It has been revealed that a large sinkhole 13 metres in depth trapped two mining vehicles at an open pit mine in Western Australia last October.
The incident was outlined publicly in a report filed by the Department of Mines, Industry Regulation and Safety (DMIRS) last Friday.
While no one was hurt and the vehicles were not occupied, four workers were in close proximity at the time of the incident.
The sinkhole occurred when a pit floor undergoing surface drill and blast operations at the mine (not named in the report, but identified by various news outlets as EMR Capital’s Gossan Hill gold-silver-zinc mine) receded into a backfilled slope.
An explosives truck, integrated tool carrier, and several charged blast holes on the working floor’s blast pattern were subsequently engulfed.
A risk assessment carried out at the site in December 2017 identified the stope void hazard but the recommendations of the assessment were not followed, according to the DMIRS.
The report cited management’s decision to move from strict void management protocols to standard mining practices in July 2018 on the erroneous assumption that the backfilled stope void was tight-filled a contributory cause to the incident.
“At the time of subsidence, the backfilled underground workings were not treated as a void allowing work to be undertaken above an area of unknown stability,” the report stated.