Copyright in published works generally lasts for the life of the author plus 70 years. The duration of copyright in subject matter other than works (films and sound recordings for example) is more variable, but generally is 70 years from the end of the year of first publication. You will find the variations from these general rules in the document Duration of Copyright. You should be aware that copyright in unpublished material can be perpetual in some cases.
Before 1 January 2005, the term of copyright in Australia was life of the author plus 50 years for published works, and 50 years after publication for audiovisual items. The extended term of 70 years applies only to material that was still in copyright on 1 January 2005. If the copyright had expired by that date, it stays expired.