HEAVY MINERALS AND ZIRCON MORPHOLOGY: PROXIES BETWEEN RONDON DO PARÁ BAUXITES AND ITAPECURU ROCKS

Abstract

The Eastern Amazon bauxite districts are located in the domain of the sedimentary rocks of the Itapecuru Group, which are considered to be their probable parent rocks. To assist in the elucidation, it was investigated the heavy minerals from Rondon do Pará bauxites. The assemblage is formed by ultrastable minerals, both in the Itapecuru and in the bauxite in similar concentrations: zircon, tourmaline, rutile and staurolite. They showed wide varieties of shapes, textures and structures, particularly for zircons, that suggest different sources of provenance. The euhedral zircons in general display the bipyramids {101} and the prisms {100}, which correspond to the S and P zircons, indicative of alkaline granites as source rocks for the Itapecuru, and that in turn are in the bauxite profile. Zircon ́s cathodoluminescences also similarly indicate different sources. They also exhibit variable concentrations of Zr, Hf, Th, U, Nb and Y, but the Zr/Hf ratios are quite constant. Therefore, the Zr/Hf ratios and the do-main of S-types and P zircons, both in the Itapecuru and in the bauxites, demonstrate that in fact its rocks, specifically those that occupied the current bauxite profile, were their parent rocks, thus strengthening the link between the two, bauxite and Itapecuru rocks. Keywords: cathodoluminescence; typology of zircon; zircon chemistry.