American Rare Earths (ARR) has updated the Cowboy State Mine (CSM) mineral resource estimate (MRE) for its Halleck Creek rare earths project in the US, incorporating new channel sampling data and the acquisition of exploration drilling permits.
The revised estimate, based on 102 channel samples collected in 2025, reflects changes to the geological resource model for the CSM area.
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The updated MRE for the CSM area now totals approximately 547.5 million tonnes (mt), using a total rare earth oxide (TREO) cut-off grade of 1,000 parts per million (ppm).
Odessa Resource, based in Perth, Australia, has completed the update, incorporating 18 additional channel samples collected during the 2025 exploration season.
These samples enabled the reclassification of approximately 63.9mt from the inferred to the indicated category, as compared to the MRE presented in the February 2025 CSM scoping study.
The samples returned an average value of 5,471ppm TREO.
One standout sample (cs25-rm111) reported a TREO grade of 13,816ppm, around four-times higher than the resource average, the highest assay recorded to date for the Halleck Creek resource.
ARR received two new drilling permits in October 2025 from the Wyoming Department of Environmental Quality Land Quality Division (WDEQ-LQD).
A total of 27 drill-hole locations were granted across the CSM area, intended for in-fill drilling required for future technical studies beyond the forthcoming pre-feasibility study.
Additionally, 29 drill-hole locations were permitted across the Bluegrass Area, a potential exploration target that could add to Halleck Creek’s current 2.6 billion tonnes resource estimate.
Resource estimates exclude areas where ARR does not control mineral resources.
Last year, in August, ARR announced operational and structural changes to expedite the development of the Halleck Creek project in Wyoming.
