The Calypso geothermal field, mapped by the R V Sonne
(cruise SO-135) in 1998, includes four main sites, the Northern Vent Area
(centred on 37 36.7'S, 177 06.2'E, area 1.5 km2), Central Vent Area
(37 39.4'S, 177 05.2'E, 1 km2), Southern Vent Area (37 41.7'S,
177 06.0'E, 1 km2) and Mercury Vent Area (37 41.3'S, 177 07.3 'E,
0.5 km2). Hydrothermal activity at the vent sites is controlled by
minor, sub-parallel NE-trending normal faults. Gas bubble trails (C02) and
shimmering hot water vent from fractures and joints between large blocks of
silicified volcaniclastics and in depressions in the sediments at the base of
these outcrops. Measured maximum vent temperatures are between 180C and 201C.
Venting fluids are at, or just below, boiling for water depths of 200 m. Rock
samples recovered by dredge from the sites include massive anhydrite,
clay-altered pumiceous ash, silicified volcaniclastic sediments and
volcaniclastic breccias cemented by sulphur. Clay-altered samples, dominated by
randomly interstratified illite-smectite and accessory chlorite, indicate
formation environments of 70C to 90 C. Native sulphur is abundant throughout
the samples. Fine-grained (<1 mm) disseminated pyrite and vein pyrite occurs>
in the clay-altered pumiceous volcaniclastics and argillites. In the Southern
and Mercury Vent Areas, fine-grained orpiment, realgar and cinnabar have
deposited in the sandy matrix of volcaniclastic breccias. Amongst the cinnabar,
small (<2 mm) beads of native hg formed on the surface of several rocks>
following their recovery. These samples also contained abundant light
hydrocarbons, which coat the rocks with an oily sheen.