100 Dollars - Elizabeth II 4th Portrait - Koala - Platinum

The Perth Mint's platinum Koala series launched in 1988, positioning Australia as one of the first sovereign issuers to produce a continuous platinum bullion program outside the Soviet Paladium and South African Platinum Leaf issues. By 1999, the series had accumulated a collector following substantial enough that the Mint maintained both bullion and proof variants — a split that complicated mintage tracking across the two-year span this type covers.

Ian Rank-Broadley's fourth portrait of Elizabeth II, introduced across Australian coinage in 1999, debuted on this issue at rollout.