Sulfur isotope signatures of sulfides from the Khibina and Lovozero massifs (Kola Alkaline Province, Fennoscandian Shield)

The sulfur isotope geochemistry of the Khibina and Lovozero agpaitic massifs provides an opportunity to understand the role of plume-lithosphere interaction processes responsible for the Paleozoic alkaline igneous activity in the north-eastern part of the Fennoscandian Shield. The stable sulfur isotope δS analysis using triple collector isotope ratio mass spectrometer (IRMS) has been carried out on the pentlandite, chalcopyrite and pyrite from nepheline syenites. The δS values for pentlandite from Khibina rocks range from +0.69 to +2.06 ‰ relative to the Vienna Canyon Diablo Troillite standard (VCDT), and the pyrite has significantly higher δS values up to +4.92 ‰ VCDT. The pentlandite from the Lovozero samples has value +1.48 ‰ VCDT, δS values of chalcopyrite is +2.85 ‰ VCDT. The maximum positive δS values are obtained for Lovozero pyrite, which vary from +5.41 to +6.30 ‰ VCDT. Comparison of sulfur-geochemical features of Khibina and Lovozero nepheline syenite with δS data for the carbonatites from the Khibina, Sallanlatvi, Seblyavr, Vuoriyarvi, Salmagora and Kovdor massifs show later carbonatite formation relatively to associated alkaline rocks. Geochemical sulfur isotope δS investigations emphasizes that parental magmas of the Khibina and Lovozero alkaline massifs were derived from a metasomatized subcontinental lithospheric mantle (SCLM). We suggest that high-δS signature on the SCLM (δS of +1 to +6 ‰ VCDT) can be explained by subduction of the high-δS Archaean crust.

Melt inclusions in olivines from phoscorites and olivinites of the Kovdor massif.

<p>The Kovdor massif is a part of the Paleozoic Kola alkaline province and located in the eastern part of the Baltic Shield. Kovdor carbonatites host a unique complex baddeleyite-apatite-magnetite deposit from which iron ores and zirconium have been mined. New data on melt inclusions in olivine crystals from phoscorites and olivinites of the ore complex are presented in this contribution. Daughter minerals in crystallized melt inclusions were identified by Raman spectroscopy and scanning electron microscopy. The trace element composition of inclusions was determined using LA-ICP-MS.</p><p>Melt inclusions in olivine from Kovdor phoscorites are negative crystal or round in shape, with sizes ranging from 5 to 50 microns. They form groups or line up. According to the mineral composition, two types of melt inclusions can be distinguished: carbonate and silicate-carbonate. In the first type, Ca-Na-Mg- (Sr?) - REE carbonates are dominant among daughter phases. In the second one, silicate phases (phlogopite, monticellite, diopside), Ca-Na-Mg carbonates and magnetite are found together. Melt inclusions in olivine from olivinites are isometric or elongated, 5–25 μm in size. They form groups or occur as isolated inclusions. Benstoneite, geylussit, ankerite, calcite and hydroxyl-bastnesite along with phyllosilicates (phlogopite, paragonite?) were identified among daughter minerals.</p><p>The rare earth elements composition of melt inclusions from both types of rocks is characterized by the predominance of light REE. The content of REE, especially light ones, in inclusions from phoscorites is higher. Strontium and barium contents in most melt inclusions have negative correlations with niobium and zirconium concentrations.</p><p>Melt inclusions from phoscorites and olivinites contain carbonate and silicate mineral phases in various proportions, which may imply heterogeneous trapping of crystalline phases and two immiscible melts, silicate and carbonatite. Inclusions from phoscorite represent a more evolved magma with higher concentrations of rare metals.</p><p>This work was supported by the Russian Science Foundation, grant No 19-17-00013.</p>

Lamprophyres from Turiy Cape and Kandalaksha Devonian dykes (Kola peninsula, Russia) : petrography,geochemistry and mineral composition

<p>Study of phenocryst and megacryst mineral associations of alkali rocks is the key to understanding an evolution and a source of the rocks.</p><p>In the Devonian Kola alkaline province (KAP) along with large mafic-ultramafic massifs there are several synchronous swarms of lamprophyre dykes. The dyke swarms occur mainly in the Kandalaksha graben. As suggest, their compositional diversity is caused by fractional crystallization and crustal contamination and a primary melt of lamprophyre was generated from a common source.  </p><p>We have studied two dykes of the Turiy Cape swarm and  the Kandalaksha swarm in the vicinity of the Kandalaksha town. The aim of  study was to determine the source of lamprophyre melts based on petrography, geochemistry and detailed investigation of clinopyroxene and olivine.</p><p>Two principal petrographical types: alkali lamprophyres (Cb-Anl monchiquite) and ultramafic lamprophyres (Cpx ailikites and mela-alikites) in the Kandalaksha swarm were observed. Alkali lamprophyres contain medium size (0.3 – 1 cm) phenocrysts of olivine, clinopyroxene, magnetite, phlogopite. A groundmass contains analcime, clinopyroxene, various amounts of carbonate (from 0 to 30-40 %), pyrite, apatite, ilmenite.</p><p>Ultramafic lamprophyres contain medium size (0.5 – 1 cm) phenocrysts of olivine, clinopyroxene, phlogopite and amphibole. A groundmass contains phlogopite, carbonate, apatite, clinopyroxene, garnet, titanite and opaque minerals.</p><p>The most important chemical features of the  alkali lamprophyres are undersaturation of SiO2 (31.04-40.54 wt%), high alkali contents (3.86 – 6.47 wt% K2O+Na2O) and their sodium specification (K2O/Na2O - 0.36-0.68), whereas ultramafic lamprophyres  have lower alkali contents (1.73-3.39 wt% K2O+Na2O), and potassium specification (K2O/Na2O -  1 -2.31). They also contain less SiO2 (27.73 – 34.11 wt%).</p><p>The Turiy Cape dykes are characterized by only a single petrographic type  - alkali lamprophyres (Cb-Anl and Ne-Anl monchiquites). They contain small and medium size (0.1 – 1 cm) phenocrysts of olivine, clinopyroxenes, amphiboles, magnetite, phlogopite. A groundmass contains analcime, nepheline, aegirine, phlogopite, garnet, perovskite, apatite and opaque minerals.</p><p>Rocks of the Turiy Cape dykes are SiO2 undersaturated (33.93 - 41.86 wt%), and contain extremely high alkalis (5.62-14.51 wt% K2O+Na2O) and all of them have sodium specification (0.11-0.68 K2O/Na2O).</p><p>The most primitive core of clinopyroxenes in the Kandalaksha dykes are high magnesian (#Mg – 0.76 – 0.87), low titanian (0,5 – 1,09 wt% TiO2) and contains chromium (0.1-1.1 wt% Cr2O3). The clinopyroxenes of the Tyriy Cape dykes have high magnesian core (#Mg 0.79-0.83, 1.48-2.05 wt% TiO2, 0.12-0.4 wt% Cr2O3).</p><p>Olivines in the Kandalaksha lamprophyres have more primitive composition in comparison with olivines from the Turiy Cape ones. The #Mg of Kandalaksha olivines varies from 0.84 to 0.87, nickel concentration varies from 1500 to 2500 ppm and the  #Mg of Turiy Cape olivines varies from 0.82 to 0.85, nickel concentration varies from 500 to 1000 ppm.  </p><p>Based on composition of primary minerals we suggest that compositional diversity of both dyke swarms were formed due to crystal fractionation processes. Though, the significant difference in chemistry of whole rocks and clinopyroxene and olivine composition do not support a common source for of the  Turiy Cape and Kandalaksha dykes.</p><p>This work was supported by the Russian Science Foundation under Grant No. 19-17-00024.</p><p> </p>

Binding Properties of Mechanically Activated Nepheline Containing Mining Waste

The development of apatite and rare-metal deposits of the Khibiny and Lovozero—the world’s largest ultrabasic massifs located in the Kola Alkaline Province—is accompanied by accumulation of huge amounts of sandy tailings dumps, about half consisting of nepheline. These tailings, on the one hand, pose a real threat of environmental pollution. On the other hand, they are “technogenic deposits” that contain reserves of valuable components (Na2O, K2O, Al2O3, etc.). In this paper, methods of processing of the nepheline-containing mining waste using mechanical activation to produce binding materials—geopolymers and blended cements—are observed. The advantages of combining the nepheline containing tailings dumps with other mining wastes accumulated in the region, such as Cu–Ni slag, are presented.

U-Pb age of sphene grains, petrochemical, mineralogical and geochemical features of alkaline rocks of the Bogdo complex (Arctic Siberia)

In the north of the Siberian Platform, east of the Anabar Shield, several identified massifs of alkaline rocks with carbonatites are known: Tomtorsky, Bogdo, Promezhutochniy, as well as Bualkalakh, Chuempe, Uele, which are projected according to geophysical data and forming a large alkaline-carbonatite province. The first data on the composition of alkaline rocks of the Bogdo massif were obtained, which correspond to a group of feldspathic rocks of the main composition: rischorrites, biotite-aegirine libenerite syenites, carbonatized, with symplectites and nepheline-feldspar aggregates, pseudo-leucite nepheline syenites. Sphenes were extracted from various types of rocks of the Bogdo massif and their U-Pb age was determined using the SHRIMP-II secondary-ion microprobe. The calculated U-Pb age corresponds to 394,4 3,2 Ma, which is close to the age stage established for the Tomtor massif and the age of the rocks of the Kola alkaline province. One of the reasons for the manifestation of alkaline plume magmatism in this territory may be the influence of the peripheral zone Africa Large Low Shear Velocity Province (Tuzo) in the Baltic and Siberia during the Devonian era.

Elemental, lead and sulfur isotopic compositions of galena from Kola carbonatites, Russia – implications for melt and mantle evolution

Galena from four REE-rich (Khibina, Sallanlatvi, Seblyavr, Vuoriyarvi) and REE-poor (Kovdor) carbonatites, as well as hydrothermal veins (Khibina) all from the Devonian Kola Alkaline Province of northwestern Russia was analysed for trace elements and Pb and S isotope compositions. Microprobe analyses show that the only detectable elements in galena are Bi and Ag and these vary from not detectable to 2.23 and not detectable to 0.43 wt.% respectively. Three distinct galena groups can be recognized using Bi and Ag contents, which differ from groupings based on Pb isotope data. The Pb isotope ratios show significant spread with 206Pb/204Pb ratios (16.79 to 18.99), 207Pb/204Pb (15.22 to 15.58) and 208Pb/204Pb ratios (36.75 to 38.62). A near-linear array in a 207Pb/204Pb vs.206Pb/204Pb ratio diagram is consistent with mixing between distinct mantle sources, one of which formed during a major differentiation event in the late Archaean or earlier. The S isotopic composition (δ34S) of galena from carbonatites is significantly lighter (–6.7 to –10.3% Canyon Diablo Troilite (CDT) from REE-rich Khibina, Seblyavr and Vuoriyarvi carbonatites, and – 3.2% CDT from REE-poor Kovdor carbonatites) than the mantle value of 0%. Although there is no correlation between S and any of the Pb isotope ratios, Bi and Ag abundances correlate negatively with δ34S values. The variations in the isotopic composition of Pb are attributed to partial melting of an isotopically heterogeneous mantle source, while those of δ34S (together with Bi and Ag abundances) are considered to be process driven. Although variation in Pb isotope values between complexes might reflect different degrees of interaction between carbonatitic melts and continental crust or metasomatized lithosphere, the published noble gas and C, O, Sr, Nd and Hf isotopic data suggest that the variable Pb isotope ratios are best attributed to isotopic differences preserved within a sub-lithospheric mantle source. Different Pb isotopic compositions of galena from the same complex are consistent with a model of magma replenishment by carbonatitic melts/fluids each marked by quite different Pb isotopic compositions.