Australian critical metal exploration for analogues of Chinese ionic-clay REE deposits

Abstract

The clean energy transition has focused attention on the critical metals required for manufacture of new energy technologies. The extremely heterogeneous distribution of critical metal mineral deposits requires that countries must make new discoveries of key critical metals to avoid potential future geopolitical risks. Although Australia has REE resources, they are mainly of LREEs, so deposit styles with significant HREEs are key targets. The most obvious are the so-called ionic-clay REE deposits of southern China that are the major global suppliers of HREEs. Mineral exploration in Australia using the Chinese model is producing hitherto unrecognized REE concentrations, here termed regolith-hosted REE mineralization, in a variety of regolith types in several weathering environments, particularly in Western and South Australia. Amongst these has been the discovery of near-surface, regolith-hosted REE mineralization in the Albany-Fraser Orogen which has the potential to complement REE production from the giant Mount Weld carbonatite and other monazite-sand deposits in Western Australia. Widespread near-surface, regolith-hosted REE mineralization is present over an area of 12,000 km² in the Esperance District. As much of this area is beneath barren Eocene-aged cover clays, all the new REE discoveries have been made, and are being delineated using shallow drilling, to depths of less than 80 m. The exploration implication is that the search space for regolith hosted REE deposits in Western Australia remains immature. These recently discovered deposits have both similarities and contrasts with geological features of ionic clay hosted REE deposits in China. Similarities include their apparent paragenesis and geometry, particularly their blanket morphology, sub-horizontal and gentle dips, and the common, but not exclusive, relationship with felsic basement terranes. However, Western Australian prospects are related to Upper Cretaceous to Eocene climates rather than more recent weathering under sub-tropical conditions. Whether the deposits can be developed to production remains unclear, with project economics tied closely to the efficacy of mineral processing technologies that target high REE extraction rates and recoveries.