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

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Abstract
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 ∼1 μm to 10 μm 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.

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