scholarly journals Depositional Environment and Genesis of the Nabeba Banded Iron Formation (BIF) in the Ivindo Basement Complex, Republic of the Congo: Perspective from Whole-Rock and Magnetite Geochemistry

Minerals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 579
Author(s):  
Chesther Gatsé Ebotehouna ◽  
Yuling Xie ◽  
Kofi Adomako-Ansah ◽  
Blandine Gourcerol ◽  
Yunwei Qu
Keyword(s):  
High Temperature ◽  
Distribution Patterns ◽  
Iron Formation ◽  
Iron Deposit ◽  
Northwestern Part ◽  
Banded Iron Formation ◽  
Basement Complex ◽  
Icp Ms ◽  
Post Archean Australian Shale ◽  
Republic Of The Congo

The Nabeba high-grade iron deposit (Republic of the Congo) is hosted by banded iron formation (BIF) in the Ivindo Basement Complex, which lies in the northwestern part of the Congo Craton. The Nabeba BIF is intercalated with chlorite-sericite-quartz schist and comprises two facies (oxide and a carbonate-oxide). In this study, whole-rock and LA-ICP-MS magnetite geochemistry of the BIF was reported. Magnetite samples from both BIF facies had fairly similar trace element compositions except for the rare earth element plus yttrium (REE + Y) distribution patterns. The high V, Ni, Cr, and Mg contents of the magnetite in the Nabeba BIF could be ascribed to the involvement of external medium-high temperature hydrothermal fluids during their deposition in relatively reduced environment. The Post-Archean Australian Shale (PAAS)-normalized REY patterns of the Nabeba BIF magnetite were characterized by LREE depletion coupled with varying La and positive Eu anomalies. Processing of the information gathered from the geochemical signatures of magnetite and the whole-rock BIF suggested that the Nabeba BIF was formed by the mixing of predominantly anoxic seawater (99.9%) with 0.1% of high-temperature (>250 °C) hydrothermal vent fluids, similar to the formation mechanism of many Archean Algoma-type BIFs reported elsewhere in the world.

scholarly journals Petrography and Geochemistry of the Banded Iron Formation of the Gangfelum Area, Northeastern Nigeria

2017 ◽  
Vol 7 (1) ◽  
pp. 25
Author(s):  
Anthony Temidayo Bolarinwa
Keyword(s):  
Iron Oxide ◽  
Inductively Coupled Plasma ◽  
Optical Emission ◽  
Iron Formation ◽  
Icp Oes ◽  
Banded Iron Formation ◽  
Basement Complex ◽  
Inductively Coupled ◽  
Iron Precipitation ◽  
Icp Ms

The Gangfelum Banded Iron Formation (BIF) is located within the basement complex of northeastern Nigeria. It is characterized by alternate bands of iron oxide and quartz. Petrographic studies show that the BIF consist mainly of hematite, goethite subordinate magnetite and accessory minerals including rutile, apatite, tourmaline and zircon. Chemical data from inductively coupled plasma optical emission spectrometer (ICP-OES) and inductively coupled plasma mass spectrometer (ICP-MS) show that average Fe2O3(t) is 53.91 wt.%. The average values of Al2O3 and CaO are 1.41 and 0.05 wt.% respectively, TiO2 and MnO are less than 0.5 wt. % each. The data suggested that the BIF is the oxide facies type. Trace element concentrations of Ba (67-332 ppm), Ni (28-35 ppm), Sr (13-55 ppm) and Zr (16-25 ppm) in the Gangfelum BIF are low and similar to the Maru and Muro BIF in northern Nigeria and also the Algoma iron formation from North America, the Orissa iron oxide facies of India and the Itabirite from Minas Gerais in Brazil. The evolution of the Gangfelum BIF involved metamorphism of chemically precipitated or rhythmically deposited iron-rich sediments into hematite-quartz rocks. The banding of the BIF suggested a break in iron precipitation probably due to iron oxide deficiency. 

Polynomial-based density inversion of gravity anomalies for concealed iron-deposit exploration in North China

Geophysics ◽  
2019 ◽  
Vol 84 (5) ◽  
pp. B325-B334 ◽  
Author(s):  
Jie Liu ◽  
Jianzhong Zhang ◽  
Li Jiang ◽  
Qi Lin ◽  
Li Wan
Keyword(s):  
North China ◽  
Gravity Anomalies ◽  
Iron Formation ◽  
Iron Deposit ◽  
Polynomial Functions ◽  
Banded Iron Formation ◽  
Linear Inversion ◽  
Density Mapping ◽  
Ore Bodies ◽  
Approximate Distribution

Inversion of residual gravity anomalies is an important geophysical technique for depicting subsurface density contrasts, for example, for mineral deposits. We have expressed subsurface density variations using depth-variable polynomial functions and developed the polynomial coefficient inversion (PCI) method, which is an alternative method for mapping subsurface density distributions by inverting the coefficients of density-contrast functions. PCI enables the linear inversion of density variations without vertically subdividing the subsurface. Synthetic tests indicate that PCI combines polynomial functions and multiple constraints to highlight the anomalous masses through an iterative process with appropriate weighting parameters. We apply our method to a local investigation of banded iron formation (BIF) deposits in the Hebei Province, North China. The inversion results depict the approximate distribution of the subsurface density contrasts to identify the stratigraphic boundaries of different lithologies and BIF-favorable zones, thus implying that local iron-rich ore bodies may be located at the syncline axis or dip along the faults. The successful application of PCI for the BIF deposits indicates that this method is a promising strategy for density mapping.

scholarly journals Fluid Inclusion and Oxygen Isotope Characteristics of Vein Quartz Associated with the Nabeba Iron Deposit, Republic of Congo: Implications for the Enrichment of Hypogene Ores

Minerals ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 677
Author(s):  
Ebotehouna ◽  
Xie ◽  
Adomako-Ansah ◽  
Pei
Keyword(s):  
Iron Ore ◽  
Early Stage ◽  
Laser Raman Spectroscopy ◽  
Iron Formation ◽  
Iron Deposit ◽  
Banded Iron Formation ◽  
Republic Of Congo ◽  
Ore Deposit ◽  
Laser Raman ◽  
Ore Mineralization

The Nabeba iron ore deposit is located at the northern part of Congo Craton, Republic of Congo. The ore deposit consists of supergene and hypogene ores, both of which are hosted in the Precambrian Nabeba banded iron formation (BIF). This study focuses on the hypogene iron ore mineralization associated with quartz veins in the Nabeba deposit, for which two hypogene ore stages have been recognized based on geologic and petrographic observations: early-stage high‐grade hematite‐rich ore (HO‐1) and late-stage magnetite‐rich ore (HO‐2). Based on microthermometric measurements and laser Raman spectroscopy of the fluid inclusions, the H2O‐NaCl ± CO2 fluids interacting with the Nabeba BIF at the HO‐1 stage evolve from high‐to‐moderate temperatures (203–405 °C) and contrasting salinities (moderate-to-low: 1–15 wt. % NaCl equiv.; high: 30–35 wt. % NaCl equiv.) to H2O‐NaCl fluids of moderate‐to‐low temperatures (150–290 °C) and salinities (1–11 wt. % NaCl equiv.) for the HO‐2 ore stage. Assuming equilibrium oxygen isotopic exchange between quartz and water, the δ18Ofluid values range from 4.7–8.1‰ for the HO‐1 stage and −2.3‰ to −1.5‰ for the HO‐2 stage. This implies the ore‐forming fluid of initially-mixed metamorphic–magmatic origin, later replenished by seawater and/or meteoric water during the formation of the HO‐2 stage. These mixtures of different fluids, coupled with their interaction with the BIF lithology followed by phase separation, are responsible for the enrichment of hypogene iron ore in the Nabeba deposit.

scholarly journals ESTUDOS GEOQUÍMICOS DE ITABIRITOS DA SERRA DO SAPO, ESPINHAÇO MERIDIONAL, MINAS GERAIS

2014 ◽  
Author(s):  
Amanda A. Pires e Souza ◽  
Rosaline Cristina Figueiredo e Silva ◽  
Carlos Alberto Rosière ◽  
Geraldo Sarquis Dias ◽  
Fernando Prudêncio Morais
Keyword(s):  
High Temperature ◽  
Iron Ore ◽  
Morphological Characteristics ◽  
Minas Gerais ◽  
Iron Formation ◽  
Geochemical Analysis ◽  
East Side ◽  
Banded Iron Formation ◽  
Geochemical Studies ◽  
The City

A Serra do Sapo localiza-se na porção leste da Serra do Espinhaço Meridional, nas proximidades do município de Conceição do Mato Dentro, Minas Gerais, Brasil. Nessa região, formações ferríferas bandadas são metamorfizadas e intensamente cisalhadas. De acordo com o grau de intemperismo e compacidade, minérios de ferro com teores entre 31 e 39% Fe são classificados em itabirito, itabirito semifriável e itabirito friável. Cristais de hematita são classificados de acordo com suas características texturais e morfológicas em microlamelar, anédrica, lamelar e martita. Análises químicas de rocha total mostram que os três tipos de itabirito são semelhantes com conteúdo de CaO (≤0,14wt%), MgO (≤ 0,04wt%), MnO (≤ 0,21wt%), Al2O3 (≤ 0,94wt%), K2O (≤ 0,27wt%), TiO2 (≤ 0,05wt%) e P2O5 (≤ 0,11wt%), entretanto com as maiores concentrações de Al2O3, MgO e K2O presentes nos itabiritos semifriável e friável, e as de CaO e P2O5 no itabirito. O teor em U autigênico, e as relações V/Cr e Ni/Co do itabirito apontam para um ambiente de sedimentação oxidante para a formação ferrífera bandada. Razões (Eu/Sm)SN, (La/Sm)CN, (Sm/Yb)SN, (Eu/Eu*)SN, e (Sm/Yb)CN indicam que a formação ferrífera bandada mais fresca, representada pelo itabirito, está livre de contaminação clástica. Já as razões de Sm/Yb vs. Eu/Sm e de Eu/Eu*(CN) vs. (Sm/Yb)(CN) indicam contribuição insignificante por fluidos hidrotermais de alta temperatura.Palavras Chave: Serra do Sapo; Serra do Espinhaço Meridional; Formação ferrífera bandada; Geoquímica. Abstract: GEOCHEMICAL STUDIES OF ITABIRITES FROM SERRA DO SAPO, SOUTHERN ESPINHAÇO, MINAS GERAIS. The Serra do Sapo is located on east side of the southern portion of Serra do Espinhaço, near the city of Conceição do Mato Dentro, Minas Gerais, Brazil. In the area banded iron formation are metamorphosed and slightly sheared. Supergene low to medium- grade iron ore (31 to 39% Fe) are classified in itabirite, semi-friable itabirite and friable or soft itabirite, according to the degree of weathering and compactness. Hematite crystals were classified after their textural and morphological characteristics as: microplaty, anhedral, platy, and martite (pseudomorphic after magnetite). Geochemical analysis show that the three types of itabirites are similar regarding the content of CaO (≤ 0,14wt%), MgO (≤ 0,04wt%), MnO (≤ 0,21wt%), Al2O3 (≤ 0,94wt%), K2O (≤ 0,27wt%), TiO2 (≤ 0,05wt%) e P2O5 (≤ 0,11wt%), with higher grades of Al2O3, MgO and K2O present in semi-friable and friable itabirites and, of CaO and P2O5 in itabirite. The autigenic U, V/Cr and Ni/Co indexes point to an oxic environment of sedimentation. Ratios of (Eu/Sm)SN, (La/Sm)CN, (Sm/Yb)SN, (Eu/Eu*)SN, and (Sm/Yb)CN indicate that the banded iron formation represented by the itabirite is free of clastic contamination and the ratios of Sm/Yb vs. Eu/Sm and of Eu/Eu*(CN) vs. (Sm/Yb)(CN) indicate insignificant contribution of high temperature hydrothermal fluids.Keywords: Serra do Sapo; Serra do Espinhaço Meridional; Banded iron formation; Geochemistry.

The Central Slave Basement Complex, Part I: its structural topology and autochthonous cover

1999 ◽  
Vol 36 (7) ◽  
pp. 1083-1109 ◽  
Author(s):  
Wouter Bleeker ◽  
John WF Ketchum ◽  
Valerie A Jackson ◽  
Michael E Villeneuve
Keyword(s):  
Detrital Zircon ◽  
Hanging Wall ◽  
Volcanic Rocks ◽  
Iron Formation ◽  
Structural Topology ◽  
Banded Iron Formation ◽  
Basement Complex ◽  
South Central ◽  
Slave Province ◽  
Lake Formation

New field and geochronological data are used to define the distribution of Mesoarchean basement rocks in the south-central Slave Province. This distribution reflects a single contiguous basement terrane that we propose to call the Central Slave Basement Complex. It shows a structural topology that is internally consistent and compatible with known regional folding and faulting events. A sample of a proposed basement gneiss below the Courageous Lake greenstone belt, central Slave Province, has been dated by U-Pb methods and yields an age of 3325 ± 8 Ma, consistent with the new basement distribution. This sample also contains 2723 ± 3 Ma metamorphic zircon and ca. 2680 Ma titanite. The Central Slave Basement Complex is overlain by a thin, discontinuous, but distinctive cover sequence that includes minor volcanic rocks, clastic sedimentary rocks, and banded iron formation. All previously known and some new occurrences of this distinctive cover sequence occur in the immediate stratigraphic hanging wall of the Central Slave Basement Complex, locally overlying a preserved in situ unconformity. We propose to call this post-2.93 Ga cover sequence the Central Slave Cover Group. It is perhaps best typified by detrital chromite-bearing, fuchsitic quartzites. Formal formation names are proposed for the spatially separate occurrences of the Central Slave Cover Group. Detrital zircon ages are presented for one of the formations of the Central Slave Cover Group, the Patterson Lake Formation, which occurs on the western flank of a local basement culmination known as the Sleepy Dragon Complex. The detrital zircon data provide evidence for two discrete basement sources dated at ca. 2943 Ma and ca. 3147-3160 Ma. These detrital ages reinforce the depositional link between the Central Slave Cover Group and underlying crystalline rocks of the Central Slave Basement Complex.

The Central Slave Basement Complex, Part II: age and tectonic significance of high-strain zones along the basement-cover contact

1999 ◽  
Vol 36 (7) ◽  
pp. 1111-1130 ◽  
Author(s):  
Wouter Bleeker ◽  
John WF Ketchum ◽  
W J Davis
Keyword(s):  
High Strain ◽  
Volcanic Rocks ◽  
Iron Formation ◽  
Banded Iron Formation ◽  
Basement Complex ◽  
Maximum Displacement ◽  
Regional Deformation ◽  
Slave Province ◽  
Group A ◽  
Extensional Model

The basement-cover high-strain zone enveloping parts of the Sleepy Dragon Complex, northeast of Yellowknife, Slave Province, Canada, has been reinvestigated. Integrated stratigraphic, structural, and geochronological data show that the high-strain zone is of regional extent and is best interpreted as a décollement between crystalline, ca. 2.9-3.3 Ga rocks of the Central Slave Basement Complex and pre-2687 Ma cover rocks. Three temporally distinct mafic dyke swarms occur within the high-strain zone. The two oldest of these constrain the timing of the high-strain event to between 2734 ± 2 and 2687 ± 1 Ma. At the time of décollement development, the cover stratigraphy consisted of (i) the Central Slave Cover Group, a thin, pre-2734 Ma succession of mafic and ultramafic volcanic rocks, conglomerates, fuchsitic quartzites, minor rhyolites, and banded iron formation; and (ii) an overlying sequence of tholeiitic pillow basalts. The Central Slave Cover Group is considered to be autochthonous, whereas a variety of evidence suggests that the pillow basalts are parautochthonous to possibly allochthonous. The transport direction in the décollement was from northeast to southwest, and maximum displacement was probably on the order of 10 to several tens of kilometres. Presently, the décollement appears discontinuous due to younger intrusive and erosional events. Around most of the southern flanks of the Sleepy Dragon Complex, the crystalline core of the complex consists of post-décollement intrusive rocks and (or) is unconformably overlain by parts of the Yellowknife Supergroup that are younger than 2687 Ma. Lineation patterns in these younger rocks reflect regional deformation events that postdate and are unrelated to the décollement. The new data allow two tectonic models for development of the décollement: (i) a contractional thrusting model, involving collision of an eastern Slave Province arc terrane; or (ii) a syn-greenstone belt extensional model.

Earth’s Middle Ages: What Came after the GOE

2017 ◽  
Author(s):  
Donald Eugene Canfield
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Middle Ages ◽  
Atmospheric Oxygen ◽  
Iron Formation ◽  
Banded Iron Formation ◽  
Dissolved Iron ◽  
Great Oxidation Event ◽  
Low Levels ◽  
Substantial Rise

This chapter considers the aftermath of the great oxidation event (GOE). It suggests that there was a substantial rise in oxygen defining the GOE, which may, in turn have led to the Lomagundi isotope excursion, which was associated with high rates of organic matter burial and perhaps even higher concentrations of oxygen. This excursion was soon followed by a crash in oxygen to very low levels and a return to banded iron formation deposition. When the massive amounts of organic carbon buried during the excursion were brought into the weathering environment, they would have represented a huge oxygen sink, drawing down levels of atmospheric oxygen. There appeared to be a veritable seesaw in oxygen concentrations, apparently triggered initially by the GOE. The GOE did not produce enough oxygen to oxygenate the oceans. Dissolved iron was removed from the oceans not by reaction with oxygen but rather by reaction with sulfide. Thus, the deep oceans remained anoxic and became rich in sulfide, instead of becoming well oxygenated.

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