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culminating with the formation of Rodinia (Wingate et al., 2002; Li et al., 2008). Alteration
of uraninite at ca. 1380 Ma and 1100 Ma is also recorded at Jabiluka and Nabarlek (Gulson
and Mizon, 1980; Polito et al., 2004).
Figure 4.16. Distribution of 207 Pb/ 206 Pb ages for 176 uraninite grains along with the timing of
various U mineralization and tectonic events that affected the South Alligator Valley area.
Alteration peaks at ca. 1000 Ma and 800 Ma (Fig. 4.16) are consistent with periods of
Rodinia breakup (Dalziel, 1991; Li et al., 2008) with the rifting of Laurentia and Gondwana
along the eastern margin of Proterozoic Australia at ca. 900 Ma-850 Ma and formation of
the Paleo-Pacific Ocean (Wingate and Giddings, 2000; Harlan et al., 2003b). These
alteration events are also recorded in uraninite from Ranger, Jabiluka, Nabarlek and
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