JOHANNESBURG (miningweekly.com) – Development of the innovative new mining method for narrow tabular steep dipping orebodies and the mobile tunnel boring to enable it are both going exceptionally well.

The game-changing narrow-reef-cutting advance on the way provides a mechanised mining solution to extract upper group two (UG2) platinum group metals (PGM) reef more selectively and efficiently from a very narrow 60 cm reef width.

Tunnelling will be done with the mobile tunnel borer for some distance, and then the on-reef cutting will follow.

The reef cutting system has been custom designed to suit the UG2 reef layout of ARM’s Bokoni PGM asset, with the reef-boring machine having been extensively tested on artificial UG2.

It uplifts PGM grades through more selective mining, which then lowers unit costs, betters safety, streamlines downstream materials and slashes the size, risk and environmental impact of tailings storage facilities.

“It’s meeting and beating all expectations,” a very upbeat African Rainbow Minerals (ARM) executive: growth and strategic development in the executive chairperson’s office Mike Schmidt said in response to Mining Weekly during question time following ARM’s presentation of dividend-yielding results last Friday, September 5.

Schmidt reported that all on-surface test work and trials for the non-explosive narrow-reef cutting had gone exceptionally well. These involve rigorous processes of cutting various grade densities and hardnesses on concrete slabs. 

“In the meanwhile, we've gone ahead and established a completely new site for the underground trials. That's far advanced. Site establishment’s done. The portals are ready. We’re busy taking up electric cables.

“We’ll start commissioning mid-November and by March, we’ll be very well advanced with the tunnel boring. Then in March, the narrow-reef cutting follows through and we’ll probably go for a final commercial decision by June - and I’m very confident,” Schmidt added.

The investment of the Johannesburg Stock Exchange-listed ARM at Bokoni was based on full mechanisation and the capital that's gone into Bokoni is to re-establish the mine from what was historically a mine extracting Merensky reef to a mine extracting UG2.

During its period of the ownership of Bokoni, ARM has commissioned a 60 000 t plant and also built and commissioned a chrome plant.

It has sunk a decline shaft directly into the orebody to concentrate all ore from one shaft instead of the historic three shafts and then to focus, as of now, on the UG2 development.

“UG2’s still the preferred grade and the preferred orebody with the preferred returns,” Schmidt outlined.

“We anticipate, within the next three years, to recommission the 60 000 t plant, phase up to 120 000 t and ultimately phase back to 240 000 t.

“The indications are that this year’s capital expenditure will be just over R1-billion, and that's the type of expenditure we see over the next three years, subject to board approval on the full feasibility which we will present towards the end of the year,” Schmidt said in response to analyst questions.

The narrow-reef-cutting technology on the way enables mechanised mining at scale, for which ARM has partnered with Herrenknecht, a German company known for its excellence in designing and manufacturing tunnel boring machines worldwide, and also Master Drilling, the South African, Fochville-based company that specialises in reef boring solutions.