Editorial for Special Issue: “Geochemistry and Mineralogy of Basic–Ultrabasic and Alkaline Intrusions and Related Magmatic Deposits”

Magmatic deposits are sources of strategic metals provided to the global market. Ultramafic–mafic intrusions contain PGE, Cu-Ni, Cr, Ti, and V deposits, while many rare metal deposits (e.g., Zr, Ta, Nb, Be, Y, Sc, Li, and Ge) are linked to alkaline intrusions. These metals are crucial for high-tech and green technologies. The genesis of metal concentrations, especially for super large deposits, is important for the prospecting of new deposits.

This Special Issue is dedicated mostly to large PGE-Cu-Ni deposits in Russia (seven publications), including the Siberian deposits and deposits within the Kola-Karelia area. One article characterizes a new rare earth element deposit in the Eastern Sayan mountains (Russia) composed of alkaline rocks and carbonatites.

Three of the articles in this Special Issue characterize the unique deposits of the Norilsk district. Kostitsyn et al. [1] statistically process a large amount of published geochemical data and study several newly discovered massifs in the eastern part of the Norilsk region. They show that well-known intrusions with economically significant mineralization (Talnakh, Kharaelakh, Norilsk 1, Chernogorsky, etc.), are characterized by a high MgO and low TiO₂ content and a very narrow range of εNd(T) varying around +1.0 ± 1 (2σ, n = 139). In contrast, barren intrusions and volcanic rocks exhibit a wider range of ε_Nd(T), from −10 to +7 (n = 256). Therefore, this isotopic parameter can be used to evaluate new sulfide-rich intrusions. It is tested in the Mikchangda area.

The other geochemical characteristics of the rocks in the Norilsk intrusions, such as the distribution of platinum metals, gold, and silver, were studied by Canhimbue and Talovina [2]. They consider the Kharaelakh, Talnakh, and Vologochan intrusions, as well as the sill of the Kruglogorsky type. The ore-bearing intrusions are composed of two types of rocks (picritic and taxitic gabbro-dolerites) which are enriched in platinum-group elements (PGE), gold, and silver. There is a clear correlation between PGE, copper, and nickel in the first rock type, while the relationship between these elements in the second type is less obvious. The geochemical characteristics of the studied rocks from different ore-bearing intrusions are similar, i.e., patterns in the accumulation of gold, silver, and platinum metals. These authors suggest that the conditions for the formation of mineralization were similar for these ore-bearing intrusions.

The relationship between ore-bearing intrusions and basalt in the Siberian Large Igneous Province (SLIP) is studied by Krivolutskaya et al. [3]. Within the SLIP, there are two types of basalt: rift and platform. Geochemical features indicate similarities between the SLIP and the Norilsk intrusions that contain sulfide mineralization. These authors suggest that rift structures play a genetic role in sulfide mineralization.

The Karelo-Kola area ranks second in terms of PGE and Ni resources in Russia and contains numerous layered intrusions with economic mineralization [4,5]. Smol’kin et al. [4] focus on peridotite–pyroxenite–gabbronorite layered intrusions that contain Cr, PGE, and Cu-Ni ores and were emplaced into the Baltic paleocontinent between 2.50 and 2.45 billion years ago. The goal of their study is to reconstruct the mechanisms behind the formation of Paleoproterozoic layered intrusions based on Mount Generalskaya in the Kola region and Kivakka, Kovdozero, and Burakovsky plutons in Karelia. The authors use U-Pb zircon ID-TIMS and Sm-Nd isotopic analyses to correlate these intrusions with komatiitic basalts from the Vetreny Belt and Polisar formations. They propose several stages of geological development, including superplume uplift during the Early Paleoproterozoic, the generation of mantle magmas and their injection into the lower crust, and the creation of deep-seated and intermediate magma chambers. The intense contamination of the granulite–metamorphic complex also occurs, followed by the formation of magma chambers triggered by single or multiple injections.

Sushchenko et al. [5] study the largest layered intrusion in the Kola Peninsula, the Fedorov–Pana pluton. They use apatite from the anorthosite rocks of the Kievey deposit as an indicator for the fluid regime during magmatic crystallization, especially for the formation of platinum group elements’ mineralization. Apatite is analyzed using petrographic methods, X-ray energy-dispersive spectroscopy (EDS), laser-ablation inductively coupled plasma mass spectrometry, and Raman spectroscopy. Two types of apatite are identified: one in plagioclase crystals (40–100 microns) and another in the interstitial space (300–600 microns). All apatite compositions lie along the F-OH side of the Cl-F-OH diagram. The apatite in plagioclases crystallized before the other type and contains much a lower content of Cl than apatite from Bushveld. These authors suggest that this difference may be due to the in situ percolation of sulfide liquids that were not enriched in platinum group elements.

Gongalsky et al. [6] describe layered intrusions of Northern Transbaikalia, which is economically very significant for Russia with notably large Cu, Fe, Ti, and V deposits. The authors find differences in the mineral composition and sulfur isotope ratios in several Cu–sandstone deposits, as well as in gabbro intrusions. The δ34S values vary from mostly negative (<0, as low as −28‰) in the Udokan, Burpala, and Skvoznoy deposits to the positive δ34S values in the Chineysky and Luktursky layered intrusions (as high as +2.6‰) and in the Pravoingamakitsky deposit (+4.0 ‰). These authors suggest the presence of complex copper (basic rocks) and sulfur sources (deep fluids) in ores of this metallogenic province.

Konyshev [7] discusses the link between basic rocks and granites from the Salmi batholith in the Fennoscandian Shield. He analyzed solid-phase inclusions in mafic rocks, as well as sulfide melt inclusions in zircons by various analytical methods, such as electron and ion probe microanalyses (EPMA and SIMS) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). He postulates that the granite porphyry intrusion and dykes formed from two connected chambers with acid and mafic melts.

Kolotilina et al. [8] provide the first detailed mineralogical description of carbonate rocks and albitite in the Podlysansky Massif of the Neoproterozoic alkaline–ultramafic Lysan complex. Albitites form dykes in the massifs with gradual transition to the host rocks. They are regarded as resulting from fenitization of leucocratic gabbro by alkali-rich carbonate-hydrothermal fluids in zones of tectonic fracture development. Only carbonatites, forming veins in gabbro, are enriched with light rare earth elements. They contain calcite, siderite, phengitic muscovite, albite, K-feldspar, apatite, monazite-(Ce), Nb-bearing rutile, bastnäsite-(Ce), parisite-(Ce) and synchysite-(Ce), pyrite, and sphalerite.

This Special Issue provides new information about magmatic deposits from significant regions of Russia, including Norilsk, Kola Peninsula, and Southern Siberia. We believe that these data and their interpretation will contribute to a better understanding of the origin of these deposits.