TREK Mapping Project Year 2: A Structural Framework for the northern Interior Plateau J.J. Angen1, C.J.R. Hart1, J.M. Logan2, R. Kim1,M. Rahimi1 1Mineral Deposit Research Unit, The University of British Columbia, Vancouver; 2Consulting Geologist

126°W 125°W 124°W 123°W

( ( a) Preliminary Bedrock Geology of the TREK Area IV. CRETACEOUS DEFORMATION b)

( ( 4 a)

4

( Quesnel WMC4 4 ( ( 4 350000 E 375000 E 400000 E 425000 E Stikine ( The Jurassic strata south of the Tatuk Fault were deformed during ENE- ( ( Terrane 125°30'0"W 125°0'0"W 124°30'0"W 124°0'0"W

6000000 4 ( ( Terrane 4 4

Francois !( & ! VOLCANIC AND SEDIMENTARY ROCKS OTHER FEATURES ( 5Prince 4 !(!(NIT!(HI MOUNTAIN Vanderhoof 54°0'0"N and WSW-vergent fold and thrust deformation (Figure 5a). This is likely

4 4 Lake !

( 4 !( !(!( Miocene to Holocene City

( 4 !(!( 4 !( !( 4

4 !(

54°N Plutonic 4

4

4 George Anahim Volcanics

( ( Pinchi Fault Road

Fraser-Straight Creek Fault 4

4 4 !(

4 !( !( !( Basanites to basaltic trachyandesites and trachytes 4

4 ( River related to the 700 km long fold and thrust belt that anks the east side of

? ( 4 450000 E

4 4 4

4 4 Miocene to Pliocene 4 4 ( Lake

4 4 4 4

4 ( 5975000 N Cabin 5975000 N

4 4 Chilcotin Group 4

4 4

I. INTRODUCTION 4 Lake 4 4

4 4 the Coast Belt (Rusmore and Woodsworth, 1991; Evenchick et al., 1991;

VMC 4

4 Olivine basalt lava flows

( 4 4

4 4

4 4 Mineral Occurrences

4 4 4

4 4

GF 4 Eocene to Oligocene 4

4 4 !(

Tatuk Fault ( 5950000 4 4 4

4 4 Porphyry Cu-Au: vein, breccia

Bobtail Shear Zone 4 ") 4 4

4

The Targeting Resources through Exploration and Knowledge 4 4 Endako Group !( Schiarizza et al., 1997; Rusmore et al., 2000). Field structural evidence and 4 4

4 4 Porphyry Mo (Low F- type) 4 4 4 4

4 (

4 Basaltic andesite and andesitic lava flows )" 4 4 4 4 4

4 4 Epithermal Au-Ag-Cu: high sulphidation

4 *# 4

4 4 4

(( 4 4 ") 4 4

4 )" 4 ") 4 Eocene

4 Epithermal Au-Ag: low sulphidation

4 4

project is a multidisciplinary project aimed at bringing 4 4 ")!(") 4

HOLY CROSS 4 ' geophysical anomalies exhibit a curvature from NNW-SSE to WNW-ESE

4 ( ") 4 ") 4 Ootsa Lake Group Subvolcanic Cu-Ag-Au (As-Sb) 4 4

Stikine 4 4 53°30'N 4 4 4 XW

4 Rhyolite to andesite flows and volcaniclastic rocks Polymetallic veins Ag-Pb-Zn+/-Au 4 ( 4 4

4 4 4 Frank Lake

") 4 4 XW Carbonate-hosted disseminated Au-Ag

( 4

together a variety of datasets in order to improve our ( 4 Upper Cretaceous

4

!( 4 +$ 4

4 pluton with proximity to the Tatuk Fault (Figure 2; Figure 3b,c). The

Terrane 4

4 !( 4 Cu skarn 4

4

4

4 4 4 Kasalka Group +$

4

4 Kenney Dam FSR 4 Fe skarn

4 4 4 4 4 4

4 4 Hornblende andesite #* 4 4 Ultramafic-hosted asbestos

5900000

understanding of the geological framework and mineral 5950000 N 4 4 5950000 N

4 predominantly volcanic and plutonic rocks to the north of the Tatuk Fault

4 Crystal-lithic tuff

4

4 Cache 4 GF 4 Lignite 4 4 c)

") 4 Vitric tuff

4 Volcanic redbed Cu 4

4

4

( 4

4 4 4 4

4 4 4 Grizzly

( 4

Creek 4 4 Flow-laminated rhyolite

potential of the Interior Plateau. In particular, little is known 4 pluton 4 4 appear unaected by the mid-Cretaceous deformation so it behaved as a

4 ( 4

( 4 4 Undifferentiated andesite to rhyolite flows and volcaniclastic rocks

") 4 123°30'0"W

4 4

4

53°N 4 4

( Terrane 4 Lower Cretaceous

4 4 4 4

4 Figure 5: a) Example of fold and thrust

4 ") 4

4 4 4

about the structural framework of this region. This region 4

") 4

4

4 Skeena Group

4 sinistral fault to accommodate the shortening within the basin. The 4 4

4 4

4

( 4 4

4

4 4 4

4

Yalakom Fault 4

4 4 Chert- and quartz-rich sandstone and conglomerate deformation in thin bedded mudstone and

4 4 4

4 ( 4 4 4 4 475000 E

4

4 4

4 Upper Jurassic

4 4

4 4

4 4

encompasses southern Stikine terrane, Cache Creek terrane, 4

( 53°30'0"N ") 4 Nazko-Redstone belt, along the eastern margin of this fold and thrust tu of the Entiako Formation, looking 5850000

4 4

4 4

4 4

4 Nechako Formation

4 !(

4 ( ( 4 4

4

( 4

4 ( 4

4

4 4 Pyroxene- and hornblende-phyric basalt

4 southeast; b) Bedding measurements within

4 4 4 4

(

Knewstubb Lake 4 4

4 Bobtail Shear Zone

4 Natalkuz Fault 4

( 4

Cadwallader terrane, and several metamorphic complexes ( 4 (

4 Middle and Upper Jurassic

4 belt, is interpreted to have formed similar to the Sustut Basin to the north.

5925000 N 4 4 4 4 4 ") 20 km of the Tatuk Fault; c) Bedding

( 4 4 Bowser Lake Group ( (

4

4

Nechako Reservoir 4 4

( Tatuk Fault

4 ( 4 4 PICKLE Chert pebble conglomerate, sandstone, siltstone and mudstone

4

Cadwallader( 4 measurements more than 20 km from the

4 4

4 (

4 (Figure 1). These are extensively mantled by 4

4 TLMC ? 4 *#

( ( Deformation continued at least until the Campanian as indicated by 4 ( Stikine terrane 4

LIESEGANG 4 Tatuk Fault. 52°30'N (

Terrane( ( 125°30'0"W 4

( CHU Lower and Middle Jurassic 4

4 !( 4 Sinkut Detachment

volcanosedimentary overlap assemblages and thick glacial ( ( ( Hazelton Group ") !( 4 palynology of well logs showing Albian to Cenomanian strata on top of CH 4 CPC ( 5800000 4 ( 350000 E Fawnie pluton 4 Naglico Formation

( ( Dome ( 4 Pyroxene-phyric basalt, lapilli tuff and sedimentary rocks CAPOOSE ( 4

till. Publicly available aeromagnetic and gravity data have 4 Capoose Campanian strata (Riddell, 2011). ( ( 4 4 4

( Entiako Formation

4

4 ' 4

pluton 4

( 4

4 ( 4 (

+$ 4

4 Crystal-lithic tuff

4

4 4

4 (

4 Red tuff 4

been integrated with bedrock mapping to develop a 4

4

4 4

4 ( Red dacite

300000 350000 400000 450000 500000 5900000 N 4 V. EOCENE DEFORMATION 4 ") Blackwater 4 Liesegang basalt

Kluskus Blue FSR 4

4 4 ( structural framework for the northern Interior Plateau. This Prince George Access Rd 4 !( Undifferentiated sedimentary and bimodal volcanic sequence

4 4

Malaput FSR 4 !( 4 !H !( 4

") 4 G 4 Eocene deformation was characterized by extension that can be separated into two phases. The

BLACKWATER ( !( Telkwa Formation

") 4 4

4 !( Laidman ( 4

4 Rhyolite to basalt flows and volcaniclastic rocks 4 4

4 4

new framework outlines several major faults that were batholith BLACKWATER SOUTH( 4 4 125°30'0"W !( 4 4 Undifferentiated 4 (

4

4 early phase of nearly E-W extension is recorded by NW-SE striking dextral faults, including KEY WEST 4 4

( Rhyolite to basalt flows and associated volcaniclastic rocks Continental

4

4 4 4

325000 E ") ( 4 Arcs

previously unidenti ed. These faults, in part, controlled the ")!( 4 4 ( Triassic

KEY 4 4

!( 4

4 OIB (

4 4 Limestone 4 reactivation of the Tatuk Fault, and N-S striking normal faults, including reactivation of some

4

( 4 4 4

HAVANA Blackwater 4

4

4 Cache Creek terrane 4 ( 4

4 development and inversion of the marine Nechako Basin. 4

4

pluton 4 ( !( XW 4 4 Permian – Triassic

4 4 3TS 4

4 4 mid-Cretaceous thrust faults (Bordet, 2014). It accompanied eruption of the Ootsa Lake Group ( ( Capoose 4 Metasedimentary rocks and basalt 4 4 4 4 4

Kluskus 4 4

4 Vancouver stock 4 ! 4 Serpentinite 4 4 4 Nazko

!H 4 4 4 4

4

4 4 Ootsa FSR 4 (Bordet, 2014) and exhumation of the Tatla Lake Metamorphic Complex (Friedman and 4

4 4

Victoria 4 4 4 PLUTONIC ROCKS 4

4

!H 4

4

4 4

4 4 Eocene Th/Yb E-MORB

4

4

4

4 4 4 4

4 Quanchus Plutonic Suite Armstrong, 1988). The late phase represents NW-SE extension recorded by N-S striking dextral 4 4 4 4

Figure 1: Location of the study area with tectonic domains and major structures based on a combination of 4

4 4 4

4 Biotite-hornblende granodiorite to tonalite Oceanic 4 4 4

4 MORB-OIB

4 4 4 Arcs 4

4 Assumed Eocene mafic intrusions inferred from aeromagnetic data

4

4 4

British Columbia map compilation, airborne magnetic and gravity data. Some of the structures presented 4 4 Array

4 4 faults, NE-SW striking normal faults, and exhumation of the Vanderhoof Metamorphic Complex

4 4

4 Late Cretaceous

4

4 4 4 4

here have not previously been documented. The red line corresponds to the extent of the TREK 4 4 4

4

4 Blackwater Plutonic Suite

4 4

4 4

4

4 4

4 4 4 Biotite-hornblende quartz monzonite to monzogranite

4 along the Sinkut Detachment (Figure 2a; Wetherup and Struik, 1996). It is assumed that the aeromagnetic survey. TLMC - Tatla Lake Metamorphic Complex, VMC - Vanderhoof Metamorphic Complex, 4 N-MORB

4

4

4 4

4 Plagioclase-phyric diorite

4 4

4

4

4 4

4 4

4

WMC - Wolverine Metamorphic Complex, CPC - Coast Plutonic Complex. 4 Jurassic to Paleogene

4 4

4 4

") 4 4 4 Bobtail Shear Zone accommodated some amount of dextral shear at this time given the current 4

BAEZ 4

4 Coast Plutonic Complex

4 4 4 4

ITCHA - 4 Diorite to granodiorite related volcanic rocks

4 4

4 CLISBAKO 4 4 4 ")

ILGACHUZ PARK 4

4 4 4 4

4 Late Jurassic to Early Cretaceous 4 475000 E

4 juxtaposition of geological units and its orientation parallel to other late Eocene dextral faults.

4

4 4 4 Excluded from 2013 Airborne Magnetic Survey 4 4 123°30'0"W

b) 4 Francois Lake Plutonic Suite 4

4

a) 4 4

4 4 Biotite monzogranite to hornblende-biotite granodiorite Native Cu 4

II. JURASSIC STRATIGRAPHY AND MINERALIZATION 4 4

4

4 4 Nb/Yb Yalakom Fault Early and Middle Jurassic Eruption of the Endako Group accompanied development of this later phase of extensional

4 4

4 4

4 4 4

Continental 4 Stag Lake Plutonic Suite 4

4

The upper Hazelton Group volcanosedimentary sequence is locally 4 4 450000 E Quartz monzonite to tonalite Arcs 4 Figure 6: Endako Group samples plotted on

4 deformation, with the Natalkuz Fault locally forming a boundary for the basalt (Figure 2a). The 4 4

OIB 4 4 4 Triassic to Jurassic 4 4

4 4 4 N the Th-Nb proxy diagram of Pearce (2008, 4 Brooks Diorite Complex

4 4 4 4 comprised of the Entiako and Naglico formations (Diakow et al., 1997). The 4 124°0'0"W

4 4 4

4 Variably foliated gabbro to monzonite Endako Group geochemistry shows evidence for melting of an enriched mantle source, 4 4 4 2014). The samples lie along a vector

4

4 4

4 4 4 !( 4

4

!(4 4

4 425000 E 4 METAMORPHIC ROCKS indicating variable contamination of an

stratigraphically lowest of three new units identi ed at the base of the 4

4 4 consistent with an extensional setting (Figure 6). Anahim Lake ! 4 0 5 10 15 20 25 Jurassic to Cretaceous

4 original E-MORB source with crustal material. 4 52°30'0"N Tatla Lake metamorphic complex Entiako Formation, the Liesegang Basalt Unit (Figure 2a) exhibits 4 kilometres Mylonite and migmatitic gneiss Th/Yb E-MORB 4

4 Triassic to Jurassic !( 400000 E Oceanic c) geochemical similarities to the crustally contaminated rift related basalts of Vanderhoof metamorphic complex Arcs MORB-OIB Orthogneiss and schist VII. DISCUSSION Array ( ( ( ( ( ( ( ( Thrust fault, approximate / inferred / interpreted from geophysics / concealed the Iskut River Formation (IRF) (Type 2 of Barresi et al., 2015; Figure 3a). It 5800000 N The presence of a rift related basalt at the base of the upper Hazelton Group suggests that the Jurassic transtension recorded by N-MORB hosts volcanic redbed Cu mineralization at the new Liesegang and Pickle 375000 E 4 4 4 4 4 4 4 4 Normal fault, approximate / inferred / interpreted from geophysics / concealed 125°0'0"W the Tatuk Fault and Bobtail Shear Zone may have initiated in the Early Jurassic. This is in agreement with a proposed Early Jurassic showings (Figure 2a, 3b). The ubiquitous presence of of Liesegang rings in Undefined fault, approximate / inferred / interpreted from geophysics / concealed 125°30'0"W transtensional origin for the Bowser Basin to the north (Greig et al., 1991). A sinistral component to convergence is supported by this new basalt unit but not in the younger Naglico Formation or Nechako 325000 E Contact, defined / approximate / inferred / interpreted from geophysics relative plate motion models (Engebretson et al., 1985), and by paleomagnetic results (McCausiland, 2006). Similarly oriented Nb/Yb volcanics suggests that a large hydrothermal system was active shortly after structures bounding the Bowser Basin in the Spatsizi River area documented by Evenchick and Thorkelson (1995) may have a deposition. Figure 3: Characteristics of the Liesegang Basalt Unit and associated b) Reduced to Pole Magnetic Intensity (nT) c) Isostatic Residual Gravity Response (mgal) shared Early to Middle Jurassic history. Volcanic Redbed Cu mineralization: a) Th-Nb proxy of Pearce (2006; 2014). The Hazelton Group is conformably overlain by chert rich siliciclastic rocks of Liesegang Basalt samples plotted in orange. Group 1 and 2 basalts of the IRF are plotted in blue and green respectively. Grey arro shows contamination the Bowser Lake Group. This group includes a northeastward thickening IX. CONCLUSIONS 125°30'0"W 125°0'0"W 124°30'0"W 124°0'0"W 125°30'0"W 125°0'0"W 124°30'0"W 124°0'0"W trend towards average IRF rhyolite (modi ed after Barresi et al., 2015; b) 18 885 54°0'0"N Native Cu within an epidote, quartz, calcite vein at the Liesegang showing. wedge of coarse clastic rocks, potentially up to 1500 m thick in the northern 54°0'0"N The Tatuk Fault is a cryptic southeast striking normal fault that formed the northeastern margin of the Nechako basin in the latest This sample yielded >1% Cu and 7.05 g/t Ag; c) Intense Liesegang rings Nechako Range (Diakow et al., 1997). 625 9 Middle Jurassic. It may be cogenetic with the north striking sinistral Bobtail Shear Zone, consistent with NE-SW directed developed in basalt. extension, or overall sinistral transtension. The newly identi ed Liesegang basalt unit which hosts native Cu mineralization may 360 -1 be genetically related to initial opening of the Nechako basin. The Tatuk Fault is a major structural break that was reactivated 123°30'0"W 123°30'0"W 95 -10 during mid-Cretaceous compression Eocene extension.

-19 53°30'0"N III. MIDDLE JURASSIC DEFORMATION a) N -170 53°30'0"N C S 53°30'0"N 53°30'0"N

The newly identi ed Tatuk Fault (Figure 2a) was de ned by strong parallel -435 -28 125°30'0"W 125°30'0"W aeromagnetic and gravity anomalies (Figure 2b,c). It marks the northeastern b) REFERENCES: limit of Bowser Lake Group marine strata. When combined with the Barresi, T., Nelson, J.L. and Dostal, J. (2015): Geochemical constraints on magmatic and metallogenic processes: Iskut River Formation, volcanogenic massive sulfide-hosting basalts, NW British Columbia, Canada; Canadian Journal of Earth Sciences, v. 52, p. 1–20. northeastward thickening of the Bowser Lake Group, this suggests that the Bordet, E. (2014): Eocene volcanic response to the tectonic evolution of the Canadian Cordillera; Ph.D. thesis, University of British Columbia, 220 p. Buckingham, A. (2014a): Enhancement filtering and structure detection, magnetic data, MDRU TREK project; unpublished report, Fathom Geophysics, August 2014, 22p. Buckingham, A. (2014b): Enhancement filtering and structure detection, gravity data, MDRU TREK project; unpublished report, Fathom Geophysics, August 2014, 22p. Tatuk Fault was present as a basin bounding fault at least by the Middle 53°0'0"N 53°0'0"N 53°0'0"N 53°0'0"N Diakow, L.J. and Levson, V.M. (1997): Bedrock and surficial geology of the southern Nechako plateau, central British Columbia; BC Ministry of Energy and Mines, BC Geological Survey, Geoscience Map 1997-2, scale 1:100 000. Jurassic. Diakow, L.J., Webster, I.C.L., Richards, T.A. and Tipper, H.W. (1997): Geology of the Fawnie and Nechako ranges, southern Nechako Plateau, central British Columbia (93F/2, 3, 6, 7); in Interior Plateau Geoscience Project: Summary Figure 2: a) Bedrock geology map of the of Geological, Geochemical and Geophysical Studies, L.J. Diakow, J.M. Newell and P. Metcalfe (ed.), BC Ministry of Energy and Mines, BC Geological Survey, Open File 1997-2 and Geological Survey of Canada, Open File 3448, p. 7–30 The newly identi ed Bobtail Shear Zone (Figure 2a) is represented by a TREK area developed from geophysical Engebretson, D.C., Cox, A., Gordon, R.G. (1985): ERelative Motions between Oceanic and Continental Plates in the Pacific Basin. Geological Society of America,Special Paper 206, p. 1-59. interpretation, targeted bedrock mapping, Evenchick, C.A. (1991): Geometry, evolution, and tectonic framework of the Skeena Fold Belt, North Central British Columbia; Tectonics, v. 10, p. 527-546. linear aeromagnetic low which juxtaposes distinct domains (Figure 2b). It and compilation of previous mapping Evenchick, C.A. and Thorkelson, D.J. (2005): Geology of the Spatsizi River map area, north-central British Columbia; Geological Survey of Canada Bulletin 577, p. 276. Greig, C.J., Gehrels, G.E., Anderson, R.G., Evenchick, C.A. (1991): Possible transtensional origin of the Bowser Basin, British Columbia. In: Geological Society of America, Abstract with Programs, vol. 23, p. 30.Pearce, J.A. (2008): 123°30'0"W 123°30'0"W including Tipper, 1959, 1963, 1969; Diakow Geochemical fingerprinting of oceanic basalts with applications to ophiolite classification and the search for Archean oceanic crust; Lithos, v. 100, p. 14-48. corresponds to intensely deformed mylonite and gneiss (Figure 4a). Poles to foliation (n = 15) and Levson, 1997; Struik et al., 2007; and McCausland, P.J.A., Symons, D.T.A., Hart, C.J.R., and Blackburn, W.H. (2006): Assembly of the northern Cordillera: New paleomagnetic evidence for coherent, moderate Jurassic to Eocene motion of the Intermontane belt and Stretching lineations (n = 3) Yukon-Tanana terranes, in Haggart, J.W., Enkin, R.J. and Monger, J.W.H, eds., Paleogeography of the North American Cordillera: Evidence For and Against Large-Scale Displacements; Geological Association of Canada, Special Structural measurements include steep foliation and shallow stretching Bordet, 2014; b) Reduced to pole magnetic 52°30'0"N 124°0'0"W 52°30'0"N 124°0'0"W 500 um intensity with faults as dashed black lines 52°30'0"N ¯ 52°30'0"N Paper 46, p. 147-170. lineations (Figure 4b), consistent with strike slip shear. S Pearce, J.A. (2014): Immobile element fingerprinting of ophiolites; Elements, v. 10, p. 101-108. and folds as dashed white lines (modi ed 0 5 10 20 30 40 Rusmore, M.E. and Woodsworth, G.L. (1991): Coast Plutonic Complex: A mid-Cretaceous contractional orogen; Geology, v. 19, p. 941-944. 124°30'0"W 124°30'0"W It is postulated that normal shear on the Tatuk Fault and sinistral shear on the Figure 4: Characteristics of the Bobtail Shear Zone: a) Plane after Buckingham, 2014a); c) Isostatic resid- ¯ km ¯ Rusmore, M.E., Woodsworth, G.L., and Gehrels, G.E. (2000): Late Cretaceous evolution of the eastern Coast Mountains, Bella Coola, British Columbia; in Tectonics of the Coast Mountains, southeastern Alaska and British Columbia, For more information, contact: polarized light photomicrograph exhibiting s-c fabric indicative ual gravity response, faults and folds repre- edited by H.H Stowell and W.C. McClelland. Geological Society of America, Special Paper, v. 343, p. 89-105. 0 5 10 20 30 40 0 5 10 20 30 40 Schiarizza, P., Gaba, R.G., Glover, J.K., Garver, J.I., and Umhoefer, P.J. (1997): Geology and mineral occurrences of the Taseko - Bridge River area, B.C; Ministry of Employment and Investment, Energy and Minerals Division, 125°0'0"W 125°0'0"W Joel Angen, MSc, G.I.T. Bobtail Shear Zone may be coeval as they are both consistent with of north-striking sinistral shear; b) Stereonet showing structural sented as above (modi ed after Bucking- km km Geological Survey Branch, Bulletin 100, 292 p. 125°30'0"W measurements consistent with strike-slip shear. ham, 2014b). All maps were produced in 125°30'0"W Struik, L.C., MacIntyre, D.G., and Williams, S.P. (2007): Nechako NATMAP Project: A Digital Suite of Geoscience Information for Central British Columbia(NTS Map Sheets 093N, 093K, 093F, 093G/W, 093L/9,16, & 093M/1,2,7,8); [email protected] northeast-southwest directed extension. NAD 83 BC Environment Albers Projection. BC Ministry of Energy and Mines, Open File 2007-10. Tipper, H.W. (1959): Quesnel, British Columbia. Geological Survey of Canada, Map 12-1959; scale 1:253 440. Tipper, H.W. 1963): Nechako River, British Columbia; Geological Survey of Canada, Map 1131A; scale1:253 440. Tipper, H.W. (1969): Anahim Lake, British Columbia; Geological Survey of Canada, Map 1202A, scale 1:253 440.