Open cut mining
History of Open Cut mining at Northparkes
Open Cut mining was used to access the near
surface portions of copper-gold deposits at Northparkes. Initially
it was used to allow accelerated ore processing prior to
the commissioning underground operations, but also to
supplement underground production during the transition from one
cave to another.
As a result open cut mining has typically
been undertaken on a campaign basis, often reyling on contractor
mining. The most recent campaign in the E22 open cutpit was
completed in September 2010.
Open cut mining commenced with the E27 pit in December 1993 and
the E22 in January 1994. The gold enriched oxide ore was
processed through a separate CIP (Carbon-in-Pulp) gold circuit
prior to the construction of the copper-gold sulphide processing
circuits in 1995. Ore was then stockpiled for blending with E26
underground material. These initial open cut mining campaigns were
completed in November 1998.
Mining of the E22 pit recommenced in July
2000, this cutback was completed in 2002 without reaching design
depth due to deteriorating wall conditions. Open-cut mining in the
E27 pit then recommenced in 2003 adopting a different mining method
to the E22 campaign, focusing on pre-splitting all final walls and
reducing blast damage with buffered blasting near final
These measures, which increased mining
costs by a relatively small amount, allowed inter-ramp wall angles
to be substantially steepened from 52.5 degrees to 60 degrees. As a
result, 5.6 million tonnes of ore was recovered from E27 pit
against an original plan of 3.4 million tonnes ore. That cutback of
the E27 pit was completed in 2005.
In 2009 the E27 pit was granted approval to commence in-pit
tailings, which is the disposal of tailings from the ore processing
facility to fill the void left from the previous mining campaign.
This ensures that post mining, the void would no longer exist, and
rehabilitation of the area would be able to proceed.
The E22 pit was reopened in 2007 to
supplement production during the construction of the underground
block cave mines of the E26 and E48 projects.
Mining was conducted on a 24/7 basis and was expected to
be completed in July 2010. The existing pit is being widened and
deepened by undertaking a 40 metre wide cut-back of the full
perimeter. That cutback width is considered the minimum for
efficient and cost-effective mining practice.
Final pit dimensions will be 550 metre diameter and 230 metres
deep. The E22 pit will yield a total of 12.3 million tonnes of ore
grading 0.49 per cent Cu and 0.35 grams/tonne Au, including 3.2
million tonnes of high-grade ore grading 0.59 per cent Cu and 0.46
grams/tonne Au and 9.1 million tonnes of ore grading 0.45 per cent
Cu and 0.30 grams/tonne Au. Overall ore/waste strip ratio will be
Waste was stockpiled in a waste dump immediately south of the
pit where it is available to be used in the construction of
tailings storage facilities.
Mining was undertaken with a fleet comprising one 300 tonne
primary excavator, one 120 tonne secondary excavator and twelve 100
tonne Caterpillar 777D trucks with ancillary support equipment
including dozers, graders and water carts.