I have recently purchased and have began to fall in love with many of the Sovereigns, especially the Aussie ones. I read a nice article online from an Australian coin collector, charting the history of gold and gold coins in Australia. He stated that these models were the first to be minted using the newly discovered gold from a flurry of prospectors. The first series are really rare, under 20 in existence the article states, and this series has around 2000 or so minted IIRC. A true piece of history, to be sure!
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