Acid sulphate alteration in a magmatic hydrothermal environment, Barton Peninsula, King George Island, Antarctica

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<jats:title>Abstract</jats:title><jats:p>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, (Na<jats:sub>0.36</jats:sub>Ca<jats:sub>0.27</jats:sub>K<jats:sub>0.1</jats:sub>□<jats:sub>0.27</jats:sub>)Al<jats:sub>3</jats:sub>(SO<jats:sub>4</jats:sub>)<jats:sub>2</jats:sub>(OH)<jats:sub>6</jats:sub>, and zunyite, Al<jats:sub>13</jats:sub>Si<jats:sub>5</jats:sub>O<jats:sub>20</jats:sub>(OH,F)<jats:sub>18</jats:sub>Cl, 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.</jats:p><jats:p>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.</jats:p>

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