Abstract
Sulfide and sulfate minerals recovered from Loihi Seamount during PISCES V submersible dives in October 1996 are the first occurrence of high-temperature hydrothermal mineralization documented for ocean island volcanoes. Millimeter- to centimeter-sized particles recovered in talus deposits on the north rim of the newly formed Pele's pit consist of aggregates of pyrite, marcasite (?), pyrrhotite, wurtzite, and barite. The barite occurs as single, clear, euhedral crystals or as acicular, radial crystal clusters on sulfide or rock fragments. The mineral assemblage and the composition of the sulfide phases are similar to those of hydrothermal sulfide from mid-ocean spreading centers. The sulfide assemblage confirms the presence of high-temperature fluids (>250 °C) in the Loihi hydrothermal system. The sulfide samples are not pieces of broken chimney or basal mound structures, or stockwork from lower levels in the hydrothermal system. The euhedral crystals and homogeneous compositions suggest rapid precipitation from a high-temperature plume injected into cold seawater along fractures and fissures that define the north wall of the new pit crater formed during the seismic swarm in July and August 1996.
