One of the more interesting aspects of Australia pre-decimal history is the nature of gold’s conversion into colonial currency. Whereas the UK minted currency is 22k with remaining copper, natural gold tends to alloy with various metals.
Furthermore, did you know that gold is believed to be created in the destruction of stars; when they collapse and go supernova? (fig. 0) I didn’t either, until about two years ago. So when I wax lyrical over the gold Darius in my collection, I am reminded that this 2400yr old culturally important artefact is actually one of the more ancient materials of this universe.

credit: Wikipedia
Which gives me to thinking of the following question. How did the earliest civilizations have the processes to create 98% gold purity when Alexander the Great was conquering the known and unknown world, yet mint officials in the NSW Colony couldn’t manage the separation of gold alloy until the late 1860’s? These are the sort of thoughts that plague my mind, yet give rise to articles that hopefully interest CAB readers.
Geoffrey Heidemann of Cockatoo Coins (and moonlighting gold geologist) reports the following mines as supplying Sydney Mint – Sofala & Bathurst – while Beechworth, Ballarat and Bendigo fed the Melbourne Mint. Barring a more detailed analysis of gold shipments that illustrates otherwise, the following gold alloys were likely mined in NSW. The alloys are composed of gold (Au), silver (Ag) and copper (Cu), with trace Iron (Fe).
Fig. 1 | Fig. 2 | Fig. 3 |
Au 91.78 |
Au 91.38 |
Au 91.84 |
Ag 5.52 |
Ag 5.81 |
Cu 4.73 |
Cu 2.70 |
Cu 2.52 |
Ag 3.43 |
+ trace Fe |
FIG. 1 – 3
The Sydney mint produced half sovereigns until 1869 (from memory, 62,000 in 1867 and 154,000 in 1869), these were most likely dated 1866. Given that the sovereigns moved towards a gold copper alloy around 1868, it makes sense that some 1866 half sovereigns will have more copper.
If I recall David Briggs’s comments in his 2nd ed. Half Sovereign book, they didn’t manage to extract the silver straight off the bat. It took some years to perfect. It’s a period of Australian gold I will analyse more frequently as time and stock permits. I’ll be curious to see if we can find 20-23% of the date heavier in silver (62,000/154,000 is less than 25/75 in proportion), illustrative of improvements in the Miller process as the various mintages were released. Cheers, Les