53

The Canqdian M ine raln gi st Vol.35, pp.53-78 (199)

MINERALOGYOF LEUCITE.BEARINGDYKES FROM NAPOLEON BAY, BAFFINlSl-AND: MULTISTAGE PROTEROZOIC LAMPROITES

DONALDD. HOGARTII Departmentof Geology,University of Oxawa Ottawa"Ontario KIN 6N5

ABsrRAcr

Vertical, W- and NW-trending, post-tectonic,Proterozoic dykes at Napoleon Bay, southeasternBaffin Island, Northwest Territories, contain mineral assemblagestypical of lamproites: 1) phenocrystsof Fe-bearingleucite and sanidine' Ti-rich phlogopite,and high-Mg olivine anddiopside, and 2) a groundmassofTi-rich phlogopite,Fe-bearing sanidine and apatite. Except wherepreserved in chill zones,leucite has decomposedto a sanidine- kalsilite intergrowth or hasbeen replaced completely by sanidine.Phlogopite grains are emichedin Fe (to annite and ferri-annite)on their margins,relative to cores.Late-stage titanian potassium maguesio-arfvedsoniteappeaxs in some dykes and is also progressively emiched in Fe (o titanian potassium arfuedsonite)toward the margins of grains. In a few crystals, aegirine and aegirine-augite(some grains Tirich) overgrow diopside.Rare and very late-stage,possibly magmaticdevelopment of ninerals involves overgrowthsof potassiummagnesio- arfvedsoniteon Fe-rich amphibole,and phlogopite and 'feniphlogopite' on Fe-rich mica- With the exceptionof aegirineand aegirine-augite,all fenomagnesiansilicates are undersaturatedin Si + ryAl, with averagedeficits in the tetrahedralposition extendingfrom 15.770n aailte atdferri-annite (grain margins)to 1.57oin magnesio-arfvedsonite(overgrowths). The vacancies in the tetrahedralposition canbe fil1edwith Fe*. Rareminerals in the Baffur dykes,that arecharacteristic ofknown occunences of lamproite, are K Ti-rich sodic--calcicamphiboles, shcherbakovite, Ti-rich cbromite, and K-Ti-Fe oxide. However, some minor minerals in these dykes have not been described from lamproite [pectolite, lorenzenite, barytolamprophyllite' calcioancylite-(Ce),djerfisheritel, and the late Na-Fe overprint seernsexteme for lamproite.Evidence suggests differentiation with repeated post-consolidation i{ections. Rocls that are possibly related include a porphyritic volcanic rock containingpseudoleucite (sanidine) - forsterite - diopside- titanian phlogopite,lacated ca. 20 km west of NapoleonBay, not found in sita, small diatremedykes and sills (cementedwith K-rich, peraluminousglass), 8 kmWSW, andcoeval, mineralogtcally similar lamproitedykes at Sisimiut, southwestGreenland.

Keryords: lamproite,ultrapotassic rocks, leucite, pseudoleucite,alkali amphibolg titanian mic4 dyke reopening,peraluminous glass,Baffin Island,Nor0rwest Territories.

Sonauann

Des filons verticauxpost-tectoniques, d'orientation vers I'ouest ou le nord-ouest,d'dge prot6rozolque, d6couverts i la baie de Napol6on,sur l'lle de Baffrq aux Territoires du Nord-Oues! contiennentdes associationsde min6rauxtypiques de lamproltes: (l) phdnocristauxde leucite ferrifdre et de sanidine,phlogopite riche en Ti, olivine magn6sienneet diopside,et (2) une pate conGnantphlogopite titanifbre, sanidineriche en Fe et apatite.Sauf dansles cas de borduresfig6es, la leucite s'est d6stabilis6e en intercroissancede sanidineet de kalsilite, ou bien a 6t6 complbtementremplacde par la sanidine.Les cristaux de pblogopite sont emichis en Fe vers leur bordure,et deviennentdonc de I'annite ou de la ferri-annite.La magn6sio-arfvedsonitetitanifdre et potassiqueapparalt tardivement dans certains filons, et se trouve progressivementemichie en Fe, pour devenirde I'arfuedsonite titanifbre potassique.Dans quelquescas, aegyrineet augite aegyrinique(ici et li titanifdre) forment une surcroissancesur le diopsitle.Plus raremen! et i un stadetrbs tardif, possiblementencore magmatique, il y a d6veloppementde surqoissancesde magn6sio-arfuedsonitepotassique sur I'amphiboleriche en Fe, et de phlogopiteet 'Terriphlogopite"sur le mica riche en Fe. Sauf dansle cas de l'aegyrine et de1'augite aegyrinique,tous les silicatesferromagn6siens sotrt sous-satur6sen Si + ryAl, le d6ficit moyendans la position t6ta6drique s'dGndantde l5.7Vo dansl'annite et la feni-annite (borduredes grains)jusqu'd l.S%odans la magn6sioarfvedsonite(en surcroissance).ks lacunes4plrarentes darui la position t6traddriquepourraient 6tre rempliespar le Fe}r. Parmi les min6rauxdes filons de Baffin qui sont caract€ristiquesdes lamproltesconnues, il faut sipaler les amphiboles sodiques-

Mots-cl6s: lamproite,roches ultrapotassiques, leucite, pseudoleucite,amphibole alcaline, mica titanif0re,rdouverture des filons, verre hyperalumineux,fle de Bafful Tenitoires du Nord-Ouest 54

INTT.ODUcToN This paperpresents the mineralogicaldata. A paper on petrochemicalcharacteristics is planned@eterson & Hogarth,in prep.). On Baffin Island, Northwest Territories (62"531{, 65'2I\{), metamolphicrocks of the CanadianShield GsolocrcAl SE"rrNG are intruded by na:row lamproite dykes. This adds an occurrence,in the Canadiannortheast, to the belt of The Proterozoicmetarnorphic rocks in southeastern ulfrapotassicrocks that extendsfrom Wyoming to west Baffin Island were derivedfrom igneousand sedimen- Greenland,a distance of over 4000 km (Hogarth & tary protoliths that have since been metamorphosed Peterson1996). to the upper amFhibolite or lower granulite facies (Blackadar The initial discovery was made n 1992, during a 1967, Jackson& Morgan 1978). Biotite- gneissespre- search for unrelated metamafic and meta-ultamafic orthopyroxene and biotite-hornblende rocks of Martin Frobisher's mines, which were tested dominate: biotite-almandine and biotite-sillimanite for gold four centuriesago (Hogarth et al. 1994).T\e gneisses are comparatively rare. At Napoleon Bay (Fig. DiscoveryDyke wasno ordinarydyke, nor an associate 2), weakly foliated, stark-white anorthositeis grey gneiss of local pre-orogenicbasic or ultrabasicroctrs, such as conformablewith dark biotite-hornblende gneisso' thoseofFrobisher's Countess ofSussex mine (Fig. 1). in three localities. Local "mafic includes heliminary testsshowed hornblende-plagioclase,diopside-plagioclase and the rock to be enrichedin K - - and Ti, depletedin Si and Ca, and clearly post-tectonic. diopside orthopyroxene plagioclaseassemblages. As a result of a haverse100 km NNW, along srike The areawas re-examined by the authorin 1994but, with metamorphicstrata at NapoleonBay, Scott (1996) xnce 1992, the Discovery Dyke exposure@; Fig. 2) concludedthat "lte rocks... may representthe north- had beencovered by a tongueoffrozen rubble. Further ward continuationof the ca. 1.9 Gametaplutonicrocks investigationrevealed several small satellite dykes on ofthe Torngatorogen [northern Labrador]". This ageis both sidesof the ice-filled valley, as well as six dykes consistentwith agesof high-grademetamoryhism and in four areasnearby (A, C, D, E; Fig. 2). Additional plutonism in southeasternBaffin Island (Hogarth & exposureswere found behind a reservoir of ice and Roddick 1989, Jacksonet aL L990, Hogarth et al. de},rj;s,2/zkm northwest(F; Fig. 2). Detailed minera- 1994).An episodeat ca. 1.5 Ga marks the final meta- logical study in Ottawaand Montreal followed. morphism of the region, although this event may

NSIAND

'rPnX,trr, o

\\ \-\,,\\

\ \(: $ d\ -'JFo lll \:, wAn/i/lcK -t t SOUND I i\l -F I l.l" til'I llli o**n*u650 ruffirHd 5

\ /-\'lRg"lDoF

Hc. 1. Map locatingsites mentioned in text. LAMPROITE DYKES. BAFFIN ISLAND

.-Trend F:-:-_-:-l Peat BiotiteGneiss r------J t Felsenmeer, Maficgneiss LamproitedYke sand,gravel ,tt Anorthosite .( ,r' Foliation( vertical, inclined)

Frc. 2. Geology,ultrapotassic dyke area,Napoleon Bay, Baffin Island. 56 TTIE CANADIAN MINERALOGIST

oocooling representa age" [11 K-Ar determinationson METH0DS OFRFSEARCH metamafic and meta-ultramafic rocks reported by Hogarth et al. (1994)1. The pristine Baffin dykes, Polished thin sections for electron-microprobe l'240Ma old (T.D. Peterson;pers. comm.; K-Ar phlo- analyseswere made from the Baffin dykes,the beach gopite age), appear to have penetated a stabilized cobble of GreaterSumner Island. the two diatremeson cratonduring post-orogenicrelaxation. Kodlunarn Islan{ and country rocks. Minerals were At NapoleonBay, the prevalentsffike of the coun- analyzedwith a JEOL 733 electron microprobe and try-rock foliation is northerly (with numerousminor wavelength-dispersionspectrometry (WDS); it is fluctuations), the dip, 50-80'W, and the plunge, equippedwith Tracor Northem 55(F and 5600 auto- 40-50'W. Pronouncedjoint pattemsare NW- and W- mation and housedin the Mineral SciencssDivision of to WNW-frending. The E-W set tends to converge the CanadianMuseum of Nature.Operating conditions landward(W), and the northwestset tends to converge were 15 kV, a beam current of 20 nA, and a beam seaward(SE). 10-30 trtm in width. Data were collected for 25 s or 0.25Voprdsion per elemen! whichevercame first, and FEr-DRH.ATIoNsrms or Pos:r-ORocENIcDyKEs werereduced with a ZAF program.Calcite and some of ANDVorcANIc RocKS the chromite grains were analyzed with the JEOL 8900L (WDS) elecfronmicroprobe at McGill Univer- Dark-colored,post-orogenic dykes are localized in sity. Glassin the vitric diatremesill on Kodlunarn was bottr sets of linear features of southeasternBaffin analyzedby PeterJones at CarletonUniversity, with a Cambridge Instruments MK4 electron microprobe Island. Thoseat locationsA, B, C, D and F @g. 2) lie in northwestlineaments, but the dyke at E has an E-W (wDs). trend. The dykes, henceforthcalled the Baffin dykes, Wherever possible, results of two, or preferably are easily locatedby color confast with the host rock, three or more, analysesfrom within a single polished especially where the brownish black dykes intude thin sectionwere averaged.The range within a cluster white anorthosite.They are also recessive,leaving ver- is shown, in parentheses,as standarddeviation (Sx). tical to sub-vertical clefts near the sea. Leucite and Standard deviations of iron oxides are in terms of pseudoleuciteare removed preferentially, commonly oxides reported in analyses(total iron expressedas producingan indented ol evena perforatd surface. Fe2O3in feldspars and feldspathoids,and as FeO in Weight per cent Fezor, FeO and H2O were The Baffin dykes are narow and composite.The others). Oxygen equivalentsof F were thickest (northerndyke of areaD) is 2 m acrossand derived by calculation. in makingtotals. Oxides are based onl00%o crops out, intermittently, aTong/70 m. Some dykes subtracted (al1constituents included) in tablesusing wt7a,and show internal (as well as marginal) chill-zones,easily total tnwt%ovalues quoted in the text. identified in the field. For example, the l.7-m-wide Discovery Dyke containstwo internal chill-zones,and Nomenclatureand formulae generallyfollow those the l.5-m-wide dyke at A containsseven intemal chill- of Nickel & Nichols (1991) andNickel (1992).Abbre- zones.A searchfor similgx dytrst nearby was unsuc- viations are those of Kretz (1983) or adaptedfrom cessfirl,but possiblyrelated occunences at Sumnerand them.The following abbreviationsare used in this paper Kodlunam Islands@ig. 1) deserveconsideration. crf: 100 Cr(Cr + Al) A small black cobble was, in 1991, collected by Fe3t: 100 Fe3+(Fe3++ Al) JamesieSataa from the beachat GreaterSumner Island, Fe3*' 100FeVFe about 20 km west of the study area. It is microcrys- Fet: 100Fe/@e + Mg) talline, with its roundedsurface liberally perforatedby Met: 100 Mg/QvIg+ Fe) tiny holes.Its pocked surfacesuggested a rock similar Mg*: 100 Mg(Mg + Fd*) to the Baffin dykes, and provided an additional speci- Tif: 100 Ti/(Ti + Al + Cr) rvAl)/Zd",r men for investigation. A: lN (Qaa- Si - - - - quadrilateral In August 1983, two small inEusive bodies were Q: dp hd fs en located on the south side of Kodlunam Island, 8 km TE: Sum of end members SSW of the Baffin dykes, then calld lryaline dykcs CaMgeTi%AlSiO6and (Hogarth & Gibbins 1984), but here termed diatreme NaFd*%Ti%Si2O6 dyleesafi silh, becausethey are largely composedof In: SumofA cations fragments,apparently derived from near-surfacewall- Xs: SumofB cations rock by gasgousexplosion. These occurrenceswere Xc: Sum of C cations re-investigatedinIily 1992.One is a vein (partly con- I'z: SnmofZ cations cordant, partly discordant) cutting leucocratic biotite apfu. atomsper formula unit gneiss.It is up to 5 cm wide and can be followed along n'. Number of electon-microprobe the seasca4rfor 4 m. The otheris a naxrow(1 cm wide) analysesprocessed within a sill, faced for about 2 m. compositionalcluster LAMPROIIB DYKFS. BAFFIN ISLAND 57

TABLEI. MODALCOMPOSNONOFTYPICALROCKS TABI.E2. MINERALSIN THEBAFFIN I.AMPROME SUITE

'14 S€cti@ T1 T2 T3 T5 T6 TI T8 T9 A- Phw4n6 D. c4vro FtlttuSr AFABBBBDEFSI eidhs pctresim fri$Fosfv€ds!ft, I€trcit€ p@$iB6mcd@it€ pbbCopn dcne 38.7 tI.t 14.6 41.4 49.0 342 302 )39 13,3 fclsicphs "eGiphlogopit " -'gB-te %iooilg 34.0 s c 26.8 nS 39.0 25.3 21.9 1.3 potaeiuq8trsHsoite dol@no bImm 0 0 0 0 lJ 2.7 15.5 0.6 r p@ssi@ rftrd!@ib g@@ 0 000tr0.62.10.10 diQside E Gr@dtuts @d rrdmrrdwrals pitrk@ 0.4 0 0 0.4 1.3 0.2 0.4 0.1 0 p€dolit zim dioprido 11.8 7.8 5.8 212 t62 4.5 4.0 3.3 2,6 timile 'g@pr' olivide 3.5 9g2.9 1.43.50294 looaits pedolib 1.6 000000008. 'olivins' Xsplqenql @d reiogrude Wdlca str,nr!ta&o/n! 5.4 3.6 32 3.2 0 10.8 2.4 2,8 A2 midim phloFpib titeitr 1.6 o 02 1.8 0.1 0.8 02 0.1 r I'hilit bqytolqrQbyllit cat@nt6 1.4 0 0 0.7 g 22 r5:7 7.4 C 8lgniE @idile apdite 0.6 cc0.60.1t0.802c egiriF@gto galqg opaqueph6 0.8 0 0, 1.0 0.9 r 0.9 2.4 g potlsineGriahEn't sphalsits ctlq 02 000.1b1.5230.50 poE8rf @ o4FrdokatoebEi, gytie goredos 0 7t.5 15.9 0.0 6.9 0 0 u.7 74.4 m'gqiegfvFdsrite djqfishsib pobsf@negBicfifr€d@ib TrO, (qdil€?) poiffi 7831 3117 3460 8790 8805 8308 9681 8157 6793 @no il@itc &qi@ito @gce, Atlorcd Mqge l@g &nqst@ ofphwrrtb (w) qbllqne olv&pilel s€p@ib d@ne ebiode 1.1 02 0r5 0.45 025 0.4 0.7 0.3 0.1 qhjede p@iddb 'olivire" 0.8 0.7 0.6 0.6 - 0.6 0.5 0J h@dit€ K-Ti cid€ diQside 0.6 0.6 0.6 0.8 0.5 0.9 0.4 0.5 0.45 €bite @Irile p€stolit 0.4 dolodto !t odi@nF bmm : : I o.r i.' i.' <)-l 0.1 dol@ne 'bio@' 0.5 4.05 4.05 0.8 0.5 025 0J 02 4.0:t c C@tuct rrnreru|s €lciqelylit! (Ca) doedde bEite a€giriE fltr@pafle Ihlr sqtlorc: Tl, '@ Edgi@l dl zoq T2, eEgiial dfl @e, nie@ery Dke; T3, argiira@gt iffial&ila!e,DmeryDldc; T4@@id@dme,Di@vqyry&e; T5,cr@, a k[raib @@iddin€dNFZislisb @d&qbf,4edt&{T6,@.,iill@q2-m-vi&drqT7,@qhilr@s, l-a-widodrr@; lllllwnb tm uidrdified C&Z sililes Ill,Fe (SD. T8, @!q, 15@ dykq T9, bec! ctbble, S@ Spedal abbwlattow. a, @idbe @ @id{tifi€d l'19-Ti 8iliqle *hdE snlhibole g; khded vith gpElhls; p8, dirop!@ Felrtcpioa lorie, h8pielhe' niie, @idilq otn r?" ilrhdx olivile, dqne, swib. wlgli8 8@ Ww @g!€dto hhdF s€irtoesdaqihr{Eb Dladr irlude atl forognioBi@; odq i@lqde otls niqale @d s"iddin€d 8P@i8

Tru SutvtNsRIsI-A,ND BEAcH CoBBLE ANDKODLIJNARN ISLAND DYKFS AND SnlJ n.a.: Not analyzed n.c.: Not calculated The rock consistsof phenocrystsand micropheno- N: Numberof compositionalcluste$ crysts in fine-grained groundmass.The largest phe- processed. nocrysts (up to 2 mm in long dimension) consist of otvine, now mainly alteredto a golden phyllosilicate. MnmAL AssocIAToNs The phenocrystsare commonly seenin clusters,more rarely in rectilinear,cruciform twins (twin planeidenti- 119 mineral associationsare summarizedin Table 1. fied optically as the Uz04zone). Similar olivine twins The mode is dominatedby felsic phasss,which in- were describedand illustated by Gonnard (1909), in cludes pseudoleucite,leucite itself, and sanidine that phenocrystsin volcanic rock (type not specified)from doesnot replaceleucite. Magnesium- iron micas,col- Cantal, France. At Sumner Island microphenocrysts lectively termed"biotite", are somewhatless importanl. include diopside prisms, some rimmed with green Lesscommon are clinopyroxene(mainly diopside)and aegirine-augite,some in stellate clusters, as well as olivine. Together, these four groups, felsic phases, equant crystals and clusters of crystals of sanidine, oobiotiteo',clinopyroxene and olivine, commonly make possibly rernnantsof pre-existing leucite. Thesephe- np 95Voof the rock volume, although amphiboleand nocrystsand microphenocrystsshow no prefered ori- carbonateare important in partsof dykesat E andF. All entation. The groundmassis composedof diopside, of these minerals may be megacrystic, although biotite, titanite, perovskite (partly alt€red to titanite), "biotite" is laJe,and olivine is not presentin the more chromite,badte, pyrite, calcite,and a carbonateclose in evolvedrocks. composition to CaSdCO3)2.Other, very fine-grained Over 40 minerals occur in these rocks (fable 2), phases were beyond the range of microscopic and including small amounts of the rare species"Fefral chemicalidentifi cation. ferriphlogopite", titanian potassium ferro-richterite, The Kodlunarn dyke contains highly rounded to shcherbakovite,and a rare mineral similal 1spriderite. fractured fragmentsof wallrock. The exfremely fine- 58 TIIE CANADIAN MINERALOGIST gminedmafix includedprimary spiculesof alkali feld- probe (n = 4). This glass is rich in Al ll7.87o AJzOs, spar (Oq5.5Ab23.sAne.7),some radiating from quartz AV(Ca+ Na + K) = 1.61,poor in Mg (4.3VoMgO, Mgf nucleii. A few slenderprisms of ferro-actinolitic hom- = 50), andrich inKI5.4Vo KzO,I?(Ca + Na) = 1.41. blendeare interspersed.The matrix also containsmag- netite,pyrite, apatite,indeterminate Fe-Al silicates,and FtsI-sTcPgasTs IN TTIEBAFFIN DYKFS tiny spherulesof quartz, cored with ferroan dolomite and calcite. Izucite, lealsilite,sanidinp and' nepheline" The sill includes scatteredpatches of devitrified glassat the contact,which extendinto the interior along Feldspars and feldspathoids are, collectively, ttre fractures in unaltered glass. Numerous macro- and most abundantminerals of the Baffin dykes. kucite, micro-scale rounded xenoliths (mainly feldspar and ond of the eadiestminerals, crystallizes as micropheno- quartz)are cemented with yellowish brown glass,iden- crysts in the cbill zones,gtows to a macroscopicsize, tified microscopicallyand analyzedby elecfion micro- but disappearsin the coarse-grainedfraction of the

Ftc. 3. Leucitecrystal exsolved to kalsilite (ight) andsanidine (dark). Surrounding minerals are pblogopite (vmiable shadesof grey), sanidine (dark gre9 and an unidentified Ti-Fe-K oxide (white). Back-scatteredelectron image. Area D. Bar scale 1.0mm. LAMPROITE DYKES. BAFFIN ISI,AND 59

TABLE 3. SELECTED COMPOSMONS OF FELSIC PHASES

- al@lrfew@ l?utte 'naphsltne'

No st s2 s3 s4 KI K2 LI NT 0 t2l 6 39 -B- B BB BE

si02 &.76 63.22(N) 6L23 52.3(70) 31.7q34 382130) 55.48(88) 44.76(54) a:or 18.26 19.00(o) 18.14 18.16(7r) 3l.l(54) 30.41(37) 2.39(M) 24.X(29) F%og o 0iq01) 0.06 0.7q42) 1.70(10) r.52\23\ 0.7700) 0.18(02) C8O <.q2 0.03(0D 4,4 4.02 0.15(0t 4.o2 4.V2 9.150n BaO 4.03 {.03 2.43 l.6r(5t 4.03 4.03 <.m 0.n6n N%o 0.05 0.31(20) 0.16 0.12(m)" 0.58(10) 0.54(20) 0.0102) l3.e70e) K2o 17.18 y3(08) 15.58 !,6!463) 2E3l(30) 2&6(36) ^2G2) t@(20 Totrl 100.51 100.t5 99.m 99.36 9,6 935 993 99,61

Chdge -64 - 12 64

si L993 2,945 2,953 L94f 7.981 E.115 2.011 8.479 AI 0.995 1.043 1.048 t.U29 7.769 7.@ 0.959 5.E2r r-F 0.009 0.013 0.002 0.025 0271 0243 0.02! o.w zz 3.ry1 4.000 4.@t 4.w2 r6.021 t5.967 L998 t4,7/t

0 0.001 0 0 0.034 0 0 1@8 Ba 0 0 0.045 0.031 0 0 0 0.057 NE 0.004 0.028 0.015 0.011 0.238 o.u, 0.005 5.313 t.ot2 1.v24 0.943 0.9n 1.650 0.984 t.437 t^ t.0t1 1.053 1.003 l.olJ 7.9n 79U 0.989 8.875

Speoimmnrmben: Sl glas of wraftze coryosition,veinlst in morlbsib nec dy&e;S2 sod&u fu lorcis pbeirocrys0in ncginal chill-zone;33 snldhe @joint srfre in mortrm'te, n€6 sdellib 6yl&t y safu,e after leucib, in mcgin l ohill-zone;K\ kalsllbeafter l€ilcib, csisb with 54 K2 kalstltrcfulaGit4 in narginalchill-zone, ccxisb wih 9; Ll brlcile,fumlehifr'.7tr@,Nl tqlelbu' nisla&' tf" rnineral in elass,c@tact of dyko d homblmdggn€fu& ProPudm of mqio olemends repor&dasmidos, in wt7o. dykes,owing to overprint by sanidineas a decomposl- that of "pseudoleucite"in the Sisimiut lamproites,illus- tion product replacementor as an independentmineral. fated by Thy et al. (1987;their Fig 2c). Leucite (unaltered)is preservedin a single specimen Feldsparhas the optical propertiesofhigh sanidine from an internal chill-zone at the Discovery Dyke (the (inclineddispersion, v > r,2V\= 45o,X lt (001)= 5'1. only inlernat cbill-zone examined).It has the typical Besides its formation during breakdown of leucite, frapezohedraloutline, twinniry and optical prcperties sanidineoccurs as discrete,unzoned phenocrysts that of tetagonal leucite. have had an independentorigin (and from which the More commonly, pseudomorphs after leucite optical measurementswere taken).Glass in the contact (Fig. 3) preservethe {21 1} oufline, evenin the largest zone in the wallrock also has the composition of crystals, and consist of tabular kalsilite, interleaved sanidine(Iable 3, specimenS1), as material with iso- with sanidine.These packets (several units with distinct tropic optics andtypical flow-structure.Sanidine is also orientationper "crystal" of pseudoleucite)may repre- presentas microcrystalscoating fracturesin wallrock sent domainsof former tetragonalleusite and relics of nearthe dykes (Table 3, specimenS3). -> transformation twins resulting from the cubic A narow rind of cross-fiber'hepheline" separatqs tefragonalinversion. dyke from wallrock in all six ocqurences.The same Compositionsof two pairsof coexistingsanidine and mineral lines tiny fracnrresin wallrock near the dyke. kalsilite 52 - Kl and 54 - K2 arc Iisted in Table 3. Thesefibers had straight extinction and positive elon- These pairs appear to result through breakdown of gation,although some fibers in the wallrockhave nega- tetragonalleucite accordingto the scheme: tive elongation. This mineral was extacted from a 2 leucite+ 1 sanidine+ 1 kalsilite polished rhin section and tested with X-ray powder This fansition takes place sluggrshlyat ca. 500'C diffractometry:its patternis virtually indistinguishable (amosphericpressue; positive P-T slope),but P(HzO) from nepheline,but high levels of Ca and low levels of enhancesthe breakdown (Scarfe et al. 7966, Gitrjns Al Clable 3, sampleNl) suggestan unusualvariant or persists new species.Further researchon this material is in et al. L98O)Thus, in the Baffin dykes, leucite 'T.{epheline", in the chill-zones,but underwentsubsolidus decompo- progress. resticted to the gxocontactof sition in the more permeable,coarse-grained fractions. the Baffin dykes, has not been found with lamproites The intergrowth differs from that of sanidine-talsilit€ elsewhere. i1 fte alkalineBatbjerg infrusion, illustated by Gittins Sanidine, leucite and kalsilite fit into restricted et al. (1980;their Figs. 1A, B), but seemsidentical with compositionaldomains that are close to end-member 60 T}IE CANADIAN MINERALOGIST

Ftc. 4. Fields of sanidine(Sa; n = l5), leucite (Lct; z = 3), kalsilite (Kls; n = 4) from Baffin dykesand volcanic rocks, and plagioclase@; rl = 3) from wallrrck, plotted on a Si - .R* -A diagram.Individual plots havebeen omitted for simplicity. Ideal compositions are shownas six-rayedstars, with Pl representingAn5a. A representsthe alkalis. compositions (Fig. 4). The relationship of kalsilite they are red, brown, orangeor yellow, and show vari- (Kls) and sanidine(Sa) to leucite (Irt) is clearly seen ous degrcesof pleocbroism.Like amphibole,pyroxene but, on this plot, the two varietiesof sanidineoverlap. and someolivine, they are characterizedby a shortage Compositionsof coexisting kalsilite and sanidine, of Si + Al andolike most of the amphiboleand someof plotled on aFe2O3- Na2Odiagram (Fig. 5), show that the pyroxene,they have an unusually high content of Fe and Na are selectivelyconcentated in kalsilite. The Ti, as revealedby 30 compositionsfrom sevendykes ten samplesof primary sanidine plot in two fields: and the SumnerIslaad sample.Mica crystalsare com- low-Fe (4.3Vo FezOa)and high-Fe (>lVoFezO).T\e monly zonedfrom a pale core to a dark margin. Some low-Fe field includessanidine asjoint coatings,glass of have a n:urow overgtowth of pale mica. Irss com- sanidinecomposition, and phenocrysts,considered to monly,they areunzoned, such as themicaftomSumner have formed independentlyof leucite decomposition. Island and from a dyke at D. In conftast, there are four casesof high-Fe sanidine In thesesamples of mica the shorfall of Si + Al was without associatedkalsilite, including crystalsfrom the balancedwith Fe3*in terahedral sites.The remaining SumnerIsland cobble,which havevague frapezohedral iron was assignedto Fd+ in octahedralsites, and the outlines and are consideredto have beenderived from formula was calculatedto an overall chatgeof.44. leucite. A high-Fe,low-Na glass,of sanidinecomposi- In this study,mica speciesare classified according to tion, may genetically belong with the low-Fe group. their dominantions asrecommended by Nickel (1992), Possibly,n high \a contentrendered leucite unstable, with end members annite:, K2F&*6Si6.Al2O2a(OlI)a, with only low-sodium variants (like Ll, Table 3) per- feni-annite: K2Fd*6Si6Fd*2Ozo(OII)+,phlogopite: sistingtbrough trme. KzMgaSioAlzOzr(OH)a and 'ferriphlogopite": Barium and Ca are distributederratically in sanidine KzM*SioFd*zOzo(OIDa(Nickel & Nichols 1991). and kalsilite. Generally,Ba is concentratedin sanidine, Note that in this scheme,biotite intermediatebetween Ca in kalsilite.Very minor St (ca.0.lvo SrO)is present phlogopite and annite has no place. Accordingly, the in two crystalsof sanidine,but was found to be below mica compositionsin the Baffin suite can be separated oonepheline". the detectionlimit (O.05Vo)in into four fields, divided at 50 Mg* and50 Fdt Gig. 6). The three coreomargin and overgrowthfriplets shown Mca alll AMpnrsors Gnows representtypical zonations:the early-formed core of crystalsconsists of phlogopite,the intermediatezones Trtoctuh.edralmica are annite- feni-annite,and the out€rmostzonqs consist of phlogopite - 'Teniphlogopite". Unzoned mica at Phenocrystsof trioctahedralmica areabundant in all SumnerIsland is rich in Fd+, but unzonedmica replacing dykes,but are absentfrom the chill zones.The crystals forsterite at NapoleonBay is poor in Fdt. have long dimensionsof 0.2 to 0.8 mm and may In the Baffin suite, titanium is tle most distinctive account for 40Voof the rock volume. In thin section. element.Tweffy-two compositionalpopulatioos, after TEMPROITE DYKES. BAFFIN ISLAND 61

2.5 Fan Fph 100 Ferri-annite 80 2.4 _3f FE \ 60

/ 3 1.5 40 3 d) 20

o(\l o lt 1.0 0L 0 60 80 100 Ann Mg* Phl Ftc. 6. Mca diagram,with end membersferri-annite, Fan 0.5 (KFeltsi3Fellorolol{r); annite,Ann (KFe3+lSi:All O'OHD; pblogopite,Pbl (KMg3[Si3Al]OrolOI{J;'Ter- riphlogopite',Fph (KMg:[Sife]lO'olOI{). d161ry3link + coreto marginto overgrowth(tbree triplets shown, tbree onittedfor simplicity).Continuous-line arlsvrs link corn- 0 positionsshowing nonnal zonation, whereas broken-line u arrowslink compositionsshowing reverse zonation. 0.0 0.0 0.2 0.4 0.6 Symbols:tr grain core,r grainmaryin, V overgrowth" a fosteritemantle, o unzonedcrystal (dyke), o lnzg1s{ Na2O(wto/o) crysal (volcanic).

Flc. 5. Diagram showingFezOr and NarO iu feldspar p. 7-06),some mica pairs from lamproite at Sisimiut, (sanidine,glass) andfeldspathoids ftalsilite, leucite). Tie Greenland(Scott 1981) and Hills Pond, Kansas link glassin polished lines sanidinewith sanidine thesame (Mitchell Baffin suite. thin section(four specimens,three dykes represented). 1985)have slopessimilar to the Symbols:I kalsilitein Baffrndyke, . sanidineassociated The four mica compositionsreported by Cundari with kalsilite,O isolatedsanidine crystals in Baffindyke, (1973) from central New South Wales cut acrossthe o sanidinecrystals in wallrocknear dyke, + glassof upper part of the lamproite field; those from minette sanidinecomposition in wallrocknear dyke, 11 sanidine and RomanProvince leucitite plot to the left and above crystalsin volcanicrock (Sumner Islaad cobble), * leucite it (Mitchell & Bergman1991, Fig. 6.33). in marginalchill-zone, Discovery Dyke. In Figure 8, compositionsof the Baffin mica are compared,in termsof AlzO: andFeOr, with mica from normalizing totals to lO0Vo,range from 5.38 lamproite,worldwide. Coresof mica phenocrystsfrom (0.67apfu) to 9.08 (1.06apfu) andaverage 7.33 wt.Vo Baffin dykes lie in the Al-rich end of the lamproite TiO2 (two anomalously low-Ti specimenswith field, or on the Fe-rich sidejust beyondit. The exterior 2.98 and 3.25 vtt.VoTiO2 were excluded). Titanium of thesemica flakes departsfurther from the lamproite tendsto be highestin the core of crystals. field, and extendsinto the Fe-rich, Al-poor area.This The TiO2 - AlzOs field outlined by Mitchell (1985; tend, although different from that of mica composi- his Fig. 2) for phlogopite from lamproite of Western tions in lamproite,shows similarities to the zonationof Australia and Montana accommodatesseven of the mica phenocrystsin orangeitefrom SoverNorth, South Baffin core andmargin pairs, one core (exteriorunsuit- Africa (Ir4itchell1995, Figs. 2.17,2.24). However, the able for analysis), and five cases of u'rzoned mica nanow overgro'*'1hsof light-colord intermediate-Fe (Frg. 7). In addition, two pairs have comFositionsof mica ["tetraferriphlogopite"absorption; Fet 36.8 (9.0), grain margins that lie somewhatoutside the field of N = 61,in sharp contactwith the exterior of the main mica compositions typical of lamproite. Although crystal,a dark high-Femica lno differential absorption; negativeTiO2 slopes,core to margin,are relatively rare Fet 17.l (4.6), N = 61,seem to be peculiarto the Baffin in mica from lamproite (Mirchell & Bergman 1991, dykesand differ from the zonationof low-Ti phlogopite 62 THE CANADTAN MINERALOCIST

from carbonatitesof Uganda (McCormick & Le Bas 1996),where Mg graduallyincreases toward the rim of by a low-Mg, JI] the central crystal, which is overgrcwn E low-Al mica, saturatedwith Si + Al at the very edge. tra If A, Yoand Z representinterlayer, octahedrallyand A tefiahedrallycoordinated ions in mica respectively,the mostimportant compositional variations in the suitecan 8 be explainedby the following substitutionalschemes v. t r (coreto exteriorofzoned grains)in decreasingorder of Alros l. (wt7") importance: I t rIVIg--+ rFe2* (1) 4 J/ lo-.. a/ zN-->4€" (2)

F-+ OH (3)

T'iOr(vvt7o) vTi + vn __>2vMg (4) Ftc. 7. The compositionsof mica plottedin termsof Al2O3and TiO2.Symbols are as in Figure 6, and arrowslink the sarrr Cation underfilling averagesI0Vo n the lposition, compositionsas in Figne 6. The plots fall mainly within SVornthe A position.Vacancies inA and a layer charge the higb-Ti, low-Al field outlinedby Mirchell & Bergman of approximately 1.0 are causedby the presenceof (1991,Fig. 6.33), which is distinctive for mica from lam- divalentA cationsand the substitution: proite andcertain ultapotassic rocks in Uganda,but exclu- sive of mica for minetfe and volcanic rocks of the Roman Province(Mitchell & Bergmanl99L,p.2l4-215). 2jK--> A(BACa) +an (5)

"lt"

wt% Al2os

10

oot wt% FeOl

Flc. 8. Mica compositionsplotted on an Al2O3-FeOldiagram. Symbols are as in Figure 6, and arrows link the same compositionsas in Figure 6. The area outlined (data of Mitchell & Bergman1991) circumscribes mica compositionsin lamproitic rocks and excludesnicas in the vast majority ofigneous rocks. I,AMPROITE DYKES. BAFFIN ISLAND 63

TABLE 4. Sw-FCIFD COITtrOSITIONS OF AMPHIBOLES AND MICAS

- Anpuboles Na AI A2 A3 A4 Ml ttl2 M3 M4 M5 tr t6 2 36 955 m B AE EBa"D

SiO2 4r20{r3) 50,75 53.14(m) 44.64(08) 3E.51(6D 37.03(2) 35.,t4(64),10.tE52)3E.10(3O IlO2 E.rE(44) 220 5.85(20 7.64149) 6.14(43) 8.5qlr) 6.8q53) 2.88(19) t.B(n) A12q 0r4(0o 02r 0.04(01) 0.46(06) 10.83(60) 11.64(22) 6.49(57' 6.00(40 r8.58(r9) cao3 4.(D 4.O2 03(06) 4.O2

Choge -zi- 44-

si 7.476 7.U3 7.t19 7.129 5.575 5.447 5.656 6.155 5.491 AI 0.M4 0.031 0.007 0.016 1.848 2.01t t.2l 1.065 2.599 0.,|E0 0.120 0.ll4 0.785 0.5% 0.535 t.t23 0.780 0

Ti 0.954 02s6 o.Qs 0.918 0.668 0947 0.n4 0325 0.t2. AI 0 000 00 0 0 0.@1 Cr 0 0 0.021 0 00 0 00 FeL 0.013 0.056 0.093 0261 00 0 0- Pd* 2,TD 2.7& LU2 2.8:'5 0.610 0.814 L9t3 1.63E 1.163 Mn 0.062 0.090 0.009 0.090 0.009 0.009 0.041 0.028 0 Mg 0.8t7 1.75t 2.6t2 0.681 4.23 3.572 1.6t4 3.s93 4.M5 >1 4.69 4.93 4.83 4.7m 5.57 534 5.3E 5.585 5.98 0rl8 0.724 0.0t2 0.\72 0.006 0 0 0.023 0.v2. Sr 0.@9 0.005 0.0!5 0.004 0.006 0- Ba 0 0000.0630.fl6 0.v29 0 0.013 Na 1.E93 t3t2 1.984 l.9ll 0.067 0.M2 0.030 0.@3 0.154 K 0.880 0.964 09s9 0.903 1.143 t.755 1.634 r.884 t.441 >4 3 3331.8m1.897 1.9@ 2.00 1.63

F 0.093 0 0.18t 0 0.293 0.341 0 027t 0.155 cl 0 000000 0 0.005

Specimennmbas: A1 brom titnian Int@shn efve&onlte, m of crystal; M link tfimiLn ptxtun fetM.ltert4 A3 gffipotasiwnnagwicefvedsonbetA4 &*btompot,srionafle^iltg e&'j.arot qyfil;Ml orng}ptnogoptte, unzonedpeudmorph aftsrfon0€dq M2-M4 zon€dphacry$, M2 plebrown ptlogoptte w, Ml deep bmm amite ffi,M4 ple brwn phlogoptte rim (overgrowth) M5 unzoned bromphlogopte,rt$l frm msb-ulfamafic sillnerD. The proportion of &e mjoolmeffi, oc6pt for F ad Cl, is expressedm uid€s, b wL%.

Typical compositionsare given in Table 4 and com- ions [X in the range 3.01 - 3.11; x = 3.05(03); parcd wifh a more nonnal phlogopite (higher Mgf, 15 populations,4 specimensl,if calculationsare based filled octahedralsites) frommeta-ultramafic rock, afew on 46 charges.Similar calculationsproduce high totals tens of meterssouth of the dvkes at D. for most examplesof amphibolefrom otherlamproites. For example,six of the nine compositionsin Mirchell Amphiboles & Bergman(1991, Table 6.22) from the Mt. Bayliss (Antarctica) lamproite atso yield high A + B sums if - Amphiboles are minor, exceptin a samplefrom E, calcul4tedaccording to charge [X in the range 3.M where in one specimen, their mode exceds 17Vo. 3.19;x = 3.12 (05)1.dssnming that the analyticaldata Brown is the most commoncolor in hansmittedlight, on the Baffin amphibolescorrect' the offendingfornu- greenis local, and pink is rarc. The habit is prismatic, lae canbe explainedas follows: the cationshave a total wifh someprisms faoning out from a silicate interface charge in excessof 46, resulting in oxygen at O(3) into calsite segregations.Very fine-grained piDk am- rather than F and OH, or K + Na + Ca should be phibole se€rnsto replace pyroxene and olivine; rare calculatedto 3 ions (or less),resulting in a cation defi- blue amphibole overgrows brown at one locality. At ciencyin octahedralsites. In this paper,the latter model area E, amphibolesare most common near internal is chosen,with K + Na + Ca = 3, thus permitting cbill-zones. resolutionof Fe2*and Fe3r. The chemicalformula of amphibolesfrom the Baffin The assignmentof ions to tetrahedralsites imposes dykes is characterizedby a high sum of K Na and Ca an additional problem. When dealing with potassium & TIIE CANADIAN MINERALOGIST

1.0 ing to a markedpleochroism and absorption,e.g., for Ferro- Magnesio- amphibole 44, Table 4, a is rich yellow brown, D i opaqueand c chocolatebrown; b >> c > a. 0,8 richterite i katophorite Amphibolesrange from sodic-calcic (pink) to alkali triu (brown, blue, green). Sodic-+alcic amphiboleshave 0.67 < Ca < 1.34apfu, andMg-rich andMg-poor mem- t e 0.6 Magnesio- bers have Si greater and less, respectively,than 7.5. (!o- Arfuedsonite Conversely,the alkali amphibolesof the Baffin suite . arfuedsonite have Ca < 0.67 apfu, and Fe3*> vIAl. On a Ca-Mg* I o.o diagram, these features permit according to trake .y'' (1978), a four-fold division of the 15 amphibolecom- positions into tle fields of.ferrorichterite, magnesio- 0.2 .:___---+--{Ieatoplwrite,magwsio-arfuedsonite and arfvedsonite, a as shown on Figure 9. One composition of pink oa amphiboleand nine of brown amphibolelie on a frend extendingfrom magnesiokafophorite,through magnesio- 0.0 o 20 40 60 80 100 arfvedsonite. to arfvedsonite. with Fe-rich brown amphibole later than Mg-rich, as shown by a zoned Mgn crystal from areaC (solid arrow, Fig. 9). This trend is similar to the richterite -+ arfvedsonitetend of Thy Ftc. 9. Amphibolesfrom Baffin dykesplotted with respectto (1987). (e.9., Ca and Mg*. Two typesof zonationare shown:normal or et al. Someovergrowths reverse this trend nznsitional, core to margin (short arrow), and reverseor overgrowthat B, broken-linearrow, Fig. 9). abrupl maryin to overgro\rth (broken-line arrow). Two Titanium is higher here than in most examplesof trendsare shorrn for simplicity. Symbols:E pink sodic-cal- igneous amphiboles,worldwide. Except for a s@on- cic amphibole,O brown alkali amphibole,O greenalkali dary blue amphiboleatC (rw.rth0.3%oTiO), the amphi- amphibole,r blue alkali amphibole. boles of this study contain 2.2 (pirrk) to 8.1 (brown), and average5.5 wtVoTiO2. These very high Ti (but low Al) contentsare similar to amphibolefrom lamproites richterite undersaturated in Si + N,Oberfr, et al. (1992) Mtchell & Bergman1991, Fig. 6.41).Eleven of the filled vacant tetahedral sites with Tia+ in preference to 15 arnphibolecompositions (Fig. 10) traversethe amphi- Fe3*. However, the amphiboles considered by these bole field of lamproite and lie outside the fields of authors contained comparatively [ttle Fe, and in the leucitite, MARID-suite xenolithsominette and kajanite, Baffin suite, Tions have been provisionally assigned in a diopside- leucite - nepheline- phlogopile- olivine the order Si, Al, Fe3+. Ti was accommodated in the volcanicrock (Mitchell & BergmanL99L,p.90,232). octahedral sites, tlus facilitating a uFePt -+ uTia The level of potassiumis also high; it rangesfrom charge tansfer in the strip of octahedra and conhibut- 4.3 (brown) to 5.2VoK2O (green)and, by itself, fills the

(g F

BohemianMinettes, PendennisMinette and NewSouth Wales Leucitite

Na/K (atomic) Ftc. 10.Variation of Ti with raspecttoNa/Kin amphiboles.Compositional fields havebeen adaptedfrom Mtchell & Bergman(1991, Fig. 6.41). Symbolsare as in Figure 9, and arrowslink the samecompositions as in Figure 9. I.AMPROITB DYKES. BAFFIN ISLAND 65

Flc. ll. a. Amphibole cross-sectionsshowing extinction of {010} in Mg-rich overgrowths.b. Crystals of phlogopite (core) transitionalto annite (margin),with an overgrowthof very pale pblogopite.Area E; photomicrograph;plaae-polarized light. Bar scale= 0.2 mm.

A site almost completely.The decreasein Na/I( from hned amphibolesand micas in specimzn5101A the normal level of 2 to 1.5 (Fig. 10) in a dyke at D, is (area E) due, not to an increasein K but to the substifutionof Na by Ca accordingto the scheme Snongly zoned phenocrystsof amphibole, with a sharply definedrim (overgrowth),were analyzedfrom 8Na+ zSi_> aca+ry& (6) tbree dykes (three compositionalclusters), and zoned crystalsof mica, also with a sharply definedrim, were (six All amphibolecompositions havelow Si+ A1,which aralyz,edfrom four dykes compositionalclusters). fills 93 (brown) to99Vo (blue) ofthe availabletetrahe- The generaltrend, for both, is a continuoustransition in dral sites.Low-Mg amphiboleshave the lowest Si + Al color, from a light tari core to a deepbrown exterior, pale filling, high-Mg amphiboleshave the highest.Thus late which in somecases is overgtownby a narrowrim, green pale brown arfvedsonitehas lower Si + Al than early brown in amphibole, orangein mica. magnesio-arfvedsonite,but late, mantling, blue and Typical are strongly zoned amphibole and mica greenamphiboles do not follow this paragenesis. grainsin specimen5101A @igs. 1la, b), takenfrom the Octahedralsiies are incompletelyfilled, with 89 to dyke at E. The overgrowthpreferentially extends c of 99Voof the available positions occupied.Amphibole the host mica and D of the amphiboles, ultimately compositionshaving low Si + A1,low C-ion totals,high changingthe crystalhabit of the latter by disappearance Ti and high K were all describedfrom lamproitesby of {010}, with {110} only presentin the prism zone Mitchell & Bergman(1991, p. 21U232).In the brown but, in a few amphibole crystals, the overgrowths amphibolesfrom the Baffin suite, the major composi- extendthe prism length. Expecially pronouncedis the tional variations can be explained by the following optical absorption of micas. Differential absorption substitutionalschemes notably decreaseson traversinga phenocrystfrom pale core (AX << AZ) to an almostopaque exterior, where biabsorptionand pleocbroismare not evident (i.e., AX c\llg _-> cFe2+ a) * AZ). Thesemargins, therefore, differ in absorption fromthe high-Fe,low-Al mica describedby Veresel aL cMg + 2zSi --+ cTi + 24et* (8) (1955),Wones (1963), Rimskaya-Korsakova & Soko- lova (L964) and Myano & Myano (1982), where AX 3clvlg --+ zcF€* + ctr (e) > AZ.T\ereason for this discrepancyis unclear;it may be connectedwith unusually high Ti in mica of the Baffin suite, which is lacking in mica studied by the rCa + cMg -+ rl.,Ti + cFe3* (10) above-citedauthors, and is the only significant differ- encein composition.The dark mica revertsto pale mica Compositionsof four amphibolesthat characterize on the extremerim, here unzonedand with a reversed the extremerange of compositionare given in Table 4. absorption-scheme,i.e., N( > AZ (ooreversedpleo- The Bafftn suite of amphibolecompositions resemble, chroism"').The Al + Si deficit in the 7 site is aboutthe in many respects,those from known lamproites.How- sameas mica in the corg which hasa norrnalabsorption- ever, the variable,but generallylow, mapesium num- scheme,i.e., AZ > AX ("normal pleocbroism'). How- bers(Mgf L4--75,average 42; n = 15,N = 4), andhigh ever,Ti is muchlower (1/3 of theions in the core;1/3 to Na contents,are not typical of lamproites. 1/13 in the other specimens).Octahedrally coordinaied 66 THE CANADIAN MINERALOGIST

'B' elterlor rlm TABLE 5. ZONATION TRENDS IN AMPHIBOLFS AND MICAS IN DYKE AT

CoB6@id Rim

Si+AI d€.l@plogBirely i|l@ d6@pmgBstv6ly io@ Ii td@ssltghtly d!@@ mallydag$ d*ffinr&a Cr dwbdl &dl aliEFMl ed;@6bd FO fncl@mBholy d@ ij1@prog@irty d@ Mn i@progBively deI@ hc@ptogaiyoly d@ MC d@prog@iwly i|l@ d@pto8@tvoly In@ Co de@mBtuoly dal@gtuh9r t€hmh@siedly Sr lowtholghd d@ffis l@thowhd deeaftrther Ba al*ys bd bdl Na in@Frog@tvEly inll@ir&er i|lc|€6prog@twly inc1@firtl3r F d@proeBiBly i|li,@ dr@prcg$d$ly h@

Abbeidim: Mlb6lddtuio!lieit,sdlsligtdlyaboveddEcddllnil Mininm d@im llnte 0.027ocr2Q, 0.04%Sro, 0.05%BaQ 0,l7oF.

Amphiboles and micas exlhibit similar patterns of zonation.The close similarity in grains of amphibole and mica cannotbe fortuitous. The few differencesare minor, and are either inconsistentCIi and Ca) or stuc- turally controlled @a). Both of thesemineral groups formed late in the crystallizationhistory; it is possible that the overgrowths were contemporaneousand formed as result ofdyke reopeningand introduction of magmaticfluid.

TYRo)mE. FTROXB{OID AND OLTVINB GNOUPS

Clirnpy roxenes and pectolite

The major pyroxeneis long-prismaticdiopside, col- orless in thin sesfiqa,with some crystals twinned on {100}. A few pdsmsare rimmed by grass-greenaegirine- augite (more rard, deep green to brownish green aegirine); in the matrix, some isolated tiny grains of aegirine-augiteand aegirine are independentof diop- side. At locality C, rare pale blue-greendio'pside over- gows prisrns of brown amFhibole and develops as of amphibole;at B, deep 50Prn acicular crystalswithin 1flN , , green aegirine-augitemantles brown amphibole and replacescolorless diopside. r mlca tr amphlbole Parageneticrelationships, such as veining and zon- main types of pyroxene, viz., earJy Ftc. 12.Zoning in micasand amphiboles of areaE. ing, indicate two colorlessdiopside and late greenaegirine-augite, which replacesdiopside as diffrrsepatches and tips to prisms. Early diopsideis oscillatorily zoned,with a tendencyto Ti may strongly enhancein-plane chargetansfer, in be moreNa- andFe-rich at the rim than at the core (e.9., agreementwith the findings of Rossman(1984). C4 and C5, Table 6). Theseeady crystalsdevelop from Figure 12 is basedon results of WDS electron- Die5HdaAelalong the diopside - hedenbergitetrend, microprobe analyses and energy-dispersionspecta reaching a final composition of about DizzHdzoAer (EDS) and image observationsof specimen5101A. It (Fig. 13a). Beyond this poinl the trend shifts toward shows patterns characteristicof all zoned grains of aegirine [Ca + @4g,Fe2*)-+ Na + Fe]1, with enrich- amphiboleand mica in the dykes: progressivecompo- ment in Ti, accordingto the schemeMg + 2Si -+ Ti + sitional variation from core to exterior paralleling the 2(A1"Fe3')[substitution 4 of Morimoto (1989)]. Tita- color transitions with, in some crystals, a marked nium-rich pyroxenecan be consideredin terms ofthe changeon the extremerim. Table 5 summarizeschemi- hypothetical end-membersCa Mgy"TiAlSiO6 and Na cal trends.In a few grainsofamphibole, an areaoflow Fe*;fUSizO6, with a marimum of 16 mol.VoTi end- density of back-scatleredelectrons (BSE) is evident members(TE), in a TE-Di-Ae system l3b), or 'l..3 @g. within the rim, correspondingto low Fe concentration. mol.Vo, when all end members are consideredo LAMPROITE DYKES. BAFFIN ISLAND 67

TABLE 6. SELECTED COMPOSMONS OF PYROXEMS. PECTOLITEAND FORSTERITE

-oltu- No. ct c2, c3 c4 c, c6 DI Fl F2 13 B- - A- S 432 624 5 2217

Sl02 52.841.tn 5lr8(lo 5r34U1) 5X9(5E) 50.?8(42)5lJ0(55) 53.8100 40.00(ro 38.40(30) 36.16(28) Ti02 r.l5(09) 280(50) 4.(D lr8(ro l.E4(lt) 8.J1Jo <.o2 <.q2 <.02 4.92 a2q 0.6103) 034(08) 0.110o 0.84(20 r.16(01) 02100) 0.03(01) {.02 4.t2 4.4 cDos 0.48(09) 0.03(02) 4.(D 039@) 0.r2-(0t <.o 4.02 4.q2 4.02 4.U2 Faq l.9l 1930 33J0 2.44 4.t9 10.73 o.44 Ln 0.98 0.d) r.6s0t 633(13) o.0dt4) rnQq Ls4(Y, to94(%, o.o5(09) 9.$Q1) l83O(21) 34.7(54) MnO 0.08(02) 036(09) 4.02 0.08{01) 0.10(02) 025(06) 036(10) 0.15(01) 0.40(0D 0.5qm) Mso t7.t2(6) 2.n(lo) 0.0E(04) 16.6121)14.68(3t 1.88(89) 0.1q05) 48.54(lo 41.r8(lo x.64(49) CaO ?-3.92116, 725Q4) 0.1q06) 24.08(2r)22.9(59) J.43(9) 3249(31) 02E(0r) 0.16(14)<.02 SrO && [a @ @ r& 0.0(03) um N62O 0r&o2) 9.r(rt l3rq03) 0Jr(06) 0.80(lo 10.2q49) 93E(0t <.03 <).03 {.03 K2o .o.02 4.4 <0.4 <.02 0.05(04) 0.02(0r) <.02 <.02 4.02 4.t2 IlzO 9.@ S@ s@ s@ 9,@ q@ zse. s@ p.@ p.@ Toel 100,13 9931 9&18 lm,t6 9.54 9.6 99.41 100,17 9.42 Im.m

CfuB Chry t7

si t.931 1.9t6 zw' 1.919 1.92 Ln4 2.9% 0.984 0.990 1.001 0.d29 0.014 0 0.036 0.051 0.010 0.lp2 0 0 0 0,040 0 0 0.045 0.057 0,017 0.002 0.016 0.010 0

Ti 0.032 0.0&l 0 0.035 0.0J2 02,f 0 0 0 0 A 0.0{t) 0.@2 0.@6 0.m 0.@ 0.(x)0 0.0m 0 0 0 0.014 0.@t 0 0.010 0.003 0 0 0 0 0 fe$ 0.013 0.562 0.979 0.021 0.061 0294 0.017 0.01? 0.@9 0.000 Felt 0.0J1 0.n5 0 0.033 0.088 0.3J3 0.@2 0.194 0,395 0.m5 Mn 0.dn 0.012 0 0.002 0.@3 0.@8 0.01? 0.m3 0.@9 0.012 w 0.932 0,121 0.@5 0.910 0.815 0.108 0.013 t.79 1.583 1.182 Ca 0.936 0.301 0.00 0.945 0.917 0.u4 1.938 0.wl 0,@4 0 Sr 0.002 No oCIo o-4 l.@) 0.c2, 0.057 0.765 1.013 0 0 ; 0 0 0 0 0.q)2 0.(x)l 00 0 0

OH 0 0 000 0 l0 0 0

Msl 90.0 t3.7 0.5 88,5 79.E I4.0 39 88.7 n.3 59.5 M; 94.E t00 94.5 902 23.4 85 90.2 m.0 59.5 sirAt 1.960 LW2 2010 1.955 1.943 1.983 /98 0.9E1 0.90 1.001 a 98.0 30.5 0,6 q7.7 94.1 50.8

Sp*im mbw Cl qlslx dloptde, M edgpdyke; C2 gm aegfup - a8Ae,replcd tip of Cl; C3 brcmieh g@@gbbre,ietdrdlfaiqMedgsdy&et c4, C5 aredgrain, m8d dm, !€spec,tirdy,of@lolsd@izL, min tybC6blwttadnatgbbtmryte,fiellf@dyketDl Wtoltu,M edgpdkc6Fl, F2 olorlcs, medoltvbp,ffi md rim, cepwtirely, |E dge dyftE F3 wm€d o/tdr?, n€'t!-ultm8fiq sill 15 kn w€ssontr€st of dyk6 (8@ SI Ih€ ptopqtim oftlF n4io ol€me'Gis qpr6€d I qid€q in wl%. equivalentto 2.3 wt%oTiO2. A small but persistentCr E Il ,). Plots lie mainly below the diopside-aegirine content (normally 0.4 - 0.8 wt%oCr2O) and low Mn trend line on the Di-Hd-Ae diagram (Fig. 13a) and @a.a.l%o MnO) characterizethis early plroxene. abovethe diopside- aegirinetrend on the TE-Di-Ae No *main-line" pyroxene compositions were ob- diagram (Frg. 13b). Grains contain appreciableMn servedbetween Aq and Ae37@ig. 13a),at which point (0.3 - 0.6VoMnO), but no detectableCr. Thesevari- green aegirine-augite appeared. One diopside phe- ants, found in matrix and as overgrowths otr phe- nocryst (areaA), with a compositionAe1, was mantled nocrysts,axe relatively late in the parageneticsequence; by aegirine-augite,Aqo (Fig. 13a;Cl a\dc2, Table 6). in one instance,Ti-rich aegirine-augitemantles potas- Aegirine-augitedeveloped along the diopside-aegirine sium arfvedsonite. fend line as the concentationofTi decreasedfrom ca. Such Ti-rich pyroxenecompositions are not restric- TE40CIE-Di-Ae system;Fig. 13b) to TEo,mainly ac- ted to the Baffin suite. For example, clinopyroxene cordingto the schemeFe?+ + Ti --> 2Fe3*.The aegirine- grains containingup to 87oTiO2 were describedfrom augitecontains appreciable Mn (0.2 - O.4VoMnO) but malignite, syeniteand metasomatized gneiss of the Red little Cr (pyroxenes(all dependson the amountofTi presenl and was ascdbed types)is invariablylow (ca.0.17oSrO). to a strong absorptionpeak centeredat 665 nm (Abu- Some compositionsof blue-greento blue pyroxene Eid 1976). Sfrenset aL (1982) assignedit to a Fd* --> of areasB and C do not follow the trend of "main-line" Tia charge fransfer. The blue-greento blue color of pyroxenes: they are particularly rich in Ti (4.6 - pyroxenegrains in the Bffin suite may be due to the 8.6 wt%oTiO2; e.g., pyroxene C6, Table 6). Depth of samemechanism. color appearsto dependon Ti content,with the most Tetrahedralsites, in colorlessand blue-greencrys- Ti-rich crystalsgving the deepestblue (navy blue with tals, appearto be slightly undersahnatedin Si + Al (e.g., 68 THE CANADIAN MINERALOGIST

Di AE

Ftc. 13. Pyroxenediagrams: a- hedenbergite(Hd) - diopside@i) - aegirine(Ae), and b. CaMgeTieAlSiO6+ NaF€p*3Ti%Si2O6CIE) - diopside @i) - aegirine (Ae). Straight- line arrows (three for simplicity) link cores to rims, curved-line arrows indicate approximatefiend during'hormal" mineraldevelopment. $noxene colors: O colorless (diopside),o green(low-Ti aegirineand aegirine-augite), * blue-greento blue (higl-Ti aegirineand aegirine-augite).

CL, C4, C5, C6, Table 6), but saturatedin deep iddingsite (in the interiors). A micaceousgrey pseudo- brownish green crystals (e.g., C2, C3, Table 6). A morph at F hasthe composition shortage of Al is common in other ferromaglesian Cae.1[Mg5.1FeP+o.eb =6[Si7.6Ahz]2=sO2sI OIIIa silicates(amphiboles and micas) of the Baffin suite. and is consideredto be saponite. Megacrystsof colorlesspectolite occur in dyke A The olivine is magnesium-rich.The core of phe- (Iable 6, Dl). They approacha compositionnormal for nocrysts(four dykes,N = 6) spansthe narrow compo- alkalineigneous rocl6, exceptfor Mn, which is low for sitional range Mgf 88-90. Most of these crystals are pectolitefrom this group (cf, Semenovet aI. 1916). virtually unzoned,but some are enriched in Fe at a nanow rim. Notable is a phenocrystfrom A, where a crystal varies from Mgf 88.7 in tle core to Mgf Olivine 79.3 at the rim; it also containsrp ta 0.4VoMnO. The interfaceis poorly defi:red,and the rim may represent Phenocrystsof fresh olivine, locally approaching Fe-diffrrsion rather than prinary (igneous) zonation. l0 modal 7o, are scaftered.through the marginal and Nickel (0.47oNiO) is presentin the coreof a phenocryst internal chill-zonesbut outwardfrom thesezones, the from D, but was not detectedat the rim and in olivine phenocrystsprogressively were altered and generally from other ocqurences. The rock (area D) contains disappearwithin a few centimeters.Here, olivine is 324 ppm Ni, more than twice the amount of other replacedby phlogopite (on the rims) and chlorite and specimensanalyzed. Olivine grainscontain 0.2 - 0.4Vo LAMPROITE DYKES. BAFFIN ISLAND 69

TABLB 7. TIIE COMPOSMON OF TITANIUM SILICATES

Shchqbalsvtt4-bdlslte buttolmpoprtflil. titeite lorwite No. TSl TS2 TS3 TS4 155 T56 TS7 n 3

Nbro, n.a 0.51 u.& n.& n.a" n.a 1.40 sio2 39.33 39.rE 28.08 27.82 29.030n 35.9000 35.03 Tio, a.ao 23.94 3024 n.70 39.UQo) K.09(24) 45.t3 AI,o3 o.12 0.07 0.46 4.6t o.olol) 0.0(03) n.& c%o: n.a n.a. n.& 027(10) u.a n.a.

Feo 2.70 t.3l 5.49 2.70 0.93(06) 0.43(04) 0.34 MnO 0.06 n.a 1.36 0.51 4.02 4.U2 n.a Mgo 0.08 0.30 0.64 0.35 0.08(0D tr.& n.a. CaO 1.93 0.97 1.08 0.E0 n.MQ0) 0.66QD n.& BaO 12.58 16.U 18.67 ?2.40 n.a. 0,31C2) L&

Nqo 4sE 5.99 7.t4 10.86 0.51(02) 1722(03) t7.74 Kzo 9.39 821 qaA 1.58 0.06(02) 0.08(03) n.& F 0.78 n a, 0.73 1.32 {.10 n.& n.& ct 4.03 La 4.03 0.19 q.03 D.a n.& Hzo a.oe 932 00x 0.09 023 Total 93.71 98.39 98.87 99.93 9t.06 100J6 9a

Cdlom -9__ -12_ 12 - t2- Choge 27.3i 27.51 35.i0 34.64 39.60 36.28 36.13

Si 4.065 4.012 3.t69 3.7t6 3.866 4.Wt 4.031 AI 0.000 0.000 0.075 02u 0.000 0.000 4.065 4.012 3.944 4 4.091 4.031

Nb 0.923 0.073 Ti 1.7t0 r.8u 3.t34 2.7V2 3.991 3.950 3.905 AI 0.0t5 0.008 0.000 o.441 0.011 0.009 ce* 0.013 Fea 0233 0.110 0.633 0.302 0.t04 0.04t 0.033 Mn 0.005 0.159 0.05t 0 0_ MC 0.012 0.045 0.13I 0.070 0.016 4 r.976 r-99s 4.000 4.011 Ca 02t4 0.105 0.159 0.114 3.858 0.08t Ba 0.509 0.6il 1.008 t.t5l 0.014 Na 0.998 1.168 1.908 2.812 0.130 3.804 3.95E K 1,38 1.054 0.q25 0269 0.01t 0.011 : 2,a 2.994 2.990 8.056 8 3.909 3.958

Rock typ€s and localities: TSI Baffin dyke at B; TS2 lmproite, Emmonslviesa, Wyming (Mitchell & Bergmanl99l); TS3 Batrn dyke at D; TS4 ijolite, RedwinoRiver, tabrador (Singh 1972);TS5 Bafrn dylo d D; T56 Baffin dyks at E; TS7 nepholinesyenito, tngedalsn, NoflEy Q-ts€'na aI 199). All iron is assnred divalenl H2Ocaloulded from anioncone4 S/ hclud€s C cationsin TS3 md TS4. The poportion of tho najor elernents,except for F md Cl is oqprecsedas oxides,invt%.

CaO, similar to thoseof volcanic and hypabyssalrocks pretectonicultramafic sill analyzedby the sametech- in general(Simkin & Smith 1970).Cbromium is close nique and the samedata-reduction protocol. to the detectionlimit of the electron microprobe (ca. Olivine from SumnerIsland is similar in composi- 0.02VoCr2O). tion to olivine in the dykesat NapoleonBay. It contains The most distinctive feature of the olivine suite is a small but significant amountof Ca (0.3VoCaO), and a low silica content.All olivine grains studiedare Si- low levels of Mn (0.1-0.2VoMnQ), Cr (ca. 0.05Vo depleted(nepheline syenite in the Kola 70 TI{E CANADIAN MINERALOGIST

MnO (\rff/")

0.1

0.05

R c oo .a

no,0t %)

Ftc. 14. Concentrationof TiOz versrc that of MnO (wt7o)for lamprophylite - barytolam- prophyllite (circles;L), scherbakovite-batisite(squares; S) and lorenzenite(diarnonds; R). Open symbolsrepresent compositions of minerals,worldwide, derived ftom the following sourc€s:L, Pecora(1942), Semenov(1972), Sineh (1972), Yakovlevskaya (192), Kostyleva-Labunstovaet aL (1978), Johnsenet al. (1994), RA. Gault (Mont Saint-Hilaire, unpublished); S, Kostyleva-Labuntsovaetal (1978), laquLeset aL (1986), Schmall & Tillmanns (1987, calculatedfrom given formula); & Sahama (1947), Semenov(1972), Ferguson (1977 , 1978),Kostyleva-Iabuntsova et al. ("nm- sayite', 198), KarupMOller (1986).Solid symbolsrepresent minerals from the Baffin dykes. Manganese(MnO) values given as '"below detection", "not detected" and *

zSttOA, Peninsul4 Russia @s'kova & Kazakova 1954),peral- hasbeen identified from aegirine-arfvedsonite kaline volcan:icrocks at Eifel, Germany('"batisite" of pegmatite in ttre Aldan Mountains, Russia, only Hentschel 1980, Schmahl et al. l98I) and lamproite (Kravchenko & Vlasova 1959), but "shcherbakovite" from West Kimberly, Austalia and Leucite Hills, from lamproite of the Leucite Hills (Mitchell & lYyoming (Mitchell 1990,Mirchell & Bergman1991). Bergman 1991) has Na slighfly dominantin A and is, Its sodium counterpart,batisite, ideally A[BaNa2]ti2 therefore,just within the batisiterange. Minor substitu- T.AMPROITE DYKES. BAFFIN ISLAND 7L tions in the shcherbakovite- batisite seriesinclude Ca for K M, Mg, Fe, and Mn for Ti, A1 for Si, and OH, Cl and F for O. Tiny, round, greylsh green grains occur in sanidine derivedfrom leucite, in a Baffin dyke (areaB). Analy- sis of the largestgrain gavea low total, possiblyowing to failure to determineM2O5 and SrO, but its compo- sition (Table 7, TSl) agreeswell with the structural forrnulaof Schmahl& Tillna:ms (1987):@a,K)(K,Na) Na(fi,Fe,Al,Mg"i\4n)2si4o14.It is here comparedwith the Leucite Hills batisite (Iable 7, TS2). Barytolnmprophyllite,a minor mineralin felsic alka- line rocks, ijolite and related peralkaline pegmatites (e.9., Kostyleva-Labuntsovaet aL 1978, Iobnsenet al. 1994), has not been reporled from lamproite. In the Baffin dykes, it is tentatively identifled in a polished thin seption from the southern dyke at D, where it showsextinction parallel (or approximatelyparallel) to a well-developedtwin parting and crystal extension, FIc. 15.ACZ plot of schcherbakovite-barisite(S) and loren- positive elongation,and strongpleochroism (X yellow, zenite(R) in alkalineand ultrapotassicrocks. Rounded Z brown), all propertiesthat overlap those of phlo- axeasdelimit I I compositionsof S givenby Prider(1965), gopite nearby. It is, however, readily distinguished Kostyleva-Labuntsovaet al, (1978),Jaques et al. (1986), from phlogopite by a much brighter BSE image and schmabl& Tillmanns(1987), Mitchell (1990), Mitchell & pronouncedBa peakwith EDS.The grainsare tiny lamel- Bergman(1991), and 19 compositions ofR givenby Sa- la€,dispersd in sanidinein two partsofthe section. har:rra(L947), Semenov (1972), Ferguson (1977, 1'978), A[NaBa2]c;NaFd- Kostyleva-Iabuntsovaet aL (1978),Karup-Moller (1986), The series barytolamprophyllite (1992).Ideal compositionsare shownby a[NaSrz]c[NaFd* l-arsenet aL TglzSqOls - lamprophyllite crosses,minerals in theBaffrn dykes by a solidsquare (S) TralzSiaO6is completein nature @engTze-chung & anda diamond(R). Chang Chien-hung 1965, Yakovlevskaya1972). The mineral in the Baffin dyke (fable 7, TS3) is strongly skewedto the Ba side,although up to l%oSrO could be presentlocally. In addition to the elementsspecified in In the Baffin dyke at E, lorenzeniteis presentin the formulae,imFortant substitutions are evidentin the fine-grainedpatches in the coarsefraction ofthe rock. liierature, viz. K rn A, A[ Fe3*,Mn, Mg and Ca in C Normally, the patchesare zoned with a core of loren- N n Z, F and OH for O. The compositionof X-ray- zenite,surrounded by two unidentified Ca-Zr silicates, identified barytolamprophyllite from Labrador aNa-Zr silicateand aMg-Ti silicate,t}roughoutwhich (Iable 7, TS4) is comparedwith that of the Baffin minute grainsof TiO2 and calcio-ancylite(Ce) produce specimen(Table 7, TS3). bright spo* on the BSE image. Toward the edge of In the Baffin dykes, titanite can attain 2Vo b the these patchesare local concentrationsof one of the mode and 0.4 mm in long diameterof crystalsin the Ca-? silicatesand a K-Ti oxide. At the extremerim coarse-grainedfraction near the dykes' center. This are irregular accumulationsof titanite. titanite Clable7, TS5) hasan unusuallyhigh contentof Tiny colorless prisms of lorenzenitealso occur in alkalis, a featurethat appearsto characterizethe mineral microveinletsthat cut wallrock and parallel the contact in alkaline and peralkaline igneous rocks. In other of the dyke at areaE.The veinletsare lined with fib'rous 'onepheline" aspects,the compositionis normal. Much of tJle 2Vo and filled with glass.In Table 7, the com- deficitin total is probablydue to thepresenceof Nb,l,a position of lorenzenite from Baffin Island CIS6) is Nd and Sr (not determined).The mineral also occursin comparedwith that of lorenzenitefrom Norway (IS7). lamproitesfromWestem Ausfralia (Jaqueset al. 1986, In the Ti silicates, Mn appearsto be enriched in p.53). the order lamprophyllite - barytolamprophyllite > Inrenzenite, a common accessorymineral in peral- shcherbakovite- batisite = lorenzenite,and Ti, in the kaline sysnit€an6 granite, some cases of phonolite,and orderlorenzenite > lamprophyllite- barytolamprophyl- pegmatiticpockets (e.9., "ramsayite"of Kostyleva- lile > shcherbakovite- batisite (Fig. 1 ). Eachmineral Labuntsovaet al. L978. De Mark L984. I-asen et aL hasits own domain of composition,so that, along with L992), has a composition that normally approaches other data Mn and Ti can be used to discriminate aNa+ti+zSi+O1s,but minor amountsof Ca" K and Sr betweenthe three groups. The compositionof loren- substitute for Na whereasNb, A1, Fe, Ce and Mn zenite is compared with that of shcherbakovite - substitutefor Ti, and F and OH for O. batisite,with.respect to A, C aridZions,in Figure15. 72 T}IE CANADIAN MINERALOGIST

TABLE 8. SELECTEDCOMPOSITIONS OF OX]DBS

tuIqgretlte chromlle ulv:&phel lhsqile Ti-Fe-K6tde No. xl x2 x3 x4 x5 x6 x't x8 n I 5 7l t4 4l

Nbror n.a &a <.03 n.& 4.03 4.03 0.3600) tr.4 siq

V:Q o 0.r0(02) 028(04) n.a 0.s 0.0q02) 0.6e(0o tr.& c€ro: LA n.a LA n.a [a n.a 0.60(07) [& F%q 6E.46 9.92038) 30.91165121.03 0.@ 131(r) 1.3561 6.68 FeO 3120 zu.)f, 47.45 4',t.76 34.41 N.89 6.17 lvltrO 4.U2 0J6(18) r.47(27) 1.lt0 rr.76 4.5439) 4.O2 n.a

7^O

Cdto6 24- -4- -88- Choge 64- *12- -32-

Nb 0* 0 0 0.019 Ti t 0.740 4.376 s.444 1.988 t.973 7.t45 ,.r* AI 0.069 2.020 0.163 0303 0.015 0 0.003 0.003 Cr 0.07 10.447 0.@5 0.m6 0 0 0.@8 0.03: v 0.059 o.c2. 0.070 0.026 0.003 0.065 o,v26 Fo} 1;; -" 7.010 4.74 0 0.051 0.119 o.577 Fel 0 o.74 4.976 5.444 0 0 0.606 0.336 Mg 0 0.000 0.000 0 -s -s 0.frD : 2p l6 t6 16 t6 2.O3 2.O3 8 8

Fs& E.000 3.935 7.5E3 6.624 t.442 rJ6o 0 0 Mn 0 0.130 0.385 0.358 0.498 o.t97 0 0 7a 0 0.020 0_ 0.(m4 0 Mg 0 3.N4 0.031 1.018 0.017 0.013 0 0 Cg 0.012 00 0.010 0.003 0.M8 Ba 0 *" K : : : 1 144 J26C 21 8 888 t.97 1.97 1.38 128

Rockl}.ps @d lslitios: Xl didme, Kodhm; XZ X3 Baffii dykod B; X4 Iampmib,Kapamba, Zmbia (Scor Snith, in Mtohel & Bergmrnl99t); )<5,X6 Batrn dyktr d B, E; XZ Baffin dyked F; X8 Iamp'roited Sbinft4 creenland(Sco lgSl). TIteFoportion ofthe najor olememis o.trssGd asoxidos, inwL%.

Oxides growth resemblesthe "sandwich type" of Haggerty (1991).Equilibrium conditions of thepair areT=967 X Titanium-free megnetiteoccurs sparingly in diahe- 30oC,at a 1ogflO) of ll.2 t 0.3 and AFMQ +0.07, mes at Kodlunam and as a contactmineral in anortho- using the reduction of Andersen et al. (1993). T\ts, site at the Discovery Dyke. Tiny grains of chromite, equilibrium was attained in the subsolidus,slightly ilmenite and a Ti-Fe-K oxide are disributed through abovethe oxygenfugacity of the fayalite - the Baffin dykes and the volcanic rock at Sumner quartzbuffer. The texture may representthe oddafion Island.An iilvospinel-ilmeniteintergrowth was observ- of ilmenite to a magnetitephase, but the paragenetic ed in the DiscoveryDyke. Compositionsof oxide min- relationship with nearby chomite is unknown. A erals from the Baffin rocks, and of similar iilvospinel composition CX4) of a similar spinel mineral is pre- and Ti-Fe-K oxide, from Zambn and Greenland, sentedfor comparison. respectively,are listed in Table 8. $mall crystals of interstitial ilmenite (e.8., Table 8, The iilvospinel - ilmenite intergrowth is presentin X5 and X6) are presentin all dykes.As in lamproites the coarse-grainedfraction of the dyke. Here, ilmenite worldwide Mtchell & Bergman 1991, p. nG278), (Xs"- - O.LLL;2.3VoMnO, O.lVoMgO) coexistswith the ilmenite is rich in Mn (2.3 - LL.8VoMnO), but poor iilvospinel CKrurug= 0.443:Table 8, anal.X3). The inter- tnCr (<0.O2VoCr2O3) (Iable 8, X5, X6). It differs from LAMPROITE DYKFS. BAFFIN ISLAND 73

ilmenite in most lamproitesby the virtual absenceof 100 Mg (0.1 - 0.3VoMgO), but it containslevels of Mg similar to that in ilmenite in lamproite from Sisimiut trtr (T\y et aL 1987). o f-ry' *o Spinel was observedas minute octahedrain olivine, 80 diopside and pseudoleucitein three dykes and the t SumnerIsland volcanic rock. It is rich in Cr A2497o Crt Cr2O3)and Ti (34Vo TiO), but poor in N (3-:7Vo Al2O) andMg (Z-ll%o MgO), resemblingspinel from 60 certain Alaskan-typeperidotites (rvine 1967, 1974), orangites(lr4itchell 1995) and lamproites (Ivlitchell & Bergman 1991). Spinel from the Baffin suite is com- pared with spinel from establishedexamples of lam- 40 proite in Figwe 16, anda composition(X2) is presented 't2 in Table8. The Baffin spinel, chromitesensu stricto, resembles spinel of groups 2 and 3 of Mtchell (1985), although 10 the compositionhere may not be primary. Both Fef (Frg. 16) and Fe* (48.7-89.0) vary considerably,with 8 iron concentated on the rims of crystals, suggesting that the mineral has been hydrotlermally altered Tif (Kimball 1990).This model is in accordwith the wl- 6 nerability of tiny grains (<50 pm diameter)to altera- tion. It explainsthe departureof the two most Fe-rich 4 populafions from the field of spinel typical of lam- proite. Nevertheless,because Crf is relatively constant within the three rock variants, and becauseFet of 2 chromite from an internal chill-zone overlapsFef of chromitefrom the coarse-grainedinteriors of the Baffin 0 dykes,the hypothesisof secondaryenrichment in iron 40 60 80 100 must be regardedas tentative. FET An opaque,Ba-free Ti-Fe-K oxide (Iable 8, X7) occursin dykes at A, B, E and F. It is normally anhe- Flc. 16. Chromite diagram,with Fet plotted againstCrt and dral, but in somecases shows rectangular sectionso and Tif. Broken line circumscribesthe field of lamproite, includes 18 datapoints taken from Mitchell (1985) in reflectedlight is distinctly aniseflspig.This which mineral and Mirchell & Bergman (1991). Symbols: O crystals appearsto be similar to an oxide from lamproite at from an internal chill-zone of dyke, u crystals from the Sisimiut (Iable 8, X8), syeniteat Liule Murun (Siberia) coarse-grainedinterior, * crystals from Sumner Island and orangeitein the Lace, SoverNorth and Star occur- volcanicrock rences (South Africa). The composition is close to K;T!13O7 (Mitchell 1995, p. 21,3-216).However, its compositioncan also be representedby a generalhol- landite formula AtBaOrc,calculated according to cat- ions and charge(Iable 8; X7, X8), with considerable galen4 sphalerite,perovskite, pyrite, dolomite, calcio- shortfall of A cations,and Fe2+as well as Fe3tin B. ancylite-(Ce),strontianite, baxite and zicon. The remaining minerals are mostly distributed throughthe groundmass.By far the most cornmonare DIscussIoN flwrapatite, calcite andpyrite. Tiny, roundedgrains of a mineral giving the distinctive EDS signatureof djer- Lamproitesworldwid.e and the Bffin roclcs: fuherite (ideally, K6l.{aFe2aS26C1)occur in dykes at B mineralogicalsimiLa.rities and dffirences and D (major peaksat S, K, Fe; minor peaksat NA Cu; smallerpeaks at Cl, Ni). Calcite associatedwith brown Minerals in the Baffin suitesupport a lamproiteclas- amphibolegives a mottled BSE image, with low BSE sification. The rocks are porphyritic, with phenocrysts intensitypertaining to minorMg (0.lVoMgO),Sr(0.17o ofphlogopite, leuciteand sanidine(more rarely, olivine SrO) and Ba (

o Ac pohsslum rnagnesbadvedsonits (cdE) O Av potassfummagneiqatfvedsonfte (wergrodt) o Ax potasetumarlvedsanite(ederkr)

E Ma phlogophe (oote) 20 v Mv phlogoplte &lenlphlogopite (o/ergronfi) r Mx annite &feni-annite (exterior)

Oo torsterite (ph€nocry€G,cote) DFu dlopeldE(undMded)

15

A

10

20 40 100 Mgt Flc. 17. Percentagedeficit of Si + A1, A in the tetrahedralposition rersus magnesium number, l@ Mg/(Mg + Fe) = Mgt, in micas,amphiboles, diopside and olivine of the Baffin dykes.Individual plots of undifferentiateddiopside @i-q N = 1l) and olivine cores(Oc, N = 6) havebeen omitted for simplicity.

p. 37-38) are met For example,major Ti and K in the depletedin Si + ryAl. Determinedas A = l(D (zdear- Si samemineral chuactstizn certain silicatesand oxides -NlJ)l4a*t, theseminerals give the following average of the Baffin suite and lamproites worldwide (e.9., compositions,listed in descendingorder oftetrahedral- amphiboles,micas and shcherbakovite)obut are rare site deficit titanian annite and ferri-annite margins 'Terriphlo- co-constituentsi1 minsrals from other environments. L5J (3.2)Vo,N = 7, titanian phlogopiteand Other typical variantsare low-Fe olivine, low-Na diop- gopite" overgrowths8.4 (2.5)Vo,N = 6, titanian phlo- side (the most commonpyroxene in the Baffin suite), gopite cores7.2 (1.O)Vo,N = 8, potassiumarfvedsonite Fe-rich leucite and sanidine and Ti-rich chromite. margins7.2 (7.6)Vo,N = 6, potassiummagnesio- "fletral ferriphlogopite" is present(though rare), but arfredsonite cores 4.7 (0.6)Vo,N = 3, diopside cores plagioclase,melilite, monticellite and garnet(all types) 2.4 (O.4),N = 11, forsteritecores 1.8(0.3),N = 6, are absent.A nepheline-likephase appears, but only as potassium magnesio-arfvedsoniteovergrowths a reactionrim at the contactwith feldspathicwallrock; 1.5 (0.4), N = 3. Mineral groups show a tendency kalsilite is a breakdownproduct of leucite. for tetahedral-sitevacancies to increasewith decreas- Mrchell (1985) and Mitchell & Bergman (1991) ing magnesiumnumber (Fig. 17), but aegirine and have noted that in lamproites,micas, amphibolesand aegirine-augiteare within the limits of error. pyroxenescommonly'tontain insufftcient aluminum Certainminor mineralsin the Baffin dykeshave not [i.e., Si + Al] to filI the tenahedralsites". In the Baffin been heretofore describedfrom lamproite. New are dykes,all micas,amphiboles, forsterite and diopside are pectolite,baaytolamprophyllite, calcio-ancylite-(Ce) and LAMPROITB DYKF.S. BAFFIN ISLAND 75

TABLE 9. COMPARISON OF LAMPROIIE FROM SISIMruTANDNAPOLEONBAY

Sistrzttn Nryokon Bay Phrogopitsag{s) l24O* 130,1227 + 12 my. (KlAr) r24O*9,(K/AI)

Intrusives narrowdykes narrowdykes

Dispositionofdykc BWtoNW-SE, vertical BW to NW-SE,vertical

Chill zones marginalmd internal marginaland intrrnal

Iare fednos of dykes reopeningcarbonatization rspsdng; carbonatization

Dyko textur€ porphyritic porphyritic

PhenocrysB phlogopite,pseudoleucite, olivine, phlogopito,psoudoleucite, olivine, diopsidomost common diopsidemost common

Olivine forsleriio,fo 87-93,ave A={ forstoite, fo 8G92,ave A=1.8%

Eadypyrorcne diopside,02-1.9% TiO,, 0.2- diopside 4.02-2.3% TiO,, 0.G 1.0%Al2O3, ave A=1.0 l.3o/oAJ2O*avo l;2.4

Amphibole normallyK-ricb, alkali amphiboles normallyK-rich" alkali amphibolos common,Na-Ca amphiboles less oommorgNa{a amphibolq less comnon,ave A=2.2 common,avo A=4.5

Phlogopite iron enrichmentm margin, iron miohment on margirg 2.8- I0.3o/oTiOaweL=7.4 29 - 9.0% TiOv aveL=11.4 'femiphlogopito' Overgrowthsonmica "feniphlogopite', 19.4-20.V/o andphlogopite, MgO,aveA=16.9 12,2- 19,3o/oMgA,ave A=8.4

lsucitg, sen&rsfrcta rare,in marginalchill zoneonly rare,in internalchill zoneonly

Pseudoleucite oommon ommon (sanidine+ kalsilite)

Sanidine common,0.1 - 3.E%Fe2O3 common,0.l- 1.6%Fe2O3

Carbonate oalcitolocally mmmon oalcitelocally common

Sourcs: ,Srrinira- Br@ks et aL (1978),t*rsen et a/. (1983),Scofi (1977, 1981), Thy (1982),Thy el a/. (1987),Winter (1974) Nqoleon Bay - GaL Surv.Canada (unpublished K/Ar age).

lorenzenite,mingrals characteristic of peralkalineinfru- part ofthe Tertiary north Atlantic volcanicprovince, on sive suiles, and djerfisheriteoa phase noted in peri- the coast of Baffin Island 450 km NNE (Clarke & dotites, kimberlites, and chondritic meteorites.Rather Upton 1971). different from most lamproitesare the high elkali and Of the variousultrapotassic rocks describedto date, iron contentsof someminerals in the dykes.Potassium the Baffin dykescorrespond most closelyto lamproites arfvedsonite,annite and aegirineare not characteristic near Sisimiu! in west Greenland.This similarity is of lamproite,though eachhas beenreported. summarizedin Table 9. The Sisimiut lamproiles are The diatremeson Kodlunam, chokedwith xenoliths 700 km northeastofNapoleon Bay, and the correspon- but cementedwith peraluminousand high-potassium denceof dyke trends suggestsa post-intrusivesepara- glass, are provisionally placed in this volcanogenic tion of Baffin Island from Greenlandin a sinistal suite and consideredto be a forerunner of the Baffin sense.without rotation. dykes.This coupling is madeby analogyto other lam- Lamproites are generally restrictedto mobile belts proites,where an eaxlyexplosive facies is presentin the surroundingcontinental cftrtons (Mirchell & Bergman majority of occurrencesO4itchell & Bergman 1991, 199L,p.406). The Baffin and Sisimiut dykes,lying at p. L37-1,57).Glass in Precambrianrocks requiresspe- the edge of the North American cratonofit admirably cial conditions for preservation,and is rare. Another into this frarnework As with many other occlurences, model, which cannot be summarily dismissed,states the lamproiteswere not emplaceduntil tensionalftac- that the diatremedykes may be manifestationsof Ceno- tures permitted inffoduction of subcrustalmelts, long zoic volcanisrn,which includes exftusion of basalt as after the last deformationhad ceased. 76

CoNcLUsIoNs REFEREI.{CES

Mineral developmentin the Baffin suitecan be sum- ABU-ED, R,M. (1976): Absorption spectra of transitional marized,tentatively, in the following stages: metal-bearingminerals at high pressures.In The Physics and Chemistryof Minerals and Rocks (R.GJ. Strens,ed.). 1) Innusion of diatremedykes and sills. Cementation Wiley, London,U.K. Qn-346). with peraluminous,K-rich glass(Kodlunam Island). 2) Emplacementof lamproitedykes (NapoleonBay) AmsRsmlr,D.J., Lnvosev, D.H. & DAvDsoN, P.M. (1993): and lamproite flows (source of the Sumner Island QUILF: a PASCAL program to assessequilibria among pyroxenes, quartz. cobble).Characteristic minerals: forsterite, phlogopite- Fe-Mg-Mn-Ti oxides, olivine and Comput,Geosci. 19, 1333-1350. annite, diopsideoleuciteo sanidine. Late-stage alkali amphiboles.Main chemicaltrends of micasand amphi- BLAcKADA&R.G. (1967): Geologicalreconnaissance, soutl- boles:Fe-emichment, and depletionin Si, Al, and F. ern Baffin Island" District of Franklin. Geol. Sarv. Can, 3) Cooling, solidification andfracturing of lamproite Pap.ffi47. dykes. BRooKs"C.IC, Nos-NvcAARD,A., RDq D.C. & RoNsBo,J.G. 4) Introduction of new material along fractures. (1978): An occurence of ultrapotassicdikes in the neigh- Characteristicminerals: overgrowths of aegirine and bourhood of Holsteinsborg,west Greenland,Bull. Geol. aegirine-augite,phlogopite and "feriphlogopite", mag- Soc,Dennnrk?.i1.l-8. nesio-arfuedsonite.Compositional tends of pyroxene: enrichmentin Na, Fe. Possibly,pectolite belongs to this Cmnxr, D.B. & Uprot.t, B.G.I. (1971): Tertiary basalts of generation.Calcite postdates magnesio-arfvedsonite. Baffin Island: field relations a:rd tectonic settins. Ca?"J. Earth Sci.8.248-258. 5) Post-consolidationeffec8: phase inversion and exsolutionof leucite; oxidation of ilnenite. CUNDART,A. (1973): Petology of the leucite-bearinglavas in The chemicalevolution of mineralsduring stage2 is New SouthWales. J. Geol. Soc.Awtralia 20.465492, an extreme example of magmatic differentiation, but the abrupt efuangefrom stage2 to 4 requiresan over- Cunns, L.W. & Grnws, J. (1979):Aluminous andtitaniferous haul ofthe systemand presents a specialproblem. Stage clinopyroxenesfrom regionally metamorphosedagpaitic 4 may representpostmagmatic, hydrothermal develop- rocksin cenfal Labrador,J, Petrol.20. 165-186. ment although very sharp zoning in some amphibole DE MAR& R.S. (1984): Minerals of Point of Rocks, New crystals favors magmamixing and introduction of an Mexico.Minzral. Rec. 15, 150-156. H2O-saturatedsilicate melt. However,amphibole-lined cavities,filled with low- to moderate-Mg,low- to mod- Es'rovA, E.M. & Kazarova, M.E. (1954): Shcherbakovite- erate-Srcalcite, imply late-stagecirculation of hydro- a new mineral. DoH. Akad iVarz&SSS.IR 99.837-Ml 6n thermal, CO2-rich fluid. That Precambrian glass Russ.).Abst tn Am. Mineral.40. 788. survives in the contact zone imptes the melt was quenchedand was not followed by later introductionof FERGUSoN,A.K. (1977):Note on a ramsayite-bearingpegna- H2O or by a thermal event. toidal clot in a mela-nephelinitefrom the older volcanics near Bacchus Marsh, Victoria- J, Geol, Soc. Aust. ?4, 49t494. ACrc{owr-EDGEvm.lTs (1978): The occr.rrenceof rarnsayite,titanJivenite Thanks are due to the following personsfor conhi- and fluorine-rich eucolitein a nqrheline-syeniteinclusion butions to this reasearch:Bill Fitzhugh (Smithsonian from Tenerife, Canary Islands. Contrib. Mineral. PetroL 66. 15-20. Institution) and Reg Auger (Universit6 Laval) for in- cluding the author in their field parties of 1992 aad G['rr.rs, J., FAw@rr, J-I., BRooKs,C.K. & Rum.ocg J.C. 1994; Andr6 Gonciar and PaulusiePishultie for field (1980): Intergrowths of nepheline- pota$siumfeldspar assistance;Scott Ercit Glenn Poirier and Peter Jones and kalsilite - potassiumfeldspar: a re-examinationof tle for help with electron-microprobeanalyses; George 'pszudelzuciteproblem' . Contrib.Mbcral PetroL73, ll9-L26. Rossmanand BarbaraScott-Smith for valuablediscus- sions; Roger MitcheU and Steve Bergmanfor writing Gomlano, F. (1909): Sur les groupementscristallins de l'oli- the definitive text on larnproites,which facilitated com- vine de Maillargues (Cantal). BUIL Soc.fr. Minlral. 32, parisonsand from which many ideas in this paper are 81-82. based. Helpful comments by Dan Barker (referee), (1991): - mini-atlas. Keith Bell, (referee), HAGGRTY,S.E. Oxide textures a Rav. SteveBergman NelsonEby, Tony Mineral.25, 129219. Fowler, Bob Martin and Tony Petersongreatly im- proved the manuscript.H6ldne DeGouffe and Sylvie HB{rscIrE, G. (1980):Weiterebemerkenswerte Mineralfunde Downing typed the manuscript. Computer drawings aus quartiiren Vulkanvorkommen der Eifel. Mairaer were madeby EdwardHearn. geowis s. Mitt. 6, L69-17 2. TAMPROITE DYKES. BAFFIN ISLAND 77

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SAHAMA,T.G. (1947): Analysis of ramsayiteand lorenzenite. Swcn, S.K. (1972):Petrolagical andMh.eralogical Sudies of Am. Mineral. 32,59-63. the Joan la*e Agpaitic Compbx, Centrallabradon Ph.D. thesis,Univ. Ottaw4 Ottawa,Ontario. Scanrg C.M., Lunr, W.C. & ftrrn B, O.F. (1966):An experi- mental study on the absenceof leucite in pluonic rocks. SrREIIS,RG.J., MAo, H.K. & BFrr.,P.M. (1982):Quantitative Am" Mineral. 51, 726:735. spectraand optics of some meteoritic and Grre$trial cli- nopyroxenes./n Advances in Physical Geochemistry Scnaenr. W.W. & T[:uemw, E. (1987):Isomorphic substi- 2 (S.K. Saxena,ed.). Springer-Verlag,New York, N.Y. tutions, straight Si-Ni geometry,and disorderof tetra- Gn-346). hedral tilting in batisire, @a K) (K Na) Na CIi, Fe, Nb, Zr) S4Os. NeuzsJahrb. Mineral., Morwtsh., 107-118. Tnr, P. (1982):Richterite - arfvedsonite- riebeckits- actino- lite assemblagefrom MARID dikes associatedwith ul- & ASRAHAI{,K. (1981): Struktur und trapotassicmagmatic activity in cenfal west Greenland. Kristallchemie von Batisit aus der Westeifel. Fortschr. Tena Cognita 2, 247-249. M ineral. 59(l), I7 +l'7 6. Srscrm" O. & KopsrcAno, J.A. (1987): Mineral Scorr, B.H. (LTl7): Petrogmzsisof Kimberlites and.Associ- chemisry and crystallizationsqpences in kimberlite and ated Potassic Lamproplryresfrom Central West Green- lamproitedikes from the Sisimiut area cenml westGreen- lard Ph.D. thesis,Univ. Edinburgh"Edinburgb, U.K. latd- Lithos 20. 391417.

(1981):Kimberlite and lamproite dykes from Hol- Vmss, G.I., MERENKovA,T.B. & Osrnovsxm,I.A. (1955): steinsborg,west Greenland.Medd- om Gr4nlan4 Geosci. Syntheticironhydroxyl mica-Dokl.Akad Naal

Scorr, DJ. (1996): Geology of the Hall Peninsula,east of Wtrrrm, J. (194). The hecambrian geologyof the Tfngamit Iqaluit southern Baffin Island, Northwest Territories. nunat arca outer Nordre Strgmtor4 cental west Green- Geol. Surv. Can, Cunent Res.196C, 83-91. land, Rapp. GrlnL Geol. Undzrs.6|.

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