Detecting micrometer-scale platinum-group minerals in mantle peridotite with microbeam synchrotron radiation X-ray fluorescence analysis

Platinum-group elements (PGE) in the Earth's mantle are key tracers for understanding the differentiation history of the Earth. PGE in mantle peridotite are strongly concentrated in Fe-Ni-Cu sulfides, whereas platinum-group minerals, rarely found in peridotite, are additional potential phases that host PGE in the mantle. However, the abundances of platinum-group minerals are not well constrained because they are generally too small to be detected with conventional analytical tools. We employed microbeam synchrotron radiation X-ray fluorescence to efficiently detect micrometer-scale platinum-group minerals in rock samples. This nondestructive technique allows location of micrometer-scale minerals from the interior of rock thin sections. With this method, we detected micrometer-scale platinum-group minerals in an orogenic lherzolite sample. The platinum-group minerals range from similar to 1 mu m to 10 mu m in maximum dimension. They are located near or within Fe-Ni-Cu sulfides, which were not exposed on the thin section surface. Nine grains of platinum-group minerals in total were detected in just one peridotite thin section, demonstrating the high efficiency of this method for detecting micrometer-scale minerals from the inside of rock samples.