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The Talnakh deposit is one of the largest PGE-Cu-Ni deposits in the world. It is located inside the NorthWestern part of the Siberian Trap province and consists of three branches. The problem of massive ore origins has been discussed for several decades. The structure of the SouthWestern branch and the mineralogy of related its Cu-rich ore are discussed in this article. The Southern 2 orebody has a deep inclination (45 •) inside the intrusive body, close to its wall, in contrary to the horizontal orebodies of the NorthEastern branch. Mineral composition of the Southern 2 orebody differs from the composition the other orebodies of the Talnakh intrusion as well. It consists ofchalcopyrite, pentlandite with subordinate cubanite, and pyrrhotite. Its specific feature is a large amount of bornite and chalcocite. These minerals occur in disseminated and massive ores. The ores of the other branches of the Talnakh intrusion have chalcopyrite-pyrrhotite compositions whilethe Southern 2 massive ore is enriched in Cu (19.03-25.8 wt %; Cu/Ni = 3.8-8.6) and PGE: ΣPGE changes from 39.1 to 279 ppm, Pd/Pt = 1.3-32. Twelve minerals of the systems Pd-Sn-Cu, Pd-Pb-Bi, Pd-Ni-As, Au-Ag-Pd-Cu, and intermetallics of the Pt-Fe-Cu-Ni types were discovered in ores, but are also widespread in other orebodies. Isoferroplatinum, sperrilite and cooperitewere not found. The unusual structure and composition of the Southern 2 orebody suggest its origin from a separate magma impulse. The correlation between disseminated and massive ores of the Southern 2 orebody in term of chemical and mineralogical composition is evidence of the formation of massive oresin situ, without displacement along the bottom of the massif.

The unique and very large PGE–Cu–Ni Noril’sk deposits are located within the Siberian trap province, posing a number of questions about the relationship between the ore-forming process and the magmatism that produced the traps. A successful answer to these questions could greatly increase the possibility of discovering new deposits in flood basalt provinces elsewhere. In this contribution, we present new data on volcanic stratigraphy and geochemistry of the magmatic rocks in the key regions of the Siberian trap province (Noril’sk, Taimyr, Maymecha-Kotuy, Kulyumber, Lower Tunguska and Angara) and analyze the structure of the north part of the province. The magmatic rocks of the Arctic zone are characterized by variable MgO (3.6–37.2 wt %) and TiO2 (0.8–3.9 wt %) contents, Gd/Yb (1.4–6.3) and La/Sm (2.0–10.4) ratios, and a large range of isotopic compositions. The intrusions in the center of the Tunguska syneclise and Angara syncline have much less variable compositions and correspond to a “typical trap” with MgO of 5.6–7.2 wt %, TiO2 of 1.0–1.6 wt %, Gd/Yb ratio of 1.4–1.6 and La/Sm ratio of 2.0–3.5. This compositional diversity of magmas in the Arctic zone is consistent with their emplacement within the paleo-rift zones. Ore-bearing intrusions (the Noril’sk 1, Talnakh, Kharaelakh) are deep-situated in the Igarka-Noril’sk rift zone, which has three branches, namely the Bolsheavamsky, Dyupkunsky, and Lower Tunguska, that are prospected for discovering new deposits. One possible explanation for the specific position of the PGE–Cu–Ni deposits is accumulation of sulfides in these long-lived zones from the Neoproterozoic to the Mesozoic era during magmatic and metamorphic processes. Thus, trap magmatism, itself, does not produce large deposits, but mobilizes earlier formed sulfide segregations in addition carrying metals in the original magmas. These deposits are the results of several successive magmatic events, in which emplacement of the traps was the final event.

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