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

Abstract

Uranium mineralization in the Kiggavik area, on the eastern border of the Thelon basin (Nunavut, Canada), hosts significant uranium resources within the basement and its understanding is critical to comprehending the genesis of unconformity-related deposits' structural controls and therefore exploration of these types of deposits in this prospective district. This article deciphers the complex multiphase fracture network associated with uranium mineralization of the most recently discovered, basement-hosted prospect in the Kiggavik area, named Contact. The Contact prospect is located along the Andrew Lake Fault (ALF), a major NE-SW fault corridor in the area. This study combines field work, drillcore logging, sampling, and macro-to micro-petro-structural analyses. Key results from this study highlight that the NEtrending ALF, along with the ENE-trending Thelon (TF) and Judge Sissons (JSF) faults, formed early during intracratonic rifting and deposition of the Baker Lake and Wharton groups (ca. 1850-1750 Ma) in response to the Thelon and Trans-Hudsonian orogeny. The ALF was affected by a strong silicification-brecciation event that likely developed at ca. 1750 Ma, and partitioned later deformation and fluid circulation. In the Contact prospect, the ALF was reactivated multiple times and mineralized in three stages with distinctive secondary fracture patterns, alteration, and mineralization types. Ten fracture stages have been identified at the Contact prospect, f1 to f10. The first stage of mineralization, coeval with f5, is related to fluids of unconstrained origin that circulated through E-W faults in the area that locally re-activated quartz veins of the brecciation event at the intersection with the ALF. Mineralization at this stage is polymetallic and associated with weak clay alteration. The second stage of uranium mineralization occurred coeval with transtensional reactivation of the NE-SW trending ALF (f6c) and in relation to circulation of oxidizing basinal brines within the fault zone. Mineralization at this stage is monometallic and associated with illite and sudoite alteration. Later reactivation of the inherited fracture network (f8) led to strong illitization and bleaching of the host rock, with local reworking of the ore body. Finally, reactivation of the fracture network during f9 and 10 lead to circulation of meteoric fluids that remobilized mineralization in a third stage of uranium re-concentration along redox fronts, with strong illitization and bleaching of the host rock. Unlike the classic unconformity-related uranium deposits in the Athabasca Basin where clay alteration halos occur around the ore bodies related to mineralizing processes, in the Contact prospect the strongest clay alteration event (f8) postdates both main stages of mineralization. Along with uranium remobilization, the basement-hosted Contact prospect is likely a relict of what was once a larger deposit.

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

“…This kind of observation is common in drill holes. Lithologies within and around the QB display a pervasive red-purple hematization, as documented at the Contact prospect [31]. Clasts bearing veins of the QB are observed in the sandstones of the Thelon formation ( Figure 2D), indicating that QB predates formation of the Thelon Basin, as already suggested by several authors [29,31] and crosscuts, thus postdates, Hudsonian intrusions (ca.…”

“…In this contribution, we focus on one structural feature encountered in many fault zones within the Uranium (U)-rich district of the Kiggavik area (Nunavut, Canada): The so-called hydrothermal Quartz Breccia (QB). The importance of this breccia, only briefly described by previous authors [26][27][28][29][30] was recently highlighted by Grare et al [31] who documented the control exerted by this breccia on later fracturing events, hydrothermal alterations and uranium mineralization at the Contact uranium prospect. However, despite observations in several locations of the Kiggavik area and its seemingly strong control on the current distribution of the uranium mineralization, the genetic model of the QB remains poorly characterized and explained to date.…”

“…The main structural features in the Kiggavik area are the ENE-trending Thelon fault (TF) and the Main Zone fault (MZF) in the northern part of the property, the ENE-trending Judge Sisson fault (JSF) in the central part, and the NE-trending Andrew Lake Fault (ALF) in the southwestern part of the study area ( Figure 2). These faults date back to at least~1920 Ma [56] and had a subsequent complex structural and kinematic evolution with several episodes of reactivation and fluid circulation during Proterozoic time [31,56]. These faults host several uranium orebodies; prospects and deposits, the main uranium mineralizing events being bracketed between 1540 and 1270 Ma [28,29,31].…”

“…These faults date back to at least~1920 Ma [56] and had a subsequent complex structural and kinematic evolution with several episodes of reactivation and fluid circulation during Proterozoic time [31,56]. These faults host several uranium orebodies; prospects and deposits, the main uranium mineralizing events being bracketed between 1540 and 1270 Ma [28,29,31]. The MZF hosts various deposits and prospects: 85 W, Granite Grid and Kiggavik (Main, Central and East Zones, Figure 1C).…”

“…However, despite observations in several locations of the Kiggavik area and its seemingly strong control on the current distribution of the uranium mineralization, the genetic model of the QB remains poorly characterized and explained to date. Grare et al [31] showed that the QB emplaced along faults of inferred Archean age, and that this emplacement was a key event within a long-lasting (~1000 Ma) complex brittle tectonic history that led to uranium mineralization within or in the vicinity of the quartz breccia ( Figure 1C). In order to better constrain the nature, emplacement, significance and role of the QB, we carried out a structural analysis combined with vein cement petrography using optical and cathodoluminescence observations, trace elements, and oxygen stable isotope analysis of quartz.…”