It may be "currency" but its a joke on you, me and every other Australian citizen.
if you were to ask the Mint for the reason for such a silly value being stamped on it, they would probably give you Ben Bernanke"s famous comment "it"s just tradition".
You are not going to tender it for a $100 dollar purchase.
In fact it"s MONEY. Because it"s GOLD.
And money trumps currency any day.