2013 Australian Mining Two Coin Proof Year Set including commemorative $1 and 20 cent coins. The Australian gold rush of the 1850's transformed a developing colony into an economic contender. Gold, the siren song of prosperity, drew migrants from Europe, North America and China, boosting Australia's population from 430,000 to over a million people in just a decade. From these beginnings grew a mining industry that constitutes more than five per cent of Australia's gross domestic product today. Mintage no more than 25,000. $1 Diameter 25.00 mm, weight 9.00 grams, 20c Diameter 28.52 mm, weight 11.30 grams.