This is a silver proof version of the mint set issued in Australia just before the Rank-Broadley Effigy of Queen Elizabeth II was replaced with her Jody Clark portrait.
The Mint says:
"The end of an era for Australian currency, the Ian Rank-Broadley design has been proudly included on the obverse of Australia’s coin currency since 1998, and was the fifth effigy of the Queen to be featured.
Ian Rank-Broadley and his effigy design, highly regarded for its realism, joins an alumnus of previous effigy artists including Mary Gillick, Arnold Machin OBE RA, Raphael Maklouf, and Vladmir Gottwald.
In September 2018, the sixth effigy to appear on Australian currency was unveiled. The new Commonwealth design by Jody Clark will begin its gradual transition onto Australian coinage in 2019 and continue into 2020.
To commemorate the conclusion of the fifth effigy by Ian Rank-Broadley, the Mint has produced a limited mintage of 2019 Six Coin Proof Sets in gold and fine silver." | 
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