We examine overall compositional ranges and substitutions of elements in intermetallic compounds of Pd, Pt, Cu, and Sn (cabriite, taimyrite, “stannopalladinite”, and tatyanaite), on the basis of (1) new results based on electron microprobe analyses of these stannides from Noril'sk (Krasnoyarskiy kray, Russia) and Lukkulaisvaara (northern Karelia, Russia), and (2) data published in the literature on natural and synthetic stannides. These results are consistent with the existence of a single and extensive field of solid solutions of the stannides of Pd-Pt-Cu, related to cabriite–taimyrite and tatyanaite, with generalized formulae (Pd,Pt)2+xCu1–x(Sn,Sb) – (Pt,Pd)2+xCu1–x(Sn,Sb), where 0 < x < 0.5. In addition, the compositional ranges extend toward Fe- and Sb-dominant endmembers (unnamed) of the type (Pd,Pt)2+x(Fe,Cu)1–x(Sb,Sn). No miscibility gap is evident. An unlimited substitution of Pt-for-Pd appears to exist; in addition, Pd partly substitutes for Cu, whereas there is no evidence for the existence of a Pt-for-Cu substitution in these solid solutions.
The stannides of Pd-Pt-Cu were likely deposited relatively late in the crystallization history of mineral associations, at low temperatures, likely as a result of a significant drop in temperature and increase in activity of Cu and Sn in a fractionated sulfide melt or a fluid phase. An atypical combination of relatively low levels of fugacities of O2 and S2 could account for the appearance of these rare compounds instead of common oxide or sulfide minerals, and could explain the observed scarcity of phases of the Pd-Pt-Cu stannides in nature.
- Pd-Pt-Cu stannides
- intermetallic compounds
- platinum-group elements
- solid solutions
- platinum-group minerals
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