Hydrothermal coprecipitation experiments in NH 4 Cl solutions have been used to establish values for sulfur isotope fractionation between sphalerite and galena over the temperature range 600 degrees to 275 degrees C. The experimental data yield a linear function described by the equation 1,000 1n alpha (sub sph-gal) = 7.0 X 10 5 T (super -2) . This result is slightly different from results published by other workers.Sphalerite and galena crystallized in NH 4 I solutions at 500 degrees C show a reversed order of S 34 enrichment, delta S 34sph < delta S 34gal instead of delta S 34sph > delta S 34gal . This striking effect is interpreted to reflect differences in the energetics of growth on the octahedral faces typical of galena grown in NH 4 I and the cubic faces of galena grown in NH 4 Cl.

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