"The company expresses its sincere condolences to the family, work colleagues and community at this time and support is being provided," St Barbara said in a statement.
The incident has resulted in a halt to operations at Simberi as a state-wide safety briefing is conducted.
A detailed investigation into the incident is also being undertaken.
The loss at Simberi comes following a period of operational improvement at the mine, which went cash flow positive for the first time in December 2014 after its acquisition in 2012.
Despite returning a $A14 million half-year loss at the mine production was up 37% during the December quarter over the previous quarter.
Before this, underperformance at Simberi and the troublesome Gold Ridge mine in the Solomon Islands had proved problematic for the company, with the pair the main culprits behind the $501 million loss last financial year.
At that time, St Barbara managing director and chief executive Bob Vassie said the company was focused on turning Simberi into a cash-generating operation.