British Sovereign Queen Victoria "Australia Mint"
Grade range:  Very Fine - Extra Fine+
Minted: 1857-1870
Actual Gold Content: .2354 troy ounces

“The sovereigns from 1855 to 1870 are among the most important and valuable series in Australian numismatics. These were the first coins struck by the Royal Mint in Sydney that was established in 1855 as the first branch of the British Royal Mint.  These sovereigns have a distinctive ‘Sydney Mint’ reverse. This is the only time the Royal Mint permitted a design unique to a branch mint."

The design is unlike an other minted Sovereign, featuring a young Victoria with a sprig of banksia (a type of wildflower unique to Australia) in her hair and the 'Sydney Mint' reverse just mentioned.  With a total mintage of just 1.22 million, 1870 is also the fourth rarest date by mintage in the series (1857-1870) and the last year the coins were minted prior to the change to the standard British design of the era.  The World Gold Coin Catalog suggest a retail price of $500-$550 in similar condition.  

Historical commentary (courtesy of Michael Marsh - "The Gold Sovereign"):

With large tracts of gold being discovered in the Australian interior, west of the young Sydney colony, the colonial government of New South Wales sought approval from Britain to open a branch of the Royal Mint.  Approval was granted in August 1853, and several pattern sovereigns were struck in London for consideration.  These patterns, dated 1853, bore a uniquely Australian design: the obverse carried a new rendition of the Queen by James Wyon, while the words SYDNEY MINT ONE SOVEREIGN with a crowned AUSTRALIA within a wreath of banksia graced the reverse.  This was the first time anywhere in the Empire that the coin stated its denomination.

Meanwhile, in Sydney, work had begun on establishing the premises of the new mint.  The facility occupies the south wing of the old "Rum" hospital, and was opened on May 14, 1855.  The transformation of raw gold from the gold fields into coinage begun in earnest, and by the end of 1856 over a million of the new colonial sovereigns had been struck.

In 1856, Leonard Charles Wyon, who had designed the reverse a few years earlier, was ordered to begin redesigning the obverse, perhaps in response to criticism that the obverse bust of the Queen was somewhat too mature.  The new disign, which featured a younger Queen wreathed in native Australian banksia, appeared on an 1856 pattern and later on currency issue coins dated 1857.  This well-received design graded the Australian sovereign until 1870.