A structural model of the Fábrica Nova region, Santa Rita syncline, Quadrilátero Ferrífero: flanking folds as a folding mechanism

AbstractThis study focuses on the eastern flank of the Santa Rita syncline (Dorr 1969), with specific emphasis on the region known as Fábrica Nova. Important iron ore deposits are located on the flanks of this structure, such as Timbopeba, Alegria, São Luiz, Tamanduá, Almas and Fábrica Nova. The Santa Rita syncline is a fold with N-S axial direction and of subregional scale, with roots in the adjacent basement of the Santa Bárbara Complex and sectioned by the Água Quente thrust fault. The hypothesis of this study is that the structural framework of the region resulted from the superposition of at least three deformation phases on the Ouro Preto nappe. The Fábrica Nova mine, located in the central portion of the study area, is embedded in a synformal structure with a 100/20 trending axis named Fábrica Nova synform. The proposed model to explain the particular structural geometry of this region is based on the flanking folding mechanism (Passchier 2001). This mechanism may have been developed by E-W crustal shortening during the F4 tectonic deformation phase.

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The Itabirites of the Quádrilátero Ferrífero and Related High-Grade Iron Ore Deposits: An Overview

Banded Iron Formation-Related High-Grade Iron Ore ◽

10.5382/rev.15.09 ◽

2008 ◽

Cited By ~ 6

Author(s):

Carlos A. Rosière ◽

Carlos A. Spier ◽

Francisco Javier Rios ◽

Viktor E. Suckau

Keyword(s):

Iron Ore ◽

Ore Deposits ◽

High Grade ◽

Quadrilátero Ferrífero ◽

Iron Ore Deposits

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Using oxygen isotope chemistry to track hydrothermal processes and fluid sources in itabirite-hosted iron ore deposits in the Quadrilátero Ferrífero, Minas Gerais, Brazil

Mineralium Deposita ◽

10.1007/s00126-013-0486-z ◽

2013 ◽

Vol 49 (3) ◽

pp. 293-311 ◽

Cited By ~ 8

Author(s):

Ana-Sophie Hensler ◽

Steffen G. Hagemann ◽

Philip E. Brown ◽

Carlos A. Rosière

Keyword(s):

Oxygen Isotope ◽

Iron Ore ◽

Minas Gerais ◽

Ore Deposits ◽

Hydrothermal Processes ◽

Quadrilátero Ferrífero ◽

Iron Ore Deposits ◽

Fluid Sources

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Mineralogy and trace-element geochemistry of the high-grade iron ores of the Águas Claras Mine and comparison with the Capão Xavier and Tamanduá iron ore deposits, Quadrilátero Ferrífero, Brazil

Mineralium Deposita ◽

10.1007/s00126-007-0157-z ◽

2007 ◽

Vol 43 (2) ◽

pp. 229-254 ◽

Cited By ~ 22

Author(s):

Carlos Alberto Spier ◽

Sonia Maria Barros de Oliveira ◽

Carlos Alberto Rosière ◽

José Domingos Ardisson

Keyword(s):

Trace Element ◽

Iron Ore ◽

Ore Deposits ◽

Trace Element Geochemistry ◽

High Grade ◽

Iron Ores ◽

Element Geochemistry ◽

Quadrilátero Ferrífero ◽

Iron Ore Deposits

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From Fresh Itabirites and Carbonates to Weathered Iron Ore: Mineral Composition, Density and Porosity of Different Fresh and Altered Rocks from the Quadrilátero Ferrífero, Brazil

Minerals ◽

10.3390/min11010029 ◽

2020 ◽

Vol 11 (1) ◽

pp. 29

Author(s):

Diniz Ribeiro ◽

Israel Moraes ◽

Rogerio Kwitko-Ribeiro ◽

Deivid Braga ◽

Carlos Spier ◽

...

Keyword(s):

Manganese Oxides ◽

Iron Ore ◽

Free Water ◽

Mineralogical Composition ◽

Ore Deposits ◽

Rock Matrix ◽

Banded Iron Formations ◽

Quadrilátero Ferrífero ◽

Mineral Assemblages ◽

Iron Ore Deposits

The weathering of Paleoproterozoic itabirites (metamorphic-banded iron formations) and dolomites from the Cauê and Gandarela Formations in the Quadrilátero Ferrífero (QF), Brazil, produces supergene iron ore with different mineralogical, chemical, and physical properties. In this work, we present a methodology to assess the changes in chemical and physical features of those rocks during weathering, via quantitative analyses of mineral assemblages. These mineral assemblages were calculated from chemical analyses of fresh and weathered samples collected from drill holes drilled in different iron ore deposits in the QF. In general, the number of mineral species found in fresh or/and weathered itabirite is restricted, which helps the quantification of the mass and volumes of minerals by normative calculation in a large dataset of drilling and channel samples. The calculation of the bulk density takes into consideration, besides the mineral phases, the voids and free water in the altered rock matrix. This study shows that the estimated porosity in supergene ore varies from 0% to 20%, for compact materials, and from 15% to 55% for friable rocks, indicating an important process of rock matrix dissolution during the weathering of itabirites. In this process, MgO, CaO, and FeO are leached out from carbonates, talc, and amphiboles. Magnetite is oxidized to hematite, releasing Fe2+, which is oxidized and precipitates as Fe-hydroxide. There is a concentration of Fe2O3, MnO, Al2O3, and SiO2 in the supergene ore (saprolite) by residual enrichment or recrystallization of hematite, goethite, quartz, manganese oxides, and kaolinite. A calculation of weathering effects on the original protoliths allowed for the establishment of a correlation between different types of fresh itabirites and their corresponding weathered materials. The calculation was carried out in several steps, to account for changes in porosity and masses and has taken into consideration differences in the mineralogical composition of the protolith. Within the weathered zones, a strong link is observed between the existence of collapse on the topographic surface and the presence of supergene ore underneath. The partial to total dissolution of quartz and carbonates from the protolith itabirite results in very porous materials and leads to gravitational collapses.

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Evidence for metre-scale variations in hematite composition within the Palaeoproterozoic Itabira Iron Formation, Minas Gerais, Brazil

Mineralogical Magazine ◽

10.1180/0026461067050352 ◽

2006 ◽

Vol 70 (5) ◽

pp. 591-602 ◽

Cited By ~ 6

Author(s):

A. R. Cabral ◽

B. Lehmann ◽

H. F. Galbiatti ◽

O. G. Rocha Filho

Keyword(s):

Chemical Composition ◽

Spatial Relationship ◽

Mineral Chemistry ◽

Minas Gerais ◽

Ore Deposits ◽

Iron Formation ◽

Quadrilátero Ferrífero ◽

Iron Ore Deposits ◽

Iron Formations ◽

Gold Bearing

AbstractHematite is a mineral the chemical composition of which rarely differs significantly from stoichiometric Fe2O3. As such, little attention has been paid to the mineral chemistry of hematite in Precambrian iron formations, where hematite forms monomineralic high-grade orebodies. Electron microprobe analysis of hematite from two iron-ore deposits, Cauê (Itabira district) and Gongo Soco, in the Palaeoproterozoic Itabira Iron Formation, Quadrilátero Ferrífero of Minas Gerais, Brazil, has revealed distinct variations in chemical composition with respect to Ti and Cr. Hematite containing Ti and/or Cr is of very local occurrence in the itabirite unit and shows a spatial relationship to hematitic, palladiferous gold-bearing veins (known as ‘jacutinga’), occurring either within the veins (adjacent to, or included in, palladiferous gold grains) or in their vicinity. Where present, titaniferous hematite (to ∼1.3 wt.% TiO2) is lepidoblastic and defines a pervasive tectonic foliation (S1). In contrast, Ti-free, chromiferous hematite (to ∼6.4 wt.% Cr2O3) characteristically occurs as inclusions in palladiferous gold within S1-truncating ‘jacutinga’. Replacement of granoblastic, Ti-free, chromiferous martite with relicts of magnetite by lepidoblastic, Cr-depleted, titaniferous hematite proves that Cr and Ti were mobile during metamorphism. Chromium was ultimately fractionated into the hematite found in auriferous aggregates within cross-cutting ‘jacutinga’. A positive correlation between Cr and Pt in bulk-rock samples from the Itabira district suggests that Cr is a potential prospective guide for Au-Pd-Pt-bearing hematitic veins (‘jacutinga’).

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