Epithermal Au-Ag veins have wall rocks that are altered to various hydrothermal minerals, some of which have zoned distributions. Mapping of individual alteration minerals can be useful because, based on the occurrences and distribution of these same minerals in geothermal systems, they can be used to infer temperature, permeability, fluid composition, formation depths and permit reconstruction of the former hydrothermal system (eg Simmons and Browne, 2000). Several key alteration minerals have been recognised that can help identify areas most likely to host gold-bearing quartz veins, based on the occurrence of these minerals associated with epithermal Au-Ag veins of the Hauraki goldfield (+12.3 Moz Au, +54.9 Moz Ag) and geothermal systems of the Taupo Volcanic Zone (TVZ) in the North Island of New Zealand (Fig. 1); both of which are mainly hosted in volcanic rocks. CITATION: Simpson, M P, 2019. Alteration in epithermal Au-Ag and geothermal systems in New Zealand: insights for mineral exploration, in Proceedings PACRIM 2019, pp 149153 (The Australasian Institute of Mining and Metallurgy: Melbourne).