Parkes, NSW Australia
Ordovician volcanic belt (porphyry deposit)
Gold and copper
Open pit copper: 0.003 million tons, with 0.325 underground. Open pit gold 0.008 million ounces, 0.357 underground.
Production Open Cut
260,000t a month
4.7 million tons a year
Open pit and underground
220 full time, 200 contractors
Ownership Rio Tinto ( 80 percent ) Sumitomo ( 20 percent)
Northparkes Mines is a copper-gold mine near the remote Australian town of Goonumbla, about 27km north-north-west of Parkes, a regional centre in central-west New South Wales.
The project is a joint venture between Rio Tinto (80%) and Japanese multinational Sumitomo Group (20%). Northparkes produces high-grade copper-gold concentrate, which is shipped to international smelters.
Exploration commenced in the district in the early 1970s when geologists were attracted to the lead-zinc potential of the volcanic belt. Approval for mining was granted in 1992. Exploration continued throughout this time and led to the discovery of three other deposits (E26, E27, and E48) and numerous smaller prospects.
Following an initial open-pit operation at Northparkes, underground block-cave mining has been undertaken since 1997, the first Australian mine to do so. There are currently two open-cut mines and one underground mine.
In November 2006, the joint venture partners approved the development of the E48 block-cave project, which is valued at A$280m, of which A$202m has been spent. The development will extend the mine’s life until 2024.
However, the development was temporarily suspended in January 2009 due to the global financial crises and a fall in the price copper price by 60%. Shareholders approved the restart of E48 project development in September 2009.
It is expected that the E48 project will be completed in 18 months including achieving complete underground mine production.
Northparkes geology and reserves
The ore bodies at Northparkes Mines belong to a class of deposits called porphyry copper-gold deposits. Northparkes occurs within the northernmost exposed part of a long belt of volcanic rocks that extends from Temora in the south.
This volcanic belt is Ordovician in age ranging from approximately 480 to 440 million years old. The mine at the Endeavour 26 ore body, the largest at Northparkes, had pre-mining reserves of around 50 million tons at grade 1.4% copper and 0.4g/t gold.
Total proven and probable reserves for copper are approximately 56 million tons at a grade of 1.1%.
Northparkes supports two open pits and a block-cave underground mine. The latter was developed in two lifts, initially to 480m below surface accessing the first lift of approximately 25 million tons. The second lift extending to the full depth of 830m below the surface accessing 25 million tons.
Block caving is possible at Northparkes due to the nature of the rock and the size of the ore body. Caving occurs when a sufficient area of rock is undercut to the point where the rock mass fails and breaks up. This occurs without the requirement for drilling and blasting and continues to fail and break up whilst the broken rock beneath is removed.
Two coarse ore stockpiles receive coarse material from the surface and underground crushers. Total capacity of each stockpile is 100,000t. Crushed ore is reclaimed by four vibrating feeders from each stockpile.
The grinding circuit is comprised of two separate modules, each incorporating semi-autogenous grinding (SAG), oversize crushing technology, two stages of ball milling and flash flotation. Flotation takes place in two separate modules, each with its own grinding circuit. The flotation process aims to float a sulphide concentrate to recover the major copper and gold bearing minerals (the circuits consist of rougher, scavenger, cleaner, cleaner-scavenger and recleaner treatment stages).
The final concentrate produced for each module assays 36% to 40% copper and is pumped to a concentrate thickener. Final tailing from each module is pumped to a common tails thickener for dewatering.
Final concentrate from the flotation circuits is pumped to thickeners where it is thickened to an average underflow density of 60% solids. Thickened concentrate is then pumped to concentrate storage tanks prior to treatment through the filtration circuit, using ceramic disc filters. The filtered concentrate is discharged onto slow moving conveyor belts, each equipped with a weightometer to determine final production of concentrate.
Production and costs
During fiscal year 2007, a total of 5,297t of ore was mined at Northparkes’ operations. Approximately 43.1 million tons of copper (50% less than in 2006) and 79 million ounces of gold (20% down on 2006) were produced. Copper head grade for 2007 was 0.91%, 0.62% for gold. Both were down on the previous year.