Heavy Mineral Prospectivity in the Eucla Basin

摘要

The Eucla Basin in southern Australia is emerging as an important global source of zircon from heavyrnmineral sands. Understanding the geological evolution of the basin and movement of heavy mineralsrndown peripheral paleovalleys and along paleocoastlines is essential to effectively refi ne explorationrnstrategies for heavy minerals in the basin. Integration of geoscientifi c datasets in a GeographicrnInformation System (GIS) environment has proved to be effective in reconstructing depositionalrnenvironments along the Cenozoic basin margin and in tracing the buried paleorivers that oncerndrained broad areas of the Archean-Paleoproterozoic Yilgarn and Gawler cratons, the dominantlyrnMesoproterozoic Musgrave and Albany-Fraser Provinces, and the Neoproterozoic-Early PaleozoicrnOffi cer Basin. Sea level highstands during the late Middle Eocene (39 - 36 Ma) are associated withrnformation of the Ooldea coastal barrier complex and the zircon-rich heavy mineral deposits at Jacinth,rnAmbrosia and Tripitaka. More extensive transgression during the Late Eocene (36 - 34 Ma) builtrnthe complex Barton shorelines that host the Cyclone deposit and the extensive ilmenite-dominatedrnoccurrences of the Barton West prospect. Multi-generation reworking of the source sands is indicatedrnby the high proportion of deposits that are zircon-rich relative to titanium minerals. The agerndistribution of zircon grains in heavy mineral concentrates from the Ooldea and Barton barrier systemsrnpoints to the Musgrave Province as the predominant ultimate zircon source. Paleorivers dischargingrnalong the northern basin margin presumably carried a sediment load that was then redistributed byrneasterly longshore drift to build the extensive coastal sand deposits along the northern and easternrnbasin margin. The south-eastern extension of these deposits was reworked during Miocene-Pliocenern(15 - 2 Ma) times into a series of regressive strandlines that show angular discordance with the Eocenerncoastlines. This discordance is consistent with evidence for long-wavelength tilting of the Australianrncontinent from Middle Miocene times, as the continent drifted toward a dynamic topographic lowrninduced by convective mantle processes associated with the South East Asia subduction systems.rnThe Dromedary and Gulliver’s deposits probably formed at this time. Ongoing research is focusedrnon the geological features of the basin that infl uence heavy mineral transport, concentration andrnpreservation, and the processes leading to deposits with high zircon content.