The Vazante Northern Extension is a continuation of the structurally controlled, hypogene nonsulfide zinc deposit from the Vazante Mine, Minas Gerais, Brazil. The deposit is hosted in Neoproterozoic carbonates of the Serra do Poço Verde Formation located in the Brasília Fold Belt along the western margin of the São Francisco Craton. The Northern Extension deposit is hosted within a shear zone that strikes 200 to 225 and dips 30º-70º NW and is associated with substantial folding that occurred in the same deformation (D2) event and later transcurrent faulting. The shear zone is composed of a tectonic-hydrothermal breccia that can be subdivided into four types: Type 1 Breccia– distally located from the willemite (Zn2SiO4) ore, weakly brecciated dolostone with some Fe-carbonate alteration; Type 2 Breccia–Strong Fe-carbonate alteration, intense brecciation; Type 3 Breccia–hematite replacement breccia, usually proximal to the Type 4 Breccia; Type 4 Breccia–willemite ore breccia, containing three generations of hypogene willemite (Zn2SiO4) as well as hematite (Fe2O3), and franklinite (ZnFe2O4). In the southern part of the deposit, late sulfide-rich veinlets are observed cutting the hypogene zinc silicate mineralization, and contain galena, sphalerite, native silver, covellite, and stromeyerite (Cu1-xAg1-xS). Geochemical studies conducted on the tectonic-hydrothermal breccia showed a strong regional signature enriched in Ag, Cd, Pb, and Zn. The presence of willemite as opposed to sphalerite and the ubiquity of hematite suggest that the zinc silicate mineralization has formed from the mixing between a low sulfur, acid, oxidizing metalliferous basinal brine similar to the fluids found in MVT deposits with a cooler, more oxidizing, meteoric fluid. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2012-02-29 16:45:36.41

Exploration for large zinc silicate deposits is more challenging than zinc sulfide deposits, as they do not exhibit similar geophysical anomalies. The Vazante deposit, which is the world’s largest zinc silicate deposit, occurs in brecciated dolomite and comprises mainly willemite with various proportions of hematite, and minor franklinite and sphalerite. In the Vazante region, the exploration challenge is enhanced as outcrops are rare, bedrock generally sits below 10s of metres of laterite cover and barren hematite-rich breccias have a similar geophysical signature to willemite ore bodies. In order to evaluate the applications of geophysical surveys in the exploration of this type of deposit, data from 475 samples were investigated from drill holes representative of the various types of ore, host rocks and zones of known geophysical anomalies in the Vazante District. Geochemical (ICP-MS and XRF) and mineralogical (optical, EMPA, SEM and MLA) data were integrated with physical rock properties (density, magnetic susceptibility and K-U-Th gamma ray spectrometry) to assist in finding new ore zones. The most distinct physical property of the ore is density (3.0-4.3 g/cm3), compared with the host rocks (2.7-3.0 g/cm3). This is due to high proportion of denser minerals (hematite and willemite) in the ore. However, barren hematite breccias also have high densities (3.0-4.5 g/cm3). The zinc ore and hematite breccias yielded higher magnetic susceptibilities (0.1-38 x10-3 SI) than the surrounding host rocks, with the highest values associated with greater proportions of franklinite and magnetite (7-38 x10-3 SI). The zinc ore has an elevated U concentration (up to 33ppm) relative to the various host rocks (up to 7 ppm), yielding higher gamma spectrometric values. The results of this investigation indicate that an integration of magnetic, gravimetric and radiometric surveys would be required to identify zinc silicate ore zones and potentially differentiate them from barren hematite breccias and host rocks. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2014-03-27 13:32:54.132

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Orientador: Alexandre Mesquita / Resumo: Os materiais nanoestruturados vêm sendo extensivamente estudados, não somente pelas novas propriedades e suas possíveis aplicações tecnológicas, mas também pela busca de uma melhor compreensão dos aspectos físicos e químicos. Em relação a materiais semicondutores, estudos da estrutura em escala nanométrica tem recebido considerável interesse em razão do efeito de tamanho que exibem. Semicondutores nanocristalinos apresentam propriedades eletrônicas intermediárias entre aqueles de estrutura molecular e sólidos macrocristalinos e são objeto de intensa pesquisa, apresentando uma grande diversidade de aplicações quando na forma nanoestruturada. Dentre esses materiais, o silicato de zinco (Zn2SiO4) puro ou dopado tem recebido atenção em razão de notáveis propriedades fundamentais, versatilidade e potencial para diversas aplicações tecnológicas. Nesse contexto, essa dissertação teve como objetivo realizar a síntese e a caracterização de Zn2SiO4 puro e dopado com átomos de manganês e sua correlação com propriedades fotoluminescentes. Neste trabalho, foi utilizado o método químico de preparação conhecido por co-preciptação. Deste modo, a caracterização morfológica foi realizada através da técnica de microscopia eletrônica de varredura de alta resolução (FEG-MEV), a qual demonstra um aglomerado de grãos, tornando a determinação do tamanho do mesmo difícil. As propriedades estruturais das nanopartículas, bem como suas propriedades físicas e químicas, foram determinadas através das técn... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Nanostructured materials have been extensively studied, not only for new properties and their possible technological applications, but also for a better understanding of the physical and chemical aspects. With regard to semiconductor materials, nanoscale structure studies have received considerable interest because of the size effect they exhibit. Nanocrystalline semiconductors have intermediate electronic properties between those of molecular structure and macrocrystalline solids and are the subject of intense research, presenting a great diversity of applications when in nanostructured form. Among these materials, pure or doped zinc silicate (Zn2SiO4) has received attention because of its remarkable fundamental properties, versatility and potential for various technological applications. In this context, this dissertation aimed to synthesize and characterize pure and doped Zn2SiO4 with manganese atoms and its correlation with photoluminescent properties. In this work, the chemical preparation method known as co-precipitation was used. Thus, the morphological characterization was performed by the high resolution scanning electron microscopy (FEG-SEM) technique, which demonstrates a grain cluster, making the size determination difficult. The structural properties of nanoparticles, as well as their physical and chemical properties, were determined by X-ray diffraction, Raman spectroscopy and photoluminescence techniques, with which it is possible to observe the formation of na... (Complete abstract click electronic access below) / Mestre

Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2015-03-30T13:38:33Z No. of bitstreams: 3 1_pdfsam_Tese - Michelly Patrícia Santana de Almeida Fógia - 2014 - (1).pdf: 19290836 bytes, checksum: 2968ddb5cb0f3df6082b9b4716172cff (MD5) 109_pdfsam_Tese - Michelly Patrícia Santana de Almeida Fógia - 2014 - (2).pdf: 5395221 bytes, checksum: 4db4ad13c96adee2667748bc5321c48f (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2015-03-30T15:36:48Z (GMT) No. of bitstreams: 3 1_pdfsam_Tese - Michelly Patrícia Santana de Almeida Fógia - 2014 - (1).pdf: 19290836 bytes, checksum: 2968ddb5cb0f3df6082b9b4716172cff (MD5) 109_pdfsam_Tese - Michelly Patrícia Santana de Almeida Fógia - 2014 - (2).pdf: 5395221 bytes, checksum: 4db4ad13c96adee2667748bc5321c48f (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2015-03-30T15:36:48Z (GMT). No. of bitstreams: 3 1_pdfsam_Tese - Michelly Patrícia Santana de Almeida Fógia - 2014 - (1).pdf: 19290836 bytes, checksum: 2968ddb5cb0f3df6082b9b4716172cff (MD5) 109_pdfsam_Tese - Michelly Patrícia Santana de Almeida Fógia - 2014 - (2).pdf: 5395221 bytes, checksum: 4db4ad13c96adee2667748bc5321c48f (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2014-09-24 / In this work the structural and optical properties of SiO2-ZnO-TiO2 system doped with of Eu3+ (1% in mol) or Er3+ ions (0,2% to 2,0% in mol) were investigated. The compositions xSiO2-([100-x]/2)ZnO-([100-x]/2)TiO2 with x ranging from 40 to 80 were synthesized and studied. A mixed methodology using the traditional sol-gel process and Pechini method was employed to prepare stable and transparent sols, homogeneous gels, powders and transparent thin films without cracks. The prepared powders were heat treated from 100°C to 1100°C. The optical “band gap” values, the lifetime of Eu3+ 5D0 level, the R/O ratio of Eu3+ emissions and refractive index are dependent on the composition and thermal treatment of the powders. Multilayered thin films were deposited onto silica substrates using the “spin coating” technique. Afterwards, the as-prepared thin films were calcined at 500°C followed by annealings from 700°C to 1000°C. The X-ray diffraction of powders showed that the crystallization starts at 800°C with a mixture of zinc titanate phases (ZnTiO3, Zn2TiO4) and titanium rutile (TiO2). In compositions with low silica content (x = 40 or 50) the formation of zinc silicate (Zn2SiO4) occurs at high temperatures. The optical properties were evaluated for both powders and thin films. Particularly, thin films exhibit transmittance above 80% in the visible region. The refractive index at 632.8 nm and thickness of thin films were estimated using the envelope method and m-Line spectrocopy. Furthermore, morphological analysis of the thin films surface was performed by scanning electron microscopy. The characteristic emission peaks of Er3+ or Eu3+ doped powders and thin films were measured. The photoluminescent emission of Eu3+ ions, obtained the highest intensities for the powders treated at 800°C, for films treated at 700°C, under excitation at 394 nm, where the system remains primarily amorphous. The photoluminescent emission of the Er3+ ions was more intense for the powders treated at 1100°C under excitation at 980 nm, mainly due to reduction of hydroxyl groups which act as photoluminescence quenchers. In the film the highest intensity occurred at a temperature of 700°C under excitation at 378 nm and showing only one guided mode. Thus, the obtained thin films can be suitable for application as waveguides in integrated optical systems. Moreover, the Eu and Er doped powders can be used as phosphors in displays. / Este trabalho avalia as propriedades estruturais e ópticas do sistema ternário SiO2-ZnO-TiO2 dopado com íons Eu3+ (1% em mol) ou Er3+ (0,2% a 2,0% em mol). As composições xSiO2-([100-x]/2)ZnO-([100-x]/2)TiO2, com x = 40, 50, 60, 70 e 80 foram estudadas. Através de metodologia mista do processo sol-gel com o método Pechini foi possível obter sóis estáveis e transparentes, géis homogêneos, pós tratados termicamente de 100ºC a 1100°C e filmes finos transparentes e sem trincas. Filmes finos multicamadas foram depositados sobre substratos de sílica usando “spin coating” e calcinados a 500°C, seguido de um tratamento térmico entre 700°C e 1000°C. Por fotoluminescência foram observadas as transições de emissão características de íons Er3+ e Eu3+. A caracterização por difração de raios X dos pós mostrou que a cristalização tem início a partir de 800°C, com uma mistura de fases de titanatos de zinco (ZnTiO3, Zn2TiO4) e segregação de titânio rutilo (TiO2). Em composições com menores proporções de sílica (x= 40 ou 50) também ocorreu a formação de silicato de zinco (Zn2SiO4) em temperaturas mais elevadas. Os espectros de transmissão dos filmes apresentaram transmitância superior a 80%. Os valores de “band gap” óptico, o tempo de vida, as razões R/O e o índice de refração são dependentes do tratamento térmico e da composição dos pós. Usando o método da envoltória, pôde-se calcular o índice de refração a 632,8 nm e a espessura dos filmes finos, sendo que esta também foi estimada por microscopia eletrônica de varredura (MEV) e espectroscopia m-Line. A emissão fotoluminescente dos íons Eu3+ tem maior intensidade nos pós tratados à 800°C e nos filmes tratados à 700°C, sob excitação a 394 nm. Nestas temperaturas o sistema permanece predominantemente amorfo. A emissão fotoluminescente dos íons Er3+ foi mais intensa para os pós tratados a 1100°C, sob excitação a 980 nm, devido à eliminação de grupos OH supressores das emissões de Er3+. Nos filmes a maior intensidade se deu à temperatura de 700°C, sob excitação a 378 nm. Os filmes apresentaram apenas um modo guiado, sendo o mais apropriado para uso como guia de onda e os pós são indicados como fósforos podendo ser aplicados em “displays".