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A Case Study on the Assessment, Planning and Extraction of the Crown Pillar at Sunrise Dam Gold Mine

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Author A Robeson, M Cowan and M Brockman

Description

Sunrise Dam Gold Mine (SDGM) is located 820 km from Perth, 220 km from Kalgoorlie—Boulder and 55 km south of Laverton in Western Australia. The SDGM main pit had successfully operated since 1997 and was due to be completed during 2012. An opportunity existed to extract the high-grade crown pillar – 600 kt @ 7 g/t for 135 koz by either open pit or underground methods.

The crown pillar was the 60 m (vertically) thick remaining part of the high-grade Cosmo orebody between the top of the paste filled underground mine stopes and the planned base of the final open pit shell.

There were two major difficulties being considered when choosing the underground or open pit options:

  • a major wall failure in the upper section of the main
    pit wall directly above the crown pillar restricting access from the base of
    the open pit to the top of the crown pillar

  • impact of a high rainfall event while the crown pillar was being mined from either surface or underground resulting in flooding of the underground mine workings.

This paper will discuss the following issues:

  • the process to identify and evaluate the risks in
    both options using knowledge based modelling software; this technique allowed
    the evaluation of a complex set of assumptions to arrive at the preferred
    option

  • remediation of the Watu failure
  • the selection of the preferred option and the
    challenges encountered before, during and after the extraction of the crown
    pillar

  • the planning and geotechnical work to ensure the safe
    extraction of the crown pillar

  • successful outcomes transitioning from open pit operation to a solely underground operation.

Citation:

Robeson, A, Cowan, M and Brockman, M, 2016. A Case Study on the Assessment, Planning and Extraction of the Crown Pillar at Sunrise Dam Gold Mine, in Proceedings Ninth AusIMM Open Pit Operators’ Conference 2016, pp 115–136 (The Australasian Institute of Mining and Metallurgy: Melbourne).