Selenides and sulfides from Iron Monarch, South Australia

The selenide assemblage at Iron Monarch, South Australia, has been characterized using electron microprobe analyses. The principal selenide minerals are: eucairite (Ag _1.03Cu _0.98Se _0.99S _0.01), naumannite (Ag _2.03Cu _0.02Se _0.96S _0.04) and bohdanowiczite (Ag _0.96Cu _0.04Bi _1.01Se _1.98S _0.02) and these occur with francisite in barite. Also present are clausthalite, bismuthinite, wittichenite and a number of copper sulfides. The occurrence is of hydrothermal origin and is thought to be associated with the intrusion of quartz diorite dykes, at temperatures between 133°C and 250°C. The compositions of coexisting sulfides and selenides show strong partitioning of Se into the Ag rich minerals and S into the Cu rich minerals.