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 Unsupervised geochemical classification and automatic 3D mapping of the Bolshetroitskoe high-grade iron ore deposit (Belgorod Region, Russia)

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Andrey O. Kalashnikov ◽  
Ivan I. Nikulin ◽  
Dmitry G. Stepenshchikov
Keyword(s):  
Iron Ore ◽  
Geological Mapping ◽  
Iron Formation ◽  
Geochemical Data ◽  
High Grade ◽  
Banded Iron Formation ◽  
Raw Data ◽  
Ore Deposit ◽  
Iron Ore Deposit ◽  
Log Ratio

Abstract We stated and solved three successive problems concerning automatization of geological mapping using the case of the Bolshetroitskoe high-grade iron ore deposit in weathered crust of Banded Iron Formation (Kursk Magnetic Anomaly, Belgorod Region, Russia). (1) Selecting a classification (clustering) method of geochemical data without reference sampling, i.e., solution of an “unsupervised clustering task”. We developed 5 rock classifications based on different principles, i.e., classification by visual description, by distribution of economic component (Fe2O3), by cluster analysis of raw data and centered log-ratio transformation of the raw data, and by artificial neural network (Kohonnen’s self-organized map). (2) Non-parametric comparison of quality of the classifications and revealing the best one. (3) Automatic 3D geological mapping in accordance with the best classification. The developed approach of automatic 3D geological mapping seems to be rather simple and plausible.

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.

Microstructures in a banded iron formation (Gua mine, India)

2007 ◽  
Vol 144 (2) ◽  
pp. 271-287 ◽  
Author(s):  
MANISH A. MAMTANI ◽  
A. MUKHERJI ◽  
A. K. CHAUDHURI
Keyword(s):  
Iron Ore ◽  
Iron Formation ◽  
Eastern India ◽  
Banded Iron Formation ◽  
Rigid Core ◽  
Quartz Veins ◽  
Planar Structures ◽  
Diffusive Mass Transfer ◽  
Ore Minerals ◽  
Deformation Processes

This paper provides a detailed documentation of microstructures developed in the banded iron formation (BIF) of Gua mine, located in the Bonai Synclinorium (eastern India), where the rocks have been subjected to three deformations (D1 to D3). Folded iron ores, quartz strain fringes around rigid core objects and folded iron ore layers, and refracted quartz veins are described from samples taken from D2 folds in the banded iron formation. Orientations of microstructures are compared with mesoscopic structures to interpret the generations of ore minerals, planar structures and the time relationship between deformation and development of different microstructures. The mechanism of D2 folding is worked out and its bearing on microstructure development is discussed. The D2 folds are inferred to have developed by a combination of tangential longitudinal strain in the competent layer, flexural flow in the incompetent layers and flexural slip at the interface between layers of differing competence. Homogeneous flattening strain superposed the earlier strain, which led to modification of the folds in the competent layer from class 1B to 1C. This strain is quantified and is found to be higher in the limb than the hinge of a fold. Diffusive mass transfer by solution and bulging dynamic recrystallization in quartz are inferred as the dominant deformation processes during folding. Moreover, based on comparison with published deformation microstructure maps, the microstructures of the present study are estimated to have developed between 300 and 350 °C temperatures at a strain rate of 10−14–10−12 s−1, which are geologically realistic conditions for naturally deformed rocks.

Tiny particles building huge ore deposits – Particle-based crystallisation in banded iron formation-hosted iron ore deposits (Hamersley Province, Australia)

2019 ◽  
Vol 104 ◽  
pp. 160-174 ◽  
Author(s):  
Mathias S. Egglseder ◽  
Alexander R. Cruden ◽  
Andrew G. Tomkins ◽  
Siobhan A. Wilson ◽  
Hilke J. Dalstra ◽  
...  
Keyword(s):  
Iron Ore ◽  
Ore Deposits ◽  
Iron Formation ◽  
Banded Iron Formation ◽  
Iron Ore Deposits
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