Rare Earth Elements of Sarawak: An Overview

Rare earth elements (REEs) are indispensable to permanent magnets, electronics, catalysts and defence systems, but the geological occurrence of REEs does not by itself establish an economically recoverable resource. This review critically evaluates the evidence for REEs in Sarawak, with particular emphasis on the Riih area of Serian, West Sarawak. The strongest published Sarawak-specific evidence is a 2025 study of two laterite profiles developed over basaltic trachyandesite of the Serian Volcanics. The parent rock contained approximately 209 mg kg⠻¹ total REE, whereas intensely weathered material (chemical index of alteration, CIA, 99–100%) reached 1,715.98 mg kg⠻¹. Kaolinite dominance, the reported absence of discrete REE minerals in analysed laterite, and ion-exchangeable REY recoveries exceeding 75% in selected samples support an ion-adsorption interpretation. These results demonstrate a mineralised weathering system at the sampled locality; they do not yet establish lateral continuity, tonnage, a compliant mineral resource, or commercial viability. Elsewhere in Sarawak, granitoids, volcanic rocks and alluvial systems are geologically plausible source or host environments, but published deposit-scale evidence remains sparse, and claims for Bau or statewide HREE resources should be treated as exploration hypotheses. The review integrates Sarawak geology, ion-adsorption processes, mineralogical and geochemical controls, exploration and analytical methods, economic considerations, environmental risks and Malaysia’s evolving regulatory framework. It proposes a staged research programme centred on representative regolith mapping, size- and horizon-controlled sampling, sequential extraction, hydrometallurgical testing, hydrogeological baselines and transparent resource classification. Sarawak has credible REE prospectivity, but responsible development requires converting promising geochemistry into reproducible geological, metallurgical, environmental and socioeconomic evidence.