LAFLAMMEITE, Pd3Pb2S2, A NEW PLATINUM-GROUP MINERAL SPECIES FROM THE PENIKAT LAYERED COMPLEX, FINLAND

Abstract

Laflammeite, Pd 3 Pb 2 S 2 , is a new parkerite-type sulfide discovered in the Penikat layered complex, Finland. It occurs in altered pyroxenite in the Kirakkajuppura deposit in association with actinolite and clinochlore, accessory chromite, various platinum-group minerals [vysotskite, zvyagintsevite, cuprorhodsite – (ferrorhodsite) – malanite, laurite – erlichmanite, irarsite, keithconnite, unusual Pb–(Pd)-rich thiospinels of Cu, Fe, Rh and Ir, unnamed Pd 9 PbO 10 and Rh(Ni,Fe,Cu) 2 S 3 ], Pd-rich gold, and minor base-metal sulfides (chalcopyrite, bornite and millerite). Laflammeite occurs as individual subhedral to euhedral crystals up to 0.3 mm in size, and in intergrowths with Pt–Ni-poor vysotskite. Laflammeite is opaque and cream-colored with a brownish tint in reflected light in air. The anisotropy is weak, from brownish gray to grayish brown. The bireflectance is weak; pleochroism was not observed. Reflectance percentages in air (and in oil) are, for R 1 and R 2 , 45.3, 46.2 (31.55, 32.45) at 470 nm, 46.5, 47.55 (32.6, 33.75) at 546 nm, 47.7, 48.8 (33.9, 35.05) at 589 nm, and 49.6, 50.0 (36.0, 36.3) at 650 nm. Fine twins are present. Microhardness values VHN 50 are 156 and 185; the average is 171 kg/mm 2 . Cleavage is {010}, perfect. The average results of 26 wavelength-dispersion electron-microprobe analyses are Pd 39.16, Ir 1.08, Pb 52.01, S 7.90, total 100.15 wt.%, corresponding to (Pd 2.96 Ir 0.05 ) ∑3.01 Pb 2.02 S 1.98 (basis: 7 atoms per formula unit). The powder pattern was indexed on a monoclinic cell with a 11.521(11), b 8.294(10), c 8.321(6) A, β 134.38(5)°, V 568.3(6) A 3 . The space group is probably C 2/ m , with Z = 4. D calc is 9.41 g/cm 3 . The strongest lines in the pattern [ d in A(I)( hkl )] are: 5.953(6)(001), 4.144(10)(020), 2.917(9)(220), 2.413(8)(022), 2.365(7)(422) and 2.082(5)(040). Laflammeite likely crystallized from a hydrothermal fluid or a late-stage liquid in an environment poor in overall sulfur and rich in the PGE , Pb and volatiles.