Volcanic-hosted advanced argillic alteration on Barton Peninsula comprises an assemblage of chalcedonic silica, alunite family minerals, pyrophyllite, pyrite, native sulphur, zunyite and rutile, characteristic of an acid sulphate-type epithermal system. The minerals minamiite, (Na0.36Ca0.27K0.1□0.27)Al3(SO4)2(OH)6, and zunyite, Al13Si5O20(OH,F)18Cl, are reported at this locality, and in Antarctica, for the first time. The WNW-striking, 1 km-long zone of alteration is hosted by early Tertiary andesitic rocks and contained in a 1.5 km-wide depression, rimmed by an arcuate ridge, probably representing a volcanic crater or small caldera structure.
Stability relations of minerals in the advanced argillic alteration zone indicate alteration took place under acidic conditions in the near-surface environment. Mineralogical and textural evidence also suggest alteration occurred in a magmatic hydrothermal system, possibly with a magmatic steam component, rather than in a supergene or steam-heated environment.
