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Geology of the Garnet Mountain-Aquila Ridge area, Ice River, British Columbia Jones, William Charles 1955

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GEOLOGY OF THE GARNET MONTIN-]4QUILARIDGE AREA, ICE RIVER, BRI’USH COLTJIBIAbyWILLIJM CHARLES JONESA THESIS SUViITTED IN PARL FUIFIUIIENT OFTHE REcUIREMENT8 FOR THE DEGREE OFMTER OF SCIENCEin the DepartmentofGeology and GeographyWe accept this thesis as conforming to thestandard required from candidates for thedegree of MASTER OF CIENCEMembers of the Department ofGeology and GeographyTHE UNIVERSITY OF BRITISH COLUMBIAApril, 19551.ABSTRACTThe Ice River igneous complex, exposed in thesouthern part of Yoho National Park in the Field area, BritishColumbia, is an asymmetrical laccolith made up of severalvarieties 01’ undersaturated alkaline igneous rooks. Neohelinesodalite sye.nite and urtite, two of the major types, aredescribed.Several theories on the origin of undersaturatedalkaline igneous rocks are discussed and it is concluded thatDaly’s limestone syntexis theory best explains the origin ofthe Ice River complex.In the vicinity of Garnet Mountain and Aquila Ridge,the north—west extension of the laocolith has contactmetasomatised enclosing limestone and limestone inclusions.The mineralogy and petrology of several extensive skarn zoneswhich carry pyrochiore and radioaotiye minerals are described.The concentration of certain elements in alkaline igneous rooksis considered and the, addition of Na, K, Cb, Zr and others toIce River limestone is described.•ii..ACKNOWLEDGEMENTThe author wishes to express his appreciation to Drs.R.M. Thompson and K.C. MoTaggart o the Department of Geologyand Geography for their helpful suggestions and criticismsthroughout the course of this investigation; to Dr. v.r.Okulitch, Chairman of the Department of Geo1or and Geography,for his aid with photographing of thin-sections; to Mr. J.Donnan for the preparation of the thin-sections and to Miss P.Everett for the typing of the manuscript.IIii’.TABLE OF CONTENTSPageABSTRACT I.ACKNOIiEDGEMENT8 ii.ChAPTER I: INTRODUCTION AJND GENEF GEOLOGY 1.Introduction 1.Physiography and Stratigraphy 3.Igneous Geology 4.Structure 4.Igneous Rock Types 5.Introduction 5.Leucooratic Group 6.Mesotype Group 7.Melanooratio Group 7.Metamorphism and Metasomatism 8.Age of Intrusion 9.CHAPTER II: GEOLOGY OF TRE GARNET MOtJTAIN-AQtJIIARIDGE AREA 10.Introduction 10.Igneous Rocks 10.Nepheline-sodalite syenite 10.Urtite 11.Acmite-niicrooline rook 12.Metasomatised Limestone 13.Lower Contact, Garnet Mountain 13.Limestone Inclusions in Igneous Rook 17.Garnet Mountain Inclusions 17.iv.Main Aquila Ridge Inclusion 19.CIL4PTER III: INERILOGY 22.Pyroxenes 22..Amphiboles 23.Microcline 24.Natrolite 25.Garnet 25.Rutile 25.Unidentified mineral (1) 26.Unidentified mineral (2) 26.Pyroohiore 26.Unidentified radioactive mineral 27.CEPTER IV: T1IEOREflCL CONSIDERATIONS 35.Theories on the Origin of Undersaturated. AlkalineIgneous Rocks 35.Origin of the Ice River Complex 40.,Rare Elements in Igneous Rocks 42.Metasomatism by Undersaturated Alkaline Igneous Rocks 44.BIBLIOGRAPHY 56.LIST CF ILLUSTRATIONSPLATE I 47.PLA’IE iiPLATE III 51.PLATE IVPLATE V 54.PLATE viV.2.Figure 1:Figure 2:Figure 3:34.Figure 4:Figure 5:Table 1:18.32Table 3:42.43.Table43.TableIn pocket.MapTable 2:4sketch-mapShowing Location of Ice River ComplexIsometric Drawing of Ice River ComplexAomite - Universal Stage DeterminationMicro dine - Universal Stage DeterminationPhase Diagram for the System NephelineKaliophilite-SilicaMineral Assemblages in Metasomatised Limestoneat the Lower Contact, Garnet MountainDistribution of Radioactivity in Aquila RidgeRadioactive ZoneAverage Cb and Ta Content and Cb-Ta Ratios inIgneous Rooks4: Abundance of Uranium in Igneous Rocks5: Concentrations o Rare Elements in Magnias1.GEOLOGY OF TEE GAR1\ET IOUNTAIN-AQUILARIDGE AREA, ICE RIVER, BRITISH COLUMBIACHAPTER IINTRODUCTION A1’fl) GENERAL GEOLOGYIntroductionThe area under discussion in this paper lies withinthe southern tip of Yoho National Park in the western part ofthe Rocky Mountains in British Columbia. It is easily reachedby motor road from Leanchoil which is situated on the main lineof the Canadian Pacific Railway and on the Trans-Canada Highway.From Leanchoil, a twelve mile long unpaved government roadfollows southerly along the north—east side of the BeaverfootRiver to a point one mile upstream from the mouth of its southflowing tributary, Ice River. From this junction, a good packtrail leads up Ice River Valley. Garnet Mountain and AquilaRidge, the areas discussed in this report, are located on thewest side of Ice River Valley about six miles from the mouth ofthe river (see sketch—map, Fig. 1, p. 2).Some four hundred, square miles of Yoho Park and theSKETCH- M,P SHOWING LOCATIONIu1, 1t1t GOQDS,RI lC RIVERSCALt I’2 MLZ5OF ICE RIVER COMPLE)(:3.surrounding region werestudied and mapped by T.A. Allan of theCanadian Geological Survey in 1910—1912. His report is entitled:“Geology of Field Map—Area, British Columbia and Alberta”, G.S.C.Memoir 55.Three days were spent by the author in company withDrs. R.M. Thompson and K. C. McTaggart of the Department ofGeology and Geography, University of British Columbia, in studyingthe geology and collecting rock and mineral specimens in thevicinity of Garnet Mountain and Aquila Ridge. Because of the verylimited time spent in he area, much of the following generaldescription is taken from Allan’s account (1914).Physiography and StratigraphyThe Ice River area displays an early mature stage oferosion and consists of rugged, narrow ridges and peaks betweenwhich occur broad, relatively flat valleys. Wide streams flowalong the valleys and numerous smaller .obsequent streams incisethe slopes forming the sides. Some peaks attain a height of over10,000 feet but the average interstream ridge is about 8,000 feetabove sea level. Ice River Valley, like other valleys in thedistrictf is believed by Allan to be of pre—glacial origin buthas become trough—shaped and deepened by glacial action. It nowcontains thick alluvial sands and gravels on which the riverassumes a meandering course in its upper few miles. Toward itsmouthhowever, the river becomes turbulent. Chancellor Ridge,which forms the west side of Ice River Valley and which separatesIce River Valley from the Beaverfoot Valley, is a rugged, sharpridge, most of which is over 8,000 feet in elevation. The eastside of the valley is formed by a similar ridge which separates4.Ice River Valley froi M9ose Creek Valley and culminates in Mt.Goodsir (elev. 11,676 feet), the highest peak in this sectionof the Rockies.In the area mapped by Allan, a thick sedimentaryseries ranging in age from Pre-Cambrian to Silurian is exposedand within the Ice River Valley, various types of fine-grainedmarine sediments ranging in age from Upper Cambrian to Ordovicianare exposed. These rocks have been folded into a broadasymmetrical anticline, the axis of which trends north—southapproximately along the course of Ice River.Formations Exposed in Ice River ValleyName Thickness Rock TypesOrdovician Goodsir 6000’ Shale; slate; lms; cherty 1msU. Cambrian Ottertail 1550’ Limestone; some shale.Chancellor 1160’ rgi11ite; shale.Igneous GeologyStructureThe alkaline Ice River intrusive complex, which isexposed in Ice River Valley, Moose Creek Valley and on the intervening ridge, is believed by Allan to form an asymmetricallaccolith with a stock—like feeder (see fig. 2, p. 5). om thestock, which is located in the southern part of Ice River Valley,a still—like extension projects northward along the east side ofChancellor Ridge for a distance of pproximate1y seven miles.This extension ends abruptly in Ottertail limestone a few hundredyards south of Chancellor Peak. Another sill—like extensionprojects north—eastward from the stock and trends across MooseCreek Valley. Much of this extension has been removed by erosionIDEALIZEDFig.2I5O11ETRICDRAWINGLEUCCCATiCTYPOFICER?VERCOMPLEX—AFTERA.ALLAN(I)4)LEGENDMESOTYPE5MELANQCRAT,CTYP56.but a small, isolated eOsional remnant of it is exposed on theeast side of Moose Creek Valley near the headwaters of MooseCreek.A rough layering is evident in the stock, the darkercoloured rook types generally occuring lower than the lightercoloured types. In thin parts of the complex, layering is lessconspicuous. However, layering was observed in the north-westextension on the north side of Garnet Mountain. Because of thesteepness of the cliffs in the latter area, the layering couldnot be studied in detail.Igneous Rook TypesIntroduction:Allan divided the rooks of the complex into three majorgroups based on mineral composition. Many diverse types exist ineach group and all gradations are present which makes dividinglines only approximate.Leuco orati c Group.Rocks of the leucocratic group compose about two-thirdsof the complex. They form the stock and smaller outcrops arefound on the eastern slopes of Garnet Mountain and Aquila Ridge,on Zinc Mountain which is located about one mile north-east ofthe main stock and at the extreme tip of the eastern extension.Nepheline syenite is by far the most abundant rock typeof this group. In general, rocks of this group are light incolour, coarse-grained and somewhat inequigranular. They arecomposed essentially of nepheline and potash feldspar withsubordinate amounts of pyroxene and amphibole. Sodalite is7.generally present and becomes so abundant in some varieties thatthe rook is sodalite syenite. A.lthough all nepheline syenitesin the Ice River complex appear similar in hand specimen, anumber of slightly different varieties have been determinedmicroscopically. The reader is referred to Chapter II for adetailed description of nepheline syenite.Leucocratio pegmaties cut all other igneous rocks.These are of three major types: aomite-orthoolase pegmatites;perthitic feldspar pegm.atits and nepheline-aegirine-augitepegmatites. No detailed work on these rocks was done by theauthor.Mesotype Group:The two main mesotype rocks present are ijolite andurtite. Ijolite is by far the most common and is a coarse—grained, equigranular rock consistng essentially of nepheline,pyroxen.e and amphibole with the light and dark constituents beingabout equal in amounts. Ice River ijolite is a rather specialtype since barkevikite replaces, in part, the pyroxenes. Urtite,a rock generally of coarser grain than ijolite, consistsessentially of nepheline, pyroxene. and sohorlomite. For adetailed description of a specimen of urtite the reader isreferred to Chapter II.Melanooratic Group:Rocks of the melanocratic group occur in the thin edgesof the laocolith. They are exposed in the northern end of theeastern extension; in two other localities in the eastern extensionand between Garnet Mountain arid Chancellor Peak. Members of thisgroup include only types in which light coloured minerals are8.accessory or entirely Iacking. By far the most common type isjacupirangite which is a coarse—grained rock consisting essentiallyof pyroxene, m.gnetite or ilmenite and sphene. Small outcrops ofpyroxenite have also been reported.Metamorphism and MetasomatismAllan made a very brief study of contact metamorphismand metasomatism of shale and limestone along the roof of thenorth-west extension of the laccolith. In this area, a band ofreddish hornfels ranging in thickness from a few feet to 350 feetoccurs. In thin-section, Allan found this hornfels to consistmainly of quartz, feldspar, biotite and clinozoisite. The hornfelsand the overlying limestone have sharp contacts and where nohornfels is present, the limestone has been recrystallized forseveral hundred of feet from the contact, and tremolite, diopside,garnet, epidote and wollastonite are found in it. He attributesvariations in widths of the metamorphic and metasomatic bandslargely to variations in concentrations of fluids which emanatedfrom the magma.i The sedimentary rocks along the upper contact of thenorth—west extension are breooiated and inclusions of both hornfelsand limestone occur within the igneous rock, particularly nearthe roof. The inclusions differ greatly in size and except forone, which outcrops on Aquila Ridge, do not exceed 100 feet indiameter.Shearing forces were active at the close of the emplacement of the conplex They resulted in shearing and brecciationof the surrounding sediments but had little effect on the competentigneous rocks.9.Age of IntrusionThe age of the Ice River complex is believed by Allanto be post—Cretaceous. Evidence is supplied by the Cretaceousrocks of the Cascade Basin, located some 35 miles north-eastof Ice River. In the Cascade Basin area, Cretaceous rocks havebeen folded and the age of the folding is believed to correspondto the formation of the Ice River antioline. Sinoe the Ice Rivercomplex has been intruded into folded strata, the intrusion mustbe post-Cretaceous in age. Allan believes that the Ice Rivercomplex is of the same age as alkaline intrusive rocks of theMontana petrographic province which are known definitely to bepost-Cretaceous in age.10.CIL4PTER IIGEOLOGY OF GARNT MOIINTAIN-AQUILA RIDGE REAIntroductionThe accompanying geologic map and cross sectionsillustrate the structure and distribution of rock types in theGarne.t Mountain-Aquila Ridge area.The large inclusion previously mentioned is well exposedon Aquila Ridge and on the south side of Garnet Creek basin whereit forms cliffs about 300 feet high. This inclusion parallelstheupper contact of the laccolith and the overlying sedimentaryrocks in attitude and is at most 1250 feet thick and slightly lessthan one mile in length. Except for the basal 80-100 feet, theinclusion is stained deep brown by limonite, a feature which makesit especially conspicuous from a distance.Igneous RocksNepheline-sodalite SyeniteNepheline—sodalite syenite forms numerous small outcropson the nose of Aquila Ridge. Hand specimens of this rock arelight greenish, medium to coarse-grained, somewhat inequigranularand display a pitted surface due to the relatively rapid weatheringof nepheline. Nepheline, K-feldspar, pyroxene, amphibole andsphene were recognized in hand specimen, the mafics making upabout 15% of the rock. In all the following thin—sectiondescriptions, mineral percentages are from visual estimates only.In thin—section, nepheline—sodalite syenite is seen tobe composed of:11,Perthite 45%nepheline 20%aegirine-augite 15%Na-Fe rich amphibole 5%sodalite 5%aphene 5%cancrinite 3%apatite- 2fmagnetite(?)5The texture is inequigranular and hypidiomorphic.Nepheline, perthite, pyroxene and amphibole occur as largesubhedral crystals. Sphene forms euhedral crystals which rangegreatly in size, a few of the smaller crystals being enclosedin pyroxene. Apatite occurs as coarse euhedral crystals, someof which, along with a few grains of magnetite, are enclosed insphene. Sodalite forms irregular interstitial masses andcancrinite occurs as irregular grains around nepheline, of whichit is probably an alteration product. A small amount of sericitehas been developed in the feldspars. From the relationshipsoutlined above, the sequence of crystallization of the constituentsappears to be: magnetite (?) and apatite; sphene; pyroxene andamphibole; nepheline and feldspar; sodalite.UrtiteSeveral specimens of mesotype igneous rocks werecollected about 100 yards west of the lower contact on GarnetMountain. A type corresponding rather closely in mineralcomposition to urtite described by Allan ( p. 14’?) is describedbelow.In hand specimen, this rock is dark green, coarsegrained and equigranular. Nepheline, pyroxene, biotite, schorlomite,sphene, magnetite and ilmenite are recognizable in the hand12.specimen.In thin section, the rock is seen to be composed of:Nepheline 50%augite and aegirine-augite 20%schorlomite)magnetite 10%ilmenitebiotite 5%sphene 3$apatitecalcite 2%can crinite)The texture is equigranular and hypidiomorphic.Nepheline occurs as fresh subhedral crystals and the pyroxenesform both subhedral crystals of aegirine-augite and subhedralzoned crystals with augite cores and aegirine—augite rims(plate IB). Biotite is closely associated with the pyroxenes.Sohorlomite is deep red in thin-section and is closely associatedwith the iron oxides. The iron oxides form soalloped contactswith the pyroxenes suggesting partial replacement of the latter.Calcite occurs interstitial to the other minerals. Alterationconsists of the development of cancrinite around nephelinecrystals, minor development of muscovite along fractures in thenepheline and the formation of fine-grained iron oxides in cracksand around the edges of pyroxene crystals. The sequence ofcrystallization of the constituents was not determined.Aoniite—microcline Rock (plate II).This rock, specimens of which were collected about100 yards west of the lower contact on Garnet Mountain, consistsof acicular and radiating groups of pyroxene crystals up to 1 inchlong in a white, finely crystalline feldspar groundmass.In thin—section, the rock is seen to be composed of::1.3.Microcline 70%acmite 20$natrolite 5%soda.lite 5$The acmite occurs as dark green, weakly pleochroic,euhedral crystals twinned on (100) and elongated along (010).Microcline forms small anhedral to subhedral crystals which have,in part, replaced acnaite. A remarkable feature of the microclineis that only Carlsbad and Albite twinning are developed in it andthe rainiliar “plaid” twinning is not seen. A detailed descriptionof this and other minerals found in Ice River rocks is included inChapter III. Natrolite occurs as irregular masses surrounding and.replacing crystals of inicrooline. Sodalite is closely associatedwith the natrolite. From the relationships outlined above, thesequence of events in the formation of this rock was: crystallization of acmite; crystallization of microcline which partly replacedthe ac.mite; introduction of natrolite and sodalite with very minorbrecciation of and partial replacement of microcline.This rock is included here only because it possessesan igneous appearance and texture. Its relationship to theenclosing urtite was not determined and it may be a metasomatisedinelusion.Metasomatised LimestoneLower Contact, Garnet MountainEleven specimens of limestone representing a stratigraphic thickness of approximately 7 feet and showing variousdegrees of alteration were collected near the lower contact ofthe intrusion on Garnet Mountain. The effects of metasomatismcan be detected in hand specimen only within 4 feet of the contact.14.The unaltered limestone is finely crystalline, lightgrey and thin-bedded, the bedding being exaggerated by surfaceweathering. Etching with dilute hydrochloric acid revealedabout 10% dolomite and insoluble residues.In thin—section, limestone 7 feet below the contactconsists of fine-grained, subhedral crystals of carbonate andminor amounts of phiogopite, amphibole and fine-grained ironoxides. The amphibole occurs as minute acicular crystalsrandomly distributed throughout the rock. The phlogopite, ironoxides and some amphibole form narrow bands and lenses parallelto the bedding.4 feet below the contact, the limestone is seen to becomposed of:Carbonates 80%phiogopite 10%microcline 5%amphiboleiron oxides 5%sphene )The amphibole appears to be of two varieties: tremoliteand a colourless variety with high dispersion and ZAG of 39.Only one fairly large crystal of the latter was found and theoptical properties could not be accurately determined even withthe aid of the universal stage. The phiogopite, microcline andamphiboles form irregular vein-like masses and “knots” in thecarbonates. The inicrocline occurs as small subhedral crystalslargely confined to these “knots”. It shows only Carisbad—albitetwinning as was evident in the aemite-microcline rock describedabove. A few irregular grains of sphene and some amphibole alsooccur randomly distributed throughout the rock.Within 3 feet of the contact, the bedding in the lime-15.&bone has become completely destroyed and the rook is coarselycrystalline (calcite grains up to 1/8 inch) with irregular “knots”of fine-grained minerals scattered throughout it. The mostnoticeable mineralogical change is the disappearance of amphiboleand the formation of small acicular crystals of ac.mite. Theaomite is largely confined to the jj.ots” where it forms groupsof crystals oriented parallel to the borders of the “knots”ma1l irregular groups of aemite crystals also occur throughoutthe rock. The “knots” and irregular veinlets are composed ofphiogopite, acmite, fine—greained iron oxides (chiefly limonite)and possibly other fine-grained minerals. Iron oxides, whichare more abundant than in limestone 4 feet from the contact, alsooccur as dust-like inclusions throughout the carbonate.Within 1 foot of the contact, the rock changes markedly.In hand specimen it becomes a dark reddish-green, hematite-stained skarn in which pyroxene, calcite and feldspar arerecognizable. In thin—section, the rock is seen to be composedof:Microcline 45%acm.ite 35%natrolite 10%iron oxides (chiefly hematite) 7%calcite‘ 3%chlQritelThe aomite occurs as small needles and subhedralorystals up to 3 ruin, long, many of which are slightly breociated.This mineral is only very weakly pleochroic and the pleochroismvaries slightly even within the same crystal. Miorocline, whichagain shows only Carlsbad-albite twinning occurs as anhedral tosubhedral crystals commonly highly brecciated. The brecciafragments are generally surrounded by calcite and natrolite.16.Natrolite Occurs as feathery masses, some of which are replacedpseudomorphously by calcite, The iron oxides occur in or closelyassociated with natrolite, and minute black grains of an unidenti—fled mineral, visible only under high power, occur throughout thenatrolite (plate lilA). Hematite dust is concentrated aroundthese black grains and breccia fragments of microcline enclosedin natrolite also have hematite dust concentrated around them. Afew small pyrite crystals occur along grain boundaries and fillfractures. Chlorite occurs as small nodular masses of minutecrystals forming veinlets cutting aemite and also occurs asttknotst? of tiny crystals along crystal borders. The chloriteshows green to reddish pleochroism. and its X-ray diffractionpattern agrees rather closely with penninite from Rinipf’ischwange,Zermatt, Valais, Switzerland (A.S.T.M. No. 2—0102).The amount of feldspar and iron oxides differs considerably in rocks close to this contact. A specimen taken only afew feet along strike from the skarn described above consistsalmost entirely of niiorocline with only subordinate amounts ofnatrolite, carbonate, acmite and iron oxides. In hand-specimen,this rock is a dark grey, fine-grained skarn not showing thehematite staining or acmite of the rock described above.ithin a few inches of the contact, the skarn is alight reddish-green, rather coarse—grained rook in which brecciatedcrystals of pyroxene up to inch long occur in a matrix ofzeolite and K—feldspar. In thin—section, this rock 1 seen to bea coarse-grained aggregate of:Natrolite 60%microcline o%acmite 15%17.iron oxidescarbonatebiotitechlorite 5pyritepyro chioresen citeA few minute black specks surrounded by hematite dustsimilar to that described in skarn 1 foot from the contact occurthroughout the natrolite. Natrolite, which forms t ground mass,encloses and partly replaces breccia fragments of aomite, niicroclineand carbonate. The iron oxides and fine-grained black mineralsurrounded by hematite are concentrated chiefly around microolinebreccia fragments. Pyroohlore occurs as a few, minute, euhedral Vcrystals surrounded by hematite dust and partly enclosing thefine-grained black mineral (plate IVA). A few minute veinlets ofchlorite cut aomite crystals and a few cubes and irregular massesof pynite are closely associated with biotite. 4iteration consistsof minor senicitization of the miorocline.A summary of the mineralogical changes in the alteredlimestone at the lower contact on Garnet Mountain is given intable 1, p. 18.Radioactivity was detected in some of the skarn rocksdescribed above. It will be discussed in detail in chapter III.Limestone Inclusions in Igneous RocksGarnet Mountain InclusionsTwo inclusions of limestone (see section A—B), eachabout 10 feet thick, were examined. These inclusions consist ofcoarse calcite (crystals up to * inch) stained deep brown bylimonite. A few small veinlets of nearly black chlorite cut theserocks. Radioactivity, sufficient to make a small portable geiger?feetcarbonates(95%)ainphibolesphiogopite(5%)ironoxides4feetcarbonates(80%)ainphibolesphlogopite(10%)ironoxides(5%)microcline(5%)spheneacinite(5%)natrolite(10%)pyriteradioactiveconstituentschlorite(2%)Contactcarbonates(2%)ironoxides (2%)mlcrocline (20%)acinite(15%)natrolite(60%)pyriteradioactiveconstituentschloritebiotite(1%)sencitepyrechioreTable1MineralAssemblagesinMetasomatisedLimestoneatVariousDistancesfromtheIgneousRock;LowerContact,GarnetMountain3feet1footcarbonates(75%)carbonates(1%)phlogopite(5%)—ironoxides(20%)ironoxides(7%)—inicrocline(45%)acmite(1%)19.counter count twice background, was detected in both inclusions.The distribution of minerals within the inclusionsappears to be quite erratic. Two thin—sections were made of thealtered limestone of the most westerly inclusion shown on sectionA-B. In one, coarse, euhedral crystals of calcite are replacedalong crystal boundaries and cleavage planes by hematite. A few,subhedral, colourless, altered crystals of an unidentifiedmineral (1) also occur in this altered limestone.The second thin—section, made from limestone collectedfrom the same inclusion only a few feet from the above showed therook here to be composed of calcite (45%), chlorite (40%) and. 15%of iron oxides and pyrite. The chlorite occurs as irregular massesof tiny botryoidal clusters of crystals which vein end replacecalcite. Fine-grained pyrite an iron oxides occur as veins andirregular d.isseminations in and especially along the borders ofthe chlorite masses.No thin—sections were made of specimens of the otherinclusion on Garnet Mountain.Main Aquila Ridge InclusionNumerous specimens of altered limestone were collectedfrom the large inclusion outcropping on Aquila Ridge. The positionof each specimen is shown on section C—D.The basal 80-100 feet of this inclusion was found to beradioactive throughout and it was found that this zone persistedsouthward for at least mile. Radioactivity was also detectedin the upper few feet of the inclusion but its extent was notdetermined. In hand specimen, radioactive rocks of this inclusiondiffer from non-radioactive rocks in that the former lack the20.limonitic staining characteristic of the latter.Specimen 1: Non—radioactive rock collected from near the centreof the inclusion was found, in thin—section, to consist of:Hematite and limonite 55%calcite 40%chlorite 5%pyrochloreunidentified mineral (2) .. —The calcite is replaced along cleavage planes and alonggrain boundaries by fine-grained iron oxides, many of the calcitecrystals being entirely replaced pseudomorphously with the retentionof the cleavage. Pyrochlore occurs as small, euhedral, somewhatfractured crystals generally associated with iron oxides. Thechlorite forms small botryoidal masses as it does in altered limestone from Garnet Mountain. A few minute veinlets of chloriteand, calcite cut all other minerals including pyrochlore.Specimen 2: Non-radioactive rock collected immediately above thebasal radioactive zone was found, in thin section, to consist of:Apatite 70%calcite 10%iron oxides 10%acmite 5%chlorite 5%pyrochiore *%The apatite forms irregular masses of small euhedra].crystals cyclically twinned probably by reflection in a planeparallel to the c-axis (plate IA)0 The acmite occurs as smallsubhedral crystals generally concentrated in the apatite massesand the pyrochlore occurs as subhedral to euhedral crystals alsoconfined to the apatite masses.Specimen 5: Radioactive rock collected from the upper radioactivezone was found, in thin—section, to consist of21.Apatite 75%calcite and iron oxides 20%chlorite 5%pyrochiorepyrite -unidentified mineral (2) —The texture of this rock is very similar to the apatite—rich rock described above except that the calcite crystals in thisrook are somewhat breeciated.Specimens from the Basal Radioactive Zone: Several thin-sectionswere cut from specimens of the main radioactive zone. In thin—section, altered limestone from this zone was found to consist of:Calcite 55%apatite 30%chlorite 10%iron oxides and pyrite 2%altered rutile(?) 2%pyrochiore 1%The textures and mineral relationships are very similarto those described above. The most noticeable difference betweenthis rock and others of the inclusion is the greater abundance ofpyrochlore and lesser quantity of iron oxides. The pyrochloreforms brecciated eiihedral crystals up to about .2 mm. in width(plate IIIB) and the pyrite occurs as anhedral to subhedral crystalslargely confined to the apatite masses. Small euhedral crystalsof a brownish mineral, thought possibly to be rutile largelyreplaced by iron oxides, occurs confined mainly to the chloritepatches.A detailed description of the pyrochlore, other radio—active constituents and. several other minerals found in the aboverocks is given in Chapter 1110220CHAPTER IIIMINERALOGYThe following minerals were identified by the authorin rocks from the Ice River area:Acmite ilmeniteaegirine-augite pyrochioreaugite apatitetreniolite nephelinehornblende (Na-Fe rich) natroliteunknown amphibole sodalitemicrocline garnet (schorlomite)perthite sphenechlorite cancrinitephiogopite carbonatesbiotite pyritesericite rutilehematite unidentified radioactive minerallimonite unknown (1)magnetite unknown (2)Pyroxene sacmite: See fig. 3 for universal stage determination,light greenweakly pleochroicnx= 1.76 n= 1.782V = 68opt. (-i-)Z,%C = 87°S.G-. (average of 5 reading) 3.38Except for the weak pleochroism, the properties listedabove agree closely with those given in Rogers and Kerr (1942, p.270) for acmite. Washington and Merwin (1927) have describedacmite from the Islet of Rockall and from Rundemyr, Norway showingweak pleochroism. Spectrographic analyses showed both, to becomparatively high in zirconium and certain rare earths. Q,ualitative spectrographic analysis carried out by the author on IceRiver material showed:23.Strong lines: Mg and the primary constituents Na, Fe and Si.Moderate lines: V and Zn.Weak lines: B, Cr, Cu, Ti, Mn and Zr.Since Cu and Mg occur as impurities in the carbon electrodes,it is not certain that they are present. No rare earths weredetected.From the above analyses, it appears therefore that IceRiver aemite is somewhat more deficient in Zr than specimensexamined by Washington and Merwin, However, the fact that certainuncommon elements were detected in Ice River acmite tends tosupport their hypothesis that impurities may cause anomalousoptical properties in acmite.aegirine-augite and augite: In urtite, there minerals occuras zoned crystals, usually with augite forming an inner core andaegirine-augite, the outer rim (plate 13).aegirine-augite augitepale green coloui’lesspleochroism: X>Y<Z:grass green; yellowish green:brownish greenXAC 230 Z,o 450The above properties agree closely with those givenfor aegirine-augite in Winohell and Winchell (1951, pp. 416-41?)and, for augite in Rogers and Kerr (1942, p. 264).Amphibolestremolite: colourless2V 78°opt. (—)Z,o=l?0The above properties, determined on the universalstage, agree closely with those given for tremolite in Rogersand Kerr (1942, p0 282).24.hornblende (Na-Fe-rich):dark greenish brownstrongly pleoohroic: X<Y<Z:light brown:dark brown:brownish green.2V ?Zc l3 (?) approximatelyoptic plane parallel to a—cThe optic orientation and pleochroism indicate thatthis mineral is not a member of the soda-hornblende group. Itis suggested that this variety is a common hornblende containingsoda and an excess of iron as described in Wincheil and Winchell(1951, p. 435).unknown amphibole: colourlesshigh dispersionlAG = 390The few properties that the author was able to determine agree with no amphibole described in modern texts, the onlyknown species approximating it being an asbestiform amphiboledescribed by Wahlstrom (1940) from Boulder County, Coloradowhich has a ZAC =44° and is pleochroic light yellow to darkyellow. The latter is close to arfvedsonite in composition.MioroclineSee fig. 4 for universal stage determination.n<l.542V 84°opt. (—)twinned according to the Carlsbadand Albite laws only (plate hA and IIB)The identity of this species was confirmed by I-raydiffraction powder photographs. Microcline, displaying onlyCarlsbad and Albite twinning is exceedingly rare. However, itis known from uincy, Mass. where it occurs in vugs in aegirineriebeckite bearing pegmatites (Warren and. Palache, 1911).Apatite.25.Optic properties as in modern texts. Confirmed byX—ray powder diffraction photographs. A remarkable feature ofthe Ice River apatite is its cyclic twinning (plate IA). Eachtwin generally consists of 3 interpenetrating members whichresemble, in appearance, cyclic twinning in cordierite.Natrolite colourlessbirefringence .01low reliefparallel extinctionlength slowperfect cleavage parallel to c axis2V = l5 — 300opt. (÷)The identity of numerous specimens of natrolite fromvarious Ice River rocks was confirmed by X-ray powder diffractionphotographs (plate V). This mineral occurs both as feathery andirregular masses and as euhedral, orthorhombic crystals. The2V, which varies slightly in natrolite from various rocks, isabnormally low for natrolite. However, the optical propertiesagree closely with those given for natolite in Winchell andWinchell (1951, Po 340) and the X—ray diffraction pattern withthat of natrolite from Aussig, Bohemia.GarnetIn hand specimen, the garnet is pitch black in colourand in thin-section, a deep red0 Chemical analyses carried outby Allan (1914, p. 177) on similar garnet revealed up to 22%Ti02 thus indicating the species schorlomite.Rutil eA brownish mineral, occuring as small, euhedralcrystals largely confined to patches of chlorite in alteredlimestone, was determined as rutile by X—ray powder diffractionphotographs. However, in thin-section, the relief is obnormally26.low for rutile. A possible explanation is that the originalrutile has largely been pseudomorphously replaced by finegrained limonite and possibly some chlorite with the retentionof sufficient rutile to enable a fairly good diffraction patternto be obtained.Unidentified mineral (1)A few highly altered crystals of an undeterminedmineral occur in limestone of the lowest inclusion on GarnetMountain.colourlessbirefringence = .008 approximatelyn>l.54parallel extinction (?)length fast (?)biaxial; large 2VUnidentified mineral (2)This mineral occurs as minute, euhedral, possiblyhexagonal crystals in apatite-rich bands in the upper radioactive zone on Aquila Ridge.colourlessbirefringence .025 approximatelyn>l.65 (apatite)<l.76 (acmite)2 poor cleavages parallel to the c axiscleavages approximately at 900 in basal sectionsuniaxial (+)PyroohioreIn hand specimen, this mineral occurs as dead whiteto light yellow, vitreous octahedrons and fragments up to .2mm. in diameter. In thin—section, it is colourless, unaltered,of very high relief and isotropic (plates 11Th and IVA). It’sidentity was determined by i-ray powder diffraction photographs,data for which is given with plate VI. A semi-quantitativespectrographic analysis carried out by the 3.0. Dept. of Mines2?.at Victoria gave the following results:Si: less than 10%Al: 3-30%Mg: 0.2—2%Ca: greater than 5%Fe: 0.3-%Ti: greater than 1%Na: greater than 1%Gb: greater than 10%Sr, Cr, Ba, Cu, IiIn: traceQualitative spectrographic analysis carried out by the author onimi1ar material yielded a trace of Ta, Y, Ce and K in additionto the above. From the above analyses, it is evident that thevariety is very near the pyrochlore end of the pyroohioremicrolite series.Pyrochlore-bearing rock was crushed, screened and aheavy tip was concentrated by super—palming. The tip wasexposed on Kodak Nuclear Track Plates for several weeks and upondevelopment, the pyrochiore was seen to display weak and sparsetracks which indicates a very small percentage of radioactiveconstituents. By comparing the density of tracks against thecolour, it was found that the darker the pyrochlore, the greaterthe amount of contained radioactive material.Unidentified radioactive mineralChemical analysis of radioactive skarn from the maininclusion on Aquila Ridge carried out by J.R. Williams and Sons,Provincial Assayers at Vancouver, gave 0.1% 13308. A bulk semi-quantitative spectrographic analysis by the B.C. Dept. of Mineson weakly radioactive skarn gave the following results:Si: greater than 10%Al: 0.5-5%Mg: 0.2—2%Ca: greater than 5%Fe: 1—10%28.Mn: 0.3—3%V: 0.007—0.07%Ni. 0.003—0.03%Go: 0.2—2%Sr: 0.3—3%P: greater than 1%As: 0.05—0.5%Gb. 0.03—0.3%Th. 0.03—0.3%Pb, Cu, Ti, Y, Yt, Ce, Na, La, Cr, Ba: traceAs the lower limit of detection of uranium by this method is0.1%, this element was not detected in the sample analysed.The 1% (approximate) of weakly uraniferous pyrochiorecontained in most radioactive skarn is insuffieient to accountfor approximately 0.1% U308. Also, the best grade materialobtained from the lower contact on Garnet Mountain (about twicebackground using the hand counter) is deficient in pyrochiorewhereas material from the same locality giving a. lower countcontains a small amount of pyrochiore. Therefore the bulk ofthe radioactive material must be contained in another mineral orminerals.In the radioactive material from Garnet Mountain, takenabout 1 foot below the contact, minute black grains in natrolitesurrounded by hematite dust are visible under high power (platelilA). In the same rock, a few pleochroic haloes are visiblein biotite but their nucleii are not visible. A 200 gm. sampleof this material was crushed, screened and super-panned. A tipof pyrite and minor acmite, a middling of almost pure acniite anda tail consisting of hematite-stained natrolite, niicrooline andcalcite was obtained. The amount of tip obtained was too smallfor an accurate radiometric determination of its radioactiveconstituents. However, the middling gave no count above background whereas the tail gave a count almost as high as the bulk29.sample. Hematite—stained natrolite was then isolated under thebinocular microscope and an X-ray powder diffraction photographmade0 Only a natrolite pattern was obtained and from this itis concluded that either the contained black grains are too fewand too small to give a pattern or the contained mineral ismetamict. No larger black grains were visible in any of thefractions.The heavy tip obtained by auper-patming material fromthe main radioactive zone (see under pyrochiore) containedapproximately. 5O each of pyrochlore and pyrite plus a smallamount of impurities. The pyrochiore was easily identified onthe track plates. A few opaque grains, some of which wereattached to pyrochiore (plate IVA) were surrounded by a densepattern of tracks. These were isolated under the medium powerof the petrographic microscope and re-examined under the binocularmicroscope. They were found to be either pyrite or pyrochiorecontaining small black specks. Only a few very small grains wereobtained although numerous track plates were prepared and attemptsto obtain i-ray powder diffraction photographs of the containedradioactive mineral resulted only in weak patterns of eitherpyrite or pyrochiore.A small amount of the pyrite-pyrochiore tip was mountedin bakelite and super—polished. Under the reflecting microscope,the pyrite was seen to be cut by irregular veinlets of hematite.However, a few minute crystals, some of them perfect cubes,were observed (plate IVB). These did not show the deep redinternal reflection characteristic of hematite. Etching 1:1 HC1 did not tarnish these grains which seems to eliminatethe possibility of their being magnetite. The grains, unfortunately, were too small to be isolated for X-ray determination.Numerous grains of pyrite were picked from the heavy tip andfused with LiF. Upon exposure to ultraviolet light, some of thebeads thus obtained showed a weak greenish fluorescence, thusindicating the presence of uranium.A 4473 gm. sample of the radioactive grey alteredlimestone from Aquila Ridge, which showed little hematite stainingand no natrolite was crushed and screened to 6 fractions. Eachfraction was super—panned and a tip, middling and tail obtained.The resulting fractions were then radiometrically assayed usinga stationary geiger counter. The assay results are recorded intable 2, p. 32. From table 2, it appears that the radioactivityis concentrated in the tip and middling whereas in the specimensfrom Garnet Mountain, it is concentrated in t1 tail.From the above observations, it appears that at leastone other radioactive mineral besides pyrochlore is present incontact limestones of the Garnet Mountain-Aquila Ridge area.Because the grains are too small, this mineral or minerals wasunidentified. However, a few general statements can be made.In rocks high in natrolite, the radioactivity is concentratedin the natrolite and hematite is closely associated with theradioactive minerals. In rocks containing no natrolite andlittle hematite, such as that of the radioactive zone on AquilaRidge, the radioactive mineral is concentrated in pyrite. Theetch reactions, colour and crystal outline as seen in polishedsection and the density of tracks on nuclear track plates suggest31.uraninitea loss toanalysis.uranini te(Palache,as the main radioaotive mineral. The writer is atexplain the presence o thorium in the spectrographicA possible explanation is that it is contained inwhich is known to carry up to 14% Th02 in some depositsBerman and Frondell, p. 612).32.Table 2Distribution of Radioactivity in AQuila Ridge Radioactive ZoneRadiometric determinations. 10 counts/mm. .02%Wt. of sample: 447.3 gras. 100 counts/mm. .18%Heads: 18 countsJmmn. .043%Size Wt.(gms.) Counts/mm. Fraction Wt.(gms.) Cts./min.tail 33.6 1448 43.9 19 middling 5.1 33tip .5 -—tail 47.6 1465 60.1 18 middling 9.0 31tip .5 ——tail 47.6 9100 66.8 14 middling 11.5 21tip .8 -—tail 29.8 4150 38.5 12 middling 46 40tip .5 ——tail 39.9 9200 47.4 17 middling 2.1 97tip .4 -—(—)200 190.6 17Combined tips: 2.7 gras. 82 counts/mm. (approx. .16%).18 gm. sample used where possible. Middling and tail assayerscorrected to 18 gui. values033.Y 35EZ 255 6optlc axis 3DtC].1 44 l3’Cl2 309±Qoo). 12.OPTJC AXI5ft10Nb Al]. values corrected ror G iftr,ncs in rfract1ve ind1cbtwn niriral at-id hernisphr, ing drowbs diaram.ACMITThrior;Fig. 50(100) 57 10ZAC-$7; Vz=56; 2V,71l2°: 2V63°—i-cl3(iift03.F1,CARLSBA 4IBIT TWiNNIIG IN MTCROCLINCombined twins4 IIX1 516 5L2 ii 132 1D2 9Sin1e tIn14 :)X 3j 24A 22 I.Cl(3Oi) 46 124—z4X1CP= 710113A1..3 Parallel or conpiex twin (Carlsbad)2V C.-) 84°Az4 Norna1 twin (4lhit):35.CHIiPTER IVTHECRETIC.L CONSIDERATIONSTheories on the Origin of Undersaturated Alkaline Igneous RocksSeveral theories have been brought forward to explainthe origin of undersaturated alkaline igneous rocks. Briefsummaries of a few of the more important of these theories aregiven below,Bowen, in 1915, postulated that a nepheline syenitemagma could be produced by the prolonged fractional crystallizationof a basaltic magma. During an early stage in the differentiationof basaltic magma, calcic plagioclase and pyroxenes are believedto form which deplete the magma in calcium, some magnesium andiron and enrich it in alkaline constituents and volatiles. Asthis alkaline residuum is evolved, certain reactions are believedto take place which involve the breakdown of complex silicatemolecules to simpler molecules. Two of the m.ore importantreactions, believed to be aided by a concentration of water andother volatiles, are as follows:NaA1Si3OB— NaA1SiO4-i-25i02KA1Si3O—> KA1SIO4+2SiO2For a certain concentration of NaAlSi3O8 and KA1S1:308, there isa corresponding concentration of NaAlSiO4 and KA1SiO4 and theamounts of each of these four constituents increases withincreasing differentiation. At a certain stage in this process,silica becomes so concentrated that it begins to crystallize asq.uartz ICAlSiO4, UA1SiO4, certain complex ferromagnesian1 Bowen believes that the molecules which separate out are notnecessarily those which are mosb concentrated but are those leastsoluble. For example, silica is less soluble than NaMSiO4.36.molecules, and a limited amount of NaAiSiO4 separate out toform biotite. Some feldspar also crystallizes at this stage and.the result is biotite granite.It is easily seen that a magma rich in NaA1SIO4, othersoda compounds, certain soluble potash compounds and volatilesmight be formed by the above processes. This soda-rich m.agrn.amay be removed from the underlying granite by filter pressingor it may crystallize in place giving rise to a layered bodywhich is silica-rich near the base and, silica-deficient near thetop.As evidence for his hypothesis, Bowen has pointed tothe post-Cretaceous undersaturated intrusives of the Black Hills,South Dakota, the nepheline syenites of the Bancroft area,Ontarioand many other localities where both silica—rich and under—saturated igneous rocks occur closely associated.Bowen believes that volatiles are expelled from thegranitic magma and become concentrated in the late soda—rich I’differentiate. He thinks volatile-bearing compounds areformed by what may be termed a decomposition of the silicates.This decomposition is the result of the action of H20, C02, Cl,F, etc. on silicates with the formation of soluble hydrates,carbonates, chlorides, etc. The latter are precipitated at avery late stage in and. around the nepheline syenite to form suchminerals as sodalite and cancrinite.Bowen postulates that rare elements are eliminated fromthe granitio magma as ions because of their geochemicalincompatibility with common silicates. These rare elementsare deposited at a late stage in the solidification of the37.nepheline syenite magma.In 1928, Bowen pointed out several other reactionswhich could produce silica—deficient magmas. These reactionswill not be discussed here.The nepheline—kaliophilite--silica system was investigated by Shairer and Bowen in 1935. The phase diagram forthis system is given in fig. 5.fig. 5phase Diagram for the System Nepheline-Kaliophilite-SilicaRocks forming from melts of composition below the.albite—orthoclase join will obviously be silica—deficient, Apart of the system that requires some explanation is thatexisting in the leucite field. Let us consider a melt of composition A. Leucite begins to crystallize on cooling and thecomposition of the melt moves towards S. At 6, leucite reactswith the melt and K—Na—feldspar crystallizes, the melt meanwhileStCAI5ToaqLIyGN,AI5i3c8KAISi2OSqI5Io1.following the curve SR. At R, leucite continues to dissolve38.and K-Na-feldspar and nepheline crystallize simultaneously.When all of the leucite is used up, K-Na-feldspar and nephelineseparate together and. the melt moves towards E until entirelyused, up. The final product is nepheline syenite. Bowen believesthat such reactions explain the existence of pseudoleucite, ie.,finely crystalline K-Na-feldspar and nepheline pseudomorphousafter leucite.Melts of composition B normally yield quartz-bearingrocks. However, if leucite crystals are concentrated duringthe early stages of cooling and the siliceous melt is largelyeliminated by some process such as filter pressing, the remainingmixture may be so enriched in leucite as to be deficient insilica. During its cooling this mixture would have the Samehistory as a magma of composition A giving rise to an under-saturated rock. A necessary result of this process would be theinjection nearby of siliceous rocks representing the expelledfraction.The mechanisms described above may not operate. undervery deep seated conditions. Bowen and Tuttle (1950) have shownthat if water reaches a relatively high concentration under apressure of approximately 2600 atxzi., the leucite field may be sorestricted as to be excluded from the albite-orthoolase-silicatriangle. Under these conditions, leucite would not precipitatefrom a melt of any composition lying in the albite—orthoclasesilica triangle.Daly (1933) postulated dissolution of limestone bysub-alkaline niagmas with consequent formation of caic-silicatesand depletion of the original magma in silica, as the flode of39.origin of undersaturated alkaline igneous rocks. He believesthat reactions such as he following go on when limestone isassimilated by a granitic magma.2NaA1Si3O8+5CaCO3 ‘ Na2SiO3±Ca3A.l2SiO12+ 2Ca3iO3 +2NaA1S1-i- 6CaCO3—> Na2003+CaA12Si3D12+ 3Ca5IO3-l-- 5C02Garnet and other minerals so formed are believed to settle outwhereas Na26i03 and Na2CO3 rise toward the top of •the magmachamber where they react with albite and anorthite molecules toproduce nepheline. The chemistry of the latter reactions isthought to be as follows:Na.A1Si3O8±2NaCO3— Na1SiO4-i-- 2Na2S1D3+2002CaA12SIZO8+Na2SiO—- 2NaIdSiO4+CaSiO3and, at lower temperatures:Ca.l2SiO8+Na2CO3 2NaAiSiD4-1--CaCO3Daly, like Bowen, advocated a concentration of 1120,CO2 and other volatiles in undersaturated magmas. Daly believedthat rare elements combine with certain volatiles to form solublecompounds. These soluble compounds do not crystallize until avery late stage and thus delay the final freezing of the magma.Gummer and Burr (1943) and Baragar (l94), after studyingnepheline gneisses in the Bancroft area, Ontario and, at York River,Ontario, respectively, concluded that these rocks, which areinterbanded with Grenvi1l-like paragneisses and crystallinelimestones, are the result o± replacement of metamorphosedsedimentary rocks. Gradations from normal siliceous gneissesthrough nepheline-poor to nepheline—rich gneisses were observedat both localities. Gummer and Burr (1943) believe that theserocks may have resulted from granitic or syenitic liquids reacting40.with limestone to form nepheline. Evidence for such reactionsis offered by calcite and other calcic minerals which are foundin these rocks0Origin of the Ice River ComplexIf Bowen’s original theory is correct, biotite graniteshould exist at Ice River. Although no biotite granite isexposed in the area, such granite may exist beneath the stock.Let us briefly consider the nepheline-kaliophilitesilica system (fig, 5) in reference to the formation of theIce River complex. Free silica has not been detected in anyof the Ice River rocks which suggests that the composition ofthe soda-rich residuum was in the field below the albiteorthoclase join. However, as previously stated, silica-deficientresiduums can be formed in the leucite field above the albite—orthoclase join by the squeezing off of interstitial silica. Asno silica-rich rocks were found, this hypothesis appearsinapplicable at Ice River. It also appears that the compositionof the residuum did not lie within the leucite field as nopseudo-leucites have been found in any Ice River igneous rocks.As previously stated, the development of leucite is considerablyrestricted under conditions of very high pressure. Very highpressures did not likely exist during the emplacement of the IceRiver complex as the maximum rock cover existing at that timeprobably did not exceed 2 miles (2 miles 600-800 atm.).The replacement theory as postulated by Gu.nnner and Burr(l943) and Baragar (1954) appears untenable for the formationof the Ice River complex for several reasons. Discordant andbrecciated contacts of igneous and. sedimentary rocks, the presence41.of inclusions of country rock in the complex and the bowing upof overlying strata indicate an igneous origin. However, theauthor is at a loss to explain the apparent layering in igneousrocks at Garnet Mountain which some geologists might interpretas a replacement phenomenom.In accordance with Daly’s limestone syntexis theory,Allan (1914) believes that the addition of CaCO3 has resultedin the desilication of an original sub-alkaline magma at IceRiver with the resultant formation of silica-deficient alkalineassemblages. Daly’s theory appears to apply at Ice River fortwo reasons. First, in order to attain its position, the magmawould have to pass through approximately 13,000 feet of Cambrianlimestone and limy sedinients. Secondly, aegirine-augite andcalcic plagioclase which were detected by Allan in the deeperportions of the exposed igneous rocks and the existence of suchcalcic minerals as calcite, schorlomite, perovekite and cancriniteveins throughout the complex points to an addition of CaCO3.Allan believes that the Ice River complex representsa single intrusion and that processes of differentiation haveresulted in the diverse types. He states:“The hypothesis offered for the explanationof the diverse types within this complex,which are transitional into one another, isa combination of the result of separation bygravitative adjustment, and a rapid coolingof a portion of the original heterogeneousmagma in the thinner and cooler portionsof the chamber. There has been a sinking ofthe heavier minerals and a rising of thelighter ones”.That darker coloured rocks solidified first is reinforced by thefact that fragments of darker material are enclosed in lightercoloured material near the contacts of the two and fractures in42.dark rooks are filled with lighter coloured material. Patchesof darker rock types occur near the roof of the magma chamberin a few places in the thinner portions of the complex. illanbelieves that the magma did not have time to differentiatecompletely in these thinner portions.As pointed out in previous chapters, mineralizers and.rare elements are abundant in the rocks at Ice River. The rolethat these mineralizars (chiefly F, Cl and probably 1120) haveplayed in the formation of the Ice River alkaline rocks or inthe extraction of rare elements, remains a matter of conjecture.However, the fact that mineralizers and rare elements are closelyassociated suggests to the author that they were probablyconcentrated and deposited together.Rare Elements in Igneous RocksThe relative abundance of columbium and, tantalum invarious igneous rock types has been compiled by Rankania and.Sahama (1949) (Table 3).Table 3Average Cb and Ta Content and Cb-Ta Ratios in Igneous RocksRock Type Cb(gms./ton) Ta(grus./ton) Cb:Ta Ratiomonomineralic rocks 0.3 0.? 0.4ultrabasic rocks 16.0 1.0 16.0eclogites 3.0 0.? 4.3gabbros 19.0 1.1 17.3diorites 3.6 0.? 5.1granites 20.0 4.2 4.8syenites 30.0 2.0 15.0nepheline syenites 310.0 0.8 387.5basic alkalic rocks 10.0 1.2 8.3In the above table it is seen that columbium becomesconcentrated in far greater amounts than tantalum in nephelinesyenites. This seems to hold true at Ice River for the py’ relatively richer in colu.mbium than tantalum. Deposits ofpyrochiore-microlite at Lake Nipissing, Ontario (Rowe, 1954)in which the source rock is diorite, have a tantalum contentof almost 30%.Rankama and Sahama (1949) have also shown that thecontent of columbium in alkaline igneous rocks is proportionalto be content of zirconium in the ratio of about 1:10. Althoughthe Ice River rocks are deficient in zircon, zirconium is presentin the acmite and since the acmite forms a major constituentof many of the rocks in the area, this 1:10 proportion may wellhold true.Radioactive elements become concentrated in latemagmatio differentiates as illustrated by tables 4 and 5.Table 4(Rankama and Sahama, 1949)Abundance of Uranium in Igneous RocksRock Type Uranium (gms./ton)ultrabasic igneous rocks igneous rooks 2.61granitic rooks 3.96Table 5(Washington, 1909)Concentrations of Rare Elements in MagmasAlkaline Rocks Sub-alkaline RooksNa-rich K-rich Fe-rich Mg-rich Ca-richLi Ba Ti Cr Cr(?)Be Va Pt P(?)Ce MnYt NiZr CoUTh44.SFClSn(?)More recent analyses using improved methods carriedout by Evans and Goodman (1941) and Senftle and Keevil (1947)have also demonstrated the increased concentration of radioactive elements in late differentiates.Metasomatism by Undersaturated Alkaline Igneous RocksAn intense search of the literature revealed thatlittle work has been done on contact metamorphism or nietasoiuatismby undersaturated alkaline igneous rocks. This is possiblydue to the fact that these rocks do not often generate extensivemetamorphic aureoles or skarn zones especially in areas wherethey are bounded by gneisses.Callisen (1943), in describing alkaline rocks atIvigtut, Greenland, noted that the contact effects on theenclosing gneisses was merely conversion of certain dark colouredminerals to orocidolite and phlogopite. He also reported minorimpregnations of fluorite, carbonate and phosphates in thegneisses.A description of metasomatism was given by Chayes(1942) who noted tremolite, spinel, phlogopite, diopside andapatite developed in limestones contacting alkaline rocks inthe Baiacroft area, Ontario.Metasomatism of Ice River limestone consisted of anintroduction of sodium to form such minerals as aoniite,natrolite and soda—rich amphiboles; potassium to form microclineand phiogopite; iron to form iron oxides, pyroxenes andr45.aniphiboles; fluorine and. phosphorous to form apatite and therare elements columbiuni, tantalum, zirconium, yttrium, cerium,e-to. to form pyrochiore, uraninite(?), and other uncommonminerals.a•.CDC)_j.I__iI-I-’.HC)CDciI s I-•Hci-CDOo‘I-‘dci-CDci‘-S.t’1ci-HoCDI-,.—t:4I__S.C) 0cici-CD (7) 04?.PLATE IAB48.PLATE IIi.. 1bite twinning in mierocline (x 400),B Carisbad-albite twinning in niicrooline.Acnaite—microcline rook (x 150). 1L—,.—‘,___-—__.4_____—50PLATE IIIA. Minute radioactive (?) grains in hematite-stained natrolite.Metasomatised Garnet Mountain limestone (x 400)B. Pyrochiore in apa.tite. Main Aquila Ridge radioactive skarnzone (x 150).51.ILPLATE: IIIrRAP,OACT,VE (9) GIA?NSAPYR QC H L.O r‘452.PLATE IVA. Pyroohiore and uraninite (?) surrounded by hematite “dust’in natrolite (x 400).3. Uraninite (?) in super—polished pyrite (x 200)Ii53.PLATE IVAUR4Ng/l r??B54.PLATE VNatrolite, Ice River, 13.0. Fe/MnOL 2 2’2 ‘7,75 7.18 1 21.05 270 1 36.35 1.6347 8.45 6.59 2 22.15 2.57 1 36.95 1.6115 9.35 5.96 2 23.35 2q44 37.85 1.5791 10.75 5.19 2 23.65 2.41 1 38.95 1.5411 11.45 4.88 1 24.55 2.33 39.85 1.5124 1215 4.64 25,45 2.25 3 41.25 1.4695 12,65 4q42 2 26.35 2q18 1 42.85 1.4244 13.55 4.13 2805 2.66 1 44,15 1.39114.55 3.86 29.15 1.989 44.95 1.3712 16.05 3.50 1 30,85 1.889 1 45.95 1.34810 17.85 3,16 3 32.35 1.810 46.95 1.3261 19.05 2q95 1 34,05 1730 1 47.65 1.31110 19.75 2.87 1 34.45 1.712 3 52.55 1.220All values adjusted for film shrinkage.55.I3310’21818212243121222432AllPyroohiore, Ice River, B.C. Cu/NiO.d (nieas.,)7.35 6.0414.15 3.1514.40 3.0117.20 2.6022.65 2.0024,70 1.8442.03 1.75729.45 1.56830.85 150331.86 1.46034.66 1.35536.40 1.29940.30 1.19241.60 1.16142.40 1.14345.15 1.08746.75 1.05850.30 1.00261.30 .87962,75 .86769.65 .822values adjusted for film shrinkage.a fca1c.) 10.408 Ahid d (cab.)(111) 6.01(113) 3.14(222) 3.01(004) 2.601(1l5 2.00‘ (333 S(044) 1.840(135) 1.759(226) 1.569(444) 1.502((117) 1.457‘(155)f(137((3555 1.355(008) 1.301(266) 1.194(048) 1.164((119) 1.143((357)(139) 1.091(448) 1.062(666) 1.002[(26,10).880(668).867(04,12) .823PLATE VI[56.BIBLIOGRAPHYAllan, J.A. U914): Geology of Field Map-area, British Columbiaand Alberta — G.SC. Men. 55.Baragar, W.R.A. (1953): Nepheline Gneisses of York River,Ontario - Proc. Geol. Assoc. Canada, Vol. 6, Part I, pp.83—ill.Bowen, N.L. (1915): Later Stages of Evolution of Igneous Rocks -Jour. Geol., supplement to Vol. 23.Bowen, N.L. (1928): The Evolution of the Igneous Rocks- Princeton University Press.Bowen, N.L. and O.F. Tuttle (1950): The System NaAlSi308—KA.lSQH20 — Jour. Geol., Vol. 58, No. 5.Callisen, K (1943): Igneous Rocks of the Ivigtut Region,Greenland — Meddelelser on Gronland, Vol. 131, No. 8,pp. 7-74.Chayes, F (1942): Alkaline and Carbonate Intrusives nearBancroft, Ontario — G.S.A. Bull., Vol. 53, pp. 449—512.Daly, R.A. (1933): geous Rocks and the Depths of the Earth —McGraw-Hill Book Co. Inc., New York and London,Evans, R.D. and C. Goodman (1941): Radioactivity of Rocks -G.S.A. Bull.,Vol. 52, PP. 459—490.Gummer, W.K0 and S.V. Burr (1943): The Nephelinized Paragneissesof the Bancroft Region, Ontario— Science, Vol. 9’7, No.251?, pp. 286—28?,Palache, C, H. Berman and C0 Frondel (1944): Dana’s System ofMineralogy - John Wiley and Sons, Inc., New York, Vol. laRankama,K and T0G. Sahama (1949): Geochemistry - University ofChicago Press.Roger, A.F. and P.F. Kerr (1942): Optical Mineralogy — McGraw—Hill Book Co. Inc., New York and London.Rowe, R.B. (1954): Notes on Geology and Mineralogy of theNewman Colunibiun—uranium Deposit, Lake Nipissing, Ontario-G.S.C. Paper 54-5.Senftle, F.E. and N.B. Keevil (194?): Thorium—uranium Ratios inthe Theory of Genesis of Lead Ores- Trans. Am. Geophy.Union, Vol. 28, No. 5, pp. ‘732—738.Lhairer, J.F. and N.L. Bowen (1935): ?reliniinary Report onEquilibrium Relations Between Feldapathoids, Alkali—I57.Feldspars, and Silica, Trans. Jim, Geophy. Union, pp. 325-328Turner, F.J, and J. Verhoogen (1951): Igneous and MetamorphicPetrology - McGraw-Hill Book Co. Inc., New York andLondon.Wahistrom, E.E. (1940): Ore Deposits at Camp Albion, BoulderCounty, Colorado — Econ. Geol., Vol. 35, No, 4, pp.477—5O0Warren, C.H0 and C. Palache (1911): The Peatitez of theRiebeckite—Aegirite Granite of .uincy, Mass., U.S.A.;Their Structure, Minerals and Origin — Proc. Am. .Acad.Arts and Science., Vol. 47, No. 4, pp. 123—168.Washington, H.S. (1909): Chemical Analyses of Igneous Rocks -U.S.G.S. Prof. Paper, No. 4.Washington, HS. ánd H.E. Merwin (1927): The Aemite Pyroxenes -Am. Mm., Vol. 12, pp. 233—252.Winchell, A.N0 and H. Winchell (1951): Elements of Optical!‘ineralogy - ohn ‘Ti1ey and Sons, Inc., New York.r/0,0009, ‘0 08,0004,000GEOLOGY OF10,0009.0008,0004 000GARNET MTN./ 0,0008,00060004’, OoOAQUILA RIDGELE GNDAREA(.JN.DER3A7’UFATED A1Lr.JE/ONEOLJS 0l$uPE Ar.,9Rj,q,,,A — L Li V I U MG LA C A LLEUCOCRATIG TYPE5J’vIEGOTYPESMEL-A NOC RAT/c TYPESGOOD51f FM -- ShIe slo+. I”s.oTrERTAIt FM.— L’,,sCHANCELLCP. FM. — /-,,)ADiOAcTI\E SfrcARNCONTOUR Ir’,ITER,VAL loot’’ SCALE9,0008,0004 000SECTION A-.SECTION C-DAFTffR 3A. ALLAN sI4-)


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