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coincident with the initiation of sedimentation in the McArthur Basin (Wyborn et al.,
1997).
All of these rocks are uncomformably overlain by the Paleoproterozoic fluvial redbed
sandstone successions of the Kombolgie Basin (Ojakangas, 1979; Sweet et al., 1999),
which is part of the McArthur Basin sequence (Kyser et al., 2000). Rocks of the Kombolgie
Basin were intruded by the late Paleoproterozoic 1723±6 Ma Oenpelli dolerite (e.g. Kyser
et al., 2000).
In the South Alligator Valley, the Pine Creek Orogen rocks were deformed during the
1870-1780 Ma Top End Orogen (Needham and DeRoss, 1990). Johnston (1984) and
Valenta (1990) identified three deformation phases. D 1 occurred during the 1890–1870 Ma
Barramundi Orogen (Page and Williams, 1988) and produced meso-scale isoclinal folding
and bedding-parallel cleavage, related to major low-angle reverse faulting, at the base of
the Koolpin Formation. D 2 occurred during the 1860-1840 Ma Nimbuwah tectonic event
and formed regional-scale, northwest trending, upright, tight to isoclinal folds, and a
penetrative axial-plane cleavage. Open, upright northeast-trending southeast-plunging folds
and fault movements formed during D 3 and affected the El Sherana and Edith River Group
rocks. (Valenta, 1991; Lally and Bajwah, 2006).
4.2.2. Uranium mineralization
Uranium deposits of the SAVMF are on or near the El Sherana–Palette fault system
(Fig. 4.1; Valenta, 1990), and were formed in dilatational zones at fault bends or
intersections (Valenta, 1991). The mineralization occurred as vein-type lodes in faults at the
unconformity between the El Sherana Group and the underlying Koolpin Formation
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