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Über dieses Buch

This book addresses fundamental problems in the evolution of magmatic and ore-forming processes in the Noril’sk area of northern Central Siberia. Based on data on the geology and geochemistry of rocks, obtained by the author in the course of fieldworks and new analytical studies (applying XRF, ICP-MS, microprobe analysis, ion-probe analysis and studying melt and fluid inclusions in olivine, as well as stable and radiogenic isotopes in the rocks), it was proposed a new scheme for the evolution of magmatism, including two episodes: rift and trap per se. The ultramafic-mafic massifs are classified into three geochemical types, the most important of which (the ore-bearing Noril’sk type) was formed in post-Nadezhdinsky time as an independent pulse of magmatic activity. The primary melts for ore-bearing intrusions had tholeiitic composition with elevated MgO (8 wt%) and low volatile contents (data form melt inclusions in olivine and pyroxenes, in combination with numerical simulations using the COMAGMAT program package). The assimilation of host rocks by the parental melts was studied in the contact zones of the Maslovsky and Talnakh intrusions. It was shown that it had taken place only in narrow zones (about 1-2 m) and did not played sufficient role in ore formation. It was suggested that the source of the material was lower crustal rocks in long-lived rift zones, where sulfides accumulated in several stages.

The book offers a valuable resource for specialists in the geology of ore deposits and petrology, as well as for advanced Geology students.

Inhaltsverzeichnis

Frontmatter

1. Introduction: Formulation of the Problem and Its Urgency

In previous years, the genesis of uniquely large mineral deposits became one of the most urgent geological problems because of the key role played by giant deposits: accounting for <5 % of the currently developed mineral deposits, these deposits satisfy 85 % the world’s consumption of mineral resources. The development of these deposits should provide a basis for the stable progression of our civilization (Rundkvist and Kravchenko 1996). Another important aspect in the analysis of super-large mineral deposits is their genesis because these deposits are, in fact, giant geochemical anomalies in the Earth’s crust (e.g., the PGE concentrations in the Noril’sk ores are six to seven orders of magnitude higher than those in the clarkes).
Nadezhda A. Krivolutskaya

2. Overview of the Geology of the Noril’sk Area and the Problems of Ore Genesis

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.
Nadezhda A. Krivolutskaya

3. Specifics of the Tuff–Lava Sequence: Geological and Geochemical Evidences

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.
Nadezhda A. Krivolutskaya

4. Intrusive Rocks

Intrusive rocks of the Noril’sk region were subdivided into several complexes according to their internal structure. Intrusions of basic–ultrabasic composition form three types, taking into account the distribution of rare elements in rocks—Dyumtaleysky, Low Talnakh, and Noril’sk close to Gudchikinsky, Nadezhdinsky, and Morongovsky lavas. Main ore-bearing intrusions of the Noril’sk Complex are described based on 1–2 sections. They are as follows: Talnakh, Kharaelakh, Noril’sk 1, Maslovsky, Noril’sk 2, Chernogorsky, Zub-Marksheydersky, Bol’shaya Bar’ernaya, and Mikchangdinsky. They have similar distribution of rare elements in rocks which are very close to the spectra of the crust.
Nadezhda A. Krivolutskaya

5. Composition of the Parental Melts for the Intrusions

The compositions of the initial melts of the ore-bearing intrusions were studied based on the inclusions in the olivines and pyroxenes (major, rare, and volatile components). These have compositions approximating those of the rocks. The magmas contained 0.5–0.7 % H2O, up to 0.2 % Cl, and 300 ppm F. The magma composition of the Talnakh intrusion was estimated with the aid of KOMAGMAT software. It was demonstrated that the magma contained 10 % olivine and 7 % plagioclase crystals and that MgO content in melt was 8 wt %.
Nadezhda A. Krivolutskaya

6. Relationship Between the Lavas and the Ore-Bearing Massifs

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).
Nadezhda A. Krivolutskaya

7. Basic–Ultrabasic Intrusions in the Kola-Karelia Area

Geochemical features of basic–ultrabasic intrusions, including massifs with Pt–Cu–Ni mineralization, have been studied in the Kola–Karelia area. Major and rare elements were determined in several samples from famous Ni deposits as Monchepluton, Fedorova–Pansky Tundras, and Burakovsky as compared to intrusions of the South Kovdor area, perspective on founding sulfide mineralization. All intrusions of the Kovdor area were related to the drusite (corona) complex. Their geochemical study demonstrated their difference in distribution of rare elements. According to these data, they were subdivided into three groups. The first one is close to Monchepluton rocks and most characteristic for Ni mineralization. The geochemical features of these massifs are very similar to the features of the Noril’sk Intrusive Complex. The patterns of these massifs are close to the crust; they have negative Ta–Nb and positive Pb anomalies. Their age is 2,410 ± 10 Ma showing their later formation as compared with layered intrusions.
Nadezhda A. Krivolutskaya

8. Assimilation of the Host Rocks by Basic Magma

The contact zones around the intrusions were studied to estimate the extent of assimilation of the host rocks by the magmas. Assimilation by the Maslovsky intrusion, which intruded the Nadezhdinsky basalt, is absent (central zone of the upper contact) or occurs in a narrow zone (1 m). The Kharaelakh intrusion, which intruded Devonian sediments, did not assimilate anhydrite, based on the isotope distribution of the rare elements. The anhydrite’s isotopic composition (Sr, Nd, Pb) does not permit it to be regarded as a contaminant in the sulfide ore formation.
Nadezhda A. Krivolutskaya

9. Resume: Interpretation of Results - Possible Magma Sources and Ore-Forming Processes

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.
Nadezhda A. Krivolutskaya

10. Appendix

Rock compositions of the Maslovsky deposit
Nadezhda A. Krivolutskaya
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