Caracterização geológica e geoquímica do dique máfico do complexo máfico-ultramáfico da fazenda Mirabela (Mina Santa Rita), Itagibá – BA

• Autor(a) principal: Silva, Daniel dos Santos
• Data de Publicação: 2021
• Tipo de documento: Trabalho de conclusão de curso
• Idioma: por
• Título da fonte: Repositório Institucional da UFS
• Texto Completo: https://ri.ufs.br/jspui/handle/riufs/18463
• topic: Geologia; Ensino superior (UFS); Dique; Máfico; Ultramáfico; Sulfeto; Níquel; Mineralogia; Mina Santa Rita (Itagibá – BA); Dikes; Mafic; Ultramafic; Sulphide; Nickel; CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS::GEOLOGIA::MINERALOGIA

This work comprises the first technical-scientific study of the mafic dyke from Santa Rita Mine. It aims the geological characterization of this structure, based on bibliographical survey, descriptions of drill cores and interpretation of the whole rock geochemical data. The mafic dyke lodged at the Fazenda Mirabela Intrusion, corresponds to a mafic-ultramafic body that intruded the high-grade metamorphic rocks of the Itabuna-Salvador-Curaçá Belt (CISC), at the end of the paleoproterozoic orogeny at 1.99 Ga. This intrusion comprises a stratiform body, with an ultramafic lithological sequence composed of dunite, harzburgite, olivine-orthopyroxenite, orthopyroxenite and websterite, overlaid by gabronorites. The ultramafic sequence hosts the stratabound/stratiform Ni-Cu magmatic sulfide deposit of the Santa Rita (Santa Rita Mine), with measured and indicated resources of 59,173 Mt. The mafic dyke intercepts the Fazenda Mirabela Intrusion according to azimuth N 120°, outcropping only on the East and West walls, between the North and Central pits of Santa Rita Mine. Descriptions of drill cores have used to identify lithological characteristics such as lithological contact relationships, color, grain size, textures, structures, primary and secondary mineralogy, in addition to the sulphides occurrence. These descriptions show that the mafic dyke of the Santa Rita Mine represents a dolerite, with strong magnetism, which intersects all lithologies of the Fazenda Mirabela Intrusion. Chalcopyrite, pentlandite and pyrrhotite occur as intercumulus and remobilized sulfides, in concentrations ranging from 0.1 to 0.5%. Geochemical analyses have used to discourse about major (Al2O3, CaO, FeOt, TiO2, P2O5, K2O, Na2O) and trace (Ni, Co, Cr, V, Cu, Sr) elements fractionation, aiming identifying the geochemical affinity and geotectonic environment, in addition to analyse the distribution contents of Cr, Ni, Cu, Pt and Pd elements, compared to the Santa Rita Mine mineralized range. The geochemical interpretations indicate that the mafic dyke has formed from a tholeiitic magmatism, in an intraplate extensional regime. The comparison of whole rock geochemical data of the Santa Rita mafic dyke and tholeiitic basalts and transitional tholeiitic basalts of the subalkaline mafic of dykes swarms from Ilhéus-Olivença, which belongs to the Coastal Province, allowed to establish similarities in terms of fractionation patterns of major and trace elements and in terms of geochemical affinity and tectonic environment type. Thus, this work contemplates the proposed objectives and opens possibilities for new studies and interpretations about the geology of Santa Rita Mine, as well as the occurrences of mafic dykes along the East bank of the São Francisco Craton.