Sultans of silt

One minesite has employed a civil construction approach to tunnel excavation to combat a wall of clay and silt.

Being confronted by a wall of clay at the top of a decline when the plan said fresh rock isn’t an ideal starting point for a new mining project.

Terramin Australia’s zinc-lead-copper mine manager Jol Jardine has seen a lot of things in his 18 years in underground mining.

Deepening the boxcut at Angas by about 15 m to take the portal below the silt-stone horizon it faced seemed irresistible at first, however, that quickly changed when Jardine saw the sign and managed to wrangle an alternative.

According to the mine manager, an innovative approach to mining through the 80 m stretch of silt, patience and a lot of hard work, got the project over (or through) the initial hurdle.

The approach involved taking a civil construction-type approach to tunnel excavation, using a drilling jumbo to erect initial roof support, and cautiously digging out the face in two stages. As hard rock appeared in the decline floor, and then increasingly became part of the advancing face, the material had to be broken in a way that wouldn’t shake up the silt too much.

Mining the extra six million tonnes out of the boxcut at Angas to deepen the entrance wasn’t really an option for Jardine and his mining team due to space restrictions and the prohibitive cost.

“We decided to stick to Plan A, which meant mining through the weaker material,” Jardine said.

“We used a tunnelling method called spiling, where we had an Atlas Copco M2D jumbo pushing NQ drill pipe into the top of the face to establish initial support, and then shotcreting and installing steel lattice girders.

“As we were mining down the 1-in-6.5 decline, we started picking rock up in the floor and it slowly worked its way up in the face as we got deeper. So as we were mining down into the rock the challenge was that we were

not only mining through silt, we then had rock in the floor which has got to be blasted.

“As soon as you blast you start knocking around all the silt. So the process was pretty involved. We were taking a metre at a time, and we were part-facing as well, which means mining the top half of the face, putting in the ground support, including spiralling tubes and shotcrete, and then coming back and mining the bottom half out.

“Then we were shotcreting the face as well, so it was an intense experience and we got about 1 m of advance at a time,” Jardine said.

The 400,000 tpa Angas underground mine, 2 km from the rural town of Strathalbyn and about an hour out of Adelaide, is due to start production this year.

Jardine said decline development was now back on track after several mishaps including an increase in anticipated costs and a schedule extension caused by the project’s slow progression at the start of the operation.

He paid tribute to the mining crews working on the decline, affectionately known as ‘the silt miners’or ‘sultans of ilt’, who triumphed in the face of a particularly challenging job.

Jardine also praised the support of Atlas Copco, and versatility of the machine used in the operation, the Boomer M2D.

“We actually got the new drill rig doing something it normally doesn’t do, and it demonstrated that it was a very flexible bit of gear and it helped us out to get through the situation,” he said.

as well as the M2D, Atlas Copco has supplied ST1030 and ST1520 loaders to Terramin at Angas.

“Certainly they [Atlas Copco] supply good products, but one of the reasons I went for Atlas Copco at this site was service and support back-up. They are pretty strong in that area in this part of the world,” Jardine said.

Angas is expected to produce up to 65,000 tonne of zinc and 24,000 tonne of copper-lead concentrate annually when in full production.

A $29 million per year boost for the local economy has been estimated in a study by the South Australian Centre for Economic Studies.

Stevan Topalovic

Business Line Manager

Atlas Copco

08 9262 9715

Stevan.topalovic@au.atlascopco.com

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