This paper details successful implementation of a revolutionary pit access
system involving excavation of an 'in-the-wall' ramp at Three Mile Hill
open pit operated by Gold Mines of Coolgardie, formerly Goldfan
Limited, at Coolgardie, Western Australia. Three Mile Hill is a
medium-size, open pit, gold operation typified by hard, competent, fresh
rock conditions from near surface. The project involved construction of a
haulage tunnel or decline access located in the wall of an open pit in place
of a conventional pit access ramp. Works undertaken as discussed herein
included excavation, support, ventilation, dewatering, services
installation, commissioning and monitoring. Prior to implementation, the
conventional hardrock pit slopes and designs were constrained by the
presence of infrastructure and a main road to the North and by adjoining
leases to the Southeast. The combination of these factors and economic
considerations resulted in a decision to proceed with an innovative
in-the-wall ramp access system that is believed to be the first of its type in
Australia. Back-analysis indicates that implementation resulted in a cost
saving of as much as A$3.6 million and increased mineable pit reserves.
The paper deals with the successful implementation and operation of the
in-the-wall ramp haulage as well as an economic evaluation that is aimed
at drawing some general conclusions on favourable conditions for
implementation in other mining scenarios.