30 Dollars - Elizabeth II 4th Portrait - Koala - Silver Bullion Coin

Australia's 1-kilogram silver Koala series has been issued annually by the Perth Mint since 2007, with the reverse design changed each year — a deliberate strategy to encourage collector repurchases rather than simple bullion accumulation. The 2015 issue falls under Ian Rank-Broadley's fourth portrait of Elizabeth II, which had been the Australian standard since 1999.

Perth Mint kilosilvers from this period were struck to .999 fineness rather than the .9999 standard the Mint applies to its gold issues — a pragmatic distinction driven by silver's greater susceptibility to surface spotting at ultra-high purities when exposed to atmospheric sulfur compounds during storage.