UNUSUALLY PGE-RICH CHROMITITE IN THE BUTYRIN VEIN OF THE KYTLYM URALIAN-ALASKAN COMPLEX, NORTHERN URALS, RUSSIA

The so-called Butyrin vein in the dunite of the Kytlym Uralian-Alaskan complex, of the north-central Urals in Russia, consists mainly of amphibole clinopyroxenite and chromitite. The chromite of the Butyrin vein chromitite is enriched in Fe and Ti. Chromitites of the Butyrin vein contain up to 22972 ppb of platinum-group elements, and show a pronounced Pd anomaly compared with dunite-hosted chromitites at Kytlym. Consistent with this anomaly, the paragenesis of platinum-group minerals (PGM) includes abundant Pd-bearing PGM, two unnamed phases, (Pd,Fe,Cu,Ni)(9)(S,Hg,As)(8) and Rh(Te,Hg), and alloys in the system Pt-Fe-Cu-Ni. The PGM commonly occur associated with pentlandite and other sulfides containing Ni-Cu-Fe in various proportions. Most of these sulfides also contain appreciable amounts of Rh, Pt and Pd. The mineral assemblage indicates that a high fugacity of sulfur and high-temperature fluids enriched in Hg, Te and Cu played an important role during the formation of the mineralization in the Butyrin vein.