Gold, Ag, Cd, Pb, and Sb behave similarly to Cu and Zn and are enriched close to the surface of the mound. This is interpreted as evidence for zone refining, a process in which elements that are mobilized from previously deposited sulfides in the interior of the mound by later hydrothermal fluids are transported to the surface, where they reprecipitate as a result of mixing with ambient seawater. The trace-element composition of pyrite and chalcopyrite separates is similar to the bulk geochemistry. However, down to about 50 mbsf, Au, As, Sb, and Mo values in pyrite separates are generally higher than in bulk samples and chalcopyrite separates. Below this depth, these elements appear to be enriched in chalcopyrite separates.
Cobalt is typically more enriched in pyrite than in chalcopyrite throughout.
A major difference between pyrite and chalcopyrite separates is the strong enrichment of Se in chalcopyrite at the top of the mound, whereas pyrite separates show a moderate increase of Se with depth. These values do not change significantly downhole, but samples collected from the top of the mound appear to have somewhat lower delta 34 S values than samples from the interior. Mineralogie, Technische Universit t Bergakademie Freiberg, Brennhausgasse 14, D-09599 Freiberg, Federal Republic of Germany.