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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 mu m, with an average of 73 mu m (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 R-1 and R-2 are: 50.2, 50.5 (37.6, 38.0) at 470 nm, 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 nm. The average result of 16 electron-microprobe 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) Pd-4.062(Sb2.893Fe0.017Bi0.017Hg0.006Te0.005)(Sigma 2.938), ideally Pd4Sb3. The mineral is the Pd-dominant analogue of genkinite. It is tetragonal, crystallizing in one of the possible space-groups P4(1)2(1)2, P4(1)22, P4(3)2(1)2, P4(2)2(1)2, or P4(2)22. Cell dimensions are: a 7.7388 (4), c 24.145(1) angstrom, with V = 1446.02(1) angstrom(3) and Z = 8. The calculated density is 7.264(1) g/cm(3). The strongest six lines in the X-ray powder-diffraction pattern [d in angstrom(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 degrees C, possibly through a solid-state order-disorder transformation.

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