A question for sulfur aficionados. Has anyone encountered sedimentary
sulfides with very high delta34S values? We obtain delta34S values of 42
and 58 per mil (N = 1 and 2 respectively) for disseminated sulfides
extracted by Cr2+ solution (Fossing and Jorgensen, 1989, Biogeochemistry
8:205-222) from an Eocene sand aquifer. Total reduced sulfur (Cr2+
reducible) is low in these beds, about 20 umol/gm, but sample size used was
relatively large, 20 to 100 mg. Acid volatile sulfide is low in all the
We have the largest number of sulfate reducing bacteria in the S-34 rich
sediments, so we suspected that the sulfide could be modern.
Unfortunately, groundwater sulfate delta34S values are much lower than the
sulfide, 8 per mil, arguing that the sulfide is not modern. Silt and clay
confining beds have higher concentrations of sulfide and yield more typical
delta34S values for sulfides of -5 to 23 per mil.
I feel compelled to interpret the heavy sulfides as the final stages of
Rayleigh distillation. We have considered the possibility that partial
oxidation of the dissolved sulfide pool enriched the residual in S-34, but
the fractionations in the literature do not seem to support this
conclusion. Does anyone have other interpretations or opinions? Does
anyone know of literature on sulfide mineralization in aquifer systems (in
addition to Kimblin and Johnson, 1992)?
Thanks for your help.
Department of Geology & Geophysics (409) 845-0637
Texas A&M University fax (409) 845-6162
College Station, TX 77843