OD6 Metals (ASX: OD6) says ANSTO has delivered higher-than-expected metallurgical magnet rare earths recoveries of up to 86 per cent following testwork on 11 clay samples from its Grass Patch deposit in Western Australia’s deep south.
The samples were selected from three key areas within the 2248-square-kilometre Grass Patch project, about 30km north of Esperance, where the company’s 93-hole reconnaissance drilling early last year identified rare earths mineralisation.
That program determined grades of up to 3340 parts per million total rare earths oxides (TREO), containing up to 38.5 per cent of the magnet rare earths oxides (MREO) that are currently more valuable owing to their essential requirement in ultra-efficient electric motors and generators such as wind turbines.
Importantly, the drilling encountered clay thicknesses ranging from 3m to 20m, but as thick as 59m. Three prospects – Belgian, Circle Valley and Scaddan – were identified as warranting further evaluation, including metallurgical testwork to determine recoveries.
Whilst our focus over the last 12 months has been firmly on our world-class Splinter Rock Project, we have continued to leverage that work and apply it at Grass Patch. Testwork results confirm further targeted drilling should occur primarily at the Belgian, Circle Valley and Scaddan Prospects.
OD6 Metals managing director Brett Hazelden
Management says the testwork on samples from the priority areas, undertaken by ANSTO (the Australian Nuclear Science Organisation), achieved excellent recoveries from low-density bottle-roll leaching at 25 grams per litre hydrochloric acid across the full suite of 15 rare earths. The tests used a relatively low slurry density of 4 weight per cent, maintained over a 24-hour period.
Those parameters had been benchmarked for laboratory purposes against previous development tests to achieve results equivalent to diagnostic leach tests using 25g/l hydrochloric acid under the same ambient conditions in a six-hour period.
Typically, once further bench-scale testwork has been completed, slurry densities would be increased to represent actual continuous production conditions more closely, potentially up to between 25 and 30 per cent density, thereby building the throughput to real-world requirements.
The minerals include the lanthanide element yttrium, which is often included in the rare earths suite due to its similar properties. But ANSTO’s analyses focussed particularly on the principal magnet rare earths components, praseodymium, neodymium, terbium and dysprosium.
The testwork across the three prospects recorded overall magnet rare earths recoveries averaging 69 per cent. The highest TREO grade of 3435ppm came from Belgian, which also had the highest MREO grade of 1374ppm.
Management noted that all of its MREO recoveries are similar, which it considers a key to overall project economics for any clay-hosted rare earths project.
OD6 uses an innovative airborne electromagnetic (AEM) surveying technique that has been widely employed for aquifer studies and analysis of problematic saline terrains, such as in the Murray Basin. It is designed to rapidly scan its extensive tenement area to identify and map clay location, expanse, depth and thickness using processing techniques it has evaluated in conjunction with the CSIRO.
The method enables the rapid identification of priority target areas and saves potentially wasted time and meterage using drilling to determine clay depths in what could easily become hundreds of line kilometres.
The company takes the view that in contrast to the mining of hard rock rare earths deposits – where mine drill-and-blast is a common necessity, followed by crushing, grinding and heating to liberate the commodity elements – leaching of rare earths clay deposits is ultimately simpler and cheaper. While grades can be lower, potential ore volumes can amount to billions of tonnes and production costs are significantly lower.
OD6 is retaining a key focus on its nearby giant Splinter Rock resource areas, where it has also reported similar excellent metallurgical recoveries from the Prop, Centre, Scrum and Flanker prospects.
However, these first metallurgical results from Grass Patch, in conjunction with its first-pass drilling assays, clearly indicate that the company’s Belgian, Circle Valley and Scaddan prospects justify priority higher-density drilling and follow-up metallurgical testwork – both of which are already in the company’s sights.
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