Polymetallic Sulfide Formation And Gold Enrichment On Hydrothermal Vents Of Pacific Seamounts

Mineral zonation studies were conducted on hydrothermal vents of two hot spot volcanoes. One study site is located within the Axial Caldera of the axial hot spot volcano of the Juan de Fuca Ridge. The young high-temperature hydrothermal vent field consisting of two polymetallic sulfide chimneys, five meters high, located at 130°01.5'W, 45°56.5'N, along a fault complex at the base of the southwestern wall of Axial Caldera was sampled during four ALVIN dives in 1983. Temperatures of up to 270°C were measured within the orifice of one of the chimneys, which was then broken off and recovered with the submersible. Both black and white "smoke" was observed to be emanating from the one chimney sampled. The high-temperature chimney extends directly from a field of broken lobate lavas which are located at a water depth of 1,550 meters, about 200 meters east of the caldera wall. The chimney makes one of the shallowest active high-temperature vents studied to date. The vent is surrounded by clumps of vestimentiferan worms and is located within an elongate field of red-colored iron smectite blankets and chimneys. The low-temperature field forms a ribbon 150 meters wide, extending for about 1,300 meters at the base of the wall. Chemical analyses of the hydrothermal deposits ranging from the polymetallic sulfides of the chimney to the outer zones of the low-temperature field show a range of elemental assemblages consistent with temperature zonation around the vent. Chemical zonation within the high-temperature