Early developments in treating pyritic and refractory gold ores in Australia

After quartz, pyrite (iron sulphide) is the mineral most commonly associated with gold. In many pyritic gold ores significant gold occurs as intergrowths and small inclusions in the pyrite and probably in some cases in solid solution. Extracting this gold from pyrite presented a major challenge to early metallurgists, particularly when using traditional methods of crushing and gold extraction by mercury amalgamation. In the late nineteenth century new techniques were developed in an attempt to treat these refractory gold ores. In Australia experiments and developments were made at key pyritic gold deposits and gold mining centres including in: central Victoria; New South Wales at Harden and Majors Creek; in Queensland at Ravenswood, Charters Towers and Mount Morgan; and Western Australia mainly at Kalgoorlie. Treatment processes evolved from concentration and finer grinding of the pyrite to release the gold for amalgamation, roasting to assist the release of the gold and chemical treatments, including chlorination and eventually cyanidation, to extract the very fine gold particles into solution. None of these techniques were developed in isolation; rather there was a vigorous transfer of ideas and information between mining areas in Australia and across the world, leading to improvements for local conditions and different ore characteristics.