In the early days, miners became aware of a general rule when prospecting for new silver deposits: "Without fahlband and calcite vein, no silver." Silver was always found at the intersections between calcite veins and fahlbands, not in every case, but never outside such intersections.
Isotopic [[delta].sup.34]S values in barite correspond to sulfate in contemporary Permian sea water (12 per mil, CDT), while fahlband sulfur (0 per mil) is a likely source for the vein sulfides, showing corresponding equilibrium isotopic values (Segalstad et al., 1986).
These zones, showing a variable rusty appearance both on the surface and in the mines, are called fahlbands after the old German designation.