Uranium ore-forming systems of the - Geoscience Australia

Uranium ore-forming systems of the Lake Frome region8.3 EXPLORATION CRITERIAExploration criteria for basin-hosted uranium mineral systems in the Lake Frome region aresummarised in Table 8.1. In addition, the hypothesis of three basin-hosted uranium systems in theLake Frome region (Fig. 8.1) leads to the following implications for exploration.1. Late Cretaceous-Early Cenozoic uranium mineral system: Post-Eromanga Basin uplift ofbasement that was deeply weathered during the Mesozoic is predicted to have triggeredgravitationally-driven flow of uranium-rich groundwaters into aquifers of the EromangaBasin. Where suitable reductants were available, uranium mineralisation could have formedin the late Cretaceous or Paleocene. These systems potentially were large due to the effectsof up to three episodes of oxidised fluid flow, although recently reversed fluid flow mayhave destroyed the early uranium mineralisation. Sub-basins isolated from present daygroundwater flow in the Eromanga Basin may be most prospective for preservedmineralisation.2. Late Eocene-Oligocene uranium mineral system: Post-Eyre Formation uplift andexhumation inferred in the Mt Painter Inlier may have triggered fluid flow from basementareas (deeply weathered at least twice) into the Eyre Formation, utilising broadly south-tonorthoriented paleochannels. In this uranium mineral system, fluids would have beenconfined by aquitards and aquicludes within the Eyre Formation, with mineralisation in thelate Eocene to early Oligocene (~37-28 Ma). Larger systems than in the Namba Formationare possible particularly to the north, due to the opportunity for the Eyre Formation to haveexperienced at least two episodes of oxidised fluid flow by this time.3. Pliocene-Pleistocene uranium mineral system: Post-Namba Formation uplift andexhumation of basement rocks in the Lake Frome region occurred since ~5 Ma, producingmost 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 forleaching of uranium and transport into permeable units of the Namba Formation, EyreFormation or Eromanga Basin. The larger systems may exist to the north, wherepaleochannels converged or met paleo-lake systems.The Beverley deposit formed during the latest system (i.e., since ~5 Ma), whereas the Four Mile Eastdeposit may have formed during either the second or third ore-forming episode (i.e., since ~35 Ma).During each of these episodes of uranium mineralisation, multiple styles of uranium mineralisationwere possible, including tabular styles controlled by sub-horizontal redox boundaries, ‘roll-front’styles, and structurally controlled styles proximal to faults where mixing of oxidised and reducedfluids may have been important. These styles are illustrated schematically in Figure 8.1.8.3 RECOMMENDATIONS FOR FURTHER WORKThe following further work is recommended to better constrain and test the hypotheses outlined inthis study. Provenance studies of sedimentary sequences hosting mineralisation, to test and refinemodels of sediment transport and paleochannel development. Mapping redox interfaces within basin sediments to test whether mineralising fluids flowedfrom south (or southwest) to north (or northwest) in the Eyre and Namba Formations.Page 111 of 151