The O'Toole deposit is a Cu-Ni-Co sulfide lens hosted by ultrabasic rocks. The orebody has undergone postdeformational metamorphism and shearing.The main sulfides of the O'Toole deposit are pyrrhotite (po), pentlandite (pn), and chalcopyrite (cp) in average proportions (%) of 65po:30pn:5cp. Cobaltite-gersdorffite and sphalerite are the most frequent accessories minerals. Assay data indicated the presence of platinum-group elements (PGE). Platinum-group minerals (PGM) were identified during microscopy on ore from the O'Toole deposit. Mineral identifications were made and confirmed by electron microprobe.Kotulskite-melonite followed by irarsite and sperrylite are the most abundant PGM. Other identified phases include OsAs 2 , OsAsS, OsRhAsS, RuTeAs, OsRuAs, OsAs 5 , and a complex Os-Re-As-Te-Fe-Y-Rh mineral. Platinum-group minerals occur frequently as inclusions in cobaltite-gersdorffite, suggesting that the PGM formed first. Since pyrrhotite replaces cobaltite-gersdorffite indicating its later crystallization, it can be deduced that the PGM formed during the first stages of magma crystallization, before sulfides and arsenides.Routine microprobe analysis identified a rhenium sulfide (ReS 2 )--the second reported global occurrence.