Magnetite Component Research Articles

The Olivine-Spinel-aSiO2melt (OSaS) Oxybarometer: A New Method for Evaluating Magmatic Oxygen Fugacity in Olivine-Phyric Basalts

Abstract The compositions of cotectic olivine-spinel pairs in mafic magmas provide information on the oxygen fugacity of their host liquid, which can be accessed with a thermodynamic analysis of the olivine-spinel-liquid peritectic reaction: 3 F e 2 S i O 4 o l i v + O 2 s y s = 2 F e 3 O 4 s p + 3 S i O 2 m e l t The extraction of redox information from cotectic olivine-spinel pairs requires a well-defined silica activity value (aSiO2melt) for the melt of interest, as well as a method to calculate aFe2SiO4oliv and aFe3O4sp from chemical analyses of olivine and spinel, respectively. In this work, we develop a new olivine-spinel-aSiO2melt (OSaS) oxygen barometer that utilizes MELTS to obtain values of aSiO2melt, which are used with values aFe2SiO4oliv and aFe3O4sp determined from established solution models for olivine and spinel. We find that two implementations of the spinel-liquid peritectic equilibria can successfully generate magmatic oxygen fugacity values, (1) using a combination of mineral activity models from the literature (classical-OSaS) and aSiO2melt determined from MELTS, and (2) directly from chemical potentials obtained from MELTS, where a correction is added to the MELTS-derived chemical potentials for the magnetite component of the spinel (MELTS-OSaS). The two implementations of the OSaS were tested by using each model to recover the experimentally reported fO2 values for a dataset consisting of 50 olivine-spinel-glass assemblages derived from 14 published experimental studies. This dataset was filtered to remove potential disequilibrium phase assemblages, experiments with failed redox buffers, and poor-quality EMP analyses. Data quality metrics for the dataset filtration included Fe-Mg partitioning between olivine and melt, Fe-Mg partitioning between olivine-spinel, and an examination of whether aSiO2melt values were consistent with the reported phase assemblages. The classical-OSaS implementations reproduced the fO2 values reported from the experimental dataset with a standard error estimate (SEE) of ±0.39, root mean standard error (RMSE) of ±0.40 and average deviation of ±0.31. In testing the MELTS-OSaS model, we identified that the solution model for magnetite underpredicted the values of aFe3O4sp; therefore, we used the 50 experiments to assign a correction to the MELTS-predicted chemical potentials of magnetite. We tested 35 the MELTS-OSaS model with the magnetite correction on a dataset of 18 additional buffered experiments, filtered for redox equilibrium and not included in the original experimental dataset. We find that the MELTs-OSaS model, which includes the correction for the magnetite chemical potential, reproduces fO2 values for the 18 experiments with an SEE of ±0.20, root mean standard error (RMSE) of ±0.23 and average deviation of ±0.18. The OSaS oxybarometer can return magmatic fO2 values with a standard error of ± 0.20 to 0.39 log units, depending on the model selected, provided that the olivine-spinel cotectic temperature is known to an accuracy of ±25°C, the H2O content of the melt can be estimated within ±1.5wt%, and that the crystallization pressure of the olivine-spinel pair is < 500 MPa. We also propose that the OSaS models can be applied to experimental run products to determine or confirm oxygen fugacity values. We additionally suggest that the careful application of the OSaS oxybarometer can provide a reliable and robust alternative for performing redox studies on samples that do not contain sufficient glassy material to support the application of spectroscopic techniques (i.e., XANES and Mössbauer).

Paleomagnetic study of terrigenous rocks of the Uryuk Formation in the Southern Urals

In order to obtain new paleomagnetic data on Vendian rocks in the Southern Urals, we studied the high-temperature magnetization component in sandstones of the Uryuk Formation, the carrier of which is hematite. The distinguished hematite vector in the collection of samples differs from the previously obtained intermediate-, intermediate-high-temperature magnetization component of magnetite, which is part of the same rocks. The average directions of the hematite component of magnetization of the Uryuk Formation were compared with the average directions of the overlying Basu Formation. The metachrony of the magnetite component and the synchrony of the hematite component are suggested.

Micromagnetic calculation of the magnetite magnetosomal morphology control of magnetism in magnetotactic bacteria.

Magnetotactic bacteria (MTB), which precisely bio-synthesize magnetosomes of magnetite or greigite nanoparticles, have attracted broad interdisciplinary interests in microbiology, magnetic materials, biotechnology and geobiology. Previous experimental and numerical investigations demonstrate a close link among MTB species, magnetosome crystal habits, and magnetic characteristics, but quantitative constraints are currently lacking. In this study, we build three-dimensional finite-element micromagnetic models of intact magnetosome chains in common MTB species and corresponding collapsed chains. Realistic numerical microstructures were constructed for the three typical biogenic magnetite crystal forms-cuboctahedron, prism and bullet. Our calculations reveal characteristic magnetic properties associated with specific magnetite crystal forms and MTB species. Cuboctahedron and bullet crystals show distinct low coercivity (less than 30 mT) and high coercivity (greater than 50 mT) clusters, respectively. Prismatic crystals have a broad range of hysteresis parameters that are strongly controlled by chain structure. This magnetic property clustering, combined with magnetic unmixing methods and electron microscopy observations, can fingerprint biogenic magnetite components in geological and environmental samples. The passive magnetic orientation efficiency of various magnetosome chains was calculated. Some bullet-shaped magnetosome chains have higher magnetic moments than those with cuboctahedron and prism magnetosomes, which may enable larger MTB cells to overcome viscous resistance for efficient magnetic navigation.

Quantifying Internal Stress and Demagnetization Effects for Natural Multidomain Magnetite and Magnetite‐Ilmenite Intergrowths

AbstractDemagnetizing effects and internal stress are difficult to distinguish in natural magnetite samples, but quantitative stress estimates can provide valuable information about microstructure formation, surface oxidation, impacts, tectonic stresses, or interface properties in exsolution structures. Quantifying demagnetizing effects informs about magnetite particle shape, magnetostatic interaction, or anisotropic texture. Here, we establish an improved measurement workflow to separate demagnetizing effects from internal stress for natural magnetite. The method is based on temperature‐dependent hysteresis measurements, and for natural samples require accurate estimates of Curie temperature and temperature‐dependent saturation magnetization to ensure that near‐end‐member magnetite is the dominant magnetic mineral, and to calibrate the temperature‐dependent scaled reversible work (SRW). SRW is the fundamental quantity to determine stress and demagnetizing factor. The improved SRW method is applied to three natural samples with different stress histories where it proves that large magnetite crystals in the metamorphosed Modum complex (Norway) have low internal stress (<100 MPa), while in highly exsolved magnetite‐ilmenite intergrowths from Taberg (Sweden) and Bushveld (South Africa) the magnetite component is highly stressed (>230 MPa). This confirms experimentally that interface strain in complex microstructures due to spinodal decomposition and partial oxidation creates large average internal stress in the magnetite minerals. Because sister specimens have similar internal stress but noticeably (>20%) different demagnetizing factors, textural, and shape anisotropy contribute substantially to SRW in these samples.

Rock Magnetism and Magnetic Fabric Study of the Icelandite and Rhyodacite Long Volcanic Sequence at Mauna Kuwale, Wai’anae Volcano, Oahu, Hawaii, USA

In order to understand further the emplacement (i.e., volcanic growth) of 22 Icelandite and 3 Rhyodacite cooling units in one of the long volcanic sequences known as Mauna Kuwale of the Wai’anae volcano (ca. 3.3 Ma), Oahu Hawaii we have conducted appropriate rock magnetic experiments described below as well as anisotropy of magnetic susceptibility (AMS) studies of such 25 units. We have undertaken rock magnetic investigations such as continuous and partial thermo-magnetic cycles of low field magnetic susceptibility versus temperature dependence, (k-T) curves experiments. We classified the k-T heating-cooling dependence of susceptibility in three groups A, B and C. Type A: yielded two components of titano-magnetite with a predominat Ti rich phase and occasionally a relevant magnetite component phase. Type B: samples are characterized by Ti poor magnetites. Magnetite dominates as the main magnetic carrier. Type C: k-T curves show one single phase of titanomagnetite, and Ti poor magnetite. The coercivity or remanence, determined by back field magnetization is always <60 mT, which suggest the predominance of magnetic components of low coercivity, like magnetite. Usually, two coercivity components are identified in the specimens. In addition we also conducted magnetic granulometry analyses on 27 specimens to determine the domain state of the flows. The ratio of hysteresis parameters (Mr/Mrs versus Hcr/Hc) show that overall samples fall in the Pseudo-Single Domain (PSD) region with high values of Mr/Mrs and very low values of Hcr/Hc. Only two samples from cooling units 17 and specially 22 show a Single Domain (SD) magnetic behavior and a sample from one unit approaches the SD-MD mixture region. We measured the magnetic susceptibility of all cooling units and we found out that in all analyzed units the magnetic susceptibility is low 13.7 ± 8.8 (10−3 SI). Magnetic anisotropy/magnetic fabric is used as a tool in rock fabric analyses to investigate the preferred orientation of magnetic minerals in rocks. Magnetic anisotropy is low on all (measured) flows from the Icelandite cooling units from 1 to 17 (mean P’ = 1.010), but becomes noticeably distinct and high in rhyodacite cooling units 23, 24 and 25 (mean P’ = 1.074). Four units show a magnetic fabric with k3 axes vertical to sub-vertical which may be denoted as normal for the horizontal to sub horizontal units. Two Icelandite cooling units display oblate shapes and two other cooling units triaxial shapes. K1 axes are horizontal but point in different directions, i.e., NE and NW. Remaining cooling units show different magnetic fabric. Units 17, 23, 24 and 25, despite important variations in anisotropy (low for units 25 and high for units 23 and 24) and shape of ellipsoid (oblate in cooling unit 23, prolate in 24 and triaxial in 25) the k3 axes show the same orientation, SW to SSW dipping around 45° and a very steady magnetic lineation azimuth NW nearly horizontal to sub horizontal. The magnetic mineralogy and magnetic fabric indicate that both the Icelandite and Rhyodacite cooling units the magmatic evolution during the shield stage of the entire Wai’anae volcano and that such growth was not affected by tectonic deformation.

Petrology and geochemistry of the Palaeo‐Mesoarchean Banded Iron formations (BIFs) from the central Bundelkhand greenstone belts, Bundelkhand Craton, India: Source characteristics and depositional environment

Palaeo‐Mesoarchean Banded Iron formations (BIFs) of central Bundelkhand greenstone belts occur from Babina (in the west) to Mahoba (in the east) via Mauranipur along with the E–W trending of the Bundelkhand Tectonic Zone (BTZ). In the present study, we report petrological, geochemical, and mineralogical data of BIFs from the Babina, Mauranipur, and Mahoba greenstone belts of central Bundelkhand Greenstone Complex to address their source characteristics and deposition environment. The lithological association of BIFs in the Babina and Mauranipur greenstone belts consists of pillowed basic–ultrabasic volcanics and metasediments, whereas in the Mahoba greenstone belt, BIFs and quartzite occur within basic volcanics. These lithological associations collectively suggest that the entire succession was deposited in a marine environment. Based on geological setting, they are classified as Algoma‐type. The main mineral assemblages of the Babina and Mauranipur BIFs are composed of magnetite, quartz, ±garnet, hornblende, chlorite, and apatite, whereas the Mahoba BIFs along with magnetite and quartz, poised of two distinct mineral assemblages; the first one is Opx–Cpx–Grt and the other one is Grt–Hbl. The preliminary P–T study of these BIFs implies that they had gone through amphibolite‐ to granulite‐facies metamorphism. The geochemical characteristics show that BIFs from the Babina and Mauranipur greenstone belts are dominated by higher quartz and magnetite (total content = 90.63–99.95 wt.%), whereas the Mahoba greenstone belt is characterized by lesser quartz and magnetite components (total content = 86.68–94.58 wt.%). The PAAS (Post Archean Average of Australian Sediments)‐normalized REE patterns display significant positive Eu anomaly (Eu/Eu* up to 2.50) with well‐represented negative Ce anomalies (Ce/Ce* = 0.27–1.20). The REE and trace element ratios of BIFs from the Babina and Mauranipur greenstone belts suggest that they were formed by high‐T hydrothermal fluid activity without or very less continental input. Moreover, the Mahoba greenstone belt BIFs are formed by low‐T hydrothermal fluid activity with substantial continental input. Their chemical variation suggests the shallowing of the proto‐basin from the Babina in the west to Mahoba in the east. Tectonic discrimination plots imply the BIFs of the Babina, Mauranipur, and Mahoba greenstone belts of the central Bundelkhand Greenstone Complex are formed in a back‐arc tectonic setting.

The application of GO-Fe3O4 nanocomposite for chromium adsorption from tannery industry wastewater

The discharge of untreated tannery industrial wastewater into the environment has resulted in an adverse effect on the ecosystem and public health. Therefore, this work aimed to remove chromium ions from tannery wastewater through magnetite graphene oxide-nanocomposite (GO-Fe3O4). The experimental design of the study was a full factorial 24 approach using pH, adsorbent dose, contact time, and initial chromium concentrations. The results of FTIR analysis revealed the presence of functional groups such as hydroxyl (3438 cm−1), alcohol (1230 cm−1), aromatic (1467 cm−1), ketone (1629 cm−1), and ether (1120 cm−1). Similarly, GO-Fe3O4 acquired a high surface area of 296.2 m2/g whereas the XRD analysis showed the presence of predominant peaks which are attributed to the magnetite component. Moreover, the SEM image showed many ups and downs on the surface of the adsorbent. These cracks of morphology can create a conducive environment for the interaction of adsorbent and adsorbate. The maximum chromium removal of 95.9% was achieved at the optimum conditions of the initial chromium concentration of 40 mg/L, pH 4, adsorbent dose 1 g/100 mL, and contact time of 120 min whereas the removal of chromium from real tannery wastewater was found to be 90.3%. Based on the adsorption isotherm, the Langmuir model was the best fit for experimental data at R2 0.99, indicating homogeneous and monolayer adsorption. Finally, it can be concluded that GO-Fe3O4 was effective for chromium removal, which is a promising technology to be scaled up at the industrial level for wastewater treatment.

Mechanical characteristics of magnetite as a function of particle size during column-based magnetic separation

ABSTRACT Column-based magnetic separation can concentrate magnetite while preventing magnetic particle agglomeration. Changes in the force characteristics during this process greatly affect the separation of different magnetite components. Here, the mechanical characteristics of magnetite with different particle sizes during column-based magnetic separation are studied. Upon reducing the particle size (passing 74 μm) from 45% to 90%, the magnetic force () required to separate the magnetite concentrate gradually increased. The difference in the magnetic force required to capture magnetite concentrate and rich interlocking concentrate by a magnetic field decreased from 39.53% to 13.92%. The difference in the magnetic force required to capture lean interlocking concentrate and gangue minerals by a magnetic field decreased from 75.87% to 54.26%. Verification tests showed that pre-separating magnetite concentrate and gangue from individual coarse particles reduced the workload of subsequent grinding and separation, making it easier to separate magnetite from the concentrate.

Study on the particle interaction in a hydrocyclone classifier with multi-component feed blend at a high solids content

In mineral processing circuits, the feed to hydrocyclone consists of different density particle system at varying degrees of liberation and sizes, leading to a multi-component system. These different density components' interaction affects the separation in the hydrocyclones, particularly at high feed solids concentrations. In this work, an attempt is made to account for bi-component particle interaction in a hydrocyclone at different feed solids concentrations (10–50 wt%). For classification experiments, pure silica and pure magnetite components were utilized as a ratio of 1:1 in the feed mixture. Customized orthogonal array experiments were carried out using three-spigot and pressure level for 3″ and 4″ hydrocyclones. Components' grade efficiency curves and the performance parameters (d50; Rf; Rs;α;β) were estimated and analysed using the Whiten Equation. The cut-size and beta parameter of the mixture and individual components witnessed to increase with increasing feed solids concentration. Suspension rheology and hindered settling rate studies were carried out to understand the influence of the fine and coarse particle interaction on the performance of the hydrocyclone processing bi-component mixture at different feed solids concentrations. The enhanced viscous flow at the conical region attributes the crowding effect and the dense medium effect near apex zone, and consequential coarse and fines inflections are observed. The lighter particle displacement in the presence of heavier component is further supported by the locus of maximum volume fraction and equilibrium position from the numerical analysis.

아연 이온화 장치의 상수 중 철 시편과 수도 배관에 미치는 부식억제 효과 예측

This study quantitatively investigated the inhibition effect of corrosion on iron coupons and water pipes by ionization of zinc metal in tap water line. After installing iron coupons into water pipes and running tap water for 20 days, the average difference of the annual corrosion rates calculated from the weight losses of iron coupons with or without the ionization device was estimated to be 12.8 %. Comparing corrosion rates with or without corrosion inhibitor on new iron coupons showed higher difference in corrosion rates, but over time, the difference of corrosion rates between absence and presence of inhibitor had decreased gradually. It was also confirmed that the less rust-free pure iron area on the iron specimen and the less pure iron surface to react with oxygen in water gradually reduces the corrosion rate. X-ray diffraction analysis of the rust generated on iron coupons confirmed that most of them were red hematite(Fe₂O₃), and that some of the blackish parts were magnetite. It is known that the rust generated causes red tap water to fall, some of which develop into foot corrosion, resulting in pin-holes in the water pipes. Therefore, based on existing research results, we predicted the breaking time due to foot corrosion of iron coupons with or without corrosion inhibitors. Zinc corrosion suppressors were installed in water pipes where corrosion had already progressed and rusted, and the internal surface of the water pipes was observed to increase the relative ratio of the black magnetite components over time, and it was believed that corrosion suppressors could be expected for a long time.

Formation of serpentinite-hosted, Fe-rich arsenide ores at the latest stage of mineralization of the Bou-Azzer mining district (Morocco)

The Bou Azzer district in the central Anti-Atlas of Morocco is the world’s unique mining district where Co is exploited from serpentinite-hosted hydrothermal Co-Ni-Fe arsenide ores. This paper provides the first-ever mineralogical and geochemical characterization of a suite of Fe-rich arsenide orebodies found during recent mining in the Ait Ahmane area, in central Bou Azzer district. These are lens-like orebodies of massive and disseminated Fe-rich ores fully hosted in serpentinites (hereafter named as serpentinite-hosted ores) that are typically enveloped by arsenide-poor, carbonated serpentinite, evolving irregularly outwards to talc-rich serpentinite. The central part of these orebodies mainly consists of massive ore made up of aggregates of zoned spindle-like crystals of löllingite whereas the outer zone of disseminated ore consists of rosette-like löllingite. These ores often contain accessory grains of chromite that display strong fracturation, zoning and alteration.We propose a general model for the formation of the Bou-Azzer Co-Ni-Fe arsenide ores associated to the infiltration of high-temperature (>400 °C) slightly alkaline, oxidized and CaCl2-rich fluids through opening fault and fractures. When channeled through faults separating serpentinite and quartz diorite (or other rocks) the fluids deposited Ni- and Ni-Co-rich ores in these fault-related open spaces (here re-defined contact-type ores). Over the course of mineral deposition, the generated Ni-poor fluids tended to migrate into serpentinite, first through networks of thin entwined veins and progressively by intergranular percolation, promoting dissolution of the infiltrated serpentinite and precipitation of Co-Fe ores (the presence of remnants of chromite included in coexisting arsenides and calcite sustains the role played by dissolution/precipitation, ore-forming process). Further circulation of the evolving fluids through weak zones of massive serpentinite away from the serpentinite-quartz diorite (or other rocks) contact (intra serpentinite faults), formed the serpentinite-hosted, Fe-rich ore type represented by the F55 lens. These fluids most probably evolved at low temperature (~200 °C) towards slightly higher pH values and oxidizing conditions increasing the proportions of CO2 and CO32−, promoting the dissolution of serpentine, the increase in the magnetite component of chromite, the formation of Cr and Fe hydroxides, the mobilization of silica out of the reactive zone and the precipitation of calcite + Fe-rich arsenides.

Experimental study on the effects of H2O upon crystallization in the Lower and Critical Zones of the Bushveld Complex with an emphasis on chromitite formation

Mafic–ultramafic layered rocks of the Lower and Critical Zones of the Bushveld Complex are believed to have formed from a parental magma usually labelled B1 with SiO2 content at 55 wt.%, MgO at about 12 wt.% and Cr2O3 concentration at 0.15 wt.%. Previous experimental study at 300 MPa and nominally dry conditions showed that this composition had orthopyroxene on liquidus between 1250 and 1300 °C, and the mineral was joined by plagioclase and clinopyroxene at and below 1166 °C. The objective of this study was to investigate the effects of variable additions of H2O (2, 4 and 6 wt.% in starting compositions) on liquidus and sub-liquidus phase equilibria. Main attention was given to the solubility of Cr-spinel and Cr distribution between melt and crystalline phases. Six experiments were carried out in the internally heated pressure vessel (IHPV) at 300 MPa and in the temperature interval 1100–1300 °C. Redox conditions were not controlled and thermal dissociation of the H2O component followed by hydrogen diffusion through container walls resulted in a noticeable oxidation of run products. The effective values of fO2 in experiments were calculated using SPINMELT 2.0 software bases on the regression of experimental data on the spinel-melt equilibrium. According to the calculations, H2O additions in isothermal series of experiments increased fO2 by 0.8–1.6 log-units from the level in a nominally dry run. Overall, the experiments showed that H2O additions suppressed crystallization of silicates, shifted olivine-orthopyroxene peritectic equilibrium towards higher olivine stability (olivine first appears in H2O-bearing compositions at 1175 °C) and increased the proportion of magnetite component in spinel solid solution. The addition of 4 wt.% H2O to the starting composition at 1200 °C resulted in complete melting of orthopyroxene, which left Cr-spinel as the only liquidus phase. Equal amount of H2O at 1125 °C leads to complete melting of plagioclase, orthopyroxene and clinopyroxene, which leaves only olivine and spinel stable and increases the liquid mass fraction from 0.62 in the nominally dry compositions to 0.9. The results of this study appear to support the idea that chromitite layers in the Critical Zone of the Bushveld Complex were formed by episodes of hydration melting of silicate cumulates.

Magnetofossil Abundance and Diversity as Paleoenvironmental Proxies: A Case Study From Southwest Iberian Margin Sediments

AbstractIt is still contentious how the abundance and diversity of magnetofossils reflect varying paleoenvironmental conditions. Here, we apply rock magnetic methods and transmission electron microscopy to identify magnetofossils in the core MD01‐2444 from the southwestern Iberian margin during the period 49.6–18.5 ka and 193.8–171.7 ka. Results show a correlation between the biogenic magnetite component and contrasting paleoenvironmental conditions. Specifically, remanence ratio (Mrs/Ms), the ratio of anhysteretic susceptibility (χARM) to saturation isothermal remanant magnetization (SIRM), fractions of biogenic soft and biogenic hard components (BS + BH), and delta–delta ratio (δFC/δZFC) have a negative relationship with planktonic δ18O, suggesting that more magnetofossils existed in sediments during warmer periods. Combining transmission electron microscopy images with paleoenvironmental proxies, we found that the proportions of bullet‐shaped magnetofossils increased in a warmer and less oxic environment, while isotropic shapes dominated in cooler and oxic environments.

Iron oxide mineralogy in Mollisols, Aridisols and Entisols from southwestern Pampean region (Argentina) by environmental magnetism approach

Ferromagnetic compounds of seven southwestern soils from Pampean region comprise iron oxides and oxyhydroxides that have an important role, because of their high surface reactivity, controlling soil adsorption and formation/conservation of soil structure among other properties. We detected minutes of iron oxides quantities by selective dissolution techniques: acid oxalate extraction (<12% of the total Fe) and dithionite-citrate-bicarbonate (<44% of the total Fe), moreover, we identified/quantified mixtures of magnetite, maghemite, goethite and hematite minerals by environmental magnetism approach. The magnetic particle size dependent parameters evidence a relationship with extractable Fe oxides, indicating that magnetic particle size distribution on these soils is a relevant property associated to poorly crystalline and free amorphous Fe oxides. In addition, the particle size and SP concentration of ferromagnetic iron oxides are associated with increments of cation exchange capacity and the specific surface area of soil samples. The estimated amounts of hematite are below 2.20 wt%, and lower contents of about 0.25 wt% correspond to magnetite components. Both magnetic iron oxides concentration, as well as the remanent coercivity, increase towards the western region, on the contrary, anhysteretic ratios decrease and hence relatively coarser magnetic particles are dominant in this western region. The present study provides valuable data to characterize Aridisols, Entisols and Mollisols in a region of high fertility that comprises ones of the world’s most productive agricultural soil region.

The Stability of Titanomagnetite Basalt of the Red Sea during Heating in Air and Argon

To optimize heating conditions during the Thellier procedure and to improve the reliability of paleofield determination, thermal stability experiments with titanomagnetite and titanomaghemite obtained by laboratory heating were conducted. The experiments were performed on P72/2 and P72/4 basalts of the rift zone of the Red Sea that contain titanomagnetite with a concentration of the magnetite component equal to (44.7 ± 3.9)% and (46 ± 5)%, respectively. It has been shown that the single-phase oxidation process prevails in annealing of titanomagnetite for 10 hours in a temperature range of 290–410°C in air. An increase in the annealing temperature up to 460–535°C means that single-phase oxidation is replaced by oxi-exsolution. The temperature range of thermal stability of the single-phase oxidized titanomagnetite expands with the degree of oxidation. In particular, at an oxidation state close to 0.9, titanomaghemite is stable up to temperatures of 410–460°C. The use of the Thellier technique for studying the properties of the chemical remanent magnetization of single-phase oxidized titanomagnetite with an oxidation state above z ≥ 0.6 is limited to approximately 20% of its value. It is possible to stabilize the single-phase oxidized state of titanomagnetite at temperatures above 460°C and thereby to improve the quality of CRM research using the Thellier method by adjusting the value of the oxygen partial pressure.

Состав минералов (апатит, магнетит, ильменит и др.) как отражение процессов формирования рудных тел и расслоенности в Кусинской габбровой интрузии (Южный Урал)

Research subject . In this research, we carried out a series of mineralogical, petrological and geochemical studies to investigate ore zones present in the Kusa ilmenite-magnetite deposit located within the boundaries of a similarly-named laminated gabbro massif. Here, ore bodies occur at various intrusion horizons among laminated apogabbroid amphibolites of a different basicity. In the intrusion section, the composition of halogens (Cl, F) in co-existing fluid-bearing minerals (apatite, am-phibole, staurolite) was analyzed. Materials and methods . In order to investigate the composition of mineral samples, their polished sections were examined using an electronic-microprobe analyzer JXA-5. The content of petrogenic and microelement components (CRF and ICP-MS methods) in the rock and ore samples was determined using the facilities of the Laboratory of Physical and Chemical methods, UBRAS Institute of Geology and Geochemisty. Results. It is established that the content of Cl and F in the apatite, amphibole and staurolite under study, as well as the chemical composition of ilmenite, magnetite, and hombombite components, depend on the position of the ore bodies in the intrusion. Thus, the apatites from the near-ore rocks in the central part of the deposit showed the highest Cl concentrations of up to 4.1%, while those located in the near-contact parts of the intrusion demonstrated a much lower Cl content of 2%. The central ore-bearing zone having the maximal Cl content features the largest formation of ore bodies, which (including magnetite) contain higher amounts of Fe 2 O 3 , Cr and V The presence of fluid-bearing minerals (apatite, scapolite, etc.) with high chlorine concentrations of up to 2.44% is this deposit is established. Conclusions. The identified peculiarities of halogen distribution in the apatite of bipyroxene gabbro, as well as the inheritance of relations TiO 2 /FeO in bipyroxene gabbro, in massive magnetite-ilmenite ores and in near-ore rocks point to a single magmatic source of these formations.

Diffusion pathways of Fe2+ and Fe3+ during the formation of ferrian chromite: a µXANES study

The alteration of chromian spinel is a key process during serpentinization and metamorphism of ultramafic rocks controlled by oxygen fugacity (fO2) and Fe2+ ↔ Fe3+ exchange during fluid–rock interaction. Chromian spinel alteration is better recorded in less permeable chromitite than in peridotites where extensive fluid–rock interaction frequently overprints the record of earlier stages of alteration. To shed light on that process we have studied the distribution of Fe2+ and Fe3+ in variably altered chromian spinel grains from a set of chromitite samples from the same mining district using synchrotron-based microscopic chemical imaging and spatially resolved X-ray absorption near edge structure spectroscopy. Our results show that early stages of alteration do not involve changes in Cr3+ and Fe2+ contents or in Fe speciation but only depletion in Al3+ and Mg2+ resulting in the formation of porous chromite. With ongoing alteration Fe3+ migrates into porous chromite mainly along fracture walls and fracture zones as well as along grain boundaries. Sheared-type chromitites record the maximum rates of fluid–rock interaction because in these chromitite-types the accommodation of deformation on porous chromite allowed higher rates of diffusion of Fe3+ and Fe2+ (a magnetite component with Fe3+/Fetotal = 0.66) into the newly formed neoblasts. In porous chromite-type texture (all the original chromite grains fully transformed to porous chromite) the deformation and accompanying diffusion processes result in the formation of homogenous ferrian chromite grains. In contrast, in partly altered-type texture (chromite grains with original cores surrounded by porous chromite), such processes are only restricted to the porous rims, giving rise to zoned chromian spinel-ferrian chromite grains.

Origin of Platinum Group Minerals (PGM) Inclusions in Chromite Deposits of the Urals

This paper reviews a database of about 1500 published and 1000 unpublished microprobe analyses of platinum-group minerals (PGM) from chromite deposits associated with ophiolites and Alaskan-type complexes of the Urals. Composition, texture, and paragenesis of unaltered PGM enclosed in fresh chromitite of the ophiolites indicate that the PGM formed by a sequence of crystallization events before, during, and probably after primary chromite precipitation. The most important controlling factors are sulfur fugacity and temperature. Laurite and Os–Ir–Ru alloys are pristine liquidus phases crystallized at high temperature and low sulfur fugacity: they were trapped in the chromite as solid particles. Oxygen thermobarometry supports that several chromitites underwent compositional equilibration down to 700 °C involving increase of the Fe3/Fe2 ratio. These chromitites contain a great number of PGM including—besides laurite and alloys—erlichmanite, Ir–Ni–sulfides, and Ir–Ru sulfarsenides formed by increasing sulfur fugacity. Correlation with chromite composition suggests that the latest stage of PGM crystallization might have occurred in the subsolidus. If platinum-group elements (PGE) were still present in solid chromite as dispersed atomic clusters, they could easily convert into discrete PGM inclusions splitting off the chromite during its re-crystallization under slow cooling-rate. The presence of primary PGM inclusions in fresh chromitite of the Alaskan-type complexes is restricted to ore bodies crystallized in equilibrium with the host dunite. The predominance of Pt–Fe alloys over sulfides is a strong indication for low sulfur fugacity, thereby early crystallization of laurite is observed only in one deposit. In most cases, Pt–Fe alloys crystallized and were trapped in chromite between 1300 and 1050 °C. On-cooling equilibration to ~900 °C may produce lamellar unmixing of different Pt–Fe phases and osmium. Precipitation of the Pt–Fe alloys locally is followed by an increase of sulfur fugacity leading to crystallize erlichmanite and Ir–Rh–Ni–Cu sulfides, occurring as epitaxic overgrowth on the alloy. There is evidence that the system moved quickly into the stabilization field of Pt–Fe alloys by an increase of the oxygen fugacity marked by an increase of the magnetite component in the chromite. In summary, the data support that most of the primary PGM inclusions in the chromitites of the Urals formed in situ, as part of the chromite precipitation event. However, in certain ophiolitic chromitites undergoing annealing conditions, there is evidence for subsolidus crystallization of discrete PGM from PGE atomic-clusters occurring in the chromite. This mechanism of formation does not require a true solid solution of PGE in the chromite structure.

Empirical constraints on partitioning of platinum group elements between Cr-spinel and primitive terrestrial magmas

Recent experimental studies and in situ LA-ICP-MS analysis on natural Cr-spinel have shown that Rh and IPGEs (Ir-group platinum group elements: Ru, Ir, Os) are enriched in the lattice of Cr-spinel. However, the factors controlling the partitioning behaviour of these elements are not well constrained. In this study, we report the Rh, IPGE, and trace element contents in primitive Cr-spinel, measured by LA-ICP-MS, from nine volcanic suites covering various tectonic settings including island arc picrites, boninites, large igneous province picrites and mid-ocean ridge basalts. The aim is to understand the factors controlling the enrichment of Rh and IPGEs in Cr-spinels, to estimate empirical partition coefficients between Cr-spinel and silicate melts, and to investigate the role of Cr-spinel fractional crystallization on the PGE geochemistry of primitive magmas during the early stages of fractional crystallization.There are systematic differences in trace elements, Rh and IPGEs in Cr-spinels from arc-related magmas (Arc Group Cr-spinel), intraplate magmas (Intraplate Group Cr-spinel), and mid-ocean ridge magmas (MORB Group Cr-spinel). Arc Group Cr-spinels are systematically enriched in Sc, Co and Mn and depleted in Ni compared to the MORB Group Cr-spinels. Intraplate Group Cr-spinels are distinguished from the Arc Group Cr-spinels by their high Ni contents. Both the Arc and Intraplate Group Cr-spinels have total Rh and IPGE contents of 22–689ppb whereas the MORB Group Cr-spinels are depleted in Rh and IPGE (total<20ppb). Palladium and Pt contents are below detection limit for all of the studied Cr-spinels (<1–5ppb). The time-resolved spectra of LA-ICP-MS data for Cr-spinels mostly show constant count rates for trace element and Rh and IPGEs, suggesting homogeneous distribution of these elements in Cr-spinels. The PGE spikes observed in several Cr-spinels were interpreted to be PGE-bearing mineral inclusions and excluded from calculating the PGE contents of the Cr-spinels.On primitive mantle normalized diagrams the Arc Group Cr-spinels are characterized by a fractionated pattern with high Rh and low Os. The Intraplate Group Cr-spinels show flat patterns with positive Ru anomalies. Our results, together with the experimental and empirical data from previous studies, show that PGE patterns of Cr-spinel largely mimic that of the rock in which they are found, and that Rh, Ir and Os contents increase with increasing Fe3+ contents (i.e. magnetite component) in Cr-spinel, although Ru does not. These observations suggest that the enrichment of Rh and IPGEs in Cr-spinel is controlled by a combination of the Rh and IPGE contents in parental melts and the magnetite component of the spinel. Empirical partition coefficients (D) for Rh and IPGEs between Cr-spinels and silicate melts were calculated using the Rh and IPGE contents of the Cr-spinel and their host volcanic rocks after subtracting the accumulation effect of Cr-spinel. The D values for the Intraplate and MORB Group Cr-spinels increase with increasing magnetite component in Cr-spinel and range from 6 to 512, which is consistent with previously reported experimental and empirical values. In contrast, the Arc Group Cr-spinels have significantly higher D values (e.g. up to ∼3700 for Ru) than those of the Intraplate and MORB Group at the same magnetite concentration in the Cr-spinel, suggesting Rh and IPGEs dissolved in silicate melt have stronger affinity for Cr spinel under arc magma conditions than in intraplate magmas. This may be partly attributed to the low temperature of arc magmas relative to intraplate magmas, which leads to the Arc Group Cr-spinels having more octahedral sites at the same magnetite components than the Intraplate Group Cr-spinels. Because of significantly higher D values for the Arc Group Cr-spinels, compared with the Intraplate Group and MORB Group spinels, fractional crystallization of Cr-spinel will more efficiently fractionate Rh and IPGE from Pd and Pt in arc systems than in intraplate and MORB systems, which accounts for the highly fractionated PGE patterns in arc basalts.

A novel magnetic chitosan/clinoptilolite/magnetite nanocomposite for highly efficient removal of Pb(II) ions from aqueous solution

A novel nanocomposite (with components of chitosan, clinoptilolite and magnetite) was synthesized featuring magnetic properties, and was used for the removal of Pb(II) as a toxic heavy metal from aqueous solutions. The effects of temperature, contact time, Pb(II) concentration, pH value of the solution and adsorbent dosage on the adsorption capacity of the nanocomposite were investigated. The kinetics data of adsorption process were analyzed by the models of pseudo-first order, pseudo-second order, the Elovich and intra-particle diffusion. The adsorption kinetics was well described by the pseudo-second order equation. The adsorption isotherms were more accurately fitted by the Langmuir equation and the maximum theoretical Pb(II) adsorption capacity of the nanocomposite was found to be 136.99mg/g at pH6 and 333K. The negative Gibbs free energy values of adsorption illustrated the spontaneity of the adsorption of Pb(II) ions on the nanocomposite. The magnetic nanocomposite gave a saturation magnetization value of 9.50emu/g, therefore, it was efficiently separated from the solution by a fast and simple magnetic separation process. Desorption of the Pb(II) ions from the nanocomposite was achieved by using 0.01M HNO3, CaCl2 and NaCl solutions. The prepared nanocomposite exhibited proper magnetic property, high thermal strength and large specific surface area while being synthesized at low cost. Hence, it offers possibilities for future practical use.