Isotopic fractionations between given sulfide minerals are relatively constant throughout the B-1 orebody and between all six deposits [studied]. The mean pyrite-sphalerite, sphalerite-galena, and pyrite-galena fractionations [differences] are approximately 1, 2, and 3 permil, respectively. These consistencies together with the similarity of the silicate mineralogies in the sulfide deposits, their wall rocks, and the country rocks indicate that sulfur isotopic equilibrium was closely approached at a fairly uniform temperature. It is suggested that low-rank regional metamorphism has generated the observed fractionations and caused local isotopic homogenization with respect to given minerals.
Gold, Ir and Pd were determined by neutron activation in hydrothermal mineralization from two mid-ocean ridges, the Juan de Fuca and the Mid-Atlantic at 26N. In the Juan de Fuca suites, Au ranges from 9.5 to 5403 ppb. Most samples with > 1000 ppb are from Axial Seamount, a recently active volcano. Those with 1000 ppb in sulfides from the hydrothermal mound area and in sediments high in hydrothermal vent precipitate. With one exception, Pd ranges from 2.6 to 136 ppb, and lr averages 0.50 and 0.77 ppb in mound sulfides and sediments. The Mid-Atlantic suites are comparable to Axial Seamount in Au but higher in Pd and Ir. Metals are derived from a basalt rock column; Au/Ir values of rockequilibrated fluids are probably comparable to MORBhosted sulfide globules, or about 16. The Au/Ir ratio in Juan de Fuca and Mid-Atlantic fudge sulfides ranges from 1700 to 41,000. In active systems, such fractionation likely occurs at the site of precipitation, usually within tens of meters of the seafloor.
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