Structural controls and metallogenic model of polyphase uranium mineralization in the Kiggavik area (Nunavut, Canada)

The Kiggavik area is located on the eastern boundary of the Paleo- to Mesoproterozoic Thelon Basin (Nunavut, Canada) and hosts uranium mineralization in Archean basement rocks. The major fault/fracture network in the Kiggavik area is mainly oriented ENE-WSW and NE-SW, consisting of polyphased fault zones initiated during the Thelon and Trans-Hudsonian orogenies (ca. 1900–1800 Ma). These faults were subsequently mineralized in four stages referred to as U0, U1, U2, and U3. The first event U0 is inferred to be of magmatic origin and is related to microbrecciation and weak clay alteration under a WSW-ENE σ1. U0 is a ca. 1830 event which predates intense quartz brecciation (QB) and veining at ca. 1750 Ma. QB is associated with emplacement of the Kivalliq Igneous Suite and caused pervasive silicification of former fault zones, which in turn controlled subsequent fracture development and behaved as barriers for later U mineralizing fluids (U1 to U3). U1, U2, and U3 postdate deposition of the Thelon Basin. U1 and U2 occurred under a regional strike-slip stress regime, with the direction of σ1 evolving from WNW-ESE (U1) to NE-SW /ENE-WSW (U2); both formed at ~ 1500–1330 Ma and are related to circulation of Thelon-derived uranium-bearing basinal brines. A post U2, but pre-Mackenzie dykes (ca. 1270 Ma), extensional/transtensional stress regime with σ3 oriented NE-SW caused normal-dextral offset of the orebodies by reactivating NNW-SSE and E-W trending faults. This fracturing event triggered circulation of hot (~ 300 °C), probably acidic, fluids that dissolved quartz, and caused illitization and bleaching of the host rocks. Finally, U3 records remobilization of the previous mineralization along redox fronts through percolation of low-temperature meteoric fluids during two main tectonic events at ca. 550 and 350 Ma. This study provides evidences for the presence of a primary, pre-Thelon Basin uranium stock within the Kiggavik prospects, and a strong structural control on mineralization in the Kiggavik area. Our study also shows a nearly similar evolution of uranium mineralization in this area compared to the world-class uranium district of the Athabasca Basin (Saskatchewan, Canada).