Red Metal Limited has turbocharged the value proposition of its Sybella rare earths discovery in Queensland after fresh test work confirmed the project’s strong heap leach potential to deliver high recoveries of the more lucrative magnetic rare earths and ultra-low iron impurities, all while using just minimal amounts acid.
Bottle roll leach tests carried out on weathered granite from the project’s Kary Zone revealed a pH sweet spot between 2.0 and 2.5, where high recoveries of magnet rare earth oxides (MREOs) including neodymium and praseodymium could be recovered using just room-temperature sulphuric acid.
When the acid’s pH was kept at 2.0 or higher, acid use and iron levels stopped increasing, hinting at the possibility of not needing to build special barriers, called “inter-lift liners”, between heap layers, thereby saving time and money.
Notably, the weaker acid levels still delivered the goods, with extraction rates for neodymium and praseodymium (NdPr) clocking in as high as 81 per cent. Even the expensive heavy rare earths - dysprosium and terbium returned impressive average recoveries of up to 60 per cent.
The company says, as a key input cost of the project, the uber-low acid consumption - requiring only 17 and 22 kilograms of sulphuric acid per tonne – undelines the project’s potentially unique economics.
Further testing showed that by mixing the acid with crushed rock before it is heaped up, dubbed “acid agglomeration”, the acid spreads more evenly and reacts faster with the rock. This could shorten processing time and extract more valuable rare earths.
Remarkably, if the leach liquor was then re-used, it caused iron to precipitate as goethite over time, further cleansing the leach solution while generating additional acid to prolong rare earths extraction.
The technique has slashed iron impurities from 13 per cent down to just 1 or 2 per cent — a game-changing drop that should sharply cut downstream processing costs. With cleaner leach liquor in play, margins on rare earths carbonate production could get a serious boost.
Red Metals Limited managing director Rob Rutherford said: “Our optimised leach tests on the Sybella ore samples have shown we can achieve strong rare earths extractions at weaker acid strengths than was previously indicated enhancing this unique deposit’s economic potential.”
The company is now prepping for its next critical step of conducting column leach tests on nine, 85- millimetre diamond core samples recently drilled at Kary. The tests will simulate full-scale heap leach conditions on crushed ore and should provide the all-important data needed for mine scoping studies.
Five of the core holes are also being put under the microscope using advanced HyLogger spectral scanning to zero in on key mineral zones that could hold the keys to unlocking better leach performance.
Together with plans to run similar bottle-roll tests on its nearby Templeton zone, Red Metal intends to keep pushing the envelope at Kary to unearth the full potential of the deposit’s depth and strike, which has already doubled in surface area from 3.5 to 8 square kilometres. Heritage surveying is being prepared for a drill campaign later in the year after the wet season.
Apart from being easy on the acid, the Sybella deposit, which sits 20 kilometres south-west of the major mining hub at Mount Isa, should also benefit from its sheer scale. With 4.8 billion tonnes grading 302ppm NdPr and 28ppm DyTb, the granite-hosted behemoth packs the kind of tonnage that could turn a low-cost leach operation into a long-life cash machine.
Whilst in reality rare earths are not actually that rare, low capex and low opex projects that can be catapulted into production with relative ease probably are.
Throw in an Australian Prime Minister and an American President that are on the hunt for rare earths stockpiles and Red metal just might find itself in the box seat later this year as its testing progresses.
Is your ASX-listed company doing something interesting? Contact: matt.birney@businessnews.com.au
By James Pearson
