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Granny Smith conversion first of its kind - Paydirt

Tuesday, 12 July 2016

Nearly three years on from its acquisition, Gold Fields Ltd continues to find fresh impetus at its Granny Smith gold mine in Western Australia’s Eastern Goldfields.

There was plenty of scepticism in the industry when Gold Fields paid $US270 million for Granny Smith, Darlot and Lawler (collectively the Yilgarn South assets) with an assumption Barrick Gold Corp was divesting tired assets. However, the South African gold mining major has dispelled any doubts, driving production up from 230,000 ozpa to 300,000 ozpa and keeping AISC below the $1,000/oz mark.

Gold Fields vice president Australasia, Richard Weston, told Gold Mining Journal it had been the company’s focus on both production efficiencies and exploration which had turned Granny Smith around.

“Gold Fields made immediate improvements and has since invested in other opportunities,” he said. “The plant needed some attention and we have done that and we have had a big uptick in reserves last year.”

Granny Smith ’s improvement can be attributed to both Gold Fields’ willingness to back its exploration team and its ability to drive down costs in the processing plant. The company has invested heavily in refurbishment of the Granny Smith CIP plant and has also added a new gravity circuit which is already paying its way with 30% of gold recovery coming from the lowcost process. In June, it unveiled its latest cost-saving measure when power provider Aggreko switched on its high-speed reciprocating engine power station at the mine. Taking feed from APA Group’s Eastern Goldfields gas pipeline which runs through to Tropicana, Aggreko has built a state-of-the-art modular system to fully service Granny Smith. Weston said the move to gas power would bring cost efficiencies and reliability benefits as well as reducing the mine’s carbon emissions by 85,845t over the 10-year contract with Aggreko. “We took advantage of the Tropicana pipeline to upgrade a 25-year old diesel-generated power station and reduce our carbon emissions, making Granny Smith eligible for the Australian Emissions Reduction Fund,” he said. Aggreko is using new generation reciprocating engines, a piston combustion gas engine, which will deliver a 24MW power generating system to the mine. The Granny Smith power station is modular with each 60l engine providing 1.5MW of power to the Wallaby underground mine and Granny Smith processing plant.

Aggreko has operated in the WA gold mining space for more than 20 years, providing short-term power solutions to a number of miners. However, managing director George Whyte said the Granny Smith power station was the first example of its move to longer term power projects. “Traditionally, we have been onsite for two to five years and our service to the mining sector has been built around the unpredictability of mine life; either at the startup or shutdown phase but we are now looking at longterm opportunities. This kind of modular power station is more flexible and is a saving on the capex of a permanent power station.”
Gas-generated power can also have operating cost savings, according to Whyte. “Mining is currently going through a lot of challenges and the industry is looking for ways to reduce operating costs. Power accounts for more than 30% of operating costs but in WA there are a lot of older assets which suffer from inefficiencies.” Aggreko’s modular plant could overcome many of the inefficiency problems associated with diesel plants, Whyte said.

“Rather than the engines going up and down, a controller on site switches individual engines on and off depending on requirements. If one engine is offline for maintenance, another can start up immediately,” he said.
APA ’s gas pipeline is yet to deliver the kind of return investors were anticipating but Whyte expects the trend of moving away from diesel generated power to continue in WA. “There is a definite trend towards cleaner energy and that means conversion from diesel to gas,” he said. “There has been a lot of talk about renewable energy but for industrial applications they are still very risky and don’t provide the required flexibility.”

Whyte anticipated more gold miners to follow Gold Fields ’ lead.

“We are doing very similar set-ups with other clients in Australia but this is the first long-term set up and the first to use this new technology,” Whyte said. “I think now such a respected miner as Gold Fields has adopted the technology, others will follow.”
Access to gas is still the most obvious challenge for other miners but Whyte said it could provide long-term planning to meet various stages of project development.

“We can put in diesel early, particularly for juniors starting up, but still retain the opportunity down the track to replace the diesel with gas.”

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