Sao Bento

Minas Gerais, Brazil

Main commodities: Au
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The São Bento mine is located in the eastern portion of the Quadrilátero Ferrífero district, approximately 50 km to the east of the city of Belo Horizonte, Minas Gerais, Brazil.

The geology of the Quadrilátero Ferrífero is dominated by Archaean and Proterozoic volcano-sedimentary sequences and Precambrian granitic complexes. The oldest rocks in the district are an Archaean gneiss-migmatite complex which is overlain by the late Archaean Rio das Velhas Supergroup.

This supergroup is sub-divided into the basal Quebra Osso Group, succession of komatiitic ultramafic and mafic rocks with BIF intercalations, overlain by the Nova Lima Group, a middle sequence of schists and phyllites that contain lenses of dolomitic and calcic white marble and by thin beds of iron formation, and finally the upper Maquine Group of quartzites, conglomerates and phyllites. These are discordantly overlain by the Palaeoproterozoic Minas Supergroup quartzites, schists, phyllites, meta-conglomerates, carbonates and iron formations that produce the major iron deposits of the district.

Mineralisation at São Bento is restricted to the fine grained sediments, tuffs and chemical sediments of the Nova Lima Group. Four formations have been differentiated on the property, namely the Carrapato, the Lower Iron, the Basal Iron and the São Bento Formations.

The ore at São Bento is localised within the Basal Iron Formation which has been continuously mined from the surface to a depth of 1100 m. Based on lateral lithologic variations, the basal Iron Formation has been divided along strike into three portions, namely Orebody No. 1, Orebody No. 2 and Orebody No. 3 (otherwise known as the São Bento/Pinta Bem Orebody).

The No. 1 Orebody represent the best developed mineralisation, reaching a thickness of 35 m and displaying al least 6 periods of gold/sulphide mineralisation. The ore zone is distinctly banded and comprises alternating layers of sulphide and iron carbonate.

Gold is closely associated with the sulphides, being present either as free metal, on crystal boundaries or enclosed within sulphide grains. The gangue and sulphides are generally 0.5 to 5 mm across, while the gold varies from 1 to 250 µm, averaging 70 µm. The average gold content is very consistent as are the ratios between gold, arsenic and sulphur.

The ore deposits dip at 55 to 60° and have an average true thickness of 1.4 m. In 1999 540 014 tonnes of ore were milled to produce 3.9 t (0.127 Moz) of gold at an average grade of 8.18 g/t Au. The total cash cost was USDS 189 per oz. The mineable reserves were 3.238 Mt @ 8.95 g/t Au for 29 t (0.932 Moz) of gold while the in-situ resource was 4.04 Mt @ 10.6 g/t Au for 43 t (1.38 Moz) of Au. Total production to that stage was 35.1 t (1.13 Moz) of Au. The mine is operated by Eldorado Gold Corp., which is 36% owned by Gold Fields Ltd.

The most recent source geological information used to prepare this summary was dated: 2001.    
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:
Anonymous  2001 - Eldorado Gold Corp: in    extract from Eldorado Gold Corp. web site http://www.eldoradogold.com    5p
Pereira S L M, 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   v32 pp 571-595

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

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