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Quadrilatero Ferrifero Iron - Aboboras, Aguas Claras, Alegria, Andrade, Bocaina, Caue, Capitao do Mato, Concercao, Corrego do Meio, Casa de Pedra, Capa Xavier, Esperanca, Fabrica, Fazendao, Itatiaiucu, Galinheiro, Jangada, Pico, Tamandua, Timbopeba
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.

For a much more detailed description of the stratigraphy and structure, see the Quadrilátero Ferrífero District Gold - Geological Setting record.

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. This structural framework is the result of at least two main tectonic events that occurred during the Proterozoic. The earliest is the Transamazonian event at ~2.1 Ga (Alkmim and Marshak 1998) that encompasses two main pene-contemporaneous deformational phases. The first phase is defined by folds with NE-SW trending axes (Alkmim and Marshak, 1998), superposed by approximately NW-SE trending structures, producing flexural and flexural-slip folds (Hippertt et al., 2001) and thrust faults with a heterogeneous foliation, as well as the development of a large scale cross-fold interference pattern reflected at both regional and mesoscopic scale. Major examples of the latter are the NNW-SSE Moeda and the east-west Dom Bosco Syncline, and the NE-SW Gandarela Syncline (see imge below). These synclines are interconnected to form a regional dome and basin pattern. The basement Archaean granitic bodies, apart from being uplifted, have not been substantially affected by this folding, but acted as rigid buttress-like bodies, remaining virtually un-displaced, although they were reactivated late during the Transamazonian orogeny, probably triggered by the intrusion of the younger, ~2.1 Ga granites (Rosiere et al., 2008).

The second major tectonic event was the ~800 to 600 Ma Brasiliano Orogeny which generated a series of west vergent thrust and fault structures associated with the development of pervasive tectonic fabrics including schistosity, mylonitic foliation, crenulation cleavage and mineral stretching lineations (Chemale et al., 1994). Major thrusts such as the NE-SW trending Cambotas-Fundao Thrust System on the northwestern limb of the Gandarela Syncline, were developed on a regional scale, as well as subordinate tight to isoclinal folds and ductile shear zones, which modified the older mega-synclines. This event resulted in inversion, translation and rotation of the synclines and the recrystallisation of the iron mineralisation. Two types of metamorphism are recognised within the Minas Supergroup (Herz, 1978), namely regional and contact metamorphism, the latter along the structural contact between gneissic domes and supracrustal rocks.

These tectonic events culminated in a regional metamorphic zonation superimposed on the thermal aureoles around the domes (Herz, 1978; Marshak et al., 1992), with Herz (1978) delineating isograds that separate three main zones characterised by chlorite, biotite and staurolite respectively, with an eastward increasing equilibration temperatures that range from ~300 to 600°C. Pires (1995) redefined those isograds for pelitic rocks and iron formations of the Itabira Group, represented by a west to east progression from grunerite → cummingtonite → actinolite → tremolite-anthophyllite metamorphic zones (see image below). This west to east zonation of increasingly strong metamorphism is accompanied by a corresponding deformational gradient, dividing the Quadrilatero Ferrffero into: i). a western low-strain structural domain, which mainly incorporates the grunerite and cummingtonite metamorphic zones and contains well-preserved mega-synclines as the main regional structures; and ii). an eastern high-strain domain that predominantly corresponds to the higher grade actinolite and tremolite-anthophyllite metamorphic zones, dominated by thrusts and transcurrent shear zones generating tight to isoclinal folds and thick mylonitic corridors (Chemale et aI., 1994). Discontinuous shear zones and thrust faults related to this second phase cut the earlier megascopic structures. Iron formations preserve some sedimentary and diagenetic features, such as meso- and micro-banding, pods formed by differential compaction, and pisolites (Beukes, 1980).

Specular hematite ore from the Mariana Deposit
Image right - Foliated, specular hematite itabirite from the Fazenda Mine of the Mariana Mine Complex in the High Strain Domain of the Quadrilátero Ferrífero. Image by Mike Porter, 2010.

The main iron deposits of the Quadrilátero Ferrífero have been developed within the iron formations of the Minas Supergroup, that are largely confined to the 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 three compositionally distinct lithofacies, namely quartz, dolomitic and amphibolitic itabirite respectively, 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, and is composed of iron oxides (hematite, magnetite, martite), abundant quartz, very rarely mica, and other accessory minerals and gangue (Rosiere et al., 2008). 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.
High-grade iron ores replace itabirites in tectonically favorable, low-strain sites. Faults are interpreted to have acted as conduits, while large fold hinges were sinks for mineralising 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 recrystallisation and development of distinctly schistose high-grade specular hematite ores characteristic of the eastern high-strain domain.

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 eastern high strain zone;
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.

Rosiere et al. (2008) suggest the high-grade iron ores of the Quadrilátero Ferrífero are the result of a combination of hypogene and geologically recent supergene processes. They have recognised three stages of hypogene ore formation. The first two occurred early, during the 2.1 to 2.0 Ga Transamazonian orogeny and are best preserved in the western low-strain domain. These stages are as follows: i). the first stage involved metamorphic fluids which leached SiO
2 and carbonates, and mobilised iron, resulting in the formation of massive magnetite bodies, Fe oxide veins, and Fe-rich itabirite bodies; ii). in the second stage, low-temperature, low-salinity fluids oxidised magnetite and Fe-rich dolomite to hematite. The resulting mineralisation is porous to massive with a granoblastic fabric. iii). the third and final hypogene stage is interpreted to be 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. This stage is characterised by the crystallisation of tabular hematite and large platy specularite crystals that overprint the pre-existing granular fabric in the presence of high-salinity hydrothermal fluids.

Neogene supergene residual enrichment processes, resulted in the formation of soft to friable hematite orebodies. The larger of these soft orebodies surround some smaller hard high-grade orebodies, and 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 widespread, but are considerably smaller, and do not extend to deeper levels below the erosion surface (Rosiere et al., 2008).

See also descriptions for individual deposits including Aguas Claras, Pico, Casa de Pedra, Itabira Complex.

Quadrilatero Ferrifero - 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 iron deposits

Key to iron mines:   AB - Abóboras;   AC - Aguas Claras;   AG - Alegria;   AL - Agua Limpa;   AN - Andrade;   BA - Baú;   BM - Brumado;   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;   GS - Gongo Soco;   IT - Itatiaiuçu;   JG - Jangada;   MA - Morro Agudo;   MT - Mutuca;   MZ - Mar Azul;   OF - Oro Fino;   PB - Pau Branco;   PI - Pico;   PR - Pires;   RA - Retirodas Almas;   SE - Serrinha;   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.

Geologyl of the Quadrilatero Ferrifero

The most recent source geological information used to prepare this decription 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:
Baltazar, O.F. and Lobato, L.M.,  2020 - Structural Evolution of the Rio das Velhas Greenstone Belt, Quadrilatero Ferrifero, Brazil: Influence of Proterozoic Orogenies on its Western Archean Gold Deposits: in    Minerals (MDPI)   v.10, 38p. doi:10.3390/min10110983.
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. and Ladeira, E.A.,  2000 - Geochemistry and Petrology of Some Proterozoic Banded Iron-Formations of the Quadrilatero Ferrifero, Minas Gerais, Brazil: in    Econ. Geol.   v.95, 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. DOI 10.1007/s00126-016-0649-9.
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, 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
Rosiere C.A., Siemes H., Quade H., Brokmeier, H.G. and Jansen E.M.,  2001 - Microstructures, textures and deformation mechanisms in hematite.: in    J. of Structural Geology   v.23, pp. 1429-1440.
Rosiere, C.A. and 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.   v.99, pp. 611-624.
Rossignol, C., Lana, C. and Alkmim, F.,  2020 - Geodynamic evolution of the Minas Basin, southern Sao Francisco Craton (Brazil), during the early Paleoproterozoic: Climate or tectonic ?: in    J. of South American Earth Sciences   v.101, 22p. doi.org/10.1016/j.jsames.2020.102628.
Selmi, M., Lagoeiro, L.E. and Endo, I.,  2009 - Geochemistry of hematitite and itabirite, Quadrilatero Ferrifero, Brazil: in    Revista Escola de Minas, Ouro Preto   v.62, pp. 35-43.
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, its employees and servants:   i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and   ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.

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