Geochronological and isotope geochemical characteristics of mafic intrusions of the Norilsk region

Layered intrusions of the Norilsk group contain unique deposits of copper-nickel, cobalt and plati� noid ores, and platinoids. The origin of silicate matrix was traditionally considered to be mantle. However, the first study of the isotopic composition of fluid components (He and Ar (1) and sulfur (2)) revealed largescale mantle-crust interaction. The complex isotopic investigations of rocks and ores of mafic intrusions of the Norilsk region performed at the Karpinskii Geological Research Institute in 2003- 2008 demonstrated the quantitative genetic indicators allowing us to refine the models of the formation of unique Cu-Ni-PGE deposits. We performed several hundred isotopic analyses: isotopic composition of helium and argon from fluid microinclusions in rocks and ores; sulfur, copper, and nickel from sulfides. The absolute (isotopic) age of sul� fide ores and zircons from rocks in intrusions with var� ious ore potential was determined. To obtain an inte� grated pattern, we also used the latest data of Russian and foreign researchers in this region (3-5 and refer� ences therein). The helium isotopic composition ( 3 Не/ 4 Не ratio) is considered to be the only reliable and strong criterion of the link between mineralforming fluids and the mantle. It is revealed that the ratio of helium isotopes in the Earth's upper mantle (1.2 × 10 -5 ) is ~1000 times higher than in helium formed in rocks of the Earth's crust (~ 2 × 10 -8 ). This allows us to reveal and calculate the portion of mantle helium, if it exceeds 1% of the total helium in the sample. Measurements demon� strated that crustal helium dominated in paleofluids from the Norilsk intrusions and the contribution of mantle helium ranged from 1 to 22%. The contribu� tion of helium of such origin is especially low (1-4%) in rich and intermediate intrusions. Poor intrusions significantly differ by this parameter (4-22%). The argon isotopic composition ( 40 Ar/ 36 Ar) pro�