Dear Dr.Yiang,

For studies of sulfur and oxygen istope ratios in
ahydrite you can safely extract SO4 ion by leaching
with distilled and boiled water which is practically
degased.To avoid contamination of the solution by
SO4 from oxidation of the sulfides the first portion
of the solution treat separately.
 By excess of water and intense mixing,eg. by
ultrasonic agitation, you can remove all soluble sulfate (i.e. in
ahydrite  and gypsusum). Then you can precipitate it as BaSO4.
 The remaining unsoluble mixture can be treated as follows:
1. Total sulfur can be easily analyzed by oxidation of an
    aliquot of the mixture to SO2 in usual manner.
2. If chalcopyrite and pyrite can be selected ( from another aliquot
    of the mixture) by hand picking under binokular then
    separate phases can be converted to SO2.
With best wishes,
                              Stan Halas