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Abstract
Discharge of hydrothermal fluids on the seafloor 13 km southwest of White Island volcano has been directly observed at 167 m depth by submersible of the research vessel Calypso. The vents were located on an anhydrite mound several metres high, which we name the Calypso vents. Activity had been inferred by previous cruises to the area, which reported bubble zones at the surface.
The anhydrite cone and adjacent muds were sampled and their mineralogy and chemistry analysed. The anhydrite has not concentrated trace metals in its formation. The finely laminated muds are comprised of nontronite and beidellite smectite clays of probable hydrothermal origin; their trace element enrichment patterns are different from those observed in metalliferous muds near White Island. The Calypso clays are anomalously high in arsenic (530 mg/kg), antimony (150 mg/kg), mercury (90 mg/kg) and thallium (˜500 mg/kg), all volatile metals also found concentrated in subaerial hot spring precipitates; in addition, uranium (138 mg/kg) and molybdenum (1000 mg/kg) are high. The uranium enrichment may be due to locally reducing conditions, as indicated by the high (10 wt%) carbon content of the muds.
The newly discovered seafloor hot springs contrast with the acid springs discharging on White Island, 13 km to the northeast. They represent the relatively low temperature discharge from a submarine geothermal system. Similar active systems can be expected further north in deeper water of the back arc basin, probably with higher temperature discharges and associated with base (and precious?) metal precipitates.