Mineral Mines & Quarries Inspectorate | Alert | No.425 V 1 | 17 February 2023

Fall of equipment and persons into a stope void

What happened?

On 15 February 2023, a light vehicle and drill rig fell approximately 15 metres into a stope void in the underground workings of the Dugald River mine in North-West Queensland. The operator of the drill rig was rescued with minor injuries but sadly on 16 February, when the light vehicle was recovered from the stope, it was confirmed that two workers were deceased in the vehicle.

How did it happen?

Early investigations suggest that the stope void had been caused due to bogging operations on the level below the area where the light vehicle and drill rig had been operating. It is unknown at this stage why those bogging operations were being carried out.

Key issues

• Mining to remove ore and subsequent backfilling activities can result in hazards, including the formation of voids within stopes.
• A void within a backfilled stope can result in slumping of the fill material and this can impact on the structural integrity of roadways crossing the stope area.
• Stope voids can be created in a number of ways, including when material is bogged or mucked from below, or due to the movement of ground.
• Where the potential for backfill slumping in a stope is identified, the risk control measures that are required will vary depending on the specific circumstances of each stope.

Recommendations

All Operators and Site Senior Executives of underground mines that contain stopes should immediately:

• take steps to ensure all stopes at their mine that have been backfilled, including roadways above backfilled areas, are structurally sound and where any voids and/or slumping is identified, implement controls to ensure risk to workers is managed to an acceptable level. This may include:
• controls to prevent the loss of material from the bottom of the stope which may lead to the formation of a void.
• controls to prevent any inadvertent bogging or mucking of material from the bottom of the stope.
• controls to manage the risk to workers in the vicinity of, or travelling over, areas of the mine that may be affected by slumping in stopes.
• audit and review the effectiveness of the mine's safety and health management system, as it relates to controlling hazards and risk to workers associated with working in the vicinity of backfilled stopes.