Search

The Siberian large igneous province (SLIP) is an enormous continental province in the world comprising the extra-large PGE-Cu-Ni deposits [1-3]. Its origin is under discussion for several decades including genesis of sulfide ores. Many models were suggested [4-6] where a plume activity and delamination of the crust are the main agents of its origin. Meanwhile, the link of deposits’ formation with these processes is unknown and still controversial. Almost all genetic constructions do not take into account the real geological structure of magmatic rocks within the province which reflects evolution of magmatism in space and time at the P-T boundary. The main feature of the province is an occurrence of rocks, fundamentally different in genesis. Two types of igneous rocks take part in the SLIP structure, i.e., platform (or traps per si) and rift basalts. The first of them have sustained thickness, tholeiitic composition (6-7 wt.% MgO, 0.8 -1.6 wt.% TiO2, εNd = 0.14–1.90) and cover huge areas on ancient Siberian craton. The latter form small, rapidly pinching out flows of different composition in the Yenisey-Khatanga trough (YKT) and its feathering structures including the Norilsk-Igarka paleorift with PGE-Cu-Ni deposits. The maximum compositional diversity characterizes the rift rocks varying from picrites to trachyandesites (3 -33 wt% MgO, 1.3-6 wt% TiO2, εNd = −11.0 - +6.6). The fundamental difference between two types of magmatisms is crucial both for the SLIP formation and origin of the magmatic sulfide deposits. Primary it was suggested that rift magmatism preceded the trap magmatism but we proved that they operated synchronically within different tectonic elements during whole period of province formation. Magmatic activity began in the western part of the YKT from formation of subalkaline basalts of the Ivakinsky (Norilsk area) and Syradasaysky (South Taimyr) formations. They were overlapped by the Syverminsky, Gudchikhinsky (Norilsk) and Labaksky, Verkhnetamsky (Taimyr) formations. First platform basalts appeared in the Tunguska syneclise (Tuklonsky Formation) at the same time when rift basalts continued to erupt (Khakanchansky and Nadezhdinsy formations). The main impulse of the trap magmatism includes the Morongovsky, Mokulaevsky, Kharaelakhsky, Samoedsky, formations in the Norilsk area, and Nidymsky, Kochechumsky formatiom in the Tunguska syneclise, and Betlingsky formation in Taimyr. Rift basalts synckonically exploded along the northern and southern boundaries of the YKT (Ayansky picrites, and Fadyukundinsky, Arydzhangsky, Maymechinsky formations) demonstrating its evolutions from the west to the east. It is supposed that this magmatic development and deposits’ formation realized due to a collision of the Kara and Siberian cratons at the Late Paleozoic – Early Mesozoic epochs.This study was supported by RSF (project No 21-27-00387).

The problem of the world-class PGE-Cu-Ni Norilsk deposits’ origin has attracted geologists for several decades. The main goal of this study is to determine the specific features of ore-bearing intrusions in comparison with thousands of similar barren intrusions widespread within the Siberian igneous province, and to establish their genesis. As a result of statistical processing of previously published isotope-geochemical data and obtained by the authors, systematic differences were found in the distribution of the isotopic ratio of Nd in ore-bearing and barren intrusions, as well as in volcanic rocks at the Norilsk region. Thus, ore-bearing rocks in ten deposits (Talnakh, Kharayelakh, Norilsk 1, South-Maslovsky, North-Maslovsky, Norilsk 2, Chernogorsky, Zub-Mrksheydersky, Pyasino-Vologochansky, Imangdinsky), different in Ni and PGE reserves, show a very narrow range of Nd isotopic ratio, ԐNd(T) = 1.0 ± 1.0 (2σ, N = 139), whereas barren and volcanic rocks are characterized by a rather wide ԐNd(T) range, from −10 to +7 units (N = 256). Furthermore, ore-bearing intrusions are characterized by reduced and compact variations of the La/Lu ratio due to lower concentrations of light lanthanides. For the first time the authors studied two new intrusions penetrated by MD-48 and MD-60 boreholes drilled by Norislkgeologia LLT at the eastern part of the Mikchangda area. Their economic values are still unclear and should be estimated using geochemical methods. Both intrusions lie in the Devonian rocks, have similar thickness and mineral composition, but differ in textural and structural features, which indicate a rapid crystallization of the MD-48 intrusion. According to the contents of the major oxides, the rocks in MD-48 and MD-60 are identical, but they differ in U/Nb, La/Sm, and Gd/Yb ratios. It is important that the rocks in the MD-60 borehole are characterized by ԐNd(T) = 1.0 ± 0.6 (2σ) and fall into the range of ore-bearing intrusions, whereas the rocks in MD-48 have ԐNd(T) 2.4 ± 0.9, and, thus, are outside of ore-bearing intrusions. Therefore, ԐNd(T) values can be used as a local criterion for the estimation of economic potential of mafic intrusions, which is demonstrated for the Mikachangda area.

One of the pivoting problems in the genesis of magmatic deposits is the role of silicate melt in the origin of sulfide ores. A way of solving this problem is to compare massifs with different mineralization, using contents of major and trace elements in the rocks. However, intrusions of the Norilsk intrusive complex are rarely compared with one another in terms of ore composition and volume in them. This paper is the first geochemical data, all of which were acquired with the application of modern analytical techniques, on the Chernogorsky intrusion in the Norilsk trough. The structure and composition of this intrusion are well comparable to the intrusions of the same complex hosting the uniquely large deposits: Talnakh, Kharaelakh, and Norilsk 1. The weighted mean composition of the Chernogorsky intrusion (wt %) is as follows: 47.2 SiO2, 0.62 TiO2, 16.7 Al2O3, 9.94 FeO, 0.16 MnO, 11.7 MgO, 11.3 CaO, 1.53 Na2O, 0.46 K2O, 0.07 P2O5, and 0.18 Cr2O3,, and the ratios of trace elements (La/Sm)n = 1–2, (Gd/Yb)n = 1.2–1.4, and (Th/Nb)n = 1–4 are same as typical of other rocks of the Norilsk complex. The ores of the Chernogorsky intrusion are close to the ores of Norilsk 1, their Cu/Ni ratio slightly exceeds 1, and the Pt + Pd = 5–6 ppm on average. However, the predicted resources of metals in this massif (0.8 Mt Cu + Ni and 0.5 kt Pt + Pd) are 140 times lower than the resources of the Kharaelakh intrusion (113 Mt Cu + Ni, 17.5 kt Pt + Pd), and 50 times lower than in Talnakh (40 Mt Cu + Ni, 8.3 kt Pt + Pd). This confirms that the ore content in an intrusion does not depend on the composition of its silicate rocks, and hence, the compositions of these rocks cannot be used as an exploration guide for new deposits.

—The Kulumbe River area occupies a transitional position in the Siberian Traps province due to being located in the junction zone of the structures of the Norilsk region and the Tunguska syncline. The Kulumbe river valley combines the characteristic volcanic formations of both regions; however, the sequence of the formation of the intrusive complexes and their correlation with the volcanics are still unclear. The paper presents new paleomagnetic data on the intrusive bodies of the Kulumbe river valley. It is shown that intrusive magmatism in the region continued for a long time spanning at least one interval of the reversed polarity and one interval of normal polarity. Based on the comparison of virtual geomagnetic poles, the Siluriyskaya intrusion (Norilsk complex) containing sulfide mineralization can be correlated to the Morongovskaya-Mokulaevskaya (Morongovsky-Mokulaevsky) formations and close to the formation time of the ore-bearing intrusions of the Norilsk region. The formation of the Kulyumbinskaya intrusion (Kureyskii (Kureysky) complex) and some other bodies of the Kureyskii and Kuzmovskii (Kuzmovsky) complexes is most likely to correspond to the Morongovskaya-Mokulaevskaya (Morongovsky-Mokulaevsky) time and also is close to the formation time of the ore-bearing intrusions. The reversely magnetized intrusive bodies in the Kulumbe River valley were formed after the completion of the main volcanic phase and are approximately synchronous with the Daldykan complex in the Norilsk region. The formation of the Katangskii (Katangsky) intrusions, just as in the central part of the Tunguska syncline, spans a long period of time and cannot be correlated to any particular volcanic formation. Finally, based on the detailed analysis of the paleomagnetic data we hypothesize that most of the intrusions of the Kulumbe River valley except for part of the reversely magnetized bodies have been formed before the end of the main regional deformations which roughly coincides with the termination of trap magmatism.

The volcanic rocks in the Vologochan syncline, the Khikey River valley, and Mount Sunduk, within the Norilsk area in the NW Siberian large igneous province, have been studied. They belong to the Ivakinsky, Syverminsky, Gudchikhinsky, Khakanchansky, Nadezhdinsky, Tuklonsky, and Morongovsky Formations. These Formations consist of trachybasalts, picritic basalts and tholeiitic basalts with aphyric and porphyritic textures, and intersertal and poikiloofitic structures. For the first time, we demonstrate the variations in the structure and composition of these Formations along the strike, based on 151 analyses of the major and trace elements in the rocks. The thickness of all the Formations, excepting the Morongovsky, reduce dramatically from the Yenisey–Khatanga trough to the Tunguska syneclise, and they pinch out in the east of the Norilsk area and are attributed to riftogen (rift) basalts. The rock compositions also change in this direction, especially in the Gudchikhinsky and Nadezhdinsky Formations. The two subformations of the Gudchikhinsky formation, the lower and upper, disappear in the east, so the Gudchikhinsky consists only of high-Mg rocks, picritic basalts, and picrites. The composition of the Nadezhdinsky formation varies intensely in its (Gd/Yb)n and (Th/Nb) ratios from the Vologochan syncline to the Khikey River valley. These structural and compositional variabilities differ between the rift formations and the platform ones. Two gabbro–dolerite sills from these areas that are close to the Norilsk and Ergalakh intrusive complexes have been studied. The metal contents in volcanic and intrusive rocks are similar and do not differ from the barren rocks of the South Pyasinsky massif comprising the PGE-Cu-Ni deposits. Only the Gudchikhinsky Formation contains elevated Cu and Ni concentrations. These features and the coinciding spatial distribution of the ore-bearing intrusions and picrites of the Gudchikhinsky rocks in the Norilsk–Igarka paleorift suggest their genetic link. It is proposed that the initial sulfides could have been formed in the mantle, as the Gudchikhinsky picrites, transported to the lower crust, and then involved by the trap magmas in the origin of the ore-bodies in the Norilsk deposits.

The Nadayansky Flow is one of the main markers of the volcanic pile of the Siberian Trap Province and covers an area of approximately 48 000 km2 at an average thickness of 30 to 50 m. The paper is the first to present data demonstrating the constancy of the major- and trace-element composition of the Nadayansky Flow, typifying basalt lava flows in the province. The flow makes up the bottom part of the Mokulaevsky Formation in the Norilsk area and the bottom of the Khonnamansky Formation at the Putorana Plateau and, correspondingly, overlies the Morongovsky and Ayansky formations (the names of these formations differ because they are used in different schemes for the stratigraphic subdivision of the volcanic rock sequence). The rocks show an obvious glomerophyric texture, which makes this flow clearly distinguishable from the under- and overlying rock units. The composition of the Nadayansky Flow was studied throughout its length of a few hundred kilometers and shows very little varying concentrations of major components (48.31 SiO2, 1.26 TiO2, 15.8 Al2O3, 12.71 Fe2O3, 0.19 MnO, 6.89 MgO, 11.1 CaO, 2.25 Na2O, 0.37 K2O, 0.14 P2O5, 0.02 Cr2O3) and trace elements (2.44 La/Sm and 1.56 Gd/Yb), whose variations are within the analytical uncertainties (XRF and ICP-MS analyses). The basalt of the flow crystallized from tholeiitic melt, whose composition was analogous to those of melts that produced all other flows of the Mokulaevsky Formation. For comparison, the paper displays the inner structures of the underlying Morongovsky and Mokulaevsky formations in the basin of the Mikchangda River in the eastern part of the Norilsk area. The composition of the basalts of these formations also varies insignificantly. The main difference is an increase in TiO2 concentration from 1.19 to 1.3 wt % with the transition from the lower formation to the upper one. In spite of the insignificant difference between the concentrations, it is of principal importance and makes it possible to distinguish between the basalts of these formations. The detected constancy of the compositions of the formations as a whole and the Nadayansky Flow in particular are principally important for studying continental flood basalt provinces and demonstrates the compositional homogeneity of the erupted magmas and their sources. These results are important as an example how geochemical data can be used to correlate widely spaced sequences of volcanic rocks.

Patterns of magma transport during the emplacement of Large Igneous Provinces (LIPs) are extremely important for the understanding of their formation. The Permian-Triassic Siberian Traps LIP is considered to be one of the largest in the Phanerozoic; however, mechanisms of magma transfer within and under the crust are still poorly studied. This problem is vital for the reconstruction of the dynamics of magmatic activity and eruption styles, ascertaining the position of magmatic centers and feeding zones, and conception of ore deposits genesis. Here, we present the detailed results of anisotropy of magnetic susceptibility measurements for lava flows and intrusions from the Noril’sk and Kulumbe regions (the northwestern Siberian platform). We reconstructed patterns of magma flow based on the magnetic fabric analysis of more than 100 sites. Distribution of the magnetic lineation in the studied intrusions and flows points out that the lateral magma flow of NW-SE directions was predominant. Our results support the idea of a magma-controlling role of Noril’sk-Kharaelakh and Imangda-Letninskiy regional fault zones. Furthermore, the reconstructed geometry of magma transport in intrusions is contrasting with that in the Angara-Taseeva depression (the southern part of the LIP) due to the presence of the long-lived mobile zones in the northwestern Siberian platform.

The Oktyabr&rsquo, skoe deposit in the Norilsk ore district is the largest platinum-copper-nickel deposit in the world. It contains a huge main orebody (2.4 km3) of massive sulfide ores and some smaller sulfide bodies. Almost all publications on this deposit are devoted to the main orebody. However, to solve the problems of the deposit genesis, it is necessary to take into account the geological structure of the entire area and the composition of all orebodies. For the first time we present data on the inner structure, geochemical and mineralogical characteristics of the intrusive body, and related the disseminated and massive sulfide ores (orebody number C-5) in the northeastern flank of the deposit. The intrusion studied in the core of the borehole RG-2 consists of several horizons including the following rock varieties (from bottom to top): olivine gabbro-dolerites, taxitic gabbro-dolerites, picritic gabbro-dolerites, troctolites, olivine-free gabbro-dolerites, ferrogabbro, and leucogabbro. The intrusion shows a strong differentiated inner structure where high-Mg rocks (up to 25 wt.% MgO troctolites and picritic gabbro-dolerites) in the bottom are associated with low-Mg rocks (6&ndash, 7 wt.%, gabbro-dolerites, leucogabbro, ferrogabbro) without intermediate differentiated members (8&ndash, 12 wt.% MgO olivine gabbro-dolerites). Rocks are characterized by low TiO2 content (&le, 1wt.%). Taxitic gabbro-dolerites, picritic gabbro-dolerites, and troctolites contain disseminated sulfide chalcopyrite-pyrrhotite mineralization (32 m thick). Cu and Ni concentrations reach up 0,74 and 0.77 wt.%, respectively. Massive ores (27 m) occur in the bottom part of the intrusion. The ores consist of pentlandite, chalcopyrite and pyrrhotite, the latter mineral dominates. Their chemical composition is stable: Cu/Ni ~1, Pd/Pt varies from 5 to 6. The C-5 orebody is similar to the C-3 orebody in terms of mineral and chemical compositions, and differ from the nearby the C-4 orebody which is characterized by a Cu/Ni ratio changing from 5 to 8. On the basis of geochemical and mineralogical data, it is assumed that orebodies C-3 and C-5 are associated with one intrusion, while the orebody number C-4 is related to another intrusive body. Thus, the deposit has a more complex structure and includes several more intrusions than is usually considered.

The composition of the parental magmas of Cu–Ni deposits is crucial for the elucidation of their genesis. In order to estimate the role of magma in ore formation, it is necessary to compare the compositions of silicate rock intrusions with different mineralization patterns, as observed in the Norilsk region. The rock geochemistry of two massifs located in the same Devonian carbonate rocks—the Kharaelakh intrusion, with its world-class platinum-group element (PGE)–Cu–Ni deposit, and the Pyasinsky-Vologochansky intrusion, with its large deposit—was studied. Along with these massifs, the Norilsk 2 massif with noneconomic mineralization intruded in the Ivakinskaya-Nadezhdinskaya basalts was studied as well. Their settings allow the estimation of the parental magma composition, taking into account the possible assimilation of host rocks. Analyses of 39 elements in 97 samples demonstrated the similarity of the intrusions in terms of their major components. The Pyasinsky-Vologochansky intrusion contains the highest trace element contents compared with the Kharaelakh and Norilsk 2 massifs, evidencing its crystallization from evolved parental magma. No influence of host rocks on the silicate rock compositions was found, except for narrow (1–2 m) endo-contact zones. There is no correlation between the mineralization volume and the rock compositions of the studied intrusions. It is assumed that the intrusions were formed from one magma crustal source irregularly rich in sulfur (S). This source inhomogeneity in terms of the sulfur distribution resulted in deposits of varying sizes. The magmas served as a transporting agent for sulfides from deep zones to the surface.

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.

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

The origin of the Siberian trap province is under discussion even though numerous models of its formation have been created over the last three decades. This situation is mainly due to lack of modern geochemical data on magmatic rocks around the province. These data are a very important tool to reconstruct of magmatic evolution within the province in time and space and to understand a mechanism of province formation. Geochemical study has only been carried out so far for the Norilsk and Meimecha&ndash, Kotuy areas. For the first time, we have studied the geochemical and mineralogical characteristics of magmatic rocks at the Kulyumber river valley located 150 km to south from the Norilsk ore district, in the junction of the Tunguska syneclise and Norilsk&ndash, Igarka zone. It comprises three sites, i.e., Khalil, Kaya, and Kulyumber. The geochemical data on the magmatic rocks of the Khalil and Kaya sites were published earlier (Part I). This article (Part II) regards geochemical and mineralogical data on igneous rocks at the Kulyumber site. Seventeen intrusive bodies (41 samples) and six samples of sedimentary rocks were studied by X-ray fluorescence (XRF) and inductively coupled plasma mass spectrometry (ICP-MS). Isotopes analyses (Sr, Nd, Pb) were conducted for 12 samples. These data were compared with data for intrusions of the Norilsk area, the Dzhaltulsky massif, Kureyka river, and intrusions in Angara river valley published earlier. The whole list of analyses includes 102 items. Three groups of intrusive rocks were recognized: (1) Mafic rocks with elevated K2O without negative Ta-Nb and Pb-positive anomalies, with (Gd/Yb)n = 2.0 and &epsilon, Nd = &minus, 1.0, attributed to a new Kulyumbinsky complex, (2) subalkaline rocks with elevated SiO2,TiO2, P2O5, and K2O with small negative Ta-Nb and positive Pb anomalies and (Gd/Yb)n = 1.8, &epsilon, 3.8, Ergalakhsky complex, and (3) mafic rocks with strong Ta-Nb and Pb anomalies and (Gd/Yb)n = 1.2&ndash, 1.4, &epsilon, Nd = +0.4&ndash, +2.2. The third group is rather nonhomogeneous and includes intrusions of the Norilsk, Kuryesky, Katangsky, Ogonersky, and Daldykansky complexes differing in MgO content and trace element distribution (values of Ta-Nb, Pb, and Sr anomalies). Three groups of intrusive bodies had different magma sources and different condition of crystallization reflecting their origin in rift and platform regimes.

The origin of the Siberian Traps province has been under discussion for the last three decades. Up to now, there is no real model of its formation in a good agreement with geological data on the magmatic evolution at P–T boundary in Eastern Siberia. Modern geochemical data on magmatic rocks around the province is a key to reconstructing magmatic development in time and space. Such data have been obtained for the Norilsk and Meimecha–Kotuy and not for other parts of the Siberian province. For the first time, we studied the geochemistry and mineralogy of magmatic rocks at the Kulyumber river valley, located in the intersection of the Tunguska syneclise and Norilsk–Igarka zone in the NW Siberian platform. In this article, we present data from the Khalil and Kaya sites of this area belonging to the Syverminsky, Gudchikhinsky, Khakanchansky and Nadezhdinsky formations. Their mineralogical and geochemical features (including Sr, Nd and Pb isotope data) are similar to the same formations in the Norilsk area, while the rocks belonging to the Gudchikhinsky formation show differences. The Syverminsky tuffs are also described for the first time. The intrusive rocks are attributed to four intrusive complexes, i.e., Ergalakhsky, Kureysky, Katangsky and Norilsk. The Ergalakhsky complex comprises trachydolerites similar to the trachydolerites of the Norilsk area. The rocks of the Norilsk complex at the Khalil site differ from the rocks of the same complex at the Norilsk area by the (U/Nb)n = 1.8, (La/Yb)n = 2.1 in comparison with 3.7 and 2.3 of the rocks of the Norilsk 1 intrusion. The intrusions of the Kureysky complex are more differentiated than those of the Katangsky intrusions but show comparable TiO2 and trace elements distribution. Thus, the magmatism of the Kulyumber area is characterized by features matching those of the Tunguska syneclise and Norilsk area, i.e., suggesting rift and platform regimes.

A periodic character of the evolution of trap magmatism was inferred by many researchers from the fact that sequences of volcanic rocks consist of alternating units of lava flows and tuff. A new phase of studying magmatic rocks in the Siberian Platform was related to the possibility of apply high-precision geochemical techniques in studying trace elements and Sr, Nd, and Pb isotopic compositions. The use of these techniques made it possible not only to identify small individual cycles in the vertical sections of volcanic rocks but also to distinguish larger stages. The currently most widely acknowledged scenario of the origin of volcanic rocks involves three stages, during which oceanic-island basalts (OIB), transitional series (intermediate between OIB and WPB), and within-plate basalts (WPB) were formed. This scenario was inferred mostly from data on rocks in the western part of the Norilsk area (Kharaelakh Trough). This publication presents recently obtained data on the inner structure of the sequences of volcanic rocks and the geochemistry of basalts in the eastern part of the territory, where no rocks show transitional characteristics have ever been found. They can be classified into two types that have clearly different composition and occur in different areas. These types characterize two major stages of the origin of volcanic rocks: rift-related and trap magmatism itself. The rocks produced during these stages occur at neighboring territories.

The Norilsk ore region is characterized by the occurrence of numerous intrusions comprising the PGE&ndash, Cu&ndash, Ni deposits. The Turumakit area, within the Southern Norilsk Trough, also contains many mineralized mafic intrusions of probably similar economic potential to the known Norilsk deposits. We study igneous rocks from three boreholes within the Turumakit area, sampling gabbro-dolerites and trachydolerites related to the Norilsk and Ergalakh complexes, as well as an outcrop of the Daldykan gabbro-dolerite intrusion. Our petrographical, mineralogical and geochemical data, as well as the U&ndash, Pb dating of extracted baddeleyites and zircons, primarily discriminate between the sub-alkaline rocks of the main Turumakit area and the Ergalakh trachydolerites located in the Norilsk and Talnakh ore junctions. Coarser grained Turumakit trachydolerites (with pegmatite segregations) contrast finer grained Ergalakh trachydolerites by having: (1) higher TiO2 (up to 5.5 wt %) compared with 2.2 wt %&ndash, 3.3 wt % in the typical Ergalakh rocks, (2) low U, lower La/Yb and La/Sm ratios (5&ndash, 7), in contrast to 8&ndash, 10 ppm, 2.5&ndash, 2.6 and 3.0&ndash, 3.3, respectively, for the Ergalakh trachydolerites, and (3) their age was determined by U&ndash, Pb methods on baddeleyite and zircon (244.8 &plusmn, 2.7 Ma), and it appears likely that the mafic rocks traditionally attributed to the Ergalakh complex within the Turumakit area are younger than the Norilsk intrusions (250 &plusmn, 1.4 Ma). These data strongly indicate an emplacement of Turumakit intrusions during the end of a ~5 Myr magmatic evolution of the Norilsk district. It is therefore proposed that the sub-alkaline rocks of the Turumakit area belong to a separate intrusive complex within the Norilsk district.

The Norilsk region is a key area within the Siberian Traps Large Igneous Province, due to the thickest sections of the Permian-Triassic extrusive rocks and high diversity of intrusions and volcanics in composition. The unique Cu-Ni-PGE deposits related to the Siberian Traps intrusions are present here. On the basis of the new representative paleomagnetic and geochemical data, we distinguished three stages of intrusive magmatic activity. At the initial stage, high-Ti trachydolerites of the Yergalakhsky complex were emplaced synchronously with the lower part of the Norilsk volcanic section. The middle stage was manifested by emplacement of ore-bearing intrusions of the Norilsk type, leucogabbro of the Kruglogorsky type, and barren gabbro-dolerites of the Oganer complex, coeval with the Morongovsky and Mokulaevsky volcanic formations (about 251.8–251.6 Ma). At this stage, magmatic activity occurred as a series of brief and powerful events. Finally, the terminal stage is represented by geochemically contrasting dikes of the Avamsky and Daldykan complexes, cutting the entire volcanic section of the Norilsk region. Our new paleomagnetic results together with U-Pb show that the Permian-Triassic boundary in the Norilsk volcanic section should be set at the base of the Morongovsky Formation (the middle part of the Norilsk tuff-lava pile), and the duration of volcanic activity after this boundary can be estimated as ~0.5 Myr.

We present new geochemical and mineralogical data from the Southern-2 orebody, located in the South-Western branch of the Talnakh intrusion (Russia) and composed of massive and disseminated sulphides. The Southern-2 orebody consists dominantly of chalcopyrite along with lesser pentlandite and subordinate cubanite, bornite and pyrrhotite, and differs from Cu-rich ores of the Oktyabr'sky deposit due to the absence of moikhukite-talnakhite assemblages. Ores from the Southern-2 orebody are highly enriched in copper, nickel and platinum-group elements (PGEs): Cu up to 28.12 and 10.58 wt%, Ni up to 6.29 and 2.45 wt%, and Pt + Pd up to 220 and 173 ppm in the massive and disseminated ores respectively. The ratios of Cu/Ni = 3.85–7.34 in massive and 2.64–6.58 in disseminated ores. The ratios of the platinum to iridium group elements (PPGE/IPGE) reaches more than 40000. These features indicate an extremely different degree of fractionation of the sulphide melt during the formation of ores. The sequence of crystallization of the PGE minerals (PGMs) on the basis of textural information was as follows: Pt-Pd-Sn (rustenburgite, atokite) → Pd-Cu-Sn (stannopalladinite) → Pt-Fe-Cu-Ni (tetraferroplatinum) → Pd-Ni-As (majakite) → Pd-As (palladoarsenide) → Pd-Pb(Bi) (zvyagintsevite, polarite and Pd5Pb3 unnamed phase) → Au-Cu-Pd (tetra-auricupride and auricupride) → Au-Ag alloys. This is consistent with experimental data on PGE minerals. The PGM assemblage was caused by the evolution of a significantly fractionated sulphide melt that was enriched in Cu, Ni, Pt, Pd, Pb and Au, and as a result produced minerals with peculiar compositions (e.g., Cu-rich stannopalladinite, Pb-rich polarite, Ni-rich palladoarsenide), which do not occur in other ores. Furthermore, Pt-Fe-Cu-Ni alloys are abundant and sperrylite is absent, which is a very common phase in all ores of the Noril'sk area. The composition of pentlandite with Ni/(Ni + Fe) ratios ranging from 0.48 to 0.68 indicates that it formed between 560 °C (Ni-poor) to 500 °C (Ni-rich) and −10.5 to −7 lgfS2, respectively. The PGMs and Au-minerals were formed at temperatures ranging from 550 to 225 °C. The specificity of sulphide (with PGMs) association is due to the evolution of the Cu-rich (and Ni-rich) melt under elevated sulphur fugacity conditions. The mechanism of filter-pressing, which precipitated sulphide drops at the bottom of the chamber, and penetration of sulphide melts into the country rocks is supported by the same geochemical composition of disseminated and massive ores.

There are five main sulfide deposits related to the Chiney pluton: Kontaktovyi, Skvoznoe, Pravoingamakitskoe, Verkhne-Chineyskoe, and Rudnoe. The high Cu/Ni ratio (Cu:Ni:Co = 76:7:1) is a distinguishing feature of the sulfide mineralization. The highest PGE tenor (up to 355 ppm PGE, Pd/Pt ~3–4) typically occurs in the massive ore. In contrast, the average grades of Pd and Pt in the disseminated sulfide are ~2 and ~0.5 ppm, respectively. The Rudnoe and Kontaktovyi deposits have the most important potential economic value. The Rudnoe is localized in gabbro rocks of the endocontact zone in the eastern offset of the Chiney pluton and in the exocontact zone with sedimentary rocks of the Udokan Supergroup. The disseminated sulfide in the endocontact is frequently related to magmatic breccia. Chalcopyrite dominates among sulfides, whereas pentlandite is a subordinate and even a rare mineral. Pyrrhotite and pyrite are also major sulfides, especially in the Kontaktovyi deposit. The other sulfide minerals are sphalerite, siegenite, galena, violarite, millerite, cobaltite, gersdorffite, safflorite, loellingite, argentopentlandite, michenerite, merenskyite, sperrylite, and other platinum group minerals.

There are two Fe-Ti-V deposits in the Chiney pluton—Magnitnyi and Etyrko. They represent the largest deposits of commercially viable vanadium ore in Russia, with average content of 0.5 wt% V2O5 and 6.3 wt% TiO2 in ores. The Etyrko deposit hosts stratabound, mostly disseminated titanomagnetite, whereas the Magnitnyi deposit consists predominantly of cross-cutting ore veins and irregular bodies in gabbronorite. The Magnitnyi deposit contains about 1.5 billion tons of ore in several orebodies. The major orebodies account for 89.1% of the total ore reserves and 86.1 to 92% of mineable metal reserves. The individual orebodies are between 5.7 m and 26.5 m thick, with the total iron content gradually decreasing westward from 39.4 wt% to 28.9 wt%. Titanomagnetite and ilmenite (the amount of the latter rarely exceeds 10% of the total) are the major ore minerals. According to the Mossbauer spectroscopy, magnetite in the titanomagnetite ore is close to stoichiometric, and titanium is mainly contained in ilmenite (11–13%).

In addition to the giant Udokan deposit, the rocks of the Udokan Supergroup contains several satellite Cu-Ag-Fe deposits. They are located in different formations at different stratigraphic levels. They differ strongly in mineral and chemical composition from the Udokan ores, often displaying much higher silver grades. The hypogene copper mineralization in these deposits consists of chalcopyrite, bornite, and, to a much lesser extent, chalcocite. Many rare minerals were found here. The deposits are of complex genesis, and for some, the hydrothermal origin was proven.

Chemical composition of the Chiney mafic-ultramafic layered intrusion was studied in two main sections and from other rock types in the eastern part. All rocks, except norite, are enriched in Fe and Ti. The MgO and TiO2 variations demonstrate a rhythmic structure of the Chiney pluton. Distribution of rare elements in rocks is similar to the distribution in typical crustal rocks with negative Ta-Nb and positive Pb anomalies. Techniques of geochemical thermometry with the use of the COMAGMAT computer program allowed to estimate the phase and chemical composition of the parental magma. The Chiney magma was represented by differentiated suspension of olivine, plagioclase, and magnetite crystals in ferrobasaltic melt at a temperature of approximately 1130 °C. The gravitational separation of these phases in the melt before its emplacement into the chamber and during the subsequent emplacement of various portions of the initial magma into the modern chamber predetermined the heterogeneity of the pluton.

Uranium mineralization in the Kodar-Udokan zone was discovered in 1950 in the rocks of the Udokan Supergroup (the Chitkanda prospect). But new occurrences of uranium mineralization were found in the rocks of the Chiney pluton and surrounding rocks only in the beginning of the twenty-first century. Mineralization is related to metasomatized rocks and is represented by brannerite, uraninite, and other minerals. Inside the Chiney pluton, many rare earth minerals were found as well. In this chapter, we report the first results (Gongalsky BI, Krivolutskaya NA, Makariev LB, Murashov KYu, Pavlovich GD, Timashkov AN: Concentration of U + REE at the final stage of operation of the Udokan-Chiney ore-magmatic system. Alkaline magmatism and associated deposits of strategic metals. Proceedings XXXIII international conference of Moscow, GEOKHI RAS, pp 28–29 (in Russian), 2016).

The cupriferous sandstones occur within the Paleoproterozoic Kodar-Udokan basin, superimposed onto Archean crystalline rocks of the Aldan Shield. In addition to the giant Udokan deposit, the basin hosts many smaller satellite deposits and occurrences. The Paleoproterozoic Sakukan Formation, hosting cupriferous sandstone units, and the overlaying Naminga Formation are principal hosting stratigraphic units of the Udokan deposit, forming a Naminga brachysyncline. The ore-bearing stratum was traced for 25 km along strike and includes four mineral levels in the vertical sequence. The Udokan deposit contains a huge endowment of Cu (>25 Mt), Fe (10 Mt), Ag (12 kt), and modest Au (13 t). The mineralization is subdivided into sulfide (70–100% sulfides), oxide (0–30% sulfides), and mixed (30–70% sulfides) ores. The ore principally consists of bornite-chalcocite and less frequently of pyrite-chalcopyrite. New data on mineral composition of ores and its sulfur isotopes are summarized here in order to constrain the genesis of the Udokan deposit.

The large Paleoproterozoic Nb-Ta-Zr-REE-Y Katugin deposit is situated in the southern part of the Kodar-Udokan district. Together with the Tomtor deposit in northern Siberia, Katugin deposit comprises the main Ta-Nb resources of the Russian Federation that can be developed in the future. The deposit occurs within a zone of fault-controlled alkaline alteration at the contact of rapakivi granite pluton. The ore-bearing quartz-albite-microcline alteration in a combination with alkaline granite form a steeply dipping lode exposed at the surface over an area of 5 km2 and traced to a depth of 800 m. The ore contains 1.62 wt% ZrO2, 0.026 wt% Ta2O5, 0.374 wt% Nb2O5, 0.16 wt% Y2O3, 0.22 wt% REE2O3, and 0.0078 wt% U3O8. Pyrochlore, zircon, gagarinite, REE-fluorite, monazite, and cryolite are the major minerals. Fergusonite, ilmenite, and ilmenorutile are widespread in the metasomatized country rocks. It was suggested that deposit was formed as a result of metasomatism, but nowadays there is an opinion on its magmatic origin.

The Chiney pluton is unique in distinct layering and rhythmic structure in Russia. It contains enormous vanadium resources (up to 30 Gt of ore) and PGE-Cu-Ni. The ores related to the Chiney intrusion differ from the ores of other Cu-Ni deposits in their high Cu/Ni ratio (~100). Its age is estimated as 1880–1850 Ma. It consists of the Western, Central, Eastern, and Southeastern blocks. Four main groups of intrusive rocks were recognized within the Chiney pluton, with two types of layering:(1) sharply bound isomodal layers, forming sandwiched leucocratic and melanocratic rocks (usually anorthosite and titanomagnetite gabbro and melagabbro), and (2) density-graded layers with titanomagnetite and/or pyroxene near the base. Maximum thickness of gabbro rocks has been estimated as 2.5 km. Internal structure and distribution of major components have been studied in the vertical sequence of the pluton. Composition of rock-forming minerals varies in separate rhythms but not in sequence.

The Kodar-Udokan mineral district is spatially constrained to a narrow spur of the western margin of the Aldan Shield in the southeast of the Siberian Craton, sandwiched between the Phanerozoic Baikal-Muya and Mongol-Okhotsk mobile belts. It comprises many deposits of Cu, V, Fe, Ag, Ti, V, Ta-Nb, Zr, and REE-Y of different genetic types in sedimentary and magmatic rocks. The sandstones of the Udokan Supergroup, the gabbro rocks of the Chiney Intrusive Complex, and the alteration assemblages of the Katugin granite are hosts to the main deposits. New geological, mineralogical, and geochemical data on the rocks and mineralization are summarized here.

The mafic-ultramafic rocks occur on the periphery of the Kodar-Udokan basin. They belong to the Chiney Intrusive Complex. The largest bodies are the Chiney and Luktur plutons, as well as the Upper Sakukan and Mylovskiy layered mafic-ultramafic intrusions. Gabbronorite dikes also belong to the Chiney Complex, with the Main Udokan Dike (up to 200 m thick) being the largest. The geochemical and geophysical data indicate that outcrops of mafic and ultramafic rocks at the margins of the Lurbun granite-granodiorite pluton, which cuts through the Chiney pluton, also belong to the Chiney Complex.

The present work involves a study of the internal structure, rock and ore compositions of the Oktyabr’skoe deposit. Two massive orebodies, C-3 and C-4, located in the north and south of the deposit central part are related to gabbro-dolerites subdivided by the Devonian sediments in space. Despite the closely similar structure and composition of the intrusive rocks, the disseminated and massive ores prove to display different chemical and mineralogical compositions. The C-3 orebody consists mostly of tetragonal chalcopyrite and pyrrothite, while the C-4 orebody appears to enclose sulfur-poor chalcopyrite group minerals, namely, talnakhite, putoronite etc. The C-4 orebody turns out to be rich in Cu and PGE in respect of the C-3 one. This ore-associated mineralogical diversity appears to result from differing fs2 taking place during the sulfide melts relating crystallization. It is also suggested that the orebodies, as originating from different portions of magmas, culminated in the formation of two intrusive branches.

The Northeastern Transbaikalia is one of the largest metallogenic provinces in Russia. It comprises three world-class deposits: Fe-Ti-V Chiney, Zr-Ta-Nb Katugin, and Cu Udokan. Besides these giant deposits there are many small deposits and prospectings in this area. All these deposits belong to the Paleoproterozoic epoch. New data on the structure, geochemistry, and mineralogy of these deposits were obtained by authors for the last three decades. The main results demonstrate the huge volume of basic-ultrabasic magmas intruded in sedimentary rocks of the Udokan Supergroup. They formed intrusive bodies; part of them are exposed on the surface as the Chiney, Luktur, and Mylovskiy layered mafic-ultramafic plutons. The chemical and mineralogical similarities of massifs demonstrate the common source of their parental magmas. It was found that Cu deposits in sandstones are characterized by different chemical ore compositions (Cu, Ag, Fe, Bi, Ni, Co, PGE) that demonstrate the essential role of hydrothermal processes in their origin, especially in Pravoingamakitskoe deposit. It was suggested that not only magmatic fluids but metheoritic water took place in ore origin due to their involving in circulation under heating caused by a huge magmas volume intrusion. Thus, the modern look of the deposits is a result of many long-lived geological processes operating in this area.

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.

The origin of the Siberian Traps province has been under discussion for the last three decades. Up to now, there is no real model of its formation in a good agreement with geological data on the magmatic evolution at P–T boundary in Eastern Siberia. Modern geochemical data on magmatic rocks around the province is a key to reconstructing magmatic development in time and space. Such data have been obtained for the Norilsk and Meimecha–Kotuy and not for other parts of the Siberian province. For the first time, we studied the geochemistry and mineralogy of magmatic rocks at the Kulyumber river valley, located in the intersection of the Tunguska syneclise and Norilsk–Igarka zone in the NW Siberian platform. In this article, we present data from the Khalil and Kaya sites of this area belonging to the Syverminsky, Gudchikhinsky, Khakanchansky and Nadezhdinsky formations. Their mineralogical and geochemical features (including Sr, Nd and Pb isotope data) are similar to the same formations in the Norilsk area, while the rocks belonging to the Gudchikhinsky formation show differences. The Syverminsky tuffs are also described for the first time. The intrusive rocks are attributed to four intrusive complexes, i.e., Ergalakhsky, Kureysky, Katangsky and Norilsk. The Ergalakhsky complex comprises trachydolerites similar to the trachydolerites of the Norilsk area. The rocks of the Norilsk complex at the Khalil site differ from the rocks of the same complex at the Norilsk area by the (U/Nb)n = 1.8, (La/Yb)n = 2.1 in comparison with 3.7 and 2.3 of the rocks of the Norilsk 1 intrusion. The intrusions of the Kureysky complex are more differentiated than those of the Katangsky intrusions but show comparable TiO2 and trace elements distribution. Thus, the magmatism of the Kulyumber area is characterized by features matching those of the Tunguska syneclise and Norilsk area, i.e., suggesting rift and platform regimes.

We present the new geochemical, paleomagnetic and anisotropy of magnetic susceptibility data from the Kulumbe river area (the Siberian Traps Large Igneous Province). The majority of the studied intrusions have the normal polarity, belong to the Katangsky complex and can be correlated with the upper part of the volcanic section of the Norilsk region. Furthermore, the first intrusive analogues of the Gudchikhinsky Formation are found. The only intrusion showing the reverse magnetic polarity has the geochemical features similar to the ore-bearing Norilsk-type intrusions. Based on the study of the magnetic fabric of the intrusions, we suggest that they were fed from the magma-conducting Imangda-Letninskiy fault.

The Talnakh deposit is one of the largest PGE-Cu-Ni deposits in the world. It is located inside the North-Western 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 South-Western 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 North-Eastern 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 significantly distinct geochemical peculiarities of the rocks of the layered plutons with titanomagnetite and sulfides (the Dyumtaleysky gabbroperidotite intrusive in the Taimyr Peninsula and the Chineysky gabbroanorthosite pluton in the Northern Transbaikalia) indicate different types and sources of the parental magmas. The rare element pattern of the rocks and their 87Sr/86Sr isotope composition (+0.704 and ɛNd = +5.5) of the Dyumtaleysky intrusive point to its crystallization from the mantle in contrast to the crustal characteristics of the Chineysky rocks (La/Sm = 3–6, 87Sr/86Sr = +0.707, ɛNd = −0.5). At the same time, the sulfide ores from these plutons are almost identical in the composition of the major elements (Cu, Ni, Co, PGE), but are distinct in the sulfur isotopic composition. The heavy values (+10 to +12%) of ores from the Dyumtaleysky intrusive are similar to those of ores from the Talnakh and Noril’sk ore districts in contrast to almost mantle δ34S values (2) of the Chineysky ores. The geochemical features of the Dyumtaleysky rocks are similar to those of the Chineysky basalts and, thus, the pluton is the first identified intrusive body that was formed from the primitive magmas in the north of the Siberian platform. It is suggested that the heavy sulfur isotopic composition was peculiar for the mantle source parental for the primary magmas of the Dyumtaleysky pluton. Such an atypical correlation of geochemical peculiarities of the rocks and ores is probably explained by its significantly younger age (Early Triassic) relative to the Paleoproterozoic Chineysky pluton, when the composition of the mantle substrate changed due to involvement of biogenic (?) or abiogenic (?) sulfur as a result of mantle-crustal interaction (e.g., subduction processes).

Composition of clinopyroxenes in vertical sections of some ore-bearing basic intrusions in the Noril’sk area has been studied by EPMA. These data formed the basis for the calculation of the pyroxene crystallization temperatures using the El Negro monopyroxene geothermometer (Fe-Mg exchange between M1-M2 positions). The results of the calculations allowed estimating the variations of temperature crystallization within the magmatic chambers from early to the late stages. The temperature varies from 1200 for idiomorphic crystals in equilibrium to liquid and up to 400 degrees (in solid intra exchange) for xenomorphic grains and marginal zones of pyroxenes. We reconstructed the regimes of crystallization of the magmatic chamber by this data. The vertical distribution of paleotemperatures of the intrusive chamber there is the evidence of absence vertical move crystals into such magmatic chambers.

To understand the origin of the Siberian trap province, it is necessary to know its internal structure in detail. Only two areas were described, the Noril’sk and Maimecha-Kotuy, while the most important part of the province, the Tunguska syneclise, is still poorly characterized. The main goal of our study is an investigation of the structure and geochemistry of volcanic rocks located in the central part of the province. We have studied basalts and tuffs and compared them with the rocks of the Noril’sk area. All studied rocks belong to three formations: Korvunchansky, Nidymsky and Kochechumsky. The whole thickness of this cross-section is around 1,000 m. Our geochemical data demonstrate that the lower part of the cross-section comprises basalts with TiO2=1 wt% while the upper part consists of the basalts with the average TiO2 content 1.4-1.5wt%. Based on this data, these rocks can be correlated with Morongovsky and Mokulaevsky formations located in the Noril’sk area. Despite many similarities between the volcanic rocks of these two areas, the basalts and tuffs of the Tunguska syneclise have their specific features, i.e. many tuff horizons, small thickness of flows and their poikiloophitic structure that reflect the rock formation near the boundary of the Tunguska syneclise.

Fe-Ti-V deposits related to the basic-ultrabasic intrusions are widespread within eastern Siberia, in its northern and southern parts. Two large massifs are located in the Kodar-Udokan trough Siberian Platform, and in the Taimyr Peninsula. They are the Chineysky intrusion and the Dyumtaleysky massifs consequently. The problem of ore origin includes an estimation of parental melt composition and its evolution. To solve it, we have studied the internal structure, composition of rocks and ores from these massifs. The Chineysky lopolith has a thickness of 2.5 km and consists of four rock groups formed during different stages. Layering is a typical feature of the second group of rocks enriched in titanomagnetite. Economic Cu-Ni sulfide mineralization (Cu/Ni=10-100) concentrates within the lower boundary of the massif and includes the endo-and exocontact ore. Chineysky massif consists of basic rocks with typical crustal characteristics (Ta-Nb negative and Pb positive anomalies). The Dyumtaleysky intrusion represents a tabular body of 600 m in thickness. It consists of two groups of rocks - gabbro (upper zone, 300 m) and peridotites (lower zone, 300 m). It was suggested that they were formed at two stages. The upper zone is characterized by thin layering which is similar to the layering of the Chineysky massif. Sulfides are concentrated within the massif (between upper and lower zones) and in its endocontact zone. The mineralization consists of chalcopyrite, pyrrhotite, pentlandite, millerite, cubanite; Cu/Ni= 1-0.5. In contrast to the rocks of the Chineysky massif, the rocks of the Dyumtaleysky intrusion are characterized by patterns without Ta-Nb anomaly. Gd/Yb ratio demonstrates the origin of these two massifs from different magma sources: shallow for the Chineysky intrusion and deep (with garnet) for the Dyumtaleysky one. Thus, Fe-Ti-V deposits could be formed from different magmas but contain the same type of ores because the leading process of ore formation is a multiple fractional crystallization.

In models for the genesis of the Noril’sk Pt-Cu-Ni ore deposits, much importance is attached to the processes of assimilation of host rocks by basaltic melts. This idea is based on unusual relations between the silicate and sulfide constituents of this type of ore deposits and also on the heavy sulfur isotopic composition of the sulfide ores. The reason for this unusual composition is thought to be the assimilation of anhydrite from the host rocks. However, no other factors able to influence this process have ever been analyzed in the literature. We were the first to thoroughly analyze the inner structure of contact aureoles of the intrusions hosted in various rocks: the Maslovsky intrusion in Early Triassic basalts of the Ivakinsky and Nadezhdinsky formations and the Talnakh intrusion in Devonian anhydrite-bearing carbonate-terrigenous rocks. The distributions of trace elements, the 87Sr/86Sr isotopic ratio, and Sm and Nd isotopes indicate that host rocks were either not assimilated at all, or their effect is perceptible only within a very narrow (1 m) zone in the eastern apophyse in the southern portion of the Maslovsky intrusion. The Sr, Nd, and particularly, Pb isotopic composition indicate that the anhydrite could not be the source of isotopically heavy sulfur for sulfides at Noril’sk deposits. The ores of the Maslovsky and Talnakh intrusions have similar sulfur isotopic composition of their sulfides (the maximum δ34S values of these sulfides reach +10.8 and +14.2‰, respectively), in spite of the significant differences in the rocks hosting these intrusions. Our newly obtained data indicate that assimilation was insignificant and could not affect the origin of the ores.

We present new results on the geochemistry and mineralogy of the disseminated ores from the Maslovsky deposit, Noril’sk area, Russia. On the basis of the composition of rocks and of the rock-forming minerals, the deposit consists of two magmatic bodies: the northern one is a continuation of the Noril’sk-1 intrusion, whereas the southern one represents a separate massif. The disseminated ores from these two intrusions have distinctive differences: the Pd:Pt ratio of the northern ores is in the range 5–6, and Ni:Cu is in the range 2–16, whereas in the southern ores, these values are close to 1. The precious metal mineralogy of the disseminated ores reflects their chemical differences. The main PGM of the northern deposit are zvyagintsevite, atokite– rustenburgite and Fe–Pt alloys, whereas Au–Ag and Fe–Pt alloys are typical for the southern part of the deposit. The ore geochemistry and PGM composition of northern part of the Maslovsky deposit is similar to those of the Noril’sk-1 deposit. Calculations of weighted mean compositions (data from cores OM–4, OM–24 and MS–31) show that there is no correlation between ore and rock compositions for these three deposits.

The evolution of magmatism within the large trap� pean provinces both in time and in space is one of the most important aspects of their formation on Earth. Reconstruction of the history of the evolution of vol� canism in the Norilsk region is an important task for determination of regularities of the formation of the Siberian province as a whole, since this region differs from its other parts by the higher thickness (up to 3.7 km) and significant diversity of effusive rocks com� posing it, as well as by the presence of unique Pt–Cu– Ni deposits. We obtained principally new data on the structure and composition of some formations in the Norilsk region, which allows us to specify the history of tectonomagmatic evolution of this territory in the Early Triassic. Basalts of the Norilsk region have been studied by many researchers for several decades [2, 3, 7]. The

We report new data on the stratigraphy, mineralogy and geochemistry of the rocks and ores of the Maslovsky Pt–Cu–Ni sulfide deposit which is thought to be the southwestern extension of the Noril’sk 1 intrusion. Variations in the Ta/Nb ratio of the gabbro-dolerites hosting the sulfide mineralization and the compositions of their pyroxene and olivine indicate that these rocks were produced by two discrete magmatic pulses, which gave rise to the Northern and Southern Maslovsky intrusions that together host the Maslovsky deposit. The Northern intrusion is located inside the Tungusska sandstones and basalt of the Ivakinsky Formation. The Southern intrusion cuts through all of the lower units of the Siberian Trap tuff-lavas, including the Lower Nadezhdinsky Formation; demonstrating that the ore-bearing intrusions of the Noril’sk Complex post-date that unit. Rocks in both intrusions have low TiO2 and elevated MgO contents (average mean TiO2

First isotopic-geochemical data were obtained on basite-ultrabasite rocks from the southern Kovdor area that were previously provisionally ascribed to the drusite (coronite) complex based on the occurrence of drusite (coronite) textures. The mineral and whole-rock Sm-Nd isochron age determined for five rock samples from the Sorkajoki and Poioiva massifs and the massif of Elevation 403 m turned out to be close (within the error): 2485 ± 51, 2509 ± 93, and 2517 ± 75 Ma, respectively. The crystallization age was evaluated for the two massifs (Poiojovski and Mount Krutaya Vostochnaya) by the U-Pb system of zircons. Our samples contained both magmatic and xenogenic crustal zircons, whose age was estimated at 2700 Ma. The crystallization age of the massifs themselves (data on the magmatic zircons) is 2410 ± 10 Ma. The undepleted character of the mantle source (ɛNd = +0.9) and the much younger age of the massifs than that of other known manifestations of ultrabasic magmatism in the territory of Karelia and the Kola Peninsula (including the layered pluton classic drusite massifs) suggest that the central part of the Belomorian Mobile Belt hosts one more independent intrusive rock complex, which has never been recognized previously and which is different from typical drusites.

The comparativegeochemical study was first cond ucted for the ultrabasic-basic massifs of the cen� tral part of the Belomorian mobile belt, which were previously ascribed to the drusite complex on the basis of the presence of coronal textures. The studied magmatic bodies are geochemically heterogeneous and can be subdivided into three groups: (1) highMg rocks (MgO > 20 wt %) with elevated Cr content, enriched trace ele� ment patterns, and deep negative Ta-Nb anomaly (Sorkajoki Massif). Intrusions of this group are geochemi� cally close to the layered plutons of Northern and Eastern Karelia (Kivakka, Burakovsky) and to the intrusions of the Kola Peninsula (Monchepluton and others); (2) lowMg intrusions (MgO < 10 wt %) with elevated con� tents of Fe, Ti, and P (403�m Height Massif). The ro cks composing these intrusions are characterized by sub� horizontal trace element patterns and weak Ta-Nb anomaly; (3) intrusions with intermediate MgO contents (10-20 wt %), flat, occasionally depleted REE patterns, and lack of Ta-Nb anomaly (Mt. Grob Tundra). The identified geochemical differences do not depend on the degree of metamorphic transformations, but were pre� sumably caused by differences in phase and chemical composition of parental magmas, as well as by conditions of their crystallization. It was substantiated that ultrabasic-basic massifs presently united into the drusite com� plex are genetically diverse and acquired similar textural appearance due to regional metamorphism. Thus, the presence of coronal textures is insufficient to ascribe the intrusions to the drusite complex, their mineralogical and geochemical composition should be taken into account.

The specifics of the morphology, internal structure, and composition of olivine, one of the major rock� forming minerals of ultrabasic and basic rocks, contains valuable information on the conditions of its formation and are widely used in petrology [11, 8, 3, 7, 12]. One of its important characteristics is zoning, which is most pronounced in lunar [8] and Martian [2] meteorites. Olivine exhibits both normal and reverse zoning, with the core–rim difference reaching 25 mol % forsterite. However, this phenomenon is uncommon in the ter� restrial intrusive rocks, because subsolidus diffusion usually “smoothes out” the initial compositional het� erogeneities of the mineral. At present, the available data are reduced to scarce olivine grains with zoned distribution of major (Fe and Mg with Fo gradient of 8–10 mol % [1, 4, 5]) and trace elements Ca, Ni, as well as Al, Cr, and P [4, 9]. Therefore, the find of zoned olivines with the core–rim difference more than 20 mol % Fo in the magmatic rocks of the Noril’sk district is a unique phenomenon not only for this region but also for ultrabasite–basite complexes around the world. The Noril’sk district is located in the NW Siberian trap province. It consists of the rocks of the crystalline basement and platform cover represented by the Early Cambrian–Late Permian terrigenous–carbonate rocks and Early Triassic basalts. Numerous ultrabasite– basite hypabyssal massifs in the forms of chonoliths and bodies of irregular shape are localized among the sedimentary and volcanic rocks of the area. Distinctly differentiated intrusions are combined into the pro� ductive Noril’sk complex, which is characterized by an elevated average weighted MgO content (10–12 wt %) relative to tholeiitic basalts predominant in the section (6–7 wt %). Some of them contain superlarge Pt– Cu–Ni deposits (Talnakh, Oktyabr’skoe, Noril’sk�1), whereas others are either weakly mineralized or bar� ren. Their age relations with volcanic rocks were not established exactly, because in most cases the intru� sions are localized in the underlying sedimentary rocks. One of the representatives of this type of magmatic complexes is the massif studied by us in the eastern part of the area, in the Mikchangda River basin. It is located in the Devonian carbonate–terrigenous rocks

Modern analytical methods (XRF and ICP-MS) were employed for the first time to investigate the geochemical characteristics of rocks from the Noril’sk Trough. It differs from other folded structures of the region in the presence of massifs with high-grade Pt-Cu-Ni ores at relatively high levels in the section of the platform cover, in the middle part of the tuff-lava sequence. This provides an opportunity of directaions of observe geologic relationships between the extrusive and intrusive rocks of the Siberian Traps and more reliably test the possibility of their comagmatic origin, because other intrusions with massive ores occur at a deeper stratigraphic level in the Devonian sequences (Kharaerlakhsky and Talnakhsky massifs in the Kharaerlakhsky Trough). A comparison of the volcanic sections of the Noril’sk Trough and other parts of the region suggests that the tectonic structures were initiated before or simultaneously with trap development. By the example of the sill of the Maslovsky intrusion, it was shown that the ore-bearing gabbro-dolerites were formed in post-Nadezhdinsky time. The geochemical characteristics of the rocks of the Noril’sk 1 and Maslovsky intrusions were compared with those of the supposedly comagmatic rocks of the Gudchikhinsky, Tuklonsky, Nadezhdinsky, and Morongovsky formations. It was found that the Gudchikhinsky picritic basalts show higher Gd/Yb values compared with the picritic gabbro-dolerites (on average, 2.5 and 1.5, respectively) and higher nickel and calcium contents in olivine (0.44 and 0.22 wt % NiO and 0.30 and 0.12 wt % CaO for Fo82, respectively). The high-magnesium rocks of the Tuklonsky Formation are depleted in U and enriched in Eu relative to their intrusive analogues and also differ with respect to NiO and CaO contents in olivine (0.11 and 0.21 wt % NiO and 0.21 and 0.12 wt % CaO for Fo78, respectively). The rocks of the Nadezhdinsky Formation show strongly enriched incompatible trace element patterns, especially for LREE. Although the Morongovsky Formation is geochemically similar to the intrusions of the Noril’sk complex, it shows a lower weighted mean MgO content (6–7 wt % as compared with 11–12 wt % for the gabbro-dolerites). Thus, it was shown by the example of the geologic setting and compositional features of the Maslovsky intrusion that the massifs with high-grade mineralization are not analogues of volcanic complexes, but were produced by an independent magmatic stage.

The Chineiskii anorthosite-gabbronorite massif is the most typical layered intrusion in Russia, which is accompanied by large V and Cu deposits. This massif is first considered to be a component of the Proterozoic volcanic-plutonic system of the Kodar-Udokan district, whose largest massifs are Chineiskii and Lukturskii. This system also comprises numerous dikes (including the Main gabbronorite dike at the Udokan deposit, whose thickness reaches 200 m), which are likely the magmatic feeders of ancient volcanism. An intermediate position in the vertical section of the magmatic system is occupied by gabbroids, whose exposures occur in the peripheral part of the Lurbunskii granite massif. The intrusive rocks were proved to be genetically interrelated and show certain similar geochemical features: they bear elevated TiO2 concentrations and have similar trace element patterns and (La/Sm)N and (Gd/Yb)N ratios (1.5–2.3 and 1.87–2.06, respectively). The Chineiskii Massif is thought to have been formed by the successive emplacement of genetically similar basic magmas, which produced four rock groups with fine and coarse layering and cyclicity of variable rank (microrhythms, rhythms, units, and series). The results of cluster analysis indicate that the rocks can be classified into 13 petrochemical types. The phase and chemical characteristics of the parental melts of these compositions were simulated with the use of the COMAGMAT-3.5 computer model, which was also applied to evaluate the composition of the most primitive initial magma of the whole Chineiskii Massif. Our results indicate that the primitive magma was heterogeneous (olivine + plagioclase ± titanomagnetite + melt) at a temperature of approximately 1130°C. The initial melt had a ferrobasaltic composition and was close to saturation with magnetite at ∼NNO ± 0.5

The history, subdivision, and characteristics of the volcanic rocks (251 Ma) of the Noril’sk region may be described thusly: The structures of the extrusive rocks differ from one tectonic element to the next (the Kharaelkh and Noril’sk Troughs and the Tunguska Syneclise). Many of the basal basalts were studied, particularly with regard to their concentrations of major and rare elements. The lower formations (Ivakinsky, Syverminsky, Gudchikhinsky, and Nadezhdinsky) are located only in the paleorift zone (including Yenisei–Khatangsky depression), whereas the upper formations (Tuklonsky, Morongovsky, Mokulaevsky, Kharaelakh, Kumginsky, Samoedsky) are widespread in the Tunguska syncline. Based on this distribution of volcanic rocks, two main stages of their formation were suggested. Based on their geochemical features, the widespread basalts were deposited in four cycles, and thus, a new schema of their magmatic evolution was constructed.