CULLINAN (miningweekly.com) – Raise boring and drilling services group Master Drilling is nearing completion of a 220 m horizontal raise bore (HRB) trial project at Southern Africa-focused miner Petra Diamonds’ Cullinan diamond mine, in Gauteng.

On Thursday during a site visit to the mine, Petra mining manager Steven Klopper highlighted that the HRB method of developing access points to the kimberlite orebody had recorded faster development rates than traditional drill and blast methods meter per day production targets to date.

Master Drilling executive director Koos Jordaan noted that the key performance indicators for the project included the ability to drill a straight pilot hole over the length of the tunnel, the ability to drill in dry way that is not reactive with the kimberlite and the ability to cut material, load and support the tunnel.

He said that the trial project had been running since July 2014 and to date 180 m tunnel had been piloted through the use of “a dry and accurate directional method”. Jordaan added that the 30 m of reaming had been completed with 2 m/d of tunnel development having been achieved along with material cutting, loading and support also having been achieved.

“Some of the major challenges that we have had to overcome was dealing with rocky stresses, blocky ground and fines in the project area,” he said.

Further, Jordaan stated that going forward the aim was to increase production to 6 m/d, while also optimising the concept in regards to mobility and productivity of the HRB method. “Advances of between 9 m and 12 m seem possible.”

Other goals initiated through the use of the HRB method include tunnelling without the need for pilot holes in a straight line,  and mobile tunnelling at curves and different cross sections.

Master Drilling CEO Danie Pretorius pointed out that a standard vertical raise bore machine had been adapted for use in the project. However, he said that the company intended to specifically develop an HRB machine.

The remaining 40 m of the tunnel will be developed using conventional mining methods owing to challenging geology. However, the completion of the remainder of the tunnel is scheduled to be completed during the course of the next three months.