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No description available.

An investigation as to the characteristics of flow and fracture for alpha-uranium were carried out over the temperature range -196°C to 270°C. The parameters relevant to grain size and strain rate were investigated. It was established that the flow stress and the fracture stress in the semi-brittle region vary linearly with the grain size parameter (1/D½). Evidence suggests that the sensitivity of flow stress to grain size is directly related to the importance of glide dislocation action as the deformation mode. Strain rate change irreversibility was found to exist at low strains for all temperatures investigated. This evidence, correlated with the effect of grain size, indicates that massive structural changes occur in the early stages of flow. This agrees with electron transmission microscopy results as established by other workers. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Rectangular beams of high density single-crystal UO₂ were prepared from large grains of fused UO₂.They were deformed under constant load in four-point bending in hydrogen at temperatures from 1340 to 1420°C. The results appear to fit a creep equation of the form (formula omitted) where e = steady-state creep rate (formula omitted) Q = 118 ± 23 kcal/mole C = constant ; and 3 < n <4 in the regions of stress and temperatures examined. Faint slip lines were observed. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Le Paléoprotérozoïque est une période charnière de la métallogénie de l'uranium marquée par l'oxyatmoversion (le GOE, ca. 2,4 Ga) rendant possible une mobilité sans précédent de l'U en solution. Dans ce contexte, cette thèse porte sur l'étude de deux types de minéralisations provenant du district de Cage (Québec). Une première minéralisation « stratoïde » à U, Ba, V, Mo, Pb, Zn, sans Th localisée dans des séries carbonatées paléoprotérozoïques du Groupe du Lake Harbour métamorphisées pendant l'orogène Torngat (1,87-1,77 Ga). La minéralisation uranifère s'est formée par l'interaction entre un fluide météorique oxydant, qui en percolant le long de la plateforme carbonatée s'est enrichi en U au contact de matériel volcanique, et des minéralisations de type MVT préalablement déposés avec de la matière organique. Une seconde minéralisation à U-Th portée par des « skarn s.l. » est liée à des pegmatites ainsi que des fluides hydromagmatiques ayant une source commune profonde provenant de la granutilisation de l'Archéen sur lequel repose le Groupe de Lake Harbour. Les résultats de cette thèse contribuent à une meilleure connaissance des processus qui ont conduit à l'enrichissement en U de la croute paléoprotérozoïque, en mettant en évidence deux nouvelles possibilités : - Des concentrations liées au fonctionnement de plateforme carbonatées enrichies en sulfates après le GOE, en contexte de rifting, au cours de la dislocation des méga-continents formés à la fin de l'Archéen ; - Des concentrations liées aux métamorphismes UHT qui granutilisent la CCI pendant le processus d'amalgamation du supercontinent Nuna. / Paleoproterozoic is a key transitory period for Uranium deposits. The appearance of an atmosphere with free oxygen (GOE, ca. 2,4 Ga), event generally know as oxyatmoversion, made it possible U mobility via aqueous solutions. The present thesis deals with two types of uranium mineralizations that are related to this period (Cage district, Québec). The first “stratoïd” deposit is characterized by U, Ba, V, Mo, Pb, Zn, mineralizations without Th. Host-rocks are carbonate paleoproterozoic series, from Lake Harbour Group, that were metamorphosed during the Torgnat orogen (1,87-1,77 Ga). The percolation along the carbonate platforms of an oxidized meteoric fluid lead to Uranium deposits by interaction with U enrichment from volcanic material, and organic rich MVT type mineralization. The second U-Th mineralization is hosted by “skarn s.l.”. It is related to pegmatites and hydro-magmatic fluids with the same deep origin: granutilization of archean terranes on which Lake Harbour Group is situated. The present work permits a better comprehension of U enrichment of paleoproterozoic crust with two new hypotheses: - Ore concentrations related to the carbonate platforms, enriched in sulfate, during rifting and dislocation of mega-continents at the end of Archean times; - Ore concentrations related to UHT metamorphism and granutilization of continental crust during hypercollision and formation of the so-called Nuna continent.