THE TAIMYRITE-TATYANAITE SERIES AND ZONING IN INTERMETALLIC COMPOUNDS OF Pt, Pd, Cu, AND Sn FROM NORIL'SK, SIBERIA, RUSSIA

Abstract

We report on the existence of a newly recognized extensive solid-solution series between taimyrite and tatyanaite, its Pt-dominant analogue. Copper probably occupies a separate site. Substitution involving Pd and Cu also is important, such that taimyrite–tatyanaite forms a solid-solution series with cabriite, which is structurally closely related to taimyrite and tatyanaite. These platinum-group minerals ( PGM ) occur in base-metal sulfide ( BMS ) ores in the Oktyabr’sky deposit, Noril’sk complex, Siberia, Russia. The taimyrite–tatyanaite is present as single grains and aggregates, associated with a heterogeneous Ag–Au alloy, and also as zoned intergrowths of Pt–Pd–Cu stannides. These intergrowths commonly, but not necessarily, occur within chalcopyrite and typically display the following sequence of crystallization, based on textural and compositional data: atokite–rustenburgite → tatyanaite → Pt-rich taimyrite → taimyrite poorer in Pt → late-stage Ag–Au alloys. Subsolidus re-equilibration of the atokite–rustenburgite core with the Cu-rich host is considered unlikely to produce the peripheral zones of the Cu-rich PGM around this core. These zoned PGM probably formed from a trapped liquid rich in noble metals, Cu, and Sn. Decrease in temperature and increase in activity of Cu in the remaining liquid seem to have been the main factors to control the order of crystallization of the PGM in the zoned intergrowths.