GEOLOGY Ill of the Fraserriver Valley Between Lillooet Andbig Bar Creek

BRITISHCOLUMBIA DEPARTMENT OF MINES AND PETROLEUMRESOURCES HON.W. K. KIERNAN,Minister P. J. MULCAIIY,Deputy Minister

BULLETIN No. 44

GEOLOGY Ill of the FraserRiver Valley between Lillooet andBig Bar Creek

A Thesis Submitted in Partial Fulfilment of The Requirements for the Degree of Doctor of Philosophy in the Department of Geology at the University of British Columbia

HANS PETER TRETTIN

1861

BEST-PHINTEII CO. LTD. I.Vertical aerial view of Fraser River at site proposed for Moran Dam. Island in river is upstream from centre line of dam-P.G.E. track on eastside of River. 11. FraserRiver at site proposed for Moran Dam, looking upstream. 111. French Bar Canyon, Fraser River Poorly lithified Eocene-Oligocene conglomerates and sandstone in upper right hand section of photo show effects oferosion. FOREWORD

Thisbulletin is based on studies made in the 1957 and 1958 fieldseasons for the Fraser River Board underthegeneral supervisionof the Mineralogical Branch ofthe Department of Mines. The cost of the field work was contributedmainly by theFraser River Board.

The workwas doneas the basis fora thesis that was submitted to theDepartment of Geology atthe Uni- versityof British Columbia. Except for some simplifi- cation in themapof the area (Figure 1) and related mi- nor changes in thetext, the bulletin is areproduction of thethesis, with some changes in thephotographs.

i ABSTRACT

An areaof 550 square miles betweenLillooetand Big Bar, Brit- ish Columbia.was mapped by thealrthor using the scaleof 1 mile to the inch. In the so-lthernpart of the Bowman Rangefour members are recognized in the Middle (?I and UpperPermian Blarble Canyon formation which is partly composedof reefallimestone. This formation forms a northwesterlytrending anticlinorium overturned to the northeast. Thecherts, argillites. limestones. and volcanic rocks west of the Bowman Range,oriGinally referred to the Permo-Pennsylvanian Cache Creekgroup. are shown to be Permo-Triassicand are here assignedto the Paviliongroup. a new groupwhich is made up of two divisions. Microscopicand stratigraphic evidence is giventhat the cherts of this groupare of radiolarian origin. The Lower Cretaceolus Lillooet group here is subdividedinto three units. Divisions A and B are shown to form a northwesterlytrending anticline. Threemembers are now recognized inDivision Aofthe Lower Cre- taceousJackass Alountain gro\lp. The Lower CretaceousSpences Bridge group is subdivided into severallocal and stratigraphic units. Two unitsprevioxsly assigned to the Spences Bridge group are correlated with the Kingsvale group on the basis of new fossilcollections. Some volcanicand sedimentary rocks originallyreferred to the ilioceneKamloops group are here correlated with Miocene to Pleisto- cene rocks of the Quesnel map area. West of Lillooetabeltof serpentinite wasmapped that has struc- tural and lithologicalsimilaritiesto the Upper Triassicultrabasic intrusionsof the ShulapsRange. Granitic rocks of three agesare recognized and range from early Lower Cretaceogs or older to mid Lower Cretaceous. It hadearlier been shown thattheFraser River fault zone consists of several normal faults with relative downwardmovement to the east. East of thesefaults the author recognizes another fault with relative downwardmovement to the west. Lower Cretaceousand early Tertiaryrocks thus occupy a arabenbetween Permo-Triassic units to thenortheast and to thesouthwest. This graben probably controlled the depositionof Divisions B and C of the JackassUountain group. Thefa:rlting may berelated to the isostaticrise of adjacent aran- itic masses.Evidence is (riventhat the latest movementon one of the fasltstook place in mid Tertiary time.

ii i

1 1 1 2 3 4

5 6

13 13 15 16 17

20 20 22 23 24 25

25 25 25 26 26 26 30 33 34 34

34 34 34 35 40 44 45 45 46

46 47

49 50 51 51 56 56 56 58

59 60 60 60 60 61 62 62

62 63 64

64 64 64 64 65 63

69 69 69 68 69 60

70 7G 71 71

74 74 74 75 75 75

76 77 77 77

a3 a3 a4 a4 84

84 85 88 88 88

89 89 89

90 90 90 90

91 91 94 94

95 96 98 98 99

vi FIGURES Fiaure Page

1. Geologyof theFraser River Valley betweenLillooet and Big BarCreek. (Inpocket)

2. Compositionof fragments, sandstones, Lillooet """_""""""""""~"""""~ 43

3. Compositionof fragments. sandstones, Jackasshlountain group ______------53

4. JackassMountain group, grainsize, distribution in sandand coarse silt grades. ------55

5. GeologyofGlen Fraser area ...... 66 6, The FraserRiver fault zone ...... 07

TABLES

Table 3 - Mineralcomposition of seven specimens of olivine basalt """""__"__""""""""""""""" 79

Table 4 - Mineralcomposition of eightspecimens from Coast Intrusions,Early Lower Cretaceous or older ------06 Table 5 - Mineralcomposition of four specimensof altered gabbroicand dioritic rocks __-______----______93

PHOTOGRAPHS (see front of Bulletin)

I. Verticalaerial viewofFraser Riverat site proposed for Moran Dam. Island in river is upstream from centreline of dam-P. G.E. track on east side ofRiver. 11. FraserRiverat site proposedfor Moran Dam. lookingupstream. 111. French Bar Canyon,Fraser River. Poorlylithified Eocene-Oligocene conglomerates and sandstone in upperright hand section of photo show effectsof erosion.

vii ACKNOWLEDGEMENTS

The work was carried out for the Fraser River Board of the Prov- inceof British Columbia under the s,>pervisionof the Department of Mines.The author is indebtedto Drs. H. Sargentand S.S. Holland for supportand encouragement. Durina the seasons of 1957 and 1958 the author wasvery ably assisted by Mr. L.V. Hills,and during one monthof 1958 by Xr. D. Leeming.Professor K.C. McTappartvisited the author on several occasions in the field, advised him in the course ofthin-section studies, and read the manuscript.Uelp with field work.laboratory work. andmanuscript was also receivedfrom Profes- sor W.H. Vathews.The author is furtherindebted to Professors W.R. Danner. V.J. Okulitch, J.V. Ross, J.S. Stevenson, R.U. Thomson.and W. H. White foradvice. The identificationof fossils by Professor W.R. Danner. Dr. J. Jeletzky.and Professor G.E. Rouse is gratefully acknowledged. In the FraserRiver area friendly help wasgiven by Mr. and hlrs. Ostensoe of Lillooet. Mr. and Mrs. Hay and Mrs. Highof Pavilion,and Mr. and 31rs. 3larriotof Big Bar.

viii INTRODUCTION 1. LOCATION ANDACCESS

Thearea mapped, elongate and irregular, lies along the Fraser Riverbetween Lillooet and French Bar Canyonand includes the adja- centMarble Range and parts of the Pavilionhlountains. the Camelsfoot Range,and Fountain Ridge. The easternside of the FraserRiver, and the west side in the vicinityof Lillooet, are served by highway, the PacificGreat East- ern Railway,andsecondary roads and trails. In the central andnorth- ern partsofthe map area the west side is accessible by a cablecar nearPavilion and a ferryat the mouth of BigBar Creek. From these two crossingsonly pack trails anda few wagon roadsprovide further access to the western parts of the map area.

2. PREVIOUS GEOLOGICAL WORK

The earliestgeological work in the area wasdone in 1871 by J, RichardsonandA.R.C. Selrvyn. The Cache Creek groupand the Jackass Mountaingroup are named and described for the first time in Selwyn's report(1872). In 1877 G.BI.Dawson (1877-78) mapped the Kamloops area on a scale of 8 miles tothe inch. Furtherstudies were carried out in the seasons of 1888. 1889. and 1890. and in 1895 a reportand a mapon a scale of 4 miles to the inchwere p'lblished. Daivson established all of the majorrock units ofthe present map area, and his map and reportare still theonly sourceof information for some of the northernparts of the Kamloops area. In1918 and 1919 Leopold Reinecke (1920) who examined the mineraldeposits adjacent to the PacificGreat Eastern railaay between Lillooetand Prince George described a felv deposits in the present map area. A reconnaissancesurvey from the Fraser River toTaseko Lake was carried out in 1920by J.D. IlacKenziewhose map andreport cover the west side of the FraserRiver between Watson Bar Creek and FrenchBar Creek. From 1945 to 1947 S. Duffel1and K. C.IIcTaggart re-mapped the Ashcroftareaona scale of 4 miles to the inch,Their most import- antcontributions to the geolopyof the present map areaconcern the Lower Cretaceoussedimentary rocks, and theFraser River fault zone. In 1955 J. NcCammon and 13. Nasmith(1956) studied possible dam sites in thegorthernpart ofthe map area, Theydiscovered several faults which prov+ed ,,tobe northern extensions of the Fraser!liver faultzone. Some of the northwesternparts ofthe area mapped arehere des- cribedfor the first time.

3. FIELD WORK

Field workwas carried out for a total of nine monthsduring the summers of 1957 and1958 and for one week in 1959.The dry climate andgood accessibility of thearea allowed uninterrupted work. In most of thearea the geoloyy {vas plotted on base maps on a scale of one-halfmile tothe inch. Nearthe Fraser River base maps on scales

1 of1,000 feetand 500 feetto the inch were available.Locations were established by crossbearings, altimeter readings, andpace and com- passtraverses. The geology of the MarbleRange was plotted on air photographsand,bymeansof radial plotting, transferredto base ma2s showingphoto centres.

4. PHYSIOGRAPHYAND PLEISTOCENE AND RECENT GEOLOGY

Threemajor elements ofthe topography canbedistinguished: Mid Tertiary andolder mountain ranges. Middle or LateTertiary upland surfaces,and Pleistocene and Recent valleys. Themain Mountain ranges ofthe map area are the Pavilion Moun- tains and the Marble Range in the east underlain by the Upper and (?) MiddlePermian Marble Canyon formation, and thecameisfoot Range and FountainRidge inthe west, underlainby Lower Cretaceoussedimentary rocks. The Bowman Rangeand the Pavilion Mountains consist mostly of parallelridges formed by steeply dipping limestones. In the northernpart ofthe Warble Range a plateau-liketopography has been pro- ducedbygently dipping limestone beds. As inthis aridclimate limestone is veryresistant to weathering the highestmountains of the map area are foundin this belt (hlount Bowman 7.360 feet). TheCarnelsfoot Range is underlainby moderately dipping lithic sandstones and conglomerates that are highly resistant to weathering. It hassteep slopes, and is transected by numerousvalleys, some of whichare deeply incised and narrow. Fountain Ridge isa narrow rem- nantof the samemountain mass. In thepresent map area the eleva- tionsoftheCamelsfoot Rangeare mostly between 4,500 and 5,500 feet but riseup to 6,900 feet. Thealtitudesof Fountain Ridge range from 4,200 to 5,500 feet. ilountMartley, whose rounded top reaches an altitude of 6.700 feetat the southeastern edge of the present map area, is formed in highly resistant granitic rocks. The steeplydippina bslt weakly resistant sedimentary and volcanicrocks of the Pavilion group form hilly tracts or mountainsof lesserheight which rarely rise above 5,000 feet. Gently dipping Cretaceous andearly Tertiary volcanic rocks, not veryresistant to weathering form a beltof low mountainsthat only in the northern part ofthe area riseto elevationsofmore than 6,000 feet. Flat lying sedimentary and volcanic rocks of Middle or Late Ter- tiary age form small plateaus at altitudes ranging approximately from 3,000 to 4,000 feet near Pavilion, between McKay Creek andWatson Bar Creek,and on BigBar Creek, North ofPavilion, south of Watson Bar Creek,and in the vicinity ofBig Bar Creek someof these depositional surfaces are continuous with youngergently sloping erosional surfaces,which are covered only with a thinveneer of unconsolidated Pleistoceneand Recent deposits, These hliddle or LateTertiary sur- facesare parts of the floor ofa valley that possibly extended from Glen FrasertoBig Bar Mountain and was connectedalong Big Bar Creek with theextensiveplateau east ofthe Marble Range. The valley part- lycoincides with thepresent Fraser River valley but has not been recognized south of Glen Fraser, The present valley ofthe Fraser River is younger than these Vid- dle or LateTertiary surfaces and wasprobably developed in Pleisto-

'J & cene time. In mostof the area it is approximatelyparallel to the strike oftherocks and to the FraserRiver fault zone. except for a peculiarS-shaped turn nearFountain. It mightbe suggested that the riveroriginally flowed along Fotlntain Valley but was diverted into theBridge River. The Pleistocenevalley bottom probably coincided approximately with the present surface of the river which lies between 900 and 650 feetabove sea level. This valley was filled.probablyinthe latest Pleistocene,with more than 1,000 feetof unconsolidated materials rangingfrom boulder gravel to mud. Thestratigraphy of these de- positschanges over short distancesand their history is complicated. Nuch of the materialshowing deltaic cross-bedding appears to have beendeposited by braidedstreams. Some of the extensive silt de- positsbetween Pavilion andBig Bar Creek may havebeen laid down in

alaciallakes. Mudflowsappear ~~ to have been deposited on alluvial ransof tributaries. .~~~In Recent. ~. time the river has been reiuvenated and has cut throuah the unconsolidatedsediments into bedro&. This rejuvenation may have beencaused by a decreaseof the detritalload in post-glacial time (Thornbury,1954. p.144) or by isostatic uplift. Although the area was covered by glaciers (Duffell and LIcTaggart. 1953, p.69)glacial erosion is slight and till veryrare. Probably norapid movements took place in thisregion which lies only some 50 miles to the south of a majorglacial divide (Geol. Assn.ofCanada, 1958; W.H. Nathews.1941, p.64). A thin layerof Recent volcanicash has been found in the vicinity of Big Bar'andJesmond. W.H. Mathews (oral communication)suggeststhat the ash was ejectedby a cindercone on the upperBridge River. H. Nasmith(oral communication) reports Recent volcanic ash in the vicinity of Pavilion.

5. CLIMATE, VEGETATION, WILD LIFE

Thearea lies in the"dry belt" of the Interiorof British Co- lumbiawhich is sheltered from rainand snow by the CoastMountains. lheaverageannual precipitation atLillooet over forty-one years was 12.35inches. The summers are warm and the winterscool. Theex- tremes atLytton. some 30 milessouth of the map area in 1956 were -9 degrees in Januaryand 106 degreesin Ju1y;theextremes recorded within thirty yearsare -25 degreesand112 degrees (B.C. Department ofAgriculture. 1957). The vegetation is relativelysparse. Some partsofthe area are coveredby forests, some are park-like,and others opengrassland. The slopes of thewestern part are more densely forested than those of the easternpart. Most of thetrees are pines (lodge-pole pine, ponderosapine); white spruce, balsam fir, and Douglas fir are common only in the higherand cooler areas that receive more precipitation. Only a fewmountains rise abovetimber line which lies near 6,500 feet. Valley flats are characterized by sage brush, bunch grass. andcactus. Thearea is notedfor big game.Deer, moose, and black bears are common in the Marble Range and on the west side of the Fraser Riv- er; goats were observedan the west sideof the river,southwest of Pavilion.

3 6. INDUSTRIES

Themain industry of the area is cattleranching. The soils of the FraserRiver valley, particularly wind blown silts, which were seen in many localities,are very fertile, but the raisingofcattle feeddepends on irrigation,and few creekscarry water all summer. Logging is second in importance.In 1956 and 1957 forests on the eastside ofthe Fraser River near Pavilion, Kelly Lake, andJes- mond were logged.and preparations for the exploitation of the west side were beingmade. >lining is relativelyunimportant. In 1950 two placermines were operating,one on the FraserRiver, opposite Fountain (M3),.and the otherone onWatson Bar Creek. Some exploration workwas done on the claims of the Monty group 012). southwestof Ward Creek. Tourismand big game huntingprovide another source ofincome forlocal people. A power dam ontheFraser River would help the local industries greatlyby providing cheap electricity. allowing extensive irrigation,and by attracting tourists (Warren. 1959).

4 CHAPTER I. GENERAL GEOLOGY

INTRODUCTORYSTATEMENT

The generalgeology of the area is summarized on thefollowing tableof formations. The term "Division" was usedfor certain units by Duffelland VcTagflart (1952). Theusage is followed here and the term is applied to other units thatare roltghly equivalent to form- ationsbut not well enough known tojustify formational names. Local units ofsomewhat uncertain stratigraphic position an? termed "aspem- blage"and designated by the name ofthe area in whichthey occur.

5 TABLE 1. TABLE OF FORMATIONS - Formation Assem- iuccession SystemSeries Stage Group Division or blage MemberLithology andContacts Quater-Recent and alluvium, volcanic ash, river Pleisto- gravel, sand, and silt, mud- silt, and sand, narygravel, Pleisto- cene flows, tuff, conglomerate. glacial outwash and till. - unconformity - Miocene- olivine basalt. minor andesite. !nozoic TertiaryPliocene - conformable contact - lithic arenite. conglomerate, minor shale. - angular unconformity - Oligocene? tuff, felsite, andesite, basalt, minor coal. - conformable contact - Eocene- French Bar French Eocene- conglomerate, volcanic arenite. Oligocene Formation Oligocene minor siltstone, plant seams. - unconformitv - Pre-Oligo- Ward andesite, dacite, felsite, tuff, !nozoic cene post- Creek minor basalt, volcanic arenite. ' Mesozoic Mid Lower assem- coal. Cretaceous blaae - not in contact - !nozoic Lower Cretaceous gabbro and diabase dykes. ' Mesozoic or vounaer - not in contact - Formation Assem- System Series Stage Group or Division blage Lithology and Contacts Member Albian Spences Fountain C andesite, minor Bridge Valley volcanic breccia, plant seams, Gp.? or assem- B felsite. blage Kings-A andesite, felsite, minor conglom- or vale Gp.? erate. - not in contact - Spences Bridge Gp. Glen (ptian? Fraser Lower Div.orandesite, Kings- dacite. vale Gp. Div. B. assemblage - contact not exposed - Div. B andesite, dacite. minor tuff, volcanic arenite. Lower Cretaceouz :retaceou - conformable contact - " volcanic arenite, conglomerate. Div. A minor siltstone, plant seams. - unconformity - - Upper andesite, minor basalt, rhyo- Division lite, tuff. Spences - not in contact - Apt- Bridge ~- ian? Lower Gp. Lower Gibbs andesite,C minor dacite. vol- Cretaceous retaceou Division Creek canic arenite. siltstone. assem- andesite, felsite, volcanic ar- blage B enite. siltstone, conglomerate. argillite, tuff, agglomerate. A andesite. Formation Assem- Succession System Series Group orStage Division blage Member Lithology and Contacts - not in contact - Lower Basal andesite, dacite, tuff, ande- Division sitic breccia. member I- angular unconformity with I Pavilion Group - IDorPhvritic auartz diorite 1dykes"and siils. - - intrusive contact - volcanic arenite. argillite, Div. C conglomerate; minor plant seams - conformable contact - Ickass conglomerate, volcanic arenite. :n.Gp. Div. B minor argillite. - local unconformities - AI11 siltstone,volcanic arenite Div. A argillite, minor limestone, AI1 volcanicarenite. minor silt- ,esozoic Cretaceou! - stone, argillite. conglomerate. conglomerate, tuffaceous sandstone, volcanic arenite. minor plant seams. - unconformity - volcanic arenite (tuffaceous), .illooet Div. C conglomerate, siltstone, argil- GP.? lite. Formation Assem- Succession System Group or Division blage Member Lithology and Contacts - fault contact with Division B. angular unconformity? - porphyritic quartz diorite dykes and sills and a small quartz esozoic I Cretaceour tretaceous mian? diorite oluton. I- intrusive contact - illooet volcanic arenite. siltstone, GP. LDiv. B argillite, conglomerate. I- gradational contact - Div. A largillite. siltstone, volcanic I t-I I larenite. minor coal. L ~~ - not in contact - quartz diorite, diorite, grano- Cretaceous diorite stocks and porphyritic or older dykes and sills. - intrusive contact with I Pavilion arouo - serpentinized peridotite and carbonate- silicaalteration. - intrusive contact with esozoic Pavilion group - tuff, volcanic arenite and greywacke. volcanic flows. argillite Tri- assem- chert, limestone: minor breccia, assic (?I blage siltstone, amphibolite, hornfels IDiv. I1 meta-quartzite. Formation Assem- Succession MemberSystem Series Stage Group or Division blage Lithology and Contacts I - - I- not i n contact Pavilion Big Bar tuff, lithic sandstone, argil- GP . assem- lite, chert, volcanik flows. blage - gradational contact or unconformity - Mesozoic and/ Triassic and/ Pavilion chert, argillite, minor tuff, or Palaeozoic or Upper Permian Gp. Div. I limestone, volcanic flows. - gradational contact I or unconformity -

IV Ichert..I araillite. limestone., Upper fiows. Permian tuff. volcanic limestone. Upper Perm- Marble Southern chert, argillite, limestone, Permian ian and/or Canyon Marble tuff, volcanic flows. Middle Formation Range I limestone with interbedded Permian ribbon chert. - conformable contact - Middle Mt. Soues chert. argillite, tuff, volcanic I Permian and/ Div. flows, limestone. 1. SEDIMENTARYAND VOLCANIC ROCKS

CACHECREEK GROUP

INTRODUCTION TheCache Creek group was firstdescribed bySelwyn. in 1872, who divided it into a lower andanupper part, The lower part.studied in outcrops along thecariboo Highwaybetween Ilartel and Clinton, was saidto contain limestone, black shale, rocks rich in epidoteand chloriteassociated with talc andserpentine, diorite, and felsitic porphyries.Brachiopods from this unit indicatedan age somewhere between the oldestDevonian and theyoungest Permian. The upper part, investigatedbetween Clinton and Pavi1ion.was found to contain limestone,marble, dolomite, chloritic andepidotic rocks, and black shales. Foraminifera from thehlarble Canyon limestoneweremisidenti- fied by J.W. Dawson asLoftusia and considered to be Eocene or Cre- taceous in age. G. 21. Dawson'sreport on the Kamloops area(1895) contains the first comprehensive description of the CacheCreek "formation"of the typearea. Dawson described the distribution of majorlithological units as follows:..the hlarble Canyon limestones, shown as a separate map unit. form a northwesterlytrending belt, that extends from the Cornwall Hills to the northwesternextremity of the map areabut is concealedby Tertiary rocks inthe vicinity ofHat Creek, Immediately to the eastof the limestone,in the area of CattleValley, McLean Lake,and Medicine Creek, volcanic rocks associated with limestone aredominant. Farther east, on BonaparteRiver and Thompson River, chertyquartzites and argillites are most abundant. To thewest of thelimestone belt, in the Edge Hills. in the western part of the Pa- vilionNountains. and onklount Martley. chert and argillite are dominant;farther west, onPavilion Creek andLeon Creek,most of the rocksare volcanic. Dawson. asdid Selwyn. considered the Marble Canyon limestones to bethe upper part ofthe formation but stressed theirstratigraphic continuity with the underlyingrocks. As thelimestone belt is flankedto the east and westby"o1der" rocks he thought that the regional structslre was amajor syncline modified by nlumerous minorfolds. Ilis summary of thestratigraphy of theCache Creek group is based on a compositesection through the eastern limb of that "syncline"(1895, p.46B): Feet 1. Massive limestones (hlarble Canyon limestone) with some minorintercalations of volcanic rocks,argillites andcherty quartzites. At least 1,000 feet seen. in some singleexpos- ures. Total thickness probably atleast 3,000 2.Volcanic materials and limestones, with some argillites,cherty quartzites, etc. Minimum thickness about 2,000 about thickness 3. Chertyquartzites. argillites, volcanic materials andserpentines with some limestone. Thethickness of these beds, or of a partof them,was roughly estimated in two placesas between 4,000 and 5,000 feet. Minimum total thickness

11 Dawson retained the original identification ofLoftusia but because of accompanying fusulinids referred it tothe Carboniferous and definedthe Cache Creek as an essentially Carboniferous formation. As moreinformation about the fusulinids accumulated, Dawson's agedetermination was revised. Dunbar (19321, Thompsonand Wheeler (1942).and Wickenden (Duffell and McTaggart, 1952, p.23) all agreed on aPermian agebut disagreed on the specific position in thatperiod. Duffell andilcTaggart called the CacheCreek a group and the MarbleCanyon limestones aforrnation. Their report is in close agree- ment with Dawson'sbut offers two alternativehypotheses about the majorstructure and stratigraphicorder within thearoup. The first is Dawson's concept that two majorunits are arranged inasyncline; thesecond that the "group consistsoftwo successions ofargillites, cherts,greenstones, minor limestones,and quartzites, separated by the thick seriesof the Marble Canyon limestones"(p.17). According to the first hypothesis thecache Creek group is approximately10,000 feet thick, according tothe secondhypothesis 20,000 feet. The latter thicknessis comparable, as Duffell and McTaggart have pointed out, to a sectionof 24,000 feet measured by Armstrong in the Fort St.James area (1949) that includes three limestone units andfour separatechert successions. In an attempt to solve the problemsresulting from the earlier work theMarble Canyon formation was studied in some detail. Fossils fromthe upper part ofthat formation are assigned by W.R. Oanner to the Upper and (?I Middle Permian. In the southern part ofthe Mar- ble Range the MarbleCanyon formation is approximately 6,000 feet thick and containschert, argillite, tuff, volcanic flows, andabout 2,500 feet of limestone. It here forms anorthwesterly trending anticlinorium that isoverturned to thenortheast. In the coreof the anticlinorium, on the south slopeofMount Soues anolder unit, about 1.500feet thick containing a little limestone, is exposed which is herecalled Mount SouesDivision. The rocks to thewest of Marble Range andpavilion Mountains appear to overlie the Marble Canyon form- ationconformably. A fossilfound in these rocks is probablyofTri- assicage. As theCache Creek group has been defined as aPermo- Pennsylvanian unit (Armstrong, 1949, p.50) thePermo-Triassic rocks overlyingthe Marble Canyon formationare assigned toa new unit, the Paviliongroup. MOUNT SOUES DIVISION

On thesoutheast slope of Mount Souesribbon chert, argillite, volcanicflow-rocks mostly ofbasiccomposition, tuff, and limestone areexposed. The assemblagediffers from rocks ofthe Pavilion group in two respects:the presence of limestones that are interlaminated with ribbon chert, and therelative abundanceof basic volcanic flows. The outcropzone is about 2 mileswide andpinches out tothe northwest. The thicknessofthe unit which is overlainconformably by the Marble Canyon formationisestimated asapproximately 1,500 feet. The rocks arefolded and faulted and seem to occupy the core of an anti- clinoriumformed by the basal member ofthe Marble Canyon formation. As the MarbleCanyon formation is Middle (?I andUpper Permian the Mount SouesDivision probably is Middle Permianand/or older.

12 MARBLE CANYON FORMATION

1. DISTRIBUTION In the present map area the Marble Canyon formation underlies the Narble Range and the central part of the Pavilion hlountains. In the Marble Range where formationthe has been mapped in its full width it occupies a belt approximately 8 miles wide.

2. LITHOLOGY AND THICKNESS

Because of facies changes,complications by faulting and folding. and the scarcity of marker beds, bedding attitudes, and stratigraphic top determinations it has been almost impossible towork out the structure and stratigraphy of the Marble Canyon formation. An attempt to establisha stratigraphic sequence could be made only in the southern part of the Marble Range. Four members, I. 11. III. IV are distinguished here,and a fifth IIIa is recognized in the central and northern parts of the area. The stratigraphy described on the following pages is valid only for the southern part of the Marble Range; it is impossible, for example, to recognize the same members in the Harble Canyon. Member I. approximately 200 to 300 feet thick, is composed of limestone and ribbon chert. The limestone is partly massive, and partly interlaminated with ribbon chert. Laminae of chert are 1 to 3 inches thick. Most of the laminae are extensive butat some localities they form short units one to several feet long. The limestone seems to be continuousover most of the area, but in the vicinity of Fiftyseven Creek it apparently forms discontinuous lenses that interfinger with chert. No fossils were found in the unit. Nember 11, which overlies I. is poorly exposed. It comprises chert, argillite, tuff, small lenses and bedsof limestone, and volcanic flow rocks. Although the member appearsto be 3,200 feet thick it probably has been repeatedby folding, and the true thickness perhaps lies between 500 and 1,000 feet. Member SIT, iscomposedmainly of limestone but locally contains small amounts of interbedded chert and argillite. The member forms a high ridge, about 13 miles long, that culminates in Mount Bowman. South of Porcupine Creek the limestone is approximately 1,000feet thick; southofTwo Mile Creekit tapers andfinally disappears. North of Porcupine Creek the structureprobably is complicated byfaulting and folding and neither the full strikelength nor the stratigraphic thickness of the limestone mass are certain. The limestone masses on Mount Kerr (about 2,500 to 3,000 feet thick) are perhaps in the same stratigraphic position as the ones on Mount Bowman but the two are not connected by outcrop; possibly these bodies are lenticular. hlost of the limestone is pure and massive and shows no bedding. In some localities, however, alternating light grey and dark grey layers are visible that arefrom afew millimeters to one centimeter thick. Under the microscope thelayers are seento differ in grain size and in the proportion ofminute inclusions in the carbonate. Some of the rocks are calcarenites and show graded bedding. ripple marks,and in- traformational breccias. Breccias made up of fragments that range from a felv millimeters to one inch in size locally occur within the massive limestone. In the northern part of the map area some rocks

13 thatmaybe correlative with Member I11 containoolites. Fossils are relativelyrare; remains of colonial corals, ofcrinoids, echinoids, algae,and fusulinids have been found at a few localities. In the syncline onhlount Kerr the thick massive limestone of Mem- ber I11 is overlain bya bed of limestone, approximately 500 feet thick, thatcontains laminae of chert. A sheetof interlaminated limestone and chertforms the crest of the Marble Range between Mann Creekand Jesmond Creek.Scattered outcrops of a similartype occur between JesmondCreek and the northern extremity of the Warble Range. These rocksare tentatively referred to Member IIIa,but it is not certain whetherall of them are in the same stratigraphic position. A thin-section ofchert from this unit consistsofan- hedral quartz grains showing undulose extinction that range from a few microns to .2 millimeter in diameter. Some spher- icalaggregates witha diameter of .08millimeter anda few spine-like structures about.4 millimeter longand .05mill- imeterwide composedof very fine-grainedsilica are visible; they areprobably of radiolarian origin, A handspecimen of limy chert consists offine blue greystringers, that are 1to2 centimeters long and afew millimeters thick, embedded ina light greygroundmass. The stringersare crenulated and fractured. Under the micro- scopethey are seen to consistoffine-grained silica, dominantly quartz with unduloseextinction, and smallamounts ofchalcedony. The light greymatrix comprises about 50 per cent carbonategrains part of which, showing rhombo- hedralhabit, are probably dolomite,and 50 percent quartz andchalcedony, Silica and carbonate are uniformly distributed. A sphericalstructure, about .2 millimeter in diameteris madeup of fine-grained silica in thecentre and relativelycoarse-grained quartzwith undulose extinc- tionat the periphery. Member IV consistsof argillite, chert, limestone, tuff, tuff- aceoussandstone, and volcanicflow rocks, butonly the limestones are well exposed. The latteroccur in lensesand beds ranging from afew hundred feet to 8 miles in strikelength. Some are of fairly constant thickness, others vary considerably in thickness along strike. A mass on PavilionBountain, for example, that is about2mileslong, rangesfrom 200 feet to about 2,000 feet in thickness. Most of the limestones do not show bedding. In afew localitiesoolites were noticed. and in others fusulinids. algae, corals,pelecypods, and ecbi- noderms (?). Inthe vicinity of intrusions the limestone has recrystallized toa fine-grained marble which locally shows a foliation in the formof finedark layers rich in carbonaceousmatter. The thickness ofthis member isuncertainbecause its structurecould not beworked oxut. On thewest side of the Marble Range it occupies a belt 1 mile to 1% mileswide. The thicknessof the unit is perhaps between 3,000 and 6,000 feet. The succession in theMarble Canyon formation in thesouthwest- ernpart of the Marble Range may besummarized asfollows: Member IV 3,000 - 6,000 feet. Chert, argillite,1imes.tone. tuff, volcanicflows. " 111 1,000 Limestone. I1 500 - 1,000 " Chert,argillite, limestone, tuff, volcanicflows. 1- 200 -300 '* Limestone with interbeddedribbon 4,700 - 8.300feet chert. 14 TheMarble Canyon formation in this areathen is approximately 6,000 feet thick and containsperhaps 2,500 feetof limestone. As thelimestone forms conspicuous cliffs and theother rocks aremostly concealed by overburden the proportionof limeqtone in theformation hasbeen overestimated by previous workers.

3. STRUCTURE

Becauseof facies changes,lackof marker beds,and the scarcity ofbedding attitudes andstratigraphic top determinations (related to the reefalcharacter ofthe limestones) the whole structuralpic- turehas not been worked out. Some success,however, was achieved in the southern part of the Narble Range, and the information obtained in thisarea may besufficient to establish the age relation of the MarbleCanyon formation to the Paviliongroup. Thefollowing three criteria have been used fortherecognition of folds: Themost important criterion are bedding attitudes. However, systematicchanges in strike and dipcould not be observedin all of thepostulated folds. A V-shaped or U-shapedlimestone outcrop visible on air photographs is suggestiveofthe nose ofa plunging fold because the limestones inmost localities form conspicuous outcrops whereas the other rock types.which are less resistant to weathering,are mostly covered by overburden.However,. this criterion alone, is not usedto establish afold because the same outcropsituation could he produced by thedifferential weathering ofa solid mass of limestone orhyfa- cies changes. The thirdcriterion is faulting in thecrestal areas of anticlines or in thetroughs of synclines. Apparently the folding was accomplishedbyvery little flowageandmuch fracturingofthe strata. In the extreme caseabox-typeof fold is produced with steeplydip- pinglimbs, a flatlying crest, and faultsbetween the crest and the limbs.However, in most localities the crests ortroughs are char- acterizedby irregular contortions. In thesouthern part of the MarbleRange, Member I appears to form a northwesterlyplunging anticlinorium which is overturnedto the northeast and is composed of at least five anticlines and the cor- respondingsynclines (cross-section F-F’). A few faults,modifying the anticlinorium, are shown on the map; othersare probablyconceal- edby overburden. Theonly fold recognized with assurancein the central part of the MarbleRange is anupright, broad, open syncline onMount Kerr. whichplunges to the southeastand fits between two northwesterly plunginganticlines outlined by Member I. A change in the direction of dips and strong distortions arewell displayed in the central part ofthe syncline which is formedby the interlaminated limestone and chertof Member IIIa. Inthe northern part of the Marble Range the dips ofthe strata are mostly moderate to low; their directions are uniform within small areasbut change abruptly from one area to another. No foldscould beoutlined. A few faultsare shownon the map. It is believedthat many othersare hidden by overburden. It seems thatthe strata here arebroken into numerous fault blocks tilted into variousdirections. Thedominance of faultingover folding in the northern partof the

15 map areaprobably isdue to thegreat thickness of the strata, to their lenticular (?I shape,and to low heat and pressure during the time ofdeformation.

4. MODE OF ORIGIN

Theabsence of coarse-grained clastic rocks and the dominance ofbiological, chemical, or fine-grained clastic material suggests thatthe source area was of low relief or at a greatdistance from thebasin of deposition. Threetypes of limestone can be distinguished. The firsttype is interlaminatednith ribbon chert (>!embers I and IIIa).These deposits aremoderately thick, ranging from 200 to 500 feet in thickness and may cover as much as 100 squaremiles. As they areassoci- ated with chertthat is possiblyof radiolarian origin, an analogous origin issuggested for the 1imestone;it may haveformed by the ac- cumulationoffree floating calcareous organisms, possibly foraminifera. However, no fossilshave been found in theserocks. Perhaps thesediments were deposited very slowly and subjected to solution and recrystallization on the seafloor. The alternative is inorganic precipitation, but it isuncertainwhether the conditionsfor such a process existed. Thesecond type of limestone deposit is extremely thick (up to 2.500feet) but probablynarrow. Corals, algae,bryozoa. and echinoids (together with fusulinids)have been found in these rocks. The fossils and theshapes of the deposits suggest that they are reefs. However, Lowenstam (1950)argues that not anymass of fossiliferous limestone showing reef-likedimensions should be called a reef and requiresevidence that sediment-binding organisms were present which wereable to erect wave resistantstructures. Certain colonial corals suchaswaaqenophyllum (7) which arelocally fairly abundant may havebeen reef builders of the type required. The thick limestone masses in the vicinity of Nount Kerrare believed to be reefs. A third type,occurring in the Nembers I1 and IV. is lenticular or pod-likeandranges from 100 feet to several miles in strike length. Many of thesebodies have dimensions similar to thoseof reefs but most of them arelacking in fossils.Perhaps some were reefs composedof algal structures that are no longerrecognizable. The origin ofthese deposits is uncertain. Calcarenites and breccias in the Alembers I11and IIIa indicate localcurrent activity. Some ofthebeds containing oolites may have beendeposited at shallow depth in thezone of wave action(Illing. 1954, PP. 35-44). The origin ofthe ribbon chert isacontroversialsubject. Ac- cordingtomodern experimental work (Krauskopf.1956) both fresh water andsea water are highly undersaturated with respectto silica and neitherchanges in pH (belowa pH of9) nor in salinity appreci- ablyaffect the solubility ofthat substance. Only threeofthevari- ous hypotheses for the origin of chert seem reasonable in vierv of the required chemical conditions established by Krauskopf: thedeposition ofcolloidal silica from siliceoussolutions that may berelated to volcanism(Davis, 1918; Cairnes. 1924b, p.41); the leachingand re- deposition of silica from vitric tuff, amaterial that dissolves much fasterthan mineralic matter (Goldstein and Hendricks,1953). and the accumulationof debris from siliceousorganisms (Bramlette. 1946).

16 Bothvolcanic flows. and tuffs are present in theYarhle Canyon formation.There is, however. no strikingassociation of chertand volcanicflows and the relatively small proportion of tuffappears in- sufficientas source of the m2ch largervolume of chert. However. thin-sectionsof chert show spine-likeand nodular structures that couldbe of orpanicorigin. Better preserved specimens of the same typehave been found in greaterquantity in thecherts of Division I of the Paviliongroup. Therefore it is believed that the chert of the MarbleCanyon formation is largely of organic origin.

5. AGE OF CORRELATION

Fossilscollected at eleven localitiesin the Marble Range (see Geological Rlap) were identified by W.R. Danner:

F1 Locality:F1 On ridge,about 1 mile eastJesmondof road, 1.25 miles northwest of PorcupineCreek, upper part. Nember IV Yabeinasp. Schlvaqerinasp. Verbeekina sp. Glomospirasp. Gyroporellasp. Associated:algae, coral, small fusulinids A ge: Upper Permian, Upper Age: F2 Locality: On ridge,about 1 mile eastJesmondof road, 2 miles southeast of ?daunt Bowman. blember 111 Yabeinasp. onesmall Verbeekina type fus!ulinid foraminifera,one similar to Pachvploia Tetrataxissp. Gyroporellasp. Associated:echinoid debris. mollusc shells, and a coral. Age : Upper Permian. The assemblagecould kslight- ly olderthan those from the other localities.

F3Locality: On ridgeabout 2 miles eastJesmondof road, 2 miles northeastof head of Porcupine Creek. Member: I11 Yabeina minuta Schwaqerina Condonofusinella sp

17 Textulariasp. Age : Upper Permian.

F4 Locality: 2 miles solrtheastofMor~nt Kerr. .7mile northwest of FiftysevenCreek. Xember Ill Yabeinacolumbiana ‘tNeoschwaqerinasp. PVerbeekinasp. Associated:other foraminifera (?), corals.algae, coarse plates of echinoderms,crinoid stems, a bryo- zoanfragment. and oolites. Age : Upper Permian.

F5 Locality: . 1.5 miles west of Mount Kerr. Member I11 Yabeina minuta Schwaqerina acris Condonofusinellasp. Age : Upper Permian.

F6 Locality: 3.2 mileseast of Mount Bowman, .2 mile north of Mann Creek. Member I1 l? Yabeinasp. Condonofusinellasp. Clomospirasp. Ape : Upper Permian.

F7 Locality: 3.5 mileseast-northeast of hlor~nt Bowman. .5 mile northof hlann Creek. Vember III? PWaaqenophyllum sp. Associated:least.at two Permiantype fosulinids. Age : Permian.

F8 Locality: 2 miles eastof hlount Bowman. .5 mile southwest of head of Nann Creek. ivlember III? Yabeinasp. Age: I!pper Permian. F9 Locality:about Smiles east Jesmond,of 1 mile northeast ofhead of JesmondCreek. Member III? Two bryozoanfragments. corals (?I, primitive fusulinids ('?I algalremains (?), oolites. Age : unknownprobably but !Ipper Palaeozoic.

F10Locality: About 3 mile north northwest of F9. hlember III? Corals,foraminefera, echinoid stems. Age : unknown

F11Locality: Eastern bank ofBig Bar Creek, about 2.5 miles northwestof Jesmond. hnber IV Fusulinids,pelecypods, coral, algae or echinoderms. Age: Permian.

W.R. Danner statesthat most of the collections contain fusulinids common to the Americanand Asiatic Tethys sea. "The associ- at.ionof Yabeina-Schwaqerina-Condonofusinella is typicalas far as is known for the uppermost fusulinid zone in North Americaand is consideredto be Upper Permian."According to Danner collection No.2 mightbe slightly older than the othersbut the fusulinids are too recrystallized to establish whether they are Neoschwaoerina and hence a zone lower in the Upper NiddlePermian. All fossils were collected in the Alembers I11 and 1V or in rocks thatare believed to be correlative with these members.Both mem- berstherefore appear to be mostly Upper Permian;but the lower part of I11 may be UpperMiddle Permian. The ilembers I and I1 areper- hapsNiddle Permian.

19 PAVILION GROUP

INTRODUCTION

ThePermo-Triassic Pavilion group is composed ofchert, arpillite,volcanic flow-rocks and tuff, volcanic sandstones, limestone, siltstone,conglomerate, sedimentary breccia, and the metamorphic equivalentsof these rocks. Two Divisionsare distinguished. Chert andargillite are dominant in the lowerpart (Division I) andvol- canic rocks andsandstones in the upperpart (Division TI). The top ofthe Upper PermianMarble Canyon limestone marks the boundary of thePavilion group with the Permo-PennsylvanianCache Creek group. Therocks now assignedto the Paviliongroup were formerly included with theCache Creek group. Stratigraphic relations in northwestern British Columbiasuggestsamajor unconformity either at the base of the qroup or betweenDivision I andDivision I1 (K. Rigby,personal communication)but that unconformity has not been observed. DIVISION I

1. DISTRIBUTIONAND THICKNESS

Division Iextends from thesoutheastern to the northern extremityof the map area. On BigBar Creek, where the Divisioniscontinu- ouslyexposed and its boundaries with the underlyingand.overlying formationsarewell exposed, itformsa zone about 5% mileswide. Its thickness may beanywhere between 1,000 and 5,000 feet and is possibly in the vicinityof 3,000 feet.

2. LITHOLOGY

Division I consistsdominantly of chert and argillite and their metamorphicequivalents and some limestone, tuff. and lithic sandstone.Volcanic flows arerare or absent. Largebodiesof tuff and limestone, locally accompaniedby lithic sandstone,are folund onlyin the vicinity of the Fraser River between Kellyand Butcher Creeks. Theyprobably belong in the upper partof Division I. Smallmasses of tuff. limestone, and rarely lithicsandstone occur at various localities andprobably occupy differ- entstratigraphic positions. Thechert varies from light grey to bluish black in colour. It mostly occurs as "ribbonchert," that is, in layers which are in the order of1 to 3 inches thick andare separated by thin sheets of argillite or pbyllite. The chert layershave a characteristic swell- ingand pinching cross-section. Cherty argillites or cherts that containahigh proportion of argillaceous materialare mostly massive. Lightgrey chert is composeddominantlyof quartz. and toa small proportionof chalcedony and "clay," that is, clay-sized minerals of the chlorite-epidotemica groups. Dark chert contains small amounts ofcarbonaceous matter. The quartz is present in anhedralgrains which rangefrom a few to approximately 30 microns in diameterand showlundulose extinction. Thequartz either forms a structureless mosaicor nod,rles. These nodulesare coarser grained than the "mosaic"and have a higher content of chalcedonyand a lowercontent of "clay."The nodules arespherical or elliptical in sectionand

20 rangefrom .03 to .3 millimeter in diameter;the average diameter probablylies between .15 and .2 millimeter. A fewnodules show a radiatingpattern around the margin; one has aspine-like projection. Theybear aclose resemblance to radiolarian cherts inwell-preserved specimens of California(Jenkins, 1943, pp.315. 319). Chert of this type was seen in thirteen out ofeighteen thin-sections of specimens fromvarious localities. Most sectionscontain numerous minutevein- letsof quartz and carbonate. Carbonate also occurs in isolated grains within the chert. The argillite is bluishblack and laminated to massive. Under the microscope minute crystals of mica,chlorite, carbonate,and particles ofcarbonaceous matter are seen tobe embedded ina(lro?lndmass of low birefringencethat is toofine-grained for identification. Theorganic matter is dispersedthroughout the argillite.but in phylliticspecimens it is concentrated in parallellayers. Some of the argillite contains massive or nodularaggregates of fine-grained silica andgrades into chert. hlost ofthe argillite hasa silt-fraction. composed largely of feldsparfragments. The tuffs do notform beds but lenticular masses which in most localitiesare associated with limestone. A handspecimen of a little alteredtuffaceous rock is brownishgreen and composedof angular or lenticular fragments rangingfrom a fraction of a millimeter to aboslt 3 millimeters indiameter. The section consists dominantly offine-grained highly altered grains of volcanicrocks someof which arevesicular oramygdaloidal. a smallerproportion ofchlorite, which may representaltered volcanic glass, and a few per cent ofquartz, feldspar. hornblende. clino-pyroxene,and "iron ore." The tuffaceous origin of the rock is apparentfrom two features: the clino-pyroxene. a mineral which has not beenobserved by the writer as a detrital mineral in any sedimentaryrock of the map area, showssubhedral to eubedralforms; and the quartzhas in- clusionsand rimsofextremely fine-grained volcanic rock, probablyrhyolite or dacite. As the tuff was deposited in water it may haveincorporated some detritalmaterial. A specimenfrom the slopenorth of the ,upper part of SiwashCreek probably represents ashearedandaltered limy tuff. Thehand specimen isbluish green and contains light to darkcoloured, rather angularfragments ina light green groundmass.The fragments range fromlcentimeter to about 1 millimeter in size. The thin-section shorvs fragmentsof volcanicrocks embedded in an abundant matrix ofchlorite andcarbonate. The fragments are porphyritic and vitro- phyricandmostly amygdaloidal. They show lath-likemicro- lites andbroad prisms of plagioclase inagroundmass that is alteredto chlorite andvery fine-grained deep brown carbonate.The carbonateof the cement is stronglytwinned, in some placesina feathery fashion. The chloriteof the groundmassoccurs in narrowstringers and large patches madeup of radiatingsheaves or feltedmasses. The limestones ofDivision I formpods and lenses, Short beds were observed in onlyafew localities. The largest ofthe lenticular masses is located on the slope north ofthe upper partofsiwash Creek andhas been mapped as a separate unit. Exceptfor gastropods, no fossilshave been found in these limestones. Some of thelimestones containoolites and pisolites that range from a fractionofamillimeter to several millimeters in diameter. Most ofthemare ellipsoidal; less commonly they are spherical orspindle-shaped. The oolites are made upofconcentric layers of veryfine-grained carbonate. Ra- dial structures arerarely developed. The centre of the oolites is occupiedby coarse-grained calcite, in some specimensby a single crystalor, less commonly, bychlorite and chert nodules. Most of the limestonesare associated with tuffs,and near the contacts the two rocks aremixed. Someofthe limestone near the con- tactscontains greenish or brownish weathering stringersof chlorite which in some specimensare associated with chalcedony.Angular fragments oflimestone or irregularblebs with roundedoutlines are incorporated in the tuff. The sizeof these inclusionsranges from.tens of feet to a fractionof a centimeter. The lithicsandstones occur with tuff,argillite, and chert. At some localitiesthey show gradedbedding and are similar in ap- pearanceto those of Division 11.

3. METAMORPHISM

Where rocks of Division I arein contact with Coast Intrusions theyare highly metamorphosed. Most of themetamorphism is related to the plutonbetween Kelly Creek and Leon Creekand the best expo- Sures are on bothbanks of the FraserRiver near the mouth of Kelly Creekwhere a migmatitecomplex consistingofdioriticdykes. amphibolites.and banded hornfelses has been mapped as a separateunit. It is notcertain, however, if all of the rocksbelong to Division I; some of the rockson the west shore may be part of Division 11. Nearthe mouth of Kelly Creek, a faciesof Division I richin tuffaceousrocks has been intruded by dioritic dykes. The contact between the dykesand the host rock is generallygradational and the hostrock is cut by numerous lensesand vein-like stringers rich in quartzand feldspar. A typical specimen of the transition cock. ablue-grey. fine-grained.massive amphibolite is cut by fine greyish white quartz-feldsparveinlets that are from one to a few millimeterswide. A thin-sectionfrom this rockcontains approximately 75per cent of hornblende (grain size approximately .05-.5 millimeter) associated with "iron ore" and a trace of biotite, and25 per cent of finer grained (.a05 -.25 millimeter)quartz and feldspar. The plagioclase, calcicandesine. is partlyanhedral, partly subhedra1,and mostlytwinned. A largeproportion of the feldspar is water-clear. A partof the rocks on the westernbank of the FraserRiver in the samearea is finelylayered amphibolites and hornfelses. The rocksbelong in thehornblende-hornfels facies (Fyfe, Turner, and Verhoogen,1958, p. 209). and may originallyhave been phyllites or strongly jointed argillites. A specimen of these foliated rocks is composed of light grey and black layers ranging from lmillimeter to 1.5 centimeters in thicknessthat show finecrynulations. The dark layersconsist mainly of subhedral hornblende crystals, about.1 millimeter longthat are strongly pleochroic (z: ,

bluishgreen:y: green, x: pale brownish green). The light- colouredlayers are made upofcloudy, partly twinned calcic oligoclase withagrain sizeof approximately .05milli- meter,and a littlequartz, Hornblende and plagioclase arepresent in approximatelyequal proportions. A grey,massive, very fine-grained specimen showing some medim- sizedgrains of feldspar is characteristicofanother large group of rocks on the west sideofthe Fraser River, opposite the mouth of Kel- ly Creek. The originalnature of the rock, which now belongs in the epidote-albitehornfels facies, is uncertain:perhaps it wasanacid- ic volcanicflow. It consistsof approximately50per cent offeldspar, 42 per centofquartz, 5 percent of epidote.:! percent of chlorite,lper cent of carbonate and traces of sphene and "ironore". The groundmass isatightly interlocked agare- gateof anhedral quartz, and subhedral toanhedral feldspar. bothranging approximately from .05 to .5 millimeter in size.that is cut by stringersof epidote, chlorite, and carbonate.The feldspar consists mostly of twinned sodic albite:potassic feldspar israre or absent. The albiteof the groundmass is cloudy with inclusionsof epidote: the largercrystals, forming anhedral, twinned grains up to 1.5 millimeterslong contain inclusions of quartz, but not of epidote,The fine-grained cloudy feldspar of the groundmassand someofthe quartz are thought tobeoriginal constituents ofthe rocks: the inclusion-freeplagioclase, and some ofthe quartz may havebeen introduced.

4. STRUCTURE

Thecontact between Division I and the MarbleCanyon formation is exposedonly in the vicinity of SallusCreek and Keatley Creek, northof Pavilion Lake, and on Big Bar Creek. In these localities neitheran unconformity noramajor fault could be observed althollah the contacts between limestone beds and argillite are locally sheared. Thecontact appearstobe gradational and the proportion of interhed- dedlimestone increases in aneastward direction. As Division Iis in contact with the uppermost partof the Xarble Canyon formationone mightconclude that it overliesthe limestones. However the westward transitionfrom limestone to chert and argillitecould represent a facieschange in isoclinally folded strata, and in this caseDivision I would be partly contemporaneous with theupper hlarble Canyon formation. In most localities the strata of Division I strike northwesterly and dipsteeply. Marker beds are scarce and stratigraphic tops could bedetermined only ata few localities. Judging from thewell strati- fied and plasticnatureoftbe rocks they are tightly fo1ded:thepat- tern offolding may be similar tothatofthe younger Lillooet group, which has a comparable lithology.Dragfolds are developed only in the vicinity of faultsand are here of very varied plunge. In some localities the limestones show a lineationin the form of grooves, but the plungesofthese lineations are also irregular. Division Iis partly boundedby faults but noextensive internal faults were recognized.However, therearebroad areas underlain by shearedrocks that arecrossedhynumerous minor irregular faults. The most extensive of these shearzones is exposedbetlveen Moran andKelly Creek, Other '3 shearzones of this type were seenontheslope northofGibbs Creek, in HighBar Canyon, and on the slopesabove Big Bar Creek, near the mouth ofStable Creek. In additionto these laraezones shownon the map, there arenumerous small ones thathavenotbeen indicated. Al- most allcontacts between massive rocks, such aslimestone, tuff, or lithicsandstone on the onehand, and laminated argillite and chert on the other hand aresheared, Some ofthedistortions may havebeen causedby differential movements of sedimentary strata during folding.others seem tobe related to movementsof Coast Intrusions.

5. MODE OF ORIGIN

Remnantsof radiolarian skeletonsin the chert suggestthat Di- vision I was laid down in amarineenvironment. The presence of carbonaceousmatter indicates a "restricted"environment (Krumbein and Garrels.1952). The scarcity ofcoarse-grained clastic sediments and thedominance offine-grained clastic and bioclastic sediments indicatesthat the sourcearea was of low relief or at a greatdistance from the site ofdeposition. There was little volcanicactivity in the area.The environment of Division I appearssimilar to that of the AlarbleCanyon formation, except that conditions for thegrowth of reefs were rareor lacking. If Division I is partlycontemporaneous with theMarble Canyon formation it probablywas deposited seaward from the reefzone. The originof the chert,tuff, andlimestone pose special prob- lems. Microscopicexamination shows that thecherts are composedof a considerableproportion ofnodules that resemble the radiolarian remains ofrelatively well-preserved (compare Jenkins, 1943, pp. 315, 319) rocks. A few of thesenodules show radiatingspine-like structures around the marginsthat are strongly suggestive of an organic origin.Becauseof the microscopic evidence and the scarcity ofvolcanic centres in the area, it is believed that the chert is of organic origin. The alternationsof chert and argillite may bedue to season- alchanges that governed the lifeof the siliceousorganisms or the depositionof the associated inorganic matter, The lenticular shapeof the tilff bodies and features of brecciation near their margins indicate that the tuffs were deposited by currents,perhaps density mrrents. thatoripinated when the tuffaceous materialentered the water. The originof the limestone in Division I is a difficvltprob- lem, Thebig, pod-like mass north of Siwash Creek is reef-like in shape,but no fossils have been found in it. Regarding the smaller bodies two consistentfeatures may beof genetic significance: the associationDfthe limestone with tuffs, and the signsofcurrentac- tivity such asoolites and certain features of brecciation. These relationscould be explainedin different ways. Thelimestones maybe inorganicand their precipitationcould have been ca,usedby theclir- rentsthat carried the tuffaceous matter. The solubility of calcium carbonate in seawater (Revelle, 1934) depends on the carbondioxide contentof the water, on its temperature,pressure and pH. Thecur- rents descendinqfrom the surface may have warmed up the bottom wa- ters andthus caused the precipitation of some calciumcarbonate. However, the amountof 1imest.one produced by sucha process would be relatively small. It is also possible that the currents collected un- 24 consolidatedlimy material fromthesea bottom and saept italong together with the tuffaceousmaterial. A third possibility is thatthe deposition of both tuff and limestone was controlled bydepressions on the seafloor. The limestone may havebeen deposited in suchdepres- sions owing tobiological or physico-chemicalconditions and the den- sitycurrents may havedropped their load here becauseof dynamic factors.

G. AGE

The structuralrelations show thatDivision1 is either contemporaneous with the upper part of the ~larble Canyon formation or younger. Itis overlainby Division I1 which is probablyTriassic. There- fore it is UpperPermian and/or Triassic in age.

DIVISION 11

1. DISTRIBUTIONAND THICKNESS

Rocks assignedtoDivision I1 underlie two separateareas. They havebeen correlated becauseof their similar lithology but they may not be exactlyof the same age. The outcrops ofthe Big Barassemblage forma zone about 3 miles long and up to 1% miles wide in the vicinity of the lower part of Big BarCreek. Their thickness is of the orderof 2,500 feet. ThePavilion assemblage underlies an areaabout IO miles long andup to3miles wide situated mostly on the eastsideofthe Fraser Riverbetween Sallus Creek and hloran. The unit is boundedbyfaults, and so little is known about its internalstructare thatan accsrate statementof the thickness cannot begiven. Several thousand feet of strataare probably present.

2. BIG BARASSEMBLAGE

A. Litholog~

Becauseof facies changes and lack of outcrop the stratigraphy of theBig Bar assemblage has notbeen worked out. A broadbelt of lithic sandstone with interlaminatedargillite extends from the west slopeof ;vlount Kosterinp across BigBar Creek tothe south slope of Big Bar Mountain. The contacts of this belt aregradational. The rocks show gradedbeddina and abgndant contortions thatapparently were produced before the lithification of the sediments. To theeast of this belt inthe vicinityofBigBar Creek. flowsofandesite and dacite are exposed. The other parts ofthe area areunderlain by tuff. ribbon chert, argillite, andlimestone. The limestoneoccurs in beds.not exceeding halfa milein strikelength, inlenses and pods associated with tuff,or in thin layersinterlam- inated with argillite. A typicalspecimen of interlaminated argillite. siltstone, and sandstonefrom the west slopeof Mount Kosteringweathers brownish green. Its laminaeof argillite are from 1 centimeterto a fraction of a millimeter thick: a layerconsisting mostly of sandstone and siltstone is about3centimetersthick. Approximately two-thirds of the argillite consist of clay-sizedminerals, one-thirdof silt-sized carbonate.feldspar, and quartz, and a smallfraction of carbonaceous 25 matter.The sandstone and the siltstone are made updominantly of carbonate,feldspar, and quartz, and a smallerproportion of clay. Thespecimen shows graded bedding and some cross-bedding. A graded unit rangesfrom very fine-grained sandstone at the bottomthrough siltstone to argillite. Thecontact between twograded units ismark- edbyaconcentration of carbonaceous matter and flsltings in the argillite, andby an abrupt change in grain size. Thevolcanic flow rocksweather greenish grey and are mostly porphyritic. Two specimens of alteredandesite consist dominantly of albite whichforms microlites andphenocrysts, andasmaller proportionof epidote, (largely pistacite). chlorite, and carbonate; one specimenshows replacement by prehnite. The lack of zoning,the al- biticcomposition, and the abundance of epidote indicates that the plagioclasehas been altered. Ina thin-section of meta-dacite,phenocrysts of calcic albite are embedded in a fine-grainedgroundmass con- sistinglargely of albiteand quartz. The plagioclase has relativelyfew inclusions. The partly jagged outlines of thecrystalsandnndulose extinction indicate recrystallization.The rock is veinedby quartz and epidote.

6. Stwrctxre TheSouthwestern contact ofthe Big Bar assemblage,exposed near theroad to the HighBar ferry, probably is faulted.The rocks are stronglysheared, and the transition from tuff to chertandargillite is abrupt. Thenortheastern contact appears tobe gradational. An unconformity couldnot he observed although it may bepresent. No major fault is visible here, hutthe contacts between masses of tuff and chert andargillite are locally sheared and altered.In the southeastthe unit tapers and forms anose. Thenorthwestern contact is notexposed. The strata strike approximately north 40 degrees west anddip moderately to steeplynortheast. At many different 10- calitiesin the southwestern half ofthe unit the stratigraphictops were found to facethe northeast. At three localities in the north- easternhalf they were seen to facethe southwest. It appearsthat the strata form a synclinewhich is overturnedto the SoUthwest and probablyplunges to the northwest. In the centralpart of the unit on the slope north ofBig Bar Creek gentlydipping strata were seen thatappearedtolie upside down. It isuncertainwhether these anomalous attitudes were producedby distrubances before or after the lithification of therocks. The foldingofthe unit probably wasac- companiedby much differential slippage on beddingplanes whichmay ex- plainthe sheared and faulted contacts. A schistosity which strikes northwesterlyand dips steeplyto the northeast wasonly observed in thecentral parts of the BigBar assemblage, thatis. near the axial planeof the inferred syncline.

3. PAVILIONASSEMBLAGE

A. Lithology

Approximately two-thirds ofthe Pavilion assemblage is madeupof volcanicrocks, mostly tuffs and less flows,and about one-third consists oflithicsandstone, argillite, limestone, siltstone, breccia, andconglomerate. 26 The tuffsare greenish weathering massive rocks which showfine, angularfragments onlyon fresh surfaces. Tuffs rich in lithic material can hardlybe distinguished from volcanicgreywacke. The vitric fragmentsare altered to chlorite or finelyrecrystallized; shard- like outlinesare rarely preserved. The crystal fraction consists mostlyof twinned plagioclase anda small proportionof quartz; horn- hlende is rare. Some pyroclasticcrystals are euhedral. others are broken; they are fresher looking and less roundedthan detrital grains in the sedimentaryrocks. The volcanic rocksofthe Pavilion area range from basalt to felsite, Many of them containphenocrysts of quartz. A greyishgreen weathering aphanitic (tholeitic) basalt containsapproximately 8 percent of quartz, 3 per cent of endiopside (t2v moderate; n,, 1.673) which forms micro-phenocrysts,and 10 per cent of chlorite and fine-grain- edalteration minerals; the balance is made up oftwinned andzoned plagioclase microlites which range from calcic labradorite to sodicbytownite in composition. The rock is crossed by narrowzonesofmylonite and by veins of carbonate and chlorite. A blue grey porphyritic aphanitic flow rockoffelsitic- compositioncomprises about 40 percent of fractured and corrodedphenocrysts (grain size2millimeters - .5 millimeter) inan extremely fine-grained partly glassy groundmass(grain size approximatelyl- 5 microns).Most of the phenocrysts areof quartz;a smaller number consistsof zoned and twinned andesine, and a few grains are of "iron ore". whichprobably has replaced a maficmineral. The groundmass is too finegrained for indentification. Besides quartz andfeldspar minerals ofthe chlorite and mica groups are abundant.The specimen includes a few fragments of relativelycoarse-grained acidic flow rocks. It is veinedand replacedby quartz. carbonate, and radiating chlorite. A greyishporphyritic volcanic rock which apparently hasbeen metamorphosed has about 3per cent of plagioclase phenocrysts(grain size .5 millimeter -3millimeters) and a mosaic-likegroundmass composedofanhedral quartz. plagioclase, and potassicfeldspar. Thephenocrysts, unzoned buttwinned albite are replaced around the margins by the groundmassand contain numerous inclusionsofquartz, epidote, andminor feldspar. Some veryfine-grained aligned inclusionsof quartz resemble myrmekitic inter-growths. Quartzprobably has been introduced into the rock.The specimenisveined by minerals ofthe epidote group. mostly pistacite. A belt of laminatedlithic sandstone with some argillite, conglomerate,breccia, and siltstone is exposed in thevicinity of the railroadbetween Pavilion and $loran. As the contactsof this belt are gradationaland poorly exposed it could not bemapped as a separate unit. Therocks show gradedbedding and contortions formed before the lithificationof the sediments. The lithicsandstone weathers brownishgreenandisgreyon fresh surfaces.Three specimens analyzed contain approximately 10 to 40 per cent of feldspar, 1 per cent of quartz, 45 to 85 per cent of lithic fragmentsand chlorite, and less than 1 percent of "iron ore"and epidote. The feldspar is mostly twinnedand zoned plagioclase that has not beenalbitized. The lithicfragmentsare mostly derived from volcanicrocks (dominantlyofintermediate composition)and some from chert and argillite. Some specimens show gradedbedding and arewell sortedbut in others thesorting is poor. A comparatively unaltered rockhas onlya small contentof clay matrix (lessthan 10 percent). and its particlesare rounded or subrounded.Others are too highly altered to determinethe original roundness and clay content. These rocks areclassified as volcanic arenites. A sedimentaryrocktransitionalfrom coarse-grained greywacke to granuleconglomerate has the following composition: plagioclase 10% quartz 1% chlorite and epidote 1% hornblendeand "iron ore" -1% volcanicfragments 67% limestone 20% chert 1% The frapents are embedded in a claymatrix which probably makes up more than10 per cent of the rock. Both rounding and size sorting arepoor, The grainsize ranges from4millimet.ers to .1 millimeter. Associated with thelithic sandstone andconglomerateare brec- ciasthat are made up ofthe samecomponents but locally contain a largerfraction of limestone, chert, and argillite.These breccias are between2and 20 feet thick andcan be traced along strike for a fewhundred feet. In mostbreccias the fragmentsdonot exceed afew centimetersin diameter. However.on the ridge northof Keatley Creek, about 2 milesnortheast of Glen Fraser. a section wasmeasured that containsseveral very coarse breccias or conglomerates.

Thickness in Feet Lithology

Top ofmeasured section 4 Lithicsandstone with granules and sand-sized grainsof limestone. 3 Laminatedsandstone andsiltstone showing some cross- bedding. 12 Lithic sandstone with fragments of limestone up to 1 inch long. 3 Lithicsandstone with abundantargillaceous matrix and a smaller proportion ofsand than normal. 24 Limy conglomerate,consisting mostly of limestone cobbles, about 4 inches in diameter, some fragmentsof lithicsandstone and chert, and onelensof argillite, about 6 inches long. Laminatedsandstone and siltstonelocal- ly show gradedbedding. The conglomerate is closely packedand the fragments are well rounded and size-sorted. 2 Coveredinterval. 2 Calcarenite and granuleconglomeratewith limy fragments in a matrixof lithic sandstone.

28 Thickness inFeet Lithology

2 Calcareniteandgranuleconglomerate consistingoflime- stonefragments in a matrixof lithic sandstone. Coveredinterval. Lithicsandstone. Fine-grainedcalcarenite. Lithic sandstone withgranules of limestone grading downward into cobble conglomerate containing dominantly fragments of limestone andminor argillite. Towards the top of the layer the sandgrains become scarcerandthema- trix more argillaceous. 12 Dominantlyargillite mixed with marland lithic sandstone.The upper6feet contain well-rounded cobbles of limestone and argilliteabout 6 inches in diameter. 4 Lithic sandstone. 6 Granuleconglomerate. One-third of the fragments is of limestone and two-thirdsof chert. The matrixconsists dominantlyof limestone. 6 Lithic sandstone. 5 Coveredinterval. 16 Brecciaconsisting dominantly of limestonepebbles, approximately 1 inch in diameter, and a fewfragments of argillite ahoutbinches long in amatrix of lithic sandstone. 6 Coarselimestone breccia. Most of the limestone is blue grey, some brownishfragments may bedolomitic, Some bouldersareangularothers rounded, A smallfractionof thefragments ranging up to6inches in length are com- posedofchert. Thematrix consistsof lithic sandstone. 6 Lithicsandstone with scattered granules of limestone. 6 Lithicsandstone. 6 Argillite. 1 Coveredinterval: fault? 32 Coarsebreccia composed mostlyof limestone and some chert.The size of thelimestone fragments ranges from pebblesone-half inch in diameter to a boulder 8 feet long, 4 feet wide. Most fragments are well rounded:the largerones mostly ellipsoidal. The matrix is lithic sandstone;the granule grade is poorlyrepresented. 4 Lithicsandstone. 1 Finebreccia. Fragments dominantlyoflimestone and mi- nor chert, argillite. and volcanic rocks are embedded in a matrix of lithicsandstone. The fragments are up to1 inch in diameterand mostly well roonded. Fault. 29 Thickness in Feet Lithology

10 Lithic sandstone with granule to pebble-sizedfragments oflimestone. 1 Argillite. 48 Lithic sandstonethat is mostlymassive but shows bedding in the form of bluish, silty or argillaceous laminae nearthe contact with the overlying argillite. Contains afew ellipsoidalfragmentsofargillite and some limestonepebbles. 60 Coveredinterval 5 Fine-graineddiorite sill. 3 Fossiliferouslimestone containing corals, gastropods, brachiopods,and echinoids and some oolites. Thelime- stone is intermittentlyexposed 'for about 200 feet. In some placeslithic sandstone andtuffaceous material is interlaminated. 4 Ribbon chert. Bottomof measured section

323 feet

Limestone,aminorcomponent of this Division, occursin pods or lensesthat donot exceed 200 feet in length.The greatest concentra- tion of suchbodies occurs near Pavilion Creek about one-half mile east of the FraserRiver. At only two localitiesfossils were found. Crinoidstems were collected on the eastside ofthe Fras6r River aboutlmilesouth of the mouthof McKay Creek,and fragments of corals.pelecypods, gastropods, andechinoids about 2 milesnortheastof Glen Fraser(F12).

E. Mrtamorphism and Alteration

Asthe Pavilion assemblage is intruded by numerous dioritic bod- iesaconsiderablepropor.ionofthe rocks show contactmetamorphism. Both thehornblende-hornfels and the albite-epidote hornfels facies arerepresented. Some specimensare transitional between these two groups(See Table 1). Mostof themetamorphic rocks are dark green, fine-grained (grainsize .01 - .15 millimeter)massiveor weakly foliated amphibolites whichmayhavebeen derived from tluffs. lithic sandstones,and basalts. In some ofthe specimens an originalfragmental character can stillbe detected underthemicroscope. but pyroclastic rocks cannot bedistinguished fromsedimentary rocks. All ofthese rocks contain more than 40 percent of amphibole and most of them have 20 to 45 per centof plagioclase. In rocksofa moderate grade of metamorphism the amphibole isrepresentedby hornblende. The mineralvaries in habitfrom broad to slenderprismatic and isstrongly pleochroic (z: blue-green; y: greenor greenish witha brown tint;x: pale brownish greenor pale brown.) In a specimenshowing retrogressive meta- 30 morphism the hornblende is partlyreplaced by chlorite. A low-grade metamorphicrockconsists dominantly of acicular, pleochroic (z: bllue- green)actinolite. Theplagioclase. ranginain composition from calcic andesine to albite, is anhedral. full of inclusions of epidote and amphibole. andpartly twinned. Epidote appears in appreciable quantityonly in rocks ofintermediate to lorv gradeofmetamorphism. Quartz forms~up to 30 percent of some specimens. As accessories “ironore”, sphene, and apatite are present. Some metamorphosed lithic sandstoneshave the same mineral as- sociationsas these amphibolites butare relatively poor in amphibole. Where lithic sandstonewas interlaminated with arpillite,alternationsof hornblende-rich and felsic layers are visible which in some localities showboudinage structures. Two greyish,fine-grained, massive rocks consisting d.ominantly of feldspar(albite in one specimen; albite and orthoclase in the other). quartz.and small amounts of chlorite,epidote, “iron ore’. andcarbonate apparently have beenmetamorphosed under conditions of the albite-epidotehornfels facies. The porphyritic texture of one specimenand the fine-grained lath-like habit of the plagioclase in theother one indicate that they were (acidic) volcanic floiv rocks. Nearintrusions the ribboncherts have been metamorphosed to quartzite and the limestonesto marble. As the unit is boundedbymajorfaults and broken internally by numerousminor ones, brecciationandmylonization are common in these rocks. Associated with thedynamic metamorphism is alteration by carbonate,epidote. chlorite. and quartz.

31 TABLE 2.

MINERAL-COMPOSITION OF SOME METAMORPHIC ROCKS,PAVILION GROUP, DIVISION 11.

Determination of % of % of % of % of % of % of % An Plagioclase Quartz __:pidote Iron Ore Metamorphic Facies I An 1 46 1 .5 49 minor minor Hornblende- on ) = 1.5485 44 I nx1 (001 1 hornfels

41 I minor 10 Hornblende- hornfels 58 (+IN Iiornblende- M3 IO10. xlA010 = 14' max 50 3 minor hornfels transitional to albite- epidote hornfels 57 5% but Retrogressive from Au- artly re- 25 minor hornblende-hornfels 104 laced by to albite-epidote hlrte 1 5o hornfels Albite-epidote 10 0 hornfels To the west thePavilion assemblage is inferred to be in fault contactwith Lower Cretaceousvolcanic rocks. The contact is nowhere exposedbut is believed to be a faultbecause the Lower Cretaceous strata seem todip under those ofthe Cache Creek group. The rocksof the Pavilionassemblage in the vicinityofthiscontact are sheared, brecciated, and locallyaltered. To the east theassemblage is in contact with Division I. The nature and exact locationof this boundaryare only partly known. The contact is well exposed onlyonthe slope north of Pavilion Creek. Here an abruptbreak from amphibolites in the southwestto ribbon chertin the northeast can beseen. The chertadjacent to the contact is stronglyshearedand partly carbonatized; theamphibolite is sheared and alteredin some places and apparently little disturbed in others. Between this locality and theslopeabove Moranthe boundary Of the two units is coveredby overburden. It seems to cutacross the regional strike of the strata in a northwesterlydirection. South- eastof Moran thecontact is notexposed but canbe located within a fewhundred feet. The appearance of the rocks on either side of the contact is the same as on Pavilion Creek. It seems tobe certain thereforethat between Pavilion Creek andhlorantheboundary between the two divisions is a fault. There arealmost no outcropsbetween the railroad and theFraser River in this vicinity. On the west side ofthe Fraser River, approximately Zmiles downstreamfrom the mouth ofKelly Creek, a sharpbreak was noticed from hornfelsic rocks in the northeast to little metamorphosed sedimentary and tuffaceousrocks in the southwest.The contact between the two rocks is notexposed. Thehornfelses near the contact appear little disturbed butthe sedimentaryand tuffaceous rocks are in some placesschistoseandcarbon- atized.This contact approximately lines upwith the faultsoutheast of kloranand may be its continuation. However, it is not entirely certainwhether the metamorphicrocks belong to Division I. Southof Pavilion Creek the contact is poorlyexposed. Only on the ridgenortbof Keatley Creek can itbe located with accuracy,but its nature is uncertain.The lack of atransition zone between lithic sandstone,tuff, and amphiboliteinthe west and chert and argillite in the east, the unusualnarrowness of Division I whichis here onlyaboutlmile wide, and the orientationof the stratigraphictops which face the northeastsuggest a faultcontact. Becauseof the scarcity of markerbeds, insufficient exposure, and the difficultyto determine the relative position ofthe stratigraphictops in shearedand altered areas, the internalstructure of Division I1 is understoodlittle. BetweenPavilion and Moran thegeneral strike of the strata is 5 degrees to 10 degrees west ofnorth, and the dipsare steep. A markerbed of chert showsextreme local distortions but a uniform trendover large distances. A few stratigraphictops in the eastern part of the area face the east and at one locality in the western part at the west. A great numberof zones composedof rusty or schistoserocks are exposedbetween Pavilion and Woran.Most ofthese zones, probably faults, are parallel to the regionalstrike. A fewofthe larger ones are shown on the map.

33 4. MODE OF ORIGIN

Fossilsindicateamarine environment, and thepresence of carbonaceousmatter in the argillite shows that it wasofthe "restricted" type in which thecarbonaceous matter has not been oxidized. Gradedbedding and the deposition ofbreccias are attributed to turbiditycurrents. Contortions that probably formed beforethe lithif- icationofthe sediments areprobably due to submarineslumping. Both turbiditycurrents andslumping maybe related to tectonic movements that wereprobably accompaniedby volcanic activity. The presenceof acidicvolcanic flows sluggests that someof the volcanic centres lay in thevicinity of Pavilion andBig Bar.

5. AGE ANDCORRELATION

Division I1 appearstobe younger thanthe UpperPermian Marble Canyon formationand the Permian and/or Triassic Division I, and it is older than ultrabasic intrusions ofaprobably Upper Triassicage. Theserelations suggesta Triassic age. This conclusion is supported by fossils found on theridge north of Keatley Creek on which Helen Duncanof the United StatesGeological Survey reports as follows: The coralsare very much recrystallized andcorroded,, but I am virtually positivethey are hexacorals. So faras I can tell,they look like things that have been identified asMontlivaultia by Squires and in theliterature.. The specimenscertainly are not thetypeof thing I should ex- pectto find in thePermian, so I thinkaTriassic assign- ment isthe best possibility on theevidence available. As no Lower Triassic fossils have so farbeen found in adjacent parts of British Columbia,a Middle Triassicage is probable. The strati- graphicrelation to theNicola group has still to be worked out. LILLOOET GROUP

1. DISTRIBUTIONAND THICKNESS

The Lillooet group isexposedin the vicinity ofthe FraserRiver between the mouth of the BridgeRiver and the town of Lillooet. It hasbeen subdivided into three divisions, A. B. and C. Becauseof foldingand faulting the true thicknesses of these units are not known. The baseof Division A, which appears in the centreof an anticlinorium, is not exposed. In the present map area it is probablyless than 3,000 feet.Division B has a minimum thickness of 2,500 feet. C does not directly overlie Bbut is in fault contact with that division. The exposedthickness ofC is approximately 900 feet. The con- cealedpart of Division C may beof considerable thickness.

2. LITHOLOGY

DivisioE A

Division A consists mostlyof argillite that is massive or interbedded with silty argillite,siltstone, andfine-grained lithic sandstone.Individual laminae range from a few millimeters to a few centimetersinthickness. Graded bedding and crenulations attributed to deformationsofthe sediments before their lithification are com-

34 mon features;cross-bedding is rare.Locally the argillitecontains limyconcretions. The argillite is darkblue-grey. It contains about 10 per cent ofcarbonaceous matter and a fewper cent of silt in a claymatrix. Thecarbonaceous matter in many specimens is concentrated in layers a fractionofamillimeter thick along which jointsare developed. The silt fractionconsistsoffeldspar. chlorite, quartz. and carbonate. Lithic sandstoneand granqle conglomerate are rare in Division A. About2milessouth of SetonCreek on the west sideof the Fraser River a few feet volcanicof areniteand a seam ofcoal are interbedded with the argillite. The arenitehas approximately the followingcomposition: feldspar 30% lithic fragments 4 3% chlorite and mica andchlorite 2% carbonateand "iron ore" 5% quartz 20% The feldspar is mostlyalbite. The lithicfragments arelargely fromvolcanic rocks andhighly altered; someare probably chert. The fragmentsare of medium tofine sand grade. subangularto subrounded. andfairly well sorted.Their cement consistsof rusty weathering carbonateand iron oxide.

Dieisimt C

Division B consists of lithic sandstone,siltstone, argillite, andconglomerate. The lowest beds of sandstone or conglomerate in the Lillooetgroup that are at leasta few feetthick, mark the base ofthat division. Argillite is the most common rock in the lower part,but higher in the section lithic sandstonebecomes dominant, and the proportionof pebble conglomerate increases. A stratigraphicsection measured in the upperpart of DivisionB near the mo!jth ofBridge River on the west shore of theFraser River shows the increase of coarser sediments upwards, (Percentages of rock- typesare based on rapidestimates.)

Feet

Top ofmeasured section. 26 Lithic sandstone,blue-grey. blue-grey to (Ireen weathering.mostly fine grained. pyrite. thick bedded to laminated.graded bedding, resistant; grades downward into siltstone,light grey toblue-grey, lightgrey to blue- greyweathering; siltstone grades into argillite. dark bluishgrey, dark bluish grey weathering, recessive; siltstone and argillitelaminatedto thin bedded;pene- contemporaneousdeformations. ss: 90% st: 5% arg: 5% 7 Lithicsandstone, medium veryto coarse grained. grades downward intogranule conglomerate. includes fragments ofargillite. up to 2 feetlong. 9 Lithicsandstone, mostly finegrained, thick bedded to laminated,siltstone with pyrite,argillite. ss: 50% st: 45% arg: 5%

35 Feet 8 Covered interval 1.5 Lithic sandstone, medium grained, laminated. 1 Argillite, grading downward into siltstone. pyrite. Fault, contortions. 10 Lithic sandstone, medium to fine grained, siltstone, argillite; thin bedded. ss. st: 90% arg: 10% Fault. 10 Conglomerate, volcanic pebblesand granules, rounded to subangular, matrix of lithic sandstone, poorly sorted, massive, cliff-forming. 8 Lithic sandstone, mostlyfine grained, siltstone,argillite: thin bedded to laminated. ss: 50% st: 30% arg: 20% Lithic sandstone, fine tomedium grained, pyrite,fragments of argillite2 mi.llimeters long, massive. 2 Siltstone, thin bedded to laminated. 5 Argillite, massive, strongly contorted. 45 Lithic sandstone, fine to medium grained,massive. 1 Argillite. medium bedded. 16 Siltstone, mostly massive, partly thin heddedto laminated. argillite massive. st: 60% arg: 40% 7 Siltstone, argillite; thin bedded to laminated. st: 80% arg: 20% 2 Siltstoneand argilliteas above, shearedand carbonated. Fault. 1 Lithic sandstone, thick bedded, strongly carbonated. 1 Siltstone, argillite, thin beddedto laminated, carbonated. st: 50% arg: 50% 1.5 Lithic sandstone, medium grained, carbonated. 4.5 Siltstone, massive. 1 Siltstone, argillite; thin beddedto laminated, carbonated. st: 60% arg: 40% Siltstone. argillite; thin bedded tolaminated. st: 90% arg: 10% 15 Lithic sandstone, fine grained, mostly massive. 20 Siltstone, argillite, lithic sandstone:medium beddedto laminated, pene-contemporaneous deformations. st: 40% arg: 40% ss: 20%

36 Feet 12 Lithic sandstone, fine to medium grained. massive. 10 Siltstone, argillite: thin bedded to laminated. st: 90% arg: 10% 4 Lithic sandstone, fine to medium grained, thin bedded to laminated. 4 Siltstone, argillite: thin bedded to laminated st: 90% arg: 10% 17 Conglomerate, mostly granules,partly pebbles of volcanic rocks, poorly tomoderately sortedand rounded,large fragmentsof siltstoneand argillite forming intraforma- tional breccia: massive. 4 Siltstone, argillite, lithic sandstone,medium grained: thin bedded to laminated. st: 85% arg: 10% ss: 5% Fault. 6 Siltstone, lithic sandstone, coarseto fine grained,argillite; thin bedded to laminated. st: 50% ss: 40% arg: 10% 11 Siltstone, argillite. lithic sandstone, fine grained: thin bedded to laminated. st: 60% arg: 30% ss: 10% 5.5 Diabase sill. 25 Siltstone, argillite, lithic sandstone, coarse to fine grained: thin bedded to laminated,graded bedding. st: 65% arg: 30% ss: 5% 1 Siltstone, argillite, lithic sandstone, coarse to fine grained: medium bedded, graded bedding. st: 65% arg: 30% ss: 5% 14 Siltstone, argillite, lithic sandstone, fine grained; thin bedded to laminated. st: 50% arg: 40% ss: 10% 3 Argillite, massive, platy jointing. 4 Lithic sandstone, medium tofine grained. siltstone, argillite: medium bedded to laminated, graded bedding. ss: 50% st: 30% arg: 20% 12 Siltstone, massive. 26 Lithic sandstone. medium to coarse grained. massive. 5.5 Lithic sandstone, fine grained, argillite. siltst,one: thin beddedto laminated, pene-contemporaneous deformations. ss: 40% arg: 40% st: 20% 2.5 Diabase sill. .5 Siltstone, argillite; thin bedded to laminated, strongly indurated by sills.

37 Feet 1.5 Diabase sill. 13 Lithic sandstone, fine to medium grained. siltstone, argillite; medium bedded to laminated, gradedbedding. ss: 50% st: 35% arg: 15% 5 Argillite, silty, massive. 8 Lithic sandstone, fine to medium grained, massive. 24 Lithic sandstone, fine grained, siltstone, araillite; medium beddedto laminated. graded bedding pene-contemporaneous deformations. ss: 50% st: 30% arg: 20% 18 Covered interval. 2 Lithic sandstone, mediumto coarse grained. thick bedded. 12 Lithic sandstone, medilum to fine grained, siltstone, argillite; thick bedded to laminated, graded bedding. ss: 50% st: 40% arg: 10% 4 Lithic sandstone, mostly medium grained, mostly thin bedded, locally massive. 13 Siltstone, lithic sandstone, fine grained, argillite; medium bedded to laminated, pene-contemporaneousdeformations. st: 60% ss: 20% arg: 20% 7 Lithic sandstone, coarse grained, with granulesand pebblesof altered volcanic rockand fragmentsof argillite up to 2 inches long: massive. 14 Siltstone, argillite, lithic sandstone, fine grained: thin bedded to laminated. st: 55% arg: 25% ss: 20% 2 Diabase sill. 4 Lithic sandstone, fine grained, siltstone: medium to thin bedded. ss: 80% st: 20% 9 Siltstone, argillite. lithic sandstone, fine arained; thin bedded to laminated. st: 40% arg: 40% ss: 20% Lithic sandstone, medium to fine grained, siltstone, argillite: thin bedded to laminated. ss: 80% st: 10% arg: 10% 20 Argillite, lithic sandstone, coarse to fine grained. siltstone. argillite; thin bedded to laminated.. araded.. bedding. arg: 40% ss: 30% st: 30% 3 Lithic sandstone, medium to coarse grained. massive. 15 Siltstone, argillite, lithicsandstone, mostly fine grained; thin bedded to laminated, upper part carbonated.

38 Feet 5 Lithic sandstone, mostlyfine grained, siltstone,argillite: thick bedded to laminated, graded bedding. ss: 80% arg: 10% st: 10% 20 Lithic sandstone, mostlyfine grained, siltstone, argillite; mostly thin bedded tolaminated. a few beds 1 foot thick. ss: 40% arg: 30% st: 30% 5.5 Lithic sandstone, coarse grained, grades downward into pebble conglomerate. includes fragments of laminated siltstone and argillite; massive. 6.5 Lithic sandstone, medium to fine grained, siltstone,argillite: medium beddedto laminated, pene-contemporaneous deformations, graded bedding. ss: 50% arg: 30% st: 20% 6 Lithic sandstone, fine grained, partly thick bedded, siltstone, argillite: thin bedded to laminated, all strongly carbonated. ss: 70% st: 20% arg: 30% 5.5 Siltstone, lithic sandstone, fine grained, argillite: thin bedded to laminated, carbonated. st: 40% ss: 30% arg: 30% 4 Lithic sandstone, finegrained. thick beddedtolaminated. siltstone, argillite: thin bedded to laminated, all carbonated. ss: 70% st: 20% arg: 10% 5.5 Lithic sandstone, fine grained, siltstone, argillite: thin bedded to laminated, graded bedding, carbonated. ss: 40% st: 40% arg: 20% 2 Lithic sandstone, fine grained, massive, carbonated. 1.5 Siltstone, argillite, lithic sandstone, fine grained: thin bedded to laminated, carbonated. st: 50% arg: 30% ss: 20% 4 Lithic sandstone, fine grained, massive, carbonated. 4 Siltstone, argillite, lithic sandstone, fine grained: thin bedded to massive, carbonated. st: 50% arg: 30% ss: 20% 10 Lithic sandstone, coarse grained, locally grading into granule conglomerate,siltstone, arvillite: lithic sandstone mostly massive; siltstoneand araillitethin bedded to laminated. 20 Siltstone. argillite, lithic sandstone, fine grained; thin bedded to laminated, graded bedding, pene-contemporaneous deformations. 3 Lithic sandstone, coarseto fine grained, siltstone,argillite: medium bedded to laminated. ss: 90% st: 5% arg: 5%

39 Feet 16 Lithic sandstone,mostly finegrained. siltstone, argillite; thin beddedto 1aminated;one bedof argillite with strongpre-lithification contortions. ss: 40% st: 40% arg: 20% 3.5 Lithic sandstone, medium to fine grained, medium to thin bedded. 15 Siltstone,argillite, lithic sandstone, mostlyfine arained; medium beddedtolaminated, pene-contemporaneogsde- formations,graded beddina. st: 60% arg: 30% ss: 10% Fault. Bottom ofmeasured section. - 685

The lithic sandstones areblue-grey. Sixspecimens analyzed contain 10 to 40 percent of feldspar and 1 to 5 percent of quartz. Thebalance consists dominantly of volcanic fragments, a small proportion of chlorite, and a claymatrix. In unaltered specimens thematrix constitutes onlya few percent of the rocks; in many alteredspecimens the clay content Seemsto be higher. But inthese rocks the matrixcannot be distinguished from themargins of altered volcanic fragments, and the results ofpoint counteranalyses that range up to 20 percent of claycontent are probablytoo high. The lithicfragments are mostly volcanic but include particles ofargillite ranging from sandtopebble size. probably derived from contemporaneoussediments. Thevolcanic fragmentsarefine grainedandhighly altered. They consist largely ofplagioclase and chlorite but also contain potassic feldspar,quartz, "iron ore", and secondary minerals such as carbonate,sericite. epidote, chlorite, and zeolites. The largest number offragments resemble original andesites or keratophyres;smaller proportions seem tobederived frombasalts or spilites. from dacites or quartz-keratophyres,and from felsiticrocks. Some completely chloritizedfragments maybe altered volcanic glass. Some ofthe detrital feldspar and quartz may haveformed phenocrysts in such rocks. Thefragments are mostly subangular. The sorting is betterthan in typicalgreywackes but poorer than in typicalquartz arenites. Theconglomerates are made upof granules or pebbles. In many localities the fragmentsare rather angular. They seem tohave been derived fromthe same source asthe sandstones but are richer in lithic fragmentsand poorer in feldsparand qlartz.

Divisioa C

Division C. separatedfrom B byafault, is made upessentially ofthe same rocktypes as B butcontains a largerproportion of the coarsergrades and is mostlymassive. Lithic sandstone is the domi- nantrock-type and granule andpebble conglomerates composed ofrath- er angularfragments are not uncommon in thelower part of the division, Siltstone and argillite whichform only a smallfraction of

40 theexposed rocks are present in laminaeand thin beds. A covered intervalof 350 feet in theupper part ofthe division may contain a higherproportion of theserocks. Thefollowing stratigraphic section was measured on the west sideof the FraserRiver, approximatelylmile north of the mouthof BridgeRiver. Percentagesof rock types are basedon rapid estimates,

Top ofIleasured Section:

Ilember Al. JackassNountain Group

Feet 61 Lithic sandstone.light bluish grey. areenish grey, locally brownish grey weathering. medium to fine qrained. mostlymassive with a few thin interbeds of siltstone, lightgrey, greenish grey weathering, and argillite, darkbluish qrey. dark bluish grey weathering. Fault. 23 Lithicsandstone as above,upper 3 feetcarbonated. 1 Lithic sandstone, fine grained.siltstone, argillite; medium bedded to laminated. ss: 70% st: 20% arg: 10% 9 Lithicsandstone, coarse to fine grained, partly massive,partly thin beddedtolaminated, includes a 1 foot lens of volcanicpebble conglomerate. 3 Siltstone,argillite. lithic sandstone, coarse to fine grained; thin bedded to laminated,Strongly sheared. st: 50% arg: 30% ss: 20% 16 Lithicsandstone, very coarse grained. granule conglomerate, 1 inchfragments of argillite, some pebblesof volcanicrocks, poorly sorted, massive, 370 Coveredinterval. 38 Lithicsandstone, fine to coarse grained, massive: thin interbedsof siltstone and argillite. ss: 98% st: arg: 2% 4 Coveredinterval, recessive. 44 Lithicsandstone, fine to coarse grained. massive. 2 Lithicsandstone, fine grained. siltst.one, argillite; thin bedded LO laminated. 8 Coveredinterval, recessive. 33 Lithic sandstone,fine to coarse grained, massive, thin interbeds of siltstone and arpilliteforming less than 1 percent of the unit. 47 Lithicsandstone, coarse to fine grained. with somegran- ulesandpebbles of volcanic rockand frapmentsof argillite,mostly massive, partly thin bedded, a few thin interbedsof siltstone and argillite. ss: 95% st: arg: 5%

41 Feet 4 Lithicsandstone, siltstone; medium tothin bedded, recessive. ss: 60% st: 40% 40 Lithic sandstone,coarse to fine grained,upper part fine grained, massive. some granules and pebblesof volcanicrocks, poorly sorted. 7 Lithic sandstone, coarse to fine grained, grading upward intosiltstone, siltstone grades upward intoargillite; mostlymassive, thin bedded in upperpart. ss: 60% st: 30% arg: 10% 40 Lithic sandstone,coarse to finearained. coarser in lower part,massive. 0 Lithicsandstone, coarse to finegrained, siltstone, argillite.thin bedded to laminated,graded beddina. ss: 40% st: 30% arg: 30% 32 Conglomerate,volcanic pebblesandgranules. rounded to subangular.matrix of lithic sandstoneand siltstone, withfragments of siltstone and argillite 2 inches to 5 feet long;poorly sorted, massive. 3 Lithicsandstone, fine grained. siltstone, argillite; thin bedded to laminated,upper part fissile, pene-contemporaneousdeformations. ss: 40% st: 30% arg: 30% 2.5 Lithicsandstone, coarse to fine grained, thinbedded to laminated,graded bedding. 2 Lithicsandstone, fine grained, siltstone. argillite, thin bedeedto laminated. ss: 60% st: 30% arg: 10% 0 Lithic sandstone, lower partvery coarse grained, with granules,massive, upper part medium to fine grained, partlymassive, partly medium bedded to laminated. 1 Argillite,fissile, siltstone; thin bedded. .arg: 70% st: 30% 1.5 Sandstone, medium to finegrained, grades upward into siltstoneand argillite; medium bedded to laminated. .5 Siltstone,argillite, lithic sandstone, fine grained; thinbedded to laminated. st: 40% arg: 40% ss: 20% 2 Lithicsandstone, fine grained. medium beddedtolaminated. ss: 90% st: 2% 1 Coveredinterval, road. 8 Lithic sandstone, finegrained. grades upward into siltstone:mostly massive, partly thin beddedto laminated. 1 Argillite,siltstone, lithic sandstone,fine grained; thinbedded to laminated. arg: 40% st: 40% ss: 20% 42 QUARTZ

VOLCANICARENITE

FELDSPARS ROCKFRAGMENTS CHLORITE,MICAS, EPIDOTE Fig.2:COMPOSITION OF FRAGMENTS SANDSTONES.LILLOOET GROW6

Classification adaoted from Gilbert(1955).

43 Feet 20 Lithicsandstone, lower partcoarse grained, upper part mediumtofine grained, mostly massive, upper part thin bedded: lens of limestone 3 X 0.5 feet, light grey,brownish weathering.fine grained. 1.5 Siltstone, lithic sandstone, medium tofinegrained. argillite: thin beddedto laminated. st: 50% ss: 30% arg: 20% 4 Lithicsandstone, mostly fine grained,mostlythin beddedto laminated, partly medium bedded: some interlam- inatedsiltstone. 2.5 Lithic sandstone,coarse to fine grained,siltstone, ar- gil1ite:thinbeddedto laminated, graded bedding. pene- contemporaneousdeformations. ss: 55% st: 30% arg: 15% 4 Lithic sandstone, medium to fine grained, thin bedded to laminated. 1 Limestone,light grey, greyish buff weathering, grainsof silt size. 27.5 Lithicsandstone, mostly fine tomedium grained, partly coarse grained, mostly massive, partly thin bedded. siltstone,argillite. both thin bedded to laminated. At 20 feet frombottom lens oflimestone 7 X 0.75 feet, medium grey,light greenish grey weathering, very fine micro-crystalline,pyrite. ss: 99% st: arg: 1%

88 1 Bottom:water levelFraser of River

A typicalgranule-conglomerate contains approximately 10 percent offeldspar, largely albite, 40 per cent of volcanicrock fragments, and 10 percent of chlorite: the claymatrix makes up about 40 per centof the rock. Some of the sandstonesand conglomerates carry highlyaltered tuffaceous material. This unit shorvsahigh degreeof alteration to albite, chlorite, andcarbonate, the alterationapparently being related to several branchesof the Fraser River fault zone. Figure 2 shows therelative proportion of three components of these rocks:feldspar, quartz. and lithic fragments together with chloriteandmica. In the frameworkof Gilbert's classification (Wil- liams.Turner, Gilbert, 1955, p.293) the rockswould be classified as volcanicarenites. A fewvolcanic greywackes may berepresented, butthe content of original clay matrix in these rocksisuncertain.

3. THEPROBLEM OF ALBITIZATION

As pointedoutby Duffell and McTaggart (1952, p.37) most of the feldspar is plagioclaseand has the compositionofsodicalbite, al- thoughone grain observed by the author in one out of seventeenthin- sections is zonedfrom An6 to Anlo. Abundantinclusions of epidote,

44 and the zonaldistribution of sericite in some grainsindicate that the albite wasderived from more calcic plagioclase by alteration. The albitization may haveoccurred in anyof three periods: as alteration byhydrothermal solutions soon after the formationofthe lavasfrom which the arenites are derived, by metamorphism of these volcanicrocks, or by albitizationofthe derived sed'imentary rocks. Latemagmatic albitization is suggestedbythe following observation.In one thin-section an amygdule in a scoriaceousvolcanic fragment is filled with water-clear plagioclase which is probably albite:but no such plagioclasecan be seen in fracturesor cavities of the sedimentaryrock. Another thin-section containsboth albite andzonedcalcic plagi- oclasewhich indicates that the albite in this rock is detrital. On theother hand, a sill intruding the Lillooetgroup near a majorfault has been prehnitized (Duffell andhlcTaggart. 1952, p.92). and the gabbros west ofLillooet which arespatially close to the strataof the Lillooet grouphave been albitized and prehnitized. Probablythe sedimentary rocks were exposed locally to the same al- teringsolutions. The relativeimportance of each of the threepossible periods ofalteration remains uncertain.

4. STRUCTURE

The bedsof Divisions AandBstrike northwesterly and dip steeply.Judging from the distributionof rock types anda few determina- tionsof stratigraphic tops their major structure isan isoclinal anticline which is in partoverturned to the southwest.In Division A themajor anticline is modifiedbyagreater number ofminor folds thatare indicated by the relativedirections of the stratigraphic tops. A few foldsnear the lower partof Dickey Creek are shownon the map.The thicknessof their limbsprobably is of the orderof a fewhundred feet. The more competent beds of Division B do not show this patternof tight secondary folding. To the westthe rocks are probably in faultcontact with basic andultrabasic intrusions. The contact is not exposed. To the east theyare in faultcontact with flatlying or gentlydipping strata of Division C andof the Jackass Mountain group. Division C, probablyof marine origin, is overlainby the continental member AI of the Jackass hlountaingroup. The transition frommarine to continental deposits suggests an unconformity but an angulardiscordance between the twogroups has not been observed.

5. MODE OF ORIGIN

Thepresence of Aucella indicates that Division Awas deposited in a marineenvironment, and the associationof carbonaceous matter with thesediments shows that it was at times ofthe restricted type in whichreducing conditions prevail. As most ofthe rocks show graded bedding the sediments probablywere deposited by turbidity wrrents. Thethickness of uniformly laminated rocks is remarkable.Contor- tions andcrenulations in the rocks apparently formed before thelith- ification of the sedimentssuggest that some of these turbidity currents are related to submarine slumping.The causes of s!~ch slumping may betectonic disturbances of the basin.

45 Thesame conditionsapparently persisted during thedeposition ofDivision B. Thegradual transition in thisunit from argillite tosandstone and conglomerate, however. suggests an uplift of basin orsource area. A small seam of coal in Division B probablyoriginated in a continentalor near-shore marine environment. Divisions A and B aretightly folded andintruded by numerous dykesand sills whereasDivision C andthe overlying strata of the JackassMountain group lie almost horizontally and are cut byvery few intrusiverocks. These relations suggest that the foldingand the intrusion took placeshortly after the depositionof Division B, andthat B and C areseparated,by an angularunconformity. But as B and C areinfault contact, and the strata between them arenot exposed,such an unconformity can only be inferred and not observed. Aftera periodof uplift anderosion the area wasagain submerged;the belemnites in Division C indicate a marineenvironment. As this unit consists mostlyof sandstone and some conglomerate,the sedimentsprobably were depositednot far from the shore.The tuffaceousmaterial in theserocks suggests contemporaneous volcanism. At the endof the time representedby the Lillooetgroup the areaagain rose above sea level. The basal sandstone conglomerate unit of the JackassMountain group probably was laid down in a continentalenvironment.

F. AGEAND CORRELATION

The Lillooetgroup was first defined and described by Duffell andMcTaggart. Specimens found by these authors in thelower part of thegroup were identified by J.A. Jeletzkyas "Aucella sp. ind. (ex aff.crassicollis) Keyserling" and considered to beearly Lower Cre- taceous(Lower Neocomian) in age (Duffell andMcTaggart.1952, p.39). Some fossils foundduring the presentinvestigation in Division B (F13)are according to Jeletzky "indeterminate true belemnoids of general Jurassic or Cretaceousage".Similarbut verypoorly preserv- edspecimens were noticedin Division C. Duffell andMcTaggart 'have correlated the Lillooetgroup with Division A of the modified Dewdney Creekgroup ofthe Princeton area and with the Dewdney Creekgroup ofthe Coquihalla area. The correlation is basedmainlyon lithology and stratigraphic position of the respective units, Ifthe unconformitybetween Divisions B and C wereproved Divi- sioncshould be treated asa separate unit or included with the Jack- ass Mountaingroup. However, sinceat this time its presencecan onlybe inferred, these rocks,following earlier workers, have been left in the Lillooetgroup.

JACKASSMOUNTAIN GROUP

1. DISTRIBUTIONAND THICKNESS

Duffell and McTaggart have subdivided the Jackass Mountain group intothree stratigraphic units called Division A, Division B, and Division C. Inthe present work three lithologicalunits, members AI, AII. and AI11 aredistinguished in Division A. Division A underlies the lower andintermediate 1evelsofFoun- tainRidge and ofthe north sideofthe Fraser River between Fountain

46 andthe mouth of Bridge River. Division B formsconspicuous cliffs on the higherlevels of the same area,Division C underlieslarge partsof Fountain Ridge and of the CamelsfootRange. hlember AI has an approximatethickness of150 feet. On the north slopeof Fountain Ridge AI1 is about 2,500 feetthick b'lt possibly repeatedby faulting. On the southslope of the Camelsfoot Range. 1% miles northeastof the mouth ofBridge River, AI11 comprisesap- proximately1,000 feet of strata. About 1% miles north ofFountain on the north side of the Fraser River,Division Bis about 1,000feet thick and onFountain Ridgeap- proximately 1,500 feet.Duffel1 and McTaggart state (p.40) that the divisionis 1,750 feet thick onthe west slope ofthe Camelsfoot Range near the northwesternedge of the Ashcroft map areaoutside Of the present map area. The topof Division C is removedby erosion.According to Duf- fell andhlcTaggart at least 5,000 feet of strata are represented '(p. 91).

2. LITHOLOGY

/Iivisioa A

Mrntbcv AI

Member AI comprisesconglomerateandlithic sandstone that car- ries some plantremains. The conglomerate is exposedonly for 1 mile along the shoresof the Fraser River inthewestern part of the area UnderlainbyDivision A. It disappears further east,probably because ofa gentle dip tothe east. Thesandstone wi,th plantremains extends to the easternboundary of Division A butwhere the conglomerate is lacking hlember AI is difficultto distinguish from AII. Thefollowing stratigraphic section of AI wasmeasured on the northside of the Fraser River about 1 mile northeastof the mouth ofBridge River. Percentages of rock types are based on rapid estimates.

Feet Top of section

8 Conglomerate,brownish green weathering. volcanic pebbles, 1 to3 inches, well rounded,matrixof lithic sandstone,massive. 9 Conglomerate,granules fineandpebbles, well rounded to subrounded,massive. 16 Conglomerate,volcanic pebbles, mostly 1 to 4 inches, well rounded,abundant matrix of lithicsandstone, stronglycarbonated. '8 Lithic sandstone,light bluish grey, greenish grey to brownishgreyweathering, scattered lenses ofpebble conglomerate;massive, strongly carbonated. 2 Conglomerate, 15 feetlens, volcanic pebbles, mostly 1 to 3 inches, well rounded. 2 Lithic sandstone,medium-grained. comparatively loosely cemented,lenses of pebble conglomerate, thin bedsof argillite;strongly carbonated. 47 Feet c 3 Lithicsandstone, mediom grained, thin bedded,compara- tivelyloosely cemented. 1 Lithicsandstone, siltstone, light bluishgrey. greenish greyweathering, argillite, dark bli~ish grey. dark bluish greyweakening. thin beddedto laminated. strongly shearedand laminated. 8 Lithicsandstone. medium to finegrained, massive. 1 Conglomerate,volcanic pebbles, well rounded,mostly .5 to 2 inches. 4 Lithicsandstone, fine tomediumgrained,massive, lenses ofvolcanic pebble and granule conglomerate. Conglomerate,volcanic pebbles, well rounded, mostly .5 to 2 inches. 1 Lithicsandstone, meditm grained. massive. 3 Conglomerateas above. 1 Lens of lithicsandstone as above. 12 Conglomerateas above. 4 Conglomerate.granules and pebbles of volcanic rocks, comparatively loosely cemented, massive. 15 Lithic sandstone, medium to fine prained, mostly massive, a few thin beds very looselycemented, probably tl.lfface- ous, a few thin interbedsof siltstone and argillite; stronglycarbonated. Fault.continuity of sectionuncertain. 15 Lithicsandstone, mediom tocoarse grained, massive, a few thin interbeds of argillite and siltstone, strongly sheared. 1O? Lithic sandstone, medium to fine grained. massive; thick- nessuncertain because of fa.rlting. Fault. 5? Lithicsandstone, medim to fine grained, massive, with a few thininterbeds of siltstone and argillite; thickness uncertainbecause of faulting. 4 Lithicsandstone, fine grained, siltstone, argillite; medium to thinbedded. ss: st: 80% arg: 20% 11 Lithic sandstone, medium to coarsegrained, tuffaceous. with fragmentsof plant matter, some coaly wood. a few granulesand pebbles ofvolcanic rocks, loosely cemented,mostly thin bedded, partly massive: recessive. Bottomof section: top of Division C. Lillooet gro:lp.

48 The stratachange considerably over distances as short as LOO feet. Thero,undstonesof the conglomerateare mostly made spof light grey weathering massive aphanitic rocks some ofwhich showa few fine grainedphenocrysts. Two typicalspecimens examined in thin-section arequartz-keratophyres. They contain micro-phenocrysts of albite andchlorite associated with "ironore" pseudomorphous aftera pyribole.The groundmass consists dominantly of plagioclase microlites, some quartz,and minerals too fine-grained for identification. The plagioclase is alteredto sericite andcarbonate. Relatively weak cementationand the presence of plant matter, mostlyremnants of stems. arecharacteristic of some ofthe lithic sandstonesassociated with the conglomerate.The lithic sandstones containlittle quartz (I per cent orless) andfeldspar (3 per c(vt. or less) and are composed mainlyofvolcanicfragments and chlorite. Some of the fragments show shard-likeoutlines, others appear to he vesicularand probably many of them areof tuffaceous origin. As the volcanicfragments are highly altered they cannotbe distinguished easilyfrom the originalclay matrix. Thefragments are subrounded to subangularand moderately well sorted. In their roundnessand sorting the sandstones resemble volcanicarenites. A carbonatizedlithic sandstone from the vicinityof Fountainstation is ofvery fine sand grade, fairly well sorted and contains fragments that are subrounded to soban- gular in shapebut replaced at the margins by chlorite. The rock containsapproximately 30 percent of feldspar, 15 percent of quartz. and7per cent of recognizable rock fragments.Chlorite, mica, epidote. and clay makeup abo'ut 20 percent of the rock. Thebalance consists ofcarbonate andderived "iron ore" which has replaced the original clay matrix toa large extent. Thefeldspar, mostly plagioclase. is partlyclear, partly altered. and rich inepidote. All grainsof plagioclase determined have the composition of albite.

Jlr.rnbo. AI1

:lemberAIIstrongly altered. faulted, and poorly exposed consists largelyof lithic sandstone blut containsbeds of conglomerate that area few feetthick, seamsof plant matter in the lowerpart of the section.and an increasingproportionof interhedded siltstone in the upperpart. On thewest slope of Fountain Ridge, east of the rail- roadbridge near Lillooet the typical greenish weathering massive lithic sandstone is underlain by dark siltstone ofconsiderable thickness. The typical lithic sandstone is massive,blue-grey on fresh s1.1~- faces,and greenish on weatheredfaces. Six specimens analyzed contain 3 to 10 per centof feldspar, mostly albite.2to 5 per cent of quartz,and a fewper cent of epidote and mica;the balance consists dominantlyof volcanic fragments. The fragments are fairly closely packed.Interstices are filled by chlorite. Thefragments are altered on theoutside to "clay". >!inor constituentsare "iron ore" andcarbonaceous matter. Some of the lowest bedsof the member sholv greyishlaminae about 1 millimeter thickand spaced a fraction of a

4c) centimeterapart. hiicroscopic examination shows that they are layers rich in pyrite. As the mineral is moderately well rounded it probably is of detritalorigin. Theparticles are mostly subrounded.' of finegrade, and better sorted than inany other unit of the JackassMountain group. The lithic sandstone of klember AI1 can beclassified as "volcanic arenite"

(Gilbert. 1955). . '

Mcwbcv AIII

Member AI11 consists of argillaceous siltstone, laminated argillite,' lithic sandstone,and lenses and beds of limestone that are a few feetthick. A section measured on the south slope of the CamelsfootRange canbe summarized as follows: Feet 520 Siltstone,darkblue-grey, darkblue-grey weathering, partlyconcretionary, lithic sandstone, grey, greenish weathering, fine tocoarse grained, argillite, dark blue- grey;dark blue-grey.weathering, lensesandbeds oflimestone, light grey, light grey weathering; massive to lam- . . inated. st: 50% ss: 35% arg: 10% lms: 5% 450 Siltstone, as abovewithargillite fragments, fossil- - iferous.belemnites, pelecypods, mostly massive, with a 970 ,few lensesandbeds of limestone as above.

The stratavary considerably over distances ofa few miles,and lithicsandstone and limestone are not present in everysection. A-typicalmassive argillaceous siltstone is madeup of about 50 percent of silt-sized minerals, mostly feldspar,quartz, epidote, mica, and chlorite. The matrix consists largelyof clay but inclludes a fewper cent ofcar- bonaceousmatter. The specimen contains approximately 40 percent of spherical or ellipticalpellets of argillite that aredarker coloured and richer in carbonaceousmatter than the siltstone. A typicallaminated specimen is composed mainlyoflay ers ofdark argillite ranging from a few millimetersto 1 centimeterin thickness andasmaller fractionoflaminaeof greyish silty argillite that are Lmillimeteror a fervmilli- meters thick. Thedark argillite contains about8per cent ofsilt-sized minerals and5per cent of carbonaceousmatter. and the balanceconsists of clay-sizedmaterial. The greyishargillite,comprises approximately 45 percent of silt, 3 percent ofcarbonaceous matter and 52 percent of clay.The silt fraction consists offeldspar, mica, epidote,chlorite., and carbonate. The specimen is well size- sortedand shows graded'bedding. The dark colour is produced by thecarbonaceous matter.

50 Diuirioa C

In the presentinvestigation Division Bof the Jackassllountain groupwas examined only briefly. Few additionscan be made tothe accountgiven by Duffell and SlcTaggart. The divisionconsists, in the orderofabundance.of conglomerate,lithic sandstone, argillite. and siltstone. The conglomerateis made upmostly of cobbles and partlyof bould- ersand pebbles. Granule conglomerate is comparativelyrare. !lost of the roundstonesare derivedfrom granitic rocks, others from volcanicrocks, chert, and argillite. They are embedded in anabundant matrixof lithic sandstone and fairly well sorted with respectto size.Imbricate structures are very rare. In some localities the longaxes of the roundstones seem to lie in the planeof bedding. butexact bedding attitudes cannot be measured in theserocks. In a sectionmeasured by Duffelland AlcTagqart on Jackass Mountain the conglomeratebeds ranpe in thicknessfrom 5to 100 feet, mostof them being 8 to 20 feet thick. They are not conspicuouslylenticular but canbe traced for scores offeet. The lithic sandstone weathers preenish. is medirlm to fine prained,and resembles the sandstoneof Division C. Therocks showno in- ternalstratification. On Jackass3lountain the sandstonebeds are from 1 foot to 50 feetthick andhave an approximate thickness of 10 feet. Theinterbedded siltstones and argillitesare similar to the ones in member AIl. In the present map areaonly afew poorly exposedstrata were seen. In the present map areathe lowest beds of confllomerateinmost placesrest conformably on 200 to 300 feet of lithic sandstone. On- ly at the road-cutwest of Fountainand at two localitiesonFountain Ridge were they seen to overlie dark siltstone and argillite. at least 10 feetthick, with erosionalunconformity. Lithicsandstone makes up perhaps one-quarter of themiddle and upperpartofDivision B. It becomesmore abundant in the upward di- rectionand is dominant in thebasal part of Division C. The lithic sandstone is continuous with the matrixofthe conglomerate, and the relation between the two rock types inmost localitiesis conformable. The onlyexample ofacut-and-fill structure in the present map area wasnoticedon the southslopeofthe Camelsfoot Range where conglom- erateoverlies a bed of argillite with erosionalunconformity. nivinio,r C

Accordingto Duffell and llcTagpart (p.43) DivisionC of the Jack- ass hlountainGroup has approximately the following composition: greynacke,i.e.. lithicsandstone 60-70% argillite 25-336 conglomerate 4% Thefollowing stratigraphic section of a part of Division C was measuredby the author on theeast slope of Fountain Ridge, about 1 mile southwestof the Indian settlement of FountainValley.

51 Feet Top ofsection. 100 Lithicsandstone, lightblluish grey. ureenish grey weathering,fine to coarsegrained. massive, siltstone, araillite;laminated to thinbedded. ss: 98% st,arg: 2% 215 Coveredinterval. slightly recessive. 500 Lithicsandstone, as above. mostly massive. At 430feet from the bottom lithic sandstone fine to very finegrained,laminated;80toe5feet lithic sandstone with scattered,poorly sorted pebbles and cobbles, well rounded, mostly granitic, partly volcanic; at 45 feet from bottom of unit a fewlaminae of siltstone and araillite. 80 Lithic sandstone, as above.grading upward into siltstone and argillite,scattered cobbles andpebbles,rvell rounded,mostly granitic. 850 Lithic sandstone,as above, mostly massive. At 700 feet fromthe bottom a fewlaminae of lithic sandstonefine tovery fine grained; at 650 feeta5-foot lens ofcon- glomerate, pebbles mostly of volcanic rocks, well rounded; at 330 feet a few laminae of siltstone and argillite; at 140 feet fromthe bottom laminaeof lithic sandstone fine tovery fine grained and siltstone. - 1,745

The typicallithic sandstone ismassive. light bluish grey. and weathersgreenish. Four specimens analyzed contain: feldspar 10feldspar - 42% quartz 3 - 14% mica 4 - 5% epidote 1 - 2% rockfragments and chlorite 15- 55% "ironore", carbonaceousmatter, apatite,sphenetrace As thelithic fragmentsare mostly altered around their margins the contentof original clay matrix is verydifficult to determine. Allfeldspar crystals examined areofsodic albite. Mostof the rockfragments are volcanic and some aremetamorphic. Angular fragments ofargillite ranging \up topebble size and pebbles of other rocksare present in some beds in smallamounts. The fragments are subroundedto subangular. The sorting is poorerthan in Alember AI1 ofDivision A butbetter than in typicalhiqh rank areywackes. All specimensexamined are of fine or medium sandgrade. In sectionsmeasured by Duffell and\IcTa(rgart the beds of lithic sandstoneaverage 60 feet in thickness. Argilliteisinterbedded with the lithic sandstoneindiscontin- !.IO'JS stringers. >up to3feet long, or in moreextensive laminae that arelto 2 inchesthick. The argillite commonly contains a relative- 1y largefraction of sandand silt which in onespecimen studied consists offeldspar, quartz.and epidote.

52 QUARTZ

FEL.DSPARS ROCK FRAGMENT: CHLORITE,MICAS, EPIDOTE Fig.3: COMPOSITION OF FRAGMENTS, SANDSTONES JACKASS MObNTAlN GROUP. Classificationadapted from Gilbert (1955).

53 In compositionthe conglomerate of DivisionCclosely resembles theconglomerate of Division B. In most localitiesthe beds are not thickerthan30feet: butaconglomerate underlying the slopessouth- west of Ward Creek may beseveral hundred feet thick. Near the mouthofFountain Creekafew hundred feet of continen- talbeds are exposed. The rocks consistmostly of lithic sandstone butalso comprise beds of pebbleand cobble conglomerate that are a few feet thick andseveral seams of fossil plant matter. Three characteristic specimensofafine-grained lithic sandstone contain 4 to 18 per cent of feldspar, mostly albite, and 3 to7 per cent of quartz. Thebalance consists mostlyoffine-grained, highly altered volcanic fragments, less chlorite,and small amountsof epidote and mica. The particlesare subrounded to angular. Theproportion of original claymatrix cannot be determined. A specimenof volcanic arenite has approximately the followingcomposition: feldspar(mostly albite) 36% quartz 19% mica,epidote, andchlorite 4% lithic,dominantly volcanic fragments 31% carbonateand "iron oxide" 10% The grainsareof fine sand gradeand angular to subrounded. The cementconsists of carbonateand "iron oxide" which may havebeen introduced by hydrothermal solutions as thesebeds are near a major fault zone. Seams ofplant matter interbedded with lithic sandstone are also exposedon the western banksof the FraserRiver, near Fountain. Stratacontaininga small percentageof plant remains were found near the mouthof Sallus Creek atafew localities in the vicinityof Lee Creek andBlackhill Creek. Figure3shows the relativeproportion of quartz. feldspar, and lithicfragments with their alteration products in twelvespecimens from the Jackasslilountain group. All specimensare in therange as- signedby Gilbert to volcanic arenite. volcanic wacke, or volcanic greywacke.According to the fair sorting and relatively close pack- ingmostofthe rocks are arenites rather thanwackes or greywackes. InFigure 4 the sizedistribution in the sandand coarse silt grades of three characteristic specimens from Member AI1 andDivision Cis shown.The maximum sectionaldiameter of 400 grains was measured and the cumulative size distribution curve obtained wasreconstruct- ed with the aidof tables given by Packham (1955). Thesorting coefficient ofthe specimen from AIIis 2.2; the two specimens of DivisionChavesorting coefficients of 2.0 and 3.2 re- spectively. On the basisof 170 sedimentsfrom many differenttypes of en- vironmentsTrask (1932, pp. 71-72)obtained the followingdistribu- tionof sorting coefficients (So): So less than 1.9 - 10% '' 2.5 - 25% 11 4.5 - 75% " 5.0 - 90% The extremes are1.26 and 9.4. The mode is 2.9. He concludes: If So is less than2.5 the sample is well sorted; if it is greater than4.5 the sediment is poorlysorted: and if it is about 3.0 the deposit is normallysorted. 54 Fig.4: JACKASSMOUNTAIN GROUP.GRAIN SIZE DISTRIBUTION IN SANDAND COARSE SILT GRADES. Thin sostion onolyais of 314000rain~.~~lsul~lsa alterPockharnl19551.

55 ,. ,. AccordingtoTrask's classification the specimen from 3lember AI1 would hewellsorted, and the specimens from Division C arenormally sorted.However, compared with studies by Krumbeinand Tisdel (1940). and Hough (1942) the results obtainedare too high. Krumbeinand Tisdel found that crystalline rocks which havedisintep-ated in place have a coefficient of sortinythat places them into the range of Trask'swell-sorted sediments. Hough pointsoutthat most near-shore marine sedimentshave sorting coefficients between 1.0 and 2.0. Thesubjects of size analysisfrom thin-section and sorting co- efficientsof greywackes and related rocks need more investigation (comparealso Greenman. 1951; Krumbein. 1953; Rosenfeld, Jacobsen, andFerm. 1953) 3. THEPROBLEM OF ALBITIZATION

The plagioclase in the Jackass Mountain group consists dominantlyof albite although a few grains of oligoclasewere noted. As ad- jacentstrata ofthe younger Spences Bridge and Kingsvale groups and the olderPavilion group are not albitized the albiteofthe Jackass Woluntain groupappears to bedetrital. From differentobservations Duffel1and McTaggart arrived at the same conclusion (p.92f). The problemremains, however, whether the albite was produced by spiliti- zation or byregional metamorphism of the source rocks.

4. STRUCTURE

The strataofthe JackassMountain group lie mostlyflat or dip at low angles. In the vicinity ofmajor faults, however, they have beentitled into almost vertical positions. On the northernpart of FountainRidge the three divisions form a shallowsyncline. As the contacts here areall stronglyaltered and sheared, the foldingprob- ably wasaccompanied bymuch differentialslippageon bedding planes. Thegroup is brokenby several longitudinal and transverse faglts that will bediscussed.in a laterchapter.

5. MODE OF ORIGIN

Informationabout the mode oforigin of the JackassMountain groupcan beobtained from three sources: from the texture and compositionof the sedimentaryrocks, from the includedfossils, and from the historyof the Fraser River fault zone. Member AI containingconglomerate, much plantmatter, and no marinefossils probably was laid down in a continentalenvironment. Volcaniceruptions resulting in the depositionoftuff proSably took . placeat the same time. Fossilsindicateamarine environment for \?embers AI1 and AIII, and associated carbonaceous matter shows that the basin was "restricted." As the grainsize in these members is comparatively fine the sediments were laid down relatively far from the shore orwere derivedfrom a sourcearea without pronognced relief. Therelatively coarse grain size in the bedsof the lower part ofDivisionBis suggestive of anear-shore environmentof deposition or uplift of the sovrcearea. The originoftheconglomerate in Division Bposes several prob- lems. Thegreat thickness of the conglomerate suggestsa rapid uplift of the sourcearea and may havebeen caused, asDuffel1 and McTaggart 56 suggested(p. 47), by early movements of the Fraser River faultzone. The present study ofthis fault zone indicatesthat before thedeposition oftheSpences Bridge group agraben had formed which controlled the sedimentationof DivisionCand perhaps also of DivisionBof the JackassMountain group. The present fault zone is complexand com- prisesat least four major longitudinal faults with relative downwardmovement oftheeastern fault block and one fault with relative downwardmovement ofthe western block. In thesouthern part of the area the faultzone has awidthof approximately7miles and the graben itself of approximatelylmile.The graben hasbeen traced throuyh- out thewhole map area and probably extends much farther to the northwest and tothe southeast.The latest movements on one of the faults tookplace in early or middle Tertiary. The faults visible now may not coincide with the faults of the early Lower Cretaceous.But the present situation perhaps pives a pictureof the conditionsinthe past. There may haveexisted a narrow,elongate trough which wasperhaps in the orderof 10 mileswide andmore than l00miles long.The conglomerate of Division Ris found in the western part of the presentfault zone and perhaps was laid down along the westernmargin of the inferredtrough. The strati- graphicequivalents of the conglomeratein the middle and eastern part of the areaare not exposed. Recause of the scarcity ofbed- dingattitudes andcomplications by faulting not enough information couldbe obtained aboutthe variations in thethickness of the conglomerate. But it wasmentioned that the conglomerateon the northwestern edge of the Ashcroft map area is perhaps 750 feet thicker thanopposite Fountain. These scanty data suggest an increase in thicknessto the northeast. DivisionB is the oldest known stratigraphic unit in the present map areathat contains a majorproportion of graniticmaterial. Some argilliteinterbedded with conglomeratecontains marine fossils, butit is uncertainwhether the basin was permanentlyor on- lytemporarily flooded by the sea.The lack of plant matter perhaps supports the theory of a permanentlymarine environment. If the environmentwas marine the detrital material may in part havebeen roundedby transportion in streamswhich descended from the borderingmoantains witha steep gradient and in partby wave action onbeaches. A problem is the mechanism of distribution in the basin over a widthof more than 1 mile. It may beassumed that currents were active. The erosion surfaceslocally observed may havebeen produced by suchagents. The nature and origin of the postulated currents,however, are uncertain. The sediments of DivisionBdo not resemble the turbiditycurrent depositsofthe Lillooet group or the Cache Creek group.Laminations, graded bedding, sllrmp structures, andintraformational breccias are inconspicuous or lacking. Perhaps the distributionof the gravel was greatlyaidedbyrelatively steep submarineslopes producedbyfaulting. The areas of greatest depres- sionalso may haveshifted laterally in the basin. In order to explain the great width of the conglomerate,Duffell andhlc'l'aggart supgested deposltion ona flood plain that was onlyat times inundatedby the sea. They mention,however, that such char- acteristicfeatures of a floodplain as cut-and-fill structure and lenticularshape of the deposits are uncommon, Some of the strata of Division C containinpconplomerate and plantmatter were deposited inacontinentalornear shore marine environment. Others. includinginvertebrate fossils, are of marine 57 origin.Carbonaceous matter associated with the argillite indicates thatthe environment at times was reducing. The rocksrarely show structuressuggestive of current action. A fairly continuous uplift Of theborderland can be inferred from the generally coarse grain sizeof the sediments. The sourcearea was underlain dominantly by volcanicrocks and a smallerproportion of Coast Intrusions. In summary it canbe stated that Division C andprobably also Division B weredeposited in anarrow elongate trough that subsided rapidly with respectto bordering highlands but fluctuated with respect to sealevel. Most of thetime it may haveformed a restrictedmarine environment but temporarily it may havebeenacontinental valley that was possiblyoccupied by a large river.

6. AGE AND CORRELATION

The name "Jackass Mountain Conglomerate group" was given by Sel- wyn to the sandstone,quartzite, shale, andpebble conglomerate of JackassMountain. He recognizedthat the rocks areyounger than the CacheCreek group. Dawson refersto the rocks as "Queen CharlotteIsland" group which heassigned to the Cretaceous. Duffell and McTaggartapplied the name JackassMountain group and established a mid Lower Cretaceousage. On ground of litholopi- cal and palaeontologicalcorrespondences they correlate DivisionsA. B, andCof the Jackass Mountain group with Divisions B, C, and D of the Dewdney Creekgroupofthe Princeton area, the Pasayten croup of theSimilkameen River district, and"Lower Cretaceous"rocks of the Coquihalla map area, Fossilsfound during the presentmapping and identifiedbyJ.A. Jeletzkyconfirm themid Lower Cretaceous age of the JackassMountain group. In Member AI1 on thenorthwestern slopeofFountain Ridge about one-halfmile east of the mouth ofthe Bridge River the following fossils,identified by J.A. Jeletzky.were found (F14): Pseudomelania ? sp. indet. (agastropod) "Pterocera"? sp, indet (agastropod) Ostrea sp. indet. Pecten (Entolium) sp. indet. Mvtilus sp. indet. -? sp. indet. Accordingto Jeletzkv the collection "cannot be dated beyond a tentativesuggestion that' its gastropodsand pelecypods show some similarity with thoseof the undescribed mid Lower Cretaceous(Bar- remian or ? Aptian)faunasofthe Quatsino Sound, Vancouver Island." Jeletzkyidentified a fossilfound approximately 1% milesdue north of the mouth ofBridae River in Member AI11 (F15) as: Ancyloceras(Helicancvlus) cf. aequicostatum Gabb This ammonite "ischaracteristicofthe Aptian rocks (so called Alderson andArgonaut zones of Anderson, 1930,G.S.A. Sp. Paper 16, p. 65-66, table 2). The state of preservationof the only specimen availableis, however, too poor to exclude its reference to other al- lied forms of Ancvloceras, which range down into Upper Barremian rocks in Californiaand elsewhere. The writer preferstherefore to date the lot here discussedas of Upper Barremian (?) orAptian age in terms ofthe international standard stages. "In British Columbia,faunas of similar and slightly older mid Lower Cretaceousage have been knownfor some timefrom the rocksof the Jackasshlountain groupofthe Ashcroft area (see Duffelland SIC- Taggart,1952, pp. 48-52) andfrom the Dewdney Creekgroup of the Princetonarea (see Rice, 1947, p.18-19)" A fossilcollectedonthe south slopeof the CamelsfootRange.at anelevation of 1,700 feet,approximately 1% miles northeast of the mouth of the BridgeRiver (Fl6) was identified by Jeletzky as: Acroteuthissp. indet. He states:"This belemnite genus isrestricted to theearly mid Lower Cretaceous rocks not older thantheBerriasian (=Infravalangin- ian)and not younger than the Barremianstages of the international standard. It is not known to rangeinto the Aptianstage either in NorthAmerica or in Eurasia." An "indeterminate(phylloceratid?) ammonite" found on thenorth sideof the FraserRiver opposite the mouth of Fountain Creek (F17) "canonly be dated asofthe general Jurassic or Cretaceousage" but indicates a marineenvironment.

SPENCESBRIDGE GROUP

1. INTRODUCTION

A beltof intercalated volcanic and sedimentary rocks is exposed between thesoutheastern extremity of the map area and the slopes northof McKay Creek. Dawson included these rocks with his "lower Volcanicgroup" which he consideredto be Miocene. Drysdale (1914) renamed thisgroup Spences Bridge group, and F.K. Knowlton regarded plantfossils found by Drysdale tobeLower Cretaceous but with Jur- assic affinities. Bell referredthe same fossilsandnew collections madeby Duffelland McTaggart to the early Upper Lower Cretaceolrs (Aptianstage). New fossilsfound during the presentinvestigation show that some of the rocks are late Lower Cretaceous(Albian) and thereforecorrelative with the Kingsvalegroup. Consequently the volcanicrocks have been subdivided into several units. Some units havebeen correlated with theSpences Bridge group, others with the Kingsvalegroup. The age and correlation of several units isolated by faultingare unknown.

LOWERDIVISION

A. nASAL MEMBER

Between Sallus Creek andGibbs Creek are two isolated small areas underlain by volcanicrocks. The northernoutcrops, located approximately 1% miles north of GibbsCreek, consistofaphaniticand aphanitic-porphyritic andesite, of andesiticflow-breccia, tuff and dacite. A layer of tuffcontains remnantsof plant stems. Thecontacts between two flowsdip 70 degreesto the northeast. The other area,situated about one-half mile to the southeast. is made upof porphyriticdacite. In the eastern half of the area 59 the daciteweathers reddish brownand locally shows fine flowlayer- ingand parallel orientation of plagioclase phenocrysts. Some of theseflow layers show strongcontortions. In thewestern half the dacite is uniformlygreenish grey and contains coarse phenocrysts. In afewlocalitiesthe plagioclase phenocrysts form flow layers that generallyhave constant attitudes over several hundred feet; but in oneplace a tightanticline of flowlayers, about 2 feet across was seen. The-dips of the flow layers range from 80 degreesto 25 degrees and thestrikes from northeast to northwest. A specimen ofthegrey porphyritic daciteconsists dominantly of plagioclase, and chloritized palagonite or chlor- ophaeite. and contains approximately 10 per cent of quartz, 15per cent of chlorite, and small porportions of "iron ore", biotite,and apatite. Mostof the phenocrysts are plagioclase.buta few consistof quartz or biotite. A grainof plagioclaseshowing oscillatory normal zoning has anap- proximatecomposition of An42 in the coreand An30 at the margin.Both plagioclase and quartz phenocrysts include finegrained minerals ofthe groundmass. The quartz phenocrystsare surrounded by rimsoffeldspathic material, and some includeplagioclase crystals of intermediate size. No flowstructures are apparent in the rock. Thecontacts of thesevolcanic rocks are not exposed but topo- graphyand structure suggest thatthey overlie Division Iof the Pavil- ion groupunconformably. Near the marginof the southernoutcrop arearemnants of a breccia, one to a fewinches thick were seen to overliebedrock of.chert and argillite. The breccia is composedof the samerock types (chert and argillite).cemented by carbonate, andtraversed by veinlets of quartz. It probablyoriginated on the Lower Cretaceo1.t~erosion surface andlocally mderlies the volcanic flows, AccordinptoDuffel1 and blcTaggart the SpencesBridge group locally rests unconformablyontheCache Creek group(p.54). Therefore theserocks are thought to representthe basal unit of the Spences Bridgegroup.

R. GIRRS CREEKASSEMBLAGE

1. DISTRIBUTIONAND THICKNESS

Theunit' underlies t.he ridpesouth ofGibbs Creek and small ar- easnorth of that creek. It hasbeen subdivided into three members. Thebase of A, the lowest member, is notexposed. It has a minimum thicknessof 200 feet. On the slopeimmediately south ofGibbs Creek Member B is approximately 700 feetthick but it thinsto the south anddisappears about 1 mile southof Gibbs Creek. The top of Member C hasbeen removed by erosion; its minimum thickness is 500 feet.

2. LITHOLOGY

.?IPmhur A

MemberA is very uniform consisting only of dark grey or greenish weathering porphyritic andesitewithmedium- to coarse-grained phenocrysts of plagioclaseand mediumtofine-grained phenocrystsofau- gite. No directional textures were seen.

60 About 50 percent of a typicalspecimen consists of plagioclase phenocrysts, ranging approximately from 2 millimeters to .1 millimeter in size. Theplagioclase. complex- lytwinned and zoned. ranges from intermediate oligoclase to calcic andesine. Themineral is much altered andhasin- clusions of sericite. carbonate;andchlorite. Crystals of augite form a smallerfraction of the phenocrysts.The augitehas anapproximate composition ofCaqlMg48Fell. (ny = 1.684).The mineral is partlyto completely replaced by chlorite. Thegroundmass consists mostly of veryfine- grainedplagioclase microlites and small amounts of chlorite,"iron ore*'. augite,and quartz. Cavities are lined bychlorite and filled by quartz and carbonate. Clots of anextremely fine-grained mineral ofhigh birefringenceami highrelief are dispersed through the rock. The mineral is possibly a carbonate.

Member B is composedof sedimentary and pyroclastic beds and of volcanicflows. Its compositionvaries within smallareas and the contacts with theunderlying andoverlying rocks are mostly gradational. Thesedimentary rocks are most abundant in the vicinity ofGibbs Creek, particularly in thenortheastern part of the area. A section herecontains approximately 450 feet of sandstone,siltstone, silty argillite, andconglomerate. Intercalated volcanic flow rocks range from andesite to rhyolite in composition.Light coloured flow rocks form conspicuous cliffs around the ridgesouthofGibbs Creek and mark the upperboundary of h1emberB.Afew specimens examined in thin-section have the composition of dacite.quartz-latite, and rhyolite. They all are very poor inbiotite, chlorite, and"iron ore" andcontain 10 per centor more orquartz which in some specimensforms phenocrysts or microphenocrysts.Significant mineralogical differences exist onlyinthe composition of the feldspar.The dacite contains plagioclase in zoned phenocrysts ranging from oligoclase to calcic andesineandmicrolites of oligoclase. The quartz-latite contains sodic oligoclaseandpotas- sic feldsparwhich both formmicrophenocrysts. The rhyolite haspheno- crysts of sodicandesine and a groundmass consisting dominantly of potassicfeldspar. Therock formsaflow breccia and shows under the microscopeaspherulitic texture. Nost of thespherulites are madeup of radiatingfibres but one shows concentricdifferentiation. The andesites of hlember B resemble the onesfound in the hlembers A and C. Pyroclasticrocks are widely distributed but form only a small proportion of thetotal assemblage. A tufffrom the north sideofthe lower part of Gibbs Creek weatherslight greyish greenbut contains dark fragments thatare up to 5 millimeters long. It consistsof approximately50 per cent of large partly broken crystalsof plagioclasethat have the appearance of phenocrysts. They show complex twinningand in many instancesfine zoning. A grainexhibiting the typical oscillatory zoningis sodic labradorite in the coreand sodic andesine at the outer margin. Some grainshave abundant inclusionsofrelatively 61 coarse-grained apatite and of "iron ore." A small number of crystals are of clinopyroxene. Lithic fragments con- stitute a little less than half of the rock.Most of them are from volcanic rocksof intermediate composition but sane arefm metamorphic rocks, including carbonaceous siltstone and fine-grained meta-quartzite, Crystals and lithic fragments areembedded in amatrix of glass shardsand dust-like glassy matter. Cavities are filled with radiating or felted aggregatesof chlorite and carbonate.

Mwnbw C

Member C consists mostly of porphyritic andesite, less dacite. and a small proportion of intercalated sandstone and siltstone. The andesite is uniform in composition and texture. It is dark grey, porphyritic, and lacking in flow structures. The phenocrysts in the order of their abundance are plagioclase, clinopyroxene, and hornblende. The plagioclase is twinned and zoned and ranges in composition from intermediate oligoclaseto calcic andesine. Some grains have a spongy or skeletal structure and contain inclusions of sericite, carbonate, chlorite, and volcanic glass. The clinopyroxene, partly replaced by chlorite, is twinned. Some grains have a lower birefringence around the margins. The composition of the minerals lie in the boundary field of augite, endiopside, and diopside (n = 1.6875. 2v = 53.5O; Fel3Caqq Ilg auaite; n = 1.6755. 2v = 4qoq Fe6Ca38Sfg56, endiopside;ny = 1.83.2~ 540. JelO~aqq~gq6,augite). The groundmass is very fine grained and consists dominantly of oligoclase microliteswith minor "iron ore"and chlorite. Other mafic minerals and glassy mattermaybe present but are difficult to identify. Some rocks containa low percentageof quartz. Apatite is a common accessory. The rocks aredominantly alteredby carbonateand chlorite.Veins are filled with quartz, carbonate,and zeolites (too fine grained and too scarce for further identification).

3. STRUCTURE,CORRELATION, MODE OF ORIGIN

The rocks dip uniformly at moderate angles to the northwest. To the west they are inferred to be in fault contact with the Foun- tain Valley assemblage (see below). Unless the unit is separated from the rockstothe north bya concealed fault, Member Ais correlative with thebasal memberof the Spences Bridge group which appears to rest unconformably on a Lower Cretaceous land surface. The problem of correlationhasnot beensolved. Neither has evidencefor such a fault been obtained norhave underlying rocksofthe Pavilion group been observed south of Gibbs Creek. Perhaps the Lower Cretaceous erosion surface sloped down to the south. The unit is tentatively referred to the lower division of the Spences Bridge group. UPPER DIVISION

1. DISTRIBUTION

The rocks referred to the uppermostpart of the Spences Bridge group are exposed on the west side of the Fraser River betweenthe bL mouthof Lee Creek and the slopes north of McKay Creek. South of Leon Creekthey are concealed by overburdenand overlying middle or lateTertiary olivine basalts. As the structrlreof these rocks is mostly unknown their thickness is uncertain.

2. LITHOLOGY

The unitconsists mostlyofandesite; basalt, rhyolite, and tuff are less common. The andesites are grey or red and aphaniticor aphanitic-porphyritic. Thephenocrysts are of finer grainthan in the GibhsCreek assemblage.Flow structures arerare. Thephenocrysts consist mostly of plagioclase butin some thin- sections crystals of clinopyroxene.hornblende, or biotiteor their altered equivalents are present. Insome rocks transitionaltodacite. a few of the phenocrystsare of quartz. Thegroundmass consists dominantly ofplagioclase microlites. a few per cent of"iron ore". and varying amounts of glass. In most specimens theplagioclaseis calcic andesineor andesine- labradoritezoned over a narrowrange. Plagioclase phenocrysts are mostlytwinned; the groundmassmicrolites are in partuntwinned. The mineral is replacedby carbonate, sericite, andan unidentified zeolite. Themafic phenocrysts are partly or completelyreplaced by chlorite, "iron ore",and chalcedony. Other minerals present as alteration or cavityfilling are prehnite. chalcedony, and zeolites. The textures areintergranular, trachytic, or hyalophitic. Some specimensare flow breccias. A typicalspecimen of basalt is brownishgrey, aphanitic, andvesicular. Macroscopically it canhardly be dis- tinguishedfrom the andesitesof the unit. A thin-section containsapproximately 80 per cent ofplagioclase: the re- mainderconsists dominantlyof clinopyroxeneand some "iron ore".The plagioclase is euhedral or subhedraland forms lath-likecrystals. It is twinnedand shows fine zoning, the composition ranging from An45 to An70.The clinopyroxene is euhedral,subhedral. or anhedral and partly zoned. The compositionofthe larger grains was determinedasFe7 Ca43 Mg50, endiopside(ny = 1.679.2v = 53' 1. A specimenof rhyolite is light buff, porphyritic-aphanitic, andlacking in flow structures. Thephenocrysts are up to2millimeterslong and consist of plagioclase, andesine,quartz, and a fewsmaller crystals of biotite. The andesine is clear,untwinned. fractured, and includes quartz, biotite, andplagioclase crystals of fine tointer- mediate size. Theplagioclase has an approximate com,posi- tionof An33, Most grainsare twinned. The plagioclase has inclusionsof sericite and glass and one grain is replacedby a zeolitewhich is possiblylaumontite. Some grainshave a spongy structure. The quartz is roundedand embayedby minerals of the groundmass.The crystals are rimmedby fibrousintergrowthsof feldspar and silica that areoriented approximately perpendicularto the faces. The groundmassconsistsdominantly offibrouspartly spherulitic intergrowthsof silica and potassic feldspar, of quartz, andsmall amountsof biotite. Apatite and "iron ore" occur asaccessories. 63 3. STRUCTURE, AGE,CORRELATION

Near the mouth of SlokCreek the rocks dipat low angles to the southeast andseemto underlie the Kingsvale group. To thewest they areinferred to be in faultcontact with theJackass Mountain group and to the east with theCache Creek group. As the unit underliessedimentary rocksof Albian age it probably is Aptian. KINGSVALE GROUP

1. DISTRIBUTION AND THICKNESS

Sedimentaryand volcanicrocks on theeast side of theFraser River about 1% miles northof Glen Fraser formerly included with the SpencesBridge group are now correlated with theKingsvale croup. The rockshave been subdivided into two divisions,A and B. Division A is approximately 700 feet thick. Althoughthe top of B hasbeen removed by erosion,more than 700 feetof volcanic rocks are still present(Reinecke. 1912. p. 12).

2. LITHOLOGY

Dizisio,?. A

Division A consistsdominantly of volcanicarenite that grades into bothpebble conglomerate andsiltstone. Conglomerate forms per- hapsone-third of thesequence; siltstone is comparativelyrare. Most ofthe volcanic areniteis grey but some bedsare red. The rocksconsist dominantly of volcanicfragments, of lessthan 50 per cent of plagioclase andsmall amounts of quartz. "iron ore".and hio- tite. The lithicfragments are mostly andesiticincomposition; some are basaltic and felsitic. Where the grainsare not replaced by the groundmassthey are subrounded to rounded. In onespecimen neither carbonate nor "iron oxide" nor quartzcanbedetected as cement. An- other specimen contains approximately50per cent of rusty weathering carbonateas matrix. Perhaps the carbonate was introduced by hydro- thermalsolutions and has replaced some ofthesedimentary material. Most rocksare well bedded and size-sorted. Locally the "iron 0re"isconcentrated in thin laminae. In some localitiesgraded bed- dingand cross-bedding can be observed. A cobble conglomerateonthe east sideofthe Fraser River, near the hidden contact with theSpences Bridge group, consists dominantly ofvolcanic roundstones but also contains some graniticcobbles.

Diuisiox C

Division B consistsdominantly of andesite, afew flows of dacite, and several thin layers of tuffaceous andsedimentary rocks. The andesite is darkgrey, light grey, or red-brown. Most of therocks are aphanitic-porphyritic but some areaphanitic. Most Of thephenocrysts are twinned and zoned plagioclase that rangesincomposition from intermediate andesineto intermediate labradorite; the average composition seems to becalcic andesine. Some rocksalso contain phenocrysts of oxyhornblende. In thegroundmass.

64 which is inmost specimens very fine grained, abundant microlites of plagioclase and a few per cent of "iron ore" canbe recognized. Mafic silicates, too fine grained for identification, and volcanic glass are present in small amounts. Apatite occurs as an accessory. Light coloured rocks that are transitional to dacite containfine-grained quartz in the groundmass. The rocks arealtered hy sericite. chlorite, and carbonate. Some specimens have a trachytic texture. A specimenofdaciteis porphyritic-aphanitic and contains elongate prisms of amphibolein a light greenish grey groundmass. iilicroscopic examination shows that the amphibole is oxyhornblende. In the groundmassa few micro-phenocrystsof plagioclase, lath-like plagioclase microlites.a small fraction of "iron ore", and very fine-grained interstitial quartz canheidentified.The microlitesare sodic andesine; the micro-phenocrysts are zoned and range in composition from sodic to calcic andesine.

3. STRUCTURE

The contact of DivisionA with the Spences Bridge group isnot exposed. The presence of cobble conglomerate near the baseDivi- of sion A suggests.an unconformity. DivisionB probably overlies A conformably. To the west the Kingsvale group is in fault contact with the Jackass Rlountain group, to the east in fault contact with the Pavilion group and possibly with rocks of the Spences Bridge group overlying the Cache Creek group. In the vicinity of the fault contacts the strata dip steeply, elsewhere the dips arelow tomoderate.

4. MODE OF ORIGIN, AGE, CORRELATION

The well-sorted and generally coarse-grained character of the sediments of Division A indicates deposition by running water, and the abundance of plant matter a continental environment. Apparently they were laid down on the flood plain of a stream that drained a terrain underlain by volcanic rocks, mostlyandesites. Plant fossils found in the lower half of blember A (F18) were identified by Professor G.E. Rouse as follows: Menispermites Upper Blairmore-Whitemud (cf. with Bell (1957). p. 130)) (Alhian-Rlaestrichtian) Celas.trophyllum (celastrinites?) (Albian-Basal Eocene) (acutidens) Trochodendroides (Cereidiphyllum?) Upper Blairmore (cf. potomacensis) (Albian) Platanus sp. (Albian through Tertiary) cf. Myrtophyllum boreale (Albian-Tertiary) or: cf. Rlaanoliaephyllum (Upper Cretaceous) Cissites sp. (Albian of Portugal) (Patapsco of Rlaryland) (Lower Cretaceous) (Upper Cretaceous of U.S. Rockies)

65 - FouIi. location known

A,0" Aliernotivecontinuations of fault

/ Contoci ...... :j...... Outcrop boundary

Schistosity. I\ layering of volconicrocks

30 Coast Intrusion

Kingsvole group,Divirion B 0 .5 I 20 or Spences Bridge group. Lower Division MILES

19 Kingsvalegroup,Division B "" Road

4 Paviliongroup, Division II Railroad

Fig.5:GEOLOGY OF GLENFRASER AREA

66 ProfessorRouse states in his reportthat “four and possibly fiveof the sixspecies have been recordedinthe (Albian) Kingsvale by Bell. but noneof these is foundin the SpencesBridge (Aptian) ... thematerial ... is youngerthan Aptian and hence younger than the SpencesBridge group.” Duffell and hkTaggart state that the Kingsvale groupin the Ash- croft map areahas a sedimentary unit at its basewhich is locally 800 to 1,000feet thick and consists ofarkose,grit, mudstone, conglomerate,and argillite. Outcropsofthese rocks extend for16miles alongNicola River. Many of the beds on NicolaRiver contain fragmentsof stems andleaves, and the mudstonescarry well-preserved plantfossils. One ofthe fossils collectednear Glen Fraser. m- Germites. was also found in the belt onNicola River (Duffell and McTaggart. 1952, pp. 57-58), These relationssuggest that Division A at Glen Fraserand the sedimentarybelt on NicolaRiver are perhaps correlative andmayrepresent the same floodplain. However, as these are continentaldepositsofpossibly small extent the correlation is not certain.

SPENCESBRIDGE GROUP OR KINGSVALEGROUP

Flowsof andesite and dacite which could be assigned either to the SpencesBridgeorKingwale groups areexposed immediately northeast ofGlen Fraser, on the east sideof the roadto Pavilion. A specimenofandesitetransitionaltobasalt contains coarse phenocrystsof plagioclaseand completely chloritiz- edpyriboles and a veryfine-grained groundmass in which plagioclase microlites and“iron ore” canbe identified. Theplagioclase of thephenocrysts hasa spongy structure, is twinnedand zoned, and rangesin composition from andesine-labradorite to labradorite-bytownite.The microlites are ofandesine-labradorite. The rock shows carbonate and chlorite alteration. The dacite weathers light grey andformsflow breccias which contain fragments of darkcoloured volcanic rocks. A specimenhasphenocrystsofcalcic andesinethat are twinned,zoned. and strongly altered, of a pyribole that is completelyreplaced by chlorite and “iron ore“. and of quartz. Thegroundmass contains plagioclase, a relatively high proportion of quartz anda low proportion of “iron ore“ and chlorite. Apatite is relatively coarse grained and abundant. Some of thephenocrysts are replaced near cleavages by a mineral with a low negativerelief andlow hirefrin- gencewhich is either orthoclase or a zeolite. No ortho- clasecould be identified in the groundmass. The outcropsare separated fromcliffs of Division Bof the Kings- valegroup by an expanseof overburden about one-half mile wide. Thestratigraphic position of these rocks is uncertainbecause the locationof the boundaryfault between the Pavilion group and the Kingsvalegroup in this area is unknown. If this longitudinalfault is not offset bya transverse fault it continuesunder the overburden in thevicinityof the Pavilion road and the rocks belong tothe lower division of the SpencesBridge group which overlies thePavilion group.However, the rocks in the vicinityof theroad show no signs ofalteration and shearing. The longitudinal fault may beoffset by

67 a transversefault along the southernborder of the stock south of Pavilion in which casethe volcanic rocks would be part of Division B ofthe Kinpsvale group, The alternatives are shown on Fipure 5.

FOUNTAINVALLEY ASSEMBLAGE

1. DISTRIBUTION AND THICKNESS

The FountainValley assemblage made up largelyofvolcanic rocks, is exposed on bothsides of the Fraser River east.ofFountain Creek. It hasbeen subdivided into three members, A, B. and C. Thebase of Member A, which is in faultcontact with the JackassMountain group, is notexposed. Xember Abasaminimumthickness of 1,200 feet. Xem- ber B is lenticular; its thicknessranges from 600 feetto2.500 feet. Theupper part of Member C which is ininferred fault contact with theGibbs Creek assemblage is notexposed. The member is about 1,000 feet thick.

2. LITHOLOGY

Membev A

Member A consists mostlyofinterlayered felsitic and andesitic rocks.About 1,000 feet southwest of the longrailroad tunnel near Gibbs Creek a short lens of conglomerate is intercalated with the volcanicflows. Successionsofandesiticrocks form units about 100 feet thick, andindividual felsitic flows range up to 20 feet in thickness. The felsiticrocks are light grey tobuff, aphanitic, andlack- ingin flow structures. A thin-sectionofadacite consists mainlyofandesine microlites, 10 to 15 per cent of quartzand small amounts of"iron ore"andvo1canic glass. The microlites show subparallel orientation. The rock is altered bycarbonate and chlorite. Otherspecimens examined are probably latite or quartz latite andrhyolite; but the exact composition of theserocks cannot be de- terminedbecause of their extremely fine grain .size. A typicalspecimen of andesiteis reddishbrown. aphanitic, andforms a flowbreccia. In thin-section a few micro-phenocrysts ofplagioclase are visible in a groundmass that consistsmostly of microlites of andesine.Within small areas of the thin-section the microlites show parallelalignment. Incorporated fragments have the samemineral composition as thematrix but differ in grain size and in theorientation of the microlites. Cavities are filled by very fine-grainedquartz and chlorite. The section is stainedby "iron oxide".

Member B

XemberB, a conspicuous,cliff-forming unit, is made upof acidic volcanicflows ranging from dacite to rhyolite. It seems to consist of a multitudeof flows but the boundariesbetween individual flows aredifficult to determine. The rocks are lightgrey on fresh surfaces andreddish or brownish buff onweathered surfaces andaphani- tic or aphanitic-porphyritic. In some localities the plagioclase 60 phenocrystsare aligned and probably oriented parallel to the layer- ingof the flows. A thin-section ofaporphyritic-aphanitic dacite consists of about 30 percentofphenocrysts. and 70 percent of groundmass.Most of the phenocrystsareofplagioclase; a few consist of biotite, "iron ore" that has replaced biotite, andquartz: The plagioclase, which has the composition of calcicandesine, is twinnedand zoned. The plagioclase phenocrysts show a spongy strlucture which is dueto replacementby minerals of thegroundmass and carbonate. The biotiteisreplaced inward from its marginsand cleavages.The groundmass consists dominantly of lath-like so- dicoligoclase. About 10 to 15 per cent ofthe groundmass is madeupof anhedral quartz, Smaller fractions are formedby "iron ore", biotite, and volcanic glass. Potassic feldspar is rareor absent. Apatite occursas an accessory mineral. A specimenof rhyolite weathers brownish buff and is lightgreyish huff onfresh surfaces. Under the microscope fine-grainedphenocrystsofandesine and qllartzare visible inamicrofelsiticgroundmass. The mineralsof the groundmass,probably intergrowthsof potassic feldsparand cristo- balite (?) arefibrous and form aggregates most of which show a radiatingstructure. Undulating, brecciated flow layers made upof relatively fine-grainedaggregates alter- nate with layersof coarser aggregate size. Fractures in thespecimen are filled with "ironoxide".

Member C

Only the lowestpart of MemberCis exposed. It consistsof andesite.andesitic flow breccia, and a few feet oflithic sandstone thatcontains seams of plant matter. A typicalandesite specimen fromtheeast shoreofthe Fras- er Riverweathers purple to greyish green. The rock is aphanitic-porphyriticand contains a smallpercentage of plagioclasephenocrysts that are largely replaced by carbonate.The groundmass is madeup dominantlyofmicrolites of sodicandesine. and a.few per cent of"iron ore" and chlorite. The microlites show subparallelorientation, Therock contains veinletsof carbonate, quartz. and chlorite.

3. STRUCTURE, MODE OF ORIGIN,AGE

Thevolcanic flows strike approximatelynorth 20 degrees west anddip at moderatetosteep anglesto the northeast. At onelocality near the contactof the Alemhers A andBafelsitic flowofB includes fragmentsof a morebasic rock probably from Member A: thestrati- graphictops therefore probably face to the northeast. The unit seemstooccupyagraben between older rockstothe west and tothe east. The fault contact with theJackass Uountain group to the west is exposedat several localities on bothsides of the FraserRiver. The contact with the lowerpart of the SpencesBridge group is coveredby an expanse of overburden; a faultbetween these

69 two units is suggestedby cross-section B-B' (Figure1). This in- ferredfault perhaps is connectedwith the normal fault that forms the western boundary ofthe CacheCreek group in the central and northern parts of the map area. Theassociation of thesevolcanic rocks with conglomerateand with sandstone carrying seams of plant matter indicatesa continental origin. The structuresuggests that the Fountain Valley assemblage is youngerthan the GibbsCreek assemblage. Its age may lie anywhere betweenthe Aptian stage of the Lower Cretaceousand the early or middleTertiary.

WARD CREEK ASSEMBLAGE

1. DISTRIBUTION AND THICKNESS

Volcanicrocks of Cretaceous or EarlyTertiary age form a nar- rowelongate belt on the west sideof the Fraser River between Leon Creek and the northwestern extremityof the map area. As the belt isin fault contact with other units on two sides, and as its internal structure is largely unknown, no accuratestatement of its thickness canbe given; several thousand feetofvolcanic rocks maybe present.

2. LITHOLOGY

The unitis madeup dominantlyofandesite, less dacite and felsiticrocks, andminor tuff, basalt, lithic sandstone,and.coa1. The andesite weathers dark grey orpurple and ismostly massive. Flowbandinq and porphyritic textures were rarelyseen. A thin-sectionof a typicalandesite flow breccia is made updominantly of microlites ofcalcicandesine. about .05 millimeter long,and a few crystalsof biotite in an extremelyfine-grained, partlyglassy groundmass. Although the mineralcompositionis uniform throughoutthe slide individual breccia fragments can bedistinguishedby the var- iationin the orientationofthe microlites. The sectionis veinedby chalcedony. Ina few localities flow-banded dacite (?I was observed. ,$1' icro- scopically the rocksare finely layered and porphyritic. The flow layers range from purple tocream in colour and area few millimeters thick. Theyshow smallflow folds one or a few feet acrossand fine crenulations. Under themicroscope phenocrysts are seento consist of plagioclase,quartz. andbiotite. 'Iheplagioclase, most- lysodic andesine, is twinned,zoned and has inclusions of glass. The quartzphenocrysts are partly embayedand cor- rodedby minerals of thegroundmass. The groundmass consists of minutemicrolites of plagioclase,and very small crystalsofquartzandbiotite embedded inamatrixofglass. The microlites form flow layers that curve around the phenocrysts. Some flowlayers, more coarse-grainedthan most& the groundmass,are relatively rich in quartz. A specimenof basalt from the upperpart of Trimble Creek is verydarkon fresh surfaces, weathers darkgreen, and is aphanitic. It containsmicrophenocrysts ofplagio-

70 clase andclinopyroxene. The plagioclase. sodic bytomite in composition, is lath-like,twinned. and finely zoned. Some of the clinopyroxene.diopside-augite. (ny=1.b035, 2~55~.Ca45lIgqbFeq) shows twinning, and a few grainshave rims of lower birefringence. Some ofthe crystals are replaced by chlorite. Thegroundmass consists dominantly of minuteplagioclase microlites. some "ironore". chlorite, and other maficminerals too fine arainedfor identification,and volcanic glass. The rocksof this unit show no signsofmetamorphismbut are 10- callyaltered. Someare veinedorpartly replacedhycarbonate. chlorite,chalcedony, or epidote.Felsitic rocksin the shearzone southwest ofthe Bia Bar ferry contain crystals of pyrite; the amygdules in anandesite flow are filled with quartzand pistacite.

3. STRUCTURE

The Ward Creek assemblage lies approximately on strike with parts of the Kingsvalegroup, the SpencesBridge group. and the Fountain Valleyassemblage, and like these it is believed to occupy a graben. Between Leon Creek andBig Bar Creek the unit is in fault contact with the Paviliongroupto northeast. Northof Big Bar Creek it is uncon- formahlyoverlain by the French Barformation. To the southwest the rocks are inferred to be in fault contact with Division Cof the Jack- ass Nountain group.They are separated from the upperdivision of theSpences Bridge group by overburden and overlying middle or late Tertiary olivine basalt. About 1 milesouthwest of the BigBar ferry a zoneof shearing andalterationis exposedfor approximately 1.000 feet. Theschistos- ity of this zonedips steeply to the west. Theshear zone possiblyis part of amore extensive fault that may terminate the French Bar formation on theeast side of the FraserRiver. However, the possible continuationsof the shear zoneto the northas well as to the south are coveredby expanses of overburden. Little is known about the internalstructure of the Ward Creek assemblage because determinations of attitudesand stratigraphic tops in mostlocalities are difficultto obtain. Between WatsonBar Creek andBig Bar Canyon the rocksin the western partof the volcanic belt dipsteeply and strike approximatelynorth 35 degreeswest. The stratigraphic tops face to the northeast. At several localities northwest of BigBar Canyon moderatenortheasterly dips were observed.

4. MODE OF ORIGIN,AGE, CORRELATION

Thepresence of coal seams indicatesa continental environment. Theunit is olderthan the unconformablyoverlying French Bar formation. It maybe correlative with the upperdivisionof the Spen- cesBridge group, with parts ofthe Kingsvale groupor Early Tertiary volcanicrocksof the Quesnel map area. Its age may lie anywherebetween the Aptianstage of the Lower Cretaceousand the Oligocene. MacKenzie (1920) referred these rocksto his OligoceneTaseko formation.However, as this formationalso includes olivine hasalts it probablycomprises rocks ranging from EarlytoMiddleor Late Ter- tiary and may have to heredefined.

71 FRENCH BAR FORMATION

The FrenchBarformation extends from BigBar Creek to the northwesternextremity of the map area nearFrench Bar Canyon. Near Big BarCreek it is atleast 2,100 feet thick. Theformation consists mostlyofcobble-pebbleand granule conglomerate, less volcanic arenite. andsmall amounts of siltstone. Bedsof arenite and conglomerate are mostly from 1 to 20 feet thick, andindividual bedsofarenite and conglomerate can be traced forseveral hundred feet. A unit composeddominantly of volcanic areniteand some interbeddedconglomerate is exposedfor about 1% miles. Therocks weather yellowishorhrownish and conglomerate strata aredarker coloured than arenite. Thesediments all seem tohave beenderived from volcanic rocks that were mostly of andesitic composition.The conglomeratesconsist almost entirelyof volcanic fragments.The arenites, in addition to thevolcanic fragments,contain a smallamountof feldspar, quartz, biotite, and "iron ore". The silt- stonesare madeup of the same mineralsand chlorite. Rounding and sorting vary considerably, but in general the bedsare moderately well size-sorted and thefragments subrounded. Conglomerates and arenites have a matrixof silt-sized rock-flour and are partly cemented by "ironoxide"and rarely carbonate. Some arenitesarevery poorly consolidated,Locally the arenitecontains seams of fossil plants. Gradedbedding andcross-bedding are rareandwere observed only where the sandstone is interlaminatedwith siltstone. TheFrench Bar formation overliesthe Ward Creekassemblage unconformably. It is overlainby a volcanicsequence that is infault contact with the Paviliongroup, The strata strike uniformlyabout north25degrees west and dip steeply or moderatelytothe northeast. In the southeastern part near the boundary fault of the Pavilion group the dips are approximately 80 degreesand in the northwestthey are close to 45 degrees.Near Big Bar Creek exposures of the conglomer- ateend abruptly. Possibly the formation here is cutoff bya fault: a strongshear zone that may bepart of such a fault is exposedin the volcanicrockson the west side of theriver. Alternatively, the basinofdeposition may haveended here. The formation is intrudedby numerousbasaltic dykes and sills. The associated plant matter indicatesacontinental environment for the formation. Thegenerally roundednatureofthe fragments and locallaminations suggest deposition by running water, Beds that show poorsorting and rounding may havebeen deposited as mudflows. Thecoarse size of the fragments is indicativeof steep gradients. These gradients may be related to contemporaneous volcanismor tectonism. Plantfossils found in theupper partof the formation,near Bia BarCreek were identified byProfessor G.E. Rouse as follows: DIVISION SPERMATOPHYTA Class GYMNOSPERMAE Order CONIFERALES 1. Metasequoiaoccidentalis (Newb.) Chaney. Paleocene-Miocene 2. ? Sequoianordenskioldi Heer. Paleocene-Eocene Class ANGIOSPERIAE Sub-class DICOTYLEDONAE 3. Cinnamomum sp. - cf. affine Lg. Upper Cretaceous-Eocene 4. Carpinus qrandis Unger. Tertiary 5. ? Salix sp. - cf. s. wyominaensis Kn. Paleocene-Miocene and Cock 6. ? Laurophyllum sp. - cf. L. laraminurn Paleocene (DN) Bell 7. Tetracera sp. - cf. x. castaneafolia Eocene Slac G. 8. Hamamelis ? -Hollick Paleocene-Eocene 9. Ainus sp. cf. 4. cremastoqynoides Berry Eocene-Oligocene Rouse states in his report: "As can be noted, the determinations indicateadefinite Terti- ary age for the strata, witha preference towards an Eocenedating. However, it is possible that the beds are eitherearlier Tertiary or Oligocene; a more definite age determination cannot bebased on the relatively poorly preserved fragmentary remains. It is thewriter's considered opinion that theBig Bar flora is closely contemporaneous with those from other Tertiary basins in B.C. e.g. Chu-Chua, and Princeton. The ages of these latter sediments have been variously ascribed as Eocene toMiocene. The closest more probably age would seem to be Upper-Eocene or Oligocene for the Big Bar flora." In 1920 MacKenzie describedanddefinedtheFrench Bar formation as follows: (pp. 76A - 77A) "This formation is well exposed on upper French Bar creek, and underlies the country westward across the ridges in which Yalakom river heads as far as upper Churn Creek drainagebasin. It may have a considerable extensionin the area southeast of that justdescribed. "The French Bar formation is made up ofvery coarse conglomer- ateswith lenticular sandstone bedsin subordinate amounts. The rocks are much less indurated than any ofthe sedimentsof thoseincluded in the Eldorado series" (Lower Cretaceous). "and the pebbles and boulders easily weather outoftheirsandy matrix. The formationischar- acterized bya high percentageof large, wellrounded boulders of the plutonic rocksofthe Coast Mountains... The conglomerate beds range from 10 to 100 feet thick, and the formation as a whole gives the im- pression of being of fluviatileorigin. ....The thickness of the FrenchBar formation as exposed near the creek of that name is approximately 2,000 feet." "On lithologic and strluctural grounds. this formation is tentatively correlated with the Coldwater group ofDamon. supposedly of Oligocene age". As the conglomerate and arenite on the Fraser Riverlie onlyap- proximately 6 miles to the east of the French Bar formationand as they havea comparable lithology, sedimentary structureand thickness they are tentatively correlated with that formation. The pranitic boulders reported by LlacKenzie are probablyof local origin and were not transported into the Big Bar area, The deposits appear to be older than the Tertiary sedimentary rocks on Big Bar Creek, on Leon Creek, and near Pavilion because they are muchstronger deformed.

73 VOLCANIC ROCKS OVERLYING THE FRENCH BAR FORMATION

TheFrench Bar formation is overlainby aminimum of 2,000 feet oftuff, andesite, basalt, felsite. andminor seams of coal. The andesite is generallygreyish brown, aphanitic, and mostly massive. A specimenof basalt weathers greyish brown and has a ves- ic,ular.aphanitic texture. It consistsof abundant microphenocrystsof plagioclase and augite in a groundmassof very fine-grained plagioclase, clinopyroxene. "iron ore". and volcanicglass and its alter- ationproducts. The plagioclase microphenocrysts. inter- mediateto sodic labradorite, are lath-like, twinned, and show oscillatorynormal zoning. They have a subparallel orientation. Some of the alugitephenocrysts (ny=1.6905: 2v=5Zo;Caq3Jlgq1Fe16) also shoa twinning. A thin-section of awhitishrelatively light felsitic rock containsa few corroded phenocrystsof plapioclase and quartzin a vesicularglassy groundmass. To the northeastthe volcanic rocks are in faultcontact with thePavilion group. Thic contact is notexposed but a faultcan be inferredfrom the factthat thepavilion group strikes into the Ter- tiaryvolcanics, from the steep dips near the contacts, and from shearing and alteration. MIOCENE-PLIOCENE SEDIMENTARY AND VOLCANIC ROCKS

1. SEDIMENTARY ROCKS NEARPAVILION

A. Distribution and Thickness

?iliddleor Late Tertiary outcrops near Pavilion lie in a north- easterlytrending zone thatis approximately.5miles longand 1% miles wide. Theexposnres are confined to narrowzones along hillsides. Theelevationof the lowesto'ltcrops is 3,200 feetat the northeastern extremityand nearly 4,000 feetat the southwesternextremity. In- divid,.!alexposuresdo not exceed 200 feetin thickness hut the verti- calrange of the depositson the slopesouth of Pavilion Creek is greaterthan 500 feet.Onthe north sideofthe same valley,however. the rocksare less than100 feet thick. A small o,rtcropofsimilar rock was noted at approximately 4,000 feetelevation on the slopeabove \loran, and anotherone lies immediately northeast of the railroadCrossing near Glen Fraser.

E. Lithology

Therocks consist of lithic arenite. conglomerate, and a small proportionof carbonaceous shale. The contacts between these rock typesare well defined,but the rocks showno pronounced internal stratification. Therocks and the soilderived from them arebrick- red.In hand specimens ofconglomerateandarenite. argillite.chert, quartz,and rarely chlorite fragments can be recognized. These par- ticlesrange fromsand to cobbles. The weakness of their cementhas resulted in the formation of numerous caves,and inamajor landslide about I mile eastof Pavilion.

74 Threespecimensof lithic areniteexamined under the microscope contain 10 to 35 per cent quartz, 0 to9per cent feldspar. 11 to 35 percent chert, and 20to SO percent lithic fragments, mostly ofargillite and a smallproportion of other sedimentary and metamorphic rocks.Minor detrital constituents arecarbonate, muscovite. and tolJrmaline. Thefragments inmost specimens are well size-sorted.Original- lythey were subroundedto roundedbut they havepartly been replaced by thematrix which consists of carbonate and "iron oxide". c. Stl'ZrcbLre

The unit overliesunconformably strataofthePavilion group and smallbodies of igneous rocks assigned to the Coast Intrusions. The beds lie horizontallyor dip at angles of lessthan 10 degreesand appearnearly everywhere little disturbed. An isolatedoutcrop by the Pavilion Mountain road,however, has.prono1.tnced jointing. possibly parallelto bedding, thatdips 55 degreeseast. Althoughthe exposures of the Tertiaryrockson the slope north of PavilionCreek terminateat the faultcontact between Divisions I and I1 ofthe Pavilion group. there is noevidencethat the Tertiary sedimentary rocks were displacedby that fault. It is more likely thatthe contact formedatopographic control of deposition.The amphibolites to the west of thatcontact which are indurated byadio- ritic intrusion are probablymore resistant to weathering than the ribbonchertsto the east. In Tertiary time they may haveformed the margin of a basinand received no sediments.

D. Mode of Origin

The sediments appear to be derived mostly frm rocks of the Cache Creekand Pavilion groups andtominor extent from Coast Intrusions. As they consistof relatively coarse, well-sorted material they prob- ablyrepresent a floodplain. Thered coIo?tr of the rocks indicates oxidizingconditions which prevail only in aell-drainedareas. The blackshale, however. shows that locally swamp conditionsexisted. Theoriginal limits of the depositsare only partly known. On the northeastthey lap againsta piston which rises above the Terti- arybeds, and north of Pavilion Creek theybecome thin andprobably disappear.Theymay have been laid down in avalley that wasconnect- ed with the areasouth of Leon Creekand partly coincided with the presentFraser River valley.

E, Agc

Dawson correlatedthe sediments with thesandstones underlying the basalt plateau onLeon Creekand placed them in the middlehliocene (Dawson. 1895, p.2128). Duffell and3lcTaggart include them with the ColdwaterBeds (?I of the Kamloopsgro?lp which is consideredto be Mioceneor earlier (p. 66). Althoughthe rocks near Pavilion are similar in lithologyto those on Hat Creek theydiffer in structure. The strataonfiat Creek dip at angles up to60 degrees whereas thebeds near Pavilion lie almost horizontally. Dawson'scorrelation of the sediments near Pavilion with those south of Leon Creek is supportedby several features. Both strata areapproximately at the same elevation,both seem toheundisturbed andboth appear to be older than the latestvolcanic rocks of the area. It willbementionedthat the stratasouth of Leon Creek probablyunderlie Middleto Late Tertiary olivine basalts. The sediments on PavilionCreek are at aslightly lower elevationthan an isolated remnant of Tertiary andesite situatedabout 1% miles to the northeast on the plateau on PavilionMountain. Duffell andMcTaggart pointed out that the sedimentaryoutcrop near Glen Fraseris cut by two dykes (p. 65~).Such dykes may well berelated to the latestvolcanic activity. Theupper surface ofthe sedimentary rocks near Pavilioniscon- tinuous with a well-preservederosion plain on Pavilion Alountain of approximately 20 square miles. It is believedthat surfaces of this typeare not older than Miocene (Thornbury.1954, p. 26).

2. SEDIMENTARYROCKS ASSOCIATED WITH THE OLIVINE BASALTS

NEARLEON CREEK AND ON BIG BAR CREEK

About 2 miles southof Leon Creekand 1 mile west ofthe Fraser River poorly consolidated sedimentsare exposed for aboutlmile along the steeplysloping margin of a plateauat an elevationof approximately 3,500 feet. Thethickness of the exposedstrata is less than 100 feet,but the unitmaybemuch thicker. Therocks, mostly brownish andreddish, range from sandstone to boulder conglomerate and are in part well bedded.Different layers canbe distinguished by colour orgrain size. Thebeds are from 1 to 10 feet thick. The detrital material consists mainly of chert and argillite.and some granitic fragments.Pebbles and sand grains are poorly rounded. The cement consistingof carbonate and "iron oxide" is mostlyweak. The beds rest unconformably on quartzdiorite. A low diphas probably been producedby recent slumping. The sediments seem tohave been derived fromrocksof the immediatevicinity. They probablyunderlie olivine basalt but may onlybe slightly older than that volcanic rock. At many localities around themargins ofthe Tertiary basalt the soil containsunusually well-rounded pebbles andcobbles.These roun&- stonesare probably derived from conglomerates which underlie the basaltsbut are hidden by the abundanttalus that surrounds their cliffsat the margins. Such conglomerateswould he correlative with the outcrop described aboveand with the sedimentary rocks near Pavil- ion. Flatlying sedimentary rocks, 200to 300 feet thick, are exposed forapproximatelylmile along the uppermargin of the plateaunorth of BigBar Creek. To the east theyinterfinger with olivine basalt, andto the west their contact is covered.The rocks are mostly pebble or cobble conglomerate but include boulder conglomerate, sandstone, and minor amountsof mudstone. The roundstones are made upofchert, argillite,limestone, andgreenstone,all derived fromthe Cache Creek or Paviliongroups and fromgranitic rocks, andhighly vesicular Ter- tiary basalts. Thefragments are well rounded and fairly well sorted andcemented by carbonate. The strength of the cement variesirreg- ularlythroughout the rock. The sediments seem tohavebeen depositedby running water and apparently are contemporaneous with the ol- ivinebasalts. They areprobably slightly yolunger than the Tertiary sedimentaryrocks near Leon Creekand near Pavilion. Recently lilcCammon (1960,p.160) has found plant fossils in di- atomiteof the Quesnelarea which ?Inderlies olivine basalts andoc- cupiesapproximately the same stratigraphic position as the sedimentaryrocks on BigBar Creek, Leon Creek,and near Pavilion. This fauna \vas identified by professor G.E. Rouseand tentatively assigned tothe lower UpperMiocene althouah its age may lie anywherebetween the earlyPliocene and the Upper Xiocene.

3. OLIVINEBASALT

A. Distribution and Thiokness

Theoutcrops of Miocene-Plioceneolivine basalts are confined to twonarrow zones. One is situated on the west sideof the Fraser Riverbetween hlcKay Creek andWatson Bar Creek: the other one, locat- edapproximately 10 miles tothe north,extends along the lower part ofBig Bar Creek. Theelevation of the uppersurface of the first zonegradually drops from 4,400 feet in the southto 3,900 feet in thenorth overa distanceof approximately10miles; the upper surface of thesecond zone drops from 3,900 feet in the west to 3.600 feet inthe east over a distanceof approximately 5 miles.These upper surfaces seem torepresentthe original top ofthe volcanic flows becausethey are of greatregularity andmarked by coarse vesicles. They areoverlain only by a thin veneer of soil andform plateaus whichare well axpressed on topographicmaps. The elevations of the lowercontacts are known with less accuracy becausethey are hidden by talus andbecause the outer margins ofthe volcanicplateaus have slumpedalmost everywhere. Probably the basaltsare nowhere thicker than 200 feet. Thesheet south of Leon Creek seems to thin outto the west: theflowsonBig Bar Creek appearto be thicker in the west than in the eastwhere they interfinger with sediments.Individual flowsare from 10 to 50 feetthick, Some of themwere tracedalong the margin of theplateaus for severalhundred feet but they may be much more extensive.

E. Lithologv

The rocks are red-brownand some of them are relatively coarse grained. Dark green crystalsofolivine aboutlto2millimeters long canbe detected with theunaided eye. The upper parts of the flows arehighly vesicular. Columnar jointing is commona feature.North of BigBar Creek ellipsoidalstructures about 1 footor a few feet thickthat resemble pillows were seen. Sevenspecimens studied in thin-section consist approximately of 50 to 60 per cent plagioclase, 7to 22per cent olivine, and 3 to 5 percent “iron oxide”. The balance is made updominantly of clinopyroxene.Orthopyroxene, not identified in all of the specimens, forms less that 1 per cent ofthe rock. Apatite, zircon (?I,and an unknown mineral occurring asvery fine-grained needle-like inclusions in theplagioclase are presentonly in minuteproportions. Theplagioclase forms euhedralto slubhedral microlites that ex- hibitCarlsbadandalbite twinning. The other twin lawsare less com- monlyrepresented. The mineral shows zoning, mostly of the normal type,andhas an averagecomposition near An60. It is little altered. 77 Some crystalsof olivine are subhedral. but most of the grains areanhedral. Thecomposition of the mineralranges from Fog4 to Fo72 and averagesFogo, In several specimens the olivine is partly alteredto brownish “iron oxide”. The alterationis strongest around the outermargins of the grainsand near fractures bilt also occurs in their interior. Theorthopyroxene is subhedraland colourless unless altered. In onespecimen itscomposition wasdetermined as En79 (ny = 1.685. - 2v). In some specimens the mineral is alteredby “iron oxide.“ The clinopyroxeneforms very fine-grained s.rbhedraloranhedra1 grains the compositionof which is diffimltto identify. ilost of theclinopyroxene seems tobe augite hut some pigeonite may bepresent. In onespecimen the augite has an approximate composition of CaqlMg4qFel5 (ny = 1.689). Of the “ironore“ minerals ilmenite is much moreabundant than magnetite. The textureof the rocks is seriate and intergranular. In some specimenstheplagioclasemicrolites show subparallelalignment. The sizeof the essential minerals ina relatively coarse-grainedspecimen rangesapproximately from 2 millimetersto .02 rnillimeter and in a fine-grainedrock from 1 millimeterto ,015 millimeter. Two types of textlure maybedistinguished: either olivinealone formsthe large grains(type 1)or the largegrains consistof plagioclase and ortho- pyroxeneas well asolivine (type 11). The intermediaterange is dominatedby plagioclase but also contains some olivineandclinopy- roxene.The finest grade ismade upof mostly clinopyroxene and small amountsof plagioclase.

78 TABLE 3

JIINERAL COMPOSITION OF SEVEN SPECIMENS OF OLIVINE BASALT

COmDOS- I Comp. ition in in % % of An ' olivine t 1% Texture 3" 61 1.6855 I +- .GO2 60 1.6893 t- .GO2 60 1.6900 -t .002 60 1.6991 + .001 61 1.7100 72.5 t ,001 pilo- l- taxitic 1.6900 81.5 + ,001 trachytic 1,6910 81 + .002

Specimens la, b. and c, are taken from three successive flows of the plateau south of Leon Creek, and specimens Za, b. ana c, arefrom three successive flows from the plateau northof Leon Creek. The two localities are approximately Z miles apart. Specimen 3 is from north of Big Bar Creek. The present sampling indicates nosystematic variation in composition. The presence oforthopyroxene in some flowsprobably is notsignificant because the mineral occurs onlyin small quantities. Theone flow (2b) that contains an olivine comparatively rich in iron showsnodeviation from the average in thecompositionof its plagioclase.This lack of correlation between olivine and plagioclase may perhapsbe explained by the factthat the textureof the rock is of type (1) andapproaches that of an olivine porphyry, c. stl.nct2

Thebasalts rest unconformably on rocksof the Paviliongroup andon poorly consolidated Tertiary sediments. Their upper surface slopesabout 50 feetper mileto the northcorresponding to a dipof less than1degree. They overlie the Fraser River fault zone without anysigns of disturbance. Being relatively resistant toweathering the basalts form cliffs andhave produced uncommonly steepprofiles in the underlyingrocks which theyprotect. Apparently these weakerrocks are not able to support the loadofthe basaltsat such slopes and yield by slumping. The marginsofthe basalt plateaus are also characterized by numerous fracturesalong which openings from a few feetto tens of feet wide develop. Theterrace-like fault blocks around the basalt plateaus near Leon Creekare visible on airphotographs.

D. Mode of Oyiqin

There can be little doubt that the fouroutcrop areas between McKay Creekand Watson Bar Creek areremnants of a continuoussheet ofvolcanic flows which originally filledavalley. Someofthe mountain slopesthat bounded this valley on the westare still preserved. Theslopes are underlain by rocks of the Jackass Mountain group and ofthe Ward Creek assemblage.The valley in which the basalts were laid down apparently containedsands and gravels that may havebeen partlyof fluviatile origin. The distributionof the basaltsonBig Bar Creek, their associa- tion with fluviatilesediments, and the presenceof possible pillow strluctluressuggesting submerged deposition indicate that theseflows like the underlyingTertiary sediments, also occupied a valley. Becauseof the uniformityoflithology andelevationand the sim- ilarityof environment itis probablethat the basalts along Big Bar Creek wereconnected with thosesouth of WatsonBar Creek. Asnobasalts are preserved between Watson Bar Creek andBigBar Creek such a connection must haveunderlain areas that have subse- quentlybeen eroded down toelevations lower than 3,900 feet;therefore it must haveoccupiedanarrow zone along the line ofthe present valleyof the FraserRiver. It wasmentioned that the upper surfaceof the northernoutcrop zone dips ata gradient of approximately 50 feet per mile to the north andthat the uppersurface of the flowsonBig Bar Creek slopewith a similargradient to theeast. One is tempted to concludethat the sourceof the volcanic flows was locatednot far from the southern extremityof their presentoutcrops and that they flowed northward andeastward along valleys that coincide in part withthepresentval-

80 leys ofFraser River andBig BarCreek, The fact, however. that the upper surfaces of the basalts south ofWatson Bar Creekand north of Big Bar Creek have thesame elevationof3,900 feet 2 50 feetandthat nogradient is noticeableindicates that some tiltinghas occlrrred sincethe deposition of theflows. The direction of tilt and there- forethe original slope of the ancientvalleys are unknown. Thesebasalts are the oldest volcanic rocks inthe present map areathat contain olivine. Their appearancemarks the endof the phasedominated by andesite, It is generallythought tha.t sslch flows are derived from abasaltic layer in the earth's crust andrise through deep reaching fractures. As the flows overlie one or two major faults they may well haveascended through fractures associated with the FraserRiver fault zone butafter they ceased to beactive. Thisconclusion conforms inageneral way with Dawson'sconcept the the flowsare of local origin (Dawson.1895. p. 216B).

E. Age

Dawson included the basalts inhis "UpperVolcanic Group" which he placed in the Upper Miocene.DuffellandWcTaggart correlated them with the Kamloops groupconsidered as Miocene or earlier. However, inthe Kamloops areathe olivine basalts rest unconformably on the Kamloops group (W.H. Mathews,personal communication.) As Dawson remarked"their present appearance represents a very great amount ofriver erosion since thedate of their formation" (1895, p.216B). The depthof erosion since their deposition is more than 3,000 feet. As theFraser River contains Pleistocene deposits it is improbablethat the volcanic rocksare youngerthanearly Pleis- tocene. Ontheother hand, they are younger than the French Bar conglomerate becauseunlike that formation they have not been affected by movementsof.theFraser River fault zone. They arealso younger than the lower Upper (?) Miocenediatomite of the Quesnel area (compare McCammon. 1960,p.160). The unit is correlative with basaltsof the Quesnel map areaassignedby Tipper (1959) to the Niocene.Pliocene, andpossibly Pleistocene. A recent as yetunpublished radioactive agedetermination suggestsahliocene-Plioceneage (W.H. Mathews.per- sonalcommunication). 2. INTRUSIVEROCKS ULTRABASICINTRUSIONS ULTRABASIC ROCKS NEAR LILLOOET

1. DISTRIBUTION

A beltof ultrabasic rocks lies betweenTriassicorolder rocks to the west and the Lillooet groupto the east in the vicinityof Lillooet. Althoughoutcrops are scarce the serpentinitesappear to beone-half mile wide.The belt probably extends beyond the present map areatothenortheast and maybelinked with the ultrabasic rocks of theShulaps Range. 2. LITHOLOGY

All specimensexamined are serpentinizedharzburgite. In most of them medium- tocoarse-grained light green enstatite or bastite is set in a blackor dark olive-green groundmass. A partlyserpentinized specimen has approximately the followingcomposition of primaryminerals: olivine 66% olivine enstatite 30% clinopyroxene 3% chromite 1% The textureof the rock is allotriomorphic-seriate. The olivine is anhedraland relatively fine-prained. rangingapproximately from .5 to .2 millimeter in section- a1diameter. The composition of the mineral is Falo (ny = 1.674). Some grainscontain inclusions of chromite, The enstatite En91 (rmY = 1.670) is subhedralor an- hedralandranges in grainsize approximately from 1 centimeter toone-half millimeter. It hasinclusions of clino- pyroxenethat are oriented parallel to the opticplane of the host. Two typesof inclusions canbe recognized: lamel- laeof uniform width C.025 millimeterx .S millimeter) and spindle-shapedor irregular patches(e.g., .4 x .8 millimeter). All inclusionswithina single grain have the same crystallographicorientation. The orientationof the inclusions is not the same as that ofthe host b,.!t in certain sections the extinction position of guest and host coincide. The birefringenceof the inclusions decreases from their centre toward their outermargin:as many as ten different zonesof distinct interference co1o:Ircan beobserved. servcd. Clinopyroxene also occurs as individualgrains that probablyhave the Composition of diopside (ny = 1.678). The grainsare subhedral to anhedraland of smallersize than the orthopyroxene.Their sectional diameter lies between l andone-half millimeter. Thechromite is opaque'orbrownish translucent and anhedral. It is relativelyfine grained. rangin? from aho'dt one-quarterto one-eighth ofamillimeter in sectionaldi- meter.

3. SERPENTINIZATION

\lostof the ultrabasicrocks are strongly or completely serpentinized;theleast altered specimen seen consistsofabovt65 per cent serpentine. The three main silicatesare affected differently by the serpentinization. The diopside is littlealtered. Some completely serpentinized crystals of enstatite contain unaltered inclusions of diopside. Most of the enstatite is partlyor completely replacedbyanti- gorite. Theserpentinization has progressedfromthemargin and from cleavagesand the blades ofantigorite lie approximately parallel to thecleavage of the host.. Theolivine is stronglyaffected by the serpentinization. Re- placementfrom the margin and from fractures has produced two types 82 of mesh structures. In the first type "serpophite" is surroundedby a few bladesof antigorite. In some specimens the antigoritg shows very roughlyapreferred orientation which maybethe result of stress (Leech. 1953,p. 32). In others the serpophite is surrounded by one orseveral layers of very fine fibres that grow perpendicularly to the wallsoftheserpophite core. The fibres (length slow, low birefringence)are possibly "chrysotile". The interstices between chrysotile layers contain material that is isotropicor has low birefringence together with grains of an opaque mineral which is probably sec- ondarymagnetite. These grains range from a fraction of a micron in size tolarger, vein-like aggregates ranging tup to .4 millimeter in lengthand .02 millimeter in width. The"serpophite" and someof the fibrous serpentine contain min- ilte acicularinclusions which range from ,005 to .03 millimeter in lengthand are approximately ,001 millimeter thick. The inclusions arealso found in the marginalzones of olivine grains but never in the core of thatmineral, These outer zones apparently have been al- teredas they show a lowerbirefringence than the inner partof the grains. The refractive indicesofthe mineral lie between 1.51 and 1.53. It maybesepiolite. amineral which occurs in serpentine.Sepiolite associated with talc was synthesizedby Bowen and Tuttle at temperatures around 350 degreescentigrade and a pressureof 15,000 pounds perinch (Bowen and Tuttle,1949, p. 443).

4. CARBONATE-SILICAALTERATION

On the ridge northeast of Town Creek the serpentinized ultrabasic rockshave been replaced by carbonate and quartz. The alteredrocks formconspicuous. rusty weathering cliffs. In some specimensfrom these outcrops remnantsof serpentine are preserved but in others only the presenceofchromite indicates that the rocks originally were ultrabasic. The compositionofthecarbonate lies near the boundaryof mag- nesiandolomite and parankerite (no = 1.699). It is present in anet- work ofveinlets that encloses quartz and nodules of carbonate some ofwhich include a few finegrains of "iron ore". The centreof the veinletscontain much secondary"iron oxide". In some specimens the carbonate is cutby veinlets of quartz.

5. AGE AND ORIGIN

Because of insufficientexposure the natureofthecontacts and the internalstructureof the ultrabasicrocks are )unknown.Howeuer, the follorvinpobservationsmay have some bearing on their ageand origin. (1) The ultrabasicrocks occupy a zone betweenTriassic or earlier rockstothe west and the Lillooetgroup tothe east which south Of the present map areaare in faultcontact (Duffell andMcTaggart, 1953,p. 27). (2) Other ultrabasicintrusions in the map areaoccur only in rocks of the Paviliongroup. (3) The serpentinitesareonstrikeand possibly continuouswith the ultramafic complex ofthe Shulaps Range to which they bear a close lithologicalresemblance. Leech foundthat the mainmass of the in- truSiOnS in the ShulapsRange cuts Upper Triassicstrata, andheob- 83 servedchromite, probably derived from these intrusions,in Lower Jurassicsediments (p. 39). He inferredthat the ultrabasic rocks were emplaced in the Upper Triassic. (4) Intrusionsof similar litholoyy are wide spread in British Columbiaand attributed by White to the @per Triassic Cassiar orogeny (White, 1959). Becauseof the last three points it is thought that theserpen- tinites westof Lillooet areof anoriginal Upper Triassic age.Their associationwith the regional fault canbe explained in two ways. Eitherthey are in intrusive contact with CacheCreek type of rocks to the west andinfault contact with the Lillooet group to the east andantedate the faulting,or the ultrabasicrocks, originally em- placedin the Triassic, were remobilized in or after the Lower Creta- ceousand squeezed into the fault. "Cold intrusions" have been des- cribedby Taliaferro (1943, p. 205)and Thayer (1948. pp.64-651,and the concept was referred to the Fraser River faultzone by Duffel1 and McTaggart(1953, p. 76). and to the Shulaps Rangeby Leech (1953. p. 39). PERIDOTITE INTRUDING THE PAVILION GROUP

At a fewlocalities serpentinized dykes were seen to intrude Divisions I and I1 ofthe Pavilion group. A handspecimen from a dykeexposed on theeast bank ofthe Fraser River, approximatelylmile north of the mouth ofSiwash Creek, is reddish brownon weathered surfaces, blackto olive green on fresh surfaces, and fine-grained. About 15 percent of the primaryminerals are clinopyroxene(endiopside ? ny = 1.675), thebalance consists of forsterite (+2v larger than 87 degrees) and a small amount of a brownishopaque mineral which is probablychromite. The endiopside is subhedral and the olivine and the chromite areanhedral. The grainsize is near .5 millimeter. Serpentinization has produced a mesh structure consistingof olivineor serpophite cores surrounded by relatively broadbladesof antigoritethat lie insubparallel orientation. The clinopyroxene hasbeen affected by the serpentinizationto mucha lesser extent thanthe olivine. There is also some carbonatereplacement. As thesedykes cut rocksthatare possiblyofLower Triassic age buthave not beenseenin the adjacent Lower Cretaceousstrata their age may lie anywherebetween those limits. Lithologically they are notidentical with theultrabasic rocks west of Lillooet. But as the emplacementof ultrabasic rocks is a rareevent in the history of a smallareait is likelythat these dykesarecontemporaneous with the massesnear Lillooet and in theShulaps Range, Therefore they.are tentativelyreferred to the Upper,Triassic. COAST INTRUSIONS 1. EARLYLOWER CRETACEOUS OR OLDER

1. DISTRIBUTION

In thepresent area dioritic rocks considered to be early Lower Cretaceousorolderare the mostabundant of the igneousrocks assignedto Coast Intrusions. 84 A stock underliesilount Nartley on t .he southeastern edge of I.he map area(see Figure6). Another, about 5miles long and up to 2miles wide,extends from the mouth of Kelly Creek to Leon Creek.Parts of a small stockare exposed south of Pavilion.The present map (Figure 1) suggests that it is lessextensive than indicated on previousmaps, andinsteadof one large mass anumbcr of small intrusions are shown. Someof these may be off-shoots of a stock or batholith hidden ai depth. A zoneof small intrusions extendsfrom Pavilion to Kelly Creek. A relatively small plslg ,.~nderlies the slopes at the north endof Pavilion Lake. In the northernpart ofthe area the CoastIntrusions arc represented only by a dyke-like mass on the lotvest part ofBig Bar Creek which is about I mile long and a few h:mdred feet wide.

2. LITHOLOGY

The intrusions are composedof diorite.quartz diroite. arano- diorite, anddacite. Quartz dioriteis the commonestrock type. The plutonicrocks have a hypidiomorphicequigranular texture and arc mostly medium grained. Many of the dykerocks are porphyritic. The essential mineralspresent are plagioclase. quartz, hornblende.and biotite; augite was noticedonly in onespecimen. "Iron ore"constitutes up to 2 percent of therock. Apatite is comparatively common asan accessory mineral; and zirconand sphene are rare. One dykerock contains muscovite but no maficsilicates. The plagioclase is mostly subhedral.zoned. and twinned; the zoning is most commonly of the normaloscillatory type. The mineral containsinclusions of sericite, epidote. and carbonate. Potassic feldspar,if present at all. forms less than 1 percent of therocks. Thehornblende is subhedraland some grainsare twinned. It shows pronouncedpleochroism being dark greenin the z-direction and palebrownish green in the x-direction. The biotite is anhedralor subhedraland brown orgreen in colour. Bothhornblendeandbiotite cont.ain inclusionsof "iron ore" and apatiteand arc in many specimenspartly or completelyreplaced by chloritc. The quartzisanhedral and most grainsare free from inclusions, Table 4 shows the range in the compositionof the rocks. It seems to be true in a general way that the plagioclasebecomes more sodic and that the percentage of mafic 'minerals decreases as the content ofquartz increases; but there arc exceptions. Near th? contacts with rocksof the Paviliongroupthe Coast In- trusionsare locally contaminatedand containa relatively high proportionof hornblende.

85 TABLE 4

MINERAL COMPOSITION OF EIGHT SPECIMENS FROM COAST INTRUSIONS. EARLY LOWER CRETACEOUSOR OLDER % of Composition of % of mafic Localitv plagioclase quartz Classification of rock minerals Dyke on loser Big Bar Creek Calcic andesine. I 0 I 35 I diorite

South of mouth of Kelly Creek Zoned from calcic 5 Lb diorite oligoclase to sodic labradorite Pluton, southeast of Pavilion,east side altered to albite 0 27 diorite, transitional to a 5 auartz diorite Dyke near Moran Calcic andesine. I1 quartz diorite zoned Pluton between Leon Creek and Kelly CreekIntermediate 23 quartz diorite andesine. zoned Stock southeast of Pavilion, west side Zoned from sodic to 33 22 quartz diorite intermediate andesine Mount Martley Stock Zoned from calcic 30 19 quartz diorite, trans- oligoclase to sodic itional to granodiorite andesine Stock at north end of Pavilion Lake Zoned from calcic 32 13 quartz diorite, trans- oligoclase to sodic itional to granodiorite andesine 87 3. ASSOCIATEDMINERALIZATION

Smallsulphide deposits are associatedwith these intrusions in many localitiesbut only,the Big Slide Mine (311 near the mouth of Kelly Creek whichoperated fora few months in 1887has been of some economicimportance. The property was inspected by G.M. Dawson in 1887 andby A.11. Richmondof the British ColumbiaDcpartmentof \lines in 1932. A compilationof all previousreports was givenby Duffell andMcTaggart (p.103f.). The mineralization here consistsofpyrite. pyrrhotite.arsenopyrite, chalcopyrite, marcasite, limonite, native gold.and carbonate in tx'o pinchingand swelling quartz veins that areup to4 feet wideand have an average thickness of8 inches. The host rock is a smalldioritic mass that intrudes chert, argillite, and minor volcanicrocks of Division I ofthe Pavilion group. South of Kelly Creek, in the same vicinity.another small deposit was ex- ploredbya shaftandtwo short levels. The writer noted some pyrite, bornite,malachite, and azurite in an abundantgangue of quartz and carbonate on a surface dump. Disseminatedpyriteandarsenopyrite form rusty zones in the di- oriteoutcrops on TiffinCreek and in chert,argillite. and diorite on the upperpart of Sallus Creek. A specimen of bornite shown to the writer was saidtohave been collected on the gpperpartof Siwash Creek near the contactbetween graniticdykes and limestone. Small amo?lntsof copper minerals have beenfoxnd in thepluton south of Leon Creek.

4. STRUCTURE,MODE OF ORIGIN

Althoughelongate masses are parallel to thestrikeof the host rocks the intrusionslocally cut across thepre-existing structures. Foliations and lineationsare rarely apparent. The majorregional faultspass around the pl7Jtonic masses, bvt minor zones of shearinr and alterationare present locally. That the quartzdiorite has been emplaced by intrusion andnot by processesof granitization is s,Jggestedbythe crosscutting relation of the graniticrocks and the very loxl gradeof reqional metamorphism in the countryrocks suggestinpa shallow depth of emplace- ment. Crystallizationfromamagma is alsoindicated by the oscillatorynormal zoning of the plagioclase.

5. AGE

Therocks intrude Divisions I and 11 of the Paviliongroup and thereforethey are not older than Triassic. Theywere not observed in intrlusivecontact with the SpencesBridge group or the Kingsvale gro.rpof tnidLower Cretaceousage. It is also probable that they were emplaced before the earliest movement on faxlt "e" of the Fraser River faultzone (see Fig:lre 61, which is tho'ightto have taken place in theearly Loiver Cretaceo'ls. In the present map area this group of Coast1ntr.tsions cannot be distinpished lithologically from the early Loiver Cretaceolis qlmrtz dioritethat intrvdes the Lillooet group. kTagpart and Duffell. however.correlate them with the 'iiount Lyttonbatholith and present struct!jralst2dies support this correlation,Duffell andhlcTagprt suggestthat the hlount Lyttonbatholith is olderthan the intrusions

08 westof the Fraser River and perhapscontemporaneous with theGuichon Creekbatholith, and refer it to the Jurassic (p.01).

11. EARLYLOWER CRETACEOUS

1. DISTRIBUTION

TheCoast Intrusions known tobe early Lower Cretaceousoccur asdykes and sills in the Lillooetgroup. The largest of these intrusions isalenticular pluton about one-half mile longand several hslndred feetwide which is exposed on theeast side of theFraser Rivernear the railroad bridge in the vicinity of Lillooet.

2. LITHOLOGY

All specimensexaminedare quartz diorite or dacite.Coarse- or medium-grainedrocks havea hypidiomorphic granular texture butpor- phyritictypes consist of medium- to coarse-grainedphenocrystsin a fine-grainedoraphaniticgroundmass. Some rocksare entirely aphanitic. A specimen from the lenticular sill-likepluton nearthe railroad bridge northeast of Lillooetis composedof the following primary minerals: feldspar 70% quartz 21% hornblende 0% biotite 1% "iron ore",apatite, sphene trace The feldsparconsists dominantly of subhedral sodic andesine that is twinnedand shows normal or oscillatory normalzoning. Orthoclase which is subhedralor anhedral makesuponlyasmall fraction of the totalfeldspar. Some of thefeldspar is stronglysericitized. Most of the hornblende is subhedral.The mineral is darkgreen in thez-direction. The biotite is subhedral or anhedraland pleochroic .in browns.The quartz is anhedraland relatively free from inclusions. As alterationminerals sericite. carbonate, and chlor- iteare fairly abundant. The texture of the rock is graniticand the size of the essential minerals ranges from 2.5millimeters to 1 millimeter. Thephenocrysts of dykerocks consistofplagioclase which commonly is zonedandesine. Hornblende and quartz are rare as phenocrysts. Thegroundmass of the porphyries contains in additionto theseminerals biotite, and in some specimensmuscovite. Highlyaltered rocks found in the vicinityof major faults are rich in chlorite,muscovite, carbonate, and pqehnite.

3. AGE

Graniticdykes are abundant in the lowerand middle part of the Lillooet group whichare tightly foldedbut lackinlrin the flat lying slpper part,DivisionC. and very scarce in the Jackass Mountain group. It is possible that the intrusion took place shortly after the deposi-

09 tionof the sediments and was nearly contemporaneous with the main periodof folding. The ageof these qdartz diorites probably is early Lower Cretaceous.

111. LATEBARREMIAN

1. DISTRIBUTION

The CoastIntrusions of this grolup occgronly as dykes or small plugsin the JackassMountain group. In the southernand central partsof the map areathey are rare. A fewdykes are exposed on the northside of the Fraser River opposite the mouthof Fountain Creek. BetweenFountain and the mouthofBridge River several zones of car- bonatealteration are visible on the shoresof the FraserRiver some of whichare associated with smallgranitic dykes. Similar zones of alteration in the vicinityof Lee Creek andBlackhill Creek that ap- parentlyare not related to major faultsmay indicate intrlusive bodies at greater depth, In thenorthern part of the map area, in the vicinity of Watson BarCreek, granitic rocksaremore abundant. The lara- est of these intrusions is shown on Figure 1.

2. LITHOLOGY

Lithologically thesedykes do not differ from the two other groups ofCoast Intrgsions in the area:they are porphyritic quartzdiorites. A typical specimen has coarse phenocrystsof zoned andesineanda fine- grainedgroundmass consistingof plagioclase, quartz, hornblende.biotite. andminor orthoclase. “Iron Ore” and apatite were noted as accessories,Secondary minerals present are sericite, epidote, chlor- it.e. andcarbonate. A dyke which probablylies in the immediatevicinity of fa!!lt “d” of theFraser River fault zone has been altered completely. The plagioclase has been altered to albite and epidote and the mafic min- eralsto chlorite. Therock is extensivelyreplaced by carbonate.

3. ASSOCIATEDMINERALIZATION

On theupperpart of Stirrirp Creek foursmall (epithermal?) deposits of stibnite,cinnabar, gold, wehrlite, and barite (Professor H.V. Warren,personal communication) is associated with porphyritic quartzdiorite that hasintruded lithic sandstone of Division C of the JackassMountain group (M2). The mineralsoccur in quartz veins thatcut bleached porphyritic quartz dioriteand stronglycarbonatiz- edcountry rock. Occurrences of this typeare probably the source of t.henumerous gold placerson Stirrup Creek (outsidethe map area).

4. AGE

As thesr dykesintrude DivisionCof the Jackass Mo!lntain groop b!lt have not been foxnd in the Spences Bridge group or Kingsvale group theyprobably were emplaced in thelate Barremian. They arethe youngestCoast lntr!~sions known in thegeneral area.

90 GABBRO ANDDIABASE NEAR LILLOOET

1. DISTRIBUTION,STRUCTURE

Gabbrosand diabases are exposed for about .6 miles between a point on the westbank of the Fraser River about 2 miles southe.ast of Lillooet andthe head of Town Creekonthe ridge northwest of Lil- looet.The o?ltcrops are mostly small and separated by expanses of overburden;larger massesare.exposed onlyin the vicinity ofthe pow- erhouse on Seton Creek. It is not known whether the outcropsareconnected and thus form one large intrlusion orwhether they represent numerous small intrusions. The belt asawhole strikes approximatelynorth 30 degrees west andforms the easternmargin ofa zone occupied dominantly by ultrabasicrocks. To the easttheintrusions are possiblyin fault contact with the Lillooetgroup, but this contact is nowhereexposed.

2. LITHOLOGY

Therocks on the eastshoreof the FraserRiver, outside of the map areahave not been studied duringthe present investigation. Ac- cordingtoBrock (1956) theyare hypersthene gabbros that show differ- entiation. The intrusionson the west sideare greyish green, medium to fine grained,and show no stratification. They arehighly altered, and theirorioinal composition is recognizableonly in a fewspecimens thatrange from bronzitegabbro to augite diorite. All specimenscontain augitewhich showsnc systematic variation in composition. In onethin-section the augite has "hour glass" structure. In two out of nineteenspecimens orthopyroxene was recognized. In onespecimen it was bronzite in the otherone hypersthene, but the two mineralsprobably do not differ in composition by more than5per centof the enstatitemolecule. In some of theother rocks orthopyroxene may havebeen present originally but probablyhas been replacedby minera1.s of thechlorite group. Only in two specimens the originalplagioclase appears to be preserved. In the bronzite gabbro its composition lies nearAn60, In theaugite diorite it is zonedfrom calcic andesine to calcic oligoclase. But as the cores of many plagioclase crystalsin this rockare highly altered they may havehad a more calciccomposition originally. Although most of the rockscontain hornblende perhaps only in the ailgitediorite is this mineral of primaryorigin. The differencesbetween the basic and acidictypes is apparent in the followingtable: bronzi te qabbro plagioclase 50% augite 37% bronzite 5% chloritegroup, replacing (bronzite 7) 6% "ironore" 2%

91 auqite diorite plagioclase 60% augite 30% hornblende 8% chloritegroup 1% "iron ore" 1% Table 5 shows the determinations of the main primary minerals in four characteristic specimens. Itis apparent that these gabbros arenot uniformin composition but owing to the lack of exposure and the high degree of alteration the trends and mechanismsofdifferentiation could notbe worked out. The outcrops north of Lillooet are of medium- to fine-grained gabbro and have a hypidiomorphic granular texture. Most of them are equigranular, but some are seriate. In some of the specimens the augite appears strained. The original texture of the rocks has been obliterated to a large extent by alteration. In the outcrops on Seton Creek the degreeof alterationis even higher. Some rocks seem to have been fine-grained gabbros with a hypidiomorphic granular texture. Two specimens resemble originaldi- abases; one of them shows a variolitic texture.

92 TABLE 5

MINERAL COMPOSITION OF FOUR SPECIMENS. OF ALTEREO GABBROIC AND DIORITIC ROCKS

Orthopyro- Plagioclase Spec xene, comp. Measurements CompositionMeasurements Hornblende Measurement - X

En89 -i- 1% Ca41Mg44Fe15 1 nv = 1.604+ Absent An61+ 2% nx' = 1.559+ bronzite ,002 I I +2% .001- 2v = 490 1 Magnesian (-12~close An,, nx' = Ca37"49Fe14 = 1.685: present but Lfu I hypersthene to 90° ,002 probably 1.5472+ 9 probably - w -+a zv = 440 secondary ,001 altered absent or completely absent completely altered altered absent or present nx' = altered replacing 1.554- augite 1.540 I

x H.H. Hess and H.A. Phillips(1940) + H.H. Hess 11949) * R.M. Crump and K.H. Ketner(1953) 3. METAMORPHISM AND ALTERATION

Inseventeen outof nineteen specimens the plagioclase has been altered to albite and minerals of the epidote group among which pistacite seems tobeabundant. The orthopyroxenehas been replaced partly orcompletely by minerals of the chloritegroup. A mineral of that groupshowing bladed,habit. low birefringence,and positive elonga- tionprobablyisantigorite. The augite is betterpreserved than the other minerals but partly replacedbymineralsof the chloritearoup. byhornblende, or "iron ore". The rocksarereplaced by prehnite.carbonate, and less commonly by tremolite andpossibly the amphibolenephrite. As veinfilling prehnite,carbonate, and albite occur. One specimen is my1onitized;inothers the augiteappears to be strained and bent.

4. AGE

Thecontacts of the gabbros were not seen. An indication of theirage is givenby the followingobservation. East of Fountain Creek,in the vicinity of fault"d"a specimen was collected that is composedof chloritized clinopyroxene and hornblende in a matrixof prehniteand showsa strong schistosity. It resembles the highlyal- teredgabbros or diorites west ofLillooet. The occurrence of these rocks suggeststhat they were intruded into majorfault zones and thereforeare early Lower Cretaceous or younger.Their alteration may havebeen produced by late magmatic solutions.

ANDESITICAND BASIC DYKES

All rockunits, except for theMiddle or Late Tertiary olivine basalts are intrudedbyandesitic.diabasic,orbasaltic dykes. These dykes may rangein age from earlyMesozoic to Late Tertiary. They aretoo small to be shown on the accompanyingmap.

94 CHAPTER 11. THEFRASER RIVER FAULT ZONE

1. INTRODUCTION

Although Dawson (1895)considered the structure of the Fraser Riverarea as a seriesof tight foldshe noticed the shattered and altered natureof the rocks in many localitiesandsugaested that some ofthe major contacts are faults. He described,for example, the structure in thevicinity of Stein Creek as follows: "but in this vicinity, on bothsides of the river entire massesof therocks have become reddened anddecomposed by actionsubsequent to their deposition. The bedsare all much shattered, and linesof faulting in this placeundoubtedly run along the valleyoneof which apparentlybounds the Cretaceous trough on theeast sideof the valley." (p. 1478, f.) He statedof the contactof the Jackass Mountain group with the rocks oftheSpences Bridge group (whichhe considered to be Tertiary) between McKay Creekand Leon Creek: "The boundarybetween the Cretaceousrockson the west and vol- canicTertiary rocks, is here remarkably distinct and straight, and followsawell-markedvalley which is nearlyparallel to that of the Fraser.There is some reasonto suppose that this boundary may bea faultedone, but this is not so certain." (p. 2158.1 In 1912 N.L. Bowen inareconnaissancesurveyof the FraserRiv- er valley from LyttontoVancouver observed thatthe Cretaceous strata south of Lytton occupya graben between granitic rocks: "The average strike of the Cretaceous beds is about north 15de- grees westand the beds are commonlyat low angles,but close to the granitesthe attitude may benearly or quitevertical. The granite does not, however,give any evidence of being intrusive. The relation shown is due to the down faulting of the Cretaceousbeds. This part of theFraser Valley is, in fact,excavated alongabelt of com- parativelysoft sedimentaries themselves preserved by grabenfault- ing. The stripsof Paleozoic rocks, too, probably owe their present positiontothis faulting, for the strike of their beds makes asharp angle with theelongation of thestrips." Duffel1 and McTaggartcorroborated Bowen's observation that in the southern partof the Ashcroftarea the Fraser River Cretaceous beltoccupiesa graben. North of Cinquefoil Creek however, they not- eda series of faultsin which therocksto the west have been elevated relative to those in theeast. They gaveevidenceof intermittent activity from Lower Cretaceousto post Eocenetime and showed that carbonate,prehnite, and albite alteration are associated with the faultzone. As the probablecauseofthe faulting they suggested uplift and tilting ofthe Coast Mountains. Leech(1953) mapped a faultzone in the Yalakom areathat is probablyconnected with amajor fault discovered by Duffel1 and Mc- Taggartnear Lillooet. McCammon andNasmith (1956) duringa study ofpossible damsites on theFraser River observedseveral faultsin the northern parts of thepresent map areawhich they considered tobe possible extensions of theFraser River fault zone of the Ashcroft area. The present study hasadded the following information: (1)Those faultsof the Ashcroftsheet (Duffelland McTaggart, 1953) 95 thatare situatedin the present map areahave been mappedingreater detail but without majorchanges. (2) It is shown thatthe western contact of the Pavilion group is anotherfault of the Fraser River faultzone. Themovement on this faultis in the opposite sense to that of the other faults of the zone. showinga relative downwardmovement ofthe western block. The structure of the present map area therefore appears to be a complex graben. It is suggestedthat fault movements on this grabencontrolled the depositionof Divisions B and C ofthe Jackass Mountain group. (3) Anotherlongitudinal fault. the natureof its movementunknown, hasbeen mapped within thePavilion group. (4) It is shown thatthe latest movement on oneof the longitudinal faultsprobably took.place in MiddleTertiary time.

2. DESCRIPTION OF THE FRASER RIVER FAULT ZONE

The main branchesof the Fraser River faultzone are shown on Figure 6. The main faults of the zone trend northwesterly to north- erly and arereferred to aslongitudinal faults. Faults trending westerly,inpart apparently offsetting the longitudinal faults, are referred to ascross-faults. Sixmajor longitudinal faults have been recognized in the map area. At least two of them arecontinuous throughout thearea and some ofthem have been shown to extendfar to the south. It is as- sumed thatother faults exist but have not been recognizedbecause ofthick overburden and lack ofobvious offset in theformations transected. The longitudinalfaults strike northwesterly to north- erly, and, judged by theirlack of deflectionon the map in crossing ridges or valleys, 'dip steeply. Fault"a" (see Figure 6) separatesthe Lillooet group on the east from Triassicor older rocks to the west. The fault is not exposed in the map areabut has been seen farther south (Duffell and McTaggart,1953) and is probably continuous to the northwithamajor fault in the Yalokom area(Leech. 1953). In the present map area it hasassociated with it serpentinizedultrabasic intrusions, gabbros and diabase which eitherlocalized the break or intruded the fault zone. Fault "b" bringstheiillooet group into contact with the Jack- assMountain group. It has several branches near the mouth ofBridge Riverthat seemto convergetoa single break to the south and to the north. The fault is poorly exposedand has no topographicexpression on thewestern slopes of the Camelsfoot Range andof Fountain Ridge. Where theindividual branches cross FraserRiver, the strataare dis- turbedover widths up to severalhundred feet. Fault "c" divides the Jackass Mountain group into two main blocks. All three divisionsofthe group are exposedin the western block but onlyDivision C in the easternblock. Near Fountain Station three closelyspaced branches were observedor inferred but elsewhere only one could beestablished. The easternbranch is indicated by anarrow beltof steeply dipping and distorted strata east and northeast ofFountain Station along the west shore of the Fraser River. The western branch is marked by intenselystained andsheared cliffs a fewhundred feet above the road west of FountainStation. The cen- tralbranch is exposed only on theshore of the river but probably continues to thesouth. It truncatesDivision B and brings it into contact with a fault slice ofDivision C. 96 Fault "d"forms the contact of Division C of the Jackass Poun- tain group with volcanic rocks of the Fountain Valley assemblage, the upperdivisionof the Spences Bridge group. and the Nard Creek assemblage.The fault zone is exposedeast of Fountain Creek at the south shore of the Fraser River, and again northeast ofthe mouthof Black- hill Creek. Severalminor faults parallel with fault "d" occurnear the mouth ofFountain Creek. Between the mouths of GibbsCreek and BlackhillCreek, on the west sideoftheFraser River, the strata of Division C. commonly flatlying or gentlydipping. have been tilted intoalmost vertical attitudes for distances of at least one-half mile west ofthe fault zone. Minor hranches of the zone are exposed at the mouthsof Sallus and Blackhill Creeks. In this vicinity, the main fault seems tohave controlled the courseof the FraserRiver. Between the upperpart of McKay Creekand Leon Creek the fault is coveredfor about 2% miles by flatlying Miocene or Pliocene (?I basalts that apparentlyhavenotbeenoffsetbythe fault. To thenorth, onWatson Bar Creek, the fault is markedby intense carbonate alteration in the lithicsandstones and the volcanicrocks. Fault "e" the westernboundary fault of the Paviliongroup is well exposed on a cliffin Big Bar Canyon, where the faultdips 74 degreesto the southwest.The trace of the faultplane on the cliff is straight,suggesting little variation in dip. Thefootwall here consists of ribbon chert that lies approximately paralleltothe fault planeand contains numerous veinlets of quartz and carbonate. The hangingwall is andesitethat has been converted into alayerof gouge about40 feet thick. Between WatsonBar Creek andFrench Bar Canyon the existence of a fault contact is indicatedby the steep dips ofthe otherwise flat lying or moderatelydipping volcanic rocks. From WatsonBar Creek to McKay Creek the rocksadjacent tothe contact are poorly exposed. Between b1cKay Creekand a localityabout 1 mile northwestof Glen Fraser the fault is notexposed but indicated by anomalous dips and signsof shattering and alteration, Immediately north ofGlen Fraser the location ofthe fault is uncertain. From GlenFraser to the mouth of GibbsCreek the eastern contactof the Paviliongroup is covered byoverhurden. Southwest of the mouth ofGibbs Creeka fault between the lowerdivision of the SpencesBridge group andthe Fountain Val- leyassemblage was inferredfrom a cross-section (B-B'). Thisin- ferredfault probably is continuous with theeastern boundary fault ofthe Pavilion group tracedfrom northwest of Glen Fraser to north ofBig Bar Creek. Fault "e" lies close to thewestern margin of severalgranitic masses. No majorplutons in the present map areaare exposed to the eastof this fault. Fault "f" forms the contact between Division I andDivision I1 of the Paviliongroup. The fault is exposedon the slopenorth of Pavil- ion Creekand indicated by shearing and alteration south of Moran. Thenorthwestern continuation of the contact is obscured by lackof outcropand metamorphism. South of Pavilion Creek the contact is verypoorly exposed. On Keatley Creek a faultrelation was inferred froman abrupt lithological change, from the unusualnarrowness of Division I and an anomalousstratigraphic top near the contact. The faults "a", "b"."c". and "d" appear to be normal faults with relative downward movementofthe eastern block; fau1t"e" is anormal fault with relative downwardmovement ofthe western block.These fivelongitudinal faults forma complex graben. The senseof movement on fault "f" is uncertain. 97 Cross-faults, approximately normal to the longitudinal faults, seem to be comparatively short and to show small offsets. Although horizontalandvertical displacements canbeestablishedin some places, in others offsets cannot berecognizedat all and faulting is indicated only by abrupt changes in attitude. The cross-fault zones consist of single breaks or, as on Fountain Ridge, of a series of closely spaced faults. One of the cross-faults offsetsa longitudinal fault hut others appear to stop atthem.

3. ASSOCIATEDALTERATION

The most common alteration associated with the Riverfault Fraser zone is carbonatization. The carbonate weathers rustybrown. In an altered rock fromBig Bar Canyonit has the composition ofmagnesiodol- omite (no = 1.6795). In conglomerates, sandstones, and siltstones the carbonate replaces mostly the matrix, butin the other rocks it occurs in veinlets and irregular patches. In many localities veinlets of quartz are associated with the carbonate. Igneous rocksand lithic sandstonesnear major faults show signs of low-grade or retrogressive metamorphism. Calcicand intermediate plagioclase have been converted to albite and epidote and the mafic minerals to chlorite. Chlorite and epidote in many of these rocks form veinlets and apparently have been redistributed by solutions. Duffel1 and McTaggart have pointed out that in many localities the albitization is accompanied by prehnitization. The prehnite appears in veinlets or replaces the plagioclase of thehost. In the present map area the mineral wasfound inthe gabbroic belt westof Lillooet, in a dioritic dyke near the mouth of Bridge River,in a gabbroic or dioritic dyke and a lithic sandstone east of Fountain Creek, and in the diorite mass southeast of Pavilion. All these localities in are the vicinity of major fault zones. Itis possible that the altering solutions and the gabbroic dykes ascended throughsuch fractures and that dykes and solutions are relatedin origin. West of Lillooet the gabbros are also veinedbytremoliteand possiblytheamphibole neph- rite.

4. HISTORY OF THE IPRASER RIVER FAULT ZONE

The history of the Fraser River fault zone probably isa long and complex sequenceofintermittent movements. The evidencefor the earlier movements is incomplete, indirect, and lies mostly in the stratigraphic record. Only the latest movements can be established directly from the present structure. Cross-section C-C' shows that the faulting is youngerthan the folding of the Lillooet group which probablytook place in the Neocom- ian. The earliest indication of the existence of the fault zone is the conglomerate of Division B (Barremian) of the Jackass Mountain group. The great thicknessof coarse sedimentsin this unit suggests rapid uplift of the source area which may have been accomplished by normal faulting. There is also some evidence thatthe fault zonewas active during the deposition of DivisionC (Barremian) orat the end of that time. About 1 mile north of the mouthof Gibbs Creek volcanic rocks ofthe Spences Bridgegroup apparently overliethe Pavilion group with

98 unconformity.Aboutlmile to thewest strata of Division C. several thousand feet thick areexposed. The units areprobably separated by two faults the latest movementon which took place in the middle (?) Tertiary(cross-section C-C'). The situationcan be explained in twoways. Either the strata of theJackass Mountain group never extendedto the locality where theSpences Bridge groupwas laid down later; or the easternpart of Division C wasremoved by uplift and erosionbefore the depositionof the SpencesBridge group. In the firstcase the sediments ofDivisionCmust have been deposited in a rapidlysubsiding trough whoseeasternboundaryapproximately coincided with the presentfault. The second explanation implies a rapid upliftofgreat magnitude immediatelyto the eastof the present fault zone.Both explanations suggest movementsofthe present fault zone; in the firstcase it wouldhave taken place in the midLower Creta- ceol(s(Barremian);in the secondcase slightly later (early Aptian?). Ifthe rocks north ofGibbs Creek are not correlative with the basal unit of the SpencesBridge group in the typearea, but younper. the faultingmight be middle or late Aptian. Middleand Upper CretaceousandEarlyTertiary movements cannot beestablished, but perhaps the volcanismof this time is related to theFraser River fault zone (compareCloos, 1939). Theyoungest rocks disturbedbyfault movements are the volcanic flowsand tuffs that overlie the FrenchBar formation (Eocene-Olig- ocene). Thelliocene - Plioceneolivine basalts overlie fault "d" without signsofdisturbance, andtopographic evidenceof Pleistocene or Recent faultinghas not been found.

.5. CAUSES OF FAULTING

Duffel1and McTaggart have related the movementon faults a, b. c,and d, which show relativedepression of the easternblocks, to upliftand tiiting of the Coast Mountains in the west. By analogy fault "e". showingrelative depression of the western block,could berelated to uplift of the plutonicmasses situated immediately to theeast. Perhaps these plutons are part of a largermass hidden at greaterdepth that is connected with the Mount Lyttonbatholith. On the otherhand, flans Cloos (1930) hassuggested that the greatestgrabens of the worldprobably were producedby broad domal upliftsand are the result oftension. An upliftof the FraserRiver area in.the Lower Cretaceous is indicated by the gradualshift from marineto continental conditions. Perhapsboth processes are related.

99 CHAPTER 111. GEOLOGICAL HISTORY OF THEAREA

In the Permianand Triassic the area waspart of a somewhat restricted marine basin in which carbonaceous matter was not oxidized, In the Upper Permianareefzone extended through the presentMarble Rangeand Pavilion Mountains. In UpperPermian or Tertiary time to the west of the MarbleRange alternating 1ayers.ofmud and radiolariandebris were laid down.The conditionswere moderately stable but some volcaniceruptions took place. It is unknown whetherthese de- positsareseparated from the underlyingreefal unit or the overlying clastic-volcanic suite byamajorunconformity. In thehliddle or Up- perTriassicthe area was extremely unstable. Tectonic movements re- sultingin submarine slumpingand turbidity currents were accompanied bystrong volcanism.The deposits of this epochconsisted of lithic sand, tuff, volcanicflorvs,argillaceousmud. radiolariandebris, lime, and silt. The tectonic activity may have culminated in the Cassiar orogeny (White. 1959). However. in the present map area the only in- trusionsmarking that eventare Upper Triassic (?) ultrabasic intrusions west ofLillooet and east of the Fraser River, No sedimentary or volcanic rocks of the timeinterval between Triassicand Lower Cretaceousare exposed. TheLower Cretaceous sediments, however,were derived from volcanic rocks that probably were depositedduring this interval.These volcanic rocks were rich in albiteand probably belong to the spilite-keratophyre suite. They werepossibly Jurassic and exposed to the northeast and/or southwest ofthe Fraser River fault zone. The source rocks may havebeen re- latedto the Aliddle Jurassickeratophyres exposednear Harrison hlills. British Columbia(Burley. 1954). Intrusionof granitic rocks into the Paviliongroup may have takenplace in the Jurassic. In the earliest Lower Cretaceousduring the depositionofDivi- sions A and Bofthe Lillooet group the area was part ofa restricted marinebasin which was tectonically unstable, The mud ofDivisions A and B andan increasing proportionof lithic sand in Division B were depositedby turbidity currents that were accompaniedby submarine slumping.During the depositionof DivisionB the area gradually rose and then was folded,intruded by dioritic dykes, elevated above sea leve1,anderoded. The uppermost partof the Lillooetgroup, Division C. consisting oftuffaceolts lithic sandstone,granule conglomerate, and a smallproportion of argillite was deposited inamarineenvir- onmentperhaps under near-shore conditions. At the endof that time (Neocomian ?) the areaagain rose above sea level, and the basalcon- glomeratesandstone unit oftheJackass Mountain group was laid down inacontinental environment.'Associated tuffaceous matter indicates contemporaneousvolcanism. During the deposition ofthe Members AI1 and AI11 ofDivision A andof the basalpart of Division B of the JackassMountain group (Barremian)the area was partofa restricted marine basin. Thesed- imentsof AI1 consisteddominantlyof fine sand, thoseof AI11 of mud, silt and fine sand,and the basalpartof Division B wascomposed of medium-grainedsand. This change in grain size may reflect a relativedepression of the basin followed by a gradualrise. Thethick conglomerate of Division B is the earliest evidence ofactivityonthe Fraser River fault zone which continued intermit- 100 tentlyto the MiddleTertiary. The faulting may berelated to the rise ofCoast Intrusionstothe east andto the west or anuplift of the whole area. A complexgraben structure was produced which probably controlled the sedimentationof Divisions B and Cofthe Jackass Mountaingroup. Divisions B and C consistingofconglomerate, lithic sandstone,and minor argillite probably were laid down in a narrow elongate trough which subsided rapidly with respect to the bordering mountainshut fluctuated with respectto sea level. During most of the time, it probablyformed a restrictedmarine basin; temporarily itmayhave beena continental valley occupied bya large river. Grad- edbedding and slump structures are veryrare, and in this respect these"post tectonic" rocks differ markedly from the oldergeosyn- clinalfacies. Thesediments were mostlyderived from albite rich volcanicrocks and to a lesser extentfrom granitic intrusions. Rocksyounger thanthe early Lower Cretaceousare only found to the east of the Lower Cretaceoussedimentary belt, and all of them are ofcontinental origin. Inthe middle and late Lower Cretaceousvolcanic rocksofgreat thicknessconsisting dominantly of andesite were depositedthat are locallyintercalated with continental sediments. Perhapsthe volcanic flows ascendedthrough fractures of the Fraser River fault zone. Becauseofthe lackof fossils the Upper Cretaceous and Paleocene- Eocenehistory of the Fraser River valley is uncertain.Probably the volcanicactivity continued. InEocene-Oligocene time graveland lithic sandof great thick- nessderived from volcanic rocks were laid down onaflood plain between BigBar Creek and theFrench Bar Canyon. The river deposits were overlaidby another series of volcanicrocks ranging from basaltic to felsitic compositions.These volcanic flows and tuffsare the youngestrocks found in thearea that have been disturbedbymove- ments ofthe Fraser River fault zone. In theMiocene (?) lithic sands were deposited on floodplains nearPavilion, south of Leon Creek,and on BigBar Creek. Possibly thesedeposits were connectedand formed inavalley that partly CO- incidedwith the present Fraser River valley. These sediments were succeededby olivine basalts which may have risen throughfractures associated with the FraserRiver fault zone. Their appearance marks the end ofa longperiod of volcanicactivity dominated by andesitic rocks. Althoughthearea was covered by glaciers in the Pleistoceneap- parently little glacialerosion took place. Probably at the end of thelast glaciation the valley was occupiedby braided streams and glaciallakes and more than 1.000 feet of gravel,sand, silt, and mud flows were deposited. In Recent time the FraserRiver has been re- juvenatedand has cut through the unconsolidatedmaterial into bed- rock.The northwestern and central part of the areareceived thin depositsof volcanic ash.

101 RIRLIOGRAPHY

Armstrong. J.E. (1949):Fort St. James Map-Area, British Columbia, Columbia, Geol. Surv.,Canada, Mem. 252. Bowen. N.L. (1914):Geological Reconnaissance of the Fraser River Valleyfrom Lytton to Vancouver, British Columbia, Geol. Surv..Canada, Sum. Rept..1912, pp. 108-114. Bowen. N.L. andTuttle, O.F. (1949): The system WgO-Si02-H20, Geol. SOC.America, Bull., Vol. 60, pp. 439-460. Bramlette. W.N. (1946): The hlonterey FormationofCalifornia and the OriginofIts Siliceous Ro-cks. U.S. Geol. Sum.. Prof.Paper 212. British ColumbiaDepartment of Agriculture (1957): Climate of Brit- ishColumbia, Report for 1956. Brock,P.(1956): A StudyofLayered Norite near Lillooet. B.C.. B.A. Sc.thesis, University of British Columbia,Unpubl. Burley. B.J. (1954): A Study of Some Volcanic Rocks fromHarrison Mills, British Columbia, M. Sc.thesis, Universityof Brit- ish Columbia,Unpubl. Cairnes, C.E. (1923):Geological'Exploration in the Yaleand Simil- kameenhlining Divisions, Southwestern British Columbia, Geol. Surv..Canada, Sum. Rept.,1922, Pt. A, pp.00-127. (1924a): Reconnaissance of the Silver Creek, Skagit and SimilkameenRivers, Yale District, Geol. Surv.,Canada, Sum. Rept., 1923. Pt. A, pp. 46-03. (1924 b): CoquihallaArea, British Columbia,Geol. Surv., Canada, Mem. 139. Cloos. H. (1939): Hebung - Spaltung - Vulkanismus,Geol. Rundsch. XXX (4a). Crump. R.M. and Ketner. K.B. (1952):Feldspar Optics, in Emmons, R.C. et al..Selected Petrogenic Relationships of Plagioclase, Geol. SOC.America, Mem. 52.pp. 23-38. Davis,E.F. (1918): The RadiolarianCherts of the FranciscanGroup, Pub.of the Universityof California, Dept. Geoi.Sci., Bull,Vol. 11, No. 3, pp. 235-432. Dawson. G.N. (1079):Report on Exploration in the SouthernPortion of British Columbia, Geol. Surv..Canada, Rept. ofProg., 1877-78, Pt. B. pp.1-173. (1895):Geol. Surv.. Canada, Map 556,Kamloops Sheet. (1896): Report on the Areaof the KamloopsMap-Sheet. Geol. Surv..Canada, Ann. Rept.,1094. New Series, Vol. VII, Pt. B. PP. 1-427. Duffell, S. andMcTaggart. K.C. (1952):Ashcroft Map-Area, British Columbia, Geol. Surv.,Canada, Mem. 262. Drysdale. C.W. (1914):Geology of the Thompson River Valley below KamloopsLake, B.C.. Geol.Surv.. Canada, Sum. Rept.. 1912. pp. 115-150.

102 Dunbar, C.O. (1932):Neoschwagerina in the Permian Faunas Of Brit- ish Columbia, Trans., Roy. SOC., Canada, Sec. IV, pp. 45- 50. Fyfe, W.S.. Turner, F.J.. and Verhoogen. J. (1958): Metamorphic Re- actions and Metamorphic Facies,Geol. Soc. America, Mem. 73. GeologicalAssociation of Canada (1958):Glacial Map of Canada. Goldstein,A.ad Hendricks, T.A. (1953):Siliceous Sediments Of the OuachitaFacies in Oklahoma, A.A.P.G., Vol.64, pp. 421- 442. Greenman, N. N. (1951): The Mechanical Analysis of Sediments from Thin-Section Data, Jour. Geol.. Vol. 59, pp. 447-462. Hess, H.H. and Phillips, A.H. (1940):Optical Properties and Chem- ical Composition of Magnesian Orthopyroxenes. Pm. Mineral.. Vol.25, pp. 271-285. (1949): Chemical Composition and Optical Properties of Common Clinopyroxenes, Pt. I, Am. Mineral., Vol. 34,pp. 621-666. Hough, J.L. (1942):Sediments of Cape Cod Bay, Massachussets,Jour. Sed.Petrog.. Vol. 12, pp. 10-30. Illing, L.V. (1954): Bahaman CalcareousSands, A.A.P.G., Vol. 38. pp. 1-95. Jenkins, O.P. (1943):Manganesein California, State of Calif. Dept. Nat.Resources, Div. Mines. Bull. 125. vander Kaaden, Gerrit(1951): Optical Studieson Natural Plagioclases with High and Low-Temperature Optics, Ph. D. thesis, Uni- versity of Utrecht. Krauskopf, K.B. (1956): Dissolution and Precipitation of Silicaat Low Temperatures; Geochim. et Cosmochim. Acta,Vol. 10, pp. 1-26. Krumbein. W.C. and Garrels. R.M. (1952): Orioin and Classification of ChemicalSediments in terms of pH and Oxidation-Reduc- tionPotentials, Jour. Geol.. Vol. 60, pp. 1-33. Krumbein, W.C. and Tisdel, F.W. (1940):Size Distribution of Source RocksofSediments, Am. Jour. Sci.. Vol.238, pp. 296-305. Krumbein. W.C. (1953):Thin-Section Mechanical Analysis of Indurated Sediments, Jour. Geol.. Vol. 43, pp. 482-496. Lay,Douglas (1940):Fraser River Tertiary Drainage-history in relation to placer-gold Deposits, B.C. Dept. of Nines. Bull, 3. Leech, C.B. (1953): Geology and MineralDeposits of theShvlaps Range, SouthwesternBritish Columbia, B.C. Dept. of Mines, Bull, 32. Lowenstam,H.A..(1950):Niagaran Reefsofthe Great Lakes Area, Jour. Geol.. Vol. 58, pp. 430-466. RlcCammon, J. and Nasmith, H. (1956): Geologyof Low LevelDamsites on theFraser River, B.C. Dept.of Mines. Unpubl. 103 MacKenzie, J. D. (1921): A Reconnaissance between Taseko Lake and Fraser River, British Columbia, Geol. Surv., Canada, Sum. Rept.. 1920, Pt. A, pp. 70A-81A. Mathews. W. H. (1941): Climbs in the Lillooet Range, Can. Alpine Jour., pp. 60-64. (1944): Glacial Lakes and Ice Retreat in South-Central British Columbia, Trans., Roy. Soc., Canada, Sec. N. pp. 39-57. Packham, G.H. (1955): Volume-, Weight-. and Number-Frequency Anal- ysisof Sediments from Thin-Section Data, Jour. Geol.,VOl. 63, pp. 50-58. Poldervaart, Arie (1950): Correlation of Physical Properties and Chemical Composition in the Plagioclase, Olivine,andOrth- opyroxene Series, Am. nlineral.. Vol. 35, pp. 1067-1079. Reinecke. L. (1920): Mineral Deposits between Lillooet and Prince George, British Columbia, Geol. Surv.. Canada, Mem. 118. Revelle. R. (1934): Physico-Chemical Factors Affecting the Solubil- ityof Calcium-Carbonate in Sea Water, Jour. Sed. Petrog., Vol. 4, pp. 103-110. Rice, H.M.A. (1947): Geology and klineral Deposits of the Princeton Map-Area, British Columbia, Geol.Surv.. Canada, Allan. 243. Rosenfeld, M.A., Jacobsen. L., and Ferm. J.C. (1953): A Comparison of Sieve and Thin-Section Techniques for Size-Analysis, Jour. Geol., Vol. 61, pp. 114-133. Selwyn, A.R.C.(1872): Journal and Report of Preliminary Explorations in British Columbia, Geol. Surv.. Canada, Rept. of Prog., 1871-72, pp. 16-72. Taliaferro. N. L. (1943): Franciscan-Knoxville Problem, A.A.P.G., Bull.. Vol. 26, pp. 10-219. Thayer. T.P. (1948): Relation of Serpentine toUpper Triassic Over- Thrusting in Northeastern Oregon,Geol. Soc. America, Bull., v01. 59, pp. 1358-1359, Tipper, W.H. (1959): Blap 12-1959. Quesnel. British Columbia, Geol. Surv., Canada, Thompson, W. L. and Wheeler, H. E. (1942): Permian Fusulinids from British Columbia, Washington,and Oregon, Jour.Palaeont.. Vol. 16, pp. 700-711. Thornbury. W.D. (1954): Principles of Geomorphology. Wiley. Tra’sk, P.D. (1932): Origin and Environment of Source Sediments of Petroleum, Gulf Publ. Co.. Houston. Warren,H.V. (1959): The WoranDam, Canadian Win. Jour.,hlarch, 1959. White, W.H. (1959): Cordilleran Tectonism in British Columbia, A.A. P.G.. Vo1. 43, pp. 60-100. Williams, H.. Turner. F.J.. and Gilbert, C.I. (1955): Petrography, W.H. Freeman and Co.

Winchell. A.N. and Winchell. H. (1951): Elements of Optical ?I’I lner- alogy. Part 11. Wiley. 104 APPENDIX I. DETERMINATION OF MINERALCOMPOSITIONS

The following optical properties and references have been used Hiqh - temperature plaqioclase: extinction angles in zone normal to (010); van der Kaaden, 1.951. Where extinction angles could not be measured, the Tsuboi-index. nx' of 001 - cleavage fragmentswas used; Crump and Ketner. 1952.

The Tsuboi indices have been worked out,so far, onlyfor low-temperature plagioclases. But in the present study it was found that determinations based on Crump and Ketner's curves do not deviate far from those based on van der Kaaden's extinction angle curves. Low-temperature plaqioclase: Tsuboi-indices; Crump and Ketner 1952. Extinction-angles; Winchell and Winchell. 1951.

Owingto the uncertainty about theoptical properties of plagioclase the determinations probably havean accuracy onlyof?2-5%. However, the curves used have been interpreted as closely as possible.

Clinopvroxene: nY, 28; Hess, 1949. Orthopyroxene: ny, optical sign; Hess and Phillips, 1940, Polder- vaart, 1950. Olivine:ny optical sign;Poldervaart. 1950. Carbonates: No; Winchell and Winchell. 1951. The Tsuboi-indices have been determined with anaccuracy of approximately 2 .001. other indices withan accuracyof approximately+.002.

105 "

INDEX POW access ...... I ...... 88 lcknaivlcdgemenfr ...... "jij JfrYCf"re ...... 88 "De . Coarl I"ir"*io"r ...... 88,89, no *merate...... 6 . 7 . 8. 9 . 72 rounilin "alley ussembiage ...... 69 coralp...... ,4 . 17 g"bbro and diabase ...... 9.2 crinoida _""""""""""""""""" 14 . 16 JIclirrr Mountain group ...... 50, 59 cretaoeous. intrvsions ...... 84 Kin<,wale <,youp ...... 65 . 67 rOcXI ...... " 9 LiilOOC, group ...... 46 IedimenfS ...... 2 i,rr,,, e conyon iormntion ...... 1, "oicanics """"""""""""""" 2. 70 liiocene-Pliocene billrlts ...... 8, Biocene-Plinccne Sedinentr ...... 75 0 ,,>vi, ion grnyp ...... 25 I 34 5pencei midge group ...... 62, 64 daciie fiars 6 ...... , 7 . 67 u,, nbasics ...... 83 W.R...... 1* .19 nii'ilamernle . Gibbr Creek osscnbiaye ...... 7 Dau.son, G.W...... 1. 11 ill biz" ...... ,, 67 Oarson, J.W...... 11 elbitintion . >>cXari Yotwtrin group ...... 56 Dardney Creek ...... 46 ,.i,looe, groap ...... 44 diabase dykes. gabbra 2nd ...... 6 91 a, ...... 1.1 diorite, ...... 9 al1,'Yi"m ...... 6 ...... 9 BlWratiOO . Carbonl, c.silicn ...... 0 . 03 dioritic rocks . Lower Cretroeous ...... ad gnbllro ani <, jabrse ...... 94 minerai composition ...... 93 PZViiiO" "'IFmblrye ...... 30 dolomite, Cache Creek ...... ,I rmmonite . Jech:isr hloul'trin 0'0, ip ...... 58 Duffe,,. s ...... 1 onphibolife ...... 9 Duncan ,lele" ...... 34 ln,~rri,...... ? iln,.* ...... ,. i " n dykes, ...... 94 andesitic riyhes . ,.ate Tertiary ...... 98 blric ...... 94 nl,ticlinori,,n. Mom,, S0"CS ...... 12 ...... ,>....9, ...... "Oe ...... 7 . 50, 6d gabbro ...... 6 .91 ...... h 7 n , peridotite ...... 81 porphyritic qurrte diorite ...... a . 9 E Pavilion gr~"p...... 20 eehinoid3 ...... 14 .l "cellu ...... ,is . 46 Edge Hill8 limcStone...... ,, Eocene T0CXS ...... 6 R

Barremian ...... 0,90 bnrs,, . 0, ivine ...... 6, 7 . 76 . Ti baric dykes . Lale Tertiary ...... "1 belemnite . Jackass aountain CIIOUI) ...... 14

field work ...... 26 1 "~,Cii,, io ...... 9 ash near ...... 3 flows . .10 fossil5 at ...... In ...... 1 / French Bar fomrfion near ...... 72 olivine brraif near ...... 76 Pavilion group "ear ...... 20 sedimentary rocks at ...... 76 ...... Big mr Ferry . shear zone near ...... 71 Kingsurio '5 Big Bar Mountain . Big Bar nssembivge at ...... 25 Li*iooef group ...... 45, 4' big game ...... Diarble Canyon formalion ...... 14 . 16- 19 3, 4 W>,i,i." groyp ...... 34 BOnapaife niuer . quartzites neer ...... I1 Upper Miocene ...... 77 argillite* ...... il Bilbbro alteration near 94 Bonmln Range ...... 2 rountain Creek ...... Fountain ,Ridge alfit,,der D* ...... 2 brooniopodr ...... I8 . Jaakrss Ilountrin group ne31 ...... 4, hreccin . andorifc~~ ...... n . rovntsin "alley arsemblngc ...... 7 in Nurble Canyon formation ...... 13 age ...... near Kealiey Creek ...... 28 69 distrib"lion ...... bo ...... 7 9 iitiiOlogy...... Bridge Riuer ...... '* ...... " ...... 69 IfllYCfUre ...... 69 Frsrer River, congiomerare nenr ...... 47 .TaCXsBI Nounfain group ...... 47 ?mer River fault %one, ossocivted alteration .90 C causes of faulting ...... 99 Cache Creek group ...... 10. ,I desciipiion ...... 90 ...... 11 early mavCnenir of ...... 5, , 10 history ...... crlelrenife . in hlrrbie canyon formtion ...... I6 98 mui, ion assemblage ...... 28 map "dng ...... 87 came, $footeange ...... 2. 4, f".$"li"idi ...... 11. 14 Garbonate-rilior alteration ...... 9. 83 curbonltizafion . Froser River fault none ...... 98 G "0, Cattle "alley ornic rocks ...... ~~ . ,, and 6, Limestone ...... 1, gabbro diabase dykes ...... ninera, Eompo6ifion ...... geologicai history Of area ...... geoiagicsl Wrk ...... geology . genera1 ...... in P8"iliO" grwp ...... 20 Fleiifecene ...... origin *f ...... 24 Recent ...... Gibbs as~ernblage chromite ...... 82 Creek ...... climate ...... 3 diStribUti0" ...... cor, ...... A 0 lithology ...... -* or1g.n.. above French Ear ...... formation ...... 74 structure in Ward Creak arremblrge ...... 7, ...... Gibbs Creek nelr coast Infrusionr Bge ...... 8a -90 . sedimentary rock8 ...... assoeivte4 "ineralizrfio" 88 90 "OlcPniC rocks near ...... 59, ...... gieeio, ',a distribution ...... 84 90 W8BD ...... , 89 . Glen Frsser ...... lithology ...... 85, 80, 90 gealopy Of ...... mineir, ...... 06 107 ~ingsvrlegroup near ...... 64 hlarble Range ...... 2 Tertiary sedimentary rocks near ...... 74 $outher" asaemh, age ...... 10 Glen Fraser arremb, age ...... 7 UediOine Creek . limestone near ...... i1 ...... 57 . LO, YolCBniCnear ...... 11 ...... 9 metamorphic iaekr . Pavilion group ...... 32 If(lCXI 1...... 9 metamorphism, gabbro and diebase ...... 94 g'eywscLe ...... 9 pavilion assemblage ...... 30 ...... PI"ili"" nln,,=. ... " ...... 22 H meto-q"ar'z;fe ...... 9 dnerai composifian . Coast Intrusions ...... 86 harzb"rgife, serpen'inized ...... 82 and diabase ...... 93 Hat Creek. Tertiary rooks near ...... 11 metamorphic IIQCXI, ~euiliongroup ...... 32 High Bar Ferry . Big Bar assemblage ...... 26 mineralizationCor8 . i. Inlrulio"a ...... BB history . i. ~i~~~ fault ...... 98 ute~~~~~~i~~ ...... 90 gee,ag.cal hisfory ...... iw m~m"g...... 4 hornfels ...... 9 . 32 h, iocener,, ...... 6 ...... 74 . 75 I volcanio ...... 75 . 76 h, Dnfli"r"li.u ...... 34 industries ...... 4 hloran . pavilion group nerr ...... 25 . 33 intrusio"r coast ...... 84 Terii3ry sedimentary rocks "err ...... 74 gabbro md diabase ...... 91 h, p,Oi"," an ...... 13 intrurive rockr ...... 8, fosli, ...... is "iron ore" 5penees Bridge group ...... 63 no"nt Kerr fossil at ...... 18 . ,imestone near ...... 13 J Llounf Kosiering Big Bar rssembioge "ea1 ...... 25 hlurfley ...... 2 Jackasr &,o"ntoin ...... 8 ...... 85 age ...... 58 . 59 mount soues . rntiClinOrium ...... 12 nlh;f;zatiOn ...... 56 Mount so"es Oi"iBion ...... LO, 12 distribution ...... 46 ,ifha, ogy ...... 47 n ".gl" ...... 56 . 59 ItruOture ...... 56 Narmifh ,r...... ,. 95 ~~l~t~~~J.A...... 46 . 58 Neoco.ian ...... 9 ~~~~~~d fossils af ...... 19 "*, "ear ...... 3 0 O, rOC*I ...... b olivinebasalt ...... 6 "'inera, cQ.position ...... 79 Keriley Creek . breocia near ...... 28 near ...... 23 neal L~~~ Creek ...... 76 near ...... 20 nevr &lcgay Creek ...... 77 Kelly Creek. Pavilion group neP/_ )gatron Bar Creek ...... 77 Kingsvale g'o"p ...... 7 age ...... 65 distribution ...... 64 P fossils ...... 65 ,itnology ...... 64 pa.i.io.. landrlide near ...... 74 ...... 65 Tertiary ~edimenfaiy rocks near ...... 74 ...... 64 pa"ilion rssemb, ...... 9 Stru~fure...... 65 ...... 34 iDokl ...... 64,65

L ..l. Landslide neajl ion ...... 70 Str"et"re ...... 33 Lee Creek Lee . voloenio rocks near ...... 63 ...... 26 Leon Creek . sedimentary racks near ...... 76 PaYilion group, metamorphic roeir ...... 32 olivine basalt near ...... 70 63, . 76 peridot;ie intruding ...... on Lillooef, gabbro and diabase near ...... 91 rocks ...... 20.22 , 25 . 26 Lillooef group rocks near ...... 34 valcinicI ...... 26. 27 Lillooet 4'~"p ...... 8- 9 Pa"i,ion g'o"p ...... 2,10 age ...... 46 I ~ge...... 25 a,biii.at;(l" ...... 44 distribution ...... 20 diStrjbufiQn ...... 34 ,ilhology ...... 20 litho, ogy ...... 34- 44 neiamorphism ...... 22 ~"gln...... 45 ItrYCt"re ...... 45 ...... 23 limestone ...... 8 . 9, 10 Cache Creek ...... I, ...... blrrble canyon formation ...... 14 .. Pa"$, ion ...... 20 lithology ...... 25 group o', ..B'" ...... 34 ...... i, -...... 4 ...... 26 Lytton...... 3 Pruilim urrembirge age -"------" 34 dislrib,, ...... 25 Mac and MC lithology ...... 26 metamorphism ...... 30 LlcCamon, .,...... 1 . 95 ...... 34 L,acKenc.e. D...... 1 Sfl"Cf"re ...... 33 .,...... 2 ),rKry Creek...... 2 pavilion ...... VoiCani~ ro~k~"ear ...... 63 peridotite . intruding Pavilion gr0Np ...... 84 McTaggart K.C...... I nenr SiwaJ), Creek ...... 04 reroenfinized ...... 9 hl permian kocxr ...... LO . 12 pavilion ...... 25 la,, " Creek fossils ...... 18 phyriography ...... 2 *,athews ,Vi."...... 3 miner...... 4 blarble canyon formation ...... 2 . 10 plant fmsil~,near Big Bar Creek ...... 72 "ge ...... 17 p, a"* lejmS ...... 6 . 7 . 0 inDlliUm...... L5 P, eisfocene geology ...... 2 0~1carenire.q ...... 16 plioeene, ...... 6 distribution ...... 13 sedimentary rocks ...... 74 . 75 fa", and folding ...... 1, volcanic rocks ...... 75, 76 fossi,s ...... I7 Porcupine Creek . Limesfme near -"------"--- 13 litho, ogy ...... 13 aon.er dam ...... 0 Drlgln...... 16 Ptr"ei"re...... 15 marble Canyon . limestone ...... 1, 108

. qUUrf' diorite. dykes ...... 8 Tawn Crcek . gabbro and diabase near ...... 91 ...... 9 "LlrabasiCI . serpentinired neor ...... 03 sills ...... 8 Triassic, fossil ...... 12 siocks ...... 9 Pavilion O~UD..rocks ...... 25 . 34 Cache Creekquartzite . Cache ...... 11 ...... 9:10 mefa.q"arfzi,e ...... 9 UitrrboSiC inlrurioni ...... 84 tuff ...... 6-10 R Cache Creek gio"p ...... 12 Marble Canyon formation ...... 10 radioinria ...... 14 Pa"ilio" ...... 20 Pavilion ...... s'o"p 24 turfreeDus Ir"dPfsne ...... 8 rrnching 4 TWOLlile ...... 13 Reinecle, L ...... , Creek . iimesfone ~t ribbon ...... 10 u blorble canyon formrtion ...... 14 hiD" "t soues ...... 12 ...... origin ...... 16 .. ulfiabrsic rocks age 83 Richardron, near Lillooet ...... J ...... , alterrtion 83 45, 72 carbonate-silioo ...... nouse . G.E...... dist rib"iion ...... 81 liihoiogy...... 82 5 "'gr" ...... 03 serpentinizr, ion...... 03 Srllui Creek, hinrble Canyon formation near ..... 23 group near 23 Pavilion ...... V spencer Bridge ...... 59 Sandsfone, in Wvilion group ...... 20 ation ...... lithic 3 ...... 10 "0, crnic arenife...... 69 ...... 8 volcanic ...... 6 sedimentary rocks . Cache Creek group ...... 11 near Big Drr ...... 3 2 Cre,jlceo.s ...... near Jesmond ...... 3 "e.,l Rig Bar Creek ...... 76 R"i, inn ...... 3 neii Leon Creak ...... 76 uo,canio . breccia ...... 7 near hri,io,, ...... id flows ...... Selo" Creek ...... 35 9 . 10 . id ...... 2 voLcanic rocks . Cache Creek group ...... LL Tertiary Bill 0 seiayn,u.p.c...... 1,,1 near BiQ Creek ...... , near Leon Creek ...... ,I .76 rerpen*ine . c3che Creel group ...... 11 near McLenn Creek ...... LL serpentiniter, west or Liiinoet ...... 8.4 "ear Farilia" Creek ...... peridmite 84 ,, serpentinizetian . Of ...... DYerlying French Bar ...... 76 or ,,,trabriic rock6 ...... 82 formofian seton Creek . ma, ...... 35 $ aibhro and dinbare near ...... 91.. , redimentilry rocks near ...... 35 WruqenaDhy, ,"in...... ,6 IO 5b8165 . lrckerr B0""tli" group ...... 49 Ward Creek rssenblage ...... 6 shear ZO"D ne;:r Big wr Terry ...... 71 . age ...... 71 CnrbDna~eatteriltion ...... nB distribution ...... 70 siitstone ...... 7 . 8. .i liihoiogy ...... 70 laekvrr >,wntrin ...... 50 Orlgln...... quartz 8, 71 sills . diorite ...... 9 SililClUle ...... 7, Siwaah group near .. 2,. 24 Creek. Pavilion """- Watson Bnr Creek . rocks ncar ...... 2 peridolife dyke ...... 04 didlife ...... 3 Slok Creek . Spencer midge group near ...... 64 soiis ...... 4 Spences Bridge group ...... 7. 67 Loner muision . mrrl ...... 59 Gibbs Creek OsIremblage ...... 62 disirib"iion ...... 60 iiiholoSy ...... M origin ...... 62 I, r"Ct"le ...... 62 Upper Di"iSi0" . b,Ember* A . R and c ...... 64 distribution ...... 62 Litho, 0gy ...... 63 StrUCtUre ...... 64 Stein Creek . Fra~erRiver fault al ...... 95 ItrUEtVre . Big Bnr assemblage ...... 26 coast ,"trurionr ...... 88 rountrin "alley assembiage ...... 69 g"bbro md diabu*e ...... 91 Gibbs Creek assemblage ...... 62 lackasr Baunfvin group ...... 56 KingBVBie group ...... 65 Lillooet group ...... 45 mrble canyon iormtion ...... 15 liiocene-Plioeene roCXB ...... 75 . 80 Pavilion asrembloge ...... 33 R"iii0" gmYp ...... 23, 26 . 33 Spencer Bridge group ...... 62 . 64 Word Creek arrenblrge ...... 71 T fable of formations ...... 6-10 Tertiary rocks ...... 2 .70 sediments . age ...... 75 disiriblliio" ...... 74 , ...... 74 ong,.. n ._...... 75 Stl"Oture ...... 15 volcanics ...... 01 diStribulion ...... 7, lithology...... 77 Ongln ...... 00 rtruCfYre ...... 80 till ...... 6 I09