Fazenda Brasileiro - Maria Preta

Bahia, Brazil

Main commodities: Au
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The Fazenda Brasileiro or Maria Preta gold deposit is located at Serrinha in Bahia State, Brazil, some 250 km north-west of Salvador.   It falls within the Palaeoproterozoic Rio Itapicuru greenstone belt, near the north-eastern margin of the Archaean to Palaeoproterozoic São Francisco Craton,

The gold deposit is associated with polyphase shearing associated with two regional-scale, sinistral-oblique brittle-ductile shear zones.

Structural relationships indicate that the primary control of mineralisation was a D1 ductile simple shear zone with an 8 km east-west extension which developed contemporaneously with granitic diapirism and greenshist grade metamorphism.   The main gold lode is interpreted to have formed after the ductile phase, during D2 brittle-ductile dextral transpressive shearing and folding.

The deposit is hosted by, or is directly associated with, a highly deformed greenschist facies metamorphosed volcano-sedimentary sequence, occurring along the margin of a mafic (gabbroic) sill at the contact of tholeiitic basalts and a sequence of pelitic schists and psammites intercalated within the volcanic succession.   The ore occurs within carbonaceous volcaniclastic rocks, breccia and stockwork systems as hydrothermal quartz-gold shear veins within iron rich chlorite-magnetite schists, and as disseminations in felsic and mafic sub-volcanic bodies.   Alteration is pervasive throughout the shear zones and is characterised by carbonatisation and sericitisation of intermediate volcanic, volcaniclastic, and sub-volcanic rocks.

The mineralised veins are composed of quartz-albite-carbonate-arsenopyrite-pyrite-gold.   There were at least four overlapping periods of veining to produce a complex lode zone with veins at different angles and orientations to the structural fabric.

Reserves originally totalled: 15 Mt @ 8 g/t Au.

Reserves and resources at 31 December, 2010 (Yamana Gold website) were:
    Proven + probable reserve - 1.80 Mt @ 3.04 g/t Au for 5.47 t Au; plus
    Measured + indicated resource - 7.88 Mt @ 1.86 g/t Au for 14.7 t Au; plus
    Inferred resource - 2.02 Mt @ 3.11 g/t Au for 6.3 t Au

For detail consult the reference(s) listed below.

The most recent source geological information used to prepare this summary was dated: 2010.    
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:
Mello E F, Xavier R P, McNaughton N J, Hagemann S G, Fletcher I and Snee L,  2006 - Age constraints on felsic intrusions, metamorphism and gold mineralisation in the Palaeoproterozoic Rio Itapicuru greenstone belt, NE Bahia State, Brazil: in    Mineralium Deposita   v40 pp 849-866
Reinhardt M C, Davison I  1990 - Structural and lithologic controls on Gold deposition in the shear zone-hosted Fazenda Brasileiro Mine, Bahia state, northeast Brazil: in    Econ. Geol.   v85 pp 952-967
Teixeira J B G, Kishida A, Marimon M P C, Xavier R P, McReath I,  1990 - The Fazenda Brasileiro Gold deposit, Bahia: geology, hydrothermal alteration, and fluid inclusion studies: in    Econ. Geol.   v85 pp 990-1009
Xavier R P and Foster R P,  1999 - Fluid evolution and chemical controls in the Fazenda Maria Preta (FMP) gold deposit, Rio Itapicuru Greenstone Belt, Bahia, Brazil: in    Chemical Geology   v.154 pp. 133-154

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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