Structure and iron mineralisation of the Carajás Province

Abstract

The Caraja ´s Province presents several volcano-sedimentary sequences that comprise the Itacaiu ´nas Supergroup. The rocks represent bimodal volcanism, and clastic and chemical sedimentation in relatively unstable basins subject to recurrent structural events with subsidence and volcanism. The Gra ˜o Para ´Group represents one of these sequences with mafic volcanic rocks that enclose discontinuous jaspilite lenses, with development of large high-grade orebodies (Fe.65%). This unit is named the Caraja ´s Formation and presents peculiar characteristics compared with other iron districts in the world, thereby departing from the classic Lake Superior or Algoma iron formation types. Owing to the dense vegetation, lack of outcrops and harsh landscape, the structural analysis of the district can only be accomplished by combination of regional field work, detailed structural work on the open pits and remotely sensed image interpretation, in this case Landsat ETM7, JERS-1 images and the shuttle radar topography mission (SRTM) digital terrane model. The regional trend of the several sequences of the area is approximately N-S and the structure is dominated by a flattened flexural fold system with axes moderately dipping WNW, intersected by several strike-slip faults subparallel to their axial plane. The Serra dos Caraja ´s represents an s-shaped synform-antiform pair, herein named the Caraja ´s Fold. This regional structure is partially disrupted by the Caraja ´s Shear Zone that divides it in the northern (Serra Norte) and the southern (Serra Sul) Ranges and also probably prepared the terrane with the development of pathways for mineralising hydrothermal fluids forming large highgrade massive iron bodies. Syntectonic granitic bodies played an important role in the structural evolution of the area as well. They caused localised ductile flattening deformation and thermal contact metamorphism in surrounding terranes. The Estrela pluton, for instance, was responsible for the discontinuity of the regional trend between the Serras do Rabo and Leste. The Caraja ´s Province is regionally the upper crustal product of a very shallowly eroded dome-and-keel geometry of Neo-Archaean volcano-sedimentary units intruded by syntectonic calc-alkaline intrusives and overlying pre-existing infracrustal rocks. The lithostructural data suggest continental-margin back-arc basin development and closure in an oblique collision belt, with N-S shallow crustal shortening, parallel to the inferred pre-existing strike of the stratigraphy.

Upland Lakes of the Carajás Region: Origin and Development through Time

“…1), which is an important metallogenic province on a global scale (Tolbert et al, 1971). This province is represented by felsic and mafic granulites (Pium Complex), granodioritic and tonalites (Xingu Complex), which form the Meso-archean basement, and by supracrustals Neo-archean metavolcanic-sedimentary sequences and banded iron formations (BIFs) related to Greenstone Belts of the Itacaiúnas Supergroup (Barros et al 2010;Macambira 2003;Rosière et al 2005). Sedimentary successions of the Águas Claras Formation were deposited over the Greenstone Belts (Nogueira et al, 1995).…”

Maghemite in Brazilian Iron Ores: Quantification of the Magnetite-Maghemite Isomorphic Series by Χ-ray Diffraction and the Rietveld Method, and Confirmation by Independent Methods

“…There is an ample discussion about the reconstruction of mineralization processes in BIF and other iron ores deposits. In Carajás, the most accepted model [1,70] proposes that both hypogene and supergene fluids are involved in deposit genesis. However, the availability of studies approaching supergenic enrichment within this model are still scarce, and most recent work describes only hypogenic iron mineralization.…”

“…Iron ore concentrates and pellets are a major export product of Brazil. Its mineralogy is generally simple, the main iron-bearing minerals being hematite and magnetite in the Carajás (state of Pará, northern Brazil) ore, and hematite with goethite in very variable amounts and rare magnetite in the ones from the Quadrilátero Ferrífero (state of Minas Gerais, southeast of Brazil), as well as diverse gangue minerals [1,2].…”

Anoxygenic photosynthesis linked to Neoarchean iron formations in Carajás (Brazil)

“…The Carajás Basin, within the CMP (Figure 1b), has a Mesoarchean (c. 3.0-2.86 Ga) basement composed of mafic granulites, migmatites, and metavolcanic rocks (Machado et al, 1991). The crystalline basement is overlain unconformably by Neoarchean and Paleoproterozoic volcanosedimentary sequences from the Grão Pará Group that have undergone subgreenschist to low-greenschist facies metamorphism (Krymsky et al, 2007;Machado et al, 1991;Rosière et al, 2006).…”