BRITISH COLUMBIA DEPARTMENT OF MINES Hon. W.J. ASSELSTINE, Minister JOHN F. WALKER, Deputy Minister BULLETIN No. 11 Fraser River Tertiary Drainage-history in relation to Placer-gold Deposits (PART 11.) by DOUGLAS LAY 1941 VICTORIA, B.C.: Photooffset by CHARLES F. BANFIELD. Prinkr to the King's Most Excellent Majeay. 1941. CONTBNTS Page INTRODUCTION . 1 SmmY 3 TOPOGRAPEY 7 Fraser River Valley 7 MeGregor River 12 Neohako River 14 . ILLUSTiiATIONS Facingpage Plate I A. Pinnacle in Tertiary gravel of the inter-volcan-ic Fraser River at the BigBend, 10 miles north of Quesnel. .................................. 46 B. Differential weathering in intra-Upper Volcanics - sedimentslying between lava beds, near Macalister. ....................................................................... 46 Plate I1 A. Drag-linedredge of the North American Goldfields Ltd., Praser River 1 1/2 milesup-stream from AlexandriaFerry. ..................................................................................................................... 50 B. Placeroperation of H. Craig,Fraser River 2 milessouth of Quesnel 50 Keymap showing location of Figures 1, 2 and 3........................... 9 Fig. 1. ?lan of FraserRiver extending from WilliamsQuesnel. Lake to 21 Fig. 2. Plan of FraserRiver extending from Quesnel to Summit Lake .......................................................................................... 23 Fig. 3. Tlan of FraserRiver extending from Prince George to Monkman Pass. ...................................................... 31 Fig. 4. Plan of Nechako RiverDelta 37 Fig. 5. Plan ofTertiary the Mine. 49 FRASZR RIVZRTlRTIARY DRAINAGZ HISTORY IN RZLATION .TO .PLACZR-GOLI) DZTOSITS (Part11) 1NTROI)VCTION This report supplements 3ritish Columbia jjepartmentof nines Bulletin No. 3, 194.0, and continues the investigation the of Fraser River drainage as far as the Grand Canyon, 109 miles up-stream from Frince George. The river, confinedfor 120 miles up-stream from this point, emerges from the Rocky MountainTrenc'h through a wide local breakin the north-westerly continuity thht of great valley. Reference is invited to British Columbia Departmentof' Mines Bulletin No. 3, 1940, for much preliminary information whioh is not repeated in this report. For convenience the terms usedto desipate' the Fraser River at different periodsin its history, givenon page 2 of Bul.letin No. 3, 1943, are repeated here. The terms "pre" and "inter" are used ip the ordinary geologic sense. The term "pre-volcanic Fraselr' River" designates tne river antedating the volcanismex- presssd by the Lower Lavas. The term "inter-volcanic Fraser River" is applied to the river flowing between the two periods of volcanism expessed respectively by the Lower Lavas and the Upper Volcanics. The term "intra-Lower Lavas Fraser River" is applied .to the river flowing during or before actual cessat.ion of volcanism expressedby the Lower Lavas. The term "intra-Lipper Voloanics Fraseriiiver" is applied to the river flowing duringor before actual cessationof the volcanism expressed by theCpper Volcanics. Zxposures of sediments of the last-mentioned were found during the field work of 1940. To facilitate examinationof all rock-outcrops on both banks of the Fraser River, investiration during 1943 was made by outboard-enginad motor-boat, between Macalister and the Grand Can- yon. The XcGregor iiiver and Herrick Creek were ascended as far as the junction of Fontoniko Creek with the latter.'&ere deemed necessary mountains adjacent to the river were examined, and after completion of reconnaissance by boat, regions more remote from the Fraser River adjacent to its large tributary, the Nechako River, were explored. Although this report does not deal with the Pleistocene drainage-history of the Fraser River, it was found necessary to devote some time to study of Pleistocene features to decipher Tertiary drainage-history. -1- Nostelevations mentioned were determined. by altimeter, the instrument being checked as frequently as practicable bycomparison withGeodetic Survey monuments at Prince George,Stratnnaver and 2uesnel. .In some casesthe context renders clear that elevations givenare those determined by the Department of Lands. It is desired to tenderthanks to C. C. K.ellyof the British ColumbiaDepartment of Agriculture,in charge of thesoil survey of a large area centerinc in ?rinceGeorga, for kindassistance ex- tended in various ways. Thanks are also due 3. IIobe and X. Framstatfor timely and invaluable assistance in navigating the difficult waters of Herrick Creek. Assistance in the field was renderedby Alan R. Smith and Lorne 2. Rowebottom. -2- A summary of the more important facts ascertained in the course of field work during1940 is g.ivenbelow. Detailsfollow in the body of thereport. .. (1) On theeast bank of theFraser River, somewhat over 3 miles north of Shelley,exposures of sediments(conglomerate.and sandstone) of thepre-volcanic Fraser River, occur in the Canadian NationalRailway-cutting and .extend below river-level. Eo fossils werefound inthese sodiments and the state of preservation of silicifieddriftwood proved.too poor for identification. The hi&h degree of lithification of thesediments suggests that their age is early Zocene or possiblyeven iate Cretaceous. This exposure is deemed of high critical value as it proves not.. only . the far northern early deep incision accomplished by the pre-volcenic Fraser River, but also the exact position of the river at tnat t ime . (2) This examinationdisclosed a wide brea!c in the Rocky MountainTrench near the Grand Canyon. At thispoint the southern wall of the Trenchends abrupt1y;while the northern wall coztinues but a few miles farther to terminate near Sinclair Mills at the great gap about 12 mileswide, caused by thejunction of the McGregcr RiverValley with theFraser River Valley. This break in the continuity of the Rocky XountainTrench continues until it is restor.ed to norm1 proportions at the junction af the valleys of the Paclc.andFarsnip Rivers, from when-ce it continues north.- westerly for many miles.After flowing confined within the Rocky MountainTrench for 120miles, the.Fraser RivSr emerges from it . .just above the Grand Canyon; and then'flows over the eastern edge of the Nechalco Plateau.. The river makes a bend at its most north- erlypoint by reason of thesurrounding structural features. The Arctic-Pacific Divide, but a few miles west of the McGregor River Valley, trends directly across the direction of flow of the river up to this point, and it is apparent that at no time in its history canthe Fraser River have continued to flow in a north-westerly directionpast the mouth of the KcGregor River. It is, hoxever, quite possible that there hasbeen a reversal of-flow of t:he waters in that part of the Fraser River down-streamfrom the mouth of theMcGregor.River, as sugEestedin (4) below. (3) . In thecourse of thisexamination, an intrusive .tongue of diorite was discovered at the north-western endof the jearpaw Mountains,,north-east of Sinclair Mills (Fii.3). This' range of mountainshe.re forms the northern wall of the Rocky ?lounta.in Trench,the north-we'sterly continui,ty of which is at this point interrupted by a .wide breakas rnentioned in (2.) above. The occur- rence of intrusive rocks in the northern wall.of. the Rocky Mountain Trench ani north of Eaglet Lake indicates the far eastward extent of theeffects of theJura-Cretaceous revolution. The presence of intrusiverocks at thesepoints, also suggests the likelihood that the Rocky MountainTrench and some parallel trenches in this region were developed prior to the Laramide revolution and gradual uplift of the Rocky Mountains.Pronounced trellis-typedrainage is ex- hibitedlocally to the south-east of the McGregor River(Fig. 3). (4) The evidenceobtained suggests that drainage in thesouth- westerly flowing parts of Berrick Creek and'the McGregor River has beenreversed (these waters are virtually oneand the same stream occupyingthe same valley, and are referred to in this report as the "SerricL"McGregor" River). In lateCre-taceous time; possibly extending to early Tertiary time, these waters were likely the headwaters of the Murray River, then flowing north-easterly through the site of theMonhan Pass in the Rocky Mountains.Quite possibly the r'raser River at the great bend at its most northerly point nowoccupiesthe deepened bed of a former tributary of the Herrick-McGregor River,then flowing in the opposite direction. Reversal of drainage was due to two causes:(a) Cap-ture of its headwaters by the ra~idly-rejuvanating southerly-flowing Fraser River(evidence cited in (1) above), nlhich sappedthe power o'f the IIerrick-McGregorRiver to maintain its flow,as did the Peace River,against (b) the slowupheaval of the Roclcy Kountainsduring the Laramide revolution in early Tertiary time. (5) Supported by strongalthough indirect evidence, it is postulated that in late Cretaceous time the ancestral Fraser Riverdrainage was northerly.&ether this drainage was mainly by the Peace River and partly by the Herrick-McGregorRiver, or partly by thePeace Ziver and mainly by the Berrick-McGregor is conjectural, but the result of this examination favours the adop- tion of the latter hypothesis. (6) Reference(Fie. 2) will renderclear, that the Fraser River makes a wide detour to the west between %kites Landing and tie mouth of theCottonwood.River. Exposures leave no doubt as tothe reason. The pre-volcanicsoutherly-flowing Fraser River, intra-LowerLavas Fraser River and the inter-volcanic Fraser River,