Ungavaite, Pd4Sb3, a new intermetallic mineral species from the mesamax northwest deposit, Ungava region, Quebec, Canada: Description and genetic implications
Ungavaite, Pd4Sb3, is a new intermetallic mineral species discovered in the Mesamax Northwest deposit, Cape Smith fold belt, Ungava region, northern Quebec. It is associated with monoclinic pyrrhotite, pentlandite, chalcopyrite, galena, sphalerite, cobaltite, a chlorite-group mineral and magnetite. Associated precious-metal minerals include another new mineral species, naldrettite (Pd2Sb), sperrylite, sudburyite, michenerite, Au-Ag alloy, altaite, petzite (Ag3AuTe4) and hessite (Ag2Te). Ungavaite occurs as rare anhedral grains with inclusions of Au-Ag alloy or with attached chalcopyrite and a chlorite-group mineral. Grains of ungavaite vary in size (equivalent circle diameter) from ca. 36 to 116 μm. with an average of 73 μm (n=4). Neither cleavage nor fracture was observed. It is distinctly anisotropic, non-pleochroic, has weak bireflectance and does not exhibit discernible internal reflections. Ungavaite appears bright creamy white in association with pentlandite, pyrrhotite, the chlorite-group mineral and chalcopyrite. Reflectance values in air (and in oil) for R1, and R2 are: 50.2, 50.5 (37.6, 38.0) at 470 urn, 55.6, 55.9 (43.2, 43.5) at 546 nm, 57.9, 58.3 (45.9, 46.3) at 589 nm and 60.2, 60.7 (48.1, 48.5) at 650 mn. The average result of 16 electronmicroprobe analyses on one particle is: Pd 54.53, Fe 0.13, Te 0.09, Sb 44.59, Bi 0.42, Hg 0. 19, and As 0.20, total 100. 15 wt. %, corresponding to empirical formula (based on seven atoms) Pd4.062(Sb2.893 Fe0.017Bi0.017Hg0.006 Te0.005)∑2.938, ideally Pd4Sb3. The mineral is the Pd-dominant analogue of genkinite. It is tetragonal, crystallizing in one of the possible space-groups P41212, P4122, P43212, P42212, or P4222. Cell dimensions are: a 7.7388 (4), c 24.145(1) Å, with V=1446.02(1) Å3 and Z=8. The calculated density is 7.264(1)g/cm3. The strongest six lines in the X-ray powder-diffraction pattern [d in Å(I)(hkl)] are: 3.008(90)(008), 2.268(100)(134), 2.147(30)(230), 1.9404(60)(400), 1.2043(30)(2218, 452), 1.2002(30)(624). The mineral formed in a narrow (Pd + Sb)-rich zone separating massive and disseminated sulfides. It is likely a product of the hydrothermal remobilization of Pd (and possibly Sb) from the pre-existing massive sulfides. Phase relations suggest that ungavaite developed at a temperature below 400°C, possibly through a solid-state order-disorder transformation.
|Keywords||Cape Smith fold belt, Hydroseparation, Mesamax Northwest deposit, New intermetallic mineral species, Pd-Sb, Platinum-group elements, Platinum-group mineral, Quebec, Ungava, Ungavaite|
McDonald, A.M. (Andrew M.), Cabri, L.J. (Louis J.), Stanley, C.J. (Christopher J.), Rudashevsky, N.S. (Nikolay S.), Poirier, G. (Glenn), Mungall, J.E, … Rudashevsky, V.N. (Vladimir N.). (2005). Ungavaite, Pd4Sb3, a new intermetallic mineral species from the mesamax northwest deposit, Ungava region, Quebec, Canada: Description and genetic implications. Canadian Mineralogist, 43(5), 1735–1744. doi:10.2113/gscanmin.43.5.1735