Ark Mines Boosts Sandy Mitchell Resource to 379Mt
Ark Mines expands its Sandy Mitchell rare earths resource by 428% to 379.4Mt, with 97% classified as Measured and Indicated.
Key points
- Sandy Mitchell resource grows 428% to 379.4Mt at 5,430ppm MzEq, with 97% in Measured and Indicated categories.
- Stage 3 drilling expands the mineralised domain to 23.3km², covering 14% of the 169km² tenure area.
- In situ content includes 508,000t monazite and 140,000t rare earth oxides plus yttrium, ahead of a 2027 PFS.
Ark Mines (ASX: AHK) has revised the mineral resource estimate at its Sandy Mitchell project in North Queensland, increasing total tonnage by 428% to 379.4 million tonnes. The deposit now contains an average grade of 5,430ppm monazite equivalent (MzEq). According to Stockhead, the company identifies this as the largest rare earth resource hosted in a residual heavy mineral sand derived from a metamorphic basement complex under the JORC 2012 Code.
The update is driven by Stage 3 drilling, which expanded the interpreted mineralised domain from 4.05 square kilometres to 23.3 square kilometres. This footprint represents approximately 14% of the company’s 169-square-kilometre tenure. The resource comprises 73.2 million tonnes of Measured material, 296.4 million tonnes of Indicated material, and 9.8 million tonnes of Inferred material. With 97% of the tonnage now in the higher-confidence categories, the company states this provides a stable foundation for its next study phases.
Drilling expands mineralised domain footprint
The tonnage increase results from extending the tested footprint rather than grade discovery. The previous October 2024 estimate of 71.8 million tonnes was entirely classified as Measured. The new estimate keeps the Measured inventory broadly unchanged at 73.2 million tonnes but adds 296.4 million tonnes of Indicated material defined by 218 valid drill holes. These holes returned heavy mineral sands from the surface to metamorphic bedrock, confirming a consistent mineralisation profile across the expanded area.
The geological model describes a shallow, flat-lying sheet averaging about 11 metres in depth. Ark Mines notes that grades are evenly distributed, without significant surface lag enrichment or basal gravity settling. The company also revised its calculation methodology, expanding the MzEq formula from eight to eleven minerals and raising the lower cut-off from 700ppm to 1,957ppm. This methodological change means the new grades are not directly comparable to the previous estimate, though the physical scale has grown substantially.
In situ rare earth content details
The updated resource contains an estimated 508,000 tonnes of monazite and 140,000 tonnes of total rare earth oxides plus yttrium in situ. These figures are pre-metallurgical recovery. Managing Director Ben Emery stated that the scale and consistency of the deposit strengthen the project’s foundation for advancing to a Pre-Feasibility Study. He emphasized that a shallow, free-digging deposit of this size is straightforward to plan around, supporting the company’s confidence in the upcoming technical assessments.
Next steps for technical studies
Ark Mines plans to complete metallurgical testwork with IHC Mining and release an updated Scoping Study incorporating the revised resource and recovery data. The company also intends to conduct infill drilling to upgrade the Inferred area in the central south-east, subject to pastoral access. Following this, the exploration target will be restated on the new MzEq basis. A Pre-Feasibility Study with third-party processing specialists is targeted for completion in calendar year 2027.
