Acid Sulphate Alteration in a Magmatic Hydrothermal Environment, Barton Peninsula, King George Island, Antarctica

Debbie C. Armstrong*
British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET, UK
*Present address: 113 Longacre Road, Singleton, Ashford, Kent, TN23 5FR, UK

Abstract: 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, (Na0.36Ca0.27K0.10.27)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.

Keywords: volcanic-hosted argillic alteration • acid sulphate-type epithermal system • Antarctica

Mineralogical Magazine; September 1995 v. 59; no. 396; p. 429-441; DOI: 10.1180/minmag.1995.059.396.05
© 1995, The Mineralogical Society
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