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• Some Fe-oxide grains crystallized from silicate melt were incorporated into downward percolated sulfide liquid. • Fe-oxide in massive ores crystallized from the sulfide liquid pool mingled with the downward percolated sulfide liquid. • Downward percolation of sulfide liquid is crucial in the formation of the net-textured and massive ores. The mineralogy and chemical composition of magnetite and chromite series (simplified as magnetite) can provide valuable insights into the formation processes of magmatic Ni-Cu-(PGE) sulfide deposits. Previous studies mainly focus on magnetite in disseminated ores and massive ores, but very little is known about the magnetite in net-textured ores. In this study, magnetite in net-textured ores (type 1 magnetite) and massive ores (type 2 magnetite) from the Zhdanov Ni-Cu-(PGE) deposit in the Pechenga ore field, were recognized and analyzed using scanning electron microscope (SEM), electron probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Both the type 1 and type 2 magnetite grains show zoned textures with Cr concentration decreasing from the core to the rim. Type 1 magnetite has higher Al and Mg concentrations than type 2 magnetite. These observations indicate that type 1 and type 2 magnetite crystallized from and record the solidification process of silicate melt and sulfide liquid, respectively. Type 1 magnetite within sulfides of net-textured ores has identical chemical composition to that within silicates, which suggests that the chemical composition of magnetite is not significantly affected by sub-solidus re-equilibrium with sulfide minerals. It also suggests that the type 1 magnetite within sulfides was incorporated into sulfide liquid later during the downward percolation of sulfide liquid through the magnetite-bearing olivine crystal mush. On the other hand, type 2 magnetite has comparable concentrations of W, Sc, Ga, Cr, Mo, and Mn to the type 1 magnetite. Such compositional similarity can be explained by the crystallization of type 2 magnetite from the sulfide liquid pool that have been mingled with the downward percolated sulfide liquid. Accordingly, the downward percolation of sulfide liquid plays an important role in the formation of net-textured ores and massive ores in the Zhdanov deposit. [ABSTRACT FROM AUTHOR]

The paper presents petrochemical, geochemical, and mineralogical data on rocks of the phoscorite–carbonatite complex in the Kovdor alkaline–ultramafic massif, Kola Peninsula, Russia. In contrast to what is usually thought, trace elements were determined to be concentrated not in the carbonatites themselves but in the related phoscorites. The paper presents data on the evolution of the compositions and zoning of minerals in successive generations of both rock types as a result of the fractional crystallization of their parental magmas, and data on general trends in the concentrations of trace elements. The Fe-rich phosphate–carbonate melt seems to have separated from the primitive alkaline–ultramafic silicate melt during its advanced differentiation. The Fe-rich phosphate–carbonate magma was parental for the phoscorite–carbonatite complex. The possibility of its splitting into immiscible Fe-rich phosphate and carbonatite melts is discussed. [ABSTRACT FROM AUTHOR]

The lower continental crust, representing up to 50% of the continental mass, is largely inaccessible, making its composition difficult to constrain. Previous composite models based on geophysical evidence and geochemical data of granulite terrains and xenoliths have proposed varying results, from a mafic, relatively refractory lower crust to an intermediate-felsic, more enriched composition. Here, we investigated the mineralogy and geochemistry of predominantly mafic granulite xenoliths from eastern Australia and the Kola Peninsula, Russia, using an in situ analytical approach that minimises host magma contamination. The resulting xenolith compositions are variably and often strongly depleted in most highly incompatible trace elements, including the heat-producing elements. These xenoliths represent an extremely refractory component of the lower continental crust, likely formed after high degrees of partial melting or crystallisation from a depleted source. A lower crust composed solely of this refractory endmember would be too exhausted in heat-producing elements to satisfy heat-flow constraints. However, a volumetrically significant component of the lower crust is this mafic and refractory material, combined with undifferentiated material and a felsic or metapelitic portion. Using geophysical constraints on proportions of refractory (55%), undepleted (38%) and enriched (7%) components, a new estimate for average lower continental crust that satisfies heat flow limits was calculated, including for elements such as Be, B, Cs, W and Tl, where previous estimates relied on very few data. Finally, we show that because much of the lower continental crust is so refractory and depleted in incompatible elements, it is unlikely to be a reservoir that can balance radiogenic isotope (unradiogenic Pb) and trace element ratios (e.g. Rb/Cs, Nb/Ta) for which bulk silicate Earth departs from chondritic ratios. • Granulite xenoliths are investigated to constrain the composition of the deep crust. • Most of the lower crust is extremely depleted in highly incompatible trace elements. • An updated compositional estimate for the lower crust is presented. • Deep crust has limited potential as a "hidden" reservoir for mass balance issues. • Only ancient delaminated deep crust can contribute significantly to the bulk Earth. [ABSTRACT FROM AUTHOR]

This paper presents new geochemical data on the complex of alkaline metasomatic rocks and carbonatites, which hosts the rare-metal mineralization of the Gremyakha-Vyrmes massif. The contents of major and trace, including rare-earth elements were determined in the albitites, aegirinites, and carbonatites. Two types of the rare-metal ores are distinguished: niobium albitite and zirconium aegirinite ores. It was shown that the albitites and aegirinites have similar trace element distribution patterns, being most geochemically close to the foidolites. The carbonatites, albitites, and aegirinites were dated by Rb-Sr and Sm-Nd methods at 1887 ± 58 Ma, which corresponds to the formation age of the Gremyakha-Vyrmes massif. The ultrabasic rocks, foidolites, alkaline metasomatic rocks, and carbonatites were formed successively within a relatively narrow range. The geological observations and geochemical data led us to conclude that the emplacement of the fluid-saturated carbonatite solutions-melts at the final stages of the massif formation against a background of fault tectonics caused a pervasive metasomatism of the ultrabasic and alkaline rock complexes and, as a result, the formation of the alkaline albitites and aegirinites. The carbonatites could be sources of rare-metals, while foidolites served as a geochemical barrier, and their metasomatic alteration led to the formation of Zr-Nb mineralization in the albitites and aegirinites. [ABSTRACT FROM AUTHOR]

The article presents study which investigates the isotope and age geochemistry of ore-hosting granodiorites of the Nyal'm-1 gold deposit at Kola Peninsula, Russia. It says that the Archean greenstone belts (GSBs) are localized in Paleoproterozoic volcanogenic-sedimentary complexes and are linked to the ore-metasomatic procedures in areas of shift deformations. It states that the investigation was done with the use of modern local isotope geochemical methods, along with the description of geological composition and structure of the volcanogenic-sedimentary complex of the GSB Kolmozero-Voron'ya (KV). Conclusion suggests that the age and genetic relationship of gold deposits enables the reconsideration of the concepts of the age of the gold formation.

The nature of tectonic processes on the early Earth is still controversial. The scarcity of high-pressure metamorphic rocks such as eclogite (the high-pressure equivalent of basalt) in Archean cratons has been used to argue that plate tectonics did not operate until Earth had cooled to a critical point, perhaps around the 2.5 Ga Archean-Proterozoic transition. However, eclogites occur as meter- to kilometer-sized lenses enclosed in Archean gneisses of the Belomorian Province of the Fennoscandian shield. Geochemistry and internal features suggest that the protoliths of the eclogites were interlayered olivine gabbros, troctolites, and Fe-Ti oxide gabbros. Greenschist facies mineral parageneses are enclosed in prograde-zoned eclogite garnets, and peak metamorphic conditions define an apparent thermal gradient (12-15 °C/km), consistent with metamorphism in a warm Archean subduction zone. We show here that these eclogites represent the oldest known high-pressure metamorphic rocks. U-Pb dating and Hf isotope analyses of zircons from the eclogites and a crosscutting felsic vein define a minimum age of 2.87 Ga for the Uzkaya Salma eclogite; a 2.70 Ga age for the Shirokaya Salma eclogite is interpreted as the age of a granulite facies overprint. Thermal overprinting and growth of new zircon also occurred during the Svecofennian (1.9-1.8 Ga) orogeny. These new data imply that plate tectonic processes operated at least locally in late Mesoarchean time. The adakitic nature of the felsic vein suggests that partial melting of hydrated eclogites could produce Archean tonalite-trondhjemite-granodiorite-type magmas. [ABSTRACT FROM AUTHOR]

The article presents a study which investigates the geochemistry and U― Pb age estimation of Zircons in the Salma Eclogites discovered at the eastern part of Belomorian mobile belt (BMB) in Kola Peninsula, Russia. The study made use of two eclogite metamorphism with ages of 2.72 and 2.82 for the interpretation of the granulite metamorphism age and the absence of the eclogite metamorphism through the use of scanning electron microscope. The result of the study indicates that the two types of the Salma eclogites contain zircon crystals rims and grains with typical geochemical characteristics. Moreover, it adds that the age estimation of the eclogite crystallization with the youngest geological process was found in the eclogite region.

The article reports on the study which contains new geochemical and isotopics data for volcanogenic complexes of the Arvarench Unit of the Imandra-Varzug structure (IVS) in Kola Peninsula, Russia. It mentions the use of traditional lithological and stratigraphic methods on the basis of signs when studying problems of stratigraphy and correlation of volcagenic-sedimentary sections of the Paleoproterozoic intracratonic riftogen IVS. It provides four conclusions based on the results obtained such as that the formation of primary melts for komatiite, some basalt, and andesite of the Arvarench Unit was controlled by melting of the Archean enriched mantle component.

The article presents an analysis of Paleozoic tholeiite magmatism manifestation in the Kola alkaline province in northeastern Fennoscandia. It states that the manifestations are presented by dolerite dikes composed of swarms such as Pechenga, the Barents Sea, and East Kola. Potassium-Argon (K—Ar) dating shows that the estimated age of Pechenga swarm ranges from 355-600 million years, which is the same with the Barents Sea swarm. The Pechenga Swarm has 1-8% olivine-normative and quartz-normative of 1-3% while rocks found in Barents Sea and East Kola contains normative-quartz of 1-10%. It concludes that the partial melting of mantle substrate in the spinel lherzholite facies is associated with tholeiites that matched to the initial stage of plume-lithosphere interaction.

The Turiy Massif, lying within the Kandalaksha Graben, and on the southern coast of the Kola Peninsula, contains carbonatites, phoscorites, melilitolites, ijolites and pyroxenites within one central and four surrounding satellite complexes. Sr–Nd isotopic data from the central complex phoscorites and carbonatites, and the nearby Terskii Coast kimberlites, combined with other recently published data on the Devonian Kola Alkaline Province, allow us to redefine the position of the Kola Carbonatite Line (KCL) of Kramm (European Journal of Mineralogy 5, 985–989, 1993). We propose that the revised-KCL mantle sources include a lower-mantle plume, and a second enriched source, which also contributed to the Terskii Coast and Archangelsk kimberlites. The Turiy Massif silicate rocks and northern complex carbonatites have more enriched isotopic signatures than the distinct, and depleted signatures of the central complex phoscorites and carbonatites, particularly with respect to εSr. This is probably due to the contamination of parental magmas, originally derived from the KCL end-members, by crustal material. The phoscorites and carbonatites show unusually enriched stable isotope δ13CPDB values with respect to their conjugate δ18OSMOW values. The trace element signatures of the silicate rocks are generally consistent with derivation from the magma sources proposed above. [ABSTRACT FROM PUBLISHER]