Don't see the real deal very often. This appears to be a 19th C. Argentinian facon. Just finished on eBay.
http://cgi.ebay.com/ws/eBayISAPI.dll...m=170038527686
The attached old picture (published 1890-1924, Carpenter Collection) shows a staged duel between two gauchos using similar long-bladed facon.
Ian.