Mines near the city of Rossland in the West Kootenay district of southeastern British Columbia were important producers of copper and gold from 1894 to 1928 and of molybdenum since 1966 from an open-pit mine near the copper-gold camp.Eighteen new K-Ar dates of plutonic, dike, and volcanic rocks indicate that the age of the oldest pluton (the Rossland monzonite) is more than 90 m.y. and that all the other rocks are between 46 and 52 m.y.Geological relationships show that the molybdenite is older than the copper-gold mineralization. The molybdenite is about 48 m.y. because it is cut by 48.1 m.y. dikes and occurs in fractures which cut quartz diorite with an apparent age of 48.7 m.y.The copper-gold mineralization is younger than lamprophyre dikes with an average age of 48.2 m.y. and is thought to be about this age.Mineralization in the Rossland camp, therefore, is Tertiary and appears to be genetically associated with two bodies of quartz diorite and granodiorite formerly regarded as part of the Nelson plutonic suite.