One of the world's biggest independent commodity-trading companies, Trafigura Group, is expected to be the new majority owner of Nyrstar.
Trafigura has entered an agreement and committed to interim funding arrangements of $348 million in a process to secure a restructuring deal with Nyrstar's financiers.
News of the deal came from Treasurer Rob Lucas on Monday.
He said the agreements were an important step towards the successful completion of the restructuring which would result in Trafigura becoming the majority owner of the operating business of Nyrstar, including the Port Pirie smelter.
The announcement by Trafigura comes after a separate announcement by Nyrstar on the outcome of its capital structure review in which Nyrstar confirmed that the South Australian taxpayer-guaranteed funding for Nyrstar Port Pirie was unaffected by the capital restructure. Under the guaranteed funding arrangements, state consent to a change of control of Nyrstar is needed.
Mr Lucas said he had been formally briefed on the planned capital restructure by Trafigura's chairman and chief executive officer, Jeremy Weir, who re-affirmed the importance of Port Pirie's operations to his company's global operations.
"In my conversation with Mr Weir, I sought - and received - his commitment to ongoing constructive talks regarding the repayment of our taxpayer-guaranteed $291 million loan for the Port Pirie smelter operations,'' he said.
"He recognised and re-affirmed the importance of Port Pirie to the company's global operations and understood the state government's clear objective to protect jobs at the smelter.
"Nyrstar and the state will continue to hold talks relating to the guaranteed funding arrangements, targeting a mutually-binding agreement as soon as possible. We hope for a successful resolution, not only for taxpayers, but for the people of Port Pirie, the smelter's employees and their families."
Headquartered in Geneva, Trafigura has $75 billion in total assets and has been Nyrstar's single biggest shareholder with 24.42 per cent of the company's shares.
Founded in 1993, Trafigura is one of the biggest physical commodities trading houses in the world and co-investors in copper mining and smelting as well as oil refineries. It sources, stores, transports and delivers a range of raw materials, including oil and refined products and metals and minerals, to clients around the world.
It has yearly group revenue of $250 billion with total group assets worth $75 billion.
It is the world's second-biggest metals and minerals trader with 95.9 million tonnes last year.
The company is ranked in the top three oil traders globally (2.1bn oil and petroleum products, total barrels traded last year) rivalling Vitol and Glencore.
It co-owns copper mines in Spain, copper smelters in China and oil refineries in India.
The company has 4300 workers in 66 offices in 38 countries.