Navegando por Assunto "Cassiterita"

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Acesso aberto (Open Access)
Evolução magmático-hidrotermal do granito mocambo, Província Estanífera do Sul do Pará: um estudo morfológico e composicional de quartzo e cassiterita
(Universidade Federal do Pará, 2018-10-02) BARROS NETO, Rubem Santa Brígida; LAMARÃO, Claudio Nery; http://lattes.cnpq.br/6973820663339281
The present research deals with the morphological, compositional and textural aspects of quartz and cassiterite crystals of the Mocambo Granite (MG) and of associated greisens bodies, belonging to the Velho Guilherme Intrusive Suite, Carajás Province, and its relation with the tin mineralization. The study was performed with the aid of scanning electron microscope (SEM), using catodoluminescence (CL) images, semiquantitative analyzes by energy dispersive spectroscopy (EDS) and by electronic microprobe (EM) analyzes. Different facies and greisenized rocks of the MG were studied and it was possible to identify five types of quartz, called Qz1, Qz2, Qz3, Qz4 and Qz5. The Qz1, considered the most earlier type and of magmatic origin, can be found in all facies, being less frequent in the greisens. It appears as anhedral phenocrysts to luminescent sub-rounded (light gray), with varying degree of fracturing, as well as fine-to medium-grained crystals dispersed in the groundmass. Luminescent nuclei with alternating or reasorbed alternating light-dark zonations are common. Qz2 is posterior to Qz1 and not luminescent (dark gray); is present in all facies, but is rare in the greisen. It usually occurs as irregular discontinuous stains or filling fractures and shafts that section the Qz1, suggesting a process of intense replacement. The Qz3 does not show luminescence. It occurs in almost all facies filling a fracture that cuts Qz1 and Qz2. The Qz4 is present in the most evolved and intensely altered rocks, in the greisen and in veins or interstitial cavities, usully associated with cassiterite crystals. It is represented by euhedral, medium-greined, slightly fractured crystals, with well-defined light-dark zoning and variable thickness. Qz5 occurs sectioning and forming irregular spots on Qz4, being associated generally with wolframite or wolframite + cassiterite in quartz veins. They are slightly fractured, luminescent, meduium-to-coarse greined anhedral crystals. Qz1 and Qz2 from porphyritic syenogranite to monzogranite facies show high Ti concentration (9.5 - 104 ppm) and low Al (10 - 149 ppm). Qz1, Qz2 and Qz3 crystals from the aplitic alkali-feldspar granite facies presented slightly lower Ti contents (5 - 87 ppm) in comparison to SGMP quartz values and Al values that reach 2065 ppm. In the Qz1, Qz2 and Qz3 of the greisenized rocks, the Ti presented lower contents (0.0 and 62 ppm) and variable Al content (0 - 167 ppm). In the Qz4 crystals of the mineralized greisenized rocks in cassiterite, the Ti did not exceed 20 ppm, while Al presented strong enrichment, exceeding 3000 ppm. In the mineralized quartz veins in wolframite or wolframite + cassiterite, consisting mainly of Qz5, the Ti and Al concentrations presented generally low values, with maximum contents of 7 and 77 ppm, respectively. The cassiterite is occur as anhedral to subhedral fine-to coarse-grained crystals, anhedral to subhedral, associated to chlorite, muscovite, fengite and siderophyllite in gresenizeds rocks or commonly included in wolframite crystals in quatz veins. Shows light brown to reddish color and high colors of interference. More developed crystals show concentric zoning. Analyzes carried throug ME showed that in addition to Sn, cassiterites have lower concentrations of Fe, Ti, W, Nb and Mn traces. The concentrations of Fe, Nb, Ti and W are higher in the darker spots, while Sn shows higher purity in the lighter parts of the crystals. Cassiterites associated with Qz5 (hydrothermal) are often included in wolframite crystals or are partially substituted by it. This study showed that quartz was an excellent marker of the magmatic evolution and late alteration resulting from hydrothermal processes that operated in the Mocambo granite. It was possible to distinguish one magmatic and four hydrothermal types of quartz. The CL images indicate that the tin mineralization is present in the most evolved rocks and hydrothermally altered as in greisenized rocks and quartz veins, where the cassiterite is associated with Qz4 or Qz5 + wolframite. Qz5 suggests a possible mineralizing hydrothermal event of wolframite, subsequent to the origin of the cassiterite associated with Qz4.
Acesso aberto (Open Access)
Geologia, petrografia e geoquímica do granito Bom Jardim, região de São Félix do Xingu, Província Mineral de Carajás
(Universidade Federal do Pará, 2009-05-22) PINHO, Sabrina Cristina Cordovil; LAMARÃO, Claudio Nery; http://lattes.cnpq.br/6973820663339281; https://orcid.org/0000-0002-0672-3977
In the Carajás mineral province, located in the Amazonia Central geochronologic province, three important granite suites (Fig 1) were individualized on geologic, petrochemical, geochronological and isotope data in Jamon, Velho Guilherme and Serra dos Carajás (CPRM/DNPM 1999, Teixeira et al. 2002a, Dall´Agnol et al. 2005). These three suites are composed of ~1.89 to 1.86 Ga (Tab. 1) nondeformed stocks and batholiths. The absence of deformation along the massifs, the discordant character of the plutons and the presence of micrographic intergrowths suggest a high level of emplacement. All granites display characteristics of A-type granites and within-plate signature. The plutons of the Jamon suite show oxidized character, while the plutons of the Serra dos Carajás and Velho Guilherme suites are moderately reduced and reduced, respectively. In the domain of the Velho Guilherme suite, São Felix do Xingu region, the massifs Antonio Vicente, Serra da Queimada, Velho Guilherme, Mocambo, Ubim-sul and Benedita are tin (±W)-mineralized granites. The mineralization is related to evolved granitic facies affected by late to postmagmatic alteration or hosted in small bodies of greisens. The granitic rocks of the Velho Guilherme suite are dominantly hololeucocratic to leucocratic, monzogranite to syenogranite with subordinate alkali-feldspar granite. Show low contents of TiO2, Al2O3, CaO, MgO, P2O5, Sr, Ba and Cl and moderate of Hf, U and Zr. Rb, Y, F, Li, Th, Nb, Ta, Ga, and Rb/Sr, Rb/Ba, F/Cl ratios are systematically high. The Bom Jardim granite, inserted into Velho Guilherme suite, is a rounded Sn-W mineralized massif that cover ~ 400 km2, outcrops south of São Felix do Xingu city, and is intrusive in intermediate to felsic volcanic rocks of the Uatumã Group. It is dominantly constituted by isotropic, pink and medium-to coarse grained monzogranite and syenogranite. Chloritized biotite is the main primary mafic phase. Aplite dikes are common cross cutting the granite in different directions. These rocks are affected in different intensities by late- to posmagmatic alteration. Greisenized rocks containing small primary concentrations of cassiterite+wolframite, besides quartz veins with milimetre to centimetre-sized crystals of wolframite+pyrite+fluorite, were identified in pervasively altered cupolas. Magnetic Susceptibility (MS) data showed values of 5,34x10-4 SIv (minimum valor) to 9,18x10-4 SIv (maximum valor), similar to those found in the syenogranitic rocks of the Antonio Vicente pluton. Scanning Electron Microscopy (SEM) studies indicate that the Sn and W mineralization are dominantly associated with syenogranite and greisenized rocks. The zircons of the different facies of the Bom Jardim granite are characteristically enriched in Hf, Y, Th and U, and display low Zr/Hf ratios, such as zircon crystals of other specialized tin-granites of the Amazonian Craton. The obtained results demonstrate that a preliminary evaluation of the potential for Sn and W (±Nb+Ta) in evolved granites may be based on zircon compositional studies and in EDS semi-quantitative analyses obtained with a SEM. Geochemically, the rocks of the Bom Jardim granite have low contents of TiO2, MnO, MgO, CaO e P2O3. The Al2O3 is near of 13%, with RG1 displaying higher values (14%). Na2O e K2O show medium contents, except in the RG. The Fe2O3 rarely is superior to 2.0%, but it is higher in the greisenized rocks 1 (GR1), with ~7% (medium value) and greisenized rocks 2 (GR2), with ~3.7% (medium value), probably resulting from the presence of syderophyllite. Rb and Ba show inverse behavior. Rb increase in the sense of MzG-LMzG-SGRG1-RG2, with average of 294, 711,790, 874 and 1835 ppm, respectively. Ba display, in this same sense, medium contents of 670, 87, 18, 9 and 2 ppm, respectively. Sr shows similar behavior of the Ba, except in the GR, originating an increase in the Rb/Sr ratios in the sense of the more fractionated rocks. Sn and W show enrichment from less evolved to the more evolved rocks, with the GR2 displaying higher concentrations. F and Li are high in all studies facies (1400 to 3000 ppm and 15 to 134 ppm, respectively), but the higher values are found in the GR1 (21000 ppm and 698 ppm). The Rare Earth Elements (REE) show similar fractionated patterns, with negative Eu anomalies increasing from monzogranite to syenogranite rocks. The GR have similar patterns, but the GR1 are more enriched in REE than the GR2. The geochemical diagrams indicate that the fractionated crystallization was the dominant process during the magmatic evolution of the Bom Jardim granite, such as observed in others granitic bodies of the Velho Guilherme suite. Based in the obtained data and in the petrographic, geochemical and geochronological similarity with others granites of the Velho Guilherme suite, the Bom Jardim granite can be included in the context of this important Paleoproterozoic granitic suite.
Acesso aberto (Open Access)
Morfologia e química mineral de zircão e cassiterita, em concentrados de bateia, como guia prospectivo para mineralizações de Sn na Província Estanífera de Rondônia
(Universidade Federal do Pará, 2018-07-23) SILVA, Luciano Castro da; LAMARÃO, Claudio Nery; http://lattes.cnpq.br/6973820663339281
The contents of trace elements in certain minerals could help to revels tectonic, petrologic, hydrothermal or weathering processes which it was submitted. In addition to being a common accessory mineral, chemically and physically resistant to sedimentary transport and weather, high temperature metamorphic processes and anatexia, the abundance of certain trace elements in igneous zircons has allowed a connection with its type of rock source, its environment of crystallization and with certain mineral deposits. High levels of Hf and low Zr / Hf ratios in zircons are characteristic of mineralized granites in Sn and associated metals (Nb, Ta, ETR, etc.). Concentrations of Y and Nb, elements slightly mobile in aqueous environment, of granites type A can be used as good indicators of the crustal or juvenile nature of the magmas from which these rocks crystallized. Zircon crystals tend to incorporate Y and Nb in their structure and may present Y / Nb ratios close to the initial ratio of their generating magma. From the morphology and composition of zircon detrital crystals, it is possible to estimate the number of sedimentary rocks in the active river beds and their transport distance. The chemical compositions of cassiterites can also be used to indicate sources and generating processes. The present work is based on MEV images and semiquantitative analyzes by EDS (Energy Dispersive Spectrometry) of zircon and cassiterite detrital crystals from baton concentrate of the Rondônia Tin-Province (RTP). The main objective is to characterize the sources of these minerals, to confirm the location of deposits in exploration and to indicate potential areas for the prospection of Sn and associated metals. The use of morphology and mineral chemistry of detrital grains on a regional scale could be used as a fast and efficient tool for the prospecting of certain mineral goods. The work area, located in RTP, north-central portion of State Rondônia, is contained in the sheets Alto Jamari SC-20-Y-B and Ariquemes SC-20-V-D, both mapped by CPRM in the 1: 250,000 scale. Samples of baton concentrate from these projects were collected in active drainage from an initial volume of 20 liters of sediment retained between strainer of 5 and 0.5 mm. From these concentrates, light minerals were separated by micro-batting with water, heavy liquids (bromoform), magnetic by hand Nd magnet, and crystals of zircon (one hundred grains) and cassiterite (all grains screened in 5g of concentrate) using a binocular loupe, in addition of criteria such as color, granulometry and morphology representative of the populations of these minerals. Subsequently, zircon and cassiterite mounts were prepared for MEV / EDS analysis. The zircon crystals with contents of Hf>3% were interpreted as coming from rocks with high potential to mineralization in Sn and associated metals. These crystals were used in the geostatistical treatment and compared with the geographic positioning of mines and digging of Sn, known in the study area, to verify the veracity of the method. The geostatistical treatment used the ordinary kriging method and, from the results, isoteores curves were generated. The isothermal maps, using Zr / Hf ratios in detrital zircons of baton concentrate, were efficient because they coincided with known cassiterite deposits in the region. In the area selected for this study a significant compositional and morphological variety of zircon detrital grains were identified. Even in the most Hf enriched crystals (Hf>3%), these contents and their Zr / Hf ratios vary strongly. The most altered crystals tend to be more enriched in Hf and have lower Zr / Hf ratios, are more fractured and fragile to transport, indicating proximal sources. On the other hand, the less altered grains have low Hf contents, high Zr / Hf ratios and show little to moderately rounded, indicating proximal to intermediate sources. While Zr and Hf are variable within the same grain, the contents of Y and Nb are virtually constant. In the ternary diagram Hf-Nb-Y, the zircons of the RTP are enriched in Nb and impoverished in Y, while in the South of Pará Tin-Province (SPTP) and Pitinga they present Y enrichment and Nb impoverishment. The high values of Nb in the zircons of RTP and those of Y in the SPTP are interpreted here as a response of the magmatic source where they were formed. While the zircons of RTP are from rocks with positive εNd (t) values close to zero, the εNd (t) values of the SPTP are strongly negative. Thus, it can be assumed that zircons with high Y / Nb ratios would come from predominantly crustal sources, while zircons with low Y / Nb ratios would have mixed (crustal and mantle) sources. Cassiterite crystals of this study are prismatic or granular, with pyramidal terminations, bordered edges, suggesting absente to moderate sedimentary transport. They have high purity content (Sn between 73 and 79%) with concentrations of substitution cations of Sn around 1.5%. The high relative contents of Nb and Ta indicate magmatic sources and the subordinate Ti and Fe contents show the hydrothermal stage in which these minerals were generated.
Acesso aberto (Open Access)
Morphological and compositional variations of zircon and their metallogenetic implications: the example of the Jamon, Serra dos Carajás and Velho Guilherme suites, Amazonian Craton
(2014-03) LAMARÃO, Cláudio Nery; SILVA, Joseanna dos Santos; BORGES, Régis Munhoz Krás; DALL'AGNOL, Roberto
Zircon from granites of the Jamon suite (JS), Serra dos Carajás suite (SCS) and Velho Guilherme suite (VGS) were studied by scanning electron microscope (SEM) through backscattered electron and cathodoluminescence images and energy dispersive spectroscopy (EDS) analyses. Granites and greisens of the VGS have predominantly anhedral zircons that are altered and intensely corroded, are enriched in Hf and have the lowest Zr/Hf ratios of the studied suites. In the granites, these ratios decrease towards the more evolved varieties. Zircons of the JS are euhedral to subhedral, zoned and slightly altered; they are also comparatively depleted in Hf and display the highest Zr/Hf ratios, indicating limited potential for tin-associated mineralization. Zircons from granites of the SCS are subhedral to anhedral, altered and corroded, and show Hf contents and Zr/Hf ratios intermediate to those of the JS and VGS. The granites of the VGS with Sn-, Ta- and W-associated mineralization contain zircons with Zr/Hf ratios varying from 7 to 22. It is concluded that ratios of similar magnitude can be used as a prospecting guide for specialized granites. Zircons from the greisens associated with the Cigano granite of the SCS have average Zr/Hf ratios of approximately 23, but no cassiterite was found in these rocks, indicating that the zircons preserved their magmatic geochemical signature. This study distinguished the three granitic suites in terms of zircon composition and demonstrated the importance of their geochemical signature, especially in terms of their Zr/Hf ratio, in the identification of specialized granites. EDS-SEM analysis can thus be used in a preliminary assessment of the metallogenic potential of tin granites.