Uranium ore-forming systems of the - Geoscience Australia

Uranium ore-forming systems of the Lake Frome region2.2.1 Paleozoic – Arrowie BasinIn the study area the Arrowie Basin is represented by the Moorowie and Yalkalpo ‘Synclines’ orsub-basins which contain thick unfolded strata to the west and east, respectively, of the BenagerieRidge (Gravestock and Cowley, 1995, Figs. 2.1, 2.2). The Arrowie Basin is comprised ofshallow marine sedimentary siliciclastic and carbonate deposits. The succession has beensubdivided into three sequences: Є1, a carbonate dominated sequence that progrades intoevaporite facies at the top the sequence; Є2, a redbed and carbonate sequence, and Є3, a thickpackage of red sandstones that coarsen up-sequence (Drexel, et al., 1993). Between sequences Є1and Є2 minor episodic tectonic and volcanic activity occurred.Petroleum exploration in the Moorowie sub-basin delineated a number of ‘shows’ but nosignificant discoveries have been made.Figure 2.2: Stratigraphic relationship diagram for the Arrowie Basin showing the correlation betweenlithologies and sequences. Source: Gravestock and Cowley (1995).2.2.2 Mesozoic – Eromanga BasinThe Eromanga Basin is an intracratonic sag basin covering some million square kilometres ofeast-central Australia (Fig. 2.3). A detailed stratigraphic framework for the Eromanga andadjacent basins was constructed by Gravestock et al. (1986), Krieg (1995) and Radke et al. (2000),among others. The Eromanga Basin has been subdivided into three main stratigraphic sequences:a lower non-marine sequence (early Jurassic to earliest Cretaceous), a middle marine sequence(early Cretaceous) and an upper non-marine sequence (late Cretaceous).The lower non-marine sequence consists of medium-grained sands deposited in a braided fluvialenvironment, followed by fine-grained lacustrine sands, silts and shales. Volcaniclastic material ismore abundant in the lower non-marine succession to the north and east of the Frome Embayment,Page 14 of 151