Australia is a treasure trove of rare earth elements (REEs), boasting an impressive array of deposits spanning diverse geological settings and periods. These deposits, beyond their geological intrigue, hold significant economic value. A geologist who has studied these fascinating deposits in detail is excited to share their insights. In this comprehensive blog post, the reader will journey through the significant REE deposit types found across the Australian continent, exploring their unique characteristics, geological origins, and the economic significance they bring to the country.
Australian Rare-Earth-Element (REE) Deposits and Prospects
Heavy Mineral Sands:
Australia’s Coastal REE Treasures Australia’s extensive coastlines host some of the country’s most significant REE resources in heavy mineral sand deposits. These deposits, ranging in age from Holocene to Eocene, are mainly concentrated in three key regions: the southwest of Western Australia, the east coast from New South Wales to Queensland, and the inland Murray Basin. The REEs in these deposits are primarily hosted by monazite, a phosphate mineral that contains significant amounts of light rare earth elements (LREEs). Monazite is typically recovered as a by-product of mining other valuable heavy minerals, such as ilmenite, rutile, and zircon, which are sought after for their titanium and zirconium content.
Australia’s heavy mineral sands have been a significant source of REEs for decades, with the Eneabba deposit in Western Australia being a notable example. However, in recent years, the extraction of REEs from monazite has been limited due to the presence of thorium, which poses environmental and regulatory challenges.
Carbonatites:
Igneous Powerhouses of REE Mineralisation Carbonatites, igneous rocks composed primarily of carbonate minerals, are renowned for hosting some of the world’s most impressive REE deposits. Australia is no exception, with several notable carbonatite-associated REE deposits scattered across the continent.
The ~2025 Ma Mount Weld deposit in Western Australia is a prime example, boasting some of the highest REE grades globally at 8.1% rare earth oxides (REO). This deposit is hosted within a thick laterite profile undergoing extensive weathering and supergene enrichment, concentrating the REEs to economic levels.
Other significant carbonatite-associated deposits in Australia include Ponton Creek (WA), Cummins Range (WA), and Mud Tank (NT). These deposits share characteristics similar to Mount Weld’s, with the REEs hosted in the profoundly weathered regolith above the primary carbonatite intrusions.
Alkaline Igneous Complexes:
Hyper-Enriched in REEs In addition to carbonatites, alkaline igneous rock suites that have undergone extreme fractional crystallisation are also known to host polymetallic deposits enriched in REEs, along with other valuable metals such as zirconium, niobium, and yttrium. These deposits typically form from volatile-rich magmas in intraplate tectonic settings, resulting in a unique assemblage of REE-bearing minerals.
Brockman (WA) and Toongi (NSW) are the two most advanced projects in this category. At Brockman, the REEs are associated with exotic silicate, carbonate, and oxide minerals, including aeschynite, bastnäsite, parisite, and rhabdophane. The Toongi deposit, on the other hand, is hosted by a hydrothermally altered trachyte pipe, with the REEs occurring in fine-grained calcium-REE-zirconium silicates and calcian bastnäsite. These alkaline igneous complexes represent a vital exploration target for REEs, as they often contain a diverse suite of REE-bearing minerals and can have high grades.
The Olympic Dam Behemoth:
REEs in Iron-Oxide Breccia Complexes The world-class Olympic Dam copper-gold-uranium deposit in South Australia is a true geological wonder. While primarily known for its immense copper, gold, and uranium resources, the Olympic Dam also contains vast REEs, particularly LREEs.
However, despite its significant REE endowment, the extraction of these elements currently needs to be economically viable, as the value of the other commodities present overshadows them. The REEs at Olympic Dam are associated with the massive hematite-rich hydrothermal breccia system that formed the deposit, with minerals such as bastnäsite, Florence, monazite, and xenotime hosting the REEs.
Similar iron-oxide breccia systems are found in the Curnamona Province of South Australia, such as the prospects in the Mount Painter and Mount Babbage inliers. These deposits share many characteristics with the Olympic Dam and highlight the potential for REE mineralisation in these unique geological settings.
Nolans Bore:
An intriguing geological puzzle, the Nolans Bore REE deposit in Australia’s Northern Territory is hosted by a series of fluorapatite veins and breccias that cut through Proterozoic granite gneiss.
The deposit is characterised by an unusual mineral assemblage highly enriched in LREEs, with minerals such as cheralite, monazite, and bastnäsite dominating the REE mineralogy. Additionally, the deposit is spatially associated with other alkaline rocks and pegmatites in the region, hinting at a possible genetic link.
Despite extensive research, geologists debate the origin of the Nolan’s Bore deposit. Some researchers suggest that the REEs were sourced from the surrounding alkaline rocks and pegmatites, while others propose a more complex genesis involving multiple stages of REE enrichment and remobilisation.
As exploration and research continue at Nolans Bore, geologists are working to unravel the mysteries surrounding this unique deposit and its potential implications for REE mineralisation in similar geological settings.
Conclusion
Australia’s REE deposits are not just a testament to the continent’s rich and varied geological history, but also a beacon of hope for the global REE demand. As the world’s need for REEs continues to surge, driven by their crucial roles in clean energy technologies, electronics, and defence applications, Australia stands tall as a potential key player in the global REE supply chain. With its diverse portfolio of REE deposits and a robust mining industry, Australia has the potential to meet a significant portion of the world’s REE needs. However, the development of these resources is not without its challenges. Environmental concerns, particularly surrounding the radioactive elements often associated with REE deposits and social and regulatory hurdles, must be carefully navigated to ensure responsible and sustainable REE production.
