Lithostratigraphic and structural controls of uranium mineralization in the Kiggavik East Zone, Centre Zone, and Main Zone deposits, Thelon Basin, Nunavut
The Kiggavik uranium deposits are located in the north-central Rae Subprovince of the Western Churchill Province and are hosted in highly deformed Archean and Paleoproterozoic basement rocks proximal to, and underlying the Thelon Basin. This field-based study documents the lithostratigraphic and structural character of Kiggavik’s basement rocks and their controls on the uranium deposits. Field investigation, coupled with structural analysis, geochemistry and geochronology indicates that the basement rocks comprise two main tectonostratigraphic packages: a structurally ‘lower-package’ comprising ~2.71 Ga Pipedream assemblage metagreywacke and a structurally ‘upper-package’ consisting of multiple intervals of ~2.6 Ga Snow Island Suite felsic epiclastic and metarhyolite intercalated with less than 2.3 Ga quartzite of the Ketyet River group. Of particular significance are the epiclastic rocks, which, based on their textural variability, felsic composition, negative europium anomaly and association with metarhyolite, are correlated with previously identified epiclastic volcanic rocks in the western part of the area, rendering this the most spatially extensive rock unit at Kiggavik. Further, field investigation, coupled with structural analysis, confirms that all units form a homoclinal sequence that dips gently NNW in the eastern map area (Domain 1) and ENE in the western map area (Domain 2). Based on regional stratigraphic relationships, down-section profiles in both domains contain multiple younging direction reversals. This, coupled with strongly transposed bedding, ubiquitous foliation and highly strained contacts, plus the direct observation of isoclinal, recumbent folds in both outcrop and drill core, indicates that these repetitions are tectonic. In addition, across both domains, all units carry a well-developed stretching lineation. The collective 3D geometry and associated fabric elements are diagnostic of sheath folding and related thrusting under an ENE-WSW tectonic transport direction during DP1 when the upper (epiclastic-metarhyolite-quartzite) package is interpreted to have been translated over the more competent metagreywacke below. Although once misunderstood, the difference in dip direction between domains is ascribed to a domain-bounding NNW-trending fault that misoriented blocks, causing late-stage dragging and down-dropping of all units in the east during late, dip-slip motion along the Thelon Fault. In general, late brittle deformation is manifested by ENE-trending regional-scale Group 1 faults and local-scale Group 2 faults that collectively define a Riedel shearing system driven by dextral strike-slip displacement along the Thelon Fault. Detailed study at the Centre Zone deposit revealed that during Phase 1 mineralization steeply dipping D- and P-shears served as conduits for fluids to move through and penetrate earlier-formed ductile structures. The fluids preferentially infiltrated through, and precipitated uranium in, the more porous-permeable epiclastic and metagreywacke, while the quartzite served as an overlying aquitard. Phase 2 mineralization resulted from the reactivation of these structures, when remobilizing fluids redistributed uranium along planar brittle structures. In addition to the Hudson and Kivalliq granites, felsic Snow Island Suite rocks may have also been a significant source of uranium.
Networked Digital Library of Theses and Dissertations
Faculty of Graduate Studies and Research, University of Regina