DEGEO - Departamento de Geologia
URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/8
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Item Pedogeochemistry of ultramafic soils from the Córrego dos Boiadeiros Body, Quadrilátero Ferrífero, Minas Gerais, Brazil.(2018) Fernandes, Victor Matheus Tavares; Evangelista, Hanna Jordt; Queiroga, Gláucia NascimentoThe Córrego dos Boiadeiros Body (CBB) comprises a metaultramafic-metamafic sequence located in the vicinities of Nova Lima town, central area of the Quadrilátero Ferrífero province. The main rock type is a serpentinite that grades upwards to weathering mantles with well-preserved pedogenetic horizons composed, from bottom to top, of four facies: the R Horizon (Fresh rock facies), the C Horizon (Alterite facies), the B Horizon (Transition facies) and the A Horizon (Solum facies). This article presents the results of geochemical and mass balance studies along a representative pedogenetic profile in order to evaluate the chemical transformations concerning major, trace and Rare Earth Elements. From bottom to top of the selected profile, there is enrichment in Fe2O3, Al2O3 and depletion in MgO and SiO2. There are also relative gains of metallic elements as Ni, Co, V and loss of Au. Cr is enriched at the uppermost horizon. Pt is enriched at the basis of the profile, but decreases towards the upper layers. The weathering mantle is REE-enriched and shows major fractionating of LREE over HREE. In order to evaluate the economic potential of the lateritic deposits, especially concerning Cr content, additional chemical analyses should be distributed over the entire body and its surroundings.Item The Statherian itabirite-bearing sequence from the Morro Escuro Ridge, Santa Maria de Itabira, Minas Gerais, Brazil.(2015) Braga, Flávia Cristina Silveira; Rosière, Carlos Alberto; Queiroga, Gláucia Nascimento; Rolim, Vassily Khoury; Santos, João Orestes Schneider; McNaughton, Neal JesseThe itabirite-bearing metasedimentary sequence from Morro Escuro Ridge comprises the basal units of the Espinhaço Supergroup and makes up a small tectonic inlier developed during one of the Brasiliano orogenic events (800-500 Ma), amongst horses of the Archean TTG gneisses, including sheared granites of the anorogenic Borrachudos Suite (~1700 Ma). The metasedimentary rocks are comprised of low-to intermediate-amphibolite facies schists, quartzites, conglomerates and banded iron formation (itabirite) correlatable with the sequences of the Serro Group, which underlies the metasedimentary rocks of the Espinhaço Supergroup in the Serra da Serpentina Ridge. A maximum Statherian deposition age (1668 Ma) was established using SHRIMP UePb isotopic constraints on zircon grains from conglomerate and quartzite units overlying the itabirite. The itabirite is predominantly hematitic and its geochemical characteristics are typical of a Lake Superior-type BIF deposited in a platformal, suboxic to anoxic environment distant from Fe-bearing hydrothermal vents. Close to the contact zone with amphibolites of the Early Neoproterozoic Pedro Lessa mafic suite, an increase of the magnetite content and crystallization of metasomatic Mg-hornblende and Ce-allanite can be observed. These mineralogical changes developed preferentially along the igneous contact zone but are probably co-genetic with the formation of alteration haloes in zircon grains during the Neoproterozoic Brasiliano orogeny (506 ± 6 Ma).