First Find of Platinum in Cosmogenic Spherules of Ferromanganese Crusts (Fedorov Guyot, Magellan Seamounts, Pacific Ocean)

More than 250 magnetic spherules 40–200 µm in size were mechanically separated from a ferromanganese crust sample of Fedorov Guyot in the Magellan Seamounts. The composition of the spherules corresponds to stony-iron and iron (with a nickel admixture) meteorites oxidized to varying degrees. The surface morphology and the internal texture of these spherules are similar to modern micrometeorites. Some spherules have a zonal structure with a core consisting of unoxidized nickel iron, with a nickel content of 7.5%–53% and a cobalt admixture up to 3.7%. Microinclusions (up to 0.5 μm) of rhodium platinum were found for the first time in a spherule consisting of wustite and magnetite in the ferromanganese crust. The presence of cosmogenic spherules in the sample studied indicates the accumulation of a certain fraction of platinoids in the ferromanganese crusts due to the burial of cosmic dust in them.