Basement geology beneath the northeast Thelon Basin, Nunavut: insights from integrating new gravity, magnetic and geological data

Abstract

Current models for unconformity‐associated uranium deposits predict fluid flow and ore deposition along reactivated faults in >1.76 Ga basement beneath Mesoproterozoic siliciclastic basins. In frontier regions such as the Thelon Basin in the Kivalliq region of Nunavut, little is known about the sub‐basin distribution of units and structures, making exploration targeting very tenuous. We constructed a geological map of the basement beneath the unconformity by extrapolating exposed features into the subsurface. The new map is constrained by detailed geological, geophysical, and rock property observations of outcrops adjacent to the basin and by aeromagnetic and gravity data over the geophysically transparent sedimentary basin. From rock property measurements, it is clear that the diverse magnetic and density characteristics of major rock packages provide quantitative three‐dimensional constraints. Gravity profiles forward modelled in four cross sections define broad synforms of the Amer Belt and Archean volcanic rocks that are consistent with the structural style outside the basin. Major lithotectonic entities beneath the unconformity include: supracrustal rocks of the Archean Woodburn Lake group and Marjorie Hills meta sedimentary gneiss and associated mixed granitoid and amphibolitic gneiss; the Amer Mylonite Zone and inferred mafic intrusions oriented parallel and sub‐parallel; other igneous intrusions of 2.6 Ga, 1.83 Ga, and 1.75 Ga vintage; and the <2.3 Ga to >1.84 Ga Amer Group. Four main brittle regional fault arrays (040°–060°, 075°–90°, 120°, and 150°) controlled development and preservation of the basin. The reactivated intersections of such faults along fertile basement units such as the Rumble assemblage, Marjorie Hills assemblage, Nueltin igneous rocks, and Pitz formation are the best targets for uranium exploration.

The Contact uranium prospect, Kiggavik project, Nunavut (Canada): Tectonic history, structural constraints and timing of mineralization

“…Major ENE-trending dextral strikeand oblique-slip faults, including the Thelon-Fault ( Fig. 1 Ma supracrustal rocks of the Woodburn Lake Group , and a distinctive package of 2620-2580 Ma felsic volcanic and related hypabyssal rocks known as the Snow Island suite (Jefferson et al, 2011a(Jefferson et al, , 2011bMcEwan, 2012;Tschirhart et al, 2013Tschirhart et al, , 2017Peterson et al, 2015a;Johnstone et al, 2016). These rocks, together with overlying Paleoproterozoic (2300-2150 Ma) rocks of the Ketyet River Group (Rainbird et al, 2010), include a prominent unit of orthoquartzite (Zaleski et al, 2000).…”

“…3). The ALF is delineated from interpretation of aeromagnetic and ground gravity maps (Tschirhart et al, 2017;Roy et al 2017), as outcrops are almost non-existent. Its trend is reported on Figure 3.…”

Uncertainty reduction through geologically conditioned petrophysical constraints in joint inversion

“…However, while geological measurements and orientation data can be used as constraints during inversion (Fullagar et al, 2008, Lelièvre and Oldenburg, 2009, and Scholl et al, 2016, less effort has been put on the quantitative integration of geostatistical modeling into geophysical joint inversion. Several studies show examples where different disciplines of geology and geophysics are integrated in a cooperative manner using expert knowledge (Jessell and Valenta, 1996, Betts et al, 2003, Lane et al, 2009, and more recently Mantovani et al, 2016 andTschirhart et al, 2016). Quantitative integration of these two disciplines is an active, yet underexplored research area.…”

Fault Zone Evolution and Development of a Structural and Hydrological Barrier: The Quartz Breccia in the Kiggavik Area (Nunavut, Canada) and Its Control on Uranium Mineralization

“…The diabase dikes of the Mackenzie diabase swarm form prominent linear aeromagnetic features trending NNW-SSE [44,45] and cut across all previous lithologies. This intrusive event is dated at 1267 ± 2 Ma [54,55], and represents the last magmatic-tectonic event in the region.…”

“…This volcano-sedimentary pile unconformably overlies a metamorphosed basement consisting of Archean rocks that include Mesoarchean (ca. 2870 Ma) granitic gneisses, 2730-2680 Ma, supracrustal rocks of the Woodburn Lake Group [40], and a distinctive package of 2620-2580 Ma felsic volcanic and related hypabyssal rocks known as the Snow Island Suite [41][42][43][44][45][46][47].…”