High-Pressure K.Feldspar . Vesuvianite.Bearing

t269 TheC anolian M ineralo gtst Vol. 35, pp.1269-1275(1997 t

HIGH-PRESSUREK.FELDSPAR . VESUVIANITE.BEARING ASSEMBLAGE IN THECENTRAL METASEDIMENTARY BELT OF THE GRENVILLE PROVINCE, SAINTJOVITE AREA, OUEBEC

RON BOGOCHI

Geological Survey of Israel, 30 Malkhe Israel Street, Jerusalem 95501, Israel

STEVE KUMARAPELI

Department ofGeology, ConcordiaUniversity, Tl4I Sherbrooke StreetWest, Montreal, Quebec H4B 1R6

ALANMATTHEWS Institureof EanhSciences, The Hebrew University, Jerusalem 91904, Israel

ABSTRACT

A lens consisting largely of calcite, microcline, vesuvianilg, quartz, diopside, calcic plagioclase, and wollastonite occws within calcite marble of the Central Metasedimentary Belt (CMB) of the Grenville hovince, in the Saint Jovite area of Quebec. This unusual assemblage exhibits a polygonal granoblastic texture and reflects high-grade phase equitbrium durilg a Grenvillian metamorphic event. The coarse grain-size of the calcite, microcline, vesuvianite and quaxtz in patchy zones within the lens is attributed to grail growth in macro-pressure shadows during shearing. There is no evidence for fluid infiltration, but water may have concentrated by solution-transfer into the patches. A T-X(CO) phase diagram constructed for 26 kbar total pressure suggeststemperatues in the order of >750'C ard X(CO ) at -O.2.

Keywords: K-feldspar, vesuvianite, high pressure, Grenville kovince, Saint Jovite, Quebec.

SoN{ruene

Nous d6crivons une lentille contenant I'assemblage calcite + microcline + v6suvianite + quartz + diopside + plagioclase calcique + wollastonite dans une s6quence de marbre i calcite prds de Saint-Jovite, Qu6bec, dans la ceinture m6tas6dimentaire centrale de la Provhce du Grenville. Cet assemblageinusit6 d6finit une texture polygonale granoblastique et t6moigne d'un 6quilibre de ces phases lors de l'6v6nement m6tamorphique grenvillien. On attribue la granulom6trie grossiBre de la calcite, du microcline, de la v6suvianite et du quartz dans des domaines individualis6s de la lentille I la croissance des cristaux dans des zones prot6g6es i pression isotrope lors d'un cisaillement. Nous ne fiouvons aucune indication d'infiltration d'une phase fluide, mais il est possible que I'eau se soit concentr6e par solution et tranfert vers ces domaines individualis6s. Un diagramme de phases T-X(CO) construit pour une pression totale de 6 kbar ou plus indique une temp6rature de I'ordre de 750oC et une valeur de X(COr) d'environ 0.2. (fraduit par la R6daction)

Mots-clds: feldspath potassique, v6suvianite, pression 61ev6e,kovince du Grenville, Saint-Jovite, Qu6bec.

INrr.olucrroN Edwards 1972), a terrane tlat representsjuvenile Grenvillian crust metamorphosedto a peak of Vesuvianiteis a constifuentof contactmetamorphic granulite-faciesconditions (100 MPa and 950'C), calc-silicaterocks. To date, it has only rarely been as recordedwithin gneisscomplexes (Boggs et al. reportedwithin regionalmetamorphic rockso where it 1994).Other areas, including that west of SaintJovite, occurs,generally in minoramounts, in all facies.Many havebeen reactivated and do not reflect peakconditions of ttre high-pressure- high-temperatureoccurrences of metamorphism(Corriveau & van Breemen1994). are in the Central MetasedimentaryBelt of the Experimental and theoretical phase-equilibrium Grenville Provincein Ontario and Quebec(Wynne- studiesof vesuvianitesuggest that it is stableover a

1E-mail address: [email protected] t270 THE CANADIAN MINERALOGIST wide range of temperatures and pressures. In the presenceof quartzoits stability at low pressuresseerrrs limited to temperaturesnear or below 400"C and very low X(Or) (Hochella et al. 1982). In this study, we examine an unusual lens-shaped body consisting of calcite, K-feldspar, vesuvianiteo q]uartzo clinopyroxene, wollastonite and calcic plagioclase, entrained within granulite-facies marble of the Central Metasedimentary Belt. It is located along Highway 117, some 12 km northwest of Siint Jovite, Quebec).The associationof vesuvianitewith K-feldspar and quartz as major phases in a high-grade assemblage has not been previously reported. A prominent feature that characterizesthe lens is the very coarsegrain-size FIc. 1. Photographofcoarse-grained, subhedral to euhedral of the K-feldspar, vesuvianite, qtrafiz and calcite. microcline. Spacesbetween crystals are the result of acid_leachingof calcite. Gsot,ocrcal. StrrrtrNc

The Meso- to Neoproterozoic rocks (Grenvillian) in the Saint Jovite area of western Quebec consist of two clinopyroxene and calcic plagioclase together form up main groups: the Central Metasedimentary Belt (CMB) to 5Vo, wbereas wollastonite is sporadic, locally reaching to the west, and the Morin igneous complex, domi- l-2%o. Accessory minerals are graphite and titanite. nantly charnockitic rocks of the Central Granulite The rock is typified by the extreme heterogeneity in Terrane (CGT), to the east. These are separated by the grain size. Thus calcite varies from mm size to 2 cm, Labelle shear belt (LSB), a north-south-trending unit microcline, from -0.5 mm to 3 cm (Fig. l), vesuvianite, traversing lithologies of both the CMB and the Morin from mm size to 8 cm, quartz, from -0.2 mm to 3 cm, complex @ivers et al. 1989), folded in this area into an and plagioclase, from -O.2to 5 mm. Clinopyroxene S-shapedkilometer-scale reclined fold (Martignole & (0.1-2 mm), wollastonite (0.5 -2 mm), gaphite (0.5-3 Corriveau 1991). mm), and titanite (0.1-0.2 mm) are more or less The CMB includes calcite marble units meters ro equigranular. The coarser-grained minerals tend to occur hundreds of meters thick, which contain hetero- together as nebulous patches within the lens, although geneously distributed diopside, titanite, and accessory their distribution could not be mapped because of the dolomite, plagioclase, tremolite, vesuvianite, and abundanceof enveloping calcite. wollastonite (Marrignole & Corriveau 1991, L993). Crystal boundaries are straight to slightly curved Thinner calc-silicate units within 16" **6le are rich in (equilibrium boundaries; Spry 1969), and 120" diopside, with variable amounts of grossular, triple-point junctions are common, even where ttre wollastonite, titanite, scapolite, quartz, K-feldspar and grains are coarse.The overall texfure is thus massive, plagioclase. Titanite ages from marble and calc-silicate inequigranular, polygonal granoblastic (Fig. 2). The units occurring -30 km to the west range befween 1133 following equilibrium assemblagesof minerals were and l165 Ma @oggs et aI. 1994). Most of the area lies observed petrographically: Cal-Kfs-Cpx, Kfs-Cpx, within t1t" O-ulite facies, with maximum temperatures Cal-Kfs, Ves-Cal, Ves-Qtz-Kfs, Kfs-Ves, Cal-Cpx, and pressures in the order of 740--790oC and 8 kbar Qtz-Wo, Kfs-Qtz-Cpx, Ves-Cal{px, Wo-Ves-Kfs, (Boggs et al. 1994, Martignole & Corriveau 1991). A marble and calc-silicate unit occurring within and near the eastern boundary of the LSB is bordered to tle west (-200 m) by charnockite, and to the east it is covered by glacial sediments. The assemblage described here occurs along a road-cut of Hi ghway ll7 (now largely quarried by mineral collectors) in a lens approximately 2.5 m long and up to 50 cm wide within coarse-grainedgranoblastic calcite marble. The lens is parallel to the trend of nearby calcite-bearing calc-silicate layers.

Mn\rERALocy

The main minerals in the lens are calcite (8V9OVo), Ftc. 2. Photomicrograph of microclile with typical polygonal K-feldspar (5-lo7o) and vesuvianite (-2-5Vo); quartz, granoblastic texture. Crossed nicols. K-FELDSPAR - VESTIVIANITE ASSEMBLAGE, GREI{VILLE PROVINCE t271

by fractures and with subtle changes in the greyish shade (plane-polarized light) suggest replacement of an earlier mineral. The quartz prisms show marked striations. In general, quartz is coarse-grained where associated with microcline, and finer in the calcite-dominated masses. Euhedral to subhedral crystals of wollastonite were observed in contact with all major phases (Fig. 4). Subhedral to euhedral grains of slinspyloleas

Frc. 3. Photomicrograph of calcite (light $ey), microcline (medium grey) and pyroxene inclusions (arrow). Plain liCht.

and Kfs-Qtz-Cal (minerals for each assemblage listed in decreasing order of relative abundance).The symbols are those of Kretz (1983). Calcite shows twin lamellae in fwo, and locally in three planes. It is coarser grained where associated with the silicate minerals, and finer where it is the dominant Frc. 4. Photomicrograph of vesuvianite (grey), wollastonite phase, although in the latter, it is still at least twice as Qight grey, center), microcline (cross-harching) and quartz coarseas in the host marble. In single sectionsoit occurs (white, top). Crossed nicols. both as a coarse-grained major phase with straight to curved boundaries with the silicate species, and as a finer-grained interstitial phase, particularly with occur randomly as a poikilitic phaselargely within K-feldspar, which it also envelops (Fig. 3). microcline, calcite and vesuvianite.Their form and The K-feldspar (perthitic microcline) exhibits optical propertiesare similar to the clinopyroxene typical cross-hatchedtwinning with elliptical to lobate occurringwithin calc-silicaterocks in the area.Flakes shapes outlining crystal boundaries. A section fortui- of graphite have a similar distribution. Calcic tously cut parallel to (010) exhibits pericline lwinning plagioclaseoccurs sporadically as largecrystals up to with elongate "patches" representing cross-sectionsof -0.5 cm in sharp contact with microcline, calcite, coarse plate- or vein perthite (with minor albite quartz,and vesuvianite, and is locally replacedby the twinning). Most of the albite present occurs as film quartz. Small subhedralto anhedralgrains also are perthite parallel to the Murchison plane. In local embeddedwittrin calcite and microcline.Titanite is domains olsesmingly untwinned microcline, the albite rare, occurringas roundedgrains within vesuvianite lamellae appear to be longer (-2<) than in zones of andmicrocline. cross-hatching. Certain zones of film perthite appear to be distorted, apparent plate perthite exhibits z-forms, Mnvpnar CrmvnsrrY and a microfault slightly displacing some, but not all of the film perthite it crosses,is itself filled with albite. Pulverized concentratesof the minerals were These features suggest albite exsolution during rock scanned using a Philips PWL730/17lO X-ray deformation, as suggestedby Evans & Guidotti (1966) diftactometer with CuK radiation.Chemical analyses based on a "spiral" arrangement of perthitic albite. of tlose mineralswere madeusing a JEOL 840 SEM Eskola (1952) and.others (as summarized in Smith with an attached Link 10000 energy-dispersion 1974) suggested that shearing stress is important for the spectrometer(EDS; ZAF4 program) on polished formation of microcline. sections (comparison with standard block files). On a fresh surface, the vesuvianite is honey-brown, The accuracyis !57o. Concentrationsof major and with a vitreous luster. It forms "stocky" prisms, in traceelements in selectedsamples of vesuvianiteand general with a length-to-width ratio of 2-3:1, and K-feldspar were measuredby inductively coupled where relatively fine-grained, occurs as rectangular plasma- atomic emissionspectroscopy (ICP-AES) forms in thin section, A distinct cleavageis absent,and and inductivelycoupled plasma - massspectrometry the fracture is irregular. In one crystal observed under (ICP-MS), and KrO and Na2Oby atomic absorption the microscope, remnant crystal forms, partly outlined spectroscopy(AAS).For the major elements,samples r272 THE CANADIAN MINERALOGIST

TABLEIA" CHEMICALCOMPOSITION OF TABLE IB. CHEMICAL COMPOSMON OF VEST'VIANITESAINTJOVITE QUEBFC: vEsrwrANITq SNNT JOVITq QUEBEC: MAIORELEMENTS TRACEELEMENTS E @ -il l0 Tiq 1.8 1.9 t.a t.n 2.0 2.0 z0 Cr 90 103 I40 - 168 90 95 Alrq 16.5 t7.4 16.3 17.M t73 t72 17.5 NI ' t0 l0 l0 FqOl 4.0 3.9 3.9 3.62 3.4 3.5 3.4 -2& 20 TO MnO 0.04 0.04 0.04 0.03 0.03 0.m Pb - 8.4 I I.6 1.7 MgO 1.9 1.9 1.8 201 1.9 1.9 1.8 7^ 93 tO1 t05 ,q) y.74 95 % m 34.0 35.0 33.8 3s.5 343 35.t c\ ': '0, -25 1 <5 NqO 02 0.5 02 0.43 0.1 0.1 02 Mo - <10 <10 <10 - KzO 0.1 - 027 - 0.06 0.05 0l ' - € s3 0.6 02 0.5 0.t R5 <10 10 <10 - t0 l2 t0 PrO. 0.t 0.r 0.1 k 787 - 't.8 7.7 8.8 - LOI 3.6 2.8 2.8 L6 2.6 1.6 Sr 32n 300 270 - 280 280 275 ffi h 9 1 LI - 280 300 315 B -58 50 58 Nmber of ims basedon 50 total cims U - 5.4 5.1 5.4 Th '23 20 24 Al3' 9.50 t023 9.55 9.88 l0.l? t0.t5 t0.67 Y 52 63 62 _53 51 53 Tr 0.66 0.7t 0.67 0.6 0.15 0.75 0.78 b 62 75 76 -75 81 69 MgP 1.38 lAl 133 1.41 I.4l 1.42 1.39 G t': 'r: 11 - 143 t55 138 Mn* O.tZ 0.m O.92. - 0.0| 0.0I 0.0I '17 t9 t1 Fd' 1.47 1.46 t.46 1.34 Ir8 t.32 t.32 Nd 1l 66 c€' 17.79 18.70 18.(F l8r9 18.95 18.40 19.45 l4 t3 Na" 0.19 0.49 0.19 0Al 0.10 0.10 020 Eu 2.6 2.8 2.a - 3.0 3-4 2.8 - K' 0.0? - 0.17 - 0.04 0.fi1 ft - 1.9 2.0 2.0 P" o.o4 0.04 0.04 Gd I3 t3 s- 02. - 0.01 - 0.t9 0.04 Dy - II ]I ]I oH' 1t.13 9.3t 928 10.9t 8.A 8.6E 5.52 Ho 22 rx 17.98 1926 18.19 t8.87 19.05 18.54 19.68 E - 6.8 12 6.E >Y r3.0? 13.87 t3.07 t335 t3.62 t3.6 14.17 Td - 1.0 1.0 I.0 >z 18.47 18.36 6.8 - 7.O 1.4 Lu ll II Proportion of mjor

were heated to 1050"C (loss on ignition, LOI), fused chalcophile metal deposit, REE it association with with LiBO2, and dissolved in HNO3. For trace elements, alkaline rocks: Deer et al. (1982), and transition metals samples were sintered with NarO2 and dissolved in in vesuvianite from ultramafic settings: Economou & HNO,. Accuracy for major elements is better that2%o, Marcopoulos (1980)1, and perhaps to the nature of and for trace elements, 10%. skarn-forming fluids. The trace-element data for The microcline (Abr_,,) and albite (Abs2_r6)are close vesuvianite from the lsas hinfs at slightly anomalous to end-member compositions, consistent with retro- values for Ni + V Zn + Cu, and Sr. gression to a lower temperature, and the plagioclase is calcic (An-rJ.The clinopyroxene within the lens DrscussroN is (ferroan) diopside; within aea16t calcite-bearing calc-silicate layers, it is apparently slightly richer in Ca The coarse grain-size of the K-feldspar, vssgvianifs, and total Fe at the expense of Mg. The wollastonite quartz and calcite within the lens are reminiscent typically contains 53VoSiO2, 45Vo CaO, l7o Fe2O3and of contact-metasomatic skarns, which are present O.I to O.sEoeach of Al2O3, K2O, and NarO. throughout the Grenville, especially where marble is Compositions of the vesuvianite are presented in found, and are cornmon in regions of high-grade Table 1. There are minor variations in the composition metamorphism (Shaw el al. 1963). Nevertheless, a of the vesuvianite taken from different parts of the lens. regional metamo{phic origin is preferred for the Compared to an average of the twenty-four composi- following reasons: 1) The host marble in the area are tions of vesuvianite in Der;r et aL (1982) and the twenty not intruded by syn- or late-tectonic granite massifs, compositions in Groat et al. (1992), our samples are such as those noted by Martignole & Corriveau (1.993). slightly elevated in their Ti contents and depleted in Mg 2) "Classic" skarns or skarn-like bodies are absent in and Ca, although they are within ranges of those the area, and textures of the host marbles and spatially reported therein. The magnesian vesuvianite of Valley associatedcalc-silicate rocks are those encountered in et al. (1985) is not significantly differento containing regionally metamorphosed rocks. Skarns tend to have more Al, less total iron, and slightly more Mg. irregular textures indicative of disequilibrium (Spry There has only been limited trace-element data 1969). 3) Geochemical evidence for skarn-related reported for vesuvianite. Unusually high enrichments vesuvianite, such as high Be contents (-800 ppm: in vesuvianite have been reported for B, Be, Bi, Pb, Cr, Watters & Brooks 1982), are lacking (<10 ppm Be in REE, Cl, Cu, Zto Sb, Li, Cr, U and Th, (Deer et al. vesuvianite from lens). 4) The calcite marble in the 1982, Groat et al. 1992). In certain cases, metal enrich- Saint Jovite area originated as shallow marine ment in vesuvianite may relate to the host litlology sediments @ivers et al. 1.989),within which are thin le.g., Cu, Zn, and Be at the planklia, New Jersey layers and erratic pods of calc-silicate rocks likely K-FELDSPAR - VESITVIANTTE ASSEMBLAGE, GRENVTTT F PROVINCE t273 derived by the metamorphismof marls (Martignole & An additional enhancementfor coarsening may relate Corriveau 1991). A1l minerals within the lens are to the presenceof areasof varying rigidities, depending, present,as major components or asaccessories, within 161elample on differential compaction of the sediment eitherthe regionalmeramorphic calc-silicate rocks or matrix (Spry 1969) or original heterogeneousmineral calc-silicate-bearingmarbles. Although the assemblage distributions.,{ssrrming opposing-senseshearing near within the lens differs in terms of mineral proportions the walls of the lens, these "rigid heterogeneities" or *rigldity from both of tlese rocks, its overall chemical contrasts'ocould yield relatively low-pressure compositionwould be compatiblewith, for example, zones, similar to pressure shadows (Spry 1969) on a illite-bearingmarls. It is thus not necessaryto invoke macroscopic scale. This could explain the "patchy" an "outsideo'source (such as a skarnfluid) for any of nature of the coarse-grainedminerals. the major elementspresent in the lens.The level of concentrationof REE and most other traceelements T-X( C O 2) phnse relations are of the sameorder of magnitudeof thosereported in theNASC (NorthAmerican Shale Composite: Gromet Hochella et al. (1982) and Valley et al. (1985) have et al. 1984).A plot of the REE data normalizedto shown tlat the stability field of vesuvianite + quartz the NASC shows a fairly smooth, near-horizontal at a fluid pressrue less than 2 kbar is restricted to low distribution(Fig. 5), thussuggesting a similil.p16surs1 T (<400"C) and low X(CO) (<0.06). Howevero since for theREE in vesuvianitefrom the SaintJovite lens. the quartz - vesuvianite association is found in amphibolite-faciesrocks, YaJIeyet aI. (1985) suggested that solid solutions in vesuvianite (principally the incorporation of F, Fe3*,Tia) may extend the thermal stability of the assemblagevesuvianite + quafiz. ln an attempt to constrain the conditions of metamorphism, we have made calculations of T- X(COr) equilibria involving the minelal assemblages. The calculations are made using the end-member compo- I-a Ce k Nd Sm Eu Gd Tb Dy Ho Er Tm yb Lu sitions rather than measured compositions. This approach allows the equilibria to be represented as a Frc. 5. Plot of the REE dataDLormalizedto the North American series of stable nnivariant reactionsoand seemspreferable shale composite (Gromet et aI. 1984). to a more complicated analysis involving the calculation of divariant and univariant equilibria. The T-X(CO2) equilibria were calculated for 6 kbar using the program As defined by metallurgists(references cited by Thermocalc v2.3 @owell & Holland 1988, Holland & Karcz 1964),grain growth is a processof migration of Powell 1990) in the KCMASH system (CaO-KzO- grain boundariesby which the grain mosaicadjusts MgO-AlrO3-SiO2-H2NOt using end-memberphases: itself to the requirementsof minimum surface-tension. calcite (cal), vesuvianite (ves), potassium feldspar ln sedimentarydolomites, grain-growth fabrics are (kfs), quartz (qtz), diopside (di), wollastonite (wo), indicated by (i) a high proportion of triple-point anorthite (an), muscovite (ms), CO2, and H2O. The junctionsat anglesin the 100-140orange, and (ii) equilibria are plotted in Figure 6. The mineral assem- boundariesat the junctions that are usually concave blage in the lens is approximately centered around awayfrom the smallestangle (incomplete adjustment). invariant point (I) (ms-absent; wo-present), with Both thesefeatures are found within the coarse-grained X(CO) of -0.2 and T close to 740"C. The field of "patches" in the lens. Karcz (1964) also found that stability of the whole assemblage is delimited by the featuresof grain growth are common near "planes of reactions forming muscovite on the low-temperature dislocation" and suggestedthat tectonic stressmay and low-X(CO2) sides. The shaded area shows the more have suppliedthe energynecessary to "unlock" the restricted stability field in terms of T- X(CO2) for the boundaries.For the lens assemblage,deformation in assemblagekfs + wo + ves @g. 6). the LSB may haveinitiated crystal-facere-adjustmenrs, The choice of 6 kbar for the T- X(CO) calculation with the shapeof the grain boundariescontrolled by is meant to give a representative value for the 4- to grain-boundaryenergy (Spry 1.969)to produce the S-kbar range of pressure, at which tle assemblage polygonalgranoblastic texture. The regionaland local could have formed. The position of the invariant point lithologies lie within the granulite facies@oggs et al. is dependenton pressure;fe1 slampleo with a pressure 1994,Martignole & Corriveau1991), and all minerals of 8 kbar, the point is moved to 820oC and X(CO2) = within 6" lensare individually stable yithin granulite- 0.27. This is a slightly higher temperature than the facies terranes. Coarse grain-sizes in high-grade estimated 64alprrm regional temperature of metamor- calc-silicaterocks may be enhancedby the presenceof phism, 750-790oC. However, bearing in mind that the abundantcalcite, which could promoteionic mobility calculations have used end-member phases (1.e.,are not (spry 1969). activity-corrected for real compositions), conditions of THE CANADIAN MINERALOGIST wo+ves+kfsassembl

^-/ .Jgi- /^\ -.;F - - - 6tiq, *it- :j _---;;f-'-,,-Jt,-, ),:- -Xy:tt''- .', -,.: -;>' (ms,kfs) U F ";'..\i:-"".-- /,: I ms+qtz+cal \tt-.rfti 3i::'-\(wo)

"4)

(l) ms+ves+cal= Ks+an+di (2) ms+ves+di+cal= kfs+an (3) ms+di+cal+an= kfs+ves = (4) an+di+cal+ms+kfs ves x(co2) 0.15 0.30 a(LrJ2la,/a"1/\ \

Frc. 6. Calculated univariant T- X(CO) equilibria diagram at 6 kbar for the system CaO-K2O-MgO-AI2O3-SiOz-H2HO2. End-member phasesused in the calculations are muscovite (rns), potassium feldspar @s), wolastonite (wo), calcite (cal)' point (D: all phases present, ms and kfs +afiz (qtz), diopside (di), anorthite (an), vesuvianite (ves), CO, and HrO. Invariant absent; invariani point (tr): all phasespresent except wo. Inset shows how position of invariant point I varies with pressure. The shaded area shows the stability field for the crifical assemblage kfs-ves.

750-800"C, 6-8 kbar and X(CO, in the range 0.2 to tratedby solution-transfer@urney 1972)nto the rela- 0.27 for the invariant-point assemblageare seen to be tively low-pressurezones that resultedin the forrnation consistent with those of regional metamorphism. of the coarse-grainedvesuvianite-bearing assemblage. The fluid phase is thus seen to be H2O-rich, as noted in other studies on the stabiliry of vesuvianite- Acre{owLEDGEN{ENTS wollastonite-bearing assemblages (Valley et al. 1985). The presenceof a mineral assemblagethat is close We thank Louise Corriveauand Walt Trzcienskifor to or at an invariant point condition suggests that the their detaited and most helpful reviewso and fluid composition was "rocK'-buffered. This does not Sarah Ehrlich, Olga Yaffe and Dina Stieber (GSI eliminate the possibility of infiltration of metamorphic GeochemicalLaboratory) for the analyses. fluid, but may be taken as further support for the notion that there is no involvement of an externally derived REFERENCES fluid. The "formation water" within the sediments that BAER,A.J., Poor-e,W.H. & Ser.rnoRD,B.V. (1971):Rividre formed the lens (trapped by the host marble, an Gatineaugeological map. GeoI. Sarv. Can., Map L3344 impenetrable barrier) may have been locally concen- (1:100,000). K-FELDSPAR _ VESI'VIAMIE ASSEMBLAGE. GRENVILLE PROVINCE r275

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