THE GEOCHEMISTRY AND GEOCHRONOLOGY OF THE END DEPOSIT, NE THELON REGION, NUNAVUT, CANADA: INSIGHT INTO THE ATHABASCA BASIN’S CLOSEST RELATIVE by Greg Ashcroft A Thesis Submitted to the Faculty of Graduate Studies of The University of Manitoba In Partial Fulfillment of the Requirements For the Degree of MASTER OF SCIENCE Department of Geological Sciences University of Manitoba Winnipeg, Manitoba Copyright © 2020 by Greg Ashcroft 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. i Acknowledgements I would like to firstly like to thank my advisor, Dr. Mostafa Fayek, for providing much insight into the preparation of this thesis. A sincere thank you to David Quirt for his help on the final revisions along with his wealth of knowledge on the local and regional geology of the Baker Lake area while I was in the field. Thank you to Ryan Sharpe for your guidance with the operation of the SIMS along with revising the early drafts of this thesis. As well thank you to Alfredo Camacho, Ravi Sedu and Neil Ball for their technical support with the Ar-Ar, EMPA and XRD analysis. I would like to express my appreciation and gratitude in the patience of my family and friends and colleagues during the preparation and final stages of this thesis. Financial support for this thesis was from the Natural Sciences and Engineering Research Council of Canada NSERC), Natural Resources Canada (NRCan), Areva Resources Canada (now Orano Canada Inc.,), and the Canadian Foundation for Innovation (CFI). Finally, to my partner, Cheryl Simoens, your continual motivation, love and support to see this to the end gave me the inspiration to overcome any obstacles and setbacks that I faced. ii Table of Contents Abstract ............................................................................................................................................ i Acknowledgements ......................................................................................................................... ii Table of Contents ........................................................................................................................... iii List of Figures ..................................................................................................................................v List of Tables ................................................................................................................................ vii List of Copyrighted Material for which permission was obtained ............................................. viii Chapter 1.0: Introduction .............................................................................................................1 1.1 Kiggavik Project History ...............................................................................................5 1.2 Previous Work ...............................................................................................................6 1.3 Scope of work ................................................................................................................7 Chapter 2.0: Geologic Setting .......................................................................................................8 2.1 MesoArchean Basement ................................................................................................8 2.2 Woodburn Lake Group (WLg) ....................................................................................10 2.2.1 Halfway Hills, Turqavik and Meadowbank Assemblages ............................12 2.2.2 Pipedream Assemblage (Ppd) .......................................................................12 2.2.3 Wading and Amarulik Assemblages .............................................................13 2.3 Rumble Assemblage ..............................................................................................13 2.4 Marjorie Hills Assemblage ....................................................................................14 2.5 Snow Island Suite (SIS) .........................................................................................15 2.5.1 Pukiq Formation ...........................................................................................15 2.6 Ketyet River Group (KRg).....................................................................................16 2.7 Dubawnt Supergroup ...................................................................................................18 2.7.1 Baker Lake Group .........................................................................................19 2.7.2 Wharton Group .............................................................................................21 2.7.3 Barrensland Group ........................................................................................21 2.7.4 Hudsonian Igneous Suites .............................................................................22 2.8 Local Geology of the End Deposit...............................................................................23 2.8.1 Host-rock Alteration within the End Deposit ...............................................28 2.8.2 U Mineralization within the End Deposit .....................................................29 2.8.3 Structures associated with the End Deposit ..................................................30 Chapter 3.0: Sampling and Analytical Methodology ...............................................................35 3.1 General Analytical Methodology .................................................................................35 3.2 Optical and Scanning Electron Microscopy (SEM) .....................................................36 3.3 Electron Microprobe Analysis (EMPA) ......................................................................36 3.4 X-Ray Diffraction (XRD) ............................................................................................37 3.5 Geochronology .............................................................................................................37 3.5.1 In Situ Secondary Ion Mass Spectrometry (SIMS).......................................37 3.5.1.1 U-Pb and Pb-Pb Analysis..................................................................38 3.5.2 40Ar/39Ar Analysis .........................................................................................40 3.6 Stable Isotope Methodology ........................................................................................42 3.6.1 Oxygen Isotope Analysis ..............................................................................42 3.6.2 Hydrogen Isotope Analysis ...........................................................................42 iii Chapter 4.0: Results.....................................................................................................................44 4.1 Petrography ..................................................................................................................44 4.1.1 Pipedream (Ppd) Metagreywacke ................................................................44 4.1.2 Lamprophyre Dykes......................................................................................49 4.1.3 Quartz-feldspar porphyritic