Permian-Triassic Intrusions of the South Norilsk trough, Siberian Traps Province: Mineralogy and Geochemistry

Abstract

The Norilsk ore region is located within the Siberian traps province which includes volcanic and intrusive rocks comprising the PGE-Cu-Ni deposits. The Turumakit area, which is situated within the southern Norilsk trough, also contains many different intrusions sometimes with related mineralization. We have studied magmatic rocks within the Turumakit area (83 samples). They are attributed to the Norilsk, Ergalakh, Daldykan and Ogonersky intrusive complexes. The obtained mineralogical and geochemical data, as well as the U-Pb system of baddeleyites, have shown difference between sub-alkaline rocks of the Turumakit area and the typical Eragalakh trachydolerites located in the Norilsk and Talnakh ore junctions. The Turumakit subalkaline rocks are coarse-grained, with segregations of pegmatite gabbro in contrast to typically fine-grained Ergalakh trachydolerites. They also contain higher TiO₂ (up to 4.7 wt%) in comparison with 2.2-3.3 in the typical Ergalakh rocks. Low U, lower La/Yb and La/Sm ratios (5-7 in contrast with 8-10 for and 2.5-2.6 versus 3.0-3.3 for the Ergalakh dolerites) are typical features of the Turumakit sub-alkaline rocks. Their age was determined by U-Pb methods on baddeleyite and zircon (244.8±2.7 Ma) and it appears likely that the mafic rocks traditionally attributed to the Ergalakh intrusion within the Turumakit area are younger than the Norilsk intrusions (250±1.4 Ma). These data strongly indicate an emplacement of the Turumakit intrusions during the end of the magmatic evolution of the Norilsk district. It is proposed that the sub-alkaline magmas within the Norilsk district intruded during two different magmatic events.