BHP Billiton successfully evacuated 79 employees Oct. 7 following a rock fall incident at its Perseverance underground nickel mine at its Nickel West Leinster operation in Western Australia.

The incident was caused by a seismic event, which caused a power outage, BHP told the news media.

A spokeswoman for the company told Dow Jones Newswires that contact was maintained at all times with employees and that no one was injured.

In July 2009 the mine was nearly closed after two rock fall incidents within a period of three weeks, which injured and trapped a total of three workers. These incidents prompted the Western Australia State Mining Engineer to direct the company to undertake an independent engineering study of its operations.

The mine is part of the Nickel West operations which includes Mt. Keith, Kwinana and the Kalgoorlie smelter.

A BHP spokeswoman said the company will immediately begin a comprehensive investigate to find the root cause of the rock fall and the subsequent power outage.