Deciphering the evolution of ecological interactions among the metabolic types during the early d... more Deciphering the evolution of ecological interactions among the metabolic types during the early diversification of life on Earth is crucial for our understanding of the ancient biosphere. The stromatolites from the genus Conophyton cylindricus represent a datum for the Proterozoic (Meso to Neoproterozoic) on Earth. Their typical conical shape has been considered a result of a competition between microorganisms for space, light and nutrients. Well-preserved records of this genus from the “Paleontological Site of Cabeludo”, Vazante Group, São Francisco Craton (Southern Brazil) present in situ fossilized biofilms, containing preserved carbonaceous matter. Petrographic and geochemical analyses revealed an alternation between mineral laminae (light grey laminae) and fossilized biofilms (dark grey laminae). The dark grey laminae comprise three different biofilms recording a stratified microstructure of microbial communities. These three biofilms composing the dark grey laminae tend to be ...
The most frequent crystallographic preferred orientations developed during the progressive phase ... more The most frequent crystallographic preferred orientations developed during the progressive phase transformation of magnetite-hematite-goethite are described and analyzed in two natural samples of banded iron formations from Carajás Mineral Province. Microtextures of martitized grains containing the three phases and the microplaty matrix were analyzed in a scanning electron microscope equipped with a detector for electron backscatter diffraction. For identifying the correlation between magnetite, hematite and goethite lattice and topotaxity during transformation, multiple orientation relationships between the three phases were tested and verified using three-dimensional misorientation analysis. The results show that basal planes of goethite coincide with basal planes of hematite, which coincide with octahedral planes of magnetite. This indicates that transformation between the three minerals happens topotactically, and the oxygen lattice framework is preserved in all members of the r...
Abstract Establishing the positions of continents during the initial stages of Earth's evolut... more Abstract Establishing the positions of continents during the initial stages of Earth's evolution is one of the most important challenges in geosciences today. This challenge is mainly due to the severe limitations in obtaining geological and/or geophysical data from early Earth time, particularly robust paleomagnetic data. Here, we report the first paleomagnetic data from an Archean block in the Amazonian craton, the Carajas Province, for ∼2.76–2.74 billion years ago (Ga), when extensive dominantly mafic volcanism (Parauapebas Formation) covered an area of ∼18,000 km2. The paleomagnetic investigation was conducted on fresh drill cores drilled into the Carajas iron ore mine and cutting across the Parauapebas Formation. After rotating the drill core segments to geographic coordinates using the viscous magnetic component, two characteristic components, Carajas 1 and 2 (C1 and C2) were identified and further used to calculate paleomagnetic poles: C1 (∼2759 Ma; 40.5°E, −44.6°S, N = 5 A95 = 6.5°, K = 18.5) and C2 (∼2749 Ma; 342.4°E, −54.3°S, N = 28, A95 = 14.8°, K = 27.8). Pole C2 is based on a bigger number of sites, passes a reversal test and is considered robust. A baked contact test was attempted for this component, but it is not conclusive. Our results, integrated with geological evidence reveals that the Carajas block occupied low latitudes at the time, and could have been part of the Superia supercraton during the Neoarchean (∼2.75 Ga) at equatorial latitudes. Finally, a consistent succession of six magnetic reversal events was identified in the lava flow sequence from the Parauapebas Formation, pointing to an already dynamic geodynamo pre-2.7 Ga.
O entendimento da assinatura geofísica em depósitos torna-se essencial na prospecção mineral, uma... more O entendimento da assinatura geofísica em depósitos torna-se essencial na prospecção mineral, uma vez que a compreensão do footprint em profundidade é cada mais necessário devido a alvos e depósitos superficiais estarem cada vez mais escassos. A integração de outros tipos de dados aos dados geofísicos pode auxiliar na criação de processos de interpretações a partir do conhecimento avançado da resposta geofísica de diferentes rochas, alterações hidrotermais e mineralizações que futuramente podem aumentar a descoberta de novos alvos ou novas abordagens na prospecção. Esta pesquisa tem como alvo o depósito epitermal de Pb-Zn-(Cu-Ag) de Santa Maria, situado no distrito de Minas do Camaquã, município de Caçapava do Sul, Rio Grande do Sul, Brasil. Trata-se de um sistema magmático-hidrotermal distal, com mineralizações controladas por sistemas de falhas em arenitos e conglomerados, que hospedam zonas de alterações hidrotermais que contêm ilita, clorita e pirita, além de galena, esfalerita,...
9th International Congress of the Brazilian Geophysical Society & EXPOGEF, Salvador, Bahia, Brazil, 11-14 September 2005, Sep 14, 2005
Airborne geophysical data acquired over the Tapajos Gold Province (TGP) in west Central Amazon Pr... more Airborne geophysical data acquired over the Tapajos Gold Province (TGP) in west Central Amazon Province display different patterns previously not identified in geological field mapping. Integrated analysis of airborne magnetic and gamma-ray spectrometric data plus available geological data was conducted to map and analyze these patterns, and to obtain insight in their regional significance. Enhancement of the airborne magnetic and gamma-ray spectrometric data have resulted in better definition of both geological structure and lithological boundaries than indicated on previous maps. Comparison of multiple geophysical signatures and known mining occurrences were particularly valuable for defining old targets and direct new ways for gold prospecting in the area. Areas with high to moderate favorableness encompass wellknown gold deposits, as well as new signatures that may have economic importance. Geophysical data were successfully used to highlight relationships between main crustal domains, as well as their internal structures and boundaries. The northeast domain bears the signature of older crustal material covered by rocks of the Uatuma Supergroup generated through partial crustal melting. The western limit of this domain is close to the supposed limit that divides the Central Amazon and Ventuari-Tapajos provinces. A large structure marked by high amplitude in the western part may record oceanic crust subduction and formation of the Cuiu-Cuiu arc.
A group of image-processing methods and an unsupervised classification were applied to the Rio da... more A group of image-processing methods and an unsupervised classification were applied to the Rio das Velhas airborne geophysical data. The products show potential application to mineral exploration, because the enhancement improved the information content of the single geophysical channels. The images have been processed with various combinations. The best product was the analytical signal amplitude and phase integrated by IHS transformation. Information extracted maps the geology and lineament patterns at regional and local scales. The K-means technique was applied to the geophysical data and resulted in 10 classes. These classes show the lithologies mapped by the field geologists at the 1:100.000.
Airborne geophysical data acquired over the Tapajos Gold Province (TGP) in west Central Amazon Pr... more Airborne geophysical data acquired over the Tapajos Gold Province (TGP) in west Central Amazon Province display different patterns previously not identified in geological field mapping. Integrated analysis of airborne magnetic and gamma-ray spectrometric data plus available geological data was conducted to map and analyze these patterns, and to obtain insight in their regional significance. Enhancement of the airborne magnetic and gamma-ray spectrometric data have resulted in better definition of both geological structure and lithological boundaries than indicated on previous maps. Comparison of multiple geophysical signatures and known mining occurrences were particularly valuable for defining old targets and direct new ways for gold prospecting in the area. Areas with high to moderate favorableness encompass wellknown gold deposits, as well as new signatures that may have economic importance. Geophysical data were successfully used to highlight relationships between main crustal domains, as well as their internal structures and boundaries. The northeast domain bears the signature of older crustal material covered by rocks of the Uatuma Supergroup generated through partial crustal melting. The western limit of this domain is close to the supposed limit that divides the Central Amazon and Ventuari-Tapajos provinces. A large structure marked by high amplitude in the western part may record oceanic crust subduction and formation of the Cuiu-Cuiu arc.
Due to the relevance and size of Mara Rosa Magmatic Arc, as well as the general lack of outcrop, ... more Due to the relevance and size of Mara Rosa Magmatic Arc, as well as the general lack of outcrop, airborne geophysics plays a major role in mineral exploration. Gold and gold-copper deposits of the Mara Rosa Magmatic Arc, Central Brazil, occur in four main associations: Au-Ag-Ba; Cu-Au; Au only and Au-Cu-Bi. New regional airborne geophysics have been undertaken to assist in geological mapping and select new favourable environments. The airborne geophysical results are compared with the distribution of known hydrothermal host rocks and outcrops where Au, Au-Ag-Ba and Cu mineralization occurs. Analysis of the data indicates high positive correlation between magnetic and gamma ray anomalies. Our study is focused on characterizing the geophysical properties of the hydrothermal rocks and associated mineralization that can host gold and copper. New spots, as two new geological targets for copper minerals, have been identified in the Mara Rosa Magmatic arc. The new copper-gold targets have clear physical property contrasts with their host rocks and therefore lend themselves to detection and mapping by airborne geophysical methods.
A statistical modeling approach was applied to airborne geophysical data to locate areas favorabl... more A statistical modeling approach was applied to airborne geophysical data to locate areas favorable for gold mineralization in Rio das Velhas Greenstone Belt, Quadrilatero Ferrifero (QF). A positive spatial coincidence exists between banded iron formation (BIF) host-rocks, structures, and mineralogy that are indicative of gold mineralization. Quantitative relationships between airborne geophysical and geological data with known gold occurrences were determined and combined to produce predictive models to explore for Archean oxide-BIF-hosted deposits. Results map areas within exposed and subsurface rocks favorable for gold mineralization. Selected target areas for gold mineralization were checked in the field and provide validation that encourages future ground follow-up in the Rio das Velhas Greenstone Belt. The approach used in this study has shown great capability for linking geological and geophysical data and illustrates an approach that may significantly increase the odds of exp...
Resumo: Neste trabalho, as informações provenientes das geotecnologias, notadamente dos levantame... more Resumo: Neste trabalho, as informações provenientes das geotecnologias, notadamente dos levantamentos aerogeofísicos, foram usadas para mapear regiões permissíveis para água subterrânea e, constituem uma alternativa para a avaliação do potencial hidrogeológico de terrenos cristalinos nos programas de exploração hídrica no nordeste brasileiro. A área de estudo situa-se em Irauçuba, Estado do Ceará. O arcabouço hidrogeológico da área consiste de um substrato aflorante de rochas cristalinas, onde a ocorrência de água subterrânea está nos bolsões de intemperismo e é favorecida pelo acúmulo de condutores hidráulicos (juntas e foliação). Localmente, aluviões e mantos de regolito (< 2 m de espessura), facilitam a drenança da água superficial para os bolsões. O banco de dados usado para a modelagem consiste de levantamentos aerogeofísicos regionais e de detalhe, contemplando os métodos magnetométricos, radiométricos e eletromagnetométricos-HEM, no domínio da freqüência (conjuntos HEM-330...
Deciphering the evolution of ecological interactions among the metabolic types during the early d... more Deciphering the evolution of ecological interactions among the metabolic types during the early diversification of life on Earth is crucial for our understanding of the ancient biosphere. The stromatolites from the genus Conophyton cylindricus represent a datum for the Proterozoic (Meso to Neoproterozoic) on Earth. Their typical conical shape has been considered a result of a competition between microorganisms for space, light and nutrients. Well-preserved records of this genus from the “Paleontological Site of Cabeludo”, Vazante Group, São Francisco Craton (Southern Brazil) present in situ fossilized biofilms, containing preserved carbonaceous matter. Petrographic and geochemical analyses revealed an alternation between mineral laminae (light grey laminae) and fossilized biofilms (dark grey laminae). The dark grey laminae comprise three different biofilms recording a stratified microstructure of microbial communities. These three biofilms composing the dark grey laminae tend to be ...
The most frequent crystallographic preferred orientations developed during the progressive phase ... more The most frequent crystallographic preferred orientations developed during the progressive phase transformation of magnetite-hematite-goethite are described and analyzed in two natural samples of banded iron formations from Carajás Mineral Province. Microtextures of martitized grains containing the three phases and the microplaty matrix were analyzed in a scanning electron microscope equipped with a detector for electron backscatter diffraction. For identifying the correlation between magnetite, hematite and goethite lattice and topotaxity during transformation, multiple orientation relationships between the three phases were tested and verified using three-dimensional misorientation analysis. The results show that basal planes of goethite coincide with basal planes of hematite, which coincide with octahedral planes of magnetite. This indicates that transformation between the three minerals happens topotactically, and the oxygen lattice framework is preserved in all members of the r...
Abstract Establishing the positions of continents during the initial stages of Earth's evolut... more Abstract Establishing the positions of continents during the initial stages of Earth's evolution is one of the most important challenges in geosciences today. This challenge is mainly due to the severe limitations in obtaining geological and/or geophysical data from early Earth time, particularly robust paleomagnetic data. Here, we report the first paleomagnetic data from an Archean block in the Amazonian craton, the Carajas Province, for ∼2.76–2.74 billion years ago (Ga), when extensive dominantly mafic volcanism (Parauapebas Formation) covered an area of ∼18,000 km2. The paleomagnetic investigation was conducted on fresh drill cores drilled into the Carajas iron ore mine and cutting across the Parauapebas Formation. After rotating the drill core segments to geographic coordinates using the viscous magnetic component, two characteristic components, Carajas 1 and 2 (C1 and C2) were identified and further used to calculate paleomagnetic poles: C1 (∼2759 Ma; 40.5°E, −44.6°S, N = 5 A95 = 6.5°, K = 18.5) and C2 (∼2749 Ma; 342.4°E, −54.3°S, N = 28, A95 = 14.8°, K = 27.8). Pole C2 is based on a bigger number of sites, passes a reversal test and is considered robust. A baked contact test was attempted for this component, but it is not conclusive. Our results, integrated with geological evidence reveals that the Carajas block occupied low latitudes at the time, and could have been part of the Superia supercraton during the Neoarchean (∼2.75 Ga) at equatorial latitudes. Finally, a consistent succession of six magnetic reversal events was identified in the lava flow sequence from the Parauapebas Formation, pointing to an already dynamic geodynamo pre-2.7 Ga.
O entendimento da assinatura geofísica em depósitos torna-se essencial na prospecção mineral, uma... more O entendimento da assinatura geofísica em depósitos torna-se essencial na prospecção mineral, uma vez que a compreensão do footprint em profundidade é cada mais necessário devido a alvos e depósitos superficiais estarem cada vez mais escassos. A integração de outros tipos de dados aos dados geofísicos pode auxiliar na criação de processos de interpretações a partir do conhecimento avançado da resposta geofísica de diferentes rochas, alterações hidrotermais e mineralizações que futuramente podem aumentar a descoberta de novos alvos ou novas abordagens na prospecção. Esta pesquisa tem como alvo o depósito epitermal de Pb-Zn-(Cu-Ag) de Santa Maria, situado no distrito de Minas do Camaquã, município de Caçapava do Sul, Rio Grande do Sul, Brasil. Trata-se de um sistema magmático-hidrotermal distal, com mineralizações controladas por sistemas de falhas em arenitos e conglomerados, que hospedam zonas de alterações hidrotermais que contêm ilita, clorita e pirita, além de galena, esfalerita,...
9th International Congress of the Brazilian Geophysical Society & EXPOGEF, Salvador, Bahia, Brazil, 11-14 September 2005, Sep 14, 2005
Airborne geophysical data acquired over the Tapajos Gold Province (TGP) in west Central Amazon Pr... more Airborne geophysical data acquired over the Tapajos Gold Province (TGP) in west Central Amazon Province display different patterns previously not identified in geological field mapping. Integrated analysis of airborne magnetic and gamma-ray spectrometric data plus available geological data was conducted to map and analyze these patterns, and to obtain insight in their regional significance. Enhancement of the airborne magnetic and gamma-ray spectrometric data have resulted in better definition of both geological structure and lithological boundaries than indicated on previous maps. Comparison of multiple geophysical signatures and known mining occurrences were particularly valuable for defining old targets and direct new ways for gold prospecting in the area. Areas with high to moderate favorableness encompass wellknown gold deposits, as well as new signatures that may have economic importance. Geophysical data were successfully used to highlight relationships between main crustal domains, as well as their internal structures and boundaries. The northeast domain bears the signature of older crustal material covered by rocks of the Uatuma Supergroup generated through partial crustal melting. The western limit of this domain is close to the supposed limit that divides the Central Amazon and Ventuari-Tapajos provinces. A large structure marked by high amplitude in the western part may record oceanic crust subduction and formation of the Cuiu-Cuiu arc.
A group of image-processing methods and an unsupervised classification were applied to the Rio da... more A group of image-processing methods and an unsupervised classification were applied to the Rio das Velhas airborne geophysical data. The products show potential application to mineral exploration, because the enhancement improved the information content of the single geophysical channels. The images have been processed with various combinations. The best product was the analytical signal amplitude and phase integrated by IHS transformation. Information extracted maps the geology and lineament patterns at regional and local scales. The K-means technique was applied to the geophysical data and resulted in 10 classes. These classes show the lithologies mapped by the field geologists at the 1:100.000.
Airborne geophysical data acquired over the Tapajos Gold Province (TGP) in west Central Amazon Pr... more Airborne geophysical data acquired over the Tapajos Gold Province (TGP) in west Central Amazon Province display different patterns previously not identified in geological field mapping. Integrated analysis of airborne magnetic and gamma-ray spectrometric data plus available geological data was conducted to map and analyze these patterns, and to obtain insight in their regional significance. Enhancement of the airborne magnetic and gamma-ray spectrometric data have resulted in better definition of both geological structure and lithological boundaries than indicated on previous maps. Comparison of multiple geophysical signatures and known mining occurrences were particularly valuable for defining old targets and direct new ways for gold prospecting in the area. Areas with high to moderate favorableness encompass wellknown gold deposits, as well as new signatures that may have economic importance. Geophysical data were successfully used to highlight relationships between main crustal domains, as well as their internal structures and boundaries. The northeast domain bears the signature of older crustal material covered by rocks of the Uatuma Supergroup generated through partial crustal melting. The western limit of this domain is close to the supposed limit that divides the Central Amazon and Ventuari-Tapajos provinces. A large structure marked by high amplitude in the western part may record oceanic crust subduction and formation of the Cuiu-Cuiu arc.
Due to the relevance and size of Mara Rosa Magmatic Arc, as well as the general lack of outcrop, ... more Due to the relevance and size of Mara Rosa Magmatic Arc, as well as the general lack of outcrop, airborne geophysics plays a major role in mineral exploration. Gold and gold-copper deposits of the Mara Rosa Magmatic Arc, Central Brazil, occur in four main associations: Au-Ag-Ba; Cu-Au; Au only and Au-Cu-Bi. New regional airborne geophysics have been undertaken to assist in geological mapping and select new favourable environments. The airborne geophysical results are compared with the distribution of known hydrothermal host rocks and outcrops where Au, Au-Ag-Ba and Cu mineralization occurs. Analysis of the data indicates high positive correlation between magnetic and gamma ray anomalies. Our study is focused on characterizing the geophysical properties of the hydrothermal rocks and associated mineralization that can host gold and copper. New spots, as two new geological targets for copper minerals, have been identified in the Mara Rosa Magmatic arc. The new copper-gold targets have clear physical property contrasts with their host rocks and therefore lend themselves to detection and mapping by airborne geophysical methods.
A statistical modeling approach was applied to airborne geophysical data to locate areas favorabl... more A statistical modeling approach was applied to airborne geophysical data to locate areas favorable for gold mineralization in Rio das Velhas Greenstone Belt, Quadrilatero Ferrifero (QF). A positive spatial coincidence exists between banded iron formation (BIF) host-rocks, structures, and mineralogy that are indicative of gold mineralization. Quantitative relationships between airborne geophysical and geological data with known gold occurrences were determined and combined to produce predictive models to explore for Archean oxide-BIF-hosted deposits. Results map areas within exposed and subsurface rocks favorable for gold mineralization. Selected target areas for gold mineralization were checked in the field and provide validation that encourages future ground follow-up in the Rio das Velhas Greenstone Belt. The approach used in this study has shown great capability for linking geological and geophysical data and illustrates an approach that may significantly increase the odds of exp...
Resumo: Neste trabalho, as informações provenientes das geotecnologias, notadamente dos levantame... more Resumo: Neste trabalho, as informações provenientes das geotecnologias, notadamente dos levantamentos aerogeofísicos, foram usadas para mapear regiões permissíveis para água subterrânea e, constituem uma alternativa para a avaliação do potencial hidrogeológico de terrenos cristalinos nos programas de exploração hídrica no nordeste brasileiro. A área de estudo situa-se em Irauçuba, Estado do Ceará. O arcabouço hidrogeológico da área consiste de um substrato aflorante de rochas cristalinas, onde a ocorrência de água subterrânea está nos bolsões de intemperismo e é favorecida pelo acúmulo de condutores hidráulicos (juntas e foliação). Localmente, aluviões e mantos de regolito (< 2 m de espessura), facilitam a drenança da água superficial para os bolsões. O banco de dados usado para a modelagem consiste de levantamentos aerogeofísicos regionais e de detalhe, contemplando os métodos magnetométricos, radiométricos e eletromagnetométricos-HEM, no domínio da freqüência (conjuntos HEM-330...
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