Till and bedrock heavy mineral signatures of the Kiggavik uranium deposits, Nunavut

Abstract

In 2010, a drift prospecting study was initiated over the Kiggavik uranium (U) deposit under the Geomapping for Energy and Minerals (GEM) Program. The objective of this study was to document the till geochemical and heavy mineral signatures of the Kiggavik U deposit and to identify potential applications of those characteristics in future exploration for drift-covered, basement-hosted, unconformity-related U deposits. The study area is within the zone affected by the migration of the Keewatin Ice Divide of the Laurentide Ice Sheet. Mineralized and non-mineralized bedrock and near-surface till samples (n = 71) were collected directly overlying, up-ice, and at various distances (50 m, 100 m, 200 m, 500 m, 1 km, 2 km, 3 km, 5 km, and 10 km) in a fan-shaped pattern down-ice from the deposit with respect to the dominant north-northwest, northwest, and west ice-flow directions. Detailed microscopy and microprobe analysis of ore samples from drill core reaffirmed uraninite and coffinite as the dominant ore minerals at the Kiggavik U deposit, with accessory galena, pyrite and very minor native gold associations. These minerals are predominantly very fine-grained and rarely exceed 100 ?m in diameter, with the exception of rare massive crystalline uraninite. Examination of the sand-size heavy mineral concentrate (HMC) from till yielded no U-rich or directly associated accessory ore minerals, reflecting the overall fine-grained nature and instability of these minerals in oxidizing conditions such as those found in near-surface till. This ultimately limits the utility of these minerals as empirical indicators of U deposits. Native gold grains in till samples collected in this study are, however, more abundant than those in regional background samples. Elevated counts were found up to 3 km down-ice of the Kiggavik Main Zone (KMZ) in a west-northwest direction. The sample containing the highest gold grain count in till was collected directly overlying the KMZ, suggesting local provenance and the applicability of native gold as an indicator mineral for Kiggavik-style unconformity-type U deposits. Moreover, Pb-rich fluorapatite grains (up to 8% PbO), from the alteration zone around the KMZ U deposit, are of particular interest due to their uniqueness, stability under near-surface weathering conditions, and thus their potential to be an indicator mineral for such deposits. However the fluorapatite grains are very finely crystalline, as are the main Ubearing phases observed in ore samples, therefore a new technique to separate, collect, and identify the finer fraction of the HMC needs to be developed.

Geochemistry of magnetite and hematite from unmineralized bedrock and local till at the Kiggavik uranium deposit: Implications for sediment provenance

“…The Geological Survey of Canada (GSC) collected a total of forty-two bedrock samples and seventy-one bulk till samples in the Kiggavik area during the summer of 2010 (Robinson et al, 2016). Bedrock samples were taken from outcrop and drill core including solid outcrop, frost heaved outcrop, and also monolithological felsenmeer representing the local bedrock.…”

“…The till samples were collected mostly from a fan-shaped distribution of sample sites extending to the west and northwest of the Kiggavik deposits in an attempt to sample till that was glacially eroded and transported by the main ice flow events to the west and northwest (Table 1B; Robinson et al (2016). In this study, the geochemical characteristics of magnetite and hematite from the 0.25-0.5 mm and 0.5-2.0 mm FHMC of ten samples from the sample suite collected by the GSC, representing material from up-ice, overlying, and down-ice of the Kiggavik…”

“…Bulk till samples (5-15 kg) collected from the Kiggavik area were processed by Overburden Drilling Management (ODM) as described below from Robinson et al (2016). Samples were sieved, the <2.0 mm material passed over a shaking table, and then sieved to isolate the 0.25-2.0 mm fraction for further processing using heavy liquid separation at a specific gravity of 3.2 to concentrate heavy minerals.…”

“…The non-ferromagnetic concentrate of each sample was sieved into 0.25-0.5, 0.5-1.0, and 1.0-2.0 mm size fractions. Hematite was picked from the 0.25-0.5 mm nonferromagnetic fraction by ODM (Robinson et al, 2016) and provide by GSC for use in this study.…”

“…The eight rock samples investigated in this study were disaggregated at Queen's University using a selFrag™ high-voltage pulse power fragmentation instrument (Robinson et al, 2016). The selFrag™ disaggregation breaks the rock along grain boundaries, and thus, the morphology of liberated minerals reflects their original shape and grain size (Cabri et al, 2008).…”