By Agence France-Presse
The 268-wagon train started on its solo journey when the driver got down from his cab to carry out an inspection, and was soon hurtling along at up to 110 kilometres (68 miles) per hour.
Mining giant BHP, which owns the four-locomotive train, decided to derail before it reached the town of Port Hedland near its Western Australia Pilbara site, and flicked the points.
The train crashed off the rails, damaging around 1,500 metres (1,600 yards) of tracks, but hurting no one.
Aerial images published by The West Australian showed a trail of twisted wreckage after Monday's incident, with some wagons covered by their loads.
Australia is one of the world's major sources of iron ore.
BHP said Wednesday more than 130 people were working to recover the train and fix the track -- a key access route for the enormous mining facility -- with partial rail operations expected to start up again in about a week.
The mine sites were still running and reserves would be used to maintain port operations, "however they are not expected to cover the entire period of interruption", a BHP spokeswoman said in a statement.
"We will be liaising with our customers in relation to our contractual commitments over this period," she added.
The Australian Transport Safety Bureau said it was investigating the incident. There was no indication of what had caused the train to move without its driver.
"We cannot speculate on the outcome of the investigation however we are working with the appropriate authorities and our focus remains on the safe recovery of our operations," the BHP spokeswoman said.
BHP's shares closed 0.48 percent lower to Aus$33.39 (US$24.18) in Sydney Wednesday as reports in Britain said the Anglo-Australian firm was facing a £5 billion (US$6.5 billion) lawsuit over the deadly Samarco dam failure in Brazil in 2015.
BHP is also facing an Australian class action involving investors pursuing the miner for losses relating to the collapse.
Nineteen people were killed and a wave of toxic waste was unleashed when a dam burst at the mine in one of Brazil's worst environmental disasters.