Regional geology and metallogeny of the eastern Aileron and Irindina Provinces: A Field Guide

The last five to seven years have seen a major revision in our understanding of the geology of central Australia, with advancements in the field of geochronology redefining the geological framework and history of this area. Prior to about 1995, the eastern Arunta region was thought to consist of moderate to high grade metamorphic Palaeoproterozoic rocks with a complex geological history. This basement was interpreted to be overlain by low grade, mainly sedimentary rocks of the Georgina and Amadeus Basins, which are part of the extensive Neoproterozoic to late Palaeozoic Centralian Superbasin (Walter et al., 1995). However, workers at Adelaide, La Trobe, Australian National and Monash Universities found that rocks of the Harts Range Group (also referred to as the Irindina Supracrustal Assemblage) have a Neoproterozoic to early Palaeozoic depositional age, and were intensely metamorphosed and deformed during the Ordovician (e.g. Miller et al., 1998, Mawby et al., 1999). Subsequent work by the Northern Territory Geological Survey (NTGS) and Geoscience Australia (GA) indicates that the Palaeoproterozoic part of the Arunta region can itself be divided into two discrete provinces: (1) the older (1840-1760 Ma) Aileron Province, and (2) the younger (1680-1610 Ma) Warumpi Province. Further work by the two geological surveys and the Australian National University suggests that in the eastern Arunta region, the Aileron Province can be divided into two sequences, the older (1820-1800 Ma) Strangways Metamorphic Complex and the younger (~1760 Ma) Oonagalabi Assemblage. Definition of these sequences became possible only because of the availability of a critical mass of geochronological data. One of the purposes of this field trip is to illustrate the characteristics of the Palaeoproterozoic basement and the overlying Neoproterozoic to Palaeozoic rocks, with emphasis on the role of modern geochronology in resolving the newly defined terrains. The rocks of the eastern Arunta region have also undergone multiple deformation and metamorphic events that are now being unravelled. This complex history will also be illustrated during the excursion. The second aspect that will be illustrated in this field trip is the metallogeny of the eastern Arunta region. The region is characterised by a large variety of mineral deposits, including lode gold, volcanic-hosted massive sulphide (VHMS), carbonate replacement Zn-Cu, iron-oxide Cu-Au (IOCG), skarn W-(Mo-Cu-Au), carbonatite and aeolian/alluvial garnet deposits. However, most of the known deposits are small, with only the Molyhil W(-Mo-Cu-Au?) deposit, the Mud Tank vermiculite and the White Range Au deposits mined in recent times. Potentially the most economically important deposits are the garnet deposits and the Nolans Bore rare-earth-element (REE)-phosphate-U deposit. This excursion will visit examples of all of these deposit types.