Initial ɛNd isotope data for the four granites related to the Ardlethan Sn deposit in the Wagga Sn belt of the central Lachlan fold belt of eastern Australia range from −11.6 to +2.1, increasing with increasing fractionation. The four granites beneath the Renison tin mine in western Tasmania range from −6.1 to −3.9. The data clearly establish the presence of light rare earths of mantle origin in the fractionated granites associated with the Ardlethan porphyry Sn deposits and hint at the same relationship for the Renison granites, though in this case the mineralizing pluton is probably yet to be discovered. Sulfur and carbon isotope data from the Ardlethan and Renison ores, and from similar deposits in Tasmania, suggest that mantle volatiles played a significant role in the genesis of Sn granites and deposits. Mantle input may have occurred either by mixing of crustal and mantle melts or metasomatism by mantle-derived fluids.