The lost production is estimated at around 8000 ounces, equivalent to a 2 per cent decrease in annual production in the September quarter.

St Barbara expects to recover the lost output in the December period, therefore maintaining its full year production guidance for the 2021 financial year at 175,000–190,000 ounces.

The fall of ground at Gwalia occurred after a large firing triggered a number of seismic events, the largest of which was measured at 1.9 local magnitude.

St Barbara confirmed that there was no personnel underground at the time, with the ground fall identified only upon re-entry to the Hoover Decline.

This was estimated to contain around 30 tonnes of material.

St Barbara suspended all work at depth as authorities worked to assess the seismic information.

Investigation and rectification work took longer than expected as a total of 30 metres lateral rehabilitation was required.

The decline has now reopened and mining activity has resumed below this level.

The Gwalia mine is estimated to have 2.1 million ounces of gold in reserves at a grade of 6.4 grams per tonne.