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Plutons Event at 1.4 Ga (Barinek et al., 1999), the 1.27 Ga Mackenzie mafic dike swarms
(Ernst and Buchan, 2001b) coincident with the final breakup of the Nuna supercontinent
(Rogers and Santos, 2002), the Grenville Orogen at ca. 1.2–0.9 Ga (Carr et al., 2004)
reflecting the assembly of Rodinia (Moores, 1991), the diachronous breakup of Rodinia at
0.7-0.8 Ga and 0.6-0.5 Ga (Li et al., 2008), and the Appalachian Orogen at 0.3-0.4 Ga
linked to Pangea assembly (Cocks and Torsvik, 2002). Lower intercept ages in the U-Pb
system reflect tectonic activity during the Cordilleran Orogen (Molnar and Atwater, 1978)
and recent reactivation during the Pleistocene glaciations (Adams, 1989).
In the South Alligator River area, deposits also have been significantly affected by
late fluid events related to fault reactivation during successive regional thermotectonic
events that occurred over a period of at least 1.8 Gyrs. The first coincided with the timing
of the ca. 1720 Ma Oenpelli dolerite intrusion (Sweet et al., 1999). Uraninite from the
Coronation Hill deposit record the Isan Orogen (1600-1580 Ma) in northern Australia
(Hand, 2006), shortly after formation of unconformity-related U mineralization in the
Kombolgie Basin (Polito et al., 2004). From the Mesoproterozoic to recent time, far field
tectonic events affected deposits in the South Alligator River area as discussed in a greater
detail in Chapter 4.
Electron microprobe analyses of various chlorite phases in deposits of the
Beaverlodge and South Alligator River areas indicate also that these deposits were
subsequently altered to low-temperature, recording the effect of late fluid events. These
events may represent incursion and circulation of meteoric water through fault zones
(Kotzer and Kyser, 1995). Hydrogen isotopic composition of chlorites in the Beaverlodge
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