Energiand Mink& Division Geological Survey Branch GEOLOGY AND MINERAL DEPOSITS OF THE QUESNEL RIVER- HORSEFLY MAP AREA, CENTRAL QUESNEL TROUGH, BRITISH COLUMBIA NTS MAP SHEETS 93A/5,6,7, 11,12,13; 93B/9,16; 93G/1; 93W4 By A. Panteleyev, P.Eng., D.G. Bailey, P.Geo. M.A. Bloodgood, P.Geo. and K.D. Hancock, P.Geo. BULLETIN 97 Canadian Cataloguingin Publication Data Main entry under title: Geology and mineral deposits of Ule Quesnel Riva~ Horsefly mal area, central Qnesnel Trough, British Columbia NIS map sheets 93A15,6.7.11,12,13: 93BR. 16: 93W1; 93W4 (Bulletin ; 97) Issued bv Gecloeical- Survev Branch. Includes bibliographical references: p. VICTORIA ISBN 0-7726-2973-0 BRITISH COLUMBIA CANADA 1. Geology - British Columbia - Quesrvel Riva Region August 1996 2. Geochemistry - British Columbia - Qnesnel River Region. 3. Geology, Economic - British Columbia - Qwsnel River Region. 4. Mines and mined resources - British Columbia - Quesnel River Region. I. Panteleyev, Andrejs, 1942 U. British Columbia. Ministryof Employment and Investment m.Bhh Cohnnbia. Ceorogical Survey Branch. N.Title. V. Series: Bulletin (British Columbia. Ministryof Employmentandlnvesunent) ; 97. QE187.G46 1996 557.11'75 w-9-9 Frontispiece. Quesnel River, viewlooking east (upstream)from the QR deposit towards Quesnel Forks British Columbia iv Geological Survey Branch Ministry of Employment and lnvesnnent The Quesnel and Horsefly rivers traverse the north- the easternmostpart of the map area. Metamorph,c gradein westerly trending axis of the central Qnesnel belt, also the volcanic rocksis subgreenschist, consistent with burial known as the 'Quesnel Trough'. Since 1859 the region has metamorphism. Commonlythere is extensive chl'xitization been thesite of significantplacer gold prcductiou including of mafic minerals; zeolite and calcite fill arnyf;dules and some very large-scale mining operations.The identification occur in fractures in rocks throughout the regi.on. Some of Mocksource areas for the placer gold and definition of zones of epidote, chlorite, tremolite, calcite and minor the various mineral deposittypes in this regionare the main quartz represent locally developed propylitic alteration that objectives of this field study. Recent economicinterest has can be related to nearby intrusive activity. Copper-gold and been concentrated on the Mount Polley (Caritno-Bell)al- gold mineralizationis associated witha number cf the Ikiy kalic porphyry copper-gold deposit, the QR intrusion-re- lurassic diorite and zoned alkalic gabbro to syenite sl.ocks lated propylite-type gold deposit and the Frasergold and that are intrudedalong the axisof the volcanic arc at CPW (Spanish Mountain)auriferous quartz vein prospects intervals of about 11 kilometres. in the black phyllite basal map unit. Recent road building The predominantly fine-grained clasticbasil-fill rocks related to ongoing logging inthe area provides new bedrock structurally overlie a thin, tectonically emp1acf:d oc(:anic exposures in this region of otherwise sparse outcrop. crustal slice, the Crooked amphibolite, part of the Slide Studies in the map area, all within 'Quesnel Terrane', Mountain Terrane. It defines the terrane boundary with the confirm the presence of a regional synclinal structure older metamorphic rocks of the Barkerville Subterrane (a formed within a Triassic continent-margin basin. It was subdivision of Kootenay Terrane)to the east. Middle Juras- infilled first with Triassic sediments and then Triassic to sic and (?) younger polylithic conglomerate lenses and Jurassic volcanic rocks. Together these rocks constitutethe thinly bedded, fine-grained clastic rocks are preserved in Qnesnel Trough. The basal lithologic unitsconsist of mid- narrow fault-bounded wedges along the west--rn te:rrane Triassic siliceous rocks to mainly younger pelitic, thinly boundary of the Quesnelrocks with Cache Creek Terrane. bedded deposits with overlying, more massive volcaniclas- In addition, a sinuous band ofdistinctive conglomerates of tic sediments. The younger epiclastic units pass upward or possible Cretaceousage and fluvial origin overlaps Quesnel interfinger with Upper Triassic subaqueous volcanic depos-arc rocks along Quesnel Lake and Quesnel River iln the its, mainly volcanic flow and breccia units. They are over- central part of the map area. lain, in turn, by subaqueous to subaerial Lower Jurassic volcanic flow andpyroclastic rocks and overlapping Lower Eocene extensional faulting and magmatis~ndisrupted to Middle Jurassic sedimentary assemblages.The volcanic the Quesnel Trough following a period of dc:ep tropical weathering. Graben development, with attendant ash-flow rocks, and some Early Jurassic plutons, form extensivethe magmatic edifice that defines the medialaxis of the Quesnel eruptions and lacustrine deposits, characteriu:s thi!; time island arc. period. Hydrothermal activity, possibly related to subvol- The older, submarine lavas, mainly olivine and py- canic intrusions, produced tourmaline-sericite and propyii- roxene basalts of alkalic basalt to basaltic trachyandesite tic alteration (for example, the Megabucks copper-gold composition, are overlain by both subaqueous and subaerial, prospect). Elsewhereincipient epithermal quanz-carbonate dark green-grey to maroon-purple feldspathic lavas and veining is evident. Mid-Miocene and younger basalts cov- pyroclastic deposits of trachybasalt to trachyandesite com- ered parts of the Eocene grabens and older arc rocks of position, alternatively classified as rocks of the absarokite- Quesnel Terrane, and the tectonic boundary with Cache shoshonite series or shoshonite association. Many of the Creek rocks to the west, a high-angle fault. II plac:es the lavas are characterized by analcite phenocrysts. Modal basalt flows capolder Miocene fluvial systems that contain quartz does not occur in anyof the arc rock, the majority placer gold. Both preglacial and postglacial rivers flowing of chemical analyses reveal alkalic whole-rock composi- out of the metamorphic highlands to the east have trans- tions with characteristicnormative nepheline. ported additional gold. Perhaps more importantly, post- The basal clastic rocks now form a continuous structur-glacial rivers and some of the smaller creeks have 'locally ally complex black phyllite to metapelite unit along the redistributed and concentrated gold from oldcr placer de- eastern side of the map area. The rocks are well foliatedat posits. The main bedrocksources for the place~.goldappear deeper structurallevels but pass upwardinto weakly cleavedto be in the eastern part of the study area where ('?)Late rocks. They are overlain by thick panels of the extensively Jurassic quam veins occnr in the basal black phy1l:ite unit block faulted volcanic successions. The basal sedimentary near the terrane boundary of Quesnellia and the high-grade rocks are regionally metamorphosedto greenschist facies in metamorphic rocksof the BarkervilleTerrane. " Bullerin 97 V Brirish Columbia vi Geological Survey Branch Ministry of Employment rmd Znveslment TABLE OF CONTEIV'TS Page Page SUMMARY ........................................................................ v Unit Trc. Volcaniclastic Breccia................. 26 Unit Trd .Volcanic Sandstone and'Nacke .. 26 CHAFTER 1 Units TrJa And TrJb .Massive Flows. INTRODUCTION.............................................................. 1 Agglomerate. Tuffs. Pillow Basalts Project Location and Objectives................................. 1 and Mafic Dikes: Massive Project Summary and Publications............................. 1 Porpbyrytic Flows.Breccia and Access ......................................................................... 2 Tuff ...................................................... 26 Physiography............................................................... 2 Volcanicand Epiclastic RocksUnit . la............. 26 Previous Work ............................................................. 5 Volcanic Successions ofthe QuesnelArc ............... 27 Acknowledgments....................................................... 6 Basalts .Unit 2 ...................................... , ............. 27 Alkali Olivine FyroxeneBasalt CHAPTER 2 (Unit 2a) ............................................... 27 REGIONAL GEOLOGY................................................... 7 Alkali (Pyroxene) Basalt(Unit 2b .md Tectonic Subdivisions- Belts, Terranes and ClastsWithin Unit 2c; Unit 2c) ..........28 Tectonic Assemblages............................................. 7 Hornblende Pyroxene Basalt Regional Map Units and Map Patterns..................... 10 2d) and 2a/2d(Units ........................... 28 Barkerville Terrane (KOB).................................. 10 Analcite-bearing Pyroxene Basalt Snowshoe Group(PP) and Quesnel Lake 2e) (Unit .............................................. 28 Gneiss (DMqQ) Gneiss ................................... 10 Sedimentary Successions Capping Cache Creek Terrane (CC) 10 (CC) TerraneCreek Cache .................................. Unit 2 (Unit 2f)................................... 29 Cache Creek Group (MTC)GroupCreekCache ......................... 10 Plagioclase-lath Pyroxene-Phyric :Basalt Slide11 Mountain (SM)Terrane ............................. (Unit 2g).............................................. 29 Croaked Amphibolite@art of DTS) ............ 11 Polylithic 'Felsic' Breccias- Unit 3 ..................... 30 Quesnellia (Quesnel) Terrane (QN).................... 11 Subaerial Basalt- Unit 4 ...................................... 30 Harper Ranch Subterrane(DTH)