CRERARITE, A NEW PT-BI-PB-S MINERAL FROM THE CU-NI-PGE DEPOSIT AT LAC-SHEEN, ABITIBI-TEMISCAMINQUE, QUEBEC, CANADA

Crerarite, a new Pt-bearing Bi-Pb sulfide from the Lac Sheen Cu-Ni-PGE deposit in the Abitibi-Temiscaminquet district of Quebec is described . The mineral is typically under 50 mum in size and is associated with pyrrhotite and an actinolitic amphibole. In reflected light, Crerarit e is white-grey in color. Reflectance spectra are listed for the miner al in air and immersion oil. Color values are: Y = 49.88, d = 474.4 nm , Pe = 2.71 and Y = 50.58, d = 477.7 nm, Pe = 2.56% in air and oil res pectively. Precession studies showed that Crerarite is cubic with unit cell dimensions of a(o) = 5.86(5) angstrom, V = 201.2 angstrom3, Z = 1, space group Fm3m. The calculated density is 7.75 g cm-1. The four s trongest lines of the powder diffraction pattern are 2.90 (100), 3.35 (50), 1.450 (50) and 2.05 (30). Electron probe microanalysis gives an average composition of 10.14% Pt, 65.26% Bi, 13.85% Pb, 10.55% S, 0.86 % Se, 0.08% Fe, 0.09% Cu, and trace (<0.12%) amounts of Ni, Pd and Te in some grains. The crystal structure has been determined to be of NaC l type, with one formula unit of Bi3Pt0.5Pb0.5S3.185Se0.105 per unit c ell. The single crystal refinement suggests about 10 - 20% vacancies i n the anion sublattice. The chemical formula, as calculated from elect ron microprobe analyses, fit this closely. The proposed simple formula is (Pt,Pb)Bi3(S,Se)4-x, where x represents the vacancies in the anion ic sublattice. Both mineral and name have been approved by the IMA Com mission on New Minerals and Mineral Names.