Gold ore identification in Santa Catarina Gabbro using electrical resistivity tomography (ERT) and visualization of mineralization in three dimensions, São Sepé, Rio Grande do Sul, Brazil

Este trabajo presenta la caracterización geológica-geofísica de una probable ocurrencia de oro en Santa Catarina Gabro, en la región de São Sepé, estado de Rio Grande do Sul, sur de Brasil. Trabajos anteriores han indicado la presencia de oro en la región en las actuales campañas de prospección geoquímica de sedimentos y sugieren que el área de origen sería Santa Catarina Gabro. Para investigar sobre esta probable ocurrencia de oro, se realizaron estudios geológicos y estructurales, seguidos de la adquisición de información geofísica utilizando los métodos de resistividad DC e IP, con el arreglo dipolo-dipolo. Los datos geofísicos fueron procesados en inversión 2D y luego interpolados para permitir la visualización tridimensional de la posible mineralización. Interpretaciones basadas en la recopilación de datos geológicos y geofísicos, en asociación con el contexto estructural regional, sugieren que la probable mineralización se originó a partir de la intrusión del Granito São Sepé, cuyos fluidos hidrotermales se alojaron en fracturas durante los eventos tectónicos ocurridos en la región. Los resultados obtenidos en este trabajo permiten delinear una arquitectura de yacimiento factible con el contexto geológico de la región y ayudar a una futura estrategia de perforación dirigida a los objetivos probables identificados

MAPPING OF CHROMITE OCCURRENCE IN A META-ULTRAMAFIC COMPLEX BY MAGNETOMETRIC PROSPECTING, SUL-RIOGRANDENSE SHIELD (SOUTHERN BRAZIL): Mapeamento de ocorrência de cromita em complexo metaultramáfico por meio de prospecção magnetométrica, Escudo Sul-Riograndense (Sul do Brasil)

This study presents the use of terrestrial magnetometry method in the characterization of a metamorphic and chromium-mineralized ultramafic body in the São Sepé region (RS). Several serpentinite exposures were recognized in the study area, characterized by a very evident schistosity marked by amphiboles and micas. The most preserved rocks are gray to dark green in color, silky to the touch and with folds and variable fracturing. The chromite present in serpentinites is associated with magnetite, and occurs in the form of small lenses. 1677 reading lines were made perpendicular to the main direction of the meta-ultramafic body, with 25m spacing between measurement points. The magnetometric maps revealed high-intensity anomalies related to meta-ultramafic rocks. 1677 reading lines were made perpendicular to the main direction of the meta-ultramafic body, with 25m spacing between measurement points. The magnetometric maps revealed high-intensity anomalies related to meta-ultramafic rocks. The results revealed the existence of highly magnetic individualized lenses orientated according to NE / SW, related to regional deformation events, with remobilization and mineral reconcentration. The direct relationship between high magnetization and chromite/ferro-chromite concentrations allows relatively detailed mapping of potentially mineralized areas, revealing dimensions more significant than the limits of the meta-ultramafic sequence defined in the geological map. The results indicate that the analytical signal amplitude map is a highly recommended product for planning sampling actions and reserve quantification, improving classical geological mapping.ABSTRACT - This study presents the use of terrestrial magnetometry method in the characterization of a metamorphic and chromium-mineralized ultramafic rocks in the São Sepé region (RS). The most preserved rocks are gray to dark green serpentinites and occasionally magnesian schists with folds and variable fracturing that occur as a lenticular body enclosed within the host meta-volcano-sedimentary rocks. The chromite present in serpentinites is associated with magnetite and occurs in the form of small lenses. 1677 reading lines were made perpendicular to the main direction of the meta-ultramafic rock, with 25m spacing between measurement points. The magnetometric maps revealed high-intensity anomalies related to meta-ultramafic rocks. The results revealed the existence of highly magnetic individualized lenses orientated according to NE/SW. The direct relationship between high magnetization and chromite/ferro-chromite concentrations allows relatively detailed mapping of potentially mineralized areas, revealing dimensions more significant than the limits of the meta-ultramafic sequence defined in the geological map. The results indicate that the analytical signal amplitude map is a highly recommended product for planning sampling actions and reserve quantification, improving classical geological mapping. Keywords: Mineral research. Chrome. Meta-ultramafic. Magnetometry. Analytical signal amplitude.   RESUMO - Este estudo apresenta a utilização do método de magnetometria terrestre na caracterização de rochas ultramáficas metamórficas e mineralizadas com cromo na região de São Sepé (RS). As rochas mais preservadas são serpentinitos cinzentos a verde-escuros e ocasionalmente xistos magnesianos com dobras e fraturamento variável, que ocorrem como um corpo lenticular contido em rochas meta-vulcano sedimentares hospedeiras. A cromita presente nas serpentinitas está associada à magnetita e ocorre na forma de pequenas lentes. Foram feitas 1.677 linhas de leitura perpendiculares à direção principal da rocha meta-ultramáfica, com espaçamento de 25m entre os pontos de medição. Os mapas magnetométricos revelaram anomalias de alta intensidade relacionadas às rochas meta-ultramáficas. Os resultados revelaram a existência de lentes individualizadas altamente magnéticas orientadas conforme NE/SW. A relação direta entre a elevada magnetização e as concentrações de cromita/ferrocromita permite um mapeamento relativamente detalhado de áreas potencialmente mineralizadas, revelando dimensões mais significativas que os limites da sequência meta-ultramáfica definida no mapa geológico. Os resultados indicam que o mapa analítico de amplitude de sinal é um produto altamente recomendado para planejamento de ações de amostragem e quantificação de reservas, melhorando o mapeamento geológico clássico. Palavras-chave: Pesquisa mineral. Cromo. Meta-ultramáfica. Magnetometria. Amplitude do sinal analítico

Prospecção geofísica em ocorrência de cobre localizada na bacia sedimentar do Camaquã (RS)

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

Estudo geofísico de vazamento de combustíveis em posto de abastecimento

The geoelectrical methods have been widely used in research involving the evaluation and monitoring of areas with environmental risk. This paper presents the results of applying the Electrical Resistivity method by electrical profiling technique to investigate the fuel presence in soil and groundwater proceeding in station gas, located in an urban area Caçapava do Sul (RS), on soil in situ, from modification of Caçapava granite. The results suggest an association between low resistivity anomalies zone with potentially degraded from underground tanks worthless on the form of free phase, now represented as residual phase. The results of the model inversion are consistent with the standards expected for hydrocarbons present in the saturated zone. The electrical resistivity method proved to be an important tool for assessment and environmental monitoring in conjunction with direct methods of investigation.Os métodos geoelétricos têm sido amplamente utilizados em pesquisas que envolvam o processo de avaliação e monitoramento de áreas com risco ambiental. Este trabalho apresenta os resultados da aplicação do método da Eletrorresistividade, através da técnica de caminhamento elétrico para investigar a presença de combustíveis no solo e águas subterrâneas provenientes de um posto de combustíveis, localizado na zona urbana de Caçapava do Sul (RS), sobre solo in situ, produzido por alteração do granito Caçapava. Os resultados sugerem uma associação entre anomalias de baixa resistividade e zonas com combustível degradado proveniente de tanques enterrados inutilizados, sobre a forma de fase livre, atualmente representada como fase residual. Os resultados dos modelos de inversão são condizentes com os padrões esperados para hidrocarbonetos presente na zona saturada do perfil de alteração. O método da Eletrorresistividade demonstrou ser um instrumento importante para avaliação e monitoramento ambiental em conjunto com métodos diretos de investigação. Palavras-chave: combustíveis, NAPLs, eletrorresistividade, resistividade

DC resistivity investigation in a fractured aquifer system contaminated by leachate from an old dump

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. doi: https://doi.org/10.22201/igeof.00167169p.2017.56.4.182

Geophysical prospection in tin mineral occurrence associated to greisen in granite São Sepé (RS)

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

Geophysical modeling in gold deposit through DC Resistivity and Induced Polarization methods

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

Geophysical prospection in tin mineral occurrence associated to greisen in granite São Sepé (RS)

<div><p>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.</p></div