COMPOSITION AND PARAGENESIS OF Pt ALLOYS FROM CHROMITITES OF THE URALIAN–ALASKAN-TYPE KYTLYM AND UKTUS COMPLEXES, NORTHERN AND CENTRAL URALS, RUSSIA

摘要: Chromitites from the Kytlym and Uktus zoned Uralian–Alaskan type complexes in northern central Urals, Russia, contain abundant inclusions of Pt alloys compositionally attributable to one three main groups: 1) Pt–Fe with an isoferroplatinum-type composition, Pt3Fe; 2) Ni-rich Pt–Fe–Ni–(Cu) a stoichiometry isoferroplatinum Pt2.5(Fe,Ni,Cu)1.5, tetraferroplatinum Pt(Fe,Ni,Cu), ferronickelplatinum Pt2FeNi, 3) Cu-rich Pt–Fe–Cu–(Ni) tulameenite type, Pt2Fe(Cu,Ni). The occur as primary unaltered chromian spinel are considered have formed high-temperature pre-chromite stage. A sulfide-rich assemblage (erlichmanite, Rh–Ir–Pt thiospinels, cooperite, unknown Rh–Ir-bearing base-metal sulfides, pyrrhotite pentlandite) accompanies Pt3Fe alloy, indicating that it was stable phase under relatively high sulfur fugacity. at low fugacity, suggested by absence sulfides exclusive presence native osmium assemblage. exclusively located along cracks contact secondary ferrian chromite, magnetite chlorite, or constitute metasomatic replacement alloys, low-temperature hydrothermal origin. PGM also includes potarite, prassoite, rhodian pentlandite, Cu–Pd osmium, Ir–Fe oxides. These data strongly suggest Ural–Alaskan-type chromitites major contributors encountered associated nuggets placer deposits Ural Platinum-bearing Belt.