Geochronology and Genesis of the Bong Uranium Deposit, Thelon Basin, Nunavut, Canada

Abstract

The Thelon basin, Nunavut, shares many similarities with the uranium-producing Athabasca basin, Saskatchewan; however, the uranium deposits associated with the Thelon basin are still poorly understood. The Kiggavik project area (AREVA Resources Canada) is located near the northeastern terminus of the Thelon basin and comprises multiple uranium deposits hosted exclusively in basement rocks. The Bong deposit is hosted dominantly by Neoarchean metagraywacke of the Woodburn Lake group. A five-phase metallogenetic model is proposed for the Bong deposit, with three stages of uraninite identified. The premineralization phase is characterized by host-rock silicification. Mineralization is separated into three main stages. Stage 1 uraninite (U1; ca. 1500 Ma) is preserved in highly fractured and altered disseminated grains that are overgrown by later stages of uraninite. Stage 2 uraninite (U2; ca. 1100 Ma) forms veinlets parallel to D1 foliation and coats and fills fractures in organic matter nodules and blebs. Stage 2 uraninite is associated with pervasive illite that formed from ~190°C fluids (δ 18 O: -6.4‰, δ 2 H: -97‰), which remobilized much of Stage 1 uraninite and completely overprinted Stage 1 alteration. At ~1000 Ma an oxidizing fluid deposited uraninite along redox fronts (U3) while altering and remobilizing Stage 1 and 2 uraninite. Post-uranium-oxide minerals include drusy quartz, calcite, and illite accompanied by uranyl phases (e.g., uranophane, Ca-U).

Nanoscale relationships between uranium and carbonaceous material in alteration halos around unconformity-related uranium deposits of the Kiggavik camp, Paleoproterozoic Thelon Basin, Nunavut, Canada

“…The BG4238 sample contain in average up to 66% carbon and record highly negative isotopic composition with δ 13 C org of -39.1 ‰. Such value has also been observed in carbonaceous mineralized nodules in samples from Bong Uranium deposit in the same ara (Sharpe et al, 2015). The low Al, K, and Mg amounts are consistent with the absence of clay minerals within the MCM.…”

“…remobilization events (in any case both require reducing conditions to precipitate) as suggested in Sharpe et al (2015). In such a process, the enhanced surface area of the CM could have acted as a favourable site for nucleation of uraninite crystals.…”

“…The main goal of the present study is to identify the origin of the CM associated with U minerals in the Kiggavik exploration camp located at the southeastern margin of the Paleo-to Mesoproterozoic Thelon Basin, building on the paragenetic context developed by (Riegler 2013;Riegler et al 2014;Riegler et al 2015;Sharpe 2013;Sharpe et al 2015). The second focus is on the solid properties of the CM to better understand their very unusual spatial and textural associations with U oxide minerals.…”

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

“…Uranium deposits in the Kiggavik area ( Fig. 2) have recently been interpreted to have some characteristics of unconformity-related deposits (Kiggavik Main and Central Zone deposits: Farkas, 1984;Shabaga et al, 2017b;Bong deposit: Riegler et al, 2016;Sharpe et al, 2015;Quirt, 2017;End deposit: Chi et al, 2017; see also Fayek et al, 2017). In contrast to the Athabasca Basin, where ductile deformation involving graphitic and mineralized shear zones are commonly observed, the tectonic style of deformation and mineralization in the Kiggavik area is dominantly brittle, as exemplified by the presence of cataclastic to ultracataclastic fault rocks and mineralized veins.…”

“…Ductile to ductile-brittle shear zones are rarely observed and their reactivation appears not to be a key process controlling uranium mineralization there (Johnstone et al, 2017). Previous studies of the various deposits in the Kiggavik area focused on the characterization of mineralizing fluids and their alteration products, through geochemical and isotopic analyses of uranium oxides and clay minerals (Farkas, 1984;Riegler et al, 2016a;Shabaga et al, 2015;Sharpe et al, 2015;Potter et al, 2015;Chi et al, 2017;Fayek et al, 2017;Quirt, 2017;Shabaga et al, 2017aShabaga et al, , 2017b. While the knowledge in these various fields has greatly improved in the last years, the tectonic history, the structural controls, and the relative timing of the deposits in the Kiggavik area remain poorly understood.…”