Th-rich loparite from the Khibina alkalinecomplex Kola Peninsula isomorphism and paragenesis

ROGER H MITCHELL

AND

ANTON R CHAKHMOURADIAN

Department of Geology Lakehead University 955 Oliver Road Thunder Bay Ontario P7B 5E1 Canada

ABSTRACT

Th-rich (up to 184 wt ThO2) loparite occurs as an accessory phase in foyaite pegmatites at MtEveslogchorr Khibina complex Russia It is associated with aegirine astrophyllite eudialytelorenzenite lamprophyllite magnesio-arfvedsonite and gerasimovskite Loparite crystals are zonedfrom niobian loparite (core) to niobian thorian and thorian niobian loparite (rim) Th-enrichment isaccompanied by a decrease in Na LREE Sr and increase in A-site vacancies The most Th-richcomposition approaches (Na039LREE019Th012Ca005Sr002)S077(Ti076Nb027)S103O3 The mineral ispartly or completely metamict and after annealing gives an X-ray diffraction powder pattern similar tothat of synthetic NaLaTi2O6 and naturally occurring loparite of different composition For the Th-richrim sample the five strongest diffraction lines (AEcirc ) are 272 (100) 110 1575 (60) 211 1925 (40)1368 (30) 220 1222 (20) 310 a = 3867(2) AEcirc The X-ray diffraction patterns do not exhibit peaksplitting or other diffraction lines typical of low-symmetry and ordered perovskite-type structuresComposition determinations infrared transmission spectroscopy and X-ray diffractometry show thatthorian loparite is partly replaced by betafite with LREE and Th as dominant A-site cations(lsquoceriobetafitersquo) Some loparite samples also exhibit thin replacement mantles of belyankinite with highLREE2O3 and ThO2 contents Both lsquoceriobetafitersquo and belyankinite were formed due to metasomaticalteration of loparite

KEY WORDS loparite betafite belyankinite nepheline-syenite pegmatite Khibina alkaline complex KolaPeninsula Russia

Introduction

PEROVSKITE-GROUP minerals from alkaline rocksexhibit wide ranges in composition and may serveas sensitive indicators of evolutionary trends(Kukharenko and Bagdasarov 1961 Mitchell1996 Mitchell and Chakhmouradian 1996Tikhonenkova et al 1982) Comprehensivestudies of isomorphic substitutions in naturally-occurring perovskites are also very important forunderstanding the crystal chemistry of syntheticperovskite-type compounds that show a broadspectrum of electric and magnetic properties

Among the least studied of perovskite-groupminerals are species containing large-size high-

valency cations in particular Th other tetra-valent actinides and Ce4+ The initial study ofnaturally-occurring perovskites enriched in acti-nide elements was undertaken by Borodin (1954)who suggested that accommodation of high-valency elements with large ionic radii inperovskite-group minerals is accompanied by thecreation of vacancies at A sites in the lattice andpartial substitution of oxygen atoms by hydroxylanions The generalized formula proposed byBorodin (1954) for hydrous perovskite-groupminerals containing considerable amounts ofrare-earth or actinide elements is A1shy xBO3 shy x

(OH)x (x = 0 shy 05) Borodin and Kazakova(1954) reported the occurrence of Th-rich

Mineralogical Magazine June 1998 Vol 62(3) pp 341ndash353

1998 The Mineralogical Society

(130 wt ThO2) loparite (termed lsquoirinitersquo) withminor amounts of Fe2O3 and CaO in a foyaitepegmatite at Mt Eveslogchorr in the Khibinaalkaline complex Kola Peninsula The structuralformula deduced from bulk wet-chemical analysisindicated that this mineral had significant cationdeficiency at the A sites which was associatedwith O2shy gt (OH)shy substitution (Borodin andKazakova 1954) Recent studies of loparitemineral iza tion at the Khibina complex(Kozyreva et al 1991 Tikhonenkova et al1982) also report the occurrence of Th-richloparite in foyaite or related pegmatites Parkerand Sharp (1970) have described rsquoirinitersquo as anaccessory constituent of vermiculite rock at theGem Park Complex Colorado However identi-fication of this mineral as lsquoirinitersquo was basedmerely on its metamict state and resemblance ofthe X-ray diffraction pattern of the heated sampleto that of Borodin and Kazakovarsquos (1954)material (Parker and Sharp 1970) Perovskitewith ThO2 content of up to 17 wt occurs in thePolino carbonatite diatreme Italy (Lupini et al1992) and up to 49 wt in the carbonatitecomplexes of Kola Peninsula (Chakhmouradianand Mitchell 1997) Finally fenite-like rocks inthe carbonatite complexes of the Parana BasinSouth America host loparite of widely varyingSrO Na2O Nb2O5 LREE2O3 and ThO2 (up to 62wt) contents (Mitchell 1996)

Initial synthesis of Th-bearing perovskite-typeoxides produced compounds of the type AThO3 (A= Ca Sr Ba Pb) in which Th4+ occupiesoctahedrally-coordinated B-sites (Naray-Szabo1947 Smith and Welch 1960) SubsequentlyKovba and Trunov (1962) synthesized a series ofniobates and tantalates accommodating Th U andCe4+ at twelve-coordinated A-sites in theperovskite structure These compounds werehighly cation-deficient relative to ideal ABX3

perovskite having the general formula A14BO3 (A= Th U Ce B = Nb Ta) Trunov and Kovba(1963) also prepared perovskite-type tungstates ofTh tolerating even higher cation deficiency at theA sites ie Th14WO3 to Th130WO3 Othersynthetic perovskites with A-site Th includeCaThV2O6 and SrThV2O6 (Vidyasagar andGopalakrishnan 1982) Na23Th13TiO3 (Zhu andHor 1995) and the solid solution seriesNaNbO3 shy Th025NbO3 (Labeau and Joubert1978) The above examples demonstrate that (i)Th4+ in perovskite-type compounds may occupyeither twelve-coordinated A sites or smalleroctahedral B sites depending on the type of

associated cations (ii) accommodation of Th inthe perovskite structure may or may not beaccompanied by the appearance of vacancies atthe A sites

The current study was undertaken to determinehow Th is accommodated in the structure ofloparite a Na-LREE-Ti member of the perovskitefamily containing significant amounts of Nb Caand Sr A second objective was to study theparagenesis of Th-rich loparite

Analytical methods

All mineral compositions were determined by X-ray energy-dispersion spectrometry using aHitachi 570 scanning electron microscopeequipped with a LINK ISIS analytical systemincorporating a Super ATW Light ElementDetector (133 eV FwHm MnK) at LakeheadUniversity Ontario EDS spectra of loparitebetafite and belyankinite were acquired for 300seconds and those of silicates for 100 seconds(live time) with an accelerating voltage of 20 kVand beam current of 086 nA The following well-characterizednatural and synthetic standards wereemployed for the determination of mineralcompositions Khibina loparite (Na LREE Nb)Magnet Cove perovskite (Ca Fe Ti) jadeite (AlSi) periclase (Mg) orthoclase (K) manganoanfayalite (Mn) synthetic SrTiO3 (Sr) BaSiO3 (Ba)metallic Th Ta and Zr The accuracy of themethod was cross-checked by wave-length-dispersion electron microprobe analysis using anautomated CAMECA SX-50 microprobe locatedat the University of Manitoba following methodsdescribed by Mitchell and Vladykin (1993)

X-ray diffraction (XRD) powder patterns (Curadiation) were obtained with a Philips 3710diffractometer at Lakehead University using aPhilips Debye-Scherer type camera with adiameter of 1146 mm The diffractometer wasoperated at 40 kV and 25 mA Relative intensitiesof the diffraction lines were estimated visuallyfrom the films

Infra-red transmission spectra were recordedwith a FTIR spectrometer IFS-66 equipped with amicroscope Spectra were obtained on 02shy 03mm thick unfractured slabs of loparite from 256scans using the 03-mm aperture of the micro-scope For each measurement the referencespectrum was obtained from 256 scans at thesame operating conditions in order to eliminatethe effect of H2O vapour apparently present in thespectrometer

R H MITCHELL AND A RCHAKHMOURADIAN

342

Occurrence

Until recently loparite with the ThO2 content ofmore than 10 wt has been recognized only fromthe Khibina alkaline complex in the KolaPeninsula Russia Its occurrence is restrictedmainly to foyaite and related pegmatoid andmetasomatic rocks comprising the central part ofthe Khibina pluton The general geologypetrology and mineralogy of the complex havebeen described in detail by Galakhov (1975)Kostyleva-Labuntsova et al (1978ab) Zak et al(1972) and summarized by Kogarko et al (1995)

Th-rich loparite examined in the current studyoccurs in foyaite pegmatites exposed on thesouthern slope of Mt Eveslogchorr southKhibina Most of the pegmatites are simplepoorly-differentiated veins emplaced into fine-to-medium grained nepheline syenite of gneissoidtexture The veins are composed mainly of alkalifeldspar nepheline aegirine and astrophylliteThe latter two minerals occur in intimate inter-growths as fibrous or radial aggregates partly orentirely replacing the earlier formed paragenesisof alkali feldspar and nepheline In Russianmineralogical literature the late-stage zones of

fibrous aegirine in nepheline-syenite pegmatitesare commonly interpreted as being of deuteric(lsquoautome tasoma ticrsquo ) or igin (Kostyl eva -Labuntsova et al 1978a) The aegirine-astro-phyllite aggregate encloses numerous irregular- orlens-shaped polygranular segregationsof analcitephillipsite natrolite and gibbsite plus Fe-hydr-oxides These segregations commonly containrelics of nepheline and undoubtedly representalteration products of the latter Accessoryminerals developed in the aegirine-astrophylliteaggregate are eudialyte loparite lamprophyllitelorenzenite and rare magnesio-arfvedsoniteRepresentative compositions of the major andaccessory silicates from the aegirine-astrophylliterock are given in Table 1

In the aegirine-astrophyllite aggregate lopariteoccurs as lsquofluoritersquo-type interpenetration twinsranging from 3 shy 7 mm across The mineral isdeep reddish-brown in thin sections andcommonly has a yellow-coloured rim up to03 mm in thickness Some loparite crystalspoikilitically enclose fine (less than 10 mm)needles of aegirine In this study we examinedzoned crystals of loparite from two pegmatiteveins KHB-44 and KHB-70

FIG 1 Back-scattered electron images of a zoned Th-rich loparite crystal (a) rim of thorian niobian and niobianthorian loparite (light grey) on niobian loparite (dark grey) scale bar is 400 mm (b) lsquoceriobetafite rsquo (dark grey)

developed along fractures and margins of thorian niobian loparite (light grey) scale bar is 30 mm

TH-RICH LOPARITE

343

Phase relationships

Back-scattered electron (BSE) imagery combinedwith line scanning reveals that loparite crystalsexhibit strong compositional zonation reflectingenrichment in ThO2 from the core towards the rim(Fig 1a) The Th-rich rims of the crystals areheterogeneous and consist of two phases Phase 1having a lower average atomic number isdeveloped as dendrite-like narrow (3 shy 30 mm)zones decorating margins of the crystals andfractures within phase 2 (Fig 1b) Compositiondeterminations show that both phases havecomparable CaO SrO LREE2O3 TiO2 andNb2O5 (Ti gt Nb) contents However phase 1gives low analysis totals (936-970 wt) andcontains considerably less Na2O (03shy 10 wt)and generally more ThO2 (178shy 220 wt) thanphase 2 X-ray diffraction study (see below)demonstrates that phase 1 comprising the bulkof the sample extracted from the rim of the crystalis loparite Three lsquoadditionalrsquo weak diffractionlines observed on the XRD film could not beassigned to loparite or any structure derived fromthe perovskite parent but corresponded well withthe three strongest diffraction lines of betafite(ASTM 13-197 Hogarth 1961)

Infrared transmission spectra recorded from thecore and rim of a loparite crystal are compared inFig 2(ab) Both spectra show a broad absorptionband at 650shy 900 cmshy 1 This band corresponds tobond vibrations in the octahedral complexes(TiNb)O6 and is typical of various perovskite-and pyrochlore-group minerals (Kostyleva-Labuntsova et al 1978b Pilipenko et al 1971)and their synthetic analogues (Nyquist and Kagel

1971 Sych et al 1973) The relative position ofthis absorption band in the spectrum depends onthe Ti vs Nb ratio of the mineral Splitting of the(TiNb)O6 band commonly observed in theinfrared spectra of low-symmetry perovskite-type compounds (Pilipenko et al 1971 Sych etal 1973) is not observed in our spectra(Fig 2ab) Similar coalescence of severalabsorption lines into one broad band has beenobserved in metamict pyrochlore (Krivokonevaand Sidorenko 1971) In addition to the(TiNb)O6 absorption band the infrared spectrumof the rim (Fig 2b) contains bands at 1650 23303300shy 3320 and 3530 cm shy 1 the latter twopartially overlapping each other The OHstretching bands at 3300shy 3320 and 3530 cmshy 1

and Nb shy OH band at 1650 cmshy 1 are characteristicof pyrochlore-group minerals (Voloshin et al1989) and most probably result from micro-intergrowths of ceriobetafite in the studiedsamples In the current study we could notassign the absorption band at 2330 cmshy 1

As evidenced by back-scattered electronimagery loparite from the vein KHB-70 hasundergone further alteration giving rise to thecomplex Ti hydroxide belyankinite The mineraloccurs as thin (20shy 30 mm) replacement mantleson loparite Its Nb-dominant analogue gerasi-movskite forms rare rectangularplates enclosed infibrous aegirine Both minerals have beeninsufficiently studied and were originallydescribed in peralkaline pegmatites of theLovozero alkaline complex Kola Peninsulawhere they occur predominantly as pseudomorphsafter titanium-silicates (Gerasimovskii andKazakova 1950 Semenov 1957)

Composition

LopariteRepresentative compositions of zoned loparite

crystals are given in Table 2 From core to rimloparite compositionally evolves by enrichment inThO2 and depletion in Na2O LREE2O3 and SrO(Table 2) In order to reveal possible end-membercompositions which may account for the accom-modation of Th in the structure of lopariterelationships between the amounts of Th (apfu)and other major elements (Fig 3) were analysedWith strongly decreasing Na LREE and to a lesserdegree Sr and increasing Th (Fig 3abd) theoccupancy of the B sites remains relativelyunchanged (Fig 3ef) As the most Th-richcompositions also exhibit the greatest cation

FIG 2 Infra-red transmission spectra of Th-rich loparite(a) core sample (b) rim sample

R H MITCHELL AND A RCHAKHMOURADIAN

344

deficiency (Fig 3g) it is deduced that Th4+ cationsare accommodatedat the A site of loparite and thatthe correspondingsubstitution scheme involves theappearance of vacancies at these sites Calculationsshow that the observed relationship between Thcontent and number of vacancies at the A-site mostclosely corresponds to the solid solution seriesbetween loparite and two hypothetical end-members ThNb4O12 and ThTi2O6 (Fig 3) Theso l id solu t ion se r ies between lopari te

NaLREETi2O6 and Na23Th13TiO3 believed tobe present is not present as the A- and B-sitesoccupancy remains constant The isomorphicsubstitutions are as follows

2Na+ + 2LREE3+ + 4Ti4+ gtTh4+ + 3amp + 4Nb5+ (1)

Na+ + LREE3+ gt Th4+ + amp (2)

ThNb4O12 (= Th025NbO3) has been synthe-sized and shown to have a perovskite-type

TABLE 1 Representative compositions of major and accessory silicate minerals

Wt 1 2 3 4 5 6 7 8 9 10 11 12

Na2O 1281 1220 227 216 1124 1094 1066 1104 1707 1696 889 871K2O 004 008 602 606 041 035 064 061 nd nd 204 218CaO 225 267 141 155 929 879 045 040 005 008 056 067SrO na na nd nd 149 118 1306 1162 nd nd na naBaO na na nd nd nd nd 085 322 nd nd na naMgO 102 103 189 191 009 037 043 045 035 023 820 808MnO 037 039 1292 1329 383 452 558 526 nd 012 373 383FeO 060 136 1904 1850 392 324 na na na na 1393 1351Fe2O3 2670 2535 na na na na 293 250 080 069 592 662La2O3 na na nd nd 067 106 060 042 na na na naCe2O3 na na nd nd 140 131 052 026 na na na naAl2O3 165 117 086 104 nd nd 029 002 nd nd 101 130SiO2 5326 5196 3555 3550 4995 4852 3100 3035 3331 3382 5320 5236TiO2 181 197 1160 1157 040 023 2959 2991 4479 4516 098 125ZrO2 na na 065 049 1326 1220 nd nd nd nd na naNb2O5 na na 065 077 290 331 009 041 212 188 na na

Total 10052 9818 9286 9284 9885 9602 9669 9647 9849 9894 9846 9851

Structural formulaeO = 6 Si = 8 Si = 24 Si = 4 O = 9 O = 23

Na 0934 0913 0990 0944 10471 10492 2667 2821 1929 1904 2576 2530K 0002 0004 1728 1742 0251 0221 0105 0103 0shy 0shy 0389 0417Ca 0091 0111 0340 0374 4782 4658 0062 0056 0003 0005 0090 0107Sr 0shy 0shy 0shy 0shy 0415 0338 0977 0888 0shy 0shy 0shy 0shyBa 0shy 0shy 0shy 0shy 0shy 0shy 0043 0166 0shy 0shy 0shy 0shyMg 0057 0059 0634 0642 0064 0273 0083 0088 0030 0020 1827 1804Mn 0012 0013 2463 2537 1559 1894 0610 0587 0shy 0006 0472 0486Fe2+ 0020 0047 3583 3486 1575 1340 0shy 0shy 0shy 0shy 1742 1693Fe3+ 0756 0735 0shy 0shy 0shy 0shy 0284 0248 0035 00300 0666 0747La 0shy 0shy 0shy 0shy 0119 0193 0029 0020 0shy 0shy 0shy 0shyCe 0shy 0shy 0shy 0shy 0246 0237 0025 0013 0shy 0shy 0shy 0shyAl 0073 0054 0228 0276 0shy 0shy 0044 0003 0shy 0shy 0178 0229Si 2003 2007 8000 8000 24000 24000 4000 4000 1942 1958 7951 7845Ti 0052 0057 1963 1961 0145 0086 2871 2964 1963 1966 0110 0141Zr 0shy 0shy 0071 0054 3107 2943 0shy 0shy 0shy 0shy 0shy 0shyNb 0shy 0shy 0066 0078 0630 0740 0005 0024 0056 0049 0shy 0shy

Compositions 1 and 2 aegirine 3 and 4 astrophyllite 5 and 6 eudialyte 7 and 8 lamprophyllite 9 and 10lorenzenite 11 and 12 magnesio-arfvedsoniteAll data this work Fe2+Fe3+ ratio calculated using Drooprsquos (1987) method

TH-RICH LOPARITE

345

structure (Keller 1965 Kovba and Trunov1963) Thorium dititanate (ThTi2O6) occurs intwo polymorphs of monoclinic symmetryStructures of both polymorphs differ from thatof perovskite in being built of sheets of edge-sharing TiO6 octahedra bound by Th atoms ineither six-fold or eight-fold coordination (BalicZIuml unic et al 1984 Ruh and Wadsley 1966)Given the considerable structural differenceloparite and thorium dititanate apparently should

not form a continuous solid solution serieshowever limits of the solubility between thesetwo end-members are unknown Our data suggestat least 23 mol ThTi2O6 is possible

The compositions of Th-rich loparite wererecalculated into major perovskite-group end-members (Mitchell 1996) plus the two thoriumcompounds ThNb4O12 and ThTi2O6 (Table 2Fig 4) The loparite composition evolves bybecoming enriched in the thorium end-members

TABLE 2 Representative compositions of loparite

Wt 1 2 3 4 5 6 7 8 9

Na2O 1043 868 850 742 669 971 918 766 662CaO 153 159 171 150 163 182 208 162 186SrO 140 133 129 133 109 165 177 131 120La2O3 972 888 647 646 541 1142 937 824 579Ce2O3 1477 1421 1119 1027 891 1691 1464 1337 987Pr2O3 186 172 156 nd 114 103 220 254 138Nd2O3 204 202 156 196 186 161 247 198 195ThO2 346 738 1029 1540 1845 234 366 869 1728TiO2 3239 3308 3046 3365 3372 3437 3241 3355 3480FeO 012 007 007 nd 011 007 nd 011 048Nb2O5 2138 2198 2716 2210 2018 1872 2213 2034 1962Ta2O5 037 022 032 043 030 033 049 059 058

Total 9947 10116 10058 10052 9949 9998 10040 10000 10143

Structural formulae (O = 3)Na 0589 0486 0477 0420 0387 0545 0515 0436 0375Ca 0048 0049 0053 0047 0052 0056 0064 0051 0058Sr 0024 0022 0022 0022 0019 0028 0030 0022 0020La 0104 0095 0069 0070 0060 0122 0100 0089 0062Ce 0158 0150 0118 0110 0097 0179 0155 0144 0106Pr 0020 0018 0016 0000 0012 0011 0023 0027 0015Nd 0021 0021 0016 0020 0020 0017 0026 0021 0020Th 0023 0048 0067 0102 0125 0015 0024 0058 0115Ti 0710 0719 0663 0739 0756 0749 0705 0741 0764Fe 0003 0002 0002 0000 0003 0002 0000 0002 0012Nb 0282 0287 0355 0292 0272 0245 0290 0270 0259Ta 0003 0002 0002 0003 0002 0003 0004 0005 0005

Mol end-membersNaCeTi2O66010 5799 4593 4306 4047 6580 6103 5833 4368NaNbO3 2820 2062 2706 2368 2120 2160 2118 1609 1850ThNb4O12 000 868 1017 775 792 290 793 1194 936ThTi2O6 456 546 897 1808 2281 155 043 607 2006CaTiO3 476 500 556 506 557 560 642 529 625SrTiO3 238 225 231 237 203 255 301 228 215

Compositions 1 shy 2 core and 3 shy 5 rim of a zoned loparite crystal KHB-44 6 shy 7 core and 8 shy 9 rim of a zonedloparite crystal KHB-70All data this workTotal Fe expressed as FeO nd = not detected

R H MITCHELL AND A RCHAKHMOURADIAN

346

at essentially constant lueshite content Usingnomenclature principles suggested for the perovs-kite-group minerals by Mitchell (1996) theexamined samples compositionally evolve fromniobian loparite toward niobian thorian andthorian niobian loparite

BetafiteRepresentative analyses of betafite developed

in thorian loparite are given in Table 3 LREEdominated by Ce and Th are the major A-cationsAccording to the classification scheme proposedby Hogarth (1989) for the pyrochlore-groupminerals this mineral should be regarded asceriobetafite or thorium ceriobetafite (LREE gtThgt 20 cation sum at the A sites) In this studywe prefer to refer to the mineral using quotationmarks as lsquoceriobetafitersquo is not approved as adistinct mineral species by the Comission on NewMinerals and Mineral Names of the IMA

At the Khibina complex pyrochlore-groupminerals were previously described as accessoryconstituents of aegirine-feldspar veins (Kozyreva

1990) and peralkaline pegmatites (Kapustin 1989Shilin et al 1966) These minerals correspond topyrochlore sensu stricto that may be somewhatenriched in SrO (Shilin et al 1966) or LREE(Kapustin 1989) Ti-dominant species ie membersof the betafite subgroup have not been previouslyrecognized in the Khibina alkaline complex

BelyankiniteCompositional data on belyankinite and related

Ti-Nb hydroxides available from literature arelimited to a few bulk wet-chemical analyses(Gerasimovskii and Kazakova 1950 Semenov1957 Vlasov et al 1966) Semenov (1957) hassuggested that Ti-dominant belyankinite formssolid solution series with its Mn-analoguemanganbelyankinite and Nb-dominant gerasi-movskite The mineral examined in the presentstudy is a member of the belyankinitendashgerasi-movskite series with negligible content ofmanganbelyankinite (Table 4) A generalizedstructural formula of belyankinite calculated onthe basis of 12 atoms of oxygen is

FIG 3 Variations (apfu) of (a) Na (b) LREE (c) Ca (d) Sr (e) Ti (f) Nb and (g) cation totals at the A and B siteswith respect to Th for Th-rich loparite Circles correspond to loparite KHB-44 squares to KHB-70 Variation of A-cation totals in the solid solution series NaLREETi2O6shy Na2ThTi3O9 is shown by solid line in the series

NaLREETi2O6shy ThTi2O6 by dashed line and in the series NaLREETi2O6shy ThNb4O12 by dash-dotted line (g)

TH-RICH LOPARITE

347

FIG 4 Compositions (mol) of Th-rich loparite in the system loparite (NaCeTi2O6)ndashlueshite (NaNbO3)ndashThTi2O6ndashThNb4O12

R H MITCHELL AND A RCHAKHMOURADIAN

348

(Ca ThLR EE )1 3(T i Nb Si Fe )5O12 nH2O(average of 18 determinations) and approachesthat deduced by Fleischer from Semenovrsquosanalytical data (see reference to Semenov1957) Ca 0 9(T i Zr NbS i )5 5O12 10H2O

However the mineral from Khibina differs fromLovozero belyankinite in having much higherThO2 (up to 2417 wt) and LREE2O3 (up to116 wt) contents both of which are undoubt-edly lsquoinheritedrsquo from the loparite parent

TABLE 3 Representative compositions of lsquoceriobetafitersquo

1 2 3 1 2 3

Wt Structural formulae(SB-cations = 2)

Na2O 101 054 034 Na 0111 0060 0036CaO 179 167 176 Ca 0108 0102 0103SrO 117 115 130 Sr 0038 0038 0041La2O3 579 481 510 La 0121 0101 0103Ce2O3 901 865 846 Ce 0186 0180 0169Nd2O3 152 262 114 Nd 0034 0053 0022ThO2 1965 2088 2041 Th 0244 0270 0253TiO2 3382 3506 3750 Ti 1438 1499 1539Fe2O3 nd 003 047 Fe 0000 0001 0017Nb2O5 2177 1926 1776 Nb 0556 0495 0438Ta2O5 037 034 039 Ta 0006 0005 0006

Total 9540 9501 9463

Compositions 1 and 2 KHB-44 3 KHB-70All data this workTotal Fe expressed as Fe2O3 nd = not detected

TABLE 4 Representative compositions of belyankinite

1 2 1 2

Wt Structural formulae(O = 24)

Na2O 003 028 Na 0014 0122CaO 412 162 Ca 1027 0402MgO 016 017 Mg 0055 0060MnO 011 028 Mn 0022 0053La2O3 208 200 La 0179 0169Ce2O3 862 221 Ce 0733 0186Nd2O3 081 076 Nd 0067 0062ThO2 1242 2417 Th 0657 1264SiO2 1303 1221 Si 3033 2805TiO2 2281 2473 Ti 3991 4273Al2O3 121 166 Al 0331 0450Fe2O3 616 507 Fe 1078 0877Nb2O5 1502 1587 Nb 1578 1649

Total 8658 9103

Compositions 1 and 2 replacement mantles on thorian loparite KHB-70Total Fe expressed as Fe2O3 ZrO2 was sought but not found

TH-RICH LOPARITE

349

X-ray powder diffractometry

An XRD powder pattern of a sample of the coreof a thorian loparite showed only a few faintdiffraction lines with relatively high d-spacingswhereas a rim sample appeared to be completelymetamict After heating to 7008C for 1 hour thecore and rim samples gave XRD powder patterns(Table 5) similar to those of La-dominantsynthetic loparite NaLaTi2O6 and lsquoirinitersquo asdescribed by Borodin and Kazakova (1954) Theformer has been proposed to have the undistortedcubic lattice (ASTM 39-65 Belous et al 1985)However Rietveld refinement of an XRD powderpattern of NaLaTi2O6 suggests that thiscompound is orthorhombic (space group Pnma)rather than cubic (Mitchell and Chakhmouradianin preparation) The pattern of the rim sample ofthorian loparite also includes three diffractionlines with d-spacings of 295 1795 and 1535 AEcirc that cannot be produced by the perovskite-typestructure These are characteristic of pyrochlore-type phases and correspond to the most intenselines 222 440 and 622 respectively (ASTM 13-197 ASTM 17-746)

Data available from the literature show thatXRD powder patterns similar to those obtained inthis study are produced by naturally occurringloparite of various Nb2O5 CaO Na2O TiO2 andSrO contents (Haggerty and Mariano 1983Kostyleva-Labuntsova et al 1978b Mitchell etal 1996) Given a significant difference in ionicradius between Th4+ Na+ and Ce3+ (121 139and 134 AEcirc respectively Shannon 1976) it isexpected that Th-rich loparite should have astrongly distorted perovskite-type structureHowever the obtained patterns (Table 5) do notexhibit lsquoextrarsquo diffraction lines reflecting cationordering or geometric distortion of the ideal cubicperovskite-type lattice Such diffraction lines eg769 shy 790 344shy 350 257shy 260 187 shy 189 AEcirc are present in patterns of most syntheticperovskite-type titanates and niobates with Th4+

localized at the A sites (Keller 1965 Kovba andTrunov 1963 Labeau and Joubert 1978 Zhu andHor 1995) The only known exceptions so far arecompounds from the Na06shy 08Th01 shy 02NbO3

range of the NaNbO3shy Th025NbO3 solid solutionseries (ASTM-34-1068 Labeau and Joubert1978 Table III)

TABLE 5 X-ray diffraction patterns of loparite lsquoirinitersquo and Th-rich loparite

1 2 3 4 5hkl d IIo d IIo d IIo d IIo d IIo

100 3870 2110 2730 100 271 100 276 100 264 100 272 100111 2225 50200 1933 92 1919 90 1950 10 1905 30 1925 40

1860 200b211 1578 95 1569 80 1598 30 1562 60 1575 60

1503 10220 1367 70 1360 40 1383 20 1355 30 1368 30300 1290 4310 1225 25 1216 30 1233 15 1214 20 1222 20311 1168 8 1197 10222 1117 13 1111 5 1118 5320 1075 3321 1035 38 1028 60 1042 20 1029 10 1034 10400 09680 5411 0908 10 0912 5420 0864 10 0865 5332 08245 5 08260 3422 07910 3

1 synthetic NaLaTi2O6 a = 3873 AEcirc (ASTM 39-65) 2 lsquoirinitersquo (heated) a = 383 AEcirc (Borodin and Kazakova 1954)3 thorian loparite KHB-70 core (unheated) a = 3902(2) AEcirc 4 thorian loparite KHB-70 core (heated) a = 3841(1)AEcirc 5 thorian loparite KHB-70 rim (heated) a = 3867(2) AEcirc + 3 weak lines with d = 295 1795 1535 AEcirc (3-5 thiswork) b = broad line

R H MITCHELL AND A RCHAKHMOURADIAN

350

The absence of superstructure reflections in thepatterns of thorian loparite may result from itsmetamict state prior to heating ie from failure torestore an initial apparently distorted structure ofthe mineral Alternatively stabilization of thecubic structure may result from the presence ofminor cations in thorian loparite eg Ca or SrThis phenomenon refered to as stabilized poly-morphism (Smirnova and Belov 1969) is well-known for TiO2 and ZrO2 polymorphs (Filatovand Frank-Kamenetskii 1969 Grunin et al1983) To select between the two abovealternatives experimental studies of the solidsolution series between loparite and Th-bearingend-members are being undertaken by us

Discussion

At Khibina Th-rich loparite occurs only inrelation to the foyaite series (Borodin andKazakova 1954 Chakhmouradian and Mitchell1998 Kozyreva et al 1991 Tikhonenkova et al1982) Zoned Th-rich loparite examined in thisstudy crystallized at a late deuteric stage of theformation of foyaite pegmatites At this stagefluids enriched in Ti and incompatible elements(Zr Nb Sr LREE Th) gave rise to theassemblage of aegirine with loparite eudialyteand Ti-silicates (astrophyllite lorenzenitelamprophyllite) In a similar paragenesis lopariteoccurs in the foyaite pegmatites at MtNiorkpakhk (east of Mt Eveslogchorr) andkhibinite pegmatites at a number of localities inwestern Khibina (Chakhmouradian and Mitchell1998) In most of these occurrences loparite isrelatively Th-poor and compositionally evolvesby enrichment in Na2O and Nb2O5 and depletionin LREE2O3 and TiO2 contents toward the rimThis trend coincides with the main magmatictrend of the compositional evolution of loparite int h e n e p h e l i n e - s y e n i t e c o m p l e x e s(Chakhmouradian and Mitchell 1998 Mitchelland Chakhmouradian 1996) The evolutionarytrend from niobian loparite to thorian niobianloparite recognized in the present study has notbeen previously observed in alkaline rocksLoparite from fenite-type rocks of the ParanaBasin carbonatite complexes has high ThO2

contents (up to 62 wt) accompanied byenrichment in Na2O and Nb2O5 (lueshite) anddepletion in SrO and TiO2 (tausonite) (Mitchell1996 Table 36) Th-enrichment (up to 49 wtThO2) in the composition of perovskite from thecarbonatite complexes of the Kola Peninsula is

coupled with increasing LREE2O3 Na2O andNb2O5 ie loparite and lueshite components(Chakhmouradian and Mitchell 1997) In thePolino carbonatite Th-bearing (15 shy 17 wtThO2) perovskite has high Fe2O3 and ZrO2

contents (Lupini et al 1992)The limits of solubility between loparite

(NaLREETi2O6) and the thorium end-membercompositions ThNb4O12 Na23Th13TiO3 andThTi2O6 are unknown From structural data(Balic ZIuml unic et al 1984 Kovba and Trunov1963 Ruh and Wadsley 1966 Zhu and Hor1995) it is expected that loparite forms acomplete solid solution series with the formertwo compounds and only a limited series withThTi2O6 Experimental studies of the NaLaTi2O6

-ThNb4O12 NaLaTi2O6ndashNa2ThTi3O9 andNaLaTi2O6ndashThTi2O6 systems are being under-taken by the authors of this paper

As evidenced by textural relationships andcompositional data the appearance of Na-poorTh-rich lsquoceriobetafitersquo and belyankinite asmantles on thorian loparite was a result ofmetasomatic processes involving alkali-cationleaching and hydration Note that the sameprocesses brought about the replacement ofnepheline and alkali feldspar present as relics infibrous aegirine by zeolites and eventually bygibbsite Metasomatites including albitites albite-aegirine and albite-astrophyllite rocks are verycommon in the vicinity of pegmatite veinscontaining thorian loparite at Mt EveslogchorrHydrothermal solutions responsible for themetasomatic alteration most probably werederived from the phonolitic magma whichproduced the differentiated intrusion of nephelinesyenites including foyaite and its precursorkhibinite An alternative source of such solutionscould be a foidolite melt as some authors suggestthat the foidolites were emplaced later than thenephel ine syenite intrusion (Kostyleva-Labuntsova et al 1978a Sniatkova et al 1986)

Conclusions

In Na-LREE-Ti-dominant species of the perovs-kite group Th4+ cations occupy large twelve-coordinated A sites in the structure Theaccommodation of Th into the structure isaccompanied by appearance of vacancies at theA sites at the expense of Na LREE and SrThorian loparite is essentially a member of theloparite (NaLREETi2O6)ndashlueshite (NaNbO3)ndashThTi2O6ndashThNb4O12 quaternary system with low

TH-RICH LOPARITE

351

or negligible contents of other end-membercompositions The mineral compositionallyevolves from niobian loparite to niobian thorianand thorian niobian loparite Metasomatic altera-tion of thorian loparite gave rise to lsquoceriobetafitersquoand belyankinite with high ThO2 content Thorianloparite is metamict or partly metamict and uponheating regains a structure close to that ofsynthetic loparite NaLaTi2O6

Acknowledgements

This work was supported by the Natural Sciencesand Engineering Research Council of Canada andLakehead University Ontario (RHM ARC) ARCalso acknowledges support from St PetersburgState University Russia (grant Evolution offramework niobium-titanium oxides in carbona-tite-bearing nepheline-syenite complexes) AlanMacKenzie and Keith Pringnitz are thanked fortheir assistance with the analytical work AnnHammond and Sam Spivak are thanked for thinsection preparation and drafting services respec-tively

References

Balic ZIuml unic T SIuml cavnicIuml ar S and Grobenski Z (1984)The structure of thorium (IV) dititanium (IV) oxideThTi2O6 Croat Chem Acta 57 645 shy 51

Belous AG Novitskaya GN Gavrilova LGPolyanetskaya SV and Makarova ZYa (1985)Lanthanum titanate-zirconates with the perovskitestructure Sov Prog Chem 51 13 shy 15

Borodin LS (1954) On accommodation of water in thecrystal lattice of perovskite-group minerals DokladyAN SSSR 95 (in Russian) 873 shy 5

Borodin LS and Kazakova ME (1954) Irinite shy anew mineral from the perovskite group Doklady ANSSSR 97 (in Russian) 725 shy 8

Chakhmouradian AR and Mitchell RH (1997)Compositional variation of perovskite-group miner-als from the carbonatite complexes of the KolaAlkaline Province Russia Canad Mineral 351293 shy 310

Chakhmouradian AR and Mitchell RH (1998)Compositional variation of perovskite-group miner-als from the Khibina alkaline complex KolaPeninsula Canad Mineral 36 (in press)

Filatov SK and Frank-Kamenetskii VA (1969)Structural characteristics of cubic ZrO2 stabilizedby calcium Sov Phys Cryst 14 414 shy 5

Galakhov AV (1975) The petrology of the KhibinaAlkaline Massif Nauka Press Leningrad (in

Russian) 256 ppGerasimovski i VI and Kazakova ME (1950)

Belyankinite shy a new mineral Doklady AN SSSR 71 (in Russian) 925 shy 7

Grunin VS Razumenko MV Patrina IV FilatovSK and Alekseyeva TV (1983) Mode of existenceand abundance of TiO2-rutile anatase and brookiteDoklady Earth Sci Sect 268 149 shy 50

Haggerty SE and Mariano AN (1983) Strontian-loparite and strontio-chevkinite two new minerals inrheomorphic fenites from the Parana Basin carbona-tites South America Contrib Mineral Petrol 84365 shy 81

Hogarth DD (1961) A study of pyrochlore andbetafite Canad Mineral 6 610 shy 33

Hogarth DD (1989) Pyrochlore apatite and amphi-bole distinctive minerals in carbonatites InCarbonat ites (K Bell ed) Unwyn HymanLondon 105 shy 48

Kapustin YuL (1989) Rare earth-bearing pyrochlorefrom peralkaline pegmatites of the Khibina massifNew data on minerals (Trudy Mineral Muz ANSSSR ) 36 (in Russian) 155 shy 61

Keller C (1965) Die Reaktion der Dioxide derElemente Thorium bis Americium mit Niob- undTantalpentoxid (The reaction of dioxides of theelements from thorium to americium with niobiumand tantalum pentoxides) J Inorg Nucl Chem 271233 shy 46

Kogarko LN Kononova VA Orlova MP andWoolle y AR (1995 ) Alkaline Rocks andCarbonatites of the World Part 2 Former USSRChapman amp Hall London UK 226 pp

Kostyleva-Labuntsova EE Borutskii BE SokolovaMN Shliukova ZV Dorfman MD DudkinOB Kozyreva LV and Ikorskii SV (1978a) TheMineralogy of the Khibina Massif Vol 1 NaukaPress Moscow (in Russian) 228 p

Kostyleva-Labuntsova EE Borutskii BE SokolovaMN Shliukova ZV Dorfman MD DudkinOB Kozyreva LV and Ikorskii SV (1978b) TheMineralogy of the Khibina Massif Vol 2 NaukaPress Moscow (in Russian) 588 p

Kovba LM and Trunov VK (1962) Double oxidescontaining tungsten tantalum or niobium DokladyAN SSSR 147 (in Russian) 622 shy 4

Kozyreva LV (1990) Aegirine-feldspar veins in thenorth-eastern part of the Khibina massif In AlkalineMagmatism in the North-eastern Part of the BalticShield Kola Sci Centre Press Apatity (in Russian)42 shy 56

Kozyreva LV Menrsquoshikov YuP and Lednev AI(1991) Loparite mineralization of the Khibinamassif In New Data on the Rare-metalMineralogy of the Kola Peninsula Kola SciCentre Press Apatity (in Russian) 37 shy 44

R H MITCHELL AND A RCHAKHMOURADIAN

352

(130 wt ThO2) loparite (termed lsquoirinitersquo) withminor amounts of Fe2O3 and CaO in a foyaitepegmatite at Mt Eveslogchorr in the Khibinaalkaline complex Kola Peninsula The structuralformula deduced from bulk wet-chemical analysisindicated that this mineral had significant cationdeficiency at the A sites which was associatedwith O2shy gt (OH)shy substitution (Borodin andKazakova 1954) Recent studies of loparitemineral iza tion at the Khibina complex(Kozyreva et al 1991 Tikhonenkova et al1982) also report the occurrence of Th-richloparite in foyaite or related pegmatites Parkerand Sharp (1970) have described rsquoirinitersquo as anaccessory constituent of vermiculite rock at theGem Park Complex Colorado However identi-fication of this mineral as lsquoirinitersquo was basedmerely on its metamict state and resemblance ofthe X-ray diffraction pattern of the heated sampleto that of Borodin and Kazakovarsquos (1954)material (Parker and Sharp 1970) Perovskitewith ThO2 content of up to 17 wt occurs in thePolino carbonatite diatreme Italy (Lupini et al1992) and up to 49 wt in the carbonatitecomplexes of Kola Peninsula (Chakhmouradianand Mitchell 1997) Finally fenite-like rocks inthe carbonatite complexes of the Parana BasinSouth America host loparite of widely varyingSrO Na2O Nb2O5 LREE2O3 and ThO2 (up to 62wt) contents (Mitchell 1996)

Initial synthesis of Th-bearing perovskite-typeoxides produced compounds of the type AThO3 (A= Ca Sr Ba Pb) in which Th4+ occupiesoctahedrally-coordinated B-sites (Naray-Szabo1947 Smith and Welch 1960) SubsequentlyKovba and Trunov (1962) synthesized a series ofniobates and tantalates accommodating Th U andCe4+ at twelve-coordinated A-sites in theperovskite structure These compounds werehighly cation-deficient relative to ideal ABX3

perovskite having the general formula A14BO3 (A= Th U Ce B = Nb Ta) Trunov and Kovba(1963) also prepared perovskite-type tungstates ofTh tolerating even higher cation deficiency at theA sites ie Th14WO3 to Th130WO3 Othersynthetic perovskites with A-site Th includeCaThV2O6 and SrThV2O6 (Vidyasagar andGopalakrishnan 1982) Na23Th13TiO3 (Zhu andHor 1995) and the solid solution seriesNaNbO3 shy Th025NbO3 (Labeau and Joubert1978) The above examples demonstrate that (i)Th4+ in perovskite-type compounds may occupyeither twelve-coordinated A sites or smalleroctahedral B sites depending on the type of

associated cations (ii) accommodation of Th inthe perovskite structure may or may not beaccompanied by the appearance of vacancies atthe A sites

The current study was undertaken to determinehow Th is accommodated in the structure ofloparite a Na-LREE-Ti member of the perovskitefamily containing significant amounts of Nb Caand Sr A second objective was to study theparagenesis of Th-rich loparite

Analytical methods

All mineral compositions were determined by X-ray energy-dispersion spectrometry using aHitachi 570 scanning electron microscopeequipped with a LINK ISIS analytical systemincorporating a Super ATW Light ElementDetector (133 eV FwHm MnK) at LakeheadUniversity Ontario EDS spectra of loparitebetafite and belyankinite were acquired for 300seconds and those of silicates for 100 seconds(live time) with an accelerating voltage of 20 kVand beam current of 086 nA The following well-characterizednatural and synthetic standards wereemployed for the determination of mineralcompositions Khibina loparite (Na LREE Nb)Magnet Cove perovskite (Ca Fe Ti) jadeite (AlSi) periclase (Mg) orthoclase (K) manganoanfayalite (Mn) synthetic SrTiO3 (Sr) BaSiO3 (Ba)metallic Th Ta and Zr The accuracy of themethod was cross-checked by wave-length-dispersion electron microprobe analysis using anautomated CAMECA SX-50 microprobe locatedat the University of Manitoba following methodsdescribed by Mitchell and Vladykin (1993)

X-ray diffraction (XRD) powder patterns (Curadiation) were obtained with a Philips 3710diffractometer at Lakehead University using aPhilips Debye-Scherer type camera with adiameter of 1146 mm The diffractometer wasoperated at 40 kV and 25 mA Relative intensitiesof the diffraction lines were estimated visuallyfrom the films

Infra-red transmission spectra were recordedwith a FTIR spectrometer IFS-66 equipped with amicroscope Spectra were obtained on 02shy 03mm thick unfractured slabs of loparite from 256scans using the 03-mm aperture of the micro-scope For each measurement the referencespectrum was obtained from 256 scans at thesame operating conditions in order to eliminatethe effect of H2O vapour apparently present in thespectrometer

R H MITCHELL AND A RCHAKHMOURADIAN

342

Occurrence

Until recently loparite with the ThO2 content ofmore than 10 wt has been recognized only fromthe Khibina alkaline complex in the KolaPeninsula Russia Its occurrence is restrictedmainly to foyaite and related pegmatoid andmetasomatic rocks comprising the central part ofthe Khibina pluton The general geologypetrology and mineralogy of the complex havebeen described in detail by Galakhov (1975)Kostyleva-Labuntsova et al (1978ab) Zak et al(1972) and summarized by Kogarko et al (1995)

Th-rich loparite examined in the current studyoccurs in foyaite pegmatites exposed on thesouthern slope of Mt Eveslogchorr southKhibina Most of the pegmatites are simplepoorly-differentiated veins emplaced into fine-to-medium grained nepheline syenite of gneissoidtexture The veins are composed mainly of alkalifeldspar nepheline aegirine and astrophylliteThe latter two minerals occur in intimate inter-growths as fibrous or radial aggregates partly orentirely replacing the earlier formed paragenesisof alkali feldspar and nepheline In Russianmineralogical literature the late-stage zones of

fibrous aegirine in nepheline-syenite pegmatitesare commonly interpreted as being of deuteric(lsquoautome tasoma ticrsquo ) or igin (Kostyl eva -Labuntsova et al 1978a) The aegirine-astro-phyllite aggregate encloses numerous irregular- orlens-shaped polygranular segregationsof analcitephillipsite natrolite and gibbsite plus Fe-hydr-oxides These segregations commonly containrelics of nepheline and undoubtedly representalteration products of the latter Accessoryminerals developed in the aegirine-astrophylliteaggregate are eudialyte loparite lamprophyllitelorenzenite and rare magnesio-arfvedsoniteRepresentative compositions of the major andaccessory silicates from the aegirine-astrophylliterock are given in Table 1

In the aegirine-astrophyllite aggregate lopariteoccurs as lsquofluoritersquo-type interpenetration twinsranging from 3 shy 7 mm across The mineral isdeep reddish-brown in thin sections andcommonly has a yellow-coloured rim up to03 mm in thickness Some loparite crystalspoikilitically enclose fine (less than 10 mm)needles of aegirine In this study we examinedzoned crystals of loparite from two pegmatiteveins KHB-44 and KHB-70

FIG 1 Back-scattered electron images of a zoned Th-rich loparite crystal (a) rim of thorian niobian and niobianthorian loparite (light grey) on niobian loparite (dark grey) scale bar is 400 mm (b) lsquoceriobetafite rsquo (dark grey)

developed along fractures and margins of thorian niobian loparite (light grey) scale bar is 30 mm

TH-RICH LOPARITE

343

Phase relationships

Back-scattered electron (BSE) imagery combinedwith line scanning reveals that loparite crystalsexhibit strong compositional zonation reflectingenrichment in ThO2 from the core towards the rim(Fig 1a) The Th-rich rims of the crystals areheterogeneous and consist of two phases Phase 1having a lower average atomic number isdeveloped as dendrite-like narrow (3 shy 30 mm)zones decorating margins of the crystals andfractures within phase 2 (Fig 1b) Compositiondeterminations show that both phases havecomparable CaO SrO LREE2O3 TiO2 andNb2O5 (Ti gt Nb) contents However phase 1gives low analysis totals (936-970 wt) andcontains considerably less Na2O (03shy 10 wt)and generally more ThO2 (178shy 220 wt) thanphase 2 X-ray diffraction study (see below)demonstrates that phase 1 comprising the bulkof the sample extracted from the rim of the crystalis loparite Three lsquoadditionalrsquo weak diffractionlines observed on the XRD film could not beassigned to loparite or any structure derived fromthe perovskite parent but corresponded well withthe three strongest diffraction lines of betafite(ASTM 13-197 Hogarth 1961)

Infrared transmission spectra recorded from thecore and rim of a loparite crystal are compared inFig 2(ab) Both spectra show a broad absorptionband at 650shy 900 cmshy 1 This band corresponds tobond vibrations in the octahedral complexes(TiNb)O6 and is typical of various perovskite-and pyrochlore-group minerals (Kostyleva-Labuntsova et al 1978b Pilipenko et al 1971)and their synthetic analogues (Nyquist and Kagel

1971 Sych et al 1973) The relative position ofthis absorption band in the spectrum depends onthe Ti vs Nb ratio of the mineral Splitting of the(TiNb)O6 band commonly observed in theinfrared spectra of low-symmetry perovskite-type compounds (Pilipenko et al 1971 Sych etal 1973) is not observed in our spectra(Fig 2ab) Similar coalescence of severalabsorption lines into one broad band has beenobserved in metamict pyrochlore (Krivokonevaand Sidorenko 1971) In addition to the(TiNb)O6 absorption band the infrared spectrumof the rim (Fig 2b) contains bands at 1650 23303300shy 3320 and 3530 cm shy 1 the latter twopartially overlapping each other The OHstretching bands at 3300shy 3320 and 3530 cmshy 1

and Nb shy OH band at 1650 cmshy 1 are characteristicof pyrochlore-group minerals (Voloshin et al1989) and most probably result from micro-intergrowths of ceriobetafite in the studiedsamples In the current study we could notassign the absorption band at 2330 cmshy 1

As evidenced by back-scattered electronimagery loparite from the vein KHB-70 hasundergone further alteration giving rise to thecomplex Ti hydroxide belyankinite The mineraloccurs as thin (20shy 30 mm) replacement mantleson loparite Its Nb-dominant analogue gerasi-movskite forms rare rectangularplates enclosed infibrous aegirine Both minerals have beeninsufficiently studied and were originallydescribed in peralkaline pegmatites of theLovozero alkaline complex Kola Peninsulawhere they occur predominantly as pseudomorphsafter titanium-silicates (Gerasimovskii andKazakova 1950 Semenov 1957)

Composition

LopariteRepresentative compositions of zoned loparite

crystals are given in Table 2 From core to rimloparite compositionally evolves by enrichment inThO2 and depletion in Na2O LREE2O3 and SrO(Table 2) In order to reveal possible end-membercompositions which may account for the accom-modation of Th in the structure of lopariterelationships between the amounts of Th (apfu)and other major elements (Fig 3) were analysedWith strongly decreasing Na LREE and to a lesserdegree Sr and increasing Th (Fig 3abd) theoccupancy of the B sites remains relativelyunchanged (Fig 3ef) As the most Th-richcompositions also exhibit the greatest cation

FIG 2 Infra-red transmission spectra of Th-rich loparite(a) core sample (b) rim sample

R H MITCHELL AND A RCHAKHMOURADIAN

344

deficiency (Fig 3g) it is deduced that Th4+ cationsare accommodatedat the A site of loparite and thatthe correspondingsubstitution scheme involves theappearance of vacancies at these sites Calculationsshow that the observed relationship between Thcontent and number of vacancies at the A-site mostclosely corresponds to the solid solution seriesbetween loparite and two hypothetical end-members ThNb4O12 and ThTi2O6 (Fig 3) Theso l id solu t ion se r ies between lopari te

NaLREETi2O6 and Na23Th13TiO3 believed tobe present is not present as the A- and B-sitesoccupancy remains constant The isomorphicsubstitutions are as follows

2Na+ + 2LREE3+ + 4Ti4+ gtTh4+ + 3amp + 4Nb5+ (1)

Na+ + LREE3+ gt Th4+ + amp (2)

ThNb4O12 (= Th025NbO3) has been synthe-sized and shown to have a perovskite-type

TABLE 1 Representative compositions of major and accessory silicate minerals

Wt 1 2 3 4 5 6 7 8 9 10 11 12

Na2O 1281 1220 227 216 1124 1094 1066 1104 1707 1696 889 871K2O 004 008 602 606 041 035 064 061 nd nd 204 218CaO 225 267 141 155 929 879 045 040 005 008 056 067SrO na na nd nd 149 118 1306 1162 nd nd na naBaO na na nd nd nd nd 085 322 nd nd na naMgO 102 103 189 191 009 037 043 045 035 023 820 808MnO 037 039 1292 1329 383 452 558 526 nd 012 373 383FeO 060 136 1904 1850 392 324 na na na na 1393 1351Fe2O3 2670 2535 na na na na 293 250 080 069 592 662La2O3 na na nd nd 067 106 060 042 na na na naCe2O3 na na nd nd 140 131 052 026 na na na naAl2O3 165 117 086 104 nd nd 029 002 nd nd 101 130SiO2 5326 5196 3555 3550 4995 4852 3100 3035 3331 3382 5320 5236TiO2 181 197 1160 1157 040 023 2959 2991 4479 4516 098 125ZrO2 na na 065 049 1326 1220 nd nd nd nd na naNb2O5 na na 065 077 290 331 009 041 212 188 na na

Total 10052 9818 9286 9284 9885 9602 9669 9647 9849 9894 9846 9851

Structural formulaeO = 6 Si = 8 Si = 24 Si = 4 O = 9 O = 23

Na 0934 0913 0990 0944 10471 10492 2667 2821 1929 1904 2576 2530K 0002 0004 1728 1742 0251 0221 0105 0103 0shy 0shy 0389 0417Ca 0091 0111 0340 0374 4782 4658 0062 0056 0003 0005 0090 0107Sr 0shy 0shy 0shy 0shy 0415 0338 0977 0888 0shy 0shy 0shy 0shyBa 0shy 0shy 0shy 0shy 0shy 0shy 0043 0166 0shy 0shy 0shy 0shyMg 0057 0059 0634 0642 0064 0273 0083 0088 0030 0020 1827 1804Mn 0012 0013 2463 2537 1559 1894 0610 0587 0shy 0006 0472 0486Fe2+ 0020 0047 3583 3486 1575 1340 0shy 0shy 0shy 0shy 1742 1693Fe3+ 0756 0735 0shy 0shy 0shy 0shy 0284 0248 0035 00300 0666 0747La 0shy 0shy 0shy 0shy 0119 0193 0029 0020 0shy 0shy 0shy 0shyCe 0shy 0shy 0shy 0shy 0246 0237 0025 0013 0shy 0shy 0shy 0shyAl 0073 0054 0228 0276 0shy 0shy 0044 0003 0shy 0shy 0178 0229Si 2003 2007 8000 8000 24000 24000 4000 4000 1942 1958 7951 7845Ti 0052 0057 1963 1961 0145 0086 2871 2964 1963 1966 0110 0141Zr 0shy 0shy 0071 0054 3107 2943 0shy 0shy 0shy 0shy 0shy 0shyNb 0shy 0shy 0066 0078 0630 0740 0005 0024 0056 0049 0shy 0shy

Compositions 1 and 2 aegirine 3 and 4 astrophyllite 5 and 6 eudialyte 7 and 8 lamprophyllite 9 and 10lorenzenite 11 and 12 magnesio-arfvedsoniteAll data this work Fe2+Fe3+ ratio calculated using Drooprsquos (1987) method

TH-RICH LOPARITE

345

structure (Keller 1965 Kovba and Trunov1963) Thorium dititanate (ThTi2O6) occurs intwo polymorphs of monoclinic symmetryStructures of both polymorphs differ from thatof perovskite in being built of sheets of edge-sharing TiO6 octahedra bound by Th atoms ineither six-fold or eight-fold coordination (BalicZIuml unic et al 1984 Ruh and Wadsley 1966)Given the considerable structural differenceloparite and thorium dititanate apparently should

not form a continuous solid solution serieshowever limits of the solubility between thesetwo end-members are unknown Our data suggestat least 23 mol ThTi2O6 is possible

The compositions of Th-rich loparite wererecalculated into major perovskite-group end-members (Mitchell 1996) plus the two thoriumcompounds ThNb4O12 and ThTi2O6 (Table 2Fig 4) The loparite composition evolves bybecoming enriched in the thorium end-members

TABLE 2 Representative compositions of loparite

Wt 1 2 3 4 5 6 7 8 9

Na2O 1043 868 850 742 669 971 918 766 662CaO 153 159 171 150 163 182 208 162 186SrO 140 133 129 133 109 165 177 131 120La2O3 972 888 647 646 541 1142 937 824 579Ce2O3 1477 1421 1119 1027 891 1691 1464 1337 987Pr2O3 186 172 156 nd 114 103 220 254 138Nd2O3 204 202 156 196 186 161 247 198 195ThO2 346 738 1029 1540 1845 234 366 869 1728TiO2 3239 3308 3046 3365 3372 3437 3241 3355 3480FeO 012 007 007 nd 011 007 nd 011 048Nb2O5 2138 2198 2716 2210 2018 1872 2213 2034 1962Ta2O5 037 022 032 043 030 033 049 059 058

Total 9947 10116 10058 10052 9949 9998 10040 10000 10143

Structural formulae (O = 3)Na 0589 0486 0477 0420 0387 0545 0515 0436 0375Ca 0048 0049 0053 0047 0052 0056 0064 0051 0058Sr 0024 0022 0022 0022 0019 0028 0030 0022 0020La 0104 0095 0069 0070 0060 0122 0100 0089 0062Ce 0158 0150 0118 0110 0097 0179 0155 0144 0106Pr 0020 0018 0016 0000 0012 0011 0023 0027 0015Nd 0021 0021 0016 0020 0020 0017 0026 0021 0020Th 0023 0048 0067 0102 0125 0015 0024 0058 0115Ti 0710 0719 0663 0739 0756 0749 0705 0741 0764Fe 0003 0002 0002 0000 0003 0002 0000 0002 0012Nb 0282 0287 0355 0292 0272 0245 0290 0270 0259Ta 0003 0002 0002 0003 0002 0003 0004 0005 0005

Mol end-membersNaCeTi2O66010 5799 4593 4306 4047 6580 6103 5833 4368NaNbO3 2820 2062 2706 2368 2120 2160 2118 1609 1850ThNb4O12 000 868 1017 775 792 290 793 1194 936ThTi2O6 456 546 897 1808 2281 155 043 607 2006CaTiO3 476 500 556 506 557 560 642 529 625SrTiO3 238 225 231 237 203 255 301 228 215

Compositions 1 shy 2 core and 3 shy 5 rim of a zoned loparite crystal KHB-44 6 shy 7 core and 8 shy 9 rim of a zonedloparite crystal KHB-70All data this workTotal Fe expressed as FeO nd = not detected

R H MITCHELL AND A RCHAKHMOURADIAN

346

at essentially constant lueshite content Usingnomenclature principles suggested for the perovs-kite-group minerals by Mitchell (1996) theexamined samples compositionally evolve fromniobian loparite toward niobian thorian andthorian niobian loparite

BetafiteRepresentative analyses of betafite developed

in thorian loparite are given in Table 3 LREEdominated by Ce and Th are the major A-cationsAccording to the classification scheme proposedby Hogarth (1989) for the pyrochlore-groupminerals this mineral should be regarded asceriobetafite or thorium ceriobetafite (LREE gtThgt 20 cation sum at the A sites) In this studywe prefer to refer to the mineral using quotationmarks as lsquoceriobetafitersquo is not approved as adistinct mineral species by the Comission on NewMinerals and Mineral Names of the IMA

At the Khibina complex pyrochlore-groupminerals were previously described as accessoryconstituents of aegirine-feldspar veins (Kozyreva

1990) and peralkaline pegmatites (Kapustin 1989Shilin et al 1966) These minerals correspond topyrochlore sensu stricto that may be somewhatenriched in SrO (Shilin et al 1966) or LREE(Kapustin 1989) Ti-dominant species ie membersof the betafite subgroup have not been previouslyrecognized in the Khibina alkaline complex

BelyankiniteCompositional data on belyankinite and related

Ti-Nb hydroxides available from literature arelimited to a few bulk wet-chemical analyses(Gerasimovskii and Kazakova 1950 Semenov1957 Vlasov et al 1966) Semenov (1957) hassuggested that Ti-dominant belyankinite formssolid solution series with its Mn-analoguemanganbelyankinite and Nb-dominant gerasi-movskite The mineral examined in the presentstudy is a member of the belyankinitendashgerasi-movskite series with negligible content ofmanganbelyankinite (Table 4) A generalizedstructural formula of belyankinite calculated onthe basis of 12 atoms of oxygen is

FIG 3 Variations (apfu) of (a) Na (b) LREE (c) Ca (d) Sr (e) Ti (f) Nb and (g) cation totals at the A and B siteswith respect to Th for Th-rich loparite Circles correspond to loparite KHB-44 squares to KHB-70 Variation of A-cation totals in the solid solution series NaLREETi2O6shy Na2ThTi3O9 is shown by solid line in the series

NaLREETi2O6shy ThTi2O6 by dashed line and in the series NaLREETi2O6shy ThNb4O12 by dash-dotted line (g)

TH-RICH LOPARITE

347

FIG 4 Compositions (mol) of Th-rich loparite in the system loparite (NaCeTi2O6)ndashlueshite (NaNbO3)ndashThTi2O6ndashThNb4O12

R H MITCHELL AND A RCHAKHMOURADIAN

348

(Ca ThLR EE )1 3(T i Nb Si Fe )5O12 nH2O(average of 18 determinations) and approachesthat deduced by Fleischer from Semenovrsquosanalytical data (see reference to Semenov1957) Ca 0 9(T i Zr NbS i )5 5O12 10H2O

However the mineral from Khibina differs fromLovozero belyankinite in having much higherThO2 (up to 2417 wt) and LREE2O3 (up to116 wt) contents both of which are undoubt-edly lsquoinheritedrsquo from the loparite parent

TABLE 3 Representative compositions of lsquoceriobetafitersquo

1 2 3 1 2 3

Wt Structural formulae(SB-cations = 2)

Na2O 101 054 034 Na 0111 0060 0036CaO 179 167 176 Ca 0108 0102 0103SrO 117 115 130 Sr 0038 0038 0041La2O3 579 481 510 La 0121 0101 0103Ce2O3 901 865 846 Ce 0186 0180 0169Nd2O3 152 262 114 Nd 0034 0053 0022ThO2 1965 2088 2041 Th 0244 0270 0253TiO2 3382 3506 3750 Ti 1438 1499 1539Fe2O3 nd 003 047 Fe 0000 0001 0017Nb2O5 2177 1926 1776 Nb 0556 0495 0438Ta2O5 037 034 039 Ta 0006 0005 0006

Total 9540 9501 9463

Compositions 1 and 2 KHB-44 3 KHB-70All data this workTotal Fe expressed as Fe2O3 nd = not detected

TABLE 4 Representative compositions of belyankinite

1 2 1 2

Wt Structural formulae(O = 24)

Na2O 003 028 Na 0014 0122CaO 412 162 Ca 1027 0402MgO 016 017 Mg 0055 0060MnO 011 028 Mn 0022 0053La2O3 208 200 La 0179 0169Ce2O3 862 221 Ce 0733 0186Nd2O3 081 076 Nd 0067 0062ThO2 1242 2417 Th 0657 1264SiO2 1303 1221 Si 3033 2805TiO2 2281 2473 Ti 3991 4273Al2O3 121 166 Al 0331 0450Fe2O3 616 507 Fe 1078 0877Nb2O5 1502 1587 Nb 1578 1649

Total 8658 9103

Compositions 1 and 2 replacement mantles on thorian loparite KHB-70Total Fe expressed as Fe2O3 ZrO2 was sought but not found

TH-RICH LOPARITE

349

X-ray powder diffractometry

An XRD powder pattern of a sample of the coreof a thorian loparite showed only a few faintdiffraction lines with relatively high d-spacingswhereas a rim sample appeared to be completelymetamict After heating to 7008C for 1 hour thecore and rim samples gave XRD powder patterns(Table 5) similar to those of La-dominantsynthetic loparite NaLaTi2O6 and lsquoirinitersquo asdescribed by Borodin and Kazakova (1954) Theformer has been proposed to have the undistortedcubic lattice (ASTM 39-65 Belous et al 1985)However Rietveld refinement of an XRD powderpattern of NaLaTi2O6 suggests that thiscompound is orthorhombic (space group Pnma)rather than cubic (Mitchell and Chakhmouradianin preparation) The pattern of the rim sample ofthorian loparite also includes three diffractionlines with d-spacings of 295 1795 and 1535 AEcirc that cannot be produced by the perovskite-typestructure These are characteristic of pyrochlore-type phases and correspond to the most intenselines 222 440 and 622 respectively (ASTM 13-197 ASTM 17-746)

Data available from the literature show thatXRD powder patterns similar to those obtained inthis study are produced by naturally occurringloparite of various Nb2O5 CaO Na2O TiO2 andSrO contents (Haggerty and Mariano 1983Kostyleva-Labuntsova et al 1978b Mitchell etal 1996) Given a significant difference in ionicradius between Th4+ Na+ and Ce3+ (121 139and 134 AEcirc respectively Shannon 1976) it isexpected that Th-rich loparite should have astrongly distorted perovskite-type structureHowever the obtained patterns (Table 5) do notexhibit lsquoextrarsquo diffraction lines reflecting cationordering or geometric distortion of the ideal cubicperovskite-type lattice Such diffraction lines eg769 shy 790 344shy 350 257shy 260 187 shy 189 AEcirc are present in patterns of most syntheticperovskite-type titanates and niobates with Th4+

localized at the A sites (Keller 1965 Kovba andTrunov 1963 Labeau and Joubert 1978 Zhu andHor 1995) The only known exceptions so far arecompounds from the Na06shy 08Th01 shy 02NbO3

range of the NaNbO3shy Th025NbO3 solid solutionseries (ASTM-34-1068 Labeau and Joubert1978 Table III)

TABLE 5 X-ray diffraction patterns of loparite lsquoirinitersquo and Th-rich loparite

1 2 3 4 5hkl d IIo d IIo d IIo d IIo d IIo

100 3870 2110 2730 100 271 100 276 100 264 100 272 100111 2225 50200 1933 92 1919 90 1950 10 1905 30 1925 40

1860 200b211 1578 95 1569 80 1598 30 1562 60 1575 60

1503 10220 1367 70 1360 40 1383 20 1355 30 1368 30300 1290 4310 1225 25 1216 30 1233 15 1214 20 1222 20311 1168 8 1197 10222 1117 13 1111 5 1118 5320 1075 3321 1035 38 1028 60 1042 20 1029 10 1034 10400 09680 5411 0908 10 0912 5420 0864 10 0865 5332 08245 5 08260 3422 07910 3

1 synthetic NaLaTi2O6 a = 3873 AEcirc (ASTM 39-65) 2 lsquoirinitersquo (heated) a = 383 AEcirc (Borodin and Kazakova 1954)3 thorian loparite KHB-70 core (unheated) a = 3902(2) AEcirc 4 thorian loparite KHB-70 core (heated) a = 3841(1)AEcirc 5 thorian loparite KHB-70 rim (heated) a = 3867(2) AEcirc + 3 weak lines with d = 295 1795 1535 AEcirc (3-5 thiswork) b = broad line

R H MITCHELL AND A RCHAKHMOURADIAN

350

The absence of superstructure reflections in thepatterns of thorian loparite may result from itsmetamict state prior to heating ie from failure torestore an initial apparently distorted structure ofthe mineral Alternatively stabilization of thecubic structure may result from the presence ofminor cations in thorian loparite eg Ca or SrThis phenomenon refered to as stabilized poly-morphism (Smirnova and Belov 1969) is well-known for TiO2 and ZrO2 polymorphs (Filatovand Frank-Kamenetskii 1969 Grunin et al1983) To select between the two abovealternatives experimental studies of the solidsolution series between loparite and Th-bearingend-members are being undertaken by us

Discussion

At Khibina Th-rich loparite occurs only inrelation to the foyaite series (Borodin andKazakova 1954 Chakhmouradian and Mitchell1998 Kozyreva et al 1991 Tikhonenkova et al1982) Zoned Th-rich loparite examined in thisstudy crystallized at a late deuteric stage of theformation of foyaite pegmatites At this stagefluids enriched in Ti and incompatible elements(Zr Nb Sr LREE Th) gave rise to theassemblage of aegirine with loparite eudialyteand Ti-silicates (astrophyllite lorenzenitelamprophyllite) In a similar paragenesis lopariteoccurs in the foyaite pegmatites at MtNiorkpakhk (east of Mt Eveslogchorr) andkhibinite pegmatites at a number of localities inwestern Khibina (Chakhmouradian and Mitchell1998) In most of these occurrences loparite isrelatively Th-poor and compositionally evolvesby enrichment in Na2O and Nb2O5 and depletionin LREE2O3 and TiO2 contents toward the rimThis trend coincides with the main magmatictrend of the compositional evolution of loparite int h e n e p h e l i n e - s y e n i t e c o m p l e x e s(Chakhmouradian and Mitchell 1998 Mitchelland Chakhmouradian 1996) The evolutionarytrend from niobian loparite to thorian niobianloparite recognized in the present study has notbeen previously observed in alkaline rocksLoparite from fenite-type rocks of the ParanaBasin carbonatite complexes has high ThO2

contents (up to 62 wt) accompanied byenrichment in Na2O and Nb2O5 (lueshite) anddepletion in SrO and TiO2 (tausonite) (Mitchell1996 Table 36) Th-enrichment (up to 49 wtThO2) in the composition of perovskite from thecarbonatite complexes of the Kola Peninsula is

coupled with increasing LREE2O3 Na2O andNb2O5 ie loparite and lueshite components(Chakhmouradian and Mitchell 1997) In thePolino carbonatite Th-bearing (15 shy 17 wtThO2) perovskite has high Fe2O3 and ZrO2

contents (Lupini et al 1992)The limits of solubility between loparite

(NaLREETi2O6) and the thorium end-membercompositions ThNb4O12 Na23Th13TiO3 andThTi2O6 are unknown From structural data(Balic ZIuml unic et al 1984 Kovba and Trunov1963 Ruh and Wadsley 1966 Zhu and Hor1995) it is expected that loparite forms acomplete solid solution series with the formertwo compounds and only a limited series withThTi2O6 Experimental studies of the NaLaTi2O6

-ThNb4O12 NaLaTi2O6ndashNa2ThTi3O9 andNaLaTi2O6ndashThTi2O6 systems are being under-taken by the authors of this paper

As evidenced by textural relationships andcompositional data the appearance of Na-poorTh-rich lsquoceriobetafitersquo and belyankinite asmantles on thorian loparite was a result ofmetasomatic processes involving alkali-cationleaching and hydration Note that the sameprocesses brought about the replacement ofnepheline and alkali feldspar present as relics infibrous aegirine by zeolites and eventually bygibbsite Metasomatites including albitites albite-aegirine and albite-astrophyllite rocks are verycommon in the vicinity of pegmatite veinscontaining thorian loparite at Mt EveslogchorrHydrothermal solutions responsible for themetasomatic alteration most probably werederived from the phonolitic magma whichproduced the differentiated intrusion of nephelinesyenites including foyaite and its precursorkhibinite An alternative source of such solutionscould be a foidolite melt as some authors suggestthat the foidolites were emplaced later than thenephel ine syenite intrusion (Kostyleva-Labuntsova et al 1978a Sniatkova et al 1986)

Conclusions

In Na-LREE-Ti-dominant species of the perovs-kite group Th4+ cations occupy large twelve-coordinated A sites in the structure Theaccommodation of Th into the structure isaccompanied by appearance of vacancies at theA sites at the expense of Na LREE and SrThorian loparite is essentially a member of theloparite (NaLREETi2O6)ndashlueshite (NaNbO3)ndashThTi2O6ndashThNb4O12 quaternary system with low

TH-RICH LOPARITE

351

or negligible contents of other end-membercompositions The mineral compositionallyevolves from niobian loparite to niobian thorianand thorian niobian loparite Metasomatic altera-tion of thorian loparite gave rise to lsquoceriobetafitersquoand belyankinite with high ThO2 content Thorianloparite is metamict or partly metamict and uponheating regains a structure close to that ofsynthetic loparite NaLaTi2O6

Acknowledgements

This work was supported by the Natural Sciencesand Engineering Research Council of Canada andLakehead University Ontario (RHM ARC) ARCalso acknowledges support from St PetersburgState University Russia (grant Evolution offramework niobium-titanium oxides in carbona-tite-bearing nepheline-syenite complexes) AlanMacKenzie and Keith Pringnitz are thanked fortheir assistance with the analytical work AnnHammond and Sam Spivak are thanked for thinsection preparation and drafting services respec-tively

References

Balic ZIuml unic T SIuml cavnicIuml ar S and Grobenski Z (1984)The structure of thorium (IV) dititanium (IV) oxideThTi2O6 Croat Chem Acta 57 645 shy 51

Belous AG Novitskaya GN Gavrilova LGPolyanetskaya SV and Makarova ZYa (1985)Lanthanum titanate-zirconates with the perovskitestructure Sov Prog Chem 51 13 shy 15

Borodin LS (1954) On accommodation of water in thecrystal lattice of perovskite-group minerals DokladyAN SSSR 95 (in Russian) 873 shy 5

Borodin LS and Kazakova ME (1954) Irinite shy anew mineral from the perovskite group Doklady ANSSSR 97 (in Russian) 725 shy 8

Chakhmouradian AR and Mitchell RH (1997)Compositional variation of perovskite-group miner-als from the carbonatite complexes of the KolaAlkaline Province Russia Canad Mineral 351293 shy 310

Chakhmouradian AR and Mitchell RH (1998)Compositional variation of perovskite-group miner-als from the Khibina alkaline complex KolaPeninsula Canad Mineral 36 (in press)

Filatov SK and Frank-Kamenetskii VA (1969)Structural characteristics of cubic ZrO2 stabilizedby calcium Sov Phys Cryst 14 414 shy 5

Galakhov AV (1975) The petrology of the KhibinaAlkaline Massif Nauka Press Leningrad (in

Russian) 256 ppGerasimovski i VI and Kazakova ME (1950)

Belyankinite shy a new mineral Doklady AN SSSR 71 (in Russian) 925 shy 7

Grunin VS Razumenko MV Patrina IV FilatovSK and Alekseyeva TV (1983) Mode of existenceand abundance of TiO2-rutile anatase and brookiteDoklady Earth Sci Sect 268 149 shy 50

Haggerty SE and Mariano AN (1983) Strontian-loparite and strontio-chevkinite two new minerals inrheomorphic fenites from the Parana Basin carbona-tites South America Contrib Mineral Petrol 84365 shy 81

Hogarth DD (1961) A study of pyrochlore andbetafite Canad Mineral 6 610 shy 33

Hogarth DD (1989) Pyrochlore apatite and amphi-bole distinctive minerals in carbonatites InCarbonat ites (K Bell ed) Unwyn HymanLondon 105 shy 48

Kapustin YuL (1989) Rare earth-bearing pyrochlorefrom peralkaline pegmatites of the Khibina massifNew data on minerals (Trudy Mineral Muz ANSSSR ) 36 (in Russian) 155 shy 61

Keller C (1965) Die Reaktion der Dioxide derElemente Thorium bis Americium mit Niob- undTantalpentoxid (The reaction of dioxides of theelements from thorium to americium with niobiumand tantalum pentoxides) J Inorg Nucl Chem 271233 shy 46

Kogarko LN Kononova VA Orlova MP andWoolle y AR (1995 ) Alkaline Rocks andCarbonatites of the World Part 2 Former USSRChapman amp Hall London UK 226 pp

Kostyleva-Labuntsova EE Borutskii BE SokolovaMN Shliukova ZV Dorfman MD DudkinOB Kozyreva LV and Ikorskii SV (1978a) TheMineralogy of the Khibina Massif Vol 1 NaukaPress Moscow (in Russian) 228 p

Kostyleva-Labuntsova EE Borutskii BE SokolovaMN Shliukova ZV Dorfman MD DudkinOB Kozyreva LV and Ikorskii SV (1978b) TheMineralogy of the Khibina Massif Vol 2 NaukaPress Moscow (in Russian) 588 p

Kovba LM and Trunov VK (1962) Double oxidescontaining tungsten tantalum or niobium DokladyAN SSSR 147 (in Russian) 622 shy 4

Kozyreva LV (1990) Aegirine-feldspar veins in thenorth-eastern part of the Khibina massif In AlkalineMagmatism in the North-eastern Part of the BalticShield Kola Sci Centre Press Apatity (in Russian)42 shy 56

Kozyreva LV Menrsquoshikov YuP and Lednev AI(1991) Loparite mineralization of the Khibinamassif In New Data on the Rare-metalMineralogy of the Kola Peninsula Kola SciCentre Press Apatity (in Russian) 37 shy 44

R H MITCHELL AND A RCHAKHMOURADIAN

352

Occurrence

Until recently loparite with the ThO2 content ofmore than 10 wt has been recognized only fromthe Khibina alkaline complex in the KolaPeninsula Russia Its occurrence is restrictedmainly to foyaite and related pegmatoid andmetasomatic rocks comprising the central part ofthe Khibina pluton The general geologypetrology and mineralogy of the complex havebeen described in detail by Galakhov (1975)Kostyleva-Labuntsova et al (1978ab) Zak et al(1972) and summarized by Kogarko et al (1995)

Th-rich loparite examined in the current studyoccurs in foyaite pegmatites exposed on thesouthern slope of Mt Eveslogchorr southKhibina Most of the pegmatites are simplepoorly-differentiated veins emplaced into fine-to-medium grained nepheline syenite of gneissoidtexture The veins are composed mainly of alkalifeldspar nepheline aegirine and astrophylliteThe latter two minerals occur in intimate inter-growths as fibrous or radial aggregates partly orentirely replacing the earlier formed paragenesisof alkali feldspar and nepheline In Russianmineralogical literature the late-stage zones of

fibrous aegirine in nepheline-syenite pegmatitesare commonly interpreted as being of deuteric(lsquoautome tasoma ticrsquo ) or igin (Kostyl eva -Labuntsova et al 1978a) The aegirine-astro-phyllite aggregate encloses numerous irregular- orlens-shaped polygranular segregationsof analcitephillipsite natrolite and gibbsite plus Fe-hydr-oxides These segregations commonly containrelics of nepheline and undoubtedly representalteration products of the latter Accessoryminerals developed in the aegirine-astrophylliteaggregate are eudialyte loparite lamprophyllitelorenzenite and rare magnesio-arfvedsoniteRepresentative compositions of the major andaccessory silicates from the aegirine-astrophylliterock are given in Table 1

In the aegirine-astrophyllite aggregate lopariteoccurs as lsquofluoritersquo-type interpenetration twinsranging from 3 shy 7 mm across The mineral isdeep reddish-brown in thin sections andcommonly has a yellow-coloured rim up to03 mm in thickness Some loparite crystalspoikilitically enclose fine (less than 10 mm)needles of aegirine In this study we examinedzoned crystals of loparite from two pegmatiteveins KHB-44 and KHB-70

FIG 1 Back-scattered electron images of a zoned Th-rich loparite crystal (a) rim of thorian niobian and niobianthorian loparite (light grey) on niobian loparite (dark grey) scale bar is 400 mm (b) lsquoceriobetafite rsquo (dark grey)

developed along fractures and margins of thorian niobian loparite (light grey) scale bar is 30 mm

TH-RICH LOPARITE

343

Phase relationships

Back-scattered electron (BSE) imagery combinedwith line scanning reveals that loparite crystalsexhibit strong compositional zonation reflectingenrichment in ThO2 from the core towards the rim(Fig 1a) The Th-rich rims of the crystals areheterogeneous and consist of two phases Phase 1having a lower average atomic number isdeveloped as dendrite-like narrow (3 shy 30 mm)zones decorating margins of the crystals andfractures within phase 2 (Fig 1b) Compositiondeterminations show that both phases havecomparable CaO SrO LREE2O3 TiO2 andNb2O5 (Ti gt Nb) contents However phase 1gives low analysis totals (936-970 wt) andcontains considerably less Na2O (03shy 10 wt)and generally more ThO2 (178shy 220 wt) thanphase 2 X-ray diffraction study (see below)demonstrates that phase 1 comprising the bulkof the sample extracted from the rim of the crystalis loparite Three lsquoadditionalrsquo weak diffractionlines observed on the XRD film could not beassigned to loparite or any structure derived fromthe perovskite parent but corresponded well withthe three strongest diffraction lines of betafite(ASTM 13-197 Hogarth 1961)

Infrared transmission spectra recorded from thecore and rim of a loparite crystal are compared inFig 2(ab) Both spectra show a broad absorptionband at 650shy 900 cmshy 1 This band corresponds tobond vibrations in the octahedral complexes(TiNb)O6 and is typical of various perovskite-and pyrochlore-group minerals (Kostyleva-Labuntsova et al 1978b Pilipenko et al 1971)and their synthetic analogues (Nyquist and Kagel

1971 Sych et al 1973) The relative position ofthis absorption band in the spectrum depends onthe Ti vs Nb ratio of the mineral Splitting of the(TiNb)O6 band commonly observed in theinfrared spectra of low-symmetry perovskite-type compounds (Pilipenko et al 1971 Sych etal 1973) is not observed in our spectra(Fig 2ab) Similar coalescence of severalabsorption lines into one broad band has beenobserved in metamict pyrochlore (Krivokonevaand Sidorenko 1971) In addition to the(TiNb)O6 absorption band the infrared spectrumof the rim (Fig 2b) contains bands at 1650 23303300shy 3320 and 3530 cm shy 1 the latter twopartially overlapping each other The OHstretching bands at 3300shy 3320 and 3530 cmshy 1

and Nb shy OH band at 1650 cmshy 1 are characteristicof pyrochlore-group minerals (Voloshin et al1989) and most probably result from micro-intergrowths of ceriobetafite in the studiedsamples In the current study we could notassign the absorption band at 2330 cmshy 1

As evidenced by back-scattered electronimagery loparite from the vein KHB-70 hasundergone further alteration giving rise to thecomplex Ti hydroxide belyankinite The mineraloccurs as thin (20shy 30 mm) replacement mantleson loparite Its Nb-dominant analogue gerasi-movskite forms rare rectangularplates enclosed infibrous aegirine Both minerals have beeninsufficiently studied and were originallydescribed in peralkaline pegmatites of theLovozero alkaline complex Kola Peninsulawhere they occur predominantly as pseudomorphsafter titanium-silicates (Gerasimovskii andKazakova 1950 Semenov 1957)

Composition

LopariteRepresentative compositions of zoned loparite

crystals are given in Table 2 From core to rimloparite compositionally evolves by enrichment inThO2 and depletion in Na2O LREE2O3 and SrO(Table 2) In order to reveal possible end-membercompositions which may account for the accom-modation of Th in the structure of lopariterelationships between the amounts of Th (apfu)and other major elements (Fig 3) were analysedWith strongly decreasing Na LREE and to a lesserdegree Sr and increasing Th (Fig 3abd) theoccupancy of the B sites remains relativelyunchanged (Fig 3ef) As the most Th-richcompositions also exhibit the greatest cation

FIG 2 Infra-red transmission spectra of Th-rich loparite(a) core sample (b) rim sample

R H MITCHELL AND A RCHAKHMOURADIAN

344

deficiency (Fig 3g) it is deduced that Th4+ cationsare accommodatedat the A site of loparite and thatthe correspondingsubstitution scheme involves theappearance of vacancies at these sites Calculationsshow that the observed relationship between Thcontent and number of vacancies at the A-site mostclosely corresponds to the solid solution seriesbetween loparite and two hypothetical end-members ThNb4O12 and ThTi2O6 (Fig 3) Theso l id solu t ion se r ies between lopari te

NaLREETi2O6 and Na23Th13TiO3 believed tobe present is not present as the A- and B-sitesoccupancy remains constant The isomorphicsubstitutions are as follows

2Na+ + 2LREE3+ + 4Ti4+ gtTh4+ + 3amp + 4Nb5+ (1)

Na+ + LREE3+ gt Th4+ + amp (2)

ThNb4O12 (= Th025NbO3) has been synthe-sized and shown to have a perovskite-type

TABLE 1 Representative compositions of major and accessory silicate minerals

Wt 1 2 3 4 5 6 7 8 9 10 11 12

Na2O 1281 1220 227 216 1124 1094 1066 1104 1707 1696 889 871K2O 004 008 602 606 041 035 064 061 nd nd 204 218CaO 225 267 141 155 929 879 045 040 005 008 056 067SrO na na nd nd 149 118 1306 1162 nd nd na naBaO na na nd nd nd nd 085 322 nd nd na naMgO 102 103 189 191 009 037 043 045 035 023 820 808MnO 037 039 1292 1329 383 452 558 526 nd 012 373 383FeO 060 136 1904 1850 392 324 na na na na 1393 1351Fe2O3 2670 2535 na na na na 293 250 080 069 592 662La2O3 na na nd nd 067 106 060 042 na na na naCe2O3 na na nd nd 140 131 052 026 na na na naAl2O3 165 117 086 104 nd nd 029 002 nd nd 101 130SiO2 5326 5196 3555 3550 4995 4852 3100 3035 3331 3382 5320 5236TiO2 181 197 1160 1157 040 023 2959 2991 4479 4516 098 125ZrO2 na na 065 049 1326 1220 nd nd nd nd na naNb2O5 na na 065 077 290 331 009 041 212 188 na na

Total 10052 9818 9286 9284 9885 9602 9669 9647 9849 9894 9846 9851

Structural formulaeO = 6 Si = 8 Si = 24 Si = 4 O = 9 O = 23

Na 0934 0913 0990 0944 10471 10492 2667 2821 1929 1904 2576 2530K 0002 0004 1728 1742 0251 0221 0105 0103 0shy 0shy 0389 0417Ca 0091 0111 0340 0374 4782 4658 0062 0056 0003 0005 0090 0107Sr 0shy 0shy 0shy 0shy 0415 0338 0977 0888 0shy 0shy 0shy 0shyBa 0shy 0shy 0shy 0shy 0shy 0shy 0043 0166 0shy 0shy 0shy 0shyMg 0057 0059 0634 0642 0064 0273 0083 0088 0030 0020 1827 1804Mn 0012 0013 2463 2537 1559 1894 0610 0587 0shy 0006 0472 0486Fe2+ 0020 0047 3583 3486 1575 1340 0shy 0shy 0shy 0shy 1742 1693Fe3+ 0756 0735 0shy 0shy 0shy 0shy 0284 0248 0035 00300 0666 0747La 0shy 0shy 0shy 0shy 0119 0193 0029 0020 0shy 0shy 0shy 0shyCe 0shy 0shy 0shy 0shy 0246 0237 0025 0013 0shy 0shy 0shy 0shyAl 0073 0054 0228 0276 0shy 0shy 0044 0003 0shy 0shy 0178 0229Si 2003 2007 8000 8000 24000 24000 4000 4000 1942 1958 7951 7845Ti 0052 0057 1963 1961 0145 0086 2871 2964 1963 1966 0110 0141Zr 0shy 0shy 0071 0054 3107 2943 0shy 0shy 0shy 0shy 0shy 0shyNb 0shy 0shy 0066 0078 0630 0740 0005 0024 0056 0049 0shy 0shy

Compositions 1 and 2 aegirine 3 and 4 astrophyllite 5 and 6 eudialyte 7 and 8 lamprophyllite 9 and 10lorenzenite 11 and 12 magnesio-arfvedsoniteAll data this work Fe2+Fe3+ ratio calculated using Drooprsquos (1987) method

TH-RICH LOPARITE

345

structure (Keller 1965 Kovba and Trunov1963) Thorium dititanate (ThTi2O6) occurs intwo polymorphs of monoclinic symmetryStructures of both polymorphs differ from thatof perovskite in being built of sheets of edge-sharing TiO6 octahedra bound by Th atoms ineither six-fold or eight-fold coordination (BalicZIuml unic et al 1984 Ruh and Wadsley 1966)Given the considerable structural differenceloparite and thorium dititanate apparently should

not form a continuous solid solution serieshowever limits of the solubility between thesetwo end-members are unknown Our data suggestat least 23 mol ThTi2O6 is possible

The compositions of Th-rich loparite wererecalculated into major perovskite-group end-members (Mitchell 1996) plus the two thoriumcompounds ThNb4O12 and ThTi2O6 (Table 2Fig 4) The loparite composition evolves bybecoming enriched in the thorium end-members

TABLE 2 Representative compositions of loparite

Wt 1 2 3 4 5 6 7 8 9

Na2O 1043 868 850 742 669 971 918 766 662CaO 153 159 171 150 163 182 208 162 186SrO 140 133 129 133 109 165 177 131 120La2O3 972 888 647 646 541 1142 937 824 579Ce2O3 1477 1421 1119 1027 891 1691 1464 1337 987Pr2O3 186 172 156 nd 114 103 220 254 138Nd2O3 204 202 156 196 186 161 247 198 195ThO2 346 738 1029 1540 1845 234 366 869 1728TiO2 3239 3308 3046 3365 3372 3437 3241 3355 3480FeO 012 007 007 nd 011 007 nd 011 048Nb2O5 2138 2198 2716 2210 2018 1872 2213 2034 1962Ta2O5 037 022 032 043 030 033 049 059 058

Total 9947 10116 10058 10052 9949 9998 10040 10000 10143

Structural formulae (O = 3)Na 0589 0486 0477 0420 0387 0545 0515 0436 0375Ca 0048 0049 0053 0047 0052 0056 0064 0051 0058Sr 0024 0022 0022 0022 0019 0028 0030 0022 0020La 0104 0095 0069 0070 0060 0122 0100 0089 0062Ce 0158 0150 0118 0110 0097 0179 0155 0144 0106Pr 0020 0018 0016 0000 0012 0011 0023 0027 0015Nd 0021 0021 0016 0020 0020 0017 0026 0021 0020Th 0023 0048 0067 0102 0125 0015 0024 0058 0115Ti 0710 0719 0663 0739 0756 0749 0705 0741 0764Fe 0003 0002 0002 0000 0003 0002 0000 0002 0012Nb 0282 0287 0355 0292 0272 0245 0290 0270 0259Ta 0003 0002 0002 0003 0002 0003 0004 0005 0005

Mol end-membersNaCeTi2O66010 5799 4593 4306 4047 6580 6103 5833 4368NaNbO3 2820 2062 2706 2368 2120 2160 2118 1609 1850ThNb4O12 000 868 1017 775 792 290 793 1194 936ThTi2O6 456 546 897 1808 2281 155 043 607 2006CaTiO3 476 500 556 506 557 560 642 529 625SrTiO3 238 225 231 237 203 255 301 228 215

Compositions 1 shy 2 core and 3 shy 5 rim of a zoned loparite crystal KHB-44 6 shy 7 core and 8 shy 9 rim of a zonedloparite crystal KHB-70All data this workTotal Fe expressed as FeO nd = not detected

R H MITCHELL AND A RCHAKHMOURADIAN

346

at essentially constant lueshite content Usingnomenclature principles suggested for the perovs-kite-group minerals by Mitchell (1996) theexamined samples compositionally evolve fromniobian loparite toward niobian thorian andthorian niobian loparite

BetafiteRepresentative analyses of betafite developed

in thorian loparite are given in Table 3 LREEdominated by Ce and Th are the major A-cationsAccording to the classification scheme proposedby Hogarth (1989) for the pyrochlore-groupminerals this mineral should be regarded asceriobetafite or thorium ceriobetafite (LREE gtThgt 20 cation sum at the A sites) In this studywe prefer to refer to the mineral using quotationmarks as lsquoceriobetafitersquo is not approved as adistinct mineral species by the Comission on NewMinerals and Mineral Names of the IMA

At the Khibina complex pyrochlore-groupminerals were previously described as accessoryconstituents of aegirine-feldspar veins (Kozyreva

1990) and peralkaline pegmatites (Kapustin 1989Shilin et al 1966) These minerals correspond topyrochlore sensu stricto that may be somewhatenriched in SrO (Shilin et al 1966) or LREE(Kapustin 1989) Ti-dominant species ie membersof the betafite subgroup have not been previouslyrecognized in the Khibina alkaline complex

BelyankiniteCompositional data on belyankinite and related

Ti-Nb hydroxides available from literature arelimited to a few bulk wet-chemical analyses(Gerasimovskii and Kazakova 1950 Semenov1957 Vlasov et al 1966) Semenov (1957) hassuggested that Ti-dominant belyankinite formssolid solution series with its Mn-analoguemanganbelyankinite and Nb-dominant gerasi-movskite The mineral examined in the presentstudy is a member of the belyankinitendashgerasi-movskite series with negligible content ofmanganbelyankinite (Table 4) A generalizedstructural formula of belyankinite calculated onthe basis of 12 atoms of oxygen is

FIG 3 Variations (apfu) of (a) Na (b) LREE (c) Ca (d) Sr (e) Ti (f) Nb and (g) cation totals at the A and B siteswith respect to Th for Th-rich loparite Circles correspond to loparite KHB-44 squares to KHB-70 Variation of A-cation totals in the solid solution series NaLREETi2O6shy Na2ThTi3O9 is shown by solid line in the series

NaLREETi2O6shy ThTi2O6 by dashed line and in the series NaLREETi2O6shy ThNb4O12 by dash-dotted line (g)

TH-RICH LOPARITE

347

FIG 4 Compositions (mol) of Th-rich loparite in the system loparite (NaCeTi2O6)ndashlueshite (NaNbO3)ndashThTi2O6ndashThNb4O12

R H MITCHELL AND A RCHAKHMOURADIAN

348

(Ca ThLR EE )1 3(T i Nb Si Fe )5O12 nH2O(average of 18 determinations) and approachesthat deduced by Fleischer from Semenovrsquosanalytical data (see reference to Semenov1957) Ca 0 9(T i Zr NbS i )5 5O12 10H2O

However the mineral from Khibina differs fromLovozero belyankinite in having much higherThO2 (up to 2417 wt) and LREE2O3 (up to116 wt) contents both of which are undoubt-edly lsquoinheritedrsquo from the loparite parent

TABLE 3 Representative compositions of lsquoceriobetafitersquo

1 2 3 1 2 3

Wt Structural formulae(SB-cations = 2)

Na2O 101 054 034 Na 0111 0060 0036CaO 179 167 176 Ca 0108 0102 0103SrO 117 115 130 Sr 0038 0038 0041La2O3 579 481 510 La 0121 0101 0103Ce2O3 901 865 846 Ce 0186 0180 0169Nd2O3 152 262 114 Nd 0034 0053 0022ThO2 1965 2088 2041 Th 0244 0270 0253TiO2 3382 3506 3750 Ti 1438 1499 1539Fe2O3 nd 003 047 Fe 0000 0001 0017Nb2O5 2177 1926 1776 Nb 0556 0495 0438Ta2O5 037 034 039 Ta 0006 0005 0006

Total 9540 9501 9463

Compositions 1 and 2 KHB-44 3 KHB-70All data this workTotal Fe expressed as Fe2O3 nd = not detected

TABLE 4 Representative compositions of belyankinite

1 2 1 2

Wt Structural formulae(O = 24)

Na2O 003 028 Na 0014 0122CaO 412 162 Ca 1027 0402MgO 016 017 Mg 0055 0060MnO 011 028 Mn 0022 0053La2O3 208 200 La 0179 0169Ce2O3 862 221 Ce 0733 0186Nd2O3 081 076 Nd 0067 0062ThO2 1242 2417 Th 0657 1264SiO2 1303 1221 Si 3033 2805TiO2 2281 2473 Ti 3991 4273Al2O3 121 166 Al 0331 0450Fe2O3 616 507 Fe 1078 0877Nb2O5 1502 1587 Nb 1578 1649

Total 8658 9103

Compositions 1 and 2 replacement mantles on thorian loparite KHB-70Total Fe expressed as Fe2O3 ZrO2 was sought but not found

TH-RICH LOPARITE

349

X-ray powder diffractometry

An XRD powder pattern of a sample of the coreof a thorian loparite showed only a few faintdiffraction lines with relatively high d-spacingswhereas a rim sample appeared to be completelymetamict After heating to 7008C for 1 hour thecore and rim samples gave XRD powder patterns(Table 5) similar to those of La-dominantsynthetic loparite NaLaTi2O6 and lsquoirinitersquo asdescribed by Borodin and Kazakova (1954) Theformer has been proposed to have the undistortedcubic lattice (ASTM 39-65 Belous et al 1985)However Rietveld refinement of an XRD powderpattern of NaLaTi2O6 suggests that thiscompound is orthorhombic (space group Pnma)rather than cubic (Mitchell and Chakhmouradianin preparation) The pattern of the rim sample ofthorian loparite also includes three diffractionlines with d-spacings of 295 1795 and 1535 AEcirc that cannot be produced by the perovskite-typestructure These are characteristic of pyrochlore-type phases and correspond to the most intenselines 222 440 and 622 respectively (ASTM 13-197 ASTM 17-746)

Data available from the literature show thatXRD powder patterns similar to those obtained inthis study are produced by naturally occurringloparite of various Nb2O5 CaO Na2O TiO2 andSrO contents (Haggerty and Mariano 1983Kostyleva-Labuntsova et al 1978b Mitchell etal 1996) Given a significant difference in ionicradius between Th4+ Na+ and Ce3+ (121 139and 134 AEcirc respectively Shannon 1976) it isexpected that Th-rich loparite should have astrongly distorted perovskite-type structureHowever the obtained patterns (Table 5) do notexhibit lsquoextrarsquo diffraction lines reflecting cationordering or geometric distortion of the ideal cubicperovskite-type lattice Such diffraction lines eg769 shy 790 344shy 350 257shy 260 187 shy 189 AEcirc are present in patterns of most syntheticperovskite-type titanates and niobates with Th4+

localized at the A sites (Keller 1965 Kovba andTrunov 1963 Labeau and Joubert 1978 Zhu andHor 1995) The only known exceptions so far arecompounds from the Na06shy 08Th01 shy 02NbO3

range of the NaNbO3shy Th025NbO3 solid solutionseries (ASTM-34-1068 Labeau and Joubert1978 Table III)

TABLE 5 X-ray diffraction patterns of loparite lsquoirinitersquo and Th-rich loparite

1 2 3 4 5hkl d IIo d IIo d IIo d IIo d IIo

100 3870 2110 2730 100 271 100 276 100 264 100 272 100111 2225 50200 1933 92 1919 90 1950 10 1905 30 1925 40

1860 200b211 1578 95 1569 80 1598 30 1562 60 1575 60

1503 10220 1367 70 1360 40 1383 20 1355 30 1368 30300 1290 4310 1225 25 1216 30 1233 15 1214 20 1222 20311 1168 8 1197 10222 1117 13 1111 5 1118 5320 1075 3321 1035 38 1028 60 1042 20 1029 10 1034 10400 09680 5411 0908 10 0912 5420 0864 10 0865 5332 08245 5 08260 3422 07910 3

1 synthetic NaLaTi2O6 a = 3873 AEcirc (ASTM 39-65) 2 lsquoirinitersquo (heated) a = 383 AEcirc (Borodin and Kazakova 1954)3 thorian loparite KHB-70 core (unheated) a = 3902(2) AEcirc 4 thorian loparite KHB-70 core (heated) a = 3841(1)AEcirc 5 thorian loparite KHB-70 rim (heated) a = 3867(2) AEcirc + 3 weak lines with d = 295 1795 1535 AEcirc (3-5 thiswork) b = broad line

R H MITCHELL AND A RCHAKHMOURADIAN

350

The absence of superstructure reflections in thepatterns of thorian loparite may result from itsmetamict state prior to heating ie from failure torestore an initial apparently distorted structure ofthe mineral Alternatively stabilization of thecubic structure may result from the presence ofminor cations in thorian loparite eg Ca or SrThis phenomenon refered to as stabilized poly-morphism (Smirnova and Belov 1969) is well-known for TiO2 and ZrO2 polymorphs (Filatovand Frank-Kamenetskii 1969 Grunin et al1983) To select between the two abovealternatives experimental studies of the solidsolution series between loparite and Th-bearingend-members are being undertaken by us

Discussion

At Khibina Th-rich loparite occurs only inrelation to the foyaite series (Borodin andKazakova 1954 Chakhmouradian and Mitchell1998 Kozyreva et al 1991 Tikhonenkova et al1982) Zoned Th-rich loparite examined in thisstudy crystallized at a late deuteric stage of theformation of foyaite pegmatites At this stagefluids enriched in Ti and incompatible elements(Zr Nb Sr LREE Th) gave rise to theassemblage of aegirine with loparite eudialyteand Ti-silicates (astrophyllite lorenzenitelamprophyllite) In a similar paragenesis lopariteoccurs in the foyaite pegmatites at MtNiorkpakhk (east of Mt Eveslogchorr) andkhibinite pegmatites at a number of localities inwestern Khibina (Chakhmouradian and Mitchell1998) In most of these occurrences loparite isrelatively Th-poor and compositionally evolvesby enrichment in Na2O and Nb2O5 and depletionin LREE2O3 and TiO2 contents toward the rimThis trend coincides with the main magmatictrend of the compositional evolution of loparite int h e n e p h e l i n e - s y e n i t e c o m p l e x e s(Chakhmouradian and Mitchell 1998 Mitchelland Chakhmouradian 1996) The evolutionarytrend from niobian loparite to thorian niobianloparite recognized in the present study has notbeen previously observed in alkaline rocksLoparite from fenite-type rocks of the ParanaBasin carbonatite complexes has high ThO2

contents (up to 62 wt) accompanied byenrichment in Na2O and Nb2O5 (lueshite) anddepletion in SrO and TiO2 (tausonite) (Mitchell1996 Table 36) Th-enrichment (up to 49 wtThO2) in the composition of perovskite from thecarbonatite complexes of the Kola Peninsula is

coupled with increasing LREE2O3 Na2O andNb2O5 ie loparite and lueshite components(Chakhmouradian and Mitchell 1997) In thePolino carbonatite Th-bearing (15 shy 17 wtThO2) perovskite has high Fe2O3 and ZrO2

contents (Lupini et al 1992)The limits of solubility between loparite

(NaLREETi2O6) and the thorium end-membercompositions ThNb4O12 Na23Th13TiO3 andThTi2O6 are unknown From structural data(Balic ZIuml unic et al 1984 Kovba and Trunov1963 Ruh and Wadsley 1966 Zhu and Hor1995) it is expected that loparite forms acomplete solid solution series with the formertwo compounds and only a limited series withThTi2O6 Experimental studies of the NaLaTi2O6

-ThNb4O12 NaLaTi2O6ndashNa2ThTi3O9 andNaLaTi2O6ndashThTi2O6 systems are being under-taken by the authors of this paper

As evidenced by textural relationships andcompositional data the appearance of Na-poorTh-rich lsquoceriobetafitersquo and belyankinite asmantles on thorian loparite was a result ofmetasomatic processes involving alkali-cationleaching and hydration Note that the sameprocesses brought about the replacement ofnepheline and alkali feldspar present as relics infibrous aegirine by zeolites and eventually bygibbsite Metasomatites including albitites albite-aegirine and albite-astrophyllite rocks are verycommon in the vicinity of pegmatite veinscontaining thorian loparite at Mt EveslogchorrHydrothermal solutions responsible for themetasomatic alteration most probably werederived from the phonolitic magma whichproduced the differentiated intrusion of nephelinesyenites including foyaite and its precursorkhibinite An alternative source of such solutionscould be a foidolite melt as some authors suggestthat the foidolites were emplaced later than thenephel ine syenite intrusion (Kostyleva-Labuntsova et al 1978a Sniatkova et al 1986)

Conclusions

In Na-LREE-Ti-dominant species of the perovs-kite group Th4+ cations occupy large twelve-coordinated A sites in the structure Theaccommodation of Th into the structure isaccompanied by appearance of vacancies at theA sites at the expense of Na LREE and SrThorian loparite is essentially a member of theloparite (NaLREETi2O6)ndashlueshite (NaNbO3)ndashThTi2O6ndashThNb4O12 quaternary system with low

TH-RICH LOPARITE

351

or negligible contents of other end-membercompositions The mineral compositionallyevolves from niobian loparite to niobian thorianand thorian niobian loparite Metasomatic altera-tion of thorian loparite gave rise to lsquoceriobetafitersquoand belyankinite with high ThO2 content Thorianloparite is metamict or partly metamict and uponheating regains a structure close to that ofsynthetic loparite NaLaTi2O6

Acknowledgements

This work was supported by the Natural Sciencesand Engineering Research Council of Canada andLakehead University Ontario (RHM ARC) ARCalso acknowledges support from St PetersburgState University Russia (grant Evolution offramework niobium-titanium oxides in carbona-tite-bearing nepheline-syenite complexes) AlanMacKenzie and Keith Pringnitz are thanked fortheir assistance with the analytical work AnnHammond and Sam Spivak are thanked for thinsection preparation and drafting services respec-tively

References

Balic ZIuml unic T SIuml cavnicIuml ar S and Grobenski Z (1984)The structure of thorium (IV) dititanium (IV) oxideThTi2O6 Croat Chem Acta 57 645 shy 51

Belous AG Novitskaya GN Gavrilova LGPolyanetskaya SV and Makarova ZYa (1985)Lanthanum titanate-zirconates with the perovskitestructure Sov Prog Chem 51 13 shy 15

Borodin LS (1954) On accommodation of water in thecrystal lattice of perovskite-group minerals DokladyAN SSSR 95 (in Russian) 873 shy 5

Borodin LS and Kazakova ME (1954) Irinite shy anew mineral from the perovskite group Doklady ANSSSR 97 (in Russian) 725 shy 8

Chakhmouradian AR and Mitchell RH (1997)Compositional variation of perovskite-group miner-als from the carbonatite complexes of the KolaAlkaline Province Russia Canad Mineral 351293 shy 310

Chakhmouradian AR and Mitchell RH (1998)Compositional variation of perovskite-group miner-als from the Khibina alkaline complex KolaPeninsula Canad Mineral 36 (in press)

Filatov SK and Frank-Kamenetskii VA (1969)Structural characteristics of cubic ZrO2 stabilizedby calcium Sov Phys Cryst 14 414 shy 5

Galakhov AV (1975) The petrology of the KhibinaAlkaline Massif Nauka Press Leningrad (in

Russian) 256 ppGerasimovski i VI and Kazakova ME (1950)

Belyankinite shy a new mineral Doklady AN SSSR 71 (in Russian) 925 shy 7

Grunin VS Razumenko MV Patrina IV FilatovSK and Alekseyeva TV (1983) Mode of existenceand abundance of TiO2-rutile anatase and brookiteDoklady Earth Sci Sect 268 149 shy 50

Haggerty SE and Mariano AN (1983) Strontian-loparite and strontio-chevkinite two new minerals inrheomorphic fenites from the Parana Basin carbona-tites South America Contrib Mineral Petrol 84365 shy 81

Hogarth DD (1961) A study of pyrochlore andbetafite Canad Mineral 6 610 shy 33

Hogarth DD (1989) Pyrochlore apatite and amphi-bole distinctive minerals in carbonatites InCarbonat ites (K Bell ed) Unwyn HymanLondon 105 shy 48

Kapustin YuL (1989) Rare earth-bearing pyrochlorefrom peralkaline pegmatites of the Khibina massifNew data on minerals (Trudy Mineral Muz ANSSSR ) 36 (in Russian) 155 shy 61

Keller C (1965) Die Reaktion der Dioxide derElemente Thorium bis Americium mit Niob- undTantalpentoxid (The reaction of dioxides of theelements from thorium to americium with niobiumand tantalum pentoxides) J Inorg Nucl Chem 271233 shy 46

Kogarko LN Kononova VA Orlova MP andWoolle y AR (1995 ) Alkaline Rocks andCarbonatites of the World Part 2 Former USSRChapman amp Hall London UK 226 pp

Kostyleva-Labuntsova EE Borutskii BE SokolovaMN Shliukova ZV Dorfman MD DudkinOB Kozyreva LV and Ikorskii SV (1978a) TheMineralogy of the Khibina Massif Vol 1 NaukaPress Moscow (in Russian) 228 p

Kostyleva-Labuntsova EE Borutskii BE SokolovaMN Shliukova ZV Dorfman MD DudkinOB Kozyreva LV and Ikorskii SV (1978b) TheMineralogy of the Khibina Massif Vol 2 NaukaPress Moscow (in Russian) 588 p

Kovba LM and Trunov VK (1962) Double oxidescontaining tungsten tantalum or niobium DokladyAN SSSR 147 (in Russian) 622 shy 4

Kozyreva LV (1990) Aegirine-feldspar veins in thenorth-eastern part of the Khibina massif In AlkalineMagmatism in the North-eastern Part of the BalticShield Kola Sci Centre Press Apatity (in Russian)42 shy 56

Kozyreva LV Menrsquoshikov YuP and Lednev AI(1991) Loparite mineralization of the Khibinamassif In New Data on the Rare-metalMineralogy of the Kola Peninsula Kola SciCentre Press Apatity (in Russian) 37 shy 44

R H MITCHELL AND A RCHAKHMOURADIAN

352

Phase relationships

Back-scattered electron (BSE) imagery combinedwith line scanning reveals that loparite crystalsexhibit strong compositional zonation reflectingenrichment in ThO2 from the core towards the rim(Fig 1a) The Th-rich rims of the crystals areheterogeneous and consist of two phases Phase 1having a lower average atomic number isdeveloped as dendrite-like narrow (3 shy 30 mm)zones decorating margins of the crystals andfractures within phase 2 (Fig 1b) Compositiondeterminations show that both phases havecomparable CaO SrO LREE2O3 TiO2 andNb2O5 (Ti gt Nb) contents However phase 1gives low analysis totals (936-970 wt) andcontains considerably less Na2O (03shy 10 wt)and generally more ThO2 (178shy 220 wt) thanphase 2 X-ray diffraction study (see below)demonstrates that phase 1 comprising the bulkof the sample extracted from the rim of the crystalis loparite Three lsquoadditionalrsquo weak diffractionlines observed on the XRD film could not beassigned to loparite or any structure derived fromthe perovskite parent but corresponded well withthe three strongest diffraction lines of betafite(ASTM 13-197 Hogarth 1961)

Infrared transmission spectra recorded from thecore and rim of a loparite crystal are compared inFig 2(ab) Both spectra show a broad absorptionband at 650shy 900 cmshy 1 This band corresponds tobond vibrations in the octahedral complexes(TiNb)O6 and is typical of various perovskite-and pyrochlore-group minerals (Kostyleva-Labuntsova et al 1978b Pilipenko et al 1971)and their synthetic analogues (Nyquist and Kagel

1971 Sych et al 1973) The relative position ofthis absorption band in the spectrum depends onthe Ti vs Nb ratio of the mineral Splitting of the(TiNb)O6 band commonly observed in theinfrared spectra of low-symmetry perovskite-type compounds (Pilipenko et al 1971 Sych etal 1973) is not observed in our spectra(Fig 2ab) Similar coalescence of severalabsorption lines into one broad band has beenobserved in metamict pyrochlore (Krivokonevaand Sidorenko 1971) In addition to the(TiNb)O6 absorption band the infrared spectrumof the rim (Fig 2b) contains bands at 1650 23303300shy 3320 and 3530 cm shy 1 the latter twopartially overlapping each other The OHstretching bands at 3300shy 3320 and 3530 cmshy 1

and Nb shy OH band at 1650 cmshy 1 are characteristicof pyrochlore-group minerals (Voloshin et al1989) and most probably result from micro-intergrowths of ceriobetafite in the studiedsamples In the current study we could notassign the absorption band at 2330 cmshy 1

As evidenced by back-scattered electronimagery loparite from the vein KHB-70 hasundergone further alteration giving rise to thecomplex Ti hydroxide belyankinite The mineraloccurs as thin (20shy 30 mm) replacement mantleson loparite Its Nb-dominant analogue gerasi-movskite forms rare rectangularplates enclosed infibrous aegirine Both minerals have beeninsufficiently studied and were originallydescribed in peralkaline pegmatites of theLovozero alkaline complex Kola Peninsulawhere they occur predominantly as pseudomorphsafter titanium-silicates (Gerasimovskii andKazakova 1950 Semenov 1957)

Composition

LopariteRepresentative compositions of zoned loparite

crystals are given in Table 2 From core to rimloparite compositionally evolves by enrichment inThO2 and depletion in Na2O LREE2O3 and SrO(Table 2) In order to reveal possible end-membercompositions which may account for the accom-modation of Th in the structure of lopariterelationships between the amounts of Th (apfu)and other major elements (Fig 3) were analysedWith strongly decreasing Na LREE and to a lesserdegree Sr and increasing Th (Fig 3abd) theoccupancy of the B sites remains relativelyunchanged (Fig 3ef) As the most Th-richcompositions also exhibit the greatest cation

FIG 2 Infra-red transmission spectra of Th-rich loparite(a) core sample (b) rim sample

R H MITCHELL AND A RCHAKHMOURADIAN

344

deficiency (Fig 3g) it is deduced that Th4+ cationsare accommodatedat the A site of loparite and thatthe correspondingsubstitution scheme involves theappearance of vacancies at these sites Calculationsshow that the observed relationship between Thcontent and number of vacancies at the A-site mostclosely corresponds to the solid solution seriesbetween loparite and two hypothetical end-members ThNb4O12 and ThTi2O6 (Fig 3) Theso l id solu t ion se r ies between lopari te

NaLREETi2O6 and Na23Th13TiO3 believed tobe present is not present as the A- and B-sitesoccupancy remains constant The isomorphicsubstitutions are as follows

2Na+ + 2LREE3+ + 4Ti4+ gtTh4+ + 3amp + 4Nb5+ (1)

Na+ + LREE3+ gt Th4+ + amp (2)

ThNb4O12 (= Th025NbO3) has been synthe-sized and shown to have a perovskite-type

TABLE 1 Representative compositions of major and accessory silicate minerals

Wt 1 2 3 4 5 6 7 8 9 10 11 12

Na2O 1281 1220 227 216 1124 1094 1066 1104 1707 1696 889 871K2O 004 008 602 606 041 035 064 061 nd nd 204 218CaO 225 267 141 155 929 879 045 040 005 008 056 067SrO na na nd nd 149 118 1306 1162 nd nd na naBaO na na nd nd nd nd 085 322 nd nd na naMgO 102 103 189 191 009 037 043 045 035 023 820 808MnO 037 039 1292 1329 383 452 558 526 nd 012 373 383FeO 060 136 1904 1850 392 324 na na na na 1393 1351Fe2O3 2670 2535 na na na na 293 250 080 069 592 662La2O3 na na nd nd 067 106 060 042 na na na naCe2O3 na na nd nd 140 131 052 026 na na na naAl2O3 165 117 086 104 nd nd 029 002 nd nd 101 130SiO2 5326 5196 3555 3550 4995 4852 3100 3035 3331 3382 5320 5236TiO2 181 197 1160 1157 040 023 2959 2991 4479 4516 098 125ZrO2 na na 065 049 1326 1220 nd nd nd nd na naNb2O5 na na 065 077 290 331 009 041 212 188 na na

Total 10052 9818 9286 9284 9885 9602 9669 9647 9849 9894 9846 9851

Structural formulaeO = 6 Si = 8 Si = 24 Si = 4 O = 9 O = 23

Na 0934 0913 0990 0944 10471 10492 2667 2821 1929 1904 2576 2530K 0002 0004 1728 1742 0251 0221 0105 0103 0shy 0shy 0389 0417Ca 0091 0111 0340 0374 4782 4658 0062 0056 0003 0005 0090 0107Sr 0shy 0shy 0shy 0shy 0415 0338 0977 0888 0shy 0shy 0shy 0shyBa 0shy 0shy 0shy 0shy 0shy 0shy 0043 0166 0shy 0shy 0shy 0shyMg 0057 0059 0634 0642 0064 0273 0083 0088 0030 0020 1827 1804Mn 0012 0013 2463 2537 1559 1894 0610 0587 0shy 0006 0472 0486Fe2+ 0020 0047 3583 3486 1575 1340 0shy 0shy 0shy 0shy 1742 1693Fe3+ 0756 0735 0shy 0shy 0shy 0shy 0284 0248 0035 00300 0666 0747La 0shy 0shy 0shy 0shy 0119 0193 0029 0020 0shy 0shy 0shy 0shyCe 0shy 0shy 0shy 0shy 0246 0237 0025 0013 0shy 0shy 0shy 0shyAl 0073 0054 0228 0276 0shy 0shy 0044 0003 0shy 0shy 0178 0229Si 2003 2007 8000 8000 24000 24000 4000 4000 1942 1958 7951 7845Ti 0052 0057 1963 1961 0145 0086 2871 2964 1963 1966 0110 0141Zr 0shy 0shy 0071 0054 3107 2943 0shy 0shy 0shy 0shy 0shy 0shyNb 0shy 0shy 0066 0078 0630 0740 0005 0024 0056 0049 0shy 0shy

Compositions 1 and 2 aegirine 3 and 4 astrophyllite 5 and 6 eudialyte 7 and 8 lamprophyllite 9 and 10lorenzenite 11 and 12 magnesio-arfvedsoniteAll data this work Fe2+Fe3+ ratio calculated using Drooprsquos (1987) method

TH-RICH LOPARITE

345

structure (Keller 1965 Kovba and Trunov1963) Thorium dititanate (ThTi2O6) occurs intwo polymorphs of monoclinic symmetryStructures of both polymorphs differ from thatof perovskite in being built of sheets of edge-sharing TiO6 octahedra bound by Th atoms ineither six-fold or eight-fold coordination (BalicZIuml unic et al 1984 Ruh and Wadsley 1966)Given the considerable structural differenceloparite and thorium dititanate apparently should

not form a continuous solid solution serieshowever limits of the solubility between thesetwo end-members are unknown Our data suggestat least 23 mol ThTi2O6 is possible

The compositions of Th-rich loparite wererecalculated into major perovskite-group end-members (Mitchell 1996) plus the two thoriumcompounds ThNb4O12 and ThTi2O6 (Table 2Fig 4) The loparite composition evolves bybecoming enriched in the thorium end-members

TABLE 2 Representative compositions of loparite

Wt 1 2 3 4 5 6 7 8 9

Na2O 1043 868 850 742 669 971 918 766 662CaO 153 159 171 150 163 182 208 162 186SrO 140 133 129 133 109 165 177 131 120La2O3 972 888 647 646 541 1142 937 824 579Ce2O3 1477 1421 1119 1027 891 1691 1464 1337 987Pr2O3 186 172 156 nd 114 103 220 254 138Nd2O3 204 202 156 196 186 161 247 198 195ThO2 346 738 1029 1540 1845 234 366 869 1728TiO2 3239 3308 3046 3365 3372 3437 3241 3355 3480FeO 012 007 007 nd 011 007 nd 011 048Nb2O5 2138 2198 2716 2210 2018 1872 2213 2034 1962Ta2O5 037 022 032 043 030 033 049 059 058

Total 9947 10116 10058 10052 9949 9998 10040 10000 10143

Structural formulae (O = 3)Na 0589 0486 0477 0420 0387 0545 0515 0436 0375Ca 0048 0049 0053 0047 0052 0056 0064 0051 0058Sr 0024 0022 0022 0022 0019 0028 0030 0022 0020La 0104 0095 0069 0070 0060 0122 0100 0089 0062Ce 0158 0150 0118 0110 0097 0179 0155 0144 0106Pr 0020 0018 0016 0000 0012 0011 0023 0027 0015Nd 0021 0021 0016 0020 0020 0017 0026 0021 0020Th 0023 0048 0067 0102 0125 0015 0024 0058 0115Ti 0710 0719 0663 0739 0756 0749 0705 0741 0764Fe 0003 0002 0002 0000 0003 0002 0000 0002 0012Nb 0282 0287 0355 0292 0272 0245 0290 0270 0259Ta 0003 0002 0002 0003 0002 0003 0004 0005 0005

Mol end-membersNaCeTi2O66010 5799 4593 4306 4047 6580 6103 5833 4368NaNbO3 2820 2062 2706 2368 2120 2160 2118 1609 1850ThNb4O12 000 868 1017 775 792 290 793 1194 936ThTi2O6 456 546 897 1808 2281 155 043 607 2006CaTiO3 476 500 556 506 557 560 642 529 625SrTiO3 238 225 231 237 203 255 301 228 215

Compositions 1 shy 2 core and 3 shy 5 rim of a zoned loparite crystal KHB-44 6 shy 7 core and 8 shy 9 rim of a zonedloparite crystal KHB-70All data this workTotal Fe expressed as FeO nd = not detected

R H MITCHELL AND A RCHAKHMOURADIAN

346

at essentially constant lueshite content Usingnomenclature principles suggested for the perovs-kite-group minerals by Mitchell (1996) theexamined samples compositionally evolve fromniobian loparite toward niobian thorian andthorian niobian loparite

BetafiteRepresentative analyses of betafite developed

in thorian loparite are given in Table 3 LREEdominated by Ce and Th are the major A-cationsAccording to the classification scheme proposedby Hogarth (1989) for the pyrochlore-groupminerals this mineral should be regarded asceriobetafite or thorium ceriobetafite (LREE gtThgt 20 cation sum at the A sites) In this studywe prefer to refer to the mineral using quotationmarks as lsquoceriobetafitersquo is not approved as adistinct mineral species by the Comission on NewMinerals and Mineral Names of the IMA

At the Khibina complex pyrochlore-groupminerals were previously described as accessoryconstituents of aegirine-feldspar veins (Kozyreva

1990) and peralkaline pegmatites (Kapustin 1989Shilin et al 1966) These minerals correspond topyrochlore sensu stricto that may be somewhatenriched in SrO (Shilin et al 1966) or LREE(Kapustin 1989) Ti-dominant species ie membersof the betafite subgroup have not been previouslyrecognized in the Khibina alkaline complex

BelyankiniteCompositional data on belyankinite and related

Ti-Nb hydroxides available from literature arelimited to a few bulk wet-chemical analyses(Gerasimovskii and Kazakova 1950 Semenov1957 Vlasov et al 1966) Semenov (1957) hassuggested that Ti-dominant belyankinite formssolid solution series with its Mn-analoguemanganbelyankinite and Nb-dominant gerasi-movskite The mineral examined in the presentstudy is a member of the belyankinitendashgerasi-movskite series with negligible content ofmanganbelyankinite (Table 4) A generalizedstructural formula of belyankinite calculated onthe basis of 12 atoms of oxygen is

FIG 3 Variations (apfu) of (a) Na (b) LREE (c) Ca (d) Sr (e) Ti (f) Nb and (g) cation totals at the A and B siteswith respect to Th for Th-rich loparite Circles correspond to loparite KHB-44 squares to KHB-70 Variation of A-cation totals in the solid solution series NaLREETi2O6shy Na2ThTi3O9 is shown by solid line in the series

NaLREETi2O6shy ThTi2O6 by dashed line and in the series NaLREETi2O6shy ThNb4O12 by dash-dotted line (g)

TH-RICH LOPARITE

347

FIG 4 Compositions (mol) of Th-rich loparite in the system loparite (NaCeTi2O6)ndashlueshite (NaNbO3)ndashThTi2O6ndashThNb4O12

R H MITCHELL AND A RCHAKHMOURADIAN

348

(Ca ThLR EE )1 3(T i Nb Si Fe )5O12 nH2O(average of 18 determinations) and approachesthat deduced by Fleischer from Semenovrsquosanalytical data (see reference to Semenov1957) Ca 0 9(T i Zr NbS i )5 5O12 10H2O

However the mineral from Khibina differs fromLovozero belyankinite in having much higherThO2 (up to 2417 wt) and LREE2O3 (up to116 wt) contents both of which are undoubt-edly lsquoinheritedrsquo from the loparite parent

TABLE 3 Representative compositions of lsquoceriobetafitersquo

1 2 3 1 2 3

Wt Structural formulae(SB-cations = 2)

Na2O 101 054 034 Na 0111 0060 0036CaO 179 167 176 Ca 0108 0102 0103SrO 117 115 130 Sr 0038 0038 0041La2O3 579 481 510 La 0121 0101 0103Ce2O3 901 865 846 Ce 0186 0180 0169Nd2O3 152 262 114 Nd 0034 0053 0022ThO2 1965 2088 2041 Th 0244 0270 0253TiO2 3382 3506 3750 Ti 1438 1499 1539Fe2O3 nd 003 047 Fe 0000 0001 0017Nb2O5 2177 1926 1776 Nb 0556 0495 0438Ta2O5 037 034 039 Ta 0006 0005 0006

Total 9540 9501 9463

Compositions 1 and 2 KHB-44 3 KHB-70All data this workTotal Fe expressed as Fe2O3 nd = not detected

TABLE 4 Representative compositions of belyankinite

1 2 1 2

Wt Structural formulae(O = 24)

Na2O 003 028 Na 0014 0122CaO 412 162 Ca 1027 0402MgO 016 017 Mg 0055 0060MnO 011 028 Mn 0022 0053La2O3 208 200 La 0179 0169Ce2O3 862 221 Ce 0733 0186Nd2O3 081 076 Nd 0067 0062ThO2 1242 2417 Th 0657 1264SiO2 1303 1221 Si 3033 2805TiO2 2281 2473 Ti 3991 4273Al2O3 121 166 Al 0331 0450Fe2O3 616 507 Fe 1078 0877Nb2O5 1502 1587 Nb 1578 1649

Total 8658 9103

Compositions 1 and 2 replacement mantles on thorian loparite KHB-70Total Fe expressed as Fe2O3 ZrO2 was sought but not found

TH-RICH LOPARITE

349

X-ray powder diffractometry

An XRD powder pattern of a sample of the coreof a thorian loparite showed only a few faintdiffraction lines with relatively high d-spacingswhereas a rim sample appeared to be completelymetamict After heating to 7008C for 1 hour thecore and rim samples gave XRD powder patterns(Table 5) similar to those of La-dominantsynthetic loparite NaLaTi2O6 and lsquoirinitersquo asdescribed by Borodin and Kazakova (1954) Theformer has been proposed to have the undistortedcubic lattice (ASTM 39-65 Belous et al 1985)However Rietveld refinement of an XRD powderpattern of NaLaTi2O6 suggests that thiscompound is orthorhombic (space group Pnma)rather than cubic (Mitchell and Chakhmouradianin preparation) The pattern of the rim sample ofthorian loparite also includes three diffractionlines with d-spacings of 295 1795 and 1535 AEcirc that cannot be produced by the perovskite-typestructure These are characteristic of pyrochlore-type phases and correspond to the most intenselines 222 440 and 622 respectively (ASTM 13-197 ASTM 17-746)

Data available from the literature show thatXRD powder patterns similar to those obtained inthis study are produced by naturally occurringloparite of various Nb2O5 CaO Na2O TiO2 andSrO contents (Haggerty and Mariano 1983Kostyleva-Labuntsova et al 1978b Mitchell etal 1996) Given a significant difference in ionicradius between Th4+ Na+ and Ce3+ (121 139and 134 AEcirc respectively Shannon 1976) it isexpected that Th-rich loparite should have astrongly distorted perovskite-type structureHowever the obtained patterns (Table 5) do notexhibit lsquoextrarsquo diffraction lines reflecting cationordering or geometric distortion of the ideal cubicperovskite-type lattice Such diffraction lines eg769 shy 790 344shy 350 257shy 260 187 shy 189 AEcirc are present in patterns of most syntheticperovskite-type titanates and niobates with Th4+

localized at the A sites (Keller 1965 Kovba andTrunov 1963 Labeau and Joubert 1978 Zhu andHor 1995) The only known exceptions so far arecompounds from the Na06shy 08Th01 shy 02NbO3

range of the NaNbO3shy Th025NbO3 solid solutionseries (ASTM-34-1068 Labeau and Joubert1978 Table III)

TABLE 5 X-ray diffraction patterns of loparite lsquoirinitersquo and Th-rich loparite

1 2 3 4 5hkl d IIo d IIo d IIo d IIo d IIo

100 3870 2110 2730 100 271 100 276 100 264 100 272 100111 2225 50200 1933 92 1919 90 1950 10 1905 30 1925 40

1860 200b211 1578 95 1569 80 1598 30 1562 60 1575 60

1503 10220 1367 70 1360 40 1383 20 1355 30 1368 30300 1290 4310 1225 25 1216 30 1233 15 1214 20 1222 20311 1168 8 1197 10222 1117 13 1111 5 1118 5320 1075 3321 1035 38 1028 60 1042 20 1029 10 1034 10400 09680 5411 0908 10 0912 5420 0864 10 0865 5332 08245 5 08260 3422 07910 3

1 synthetic NaLaTi2O6 a = 3873 AEcirc (ASTM 39-65) 2 lsquoirinitersquo (heated) a = 383 AEcirc (Borodin and Kazakova 1954)3 thorian loparite KHB-70 core (unheated) a = 3902(2) AEcirc 4 thorian loparite KHB-70 core (heated) a = 3841(1)AEcirc 5 thorian loparite KHB-70 rim (heated) a = 3867(2) AEcirc + 3 weak lines with d = 295 1795 1535 AEcirc (3-5 thiswork) b = broad line

R H MITCHELL AND A RCHAKHMOURADIAN

350

The absence of superstructure reflections in thepatterns of thorian loparite may result from itsmetamict state prior to heating ie from failure torestore an initial apparently distorted structure ofthe mineral Alternatively stabilization of thecubic structure may result from the presence ofminor cations in thorian loparite eg Ca or SrThis phenomenon refered to as stabilized poly-morphism (Smirnova and Belov 1969) is well-known for TiO2 and ZrO2 polymorphs (Filatovand Frank-Kamenetskii 1969 Grunin et al1983) To select between the two abovealternatives experimental studies of the solidsolution series between loparite and Th-bearingend-members are being undertaken by us

Discussion

At Khibina Th-rich loparite occurs only inrelation to the foyaite series (Borodin andKazakova 1954 Chakhmouradian and Mitchell1998 Kozyreva et al 1991 Tikhonenkova et al1982) Zoned Th-rich loparite examined in thisstudy crystallized at a late deuteric stage of theformation of foyaite pegmatites At this stagefluids enriched in Ti and incompatible elements(Zr Nb Sr LREE Th) gave rise to theassemblage of aegirine with loparite eudialyteand Ti-silicates (astrophyllite lorenzenitelamprophyllite) In a similar paragenesis lopariteoccurs in the foyaite pegmatites at MtNiorkpakhk (east of Mt Eveslogchorr) andkhibinite pegmatites at a number of localities inwestern Khibina (Chakhmouradian and Mitchell1998) In most of these occurrences loparite isrelatively Th-poor and compositionally evolvesby enrichment in Na2O and Nb2O5 and depletionin LREE2O3 and TiO2 contents toward the rimThis trend coincides with the main magmatictrend of the compositional evolution of loparite int h e n e p h e l i n e - s y e n i t e c o m p l e x e s(Chakhmouradian and Mitchell 1998 Mitchelland Chakhmouradian 1996) The evolutionarytrend from niobian loparite to thorian niobianloparite recognized in the present study has notbeen previously observed in alkaline rocksLoparite from fenite-type rocks of the ParanaBasin carbonatite complexes has high ThO2

contents (up to 62 wt) accompanied byenrichment in Na2O and Nb2O5 (lueshite) anddepletion in SrO and TiO2 (tausonite) (Mitchell1996 Table 36) Th-enrichment (up to 49 wtThO2) in the composition of perovskite from thecarbonatite complexes of the Kola Peninsula is

coupled with increasing LREE2O3 Na2O andNb2O5 ie loparite and lueshite components(Chakhmouradian and Mitchell 1997) In thePolino carbonatite Th-bearing (15 shy 17 wtThO2) perovskite has high Fe2O3 and ZrO2

contents (Lupini et al 1992)The limits of solubility between loparite

(NaLREETi2O6) and the thorium end-membercompositions ThNb4O12 Na23Th13TiO3 andThTi2O6 are unknown From structural data(Balic ZIuml unic et al 1984 Kovba and Trunov1963 Ruh and Wadsley 1966 Zhu and Hor1995) it is expected that loparite forms acomplete solid solution series with the formertwo compounds and only a limited series withThTi2O6 Experimental studies of the NaLaTi2O6

-ThNb4O12 NaLaTi2O6ndashNa2ThTi3O9 andNaLaTi2O6ndashThTi2O6 systems are being under-taken by the authors of this paper

As evidenced by textural relationships andcompositional data the appearance of Na-poorTh-rich lsquoceriobetafitersquo and belyankinite asmantles on thorian loparite was a result ofmetasomatic processes involving alkali-cationleaching and hydration Note that the sameprocesses brought about the replacement ofnepheline and alkali feldspar present as relics infibrous aegirine by zeolites and eventually bygibbsite Metasomatites including albitites albite-aegirine and albite-astrophyllite rocks are verycommon in the vicinity of pegmatite veinscontaining thorian loparite at Mt EveslogchorrHydrothermal solutions responsible for themetasomatic alteration most probably werederived from the phonolitic magma whichproduced the differentiated intrusion of nephelinesyenites including foyaite and its precursorkhibinite An alternative source of such solutionscould be a foidolite melt as some authors suggestthat the foidolites were emplaced later than thenephel ine syenite intrusion (Kostyleva-Labuntsova et al 1978a Sniatkova et al 1986)

Conclusions

In Na-LREE-Ti-dominant species of the perovs-kite group Th4+ cations occupy large twelve-coordinated A sites in the structure Theaccommodation of Th into the structure isaccompanied by appearance of vacancies at theA sites at the expense of Na LREE and SrThorian loparite is essentially a member of theloparite (NaLREETi2O6)ndashlueshite (NaNbO3)ndashThTi2O6ndashThNb4O12 quaternary system with low

TH-RICH LOPARITE

351

or negligible contents of other end-membercompositions The mineral compositionallyevolves from niobian loparite to niobian thorianand thorian niobian loparite Metasomatic altera-tion of thorian loparite gave rise to lsquoceriobetafitersquoand belyankinite with high ThO2 content Thorianloparite is metamict or partly metamict and uponheating regains a structure close to that ofsynthetic loparite NaLaTi2O6

Acknowledgements

This work was supported by the Natural Sciencesand Engineering Research Council of Canada andLakehead University Ontario (RHM ARC) ARCalso acknowledges support from St PetersburgState University Russia (grant Evolution offramework niobium-titanium oxides in carbona-tite-bearing nepheline-syenite complexes) AlanMacKenzie and Keith Pringnitz are thanked fortheir assistance with the analytical work AnnHammond and Sam Spivak are thanked for thinsection preparation and drafting services respec-tively

References

Balic ZIuml unic T SIuml cavnicIuml ar S and Grobenski Z (1984)The structure of thorium (IV) dititanium (IV) oxideThTi2O6 Croat Chem Acta 57 645 shy 51

Belous AG Novitskaya GN Gavrilova LGPolyanetskaya SV and Makarova ZYa (1985)Lanthanum titanate-zirconates with the perovskitestructure Sov Prog Chem 51 13 shy 15

Borodin LS (1954) On accommodation of water in thecrystal lattice of perovskite-group minerals DokladyAN SSSR 95 (in Russian) 873 shy 5

Borodin LS and Kazakova ME (1954) Irinite shy anew mineral from the perovskite group Doklady ANSSSR 97 (in Russian) 725 shy 8

Chakhmouradian AR and Mitchell RH (1997)Compositional variation of perovskite-group miner-als from the carbonatite complexes of the KolaAlkaline Province Russia Canad Mineral 351293 shy 310

Chakhmouradian AR and Mitchell RH (1998)Compositional variation of perovskite-group miner-als from the Khibina alkaline complex KolaPeninsula Canad Mineral 36 (in press)

Filatov SK and Frank-Kamenetskii VA (1969)Structural characteristics of cubic ZrO2 stabilizedby calcium Sov Phys Cryst 14 414 shy 5

Galakhov AV (1975) The petrology of the KhibinaAlkaline Massif Nauka Press Leningrad (in

Russian) 256 ppGerasimovski i VI and Kazakova ME (1950)

Belyankinite shy a new mineral Doklady AN SSSR 71 (in Russian) 925 shy 7

Grunin VS Razumenko MV Patrina IV FilatovSK and Alekseyeva TV (1983) Mode of existenceand abundance of TiO2-rutile anatase and brookiteDoklady Earth Sci Sect 268 149 shy 50

Haggerty SE and Mariano AN (1983) Strontian-loparite and strontio-chevkinite two new minerals inrheomorphic fenites from the Parana Basin carbona-tites South America Contrib Mineral Petrol 84365 shy 81

Hogarth DD (1961) A study of pyrochlore andbetafite Canad Mineral 6 610 shy 33

Hogarth DD (1989) Pyrochlore apatite and amphi-bole distinctive minerals in carbonatites InCarbonat ites (K Bell ed) Unwyn HymanLondon 105 shy 48

Kapustin YuL (1989) Rare earth-bearing pyrochlorefrom peralkaline pegmatites of the Khibina massifNew data on minerals (Trudy Mineral Muz ANSSSR ) 36 (in Russian) 155 shy 61

Keller C (1965) Die Reaktion der Dioxide derElemente Thorium bis Americium mit Niob- undTantalpentoxid (The reaction of dioxides of theelements from thorium to americium with niobiumand tantalum pentoxides) J Inorg Nucl Chem 271233 shy 46

Kogarko LN Kononova VA Orlova MP andWoolle y AR (1995 ) Alkaline Rocks andCarbonatites of the World Part 2 Former USSRChapman amp Hall London UK 226 pp

Kostyleva-Labuntsova EE Borutskii BE SokolovaMN Shliukova ZV Dorfman MD DudkinOB Kozyreva LV and Ikorskii SV (1978a) TheMineralogy of the Khibina Massif Vol 1 NaukaPress Moscow (in Russian) 228 p

Kostyleva-Labuntsova EE Borutskii BE SokolovaMN Shliukova ZV Dorfman MD DudkinOB Kozyreva LV and Ikorskii SV (1978b) TheMineralogy of the Khibina Massif Vol 2 NaukaPress Moscow (in Russian) 588 p

Kovba LM and Trunov VK (1962) Double oxidescontaining tungsten tantalum or niobium DokladyAN SSSR 147 (in Russian) 622 shy 4

Kozyreva LV (1990) Aegirine-feldspar veins in thenorth-eastern part of the Khibina massif In AlkalineMagmatism in the North-eastern Part of the BalticShield Kola Sci Centre Press Apatity (in Russian)42 shy 56

Kozyreva LV Menrsquoshikov YuP and Lednev AI(1991) Loparite mineralization of the Khibinamassif In New Data on the Rare-metalMineralogy of the Kola Peninsula Kola SciCentre Press Apatity (in Russian) 37 shy 44

R H MITCHELL AND A RCHAKHMOURADIAN

352

deficiency (Fig 3g) it is deduced that Th4+ cationsare accommodatedat the A site of loparite and thatthe correspondingsubstitution scheme involves theappearance of vacancies at these sites Calculationsshow that the observed relationship between Thcontent and number of vacancies at the A-site mostclosely corresponds to the solid solution seriesbetween loparite and two hypothetical end-members ThNb4O12 and ThTi2O6 (Fig 3) Theso l id solu t ion se r ies between lopari te

NaLREETi2O6 and Na23Th13TiO3 believed tobe present is not present as the A- and B-sitesoccupancy remains constant The isomorphicsubstitutions are as follows

2Na+ + 2LREE3+ + 4Ti4+ gtTh4+ + 3amp + 4Nb5+ (1)

Na+ + LREE3+ gt Th4+ + amp (2)

ThNb4O12 (= Th025NbO3) has been synthe-sized and shown to have a perovskite-type

TABLE 1 Representative compositions of major and accessory silicate minerals

Wt 1 2 3 4 5 6 7 8 9 10 11 12

Na2O 1281 1220 227 216 1124 1094 1066 1104 1707 1696 889 871K2O 004 008 602 606 041 035 064 061 nd nd 204 218CaO 225 267 141 155 929 879 045 040 005 008 056 067SrO na na nd nd 149 118 1306 1162 nd nd na naBaO na na nd nd nd nd 085 322 nd nd na naMgO 102 103 189 191 009 037 043 045 035 023 820 808MnO 037 039 1292 1329 383 452 558 526 nd 012 373 383FeO 060 136 1904 1850 392 324 na na na na 1393 1351Fe2O3 2670 2535 na na na na 293 250 080 069 592 662La2O3 na na nd nd 067 106 060 042 na na na naCe2O3 na na nd nd 140 131 052 026 na na na naAl2O3 165 117 086 104 nd nd 029 002 nd nd 101 130SiO2 5326 5196 3555 3550 4995 4852 3100 3035 3331 3382 5320 5236TiO2 181 197 1160 1157 040 023 2959 2991 4479 4516 098 125ZrO2 na na 065 049 1326 1220 nd nd nd nd na naNb2O5 na na 065 077 290 331 009 041 212 188 na na

Total 10052 9818 9286 9284 9885 9602 9669 9647 9849 9894 9846 9851

Structural formulaeO = 6 Si = 8 Si = 24 Si = 4 O = 9 O = 23

Na 0934 0913 0990 0944 10471 10492 2667 2821 1929 1904 2576 2530K 0002 0004 1728 1742 0251 0221 0105 0103 0shy 0shy 0389 0417Ca 0091 0111 0340 0374 4782 4658 0062 0056 0003 0005 0090 0107Sr 0shy 0shy 0shy 0shy 0415 0338 0977 0888 0shy 0shy 0shy 0shyBa 0shy 0shy 0shy 0shy 0shy 0shy 0043 0166 0shy 0shy 0shy 0shyMg 0057 0059 0634 0642 0064 0273 0083 0088 0030 0020 1827 1804Mn 0012 0013 2463 2537 1559 1894 0610 0587 0shy 0006 0472 0486Fe2+ 0020 0047 3583 3486 1575 1340 0shy 0shy 0shy 0shy 1742 1693Fe3+ 0756 0735 0shy 0shy 0shy 0shy 0284 0248 0035 00300 0666 0747La 0shy 0shy 0shy 0shy 0119 0193 0029 0020 0shy 0shy 0shy 0shyCe 0shy 0shy 0shy 0shy 0246 0237 0025 0013 0shy 0shy 0shy 0shyAl 0073 0054 0228 0276 0shy 0shy 0044 0003 0shy 0shy 0178 0229Si 2003 2007 8000 8000 24000 24000 4000 4000 1942 1958 7951 7845Ti 0052 0057 1963 1961 0145 0086 2871 2964 1963 1966 0110 0141Zr 0shy 0shy 0071 0054 3107 2943 0shy 0shy 0shy 0shy 0shy 0shyNb 0shy 0shy 0066 0078 0630 0740 0005 0024 0056 0049 0shy 0shy

Compositions 1 and 2 aegirine 3 and 4 astrophyllite 5 and 6 eudialyte 7 and 8 lamprophyllite 9 and 10lorenzenite 11 and 12 magnesio-arfvedsoniteAll data this work Fe2+Fe3+ ratio calculated using Drooprsquos (1987) method

TH-RICH LOPARITE

345

structure (Keller 1965 Kovba and Trunov1963) Thorium dititanate (ThTi2O6) occurs intwo polymorphs of monoclinic symmetryStructures of both polymorphs differ from thatof perovskite in being built of sheets of edge-sharing TiO6 octahedra bound by Th atoms ineither six-fold or eight-fold coordination (BalicZIuml unic et al 1984 Ruh and Wadsley 1966)Given the considerable structural differenceloparite and thorium dititanate apparently should

not form a continuous solid solution serieshowever limits of the solubility between thesetwo end-members are unknown Our data suggestat least 23 mol ThTi2O6 is possible

The compositions of Th-rich loparite wererecalculated into major perovskite-group end-members (Mitchell 1996) plus the two thoriumcompounds ThNb4O12 and ThTi2O6 (Table 2Fig 4) The loparite composition evolves bybecoming enriched in the thorium end-members

TABLE 2 Representative compositions of loparite

Wt 1 2 3 4 5 6 7 8 9

Na2O 1043 868 850 742 669 971 918 766 662CaO 153 159 171 150 163 182 208 162 186SrO 140 133 129 133 109 165 177 131 120La2O3 972 888 647 646 541 1142 937 824 579Ce2O3 1477 1421 1119 1027 891 1691 1464 1337 987Pr2O3 186 172 156 nd 114 103 220 254 138Nd2O3 204 202 156 196 186 161 247 198 195ThO2 346 738 1029 1540 1845 234 366 869 1728TiO2 3239 3308 3046 3365 3372 3437 3241 3355 3480FeO 012 007 007 nd 011 007 nd 011 048Nb2O5 2138 2198 2716 2210 2018 1872 2213 2034 1962Ta2O5 037 022 032 043 030 033 049 059 058

Total 9947 10116 10058 10052 9949 9998 10040 10000 10143

Structural formulae (O = 3)Na 0589 0486 0477 0420 0387 0545 0515 0436 0375Ca 0048 0049 0053 0047 0052 0056 0064 0051 0058Sr 0024 0022 0022 0022 0019 0028 0030 0022 0020La 0104 0095 0069 0070 0060 0122 0100 0089 0062Ce 0158 0150 0118 0110 0097 0179 0155 0144 0106Pr 0020 0018 0016 0000 0012 0011 0023 0027 0015Nd 0021 0021 0016 0020 0020 0017 0026 0021 0020Th 0023 0048 0067 0102 0125 0015 0024 0058 0115Ti 0710 0719 0663 0739 0756 0749 0705 0741 0764Fe 0003 0002 0002 0000 0003 0002 0000 0002 0012Nb 0282 0287 0355 0292 0272 0245 0290 0270 0259Ta 0003 0002 0002 0003 0002 0003 0004 0005 0005

Mol end-membersNaCeTi2O66010 5799 4593 4306 4047 6580 6103 5833 4368NaNbO3 2820 2062 2706 2368 2120 2160 2118 1609 1850ThNb4O12 000 868 1017 775 792 290 793 1194 936ThTi2O6 456 546 897 1808 2281 155 043 607 2006CaTiO3 476 500 556 506 557 560 642 529 625SrTiO3 238 225 231 237 203 255 301 228 215

Compositions 1 shy 2 core and 3 shy 5 rim of a zoned loparite crystal KHB-44 6 shy 7 core and 8 shy 9 rim of a zonedloparite crystal KHB-70All data this workTotal Fe expressed as FeO nd = not detected

R H MITCHELL AND A RCHAKHMOURADIAN

346

at essentially constant lueshite content Usingnomenclature principles suggested for the perovs-kite-group minerals by Mitchell (1996) theexamined samples compositionally evolve fromniobian loparite toward niobian thorian andthorian niobian loparite

BetafiteRepresentative analyses of betafite developed

in thorian loparite are given in Table 3 LREEdominated by Ce and Th are the major A-cationsAccording to the classification scheme proposedby Hogarth (1989) for the pyrochlore-groupminerals this mineral should be regarded asceriobetafite or thorium ceriobetafite (LREE gtThgt 20 cation sum at the A sites) In this studywe prefer to refer to the mineral using quotationmarks as lsquoceriobetafitersquo is not approved as adistinct mineral species by the Comission on NewMinerals and Mineral Names of the IMA

At the Khibina complex pyrochlore-groupminerals were previously described as accessoryconstituents of aegirine-feldspar veins (Kozyreva

1990) and peralkaline pegmatites (Kapustin 1989Shilin et al 1966) These minerals correspond topyrochlore sensu stricto that may be somewhatenriched in SrO (Shilin et al 1966) or LREE(Kapustin 1989) Ti-dominant species ie membersof the betafite subgroup have not been previouslyrecognized in the Khibina alkaline complex

BelyankiniteCompositional data on belyankinite and related

Ti-Nb hydroxides available from literature arelimited to a few bulk wet-chemical analyses(Gerasimovskii and Kazakova 1950 Semenov1957 Vlasov et al 1966) Semenov (1957) hassuggested that Ti-dominant belyankinite formssolid solution series with its Mn-analoguemanganbelyankinite and Nb-dominant gerasi-movskite The mineral examined in the presentstudy is a member of the belyankinitendashgerasi-movskite series with negligible content ofmanganbelyankinite (Table 4) A generalizedstructural formula of belyankinite calculated onthe basis of 12 atoms of oxygen is

FIG 3 Variations (apfu) of (a) Na (b) LREE (c) Ca (d) Sr (e) Ti (f) Nb and (g) cation totals at the A and B siteswith respect to Th for Th-rich loparite Circles correspond to loparite KHB-44 squares to KHB-70 Variation of A-cation totals in the solid solution series NaLREETi2O6shy Na2ThTi3O9 is shown by solid line in the series

NaLREETi2O6shy ThTi2O6 by dashed line and in the series NaLREETi2O6shy ThNb4O12 by dash-dotted line (g)

TH-RICH LOPARITE

347

FIG 4 Compositions (mol) of Th-rich loparite in the system loparite (NaCeTi2O6)ndashlueshite (NaNbO3)ndashThTi2O6ndashThNb4O12

R H MITCHELL AND A RCHAKHMOURADIAN

348

(Ca ThLR EE )1 3(T i Nb Si Fe )5O12 nH2O(average of 18 determinations) and approachesthat deduced by Fleischer from Semenovrsquosanalytical data (see reference to Semenov1957) Ca 0 9(T i Zr NbS i )5 5O12 10H2O

However the mineral from Khibina differs fromLovozero belyankinite in having much higherThO2 (up to 2417 wt) and LREE2O3 (up to116 wt) contents both of which are undoubt-edly lsquoinheritedrsquo from the loparite parent

TABLE 3 Representative compositions of lsquoceriobetafitersquo

1 2 3 1 2 3

Wt Structural formulae(SB-cations = 2)

Na2O 101 054 034 Na 0111 0060 0036CaO 179 167 176 Ca 0108 0102 0103SrO 117 115 130 Sr 0038 0038 0041La2O3 579 481 510 La 0121 0101 0103Ce2O3 901 865 846 Ce 0186 0180 0169Nd2O3 152 262 114 Nd 0034 0053 0022ThO2 1965 2088 2041 Th 0244 0270 0253TiO2 3382 3506 3750 Ti 1438 1499 1539Fe2O3 nd 003 047 Fe 0000 0001 0017Nb2O5 2177 1926 1776 Nb 0556 0495 0438Ta2O5 037 034 039 Ta 0006 0005 0006

Total 9540 9501 9463

Compositions 1 and 2 KHB-44 3 KHB-70All data this workTotal Fe expressed as Fe2O3 nd = not detected

TABLE 4 Representative compositions of belyankinite

1 2 1 2

Wt Structural formulae(O = 24)

Na2O 003 028 Na 0014 0122CaO 412 162 Ca 1027 0402MgO 016 017 Mg 0055 0060MnO 011 028 Mn 0022 0053La2O3 208 200 La 0179 0169Ce2O3 862 221 Ce 0733 0186Nd2O3 081 076 Nd 0067 0062ThO2 1242 2417 Th 0657 1264SiO2 1303 1221 Si 3033 2805TiO2 2281 2473 Ti 3991 4273Al2O3 121 166 Al 0331 0450Fe2O3 616 507 Fe 1078 0877Nb2O5 1502 1587 Nb 1578 1649

Total 8658 9103

Compositions 1 and 2 replacement mantles on thorian loparite KHB-70Total Fe expressed as Fe2O3 ZrO2 was sought but not found

TH-RICH LOPARITE

349

X-ray powder diffractometry

An XRD powder pattern of a sample of the coreof a thorian loparite showed only a few faintdiffraction lines with relatively high d-spacingswhereas a rim sample appeared to be completelymetamict After heating to 7008C for 1 hour thecore and rim samples gave XRD powder patterns(Table 5) similar to those of La-dominantsynthetic loparite NaLaTi2O6 and lsquoirinitersquo asdescribed by Borodin and Kazakova (1954) Theformer has been proposed to have the undistortedcubic lattice (ASTM 39-65 Belous et al 1985)However Rietveld refinement of an XRD powderpattern of NaLaTi2O6 suggests that thiscompound is orthorhombic (space group Pnma)rather than cubic (Mitchell and Chakhmouradianin preparation) The pattern of the rim sample ofthorian loparite also includes three diffractionlines with d-spacings of 295 1795 and 1535 AEcirc that cannot be produced by the perovskite-typestructure These are characteristic of pyrochlore-type phases and correspond to the most intenselines 222 440 and 622 respectively (ASTM 13-197 ASTM 17-746)

Data available from the literature show thatXRD powder patterns similar to those obtained inthis study are produced by naturally occurringloparite of various Nb2O5 CaO Na2O TiO2 andSrO contents (Haggerty and Mariano 1983Kostyleva-Labuntsova et al 1978b Mitchell etal 1996) Given a significant difference in ionicradius between Th4+ Na+ and Ce3+ (121 139and 134 AEcirc respectively Shannon 1976) it isexpected that Th-rich loparite should have astrongly distorted perovskite-type structureHowever the obtained patterns (Table 5) do notexhibit lsquoextrarsquo diffraction lines reflecting cationordering or geometric distortion of the ideal cubicperovskite-type lattice Such diffraction lines eg769 shy 790 344shy 350 257shy 260 187 shy 189 AEcirc are present in patterns of most syntheticperovskite-type titanates and niobates with Th4+

localized at the A sites (Keller 1965 Kovba andTrunov 1963 Labeau and Joubert 1978 Zhu andHor 1995) The only known exceptions so far arecompounds from the Na06shy 08Th01 shy 02NbO3

range of the NaNbO3shy Th025NbO3 solid solutionseries (ASTM-34-1068 Labeau and Joubert1978 Table III)

TABLE 5 X-ray diffraction patterns of loparite lsquoirinitersquo and Th-rich loparite

1 2 3 4 5hkl d IIo d IIo d IIo d IIo d IIo

100 3870 2110 2730 100 271 100 276 100 264 100 272 100111 2225 50200 1933 92 1919 90 1950 10 1905 30 1925 40

1860 200b211 1578 95 1569 80 1598 30 1562 60 1575 60

1503 10220 1367 70 1360 40 1383 20 1355 30 1368 30300 1290 4310 1225 25 1216 30 1233 15 1214 20 1222 20311 1168 8 1197 10222 1117 13 1111 5 1118 5320 1075 3321 1035 38 1028 60 1042 20 1029 10 1034 10400 09680 5411 0908 10 0912 5420 0864 10 0865 5332 08245 5 08260 3422 07910 3

1 synthetic NaLaTi2O6 a = 3873 AEcirc (ASTM 39-65) 2 lsquoirinitersquo (heated) a = 383 AEcirc (Borodin and Kazakova 1954)3 thorian loparite KHB-70 core (unheated) a = 3902(2) AEcirc 4 thorian loparite KHB-70 core (heated) a = 3841(1)AEcirc 5 thorian loparite KHB-70 rim (heated) a = 3867(2) AEcirc + 3 weak lines with d = 295 1795 1535 AEcirc (3-5 thiswork) b = broad line

R H MITCHELL AND A RCHAKHMOURADIAN

350

The absence of superstructure reflections in thepatterns of thorian loparite may result from itsmetamict state prior to heating ie from failure torestore an initial apparently distorted structure ofthe mineral Alternatively stabilization of thecubic structure may result from the presence ofminor cations in thorian loparite eg Ca or SrThis phenomenon refered to as stabilized poly-morphism (Smirnova and Belov 1969) is well-known for TiO2 and ZrO2 polymorphs (Filatovand Frank-Kamenetskii 1969 Grunin et al1983) To select between the two abovealternatives experimental studies of the solidsolution series between loparite and Th-bearingend-members are being undertaken by us

Discussion

At Khibina Th-rich loparite occurs only inrelation to the foyaite series (Borodin andKazakova 1954 Chakhmouradian and Mitchell1998 Kozyreva et al 1991 Tikhonenkova et al1982) Zoned Th-rich loparite examined in thisstudy crystallized at a late deuteric stage of theformation of foyaite pegmatites At this stagefluids enriched in Ti and incompatible elements(Zr Nb Sr LREE Th) gave rise to theassemblage of aegirine with loparite eudialyteand Ti-silicates (astrophyllite lorenzenitelamprophyllite) In a similar paragenesis lopariteoccurs in the foyaite pegmatites at MtNiorkpakhk (east of Mt Eveslogchorr) andkhibinite pegmatites at a number of localities inwestern Khibina (Chakhmouradian and Mitchell1998) In most of these occurrences loparite isrelatively Th-poor and compositionally evolvesby enrichment in Na2O and Nb2O5 and depletionin LREE2O3 and TiO2 contents toward the rimThis trend coincides with the main magmatictrend of the compositional evolution of loparite int h e n e p h e l i n e - s y e n i t e c o m p l e x e s(Chakhmouradian and Mitchell 1998 Mitchelland Chakhmouradian 1996) The evolutionarytrend from niobian loparite to thorian niobianloparite recognized in the present study has notbeen previously observed in alkaline rocksLoparite from fenite-type rocks of the ParanaBasin carbonatite complexes has high ThO2

contents (up to 62 wt) accompanied byenrichment in Na2O and Nb2O5 (lueshite) anddepletion in SrO and TiO2 (tausonite) (Mitchell1996 Table 36) Th-enrichment (up to 49 wtThO2) in the composition of perovskite from thecarbonatite complexes of the Kola Peninsula is

coupled with increasing LREE2O3 Na2O andNb2O5 ie loparite and lueshite components(Chakhmouradian and Mitchell 1997) In thePolino carbonatite Th-bearing (15 shy 17 wtThO2) perovskite has high Fe2O3 and ZrO2

contents (Lupini et al 1992)The limits of solubility between loparite

(NaLREETi2O6) and the thorium end-membercompositions ThNb4O12 Na23Th13TiO3 andThTi2O6 are unknown From structural data(Balic ZIuml unic et al 1984 Kovba and Trunov1963 Ruh and Wadsley 1966 Zhu and Hor1995) it is expected that loparite forms acomplete solid solution series with the formertwo compounds and only a limited series withThTi2O6 Experimental studies of the NaLaTi2O6

-ThNb4O12 NaLaTi2O6ndashNa2ThTi3O9 andNaLaTi2O6ndashThTi2O6 systems are being under-taken by the authors of this paper

As evidenced by textural relationships andcompositional data the appearance of Na-poorTh-rich lsquoceriobetafitersquo and belyankinite asmantles on thorian loparite was a result ofmetasomatic processes involving alkali-cationleaching and hydration Note that the sameprocesses brought about the replacement ofnepheline and alkali feldspar present as relics infibrous aegirine by zeolites and eventually bygibbsite Metasomatites including albitites albite-aegirine and albite-astrophyllite rocks are verycommon in the vicinity of pegmatite veinscontaining thorian loparite at Mt EveslogchorrHydrothermal solutions responsible for themetasomatic alteration most probably werederived from the phonolitic magma whichproduced the differentiated intrusion of nephelinesyenites including foyaite and its precursorkhibinite An alternative source of such solutionscould be a foidolite melt as some authors suggestthat the foidolites were emplaced later than thenephel ine syenite intrusion (Kostyleva-Labuntsova et al 1978a Sniatkova et al 1986)

Conclusions

In Na-LREE-Ti-dominant species of the perovs-kite group Th4+ cations occupy large twelve-coordinated A sites in the structure Theaccommodation of Th into the structure isaccompanied by appearance of vacancies at theA sites at the expense of Na LREE and SrThorian loparite is essentially a member of theloparite (NaLREETi2O6)ndashlueshite (NaNbO3)ndashThTi2O6ndashThNb4O12 quaternary system with low

TH-RICH LOPARITE

351

or negligible contents of other end-membercompositions The mineral compositionallyevolves from niobian loparite to niobian thorianand thorian niobian loparite Metasomatic altera-tion of thorian loparite gave rise to lsquoceriobetafitersquoand belyankinite with high ThO2 content Thorianloparite is metamict or partly metamict and uponheating regains a structure close to that ofsynthetic loparite NaLaTi2O6

Acknowledgements

This work was supported by the Natural Sciencesand Engineering Research Council of Canada andLakehead University Ontario (RHM ARC) ARCalso acknowledges support from St PetersburgState University Russia (grant Evolution offramework niobium-titanium oxides in carbona-tite-bearing nepheline-syenite complexes) AlanMacKenzie and Keith Pringnitz are thanked fortheir assistance with the analytical work AnnHammond and Sam Spivak are thanked for thinsection preparation and drafting services respec-tively

References

Balic ZIuml unic T SIuml cavnicIuml ar S and Grobenski Z (1984)The structure of thorium (IV) dititanium (IV) oxideThTi2O6 Croat Chem Acta 57 645 shy 51

Belous AG Novitskaya GN Gavrilova LGPolyanetskaya SV and Makarova ZYa (1985)Lanthanum titanate-zirconates with the perovskitestructure Sov Prog Chem 51 13 shy 15

Borodin LS (1954) On accommodation of water in thecrystal lattice of perovskite-group minerals DokladyAN SSSR 95 (in Russian) 873 shy 5

Borodin LS and Kazakova ME (1954) Irinite shy anew mineral from the perovskite group Doklady ANSSSR 97 (in Russian) 725 shy 8

Chakhmouradian AR and Mitchell RH (1997)Compositional variation of perovskite-group miner-als from the carbonatite complexes of the KolaAlkaline Province Russia Canad Mineral 351293 shy 310

Chakhmouradian AR and Mitchell RH (1998)Compositional variation of perovskite-group miner-als from the Khibina alkaline complex KolaPeninsula Canad Mineral 36 (in press)

Filatov SK and Frank-Kamenetskii VA (1969)Structural characteristics of cubic ZrO2 stabilizedby calcium Sov Phys Cryst 14 414 shy 5

Galakhov AV (1975) The petrology of the KhibinaAlkaline Massif Nauka Press Leningrad (in

Russian) 256 ppGerasimovski i VI and Kazakova ME (1950)

Belyankinite shy a new mineral Doklady AN SSSR 71 (in Russian) 925 shy 7

Grunin VS Razumenko MV Patrina IV FilatovSK and Alekseyeva TV (1983) Mode of existenceand abundance of TiO2-rutile anatase and brookiteDoklady Earth Sci Sect 268 149 shy 50

Haggerty SE and Mariano AN (1983) Strontian-loparite and strontio-chevkinite two new minerals inrheomorphic fenites from the Parana Basin carbona-tites South America Contrib Mineral Petrol 84365 shy 81

Hogarth DD (1961) A study of pyrochlore andbetafite Canad Mineral 6 610 shy 33

Hogarth DD (1989) Pyrochlore apatite and amphi-bole distinctive minerals in carbonatites InCarbonat ites (K Bell ed) Unwyn HymanLondon 105 shy 48

Kapustin YuL (1989) Rare earth-bearing pyrochlorefrom peralkaline pegmatites of the Khibina massifNew data on minerals (Trudy Mineral Muz ANSSSR ) 36 (in Russian) 155 shy 61

Keller C (1965) Die Reaktion der Dioxide derElemente Thorium bis Americium mit Niob- undTantalpentoxid (The reaction of dioxides of theelements from thorium to americium with niobiumand tantalum pentoxides) J Inorg Nucl Chem 271233 shy 46

Kogarko LN Kononova VA Orlova MP andWoolle y AR (1995 ) Alkaline Rocks andCarbonatites of the World Part 2 Former USSRChapman amp Hall London UK 226 pp

Kostyleva-Labuntsova EE Borutskii BE SokolovaMN Shliukova ZV Dorfman MD DudkinOB Kozyreva LV and Ikorskii SV (1978a) TheMineralogy of the Khibina Massif Vol 1 NaukaPress Moscow (in Russian) 228 p

Kostyleva-Labuntsova EE Borutskii BE SokolovaMN Shliukova ZV Dorfman MD DudkinOB Kozyreva LV and Ikorskii SV (1978b) TheMineralogy of the Khibina Massif Vol 2 NaukaPress Moscow (in Russian) 588 p

Kovba LM and Trunov VK (1962) Double oxidescontaining tungsten tantalum or niobium DokladyAN SSSR 147 (in Russian) 622 shy 4

Kozyreva LV (1990) Aegirine-feldspar veins in thenorth-eastern part of the Khibina massif In AlkalineMagmatism in the North-eastern Part of the BalticShield Kola Sci Centre Press Apatity (in Russian)42 shy 56

Kozyreva LV Menrsquoshikov YuP and Lednev AI(1991) Loparite mineralization of the Khibinamassif In New Data on the Rare-metalMineralogy of the Kola Peninsula Kola SciCentre Press Apatity (in Russian) 37 shy 44

R H MITCHELL AND A RCHAKHMOURADIAN

352

structure (Keller 1965 Kovba and Trunov1963) Thorium dititanate (ThTi2O6) occurs intwo polymorphs of monoclinic symmetryStructures of both polymorphs differ from thatof perovskite in being built of sheets of edge-sharing TiO6 octahedra bound by Th atoms ineither six-fold or eight-fold coordination (BalicZIuml unic et al 1984 Ruh and Wadsley 1966)Given the considerable structural differenceloparite and thorium dititanate apparently should

not form a continuous solid solution serieshowever limits of the solubility between thesetwo end-members are unknown Our data suggestat least 23 mol ThTi2O6 is possible

The compositions of Th-rich loparite wererecalculated into major perovskite-group end-members (Mitchell 1996) plus the two thoriumcompounds ThNb4O12 and ThTi2O6 (Table 2Fig 4) The loparite composition evolves bybecoming enriched in the thorium end-members

TABLE 2 Representative compositions of loparite

Wt 1 2 3 4 5 6 7 8 9

Na2O 1043 868 850 742 669 971 918 766 662CaO 153 159 171 150 163 182 208 162 186SrO 140 133 129 133 109 165 177 131 120La2O3 972 888 647 646 541 1142 937 824 579Ce2O3 1477 1421 1119 1027 891 1691 1464 1337 987Pr2O3 186 172 156 nd 114 103 220 254 138Nd2O3 204 202 156 196 186 161 247 198 195ThO2 346 738 1029 1540 1845 234 366 869 1728TiO2 3239 3308 3046 3365 3372 3437 3241 3355 3480FeO 012 007 007 nd 011 007 nd 011 048Nb2O5 2138 2198 2716 2210 2018 1872 2213 2034 1962Ta2O5 037 022 032 043 030 033 049 059 058

Total 9947 10116 10058 10052 9949 9998 10040 10000 10143

Structural formulae (O = 3)Na 0589 0486 0477 0420 0387 0545 0515 0436 0375Ca 0048 0049 0053 0047 0052 0056 0064 0051 0058Sr 0024 0022 0022 0022 0019 0028 0030 0022 0020La 0104 0095 0069 0070 0060 0122 0100 0089 0062Ce 0158 0150 0118 0110 0097 0179 0155 0144 0106Pr 0020 0018 0016 0000 0012 0011 0023 0027 0015Nd 0021 0021 0016 0020 0020 0017 0026 0021 0020Th 0023 0048 0067 0102 0125 0015 0024 0058 0115Ti 0710 0719 0663 0739 0756 0749 0705 0741 0764Fe 0003 0002 0002 0000 0003 0002 0000 0002 0012Nb 0282 0287 0355 0292 0272 0245 0290 0270 0259Ta 0003 0002 0002 0003 0002 0003 0004 0005 0005

Mol end-membersNaCeTi2O66010 5799 4593 4306 4047 6580 6103 5833 4368NaNbO3 2820 2062 2706 2368 2120 2160 2118 1609 1850ThNb4O12 000 868 1017 775 792 290 793 1194 936ThTi2O6 456 546 897 1808 2281 155 043 607 2006CaTiO3 476 500 556 506 557 560 642 529 625SrTiO3 238 225 231 237 203 255 301 228 215

Compositions 1 shy 2 core and 3 shy 5 rim of a zoned loparite crystal KHB-44 6 shy 7 core and 8 shy 9 rim of a zonedloparite crystal KHB-70All data this workTotal Fe expressed as FeO nd = not detected

R H MITCHELL AND A RCHAKHMOURADIAN

346

at essentially constant lueshite content Usingnomenclature principles suggested for the perovs-kite-group minerals by Mitchell (1996) theexamined samples compositionally evolve fromniobian loparite toward niobian thorian andthorian niobian loparite

BetafiteRepresentative analyses of betafite developed

in thorian loparite are given in Table 3 LREEdominated by Ce and Th are the major A-cationsAccording to the classification scheme proposedby Hogarth (1989) for the pyrochlore-groupminerals this mineral should be regarded asceriobetafite or thorium ceriobetafite (LREE gtThgt 20 cation sum at the A sites) In this studywe prefer to refer to the mineral using quotationmarks as lsquoceriobetafitersquo is not approved as adistinct mineral species by the Comission on NewMinerals and Mineral Names of the IMA

At the Khibina complex pyrochlore-groupminerals were previously described as accessoryconstituents of aegirine-feldspar veins (Kozyreva

1990) and peralkaline pegmatites (Kapustin 1989Shilin et al 1966) These minerals correspond topyrochlore sensu stricto that may be somewhatenriched in SrO (Shilin et al 1966) or LREE(Kapustin 1989) Ti-dominant species ie membersof the betafite subgroup have not been previouslyrecognized in the Khibina alkaline complex

BelyankiniteCompositional data on belyankinite and related

Ti-Nb hydroxides available from literature arelimited to a few bulk wet-chemical analyses(Gerasimovskii and Kazakova 1950 Semenov1957 Vlasov et al 1966) Semenov (1957) hassuggested that Ti-dominant belyankinite formssolid solution series with its Mn-analoguemanganbelyankinite and Nb-dominant gerasi-movskite The mineral examined in the presentstudy is a member of the belyankinitendashgerasi-movskite series with negligible content ofmanganbelyankinite (Table 4) A generalizedstructural formula of belyankinite calculated onthe basis of 12 atoms of oxygen is

FIG 3 Variations (apfu) of (a) Na (b) LREE (c) Ca (d) Sr (e) Ti (f) Nb and (g) cation totals at the A and B siteswith respect to Th for Th-rich loparite Circles correspond to loparite KHB-44 squares to KHB-70 Variation of A-cation totals in the solid solution series NaLREETi2O6shy Na2ThTi3O9 is shown by solid line in the series

NaLREETi2O6shy ThTi2O6 by dashed line and in the series NaLREETi2O6shy ThNb4O12 by dash-dotted line (g)

TH-RICH LOPARITE

347

FIG 4 Compositions (mol) of Th-rich loparite in the system loparite (NaCeTi2O6)ndashlueshite (NaNbO3)ndashThTi2O6ndashThNb4O12

R H MITCHELL AND A RCHAKHMOURADIAN

348

(Ca ThLR EE )1 3(T i Nb Si Fe )5O12 nH2O(average of 18 determinations) and approachesthat deduced by Fleischer from Semenovrsquosanalytical data (see reference to Semenov1957) Ca 0 9(T i Zr NbS i )5 5O12 10H2O

However the mineral from Khibina differs fromLovozero belyankinite in having much higherThO2 (up to 2417 wt) and LREE2O3 (up to116 wt) contents both of which are undoubt-edly lsquoinheritedrsquo from the loparite parent

TABLE 3 Representative compositions of lsquoceriobetafitersquo

1 2 3 1 2 3

Wt Structural formulae(SB-cations = 2)

Na2O 101 054 034 Na 0111 0060 0036CaO 179 167 176 Ca 0108 0102 0103SrO 117 115 130 Sr 0038 0038 0041La2O3 579 481 510 La 0121 0101 0103Ce2O3 901 865 846 Ce 0186 0180 0169Nd2O3 152 262 114 Nd 0034 0053 0022ThO2 1965 2088 2041 Th 0244 0270 0253TiO2 3382 3506 3750 Ti 1438 1499 1539Fe2O3 nd 003 047 Fe 0000 0001 0017Nb2O5 2177 1926 1776 Nb 0556 0495 0438Ta2O5 037 034 039 Ta 0006 0005 0006

Total 9540 9501 9463

Compositions 1 and 2 KHB-44 3 KHB-70All data this workTotal Fe expressed as Fe2O3 nd = not detected

TABLE 4 Representative compositions of belyankinite

1 2 1 2

Wt Structural formulae(O = 24)

Na2O 003 028 Na 0014 0122CaO 412 162 Ca 1027 0402MgO 016 017 Mg 0055 0060MnO 011 028 Mn 0022 0053La2O3 208 200 La 0179 0169Ce2O3 862 221 Ce 0733 0186Nd2O3 081 076 Nd 0067 0062ThO2 1242 2417 Th 0657 1264SiO2 1303 1221 Si 3033 2805TiO2 2281 2473 Ti 3991 4273Al2O3 121 166 Al 0331 0450Fe2O3 616 507 Fe 1078 0877Nb2O5 1502 1587 Nb 1578 1649

Total 8658 9103

Compositions 1 and 2 replacement mantles on thorian loparite KHB-70Total Fe expressed as Fe2O3 ZrO2 was sought but not found

TH-RICH LOPARITE

349

X-ray powder diffractometry

An XRD powder pattern of a sample of the coreof a thorian loparite showed only a few faintdiffraction lines with relatively high d-spacingswhereas a rim sample appeared to be completelymetamict After heating to 7008C for 1 hour thecore and rim samples gave XRD powder patterns(Table 5) similar to those of La-dominantsynthetic loparite NaLaTi2O6 and lsquoirinitersquo asdescribed by Borodin and Kazakova (1954) Theformer has been proposed to have the undistortedcubic lattice (ASTM 39-65 Belous et al 1985)However Rietveld refinement of an XRD powderpattern of NaLaTi2O6 suggests that thiscompound is orthorhombic (space group Pnma)rather than cubic (Mitchell and Chakhmouradianin preparation) The pattern of the rim sample ofthorian loparite also includes three diffractionlines with d-spacings of 295 1795 and 1535 AEcirc that cannot be produced by the perovskite-typestructure These are characteristic of pyrochlore-type phases and correspond to the most intenselines 222 440 and 622 respectively (ASTM 13-197 ASTM 17-746)

Data available from the literature show thatXRD powder patterns similar to those obtained inthis study are produced by naturally occurringloparite of various Nb2O5 CaO Na2O TiO2 andSrO contents (Haggerty and Mariano 1983Kostyleva-Labuntsova et al 1978b Mitchell etal 1996) Given a significant difference in ionicradius between Th4+ Na+ and Ce3+ (121 139and 134 AEcirc respectively Shannon 1976) it isexpected that Th-rich loparite should have astrongly distorted perovskite-type structureHowever the obtained patterns (Table 5) do notexhibit lsquoextrarsquo diffraction lines reflecting cationordering or geometric distortion of the ideal cubicperovskite-type lattice Such diffraction lines eg769 shy 790 344shy 350 257shy 260 187 shy 189 AEcirc are present in patterns of most syntheticperovskite-type titanates and niobates with Th4+

localized at the A sites (Keller 1965 Kovba andTrunov 1963 Labeau and Joubert 1978 Zhu andHor 1995) The only known exceptions so far arecompounds from the Na06shy 08Th01 shy 02NbO3

range of the NaNbO3shy Th025NbO3 solid solutionseries (ASTM-34-1068 Labeau and Joubert1978 Table III)

TABLE 5 X-ray diffraction patterns of loparite lsquoirinitersquo and Th-rich loparite

1 2 3 4 5hkl d IIo d IIo d IIo d IIo d IIo

100 3870 2110 2730 100 271 100 276 100 264 100 272 100111 2225 50200 1933 92 1919 90 1950 10 1905 30 1925 40

1860 200b211 1578 95 1569 80 1598 30 1562 60 1575 60

1503 10220 1367 70 1360 40 1383 20 1355 30 1368 30300 1290 4310 1225 25 1216 30 1233 15 1214 20 1222 20311 1168 8 1197 10222 1117 13 1111 5 1118 5320 1075 3321 1035 38 1028 60 1042 20 1029 10 1034 10400 09680 5411 0908 10 0912 5420 0864 10 0865 5332 08245 5 08260 3422 07910 3

1 synthetic NaLaTi2O6 a = 3873 AEcirc (ASTM 39-65) 2 lsquoirinitersquo (heated) a = 383 AEcirc (Borodin and Kazakova 1954)3 thorian loparite KHB-70 core (unheated) a = 3902(2) AEcirc 4 thorian loparite KHB-70 core (heated) a = 3841(1)AEcirc 5 thorian loparite KHB-70 rim (heated) a = 3867(2) AEcirc + 3 weak lines with d = 295 1795 1535 AEcirc (3-5 thiswork) b = broad line

R H MITCHELL AND A RCHAKHMOURADIAN

350

The absence of superstructure reflections in thepatterns of thorian loparite may result from itsmetamict state prior to heating ie from failure torestore an initial apparently distorted structure ofthe mineral Alternatively stabilization of thecubic structure may result from the presence ofminor cations in thorian loparite eg Ca or SrThis phenomenon refered to as stabilized poly-morphism (Smirnova and Belov 1969) is well-known for TiO2 and ZrO2 polymorphs (Filatovand Frank-Kamenetskii 1969 Grunin et al1983) To select between the two abovealternatives experimental studies of the solidsolution series between loparite and Th-bearingend-members are being undertaken by us

Discussion

At Khibina Th-rich loparite occurs only inrelation to the foyaite series (Borodin andKazakova 1954 Chakhmouradian and Mitchell1998 Kozyreva et al 1991 Tikhonenkova et al1982) Zoned Th-rich loparite examined in thisstudy crystallized at a late deuteric stage of theformation of foyaite pegmatites At this stagefluids enriched in Ti and incompatible elements(Zr Nb Sr LREE Th) gave rise to theassemblage of aegirine with loparite eudialyteand Ti-silicates (astrophyllite lorenzenitelamprophyllite) In a similar paragenesis lopariteoccurs in the foyaite pegmatites at MtNiorkpakhk (east of Mt Eveslogchorr) andkhibinite pegmatites at a number of localities inwestern Khibina (Chakhmouradian and Mitchell1998) In most of these occurrences loparite isrelatively Th-poor and compositionally evolvesby enrichment in Na2O and Nb2O5 and depletionin LREE2O3 and TiO2 contents toward the rimThis trend coincides with the main magmatictrend of the compositional evolution of loparite int h e n e p h e l i n e - s y e n i t e c o m p l e x e s(Chakhmouradian and Mitchell 1998 Mitchelland Chakhmouradian 1996) The evolutionarytrend from niobian loparite to thorian niobianloparite recognized in the present study has notbeen previously observed in alkaline rocksLoparite from fenite-type rocks of the ParanaBasin carbonatite complexes has high ThO2

contents (up to 62 wt) accompanied byenrichment in Na2O and Nb2O5 (lueshite) anddepletion in SrO and TiO2 (tausonite) (Mitchell1996 Table 36) Th-enrichment (up to 49 wtThO2) in the composition of perovskite from thecarbonatite complexes of the Kola Peninsula is

coupled with increasing LREE2O3 Na2O andNb2O5 ie loparite and lueshite components(Chakhmouradian and Mitchell 1997) In thePolino carbonatite Th-bearing (15 shy 17 wtThO2) perovskite has high Fe2O3 and ZrO2

contents (Lupini et al 1992)The limits of solubility between loparite

(NaLREETi2O6) and the thorium end-membercompositions ThNb4O12 Na23Th13TiO3 andThTi2O6 are unknown From structural data(Balic ZIuml unic et al 1984 Kovba and Trunov1963 Ruh and Wadsley 1966 Zhu and Hor1995) it is expected that loparite forms acomplete solid solution series with the formertwo compounds and only a limited series withThTi2O6 Experimental studies of the NaLaTi2O6

-ThNb4O12 NaLaTi2O6ndashNa2ThTi3O9 andNaLaTi2O6ndashThTi2O6 systems are being under-taken by the authors of this paper

As evidenced by textural relationships andcompositional data the appearance of Na-poorTh-rich lsquoceriobetafitersquo and belyankinite asmantles on thorian loparite was a result ofmetasomatic processes involving alkali-cationleaching and hydration Note that the sameprocesses brought about the replacement ofnepheline and alkali feldspar present as relics infibrous aegirine by zeolites and eventually bygibbsite Metasomatites including albitites albite-aegirine and albite-astrophyllite rocks are verycommon in the vicinity of pegmatite veinscontaining thorian loparite at Mt EveslogchorrHydrothermal solutions responsible for themetasomatic alteration most probably werederived from the phonolitic magma whichproduced the differentiated intrusion of nephelinesyenites including foyaite and its precursorkhibinite An alternative source of such solutionscould be a foidolite melt as some authors suggestthat the foidolites were emplaced later than thenephel ine syenite intrusion (Kostyleva-Labuntsova et al 1978a Sniatkova et al 1986)

Conclusions

In Na-LREE-Ti-dominant species of the perovs-kite group Th4+ cations occupy large twelve-coordinated A sites in the structure Theaccommodation of Th into the structure isaccompanied by appearance of vacancies at theA sites at the expense of Na LREE and SrThorian loparite is essentially a member of theloparite (NaLREETi2O6)ndashlueshite (NaNbO3)ndashThTi2O6ndashThNb4O12 quaternary system with low

TH-RICH LOPARITE

351

or negligible contents of other end-membercompositions The mineral compositionallyevolves from niobian loparite to niobian thorianand thorian niobian loparite Metasomatic altera-tion of thorian loparite gave rise to lsquoceriobetafitersquoand belyankinite with high ThO2 content Thorianloparite is metamict or partly metamict and uponheating regains a structure close to that ofsynthetic loparite NaLaTi2O6

Acknowledgements

This work was supported by the Natural Sciencesand Engineering Research Council of Canada andLakehead University Ontario (RHM ARC) ARCalso acknowledges support from St PetersburgState University Russia (grant Evolution offramework niobium-titanium oxides in carbona-tite-bearing nepheline-syenite complexes) AlanMacKenzie and Keith Pringnitz are thanked fortheir assistance with the analytical work AnnHammond and Sam Spivak are thanked for thinsection preparation and drafting services respec-tively

References

Balic ZIuml unic T SIuml cavnicIuml ar S and Grobenski Z (1984)The structure of thorium (IV) dititanium (IV) oxideThTi2O6 Croat Chem Acta 57 645 shy 51

Belous AG Novitskaya GN Gavrilova LGPolyanetskaya SV and Makarova ZYa (1985)Lanthanum titanate-zirconates with the perovskitestructure Sov Prog Chem 51 13 shy 15

Borodin LS (1954) On accommodation of water in thecrystal lattice of perovskite-group minerals DokladyAN SSSR 95 (in Russian) 873 shy 5

Borodin LS and Kazakova ME (1954) Irinite shy anew mineral from the perovskite group Doklady ANSSSR 97 (in Russian) 725 shy 8

Chakhmouradian AR and Mitchell RH (1997)Compositional variation of perovskite-group miner-als from the carbonatite complexes of the KolaAlkaline Province Russia Canad Mineral 351293 shy 310

Chakhmouradian AR and Mitchell RH (1998)Compositional variation of perovskite-group miner-als from the Khibina alkaline complex KolaPeninsula Canad Mineral 36 (in press)

Filatov SK and Frank-Kamenetskii VA (1969)Structural characteristics of cubic ZrO2 stabilizedby calcium Sov Phys Cryst 14 414 shy 5

Galakhov AV (1975) The petrology of the KhibinaAlkaline Massif Nauka Press Leningrad (in

Russian) 256 ppGerasimovski i VI and Kazakova ME (1950)

Belyankinite shy a new mineral Doklady AN SSSR 71 (in Russian) 925 shy 7

Grunin VS Razumenko MV Patrina IV FilatovSK and Alekseyeva TV (1983) Mode of existenceand abundance of TiO2-rutile anatase and brookiteDoklady Earth Sci Sect 268 149 shy 50

Haggerty SE and Mariano AN (1983) Strontian-loparite and strontio-chevkinite two new minerals inrheomorphic fenites from the Parana Basin carbona-tites South America Contrib Mineral Petrol 84365 shy 81

Hogarth DD (1961) A study of pyrochlore andbetafite Canad Mineral 6 610 shy 33

Hogarth DD (1989) Pyrochlore apatite and amphi-bole distinctive minerals in carbonatites InCarbonat ites (K Bell ed) Unwyn HymanLondon 105 shy 48

Kapustin YuL (1989) Rare earth-bearing pyrochlorefrom peralkaline pegmatites of the Khibina massifNew data on minerals (Trudy Mineral Muz ANSSSR ) 36 (in Russian) 155 shy 61

Keller C (1965) Die Reaktion der Dioxide derElemente Thorium bis Americium mit Niob- undTantalpentoxid (The reaction of dioxides of theelements from thorium to americium with niobiumand tantalum pentoxides) J Inorg Nucl Chem 271233 shy 46

Kogarko LN Kononova VA Orlova MP andWoolle y AR (1995 ) Alkaline Rocks andCarbonatites of the World Part 2 Former USSRChapman amp Hall London UK 226 pp

Kostyleva-Labuntsova EE Borutskii BE SokolovaMN Shliukova ZV Dorfman MD DudkinOB Kozyreva LV and Ikorskii SV (1978a) TheMineralogy of the Khibina Massif Vol 1 NaukaPress Moscow (in Russian) 228 p

Kostyleva-Labuntsova EE Borutskii BE SokolovaMN Shliukova ZV Dorfman MD DudkinOB Kozyreva LV and Ikorskii SV (1978b) TheMineralogy of the Khibina Massif Vol 2 NaukaPress Moscow (in Russian) 588 p

Kovba LM and Trunov VK (1962) Double oxidescontaining tungsten tantalum or niobium DokladyAN SSSR 147 (in Russian) 622 shy 4

Kozyreva LV (1990) Aegirine-feldspar veins in thenorth-eastern part of the Khibina massif In AlkalineMagmatism in the North-eastern Part of the BalticShield Kola Sci Centre Press Apatity (in Russian)42 shy 56

Kozyreva LV Menrsquoshikov YuP and Lednev AI(1991) Loparite mineralization of the Khibinamassif In New Data on the Rare-metalMineralogy of the Kola Peninsula Kola SciCentre Press Apatity (in Russian) 37 shy 44

R H MITCHELL AND A RCHAKHMOURADIAN

352

at essentially constant lueshite content Usingnomenclature principles suggested for the perovs-kite-group minerals by Mitchell (1996) theexamined samples compositionally evolve fromniobian loparite toward niobian thorian andthorian niobian loparite

BetafiteRepresentative analyses of betafite developed

in thorian loparite are given in Table 3 LREEdominated by Ce and Th are the major A-cationsAccording to the classification scheme proposedby Hogarth (1989) for the pyrochlore-groupminerals this mineral should be regarded asceriobetafite or thorium ceriobetafite (LREE gtThgt 20 cation sum at the A sites) In this studywe prefer to refer to the mineral using quotationmarks as lsquoceriobetafitersquo is not approved as adistinct mineral species by the Comission on NewMinerals and Mineral Names of the IMA

At the Khibina complex pyrochlore-groupminerals were previously described as accessoryconstituents of aegirine-feldspar veins (Kozyreva

1990) and peralkaline pegmatites (Kapustin 1989Shilin et al 1966) These minerals correspond topyrochlore sensu stricto that may be somewhatenriched in SrO (Shilin et al 1966) or LREE(Kapustin 1989) Ti-dominant species ie membersof the betafite subgroup have not been previouslyrecognized in the Khibina alkaline complex

BelyankiniteCompositional data on belyankinite and related

Ti-Nb hydroxides available from literature arelimited to a few bulk wet-chemical analyses(Gerasimovskii and Kazakova 1950 Semenov1957 Vlasov et al 1966) Semenov (1957) hassuggested that Ti-dominant belyankinite formssolid solution series with its Mn-analoguemanganbelyankinite and Nb-dominant gerasi-movskite The mineral examined in the presentstudy is a member of the belyankinitendashgerasi-movskite series with negligible content ofmanganbelyankinite (Table 4) A generalizedstructural formula of belyankinite calculated onthe basis of 12 atoms of oxygen is

FIG 3 Variations (apfu) of (a) Na (b) LREE (c) Ca (d) Sr (e) Ti (f) Nb and (g) cation totals at the A and B siteswith respect to Th for Th-rich loparite Circles correspond to loparite KHB-44 squares to KHB-70 Variation of A-cation totals in the solid solution series NaLREETi2O6shy Na2ThTi3O9 is shown by solid line in the series

NaLREETi2O6shy ThTi2O6 by dashed line and in the series NaLREETi2O6shy ThNb4O12 by dash-dotted line (g)

TH-RICH LOPARITE

347

FIG 4 Compositions (mol) of Th-rich loparite in the system loparite (NaCeTi2O6)ndashlueshite (NaNbO3)ndashThTi2O6ndashThNb4O12

R H MITCHELL AND A RCHAKHMOURADIAN

348

(Ca ThLR EE )1 3(T i Nb Si Fe )5O12 nH2O(average of 18 determinations) and approachesthat deduced by Fleischer from Semenovrsquosanalytical data (see reference to Semenov1957) Ca 0 9(T i Zr NbS i )5 5O12 10H2O

However the mineral from Khibina differs fromLovozero belyankinite in having much higherThO2 (up to 2417 wt) and LREE2O3 (up to116 wt) contents both of which are undoubt-edly lsquoinheritedrsquo from the loparite parent

TABLE 3 Representative compositions of lsquoceriobetafitersquo

1 2 3 1 2 3

Wt Structural formulae(SB-cations = 2)

Na2O 101 054 034 Na 0111 0060 0036CaO 179 167 176 Ca 0108 0102 0103SrO 117 115 130 Sr 0038 0038 0041La2O3 579 481 510 La 0121 0101 0103Ce2O3 901 865 846 Ce 0186 0180 0169Nd2O3 152 262 114 Nd 0034 0053 0022ThO2 1965 2088 2041 Th 0244 0270 0253TiO2 3382 3506 3750 Ti 1438 1499 1539Fe2O3 nd 003 047 Fe 0000 0001 0017Nb2O5 2177 1926 1776 Nb 0556 0495 0438Ta2O5 037 034 039 Ta 0006 0005 0006

Total 9540 9501 9463

Compositions 1 and 2 KHB-44 3 KHB-70All data this workTotal Fe expressed as Fe2O3 nd = not detected

TABLE 4 Representative compositions of belyankinite

1 2 1 2

Wt Structural formulae(O = 24)

Na2O 003 028 Na 0014 0122CaO 412 162 Ca 1027 0402MgO 016 017 Mg 0055 0060MnO 011 028 Mn 0022 0053La2O3 208 200 La 0179 0169Ce2O3 862 221 Ce 0733 0186Nd2O3 081 076 Nd 0067 0062ThO2 1242 2417 Th 0657 1264SiO2 1303 1221 Si 3033 2805TiO2 2281 2473 Ti 3991 4273Al2O3 121 166 Al 0331 0450Fe2O3 616 507 Fe 1078 0877Nb2O5 1502 1587 Nb 1578 1649

Total 8658 9103

Compositions 1 and 2 replacement mantles on thorian loparite KHB-70Total Fe expressed as Fe2O3 ZrO2 was sought but not found

TH-RICH LOPARITE

349

X-ray powder diffractometry

An XRD powder pattern of a sample of the coreof a thorian loparite showed only a few faintdiffraction lines with relatively high d-spacingswhereas a rim sample appeared to be completelymetamict After heating to 7008C for 1 hour thecore and rim samples gave XRD powder patterns(Table 5) similar to those of La-dominantsynthetic loparite NaLaTi2O6 and lsquoirinitersquo asdescribed by Borodin and Kazakova (1954) Theformer has been proposed to have the undistortedcubic lattice (ASTM 39-65 Belous et al 1985)However Rietveld refinement of an XRD powderpattern of NaLaTi2O6 suggests that thiscompound is orthorhombic (space group Pnma)rather than cubic (Mitchell and Chakhmouradianin preparation) The pattern of the rim sample ofthorian loparite also includes three diffractionlines with d-spacings of 295 1795 and 1535 AEcirc that cannot be produced by the perovskite-typestructure These are characteristic of pyrochlore-type phases and correspond to the most intenselines 222 440 and 622 respectively (ASTM 13-197 ASTM 17-746)

Data available from the literature show thatXRD powder patterns similar to those obtained inthis study are produced by naturally occurringloparite of various Nb2O5 CaO Na2O TiO2 andSrO contents (Haggerty and Mariano 1983Kostyleva-Labuntsova et al 1978b Mitchell etal 1996) Given a significant difference in ionicradius between Th4+ Na+ and Ce3+ (121 139and 134 AEcirc respectively Shannon 1976) it isexpected that Th-rich loparite should have astrongly distorted perovskite-type structureHowever the obtained patterns (Table 5) do notexhibit lsquoextrarsquo diffraction lines reflecting cationordering or geometric distortion of the ideal cubicperovskite-type lattice Such diffraction lines eg769 shy 790 344shy 350 257shy 260 187 shy 189 AEcirc are present in patterns of most syntheticperovskite-type titanates and niobates with Th4+

localized at the A sites (Keller 1965 Kovba andTrunov 1963 Labeau and Joubert 1978 Zhu andHor 1995) The only known exceptions so far arecompounds from the Na06shy 08Th01 shy 02NbO3

range of the NaNbO3shy Th025NbO3 solid solutionseries (ASTM-34-1068 Labeau and Joubert1978 Table III)

TABLE 5 X-ray diffraction patterns of loparite lsquoirinitersquo and Th-rich loparite

1 2 3 4 5hkl d IIo d IIo d IIo d IIo d IIo

100 3870 2110 2730 100 271 100 276 100 264 100 272 100111 2225 50200 1933 92 1919 90 1950 10 1905 30 1925 40

1860 200b211 1578 95 1569 80 1598 30 1562 60 1575 60

1503 10220 1367 70 1360 40 1383 20 1355 30 1368 30300 1290 4310 1225 25 1216 30 1233 15 1214 20 1222 20311 1168 8 1197 10222 1117 13 1111 5 1118 5320 1075 3321 1035 38 1028 60 1042 20 1029 10 1034 10400 09680 5411 0908 10 0912 5420 0864 10 0865 5332 08245 5 08260 3422 07910 3

1 synthetic NaLaTi2O6 a = 3873 AEcirc (ASTM 39-65) 2 lsquoirinitersquo (heated) a = 383 AEcirc (Borodin and Kazakova 1954)3 thorian loparite KHB-70 core (unheated) a = 3902(2) AEcirc 4 thorian loparite KHB-70 core (heated) a = 3841(1)AEcirc 5 thorian loparite KHB-70 rim (heated) a = 3867(2) AEcirc + 3 weak lines with d = 295 1795 1535 AEcirc (3-5 thiswork) b = broad line

R H MITCHELL AND A RCHAKHMOURADIAN

350

The absence of superstructure reflections in thepatterns of thorian loparite may result from itsmetamict state prior to heating ie from failure torestore an initial apparently distorted structure ofthe mineral Alternatively stabilization of thecubic structure may result from the presence ofminor cations in thorian loparite eg Ca or SrThis phenomenon refered to as stabilized poly-morphism (Smirnova and Belov 1969) is well-known for TiO2 and ZrO2 polymorphs (Filatovand Frank-Kamenetskii 1969 Grunin et al1983) To select between the two abovealternatives experimental studies of the solidsolution series between loparite and Th-bearingend-members are being undertaken by us

Discussion

At Khibina Th-rich loparite occurs only inrelation to the foyaite series (Borodin andKazakova 1954 Chakhmouradian and Mitchell1998 Kozyreva et al 1991 Tikhonenkova et al1982) Zoned Th-rich loparite examined in thisstudy crystallized at a late deuteric stage of theformation of foyaite pegmatites At this stagefluids enriched in Ti and incompatible elements(Zr Nb Sr LREE Th) gave rise to theassemblage of aegirine with loparite eudialyteand Ti-silicates (astrophyllite lorenzenitelamprophyllite) In a similar paragenesis lopariteoccurs in the foyaite pegmatites at MtNiorkpakhk (east of Mt Eveslogchorr) andkhibinite pegmatites at a number of localities inwestern Khibina (Chakhmouradian and Mitchell1998) In most of these occurrences loparite isrelatively Th-poor and compositionally evolvesby enrichment in Na2O and Nb2O5 and depletionin LREE2O3 and TiO2 contents toward the rimThis trend coincides with the main magmatictrend of the compositional evolution of loparite int h e n e p h e l i n e - s y e n i t e c o m p l e x e s(Chakhmouradian and Mitchell 1998 Mitchelland Chakhmouradian 1996) The evolutionarytrend from niobian loparite to thorian niobianloparite recognized in the present study has notbeen previously observed in alkaline rocksLoparite from fenite-type rocks of the ParanaBasin carbonatite complexes has high ThO2

contents (up to 62 wt) accompanied byenrichment in Na2O and Nb2O5 (lueshite) anddepletion in SrO and TiO2 (tausonite) (Mitchell1996 Table 36) Th-enrichment (up to 49 wtThO2) in the composition of perovskite from thecarbonatite complexes of the Kola Peninsula is

coupled with increasing LREE2O3 Na2O andNb2O5 ie loparite and lueshite components(Chakhmouradian and Mitchell 1997) In thePolino carbonatite Th-bearing (15 shy 17 wtThO2) perovskite has high Fe2O3 and ZrO2

contents (Lupini et al 1992)The limits of solubility between loparite

(NaLREETi2O6) and the thorium end-membercompositions ThNb4O12 Na23Th13TiO3 andThTi2O6 are unknown From structural data(Balic ZIuml unic et al 1984 Kovba and Trunov1963 Ruh and Wadsley 1966 Zhu and Hor1995) it is expected that loparite forms acomplete solid solution series with the formertwo compounds and only a limited series withThTi2O6 Experimental studies of the NaLaTi2O6

-ThNb4O12 NaLaTi2O6ndashNa2ThTi3O9 andNaLaTi2O6ndashThTi2O6 systems are being under-taken by the authors of this paper

As evidenced by textural relationships andcompositional data the appearance of Na-poorTh-rich lsquoceriobetafitersquo and belyankinite asmantles on thorian loparite was a result ofmetasomatic processes involving alkali-cationleaching and hydration Note that the sameprocesses brought about the replacement ofnepheline and alkali feldspar present as relics infibrous aegirine by zeolites and eventually bygibbsite Metasomatites including albitites albite-aegirine and albite-astrophyllite rocks are verycommon in the vicinity of pegmatite veinscontaining thorian loparite at Mt EveslogchorrHydrothermal solutions responsible for themetasomatic alteration most probably werederived from the phonolitic magma whichproduced the differentiated intrusion of nephelinesyenites including foyaite and its precursorkhibinite An alternative source of such solutionscould be a foidolite melt as some authors suggestthat the foidolites were emplaced later than thenephel ine syenite intrusion (Kostyleva-Labuntsova et al 1978a Sniatkova et al 1986)

Conclusions

In Na-LREE-Ti-dominant species of the perovs-kite group Th4+ cations occupy large twelve-coordinated A sites in the structure Theaccommodation of Th into the structure isaccompanied by appearance of vacancies at theA sites at the expense of Na LREE and SrThorian loparite is essentially a member of theloparite (NaLREETi2O6)ndashlueshite (NaNbO3)ndashThTi2O6ndashThNb4O12 quaternary system with low

TH-RICH LOPARITE

351

or negligible contents of other end-membercompositions The mineral compositionallyevolves from niobian loparite to niobian thorianand thorian niobian loparite Metasomatic altera-tion of thorian loparite gave rise to lsquoceriobetafitersquoand belyankinite with high ThO2 content Thorianloparite is metamict or partly metamict and uponheating regains a structure close to that ofsynthetic loparite NaLaTi2O6

Acknowledgements

This work was supported by the Natural Sciencesand Engineering Research Council of Canada andLakehead University Ontario (RHM ARC) ARCalso acknowledges support from St PetersburgState University Russia (grant Evolution offramework niobium-titanium oxides in carbona-tite-bearing nepheline-syenite complexes) AlanMacKenzie and Keith Pringnitz are thanked fortheir assistance with the analytical work AnnHammond and Sam Spivak are thanked for thinsection preparation and drafting services respec-tively

References

Balic ZIuml unic T SIuml cavnicIuml ar S and Grobenski Z (1984)The structure of thorium (IV) dititanium (IV) oxideThTi2O6 Croat Chem Acta 57 645 shy 51

Belous AG Novitskaya GN Gavrilova LGPolyanetskaya SV and Makarova ZYa (1985)Lanthanum titanate-zirconates with the perovskitestructure Sov Prog Chem 51 13 shy 15

Borodin LS (1954) On accommodation of water in thecrystal lattice of perovskite-group minerals DokladyAN SSSR 95 (in Russian) 873 shy 5

Borodin LS and Kazakova ME (1954) Irinite shy anew mineral from the perovskite group Doklady ANSSSR 97 (in Russian) 725 shy 8

Chakhmouradian AR and Mitchell RH (1997)Compositional variation of perovskite-group miner-als from the carbonatite complexes of the KolaAlkaline Province Russia Canad Mineral 351293 shy 310

Chakhmouradian AR and Mitchell RH (1998)Compositional variation of perovskite-group miner-als from the Khibina alkaline complex KolaPeninsula Canad Mineral 36 (in press)

Filatov SK and Frank-Kamenetskii VA (1969)Structural characteristics of cubic ZrO2 stabilizedby calcium Sov Phys Cryst 14 414 shy 5

Galakhov AV (1975) The petrology of the KhibinaAlkaline Massif Nauka Press Leningrad (in

Russian) 256 ppGerasimovski i VI and Kazakova ME (1950)

Belyankinite shy a new mineral Doklady AN SSSR 71 (in Russian) 925 shy 7

Grunin VS Razumenko MV Patrina IV FilatovSK and Alekseyeva TV (1983) Mode of existenceand abundance of TiO2-rutile anatase and brookiteDoklady Earth Sci Sect 268 149 shy 50

Haggerty SE and Mariano AN (1983) Strontian-loparite and strontio-chevkinite two new minerals inrheomorphic fenites from the Parana Basin carbona-tites South America Contrib Mineral Petrol 84365 shy 81

Hogarth DD (1961) A study of pyrochlore andbetafite Canad Mineral 6 610 shy 33

Hogarth DD (1989) Pyrochlore apatite and amphi-bole distinctive minerals in carbonatites InCarbonat ites (K Bell ed) Unwyn HymanLondon 105 shy 48

Kapustin YuL (1989) Rare earth-bearing pyrochlorefrom peralkaline pegmatites of the Khibina massifNew data on minerals (Trudy Mineral Muz ANSSSR ) 36 (in Russian) 155 shy 61

Keller C (1965) Die Reaktion der Dioxide derElemente Thorium bis Americium mit Niob- undTantalpentoxid (The reaction of dioxides of theelements from thorium to americium with niobiumand tantalum pentoxides) J Inorg Nucl Chem 271233 shy 46

Kogarko LN Kononova VA Orlova MP andWoolle y AR (1995 ) Alkaline Rocks andCarbonatites of the World Part 2 Former USSRChapman amp Hall London UK 226 pp

Kostyleva-Labuntsova EE Borutskii BE SokolovaMN Shliukova ZV Dorfman MD DudkinOB Kozyreva LV and Ikorskii SV (1978a) TheMineralogy of the Khibina Massif Vol 1 NaukaPress Moscow (in Russian) 228 p

Kostyleva-Labuntsova EE Borutskii BE SokolovaMN Shliukova ZV Dorfman MD DudkinOB Kozyreva LV and Ikorskii SV (1978b) TheMineralogy of the Khibina Massif Vol 2 NaukaPress Moscow (in Russian) 588 p

Kovba LM and Trunov VK (1962) Double oxidescontaining tungsten tantalum or niobium DokladyAN SSSR 147 (in Russian) 622 shy 4

Kozyreva LV (1990) Aegirine-feldspar veins in thenorth-eastern part of the Khibina massif In AlkalineMagmatism in the North-eastern Part of the BalticShield Kola Sci Centre Press Apatity (in Russian)42 shy 56

Kozyreva LV Menrsquoshikov YuP and Lednev AI(1991) Loparite mineralization of the Khibinamassif In New Data on the Rare-metalMineralogy of the Kola Peninsula Kola SciCentre Press Apatity (in Russian) 37 shy 44

R H MITCHELL AND A RCHAKHMOURADIAN

352

FIG 4 Compositions (mol) of Th-rich loparite in the system loparite (NaCeTi2O6)ndashlueshite (NaNbO3)ndashThTi2O6ndashThNb4O12

R H MITCHELL AND A RCHAKHMOURADIAN

348

(Ca ThLR EE )1 3(T i Nb Si Fe )5O12 nH2O(average of 18 determinations) and approachesthat deduced by Fleischer from Semenovrsquosanalytical data (see reference to Semenov1957) Ca 0 9(T i Zr NbS i )5 5O12 10H2O

However the mineral from Khibina differs fromLovozero belyankinite in having much higherThO2 (up to 2417 wt) and LREE2O3 (up to116 wt) contents both of which are undoubt-edly lsquoinheritedrsquo from the loparite parent

TABLE 3 Representative compositions of lsquoceriobetafitersquo

1 2 3 1 2 3

Wt Structural formulae(SB-cations = 2)

Na2O 101 054 034 Na 0111 0060 0036CaO 179 167 176 Ca 0108 0102 0103SrO 117 115 130 Sr 0038 0038 0041La2O3 579 481 510 La 0121 0101 0103Ce2O3 901 865 846 Ce 0186 0180 0169Nd2O3 152 262 114 Nd 0034 0053 0022ThO2 1965 2088 2041 Th 0244 0270 0253TiO2 3382 3506 3750 Ti 1438 1499 1539Fe2O3 nd 003 047 Fe 0000 0001 0017Nb2O5 2177 1926 1776 Nb 0556 0495 0438Ta2O5 037 034 039 Ta 0006 0005 0006

Total 9540 9501 9463

Compositions 1 and 2 KHB-44 3 KHB-70All data this workTotal Fe expressed as Fe2O3 nd = not detected

TABLE 4 Representative compositions of belyankinite

1 2 1 2

Wt Structural formulae(O = 24)

Na2O 003 028 Na 0014 0122CaO 412 162 Ca 1027 0402MgO 016 017 Mg 0055 0060MnO 011 028 Mn 0022 0053La2O3 208 200 La 0179 0169Ce2O3 862 221 Ce 0733 0186Nd2O3 081 076 Nd 0067 0062ThO2 1242 2417 Th 0657 1264SiO2 1303 1221 Si 3033 2805TiO2 2281 2473 Ti 3991 4273Al2O3 121 166 Al 0331 0450Fe2O3 616 507 Fe 1078 0877Nb2O5 1502 1587 Nb 1578 1649

Total 8658 9103

Compositions 1 and 2 replacement mantles on thorian loparite KHB-70Total Fe expressed as Fe2O3 ZrO2 was sought but not found

TH-RICH LOPARITE

349

X-ray powder diffractometry

An XRD powder pattern of a sample of the coreof a thorian loparite showed only a few faintdiffraction lines with relatively high d-spacingswhereas a rim sample appeared to be completelymetamict After heating to 7008C for 1 hour thecore and rim samples gave XRD powder patterns(Table 5) similar to those of La-dominantsynthetic loparite NaLaTi2O6 and lsquoirinitersquo asdescribed by Borodin and Kazakova (1954) Theformer has been proposed to have the undistortedcubic lattice (ASTM 39-65 Belous et al 1985)However Rietveld refinement of an XRD powderpattern of NaLaTi2O6 suggests that thiscompound is orthorhombic (space group Pnma)rather than cubic (Mitchell and Chakhmouradianin preparation) The pattern of the rim sample ofthorian loparite also includes three diffractionlines with d-spacings of 295 1795 and 1535 AEcirc that cannot be produced by the perovskite-typestructure These are characteristic of pyrochlore-type phases and correspond to the most intenselines 222 440 and 622 respectively (ASTM 13-197 ASTM 17-746)

Data available from the literature show thatXRD powder patterns similar to those obtained inthis study are produced by naturally occurringloparite of various Nb2O5 CaO Na2O TiO2 andSrO contents (Haggerty and Mariano 1983Kostyleva-Labuntsova et al 1978b Mitchell etal 1996) Given a significant difference in ionicradius between Th4+ Na+ and Ce3+ (121 139and 134 AEcirc respectively Shannon 1976) it isexpected that Th-rich loparite should have astrongly distorted perovskite-type structureHowever the obtained patterns (Table 5) do notexhibit lsquoextrarsquo diffraction lines reflecting cationordering or geometric distortion of the ideal cubicperovskite-type lattice Such diffraction lines eg769 shy 790 344shy 350 257shy 260 187 shy 189 AEcirc are present in patterns of most syntheticperovskite-type titanates and niobates with Th4+

localized at the A sites (Keller 1965 Kovba andTrunov 1963 Labeau and Joubert 1978 Zhu andHor 1995) The only known exceptions so far arecompounds from the Na06shy 08Th01 shy 02NbO3

range of the NaNbO3shy Th025NbO3 solid solutionseries (ASTM-34-1068 Labeau and Joubert1978 Table III)

TABLE 5 X-ray diffraction patterns of loparite lsquoirinitersquo and Th-rich loparite

1 2 3 4 5hkl d IIo d IIo d IIo d IIo d IIo

100 3870 2110 2730 100 271 100 276 100 264 100 272 100111 2225 50200 1933 92 1919 90 1950 10 1905 30 1925 40

1860 200b211 1578 95 1569 80 1598 30 1562 60 1575 60

1503 10220 1367 70 1360 40 1383 20 1355 30 1368 30300 1290 4310 1225 25 1216 30 1233 15 1214 20 1222 20311 1168 8 1197 10222 1117 13 1111 5 1118 5320 1075 3321 1035 38 1028 60 1042 20 1029 10 1034 10400 09680 5411 0908 10 0912 5420 0864 10 0865 5332 08245 5 08260 3422 07910 3

1 synthetic NaLaTi2O6 a = 3873 AEcirc (ASTM 39-65) 2 lsquoirinitersquo (heated) a = 383 AEcirc (Borodin and Kazakova 1954)3 thorian loparite KHB-70 core (unheated) a = 3902(2) AEcirc 4 thorian loparite KHB-70 core (heated) a = 3841(1)AEcirc 5 thorian loparite KHB-70 rim (heated) a = 3867(2) AEcirc + 3 weak lines with d = 295 1795 1535 AEcirc (3-5 thiswork) b = broad line

R H MITCHELL AND A RCHAKHMOURADIAN

350

The absence of superstructure reflections in thepatterns of thorian loparite may result from itsmetamict state prior to heating ie from failure torestore an initial apparently distorted structure ofthe mineral Alternatively stabilization of thecubic structure may result from the presence ofminor cations in thorian loparite eg Ca or SrThis phenomenon refered to as stabilized poly-morphism (Smirnova and Belov 1969) is well-known for TiO2 and ZrO2 polymorphs (Filatovand Frank-Kamenetskii 1969 Grunin et al1983) To select between the two abovealternatives experimental studies of the solidsolution series between loparite and Th-bearingend-members are being undertaken by us

Discussion

At Khibina Th-rich loparite occurs only inrelation to the foyaite series (Borodin andKazakova 1954 Chakhmouradian and Mitchell1998 Kozyreva et al 1991 Tikhonenkova et al1982) Zoned Th-rich loparite examined in thisstudy crystallized at a late deuteric stage of theformation of foyaite pegmatites At this stagefluids enriched in Ti and incompatible elements(Zr Nb Sr LREE Th) gave rise to theassemblage of aegirine with loparite eudialyteand Ti-silicates (astrophyllite lorenzenitelamprophyllite) In a similar paragenesis lopariteoccurs in the foyaite pegmatites at MtNiorkpakhk (east of Mt Eveslogchorr) andkhibinite pegmatites at a number of localities inwestern Khibina (Chakhmouradian and Mitchell1998) In most of these occurrences loparite isrelatively Th-poor and compositionally evolvesby enrichment in Na2O and Nb2O5 and depletionin LREE2O3 and TiO2 contents toward the rimThis trend coincides with the main magmatictrend of the compositional evolution of loparite int h e n e p h e l i n e - s y e n i t e c o m p l e x e s(Chakhmouradian and Mitchell 1998 Mitchelland Chakhmouradian 1996) The evolutionarytrend from niobian loparite to thorian niobianloparite recognized in the present study has notbeen previously observed in alkaline rocksLoparite from fenite-type rocks of the ParanaBasin carbonatite complexes has high ThO2

contents (up to 62 wt) accompanied byenrichment in Na2O and Nb2O5 (lueshite) anddepletion in SrO and TiO2 (tausonite) (Mitchell1996 Table 36) Th-enrichment (up to 49 wtThO2) in the composition of perovskite from thecarbonatite complexes of the Kola Peninsula is

coupled with increasing LREE2O3 Na2O andNb2O5 ie loparite and lueshite components(Chakhmouradian and Mitchell 1997) In thePolino carbonatite Th-bearing (15 shy 17 wtThO2) perovskite has high Fe2O3 and ZrO2

contents (Lupini et al 1992)The limits of solubility between loparite

(NaLREETi2O6) and the thorium end-membercompositions ThNb4O12 Na23Th13TiO3 andThTi2O6 are unknown From structural data(Balic ZIuml unic et al 1984 Kovba and Trunov1963 Ruh and Wadsley 1966 Zhu and Hor1995) it is expected that loparite forms acomplete solid solution series with the formertwo compounds and only a limited series withThTi2O6 Experimental studies of the NaLaTi2O6

-ThNb4O12 NaLaTi2O6ndashNa2ThTi3O9 andNaLaTi2O6ndashThTi2O6 systems are being under-taken by the authors of this paper

As evidenced by textural relationships andcompositional data the appearance of Na-poorTh-rich lsquoceriobetafitersquo and belyankinite asmantles on thorian loparite was a result ofmetasomatic processes involving alkali-cationleaching and hydration Note that the sameprocesses brought about the replacement ofnepheline and alkali feldspar present as relics infibrous aegirine by zeolites and eventually bygibbsite Metasomatites including albitites albite-aegirine and albite-astrophyllite rocks are verycommon in the vicinity of pegmatite veinscontaining thorian loparite at Mt EveslogchorrHydrothermal solutions responsible for themetasomatic alteration most probably werederived from the phonolitic magma whichproduced the differentiated intrusion of nephelinesyenites including foyaite and its precursorkhibinite An alternative source of such solutionscould be a foidolite melt as some authors suggestthat the foidolites were emplaced later than thenephel ine syenite intrusion (Kostyleva-Labuntsova et al 1978a Sniatkova et al 1986)

Conclusions

In Na-LREE-Ti-dominant species of the perovs-kite group Th4+ cations occupy large twelve-coordinated A sites in the structure Theaccommodation of Th into the structure isaccompanied by appearance of vacancies at theA sites at the expense of Na LREE and SrThorian loparite is essentially a member of theloparite (NaLREETi2O6)ndashlueshite (NaNbO3)ndashThTi2O6ndashThNb4O12 quaternary system with low

TH-RICH LOPARITE

351

or negligible contents of other end-membercompositions The mineral compositionallyevolves from niobian loparite to niobian thorianand thorian niobian loparite Metasomatic altera-tion of thorian loparite gave rise to lsquoceriobetafitersquoand belyankinite with high ThO2 content Thorianloparite is metamict or partly metamict and uponheating regains a structure close to that ofsynthetic loparite NaLaTi2O6

Acknowledgements

This work was supported by the Natural Sciencesand Engineering Research Council of Canada andLakehead University Ontario (RHM ARC) ARCalso acknowledges support from St PetersburgState University Russia (grant Evolution offramework niobium-titanium oxides in carbona-tite-bearing nepheline-syenite complexes) AlanMacKenzie and Keith Pringnitz are thanked fortheir assistance with the analytical work AnnHammond and Sam Spivak are thanked for thinsection preparation and drafting services respec-tively

References

Balic ZIuml unic T SIuml cavnicIuml ar S and Grobenski Z (1984)The structure of thorium (IV) dititanium (IV) oxideThTi2O6 Croat Chem Acta 57 645 shy 51

Belous AG Novitskaya GN Gavrilova LGPolyanetskaya SV and Makarova ZYa (1985)Lanthanum titanate-zirconates with the perovskitestructure Sov Prog Chem 51 13 shy 15

Borodin LS (1954) On accommodation of water in thecrystal lattice of perovskite-group minerals DokladyAN SSSR 95 (in Russian) 873 shy 5

Borodin LS and Kazakova ME (1954) Irinite shy anew mineral from the perovskite group Doklady ANSSSR 97 (in Russian) 725 shy 8

Chakhmouradian AR and Mitchell RH (1997)Compositional variation of perovskite-group miner-als from the carbonatite complexes of the KolaAlkaline Province Russia Canad Mineral 351293 shy 310

Chakhmouradian AR and Mitchell RH (1998)Compositional variation of perovskite-group miner-als from the Khibina alkaline complex KolaPeninsula Canad Mineral 36 (in press)

Filatov SK and Frank-Kamenetskii VA (1969)Structural characteristics of cubic ZrO2 stabilizedby calcium Sov Phys Cryst 14 414 shy 5

Galakhov AV (1975) The petrology of the KhibinaAlkaline Massif Nauka Press Leningrad (in

Russian) 256 ppGerasimovski i VI and Kazakova ME (1950)

Belyankinite shy a new mineral Doklady AN SSSR 71 (in Russian) 925 shy 7

Grunin VS Razumenko MV Patrina IV FilatovSK and Alekseyeva TV (1983) Mode of existenceand abundance of TiO2-rutile anatase and brookiteDoklady Earth Sci Sect 268 149 shy 50

Haggerty SE and Mariano AN (1983) Strontian-loparite and strontio-chevkinite two new minerals inrheomorphic fenites from the Parana Basin carbona-tites South America Contrib Mineral Petrol 84365 shy 81

Hogarth DD (1961) A study of pyrochlore andbetafite Canad Mineral 6 610 shy 33

Hogarth DD (1989) Pyrochlore apatite and amphi-bole distinctive minerals in carbonatites InCarbonat ites (K Bell ed) Unwyn HymanLondon 105 shy 48

Kapustin YuL (1989) Rare earth-bearing pyrochlorefrom peralkaline pegmatites of the Khibina massifNew data on minerals (Trudy Mineral Muz ANSSSR ) 36 (in Russian) 155 shy 61

Keller C (1965) Die Reaktion der Dioxide derElemente Thorium bis Americium mit Niob- undTantalpentoxid (The reaction of dioxides of theelements from thorium to americium with niobiumand tantalum pentoxides) J Inorg Nucl Chem 271233 shy 46

Kogarko LN Kononova VA Orlova MP andWoolle y AR (1995 ) Alkaline Rocks andCarbonatites of the World Part 2 Former USSRChapman amp Hall London UK 226 pp

Kostyleva-Labuntsova EE Borutskii BE SokolovaMN Shliukova ZV Dorfman MD DudkinOB Kozyreva LV and Ikorskii SV (1978a) TheMineralogy of the Khibina Massif Vol 1 NaukaPress Moscow (in Russian) 228 p

Kostyleva-Labuntsova EE Borutskii BE SokolovaMN Shliukova ZV Dorfman MD DudkinOB Kozyreva LV and Ikorskii SV (1978b) TheMineralogy of the Khibina Massif Vol 2 NaukaPress Moscow (in Russian) 588 p

Kovba LM and Trunov VK (1962) Double oxidescontaining tungsten tantalum or niobium DokladyAN SSSR 147 (in Russian) 622 shy 4

Kozyreva LV (1990) Aegirine-feldspar veins in thenorth-eastern part of the Khibina massif In AlkalineMagmatism in the North-eastern Part of the BalticShield Kola Sci Centre Press Apatity (in Russian)42 shy 56

Kozyreva LV Menrsquoshikov YuP and Lednev AI(1991) Loparite mineralization of the Khibinamassif In New Data on the Rare-metalMineralogy of the Kola Peninsula Kola SciCentre Press Apatity (in Russian) 37 shy 44

R H MITCHELL AND A RCHAKHMOURADIAN

352

(Ca ThLR EE )1 3(T i Nb Si Fe )5O12 nH2O(average of 18 determinations) and approachesthat deduced by Fleischer from Semenovrsquosanalytical data (see reference to Semenov1957) Ca 0 9(T i Zr NbS i )5 5O12 10H2O

However the mineral from Khibina differs fromLovozero belyankinite in having much higherThO2 (up to 2417 wt) and LREE2O3 (up to116 wt) contents both of which are undoubt-edly lsquoinheritedrsquo from the loparite parent

TABLE 3 Representative compositions of lsquoceriobetafitersquo

1 2 3 1 2 3

Wt Structural formulae(SB-cations = 2)

Na2O 101 054 034 Na 0111 0060 0036CaO 179 167 176 Ca 0108 0102 0103SrO 117 115 130 Sr 0038 0038 0041La2O3 579 481 510 La 0121 0101 0103Ce2O3 901 865 846 Ce 0186 0180 0169Nd2O3 152 262 114 Nd 0034 0053 0022ThO2 1965 2088 2041 Th 0244 0270 0253TiO2 3382 3506 3750 Ti 1438 1499 1539Fe2O3 nd 003 047 Fe 0000 0001 0017Nb2O5 2177 1926 1776 Nb 0556 0495 0438Ta2O5 037 034 039 Ta 0006 0005 0006

Total 9540 9501 9463

Compositions 1 and 2 KHB-44 3 KHB-70All data this workTotal Fe expressed as Fe2O3 nd = not detected

TABLE 4 Representative compositions of belyankinite

1 2 1 2

Wt Structural formulae(O = 24)

Na2O 003 028 Na 0014 0122CaO 412 162 Ca 1027 0402MgO 016 017 Mg 0055 0060MnO 011 028 Mn 0022 0053La2O3 208 200 La 0179 0169Ce2O3 862 221 Ce 0733 0186Nd2O3 081 076 Nd 0067 0062ThO2 1242 2417 Th 0657 1264SiO2 1303 1221 Si 3033 2805TiO2 2281 2473 Ti 3991 4273Al2O3 121 166 Al 0331 0450Fe2O3 616 507 Fe 1078 0877Nb2O5 1502 1587 Nb 1578 1649

Total 8658 9103

Compositions 1 and 2 replacement mantles on thorian loparite KHB-70Total Fe expressed as Fe2O3 ZrO2 was sought but not found

TH-RICH LOPARITE

349

X-ray powder diffractometry

An XRD powder pattern of a sample of the coreof a thorian loparite showed only a few faintdiffraction lines with relatively high d-spacingswhereas a rim sample appeared to be completelymetamict After heating to 7008C for 1 hour thecore and rim samples gave XRD powder patterns(Table 5) similar to those of La-dominantsynthetic loparite NaLaTi2O6 and lsquoirinitersquo asdescribed by Borodin and Kazakova (1954) Theformer has been proposed to have the undistortedcubic lattice (ASTM 39-65 Belous et al 1985)However Rietveld refinement of an XRD powderpattern of NaLaTi2O6 suggests that thiscompound is orthorhombic (space group Pnma)rather than cubic (Mitchell and Chakhmouradianin preparation) The pattern of the rim sample ofthorian loparite also includes three diffractionlines with d-spacings of 295 1795 and 1535 AEcirc that cannot be produced by the perovskite-typestructure These are characteristic of pyrochlore-type phases and correspond to the most intenselines 222 440 and 622 respectively (ASTM 13-197 ASTM 17-746)

Data available from the literature show thatXRD powder patterns similar to those obtained inthis study are produced by naturally occurringloparite of various Nb2O5 CaO Na2O TiO2 andSrO contents (Haggerty and Mariano 1983Kostyleva-Labuntsova et al 1978b Mitchell etal 1996) Given a significant difference in ionicradius between Th4+ Na+ and Ce3+ (121 139and 134 AEcirc respectively Shannon 1976) it isexpected that Th-rich loparite should have astrongly distorted perovskite-type structureHowever the obtained patterns (Table 5) do notexhibit lsquoextrarsquo diffraction lines reflecting cationordering or geometric distortion of the ideal cubicperovskite-type lattice Such diffraction lines eg769 shy 790 344shy 350 257shy 260 187 shy 189 AEcirc are present in patterns of most syntheticperovskite-type titanates and niobates with Th4+

localized at the A sites (Keller 1965 Kovba andTrunov 1963 Labeau and Joubert 1978 Zhu andHor 1995) The only known exceptions so far arecompounds from the Na06shy 08Th01 shy 02NbO3

range of the NaNbO3shy Th025NbO3 solid solutionseries (ASTM-34-1068 Labeau and Joubert1978 Table III)

TABLE 5 X-ray diffraction patterns of loparite lsquoirinitersquo and Th-rich loparite

1 2 3 4 5hkl d IIo d IIo d IIo d IIo d IIo

100 3870 2110 2730 100 271 100 276 100 264 100 272 100111 2225 50200 1933 92 1919 90 1950 10 1905 30 1925 40

1860 200b211 1578 95 1569 80 1598 30 1562 60 1575 60

1503 10220 1367 70 1360 40 1383 20 1355 30 1368 30300 1290 4310 1225 25 1216 30 1233 15 1214 20 1222 20311 1168 8 1197 10222 1117 13 1111 5 1118 5320 1075 3321 1035 38 1028 60 1042 20 1029 10 1034 10400 09680 5411 0908 10 0912 5420 0864 10 0865 5332 08245 5 08260 3422 07910 3

1 synthetic NaLaTi2O6 a = 3873 AEcirc (ASTM 39-65) 2 lsquoirinitersquo (heated) a = 383 AEcirc (Borodin and Kazakova 1954)3 thorian loparite KHB-70 core (unheated) a = 3902(2) AEcirc 4 thorian loparite KHB-70 core (heated) a = 3841(1)AEcirc 5 thorian loparite KHB-70 rim (heated) a = 3867(2) AEcirc + 3 weak lines with d = 295 1795 1535 AEcirc (3-5 thiswork) b = broad line

R H MITCHELL AND A RCHAKHMOURADIAN

350

The absence of superstructure reflections in thepatterns of thorian loparite may result from itsmetamict state prior to heating ie from failure torestore an initial apparently distorted structure ofthe mineral Alternatively stabilization of thecubic structure may result from the presence ofminor cations in thorian loparite eg Ca or SrThis phenomenon refered to as stabilized poly-morphism (Smirnova and Belov 1969) is well-known for TiO2 and ZrO2 polymorphs (Filatovand Frank-Kamenetskii 1969 Grunin et al1983) To select between the two abovealternatives experimental studies of the solidsolution series between loparite and Th-bearingend-members are being undertaken by us

Discussion

At Khibina Th-rich loparite occurs only inrelation to the foyaite series (Borodin andKazakova 1954 Chakhmouradian and Mitchell1998 Kozyreva et al 1991 Tikhonenkova et al1982) Zoned Th-rich loparite examined in thisstudy crystallized at a late deuteric stage of theformation of foyaite pegmatites At this stagefluids enriched in Ti and incompatible elements(Zr Nb Sr LREE Th) gave rise to theassemblage of aegirine with loparite eudialyteand Ti-silicates (astrophyllite lorenzenitelamprophyllite) In a similar paragenesis lopariteoccurs in the foyaite pegmatites at MtNiorkpakhk (east of Mt Eveslogchorr) andkhibinite pegmatites at a number of localities inwestern Khibina (Chakhmouradian and Mitchell1998) In most of these occurrences loparite isrelatively Th-poor and compositionally evolvesby enrichment in Na2O and Nb2O5 and depletionin LREE2O3 and TiO2 contents toward the rimThis trend coincides with the main magmatictrend of the compositional evolution of loparite int h e n e p h e l i n e - s y e n i t e c o m p l e x e s(Chakhmouradian and Mitchell 1998 Mitchelland Chakhmouradian 1996) The evolutionarytrend from niobian loparite to thorian niobianloparite recognized in the present study has notbeen previously observed in alkaline rocksLoparite from fenite-type rocks of the ParanaBasin carbonatite complexes has high ThO2

contents (up to 62 wt) accompanied byenrichment in Na2O and Nb2O5 (lueshite) anddepletion in SrO and TiO2 (tausonite) (Mitchell1996 Table 36) Th-enrichment (up to 49 wtThO2) in the composition of perovskite from thecarbonatite complexes of the Kola Peninsula is

coupled with increasing LREE2O3 Na2O andNb2O5 ie loparite and lueshite components(Chakhmouradian and Mitchell 1997) In thePolino carbonatite Th-bearing (15 shy 17 wtThO2) perovskite has high Fe2O3 and ZrO2

contents (Lupini et al 1992)The limits of solubility between loparite

(NaLREETi2O6) and the thorium end-membercompositions ThNb4O12 Na23Th13TiO3 andThTi2O6 are unknown From structural data(Balic ZIuml unic et al 1984 Kovba and Trunov1963 Ruh and Wadsley 1966 Zhu and Hor1995) it is expected that loparite forms acomplete solid solution series with the formertwo compounds and only a limited series withThTi2O6 Experimental studies of the NaLaTi2O6

-ThNb4O12 NaLaTi2O6ndashNa2ThTi3O9 andNaLaTi2O6ndashThTi2O6 systems are being under-taken by the authors of this paper

As evidenced by textural relationships andcompositional data the appearance of Na-poorTh-rich lsquoceriobetafitersquo and belyankinite asmantles on thorian loparite was a result ofmetasomatic processes involving alkali-cationleaching and hydration Note that the sameprocesses brought about the replacement ofnepheline and alkali feldspar present as relics infibrous aegirine by zeolites and eventually bygibbsite Metasomatites including albitites albite-aegirine and albite-astrophyllite rocks are verycommon in the vicinity of pegmatite veinscontaining thorian loparite at Mt EveslogchorrHydrothermal solutions responsible for themetasomatic alteration most probably werederived from the phonolitic magma whichproduced the differentiated intrusion of nephelinesyenites including foyaite and its precursorkhibinite An alternative source of such solutionscould be a foidolite melt as some authors suggestthat the foidolites were emplaced later than thenephel ine syenite intrusion (Kostyleva-Labuntsova et al 1978a Sniatkova et al 1986)

Conclusions

In Na-LREE-Ti-dominant species of the perovs-kite group Th4+ cations occupy large twelve-coordinated A sites in the structure Theaccommodation of Th into the structure isaccompanied by appearance of vacancies at theA sites at the expense of Na LREE and SrThorian loparite is essentially a member of theloparite (NaLREETi2O6)ndashlueshite (NaNbO3)ndashThTi2O6ndashThNb4O12 quaternary system with low

TH-RICH LOPARITE

351

or negligible contents of other end-membercompositions The mineral compositionallyevolves from niobian loparite to niobian thorianand thorian niobian loparite Metasomatic altera-tion of thorian loparite gave rise to lsquoceriobetafitersquoand belyankinite with high ThO2 content Thorianloparite is metamict or partly metamict and uponheating regains a structure close to that ofsynthetic loparite NaLaTi2O6

Acknowledgements

This work was supported by the Natural Sciencesand Engineering Research Council of Canada andLakehead University Ontario (RHM ARC) ARCalso acknowledges support from St PetersburgState University Russia (grant Evolution offramework niobium-titanium oxides in carbona-tite-bearing nepheline-syenite complexes) AlanMacKenzie and Keith Pringnitz are thanked fortheir assistance with the analytical work AnnHammond and Sam Spivak are thanked for thinsection preparation and drafting services respec-tively

References

Balic ZIuml unic T SIuml cavnicIuml ar S and Grobenski Z (1984)The structure of thorium (IV) dititanium (IV) oxideThTi2O6 Croat Chem Acta 57 645 shy 51

Belous AG Novitskaya GN Gavrilova LGPolyanetskaya SV and Makarova ZYa (1985)Lanthanum titanate-zirconates with the perovskitestructure Sov Prog Chem 51 13 shy 15

Borodin LS (1954) On accommodation of water in thecrystal lattice of perovskite-group minerals DokladyAN SSSR 95 (in Russian) 873 shy 5

Borodin LS and Kazakova ME (1954) Irinite shy anew mineral from the perovskite group Doklady ANSSSR 97 (in Russian) 725 shy 8

Chakhmouradian AR and Mitchell RH (1997)Compositional variation of perovskite-group miner-als from the carbonatite complexes of the KolaAlkaline Province Russia Canad Mineral 351293 shy 310

Chakhmouradian AR and Mitchell RH (1998)Compositional variation of perovskite-group miner-als from the Khibina alkaline complex KolaPeninsula Canad Mineral 36 (in press)

Filatov SK and Frank-Kamenetskii VA (1969)Structural characteristics of cubic ZrO2 stabilizedby calcium Sov Phys Cryst 14 414 shy 5

Galakhov AV (1975) The petrology of the KhibinaAlkaline Massif Nauka Press Leningrad (in

Russian) 256 ppGerasimovski i VI and Kazakova ME (1950)

Belyankinite shy a new mineral Doklady AN SSSR 71 (in Russian) 925 shy 7

Grunin VS Razumenko MV Patrina IV FilatovSK and Alekseyeva TV (1983) Mode of existenceand abundance of TiO2-rutile anatase and brookiteDoklady Earth Sci Sect 268 149 shy 50

Haggerty SE and Mariano AN (1983) Strontian-loparite and strontio-chevkinite two new minerals inrheomorphic fenites from the Parana Basin carbona-tites South America Contrib Mineral Petrol 84365 shy 81

Hogarth DD (1961) A study of pyrochlore andbetafite Canad Mineral 6 610 shy 33

Hogarth DD (1989) Pyrochlore apatite and amphi-bole distinctive minerals in carbonatites InCarbonat ites (K Bell ed) Unwyn HymanLondon 105 shy 48

Kapustin YuL (1989) Rare earth-bearing pyrochlorefrom peralkaline pegmatites of the Khibina massifNew data on minerals (Trudy Mineral Muz ANSSSR ) 36 (in Russian) 155 shy 61

Keller C (1965) Die Reaktion der Dioxide derElemente Thorium bis Americium mit Niob- undTantalpentoxid (The reaction of dioxides of theelements from thorium to americium with niobiumand tantalum pentoxides) J Inorg Nucl Chem 271233 shy 46

Kogarko LN Kononova VA Orlova MP andWoolle y AR (1995 ) Alkaline Rocks andCarbonatites of the World Part 2 Former USSRChapman amp Hall London UK 226 pp

Kostyleva-Labuntsova EE Borutskii BE SokolovaMN Shliukova ZV Dorfman MD DudkinOB Kozyreva LV and Ikorskii SV (1978a) TheMineralogy of the Khibina Massif Vol 1 NaukaPress Moscow (in Russian) 228 p

Kostyleva-Labuntsova EE Borutskii BE SokolovaMN Shliukova ZV Dorfman MD DudkinOB Kozyreva LV and Ikorskii SV (1978b) TheMineralogy of the Khibina Massif Vol 2 NaukaPress Moscow (in Russian) 588 p

Kovba LM and Trunov VK (1962) Double oxidescontaining tungsten tantalum or niobium DokladyAN SSSR 147 (in Russian) 622 shy 4

Kozyreva LV (1990) Aegirine-feldspar veins in thenorth-eastern part of the Khibina massif In AlkalineMagmatism in the North-eastern Part of the BalticShield Kola Sci Centre Press Apatity (in Russian)42 shy 56

Kozyreva LV Menrsquoshikov YuP and Lednev AI(1991) Loparite mineralization of the Khibinamassif In New Data on the Rare-metalMineralogy of the Kola Peninsula Kola SciCentre Press Apatity (in Russian) 37 shy 44

R H MITCHELL AND A RCHAKHMOURADIAN

352

X-ray powder diffractometry

An XRD powder pattern of a sample of the coreof a thorian loparite showed only a few faintdiffraction lines with relatively high d-spacingswhereas a rim sample appeared to be completelymetamict After heating to 7008C for 1 hour thecore and rim samples gave XRD powder patterns(Table 5) similar to those of La-dominantsynthetic loparite NaLaTi2O6 and lsquoirinitersquo asdescribed by Borodin and Kazakova (1954) Theformer has been proposed to have the undistortedcubic lattice (ASTM 39-65 Belous et al 1985)However Rietveld refinement of an XRD powderpattern of NaLaTi2O6 suggests that thiscompound is orthorhombic (space group Pnma)rather than cubic (Mitchell and Chakhmouradianin preparation) The pattern of the rim sample ofthorian loparite also includes three diffractionlines with d-spacings of 295 1795 and 1535 AEcirc that cannot be produced by the perovskite-typestructure These are characteristic of pyrochlore-type phases and correspond to the most intenselines 222 440 and 622 respectively (ASTM 13-197 ASTM 17-746)

Data available from the literature show thatXRD powder patterns similar to those obtained inthis study are produced by naturally occurringloparite of various Nb2O5 CaO Na2O TiO2 andSrO contents (Haggerty and Mariano 1983Kostyleva-Labuntsova et al 1978b Mitchell etal 1996) Given a significant difference in ionicradius between Th4+ Na+ and Ce3+ (121 139and 134 AEcirc respectively Shannon 1976) it isexpected that Th-rich loparite should have astrongly distorted perovskite-type structureHowever the obtained patterns (Table 5) do notexhibit lsquoextrarsquo diffraction lines reflecting cationordering or geometric distortion of the ideal cubicperovskite-type lattice Such diffraction lines eg769 shy 790 344shy 350 257shy 260 187 shy 189 AEcirc are present in patterns of most syntheticperovskite-type titanates and niobates with Th4+

localized at the A sites (Keller 1965 Kovba andTrunov 1963 Labeau and Joubert 1978 Zhu andHor 1995) The only known exceptions so far arecompounds from the Na06shy 08Th01 shy 02NbO3

range of the NaNbO3shy Th025NbO3 solid solutionseries (ASTM-34-1068 Labeau and Joubert1978 Table III)

TABLE 5 X-ray diffraction patterns of loparite lsquoirinitersquo and Th-rich loparite

1 2 3 4 5hkl d IIo d IIo d IIo d IIo d IIo

100 3870 2110 2730 100 271 100 276 100 264 100 272 100111 2225 50200 1933 92 1919 90 1950 10 1905 30 1925 40

1860 200b211 1578 95 1569 80 1598 30 1562 60 1575 60

1503 10220 1367 70 1360 40 1383 20 1355 30 1368 30300 1290 4310 1225 25 1216 30 1233 15 1214 20 1222 20311 1168 8 1197 10222 1117 13 1111 5 1118 5320 1075 3321 1035 38 1028 60 1042 20 1029 10 1034 10400 09680 5411 0908 10 0912 5420 0864 10 0865 5332 08245 5 08260 3422 07910 3

1 synthetic NaLaTi2O6 a = 3873 AEcirc (ASTM 39-65) 2 lsquoirinitersquo (heated) a = 383 AEcirc (Borodin and Kazakova 1954)3 thorian loparite KHB-70 core (unheated) a = 3902(2) AEcirc 4 thorian loparite KHB-70 core (heated) a = 3841(1)AEcirc 5 thorian loparite KHB-70 rim (heated) a = 3867(2) AEcirc + 3 weak lines with d = 295 1795 1535 AEcirc (3-5 thiswork) b = broad line

R H MITCHELL AND A RCHAKHMOURADIAN

350

The absence of superstructure reflections in thepatterns of thorian loparite may result from itsmetamict state prior to heating ie from failure torestore an initial apparently distorted structure ofthe mineral Alternatively stabilization of thecubic structure may result from the presence ofminor cations in thorian loparite eg Ca or SrThis phenomenon refered to as stabilized poly-morphism (Smirnova and Belov 1969) is well-known for TiO2 and ZrO2 polymorphs (Filatovand Frank-Kamenetskii 1969 Grunin et al1983) To select between the two abovealternatives experimental studies of the solidsolution series between loparite and Th-bearingend-members are being undertaken by us

Discussion

At Khibina Th-rich loparite occurs only inrelation to the foyaite series (Borodin andKazakova 1954 Chakhmouradian and Mitchell1998 Kozyreva et al 1991 Tikhonenkova et al1982) Zoned Th-rich loparite examined in thisstudy crystallized at a late deuteric stage of theformation of foyaite pegmatites At this stagefluids enriched in Ti and incompatible elements(Zr Nb Sr LREE Th) gave rise to theassemblage of aegirine with loparite eudialyteand Ti-silicates (astrophyllite lorenzenitelamprophyllite) In a similar paragenesis lopariteoccurs in the foyaite pegmatites at MtNiorkpakhk (east of Mt Eveslogchorr) andkhibinite pegmatites at a number of localities inwestern Khibina (Chakhmouradian and Mitchell1998) In most of these occurrences loparite isrelatively Th-poor and compositionally evolvesby enrichment in Na2O and Nb2O5 and depletionin LREE2O3 and TiO2 contents toward the rimThis trend coincides with the main magmatictrend of the compositional evolution of loparite int h e n e p h e l i n e - s y e n i t e c o m p l e x e s(Chakhmouradian and Mitchell 1998 Mitchelland Chakhmouradian 1996) The evolutionarytrend from niobian loparite to thorian niobianloparite recognized in the present study has notbeen previously observed in alkaline rocksLoparite from fenite-type rocks of the ParanaBasin carbonatite complexes has high ThO2

contents (up to 62 wt) accompanied byenrichment in Na2O and Nb2O5 (lueshite) anddepletion in SrO and TiO2 (tausonite) (Mitchell1996 Table 36) Th-enrichment (up to 49 wtThO2) in the composition of perovskite from thecarbonatite complexes of the Kola Peninsula is

coupled with increasing LREE2O3 Na2O andNb2O5 ie loparite and lueshite components(Chakhmouradian and Mitchell 1997) In thePolino carbonatite Th-bearing (15 shy 17 wtThO2) perovskite has high Fe2O3 and ZrO2

contents (Lupini et al 1992)The limits of solubility between loparite

(NaLREETi2O6) and the thorium end-membercompositions ThNb4O12 Na23Th13TiO3 andThTi2O6 are unknown From structural data(Balic ZIuml unic et al 1984 Kovba and Trunov1963 Ruh and Wadsley 1966 Zhu and Hor1995) it is expected that loparite forms acomplete solid solution series with the formertwo compounds and only a limited series withThTi2O6 Experimental studies of the NaLaTi2O6

-ThNb4O12 NaLaTi2O6ndashNa2ThTi3O9 andNaLaTi2O6ndashThTi2O6 systems are being under-taken by the authors of this paper

As evidenced by textural relationships andcompositional data the appearance of Na-poorTh-rich lsquoceriobetafitersquo and belyankinite asmantles on thorian loparite was a result ofmetasomatic processes involving alkali-cationleaching and hydration Note that the sameprocesses brought about the replacement ofnepheline and alkali feldspar present as relics infibrous aegirine by zeolites and eventually bygibbsite Metasomatites including albitites albite-aegirine and albite-astrophyllite rocks are verycommon in the vicinity of pegmatite veinscontaining thorian loparite at Mt EveslogchorrHydrothermal solutions responsible for themetasomatic alteration most probably werederived from the phonolitic magma whichproduced the differentiated intrusion of nephelinesyenites including foyaite and its precursorkhibinite An alternative source of such solutionscould be a foidolite melt as some authors suggestthat the foidolites were emplaced later than thenephel ine syenite intrusion (Kostyleva-Labuntsova et al 1978a Sniatkova et al 1986)

Conclusions

In Na-LREE-Ti-dominant species of the perovs-kite group Th4+ cations occupy large twelve-coordinated A sites in the structure Theaccommodation of Th into the structure isaccompanied by appearance of vacancies at theA sites at the expense of Na LREE and SrThorian loparite is essentially a member of theloparite (NaLREETi2O6)ndashlueshite (NaNbO3)ndashThTi2O6ndashThNb4O12 quaternary system with low

TH-RICH LOPARITE

351

or negligible contents of other end-membercompositions The mineral compositionallyevolves from niobian loparite to niobian thorianand thorian niobian loparite Metasomatic altera-tion of thorian loparite gave rise to lsquoceriobetafitersquoand belyankinite with high ThO2 content Thorianloparite is metamict or partly metamict and uponheating regains a structure close to that ofsynthetic loparite NaLaTi2O6

Acknowledgements

This work was supported by the Natural Sciencesand Engineering Research Council of Canada andLakehead University Ontario (RHM ARC) ARCalso acknowledges support from St PetersburgState University Russia (grant Evolution offramework niobium-titanium oxides in carbona-tite-bearing nepheline-syenite complexes) AlanMacKenzie and Keith Pringnitz are thanked fortheir assistance with the analytical work AnnHammond and Sam Spivak are thanked for thinsection preparation and drafting services respec-tively

References

Balic ZIuml unic T SIuml cavnicIuml ar S and Grobenski Z (1984)The structure of thorium (IV) dititanium (IV) oxideThTi2O6 Croat Chem Acta 57 645 shy 51

Belous AG Novitskaya GN Gavrilova LGPolyanetskaya SV and Makarova ZYa (1985)Lanthanum titanate-zirconates with the perovskitestructure Sov Prog Chem 51 13 shy 15

Borodin LS (1954) On accommodation of water in thecrystal lattice of perovskite-group minerals DokladyAN SSSR 95 (in Russian) 873 shy 5

Borodin LS and Kazakova ME (1954) Irinite shy anew mineral from the perovskite group Doklady ANSSSR 97 (in Russian) 725 shy 8

Chakhmouradian AR and Mitchell RH (1997)Compositional variation of perovskite-group miner-als from the carbonatite complexes of the KolaAlkaline Province Russia Canad Mineral 351293 shy 310

Chakhmouradian AR and Mitchell RH (1998)Compositional variation of perovskite-group miner-als from the Khibina alkaline complex KolaPeninsula Canad Mineral 36 (in press)

Filatov SK and Frank-Kamenetskii VA (1969)Structural characteristics of cubic ZrO2 stabilizedby calcium Sov Phys Cryst 14 414 shy 5

Galakhov AV (1975) The petrology of the KhibinaAlkaline Massif Nauka Press Leningrad (in

Russian) 256 ppGerasimovski i VI and Kazakova ME (1950)

Belyankinite shy a new mineral Doklady AN SSSR 71 (in Russian) 925 shy 7

Grunin VS Razumenko MV Patrina IV FilatovSK and Alekseyeva TV (1983) Mode of existenceand abundance of TiO2-rutile anatase and brookiteDoklady Earth Sci Sect 268 149 shy 50

Haggerty SE and Mariano AN (1983) Strontian-loparite and strontio-chevkinite two new minerals inrheomorphic fenites from the Parana Basin carbona-tites South America Contrib Mineral Petrol 84365 shy 81

Hogarth DD (1961) A study of pyrochlore andbetafite Canad Mineral 6 610 shy 33

Hogarth DD (1989) Pyrochlore apatite and amphi-bole distinctive minerals in carbonatites InCarbonat ites (K Bell ed) Unwyn HymanLondon 105 shy 48

Kapustin YuL (1989) Rare earth-bearing pyrochlorefrom peralkaline pegmatites of the Khibina massifNew data on minerals (Trudy Mineral Muz ANSSSR ) 36 (in Russian) 155 shy 61

Keller C (1965) Die Reaktion der Dioxide derElemente Thorium bis Americium mit Niob- undTantalpentoxid (The reaction of dioxides of theelements from thorium to americium with niobiumand tantalum pentoxides) J Inorg Nucl Chem 271233 shy 46

Kogarko LN Kononova VA Orlova MP andWoolle y AR (1995 ) Alkaline Rocks andCarbonatites of the World Part 2 Former USSRChapman amp Hall London UK 226 pp

Kostyleva-Labuntsova EE Borutskii BE SokolovaMN Shliukova ZV Dorfman MD DudkinOB Kozyreva LV and Ikorskii SV (1978a) TheMineralogy of the Khibina Massif Vol 1 NaukaPress Moscow (in Russian) 228 p

Kostyleva-Labuntsova EE Borutskii BE SokolovaMN Shliukova ZV Dorfman MD DudkinOB Kozyreva LV and Ikorskii SV (1978b) TheMineralogy of the Khibina Massif Vol 2 NaukaPress Moscow (in Russian) 588 p

Kovba LM and Trunov VK (1962) Double oxidescontaining tungsten tantalum or niobium DokladyAN SSSR 147 (in Russian) 622 shy 4

Kozyreva LV (1990) Aegirine-feldspar veins in thenorth-eastern part of the Khibina massif In AlkalineMagmatism in the North-eastern Part of the BalticShield Kola Sci Centre Press Apatity (in Russian)42 shy 56

Kozyreva LV Menrsquoshikov YuP and Lednev AI(1991) Loparite mineralization of the Khibinamassif In New Data on the Rare-metalMineralogy of the Kola Peninsula Kola SciCentre Press Apatity (in Russian) 37 shy 44

R H MITCHELL AND A RCHAKHMOURADIAN

352

The absence of superstructure reflections in thepatterns of thorian loparite may result from itsmetamict state prior to heating ie from failure torestore an initial apparently distorted structure ofthe mineral Alternatively stabilization of thecubic structure may result from the presence ofminor cations in thorian loparite eg Ca or SrThis phenomenon refered to as stabilized poly-morphism (Smirnova and Belov 1969) is well-known for TiO2 and ZrO2 polymorphs (Filatovand Frank-Kamenetskii 1969 Grunin et al1983) To select between the two abovealternatives experimental studies of the solidsolution series between loparite and Th-bearingend-members are being undertaken by us

Discussion

At Khibina Th-rich loparite occurs only inrelation to the foyaite series (Borodin andKazakova 1954 Chakhmouradian and Mitchell1998 Kozyreva et al 1991 Tikhonenkova et al1982) Zoned Th-rich loparite examined in thisstudy crystallized at a late deuteric stage of theformation of foyaite pegmatites At this stagefluids enriched in Ti and incompatible elements(Zr Nb Sr LREE Th) gave rise to theassemblage of aegirine with loparite eudialyteand Ti-silicates (astrophyllite lorenzenitelamprophyllite) In a similar paragenesis lopariteoccurs in the foyaite pegmatites at MtNiorkpakhk (east of Mt Eveslogchorr) andkhibinite pegmatites at a number of localities inwestern Khibina (Chakhmouradian and Mitchell1998) In most of these occurrences loparite isrelatively Th-poor and compositionally evolvesby enrichment in Na2O and Nb2O5 and depletionin LREE2O3 and TiO2 contents toward the rimThis trend coincides with the main magmatictrend of the compositional evolution of loparite int h e n e p h e l i n e - s y e n i t e c o m p l e x e s(Chakhmouradian and Mitchell 1998 Mitchelland Chakhmouradian 1996) The evolutionarytrend from niobian loparite to thorian niobianloparite recognized in the present study has notbeen previously observed in alkaline rocksLoparite from fenite-type rocks of the ParanaBasin carbonatite complexes has high ThO2

contents (up to 62 wt) accompanied byenrichment in Na2O and Nb2O5 (lueshite) anddepletion in SrO and TiO2 (tausonite) (Mitchell1996 Table 36) Th-enrichment (up to 49 wtThO2) in the composition of perovskite from thecarbonatite complexes of the Kola Peninsula is

coupled with increasing LREE2O3 Na2O andNb2O5 ie loparite and lueshite components(Chakhmouradian and Mitchell 1997) In thePolino carbonatite Th-bearing (15 shy 17 wtThO2) perovskite has high Fe2O3 and ZrO2

contents (Lupini et al 1992)The limits of solubility between loparite

(NaLREETi2O6) and the thorium end-membercompositions ThNb4O12 Na23Th13TiO3 andThTi2O6 are unknown From structural data(Balic ZIuml unic et al 1984 Kovba and Trunov1963 Ruh and Wadsley 1966 Zhu and Hor1995) it is expected that loparite forms acomplete solid solution series with the formertwo compounds and only a limited series withThTi2O6 Experimental studies of the NaLaTi2O6

-ThNb4O12 NaLaTi2O6ndashNa2ThTi3O9 andNaLaTi2O6ndashThTi2O6 systems are being under-taken by the authors of this paper

As evidenced by textural relationships andcompositional data the appearance of Na-poorTh-rich lsquoceriobetafitersquo and belyankinite asmantles on thorian loparite was a result ofmetasomatic processes involving alkali-cationleaching and hydration Note that the sameprocesses brought about the replacement ofnepheline and alkali feldspar present as relics infibrous aegirine by zeolites and eventually bygibbsite Metasomatites including albitites albite-aegirine and albite-astrophyllite rocks are verycommon in the vicinity of pegmatite veinscontaining thorian loparite at Mt EveslogchorrHydrothermal solutions responsible for themetasomatic alteration most probably werederived from the phonolitic magma whichproduced the differentiated intrusion of nephelinesyenites including foyaite and its precursorkhibinite An alternative source of such solutionscould be a foidolite melt as some authors suggestthat the foidolites were emplaced later than thenephel ine syenite intrusion (Kostyleva-Labuntsova et al 1978a Sniatkova et al 1986)

Conclusions

In Na-LREE-Ti-dominant species of the perovs-kite group Th4+ cations occupy large twelve-coordinated A sites in the structure Theaccommodation of Th into the structure isaccompanied by appearance of vacancies at theA sites at the expense of Na LREE and SrThorian loparite is essentially a member of theloparite (NaLREETi2O6)ndashlueshite (NaNbO3)ndashThTi2O6ndashThNb4O12 quaternary system with low

TH-RICH LOPARITE

351

or negligible contents of other end-membercompositions The mineral compositionallyevolves from niobian loparite to niobian thorianand thorian niobian loparite Metasomatic altera-tion of thorian loparite gave rise to lsquoceriobetafitersquoand belyankinite with high ThO2 content Thorianloparite is metamict or partly metamict and uponheating regains a structure close to that ofsynthetic loparite NaLaTi2O6

Acknowledgements

This work was supported by the Natural Sciencesand Engineering Research Council of Canada andLakehead University Ontario (RHM ARC) ARCalso acknowledges support from St PetersburgState University Russia (grant Evolution offramework niobium-titanium oxides in carbona-tite-bearing nepheline-syenite complexes) AlanMacKenzie and Keith Pringnitz are thanked fortheir assistance with the analytical work AnnHammond and Sam Spivak are thanked for thinsection preparation and drafting services respec-tively

References

Balic ZIuml unic T SIuml cavnicIuml ar S and Grobenski Z (1984)The structure of thorium (IV) dititanium (IV) oxideThTi2O6 Croat Chem Acta 57 645 shy 51

Belous AG Novitskaya GN Gavrilova LGPolyanetskaya SV and Makarova ZYa (1985)Lanthanum titanate-zirconates with the perovskitestructure Sov Prog Chem 51 13 shy 15

Borodin LS (1954) On accommodation of water in thecrystal lattice of perovskite-group minerals DokladyAN SSSR 95 (in Russian) 873 shy 5

Borodin LS and Kazakova ME (1954) Irinite shy anew mineral from the perovskite group Doklady ANSSSR 97 (in Russian) 725 shy 8

Chakhmouradian AR and Mitchell RH (1997)Compositional variation of perovskite-group miner-als from the carbonatite complexes of the KolaAlkaline Province Russia Canad Mineral 351293 shy 310

Chakhmouradian AR and Mitchell RH (1998)Compositional variation of perovskite-group miner-als from the Khibina alkaline complex KolaPeninsula Canad Mineral 36 (in press)

Filatov SK and Frank-Kamenetskii VA (1969)Structural characteristics of cubic ZrO2 stabilizedby calcium Sov Phys Cryst 14 414 shy 5

Galakhov AV (1975) The petrology of the KhibinaAlkaline Massif Nauka Press Leningrad (in

Russian) 256 ppGerasimovski i VI and Kazakova ME (1950)

Belyankinite shy a new mineral Doklady AN SSSR 71 (in Russian) 925 shy 7

Grunin VS Razumenko MV Patrina IV FilatovSK and Alekseyeva TV (1983) Mode of existenceand abundance of TiO2-rutile anatase and brookiteDoklady Earth Sci Sect 268 149 shy 50

Haggerty SE and Mariano AN (1983) Strontian-loparite and strontio-chevkinite two new minerals inrheomorphic fenites from the Parana Basin carbona-tites South America Contrib Mineral Petrol 84365 shy 81

Hogarth DD (1961) A study of pyrochlore andbetafite Canad Mineral 6 610 shy 33

Hogarth DD (1989) Pyrochlore apatite and amphi-bole distinctive minerals in carbonatites InCarbonat ites (K Bell ed) Unwyn HymanLondon 105 shy 48

Kapustin YuL (1989) Rare earth-bearing pyrochlorefrom peralkaline pegmatites of the Khibina massifNew data on minerals (Trudy Mineral Muz ANSSSR ) 36 (in Russian) 155 shy 61

Keller C (1965) Die Reaktion der Dioxide derElemente Thorium bis Americium mit Niob- undTantalpentoxid (The reaction of dioxides of theelements from thorium to americium with niobiumand tantalum pentoxides) J Inorg Nucl Chem 271233 shy 46

Kogarko LN Kononova VA Orlova MP andWoolle y AR (1995 ) Alkaline Rocks andCarbonatites of the World Part 2 Former USSRChapman amp Hall London UK 226 pp

Kostyleva-Labuntsova EE Borutskii BE SokolovaMN Shliukova ZV Dorfman MD DudkinOB Kozyreva LV and Ikorskii SV (1978a) TheMineralogy of the Khibina Massif Vol 1 NaukaPress Moscow (in Russian) 228 p

Kostyleva-Labuntsova EE Borutskii BE SokolovaMN Shliukova ZV Dorfman MD DudkinOB Kozyreva LV and Ikorskii SV (1978b) TheMineralogy of the Khibina Massif Vol 2 NaukaPress Moscow (in Russian) 588 p

Kovba LM and Trunov VK (1962) Double oxidescontaining tungsten tantalum or niobium DokladyAN SSSR 147 (in Russian) 622 shy 4

Kozyreva LV (1990) Aegirine-feldspar veins in thenorth-eastern part of the Khibina massif In AlkalineMagmatism in the North-eastern Part of the BalticShield Kola Sci Centre Press Apatity (in Russian)42 shy 56

Kozyreva LV Menrsquoshikov YuP and Lednev AI(1991) Loparite mineralization of the Khibinamassif In New Data on the Rare-metalMineralogy of the Kola Peninsula Kola SciCentre Press Apatity (in Russian) 37 shy 44

R H MITCHELL AND A RCHAKHMOURADIAN

352

or negligible contents of other end-membercompositions The mineral compositionallyevolves from niobian loparite to niobian thorianand thorian niobian loparite Metasomatic altera-tion of thorian loparite gave rise to lsquoceriobetafitersquoand belyankinite with high ThO2 content Thorianloparite is metamict or partly metamict and uponheating regains a structure close to that ofsynthetic loparite NaLaTi2O6

Acknowledgements

This work was supported by the Natural Sciencesand Engineering Research Council of Canada andLakehead University Ontario (RHM ARC) ARCalso acknowledges support from St PetersburgState University Russia (grant Evolution offramework niobium-titanium oxides in carbona-tite-bearing nepheline-syenite complexes) AlanMacKenzie and Keith Pringnitz are thanked fortheir assistance with the analytical work AnnHammond and Sam Spivak are thanked for thinsection preparation and drafting services respec-tively

References

Balic ZIuml unic T SIuml cavnicIuml ar S and Grobenski Z (1984)The structure of thorium (IV) dititanium (IV) oxideThTi2O6 Croat Chem Acta 57 645 shy 51

Belous AG Novitskaya GN Gavrilova LGPolyanetskaya SV and Makarova ZYa (1985)Lanthanum titanate-zirconates with the perovskitestructure Sov Prog Chem 51 13 shy 15

Borodin LS (1954) On accommodation of water in thecrystal lattice of perovskite-group minerals DokladyAN SSSR 95 (in Russian) 873 shy 5

Borodin LS and Kazakova ME (1954) Irinite shy anew mineral from the perovskite group Doklady ANSSSR 97 (in Russian) 725 shy 8

Chakhmouradian AR and Mitchell RH (1997)Compositional variation of perovskite-group miner-als from the carbonatite complexes of the KolaAlkaline Province Russia Canad Mineral 351293 shy 310

Chakhmouradian AR and Mitchell RH (1998)Compositional variation of perovskite-group miner-als from the Khibina alkaline complex KolaPeninsula Canad Mineral 36 (in press)

Filatov SK and Frank-Kamenetskii VA (1969)Structural characteristics of cubic ZrO2 stabilizedby calcium Sov Phys Cryst 14 414 shy 5

Galakhov AV (1975) The petrology of the KhibinaAlkaline Massif Nauka Press Leningrad (in

Russian) 256 ppGerasimovski i VI and Kazakova ME (1950)

Belyankinite shy a new mineral Doklady AN SSSR 71 (in Russian) 925 shy 7

Grunin VS Razumenko MV Patrina IV FilatovSK and Alekseyeva TV (1983) Mode of existenceand abundance of TiO2-rutile anatase and brookiteDoklady Earth Sci Sect 268 149 shy 50

Haggerty SE and Mariano AN (1983) Strontian-loparite and strontio-chevkinite two new minerals inrheomorphic fenites from the Parana Basin carbona-tites South America Contrib Mineral Petrol 84365 shy 81

Hogarth DD (1961) A study of pyrochlore andbetafite Canad Mineral 6 610 shy 33

Hogarth DD (1989) Pyrochlore apatite and amphi-bole distinctive minerals in carbonatites InCarbonat ites (K Bell ed) Unwyn HymanLondon 105 shy 48

Kapustin YuL (1989) Rare earth-bearing pyrochlorefrom peralkaline pegmatites of the Khibina massifNew data on minerals (Trudy Mineral Muz ANSSSR ) 36 (in Russian) 155 shy 61

Keller C (1965) Die Reaktion der Dioxide derElemente Thorium bis Americium mit Niob- undTantalpentoxid (The reaction of dioxides of theelements from thorium to americium with niobiumand tantalum pentoxides) J Inorg Nucl Chem 271233 shy 46

Kogarko LN Kononova VA Orlova MP andWoolle y AR (1995 ) Alkaline Rocks andCarbonatites of the World Part 2 Former USSRChapman amp Hall London UK 226 pp

Kostyleva-Labuntsova EE Borutskii BE SokolovaMN Shliukova ZV Dorfman MD DudkinOB Kozyreva LV and Ikorskii SV (1978a) TheMineralogy of the Khibina Massif Vol 1 NaukaPress Moscow (in Russian) 228 p

Kostyleva-Labuntsova EE Borutskii BE SokolovaMN Shliukova ZV Dorfman MD DudkinOB Kozyreva LV and Ikorskii SV (1978b) TheMineralogy of the Khibina Massif Vol 2 NaukaPress Moscow (in Russian) 588 p

Kovba LM and Trunov VK (1962) Double oxidescontaining tungsten tantalum or niobium DokladyAN SSSR 147 (in Russian) 622 shy 4

Kozyreva LV (1990) Aegirine-feldspar veins in thenorth-eastern part of the Khibina massif In AlkalineMagmatism in the North-eastern Part of the BalticShield Kola Sci Centre Press Apatity (in Russian)42 shy 56

Kozyreva LV Menrsquoshikov YuP and Lednev AI(1991) Loparite mineralization of the Khibinamassif In New Data on the Rare-metalMineralogy of the Kola Peninsula Kola SciCentre Press Apatity (in Russian) 37 shy 44

R H MITCHELL AND A RCHAKHMOURADIAN

352

Krivokoneva GK and Sidorenko GA (1971) Theessence of the metamict transformation in pyro-chlores Geochem Int 1971 113 shy 22

Kukharenko AA amp Bagdasarov EA (1961 )Perovskite from ultramafic-alkaline rocks of theKola Peninsula Trudy VSEGEI 45 (in Russian)37 shy 66

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[Manuscript received 6 May 1997revised 9 September 1997 ]

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