The first data on the composition and inner structure of zircon, one of the main ore minerals of the rare-metal metasomatites of the Gremyakha–Vyrmes alkaline-ultramafic massif, are reported. Early zircon generations are enriched in Y and REE and contain numerous inclusions of rock-forming and accessory minerals of metasomatites, as well as syngenetic fluid inclusions of calcite, thorite and thorianite. Late generations differ in the elevated Hf content and contain no inclusions. The elevated concentrations of Ca and Th in the central zones of crystals are related to the presence of numerous micron-sized inclusions of calcite and thorium phases. All zircon varieties have extremely low U and Pb contents. Concentrations and distribution patterns of incompatible and rare-earth elements in zircon from the metasomatites of the Gremyakha–Vyrmes Massif are similar to those of syenite pegmatites and magmatic carbonatites around the world. Mineral from these associations shows a positive Ce anomaly and elevated HREE contents. According to the compositions of zircon and thorite inclusion in it and experimental data on the simultaneous synthesis of these minerals, the crystallization temperature of zircon was 700–750°С. Using Ti-in-zircon temperature dependence, late zurcon was formed at temperature of 700–750°С. The rare-metal metasomatites are formed at the final stages of the massif formation, presumably after foidolites. Carbonatites could initiate metasomatic reworking of foidolites and accumulation of trace metals in them. The evolution of the primary alkaline–ultramafic melt toward the enrichment in trace elements was mainly controlled by crystallization differentiation.

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.

Jinshanjiangite (acicular crystals up to 2 mm in length) and bafertisite (lamellar crystals up to 3 × 4 mm in size) have been found in alkali granite pegmatite of the Gremyakha-Vyrmes Complex, Kola Peninsula. Albite, microcline, quartz, arfvedsonite, zircon, and apatite are associated minerals. The dimensions of a monoclinic unit cell of jinshanjiangite and bafertisite are: a = 10.72(2), b=13.80(2), c = 20.94(6) Å, β = 97.0(5)° and a = 10.654(6), b = 13.724(6), c = 10.863(8) Å, β = 94.47(8)°, respectively. The typical compositions (electron microprobe data) of jinshanjiangite and bafertisite are: (Na0.57Ca0.44)Σ1.01(Ba0.57K0.44)Σ1.01 (Fe3.53Mn0.30Mg0.04Zn0.01)Σ3.88(Ti1.97Nb0.06Zr0.01)Σ2.04(Si3.97Al0.03O14)O2.00(OH2.25F0.73O0.02)Σ3.00 and (Ba1.98Na0.04K0.03)Σ2.05(Fe3.43Mn0.37Mg0.03)Σ3.83(Ti2.02Nb0.03)Σ2.05 (Si3.92Al0.08O14)(O1.84OH0.16)Σ2.00(OH2.39F1.61)Σ3.00, respectively. The minerals studied are the Fe-richest members of the bafertisite structural family.

La paragenese et la variation en composition de la solution solide banalsite-stronalsite, Ba 1-x Sr x Na 2 Al 4 Si 4 O 16 , provenant de cinq nouveaux indices dans la syenite nephelinique ou des roches ultramafiques alcalines, ont fait l'objet d'une description. Nous presentons aussi de nouvelles donnees pour la banalsite et la stronalsite de la mine Benallt, au Pays de Galles, Lângban, en Suede, et a Khibina, dans la peninsule de Kola, en Russie. En general, les membres de la solution solide entre banalsite et stronalsite decorent la bordure de grains de nepheline en contact avec l'analcime tardive ou l'albite, et se presentent en aggregats allant de banalsite dans le noyau a stronalsite barifere et stronalsite a la bordure. Les relations texturales montrent que la banalsite pourrait se former a un stade magmatique tardif, avec la nepheline, tandis que la stronalsite cristallise en general comme sous-produit de la conversion postmagmatique de la nepheline a 1 'analcime, en remplacement a la fois de nepheline et banalsite. Cette conversion est facilitee par la ressemblance structurale de la nepheline et de ces tectosilicates Ba 1-x Sr x Na 2 Al 4 Si 4 O 16 , les deux possedant une trame infinie a Si-Al ordonnes faite d'anneaux -UDUD-. Le fait que la serie Ba 1-x Sr x Na 2 Al 4 Si 4 O 16 est complete et la solution solide tres limitee vers la lisetite, CaNa 2 Al 4 Si 4 O 16 , resultent de la ressemblance topologique de la banalsite et la stronalsite, et des differences importantes avec la lisetite par rapport au degre d'ordre des cations.

Natural γ-CrOOH was first found and studied in rischorrite of the Khibina Massif, in which this mineral is associated with gonardite, natrolite, phillipsite, and saponite and usually forms microcrystallites in a matrix of amorphous CrOOH hydrogel or, more rarely, occurs as fine-crystalline, thin acicular, and lumpy aggregates of a green and emerald-green color. X-ray powder diffraction data indicate that crystalline blocks consist of a mineral with a rhombohedral unit cell, Cmcm, a = 3.86 Å, b = 12.78 Å, and c = 3.04 Å. Chromium oxyhydroxide from the Khibina Massif is isostructural with γ-CrOOH from the Iksinskoe deposit, but significantly differs from it in bearing low Al concentrations. The empirical formula of the Khibina γ-CrOOH is (Cr0.94Mg0.03Al0.02Ti0.01Fe0.01)1.01O(OH) · nH2O. The Cr oxyhydroxide and associated zeolites crystallized from low-temperature hydrothermal solutions rich in Na. The most probable source of Cr for the γ-CrOOH in the Khibina Massif was titanomagnetite in xenoliths of ultrabasic rocks in the rischorrites affected by postmagmatic alterations.

Nous avons determine la structure de la stronalsite, SrNa 2 Al 4 Si 4 O 16 , et celle de la banalsite, BaNa 2 Al 4 Si 4 O 16 , par methodes directes au moyen de donnees en diffraction X prelevees sur monocristaux et d'un detecteur a aire CCD. Les structures sont topologiquement identiques; elles adoptent le groupe d'espace non centrosymetrique Iba2 plutot que le groupe centrosymetrique Ibam attribue anterieurement a la banalsite. Les parametres reticulaires sont: a 8.4080(9), b 9.8699(11), c 16.7083(18) A, V 1386.6(3) A 3 , Z = 4, D calc 2.92 g/cm 3 pour la stronalsite (complexe de Khibina, peninsule de Kola, Russie); a 8.5400(7), b 10.0127(9), c 16.7897(14) A, V 1435.7(2) A 3 , D calc 3.05 g/cm 3 pour la banalsite provenant du Pays de Galles (mine Benallt, UK), et a 8.5068(16), b 9.9811(18), c 16.7485(31) A, V 1422.1(5) A 3 , D calc 3.08 g/cm 3 pour la banalsite de Lângban (Suede). Les structures contiennent une trame infinie de tetraedres partageant leurs coins, avec Si et Al completement ordonnes sur quatre sites independants. Les tetraedres Si(1)-A1(1) et Si(2)-Al(2) pointent en alternance vers le haut (U) et vers le bas (D) pour former des anneaux a quatre et huit membres paralleles a (001), ce qui mene a une trame -UDUD-, distincte de la trame -UUDD- des feldspaths. L'empilement mene a des anneaux a six membres paralleles au plan (100). Les interstices de cette trame contiennent les gros atomes Sr ou Ba ( X A 2+ ) et les atomes plus petits de VI Na + , ordonnes a des niveaux alternants paralleles a (001), avec une separation de 1/4 c. Le caractere isostructural de la banalsite et de la stronalsite explique la solution solide complete Ba 1-x Sr x- Na 2 Al 4 Si 4 O 16 observee dans la nature.