Northparkes Mines

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.

 

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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 walls.

 

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 1.2:1.

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.