167 Thz Canadian M incralo gist Vol. 35, pp.1,67-173(1997) LITHIUMIN SEKANINAITEFROM THE TYPE LOCALITV, DOLNIBORY. CZECH REPUBLIC PETR dERNfI anp RON CHAPMAN Departrnentof GeolagicalSciences, University of Manitoba, Winnipeg,Manitoba R3T2N2 WERNERSCHREYER Irutitut fir Mincralogie, Ruh.r-Uni'ttersitiltBoclun D44801 Bochwa Germary LIIISA OTTOLINI AND PIERO BOTTAZZI CNRCentro d.i Studio per la Cristallochimicae la Cristall.ografia I-27100 Pnia ltaly CATIIERINEA. MoCAMMON BayerischzsGeoinstitw, UniversbAtBayreutfu D-95440 Bayreuth. Germany ABSTRACI The (Si,Al)-orderedFe end-memberof the cordieritegroup, sekaninaite, from its type locality at Dohl Bory, CzechRepublic, was analyze4 and found to contain0.04 - 0.2ALi ard0,1.l -0,2-6Na apfu; (Fe + Mn)/(Mg + Fe + 1!tn) (at.) rangesfrom 0.74 to 0.97.Lithium is incorporatedby the substitutionchNavlli0\4gFe)-r . This sekaninaiteis the first memberof the cordieritegroup reportedto have substantialLi but negligible Be. All samplesof Na,Be-, NaJ-i'Be- and Nati-bearing cordierite-sekadnaite examinedto date show a minor deficit in the tetrahedralsite (0,237 in the literature, 0.036 in our data) and a slight excessof channelcations (NaKCa) over the proportion of (BeIi) (at.). The Li-bearing sekaninaitecomes from ralher simple granitic pegmatites,in which the only Li-bearing minerals are rare tiphylite and cookeite.Thus cordierite-groupminerals are crystal- 'Ihis chemicalsinks for U. ffnding stressesthe needto analyzefor tracelight elements,even in mineralsfrom poorly fractionated andrare-element-depleted environnents, provided the crystal chemistryis favorable. Keyvvords:sekaninaite, cordierite group, lithium, beryllium, CzechRepublic. SoMraans Nous avonsanalysd la sekaninalte,p61e ferrifbre ordonn6en Al,Si du groupede la cordi6rite,provenaat de sa localit6 type, i Dolnl Bory, en R6publiqueTch{ue. Elle contient entre 0.M et0.24 atomesde Li et entre 0.11 et 0.26 atomesde Na par unit6 formulaire. k rapport @e + NIn/(Mg + Fe + Mn) (ar.) va de 0.74 d0.97.I.e lithium est incorpor6 selon le schdma ooaNavtli(Mg,Fe)-1. Cette sekaninaltefoumit le premier exemple d'un membre du groupe de la cordi6rite contenantune proportion appr€ciablede Li, mais en m6me temps, une proportiotr ndgligeablede Be. Tous les exemplesde cordi6rite - sekaninaltecontenant NaFe, NaIi'Be et NaLi 6tudi6sjusqu'ici font preuve d'un l6ger d6fcit d'occupation dans le site t6traddrique(0.237 dans la litt6rature,0.036 pour nos donn6es),et d'un l6ger exc€denten teneursde (NaKCa) daasles canaux par rapport arrltteneurs en (BeIi), en proportionsatomiques. la sekadnaltei Li provient d'exemplesde pegmatitegranitique relativenent simple, danslesquels les seulsmin€raux i contenirle Li essetrtielsont triphylit€ et cookeite,rares. C'est donc dire que les min6rauxdu groupede 1acordi6rite seraient un h6te privil6gi6 du Li. Cette situationsouligne la ndcessit6de chercherb 6tablir les teneursen 6l6nents l6gerse f6tat de trace,m0me dans les min6rauxprovenant de milieux peu 6volu6set appauwis en 6l6mentsrares, pourvu quela situationcristallochimique en est favorable. (Traduit par la R6daction) Mots-cl6s: sekaninalte,groupe de la cordi6rite,lithiun" bdryllium, R6publiqueTchdque. L E-mail address: [email protected] 168 INTRODUC"noN TABLE I. SAMPLESOF THE DOTNIBORY SEKANINAITE DGMINED Sekaninaite,ideally Fe2AlaSisOrr,is the Fe-domi- nant andAl-Si-ordered memberof the cordieritegroup. Sou@ Na?O;wt.%t It was synthesizedby severalauthors ['Terrocordierite" )c R&srch collection of J. Stan& 130 of Schreyer(1965); cl Boberski& Scbreyer(1990)1, x6 Recgarc.hco|letio of J. Stantrk 130 (L928), first noticed as a natural mineral by Sekanina )(}3 DepL Mheralogf, Petrograpby and 0.45 describedas a new speciesby Standk & MiSkovskf c€@henidry, Masaryk University. No. 11220 Q975:cf. Standk& Mi5kovskf 1964),and also studied D€pL Mintralos| and Petrology, Mor$'iatr 0J0 by electronmicroprobe (Goldman et aL 1977,Selkregg Mureu6- No. 691 & Bloss 1980, Scbreyer et al. 1993) and by X-ray DepL Mrcrslory and Petrology, Moraviu 0s2 diffraction lstructure refinement by HochelTaet al. Museun" No. 1185 (1979), unit-cell dimensions and selected physical Dept, Mn€ralog| and Potrology, Muavian 095-ll)3 propertiesby Sellregg & Bloss (1980)1.In 1990,during !fusm No. a583 the initial stagesof examination of associatedferro- Depc Mneralogr and Petrology, }{6sviar 1.08-118 gedrite, elecfton-microprobeanalyses @MPA) were ![usus, No. al44l performedattheUniversity of Manitobaon sekaninaite Rearch colection of W. Schnla (0e0) from its type locality at Dolnf Bory, westemMoraviq Czech Republic. The analysesyielded totals slightly tReconnaiesancedata deterniaed by teging all of the 46 specimers lowerthan expectedfromthe previouslyknown content availablo fc sudy, qc€'pt TS25. of H2O+,and formulas deviating from tle ideal stoichiometryOigh levels of Na but deficit in the octa- hedrally coordinatedsites). The stoichiometryruled out Axalvrrcar lMBrnonsaNo MOsssAuERRESLILTS potential substitutionby Be, and Li was not seriously considere4 as the parentgranitic pegmatitesare virtu- EMPA analysesof sevenspecimens at the Univer- ally devoid of lithium-bearingminerals. The low totals sity of Manitoba were done using o CamecaSX-50 werefirst afiributedto improperstandards, but re-analysis instrument,with an operatingvoltage of 15 kV and a of the examinedspecimens at the Rubr-Universitiitcon- samplecurrent of 20 nA, measuredon a Faradaycup; firmed the resultsobtained at Manitoba. pres- Thus the counting time was 20 s for the Ka lines of Na (albite enceof Li remainedthe only viable possibility, and was standard),Fe (fayalite), Si (diopside),Mn (spessartine), subsequentlyconfirmed. We report here on our results Al (kyanite) and Mg (olivine), and 40 s for Kcr of K of extensivechemical analysesof sekaninaitefrom its (orthoclase),Ca (diopside),Ti (titanite), Cr (cbromite), type locality, and on its geochemicalsignificance. Zn Gahnite),F (fluor-richterite), andIa of Cs (pollu- cite) and Rb (rubidian microcline). The data wetrere- SevprrsExevnrro ducedusing the PAP procedureof Pouchou& Pichoir (1985). The high contentof Na found in the first Li-bearing SIMS analysesof the above specimensfor Li, Be specimensexamined suggestedtlat tle presgnceof and B wereperformed atthe CNR Centrodi Studioper octahedrallycoordinated Li could be compensatedby la Cristallochimica e Cristallografia in Pavia under incorporationof Na inlo the channelsof the stucture. analytical conditions fully describedby Oltolint et aL Atotal of 2i7samples of sekaninaitefrom the collection (1993). Briefly, positive ions of the isotopes7Li, eBe of the Moravian Museum,and eight samplesfrom the and 11B(plus 30Si, assumedas the matrix reference collectionof the Departuentof Mineralogy,Petography isotope), rvith emissionkinetic energiesranging from and Geochemistry,Masaryk University were analyzed ^:75 to L25eV, weremonitored using a CamecaMS-4f by elecfronmicroprobe for Na as a monitor of Li, along ion microprobe.Medium- to high-energysecondary ions with two samplesfrom the R3. FergusonMuseum of were usedto reducematrix effects a.trectingaspecially Mineralogyat the University of Manitoba,four samples Li-Si ionization and to improve measurementrepro- from the researchmaterial of Dr. J. Standk (Masaryk ducibility with respectto low-energyion analysis.The University) andthree samples from the researchcollec- quantification of Li, Be and B ion signalswas canied tion of P.C. Sevenspecimens covering the full rangeof out by means of the empirical approachof working Na2Oencountered 0.13 - 1.57wt.Vo, wata selectedfor curvesvla calibrationwith standards.Since the relative detailedanalysis by EMPA, secondary-ionmass spec- yields for Li ions, with emissionenergies in the range fomety (SMS) andMdssbauer spectroscopy Clable l). 75-125 eV. showeda direct correlationwith the silica A specimenof sekaninaitecollected at Dolnl Bory in contentof the matix (Ottolini s1aL 1993),an empirical 1963 by W.S. (TS 25) was analyzedat the Ruhr- correctionwas made to accountfor matix effectsat this Universitdt, and also was subjected to Miissbauer silica value: for the quantificationof lithium, we used analysisClable l). an ion yield that is typical of low-silica samples,which LJTIIIUM IN TYPE.I.OCALITY SEKANINAITE 169 is lower by abouI25%othan that of high-silica samples. Wet-chemicalanalysis was performedfor Li andBe on No specialconections were employedto quantifyberyl- material cleaned under a binocular microscope.The lium or boron contents.Under thesecircu.nstances. the concentration of both elements was determined by accuracyfor Li (aswell as Be andB) is estimatedto be inductively coupled plasma - emission specfroscopy. betterthan LIVorelative. Reproducibility for Li, Be and This sample was also subjected to the Milssbauer B measurementswithin a one-day analytical session spectroscopicexamination discussed above. was typically afew Vorelative; it was testedon homo- geneoussynthetic glass standards. CIIEI\fiCAL CONFOSIIION OF SEKANINAITE The concenfrationsofli, Be andB reportedhere are the averagesof five determinationson each sample. Table 2 shows the combined results of EMPA, Lithium was found in the range of 0.11 - 0.55 wt.Vo SMS, Mti'ssbauerand in the case of sampleTS 25, oxide; Be and B were found to be negligible (tens of wet-chemicalanalysis. The Fe2O3contents could not be ppm oxides),insignificant for the formulae. quantified.To documentthe presenceof Fe! indicated The M0ssbauerspectra were collectedat the Bayer- by the medium to deep blue color of sekaninaite,its