Banded Iron Formation

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Lianchang Zhang - One of the best experts on this subject based on the ideXlab platform.

  • earth s youngest Banded Iron Formation implies ferruginous conditions in the early cambrian ocean
    Scientific Reports, 2018
    Co-Authors: Zhiquan Li, Lianchang Zhang, Mengtian Zheng, Leslie J Robbins, John F Slack, Noah J Planavsky, Kurt O Konhauser
    Abstract:

    It has been proposed that anoxic and Iron-rich (ferruginous) marine conditions were common through most of Earth history. This view represents a major shift in our understanding of the evolution of marine chemistry. However, thus far, evidence for ferruginous conditions comes predominantly from Fe-speciation data. Given debate over these records, new evidence for Fe-rich marine conditions is a requisite if we are to shift our view regarding evolution of the marine redox landscape. Here we present strong evidence for ferruginous conditions by describing a suite of Fe-rich chemical sedimentary rocks-Banded Iron Formation (BIF)--deposited during the Early Cambrian in western China. Specifically, we provide new U-Pb geochronological data that confirm a depositional age of ca. 527 Ma for this unit, as well as rare earth element (REE) data are consistent with anoxic deposition. Similar to many Algoma-type Precambrian Iron Formations, these Early Cambrian sediments precipitated in a back-arc rift basin setting, where hydrothermally sourced Iron drove the deposition of a BIF-like protolith, the youngest ever reported of regional extent without direct links to volcanogenic massive sulphide (VMS) deposits. Their presence indicates that marine envIronments were still characterized by chemical- and redox-stratification, thus supporting the view that-despite a dearth of modern marine analogues-ferruginous conditions continued to locally be a feature of early Phanerozoic seawater.

  • changing provenance of late neoarchean metasedimentary rocks in the anshan benxi area north china craton implications for the tectonic setting of the world class dataigou Banded Iron Formation
    Gondwana Research, 2016
    Co-Authors: Changle Wang, Lianchang Zhang, Mengtian Zheng, Hua Huang, Xiaoxue Tong, Zidong Peng, Mingguo Zhai
    Abstract:

    Abstract The Anshan-Benxi (AnBen) area is situated in the northeastern part of the North China Craton and is considered to be the most important Iron metallogenic province in China. The giant Dataigou Banded Iron Formation (BIF) has the potential to be the largest Iron deposit in this area, even in Asia. Here, we present in situ zircon U–Pb-Hf-O isotopic and whole-rock geochemical data for metasedimentary rocks (metapelites and metaarenites) and trondhjemitic gneiss associated with this BIF, in order to provide constraints on the setting of the deposit, with implications for geological and exploration models. SIMS zircon U–Pb dating results indicate that the trondhjemitic gneiss crystallized at 3450 ± 19 Ma, and thus it is the oldest rock so far indentified in the Benxi area. The youngest group of detrital zircons from the metaarenite samples constrains their maximum depositional age at ~ 2.54 Ga. In combination with the earlier metamorphic age of ~ 2.51 Ga for the metaarenites, the deposition age of the Dataigou BIF can be constrained between 2.54 and 2.51 Ga. The metasediments have undergone varying degrees of source weathering. Source rocks of the metapelites have undergone moderate to severe chemical weathering, whereas those of the metaarenites have subjected to relatively weak chemical weathering. Diagnostic geochemical features such as the Al2O3/TiO2 values, trace element ratios, and REE patterns suggest that the metaarenites were predominantly derived from felsic igneous sources, whereas the metapelites were sourced mainly from mafic tholeiitic rocks. The dominant late Neoarchean detrital zircons further indicate that they were most likely sourced from almost synchronous volcanic rocks in the AnBen area. Taking into account the lithostratigraphic, geochemical, and geochronological data, the Dataigou BIF is interpreted as having been deposited in a back-arc basin, most probably on the margin of an ancient continental crust. Continuous provenance variations of these metasediments during highstand times and transgression can be ascribed to changes in natures of nearby volcanisms. Integrated with previous zircon Hf isotopic data from other supracrustal rocks in the AnBen area, our Hf-O data reveal major juvenile crustal growth stages at 3.0 Ga and during 2.8–2.7 Ga, and a crustal reworking event with minor juvenile addition at ~ 2.5 Ga in the studied area.

  • decoupled sources of the 2 3 2 2ga yuanjiacun Banded Iron Formation implications for the nd cycle in earth s early oceans
    Precambrian Research, 2016
    Co-Authors: Changle Wang, Kurt O Konhauser, Lianchang Zhang, Mingguo Zhai, Wenjun Li
    Abstract:

    Abstract The recognized worldwide gap in BIF deposition between 2.4 and 2.0 billion years ago has long been considered as an obstacle to fully determining the geochemical composition of seawater at that time. However, the recently dated 2.3–2.2 Ga Yuanjiacun Banded Iron Formation (BIF) in the North China Craton (NCC) offers a possibility to redress these uncertainties. Shale-normalized rare earth element-yttrium (REE + Y) patterns of the BIF and interlayered meta-chert samples show features characteristic of other Archean and Paleoproterozoic BIFs, with HREE enrichment relative to LREE, positive La and Eu anomalies, and superchondritic Y/Ho ratios comparable to modern seawater. Very low Al 2 O 3 ( e Nd ( t ) ∼ +3.5) derived from interaction with a depleted mantle source and associated with high Fe fluxes. The second is ambient surface seawater ( e Nd ( t ) ∼ −2.4), which obtained its signature through weathering of the nearby landmasses and associated with high Si fluxes. Our findings suggest that the REE budget of the oceans prior to 2.3 Ga was generally dominated by hydrothermal circulation of seawater through depleted mantle-derived source rocks. However, where evolved local continental crust and/or an enriched mantle source were present, this positive mantle Nd signal became discernible in the BIFs. By comparing the Nd isotopic features of similar aged BIFs and marine carbonates, it is concluded that similar to modern oceans, the early Precambrian ocean was not well-mixed with respect to its Nd isotopic composition.

  • depositional envIronment of the paleoproterozoic yuanjiacun Banded Iron Formation in shanxi province china
    Economic Geology, 2015
    Co-Authors: Changle Wang, Kurt O Konhauser, Lianchang Zhang
    Abstract:

    The Paleoproterozoic (~2.38–2.21 Ga) Yuanjiacun Banded Iron Formation (BIF), located in Shanxi Province, is a Superior-type BIF in the North China craton. This BIF is within a metasedimentary rock succession of the Yuanjiacun Formation, in the lower Luliang Group, which has undergone lower greenschist-facies metamor phism. Iron oxide (magnetite and hematite), carbonate, and silicate facies are all present within the Iron-rich layers. The eastward transition from carbonate- into oxide-facies Iron Formations is accompanied by a change in mineralogical composition from siderite in the west through magnetite-ankerite and magnetite-stilpnomelane assemblages in the transition zone to magnetite and then hematite in the east. These distinct lateral facies are also observed vertically within the BIF, i.e., the Iron mineral assemblage changes upsection from sider ite through magnetite into hematite-rich Iron Formation. The oxide-facies BIF formed near shore, whereas carbonate (siderite)- and silicate-facies assemblages formed in deeper waters. Based on detailed analyses of these variations on a basinal scale, the BIF precipitated during a transgressive event within an envIronment that ranged from deep waters below storm wave base to relatively shallow waters. The BIF samples display distinctively seawater-like REEs + Y profiles that are characterized by positive La and Y anomalies and HREEs enrichment relative to LREEs in Post-Archean Australian shale-normalized diagrams. Consistently positive Eu anomalies are also observed, which are typical of reduced, high-temperature hydrothermal fluids. In addition, slightly negative to positive Ce anomalies, and a large range in ratios of light to heavy REEs, are present in the oxide-facies BIF. These characteristics, in combination with consistently positive δ 56Fe values, suggest that deposition of the BIF took place along the chemocline where upwelling of deep, anoxic, Iron- and silicarich hydrothermal fluids mixed with shallower and slightly oxygenated seawater. The ankerite displays highly depleted δ13C values and the carbonate-rich BIF has a high content of organic carbon, suggesting dissimilatory Fe(III) reduction of a ferric oxyhydroxide precursor during burial of biomass deposited from the water column; that same biomass was likely tied to the original oxidation of dissolved Fe(II). The fact that the more ferric BIF facies formed in shallower waters suggests that river-sourced nutrients would have been minimal, thus limiting primary productivity in the shallow waters and minimizing the organic carbon source necessary for reducing the hematite via dissimilatory Fe(III) reduction. By contrast, in deeper waters more proximal to the hydrothermal vents, nutrients were abundant, and high biomass productivity was coupled to increased carbon burial, leading to the deposition of Iron-rich carbonates. The deposition of the Yuanjiacun BIF during the onset of the Great Oxidation Event (GOE; ca. 2.4–2.2 Ga) confirms that deep marine waters during this time period were still episodically ferruginous, but that shallow waters were sufficiently oxygenated that Fe(II) oxidation no longer needed to be tied directly to proximal cyanobacterial activity.

  • petrology and geochemistry of the wangjiazhuang Banded Iron Formation and associated supracrustal rocks from the wutai greenstone belt in the north china craton implications for their origin and tectonic setting
    Precambrian Research, 2014
    Co-Authors: Changle Wang, Lianchang Zhang
    Abstract:

    Abstract The Wutai greenstone belt (WGB) is one of the most extensively studied greenstone belts in China. Together with the Hengshan and Fuping complexes, these three associations compose the central segment of the Trans-North China Orogen (TNCO) in the North China Craton (NCC). The Wangjiazhuang Banded Iron Formation (BIF) is located in the bottom of the Jingangku Formation of the WGB. The associated supracrustal rocks consist of meta-basalts (amphibolites), meta-felsic volcanic rocks (leptynite) and metapelites (mica schist), which have experienced amphibolite-facies metamorphism. Amphibolites are commonly intercalated with the BIF. SIMS zircon U–Pb analyses on amphibolites suggest that the Wangjiazhuang BIF was formed at ca. 2543 ± 4 Ma. Combined with most Neoarchean Algoma-type BIFs in the NCC, these features indicate that a significant tectothermal event of the NCC have occurred at ∼2.5 Ga. Mineral assemblages of the Wangjiazhuang BIF are composed of quartz, magnetite, amphibole, and minor garnet, pyrite and calcite. The precursor deposits of this BIF were likely ferric-oxyhydroxides, fine-grained carbonate oozes, silicate phases rich in Al–Ca–Mg–Fe and amorphous silica. The appearance of garnet and ferro-pargasite, high concentrations of Al2O3, HFSEs, Sc, and positive correlations among Al2O3, TiO2, HFSEs and REE indicate that there was a significant terrigenous input. Even so, the Wangjiazhuang BIF samples display distinctively seawater-like REE+Y profiles, characterized by positive La and Y anomalies and HREE enrichment relative to LREE in PAAS-normalized REE diagrams. Consistently positive Eu anomalies are also observed, which are typically from high-T hydrothermal fluids. In addition, the true negative Ce anomalies recorded in the Wangjiazhuang BIF might indicate the onset of bottom-water oxidation at the Archean-Proterozoic boundary, at least in restricted basins. Amphibolites have geochemical affinity with both MORB- and arc-like components, and the trace element characteristics of leptynites are also consistent with a subduction zone signature. These features suggest that the Wangjiazhuang BIF was deposited in a back-arc basin. Oceanic subduction, coupled with contemporary depleted mantle upwelling related to back-arc basin extension, can account for the typical interaction between these two components.

Mathias S Egglseder - One of the best experts on this subject based on the ideXlab platform.

  • Tiny particles building huge ore deposits – Particle-based crystallisation in Banded Iron Formation-hosted Iron ore deposits (Hamersley Province, Australia)
    Ore Geology Reviews, 2020
    Co-Authors: Mathias S Egglseder, Alexander R Cruden, Hilke J Dalstra, Andrew G Tomkins, Siobhan A Wilson, Andrea Rielli, Chenghao Li, Jens Baumgartner, Damien Faivre
    Abstract:

    Abstract The world’s major source of Iron ore is hosted in Precambrian Banded Iron Formations. These chemical (meta-) sedimentary rocks are composed of alternating laminae of Iron oxide minerals and chert. Despite the economic significance of high-grade Iron ore deposits, controversy persists after decades of research on how Banded Iron Formations became upgraded to form Iron ore. The fundamental requirement for Iron ore Formation is the removal of vast amounts of chert coupled with an increased concentration of Iron oxide minerals. Here, we assess the fate of colloidal hematite inclusions encapsulated in chert after quartz dissolution and examine their role in the Formation of hematite ore. We have analysed hematite ores from the Hamersley Province (Australia) using a combination of petrography, high-resolution electron microscopy and X-ray diffraction. These techniques reveal the presence of abundant nano and microscale hematite particles that we suggest form the building blocks of larger hematite crystals within the Iron ore. Our textural observations indicate that hematite colloids that were previously encapsulated inside the microcrystalline quartz grains in chert layers are released during quartz dissolution, and subsequently reassemble in a self-similar fashion to from new microplaty hematite crystals via non-classical crystallisation pathways. Progressive growth and fusion leads to the transFormation of hematite microplates into hematite bands, which resemble pre-existing Iron oxide laminae of Banded Iron Formations. In contrast to previous models, we observe the direct transFormation of Banded Iron Formations to microplaty hematite and have not found evidence that significant amounts of hematite formed through metamorphism of goethite or that intermediate carbonate minerals were involved during the upgrading of Banded Iron Formations to pure hematite ore. Given the strong evidence for hypogene fluids found in many deposits, we have also assessed the role that such warm, highly saline fluids may have played during the evolution of Iron ore. Using insights from crystal chemistry we conclude that fluid infiltration impacts many aspects of Iron ore Formation by controlling hematite colloid liberation and aggregation, and finally controlling the transFormation of the colloids into macroscopic crystals of hematite via non-classical crystallisation mechanisms. Our study underlines the significance of hypogene fluids in the upgrading of Banded Iron Formation to Iron ore, however, we suggest that their influence was mainly passive as hematite was not precipitated directly from these fluids.

  • tiny particles building huge ore deposits particle based crystallisation in Banded Iron Formation hosted Iron ore deposits hamersley province australia
    Ore Geology Reviews, 2019
    Co-Authors: Mathias S Egglseder, Alexander R Cruden, Hilke J Dalstra, Andrew G Tomkins, Siobhan A Wilson, Andrea Rielli, Chenghao Li, Jens Baumgartner
    Abstract:

    Abstract The world’s major source of Iron ore is hosted in Precambrian Banded Iron Formations. These chemical (meta-) sedimentary rocks are composed of alternating laminae of Iron oxide minerals and chert. Despite the economic significance of high-grade Iron ore deposits, controversy persists after decades of research on how Banded Iron Formations became upgraded to form Iron ore. The fundamental requirement for Iron ore Formation is the removal of vast amounts of chert coupled with an increased concentration of Iron oxide minerals. Here, we assess the fate of colloidal hematite inclusions encapsulated in chert after quartz dissolution and examine their role in the Formation of hematite ore. We have analysed hematite ores from the Hamersley Province (Australia) using a combination of petrography, high-resolution electron microscopy and X-ray diffraction. These techniques reveal the presence of abundant nano and microscale hematite particles that we suggest form the building blocks of larger hematite crystals within the Iron ore. Our textural observations indicate that hematite colloids that were previously encapsulated inside the microcrystalline quartz grains in chert layers are released during quartz dissolution, and subsequently reassemble in a self-similar fashion to from new microplaty hematite crystals via non-classical crystallisation pathways. Progressive growth and fusion leads to the transFormation of hematite microplates into hematite bands, which resemble pre-existing Iron oxide laminae of Banded Iron Formations. In contrast to previous models, we observe the direct transFormation of Banded Iron Formations to microplaty hematite and have not found evidence that significant amounts of hematite formed through metamorphism of goethite or that intermediate carbonate minerals were involved during the upgrading of Banded Iron Formations to pure hematite ore. Given the strong evidence for hypogene fluids found in many deposits, we have also assessed the role that such warm, highly saline fluids may have played during the evolution of Iron ore. Using insights from crystal chemistry we conclude that fluid infiltration impacts many aspects of Iron ore Formation by controlling hematite colloid liberation and aggregation, and finally controlling the transFormation of the colloids into macroscopic crystals of hematite via non-classical crystallisation mechanisms. Our study underlines the significance of hypogene fluids in the upgrading of Banded Iron Formation to Iron ore, however, we suggest that their influence was mainly passive as hematite was not precipitated directly from these fluids.

  • the role of deFormation in the Formation of Banded Iron Formation hosted high grade Iron ore deposits hamersley province australia
    Precambrian Research, 2017
    Co-Authors: Mathias S Egglseder, Alexander R Cruden, Hilke J Dalstra, Leigh Nicholas
    Abstract:

    Abstract The Hamersley Province (Western Australia) hosts some of the world’s largest Iron ore deposits but despite decades of research, their genesis is still extensively debated. Many Iron ore deposits are hosted in complexly deformed Archean to Paleoproterozoic Banded Iron Formations, comprising thin chert and Iron oxide bands interlayered with silicate-rich shales and carbonates. Current Iron ore genesis models have identified a strong structural control on ore Formation linked to extensive hypogene and supergene fluid circulation along fault structures. These fluid pathways facilitate the removal of vast amounts of gangue minerals, leading to enrichment of the Iron oxide residue to Iron ore. However, the evolution of the associated structures has not yet been considered as a key element in ore genesis. Here we show through multiscale structural analyses that deFormation not only forms suitable fluid channels, but that folding and shearing also result in significant synkinematic removal of gangue minerals. Our multidisciplinary investigation of the structural evolution of the Mount Tom Price deposit combines microtectonic, field geology and 3D implicit modelling techniques to establish a link between deFormation structures at various scales. Microscale shear bands and outcrop-scale asymmetric parasitic folds share striking similarities in their evolution and their controlling mechanisms. Both features record substantial non-coaxial deFormation accompanied by volume changes due to stress-induced silica remobilisation. The closely spaced layering of rheologically different lithologies within Hamersley Province strata plays a crucial role in complex multilayer deFormation, which resulted in extensive strain partitioning. Our study suggests that deFormation was of major significance in the upgrading of Banded Iron Formation to Iron ore and was active from the early stages of Banded Iron Formation during diagenesis. DeFormation structures also established a micro- to deposit-scale lateral and vertical fluid network, which enabled infiltration by hypogene and supergene fluids during or after deFormation. These new insights have important implications for Iron ore genesis models, structural applications in the mine envIronment, and for understanding complex multilayer deFormation with volume loss.

Kurt O Konhauser - One of the best experts on this subject based on the ideXlab platform.

  • Using Ge/Si ratios to decouple Iron and silica fluxes in Precambrian Banded Iron Formations
    Geology, 2020
    Co-Authors: Tristan Hamade, Kurt O Konhauser, Robert Raiswell, Sarah Goldsmith, R.c. Morris
    Abstract:

    Banded Iron Formations are prominent sedimentary deposits of the Precambrian, yet the source of their silica remains unresolved. Here we show that Ge/Si ratios preserved in Banded Iron Formation chert layers are indicative of weathering of continental landmass. This conflicts with the accumulation of evidence suggesting that chemical components were sourced at mid-ocean-ridge hydrothermal systems. Instead, it implies that the sources of silica and Iron were decoupled during Banded Iron Formation deposition, silica being dominantly derived from weathering of continental landmass and Iron having a hydrothermal origin. Thus, the chemistry within Banded Iron Formation depositional basins underwent clear switching that varied on a periodic basis and is recorded in the alternation of Iron- to silica-rich layers.

  • earth s youngest Banded Iron Formation implies ferruginous conditions in the early cambrian ocean
    Scientific Reports, 2018
    Co-Authors: Zhiquan Li, Lianchang Zhang, Mengtian Zheng, Leslie J Robbins, John F Slack, Noah J Planavsky, Kurt O Konhauser
    Abstract:

    It has been proposed that anoxic and Iron-rich (ferruginous) marine conditions were common through most of Earth history. This view represents a major shift in our understanding of the evolution of marine chemistry. However, thus far, evidence for ferruginous conditions comes predominantly from Fe-speciation data. Given debate over these records, new evidence for Fe-rich marine conditions is a requisite if we are to shift our view regarding evolution of the marine redox landscape. Here we present strong evidence for ferruginous conditions by describing a suite of Fe-rich chemical sedimentary rocks-Banded Iron Formation (BIF)--deposited during the Early Cambrian in western China. Specifically, we provide new U-Pb geochronological data that confirm a depositional age of ca. 527 Ma for this unit, as well as rare earth element (REE) data are consistent with anoxic deposition. Similar to many Algoma-type Precambrian Iron Formations, these Early Cambrian sediments precipitated in a back-arc rift basin setting, where hydrothermally sourced Iron drove the deposition of a BIF-like protolith, the youngest ever reported of regional extent without direct links to volcanogenic massive sulphide (VMS) deposits. Their presence indicates that marine envIronments were still characterized by chemical- and redox-stratification, thus supporting the view that-despite a dearth of modern marine analogues-ferruginous conditions continued to locally be a feature of early Phanerozoic seawater.

  • decoupled sources of the 2 3 2 2ga yuanjiacun Banded Iron Formation implications for the nd cycle in earth s early oceans
    Precambrian Research, 2016
    Co-Authors: Changle Wang, Kurt O Konhauser, Lianchang Zhang, Mingguo Zhai, Wenjun Li
    Abstract:

    Abstract The recognized worldwide gap in BIF deposition between 2.4 and 2.0 billion years ago has long been considered as an obstacle to fully determining the geochemical composition of seawater at that time. However, the recently dated 2.3–2.2 Ga Yuanjiacun Banded Iron Formation (BIF) in the North China Craton (NCC) offers a possibility to redress these uncertainties. Shale-normalized rare earth element-yttrium (REE + Y) patterns of the BIF and interlayered meta-chert samples show features characteristic of other Archean and Paleoproterozoic BIFs, with HREE enrichment relative to LREE, positive La and Eu anomalies, and superchondritic Y/Ho ratios comparable to modern seawater. Very low Al 2 O 3 ( e Nd ( t ) ∼ +3.5) derived from interaction with a depleted mantle source and associated with high Fe fluxes. The second is ambient surface seawater ( e Nd ( t ) ∼ −2.4), which obtained its signature through weathering of the nearby landmasses and associated with high Si fluxes. Our findings suggest that the REE budget of the oceans prior to 2.3 Ga was generally dominated by hydrothermal circulation of seawater through depleted mantle-derived source rocks. However, where evolved local continental crust and/or an enriched mantle source were present, this positive mantle Nd signal became discernible in the BIFs. By comparing the Nd isotopic features of similar aged BIFs and marine carbonates, it is concluded that similar to modern oceans, the early Precambrian ocean was not well-mixed with respect to its Nd isotopic composition.

  • the joffre Banded Iron Formation hamersley group western australia assessing the palaeoenvIronment through detailed petrology and chemostratigraphy
    Precambrian Research, 2016
    Co-Authors: Rasmus Haugaard, Ernesto Pecoits, Stefan V Lalonde, Olivier Rouxel, Kurt O Konhauser
    Abstract:

    Abstract The Joffre Member of the Brockman Iron Formation is by volume the largest single known Banded Iron Formation (BIF) in the world. Here we present detailed petrology and chemostratigraphy through the entire 355 m core section of this ∼2.45 billion year old unit. Oxide BIF and silicate–carbonate–oxide BIF dominate the lithology, with minor amounts of interbedded stilpnomelane mudrock, stilpnomelane-rich tuffaceous mudrock and calcareous mudrock. Besides chert and magnetite, the prominent mineralogy is riebeckite, ankerite, hematite, stilpnomelane and crocidolite. The BIF is characterized by an average of 50 wt.% SiO 2 and 44.5 wt.% Fe 2 O 3 and an overall low abundance of Al 2 O 3 ( 2 ( SN of 0.24. The REY patterns also show a positive La SN anomaly, no Ce SN anomaly and a weakly developed positive Y SN anomaly. Iron isotopes (δ 56 Fe) with positive δ 56 Fe values of +0.04‰ to +1.21‰ suggest that a large part of the hydrothermal Iron was partly oxidized in the upper water column and subsequently precipitated as ferric oxyhydroxides. No epiclastic grains have been found; rather submarine hydrothermal fluids and fine-grained volcanogenic detritus controlled BIF chemistry. The former source is reflected through a constant positive Eu SN anomaly throughout the core (average Eu SN anomaly of 1.6 with a peak of 2.1 between 100 and 155 m depth), while the latter source is best reflected through the stilpnomelane-rich tuffaceous mudrock consisting of volcanic ash-fall tuff with relict shards set in a stilpnomelane matrix. The mudrock is overlain by well-preserved wavy laminae and laminae sets of stilpnomelane microgranules that likely originated from re-worked volcanic ash formed either on the seafloor or in the water column prior to deposition. An enriched HREE-to-LREE pattern, a high Iron content (∼30 wt.%), and a δ 56 Fe value of +0.59‰ collectively imply that the mudrock facies interacted with the Fe-rich seawater prior to deposition. The TiO 2 –Zr ratio of the BIF and the associated mudrocks suggest a felsic-only-source related to the same style of volcanics as the slightly younger Woongarra rhyolites. Given the observation that the dominant control on the seawater chemistry was associated with felsic volcanics, we speculate that the fine-grained pelagic ash particles may have sourced bio-available nutrients to the surface water. This would have facilitated enhanced biological productivity, including bacterial Fe(II)-oxidation which is now recorded as the positively fractionated 56 Fe Iron oxide minerals in the Joffre BIF. Alongside submarine hydrothermal input to the basin, the dominant control on the ocean chemistry seems to have been through volcanic and pyroclastic pathways, thereby making the Joffre BIF poorly suited as a chemical proxy for the study of atmospheric oxygen and its weathering impact on local landmasses.

  • depositional envIronment of the paleoproterozoic yuanjiacun Banded Iron Formation in shanxi province china
    Economic Geology, 2015
    Co-Authors: Changle Wang, Kurt O Konhauser, Lianchang Zhang
    Abstract:

    The Paleoproterozoic (~2.38–2.21 Ga) Yuanjiacun Banded Iron Formation (BIF), located in Shanxi Province, is a Superior-type BIF in the North China craton. This BIF is within a metasedimentary rock succession of the Yuanjiacun Formation, in the lower Luliang Group, which has undergone lower greenschist-facies metamor phism. Iron oxide (magnetite and hematite), carbonate, and silicate facies are all present within the Iron-rich layers. The eastward transition from carbonate- into oxide-facies Iron Formations is accompanied by a change in mineralogical composition from siderite in the west through magnetite-ankerite and magnetite-stilpnomelane assemblages in the transition zone to magnetite and then hematite in the east. These distinct lateral facies are also observed vertically within the BIF, i.e., the Iron mineral assemblage changes upsection from sider ite through magnetite into hematite-rich Iron Formation. The oxide-facies BIF formed near shore, whereas carbonate (siderite)- and silicate-facies assemblages formed in deeper waters. Based on detailed analyses of these variations on a basinal scale, the BIF precipitated during a transgressive event within an envIronment that ranged from deep waters below storm wave base to relatively shallow waters. The BIF samples display distinctively seawater-like REEs + Y profiles that are characterized by positive La and Y anomalies and HREEs enrichment relative to LREEs in Post-Archean Australian shale-normalized diagrams. Consistently positive Eu anomalies are also observed, which are typical of reduced, high-temperature hydrothermal fluids. In addition, slightly negative to positive Ce anomalies, and a large range in ratios of light to heavy REEs, are present in the oxide-facies BIF. These characteristics, in combination with consistently positive δ 56Fe values, suggest that deposition of the BIF took place along the chemocline where upwelling of deep, anoxic, Iron- and silicarich hydrothermal fluids mixed with shallower and slightly oxygenated seawater. The ankerite displays highly depleted δ13C values and the carbonate-rich BIF has a high content of organic carbon, suggesting dissimilatory Fe(III) reduction of a ferric oxyhydroxide precursor during burial of biomass deposited from the water column; that same biomass was likely tied to the original oxidation of dissolved Fe(II). The fact that the more ferric BIF facies formed in shallower waters suggests that river-sourced nutrients would have been minimal, thus limiting primary productivity in the shallow waters and minimizing the organic carbon source necessary for reducing the hematite via dissimilatory Fe(III) reduction. By contrast, in deeper waters more proximal to the hydrothermal vents, nutrients were abundant, and high biomass productivity was coupled to increased carbon burial, leading to the deposition of Iron-rich carbonates. The deposition of the Yuanjiacun BIF during the onset of the Great Oxidation Event (GOE; ca. 2.4–2.2 Ga) confirms that deep marine waters during this time period were still episodically ferruginous, but that shallow waters were sufficiently oxygenated that Fe(II) oxidation no longer needed to be tied directly to proximal cyanobacterial activity.

Changle Wang - One of the best experts on this subject based on the ideXlab platform.

  • changing provenance of late neoarchean metasedimentary rocks in the anshan benxi area north china craton implications for the tectonic setting of the world class dataigou Banded Iron Formation
    Gondwana Research, 2016
    Co-Authors: Changle Wang, Lianchang Zhang, Mengtian Zheng, Hua Huang, Xiaoxue Tong, Zidong Peng, Mingguo Zhai
    Abstract:

    Abstract The Anshan-Benxi (AnBen) area is situated in the northeastern part of the North China Craton and is considered to be the most important Iron metallogenic province in China. The giant Dataigou Banded Iron Formation (BIF) has the potential to be the largest Iron deposit in this area, even in Asia. Here, we present in situ zircon U–Pb-Hf-O isotopic and whole-rock geochemical data for metasedimentary rocks (metapelites and metaarenites) and trondhjemitic gneiss associated with this BIF, in order to provide constraints on the setting of the deposit, with implications for geological and exploration models. SIMS zircon U–Pb dating results indicate that the trondhjemitic gneiss crystallized at 3450 ± 19 Ma, and thus it is the oldest rock so far indentified in the Benxi area. The youngest group of detrital zircons from the metaarenite samples constrains their maximum depositional age at ~ 2.54 Ga. In combination with the earlier metamorphic age of ~ 2.51 Ga for the metaarenites, the deposition age of the Dataigou BIF can be constrained between 2.54 and 2.51 Ga. The metasediments have undergone varying degrees of source weathering. Source rocks of the metapelites have undergone moderate to severe chemical weathering, whereas those of the metaarenites have subjected to relatively weak chemical weathering. Diagnostic geochemical features such as the Al2O3/TiO2 values, trace element ratios, and REE patterns suggest that the metaarenites were predominantly derived from felsic igneous sources, whereas the metapelites were sourced mainly from mafic tholeiitic rocks. The dominant late Neoarchean detrital zircons further indicate that they were most likely sourced from almost synchronous volcanic rocks in the AnBen area. Taking into account the lithostratigraphic, geochemical, and geochronological data, the Dataigou BIF is interpreted as having been deposited in a back-arc basin, most probably on the margin of an ancient continental crust. Continuous provenance variations of these metasediments during highstand times and transgression can be ascribed to changes in natures of nearby volcanisms. Integrated with previous zircon Hf isotopic data from other supracrustal rocks in the AnBen area, our Hf-O data reveal major juvenile crustal growth stages at 3.0 Ga and during 2.8–2.7 Ga, and a crustal reworking event with minor juvenile addition at ~ 2.5 Ga in the studied area.

  • decoupled sources of the 2 3 2 2ga yuanjiacun Banded Iron Formation implications for the nd cycle in earth s early oceans
    Precambrian Research, 2016
    Co-Authors: Changle Wang, Kurt O Konhauser, Lianchang Zhang, Mingguo Zhai, Wenjun Li
    Abstract:

    Abstract The recognized worldwide gap in BIF deposition between 2.4 and 2.0 billion years ago has long been considered as an obstacle to fully determining the geochemical composition of seawater at that time. However, the recently dated 2.3–2.2 Ga Yuanjiacun Banded Iron Formation (BIF) in the North China Craton (NCC) offers a possibility to redress these uncertainties. Shale-normalized rare earth element-yttrium (REE + Y) patterns of the BIF and interlayered meta-chert samples show features characteristic of other Archean and Paleoproterozoic BIFs, with HREE enrichment relative to LREE, positive La and Eu anomalies, and superchondritic Y/Ho ratios comparable to modern seawater. Very low Al 2 O 3 ( e Nd ( t ) ∼ +3.5) derived from interaction with a depleted mantle source and associated with high Fe fluxes. The second is ambient surface seawater ( e Nd ( t ) ∼ −2.4), which obtained its signature through weathering of the nearby landmasses and associated with high Si fluxes. Our findings suggest that the REE budget of the oceans prior to 2.3 Ga was generally dominated by hydrothermal circulation of seawater through depleted mantle-derived source rocks. However, where evolved local continental crust and/or an enriched mantle source were present, this positive mantle Nd signal became discernible in the BIFs. By comparing the Nd isotopic features of similar aged BIFs and marine carbonates, it is concluded that similar to modern oceans, the early Precambrian ocean was not well-mixed with respect to its Nd isotopic composition.

  • depositional envIronment of the paleoproterozoic yuanjiacun Banded Iron Formation in shanxi province china
    Economic Geology, 2015
    Co-Authors: Changle Wang, Kurt O Konhauser, Lianchang Zhang
    Abstract:

    The Paleoproterozoic (~2.38–2.21 Ga) Yuanjiacun Banded Iron Formation (BIF), located in Shanxi Province, is a Superior-type BIF in the North China craton. This BIF is within a metasedimentary rock succession of the Yuanjiacun Formation, in the lower Luliang Group, which has undergone lower greenschist-facies metamor phism. Iron oxide (magnetite and hematite), carbonate, and silicate facies are all present within the Iron-rich layers. The eastward transition from carbonate- into oxide-facies Iron Formations is accompanied by a change in mineralogical composition from siderite in the west through magnetite-ankerite and magnetite-stilpnomelane assemblages in the transition zone to magnetite and then hematite in the east. These distinct lateral facies are also observed vertically within the BIF, i.e., the Iron mineral assemblage changes upsection from sider ite through magnetite into hematite-rich Iron Formation. The oxide-facies BIF formed near shore, whereas carbonate (siderite)- and silicate-facies assemblages formed in deeper waters. Based on detailed analyses of these variations on a basinal scale, the BIF precipitated during a transgressive event within an envIronment that ranged from deep waters below storm wave base to relatively shallow waters. The BIF samples display distinctively seawater-like REEs + Y profiles that are characterized by positive La and Y anomalies and HREEs enrichment relative to LREEs in Post-Archean Australian shale-normalized diagrams. Consistently positive Eu anomalies are also observed, which are typical of reduced, high-temperature hydrothermal fluids. In addition, slightly negative to positive Ce anomalies, and a large range in ratios of light to heavy REEs, are present in the oxide-facies BIF. These characteristics, in combination with consistently positive δ 56Fe values, suggest that deposition of the BIF took place along the chemocline where upwelling of deep, anoxic, Iron- and silicarich hydrothermal fluids mixed with shallower and slightly oxygenated seawater. The ankerite displays highly depleted δ13C values and the carbonate-rich BIF has a high content of organic carbon, suggesting dissimilatory Fe(III) reduction of a ferric oxyhydroxide precursor during burial of biomass deposited from the water column; that same biomass was likely tied to the original oxidation of dissolved Fe(II). The fact that the more ferric BIF facies formed in shallower waters suggests that river-sourced nutrients would have been minimal, thus limiting primary productivity in the shallow waters and minimizing the organic carbon source necessary for reducing the hematite via dissimilatory Fe(III) reduction. By contrast, in deeper waters more proximal to the hydrothermal vents, nutrients were abundant, and high biomass productivity was coupled to increased carbon burial, leading to the deposition of Iron-rich carbonates. The deposition of the Yuanjiacun BIF during the onset of the Great Oxidation Event (GOE; ca. 2.4–2.2 Ga) confirms that deep marine waters during this time period were still episodically ferruginous, but that shallow waters were sufficiently oxygenated that Fe(II) oxidation no longer needed to be tied directly to proximal cyanobacterial activity.

  • petrology and geochemistry of the wangjiazhuang Banded Iron Formation and associated supracrustal rocks from the wutai greenstone belt in the north china craton implications for their origin and tectonic setting
    Precambrian Research, 2014
    Co-Authors: Changle Wang, Lianchang Zhang
    Abstract:

    Abstract The Wutai greenstone belt (WGB) is one of the most extensively studied greenstone belts in China. Together with the Hengshan and Fuping complexes, these three associations compose the central segment of the Trans-North China Orogen (TNCO) in the North China Craton (NCC). The Wangjiazhuang Banded Iron Formation (BIF) is located in the bottom of the Jingangku Formation of the WGB. The associated supracrustal rocks consist of meta-basalts (amphibolites), meta-felsic volcanic rocks (leptynite) and metapelites (mica schist), which have experienced amphibolite-facies metamorphism. Amphibolites are commonly intercalated with the BIF. SIMS zircon U–Pb analyses on amphibolites suggest that the Wangjiazhuang BIF was formed at ca. 2543 ± 4 Ma. Combined with most Neoarchean Algoma-type BIFs in the NCC, these features indicate that a significant tectothermal event of the NCC have occurred at ∼2.5 Ga. Mineral assemblages of the Wangjiazhuang BIF are composed of quartz, magnetite, amphibole, and minor garnet, pyrite and calcite. The precursor deposits of this BIF were likely ferric-oxyhydroxides, fine-grained carbonate oozes, silicate phases rich in Al–Ca–Mg–Fe and amorphous silica. The appearance of garnet and ferro-pargasite, high concentrations of Al2O3, HFSEs, Sc, and positive correlations among Al2O3, TiO2, HFSEs and REE indicate that there was a significant terrigenous input. Even so, the Wangjiazhuang BIF samples display distinctively seawater-like REE+Y profiles, characterized by positive La and Y anomalies and HREE enrichment relative to LREE in PAAS-normalized REE diagrams. Consistently positive Eu anomalies are also observed, which are typically from high-T hydrothermal fluids. In addition, the true negative Ce anomalies recorded in the Wangjiazhuang BIF might indicate the onset of bottom-water oxidation at the Archean-Proterozoic boundary, at least in restricted basins. Amphibolites have geochemical affinity with both MORB- and arc-like components, and the trace element characteristics of leptynites are also consistent with a subduction zone signature. These features suggest that the Wangjiazhuang BIF was deposited in a back-arc basin. Oceanic subduction, coupled with contemporary depleted mantle upwelling related to back-arc basin extension, can account for the typical interaction between these two components.

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  • invisible gold in pyrite from epithermal Banded Iron Formation hosted and sedimentary gold deposits evidence of hydrothermal influence
    Minerals, 2019
    Co-Authors: Yuichi Morishita, Napoleon Q Hammond, Kazunori Momii, Rimi Konagaya, Yuji Sano, Naoto Takahata, Hirotomo Ueno
    Abstract:

    “Invisible gold” in pyrite is defined as an Au solid solution of the pyrite lattice, sub-microscopic Au nanoparticles (NPs) in the pyrite, or other chemisorption complexes of Au. Because the relationship between the Au and As concentrations in pyrite could indicate the genesis of the deposit, the purpose of this study is to assess the micro-analytical characteristics of the Au–As relationship in pyrite from epithermal and hydrothermally affected sedimentary Au deposits by secondary ion mass spectrometry. The Au and As concentrations in pyrite vary from 0.04 to 30 ppm and from 1 to 1000 ppm, respectively, in the high-sulfidation Nansatsu-type epithermal deposits; these concentrations are both lower than those of the low-sulfidation epithermal Hishikari deposit. The Au concentrations in pyrrhotite and pyrite reach 6 and 0.3 ppm, respectively, in the Kalahari Goldridge Banded-Iron-Formation-hosted gold deposit, and Au in pyrrhotite may sometimes exist as NPs, whereas As concentrations in pyrrhotite and pyrite are both low and lie in a narrow range from 6 to 22 ppm. Whether Au is present as NPs is important in ore dressing. The Au and As concentrations in pyrite from the Witwatersrand gold field range from 0.02 to 1.1 ppm and from 8 to 4000 ppm, respectively. The shape of the pyrite grains might prove to be an indicator of the hydrothermal influence on deposits of sedimentary origin, which implies the genesis of the deposits.

  • gold mineralization in Banded Iron Formation in the amalia greenstone belt south africa a mineralogical and sulfur isotope study
    Resource Geology, 2013
    Co-Authors: Kofi Adomakoansah, Napoleon Q Hammond, Toshio Mizuta, Daizo Ishiyama, Takeyuki Ogata, Hitoshi Chiba
    Abstract:

    The Blue Dot gold deposit, located in the Archean Amalia greenstone belt of South Africa, is hosted in an oxide (± carbonate) facies Banded Iron Formation (BIF). It consists of three stratabound orebodies; Goudplaats, Abelskop, and Bothmasrust. The orebodies are flanked by quartz-chlorite-ferroan dolomite-albite schist in the hanging wall and mafic (volcanic) schists in the footwall. Alteration minerals associated with the main hydrothermal stage in the BIF are dominated by quartz, ankerite-dolomite series, siderite, chlorite, muscovite, sericite, hematite, pyrite, and minor amounts of chalcopyrite and arsenopyrite. This study investigates the characteristics of gold mineralization in the Amalia BIF based on ore textures, mineral-chemical data and sulfur isotope analysis. Gold mineralization of the Blue Dot deposit is associated with quartz-carbonate veins that crosscut the BIF layering. In contrast to previous works, petrographic evidence suggests that the gold mineralization is not solely attributed to replacement reactions between ore fluid and the magnetite or hematite in the host BIF because coarse hydrothermal pyrite grains do not show mutual replacement textures of the oxide minerals. Rather, the parallel-bedded and generally chert-hosted pyrites are in sharp contact with re-crystallized euhedral to subhedral magnetite ± hematite grains, and the nature of their coexistence suggests that pyrite (and gold) precipitation was contemporaneous with magnetite–hematite re-crystallization. The Fe/(Fe+Mg) ratio of the dolomite–ankerite series and chlorite decreased from veins through mineralized BIF and non-mineralized BIF, in contrast to most Archean BIF-hosted gold deposits. This is interpreted to be due to the effect of a high sulfur activity and increase in fO2 in a H2S-dominant fluid during progressive fluid-rock interaction. High sulfur activity of the hydrothermal fluid fixed pyrite in the BIF by consuming Fe2+ released into the chert layers and leaving the co-precipitating carbonates and chlorites with less available ferrous Iron content. Alternatively, the occurrence of hematite in the alteration assemblage of the host BIF caused a structural limitation in the assignment of Fe3+ in chlorite which favored the incorporation of magnesium (rather than ferric Iron) in chlorite under increasing fO2 conditions, and is consistent with deposits hosted in hematite-bearing rocks. The combined effects of reduction in sulfur contents due to sulfide precipitation and increasing fO2 during progressive fluid-rock interactions are likely to be the principal factors to have caused gold deposition. Arsenopyrite–pyrite geothermometry indicated a temperature range of 300–350°C for the associated gold mineralization. The estimated δ34SΣS (= +1.8 to +2.5‰) and low base metal contents of the sulfide ore mineralogy are consistent with sulfides that have been sourced from magma or derived by the dissolution of magmatic sulfides from volcanic rocks during fluid migration.

  • archaean lode gold mineralisation in Banded Iron Formation at the kalahari goldridge deposit kraaipan greenstone belt south africa
    Mineralium Deposita, 2006
    Co-Authors: Napoleon Q Hammond, J M Moore
    Abstract:

    The Kalahari Goldridge Mine is located within the Archaean Kraaipan Greenstone Belt, about 60 km southwest of Mafikeng in the North West Province, South Africa. The ore body thickness varies from 15 to 45 m along a strike length of about 1.5 km within approximately N–S striking Banded Iron Formation (BIF). The stratabound ore body is hosted primarily by BIF, which consists of alternating chert and magnetite–chlorite–stilpnomelane–sulphide–carbonate bands of millimetre- to centimetre scale. A footwall of sericite–carbonate–chlorite schist underlain by mafic amphibolite occurs to the west and carbonaceous metapelites in the hanging wall to the east. Overlying the hanging wall, carbonaceous metapelites, units of coarse-grained metagreywackes fining upwards, become increasingly conglomeratic up the stratigraphy. Small-scale isoclinal folds, brecciation, extension fractures and boudinage of cherty BIF units reflect brittle-ductile deFormation. Fold axial planes have foliation, with subvertical plunges parallel to prominent rodding and mineral lineation in the footwall rocks. Gold mineralisation is associated with two generations of quartz–carbonate veins, dipping approximately 20° to 40° W. The first generation consists of ladder-vein sets (group IIA) preferentially developed in centimetre-scale Fe-rich mesobands, whereas the second generation consists of large quartz–carbonate veins (group IIB), which locally crosscut the entire ore body and extend into the footwall and hanging wall. The ore body is controlled by mesoscale isoclinal folds approximately 67° E, orthogonal to the plane of mineralised, gently dipping veins, defining the principal stretching direction and development of fluid-focussing conduits. The intersections of the mineralised veins and foliation planes of the host rock plunges approximately 08° to the north. Pervasive hydrothermal alteration is characterised by chloritisation, carbonatisation, sulphidation and K-metasomatism. Gold is closely associated with sulphides, mainly pyrite and pyrrhotite, and to a lesser extent, with bismuth tellurides and carbonate minerals. Mass balance transfer calculations indicate that hydrothermal alteration of BIF involved enrichment of Au, Ag, Bi, Te, S and CO2 (LOI), MgO, Ba, K and Rb, but significant depletion of SiO2 and, to a lesser extent, Fe2O3. Extensive replacement of magnetite and chlorite in BIF and other pelitic sedimentary rocks by sulphide and carbonate minerals, both on mesoscopic and microscopic scales, is evidence of interaction of CO2- and H2S-bearing fluids with the Fe-rich host rocks. The fineness of gold grains ranges from 823 to 921, similar to that of other epigenetic Archaean BIF-hosted gold deposits, worldwide.