Mount Ridley delivers solid rare earths recovery rates

Mineral exploration company, Mount Ridley Mines continues to kick goals at its namesake rare earth element, or “REE” project near Esperance in Western Australia. Initial metallurgical testing of 489 samples from 215 drill holes showed high recovery rates of total rare earth oxides, or “TREO”.

The company has defined a mammoth mineralised strike area at the project covering about 25 kilometres in length by 3km in width.

Mount Ridley recently uncovered the hefty mineralised envelope by re-assaying of 1,108 drill samples from historical exploration drilling conducted between 2017 and 2019.

The re-assayed data from 267 aircore holes, taking in more than 3,500 metres of drilling, returned a conga line of shallow and high-grade mineralised intervals including 16m at 2,020 parts per million TREO, 16m at 1,580ppm TREO and 5m at 3,949ppm TREO. Peak grades hit a cracking 10,461ppm TREO from just 23m in a one-metre intercept.

The initial assaying was undertaken via a ‘total digest’ fusion technique designed to report how much REE is present in each sample. In total, more than 50 per cent of the samples returned elevated REE mineralisation.

Subsequently, the company launched a metallurgical testing program to evaluate the potential of extracting the REE mineralisation via a partial leach analysis method.

Mount Ridley now reports results from 489 previously assayed samples performed through a ‘partial digest’ modified aqua regia digestion technique, or “AR”. The assaying method is designed to analyse for soluble or loosely bound REE mineralisation - a style of mineralisation typical for ionic adsorption clay REE deposits being targeted by the company at the tenure.

Management says a grade of about 800ppm TREO was taken into solution under the trial conditions. Recovery of some 80 per cent of light REO, 76 per cent of heavy REO and 80 per cent of critical REO was achieved in the testing.

Clay-hosted REE deposits potentially consist of multiple phases of mineralisation, including the targeted ionic adsorption clay, colloidal clay, and refractory primary minerals.

Typical ionic adsorption clay REE deposits are processed by leaching with a salt solution at a weakly acidic pH.

Mount Ridley says results of AR testing show that a high proportion of REE mineralisation at the project is extractable using a weak acid solution.

This analytical program was designed to give an early indication of whether the REE mineralisation was in a readily-soluble state and, while these results are indicative only, they exceeded our expectations and therefore encourages the Company to fully commit to advancing the Mount Ridley REE Project through drilling and more advanced metallurgical studies.

Mount Ridley plans to get the rods turning at the tenure once all relevant permitting is in place.

An aircore campaign will look to test for extensions of the mineralised zones, with historical holes that ended in mineralisation also to be re-drilled. Reconnaissance aircore drilling of other targets is also on the agenda.

The company is also considering core drilling to verify mineralisation from historical holes and to acquire core for metallurgical and geotechnical testing.

Following the drilling, Mount Ridley plans to conduct further metallurgical testing.

The next phase of testwork will look to establish if REE can be extracted via salt solutions under weakly acidic conditions. In conjunction, further testwork will look to gauge the leachability of REE at various acid strengths to estimate acid consumption rates for leaching.

Mount Ridley has come a long way in a short time since unveiling REE mineralisation at its namesake project in Western Australia. With a mineralised strike of more than 25km and now high REE recovery rates reported at the project, the Perth-based company could quickly emerge as an explorer to keep a close eye on in the rest of the year and beyond.

Is your ASX-listed company doing something interesting? Contact: matt.birney@wanews.com.au