Rio Tinto has apologised after a radioactive capsule appears to have fallen off the back of a lorry and been lost in western Australia sometime between 12 and 25 January.
It now faces a search over an area of 1,400km, between Newman and Perth, for the missing Cesium-137, which has sparked an official radiation alert and search by state authorities.
"We recognise this is clearly very concerning and are sorry for the alarm it has caused," said Rio Tinto iron ore chief Simon Trott.
Local authorities suggest the risk to the public is low, but direct contact with the device could cause radiation burns and sickness - similar to having ten x-rays an hour.
"We have completed radiological surveys of all areas on site where the device had been, and surveyed roads within the mine site as well as the access road leading away from the Gudai-Darri mine site," said Trott.
He added a third-party contractor had been responsible for packaging and transporting the capsule, which was part of a gauge to measure iron ore density.
Rio Tinto was previously at the centre of controversy after destroying two 46,000-year-old aboriginal rock shelters at Juukan Gorge in Australia in 2020 to expand an iron ore mine.