Abstract
The area studied is situated in the southwest part of the state of Bahia, Brazil. From Urandi to Brejinho das Ametistas, about 70 kilometers to the north, occurs an elongated sequence of metamorphic rocks. It forms part of the major geotectonic unit known as the Espinhaço Geosyncline. This part of the Brazilian Platform was probably formed during the Brazilian Orogenic Cycle. The ages of the rocks in this region, based on K/Ar determinations, lie in the range 520 to 790 m.y.. These ages correspond to the youngest rocks situated in the east of the São Francisco craton. The Precambrian rocks of the area comprise a lower sequence of gnaisses, schists and amphibolites and an upper sequence of phyllites, green schists, metaconglomerates, quartzites and limestones. The lense like shaped deposits of manganese ore are always intercaleted between the schists and phyllites. The lenses are conformable with the regional schistosity which strikes northeast and dips SE.
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