The primary geology of the Paleoproterozoic Mt Weld Carbonatite Complex, Western Australia.

This article focuses on the detailed geological, mineralogical, and geochemical characterization of the Mt Weld carbonatite complex in the Eastern Yilgarn Craton, Western Australia, which hosts one of the world’s largest Rare Earth Element (REE) deposits. The study, enabled by recent deep drilling, reveals a central ~600 m diameter magnesio- to ferrocarbonatite unit enriched in REE, surrounded by a broader ~1.2 km annulus of Nb-rich calciocarbonatite, with primary REE mineralization dominated by fine-grained monazite and late magmatic REE carbonates. The research indicates minimal horizontal migration of REE and niobium during paleoregolith formation, resulting in an approximate fivefold enrichment of these elements in the weathered paleoregolith compared to the fresh carbonatite. Mt Weld’s geological and isotopic features differ from other major global carbonatite-associated REE deposits, suggesting diverse mantle sources and evolutionary pathways can produce world-class REE ore bodies.