Viridis Mining & Minerals (ASX: VMM) says ANSTO laboratory leach tests have achieved up to 80 per cent recoveries of rare earths from clay samples out of the first diamond drillhole at its Colossus project in the Brazilian State of Minas Gerais.
The company has today revealed that the laboratory confirmed exceptional ionic recoveries from six 3m composite clay samples taken from the full intercept between 3.3m and 21.2m in its Cupim South drillhole, with minimal gangue and radioactive element leaching affinity shown.
The results included neodymium (Nd) and praseodymium (Pr) recoveries of 80 per cent in an 11.9m section from 3.3m and 66 per cent recovery of dysprosium (Dy) and terbium (Tb), also in the 11.9m from 3.3m.
The testwork undertaken by ANSTO (the Australian Nuclear Science and Technology Organisation), was the first step in a metallurgical testing campaign to help Viridis get to grips with the leaching characteristics of its ionic-absorbed clay-hosted rare earths throughout the entire saprolitic clay profile.
The company’s first diamond drillhole obtained an impressive intercept of 24m at 4573 parts per million total rare earth oxides (TREO) from surface. Four previous auger drillholes on the same section immediately next to the diamond hole also recorded a decent suite of TREO hits including 24m at 2902ppm including 13m at 3548ppm, 8m at 3535ppm ending in mineralisation at 2535ppm, 10m going 3292ppm and finishing in mineralisation with the last 2m going 4439ppm. A final intercept read 7m running 3463ppm TREO with the last 2m ending in mineralisation at 6087ppm.
The leach test samples for ANSTO’s work were taken in 3m increments between 3.3m and 21.2m, with no testing undertaken above or below that range. ANSTO used a standard ammonium sulphate (AMSUL) leach at pH4 at room temperature for 30-minute leach cycles and analysed for the full suite of 15 rare earths and the additional non-rare earths scandium, thorium, uranium and yttrium.
The internationally-renowned ANSTO laboratory says the results have been achieved under non-optimised conditions, meaning that significant scope remains to adjust desorption chemistry and provide improved results in future tests. Results to date show the highest-grade section lies closer to the surface and exhibits the best desorption characteristics, with low cerium desorption and little to no radioactive mineralisation or waste.
That is significant for the potential exploitation economics at Colossus. And, importantly, the low levels of uranium and thorium in both the feed and waste is expected to translate to a fast-tracking of environmental approvals process.
This result is a significant milestone which confirms Colossus has the potential to be a world-class ionic-adsorption clay rare earths resource, with exceptionally high recoveries for both light, medium and heavy magnet rare earth elements throughout the clay intercept. The benign leaching conditions, reagent selection and low impurity concentration in the leached solution, simplifies the process flowsheet significantly and strengthens the robust economics of the project.
Viridis Mining & Minerals chief executive officer Rafael Moreno
Moreno said the next set of metallurgical results were expected to land either late next month or early in May and the company would continue to work closely with ANSTO to optimise leaching conditions and maximise recoveries at Colossus.
Other economically significant conclusions are that the mining depth at the project is typically shallow and essentially free-dig, the AMSUL leaching reagent is cheap, gangue mineralisation such as aluminium and iron are low and cerium recovery is also low.
The fact that magnet rare earths show their best recoveries in the highest-grade zone – with 12m at 6402ppm TREO (comprising 2146ppm NdPr and 67ppm DyTb from 3m) – is another significant advantage, with shallow saprolitic clays offering many mining and processing advantages to help keep operating expenses low.
Viridis sees big upside in the outcome of its first testwork, not only because it points to Colossus having world-class potential as a rare earths resource, but that it also shows low radioactive components and low levels of impurities in the leached solution.
The company says additional samples from later diamond and reverse-circulation (RC) drillholes, in addition to other bulk samples representing more than 30 more drilled locations, have been sent to ANSTO and results are expected to flow back during the next two months.
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