Kalsilite of the Khibiny and Lovozero alkaline plutons,Kola Peninsula

Kalsilite—a typical mineral of ore-bearing zones of the Khibiny and Lovozero plutons—was formed after low-Si and high-K nepheline in one of three ways: (1) by relatively high-temperature replacement of Na with K; (2) due to orthoclase-kalsilite poikiloblastesis in foidolites and overlapping foyaites; or (3) by replacement of nepheline with zeolite.     

Corundum-group minerals in rocks of the Khibiny alkaline pluton,Kola Peninsula

Five minerals of the corundum group have been identified in the Khibiny pluton with certainty. Corundum proper and karelianite occur only in hornfels after volcanic and sedimentary rocks. Xenoliths of hornfels mark the ring faults that bound foidalite within the field of foyaite. Hematite occurs in hydrothermally altered nepheline syenite and crosscutting hydrothermal veins related to the ring faults. Minerals of the ilmenite-pyrophanite series are present in all rocks of the pluton, including veins. Accessory ilmenite in foyaite varies from the manganese variety and pyrophanite in the inner and outer parts of the pluton to manganese-free ilmenite in zone of the Main Ring Fault. In xenoliths of volcanic rocks and alkaline ultramafic rocks, ilmenite is enriched in magnesium. The zoning in distribution of the above-mentioned minerals and the character of variation in their compositions from margins of the pluton to its center are consistent with the petrochemical zoning formed as a result of foyaite alteration of near ring faults.     

Kyanoxalite,a new cancrinite-group mineral species with extraframework oxalate anion from the Lovozero alkaline pluton,Kola Peninsula

Kyanoxalite, a new member of the cancrinite group, has been identified in hydrothermally altered hyperalkaline rocks and pegmatites of the Lovozero alkaline pluton, Kola Peninsula, Russia. It was found at Mount Karnasurt (holotype) in association with nepheline, aegirine, sodalite, nosean, albite, lomonosovite, murmanite, fluorapatite, loparite, and natrolite and at Mt. Alluaiv. Kyanoxalite is transparent, ranging in color from bright light blue, greenish light blue and grayish light blue to colorless. The new mineral is brittle, with a perfect cleavage parallel to (100). Mohs hardness is 5–5.5. The measured and calculated densitiesare 2.30(1) and 2.327 g/cm³, respectively. Kyanoxalite is uniaxial, negative, ω = 1.794(1), ɛ = 1.491(1). It is pleochroic from colorless along E to light blue along O. The IR spectrum indicates the presence of oxalate anions C₂O₄²⁻ and water molecules in the absence of CO₃²⁻ Oxalate ions are confirmed by anion chromatography. The chemical composition (electron microprobe; water was determined by a modified Penfield method and carbon was determined by selective sorption from annealing products) is as follows, wt %: 19.70 Na₂O, 1.92 K₂O, 0.17 CaO, 27.41 Al₂O₃, 38.68 SiO₂, 0.64 P₂O₅, 1.05 SO₃, 3.23 C₂O₃, 8.42 H₂O; the total is 101.18. The empirical formula (Z = 1) is (Na_6.45K_0.41Ca_0.03)_Σ6.89(Si_6.53Al_5.46O₂₄)[(C₂O₄)_0.455(SO₄)_0.13(PO₄)_0.09(OH)_0.01]_Σ0.68 · 4.74H₂O. The idealized formula is Na₇(Al₅₋₆Si₆₋₇O₂₄)(C₂O₄)_0.5−1 · 5H₂O. Kyanoxalite is hexagonal, the space group is P6₃, a = 12.744(8), c = 5.213(6) -ray powder diffraction pattern are as follows, [d, [A] (I, %)(hkl)]: 6.39(44) (110), 4.73 (92) (101), 3.679 (72) (300), 3.264 (100) (211, 121), 2.760 (29) (400), 2.618 (36) (002), 2.216, (29) (302, 330). According to the X-ray single crystal study (R = 0.033), two independent C₂O₄ groups statistically occupy the sites on the axis 6₃. The new mineral is the first natural silicate with an additional organic anion and is the most hydrated member of the cancrinite group. Its name reflects the color (κɛανgoΣς is light blue in Greek) and the species-forming role of oxalate anions. The holotype is deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, registration no. 3735/1.     

Spinel-group minerals in rocks of the Khibiny alkaline pluton,Kola Peninsula

Seven spinel-group minerals in various geological settings have been revealed in the rocks of the Khibiny pluton. Hercynite, gahnite, and vuorelainenite occur only in xenoliths of hornfels after volcanic and sedimentary rocks, whereas spinel and magnesiochromite occur in alkaline ultramafic rocks of dike series. Franklinite has been discovered in a low-temperature hydrothermal vein. Ubiquitous magnetite is abundant in foyaite, foidolites, alkaline ultrabasic rocks, and pegmatite and hydrothermal veins and may even be the main mineral in some foidolite varieties. The spinel-group minerals are characterized by various chemical compositions due to the fractionation of nepheline syenites resulting in formation of the Main ring of foidolites and apatite-nepheline ore. Like most other minerals found throughout the pluton, magnetite is characterized by variation in the chemical composition along the radial line from the contact with country Proterozoic volcanic rocks to the geometric center of the pluton. Toward the center, the total Ti and Mn contents in magnetite increase from 5–15 up to 40 at %.     

Native elements in rocks of the banded iron formation,Kola Peninsula

Eleven native minerals and intermetallic alloys were identified in rocks of the banded iron formation (BIF) in the Kola Peninsula: copper, silver, gold, electrum, auricupride, cuproauride, tetraauricupride, bismuth, sulfur, tellurium, and graphite. Graphite is a common mineral of sulfide-bearing BIF and gneiss. Sulfur occurs in supergene-altered sulfide-bearing BIFs together with Fe- and Ca-sulfates. Gold of low fineness (electrum) in association with electrum, acanthite, auricupride, volynskite, hessite, cervelleite, pavonite, petzite, and bismuth is related to the areas of hydrothermally altered skarnoids with greenalite, chamosite, aegirine, and Na-Ca amphibole. Redeposited gold of high fineness associated with auricupride, hessite, silver, electrum, kostovite, cuproauride, tetraauricupride, and sperrylite occurs in low-temperature zonal hydrothermal segregations hosted in aluminous gneiss and which formed under the effect of alkalized, highly siliceous solutions at the regressive stage of BIF metamorphism.     

The Occurrence of a Catastrophic Rockburst at the Umbozero Mine in the Lovozero Massif,Central Part of the Kola Peninsula

Doklady Earth Sciences - The parameters and peculiarities of a catastrophic rockburst that occurred at the Umbozero rare-metal mine located in the Lovozero massif (central Kola Peninsula), at a...     

Hydrocarbons and other volatile components in alkaline rocks from the Ukrainian shield and Kola Peninsula

Gas chromatography and other analytical techniques (EMR, PMR, and IR spectroscopy) were used to examine volatile components (CH₄, C₂-C₃, CO₂, CO, H₂, H₂O, and others) in alkaline rocks and minerals from the Ukrainian Shield (eight massifs and dikes of grorudites) and from the Khibina and Lovozero massifs in the Baltic Shield. The alkaline rocks from the Ukrainian Shield are mostly of Proterozoic (1.7–2.1 Ga) age. The alkaline rocks from the Kola Peninsula were confirmed to be rich in methane (21 ± 14 μl/g on average) and other hydrocarbons, whereas the analogous rocks from the Ukrainian Shield are poor in methane (2.1 ± 1.6 μl/g on average at a maximum of 14 μl/g). The latter rocks are richer in CO₂, which is one of the major volatile components of alkaline rocks, including agpaitic nepheline syenites from the Kola Peninsula. The rocks from the Ukrainian Shield often have elevated contents of nitrogen (up to 20 μl/g). The reasons for the differences in the composition of volatile components of rocks from the Kola Peninsula and Ukrainian Shield are as follows: the agpaitic crystallization trends of large massifs in the Kola Peninsula and much less clearly pronounced agpaitic trends in the small massifs in the Ukrainian Shield, the affiliation of these rocks with different complexes, the deeper erosion levels of the Ukrainian alkaline massifs, different ages of these rocks, etc.     

Free hydrogen-hydrocarbon gases from the Lovozero loparite deposit (Kola Peninsula,NW Russia)

The Lovozero nepheline-syenite massif in the north-eastern Fennoscandian Shield, well-known to mineralogists and petrologists, is also interesting with its high contents of hydrogen-hydrocarbon gases in different forms of presence, which is untypical of magmatic rocks. The article systematizes and generalizes little known and unpublished data on the composition, location, character and scale (intensity) of the free gases (FG) emission within a major loparite deposit confined to the massif. СН₄ and Н₂ are dominant in the FG composition. The molecular weight distribution of hydrocarbon gas components corresponds to the classic Anderson–Schulz–Flory distribution with a steep gradient. Carbon and hydrogen of the gases are characterized by rather heavy isotope compositions, becoming lighter from the transition of methane to ethane. The FG volume has been estimated as 0.2–1.6 m³ of gas per 1 m³ of undisturbed rock. The gas recovery of walls in underground workings has been up to 0.2 ml/min/m² for СН₄ and 0.5 ml/min/m² for Н₂ in several years after their heading. The discharge of some shot holes that characterizes the gas emission intensity (1.8–2 m deep and 40 mm in diameter) is up to 300 ml/min, but its 1–2 orders lesser values dominate. The discharge time in some sections varies from several days to 20 years. The overpressure of gases towards the air mainly does not increase 100 hPa, sometimes reaching 120 kPa. It has been defined, that FG distribute irregularly (at the distance of centimeters to hundreds of meters) and their composition and particularly emission intensity perform different temporal fluctuations. The abiogenic origin of FG has been proposed, with FG appearing as a mixture of gases in various proportions: (a) gases remaining in microfissures at the massif's consolidation after the capture by fluid inclusions and those lost during degassing and (b) gases occurred in mechanic-chemical reactions, partial emission and concentration of occluded and diffusely scattered gases under the unstable stress-strain mode of the rock mass. Combustible and explosive hydrogen-hydrocarbon FG can accumulate in the air of underground workings and cause accidents, disrupting the workflow. The background for using characteristics of spatial-temporal variations of the FG emission as precursors of dangerous geodynamic phenomena has been indicated.     

Behoite and mimetite from the Saharjok alkaline intrusion,Kola Peninsula

The detailed study of the mineral composition of the nepheline syenite pegmatite from the Saharjok Intrusion has resulted in the finding of behoite and mimetite, a mineral species identified in the Kola region for the first time. The pegmatite body at the contact between nepheline syenite and essexite is unusual in textural and structural features and combination of mineral assemblages including unique beryllium mineralization. Behoite Be(OH)₂ is an extremely rare beryllium mineral. It occurs as powderlike aggregates in the leaching cavities between euhedral pyroxene crystals. Behoite was identified by comparison of X-ray powder diffraction data of the studied mineral phase and behoite from the Be-bearing tuff in the type locality of this mineral (Utah, United States). Mimetite was found in the same pegmatite of the Saharjok intrusion. It forms unusual parallel-fibrous aggregates with individual fibers as long as ∼1 mm and only ∼1 μm across. X-ray powder diffraction data and the chemical composition characterize the mineral as hexagonal phase Pb₅[AsO₄]₃Cl. Both behoite and mimetite are the products of late hydrothermal alteration of primary minerals (meliphanite, galena, arsenopyrite, and loellingite). The secondary phases freely crystallized in the cavities remaining after the leached nepheline.     

Emplacement processes and cooling history of layered cyclic unit II-7 from the Lovozero alkaline massif (Kola Peninsula, Russia)

The Lovozero alkaline massif (Kola Peninsula, Russia) is composed of three major units. The central unit (80% of the volume) comprises numerous well developed layers composed, from bottom to roof, of an urtite–juvite–foyaite–lujavrite continuous lithological sequence (ijolite–foid-bearing alkali feldspar syenite in IUGS nomenclature). The mode of emplacement of the massif and the mechanism of formation of the layering are still under debate. Petrological, mineralogical (two stages of crystallisation) and structural evidence from the detailed analysis of one of these layers (unit II-7) is interpreted in terms of both mechanical (magmatic to sub-solidus, non-coaxial deformation) and thermal differentiation operating on a crystal-laden (alkali feldspar, high T nepheline, aegirine-augite) material of foyaitic composition. Textural and mineralogical data suggest that a sheet of foiditic magma intruded into solidified earlier units of the Lovozero layered sequence and acquired a sill-like structure on cooling.     

Thorium mineralization in hyperalkaline pegmatites and hydrothermalites of the Lovozero pluton,Kola Peninsula

The Lovozero pluton (Kola Peninsula, Russia) is an unique object from the standpoint of the abundance, diversity, and originality of Th mineralization. In contrast to other igneous rocks and to such chemical elements as Ca, REE, U, and Na, Th in the hyperalkaline pegmatites and hydrothermalites of the Lovozero pluton commonly occurs as its own mineral phases. Umbozerite Na₃Sr₄Th(Mn,Zn,Fe,Mg)[Si₈O₂₄](OH) (7 samples), Ti-Th silicate Na_0–7Sr_0–1ThTi_1–2Si₈O_22–23(OH) · nH₂O (8 samples), Na-Th silicate (Na,K)₄Th₃[Si₈(O,OH)₂₄] · nH₂O (6 samples), thorite (2 samples), steenstrupine-(Ce)-thorosteenstrupine series minerals (5 samples), and Th phosphate (Th,Na,K,Ca,Mg,U,Sr,Ba)[(P,Si, Al)₁O₄] · nH₂O (1 sample) were investigated in this study. Ti-Th silicates and Th phosphate have been described for the first time. All of the above-mentioned minerals have been examined with electron microprobe, IR spectroscopy, powder diffraction, thermogravimetric and optical methods. High-Th minerals such as steenstrupine, umbozerite, Th phosphate, and Na-Th silicates crystallized mainly during the ussingite stage of the pegmatite-forming process. At the early hydrothermal high-alkaline stage, steenstrupine was replaced with REE and Th aggregates (belovite, vitusite, seidite, Na-Th silicates, Ti-Th silicates, etc.). Thorite, Ti-Th silicates, and minerals of the rhabdophane and monazite groups were formed at the late hydrothermal low-alkaline stage. Despite the metamict features of almost all samples, stoichiometric ratios of cations in umbozerites and Ti-Th silicates remain stable. Clear relationships have been revealed between umbozerites and Ti-Th silicates, on the one hand, and seidite-(Ce), a Ti-silicate that has a zeolite-like structure, on the other. This implies that, under certain conditions, these minerals may be regarded as potential suppliers of Th to the environment due to the leaching of Th from zeolite channels.     

Proterozoic Gremyakha-Vyrmes Polyphase Massif, Kola Peninsula: An example of mixing basic and alkaline mantle melts

The paper presents newly obtained data on the geological structure, age, and composition of the Gremyakha-Vyrmes Massif, which consists of rocks of the ultrabasic, granitoid, and foidolite series. According to the results of the Rb-Sr and Sm-Nd geochronologic research and the U-Pb dating of single zircon grains, the three rock series composing the massif were emplaced within a fairly narrow age interval of 1885 ± 20 Ma, a fact testifying to the spatiotemporal closeness of the normal ultrabasic and alkaline melts. The interaction of these magmas within the crust resulted in the complicated series of derivatives of the Gremyakha-Vyrmes Massif, whose rocks show evidence of the mixing of compositionally diverse mantle melts. Model simulations based on precise geochemical data indicate that the probable parental magmas of the ultrabasic series of this massif were ferropicritic melts, which were formed by endogenic activity in the Pechenga-Varzuga rift zone. According to the simulation data, the granitoids of the massif were produced by the fractional crystallization of melts genetically related to the gabbro-peridotites and by the accompanying assimilation of Archean crustal material with the addition of small portions of alkaline-ultrabasic melts. The isotopic geochemical characteristics of the foidolites notably differ from those of the other rocks of the massif: together with carbonatites, these rocks define a trend implying the predominance of a more depleted mantle source in their genesis. The similarities between the Sm-Nd isotopic characteristics of foidolites from the Gremyakha-Vyrmes Massif and the rocks of the Tiksheozero Massif suggest that the parental alkaline-ultrabasic melts of these rocks were derived from an autonomous mantle source and were only very weakly affected by the crust. The occurrence of ultrabasic foidolites and carbonatites in the Gremyakha-Vyrmes Massif indicates that domains of metasomatized mantle material were produced in the sublithospheric mantle beneath the northeastern part of the Fennoscandian Shield already at 1.88 Ga, and these domains were enriched in incompatible elements and able to produce alkaline and carbonatite melts. The involvement of these domains in plume-lithospheric processes at 0.4–0.36 Ga gave rise to the peralkaline melts that formed the Paleozoic Kola alkaline province.     

Geochemistry of radioactive elements in the rocks of the Guli Massif,Polar Siberia

The study of radioactive element distribution in the rocks of the Guli Complex revealed an increase of uranium and thorium contents in the final products of magmatic differentiation. In the carbonatite complex, the radioactive elements are mainly accumulated in the early rocks—phoscorites, while their contents in the late phases, dolomitic carbonatites, decrease. The Th/U ratio increases from near-chondritic values in the weakly differentiated highly-magnesian primary magmas to the late rocks—phoscorites, calcitic carbonatites, and dolomitic carbonatites. The majority of radioactive elements are hosted in rare-metal accessory minerals: perovskite, pyrochlore, calzirtite, and apatite. Rock-forming minerals are characterized by extremely low contents of radioactive elements.     

Pyroxenes of the Khibiny alkaline pluton, Kola Peninsula

Seven pyroxene varieties were identified in nepheline syenites and foidolites of the Khibiny pluton: enstatite, ferrosilite, diopside, hedenbergite, augite, aegirine-augite, and aegirine. Enstatite and augite are typical of alkaline and ultramafic rocks of dike series. Ferrosilite was found in country quartzitic hornfels. Diopside is a rock-forming mineral in alkaline and ultramafic rocks, alkali gabbroids, hornfels in xenoliths of volcanic and sedimentary rocks and foyaite, melteigite-urtite that assimilate them, and certain hydrothermal pegmatite veins. Hedenbergite was noted in hornfels from xenoliths of volcanic and sedimentary rocks and in a hydrothermal pegmatite vein at Mount Eveslogchorr. Aegirine-augite is the predominant pyroxene in all types of nepheline syenites, phonolites and tinguaites, foidolites, alkaline and ultramafic rocks of dike series, fenitized wall rocks surrounding the pluton, and xenoliths of Devonian volcanic and sedimentary rocks. Aegirine is an abundant primary or, more often, secondary mineral in nepheline syenites, foidolites, and hydrothermal pegmatite veins. It occurs as separate crystals, outer zones of diopside and aegirine-augite crystals, and homoaxial pseudomorphs after Na-Ca amphiboles. Microprobe analyses of 265 pyroxenes samples allowed us to distinguish ten principal trends of isomorphic replacement and corresponding typomorphic features of pyroxenes. Compositional variations in clinopyroxenes along the sampled 35-km profile from the margin of the Khibiny pluton to its center confirm the symmetric zoning of the foyaite pluton relative to semicircular faults of the Minor Arc and the Main (Central) Ring marked by Devonian volcanic and sedimentary rocks, foidolites, and related metasomatic rocks (rischorrite, albitite, and aegirinite). Changes in the composition of pyroxenes are explained mainly by the redistribution of elements between coexisting minerals of foyaites in the process of their intense differentiation under the effect of foidolite melts that have intruded into the circular fault zones.     

A Pb isotope investigation of the Lovozero Agpaitic Nepheline Syenite,Kola Peninsula,Russia

For the first time Pb isotope composition was established in Lovozero rocks and raremetal ores, which is important for identifying their sources. The world’s largest layered intrusion of agpaitic nepheline syenite-the Lovozero alkaline massif—is located near the center of the Kola Peninsula in Russia. This superlarge complex plutonic body hosts the economically important loparite and eudiallyte deposits [1]. These deposits contain immense resources of REE, Nb, Ta, Zr, and constitute a world class mineral district. The Lovozero massif belongs to the Kola ultramafic alkaline and carbonatitic province (KACP) of Devonian age. Previous bulk rock studies have shown that the initial Sr and Nd isotope ratios of Lovozero rocks plot in the depleted mantle quadrant of Sr-Nd diagrams [2]. More recently, Hf isotope data obtained by Kogarko et al. (3) confirm that the Lovozero and Khibina massifs with ?_Hf between 6 and 8 are derived predominantly from a depleted mantle source. It was shown that Sr, Nd, and Hf abundances are significantly elevated in the Kola alkaline rocks, and thus their isotopic compositions are relatively insensitive to minor contamination by the overlying crustal rocks. By contrast, Pb in the KACP rocks is a much more sensitive indicator of a crustal component. In this paper we investigate the lead isotopic signature of all resentative types of Lovozero rocks (Table 1) in order to further characterize their mantle sources. The Lovozero massif consists of four intrusive phases. Rocks of phase I (mostly nepheline syenites) comprise about 5% of the total volume, phase II (urtites, foyaite, lujavrites) forms the main portion of the massif comprising 77% in volume, and phase III (eudialyte lujavrites) contributes about 18%. Country rocks are represented by Devonian effusive rocks and Archean gneisses.