Some general problems of the formation of copper-nickel ores are discussed on the basis of new data from the Norilsk deposits. These deposits, together with the deposits of greenstone belts and some others, are classified as the deposits connected with ore-bearing volcanic-intrusive complexes of intercontinental rift zones. Massive sulfide ores, sulfide-bearing intrusions, and ultramafic vo1canites are shown to have been formed as the result of successive emplacements of magmatic melts formed in the process of deep differentiation of mantle magmas. The factors determining the zonality of distribution of sulfide mineral assemblages in sulfide-bearing intrusions of the bodies of massive sulfides and the formation conditions of platin-bearing horizons of layered intrusions are discussed.In the recent decade, studies of copper-nickel deposits have been undertaken within the International Program of Geological Correlation. A number of basic works aimed at investigating copper-nickel deposits were carried out in the USSR. These studies have contributed significantly to a better understanding of geological and petrological regularities of sulfide ore formation.A concept of the magmatic origin of copper-nickel ores as products of the evolution of ultrabasite-basite sulfide-silicate magmatic systems is emerging. Investigations of ancient copper-nickel ore deposits in greenstone belts of the Archean cratons were especially important in this respect. Presently, the results obtained, as well as the achievements in studies of evolution of structures and endogenous ore formation through the Earth's history (Kazanskii 1983, Smirnov 1982, allow us to consider the copper-nickel ores as a specific type of magmatic product formed in the course of definite structural transformations of the continental crust.Two groups of magmatic assemblages, the formation of which is accompanied by copper-nickel ore formation persist in all metallogenic epochs. The first group includes highly differentiated volcanic-intrusive magmatic assemblages occurring in the zones of near-fault depressions or intercontinental rift structures; the second group comprises magmatic assemblages forming rhythmi-

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