Uranium ore-forming systems of the - Geoscience Australia

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Uranium ore-forming systems of the Lake Frome regionpossibly sourced from volcanism in the east (Krieg, et al. 1995). The middle marine sequencecomprises basal sands, of which the Cadna-owie Formation occurs in the Frome Embayment,prograding into deeper water shales and muds. Felsic volcanic detritus from the U-rich GawlerRange Volcanics also occurs in the Mt Anna Sandstone, equivalent to the Cadna-owie Formation,along the southwestern margin of the basin (west of Lake Torrens). Of the shales and muds, theCretaceous Bulldog Shale is the uppermost of the Eromanga Basin units present in the study area.It is described by Ellis (1976) as monotonous blue-grey silty clay. The upper non-marinesequence, the Winton Formation, does not occur in the Frome Embayment. It comprises athousand-metre thick package of sediments (sandstones, shales and siltstones) that was depositedin a low-energy fluvial to lacustrine environment. Detrital feldspars and ferromagnesian mineralsare thought to have been sourced from active volcanoes in eastern Australia (Krieg et al., 1995).The Great Artesian Basin (GAB) is synonymous with the Eromanga Basin, although the aquiferunits are not coincident with the sedimentary limits. The main artesian aquifer comprises anumber of formations below and including the Cadna-owie Formation, whereas the upperconfined aquifer occurs within the upper non-marine sequence (Krieg et al., 1995). Artesianwaters from the GAB debouch onto the surface at a number of mound springs in the Lake Fromeregion.Organic matter is abundant in several units of the Eromanga Basin, including the Bulldog Shale inthe Frome Embayment. Coal seams are present in the lower and upper non-marine successions(e.g., Birkhead Formation, Winton Formation). In the Moomba region to the north, oil and gashave been recovered from almost all of the lower non-marine units. While much of thesehydrocarbons are believed to have migrated upwards from the Cooper Basin, some units in thelower marine Eromanga Basin contain abundant organic matter and are oil mature (Krieg et al.,1995). It is unclear whether Mesozoic rocks in the Frome Embayment experienced the migrationof hydrocarbons derived either from within the Eromanga Basin or from the underlying Cambrianstrata.Page 15 of 151
Uranium ore-forming systems of the Lake Frome regionFigure 2.3: Extents of Cooper and Eromanga Basins in South Australia. Source:Krieg (1995).2.2.3 Cenozoic – Lake Eyre BasinThe Lake Eyre Basin was created by tectonic subsidence commencing in the late Paleocene withepisodic fluvial and lacustrine sedimentation occurring in the basin until the present day (Callen etal., 1995). The Eyre Formation is the basal unit of the Lake Eyre Basin and unconformablyoverlies the Eromanga Basin. Sedimentation spanned the latest Paleocene to the Middle Eocene.The Eyre Formation comprises pyritic, carbonaceous mature sand of varying grain size rangingPage 16 of 151
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