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Amphibole and Pyroxene Development in Fenite From Conadian Mineralogist YoI.22, pp. 281-295(1984) AMPHIBOLEAND PYROXENEDEVELOPMENT IN FENITEFROM CANTLEY, OUEBEC* DONALD D. HOGARTH Ottawa-CarletonCentre for GeoscienceStudies, University of Ottowa,Ottawa, Ontorio KIN 6Ns PIERRE LAPOINTE Earth PhysicsBranch, Department of Energy,Mines and Resources,Ottawa, Ontario KIA 0Y3 ABSTRAcT l'h€denbergite,I'aegyrine tardive, le diopside.L'aegyrine tardivese d6veloppe lors dela croissancedes oxydes de fer Proterozoic fenites near Cantley, Quebec, formed from et de titane. Lespyriboles sodiques qui Cvoluentdans un biotite gneiss and hypersthene-augite gneiss by systbmeouvert tels ceux des f€nites de Cantley,definissent metasomatism possibly related to carbonatite, are descourbes dans les diaglammesde variation chimique; characterized by magnesio-arfvedsonite, magnesio- par contre,ceux d'un systdmeclos ont tendancei segrou- riebeckite and aegirine. The ratio Ca,/(Ca+Na+K) per, et ceuxqui proviennentde protolithes de composition decreasesfrom older to younger pyriboles. In maguesio- chimiquevariable montrent, ind6pendamment du systdme, arfvedsonite, the ratio Fe1/@e1+Mg) first increasesand une distributional6atoire. then decreases,but K remains constant with respectto Na and Ca. Magnesio-riebeckite,replacing cummingtonite or Mots-clds: f6nite, magndsio-arfvedsonite,magnCsio- hypersthene, shows a trend similar to that of magnesio- riebeickite,aegyrine, m€tasomatisme, variations chimi- arfvedsonite but is notably depleted in K and F. In ques,oxydation, graben Ottawa - Bonnechbre,Qu6bec. magnesio-arfvedsonite,and possibly magnesio-riebeckite, the-A sites are progressivelyfilled. Na-amphibole and Na- INTRoDUcToN pyroxene, in the same hand specimen, are approximately coeval. Early aegirine substitutesfor the hedenbergiteend- The chemical trends illustrated by Na-amphibole member, and later aegirine, for tle diopside end-member. and Na-pyroxene from fenite have not been clearly Iate aegirineis contenporaneouswith major growth of @e, defined. Attempts have been made to outline these Ti) oxides. Na-pyriboles from open systems,such as those trendsin a generalway (e.9., Sutherland1969, Var- of the Cantley fenite, tend to define curves on chemical tiainen & Woolley 197Q,but thesewere not entfuely variation diagrams,whereas those from closedsystems tend to cluster; those formed in either syslem, but from pro- succe$sful,in part owing to lack of care in sample toliths of different chemical g6mpo5itions, give random selection and impure mineral separates.In order to plots. define fenitic pyribole trends more precisely we will describethese minerals from a small area that shows Keywords: fenite, magnesio-arfvedsonite, magnesio- minimal variation in the protolith. We will also com- riebeckite, aegirine, carbonatite, metasomatic rocks, pare these pyriboles with those of three other - chemical trends, oxidation, Cantley, Ottawa Bonne- nonigneousocclurences, each with a distinct origin. graben, chdre Quebec. In this paper thelermpyribo/e is usedto refer col- Soruuernr lectively to pyroxene and amphibole. An areanear Cantley, Quebec(Fig. l) wherefenite Les f6nites d'6ge protdrozoique de la rdgion de Cantley replacesvarious Precambrian rocks was chosen for (Qu6bec) ort 6t6 formees i partir d'un gneiss d biotite et this research.Occurrences were selectedfrom two hypersthdne- augite par un m6tasomatismequi serait reli6 metasomatized protoliths: biotite gneiss and d une carbonatite. Elles sont caract6ris€espar la pr6sence hypersthene-augitegneiss. Fenite, Mg-Fe-Na magrr6sio-arfvedsonite,magn€sio-riebeckite "the de et aegyrine. silicate zone" in Figures I and 2, is delineated by Dansles pyriboles, le rapport Ca,/(Ca+Na+K) ddcroftdes the presence, plus anciennes aux plus r6centes. Dans la magndsio- of Na-amphibole and Na-pyroxene arfvedsonite,le rapport Fe1/@e1+Mg) crolt d'abord et basedon field observations.Sample selection was puis diminue; par contre, le rapport K{Na + Ca) restecons- basedon representativemineral associationsand the tant. La magn6io-riebeckite,qui remplacesoit la cunming- suitability of grains for microprobe and petrographic tonite, soit I'hyperstlbne, secomporte commela magn&io- examination. arfvedsonite sauf appauvrissementnotable en K et F. Dans The fenites in this area were described briefly by la magn6io-arfuedsoniteet peut4tre la magn6io-riebeckite, Hogarth & Moore (1972)alid, Hogarth (1977).Fur- I'occupationdes sites.4 sefait de fagon croissante.L'am- ther details are to be found in the thesis of Lapointe phibole pyroxtne et le sodiquc d'un m0me€chantillon sont (1979)and the regionalreport of Hogarth (1981).The d peu prbs contemporains. L'aegyrine prdcoce remplace associatedoxides have been describedby Cockburn (1960. This researchis part of an ongoing study at *Publication 05-84 of tlte Ottawa-Carleton Centre for the University of Ottawa on the geology of the GeoscienceStudies. Gatineau-Lidwe district. 281 Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/22/2/281/3446023/281.pdf by guest on 29 September 2021 282 THE CANADIAN MINERALOGIST PRECAMBRIAN .* FAULr ::......]:' F+l GRANITE APPROXIMATEUMIT OF Mg-FE-NO-SIUCATEZONE E MENADIORITE SAMPLE LOCATIONS g MARBLE A CAJ-SIUCATE ROCK r Mg-Fe-No-stucATE RocK BIOT]TE GNEISS.MINoR HYPERSIHENE- O Mg-Fe-No-sruclirE RocK wrrH Fe-Ti-oxlDEs a AUGM GNEISS A OUARTZITE Ftc. l. Map showinglocation and geologyof study area(generalized after Hogarth l98l) and samplelocations. Limits of the Mg-Fe-Na zone mark the field-observed disappearanceof Na-amphibole and Na-pyroxene. Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/22/2/281/3446023/281.pdf by guest on 29 September 2021 AMPHIBOLE AND PYROXENE DEVELOPMENT IN FENITE 283 mingtonite, saponite and biotite after hyperstene, hornblende and biotite after augite, chlorite after biotite, and sericite and scapolite after plagioclase. In addition, the monoclinic K-feldspar has inverted to microcline. Numerousbodie of fenite, tlte largest2500 m long and 150 m wide, are situated in a belt that approx- imately parallels the regional foliation. This belt at- tains a maximum thickness of 4 km near Cantley, whenceit can be traced northeasterlyfor 22kmto an occurrence near the Libwe River. The fenite replacesor transects all the above rock types and is superimposedon both the unaltered and retrograde minerals. A "silicate assemblage"characterizes most of the specimenslisted in Table l. It is composedof major amounts of Na-pyribole, lesseralbite and substan- tl ABJNDANTFE -Ti-OIIDE VEINS tial quantities of phlogopite. Associatedminerals are Mg-Fe -No-srLrcATE zoNE disseminatedhematite and minor but typical calcite, M barite and apatite. It appearsas patches, dissemina- E BIOTITEGNEISS tions and cross-cutting veinlets. Indisputable l:F..'-----Tl -AJGITE Li;jjjill HYPEFIITHENE GNESS replacement-textures,such as aegirinepseudomorphs .f..* PRINCIPALVEINS (INCUNED, VEFNCAL) (and partial pseudomorphs) after biotite, were FOUANON ( INCUNED) observedin severalthin sections. Coarse-grainedoxides of iron and titanium (the ,t.i;: SllAMP "oxide assemblage")are present in cross-cutting Ftc.2. Detailedgeology of theHaycock Mine and vicini- veins and lensesof specularite-rutile-magnetite(a9., ty. Locationis givenby rectangleon Figure l. specimen 127, Table l), veinlets of specularite- calcite-barite, and strike fracture-fillings of specularite-rutile-apatite (e.9., specimen002, Table 1). The surrounding rock is largely replacedwith the GsoLocv silicateassemblage. Cross-cutting lenses, the largest The map area lies on the western flank of an 3.5 m across,were testedfor iron ore in the 1870s almost isoclinal synform, overturnedtoward the east (the Haycock mine: Cirkel 1909).Commonly, the and plunging northward. Within this synform, the oxide veins and lensesare most abundant in the core principal rocks define a high-grade metamorphic of an occurrence; the comparatively oxide-free suite belonging to the Grenville Supergroup. The silicate assemblagecharacterizes the envelope @ig. ascendingsequence is graphitic marble and granite 2\. orthogneiss(left-hand side, Fig. l), a thin layer of Two Ca-Ba-R.EE carbonatites, associated with quartzite (omitted for simplicity), biotite gneissand fenite, crop out on the west side of the synform minor interlayered quartzofeldspathic and (north of Fig. l) and on the east side (northeast of hypersthene-augite gneisses(centre of area) and, Fig. 1), and are possiblythe sourceof metasomatic finally, a non-graphitic marble and metadiorite solutions that formed the fenites. With the excep- (right-hand side, Fig. l). Neither "glanite" (granite tion of three small syenite dykes on the east flank to granodiorite) nor "metadiorite" (quartz diorite of the synform (3 km east of the c€ntreof Fig. l), to diorite) show cross-cuttingrelationships with sur- no alkaline intrusive rock is known in the immediate rounding rocks. They are concordanfly foliated near area. tleir margins and display an igneous texture (por- The age of the fenite can be tentatively placed in phyritic and ophitic, respectively)in their cores. All the interval 850 to 1050 Ma. The Cantley fenite rock types are cut by small dykes of granite postdates granite pegmatite but probably is older pegmatite. Gneisses have attained the granulite than the K/Ar ages determined from phlogopite metamorphic facies, indicated by the associations separatedfrom fenite at the Haycock mine (980* 52 hypersthene + augite + andesine, hypersthene * Ma, M. Shafiqullah,pers. comm.; 862*31 Ma, almandine + andesine, hypersthene + K-feldspar
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