"They (inspectors) are still putting a time line together, so the details of how long this will actually take have not been established yet," a DEC spokeswoman said.

The probe at seven ports follows an investigation into bird deaths in Esperance port in the south of Western Australia state that were caused by lead poisoning. The probe forced the closure in March of the giant Magellan lead mine, owned by Canada's Ivernia Inc.

Health officials had ordered a halt to shipments of lead from Esperance before expanding their investigation to cover concerns arising from shipments of nickel and other ores and metals.

Inspectors were expecting to find some heavy metals at the additional ports being probed, particularly around loading systems and equipment, the DEC has said.

Oxiana relies on the port in Geraldton to ship out minerals from Golden Grove, which yields zinc and copper concentrates along with smaller volumes of a concentrate that contains a mixture of silver, gold, lead and copper.