The Mont Collon mafic complex (Austroalpine Dent Blanche nappe) : permian evolution of the Western European mantle

Résumé: Le complexe du Mont Collon (nappe de la Dent Blanche, Austroalpin) est l'un des exemples les mieux préservés du magmatisme mafique permien des Alpes occidentales. Il est composé d'affleurements discontinus et d'une stratification magmatique en son centre (Dents de Bertol) et est composé à 95% de roches mafiques cumulatives (gabbros à olivine et/ou cpx, anorthositiques, troctolites, wehrlites et wehrlites à plagioclase) et localement de quelques gabbros pegmatitiques. Ces faciès sont recoupés par de nombreux filons acides (aphtes, pegmatites quartziques, microgranodiorites et filons anorthositiques) et mafiques tardifs (dikes mélanocrates riches en Fe et Ti). Les calculs thermométriques (équilibre olivine-augite) montrent des températures de 1070-1120 ± 6°C, tandis que le thermomètre amphibole-plagioclase indique une température de 740 ± 40°C à 0.5 GPa pour les amphiboles magmatiques tardives. La geobarométrie sur pyroxène donne des pressions moyennes de 0.3-0.6 GPa, indiquant un emplacement dans la croûte moyenne. De plus, les températures obtenues sur des amphiboles coronitiques indiquent des températures de l'ordre de 700 ± 40°C confirmant que les réactions coronitiques apparaissent dans des conditions subsolidus. Les âges concordants U/Pb sur zircons de 284.2 ± 0.6 et 282.9 ± 0.6 Ma obtenus sur un gabbro pegmatitique et une pegmatitique quartzique, sont interprétés comme des âges de cristallisation. Les datations 40Ar/39Ar sur amphiboles des filons mélanocrates donnent un âge plateau de 260.2 ± 0.7 Ma, qui est probablement très proche de l'âge de cristallisation. Ainsi, cet age 40Ar/39Ar indique un second évènement magmatique au sein du complexe. Les compositions des roches totales en éléments majeurs et traces montrent peu de variations, ainsi que le Mg# (75-80). Les éléments traces enregistrent le caractère cumulatif des roches (anomalie positive en Eu) et révèlent des anomalies négatives systématiques en Nb, Ta, Zr, Hf et Ti dans les faciès basiques. Le manque de corrélation entre éléments majeurs et traces est caractéristique d'un processus de cristallisation in situ impliquant une quantité variable de liquide interstitiel (L) entre les phases cumulus. Les distributions des éléments traces dans les minéraux sont homogènes, indiquant une rééquilibration .subsolidus entre cristaux et liquide interstitiel. Un modèle quantitatif basé sur les équations de cristallisation in situ de Langmuir reproduisent correctement les concentrations en terres rares légères des minéraux cumulatifs montrant la présence de 0 à 35% de liquide interstitiel L pour des degrés de différenciation F de 0 à 45%, par rapport au faciès les moins évolués du complexe. En outre, les valeurs de L sont bien corrélées avec les proportions modales d'amphibole interstitielle et les concentrations en éléments incompatibles des roches (Zr, Nb). Le liquide parental calculé des cumulats du Mont Collon est caractérisé par un enrichissement relatif en terres rares légères et Th, un appauvrissement en terres rares lourdes typique d'une affinité transitionnelle (T-MORB) et une forte anomalie négative en Nb-Ta. Les roches cumulatives montrent des compositions isotopiques en Nd-Sr proches de la terre globale silicatée (BSE), soit 0.6<εNdi<+3.2, 0.7045<87Sr/86Sri<0.7056. Les rapports initiaux en Pb indiquent une source dans le manteau enrichi subcontinental lithosphérique, préalablement contaminé par des sédiments océaniques. Les dikes mélanocrates Fe-Ti sont représentatifs de liquides et ont des spectres de terres rares enrichis, une anomalie positive en Nb-Ta et des εNdi de +7, des 87Sr/86Sri de 0.703 et des rapports initiaux en Pb, similaires à ceux des basaltes d'île océanique, indiquant une source asthénosphérique modérément appauvrie. Ainsi, la fusion partielle du manteau lithosphérique subcontinental est induite par l'amincissement post-orogénique et la remontée de l'asthénosphère. Les filons mélanocrates proviennent, après délamination du manteau lithosphérique, de la fusion de l'asthénosphère. Abstract The early Permian Mont Collon mafic complex (Dent Blanche nappe, Austroalpine nappe system) is one of the best preserved examples of the Permian mafic magmatism in the Western Alps. It is composed of discontinuous exposures and a well-preserved magmatic layering (the Dents de Bertol cliff) crops out in the center part of the complex. It mainly consists of cumulative mafic rocks, which represent 95 vol-% of the mafic complex (ol- and cpx-bearing gabbros and rare anorthositic layers, troctolites, wehrlites and plagioclase-wehrlites) and locally pegmatitic gabbros. All these facies are crosscut by widespread acidic (aplites, quartz-rich pegmatites, microgranodiorites) and late mafic Fe-Ti melanocratic dikes. Olivine-augite thermometric calculations yield a range of 1070-1120 ± 6°C, while amphibole-plagioclase thermometer yields a temperature of 740 ± 40°C at 0.5 GPa. Pyroxene geobarometry points to a pressure of 0.3-0.6 GPa, indicating a middle crustal level of emplacement. Moreover, temperature calculations on the Mont Conon coronitic amphiboles indicate temperatures of 700 ± 40°C, close to those calculated for magmatic amphiboles. These temperatures confirm that coronitic reactions occurred at subsolidus conditions. ID-TIMS U/Pb zircon ages of 284.2 ± 0.6 and 282.9 ± 0.6 Ma obtained on a pegmatitic gabbro and a quartz-pegmatitic dike, respectively, were interpreted as the crystallization ages of these rocks. 40Ar/39Ar dating on amphiboles from Fe-Ti melanocratic dikes yields a plateau age of 260.2 ± 0.7 Ma, which is probably very close to the crystallization age. Consequently, this 40Ar/P39Ar age indicates a second magmatic event. Whole-rock major- and trace-element compositions show little variation across the whole intrusion and Mg-number stays within a narrow range (75-80). Trace-element concentrations record the cumulative nature of the rocks (e.g. positive Eu anomaly) and reveal systematic Nb, Ta, Zr, Hf and Ti negative anomalies for all basic facies. The lack of correlation between major and trace elements is characteristic of an in situ crystallization process involving variable amounts of interstitial liquid (L) trapped between the cumulus mineral phases. LA-ICPMS measurements show that trace-element distributions in minerals are homogeneous, pointing to subsolidus re-equilibration between crystals and interstitial melts. A quantitative modeling based on Langmuir's in situ crystallization equation successfully reproduced the Rare Earth Element (REE) concentrations in cumulitic minerals. The calculated amounts of interstitial liquid L vary between 0 and 35% for degrees of differentiation F of 0 to 45%, relative to the least evolved facies of the intrusion. Furthermore, L values are well correlated with the modal proportions of interstitial amphibole and whole-rock incompatible trace-element concentrations (e.g. Zr, Nb) of the tested samples. The calculated parental melt of the Mont Collon cumulates is characterized by a relative enrichment in Light REE and Th, a depletion in Heavy REE, typical of a transitional affinity (T-MORB), and strong negative Nb-Ta anomaly. Cumulative rocks display Nd-Sr isotopic compositions close to the BSE (-0.6 < εNdi < +3.2, 0.7045 < 87Sr/86Sri < 0.7056). Initial Pb ratios point to an origin from the melting of an enriched subcontinental lithospheric mantle source, previously contaminated at the source by oceanic sediments. The contrasted alkaline Fe-Ti melanocratic dikes are representative of liquids. They display enriched fractionated REE patterns, a positive Nb-Ta anomaly and εNdi of +7, 87Sr/86Sri of 0.703 and initial Pb ratios, all reminiscent of Ocean Island Basalt-type rocks, pointing to a moderately

UV optical absorption spectra analysis of beryl crystals from Brazil

The spectral decomposition analysis was applied to the optical absorption spectra of green and colorless beryl crystals from the Brazilian Eastern Pegmatitic province in the natural state, Submitted to heat treatment and irradiated with UV light The attributions of the lines were made taking into account highly accurate quantum mechanical calculations The deconvolution of the green beryl spectra revealed four lines, two of them around 12,000 cm(-1) (1 5eV) and two of them around 34,000 cm(-1) (4.2 eV) attributed to Fe(2+) and Fe(3+), respectively The deconvolution of the colorless beryl spectra without any treatment, after heating and for the same heat treatment followed by UV light irradiation revealed five lines The analysis of ratio relations showed that the lines at 36,400 cm(-1) (4.5 eV) and 41,400 cm(-1) (5 1 eV) belongs to a single defect attributed to a silicon dangling bond defect (=Si). Discussions and comparison with reported defects in quartz have supported the allocation of the lines at 61,000 cm(-1) (7.6 eV) and 43,800 cm(-1) (5 4 eV) to diamagnetic oxygen vacancy defect ( Si-Si ) and unrelaxed ( Si Si ) defect, respectively Finally, the line at 39.100 cm(-1) (4.8 eV), quite polarized along the c-axis, was attributed to a (Fe(2+) OH(-)) defect in the structural channels (C) 2009 Elsevier B V All rights reserved

Rankamaite from the Urubu pegmatite, Itinga, Minas Gerais, Brazil: Crystal chemistry and Rietveld refinement

A new occurrence of rankamaite is here described at the Urubu pegmatite, Itinga municipality, Minas Gerais, Brazil. The mineral forms cream-white botryoidal aggregates of acicular to fibrous crystals, intimately associated with simpsonite, thoreaulite, cassiterite, quartz, elbaite, albite, and muscovite. The average of six chemical analyses obtained by electron microprobe is (range in parentheses, wt%): Na(2)O 2.08 (1.95-2.13), K(2)O 2.61 (2.52-2.74), Al(2)O(3) 1.96 (1.89-2.00), Fe(2)O(3) 0.01 (0.00-0.03), TiO(2) 0.02 (0.00-0.06), Ta(2)O(5) 81.04 (79.12-85.18), Nb(2)O(5) 9.49 (8.58-9.86), total 97.21 (95.95-101.50). The chemical formula derived from this analysis is (Na(1.55)K(1.28))(Sigma 2.83)(Ta(8.45)Nb(1.64)Al(0.89)Fe(0.01)(3+)Ti(0.01))(Sigma 11.00)[O(25.02)(OH)(5.98)](Sigma 31.00). Rankamaite is an orthorhombic ""tungsten bronze"" (OTB), crystallizing in the space group Cmmm. Its unit-cell parameters refined from X-ray diffraction powder data are: a = 17.224(3), b = 17.687(3), c = 3.9361(7) angstrom, V = 1199.1(3) angstrom(3), Z = 2. Rietveld refinement of the powder data was undertaken using the structure of LaTa(5)O(14) as a starting model for the rankamaite structure. The structural formula obtained with the Rietveld analyses is: (Na(2.21)K(1.26))Sigma(3.37)(Ta(9.12)NB(1.30) Al(0.59))(Sigma 11.00)[O(26.29)(OH)(4.71)](Sigma 31.00). The tantalum atoms are coordinated by six and seven oxygen atoms in the form of distorted TaO(6) octahedra and TaO(2) pentagonal bipyramids, respectively. Every pentagonal bipyramid shares edges with four octahedra, thus forming Ta(5)O(14) units. The potassium atom is in an 11-fold coordination, whereas one sodium atom is in a 10-fold and the other is in a 12-fold coordination. Raman and infrared spectroscopy were used to investigate the room-temperature spectra of rankamaite.

A review of the tectonic evolution of the Sunsas belt, SW Amazonian Craton

The Sunsas-Aguapei province (1.20-0.95 Ga), SW Amazonian Craton, is a key area to study the heterogeneous effects of collisional events with Laurentia, which shows evidence of the Grenvillian and Sunsas orogens. The Sunsas orogen, characterized by an allochthonous collisional-type belt (1.11-1.00 Ga), is the youngest and southwestern most of the events recorded along the cratonic fringe. Its evolution occurred after a period of long quiescence and erosion of the already cratonized provinces (>1.30 Ga), that led to sedimentation of the Sunsas and Vibosi groups in a passive margin setting. The passive margin stage was roughly contemporary with intraplate tectonics that produced the Nova Brasilandia proto-oceanic basin (<1.21 Ga), the reactivation of the Ji-Parana shear zone network (1.18-1.12 Ga) and a system of aborted rifts that evolved to the Huanchaca-Aguapei basin (1.17-1.15 Ga). The Sunsas belt is comprised by the metamorphosed Sunsas and Vibosi sequences, the Rincon del Tigre mafic-ultramafic sill and granitic intrusive suites. The latter rocks yield epsilon(Nd(t)) signatures (-0.5 to -4.5) and geochemistry (S,1, A-types) suggesting their origin associated with a continental arc setting. The Sunsas belt evolution is marked by ""tectonic fronts"" with sinistral offsets that was active from c. 1.08 to 1.05 Ga, along the southern edge of the Paragua microcontinent where K/Ar ages (1.27-1.34 Ga) and the Huanchaca-Aguapei flat-lying cover attest to the earliest tectonic stability at the time of the orogen. The Sunsas dynamics is coeval with inboard crustal shortening, transpression and magmatism in the Nova Brasilandia belt (1.13-1.00 Ga). Conversely, the Aguapei aulacogen (0.96-0.91 Ga) and nearby shear zones (0.93-0.91 Ga) are the late tectonic offshoots over the cratonic margin. The post-tectonic to anorogenic stages took place after ca. 1.00 Ga, evidenced by the occurrences of intra-plate A-type granites, pegmatites, mafic dikes and sills, as well as of graben basins. Integrated interpretation of the available data related to the Sunsas orogen supports the idea that the main nucleus of Rodinia incorporated the terrains forming the SW corner of Amazonia and most of the Grenvillian margin, as a result of two independent collisional events, as indicated in the Amazon region by the Ji-Parana shear zone event and the Sunsas belt, respectively. (C) 2009 Elsevier Ltd. All rights reserved.

Obtenção de uma porcelana dielétrica a partir de matérias-primas do Rio Grande do Norte

The dielectric porcelain is usually obtained by mixing various raw materials proportions and is used in the production of electronic equipment for various applications, from capacitors of high and low Power to insulators for low, medium, high and extra high voltage, which are used in distribution lines and transmission of electricity.This work was directed to the s tudy of technological properties of technic porcelain, made from raw materials extracted from pegmatites found in the regions of Seridó and the Alto Oeste of Rio Grande do Norte, which are made of kaolin, quartz and feldspar, abundant and high quality in these regions. The technic ceramics were obtained by mixing in appropriate levels, kaolin, feldspar, quartz and clay, the last item from a pottery in the city of Sao Gonçalo do Amarante, Rio Grande do Norte. During the development the following characterizations correlated to raw materials were made: laser particle sizing, x-ray diffraction, DTA and TG. The compositions studied were formed by uniaxial pressing at a pressure of 50 MPa and sintered at temperatures ranging from 1150 to 1350ºC and levels (times) of sintering between 30, 60, 90 and 120 minutes. The characterization of the samples were taken from the analysis of weight loss, linear shrinkage, porosity, stoneware curve, bulk density, flexural strength of three points, SEM and X-ray diffraction, TMA, Dielectric and cross Resistivity. The studied materials can be employed in producing the objects used in electrical engineering such as: insulators for low, medium and high-voltage electrical systems, command devices, bushing insulation for transformers, power capacitors, spark plugs, receptacles for fluorescent and incandescent light bulbs and others

A mineração artesanal e de pequena escala em pegmatitos e cerâmica no município de Parelhas, região do Seridó/Rio Grande do Norte

The working conditions, occupational health, occupational illness and workers quality of life, usually referring to the artisanal activities and the workers with a poor professional support. Because this reality is still present in locals without good infrastructure of social and economic attention, there is a need for a broad knowledge of problems related to the productive processes that include features of unsanitary and unhealthy. Despite the intense process of industrialization promoted by globalization and the growth of developing nations like Brazil, the activities of artisanal and small-scale mining are still suffering from the marginalization of their production processes and their workers. This dissertation deals with the description of mineral-based activities (MBA), especially the activities related to production processes of extraction and processing of red pottery and minerals in pegmatites in Parelhas city, Seridó, Rio Grande do Norte, which are conducted by small mining companies or artisanal miners. The study of the work process was based on direct observation, photographic documentation, ergonomics, health and occupational safety analysis, interviews and structured questionnaire with workers of the two activities. The results indicate the need for improvement in both workplaces (red pottery and pegmatites), adaptation of workers to safety standards specific to the workplace, more attention and care related to ergonomics and occupational safety, greater importance to economic and social relations among performed activities, workers and firms of mineral branch and better and greater integration of social policies, supported by different sectors of society with the intention of transforming the current social, cultural, labor and education situation

Estudos sedimentológicos e o contexto estrutural da formação Serra do Martins, nos platôs de Portalegre, Martins e Santana/RN

This dissertation deals with sedimentological and structural framework of the siliciclastic rock of the Serra do Martins Formation (FSM) in the Portalegre, Martins and Santana plateau, located to the south of Potiguar Basin, in the southwest and central Rio Grande do Norte state. This formation, regarded as of Oligo-Miocene age based on intrusive relations of the Miocene Macau volcanics, has a still disputable age due to the lack of appropriate bio and/or chronostratigraphic markers. The FSSM deposits crop out along 650 to 750 m high plateau, as a remanescent sedimentary cover directly overlying topographically uplifted pre-cambrian crystalline rocks. During the last decades, these deposits were interpreted according to a Tertiary paleoclimatic evolutionary model, associated to pedogenetic processes. The sedimentological characterization of the FSM was done through a detailed study of its facies, petrography and diagenetic features. The facies study was based on description of field relations, textures and structures, the piling up of the strata and their lateral variations. The FSM was deposited by an anastomosing to coarse-meandering fluvial system, including deposits of lag, cannel-fill, ouver-bank and flood plain. The petrographic composition of the sediments, coupled to their facies and paleocurrent directions, suggest a rather distal sourcearea, to the south of the present plateau. The diagenetic study identified an incipient grain mechanical compaction, pronounced dissolution of the framework, matrix and/or cement components, intense precipitation of kaolinite, silic and, eventually, iron oxides, besides mechanical infiltration of the clays. Most of these events, regarded in the literature as associated to near-surface conditions (eo or telodiagenesis), indicate the FSM sediments were never deeply buried. Topographic relations along longitudinal and transversal sections reaching the Potiguar Basin to the north identified regional dips that allow to discuss stratigraphic correlations between the FSM and the basin formations. The sedimentological features of the different units and the intrusive relations of the Macau volcanics were also considered in these correlations,which support the Oligo-Miocene age previously accepted for the FSM. Concerning the tectonic framework of the FSM, this work investigated the pre-cambrian to cretaceous heritage and the cenozoic deformation, allowing the recognition of pre-, sin and post-FSM structures. The crystalline basement, belonging to the Seridó Belt, displays NE and WNW foliation trends related to the Brasiliano-age ductile shear zones. In this terrain, brittle-ductile and brittle NE- and NW-trending structures, associated with extensional joints filled with pegmatites and quartz veins, are related to an E-W compression by the end of Brasiliano Cycle. The E-W joints and NE-trending fractures were reactivated by N-S to N-S to NW extension during late Jurassic to Cretaceous times, controlling the emplacement of the Rio Ceará-Mirim basic dyke swarm and the opening of the Potiguar rift basin

Uranium distribution and radon exhalation from Brazilian dimension stones

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Final stages of the Brasiliano Orogenesis in SE Brazil: U-Pb and 40Ar/39Ar evidence for overprinting of the Brasília Belt by the Ribeira Belt Tectonics

Around the southern margins of the São Francisco Craton, there is a zone of tectonic interference between the Brasília belt to the west and the younger Ribeira belt to the east. U-Pb monazite and 40Ar/39Ar cooling age determinations carried out in the area reveal the cooling histories of these belts and the timing of tectonic overprint, unraveling the final stages of Brasiliano Orogeny in SE Brazil. The U-Pb monazite data from migmatized paragneisses and late-stage pegmatites in the Socorro-Guaxupé Nappe System of the southern Brasília belt show that migmatization peaked between ca. 613±1 and 607±3 Ma. 40Ar/39Ar biotite and muscovite ages of paragneisses and schists in this area indicate that the northern high-grade core of the Nappe System (Guaxupé Domain) was uplifted and cooled through the 350°C isotherm between 599±1 and 587±1 Ma. In contrast, samples from the southern high-grade core of the Nappe System, the Socorro Domain, south of the Jacutinga shear zone, yields a broader and younger spectrum of 40Ar/39Ar biotite ages between 571±1 and 562±1 Ma, attributed to a later uplift and cooling of the crust. The cooling ages can be assigned to local resetting of the 40Ar/39Ar system during transpressive tectonic overprint due to reactivation as a result of collision of the Ribeira belt. A younger group of 40Ar/39Ar mica ages (537±1 to 521±1Ma) in schists of the Socorro Domain, are associated with transpressional structures of the Ribeira belt. Rock samples from the Jacutinga and Três Corações shear zones, yield 40Ar/39Ar biotite-muscovite ages around 520 Ma. These are typical cooling ages of the Ribeira belt, and are interpreted to mark the western limit of the Ribeira belt transpressional regime within the Brasília belt. The youngest biotite-muscovite cooling ages in schists of the Socorro Domain, between 510±2 and 491±1 Ma, mark the final cooling and exhumation of that part of the Brasília belt.

Aspectos texturais do magmatismo e tramas da tectônica impostas ao Granito Chaval na Zona de Cisalhamento Santa Rosa, extremo Noroeste da Província Borborema

A região Noroeste da Província Borborema apresenta uma diversidade de corpos graníticos de natureza e evolução tectônica diversificadas, do Paleoproterozoico ao Paleozoico, com maior incidência relacionada ao Neoproterozoico e alojamento em diferentes fases da orogenia Brasiliana. Um desses exemplos é o Granito Chaval, que representa um batólito aflorante próximo à costa Atlântica do Ceará e Piauí, intrusivo em ortognaisses do Complexo Granja e supracrustais do Grupo Martinópole. Ele é, em parte, coberto por depósitos cenozoicos costeiros e rochas sedimentares paleozoicas da Bacia do Parnaíba. O Granito Chaval tem como característica marcante a textura porfirítica, destacando-se megacristais de microclina, em sienogranitos e monzogranitos, e outras feições texturais/estruturais de origem magmática, Essas permitiram interpretar sua evolução como de alojamento relativamente raso do plúton, conduzido por processos de cristalização fracionada, mistura de magmas com fluxo magmático e ação gravitacional em função da diferença de densidade do magma, levando à flutuação e ascensão de megacristais de microclina no magma residual, com alojamento de leucogranitos e pegmatitos nos estágios finais da evolução deste plutonismo. Por outro lado, em toda a metade Leste do plúton, encontra-se um rico acervo de estruturas tectógenas de cisalhamento, relacionada à implantação da Zona de Cisalhamento Transcorrente Santa Rosa, que levou a transformações tectonometamórficas superpostas às feições magmáticas, as quais atingiram condições metamórficas máximas na fácies anfibolito baixo. Cartograficamente, foram individualizados três domínios estruturais em que estão presentes uma gama de variações petroestruturais do Granito Chaval, sejam feições texturais/estruturais ígneas e tectônicas. As rochas plutônicas foram deformadas e modificadas progressivamente à medida que se dirige para Leste, no qual as rochas mudam-se para tonalidades mais escuras do cinza e os processos de cominuição e recristalização dinâmica reduzem, progressivamente, a granulação grossa desses granitos bem como o tamanho dos fenocristais para dimensões mais finas, mantendo-se suas características porfiroides. Desse modo, a trama milonítica se torna evidente, acentuando-se ao atingir a porção principal da Zona de Cisalhamento Transcorrente Santa Rosa. Como principais feições estruturais, destacam-se extinção ondulante forte; encurvamento e segmentação de cristais; geminação de deformação; rotação de cristais; microbudinagem; foliação anastomosada, inclusive S-C; lineação de estiramento; formas amendoadas de porfiroclastos, fitas e folhas de quartzo e recristalização. Os produtos desses processos de cisalhamento resultam na formação de protomilonitos, milonitos e ultramilonitos. Essas faixas miloníticas representam os locais de maior concentração da deformação, por isso é possível acompanhar progressivamente suas modificações texturais e mineralógicas, configurando uma sequência clássica de deformação progressiva heterogênea, por cisalhamento simples, em condições frágil-dúctil e dúctil. O alojamento do Granito Chaval aconteceu no final do Criogeniano (aproximadamente 630 Ma) e pode ser interpretado como magmatismo sin a tardi-tectônico em relação ao evento Brasiliano. O processo de cisalhamento que gerou a Zona de Cisalhamento Transcorrente Santa Rosa se formou nos incrementos finais da deformação de uma colisão continental em um sistema de cavalgamento oblíquo, em que se edificou o Cinturão de Cisalhamento Noroeste do Ceará, devido ao extravasamento lateral de massas crustais em fluxo dúctil acontecido no final da orogenia Brasiliana no Noroeste da Província Borborema.

Caracterização petrográfica das zonas de alteração hidrotermal associadas aos pegmatitos da mina Bom Futuro, Rondônia

The Bom Futuro tin deposit is located in Ariquemes, north-central state of Rondônia. Since its discovery in the late 80s, the tin deposit of Bom Futuro has been explored and considered one of the leading Brazilian producers of cassiterite, exploring it mainly in secondary deposits (placers) in the vicinity of the hill Bom Futuro. The primary mineralization occurs in the contacts between quartz veins and pegmatites with the rocks of the hill and its exploitation has been the goal of new studies in the area. These bodies occur in all rock types of the hill, leading edges of hydrothermal alteration with each rock. The focus of the study is the characterization of hydrothermal alteration through the analysis of the edges of pegmatitic veins intruded on each of the main rock types found on the hill Bom Futuro, which are: biotite gneiss, biotite amphibolite, subvolcanic breccia, topaz leucogranite, topaz leucoriolito and micro melassienito porphyry. The analysis and comparison showed familiarities between the edges of alteration encountered, and possible subdivision into three main zones: the inner zone or the vein itself, intermediate zone or transition zone and the change zone where the passage of hydrothermal features to rocks features is gradual. The cassiterite and sphalerite were found scattered in three zones, however in larger quantities in the intermediate zone, near the contact

Perfil econômico do lítio nos países sulamericanos e consumo mundial

The lithium industry has changed and the producers of lithium carbonate form South America play a dominant role in the world. This paper discusses the South American geological resources, production and producers of lithium considering the potential growth in lithium consumption for electric vehicle batteries. Taking into account the manufacturing companies and their external connections, their participation in corporate groups and the international market for the stocks of metal, in addition to facts and updates that affect this market and its key growth trends. This inventory of the most important reserves takes into account the geological context of the formation of these deposits, including a description of the types of deposits exploited in the world today. Besides the general description was made a brief description of the South American resources, more exploited by the media (Salar de Atacama, Salar de Hombre Muerto, Salar de Uyuni) and Pegmatites of Província Pegmatítica Oriental do Brasil and Província Seridó-Borborema).

Geologia do alvo e da mina Sol Nascente, município de Rio Crespo, Rondônia

Eight Mesoproterozoic granite suites are recognized in the Rondônia Tin Province, called Serra da Providência Intrusive Suite (1606-1532 Ma), Rio Crespo Intrusive Suite (1500 Ma), St. Anthony Intrusive Suite (1406 Ma), Teotonio Intrusive Suite (1387 Ma ), Santa Clara Intrusive Suite (1082-1074 Ma) and Younger Granites of Rondônia Intrusive Suite (998-974 Ma), represent successive magmatic type A (anorogenic) and the intra-plate basement rocks intruded in the metamorphic complex named Jamari separated into two distinct lithologic associations, a ortogneiss (U-Pb from 1.76 to 1.73 Ga) and a paragneiss (1675 + / - 12 Ma). Tin mineralization are widely found in the Tin Province and are associated with granitic intrusions known Mesoproterozoic more closely with the last two magmatic events, represented by the Santa Clara and Younger Granites of Rondônia. The tin mineralization are of primary and secondary, with the primary form deposits of different structural styles and is presented in the form of endo-or exogreisens, veins, stockworks and pegmatites. The secondary mineralization are related to natural processes of weathering and erosion of primary rocks, leading to placer deposits classified as colluvial, eluvial and colluvial-alluvial. The Target Alvo Sol Nascente is located in the central-eastern Rondônia Tin Province and has basement rocks of the metamorphic-magmatic region represented by Jamari Complex intrusive suites and Sierra Providence and Rio Crespo. The last tectonic event spa in the area was responsible for the intrusion of Younger Granites of Rondônia (São Carlos and Caripuanã Massifis). The anomalous levels of tin, sufficient to operate (Mina Rising Sun), indicate that there was possibly mineralization event, evidenced by pegmatite veins well defined, easily found relatively close to mine. Plaque deposits associated with Quaternary sedimentary sequences can also be observed

Rochas calciossilicáticas e feldspáticas na região de Castro Alves e Rafael Jambeiro (BA)

The towns of Castro Alves and Rafael Jambeiro, central-east of Bahia state, are located in the east of São Francisco Craton, in granulite terrains of Salvador-Curaçá Belt, formed in Paleoproterozoic. The region of study contains ortognaisses of Caraíba Complex, metamafic and metaultramafic rocks of São José do Jacuípe Suite, metasedimentary rocks of Tanque Novo-Ipirá Complex, granitoids, pegmatites and alkaline rocks. The study carried out regional and detailed geological mapping in addition to petrographical and geochemical characterization of six areas in the search for targets of feldspar and white diopside, minerals used in ceramic industry. The areas consist of granitic ortognaisses interspersed with lenses of mafic granulite rocks, calc-silicate rock, banded iron formations, paragnaisses, quartzites, and bodies of quartz-feldspar or feldspar pegmatites and alkaline rocks that fill discontinuities. The region of study contains four deformations phases, with a predominance of ductile structures. The foliation Sn has N30E to N70W direction, high angle of dip and is characterized by compositional banding of granoblastic and felsic bands interspersed with nematoblastic or lepidoblastic mafic bands. A mineral or stretching lineation Ln is associated with Sn and has trend of S55E to S72E. The rocks have been suffered a regional metamorphism with granulite facies peak and partial retrogression to greenschist facies. Geochemical studies indicate that the green coloring calc-silicate rocks have lower SiO2, MgO and higher Fe2O3 content compared with white calcssilicate rocks. The alkaline rocks of the studied area have higher Na2O, SiO2 and lower K2O, Fe2O3 content compared with others Paleoproterozoic alkaline rocks of Bahia state. The targets of diopside are associated with white calc-silicate rocks, while the targets of feldspar are associated with paragnaisses, pegmatites and alkaline rocks

Color Dependence on Thickness in Topaz Crystal from Brazil

It is well known that crystals of topaz from the Eastern Brazilian Pegmatite Province may turn blue by the irradiation with Co-60 gamma rays followed by heat treatment. Also, it is known that the sensation of color changes with the thickness of these crystals. The dependence of the color, given by 1931 CIE chromaticity coordinates, with the thickness of the crystal was analyzed. The absorbance used in the calculation of these coordinates was given by the sum of Gaussian lines. The parameters of these lines were determined through the decomposition of the optical absorption spectra in the ultraviolet and visible regions. The decomposition revealed several lines, whose assignment was made considering studies in spodumene and beryl crystals and highly accurate quantum mechanical calculations. The transmittance becomes very narrow with increasing thickness, and the CIE chromaticity coordinates converge to the borderline of the CIE Chromaticity Diagram at the wavelength of maximum transmittance. Furthermore, the purity of color increases with increasing thickness, and the dominant wavelength reaches the wavelength of maximum transmittance.