673

Tlu Canadian Mhe ralo gistVol. 35, pp. 673-6n 0997)

THE PHOSPHORUS.ENRICHED, S.WPE MIDDLE RIVER RHYOLITE,TETAGOUCHE GROUP, NORTHEASTERN NEW BRUNSWICK

DAVIDR. LENTZ1

New Brmswick Geological Suneys Brmch, Depanmznt of Naural Resources and' Enzrgy,P.O. Box 50. Baharst, New Brm"rwi* E2A 3ZI

ASSTRACT

In the Middle River area of the Bathurst Mining Camp, northem New Brunswick, lenses of flow-banded rhyolite are undedainby middle Ordovician sedimentary rocks of the Mramichi Group, and overlain by shales and wackes of the Tetagouche Group.The least-altered rhyolites have microscopic spherulites in which the alkali feldspar contains up to 0.32 wt.Vo PzOs @erlinitesnbstitution). These high-silicarhyolites are peraluminous (l.l <ASI < 1.4) with very low TiOz (0.043 to 0.053 tttt.Vo),7-,r (36to42 ppm), Th (1.5 to 24 pp ), Y (9 to 14 ppm), Nb (12 to 14 ppm), V (<1 to 3 ppm), Sc (2 to 3 ppm), and rare-earth elements(ZREE between 16 and 19 ppm), but have elevated PzOs contents (0.2 and 0.3 wl./o). Their high Nb/Y (>0.7), TalYb (>4.3)'

M/Ta (<6) and Rb (>2@ppm) values indicate an S-typeparentage, which is consistentwithft6 high 6180 value (13.4w 15.4%o)for three least-altered samples of rhyolite. The felsic magma is interpreted as a product of fusion of supracrustal rocks, associatedwith heal advection from intruding continental backarc mafic magmas; tle magma then underwent low-t€mtrErature fractionationofFe-Ti oxidas, zircon and apatite.

Keywords: S-type rhyolite, high-silica rhyolite, phosphorus enrichment, Tetagouche Group, Bathurst Mining Camp,New Brunswick.

SoraMans

Des lentilles of rhyolite h texture due b l'dpanchement ont 6t6 d&ouverles dons la rdglon de Middle River, dans le camp minierde Bafhunt, dans le nord du Nouveau-Brunswick ces coul6es recouvrent un socle de roches s6dimentaires d'6ge ondovicienmoyen du Groupe de Mramichi, et sont recouverGs de shales et de wackes du Groupe de Tetagouche. I,es rhyolites les moinsalt6r6es contiennent des sph6rulites microscopiques riches en feldspafh alcalin contenant juqld 032Vo de P2O5 par poids, lephosphore y 6tant incorpord selon la substitrtion dite "bedinite'. Ces roches d teneur 6lev6e en silice sont hlperalumineuses(1.1 < ASI < 1.4), avec des teneurs tOs faibles en Ti (0.M3 d,0.053Vo par poids de TiOd ,7t (36 d 42 ppm), Th (1.5 i 2.4 ppm),

Y (9 n 14ppn), Nb (l2 n l4ppm), V (<l d3 ppm), Sc (2 i3 ppm), eten terresrares @?lR entre 16 et 19 ppm), mais slles montentune teneur 61ev6e en P (PzOs en[e 0.2 et 0.37o par poids). L,a valeur 6lev6e des rapports NbAf (>0.7), TaNb (>4,3), et M/Ta(<6), et la teneur 6lev6e en Rb (>200 ppm), font penser b un ant€c6dant m6tas6dimentahe, ce qui concorde avec les valeursdlev€es en 6180 (enne 13.4 et ll,AVoo) de tois &hantillons relativement frais. Ces rhyottas repr6,senteraient las produiS de lafusion partielle de roches supracustales, cette fusion 6tant attribuable i lapport de chaleur associ6 avec la mise en place demagms mafiques dans un milieu d'arri0re-arc; le magna semble avoir ensuite 6volu6 par fractionnement d'orydes de Fe-Ti,zircon et apatite i faible temffratme.

(Traduit par la Rddaction)

Mots-c6s: rhyolite de type S, rhyolite siliceuse, enrichissement en phosphore, Groupe de Tetagouche, camp minier de BathurstNouveau-Brunswick

INTRoDUcnoN

knses of rhyolite occur at three places at the contactbetween middle Ordovician mature carbonaceoussedimentary rocks of the Parick Brook Formation(Miramichi Group) and the immature carbonaceoussedimentary rocks of the Boucher Brook Formation(fetagouche Group), along the autochthonous eastern

margin of the Bathurst Mining Camp, northern NewBrunswick (Figs. l, 2; l*ntz et aL 1996). The hostsedimentary sequence, interpreted as distal turbidites(Patrick Brook Formatioq), is tansitional upward intoa starved ocean-basin environment with minor volcanicinput @oucher Brook Formationa I'ettz et aL t996).This submarine bimodal volcanosedimentary sequence(Ietagouche Group) formed along the rifted eastem

I E-mail address: dlentz@gov.nb.ca

674

Fto. 1. Geology of fhe northeastem part of tle Bathurst Mining Camp (after van Staal et al. l99l). This study area (inset Fig. 2)is shown with respect to the Brunswick No. 6 and 12 and Key Anacon massive sulfide deposits, New Brunswick"

continental maxgin of an evolving backarc-basin system(Iapetus tr: van Staal L987, van Staal et al. 1991, vanStaal & Fytre 1995). Interestingly, the rhyolite in theselenses has a preliminary U-Pb zircon age (= 480 Ma;I-.entz & McNicoll, in prep.) tlat seems to be slightlyolder than ttre oldest known felsic volcanic rocks(472to 476Ma) in the Tetagouche Group (Sullivan &van Staal 1996, Rogers et al. 1997). Therefore, thisrhyolite may represent the fint episode of magmatismin the inner protoarc-backmc system. Although consid-erable deformation occurred druing the eady stages of theAcadian Orogeny, with coincident middle-green-schist-facie,s metamorphism in this part of the camp,there are low-strain windows that permit interpretation ofprimary volcanic and sedimelrtary feaffiel The,se distinc-tive lenses of rhyolites were re-examined and re-analyzed toenhance stratigraphic correlations along the BrunswickBelt, examine the limitations of some trace-element discri-mination tecbniques, and determine their petrogeneticsignificance.

DEscRIPfioNoF RHYoUIE I.EI{sEs ANDTIDIR STRATTGRAPIilc SETTtr.IG

In all three lenses, the rhyolite has a prominent flow-foliation (Figs. 3, 4a) oriented perpendicular to theinferred contacts and cut by several synvolcanic dikes.Pebble to cobble conglomerate of the Panick BrookFormation occurs discontinuously along its base.Coarse rhyolitic breccia and finer-grained fragmentalrhyolite (Fig. 4b), along with minor clasts of massivesulfide, are interlayered with shale above the rhyoliteG*na et al. 1996).

The regional geological map of van Staal (1995) indi-cates the presence oftwo different and parallel rhyoliteunis in tlds area: 1) rhyolite interpreted as part of the FlatTanding Brook Formarion to the east, and 2) rhyoliteinterpreted as part of the Boucher Brook Formation to thewest. However, remapping of this areaby the staffof TeckExploration Limited (lvloore 1993) indicatqs that (1) thetwo rhyolite units are, in facg lenses of the same unit, and

S-TYPE RHYOLITB. TBTAGOUC}IE GROUP. NEW BRUNSWICK 675

Frc. 2. Local geology of the study area (after Moore 1993), with the location of two drill holes @G94-1 and 2). Also shown areTeck's original sample numbers (see Table l).

(2) a third lens occurs between the two, which indicatesthat it is probably folded by Fz Gig. 2). Chemical datapresented by Moore (1993) indicate that these felsicrocks are unique in the Bathurst Mining Camp, owingto their exfremely low contents of high-field-strengthelements (IIFSE) and moderately high P content.

PEIROGRAPHY

Like many other felsic volcanic rocks in theTetagouche Group, the Mddle River rhyolite lensesexhibit variable degrees of seawater-induced alterationand development of a tectonic fabric, which are bothevident in the eastem and central lenses, However. thewestem lens is, for the most parg very minimally altered,with negligible development of a fabric on the basis ofmesoscopic and petographic observations. Very smallalkali feldspar spherulites (d.5 mm, Table 1) formmost of the rhyolite, with only minor sericitic andpossibly chloritic alteration evident in the groundmass,whereas the flow layers are marked by partially to

completely recrystallized spheruliles forming a mottledquartz-feldspar intergrowth (Figs. 5, 64 b). Some ofthe spherulites have nucleated on pre-existing feldsparphenocrysts (Frg. 6b, Table 1), whereas others formedon other spheruttes. The small size of the spherulitesreflects devinification-induced crystallization at veryhigh degrees ofundercooling (Lofgren 1971).

The compositions of spherulitic intergrowths of feld-spar were determined by electron-microprobe analysis(Table 1). The nuclei to some spherulites are albitephenocrysts (or xenocrysts), and in some cases, thespherulitic alkali feldspar has a notable enricbment inphosphorus. Table 1 presents a compositional profile ofone of the well-developed examples (sample points I to10, Fig. 6b). The P contents generally increase from thecore to the margrn of the spherulite (0.03 to 0.32 wt.VoP2O5), whereas the albite core contains no detectablephosphorus; the levels of phosphorus are generallylower than those present from other moderate- to high-Prhyolites and granites (London et aI. 1990, London1992a, Kontak et aL.1996).

676 TIIE CANADIAN MINERALOGIST

FIc. 3. Pronounced flow-induced foliarion (differential weafheredsurface) in rhyolite, western lens, Mddle River. Widfh offleld of view: 7 cm-

GEOCHBTICAL CHARACTERTZATION

Sampling and analytical c onsifurations

Thfuteen samples from the three rhyolite lenses,which are inferred to represent a folded single horizon(Fig. 2), were crushed and then pulverized in a cbromesteel swing mill. These samFles were analyzed with aPhilips 2400 X-Ray Fluorescence Q(RF) Spectrometerusing fused disks n1 the geochemical laboratory of theUniversity of Ottawa (-ajor elements and selectedtrace elements; Table2). All samples also were analyzedby neutron activation at X-Ray Assay Laboratories,Don Mlls" Ontario. Based on the 94-R[IY-1 in-housestandard Q,entz L99s), concentrafions of major elemen6are quoted with less than a 2Vo error; with most traceelemenb, the e,rror is less than 107o, although severalvery-low-abundance trace elements have slightlyhigher errors. The rare-earth elements (RZ@ are closeto their practical limits of detection (6o times anatytrcaldetection limit). Neutron-activation-derived trace-elgment data were used in preference to the equivalent)(RF data

The oxygen isotope values were determined on thethee least-altered samples of rhyolite from the westlens using an Optima mass spectrometer at the Univer-sity of Western Ontario. hecision and accuracy arejudged to be approximafely fl.2Voo.

TAFIE I. FELDSPAR COMPOSMONS FROM A SPHERUUTE IN THE WEST I.ENSOF THE IIIDDIE RIVER RHYOUTE, BATHURST, NEW BRUNSflICK

Csnt€rS p . i 1 2 3so, 69.12 68.3:! 65.62Ato. 1s,5lt 18.a 18.83FqO, 0.(X 0.04 0.O4BaO 0.m 0.06 O.07cao 0.04 0.01 0.00sro 0.m 0.00 0.01NqO 11.32 2.4 1.U2w 1.'t4 12.9:1 15.07Ppr 0.00 o.(xl o.12suM 101.2 1q).5 1d'.8

4 5 6 765.57 65.S 66.03 65.401E.56 18.54 18.46 18.40.00 0.04 0.14 0.010.08 0.16 0.08 0.040.(p 0.6 o.fi o.280.@ o.ut 0.@ 0.13o21 024 0.2, 02

16.14 16.08 15.97 18.060.04 0.09 0.'t I 020

t@.6 1012 101.1 't@.78

Edge8 9 1 0

6626 65.02 65.6118.40 18.34 18.530.01 0.00 0.00o.fi 0.05 0.(p0.38 0.32 0.100.04 0.01 0.00o20 021 0.23

16.06 16.12 18.10o.32 0.31 0.12

r(X).E 100.4 1q).7

st 2.ffi 3.008Al 0.998 0.W8F€8+ 0.@1 0.001Ba o.dF 0.001Ca 0.(X12 0.001Sr 0.@ 0.m0Na 0.951 0.217K 0.6t o.74P 0.000 0.001o 8 8

2.5C21.O12o.dt'l0.q)10.0(x)0.qD0.09t0.8770.m4I

3.qt4 3.m 3.008 2.995 2.9$ 2.9q' 3.0041.004 0.996 0.Sl 0.9S!t 0.994 0.994 0.9990.0(x) 0.00't 0.q!4 0.0m o.qF 0.000 0.m0.001 o.qE 0.m2 0.dr2 o.(XP 0.(X)1 0.(m0.0@ 0.002 0.005 0.014 0.018 0.016 0.0040.000 0.001 0.@ 0.003 0.@r 0.0m 0.0@0.019 0.02, 0.m0 0.m0 0.018 0.018 0.062o.w 0.935 0.928 0.S8 0.938 0.s48 0.S400.@1 0.003 0.004 0.@ o.o12 0.012 0.d158 8 8 8 E 8 8

NOTES: S€€ &ut€ 68 for mlcropmbe favg|r€ (sample &DL-14A). Cherdcal analys€s werootbhed byDr.D,oughs HalushgthsJEOLT3ttrdcroprobe dt|gUnlversity of NqvBrunsrlckwithan accabr&rg votrags ot '15 kV and 5 nA cunent and a b€am dbrlEbr ot 5 frrl Th€ analydcal ltnlts(3.3 'J badqround aounb) lor ths l0, abundanra elfiEnts arB: CaO - 0.(I3 rvl%, Fe - 0.06 wtol0,Sr- 0.08 rvtyo, Ba - 0.03 vnt%, ard P - 0.d1 wtTo

S-TYPE RIIYOUTB. TETAGOUCIIB GROUP. NEW BRT'NSWICK

Frc. 4. a) Refolded folds in flow-banded rhyolite, west lens, Middle River (sarnple 96-DI-14A). Tte location of thethin section is outlined" b) Breccialed flow-banded rhyolite, west lens, Middle River (sample 9GDI-148),

678

FIc. 5. Phoromicrograph of flow-banded rhyolite (sample 9GDL-14) with altemating lightyellow (spherulitic) and medium beige layers (recrystallizal spherulites and mottledfelclspar, i.a., no micas) from left mmgin (Fig. 4) of thin section, western lens, MiddleRiver. Plane-polarized light; the field of view is 5 mm.

Geochernical data

As previously indicated, the rhyolite from the eastand cenfral lenses is moderately altere{ whereas that inthe western lens is only very weakly altercd; tlerefore,data from the westem rhyolite lens are emphasized.Data on the other lenses will also be used. to enhancethe overall geochemical interpretation, with the effectsof alteration being taken into account.

The least-altered samples of rhyolite typically havehigh sitca and alkali contents and a low Ca content(Fig. 7, Table 1), although considerable mobility ofalkalis and silica is associaied with sericitization andalbitization, particularly in the eastem exposure (Lentzet aL L996). The aluminum saturation index [ASI =Alrq(CaO + Na2O + &O)l of the least-altered samplesof Mddle River rhyolite ranges between 1.1 and 1.4(Fig. 8), with the higher values enhanced by weaksericitic alteration. The antipathetic variations betweenA12O3 and SiOz Gig. 9a) are too lmge to be related tomagrna fractionation, but instead reflect mass changesowing to hydrothermal alteration in the form of serici-tization, albitization and silicification (Al dilution)(Leitch &Ix;rtz 1994). This is accompanied by consid-erable Na-K exchange, probably due to seawater-induced alteration and devifrification reactions. Theleast-altered rocls have 13 to L5 vtt-Vo AhOg and approxi-malely equal concenfrations of Na2O and I(2O, as doother least-altered felsic volcanic rocks in the BathurstCamF. Sericitization is particularly evident in rocks rich

in A1 @ig. 9b), whereas high levels of Ca reflects carbo-natization that is associated with silicification. TheFe2O3 (total), MgO, and MnO contents are typicallyless than 1.0,0.5, and 0.05 wt.7o, respectively, althoughhigher values relating to alteration also occur (Table 2).

The minor- and trace-€lemerf contenb of the rhyoliteare particularly noteworthy; Cs, Rb and Sr contents arehigher, and Ba content is lower, in the least-alteredMiddle Riverrhyolite than in otherfelsic volcanic rocksin the Bathurst Camp, although these elements werecertainly somewhat mobile during seawater-induced al-teration. Irvels of TiO2 (0.03 to 0.06 wLVo),Zr (3O ta52 ppm), Y (9 to 14 ppm), Nb (9 to 16 ppm), and V(1 to 8 ppm) are low, but P2O5content (0.16 and0.34 wtVo) is high compared to the other felsic volcanicrocls in the camp (0.03 to 0.1,8 wt.Vo; I*ntz 1996b).The sftong covariation between A12O3 and TiO2, Z,r,ll[b, and Ga (Figs. 9c, d, e,0 itdicates that they alsowere relatively immobile during alteration. Thougfi y-tium generally is considered 41 imm6file element, itsconcentration is variable.

Immobile-element ratios arc not sensitive to mass-change effects and, tlerefore, are most effective indetermining compositional affinity and evolution inaltered rocks. TheZtftiO2 values (0.5 to 0.9) arc typi-cal of felsic volcanic rocks of the Bathurst Camp@ig. 10a), whereas high \f/l values (>0.7) causethese rhyolite samples to fall erroneously within thetrachyandesite field @g. 10b). The low I/FSE contentsof these rhyolites are not typical of alkaline igneous

S-TYPE RI{YOLIIE. TETAGOUCIIB GROUP. NEW BRUNSWCK

Flc. 6. a) Intergrown spherulites (80 vol.7o) from the Middle River rhyolite (sample 9GDLI4A). The line is themicroprobe profile of the spherulitic feldspar (Fig. 6b). Crossed-polarized ligbt, field of view i5 1.! mm. b)Spherulitic alkali feldspar with albite nucleus. The points I to l0 locate the feldspar compositions presented in Table1. Crossed-polarized light; field of view is 0.3 mm.

680 IIIE CANADIAN MINERALOGIST

TABLE 2. WHOI..E.ROCK GEOCHEMICAL DATA ON THE MIDDLE RIVER RHYOUTEAND A RHYOUTE FROM THE BOUCHER BROOK FORMATION

satnplo 8090 8700 8701 n02 g10a 8769 88:18 83:17 840 88119 841 8842 8881 BBrhyLone we8t W6t Wd U@] West Mld EsCl Easl E83! Eas! ECCI Eas! @!wtohSO, 76.95 75.19 75.28 74.8 73.9 78.C2 70,09 78.63 74.65 @.r15 78.N 74.18 78.91 74,@TO2 0.046 0.050 0.q8 0.(X5 0.u7 0.w 0.(E4 0.039 o.ont 0.m0 0.ut9 0.c89 0.050 0.05AI.O, 12,85 14.19 13.87 13.61 14.21 n.n 18.45 1120 14.9t 18.17 10.10 11.39 9.92 14.24Fo2O3[D 1.11 0.97 0,96 0.91 0.91 0.51 1.13 0.61 'l.U 0.61 0.84 1.84 26 O.42MnO 0.01 o.CB 0.01 0.01 0.01 0.01 0.02 0.05 0.09 0.m O.12 0.14 0.1,t 0.00MgO 027 027 0.34 0.28 0.21 O.n 0,67 0.17 0.61 0.34 0.49 0.58 o.78 02,CaO 0.3t1 0.54 0.36 0.34 0.27 0.50 0.15 1.34 0.40 0.46 211 3.39 1.8.1 O28Na.O 3,86 3.61 4.45 2.21 3.14 4.A 0.13 4.70 0.11 5.19 2.U 0.6 0.A. 2.4&o 2.39 2,6 2.26 5.38 5.70 1.58 5.27 0.59 4.11 2.& 1.25 2.8 2.41 7.18P.Or O.21 0.m 026 0.25 0.19 0.28 0.16 0.29 0.30 0.34 O2S 023 0.24 O.2.LOr 0.80 120 1.10 lJg @ 0.70 3.00 1.30 @ 1.70 & 4.70 3.10 O.72suM 98.8 99.0 98.9 99.1 98.9 98.9 99.1 98.9 99.3 98.8 99.2 99.1 99.1 99.7ppm

v 4 < 1 1 2 1 8 3 2 7 3 1 3 1 1 8Pb /$l 19 0 0 15 51 13 I 8 69 13 12 0 Ih 43 111 3t 2A l(x' 81 A 7A 119 58 87 1U 70 2.

sb' 1.4 2.A 0.9 1.4 2.6 2.6 3.7 1.8 3.0 5.8 2.9 72 3.3Rb 130 '150 142 n3 272 101 y2 39 n7 13 82 150 145 28

Ba 2& 2& 38 U7 2$ 37 412 il 3?,3 1Q, 65 207 117 309Sr 112 I 130 60 7a 1U E7 162, 43 136 98 31 31 TlTa' 2.3 2.5 25 2.3 2.3 '1.7 3.0 1.5 2.9 32 1.0 22 1.9 1.7Nb 15 15 15 t0 15 12 19 14 16 19 10 14 12 1€Hf 1.7 1.6 1.6 1.8 1.8 1.1 2.A 1.5 2.3 2.4 1.2 1:t 1.5 1.7Zt 37 39 39 37 tr7 31 52 32 41 48 A 32 30 55Y I 12 I 11 I 11 8 11 11 14 12 11 12 14G e 2 . n 2 , 2 0 2 1 1 8 3 0 1 2 2 4 3 5 1 4 1 0 1 5 1 8

u 6.0 5.9 5.8 5.1 5.9 6.0 7.0 5.8 7A 10.5 4.3 0.6 6.4 4.O

N d ' 3 6 5 5 5 4 3 5 5 5 5 5 5 3 . 2Sm' l.Og 1.85 1.A 1.4'l 1.35 1.40 0.96 1.56 1.68 1.82 1.24 1.70 1.97 1.OgEu' 0.26 0.08 029 0.18 {.(}5 0.18 0.14 0.18 0.10 029 0.0tt 0.14 0.12 0.05Gd. - 1.4

Lu' 0.04 0.05 o.cxl 0.08 0.6 0.05 0.07 0.05 0.07 0.05 0.06 o.CXl 0.06 0.08

a/no? 0.080 0.078 0.078 0.02 0.082 0.070 0,081 0.082 0.080 0.080 0.074 0.082 0.ft10 0.110ZrlW 22 24 24 21 21 28 m 21 18 20 24 t9 20 32ZlN 4.1 3.3 4.3 3.4 4,1 2.8 6.5 2.E 3.7 3.4 2,4 2.9 2.5 3.9La/Ytd 3.9 6.8 5.8 5.2 5.7 5.1 3.9 82 3.7 5.0 6.8 4.1 5.5 6.0Nt/Ta 6.5 6.0 6.0 7.0 6.5 7.1 5.3 9.3 5.5 5.9 6.3 6.4 6.3 9.4Nb/Y 1.67 1,5 1.67 1.8 't.6t 1.'t0 2.* 127 1.& 1.9 0.&} 1.r/ 1.00 1.14

NOTES: Sarpls donobs Teck Beloredon Ltnhed's (TlQ sample numbeB. 'donob rBults obbf|gd byFtstwBnbl neufon acffvdon anelysb, BB rhy danots8 taohy-and6ls' samplB li\876 (van Staal e[ al.1991, de fle). FCOIO den&8 totBl Fe a3 F62O!, - dsnob no analysb.

suites (e.9., comenditic rhyolites), but rather are moret)?ical of S-, I-, or M-type felsic rocls on the basis ofNb--Y systematics @ig. 10c). The high TalYb value(Fig. 10d) indicates an S-type (syncollisionaln Pearceet aL L984) paxentage for the rhyolites. Although Rbcan be mobile. the Rb content in the least-altered sam-ples is greater than 2fi) ppm, which also supports anS-type parentage (see Fig. 10d).

The high concentation of Ta results inNblTavalues(6.5 t 1.0, Fig. 1l) lower than mantle (ave. 17.5) andmost crustal (ave. 11.5) maefnatic rocks (Green 1994),but within the range g?ical of S-type igneous rocks

(Iaylor 1992). \\e low Nb relative to Ta may resultfrom compositional inheritance from the souxce region,presumably sedimentary rocks, or fractionation ofFe-Ti phases or amphibole.

There are faidy well-developed trends evidentbetween TiO2 and several ftace elements (Fig. 12) thafwere enhanced by metasomatism, but they are alsoevident in the least-altered material (shaded). Covmia-tion of Zr arid Th with TiOz (Figs. 12a b) indicatessimilar behavior of zircon and the Fe-Ti silicate andoxide phases. Although V usually covaries with TiO2,its low abundance and possible analytical imprecision

S-TYPE RHYOLITB. TETAGOUCIIE GROUP. NEW BRUNSWICK 681

6'C\I\z+o2Noz

d( \ t t

F€^ 1 0g+Os

(\l

oz

SlO2 (wt7.)Ftc. 7. NqO + K2O versus SiO2 discrimination diagram (r

Mute et aL 1989) illustrating the compositional sp€ctrumof the Midclle River rhyolite samples (circle) and theBoucher Brook Formation rhyolite (trianele). Shaded meais field ofleast-altered samples.

probably account for the scatter in Figure l2c. Like V,Sc typically substitutes into Fe-Ti odde and maficsilicate phases, also accounting for the strong covaria-tion with TiOz Gig. 12d). The strong covariation of Nband Ta with TiO2 also indicales substitution into Fe-Tioxide and silicate phases (Green 1994). Trends in theleast-altered parts of the arrays could reflect eitherfractional crystallization or partial fusion.

Compared to the average continental crust (Wede?ohl1995) and relative to other felsic volcanic roctrs in theBathurst Camp, the Middle River rhyolite is depleted inBa Th, La Ce, Sro Nd, IIf, Z, Sm, Eu, Ti, Sc, Tb, Y,Yb, and Lu, and enriched in Rb, Ta and P (Fig. 13).The low levels of Ba and Sr, and high lsvsfu 6f ft!,indicate that the rhyolite is compositionally evolved.Concentrations of the light rare-earth elements (L'REE)are approximately ten times chondrite, whereas those ofthe heavy REE QIREE) are between one and two timeschondrite, yielding a LREEIHREE slope of approxi-mately 5 (XREE in the range 16 to 19 ppm). The nega-tive Eu anomaly is pronounced, but variable, even inthe least-altered samples, which indicates either frac-tionation of feldspar or very selective partial melting.T\e REE abundances we ca. IO times lower than intypical aphyric rhyolitic rocks of the Bathurst Camp0*ntzL996b).

The P content of the rhyolite is unusually high(0.16 to 034 wt.Vo,Fig. 14) compared to the felsic vol-canis rocks of the Tetagouche Group. The Ca-P tendof the least-altered samples is consistent with fractiona-tion of apatite, although it is evident that some P also istied up fu alkali feldspar (Iable 1). The concentationof P is variable relative to Al (Fig. 15a) which, if immo-bile, indicates preferentialremoval ofP relative to other

Metolumlnous

Perolkollne

Al2o3/(coo+No2o+K2o)Flc. 8. AlO:(CaO + Na2O + K2O) versus AlzOy'(NazO + I(zO)

diagram (Maniar & Piccoli 1989) iltustrating the peralumi-nous compositional spectrum (Table 2) of the Mddle Riverrhyolite samples (circle) andthe BoucherBrookFormationrhyolite (triangle). Shaded area is field of least-alteredsamples.

HFSE. The weak anticorrelation of P and K (Fig. 15b)might indicate leaching of P during devifrification andalteration. However, the moderate correlation betweenP and Y (Fig. 15c) and a weaker correlation betvreen P andIa (Fig. 15d) suggest coupled removal of these elements,whose concentation seeqrs to be largely primary.

Oxvcmt Isotops Svsrmue,lcs

Whole-rock oxygen isotopic values (6180) areI4.9Voo (TK8699)' l3.4Voo (TK870l), and 15.47oo(TK8703), all three samples being from the least-altered westem lens. Although the fluid-rock reactionsseem to be minimal there, the variation in tle alkaliscould reflect very low-temperature alkali-exchangereactions in feldspars, which can produce large shifls inthe oxygen isotopes (faylor & Sheppard 1986). Thepreservation e1 elkali feldspar spherulites and albitenuclei, however, indicates that such exchange wasminimal in the samples analyzed. Considering the least-altered nature of these samples, the 618Osyes' valuesare interpreted to reflect primary signatures, with veryminor changes due to alteration.

The l8O-enriched signature of these samples isconsistent with a derivation by anatecfic reactionsinvolving shale (faylor & Sheppard 1986). The felsicvolcanic rocks of the Nepisiguit Falls and Flat LandingBrook formations (Fig. 1) also show an enrichment in18O (Lentz & Goodfellow 1993, Lorrtz et al. L997) thalis interpreted to originate from partial melting of uppercrust sources (Avalonian margin) during backmc rifting(van Staal 1987, van Staalet al. L991,1-enzl996a,b).

f f i \ l o l q

l**l $l*.;\*'lEEl ' | \

DtscussroN

C hz rut s trati g raphic s i gnifi c anc e

The compositional similarities of the three lenses ofstrikingly flow-banded, aphyric rhyolite at Middle

River suggest that they can be correlated. This viewcontrasts with the interpretation of van Staal (1995).The three lenses occur at the contact between the carbo-naceous sedimentary rocks of the Miramichi Group andthe Boucher Brook Formation (Tetagouche Group),which is consistent with the position interpreted for the

F'd

3 4o

N\Z

270

F'ENacn

Eog

t!

F'5(\l

oF

. 8 0ol

75

a) 20

?Btu

;z

I O

b)8

6

65t e

Al2O3 (wt%)

| = o,94f 0 15 20 l 0

Al2O3 pvt%)

l 5

Al2O3 (rvt%)

I R

Al2O3 pvto/d

@rtc€ntratlon

..,,,,.v a

%E.

odiltJtlon

o r = 0.95

l5 20Al2O3 ftvt%)

zv

d) oo

25

6 4 0,J

tro.g

oo

2Cl 0

Frc. 9. Al2O3 versr"r a) SiOz, b) KzO, c) TiOz, d) Zr, e) Nb, and 0 Ga for the Middle River rhyolite (circle) and the Boucher BrookFormation rhyolite (triangle) (lable 2) illusnating the changes in mass associated with the weak to moderate alteration. r:Pearson hoduct correlation coefficient; r values greater than 0.53 (n = 13) are significant above the 957o confidence level(Le Maihe 1982).

re ..r';rory "'

o ffiS;ro. fil$il:ir.r /eosf-

,''6 Y;;ii::i:OY Offel&?

dilLfion f = 0.86

@n@filrqllono

& ...n _-dO€"

't- o

<f€-.";:.-r':."'' /ili.d;:{}.

$ffi;aeovE' olter&?@ ^

S - ^ ^ or = 0.98

Rhyollle@rcndltel

R1*,3@6lpcfiee/ tunteileilte

T@hyte

Andesiib Traclv-qrdeslie phorpllte

Subor/@/cboso/t

BoYtriicruNeph

S.TYPE RIIYOLIIE, TSTAGOUCI{B GROUP, NEW BRUNSWICK

l 00.001 r-

0.01

683

a) 80

crtot

E r00

og

2ro

b)

N

O o, t

N

0.01

bSQ

s 6 0No

ao50

EoggI

400.01 0,1

Zt lTlOz N b / Y

wtlhlnplate-ffisyr|. W.,oi

o,s,arrr gi!(i" I wtcruae

toe) I (oRtYPe)

d)"

1 0 .1' l l0 ]00 1000 o.l I l0 100

Y (ppm) \4e (ppm)

ftc. 10. a) SiO2 versas ZtftiOzandb) ZtfliO2versus l{bN discrimination diagrarns (Winchester & Floyd lWl); c) Nb versusY and d) Ta versus Yb tectonic discrimination diagram [after Pearce et al. (L9M) and modified by Cbristiansen & Keith(1996)l illusrating the compositional variation Clable 2) and tectonic affinities of the Middle River rhyolite (circles) andBoucher Brook Formation rhyolite (triangles).

Eo.o.

g2

1 0 ] 5 2 0Nb (ppm)

Frc. I1.. Nb varsa.r Ta diagram illustrating the range in compo-sitions of the Middle River rhvoliG and data for the least-altered samples Ghaded).

rhyolite on Middle River @ig .2, seel*ntz et al. L996).However, the Middle Riverrhyolite is chemically distinctfrom and possible older than flow-banded aphyricrhyolite of the Flat Landing Brook Formation(Tetagouche Group). Instead, it is compositionally verysimilar to a rhyolite mistakenly refened to as a comen-dite on the basis of tace-element compositional discrimi-nation techniques (sample WS76, van St^aI et aI.1991), located within an alkali basalt sequence(Boucher Brook Formation?) in the Lovalls Lake Anti-form, a few kilometers to the west of the area coveredby Figure 2 (se I*ntz & van Staal 1995), and twoporphyritic dikes at the top of the Flat Landing BrookFormation, to the north of Brunswick No. 12. (LentzI996a). The very low Y content of sample WS76Q*ntz & van Staal 1995) results in a Nb/Y valuegreater than 1, thus an ooapparento'nlkaline afnniry inFigure 10c. However, neither this sample (WS76) northe Middle River suite have characteristics expected ofan alkaline felsic rock; on the contrary, they are

syn-@illsb,nol(s t!4pe)

6o" 69@onbtElge

(oR fype)wletnbarc

0 , & Mtvpe)

684

^f 60

50

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30

c)'o

eQrotI

;

o ,/^g$,a9'

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r = 0.90

TlO2 (wto/o)

TiO2 (wt7d

bI

r = 0.70

E&zF

0.080.03,0320

0

d)o

TiO2 (wt'l.)

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I = 0.89

t

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subalkaline, peraluminous, phosphorus-enriche4 high-silica alkali rhyolites with anomalously low levels of Yalrd HREE. To the south, however, these low-F/FS4P-enriched, high-silica rhyolites have not been identi-fied in the Brunswick alkali basalt - comendite suite

s r 4

?.

tro9zg

I

Tloz M%)

(J. Carroll, Noranda Exploration and Mining Limite4pers. comm.). The low-/r'FSE and moderate-P contentsof the Middle River rhyolite and related Lovall's Lakerhyolite axe, at present, unique geochemical featmes inthe Baflurst Camp.

n?00

Fto.l2.TiO2versus a)Zt,b)Tbrc) V, d) Sc, e) Nb, andf) Ta diagrams illustrating the range of compositions of the Mddle Riverrhyolite and data for the least-altered samples (shaded).

; . ;t r . dq.; j

\

,i' r = 0.04

" S\

{ffi'#. i , ; , .^ .1{,E6$flidi}. r/

!rl,@)rlrl.fl

o o

1 = o,79

TiO2 (wf.o/o)

.Otrt:" r A ;

,,!'f#;,."';jo ,:€ssg''viJl@''

o

r = 0.89

S-TYPE RTIYOLITE. TETAGOUCTIE GROTJP. NBW BRUNSWICK

0.1

0.01Sm Tl Ib Vc

Zr EuSc Y LuFlc. 13. Continental-grust-normalized (Wedepohl 1995) extended face-element spider diagnm illustating the compositional

similarities between the Middle River rhyolite (Table 2), a rhyolite sample ftom the Boucher Brook Formation (BB; thisstudy) with the two other high-P felsic rocks, the Macusani tuff @chavant er aL 1987) and the SL Austell graniG (Manning& Hill 1990, Taylor 192), and an average shale composition (Taylor & Mcknnan 1985).

685

63ooCocCoo{)-'E.Eo3n

IO

CSBAUNbCEP HfRb Th To Lo Sr Nd

Cry stal- chemical considzrations

ln many cases exrmined (ondon et aI I990,Iondon1992a Konak et aJ. 1996), it is probable thar the coupledP + Al for 2Si substitution in feldspar (berlinite substi-tution, Simpson 1977) represents a primary feature.Here, tle P contents increase in the spherulitic alkalifeldspar from core to rim" Considering that spherulitesform by diffrrsion-limited glowth at high degrees ofund$s66ling (Lofgren 1971, Fenn L977,MacI*llan &Trembath 1991), tle P + Al = 2Si substitution in thespherulitic feldspar may simply represent metastable ordisequilibrium partitioning (cf, Fowler et al. 1987) rc-sulting from very slow diffrrsion 6f ftsss highly cbargedcations or complex polym.ers atthe crystal-glass interfaceduring devirification.

P etro genetic c onsiderartons

It is generally accepted that extreme fractional crys-tallization of a subalkaline felsic ma$na can pro-foundly change the compatibility of both large-ion -

lithophile elenrents (Ul'E) nd HFSE elements (Mahood& Hildreth 1983. Michael 1983. Miller & Mifilefehldt1984, Nash & Crerl:aft 1985). The low abundance ofI/FSE in the Mddle River rhyolite indicates that it washighly fractionated or a low-temperature partial melt.The absence ofrelated felsic volcanic rocks here pre-cludes a detailed petrogenetic evaluation ofthe originof this rhyolite. Instead; comparison will be made toother felsic igneous rocks with similar geochemicalcharacteristics (Ftg. 13).

The Macusani glass-bearing tuff in southeastemPeru, one of the few known extrusive high-P magmas,geochemically resembles, io patt" the Middle Riverrhyolite. It is interpreted to be a highly fractionatedproduct of a peraluminous magma @chavant et aL1987, 1988, London et al. 1989; Fig. 13), which isconsistent with the isotopic evidence. S-type peralumi-nous felsic rocks typically have higher average P2O5(0.15 t 0.1 *.Vo) than other t)?es of granite (Whalenet aI. 1987, Christiansen & Keith 1996). The highlyperaluminous nature (1.1 < ASI < 1.4) of the least-altered rhyolite is consistent with these observations.

o Gobonola

t*\

\ .a \

l oI

Apotttefroctlonotlon

3

F'E52oC)

686

0 0,1 o.2 0,3 0.4P2O5 ftvt.%l

FIG. 14. P2O5 versu.s CaO diagram illustrating the range ofcompositions of the Mddle River rhyolite and data for theleast-altered samples (shaded). Note the trend expected forfractionation of apatite and carbonate-alteration tend.

The covariation between TiOz and Zt, tffo Sc, M,and Ta is either indicative of variable degrees of solu-tion of restite phases during partial melting, xenocrystincorporation or fractional crystallization. The covaria-tion in P2O5 and Y and, to a lesser degree, La and Yb,also may indicate low-temperature fractionation orvariations in degrees of partial melting. Although reten-tion of the original heterogeneities associated with dis-equilibrium partial melting is possible, it is not probablewithin this small flow-banded rhyolite unit. Therefore,very minor degees of fiactional crysallization of zircon,Fe-Ti oxides and apatite may have occurred in thesubvolcanic magma-chamber before eruption.

In subalkaline igneous systems, the low Zr and Hfcontents (29 to 52 ppm and 1.1 to 1.8 ppm, respec-tively), which aremostly inherited (knE & V. McNicoll,in prep.), indicaie thaf these very-low-teinpcature magmas(<700"C; se€ Watson & Harrison 1983) are derived byselective melting, because of the xenocrysticnature of most of the zircon crystals (Watson 1996).

o/

l 5Al2O3 Fvt'6)

o.2 0.25 0.3 0,s5P2Os (wt%)

A

on O- F......

..... /q,,,..&)z o\...:b^\-.../

o o o o o o

6- o

r = -0.54 o0 -0 .15 o.2 0.25

P2Os grtz.1

oA 9

oo o o o

o ^

r = 0.35o.ts O,2 026 0.3 0,35

P2O5 gt"/d

b)'6

F'Ed"d o,2

sEo4

6l\z

20

'15

/^)

7E'o

;

. .'U*i'ndd'o,..."@"o o o

a.9.- O O

r = 0.83

d)

E 4o.EL

(EJ

3

50.15

FIc. 15. P2O5versa.s a) Al2O3, b) K2O, c) Y and d) la, illustrating the compositional variatiotr and tectonic affinities of the MddleRiver rhyolite (chcles) and rhyolite in the Boucher Brook Formation (hiangle) Clable 2). r: Pearson hoduct correlationcoefficienq r values greater than 0.53 (n = 13) are sipificant above the 95Vo confidence level (L€ Maitre 1982).

i:p :* !b !o ig lv

r = -0.07

S.TYPE RT{YOLITE. TETAGOUCM GROIJP. NEW BRUNSWICK 687

Strong compatibility of Hf in zircon in felsic magmasMahood & Hildreth 1983) results in IIf depletion byfractionation of zircon. However, Hf is generallyslightly more incompatible than Zt (see Chyi 1986),such that the Zrfttf decreases to low values in theserhyolites (2L to 28) via fractionation(?), which conffastswith the Z/Hf ratio for various crustal rocks, includingshalg which ranges from 33 to 4l (Iaylor & Mcknnan1985, Wedepohl 1995). The M/Ta value of the MddleRiver rhyolite also is low (6.5 t 1.0), in contast with thevalue for various crustal rocks, which ranges between10 and 17 (Taylor & Mclennan 1985, Wedepohl1995). Pearce et aI. (1984) indicated that collision-zonemagnas commonly have low M/Ia values. Green(1994) has shown that many felsic suite.s can have lowNblTa values with variable Nb and Ta abundances.Topaz granites and ongoniles typically have M/Tavalues less than 10 (Cbristiansen et al. 1986, Taylor7992).Ta is usually more compafible than Nb in variousminerals, except pargasitic amphibole (Green 1994)and biotite (Nash & Crecraft 1985). Thus, to decreasethe M/Ta ratio, amphibole or biotite may be involvedin fractionation or selective partial melting. The low Thcontent (1.3 to 1.8 ppm) is attributed to removal ofztrcon. (cf. Mahood & Hildreth 1983) and possiblyapatrte (cf. Rapp & Watson 1986) as fractionatingliquidus phases or phases remaining in restite.

The geochemical feature of particularhere is the enriched P conlent (>4.14 txt.Vo P2O5). Thissuggests that the peraluminous composition of the meltincreased the solubility of apatite @ea er aL IW2,Iandon1992u Vtchavatt etal. 1992, Taylor 1992). High Pcontents are typical 6fhighly fractionated S-type felsicmagrnas derived from low-Ca, aluminous sedimentaryprotoliths (London 199?4Beaet aL 1992, Cbristiansen& Keith 1996), but the latter generally have htgh HFSEcontents. Typically, higb-P topaz leucogranite andrhyolitehave low levels ofthe I/FSE and high seassauafiem efRb, Li, Nb, Ta and F (Manning & Hill 1990, Taylor1992, Christiansen & Keith 1996), consistent u/ith anS-type affinity. Also, evolved, high-P felsic magmascommonly are depleted in RE4 as are the Middle Riverrhyolites, whereas otherwise similar low-P type felsicmagmas remain enriched iaREE (laylor 1992),wlnchsuggests a relationship with high activity of P. Thepartition coefftcient (K7) for the ftEE in apatite is higb(>10) in rhyolitic magmas (Watson & Capobianco1981, Watson & Green l98l). The correlation amongY, La and P2O5 in the Middle River rhyolite couldindicate apatite fractionation from even higher P con-tents. The good correlation between CaO and PzOs in theleast-alt€red rhyolites (Fig. 14) supports a relationshipwith apatite fractionation.

The very low REE content of the high-P rhyolitesmay result from the stability of residual apatite or otherresidual or refractory P-bearing phase, or a silicate oroxide phase (garnet" zircon, titanite, etc.) in tle sourceprotolith that hosts the REE. Alternatively, very early

fractionation of apatite (LkE&bearing), monaziteQ.REE-tich), xenotime QIREE-tich), and zircon(H&EE-bearlng) (Watson 1980, Watson & Capobianco1981) resulting from the high activity of P may alsoreduce the REE alid Th content$.

Extreme compositional zoning in felsic magmaschambers (Hildreth 1981) is commonly int€rpret€d as theproduct of extensive crystal fractionation in the magmachamber (Mahood & Hildreth 1983, Mchael 1983, Mller& Mclefehldt 1984) as opposed to volatile-relatedliquid-state diffrsion proc€sses (Ilildrcth 1981). Concen-ftation of network modifiers (H2O, IIF, etc.) in theuppermost parts of chambers reduce extent of crystal-lization and allow fractionation to very low tempera-tures (London et al. 1989, London I992b), which isconsistent with the inferred zircon-saturation tempera-tures of less ttran 700'C for the Middle River rhyolite.The aphyric, flow-banded nature of the Mddle Riverrhyolite and lack of vesicles are consist€nt with theconlention that these magmas were undersaturated involafiles and higbly viscous dring emplace,ment, althoughthe confining pressnre exerted by seawater may haveimpeded vesiculation.

The Middle River rhyolite may be relatpd to thepartial melting of Avalon supracrustal sedimentaryrocks that underlie the Gander Zone passive marginsequence (Miramichi Group). Interestingly, the envi-ronment and magmatic association are not unlike theearly l8O-enriched Torre Alfina lavas of the Romanigneous Province (Iaylor & Sheppard 1986). Typi-cally, the most contamin4€fl magmas are the firsttbrough the magmatic conduits; the smallest volumesinteracted with hottest coun0ry-rocks. This is somewhatsimilar to the processqs that are envisaged for the episodesof protorift backarc felsic volcanism in the area (Lentz1996b). Also, the macusanite occlurences @eru) formwithin three basins situated within a continental innerarc environment in the Westem Cordillera (Kontaket al, L984, Pichavant et al. 1987). Therefore, snall-volume, evolved peraluminous S-type magmas may beassociated with eady orogenic, continental subductionenvironments (cf Pearce et al. 1984, Hanis et al.1986). Advection of heat related to upwelling astheno-spheric mantle and resultant later subalkaline felsic the'nalkaline mafic volcanism were probably responsible forthe early selective crustal melting.

CoNcl-usroNs

Three flow-banded rhyolite lenses define the base ofthe Tetagouche Group in the Mddle River area along theeastem flank of the Bathurst Mining Camp. They arespherulitic, with some evidence of Al + P = 2Si substi-firtion in alkali feldspar. Overall, the least-altered rhyolitesamples have high silica conlents and are peraluminous,with very low levels of Ca and IIFS4 but they havehigh P contents (0.16 and 0.34 tttt.Vo P2O5) relative toother subalkaline felsic volcanic rocks in the Bathurst

688 TIIE CANADIAN MINERALOGIST

Mining Camp. These features, together wift fts highNb/Y (>0.7), TalYb (>4.3), Rb contents (>200 ppm)and high ltag Q3.4ta L5.4%o) and low M/Ta ({), areconsistent with an S-6?e affinity. These P-emiched,high-silica S-type rhyolites represent evolve{ low-lemperature magmas. The variations in I/FSE and theirratios are consistent with low-temperature fractionationprocesses of phases withhi.gh specific gravity, althoughtheir low abundance,s may, in part, b inherited by low-temperature partial melting processes of a sedimentaryprotolith. These S-type rhyolites erupted in a continen-tally situated, proto-arc to backarc-rift setting, which isatypical ofthe normal tectonic interpretation for S-typemagmatic systems.

ACKNowl.DcHvm{rs

I thank 1fre managernent of Teck Exploration Limit€dfor providing the pulverized samples of the MiddleRiver rhyolites for re-analysis. Discussion withDr. Steven McCutcheon (N.B. GSB) helped in myunderstanding ofthe regional geology. The manuscriptbenefitted from reviews by him, Dr. Niel Rogers (GSC),Parl Moore (Ieck Exploration T imited), Dr. Dan Kontak(N.S. DNR) and two anonJimous critical reviewers.Special thanls to Dr. RobertMartinforhis considerableeditorial help. This represents a conftibution to theCanada - New Brunswick EXIECH II aereement(1994-re99).

REFERENCFS

BEA, F., Fhslrrarm, G. & Connrroq L.c. (192): The geo-chemistry ofphosphorus in granite rocks and the effect ofaluminum. lrrftos 29, 43-56.

Cmsuemw, E.H. & KurH, J.D. (1996): Trace-elemenr sys-temafics irl silicic magmas: a metallogenic perqrective. .IzTrace Element Geochemistry of Volcanic Rockss AFplica-tions for Massive Sulphide Exploration @.A. Wyrnan,d.). Geol. Assoc. Can , Shon Course Notes 12,115-151.

Snm.oar, MF. & Bum, D.IvI. (1986): The geologyand geochemisfy of Cenozoic topaz rhyolites from thewesGm Uniled States. Geol. Soc, Am, Spec, Pap. 2fr5,

Crrvt, L.L. (1986): Characteristics and genesis of zirconiumand hafuium deposits. In Mineral Paragenesis. TheopbrastrsPublications S.A., Athens, creece (387408).

FB{N, PJ,I. (1977): The nucleation and growth of alkali feld-spars from hydrous melts. Can Mineral, 15, 135-161.

Fowr.m, A-D., Jnlss.r, L.S. & Pfioqunl SA (1987): Variolesin Archean basalts: products of spherulitic crystallization.Cur. Minz ral. 25, n 5 -289.

GRm{, T.H. (1994): Experimental studies of face-elementpartitioning apptcable to igneous petrogetrssis - Sedona16 years later. Cltcm- Geol, tl7,l-36.

Henrus, N.B.W., hARcE, J.A. & Ttt\ol-e, A.G. (1986): Geo-chemical characteristics of collision-zone maemalism. InCollision Tectonics (M.P. Coward & A.C. Ries, eds.).Geol, Soc., Spec, Publ. 19,67-81.

Hnonmn, W. (1981): Gradients in silicic magma chambers:implications for lithospheric magmatism. J, Geopbys. Res.10.153-192.

Koure& D.J., CI.ARx, A.H. & FanneR" E. (1984): The mag-matic evolution of the Cordillera Oriental of SE Peru:crustal yerszs mantle compnents. /z Andean Magmatism:Chemical and Isotopic Constraints @.S. Harmon & B.A.Barreiro, eds.). Shiva Publishing Nmtwicb, U.K Q03-219)

MARrtrI, R.F. & Rtcuano,L. (1996): Patterns ofphosphorus enricbment in alkali feldspar, South MountainBatholitb Nova S cobl4 Caradz Eur. J. Mberal 8, 805-824.

Lrrrcr, C.H.B. & Lu\rrz, D.R (194): The Gresens' approachto mass balance constraints of alteration systems: methods,pit'alls, examples. .Iz Alteration and Alteralion ProcessesAssociated with Ore-Forming Systems @.R. kntz, ed.).Geol, Assoc. Can, Sltort Course Notes ll,16I-192,

LE Merrrr, R.W. (1982): Numerical Petrology, StatisticalIwerpretatian of Geochernical Da/aElw:'iLer, New York,N.Y.

Bers[4AN, P., DrDEK A., Kru-m, J., Lawvnn, J.,LE BAs, M.J., SABNE, P.A., Scnm, R., Sgnwsnl, H.,Smrcrs.smq A., Woor,Ley, A.R. & Zersrm, B. (1989):A Classifiration of lgncous Roclu and. Glossary of Terms,Blackwell Scientific Publications Oxfor4 U.tri

Irm.rrz, D.R. (1995): hetininary evaluation of six in-houserock geochemical standards from the Ba.thurst Camp, NewBrunswick. 1z Current Research199,4 (S.A. Merlini, ed.).New Brm*wick Deparfinent of Natural Resources and.Energy, Mburals od Enzrgy Divisioa Misc, Rep. lE, 83-91.

_ (1996a): Geology and geochemisfty of TetagoucheGroup volcanic and sedimentary rocks and related debrisflows north of the Brunswick No. 12 massive-sulphidedeposil Bathursl New Brunswick GeoI. Surv. Can, Pap.gGrD,8t-92.

_ 0996b): Trace-element systematics offelsic volcanicrocks associated with massive-sulphide deposits in theBathurst Mining Camp: petrogenetic, tectonic and chemostratigraphic implications for VMS exploration. In TraceElement Geochemistry of Volcanic Rocks: Applicationsfor Massive Sulphide Exploration @.A. Wyman, ed-).Geol. Assoc, Can . Shon Course Notes12.35942.

& Goonrs:ow, W-D. (193): Petrology and mass-balance constraints on the origin of quartz augen schistassociated with the Brunswick massive sulfide deposits,Bathurst New Brunswick Can Mheral. 31, 877 -903.

& BRooKs, E (1996): Chemosrarigra,phyand depositional environment of an @ovician sedimentarysection across the Mramichi-Tetagouche Group contac!northeastem New Brunswick" Arlartic Geol. 32. l0l-122.

S.TYPE RI{YOLITE. TETAGOUCHE GROUP. NEW BRUNSWICK 689

IIAU, D.C & Hoy, L.D. (1997): Chemostrati-graphic, alteration, and orygen isotopic trends in a profiletbrough the stratigraphic sequence hosting the Heath SteeleB Zone massive sulfide deposil New Brunswick. CaaMilural.35 (in press).

& vAN STAAL, C.R (1995): Predeformational originof massive sulfide mineralization and associatgd footwallalteration at the Brunswick No. 12, Pb-Zn-Cu depositBathurst, New Brunswick evidence from the pc'rphyrydike. Econ Geol. XJ, 453463.

LoFcRm.r, G. (1971): Experimentally prduced devihificationtextures in natural rhyolitic glass. Geol. Soc, Am., BulI. U,tLt-t 'u.

I,oNDoN, D. (L99?a): Phosphorus in S-tJ{,e magmas: the P2O5content of feldspars from peraluminous granite$ pepatites,and rhyolites. Anr Mircral.77, 12tr.145.

-(1992b} The application of experimental petrologyto the genesis and crystallization of granitic pegmatites.Can Mineral. 30. 499-540.

-, dRNf, P., I,oorvfl,s, J.L. & Par, J.P. (1990): Phos-phorus in alkali feldspars of rare-element granitic pegma-tites. Caa Mineral. 2E.771:786.

MoRGAN, G.8., VI & Hnvrc, R.L. (1989): Vapor-undersatlaf€d experiments with Macusani glass + II2O at200 MPa, and tle intemal differentiation of graniticpegmatites. Contrib, Mincral Petrol. 102, l-17,

Macl-o:arl, H.E. & Tnmmau, L.T. (1991): The role ofquartz crystalization in the development and preservationofigneous texture in granitic rocks: experimental evidenceat I kbar. Am. Mineral. 76. l29L-1305.

MAItooD, G.A. & Hnonrru, W. (1983): Iarge partitioncoeffrcien8 for trace elemens in high sitca rhyolites. Geo-chim. Cosmochim. Aaa 47, ll-30.

Mewnn, P.D. & Ptccou, P.M. (1989): Tectonic discrimina-tion of ganitoids. Geol. Soc. Am, BdL l0l,635-&3.

MANNslc, D.A.C. & IItrt P.I. (1990): The trFtrogenetic andmetallogenic significance oftopaz granite from southwestF.ngland orefield. ft Ore-bearing Granite Systems; Petro-genesis andMinoalizing Pnocesses (HJ. Stein & JL llamab,ds.). Geol. Soc. Am-, Spec. Pap.26,5I-69.

Mtqus" P.J. (1983): Chemical differentiation of the Bishoptuff and other high-silica mrgmas through crystallizationprocesses. Ge olo gy ll, 3l-34.

Mui.rn, C.F. & Mrrn sFEfl,Dr, D.W. (1984): Exreme fraction-ation in felsic magma chamben: a product of liquid-starediffrrsion or fractional crystallization? Eanh Planet Sci,ktt 6.151-158.

Moons, P.J. (1993): Report of work to January 31, 1993Brooks{aroll hoperly (Imoff and Kakalducas groups),Gloucester County, New Brunswick. New BrunswickDepartnent ofNaural Resources and Erurgy, AssessmzntFikn4n5.

NAsIr, W.P. & CRFcRAFT, H.R. (1985): Partition coefficientsfor trace elements in silicic nagmas. Geochim. CosmochintActa 49,2309-2322.

fbARcE, J.A., IIARRTS, N.B. & TINDLB, A.G. (1984): Traceelement discrimination diagrams for the tectonic interpre-tation of granitic rocks.,/. Petrol, 25, 956-983,

PrerAvANT, M., HERRIRA' J.V., Bouru:m, S., BruQusu, L.,Jono\ J-L.,Jrrnau,IU., MARN, L., Ma{ARD, A-, SITEPARD,S.M.F., TREntr, M. & VRNET, M. (1987): The Macusaniglasses, SE Peru: evidence of chemical fractionation inperaluminous magmas. /r Magmatic Processes: Physico-chenical hinciples @.O. Mysen, d.). Geoclum. Soc.,Spec. Publ. l, 359-3'1 3.

Korvrar! D.J., Brueusu, L., Verwcre l{mnma &CL{R& A.H. (1988): The Mocene-Pliocene Macusanivolcanics, SE Peru. tr. Geochemistry and origin of a felsicperatminous magma Contrib, MineraL P aroL lffi , 325-338.

MoNrnr,, J.-M. & Rtcrraro, L.R (1992): Apatitesolubility in peraluminous liquids: experimental data andan extension of the Harrison-Watson model. Geochim.Cosmochim. Acta 56, 3855-3861.

Rerp, R.P. & WATso\ E.B. (1986): Monazite solubility anddissolution kinetics: implications for the thorium and lightrare-earth chemisty of felsic magnas. Contrib, Mfueral,Petrol. 94,3W316.

Rocms, N., WoDrcKA, N., McNIcor& V. & vm Sreer,, C.R(1997): U-Pb zircon ages of Tetagouche Group felsicvolcanic rocks, northem New Brunswick. 1z RadiogenicAge and Isotopic Studies: Report lL, Geol, Sun. Can-,Pap. l9fl-F (in press).

Sn@soN, DR. (197): Aluminumphosphate variants of feldspar.Am. Mincral. A. 351-355.

Suur.waN, R.W. & vAN STAAL, C.R. (1996): Prelininarychronostratigraphy ofthe Tetagouche and Foumier groupsin nmtlem New Brunswick 1n Radiogenic Age andlsotopicStudies: Report 12. Geol. Surv. Can, Pap. l99.&I,43-56,

TAyLo& H.P., JR. & Smpeano, S.M.F. (1986): Igneous rocks.I. hocesses of isotope fractionation and isotope systematics./z Stable Isotops in High Temperature Geological Proc-esses (J.W. Valley, H.P. Taylor, Jr. & J.R. O'Neil, eds.).Rev. Mincral6,2n-nl.

TAyLoR, R.P. (1992): Petrological and geochemical charac-teristics of the Pleasant Ridge zinnwaldite - topaz granite,southem New Brunswic\ and comparisons with othertopaz-bearing felsic rocks. Can. Mirural. n,895-92L.

TAyLo& S.R. & Md.mwan, S.M. (1985): Thz ContircntalCrust: i* Composition and Evolation, Blackwell ScientifisPubl., Boston, Massachusetts.

vAN STAAL, C.R. (1987): Tectonic setting of the TetagoucheGroup in northem New Brunswick implications for platetectonic models in the northern Appalachians, Can ./.Earth Sci. U, 1329-1351.

690

(199): Geology of Teragouche Fallq New BrunswickGeoL Suw. Ca6 Mq, Open-File Rep.3163 (scale 1:20 ffi).

& FYFFE, L.R (1995): Dunnage Zone - New Bruns-wick /z Geology of Canada 6. Geolog;r of the Appala-chian - Caledonian Orogen in Canada and Greenland(H. Williams, ed.). Geological Survey of Canad4 Ottaw4Ontario (16G178).

Wn{crnsrts& J.A. & Bftiem, J.H. (1991): Geo-chemical variations in Middle Ordovician volcanic rocksof the northem Mranichi Highlands and their tectonicsignific2ass. Can J. Eanh Sci. ?A, fi3L-1049,

WArsoN, E.B. Qn\: Zircon saturation in felsic liquids:experimental results and applications to trce elementgeochemisty. Contrib. Minzral. Petrol, 70, N7 4L9.

(1980): Some experimentally determined zirconlliquid partition coefEcients for the rare earth elements.Geochim. Cosmochim- Acta U. 895-897.

(1996): Dissolution, growth and survival ofzirconsduring crustal fusion: kinetic principles, geological modelsand imFlications for isotopic inheritance. Trans. R Soc.Edinburgh E7, 43-56.

& Caroawco, CJ. (1981): Phosphorus andtherareearth elements in felsic mapas: an assessment of the roleof aoatite. Geochim Cosmochim, Acta 45. 2349-2358.

& GREN, T.H. (1981): Apafite/liquid partitioncoeffrcients for the rare-earth elements and strontium.Earth Plenet Sci. Iztt, 56. 40,5421.

& HARRrsoN, T.M. (1983): Zfucon saturation revis-ited: temperature and compositional effects in a variety ofcrustal mapma tjrpes. Earth Platrct. Sci. Iztt, 9,295-3M.

Wmeoru, K.H. (1995): The composition of the continentalcmst. Geochim. Cosmochim. Acta 59.1217-L232.

Wnar,aN, J.8., Cunnrs, K.L. & cl$rpuu, B.W. (1987): A-type granites: geochemical characteristics, discriminationand petrogenesis, Contrib, Minzral. Petrol. 95,407419.

Wn{cHBsrER, J.A. & Flovo, P.A. (1977): Geochemicaldiscrimination of different magrna series and their differ-entiation products using immobile elements. Chem, Geol.?r.325-343.

Received August 15, 1996, revised manuscript acceptedJanunry 2, 1997.