I can now confirm, thanks to the New South Wales Births, Deaths and Marriage indexes, that my Chilean ancestor was indeed, Agustin Aldetete from around the area of Valparaiso, Chile. He came to Australia in 1840 to work for the Australian Agricultural Company as a muleteer (described: huaso) and married convict Mary Connors (Barry). He is believed either to have died as the result of bushrangers in the 1850s. Other huasos to come at the same time included Santo Crina (Crena/Creanor) Bernardo Riba (Reeves)
Are there any Chileans who can help out with my Agustin? Bernardo Riba was baptised in Valparaiso cathedral. Perhaps Agustin came from nearby.