Modern Quarrying Q3 2021

Comparison of muckpile fragmentation between a Varistem and standard blast design.

this market segment are 10 mm and 20 mm road stone. The operation produces an array of top quality material sizes, including G6 (base course); ballast (for Transnet); 7,1 mm, 22 mm and 28 mm concrete stone; 10 mm, 14 mm and 20 mm road stone, as well as crusher sand. The operation is one of the few quarries in the country that still produces 28 mm stone. This is largely produced on order and is mainly supplied to Sasol. The square nature of the pit allows for particularly big blasts, which translates into cost savings. “We are probably one of the fortunate operations in our group that can do fairly big blasts,” says Sterley. “We can blast up to a 120 000 tonnes in one go. This is facilitated by the square nature of the pit; our benches are much wider and have big reserves of material. In general, we have ample space to blast.” The pit is currently about 50 m deep and will allow for mining of two more levels to about 90 m. “We will probably be busy in the existing pit until 2027, before there is need to expand,” concludes Sterley. l

The square nature of the pit allows for particularly big blasts, which translates into massive cost savings.

well. This is complemented by good blast designs. The stemming cap is also proving worthwhile when blast- ing such a tricky rock. Good fragmentation, with a special focus on fines, is a big focus for Rooikraal, especially given that the biggest demand driver is sand. Because of the competent nature of the rock on site, the quarry is also a big supplier to the asphalt market. Its product is sought after, with some asphalt producers coming from as far as the Free State to fetch the product. Products driving demand in

He says the Varistem has offered the quarry the best of both worlds – an increase in safety and cost efficiency. “We pay a bit more in the pit, but the benefits of good fragmentation in the downstream processes are well documented,” he says. Quality product Rooikraal Quarry mines a competent dolerite rock, which is blocky by nature when blasted. The direction of the blast is a crucial factor in achieving good fragmentation as

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QUARTER 3 - 2021 MODERN QUARRYING