BHP Billiton has been ordered to carry out an independent engineering study of the underground operations at the Leinster Perseverance nickel mine in west Australia after two rockfall incidents in the last month.

A seismic tremor measuring 2.3 on the Richter scale caused the most recent rockfall at the mine and caused about 25t of rock to fall near a worker, BHP said.

BHP Billiton Nickel West president and chief operating officer Wayne Isaacs and the government mine inspector have inspected the underground operations to assess the impact of the seismic event, the company said.

The company has been given eight weeks to complete the study, according to a report in WA Business News.