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Hem: hematite, Kfs: potassium feldspar, Ms: muscovite, Mnz: monazite, Py: pyrite, Qtz:
quartz, Src: sericite, Ttn: titanite, U: uraninite.
2.4.4. Geochronology of uraninite and isotopic systematics
The various generations of uraninite that formed during different stages of
deformation have been paragenetically constrained (see previous section), and analyzed.
For example the cataclasite-type ±U 1 and early-vein type ±U 2 uraninites observed at the
Ace-Fay deposits formed at depth different from the breccia-type U 4
uraninite. The
granite-related metasomatic-type U 3 uraninite is observed at Gunnar wherein moderate
uranium mineralization is derived from Na-metasomatism of the Gunnar granite prior to
brecciation. The volcanic-type ±U 5 uraninite cuts across the ductile-brittle shear zones at
Cinch Lake and Ace-Fay deposits and is spatially related to the Martin Lake mafic dikes.
Late ±U 6 uraninite veins interpreted as related to the Athabasca Basin, cross cut all types
and have a distinct alteration assemblage.
2.4.4.1. U-Pb and Pb-Pb geochronology of U-rich minerals by LA-HR-ICP-MS
Paragenetically constrained uraninite grains from the six stages of uranium
mineralization have been dated by LA-HR-ICP-MS (Table 2.1). Results of the U-Pb
concordia are summarized in Table 2.2a. The oldest 207 Pb/ 206 Pb ages are likely to be closer
to the initial formation age because Pb/Pb ratios in uraninite are less susceptible to
resetting by younger fluid events than are the U/Pb ratios (Collins et al., 1954). The
relatively high error margins for U/Pb isotopic ratios reflect uraninite heterogeneity
(Kotzer and Kyser, 1993; Chipley et al., 2007), which is indicated by the mottled and
pitted texture observed in Back-Scattered Electron Microscopy (BSEM) images of
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