Abstract
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.
Highlights
The Noril’sk deposits play a leading role in the economics of the world’s supply of Ni and PGE
They are unique among PGE–Cu–Ni deposits around the world due to their location inside the Phanerozoic Siberian traps province of continental flood basalts [1,2], in contrast to most deposits which are related to large Proterozoic layered intrusions
Were the deposits formed under special conditions, or was their origin predetermined by the evolution of the trap system as a whole? Could we expect the discovery of large Cu–Ni deposits in flood-basalt provinces elsewhere? To answer these questions, it is necessary to analyze the structure of the Siberian province and the evolution of magmatism within it
Summary
The Noril’sk deposits play a leading role in the economics of the world’s supply of Ni and PGE. They are unique among PGE–Cu–Ni deposits around the world due to their location inside the Phanerozoic Siberian traps province of continental flood basalts [1,2], in contrast to most deposits which are related to large Proterozoic layered intrusions. The Noril’sk giant bodies of massive sulfide ore (up to 54 m) extremely enriched in PGE are related to thin (100–150 m) subvolcanic basic intrusions. The location of the intrusions within the Siberian trap province and the geochemical similarities between the intrusions and lavas pose a question about the possible relationships between magmatic and ore-forming processes in this area. Were the deposits formed under special conditions, or was their origin predetermined by the evolution of the trap system as a whole? Could we expect the discovery of large Cu–Ni deposits in flood-basalt provinces elsewhere? To answer these questions, it is necessary to analyze the structure of the Siberian province and the evolution of magmatism within it
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