CARACTERIZAÇÃO GAMAESPECTROMÉTRICA E PETROGRÁFICA DE GRAFITA FLAKE DISSEMINADA EM METASSEDIMENTOS DE ALTO GRAU METAMÓRFICO NA REGIÃO DE QUATIS, SUL DO ESTADO DO RIO DE JANEIRO

Gamma spectrometric and petrographic characterization of disseminated flake graphite in high grade metamorphic sediments in the Quatis region, southern Rio de Janeiro State

Abstract

The investigated flake graphite occurs in the southern region of Rio de Janeiro State (SE Brazil), and is disseminated in high grade Neoproterozoic metasediments (metapelitic gneisses) (up to granulite facies), interdigitated with the orthogranulitic rocks (basement) of the Juiz de Fora Complex. These lithotypes are tectonically related to the Ocidental Terrain Superior Domain, belonging to the Central Ribeira Belt. Aerogamma spectrometry and aeromagnetometry data were used to recognize the signature patterns of the gneisses and surrounding rocks. The eTh concentrations are expressive throughout the area where the gneisses associated with graphite occur, exhibiting correlation with the uranium channel. In the geological-geophysical profiles, there are similarities between the airborne and ground data, however, eU and eTh are also correlated, unlike potassium, which showed variations, without a defined pattern. Graphite grains occur associated with sillimanite-granada-biotite gneiss with graphite, commonly next to biotite, being deformed by milonite foliation. The graphite shows different habits, having been classified into tabular reeds (45%), tabular with ragged edges (21%), ragged (31%) and basal (hexagonal) section (3%). Crystal size varied between very fine (dust) (41.7%), flake wide (11.7%) and extra large (11.2%) for the crystals larger than 0.30 mm of the sample.