Abstract

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 unusual depression,hosted morphology with few chimney structures. Copper-rich samples show evidence for a primary gold-copper association, as well as gold concentration during small-scale replacement and reworking processes. Evidence from vent morphologies, Au/Ag ratios, and sulfidation state suggest that, in the copper-rich samples, gold was not transported as Au(HS) (super -) 2 .

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