Jacurici Complex, Ipueira-Medrado Sill

Bahia, Brazil

Main commodities: Cr
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The chromitite bearing Ipueira-Medrado Sill is located in northern Bahia State, north-eastern Brazil, some 220 km NNW of Salvador.

The Ipueira-Medrado Sill was emplaced in the northeastern sector of the São Francisco Craton and belongs to the regionally extensive Jacurici Complex of mafic-ultramafic intrusions emplaced into an Archaean granulite gneiss terrane of the Caraíba granulite complex.   The Jacurici Complex intrusions are distributed over a north-south elongated area of 70 x 20 km.   Limited dating of the mafic-ultramafic intrusions of the complex suggests they are around 2038±19 Ma in age.   The Jacurici Complex parallels the copper bearing Caraíba mafic complex (see the Caraiba-Jaguari copper mine record) to the north, separated by the 2.1 Ma Itiúba Syenite, while the larger Campo Formoso mafic-ultramafic intrusion is located some 50 km to the west.

The Ipueira-Medrado Sill is a single intrusion that has been tectonically disrupted by faulting and folding into two segments that outcrop on the limbs of a synform.   It is conformable with the enclosing quartzo-feldsapthic gneisses, which in the hangingwall include olivine bearing marble, calcsilicates and metachert.

The sill is composed mainly of ultramafics with dunite, harzburgite and pyroxenites making up 80% of the body.   It has been divided into three zones as follows from the base:
1). Marginal Zone, 5 to 20 m thick - sheared gabbro and orthopyroxene rich harzburgite.
2). Ultramafic Zone, 250 m thick - subdivided into  i). Lower Ultramafic Unit, composed of dunite and minor harzburgite with chain textured chromitite,  ii). Main Chromitite Layer, comprising massive and chain textured chromitites  iii). Upper Ultramafic Unit, mainly of harzburgite but also with minor chain chromitite and dunite.   Pyroxene increases upwards in the Ultramafic Zone to produce a pyroxenite at the top, while magmatic intercumulus amphibole makes up around 20% of the zone.
3). Mafic Zone, up to 40 m thick - consists of leuconorites to melanorites that are partially metamorphosed to amphibolite facies.

The ore in the Ipueira-Medrado Sill is mined from a single sinuous layer that is continuously developed (but structurally disrupted) throughout the 7 km long sill and varies from 5 to 8 m in thickness within the 300 m thick sequence of cumulate mafic-ultramafic rocks that make up the sill as described above.

The measured reserves of chromite ore in the Ipueira-Medrado Sill total   4.5 Mt @ 30 to 40% Cr2O3 and have been mined since 1974.
The geologic resource in the Jacurici Complex is estimated to be around 30 Mt @ a similar grade.

For detail consult the reference(s) listed below.

The most recent source geological information used to prepare this summary was dated: 2003.    
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:
Friedrich, B.M., Marques, J.C., Ribeiro Olivo, G., Frantz, J.C., Joy, B. and Queiroz, W.J.A.,  2020 - Petrogenesis of the massive chromitite layer from the Jacurici Complex, Brazil: evidence from inclusions in chromite: in    Mineralium Deposita   v.55, pp. 1105-1126.
Lord, R.A., Prichard, H.M., Sa, J.H.S. and Neary, C.R.,  2004 - Chromite Geochemistry and PGE Fractionation in the Campo Formoso and IPueira-Medrado Sill, Bahia State, Brazil: in    Econ. Geol.   v.99, pp. 339-363.
Marques, J.C. and Feirreira Filho, C.F.,  2003 - The Chromite deposit of the Ipueira-Medrado Sill, Sao Francisco Craton, Bahia State, Brazil: in    Econ. Geol.   v.98, pp. 87-108.

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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