The role of emulsions in magmatic sulfide deposits

• Applicant: Professor Dr. Gregor Markl, since 9/2024
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 499578128

Liquid immiscibility between silicate and sulfide melt is an important prerequisite to form magmatic sulfide deposits. These are amongst the most valuable metal resources in the world, forming Ni-Cu-Co- platinum group element (PGE) deposits (e.g., Sudbury and Noril’sk; the two largest accumulations of Ni- and Cu-sulfides and the second and third largest PGE enrichments on Earth; Naldrett, 2011). Surprisingly, the textural evidence for liquid immiscibility, frozen emulsions, are not studied in detail so far and this is the topic of this proposal for a PhD candidate. Three objectives will be addressed:(1) The variability of emulsion textures (e.g. different spheroidal and interconnected emulsions) will be texturally and chemically studied and compared to similar textures (e.g. net-textured sulfides, clast fragmentation) and the host rocks of the emulsions to study the emplacement history of sulfides and emulsion formation in the course of that emplacement. The samples for this objective come from a large variety of magmatic sulfide occurrences worldwide.(2) Emulsions from the Nova deposit (Australia) are typically associated with large silicate crystals embedded by sulfides. The hypothesis is that these crystals grew within the emulsion due to changing conditions, such as cooling. After growth, the silicate melt portion of the emulsion floated up when both melts separated (due to slowing movement of the melts), leaving the crystals in the sulfides behind. To test this, the crystals will be texturally and chemically compared to the country rocks.(3) A hitherto undescribed emulsion texture comprises oxide-apatite coatings on silicate droplets of an emulsion from sulfide pods near Bautzen (Sora, Germany). The hypothesis is that this coating represents a third melt between silicate and sulfide melt and acted as an emulsifier, which has not been described before in any geological context. This physical barrier between the sulfide and the silicate melt would prevent a "conventional" partitioning of elements between them and, therefore, trace elements (besides textural observations) will be used to study and interpret this new emulsion texture.All three objectives will help to better understand the processes involved in the formation and emplacement of magmatic sulfide deposits. It will create a foundation for other researchers to classify and discriminate emulsions and to distinguish them from similar textures, which formed in different processes. The identification of emulsions in the field can help exploration for magmatic sulfide deposits in directing them from the emulsion, which is usually found in sub-economic sulfides on steep intrusive contacts, towards the main orebody.

• DFG Programme: Research Grants
• Ehemaliger Antragsteller: Dr. Sebastian Staude, until 8/2024