Pedogênese e classificação de latossolos desenvolvidos de itabiritos no Quadrilátero Ferrífero, MG

Abstract

Located in the Midwest of the State of Minas Gerais, a region called Quadrilátero Ferrífero covers an area of approximately 7,000 km2. Since the seventeenth century, it is known as goldand iron-producing province, and the geological context is therefore one of the best-studied of Brazil. The regional topography is very rugged, with mostly poorly developed pedogenesis, especially Cambissolos Háplicos, Neossolos Litólicos and Neossolos Regolíticos. In a smaller proportion and on colluvial ramps (hilly relief), very Fe-rich Latossolos Vermelhos occur, formerly Latossolos Ferríferos. This study characterized the physical, chemical and mineralogical properties of samples from nine ferric and hyperferric Latossolo Vermelho profiles, developed from itabirite and related rocks in the Quadrilátero Ferrífero, with the objectives of improving the understanding of their genesis and establish taxonomic criteria for their differentiation in the SiBCS at lower categorical levels. The high particle density values in these soils are peculiar and along with the strong, very small and granular structure, are factors that contribute to underestimate clay and overestimate silt, resulting in a higher silt/clay ratio than proposed by SiBCS for Latossolos. Variations in the levels of SiO2, Fe2O3, Al2O3, TiO2, MnO, P2O5, and of some trace elements indicate the diversity in the chemical composition of itabirite or a probable mixture with phyllitic rocks of the region. The ratios of Fe2O3/TiO2 (non-molecular) and TiO2/Fe2O3 (molecular) reported in the literature for separation of Latossolos Vermelhos differed between soils developed from itabirite and from mafic rocks. The magnetic attraction in sand, silt and clay varied greatly; due to the presence of magnetite, magnetization was higher in the former two fractions. The values of isomorphic Al-for-Fe substitution ranged from 0.07 to 0.11 and from 0.09 to 0.38 mol mol-1 in the structures of hematite and magnetite, respectively.