The Whalesback Mine is one of many copper deposits associated with Ordovician volcanic rocks in the Notre Dame Bay area, Newfoundland. The deposit consists of veins, pods, and disseminated sulfides localized within a highly chloritized shear zone cutting basaltic pillow lavas. Porphyritic dikes cut the shear zone, sulfide deposit, and the surrounding pillow lavas; all of the rocks, including the sulfide-rich rocks, have been regionally metamorphosed. Ore minerals, in decreasing order of abundance, include pyrite, chalcopyrite, pyrrhotite, sphalerite, mackinawite, pentlandite, magnetite, cubanite, galena, and ilmenite. Marcasite, covellite, and goethite are supergene minerals. Chlorite and quartz are the predominant gangue minerals. Muscovite, carbonates, sphene, albite, and epidote are minor constituents. Banding and streaking of sulfides in massive ores, crushed pyrite, and the local occurrence of pressure-shadow phenomena in the ore are indicative of shearing stress post-dating original sulfide ore formation. Present sulfide assemblages are compatible with relatively low temperatures and are the result of re-equilibration and internal reaction among the sulfides with decreasing temperature.