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Rem: Revista Escola de Minas

Print version ISSN 0370-4467

Abstract

CHAVES, Alexandre de Oliveira et al. Mineralogy and provenance of black sands from Iriri - ES. Rem: Rev. Esc. Minas [online]. 2011, vol.64, n.4, pp.421-428. ISSN 0370-4467.  http://dx.doi.org/10.1590/S0370-44672011000500006.

Black sands from the Iriri beach (ES) present a wide variety in their mineral content. From the optical and morphological properties and the chemical compositions of individual grains, it was found that crystals of quartz (45% vol.) and ilmenite (35% vol.) represent the main mineral phases of the material. In the remaining portion, the heavy minerals of magnetite, monazite, zircon, kyanite, sillimanite, almandine and grossular garnets, spinel, actinolite, chlorite, rutile, augite and aragonite have been found. Taking into account the regional geology of the continental area and sedimentary basin surrounding Iriri, the provenance analysis suggests that: a) the quartz originates from the regional paragneisses, the pre to syn-collisional granitoids and the coastal granulites, b) the association of ilmenite, magnetite, augite, and chamosite arises from Mesozoic amygdaloid tholeiitic basalts of the basin, c) grossular, spinel, and actinolite come from orthoamphibolites and calc-silicate rocks, d) almandine arises not only from paragneisses but also as syn-collisional peraluminous granitoids and coastal granulites, and the latter rocks also have been the source of rutile; e) kyanite is from the Cabo Frio terrain; f) sillimanite comes from the sillimanite-garnet-biotite paragneisses located near the Espirito Santo coast, g) a zircon subtype, along with monazite, arises from post-collisional G4 and G5 suites and another group of zircon represents crystals of the Paleoproterozoic basement away from the area of deposition; h) aragonite has a biogenic origin, from fragments of mollusk shells or coral reefs.

Keywords : Iriri; black sands; heavy minerals; mineralogy; provenance.

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