Ungavaite, Pd (sub 4) Sb (sub 3) a new intermetallic mineral species from the Mesamax Northwest Deposit, Ungava region, Quebec, Canada; description and genetic implications

Ungavaite occurs associated with monoclinic pyrrhotite, pentlandite, chalcopyrite, galena, sphalerite, cobaltite, a chlorite-group mineral and magnetite in the Mesamax Northwest deposit, Cape Smith fold belt, Ungava region, northern Quebec. Associated precious-metal minerals include another new mineral species, naldrettite (Pd (sub 2) Sb), sperrylite, sudburyite, michenerite, Au-Ag alloy, altaite, petzite and hessite. Ungavaite ccurs as rare anhedral grains with inclusions of Au-Ag alloy, or with attached chalcopyrite and a chlorite-group mineral. Grains vary in size from approximately 36 to 116 mu m; they are distinctly anisotropic, and appear bright creamy white in association with pentlandite, pyrrhotite and chalcopyrite; reflectance approximately 58% (46 in oil); D (sub calc) 7.264 g/cm (super 3) . EPMA gave Pd 54.53, Fe 0.13, Te 0.09, Sb 44.59, Bi 0.42, Hg 0.19, As 0.20, = 100.15, leading to the idealized formula Pd (sub 4) Sb (sub 3) ; it is the Pd-dominant analogue of genkinite. Indexed XRD powder data are tabulated; strongest lines 2.268(100), 3.008(90), 1.9404(60), 2.147(30), 1.2043(30), 1.2002(30) Aa; a 7.7388, c 24.145 Aa, V 1446.02 Aa (super 3) , Z = 8, possible space groups P4 (sub 1) 2 (sub 1) 2, P4 (sub 1) 22, P4 (sub 3) 2 (sub 1) 2, (sub ) P4 (sub 2) 2 (sub 1) 2 or P4 (sub 2) 22. Ungavaite formed in a narrow (Pd + Sb)-rich zone separating massive and disseminated sulphides; it is probably a product of the hydrothermal remobilization of Pd (and possibly Sb) from the pre-existing massive sulphides and may have developed at a temperature of below 400 degrees C, possibly via a solid-state order-disorder transformation. The name is for the region.