977
The Canadian M ineralo g ist Vol. 34, pp.977-990 (1996)
COMPOSITIONALVARIATION OF LOPARITE FROMTHE LOVOZERO ALKALINE COMPLEX, RUSSIA
ROGERH. MITCIIELL1 Departmentof Geology,Lakehead University, Thunder Bay, Ontario P7B \El
ANTON R. CHAKHMOURADIAN Departmzntof Minzralogy,St, Petersburg State University, St. Petersburg, 199034, Russia
ABSTRACT
Perovskite-groupminerals from tle Lovozero peralkalinecomplex, on the Kola Peninsul4 Russi4 are primarily loparite- rich membersof the perovskite- lueshite- loparite-(Ce)solid-solution series. From early-formingpoikilifls aeplslins sysnils to late eudiallte lujavrite, loparite compositionsevolve by enricbmentin Na" Sr, and Nb, and depletion in Ca Ti and light rare-earthelements. The evolutionarytrend is from calcian niobian loparite-(Ce)in the poikilitic nephelinesyenite and rocks of the differentiated complex through niobian calcian loparite-(Ce)in the differentiatedcomplex and eudialyte lujawite to cerianlueshite in eudialytelujavrite. This trend coincideswith the proposedorder of crystallizationof the major intrusive series of the massif. Intra- and interyrain compositionalvariation and diversepattems of core-to-rim zonation exhibited by loparite grains from the same samFleare characteristicof most paragenesesand may result from a combinationof re-equilibration phenomenaand late-stagemetasomatic processes.
Keyvvords:perovskite, loparite, lueshite,nepheline syenite, Lovozero, Russia.
SoNouarne
Les min6rauxdu groupe de la pdrovskite du complexehyperalcalin de Lovozero, p,6ninsulede Kola en RusSie,sont en g6n6ralproches du p6le loparite dansla solution solide p6rovskite- lueshite - loparite-(Ce).l,a compositionde la loparite 6volue progressivement,de la sydnite n6ph€liniquepoecilitique prdcocejusqu'd la lujavrite d eudialyte tardive, comme en t6moignentun emichissementen Na, Sr et M, et un appauwissementen C4 Ti, et terresrares l6gbres. Ce sch6mad'6volution va de loparite-(Ce)calcique et niobiennedans la sy6niten6ph6linique pr6coce et les rochesdu complexediff6renci6, a loparite- (Ce) niobiennecalcique dans le complexediff6renci6 et la lujawite i eudialyte,jusqu'i lueshite c6rique dans la tujawite b eudialyls. Il coincide avec l'ordre de cristallisation propos6 des membresde la s6rie intrusive principale du massif. l,es variationsen compositionh I'intdrieur des grains et d'un grain i I'autre, ainsi que la diversit6 des types de zonationdu coeur d'un grain vers la bordure de cristaux de toparite provenantd'un mOme€chantillon, sont caract6dstiquesde la plupafi des associations,et r6sulteraienti la fois de r6-6quilibrageau coursdu refroidissementet de mdtasomatosetardive.
(Traduit par la R€daction)
Mots-cl€s:ffrovskite, loparite, lueshite,sy6nite ndph6linique, Lovozero, Russie.
INTRoDUciloN as a single peralkaline complex becauseof their proximity and petrological similarities (Arzamastsev The Lovozero peralkaline complex, located in the 1994). The Lovozero complex is scientifically Kola Peninsulaof Russia,is one of a numberof large important becauseof the unusual composition and intrusionsthat collectively comprisethe Kola-Karelia diverse mineralogy of the rocks present.In addition, Alkaline hovince (Kogarko et aI. 1995). Currenrly, many membersof the complex are in placesenriched the two largest intrusions in the province, Khibina in loparite [(NaREZ')Ti2O6],and theseocclurences are Q3n k#) and Lovozero(650 km2), are considered currently exploited as a soluce of rare-earthelements (REE). The current study was undertaken primarily to establish the trends of compositional evolution of I E-mail address.' [email protected] loparite from the different rock seriesofthe Lovozero 978 THE CANADIAN MINERALOGIST
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6 HNHffiffiBffiNEEN! P E E o =cFa===E=E= .t =t s EgEgEbFEEEFae=EEE.a1*=A € *EgEggEEEF*sF F Ea3Fli';lp E'u*FE (D3F ast# LOPARITE FROM THE LOVOZEROCOMPLEX 979 massif (Fig. 1) and to define the evolutionarytrend for melanocratic nepheline syenite characterizedby a the pluton as a whole. For this pulpose, we selected trachytic texture formed by the flow alignment of loparite samplesfrom well-correlateddrill cores and feldsparprisms. outcrops from the main intrusive series occurring in (3) Eudialyte lujavrite overlies the differentiated the northwestern part of the massif (Mts. Alluaiv series and forms a plate-like body up to 800 m in and Karnasurt), from metasomatic and host rocks thickness(Frg. 1).These rocks differ from thelujawite of the northempart (Mt. Selsurt),and from pegmatites of the differentiated complex in containing euhedral and contactrocks of the differentiatedcomplex at the crystalsrather than anhedralgrains of eudialyte.AIso central and southeasternparts of the massif (Mts, presentin this unit are numerouslenses and irregular Leppkhe-Nel'm,Ninchurt, Punkaruaiv). minor intrusions of murmanite-lovozerite-bearing A secondobjective was to determineif the existing lujavrite porphyry. The body of eudialyte lujavrite is data obtained by older analytical methods obtained typically devoid of layering. It is not considered on bulk samplesof loparite are realistic. For exarnple, to be a late differentiate of the layered complex, and Mitchell (1996) has noted that many of the formed from a distinct batch of magma(Arzamastsev compositionsreported by Vlasov et al. (1966) glve 1994). poor structural formulae as a consequenceof tle (4) A minor suite of dikes representedmainly by inaccurate determination of the amounts of alkali atkali lamprophyres(carnptonite, monchiquite), alkali elements,Ti, Ta, and Nb present. picrites, nephelinitesand phonolites. In additionto the above,Bussen & Sakharov(1972) Gpor.ocrcer-SsrrrNc have describedmetamorphosed nepheline syenite and alkali syenite porphyries, and assumed that they The Lovozero complex (Frg. 1) is topographically representthe earliest intrusive stagesof tle complex. expressedas the dissectedLujavrurt Plateau, which They also subdivided the third series into discrete rises to about 800-900 m above the surrounding eudialytelujawite and murmanitelujavrite complexes. lowlands. It forms a stratified sheet-like intrusion The position of the poikilitic sodalite syenite emplaced in the Archean basement of the central (naujaite)and sodalitefoidolite (tawite) relative to the Kola anticlinorium. Emplacement was tectonically other rock series remains unclear" becauseof their controlled by a deep-seatedfault zone that may by occurence both as enclavesin the lujavrites and as traced from the Kovdor alkaline ultrabasic complex the basalunit of the complex.Some petrologists $oup eastward to the Ivanovka massif (Orlova 1993, them with the other types of poikilitic syenite and Arzamastsev 1994). Contemporaneousextrusive considerthat they representone ofthe earliestintrusive alkaline volcanic rocks and sedimentarylithologies of stages @ussen & Sakharov 1972), whercas others the Lovozero suite are found in the upper parts of the interpretthem as the latest differentiatesor immiscible massif. These.and the occurrenceof similar rocks as fractions of evolving agpaitic lujavritic melts (Vlasov xenoliths in the syenites,indicate that the currently et al. L966, Gerasimovskyet al. 1968, Kogarko & exposedparts of the pluton crystallized at relatively Ryabchikov1969). shallowdepths. Age determinationsof the pluton range from3964l2 + L2Ma (Kononova& Shanin l97I) to DISTRIBUnoN oF LoPARITE 362 + 17 Ma (Kogarko et al. 1983),thus establishing a Middle Paleozoicage. At Lovozero, loparite occurs mostly as inter- oofluorite-type'o Most petrologists@liseev & Fedorov 1953,Vlasov penetration twins of cubic and cubo- et al. 1.966,Gerasimovsky et al. 1968)distinguish four octahedralhabit, ranging in size from a few tenths intrusive rock serieswithin the pluton (Fig. 1). Each of a millimeter, in most of the intrusive series, to correspondsto a separatestage of magmaticactivity. 4-5 mm in pegmatites.The loparite twins are euhedral From the baseof the massifupward, these are: in the rocks of the differentiatedcomplex, albititites, (1) Poikilitic nepheline, nosean and sodalite microclinites and pegmatites. In contrast, loparite syenites.These rocks arecharacterized by the presence crystalsin poikittic syenitesexhibit an irregular habit, of large alkali feldsparoikocrysts, which poikilitically owing to their late crystallizationrelative to the felsic enclose the feldspathoids. Although they occur minerals. primarily in the lower part of the intrusion, they are Loparite is a common accessorymineral in the also found as inclusions in the later members of poikilitic nephelinesyenite, rocks of the differentiated the intrusiveseries (see below). complex and eudialyte lujawite. Exploration drilling (2) A differentiated complex, established by has shown that at a depth of about 1.5 km within driiling tobe 2.5 km in thickness,consisting of macro- the complex, loparite is not common, and the main rhythmically layered alternating urtite - juvite - host minerals of titanium in the nephelinesyenite are lujavrite units. Individual modally-graded units in lorenzenite and ilnenite (Aleksandrov 1973). The the layered complex arc about 15 m in thickness. dyke rocks of the fourth intrusive phase contain Lujavrite is a local name for an agpaitic hypersolvus perovskite only as a rare accessoryphase (Bussen & 980 T}IE CANADIAN MINERALOGIST
Sakharov1972) and"have not beenreported to contain were acquiredfor 300 seconds,those of lueshite for loparite. 100 seconds(live time) with an acceleratingvoltage The highest concentrationsof loparite are found in of 20 kV and beam current of 0.86 nA. X-ray spectra the rocks of the differentiated complex, particularly were collected and processed with the LINK in the northwesternpart of the pluton. In these, the ISIS-SEMQUANT software package. Full ZAF highestcontents of loparite occur in zonesadjacent to correctionswere applied to tfie raw X-ray data. The the boundariesbetween massive and trachytic-textured following well-characterizedstandards were employed rocks.Thus, within one modally gradedunit, the lower for the determinationof loparite compositions:Khibina horizon of urtite andthe upperone of lujavrite havethe loparite (Na, La, Ce, h, Nd, Nb, Ti), MagnetCove maximum contents of loparite fflasov et al. 1966, perovskite(Ca, Fe), syntheticSrTiO3 (Sr), BaSiO3 Veselovskyet al. L990).The loparite contentofurtite (Ba), andmetallic Th andTa. A multi-elementstandard is on the orderof I vol.Vo.Inmelanocratic neoheline for the REE was used, as experiencehas shown that syenites ("malignites"') in the upper parr ;f rhe this gives more accurate data than single-REE differentiated complex, loparite may gain the status standards when using EDS spectrum-stripping of a rock-forming mineral and comprise up to techniques.However, peak profiles used for the I0-l2 vol.Voof the rock. Despitetheir small thickness analyical X-ray lines were obtainedusing single REE (usuallyless than l0 cm), loparite-enrichedlayers in fluoride standards.The accuracyof the method was the differentiatedcomplex are continuousalong strike, cross-checkedby wavelength-dispersionelectron- even though the mode of the host rock may change microprobe analysis of some samples using an significantly, e.9., from urtite to juvite or from automatedCAMECA SX-50 microprobelocated at the melanocraticnepheline syenite to urtite CVeselovsky University of Manitoba, using methodsdescribed by et al. 1.990\. Mitchell & Vladykin (1993). Commonly, albitite, albite aegirinite and micro- clinite veins cutting the loparite-bearingrocks of the differentiatedcomplex also contain loparite. Some of these veins are gradational tlrough albitized rocks, with relict trachytic textures,to unaltereddifferentiated IABLE ,1. REPRESENTATIVECOMPOSTTIONS OF LOPARITEFROM POIKILIIICNEPHELINE SYENM ANDJWITE FROMTHE complex rocks. Loparite crystals in these veins are DIFFERENTIqTEDCOMPLEX LOVOZERO identical in morphology to those occurring in the host lujavrites. These loparite samples may be regarded as either relict phasesthat have persisted Nhou 6.60 5.96 5.9.1 5.94 5.71 6.2. Ta"Oo 0.37 0.40 0.s 0.& 0.80 0.v2 in an unalteredstate during alteration(metasomatism) Tioz 40.97 41.05 41.15 41.33 39.66 41.12 of the host rocks by deuteric alkaline solutions, or a FeO o.il 0.48 0.70 0.57 0.50 0.58 Thor 0.41 0.74 0.4| 0.46 0.U 0.34 new generationof loparite produced by reaction of L&o" 9.95 9.78 1.1.S 11.62 f.n Q.02 the metasomatizingfluids with pre-existing loparite- cqor 19.90 19.73 20.58 19.75 19.50 20.35 P12O3 2.'15 2.8 1.A 1.08 3.79 1.14 bearing rocks. If the latter hypothesisis correct, Ndr03 5.85 6.01 4.@ 4.08 4.Zt 4.18 loparite in the veins shoulddiffer in compositionfrom 4.U s.17 4.n 5.38 4.94 4.S sro 0.E5 1.12 1.10 1.20 0.96 1.18 that occurringin the host rocks. Na2O 7.33 7.17 7.14 7.61 7.?3 7.8 In the eudialyte lujavrite and poikilitic nepheline I ot€ll ss.23 100.33 100.11 g9.78 98.99 100.4 syenite,Ioparite is commonly,although not invariably, presentas an accessoryphase, and does not occur Strucluralformulae based on 3 etomsof oxygsn as Nb 0.087 0.078 0.078 0.078 0.076 0.081 laterally continuouslayers. The poikilitic noseanand Ta 0.003 0.003 0.007 0.m6 0.006 0.006 sodalite syeniteslack loparite, pegmatitic Tr 0.@8 0.894 0.898 0.897 0.882 0.893 although a Fe 0.013 0.012 0.017 0.014 0.012 0.014 facies of this rock commonly contains significant Th 0.@3 0.@5 0.@3 0.003 0.002 0.m2 amounts of loparite. pegmatites, La alOT 0.105 0.127 0.124 0.173 0:128 In these loparite is co 0.212 0.209 0.215 0.209 0.211 0.215 found entirely in contact zones composedof micro- Pr 0.023 0.028 0.013 0.011 0.041 0.012 cline, Nd 0.061 0.062 0.042 o.u2 0.045 0.043 nepheline and early prismatic aegirine, the ca 0.135 0.160 0.1rt8 0.163 0.157 0.149 assemblagehaving formed during the early, relatively sr 0.014 0.019 0.019 0.v& 0.017 0.@0 high-temperaturestage of pegmatiteformation. Na 0.414 0.403 0.402 0.426 0.420 0.423 Mol.%End-mqberc CaThO3 0.A7 0.67 0.38 0.3s a.n o.n ANALYTICALTECHI,[euEs SrTlOs 1.94 2.$ 2.45 2.60 2,10 2.W NaNbOs 6.07 5.31 5.45 5.29 5.74 mineral CqTizOr 7.97 8.11 8.47 4.27 7.91 6..15 All compositionswere determinedby X-ray CaTiO3 17.94 20.33 19.45 20.74 19.71 19,8 energy-dispersionspectrometry (EDS) using a Hitachi Loparfte 65.71 6.1'l 66.50 64.69 65.95 570 scanning electron microscope equipped with a LINK ISIS analytical system incorporating a Super Compositions1, 2: mE md rim ot loparfte,poikllitlc sysnnq Mt. Alluaiv; 3, 4: ATW (133 @re and rim of lopalite lrom end@nGcl juvits, Litllo PunkaruaivMl; 5, 6: @re Light ElementDetector eV FwHm MnK) at md rim of loparito, psgmatiterein in snd@ntad jwito (nos. 3 & 4), Little Punk- LakeheadUniversity. EDS spectraof loparite crystals sruaiv Ml All dala obtalnad In this investigation.Total Fe exprosssdas FoO. LOPARTTEFROM TI{E LOVOZEROCOMPLEX 981
With few exceptions, in which the composition (lueshite), SrTiO. (tausonite),PbTiO3 (macedonite), varies dramatically within the same grain, back- Ca2Fe3+Mo6(latrappite), Ca2M2o7, REEzTi2oT, scatteredelectron imagery of the sarnples studied, CaThO3,CaZxO3, KMO3 andBaTiO3. Compositional at the low beam currents used for the analyses,did data were recalculatedinto theseperovskite-group end not reveal any heterogeneityin the distribution of membersusing an APL program for PC following the major elements.However, several analyseswere methodssuggested by MitcheU(1996). undertakenat different points within each apparently The majoriry of the loparite and lueshite grains homogeneousgrain of loparite grain to ensurethat any examinedin this study were found to be essentially zoning that resultsin a similar averageatomic number membersof the CaTiO3- Na(REE)TirO6- NaNbo3 was recognized. system. They contain low levels of the SrTiO, MitcheU (1996) has demonstratedthat the compo- (tausonite),CaTho3, (REETizol and otherperovskite- sitions of most naturally occurring perovskite-group type end members.Accordingly, the temary system minerals can be expressedin terms of relatively (mol.Vo) perovskite - loparite - lueshite is used to few end-member compositions, namely: CaTiO, illustrate the compositionalvariation of the minerals (perovskite), Na(RE@Ti2O6 Qoparite), NaNbO3 analyzed(Figs. 2-7).
TABLE2. REPRESENTATIVECOMPOSITIONS OF LOPARITEFROM ROCKS OFTHE DIFFERENTIATEDCOMPLEX LOVOZERO
Nhos 7.24 7.95 7.60 7.60 9.88 9.61 '.t1.49 9.73 10.91 11.14 TarOu 1.09 0.96 0.88 1.15 n-a. n.a. n.a. n.a. n.a. n.a. Ti02 40.68 39.07 39.80 40.31 39.31 40.01 38.98 39.45 38.3i, 35.14 FeO o.22 0.33 0.39 0.9 0.32 0.19 0.16 o.25 0.08 0.2. Th02 o.40 0.40 0.46 0.48 0.72 0.99 0.58 1.05 0.87 1.18 LarO. 11.53 11.23 11.28 10.65 8.86 9.21 8.57 9.20 A.20 8.67 cqo. 19.55 19.45 19.58 19.01 17.78 17.U 17.51 18.35 17.W 17.'t4 PrrOt 2.13 2.78 2.U 2.15 2.70 1.68 2.14 2.AO 2.@ 2.43 Nd203 4.23 4.37 3.94 4.19 4.05 3.61 4.?7 3.99 4.95 3.79 CaQ 4.45 4.14 4.11 4.56 4.42 4.52 4.77 4.46 3.21 1.88 SrO 2.M 2.O9 2.O5 2.30 3.31 3.35 3.52 2.94 4.38 3.08 Naro 7.32 7.A2 7.40 7.88 8.03 7.89 8.M 7.84 7.76 9.70
Total 100.82 '100.59100.(X 100.62 99.36 98.40 1OO.14 99.27 98.37 98.82
Structuralformulae based on 3 atomsof oxygen Nb 0.094 0.105 0.100 0.099 0.129 0.126 0.149 0.128 0.145 0.156 Ta 0.009 0.008 0.007 0.009 Ti 0.883 0.857 0.873 0.874 0.856 0.872 0.839 0.860 0.848 0.820 Fe 0.005 0.008 0.010 0.008 0.008 0.@5 0.004 0.06 0.002 0.006 Th 0.003 0.003 0.003 0.003 0.005 0.007 0.004 0.007 0.006 0.008 La 0.123 0.121 0.121 0.113 0.095 0.098 0.091 0.098 0.089 0.099 Ce a.207 0.208 0.209 0.201 0.188 0.184 0.184 0.195 0.184 0.195 Pr 0.022 0.030 0.027 0.023 0.029 0.018 0.022 0.021 0.028 0.023 Nd 0.044 0.o& o.a41 0.u3 0.042 0.0i18 0.@5 0.041 0.052 0.M2 Ca 0.138 0.129 0.129 0.141 0.137 0.140 0.'146 0.139 0.101 0.0s Sr 0.035 0.035 0.035 0.038 0.056 0.056 0.058 0.M9 0.075 0.055 Na o.4M A.442 0.419 0.440 0.451 0.443 0.446 0.441 0.443 0.58i1
Mol.%End-memb€rs CaThO' 0.35 0.34 0.41 0.41 0.62 0.87 0.50 0.92 0.79 0.84 SrTiOs 4.62 4.59 4.63 s.01 7.28 7.50 7.71 6.56 10.15 5.59 NaNbO. 6.91 7.29 7.16 7.M 8.47 8.39 9.81 8.47 9.86 15.75 CeJi2Or 9.4t, 7.17 8.73 4.61 3.14 2.O0 4.30 4.22 5.63 CaTiO3 18.10 16.44 16.74 17.95 17.U 17.t2 18.80 17.47 12.95 5.46 Loparite 6O.U U.17 62.U U.98 63.15 63.42 58.88 62.8 60.62 72.8
Compositions1, 2 and3, 4: coresand rimsof lop€ritesfom successivelujavrite and urtite layers,respectively, Great PunkaruaivMt.; 5€; 7€; 9-10: coresand rims of loparitesfrom successivefoyaite, melanepheline syenite and urtitelayers, respec{ively, Ml Alluaiv.All data obtainedin this investigation.Total Fe expressedas FeO; n.a.= not analyzed. 982 THE CANADIAN MINERALOGIST
CoMposmoNALVannnon Representativecompositions of loparite obtainedin this work are given in Tables l-5. Although our data Only a few chemicalcompositions of loparite from are in generalagreement with the bulk compositional Lovozero have been previously published.These data data obtained in earlier studies, they differ in that wereobtained primarily by wet-chemicalbulk analyses we did not find any significant Si or Al contents of loparite from the differentiated complex and in any of the loparite examined.We attributeprevious pegmatites.afte sem.Fositionsof loparite from samples reports of the presenceof these elementsto the of poikilitic nephelinesyenite, eudialyte lujawite and occurrenceof micro-inclusionsof silicates(nepheline, metasomaticrocks havepreviously only beencursorily aegirine, etc.) tn the material used for bulk analysis. investigated.Vlasov et al. (1966), Semenov(1972), Data obtainedin the presentwork thus are considered and Ifantopulo & Osolon (1979) have indicated that to be more accuratethan those presentedin earlier from the bottom units of the differentiated complex studies,in that structuralformulae are satisfactory,and upward, loparite compositions evolve by becoming assignment of cations to end-member components enriched in Sr, Th, Nb, and Ta, with concomitanr typically results in less than I or 5Vodeparture from depletionin the rare-earthelements and Ti. the ideal occupancyof the perovskiteA and B site,
TABLE3. REPRESENTATMECOMPOSITIONS OF LOPARITEAND LUESHITE FROM ROCKSOF THE DIFFERENTIATEDCOMPLEX. LOVOZERO
Wt.7o12345678910
Nb2o5 9.46 11.33 7.77 22.88 27.48 10.8't 74.70 9.n 8.76 9.30 TarO5 0.63 O.U 0.62 n.a. n.a. n.a. n.d. n.a. 0.57 n.a. Tio2 39.47 38.05 40.88 31.81 29.73 39.81 2.48 4O.3O 41.14 41.@ FeO 0.18 0.08 0.22 n.d. O.12 0.18 0.18 0.'11 0.36 O.28 fro, 0.81 1.24 O.82 1.06 0.93 1.13 0.09 0.56 O.54 1.2O LarO. 8.78 9.06 9.34 9.91 9.52 8.80 n.d. 9.60 9.83 9.23 CqO. 17.61 17.90 17.95 16.82 15.20 17.25 O.25 19.03 '19.46 18.04 Pr2O3 1.63 2.39 1.74 0.75 1.18 1.89 O.17 2.42 2.'l'l 1.8 Nd2O3 5.05 5.75 6.30 2.07 '1.91 4.05 n.d. 3.67 4.15 4.36 CaO 4.47 2.23 3.99 '1.57 1.41 3.89 0.05 4.24 3.91 4.4 SrO 3.40 3.55 3.50 1.69 1.86 3.64 0.38 3.13 2.31 3.23 Na"O 7.45 8.26 7.6A 10.41 10.58 8.27 17.1s 8.Os 7.% 7.8O Total 98.95 100.48100.74 98.U 99.92 99.16 98.98 100.85101.11 [email protected]
Struc{uralformulae based on 3 atomsof oxygen Nb 0.124 0j49 0.10't 0.301 0.357 0.141 0.961 0.126 0.113 0.119 Ta 0.005 0.005 0.005 0.@4 Ti 0.84t 0.885 0.884 0.6S 0.642 0.853 0.053 0.8&1 0.880 0.879 Fe 0.004 0.@2 0.005 - 0.003 0.004 0.004 0.003 0.009 0.008 Th 0.005 0.@8 0.005 0.007 0.006 0.007 0.0m 0.0M 0.004 0.008 La 0.094 0.098 0.099 0.106 0.101 0.094 - 0.'t0'l 0.103 0.097 Ce 0.188 0.'t91 0.189 0.179 0.160 0.'183 0.003 0.199 0.203 0.188 Pr 0.017 0.025 0.0'18 0.008 o.aQ 0.02a 0.002 0.025 0.v22 0.015 Nd 0.053 0.060 0.065 0.022 0.019 0.042 - 0.037 0.042 0.u4 0.'139 0.070 0.123 0.049 0.04,i! 0.120 0.002 0.129 0.119 0.133 Sr 0.057 0.060 0.058 0.029 0.031 o.ml 0.006 0.052 0.038 0.053 Na 0.420 0.&8 0.426 0.586 0.589 0.4&4 o.u6 0.444 0.439 0.431
Mol.o/oEnd-memberg CaThO. 0,72 1.14 0.71 1.03 0.94 0.99 0.2'.1 0.48 0.48 1.05 SrTiO3 7.72 8.4 7.76 4.20 4.79 8.16 0.63 6.86 5.19 7.23 NaNbO3 8.71 10.70 7.M 2,.17 27.6A 9.45 98.12 8.35 7.97 8.12 CqTirOr 612 6.36 5j2 3J7 6.99 1.59 - 4.39 4.88 3.43 CaTiO" 18.03 8.51 15.63 6.18 5.77 15.13 - 16.69 15.75 16.90 Loparite 58.70 M.97 63.73 63.26 53.91 64.68 l.M 63.23 65.74 63.25
Compositions1: core;2€: rimof loparite,foyaite, Mt. Kamasurt;4$: core,intermediate zone and rim of loparitefom trachytoidalfoyaite,Mt. Selsurq7: lueshitefrom natrolitized foyaite, Mt . Alluaiv;&10: loparitefrom lujavrite, lujavrit+hosted albitite and microclinite,respectively, Mt. Solsurl All daia obtainedin this investigation.Total Fe expressedas FeO;n.a. = not analfzed;n.d. = not detected. LOPARITE FROM TIIE LOVOreRO COMPLEX 983
TABLE4. REPRESETITATTVECOMPOS]TIONS OF LOPARI'I-E others display the opposite compositional trend ANDLUESH]TE FROM EUDIqLYTE LUJAVRITE (Iable 5, anal. 6, 7). Variationsin Sr, Th and Ta contents do not correlate with changes in major- element contents and may differ in the sense of Nhou 12.97 14.5s 11.83 11.62 45.29 16.09 '12.06 Tarou n.a, n.a. n.a. n.a. n.a. o.74 0.42 enrichment or depletion in loparite, which exhibits Tio, 37.39 36.67 39.01 39.16 19.3s 36.35 38.78 generally similar 6sadg of zonation in Na and Nb FeO 0.19 0.03 n.d. 0.25 n.d. 0.04 n.d. (cf compositions1 and 3-5 in Table 5). Tho" 1.6 0.92 1.30 1.02 0.42 0.59 0.88 enrichment LarO. 7.70 7.U 8.67 8.11 6.57 8.39 A.V2 CqO. 15.25 15.76 16.39 16.63 5.62 15.44 17.11 Stage2: rocl TABLE5. REPRESENTATTVECOMPOSITIONS OF LOPARTTEFROM PEGMATITES OFTHE POIKILITICNOSEAN AND SODALITE SYENITES wt.%12345678910 Nhou 7.ffi 17.* 7.53 8.% 12.st 15.27 10.89 6.67 6.87 6.83 Ta.Ou o.82 1.05 o.7s 0.75 0.55 0.34 0.80 0.64 0.53 0.16 Tio, 41.76 36.03 42.12 41.21 38.92 37.& 39.77 42.23 42"05 42.28 FeO 0.30 n.d. O.22 O.12 n.d. 0.10 0.10 0.30 at4 0.31 Thoz 0.58 1.05 0.70 0.92 0.98 0.88 '1.10 0.60 0.55 0.50 LarOg 9.47 8.07 8.92 8.86 7.50 7.39 8.16 9.48 9.80 9.3rt' cqo. 19.76 ,15.98 1e.23 18.& 17.% 16.67 17.76 19.09 15.72 19.11 PrrOg 1,65 1.46 1.65 1.62 1.58 1.47 1.51 1.63 l.n 1.78 Nd203 4.80 3.80 4.U 4.58 4.24 3.95 4.36 4.8 4.42 4.51 CaO 4.98 3.30 5.14 4.47 4.90 4.95 4.60 5.18 4.56 5.51 SrO 0.94 2.75 3.10 2.83 2.72 2.97 2.72 2.17 1.45 2.14 Naro 7.77 9.22 7.& 7.89 8.14 8.27 7.U 7.8 7.74 7.3'l Total 100.34 100.30 100.90 99.81 99.89 99.91 98.71 99.75 99.60 99.77 Slrucluralformulae based on 3 atomsof orygen Nb 0.097 0.26 0.097 0.107 0.166 0.196 0.141 0.086 0.089 0.088 Ta 0.006 0.008 0.006 0.0m 0.004 0.@3 0.006 0.005 0.004 0.001 Ti 0.8w 0.771 0.898 0.887 0.832 0.803 0.856 0.908 0.907 0.909 Fe 0.007 - 0.005 0.003 0.002 0.002 0.002 0.007 0.003 0.007 Th 0.@4 0.007 0.005 0.006 0.006 0.006 0.007 0.004 0.004 0.003 La 0.099 0.085 0.093 0.094 o.A79 O.On 0.086 0.100 0.'104 0.098 Ce 0.206 0.167 0.189 0.193 0.181 0.173 0.186 O.2ffi A.2W o.19 Pr 0.017 0.015 0.017 0.017 0.016 0.015 0.016 0.017 0.019 0.018 Nd 0.049 0.039 0.a47 0.u7 0.043 0.040 0.045 0.045 0.M5 0.046 Ca 0152 AJ'OI 0.156 0.137 0.149 0.150 0.141 0.159 0.140 0.168 Sr 0.016 0.M5 0.0s1 O.O47O.MS 0.049 0.045 0.036 0.024 0.035 Na 0.429 0.509 0.416 0.438 O.W 0.455 0.440 0.2109 0.4:ll 0.403 Mol.o/oEnd-members CaThO3 0.51 O.97 0.60 0.80 0.87 o.79 0.98 0.52 0.48 0.43 SrTiO, 2.09 6.50 6.n 6.29 6.17 6.79 6.19 4.80 3.24 4.68 NaNbOg 6.94 16.79 6.79 7.55 11.75 13.78 10.09 6.08 6.26 5.91 CerTirO, 4.59 3.28 2.31 2.50 4.17 5.10 4.42 4,36 3.75 4.68 CaTiO, 19.97 13.45 20.13 17.55 19.67 20.11 18.6 20.U 18.U 2',t.U Loparite 65.90 59.00 62.40 65.31 57.36 53.43 60.36 63.60 67.93 62.47 Compositions:1, 2: coreand rim of a zonedcrystal, Little Punkaruaiv Mt.; 3, 4, 5: core, intermediatezone and rim of a zoned crystal,Mt. Leppke-Nel'm;6, 7: core and rim of a zonedcrystal, ML Leppke-Nel'm;8, 9, 10:'intermediate' zones and marginof a zonation- free crystal,Great PunkaruaivMt. All data were obtainedin thb invostigation.Total Fe expressedas FeO;n.d. s notd€termined. nepheline(Table 3, anal. 7). Our observationssupport Its composition correspondsto the calcian niobian a previousreport of the occurrenceof niobian loparite loparite-(Ce) which, where zoned, shows diverse in natrolitized urtite from Mt. Leppkhe-Nel'm patlernsof core-to-rim zonationfrom one grain to the (Semenov1972). next @ig. 2). Ca and Nb contentsvary in the range There is a continuous layer of melanocratic 3.5 - 4.9 wt.VoCaO and 7.7 - 1.1.5wt.Vo M"O.. nepheline syenite ("malignite") occurring between respectively. foyaite (uvite) and urtite that can be traced laterally The loparite in the lujawite is calcian niobian practically through the whole massif; it is used loparite-(Ce) that rarely shows any zonation (Fig. 5, as a correlation horizon within the differentiated Table2). It contains3.3 - 5.87oCaO,7.3 - L2.5Vo complex. In this rock, loparite contentslocally reach M2O5, 2.5 - 4.3VoSrO and 0.5 - l.2Vo ThO2 Its L0-lZ vol.Vo.In terms of composition, the loparite composition at the top of a macrorhythmic unit in from this melanocraticnepheline syenite unit doesnot lujawite is, similar to that occurring in the overlying differ significantly from that of loparite occurring in urtite of the next unit (Table 2, alal. 1-4). the underlyingfoyaite or the overlying urtite (Table 2). In microclinite, aegirinite, albitite and modally LOPARTTEFROM TIIE LOVOreRO COMPI-EX 985 PEROVSKJTE conE nil o1 .1 *2 ,t2 v3 vg 04 l4 E5 t5 46 A6 *7 r7 (oE to r&r etdon CATCNN MOBIAN :,/' NIOBIAN LOPARITE LUESHITE MI. % LUESHM :J Flc. 2. Compositions(mol.7o) of loparitefrom poikilitic nephelinesyenite and rocks of the differentiatedcomplex: I poikilitic nephelinesyenite, Mt. Alluaiv, 2 contactjuvite, Littte PunkanraivMtn., 3 foyaite, Mt. Alluaiv, 4 juvite, Mt. Alluaiv, 5 melanocratic nephelinesyenite, Mt. Alluaiv, 6 trachytic foyaite, Ml Karnasurt,7 trachytic foyaite, Ml Selsurt. PEROVSKITE coRr ruil 0r fl o2 .2 A3 A3 *4 *4 @ to rh erdo! GALCIANNloBlrAN ,\ I-OPARITE Frc. 3. Compositions NIOBIANCALCIAN \\. (mol.Vo) of loparite \-- \ from pegmatites in the poikilitic sodalite and nosean syenites: I Little Punkaruaiv NOBNN LOPARITE Mtn.. 2 Great Punka- ruaiv Mtn.. 3 Mt. LUESHITE lo to Ninchurt. 4 Mt. + mI.%LUESHITE Leppkhe-Nel'm. 986 TT{E CANADIAN MINERALOGIST PEROVSKJTE conE $lt 0'r ll o2 .2 +3 .3 *4 *4 + @nlo rtd 4r&n CALCIANNIOBIqN ^tAA\ @' NIOBIANCALCIAN t"o"* LUESH|TE + nJ.%LUESHIII - Flc. 4. Compositions(rnol.7o) of loparite from metasomaticrocks and pegmatite vein in juvite: 1, 2 and 3: albitite, microclinite and host lujavrite, respectively,Mt. Selsurt, 4 and 5: pegmatitevein and hostjuvite, Little PunkaruaivMtn. PEROVSKTTE COrl Rfi o't .'l A2 L2 vg v8 o4 .4 tr5 15 06 16 e7 .7 *8 *8 FIG. 5. Compositions (mol.t/o) of loparite from poikilitic nephe- line syenites and rocks of the differentiated complex: I poikilitic nepheline syenite, Mt. Alluaiv, 2 urtite, Mt. Alluaiv, 3 urtite, Great PunkaruaivMtn., 4 lujawite, Great Punkaruaiv Mtn.. 5 l-:-\,; lujavrite, Mt. Kamasurt, 6 lujawite, Mt. NIOB]AN LOPAFM Karnasurt, 7 lujavrite, ton Mt. Selsurt 8 lujavrite, LUESHTTE Mt. Kuetnyuchorr. + bl.%tUESHm I,OPARITE FROM TTIE LOVOreRO COMPLEX 987 transitional vein-rocks (e.9., microcline albitite or CaO) and LREE (17.2 - 31.4 wtVo.total [REflrOt), aegirinealbitite), accessoryloparite has a composition than loparite from the poikilitic nephelinesyenites and similar to that of loparite from the rocks of the rocks of the differentiatedcomplex. differentiatedcomplex (Table 3). Trendsof core-to-rim zonation differ from one erain to another within DrscussloN the samesample @ig.4). In the temary system perovskite - lueshite - Stage3: eudialytelujavrite loparite, the majority of the compositions of perovskite-groupminerals from the intrusive, metaso- In the eudialyte lujawite, the loparite is strongly matic rocks and pegmatitesof the Lovozero complex zoned.Two principal typesofcore-to-rim zonationare correspondto calcianniobian loparite-(Ce),with some found: compositionsbeing niobian calcian loparite-(Ce). (1) In the uppernost eudialyte lujavrite facies at Lueshiteis found as a late-stagemineral in nafrolitized Mt. Alluaiv, loparite compositions evolved by foyaite at Mt. Alluaiv, and as a mantle on loparite in enrichmentin rREEand Ti, and depletionin Nb and Sr eudialytelujavrite at Mt. Kamasurt. (Fie. 6, Table 4). This trend of zonation is similar to The general trend of compositional evolution is that observedin niobian toparitefrom pegmatiteveins essentially from calcian niobian loparite (poikilitic in the melteigite - urtite - rischorrite series of the nephelinesyenites and differentiatedcomplex) through Khibina massif (Mirchell et al. 1996). niobian calcian loparite (differentiated complex and (2) In the bottom faciesof eudialytelujawite at Mt. eudialyte lujavrite) to cerian lueshite (eudialyte Karnasurt,some loparite grainshave a rim enrichedin lujavrite) (Fig. 7). The Sr content of loparite also the lueshiteend-member and contain ap to 13.7 wt.Vo increasesaccording to this sequenceofintrusion, with Na2O and 45.4 wt.Vo MzOs. Thus, these minerals loparite from eudialytelujavrites having the highestSr evolved from calcian niobian or niobian calcian content(up to 16 mol.7oSrTiO3). loparite toward cerian lueshite during the course of The similarity in compositionof loparite within and crystallizatiqa (Fig. 6). Such loparite grains coexist between successivemacrorhythmically layered units with irregularly zonedloparite of less variable compo- of the differentiatedcomplex (foyaite or lujawite and sition (Table 4). In general, loparite from eudialyte urtite) suggeststhat each unit was produced ftom lujawite containsmore Nb (10.9 - 45.4 wt.VoMzOs) compositionally similar batches of magma. The andSr (up to 7.3 wlVo SrO)and less Ca (0.3-3.I 'lt.Vo absenceof strong cryptic compositionalvariation and PEROYSKJTE COIE nf,l A1 A1 \ Y- 0 2 a2 \\ + \ @rc6ilmendq cArclqNNIOBIAN \ Ftc. 6. Compositions(mol.7o) ll NIOBIAN LOPAFITE of loparite and lueshite 1-: from eudialyte lujavrites: TUESHtTE 30 1 Mt. Alluaiv. 2 Mt. ml. % LUESHITE Kamasurt. 988 THE CANADIAN MINERALOGIST PEROVSKITE @1 (fi.2 @3 (:) 4 t HeilA 0 rupM K -KovM ABrc S €SEJAn t"--; '."u* Ftc. 7. Composition (mol.7o) of loparite and lueshite from the Lovozero complex comparedwith that of loparite from the Khibina and Bqpala alkaline complexes,and cerian perovskite from the Kovdor, Afrikander and Sebljaw alkaline uluabasic complexes(ail data obtained in this study): 14 l_nvozero;1 poikilitic nepheline syenites,2 pegmatitesof the poikilitic sodalite and noseansyenites, 3 differentiated complex,4 eudialytelujavrites. lueshite-rich membersof the lueshite-loparite solid- this hypothesis is correct, it may be concluded solution series is particularly notable. These data that loparite is stable under conditions of alkaline might indicate that the formation of in situ modal metasomatism. layering was not accompaniedby strong chemical The weak compositional trends found among differentiation and that the parental magma was loparite samplesin the Lovozero suite coincideswith strongly enrichedn REE at the time of emplacement. the order of crystallization of the intrusive series as Alternatively, the diverse intergrain compositions proposed by most petrologists @liseev & Fedorov and variouspatterns of core-to-rimzonation exhibited 1953,Bussen & Sakharov1972, Borutsky 1988). This by individual crystals from the same sample might generaltrend is in agreementwith experimentaldata on result ftom a combinationof magmaticre-equilibration the crystallizationof loparite in the loparite-nepheline and metasomatic-hydrothermalprocesses. The fluids and lujavrite-loparite pseudobinarysystems (Veksler responsiblefor the latter might be derived from the et al.1985, Veksler& Teptelev1990), which indicate magma and thus be essentially deuteric in origin. that, with decreasingtemperature, loparite become Further discussionof these problems is beyond the depletedn REE and enrichedin Sr and Nb. Thus, our scopeof this paper, as detailed modem mineralogical data are in accord with the magmatic origin of the investigationsof the macrorhythmiclayered units are Ioparitemineralization in the Lovozerointrusive series, required. asproposed by Kogarko et al. (1984)and Veksler er a/. The observationthat loparite in albitite, midselinite (1985). and other veinlike rocks is similar in crystal It is significant that a wide range of perovskite- morphology and compositionto that occurring in the group minerals was not encounteredin this very large host rocks of the differentiatedcomplex suggeststhat layered intrusion. Lueshite is found in the eudialyte loparite in the former was "inherited" from precursor lujawite, suggestingthat Na and Nb were concentrated rocks tlat have undergonemetasomatic alteration. If in the most evolvedbatches of magma.Howevero even LOPARITE FROM TIIE LOVOruRO COMPLEX 989 in theseroctrs, lueshite is not abundantand appearsto the Lovozero intrusive series and with experimental be formed by reaction of earlier-formedloparite with studies of loparite crystallization in the system residual fluids. Less evolved, Ca-rich, REE-poor nepheline-loparite. members of the perovskite-loparite solid-solution (3) Loparite in albitite, microclinite, aegirinite and series are notably absent from all of the rocks modally transitional rocks, which occur as veins examined.This observationsuggests that either all of cutting rocls of the differentiated complex, is not a the rocks currently exposedat Lovozero are relatively product of metasomatism,but a relict mineral that was evolved membersof the complex or perovskite-group stableunder conditionsof alkaline metasomatism. minerals are not sensitive indicators of the differ- entiation processes.This latter hypothesis is not AcKNowrsocENm{Ts tenable given that perovskite-groupminerals in other alkalinecomplexes exhibit wide rangesin composition This work was supportedby the Natural Sciences (Mitchell 1996), and that the compositional trends and EngineeringResearch Council of Canada(RIII\4), observedin loparite in this work, although limited, Lakehead University GHM, ARC) and the Russian are real and correspondwith the postulated stages Foundation for FundamentalResearch (ARC). Alan of evolution of the parental magma.It is significant MacKenzie 1r ftanked for assistance with the that the loparite-bearing rocks at Lovozero are analytical work. Ann Hammond and Sam Spivak are hyperagpaiticsyenites (Khomyakov 1995), in which thanked for thin section preparation and drafting the associated minerals have near-end-member services, respectively. The critical and editorial compositions and are apparently highly evolved commentsof Frank Dudas,an anonymousreferee and (Arzamastsev1994). Consequently,it is suggested Bob Martin helped to improve substantiallyan initial that the loparite compositionsfound lie close to, or at, draft of this paper. the termination of the evolutionary trend of primary magmatic perovskite-group minerals. Further, it is RTPSRB{cES poshrlatedthat less-evolvedperovskite-group minerals may be expectedto occur in the plutonic rocks that AEKsANDRoV,I.V. (1973): Models of EndogenicTantalurn- must comprise the inaccessibleinfrastructure of the Niobium Mineralization. Nauka hess, Moscow, Russia complex. (in Russ.). Loparite from Lovozero is generally richer in Nb Anzavasrsnv, A.A. (1994): Unique PaleozoicInm'uions of and poor in Ca than that from pluton the Khibina the Koln PeninsuLa-Kola ScienceCentre hess, Apatity, (Fig. 7). The unusual Th-rich compositionsreported Russia. for Khibina loparite (Borodin & Kazakova 1954) we not found at Lovozero. Loparite from carbonatite- BoRoDD.l,L.S. & Kazarove, M.E. (1954): Irinite - a new bearing ultramafic complexesof the Kola peninsula rnineral from the perovskite group. Dol CoNcr-usroNs EusBsv, N.A. & FEDoRov,E.E. (1953): Theknozero Pluton and lts Deposits. Mater. Lab. Precambrian.Geol. (l) The majority of the loparite in the Lovozero lrningrad I (in Russ.). complex is calcian niobian loparite-(Ce), with Gsnesrl4ovsrv, V.K., VoLKov, V.P., Kocanxo, L.N., relatively low levels of Sr and Th, and negligible Ta PoLyAKov, A.I., Samvrnla, T.V. & BALAsHov,Y.A. contents.Niobian calcian loparite-(Ce)also is present (1968): The Geochemistry of the Invozero Alkaline but is less common. Lueshite was observedas a rim Massif. Univ. Toronto Press,Toronto, Ontario. surroundinga core of loparite in the eudialytelujavrite and as a late-stagephase in natrolitlzed foyaite of the Farronro, T.N. & Osorw, E.D. (1979):Accessory loparite differentiatedcomplex. from a stratified alkaline intrusion. /n New Data on the (2) The general trend of compositional evolution Mineralogy of Alkaline Formations. Inst. Mineral. Geochem.Rare ElementsPress, Moscow, Russia(20-28; of loparite from the major intrusive series of the in Russ.). complex is from calcian niobian lopaxite-(Ce)through niobian calcian loparite-(Ce) to cerian lueshite. This KHoMyAKov, A.P. (1995): Mineralogy of Hyperagpaitic correspondswith the proposedorder of formation of Roc&"s.Oxford Univ. Press.Odord. U.K. 990 TTIE CANADIAN MINERALOGIST KocARKo, L.N., KoroxovA, V.A., Oru.ova, M.P. & & VI-ADyrm{,N.V. (1993): Rare earth element- Woouxv, A.R. (1995):Alkalinc Rocl KRAMI4,U. & GnausERr,B. (1983):New dataon ORLovA,M.P. (1993): Middle-Late Paleozoicriftogenic the age and genesis of alkaline rocks of the Lovozero system./n Magmatismand Metallogenyof the Riftogenic massif (rubidium and strontium isotopy). Dokl. Al & Ryarom