At Sybella, rare earth fluoro-carbonates in the weathered host granite start right from surface and the rock can range from almost friable to easily broken under mild pressures. The company says it could be amenable to simple ripping or digging by an excavator within the upper 10m to 15m and even as deep as 20m.

Red Metal’s testwork shows excellent rare earth oxide recoveries can be achieved from both weathered and fresh rock with low acid consumption and importantly, the leach extracted low levels of impurities.

Surprisingly, and contrary to most operations, Sybella recoveries are actually reduced by the excessive grinding that simply exposes more of the barren host rock to the leachant, which creates other negative metallurgical issues and wastes acid.

To put it in layman’s terms, the metallurgy shows that the less you mess with Sybella, the more forthcoming it will be, pointing to coarse crushing and simple, low-cost heap or dump leach processing as the optimal way forward for the project’s likely ore type.

In addition to the solid extraction numbers, the recent testing at Sybella also showed a low average sulphuric acid consumption of just 37kg per tonne – a key cost input in any mining operation. The minimum was 23kg per tonne, accompanied by only low extractions of aluminium and iron impurities at 7 and 22 per cent, respectively.

Importantly, recoveries of the potentially serious deleterious components, thorium and uranium, have been low at 20 grams per tonne and 1g/t, respectively.

While the latest tests were undertaken up to a maximum of 96 hours, the recovery curves indicate that the longer residence times that are more typical of dump leaches – which can be days, weeks or even months – will likely yield even better recoveries.

Further recovery and cost reduction improvements look like they will be forthcoming with increasing particle size, residence time and careful tweaking of the pH (acidity),

The company says it is already undertaking a second phase of metallurgy test work to explore comminution characteristics, leach recoveries on varying size fractions from crushed core samples and it will run trials to remove impurities.

Planning for further drilling is also underway, likely to be on a broad grid of 800m-by-400m to scope out the extent of the potential resource to gain a sense of the rare earths grade and continuity along strike and into the deeper weathered zones and relatively fresh rock.

Red Metal’s Sybella prospect has an air of anticipation about it, of something new and potentially lucrative, nonetheless it may take a little while for punters to fully understand how its characteristics and metallurgy set it apart from the more traditional clay-hosted and hard rock rare earths discoveries.

And while metallurgy tests are not always sexy, they are nonetheless critical to understanding the economic potential of a rare earths project as poor metallurgy can kill a project overnight.

That Red Metal appears to have jumped this hurdle even before tabling a maiden resource should put to bed the question around processing – at least at this early stage.

It will now be fascinating to see the numbers in any future prefeasibility study on Sybella. They just might rewrite the traditional rare earths production cost curve.

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