Quartz Core Research Articles

FLUID EVOLUTION IN THE ZONED RARE-ELEMENT PEGMATITE FIELD AT CAP DE CREUS, CATALONIA, SPAIN

The Cap de Creus LCT granitic pegmatites, in Catalonia, northeastern Spain, belong to the beryl – columbite and beryl – columbite – phosphate subtypes and to the albite type. Fluid inclusions have been studied in all these types of pegmatite to determine the nature of the fluids involved in their formation. Beryl – columbite pegmatites are zoned; border, wall, intermediate zones and a quartz core and albite-dominant replacement bodies are distinguished. Beryl – columbite – phosphate pegmatites, in addition, feature veins of albite and quartz–muscovite. In the albite pegmatites, phosphate and albite–chlorite veins also occur. Five types of fluid inclusions have been identified: hypersaline aqueous–carbonic fluid inclusions (type A), low-salinity aqueous– carbonic inclusions (type B), carbonic inclusions (type C), multiphase aqueous fluid inclusions (type D), and late multiphase aqueous–carbonic fluid inclusions (type E). In the early stages of crystallization, a hypersaline fluid exsolved from the melt. It is CO 2 -rich, 41–46 wt.% NaCl eq., in beryl – columbite – phosphate pegmatites, and the aqueous fluid contains 23–38 wt.% NaCl eq. in albite pegmatites. A second immiscibility process occurred in the last stages of the crystallization of the intermediate zones; the fluid unmixed into two fluids: one CO 2 -rich, salt-poor (3–5% NaCl eq.) and the other hypersaline (up to 35% NaCl eq.) and CO 2 -poor. The CO 2 -rich fluid is related to the formation of the quartz core, and the second fluid formed albite veins and circulated throughout the pegmatite, owing to the development of a network of fractures, which produced a Na-metasomatic alteration of the previously formed units. These processes took place at 415–450°C and 2.2–2.7 kbar. Later, quartz–muscovite veins developed at 2.4 kbar and 400°C. The fluid that formed these veins (36–39 wt.% NaCl eq.) produced a K-rich alteration that affected the previously formed pegmatite units. In addition, in albite pegmatites, late albite–chlorite veins formed at pressures lower than 700 bars and more than 340°C.

PHOSPHATE ASSEMBLAGES FROM THE BRISSAGO GRANITIC PEGMATITE, WESTERN SOUTHERN ALPS, SWITZERLAND

We describe a first significant occurrence of graftonite–triphylite-bearing LCT-type granitic pegmatite in the Alps. In 1999, in the Brissago area, in the western Southern Alps, Canton Ticino, Switzerland, we found a boulder containing an almost complete section of a phosphate-bearing pegmatite dike. The zoned pegmatite is composed by four main units: 1) an aplite unit, 2) a plagioclase + quartz graphic unit, 3) a coarse-grained plagioclase unit, and 4) a quartz core containing several phosphate masses up to 10 cm in diameter. On the basis of textural features and results of chemical analyses, we distinguish two phosphate associations. Association I, of magmatic origin, is represented by lamellar intergrowths of graftonite and triphylite. The leaching of Li and oxidation of Fe have led to the formation of ferrisicklerite and heterosite in replacement of triphylite, whereas the origin of kryzhanovskite and stanekite remains unclear. Association II, of metamorphic origin, consists of a polycrystalline aggregate of graftonite and triphylite. Exceptionally, primary maghagendorfite grains are present. Non-oxidizing low-temperature processes led to the formation of ludlamite and vivianite in replacement of triphylite. Locally, at the rim of phosphate masses, in close association with apatite-(CaOH), jahnsite and mitridatite formed at the expenses of graftonite. The chemical characteristics of the phosphate assemblages and associated mafic silicates indicate that this phosphate-bearing pegmatite dike belongs to a geochemically primitive system. Our U/Pb dating of zircon (242 ± 2.8 Ma) allows us to relate the formation of this dike to the Mid-Triassic tectonomagmatic cycle, characterized by the evolution of a magmatic arc well represented in the Southern Alps. In this geodynamic environment, a pegmatite-forming melt formed after partial melting of metapelites belonging to the Kinzigitic Complex of the Ivrea–Verbano zone.

Photocatalytic activity on TiO 2-coated side-glowing optical fiber reactor under solar light

A novel optical fiber reactor (OFR) that employs side-glowing optical fibers (SOFs) as a means of light transmission medium and TiO 2 supporter has been developed, characterized, and investigated. Different from existing ones, the SOF here is made up of quartz core with a silicon cladding, which can emit light from side surface more uniformly and can transmit light for longer distance since attenuation of light through SOF is slow; furthermore, SOF is flexible enough to be entwined into U-shapes. The crystal phase and microstructure of TiO 2 coating are investigated by XRD and SEM. Solar light collected and transmitted to SOF by automatic sun-tracing equipment (ASE) was utilized to excite the titania coating for photocatalytic degradation of 4-chlorophenol (4-CP). Compared to traditional solar collectors, the present one can collect solar light efficiently while occupying smaller area, moreover, ASE allows a long distance light transmission to somewhere such as indoor or sub-surface for photocatalytic applications. Results show that 79% of 4-CP had been decomposed under sunlight irradiation for 8 h.

Fluid and Halide Melt Inclusions of Magmatic Origin in the Ultramafic and Lower Banded Series, Stillwater Complex, Montana, USA

Fluid andmelt inclusions trapped in igneous rocks below the platinumgroup element (PGE)-rich J-M reef in the Stillwater Complex, Montana provide a physiochemical record of a continuum of high P^T magmatic^hydrothermal and low P^T metamorphic events. Magmatic^hydrothermal volatiles ranged from NaCl-dominated halide melts (482 wt%NaClequiv) to more complexNa^Ca^K^Fe^ Mn^Ba^Si^Al^Cl brines (28^79 wt % NaClequiv) that were trapped simultaneously with a moderate density carbonic fluid (CO2 CH4). Early primary inclusions containing immiscible brine and carbonic fluid were trapped in the granophyric albite^quartz core of a zoned pegmatite body in the Gabbronorite I unit at T of 700^7158C, and P between 4 3 and 5 6 kbar.The pegmatitic body crystallized from a fluid-saturated residual silicate liquid that was channeled through the cooling igneous stratigraphy. Approximately 500 m stratigraphically below the pegmatite, in the Ultramafic Series, early halide melt inclusions representing samples of formerly molten NaClwere trapped in unaltered primary olivine overa minimum range in temperature of 660^8008C. In the same olivine that hosts the halide melt inclusions, secondary brine inclusions with a composition similar to brines in the pegmatite were trapped over a minimum temperature range of 480^6408C. As hydrothermal activity continued during post-solidus cooling of the intrusion, quartz precipitation in the vuggycore of the pegmatitebody trappedpost-magmatic, immiscible brine and carbonic fluid inclusion assemblages that record a progressive decrease in fluid salinity, T and confining P from lithostatic to near-hydrostatic conditions. Late secondary inclusions containing regional metamorphic fluids were trapped in quartz in the pegmatite after cooling to zeolite-facies conditions.The late metamorphic fluids were low to moderate salinity, CaCl2^MgCl2^H2O solutions. Hydrous salt melts, magmatic brines, and non aqueous (carbonic) fluids may have coexisted and interacted throughout much of the late crystallization and post-magmatic history of the Stillwater Complex. Hence, the potential for interaction between exsolved magmatic volatiles and grain boundary-hosted sulfide minerals below the J-M reef at near-solidus temperatures, and the post-magmatic modification of theJ-M reef PGE ore compositions by hydrothermal fluids are strongly indicated.

Radiation-hardness measurements of high [formula omitted] content quartz fibres irradiated with 24 GeV protons up to 1.25 Grad

We investigated the darkening of two high OH - content quartz fibres irradiated with 24 GeV protons at the Cern PS facility IRRAD. The two tested fibres have a 0.6 mm quartz core diameter, one with hard plastic cladding (qp) and the other with quartz cladding (qq). These fibres were exposed at about 1.25 Grad in 3 weeks. The fibres became opaque below 380 nm and in the range 580–650 nm. The darkening under irradiation and damage recovery after irradiation as a function of dose and time are similar to what we observed with electrons. The typical attenuation at 455 nm are 1.44 ± 0.22 and 2.20 ± 0.15 dB / m at 100 Mrad for qp and qq fibres, respectively. The maximum damage recovery is also observed near this wavelength.

An evaluation of synthetic fluid inclusions for the purpose of trapping equilibrated, coexisting, immiscible fluid phases at magmatic conditions

We report data that allow us to evaluate the method of trapping immiscible, saline aqueous fluids (i.e., vapor and brine in the NaCl-KCl-HCl-FeCl2-AuHCl2-H2O system) as synthetic fluid inclusions in pre-fractured quartz cores in order to quantify the concentrations of Au, Fe, K, and Na, among coexisting three-phase, immiscible fluids (i.e., haplogranite melt, brine, and vapor) at magmatic conditions. Coexisting vapor and brine were trapped experimentally at 800 °C and 100-110 MPa as synthetic fluid inclusions in both quartz microfractures and quenched silicate melt (i.e., glass), and also sampled indirectly using the recovered quenched aqueous fluid. Quartz-hosted and glass-hosted brine inclusions were analyzed by laser-ablation inductively-coupled-plasma mass spectrometry (LAICPMS) and instrumental neutron activation analysis (INAA), respectively. Quenched aqueous fluid from each experiment containing a quartz core was recovered and analyzed by atomic absorption spectrophotometry (AAS). The composition of aqueous fluids trapped as quartz-hosted inclusions, glass-hosted inclusions, and those recovered after quench yield consistent and precise data, at the 2σ uncertainty level, for the elements of interest. The overlapping Au, Fe, K, and Na concentrations in aqueous fluids trapped and analyzed via three entirely different instrumental techniques (i.e., LAICPMS, INAA, and AAS) suggest strongly that quartz microfractures heal on a slow enough time scale to permit entrapment of fully equilibrated aqueous fluids at our experimental PTX conditions. The data evince clearly that the chemical composition of fluids in quartz microfractures at the time of self-healing represents equilibrium conditions; hence, synthetic fluid inclusions in experiments with low thermal gradients across the charge provide a reasonable estimate of fluid composition at least at the experimental conditions examined in this study.

AN UNUSUAL TOURMALINE COMPOSITION FROM SITHONIA PENINSULA (NORTHERN GREECE)

The variety and wideness of substitutions shown by tourmaline group, mainly in the Ζ, Y and X sites, make possible a high number of real and hypothetical endmembers. However in some cases it is not so obvious to determine to what endmembers to refer to, but the wide stability field of tourmaline and its occurrence in different geological environments make useful to define the composition as percentages of end-members to trace back to its genesis. In this paper the followed procedure to identify the components of a complex tourmaline is given. During a study on the granitoid intrusions outcropping on Sithonia, Chalkidiki Peninsula (Northern Greece), a swarm of very small crystals of tourmaline, subhedral or more often allotriomorphic, has been found as stuffing of subparallel micro fractures in the quartz core of a pegmatite dike. Their composition, analysed by EMPA, turns out to be rather unusual and not satisfactorily referable to so far proposed solid solutions. It is characterized by remarkable Al deficiency (ZAl < 6 apfu), high amounts of magnesium and iron with Mg > Fe and Να dominating X site. On the basis of compositional and crystal-chemical evidences, supported by previous literature, it was hypothesized that Mg and Fe have to be referred to an uvite — feruvite component, while the considerable part of total iron in its trivalent oxidation state yields a povondraitic component according also with Na in X site. These data, coupled with a theoretical evaluation of bond valence sum (B VS) that allowed inferring the presence of OFT anions in the W site, make reasonable to consider Sithonia tourmaline as the new variety sodian povondraitic hydroxil uviteferuvite. On the basis of its composition, of its fabric and of the oscillatory trends shown by the main elements of Y and X sites, this tourmaline may be considered post magmatic likely of hydrothermal genesis.

Assessment of Spatial Distribution of Porosity in Synthetic Quartz Cores Using Microfocus Computed Tomography (µCT)

The effects of particle sorting and compaction pressure on spatial distribution of porosity of synthetic quartz cores were investigated. A high-resolution X-ray computed tomography (CT) system with a microfocus X-ray source was used to acquire CT scans of 12 cores. The cores consist of a mixture of quartz powder and different proportions of quartz granulates (with a particle size range of 0.126 to 0.210 mm) that were compacted at 20.68 MPa (3,000 psi), 27.58 MPa (4,000 psi), and 34.47 MPa (5,000 psi) pressures. Calibration of core density was carried out according to the ASTM standard procedure. Computer algorithms were developed to calculate local porosity (φ) values, producing about 15 million φ values per core. The results of the analysis were represented by histograms and qualitatively compared with capillary pressure versus brine saturation measurements. As a result of changing the particle sorting (i.e., using a wider range of particle sizes), the standard deviation of the porosity distribution increases for the cores compacted under the same pressure. There were mixed trends of the effects of compaction pressure on porosity. However, they are qualitatively consistent with the capillary pressure measurements.

Holey lightguides with a quartz core for nonlinear-optical conversion of laser-emission pulses

Holey lightguides based on quartz glass with a solid core 1-5 µm in diameter, surrounded by a hexagonal system of openings with a number of cycles from one to four, have been developed for converting ultrashort laser pulses into a spectral supercontinuum. It has been shown that the wavelength range from 400 to 1300 nm can be overlapped when the radiation of a Ti-sapphire laser is used.

SU‐FF‐T‐379: Radiochromic Film Dosimetry for a New Type of I‐125 Seed: Determination of TG43 Parameters

Purpose: A new prototype of I‐125 seed was studied using radiochromic EBT film in solid water for the dose distributions from 0.06cm out to 5cm. The high activity seed was designed for intravascular brachytherapy of lesions in peripheral arteries. The active source core was produced with Xenon ion implantation into a solid quartz core (without silver marker) and then encapsulated in titanium to form a sealed source.Materials and methods: A multiple film technique was employed. Each film (EBT lot #35076) was in contact geometry with the seed at the center of a solid water phantom, 30×30×20 cm. Totally 46 films were separately exposed to 12 seeds, with the product of activity and exposure time between 8 and 4910 mCi‐hr. The seed activity ranged from 12.5 to 2.4 mCi during the experimental runs. 30 calibration films were exposed to one seed at 0.5 cm above or below the seed. All experimental, calibration and background films were scanned (pixel resolution 0.2mm) using a PeC CCD100 densitometer, with red and green light sources at least one day after exposures. Conversion from optical densities to doses was achieved based on the calibration curve established for each light source used in scanning. The 2‐d dose values in cylindrical coordinates were converted to polar coordinates, and the TG43 parameters were generated. Results: The radial dose function and anisotropy function were plotted. Compared with the Implant Sciences model 3500 seed, the anisotropy function values are similar, while the radial dose function values (at distances > 1cm) are higher, possibly due to the absence of silver fluorescent x‐rays. An interim value of dose rate constant was determined. Conclusion: TG43 parameters for a new type of high activity I‐125 seed have been obtained using radiochromic EBT film for distances from 0.06 to 5 cm in solid water phantom.

Characteristics and composition of fly ash from Canadian coal-fired power plants

Fly ashes were collected from the electrostatic precipitator (ESPs) and/or the baghouse of seven coal-fired power plants. The fly ashes were sampled from power plants that use pulverized subbituminous and bituminous feed coals. Fly ash from bituminous coals and limestone feed coals from fluidized-bed power plant were also sampled. The fly ashes were examined for their mineralogies and elemental compositions. The fly ashes from pulverized low sulfur coals are ferrocalsialic, those from high sulfur coals are ferrosialic and the fly ashes from the fluidized bed coals are ferrocalcic. The concentrations of As, Cd, Hg, Mo, Ni, and Pb in fly ash are related to the S content of the coal. Generally, those feed coals with a high S content contain higher concentrations of these elements. The concentrations of these elements are also greater for baghouse fly ash compared to ESP fly ash for the same station. The S content of fly ash from high S coal is 0.1% for pulverized ESP fly ash and 7% for baghouse fly ash from the fluidized bed, indicating that most of the S is captured by fly ash in the fluidized bed. The baghouse fly ash from the fluidized bed has the highest content of Cd, Hg, Mo, Pb, and Se, indicating that CaO, for the most part, captures them. Arsenic is captured by calcium-bearing minerals and hematite, and forms a stable complex of calcium or a transition metal of iron hydroxy arsenate hydrate [(M 2+) 2Fe 3(AsO 4) 3(OH) 4·10H 2O] in the fly ash. Most elements in fly ash have enrichment indices of greater than 0.7 indicating that they are more enriched in the fly ash than in the feed coal, except for Hg in all ESP ashes. Mercury is an exception; it is more enriched in baghouse fly ash compared to ESP. Fly ash collected from a station equipped with hot side ESP has a lower concentration of Hg compared to stations equipped with cold side ESP using feed coals of similar rank and mercury content. Fly ash particles from fluidized bed coal are angular and subangular with cores of quartz and calcite. The quartz core is encased in layer(s) of calcium-rich aluminosilicates, and/or calcium/iron oxides. The calcite core is usually encased in an anhydrite shell.

Microlite-manganotantalite exsolution lamellae: evidence from rare-metal pegmatite, Karibib, Namibia

AbstractWe have analysed a rare occurrence of orange-brown manganotantalite lamellae (visible in hand specimen), intergrown with microlite [(Ca,Na)2(Ta,Nb)2(O,OH,F)7], aggregates of ferrotapiolite, bismuth minerals and apatite to understand more about the mechanisms of crystal growth and secondary modification in Ta-rich minerals. The intergrowth occurs within amblygonite/montebrasite nodules near the quartz core of the highly fractionated rare-metal Li/Be/Ta pegmatite at Rubicon, Karibib, Namibia. Electron microprobe analyses show that manganotantalite lamellae are variable in composition. Primary microlite (Ta2O5 82%, 1.97 Ta a.p.f.u.) forms the matrix mineral between the lamellae. Textural relations suggest an exsolution origin for the lamellae. Manganotantalite is represented by three generations: (1) primary late magmatic; (2) disequilibrium exsolution lamellae; and (3) subsolidus replacement. Crystallization commenced with primary microlite and likely simultaneous intergrowth between ferrotapiolite and a first generation of late-magmatic primary manganotantalite with low Ta (1.1—1.5 a.p.f.u.). On cooling this was followed by exsolution of manganotantalite lamellae, generation (2) with low—medium Ta (1.27—1.7 a.p.f.u.). The replacement of microlite by a highly fractionated late-stage melt rich in Mn2+, Ca2+ with low Na+ finally produces a third generation (3) of manganotantalite with high Ta (1.72—1.99 a.p.f.u.) at the contact with microlite. Native bismuth and bismutite cut across microlite and pseudomorph lamellae as a final hydrothermal replacement. Apatite is ubiquitous at the contact with amblygonite. The stability field of microlite may be extended by incorporation of CaTa2O6-rynersonite and Ca2Ta2O7 — idealized, components in solid solution. However, rynersonite-CaTa2O6 with distorted octahedra has some structural templates which are similar to the structure of pyrochlore (microlite). Hence, via the perovskite/pyrochlore analogy, hypothetical exsolution of manganotantalite-type structures may occur from a microlite (pyrochlore) host by solid-state diffusion via metastable rynersonite-type intermediates. Such a mechanism has the potential to explain the crystallographically controlled intergrowth textures and the compositional heterogeneity.

Origin of quartz cores in tourmaline from Roche Rock, SW England

AbstractThe nature and mode of origin of quartz-cored tourmalines (QCT) are studied from hydrothermal quartz veins within massive quartz-tourmaline (MQT) rocks at Roche, SW England. The QCT are annular, have blue maximum absorption colour and occur together with tourmalines with brown cores rimmed by blue tourmaline. Where the quartz core is not continuous throughout the length of the QCT crystals, the tourmaline core has brown maximum absorption colour, similar to tourmalines without quartz cores. Both the blue and brown tourmalines are schorl, but are compositionally distinct showing different Fe/(Mg + Ti) ratios and Ca concentrations. Fluid inclusion data indicate quartz precipitation from a moderate salinity (∼20–25 wt.% NaCl eq.) brine which periodically boiled following pressure drops within the vein system. The QCT show rheomorphic and lobate textures on their inner margins indicating selective dissolution of their brown, relative Mg-, Ti- and Ca-rich tourmaline cores and replacement with quartz. This presents a problem in terms of the nature of the fluid responsible for such selective dissolution because tourmaline is generally highly resistant under the normal range of hydrothermal fluid conditions. It is proposed that the relatively high concentrations of Ti, Mg and Ca in the brown tourmaline caused significant lattice strain, which together with an increase in pH, and probably Al, in the boiling hydrothermal fluid caused the brown cores to become unstable compared with the Fe-rich blue tourmaline rims.

Microstructured lightguides with a quartz core for obtaining a spectral supercontinuum in the femtosecond range

Quartz fiber lightguides with a core (diameter 1-5 µm) surrounded by a hexagonal system of holes and having high numerical aperture have been developed and implemented for the spectral conversion of ultrashort laser pulses into broad-band radiation (a supercontinuum). It is shown that the spectral range from 400 to 1000 nm can be covered when the radiation of a Ti-sapphire laser is used. © 2005 Optical Society of America

Microscopic deformation of the Neoarchean oceanic lithospheric mantle: evidence from the Zunhua Neoarchean ophiolitic mélange, North China Craton *

Abstract The microstructures of the mantle tectonites in the Zunhua Neoarchean ophiolitic melange are mainly coarse-mosaic structures with locally interstitial impregnated melts. Olivine and orthopyroxene occur as residual porphyroclastic blasts, dynamic recrystallization neoblasts or elongated to be tabular. The podiform chromitites are mostly strongly deformed with the development of pull-apart structure. These microstructures are typical high-temperature plastic deformation in oceanic upper mantle resulting from ocean-floor spreading. Besides the high-temperature plastic deformation, undeformed magmatic intrusions such as undeformed podiform chromitite. dunite and pyroxenite intrusions are also preserved in the mantle tectonite. Structures of high-temperature plastic deformation and intensive magmatic activity prove that the Zunhua ophiolite was formed under fast spreading oceanic ridge, similar to the Oman ophiolite. And the microstructures of country rocks, such as quartz ribbon, core and mantle stru...

Rapid generation of both high- and low-δ18O, large-volume silicic magmas at the Timber Mountain/Oasis Valley caldera complex, Nevada

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Fluid evolution in the beryl-columbite-phosphate pegmatitesof Cap de Creus (Catalonia, Spain)

In the Cap de Creus peninsula (NE Spain), four granite pegmatite types are distinguished: microcline-rich; beryl- columbite;beryl- columbite-phosphate; and albite. Beryl -columbite-phosphate pegmatites are zoned, with border, wall, intermediate zones and a quartz core. In addition, albitic and quartz-muscovite replacement bodies occur. The intermediate zones are mainly constituted by quartz, microcline, albite, beryl, Nb Ta minerals and phosphates. In early stages, crystallization takes place from a volatile-saturated magma and a hypersaline (39–46 wt.% NaCl eq.), CO 2-rich fluid exsolved from the magma. In the last stages of the crystallization of the intermediate zones, this fluid produced unmixing in two fluids: one CO 2-rich, salts-poor (3–5 wt.% NaCl eq.) and the other saline (up to 34 wt.% NaCl eq.) and CO 2-poor. The first fluid formed a quartz core at 430 °C and 2.7 kbar. The second fluid circulated through all the pegmatite due to the development of a fracture network produced by a hydraulic fracturation. This fluid replaced the previous zones. In addition, crystallization of fine-grained albitites (Ta P-rich) and late quartz-muscovite veins takes place in the fractures. The fluids that formed these veins are more saline than those from the albitites, with 36–38 wt.% NaCl eq. and with CO 2 and minor N 2.

The Proterozoic Hustad igneous complex: a low strain enclave with a key to the history of the Western Gneiss Region of Norway

The Hustad Igneous Complex (HIC) is a concentrically zoned, high K calc-alkaline intrusive complex, with a core of quartz–monzonite and granite surrounded successively by monzodiorite and pyroxenite, preserved in a 10 km2 lens within the strongly ‘caledonised’ Western Gneiss Region (WGR) of Norway. Upper intercept UPb zircon ages of 1654±1 and 1653±2 Ma, obtained from the granite and the monzodiorite, respectively, overlap with a RbSr whole rock age of 1656±49 Ma (I.R.: 0.70193±0.0009, MSWD:6.6) obtained from the felsic members of the complex and a SmNd whole rock age of 1555±180 Ma (I.R.: 0.51067±13, MSWD:3.3). The UPb age of 1654±1 Ma is interpreted to date the time of intrusion. A 50 m thick dolerite dyke that can be followed for almost 4 km across the HIC yields a UPb zircon and baddeleyite age of 1251±3 Ma. The dyke also contains a secondary polycrystalline zircon generation, which together with baddeleyite defines a lower intercept age of 384±9 Ma. The Caledonian events were also marked by the emplacement of a swarm of pegmatites, which crosscut all the other units and provide a UPb zircon age of 401±1 Ma. A RbSr whole-rock age for the pegmatites is older at 452±26 Ma (I.R.: 0.7105, MSWD:4.3) indicating some initial isotopic heterogenity and formation of the pegmatites from material with a long crustal residence time. A concordant UPb monazite age of 390±2 Ma from the pegmatite and the above 384±9 Ma lower intercept age date metamorphism caused by percolating fluids. Post pegmatite deformation transformed the complex along shear zones into gneisses indiscernible from the surrounding gneisses. The HIC is characterised by high mg-numbers (0.39–0.80), high Ni and Cr values, and depletion of Nb and Ta relative to LIL elements. Phenocrysts of ortho- and clinopyroxene have high concentrations of Cr, supporting the Cr-rich nature of the complex. The suite is LREE-enriched, has a fractionated and U- shaped REE pattern (Cen 90–143, Ybn 12–40), eNd values ranging from +0.0 to +2.7, and the felsic members display weak positive Eu anomalies while the pyroxenite has a negative Eu anomaly. The complex bears a geochemical resemblance to the late-tectonic, high-BaSr granite complexes of West Scotland, and particularly to their volcanic counterparts, the Mg-rich Old Red Sandstone andesites. Overall the data suggest generation of the suite in a subduction environment from material derived by melting of a recently enriched, but previously long-term LREE-depleted mantle. The HIC is one of the few well-preserved remnants of the igneous protoliths of the 1686–1640 Ma gneisses that make up the WGR. In fact, the pyroxenite is compositionally identical to orthopyroxene eclogite found as lenses in the surrounding gneisses and forms a likely protolith to this enigmatic rock. The metamorphism had little influence on the RbSr and SmNd systems of the felsic rocks, but it appears to have affected more strongly those in the mafic rocks, probably as a result of the more intense mineralogical transformations and metasomatic loss of Rb and LREE during high-grade metamorphism.

Radiation-hardness studies of high OH − content quartz fibres irradiated with [formula omitted] electrons

We investigated the darkening of nine high OH − fibre types irradiated with 500 MeV electrons from the Linac Injector of LEP (LIL) at CERN. The transmission of Xe light was measured in situ in the 350– 800 nm range. The induced attenuation at 450 nm is typically 1.52±0.15 dB/m for a 100 Mrad absorbed dose. Two-parameter fits for darkening and recovery are presented. After irradiation the tensile strength remains essentially unchanged. For Polymicro quartz core fibres the tensile strength is typically 4.6±0.4 GPa .

Fluid inclusion microthermometry in Be–Ta–(Li–Sn)-bearing pegmatites from the Borborema Province, Northeast Brazil

Fluid inclusions in Be–Ta–Li–Sn-bearing pegmatites have been reported in the literature as hypersaline aqueous brines or low-salinity aqueous or aqueous–carbonic fluids. The evolution paths of volatile fluids in equilibrium with the different crystallizing phases of rare-element pegmatites do not seem to be unique. The aim of this work is to contribute to this discussion, on the basis of fluid inclusion information from the Borborema Pegmatite Province (BPP) in Northeast Brazil. Some well-known heterogeneous Be–Ta–(Li–Sn) mineralized pegmatites of this province were systematically sampled along cross sections with the purpose of studying the fluid inclusions in the different pegmatite zones (I, muscovite-rich contact zone; II, homogeneous or graphic pegmatite; III, blocky feldspar zone; and IV, quartz core). The observed fluid inclusions (mainly in quartz) were almost always secondary or pseudosecondary, grouped along healed fractures with random orientation. Even some trails paralleling quartz grain limits were not undoubtedly primary. Almost all these fluid inclusions were filled with low-salinity aqueous or aqueous–carbonic fluids. Primary inclusions were recognized only in some well-formed crystals from druses with erratic distribution in the pegmatites. Microthermometric data from these samples confirm that the various crystallizing phases of the pegmatites were in equilibrium with low-salinity aqueous or aqueous–carbonic fluids (with insignificant N 2 or CH 4 contents) with frequent accidentally trapped solids. The various types of primary inclusions found in these crystals compare well with the types of secondary inclusions of the samples from the systematic cross sections. The relative age of the crystals hosting primary fluid inclusions, the relative age of primary inclusion types in successive crystal-growth zones, the relative age of secondary fluid inclusion trails and the corresponding microthermometric data allowed to establish the most probable evolution of the fluid characteristics during pegmatite crystallization. An early low-salinity aqueous–carbonic fluid with CO 2 contents of 20 mol% was present during the crystallization of early minerals, such as garnet and tourmaline of the border zone and graphic quartz, beryl, manganotantalite, and blue tourmaline of zones II and III. The end of zone III crystallization occurred in the presence of a low-salinity, aqueous fluid with very low CO 2 contents, as indicated by inclusions in the smoky core of quartz crystals at the limit between zones III and IV. Later aqueous fluids barren in CO 2 and with salinities increasing from 5% to 20% coexisted with the formation of the pegmatite nucleus and replacement bodies, as indicated by inclusions in the border of these crystals and in euclase. The estimated trapping conditions of 3.5 kbar and 580°C for the earliest inclusion types agree with the regional metamorphic conditions and with the known liquidus conditions of rare-element-bearing pegmatite crystallization. The trapping conditions of inclusions in euclase and coexisting quartz crystal rims in the pegmatitic core, at 3.5 kbar and 400°C are slightly below the conditions admitted for the solidus of rare-element pegmatites and indicate an isobaric cooling during pegmatite crystallization.