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Antimony quartz and antimony-gold quartz veins from northern Portugal

Neiva, A. M. R.; András, P.; Ramos, J. M. F.
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
ENG
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Antimony- and Pb-Sb-quartz veins from the Bragança district, Portugal, are mainly hosted by Silurian phyllites. Antimony-Au-quartz veins from the Dúrico-Beirã region are mainly hosted by a Cambrian schist-metagraywacke complex, as well as Ordovician phyllites and quartzites. The deposits were mostly exploited in the late 19th Century. Mineralogical characteristics and chemical compositions of individual ore minerals are similar in the two areas. First and second generations of arsenopyrite precipitated at 390 and 300 °C, respectively. Berthierite and stibnite are the most abundant Sb-bearing minerals and precipitated between 225 and 128 °C, native antimony at < 200 °C. Drastic fluid cooling is the main cause of mineral precipitation. The Pb isotope compositions of stibnite suggest a homogeneous crustal source of lead, from the metasedimentary sequences, for Sb, Pb-Sb and Sb-Au deposits in both areas, which is consistent with the findings for comparable mineralizations elsewhere in Europe. Remobilization of Pb is related to Variscan metamorphism and deformation.; http://www.sciencedirect.com/science/article/B6V90-4SS1KKX-1/1/0011e7cdc8549fdf26d7f4bc628b3bb8

Gruta Nova da Columbeira, Gruta das Salemas and Gruta da Figueira Brava : stratigraphy, and chronology of the pleistocene deposits

Antunes, M. T.; Cardoso, João Luís
Fonte: Universidade Aberta de Portugal Publicador: Universidade Aberta de Portugal
Tipo: Parte de Livro
Publicado em //2000 ENG
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The evidence concerning the most recent Neanderthals in Portugal and maybe in the world, comes from there basic sites: Gruta das Salemas and Gruta da Figueira Brava. For Gruta Nova da Columbeira, two human occupation lewvels were 14C dated: c. 7, 26400 ± 750 BP and c. 8, 28900 ± 950 BP. The industries (denticulates, rich in levallois facies scrapers) are exclusively late Mousterian; this , as well as the fauna and a neanderthalian tooth make this cave one of the reference Mousterian sites in the Iberian Peninsula. Gruta das Salemas - at the bottom, sediment gliding suggests that most of the basal deposits (and bones for 14C dating) came from the outside during a certain time span. Atypical implements have tentatively been ascribed to the Middle Palaeolithic. Bed 8 vielded a human decidual molar and was dated 24820 ± 550 BP,this being apparently too for the Mousterian. The concerned dating may be somewhat later than the lowermost c. 8 deposits. The Gruta da Figueira Brava is especially important because of the wealth of data it provides. The site resulted from karst erosion that broadened vertical diaclases, and mainly from marine abrasion during Tryrrhenian III event. The surfexcavated a broad and deep shelter: The consequent lowering of the sea level (until about - 60 meters) forstered the development of a littoral plain with dunes that was flooded again in the Holocene. Diagenetic CaCo3 consolidated the external part of eolic sand with its fossil contents into a hard sandstone. That...

Relação solo-relevo-substrato geológico nas restingas da planície costeira do estado de São Paulo; Relationship between soil, landscape and geological substrate of the sandy coastal plain of São Paulo state

COELHO, Maurício Rizzato; MARTINS, Vanda Moreira; VIDAL-TORRADO, Pablo; SOUZA, Célia Regina de Gouveia; PEREZ, Xosé Luis Otero; VÁZQUEZ, Felipe Macías
Fonte: Sociedade Brasileira de Ciência do Solo Publicador: Sociedade Brasileira de Ciência do Solo
Tipo: Artigo de Revista Científica
POR
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Atributos morfológicos de 28 pedons, descritos e amostrados em cronossequências, e datações absolutas por luminescência (TL e LOE) e 14C foram utilizados para elucidar os principais fatores envolvidos na formação e evolução dos Espodossolos nos depósitos marinhos quaternários da planície costeira do Estado de São Paulo. Os solos estudados localizam-se nos municípios de Bertioga (Baixada Santista), Cananeia e Ilha Comprida (Litoral Sul). Essa abordagem, pouco comum nos estudos dos ambientes de planície costeira brasileiros, possibilitou as seguintes interpretações: (a) o relevo, a dinâmica hídrica e o tempo (incluindo as variações do nível relativo do mar) são os principais condicionantes da diferenciação espacial dos Espodossolos nos terraços marinhos; (b) os Espodossolos mais antigos e bem drenados, devido às condições de relevo e rebaixamento do nível do lençol freático, apresentam grande variabilidade e diversidade de seus horizontes e atributos morfológicos, diferindo daqueles mal drenados (antigos ou jovens), em que os horizontes são mais homogêneos; (c) os Espodossolos mais antigos, quando bem drenados, mostram-se em avançado estádio de degradação, enquanto os mal drenados encontram-se bem preservados...

OSL age determinations of Pleistocene fluvial deposits in Central Amazonia

SOARES, Emílio A.A.; TATUMI, Sonia H.; Riccomini, Claudio
Fonte: Academia Brasileira de Ciências Publicador: Academia Brasileira de Ciências
Tipo: Artigo de Revista Científica
ENG
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Absolute dating methods have been used in chronological studies of geological processes and sedimentary units of Quaternary age in Central Amazonia, Brazil. Although radiocarbon dating has been very useful in archaeological research and soil studies, the temporal interval of this method is inefficient in evaluating the sedimentation aspects and geological events from the beginning of the Quaternary in the Amazon basin. The use of crystal luminescence dating has been one of the most promising tool for determining the absolute dating of Quaternary deposits in the Amazonian region. Optically stimulated luminescence (OSL) dating, following the MAR and SAR protocols, in a tectonic-sedimentary study of Quaternary fluvial deposits in the confluence area of the Negro and Solimões rivers, indicated ages from 1.3 (Holocene) to about 67.4 kyears (Late Pleistocene) for these sediments. Low radioactive isotope concentrations were found about 2ppm for 235U and 238U; 5ppm for 232Th; and the 40K concentrations were almost zero. A comparison was made between MAR and SAR protocols taking into account the fluvial depositional process.; Métodos de datação absoluta têm sido usados em estudos cronológicos de processos geológicos e unidades sedimentares de idade quaternária na Amazônia Central...

Late Quaternary sedimentation in the Paraiba Basin, Northeastern Brazil: Landform, sea level and tectonics in Eastern South America passive margin

ROSSETTI, Dlice F.; BEZERRA, Francisco H. R.; GOES, Ana M.; VALERIANO, Marcio M.; ANDRADES-FILHO, Clodis O.; MITTANI, Juan C. R.; TATUMI, Sonia H.; BRITO-NEVES, Benjamim B.
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
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Late Quaternary deposits in the northeastern Brazil have been scarcely investigated, despite their relevance to the discussion of the post-rift evolution of the South American passive margin within the context of landform, sea level and tectonic deformation. Sedimentological, stratigraphic and morphological characterization of these deposits, referred as Post-Barreiras Sediments, led to their distinction from underlying Early/Middle Miocene strata. Based on optically stimulated luminescence (OSL) dating, two sedimentary units (PB1 and PB2) were recognized and related to the time intervals between 74.8 +/- 9.3 and 30.8 +/- 6.9 ka, and 8.8 +/- 0.9 and 1.8 +/- 0.2 ka, respectively. Unit PB1 consists of indurated sandstones and breccias either with massive bedding or complex types of soft sediment deformation structures generated by contemporaneous seismic activity. Unit PB2 is composed of massive sands or sands related to structures developed by dissipation of dunes. The present work, focusing on the Post-Barreiras Sediments, discusses landform, sea level and tectonics of the eastern South American passive margin during the latest Quaternary. Non-deposition and sub-aerial exposure related to the Tortonian worldwide low sea level combined with tectonic quiescence followed the Miocene transgression. Tectonic deformation in the latest Pleistocene created space to accommodate unit PB1 in downthrown faulted blocks and...

Molecular mass distribution of dextran in Brazilian sugar and insoluble deposits of cachaca

AQUINO, Francisco W. B.; FRANCO, Douglas W.
Fonte: ELSEVIER SCI LTD Publicador: ELSEVIER SCI LTD
Tipo: Artigo de Revista Científica
ENG
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The dextran molecular mass distribution profile in 77 sugar samples from Brazil and twelve insoluble deposits (alcoholic flocks) samples from sugared cachacas (Brazilian sugar cane spirit) is described in terms of number-average molecular mass M,,, weight-average molecular mass M(w), Z-average molecular mass M,, and polydispersity. The analyses were performed by size-exclusion chromatography, using a refractive index detector. In most of the sugar samples, it was possible to identify two major groups of dextrans with Mw averages of 5 x 10(6) and 5 x 10(4) Da. Based on the evaluated parameters, the dextran distribution profile is about the same in samples analyzed over five seasons, and, therefore, it is likely that the Brazilian product pattern will not change very much over the years. In insoluble deposits from sugared cachacas, dextrans with Mw values in the order of the 10(5) Da were the most frequent ones, being present in 58% of the samples. (c) 2008 Elsevier Ltd. All rights reserved.; CNPq; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); CAPES; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); FAPESP

Raman and XRD study on brookite-anatase coexistence in cathodic electrosynthesized titania

Campos, C. S.; Spada, E. R.; Paula, F. R. de; Reis, F. T.; Faria, Roberto Mendonça; Sartorelli, M. L.
Fonte: WILEY-BLACKWELL; MALDEN Publicador: WILEY-BLACKWELL; MALDEN
Tipo: Artigo de Revista Científica
ENG
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Among the many methods developed for the synthesis of titanium dioxide, cathodic electrosynthesis has not received much attention because the resulting amorphous oxy-hydroxide matrix demands a further thermal annealing step to be transformed into crystalline titania. However, the possibility of filling deep recessed templates by the control of the solidliquid interface makes it a potentially suitable technique for the fabrication of porous scaffolds for photovoltaics and photocatalysis. Furthermore, a careful control of the crystallization process enables the growth of larger grains with lower density of grain boundaries, which act as electron traps that slow down electronic transport and promote charge recombination. In this report, well crystallized titania deposits were obtained by thermal annealing of amorphous deposits fabricated by cathodically assisted electrosynthesis on indium-tin oxide (ITO)substrates. The combined use of Raman spectroscopy and X-ray diffraction showed that the crystallization process is more intricate than previously assumed. It is shown that the amorphous matrix evolves into a rutile-free mixture of brookite and anatase at temperatures as low as 200 degrees C that persists up to 800 degrees C, when pure anatase dominates. The amount of brookite in the brookiteanatase mixture reaches a maximum at 400 degrees C. This very simple method for obtaining a brookiteanatase mixture and the ability to tune their proportions by thermal annealing is a promising alternative whose potential for solar cells and photocatalysis deserves a careful evaluation. Copyright (C) 2011 John Wiley & Sons...

Characterization of quaternary tufas in the Serra do Andre Lopes karst, southeastern Brazil

Sallun Filho, William; Sapiensa Almeida, Luis Henrique; Boggiani, Paulo Cesar; Karmann, Ivo
Fonte: SPRINGER; NEW YORK Publicador: SPRINGER; NEW YORK
Tipo: Artigo de Revista Científica
ENG
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Active tufas in the form of waterfalls and dams occur along drainage channels in the Serra do Andre Lopes region (State of Sao Paulo, southeastern Brazil) and are associated with the karst system that developed on a dolomitic plateau with a superhumid subtropical climate. The predominance of autogenic waters enables the groundwater to become enriched in calcium carbonate, with low terrigenous sediment content. The tufas that were studied are composed of calcite and have high calcium contents and low magnesium contents. Eroded tufa beds that originate from changes in the position of fluvial channels or river flow rates also occur in this region. In the Sapatu deposit, phytohermal tufas with complex morphologies are arranged in levels constituting various temporally repeated sequences that were deposited between 10,570 and 4,972 cal years BP. In the Frias deposit, distal fluvial deposits of tufa are massive with a relatively greater quantity of terrigenous material and show evidence of dissolution and reprecipitation. The base of this deposit is composed of a cemented breccia dated at 25,390 years BP, which is younger than the overlying tufas ([42,000 years BP). In the two deposits, the levels of terrigenous sediments (quartz sand and lithic pebbles) and terrestrial gastropod shells are interpreted as phases of increased flow rate of rivers during intervals of higher rainfall.; FAPESP; FAPESP [08/08583-7]; Caverna do Diabo State Park; Caverna do Diabo State Park

Geochemical and sedimentological investigations of Youngest Toba Tuff ashfall deposits

Gatti, Emma
Fonte: University of Cambridge; Department of Geography Publicador: University of Cambridge; Department of Geography
Tipo: Thesis; doctoral; PhD
EN
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The ~ 73 ka ?super-eruption? of the Toba caldera in Sumatra is the largest known eruption of the Quaternary. The products of this eruption, the Youngest Toba Tuff (YTT), have been implicated in global and regional climate deterioration with widespread ecological effects. In this thesis I study the YTT co-ignimbrite ashfall, in particular the mechanisms of transport, sedimentation and preservation of ash deposits. I use distal marine and terrestrial ash sediments: a) to estimate the volume of YTT ash fallout; b) to quantify variability in the geochemistry of YTT ash; c) to assess the reliability of YTT ash as a chronostratigraphic marker; and d) to determine local influences on the reworking of YTT ash deposits. Following the introductory chapters, I address topics a) and b) through detailed investigations of published physical and chemical evidence. Chapter three shows that particle size and sediment thickness do not decline exponentially with distance from the eruption vent, highlighting the limitations of current methods of volume estimation for co-ignimbrite super-eruptions. Chapter four analyses geochemical variation in 72 YTT samples, and reveals the signatures of magma chamber zonation and post-depositional alteration. I address topics c) and d) through fieldwork in six locations...

Ordovician-Silurian volcanogenic massive sulfide deposits on the southern Prince of Wales Island and the barrier islands, southeastern Alaska

Gehrels, George E.; Berg, Henry C.; Saleeby, Jason B.
Fonte: United States Geological Survey Publicador: United States Geological Survey
Tipo: Report or Paper; PeerReviewed Formato: application/pdf
Publicado em //1983
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Several pyritic massive sulfide deposits have been recognized in an Ordovician-Silurian volcano-plutonic complex in the southern Prince of Wales Island region (Fig. 1). These deposits have been studied as part of a U.S. Geological Survey-California Institute of Technology investigation into the geologic and mineralization history of southern Prince of Wales Island (south of 55° North Latitude; Fig. 1). This report describes the geologic setting of the deposits and presents preliminary chemical analyses of the mineralization.

Deltaic deposits at Aeolis Dorsa: Sedimentary evidence for a standing body of water on the northern plains of Mars

DiBiase, Roman A.; Limaye, Ajay; Scheingross, Joel S.; Fischer, Woodward W.; Lamb, Michael P.
Fonte: American Geophysical Union Publicador: American Geophysical Union
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 12/06/2013
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A fundamental long-standing question regarding Mars history is whether the flat and low-lying northern plains ever hosted an ocean. The best opportunity to solve this problem is provided by stratigraphic observations of sedimentary deposits onlapping the crustal dichotomy. Here, we use high-resolution imagery and topography to analyze a branching network of inverted channel and channel lobe deposits in the Aeolis Dorsa region, just north of the dichotomy boundary. Observations of stacked, cross-cutting channel bodies and stratal geometries indicate that these landforms represent exhumed distributary channel deposits. Observations of depositional trunk feeder channel bodies, a lack of evidence for past topographic confinement, channel avulsions at similar elevations, and the presence of a strong break in dip slope between topset and foreset beds suggest that this distributary system was most likely a delta, rather than an alluvial fan or submarine fan. Sediment transport calculations using both measured and derived channel geometries indicate a minimum delta deposition time on the order of 400  years. The location of this delta within a thick and widespread clastic wedge abutting the crustal dichotomy boundary, unconfined by any observable craters...

Geologia e caracterização tecnológica do minério de manganês da mina Córrego do Cocho, Itapira (SP); Geological and technological characterization of the manganese ore deposits of the Córrego do Cocho mine, Itapira (SP)

Angeli, Nelson; Khan, Henrique; Ito, Gabriel Mineo; Carvalho, Sebastião Gomes de; Jimenez-Rueda, Jairo Roberto; Penha, Ulisses Cyrino
Fonte: Universidade de São Paulo. Instituto de Geociências Publicador: Universidade de São Paulo. Instituto de Geociências
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; ; ; Formato: application/pdf
Publicado em 01/12/2011 POR
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The objects of this study are three manganese ore deposits and one mine derived from lateritic weathering of gondites (spessartine quartzites). These deposits are associated with Mn-rich garnet metasediments of the Itapira Group (Paleoproterozoic) and the reserves were estimated at approximately 2.0 x 10(6) tons with an average grade of 23% MnO2. The ore minerals are cryptomelane, pyrolusite, lithiophorite, spessartine and psilomelane. Several crystal shapes and textural characteristics were identified in this study, which are related to the degree of liberation, as confirmed by heavy media separation method. In this study, we determined the main characteristics of the liberation of manganese, which is concentrated in the fine grain-size fraction and is lost during ore dressing. Therefore, the low average content of MnO2 (28%) is due to this loss, whereas at grain size of minus 0.074 mm, contents near 40% MnO2 were observed. This suggests that the ore can be used for manufacturing manganese sulphate fertilizers. A comparative study with the ore deposits located at Ouro Fino (MG), mainly with the Caneleiras mine, showed that higher degree of liberation occurs in the coarse grain-size fractions (0.84 to 0.074 mm with MnO2 content of 38%). As a consequence...

Comparison of the Daluxiang and Maoniuping carbonatitic REE deposits with Bayan Obo REE deposit, China

Xu, Cheng; Campbell, Ian; Kynicky, Jindrich; Allen, Charlotte M; Chen, Yanjing; Huang, Zhilong; Qi , Liang
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
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Although carbonatites potentially contain a larger concentration of rare earth elements (REEs) than any rock type, the origin of the REE mineralization in the world's largest Bayan Obo carbonatite-related deposit is still disputed. In order to clarify the mechanism of REE mineralization, carbonatite samples from three large REE deposits in China, Daluxiang, Maoniuping and Bayan Obo were compared. The REE minerals in Daluxiang and Maoniuping carbonatites show constant light REE (LREE) enrichment (chondrite normalized (La/Nd)N ratios > 1), whereas those in Bayan Obo H8 dolomite marbles show variable (La/Nd)N ratios. The REE abundances and patterns of the REE minerals in Maoniuping carbonatites are similar to those in the barite, calcite and thread vein-hosted ores. The calcites in Daluxiang and Maoniuping carbonatites are characterized by enrichments of Pb, Sr and REEs, which is consistent with an igneous origin. They have similar REE contents and patterns to the corresponding bulk rocks, suggesting that these carbonatites are calcite-rich cumulates. During crystallization and accumulation of calcites, the REEs become enriched in carbonatite-expelled fluids because of the very low partition coefficients for these elements between carbonate minerals and melt. These fluids interact with the country rocks to produce fluorite-rich REE mineralization. The fluorites in Daluxiang and Maoniuping deposits are characterized by high Sr contents and REE patterns that vary from LREE enriched to LREE depleted. The former has relatively higher Sr and lower heavy REE (HREE) concentrations than those in Maoniuping...

The St Ives mesothermal gold system, Western Australia - a case of golden aftershocks?

Cox, Stephen; Ruming, K
Fonte: Pergamon-Elsevier Ltd Publicador: Pergamon-Elsevier Ltd
Tipo: Artigo de Revista Científica
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The late orogenic evolution of the Archaean greenstone sequence in the Eastern Goldfields Province of the Yilgarn Craton in Western Australia is characterised by strike-slip tectonics and locally very high, fault-controlled, fluid fluxes. Fluid flow was associated with the formation of many fault-hosted and shear-zone-hosted gold deposits, which are commonly clustered adjacent to high displacement faults or shear zones. In the St Ives goldfield, near Kambalda, fluid flow in a gold-producing hydrothermal system was localised within arrays of low displacement faults and shear zones, which form part of the NNW trending, crustal-scale, Boulder-Lefroy fault system (BLFS). The numerous ore-hosting structures are kinematically related to sinistral to sinistral-oblique slip on the Playa Fault, which is a 20-km-long splay of the 200-km-long Boulder-Lefroy Fault. Most of the known gold mineralisation at St Ives occurs within an area of 20 km2 immediately south-west of the Playa Fault. The distribution of low displacement faults and shear zones that host gold mineralisation is related to the presence of a kilometre-scale contractional jog (the Victory jog) and an associated imbricate thrust array on the Playa Fault. By analogy with modern seismogenic systems...

A system to evaluate the performance of hydraulic nozzles used in stored grain preotection trials; Sistema para avaliar o desempenho de bicos hidráulicos utilizados em experimentos de proteção de grãos armazenados

Vásquez-Castro, Javier A.; Baptista, Gilberto C. de; Gadanha Jr., Casimiro D.; Trevizan, Luiz R.P.
Fonte: Universidade de São Paulo. Escola Superior de Agricultura Luiz de Queiroz Publicador: Universidade de São Paulo. Escola Superior de Agricultura Luiz de Queiroz
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; ; ; ; ; Formato: application/pdf
Publicado em 01/12/2007 ENG
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We developed a system to evaluate the performance of hydraulic nozzles used in stored corn and wheat grain protection experiments. An insecticidal mix was used as test fluid to determine the transversal volumetric distribution and droplets spectrum of a model TJ-60 8002EVS hydraulic nozzle. A mobile application system was built to apply a rate equivalent to 5 L t-1 and obtain theoretical concentrations of 10 and 0.5 mg kg-1 of fenitrothion and esfenvalerate, respectively. The corn and wheat grains were spread out as a fine layer. Three glass slides (0.1 × 0.05 m) were placed on the top surface of the grains to ensure that the intended application rate was achieved. After treatment, the deposits on both matrices were analyzed by gas chromatography. The fenitrothion deposit was higher than esfenvalerate, and the deposit on wheat was higher than on corn grains (P < 0.05). The deposits on the glass slides reached values of 100 and 93% of the intended theoretical fenitrothion and esfenvalerate concentrations, respectively. Deposits on the grains were lower than on the glass slides, with values of 64 and 52% of the intended theoretical fenitrothion and esfenvalerate concentrations, respectively. The results obtained demonstrate a high effectiveness of the method for evaluation of the performance of hydraulic nozzles when an insecticidal mix is used as test fluid. The factors that influenced insecticide deposition on glass slides and on grains are discussed in the present work.; A tecnologia de aplicação na proteção de grãos armazenados é de fundamental importância para melhorar a uniformidade de distribuição dos agrotóxicos na massa de grãos. Foi desenvolvido um sistema para avaliar o desempenho de bico hidráulico utilizado em experimentos de proteção de grãos de milho e trigo armazenados. Para determinar a distribuição volumétrica transversal e o espectro de gotas do bico hidráulico modelo TJ-60 8002EVS...

Albite-chlorite and talc-chlorite deposits in metasedimantary and granitoid rocks of central Sardinia (Italy)

FIORI, MADDALENA; GRILLO, SILVANA MARIA
Fonte: UFPR Publicador: UFPR
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; Artigo Avaliado pelos Pares Formato: application/pdf
Publicado em 31/08/2004 POR
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The albite and talc-chlorite deposits occurring in central-eastern Sardinia are associated with metasedimentary rocks with intrusions of Hercynian granitoids which contain abundant roof pendants of Palaeozoic metasedimentary rocks. The talc-chlorite bodies are hosted by the roof pendants of mica schists and variably recrystallised metalimestones and metadolostones, whereas deposits of albite generally occur in the granitoids, and to a lesser extent, in the roof pendants represented by mica schists. The talc- and Mg-chlorite deposits are considered to have been formed during the metamorphic event coeval with the emplacement of the granitoid rocks, whereas the albitic bodies were formed during later, post-magmatic, metasomatic processes.

PETROGRAPHIC AND GEOCHEMICAL STUDIES AT GIANT SERRA NORTE IRON ORE DEPOSITS IN THE CARAJÁS MINERAL PROVINCE, PARÁ STATE, BRAZIL

Figueiredo e Silva, Rosaline Cristina; Lobato, Lydia Maria; Rosière, Carlos Alberto; Hagemann, Steffen
Fonte: Centro de Pesquisa Professor Manoel Teixeira da Costa - IGC - UFMG Publicador: Centro de Pesquisa Professor Manoel Teixeira da Costa - IGC - UFMG
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; Artigo Avaliado pelos Pares Formato: application/pdf
Publicado em 13/02/2013 POR
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ESTUDOS PETROGRÁFICOS E GEOQUÍMICOS DOS GIGANTES DEPÓSITOS DE MINÉRIO DE FERRO DA SERRA NORTE, PROVÍNCIA MINERAL DE CARAJÁS, PARÁ, BRASIL. Os depósitos de minério de ferro de Carajás, localizados no sudeste do estado do Pará no Brasil, estão hospedados na sequência metavulcanossedimentar do Grupo Grão Pará, Supergrupo Itacaiúnas. Os protólitos da mineralização de ferro são jaspilitos, soto- e sobrepostos por basaltos, ambos metamorfisados em fácies xisto verde. Os maiores depósitos de minério de ferro da Serra Norte são N1, N4E, N4W, N5E e N5S, estão distribuídos ao longo e estruturalmente controlados pelo flanco norte da dobra Carajás. Minério de alto teor (> 64 % Fe) consiste em minérios compactos e friáveis. O contato basal dos minérios de alto teor é definido por rocha basáltica alterada hidrotermalmente, composta por clorita e hematita microlamelar. Diferentes estágios de alteração hidrotermal afetaram jaspilitos para formar minérios de ferro, da zona de alteração distal, representada pelo estágio cedo-hidrotermal, às zonas de alteração intermediária e proximal, concomitantes com o evento principal de formação de minério de ferro. A zona proximal representa o estágio de alteração avançado (i.e....

Precious metaltellurides and other Te-bearing minerals in different paragenesis of Argentina: A review

de Brodtkorb,Milka K
Fonte: Revista de la Asociación Geológica Argentina Publicador: Revista de la Asociación Geológica Argentina
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2009 EN
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Severalpolymetallic deposits containing tellurides and Te-bearing minerals occur indifferent geologic terrains of Argentina. Tellurides with Ag and /or Au arewidespread in meso and epithermal environments; they are structurallycontrolled and genetically related to Jurassic or Miocene-Pliocene volcanism.These species are represented by calaverite, hessite, stützite, krennerite,sylvanite, petzite and cervellite. Other Te-bearing minerals are present notonly in epithermal deposits but also in different assemblages such asintraplutonic W deposits, skarn and mafic-ultramafic bodies. They are Te,altaite, nagyágite, melonite- merenskyite, tetradymite, telurobismuthite,kawazulite, Te-canfieldite and goldfieldite. Paragenesis of the differentdeposits and chemical data of the minerals are given.

Climatic characteristics of the late Pleistocene and Holocene continental deposits from southwestern Syria based on palynological data

Hussein,Kamal M.
Fonte: Darwiniana, nueva serie Publicador: Darwiniana, nueva serie
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2006 EN
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The goal of this research was to reconstruct the vegetational and climatic changes that took place during the late Pleisocene and Holocene in southwestern Syria. This reconstruction was based on palynological data obtained from the analysis of 27 sediments and surface samples (with a total thickness of 4.55 m) collected from Al-Hijaneh Lake basin (late Pleistocene) and from Al-Aouaj River valley (Holocene). Three pollen zones were established. The oldest one (zone A) corresponds to the late Pleistocene lacustrine deposits of Lake Al-Hijaneh. Zones B and C were defined in the Holocene fluvial- lacustrine deposits of the Al-Aouaj River valley. These three pollen assemblage zones are correlated to synchronic and similar C14 dated pollen zones from Syria, Turkey, Iran and Greece. This allows a more definite age determination for the deposits of this study. The region's past climates and vegetation are discussed.

Multi-mineral cut-off grade optimization by grid search

Cetin,E.; Dowd,P.A.
Fonte: Journal of the Southern African Institute of Mining and Metallurgy Publicador: Journal of the Southern African Institute of Mining and Metallurgy
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2013 EN
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Orebodies that contain more than one economically important mineral are generally evaluated by parametric cut-off grades. This approach often leads to mis-valuation of mineral deposits because cut-off grades are not based on the grades of each individual mineral and, because of the parametric formulation, are only indirectly related to the individual grade distributions. The only realistic approach is a formulation that accounts separately for each component mineral. The grid search method can be used as a means of multi-mineral cut-off grade optimization in this context. This paper describes the use of the grid search method in cut-off grade optimization for multi-mineral deposits. The authors introduce the general concepts of the method and formulate its application to cut-off grade optimization; they describe a software implementation of the method that can accommodate cut-off grade optimization for mineral deposits that contain up to three economic minerals.