Traditional underground mining methods have extracted much of the high grade
ore in the Fimiston Open Pit area, but huge quantities of low grade material
remain in “haloes” around the orebodies under the Golden Mile. It is these
“Haloes” that are being mined in the Open Pit.
The Fimiston Open Pit is the largest open cut gold mine in Australia. When
completed it will be some 3.8 kilometres long, 1.35km wide and go down to a
depth of more than 500 metres. Currently the open pit operation moves around 85
million tonnes of material per year making it the single largest open pit
operation of any commodity in Australia, on a tonnes per annum basis. Of this
some 12 million tonnes of gold bearing ore are produced and milled through the
Fimiston Mill. The remaining material is comprised of lower grade ore and waste.
The strip ratio for the operation is between 5.5 and 6.
Mining is carried out 7 days per week, 24 hours per day, 365 days a year in
the Open Pit.
Open pit mining on the Golden Mile is complicated by the presence of
underground workings including stope voids, shafts, drives and cross-cuts of
workings from the original underground mines that date back to 1893. There are
about 3,000 km of old mine workings under this area. These have an impact on all
aspects of the Open Pit operations from grade control to drilling and blasting
to mining, and many detailed procedures and work practices have been developed
to deal with these.
The Fimiston Open Pit currently has a remaining mine life of some 16 years,
being due to finish surface mining in 2018. During this time the mine will move
1,129 million tonnes of material and produce more than 10 million ounces (300
tonnes) of gold.