Showing papers on "Magnetite published in 1985"

Spectral and other physicochemical properties of submicron powders of hematite (alpha-Fe2O3), maghemite (gamma-Fe2O3), magnetite (Fe3O4), goethite (alpha-FeOOH), and lepidocrocite (gamma-FeOOH).

Abstract: The spectral properties (0.35-2.20 microns) of submicron powders of hematite, maghemite, magnetite, goethite, and lepidocrocite are determined. Other physicochemical data are obtained for the powders in order to determine if deviations from stoichiometry occur due to their small particle size, to determine their state of chemical and phase purity, and to determine the physical characteristics of the individual powders. The physicochemical data obtained include mean particle diameter, discrete particle shape, chemical composition, crystallographic phase, magnetic parameters, and Moessbauer parameters. The positions of the spectral features for the hematite, maghemite, and magnetite powders are independent of temperature over the interval between about +20 and -110 C. For the goethite and lepidocrocite powders, a small shift of about 0.02 micron to shorter wavelengths is observed for some of the features after cooling to about -110 C. The spectral properties of the iron oxides and oxyhydroxides are important not only for understanding the basic physics and chemistry of the compounds but also for applications such as the remote sensing of the earth and Mars.

The nature and origin of titaniferous magnetite-rich layers in the upper zone of the Bushveld Complex; a review and synthesis

Abstract: The occurrence and geologic relationships of Ti magnetite layers indicate that their genesis is intimately related to fractional crystallization processes that were responsible for the formation of their silicate host rocks. The exact mechanism by which these oxide-rich layers form is, however, still debated. Most recent models recognize that precipitation of copious quantities of Ti magnetite is triggered by episodic increases in f (sub O 2 ) , but the process whereby this occurs is not well understood. The nature and occurrence of Ti magnetite-rich layers in the Bushveld Complex is reviewed and the requirements of any satisfactory genetic model are outlined. The formation and subsequent textural evolution of Ti magnetite layers is believed to have taken place as follows:1. Favorable conditions for the precipitation of large quantities of Ti magnetite were created by a lengthy period of fractional crystallization that resulted in the concentration of large amounts of Fe, Ti, and V in the residual magma.2. Large-scale in situ bottom crystallization of plagioclase resulted in a marked increase in the total Fe content and density of the immediately surrounding melt which collected as a dense layer on the bottom of the magma chamber. This dense Fe-Ti-(V)-enriched liquid did not mix with the overlying magma and formed a stagnant layer from which copious amounts of Ti magnetite may have crystallized.3. Crystallization of Ti magnetite is controlled by the Fe 2 O 3 /FeO ratio of the liquid and is a function of f (sub O 2 ) , temperature, and the f (sub H 2 O) /f (sub H 2 ) ratio. The Fe 2 O 3 content of the liquid will also increase during the crystallization of ilmenite and Fe (super +2) -bearing silicates (clinopy-roxene, pigeonitc, and fayalitic olivine). The H 2 O content of the residual liquid will also be increased by the fractionation of anhydrous silicate phases.4. A complex interplay of these factors resulted in the precipitation of relatively large amounts of Ti magnetite required for the development of ore-rich layers. The bulk of the Ti magnetite formed by in situ bottom crystallization. The nucleation and growth of magnetite within the stagnant layer and gravitative settling of these crystals over a short distance (on the order of meters) may have augmented the growth of the layers.5. Variations in the relative proportions of coexisting oxide and silicate phases may be related to differences in concentrations and diffusion rates of ions in the liquid immediately above the crystallizing layer. This resulted in differences in the rates of nucleation and growth of individual phases.6. Precipitation of abundant magnetite lowered the density of the stagnant layer until it reached that of the overlying magma. The two liquids then mixed, thus terminating the cycle of magnetite layer formation and marking a return to silicate-dominated fractionation.7. The ore-rich layers originally consisted of Ti magnetite crystals and variable amounts of silicate crystals which contained a certain amount of interstitial residual liquid. Densification of these layers and expulsion of significant amounts of this liquid were accomplished by annealing at high subsolidus temperatures, possibly augmented by the addition of suitable material from interprecipitate liquids.8. Variations in f (sub O 2 ) during subsolidus cooling resulted in the development of a wide range of ulvoespinel and ilmenite microintergrowths.

The concentration of iron in chloride solutions equilibrated with synthetic granitic compositions; the sulfur-free system

Abstract: The concentrations of iron in 1 N chloride solutions have been determined at temperatures from 400 degrees to 700 degrees C and a pressure of 1 kb for fluids in equilibrium with synthetic magnetite- or biotite-bearing granitic (quartz monzonite) compositions. K/H and Na/H ratios in solution were controlled by reactions similar to those observed in natural alteration assemblages involving alkali feldspar and plagioclase with aluminosilicate, muscovite, or montmorillonite. Oxygen fugacity was controlled by internal or external methods using hematite-magnetite, Ni-NiO, and quartz-fayalite-magnetite assemblages. Starting compositions of fluids were solutions of HCl, 2HCl:FeCl 2 , HCl:NaCl, and NaCl:KCl:FeCl 2 . Equal masses (i.e., low liquid/solid ratios) of solid and solution were used to expedite equilibration. Iron was added as synthetic magnetite, synthetic biotite, or in solution. Run times ranged from four days to several weeks.At 400 degrees C, the dominant cations in solutions are Na, K, and Ca, with Fe concentrations of 0.01 to 0.03 molal. At 500 degrees C, Na, K, and Fe are dominant with Fe concentrations of 0.10 to 0.17 molal. At 600 degrees C, the Fe concentration reaches a maximum of 0.20 to 0.25 molal and then appears to drop to between 0.10 to 0.15 molal at 700 degrees C. The effect of f (sub O 2 ) on concentration is consistent with changes in the iron-bearing assemblage from magnetite to biotite, and along with charge balance calculations, suggests that ferrous chloride is the dominant species at low temperatures. These data indicate that in natural magmatic systems, the concentration of iron in chloride solutions coexisting with magnetite or biotite is extremely high. This high solubility may explain the large quantities of iron deposited in skarns and related deposits around some mineralized granitic stocks.

The geochemistry of titanomagnetite in magnetite layers and their host rocks of the eastern Bushveld Complex

Abstract: More than 430 analyses of magnetite separates revealed pronounced differences in composition between magnetite from magnetite layers and disseminated magnetite from the host rocks. Magnetite from the massive layers is among others enriched in elements such as Ti, Mg, Al, and Si, which suggests that this magnetite crystallized under conditions of disequilibrium with the magma, i.e., by spontaneous nucleation and rapid crystallization. Lower vanadium values in the magnetites from the massive layers suggest crystallization at higher f (sub O 2 ) than from the rocks containing the disseminated magnetite.Variation diagrams reveal a cyclicity in compositional trends upward in the sequence which is related to nucleation of the magma in the roof zone of the intrusion, the periodic collapse of this crystal-laden magma, and its incorporation in the zone of crystallization at the base of the magma chamber. Deviations of this normal trend are considered to reflect a stratification of the roof zone and a gradual incorporation of the stratified roof zone liquid into the convecting magma. A pronounced upward increase in the Cr content of magnetite is tentatively ascribed to a combination of olivine crystallization at the expense of pyroxene in the upper subzones and a possible increase in the partition coefficient of chromium between spinel and liquid with a decrease in the crystallization temperature.

Contrasted mineralogy and textural relationships in the uppermost titaniferous magnetite layers of the Bushveld Complex in the Bierkraal area north of Rustenburg

Abstract: Disseminated Fe-Ti oxides and ore-rich concentrations of these minerals in a 1,230-m vertical borehole section through the top of the upper zone of the Bushveld Complex are described. The succession consists of a layered sequence of highly fractionated olivine-rich rocks that range in composition from ferrogabbro to diorite. The Fe content of the olivine increases systematically from Fa 65 at the base to a maximum of Fa 94 at the top of the section. Fe-Ti oxides axe present throughout this interval and are divided into three distinct groups on the basis of their mineralogy and chemistry: (1) an apatite-poor, high Ti magnetite association, (2) an apatite-rich, high Ti magnetite association, and (3) an apatite-poor, low Ti magnetite association. The Ti magnetite in each of these associations exhibits a wide variety of ulvoespinel and/or ilmenite microintergrowths, the development of which can be interpreted in terms of the ambient f (sub O 2 ) at various stages of subsolidus cooling. Certain Ti magnetite crystals are characterized by the development of radiating, eutectoidlike intergrowths of magnetite and ilmenite or ulvoespinel that appear to represent duplex cell decomposition products of magnetite-ulvoespinel solutions.The apatite-poor, high Ti magnetite represents the dominant opaque oxide association and is present both as disseminations and distinct ore-rich layers, particularly toward the base of the study section. The greatest concentration of this association occurs at a depth of between 1,033 to 1,060 m below the top of the intrusion. The lowermost 14 m of this interval consist of a thick composite Ti magnetite layer that contains numerous silicate inclusions and partings. This is believed to represent the equivalent of the uppermost Ti magnetite layer (layer 21) in the eastern Bushveld Complex. Groups of minor Ti magnetite layers are also present at depths of 412 and 225 m below the top of the intrusion. The Ti content of the magnetite increases with increasing stratigraphic height from 55 mole percent ulvoespinel at the base to 65 mole percent near the top of the study section where it gives way to the Ti-poor association. The beginning of Ti-poor magnetite precipitation 225 m below the roof of the intrusion marks the onset of Ti depletion in the residual liquid. Ilmenite is virtually the only Fe-Ti oxide phase present in the uppermost 100 m of the complex. Both these associations formed in response to normal fractional crystallization processes, the formation of discrete ore-rich layers being triggered by episodic increases in f (sub O 2 ) . The apatite-rich, high Ti magnetite association is present both as disseminations and in ore-rich concentrations but is restricted to three relatively narrow horizons within the study section. These are developed at the following depths below the top of the intrusion: 233 to 283 m, 677 to 700 m, and 1,033 to 1,108 m. Discrete ore-rich concentrations consisting almost entirely of Ti magnetite + ilmenite ( approximately 70 vol %) and apatite ( approximately 30 vol %) are present in the lower 2 m of the middle horizon. The upper and lower horizons contain only disseminated opaque oxide-apatite assemblages. The formation of these assemblages is interpreted in terms of the separation of immiscible Fe-Ti-Mn-Ca-P-REE-enriched liquids from the late-stage dioritic residual melt.

Exsolution features in titanomagnetites from massive magnetite layers and their host rocks of the upper zone, eastern Bushveld Complex

Abstract: A systematic investigation of the exsolution textures in titanomagnetite grains of massive magnetite layers and their associated host rocks from the entire upper zone sequence has revealed noticeable differences that can be related to changes in the oxidation state of the magma during crystallization and cooling. The observed oxidation exsolution intergrowths indicate a higher f (sub O 2 ) during formation of the magnetite layers than during crystallization of the disseminated titanomagnetite, as well as a decrease in the f (sub O 2 ) required to precipitate successive titanomagnetite-rich layers upward in the sequence.Peculiar composite lamellar intergrowths of magnetite and ilmenite in the uppermost magnetite layers and in some magnetite plugs are ascribed to a subsolvus oxidation of ulvoespinel in ulvoespinel-rich magnetite. The configuration of the magnetite-ulvoespinel solvus dictates that ulvoespinel in Ti-rich magnetite-ulvoespinel solid solution high in the succession exsolves at considerably higher temperature than in Ti-poor solid solution lower in the sequence. Subsolvus oxidation of ulvoespinel to ilmenite at higher temperatures near the top of the intrusion facilitated diffusion of ilmenite to produce the variety of different composite exsolution textures. The textures are not developed where abundant oxidation exsolution of ilmenite has taken place at temperatures above the solvus.

Ferrimagnetic Properties of Magnetite

Abstract: Magnetite (Fe3O4, ferrous–ferric oxide) is ubiquitous as the source of the magnetism of most biological magnetic systems. Although a cation-deficient form of it, maghemite (γ- Fe2O3), and impurity-substituted magnetite (titanomagnetite) have on occasion been identified in biomagnetic systems, magnetite continues to be the primary magnetic source in biology. It is of interest, therefore, to inquire into the origin of its magnetism, or more properly, the ferrimagnetism of magnetite. In this chapter we deal with the ferrimagnetism of magnetite single crystals first. We then occupy ourselves with the application of magnetic domain theory to the particle-size-dependent properties of magnetite and the various kinds of intrinsic remanent magnetization contributed to by magnetite. The only type of natural remanent magnetization which we have not discussed here is depositional remanent magnetization (DRM), as it is still rare to find examples where biogenic magnetite has been convincingly shown to be responsible for the DRM in a sediment. Future research may prove otherwise. Finally, we deal with some practical magnetic techniques for determining the magnetic domain state, hence the effective particle size, of magnetite.

The influence of inorganic phosphate on the crystallization of magnetite (Fe3O4) from aqueous solution

Abstract: The formation of magnetite (Fe3O4) from the oxidation of FeII solutions results in small (20–60 nm) irregular-shaped crystals; in the presence of 5–10% inorganic phosphate Pi the crystal morphology is selectively enhanced whilst at 20–30% Pi-doping crystallization is severely inhibited.

An oxygen and sulfur isotope study of skarn-type magnetite deposits of the Cornwall type, southeastern Pennsylvania

Abstract: Contact metasomatic magnetite ores of the Cornwall type in Pennsylvania occur as replacements of carbonate rocks adjacent to sheets and dikes of Triassic diabase. In addition to large (10 8 tons) magnetite deposits at Cornwall and Morgantown (Grace mine), about 45 smaller occurrences are known in a zone 150 km long. Major gangue minerals include early diopside, phlogopite, and garnet followed by actinolite, ohiorite, talc, serpentine, pyrite, chalcopyrite, and pyrrhotite associated with abundant magnetite. Based on mineral assemblages, temperatures of deposition are inferred to be less than 500 degrees C for most of the magnetite.At Cornwall, 50 samples of magnetite have delta 18 O between 5.2 and 11.0 per mil (SMOW), with the highest values (mean (x) delta 18 O = 9.3ppm, standard deviation (Sigma ) = 0.66ppm, n = 19) adjacent to the diabase and the lowest values (x = 6.6ppm, Sigma = 0.69ppm, n = 14) near replaced marble. Thirty-five magnetite samples from 19 other Cornwall-type deposits fall within a similar range (x = 7.9ppm, Sigma = 1.97ppm). Silicates from the Cornwall deposit also show unusually high delta 18 O (13 actinolites, x = 12.4ppm, Sigma = 0.47ppm; 6 phlogopites, x = 12.3ppm, Sigma = 0.73ppm; 3 diopsides, x = 13.1ppm, Sigma = 0.19ppm). At Cornwall, 36 samples of pyrite and chalcopyrite have delta 34 S (CDT) of 6.3 to 19.9 per mil (x = 10.9ppm, Sigma = 2.91ppm).Calcites from the ore (delta 13 C = -5.9ppm (PDB), Sigma = 0.93ppm, delta 18 O = 17.5ppm, Sigma = 0.45ppm, n = 4) are distinctly depleted in both 18 O and 13 C relative to the unaltered host limestones (delta 13 C = -1.3ppm, Sigma = 0.44ppm, delta 18 O = 20.6ppm, Sigma = 0.68ppm, n = 15), which are similar to other Cambrian limestones in the literature. Marbles adjacent to ore are intermediate in 13 C and 18 O between carbonates in ore and unaltered limestones. Thermally metamorphosed marbles adjacent to diabase but away from ore are depleted only in 13 C relative to unaltered limestones.The magnetite, silicate, and carbonate minerals in the skarn-type ore in all 20 deposits are calculated to have formed in fluids with delta 18 O (sub H 2 O) of 13 to 16 per mil. The very high delta 18 O of the fluid is difficult to explain by conventional ideas on a magmatic origin for skarnforming fluids. The diabase, which has a normal igneous delta 18 O of 7.4 to 7.8 per mil, would have furnished fluids with delta 18 O of 7 to 10 per mil and therefore camlot be the direct source of the ore fluids.The preferred explanation of the 18 O-rich skarn is that an 18 O- and 34 S-enriched ore solution was formed by heating and circulation of meteoric, connate, or possibly magmatic waters in sedimentary rocks near the contact of the diabase. Exchange of 18 O with shales, argillaceous sandstones, or limestones at high temperatures created the 18 O-rich fluid. This fluid, upon encountering carbonate in the contact zone of the diabase, replaced it with magnetite and silicates. The relatively high Cu and Co contents of the Cornwall ore suggest that the ore fluid either contained a magmatic component or interacted with diabase to some extent. Zoning of 18 O away from the contact appears to result from decreasing temperature of deposition of the skarn farther from the contact.An alternative explanation is that the high delta 18 O values of magnetite and silicates were determined by the high delta 18 O values of the replaced carbonate in a diffusion-controlled process. In a diffusion-controlled process, the amount of water flowing through the replacement front might be negligible compared to the flux of Fe and other dissolved species. The presence of delta 18 O-rich alteration within the diabase and the lack of correlation of delta 18 O-rich of ore with delta 18 O of replaced carbonate indicate that this process is probably not the dominant one causing the high delta 18 O, but it might contribute to the range of values observed.

Heavy metals removal by high gradient magnetic separation

Abstract: Experimental data is presented on the effective removal of heavy metals such as cadmium, copper, nickel and zinc by absorption onto ferric hydroxide flocs. Ferric sulphate is used as the source of ferric ions along with a small amount of magnetite which is added to make use of high gradient magnetic separation. This paper examines the use of HGMS for this operation. The role of pH, flow rate through the filter, magnetic field strength and collection tube diameter is discussed in detail.

Mineral layering in the Bushveld Complex; implications of Cr abundances in magnetite from closely spaced magnetitite and intervening silicate-rich layers

Abstract: The Cr abundances in magnetite separates from the Main Magnetite layer, 1 magnetite layers 1 and 2, and the intervening anorthositic horizons have been determined from two widely spaced localities in the eastern Bushveld Complex. Chromium abundance is greatest at the base of the Main Magnetite layer (around 7,000 ppm) and decreases rapidly with height through this layer and the overlying anorthositic horizon. The base of layer 1 is associated with a high Cr content (about 1,500 ppm), which is followed by a steady upward decrease. The base of layer 2 is also characterized by a high Cr abundance (about 900 ppm) and detailed studies indicate a slight rise in Cr near the base of this layer.Chromium abundance profiles are examined in the light of several models which have been proposed for the origin of mineralogical layering. The general features of the abundance profiles are compatible with a variety of models; however, it appears that the detailed features of these profiles are best accounted for by a model involving bottom growth, with a slow and variable rate of supply of Cr to the crystallization zone.

Process for producing alkali metal ferrates utilizing hematite and magnetite

Abstract: Alkali metal iron (IV) and iron (VI) ferrates are produced by forming a particulate mixture of reactants including an alkali metal nitrogen oxygen compound and an iron material selected from the group of iron oxide, Fe2O3, Fe304 and an iron compound which self-reacts at a temperature less than about 1100°C to form Fe203. The mixture of reactants is subjected to a predetermined elevated temperature for a predetermined time duration sufficient to bring about a reaction between the reactants which produces at least one of iron (IV) and iron (VI) ferrates. The molar ratio of alkali metal nitrogen oxygen compound to the iron material is preferably in the range extending between about 4:1 and about 8:1.

Mössbauer spectra, magnetic and electrical properties of laihunite, a mixed valence iron olivine mineral

Abstract: Laihunite is an olivine mineral with ideal composition Fe2+Fer+(Sion)r. Alternate M1 sites are occupied by Fe2* whereas Fe3+ occupies the M2 sites. Small (-1mm) crystals from Laihe, N.E. China exhibit thermally-activated electrical conduction in the range 290-500 K with an activation energy of 0.53 eV. Resistivity at 290 K is 2.2 x 105 Qm. Mdssbauer data show that ferric iron begins to order magnetically below 160+5 K, but that hyperfine splitting for ferrous iron only appears below 100 K. An antiferromagnetic structure ir p.oposed which is consistent both with the crystal structure and with the magnetization curves that indicate antiferromagnetic interactions. Magnetization measurements also show that magnetite inclusions account for less than 0.5 wt.Vo of the sample. Analysis of the 4.2 K Mcissbauer spectrum suggests that there is a distortion of the structure at low temperatures which leads to inequivalent Ml and M2 sites, each with relative populations oi 2'1. In addition, 5+2% of the total iron is identified as Fe2* onM2 sites. This supports evidence from X-ray diffraction which indicated that roughly lO% of the crystal is composed of twin boundary regions with a concentration of divalent ions approaching that of fayalite.

Method of separation of material from material mixtures

Abstract: A method of separating the constituent minerals of a mixture of minerals requires the introduction of fine particles of magnetic material such as finely ground particles of magnetite. The control of the zeta-potential of the minerals and particles of magnetic material provides heterocoagulation of the magnetized particles with one mineral but not the other to achieve separation. The method is ideally suitable for separating carbonates and phosphate ore and the separation process is enhanced by the addition of a surfactant such as oleate. The slurry is preferably subjected to low intensity magnetic separation to remove unattached particles of magnetic material which can be recycled to keep costs to a minimum.

Formation of awaruite in the system Ni-Fe-Mg-Si-O-H-S and olivine hydration with NaOH solution, an experimental study

Abstract: The serpentinization of Mg, Fe, Ni olivine by NaOH solution at very low sulfur fugacity and in a sulfur-free system has been investigated experimentally below the stability field of the assemblage olivine + water, at 350 degrees + or - 5 degrees C and 2,000 + or - 50 bars. Serpentinization at very low sulfur fugacity produces the opaque mineral assemblage of heazlewoodite + Ni-poor magnetite + Ni-poor awaruite, while in the sulfur-free system, an opaque mineral assemblage of Ni-rich magnetite + Ni-rich awaruite is formed. The serpentine minerals (antigorite and chrysotile) obtained during the serpentinization process contain some Ni and Fe (with an Ni/Fe ratio of 0.4-2.4). The composition of the minerals produced is dependent on the composition of the original olivine, oxygen, and sulfur fugacities.

Detection, Extraction, and Characterization of Biogenic Magnetite

Abstract: Several difficulties arise when attempts are made to characterize the deposits of magnetite found in metazoans. We are usually forced to deal with very small amounts of material, dispersed in tissues, using indirect methods that are subject to contamination. Magnetite crystals in the abdomens of bees (Gould et al., 1978), and in the heads of pigeons (Walcott et al., 1979), and other vertebrates (Bauer et al., this volume; Perry et al., this volume; Walker et al., this volume) are submicroscopic (<100 nm), occupy a combined volume of 10−10 to 10−8 cm3, and have a mass of 1–100 ng. In organisms of up to 100 kg or more, detecting such quantities of magnetite from its magnetic properties depends on the crystals being highly concentrated in small, recognizable structures, and not uniformly dispersed throughout all the tissues. Extraction and recovery of the crystals likewise depend on their being sufficiently concentrated to be magnetically detectable.

Fe-Ti-oxides in metamorphic basites from the Eastern Alps, Austria: a contribution to the formation of solid solutions of natural Fe-Ti-oxide assemblages

Abstract: The development of Fe-Ti oxide assemblages in basic rocks from the Penninic series of the southern Venediger rea, Austria, during polyphase Alpine metamorphism has been studied. Textural and compositional relations indicate thorough reequilibration of the opaque mineral assemblages during late Barrovian metamorphism at essentially static conditions of lower amphibolite to greenschist facies. In contrast, silicate mineralogy of the preceeding blueschist to eclogite facies metamorphism might still be preserved to a large extent. Chemical adjustment of the Fe-Ti oxide minerals to decreasing P-T conditions is characterized by (1) formation of complex intergrowths of ilmenite and hematite solid solutions (<550° C), (2) the decomposition of hemo-ilmenite 1 to ferrianilmenite2+magnetite+rutile and of ilmeno-hematite1 to titanhematite2+rutile±magnetite (<450° C), and (3) low-grade oxidation of ferrianilmenite2 to magnetite+hematite-rutile intergrowths or hematite +rutile and of titanhematite2 to hematite-rutile intergrowths (≦400° C). Chemical equilibrium is suggested by the regular partitioning of Cr, V, Mg and Mn between coexisting hemo-ilmenite, ilmeno-hematite, and magnetite. The hematite-ilmenite miscibility gap has been delimited on the basis of the bulk compositions of the exsolved phases and the temperature estimates obtained from Fe-Ti oxide thermometry.

Apatite iron ores of the Kiruna field, northern Sweden: magmatic textures and carbonatitic affinity

Abstract: Primary textures in the Kiirunavaara apatite iron ore suggest a magmatic origin. They comprise (a) columnar development of magnetite similar to a crystal growth texture due to rapid cooling in the El Laco iron ore, Chile, (b) ‘skeleton ore’ with platy magnetite, locally dendritic - a widespread ore type also in the other iron deposits of the Kiruna Field, and (c) ore with thin tabular pyroxene crystals, partly dendritic, distributed in a way clearly indicating flow in a consolidating ‘ore magma’. In addition, the reported cross-bedding and graded bedding in the Kiruna ores might be igneous sedimentation features. The relationship between different ore types suggests a complex emplacement history. Some associated breccias and ‘conglomerates’ might be the consequence of gas discharge, i.e. tuffisites. Some of the Kiruna ores appear to have a carbonatitic affinity, with ankerite as a seemingly primary constituent; certain associated albite-rich rocks might be regarded as analogous to fenites. The in...

Magnetic recording medium

Abstract: PURPOSE:To obtain the titled magnetic recording medium having excellent magnetic characteristics without necessitating any protective layers by forming an iron oxide layer which is thinner than a magnetic layer on the metallic thin film magnetic layer formed on a substrate CONSTITUTION:The surface of an undercoat layer 2 formed on an aluminum substrate 1 is polished, and then a magnetic layer 3 (<=01mum thickness) of Co or Ni-Co is electroless-plated Subsequently, an iron magnetic layer which is thinner than the magnetic layer 3 is formed, in about 002mum thickness, on the magnetic layer 3 The substrate is then immersed in an alkaline liquid at high temps, and the iron magnetic layer is converted into a magnetite layer 10 of iron oxide Since the magnetite is a magnetic body and has high mechanical strength, the magnetic recording medium having high mechanical strength can be realized without damaging the magnetic characteristic

Behavior of Constituent Minerals in the Carbon Monoxide Reduction of Sinter at 900°C

Abstract: The reduction behavior of constituent minerals of iron ore sinter has been investigated microscopically by using two kinds of commercial sinter having different basicity and FeO content. The results are summarized as follows:(1) There is a difference in reducibility between hematite and magnetite, and hematite is reduced faster than magnetite.(i) Both hematite and magnetite are reduced rapidly to wustite, but there is a difference in the rate of reduction from wustite to iron.(ii) The reduction of wustite reduced from hematite does not proceed topochemically but homogeneously. Although the reduction of the wustite is comparatively fast in the almost whole period of reduction, part of the wustite becomes surrounded by dense iron and left unreduced in the final stage of reduction.(iii) In the reduction of wustite reduced from magnetite, almost all grains of wustite are surrounded by dense iron from the early stage of reduction, which causes the retardation of reduction.(2) Calcium ferrite is reduced much faster than the wustites mentioned above, which is shown by the fact that many grains of wustite are left unreduced even after calcium ferrite is reduced completely.(i) The reduction of calcium ferrite proceeds topochemically.(ii) Iron produced by the reduction of calcium ferrite is very porous and not sintered, which does not cause the retardation of reduction.(3) In many cases, reduction begins with the surface of mineral grains facing a macro-pore, which serves as a passage of reducing gas to each mineral grain to be reduced.

Mineralization at the Golden Grove Cu – Zn deposit, Western Australia. I: Premetamorphic textures of the opaque minerals

Abstract: The competent opaque minerals in the Archaean Golden Grove deposit, pyrite and magnetite, retain pre-regional metamorphic textures despite the lower greenschist-facies grade of metamorphism. The pre-regional metamorphic textures and structures recognized include the development of pyrite and magnetite overgrowths, the replacement of pyrrhotite by pyrite, the conversion of a primary hematite–goethite mineralogy to magnetite and, as a result of thermal metamorphism, further local replacement of pyrrhotite (and sphalerite) by magnetite. Comparisons between pyrite from the Cu-rich mineralization at the base of the deposit and that from the Zn-rich mineralization in the hanging wall indicate that postdepositional modification and recrystallization were more extreme at the base of the deposit. The pre-regional metamorphic textures and structures indicate that pyrite and magnetite overgrowths developed almost immediately after primary precipitation ceased and that overgrowths continued to develop into the late h...

Magnetite in Chitons

Abstract: Radular teeth of chitons were studied using Mossbauer spectroscopy. Their spectra gave clear evidence of the presence of magnetite and a small amount of paramagnetic substance. These are characteristic features in biogenic magnetite. Measurements on the teeth at different locations along the radula were also performed. The results show that the magnetite in the radular teeth of chitons changes considerably from its stoichiometry as the teeth mature.

Initial permeability of single crystal magnetite and Mn-ferrite

Abstract: The behaviour of the initial permeabilityμ of the single crystal magnetite and of the Mn0·5Fe2·5O4 ferrite (Mn-ferrite) is studied by two methods in the 10 to 300 K temperature range at three audio frequencies. Two anomalies in the temperature dependence ofμ were found in magnetite. The first, occurring near the Verwey transition,Tv=121 K, appeared to be independent of the measuring frequency. The other, near 40 K, was found to be frequency dependent and confirmed thus the presence of an electronic type of the relaxation process.