Platinum-Group Minerals from the Mukawa Serpentinite, Southern Kamuikotan Belt

Abstract

PGM have been detected from the bottom of a twometer-thick dunite layer intercalated by a large harzburgite mass exposed along the Mukawa River, southern Kamuikotan belt, Hokkaido, Japan. The PGM occur as a complex aggregate of alloys (Unit A) and complex mixture of a pentlandite-like sulfide and Ru-Rh alloys (Unit B) included in fibrous serpentine. The unit A can be divided into the following three parts:
A1. Pt-Pd bearing native copper with domain texture
A2. an alloy of Rh and base-metals
A3. a Pt-Pd-Cu alloy including tiny grains of Rh-Ni alloy
Many small grains of Ru-Co-pentlandite are also observed in the same specimen. The occurrences, textures and chemical compositions of the PGE-bearing aggregate and Ru-pentlandite indicate that these minerals are products of the serpentinization.