In Situ Trace Element and Fe-O Isotope Studies on Magnetite of the Iron-Oxide Ores from the Takab Region, North Western Iran: Implications for Ore Genesis

International audienceThe early Cambrian Takab iron ore deposit is situated in the northern part of the Sanandaj-Sirjan zone, western Iran. It consists of banded, nodular and disseminated magnetite hosted in folded micaschists. Trace element and Fe and O isotopic experiments reveal various hydrothermal precipitation environments under reduced to slightly oxidizing conditions. Disseminated magnetite has high Ti (945-1940 ppm) positively correlated with Mg + Al + Si, and heavy Fe (+0.76 to +1.86‰) and O (+1.0 to +4.07‰) isotopic compositions that support a magmatic/high-T hydrothermal origin. Banded magnetite has low Ti (15−200 ppm), V (≤100 ppm), Si and Mg (mostly ≤300 ppm) and variable Al. The ∂ 56 Fe values vary from −0.2‰ to +1.12‰ but most values also support a magmatic/high-T hydrothermal origin. However, variable ∂ 18 O (−2.52 to +1.22‰) values provide evidence of re-equilibration with lower-T fluid at ~200-300 • C. Nodular magnetite shows high Mn (≤1%), and mostly negative ∂ 56 Fe values (average, −0.3‰) indicative of precipitation from an isotopically light hydrothermal fluid. Re-equilibration with carbonated rocks/fluids likely results in a negative Ce anomaly and higher ∂ 18 O (average, +6.30‰). The Takab iron ore deposit has, thus, experienced a complex hydrothermal history

Resolving the source and ore-forming processes of the Takab Iranian BIF using Fe and O isotope pairs in magnetite.

International audienceIron ore deposits from Iran are spatially related to the main suture zones of the Iranian continental fragmented block. In western Iran, the Sanandaj-Sirjan structural zone (SSZ) hosts several iron ore deposits interpreted being of volcano sedimentary, hydrothermal or mixed volcano sedimentary-skarn origin. In the northern part of the SSZ the early Cambrian (~530 Ma) Takab iron ore deposit consists of disseminated, layered and nodular magnetite mainly hosted in folded micaschists, and also in calcschists or metavolcanics. Quartz may show grain boundary migration and feldspar is partly altered. Accessory minerals are Mn-Ba-oxides, barite, monazite &#177; uraninite and Mn-carbonate (in calschists) in the matrix or in cross-cutting veins.The low concentrations of Cr (1in disseminated (1.2) and nodular magnetite (2.2), but <1 in layered magnetite (0.5-0.7). Nodular magnetite shows a negative Ce anomaly, similar to that of the calcschists. These results indicate mixing of hot hydrothermal fluid and seawater during the precipitation of the Takab BIF.In nodular magnetite the average &#8706;56Fe of -0.3 &#8240; is typical of low T-hydrothermal environment, while the heavier &#8706;56Fe (1.4 &#8240;) in disseminated magnetite points to magmatic or magmatic-hydrothermal fluid. &#8706;56Fe data in the layered magnetite are variable (-0.2 to +1.12 &#8240;) but mostly in the magmatic-hydrothermal box of discrimination diagrams. &#8706;18O values are positive in disseminated and nodular magnetite (+2.15&#8240; and +5.30 &#8240; respectively on average), and vary from -2.52 &#8240; to +1.22 &#8240; in layered magnetite.Based on the trace elements and REE data it can be concluded that primary layered magnetite ore crystallized statically from a Fe-Si rich mixed seawater and hot hydrothermal fluid. Regional deformation induced dynamic recrystallization of quartz, and disruption of magnetite bands.The chemical and isotopic signature of the disseminated magnetite points to a predominant imprint of an ortho-magmatic fluid. However, post primary mineralization hydrothermal alterations complicate the signal recorded by magnetite and evidence a complex story: for example, the lighter &#8706;18O of layered magnetite suggests re-equilibration with low temperature fluid. Similarly, the low &#8706;56Fe of nodular ore results likely from the precipitation of magnetite from a light hydrothermal fluid that may have dissolved a primary magnetite with heavy iron isotope signature. Moreover, re-equilibration with carbonated rocks likely results in the observed negative Ce anomaly and higher &#8706;18O (up to 6.30 &#8240; on average)

Mineralogy and Fe-isotopic composition of iron-oxide ore from the Takab region, North Western Iran

International audienceThe major iron deposits occur in the northeast and central part of Iran. However, iron ore deposits in the northwest (e.g. Takab area) are still little studied. In this region, the most important iron deposits are hosted within para-metamorphic rocks and are attributed to Late Proterozoic age. The iron ore grades from disseminated to layered and nodular type. Disseminated ore: Magnetite forms euhedral grains (~400 µm-1.5 mm) free of inclusions. The grains are slightly hematized. The matrix minerals are quartz, minor K-feldspar and phengite. The feldspars host P (U, Th)-bearing phases, zircon and barite. Rutile and phosphates also occur interstitial to the matrix grains. The magnetite is characterized by ∂ 56 Fe (+0.7 to +2 ‰ ± 0.2 ‰). Layered ore: Coarse and discontinuous bands with interstitial quartz. Magnetite forms individual grains (~50 µm to several hundreds of µm). It is altered to hematite. Goethite is abundant around hematized magnetite and in veins crosscutting the oxides. Pyrite relics are present in goethite. Magnetite grew around detrital zircon and hosts droplet-like inclusions of PbS and ZnS, while P-bearing minerals occur in goethite and quartz. In the matrix, apart from quartz, Mn-Ba-oxides and barite (partly replacing hyalophane) and, rarely, uraninite occur. The magnetite is characterized by ∂ 56 Fe (-0.3 to +1 ‰ ± 0.2 ‰). Nodular ore: Magnetite forms mm-sized agglomerates partly elongated and disrupted in the quartz matrix. Other matrix minerals are similar to those in the layered ore. Magnetite is not hematized. P-bearing minerals, Mn-and Fe-carbonates and uraninite inclusions are hosted in magnetite. The magnetite is characterized by ∂ 56 Fe (-1 to +0.5 ‰ ± 0.2 ‰). The ∂ 56 Fe values observed for magnetite decrease from disseminated to nodular iron ore (averages: +1.3, +0.4 and-0.4 ‰ (± 0.2 ‰), respectively). Iron isotopes of hematite in disseminated and layered ore show higher ∂ 56 Fe values than those of magnetite, in the range of +2 to +4 ‰ (± 0.2 ‰). The following scenario is proposed: A hydrothermal (volcano-) sedimentary environment based on: (i) ore textures and major mineralogy (iron oxides with chemically precipitated quartz and detrital zircon); (ii) the occurrence of Mn-Fe-carbonates, barite and sulphide inclusions in magnetite and in matrix K-Ba feldspars; (iii) ∂ 56 Fe in magnetite of nodular ore slightly negative. An oxidation event based on: (i) partial transformation of magnetite into hematite; (ii) remobilisation of Mn-Ba-U as oxide and sulfate into veins; (iii) increasing ∂56Fe with progressive oxidation from nodular to disseminated magnetite reaching highest values in hematite. A shift in ∂ 56Fe towards positive values in oxidizing environments was also observed for example by Rouxel et al (2008, Chem Geol 252, 214-227)

Effects of a new emollient-based treatment on skin microflora balance and barrier function in children with mild atopic dermatitis

Background/Objectives The use of emollients is widely recommended for the management of atopic dermatitis (AD), especially between flares. An imbalance of skin microflora is suspected of playing a key role in exacerbations of AD. Our aim was to evaluate the effect of a new emollient balm on clinical parameters (SCORing Atopic Dermatitis [SCORAD], xerosis, pruritus), skin barrier function (transepidermal water loss and loricrin, filaggrin, corneodesmosin, and involucrin expression], skin microflora biodiversity, and Staphylococcus aureus and Staphylococcus epidermidis balance in children with mild AD. Methods Fifty-four children (1-4 yrs old) were enrolled in this randomized, controlled study. Subjects applied a hygiene product and the emollient balm (emollient group, n = 28) or the hygiene product only (control group, n = 26) twice a day for 28 days. Results We found improvement in favor of the emollient group in SCORAD (p < 0.001), pruritus (p = 0.06), and xerosis (p = 0.06) after 28 days of application. Moreover, transepidermal water loss decreased in the emollient group by 34% (p = 0.06) and involucrin expression by 37% (p = 0.001) at day 28 from baseline in association with improvement in barrier function, whereas other barrier-specific proteins did not vary. S. aureus increased significantly in the control group only (6.5 times, p = 0.01), whereas S. epidermidis remained stable in both groups. The Shannon index (H′ = 2.3) did not vary with treatment in either group. Conclusion Twice-daily application of a new emollient balm in children with mild AD protected the skin from S. aureus proliferation and preserved microflora biodiversity

Iron-oxide ores in the Takab region, North Western Iran

International audienceThe siliceous iron ore deposits in the NW part of Iran (Takab region) are hosted within para-metamorphic rocks, and are attributed to Late Proterozoic age. They comprise massive, banded, nodular and disseminated ore types, which are mainly composed of magnetite. Magnetite contains traces of Al. It is variously hematitized. Hematite show higher Al, Si and Ca contents than the magnetite. The iron oxides contain inclusions of zircons, apatite, uraninite, Mn-carbonate and euhedral monazite. Later hydrothermal solutions precipitated goethite surrounding the magnetite-hematite-maghemite grains and replacing hematite. Barite occurs in fractures of iron oxides, Mn-Ba-Pb oxi-hydroxides and scheelite occur interstitial to iron oxides. The ∂ 56 Fe values observed for magnetite decrease from disseminated to nodular iron ore (averages: +1.3, +0.4 and-0.4 ‰ (± 0.2 ‰), respectively). Iron isotopes of hematite in disseminated & layered ore show higher ∂ 56 Fe values than those of magnetite, in the range of +2 to +4 ‰ (± 0.2 ‰)

Iron-oxide ores in the Takab region, North Western Iran

International audienceThe siliceous iron ore deposits in the NW part of Iran (Takab region) are hosted within parametamorphic rocks, and are attributed to Late Proterozoic age..They comprise massive, banded, nodular and disseminated ore types, which are mainly composed of magnetite. Magnetite contains traces of Al. It is variously hematized. Hematite shows higher Al, Si and Ca contents than the magnetite. The iron oxides contain inclusions of zircon, apatite, uraninite, Mncarbonate and euhedral monazite. Later hydrothermal solutions precipitated goethite surrounding the magnetite-hematite-maghemite grains and replacing hematite. Barite occurs in fractures of iron oxides, Mn-Ba-Pb oxy-hydroxides and scheelite occur interstitial to iron oxides. The ∂ 56 Fe values observed for magnetite decrease from disseminated to nodular iron ore (averages: +1.3, +0.4 and-0.4 ‰ (± 0.2 ‰), respectively). Iron isotopes of hematite in disseminated and layered ore show higher ∂ 56 Fe values than those of magnetite, in the range of +2 to +4 ‰ (± 0.2 ‰). Volcano sedimentary primary processes are thus superposed by a secondary (magmatic?) hydrothermal process