Ark Mines Ltd (ASX: AHK), an Australian mineral exploration and development company focused on critical minerals, including rare earth elements and heavy minerals, has announced highly encouraging initial metallurgical testwork results for its Sandy Mitchell Rare Earth Elements and Heavy Minerals Project in North Queensland. The company reported on 8 October 2026 that scoping-level tests conducted by the Australian Nuclear Science and Technology Organisation (ANSTO) have confirmed the high amenability of its Sandy Mitchell monazite concentrate to conventional processing methods.
The ANSTO testwork demonstrated impressive light rare earth (LRE) extraction rates, achieving between 98% and 99% from milled concentrate using acid bake and water leach methods. Dysprosium extraction also reached up to 99% in these tests. The monazite concentrate itself, which assayed 48.7% total rare earth oxide (TREO) or 50.2% TREO plus yttrium, proved to be very well liberated, with 93% reporting to the 90% to 100% liberation band. Furthermore, caustic conversion techniques yielded 97% phosphate removal, with a subsequent hydrochloric acid leach delivering approximately 98% LRE extraction. These results are specific to the monazite concentrate and do not include the recovery of monazite from ore.
Managing Director Ben Emery commented on the significance of these findings, stating that the high extraction rates validate the effectiveness of conventional processing for their high-grade monazite concentrate. Mr Emery highlighted the operational flexibility gained from the concentrate’s amenability to both acid bake and caustic conversion routes as the company moves towards producing a mixed rare earth carbonate (MREC) product. Ark Mines is now advancing to larger-scale acid bake testing, which is currently underway, to generate leach liquor for subsequent impurity removal and rare earth product precipitation.
