Modern Quarrying Q4 2018

AT THE QUARRY FACE

A 20-t Doosan 225 LCV excavator equipped with a hydraulic hammer is deployed to break down oversized material.

A Volvo L150G is used for stockpiling at the ISP.

Quality matters Roodepoort Crusher’s quality is also based on the shape of its end product. There is a growing demand for cubical-shaped material in asphalt and concrete production at the expense of flaky material. Flaky material is weak and can be broken by the pressure of large vehicles, while an exposed hole will fill with water and quickly become a pothole. The water demand is also higher for flaky material compared with cubical material, and this increases the amount of cement needed to achieve the required strength of con- crete. Cubical-shaped material also greatly increases the workability of the various mixes. Cubical-shaped stone fits close together and more compactly, ensuring that less asphalt (or cement) is required in production, thereby reducing costs significantly. “We have experienced increased demand for our product as a result of these innovations,” explains Botha. To ensure optimal quality of the end product, maximum controls are implemented throughout the production process. It starts in the pit, where drilling and blasting, outsourced to contractor Demwreck, is undertaken every second month. Blasts are kept fairly large at 20 000 m³ of material on the ground. With proper fragmentation in mind, which has a significant impact on downstream processes such as

crushing and screening, as well as load and haul, management specifies the use of high-quality electronic detonators from leading South African supplier, BME. Electronic detonation has become popular due to its reliability, accuracy and flexibility, making blasting more predictable and allowing for larger and more cost-effective blasts. BME – which has built a strong reputation in the mining and quarrying sectors in Africa and Australia – has been behind some of the world’s largest surface blasts in terms of the number of electronic detonators fired in a single blast. For example, at Zambia’s Kansanshi Mine – the largest copper mine in Africa – 6,690 electronic delay detonators were successfully initiated in one blast in 2017 using the AXXIS system. Operational processes With load and haul being one of the biggest cost drivers for any opera- tion, distances from the pit to the processing plant have been kept at a maximum of 700m. Two Bell B18D articulated haulers, loaded by a 40-t Hitachi ZX400-3 hydraulic excavator, haul material from the pit to the tipping point at the primary crusher. Two 20-t Doosan 225 LCV excavators are also part of the in-pit fleet. One is equipped with a hydraulic hammer to break down oversized material, while the other unit is deployed to strip overburden and load a Bell B20C

articulated hauler. One of the key challenges in the pit is the oversize material from blasts. The pit is still in its infancy, so when you blast there is so much fall-over boulders. This is largely due to the loose joints in the granite rock; the loose the joints, the poor the management at Roodepoort opted for a cheaper Chinese processing plant which was designed specifically to meet the operation’s specific needs. The team travelled all the way to China to incorporate their “voice” in the design of the plant. However, this was a temporary solution to just get the business off the ground. A year later, parts of the plant were replaced impermanent solution. It was never going to be sustainable – our granite material is too abrasive and hard to handle, with very high silica content,” explains Botha. The crushing plant has since been replaced with a Metso C120 jaw crusher (primary), a GP220 cone crusher (secondary) and a Techroq T12R vertical shaft impactor (VSI) (tertiary crusher). Haulers tip directly into the primary jaw crusher. From there, material goes onto an intermediary stockpile (ISP). At any given point, the ISP stockpiles material worth three days of production. An additional two days’ worth of material is stockpiled fractioning when blasting. To kick-start the business, with tried and tested brands. “The Chinese plant was an

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MODERN QUARRYING QUARTER 4 - 2018