APPLICATION OF WHOLE-ROCK OXYGEN ISOTOPE PROFILES TO STUDY FLUID MIGRATION AND MINERALIZATION AT THE LAC CINQUANTE URANIUM DEPOSIT, NUNAVUT, CANADA

The Lac Cinquante basement hosted uranium deposit is located in the Hearne Subprovince of the Western Churchill Province. The deposit is hosted in Achaean greenstones that are unconformably overlain by the northeast trending Angikuni sub-basin in the Western Churchill Province. Uranium mineralization at Lac Cinquante occurs as pitchblende in discrete veins forming the main zone of mineralization with a 43-101 compliant inferred mineral resource estimate of 810,000 tonnes grading 0.79% U₃O₈, flanking gash veins in a hematite-altered mafic-tuff, and weakly mineralized basinal conglomerates. In this study we present newly obtained results for oxygen stable isotope analyses of silicate whole-rock samples and investigate the implications for fluid flow, alteration, and mineralization of the main ore zone at Lac Cinquante.

The application of oxygen stable isotope analyses has proven to be an effective tool in documenting zones of increased low-temperature hydrothermal alteration associated with the main zone. Oxygen stable isotope analyses of silicate whole rock samples have identified a 20 – 50 meter wide alteration window where values are elevated by up to 1.6‰ within, and surrounding, the main zone of mineralization. Several tuffaceous units not associated with the current main zone of mineralization also show anomalous enrichments up to 2.5‰. Additionally, 1‰ enrichment halos can be traced around structural zones in the basaltic basement rocks. All of these enrichments are associated with zones of increased low-temperature fluid flow.

Coupling geochemical alteration halos with geological mapping can be utilised as an exploration vector to refine future drill targets. Additionally, an alteration halo can be used to test historic drill core and identify zones of high grade mineralization that were intersected or potentially near misses in past drilling. This technique can also be used for testing drill core from holes that are associated with geophysical targets in the region not directly associated with the main zone mineralization.