowmead and Duaringa Basins in Queensland, contain two distinctive types of siderite in the ironstone bands: sphaerosiderite in the mudstone and coal, and finely crystalline siderite in the lamosite. The petrological evidence indicates that the siderite in the ironstone bands formed eogenetically by growing displacively within the soft sediment. Chemically the siderite is very pure though the sphaerosiderite sometimes shows compositional zoning. Stable oxygen and carbon isotope analyses of the siderite show a wide range of values from ‐12.8‰ to ‐2.4 %0 δ18O (PDB) and ‐5.5‰ to +12.9‰ δ13C (PDB) for the Lowmead Basin; and ‐9.6‰ to ‐1.2‰ δ18O (PDB) and ‐18.6‰ to +16.4‰ δ13C (PDB) for the Duaringa Basin. The oxygen isotope data indicate that the siderite formed in freshwater environments but not in isotopic equilibrium with the formation waters. Kinetic factors offer the most plausible explanation for the anomalously light δ18O values of many of the siderites. The carbon isotope data show that the carbonate for the formation of the siderite originated predominantly from methanogenic fermentation processes but there was also the varying influence of bacterial oxidation processes. The different petrological and isotopic characteristics of the ironstones broadly reflect variations in their depositional environments and the variable eogenetic conditions in which the siderite formed. There is no suitable single model to explain the genesis of all the different types of ironstones other than that a synsedimentary iron‐enrichment process is involved. 相似文献
19.
The geochemistry of two deerite‐bearing meta‐ironstones from the Emo Metamorphics of Papua New Guinea suggests that they were deposited as metalliferous cherts enriched in manganese and iron by hydrothermal exhalative activity in an ocean ridge system. Subsequent blueschist facies metamorphism resulted in the formation of the assemblage deerite‐quartz‐albite‐iron oxides‐alkali amphiboles‐spessar‐tine‐stilpnomelane‐apatite, with calcium‐manganese carbonates in one specimen. Assemblages in associated metabasites suggest P‐T conditions of 7 kb at 320°C, which overlap with the P‐T field defined by one of the meta‐ironstones. Oxygen fugacity was probably an important control in determining variations in mineralogy and mineral chemistry. Preliminary data on the trace element geochemistry of associated metabasites are consistent with an ocean ridge environment for the formation of the meta‐ironstones. 相似文献