Multi-disciplinary characterisation of the splinter rock clay-hosted REE prospect, Western Australia

• The study integrates landscape evolution, mineralogy, geophysics, and geochemistry to understand the weathering processes responsible for REE enrichment in the Splinter Rock project area in southern Western Australia. • Three distinct regolith units — saprock, saprolite, and transported cover — were identified from drill holes, with the highest REE concentrations found in the in-situ saprolite. • Changes in conductivity (AEM inversions) and kaolinite crystallinity (hyperspectral data) were instrumental in identifying key in-situ and transported interfaces within the regolith. • Combined spectral, XRD and SEM mineralogy has identified discrete REE-bearing mineral phases, including REE phosphates, Al-REE Phosphates and REE carbonates. Global efforts to find rare earth elements (REEs – including La to Lu, Y, and Sc) are increasingly focusing on clay-rich layers found in weathered landscapes, especially those formed from alkaline granites. These REEs are vital for modern technologies. In southern Western Australia, the Esperance region is now seen as a promising area for REEs in clay-rich regolith. However, how natural processes and climate have moved REEs into these materials is not fully understood. This study used a multi-disciplinary approach to better understand the Splinter Rock REE project. We combined detailed regolith mapping with airborne electromagnetic (AEM) surveys to study the regolith and identify different clay layers. We also combined detailed geochemical and spectral mineralogy to analyse the regolith layers and figure out which ones are most important for REE accumulation. At Splinter Rock, three main regolith layers were identified, starting from the bedrock and moving upward: Saprock – the weathered rock just above the bedrock. Saprolite – a deeper, in-place weathered layer. Transported sediments – materials moved and deposited in low-lying areas, often along palaeo-drainage. The boundaries between these layers helped distinguish between materials formed in situ and those transported from further afield. The highest REE concentrations were found in the saprolite layer, especially near its top. Some enrichment in REEs was also found at the base of the transported sediments, but in much lower concentrations. To explore REEs effectively in these terrains, it’s important to understand how physical and chemical processes move and concentrate these elements. By combining knowledge of landscape evolution models with data on mineralogy, geochemistry, and geophysics, it is possible to better understand how REEs become enriched in certain areas. REE phosphate phases were detected with no direct evidence for weakly bound REEs; the phosphate minerals increase in concentration with depth. Further detailed work is recommended to determine whether the REE minerals are primary (hard to leach) or secondary (easier to leach). Mineralogy and leachability will be key for these types of prospects to determine future economic potential.