Fe Enrichment Research Articles

Evaluation of Heavy Metals Pollution in Seawater, Suspended Particulate Matter and Sediment from Abu-Qir Bay, Alexandria, Egypt

The level of heavy metals (Mn, Fe, Co, Ni, Cu, Zn, Pb, and Cd) in seawater, suspended particulate matter (SPM) and sediment along Abu-Qir Bay coast, Alexandria, Egypt, were evaluated by selecting nine stations as hot spots during winter 2020. Resuls showed that, the average concentrations of the investigated heavy metals followed the following order: Fe > Zn > Mn > Ni > Pb > Co > Cu > Cd in seawater, Fe > Zn > Mn > Pb > Cu > Ni > Co > Cd in SPM, and Fe > Mn > Zn > Ni > Co > Cu > Pb > Cd in sediment. Moreover, the distribution coefficient ( 16Kd> ) revealed that, Fe was highly stable in sediments, and the log ( 16Kd> ) value was 6.521 in all water bodies. In addition, geo-accumulation index (Igeo), pollution load index ( 16PLI> ), modified degree of contamination (mCd), potential ecological risk index ( 16RI> ), as well as the mean effect range median quotient ( 16MERM-Q> ) were calculated. Calculations recorded that, the values of Igeo for Cd in surface sediments ranged between 1 and 3 indicating that, the study sites were moderate to strongly contaminated with Cd. The mCd values of Ni, Cu, Zn, Pb, and Cd ranged between 1.32 and 4.24, reflecting a low to moderate degree of contamination. The studied metals presented a moderately toxic ecological risk (150 ≤ RI > 300). Based on 16MERM-Q> classification, all samples had medium-low toxicity; Ni, Cu, Zn, and Pb may be originated from anthropogenic sources, whereas Cd emerged from natural sources with some contribution of anthropogenic source. Redundancy analysis (RDA) revealed that the TOC % and fine sand % of the sediment had a certain influence on the Fe enrichment. The data of the water quality index (WQI) revealed that St 2, St 3, St 4, St 5 & St 6 were slightly polluted, and could be considered hot spots.

Understanding genesis of iron oxide concretions present in Dhandraul (Vindhyan) Sandstone: Implications in formation of Martian hematite spherules

The iron oxide concretions of Shankargarh (Allahabad), India belongs to Dhandraul Sandstone of Vindhyan Supergroup. Petrography of concretions shows abundant quartz grains embedded within the iron oxide cementation. XRD analysis of the concretion shows diagnostic peaks for quartz, hematite, and goethite. The A–CN–K and A–CNK–FM ternary diagrams drawn for concretion and host rock bulk composition clearly indicate the interaction of concretions rock with iron-bearing diagenetic fluids. A negative Ce anomaly, lower Th/U ratio, and enrichment of redox responsive trace element (e.g., vanadium) indicate concretion formation is redox-controlled. The concretions show Fe enrichment and Si depletion as compared to the host sandstone. The mass balance calculations indicate that the total Fe2O3 in the ferruginous sandstone system is 17.63 wt%. The iron mobilization and recycling in the sandstone pore spaces have formed concretions with Fe2O3 (25–35% by volume). The sandstone volume required to produce a 6 mm diameter iron oxide concretion is 1807.83 mm3. The Fe laminae and random red colouration patterns in Dhandraul sandstone are consistent with the movement of iron-enriched fluid through pores and spaces. These iron oxide concretions have similarities with the hematite spherules discovered in the Burn Formation, Meridiani Planum, Mars.

Discriminate between magmatic- and magmatic-hydrothermal ore deposits using Fe isotopes

Although discriminating high temperature mineral systems, for example, magmatic- vs magmatic-hydrothermal origin Fe deposits, is challenging, the emerging Fe isotope systematics have shown good potentials to provide crucial information on resolving the problem. Here, Fe isotopes of multiple types of samples from one iron oxide-apatite (IOA) deposit and two skarn Fe deposits are measured, aiming to study their behaviors in high temperature magmatic and magmatic-hydrothermal environments. The primary observation of this study is that magnetite samples from high grade ores of magmatic origin IOA deposits has a heavier Fe isotopic signature relative to the associated igneous rocks, whereas a lighter Fe isotopic composition in magnetite samples from magmatic-hydrothermal origin skarn deposits relative to the causative intrusions. Another distinctive feature is that δ56Fe values of the causative intrusions in the magmatic origin IOA deposits are lighter than that of non-fertile intrusions, whereas the ore-associated intrusions of the magmatic-hydrothermal deposit are heavier in δ56Fe than that of non-fertile igneous rocks. The above two observed scenarios suggest that Fe isotope fractionation exists in both magmatic immiscibility and hydrothermal fluid exsolution processes. Magma immiscibility leads to heavy Fe isotope enrichment in immiscible Fe-rich melt phase, and resulting light Fe enrichment in Si-rich melt phase. Hydrothermal fluid exsolution results in lighter Fe isotope enrichment in the exsolved liquid phase, with a heavy Fe isotope enrichment in the residual magma. Fe isotopes behave in different ways in magmatic and magmatic-hydrothermal mineralization processes, which makes Fe isotopes an effective tool to discriminate mineral deposits of magmatic origin from those formed by magmatic-hydrothermal processes.

Ordovician volcanic rocks record rifting, Variscan metamorphism and gold mineralization processes (Truchas Syncline, NW Iberia, Spain)

Ordovician volcanic rocks outcrop in several locations of the NW Iberian Variscan belt. Their composition is mainly basaltic (with less acid types) and occur as volcanic-volcanoclastic layers within a shale-slate succession. This work focuses on volcanic and related rocks within a prominent Variscan structure, the Truchas Syncline. We studied field relations, petrography, mineralogy, geochemistry and conducted thermodynamic modelling to review the petrogenesis and establish the evolution of these volcanic rocks classified as within-plate alkaline basalts (high Ti/Y, Nb/Y and Nb/Yb). Crustal contamination is absent given the elevated Nb/La ratio (1–1.5). These features indicate low melting degrees of the upper mantle and a continental rifting environment. The finding of Ordovician orthid brachiopods in some of the volcanoclastic rocks suggests a shallow marine environment for the volcanic deposition. Variscan metamorphism occurred at lower greenschist conditions with chlorite-temperatures of 374 ± 6 °C. Quartz + carbonate veins indicate that H2O–CO2 metamorphic fluids traversed some volcanic rocks, reacting with Ca–Fe–Mg phases to produce carbonates (Mg-calcite–Fe-dolomite). For this event, T-XCO2 modelling indicates temperatures below 350–360 °C and fluid XCO2 between 0.10 and 0.45. Such fluids can be important carriers of Au and might explain gold deposits in adjacent quartzites. Metasomatic shales (Fe-chlorite + quartz) outcrop nearby and were derived from a mixed protholith of shales and minor volcanic components. Its geochemistry shows Fe enrichment and high peraluminosity. Variscan deformation further modified its geochemistry causing Si-depletions and relative increases of other elements (K, Na, Ti, Al, Rb, Sr, Ba and LREE) in shear zones domains.

Cu, Fe, and Zn isotope ratios in murine Alzheimer's disease models suggest specific signatures of amyloidogenesis and tauopathy

Alzheimer’s disease (AD) is characterized by accumulation of tau and amyloid-beta in the brain, and recent evidence suggests a correlation between associated protein aggregates and trace elements, such as copper, iron, and zinc. In AD, a distorted brain redox homeostasis and complexation by amyloid-beta and hyperphosphorylated tau may alter the isotopic composition of essential mineral elements. Therefore, high-precision isotopic analysis may reveal changes in the homeostasis of these elements. We used inductively coupled plasma–mass spectrometry (ICP-MS)-based techniques to determine the total Cu, Fe, and Zn contents in the brain, as well as their isotopic compositions in both mouse brain and serum. Results for male transgenic tau (Line 66, L66) and amyloid/presenilin (5xFAD) mice were compared with those for the corresponding age- and sex-matched wild-type control mice (WT). Our data show that L66 brains showed significantly higher Fe levels than did those from the corresponding WT. Significantly less Cu, but more Zn was found in 5xFAD brains. We observed significantly lighter isotopic compositions of Fe (enrichment in the lighter isotopes) in the brain and serum of L66 mice compared with WT. For 5xFAD mice, Zn exhibited a trend toward a lighter isotopic composition in the brain and a heavier isotopic composition in serum compared with WT. Neither mouse model yielded differences in the isotopic composition of Cu. Our findings indicate significant pathology-specific alterations of Fe and Zn brain homeostasis in mouse models of AD. The associated changes in isotopic composition may serve as a marker for proteinopathies underlying AD and other types of dementia.

Anoxic continental surface weathering recorded by the 2.95 Ga Denny Dalton Paleosol (Pongola Supergroup, South Africa)

Iron mobilization during continental weathering was pervasive before the Great Oxidation Event (GOE) that started at around 2.43 billion years (Ga) ago, due to the soluble nature of reduced iron. However, various geochemical proxies indicate transient oxygenation during deposition of the Mesoarchean (∼2.95 Ga) Pongola Supergroup, South Africa, which suggests that continental weathering could have also occurred under transiently oxic conditions before the GOE. We analyzed trace elemental and Fe, Ti, and Cr isotopic compositions of the ca. 2.95 Ga Denny Dalton paleosol in the Pongola Supergroup to better understand continental weathering and redox conditions in the ancient critical zone, and the nature of geochemical fluxes from the continents to the oceans and marine sediments. Iron isotope systematics are consistent with a model where Fe was released during intense leaching from the paleosol to concentrate in Fe-rich groundwaters in the deeper part of the soil horizon. We show for the first time that Fe isotopic fractionation during Mesoarchean continental weathering was limited, and Fe enrichments and depletions are coupled with those of divalent transition metals, Co, Ni, and particularly Zn. This suggests that Fe redox cycling was not involved in paleosol formation, and Fe2+ was mobilized under anoxic conditions. Chromium isotopes are also unfractionated relative to the parent igneous rock in this paleosol, which precludes removal of isotopically heavy Cr6+ and thus supports anoxic continental weathering. We show that previously reported Cr isotopic fractionation in another Denny Dalton paleosol profile does not follow a Cr6+ leaching trend, but instead scales with Cr enrichment and may reveal Cr enrichment from post-burial fluids. Thus, there is no clear evidence for an oxidative continental weathering during deposition of the Pongola Supergroup. Titanium isotopes are not significantly fractionated in the paleosol, suggesting that continental weathering and erosion in the Archean did not fractionate Ti isotopes. Similarly, Ni/Co and Th/Sc ratios are reasonably conserved, which validates their use as a robust proxy for upper continental crust composition in shales, whereas La/Sc, Cr/Zn and Cr/U ratios are highly variable relative to the provenance composition, which suggests that caution should be used when applying these ratios in shale studies of the ancient upper continental crust composition.

Geochemical and tectonic constraints on the genesis of iron formation-hosted magnetite-hematite deposits at the Guanhães Block (Brazil) by contact metasomatism with pegmatite intrusions

The Horto-Baratinha (HBD) and Cuité (CTE) are two high-grade iron ore deposits (>60% wt. Fe) located in the Guanhães Tectonic Block (GB), at the eastern margin of the São Francisco Craton bordering the late Neoproterozoic–Cambrian Araçuaí-West Congo Orogenic belt. The orebodies are hosted by Orosirian to early Statherian metamorphic banded iron formation (IF) associated with quartzite and aluminous schists. The metasedimentary units are time-correlated with the Serra da Serpentina and Serra de São José Groups exposed in the Southern Espinhaço fold-thrust belt. They occur as tectonic slivers inserted in the pre-Rhyacian gneissic rocks and the granitic plutons of the Statherian Borrachudos Suite that comprise the GB. In the GB, the IF was intruded by anatectic pegmatites of Ediacaran to Cambrian crystallization age with the development of massive, granular magnetite-rich high-grade orebodies at the contact zone, contrasting with the hosting schistose quartz-hematite IF. The Fe-mineralization of the IF during the Brasiliano Orogeny developed in three distinct stages. (1) Syn- to late-collisional stage (ca. 580–560 Ma) with partial Fe enrichment along sheared zones, crystallization of oriented platy hematite crystals and development of discontinuous lens-shaped schistose high-grade orebodies. (2) Syn- to late-collisional stage (ca. 560–530 Ma) with the formation of massive magnetite bodies by contact metamorphic-metasomatism with the pegmatite. (3) Late- to post-tectonic stage with the oxidation of magnetite to kenomagnetite, martite and crystallization of granular hematite, probably by increased input of meteoric fluids during gravitational collapse of the Araçuaí-West Congo Orogen (ca. 530–490 Ma). In the HBD deposit, the first mineralization stage was unimportant for the enrichment of the IF that exhibit Fe contents of 32.45 to 43.50 wt%.Whole-rock data indicates that the massive hematite-magnetite high-grade iron ore pods exhibit Fe contents between 50.24 and 69.46 wt%, and increasing content of Al2O3, MgO and CaO and the trace elements Zr, Y, Zn, and Ni near the contact with pegmatite, associated with the presence of interstitial silicates and carbonates in their composition. Lamellar hematite exhibit very low contents of trace elements as in other specularitic IFs and orebodies from the eastern São Francisco Craton. A consistent increase in the content of trace elements, mainly Mg, V, Cr, Mn, Co, Ni, Zn, and Ga, is observed in kenomagnetite. Granular hematite grains are enriched an Al, Ti, Zr, Nb, Mo, Sn, Sb, Hf, Ta, and W. Notably, Mn and Ti may occur in relatively high concentrations in kenomagnetite and hematite with the crystallization of ilmenite inclusions, associated with the contact-metasomatic stages.

Characterizing geochemistry of organic carbon, sulfur, and iron in sediments of the middle Okinawa Trough since the last glacial maximum

The diagenetic interplays of organic carbon (OC), sulfur (S), and iron (Fe) in marine sediments and their responses to changes in depositional and climatic conditions are poorly characterized. In this study, chemical speciation and isotopes were combined to characterize diagenesis of OC, S and Fe in sediments of the middle Okinawa Trough (OT), a back-arc deep basin along the edge of the East China Sea outer shelf, since the Last Glacial Maximum (LGM). Two key geochemical proxies, i.e., OC/pyrite-S ratios and the degrees of pyritization, indicate anoxic bottom-water conditions during the last Glacial/Deglacial, which promoted burial of OC and pyrite. However, a shift to oxic conditions during the Deglacial-Holocene transition facilitated aerobic respiration, resulting in lower burial of OC and pyrite. In contrast to previous studies, the environmental changes induced by large sea-level rises since the LGM have not triggered significant variations in pyrite-S isotopic compositions, probably due to persistently low sedimentation rates. Variable extents of Fe enrichment are identified in the sediments since the LGM, with lower enrichment during the Holocene probably due to increased distance of Fe shuttling and concomitant Fe ageing. Anoxic bottom water during the Glacial/Deglacial did not induce an expected intensification of OC sulfurization, probably because sedimentary Fe enrichment favored pyrite formation but competitively dampened OC sulfurization. Lines of geochemical evidence hint at a discontinuous deposition at ~200 cm depth probably caused by mass wasting.

Iron Incorporation From Seawater Into Antarctic Sea Ice: A Model Study

Sea ice acts as an iron (Fe) reservoir in the Southern Ocean (SO) where primary productivity is largely Fe limited. The mechanisms leading to Fe enrichment in sea ice result from the combination of poorly understood and largely unexplored physical and biological processes. We analyze the biogeochemical impacts of three plausible idealized formulations of dissolved Fe (DFe) incorporation into sea ice corresponding to (i) constant Fe concentration in sea ice, (ii) constant ocean‐ice Fe flux, and (iii) ocean‐ice Fe flux linearly varying with seawater Fe concentration in a global ocean‐sea‐ice‐biogeochemical model, focusing on the SO. The three formulations simulate different geographical distributions of DFe concentrations in sea ice. Iron in sea ice remains largely uncertain due to the limited number of spatial and seasonal observations, poorly constrained Fe sources and sinks, and significant uncertainties in simulated sea ice and hydrography. Despite these differences, the fertilization effect by sea ice on phytoplankton photosynthesis is qualitatively similar regardless of the formulation considered. Iron incorporation during sea‐ice formation, transport, and melt release, common to all formulations, dominates over differences in sea‐ice Fe concentrations. Formulating the Fe incorporation rate as proportional to seawater Fe concentrations gives the closest agreement to field observations. With this formulation, sediments work in synergy with Fe transport to fertilize the waters north of the continental shelf. Southern Ocean primary production and export production increase by 5–10% and 9–19%, respectively, when Fe incorporation into sea ice is considered, suggesting a moderate effect of Fe‐bearing sea ice on marine productivity.

Textural and Compositional Changes in the Lithospheric Mantle Atop the Hawaiian Plume: Consequences for Seismic Properties

AbstractWe characterized the texture, composition, and seismic properties of the lithospheric mantle atop the Hawaiian plume by petrostructural analysis of 48 spinel peridotite xenoliths from four localities in three Hawaiian islands. Coarse‐porphyroclastic peridotites with variable degrees of recrystallization, recorded by growth of strain‐free neoblasts onto the deformed microstructure, predominate. Full evolution of this process produced equigranular microstructures. Some peridotites have coarse‐granular microstructures. Coarse‐granular and coarse‐porphyroclastic peridotites have strong orthorhombic or axial‐[100] olivine crystal‐preferred orientations (CPOs). Recrystallization produced some dispersion and, locally, changed the olivine CPO towards axial‐[010]. Enrichment in pyroxenes relative to model melting trends and pyroxenes with interstitial shapes and CPO uncorrelated with the olivine CPO imply refertilization by reactive melt percolation. The unusual spatial distribution of the recrystallized fraction, Ti enrichment, and Rare Earth Element fractionation in recrystallized, equigranular, and coarse‐granular peridotites support that these microstructures are produced by static recrystallization triggered by melt percolation. However, there is no simple relation between microstructure and chemical or modal composition. This, together with marked variations in mineral chemistry among samples, implies multiple spatially heterogeneous melt‐rock reaction events. We interpret the coarse‐porphyroclastic microstructures and CPO as representative of the original oceanic lithosphere fabric. Annealing changed the microstructure to coarse‐granular, but did not modify significantly the olivine CPO. Recrystallization produced moderate dispersion of the CPO. “Normal” oceanic lithosphere seismic anisotropy patterns are therefore preserved. Yet Fe enrichment, refertilization, and limited heating of the base of the lithosphere may reduce seismic velocities by up to 2%, partially explaining negative velocity anomalies imaged at lithospheric depths beneath Hawaii.

The Effect of the Starting Mineralogical Mixture on the Nature of Fe-Serpentines Obtained during Hydrothermal Synthesis AT 90°C

AbstractThe formation conditions and stability fields of Fe-serpentines are still poorly understood in both terrestrial (natural or anthropic) and extraterrestrial environments. Knowledge of the effects of physical-chemical parameters on compositional and structural features of Fe-serpentines is lacking, and only a few thermodynamic parameters of these minerals are available in the literature. To fill these gaps, the synthesis of these minerals, while controlling all the physicochemical experimental parameters, was undertaken. Two hydrothermal syntheses were carried out at 90°C to investigate the effect of two different starting mineralogical mixtures on the nature of Fe-serpentines. The run products were identified by several analytical techniques (powder X-ray diffraction, transmission, and scanning electron microscopy). Berthierine crystals were synthesized from a starting mixture of kaolinite and metal iron. The berthierines synthesized show different morphologies and iron contents (~3–38 at.%). From a starting mineralogical mixture composed of quartz and metal iron, cronstedtite crystallizes. Most of the crystals are 1M polytypes. Magnetite is always associated with both berthierine and cronstedtite. Lepidocrocite was observed only in the experiment with kaolinite. These experimental results demonstrated that Fe enrichment in serpentines depends on the silicate precursor (kaolinite or quartz) of the starting mixture. The results are also in agreement with the geochemical equilibrium predicted by thermodynamic modeling, i.e. the formation of berthierine and cronstedtite in association with magnetite at the expense of metal iron and silicates.

Influence of host magma alkalinity on trachytic melts formed during incongruent orthopyroxene dissolution in mantle xenoliths

ABSTRACT Spectacular reactions textures developed during the non-isochemical breakdown of orthopyroxene and spinel in peridotite mantle xenoliths in intraplate alkaline basalts from the Auckland Volcanic Field and the Dunedin Volcano in New Zealand, and Jeju Island in South Korea. Mantle orthopyroxene is replaced by symplectitic intergrowths of silica-rich glass and olivine (± clinopyroxene ± orthopyroxene) with individual minerals showing large diffusion gradients at their margins proximal to the host melt. The glasses are basaltic to trachytic and formed by incongruent melting of orthopyroxene and subsequent re-equilibration by diffusion and mixing during changing boundary conditions with the host magma. Although the glass composition is strongly dependent on the alkalinity of the host magma, the distance to the reacting contact and the respective phase assemblage that develops in the reaction zone (melt + ol ± clinopyroxene ± orthopyroxene), the most evolved melts converge at trachytic composition. Diffusion-driven Fe enrichment for mantle olivine indicates residence timescales within the host magma on the order of weeks to several months.

Maternal Red Blood Cell Catabolism as a Source of Fetal Iron

Abstract Objectives The developing fetus is reliant on maternal iron (Fe) supply across gestation. Fetal Fe may be obtained from maternal red blood cell (RBC) catabolism, dietary sources or maternal stores. Relative use of these Fe pools has not been explored in humans. The objective of this study was to label the maternal RBC pool in early gestation and evaluate determinants of RBC enrichment across. A second objective was to compare fetal uptake of Fe from RBC catabolism vs recent maternal diet. Methods Fifteen women (age 17–34 y) were dosed with an oral stable ,57Fe isotope during the early second trimester of pregnancy (wk 15 ± 0.7) to label the maternal RBC pool. Enrichment of ,57Fe in maternal RBCs was monitored at regular intervals across pregnancy and in neonatal RBC's at birth. All women ingested an additional stable isotope (,58Fe) in late gestation (wk 34 ± 0.7) to quantify rapid transfer of dietary Fe to the fetus. The net amounts of each isotope in the mother and neonate were calculated using hemoglobin (Hb) concentration, body weight and estimated blood volumes. Hb, serum ferritin (SF), soluble transferrin receptor (sTfR), hepcidin and erythroferrone (ERFE) were assessed in maternal and cord blood. Results In this population, 25% of women were anemic at delivery (Hb < 11 g/dL), and 36% of the newborns were anemic at birth (wk 39 ± 1.8) (Hb < 13 g/dL). During the third trimester of pregnancy, 25% of women were Fe deficient (SF < 12 mg/L). In the group as a whole, RBC ,57Fe enrichment decreased (b = −0.2, P = 0.06) on average by 2% across the 22 wk study interval (from 13.1% to 9.6%). Of the net amount of ,57Fe released from RBC catabolism, 25.4% [95% CI: 10.0%–64.4%] was transferred to the neonate. Neonatal RBC ,57Fe enrichment was significantly inversely associated with maternal and neonatal SF, which captured 87% of the variance in neonatal RBC ,57Fe enrichment (P < 0.01). Maternal SF was significantly inversely associated with neonatal RBC ,58Fe enrichment from the dietary source in late gestation. Maternal SF captured 55% of the variance in neonatal RBC ,58Fe enrichment (P = 0.01). Conclusions Women with low Fe stores exhibited a greater loss of RBC enrichment across gestation and a higher transfer of Fe from both catabolized RBC's and dietary sources to the fetus. More research on the determinants of placental Fe trafficking of different sources of maternal Fe is needed. Funding Sources Work funded by the NIH/NIDDK.

Effects of iron oxide nanoparticles on Fe and heavy metal accumulation in castor (Ricinus communis L.) plants and the soil aggregate.

In this study, the effects of iron (Fe) nanoparticles (NPs) on Fe and heavy metal accumulations by castor (Ricinus communis L.) plants were investigated. The castor cultivar was planted in the soil contaminated with Pb and Zn for 48 days with Fe2O3 NPs treatments. The Fe and heavy metal concentrations in the plant tissues, the plant tissues' ultrastructures, and the Fe and heavy metal distributions in the soil aggregate were analyzed. The results of this study indicate that there is a mutual promotion relationship between Fe and heavy metals (Pb and Zn). The scanning electron microscopy (SEM) revealed ultrastructural differences in the xylem and phloem with Fe2O3 NPs addition, and the presence of Fe2O3 NPs may influence the synthesis of starch granules in response to heavy metal stress. Based on the analysis of the soil aggregate, α-Fe2O3 NPs and γ-Fe2O3 NPs changed the size distribution of the soil aggregate, that is, the macro-aggregate and the clay fraction contents increased and the micro-aggregate content decreased. Moreover, in the different size fractions of the soil aggregate, Fe2O3 NPs can change the Zn and Fe enrichment and migration between the macro-aggregate and clay fractions, and there is a synergistic effect between the Fe and Zn migration. In addition, in the castor organs (roots and shoots), the Zn accumulation was mainly determined by the Zn concentration of the macro-aggregate fraction, while the Fe accumulation was mainly determined by the Fe concentration of the micro-aggregate fraction. Overall, these direct observations help improve our understanding of the migration and transport characteristics of Fe and heavy metals in soil-plant systems when Fe nanoparticles are added to metal-contaminated soils.

Sedimentary iron cycling in the Benguela upwelling system off Namibia

Iron (Fe) is an essential micronutrient and its availability controls primary production in large parts of the ocean. Further, the variability of oxygen minimum zones (OMZ) exerts a major control on the availability of Fe, concentrations of which are elevated off Namibia. Therefore, to understand the sources and processes involved in the cycling of Fe off Namibia, we determined major and trace element contents (Fe, Al, Si, K, P, organic carbon, Mn, Co, Zr) and the isotopic composition of Fe (δ56Fe) in seven sediment cores along a transect from the shelf to the abyssal plain at ∼5 km water depth (Meteor cruise M76-1) as well as in the local lithogenic background (Namibian river bed sediments and dust).The depletion of Mn vs. the local lithogenic background (LLB) reflects the reducing character of sediments from the shelf to the lower slope. While depletion of Mn and enrichment of Co indicates the anoxic–sulfidic environment on the shelf, the enrichment of both elements in abyssal sediments documents highly oxidizing conditions there.Iron/Al ratios are elevated (0.6 to 1.6) and therefore equal to, or higher than the LLB. The highest Fe enrichment is seen on the shelf (core 1) and the shelf break (core 2) with a clear decrease towards the abyss. The bulk δ56Fe values range from +0.30 to −0.05‰ in the marine sediments, with an average of ∼0.08‰, which is slightly lighter than the δ56Fe of the LLB (0.16 to 0.21‰). Further, combined enrichments of K and Fe suggest the presence of detrital biotite (core 1) and authigenic glauconite (core 2), both of which are perfectly correlated with Zr/Al ratios reflecting the highly dynamic conditions of the shelf environment (0-300 m water depth).The absent large sedimentary Fe isotope fractionation in the sediments of this study compared to Peru sediments is likely due to a combination of the following: (i) a highly variable OMZ leading to random re-oxidation of any sediment-sourced Fe which prevents the export of larger amounts of dissolved Fe to the interior of the ocean, and which also prevents focused enrichments of Fe, and (ii) an enhanced dust flux, which frequently resupplies terrestrial Fe dampening any Fe isotope fractionation.This study is a snapshot on sedimentary Fe cycling in one area from the vast Namibian margin. Compared to the Peruvian margin, the data suggest little sedimentary Fe release, transport and redeposition. However, previous water column data suggest substantial Fe release. Hence, for a more subtle investigation of the Fe loss and re-supply a higher sampling resolution of multiple cores across the shelf and slope will be required.

The brecciated texture of polymict eucrites: Petrographic investigations of unequilibrated meteorites from the Antarctic Yamato collection

AbstractWe report on the petrography and mineralogy of five Yamato polymict eucrites to better constrain the formation and alteration of crustal material on differentiated asteroids. Each sample consists of different lithic clasts that altogether form four dominant textures and therefore appear to originate from closely related petrological areas within Vesta′s crust. The textures range from subophitic to brecciated, porphyritic, and quench‐textured, that differ from section to section. Comparison with literature data for these samples is therefore difficult, which stresses that polymict eucrites are extremely complex in their petrography and investigation of only one thick section may not be representative for the host rock. We also show that sample Y‐793548 consists of more than one lithic unit and must therefore be classified as polymict instead of monomict. The variety and nature of lithic textures in the investigated Yamato meteorites indicate shock events, intense post‐magmatic thermal annealing, and secondary alteration. These postmagmatic features occur in different intensities, varying from clast to clast or among coexisting mineral fragments on a small, local scale. Several clasts within the eucrites studied have been modified by late‐stage alteration processes that caused deposition of Fe‐rich olivine and Fe enrichment along cracks crosscutting pyroxene crystals. However, formation of these secondary phases seems to be independent of the degree of thermal metamorphism observed within every type of clast, which would support a late‐stage metasomatism model for their formation.

Assessment of Cu, Zn, Mn, and Fe enrichment in Mt. Kenya soils: evidence for atmospheric deposition and contamination.

Mountains are the preferred sites for studying long-range atmospheric transportation and deposition of heavy metals, due to their isolation and steep temperature decrease that favors cold trapping and condensation of particulate forms of heavy metals. Any enrichment of heavy metals in mountains is presumed to primarily occur through atmospheric deposition. In this particular study, we assessed the status of 27 subsurface soils collected along two elevation gradients of Mt. Kenya using enrichment factors (EFs) as the ecological risk assessments. The collected soils were analyzed for total organic carbon, zinc (Zn), iron (Fe), manganese (Mn), and copper (Cu). The mean concentration of Mn, Fe, Zn, and Cu was 0.376mg/kg, 47.6mg/kg, 12.3mg/kg, and 4.88mg/kg in Chogoria and 0.560mg/kg, 113mg/kg, 12.7mg/kg, and 2.70mg/kg in Naro Moru respectively. These concentrations were below the US-EPA maximum permissible levels for soils, implying that the levels recorded had low toxicity. Meanwhile, the mean enrichment factors for Mn, Cu, and Zn were 0.447, 131, and 78.8 in Chogoria and 0.463, 38.9, and 53.0 in Naro Moru respectively. This implied that Zn and Cu in Chogoria sites were extremely enriched, while in Naro Moru, enrichment levels ranged from significant to extreme. However, Mn was found to have minimal enrichment in all the sites. Lower montane forest and bamboo zone recorded relatively high enrichment due to distance from source of pollution. Ericaceous zone also had high mean enrichment due to influence of wind which favors higher deposition at mid-elevations.

A study of igneous rocks related to Zn–Pb mineralization in the Shinyemi and Gagok deposits of the Taebaeksan Basin, South Korea

AbstractThe Shinyemi and Gagok deposits, located in the Taebaeksan Basin, South Korea, display Zn–Pb mineralization along a contact between Cretaceous granitoids and Cambrian–Ordovician carbonates of the Joseon Supergroup. The Shinyemi mine is one of the largest polymetallic skarn‐type magnetite deposits in South Korea and comprises Fe and Fe–Mo–Zn skarns, and Zn–Cu–Pb replacement deposits. Both deposits yield similar Cretaceous mineralization ages, and granitoids associated with the two deposits displaying similar mineral textures and compositions, are highly evolved, and were emplaced at a shallow depth. They are classified as calc‐alkaline, I‐type granites (magnetite series) and were formed in a volcanic arc. Compositional variation is less in the Shinyemi granites and aplites (e.g., SiO2 = 74.4–76.6 wt% and 74.4–75.1 wt%, respectively) than in the Gagok granites and aplites (e.g., SiO2 = 65.6–68.0 wt% and 74.9–76.5 wt%, respectively). Furthermore, SiO2 vs K/Rb and SiO2 vs Rb/Sr diagrams indicate that the Shinyemi granitoids are more evolved than the Gagok granitoids. Shinyemi granitoids had been already differentiated highly in deep depth and then intruded into shallow depth, so both granite and aplite show the highly evolved similar chemical compositions. Whereas, less differentiated Gagok granitoids were separated into two phases in the last stage at shallow depth, so granite and aplite show different compositions. The amounts of granites and aplite are similar in the Shinyemi deposit, whereas the aplite appears in an amount less than the granite in the Gagok deposit. For this reason, the Shinyemi granitoids caused not only Fe enrichment during formation of the dolomite‐hosted magnesian skarn but also was associated with Mo mineralization in the Shinyemi deposit. Zn mineralization of the Gagok deposit was mainly caused by granite rather than aplite. Our data suggest that the variation in mineralization displayed by the two deposits resulted from differences in the compositions of their associated igneous intrusions.

Microbial communities and biogenic Mn-oxides in an on-site biofiltration system for cold Fe-(II)- and Mn(II)-rich groundwater treatment

This study investigated relationships between microbial communities, groundwater chemistry, and geochemical and mineralogical characteristics in field-aged biofilter media from a two-stage, pilot-scale, flow-through biofiltration unit designed to remove Fe(II) and Mn(II) from cold groundwater (8 to 15 °C). High-throughput 16S rRNA gene amplicon sequencing of influent groundwater and biofilter samples (solids, effluents, and backwash water) revealed significant differences in the groundwater, Fe filter, and Mn filter communities. These community differences reflect conditions in each filter that select for populations that biologically oxidize Fe(II) and Mn(II) in the two filters, respectively. Genera identified in both filters included relatives of known Fe(II)-oxidizing bacteria (FeOB), Mn(II)-oxidizing bacteria (MnOB), and ammonia-oxidizing bacteria (AOB). Relatives of AOB and nitrite-oxidizing bacteria were abundant in sequencing reads from both filters. Relatives of FeOB in class Betaproteobacteria dominated the Fe filter. Taxa related to Mn-oxidizing organisms were minor members of the Mn-filter communities; intriguingly, while Alphaproteobacteria dominated (40 ± 10% of sequencing reads) the Mn filter community, these Alphaproteobacteria did not classify as known MnOB. Isolates from Fe and Mn filter backwash enrichment studies provide insight on the identity of MnOB in this system. Novel putative MnOB isolates included Azospirillum sp. CDMB, Solimonas soli CDMK, and Paenibacillus sp. CDME. The isolate Hydrogenophaga strain CDMN can oxidize Mn(II) at 8 °C; this known FeOB is likely capable of Mn(II) oxidation in this system. Synchrotron-based X-ray near-edge spectroscopy (XANES) coupled with electron paramagnetic resonance (EPR) revealed the dominant Mn-oxide that formed was biogenic birnessite. Co-existence of amorphous and crystallized Mn-oxide surface morphologies on the Mn-filter media suggest occurrence of both biological and autocatalytic Mn(II) oxidation in the biofilter. This study provides evidence that biofiltration is a viable approach to remove iron, manganese, and ammonia in cold groundwater systems, and that mineralogical and microbiological approaches can be used to monitor biofiltration system efficacy and function.

Investigation of lithological control of iron enrichment in groundwater using geophysical techniques in Yenagoa, Southern Nigeria

Hydrochemical analysis of water samples from Yenagoa in the Niger Delta shows widespread occurrence of iron (Fe) in the groundwater. The Fe concentration is more than 0.3 mg/L at many places, and the distribution is heterogeneous both vertically and horizontally. In order to identify the cause of the high heterogeneity, we carried out an integrated study consisting of hydrogeochemical, electrical resistivity sounding and induced polarization (IP) chargeability measurements at eleven sites and 2-D electrical resistivity profiling (at 2 sites). Data processing using inversion techniques resulted in 4-layered resistivity and chargeability—depth models. The results show that clean sand and gravel exhibit high resistivity but low chargeability and normalized chargeability values, whereas clay and sandy clay exhibit relatively low resistivity but high chargeability and normalized chargeability values. In sites where the aquifer is overlain by a thick clay layer, Fe concentration is high (Fe > 0.3 mg/L) in the groundwater and redox potential values range between 118 and 133 mV. We interpret that the low-permeability clay layer creates a relatively atmosphere-isolated state in the underlying aquifer, which is responsible for the reductive ambient subsurface groundwater environment. In sites where the aquifer is capped by silt, Fe concentration is low (< 0.3 mg/L) in the groundwater and redox potential values range between 115 and 164 mv indicating a mild oxidation environment. We interpret that the clay acts as a controlling factor to the Fe enrichment in the groundwater regime. Knowledge of the clay layer, which is identified in the present study, will be helpful in selecting suitable sites for boreholes.