Sulfide partial melting and galena–tetrahedrite intergrowth texture: An experimental study

Galena–tetrahedrite intergrowth textures have been observed in some quenched run products of melting experiments conducted at 500 and 600°C in the systems ZnS–PbS–FeS–Cu2S–Sb2S3 and ZnS–PbS–FeS–Cu2S–Sb2S3–As2S3, using the evacuated silica-tube method. At 600°C the intergrowth formed an interface between sulfide melt and galena, whereas at 500°C it existed as inclusions partially embedded or completely embedded within tetrahedrite. At 600°C tetrahedrite was absent in PbS-bearing experiments, instead galena and melt were a part of the equilibrium phase assemblage. From the disposition of the galena–tetrahedrite intergrowths at 500°C it is evident that droplets of galena–tetrahedrite melt coexisted with tetrahedrite or tetrahedrite + galena and gave rise to these intergrowths upon quenching. The intergrowths coexisting with galena probably represent compositions on the galena-rich liquidus in the galena–tetrahedrite binary and those coexisting with tetrahedrite represent points on the tetrahedrite-rich liquidus. A eutectic at galena:tetrahedrite = ~30:70, very close to 500°C is apparent. It is clearly indicated that galena–tetrahedrite intergrowths can be formed by sulfide partial melting, and could be used as a potential indicator of partial melting in metamorphosed sulfide ore deposits.