The geochemistry and geochronology of the End deposit, NE Thelon region, Nunavut, Canada: insight into the Athabasca basin's closest relative
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Date
2020-06
Authors
Ashcroft, Greg
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Abstract
The Paleoproterozoic, intracratonic Thelon Basin, located ~100-500 km west of Baker Lake, Nunavut, has been studied over the past few decades by various researchers, but it is still relatively poorly understood. It displays many stratigraphic, sedimentological, and metallogenetic similarities to the uranium-producing Athabasca Basin located in Northern Saskatchewan and may share similar economic potential.
The Kiggavik uranium project area is located 80 km west of Baker Lake, Nunavut, adjacent to the northeastern extent of the Thelon Basin; the Aberdeen sub-basin. The project area contains a series of uranium deposits and showings generally located along a broad NNE-oriented structural corridor known as the Andrew Lake-Kiggavik structural trend. The End deposit, hosted by the Judge Sissions Fault (JSF) within this structural trend, and contained within the Woodburn Lake group (WLg) Pipedream metagreywacke (Ppd)
Three paragenetic stages of uranium mineralization are preserved, with the third stage comprising 3 sub-stages. The oldest dated stage is disseminated uraninite (U1; ~1500 Ma). This is transected by vein-type uraninite (U2; ~1300Ma). These in turn were remobilized as foliation-parallel (U3a), infill-type (U3b; ~970 Ma), and micro-roll-front style (U3c; ~750Ma). All uranium oxide minerals are now highly altered and the U-Pb ages obtained are highly discordant, suggesting that Pb-loss has occurred. Therefore, these ages are interpreted to represent thermal or tectonic resetting events. The U-Pb ages of uranium minerals from the End deposit are similar to the ages of uranium mineralization at the Bong deposit, which coincide with regional and tectonic thermal events.
Three alteration events were also dated at ~1600, ~1475 and ~1300 Ma using 40Ar/39Ar geochronology of muscovite and illite. The ~1475 and 1300 Ma events coincide with ages from uranium minerals in the End deposit. The fluid that deposited U1 and illite (Il1) had a temperature of 210 ± 16 °C with δ18O and δ2H values of 4.1 ± 0.8 ‰ and -131 ± 5‰ respectively. The stable isotope systematics of the uranium deposits of the Athabasca and McArthur River Basin (Australia) suggest that these deposits formed from interaction of basinal brines with basement fluids, the End deposit is likely to have formed from fluids similar to the Athabasca and McArthur basins, and illite may have been affected by present day meteoric water.
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Keywords
Kiggavik, Uranium, Nunavut, Thelon, Athabasca, Paleoproterozoic, Geochronology, Geochemistry, Isotopes, Oxygen, Hydrogen, Radiogenic, Lead, Ar-Ar, Clay thermometry