ASSOCIATIONS OF PLATINUM-GROUP MINERALS FROM THE ZOLOTAYA GOLD PLACER

The platinum-group minerals (PGM) and chromite composition of the Zolotaya River gold placer, in the Russian Far East, indicate a genetic relationship to poorly exposed Late Permian dunite – hornblendite – gabbro intrusions of Uralian–Alaskan type. Ninety percent of the PGM grains studied consist of Pt–Fe alloy, typically with a rhodium content in the 1–2 wt. % range. Pt-bearing Os–Ir–Ru alloy occurs in three variants: (1) heterogeneous grains with an exsolution texture, (2) intergrowths of Os– Ir alloy with Pt–Fe alloy, and (3) homogeneous grains. Minerals of the erlichmanite–laurite series are relatively rare. Their composition varies from pure laurite through Os-bearing laurite to erlichmanite. Cooperite occurs in multiphase inclusions (in association with cuprorhodsite and chalcopyrite) in Pt–Fe alloy, and as a secondary rim (occasionally intergrown with platarsite and sperrylite) around Pt–Fe grains. Heterogeneous aggregates of Pt–Fe and Ru–Pt–Ir alloy have inclusions of arsenides of rhodium, iridium and ruthenium (cherepanovite, iridarsenite, ruthenarsenite) and a sulfarsenide-rich rim (irarsite)