GEOLOGY Ill of the Fraserriver Valley Between Lillooet Andbig Bar Creek
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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 by 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 rec- ognized 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 subdivided into 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 assign- ed 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 con- sists 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 5 6 11 11 11 12 13 13 13 15 16 17 20 20 20 20 20 22 23 24 25 25 25 25 25 26 26 26 30 33 34 34 34 34 34 34 35 40 44 45 45 46 46 46 47 49 50 51 51 56 56 56 58 59 59 59 59 60 60 60 60 61 62 62 62 62 63 64 64 64 64 64 64 65 63 67 68 69 69 69 68 69 60 70 70 7G 71 71 72 74 74 74 74 74 75 75 75 76 77 77 77 a3 a3 a4 a4 84 84 85 88 88 88 89 89 89 89 90 90 90 90 90 91 91 91 94 94 94 95 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- cent Marble Range and parts of the Pavilion hlountains. 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 parts ofthe 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 earliest geological 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 sea- sons 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 min- eraldeposits adjacent to the PacificGreat Eastern railaay between Lillooetand Prince George described a felv deposits in the present map area. A reconnaissance survey 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 north- ernpart ofthe Warble Range a plateau-liketopography has been pro- ducedbygently dipping limestone beds. As inthis aridclimate lime- stone is veryresistant to weathering the highestmountains of the map area are foundin this belt (hlount Bowman 7.360 feet).