Search

Seismic-reflection techniques have been applied in several studies over the last 20 years as a uranium-exploration tool within the Athabasca Basin and have been utilized to provide the larger structural context for known uranium deposits within the basin. At the crustal scale, deposits within the eastern Athabasca Basin are shown to be associated with deep-seated shear zones that originated during Trans-Hudson orogeny and have subsequently been reactivated during and subsequent to deposition of the basin-fill sandstones. Seismic properties of the Athabasca sandstones and underlying basement have been determined through in situ borehole measurements. Reflectivity within the sandstones is generally weak. Seismically recognizable signatures are primarily associated with variations in fracture density, porosity, and degree of silicification. The basement unconformity and regolith, a prime target of exploration, is widely imaged as it is characterized by variable but generally distinct reflectivity. Results from the McArthur River mine site suggest that the spatial coincidence of seismically imaged high-velocity zones and deep-seated faults that offset the unconformity may be a more broadly applicable exploration targeting tool. Three-dimensional (3-D) seismic imaging near existing ore zones can define the local structural controls on the mineralization and point the way to new targets, thus leading to more efficient exploration drilling programs. Furthermore, seismically generated structural maps of the unconformity and rock competence properties may play a significant role at the outset of mine planning. La sismique reflexion a ete utilisee dans plusieurs etudes au cours des 20 dernieres anneees en tant qu'outil d'exploration pour l'uranium dans le bassin de l'Athabasca; elle a aussi ete utilisee pour fournir le contexte structural a plus grande echelle pour les gisements connus d'uranium a l'interieur du bassin. A l'echelle de la croflte, il est montre que des gisements dans le bassin Athabasca oriental sont associeesa des zones de cisaillement a grande profondeur qui ont pris naissance durant l'orogene trans-hudsonien et qui ont par la suite ete reeactiveees durant et apresla deposition des gres remplissant les bassins. Les proprieetes sismiques des gres de l'Athabasca et du socle sous-jacent ont ete determinees par des mesures in situ dans des forages. La reflectivite est geeneralement faible dans les gres. Des signatures sismiques identifiables sont surtout associees a des variations de densite des fractures, de la porosite et du degree de silicification. La discordance entre le socle et le regolite, une cible de choix en exploration, est bien imageee en raison de sa caracterisation par une reflectivite variable mais geeneralement distincte. Les resultats provenant du site minier McArthur River suggerent que la coincidence spatiale de zones de grandes vitesses imageees par sismicite et de failles a grande profondeur qui decalent la discordance puissent etre un outil plus largement applicable comme cible d'exploration. De l'imagerie sismique 3D a proximite des zones mineeralisees existantes peut definir les controles structuraux locaux sur la mineralisation et indiquer de nouvelles cibles, menant ainsi a des programmes de forages d'exploration plus efficaces. De plus, des cartes de structure, generees par sismicite;, de la discordance et des proprieetes de competence du roc pourraient jouer un role important desle debut d'une planification miniere. [Traduit par la Redaction], Introduction The Athabasca Basin has been actively explored for uranium for over a half century. Geophysical methods have played a major role in this region, as virtually all ore discoveries [...]

A study has been performed to examine the process of micropelletization on four different polyethylenes with melt index values between 1 and 5 g/10 min. The experiments were done on a 50-mm 30:1 L/D extruder with an underwater micropelletizer attached. The average micropellet size that was produced ranged from 0.4 to 0.5 mm in diameter depending on whether a plastomer or high-density grade was selected. The dimensions of the pellets were influenced strongly by the occurrence of die-hole freeze-off. Minor sharkskin was observed on the surface of the micropellets, a result of the high stresses experienced in the pelletizer die. A non-isothermal, axisymmetric flow model was used to assist in the analysis by comparing the observed results to the predicted shear stresses in the die. The calculations revealed that extremely high shear rates were present in the die holes, resulting in a significant degree of wall slip. The measured rheological properties of the micropellets did not show any change in comparison to their virgin resins, likely because of the presence of wall slippage and the short residence time of the polymer in the die holes. Polym. Eng. Sci. 44:1391-1402. 2004., INTRODUCTION Micropelletization is a relatively new technology for producing resin particulate that exhibits many of the advantages of a pellet yet possesses a size closer to that of a powder. [...]

The M-intrashell spectra from Co-like Yb43+ through Na-like Yb59+ ions produced in an electron beam ion trap (EBIT) at the National Institute of Standards and Technology have been studied in the extreme ultraviolet (EUV) range. A few N-intrashell transitions for Co-like Yb43+ and Fe-like Yb44+ are also reported. The EUV radiation was observed with a flat-field grazing incidence spectrometer in the wavelength region of about 7.5 nm to 26.2 nm. The electron beam energies were varied between 3.6 keV and 18 keV to produce the ionization stages of interest. The line identifications were based on the large-scale simulations of the EBIT plasma emission using the non-Maxwellian collisional-radiative code NOMAD. A total of 76 previously unobserved spectral lines corresponding to electric-dipole and magnetic-dipole transitions in the above mentioned ions were identified and discussed. In particular, our accurate wavelength of 24.3855 ± 0.0005 nm for a magnetic-dipole (M1) transition in the ground configuration of Co-like ion presents a solid benchmark for comparisons with the most advanced theories of atomic structure. [ABSTRACT FROM AUTHOR]