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Mylonites were then reactivated at shallower structural levels where brittle-ductile
fracturing under hydrated conditions associated with cataclasite faulting became the
dominant failure process (Fig. 2.13C).
The formation age of the cataclasite ±U 1 and early tensional veins-type ±U 2
mineralization, suggests that these two mineralizing events were coeval and their timing is
consistent with fault reactivation during late stage Arrowsmith Orogen that affected the
Beaverlodge area (Fig. 2.13C). Post-orogenic exhumation and erosion may have led to the
development of fluid-related features (Miller et al., 2002) as deformation occurred under
hydrated conditions in the ductile-brittle environment. Hydraulic tensile fracturing in
response to fluid generation via decompression and hydration reactions (Miller and
Cartwright, 2006) was probably the mechanism of the early tensional ±U 2 -veins formation.
The vein-forming fluid was likely driven into these fractures by suction pump processes
(Sibson, 1987). Interaction between the hydrothermal brine and the metamorphic host rocks
likely promoted the deposition of the ±U 2 uranium mineralization and the Cal 2 -Hem 3 -Chl 3 -
Src 2 -Cpy 2 -Py 2 mineral assemblage (Fig. 2.8).
The 207 Pb/ 206 Pb system of U 1 and U 2 uraninites displays five groups of ages reflecting
post-mineralization alteration by later fluid events that are related to fault reactivation (Fig.
2.15). The intervals 2.2-2.1 Ga and 2.1-2.0 Ga correspond to a period of global extension
and rifting related to the protracted breakup of the Kenorland supercontinent (Williams et
al., 1991; LeCheminant et al., 1997) (Fig. 2.15). For example, the 2.2-2.1 Ga mafic swarms
in the Slave, Churchill, Superior and Nain provinces (LeCheminant et al., 1996; Bleeker et
al., 2007) and the 2.2-2.0 Ga intrusive complexes in the Slave province (Buchan and Ernst,
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