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in the U-Pb systems are in large part a function of the U age (Chipley et al., 2007); older
uraninite is more likely affected by multiple alteration events so that errors obtained in the
U-Pb system are greater. Analytical results are presented in Table 4.4 and the U-Pb
concordia results summarized in Table 4.5.
4.5.4.1. U-Pb geochronology of U-rich minerals by LA-HR-ICP-MS
U 1 uraninite grains from the syn-ore stage at the Coronation Hill deposit have U-Pb
isotopic compositions that define a discordia line with an upper intercept age of 1823±140
Ma and an oldest 207 Pb/ 206 Pb age of 1719±31 Ma (2σ, MSWD=2.6) (Fig. 4.12A). Two
samples from the El Sherana deposit have upper intercept ages of 1819±150 Ma (2σ,
MSWD=7.8; Fig. 4.12B) and 1616±100 Ma (2σ, MSWD=1.02; Fig. 4.12C) and the oldest
207 Pb/ 206 Pb ages of 1810±15 Ma and 1825±90 Ma, respectively. The upper intercept and
oldest 207 Pb/ 206 Pb ages at Coronation Hill are identical to oldest 207 Pb/ 206 Pb ages at El
Sherana and can therefore be interpreted as the estimate formation age for U 1
mineralization.
The U-Pb system in uraninite from various samples from the Coronation Hill deposit
records various periods of post-mineralization alteration coincident with major tectonic
events that have affected the area. These ages include 1654±170 Ma and 1638±160 Ma
(Figs. 4.12D and 4.12E respectively), 1510±10 Ma (Fig. 4.12F), 1266±68 Ma (Fig. 4.12G),
and 837±130 Ma (Fig. 4.12H). Similar post-formation alteration dates of uraninite have
been reported from unconformity-type deposits in the Athabasca (Kotzer and Kyser 1993;
Fayek and Kyser 1997; Cloutier et al., 2009) and Kombolgie basins (Polito et al., 2004).
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