Northern Minerals Ltd has progressed its ore sorting project enhancement initiative with the commissioning and testing of the Steinert sorter system, and is now producing ore sorted material and converting this to a 30% total rare earth oxide (TREO) concentrate in its’ Browns Range beneficiation plant in Western Australia.

Northern Minerals’ CEO, Mark Tory, said: “The construction, commissioning and testing of the ore sorter circuit marks another milestone in the development of the Browns Range project.

“The positive bulk sample tests confirm the effectiveness of the ore sorting circuit on the Wolverine ore to significantly increase the head grade to the mill which is expected to result in higher production rates and lower operating costs for a full-scale operation at Browns Range.

“It’s also pleasing to see the initial ore sorting tests the Banshee ore showing promise which, if shown to be effective in future tests, has potential to significantly increase the Browns Range mineral resource estimate.”

He added: “Being able to test and operate the ore sorting circuit in conjunction with the pilot beneficiation plant is providing extremely valuable data that you just can’t get from small bench-scale tests and this will feed into our feasibility study for a potential commercial scale heavy rare earth operation at Browns Range.”

The ore sorter system was constructed during 2020 and 2021 and commissioned in June 2021. The sorter that was installed is a 2-m wide Steinert sorter that uses X-ray Transmission (XRT) and laser detectors to identify rare earth mineralisation.

The sorter has been run over two test campaigns, which included 41 test runs processing 5,300 t of ore from the run of mine stockpiles largely coming from Wolverine ore, and five test runs on Banshee ore that was bulk sampled from a surface costean that provided 285 t of Banshee ore.

The tests have confirmed that simultaneous sorting of two size fractions is possible on the sorter, allowing a single machine to sort both sortable size fractions (10 mm-25 mm and 25 mm-75 mm), Northern Minerals says. The sortable fraction (>10 mm material) of Wolverine ore can be successfully sorted (90% TREO recovery in 50% of the mass) and, when combined with non-sortable fines, achieves a 45% grade increase to the mill and over 95% TREO recovery when feeding a 0.9% TREO ore.

The sorter system is now being run to produce feed for the beneficiation plant and 4,479 t of Wolverine ore have been processed through the ore sorter circuit to the end of August. Processing of the Wolverine ore sorted material in the beneficiation plant has resulted in better recoveries in the magnetic separation plant and flotation plant compared with feeding unsorted ore, the company says. A bulk sample of 50 t of 30% TREO rare earth concentrate has being produced for test work by facilities identified with likely future capability and capacity to process the heavy rare earth xenotime concentrate produced at Browns Range.

Bulks sample tests have highlighted some key factors to consider for ore sorting that cannot be determined at bench scale using vendor equipment in laboratory settings. Understanding the impact of these factors is critical to including an ore sorting circuit in a full-scale processing facility.

Initial sorting tests of the Banshee ore have shown that the highly oxidised surface material contains a large fines fraction and that the grade of the sortable fraction (ie >10 mm) can be doubled recovering more than 60% of the TREO in 25% of the mass. An additional bulk sample is being extracted from deeper in the costean and three diamond drill holes are being drilled for further test work.

The bulk ore sorting test work is a key input for the full-scale beneficiation plant feasibility study currently underway, which will also leverage off the substantial technical, operational and economic data from the R&D test work at the Browns Range Pilot Plant since 2018, the company says.