An inventory of peralkaline rocks in Queensland for evaluation of REE enrichment potential

Highly fractionated peralkaline rocks are globally important sources of rare earth elements and other critical or new economy metals. Such metals are vital for technological advancement and a transition to a clean energy future and are therefore predicted to rise in demand. These are non-traditional commodities in Queensland and it is therefore important to gain a greater understanding of the distribution of peralkaline rocks and the potential for igneous suites to host highly fractionated, enriched components. A critical first step is to compile an inventory of the distribution, geochemistry, mineralogy and geochronology of these rocks. Rocks units that include peralkaline compositions were emplaced in post orogenic, rifting or plume-related settings during late Triassic or younger magmatic events. These crop out in a broad belt between the Bowen-Mackay area and the southern Border Ranges. They include large A- and I-type plutons, pyroclastic deposits and clusters of smaller rhyolitic to trachytic domes, lavas and shallow intrusions. Three broad age categories are recognised: late Triassic, Cretaceous, and Cenozoic (dominantly Paleogene). Some of the Cretaceous units, and many of the Cenozoic units exhibit enrichment in high field strength and rare earth elements. The Peak Range Volcanics are the most highly enriched but significant potential exists in other units if more thorough sampling can be completed and more highly fractionated rocks found. More detailed geological mapping, combined with expansion of the geochemical, geochronological and isotopic database is required to understand the distribution and crustal-scale controls on peralkaline magmatism.
Open-Access Online Publication: March 03, 2023