Some observations that bear on the origin of porphyry copper deposits

Observations at Ray, Ariz., suggest that upper crustal calc-alkaline plutons associated in time and space with the deposit might not have been capable of producing much water by differentiation and that any water released likely had restricted access to the best copper-sulfur sources in the magmas. Observation of concentrations of sulfides around isolated pockets of partially melted rocks below the Stillwater Complex. Mont., suggest to us a variant model of porphyry copper generation that does not require calc-alkaline plutons to be the vessels that transport copper and sulfur to upper crustal sites.