Pavel M. Kartashov

Chevkinite-group minerals from Russia and Mongolia: new compositional data from metasomatites and ore deposits

Abstract Electron-microprobe analyses of Russian and Mongolian chevkinite-group minerals from little-known host lithologies, including various metasomatic rocks, quartzolites and an apatite deposit, are presented. The mineral species analysed include chevkinite-(Ce), perrierite-(Ce), polyakovite-(Ce) and Sr- and Zr-rich perrierite-(Ce). Compositional variation in the Sr-rich members of the group is broadly represented by the exchange vector (Fe + Mn + Al + REE) ↔ (Ca + Sr + Ti + Zr). Despite the varied parageneses, the chevkinite-(Ce) compositions are similar to previously published data. Many crystals have strong internal compositional variations, partly produced during primary crystallization and partly during low-temperature hydrothermal alteration.

Koksharovite, CaMg2Fe3+ 4(VO4)6, and grigorievite, Cu3Fe3+ 2Al2(VO4)6, two new howardevansite-group minerals from volcanic exhalations

Two new howardevansite-group minerals were discovered in the exhalations of fumaroles related to two volcanoes in Kamchatka, Russia. Koksharovite, CaMg2Fe 3þ 4(VO4)6, is found at the Bezymyannyi volcano in association with bannermanite. Grigorievite, Cu3Fe 3þ 2Al2(VO4)6, associated with bannermanite, ziesite, hematite, etc., was found at the Second scoria cone of the NorthernBreakthroughoftheGreatTolbachikFissureEruption,Tolbachikvolcano.Koksharoviteoccursasequanttoprismaticcrystals upto30 � 70mm.Itistranslucent,yellowish-browntoreddish-brownwithanadamantinelustre.Grigorieviteformsprismatic totabular crystals up to 40 � 100 mm. It is opaque, black with a semi-metallic lustre. Both minerals are brittle. The VHN hardness is 368 and 489 kg mm � 2 , the calculated density (Dcalc) 3.39 and 3.67 g cm � 3 for koksharovite and grigorievite, respectively. In reflected light, koksharovite is light grey, grigorievite is grey; both minerals are weakly anisotropic. Reflectance values (koksharovite//grigorievite: Rmax-Rmin ,%( l, nm)) are: 15.3-14.4//16.8-16.4 (470), 14.1-13.2//15.9-15.5 (546), 13.8-13.0//15.3-14.9 (589), 13.4-12.7//14.8-14.1 (650). Chemical data (wt%, electron-microprobe analysis; first value is for koksharovite, second for grigorievite) are: Na2O 0.76, 0.00; K2O 0.05, 0.00; MgO 9.43,2.78; CaO 3.57, 0.95; MnO 0.46,0.04;CuO 0.00,17.70; NiO 0.11, 0.00;ZnO 0.00,0.14; Al2O3 3.04,11.76; Fe2O3 23.88, 10.10; TiO2 2.42, 1.47; SiO2 0.20, 0.00; P2O5 0.98, 0.13; V2O5 53.86, 54.97; total 98.76, 100.04. The empirical formulae, based on 24 O atoms per formula unit, are: Na0.24K0.01Ca0.63Mg2.30Mn0.06Ni0.01Al0.59Fe 3þ 2.94Ti0.30Si0.03P0.14V5.83O24 (koksharovite); Ca0.17Mg0.69Mn0.01Cu2.23Zn0.02Al2.31Fe 3þ 1.27Ti0.18P0.02V6.05O24(grigorievite).Bothmineralsaretriclinic,spacegroupP-1,Z ¼1.Unit-

Hydrothermal alteration of chevkinite-group minerals. Part 2. Metasomatite from the Keivy massif, Kola Peninsula, Russia

Abstract Chevkinite-(Ce) in a mineralized quartz-epidote metasomatite from the Keivy massif, Kola Peninsula, Russia, underwent at least two stages of low-temperature alteration. In the first, it interacted with hydrothermal fluids, with loss of Ca, Fe, LREE and Si and strong enrichment in Ti. The altered chevkinite was then rimmed and partially replaced by a zone of ferriallanite-(Ce) and davidite-(La), in turn rimmed by a zone of allanite-(Ce) richer in the epidote component. The allanite zone was in turn partially replaced by rutile-titanite-quartz assemblages, the formation of titanite postdating that of rutile. Aeschynite-(Y), aeschynite-(Ce) and REE-carbonates are accessory phases in all zones. The hydrothermal fluids were alkaline, with significant proportions of CO2 and F. At various alteration stages, the Ca, Si ± Al activities in the fluid were high. Formation of the aeschynite is discussed in relation to its stability in broadly similar parageneses; it was a primary phase in the unaltered chevkinite zone whereas in other zones it formed from Nb, Ti, REE and Th released from the major phases.

Hydrothermal alteration of chevkinite-group minerals: products and mechanisms. Part 1. Hydration of chevkinite-(Ce)

Abstract Samples from Russia and Scotland are used to examine the interaction of the REE-Ti silicate chevkinite-(Ce) with hydrothermal fluids. Altered zones in crystals are distinguished by using areas of low intensity on backscattered-electron images, low analytical totals, increasingly large departures from stoichiometry and, in some cases, the presence of micropores. Initial alteration of the chevkinite results in strong Ca enrichment. With increasing degrees of alteration, Ca abundances drop sharply, as do those of the REE, Fe and Si. In contrast, Ti levels increase strongly, usually accompanied by higher Nb ± Th levels. The most altered zones contain up to 36 wt.% TiO2 and the formula cannot be expressed in the standard chevkinite formula. In detail, samples follow different alteration trends, presumably reflecting different P, T, fO₂ and fluid composition. The Ti enrichment may have been related to a reaction front of dissolution-reprecipitation passing through the outer zones of the original chevkinite, leaving behind a reprecipitated Ti-enriched phase which may or may not be chevkinite.

Arsenoflorencite-(La), a new mineral from the Komi Republic, Russian Federation: description and crystal structure

Arsenoflorencite-(La) [Арсенфлоренсит-(La)], ideally LaAl 3 (AsO 4 ) 2 (OH) 6 , is a new mineral (IMA2009–078), from the Grubependity Lake cirque, Maldynyrd range, upper Kozhim River basin, Prepolar Ural, Komi Republic, Russia. It occurs in direct association with zircon, quartz, hematite, ardennite-(As), andalusite, anorthite, sericite, clinochlore, chernovite-(Y), manganiandrosite-(La), spessartine and monazite–gasparite-group minerals in Mn-rich nodules in metasediments. Arsenoflorencite-(La) forms orange–red to pink rhombohedral, pseudocubic or tabular crystals up to about 0.2 mm across. The dominant forms observed are {001} and {102}. The crystals have a vitreous lustre, are transparent to translucent, have a very light pink streak and are non-fluorescent. Mohs hardness is about 3.5 (estimated). The fracture is uneven and the tenacity is brittle. Arsenoflorencite-(La) has fair cleavage on {001}. Crystals are uniaxial (+), with the indices of refraction ω = 1.740(5) and e = 1.750(5), measured in white light, and are nonpleochroic. The empirical formula (based on 14 O atoms) is: (La 0.56 Ce 0.18 Nd 0.12 Pr 0.04 Sr 0.09 Ca 0.03 ) ∑1.02 (Al 2.94 Fe 0.06 ) ∑3.00 (As 1.80 P 0.21 ) ∑2.01 H 5.95 O 14 . The simplified formula is LaAl 3 (AsO 4 ) 2 (OH) 6 . Arsenoflorencite-(La) is trigonal, space group R 3 m , a = 7.0316(3), c = 16.5151(8) A, V = 707.16(5) A 3 and Z = 3. The crystal structure was solved from single-crystal X-ray diffraction data and refined to R 1 = 0.0112 on the basis of 287 unique reflections with F o > 4 σF and R 1 = 0.0116 for all 293 reflections. The five strongest lines in the powder X-ray diffraction pattern are [ d obs in A, ( I ), ( hkl )]: 2.982, (100), (113); 3.538, (55), (110); 1.914, (38), (303, 033); 2.211, (28), (122); 5.755, (27), (101). The name is for its relationship to florencite [and arsenoflorencite-(Ce)] with La as the dominant REE.

Hydrothermal alteration of a chevkinite-group mineral to a bastnäsite-(Ce)-ilmenite- columbite-(Fe) assemblage: interaction with a F-, CO2-rich fluid

The results are presented of a textural and mineral chemical study of a previously undescribed type of hydrothermal alteration of chevkinite-(Ce) which occurs in a syenitic pegmatite from the Vishnevye Mountains, Urals Region, Russia. The progressive alteration of the chevkinite to a bastnäsite-(Ce)-ilmenite-columbite-(Fe) assemblage through a series of texturally complex intermediate stages is described and electron microprobe analyses are given of all the major phases. Unusual Nb ± Th-rich phases formed late in the alteration sequence provide evidence of local Nb mobility. The main compositional fluxes are traced, especially of the REE, HFSE, Th and U. It appears that almost all elements, with the exception of La, released from the chevkinite-(Ce) were reincorporated into later phases, such that they did not leave the alteration crust in significant amounts. The hydrothermal fluids are inferred to have been F- and CO2-rich, with variable levels of Ca activity, and with fO2 mainly between the nickel-nickel oxide and magnetite-hematite buffers. This occurrence represents a new paragenesis for a columbite-group mineral.

Yttriaite-(Y): The natural occurrence of Y2O3 from the Bol’shaya Pol’ya River, Subpolar Urals, Russia

Abstract Yttriaite-(Y), ideally Y2O3, is a new mineral (IMA2010-039) from the alluvial deposits of the Bol’shaya Pol’ya River, Subpolar Urals, Russia. The new mineral occurs as isolated crystals, typically cubo-octahedra <6 μm in size, embedded in massive native tungsten. Associated minerals include: copper, zircon, osmium, gold, and pyrite. The main forms observed are {100} and {111}. Due to the crystal size, physical properties could not be determined; however, the properties of synthetic Y2O3 are well known. Synthetic Y2O3 crystals are colorless to white with a white streak; crystals are transparent with an adamantine luster, while massive Y2O3 is typically translucent with an earthy luster. Synthetic Y2O3 has a Vickers hardness of 653.91, which corresponds to 5.5 on the Mohs scale. Synthetic Y2O3 crystals have good cleavage on {111}. Yttriaite-(Y) is isotropic; the refractive index measured at 587 nm on synthetic Y2O3 is n = 1.931. The empirical chemical formula (mean of 4 electron microprobe analyses) calculated on the basis of 3 O is: Y1.98Dy0.01Yb0.01O3. Yttriaite-(Y) is cubic, space group Ia3̅, with parameters a = 10.6018(7) Å, V = 1191.62(7) Å3, and Z = 16. The five strongest lines in the powder X-ray diffraction pattern (measured on synthetic Y2O3 using synchrotron radiation) are [dobs in Å (I) (hkl)]: 3.0646 (100) (222), 1.8746 (55) (440), 1.5984 (38) (622), 2.6537 (26) (400), and 4.3356 (14) (211). The mineral name is based on the common name for the chemical compound, yttria.

Magnesioneptunite, KNa2Li(Mg,Fe)2Ti2Si8O24, a new mineral species of the neptunite group

A new mineral of the neptunite group, magnesioneptunite KNa2Li(Mg,Fe)2Ti2Si8O24, a Mg-dominant analogue of neptunite and manganoneptunite, has been found in the Upper Chegem caldera near Mount Lakargi, Kabardino-Balkaria, the North Caucasus, Russia in a xenolith of altered sandstone located between skarnified carbonate xenoliths and ignimbrite. Magnesioneptunite occurs as nearly isometric grains and aggregates up to 0.1 mm in size in the cores of some grains of a Mg-rich variety of neptunite with Mg/(Fe + Mn) = 0.7−1.0. The chemical composition of magnesioneptunite with a maximum Mg content is as follows, wt %: 3.63 K2O, 8.21 Na2O, 1.73 Li2O, 6.47 MgO, 0.04 MnO, 5.87 FeO, 0.07 Al2O3, 18.73 TiO2, 56.88 SiO2, 99.62 in total. The empirical formula is (K0.67Na0.32Ca0.01)Σ1.00Na2.06Li1.00 · (Mg1.39Fe0.712+)Σ2.10(Si7.90Al0.01)Σ7.91O24. Grains of magnesioneptunite are dark brown to red-brown, translucent, with vitreous luster. Dcalc = 3.15 g/cm3, and the Mohs hardness is 5–6. Cleavage parallel to the (110) is perfect. The new mineral is optically biaxial, positive, α = 1.697(2), β = 1.708 (3), γ = 1.725(3), 2Vmeas = 45(15)°. The mineral is associated with quartz, alkali feldspar, rutile, aegirine, and neptunite. Magnesioneptunite and the Mg-rich variety of neptunite were formed as products of ilmenite alteration. Magnesioneptunite is monoclinic, C2/c; unit-cell parameters: a = 16.327(7), b = 12.4788(4), c = 9.9666(4) Å, β = 115.6519(5)°, V = 1830.5(1) Å3, Z = 4. The type specimen is deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow.

Fluorocronite, the natural analogue of β-PbF2, from the Sakha Republic, Russian Federation

Fluorocronite (Фторокронит), ideally PbF 2 , is a new mineral (IMA2010–023), from the Kupol’noe deposit, Sarychev range, Sakha Republic, Russian Federation. It occurs intimately mixed with cassiterite and a potentially new Sn oxy-hydroxide with the composition Sn 4 O(OH,F) 6 , and is found in direct association with quartz, anglesite, cerussite, galena, hocartite, bindheimite and chlorargyrite. Fluorocronite forms flattened, leaf-like microcrystals up to about 20 μm across. The main form observed is {100}, while {111} may also be present. The crystals are translucent and white with a pearly lustre. The streak is also white and Mohs hardness is between 3 and 4 (estimated). No parting or twinning was observed. Fluorocronite has prefect cleavage on {111} by analogy with other minerals with the fluorite structure type. Crystals are optically isotropic; however, the refractive index could not be measured due to the small size of the crystals. The empirical formula (based on 3 apfu ) is Pb 0.98 F 2.02 . The simplified formula is PbF 2 . Fluorocronite is cubic, space group Fm 3 m , with a = 5.9306(5) A, V = 208.59(5) A 3 and Z = 4. Fluorocronite is isostructural with fluorite. The five strongest lines in the powder X-ray diffraction pattern are [ d obs in A ( I ) ( hkl )]: 3.437 (100) (111); 2.976 (46) (002); 2.103 (44) (022); 1.794 (42) (311); 1.717 (21) (222). The name is in relation to the composition; fluoro (for fluorine) and cron (κρόνος, the alchemical name for lead).

Ordering of cations in the voids of the anionic framework of the crystal structure of catapleiite

The pseudohexagonal crystal structure of the mineral catapleiite Na1.5Ca0.2[ZrSi3(O,OH)9] · 2(H2O,F) from the Zhil’naya Valley in the central part of the Khibiny alkaline massif (Kola Peninsula, Russia) is studied by X-ray diffraction (XCalibur-S diffractometer, R = 0.0346): a = 20.100(4), b = 25.673(5), and c = 14.822(3) Å; space group Fdd2, Z = 32, and ρcalcd = 2.76 g/cm3. Fluorine atoms substituting part of H2O molecules in open channels of the crystal structure have been found for the first time in the catapleiite composition by microprobe analysis. The pattern of distribution of Na and Ca atoms over the voids of the mixed anionic framework consisting of Zr-octahedra and three-membered rings of Si-tetrahedra accounts for the pronounced pseudoperiodicity along the a and c axes of the pseudohexagonal unit cell and for the lowering of crystal symmetry to the orthorhombic one. It is shown that part of the hydrogen atoms of water molecules is statistically disordered; their distribution correlates with the pattern of the population of large eight-vertex polyhedra by Na and Ca atoms.