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faults (Fig. 2.13C). The breccias were generated later at a shallow level in the brittle
environment (Fig. 2.13E). The shear zone is further cut by more brittle features associated
with veins and dikes (Figs. 2.13F and 2.13G).
The Main Ore shear zone and the Saint Louis fault display evidence for hydration
and fluid flow. Retrograde metamorphism following mylonitization involved exothermic
hydration reactions evidenced by the presence of en-échelon quartz-filled tension gashes
(Fig. 2.5G), tensional veins (Fig. 2.9B), hydraulic breccia (Fig. 2.5L) and chlorite, calcite
and albite veins (Fig. 2.7H) that occur within these shear zones. All the evidence suggests
that hydration associated with fluid circulation prevailed during the development of the
shear zones and played a key role in the alteration and ore-forming processes.
Petrographic, paragenetic mineral and ore alteration relationships, together with
geochronological data and the various deformation features within the Main Ore shear zone
and Saint Louis fault indicate six events of uranium mineralization. These are related to
episodic brittle reactivation of the fault zones (Fig. 2.8) that create dilatant areas, which are
favorable structural sites for fluid flow, hydrothermal alteration, and uranium
mineralization.
Sediments of the Murmac Bay Group were deposited in a tectonically active
extensional fault-bounded Paleoproterozoic Basin (Ashton et al., 2009b) (Fig. 2.13A). Slip
activity along fault zones was likely initiated shortly after deposition of the Murmac Bay
sediments at ca. 2.33 Ga (Hartlaub et al., 2004; Ashton and Hartlaub, 2008). The Group is
intruded by the ca. 2.33–2.30 Ga ‘North Shore Plutons’ (Macdonald et al., 1985) likely
related to tectonic extension during the Arrowsmith Orogen (Hartlaub et al., 2007). The
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