Three cross sections, 200 m apart, display the
distribution of indicator hydrothermal minerals across the Empire zone of the
Golden Cross epithermal Au-Ag deposit, Waihi, New Zealand. These minerals are
used to interpret the temperature and composition of hydrothermal fluids. The
distribution of interstratified illite-montmorillonite and illite indicate that
temperatures ranged from 140 to >220C, with temperatures above 220C
predominating. The mineral assemblage of
quartz-adularia-chlorite-illite-calcite-pyrite envelops the Empire vein system
and stockwork, and reflects formation from an alkali chloride water whereas the
mineral assemblage of replacement calcite-interstratified illite -
montmorillonite-kaolinite forms a carapace and reflects formation from a
CO2-rich steam-heated water. Alkali chloride waters
appear responsible for the epithermal Au-Ag mineralisation.