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Ore-bearing formations and copper-nickel deposits are recognized as follows:(1) Duluth-type gabbro-troctolite formation; (2) Norilsk-type gabbro-dolerite formation; (3) Bushveld and Monchegorsk-type gabbro-norite-pyroxenite-peridotite formation; (4) Pechenga-type gabbro-pyroxenite-peridotite formation; (5) Kambalda-and Allarechensk-type pyroxenite-peridotite formation; (6) Mountkeith-type peridotite-dunite; and (7) regenerated Subdury-type diorite-norite formation. Nickel-bearing structures are noted in the greater thicknesses of the Earth's crust and in downwarped Moho boundaries in weakly eroded provinces. There is a clear relationship between magmatic thicknesses of continental depressions and their ore potential: the thickness of volcanogenic units in orebearing structures is over 3 km, whereas that of barren structures is less than 2 -3 km. In undislocated areas, the relation between the morphology of intrusive bodies and their ore potential is observed. Ore-bearing magmatic bodies are typically elongated, band-chonolitelike bodies with flat roofs and downwarped bottoms; this is attributed to the excess of density of ore-bearing magmas over that of environment (at the expense of sulfide load) and gravity field effect during intrusion of the bodies that brought about one-way movement of magmatic masses.Copper-nickel deposits are associated with mafic-ultramafic magmatic formations that are divided into three series: (1) (Fig. 1 A, Table 1) mafic sulfidefree and slightly sulfide-bearing series (MgO ~ 8 mass 070 ); (2) mesomafic sulfidebearing (MgO 8-33 mass%); and (3) ultramafic sulfide-free series (MgO >33 mass%). Each of the series is subdivided into magmatic groups that correspond to magma varieties and produce magmatic rock complexes or geological formations that host various copper-nickel deposits.The following ore-bearing (sulfide-nickel-bearing) formations are recognized for copper-nickel deposits (Fig. 2): (1) Duluth-type gabbro-troctolite formation; (2) Norilsk-type gabbro-dolerite formations; (3) Bushveld-and Monchegorsktype gabbro-norite-pyroxenite-peridotite formation; (4) Pechenga-type gabbropyroxenite-peridotite formation; (5) Kambalda-and Allarechensk-type pyrox-

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