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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 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.

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 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.

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.

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 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.

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 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.

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.

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.

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

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.

The geologic relationships between the basalts and ore-bearing intrusions are described based on the example of the Southern Maslovsky massif, which intruded basalts of the Nadezhdinsky Formation. Therefore, these rocks were formed in post-Nadezhdinsky time. The ore-bearing intrusions are similar to the volcanic rocks of the Morongovsky Formation in terms of their rare elements and isotopic compositions (Sr, ƐNd), but they contain higher MgO concentrations (10–12 wt % on average) and a heavier S isotope composition (up to 18‰ compared with 6–7‰ in the basalts).

The very first studies of the Noril’sk deposits were launched by N. N. Urvantsev in 1919, and these deposits have now been studied for almost one century. During these years, the unique ores of the Talnakh and Oktyabr’skoe deposits were discovered. Their resources, composition, and mineralogical diversity have no equivalents anywhere on the planet. The uniqueness of the Noril’sk ore-bearing massifs within the extensive class of magmatic Pt–Cu–Ni deposits (the setting of the Noril’sk massifs in the world’s largest Siberian flood basalt province, their Early Triassic age, and their combination of sulfide and low sulfide types of PGE mineralization within the same massifs) continues to attract the keen interest, in both purely theoretical and applied aspects, of several researchers. The principal relations and trends revealed in the origin of the Noril’sk deposits largely facilitate exploration for analogous ores not only in the Noril’sk district itself but also throughout the Siberian Platform and elsewhere worldwide.

The Pt–Cu–Ni Noril’sk deposits were discovered in the nineteenth century on the SW Siberian Platform. They are located in a paleorift zone and display a structure that differs from that of the Siberian craton basement. Terrigenous and carbonate rocks with anhydrite and coal are exposed on the surface of the Noril’sk area. They are overlapped by volcanic rocks of the trap formation. The stratigraphy of the sediments and tuff–lava deposits is given. The intrusive rocks consist of 10 % plutonic rocks and are represented by ultrabasic to basic intrusions (sills, dykes) of mostly normal alkalinity and rarely of elevated alkalinity. There are two types of sulfide ores: disseminated and massive. These are located near the contacts with the intrusive bodies. There are three main deposits in the Noril’sk area: the Talnakh, Oktyabr’skoe, and Noril’sk deposits. Many other intrusions contain mineralizations in economic quantities.

The northern Transbaikal region situated at thesouthwestern margin of the Aldan Shield incorporates aunique ore district (Fig. 1). Giant ore deposits, such asUdokan (copper, silver), Chinei (iron, titanium, vana-dium, copper, and noble metals), and Katun (rare metaland rare earth elements), are located 30–100 km southof the Novaya Chara station along the Baikal AmurMainline [2].Despite unfavorable natural mining–geological andtechnological features of the Udokan copper deposit, itsexploitation in the nearest future is inevitable [7].Therefore, solution to problems related to enhancementof the efficiency of raw mineral mining in the depositand ore district has become a crucial issue. This districtis characterized by juxtaposition of two large deposits(Udokan and Chinei). Moreover, these deposits aresuperlarge (giant) objects with respect to resources ofmajor metals (Cu and V). This fact is of paramount sig-nificance in the strategy of economic development ofnorthern Transbaikalia. Extraction of associated orecomponents and elucidation of new types of complexores are essential for enhancement of the efficiency offuture mining–metallurgical plants in the region. In thisrespect, assessment of the genesis, abundance, andscale of gold–platinum–copper mineralization, whichwas first found in the Udokan–Chinei ore district, isvery important.Quartz veins with noble metals and copper weredetected in the nearest framing of the Chinei Massif andthe Pravoingamakit deposit. The Pravoingamakitdeposit was exploited for cupriferous sandstones by theUdokan Expedition in the 1960s. However, we scruti-nized ores of this deposit in 2004–2006 and revealedthat its structure is more complicated and differs signif-icantly from that of the standard cupriferous sandstonedeposit (Udokan). Orebodies of the Pravoingamakitdeposit are hosted in terrigenous–carbonate rocks ofthe middle section of the Chitkanda subformation of theLower Proterozoic Udokan Formation. The discontinu-ous cupriferous horizon is traced as a NW-striking (dipazimuth 350, dip angle 65°–70°) zone extending overnearly 10 km on the surface and 400–500 m along thedip. Economic grade mineralization is developed over4.5 km. The deposit includes orebodies of two types:(1) veins and lenses of milky white massive quartz withstringers and patches of sulfides (Fig. 2); (2) echelon ofmassive sulfide bodies surrounded by dissemination ofpyrite and chalcopyrite. Quartz veins (0.3–1 m thick)extend along the strike over a few tens of meters. Sul-fide bodies are 3–5 m thick and 300–440 m long. Theorebodies are characterized by significant content of Cu(0.47–2.5 wt %) and very high variation of the Cu/Niratio (from 10 to 700 in various sectors).Ores are represented by the pyrite–chalcopyritevarieties with typical stringer and breccia structures(Fig. 2). The maximal concentration of Ni in quartzveins is related to high contents of nickel minerals (mil-lerite and pentlandite). The quartz vein ore is alsoenriched in noble metals (g/t): Pt 0.1–2.2, Pd 0.9–6.2,and Au 0.1–0.4. The ore includes fine (up to 10 µm)inclusions of clausthalite Pb

To understand the origin of the Siberian Traps it is necessary to know the evolution of magmatism in space and time inside the Siberian Platform. It was suggested that volcanic rocks were formed in three stages: rift (OIB), intermediate and trap (WPB). It was studied rocks of the Tuklonsky, Nadezhdinsky and Morongovsky suits in the western part of the Norilsk area and found that they have no intermediate geochemical characteristics (major components and rare elements, especially La/Sm ratios) between OIB and WPB. Therefore, there are only two main stages in the magmatism evolution as the actual trapping stage began from Tuklonsky time.