BHP Billiton insists the toxic products from its Olympic Dam expansion can be safely transported through central Australia and exported from Darwin, despite a derailment and spill this week adding to environmental concerns about the export route.

Toxic copper concentrate owned by OZ Minerals spilled into the Edith River on Tuesday after bad weather caused a freight train to derail near Katherine, about 320 kilometres south-east of Darwin.

 

BHP was not involved in the spill, but plans to use the same rail route to export copper concentrate from its Olympic Dam expansion, which, at an estimated cost of $30 billion, ranks as arguably the company's most important growth project.

BHP expects a train to depart Olympic Dam bound for Darwin every day.

The copper concentrate includes traces of uranium, gold and silver, and BHP will build new storage at Darwin Port to house the 1.6 million tonnes of concentrate produced annually until it is ready to be loaded onto ships.

BHP spokeswoman Kelly Quirke said the company remained confident the route could be managed safely, despite the cyclones and other wild weather that typify the wet season in the Top End.

''We remain confident in our transport options for the Olympic Dam expansion, as outlined in the environmental impact statement which was approved by the federal and state governments,'' she said.

BHP has promised to use rail wagons with waterproof and airtight lids for the journey to Darwin, and has extensive plans for a ''closed circuit'' upon arrival at Darwin to prevent pollution.

OZ Minerals' export of copper concentrate through Darwin has already attracted controversy amid fears that some of it has spilled into Darwin Harbour.

OZ Minerals said about 1500 dry tonnes of copper concentrate was on the derailed train, but the exact amount of concentrate lost would not be known until better weather allowed safe access to the crash site.

OZ Minerals said it was confident the environmental impact of the incident could be minimised.

''From an environmental perspective, any concentrate that has settled will be cleaned up,'' a spokeswoman said. ''Given the large volume of water flowing through the system, it is likely that any concentrate that has been impacted by the water would be highly diluted.''

Rio Tinto-controlled Energy Resources of Australia briefly shut down operation at its Ranger uranium mine while the storm passed but has confirmed that the mine escaped damage from the diminishing cyclone.

BHP said it would continue monitoring the movements of ex-tropical cyclone Grant through the Northern Territory in case it approached the company's manganese mine at Groote Eylandt.

BHP is poised to start preparations for the Olympic Dam expansion - including works on the proposed open-pit site - within weeks.

The January works, which will include the clearing of land for the workers' village, are part of a $1.2 billion tranche of ''pre-commitment'' spending that BHP promised before a final investment decision on the project.

The company insists the works scheduled for next month will not prejudice the outcome of a final investment decision, due by mid-2012.

BHP yesterday signed a heads of agreement with ASX-listed minnow Archer Exploration, giving the big miner an 80 per cent interest in five tenements around the Olympic Dam site.