Levantamento e estudo das ocorrências de grafita do Distrito Grafitífero Aracoiába-Baturité, CE

• Ano de defesa: 2011
• Autor(a) principal: Fragomeni, Paulo Roberto Pizarro
• Orientador(a): Pereira, Ronaldo Mello
• Banca de defesa: ávila, Ciro Alexandre , Seoane, José Carlos Sicoli , Menezes, Paulo de Tarso Luiz , Silva, Francisco José da
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade do Estado do Rio de Janeiro
• Programa de Pós-Graduação: Programa de Pós-Graduação em Análise de Bacias e Faixas Móveis
• Departamento: Centro de Tecnologia e Ciências::Faculdade de Geologia
• País: BR
• Palavras-chave em Português: Grafita; Bioassinaturas; Suturas de bacias; Grafita singenética; Grafita epigenética; Prospecção; Análise termogravimétrica
• Palavras-chave em Inglês: Graphite; Biosignatures; Basin sutures; Syngenetic graphite; Epigenetic graphite; Research thermo-gravimetric analysis
• Área do conhecimento CNPq: CNPQ::CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS::GEOLOGIA::PETROLOGIA
• Link de acesso: http://www.bdtd.uerj.br/handle/1/7002

The Aracoiába-Baturité Graphite-bearing District has graphitic gneiss deposits (disseminated ore) and vein (solid ore) with different genetic origins and their own physical characteristics and geological environments. The graphite gneiss ore is of sedimentary, syngenetic origin, with 1.5% to 8% C content, which is distributed along two long parallel belts, hosted in the Baturité Sub-unit, which consists of a major regional metallotect. The association of metamorphic graphite disseminated in metasediments of the Acarápe Sequence consists of a geoindicator of an old Neo-Proterozoic sedimentary basin and also can be considered a geosuture zone, the result of the subsequent closing of a primitive ocean. The rocks of this subunit correspond in the paleogeography of the Acarápe Sequence to the facies of the bottom of a slope and of an abyssal plain. The vein ore ( deposited fluid ) is epigenetic and, with C contents of between 20% and 70%, forms tabular bodies and pockets, controlled on a local scale by relief structures (faults, fractures, contact zones, fold axes, etc.), which allowed seepage of pneumatolithic solutions relating to the plutonic body of Pedra Aguda. The variations in the values of the ratios between stable carbon isotopes (δ13C) in the graphite of the disseminated ore are -26.72 to -23.52 and of the solid ore -27.03 to -20.83 , showing a sign of biological activities (biosignatures), and it can be said that the graphite of the above samples is derived from organic matter. The main prospecting guides for graphite were presented and the following geophysical methods tested: Electro-resistivity (ER); Ground Penetrating Radar (GPR); Magnetometry; Very Low Frequency (VLF); and Spectral Induced Polarization (SIP) / Electro-resistivity (ER). It was found that the combination of the Spectral Induced Polarization (SIP) and Electro-resistivity (ER) methods proved the most efficient. In relation to determining the carbon content using thermogravimetry (TG), which is the most commonly used method for this element, it was found that the bands of burning attributed to the carbon in the ore in the Aracoiába-Baturité District (340° to 570°C and from 570oC to 1050°C) were different from the bands of the ore in Minas Gerais ( 350°C to 650°C and 650°C to 1050°C ). This finding suggests the need to determine beforehand the temperature ranges for each region studied.