GEOLOGY AND MINERAL DEPOSITS TULSEQUAH MAP-AREA, BRITISH COLUMBIA (104K) 1.(50-1971-6J44 Technical Editor H. M. A. RJCl! Critical Readers J. O. WHUL~R HNll R. B. CAMPBELL Editor D. W>UT1! Text printed OD Georgian Olfset Smooth Finish Set iD Times Roman with 20th Century captioos by CANADIAN GOVEI\NMENT PJuN'TTNG BUReAU Artwork by C,\JlTOCRAPHlC UNIT, GSC 201339 FIGURE 1. View looking 'outhwe'l from the Tohllon Highland ocro" Tohomenie lake to the inner range' of the Coo,1 Mountain<. GEOLOGICAL SURVEY OF CANADA MEMOIR 362 GEOLOGY AND MINERAL DEPOSITS OF TULSEQUAH MAP-AREA, BRITISH COLUMBIA (104K) By J. G. Souther DEPARTMENT OF ENERGY, MINES AND RESOURCES CANADA © Crown Copyrighls reserved AvailabLe by mail from Information Canada, OIlOWO, rrom Geological SOf"ey or Canada. 601 Boolh St., Ollaw" nnd tll the following Jnformalion Canada b()Qk~hops: HALl FA>.' 1735 Barringlon Slreel MONTREAL 1182 SI. Cnlherine SlreeL West OrT,\WA 171 S Ialer Slreel TORONTO '22L Yonge Streel WINNlPEG 393 Ponage Avenue VA1'JCOUV£R 657 GranvilLe Street or through your bookseller A depos\t copy or Ihis publicalion is also 3yailable ror reference in public libraries acros~ Canada Price: $3.00 Calalogue No. M46·362 Price subju.1 to c.hange wilhaut nOlice Tnformiuion Canada Ollawa. 1971 PREFACE Taku River was used as a route to the Yukon during the Klondike gold rush of 1898 and this led to extensive prospecting, but it was not until 1937 that any of the silver-gold showings discovered in the intervening years were brought into production. Declining metal prices resulted in the closure of the last producing mine in 1957, but in recent years extensive geophysical and geochemical surveys have been made by several major exploration com­ panies and new prospects have been discovered. The layered rocks of Tulsequah map-area comprise intensely folded and regionally metamorphosed Triassic, Permian and older strata, separated by a major unconformity from younger sedimentary and volcanic rocks. The western part of the area is underlain by granitic rocks of the Coast Crystalline Belt which were emplaced between early Mesozoic and Tertiary time. These varying lithologies are fully discussed in this report, the structural aod tectonic history of the area is outlined, and the mineral deposits are described in some detail. Y. O. FORTIER, Director, Geological Survey ofCanada OITAWA, December 19, 1967 ~U::\[OIR 362, -- Geo1og-ic nnd Erzlagerstiitte"n des Kartenblatts Tulscqui1h (I3ritisch-Kolumbiel1) Von Jack Gordon Souther Es wird ein Gebiet verformter und metamorphisiel'­ tet triassischer, permischer und alterer Schichten, weni­ g:er €:efalteter mesozoischer Ablagerungs- und Eruptiv­ gesteine und fruhmesozoischer bis tel'ti~irer Gl'anitge­ steine beschrieben. Silbel'- und Golderzlagerstiitten komrnen vor. MEMY AP 362· . reO,10nJ51 VI MeCTOpO)I<.lem-l51 110- "e3HblX V1CI<Onae\1hIX J<apTorpaqHlpoB8HHoro paHOHa TY_'ICeK~'a, 'SpHTaHCKa51 KOJlVMOI--I5I. ,Q>KeK r. C03ep. OrTIIChl8aeTcn p~t!OH .ue<l>op~li'lpOllaHHblx H ~eTaMoP<PH­ '1eCI<IIX TpllaCO·UI.IX, nepMCI<HX I1 flHLIX TOJlU!. [l MeH~wcil CTe­ neHlI CI<.'l<l,ll43TbIX ~'le303()~Cl<fIX OC;l:LO'IHLIX LI 113Ilepil(eHH~'X nopOll 11 rpaHHTHLIX nopOll OT paHHeMe3030~CI<Oro 110 Tperll4­ Horo BCI<a. BCTpe'-l3eTCSl .'IHHepaJIJI3<ll!lln cepe6p<l 11 30JlOTa. CONTENTS PAGE INTRODUCTION.......... .. 1 Location and access . 1 Previous geological work . I Field work . 2 Acknowledgments . 2 PHYSIOGRAPHY AND GLACIATION . 3 Physiography . 3 Landslides .. 4 Self-dumping glacier-dammed lakes , .. 6 Glaciation......... .. .. 8 GENERAL GEOLOGY... .. .. .. 10 Table of formations ". .. .. 11 Metamorphic rocks , ,,,,. 14 Map-unit 5 ,. 14 Map-unit A,, ,......................... .. IS Layered rocks . 15 Permian ,,,.. , . IS Triassic and older .. 16 Upper Triassic, , . 18 Stuhini Group ", .. 19 King Salmon Formation .. 21 Sinwa Formation . 22 Lower and Middle lurassic"" " .. 23 Laberge Group .. 23 Inklin Formation . 24 Takwahoni Formation .. 24 Upper Cretaceous and Early Tertiary............... .. 28 Sloko Group ,, .. 28 Late Tertiary and (7) Pleistocene .. 32 Heart Peaks Formation .. 32 Level Mountain Group " .. 33 PAGE PLUTONIC ROCKS , 33 Coast plutonic rocks. 34 Lower or Middle Triassic........................................... 34 Foliated quartz diorite. 34 Pre-Upper Cretaceous.. 36 Central plutonic complex....... 36 Cretaceous and early Tertiary................... 36 Younger quartz monzonite..... 36 Minor Intrusions 37 Post-Middle Jurassic................................. 37 Hornblende-biotite granodiorite................................... 37 Biotite-hornblende quartz diorite.. .. 37 Hornblende diorite................ 38 Augite diorite.... 38 Cretaceous 0) and Early Tertiary intrusions..................... 39 Felsite and quartz-feldspar porphyry.................................. 39 Basic and ultrabasic rocks......................... 40 Permian (?).... 40 Nahlin ultramafic body.................................................... 40 Other ultramafic rocks. 42 Gabbro and diorite............................................... 43 STRUCTURAL GEOLOGY... 44 Mid-Triassic and older structures............ 44 Nahlin fault........ 44 Folds............................................................................................................... 45 Upper Jurassic structures............. 45 King Salmon thrust fault.......................... 45 Folds........................... 47 Early Tertiary structures.. 48 TECTONIC HISTORy .. 49 ECONOMIC GEOLOGy........... .. 52 History of mining and p(Ospecting............................. 52 Geological associations of mineral deposits.................................................. 52 List of mineral properties.......... 54 INDEX . 82 REFERENCES .. 58 ApPENDIX 1. STRATIGRAPH1C SECTIONS .. 61 ApPENDIX n. FOSSIL LoCALITIES . 77 Illustrations PAGE Map 1262A TulseqiJah, and Juneau map-areas, British Columbia ..Tn pocket Figure View looking southwest from the Tahltan Highland across Tatsa- menie Lake to the inner ranges of the Coast Mountains Frontispiece 2 Devils Paw, elevation 8,584 feet.. .......... ...... .. ....... ....... ...... 3 3 Vertical air photograph showing rock drumlins, and landslide in Sheslay River Valley.... 5 4 Violent discharge of water from beneath the ice at the foot of Tulse- quah G lacier during the 1960 dumping of Tulsequah Lake.... ... ....... 7 5 Icebergs stranded on the bed of Tulsequah Lake after water drained under Tulsequah Glacier (background) during the 1960 flood......... 7 6 Vertical air photograph of a typicaL small valley glacier, near the southeast corner of the map-area................. ................. ......... 9 7 Index map showing the relationship of Tulsequah map-area to the major tectonic elements of northwestern British Columbia.............. 10 8 View looking northwest across Samotua River Valley...................... 16 9 Diagrammatic cross-section illustrating the stratigraphic relation- ship of the Stuhini and Laberge Groups and the King Salmon For- mation........................................................................................................ 18 10 Specimen of Inklin siltstone illustrating typical graded and convo- luted bedding.... 25 11 Takwahoni conglomerate.. 27 12 Plot of the compositions (volume per cent) of Mesozoic arenites from Tulsequah map-area..... 28 13 Distribution of Sloko and equivalent volcanic rocks and related intrusions in northwestern British Columbia and southern Yukon Territory.... 29 14 Photomicrograph showing glass shards surrounding accidental in­ clusions of andesite (dark grey) and quartz monzonite (clear angular fragments) in Sloko welded ash-flow.................................................... 30 15 Flat-lying Sloko breccia and welded ash-flows (hill in right back­ ground) resting on steeply dipping Takwahoni strata south of King Salmon Lake........................... 31 16 Proportions (volume per cent) of quartz, potash feldspar and plagio- clase in Coast plutonic rocks of Tulsequah map-area........... 35 17 Pyroxene-rich layers in Nahlin peridotite........ 41 18 Small decollement fold in interbedded siltstone and greywacke of the Inklin Formation.. 46 19 Schematic cross-section illustrating three stages in the evolution of Upper Jurassic structures and their relationship to the uplifted Atlin HorsL........................................................ 47 GEOLOGY AND MINERAL DEPOSITS OF TULSEQUAH MAP-AREA, BRITISH COLUMBIA Abstract The area comprises a deeply incised plateau, a narrow highland zone, and a mountainous area that is part of the Coast Mountains. The latter contains deeply incised valleys giving a local relief of 5,000 to 7,000 feel. Indications of Pleistocene glaciation are found on Slikine Plateau and indicate that the ice moved southwestward through Taku Valley to the sea. A gradual retreat of present-day glaciers began in the mid-nineteenth century. The layered rocks comprise intensely folded and regionally metamorphosed Triassic, Permian and older strata, separated by a pre-Upper Triassic unconformity from less folded Mesozoic sedimentary and volcanic rocks that have not been region­ ally metamorphosed. The western part of the area mapped is underlain by leucogra­ nite to pyroxene diorite of the Coast Crystalline Bell. These granitic rocks were emplaced between early Mcsozoic and Tertiary time. All consolidated rocks in the map-area are overlain unconformably by flat-lying late Tertiary and Pleistocene basalt. Three main episodes of tectonic activity culminating in mid-Triassic. Upper Jurassic