Morro do Ouro, Brasilia, Rio Paracatu

Minas Gerais, Brazil

Main commodities: Au
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The Morro do Ouro gold deposit at the Paracatu Mine of Kinross Brasil Mineração S.A., in Minas Gerais, is located some 240 km SSE of Brasilia and 500 km NNW of Belo Horizonte (#Location: 17° 10' 55"S, 46° 52' 59"W).

The deposit is hosted by late Meso- to Neoproterozoic sedimentary rocks within the north-south trending Brasília Belt that extends along the western margin of the São Fransisco Craton and lies within the Central Brazil Shield. Whilst the sedimentary character and textures of these rocks are mostly preserved in the northern part of the belt, in the southern part, where Paracatu is located, they have been subjected to intense deformation and metamorphism, with lithological contacts being primarily tectonic. A series of ENE to WNW trending thrust faults is extensively developed along the belt, whilst metamorphic grades increases to the west as the imbricated thickness of the fold belt increases. The timing of deformation is estimated at 800 Ma to 600 Ma during the Brasiliano Orogenic Cycle.

The host sequence belongs to the ~0.9 to ~1000 Ma Canastra Group which is exposed along the south-central portion of the Brasília Belt, and is composed of sandy and shaley metasedimentary rocks which were locally metamorphosed to greenschist grade, although locally, amphibolite grade assemblages have been reported. The immediate host is a thick sequence of phyllites belonging to the basal Morro do Ouro Member of the Paracatu Formation of the middle Canastra Group. The Morro do Ouro Member is an ~100 m thick layer of pyrite-bearing black carbonaceous graphitic phyllite with interbedded relatively continuous thin layers and lenses of impure quartz sandstones. The overlying Serra da Anta Member is a sericitic phyllite. Both phyllites contain fine-grained quartzite intercalations. These two members have been thrust over carbonates of the Vazante Formation that belong to the same stratigraphic package.

The host phyllites of the Paracatu Formation have undergone extensive deformation and contain well-developed quartz boudins and associated sulphide mineralisation. Gold mineralisation is closely related to a period of ductile deformation associated with shearing and overall NE vergent thrust faulting. Intense, low angle isoclinal folds are also common. The ductile deformation at the Morro do Ouro gold deposit is localised within a structure that is a subsidiary of a larger thrust. The extensive flat lying orebody lies within the horizontal segment of a monoclinal thrust that is characterised by a strong mylonitic foliation within the host graphitic phyllites. In detail, the better gold is found along the hinge zones of isoclinal folds and along S-C surfaces which were transformed into dilatant sites during progressive shearing. The same progressive shearing produced multiple vein sets and intense boudinage of quartz veining introduced in preceding episodes of the same deformational event. The mineralisation appears to be truncated to the north by a major ENE trending normal fault which may have displaced the mineralisation upwards to be eroded from the up-thrown block.

Sericite minerals are common, likely as a result of extensive metamorphic alteration of the host rocks. Primary sedimentary features and bedding planes are easily recognizable, but are intensively deformed by thrusting, particularly along bedding planes, and the development of sygmoidal and boudinage structures.

The Paracatu mineralisation has been subdivided into four horizons defined by the degree of oxidation, surface weathering, and sulphide mineralisation. The contact between unmineralised host rock and the various mineralised horizons is gradational, occurring over a 10 m thick interval that is characterised by arsenic values of 200 to 500 ppm and grades of up to 0.2 g/t Au. The sulphide content typically does not exceed 3 to 4%. The most common sulphides are arsenopyrite, pyrite and pyrrhotite. Galena is relatively common and may be accompanied by sphalerite. Chalcopyrite occurs locally in fractures within the main sulphide minerals listed above. A distinct mineralogical zoning is evident, with the arsenopyrite content increasing towards the centre and west and in the zones of intense deformation. Gold grade increases in sympathy with the arsenopyrite content. Pyrrhotite occurs in the western part of the deposit with elevated gold grades accompanying higher pyrrhotite contents. The deposit formation model proposed for Paracatu suggests that gold and arsenopyrite were introduced concurrently during the deformation event. Gold occurs either as free gold or electrum.

In the oxide zone, gold occurs as free metal in the quartz boudins, accompanied by sulphides and minor carbonate and after decomposed sulphides in the enclosing phyllite, concentrated in pressure shadows produced by the presence of the boudins. The initial viability of the deposit was determined by the flat lying attitude of the ore zone which forms a low hill with no overburden, enhanced by the deep oxidation of the ore. The oxidation has released gold from the sulphides and carbonates to be free milling, while it has also decomposed the rock so no crushing or blasting is required in the oxide zone.

In the primary zone gold is distributed in the lattice or in micro-fractures within iron and arsenic sulphides, and in association with carbonates.

The operation was one of the lowest grade profitable mines in the world in 2000. In 1999 some 17.47 Mt of ore were mined at an average grade of 0.45 g/t Au. The gold recovery was 73%, for 5.7 t (0.185 Moz) of gold at a cash cost of $US 176 per oz.
    Reserves and resources in 1999 stood at 124 Mt @ 0.41 g/t Au.

Published Ore Reserves and Mineral Resources at December 31, 2006 (Kinross Gold Corp.) were:
    Proved + Probable Reserves - 1262 Mt @ 0.4 g/t Au for 505 t of contained gold.
    Measured + Indicated Resources were - 67.5 Mt @ 0.33 g/t Au for 22 t of gold.
Production in 2006 amounted to 17.637 Mt of ore @ 0.38 g/t Au, for 5.42 t of Au produced (ie. 81% recovery of the 6.7 t contained gold).

Published Ore Reserves and Mineral Resources at December 31, 2015 (Kinross Gold Corp. Annual Reserves and Resources Report, 2016) were:
    Proved + Probable reserves - 687.990 Mt @ 0.40 g/t Au for 300 t Au;
    Measured + Indicated resources - 315.508 Mt @ 0.30 g/t Au for 102 t Au; (exclusive of reserves)
    Inferred resources - 10.515 Mt @ 0.40 g/t Au for 4.5 t Au

Published Ore Reserves and Mineral Resources at December 31, 2021 (Kinross Gold Corp. Annual Reserves and Resources Report, 2021) were:
    Proved + Probable reserves - 536.866 Mt @ 0.40 g/t Au for 225 t Au;
    Measured + Indicated resources - 309.070 Mt @ 0.30 g/t Au for 92.5 t Au; (exclusive of reserves)
    Inferred resources - 75.592 Mt @ 0.30 g/t Au for 25.5 t Au

The mine has been in production since 1988. In 2000, Rio Paracatu Mineracao was controlled by RTDM, the Brazilian subsidiary of the operator Rio Tinto (51%) with the balance held by TVX Normandy. From December 2004, the operating company was wholly owned by Kinross Gold Corporation.

Information in this record has been partly drawn from: Sims, J., 2014 - Paracatu Project Brazil; an NI 43-101 Technical Report prepared for Kinross Gold Corporation, 132p.

The most recent source geological information used to prepare this summary was dated: 2014.     Record last updated: 14/3/2022
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.

  References & Additional Information
   Selected References:
Carvalho M.O., Valeriano C.M., Neto C.C.A., Diniz Oliveira G. and Heilbron, M.,  2019 - The Vazante and Canastra groups revisited: Sm-Nd and Sr isotopes - evidence for contribution from Tonian intraplate magmatism during passive margin development along the SW Sao Francisco margin, Brazil: in    Brazilian Journal of Geology,    16p. DOI: 10.1590/2317-4889201920180081.
Freitas-Silva F H, Dardenne M A, Jost H  1991 - Lithostructural control of the Morro do Ouro, Paracatu, Minas Gerais, gold deposit: in Ladeira E A (Ed.),  Brazil Gold 91 Balkema, Rotterdam    pp 681-683
Hitzman M W  1997 - Sediment-hosted Zn-Pb and Au deposits in the Proterozoic Paracatu Vazante fold belt, Minas Gerais, Brazil: in    http://www.dregs.org/absa997.html    1p
Zini A, Forlim R, Andreazza P, de Souza A   - The Morro do Ouro gold deposit, Paracatu, Minas Gerais: in   Gold and Zinc-Lead Deposits of Paracatu and Vazante xiii IGES - II CGBq (excxursions)    pp 133-139

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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