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Corrego do Sitio, CdS - Rosalino, Cachorro Bravo, Laranjeiras, Carvoaria, Sangue de Boi, Sao Bento |
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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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The Córrego do Sítio (CdS) auriferous lineament and mine complex is located in the northern part of the Quadrilátero Ferrífero district, within the municipalities of Santa Bárbara and Barão de Cocais, ~90 km east of the city of Belo Horizonte in Minas Gerais State, southeastern of Brazil. It trends NNE-SSW and from south to north includes the ~6 km long, interconnected Rosalino, Cachorro Bravo, Laranjeiras and Carvoaria lode-gold deposits (#Location: 20° 0' 56"S, 43° 31' 8"W).
Gold has been intermittently prospected for and mined in the Santa Barbara and Barão de Cocais districts since the 19th Century. Modern exploration was undertaken within the Córrego do Sítio corridor during the 1980s by the AngloAmerican controlled Morro Velho Mineração and by São Bento Mineração. This work culminated in the approval in 1987 of a feasibility study for the mining of an open pit oxide Ore Reserve to be treated by a heap leach plant. The CdS I open pit operations that extended over the four main deposits listed above, commenced with the first phase of production between 1990 and 1998. In 2002, development of underground exploration drives began at CdS I and a feasibility study of a sulphide Ore Reserve to be mined underground and treated in a sulphide plant, was concluded in 2010. In 2007, the São Bento Mine had been acquired from Eldorado Gold Corporation by AngloGold Ashanti. São Bento is located to the NNW in CdS II, the fault offset continuation of the Córrego do Sítio auriferous lineament. In 2011-12, a major upgrade of the São Bento metallurgical plant was completed to optimise an expanded throughput that included sulphide ore from the CdS I underground mine, 15 km to the south by haul road. Sulphide ore production commenced at Cachorro Bravo, Laranjeiras and Carvoaria at CdS I in 2012, to supplement ore from São Bento, Pinta Bem and Sangue de Boi in CdS II. During this period, oxide open pit operations were also conducted at Rosalino, Carvoaria and Laranjeiras in the CdS I area. The São Bento deposit is described separately, based on the operation prior to being acquired by AngoGold Ashanti.
For details of the regional setting, see the Quadrilátero Ferrífero District Gold - Geological Setting record. See the detailed description of the Rio das Velhas Supergroup within the Santa Bárbara Domain in that record, concentrating on the Nova Lima Goup, in particular the Córrego do Sítio Formation in the upper third of that group. This outlines the geology of the sequence hosting the deposits of the Córrego do Sítio auriferous lineament. The geological map on the same link also shows the location of the deposits.
Geology
The NE-SW trending Córrego do Sítio auriferous structural lineament has been defined to include all of the gold occurrences associated with the parallel to sub-parallel, closely spaced and laterally co-extensive Córrego do Sítio, Cristina and São Bento-Donana shear zones (Lima, 2012). Along its length, it has been divided into three contiguous, fault-offset blocks, which from SW to NE, are known as the CdS I, II and III segments. Mineralisation within this lineament transects all three blocks over it's strike length of ~14 km and a width of up to 1500 m, from the Grota Funda prospect (in CdS I) in the south, to the Jambeiro prospect (in CdS III) in the north, and was developed in a compressional regime. Gold is associated with quartz and fine-grained acicular arsenopyrite hosted by either metasedimentary rocks or banded iron formation (BIF). The main gold prospects and deposits within the three SW-NE shear trends are, from SE to NW: i). the Córrego do Sítio Trend (Rosalino, Cachorro Bravo, Laranjeiras and Carvoaria which are metasediment hosted), ii). the Donana Trend (São Bento and Pinta Bem, both BIF hosted, and Sangue de Boi, metasediment hosted) and iii). the Cristina Trend (Jambeiro and Mina de Pedra prospects, both BIF hosted).
The lineament incorporates a package of metasedimentary rocks consisting of alternating greywackes and phyllites in a turbidite sequence with incomplete Bouma cycles, metamorphosed to the greenschist facies. The sedimentiary sequence, and the mineralisation, are cut by a swarm of mafic dykes of uncertain age, with a general NNE-SSW orientation, dipping to the SW, with thicknesses varying from 20 cm to 20 m. These dykes and related sills are subparallel to discordant to stratigraphy (Porto, 2008; Lima, 2012). This succession belongs to the Córrego do Sítio Formation of the Nova Lima Group, which comprises sequences of greywacke and argillite. Greywackes, quartz greywackes, sandstones and siltstones form cyclic layers, with abrupt basal contacts between cycles. These contacts between metasedimentary units are abrupt, oblique and marked by the development of hydrothermal alteration zones containing carbonate, sericite, quartz and sulphide minerals (Roncato et al., 2015).
Within the Córrego do Sítio auriferous lineament, the Córrego do Sítio Formation has been informally subdivided, from east to west, (after Lima, 2012) into:
• Lower sub-unit, a thick carbonaceous phyllite and greywacke sequence, containing subordinate BIF layers that are tens of cm to metres thick, some of which are magnetic and have intercalated carbonaceous phyllites.
• Intermediate sub-unit, a carbonaceous phyllite with an anastomosing schistosity hosting millimetre- to metre-scale quartz-carbonate veins and microfolded layers, transposed locally in axial planes of assymetric folds. This is where the auriferous mineralisation is concentrated in CdS I, with sulphide and sulphosalts in quartz-carbonate veins. The upper and lower contacts are sharp.
• Upper sub-unit, a thick greywacke sequence with subordinate intercalated carbonaceous phyllite beds forming incomplete Bouma cycles. Bedding displays an upward grain-size fining in normal and inverted sequence.
The meta-mafic dykes and sills trend NNE-SSW, dipping to the SE. Meta-mafic rocks with chlorite and muscovite alteration represent epidote-rich meta-gabbro protoliths. Quartz-bearing, schistose chlorite-carbonate dominated metamafic rocks are the most hydrothermally altered, and are locally mineralised, including with gold. An incipiently altered meta-mafic rock type represent a fine-grained meta-gabbro with relict pyroxene, amphibole and plagioclase.
Structure
The mine sequence has been affected by four deformation events, that are interpreted to, in part, be progressive. D1 is characterised by a NNE striking and ESE dipping, progressive S1-2 foliation that produced tight, asymmetric, isoclinal and dis-harmonic kink folds. D2 is typified by a NNE striking crenulation cleavage and a spaced crenulation cleavage S3, which crosscuts the regional S1-2 foliation at a high angle to the NW. D3 produced large-scale, open folds that arched S0, S1-2 and S3. D4 formed parallel fractures, spaced from centimetres to metres along with open folds or subordinate kink folds with high angle vertical axial plane, striking mainly towards NW. These latter structures may represent a more recent orogeny (Roncato et al., 2015).
Mineralisation
The Córrego do Sítio deposits occur as narrow NE-SW elongated and folded lenses of mineralisation, parallel to the main regional deformational S2 structure, and dip at 60 to 70°SE, with a plunge of 20 to 30°NE. The cores of the individual deposits that make up the 6.2 km strike length of the overlapping cluster of the CdS I block persist down plunge from the surface to vertical depths of ~1000 m at Rosalino in the SW, to 1800 m at Carvoaria in the NE. The orebodies are consistently folded, boudinaged and locally disrupted by younger structures. They comprise multiple hydrothermal lodes, composed of quartz veins and low-grade disseminated sulphide in the wall rocks. Mineralisation includes sericitic zones and quartz veinlets hosted in metapellite and BIF.
Gold is largely associated with quartz and fine-grained acicular arsenopyrite. Two different vein types are recognised (Roncato et al., 2015; after Sequetto-Pereira et al., 2013 and Ribeiro et al., 2013):
i). smoky-quartz-carbonate-sulphide-sulphosalt veins, that are highly deformed. These veins contain microscopic or sub-microscopic gold inclusions in arsenopyrite, the main mineralisation style, but also native gold; and
ii). milky-quartz-carbonate veins that are the result of recrystallisation of the smoky quartz-carbonate veins, but are largely un-mineralised.
Gold may also occasionally be associated with berthierite in quartz-Sb-Au veins (see below). Other typical sulphide minerals within the smoky quartz veins are pyrrhotite, pyrite, stibnite, sphalerite and chalcopyrite.
The main deposits have a paragenesis, whereby arsenopyrite forms after pyrite or pyrrhotite, both locally seen to originate from the alteration of magnetite. Near the meta-mafic dykes, particularly at the Cachorro Bravo deposit, arsenopyrite post-dates pyrrhotite in mineralised veins and veinlets. The pyrrhotite/arsenopyrite association occurs proximal to dykes, and is interpreted to reflect the local relatively higher temperature which formed pyrrhotite after pyrite, before the development of arsenopyrite. Arsenopyrite after pyrite is typical of alteration zones distal to meta-mafic dykes, where veins are dominated by smoky Sb-bearing quartz-carbonate veins with berthierite (FeSb2S4), stibnite, pyrite and gold. This mineral assemblage is mainly hosted in carbonaceous phyllites and has a gold-dominated association with porous arsenopyrite, which is the predominant gold-associated sulphide in the Cachorro Bravo deposit (Roncato et al., 2015). Hydrothermal alteration proximal to quartz lodes is reflected by the bleaching and sericitisation of the wall rocks and the abundance of disseminated pyrite, pyrrhotite and arsenopyrite, as well as stibnite and berthierite (Roncato et al., 2015).
Reserves and Resources
Total oxide Mineral Resources and Ore Reserves, at 31 December, 2005 (AngloGold Ashanti Mineral Resource and Ore Reserve Report, 2005) were:
Measured + Indicated + Inferred Mineral Resources - 10.965 Mt @ 7.09 g/t Au, for 77.77 tonnes of contained gold;
Proved + Probable Ore Reserves (Cachorro Bravo + Laranjeiras + Oxides) - 3.69 Mt @ 4.11 g/t Au, for 15.19 tonnes of contained gold;
Total sulphide, transitional and oxide Mineral Resources and Ore Reserves, at 31 December, 2011 (AngloGold Ashanti Mineral Resource and Ore Reserve Report, 2011) were:
Measured + Indicated + Inferred Mineral Resources - 24.24 Mt @ 5.95 g/t Au, for 144.34 tonnes of contained gold;
Proved + Probable Ore Reserves (Cachorro Bravo + Laranjeiras + Oxides) - 1.265 Mt @ 5.05 g/t Au, for 6.391 tonnes of contained gold;
Total sulphide, transitional and oxide Mineral Resources, and Ore Reserves by orebody and ore type, at 31 December, 2015 (AngloGold Ashanti Mineral Resource and Ore Reserve Report, 2015) were:
Measured + Indicated + Inferred Mineral Resources - 35.03 Mt @ 4.72 g/t Au, for 165.35 tonnes of contained gold;
Proved + Probable Ore Reserves:
Cachorro Bravo sulphides (CdS I) - 0.21 Mt @ 4.59 g/t Au, for 0.98 tonnes of contained gold;
Carvoaria sulphides (CdS I) - 0.56 Mt @ 5.55 g/t Au, for 3.10 tonnes of contained gold;
Laranjeiras sulphides (CdS I) - 0.29 Mt @ 4.78 g/t Au, for 1.41 tonnes of contained gold;
Rosalino oxides (CdS I) - 0.97 Mt @ 2.20 g/t Au, for 2.15 tonnes of contained gold;
Sangue de Boi sulphides (CdS II) - 0.32 Mt @ 5.95 g/t Au, for 1.90 tonnes of contained gold;
São Bento sulphides (CdS II) - 0.24 Mt @ 6.55 g/t Au, for 1.56 tonnes of contained gold;
CdS II oxides - 0.37 Mt @ 2.64 g/t Au, for 0.97 tonnes of contained gold;
TOTAL - 2.96 Mt @ 4.07 g/t Au, for 12.07 tonnes of contained gold.
Total sulphide, transitional and oxide Mineral Resources, and Ore Reserves by orebody and ore type, at 31 December, 2021 (AngloGold Ashanti Mineral Resource and Ore Reserve Report, 2021) were:
Measured + Indicated + Inferred Mineral Resources - 28.11 Mt @ 3.68 g/t Au, for 103.46 tonnes of contained gold;
Proved + Probable Ore Reserves:
Rosalino underground sulphides (CdS I) - 0.33 Mt @ 4.40 g/t Au, for 1.45 tonnes of contained gold;
CdS I underground secondary (CdS I) - 0.12 Mt @ 3.33 g/t Au, for 0.41 tonnes of contained gold;
Cachorro Bravo underground sulphides (CdS I) - 0.02 Mt @ 3.71 g/t Au, for 0.07 tonnes of contained gold;
Laranjeiras underground sulphides (CdS I) - 0.21 Mt @ 3.21 g/t Au, for 0.68 tonnes of contained gold;
Carvoaria underground sulphides (CdS I) - 0.72 Mt @ 4.27 g/t Au, for 3.10 tonnes of contained gold;
Sangue de Boi underground sulphides (CdS II) - 0.35 Mt @ 5.29 g/t Au, for 1.87 tonnes of contained gold;
São Bento underground sulphides (CdS II) - 0.11 Mt @ 3.88 g/t Au, for 0.43 tonnes of contained gold;
CdS Stockpile sulphides - 0.12 Mt @ 1.35 g/t Au, for 0.16 tonnes of contained gold;
Rosalino open pit sulphides (CdS I) - 0.39 Mt @ 1.94 g/t Au, for 0.76 tonnes of contained gold;
Rosalino open pit oxides (CdS I) - 0.64 Mt @ 1.06 g/t Au, for 0.68 tonnes of contained gold;
Rosalino open pit transitional (CdS I) - 0.15 Mt @ 2.16 g/t Au, for 0.32 tonnes of contained gold;
CdS II oxides - 0.30 Mt @ 1.67 g/t Au, for 0.50 tonnes of contained gold;
CdS III oxides - 0.69 Mt @ 1.66 g/t Au, for 1.14 tonnes of contained gold;
CdS Stockpile oxides - 0.19 Mt @ 0.32 g/t Au, for 0.06 tonnes of contained gold;
CdS Stockpile transitional - 0.11 Mt @ 1.02 g/t Au, for 0.11 tonnes of contained gold;
TOTAL - 4.46 Mt @ 2.63 g/t Au, for 11.75 tonnes of contained gold.
NOTE: Mineral Resources are inclusive of Ore Reserves.
The information in this summary is drawn from Roncato et al. (2015) and the AngloGold Ashanti Mineral Resource and Ore Reserve Reports (2005 to 2021).
The most recent source geological information used to prepare this decription was dated: 2021.
Record last updated: 7/1/2023
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.
Corrego do Sitio 1
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Selected References:
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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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Roncato, J.G., Lobato, L.M., Lima, L.C., Porto, C.G., Silva, R.C.F., 2015 - Metaturbidite-hosted gold deposits, Corrego do Sitio lineament, Quadrilatero Ferrifero, Brazil: in Brazilian Journal of Geology v.45 pp. 5-22. doi:10.1590/23174889201500010001
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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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