|
The tributaries of Ivalojoki and Lemmenjoki in the northermost Finland carry a total of 37 Platinum-Group Minerals (PGM) including sulfides, arsenides, antimonarsenides, tellurides, bimuthotellurides, stannides, selenides, and native PGM alloys. The main PGM, in decreasing order of abundance, are sperrylite, isoferroplatinum, cooperite, braggite, isomertieite, mertieite, moncheite, kotulskite, keithconnite, rustenburgite, atokite, stillwaterite, hongshiite, arsenopalladinite, stibiopalladinite, xingzhongite, vincentite, and Pt-oxide. The PGM inclusions hosted in isoferroplatinum include laurite, erlichmanite, irarsite, osarsite, ruarsite, cuproiridsite, and cuprorhodsite.The native PGM metals include Pt, Pt9Pd, Pt4Pd, OsIrRu in various proportions, AuPdCu, AuPtCu, AuPd, Pt7Cu, and PtCu.
The PGE selenides are rare luberoite, palladseite, and a recently approved new mineral miessiite. Luberoite Pt5Se4 occurs in a grain with undefined Pt7Cu. It is light brown in reflected light with strong anisotropism. Luberoite is monoclinic, space group P2(1)/c, average VHN=461, D=11.82 g/cm3 and reflectance at 589 nm 51.8%. Some EMP analyses show Te; the empirical formulae vary from Pt4.95Se4.05 to Pt4.86Te0.62Se3.52. Cubic miessiite, space group Fd3m, occurs as a homogenous isotropic grain with ideal composition Pd11Te2Se2 that shows a light grey colour in comparison with the associated PGM grains.
The reflectance in air is 53.9% at 589 nm, and the empirical formula is Pd11.02Te2.09Se1.90 , with D=10.94 g/cm3 and VHN=362. Palladseite Pd17Se15 occurs as homogenous isotropic whitish cream coloured grains. Palladseite is cubic, space group Pm-3m, with average D= 8.15 g/cm3, VHN=414 and reflectance 45.4% at 589 nm. The empirical formula is (Pd15.35Pt0.26Cu1.78Ag0.13Au0.04)17.56 (Se11.75S2.62Te0.04As0.02)14.43.
|
