Authors: Snyman, L; Webster, S

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Snyman, L & Webster, S 2022, 'Northparkes E48 block cave: the mining history of a successful block cave', in Y Potvin (ed.), Caving 2022: Proceedings of the Fifth International Conference on Block and Sublevel Caving, Australian Centre for Geomechanics, Perth, pp. 95-108,

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Northparkes operations consist of underground sublevel cave and block cave mines and an ore processing plant which produces copper and gold concentrate. Production is transitioning from the E48 Lift 1 to the E26 Lift 1 North block cave. Block cave ore will be supplemented with E26 sublevel cave and open cut ore. The E48 extraction level is located approximately 581 m below surface in a low to moderate stress state. The construction used a post-undercut strategy that was initiated in 2009, with production commencing in September 2010 and cave-through to the surface occurring approximately four months later in January 2011. The fast cave propagation and initial, low swell factor is uncharacteristic of block caves. The E48 cave experienced complex problems with large ground displacements that lead to drive and drawpoint closure. Lessons learned from the E48 experience were used to improve ground support design to minimise potential damage in the extension area. The mine was originally proposed with eight extraction drives and ten drives were developed. Through reserve upgrades the final extraction level now consists of 13 extraction drives and 270 drawpoints. Changes to the cutoff grade and price/earnings to growth ratio prices meant that Northparkes was able to develop an additional two drives to the north of the existing cave and one additional drive to the south. Developing the extension drives mid-way through the cave life posed further challenges and learnings in the areas of mine design, ground support, undercutting geometry, caveability and reserve recovery. The reserves recovered have exceeded initial estimates and the evaluation of cave shapes defining tonnes from the footprint have required iterative, ongoing evaluations. In the final years of E48 the mine is focusing on management of extraction level stability, grade prediction and ramp down to closure of the drives and eventually the whole level. This paper looks at the life of the E48 block cave – the challenges, the failures, and the successes.

Keywords: block cave, stability, redevelopment

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