Modern Quarrying Q3 2018

Two 30-t Astra RD32 rigid haulers with a payload of 28 t haul material from the pit to Primary B.

AT THE QUARRY FACE

days. This amounts to a total of 11 blasts per year. Blast are kept large, achieving between 60 000 and 100 000 tonnes of material on the ground. Drilling and blasting is outsourced. Hole diameter is kept at 115 mm, burden and spacing at 3,9 x 4,3 with 2,5 m stemming. “The blast design ensures good blast fragmentation to warrant correct size rock that suits both the primary plants,” explains Kruger. Efficiency of drilling and blasting patterns in open pit mining determines, to a large extent, utilisation of equipment, crushing and screening, as well as productivity and economics. Mining is currently taking place in the southerly direc- tion of the quarry, with 11 benches being mined, at an average pit depth of 110 m. Bench lengths are up to 400 m wide, with average bench heights of 10 to 12 m. “Long benches provide for both rock types simultaneously (blue and brown) on the same bench, which contributes to lower operational costs,” explains Kruger. Load and haul is also outsourced to a contractor, Lulenco Plant Hire. The contractor is running two 40-t Cat 745 articulated haulers with a payload of 38 t. These are being loaded by a 50 t Hyundai excavator and are used to feed Primary A. Two 30-t Astra RD32 rigid haulers with a payload of 28 t – loaded by a 40 t Volvo excavator – haul brown material from the pit to Primary B. Meanwhile, two 30-t Volvo ADTs are used for bin out loading and stock- piling material at the tertiary plant, while three Cat 950 front-end loaders are deployed for stockpiling and loading customer trucks at the stockpiles. In terms of equipment choices, the quarry doesn’t neces- sarily specify the type of machines to the contractor, but only stipulates production capacity per hour. “Equipment choices are largely informed by reliability and correct fleet size to meet production requirements. Mining equipment should not exceed 12 000 hours, while dispatch equip- ment can only be used to a maximum of 15 000 hours,” explains Kruger, adding that compliance to safety stan- dards and MHSA is a pre-requisite. A strict maintenance regime ensures increased crushing plant uptime. “We ensure proper scheduled maintenance plans and integrity of workmanship. This helps maintain a Product Rate Index (PRI) of 100% and plant availability of 68%,” says Kruger. In terms of resource consumption, Kruger is so particu- lar about measuring and controlling fuel consumption, which is kept at 0,3 ℓ /tonne. Water usage, both billed

and unbilled, is also closely monitored. With the current drought conditions in the Cape area, Peninsula quarry has actually reduced its municipal water consumption by 85% year-to-date, measured against the same period last year, says Kruger. This is a massive improvement from last year. This has been achieved through several interventions such as the changing over of ablutions and water supply to the readymix concrete plant to quarry pit water. Plant structure The plant at Pensinsula quarry has a design capac- ity to produce about 1,2 million tonnes per annum. Primary A plant comprises a 38/48 Osborn jaw crusher fed with an apron feeder, three conveyor belts, one screen and a Sandvik H6800 cone crusher fitted with an automatic setting regulation (ASRi) for multiple closed side setting (CSS) features. Fed by the two Cat ADTs, it has a feed rate of 450 tph. In terms of product range, it produces blue rock material for the intermediary stockpile (ISP), unwashed sand, as well as 9 mm or 13 mm ROC. Primary B plant – which is fed by the two Astra rigids – has a feed rate of 275 tph. Its equipment comprises a 30/40 Osborn jaw crusher with a vibrating grizzly feeder, 9 conveyor belts, one screen, a Sandvik CH440 cone crusher with ASRi and a Barmac. Its product range includes blue rock material for the ISP, base and sub base material (G1 to G7); 19 mm concrete stone and 9 mm or 13 mm ROC. The tertiary plant comprises ISP feeders, six conveyor belts, four screens, two Sandvik cone crushers – H4800 and H3800 with ASRi, and a Barmac. The product range here comprises 53 mm, 37 mm, 26 mm, 19 mm, 13,2 mm and 6,7 mm concrete stone, as well as -6 mm unwashed sand. There is also a sand plant which has five conveyor belts, one screen, a cone crusher and a single Barmac. This produces -6 mm unwashed sand. Kruger and his team ensure optimal crushing pro- cesses with regards to CSS and choke being fed. A key competitive edge of the plant is its flexibility, which allows Penisnula quarry to produce material to customer spec at any given time with no need for investments into new additional equipment. “As the market and demand changes, you have to be able to change with it,” con- cludes Kruger. l

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MODERN QUARRYING QUARTER 3 - 2018