Isomorphous Compounds; Galena, Clausthalite, and Altaite from the Kushikino Gold-Silver Ore Deposit, Japan-Possible Substitutional Limits

The Kushikino ore deposit is an epithermal gold-silver quartz vein type developed in Miocene to Pliocene andesites. Galena-clausthalite solid solution and altaite are abundant in the gold-silver-tellurium ores from the Shinpi No.1 vein of the mine; typical mineral associations are altaite-calaverite-clausthalite, altaite-electrum-galena, clausthalite-hessite-sylvanite, galena-petzite-sylvanite. Electron microprobe analyses were performed on the various associations in order to establish the limits of isomorphous substitutions among sulfur, selenium, and tellurium in the PbS-PbSe-PbTe series. Galena-clausthalite solid solution shows a compositional range from about 18 to 74 mol. percent PbSe, indicating a continuous solid solution series between PbS and PbSe. A rather wide miscibility gap exists between approximately 22 and 73 mol. percent PbSe in the PbSe-PbTe series, and a more extensive miscibility gap in the PbS-PbTe series. These compositional relations are explained from the viewpoint of geochemical character. No natural stable phase is expected to appear in a central part of the PbS-PbSe-PbTe system although the extent of the solid solutions is probably enlarged at elevated temperatures.