It's Potosi !!! For my evidence, please go to www.nma.gov.au/collections/highlights/holey_dollar The obverse, near the top, seems to match the photo of the coin you speak of. The reverse, with "PTSI" monogram, is just over half-way down.

The National Museum of Australia spent AUS$130,000 (hammer price AUS$111,000) to acquire a rare 1813 “holey dollar,” Australia's first official minted currency, at the International Auction Galleries' Australian & World Rare Coin auction on November 6th. There are only 300 or so holey dollars extant and this particular piece is one of only five which originated from Potosi, Bolivia.

Source: http://www.thehistoryblog.com/archives/14157

The complete Holey Dollar (obverse and reverse): http://www.thehistoryblog.com/wp-content/uploads/2011/12/NSW-Holey-Dollar.jpg

More Info: This Holey Dollar 1813 (1796/5) of the scarce Potosi Mint type and with fantastic old provenance sold for $129,315

http://iagauctions.com/files/IAG_A75_Review.pdf

Also, I found the following and very interesting web site: www.australianstamp.com/coin-web/aust/earlyaus/holey$.htm which contains a Holey Dollar population by mint and year; including valuable information about this amazing coinage.

Using the information of above web site I did some calculations about the 8 Reales host coins:

Lima, Peru - host coins from 1780-1810 - population: 30 holey dollars (10.87%)
Madrid, Spain - host coins from 1799-1805 - population: 4 holey dollars (1.45%)
Mexico City, Mexico - host coins from 1757-1810 - population: 212 holey dollars (76.81%)
New Guatemala, Guatemala - host coin from 1800 – population: 1 holey dollar (0.36%)
Potosí, Bolivia - host coins from 1783-1808 – population: 26 monedas (9.42%)
Seville, Spain - host coins from 1793-1798 – population: 2 holey dollars (0.72%)
Plus one Holey Dollar with No Mintmark Visible (0.36%) Total: 276 Holey Dollars