Experimental constraints on the behaviour of highly siderophile elements during planetary differentiation

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The highly siderophile, or iron-loving, elements (HSE) include the more familiar precious metals (platinum, palladium, rhodium and gold) as well as exotic varieties (rhenium, osmium, ruthenium and iridium). They are all useful to society, owing to exceptional thermal, surface and electronic properties. The HSE are also of value to geologists, as they are unique in their tendency to avoid oxygen, and bond to sulfur, as well as other "sulfur-like" elements, and iron. The HSE are therefore sensitive to the processes by which planets separate into a metallic core, mantle and crust. My research program involves laboratory simulation of these processes, with a specific focus on determining how the HSE get concentrated above normal background levels; be it by iron metal, other minerals, or unusual iron-sulfur (sulfide) melts. A major focus of the planned research will be to assess the efficiency of HSE extraction from magma by sulfide melt, and by compounds of the "sulfur-like" metals arsenic, bismuth, tellurium and selenium. This information helps us to understand how the HSE become concentrated by these elements in crustal mineral deposits. Knowledge of the sulfide scavenging capacity also makes it easier to inventory the HSE content of other planets from measurements of their surface lavas, whose sulfide has been removed at depth. In addition, we will determine the origin of some of the unusual behaviours of platinum, such as why it is so abundant in the Earth's mantle (when it should all be in the core) and why some magmas contain far more platinum than expected. We also plan to branch out into an emerging research area which deals with subtle variations in the composition of iron itself, and simulate the processes by which this may occur. In sum, this work seeks to provide the essential information for using the HSE to understand how planets form and evolve. Information gained from this research is also of value to the exploration and mining industry, as it provides information on how these elements may be concentrated to economic levels, and in what mineral forms they may occur.