Types Of Magnetite Research Articles

Unraveling the exhumation history of high-pressure ophiolites using magnetite (U-Th-Sm)/He thermochronometry

Magnetite is a ubiquitous oxide in ultramafic and mafic rocks, which is present in a large range of geological and tectonic settings. In the case of high-pressure ultramafic rocks, exhumation timing is commonly constrained by geochronometers in nearby lithologies. The development of the magnetite (U-Th-Sm)/He method (MgHe) has opened new perspectives to refine the exhumation history of such rocks. However no thermal history has been deduced using MgHe data so far. Here we applied MgHe dating to magnetite from an HP-LT alpine ophiolite body (Rocher Blanc) from the Schistes lustrés units (Western Alps, France) where part the P-T-t history is constrained to further refine the thermal history and demonstrate validity of the method. Textural and geochemical characterizations of the magnetite grains reveal two crystallization environments leading to distinct grain morphologies, euhedral and pseudo-euhedral, with different amounts of mineral inclusions (titanite, chlorite and augite-aegirine). Both magnetite types crystallized during the same retrograde path at T>250°C, under hydrothermal conditions shown by Si and V oscillatory zoning and low Ti content. MgHe ages derived from euhedral magnetite crystals range from 14.8 ± 2.1 to 20.9 ± 3.0 Ma, between zircon and apatite fission track (ZFT) and (AFT) ages deduced from the literature. Pseudo-euhedral grains display older ages interpreted as resulting from the implantation of He from U-rich neighboring minerals such as titanite. For the first time, MgHe data are inverted along with AFT and ZFT data to refine the thermal history of an ophiolite related to their exhumation. The MgHe data suggest that the Rocher Blanc sample has undergone an exhumation in ductile conditions related to subduction dynamics and underplating processes, followed by an exhumation reflecting denudation by erosion under brittle conditions. This exhumation regime change is found to take place at ∼20 Ma, as opposed to a less constrained ∼26 Ma cooling as would be inferred from the ZFT and AFT ages alone. Considering published thermochronometric data along the Western Alps, we propose that the exhumation is controlled by the upward indentation of the Apulian mantle producing regional tilting and associated erosion. With the present Schistes lustrés ophiolite example, we demonstrate that the MgHe method can be used as a low-temperature thermochronometer (closure temperature in the 200-250°C range) that aids in unraveling the cooling history associated with exhumation of high-pressure ultramafic and mafic rocks at the brittle to ductile transition.

Geological, mineralogical, and oxygen isotope studies of the Chandmani Uul iron oxide–copper–gold deposit in Dornogobi Province, Southeastern Mongolia

AbstractThe Chandmani Uul deposit is located in Dornogovi province, Southeastern Mongolia. Iron oxide ores are hosted in the andesitic rocks of the Shar Zeeg Formation of Neoproterozoic to Lower‐Cambrian age. Middle‐ to Upper‐Cambrian bodies of granitic rocks have intruded into the host rocks in the western and southern regions of the deposit. The wall rocks around the iron oxide ore bodies were hydrothermally altered to form potassic, epidote, and sericite–chlorite alteration zones, and calcite and quartz veinlets are ubiquitous in the late stage. Since granitic rocks also underwent potassic alteration, the activity of the granitic rocks must have a genetic relation to the ore deposit. The ore mineral assemblage is dominated by iron oxides such as mushketovite, euhedral magnetite with concentric and/or oscillatory zoning textures, and cauliflower magnetite. Lesser amounts of chalcopyrite and pyrite accompany the iron oxides. Among all these products, mushketovite is dominant and is distributed throughout the deposit. Meanwhile, euhedral magnetite appears in limited amounts at relatively shallow levels in the deposit. By contrast, cauliflower magnetite appears locally in the deeper parts of the deposit, and is associated with green‐colored garnet and calcite. Sulfide minerals are ubiquitously associated with these iron oxides. The oxygen isotope (δ18O) values of all types of magnetite, quartz, and epidote were found to be −5.9 to −2.8‰, 10.5 to 14.9‰, and 3.6 to 6.6‰, respectively. The δ18O values of quartz–magnetite pairs suggest an equilibrium isotopic temperature near 300°C. The calculated values of δ18O for the water responsible for magnetite ranged from 2 to 10‰. All the data obtained in this study suggest that the iron oxide deposit at the Chandmani Uul is a typical iron oxide–copper–gold deposit, and that this deposit was formed at an intermediate depth with potassic and sericite–chlorite alteration zones under the oxidized conditions of a hematite‐stable environment. The δ18O range estimated implies that the ore‐forming fluid was supplied by a crystallizing granodioritic magma exsolving fluids at depth with a significant contribution of meteoric water.

Preparation and Application of Complexes of Lignosulfonic Acids with Iron Cations

Lignosulfonates and lignosulfonic acids are the main commercial product on the world market of lignins. They are used in metallurgy, mining, concrete production, and agriculture. The review presents the results of studying the structure and properties of lignosulfonates, the synthesis and application of complexes of lignosulfonic acids with iron cations. Lignosulfonates possess unique physicochemical properties that other types of lignins do not have. They form chelate complexes when interacting with iron cations and other biogenic metals. These complexes can be used in agriculture to eliminate plant chlorosis. Chlorosis is particularly manifests itself on about 30 % of the world’s farmlands with high calcium carbonate content. It is possible to change the properties of lignosulfonic acids and lignosulfonates intentionally by theirmodification. Nitration and nitrosation enhances the complexing properties. This is due to the possibility of the formation of chelate complexes with ironcations. Iron chelates with nitrated and nitrosated lignosulfonates exhibit strong antichlorosis properties. Their use allows normalizing the content of chlorophyll in photosynthetic structures completely. In the synthesis of water-based magnetic fluids lignosulfonates modified by nitration and nitrosation exhibit the properties of a peptizing agent that promotes the formation of stable magnetic fluids of magnetite type. Lignosulfonates have a strong influence on the synthesis of magnetoactive compounds by the partial oxidation of iron (II) cations using chromate ions or silver ammonium hydroxide. In the former case, a compact magnetoactive compound is formed; and in the second – a magnetic fluid (if condensation is carried out in the presence of tetraalkylammonium hydroxides).For citation: Khabarov Yu.G., Veshnyakov V.A., Kuzyakov N.Yu. Preparation and Application of Complexes of Lignosulfonic Acids with Iron Cations. Lesnoy Zhurnal [ForestryJournal], 2019, no. 5, pp. 167–187. DOI: 10.17238/issn0536-1036.2019.5.167

Effect of Fe-metabolizing bacteria and humic substances on magnetite nanoparticle reactivity towards arsenic and chromium

Magnetite is a magnetic, Fe(II)-Fe(III)-mineral formed through abiogenic and biogenic pathways. It constitutes an attractive material for remediation due to its reactivity, large surface-area-to-volume ratio when present as nanoparticles, and magnetic recoverability. Magnetite can be repeatedly microbially oxidized or reduced, but it is unclear how this influences the reactivity of magnetite towards toxic metal or metalloid contaminants. In this study, magnetite (both abiogenic and biogenic) was exposed to microbial Fe(II) oxidation and Fe(III) reduction, before reacted with hexavalent chromium (Cr(VI)) or pentavalent arsenic (As(V)). Results showed microbial reduction of both magnetite types improved the removal rate of Cr(VI) from solution, though surprisingly microbial Fe(II)-oxidation also showed enhanced reactivity towards Cr(VI) compared to un-treated magnetite. Synchrotron based analysis confirmed the formation of Cr(III) at the surface of the magnetite. Reactivity with As was less dramatic and showed un-treated material was able to remove As(V) from solution faster than microbially Fe(III)-reduced and Fe(II)-oxidized magnetite. The presence of humic substances was also shown to lead to a decreased reactivity of biogenic and abiogenic magnetite towards As(V) and Cr(VI). Our results imply that Fe-metabolizing bacteria influence the immobilization of contaminants and should be considered when evaluating remediation schemes, especially where Fe-metabolizing bacteria are active.

Magnetite Geochemistry of the Jinchuan Ni-Cu-PGE Deposit, NW China: Implication for Its Ore-Forming Processes

The Jinchuan Ni-Cu-PGE deposit is the single largest magmatic Ni-sulfide deposit in the world, with three different hypotheses on its ore-forming processes (e.g., in-situ sulfide segregation of sulfide-bearing magma, deep segregation with multiple injections of magma, and hydrothermal superimposition) mainly based on study of whole-rock geochemistry and isotopes (e.g., S-Sr-Nd-Hf). In this study, we mainly concentrated on magnetite textural and geochemical characteristics from different sulfide ores to clarify the genetic types and geochemical difference of the Jinchuan magnetite, and to explore a new credible ore-forming process by magnetite formation process when combined with detailed deposit geology. Three types of magnetite from massive and disseminated sulfide ores were observed by different textural analysis, and they were shown to have different genetic types (mainly in geochemistry) and trace elemental features. Type I magnetite is subhedral to anhedral from massive Ni- (or Fe-) and Cu-rich sulfide ores, with apparent magmatic origin, whereas Type II (dendritic or laminar crystals) and III magnetite (granular crystals as disseminated structures) from disseminated Cu-rich sulfide ores may have precipitated from late stage of melts evolved from a primitive Fe-rich and sulfide-bearing system with magmatic origin, but their geochemistry being typical of hydrothermal magnetite, videlicet, depletions of Ti (< 20 ppm), Al (< 51 ppm), Zr (0.01–0.57 ppm), Hf (0.03–0.06 ppm), Nb (0.01–0.14 ppm), and Ta (0.01–0.21 ppm). Such different types of magnetite can be clearly distinguished from concentrations and ratios of their trace elements, such as Ti, V, Co, Ni, Zn, Zr, Sn, Ga, and Ni/Cr. Those different types of Jinchuan magnetite crystallized from (evolved) sulfide-bearing systems and their geochemistries in trace elements are controlled mainly by evolution of ore-related systems and geochemical parameters (e.g., T and fO2), with the former playing a predominant role. Combining the previous literature with this study, we propose that the Jinchuan deposit formed by multiple pluses of sulfide-bearing magma during fractional crystallization, with the emplacing of more fractionated and sulfide-bearing magma during sulfide segregation playing a predominant role. During this multiple emplacement and evolving of sulfide-bearing systems, Type I magmatic magnetite crystallized from primitive and evolved Fe-rich MSS (monosulfide solid solution), while Type II and III magnetite crystallized from evolved Fe-rich MSS to Cu-rich ISS (intermediate solid solution) during sulfide fractionation, with those Type II and III magnetite having much higher Cu contents compared with that of Type I magnetite.

Trace Element Composition of Igneous and Hydrothermal Magnetite from Porphyry Deposits: Relationship to Deposit Subtypes and Magmatic Affinity

AbstractThe trace element composition of igneous and hydrothermal magnetite from 19 well-studied porphyry Cu ± Au ± Mo, Mo, and W-Mo deposits was measured by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and then classified by partial least squares-discriminant analysis (PLS-DA) to constrain the factors explaining the relationships between the chemical composition of magnetite and the magmatic affinity and porphyry deposit subtypes. Igneous magnetite can be discriminated by relatively high P, Ti, V, Mn, Zr, Nb, Hf, and Ta contents but low Mg, Si, Co, Ni, Ge, Sb, W, and Pb contents, in contrast to hydrothermal magnetite. Compositional differences between igneous and hydrothermal magnetite are mainly controlled by the temperature, oxygen fugacity, cocrystallized sulfides, and element solubility/mobility that significantly affect the partition coefficients between magnetite and melt/fluids. Binary diagrams based on Ti, V, and Cr contents are not enough to discriminate igneous and hydrothermal magnetite in porphyry deposits.Relatively high Si and Al contents discriminate porphyry W-Mo hydrothermal magnetite, probably reflecting the control by high-Si, highly differentiated, granitic intrusions for this deposit type. Relatively high Mg, Mn, Zr, Nb, Sn, and Hf but low Ti and V contents discriminate porphyry Au-Cu hydrothermal magnetite, most likely resulting from a combination of mafic to intermediate intrusion composition, high chlorine in fluids, relatively high oxygen fugacity, and low-temperature conditions. Igneous or hydrothermal magnetite from Cu-Mo, Cu-Au, and Cu-Mo-Au deposits cannot be discriminated from each other, probably due to similar intermediate to felsic intrusion composition, melt/fluid composition, and conditions such as temperature and oxygen fugacity for the formation of these deposits.The magmatic affinity of porphyritic intrusions exerts some control on the chemical composition of igneous and hydrothermal magnetite in porphyry systems. Igneous and hydrothermal magnetite related to alkaline magma is relatively rich in Mg, Mn, Co, Mo, Sn, and high field strength elements (HFSEs), perhaps due to high concentrations of chlorine and fluorine in magma and exsolved fluids, whereas those related to calc-alkaline magma are relatively rich in Ca but depleted in HFSEs, consistent with the high Ca but low HFSE magma composition. Igneous and hydrothermal magnetite related to high-K calc-alkaline magma is relatively rich in Al, Ti, Sc, and Ta, due to a higher temperature of formation or enrichment of these elements in melt/fluids.Partial least squares-discriminant analysis on hydrothermal magnetite compositions from porphyry Cu, iron oxide copper-gold (IOCG), Kiruna-type iron oxide-apatite (IOA), and skarn deposits around the world identify important discriminant elements for these deposit types. Magnetite from porphyry Cu deposits is characterized by relatively high Ti, V, Zn, and Al contents, whereas that from IOCG deposits can be discriminated from other types of magnetite by its relatively high V, Ni, Ti, and Al contents. IOA magnetite is discriminated by higher V, Ti, and Mg but lower Al contents, whereas skarn magnetite can be separated from magnetite from other deposit types by higher Mn, Mg, Ca, and Zn contents. Decreased Ti and V contents in hydrothermal magnetite from porphyry Cu and IOA, to IOCG, and to skarn deposits may be related to decreasing temperature and increasing oxygen fugacity. The relative depletion of Al in IOA magnetite is due to its low magnetite-silicate melt partition coefficient, immobility of Al in fluids, and earlier, higher-temperature magmatic or magmatic-hydrothermal formation of IOA deposits. The relative enrichment of Ni in IOCG magnetite reflects more mafic magmatic composition and less competition with sulfide, whereas elevated Mn, Mg, Ca, and Zn in skarn magnetite results from enrichment of these elements in fluids via more intensive fluid-carbonate rock interaction.

Trace element geochemistry of magnetite from the Cerro Negro Norte iron oxide−apatite deposit, northern Chile

Kiruna-type iron oxide−apatite (IOA) deposits constitute an important source of iron and phosphorus, and potentially of rare earth elements (REE). However, the origin of IOA deposits is still a matter of debate with models that range from a purely magmatic origin by liquid immiscibility to replacement of host rocks by hydrothermal fluids from different sources. In order to better constrain the origin of Andean IOA deposits, we focused on the Cretaceous Cerro Negro Norte deposit located in the Chilean Iron Belt, northern Chile. The Cerro Negro Norte magnetite ore is hosted in andesitic rocks and is spatially and genetically associated with a diorite intrusion. Our results show that the deposit is characterized by three main mineralization/alteration episodes: an early Fe–oxide event with magnetite and actinolite followed by four stages that comprise the main hydrothermal event (hydrothermal magnetite + actinolite; calcic–sodic alteration + sulfides; quartz–tourmaline and propylitic alteration) and a minor supergene event. Based on textural and chemical characteristics, four different types of magnetite are recognized at Cerro Negro Norte: type I, represented by high-temperature (~ 500 °C) magnetite cores with amphibole, pyroxene, and minor Ti–Fe oxide inclusions; type II, an inclusion-free magnetite, usually surrounding type I magnetite cores; type III corresponds to an inclusion-free magnetite with chemical zoning formed under moderate temperatures; and type IV magnetite contains abundant inclusions and is related to low-temperature (~ 250 °C) hydrothermal veinlets. Electron probe and laser ablation ICP-MS analyses of the four magnetite types show that the incorporation of Al, Mn, Ti, and V into the magnetite structure is controlled by temperature. Vanadium and Ga concentrations are relatively constant within each magnetite type, but are statistically different among magnetite types, suggesting that both elements could be used to discriminate between magmatic and hydrothermal magnetite. However, our results show that the use of elemental discrimination diagrams should be coupled with detailed textural studies in order to identify superimposed metasomatic events and evaluate the impact of inclusions on the interpretation of microanalytical data. The presence of a distinct textural and chemical variation between magnetite types in Cerro Negro Norte is explained by a transition from high- to low-temperature magmatic-hydrothermal conditions. The microanalytical data of magnetite presented here, coupled with new δ34S data for pyrite (− 0.5 to + 4.3‰) and U–Pb ages of the diorite (129.6 ± 1.0 Ma), are indicative of a genetic connection between the diorite intrusion and the magnetite mineralization, supporting a magmatic-hydrothermal flotation model to explain the origin of Kiruna-type deposits in the Coastal Cordillera of northern Chile.

Depositional model for banded iron formation host to gold in the Archean Rio das Velhas greenstone belt, Brazil, based on geochemistry and LA-ICP-MS magnetite analyses

Petrographic and geochemical data were obtained for selected carbonaceous and siderite-bearing chert and banded iron formation (BIF) from the Archean Rio das Velhas greenstone belt (RVGB), Quadrilátero Ferrífero, including seven orogenic gold deposits (Cuiabá, Lamego, Raposos, Roça Grande, São Bento, Urubu and Ápis) and two barren BIFs (Sumidouro and Campo Grande). The RVGB has Algoma-type BIFs that differ in terms of lithological association, mineralogical assemblage and geochemistry. Trace element geochemistry of the BIFs is used to investigate their depositional environment, and to evaluate if primary geochemical and petrographic features have implications for gold mineralization. The chert layers of the Lamego and Urubu deposits exhibit significant, positive Eu anomalies (Eu/Eu*PAAS = 1.57–4.01) and low contents of immobile elements (Al2O3 = <0.34 wt%, TiO2 = <0.02 wt%), suggesting a high contribution of hydrothermal fluid in their formation, with relatively low detrital input. The carbonate- and the magnetite-rich BIF of the Cuiabá, Roça Grande, Ápis and Raposos deposits display Eu/Eu*PAAS = 1.34–3.25; Al2O3 = 0.04–1.47 wt%, TiO2 = <0.03 wt%, interpreted to represent an intermediate contribution of hydrothermal fluid, as well as limited detrital input. The São Bento, Campo Grande and Sumidouro BIF show a significant mineralogical variability including magnetite, carbonate and iron-rich silicates. Their Eu/Eu*PAAS = 1.1–2.6; Al2O3 = 0.11–6.82 wt%, TiO2 = 0.03–0.33 wt% suggest high detrital input and low hydrothermal fluid influence. Textural relations and mineral assemblages of magnetite-rich samples indicate three main generations of this mineral: (i) diagenetic (very low grade metamorphic), (ii) early and (iii) main-stage hydrothermal. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses show that Ti, V, Ni and Co contents of magnetite systematically fluctuate. Their concentrations of Ti (50–677 ppm), V (11–207 ppm), Ni (8–166 ppm) and Co (3–14 ppm) in magnetite (i) are the highest comparatively to types (ii) and (iii) (Ti = 7–352 ppm; V = 0.2–59 ppm; Ni = 1–22 ppm; Co = 0.1–7 ppm). Even higher trace element content of the Sumidouro (i) is related to important clastic input to seawater during BIF deposition. The composition of magnetite types (ii) and (iii) is dependent on coexisting minerals (sulfides, carbonates and silicates), and on the type of mechanism of their formation (dissolution-reprecipitation, or re-equilibration). The mineralogical, geochemical and geological diversity of the RVGB BIFs, as well as magnetite composition in BIF, point to a depositional model for the RVGB BIF within the Rio das Velhas basin related to both proximity to the hydrothermal vent and of terrigenous sedimentary input.Deposition of chert layers (e.g., Lamego and Urubu deposits) was favored near the hydrothermal vents on the abyssal plain due to high concentration of silica and organic carbon. Away from the hydrothermal source, chert transitioned to carbonate-rich BIF, typical of Cuiabá, Roça Grande and Ápis, which still formed under the influence of organic matter. Magnetite-rich BIF, i.e. Raposos deposit, was deposited further away from the volcanic center, with limited supply of organic carbon and silica. In a submarine environment with greater clastic input, such as continental shelfs and island arcs, BIF composition was influenced by detrital contamination, and iron-rich silicates (i.e., stilpnomelane and chlorite) are common, besides magnetite and carbonate; this is the case for the São Bento, Campo Grande and Sumidouro BIFs. The BIF types with abundant iron-rich carbonate and-or magnetite host gold mineralization more efficiently since they are especially favorable to sulfides replacement accompanied by gold precipitation.

Magnetite chemistry and implications for the magmatic-hydrothermal ore-forming process: An example from the Devonian Yuleken porphyry Cu system, NW China

Magnetite in the Devonian Yuleken porphyry Cu–Mo deposit located in NW China witnessed complicated magmatic-hydrothermal ore-forming processes. The magnetite grains can be divided into MagI-A (from the Beitashan Formation basalt), MagI-B (from the porphyritic syenite wall rock), MagII (from sodic-calcic alteration zone), MagIII-A (from early potassic stage with no concomitant sulfides) and MagIII-B (from late potassic alteration coexisting with sulfides).Although magnetite crystals of a single type may accommodate a wide range of trace elements, general trend among elements in various types of magnetite can still be related to their forming conditions, such as temperature, fO2, coexisting mineral assemblages, and fluid compositions. In this study, the incorporation of Ti, Si, Al, Ba, Ta, and Sc into magnetite is favored under high temperatures, as indicated by their decreasing average concentrations from igneous MagI-A and MagI-B to hydrothermal MagIII-A and MagIII-B, while fO2 has considerable influence on the substitution of V and Mn into magnetite crystals especially under low temperatures. For chalcophile elements, e.g., Co, Ni, Cu, Zn, and Bi, which are subject to be affected by coexisting sulfide assemblages, the absence of expected depletion of Ni, Cu, Zn, and Bi in MagIII-B relative to MagIII-A suggests a slightly earlier precipitation of magnetite compared to sulfides, whereas Co depletion in MagIII-B compared to MagIII-A indicates extraction of Co by the later hydrothermal fluid. Thermodynamic calculation for Zn–Fe exchange between magnetite and equilibrated hydrothermal fluids verifies the distribution coefficients extrapolated from early experimental partitioning data, implying that Zn is more effectively fractionated into hydrothermal fluids than Fe with decreasing temperature, and yields Zn/Fe ratios of hydrothermal fluids similar to those measured from fluid inclusions trapped in porphyry Cu deposit. However, a similar calculation for Mn-Fe exchange in this study shows apparent discrepancies with previously published experimental data, implying an additional role of fO2 on the incorporation of Mn into magnetite.The presence of oxy-exsolution texture of ilmenite in hydrothermal magnetite of sodic-calcic stage (MagII) indicates superimposition of later potassic alteration characterized by high fO2 (ΔMH = −1 to 2) and medium-high-temperature (408 to 444 °C) onto magnetite initially formed in the early sodic-calcic stage. Additionally, MagI-A and MagI-B are characterized by higher Cr/Ni ratios relative to MagII and MagIII, with MagI-A enriched in both Ni and Cr at the Yuleken deposit. The newly-constructed Co–Ni–Cr ternary diagram could well differentiate magnetite of various paragenesis or origins owing to the sensitive response of these elements to forming environments at the Yuleken deposit.

Diagenetic Fate of Biogenic Soft and Hard Magnetite in Chemically Stratified Sedimentary Environments of Mamanguá Ría, Brazil

AbstractMagnetotactic bacteria (MTB) synthesize magnetite and greigite crystals under low oxygen conditions in the water column or uppermost sediment (greigite‐producing bacteria are found below the oxic‐anoxic transition). Dissolved iron and oxygen contents in local environments are known to be limiting factors for the production and preservation of biogenic magnetite. Understanding the processes that link MTB to their living environments is fundamental to reconstructing past chemical variations in the water column and sediment, and for using the magnetic properties of biogenic magnetite as environmental proxy indicators. Previous studies have suggested that the frequently identified biogenic soft (BS) and biogenic hard (BH) magnetite types are associated with equant and more elongated morphologies, respectively, and that their abundance varies in accordance with sedimentary oxygen content, where MTB that produce the BH component live in less oxygenated environments. We test this hypothesis in a high‐resolution integrated environmental magnetic and geochemical study of surface sediments from Mamanguá Ría, SE Brazil. Based on magnetic and pore water profiles, we demonstrate that both the BS and BH components occur within microaerobic environments and that as sediment oxygen content decreases with depth, the BS component disappears before the BH component. With continued burial into the sulfidic diagenetic zone, both components undergo progressive dissolution, but the BH component is more resistant to dissolution than the BS component. Our observations confirm previous inferences about the relative stability of these phases and provide a firmer basis for use of these two types of biogenic magnetite as paleoenvironmental proxies.

Study of cooling rate effect on baked clay materials and its importance for archaeointensity determinations

The effect of cooling rate was investigated for various baked clay materials as an attempt to follow how different factors (clay type, the experimental temperature chosen and material‘ heterogeneity) affect the corrections obtained and to estimate the importance of correction factors on the final archaeointensity determinations. The collection analyzed includes archaeological samples taken from eight archaeomagnetically studied Bulgarian archaeological sites and artificial samples with identical heating/cooling history prepared in the laboratory from different clay types. The results from the rock-magnetic analyses carried out indicate stability of magnetic mineralogy during heating. The identified magnetic minerals are mainly of magnetite type but hematite is also detected in certain cases. The cooling rate experiment was performed at several temperatures – 450 and 520 °C for the archaeological materials (taking into account the temperature intervals used for archaeointensity determination) and 450, 520 and 620 °C for the artificial samples. The results obtained point out that the cooling rate corrections can vary significantly not only within the same archaeological structure but also within the same sample. Major part of applicable corrections is obtained using lower experimental temperature. The experiment with the artificial samples illustrates that correction factors could differ even for materials subjected to the identical heating/cooling conditions. After applying individual cooling rate corrections the mean archaeointensities are reduced by 2–16%. For the half of the archaeological collections tested, the corrected mean values are within the experimental errors. Generally, the application of cooling rate correction does not improve the scatter of the AI results but can considerably diminish the number of the results used for the final AIs determination. It is suggested that this problem could be overcome using calculated median values for the cooling rate correction per site. The applicability of the proposed approach was tested and verified using published by other authors archaeointensity data obtained from pottery fragments (coming from three archaeological sites in Greece) and baked clay samples (taken from seven Spanish kilns).

Genesis of Chating Cu-Au deposit in the Middle-Lower Yangtze River Metallogenic Belt, Eastern China: Implications from magnetite and biotite geochemistry

Porphyry deposits developed in intracontinental settings have some geological characteristics that differ from those developed in arc-related continental margins. The Chating deposit is a newly discovered Cu-Au deposit in the Middle-Lower Yangtze River Metallogenic Belt (MLYB), eastern China. We carried out detailed petrographic observations and major and trace element analyses of different types of magnetite and biotite from the host quartz diorite porphyry and different alteration zones in Chating to elucidate the genesis of Chating deposit.Alteration types in Chating include skarn, sodic-calcic, potassic and phyllic, and copper mineralization is closely associated with potassic alteration of quartz diorite porphyry. The different types of magnetite and biotite at Chating show distinctive geochemical characteristics. Higher Ti and Al in magmatic magnetites and biotites compared to the hydrothermal minerals indicate higher temperature and pressure in the quartz diorite porphyry. Higher V in magmatic magnetites and lower XMg in magmatic biotites indicate higher fO2. Similar mineral geochemistry from typical worldwide porphyry deposits, for example, Al2O3, TiO2, FeOT, MgO, Na2O, IV(F) and IV(Cl) contents in biotite, and Ni/Cr, Ti, Al, Sn and Ga in magnetite, indicate a predominately magmatic fluid source. Differences in Si, Ca, Co/Ni, Mg, and Mn in different types of magnetite, and MnO, CaO, SiO2 differences in two types of biotite from typical porphyry copper deposits show the influence of external fluids. Moreover, high IV(F) values and low IV(Cl) values in biotites demonstrate that the magmatic-hydrothermal system in Chating was enriched in Cl and lacked F, consistent with the importance of Cl in the transport of Cu. Based on different discrimination diagrams for magnetite, such as Ni/Cr versus Ti, Ni/(Cr + Mn) versus Ti + V, and Al + Mn versus Ti + V, and the geochemical similarities of biotite from Chating and other porphyry deposits, combined with the similarity of alteration assemblages, we conclude that Chating has porphyry Cu-Au affinities, but the hydrothermal system was affected by external fluids, in contrast to more typical subduction-related porphyry deposits.

Combined igneous and hydrothermal source for the Kiruna-type Bafq magnetite-apatite deposit in Central Iran; trace element and oxygen isotope studies of magnetite

The main deposits of the Bafq district (Choghart, Se Chahun and Chadormalou deposits) are magnetite-apatite ore bodies with Early Cambrian age, hosted by Early Cambrian volcano-sedimentary rocks, showing lava flow structure with miarolitic cavities and occasional brecciation. The texture and geochemistry (trace elements and O-isotope) of the studied magnetite crystals show three types of magnetite with different proportions in different parts of the district and the deposits. These are primary ignious magnetite and high-temperature hydrothermal magnetite in the massive parts of the deposits and foam-like magnetite in the veins or in the fractures of the massive part. The lack of zonation, high Ti/Fe ratios and δ18O values (2‰<) indicate that massive magnetites formed at high temperature condition, while foam-like magnetite recrystallized at lower temperature. Textures and Co, V, Ti, Al, and Pb contents are used to distinguish ignious magnetites from the high-temperature hydrothermal magnetites. Foam-like magnetites contain lower REE and has lower δ18O values (2‰>) than the massive magnetites.The magmatic origin for the main part of the ores in the Bafq is more plausible. Contamination of the primary magmas of the Bafq magmatic rocks with crustal phosphorus and evaporate units was the major agent for triggering iron-rich melt immiscibility from the original magma. Concentration of volatiles in the iron-rich melt involving in crystallization of the primary magnetite and nucleation of the aqueous fluid bubbles on magnetite surfaces led to ascending the buoyant fluid bubble-magnetite aggregates. This caused continuation of the magmatic magnetite microlites growth from the iron-rich magmatic-hydrothermal fluid and formed high-temperature hydrothermal magnetite. Formation of hypersaline fluid due to crystallization of iron-rich melt at shallow depth led to crystallization of titanite (and Th-U-REE-bearing minerals) and sodic-calcic alteration related to magnetite mineralization. Microscopic evidence (replacement of magnetite by hematite and filling of fractures of thorite by magnetite) show that degassing continued at shallow depth, which led to re-crystallization of the primary magnetites and formation of the foam-like magnetites.

Magnetic Nanoparticle-Based Lateral Flow Immunochromatographic Strip as a Reporter for Rapid Detection of Melamine.

Magnetite nanoparticles (MNPs) Fe3O4 and r-Fe2O3 were surface-modified with poly(ethylene glycol) (PEG) in order to improve their specificity and bioactivity. PEG and the anti-MEL monoclonal antibody (mAb) were successfully immobilized on the surface of MNPs and characterized using FTIR, UV-Vis and TEM analyses. Surface modification of MNPs-PEG-mAb conjugates of a variety of sizes and magnetite types was employed to design and prepare labels for use in a lateral flow immunoassay (LFIA) to test whether the size of the conjugate can affect the performance of the assay. The results showed that the detection limit was mainly determined by the size of the MNPs-PEG-mAb conjugate. Under optimized conditions, a detection limit of 0.4 ppm for melamine was achieved using Fe2O3-PEG-mAb, which was almost 5-fold lower than that of the Fe3O4-PEG-mAb conjugate (2.2 ppm).

Trace element composition of magnetite from the Xinqiao Fe–S(–Cu–Au) deposit, Tongling, Eastern China: constraints on fluid evolution and ore genesis

The Xinqiao deposit is one of several polymetallic deposits in the Tongling ore district. There are two types of mineralization in the Xinqiao: skarn-type and stratiform-type. The skarn-type mineralization is characterized by iron oxides such as magnetite and hematite, whereas stratiform-type mineralization is characterized by massive sulfides with small amounts of magnetite and hematite. We defined three types of ores within the stratiform-type mineralization by the mineral assemblages and ore structures. Type I ore is represented by magnetite crosscut by minor calcite veins. Type II is a network ore composed of magnetite and crosscutting pyrite. Type III is a massive ore containing calcite and hematite. Type I magnetite is characterized by highly variable trace element content, whereas Type II magnetite has consistently higher Si, Ti, V, and Nb. Type III magnetite contains more In, Sn, and As than the other two types. Fluid–rock interaction, oxygen fugacity (fO2), and temperature (T) are the main factors controlling element variation between the different magnetite types. Type I magnetite was formed by more extensive fluid–rock interaction than the other two types at moderate fO2 and T conditions. Type II magnetite is thought to have formed in relatively low fO2 and high-T environments, and Type III in relatively high fO2 and moderate-T environments. Ca + Al + Mn and Ti + V discrimination diagrams show that magnetite in the Xinqiao deposit is hydrothermal in origin and is possibly linked with skarn.

Constraints on the Source of the Martian Magnetic Anomalies Inferred From Relaxation Time of Remanent Magnetization

AbstractThe strong magnetic anomalies observed over Mars originate from remanence of deep crust, which should be preserved during 4 billion years. We estimate the relaxation time of remanence carried by various types of magnetite, considering temperature and pressure dependences of magnetic parameters. The estimation shows that acicular‐shaped single‐domain magnetite is needed to retain the thick magnetized layer during 4 billion years in a low‐Urey ratio scenario, whereas acicular‐shaped single‐domain, equidimensional single‐domain, and pseudo‐single‐domain magnetites can be the source of anomalies in a high‐Urey ratio scenario. In each case, fine‐grained (&lt;10 μm) and preferably high‐aspect‐ratio magnetite in deep crust is needed to explain the observed anomalies.

In-situ LA-ICP-MS trace element analysis of magnetite from Mesozoic iron oxide apatite (IOA) deposits in the Luzong volcanic basin, eastern China

The iron-copper-gold belt in the Middle and Lower Yangtze River region is among the most important metallogenic provinces in eastern China. The Luzong (Lujiang—Zongyang) ore district hosts many significant iron deposits in the Luzong Basin and is an important part of this belt. The Yangshan deposit is hosted in the Cretaceous volcanic rocks of the middle Luzong Basin. The Makou deposit in the southern-central Luzong Basin has orebodies at the contact between gabbro-diorite and volcanic rocks of the Zhuanqiao Formation. There are three types of magnetite in these two deposits: (1) magmatic magnetite from the Makou gabbro-diorite, (2) hydrothermal magnetite from the Makou deposit, and (3) hydrothermal magnetite in the volcanic rocks from the Yangshan deposit. Magmatic magnetite from gabbro-diorite in the Makou deposit has concentrations of elements, Mg, Al, K, Sc, Ti, V, Cr, Mn, Co, Ni and Zn, higher than hydrothermal magnetite. Magmatic magnetite from the Makou deposit are the highest concentrations of Cr, Sc, Ni, Al, and Zn, but hydrothermal magnetite from this deposit has the lowest concentrations of these elements, whereas hydrothermal magnetite from the Yangshan deposit contains intermediate concentrations of these elements. Overall, there are positive correlations between Mg and Al, and Ti and Mn. The Makou and Yangshan hydrothermal magnetite show highly variable Mg values, apparently influenced by clinopyroxene (diopside) crystallisation from hydrothermal fluids. The Ti, Ga and Sn contents of the Makou hydrothermal magnetite are generally higher than those from the Yangshan deposit, suggesting the Makou magnetite formed under higher temperatures. The formation of IVAl-rich clinopyroxene in the Yangshan deposit may have resulted in the low V content of magnetite, whereas the high Cr content may have been derived from the associated trachyandesite. Leaching of thick volcanic sequences via magmatic fluids may have led to the incorporation of certain elements into the ore-forming fluids, resulting in higher Al, Mn, and Zn concentrations in the Yangshan magnetite. The Makou hydrothermal magnetite has Na and K contents similar but Ca content higher than that of the magmatic magnetite, indicating that Na and K were retained in the melt, but Ca was enriched in the fluid. Both the Makou and Yangshan hydrothermal magnetites contain high V and low Cr concentrations and resemble magnetite in IOA deposits elsewhere. Combined with the wall rocks and mineral assemblages the Makou and Yangshan deposits are best classified as magnetite-apatite deposits. Intensive diopside alteration in these two deposits may be related to the marine sedimentary strata at the depth.

Constraining the origin of the Mesozoic Xishimen Fe deposit in the Taihang Mountain Range, North China using geochemistry of magnetite

The Xishimen (XSM) iron (Fe) deposit located in the Taihang Mountain Range in North China is one of the largest known Mesozoic skarn Fe deposits in China. Recent research suggests that the Fe deposit exhibits some magmatic features. Here, we report new major and trace element, mineral assemblage and Fe isotope data of magnetite from the XSM Fe deposit in the Han-Xing Fe metallogenic belt, which allows for the identification of four distinct types of magnetite (Type I, II, III and IV). Magnetite type I is characterized by anhedral shape with vesicles in the ores, and consists of minerals diopside (Di), tremolite (Tr), ±garnet (Gt) and/or augite (Aug), spreading over diopside, tremolite, phlogopite and/or Aug as an interstitial mineral, which can dissolve or melt pre-existing minerals (such as Di and Tr). Magnetite type I also contains high content of TiO2 (0.25–1.21 wt.%) and Al2O3 + MnO (0.24–0.72 wt.%). These features suggest that magnetite type I is of magmatic origin. Magnetite type IV is marked by euhedral shape, consists of Cc, Ap and/or Py, enriched in SiO2, CaO, Sr, Ba, Rb, Nb, and total REE, and depleted in TiO2. These properties suggest that magnetite type IV is of hydrothermal origin. The features of magnetite types II and III fall in between magnetite I and magnetite IV. The δ56Fe value also differs for the four types of magnetite: δ56Fe is the highest for type I magnetite (average 0.085‰); and the lowest for magnetite type IV (average 0.016‰). We also find that δ56Fe value tends to be higher under high temperature environment and in lower part of the main orebody. Statistical analysis shows that δ56Fe and altitudes are negatively correlated.In order to constrain the origin of the XSM Fe deposit, we present a new conceptual model based on our new geochemistry data. This model suggests a stepwise pattern of Fe ore genesis, including (1) “melt-fluid bearing Fe” forms in the deep magma chamber; (2) “melt-fluid bearing Fe” rises along the magmatic conduit due to fluid overpressure in the deep magma chamber; (3) changes in ambient temperature, pressure, and oxygen fugacity cause the different composition of magnetite along the magmatic conduit; and (4) Fe isotope fractionation occurs during the rising and settlement of “melt-fluid bearing Fe” in response to changes in temperature and oxygen fugacity. This model explains the magmatic characteristics of magnetite formed under high temperature in the lower part of the conduit, and the hydrothermal characteristics of magnetite occurred under low temperature in the upper part of the conduit.

Trace Element Geochemistry of Magnetite: Implications for Ore Genesis of the Huanggangliang Sn-Fe Deposit, Inner Mongolia, Northeastern China

The Huanggangliang deposit is a super-large Sn-Fe deposit in the Huanggangliang–Ganzhuermiao metallogenic belt in the southern section of the Great Hinggan Range. The Sn-Fe deposits mainly occur in the skarn contact zone and were formed via the interaction of biotite-bearing alkali feldspar granite with limestone strata of the Permian Dashizhai and Zhesi Formations. Based on the intersecting relations among the ore-bearing veins and the different types of mineral assemblages within these veins, the Sn-Fe mineralization could be divided into two periods and four stages: the skarn period, which includes the garnet–diopside–magnetite (T1) stage (stage 1) and epidote–idocrase–cassiterite–magnetite (T2) stage (stage 2); and the quartz–magnetite period, which can be divided into the quartz–cassiterite–magnetite (T3) stage (stage 3) and quartz–magnetite (T4) stage (stage 4). In this paper, we discuss the genesis of magnetite, controlling factors for magnetite compositions, and type of ore genesis based on petrographic studies and LA-ICP-MS analyses of trace elements in these four types of magnetite from the Huanggangliang Sn-Fe deposit. The results demonstrate that the four types of magnetite are generally depleted in Ti (0.002–3.030 wt %), Al (0.008–1.731 wt %), and Zr (&lt;1.610 ppm). In addition, the low Ni and Cr contents and relatively high and stable Fe contents in the four types of magnetite are indicative of hydrothermal genetic features. Compositions of the ore fluids and host rocks, formation of coexisting minerals, and other physical and chemical parameters (such as fO2) may have influenced the variable magnetite geochemistry in the different Huanggangliang ore types, with fluid compositions and fO2 probably playing the most important roles. The geological, petrographic, and geochemical characteristics of magnetite of the Huanggangliang Sn-Fe deposit lead us to conclude that the deposit is a skarn-type Sn-Fe deposit associated with Yanshanian medium-acidic magmatic activities.

Removal of Lead(II), Cadmium(II), and Arsenic(III) from Aqueous Solution Using Magnetite Nanoparticles Prepared by Green Synthesis with Box–Behnken Design

ABSTRACTTwo types of magnetite (Fe3O4) nanoparticles were investigated as adsorbents for the simultaneous removal of Pb(II), Cd(II), and As(III) metal ions from aqueous solution. Magnetite nanoparticles were prepared by two synthesis procedures, both using water as solvent, and are referred to as conventional Fe3O4 nanoparticles and green Fe3O4 nanoparticles. The latter used Citrus limon (lemon) aqueous peel extract as the surfactant. Box–Behnken experimental design was used to investigate the effects of parameters such as initial concentration (20–150 mg L−1), pH (2–9), and biomass dosage (1–5 g L−1) on the removal of Pb(II), Cd(II), and As(III) ions. The optimum parameters for removal of the studied metal ions from aqueous solutions, including the initial ion concentration (20 mg L−1), pH (5.5) and adsorbent dose (5 g L−1), were determined. The pseudosecond-order model exhibited the best fit for the kinetic studies, while adsorption equilibrium isotherms were best described by Langmuir and Freundlich models. The optimum conditions were applied for the treatment wastewater. The removal efficiencies of Pb(II), Cd(II), and As(III) using the conventional and green synthesized Fe3O4 nanoparticles were 59.4 ± 4.3, 18.7 ± 1.9 and 17.5 ± 1.6, and 98.8 ± 5.6, 46.0 ± 1.3, and 48.2 ± 2.6%, respectively. These results demonstrate the potential of magnetite nanoparticles synthesized using C. limon peel extract as highly efficient adsorbents for the removal of Pb(II), Cd(II), and As(III) ions from aqueous solution.