Quadrilatero Ferrifero Iron Province

Minas Gerais, Brazil

Main commodities: Fe
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The Quadrilátero Ferrífero occupies the southern-most part of the São Francisco Craton in Minas Gerais State, Brazil, some 1750 km SSE of the Carajás district.   The geology of the Quadrilátero Ferrífero is dominated by Archaean and Proterozoic volcano-sedimentary sequences and Precambrian granitic complexes.   The oldest rocks in the district are the 3.38 to 2.9 Ga Archaean banded trondhjemite-tonalite-granodiorite gneiss-migmatite complexes which form the basement to the late Archaean Rio das Velhas Supergroup.

The Rio das Velhas Supergroup is sub-divided into the basal Nova Lima Group which commenced with a succession of komatiitic ultramafic and mafic rocks with BIF intercalations, overlain progressively upwards by three associations, namely:
i) a volcanic-chemical and clastic-chemical association composed of tholeiitic and komatiitic basalts with abundant interbedded iron formations or alternating fine grained clastics and iron formations respectively;
ii) a volcanic association of felsic pyroclastics, autoclastics and epiclastics;
iii) a re-sedimented association of greywacke, quartz-greywacke, sandstones and siltstones. Age dating of volcanic rocks from the Nova Lima group suggest an age of around 2.77 Ga.

The Nova Lima Group is overlain by the Maquiné Group, composed of the lower Palmital and upper Casa Forte Formations which are represented by a shallowing upwards sequence of marine and coastal, then non-marine continental rocks, specifically phyllite, greywacke, quartzites and conglomerates.

The Rio das Velhas Supergroup is discordantly overlain by the mainly Palaeoproterozoic Minas Supergroup quartzites, schists, phyllites, meta-conglomerates, carbonates and iron formations that host the major iron deposits of the district. The Minas Supergroup has been sub-divided into the basal clastic Caraça Group, which is divided into the Moeda Formation quartzite and metaconglomerate (including a Witwatersrand-like metaconglomerate), overlain by metapelitic rocks of the Batatal formations, which is transitional, but punctuated by an erosional unconformity, to the chemical-sedimentary Itabira Group (oxide or carbonate facies banded iron formation with ferruginous phyllite and dolomite), the upper clastic Piracicaba Group (quartzite, phyllite and dolomite lenses) and the overlying Sabará Formation (chlorite schist, phyllite, greywacke, tuff, conglomerate, quartzite and rare itabirite). The age of deposition of this sequence is estimated to be from 2.6 to 2.12 Ga, while an age of 2.42 Ga has been obtained from a dolomite of the Itabira Group.

All of the sequences detailed above are locally overlain by late Palaeoproterozoic and Mesoproterozoic clastic sediments and minor mafic volcanics. Granitoid intrusives appear to have been concentrated in two periods, namely around 2.7 Ga and 2.0 to 2.1 Ga.

The overall structure of the district is characterised by domal granitoids, with thrust faulting and associated isoclinal folds, while the Rio das Velhas and Minas Supergroups are interpreted to have been thrust stacked to the west and north-west. In detail, the basement gneisses and Rio das Velhas Supergroup were subjected to a compressional deformation with tangential thrusting from north to south or SW. A second, Palaeoproterozoic (Trans-Amazonian) compression produced NW striking thrust faults and tight SW-vergent isoclinal folds Metamorphism increases from greenschist facies to the west, to amphibolite and granulite grade in the east. Late extension during the Palaeo- to Mesoproterozoic led to basin formation and the prominent dome and keel architecture of the Quadrilátero Ferrífero. The Neoproterozoic Brasiliano event is evident on the eastern margin of the district produced west-vergent thrust and fault belts. The overall metamorphic grade of the western part of the district is primarily greenschist facies, increasing to amphibolite to granulite grades to the east.

The main iron deposits of the Quadrilátero Ferrífero have been developed within the iron formations of the Minas Supergroup Itabira Group, specifically within the basal unit of that group, the 350+ m thick, 2.58 and 2.42 Ga (Hartmann et al., 2006) Cauê Formation (previously the Tamandua Group), which is composed of itabirite (oxide facies iron formation), dolomitic itabirite and amphibolitic itabirite, with minor phyllite and dolomite. It is overlain by the upper member of the formation, the 600 m thick Gandarela Unit comprising dolomite and minor limestone, dolomitic itabirite, itabirite and dolomitic phyllite.

Itabirite is a term widely used in Brazil to denote a metamorphosed iron formation composed of iron oxides (hematite, magnetite, martite), abundant quartz, very rarely mica and other accessory minerals. It may be schistose or compact. The un-enriched itabirites from the Quadrilátero Ferrífero tend to have little magnetite and comprise principally quartz-hematite, quartz-hematite-carbonate and hematite-carbonate.

Two distinct types of high-grade (>65 wt % Fe) iron ore bodies occur in the Quadrilátero Ferrífero:
i). Hard ores, composed of hematite, martite, specularite and iron-deficient magnetite (kenomagnetite); and
ii). Soft, friable ores, distributed as 'alteration halos' around the hard orebodies.

Considerable variations in the structure and textures of the hard iron ores can be observed within the Quadrilátero Ferrífero. A preserved banding and lamination in the thin banded compact hematite ores apparently reflects the original layering and/or the prominent foliation of partially or completely replaced itabirite. Individual deposits vary from almond-shaped and rootless masses to bedded bodies which are both concordant to the main foliation, and to mesoscopic veins and irregular bodies. The ore textures have been grouped into the following styles:
i). thin bedded and laminated itabirites, predominantly found in the west and central parts of the district;
ii). micaceous, foliated and schistose ores, composed mainly of oriented specularite plates, that are dominant to the east;
iii). brecciated mineralisation that is found mainly to the west, and to a lesser degree in the centre; and
iv). compact/massive ores which occur as structureless bodies related to the brecciated interval or as isolated bodies in the centre of the district. The bedded and micaceous ores are believed to be the result of synkinematic, acid and oxidised metasomatism under a ductile regime during metamorphism, while the brecciated and massive ores are interpreted to be the result of subsequent, static hydrothermal activity during regional metamorphism in a brittle regime.

Soft high grade orebodies may be powdery, structureless, or have a brecciated structure with relics of the original banding. Huge cavities of several metres diameter may also be present. Soft high-grade ores do not considerably differ in mineral composition from the hard ores except in the case of some discontinuous pockets of powdery blue dust composed of random textured platy hematite that occur in the middle of granoblastic ores. Goethite only occurs at the surface, rapidly decreasing in concentration with depth. Relics of gangue minerals such as quartz dolomite, quartz, chlorite, talc and apatite may be detected.

The image below illustrates the geological setting of the Quadrilatero Ferrifero, the distribution of metamorphic facies, deformational intensity and the location of the key mines operated up to 2008.

Quadrilatero Ferrifero

Key to iron mines:   AB - Abóboras;   AC - Aguas Claras;   AG - Alegria;   AL - Agua Limpa;   AN - Andrade;   BA - Baú   BO - Bocaina;   BR - Brucutú;   CA - Cauê;   CE - Capanema;   CF - Córrego Feijão;   CM - Capitão do Mato;   CN - Concerção;   CO - Córrego do Meio;   CP - Casa de Pedra;   CX - Capã Xavier;   DC - Dois Córregos;   ES - Esperança;   FB - Fábrica;   FN - Fábrica Nova;   FZ - Fazendão;   GE - Germano;   GL - Galinheiro;   IT - Itatiaiuçu;   JG - Jangada;   MA - Morro Agudo;   MT - Mutuca;   MZ - Mar Azul;   OF - Oro Fino;   PI - Pico;   PR - Pires;   RA - Retirodas Almas;   SP - Sapecado;   TA - Tamanduá;   TB - Timbopeba.
Key to structural elements:   DBS - Dom Bosco syncline;   GS - Ganderela Syncline;   IS - Itabira synclinorium;   JMS - João Monlevade synclinorium;   MS - Moeda syncline.
Key to metamorphic terranes (upper figure):   AZ - Actinolite zone;   CZ - Cummingtonite zone;   GZ - Grunerite zone;   TAZ - Tremolite-anthophyllite zone.

The most recent source geological information used to prepare this summary was dated: 2008.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.

  References & Additional Information
   Selected References:
Barbour A P,  1973 - Distribution of phosphorous in the iron ore deposits of Itabira, Minas Gerais, Brazil.: in    Econ. Geol.   v32 pp 52-64
Cabral A R, Lehmann B, Galbiatti H F and Rocha Filho O G,   2006 - Evidence for metre-scale variations in hematite composition within the Palaeoproterozoic Itabira Iron Formation, Minas Gerais, Brazil: in    Mineralogical Magazine   v70 pp 591-602
Cabral A R, Rocha Filho O G and Jones R D,  2008 - Mercury in itabirite-hosted soft hematite ore in the Quadrilatero Ferrifero of Minas Gerais: in    J. of Geochemical Exploration   v94 pp 69-76
Cabral A R, Rocha Filho O G, Jones R D  2003 - Hydrothermal origin of soft hematite ore in the Quadrilatero Ferrifero of Minas Gerais, Brazil: petrographic evidence from the Gongo Soco iron ore deposit: in    Trans. IMM (incorp. AusIMM Proc.), Section B, Appl. Earth Sc.   v112 pp 279-286
Cabral A R, Wiedenbeck M, Rios F J, Gomes Jr A A S, Filho O G R and Jones R D,  2012 - Talc mineralisation associated with soft hematite ore, Gongo Soco deposit, Minas Gerais, Brazil: petrography, mineral chemistry and boron-isotope composition of tourmaline: in    Mineralium Deposita   v.47 pp. 411-424
Dalstra, H. and Rosiere, C.A.,  2008 - Structural controls on high-grade iron ores hosted by banded iron formation: A global perspective: in Hagemann S, Rosiere C, Gutzmer J and Beukes N J, (eds.), 2008 Banded Iron Formation-Related High-Grade Iron Ore, Reviews in Economic Geology,   v.15 pp. 73-106
Hensler, A.-S., Rosiere, C.A. and Hagemann, S.G.,  2017 - Iron Oxide Mineralization at the Contact Zone Between Phyllite and Itabirite of the Pau Branco Deposit, Quadrilatero Ferrifero, Brazil - Implications for Fluid-Rock Interaction During Iron Ore Formation: in    Econ. Geol.   v.112, pp. 941-982.
Hoefs J, Muller G, Schuster K  1992 - Polymetamorphic relations of iron ore from the Iron Quadrangle, Brazil; The correlation of oxygen isotope variations with deformational history: in    Contrib. to Mineralogy & Petrology   v79 pp 241-251
Klein C, Ladeira E A  2000 - Geochemistry and Petrology of Some Proterozoic Banded Iron-Formations of the Quadrilatero Ferrifero, Minas Gerais, Brazil: in    Econ. Geol.   v95 pp 405-427
Mendes, M., Lobato, L.M., Kunzmann, M., Halverson, G.P. and Rosiere, C.A.,  2017 - Iron isotope and REE+Y composition of the Caue banded iron formation and related iron ores of the Quadrilatero Ferrifero, Brazil: in    Mineralium Deposita   v.52, pp. 159-180.
Pires FRM  2002 - Distribution of Hard Hematite Ores at the Quadrilatero Ferrifero, Minas Gerais, Brazil and its Possible Genetic Significance: in   Proceedings, Iron Ore 2002 Conference, 9-11 September 2002, Perth, Western Australia, The AusIMM, Melbourne,    pp 71-76
Rosiere C A and Rios F J,   2006 - Specularitic iron ores and shear zones in the Quadrilatero Ferrifero: in    Trans. IMM (incorp. AusIMM Proc.), Section B, Appl. Earth Sc.   v115 pp 134-138
Rosiere C A, Rios F J,  2004 - The Origin of Hematite in High-Grade Iron Ores Based on Infrared Microscopy and Fluid Inclusion Studies: The Example of the Conceicao Mine, Quadrilatero Ferrifero, Brazil: in    Econ. Geol.   v99 pp 611-624
Rosiere C A, Spier C A, Rios F J and Suckau V E,  2008 - The Itabirites of the Quadrilatero Ferrifero and Related High-Grade Iron Ore Deposits: An Overview: in Hagemann S, Rosiere C, Gutzmer J and Beukes N J, (eds.), 2008 Banded Iron Formation-Related High-Grade Iron Ore Reviews in Economic Geology   v15 pp 223-254
Spier C A, De Oliveira S M B, Rosiere C A  2003 - Geology and geochemistry of the Aguas Claras and Pico Iron Mines, Quadrilatero Ferrifero, Minas Gerais, Brazil: in    Mineralium Deposita   v38 pp 751-774
Spier C A, de Oliveira S M B, Rosiere C A and Ardisson J D,  2008 - Mineralogy and trace-element geochemistry of the high-grade iron ores of the Aguas Claras Mine and comparison with the Capao Xavier and Tamandua iron ore deposits, Quadrilatero Ferrifero, Brazil : in    Mineralium Deposita   v43 pp 229-254
Spier C A, de Oliveira S M B, Sial A N and Rios F J,   2007 - Geochemistry and genesis of the banded iron formations of the Caue Formation, Quadrilatero Ferrifero, Minas Gerais, Brazil: in    Precambrian Research   v152 pp 170-206
Spier C A, Vasconcelos P M and de Oliveiraa S M B  2007 - 40Ar/39Ar geochronological constraints on the evolution of lateritic iron deposits in the Quadrilatero Ferrifero, Minas Gerais, Brazil: in    Chemical Geology   v234 pp 79-104
Spier, C.A., Levett, A. and Rosiere, C.A.,  2019 - Geochemistry of canga (ferricrete) and evolution of the weathering profile developed on itabirite and iron ore in the Quadrilatero Ferrifero, Minas Gerais, Brazil: in    Mineralium Deposita   v.54, pp. 983-1010.

Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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