A LASER-RAMAN MICROPROBE STUDY OF PLATINUM-GROUP MINERALS FROM THE MUNNI-MUNNI LAYERED INTRUSION, WEST PILBARA BLOCK, WESTERN-AUSTRALIA

The laser-Raman microprobe has been used to identify relatively small (less than or equal to 10 mu m) grains of platinum-group minerals (PGM ) occurring in the mineralized layer just below the contact between th e ultramafic zone and the gabbroic zone of the Archean Munni Munni lay ered igneous complex, in the west Pilbara block of Western Australia. The Raman spectra of sperrylite, platarsite, moncheite, cooperite, bra ggite and potarite are reported for the first time, and their spectra are compared with those predicted from group theory. All Raman bands o ccur below 500 cm(-1), and each PGM produces a distinct spectrum, thus allowing ready identification of each mineral by Raman microspectrosc opy. The technique requires little preparation of the samples and offe rs the advantages of high spatial resolution and the relatively rapid identification of in situ micrometer-sized grains of PGM in silicate o r sulfide matrices.