A mining company has been fined $35,500 and ordered to pay $10,000 in costs after an integrated tool carrier and blast truck fell into a 13-metre deep sinkhole in October 2018.
The cavity was formed after ground subsided in the floor of an open-cut gold pit.
Minjar Gold Pty Ltd appeared in the Perth Magistrates Court on 29 March 2023 after pleading guilty to failing to provide and maintain a safe work environment.
While no one was injured in the incident, four workers from a blast crew had been working in close proximity to the bomb truck minutes earlier.
The sinkhole also engulfed a number of charged blast holes.
Investigations found the mining operators had not treated backfilled underground workings as a void, allowing work to be carried out above an area of unknown stability.
Minjar Gold had an agreement with Golden Grove Operations Pty Ltd (formerly known as EMR Golden Grove) to mine and process gold oxide ore at the company's operations located around 52 kilometres south-east of Yalgoo.
Golden Grove was fined $35,500 for its role in the same incident in June 2022.
Acting WorkSafe Chief Inspector Mines, Christina Folley said Minjar Gold should not have allowed workers and plant to operate in the pit.
"The workers in the area shortly before the incident were lucky to escape and this incident could have resulted in serious injury or loss of life," Ms Folley said.
"While the company had identified the stope void as a risk, it did not implement the recommended controls.
"Minjar Gold should have properly applied a Voids Procedure or other control such as confirmation of backfill competency, probe drilling or a geotechnical review."
Ms Folley said geotechnical hazards were well recognised in the mining industry and that mine operators must monitor and record any change in underground conditions below open cut workings.
"Voids pose a significant workplace risk, so mine operators must ensure underground workings close to active work areas are marked on all plans.
"Minjar Gold should have developed safe working practices that did not presume any stope was tight filled."
