Abstract The discovery of new mineral resources involves various research techniques through direct and indirect studies. The geophysical methods are important tools in the detection of deep deposits because they use the contrast between the physical properties of the hosting rocks and the mineralized zone. In this sense, electrical geophysical methods are widely used in the prospecting of sulfide deposits. This work presents and discusses the results of the application of the Induced Polarization geophysical method in the investigation of a tin mineral occurrence associated with greisen, located on the western border of São Sepé Granite. The study area is located in the central portion of the Rio Grande do Sul State, in the municipality of São Sepé (RS), housed in the metavolcano-sedimentary rocks of the Vacacaí Metamorphic Complex. Six lines of electrical tomography were parallel arranged in the N30W direction. The 2D inversion models allowed to identify areas of high chargeability (above 5.0 mV/V), possibly attributed to areas with sulfide accumulation. The areas with low values (below 1.9 mV/V) area associated with soil and rocks absent of mineralization. Through the 3D visualization models, it was possible to identify that the mineralized zone apparently has continuity for more than 36 m. These models also allowed identifying the morphology and the lateral continuity of the sulfide zone. Thus, the results of this work demonstrate the possibility of using Induced Polarization in the research of cassiterite deposits with associated sulfides due to the contrast of physical properties obtained from the high polarizability of the sulfides.

Abstract The dumps are areas of final disposal of solid wastes directly into the soil, with no technical criteria or collecting systems of gases or liquids. A large part of Brazilian municipalities have used this extreme damaging alternative to the environment up to the year 2010, when a federal law made compulsory the installation of sanitary landfills. However, large parts of the dumps were simply abandoned, although some eventually go through treatment after assessments of the state environmental agencies. This work presents the results of a geophysical investigation in a dump deactivated in 2004 in a small city in southern Brazil, where previous investigations have revealed contamination of soil and groundwater by leachate. Structural analyzes in the area of study combined to geological data from monitoring wells indicate the presence of contaminants in fractured granite, with a wide variation in the thickness of soil, saprolite and groundwater level. The integration of chemical analyses of the groundwater with electrical resistivity tomography (ERT) in 2D and 3D processing, revealed the existence of large contaminated areas within the limits of the dump flowing into the aquifer partially free up to 5m depth. Such areas may decrease gradually with the increase in depth and between 9m and 19m contaminated zones clearly predominate, associated with the Flow in the fractured aquifer. The indication of restricted and oriented zones suggests the targeting and accumulation of contaminants in two systems of preferential fractures. The discovery of these zones is fundamental for planning and the installation of pumping and decontamination systems of groundwater, considering a declining production of leachate since the closure of the dump.

Resumen Los basureros son zonas de depósito final de desechos sólidos directamente en el suelo, en ausencia de criterios técnicos o sistemas de recolección de gases o líquidos. Una gran parte de los municipios brasileños han utilizado esta alternativa extremadamente perjudicial para el ambiente hasta el año 2010, cuando una ley federal hizo obligatoria la instalación de rellenos sanitarios. Sin embargo, una gran parte de los basureros fueron simplemente abandonados, aunque algunos finalmente tuvieron algún tratamiento después de las evaluaciones de los organismos ambientales. Este trabajo presenta los resultados de la investigación geofísica en un basurero cerrado en 2004 en una pequeña ciudad del sur de Brasil, donde las investigaciones anteriores revelaron contaminaciones del suelo y de las aguas subterráneas por lixiviación. Los análisis estructurales en la región de estudios vinculados a datos geológicos de pozos de monitoreo indican la presencia de contaminantes en la fractura de granito, con amplias variaciones en el espesor del suelo, saprolita y el nivel del agua subterránea. La integración del análisis químico de las aguas subterráneas con los datos de la tomografía eléctrica (ERT) en el procesamiento de imágenes 2D y 3D, reveló la existencia de grandes áreas contaminadas dentro de los límites del basurero y el flujo en el acuífero parcialmente libre hasta 5m de profundidad. Estas zonas pueden disminuir gradualmente con el aumento de la profundidad y entre 9m y 19m predominan zonas contaminadas claramente orientadas, asociada con el flujo en el acuífero fracturado. La indicación de zonas restringidas y dirigidos sugiere la focalización y la acumulación de contaminantes en los dos sistemas de fracturas preferenciales. El descubrimiento de estas áreas es esencial para la planificación y la instalación de sistemas de bombeo y de descontaminación de aguas subterráneas, en vista de la disminución de la producción de lixiviado desde la clausura del basurero.

Abstract Ore mining fundamentally depends on the definition of its tenor and volume, something extremely complex in disseminated mineralization, as in the case of certain types of deposits of gold and sulfites. This article proposes the use of electrical tomography for definition of a geophysical signature in terms of electrical resistivity and chargeability, in an outcrop of mineralized quartz lode at the end of an inactive gold mine. One of the targets was to analyze the continuity of the mineralized body, the occurrence of new outcrops and the applicability of the method as an auxiliary tool in mineral extraction. Three parallel lines of electrical tomography in a dipole-dipole arrangement, being orthogonal to the orientation of the gold lode, were installed in an area outside the mine. The results allowed the geophysical characterization of the mineralized zone by high resistivity (above 1000Ω.m) and high chargeability (above 30mV/V). The results of the 2D inversion models were interpolated in 3D visualization models, which allowed definition of the contour surfaces for the physical parameters measured, and the morphological pattern modeling of the mineralization. The data reveal the existence of a new lode in subsurface, localized 30m to the south of the lode outcrop. The versatility of the acquisition and data processing indicate the application potential of electrical tomography as a criterion for sampling and tenor definition in ore extraction activities, since it is objective and low cost.

Estudos de pesquisa mineral são fundamentais para o reconhecimento e a incorporação de novas reservas. Esse trabalho apresenta os resultados de aplicação do método geofísico da eletrorresistividade numa ocorrência mineralizada em carbonatos de cobre, por meio da técnica de caminhamento elétrico em arranjo azimutal. A área de estudos está inserida na bacia sedimentar do Camaquã, formada por um conjunto de unidades estratigráficas sedimentares e vulcanogênicas, onde são descritas diversas ocorrências cupríferas. A presença de azurita e malaquita em fraturas e zonas de maior porosidade em arenito encaixante define a geologia local. Os modelos de inversão revelam anomalias circulares de resistividade moderada para até 25m abaixo da ocorrência aflorante e anomalias de baixa resistividade em profundidades abaixo de 25m, além de áreas adjacentes com alta resistividade. Indicadores de mineralização descritos para ocorrências de cobre estudadas, no âmbito da bacia sedimentar do Camaquã, ocorrem na área de estudos e permitem caracterização em termos de resistividade elétrica. Áreas com silicificação apresentam alta resistividade, enquanto que valores intermediários são atribuídos a zonas com carbonatação e, finalmente, áreas de baixa resistividade, provavelmente, indicam concentrações de sulfetos disseminados.

Mineral research studies are fundamental for the recognition and incorporation of new reserves. This paper presents the results of an application of the Electrical Resistivity geophysical method to a mineral occurrence of copper carbonates, by an electrical profiling technique in an azimutal array. The parameter of physical electric resistivity was measured, using the Electrical Resistivity method and the technique of electrical profiling. This study area is inserted in the Camaquã sedimentary basin, formed by sedimentary and volcanogenic stratigraphy units, where several copper occurrences are encountered. The presence of azurite and malachite in the fractures and high porosity zones in arenitic hosts define the local geology. The inversion models reveal circular anomalies of moderate resistivity up to 25m below the outcropping surface, and anomalies of low resistivity for depths below 25m, besides adjacent areas with high resistivity. Mineralization indicators described for the copper occurence in the Camaquã sedimentary basin are encountered in previous studies as well as the area now studied and allow for characterization in terms of electrical resistivivity. Silicified areas present high resistivity, while intermediary values are attributed to carbonated zones, and finally, low resistivity areas probably indicate concentrations of disseminated sulfites.