A GOLD-COPPER ASSOCIATION IN ULTRAMAFIC-HOSTED HYDROTHERMAL SULFIDES FROM THE MID-ATLANTIC RIDGE

Sulfide samples from the Logatchev hydrothermal field (14 degrees 45' N, Mid-Atlantic Ridge), which occurs on an ultramafic substrate, show a bimodal distribution of copper- and zinc-rich mineralogies, both of which have elevated gold contents. The copper-rich vents show an unusu al depression-hosted morphology with few chimney structures. Copper-ri ch samples show evidence for a primary gold-copper association, as wel l as gold concentration during small-scale replacement and reworking p rocesses. Evidence from vent morphologies, Au/Ag ratios, and sulfidati on state suggest that, in the copper-rich samples, gold was not transp orted as Au(HS)(2)(-).