Surface mining operations have resumed at Fortescue Metals Group's Christmas Creek mine, four days after the death of a contractor.

The man was carrying out maintenance on a large piece of mining machinery in the Pilbara mine's heavy vehicle workshop when the accident occurred on Monday.

Surface mining operations at Christmas Creek were suspended as WA Department of Mines and Petroleum (DMP) inspectors carried out a site investigation.

It is the second death at the iron ore mine in less than five months.

The DMP also issued special directions ensuring that Fortescue tightens safety procedures at all of its operations, including lock out/tag out procedures, ahead of a safety audit.

Fortescue said the heavy vehicle workshop was "released" by the coroner and DMP safety inspectors on Thursday, and will now be brought back into service.

The company is now reviewing safety isolation and lock out/tag out procedures.

DMP Director General Richard Sellers said the department was conducting a thorough investigation into the Christmas Creek death and Fortescue was assisting inspectors with investigations.

Another worker who suffered leg and hand injuries in the incident has been released from Royal Perth Hospital.