In-pit Crushers

Mobile crushers located close to the production face capable of meeting the required outputs are well established and can be operated in a number of ways. They can be fed conventionally by dump truck travelling a short distance from face to crusher on one level. Where travel distances can be maintained at less than 100-150 metres, large capacity front end loaders working as 'load-haul-dump' units (LHD) are-most effective, see Fig. 1. Finally, hydraulic excavators which sit on the shot rock pile can load directly to the crusher feed hoppers with no requirement for dump trucks, see Fig. 4.17. From the quarry face or quarry floor, primary crushed rock is fed to the secondaries and the process plants by conveyor.

Conveyor systems require considerably less space than haul roads sterilizing less reserves and are able to operate at much steeper gradients than dump trucks. The trend towards high-angle, high-capacity conveyor systems will increase the opportunities of introducing mobile crushers located at the production face of deep open pits and quarries.

At hillside quarry locations short travel distances and the use of load-haul-dump techniques are possible by feeding the primary crushers via an ore pass or by locating a semi-mobile primary over the ore pass. ARC's Criggion Quarry and Yeoman's Glendsanda Super Quarry have both adopted the technique to considerable effect. Figure 2 demonstrates the technique whereby the shot rock is crushed close to the face above the ore pass or glory hole. The travel distances of either dumpers or LHD equipment can be restricted thus reducing numbers. Movement of the primary crusher level by level downwards becomes part of the excavation planning schedules and is included in the mine design programmes.

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