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Metamorphosed banded iron formation (BIF) in granulite-amphibolite facies, tonalitic orthogneisses from a series of locations in the Kolli Massif of southern India are described and analysed with regard to their lithologies, whole rock chemistry, mineral reaction textures, and mineral chemistry. On the basis of their mineral reaction textures along magnetite-quartz grain boundaries these BIFs are grouped according to their predominant silicate mineralogy: 1) amphibole; 2) orthopyroxene; 3) orthopyroxene–clinopyroxene; 4) orthopyroxene-clinopyroxene-garnet; 5) clinopyroxene-garnet-plagioclase; and 6) Fe-Mg silicates are absent. Two-pyroxene and garnet-pyroxene Fe-Mg exchange thermometry, coupled with thermodynamic pseudo-section modelling of whole rock data from one of the magnetite-quartz-orthopyroxene-clinopyroxene-bearing lithologies, indicates that the magnetite-quartz-orthopyroxene-clinopyroxene-garnet assemblages formed at ~900 to 1200 MPa and 750 to 900 °C under relatively low H2O activities. Magnetite-quartz-orthopyroxene reaction textures were experimentally replicated at 800 and 900 °C and 1000 MPa in a synthetic BIF using isolated magnetite grains in a quartz matrix to which was added a hypersaline Mg- and Al-bearing fluid (approximately 1% by mass), which permeated along all the grain boundaries. The fact that Fe-Mg silicate reaction textures did not form in one of the BIF samples, which had experienced the same P-T conditions as the other BIF samples, suggests that, unless a BIF initially incorporated Mg, Al, and Ca during formation with or was infiltrated from the surrounding rocks by Mg-, Al-, and Ca-bearing saline fluids, these silicate minerals could not and would not have formed from the inherent magnetite and quartz during granulite-facies and amphibolite-facies metamorphism. [ABSTRACT FROM AUTHOR]

Banded iron formations (BIFs) are chemical sediments that reflect the composition of the seawater from which they were deposited. Therefore, they provide a key part of the evidence for the modern scientific understanding of paleoenvironmental conditions in Archean and Paleoproterozoic times. Although BIFs have been extensively studied, many aspects (e.g., specific mechanisms controlling iron (Fe) and silicon (Si) precipitations) of their origin still remain enigmatic because of the lack of modern analogues. In China, abundant BIFs occur throughout within the late Neoarchean volcanic and sedimentary succession and therefore are the principal source of Fe for the Chinese steel industry. Here, we examine the ~ 2.53 Ga Qidashan BIF, one of the most extensive BIFs in China, by conducting a detailed petrographic and multi-proxy investigation to well constrain its formation mechanism. The BIF consists mainly of magnetite and quartz with lesser amounts of calcite and various types of silicate minerals, of which the content of Al-rich minerals (i.e., chlorite) is rare, coupled with a low abundance of detrital geochemical indicators (e.g., Al and Ti), suggesting that the BIF is relatively pure with insignificant terrigenous contamination. A wide range of Nd isotope compositions and shale-normalized patterns and specific anomalies of rare earth elements, especially highly positive Eu anomalies, indicate that the BIF precipitated from seawater imprinted by high-temperature hydrothermal fluids. Furthermore, there is a significantly negative correlation between Nd isotope values and total Fe contents of the BIF. This suggests that such enhanced hydrothermal activity provided vast volumes of dissolved Fe(II) necessary for the formation of the BIF via alteration of ancient continental crust. In addition, the Qidashan BIF was deposited under pervasively anoxic conditions, as revealed by the absence of shale-normalized Ce anomalies and the presence of consistently positive Fe isotope values. Hence, anoxygenic photosynthesis is the most plausible mechanism responsible for Fe(II) oxidation. Given that Fe─Si bonding has a strong impact on Si isotope fractionation, the formation of primary Fe(III) oxyhydroxides should have exerted a first-order control on the negative Si isotope signatures observed in the studied BIF samples. It is also noted that the BIF possesses a variation of negative Si isotope values, further implying that diagenetic dissolution and reprecipitation of silica took place after primary Si precipitation associated with Fe. [ABSTRACT FROM AUTHOR]

There is a paucity of evidence preserved in the rock record regarding Earth's earliest enriched crust and its complementary depleted mantle during the Hadean. In recent years, vestiges of these early reservoirs have been inferred by examination of Hf isotope systematics compiled from zircons. The Singhbhum craton of Eastern India, for example, preserves only the existence of an enriched (εHf <0) crustal reservoir during the Hadean-Eoarchean, with the notable absence of a depleted mantle reservoir signature (εHf >0) until ca. 3.5 Ga. Here we report a new Sm-Nd isochron for the Lower Lava greenstones of the western Iron Ore Group from the Singhbhum craton, confirming a 3.42 ± 0.14 Ga crystallization age with an initial εNd of +5.7 ± 2.5. This is the highest positive εNd value derived from an isochron of this age. We infer that this depleted mantle source is a vestige complementary to the primary crust following planetary differentiation. Furthermore, we present U-Pb zircon ages for a 3.39 ± 0.02 Ga tuff that lies stratigraphically above the Lower Lava and <30 cm below an extensive conformable banded iron formation (BIF). This age implies that the western Iron Ore Group's BIF is the largest economic-grade iron formation of its Paleoarchean age, suggesting that free atmospheric oxygen existed as more than just whiffs at this time. [ABSTRACT FROM AUTHOR]

Over 3000 iron formation caves (IFCs) have formed in erosion-resistant Fe(III)-rich rocks throughout Brazil. Microbial Fe(III) reduction occurs in IFCs, where a microbe-rich, Fe(III)-depleted paste (sub muros) is found behind an Fe(III)-(hydr)oxide crust in the ceiling/walls. Microbial Fe(III) reduction in sub muros appears to be responsible for the transformation of Fe(III) to more soluble Fe(II), which is removed, leading to cave formation. This process of biospeleogenesis is likely controlled by O2 availability, which is linked to seasonal changes. Here, we studied the effects of alternating anoxia/oxia on the microbial community and on Fe solubility in banded iron formation (BIF), a rock type consisting of layered Fe(III)-oxide and silicate. Incubations of synthetic pore water, pulverized BIF, and sub muros were prepared and incubated under anoxia, during which BIF-Fe(III) reduction proceeded. During the Fe(III) reduction period, Firmicutes and/or Alphaproteobacteria were enriched, and genes involved in Fe(III) and sulfate reduction were detected in the metagenomes. Fe(II) oxidation genes, which were detected in the fresh sub muros, were not found. Upon the addition of atmospheric O2, Fe(III) reduction was arrested, and incomplete Fe(II) oxidation occurred. Betaproteobacteria, Gammaproteobacteria, and Chloroflexi increased in relative abundance following aeration, and Fe(III) reduction genes were still identified. Our results demonstrate that the sub muros microbial community retains the ability to reduce Fe(III) and drive speleogenesis despite fluctuations in O2 levels. [ABSTRACT FROM AUTHOR]

Recovering ancient records of Earth's magnetic field is essential for determining the role of the magnetosphere in protecting early Earth from cosmic radiation and atmospheric escape. We present paleomagnetic field tests hinting that a record of Earth's 3.7‐billion‐year (Ga) old magnetic field may be preserved in the northeastern Isua Supracrustal Belt as a chemical remanent magnetization acquired during amphibolite‐grade metamorphism in the banded iron formation. Multiple petrological and geochronological lines of evidence indicate that the northernmost part of Isua has not experienced metamorphic temperatures exceeding 380°C since the Eoarchean, suggesting the rocks have not been significantly heated since magnetization was acquired. We use "pseudo" baked contact tests (intrusions emplaced 3.26–3.5 Ga ago) and a fold test (folding 3.6 Ga ago) to demonstrate that some samples preserve a ca. 3.7 Ga record of the magnetic field. We recover a field strength of >15 µT. This suggests that Earth's magnetic field may have been weak enough to enhance atmospheric escape during the Archean. Plain Language Summary: Recovering ancient records of Earth's magnetic field is challenging because the magnetization in rocks is often reset by heating during tectonic burial over their long and complex geological histories. We show that rocks from the Isua Supracrustal Belt in West Greenland have experienced three thermal events throughout their geological history. The first event was the most significant, and heated the rocks up to 550°C 3.7‐billion‐years‐ago. The subsequent two events did not heat the rocks in the northernmost part of the area above 380°C. We use multiple lines of evidence to test this claim, including paleomagnetic field tests, the metamorphic mineral assemblages across the area, and the temperatures at which radiometric ages of the observed mineral populations are reset. We use these lines of evidence to argue that an ancient, 3.7 billion year old record of Earth's magnetic field may be preserved in the banded iron formations in the northernmost part of the field area. The magnetization was acquired during mineral transformation associated with the first thermal event and therefore only a lower limit on the strength of the ancient magnetic field was constrained. However, we are able to conclude that the ancient magnetic field was likely comparable with the strength of Earth's magnetic field today. Key Points: The north‐eastern part of the Isua Supracrustal Belt experienced two metamorphic events at 3.69 Ga and 2.85 Ga and one hydrothermal event at 1.5 GaBanded iron formations acquired a chemical remanent magnetization during the first thermal event that was not entirely overprinted by subsequent eventsPaleomagnetic results hint that a record of the Eoarchean geomagnetic field is preserved in the Isua Supracrustal Belt [ABSTRACT FROM AUTHOR]

This study aims to determine the depositional setting and deposit type of the Ereen deposit in the Bayanjargalan soum of Dundgovi province and the Dartsagt deposit in the Dalanjargalan soum of Dornogovi province, Mongolia. Both deposits are hosted within the sediments of the Neoproterozoic Oortsog Formation. The ore-hosted Oortsog Formation consists of shale with muscovite-sericite-magnetite-quartz and marbled limestone. The former is characterzid by gray to black shaly texture. Major, minor and trace elements composition of 16 ore samples of these two deposits were analyzed by XRF, ICP-MS and ICP-OES. The total iron (TFe) contents of the ore samples from the Ereen deposit range from 28.83 to 51.09 wt% with an average of 41.92 wt% whereas the TFe contents of the Dartsagt deposit from 37.61 to 49.78 wt% with an average of 43.15 wt%. In the Post-Archean Australian Shale (PAAS)-normalized REY diagram, the samples from the Ereen and the Dartsagt deposits show a weakly LREE depleted and HREE weakly enriched trend. Also, in the chondrite-normalized REY diagram, negative Eu anomaly Y-enriched trend are observed. The Eu/Eu*SN values of the Ereen deposit (0.93 to 1.25, average 1.08) and the Dartsagt deposit range from 0.93 to 1.25 (avg. 1.08) and from 1.05 to 1.61 (avg. 1.22), respectively. These trace elements characteristics indicate that these two deposits belong to the Superior-type BIF deposit formed on the passive continental margin and are not likely to be associated with volcanogenic rocks. [ABSTRACT FROM AUTHOR]

The Nkout banded iron formations (BIFs)-hosted iron deposit is located in the Ntem Complex at the northwestern part of the Congo craton, southern Cameroon. We report geochronological and geochemical data of magnetite BIFs and interlayered mica schists from the Nkout iron ore deposit. The BIFs show typical features of chemical precipitates characterized by seawater-like shale-normalized rare earth elements plus yttrium spectra. Weak positive Eu anomalies indicate the contribution of high-temperature hydrothermal fluids to the BIFs, with low detrital input. The absence of true Ce anomalies indicates that the BIFs were likely to be deposited in anoxic seawater. LA-ICP-MS U-Pb detrital zircon data for the BIFs and associated metasiliciclasltic rocks constrained the maximum depositional age at ca. 2.8 Ga, suggesting that the Nkout BIFs are likely the oldest iron formations in the Ntem Complex. Our zircon U-Pb isotope data indicate that the Nkout succession experienced lower-amphibolite facies metamorphism at ca. 2.0 Ga, which correlates with the regional tectono-thermal event linked to the convergence and assembly of terranes between the Congo and São Francisco cratons during the Eburnean-Transamazonian orogeny. [ABSTRACT FROM AUTHOR]

Zircon is not a common accessory mineral of banded iron formation (BIF), but it occurs in all BIF samples from the Kostomuksha Greenstone Belt (KGB) in the Karelian Craton of the Fennoscandian Shield. The Kostomuksha BIF is of Algoma type and is part of three variably old rock associations: BIF-1 is part of a sedimentary sequence in Mesoarchean (2.87–2.84 Ga) basaltic komatiites with dacites, BIF-2 is located in Meso-Neoarchean (2.8–2.79 Ga) felsic volcanics, and BIF-3 is part of a Neoarchean (2.76–2.74 Ga) greywacke unit with felsic volcanics. Analysis of zircon has revealed grains with cores and several generations of rims. The U-Th-Pb systems of zircon indicate that its isotopic age varies considerably from 2.98 to 1.89 Ga, forming up to 4 age clusters in each sample. Most samples contain single inherited grains. The bulk of zircon in BIF is younger than the host rocks and is interpreted as metamorphic. Most of metamorphic zircons display an oscillatory zoning, and their Th/U ratio varies from 0.01 to 4.7, i.e. their origin is hard to interpret reliably, based on the above characteristics. Paleoproterozoic (1.89–1.85 Ga) zircons from BIF-1 and 3, occurring as rims and individual grains, are related to local tectono-thermal processes simultaneous with the formation of the Svecofennian orogen and were described for the central Karelian Craton for the first time. Thus, both inherited and metamorphic zircons have been revealed in Meso-Neoarchean BIF metamorphosed repeatedly in the Neoarchean-Paleoproterozoic under up to amphibolite-facies conditions. All metamorphic generations of zircons from BIF are correlated with the tectono-thermal events in the Karelian Craton, including the effect of the Svecofennian orogeny. [ABSTRACT FROM AUTHOR]

Veloso is one of numerous and poorly documented auriferous deposits of Ouro Preto, the town that symbolises the gold rush in Brazil at the turn of the seventeenth century. We present the results of underground geological mapping, combined with a boron (B) isotopic study of tourmaline, an elusive mineral in the auriferous quartz lode of the historical Veloso deposit. Its lode is characteristically brecciated in a host rock that shows no cataclastic fabric. The host rock is itabirite, a metamorphosed banded iron formation. Tourmaline is essentially dravite and locally occurs as abundant crystals in breccia-cementing pockets of goethite, formed from the oxidation of sulfide minerals. Gold is spatially associated with tourmaline in the goethite-rich pockets. In situ measurements for B isotopes yielded δ11B values in the range of −21 to −9‰. This range is similar to that reported for tourmaline of the Passagem de Mariana deposit, the best documented auriferous lode deposit at the south-eastern edge of the Quadrilátero Ferrífero. The tourmaline B isotopic data reflect auriferous fluids of crustal origin that sourced B from metasedimentary rocks, which may include a non-marine evaporitic component. [ABSTRACT FROM AUTHOR]

Three variably old groups of banded iron formation (BIF) are known in the Kostomuksha Greenstone Belt (KGB) of the Karelian Craton. This paper deals with the earliest of them, Mesoarchean (2.87–2.81 Ga) BIF-1. BIF-1 occurs among the komatiite–basalt unit of the KGB. BIF-1 consists mainly of quartz and magnetite, with varying amounts of amphibole, biotite, and garnet; the variations of SiO2 (48.3–58.6 wt %) and (21.34–33.82 wt %) suggest that the rocks are BIF. BIF-1 of the KGB, as well as most Archean BIFs, contain high concentration, display a contrasting positive Eu anomaly, lack of Ce anomaly, and the depletion of LREE relative to HREE. However, they differ from other BIFs in the higher Al2O3, TiO2, MgO, K2O, Cr, Ni, Zr, Ba, Cu and Zn concentrations. BIF-1 was formed in a marine basin at an anoxic atmosphere due to hydrothermal fluids, the proportion of which varies from 20 to 80%, and a terrigenous component derived mainly from basalts, komatiites, and dacites of host rocks. Mesoarchean BIF-1 of the KGB was accumulated in a small rift structures within an oceanic volcanic plateau, the formation of which is associated with the influence of a mantle plume on the oceanic lithosphere. [ABSTRACT FROM AUTHOR]

The results of studies of carbonaceous matter (CM) and the S isotopic composition of associated sulfides in metapelites of the Neoarchean banded iron formation of the Kostomuksha greenstone belt of Karelia (Karelian Craton of the Fennoscandinavian Shield) are presented. The petrographic observations show that the CM occurs inside and between silicates, in sulfides, or at the grain boundaries between the sulfide crystals and biotite or amphibole. The results of scanning electron and atomic force microscopy showed the presence of several CM types distinct in structure and C content. The analysis of Raman spectra of CM revealed the presence both of well-ordered graphite and weakly structured kerogene in samples. The isotopic composition of the total organic carbon is typical of biogenic processes. The δ13Corg values from –27.9 to –30.6‰ are consistent with the fixation of carbon by photo- or chemoautotrophs. The S isotopic composition of associated sulfides is characterized by a positive Δ33S anomaly (up to +0.94‰) and negative δ34S values (from –2.06 to –4.1‰). The positive Δ33S values indicate a genetic link with photochemical elemental sulfur (S8) from the atmosphere, whereas the negative δ34S values reflect the fractionation of isotopes during bacterial-related processes. Based on these observations, we suggest that the primary CM mostly has a biogenic origin. [ABSTRACT FROM AUTHOR]

The Bipindi iron ore district is located in the central section of the Nyong Complex at the northwestern margin of the Congo Craton in Southwest Cameroon. This iron district contains numerous iron mineralization hosted by the Mewongo, Bibole, Kouambo, and Zambi banded iron formations (BIFs). These BIFs contain magnetite as the main iron ore mineral associated with pyrite, and gangue minerals are quartz with minor chlorite and amphibole. The origin of iron ore from these BIFs was investigated using a combination of in-situ magnetite and whole-rock chemistry. The studied BIF ore samples have a narrow range of TFe between 30.90 wt.% and 43.20 wt.%, indicating a low-grade ore. The geochemical signatures of magnetite such as low contents of base metals (e.g., Cu, Co, V, and Zn) and low Co/Zn ratios < 0.85 indicate a hydrothermal origin. Combined with the geochemical features of these BIFs, e. g., high Fe/Ti and Fe/Al ratios (mean > 600 and > 75, respectively), we suggest that magnetite was derived from a mixture of seawater and ∼0.1% low-temperature hydrothermal fluids in an oxidizing environment. Collectively, low-temperature hydrothermal and later metamorphic fluids were necessary for the transformation of the protolith Nyong Complex BIFs to iron ore. [ABSTRACT FROM AUTHOR]

Modified magnetite and hydrothermal apatite in banded iron formations (BIFs) are ideal minerals for studying hydrothermal and metamorphic processes and are applied to linking with high-grade Fe mineralization and metamorphism in iron deposits hosted by BIFs. In this study, we have investigated the geochemical composition of modified magnetite and hydrothermal apatite and in situ U-Pb geochronology on apatite from the Huogezhuang BIF-hosted Fe deposit in northeastern China. The magnetite in metamorphosed BIF is modified, locally fragmented, and forms millimeter- to micrometer-scale bands. The apatite is present surrounding or intergrowing with magnetite, has corroded surfaces, and contains irregular impurities and fluid inclusions, indicating that it has been partly hydrothermally altered. Original element compositions (e.g., Fe, Al, Ti, K, Mg, and Mn) of magnetite in BIFs have been modified during high-grade Fe mineralization and retrogressive metamorphism with temperature reduction and addition of acids. The hydrothermally altered apatite has been relatively reduced in the contents of Ca, P, F, La, Ce, Nd, δCe, δEu, and total REEs compared to non-altered apatite. The magnetite and apatite in low-grade BIFs are poorer in FeOT than those from the high-grade Fe ores, indicating that Fe is remobilized during the transition from BIFs to high-grade Fe ores. The magnetite and apatite in high-grade Fe ores are overgrown by greenschist-facies minerals formed during retrograde metamorphism, suggesting that the high-grade Fe mineralization may be related to retrogressive metamorphism. In situ U-Pb geochronology of apatite intergrown with magnetite and zircon LA-ICP-MS U-Pb dating at Huogezhuang deposit reveals that the BIF-hosted magnetite was altered and remobilized at ca. 1950–1900 Ma, and deposition of the BIF began during the Late Neoarchean. The changes of elements in the modified magnetite and diferent geochemical compositions of the altered and unaltered apatite confirm that the modified magnetite and hydrothermal apatite can be efective in tracing high-grade Fe mineralization and retrogressive metamorphism in BIFs. [ABSTRACT FROM AUTHOR]

Environments originating from banded iron formations, such as the canga, are important reference ecosystems for the recovery of degraded areas by mining. The objective of this work was to evaluate if the relationship between morphofunctional and photosynthetic attributes of native canga species from different functional group results in distinct responses when grown in iron mining tailings substrate. The experiment was carried out with species belonging to different functional groups: a widespread semi-deciduous tree-shrub, Myrcia splendens; an endemic deciduous shrub, Jacaranda caroba; and a nitrogen-fixing herbaceous species, Periandra mediterranea. The species were grown in two conditions, reference soil and iron ore tailing. Despite belonging to different functional groups when grown in tailings, the morphofunctional attributes presented similar responses between species.M. splendens was the species most affected by the conditions imposed by the iron ore mining tailings, with decreased light-use efficiency and electron transport. P. mediterranea had satisfactory growth and maintenance of photosynthetic attributes. J. caroba growing in the tailings increased the effective quantum yield of PSII. The photochemical and growth assessments were able to better explain the adaptive strategies developed by the species, guaranteeing a greater chance of success during the rehabilitation of mining substrates. [ABSTRACT FROM AUTHOR]

Chemical sedimentary deposits called Banded Iron Formations (BIFs) are one of the best surviving records of ancient marine (bio)geochemistry. Many BIF precursor sediments precipitated from ferruginous, silica‐rich waters prior to the Great Oxidation Event at ~2.43 Ga. Reconstructing the mineralogy of BIF precursor phases is key to understanding the coevolution of seawater chemistry and early life. Many models of BIF deposition invoke the activity of Fe(II)‐oxidizing photoautotrophic bacteria as a mechanism for precipitating mixed‐valence Fe(II,III) and/or fully oxidized Fe(III) minerals in the absence of molecular oxygen. Although the identity of phases produced by ancient photoferrotrophs remains debated, laboratory experiments provide a means to explore what their mineral byproducts might have been. Few studies have thoroughly characterized precipitates produced by photoferrotrophs in settings representative of Archean oceans, including investigating how residual Fe(II)aq can affect the mineralogy of expected solid phases. The concentration of dissolved silica (Si) is also an important variable to consider, as silicate species may influence the identity and reactivity of Fe(III)‐bearing phases. To address these uncertainties, we cultured Rhodopseudomonas palustris TIE‐1 as a photoferrotroph in synthetic Archean seawater with an initial [Fe(II)aq] of 1 mM and [Si] spanning 0–1.5 mM. Ferrihydrite was the dominant precipitate across all Si concentrations, even with substantial Fe(II) remaining in solution. Consistent with other studies of microbial iron oxidation, no Fe‐silicates were observed across the silica gradient, although Si coprecipitated with ferrihydrite via surface adsorption. More crystalline phases such as lepidocrocite and goethite were only detected at low [Si] and are likely products of Fe(II)‐catalyzed ferrihydrite transformation. Finally, we observed a substantial fraction of Fe(II) in precipitates, with the proportion of Fe(II) increasing as a function of [Si]. These experimental results suggest that photoferrotrophy in a Fe(II)‐buffered ocean may have exported Fe(II,III)‐oxide/silica admixtures to BIF sediments, providing a more chemically diverse substrate than previously hypothesized. [ABSTRACT FROM AUTHOR]

Microbial Fe(II) oxidation has been proposed as a major source of Fe minerals during deposition of banded iron formations (BIFs) in the Archean and Proterozoic Eons. The conspicuous absence of organic matter or graphitic carbon from BIFs, however, has given rise to divergent views on the importance of such a biologically mediated iron cycle. Here, we present mineral associations, major element concentrations, total carbon contents and carbon isotope compositions for a set of lower amphibolite-facies BIF samples from the Neoarchean Zhalanzhangzi BIF in the Qinglonghe supra-crustal sequence, Eastern Hebei, China. Graphite grains with crystallization temperatures (~470 °C) that are comparable to that predicted for the regional metamorphic grade are widely distributed, despite highly variable iron (12.9 to 54.0 wt%) and total organic carbon (0.19 to 1.10 wt%) contents. The crystalline graphite is interpreted to represent the metamorphosed product of syngenetic biomass, based on its co-occurrence with apatite rosettes and negative bulk rock δ13Corganic values (–23.8 to –15.4‰). Moreover, the crystalline graphite is unevenly distributed between iron- and silica-rich bands. In the iron-rich bands, abundant graphite relicts are closely associated with magnetite and/or are preserved within carbonate minerals (i.e., siderite, ankerite, and calcite) with highly negative bulk rock δ13Ccarb values (–16.73 to –6.33‰), indicating incomplete reduction of primary ferric (oxyhydr) oxides by organic matter. By comparison, only minor graphite grains are observed in the silica-rich bands. Normally, these grains are preserved within quartz or silicate minerals and thus did not undergo oxidation by Fe(III). In addition, the close association of graphite with iron-bearing phases indicates that ferric (oxyhydr)oxides may have exerted a first order control on the abundance of organic matter. Combined, the biological oxidation of Fe(II) in the oceanic photic zone and subsequent burial of ferric (oxyhydr)oxides and biomass in sediments to form BIFs, suggests that a BIF-dependent carbon cycle was important in the Archean Eon. Although significant re-adsorption of phosphorus to ferric (oxyhydr)oxides and the formation of authigenic phosphate minerals at the sediment-water interface would be expected, oxidation of biomass in BIFs may have recycled at least a portion of the P (and other nutrients) released from reactions between organic matter and ferric (oxyhydr)oxides to the overlying water column, potentially promoting further primary productivity. [ABSTRACT FROM AUTHOR]

Banded iron formations (BIFs) are widespread over the world (3.81 Ga to 1.80 Ga) as the Algoma and Superior types. The paper provides new isotope (Nd-Sr, U-Pb) data on associated noble-metal mineralization in Algoma-type BIFs of the Fennoscandian Shield. U-Pb dating of accessory zircon applied to estimate the formation time of noble-metal-bearing skarn and related rocks in the Olenegorsk and Kirovogorsk BIFs, NW Fennoscandian Shield show that they occurred in the interval between the formation of basalt protolith (2.81 Ga amphibolites) and metamorphism in BIFs (2.75 Ga) to the formation of gold-bearing iron-rich skarn with native Au, Ag, Bi and tellurides (2.65 Ga) and low-temperature quartz-zeolite veins with redeposited Au (2.55 Ga). REE distribution in zircons and corresponding rocks indicated an important role of redox reactions in Fe and REE redistribution affected by reducing fluids on haematite-quartz protolith of BIFs. [ABSTRACT FROM AUTHOR]

The current work makes integrated value-added, geological and chemical studies on the texturally intricate banded iron formation "BIF" that is represented here, as a case in point, by the Um Nar BIF located in the Central Eastern Desert of Egypt. Geologically, the Um Nar BIF is composed mainly of oxide-rich facies and silicate-rich facies mostly expressed as bands of variable thickness (90–730 µm). Magnetite, martite, goethite, and quartz are detected as the main components of the oxide-rich facies, while epidote, stilpnomelane, and garnet occupy the other facies type. The studied ore can be classified as a low-grade iron ore containing 51.23 wt.% Fe2O3 and 39.64 wt.% SiO2 along with considerable phosphorous content (1.01 wt.% P2O5). These elemental concentrations do not match the recommended benchmarks for iron and steelmaking (e.g.75.78–95.8 wt.% Fe2O3, 5–7 wt.% SiO2, and 0.04 wt.% P2O5). Moreover, the studied BIF has a poor liberation behavior on crushing and grinding due to the complex interlocking of magnetite with quartz and stilpnomelane expressed as a sieve-like texture. This textural complication directed the current work to investigate the potential exploitation of the Um Nar BIF as a precursor of nano-magnetite that is commonly synthesized by ferrous and ferric chlorides. Accordingly, HCl-based agitation leaching followed by co-precipitation was carried out, resulting in ultrafine mesoporous nano-magnetite (2.47–4.27 nm particle size, 120 m2g−1 surface area, 0.55 cm3g−1 pore volume, and 4.88 nm pore diameter) expected to serve in water treatment as an effective adsorbent for heavy metals. [ABSTRACT FROM AUTHOR]

The concentration of the bio-limiting nutrient element, phosphorus (P), in seawater is important for primary marine productivity and the evolution of life on geological time scales. The molar percentage of P/Fe in banded iron formations (BIF) and iron oxide-rich chemical sediments is a good proxy for the first-order approximation of seawater P concentration. Bio-available concentration of phosphorus in Precambrian, especially during the late Palaeoproterozoic Era (2.0–1.8 Ga), is poorly constrained. We evaluated the P/Fe ratios of iron-rich rocks from the late Palaeoproterozoic Chilpi Group, Bastar Craton, Central India. The bulk rock molar percentage of P/Fe ratios of the Chilpi rocks vary between 0.11 and 1.17 (average 0.51 ± 0.3), and the average of EPMA spot analysis P/Fe molar ratio is 0.32 ± 0.4; both have values similar to Archaean BIFs of the world. The observed low molar ratio is not an artefact of contamination from terrestrial sources, diagenetic alterations or high-temperature hydrothermal inputs; it indicates the deposition from phosphorus-lean seawater. The modelled P/Fe molar ratio in the Chilpi Group suggests that the concentration of phosphorus in the shallow marine environment was less than 0.12 μM. The low level of phosphorus concentration in seawater during the late Palaeoproterozoic Era is interpreted to be a consequence of the low primary production during a period of low atmospheric oxygen content, which might have impeded the evolution of eukaryotes. [ABSTRACT FROM AUTHOR]

Banded iron formations (BIF) are chemically precipitated sediments that can record Archean ocean geochemistry. BIFs are laminated silica- and iron-rich deposits that host a range of iron(II, III) minerals, including hematite, magnetite, siderite, greenalite, minnesotaite, and stilpnomelane. This diverse mineralogical assemblage reflects secondary mineralization reactions due to diagenesis and/or post-depositional alteration. While petrographic observations of BIFs sparingly contain the iron silicate greenalite, recent evidence of greenalite nanoparticles preserved in early-mineralizing BIF chert suggest this mineral was a primary phase in BIF progenitor sediments. Therefore, it is critical to investigate the formation and alteration of greenalite to constrain the Archean ocean environment and help unravel post-depositional processes. To examine how iron silicates precipitate and then crystallize and/or transform during diagenesis, we simulated these two processes under Archean ocean conditions. We first precipitated a poorly ordered Fe-rich serpentine with subsidiary ferrihydrite at neutral pH by performing in situ Fe(II) oxidation experiments at 25 °C in the presence of silica. Subjected to simulated diagenesis at 80 °C, the rudimentary Fe-phyllosilicate transformed into a crystalline phyllosilicate characterized as 30% cronstedtite and 70% greenalite accompanied by magnetite and persistent ferrihydrite. At temperatures ≤150 °C, we continued to observe ferrihydrite, increased magnetite formation, and elevated incorporation of Mg into the phyllosilicate as it further recrystallized into Mg-greenalite. Our findings demonstrate a possible formation mechanism of early silicates through partial Fe(II) oxidation and support petrographic observations that magnetite likely mineralizes during diagenesis. Additionally, we suggest that Mg contents in BIF iron phyllosilicates could serve as a tracer for diagenesis, with Mg signaling phyllosilicate-fluid interactions at elevated temperatures. Ultimately, our experiments help reveal how initial iron-silica coprecipitates are altered during diagenesis, providing novel insights into the interpretation of greenalite and magnetite in ancient BIF assemblages. [ABSTRACT FROM AUTHOR]

Geochemical proxies archived in banded iron formations (BIFs) can provide information on the physico-chemical conditions in the Precambrian atmosphere-hydrosphere system and the element sources to ambient Early Earth's seawater. We here report results of the first investigation of the Ga-Al systematics of BIFs and use adjacent magnetite and metachert bands of the well-studied and very pure 2.7 Ga-old Temagami BIF in Ontario, Canada, in an attempt to test the suitability of the Ga/Al ratio as a geochemical proxy. Due to very low Ga concentrations in BIFs and multiple mass interferences on the stable isotopes 69Ga and 71Ga, we conducted comparative analyses of dissolved samples with sector-field (SF-)ICP-MS and tandem ICP-MS/MS as well as laser-ablation (LA-)SF-ICP-MS on nano-particulate pressed powder tablets (NP tablets). The unexpected results indicate uniform Ga/Al weight ratios between 2.0×10−4 and 7×10−4 for the Temagami BIF, i.e. Ga/Al ratios that are slightly above those of potential clastic detritus but well below those of modern seawater or marine hydrothermal fluids. Consistent results from solution SF- and ICP-MS/MS and a two-component mixing experiment with BIF reference material IF-G and synthetic pure quartz sand corroborate the high analytical quality of these Ga and Al data. The Ga/Al ratios of the metachert bands show the same range of Ga/Al ratios as the magnetite bands and appear to be dominated by small amounts of finely dispersed Fe oxide particles that were deposited together with the chert. The Ga/Al ratios of the magnetite bands either suggest that (in contrast to other trace elements such as the rare earth elements and Y) Ga and Al were fractionated from each other during scavenging from Archean seawater by Fe (oxyhydr)oxides or that ambient Temagami seawater had significantly lower Ga/Al ratios than modern seawater, possibly due to different weathering, riverine, and estuarine processes in the Archean. While these first results demonstrate the potential of Ga-Al systematics as an additional geochemical tool for studies of Early Earth, they also reveal the knowledge gaps that still need to be addressed in future investigations. [ABSTRACT FROM AUTHOR]

A comprehensive investigation into the application of machine learning algorithms for accurately classifying mineral deposit types is presented. The study specifically focuses on iron deposits in the Portuguese Ossa-Morena Zone, employing a limited dataset of trace element geochemistry from magnetites. The research aims to derive meaningful methodological and metallogenic conclusions from the obtained results. The findings demonstrate that the combination of a restricted dataset of trace element geochemistry from magnetites with diverse machine learning models serves as a reliable tool for achieving precise classifications of mineral deposit types. Among the machine learning methods evaluated, random forest, naïve Bayes, and multinomial logistic regression emerge as the most accurate classifiers, whereas the support vector machine, the k-nearest neighbour, and artificial neural networks exhibit lower performance scores. By integrating all literature-proposed classifications, and applying them to selected iron deposits, confident classifications were obtained. Alvito and Azenhas are reliably classified as skarns, whereas Monges, Serrinha, and Vale da Arca are classified as either porphyry or a Banded Iron Formation (BIF). Notably, the classification of Orada proves cryptic, encompassing both BIF and volcanogenic massive sulphide (VMS) deposit types. Moreover, the application of machine learning models to pertinent case studies offers valuable insights not only for classifying mineral deposit types but also for discerning mixed or complex origins. This approach provides meaningful results that can aid in the interpretation of mineral deposit types and may facilitate the identification of new mineral exploration targets. The research highlights the robustness of machine learning algorithms in interpreting magnetite data and underscores their potential significance in exploration projects. [ABSTRACT FROM AUTHOR]

The Guandi and Banshigou iron deposits of southern Jilin Province, China, are Algoma-type banded iron formations (BIFs) located in the Eastern Block of the North China Craton (NCC). LA–ICP–MS U–Pb dating shows the magmatic zircons in plagioclase amphibolite from the Guandi BIF (PA–GD) and plagioclase hornblende gneiss from the Banshigou BIF (PHG–BSG) were crystallised at 2556 ± 17 Ma and 2545 ± 27 Ma, respectively, representing the formation age of the BIFs. Metamorphic overgrowth zircons from both samples gave two U–Pb ages of 2452 ± 23 Ma and 2446 ± 70 Ma, indicating the age of metamorphism. The zircon εHf(t) values of PA–GD (–1.3 to +2.8) and PHG–BSG (–1.5 to +2.7) indicate that the magma source was derived from depleted mantle with contamination of crustal material. According to our study, the PA–GD and PHG–BSG were formed in an island arc setting and support previously proposed subduction zone tectonic models for the northeastern NCC during the Neoarchean. The magmatic zircons from the PA–GD and PHG–BSG were crystallised at 2556 ± 17 Ma and 2545 ± 27 Ma, which represents the formation age of the BIFs. The metamorphic overgrowth zircons from the PA–GD and PHG–BSG gave two ages of 2452 ± 23 Ma and 2446 ± 70 Ma, which represent the age of metamorphism. Major-element and REE data indicate that BIFs precipitated in a mixture of seawater and hydrothermal fluids in an anoxic environment. Geochemical and Hf isotope characteristics of BIFs' wall rock indicate that the source magma was derived from a depleted mantle wedge metasomatised by subduction-slab melts and contaminated by ancient crust, formed in an island arc setting. [ABSTRACT FROM AUTHOR]

Plate tectonics distinguishes Earth from the other terrestrial planets but its initiation mechanism and onset time are debated. We propose plate tectonics was initiated by the deposition of magnetite‐rich banded iron formations (BIFs) through biogeochemical iron cycling in Neoarchean oceans. In the photic zone of proto‐continental margins, photoferrotrophic bacteria efficiently oxidized the dissolved Fe(II) and induced massive precipitation of ferric oxyhydroxide, which would rapidly react with Fe(II)‐rich hydrothermal fluids from coeval vigorous volcanism in Neoarchean oceans to produce magnetite‐rich BIFs. Mechanical models demonstrate that the localization of high‐density BIF deposition near proto‐continents induces collapse of the lithosphere and can initiate the earliest subduction. The peak deposition of BIFs in 2.75–2.40 Ga provides a time constraint on the inception of plate tectonics. Plain Language Summary: Plate tectonics provides a basic framework for understanding geological processes on Earth. Although the subduction of cold and heavy oceanic lithosphere can maintain the operation of plate tectonics, its initiation mechanism remains unclear. To reveal the origin mystery of plate tectonics, it is necessary to clarify how and when the first subduction on Earth began. In this study, we propose a hypothetical model that links Earth's biological processes with the origin of plate tectonics. In the photic zone of the Neoarchean continental margins, the anaerobic metabolism of photoferrotrophic bacteria greatly promoted the massive deposition of magnetite‐rich banded iron formations (BIFs). Our mechanical calculations show that within an acceptable sedimentary thickness, these heavy BIF deposits can provide enough downward force to rupture the Neoarchean continental margins and initiate the earliest subduction. The peak deposition of BIFs in 2.75–2.4 Ga further implies the onset time of global plate tectonics. Key Points: The biologically induced deposition of magnetite‐rich banded iron formations (BIFs) at proto‐continental margins can initiate plate tectonicsThe peak deposition of BIFs in 2.75–2.4 Ga indicates the onset time of plate tectonicsBiological activities have an important influence on the tectonic behavior of Earth [ABSTRACT FROM AUTHOR]

The Sijiaying iron deposit is located in the Eastern Hebei area of the southern section of the northern margin of the North China Craton (NCC) and is the largest single iron deposit in China. The deposit contains many banded iron formations (BIFs) and was proven to have more than 3 million tons of high-grade iron ore resources. This study carried out geochemistry and zircon U–Pb analysis of normal-grade iron ore, high-grade iron ore, and wall rock (biotite–leptynite, chlorite–sericite schist) in the Sijiaying deposit and discussed the genesis and metallogenic age of high-grade iron ore. BIFs have low concentrations of Al2O3 and TiO2 and high field strength element (HFSE) depletion, indicating almost no contamination via terrestrial debris. The standardized post-Archean Australian shale (PAAS) rare earth element (REE) distribution pattern indicates that the iron formation exhibits positive Eu, Y, and heavy rare earth element (HREE) anomalies and lacks negative Ce anomalies, indicating that the Sijiaying BIF was enriched with iron sources via high-temperature hydrothermal fluids from the seabed and deposited in an anoxic ancient marine environment. In addition, geological field work identified two types of high-grade iron ore in the mining area: primitive sedimentary and hydrothermally altered high-grade iron ore. Further ore geochemical research showed that the primitive sedimentary-type iron ore is similar in geochemistry to the BIF. In addition to low Eu/Eu* values, the hydrothermally altered high-grade iron ore shows geochemical characteristics similar to those of the BIF, suggesting that they share the same iron source but did not form at the same time. The total large ion lithophile element (LILE) (Sr, Ba, Pb) contents in primitive sedimentary-type high-grade iron ore are higher than those in hydrothermally altered high-grade iron ore, indicating that LILEs are carried away via fluids during the hydrothermal alteration process in normal-grade iron ore. The geochemical characteristics of biotite–leptynite and chlorite–sericite schist include high contents of SiO2 and Al2O3, light rare earth elements (LREEs), LILE enrichment (Rb, Ba, Sr, Zr), and HFSE depletion (Nb, Ta, P, Ti), characteristics that are similar to island arc volcanic rocks. The reconstruction of the original rock indicates that the wall rock is a product of volcanic sedimentary cycles in an island arc setting. Zircon cathodoluminescence images and LA–ICP–MS zircon U–Pb dating can be divided into four age groups (3283 Ma, 2547 Ma, 2500 Ma, and 2407 Ma), which correspond to the earliest volcanic activity in eastern Hebei, the main mineralization age of the Sijiaying BIF (the mineralization age of primitive sedimentary high-grade iron ore), a regional tectonic–metamorphic event, and the occurrence of migmatization (the mineralization age of hydrothermally altered high-grade iron ore), respectively. Therefore, the Sijiaying BIF and primitive sedimentary high-grade iron ores were deposited and mineralized at 2547 Ma, and the iron orebody was later altered via the hydrothermal solution at 2407 Ma, forming large-scale high-grade iron ores. [ABSTRACT FROM AUTHOR]

Self‐organizing diffusion‐reaction systems naturally form complex patterns under far‐from‐equilibrium conditions. A representative example is the rhythmic concentration pattern of Fe‐oxides in Zebra rocks; these patterns include reddish‐brown stripes, rounded rods, and elliptical spots. Similar patterns are observed in the banded iron formations, which are presumed to have formed in the early earth under global glaciation. We propose that such patterns can be used directly (e.g., by computer‐vision‐analysis) to infer basic quantities relevant to their formation giving information on generalized chemical gradients. Here we present a phase‐field model that quantitatively captures the distinct Zebra rock patterns based on the concept of phase separation that describes the process forming Liesegang stripes. We find that diffusion coefficients (the bulk self‐diffusivities of the native species and the mobility of the reaction product) play an essential role in controlling the appearance of regular stripe patterns as well as the transition from stripes to spots. The numerical results are carefully benchmarked with well‐established empirical spacing law, width law, timing law and the Matalon‐Packter law. Using this model, we invert for the important process parameters originating from the intrinsic material properties, the self‐diffusivity ratio and the mobility of Fe‐oxides with a series of Zebra rock samples. This study allows a quantitative prediction of the generalized chemical gradients in mineralized source rocks without intrusive measurements, providing a better intuition for the mineral exploration space. Plain Language Summary: Patterns in nature are observed in disparate fields of science in biology, geology, mechanics, atmospheric physics, chemistry and others. A unifying principle to decipher those patterns is using a reaction‐diffusion approach, as employed here, when implemented in numerical simulations, can deliver a perfect match to patterns observed in nature. Here we go one step further and show that dynamic coefficients describing the concentrations and mobility of valuable species such as iron oxide can be derived from the images. The proposed algorithms are benchmarked on the Zebra banded rock in Western Australia. The broader impact of the presented work includes the development of a future exploration tool based on computer‐version, revealing high grades of iron in the prominent worldwide banded iron formations which bear similar characteristic stripes. Using a physics‐based model, our formulation also captures the interesting phenomenon of transition from bands to spots that has not been addressed before. Key Points: Inversion of Cahn‐Hilliard dynamic coefficients from photographic images of Zebra rock reveals multiphysics coupled processesTransition from stripes to spots is triggered by low reaction product (here Fe‐Oxyhydroxite) mobilityApplication of computer‐vision algorithms in conjunction with inversion may allow novel geophysical exploration tools for ores [ABSTRACT FROM AUTHOR]

Goa is situated in the northwestern part of the Western Dharwar Craton (WDC) which is Asia's major metallogenic province. The iron ore of Goa is associated with greenstone and occurs as bands, reefs, and lenses of Banded Hematite Quartzite (BHQ) and Banded Magnetite Quartzite (BMQ) none of these are explored for geo-microbiological dimensions, such as detection of microbioform Gold. The presence of metalliferous WDC in Goa affords sampling of auriferous materials from mining area having hitherto BHQ at latitude 15°29′54″ N and longitude 74° 03′44″ E) and BMQ at latitude 15°24′12″ N and longitude 74° 09′31″ E were collected, surface sterilized and drilled with a sterile driller to get the endolithic material under sterile conditions and sent for metagenomic analysis using Oxford nanopore sequencing. Both the samples showed the presence of microorganisms with Archea, such as Haloferax, Nitrososphaera, and Eubacteria, i.e., Bacillus, Ralstonia, Cupriavidus, Burkholderia, and Acetobacter. The traditional model of Banded Iron Deposition assumes precipitation by the oxidation of hydrothermal Fe (II), either via abiotic oxidation or biotic oxidation through chemo lithotrophic Eubacteria, such as cyanobacteria which produce oxygen. This paper reports the diversity and the presumptive role of these microorganisms in the biogeochemical cycling of metals, such as Fe, Mn, and gold (Au). [ABSTRACT FROM AUTHOR]

Banded iron-formations (BIFs) are marine chemical sedimentary rocks composed of siliceous and ferric materials, usually with typical thin layers or sheet structures. BIFs not only record a wealth of information about the state and evolution of the lithosphere, atmosphere, hydrosphere, and biosphere but also host the majority of the economic iron resources in the world. Here, we summarize the types, mineralogical, and geochemical characteristics of BIFs; analyze their formation conditions, their oxidative mechanism, and the absence causes of BIFs; and elucidate the associations between BIFs and major atmospheric oxidation events (Paleoproterozoic great oxidation event (2.4~2.1 Ga) and Neoproterozoic oxidation event (0.8~0.55 Ga)). BIFs are intimately associated with enhanced submarine magmatic–hydrothermal activities. Finally, it is concluded that the deposition and demise of BIFs are closely related to major geological events, and these major geological events interact with each other, jointly constraining the evolution of the atmospheric and marine environment and of geo-biological and geodynamic processes. [ABSTRACT FROM AUTHOR]

The Hamersley Basin in Western Australia is one of the world's largest iron ore‐producing regions, hosting two types of ore in banded iron formations: the high‐grade martite‐microplaty haematite and the supergene martite‐goethite ores. With the high‐grade ores almost entirely mined in the last decade, the supergene ores have more recently become the dominant resource of interest. Consequently, understanding the genesis of these martite‐goethite deposits is a critical step for exploration. Yet, although various models exist, there is still no consensus on how these mineral resources formed, complicating the prediction of resource volume and location. Here, we show that the paleo‐stratigraphic permeability anisotropy (with higher permeability along strata than across) controls the supergene mimetic enrichment transport process and, subsequently, the mineralisation distribution. We introduce a flow model that implicitly represents strata with a potential function that orients the permeability tensor accurately. The numerical solver uses automatic mesh adaptivity to deliver robust solutions. By accurately reproducing the mineralisation patterns in specific deposits, we identify and quantify the paleo‐water table level and permeability anisotropy ratio as the two main controlling parameters for the mineralisation distribution. These insights provide new timing constraints for the mineralisation and the physical process of iron enrichment, suggesting much more potential mineralisation volume in the paleo‐reconstructed zones than previously anticipated. These flow models allow us to draw geological conclusions with few a priori assumptions required for the genetic model in which the transport component is dominant. The predictive power of this methodology will allow targeted drilling to narrow down the prospective areas and lower exploration costs. Furthermore, the methodology's generality applies to other commodities in sedimentary basins involving supergene processes and will improve our understanding of various genetic models. [ABSTRACT FROM AUTHOR]

The Hamersley Group in the Hamersley Basin, Western Australia, contains major deposits of banded iron formation of Neoarchean–Paleoproterozoic age (2629–2449 Ma). The 2450 Ma Weeli Wolli Formation near the top of the group includes banded iron formation with microbands (≤0.05–0.5 mm to rarely 1 mm thick) of chert and iron oxide lamina couplets that display distinctive cycles. Some adjacent, thin microbands have merged with compaction and the diagenetic removal of chert laminae, and maximum counts of cycle period by different studies is preferred, suggesting a period of ∼28 ± 2 microbands. Associated cyclic iron formation shows soft-sediment plastic deformation and brittle fracturing. Rare earth element geochemistry indicates that much of the iron in late Archean–early Paleoproterozoic banded iron formations was derived from submarine hydrothermal systems. Monitoring of hydrothermal vents on mid-ocean ridges and seamounts has identified tidal modulation of the discharge, temperature and dispersal of deep-sea hydrothermal plumes principally by semidiurnal variations in tidal loading and earth tides. Microearthquake swarms are associated with deep-sea hydrothermal systems at the crests of mid-ocean ridges, and tidal triggering of microearthquake activity is indicated for a hydrothermal system on the East Pacific Rise. The microband cycles in the Weeli Wolli Formation are interpreted as tidalites, comprising ∼28 ± 2 semidiurnal microbands per lunar (synodic) fortnightly cycle, related to the tidally modulated activity of a submarine hydrothermal system. The associated plastically deformed and brittle-fractured sediments are viewed as seismites resulting from microearthquakes also related to the hydrothermal system. The Weeli Wolli microband cycles and seismites may represent a rarely identified instance of iron-formation deposition near a submarine hydrothermal system. Submarine hydrothermal venting was a major source of iron in late Archean–early Paleoproterozoic banded iron formations. Semidiurnal variations in tidal loading and earth tides commonly modulate present-day deep-sea hydrothermal activity, and microearthquake swarms are associated with deep-sea hydrothermal systems. Early Paleoproterozoic banded iron formation from the Hamersley Basin displays cycles with an estimated period of ∼28 ± 2 microbands and associated plastic deformation and brittle fracturing. The microband cycles are interpreted as tidalites comprising ∼28 ± 2 semidiurnal increments grouped in fortnightly cycles at a tidally modulated submarine hydrothermal system, and the deformed sediments as seismites caused by related microearthquake activity. [ABSTRACT FROM AUTHOR]

Gold mineralization associated with quartz veins and sulfide minerals has been reported in Banded Iron Formation (BIF) at Girar, Bundelkhand Craton, India. The BIF is deformed with the development of tight- isoclinal folds in high strain zones and hosts four types of quartz veins viz., (i) folded veins, (ii) band parallel veins, (iii) low angle cross-cutting veins, and (iv) high angle cross-cutting veins. Folded and band parallel veins are continuous with each other and spatially restricted to zones of tight-isoclinal folds in BIF. Shape of quartz aggregates in the folded and band parallel veins is interlobate, and these veins contain pyrite and chalcopyrite as dominant sulfide minerals along with gold. Microstructure of quartz grains and presence of fragments of BIF in sulfide mineralgold bearing folded and band parallel veins indicate that the formations of these veins were related to a single deformation episode. Spatial association of folded and band parallel veins to intensely folded zones in BIF is attributed to epigenetic nature of sulfide and gold mineralization. [ABSTRACT FROM AUTHOR]

The presence of Cainozoic marine sediments in the Sperrgebiet, Namibia, was noted as early as 1908 when diamonds were found at Kolmanskop. Because of the economic interest of these deposits, geological investigations were undertaken, which led to detailed mapping of their distribution, initially by Beetz (1926). In the Central Sperrgebiet early investigators correlated the 'highest' beach deposits (ca 160 metres above present-day mean sea-level) to the Eocene, referred to in the old literature as 'Höchster Stand der Eocänsee' or the 'Eocäne Marine Inundation' (Kaiser, 1926). Liddle (1971) extended this « ancient » strandline a few kilometres northwards to Elfert's Tafelberg. Dingle et al. (1983) dated it to the late Palaeocene - early Eocene. In contrast, along the Namaqualand coastal plain in South Africa, marine deposits attributed by Pether (1986, 1994) to the 90 metre package, the 50 metre package, and the 30 metre package were correlated to the Miocene. Re-examination of the conglomerates at Eisenkieselklippenbake and Buntfeldschuh which crop out at ca 150-160 metres above sea level, reveals that some of the deposits are considerably younger than the Eocene, being instead of early Miocene (Aquitanian-Burdigalian) age. The beach conglomerates at both of these localities contain well-rounded and polished cobbles of densely ferruginised gravel and sand associated with cobbles of a great variety of other rock types (quartzite, silcrete, silicified freshwater limestone, vein quartz, agates, pebbles of banded ironstone formation (BIF), jasper etc.). The conclusion about the Miocene age of the beaches follows from the observation that the ferruginisation of near-surface deposits in the sector of the Sperrgebiet between Kerbehuk in the south and Elisabethfeld-Grillental in the north occurred during the Oligocene (more precisely, the Chattian) the process petering out during the Early Miocene (Aquitanian-Burdigalian), and ceasing altogether with the establishment of hyper-aridity in the region (onset of fully desert conditions in the Namib) ca 17 Ma. This means that cobbles derived from the break-up of the ferruginised deposits must be younger than the Chattian. Many of the cobbles of ferruginised sediment contain clasts of agate, BIF and jasper, vein quartz, silicified limestone etc. which were already present in the superficial deposits of the region prior to the Chattian, supporting the old conclusions concerning the presence of Eocene marine deposits in the Sperrgebiet. The revised age of the Eisenkieselklippenbake and Buntfeldschuh beach conglomerates means that the timing of the geomorphological development of the region, such as the back-cutting of the Buntfeldschuh Escarpment, requires revision, as do the correlations of near-surface deposits such as the fluvial Blaubok and Gemsboktal formations (Pickford, 2015) which are of Eo-Oligocene and Miocene age respectively. [ABSTRACT FROM AUTHOR]

In this study, we investigated Ni2+, Zn2+, and Co2+ mineralogical incorporation and its effect on green rust transformation to magnetite. Mineral transformation experiments were conducted by heating green rust suspensions at 85 °C in the presence of Ni2+, Zn2+, or Co2+ under strict anoxic conditions. Transmission electron microscopy and powder X-ray diffraction showed the conversion of hexagonal green rust platelets to fine grained cubic magnetite crystals. The addition of Ni2+, Zn2+, and Co2+ resulted in faster rates of mineral transformation. The conversion of green rust to magnetite was concurrent to significant increases in metal uptake, demonstrating a strong affinity for metal sorption/co-precipitation by magnetite. Dissolution ratio curves showed that Ni2+, Zn2+, and Co2+ cations were incorporated into the mineral structure during magnetite crystal growth. The results indicate that the transformation of green rust to magnetite is accelerated by metal impurities, and that magnetite is a highly effective scavenger of trace metals during mineral transformation. The implications for using diagenetic magnetite from green rust precursors as paleo-proxies of Precambrian ocean chemistry are discussed. [ABSTRACT FROM AUTHOR]

∼ 2.5 Ga banded iron formation (BIF) and Cu-Zn sulfide deposit within volcanic-argillaceous sequences (VMS-like) occurred together in NE China, recording the first appearance of oxidized ores and sulfide ores co-existing in the early Earth. They requires two requirements of tectonic setting and sedimentary environment. These conditions could be implemented only in late Neoarchean and Paleoproterozoic for a limited period of time until to the Great Oxygen Event. The study revealed a radical change in tectonic regime and paleo-environment at the end of Neoarchean. [Display omitted] Banded iron formation and Cu-Zn sulfide deposits within volcanic-argillaceous sequences (as volcanogenic massive sulphide deposits (VMS)-like type) occur together in the Qingyuan greenstone belt of the North China Craton, recording the first appearance of oxidized ores and sulfide ores co-existing in the early Earth. The unique metal co-existing deposits should meet two requirements: tectonic setting and sedimentary environment. As regards to tectonic setting, plate-like tectonics might have started since the end of the Neoarchean because continents had grown large enough and there occurred volcanic arcs and backarc basins similar to modern ones in a way. Partial melting of subducted continental crust is conductive to providing ore-forming elements. As for sedimentary environment, late Neoarchean seawater was rich in Fe2+ and anoxic. Instantaneous oxidation of the seawater resulted possibly from frequent submarine volcanic eruptions and facilitated precipitation of the banded iron formation. At this point, it is also favorable for the enrichment of Cu and Zn ions in seawater. The VMS-like deposits tended to form when the seawater was reduced again. Studies of isotopic elements like sulfur, oxygen, iron and silicon support the above geological processes. It is shown that the geologic conditions only existed in the late Neoarchean and Paleoproterozoic for a short period of time. The banded iron formations disappeared around 1.85 Ga, and the associated sulfide metal deposits also became dominant sedimentary exhalative deposits in the meso -Neoproterozoic Boring Billion, as a result of increasing oxidation of the oceans and the increasing maturity of the continental crust. This study is significant not only for decoding metallogenic genesis but also helping understand rapid change in Precambrian tectonic regimes and Earth's environments. [ABSTRACT FROM AUTHOR]

Gold (I) sulphide (Au2S) is an inorganic compound and the principal sulphide of gold. This study aimed to separate gold sulphide from ore samples such as banded hematite quartzite mined from the banded iron formation of Goa, India. The samples were dried, powdered and then concentrated by the panning method. The coarse ferromagnetic material was separated and sieved into different fractions of varying sieve sizes, i.e. 250, 150, 106 and 53 µm. Next, they were subjected to serial washing, and after drying, were tested for the presence of gold by ICP-AES, optical microscopy, phase contrast microscopy, SEM-EDS and total content of the sulphur was analysed by CHNS/O elemental analyzer. [ABSTRACT FROM AUTHOR]

Minerals and metals play a very important role in the country’s economic growth and as well as construction industries. Minerals also support automobile industries as they are required to manufacture steel and other products using various minerals. So, minerals and mining industries are the backbones of any country’s Gross Domestic Product (GDP). In the study area, Banded Iron Formation (BIF) hosted auriferous sheared zones which are indicating very good gold and associated mineralisation. In the study area, different litho units occur like metabasalt, schist, shale and pyritiferous metabasalt. Banded Iron Formations (BIFs) are dominating in the study area along with quartz vein, Banded Fe-Mn Chert and BIFs float. Different rock chip samples show encouraging gold mineralisation zones. Auriferous shear zones on top of the hilltop in the reef. In the study area, Petrography and mineralogy have played a vital role in gold and associated mineralisation in the Nagavi area. Gold is closely associated with sulphides, mainly pyrite and pyrrhotite, and to a lesser extent, with bismuth tellurides and carbonate minerals. The gold content range in BIF’s of the Nagavi area is from < 20 to <27 ppb. In the study area, geological structures like dips, strike, faults, folds, joints and unconformities support gold mineralisation. Majorly these structures control the gold and associated minerals. [ABSTRACT FROM AUTHOR]

Hematite and goethite deposits hosted in banded iron formations (BIFs) in the Pilbara craton (Western Australia) represent one of Earth's most significant Fe reserves; however, the timing and tectonic triggers underpinning deposit genesis remain contentious. Uncertainty in ore genesis stems from a lack of direct age measurements, which could aid in correlating periods of BIF mineralization with tectono-thermal events observed elsewhere. Archean-Paleoproterozoic BIFs in the Hamersley Province host extensive martite-microplaty hematite orebodies that formed at 2.2-2.0 Ga, based on indirect constraints. In contrast, combined hematite in situ U-Pb geochronology and (U-Th)/He thermochronology demonstrate that martite-microplaty hematite ores in the Chichester Range crystallized ca. 1.26-1.22 Ga and underwent cratonic denudation between ca. 0.57 and 0.38 Ga. Nanoscale imaging of dated hematite indicates that U-Th-Pb is lattice bound and not hosted in inclusions. New U-Pb hematite ages overlap with other mineral ages reported at the margins of the Pilbara and Yilgarn cratons (1.3-1.1 Ga), where mineral formation was driven by plate reorganization following breakup of the Nuna supercontinent. This age correlation suggests that a combination of increased orogenic (+diagenetic) and heat (+fluid) generative processes resulting from supercontinent reconfiguration was a key trigger for iron ore formation in the Pilbara craton. [ABSTRACT FROM AUTHOR]

Marine chemical sedimentary deposits known as Banded Iron Formations (BIFs) archive Archean ocean chemistry and, potentially, signs of ancient microbial life. BIFs contain a diversity of iron‐ and silica‐rich minerals in disequilibrium, and thus many interpretations of these phases suggest they formed secondarily during early diagenetic processes. One such hypothesis posits that the early diagenetic microbial respiration of primary iron(III) oxides in BIFs resulted in the formation of other iron phases, including the iron‐rich silicates, carbonates, and magnetite common in BIF assemblages. Here, we simulated this proposed pathway in laboratory incubations combining a model dissimilatory iron‐reducing (DIR) bacterium, Shewanella putrefaciens CN32, and the ferric oxyhydroxide mineral ferrihydrite under conditions mimicking the predicted Archean seawater geochemistry. We assessed the impact of dissolved silica, calcium, and magnesium on the bioreduced precipitates. After harvesting the solid products from these experiments, we analyzed the reduced mineral phases using Raman spectroscopy, electron microscopy, powder x‐ray diffraction, and spectrophotometric techniques to identify mineral precipitates and track the bulk distributions of Fe(II) and Fe(III). These techniques detected a diverse range of calcium carbonate morphologies and polymorphism in incubations with calcium, as well as secondary ferric oxide phases like goethite in silica‐free experiments. We also identified aggregates of curling, iron‐ and silica‐rich amorphous precipitates in all incubations amended with silica. Although ferric oxides persist even in our electron acceptor‐limited incubations, our observations indicate that microbial iron reduction of ferrihydrite is a viable pathway for the formation of early iron silicate phases. This finding allows us to draw parallels between our experimental proto‐silicates and the recently characterized iron silicate nanoinclusions in BIF chert deposits, suggesting that early iron silicates could possibly be signatures of iron‐reducing metabolisms on early Earth. [ABSTRACT FROM AUTHOR]

Most cave formation requires mass separation from a host rock in a process that operates outward from permeable pathways to create the cave void. Given the poor solubility of Fe(III) phases, such processes are insufficient to account for the significant iron formation caves (IFCs) seen in Brazilian banded iron formations (BIF) and associated rock. In this study we demonstrate that microbially-mediated reductive Fe(III) dissolution is solubilizing the poorly soluble Fe(III) phases to soluble Fe(II) in the anoxic zone behind cave walls. The resultant Fe(III)-depleted material (termed sub muros) is unable to maintain the structural integrity of the walls and repeated rounds of wall collapse lead to formation of the cave void in an active, measurable process. This mechanism may move significant quantities of Fe(II) into ground water and may help to explain the mechanism of BIF dissolution and REE enrichment in the generation of canga. The role of Fe(III) reducing microorganism and mass separation behind the walls (outward-in, rather than inward-out) is not only a novel mechanism of speleogenesis, but it also may identify a previously overlooked source of continental Fe that may have contributed to Archaean BIF formation. [ABSTRACT FROM AUTHOR]

The return of vegetation to mined lands often requires broadcast seeding of diverse native seed mixes. However, seeds are highly adapted to germination windows with specific hydrothermal thresholds that maximize the likelihood of seedling survival, and post‐mining landscapes typically offer markedly different hydrothermal conditions than pre‐disturbance ecosystems. According to niche theory, generalist species should exhibit broader hydrothermal performance niches than specialist taxa, which may influence the success of recruitment from seeds in post‐mining ecological restoration. To test this assumption, the impact of hydrothermal stress (incubation temperature (10–30°C) and osmotic potential (−0.8 to 0 MPa)) on the time to 50% germination (t50) and maximum germination (Gmax) was compared between two narrow‐range species of conservation concern (Acacia woodmaniorum and A. karina) restricted to mining‐impacted Banded Ironstone Formations (BIF) and three broadly distributed congenerics (A. assimilis, A. exocarpoides, and A. ramulosa). The hydrothermal germination niches of the study species were broadly congruent with hydrothermal conditions of their habitats. The two range‐restricted taxa were more tolerant of hydrothermal stress compared to the three widely distributed taxa, suggesting that tolerance of greater hydrothermal stress by both range‐restricted Acacia species is likely to be adaptive to establishment in uncontested niche space. Complex interactions between thermal and water stress suggest these environmental gradients may shape the germination niche as well as patterns of plant diversity in BIF ecosystems. This study highlights the importance of quantifying interactions between niche dimensions and their implications for species performance, which will aid future restoration efforts for micro‐endemic species impacted by mining. [ABSTRACT FROM AUTHOR]

The long-term history of the Earth–Moon system as reconstructed from the geological record remains unclear when based on fossil growth bands and tidal laminations. A possibly more robust method is provided by the sedimentary record of Milankovitch cycles (climatic precession, obliquity, and orbital eccentricity), whose relative ratios in periodicity change over time as a function of a decreasing Earth spin rate and increasing lunar distance. However, for the critical older portion of Earth’s history where information on Earth–Moon dynamics is sparse, suitable sedimentary successions in which these cycles are recorded remain largely unknown, leaving this method unexplored. Here we present results of cyclostratigraphic analysis and high-precision U–Pb zircon dating of the lower Paleoproterozoic Joffre Member of the Brockman Iron Formation, NW Australia, providing evidence for Milankovitch forcing of regular lithological alternations related to Earth’s climatic precession and orbital eccentricity cycles. Combining visual and statistical tools to determine their hierarchical relation, we estimate an astronomical precession frequency of 108.6 ± 8.5 arcsec/y, corresponding to an Earth–Moon distance of 321,800 ± 6,500 km and a daylength of 16.9 ± 0.2 h at 2.46 Ga. With this robust cyclostratigraphic approach, we extend the oldest reliable datum for the lunar recession history by more than 1 billion years and provide a critical reference point for future modeling and geological investigation of Precambrian Earth–Moon system evolution. [ABSTRACT FROM AUTHOR]

The role of biogenicity in the mineral world is larger than many might assume. Biological processes and physical and chemical processes interact both at the Earth's surface and far underground, leading to the formation of banded iron and manganese deposits, among others. Microbial mats can form giant sedimentary ore deposits, which include enrichment of further elements. This article reviews the ways in which microbially-mediated processes contribute to mineralization, the importance of mineralized microbial textural features, and the methods that must be used to obtain high-resolution datasets. If the chosen methodology and/or the size dimension of investigation is not appropriate, then it is not possible to recognize that a system is microbially mediated, and the conclusion will be incomplete. We call attention to variable authigenic mineralization as the result of complex mineralization of cells and extracellular polymeric substances in the starving basins, which form giant ore deposits together with ore-forming minerals. Microbial mats and other biosignatures can serve as indicators of environmental reconstruction in ore formations. We suggest tests and analyses that will allow the potential role of biomineralization to be properly investigated for a more comprehensive view of formation processes and their implications. [ABSTRACT FROM AUTHOR]

Banded Iron Formations (BIFs) are ancient marine chemical sediments that contain various Fe-bearing minerals such as hematite (Fe 2 O 3), magnetite (Fe 3 O 4), siderite (FeCO 3) and a variety of FeII - /FeIII-silicates. The prevailing opinion is that primary Fe(III) (oxyhydr)oxides, such as ferrihydrite (simplified formula of Fe(OH) 3), were precipitated from the ocean's photic zone by marine plankton, and a fraction of these minerals was subsequently transformed into secondary magnetite and siderite by dissimilatory Fe(III)-reducing bacteria (DIRB). However, aside from broad estimates, it is currently unknown what fraction of the primary Fe(III) minerals was sedimented to the seafloor where it was eventually lithified, and what fraction was reduced by DIRB in the water column, thus forming a microbial Fe cycle in the water column. To test this, we conducted Fe cycling experiments with marine phototrophic Fe(II)-oxidizing bacteria and DIRB under conditions mimicking the Precambrian ocean water column with elevated Fe(II) and Si concentrations. We followed secondary mineral formation over three consecutive redox cycles (oxidation followed by reduction) over a time interval of up to 58 days to determine which mineral phases would ultimately have settled as BIF forming sediments. We used wet geochemical methods to follow Fe speciation, measured dissolved silica and volatile fatty acid (VFA) concentrations, determined cell-mineral associations using fluorescence and electron microscopy, and characterized the mineralogy of the precipitates using 57Fe-Moessbauer spectroscopy and X-ray diffraction (XRD). Our results showed that both the absence of silica and an increasing number of Fe cycles favored the formation of more crystalline minerals, such as goethite (α-FeOOH). However, in the presence of high concentrations of monomeric silica, as suggested for ancient oceans (2.2 mM), only short-range ordered (SRO) Fe(III) minerals such as ferrihydrite were observed. These did not transform into the more thermodynamically stable goethite during repeated Fe cycling. Interestingly, no magnetite formed in any of the setups. Instead, increasing Si concentrations favored the formation of increasing quantities of Fe(II) minerals. Microscopy revealed a tight association between microbial biomass and minerals formed. Dissolved silica analysis showed the removal of Si from solution congruent with Fe(II) oxidation and a release of Si during Fe(III) reduction. Together, these results suggest an important role of co-precipitated biomass as well as silica for secondary mineral formation by either constraining crystal growth and/or inhibiting Fe(II)-induced mineral transformation. Overall, our results imply that microbial Fe cycling during settling of primary ferrihydrite through the photic zone in a Precambrian ocean would have resulted in the partial transformation of ferrihydrite into secondary Fe(II) mineral phases in the water column. This would have resulted in the accumulation of mixtures of a ferrihydrite-silica composite and Fe(II) minerals in the initial BIF forming sediments. [ABSTRACT FROM AUTHOR]

The Banda Alta Formation (Urucum district, Mato Grosso do Sul, Brazil) comprises ∼600 Ma Fe and Mn deposits, which are among the world's youngest and largest Neoproterozoic sedimentary Fe and Mn formations (IF; MnF). These have been deposited in a redox-stratified, marine sub-basin (Jacadigo Basin), which was strongly influenced by glacial advance/retraction cycles with temporary influx of continental freshwater and upwelling of metal-enriched deep anoxic seawater. Cr and Cd isotopes measured on meticulously separated hematite mesobands from drill core samples are relatively homogenous throughout the ca. 325 m thick sequence sampled in the Banda Alta Fm., with average authigenic δ53Cr values of +0.93 ± 0.24 ‰ (2σ; n = 23) and δ114Cd values of −0.14 ± 0.14 ‰ (2σ; n = 15). The significant enrichment of Cr, in parallel with the strong enrichments of other redox sensitive elements (U, Mo), attests for effective and efficient reduction removal processes in the surface waters during cycles where upwelling Fe2+-rich waters reached the oxygenated surface layer exposed to the atmosphere during episodic glacier retreat stages. Assuming a similar quantitative and efficient removal pathway of dissolved Cd by iron oxyhydroxides, the so-inferred average δ114Cd signature of −0.14 ± 0.14 ‰ in the Jacadigo Basin surface water is significantly lower than signatures of modern ocean surface waters with a range of δ114Cd of ca. ∼0.4 to ∼1 ‰ and even lower than the signature of modern ocean deep waters with δ114Cd of ∼0.3 ‰. It possibly attests to reduced primary production levels and lower nutrient utilization rates during deposition of the Late Neoproterozoic Jacadigo Group, compared to today. This despite the inferred oxidized surface water layer that must have prevailed during this time, as implied by the strongly positively fractionated Cr isotope signatures and pronouncedly negative Ce-anomalies recorded in the seawater-like, shale-normalized Rare Earth Element and Yttrium (REY) patterns exhibited by the hematite mesobands. Data presented herein speak for: (1) a stable, isotopically heavy Cr input to the Jacadigo Basin at the time of deposition, implying high atmospheric O 2 levels in the Late Neoproterozoic (2) likely quantitative, reductive incorporation / adsorption processes of dissolved Cr and Cd, respectively, into/onto precipitating iron oxyhydroxides, and (3) the prevalence of low nutrient concentrations and utilization rates in the Jacadigo Basin during glacier retreat cycles. Banded iron formations are considered suitable archives for reconstructing redox and bioproductivity levels in past marine depositional basin, including those prevalent in Neoproterozoic glacial conditions, via employing the Cr Cd isotope double tracer to iron-rich mesobands. • Positively fractionated Cr isotopes in Late Neoproterozoic Urucum iron formation. • Low bioproductivity during syn -glacial periods indicated by cadmium isotopes. • Chromium and cadmium likely derived from oxidative weathering of landmasses. • Deposition of IF in partially silled, periodically ice-covered sub-basins. [ABSTRACT FROM AUTHOR]

• Narrow range endemics are believed to be adapted to local climate conditions across their distribution. • Reproductive traits and germination niche characteristics vary in Banksia arborea populations. • Different populations adapt to display different temperature and water stress tolerances. • Warming of the region could impact on future recruitment of the species. The temperature and moisture requirements for reproduction (i.e. seed production and germination) underpin the biogeographical relationships between climate, distribution and population dynamics of plants, particularly narrow range endemic species. We aimed to investigate reproductive outputs and the responses of seeds to temperature and moisture availability across three Banksia arborea populations that are distributed over a narrow range (< 200 km2) of semi-arid habitat on banded ironstone formations of Western Australia. We conducted reproductive trait assessments by quantifying follicles per cone, proportion of viable seed and associated seed mass followed by hydrothermal germination assessments for each population to characterise temperature and water stress tolerance. We found the southern-most population, that receives marginally higher rainfall, had heavier seeds (10 ± 0.02 mg), a cooler optimum temperature (16.1 °C) and wider germination capacity under water stress at 10 °C and 15 °C (Ψ b50 = -0.66 to -0.87 MPa) compared to the two northern populations (Ψ b50 = -0.60 to -0.65 MPa). By contrast, both northern populations had slightly warmer optimum temperatures for germination (16.9–17.5 °C) and a higher capacity to germinate under water stress at warmer temperatures of 22.5 °C (Ψ b50 = -0.43 to -0.56 MPa, compared to -0.29 MPa). Our work highlights that, even within the specific requirements of a narrow range endemic, different populations adapt to marginally different temperature and water stress tolerances. Warming of the southern populations could impact on future recruitment, and conservation action to promote resilient ecosystems are suggested. [ABSTRACT FROM AUTHOR]

The Banded Iron Formations (BIFs) have been invaluable archives for the Precambrian eons, providing evidence for the paleoenvironment conditions, including the atmospheric oxygen levels. This study explores the geological origin and depositional mechanism of BIF-like Carboniferous Heiyingshan (HYS) and Mesoproterozoic Pilot Knob hematite (PKH) formations, characterized by hematite-rich (Fe-rich) layer and quartz-rich (Si-rich) jasper layer alternations within felsic volcanic rocks. Through comprehensive mineralogical analyses and geochemical modeling, we present evidence supporting their formation in intra-caldera hot spring lakes, where episodic inputs of Fe(H 3 SiO 4) 2 -bearing fluids mixed with ambient lake water. Experimental simulations and PHREEQC modeling corroborate a mechanism where ferrihydrite and amorphous silica precursors sequentially precipitate, possibly driven by the oxidation and decomposition rates of Fe(H 3 SiO 4) 2 complexes. The sharp or gradational change in the Fe- and Si-rich layering transition can be caused by varying atmospheric oxygen levels. The Carboniferous HYS specimen exhibits a sharp Fe Si boundary that is in accordance with modeling under high atmospheric O 2 condition. In contrast, the Mesoproterozoic PKH sample contains both sharp and gradual change in the Fe Si transition, implying the p O 2 lies between 10−3 and 10−5. This chemical precipitation model of BIF-like iron formations could provide insights into the Fe Si source and banding mechanism of BIFs, and Precambrian p O 2 levels. [Display omitted] • BIF-like iron formations are chemical sedimentary rocks originating from Fe-silicate metal complex hydrothermal fluid mixing with intra-caldera lake water. • Banding boundary sharpness can be a surface O 2 level proxy as layering forms when p O 2 is higher than 10−4. • The Mid-Proterozoic p O 2 concentration could be lower than 10−4. • The banding mechanism can resemble the BIF precipitation process. [ABSTRACT FROM AUTHOR]

• Review of chronometric versus chronostratigraphic basis for the Archean–Proterozoic boundary (APB) • Revised APB definition proposed based on the Mount Bruce Supergroup, Western Australia. • Rapid decline of banded iron formation and appearance of glacial diamictite defines the Archean–Proterozoic transition. The Mount Bruce Supergroup (MBS) in Western Australia has been central to debates surrounding Precambrian stratigraphic subdivision and is one of the few relatively conformable successions that records both the chronometric Archean-Proterozoic boundary (APB) and the Great Oxidation Event/Episode (GOE) which has previously been proposed as the most practical basis for a chronostratigraphic boundary. Current understanding of the lithostratigraphy, chemostratigraphy, and geochronology of the MBS supports the placement of a chronostratigraphic APB in the vicinity of the contact between the Hamersley and Turee Creek Groups, although a precise boundary awaits the generation and integration of more detailed chemostratigraphic records of the GOE with the physical record. The chronometric APB as presently defined at 2500 Ma will suffice until consensus is reached regarding a revised definition based on the GOE, and reconciliation of the physical and proxy records of this event. However, the Australian stratigraphic record suggests placement of the APB either at the base of the first glacial diamictite, or at the top of the last banded iron formation (BIF) below the GOE. The first option would exclude some BIF from the Siderian, which in both cases would be the terminal period of the Archean, whereas the second option places all diamictite in a new period at the start of the Paleoproterozoic. It is further proposed that this new period be named to primarily reflect this glacial influence, rather than for the influence of the GOE which relies on less obvious laboratory-based proxies for its identification. [ABSTRACT FROM AUTHOR]

• Rocks are derived via weak to intermediate weathering of a mixed felsic and mafic provenance. • Texture and geochemical filters distinguish primary zircons from subsequent modification under high-grade metamorphism or hydrothermal alteration conditions. • The maximal depositional age of unmodified detrital zircons at ca. 2.48 Ga is consistent with the continental arc in the context of the second stage of the two-step model. The Late Neoarchean to Early Paleoproterozoic Zhujiafang supracrustal assemblage is comprised of banded iron formations (BIF) interlayered with amphibolites, schist, felsic gneisses, and quartzite, intruded by mafic dykes and granitic intrusions or veins. Whole-rock geochemical and Nd isotopic and zircon U–Pb-Hf isotopic studies were conducted on the metasedimentary rocks from the Hengshan Complex, Trans-North China Orogen, North China Craton, to constrain their depositional age, provenance, and tectonic setting, and identify the impact of source weathering and sedimentary processes. Geochemical data classify these metasedimentary rocks as immature greywackes, showing weak- to intermediate-source weathering, poor sorting, and negligible sedimentary recycling. Relative to average Archean Cratonic Shales, the average major oxides of the Hengshan metasedimentary rocks have almost identical characteristics. The Chondrite-normalized rare earth element (REE) plots for these metasedimentary rocks show fractionated REE patterns ((La/Yb) N = 4.93–31.45), alongside moderate negative to slightly positive Eu anomalies (δEu = 0.68–1.17). Whole-rock Nd isotopic data give positive εNd (t) values ranging from + 0.34 to + 2.78. The zircons of two samples yield detrital zircon age range of ca. 2.59–2.48 Ga, with superchondrite εHf (t) values (+2.25 to + 6.08), and have experienced late modification. These findings suggest that the sediments originated from a blend of felsic and mafic sources, predominated by Late Neoarchean to Early Paleoproterozoic granitoids and metavolcanic rocks from the Huai'an, Hengshan, and Wutai complexes, excluding the TTG gneisses from the Fuping Complex. The Nd isotopic signatures, coupled with values of Th/U, δEu, Th/Sc, and other element characteristics, point to a Young Undifferentiated Arc provenance. The detrital zircon age spectrum, complemented by Hf isotope analysis, further delineates the depositional environment as a continental island arc setting, with a maximum depositional age of ca. 2.48 Ga. [ABSTRACT FROM AUTHOR]

The inclination of Planet Earth's axis of rotation by 23½° resulted in extreme climatic changes. Weak, solar radiation upon the Polar Circles during half-a-year alternated with half-a-year of darkness, turning them into freezing terrains for nearly the whole Precambrian. Exhalant hydrothermal solutions formed huge lakes over Polar Regions, undergoing intensive evaporation and condensation. Chemical interactions incidentally created primitive live forms, surviving as chemoautotrophic bacteria under the weakest UV rays. Daily changing solar radiation emitting UV rays over low latitudes prevented any life form. Some of these polar bacteria developed photosynthesis, improving their nourishment simultaneously releasing oxygen. The high content of ferrous iron in the lakes absorbed toxic oxygen forming iron oxides as banded iron formation (BIF). Excess photosynthetic oxygen molecules escaped into the anoxic atmosphere. At ~ 1.8 Ga oxygenated meteoric water infiltrated the continental subsurface oxidizing hydrothermal fluids, precipitating underground layered iron-oxides followed by silica only during the dry summers. The dilution of the rising solutions terminated biologically induced BIF precipitation. Consequently, intensive evaporation cemented sililiciclasts into stratified ferruginous formations, becoming abundant in the Late Neoproterozoic as NIF. The co-occurrence of Paleoproterozoic BIF and Neoproterozoic NIF sites evidence the tectonic and climatic stability of the Polar Circles. Magmatic convection currents split them ~ 750 Ma ago, but only after 580 Ma shifted the individual plates radially to low latitudes with advance of 'Plate Tectonics'. The polar bacteria connected with the open sterile sea for the first time had to adapt to daily changing ecosystems by combining into mobile primitive eukaryotes (Ediacaran Biota) and further diversify, erroneously referred to the 'Cambrian Explosion'. Geological evidence corroborated the activity of convection currents since Earth's consolidation controlling its inner heat budget and supplying hydrothermal solutions forming lakes on the Polar Circles where life originated and iron ores accumulated. [ABSTRACT FROM AUTHOR]

In the current study, a simple dry coating method was utilized to fabricate a super-hydrophobic super-magnetic powder (ZS@BIF) for oily water purification using zinc stearate (ZS) and banded iron formation (BIF). The produced composite was fully characterized as a magnetic sorbent for oily water treatment. The results of X-ray diffraction diffractometer (XRD), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS) and particle size analysis revealed the fabrication of homogenous hydrophobic-magnetic composite particles with core–shell structure. Contact angle and magnetic susceptibility results showed that 4 (BIF): 1 (Zs) was the ideal coverage ratio to render the core material superhydrophobic and preserve its ferromagnetic nature. The capability of the fabricated composite to sorb. n-butyl acetate, kerosene, and cyclohexane from oil–water system was evaluated. ZS@BIF composite showed a higher affinity to adsorb cyclohexane than n-butyl acetate and kerosene with a maximum adsorption capacity of about 22 g g−1 and 99.9% removal efficiency. Moreover, about 95% of the adsorbed oils could be successfully recovered (desorbed) by rotary evaporator and the regenerated ZS@BIF composite showed high recyclability over ten repeated cycles. [ABSTRACT FROM AUTHOR]