Canada accounts for 15% of the world’s uranium production (World Nuclear Association). The Athabasca Basin in northern Saskatchewan Canada contains a number of high grade, uranium ore deposits which occur at, or immediately below, an unconformity between Archean and Paleoproterozoic metasediments and intrusive rocks and overlying Proterozoic sandstones. The uranium ores are largely composed of high concentrations of uraninite and Pitchblende with naturally occurring 238U/235U ratios. U- 236 (half-life of 23.42 Myr) will be produced when 235U absorbs a neutron and the nucleus does not fission. Because it is so long lived, a small amount 236U can be maintained at equilibrium levels in the natural uranium ores. One of the main questions of this research is whether or not these equilibrium levels reflect higher grades or larger amounts of uranium minerals as a result of elevated neutron fluxes from 238U and subsequent neutron absorption on 235U. As well, are there other elements within the system that will absorb these neutrons, thereby reducing that which will impinge on 235U. In this study, we have estimated the amount of 236U that is produced by calculating the neutron flux from uranium and evaluating the effects of spatially related elements such as B, Sm and Gd using their elemental neutron cross- sections and abundances. In this project we have calculated and simulated theoretically the production of 236U and then test the theoretical calculations using measurements of uranium isotopes by accelerator mass spectrometry (AMS). Once we understand the factors controlling the 236U concentration, we hypothesize that the relationship between 236U and 238U can be used as a geochemical vector within uranium exploration, with the equilibrium level possibly distinguishing between primary mineralization and remobilization and reprecipitation of this U within spatially associated secondary U mineralization.

The first comprehensive analysis of surface waters in the Labrador Sea for 236U was completed via Accelerator Mass Spectrometry. Through the analysis of 236U the method for AMS measurement was fine-tuned to allow for more precise results. Surface samples for the anthropogenic isotopes 137Cs and 129I were also collected along with two depth profiles of 129I. Samples were also collected in the Beaufort Sea and analyzed for the aforementioned isotopes. It was found that anthropogenic 129I from reprocessing plants is easily discernible at different concentrations among water bodies in both the Labrador and Beaufort Sea. 137Cs in surface waters is close to global fallout levels with no discernable influence from reprocessing plant inputs, but follows a similar trend to that of 129I with depth in the Beaufort Sea. 236U among surface waters in the Labrador Sea did not follow the same trends as 129I but had concentrations indicative of a mix of global fallout as well as reprocessing plant influenced waters. 236U samples from the Beaufort Sea were contaminated by an unknown source of 236U and were inconclusive but were reproducible and allowed for continued development of the AMS analysis methodology.