Genesis and Significance of Sulfide-Silicate Emulsions in Magmatic Sulfide Deposits

Abstract

Sulfide-silicate emulsion textures represent complex intergrowth of two chemically and physically contrasting melts which preserve crucial information on sulfide melt mobility, redistribution, and exsolution in magmatic and metamorphic systems. This cumulative thesis investigates the chemical, physical and mineralogical processes governing sulfide-silicate emulsion across the orthomagmatic Ni-Cu-PGE deposits Nova-Bollinger, Savannah and Sora, as well as in the high-grade metamorphosed SEDEX-type Pb-Zn-Cu mineralisation at the Silberberg deposit. Combined petrographic, textural and mineral-chemical analysis were conducted to shed light on emulsion formation and to understand their role in the genesis of unique features associated with these textures. The results strengthen the hypothesis that emulsion textures can form via multiple pathways: (1) Physical mingling of a sulfide melt with an anatectic silicate melt, (2) liquid immiscibility during magma evolution and hybridisation, and (3) simultaneous anatexis of sulfide ore and silicate country rock and consequent mingling during high temperature metamorphism. Infiltration-driven emulsion formation is associated with a broad spectrum of semi-massive sulfide rocks prompting the development of a genesis-based terminology for all involved textures. The introduced terminology comprises infiltration and disaggregation textures and subdivides the emulsion texture into droplet and bicontinuous emulsions, as well as pegmatoidal pockets. These newly categorised textures reflect different stages of sulfide melt infiltration and carry direct implications for ore exploration. At the infiltration front of Nova-Bollinger, the close association of silicate megacrysts with sulfide-silicate emulsions gave insight inro their influence on silicate crystal nucleation, growth kinetics, and element partitioning within the two immiscible melt system. At Sora, mineral chemistry and field relationships indicate that hybridisation between the gabbro intrusion and an anatectic leucogranite triggered sulfide saturation, with emulsion textures preserving the composition of the sulfide-saturated parental melt. The occurrence of oxide-apatite-coated silicate droplets suggest the involvement of a third immiscible Fe-Ti-P melt, potentially acting as a geological emulsifier that enhanced emulsion stability by inhibiting coalescence. Comparable emulsion textures at Silberberg demonstrate that such structures are not restricted to primary magmatic systems but may also develop during high-grade metamorphism through sulfide anatexis. Their preservation, together with elevated concentrations of low-melting-point chalcophile elements within the sulfides, provides diagnostic evidence for simultaneous sulfide and silicate anatexis. Collectively, these findings establish sulfide-silicate emulsions as robust petrogenetic indicators of melt interaction, hybridisation, infiltration, and remobilisation processes across both magmatic and metamorphic environments, thereby refining current models of sulfide melt mobility and ore formation.

Die Dissertation ist gesperrt bis zum 24. April 2027 !