Voluminousplatinum-groupmineral（PGM）inclusionsincludingerlichmanite（Os,Ru）S2,laurite（Ru,Os）S2,andirarsite（Ir,Os,Ru,Rh）AsS,aswellasnativeosmiumOs（Ir）andinclusionsofbasemetalsulphides（BMS）,includingmillerite（NiS）,heazlewoodite（Ni3S2）,covellite（CuS）anddigenite（Cu3S2）,accompaniedbynativeiron,havebeenidentifiedinchromititesoftheZedangophiolite,Tibet.ThePGMsoccurasbothinclusionsinmagnesiochromitegrainsandassmallinterstitialgranulesbetweenthem;mostarelessthan10μminsizeandvaryinshapefromeuhedraltoanhedral.Theyoccureitherassingleorcomposite（biphaseorpolyphase）grainscomposedsolelyofPGM,orPGMassociatedwithsilicategrains.Os-,Ir-,andRu-richPGMsarethecommonspeciesandPt-,Pd-,andRh-richvarietieshavenotbeenidentified.SulfurfugacityandtemperatureappeartobethemainfactorsthatcontrolledthePGEmineralogyduringcrystallizationofthehostchromititeintheuppermantle.Iftheactivityofchalcogenides（suchasS,andAs）islow,PGEclusterswillremainsuspendedinthesilicatemeltuntiltheycancoalescetoformalloys.Underappropriateconditionsof?S2and?O2,PGEalloysmightreactwiththemelttoformsulfides-sulfarsenides.Thus,wesuggestthattheOs,IrandRumetallicclustersandalloysintheZedangchromititescrystallizedfirstunderhightemperatureandlow?S2,followedbycrystallizationofsulphidesofthelaurite-erlichmanite,solid-solutionseriesasthemagmacooledand?S2increased.TheabundanceofprimaryBMSinthechromititessuggeststhat?S2reachedrelativelyhighvaluesduringthefinalstagesofmagnesiochromitecrystallization.ThepersityofthePGEminerals,incombinationwithdifferencesinthepetrologicalcharacteristicsofthemagnesiochromites,suggestdifferentdegreesofpartialmelting,perhapsatdifferentdepthsinthemantle.Theestimatedparentalmagmacompositionsuggestsformationinasuprasubductionzone
