Pt, Pd, and Au are concentrated in a hydrothermal Cu-Ni sulfide occurrence near Rathbun Lake, northeastern Ontario. The mineralization is associated with a sheared zone of the Wanapitei intrusion where hydrothermal fluids have altered relatively pristine gabbronorite to chlorite, sericite, quartz, epidote, and biotite. Chalcopyrite and pyrite, the principal sulfide minerals, occur as massive and disseminated mineralization. Bismuthian merenskyite and to a lesser extent kotulskite, michenerite, and temagamite are the Pd-bearing minerals, whereas Pt occurs primarily in sperrylite--64 percent of the Pd mineral grains are associated with altered silicates rather than sulfides. Although grains within sulfides may have been exsolved, the size and number associated with silicates suggest many were precipitated independently.Grab samples average 9 percent Cu, 0.2 percent Ni, 20,829 ppb Pd, 9,736 ppb Pt, and 3,053 ppb Au. Values for the other platinum-group elements are near background levels. No correlation is evident between Cu and the platinum-group elements or Au. The ratio of Pt + Pd/Os + Ir + Ru is much larger than for tholeiitic-hosted deposits of magmatic origin and probably reflects the relative solubilities of the platinum-group elements.