The tunnel would be used to transport iron ore to the wharf instead of shipping it by rail over the level crossing where it would interfere with traffic.

This is one of several scenarios for port development worth hundreds of millions of dollars.

Under the plan, the conveyor belt would be linked to a similar transport system running beside the railway line into Port Pirie and lead to several storage sheds at least a couple of kilometres away.

The underground component would be a challenge for engineers with the big amount of subterranean water and associated seepage problems.

This project alone could cost $100 million.

Another scenario would involve a spur line from the east-west railway track leading to the Pirie River to bring iron ore which would then be transported across the river by conveyor belt.

Both this and the scenario with the underground conveyor belt would use barges to take the ore from the harbour to a waiting ship in Spencer Gulf.

It is envisaged that 20 to 30 million tonnes of ore would be exported each year.