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Quadrilatero Ferrifero District Gold - Geological Setting |
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Minas Gerais, Brazil |
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Au
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Quadrilátero Ferrífero district of Brazil, which surrounds the major city of Belo Horizonte in Minas Gerais, is one of the most significant mining centres in the country. It represents the home of mining in Brazil with the country's first and largest gold mines, and the hub of much of the iron mining of the country, outside of the Carajas.
Gold mining commenced in the Nova Lima district over 200 years ago, with one of the earliest mines being Morro Velho (see the seperate Morro Velho record). The historic town of Ouro Preto a little to the south, just to the west of the Passagem de Mariana deposit (see image below) was the focal point of the Brazilian gold rush in the 18th century when the country was a Portuguese colony. Between 1695 and 1696, a gold-bearing stream was discovered at Itacolomi, which would be renamed Gualacho do Sul. In 1711, several small settlements were united as a municipality called Villa Rica, which in 1823 became Ouro Preto (meaning Black Gold). 'Black Gold' comes from the gold coated with a layer of iron oxide that is found in the city. Officially, 800 tonnes of gold were sent to Portugal in the eighteenth century, not including that which was illegally traded, nor that retained in the colony, such as gold used in the lavish ornamentation of churches. The population grew from 40 000 in 1730 to 80 000, over which period it was the most populous city in Latin America.
The Quadrilátero Ferrífero occupies an area of ~7000 km2 in central and southern Minas Gerais state and represents the southern tip of the Archaean to Proterozoic São Francisco Craton. It constitutes an aggregation of Archaean and Proterozoic terranes, consolidated at the end of the Mid to Late Palaeoproterozoic Trasamazonian orogenic cycle. It is bound along its eastern and southeastern limits by the Neoproterozoic Araçuaí Orogenic Belt, to the south by the ~2.12 to 2.13 Ga Mineiro Belt, and to the west by the Meso- to Neoproterozoic Brasilia Belt. To the north, it is overlain by thick and extensive Mesoproterozoic (mainly the Espinhaço Supergroup) to Early Phanerozoic shelf sequences which isolates it from the bulk of the craton.
Archaean Basement Complexes
The Archaean basement of the Quadrilátero Ferrífero Block is exposed as a series of irregularly shaped domal structures, largely composed of Palaeo- to Mesoarchaean tonalitic-trondhjemitic-granodioritic (TTG) orthogneisses, each of which is defined by lithological differences, and considered an individual 'complex' (Aguilar et al., 2017). These domes vary from <25 to >200 km in diameter (see image below). They are largely separated by younger and smaller (<1 to 40 km diameter) aligned domes of 2.76 to 2.68 Ga medium to high-K granitoids, and linear keels composed of Neoarchaean greenstones and Palaeoproterozoic volcano-sedimentary and sedimentary rocks. The principal of these older TTG domes are the Bonfim, Bação, Belo Horizonte, Santa Bárbara, Caeté and Divinópolis. With the exception of the ~2780 Ma Caeté Complex, all are >2.85 Ga in age.
The Mantiqueira Complex, to the east, is considered to represent the periphery of the Archaean São Francisco Craton that has been deeply reworked during both the (2.02 to 1.94 Ga) Palaeoproterozoic Transamazonian and (580 to 540 Ma) Neoproterozoic Brasiliano orogenic events, and as such defines the margins of the craton (e.g., Teixeira, 1996, 2000; Heilbron et al., 2000; Duarte et al., 2004, 2005; Noce et al., 2007; Heilbron et al., 2010). This complex is very heterogeneous, with gneiss–migmatitic suites and amphibolites that have zircon crystalisation grain rim ages of 2.20 to 2.04 Ga, surrounding ~3.20 to 2.60 Ga cores. These gneisses are intruded by a range of alkaline felsic plutons, and felsic and mafic dykes dated at ~2.18 and 2.04 Ga (e.g., Fischel et al., 1998; Ragatky et al., 1999; Brueckner et al., 2000; Heilbron et al., 2001; Silva et al., 2002; Noce et al., 2007; Heilbron et al., 2010). The latter is considered to represent the Juiz de Fora Complex, a Palaeoproterozoic ocean arc (e.g., Cutts and Lana, 2019).
In the NE, the Guanhães Complex separates the Caeté and Santa Bárbara complexes and perhaps the Mantiqueira Complex. The Santo Antônio do Pirapetinga Complex to the SE is variously mapped as predominantly >2.9 Ga (e.g., Soares et al., 2021) or earliest Palaeoproterozoic leucocratic TTG gneisses (e.g., Endo et al., 2020 - which is the currently favoured interpretation), intruded by extensive plutons and dyke swarms of 1.8 to 1.6 Ga meta-mafic rocks of the Catas Altas da Noruega Suite and meta-ultramafics of the Santa Rita Suite. The TTG and ultramafic/mafic complexes temporally bracket the Palaeoproterozoic Minas Supergroup discussed below. These mafic and ultramafic suites are also described seperately below. A number of smaller Early Palaeoproterozoic Siderian metatonalites and meta-granites are also mapped along the margin of the Santa Bárbara complex (e.g., Endo et al., 2020) but, for simplicity, are not differentiated on the main image in this record.
The Archaean basement complexes and greenstone belts of the Quadrilátero Ferrífero Block were formed during four main magmatic events (Lana et al., 2013; Farina et al., 2015; Araújo et al., 2020), namely:
• The oldest was the Santa Bárbara Event, between ~3.22 and 3.20 Ga in the late Palaeoarchaean (Lana et al., 2013) which occurs as, i). an 'older' juvenile TTG with meta-granites and migmatites that constitute the bulk of the Santa Bárbara Complex in the SE, and ii). as subsequently deformed equivalents in the adjacent orogenic Mineiro Belt to the south. Although exposures of these older rocks are limited, Sm-Nd model ages of the TTG rocks (Teixeira et al., 1996), and the abundance of 3.6 to 3.0 Ga detrital zircons in Neoarchaean and Palaeoproterozoic sequences of the district, suggest Palaeoarchaean rocks were once more widely exposed (Lana et al., 2013).
• The second of these periods of accretion was the Rio das Velhas I Event between ~2.93 and 2.85 Ga in the Mesoarchaean. This event produced juvenile TTG magmatism, now orthogneiss, which account for the bulk of the complexes listed above, particularly in the Bação, and large Belo Horizonte, Divinópolis and Bonfim complexes/domes. This magmatism was accompanied by the accretion of limited mafic-ultramafic greenstone terranes to the pre-existing crust.
• The Early Neoarchaean Rio das Velhas Magmatic II Event emplaced the final pulse of TTG magmatism between 2.82 and 2.76 Ga. This was followed by deposition of the Rio das Velhas Supergroup, comprising suites of meta-komatiites and meta-tholeiites to form extensive 'greenstone belts', with intercalations of silica-iron-manganese formations in the lower section of the stratigraphic pile. Calc-alkaline felsic metavolcanic rocks are also always present. The upper part of the sequence is made up of metasedimentary rocks, subdivided into a lower succession which constitutes an association of schist, graphite, meta-pelite, meta-chert, banded iron formation and calc-silicate rock, and an upper suite of clastic rocks, mainly turbidites. This sequence is described in more detail below.
• The 2.75 to 2.68 Ga, Neoarchaean Mamona I Magmatic Event, which resulted in the intrusion of voluminous, relatively K-rich magmatic rocks that comprise: i). 2.78 to 2.72 Ga (U-Pb; zircon) metaluminous tonalite, grandiorite and calc-alkaline granite; and ii). 2.71 to 2.69 Ga (U-Pb zircon) peraluminous A-type granitoids (Lana et al., 2013; Farina et al., 2015; Dopico et al., 2017). These and the older rocks of the Quadrilátero Ferrífero were deformed to produce a dome-and-keel architecture by 2.72 Ga (e.g., Farina et al., 2015; Teixeira et al., 2017; Cutts et al., 2019), and were migmatised by two metamorphic events straddling this period, as shown by metamorphic peaks at 2.86 and 2.77 Ga (U-Pb zircon; Moreno et al., 2018; Brando Soares et al., 2020).
• The 2.65 to 2.58 Ga Neoarchaean, Mamona II Magmatic Event produced 2.61 to 2.55 Ga post-orogenic, A-type, grey granite dykes and plutons (Teixeira et al., 2000), principally as relatively minor magmatic events at ~2631 (Moreno et al., 2017) and ~2612 Ma (Romano et al., 2013). These intrusions were the continuation of an extended period in which several generations of A-type granitoid magmatism occurred between 2.72 and 2.63 Ga in both Mamona I and II events (Moreno et al., 2018; Brando Soares et al., 2020)
Rio das Velhas Supergroup
Summary - The Rio das Velhas Supergroup, in Minas Gerais, is the host to the most abundantly gold endowed deposits of the Quadrilátero Ferrífero. This suite of greenstones and sedimentary rocks contains major tectonic and stratigraphic discontinuities that require its division into three fault-bound tectonostratigraphic domains, (Araújo et al., 2020), the Santa Bárbara (to the east), Nova Lima-Caeté (to the NW) and São Bartolomeu (to the SW), each of which is divided into a separate lithostratigraphy as illustrated on the stratigraphic distribution diagram below. However, despite some marked differences between these domains, stratigraphic correlations and a similar depositional evolution is recognisable. The bulk of the sequence comprises the 2.8 to 2.76 Ga (Lana et al., 2013) Rio das Velhas Supergroup, that is, in turn, subdivided into the lower Quebra Osso Group, and the ~2.77 Ga Nova Lima and overlying Maquiné groups. The same authors suggest a volcanic architecture and sedimentary depositional model that includes:
i). fissure eruption of komatiite lavas of the Quebra Osso Group in the Santa Bárbara domain, where it mainly occurs within a NNE-SSW elongated ~15 x ~0.5 to 1.5 km strip; as narrow exposures in the São Bartolomeu Domain and over the Baçao Complex, mostly composed of meta-komatiites. The predominantly intrusive Córrego dos Boiadeiros Suite in the Nova Lima-Caeté Domain may be an equivalent;
ii). ultramafic/mafic tholeiitic MORB-like lavas and sills related to multiple volcanic centres in a subaqueous, extensional environment, with chemical-exhalative meta-sedimentary intercalations. These rocks are characteristic of the basal Nova Lima Group sedimentary sequence in the Santa Bárbara and Nova Lima-Caeté domains;
iii). intermediate to felsic volcanic and volcaniclastic rocks of the Nova Lima Group, which are related to explosive eruptions, and restricted to the Nova Lima-Caeté Domain;
iv). clasto-chemical sedimentation that is well developed in the Nova Lima Group of the Santa Bárbara Block;
v). a thick sequence of clastic sedimentary rocks deposited at the top of the Nova Lima Group in all three domains, predominantly composed of greywacke-argillite cycles, deposited by turbidity currents in tectonically active submarine basins. This section is interpreted by Delgado et al., 2003 as a post-eruptive facies of volcaniclastic and epiclastic meta-sedimentary, turbiditic rocks, deposited in a compressive regime during basin inversion;
vi). a sequence of polymitic meta-conglomerate, meta-arenite and meta-pelite of the 2.77 to 2.70 Ga (U-Pb zircon; Moreira et al., 2016) Maquiné Group. This group, which unconformably overlies the Nova Lima Goup, is a post-orogenic terrigenous sedimentary sequence deposited in alluvial/fluvial braided river, coastal and shallow marine environments (Baltazar and Zucchetti, 2007; Moreira et al., 2016).
In more detail the Rio das Velhas Supergroup, can be described as follows:
Quebra Osso Group - the lowest stratigraphic unit of the Rio das Velhas Supergroup, is largely restricted to a NNE-SSW elongated string of exposures of meta-komatiites distributed over an interval of ~15 x 0.5 to 1.5 km on the western margin of the Santa Bárbara Complex, but also as remnants over and east of the Bação Complex. It is interpreted to represent fissure eruptions of komatiitic lava. Contacts with the TTGs of the Santa Bárbara Complex and the metasedimentary rocks of the Minas Supergroup, to the east, and metavolcano-sedimentary rocks of the Nova Lima Group, to the west, are all marked by thrust-faults. In contrast to the overlying Nova Lima Group, it is mainly composed of komatiite without associated basalt, and has well preserved volcanic features, including the characteristic spinifex texture. The komatiite flows are mainly massive to brecciated, with subordinate spinifex-textured varieties, pillow lavas and minor meta-volcaniclastic rocks. The meta-komatiites are preserved as green to dark grey, fine to medium-grained serpentinites and ultrabasic schists, commonly crosscut by veins of fibrous serpentine or carbonate. The primary mineral assemblage comprises olivine and pyroxene, which were completely replaced by variable amounts of serpentine, magnetite, tremolite, talc and chlorite, with traces of Mg-carbonate, ilmenite, chromite, pyrrhotite and pentlandite. The contacts between individual lava flows are, in general sheared, and have been locally intensely deformed, with the obliteration of all primary features. The most foliated exposures comprise tremolitite, serpentine-talc schist and talc-serpentine-tremolite-(biotite)-(chlorite) schist. Rare lenses of metasedimentary rocks, including BIF, metachert, carbonaceous phyllite and fuchsite-quartz schist, are interbedded with the lava flows. Some authors, e.g., Baltazar and Raposo (1993), regard this unit as a basal member of the Nova Lima Group, rather than a separate group (This paragraph after Araújo et al., 2020).
The Córrego dos Boiadeiros suite that occurs in the northwestern part of the Nova Lima-Caeté Domain, is an association of meta-ultramafic and meta-mafic rocks that form an elongate north-south trending, ~4 x up to 2 to 3 km wide body. It is variously interpreted to be an autochthonous ophiolite (Drake and Morgan, 1980), a komatiitic sequence (Padilha, 1984), or an intrusive suite at the base of the Nova Lima Group (Schrank et al., 1990; Costa, 1995). Its contacts, including with the Nova Lima Group are invariably tectonic. Meta-ultramafic rocks predominate, with meta-mafic lithologies being subordinate. The main lithotypes are serpentinites, steatites, talc schist, chlorite-tremolite schist and tremolite-serpentinite granofels (Fernandes 2016). Serpentinites are the dominant rocks interpreted to have been derived from a range of protoliths, including dunites, orthopyroxenites and peridotites. At least part of the suite represents a layered intrusion (Araújo et al., 2020).
Nova Lima Group, which has a structural contact with the TTG basement complexes. It is composed of ultramafic and mafic volcanic rocks, interleaved with 'Algoma-type' banded iron formation (BIF), meta-greywacke, quartzite, ferruginous meta-chert, carbonaceous meta-pelites, and acid and intermediate volcanic rocks (Dorr, 1969; Zucchetti et al., 2000). The ultramafic rocks, in the lower part of the section, accompanied by some felsic eruptives, are either massive or pillowed komatiitic meta-basalt, with associated tholeiitic meta-basalts (Zucchetti 1998; Zucchetti et al., 2000). According to Zucchetti (1998) and Silva (2000), the geochemistry of these mafic lavas is compatible with N-MORB, and most likely, they were erupted in an oceanic extensional environment (Araújo et al., 2020). The mid section of the group is mainly composed of meta-pelites interleaved with BIF, meta-cherts, meta-greywackes, carbonaceous meta-pelites and acid/intermediate meta-volcaniclastic rocks deposited in a deep marine setting. The uppermost unit is composed of turbidites, epiclastic and volcaniclastic rocks (Baltazar and Zucchetti 2007).
U-Pb zircon dating of rocks from the Nova Lima Group returned ages of 2776 ±23 and 2772 ±6 Ma for felsic volcanic rocks of the basal section of the group (Machado et al., 1989, 1992); and 2792 ±11 and 2751 ±9 Ma from meta-volcaniclastic greywacke units (Noce et al., 2005). The Lapa Seca carbonate has been allocated an age-span of 2771 to 2705 Ma (Schrank and Machado, 1996), whilst quartzites at the top of the group yielded maximum depositional ages of ~2679 ±20 Ma (Dopico et al., 2017).
Over much of the main central Quadrilátero Ferrífero, the group has been divided into three formations. In addition, this area is subdivided into three tectonostratigraphic domains based on major structural trends and stratigraphic variations within the three formations (see diagram above). The three domains are: i). Santa Bárbara Domain, bound to the east by the Santa Bárbara Complex, to the NW by the Gandarela Syncline and to the SW by the southwestern margin of the Minas Supergroup that is just to the NE of the São Vincente Shear; the structural trend within this domain is mainly NE-SW to north-south; ii). Nova Lima-Caeté Domain, which extends from the Caeté Dome to the Moeda Syncline, with an arm that extends to the SE between the Santa Bárbara Domain and the São Vincente Shear. The structural trend in this domain is dominantly north-south to NNW-SSE;
iii). São Bartolomeu Domain, which takes the form of a 2 to 7 km wide halo peripheral to the Bação Complex, with a SE extension from that complex that is bounded to the north and NE by the Bem Te Vi Fault and extends to the structural nose to the SE. It is bounded by the Palaeoproterozoic Minas Basin sequence of the Moeda Syncline margin to the west and south. The structural trend in this domain dips outward, and strikes parallel to the Bação Complex margin. The Bação Complex is a metamorphic core complex that has diapirically risen during an episode of extension during the late Palaeoproterozoic, and is rimmed by a broad zone of shearing on its outer margins.
Within the Santa Bárbara Domain, the Nova Lima Group is subdivided, from the base, into the:
• Vigário da Vara Formation - which comprises green to grey, massive to foliated, and very fine-grained to aphanitic tholeiitic metabasalts that have locally preserved original igneous features, such as pillowed lava flows and 0.1 to 0.3 mm diameter amygdales. They also contain rare, centimetric, lensoid intercalations of BIF and meta-chert, and have undergone deformation and stretching along the metamorphic foliation. The primary basaltic mineral assemblage has been metamorphosed to tremolitites, actinolitites, albite-chlorite-tremolite/actinolite schists, tremolite/actinolite schists, quartz-chlorite schists, and albite-quartz-mica schists. Minor minerals include epidote, titanite, opaque minerals, quartz, tourmaline and rutile. The amphiboles are the principal matrix minerals, and may form radial fibrous aggregates. Albite occurs mostly as tabular relict phenocrysts with Carlsbad twinning and evidence of corrosion (Araújo et al., 2020).
• Santa Quitéria Formation - which constitutes a clasto-chemical meta-sedimentary sequence, comprising a thick succession of meta-pelites, carbonaceous phyllites, banded iron formations, and metachert, frequently crosscut by quartz-carbonate veining. These rocks are pervasively foliated and contain tight to isoclinal folds, suggesting thickening by tectonic repetition. The meta-pelites are laminated, with millimetric layers of variable composition and colour. Where fresh, they comprise mica-quartz schists, sericite-quartz-(carbonate)-(chlorite) schists and chlorite schists. They are very fine-gained, containing minor biotite, titanite, epidote and pyrite. The carbonaceous phyllites are black to dark grey and composed of quartz, sericite, chlorite and carbonaceous matter. The BIF beds ranges from a few centimetres to a few tens of metres in thickness of alternating mm- to cm-thick bands of hematite-magnetite aggregates, minor recrystallised chert and trace sericite, chlorite, chalcopyrite, pyrite, epidote and tourmaline. These BIFs host orogenic gold deposits at the São Bento and Pilar mines, where they contain massive or disseminated arsenopyrite and pyrrhotite, crosscut by quartz-carbonate-sulphide veins (Valladares 2004; Martins Pereira 2007; Silva 2007; Guerrero 2016).
• Córrego do Sítio Formation - which principally consists of a NE-SW trending meta-sedimentary succession composed of rhythmic cycles of meta-psammites, meta-pelites and carbonaceous meta-pelites. BIFs are rare. Each cycles is a few to tens of cm thick, and rests on a sharp to erosive contact with the top of the underlying cycle. They have an upright facing, with a gradual upward decrease in grain size to the upper carbonaceous metapelite layers. They have been described as incomplete Bouma cycles (e.g., Zucchetti et al., 2000; Baltazar and Zucchetti 2007; Roncato et al., 2015; Sepulveda 2020), and are interpreted to represent a distal turbidite sequence. They are foliated and often overprinted by hydrothermal alteration zones containing carbonate, sericite, quartz and sulphides. The meta-pelites occur as very fine-grained sericite-quartz-(chlorite) schists with planar-parallel bedding defined by an alternation of mm- to cm- bands of polygonal quartz and oriented phyllosilicates. They contain variable carbonaceous matter and traces of rutile, chloritoid, zircon, opaques and carbonate. The psammitic layers are fine- to coarse-grained meta-greywackes composed of alternating layers of quartz-albite and sericite-chlorite. Quartz occurs as rounded to stretched recrystallised porphyroclasts. This formation hosts significant gold deposits distributed along the regional NE-SWCórrego do Sítio Lineament (Porto 2008; Lima 2012), e.g., the Cachorro Bravo, Carvoaria, Laranjeiras, Cristina, Rosalino and Grota Funda deposits. These deposits occur either as disseminated arsenopyrite, pyrite, chalcopyrite, pyrrhotite, stibnite and berthierite, or quartz-carbonate sulphide ±sulphosalt veins (Roncato et al., 2015 and references therein).
- Mindá Member is characterised by meta-turbidites in which meta-psammites dominate over meta-pelites. These have been regarded as a separate formation in some localities, although Araújo et al. (2020) suggest it is merely a coarse-grained member in the upper part of the Córrego do Sítio Formation. It occurs as sericite-quartz-(plagioclase)-(chlorite) schists with layering that is usually characterised by alternating millimetre-thick laminae of polygonal quartz-albite aggregates and phyllosilicate stringers. Quartz and plagioclase occur as angular to sub-rounded porphyroclasts set in a matrix of chlorite, sericite and rare biotite. Porphyroclasts are often present and stretched parallel to the foliation. Tourmaline, titanite, rutile, biotite, zircon, and opaque minerals are minor phases.
Within the Nova Lima-Caeté Domain, the Nova Lima Group is subdivided, from the base, into the:
• Ouro Fino Formation - which comprises the basal unit of the group in this domain, and combined with the overlying Morro Vermelho Formation is correlated with the Vigário da Vara Formation in the Santa Bárbara Domain, as described above. It has been mapped in two main areas, i). on the eastern margin of the domain, outcropping as a continuous layer in tectonic contact with granodioritic rocks of the TTG basement; and ii). in the central-western part of the domain, surrounded by the youngest rocks of the Nova Lima Group with either a tectonic or gradational contact.
The interpreted protoliths of the formation are primarily mafic meta-volcanic rocks with interlayered ultramafic and felsic meta-volcanic and meta-volcaniclastic rocks, with subordinate felsic/intermediate volcanic rocks, banded iron formations (BIF), meta-chert, carbonaceous meta-pelite and other pelagic sedimentary rocks. These protoliths are dominantly represented by serpentinites, tremolitites, and serpentine-tremolite-chlorite schists, talc schists and quartz-carbonate-chlorite schists. The least metamorphosed rocks are green to dark green, fine- to medium-grained, and are massive or schistose. Locally, serpentinites contain hexagonal-shaped, 0.3 to 2 mm serpentine pseudomorphs, interpreted to have been derived from cumulate olivine crystals. Original features such as pillows are recognisable locally. The sequence has been deeply weathered.
Felsic to intermediate meta-volcanic and meta-volcaniclastic rocks are commonly intercalated with the mafic rocks, and occur as sericite-quartz schists and sericite-plagioclase-quartz schists. The meta-volcaniclastic rocks are feldspathic meta-greywackes that frequently contain clasts of volcanic rocks. Porphyroclasts of greyish-blue quartz and white plagioclase are common. These rocks underwent intense metasomatic alteration and were subjected to multiple episodes of deformation and metamorphism, and consequently, primary features are often obliterated, making differentiation between volcanic and volcaniclastic rocks difficult to impossible.
BIF and metachert are less common within the Ouro Fino Formation, but are frequently more abundant in the Morro Velho area. These rocks have been strongly oxidised, with banding preserved as quartz-rich layers alternating with those primarily composed of goethite, magnetite and hematite. Meta-chert commonly occurs as thin quartz layers interbedded with the ultramafic/mafic meta-volcanic rocks, while quartz- and sericite-bearing carbonaceous phyllite is frequently associated with BIF.
Mafic to ultramafic meta-volcanic rocks and BIFs are the principal hosts of the gold mineralisation in the Ouro Fino Formation, e.g., Raposos, Juca Vieira and Ouro Fino, which are significant historic deposits (Vial 1980; Lobato et al., 2001; Junqueira et al., 2007; Vial et al., 2007).
• Morro Vermelho Formation - which gradationally overlies the Ouro Fino Formation, corresponds to an increase in the amount of clastic meta-sedimentary rocks, both vertically and laterally. The formation principally comprises an alternating sequence of mafic meta-volcanic, clastic and chemical meta-sedimentary rocks, with subordinate felsic/intermediate meta-volcanic, meta-pyroclastic, meta-volcaniclastic rocks and carbonaceous metapelites. Mafic meta-volcanic rocks predominate at the base of the formation, while the amount of clastic and volcaniclastic rocks increases towards the top where the Roça Grande Member (see below) represents the interval where meta-sedimentary rocks predominate (Araújo et al., 2020).
The mafic meta-volcanic rocks occur as fine-grained amphibolite, chlorite-amphibole schists, quartz-sericite-chlorite schist and chlorite schist, the least weathered of which are light-green, fine-grained amphibolite and chlorite-amphibole schists. Thin quartz-rich layers are common, interpreted to represent cherts intercalated with the mafic volcanic rocks (Araújo et al., 2020).
Felsic to intermediate meta-volcanic and meta-volcaniclastic rocks are subordinate lithotypes within this formation, where they comprise meta-agglomerates, plagioclase-sericite-quartz schists, plagioclase-carbonate-quartz-chlorite schists and sericite-quartz schist that are often mylonitised. Porphyroclasts of partially sericitised plagioclase and greyish-blue corroded quartz are common. These rocks are more frequent in the Morro Velho district to the west than to the east (Araújo et al., 2020).
BIF and meta-chert layers occur throughout the Morro Vermelho Formation (Zucchetti et al., 2000), but are more concentrated in its basal section. These rocks are particularly abundant in the Morro Vermelho area, where thick continuous layers form prominent ridges. BIF layers are frequently discontinuous and strongly folded, and occur within both meta-volcanic and clastic meta-sedimentary rocks, commonly sharing a contact with carbonaceous phyllite layers. At surface, these BIFs are strongly oxidised and occur as mm to cm thick quartz-rich or meta-chert layers, alternating with goethite and remnant magnetite and hematite. In contrast, underground BIF exposures in the gold mines (e.g., Cuiabá, Lamego, Roça Grande) are composed of iron carbonates, oxides and silicates (Araújo et al., 2020).
Meta-pelites and feldspar-quartz meta-greywackes are the most common clastic meta-sedimentary rocks, represented by quartz-chlorite schists, which are meta-pelites with a significant mafic contribution, whilst chlorite-sericite-quartz schists have a mixed or more felsic source. These meta-sediments are interpreted as volcano-sedimentary deposits (Araújo et al., 2020).
Meta-volcanic rocks of this formation, as described above, are found at a number of significant gold deposits, including Lamego (Araújo et al., 2020), Cuiabá and Roça Grande (Silva, 1994; Baltazar and Silva, 1996; Baltazar et al., 2005). In the Cuiabá deposit, the meta-volcanic rocks occur as two main packages separated by a mineralised BIF layer. The lower mafic volcanic package is a thick succession of light-green, massive, fine-grained rocks composed of clinozoisite, plagioclase, amphibole, chlorite and quartz. The upper mafic package is dark olive-green, massive and fine-grained, with a restricted distribution, composed of chlorite, epidote, plagioclase and quartz (Silva 2006; Ribeiro- Rodrigues et al., 2007). The mafic metavolcanic rocks at the Lamego deposit occur as schists composed of chlorite, plagioclase, quartz, carbonate and minor amphibole (Martins et al., 2016; Araújo, 2018). At the Roça Grande deposit, the meta-volcanic rocks are chlorite-hornblende schists with minor quartz, plagioclase, epidote and carbonate (Araújo, 2018).
- The Roça Grande Member, is at the top of the Morro Vermelho Formation, where metamorphosed clastic and volcaniclastic meta-sedimentary rocks predominate. These include meta-pelites, chlorite-rich meta-pelite, lithic, feldspathic and quartz meta-greywackes, interbedded with meta-volcaniclastic rocks, subordinate BIF, meta-chert, carbonaceous phyllite and basic meta-volcanic rocks. This member has a transitional contact with the undivided Morro Vermelho Formation and the base of the Mestre Caetano Formation.
• Mestre Caetano Formation - which is generally correlated with the Santa Quitéria Formation in the Santa Bárbara Domain (as described above). It is exposed as a continuous unit within the central and western sections of the Nova Lima-Caeté Domain, but is less well exposed in the east. It is mainly composed of meta-volcaniclastic rocks and is subdivided into the Ribeirão Vermelho and Mestre Caetano members in the lower and upper sections of the formation respectively, separated by a central undivided interval.
The undivided central section of the formation is widely distributed within the domain, particularly in the central and western parts. It is composed of feldspathic and quartz-rich meta-greywackes and meta-pelites, frequently interbedded as meta-rhythmites. Meta-pyroclastic rocks within this part of the sequence comprise a range of protoliths that include ash and lapilli tuff, agglomerate and bomb layers. Subordinate lithologies include carbonaceous phyllite, felsic to intermediate meta-volcanic rocks and BIF (Zucchetti et al., 2000). The most representative lithotype of the formation are volcanogenic meta-greywackes, which frequently have an intermediate composition (Zucchetti et al., 2000; Noce et al., 2005; Baltazar and Zucchetti 2007). They comprise schists with a matrix of variable quartz, plagioclase, sericite and carbonate. Common porphyroclasts are of corroded quartz, and/or plagioclase with primary zoning growth. Both of these minerals are often rounded to sub-rounded as a result of reworking. The porphyroclasts:matrix ratio in these rocks is extremely variable. Sedimentary bedding defines fining-up cycles, each of which has a basal quartzite or meta-greywacke, grading upwards into meta-pelitic layers, with local small-scale trough and planar crossbedding (Baltazar and Zucchetti 2007). These represent reworked and re-sedimented volcaniclastic rocks. Metapelites occur as fine-grained schists with sericite, chlorite, quartz and carbonate. Subordinate meta-agglomerates, bombs and tuffs are found in the undivided Mestre Caetano Formation, mainly in the Morro Velho district.
An unusual lithology, locally known as Lapa Seca, found in the undivided middle section of the Mestre Caetano Formation, is an important host to the orogenic gold deposits of the Rio das Velhas Supergroup (e.g., Morro Velho, which produced >450 tonnes of gold; and the Bicalho and Bela Fama deposits; Lobato et al., 2001). It comprises a foliated, homogeneous to thinly banded, grey to whitish-grey rock composed of ferroan dolomite, ankerite and siderite, with variable quartz, calcite, sericite, fuchsite, chlorite and albite (Ladeira 1980; Ladeira 1985). Ladeira (1980) and Vial (1980) interpret these rocks as chemical sediments, whilst Vial et al. (1987), Vieira (1991), and Lobato et al. (2001) suggest a hydrothermal origin.
- Ribeirão Vermelho Member, which comprises the lower section of the Mestre Caetano Formation. It has tectonic contacts with the underlying Morro Vermelho and younger Ribeirão do Brumado formations and the undivided central section of the Mestre Caetano Formation. It is only found to the east near the Caeté Dome. It is principally composed of meta-pyroclastic deposits after protoliths that include agglomerate, bomb layers, lapilli tuff and ash tuffs, with subordinate carbonaceous phyllite and rare felsic/intermediate meta-volcanic rocks. The meta-agglomerates contain angular to rounded clasts up to 40 cm across that are either feldspar and quartz crystal aggregates, or mainly dacitic to andesitic lithic fragments, set in an intermediate to mafic tuffaceous matrix with variable proportions of quartz, feldspar, chlorite, sericite and occasional carbonaceous matter. The lapilli meta-tuffs are schists with fine-grained quartz, feldspar, sericite, chlorite and coarse grains of prismatic plagioclase, lithic fragments and greyish-blue corroded quartz. The metamorphosed ash tuffs are argillaceous and mainly composed of white clay and very fine-grained quartz. The subordinate volcaniclastic and volcanogenic meta-sedimentary rocks are meta-greywackes and meta-pelites. The few felsic meta-volcanic rocks present are of a dacitic composition and preserve the original porphyritic texture, with a quartz-feldspathic matrix with plagioclase and subordinate hornblende phenocrysts (Zucchetti et al., 2000). Coarse and poorly sorted conglomerates and breccias are interpreted to be alluvial-fans formed near an explosive volcanic center (Zucchetti et al., 2000; Noce et al., 2005; Baltazar and Zucchetti 2007).
- Macacos Member, which is confined to the western sections of the Nova Lima-Caeté Domain, and has tectonic contacts with all other units. However, on the basis of lithologic and depositional similarities to the Mestre Caetano Formation, it is considered to be part of that unit. Never the less, it differs from the undivided Mestre Caetano Formation, described above, in its abundance of chloritic meta-pelites and meta-greywackes, interpreted to represent volcaniclastic and volcanogenic meta-sedimentary protoliths derived from mafic to intermediate sources (Cavalcanti 2018). Meta-pelites and meta-greywackes with a felsic provenance also occur, interbedded in the package. Carbonaceous and non-carbonaceous phyllites, BIFs, and mafic and ultramafic intrusions are also present, but subordinate (Cavalcanti et al., 2020). The chlorite-rich rocks are interbedded with schists containing variable proportions of sericite, quartz and plagioclase. The meta-greywackes are composed of quartz, plagioclase and fragments of volcanic rocks that range from those that are crystalline, though angular to sub-rounded grains, indicating variable reworking.
• Ribeirão do Brumado Formation - which is generally correlated with the Córrego do Sítio Formation of the Santa Bárbara Domain (as described above). The two formations are generally similar, both being composed of rhythmic depositional cycles of greywacke-argillite, interpreted as turbidites, re-sedimented from earlier volcaniclastic lithofacies. However, as they occur in two different tectonostratigraphic domains, with varying sources, i.e., a felsic source in the Santa Bárbara Domain and a mixture of different felsic source in the Nova Lima-Caeté Domain (Baltazar and Zucchetti, 2007), they have been allocated different formal names by Araújo et al. (2020). The Ribeirão do Brumado Formation is widely distributed across the domain and comprise metasedimentary rocks that represent the proximal and distal facies of turbidites derived from the underlying greenstone belt sequence. It has been sub-divided into two members, as follows, which are separated by a gradational contact, and are structurally or unconformably overlain by the Palaeoproterozoic Minas Supergroup:
- Ribeirão Comprido Member - which has been correlated with the Mindá Member of the Córrego do Sítio Formation in the Santa Bárbara Domain. In the type-section, in the vicinity of the historic Morro Velho mine, psammitic layers dominate, with lesser pelitic facies. Meta-rhythmites contain thick meta-greywacke to quartzite bands, which grade into sericite-quartz schist after meta-siltstones and quartz-chlorite-sericite phyllite after meta-pelitic protoliths. Sericite-quartz schist and quartz-chlorite-sericite schist after quartz meta-greywackes are the most common rocks in this member. These schists are rich in sand-sized quartz with varying proportions of fine-grained matrix and contain up to 1 cm long magnetite crystals, as well as cubic boxworks that are empty or filled with ochre to red secondary minerals. The meta-rhythmites occur as fining-upward cycles, from sand at the base to mud layers at the top. The sand layers are thicker and may contain small-scale, low-angle (up to 20°) tabular cross-bedding and symmetrical to asymmetric ripple-marks. The pelitic layers at the top have planar stratification. Layers of mylonitic sericite-quartz schist are common and form small ridges, typical of this member. Subordinate feldspathic meta-greywackes, phyllites and carbonaceous phyllite are also present (Araújo et al., 2020).
- Ribeirão do Gaia Member - composed of fine-grained meta-sedimentary rocks, made up of silt and clay-sized particles with subordinate sandy layers. These rocks occur as meta-rhythmites that are also characterised by fining upward cycles that are tens of centimetres thick, with thin layers of meta-greywackes or fine quartzites at the base, grading into thicker meta-pelite layers at the top, interpreted as a turbidite sequence. Grey, red, ochre and lilac weathered meta-pelites are the most common lithology, composed of variable amounts of quartz, sericite and chlorite, with subordinate magnetite, plagioclase and carbonate. Carbonaceous phyllite layers are common, whilst sericite-quartz schist and sericite-plagioclase-quartz schist after quartz and feldspathic meta-greywacke are subordinate. Possible metamorphosed tuffaceous rocks are represented by white to beige, potassium-rich, deeply weathered rocks, occurring as centimetre to metre scale layers composed of white clay, sericite and very fine-grained quartz (Araújo et al., 2020).
Within the São Bartolomeu Domain, the Nova Lima Group is more condensed and possibly only represents equivalents to the upper Santa Quitéria and Córrego do Sítio Formations of the Santa Bárbara Domain. It is divided into three formations, from base to top (after Araújo et al., 2020):
• Fazenda Velha Formation - which is predominantly found in the northern, northeastern, eastern and western section of the São Bartolomeu Domain, radially distributed around the Bação Complex and bounded to the north by the Bem Te Vi Fault. The principal lithotypes are grey, green, white or yellow plagioclase-chlorite-quartz schists, sericite-plagioclase-biotite-chlorite-quartz schists, carbonate-biotite-plagioclase-quartz-sericite schists, and carbonaceous phyllite. These rocks have a compositional banding of mm- to cm-thick layers rich in chlorite, biotite, white mica and carbonate, alternating with layers of quartz and feldspar. The protoliths of these schists are interpreted to have included greywacke, at the base of cm- to m-thick, fining-upward, rhythmite cycles, grading to thin layered carbonatic meta-argillite and dark-grey carbonaceous meta-argillites at the top, overlain across a sharp basal contact by the next cycle. In addition to this graded bedding, preserved primary structures include small to medium-scale tabular and trough cross-bedding, whilst the presence of corroded quartz grains with bipyramidal features suggests a volcanogenic provenance for the sedimentary protolith (after Araújo et al., 2020).
• Córrego da Paina Formation, which together with the gradationally overlying Pau D'Óleo Formation, are generally correlated with the Córrego do Sítio and Ribeirão do Brumado formation of the Santa Bárbara and Nova Lima-Caeté domains, respectively. The Córrego da Paina Formation is composed of grey to dark green, occasionally reddish, siliciclastic rocks, that form alternating rhythmic cycles, as described elsewhere in the succession. Each cycle comprises a graded, foliated, succession, ranging from basal fine-grained meta-arenite, meta-greywacke, meta-siltite and meta-argillite, represented by an upper carbonaceous phyllite crosscut by white quartz veinlets and two foliations. Each cycle has sharp contacts with the overlying and underlying cycles, with planar-parallel and small scale cross-stratification in the lower layer which consists of fine-grained quartz, plagioclase and phyllosilicate, with rare dispersed granules. The phyllosilicates in all layers are composed of variable proportions of sericite, biotite and chlorite, with local thin layers of carbonaceous phyllite, interbedded stratabound tourmalinites and carbonatic and weakly magnetic BIF lenses, with concentrations of opaque minerals. This Formation hosts few gold occurrences, particularly in its western portion, along the east-west trending sinistral Cata Branca fault, which marks the contact with the Minas Supergroup (after Araújo et al., 2020).
• Pau D'Óleo Formation - which consists of white-grey to yellow, tabular to trough cross-bedded, fine- to medium-grained meta-greywacke, meta-arenite and meta-argilite. These protoliths have been metamorphosed to plagioclase-carbonate-chlorite-quartz-mica schist with folded compositional banding and transposed schistosity. The compositional banding is distinguished by thicker bands containing sericite and chlorite alternating with thinner layers of quartz, feldspar and carbonate, interpreted to represent rhythmic greywacke-argillite cycles (after Araújo et al., 2020).
Maquiné Group - which comprises the lower Palmital and upper Casa Forte formations in both the Santa Bárbara and Nova Lima-Caeté domains, whilst in the São Bartolomeu Domain, only the Andaimes Formation is recognised, an equivalent of the Palmital Formation. The group is predominantly composed of quartzites and meta-conglomerates that form scarps and steep slopes over the less resistant Nova Lima Group (Dorr II 1969).
• Palmital Formation, that comprises meta-greywacke, quartzites and meta-pelites, in which preserved primary structures such as tabular and trough cross-bedding are locally evident. The meta-greywacke/quartzite lithofacies are composed of micaceous quartzite, chloritoid quartzite, quartz-mica schist and (chloritoid)-chlorite-muscovite/sericite-quartz schist. They comprise rounded to angular, medium grained, sand- to silt-sized quartz grains set in a micaceous matrix. Oriented chlorite and sericite locally form thin anastomosed laminae bordering stretched quartz grains. Minor minerals include chloritoid and kyanite with variable magnetite, zircon, rutile and albite. Chloritoid crystals have hour-glass textures, and may form radial aggregates, whereas kyanite is common near the tectonic contacts with other units, or associated with quartz veins. Magnetite is common, as are cubic boxworks. Metapelites and carbonaceous phyllites are subordinate, occurring as fine-grained quartz-chlorite-sericite schists (after Araújo et al., 2020).
• Andaimes Formation, which occurs in the São Bartolomeu Domain, only. It has been considered to be part of the Palmital Formation (Baltazar and Silva 1996; Féboli and Signorelli 1996; Zucchetti and Baltazar 2000), or the uppermost unit of the Nova Lima Group (Belo de Oliveira 1986; Hartmann et al., 2006), whilst Freitas et al. (2020) and Silva et al. (2020) consider them a separate formation of the Maquiné Group. The Andaimes Formation is composed are medium- to fine-grained, white micaceous meta-sandstone, which weathers to yellow. Well-preserved primary sedimentary structures include small asymmetric ripple-marks and herringbone cross-stratification. Subordinate rock-types are mica-quartz schists after meta-siltstone, and cm- to m-thick layers and lenses of polymictic, matrix-supported, micro-conglomerate with clasts of meta-chert, quartz-veins, quartzite and schist. Bi-pyramidal and corroded quartz within these meta-clastics are interpreted to suggest a volcanic provenance. The meta-sandstones are interpreted to occur as the following coastal lithofacies (Baltazar and Zucchetti 2007): i). medium- to large-scale cross-bedded, deposited in an eolian environment; ii). those with small, asymmetric, straight-crested ripple-marks suggesting deposition in shallow water (Baltazar and Zucchetti 2007); iii). with herringbone cross-bedding, which indicates bidirectional cycles of tidal flow (Pedreira and Silva 1996; Baltazar and Pedreira 2000); and iv). those associated with metasiltstone, that have planar and trough cross-bedding suggesting deposition under shallow marine conditions, such as a tidal plain (Féboli and Signorelli 1996).
• Casa Forte Formation, which comprises a non-marine lithofacies association that overlies the Palmital Formation with a contact that has been variously reported to be gradational (Dorr II, 1969), an angular unconformity, or a thrust fault (Signorelli et al., 1996; Baltazar and Zucchetti 2007; Moreira et al., 2016). In both the Santa Bárbara and Nova Lima-Caeté domains, this group includes the basal:
- Chica Dona Member, which consists of alternating layers of fine-grained sericitic meta-quartz-arenite, meta-greywacke and monomictic to polymictic meta-conglomerate. The meta-quartz-arenite and meta-greywacke are the thickest rock packages, with local fining-upward cycles, progressing from conglomerate at the base to sericite-quartz schist at the top. These rocks are locally also planar stratified and tabular cross-bedded. The meta-quartz-arenite, which predominates, contains variable sericite, chlorite, chloritoid, kyanite and rutile. The meta-greywacke is composed of coarse- to fine-grained (chloritoid)-chlorite-sericite-quartz schist containing traces of carbonate, rutile, albite and opaque minerals. The meta-conglomerate is present as cm- to m-thick lenses that include both clast- and matrix-supported sections, with up to 30 cm diameter, subangular to subrounded clasts of various compositions, e.g., banded iron formation, metachert, carbonaceous phyllite, quartz veins, quartzite, mafic rock and granite. The matrix is sandy, commonly ferruginous, composed of quartz and sericite with minor biotite, opaque minerals and chloritoid porphyroblasts. Preserved primary textures include tabular and trough cross-bedding, graded bedding, cut-and-fill structures and sole marks (Signorelli et al., 1996; Zucchetti and Baltazar 2000; Moreira et al., 2016).
In the Santa Bárbara Domain, the Chica Dona Member is gradationally overlain by the:
- Córrego do Engenho Member, which, however is in tectonic contact with the overlying Palaeoproterozoic Minas Supergroup. It is composed of meta-greywacke and meta-quartz-arenite, with subordinate layers of matrix-supported meta-conglomerate, occurring as chloritoid quartzite, sericite quartzite, (chlorite)-sericite-quartz schist and biotite-sericite-quartz schist. Small- to medium-scale cross-bedding and graded-bedding are evident, whilst quartz porphyroclasts are commonly recrystallised and stretched along the foliation, accompanied by lesser rutile, plagioclase, biotite, kyanite, zircon, titanite, tourmaline and various other opaque minerals (after Araújo et al., 2020).
In the Nova Lima-Caeté Domain, the Chica Dona Member is overlain by two members, the:
- Jaguara Member, which gradationally overlies the Chica Dona Member and comprises coarse-grained to micro-conglomeratic quartzite. The latter contains coarse-grained smoky quartz clasts set in a quartz-sericite matrix, with subordinate chlorite and radial aggregates of chloritoid. Fine-grained quartzite and meta-greywacke are more frequent to the southeast, where they are interbedded with tens of cm-thick, fining upward cycles of micro-conglomerate and quartzite. Rare, thin lenses of polimitic meta-conglomerate occur within the quartzite units, containing clasts of schist, metachert, vein quartz and carbonaceous phyllite. Preserved sedimentary structures include tabular and trough cross-bedding and graded bedding. The contacts with both the underlying Chica Dona and overlying Capanema members are transitional (after Araújo et al., 2020).
- Capanema Member, which only occurs on the extreme SE of the Vargem do Lima syncline, where it is composed of fine-grained metasedimentary rocks that are considered lateral facies of the other members of the Casa Forte Formation. The characteristic lithofacies is a silvery to red package of quartz-sericite schist, interbedded with fine-grained meta-greywacke layers, arranged in rhythmic cycles, with locally preserved tabular, trough cross-bedding and graded bedding. The schist usually has a crenulation cleavage and contains minor chloritoid, kyanite and chlorite. Rare tens of cm thick layers of conglomeratic quartzite to meta-conglomerate have been mapped, with stretched pebbles of meta-chert and quartzite (after Araújo et al., 2020).
Pitangui Greenstone Belt
The Pitangui Greenstone Belt represents the northwestern extension of the Rio das Velhas Greenstone Belt, across the ENE-WSW trending Curral Shear Zone. It comprises a NW-trending synclinorium bounded by TTG gneisses and syn-to late-tectonic granitoids (Romano, 2000; Marinho et al., 2018; Brando Soares et al., 2020). It is composed of a meta-volcano-sedimentary sequence that includes ultramafic metavolcanic rocks and mafic to intermediary metavolcanic rocks, represented by talc-schist and chlorite-sericite schist respectively. This sequence is interleaved with banded iron formation (BIF), carbonaceous pelite, turbiditic meta-arenite and meta-pelite (Brando Soares et al., 2017, 2018; Marinho et al., 2018). It is divided into the lower Pitangui Group and upper Antimes Formation (Marinho 2018). The Pitangui Group comprises, from the base (Marinho et al., 2018), the,
• Rio Pará Formation, which is dominated by a mafic-ultramafic association, that has an N- to E-MORB chemistry and represents an Al-depleted affinity to meta-komatiites and komatiitic metabasalts (Brando-Soares et al., 2020). It also includes carbonaceous and ferruginous meta-pelite, meta-chert and rare BIF units.
• Rio São João Formation, represented by arkosic to lithic meta-arenite to meta-pelite with rhythmic bedding, interlayered with subordinate meta-chert, BIF and mafic to intermediate metavolcanic rocks. Geochemically, Cr and Ni are significantly within the sequence, whereas a highly fractionated REE pattern and LREE enrichment suggest an association with mafic and ultramafic rocks (Brando-Soares et al.< 2020); and
• Onça do Pitangui Formation, which is mainly composed of meta-greywacke, arkosic to lithic meta-arenite and meta-pelite, with rhythmic interlayering and intercalations of polymictic meta-conglomerate and scarce BIFs (Marinho et al., 2018; Brando-Soares et al., 2017). The same authors suggest these units are crosscut by meta-mafic dykes that are sub-parallel to the main foliation, but are overlain above an angular unconformity by fine- to coarse-grained quartzite and meta-conglomerate of the Antimes Formation.
The principal magmatic events of the Quadrilátero Ferrífero, namely the ~3.22 to 3.20 Ga Santa Bárbara; the ~2.94 to 2.84 Ga Rio das Velhas I; the ~2.82 to 2.77 Ga Rio das Velhas II; the ~2.76 to 2.64 Ga Mamona I (Farina et al., 2015, 2016) and 2.65 to 2.58 Ga Mamona II magmatic events are also evident in the Belo Horizonte and Divinopolis TTG complexes spatially bracketing the Pitangui Greenstone Belt. These TTG complexes are intruded by the massive 2755 ±8 Ma Florestal and 2750 ±13 Ma Pequi granitic batholiths which also have TTG affinities, whilst the 2711 ±11 Ma Jaguara granitoid intrudes the Pitangui Greenstone Belt (Romano et al., 2013; Teixeira et al., 2017; Brando-Soares et al., 2020). Regional scale mafic dyke swarms crosscut this section of the São Francisco Craton, including the Pitangui Greenstone Belt, corresponding to extensional events, specifically the i). ~2.55 Ga Lavras I; ii). ~1.8 to 1.7 Ga Pará de Minas; and iii). ~0,9 Ga Formiga dyke swarms (Caxito et al., 2020).
Brando Soares et al. (2020) and Melo-Silva et al. (2020) suggest the structurally juxtaposed Pitangui and Rio das Velhas greenstone belts have distinct and different magmatic-tectonic evolutionary paths. They interpret the Rio das Velhas Supergroup to be a sediment-dominated sequence with Al-undepleted meta-komatiite rocks, and contributions from a younger juvenile crust than the Pitangui Greenstone Belt. Conversely, they suggest, the Pitangui Greenstone Belt is a mafic-volcanic dominated sequence with a MORB affinity, a high and low LILE/HFSE dual geochemical character; and depleted meta-komatiite rocks (Martins et al., 2016; Brando-Soares et al., 2020; Melo-Silva et al., 2020; Silva et al., 2020). See the Turmalina, Satinoco record for more details on this greenstone belt.
Minas Supergroup
The initiation of the next phase of extension, which was predominantly within the Palaeoproterozoic, was marked by the emplacement of the ~2.55 Ga (Caxito et al., 2020) Lavras mafic dyke swarm, and deposition of the Minas Supergroup. This supergroup is an up to ~6000 m thick sedimentary pile composed of various clastic, carbonate and chemical-sediment units, deposited as a continental to marine sequence between ~2.58 and 2.10 Ga (Dorr II 1969, Renger et al., 1995, Alkmim & Martins-Neto 2012, Martinez-Dopico et al., 2017). It has been subdivided into the:
Tamanduá Group, which in much of the literature, including Endo et al. (2020), is shown to be the lowest unit of the Minas Supergroup. However, dating of detrital zircons in the clastic sedimentary rocks within the group give maximum ages of 1981 to 1770 Ma in its basal sections, and 1769 to 1740 Ma in its upper formation, while the Pedra Formosa Suite which intrudes it, has crystallisation dates of 1740 Ma (Dutra et al., 2020). It is therefore described later, assuming those ages.
Caraça Group, which is, in turn, divided into two main formations, namely the,
• Moeda Formation, mainly composed of conglomerate and sandstone units (e.g., Pomerene, 1964; Dorr, 1969) deposited in an alluvial to deltaic setting (Dorr, 1969; Alkmim and Martins-Neto, 2012) and includes auriferous and uraniferous conglomerate beds. It is estimated to have a maximum depositional age of ~2545 Ma (recalculated by Rossignol, et al., 2020, after Martinez Dopico et al., 2017) which implies a latest Archaean to Early Palaeoproterozoic transition depositional age. The sandstones of the Moeda Formation are pyritic (e.g., Koglin et al., 2010). Pb-Pb dating of carbonates from a stromatolite of 2420 ±19 Ma and an unconformably overlying 2199 ±24 Ma basalt provides a minimum age for the Caraça Group (Rossignol, et al., 2020). Detrital zircons from Moeda Formation conglomerate yield ages in the range from 3809 to 2520 Ma.
• Batatal Formation, which conformably overlies, or is at least in part, laterally equivalent to the Moeda Formation (Dorr, 1969). It mainly comprises fine-grained clastic sedimentary rocks grading to sericite-phyllite, with subordinate chert, carbonaceous black shale, and banded iron formation chemical sedimentary rocks. It is interpreted to have been deposited in a shallow marine regime (e.g., Dorr, 1969). Sulphides within the unit show mass-dependent sulphur isotope fractionation, indicating microbial sulphate reduction (Zhelezinskaia et al., 2014).
Itabira Group, which conformably overlies the Caraça Group and mainly comprise iron oxides, recrystallised chert, limestone and dolostone (e.g., Pomerene, 1964; Dorr, 1969; Maxwell, 1972; Morgan et al., 2013; Mendes et al., 2017), accompanied by subordinate shale and volcaniclastic layers (Suckau et al., 2005; Cabral et al., 2012). It is subdivided into the,
• Cauê Formation, which comprises an extensive siliceous and dolomitic banded iron formation (BIF or Itabirite) with variable composition, together with dolomitic phyllite, marble and dolostone, that grades vertically and laterally into the Gandarela Formation (e.g., Maxwell, 1972). Four types of BIF are recognised (Amorim and Alkmim 2011), namely,
i). siliceous, which accounts for the bulk of the BIF, occurring as a laminated, metamorphosed oxide-facies iron formation in which the original chert or jasper bands have been recrystallised into granular quartz and the iron is present principally as hematite and martite;
ii). dolomitic, which is more frequent in the western part of the Quadrilátero Ferrífero and comprises interlayered hematite, martite and dolomite;
iii). amphibolitic, that is more frequent to the east, and comprises hornblende and grunerite bands intercalated with tremolite and actinolite; and
iv). magnetite itabirite, which is only locally developed, but when fresh, comprises a green banded iron-formation, containing magnetite, martite, grunerite-cummingtonite, quartz, dolomite, stilpnomelane and subordinate hematite (Alkmim, 2009).
The original stratigraphic thickness of the iron formation is estimated to have been ~250 to 350 m, but due to the plastic behaviour of the Cauê BIF, the deformation processes that affected it resulted in a range of apparent thickness from a few to >1400 m (Dorr, 1964). A detrital zircon from a ferruginous meta-sandstone lens within the Cauê Formation has been dated at 2453 ±18 Ma (Cassino, 2014).
• Gandarela Formation, which is dominantly composed of stromatolitic dolomitic rocks (e.g., Babinski et al., 1995), with lesser limestone, dolomitic phyllite, dolomitic iron formation and phyllite, indicating shallow subaqueous deposition. The sedimentation age has been estimated at 2420 Ma (Babinski et al., 1995).
Piracicaba Group, which predominantly comprises a thick package of transgressive to regressive shallow marine and deltaic clastic sedimentary rocks, with minor chemical sediments, has been metamorphosed under regional greenschist and local amphibolite facies conditions (Dorr II 1969). It overlies the Itabira Group, with a contact that ranges from generally conformable to an erosional disconformable relationship (Dorr, 1969) to unconformable transgressive contacts. It has been divided into the following four formations (after Spier et al., 2007):
• Cercadinho Formation, comprising meta-sandstone with ferruginous lenses, phyllite and locally dolomitic marble lenses, as well as meta-conglomerate with clasts of phyllite, itabirite, chert and vein quartz that are mainly derived from the Itabira Group, as well as meta-sandstone fragments of indeterminate origin (Dorr II 1969). There is a significant detrital contribution from Meso- to Neoarchaean sources, with the average of the youngest cluster of zircons at 2680 ±24 Ma (Mendes et al., 2014), whilst δ13C values suggest Cercadinho Formation carbonates were deposited during the early stage of a global biogeochemical anomaly at ~2.22 to 2.10 Ga. However, the expected associated glacial deposits are absent, possibly having been eroded during the hiatus between the Gandarela and Cercadinho formations (Spier et al., 2007). Locally, this contact is marked by the Sítio Largo amphibolite dated at 2.18 Ga (Cabral and Zeh, 2015).
• Fecho do Funil Formation, composed of phyllite, meta-siltstone and impure dolomitic marble. A minimum deposition age of this formation is suggested by a Pb-Pb isochron age of 2110 ±19 Ma (Babinski et al., 1995).
• Taboões Formation, mainly fine-grained ortho-metasandstone.
• Barreiro Formation, comprising equigranular meta-sandstone and graphitic phyllite, occupying the upper section of the Piracicaba Group.
Tectonic stability and a passive margin regime persisted until deposition of the pelitic succession at the top of the Barreiro Formation of the Piracicaba Group, which was then modified at ~2.22 Ga by the beginning of the Transamazonian tectono-thermal event that continued through the deposition of the 2127.2 ±6.9 to 2098 ±33 Ma, unconformably overlying Sabará Group.
Estrada Real Supergroup
The Sabará Group, which overlies the Piracicaba Group above a regional unconformity, marks the change from a passive margin to a syn-orogenic regime. This group is variously regarded as the uppermost section of the Minas Supergroup (e.g., Spier et al., 2007; Dutra et al., 2019), or alternatively as the lower of the two formations that constitute the Estrada Real Supergroup, which unconformably overlies the Minas Supergroup (see Endo et al., 2020 - Quadrilátero Ferrífero,: avanços do conhecimento nos últimos 50 anos and Mapa Geológico do Quadrilátero Ferrífero, Minas Gerais, Brazil, coordinated by Galbiatti et al., 2019, Universidade Federal de Ouro Preto). In this latter interpretation, the Estrada Real Supergroup is composed of the Sabará and Itacolomi groups, and represents a succession of syn-orogenic flysch and molassic rocks that are at least 3625 m thick (Dorr 1969, Noce 1995, Reis et al., 2002). The marine metasedimentary rocks of the Sabará Group and the continental facies of the Itacolomi Group are seen to be locally interdigitated and may be lateral equivalents, at least in part (Barbosa 2018). Dating of detrital zircons suggest both the Sabará and Itacolomi groups were in place by ~2.1 Ga (Endo et al., 2020).
The Sabará and Itacolomi groups are interpreted to have reworked older supracrustal units, granitic complexes and a collisional magmatic arc in a foreland system during the early- to mid-Palaeoproterozoic Rhyacian to Orosirian periods (Machado et al., 1992, 1996, Reis et al., 2002, Hartmann et al., 2006, Alkmim and Martins-Neto 2012). This tectono-thermal event, that was roughly coeval with deposition of the passive margin Minas Supergroup, resulted in the magmatic arcs of the ENE-WSW trending Palaeoproterozoic Mineiro Mobile Belt to the south of the Quadrilátero Ferrífero (Teixeira, 1985), as discussed separately below.
The Sabará Group is estimated to be ~1750 m in thickness and is composed of meta-diamictite, meta-conglomerate, meta-sandstone and meta-siltstone, with localised intercalations of chemical sediments and volcanic rocks. The sequence has been divided into the following temporally and spatially overlapping lithofacies (after Endo et al., 2020):
• Córrego do Germano Formation, at the base of the Sabará Group, where it comprises banded, granular, iron formation and ferruginous quartzite, with a minimum thickness of between 50 and 100 m (Endo et al., 2020);
• Saramenha Formation, which is composed of quartz, chlorite-schist and white mica schist after pelites, with intercalations of meta-greywacke, quartzite, graphitic phyllite, dolomitic marble, meta-rhythmite, paragneiss, banded iron formation and subordinate felsic, mafic and ultramafic meta-volcanic rocks and pegmatites. In the Ouro Preto region, this formation has a minimum thickness of 978 m (Gomes Jr. 2002; Almeida et al. 2005) and also includes metadiamictites with pebble sized granitoid clasts.
• Catarina Mendes Formation, at the top of the group, comprising biotite-quartz schist, quartzite, phyllite and superimposed mylonite, with an age estimated at 2114 ±5 Ma (Freitas et al., 2019).
The Itacolomi Group, which is interpreted to comprise an up to 1800 m thick fluvial sequence, with a local marine transition (Alkmim 1987). It is composed of meta-sandstone, meta-arkose, meta-conglomerate and minor meta-pelite, deposited during the collapse phase of the Rhyacian-Orosirian age orogen (Dorr II, 1969, Alkmim & Marshak 1998, Alkmim and Martins-Neto 2012). The maximum age of deposition is 2059 ±58 Ma (Machadoet al., 1996) and 2058 ±9 Ma (Alkmim et al., 2014). It has been divided, from the base, into the:
• Florália Formation, which consists of orthoquartzite, with a thickness that varies from 80 to 350 m;
• Pico do Itacolomi Formation, predominantly composed of quartzite with channeled cross bedding that is marked by iron oxide bands; meta-conglomerate with pebbles and rare boulders of quartz; quartzite, BIF, phyllite and granite. In the type locality, the Pico do Itacolomi quartzite is interdigitated with phyllite and schist of the Itacolomi Group Saramenha Formation, whose minimum thickness is 1875 m (Barbosa 2018). Locally, layers of detrital iron formation up to a few tens of metres in thickness are exposed over strike lengths of up to 1.5 km (Endo et al., 2020).
Tamanduá Group, which in much of the literature, including Endo et al. (2020), is shown to be the lowest unit of the Minas Supergroup. However, dating of detrital zircons in the clastic sedimentary rocks within the group give maximum ages of 1981 to 1770 Ma in its basal sections, and 1769 to 1740 Ma in its upper formation, while the Pedra Formosa Suite which intrudes it, has crystallisation dates of 1740 Ma (Dutra et al., 1995). On the basis of these late Orosirian to Statherian ages, the same authors suggest a correlation with the first post-Minas rifting event within the São Francisco palaeoplate, which was the precursor of the Palaeo- to Mesoproterozoic Espinhaço Basin. The Tamanduá Group is principally composed of polymictic meta-conglomerate and meta-sandstone that grade upward and laterally into meta-sandstone, interbedded with meta-arkose, and overlain by a suite of phyllite and sericitic meta-sandstone. This sequence unconformably overlies the Belo Horizonte and other Pre-2.9 Ga granite gneiss basement complexes, and is sub-divided as follows, from the base, into (after Gomes 2017):
• Antâe;nio dos Santos Formation, which is further split into the,
- Córrego do Garimpo Member - composed of matrix- and clast-supported meta-conglomerate with pebbles of quartz, banded iron-formation, granite-gneiss and micaceous, pure and ferruginous meta-sandstones. Pebbles have diameters ranging from 1 to 30 cm and tend to be well‑rounded, although the banded iron-formation clasts are oblate in the less deformed sections. The dominant pebbles are meta-sandstone and banded iron-formation, embedded in a matrix of very fine to very coarse quartz grains with abundant mica. Medium to coarse grained sericitic meta-sandstone with sub-rounded to sub-angular grains are subordinate within the meta-conglomerate.
- Serra do Garimpo Member - fine to medium grained meta-sandstone with high angle cross-stratification and sub-rounded, well-sorted, quartz grains;
• Cambotas Formation
- Rio Vermelho Member - fine to coarse grained sericitic meta-sandstone with tabular stratification, interbedded with meta-arkose;
- São Miguel Member - yellowish to brownish or pink sericitic meta-sandstone with tabular cross-bedding, planar parallel lamination and ripple marks;
- Ribeirão Cocais Member - phyllite and very fine to fine grained, planar parallel, bedded sericitic meta-sandstone.
The contacts between the Tamanduá Group and the Rio das Velhas and Minas Supergroups, as well as the granite-gneiss complexes are marked by unconformities or by faults (Simmons and Maxwell 1961, Simmons 1968, Moore 1969, Crocco-Rodrigues 1991), whilst the internal contact between the Antânio dos Santos and Cambotas formations is abrupt and tectonised (Gomes 2017).
The Pedra Formosa Suite occurs as dykes, stocks and sills that crosscut the Tamanduá Group. It comprises a black to bluish-grey aphanitic dolerite, with fine to coarse grained, dark green metagabbro (Crocco-Rodrigues 1991, Almeida-Filho et al., 2015, Gomes 2017). A single zircon grain from the Pedra Formosa Suite has been dated at 1740 ±23 Ma.
Late Palaeoproterozoic Intrusions
A swathe of extensive, Late Palaeoproterozoic (Stratherian) mafic, ultramafic and meta-monzogranite to meta-syenogranite intrusions is developed along the eastern margin of the Quadrilátero Ferrífero, interpreted to be related to post Minas Group extension during opening of the rift that was to host the Tamanduá Group and sections of the Espinhaço Supergroup. The largest mafic and ultramafic bodies are located in the core of the probable Early Palaeoproterozoic Santo Antônio do Pirapetinga Metamorphic Complex (see above), fringed to the NW by a dense swarm of NW-SE oriented, 2 to 15 km long, metres to tens of metres thick dykes and plugs of the same compositions. These dykes exhibit superimposed sinistral shear deformation (Gonçalves et al. 2011). The meta-granitoids, in contrast, are best developed to the northeast, straddling the northeastern extremity of the Santa Bárbara and GuanhÃes complexes. The principal intrusive facies are a follows:
• The Santa Rita de Ouro Preto Suite is composed of ultramafic bodies that have been metamorphosed to greenschist facies, with a mineral paragenesis of chlorite ±serpentine ±talc ±tremolite ±carbonate (Gonçalves et al., 2011). The principal meta-ultramafic rocks are steatite (soapstone) and serpentinite (Jordt-Evangelista and Silva 2005). NW-SE meta-ultramafic dykes and stocks cut the Itacolomi Group and rocks from the Minas Supergroup, as well as gneisses of the Mantiqueira Metamorphic Complex and gneisses and orthogneisses of the Mineiro Belt (Endo et al., 2020).
• The Catas Altas da Noruega Suite represents a mafic magmatic event that followed on from the Santa Rita de Ouro Preto Suite, forming a swarm of mafic dykes intruding the chloritic schists of the Sabará Group and the orthogneisses of the Santo Antônio do Pirapetinga Metamorphic Complex (Raposo 1991), as well as a batholithic body in the Noruega district intruding similar sized mass of the Santa Rita de Ouro Preto Suite. Further north the Catas Altas Suite intrudes gneisses and orthogneisses of the Caeté Complex and the Rio das Velhas supergroups and Santa Bárbara Complex. Dykes are preferentially oriented NW-SE, rarely NE-SW in the south and east-west and north-south in other areas (Endo et al., 2019). They range from a few, to tens of metres in thickness, and commonly have a very pronounced shear foliation on their margins. The probable age of the suite is 1714 ±5 Ma (U/Pb, baddeleyite; Silva et al., 1995).
• The Borrachudos Suite is composed of meta-monzogranite and meta-syenogranite, and is generally massive and unjointed, forming prominent scarps. It is light grey to pinkish grey, coarse grained, and poorly foliated, although it has a strong lineation imparted by aligned elongate aggregates of biotite (Herz, 1970). Locally, in zones of Brasiliano shear deformation, it may be metamorphosed to augen gneiss. It was apparently emplaced at ~1.7 Ga in the Statherian, predominantly in the NE of the Quadrilátero Ferrífero, as described above. As such, it postdates the Minas deformation and structural emplacement of the Mineiro Belt from the south, but predates the Neoproterozoic Ribeiro Belt orogenesis.
Mineiro Belt
The triangular northern 'corner' of the larger ENE-WSW trending Palaeoproterozoic Mineiro Belt abuts the southern Quadrilátero Ferrífero Block, across two major structures, i). the NW-SE trending, sinistral, Congonhas Lineament (or fault), which marks the eastern termination of the Mineiro Belt, and juxtaposes it with the Santo Antônio do Pirapetinga Complex to the NE; and ii). the composite Jeceaba-Bom Sucesso Lineament (or fault), a NW vergent thrust package over which the Mineiro Belt is thrust onto the Bonfim TTG Complex.
According to Neves et al. (2021), between 2.47 and 2.13 Ga, roughly coeval with deposition of the Minas Supergroup in the passive margin rift that was the Minas Basin, an extended episode of juvenile magmatism took place to the south in the Mineiro Belt (Seixas et al., 2012, 2013; Ávila et al., 2014; Teixeira et al., 2015; Barbosa et al., 2019). The Mineiro Belt is interpreted to represent an intra-oceanic accretionary orogen above a south dipping subduction zone that consumed the oceanic crust that was the substrate of the distal Minas Basin to the north. Subsequent collision and obduction/imbrication of the Mineiro Belt arc over the passive margin of the southern Quadrilátero Ferrífero, led to the inversion of the Minas Basin at ~2.12 to 2.13 Ga, crustal shortening and thickening, and reworking of the Archaean/Siderian crustal basement. This was accompanied by A-type magmatism and high-grade metamorphism, between 2.14 and 2.05 Ga (Ávila et al., 2014; Teixeira et al., 2015; Moreira et al., 2019). This tectono-thermal event is marked by a granulite facies metamorphic peak at 2.08 Ga and intense Palaeoproterozoic calc-alkaline plutonism. This event is interpreted to have produced three suites, namely: i). calc-alkaline 2.22 to 2.13 Ga gabbro-diorite; ii). 2.18 to 2.16 Ga TTG; and iii). 2.12 Ga, highly differentiated S-type peraluminous bodies and less evolved high-K metaluminous to peraluminous granitic intrusions (Quéméneur and Noce, 2000).
On the accompanying image, three main lithostratigraphic subdivisions are differentiated. These include:
i). undifferentiated metamorphic rocks, mainly leucocratic gneisses;
ii). metagranitoids of the ~2.13 to 2.12 Ga Alto Maranhão Suite, composed of calc-alkaline allanite-bearing biotite hornblende meta-tonalites and meta-granites, commingled with dioritic mafic magmatic enclaves which covers an area of >300 km2 (Seixas et al., 2013); and;
iii). metasedimentary rocks of the Grupo Barbacena to the south, equivalent to the Saramenha Formation of the Sabará Group to the north. The former is composed of mica-schists, feldspathic quartzites, manganiferous schists containing spessartite and/or rhodonite, meta-cherts, gondites and phyllites with intercalated amphibolite, meta-ultramafic and graphite shales (Galbiatti et al., 2019).
Mineralisation
The bulk of the gold mineralisation in the Quadrilátero Ferrífero gold district lies within the Nova Lima Group. In the main deposits of the district, gold mineralisation is associated with sulphides and quartz veins in banded iron formation (BIF), mafic and ultra-mafic sequences and as disseminations within the volcano-sedimentary sequence.
Mineralisation within the district is distributed over an area of approximately 75 x 75 km and has been exploited from over 60 seperate mines. An important string of deposits hosted within the Nova Lima Group, including
Morro Velho,
Raposos,
Lamego,
Cuiabá,
Faria, Bicalho and Bela Fama are located towards the northwestern margin of the Nova Lima Caeté Domain, whilst another chain of deposits including Pilar and
Córrego do Sítio, which also includes the previously separate
São Bento mine, is located within the Santa Bárbara Domain to the SE of the Gandelaria Syncline. Both of these strings of deposit trend SW-NE.
The
Turmalina and São Sebastião mines and another cluster of deposits are found much further to the NW in the Pitangui Greenstone Belt in rocks broadly correlatable with the Nova Lima Group.
However, in contrast, a string of deposits near Ouro Preto, overlying the southeastern extremity of the São Bartolomeu Domain, includes the
Passagem de Mariana,
and adjacent mines hosted over a 15 km interval of the Batatal Formation in the upper sections of the Caraça Group of the Palaeoproterozoic Minas Supergroup.
In addition, gold and uranium are hosted by pyritic cobble conglomerates of the Palaeoproterozoic
Moeda Formation
at the base of the Minas Supergroup Caraça Group on the margins of the Moeda Syncline.
For more detail see the records to individual deposits linked above.
The most recent source geological information used to prepare this decription was dated: 2022.
Record last updated: 3/1/2023
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.
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Anonymous 2001 - Eldorado Gold Corp: in extract from Eldorado Gold Corp. web site http://www.eldoradogold.com 5p
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Anonymous 2001 - Morro Velho: in extract from AngloGold web site http://www.anglogold.com/ informationforinvestors/annualreport99/20f/i1-4susa.htm 2p
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Araujo, J.C.S., Ferreira R.C.R., Freitas F.M. and Magalhaes, J.R., 2020 - The Archean Rio das Velhas greenstone belt revisited: new insights into the stratigraphy: in Journal of the Geological Survey of Brazil, v.3, No.3, pp. 113-149. doi.org/10.29396/jgsb.2020.v3.n3.1.
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Baltazar O F and Zucchetti M, 2007 - Lithofacies associations and structural evolution of the Archean Rio das Velhas greenstone belt, Quadrilatero Ferrifero, Brazil: A review of the setting of gold deposits: in Ore Geology Reviews v32 pp 471-499
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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.
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Chauvet A, Piantone P, Barbanson L, Nehlig P, Pedroletti I 2001 - Gold deposit formation during collapse tectonics: structural, mineralogical, geochronological and fluid inclusion constraints in the Ouro Preto Gold mines, Quadrilatero, Brazil: in Econ. Geol. v96 pp 25-48
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de Alvarenga, C.J.S., Cathelineau, M. and Dubessy, J., 1991 - Au-ore deposition-rock deformation-ore fluid chemistry relationships in quartz veins from Cuiba, Brazil: in Ladeira, E.A. (Ed.), Brazil Gold 91 Balkema, Rotterdam, pp 335-338
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Dias, T.G., Figueiredo e Silva, R.C., Lobato, L.M., Caxito, F.A., Hagermann, S., Santos, J.O.S. and Barrote, V., 2022 - Ediacaran - Cambrian fluid flow in Archean orogenic gold deposits: Evidence from U-Pb SHRIMP hydrothermal monazite ages of the metaturbidite-hosted Corrego do Sitio and Pilar deposits, Quadrilatero Ferrifero, Brazil: in J. of South American Earth Sciences v.116, doi.org/10.1016/j.jsames.2022.103844.
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Kresse, C., Lobato, L.M., Hagemann, S.G. and Figueiredo e Silva, R.C., 2018 - Sulfur isotope and metal variations in sulfides in the BIF-hosted orogenic Cuiaba gold deposit, Brazil: Implications for the hydrothermal fluid evolution: in Ore Geology Reviews v.98, pp. 1-27.
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Ladeira E A 1991 - Genesis of gold in Quadrilatero Ferrifero: A remarkable case of permanency, recycling and inheritance - A tribute to Djalma Guimaraes, Pierre Routhier and Hans Ramberg: in Ladeira E A (Ed.), Brazil Gold 91 Balkema, Rotterdam pp 11-30
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Lobato L M, Ribeiro-Rodrigues L C, Vieira F W R 2001 - Brazils premier gold province. Part II: geology and genesis of gold deposits in the Archean Rio das Velhas greenstone belt, Quadrilatero Ferrifero: in Mineralium Deposita v36 pp 249-277
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Lobato L M, Ribeiro-Rodrigues L C, Zucchetti M, Noce C M, Baltazar O F, da Silva L C, Pinto C P 2001 - Brazils premier gold province. Part I: The tectonic, magmatic and structural setting of the Archean Rio das Velhas greenstone belt, Quadrilatero Ferrifero: in Mineralium Deposita v36 pp 228-248
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Lobato L M, Santos J O S, McNaughton N J, Fletcher I R and Noce C M, 2007 - U-Pb SHRIMP monazite ages of the giant Morro Velho and Cuiaba gold deposits, Rio das Velhas greenstone belt, Quadrilatero Ferrifero, Minas Gerais, Brazil: in Ore Geology Reviews v32 pp 674-680
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Martins Pereira, S.L., Lobato, L.M., Ferreira, J.E. and Jardim, E.C., 2007 - Nature and origin of the BIF-hosted Sao Bento gold deposit, Quadrilatero Ferrifero, Brazil, with special emphasis on structural controls: in Ore Geology Reviews v.32, pp. 571-595.
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Maurer, V.C., de Melo, G.H.C., Lana, C.deC., Marinho, M.deS., Batista, S.P.V., da Silveira, L.M., Queiroga, G., Castro, M.P. and Silva, M., 2021 - Trace elements in pyrite and pyrrhotite in the Pitangui Orogenic Au deposit, Pitangui greenstone belt, Sao Francisco Craton: Implications for the ore-forming fluids and metal sources: in J. of South American Earth Sciences v.111, 22p. doi.org/10.1016/j.jsames.2021.103459.
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Noce C M, Tassinari C and Lobato L M, 2007 - Geochronological framework of the Quadrilatero Ferrifero, with emphasis on the age of gold mineralization hosted in Archean greenstone belts: in Ore Geology Reviews v32 pp 500-510
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Ribeiro-Rodrigues L C, de Oliveira C G and Friedrich G, 2007 - The Archean BIF-hosted Cuiaba Gold deposit, Quadrilatero Ferrifero, Minas Gerais, Brazil: in Ore Geology Reviews v32 pp 543-570
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Scarpelli W 1991 - Aspects of gold mineralization in the Iron Quadrangle, Brazil: in Ladeira E A (Ed.), Brazil Gold 91 Balkema, Rotterdam pp 151-157
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Soares, M.B., Selby, D., Robb, L. and Correa Neto, A.V., 2021 - Sulfide Recrystallization and Gold Remobilization During the 2.0 Ga Stage of the Minas Orogeny: Implications for Gold Mineralization in the Quadrilatero Ferrifero Area, Brazi: in Econ. Geol. v.116, pp. 1455-1466.
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Vial D S, Abreu G C, Schubert G and Ribeiro-Rodrigues L C, 2007 - Smaller gold deposits in the Archean Rio das Velhas greenstone belt, Quadrilatero Ferrifero, Brazil: in Ore Geology Reviews v32 pp 651-673
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Vial D S, Duarte B P, Fuzikawa K and Vieira M B H, 2007 - An epigenetic origin for the Passagem de Mariana gold deposit, Quadrilatero Ferrifero, Minas Gerais, Brazil: in Ore Geology Reviews v32 pp 596-613
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Vial, D.S., DeWitt, E., Lobato, L.M. and Thorman, C.H., 2007 - The geology of the Morro Velho gold deposit in the Archean Rio das Velhas greenstone belt, Quadrilatero Ferrifero, Brazil: in Ore Geology Reviews v.32, pp. 511-542.
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Vieira F W R 1991 - Textures and processes of hydrothermal alteration and mineralization in the Nova Lima Group, Minas Gerais, Brazil: in Ladeira E A (Ed.), Brazil Gold 91 Balkema, Rotterdam pp 319-325
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Viera F W R, Corbani M, Fonesca J T F, Pereira A, de Oliveira G A I, Clemente P L C 1986 - Excursion to the Cuiba gold mine, Minas Gerais, Brazil: in Thorman C H, Ladeira E A, Schnabel D C (Ed.s), Gold Deposits Related to Greenstone Belts in Brazil - Deposit Modelling Workshop, Part A Excursions pp A79-A86
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Viera F W R, Lisboa L H A, Chaves J L, de Oliveira G A I, Clemente P L C, de Oliveira R L 1986 - Excursion to the Morro Velho gold mine, Minas Gerais, Brazil: in Thorman C H, Ladeira E A, Schnabel D C (Ed.s), Gold Deposits Related to Greenstone Belts in Brazil - Deposit Modelling Workshop, Part A Excursions pp A67-A73
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