The last part of my earlier message got somehow corrupted. Here it goes
again in the hope that this time it will transmit correctly.
Sorry for that!
Regarding the analysis of the pyrrhotite (i.e., H2S) in the same samples,
I suggest to have a look to the paper by Canfield et al (1986). You can
attack the sample with HCl in a nitrogen atmosphere, collect the evolved
H2S in a zinc acetate + ammonia trap and convert the sulphur acetate to
Ag2S using AgNO3 0.1 M. The method is quite well described in the paper
mentioned, but if you have further questions, contact me again. We have
some experience with it.
Stable Isotope Lab.
Canfield, Raiswell, Westrich, Reaves and Berner (1986) "the use of
chromium reduction in the analysis of reduced inorganic sulfur in sediments
and shales". Chem. Geol., 54, 149-155.
Hall, Pelchat and Loop (1988) "separation and recovery of various sulphur
species in sedimentary rocks for stable sulphur isotopic determination".
Chem. Geol., 67, 35-45.
.... as well as various more recent articles, mostly published in Chem. Geol.