A POTENTIALLY NEW KONDERITE-LIKE SULFIDE OF Fe, Pb, Cu, Rh, Pd, AND Ir FROM THE PENIKAT LAYERED COMPLEX, FINLAND

摘要

A potentially new konderite-like sulfide of Fe, Pb, Cu, Rh, Pd, and Ir [hereafter: "Pb–(Fe)+Pd Kdr"] occurs in an intimate association with platinum-group element (PGE) thiospinel (i.e., cuprorhodsite – ferrorhodsite – cuproiridsite: Cpr) in the S-poor Kirakkajuppura PGE deposit hosted by the Penikat layered complex, Finland. The "Pb–(Fe)+Pd Kdr" (a large grain, LG: 0.15 mm in size and a rim-like grain, RG) displays thiospinel-type proportions (Cu + Fe + Pb + Ni) : (Rh + Ir + Pd + Pt + Co) : S of 1 : 2 : 4, but differs from the associated Cpr in its appearance, texture and optical properties, and also in the presence of Pb (up to 9.7 wt.%) and Pd (up to 6.4 wt.%), which are positively correlated. A relationship between the "Pb–(Fe)+Pd Kdr" and konderite from the Kondyor Uralian–Alaskan-type complex [i.e., (Cu,Ni,Fe)₃Pb(Rh,Pt,Ir)₈S₁₆: hexagonal and thiospinel-derivative) likely exists. Results of multiple electron-microprobe analyses of the "Pb–(Fe)+Pd Kdr" point to coupled Pb-for-Fe and Pd-for-Rh atomic substitution mechanisms; the Fe-rich compositions of this sulfide imply the existence of an (unnamed) Fe-dominant analogue of konderite. The approximate scheme of substitution operating in the LG appears to be [Cu+ + 2 (Pb + Ni)2+] + 2 Pd2+ = 2 Fe3+ + Rh3+]. Also, variations in S could be essential in maintaining charge balance. In contrast, Cu is unlikely to be involved in the charge-balance substitution in the RG; in fact, Ni is more important than Cu in the RG. The LG and Cpr observed in a mutual intergrowth contain equal amounts of Ir, and, thus may have reached equilibrium in the distribution of Ir, whereas all Pb was selectively partitioned into the "Pb–(Fe)+Pd Kdr". The appearance of these thiospinel- and konderite-type chalcogenides, which are uncharacteristic of layered intrusions, is related to the anomalously S-poor character of the Kirakkajuppura PGE deposit, which is similar in this respect to the Uralian–Alaskan–type complexes.