Mining giant BHP will return its Olympic Dam mine to full production by the end of March after completing a $350 million upgrade.
The company was also pushing ahead with a study to potentially double copper production by 2023.
The upgrade, which involved the largest planned shutdown in the asset's 30-year history, included improvements to the smelter and works on the refinery, concentrator and other key pieces of infrastructure and site technology.
Two of the site's four furnaces were also replaced.
Olympic Dam asset president Jacqui McGill said the planned outage was a risk but expected the investment to pay off.
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"We're probably at about two-thirds of our production as a result of that outage, but we're coming back stronger, better, more efficient as a result of that strategic investment," she told reporters at the mine on Thursday.
She would not confirm the company's financial loss as a result of the shutdown, but confirmed it was in the "tens of millions".
Olympic Dam, 600km north-west of Adelaide, remains one of the world's largest copper, uranium, silver and gold deposits.
Copper production this year was expected to hit 150,000 tonnes.
That could rise to 330,000 tonnes by 2023 with the expansion to require a further investment of about $2 billion.
It was expected to go before the BHP board for approval in mid-2020.
The Olympic Dam mine plays a key role in the South Australian government's copper strategy, which aims to boost annual production to one million tonnes by 2030.
Ms McGill called the goal "audacious", but welcomed the government's support.
"We're one of the largest employers in South Australia and I think, based on the resource wealth of this state, having an audacious strategy like that is really important," she said.
Last year Ms McGill said power prices had to fall by 25 per cent before South Australia could effectively attract investors.
But she appeared more optimistic on Thursday when questioned about power.
"We've done a really comprehensive market study, and we're very optimistic about the part that that will play in our cost base going forward," she said.
Premier Jay Weatherill and Treasurer Tom Koutsantonis also toured the mine on Thursday with the premier describing the upgrade as a boost for the local and the state economy.
"BHP is deeply insinuated into the fabric of South Australia," he said.
"BHP is back after a period of uncertainty - recruiting new staff."
