Thorite in fault zones of a granitic pluton, Atikokan, Canada: Implications for nuclear fuel waste disposal

Thorite, identified under a scanning electron microscope, occurs in fault zones investigated throughout the Eye-Dashwa pluton. The undeformed nature and development of corona structures around the thorite suggest its growth during post-kinematic conditions. ThO 2 and SiO 2 constitute the major oxides in the thorite found in the pluton, while Ce 2O 3, Fe 2O 3, CaO, UO 2, P 2O 5 and S are present in minor amounts. Thermodynamic analysis shows that this thorite is a stable phase in contact with ambient groundwater in granitic environments. The antiquity (∼2.3 Ga) and the chemical inertness of this thorite in contact with granite groundwater can be used as an example of a natural analogue for some aspects of nuclear fuel waste disposal.