This paper presents the results of the investigation of a supergene manganese occurrence in the southeast of Brazil, using the Induced Polarization geophysical method. This study aims to characterize the surface and subsurface morphology of one of these occurrences, named São Roque, based on the contrast of the electrical properties of the ore and the host rocks. The ore, which is composed mainly of manganese oxides and hydroxides and subordinated graphite, occurs in the form of small discontinuous lenses hosted by quartzites and schists of the Itapira Group. The geophysical survey consisted on 10 lines of Induced Polarization Tomography using a Wenner-Schlumberger array, with an along-line electrode separation of 10 m for all lines. The IP data were modeled through commercial inversion software to generate 2D section models of chargeability. In order to create a 3D visualization model of chargeability, the 2D inversion models were then combined and interpolated in order to create a 3D visualization model. The 3D model revealed two independent ore bodies in both surface and subsurface, characterized for high chargeability (up to 20mV/V), instead of a single elongated orebody as suggested by the lateritic surface in the field. In addition, the model showed that the orebodies are elongated perpendicular to the area main structural trend and the regional alignment of the lateritic occurrences, which can bring new ideas in terms of local exploration strategies for manganese in this context.

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In this paper are presented the results of the combination between a resistivity method and geological surface mapping, applied to the study of an area with potential mineralization of copper sulfides sited on the northern edge of the Camaquã sedimentary basin, Bra-zilian southern. The copper mineralization is housted in a metamorphosed, silicified and fractured sandstone with abundant presence of malachite and azurite in the fractured planes of the rock. The geophysical survey in this work consisted of 6 lines of electric resistivity tomography in Wenner-Schlumberger array, of 520 m long and 10 m of space between the electrodes, arranged in a regular grid according to structural criteria previously established. The inversion models show a low resistivity area in a depth of 60 m that can be related to a sulphidation zone. This zone with a somewhat circular shape is aligned in the NW-SE direction and is approximately 100 meters long. High resistivity areas around it indicate that it is surrounded by a silicification zones. The evidence for an argillic zone peripheral to the deposit is expressed by the occurrence of abundant copper carbonate in surface, since clay and carbonates are formed from low temperature and final stages of hydrothermal crystallization of the deposit.

ABSTRACT.Hydrocarbons meet more than 50% of world wide demand for industries and main transportation means. Unfortunately, the use of this energetic matrix in large scale is the frequent cause of contamination of soil and groundwater, scenarios that present risks to human health and limit the use of natural resources.Geophysical methods constitute an important tool for the evaluation of these cases, as they offer relevant information in an indirect and comprehensive manner, with low relative cost, guiding remediation efforts in contaminated areas. In this work a geophysical study was performed in Electro DC Resistivity and Induced Polarization in a sandy tropical soil contaminated by a 58,000l diesel spilling a railway accident, and aimed to diagnose the contamination scenario after more than seven years from the incident. 11 lines of electrical imaging were performed with generation of resistivity and charge ability models integrated in 3D view blocks. The results indicated the punctual occurrence of shallow zones of low resistivity close to the place of contaminants infiltration, associated to the action of natural attenuation processes. The model presented zones of high chargeability associated to the probable presence of metallic minerals formed during and after the action of biodegradation processes.The results set pointed to a general scenario of an advanced stage of decontamination in the area, with effective natural attenuation processes.Keywords: accident, hydrocarbons, natural attenuation, induced polarization, DC resistivity. RESUMO.Os hidrocarbonetos atendem a mais de 50% da demanda mundial das indústrias e principais meios de transporte. Infelizmente, o uso desta matriz energética em larga escalaé a causa frequente de contaminações de solos eáguas subterrâneas, situações que representam riscoà saúde humana e inviabilizam o uso de recursos naturais. Os métodos geofísicos constituem um importante instrumento de avaliação nestes casos, pois oferecem informações relevantes de maneira indireta e abrangente, com baixo custo relativo, e orientam ações de remediação deáreas contaminadas. Este trabalho realizou um estudo geofísico de Eletrorresistividade e Polarização Induzida em solo tropical arenoso contaminado por vazamento de 58.000l de diesel em acidente ferroviário, e buscou diagnosticar o cenário da contaminação decorridos mais de sete anos do acidente. Foram realizadas 11 linhas de imageamento elétrico com geração de modelos de resistividade e cargabilidade integrados em blocos de visualização 3D. Os resultados indicaram a ocorrência pontual de zonas rasas de baixa resistividade próximas ao local de infiltração de contaminantes, associadasà ação de processos de atenuação natural. O modelo apresentou zonas de elevada cargabilidade associadasà provável presença de minerais metálicos formados durante e após a ação dos processos de biodegradação. O conjunto dos resultados apontou para um panorama geral de avançado estágio de descontaminação daárea, com atuação efetiva dos processos de atenuação natural.P...