Warm-water faunal communities and zinc- and iron-rich sulfide deposits in the axial valley of the Juan de Fuca Ridge were photographed and sampled at a site about 15 to 20 km north of the Blanco Fracture Zone, approximately 500 km west of the coast of Oregon. Fine-scale bathymetric profiling along the 1-km wide axial valley reveals a shallow apparently continuous axial depression bisecting the planar valley floor. Faunal communities were observed in 75% of the camera traverses across this depression over a distance of 4 km. Although active venting of hot water was not directly observed, higher than ambient temperatures are inferred from the presence of sulfides and fauna that resemble those associated with previously described hydrothermal-vent systems. The presence of pa agonite coatings on basalt recovered with the sulfides, the freshness of the sulfide minerals, and the thin (< 1 cm) oxidized crust on the sulfide deposits all imply that volcanism and deposition of sulfides are recent events.

Sulfides dredged from one of the vent areas include: (1) a porous black sulfide consisting of sphalerite, wurtzite, and minor chalcopyrite, pyrite, galena, and cubanite; (2) a spongy gray sulfide consisting of sphalerite and minor pyrite; and (3) a yellow sulfide consisting of pyrite, marcasite, and sphalerite. Black and gray sulfide constitutes 95% of the total recovered sulfide. Other minor phases include amorphous silica, anhydrite, gypsum, barite, sulfur, and secondary iron oxide. Sphalerite is commonly colloform, with delicate growth zonation; Fe/Zn ratios across growth zones vary, and Cd content is low. Well-formed hexagonal wurtzite crystals have broad growth zones; Fe/Zn ratios and Cd content decrease from core to rim.

The results of bulk chemical analyses by atomic-absorption spectroscopy are:

Table

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