WINNING
If you add in the drilling, charging, contractors’ time, blasting, monitoring, and all the other things that go into ensuring a successful blast, the cost rises to between R300 000 and R500 000 per blast. For the blast we were watching, 16.8 tonnes of explosives was used, producing 36 000 tonnes of blue rock.
DSS has its own on-site laboratory for outgoing testing material. Van Wyk explains that the lab allows them to test immediately if there is a potential problem with the material. If a problem is reported by a customer, a sample is collected and tested at the on-site lab, and the results are given to the customer directly. While the customer can use an independent lab to check the results, the on-site lab allows DSS to maintain quality control on site.
Equipment
DSS makes use of many older equipment, which is, in Van Wyk’ s words,“ proven and workhorse-like— it just keeps going”. Currently, the quarry does one million to 1.5 million tonnes per year with four 30-tonne trucks( two Cat 730s and two Volvo A30Es) and two 50-tonne excavators( one Cat, one Sumitomo) with 1.8m 3 buckets. The fleet also includes six Doosan front-end loaders, five Doosan excavators, and two mobile screens. According to Van Wyk, they are working on replacing one excavator or front-end loader per year.
The primary plant used by DSS is a 3042 Telsmith jaw crusher, with manganese jaw liners for better wear, as this lasts longer with harder materials. The secondary plant is a Symons 4¼ crusher, and the tertiary plant is a Symons 4¼ short head crusher. Altogether, the plant has a throughput of between 200 and 210 tonnes per hour.
DSS uses a self-manufactured, selfinstalled dust suppression system when offloading into the primary jaw crusher. When a haul truck reverses in, a series of sprayers around the truck turn on, and as the truck is tipping the material, all the dust that comes from the truck tipping the material is immediately suppressed. The system is activated via a series of gate eyes that turn on the sprayers when a vehicle crosses them.
The quarry has an on-site 850kW generator and mobile crushers to continue operations in case of power outages. The roughly 5 000 tonnes per day of product that would be lost without alternate power sources make this an extremely important investment, and they are able to output the same number of tonnes using the generator and mobile crushers as under normal operating conditions. And, Van Wyk points out, each of the five or six crushers on site takes between one and three hours to empty out by hand should power be lost.
The DSS quarry has three primary layers: sand, the weathered zone, and granite or blue rock, although some pink rock has also recently been discovered. The sand is used to produce building, river, and plaster sand, while the weathered zone is used for sub-bases, crusher run and fill material. The granite is used for concrete stone, stone, crusher sand, and crusher run.
DSS produces a variety of products for commercial and civil contractors in the building and construction industries. The quarry produces 13 – 15 materials on site: G5, G6 and G7 sub-base; G1 crusher run; river, building, pit and plaster sand; 19mm, 13mm, 9.5mm and 6.7mm stone; crusher dust; and builders mix. Each product has a different use— concrete, bitumen, bricks— all with different requirements. n