REE-Sr-Ba Minerals from the Khibina Carbonatites, Kola Peninsula, Russia

Home , Edingtonite, Harmotome, Lanthanite, Strontianite, Weloganite

Mineralogical Magazine, April 1998, Vol.62(2), pp.225–250

REE-Sr-Bamineralsf romthe Khibina carbonatites,K ola Peninsula,R ussia:t heirmineralogy,paragenesisan devolution

ANATOLY N. ZAITSEV Department of Mineralogy, StPetersburg University, StPetersburg 199034, Russia

FRANCES WALL Department of Mineralogy, The Natural History Museum, Cromwell Road, London, SW7 5BD

AND

MICHAEL J. LE BAS Department of Geology, University of Southampton, Southampton Oceanography Centre, Southampton, SO14 3ZH

ABSTRACT

Carbonatitesfrom the Khibina Alkaline Massif (360 380Ma), Kola Peninsula, Russia, contain one of themost diverse assemblages of REE mineralsdescribed thus far from carbonatites and provide an excellentopportunity to track the evolution of late-stage carbonatites and their sub-solidus (secondary) changes.Twelverare earth minerals have been analysed in detail and compared with literature analyses.Theseminerals include some common to carbonatites (e .g.Ca-rare-earthfluocarbonates and ancylite-(Ce))plus burbankite and carbocernaite and some very rare Ba, REE fluocarbonates. Overall the REE patternschange from light rare earth-enriched in the earliest carbonatites to heavy rareearth-enriched in the late carbonate-zeolite veins, an evolution which is thought to reflect the increasing ‘carbohydrothermal’ natureof the rock-forming fluid .Manyof the carbonatites have been subjectto sub-solidus metasomatic processes whose products include hexagonal prismatic pseudomorphsof ancylite-(Ce) or synchysite-(Ce), strontianite and baryte after burbankite and carbocernaite . Themetasomatic processes cause little change in the rare earth patterns and it isthought that they took placesoon after emplacement .

KEY WORDS: Khibina,carbonatite, REE,burbankite,carbocernaite, metasomatism .

Introduction containhigh levels of Ba and also commonly Sr.Theprincipal RE mineralsin carbonatites are RARE-EARTH-RICH carbonatites,containing wt . % thephosphate, monazite-(Ce); the fluocarbonates, levels of REE anddiscrete RE minerals,are bastna¨site-(Ce),synchysite -(Ce),and parisite- commonas late-stage products in carbonatite (Ce);and the hydrated carbonate, ancylite-(Ce) . complexes.Occasionally,they form the major Otherrare earth minerals such as burbankite, partof the complex and may be of economic carbocernaite,huanghoite-( Ce),calkinsite-(Ce ) importance,e .g.atMountain Pass (Olsen et al., andfluocerite-(Ce) have been reported from a 1954),Vuoriyarvi (Kukharenko et al., 1965), fewcarbonatite localities . Verkhnesayanskiiand Nizhnesayanskii (Somina, Carbonatitesfrom the Khibina alkaline massif, 1975),and Kangankunde (Wall and Mariano, KolaPeninsula, Russia, (Minakov and Dudkin, 1996)but usually their volume is small in 1974;Minakov et al.,1981)present a good comparisonwith earlier carbonatites, e .g.Fen opportunityfor a comprehensivestudy of the (Andersen,1986),and Qaqarssuk (Knudsen, mineralogyand petrogenesis of RE-richcarbona- 1991).Rareearth -richcarbon atitesusuall y tites.Takenfrom drillcore, the carbonatites are

# 1998The Mineralogical Society A. N.ZAITSEV ETAL.

fresh,coarse-grained, and consist of asequenceof Zaitsev(1996, Fig .1)gives a generalmap of earlyto late carbonatites that contain high levels theKhibina massif that shows the location of of REE, Sr and Ba. carbonatitedrill holes .ASr andNd isotope study Theaims of ourstudyare twofold: (i) topresent hasbeenmadebyZa itsevandBe ll( in mineralogicald ataon Kh ibina REE-Sr-Ba preparation). mineralsbecause little information on many of Thecarbonatites form a stockwork(Zaitsev, theseminerals is availablein the literature and (ii) 1996)in which it is possible to distinguish early todetermine the history of crystallization and calcitecarbonat ites(C I)andlater calcite, subsequentalteration of the Khibina minerals . manganoanankerite calciteand ferroan rhodochrosite manganoansiderite carbonatites (C II). Thelater carbonatites account for about 90 % by Generalgeology and geochemistry of the volumeof the Khibina carbonatite series and Khibinacarbonatites occuras veins 1 cmto 6 mwide.Otherrocks TheKhibina alkaline massif is located in the whichare not carbonatites sensustricto , but are centralpart of the Kola Alkaline Province which geneticallyconnected with them, are represented consistsof 24 ultrabas ic-alkaline-carbonatite byphoscorite (BAA) andcarbonate-zeolite rocks complexesof Devonian age .Accordingto Rb-Sr (CZIII).Thesilicate country rocks (ijolite, dating,the age of the Khibina massif ranges from foyaite,olivine melanephelinite and phonolite) 377to 362 Ma (Kramm et al.,1993;Kramm and hostingthe carbonatites are intensively fenitized, Kogarko,1994 ).TheKhibina massif is a andconsist of albite, biotite and calcite . concentricallyzoned pluton, consisting of ultra- Representativewhole-rock major and trace basic(peridotite, pyroxenite), alkaline silicate elementanalyses for the carbonatites are given (nephelinesyenite, foidolite) and apatite-nephe- inTable 1 .Interms of the major oxides (CaO, linerocks and carbonatites .Itsgeneral geology, MgO,FeO andMnO), the Khibina carbonatites geochemistrya ndmineralogyhavebeen canbe subdivided into calciocarbonatite sand describedinnumerouspublications(e.g. ferrocarbonatites(Fig .1 a)andshow a progressive Khomyakov,1995; Kogark o et al. , 1995). increasein Fe andMn from the oldest C Itothe

FIG.1.Plots showing the compositional range of the Khibina carbonatites which ( a)classify as calcio- and ferrocarbonatites according to Woolley and Kempe (1989) but ( b)sometimes contain more Mn than Fe and may be classified as manganocarbonatites .

226 REE-SR-BA MINERALS

TABLE 1.Representativewhole-rock and trace element analyses of theKhibina carbonatites

Rock C I C I C II-1 CII-1C II-2C II-2C II-3C II-3 Sample632B/ 1934632B/ 1960633/ 477.7603/165.5604/454603/ 225603/ 89604/ 90

SiO2 wt. % 4. 81 3. 68 0. 64 0. 19 0. 44 0.87 1.88 2.09 TiO2 0. 64 0. 22 0. 03 0. 02 0. 01 0.04 0.02 0.08 Al2O3 0. 88 0. 49 0. 25 0. 06 0. 10 0.29 0.69 0.70 FeOT 4. 99 3. 02 3. 79 2. 29 5. 64 8.09 19.14 22.97 MnO 0. 37 0. 39 1. 56 0. 85 5.86 11.39 12.78 12.60 MgO 1. 20 0. 97 0. 41 0. 35 2. 05 3.72 3.97 2.35 CaO 46. 50 45. 95 32. 52 35. 12 28.70 24.59 12.13 18.40 Na2O 0. 36 0. 59 3. 09 1. 68 0. 14 0.22 0.21 0.25 K2O 1. 45 0. 38 0. 09 0. 05 0. 12 0.03 0.55 0.69 P2O5 1. 25 1. 67 0. 02 0. 04 0. 09 0.08 0.11 0.91 S 0. 32 0. 20 0. 73 0. 53 0. 74 0.41 1.59 1.12 F 0. 09 0. 19 0. 06 0. 41 0. 84 1.03 0.21 0.12 Cl 0. 01 0. 01 0. 02 0. 01 0. 01 0.03 0.02 0.01 O=S,F2,Cl2 0. 20 0. 18 0. 39 0. 44 0. 73 0.65 0.88 0.61 Total* 64. 79 59. 57 61. 02 62. 92 58.21 62.19 58.16 65.16

Rb ppm 37 25 bd bd bd bd 5 9 Ba 1343 1268 13102 10205 11380 10990 28374 1280 Th 13 10 127 103 44 17 84 76 Nb 416 515 bd 10 15 28 112 86 La 437 492 28384 35565 18589 22891 2540 4064 Ce 955 1078 37990 50727 31341 37558 6823 8868 Sr 13449 12307 63819 73004 20495 16174 5533 7017 Nd 403 418 7969 10620 6395 8852 2814 3099 Zr 184 135 bd 5 bd bd 7 20 Y 62 44 113 137 98 52 43 102 Sc 40 8 56 28 21 32 19 21 V 96 112 bd 14 25 bd 201 156 Cr 22 40 bd 15 10 bd 286 4 Co 20 18 23 14 19 bd 40 4 Cu 34 27 76 39 28 47 84 45 Ni 4 6 24 18 20 24 15 16 Zn 76 44 57 120 995 2354 1850 3073

FeOT -total iron as FeO.*-including trace elements as oxides.bd -below detection Whole-rock analyses were made on fusion beads for major elements and powder pellets for trace-elements by X-ray fluorescence analysis at the University of Leicester using aPhilips PW1400 X-ray spectrometer.CO 2 and H2O not analysed

youngestCII-3 carbonatit es.However,some unusualchemical characteristics of the Khibina ferrocarbonatitescontain more Mn than Fe and carbonatitesinclude the following: theycan be classified as manganocarbonatite s 1.Somecarbonatites contain burbankite or withCaO/ (CaO+ MgO+ FeO +Fe 2O3 + MnO) carbocernaite(C II-1)and are characterized by lessthan 0 .8,MgO<(FeO+MnO) and MnO>FeO highNa contents (1 .20 4.94 wt. % Na2O), but (Table1 andFig .1 b).Themanganocarbonatite s containno Na-bearingsilicates such as pyroxene, containup to 12 .8wt. % MnOand contain Mn- amphiboleor feldspar . bearingcarbonates, such as manganoan ankerite, 2.Sy nchysite-(Ce)-bearingcarbonatites ferroankutnohorite, ferroan rhodochrosite and (CII-2)have high F contents(0 .76 1.28 wt.%) manganoansiderite(Zaits ev,1 996).Other whereasother late carbonatites (C II-1and C II-3)

227 A. N.ZAITSEV ETAL.

havelow F contents.However,the intensive fluoritizationof wall rocks around the carbona- titeswhich now have low amounts of F suggests thatthe initial F contentwas higher . 3.Thelate carbonatites (C II)havehigh BaO (0. 81 3. 22 wt. %), SrO (0.61 8. 65 wt. %) and light REE (1.25 11.35 wt.% La2O3 + Ce2O3 + Nd2O3)andthese elemen tsbecome major componentsof these carbonatites . Multi-elementvariati ondiagram sforthe Khibinacarbonatite samples (Fig .2),normalized toprimordialmantle of Wood et al.(1979),show thatthe general chemical features of the Khibina carbonatitesare similar to those described for mostcarbonatites (e .g.Nelson et al.,1988;Clarke et al.,1992).Theearly calcite carbonatites (C I) havecomparable element variation patterns to averagedata for the calciocarbonatite sofWoolley andKempe (1989), although the Khibina samples showslightly higher Sr (Fig.2 a).TheSr ishosted bycalcite which contains 1 .1 1.8 wt. % SrO (Zaitsev,1996) . Theelement variation patterns for the late carbonatitesC II(Fig.2 b)suggestthat these carbonatiteshave undergone fractional crystal- lizationsimilar to that shown by Clarke et al. (1992).Theplot shows a depletionin La,Ce, Nd andSr normalizedvalues from the relatively early-formedcalcite carbonatites with burbankite FIG.2.Multi-element variation diagrams for ( a) early orcarbocernaite (C II-1)to the late manganoan and (b)late Khibina carbonatites, normalized to ankerite-calcitecarbonatites with synchysite-(Ce) primordial mantle of Wood et al. (1979).Calcio- and (CII-2),and to the latest ferroan rhodochrosi- ferrocarbonatites are average values from Woolley and te manganoansiderite carbonatites with synchy- Kempe (1989). site-(Ce)or cordylite-(Ce) (C II-3). Althoughthe normalized Ba values are similar inthe C II-1and C II-2carbonatite types, they showwide variation in CII-3carbonatites .Some and CO2,lossof Na and F underthe electron ofthe C II-3carbonatites are depleted in Ba beam,and the high interference corrections for Ba comparedto C II-1and C II-2types and they and the REE.Inaddition, RE mineraldata containsynchysite-(Ce) as a minoror accessory availablefromthe literatu reare commonly mineral.However,most of C II-3carbonatites are incompleteand sometimes inconsistent .These enrichedin Ba and contain cordylite-(Ce) as a factsprompted us to use as many different majormineral . techniquesas possible for the mineralogic al investigationof the REE-Sr-Baminerals from theKhibina carbonatites . Analyticalmethods Identificationof mineralswas based on optical Theidentification and description of REE-Sr-Ba examination,IR-spectroscopy (UR-20 Carl Zeiss mineralsis often difficult due to their complex spectrophotometer)and X-ray diffraction (RKU chemicalcompositions, with a widevariety of camera- 57.3mm diameterand Fe- Ka radiation, solidsolutions and some polymorphs .Asa result, 114.6mm diameterand Cr - Ka radiation). theyhave variable physical properties, infra-red Electronmicroprobe analyses were made using a andX-ray diffraction patterns .Otherdifficulties CamecaSX 50wavelength-dispersiv eelectron arisefrom the limitations of electron microprobe microprobeat The Natural History Museum, analysisincluding the inability to determineH 2O London,after preliminary work had been carried

228 REE-SR-BA MINERALS

outon a HitachiS2500 scannin gelectron TABLE 2.Mineralscontaining REE,Sr and/orBa as microscopeequipped with a LinkAN10/ 55S majorelements identified in Khibina late carbo- energy-dispersiveanalysis system .TheCameca natites(C II)andcarbonate-zeolite rocks (CZ III) wasoperated at 15 kV and10 20nA, with spot sizes,as largeas possible, up to30 mm in order to minimizebeam damage .Individual REE calcium Mineral Formula aluminiumsilicate glasses obtained from the

Universityof Edinburgh were used as standards burbankite (Na,Ca)3(Sr,Ba,Ce)3(CO3)5 for the REE;jadeitewas used for Na, wollastonite carbocernaite (Na,Ca)(Sr,Ce,Ba)(CO 3)2 andapatite for Ca, celestine for Sr andbarium fluoridefor Ba and F .Detailedinformation about ancylite-(Ce) SrCe(CO3)2(OH) H2O conditionsof microprobe analyses is available fromWilliams (1996) . synchysite-(Ce) Ca(Ce,La)(CO 3)2F parisite-(Ce) Ca(Ce,La)2(CO3)3F2 bastna¨site-(Ce) (Ce,La)(CO3)F Mineralogyand mineral chemistry cordylite-(Ce) Ba(Ce,La)2(CO3)3F2 At least17 mineralscontaining REE,Sr and/orBa cebaite-(Ce) Ba3(Ce,La)2(CO3)5F2 asmajorelements have been identified in thelate kukharenkoite-(Ce) Ba 2Ce(CO3)3F carbonatites(C II)andthe carbonate-zeolite rocks (CZ III)(Table2) .Themineralogy and paragen- mckelveyite-(Y) Ba3Na(Ca,U)Y(CO 3)6 3H2O esisof these, and the associated minerals, is ewaldite Ba(Ca,Y,Na,K)(CO 3)2 summarizedin Table3 .Thistable also shows the donnayite-(Y) Sr3NaCaY(CO3)6 3H2O sequenceof formationof phoscorites,carbonatites edingtonite BaAl Si O 4H O andcarbonate-zeolite rocks in theKhibina massif . 2 3 10 2 harmotome (Ba,K)1 2(Si,Al)8O16 6H2O

AlkalineSr-Ca-REE -Bacarbonates : burbankite and strontianite SrCO3 carbocernaite baryte BaSO4 barytocalcite BaCa(CO3)2 Thealkaline Sr-Ca- REE-Bacarbonates, burbankiteand carbocernaite, are rock-forming minerals inthecalcite carbonatites (C II-1)(Table 3) .Field relationshipsshow that the carbonatites with burbankiteand carbocernaite are the earliest of Thesedata show a largevariation in major oxides: theC IIgroupof carbonatites(Zaitsev, 1996) . Na2O (4. 04 13. 89 wt. %), SrO (6. 17 32. 60 Burbankite,a raremineral known from several wt. %), CaO (9. 81 21. 09 wt. %), SREE2O3 carbonatitecomplexes, always occurs in late- (2. 50 23. 00 wt. %)andBaO (1.85 14. 60 stagecarbonatites .Ithas been described from the wt.%).Wetchemical analyses of burbankite can BearpawMountains (Pecora and Kerr, 1953), showhigh contents of Si, Al andS butthese are Vuoriyarvi(Kukharenko et al.,1965;Kapustin, probablythe result of admixtures .Published 1980),Ozernyi (Zdorik, 1966), Arbarast akh microprobeanalyses have high cation deficiencies (Zhabin et al.,1971),Nizhnesayanskii (Somina, in the A-site(up to 0 .65per formula unit), 1975),Chipman Lake (Platt and Woolley, 1990) attributedto the loss of Na under the electron andQaqarssuk (Knudsen, 1991) . beam(Platt and Woolley, 1990), or have high Burbankiteis a doublecarbonate with the totalswith calculated CO 2 (108. 26 113.49 wt.%) generalformula A3B3(CO3)5, where the A-site is (Knudsen,1991) which also indicate possible occupiedby Naand Ca and the B-sitecontains Sr, analyticalproblems . REE,Baand Ca (Effenberger et al.,1985).There Averagechemical compositions of the Khibina areon lysev enwet chemic alanalysesof burbankitedetermined by wet chemical analysis burbankitefrom carbonatites, made more than of2 gofpure hand-picked burbankite and 25yearsago (Pecora and Kerr, 1953; Kukharenko approximately40 electron microprobe analyses et al., 1965;Zdorik, 1966; Zhabin et al. , 1971; aregiven in Table 4 .Thewet chemical and Kapustin,1980) and twelve electron microprobe microproberesults are in good agreement and analysespublished recently (Effenberger et al., indicatethat the burbankite is relativelylow in Ba 1985;Platt and Woolley, 1990; Knudsen, 1991) . comparedwith other carbonat ites.Theone

229 TABLE 3. Mineralogy and paragenesis of Khibina REE-Sr-Ba minerals

BAA phoscorite-biotite-aegirine-apatite No primary rare earth minerals

CI early calcite carbonatite No primary rare earth minerals

C II-1 late calcite carbonatite with burbankite or carbocernaite Primary phases

Burbankite Carbocernaite A.

10 50% volume, yellow-brown in freshly broken hand specimens. Usually large, hexagonal 10-50% volume N. prismatic crystals (5 50 mm long 6 1 25 mm diameter). Sometimes grow in from, and about N.B. does not occur with burbankite. Lemon yellow ZAITSEV 230 perpendicular to, the contact of the veins. Distribution is heterogeneous. Also as drop-like in hand specimen. Isometric grains 1 5 mm inclusions (30 200 mm) in calcite associated with euhedral zoned apatite (Fig. 3a). diameter in distinct clusters ETAL. Alteration Either of two alteration assemblages can completely pseudomorph Carbocernaite is often partly Strontianite usually colourless anhedral crystals but burbankite, preserving its prismatic, hexagonal crystal form (Fig. replaced by porous aggre- also as prismatic zoned crystals up to 2 mm 3b). gates of strontianite, cordy- 1) Replacement assemblage of ancylite-(Ce), strontianite, and less lite-(Ce), synchysite-(Ce) and Baryte, usually colourless, anhedral, 0. 1 1 mm often, baryte and rarely harmotome and edingtonite. All stages of baryte. Carbocernaite usually grains. alteration seen: from single fine veins (5 20 mm) of ancylite-(Ce) preserved in central parts of in burbankite (Fig. 3d) to porous aggregates of ancylite-(Ce) and the former crystals. Edingtonite and harmotome, spherulitic aggregates strontianite completely replacing burbankite. Ancylite-(Ce) on ancylite-(Ce) or strontianite. usually as pink to red anhedral crystals up to 4 mm but also some euhedral crystals and zoned strontianite in cavities. 2) Porous aggregates of synchysite-(Ce), strontianite and baryte. Burbankite relics seen in strontianite crystals and also in synchysite-(Ce) and baryte. Fig. 3c. TABLE 3 (contd)

C II-2 late manganoan ankerite-calcite carbonatite with synchysite-(Ce) Primary phases

Syntaxial intergrowths (Donnay and Donnay, 1953) of synchysite- Synchysite-(Ce) which is not intergrown is a major rock-forming mineral. (Ce), parisite, and bastna¨site-(Ce) (Fig. 4a) Intergrowths are very fine White, yellow (usually with calcite) or red (usually with ferroan kutnohorite) – 1 20 mm wide and 50 500 mm long. Associated with strontianite. tabular crystals, 0.1 3 mm diameter. Often irregular to radiating agregates.

Kukharenkoite-(Ce), as late-stage 0. 01 1 mm prismatic crystals in tiny cavities. Often as stellate, Strontianite usually occurs as dendritic or irregular intergrowths up to 3 mm diameter. Rarely as anhedral, 0.05 0. 2 mm grains or colourless, subhedral crystals up platy 0.1 2 mm crystals. Associated with cordylite-(Ce), strontianite, and rarely mckelveyite-(Y). to 2 mm diameter. REE -S R C II-3 late carbonatites-ferroan rhodochrosite-manganoan ankerite with synchysite-(Ce) or cordylite-(Ce) -B A 23 MINERALS 1 Primary phases

Synchysite-(Ce) sometimes present in fine Cordylite-(Ce), is a typical mineral. Mckelveyite-(Y), ewaldite, and don- Strontianite, primary, syntaxial intergrowths with parisite-(Ce). White or yellow tabular crystals, nayite-(Y) in cavities. Yellow or usually colourless, 0.1 1 mm and sometimes up to 5 white crystals, various habits from subhedral crystals up mm, either single or in aggregates. tabular, columnar to barrel-shaped. to 2 mm. Some crystals are hemimorphic. Kukharenkoite-(Ce) (See above) Edingtonite and harmotome are common accessory minerals. Usually, euhedral crystals, up to 2 mm, in cavities. Alteration Vein-like aggregates of synchysite-(Ce), strontianite, baryte and Strontianite, usually col- Baryte, usually colourless, anhe- bastna¨site-(Ce) replace the syntaxial intergrowth in some rocks. ourless anhedral crystals. dral, 0.1 1 mm grains. TABLE 3. (contd)

CZ III-1 carbonate-zeolite veins-manganoan siderite-manganoan ankerite-natrolite

Synchysite-(Ce) sometimes Cordylite-(Ce) is a typical Cebaite-(Ce), found in cavities Mckelveyite-(Y), ewal- Edingtonite and har- present mineral. White or yellow as yellow, white or colourless dite and donnayite-(Y) motome common ac- tabular crystals, 0. 1 1 mm crystals up to 0.2 mm. Dendritic, see above. c es so ry m in er al s. and sometimes up to 5 mm, stellate or irregular intergrowths. Usually, euhedral crys- either single or in aggre- Commonly associated with tals, up to 2 mm, in gates. 2 varieties (Fig. 4b). mckelveyite-(Ce), cordylite and cavities. strontianite. Kukharenkoite-(Ce) (See above) Strontianite with cordylite- Baryte, often short, prismatic crystals in cavities (Ce), primary .A. .N. ZAITSEV

232 CZ III-2 carbonate-zeolite veins-manganoan siderite-nordstrandite-natrolite

Cordylite-(Ce) is a ‘typical’ Mckelveyite-(Y), ewaldite Barytocalcite, euhedral or sub- Strontianite with cor- Baryte, often short, ETAL. mineral. White or yellow tabular and donnayite-(Y) hedral, 1 2 mm white crystals dylite-(Ce), primary prismatic crystals in crystals, 0.1 1 mm and some- in cavities. Identification based cavities. times up to 5 mm, either single or on XRD and IR spectra. in aggregates.

CZ III-3 carbonate-zeolite veins-natrolite-manganoan siderite-dawsonite

Mckelveyite-(Y), ewaldite and Strontianite with cordylite- Baryte, often short, prismatic crystals in cavities. donnayite-(Y) (Ce), primary REE-SR-BA MINERALS

TABLE 4.Chemicalcomposition of burbankite at Khibina

Rock C II-1 Sample607/ 277 633/477. 7 633/477.7 581/013 633B/79. 5 largecrystal drop-like inclusion large crystal largecrystal mean(9) sd mean (4) sd mean (10) sd mean (9) sd

Na2O 12. 45 11. 93 0.13 11.80 0.27 12.60 0.44 12. 03 0. 85 CaO 12. 60 11. 94 0.53 12.57 0.54 10.20 0.49 10. 08 1. 22 SrO 19. 60 24. 74 0.31 24.57 0.38 18.38 0.61 17. 71 0. 92 BaO 0. 78 1. 76 0. 12 1. 86 0. 04 2. 52 0. 49 6. 65 0. 47 La2O3 5. 20 5. 65 0. 14 5. 11 0. 25 7. 05 0. 30 4. 77 0. 26 Ce2O3 9. 91 7. 15 0. 16 6.97 0.28 11.06 0.41 9. 26 0. 43 Pr2O3 0. 64 0. 47 0. 04 0. 47 0. 05 0. 80 0. 10 0. 88 0. 07 Nd2O3 1. 53 1. 24 0. 10 1. 33 0. 03 2. 53 0. 28 3. 11 0. 31 Sm2O3 0. 05 b. d. b. d. 0. 31 0. 11 0. 39 0. 12 Gd2O3 b. d. b. d. b. d. b. d. 0. 20 0. 07 ThO2 n. d. b. d. b. d. b. d. 0. 16 0. 10 CO2 35. 40 34. 68 34. 79 34.21 33. 38 Total 99.76* 99.56 99. 47 99.66 98. 62

2 Calculated to 5(CO 3) groups Na 2. 508 2. 442 2. 408 2. 615 2. 558 Ca 0. 338 0. 498 0. 529 0. 267 0. 345 Asite total 2.846 2.941 2. 937 2. 882 2. 903 Sr 1. 181 1. 514 1. 499 1. 141 1. 126 Ca 1. 065 0. 852 0. 889 0. 903 0. 840 La 0. 199 0. 220 0. 198 0. 278 0. 193 Ce 0. 377 0. 276 0. 268 0. 433 0. 372 Pr 0. 024 0. 018 0. 018 0. 031 0. 035 Nd 0. 056 0. 047 0. 050 0. 097 0. 122 Sm 0. 003 0. 011 0. 015 Gd 0. 007 Ba 0. 032 0. 073 0. 077 0. 106 0. 286 Th 0. 004 Bsite total 3.000** 3.000 3. 000 3. 000 3. 000 C 5. 021

Sample 607/277 -wet chemical analysis; other samples -electron microprobe analyses. sd -standard deviation. *-including MgO 0.02 ,K 2O0.02, MnO 0.07, FeO0 .42, SiO 2 0.20, F0.04 and H 2O0.85, all wt. %. **-including Mn0.006, Fe0.037 and Si0.021. b.d.-below detection limits.Mg, Mn, Fe, Yand Fare below detection limits in the microprobe analyses.CO 2 in microprobe analyses calculated by stoichiometry.n.d.–not determined.

exception(sample 633B/ 79.5)has 6 .65wt . % differencein morphology suggests they may BaO.Thereis no zoning in Khibina burbankite haveformed by differe ntprocess es.Large crystalsand the compositions are also uniform euhedralprismatic crystals could have crystal- withineach rock sample . lizedat an early stage of carbonatite formation, Thereare two morphological types of burban- andsometimes large burbankite crystals are kite,large prismatic crystals and small drop-like observednear the contact of veins that are inclusionswithin calcite crystals and along their characterizedby a crustificationtexture (vein- boundaries(Fig .3 a,Table3) .Althoughtheir filling).Thedrop-like burbankite inclusions in compositionsare th esame(Table 4 ),the calciteprobably did not form by exsolution of

233 A. N. ZAITSEV ETAL.

FIG. 3. Backscattered electron images (BEI) of (a) large crystals and drop-like inclusions of burbankite (white) in calcite (black); (b) a contact print of a thin section containing a pseudomorph of synchysite-(Ce), strontianite and baryte after burbankite,. The width of the burbankite pseudomorph is 9 mm. C II-1 calcite carbonatite, sample 603/ 26.5; (c) zoned altered burbankite (grey and dark-grey) with ancylite-(Ce) veins (white), C II-1 calcite carbonatite, sample 633B/79.5 (d) relics of burbankite (dark grey) in strontianite (grey) and synchysite-(Ce) (white).

234 REE-SR-BA MINERALS burbankitefrom calcite rich in Na,Sr and REE as TABLE 5.Chemicalcomposition of carbocernaite at mightbe thought at first from Fig .3 a, and as Khibina proposedfor a similaroccurrence by Knudsen (1991),because the burbanki tecrystals are Rock C II-1 associatedwith euhedral zoned apatites .They Sample 603/165 603/287 aremore likely to be the result of ‘cotectic’ mean (12) sd mean (10) sd crystallizationof burbankite and calcite after the precipitationof the apatite . Na2O 4. 98 0. 18 4. 33 0. 42 Carbocernaitehas been found in many Khibina CaO 11. 94 0. 42 13.60 0. 33 carbonatitesamples (Table 3) .Itwas described SrO 22. 33 0. 76 20.20 0. 27 originallyas a primarymineral crystallized at a BaO 0. 37 0. 13 0. 56 0. 07 latestage of carbonatite formation at Vuorijarvi, La2O3 9. 27 0. 61 10.53 0. 33 KolaPeninsula (Bulakh et al., 1961).Zdorik Ce2O3 13. 19 0. 51 14.19 0. 30 (1966)and Kapustin (1980) found that carbocer- Pr2O3 0. 97 0. 09 0. 94 0. 08 Nd O 2. 34 0. 25 2. 56 0. 19 naitein carbonat itesfrom the Ozernyi and 2 3 Sm2O3 0. 14 0. 05 0. 32 0. 04 Vuoriyarvimassifsocc ursas a secondary F 0. 10 0. 10 0. 14 0. 03 mineralafter burbanki te.Themost unusual CO2 32. 79 33.79 occurrenceof carbocernaite is the exsolution O=F2 0. 04 0. 06 lamellaeand cotectic textures for carbocernaite Total 98. 36 101.10 andcalciteinSarnu-Dandalic arbonatite 2 describedby Wall et al. (1993).Carbocernaiteis Calculated to 2(CO 3) groups alsoreported from carbonatite in the Si Pan Na 0. 431 0. 364 Range,Vietnam (Bulakh and Izokh, 1966) . Ca 0. 571 0. 632 Carbocernaite,like burbankite, is a double Asite total 1.003 0. 996 carbonatewith a generalformula AB(CO3)2 with Sr 0. 578 0. 508 Naand Ca in the A-siteand Sr, REE and Ba in the La 0. 153 0. 168 B-site.Thereare few studies of the chemical Ce 0. 216 0. 225 compositionof carbocernaite.Beforethe detailed Pr 0. 016 0. 015 investigationof Wall et al. (1993)only a fewwet Nd 0. 037 0. 040 Sm 0. 002 0. 005 chemicalanalyses were published (Bulakh et al., Ba 0. 007 0. 010 1961;Bulakh and Izokh, 1966; Zdorik, 1966; Bsite total 1.008 0. 971 Kapustin,1980) .Althoughavailable data for F 0. 014 0. 019 carbocernaiteshow so mevaria tionin th e contentof major elements, there is less variation thanin burbankite .TheNa Ovaluesrange from Mg, Mn, Fe, Gd, Y,Thand Uare below detection limits 2 CO calculated by stoichiometry 2.43to6 .12wt. %,theBaO from0 .95to5 .96,the 2 SrO from5 .58to 23 .98,the CaO from15 .93to 19.27and the SREE2O3 from17 .06to 26 .31,all wt. %.Ingeneral the compositional variations in additionalanion group (F,OH) 2 inthe mineral burbankiteand carbocernaite are similar, but formula.Ourdata show that the F contentof carbocernaitecontains less Na 2O (commonly Khibinacarbocernaite is nearthe electron micro- about 4 5 wt. %)comparedwith burbankite probedetection limit of about 0 .1wt. % and IR (commonlyabout 10 12 wt. %).Thisdifference investigationsshow an absenceof any absorption - insodium content makes it possible to identify bandrelated to OH group or H2O.Itis possible carbocernaiteand burbankite on the basis of thatthe mineral described from the Sturgeon electronmicroprobe analyses . Narrowsis a differentmineral species .Thelack Selectedaverage compositions of carbocernaite ofNa in Sturgeon Narrows carbocernaite also fromKhibina are given in Table 5 .Thesedata supportsour conclusion . showthat ca rbocernaitefrom th eKhibina Inthe Khibina carbonatite samples burbankite carbonatitesis a lowBa variet y.Khibina andcarbocernaite do not occur together so it has carbocernaite,like burbankite, is not zoned . notbeen possible to establish their relative ages . Harris(1972) reported high F (3.86wt . %) in However,both burbankite and carbocernai te- carbocernaitefrom Sturgeon Narrows, Canada, containingcarbonatites are cut by later C II-2 andproposed that F togetherwith OH couldbe andC II-3carbonatites .

235 A. N.ZAITSEV ETAL.

Alterationof burbankiteand c arbocernaite 0. 148 0.488F performula unit .Since REE and Sr arepresent in equalabundances it is suggested Burbankitein carbonatites is commonly replaced that F- substitutesfor OH -.Thus,the mineral from byancylite-(Ce),strontianite and baryte (Somina, theKhibina carbonatites can be classified as F- 1975;Kapustin 1980) and rarely by ancylite-(Ce), bearingancylite-(Ce) .Fluorinewas also detected calkinsite,lanthanite and baryte (Pecora and Kerr, intwo ancylite-(Ce) samples from Qaqarssuk 1953).Multi-stagealteration of burbankite from carbonatitesat 0 .37and 0 .58wt . % respectively theOzernyi carbonatites has been documented by (Knudsen,1991) . Zdorik(1966) where carbocernaite, strontianite, bastna¨site-(Ce),calcite, baryte, allanite -(Ce), Ca-REEfluocar bonates monazite-(Ce)and epidote have been identified asalteration products of burbankite . Synchysite-(Ce)is common at Khibina,bastna ¨site- Inthe Khibina carbonatites, burbankite and (Ce)and parisite-(Ce) are also found but are rare carbocernaiteare commonly replaced by various (Table 3). Thetextures vary, as described in Table combinationsof ancylite-(Ce),strontianite, synch- 3,and include syntaxial intergrowths (Fig .4 a). ysite-(Ce),baryte; less commonly by cordylite- Ca-REE fluocarbonatesare present in numerous (Ce)and rarely by harmotome and edingtonite carbonatites,e .g.MountainPass (Olsen et al., (Table3) .Evenwhen burbankite is completely 1954),Gatineau(Hogarth et al. , 1985), replaced,evidence of itsexistence is preserved in Kizilc¸ao¨ren(Hatzl, 1992), Tundulu (Ngwenya, theform of hexagonal prismatic pseudomorphs 1994)and are the most well-studied of the (Fig. 3b)andislands of relict burbankite (Fig .3 c carbonatite REE-minerals(e .g.Kapustin,1980; and d).Pseudomorphsof a similarform have been Hogarth et al., 1985;Andersen, 1986; Wall and mentionedfrom some other rare earth -rich Mariano,1996) .Selectedaverage microprobe carbonatites,e.g .GemPark,W iguHill, analysesof Khibina synchysite-(Ce) made on Kangankunde(Wall and Mariano, 1996) but in mineralsfrom different mineral assemblages are thesecases there is no evidence of the precursor presentedin Table 7 .Synchysite-(Ce)is char- mineral.Thepresence of primary and replaced acterizedby having little substitution of other burbankiteat Khibina is good evidence that the elementsfor Ca and REE.Primarysynchysite- pseudomorphsreported from these other carbo- (Ce)fromsyntaxial intergrow ths,secondary natitesmay well have originally been burbankite . synchysite-(Ce)from the alteration products of burbankite,carbocernaite and syntaxial inter- growthsof synchysite-(Ce) with parisite-(Ce) all Ancylite havesimilar chemical compositions .Sr,Ba and Th Ancylite-(Ce)is a hydrouscarbonate containing aretypical minor constituents in allthe synchysite- REE andSr asmajor cations .Onthe basis of a (Ce)and Fe ispresentin the red variety associated structuralstudy of material from the Mont Saint- withmanganoan ankerite or ferroan kutnohorite . Hilairemassif, its formula has been proposed as Parisite-(Ce)and bastna ¨site-(Ce)(Table 8) are REEx(Sr,Ca)2 x(CO3)2(OH)x (2 x)H2O with a neartheir theoretical compositions with only 2+ cation-anionsubstituti onof Sr + H2O > minoramounts of Sr andBa substituting for Ca REE3+ + OH (Dal Negro et al. , 1975). andTh substituting for REE. Althoughancylite-(Ce) is a relativelycommon Syntaxialintergrowths of Ca- REE fluocarbo- mineralin carbonatites there are only a few natesare considered to be evidence for their analysesavailable (Kukharenko et al. , 1965; primaryorigin, the intergrowth being related to Kapustin,1980; Knudsen, 1991), and this is the changesin the chemical composition of the host firstdetail edinvest igationofits chemic al fluid (Ni et al, 1993). composition.Selectedaverage chemical compositionsare given in Table 6 .Thecomposition of Ba-REEfluocar bonates ancylite-(Ce)from Khibina is relatively uniform withCa, Ba and Th present only as traces .The Ba-REE fluocarbonatesare extremely rare in atomicproportion of Sr and REE intheformula is carbonatites.Huanghoite-(Ce)isth eonly near1:1 with a smallexcess of REE.Animportant memberof the group previously described, from findingis thepresence of fluorinein ancylite-(Ce). anunnamed Siberian carbonatite (Kapustin, 1973) TheKhibina ancylite-(Ce) contains between 0 .75 andfrom Qaqarssuk carbonat ites(Knudsen, and 2.50 wt. % offluorine corresponding to 1991).Howevercordylite-(Ce), kukharenkoite-

236 REE-SR-BA MINERALS

TABLE 6.Chemicalcomposition of ancylite-(Ce) at Khibina

Rock C II-1 Sample 633B/79.5 646/001 646/451 mean (8) sd mean (21) sd mean (24) sd

SrO 23.97 1. 25 21. 70 1. 19 20. 65 1. 63 CaO 1. 35 0. 40 2. 09 0. 51 1. 93 0. 59 BaO 0. 59 0. 09 0. 85 0. 24 0. 85 0. 25 FeO 0. 19 0. 35 b. d. 0. 20 0. 30 La2O3 13.08 1. 18 15. 56 0. 83 16. 53 1. 17 Ce2O3 23.40 1. 04 23. 46 1. 09 23. 59 0. 89 Pr2O3 1. 94 0. 11 1. 74 0. 14 1. 69 0. 12 Nd2O3 5. 35 0. 52 4. 42 0. 38 4. 34 0. 33 Sm2O3 0. 29 0. 06 0. 28 0. 05 0. 23 0. 04 Gd2O3 0. 14 0. 13 0. 17 0. 09 b. d. ThO2 0. 53 0. 20 b. d. b. d. F 2. 15 0. 30 1. 83 0. 34 1. 19 0. 17 CO2 23.44 23. 32 23. 07 O=F2 0. 90 0. 77 0. 50 Total 95.51 94. 66 93. 77

2 Calculated to 2(CO 3) groups La 0. 300 0. 357 0. 381 Ce 0. 532 0. 534 0. 539 Pr 0. 044 0. 040 0. 039 Nd 0. 119 0. 098 0. 097 Sm 0. 006 0. 006 0. 005 Gd 0. 003 0. 004 Th 0. 008 Total 1. 012 1. 038 1. 061 Sr 0. 864 0. 783 0. 748 Ca 0. 090 0. 139 0. 129 Ba 0. 014 0. 021 0. 021 Fe 0. 010 0. 010 Total 0. 979 0. 943 0. 909 F 0. 422 0. 360 0. 235

Na, Mg, Mn, Yand Uare below detection limits CO2 calculated by stoichiometry

(Ce)and cebaite-(Ce) have all been identified at cebaite-(Ce)atKhibina is only the second Khibina(Table 3) . documentedoccurrenc e.Thefirst was from Cordylite-(Ce)is known only from Greenland BayanObo (Zhang and Tao, 1986) . (Flink,1901), Mont Saint-Hilaire, Canada (Chen Thereare no data on thechemical composition andChao, 1975) and Bayan Obo, China (Zhang ofcordylite-(Ce) from carbonatites and our report andTao, 1986) .Itsoccurrence at Khibina is the isthe first for this mineral (Table 9) .Thereare firstdocumented occurrence which is certainly threedistinct chemical compositions of cordylite- fromcarbonatites .Kukharenkoite-(Ce)is a new (Ce)from Khibina .Cordylite-(Ce)with low Ca Ba-REE fluocarbonatemineral which has been andSr (Table9) occurs in manganoan siderite- foundin the Khibina carbonatites, and from manganoanankerite-natrolite veins (CZ III-1), Vuoriyavri,Kola Peninsula, Mont Saint-Hilaire whereit forms tabula rcrystalswhich are andthe Saint-Amab lesill, Quebec, Canada associatedwith stront ianiteand sometim es (Zaitsev et al.,1996).Theocc urrenceof kukharenkoite-(Ce).HighCa and Sr cordylite-

237 A. N.ZAITSEV ETAL.

FIG. 4 (a)BEIof syntaxial intergrowths of synchysite-(Ce) (grey), parisite-(Ce) (grey) and bastna¨site-(Ce) (white), C II-2 manganoan ankerite-calcite carbonatite, sample 633A/414.1( b)BEIof large crystals of low Ca and Srcordylite- (Ce) pale grey in centre) associated with laths of high Ca and Srcordylite-(Ce) (dark grey) and kukharenkoite-(Ce) (white), CZIII-1 manganoan siderite-manganoan ankerite natrolite vein, sample 607/75.

(Ce)(Table 9) isobservedin the same samples as Kukharenkoite-(Ce)occurs in Khibina C II-2 mantleson crystals of low Ca and Sr cordylite- andC II-3carbonatites and in carbonate-zeolite (Ce)and as abundant laths in the surrounding veins(Table 3) .Itwas described as anewmineral natroliteand manganoan ankerite (Fig .4 b). It has by Zaitsev et al. (1996).Thecomposition of the alsoformed as a secondarymineral during kukharenkoite-(Ce)(Zaitsev et al., 1996),deter- carbocernaitealterat ion.Cordylite-(Ce)with moderateCa and Sr (Table9) occursin ferroan rhodochrosite-manganoanankerite carbonatites (CII-3)and is associated with strontianite . Theatomic proportions of Na-Ca and REE-Sr pairsshow a negativecorrelation with a slope near 1anda plotof Na+ REE vs.Ca+Sr (Fig.5) showsa trendin compositionfrom Sr-Ca-poor to Sr-Ca-richcordylite -(Ce).Theslope of this correlationsuggests a 1:1exchange of Na and REE forCa and Sr witha substitutionscheme of Na+ + REE3+ Ca2+ + Sr2+.Onthe basis of these observationsa generalformula for cordylite-(Ce) canbe expressedas (Na,Ca)Ba( REE,Sr)2(CO3)4F. OurX-ray and IR dataare identical for each compositionalvariety and also identical to those of ‘baiyuneboite-(Ce) ’ (Fuand Su, 1988), which isnow recogni zedto be cordylit e-(Ce)(J . FIG.5.Atomic proportions of Na+ REE vs. Ca+Sr for Zemann,personal communication, 1996) . cordylite-(Ce) .

238 REE-SR-BA MINERALS

TABLE 7.Chemicalcomposition of synchysite-(Ce) at Khibina

Rock C II-2 C II-3 C II-1 C II-1 C II-1 Sample633A/ 414.1 604/413 633/485. 5 603/26.5 603/165 syntaxialintergrowths secondaryafter burbankite secondaryafter carbocernaite mean(8) sd mean (6) sd mean(9) sd mean (15) sd mean (4) sd

CaO 17.47 0.38 16.89 0.62 16.18 0.70 16.08 0.88 17.23 0.33 FeO b.d. 0. 35 0. 49 b. d. b. d. b.d. SrO 0.24 0.12 0.43 0.18 0.87 0.66 0.59 0.28 0.56 0.21 BaO 0.09 0.05 0.15 0.04 0.12 0.07 0.06 0.05 0.11 0.06 La2O3 16.54 0.42 13.06 0.58 17.98 0.87 20.34 0.86 13.63 0.73 Ce2O3 26.19 0.85 27.21 0.79 25.91 0.65 25.77 0.50 25.26 0.85 Pr2O3 2.15 0.12 2.53 0.07 1.94 0.11 1.78 0.08 2.58 0.10 Nd2O3 6.14 0.44 7.90 0.22 5.54 0.27 4.53 0.41 9.69 0.86 Sm2O3 0.38 0.06 0.62 0.10 0.38 0.04 0.31 0.07 0.68 0.38 Y2O3 b.d. b. d. b. d. b. d. 0.11 0.09 ThO2 b.d. 0. 38 0. 21 0.15 0.09 b.d. 0.17 0.14 F 5.49 0.18 5.69 0.21 5.83 0.23 5.61 0.23 5.78 0.11 CO2 28. 12 27. 81 27.18 27. 59 28. 11 O=F2 2.31 2. 40 2. 46 2. 36 2.43 Total 100.49 100. 62 99.61 100. 30 101. 46

2 Calculated to 2(CO 3) groups Ca 0.975 0. 953 0. 934 0. 915 0.962 Sr 0.007 0. 013 0. 027 0. 018 0.017 Ba 0.002 0. 003 0. 002 0. 001 0.002 Fe 0. 015 Total 0.984 0. 985 0. 964 0. 934 0.981 La 0.318 0. 254 0. 357 0. 398 0.262 Ce 0.499 0. 524 0. 511 0. 501 0.481 Pr 0.041 0. 049 0. 038 0. 034 0.049 Nd 0.114 0. 149 0. 107 0. 086 0.180 Sm 0.007 0. 011 0. 007 0. 006 0.012 Y 0.003 Th 0. 005 0. 002 0.002 Total 0.979 0. 991 1. 022 1. 025 0.990 F 0.904 0. 948 0. 994 0. 943 0.953

Na, Mg, Mn and Uare below detection limits CO2 calculated by stoichiometry

minedfrom electron microprobe analysis is BaO probeanalyses (Table 10) .Although,analysis 48.93,SrO 0.42,MnO 0 .26,Na 2O 0. 08, CaO totalsare less then 100 %,calculatedatomic ratios 0. 05, La2O3 6. 16, Ce2O3 15. 12, Pr2O3 1.49, for Ba, REE andF arenear 3:2:2 and closely Nd2O3 4. 08, ThO2 0.10and F 3.20,wt . %. The correspondtoanidealformulaof atomicratios of Ba, REE andF arenear 2:1:1, Ba3REE2(CO3)5F2.Cebaite-(Ce)contains minor 2 requiring3 (CO 3) groupsper formula unit SrO (1.01 2.61 wt. %), CaO (0.33 1.18 wt.%) (calculatedCO 2 21. 73 wt. %)andthe ideal and ThO2 (0.49 1.26 wt.%),in addition rela- formulaforkukharenkoite-(Ce)is tivelyhigh MnO (up to 0.83wt . %)andFeO (upto Ba2REE(CO3)3F. 0. 61 wt. %)wereobserved in some analyses .All Thechemical composition of cebaite-(Ce)from cebaite-(Ce)crystals are unzoned .SeeTable 3 for Khibinawas determined by 18 electron micro- mineralogicaldetails .

239 A. N.ZAITSEV ETAL.

TABLE 8.Chemicalcomposition of parisite-(Ce) and bastna ¨site-(Ce)at Khibina

Rock C II-2 C II-3 C II-2 Sample 633A/414.1 604/413 633A/414. 1 Mineral parisite-(Ce) bastna¨site-(Ce) mean (2) mean (5) sd mean (6) sd

CaO 9. 72 9. 29 1. 03 0.84 0. 29 SrO 0. 56 0. 79 0. 18 0.85 0. 34 BaO 0. 07 0. 30 0. 29 0.08 0. 05 FeO 0. 05 0. 38 0. 28 La2O3 19.63 15. 96 0. 72 26. 35 0. 99 Ce2O3 31.72 32. 28 0. 45 37. 41 0. 54 Pr2O3 2. 30 2. 87 0. 14 2.50 0. 13 Nd2O3 6. 83 8. 74 0. 22 6.60 0. 48 Sm2O3 0. 45 0. 60 0. 02 0.36 0. 07 Y2O3 0. 10 0. 22 0. 12 b.d. ThO2 b. d. 0. 24 0. 10 b.d. F 7. 02 6. 79 0. 17 8.11 0. 22 CO2 24.33 24. 54 20. 67 O=F2 2. 95 2. 86 3.42 Total 99.82 100. 13 100. 35

2 2 Calculated to 3(CO 3) groups Calculated to 1(CO 3) group Ca 0. 941 0. 892 0.033 Sr 0. 029 0. 041 0.018 Ba 0. 002 0. 011 0.001 Fe 0. 004 0. 029 Total 0. 976 0. 972 La 0. 654 0. 527 0.357 Ce 1. 048 1. 057 0.503 Pr 0. 076 0. 094 0.033 Nd 0. 220 0. 280 0.087 Sm 0. 014 0. 018 0.005 Y 0. 005 0. 010 Th 0. 005 Total 2. 017 1. 992 1.037 F 2. 004 1. 923 0.942

Na, Mg, Mn and Uare below detection limits CO2 calculated by stoichiometry

Y-richcarbonates mcke lveyite-(Y),ewalditeand threeelectron microprobe analyses of mckelveyite- donnayite-(Y) (Y)from Vuoriyarvi carbonatites, one from the Sallanlatvicarbonat iteand two analyses of Adetaileddescription of these minerals from ewalditefrom Vuoriyarvi (Voloshin et al., 1990, Khibina,Vuoriyarvi and Sallanlatvi, is given by 1992).However,even these limited data show Voloshin et al. (1990,1992) .Thiswas the first compositionalvariation and three groups have timethat they had been documented in carbona- beenidentified: Na-free mckelveyite-(Y), Y-free tites.Mckelveyite-(Y)is the best-studied of the LREE-enrichedmckelveyite and Y-free ewaldite . groupat Khibina (Table 3) . Fiveseparate crystals of mckelveyite-(Y)were Chemicalcompositions of mckelveyite-(Y) and analysedfrom Khibina (Table 11) and are ewalditefrom Kola carbonatites are represented by uniformin chemical composition .Theformula

240 REE-SR-BA MINERALS

TABLE 9.Chemicalcomposition of cordylite-(Ce) at Khibina

Rock CZ III-1 C II-3 CZ III-1 CZ III-1 C II-1 Sample 607/75 603/264.6 603/251.5 607/75 603/165.0 Varietylow Ca and Sr moderateCa and Sr highCa and Sr mean(15) sd mean (17) sd mean (15) sd mean (10) sd mean (17) sd

Na2O 4.12 0.12 3.66 0.24 3.67 0.12 2.60 0.15 2.56 0. 16 CaO 0.73 0.18 1.54 0.31 1.50 0.08 3.82 0.18 4.10 0. 26 SrO 0.58 0.23 2.48 0.57 2.09 0.31 6.03 0.43 5.90 0. 50 BaO 22.28 0.33 22.29 0.51 22.32 0.32 23.02 0.25 23.11 0.36 La2O3 9.94 0.36 10.46 0.38 11.82 0.53 7.58 0.30 11.49 0.51 Ce2O3 24.46 0.43 23.82 0.68 22.18 0.28 20.26 0.38 17.90 0.67 Pr2O3 2.41 0.18 1.85 0.24 1.69 0.25 2.19 0.27 1.45 0. 30 Nd2O3 7.47 0.49 5.88 0.31 5.70 0.41 6.97 0.49 5.36 0. 54 ThO2 0.11 0.17 0.13 0.14 0.12 0.16 0.13 0.12 0.13 0. 16 F 2.62 0.10 2.97 0.28 2.95 0.33 2.60 0.08 2.85 0. 31 CO2 24. 92 25. 16 24. 78 25. 77 25. 75 O=F2 1.10 1. 25 1. 24 1. 10 1.20 Total 98. 55 98. 98 97. 57 99. 88 99. 40 2 Calculated for 4(CO 3) groups Na 0.945 0. 821 0. 837 0. 579 0.567 Ca 0.093 0. 191 0. 189 0. 470 0.501 Total 1.038 1. 012 1. 026 1. 049 1.068 Ba 1.032 1. 011 1. 028 1. 036 1.033 La 0.434 0. 446 0. 513 0. 321 0.483 Ce 1.058 1. 008 0. 954 0. 851 0.747 Pr 0.104 0. 078 0. 072 0. 092 0.060 Nd 0.315 0. 243 0. 239 0. 286 0.218 Sr 0.040 0. 167 0. 142 0. 402 0.390 Th 0.003 0. 003 0. 003 0. 003 0.003 Total 1.954 1. 945 1. 923 1. 955 1.901 F 0.981 1. 088 1. 096 0. 946 1.029

Fe, Mnand Smare below detection limits CO2 calculated by stoichiometry

ofmckelveyite-(Y)is still the subject of debate.In 11).Ourdata and those of Voloshin et al. (1990) theoriginal description Milton et al. (1965) gave showsignificant substitutions, the main one being 2+ 2+ theformula as Na 1. 9Ba4.0Ca1. 1Sr0. 2REE1.5U0. 3 Ba Sr whichis relatedto themckelveyite-(Y)- (CO3)9 5H2O.Later,Chao et al. (1978)suggested donnayite-(Y)pair where these minerals are Ba anisomorphous relationsh ipbetween mckel- andSr end-membersrespectively .Theassignation veyite-(Y)anddonnayi te-(Y)and gave the of REE totwo different sites in the mckelveyite- formulaof NaCaBa 3Y(CO3)6 3H2O.Ina recent (Y)formulais problematic .Itis based on formula studyof mckelveyite-(Y) and ewaldite Voloshin balanceandthe REE chondrite-normalized et al. (1990,1992) showed a similaritybetween distributionwhich is discussed below in the thesetwo minerals and suggested that they are section on ‘Rareearth patterns ’. probablypolymorphs .Theformula of ewaldite wasdeterminedas(Ca,Na, REE )(Ba,Sr ) Strontianite,baryte,barytocalcite,edingtonite and (CO ) nH Owherepart of the H Oiszeolitic . 3 2 2 2 harmotome Chemicaldata from the Khibina mckelveyite- (Y)werecalculated on the basis of the IMA Mineralsrich in Ba and Sr butwith no REE are acceptedformula NaCaBa 3Y(CO3)6 3H2O (Table representedin the Khibina carbona titesby

241 A. N.ZAITSEV ETAL.

TABLE 10.Chemicalcomposition of cebaite-(Ce) at Khibina

Rock CZ III-1 Sample 603/143.5 Analysis 14 24 25 29 30 33Mean (18) Sd

Na2O 0. 09 0. 10 0. 08 0. 11 0. 13 0. 10 0. 10 0. 03 CaO 0. 40 1. 18 0. 47 0. 61 0. 52 0. 70 0. 61 0. 21 MnO 0. 07 0. 47 0. 12 0. 73 0. 83 0. 13 0. 16 0. 24 FeO 0. 45 0. 13 b. d. 0. 14 0. 61 b. d. 0. 16 0. 19 SrO 1. 40 1. 27 1. 45 1. 25 1. 28 1. 31 1. 43 0. 36 BaO 43.93 40.51 42.19 42. 09 42. 59 42. 93 42. 77 1. 84 La2O3 5. 30 7. 28 6. 71 5. 58 5. 48 5. 72 5. 67 0. 52 Ce2O3 13.59 14.33 14.52 14. 66 13. 66 14. 91 14. 45 1. 16 Pr2O3 1. 54 1. 69 1. 83 1. 78 1. 51 1. 81 1. 63 0. 19 Nd2O3 6. 15 5. 69 5. 99 6. 32 5. 70 5. 34 5. 54 0. 48 Sm2O3 0. 60 0. 61 0. 50 0. 38 0. 42 0. 34 0. 48 0. 11 Eu2O3 0. 17 0. 18 b. d. 0. 24 b. d. b. d. 0. 07 0. 11 Gd2O3 0. 59 0. 66 0. 53 0. 49 0. 40 0. 37 0. 50 0. 13 ThO2 0. 99 0. 51 0. 49 0. 92 1. 07 0. 99 0. 92 0. 22 F 4. 24 4. 10 4. 15 3. 78 3. 99 3. 61 3. 76 0. 21 CO2 21.57 21.79 21.41 21. 79 21. 65 21. 41 21. 42 O=F2 1. 78 1. 73 1. 75 1. 59 1. 68 1. 52 1. 58 Total 99.31 98.77 98.78 99. 29 98. 15 98. 15 98. 10

2 Calculated for 5(CO 3) groups Na 0.031 0.032 0.025 0.038 0.042 0.034 0.032 Ca 0.073 0.212 0.085 0.111 0.095 0.130 0.114 Mn 0.010 0.066 0.018 0.105 0.119 0.018 0.023 Fe 0.064 0.018 0.020 0.087 0. 023 Sr 0.137 0.124 0.143 0.123 0.127 0.132 0.144 Ba 2.915 2.659 2.802 2.805 2.855 2.926 2.900 Total 3.230 3.111 3.072 3.201 3.325 3.240 3.236 La 0.331 0.450 0.419 0.350 0.346 0.367 0.362 Ce 0.841 0.878 0.900 0.911 0.854 0.948 0.914 Pr 0.095 0.103 0.113 0.110 0.094 0.115 0.102 Nd 0.372 0.340 0.362 0.384 0.348 0.332 0.342 Sm 0.035 0.035 0.029 0.022 0.024 0.021 0.029 Eu 0.010 0.011 0.014 0. 004 Gd 0.033 0.036 0.030 0.028 0.023 0.021 0.029 Th 0.038 0.019 0.019 0.036 0.042 0.039 0.036 Total 1.755 1.872 1.873 1.855 1.730 1.843 1.819 F 2.268 2.174 2.221 2.033 2.159 1.986 2.057

Y,Dy, Er, Yb and Luare below detection limits CO2 calculated by stoichiometry

strontianite,baryte, barytocalcite, edingtonite and Barytocalciteis extremely rare in carbonatites harmotome(Table 3) . Thefirst two minerals are andhas been described only from Vuoriyarvi and commonin late-stagecarbonatites, e .g.Mountain anunnamed Siberian carbonatite (Kapustin, 1980) Pass (Olsen et al. , 1954),Vuoriyarvi, Seblyavr, andpossibly Chipman Lake (Platt and Woolley, Sallanlatvi(Kapustin, 1980), Sarnu-Dandali (Wall 1990). et al.,1993)andKangank unde(Wall and Edingtoniteandharmotomea reb arium Mariano,1996) . zeolites.Theiroccurrence at Khibina is the first

242 REE-SR-BA MINERALS

TABLE 11.Chemicalposition of mckelveyite-(Y) at Khibina

Rock CZ III Sample 603/143.5 Point 1 2 4 5 9 10Mean (12) sd

Na2O 3. 12 3. 05 3. 21 3. 10 3. 33 3. 14 3. 19 0. 10 CaO 4. 56 4. 34 4. 32 4. 34 4. 20 4. 72 4. 43 0. 38 MnO 0. 06 b. d. b. d. b. d. b. d. 0. 06 FeO b. d. b. d. 0. 64 b. d. 0. 07 0. 11 0. 18 0. 26 BaO 29.43 29.89 28.47 28. 73 29. 69 27. 13 28. 97 0. 98 SrO 9. 16 9. 56 9. 29 10. 41 8. 25 12. 42 9. 56 1. 26 Y2O3 6. 39 6. 33 5. 32 7. 02 5. 84 8. 42 6. 44 0. 93 La2O3 1. 22 1. 22 1. 60 0. 85 1. 84 0. 96 1. 34 0. 34 Ce2O3 1. 93 1. 79 2. 43 1. 17 2. 96 1. 77 2. 18 0. 65 Pr2O3 0. 22 0. 22 0. 15 0. 30 0. 24 0. 15 0. 22 0. 06 Nd2O3 0. 69 0. 77 0. 91 1. 11 0. 71 0. 37 0. 84 0. 24 Sm2O3 0. 81 0. 87 0. 81 0. 89 0. 85 0. 20 0. 78 0. 23 Eu2O3 0. 49 0. 64 0. 50 0. 36 0. 60 0. 34 0. 47 0. 10 Gd2O3 2. 15 1. 94 2. 18 2. 05 2. 32 1. 05 2. 02 0. 38 Dy2O3 2. 39 2. 40 2. 97 2. 29 2. 83 2. 00 2. 48 0. 29 Er2O3 1. 03 1. 09 1. 28 0. 87 0. 68 1. 03 0. 94 0. 19 Yb2O3 0. 44 0. 44 0. 56 0. 59 0. 25 0. 61 0. 47 0. 12 ThO2 b. d. 0. 17 b. d. b. d. b. d. b. d. F 0. 18 0. 15 b. d. b. d. 0. 17 0. 16 0. 14 0. 09 CO2 25.71 25.70 25.86 25. 81 25. 71 26. 72 25. 93 H2O 10.52 10.51 10.58 10. 56 10. 52 10. 93 10. 61 O=F2 0. 07 0. 06 0. 07 0. 07 0. 06 Total 100.43 101.01 101.07 100.44 100.98 102.24 101.13 2 Calculated to 6(CO 3) and 3H2O groups Na 1.000 0.984 1.000 1.000 1.000 0.978 1.000 Ca 0.735 0.757 0.561 0.778 0.565 0.785 0.676 Na 0. 009 0.040 0.006 0.075 0. 023 La 0.075 0.075 0.099 0.052 0.113 0.057 0.082 Ce 0.118 0.109 0.148 0.071 0.181 0.104 0.132 Pr 0.013 0.013 0.009 0.018 0.014 0.009 0.013 Nd 0.041 0.046 0.054 0.067 0.042 0.021 0.050 Mn 0. 009 0. 008 0. 000 Fe 0. 089 0.010 0.015 0.025 Total 1.000 1.000 1.000 0.992 1.000 1.000 1.000 Ba 1.923 1.950 1.865 1.884 1.941 1.707 1.880 Sr 0.885 0.922 0.900 1.009 0.798 1.156 0.917 Ca 0.080 0.017 0.212 0.185 0.026 0.110 Total 2.888 2.890 2.977 2.893 2.924 2.889 2.907 Y 0.567 0.561 0.473 0.625 0.518 0.719 0.567 Sm 0.047 0.050 0.047 0.051 0.049 0.011 0.045 Eu 0.028 0.036 0.029 0.021 0.034 0.018 0.026 Gd 0.119 0.107 0.121 0.114 0.128 0.056 0.111 Dy 0.128 0.129 0.160 0.123 0.152 0.104 0.132 Er 0.054 0.057 0.067 0.045 0.036 0.052 0.049 Yb 0.023 0.022 0.028 0.030 0.013 0.030 0.024 Th 0. 007 Total 0.965 0.969 0.925 1.009 0.930 0.990 0.954 F 0. 092 0. 081 0.088 0.082 0.071

Luis below detection limit, CO 2 and H2Ocalculated by stoichiometry

243 TABLE 12. Chemical composition of strontianite at Khibina

Rock C II-2 C II-3 CZ III-1 C II-1 C II-1 C II-1 Sample 633A/414. 1 604/413. 0 603/251.5 646/451.0 603/36.3 646/001 primary strontianite associated with secondary strontianite (after burbankite) associated with synchysite-(Ce), synchysite-(Ce) cordylite-(Ce) ancylite-(Ce) synchysite-(Ce) ancylite-(Ce) and baryte parisite-(Ce) and and parisite-(Ce) and baryte and baryte bastna¨site-(Ce) mean (10) sd mean (6) sd mean (3) mean (25) sd mean (4) sd mean (6) sd mean (4) sd mean (8) sd core mantle rim

Na O b. d. b.d. b. d. 0.14 0. 05 b.d. 0. 21 0.05 0.10 0. 04 b. d. 2 A.

CaO 3. 25 0.56 3.23 0.44 3. 07 3.46 1. 00 3.37 0. 33 1. 58 0.37 3.72 0. 32 5. 97 0. 20 N.

SrO 66.21 0.68 66. 80 0.51 66. 62 63. 57 1. 26 64. 34 0. 51 68.20 0.60 63. 95 1. 00 62. 58 0. 78 ZAITSEV

244 BaO 0. 19 0.17 0.16 0.07 0. 22 1.61 0. 47 1.63 0. 15 0. 72 0.29 0.83 0. 09 2. 00 0. 57 La2O3 b. d. b.d. 0. 16 0.48 0. 20 b.d. 0. 62 0.12 0.33 0. 06 0. 15 0. 04 Ce2O3 0. 18 0.12 0.11 0.11 0. 57 0.61 0. 24 0.19 0. 08 0. 76 0.16 0.42 0. 05 0. 25 0. 05 ETAL. CO2 30.79 30. 99 31. 05 30. 71 30. 51 31.11 30. 69 31. 99 Total 100.63 101.29 101. 69 100.58 100.04 103.20 100. 04 102. 94

2 Calculated to 1 (CO3) group Na 0.006 0. 010 0.005 Ca 0. 083 0.082 0. 077 0.088 0.087 0. 040 0.095 0. 146 Sr 0. 913 0.915 0. 911 0.879 0.895 0. 931 0.885 0. 831 Ba 0. 002 0.001 0. 002 0.015 0.015 0. 007 0.008 0. 018 La 0. 001 0.004 0. 005 0.003 0. 001 Ce 0. 002 0.001 0. 005 0.005 0.002 0. 007 0.004 0. 002 Total 0. 999 1.000 0. 997 0.998 0.999 0. 999 0.999 0. 998

Mg, Mn, Fe, Pr, Nd, Sm, Y, Th and U are below detection limits CO2 calculated by stoichiometry REE-SR-BA MINERALS

documentedoccurrence in carbonatites (Zaitsev et al. , 1992). Thechemical composition of strontianite from carbonatitesis generally close to the end-member, containinga fewpercent of CaO (e.g.Kapustin, 1980;Wall and Mariano, 1996) .Averagemicro- proberesults from Khibina are presented in Table12 .Primarystrontianite is characterized byminor replacement of Sr byCa which is commonfor carbonatitic strontianite but low contentsofotherelementssuchasBa (0. 05 0. 63 wt. % ofBaO), La, Ce and Nd (REE2O3 = 0.15 0.71 wt. %).Comparedwith thisprimary strontianite, secondary strontianite at Khibinacontains more BaO (0.44 3. 34 wt.%) and REE2O3 (0. 35 2. 47 wt.%),somesecondary strontianitealso shows core-mantle-rim zoning (Table 12). Microprobeanalyses of baryte from Khibina arein good agreement with available data for otherlate-stage carbonatites (Kapustin, 1980; Walland Mariano, 1996) and show only a small replacementof Baby Sr (0.09 1.75 wt.% of SrO, Ca (0. 05 0.13 wt.% ofCaO)and Na (0 .08 0.22 wt. % of Na2O). Barytocalcitefrom Khibina (CaO 18 .96,BaO 51.82,SrO 0.28,Na 2O 0.06, CO2 calc. 29.90,total 101. 02, wt.%)hasless SrO thanthat reported previouslyfrom other carbonatites (Kapustin, 1980).

Rareearth pat terns Burbankiteand carboc ernaitefromC II-1 carbonatites,which are early, primary RE-rich minerals,show almost identical REE distribution patternswith La/ Nd cn (cn= chondrite-normalized)ratios between 5 .2and8 .5forburbankite andbetween 7 .4and7 .7forcarbocernaite .An exceptionis Ba-enriched burbankite which has a relativeenrichment in Nd (La/ Nd cn ratio 2.9) (Fig. 6a). FIG.6.Chondrite-normalized plots of ( a)burbankite and REE distributionpatterns in Ca- REE fluocar- carbocernaite from CIcarbonatites; ( b)bastna¨site-(Ce), bonatesfrom syntaxic intergrowths in C II-1 parisite-(Ce) and synchysite-(Ce) from syntaxial inter- carbonatitesare similar to those in burbankite and growths, CII-2 carbonatites; ( c)parisite-(Ce) and carbocernaite(Fig .6 b) with La/Ndcn ratios synchysite-(Ce) from syntaxial intergrowths, CII-3 5.1 6. 0, 5.4 6.3 and 7. 1 7.5forsynchysite- carbonatites; ( d)cordylite-(Ce) and kukharenkoite-(Ce) (Ce),parisite-(Ce) and bastna ¨site-(Ce)respec- from CII-3 carbonatites and CZIII-1 carbonate-zeolite tively.Averagevalues from C II-2carbonatites veins.Chondrite values from Wakita et al. (1971) aremore light- REE-enrichedthan those from the CII-3carbonatites and the minerals from C II-3 typehave relative lylow La/ Nd cn ratios of 3.0 3. 3 and 3. 2 3.8forsynchysite-(Ce) and The Ba-REE fluocarbonates,cordylite-(Ce), parisite-(Ce)respectively (Fig .6 c). kukharenkoite-(Ce)and cebaite-(Ce), from C II-

245 A. N.ZAITSEV ETAL.

3carbonatitesand CZ IIIcarbonate-zeoliteveins structurecorresponded to the Zr positionin werethe final light REE mineralsto crystallize weloganitethen Y wouldhave a co-ordination andare characterized by REE chondrite-normal- numberof 9 (ionsize 10 .75A Ê )andcould be izedplots similar to thosefor synchysite-(Ce) and substitutedby heavy REE suchas Sm-Yb where parisite-(Ce)from syntaxial intergrowths from C ionsizes range from 11 .32A Ê forSm to10 .42A Ê II-3carbonatites (Fig .6 d). The La/Ndcn ratios are forYb; all ion sizes are from Shannon (1976) . 2.5 3. 9, 2.8 3. 5 and 1. 6 2.4forcordylite-(Ce), Calculatedformulae of mckelveyite-(Y)based on kukharenkoite-(Ce)andcebaite-(Ce) respectively . REE intwo different sites (Table 11) produce Thedistribution of REE inprimary carbonates totalsclose to an ideal formula . fromKhibina shows an evolutionary trend from earlycarbonatites (C I)throughlate carbonatites REEdistribut iondur ingalterat ion (CII)tocarbonate-zeolite veins (CZ III).This trendis markedby changesin the La/ Nd cn ratio of Thewidespread alteration of REE minerals at the REE-mineralswhich gradually decreases from Khibinaallows us tomonitor the REE distribution earlyburbankiteandcarbocernaite(La/ duringthe alteration process .Themain primary- Ndcn=5.2 8.6)to later Ca- REE fluocarbonates secondarymineral pairs at Khibinaare following: (La/Ndcn=5. 1 7.5forC II-2carbonatite type and (a)burbankite ? ancylite-(Ce), 3.0 3.8forC II-3carbonatite) and finally to Ba- (b)burbankite ? synchysite-(Ce), REE fluocarbonateswith La/ Nd cn between (c)carbocernaite ? cordylite-(Ce)+synchysite- 1.6 3. 9. (Ce), Theextreme of this trend may be represented (d)cordylite-(Ce) (low Ca-Sr) ? cordylite-(Ce) bythe suite of Y andSm-Er-enriched minerals (highCa-Sr) . (mckelveyite-(Y),donnayite-(Y) and ewaldite) Chondrite-normalizedplots of REE forthese pairs whicharealway slate.Theaverage REE showtwo distinct types of REE pattern.Thefirst chondrite-normalizeddistributio nforKhibina type (Fig. 8a)isrepresented by mineralpairs with mckelveyite-(Y)is shown in Fig .7.Thereis a similarLa/ Nd cn ratiosfor primary-seco ndary bimodaldistribution of REE,probablyrelated to thepresence of more than one site for the REE. Although,the crystal structure of mckelveyite-(Y) hasnot been solved, Chao et al. (1978)provided evidencet hatitissimila rtowel oganite Na2(Sr)3Zr(CO3)6 3H2Owhichhas co-ordination numbersof 6forthe Na site, 9 forthe Zr and10 forthe Sr site.Ifthe Ca in mckelveyite-(Y) occupiesthe equivalent of the 6 co-ordinatedNa site(ion size of 10.0A Ê )itcouldbe substitutedby La(ion size 10 .32A Ê ), Ce (10.1 AÊ ), Pr (9. 9 AÊ ) and Nd (9.83 AÊ ).Ifthe Y inthe mckelveyite-(Y)

FIG.8.Chondrite-normalized plots of primary-secondary mineral pairs for ( a)burbankite–ancylite-(Ce) and ( b) FIG.7.Chondrite-normalized plot of mckelveyite-(Y) carbocernaite–synchysite-(Ce)+high Ca-Sr cordylite- from CZIII-1 carbonate zeolite vein (Ce), CII-1 carbonatites

246 REE-SR-BA MINERALS

mineralspairs .Thistype is the most common and TheLa/ Ndratio in minerals has been shown to includesburbankit e-ancylite-(Ce),burbankite- bea usefulindicator of the paragenetic type of synchysite-(Ce)and low Ca-Sr cordylite-(Ce)- occurrenceand geolog icalenviro nmentby highCa-Sr cordylite-(Ce) .Thesecond type (Fig . Fleischer(196 5,1 978)andFleischera nd 8b),seenonly in an assemblageof carbocernaite, Altschuler(1969) .Theirresults cannot be directly cordylite-(Ce)andsynchysit e-(Ce),shows a appliedto the Khibina data because they used the changein La/ Nd cn ratiofrom primar yto La/Ndratio from the atomic percent of total REE secondaryminerals . normalizedto 100 % butcomparison of the relativechanges in the La/ Ndratio can be useful.Fleischer(1978) calculated La/ Ndratios Discussionandconclusio ns (fromatomic percent of total REE)forbastna ¨site- Thegeological, geochemical and mineralogical (Ce),synchysite -(Ce)and parisite-( Ce)from datapresented in thispaper show that the Khibina variousrocks .Thesedata show a decreasingLa/ carbonatitesare unusual compared with other Ndratio in the sequence from carbonatites to carbonatites.Thisis mainly due to the strong hydrothermalrocks with average La/ Ndratios in differentiationof thecarbonatitic rocks giving the bastna¨site-(Ce)2 .7and1 .8respectivelyand sequencephoscorite, early carbonatite, at least averageLa/ Ndvalues for parisite-(Ce) are 2 .8 threetypes of late carbonatites, and finally three (carbonatites)and 1 .3(hydrothermalrocks) . typesof carbonate-zeolite veins (Table 3) . TheKhibina carbonatites are interpreted as Detailedmineralog icalinvestiga tionshave polygeneticin origin(Zaitsev, 1996) .Phoscorites revealedtwodistin ctty pesof REE-Sr-Ba andearly carbon atites(C I)areprobab ly mineralizationat Khibina: (1) primary minerals magmatic;formation of the late carbonatites (C crystallizeddirectly from a magmaor otherfluid II)islikely to be from volatile -richfluid and(2) minerals produced by secondary metaso- (carbohydrothermal)andcarbonate-zeolite veins maticprocesses (Table 3) .Ageneralsequence for fromhydrothermal fluids .Thedecreasing La/ the REE-Sr-Ba-richmineralization in the late Ndcn ratiosin Khibina carbonatites probably carbonatitesand carbonate-zeolite veins can be reflectincrease of ‘carbohydrothermal’ fraction expressedas follows: incarbonatite-forming system . Sr-REE-Ca-Na-richcarbonat es(burbanki te, Thealteration of burbankite or carbocernaite to carbocernaite) ? Ca-REE fluocarbonates(bast- assemblagesof ancylite-(Ce) + strontianite +- na¨sitegroup) ? Ba-REE fluocarbonates(cordy- baryte,synchysite-(Ce) + strontianite+baryteor lite group) ? Y-richcarbonates (mckelveyite stronianite+ cordylite-(Ce)+ synchysite-(Ce)+ group). baryteis probably an open-system hydrothermal Similarage relationships for the Sr- REE-Ca- process(Wall and Mariano, 1996) .Thisconclu- Na-richcarbonates burbankite and carbocernaite sionis confirmed by reactions calculated for two and the Ca-REE fluocarbonateshavebeen differentpaths of burbankitealteration at Khibina . establishedin carbonatites from other complexes Calculationof the equations was based on the (Zdorik,1966; Somina, 1975; Kapustin, 1980; following:1 .volumesof primary burbankite and Plattand Woolley, 1990) and probably this secondaryancylite-(Ce), synchysite-(Ce), stron- sequenceis universal for late-stage carbonatites . tianiteand baryte are the same (full hexagonal The primary RE mineralsin Khibina carbona- prismaticpseudomorphs are strong evidence for titessuch as burbankite, carbocernaite, cordylite- this);2 .proportionsof the secondary minerals (Ce)and mckelveyite-(Y) contain essential Na werecalculated from the backscattered electron (rangingfrom a minimumof 2 .22wt . % Na2O in imagesas ancylite-(Ce) 30 vol . %,strontianite50 cordylite-(Ce)to12 .12wt . % of Na2O in vol. %,baryte5 vol. %,porous15 vol . % for burbankite)and the whole rock Na 2O content of reaction(1 )andsynchysi te-(Ce)20 vol . %, theCII-1 carbonatites ranges up to 4 .95wt . %. strontianite50 vol . %,baryte10 vol . % and Thesedata show that carbonatite formation in the porous20 vol . % forreaction (2); 3 .actual Khibinamassif was characterized by a high mineralcompositions were used; 4 .coefficients contentof alkaline elements (particularly Na) at inthe reactions are numbers of mineralmoles in a allstages .Thehigh content of alkaline elements ‘single’ volume,which was assumed as 1000 (bothNa and K) duringthe early stages is also volumeunits (cm 3);5 .thenumber of mineral markedby abundant aegirine and biotite in the moleswere calculated by using mineral density phoscorites. andunit cell parameters .Thus,replacement of

247 A. N.ZAITSEV ETAL.

Equation 1 2+ 2+ 5.55(Na2.42 Ca0.50)S2.92(Sr1.50 Ca0.86REE0.55 Ba0.09)S3.00(CO3)5 + 6.00Sr + 0.52Ba + 3+ 2 0. 25REE + 5.20H2O + 1.14F + 0. 97SO4 =

3.17REE1.04(Sr0.78Ca0.14Ba0.02)S0.94(CO3)2(OH0.64F0.36) H2O + 12.86(Sr0.92Ca0.08)S1.00CO3 + + 2+ 2 + 0.97(Ba0.99Sr0.01)S1.00SO4 + 13.42Na + 6.07Ca + 8. 52CO3 + 2.03H (1)

Equation 2 2+ 2+ 2 5.48(Na2.64Ca0.30)S2.94(Sr1.22Ca0.90REE0.79Ba0.09)S3.00(CO3)5 + 3.87Sr + 1. 43Ba + 3. 00F + 1. 94SO4 =

3.03(Ca0.93Sr0.03)S0.96REE1.02(CO3)2F0.99 + 11.57(Sr0.90Ca0.09Ba0.01)S1.00CO3 + + 2+ 3+ 2 1.94(Ba0.99Sr0.01)S1.00SO4 + 14. 46Na + 2.71Ca + 1.24REE + 9. 76CO3 (2)

burbankiteby an assemblage of ancylite-(Ce) + theevolution (Zaitsev and Bell, in preparation) strontianite+ barytemay be represented by andall appear to be directly related to the equation(1) above . carbonatitecomplex .Theratio of La/ Nd cn in Replacementof burbankite by the assemblage primary-secondarymineral pairs can also be used ofsynchysite-(Ce)+ strontianite+ barytecould be togive some information about the fluids .Similar describedby equation (2) above . La/Ndcn ratiosfor the pairs burbankite-ancylit e- Bothreactions show that H 2O(equation1), F, S (Ce)and burbankite-synchys ite-(Ce)indicate that andSr withtraces of Baand REE (inequation 1) alterationtook place soon after the initial mustbe introd ucedto form anc ylite-(Ce), formationof burbankite, before the evolution of synchysite-(Ce),strontianite, and baryte .These carbonatiticfluids .DifferentLa/ Nd cn values for secondaryminerals do not contain Na and this mineralsin the system carbocernaite-sync hysite- elementtogether with Ca, REE (inequation 2) (Ce)+cordylite-(Ce)and particularly low La/ Nd cn and CO2(aq)are removed from the carbonatite . ratiosfor synchysite -(Ce)and cordylite -(Ce) Calculationof similarequations for the alteration probablyindicate involvement not only of fluids ofcarbocer naiteproduces similar results to relatedto carbonatites,but also fluids responsible equation(2) . forthe formation of the carbonate-zeolite veins . Residualsolutions enriched in Na, Ca and CO 2(aq) Finally,low, but similar La/ Nd cn ratiosfor the maybe described as alkaline carbohydrothermal pairlow-Ca-Sr cordylite-(Ce)-high -Ca-Srcordy- fluids (‘hot brines’)andmay be an additional cause lite-(Ce)indicate a fluidsource related only to the ofwall rock fenitization or may be involved in the formationof carbonate-zeoliteveins . formaionof the carbonate-zeolite veins . Thetwo differ entgeoche micalpaths of Acknowledgements burbankiteand carbocernaite alteration (ancylite- (Ce) versus synchysite-(Ce)and cordylite-(Ce)) A.Zaitsevreceived a RoyalSociety grant for two seemsto implyaction on these minerals by fluids visitsto the UK .TerryWilliams and John Spratt ofdifferentcomposition .Oneof these fluids was arethanked for assistance and advice with the 2 characterizedby ahighactivity of F and (SO4) electronmicroprobe analyses .Thiswork was and low (OH) resultingin the formation of carriedout as aportionof a comprehensivestudy synchysite-(Ce),cordylite-(Ce) and baryte .In ofthe Kola alkaline massifs carried out at St- contrast,the second type of fluid was character- PetersburgUniversity, University of Leicesterand 2 izedby ahighactivity of (OH) , (SO4) and low TheNatural History Museum .Theauthors thanks F whichresulted in the formation of ancylite- A.G.Bulakhfor discussion on mineralogy of (Ce)and baryte .Although,there are no data on REE-richcarbonatites and A .M.McDonaldfor thetemperature stability fields of ancylite(Ce) or discussionon chemistry of mckelveyite-(Y) .K. synchysite-(Ce),ancylite-(Ce) as a water-bearing Belland an anonymous reviewer made helpful mineralcontaining both (OH) and H2O groups commentson themanuscript .A.N.Zaitsevwould appearsto be stable at lower temperatures than liketo thank all staff of the Department of anhydroussynchysite-(Ce) . Geology,Leicester University, and Department of Thenature of thesefluids is unclear but there is Mineralogy,The Natural History Museum, for nochange in the Sr andNd isotope ratios during hospitality.Specialthanks go toHelen, Olga and

248 REE-SR-BA MINERALS

PolinaZaitseva for their support .Thiswork was rence. Canad.Mineral., 11, 812 18. fundedbytheRoyalSociety(project Hatzl, T.(1992) Die Genese Karbonatite-und 638072.P699)and partly by Russian Foundation Alkalivulkanit-assoziierten Fluorit-Baryt-Bastna ¨sit- forFundamental Sciences (grant 96-05-66151) . Vererzung bei Kizilc¸ao¨ren (Tu¨rkei). Mu¨nchner Geol.Hefte, 8, 271 pp. Hogarth, D.D.,Hartree, R.,Loop, S.and Solberg, T.N. References (1985) Rare-earth element minerals in four carbonatites near Gatineau, Quebec. Amer.Mineral., 70, Andersen, T.(1986) Compositional variation of some 1135 42. rare earth minerals from the Fen complex (Telemark, Kapustin, Yu.L.(1973) First find of huanghoite in the SENorway): implication for the mobility of rare USSR. Dokl.Acad.Sci.USSR., 202, 116 9. earths in acarbonatite system. Mineral.Mag., 50, Kapustin, Yu.L.(1980) Mineralogy of Carbonatites . 503 9. Amerind Publishing, NewDehli, 259 pp. Bulakh, A.G.and Izokh, E.P.(1966) Newdata on Khomyakov, A.P.(1995) Mineralogy of hyperagpaitic carbocernaite . Dokl.Acad.Sci.USSR., 175, 118 20. alkaline rocks .Clarendon Press, Oxford, 220 pp. Bulakh, A.G.,Kondrateva, V.V.and Baranova, E.N. Knudsen, C.(1991) Petrology, geochemistry and (1961) Carbocernaite, anew rare earth carbonate. economic geology of the Qaquarssuk carbonatite Zap.Vses.Mineral.Obshch., 90 (1), 42 9 (in complex.southern West Greenland. Monograph Russian). Series on Mineral Deposits, 29.Gebru¨der Chao, G.Y.,Mainwaring, P.R.and Baker, J.(1978) Borntraeger, Berlin-Stuttgart, 110 pp. Donnayite, NaCaSr 3Y(CO3)6 3H2O,anew mineral Kogarko, L.N.,Kononova, V.A.,Orlova, M.P.and from Mont St-Hilaire, Quebec. Canad.Mineral., 16, Woolley, A.R.(1995 ) AlkalineRocksand 335 40. Carbonatites of the World. Part 2: former USSR. Chen, T.T.and Chao, G.Y.(1975) Cordylite from Mont Chapman and Hall, London, 226 pp. St.Hilaire, Quebec. Canad.Mineral., 13, 93 4. Kramm, U.and Kogarko, L.N.(1994) Nd and Srisotope Clarke, L.B.,Le Bas, M.J.and Spiro, B.(1992) Rare signatures of the Khibina and Lovozero agpaitic earth, trace element and stable isotope fractionation centres, Kola Alkaline Province, Russia. Lithos, 32, of carbonatites at Kruidfontein, Transvaal, S.Africa. 225 42. International Kimberlite Conference, 5Araxa 1991. Kramm, U.,Kogarko, L.N.,Kononova, V.A.and Proceedings. CPRMSpecial publication.CPRM, Vartiainen, H.(1993) The Kola Alkaline Province Brasilia, 236 51. of the CISand Finland: precise Rb-Sr ages define Dal Negro, A.,Rossi, G.and Tazzoli, V.(1975) The 380 360 Ma age range for all magmatism. Lithos, crystal structure of ancylite, (RE) x(Ca,Sr)2 x(CO3)2 30, 33 44. (OH)x (2 x)H2O. Amer.Mineral., 60, 280 4. Kukharenko, A.A.,Orlova, M.P.,Bulakh, A.G., Donnay, G.and Donnay, J.D.H.(1953) The crystal- Bagdasarov, E.A.,Rimskaya-Korsakova, O.M., lography of bastna¨site, parisite, ro¨ntgenite and Nefedov, E.I.,Ilinsky, G.A.,Sergeev, A.S.and synchysite. Amer.Mineral., 38, 932 63. Abakumova, N.B.(1965) The Caledonian complexes Effenberger, H.,Kluger, F.Paulus, H.and Wolfel, E.R. of ultrabasic-alkaline and carbonatite rocks on Kola (1985) Crystal structure refinement of burbankite. peninsula and in Northern Karelia (geology, Neues Jahrb.Mineral.,Mh., 161 70. petrology, mineralogy and geochemistry) . Nedra, Fleischer, M.(1965) Some aspects of the geochemistry Moscow, 772 pp.(in Russian). of yttrium and the lanthanides. Geochim. Milton, C.,Ingram, B.,Clark, J.R.and Dwornik, E.J. Cosmochim.Acta, 29, 755 72. (1965) Mckelveyite, anew hydrous sodium barium Fleischer, M.(1978) Relative proportions of the rare-earth uranium carbonate mineral from Green lanthanides in minerals of the bastnaesite group. River Formation, Wyoming. Amer.Mineral., 50, Canad.Mineral., 16, 361 3. 593 612. Fleischer, M.and Altschuler, Z.S.(1969) The relation- Minakov, F.V.and Dudkin, O.B.(1974) Possible ship of rare-earth composition of minerals to presence of carbonatite in the Khibiny alkalic massif. geological environment. Geochim.Cosmochim. Dokl.Akad.Nauk SSSR (Earth Sci.Sect.), 215, Acta, 33, 725 32. 109 12. Flink, G.(1901) On the minerals from Narsarsuk on the Minakov, F.V.,Dudkin, O.B.and Kamenev, E.A.(1981) Tunugdliarfic in Southern Greenland. Meddel. aÊ m The Khibina carbonatite complex. Dokl.Akad.Nauk Gronland, 24, 42 9. SSSR (Earth Sci.Sect.), 259, 58 60. Fu, P.and Su, X.(1988) Baiyuneboite-(Ce) —anew Nelson, D.R.,Chivas, A.R.,Chappel, B.W.and mineral. Chinese J.Geochem., 7, 348 56. McCulloch, M.T.(1988) Geochemical and isotopic Harris, D.C.(1972) Carbocernaite, aCanadian occur- systematics in carbonatites and implication for the

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