Lead Isotopes in Exploration for Basement-Hosted Structurally Controlled Unconformity-Related Uranium Deposits: Kiggavik Project (Nunavut, Canada)

Abstract

Pb-isotopes have been proposed as pathfinders for sandstone-hosted unconformity-related U deposits, with isotope ratios providing information on mineralization timing and element remobilization and migration. Pb-isotopes proximal to mineralization display radiogenic signatures, often with ‘excess Pb’ suggestive of derivation from greater U concentrations than are currently present. The U deposits in the Kiggavik project area (west of Baker Lake, NU, Canada) are basement-hosted, contain several generations of pitchblende mineralization, display a strong structural control, and are located in fault-related fracture systems and foliation-parallel veinlets. Drill core samples were analysed by Inductively-Coupled Plasma-Mass Spectrometer (ICP-MS) for Pb isotopes following multi-acid total-digestion, reverse Aqua Regia partial-digestion, and weak-acid-leach attacks, to evaluate the utility of the respective dissolution methods in Pb-isotope pathfinder geochemistry. Partial-digestion results are similar to weak-acid-leach results, indicating that interpretation of Pb-isotope signatures can be carried out from partial-digestion data if weak-acid-leach data are unavailable. Application of this pathfinder method at Kiggavik shows that Pb-isotope ratios display systematic trends useful for exploration vectoring. Uranium-content-adjusted 206Pb/204Pb ratios and 206Pb/204Pb ‘excess-lead’ data highlight anomalous isotopic values. 207Pb/206Pb ratios display downhole trends complementary to location of mineralization. Three-dimensional (3D) distributions of Pb-isotope data at the Contact U prospect show systematic trends and form halos around the mineralization. Isotopic footprints are limited to <50 m from the mineralization outline, reflecting host-rock and structural control, but indicate areas with elevated potential for U mineralization and provide vectoring information within basement lithologies.

Combined U-Pb isotopic signatures of U mill tailings from France and Gabon: A new potential tracer to assess their fingerprint on the environment

“…These isotopes are widely used in geosciences and environmental sciences as a powerful source tracers, as they do not fractionate significantly during geological processes or chemical processes occurring in industrial plants. Moreover, radiogenic lead isotopes have commonly been used for U-ore exploration purposes (Dickson et al, 1985, Dickson et al, 1987Quirt and Benedicto, 2020) and also in a few studies related to isotope fingerprinting of the dissemination U mine material in the environment (France: Cuvier et al, 2016;Gourgiotis et al, 2020;Martin et al, 2020;Worldwide: Bollhöfer et al, 1989;Coetzee et al, 2006;Santos and Tassinari, 2012;Dang et al, 2018;Liu et al, 2018), as U-rich minerals (e.g. ~88 wt.…”