Occurrences and Phase Stability Relations of Minerals of the Cu-Fe-Sn-S System

Cu-Fe-Sn-S계(系) 광물(鑛物)의 산출상태(産出狀態)와 상안정관계(相安定關係)

Stannite is mainly found in hypothermal ore deposits, whereas mawsonite and stannoidite occur characteristically with bornite and chalcopyrite in subvolcanic (xenothermal) ore deposits. Mawsonite always shows the replacement on the rims of stannoidite grains or along the grain boundaries of stannoidite, bornite and chalcopyrite. In the Tada mine, Japan, the following mineral assemblages of the Cu-Fe-Sn-S minerals were observed. 1) bornite-stannoidite; 2) stannoidite-chalcopyrite; 3) stannite-chalcopyrite; 4) bornite-mawsonite-stannoidite; 5) bornite-stannoidite-chalcopyrite; 6) mawsonite-stannoidite-chalcopyrite; 7) stannoidite-stannite-chalcopyrite; 8) bornite-mawsonite-stannoidite-chalcopyrite The heating and D.T.A. experimental results indicate that natural stannoidite containing 3 weight percent of zinc decomposes to bornite, stannite and chalcopyrite at above $500^{\circ}C$, whereas zinc-free synthetic stannoidite is stable up to $800^{\circ}C$. The stability temperature of zincian stannoidite depends on the zinc content. Mawsonite is stable at temperatures below $390^{\circ}C$ and decomposed to stannoidite, bornite and chalcopyrite above it. According to the sulfur fugacity determination by the electrum tarnish method the univariant assemblage of mawsonite, bornite, stannoidite and chalcopyrite requires a higher sulfur fugacity than that of bornite, stannoidite and chalcopyrite assemblage.