The Cu association with Ordovician volcanics of Newfoundland has long been known. Production has been disappointing, and exploration has failed to respond in a large way to the probing that has been carried on. That there are underlying reasons for lack of success is apparent to anyone familiar with the host rocks in the field. The rock-types commonly regarded as favorable are described. The observation that Cu mineralization is virtually confined to the fragmental flow-tops is related to the ratio of flow-top thickness to the total thickness of an individual flow, termed the skin ratio. The formation of pyrite and chalcopyrite is thought to have been more emphatically one of sulfurization, unaccompanied by any large-scale introduction of metal.

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