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

By
Carlos A. Rosière
Carlos A. Rosière
1
Universidade Federal de Minas Gerais, Av. Antônio Carlos 6627, 31270-901, Belo Horizonte, MG, Brazil
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Carlos A. Spier
Carlos A. Spier
2
BHP Billiton-Nickel West, Leinster Nickel Operations, P.O. Box 22, Leinster, Western Australia, Australia 6437
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Francisco Javier Rios
Francisco Javier Rios
3
Fluid Inclusion and Metallogenic Laboratory (EC1), Centro de Desenvolvimento de Tecnologia Nuclear-(CDTN-CNEN), Cx. Postal 941, 30123-970 Belo Horizonte, MG, Brazil
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Viktor E. Suckau
Viktor E. Suckau
4
VALE, GAMGF, Avenida de Ligação 3580, 34000-000 Nova Lima, MG, Brazil
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Published:
January 01, 2008

Abstract

The Quadrilátero Ferrífero district, located on the southern portion of the San Francisco craton in Minas Gerais, Brazil, comprises Archean greenstone terranes of the Nova Lima Supergroup and the Paleoproterozoic cratonic cover sequences of the Minas Supergroup that consist of quartzites, metaconglomerates, phyllites, dolomites, and banded iron formations. The Minas Supergroup was affected by two orogenic events—the Paleoproterozoic Transamazonian-Mineiro (2.1–2.0 Ga) orogeny and the Neoproterozoic to Early Paleozoic Brasiliano-Araçuaí (0.65–0.50 Ga) orogeny, resulting in complex deformation and metamorphic grades that increase from greenschist facies in the West to amphibolite facies in the East. Metamorphosed iron formations, referred to as itabirites, are found in three compositionally distinct lithofacies, namely quartz itabirite, dolomitic itabirite, and amphibolitic itabirite; these lithofacies are host to a large number of economically important high-grade iron ore deposits that give rise to the name Quadrilátero Ferrífero, or "Iron Quadrangle."

High-grade iron ores replace itabirites in tectonically favorable, low-strain sites. faults acted as conduits while large fold hinges were sinks for mineralizing fluids. Hard and fine-grained hematite and/or magnetite orebodies are in the western low-strain domain of the Quadrilátero Ferrífero. Subsequent deformation led to recrystallization and development of distinctly schistose high-grade hematite ores characteristic of the eastern high-strain domain.

A combination of hypogene and geologically recent supergene processes is thus invoked to explain the formation of the high-grade iron ores of the Quadrilátero Ferrífero. Three stages of hypogene ore formation are distinguished. The first two of these stages took place early during the Transamazonian orogeny (2.1–2.0 Ga) and are well preserved in the western low-strain domain. During the first stage metamorphic fluids leached SiO2 and carbonates and mobilized iron, which resulted in the formation of massive magnetite bodies, Fe oxide veins, and Fe-rich itabirite bodies; during the second stage, low-temperature, low-salinity fluids caused oxidation of magnetite and Fe-rich dolomite to hematite. The resulting ore is porous to massive and has a granoblastic fabric. The third and final hypogene stage of ore formation is related to thrusts of uncertain age (Transamazonian or Brasiliano orogeny), which dominate the tectonic structure of the eastern high-strain domain of the Quadrilátero Ferrífero. Crystallization of tabular hematite and large platy specularite crystals that overprint the preexisting granular fabric in the presence of high-salinity hydrothermal fluids are characteristic of this stage. During the Neogene, supergene residual enrichment processes gave rise to the formation of soft to friable hematite orebodies. The larger soft orebodies that surround some smaller hard high-grade orebodies are typically associated with dolomitic itabirite. Together, both ore types comprise the giant high-grade iron deposits typical for the Quadrilátero Ferrífero, resulting from the superposition of both hypogene and supergene processes. Pure supergene deposits are considerably smaller and do not extend to deeper levels below the erosion surface.

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Contents

Reviews in Economic Geology

Banded Iron Formation-Related High-Grade Iron Ore

Steffen Hagemann
Steffen Hagemann
Centre for Exploration Targeting, School of Earth and Geographical Sciences, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia
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Carlos Alberto Rosière
Carlos Alberto Rosière
Centro de Pesquisas Prof. Manoel Teixeira da Costa, Instituto de Geociências, Universidade Federal de Minas Gerais, Av. Antônio Carlos 6627, Campus Pampulha, Belo Horizonte, MG 31270.90, Brazil
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Jens Gutzmer
Jens Gutzmer
Paleoproterozoic Mineralization Research Group, University of Johannesburg, PO Box 524, Auckland Park 2006, South Africa
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Nicolas J. Beukes
Nicolas J. Beukes
Paleoproterozoic Mineralization Research Group, University of Johannesburg, PO Box 524, Auckland Park 2006, South Africa
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Society of Economic Geologists
Volume
15
ISBN electronic:
9781629490229
Publication date:
January 01, 2008

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