Rezente marine Eisenerze auf Santorin,Griechenland

Recent iron sediments forming at present in a bay of the volcanic island Palaea Kameni within the caldera of Santorini, Aegean Sea, have been investigated for their mineralogy and geochemistry. For the first time siderite has been found in a marine environment to be major constituent of a recent sediment. Further main constituents are opal, ferric hydroxide, vivianite, ferrous hydroxide, and possibly ferrous silicate. The chemical composition both of the solid material of the sediment cores and of their pore solution indicate that the ore forming solutions have originated from the leaching of volcanic kalk-alcaline rocks by hot acid solutions. This is in agreement with experimental leaching of these rock types. No enrichment of lead, copper, zinc etc. was found in the sediments. Iron oxidizing bacteria in the reddish-brown ferric hydroxide sediments now forming in bays of the Kameni Islands have been studied by light and electron microscopic investigations. Samples from the uppermost parts of the sediment consist mainly of the ferric hydroxide stalks of the iron bacteriumGallionella ferruginea. The stalks showing their morphological characteristics occur in such masses that there is no doubt concerning the presence, activity and share of these bacteria in the process of iron sedimentation. Phases of sedimentation process and kinetics of ferric hydroxide stalk formation have been determined qualitatively and quantitatively by in-situ-experiments using artificial growing surfaces (underwater “Aufwuchs” on glass slides). The results obtained are compared to similar iron sedimentation in fresh water habitats and iron rich carbonate springs discussed in literature in connection with the problem of submarine exhalative sedimentary iron ore formation.     

铁矿石化学物相分析中硅酸铁的分离测定方法述评

对铁矿石化学物相分析中硅酸铁的分离测定方法进行了简要述评。介绍了测定硅酸铁矿物相的重要性、硅酸铁的分离和测定方法研究进展等;通过验证实验和测试数据对比,进一步介绍了化学分离测定方法中的亚铁加合计算法的重要意义和实际应用价值。引用文献55篇。     

Ferric-ferrous equilibria in natural silicate liquids at 1 bar

Ferric and ferrous iron concentrations have been measured in 57 silicate liquids equilibrated at temperatures (1,200°–1,330°C) above the liquidus and at oxygen fugacities close to those defined by quartz-fayalite-magnetite. The experimental results reported here span virtually the entire known compositional range of lavas. An empirical equation relating the mole fraction of Fe₂O₃ and FeO to oxygen fugacity, absolute temperature and liquid composition at 1 bar has been formulated, based on the present experimental results and published data. Extrapolating the proposed empirical relationship over several hundred degrees, for instance below the solidus of the 1965 Makaopuhi tholeiitic lava lake, yields calculated oxygen fugacities which are a little lower than those measured directly in drill holes; at 1,100°C this discrepancy is 0.4 log unit. However, the agreement between the oxygen fugacities calculated from our empirical equation and those indicated by the composition of Fe-Ti oxides in andesites and siliceous obsidians is much closer.     

An Improved Procedure for the Determination of Ferrous Iron Mass Fraction in Silicate Rocks Using a Schlenk Line‐Based Digestion Apparatus to Exclude Oxygen

Precise and accurate determination of ferrous iron mass fraction in silicate rocks and geological reference materials is still a significant challenge due to the labile nature of the analyte. Here, we report a modified and improved procedure for the determination of ferrous iron mass fraction, capable of yielding moderately accurate and highly precise results in a relatively shorter time than before. This modified technique requires a more convenient operational procedure than the classical method. A sample digestion apparatus was designed that included a Schlenk line to expel air in order to prevent oxidation. The advantages of this procedure over the classical procedure are shorter process flow, higher efficiency and absence of an additional redox indicator. The composition of the acid matrix used to dissolve the samples as well as the incubation temperature and time was investigated. Comparative data for twenty‐one reference materials are reported, with five of them reported for the first time by the Schlenk line procedure. A series of experiments were carried out to identify and minimise the main source of error. In addition, the possibility of eliminating the reducing substances before digestion, by pretreatment of the sample by cold 10% methanolic bromine, was also studied.     

Role of superoxide in the photochemical reduction of iron in seawater

We have conducted a series of laboratory studies to investigate the generation of ferrous iron and reactive oxygen species when solutions of seawater containing natural organic matter (NOM) and ferric iron are exposed to simulated sunlight. Total ferrous iron and hydrogen peroxide were measured at nanomolar concentrations with high temporal resolution using chemiluminescence-based methods. In all cases, ferrous iron concentrations rapidly peaked at several nanomoles per litre after a few minutes, and then declined over time, while hydrogen peroxide concentrations increased in a non-linear manner. Although concentrations of both species depended on the concentration of NOM, hydrogen peroxide concentrations were only minimally affected by the presence of iron. Increasing the NOM concentration while the total iron concentration was maintained constant led to an increase in the maximum ferrous iron concentration, suggesting that superoxide-mediated reduction of iron may be a major pathway for ferrous iron formation. This was supported by measurements of superoxide production from irradiation of NOM in the absence of iron and kinetic calculations, as well as an experiment in which superoxide dismutase was added. Further analysis of the data suggested that dissolved oxygen and photo-produced hydrogen peroxide were the primary oxidants of the Fe(II) formed. Thus we propose that superoxide and ferrous iron may be intricately coupled in the system, and that their generation is determined by the supply of NOM available to harvest light and donate electrons.     

Mössbauer spectroscopic studies of iron in organic material from natural sedimentary environments

⁵⁷Fe Mössbauer spectra have been obtained from samples of humic acid, fulvic acid and kerogen and from the organic material extracted from bituminous chalk with benzene-methanol. The spectra indicate that iron occurs in a trivalent form in the silicate residue of the humic acid fraction, as hydrated ferrous ions associated with the fulvic acid fraction, as pyrite in kerogen and in a form not detectable by Mössbauer spectroscopy in the benzene-methanol extract.     

57Fe Mössbauer study of the asbestiform silicates balangeroite and carlosturanite

⁵⁷FeMössbauer spectra of the two silicate minerals balangeroite (BAL) and carlosturanite (CST) have been collected at 80 and 295 K under normal and magic angle geometry. For both minerals the spectra have been fitted with two ferrous and two ferric doublets; Fe²⁺ accounts for 80 and 62% of Fe_tot in Bal and CST, respectively. The number of doublets used to fit the spectra supports the hypotheses that: (i) in the serpentine-like structure of CST iron occupies only octahedra which lie between the tetrahedral silicate strips; (ii) the octahedral framework of BAL (actually monoclinic) is satisfactorily described with an orthorhombic sub-cell.     

钒矿床研究进展与展望

钒是工业国家重点关注和争夺的资源,已被部分国家列为关键金属。本文对矿床类型、地质特征、时空分布以及成矿机制等方面进行了系统总结和分析,以期丰富钒成矿理论研究,为提高钒资源的预测和勘查效率提供支撑,为钒资源储备提供保障。研究发现,钒矿床主要分为岩浆型和沉积型,其中岩浆型钒矿床（主要指钒钛磁铁矿床）成矿与铁镁质–超铁镁质岩及部分斜长岩侵位密切相关,成矿年龄与成岩年龄一致,钒可能来自上地幔并在岩浆演化过程中结晶析出赋存于含钒钛磁铁矿中;沉积型钒矿床多形成于黑色岩系及部分砂岩中,成矿多集中于上寒武世,钒可能来自海水和赋矿围岩,由于氧化还原电位降低,以吸附和类质同象等形式赋存于有机质和硅酸盐矿物中。同时,钒矿床的成因研究存在较多问题,如成矿物质钒的来源、迁移过程、赋存形式及富集条件等。笔者建议在今后研究中通过分析钒化学行为、围岩沉积物理–化学–生物条件及岩浆演化的地质动力背景来解析钒矿床成因机制。     

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.     

A simple model for the effect of hydration on the distribution of ferrous iron at reduced hematite (0 1 2) surfaces

Using a simple ionic model with polarizable oxygen ions and dissociating water molecules, we have calculated the energetics governing the distribution of Fe(II)/Fe(III) ions at the reduced (2 × 1) surface of α-Fe₂O₃ (hematite) (0 1 2) under dry and hydrated conditions. The results show that systems with Fe(II) ions located in the near-surface region have lower potential energy for both dry and hydrated surfaces. The distribution is governed by coupling of the ferrous iron centers to positive charge associated with missing oxygen atoms on the dry reduced (2 × 1) (0 2 1) surface. As the surface is hydroxylated, the missing oxygen rows are filled and protons from dissociated water molecules become the positive charge centers, which couple more weakly to the ferrous iron centers. At the same time, the first-layer iron centers change from fourfold or fivefold coordination to sixfold coordination lowering the potential energy of ferric iron in the first layer and favoring migration of ferrous iron from the immediate surface sites. This effect can also be understood as reflecting stronger solvation of Fe(III) by the adsorbed water molecules and by hydrolysis reactions favoring Fe(III) ions at the immediate surface. The balance between these two driving forces, which changes as a function of hydration, provides a compelling explanation for the anomalous coverage dependence of water desorption in ultra-high vacuum experiments.     

BIF成因研究进展

BIF在全球广泛分布,BIF型铁矿是铁的重要来源。根据产出的构造背景将其分为阿尔戈玛型（Algoma-type）和苏必利尔湖型（Lake Superior-type）。BIF主要产出于前寒武纪的古老克拉通和/或年轻地体,形成时代集中在3.0～2.0 Ga,峰期为2.5 Ga左右。前人对BIF型铁矿的成因研究着重于BIF的物质来源和Fe²⁺ 氧化沉淀机制两个方面,但都尚未达成共识。物质来源的观点主要有大陆风化剥蚀、海底热液、海底热液和海水的混合物、热液淋滤洋壳、既有大陆物质来源又有热液来源,沉淀机制主要有生物沉淀和非生物沉淀两种认识,前者是指Fe²⁺ 利用微生物（如蓝藻）光合作用产生的O₂氧化成Fe³⁺,或Fe²⁺ 直接被微生物代谢氧化,后者主要包括热液与海水混合、密度流作用、相分离、紫外线引起Fe²⁺ 氧化沉淀等。     

Weathering of phlogopite in simulated bioleaching solutions

The purpose of this study was to examine structural alterations of finely ground phlogopite, a trioctahedral mica, when exposed to acid, iron- and sulfate-rich solutions typical of bioleaching systems. Phlogopite suspensions were supplemented with ferrous sulfate and incubated with iron- and sulfur-oxidizing bacteria (Acidithiobacillus ferrooxidans) at 22 °C. As bacteria oxidized ferrous iron, ferric iron thus formed partially precipitated as K-jarosite. K-jarosite precipitation was contingent on the preceding ferrous iron oxidation by bacteria and the release of interlayer-K from phlogopite. This chemically and microbially induced weathering involved alteration of phlogopite to a mixed layer structure that included expansible vermiculite. The extent of phlogopite weathering and structure expansion varied with duration of the contact, concentration of ferrous iron and phlogopite, and the presence of monovalent cations (NH₄⁺, K⁺, or Na⁺) in the culture solution. NH₄⁺ and K⁺ ions (100 mM) added to culture suspensions precipitated as jarosite and thereby effectively prevented the loss of interlayer-K and structural alteration of phlogopite. Additional Na⁺ (100 mM) was insufficient to precipitate ferric iron as natrojarosite and therefore the precipitation was coupled with interlayer-K released from phlogopite. When ferrous iron was replaced with elemental sulfur as the substrate for A. ferrooxidans, the weathering of phlogopite was based on chemical dissolution without structural interstratification. The results demonstrate that iron oxidation and the concentration and composition of monovalent ions can have an effect on mineral weathering in leaching systems that involve contact of phlogopite and other mica minerals with acid leach solutions.     

河东煤田中部晚古生代含煤岩系中宇宙尘的首次发现及其特征

宇宙尘系重要的太阳系物质.笔者在利用双目镜、扫描电镜研究河东煤田中部晚古生代含煤岩系沉积岩时,发现了沉积的宇宙尘.可见到的表面显微构造特征有:无规则全晶质构造、晶间孔构造、熔蚀构造、瘤状构造、气孔和空腔构造、球粒构造、皱纹构造和碎裂构造等八种类型。由电子探针测定的化学成分得知,本区宇宙尘有玻璃质、硅酸盐质和铁质三种。它们均与已报道的宇宙尘的化学成分相似。但铁质宇宙尘中的Ir含量高达1.09%,这种“指纹元素”的大量存在,进一步证明了它们确系地外星球物质。     

Biogeochemistry and bacteriology of ferrous iron oxidation in geothermal habitats

A survey of hot, acid springs in Yellowstone Park has shown that high concentrations of ferrous and ferric iron are often present. Total ionic iron concentrations in different springs ranged from less than 1 ppm to greater than 200 ppm, and up to 50% of the ionic iron was in the ferrous form. Some of these springs also have high concentrations of reduced sulfur species (S^2? and S⁰). Significant populations of the bacterium Sulfolobus, acidocaldarius, an autotrophic organism able to live and oxidize sulfur compounds at low pH and high temperature, were present in most of these springs. The role of this organism in the oxidation of ferrous iron was investigated by incubating natural samples of water and assaying for disappearance of ferrous iron. Controls in which bacterial activity was inhibited by addition of 10% NaCl were also run. Bacterial oxidation of ferrous iron occurred in most but not all of the spring waters. The temperature optimum for oxidation varied from spring to spring, but significant oxidation occurred at temperatures of 80–85°C, but not at 90°C. Thus, 85–90°C is the upper temperature at which bacterial iron oxidation occurs; a similar upper limit has previously been reported for sulfur oxidation in the same kinds of springs. The steady-state concentrations of ferrous and ferric iron are determined by the rate at which these ions move into the spring pools with the ground water (flow rate), by the rate at which ferric iron is reduced to the ferrous state by sulfide, and by the rate of bacterial oxidation. The bacterial oxidation rate is faster than the flow rate, so that the rate of reduction of ferric iron is probably the rate-controlling reaction. In several springs, no decrease in ferrous iron occurred, even though high bacterial populations were present. It was shown that in these springs, ferrous iron oxidation occurred but the ferric iron formed was reduced back to the ferrous state again. These springs were all high in suspended sediment and the reductant was shown to be present in the sediment. X-ray diffraction revealed that the sediment contained three major ingredients, elemental sulfur, natroalunite, and quartz. Chemical analyses showed a small amount of sulfide, too little to reduce the ferric iron. Elemental sulfur itself did not reduce ferric iron but when elemental sulfur was removed from the sediment by CS₂ extraction, the activity of the sediment was abolished. It is hypothesized that the sulfide present in the sediment (possibly bound to natroalunite) reacts with elemental sulfur to form a reductant for ferric iron. The results show that bacteria can have a profound influence on the ferrous/ferric ratios of geothermal systems, but that temperature and mineral composition of the water may significantly influence the overall result.     

Phase relations of biotite and stilpnomelane in the greenschist facies

Phase relations of biotite and stilpnomelane and associated silicate minerals have been studied in rocks of the greenschist facies, chiefly from Otago, New Zealand and western Vermont, but also from Scotland, Minnesota-Michigan iron range, and northwest Washington. That stilpnomelane in the greenschicht facies crystallizes initially with nearly all iron in the ferrous state is indicated by chemical analyses, high p-T experiments, and phase relationships. Alteration of stilpnomelane after metamorphism not only oxidizes iron but leaches potassium; corrections for both effects must be made in using analyses of brown stilpnomelane in studies of phase relations. Two discontinuous reactions which produce biotite at the biotite isograd have been identified:

1. muscovite+stilpnomelane+actinolite→ biotite+chlorite+epidote
2. chlorite+microcline→ biotite+muscovite. Biotite produced by the first of these reactions has a limited range of variation in Fe/Mg. As grade advances within the biotite zone more magnesian and ferruginous biotites become stable in consequence of the two continuous reactions:
3. muscovite+actinolite+chlorite→ biotite (Mg-rich)+epidote
4. muscovite+stilpnomelane→ biotite (Fe-rich)+chlorite.

Stilpnomelane is stable in muscovite-free rocks throughout the biotite zone, and even up to the grade at which hornblende becomes stable. Phengitic muscovite is stable throughout the biotite zone in New Zealand and thus apparently does not contribute to the formation of biotite until a higher grade is reached.     

Formation of Carbon and Hydrogen Species in Magmas at Low Oxygen Fugacity

Studies of iron-bearing silicate melt (ferrobasalt) + iron metallicphase + graphite + hydrogen equilibria show that carbon andhydrogen solubilities in melts are important for the evolutionof the upper mantle. In a series of experiments conducted at3·7 GPa and 1520–1600°C, we have characterizedthe nature (oxidized vs reduced) and quantified the abundancesof C- and H-compounds dissolved in iron-bearing silicate melts.Experiments were carried out in an anvil-with-hole apparatuspermitting the achievement of equal chemical potentials of H₂in the inner Pt capsule and outer furnace assembly. The fO₂for silicate melt–iron equilibrium was 2·32 ±0·04 log units below iron–wüstite (IW). Theferrobasalt used as starting material experienced a reductionof its iron oxides and silicate network. The counterpart wasa liberation of oxygen reacting with the hydrogen entering thecapsule. The amount of H₂O dissolved in the glasses was measuredby ion microprobe and by step-heating and was found to be between1 and 2 wt %. The dissolved carbon content was found to be 1600ppm C by step-heating. The speciation of C and H componentswas determined by IR and Raman spectroscopy. It was establishedthat the main part of the liberated oxygen was used to formOH^– and to a much lesser extent H₂O, and only traces ofH₂, CO₂ and     

石煤钠盐焙烧气氛对钒转化的研究

石煤钠盐焙烧是复杂的气、液、固多相化学反应,焙烧气氛对钒焙烧转化率有重要影响。本文在钒价态研究工作的基础上,研究了在氧化—氯化焙烧下,提高气相中HCl或Cl_2分压,使钒转化率有不同程度的提高,小试表明能提高5～20％,半工业生产试验提高5.4％。该技术简易可行,实用性强,具有较好的经济效益。 本文对氧化—氯化焙烧的技术条件、焙烧温度、时间、含碳量及钠盐配比等作了全面研究。通过气体成分分析,焙砂浸出液成分分析和物相分析鉴定,对氧化—氯化焙烧提高钒焙烧转化率的机理作了探讨。     

Alkali loss and retention in an iron-rich peralkaline phonolite dyke from the Gardar province,south Greenland

An unusually iron-rich, strongly peralkaline dyke occurring near the Ilimaussaq intrusion, south Greenland, is described. The dyke has developed two facies characterised respectively by the mafic assemblages pyroxene+amphibole+aemigmatite, and pyroxene+magnetite. The differences can be explained as an effect of loss of up to 4% Na₁O from the magnetite-bearing facies (relative to the magnetite-free facies). The effect is in accordance with the phase relations at 1 atm in the synthetic system Na₂OAl₂O₂Fe₂O₂SiO₂. Continued alkali loss and magnetic precipitation will change the differentiation trend from agpaitic with iron enrichment towards miaskitic with iron depletion. It is suggested that the extreme degree of iron enrichment in the dyke resulted from the coincidence of low oxygen fugacity and strong peralkalinity tending to stabilise both ferrous and ferric iron in the liquid.     

Differential Alteration of Ilmenite in a Tropical Beach Placer, Southern India: Microscopic and Electron Probe Evidences

Abstract. The study based on microscopic and microprobe techniques reveals that ilmenite of Manavalakurichi deposit has generally reached the alteration phase of 'leached ilmenite'. The XRD and bulk chemical analysis confirm the limited alteration undergone by ilmenite grains. Ilmenite alteration has been found to be a process of continuous leaching of iron from the mineral lattice and hydroxylisation. The enrichment of trace elements with progressive alteration is discussed. Si and Al are enriched by more than 100 fold. The prevalence of reducing environment at present in the deposit indicates that the oxidation of ferrous iron leading to pseudorutile formation would have occurred during transportation of sediments.     

Penetration of molten iron alloy into the lower mantle phase

The core–mantle boundary is the only interface where the metallic core and the silicate mantle interact physically and chemically. Many geophysical anomalies such as low shear velocity and high electrical conductivity have been observed at the bottom of the mantle. Perturbations in the Earth's rotation rate at decadal time periods require the existence of a thin conductive layer with a conductance of 10⁸ S. Substantial additions of molten iron from the outer core into the mantle may produce these geophysical anomalies. Although iron enrichment by penetration has only been observed in (Mg,Fe)O, the second dominant mineral in the lower mantle, the penetration process leading to iron enrichment in the silicate mantle has not been experimentally confirmed. In this study, high-pressure and high-temperature experiments were conducted to investigate the penetration of molten iron alloy into lower mantle phases; postspinel, polycrystalline bridgmanite and polycrystalline (Mg,Fe)O. At the interface between (Mg,Fe)O aggregate and molten iron alloy, liquid metal penetrated the (Mg,Fe)O aggregate along grain boundaries and formed a thin layer containing metal-rich blobs. In contrast, no penetration of molten iron alloy was observed at the interface between molten iron alloy and silicate phases. Penetration of liquid iron alloy into the (Mg,Fe)O aggregate is caused by the capillarity phenomenon or Mullins–Sekerka instability. Neither mechanism occurs at the boundary of pure polycrystalline MgO, indicating that the FeO in (Mg,Fe)O plays an essential role in this phenomenon. Infiltration of molten iron alloy along grain boundaries (capillarity phenomenon) is the dominant process and precedes penetration due to the Mullins–Sekerka instability. The capillarity phenomenon is governed by the balance of forces between surface tension and gravity. In the case where the ultralow velocity zone (ULVZ) with a low shear velocity is composed of Fe-rich (Mg,Fe)O, the maximum penetration distance of molten iron alloy by capillary rise is limited to 20 m. The addition of iron-rich melt to the base of the mantle is therefore unlikely to be the main cause of the high conductance of the CMB region predicted from decadal variation of the length of day. Furthermore, the absence of molten iron alloy penetration into silicate phases does not allow an extensive modification of the chemical composition of the mantle by core–mantle interaction.