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Alternating intervals of normal and reversed polarity are revealed in the sections of two Permian–Triassic trap intrusions of the Ergalakhsky complex, Norilsk region. The near-contact zones of the intrusions are magnetized reversely, whereas magnetization in the central zones has normal polarity. The arguments are presented that this change in the polarity along the intrusions section is not due to the postmagmatic remagnetization or self-reversal of remanence but marks the reversal of the geomagnetic field that occurred during the emplacement of the intrusive bodies. Highly accurate age determination for the Ergalakhsky intrusions – the oldest intrusive trap complex in the Norilsk region – is vital for time correlation of the initial stage of magmatic activity. According to the paleomagnetic data, the studied sills intruded directly at the Permian–Triassic boundary at the very end of the Ivakinsky stage. The existing estimates for the durations of the reversals indicate that the cooling of the intrusions could last a few thousand years. In the future, the examined sills of the Ergalakhsky complex can be used as a unique object for exploring the structure of the geomagnetic field during the reversals, for reconstructing the thermal history of intrusions’ cooling, and as a reference for estimating the total duration of trap magmatism.

We studied 6 sections of the Arydzhangsky lava formation (P2-T1) in the Kotuy river valley. The results of petrographic and geochemical studies of the composition of rocks of the Arydzhangsky, Khardaksky and Pravoboyarsky formations are presented. The stratigraphic columns of the sections were built and the composition of the rocks was additionally determined using a scanning electron microscope. In this regard, the relative position of these formations was established, the mantle and crust sources of magmas were confirmed. A geochemical identity of the rocks of the Khardaksky formation with the rocks of the Arydzhangsky formation was established, which suggests a similar age of their formation.

Rocks enriched in olivine, such as olivine and picritic gabbro–dolerite and troctolite are abundant in the Pyasino–Vologochan intrusion. In contrast to Norilsk type ore-bearing massifs, ultramafic rocks of the intrusion are dominated by troctolite. Picritic gabbro–dolerite and troctolite are located between olivine and olivine-bearing gabbro–dolerite. These rocks are related by gradual transitions. The rocks are enriched in olivine, but depleted in magnesium relative to the Norilsk type ore-bearing massifs. The intrusion is also distinguished by low chromium content in the rocks. Most disseminated Pt–Cu–Ni ores are confined to troctolite and picritic gabbro–dolerite, and to a lesser extent, to contact and olivine gabbro–dolerite. The ore is mainly observed as low-sulfur assemblages of sulfides with troilite, Fe-rich hexagonal pyrrhotite, Fe-rich chalcopyrite, talnakhite, Fe-rich pentlandite, and cubanite. The total content of platinum group elements (PGE) in the ore (ppm) is as follows: from 0.45–3.47 to 7.8; gold, from 0.05–0.24 to 0.49; and silver, from 0.53–4.50 to 8.30. Disseminated ores of the Pyasino–Vologochan intrusion contain the following Pt and Pd minerals: sobolevskite, Te-sobolevskite, Te-insizwaite, maslovite, paolovite, zvyagintsevite, atokite, niggliite, mertieite II, guanglinite, and Pd2(As,Sb), Pd2(Sn,As), Pd3Sb, (Pd,Ni)2As minerals. The similarities and differences between the Pyasino–Vologochan intrusion and Norilsk type ore-bearing massifs are discussed in this paper.

The timing of the emplacement of ore-bearing melts in the process of evolution of flood-basalt magmatism in the Noril’sk District is discussed. The current models of ore formation consider the emplacement of ore-bearing intrusions either under the conditions of a closed magmatic system as a product of a self-dependent magmatic event, or under the conditions of an open magmatic system, where intrusions are parts of the conduits feeding lava flows. In both cases, the composition of the initial magma, the content of volatile components therein, and the contribution of country rock assimilation are important for the development of a genetic model. The relationships between lavas and intrusions are exemplified in the South Maslov intrusion, which cuts through the rocks of the Nadezhdinsky Formation. No geological evidence for links of lavas to intrusions has been established. Substantial difference in geochemistry (Ti contents, Gd/Yb and La/Sm ratios, etc.) of the tuff and lava sequence on the northern shore of Lake Lama and the Maslov intrusions are demonstrated. It is concluded that the Noril’sk deposits were formed as products of emplacement of self-dependent portion of magma in the post-lower Nadezhdinsky time. The melt composition determined from melt inclusions in olivine corresponds to high-Mg tholeiitic basalt (up to 7–8 wt % MgO) containing up to 1 wt % H2O and 0.3 wt % Cl and undersaturated with sulfur. The fluid regime of flood-basalt volcanism had no anomalous features—the fluid was aqueous-carbon dioxide. The melts of ore-bearing and barren intrusions had similar concentrations of volatile components. The distribution of major and trace elements in intrusive rocks of the contact zone with the lower part of the Nadezhdinsky Formation characterized by high (La/Sm)N ratio in comparison with gabbroic rocks (2.8–2.3 and 1.3–1.6, respectively), indicates that contamination of the initial melt only took place in a narrow (1 m) contact zone or did not develop at all. New data on isotopic compositions of Sr (87Sr/86Sr)251 = 0.7089 and Pb (206Pb/204Pb = 20.877–24.528 in anhydrite confirm that local assimilation did not play a substantial role in the formation of rock and ores. On the basis of chemical composition of ore-forming intrusions, their isotopic characteristics, and the composition of melt inclusions in olivine, it is suggested that the lower crustal rocks were a major source of ore-bearing magmas.

Olivine is one of the most widespread minerals on the Earth, being the main component of the mantle in accordance with existing views. Olivine undergoes only minor alterations in going down to the depth of 350 km, but at deeper levels it can be transformed to β-modification (wadsleite) and, at the depth of 520 km, further to γ-modification (ringwoodite). Olivine occurs either as the main or auxiliary mineral for crust rocks (ultrabasites, basites, and kimberlites) and also as accessory mineral in acidic rocks. Depending on its genesis olivine contains isomorphous impurities of Cr, Ni, Ti, Mn, Ca, Co, etc. The composition of olivine and igneous inclusions entrapped during its growth constitutes important diagnostic criteria which identify the genesis of ore deposits. Regular variations of the content of basic end-members (forsterite and fayalite) and the availability and abundance of impurity elements make them suitable as indicators of ore formation process for various deposits. This point was exemplified by chromite-bearing massifs of the Polar Urals and platinumcoppernickel deposits of Norilsk Ore Region. Olivine is commonly used as natural fireproof raw material.

This paper presents a detailed analysis of the structure of the Trap Rock Association in the Norilsk Trough and presents data from the petrographic examination of the volcanics. We recorded new data that allow us to renew and supplement the available information on the trap association. We used the drill core from a drill hole 1100 m deep (the hole penetrated 1039 m of volcanics) as a study target. We were able to reveal the thicknesses of the formations, their flows, the petrographic composition of volcanics, and their structural and textural specific features. We examined rock variability up the section in analogous rocks belonging to different rock associations.

The influence of processing regimes on the static electric potential during processing of aminalone in a pulsating layer was studied. The potential decreased significantly as compared with that in a fluidized bed.

The role of recycled material in mantle plumes is difficult to quantify on the basis of incompatible trace elements and isotopes because of the great variability of subducted material. Another approach is to use major elements and compatible trace elements because these are more uniform in the mantle and are strongly controlled by the phase petrology of melting. Subducted crustal lithologies invariably differ from mantle peridotite, and this introduces olivine-free lithologies such as pyroxenites and eclogites into the mantle. Our massive study of olivine phenocrysts and trapped melt inclusions shows unusually high Ni and Si contents in many recent primary Hawaiian magmas. Similar compositions are found in the Canary Islands, W. Greenland, and the Siberian flood basalts. These magmas are not in equilibrium with an olivine bearing source under thick lithosphere (more than 100 km) typical of these localities, because an olivine-pyroxene assemblage would buffer both Ni and Si at lower levels. In contrast, magmas from plumes located under thin lithosphere, such as Iceland or Azores show no significant Si and Ni excess, and they could be in equilibrium with a shallow, olivine-bearing source. High-Si magmas can be produced by melting of eclogite, but this does not yield high Ni contents. Therefore, the eclogite-derived melt must acquire high Ni by converting surrounding peridotite to a solid pyroxenite, which ultimately melts a shallower level. Because unreacted peridotite may also begin to melt at shallow depths, this results in mixed melts derived from (secondary) pyroxenite and peridotite. In settings of thick lithosphere, the amount of peridotite-derived melt will be relatively small. Therefore, the recycled component represented by pyroxenite-derived melt may dominate. In settings of shallow melting, the peridotite will melt more extensively, and the signal from the recycled component will be diluted. Quantitative modeling shows that over half of the Hawaiian magma volume formed during the last 1 Myr came from secondary pyroxenite representing the recycled oceanic crust. The results are consistent with a plume with potential temperature of 1600 deg.C containing about 20 percent of recycled oceanic crust in the central part. These results are also consistent with estimates of volcano volumes, magma volume flux, and seismological observations. In the context of this model, the recent increase in Hawaiian magma flux is produced by an unusually high proportion of recycled crustal material in this part of the plume.