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Crerarite is a rare PGM originally described from the Lac Sheen Ni-Cu-PGE deposit in the Abitibi-Temiscaminque district, Quebec, Canada where it was discovered in loose boulders associated with pyrrhotite, actinolite and other PGM (moncheite, michenerite). The mineral was considered to have the simplified formula, (Pt,Pb)Bi3(S,Se)4-x and based on a single-crystal study, a NaCl-type structure (Fm3m, a = 5.86 Å) with a high concentration of vacancies (10-20%).
During examination of ore samples from chalcopyrite-millerite stringers hosted by Sudbury breccia and Levack gneiss from the 148 Zone of the Levack North Property (probable up-dip extension of the McCreedy East 153 deposit) in the north range of the Sudbury basin, a phase whose chemistry and appearance closely matched that of crerarite was encountered. The mineral occurs in subhedral, angular to elongate grains that are 30 to 250 m in size, is association with a chlorite-group mineral, quartz, a clinoamphibole and chalcopyrite. It appears to be intimately associated with chalcopyrite (with sharp grain boundaries between the two) and infrequently contains rounded, elongate inclusions of Bi-rich moncheite. This discovery precipitated a comprehensive study (single-crystal & Gandolfi XRD, electron microprobe) involving both this new material and its discovery in-situ, along with a re-examination of the type material, the goal being to more completely characterize the mineral.
Results from single-crystal XRD analysis of crerarite from the type locality indicate the mineral is triclinic, P-1 with a = 9.3521(7), b = 9.3898(6), c = 14.517(1) Å, α = 105.647(1) β = 96.780(1), γ = 108.390(1)°; a rationale relationship with this cell and that originally proposed for the mineral could not be discerned. Results also indicate that, considering observed bond distances refined-site occupancies and negative Bi-Pb crystal-chemical variations, PtPb substitution is unlikely.
A revised, simplified chemical formula for crerarite is suggested as: Pt2-x(Bi,Pb)11(S,Se)11.
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