Chilwa Minerals has identified widespread rare earth element mineralisation in clays directly beneath its Mposa heavy mineral sands deposit in Malawi, revealing potential for a dual-commodity mining operation pending metallurgical test results.
- Rare earth oxides average 525 ppm in basal clays beneath Mposa
- Magnet rare earths constitute about 21% of total rare earth oxide
- Metallurgical test-work underway to assess ionic-adsorption recoverability
- Mineralised clays extend along an 8 km corridor beneath HMS deposit
- Potential for combined heavy mineral sands and rare earth extraction
Widespread Rare Earth Mineralisation Discovered Beneath Mposa
Chilwa Minerals Limited (ASX:CHW) has revealed significant rare earth element (REE) mineralisation hosted in clays directly beneath its Mposa heavy mineral sands (HMS) deposit in southern Malawi. Assay results from 200 samples taken from the basal clay interval underlying the HMS deposit show an average total rare earth oxide (TREO) grade of 525 ppm, with a peak of 987 ppm recorded in hole MPOSD509. Notably, 57% of samples exceeded 500 ppm TREO, indicating consistent mineralisation along an approximately 8-kilometre corridor.
Magnet Rare Earths Enrich the Clay Horizon
The REE-bearing clays contain a valuable mix of magnet rare earth oxides; neodymium, praseodymium, dysprosium, and terbium; that account for about 21% of the total rare earth oxide content. Heavy rare earth oxides represent roughly 19.6% of TREO, with neodymium-praseodymium (NdPr) averaging 102 ppm across samples. This composition aligns with characteristics typical of clay-hosted systems, which are prized for their high-value rare earth components.
Assessing Ionic-Adsorption Clay Potential
While the presence of REE is confirmed, the critical question remains whether these elements occur in a recoverable ionic-adsorption clay (IAC) form. Such deposits are highly sought after globally due to their amenability to low-cost, ambient-temperature leaching using salt solutions, avoiding energy-intensive processing methods required for hard rock or mineral sands. Chilwa is currently progressing ammonium-sulfate desorption test-work at the Australian Nuclear Science and Technology Organisation (ANSTO) in Sydney to determine the leachability and recoverable proportion of the contained rare earths.
Strategic Implications of a Dual-Commodity System
The REE-bearing clay horizon lies immediately beneath the Mposa HMS deposit, opening the possibility of extracting two critical minerals from a single mine site. Chilwa’s Managing Director, Cadell Buss, highlighted the potential operational and capital efficiencies of such a dual-commodity system, including shared infrastructure and permitting. This discovery complements the company’s broader critical minerals portfolio in Malawi, which includes the expanding Mpyupyu HMS deposits and the Nakombe alkaline intrusive target with niobium and rare earths.
Next Steps: Depth Testing and Expanded Drilling
Current samples were collected from the top of the clay unit, which is known to extend tens of metres downward but has not yet been systematically sampled at depth. Chilwa plans further drilling to test the vertical extent of the REE mineralisation beneath Mposa and at other HMS deposits on its license, notably the substantially larger Mpyupyu deposits covering 15 km². This expanded drilling program aims to better define the resource potential of the clay-hosted rare earth system and its integration with existing mineral sands operations.
Bottom Line?
Chilwa’s confirmation of rare earths beneath Mposa could reshape the project’s economics if metallurgical tests validate recoverability, but key uncertainties on deposit depth and leachability remain.
Questions in the middle?
- Will metallurgical test-work confirm a recoverable ionic-adsorption clay form?
- How extensive and continuous is the rare earth mineralisation at depth beneath Mposa?
- Can Chilwa successfully integrate rare earth extraction with its heavy mineral sands operations to create a cost-effective dual-commodity mine?