875 Thz Caradian M fuc ralo g is t Vol.35, pp. 875-885(1997)
FIRSTTERRESTRIAL OCCURRENCE OF TITANIUM.RICH PYRRHOTITE, MARCASITEAND PVRITEIN A FENITIZEDXENOLITH FROMTHE KHIBINA ALKALINE COMPLEX. RUSSIA
ANDREI Y. BARKOVT nxp KAUKO V.O. LAAJOKI Irxtiruteof Geosciencesand Astrorcmy, University of Oula FIN-90570OuIW FinLand
YT]RIP.MEN'SHIKOV
Geological Instirute, Kola Science Cente, Russian Acadenry of Scimces, 14 Fersman Street, Apatity 1M200 , Russia
TUOMO T. AI.APIETI Instituteof Geoscierrcesand Astrotnnry, University of Ouh+FN-90570 OuIu Finlnnl
SEPPOJ. SryONEN Instiarcof ElcctronOptics, University of OuhaFN-90570 Ouh+ Finlnnd
ABSTRACT
The first terrestrial titanium-rich sulfides, the fust natural niobium-rich sulfide FeMgSe, fluorine-rich (ca. 6 wt.Vo D end-memberphlogopite (S().04 wLTo FeO) and ferroan alabandite occurlocally in aheterogeneous xenolit\ enclosed within nepheline syenite in the l(hifiaa alkalins gs6plex, Kola Peninsul4 northwestem Russia- This assemblage is exclusively associated with an alkali-feldspar-rich rock, probably fenite. Associat€d ninerals include corundum, Nb-Zr-bearing rutile and monazite. The maximum Ti content reaches 3.9 w.7o in pynhotite and 2 wt.7o in marcasite and pyrite, which represent prducts of replacement of the pynhotite. Titanium is distributed rather homogeneously within single grains of the pyrrhotite; however, a strong grain-to-gain variation is observed. The Tl-rich sulfides invariably contrin an elevated level ofvanadium (0.2-0 .4 wr.Vo).T\e results indicate that both Ti and V enter into solid solution in the sulfides. Presumably, there is an environmental similarity between the occurrences ofTl-bearing sulfides in trftibina and in meteorites (enstatite chondrites), where Tl-bearing hoilite occurs. As in the meteorites, strongly reducing conditions probably existed locally at the time of crystelliTation. Concentration of Mg wa a fluid phase accounts for the formation ofthe Mg-rich phlogopite, associated with the relatively Mg-poor rock.
Keyvords:Tr-beainn s"lfi6es, V-bearing sulfides, M-rich sulfide, end-member phlogopite, alabandite, fenite, xenolitb, I(hibina alkalins se6plgA Russi4 FennoscandianShield.
Souuane
Nousprdsenlons une description du premierexemple terrestre de sulfuresenrichis en titaneet du premierexemple naturel d'un sulfure cont€nant du niobium, FeMgSe, en association avec une phlogopite fluor6e (environ 6% de E en poids) et I faible teneuren fer (<0,MVoFeO) + alabandite ferreuse. Cette association est d6velopp6e dans une enchys.lans une sy6nite n6ph6linique dans le complexe alcalin de Khibin4 p6ninsule de KoIa secteur nord-ouest de Ia Russie; l'enclave serait une f6nite emichie en feldspath alcalin. Pami les min6raux associdssontcorindon, rutileenrichi en Nb etZ, et mon:zite.lspyilstitecontientjusqu'i 3.9Vo &'Ti, etla marcasite et la pyrite, qui remplacent la pyrrhotile, en contiennentenvtrot2%o,I*Ti y est r6parti de fagon assez homogBne rlgns gfuaquecristal, mais montre une grande variabilit6 parmi les grains. Les sulfifes riches en Ti sont aussi enrichis en vanadium (0.24.4Vo). D'aprds nos r6suhats, Ti et V sont incorpor6s dsns la structure des sulfures de cette enclave. tr y a proba- blement une ressemblance dans le milieu de formation de ces sulfures riches en Ti I l(hibina et dans les m6t6orites (chondrites i enstatite), dans lesquelles on peut trouver une trofite riche en Ti. Dans les deux cas, les conditions semblent avoir 6t6 fortement r6ductrices. [a concentration du Mg dgns une phase fluide pourrait expliquer Ia formation de pblogopite trBs magn6sienne dans un milisg lslatiyement pauvr,e en Mg.
(Ibaduit par la R6daction)
Mo*-clds: sulfure.s riches en Tl, sulfures riches en V, sulfure de Nb, phlogopite, mica riche en R alabandite, f6nite, x6nolithe, complexe alcalin de Khibin4 Russie, bouclier fennoscandien.
I E-mail address: [email protected] 876 TI{E CANADIAN MINERALOGIST
IxrnouucrroN the typical assemblagesof minerals.The xenoliths are presentasnunreous isolated bodies having wide variations In the courseofa detailedmineralogical study ofone in theirsize(from d m up to approximately0.5 km across) of the contactmetamorphicrockxenolitbs in the Khibina andmineralasse, blages. The mineralory of somexenolitbs alkaline complex, northwesternRussia, a unique is exceptionallydiverse. occurrenceof titanium-rich pyrrhotite, marcasiteand The assemblagedescribed here was identified in a pyrite,aniobium-rich sulfide and end-memberpblogopite relativelysmall xenolith (<()2kminthe longestdimension) wasrecorded. It is well known thatpyrrhotite, pyrite and surroundedby nephelinesyenite (foyaite). The xenolith marcasiteare abundantin a wide variety of geological is extremelyheterogeneous texfrrrally and mineralogically, environments(e.g., Deer et al. 1992).These minerals andseems to becomposed of vruiouscontact metamorphic have been the subject of numerousstudies; however, reks, accide,ntallyincorporated into foyaitic magma"The Ti-e,nrichedteneshialexampleswerenotpreviously known rcks te,ndtobefinegrained: however, medium-to coarse- The Iftibina pynhotite, reportedin this paper,contains grained rocks and pegmatitic facies locally also are up to 3.9 wt.VoT1 being considerablyricher in Ti than commonin theoccurrence. It is notewo,rthytbat, in general, troilite from enstatitechondrites (up to 1.0wtTa Tt), the the rocks in the xenolith show an essentialenricbment only otherTi-bearingsulfide sofarlnown in nature(Keil in titanium, and an abundanceof Ti-(Fe) oxide occurs &Andersen1965, Keil 1968).Inaddition, thebase-metal at the contactwith the host nephelinesyenite. snlfide mineftrlsare reported here to containremarkable Alkali feldspar,nepheline, sodalite, analcirne, mic4 concenhationsof vanadium (up to 0.4 wt.VoY rn the conmdum,nrile, danite,ilmenite and topaz occur in places pyrrhotite).The prese,nce of theNb-rich sulfide and a nealy asthe chief or essentialminerals in the xenolith. It is of iron-free,fluorine-rich phlogopite, occurring in therather interestto note1tru1m1s mineral speciesfreudenbergte, Mg-poor environment,is also of particularinterest. representingtle first Fennoscandianoccurrence, and membn of thecrichto'nite - loveringite- landauitesolid- Occunnrncp solutionseries were found to occurin a closeassociation with otheroxides in thexenolith @arkov et al.,nprep.). The uniquemineral assemblage occurs in the tftibina Zircon andminute grainsof uraninite(?) (310 pm) also '43'N; alkalineso6plsx (Kola PeninsulaNW Russia:67 wereobserved. Base-metal sulfide mineralization is rather 33'47'E), oneof thelargest (about 1330 km2) and most abundantin places. well-knownalkaline complexes in the world.As noted Within the xenolith, the unusual assemblageis taKogarkoet aL (195), only theGuIi nlkalineulfabasic intimately associatedwith amedium- to coarse-grained complex in Siberia may be somewhatlarger (1500- rock consistingpredominantly of alkali feldspar (bulk 16@km2). The Khibina complex is lcated at thecontract compositionAb ss.g-sgsOrn o-+r.oAn r.r-a.z), the modal betweenArchean granite gneissesand Proterozoic abundanceofwhich is not uniform, but seemsto exceed volcanic-sedimentarycomplexes. Ikamm et al. (1993) 75-3OVoon the whole. This rock may be regardedas an haverecently reported a very narrowrange ofRb-Sr ages, atkali-fetdspar-richvariety of fenite. Platy pblogopite, from 361.7tn 377.3Ma (i.e.,late Middle Devonianto subhedralto euhedralcorundum, pyrrhotite (up to Up'perDevonian),forigneous activity in theKola-Finnish ca.34 vol.7a)and rutile arepresent in varying propor- alkalineprovince, including that of theKhibina complex. tions. Monaziteis a wide,spreadaccessory mineral. It is This complexis composedof variousalkaline 16skso noteworthy that a graphite-like mineral (idenffied by predominantly(from theperiphery to thecenter) alkaline X-ray powderdiftaction) occursin thexenolitb, relatively syenite,nepheline syenite, khibinite, rischorrite,ijolite, closeto theTi-rich sulfideoccurrenceo as small spherules urtite,apatite-*phelinerocks, melteigite, nepheline syenite of lessthan 0.5 mm in diameter.This fenite xenolithmay andcarbonatite; it is surroundedby abundantfenites and be an exampleof "contactfenite", which may consistof homfelses(a9., Ge,rasimovskya aI l% 4, hlakhov l% 5, almostmonomineralic feldsparrock Examples of thelater Kostyleva-Iahmaovaet aI. Lg78).T\egeolory,pehography areknowninthefenitizedxenoliths in theOldoinyo kngai and mineralogy of the Khibina complex have been carbonatiticlavas (Morogan & Martin 1985). describedin numerouspublications (a9., Kuplesky 1928, The occurrenceof titanium-rich sulfides seems Eltseeve t al. 1939,Zak et al. l9T 2, Gerasimov sky et aI. to be a local featureof the trftibina xenolith. Electron- 1974,Galakhov 1975, Kostyleva-Iabuntsova et aL L978, microprobeanalyses ofpyrrhotite andchalcopyrite from Shlyukova 1986).However, in spite of a large number a related fine-grainednepheline-rich rock in the same of publications,only Kupletsky(1932) and Men'sbikov xenolithic body do not show detectableconcentrations (1978)have addressed the geologicaland mineralogical ofTi andV. featuresofheterogeneous xenolithic homfelsand fenite bodies,which are lcated within alkalinerocks in thecentral Et-ucrRoN-MrcRoPRoBEANALYSES part of the complex. It is important to emphasizethat xenoliths are widespreadover a large areain Khibina. Mineral compositionswere determinedusing Men'shikov(198) reporteda zoneof theconmdum-bearing both wavelength-dispersiontechnique (WDS) and xenolithic bodiesof over 20 km in length anddescribed energy-dispersiontechnique (EDS). The WDS analyses Ti-RICH PYRRHOTTTE, FENIIZED )GNOLITII KHIBINA 877
Flc. l. Left: back-scattered electron image @EI) showing a gra.in of the Tl-rich pynhotite @o) associaredwith rutile (Rt), alabandite (Alb), a REE phosphare (probably monazite) (RP), and the Nb-rich sulfide (NS). Phl the host phlogopite. Right X-ray scanning micrograph showing distribution of tiranium in the pyrrhotite. Note that a bright spot at the margin of the pynhotite grain is due to interference between Ti and La in the REE phosphate. Scale bar: 250 Lr.m. werecamiedoutwith aJEOL733Superprobeatthe l:sitrte beamwas apptied.Counting periods were 100seconds. of Electron Optics, University of Oulu, Finland and a The spectrawere processedwith an on-line Link ISIS CamecaM$46 electronmicroprobe at theKola Science (version3.00) program. Standard deviations in the EDS Centre,Russian Academy of Sciences,Apatity. Operating analysesfor both Tl andV are<0.1. wt.Vo. conditionsat Oulu were 15kV and 15nA. The following X-ray linesand standards were used: SKa (pyrite),YKa, Trremuu-B Bannc SULFDES FeK4 CrKa, NiKa, CoKa,MnKq MLa(pureelemenb), TiKc (rutile), SiKd, CaKa (wollastonite),MgKa Pynhotite (periclase),KKa (orthoclase),NaKc (iadeite),AtKc (syntheticAl2O3),FKc, BaZa(syntheticBaF2) and ClKc Pyrrhotiteforms relatively large (up to 4 mm in length) (syntheticKCI). At Apatity, analyseswere madeusing axhedralto subhedraldiscrete crystals, which may be an accelerafingvoltage of22kY anda beamcurrent of associatedclosely with alkalifeldspar, pblogopite (e.9., 20 nA (for S, Ti, Fe, Si andBa), 15 nA (for Y Co and Fig. 1) anda hydrous(?) Na{a aluminosilicate.Since It[n) and40nAforthe otherelementssoughr The following the Ti-bearingpyrhotite commonlyoccurs as single, lines and standardswere used:SKa (syntheticFeroSrr well-formedcrystals (e.g.,Fig.2), thatdo not exhibit any for base-metalsulfides; pyrite for Nb-rich sulfide),VKc1, replacementrelations with a precursormineral(s), it MnKar, NbZa@ureele,menB), TlKal (nrtileorlorenzenite appearsto representthe primary phase.Small (<().1mm or both),FeKar (FeroS11),SiKc (diopside),MgKa across)irregular grainsof pyrrhotite,inhomogeneously (forsterite),KKc (wadeite),NaKa (lorenzenite),AIKa distributedin the rock" also arenot uncommon. (pyrope) and,BaLar Oarite). The raw data were ZAF- Initial electron-microprobeanalyses showed that Ti corrected. couldbe anessential constituent of theKhibinapynhotite. For theTi-V-bearing snlfides,interferences between Thepossible presence of Ti in impurities,e.9., as a result TiKp and VKa emissionlines are taken into account, of submicroscopicinclusions of rutile, was taken into but the reqlired correctionswere found to be virtually account,and a numberof the grainsin polishedsections insipificant, muchlower than the minimum detection- were carefirlly examinedin reflected light" with back- Iimit for V. scatteredelectron imaging and scanning-electron The quantitativeEDS analysesof the sulfideswere microscopy(at magnificationsas high as 10,000x),but carriedout at the Instituteof ElectronOptics, University inclusionswere not found.To testthe analyticaldata with of Oulu, using a JEOL JSM-64QQsganning-electron respectto Ti and V, pynhotite from the Salmagorsky microscopeequip@ with aLINK eXL energy-dispersion alkaline ultramafic complex,Kola Peninsulq and from spectrometer.The analyticalconditions were l5 kV and Sudbury,Ontario, was analyzed using the same analytical l.2nA; the Kline wasused in the analyses.Pyrite and procedure.Both Ti andV contentsof thesesamples were puremetalswereused as standards. Themostfinelyfocused below the electron-microprobedetection limits. An 878 THE CANADIAN MINERALOGIST
Ftc. 2. A subhedral crystal of Ti-bearing pyrrhotite @o) hosted by silicate (Sil). Back-scatteredelectron image. Scalebar: 100 pm.
X-ray mapshowing the distributionof Ti in a largegrain concentrationsof vanadiurl rangingfrom0.2to O.4wt.Vo. of pyrrhotite (Frg. 1) indicateshomogeneity throughout Within the rock samplewith Ti-bearing pyrrhotite, thegrain. More thanfifteen individual grains of pynhotite, neitherTi- nor V-free pynhotite grainswere found. No varyingin shape(subhedral to irregular)and in size(from correlationbetween Ti and V concentrationsin the lesstlan 0.1mm to morethan I mm in the longest pyrrhotitewas found. Figure3 illustratesthat the sumof dimea5isn),r*rs1s analyzed to characterizecompositional Ti (+ V) hasa ratherstrong negative correlation with Fe variations.Depending on the grain size, from threeto twelve (correlationcoefficient R = -{.86, n=63). A stronger point-analyse.swere performed for eachgrain. The results correlationcan hardly beexpected because ofthe variable revealthat the individual grains are relatively homoge,lreous stoichiometryof pyrrhotite. A1l thesefindings lead to the conclusionthat Ti and V occur in solid solution in theKhibina pynhotite.Feversw Ti (+ 9 datafor eight TABLE I. REPRESENTATIVE RFSULTS OF T'DS) ELFCTRON-MICROPROBE ANALYSBS OF TITANIIJM-RICH PYRRIIOTITE FROM KHIBINA selectedWDS data-setsdefine a regressionline of = -2.13x _l) y + 0.93for theTi-bearing pyrrhotite. IM t. 51.43 l.m o32 3&34 n.ag 0.86l} 0.031 0.@, 0.896 2. 58.45 1.89 028 39.78 1m.40 0.844 0.Ct2 0.@4 0.8&) 3. 5&32 1.93 025 38.m 99.rl0 0.t61 0.033 0.m4 0.8!B 58.70 2.10 0.32 3&51 99.63 0.875 0.C17 0.m5 0.917 TABLB 2. REPRBSET.ITA'I'TVERFSULTS OF (ED$ ELBCTRON.MROPROtsE 5. 56.13 2.93 0.33 39.34 99.55 o.n4 0.030 0.m5 0.a79 ANALYSBS OF TTTANIUM-RICII F?RREOTITB FROM KIIIBINA :t636 3.01 o34 10.33 [email protected] 0.&'2 0.050 0.005 0.81t7 .39 3.6 0.37 4039 [email protected] o.Tr9 0.051 0.06 0.t56 WBIGI{T % ArIOMIcRms(B-r) 8r 56.05 3.15 0.32 &25 99.T1 0.&0 0.052 o.ctlt 0.857 T1 VS Fe n V tXl{ 9. 36.11 38 024 &.4 99.v1 0.419 0.091 0.m4 0.8:t? 10. 53.37 3.t9 0.32 40.30 100.08 .0.712 o.(bs 0.m5 0.862 t 59.r6 o.94 0.4 3t.65 9.03 0.879 0.016 0.dt5 0.9@ A@bB e lid€d h odq of |'lcl@ing'If oode4 NL Co @d IVq < 0.1 m%. 59.89 t.v2 0.35 38.81 l{n.o7 0.tE6 0.0t8 0.m6 0.910 * JBOL-713 ele6u nioqrcbq n C€rl@ MS-a5 rb(tr@ Ei6oprobo. 59.01 l.l7 0.3t 39 99.42 0.t63 o.om 0.m6 0.8E9 SeHftrolytiel o*lde. 5t.70 t.u 0.35 3t.7t 94g7 0.869 o.oil o.ffi 0.896 59.16 l.4l 0.36 38.73 9.6 0.an 0.ot4 0.m6 0.907 5&70 t.52 023 3E.J8 9.03 0.&74 0.(D6 0.dt4 0.904 1 54.09 2.17 025 38.78 99.29 0.t60 0.(B7 0.@4 0.901 E 3821 2.!t o 3t.& 99.58 0.E61 0.040 o.qx 0.905 with respect to Ti (and 9, whereas there is an essential 9 s7.71 2.sl 0.30 34.72 9.3t) 0.&,7 0.043 0.@5 0.905 grain-to-grain l0 37.T1 2.62 0.21 39.6 99.% 0.r43 0.045 0.m3 0.891 variationinTl, even onthe scaleof apolished il 9.33 2.7t 0.39 34.14 99.31 0.&t3 0.047 0.006 0.m6 section (Iables 1,2). Resultsof theWDS andEDS elecron- t2 51.70 2.4 O.25 39.33 lm.l3 o.ui2 o.Mt o.m4 0.894 l3 51.19 2.9t 024 39.,fO 9.74 0.833 0.049 0.d)4 0.tE6 microprobe analyses are in agreement with each other. t4 x.92 L98 0.30 39.51 99.11 0.@7 0.051 0.m5 0.tt3 The maximum Ti content reaches as much as 3.9 wt.Vo. l5 56.05 3.t1 0.30 38.78 98.30 0.t30 0.055 0.00J 0.890 tn addition to Ti, all the grains also exhibit remarkable Antye re liggl ia or&r of i@irg Ti o.d€d- Se toc br aolytiel ooodhio Ti-RICH PYRRHOTTIE FBNNIZED )GNOLITTL KHIBINA 879 0.08 KHIBIM
0.07 R=-0.86
0.06 o o &o '.oo o '.. o cnoo.P o J 0.05 go CL o .E "'..@ o@ '...o o + 0.(x o 'd
0.03 b9 ."d:... o'u 3o b. 0.02 o
0.01 0.78 0.8 0.82 0.84 0.86 0.88 0.9 Fe (apfu)
Ftc. 3. A plot of concentrationsof Fe verszsTl + V (atomsper formula unit, apfu: S = 1) for the Ti-(V)-bearing pyrrhotite from Khibim.
In view of a low Fe+ Ti + V content(ca.46atom.Vo\, electron-microprobe results and optical observations, the monoclinicstructural form is consideredlikelv for showing a distinct anisotropy of some of the FeS2veinlets. the metal-deficientTi-bearing pyrrhotite from Khilina. However. the latter characteristic itself does not neces- Resultsof an X-ray powder-diffractionstudy of one of sarily indicate marcasite, since anomalsgs anisotropy is the pyrrhotitesamples confirmed that it is monoclinic. known in pyrite.An exampleof themarcasite-pyriteveinlets It is of interestto notethat Kissin & Scott( 1972) reported cutting pynhotite is shown in Figure 4. In addition, some a n,urowrange of compositions(46.547 .0 atam.VoFe) pyrrhotite grains have partly been replaced by marcasite for syntheticmoasglinis pyrrhotite crystalli2sd ua4s1 and pyrite along the grain boundaries. hydrothermalconditions at I l5'C. The titanium-bearing Results of electron-microprobe analyses (Table 3) pyrrhotite with slightly higher EMet. contents(ca. 48 indicate that marcasite and pyrite contain both Ti and Y atam.Vo;Tables 1, 2) may representa low-temperature similar to the host pyrrhotite. Several veinlets and grains, polytypeof (hexagonal?)pyrrhotite; rhis possibility should analyzed using the WDS and EDS methods, gave be testedwith an X-ray study. comparable concentrationsof Ti (1.61-2.25 wt.Vo) atd Y (0.24.3 wt.Vo). Marcasiteand pyrite Assocrarnp Mnlmals An X-ray powder-ditfractionstudy revealedthat an alterationproduct of the Ti-bearingpyrrhotite contains Niobium-rich sulfide mixturesof marcasiteand pyrite. The individual veinlers are typicaly up to 0.05 mm across,but somepynhotite A new Nb-Fe sulfide mineral (edgarite; approved by grainsare extensivelyreplaced by the marcasite-pyrite theIMA CommissiononNewMnerals andMinemlNames) aggregate.The X-ray idenffication is consistentwith the was fomdto becloselyassociaredwithTi-bearingpynhotite, 880 TIIE CANADIAN MINERALOGIST
Fnr
Flc, 4. Veirlets of theTi-bearing pyrite or marcasite(Mrc) (or both) orientedalong fractures in pyrrhotite (Po). Back-scatteredelecfi'on image. Scale bac 50 pm. Magnification of a part ofFigure 2.
TABI.E 3. REPRBSENTATIVE RESTJLIII OF EI.ECTRON.MICROPROBB Monazite AI{ALYSES OF fi.BFr{RING PYRITE ORMARCASITE (OR BOfiI) FROMKHIBINA SBKETo/o ATorrIcPRoPUf,Flu(IaM=3) Relativelylarge grains (up to 3 mm across)of amember FoTIVSSI,MFoTtV>MS ofthemonazitegroup havebeen ident'rtredbyX-raypowder difftaction. No detailed elechon-microprobestudy of WDS@lW monazitewascarried out, but somepartialWDSandEDS lf 45.80 zcr 0 32.m 100.79 0.980 0.051 0.q5 l.qvt l.9dl grains((0.1 mm), suggest 2. 16.42 r.r2 010 52.9 t0l.(B 0.992 0.048 0.@t t.O4t r.9:r5 analyses,performed on tbree 3* 44.t6 22s O 50.51 9.lt 0.981 0.058 0.m6 1.045 1.954 tlhatrhis is monazite{Ce),with sip.ificant concentrafions EDS @lyta of I-a andNd.
4 4532 t.6t 030 5t.19 .42 0.9t5 0.041 o.dt 1.043 r.g:'7 5 4tj, 2.03 0.m 9.62 n.91 0.D6 0.052 o.dlJ l.rxB 1.947 Nb-Zr-bearing rurtle . JBOL-nt3 dffi ddoFmt8: F frlt€ M8.46 eld@ ddoFlb. Cq Nl and ItIn < 0.f rrl7a Se Btu€@lyd€l cdid@ Rutile is presentas abundant anhedral grains ranging from ca.20 pm to morethan 0.5 mm in their longest alabanditeand monazite. The mineral forms platy crystals dimensions.Electron-microprobe data show that rutile typically locatedat the margin of the pyrrhotite grains is aM-bearing phase,but is Nb contentisrelatively low (e.g.,Fig. 5) and,more rarely, enclosed within pyrrhotite (up to 2.5 wt.7oMzOs). For comparison,the MzOs or alabandite.It hasalso been observed to fill a fracture contentof rutile from kimberlite canbe up to 20.9 wt.Vo in pyrrhotite,indicating relatively late crystallization.In (nolo & Haggerty1987). The sampleof rutile analyzed addition, the sulfide was encounteredas intergrowtls (JEOL733 microprobe) contains up to ca l.2wt-%7'tO2. with bothatabandite and a rare-earth-elementphosphate, probablymonazite. The individualcrystals oftheNb-rich sulfide typically anain0. 15mm in length,but massesof Alabandite plate-like grains may reachmore than 0.5 mm across. Resultsofelecfron-microprrobemalyses oftheNb-Fesulfide Tlpicaly, alabanditeappears as relatively rare grains are presentedin Table4. The compositionscorrespond rcashingabout 0.3 mm in thelongest dimension (Fig. 6). well to anideal formulaFeMgS6, suggesfing thatthenew Larger grains (>1 mm), identified by X-ray powder mineral representsthe nahrralequivalent of a synthetic diftactioru alsoare present Electron-microprobe analyses FeNbaS e phase reported by vanden Berg & Cossee( I 968). yield a restrictedrange of Fe concentrationsin the A more detaileddescription of the M-rich sulfide will alabanditefrom Khibina Cfable5). The compositionsare be given separately. characteristicatlyvery closeto stoichiomeftic(Mn Fe)S. Ti-RICH PYRRHOTNE FEI\TIZED )(ENOLITI{, KHIBINA 881
Frc. 5. A platy crystal of the M-rich sulfide (NS) intergrownwith a REE phosphate(RP) at the boundarybetween pynhotite @o) and phlogopite (PbI). Mrc: marcasiteor pyrite. Back-scatteredelectron image. Scale bar: 100pm..
TABLE 4. RBPREIIENTATIVBREST,LTS OF ETECIRON.MCROPROBB A}.IALYSESOF NIOBIT'M-RrcH SULFIDE FROI{ KHIBII{A content,expressed by theeastonite end-member. It is poor primary phlogopitefrom peridotite WEIOIIT % FoRMUIA (t alo@ - l0) in TiOz, similar to lr 2.r l+ 2.r xenolitlrsand kimberlites (e.9., Carswell l975,Delaney et al. 1980, At'tnra& Edgar 1981).Another noteworthy Nb 54.10 52.33 Fe 0.896 0.961 compositionalfeature of the phlogopitein the Khibina Fe 9.48 10.21 v 0.040 0.M2 samplesis its relativeenrichment in Ba. 0.39 0.41 Ti 0.@7 0.q)4 Ti 0.06 0.04 M! 0.(n8 0.012 Tlpicaly, high-Mg phlogopitereflects the ultramafic I\'ln 0.08 0.13 E 0.951 1.019 natureofits hostrocks.Mg-richmembers ofthephlogopio- s 36.30 36.70 Nb 3.m4 2.X2 annite seriesare known to occur in various geological Total [email protected] 99.82 s 5.976 6.018 environments,including, in additionto pridotite xenoliths r JECrI-?33 dffi ntqoPtobq .i JEOLa6m dectm EtdoprSe: andkimberlites,ultramafic cumulates of layeredintusions Mtesy A"D. Edgr ad Y. Tbft@lt, Utrf@ity of Wffi O@do. (e.g.,Alaprett 1982), ultramafic rocks associated with the alkaline ultramafic complexes(e.9., Kukharenkoet aL 1965),lamproite,s (e.g.,Wtcbell er aL 198|, lamprophyres (e.9.,Rock 1991), marbles (e.g.,Bolet al. 1989),skarns Alabmditewasnotlmownto murintheKolaPeninsula (e.g.,Ahe.tff, et aI 195), catronatitss(e.9., Gaspar & Wyllie but was reported from some other localities in the 1987,McCormick & Le Bas1996) and some sapphirine- FennoscandianShield (Zakrzewski 1980, Tdmroos 1982). bearingrocks (e.9., Williams 1984). Sincethe contentof Fe in the pblogopitein this suite Pru-oc,oprrnEND-Mmmnn may be lower thanthe detectionlimit of the microprobeo themica represents the phlogopite end-member. kon-por Phlogopiteoccurs as plafelets and subhedral to euhedral phlogopite(O.II wt.VoFeO), close to the phlogopite platy crystalsranging from <2 to about4 mm in rliameter. end-member,has recently been reported by Chabu(1995) Megascopically,the mineral is characteristically from a Zn-Pb-{u depositin the DemocraticRepublic greenishblue to blue in color.The unusualcomposition of Congo.Like the trftibina material, the latter sample ofthis phlogopiteis particularlyillustrated by is depletion andthat with 0.3 wt.VoFeO citedin Deeret al. (1962) in Fe (i.e.,reflecting a strongenrichment in Mg) andhigh are extremely rich in fluorine (5.6 and 6.7 wt.VoF, concenffationsof fluorine Clable6). The concentration respectively).Very high concentrationsofFin theI(hibina of Fewas typically at the minimum detection-limit of the phlogopitealso are comparable with thosein phlogopite microprobe(<0.O4 wt% FeO),h.n in severalpoinranalyses, from lamproiteand kamafugite@dgar & Charbonneau Fewasbelowthe detection limir In additio[ theph]ogopite l99l,Hgar et a/ 1994).In0erestingly, phlogopite without is characterizedbv Si + Al > 8. andrather elevated vrAl Fe wasidentified in blast-furnaceslags (Wearing 1984). 882 THE CANADIAN MINERAL@IST
Ftc. 6. An irregulargrain of alabandite(Alb) associatedwith pyrrhotite (Po) andrutile (Rt). Note a plateletof the M-rich sulfide (NS) enclosedwithin alabandite.Pbl: phlogopite. Back-scatteredelectron image; see Figure 1 for location. Scalebar: 100pm.
TABLE 5. REPRESENTATTVERBSTILTS OF ELECTRON The presenceof both Ti-rich andTi-free base-metal MIQOPROEE ANALYSS' OF AI-ABANDITEFROMKIIIBINA sulfidesin the Khibina xenolith indicatesthat the WEIGIIT% FoRMIJIA (td@-2) Ti-(V)-rich sulfideshave formed underparticular (ocal) 123 t23 environmentalconditions. No otherterrestrialoccurrences ofTi-enrichedsulfidqs have so far beenreportd andthe Mu f6.01 55.3t 5324 Ivh 0.t96 0.ttp 0.t?E Fe 6.42 7.m 7.m Fs 0.101 0.122 0.113 onlyrelated occurre, rces (ie., Ti- bearingtroilite) areknown s 5.61 3!.94 37.@ > 0.997 l.0ll 0.991 in meteorites(Keil &Andersen1965, Keil 1968).Therefore, stJM 99.U 99.02 99.53 s l.m3 0.9&) t.0t0 a certain environmentalsimilarity appearsto exist I JEOL - 733 el€rtrcr dcroplsa 56 M ft[ olyttcal wrutlttm betweenthe Khibina and meteoriticoccurrences. In Ielg m mgh, h !d deb{i€d additionto theTi-bearing sulfidas, the probable similarity alsois implied by thepresence of ferroanalabandite and Drscussron highly'lrnusual" sulfides,such as FeCrzS+ (daubreelite) in chondritesand FeNb gS o (edgarite)in thefenite, as well As a ruleopyrrhotite containsonly small emountsof elementsotherthan FeandS (e.9., Arnold 1967, Vaughan & Craig 1978,Kelly & Vaughan1983, Campbell & Ethier 1984,Cabri et al. 1984,Stanley et al. 1987, Hamey & TABLE 6. REPRESENTATTTTERESULTS OF ELECTRON-MICROPROBE Merkle 1992).These elements are typically Ni, Co, Mn ANALYSES OF ENI}MEMBER PHIOGOPITE FROMKHIBINA andCu Accordingto themaximum minor-elementcontents citedby Vaughan& Craig (1978),marcasite may contain Wt.zo luNlLlwu|.e:rttqw4 SlO2 38 lt 3E.91 up to 80ppmTi and2@ pprmV,andpyrrhotite may contain st 5.61 5.65 066 o.6 up to 1250ppmV.No titaniumwas reported in pyrrhotite TiO2 Ar(r9 2.39 2.35 Al2o, lS lo 15.17 t 8 t by theseauthors.In common with pyrrhotite,typical minor FeO 0.M Id- Al(vD 0.22 o.25 MsO 25.43 .05 TI(VD 0.0E o.y elementsin pyrite are Ni and Co. Recently,essential BsO l.5t 1.35 0.q)5 ruthenium(up to 12 wtToRu) has been revealed in memters lIa2O 0 31 0.29 Mg s.6 J.64 t 5.965 5.!b K2O 911 9.61 of the pyrite-laurite series et al. 1997). Be 0.09 0.6 @arkov P 5.96 6.30 M 0.09 0.08 Theresults presented in this paperindicate O. F 2.31 2.65 thalTi an4 1.82 1.78 srJM 94.88 95.69 K to a lesserextent, V can be incorporatedin significant 2.q) 1.94 quantitiesin structuresofpyrrhotite, marcasite and pyrite, F 2.n 2.8lIr5 andthe maximumTi and V concentrationsin thepyrrhotite JEOL733 eled.@ Ei6oprobe C!, M4 Cr,V,Ni dd Clw$ughlh.tdd€*.@d Al can reachapproximately 4 andO.4wt.7o, respectively. Fe is qpBed I FeO; trd: rct dddEd Ti-RICH PYRRHOTTTE FENIIIZED )GNOLITII KHIBINA 883
asgxaphite and the graphite-likephase in the vicinity of Ti in terrestial dnerals is normallytetravalent the simple the Ti-bearingsulfide occurrencein Khibina.. heterovalentsubstitution 2Fez+ =Ti4+ (V4) + n canbe Meteoritictroilite containsfrom 0.2 to 1.0wt.ToTi; suggested.The very small differencet, tr u+y, between in general,the concentrationsof Ti aresomewhat lower ionic radii of Fe2+(0.69 A), 1i++ (0.69A) andV+* in troilite of type-I than in troilite of type-Il enstatite (0.67 A), consideredfor the samecoordination number chondrites[see Keil (1968)for details].However, rhe @hittaker & Muntus l97O), arein agreementwith the observeddifferences in theaverageTi contents are rather proposal.An altemativeis theincorporation o1111+ (and minor(brps 1; 0.38 wtVoTrverszs type II: 0.65wt.VoTr), y3+): 3 Fe2+= 21i3+ (or y3+) + n. The relevantradii whereasthe reportedranges are nearly identical (type I: are:Tis* 0.75A ,Yz* o.72A,and Fe2+0.69 A (whinaker 0.2C-{.93wt.Vo Tr versustype n: 0.23-l.M tut.VoTi). & Muntus 1970).The presenceof Ti3+ seemsto be a AlthoughKeil did notreportvanadirmin thetroilite, this viable alternative,as considerableftivalent Ti hasbeen elemeatalso is present(S.A. Kissin, pers. somm.). Unlike shownto enterCa-rich pyroxenein a meteorite(DowE the Khibina pyrrhotite, meteoritictroilite invariably & Clark 1973).Adetailed studyis requiredto testone containsessential cbromium (0.5-3 .4 wLEo Cr). Ke;d (L968) of thesepossibilities. suggestedthat textural and mineralogical differences On thebasis of the experimentallydetermined upper betweenthe two types of chondritemay have resulted stability limit of monoclinic pyrrhotite, its primary from different gooling histories:type-I chondritesmay formation is restrictedto temperaturesbelow 254'C have cooled quickly to temperatureslow enoughto (Kissin& Scott1982). Although tle presenceof Ti and preventextensive solid-state difrrsion and recrysallization" V may influencethis limit to somedegree, a relatively whereastype-tr chondritesmay have cooled more slowly. low-temperaturecrystsllization can be suggestedfor the In the latter case,rates of solid-statediffusion were KhibinaTi-rich monoclinicpyrrhotite. sufficientlyhigh thatextensive recrystallization and equi- From a genetic point of view, the presenceof the Iibrrationtookplace.An altemative discussed in IGil (1968) phlogopiteend-member in the Mg-poor fenite at is that type-tr enstatitechondrites originated ftom those Khibina is quite unusual.Although petrographic of typeI by reheating.During reheating,along with other observationsdo not provide exactdata on flfistiming of chemicaland textural changes, toilite of type-trchondrites phlogopiteformatioD" its earlycrystallizatiea nrior,o 1ot may havebecome relatively enrichedin titanium. with) the alkafi feldsparcan hardly be expected.It could The occurrenceof Ti in solidsolution in themeteoritic beinsteadalate-crystallZing mineral, formed from afluid Eoilite,as well asthechalcophilebehaviorof othertypically phase,after the associatedfeldspar. This suggestionis lithophile elements(Cr, Mn, Mg and Ca), are atrributed consistentwifl evidencethat phlogopitecan be formed to higbty reducingconditions in the meteorites(Keil & at low-temperaturehydrothermal conditions @elkin s6 Andersen1965). Itis ofinterestto notethatthe al. 1988).It is known that the phlogopitechemistry is behaviorof Nb, revealedin the Khibina xenolith, is affectedby variationsin temperature,pressure, oxygen rnknown in meteorites, fugacity,bulk-rock chemistry and fluid composition.Foley Apart from theTi-rich oxidezone, at leastlocally and (1990)concluded that fluid compositionmay exert in certainstages of crystnllization,moderately to higbly much greatercontrol on chemistryof the phlogopitein reducingenvironments also a'ppeartohave existed during lamproitic rocks than do either pressure-temperature recrysallizafionof thetrihibinaxenolith- Obviously, similar vaiationsor bulk compositionof thehost rock TheKhibina reducingenvironments also were characteristicfor the phlogopiteis rather poor in Ti and rich in Al (Iable 6). otherrelated xenolithic bodies, as native iron is observed In general,Ti in phlogopite increaseswith decreasing asa quite abundantphase within anotherxenolith in the pressureand increasing temperature @gu et al. 1976, complex(Men'shikov, unpubl. data). However, the extent Robert19764 Tronnes et al. l985,Foley 1990).Robert ofreductionmay have varied not only in differentbodies, (1976b)concluded that the Al contentof phlogopite but alsothmugh a singlexenolith containing Ti-rich sulfide decreaseswith increasingtemperature, and this feature minetals.The highestdegree of reductionmay well be is a peculiarproperty of phlogopite.In addition, the Al reflectedin the associationof theTl-V-rich sulfidesand contentalso dependson the HzO concentrationin the niobium-richsulfide (edgariteis not observedin the mineral-forming environment.Mica crystallized in Ti-poor pyrrhotite occurrence)and in the presenceof H2O-rich experimentalenvironments contains consid- alabandite.The highly reducingconditions, rather than erablyhigher levels of Al thanmica in experinentswith equilibration at different temperaturesor a particular lessHzO (Foley 1990).The behaviorof Al during cooling history could be the most significant factor to crystallizationof pblogopiteappears to be a function of explain the Ti-rich sulfidesassociated with the M-rich the bulk-rockAl content(Foley 1989).Finally, like the sulfide in the Khibina complex. This conclusionis other examplesof exceedinglyFe-poor phlogopite in supportedby the occurrenceof vanadiumsulfide, the literature (Deer et al. 1962,Chabu 1995),the end- patr6nite (VSa) in a bituminousore depositin Peru memberphlogopite is strongly enrichedin fluorine (Baumann19Ci4). (Table6) at Khibina. Theseexamples are in good Themechanism of incorporationofTi into thestuchre agreementwith the corollary of the so-calledFe-F of theTi-rich sulfidesat Khibinaremains rrnknown. As avoidancerule. 884 TTIE CANADIAN MINERAISGIST
AcK\owIEGHW\TS Censwsr. D.A. (1975):Primary and secondary phlogopites and clinopyroxenesin garnetthenolite xenoliths.Plrys. Chzm. This strrdywas supported by theAcademyof Finland, Earth9,4l7429. Thule Institute(University of Oulu), and the Russian CHanu,M. (1995):The geochemistryofpblogopite and cblorite (though grant Foundationfor BasicResearch 95-05-I 6503 from the Kipushi Zn-Pb-Cu deposit, Shab4 Zatre. Can. to YPM). We thank Prof. A.D. Edgar for his helptul Mtueral.33,5M-558. commentson a preliminaryversion of this paperand Dr. Y. Thibault for providing someelectron-microprobe Dmn, W.A., Hown, R.A. & ZussMAN,l. (1962):Rock-Forming analyses.The paperhas been improved as a result of Minerals.3.Sheet Silicates. Iongmans, London, U.K. constructivecomments and reviews by two referees,S.A. Kissin and J.H.G.Lajlamme, Editor R.F. Martin and & -(1992): An Innoduction to AssociateEditor R.H. Mitchell, whoseefforts are greatly the Rock-Forming Mhcrals. 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