SILVER.BEARING INCLUSIONS IN "ARGENTIFEROUS " GALENA FROM THE SILVERMINE DISTRICT IN SOUTHEASTERN MISSOURI

Galena from Sn-W greisen veins in the Silvermine dis-trict of southeastern Missouri contains between I and 3 kg,/tonne Ag and carries trace amounts of Bi, Sb, Sn, As, Fe, Cu, Zn and Au (up to 1l g,/tonne). Such galena, long considered argentiferous, has been examined optically at 1250 x and by SEM up to 12,5 @ x. It clearly contains two types ofminute inclusions: round blebs and rods. Their dis-tribution in rows suggests an exsolution origin. Optical properties and electron-microprobe/SEM-EDS analyses indicate that one ofthe cryptic phases is argentiferous tetra-hedrite containing variable arnounts of silver (up to approxi-mately l5Y0) and the other is a Cu-Fe-Sn-S mineral. verv likely mawsonite. Neither phase has been previously reported from this locality. Repeated analyses of homogene-ous domains within the galena failed to detect any silver above the limits of detection of the electron microorobe(approximately 0.02V0)