A loaded train travelling from Newman to Port Hedland stopped about 211km into its journey yesterday morning to allow the driver to inspect an issue with a wagon.
While the driver was outside the train, it took off with no one on board.
The train, comprising four locomotives and 268 wagons, travelled 92km before being deliberately derailed at a set of points operated by BHP's Integrated Remote Operations Centre, around 119km from Port Hedland.
No one was injured.
The Australian Transport Safety Bureau is looking into the incident, but says its investigation won't be complete until the second quarter of next year.
BHP said it was cooperating with investigators.
Rail operations have been suspended.