The New Platinum Selenide Luberoite Pt5se4 From the Lubero Region (kivu-province, Zaire)

The new platinum selenide luberoite, identical with the synthetic compound Pt5Se4, has been found in concentrates from placers worked for gold and platinum in the Lubero region (Kivu Province, Zaire). The mineral is present as loose crystals and fragments smaller than 0.5 mm, and as inclusions in platinum grains. It is composed of Pt = 75.76 and Se = 24.24 wt %. Its symmetry is monoclinic (space group P 2(1)/c), with a = 6.584 angstrom ; b = 4.602 angstrom ; c = 11.10 angstrom ; a : b : c = 1.430 : 1 : 2.412 ; beta = 101.6-degrees ; V = 329.5 angstrom3. The three strongest diffraction lines are 1.875(100), 2.93(80) and 1.812(60)angstrom. The calculated density is 13.02 g cm-3, and the stoechiometric formula is Pt5Se4 for Z=2. The mineral is opaque and the maximum and minimum reflectance values in air for the COM wavelengths (470, 546, 589, 650 mm) are, respectively : 48.6/42.6 ; 53.0/46.7 ; 55.0/48.6 ; 58.0/51.5. It has a mean microhardness (VHN15) of 461 kg mm-2 . The minerals found associated with luberoite in the placers, as well as the minerals enclosed in the platinum grains, indicate that luberoite belongs to a platinum deposit, whose primary source-rocks are not yet definitively known, but are very likely of granodioritic affiliation