FQM was charged with failing to provide a safe working environment by Western Australia's Department of Mines, Industry Regulation and Safety.

The company pleaded guilty to that charge in the same court before Magistrate Brie Ayling in August.

The incident happened in May 2017 when a processing tank that had previously held limestone slurry was refilled with a weak acidic mixture before being properly cleaned.

This  resulted in an uncontrolled chemical reaction that ruptured the tank's fibreglass roof and sent slurry spraying out.

A field technician working on top of the tank was forced to leap across a 3m drop to avoid the slurry spray, with the lucky worker escaping injury despite a few drops landing on his clothes.

DMIRS mines safety director Andrew Chaplyn said the incident could have been prevented if FQM had cleaned the tank and removed residual limestone before refilling it.

"There was also only one means of access or egress from the tank platform, so having to jump to an adjacent tank exposed the worker to a fall from height hazard," he said.

"All mining operators need to develop and implement change management procedures to identify the potential impact of any proposed changes on the working environment."

Chaplyn said FQM should have initiated an appropriate change management procedure when it used the tank to temporarily hold limestone slurry.

"All employees affected by the change should be provided with adequate information, instruction, training and supervision," he said.

"Worker safety should be every mining company's number one priority."

It is not the first court appearance for FQM this year, with the company also charged with failing to keep workers safe on a mine site after an incident in January.

In that incident a contractor was also fined when a telehandler machine loaded with pipes tipped over and nearly injured two workers, one of which was the contractor's 18-year-old daughter.

It was fined $19,000 for that incident.