PLATINUM-GROUP MINERALS IN THE INAGLI PLA CER (ALDAN SHIELD)

Study was given to minerals of platinum group elements (PGE) from a pl acer of the Inagli Massif of zonal-ultramafic type. Two magmatic PGE p arageneses have been revealed: iridium-isoferroplatinum and osmium-iso ferroplatinum. The first paragenesis consists of decomposition product s Pt3Fe+(Ir,Os,Pt), whose compositions suggest that the decomposition took place at 800-850 degrees C. The second paragenesis is characteriz ed by inclusions of euhedral crystals of iridosmine in isoferroplatinu m. Osmium trend of composition which reflects the typomorphous feature of Os-Ir-Ru alloys from intrusions of zoned ultramafic type. A comple te isomorphous series of sulfides RuS2-OsS2, elements of both paragene ses, has been described. The presence of erlichmanite at 800-850 degre es C indicates a high fugacity of sulfur during its formation (f(S2) = to(-1.5)-10(-2.5) atm). There are three late PGE parageneses superimp osed on primary-magmatic parageneses: CuIr2S4+PtS; CuIr2S4+CuPt2S4; Cu Ir2S4+(Os,Ir). Of them, the first preceded the second, because the exp erimental data show that PtS transforms into CuPt2S4 at a decrease in temperature. The sperrylite paragenesis with Pd mineralization is expr essed independently and coincides with magmatic parageneses only in th e placer. In general, the PGEs from the Inagli Massif are characterize d by Ir specialization with a limited role of Rh and by the highest te mperature of crystallization and sulfur activity as compared with othe r objects of the Alaska type.