Summary:
The Carajás Mineral Province hosts world-class deposits of Fe, Cu, Au, Mn, and Ni, resulting from polyphase tectonic evolution, accompanied by hypogenic and supergenic enrichment processes, developed on sedimentary and magmatic rocks of the Archean core of the Amazonian Craton.
Mineralization occurs mainly as a product of supergenic enrichment, developed on jaspilites (algoma-like BIFs interlayered with basalts) in high, flat-topped regions that make up the plateaus observable by remote sensors. The irregularity and discontinuity of the deposits along this mineral province demonstrates the existence of structures inherited from deformational events that favored the thickening of the jaspilite and the efficiency of supergenic processes through the tilting and fracturing of these rocks.
The main Carajás iron ore deposits are associated with flat-topped elevated plateaus, in general, elevated areas, between 650-800 meters, defined along two main morphological alignments corresponding to Serra Norte and Serra Sul. These alignments materialize the limbs of the Carajás Syncline.
The Serra Norte Complex corresponds to the inverted limb geological domain of the Carajás Syncline. The high deformation pattern of this domain is reflected in the geometry and the distribution of the iron formations, whose segmentation by faults and folds of different orientations and scales, individualizes plateaus from N1 to N9.
The plateaus of the Serra Norte Complex are limited to the north by the domain of volcanic rocks of the Parauapebas Formation, and to the south, by the domain of terrigenous sediments of the Águas Claras Formation.
The mineralization at The Serra Norte Complex is mainly formed from supergenic alteration of jaspilite, which constitutes the Carajás protolith. The high-grade ore is mainly represented by friable hematite, the structured canga is also considered as a mineralized lithotype.
Deposit N1 is in the extreme west of Serra Norte and corresponds to part of the homonymous plateau. This plateau has an elongated shape in the NW-SE direction. It is predominantly composed of rocks from the Carajás and Igarapé Cigarra formations. In general, the layers show medium to high angle dips to the northeast, configuring an inverted stratigraphic stack. The thickness of the layer varies between 250-600 m and is strongly controlled by folds and faults.
Deposits N2 and N3 are located on the homonymous plateaus, with an elongated shape in the E-W direction, in the central portion of the Serra Norte. The rocks of the Igarapé Cigarra Formation are predominant in these plateaus. In general, the layers show a medium to high angle dip to the north, configuring an inverted stratigraphic stacking.
Most of the iron formations of plateaus N2 and N3 were attributed to the Igarapé Cigarra Formation, they do not stand out in the relief due to the low thickness. Structural controls and their relative chronological ordering are like those described for N1, differing by the low continuity of iron formations, which reflects the importance of the faults for the local geological framework.
Plateau N4 is in the central-east portion of Serra Norte, where there are several mine pits, distributed along the homonymous plateau. The dimensions of N4 are big and it is composed of rocks from the Carajás, Parauapebas, and Igarapé Cigarra formations, with tabular shape and general dip to the west configuring a normal stratigraphic stacking. Prior to the start of mining, the plateau was already divided into the east and west portions by a drainage that separates the two main bodies of iron formations
The Carajás Formation occurs continuously in the central portion of the plateaus and corresponds to the domain with the highest thickness of iron formations, which are strongly controlled by strike-slip faults and present thickness between 200-500 meters.
On the N4 plateau, the Carajás Formation assumes a strong N-S trend and defines two occurrence belts called N4W and N4E, with a distinct structural pattern, separated by an eastward verging thrust fault. The N4W region is relatively simpler and behaves like a homocline, the N4E region is more complex, given the rotation of the banding, folding in southern portion and drag along the large dextral strike-slip faults.
The N5 plateau is in the extreme east of Serra Norte, where there are five mine pits called N5W, N5N, N5E, N5S, and M1, distributed along the homonymous plateau. This plateau has elongated geometry at the NNW-SSE direction, suffering a strong curvature in the north-central portion as a reflection of interference by folding. The iron formations occupy the central portion of the plateau layers and show general dip to the west direction, configured at a normal stratigraphic stacking. At N5, the Carajás Formation behaves like a homocline, with a trend varying from NW-SE to N-S and dips to the SE and E. The sinuous character in the northern portion of the plateau is given as a function of a syncline, which, associated with the fault system, verified throughout the plateau, controls the geometry of the iron formation.