OULANKAITE, A NEW PLATINUM-GROUP MINERAL FROM THE LUKKULAISVAARA LAYERED INTRUSION, NORTHERN KARELIA, RUSSIA

Abstract

Oulankaite, ideally (Pd,Pt)s(Cu,Fe)4SnTe2S2, is a new mineral species, occurring in pegmatoidal, plagio-clase-bearing pyroxenite hosted by a microgabbronorite in the Early Proterozoic Lukkulaisvaara mafic-ultramafic layered intrusion, Oulanka complex, northern Karelia, Russia. The mineral name is for the Oulanka river. The associated minerals include base-metal sulphides (chalcopyrite, bornite, millerite, pentlandite etc.), various plat­ inum-group minerals, and an unnamed rhenium-rich sulphide. Typically, oulankaite forms platy inclusions (up to 0.2 x 0.1 mm) in chalcopyrite. Oulankaite is an opaque mineral. In reflected light in air it is distinctly to strongly bireflectant and pleochroic from yellowish-rose to violet-rose. The anisotropy is typically strong from yellowish-white to bluish-grey. Reflectance data measured in air are [Ri and R2 % (λ nm)l: 41.6 and 36.2 (470); 48.7 and 41.0 (546); 51.7 and 43.1 (589); 54.0 and 44.6 (650). Reflectance data measured in oil are 29.1 and 23.5 (470); 35.2 and 29.5 (546); 37.1 and 30.8 (589); 39.4 and 33.8 (650). Vickers micro-indentation hardness is 156-334, the average is 221 kg/mm 2 (VHN2O;4o). The mean of three microprobe analyses gave Pd 41.60, Pt 2.85, Cu 17.53, Fe 2.51, Sn 9.73, Te 21.32, S 4.84, a total of 100.38 wt.%, corresponding to: (Po4.86Pto.i8)Σ5.O4(CU3.43Feo.56)Σ3.99Sni.o2 Te2.o8S1.88 (on the basis of Σ atoms =14). The X-ray powder diffraction pattern was indexed for a tetragonal cell with a = 9.044(3) Å, c = 4.937(3) Å, c:a = 0.5459, V = 403.8(5) Å 3. For Z = 2, the calculated density is 10.27(1) g/cm 3. The strongest five lines in the X-ray powder pattern are [d in Å (I) (hkl)]: 2.472(10) (311,002); 2.260 (9) (400); 2.022 (6) (420); 1.361 (4) (541); 1.129 (5) (800,533,651).