Uranium ore-forming systems of the - Geoscience Australia

Uranium ore-forming systems of the Lake Frome region8.1.2 Energy and timingThe timing of uplift in the hinterland to the Frome Embayment and Callabonna Sub-basin is criticalin the evolution of uranium mineral systems, partly because topography provides the potentialenergy to drive fluids down into basins, and partly for reasons involving effective leaching of sourceareas, discussed above. The three proposed episodes of uplift and exhumation were potentially thetriggers for the formation of major basin-hosted uranium systems (Fig. 3.1). Optimal conditionsexisted with the coincidence in time and space of this source of energy, the availability of readilyleacheable uranium in deeply weathered uplifted basement, and the permeability architecture anddepositional gradients (reductants) already present in paleochannels within the Eyre and NambaFormations (Fig. 1.6). The three hypothetical episodes of uranium system development in the LakeFrome region are summarised below.1. Late Mesozoic-early Cenozoic uranium mineral system: Post-Eromanga Basin uplift of basementthat was deeply weathered during the Mesozoic could have potentially triggered gravitationallydrivenflow of uranium-rich groundwaters into aquifers of the Eromanga Basin. The apatite fissiontrack results of Mitchell et al. (2002) from the Mt Painter Inlier suggest regional denudation from~90 Ma until the Paleocene, when deposition of the Eyre Formation commenced. If suitablereductants were available in aquifers of the Eromanga Basin, then uranium mineralisation potentiallycould have formed in the Late Cretaceous or Paleocene.2. Eocene-Oligocene post-Eyre Formation uranium mineral system: Cessation of deposition of theEyre Formation in the Late Eocene (~35 Ma) and development of a disconformity is roughlycontemporaneous with the initiation of intraplate stresses due to changes in motion of the Australianplate (Célérier et al., 2005). Uplift and exhumation in the Paleocene was inferred from fission trackdata from the Mt Painter Inlier (Mitchell et al., 2002), prior to deposition of the Namba Formation.This tectonism and resultant topography may have triggered fluid flow from basement areas (at leasttwice deeply weathered) into the Eyre Formation, utilising south-to-north oriented paleochannels. Inthis hypothetical uranium mineral system, fluids would have been confined by aquitards andaquicludes within the Eyre Formation, and mineralisation would have formed in the late Eocene toearly Oligocene (~35-28 Ma).3. Pliocene-Pleistocene post-Namba Formation uranium mineral system: the most recent majorperiod of uplift and exhumation of basement rocks in the Lake Frome region occurred since ~5 Ma,producing most of the present day relief in the Northern Flinders Ranges and Mt Painter Inlier.Basement that was deeply weathered in the period ~10-20 Ma would now be available for leachingof uranium and transport into permeable units of the Namba Formation, Eyre Formation orEromanga Basin.8.1.3 Permeability architecture and fluid flowFault architecture that developed during the Proterozoic controlled the formation of the ArrowieBasin, including the Moorowie and Yalkalpo sub-basins to the west and east, respectively, of theProterozoic Benagerie Ridge. North-south trending faults as well as northeast-southwest trendingfaults imaged in seismic data controlled the architecture of Cambrian half-graben.Seismic data show that several reactivated Cambrian faults cut upwards through the MesozoicEromanga Basin sediments and also cut Cenozoic sediments. Some modern topographic featuresPage 104 of 151