Sulfur gases produced by the decomposition of sulfide minerals: Application to geochemical exploration

We have evaluated the potential application of sulfur gas analysis to exploration for buried sulfide mineral deposits by: (1) calculating by use of equilibrium thermodynamics, the relative abundances of gases that should be given off by decomposing sulfide minerals; and (2) determining experimentally the abundances of gases that are actually given off. The calculations indicate that the gases that should be given off by decomposing sulfide minerals are (in order of decreasing abundance) H₂S, COS, CS₂, CH₃SH, (CH₃)₂S₂ or SO₂ or S₂ (depending on Eh and pH). In contrast, our experiments show that decomposing sulfide minerals evolve only CS₂ and COS, in order of decreasing abundance. Pyrite produces the largest amounts of sulfur gas. Moist (rather than saturated) and non-sterile (rather than sterile) conditions enhance gas generation from pyrite, although no large difference appeared between sterile and non-sterile experiments for other sulfide minerals. These experiments indicate that the sulfur gases CS₂ and COS could be useful indicators of buried metal sulfide deposits.