Ferriferous Carajás District is located in the southeastern Pará state being represented
by the Carajás ridge (main area) and East ridge (smaller areas). In these ridges occur jaspilites
of the Carajás Formation, which comprise more than 90% of this formation. In this work was
realized a study of sedimentary primary structures (meso and microscopic) preserved in the
jaspilites, aiming to characterize their depositional environment and establish parameters for
defining the pile. Sedimentary structures typical of jaspilite such as banding and lamination
represent the bedding of the rock and show that during the precipitation of a centimeter layer
would have pulses with the deposition of extremely thin sheet sand lenses, at the bands of
opaque would be lenses and lamination of silica minerals and at the bands of silica lenses and
lamination of opaque minerals. These features are interpreted as primary depositional. The
study of sedimentary features has never been used for correlation of different deposits, such as
those occurring in the North ridge, therefore the study of these features, in this work, will
suggest whether it is possible the correlation between these deposits, maybe allowing,
extensions to other ore bodies in the region. The Carajás Formation is here regarded as
Superior type BIF and are not metamorphosed. Sedimentary structures were divided into A)
primary: 1) banding, 2) plane-parallel laminations, 3) structures of scour and fill 4) levels of
intraclast sand; B) secondary: 1) inter-penetrative contacts, 2) features of thinning, 3) features
of rupture of bands, 4) pod structures, 5) spherulite sand and 6) increasing particle size of the
chert. The analysis of the features found along the jaspilite showed that in the Lower Portion
(70m) opaque bands are thicker, while in Higher Portion (150m) the silica are thicker,
reflecting a gradual depletion of iron in sea water from the beginning to the end of the
deposition. In addition, levels of intraclasts and the sedimentary structures of scour and fill
occur only in the Higher Portion, showing the action of laminar currents, while in the Lower
Portion, the absence of these structures shows that the environmental conditions were
comparatively more stable and constant. Therefore, the primary sedimentary structures in
detail, maybe criteria to differentiate the lower portion of the upper portion and be used to
establish the pile of the jaspilite deformed areas and make correlations with other deposits of
the Carajás Formation BIFs.
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