Modern Mining December 2021

fragmentation, and this has a significant positive knock-on effect on downstream productivity, costs and profits. Getting your fragmentation right is substantially

its 171 mm Varistem plugs to help the mine reduce the cost of mining waste on site. Key performance indicators for ERG included the reduction of direct drilling and blasting costs by expanding the drill pattern and using the Varistem to improve energy retention. In the end, drilling and blasting costs were reduced by 11%, translating into a net saving of R28- million per annum. How it works Plugs work by creating an additional blocking effect within the drill hole when blast energy is released, directing more energy into the block and less energy upwards out of the drill hole. Upon detonation of the explosives, the plug is forced upward into the stem- ming material and “locks up”. The explosives gases and energy are prevented from travelling (venting) up through the drill hole. Typically, the loss of explosive energy through stemming ejection reduces the performance of the blast. The fundamental theory promoting the use of blast-improvement and containment plugs is that they improve the effectiveness of stemming mate- rial in the blasthole. As a result, this better contains the explosive energy within the rock mass and yields a more controlled and efficient blast. The plugs contain blast energy for longer, result- ing in a range of benefits depending on how they are incorporated into the blast design. Preis says better blast energy retention results in improved

Eugene Preis, MD of ERG Industrial, at one of the mines where the Varistem stemming technology has been adopted.

The plugs contain blast energy for longer, resulting in a range of benefits depending on how they are incorporated into the blast design.

feature

December 2021  MODERN MINING  23