Genesis of clayey bodies in Quadrilatero Ferrifero, Minas Gerais, Brazil

摘要

This work deals with macromorphological, mineralogical, micromorphological and geochemical studies in clayey bodies from Quadrilatero Ferrifero in order to define their genesis and formation conditions in this geologic province from Minas Gerais State. Methodologies, based on the description of outcrops and drill cores, using X-ray diffraction (XRD), differential and gravimetric thermal analyses (DTA-TG), scanning electron microscopy (SEM), optical analysis of thin sections and chemical analyses allowed for the definition of two different genetic types of clayey bodies. One type, SET 1, occurs upon saprolitic material from Paleoproterozoic rocks in unconformity contact. It is constituted, from the base to the top, by four facies: nodular, ferruginous kaolinitic, mottled kaolinitic, and massive kaolinitic. The origin of this set is related to the deposition of lateritic materials by gravitational process. The faciological differentiation of this set is related to the syndepositional process and postdepositional mechanisms of ferruginization and deferruginization. The second type, SET 2, is composed by an ilmenitic-kaolinitic tabular facies in discordant relationships with the saprolite material from Paleoproterozoic rocks. The origin of this second set is related to "in situ" alteration of intrusive rocks of acidic composition. (C) 2003 Elsevier B.V. All rights reserved