Alkaline Magmatism and Porphyry Cu-Au Deposits at Galore Creek, Northwestern

By James M. Logan

KEYWORDS: , mineralization, geochronology, compare with publi shed data and data from the Mount alkaline, porphyry copper-gold, Stikinia, Stuhini Group, Polley and Iron Mask suites; and Copper Mountain intrusive suite, copper, gold, magnetite, garnet, biotite, pseudoleucite, Central zone, Junction zone, · com pare these result s with those from other alkalic in- Butte zone, Southwest zone, Copper Canyon tru sive cen tres in the prov ince to es tab lish a met al lo - gen ic model that will direct ex plo ra tion. INTRODUCTION The Ga lore Creek camp is lo cated within the lower Stikine River region of northwest ern Brit ish Colum bia, ap- Por phyry de pos its and pros pects con tain ing cop per, proxi m ately 150 km northeas t of Stewart . The propert y is mo lyb de num and gold are im por tant his tor i cal con tri bu tors 75 km northwest of the Eskay Creek gold-silver mine, on to the me tal lic min ing in dus try in Brit ish Co lum bia. El e - the west side of the Cassiar High way (Fig. 1). It con tains vated metal prices and re cent ex plo ra tion suc cesses have twelve known Cu-Au occur rence s (MINFILE 104G/90 re newed in ter est in Brit ish Co lum bia’s cop per-gold por- through 99), that are distri buted across an area measuring phyry depos it s, in parti cu lar the alkalic Cu-Au porphyry 5 km by 4 km, and over a verti cal range of 1000 m. Three of class of de posit s (e.g., Galore Creek, Mount Polley and these, the Centra l, Junc tion and Southwest zones, contai n Afton-Ajax). These and cospatial calcalkaline Cu-Mo and resource s of 284 mil lion tonnes at 0.67% Cu. NovaGold Cu-Mo-Au porphyry depos it s formed outboard of ances tral Resource s Inc is current ly in an opti on agree ment to earn North Amer ica in is land-arc tec tonic set tings in the Late 100% owner ship of the propert y. In 2003, SpectrumGold Tri as sic to Early Ju ras sic. The alkalic Cu-Au de pos its in com pleted a 3000 m drill program to test for the presence of both the Stikine and Quesnel ter ranes are the products of a increa sed gold and copper grades in the Centra l deposit . At dis crete alkaline magmatic event (210–200 Ma) at the end that time, a new zone of Cu-Au miner al iza tion, the ‘Bounti - of the Triassic. ful zone’, was dis covered be neath the Centra l zone and has In order to better under sta nd the control s on miner al - spurred re-eval ua ti on of the Galore Creek propert y. iza tion and max i mize ex plo ra tion ef fi cien cies, a part ner - This report sum mariz es the regional geol ogy and pres- ship was struck be tween the British Co lumbia Min is try of ents some of the preli m inary field obser va ti ons from the Ener gy and Mines and explo ra ti on com panies with a direct 2004 field mapping. The Galore Creek com ponent of the in ter est in re fin ing the al ka line Cu-Au por phyry ex plo ra- Cu-Au Porphyry Project conducte d 1:20 000-scale field tion model (Abacus Mining and Explo ra ti on Corp., Im pe- mapping and sam pling of the west ern and southern por- rial Met als Corp., NovaGold Resour ces Inc.) as it ap plies to tions of the Galore Creek basin, where overbur den is thin the Iron Mask, Mount Polley and Galore Creek magmatic and outcrop expo sure is good. In addi ti on, regional -scale com plexes. Addi ti onal funding was obtained through a tra verses were started out side the main intru sive complex Rocks to Riches grant provided by the Brit ish Colum bia and traced stra tigra phy back into the Galore Creek basin, and Cham ber of Mines. The new infor m ati on pro- where po tas sium metasomatism has typ i cally oblit er ated vided by these studies will update the provincial da tabase pri mary protoliths. Mag netic sus cep ti bil i ties of in tru sive and mineral deposit models , and prom ote Cu-Au porphyry and vol canic units were measured to better uti lize the low- ex plo ra tion, all of which will ul timately lead to new dis cov - level airborne geophys i cal survey and aid map com pila - eries and resource s in the province . tion. A map of the intru sive com plex, togethe r with geo- The Ga lore Creek pro ject ob jec tives are to chem i cal an a lyt i cal re sults and pe trog ra phy, will be re- leased as a GeoFile. · de ter mine the spa tial and tem po ral re la tion ships be- tween the al ka line (feldspathoid-bear ing) vol ca nic rocks, min er al iza tion and the var i ous in tru sive phases PREVIOUS WORK of the alkalic Ga lore Creek magmatic complex; Forrest Kerr carrie d out the first geolog i cal mapping · char ac ter ize min eral zones lo cated pe riph eral to, and along the Stikine and Iskut rivers from 1924 to 1929, but it as much as 1000 m verti cally above, the Centra l zone; was not unti l 1948 that his data were publi shed (Kerr, · acquire a suite of samples from the var ious min er alized 1948a, b). Kerr proposed the origi nal Perm ian and pre- zones, as well as a suite of least altered volca nic and in - Perm ian subdi vi sion of Paleo zoic strata and, from his work tru sive rocks, for major and trace el em ent anal ysis, and in the Taku River val ley of the Tulsequah map area, he de -

Geo log i cal Field work 2004, Pa per 2005-1 237 Fig ure 1. Lo ca tion of the Ga lore Creek compo nent of the Cu-Au Por phyry Project in north west ern Brit ish Colum bia (NTS 104G). In set is a terrane map of northern Cor dil lera (mod i fied from Wheeler and McFeely, 1991), show ing the tectonostratigraphic set ting of the three study ar eas. Me so zoic ini tial stron tium iso pleths are from Armstrong (1988). Box on the right shows de tailed terrane re la tion ships for NTS 092I and the project area. fined the Late Tri as sic Stuhini Group, much of which un- the Late Tri as sic Stuhini Group and the Early Juras sic derli es the current study area. In 1956, a he li copter -sup- Hazelton Group. These are overlai n by Middle Juras sic to ported re con nais sance of the Telegrap h Creek map area early Ter tiary suc ces sor-ba sin sed i ments of the Bow ser was conducte d by the Geolog i cal Survey of Canada (1957, Lake and Sustut Groups, Late Cre taceous to Ter tiary con ti- Op er a tion Stikine). Jack Souther mas ter minded Op er a tion nental volca nic rocks of the Sloko Group, and Late Terti ary Stikine and produced 1:250 000-scale geolog i cal maps of to Recent bim odal shield of the Edziza and the Tele graph Creek sheet (104G), Tulsequah sheet (104K) Spectrum ranges. and 1:50 000-scale de tailed studies of Mount Edziza (1988, The Stikine Terrane is a com posit e allochthonous (?) 1992). Other work by the Geolog i cal Survey of Canada terrane made up of an amalgam ation of vol canic is land arcs (Fig. 1) include s that of Monger (1970, 1977), Souther ranging in age from late Paleo zoic through Early Juras sic . (1971, 1972, 1992) and Ander son (1984, 1989). Modern analogs include the Pacif ic island arcs from Japan A. Panteleyev carrie d out mapping in the im medi ate south through the Phil ippines , or New Guinea to New Zea- area of Galore Creek, in conjunc ti on with a study of the de- land. Recent studies suggest that the Stikine terrane devel - posit betwee n 1973 and 1975 (Panteleyev, 1973, 1974, oped adja cent to the ances tral mar gin of North America 1975, 1976, 1983). Geolog i cal mapping was com pleted at (McClelland, 1992; Mihalynuk et al., 1994; Gunning 1:50 000 scale in the Ga lore Creek area (Sphaler Creek and 1996) and that parts of the Pa leozoic Stikine as sem blage Flood Glacie r map sheets) in 1988 (Logan et al., 1989; Lo - are cor re la tive with and depositionally tied to Pa leo zoic gan and Koyanagi, 1994). Con cur rent Brit ish Co lum bia rocks of the Yu kon-Tanana Terrane. Depositional ties be - Geo log i cal Sur vey pro jects have com pleted 1:50 000-scale tween the Quesnel and Yu kon-Tanana ter ranes are also map cover age north and west of the Iskut north project area known and this, togethe r with the hook-like geom etry of in the Scud River, Yehiniko Lake, Chutine River and the 0.706 ini tial 87Sr/86Sr line around the northern end of Tahltan Lake map ar eas (Brown et al., 1996). Stikinia (Fig. 1), led Nel son and Mihalynuk (1993) and Mihalynuk et al. (1994) to propose a single arc model con - REGIONAL GEOLOGY sisting of the Quesnel, Yu kon-Tanana, Nisling and Stikine ter ranes. The study area straddles the boundary betwee n the Up per Tri as sic vol ca nic rocks and paired, al ka line- Intermontane Belt and the Coast Belt, and is un der lain calcalkaline Cu-Au depos it s extend the length of the Ca na- mainly by rocks of the Stikine Terrane (Stikinia), the wes- dian Cor dil lera (Barr et al. 1976). In the south, in ternm ost terrane of the Intermontane Belt (Fig. 1). The Quesnellia, the Nicola and Takla groups lie east of the strati graphic and plutonic framework of northwest ern Cache Creek Terrane. Far ther north, in Stikinia, the Stuhini Stikinia is sum mariz ed by Ander son (1993), Gunning and Lewis River groups lie west of the Cache Creek. There (1996) and Logan (2000). It consis ts of a Paleo zoic to Me- is lit tle differ ence in age, li thol ogy or chem istry of the Tri- so zoic sed i men tary and volcanoplutonic arc as sem blage as sic strata from one tectonostratigraphic terrane to the next that include s the Devo nian to Perm ian Stikine as sem blage, (Barr et al., 1976; de Rosen-Spence, 1985; Mortimer, 1987;

238 Brit ish Co lum bia Geo log i cal Sur vey Lo gan and Koyanagi, 1994; Panteleyev et al., 1996; Nelson sub di vi sions un der lie the Ga lore Creek ba sin, host mul ti ple and Bellefontaine, 1996). Un con formi ties sep a rate the Up- syenite intru sions and Cu-Au miner al iza tion that make up per Tri as sic Stuhini Group, which is mainly subm arine vol- the intru sive -volca nic com plex and are, in part, extru sive canic rocks, from the Ju ras sic Hazelton Group, which is equiva lent s of these subvolcanic intru sions . mainly subaerial vol canic and sedi m entar y rocks in north - The Lower vol ca nic sub di vi sion con sists of aphyric west ern Brit ish Co lum bia. A paraconformity sep a rates the and sparse hornblende and plagioclase-phyric flows, brec- Tri as sic from Early Ju ras sic vol ca nism in north-cen tral cia and that under li e exten sive areas south of Ga lore Quesnellia (Nel son and Bellefontaine, 1996). A sim ilar hi- Creek and consti tute most of the Middle to Upper Trias sic a tus is in ter preted at Mount Polley (Logan and Mihalynuk, country rock that hosts the Hickman batholith (Logan and this vol ume), where Lower Ju ras sic sed i men tary rocks Koyanagi, 1994; Brown et al., 1996). over lie the Tri as sic vol ca nic se quence; how ever, in south- The Me dial vol ca nic sub di vi sion is dom i nated by ern Quesnellia, the Early Juras sic volca nic rocks of the polylithic vol ca nic con glom er ate, wacke, , Rossland Group (Höy and Dunne, 1997) indi cat e a substa n - siltstone and fine tuffaceous rocks, and disti ncti ve but sub - tial east ward shift of vol ca nism from the Tri as sic mag matic or di nate pyroxene-phyric ba salt flow brec cias and dikes. axis. The clast com posi ti on is variable , includ ing pale green, Galore Creek is one of a num ber intru sion-re lated Cu- grey or purple, sparsely porphy rit ic plagioclase ande sit e, Au depos it s that devel oped in the Upper Trias sic to Lower pyroxene porphyry basal t, coarse-bladed plagioclase- Ju ras sic (?) volcanoplutonic-arc rocks of the Quesnel- pyroxene porphy rit ic ba salt and rarely limestone . The Stikine arc (Barr et al.; 1976; Nel son and Mihalynuk, clasts are angu lar to subrounded and consti tute from 15 to 2004). Sim ilar depos it s extend the length of the 80% of the rock in an arkosic matri x of sim ilar com posi - Intermontane Belt (Fig. 1). The Cu-Au de posit s are asso ci - tion. Graded sandstone and siltstone beds and local , thinly ated, in the south, with the Iron Mask batholith (Afton, lam i nated, black and or ange, cal car e ous argillite ho ri zons Ajax, and Crescent ) and Copper Mountai n intrusives (Cop- are interbedded with the conglom erate on the ridge west of per Mountai n, Ingerbelle); to the north, with the Hogem the head of Ga lore Creek. They are char acter ized by soft- batholith (Lorraine); and, in the Stikine Terrane, with Ga- sedi m ent slumping, fault ing and scour-and-fill struc tures, lore Creek intrusives (Galore Creek). and crosscut by sedi m entar y dikes (Fig. 2). Interlayered The de pos its at Galore Creek are hosted within shoshonitic subm arine volca nic rocks and coeval subvolcanic syenite intru sions of the Upper Trias sic Stuhini Group. It is a high-level, sil ica-undersaturated alka - line porphyry Cu-Au system of latest Trias sic age (210 Ma; Mortensen et al., 1995) that lies 38 km southwest of the large calcalkaline Cu-Mo-Au Schaft Creek sys tem.

STUHINI GROUP ROCKS

Up per Tri as sic Stuhini Group flows, tuffs, vol ca nic brec cias and sed i men tary rocks de fine a vol ca nic ed i fice cen tred on Ga lore Creek. Con tem po ra ne ous sed i men tary rocks flank the volca nic centre and, east of the South Scud River fault, a se quence of meta vol can ic brec cias and mas- sive volca nic rocks is intrude d by the coeval calcalkaline Hickman pluton. Stuhini stra tigra phy ranges in age from early Carnian to late Norian, based on ra dio metric dates (Ander son, 1983) and fos sil ages (Souther, 1972; Logan and Koyanagi, 1994; Brown et al., 1996). Volca nic rocks consti tute the bulk of the Upper Trias - sic stra tig ra phy at Ga lore Creek, and three differ ent calcalkaline vol canic suites are recog nized: a lower subalkaline hornblende-bearing basal tic ande sit e; a medial subalkaline to alka li ne augite-porphy rit ic ba salt; and an up- perm ost alka li ne orthoclase and pseudoleucite-bearing shoshonitic ba salt. Strat i fied, sed i men tary fa cies equiv a - lent units of the lavas were depos it ed on the flanks of the ed- ific e and contai n diag nos ti c fossil s. Carnian fossil s are pre- served within the lower sed im en tary pack age; the medial Fig ure 2. Well-lami nated calcar e ous argillite rip-ups in a chaotic and up per sed i men tary pack ages are char ac ter ized by lahar-con glomer ate unit. This unit marks the tran sition from vol - conodonts and bivalve s of Norian age (Logan and ca nic con glom er ates of the Me dial subdivision up ward into the al - Koyanagi, 1994). Rocks of the medial and upper vol canic ka line vol ca nic tuffaceous rocks.

Geo log i cal Field work 2004, Pa per 2005-1 239 with the dom inantl y epiclastic rocks are pyroxene por- and tuffaceous beds are char ac ter is ti cally po tas sium feld - phyry flow brec cias, pyroxene crystal tuff, and re worked spar rich, crossbedded and show both norm al and reverse vol ca nic stone con tain ing vit re ous pyroxene crys tals. grading. Graded bedding, inter preted to be norm al, indi - The medial unit general ly coars ens upwards. Lower units cates that the beds are over turned in places (Fig. 4). are thin, re pet i tively graded AE-turbidites. Higher in the Interbedded with the and tuffs are slump depos it s of sec tion are thick-bedded, cha otic to nor mally graded lahar- massive to cha otic maroon and sand contai ning cross- conglom erate and pyroxene-phyric lava flows. The bedded rip-up clasts and large angu lar breccia blocks of turbidites and paucit y of lava flows suggest a dis tal fine-grained tuff, some showing soft-sedi m ent plasti c de- depositional en vi ron ment. form ati on. Among the sedi m ents are polylithic con glom er- The Up per al ka line vol ca nic sub di vi sion is best ex- ates that con tain syenite clasts of the Galore Creek posed west of Copper Canyon. Volca nic rocks at the base of intrusives. Rare clasts of min er alized syenite por phyry oc - the secti on (Logan and Koyanagi, 1994, Fig. 12) are per va - cur within the po tas sium feld spar crys tal-rich lapilli tuff sively po tassium metasomatized and, in some places, may unit west of Copper Canyon. A grab sam ple from a 40 cm be intru sive in ori gin. The lower unit is cut by block of well min er al ized po tas sium feld spar pseudo- pseudoleucite, potas sium feldspar syenite por phyry bodies leucite porphyry syenite from a lapilli tuff bed returne d ex- and younger fel sic and diabase dikes. Overly ing the lower ceedingl y high copper , sil ver and gold values (6.53 % Cu, pack age are less al tered in ter me di ate tuff-brec cia, 0.21 g/t Au and 174 g/t Ag; JLO04-44-504, see Ta ble 1). tuffaceous wacke and rare, interbedded orange-we ather ing Orthoclase crys tal tuffs contai n large potas sium feldspar grit contai ning shale rip-up clasts. The unit fines and be - crystal s up to 1 by 2 cm in size. Subhedral to euhedral clots comes well bedded upward; the vol canic com ponent also and crystal s of detri tal bio ti te consti tute 2–5% of a num ber re flects a change to more alka line magmatism. The top of of crystal lithic tuff beds. The euhedral crystal s provide evi - the secti on consis ts of orthoclase and bio ti te crystal tuffs dence for a pyroclastic or igin for these rocks, as does the and fine epiclastics, lithic crys tal tuffs, lapilli tuffs and pres ence of accretionary lapilli. The crosslaminations, rip- polymictic vol ca nic con glom er ates that are interbedded up clasts, soft-sed i ment de for ma tion fea tures and pres ence with well-lam inate d siltstone and fine-grained sandstone of accretionary lapilli could be in ter preted as ev idence of a beds. A disti ncti ve accretionary lapilli hori zon was recog - base surge or airfall deposit . Ar gon-ar gon step heat ing of nized near the base of the sec tion (Fig. 3). The epiclastic bio ti te from this unit gives a pla teau age of 212 Ma (Logan and Koyanagi, 1994).

Fig ure 3. Accretionary lapilli hori zon marks the tran sition from a lower pack age of heterolithic brec cias and lapilli tuff up wards into po tas sium feld spar and bi o tite-rich airfall crys tal tuffs, west of Fig ure 4. Po tas sium feldspar–rich graded crystal tuff, west of Cop- Cop per Can yon. per Can yon.

240 Brit ish Co lum bia Geo log i cal Sur vey 40 15 4.1 8.2 3.7 2.1 1.5 1.2 8.9 1.3 4.1 3.3 2.3 4.3 4.1 0.4 3.3 Zr Mo 21.6 31.8 52.4 11.5 28.7 20.5 53.3 32.7 20.9 57.8 31.5 13.7 32.7 31.5 17.1 ppm ppm 0.01 TICP TICP 65 50 24 98 1.4 0.0 101 116 224 374 210 219 210 210 210 484 194 1 Zn 0.1 Mn 2333 1477 1478 1129 1344 1256 4766 3357 4333 2300 1324 1536 2333 1320 2300 ppm ppm TICP TICP 2 YTICAL 1.5 0.4 0.8 1.4 0.4 1.9 1.4 0.9 1.9 2.4 0.4 1.8 0.5 1.9 1.8 5.4 % 2.72 0.95 1.42 1.11 2.15 2.83 0.76 1.78 2.68 0.97 0.33 0.46 2.72 2.68 Yb 0.2 Mg INA ppm 0.01 TICP 16.77 14 20 20 9.8 3.2 7.9 1.9 9.4 1.5 4.2 1.5 Y Lu 0.29 16.6 21.6 16.3 15.5 19.7 19.7 0.14 0.23 0.08 0.29 0.25 0.15 0.32 0.35 0.31 0.05 0.29 0.07 0.32 INA ppm ppm 0.05 TICP b.d. 4 1 4 8 2 25 44 3.4 3.4 5.5 3.8 1 Li 11.7 78.5 52.4 13.1 78.2 12.1 17.2 18.7 33.7 11.7 12.1 INA b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. ppm ppm TION ANAL W TICP A 6 80 14 27 33 3.1 0.6 1.9 230 211 128 232 467 535 348 223 389 324 350 348 350 2 V 25.4 14.2 12.5 15.3 26.2 23.4 20.4 15.8 25.4 26.2 La 0.5 1166 ppm ppm TICP TICP 5 2.7 1.8 2.5 1.5 1.1 4.7 4.3 6.5 1.2 4.9 4.3 4.9 K % 5.69 13.0 4.99 5.73 5.45 7.37 0.37 3.65 4.62 5.54 5.63 5.12 6.07 5.69 0.09 5.54 0.5 N ACTIV INA b.d. b.d. b.d. U ppm 0.01 TICP . 1 1.3 7.4 0.5 0.3 0.9 1.8 0.4 1.4 0.8 1.7 1.4 1.5 1.5 1.3 0.4 1.4 Ti % Hf 0.26 ppm TICP 0.102 0.177 0.387 0.353 1.061 0.241 0.372 0.569 0.544 0.189 0.566 0.194 0.569 0.566 TICP 0.001 AREA 3 2.4 2.4 4.9 2.6 1.7 3.7 1.1 4.2 3.1 4.3 3.9 2.8 3.1 2.8 3.8 3.1 % NEUTRO 4.26 Th 10.2 Fe 2.93 2.38 2.96 6.96 4.16 6.61 3.14 4.26 4.16 0.2 INA b.d. ppm 0.01 TICP 29.35 27.06 10.78 AL 7 1 0.9 0.0 0.5 0.2 0.5 0.5 0.2 1.1 0.6 0.8 0.9 1.1 0.4 0.9 0.4 0.9 571 499 633 573 576 573 429 412 283 616 259 516 576 Sr Eu NT 0.2 0.5 1083 INA ppm ppm TICP E CREEK 5.8 72.1 2 1715 Sn Cu 1.2 2.1 0.8 0.6 0.8 1.1 308.7 0.8 1.4 1.3 0.9 1.7 0.4 0.8 3.8 31.6 0.01 10960 22920 31930 20800 16550 28330 65380 30030 28330 30030 ppm ppm TICP TICP 5955.1 5673.4 ALOR 9 4 51 24 20 29 13 35 50 24 13 43 35 43 2.8 3.2 0.8 2.5 0.8 2.6 2.5 3.9 0.4 1.2 2.3 0.5 1.2 1.9 2.6 102 5 20.5 Cr 0.1 3610 Sm INA INA ppm ppm 8 3 22 48 17 21 85 75 32 24 15 15 25 24 25 N THE G 4.6 4.3 4.1 1.5 5.5 6.9 7.3 6.3 170 Sc Co 0.1 0.1 AND INSTRUME 17.3 27.2 11.6 28.4 27.2 14.2 34.4 28.4 INA ppm ppm TICP Y 1 7 7 23 25 17 47 17 42 37 39 35 20 35 37 35 1.1 2.9 0.5 0.8 0.5 0.5 0.0 5.6 0.7 0.9 1.3 0.8 2.8 3.1 0.5 3 Sb Ce TR 11.5 INA ppm 0.02 ppm TICP 1 1 1 14 0.1 0.9 0.9 0.2 1.1 0.9 3.2 0.2 1.7 0.3 0.6 0.1 0.3 0.3 0.2 0.3 0.3 0.0 0.5 2.5 0.2 1.2 2.2 0.9 S % Cd 10.5 b.d. b.d. b.d. 0.01 0.02 ppm TICP TICP LLECTED I LLECTED 3.4 8.1 7.7 0.7 % 1.97 2.61 2.78 0.98 1.84 5.05 2.77 0.63 4.24 0.36 2.79 1.51 2.77 2.79 17.4 Rb Ca CTROME 0.01 ppm 143.6 122.5 173.5 179.4 165.4 179.4 TICP 133.6 118.3 116.7 172.6 119.4 189.5 165.4 TICP 5.2 4.4 4.0 0.3 0.5 0.2 2.1 0.1 1.3 4.1 0.1 0.8 4.2 0.1 4.1 4.2 2.4 6.7 2.1 LES CO Bi 24.8 17.3 29.2 30.4 29.2 30.1 53.2 37.4 30.4 Pb 0.02 ppm 0.01 ppm TICP 111.5 701.2 TICP b.d. b.d. 2.9 AMP 120 P 10.0 0.06 % 50 Ba 3700 1800 2800 2400 1100 1700 1900 2000 2400 2300 2100 1900 2100 INA ppm 0.106 0.118 0.091 0.248 0.018 0.241 0.248 0.074 0.173 0.116 0.603 0.052 0.234 0.241 TICP 0.001 b.d. – MASS SPE – MASS 5 5 12 73 37 85 12 3.9 0.7 2.5 6.7 1.2 9.9 4.9 6.4 OM S 140 177 370 159 211 2 12.3 12.3 69.1 31.8 20.9 Ni 2340 1700 1010 1080 1010 1080 Au 0.1 ppb INA ppm TICP 3007.1 8 5 18 18 11 15 11 18 17 18 15 23 21 15 4.5 6.2 3.7 5.8 2.2 9.3 TS FR 5 106 As 30.8 20.2 22.5 21.5 69.3 16.4 16.4 Nd 0.5 b.d. b.d. INA b.d. b.d. INA ppm ppm L D PLASMA 9 2 2.9 3.8 1.4 8.1 1.3 Al % 10.4 15.8 27.6 14.2 20.6 12.7 16.5 13.1 14.2 13.1 6.69 8.33 9.58 8.21 8.22 1.33 8.33 8.22 7.69 6.96 8.74 2.74 4.73 Nb ppm 0.01 10.01 TICP TICP 10.55 RESU 2.5 0.8 0.1 0.6 0.9 2.5 4.2 0.2 5.8 2 % 1.54 45.7 22.6 22.8 22.6 22.8 10.5 21.5 Ag Na ppm 0.325 0.779 0.293 0.395 0.627 0.545 1.257 2.276 0.247 1.519 1.289 0.019 1.257 1.289 173.5 TICP TICP 0.001 COUPLE s it Y ent Unit em n Lim VEL Method El Det' 6334481 6336104 6335717 6334033 6333162 6332348 6332841 6335648 6335394 6333693 6334451 6335648 6332841 6335648 6335394 6333693 6334451 6335648 Northing Northing 6334481 6336104 6335717 6334033 6333162 6332348 ng ng ti ti 349000 349638 349021 350854 352831 352744 357785 349619 349825 357170 356589 349619 357785 349619 349825 357170 356589 349619 349000 349638 349021 350854 352831 352744 Eas Eas P P 1. INDUCTI ber ber RP1 RP1 ABLE erence erence ff ff on Num on Num T ati ati Std. W JLO04-43-480 JLO04-43-480RE % Di JLO04-39-427 JLO04-39-434 JLO04-42-479-3 JLO04-43-480 JLO04-43-484 JLO04-44-497 JLO04-44-504 JLO04-43-480Rep St JLO04-32-325 JLO04-34-355 JLO04-35-375 JLO04-36-403 JLO04-44-504 JLO04-43-480Rep Std. W JLO04-43-480 JLO04-43-480RE % Di JLO04-35-375 JLO04-36-403 JLO04-39-427 JLO04-39-434 JLO04-42-479-3 JLO04-43-480 JLO04-43-484 JLO04-44-497 St JLO04-32-325 JLO04-34-355

Geo log i cal Field work 2004, Pa per 2005-1 241 Pseudoleucite trachyte breccia flows crop out on the and I-3 are only exposed in drillcore. Due to their intens e ridge betwee n the Anuk River val ley and the head of Ga lore hy dro ther mal al ter ation, they have been in ter preted as the Creek (Fig. 5). The tuffs consis t of a sequence of orthoclase caus ative intru sion for the main stage of copper miner al iza - crys tal tuffs and crys tal-lithic tuffs and flow-banded sills or tion (Sillitoe, 1991a, 1991b; Enns et al., 1995). The I-3 out - welded tuffs. The rocks are potassically altered and cut by a crop in lower Dendrit ic Creek could not be substa nti ated. I- pro nounced and strong pen e tra tive de for ma tion that has 4 is the most com mon intru sive in the southern part of the produced foli ated and schistose rocks. The north-trending deposit . It is a medium dark grey porphyry with 10–20% extent of these potas sium-rich volca nic units is evi dent on white stubby orthoclase pheno crysts (5–20 mm in length) the po tas sium ra dio met ric im age de rived from the low- and rare euhedral pseudoleucite pheno crysts up to 5 cm in level air borne geo phys i cal sur vey (Yar row and Tay lor, diam eter (Fig. 6). The matri x to I-4 is a mixture of fine- 1990). grained orthoclase, bi oti te and chlorite. The re main ing phases are con sid er ably less altered, ORTHOCLASE PORPHYRY SYENITE cross cut min er al iza tion and are con sid ered to be postmineral. Most of these phases were de fined in drillcore The Ga lore Creek magmatic complex is lo cated in the from the Centra l zone, where cross cutti ng rela ti onships head wa ters of Galore Creek. It comprises a se ries of could be observe d and project ed betwee n holes. In the orthoclase-por phy ritic syenite in tru sions that in trude co- field, the most com monly encoun ter ed phases are the me- eval Up per Tri as sic Stuhini Group volca nic rocks and re- dium-grained equigranular syenite (I-8), an inter growth of lated sedi m ents. At least 12 main equigranular and orthoclase, hornblende and epidote and rarely 2–5 mm orthoclase porphy rit ic feldspathoid-bearing syenite intru - orthoclase pheno crysts; and the medium -grained sive units can be identi fied and have been de scribed (Enns orthoclase syenite megaporphyry (I-9a and I-9b), which is et al., 1995). equiva lent to the epidote syenite megaporphyry of Allen et The early in tru sive suite is premineral to intermineral al. (1976) and is the most abundant intru sive phase at Ga- and include s pseudoleucite por phyry and megaporphyry lore Creek. It forms thick (up to 50 m) subhorizontal dikes dikes (I-1 and I-2), grey syenite por phyry (I-3), dark that dilute the ore in the Cen tral, North Junc tion, Butte and syenite porphyry (I-4a, I-4b), and dikes of fine-grained West Rim zones. It is char acter ized by 10–30% euhedral orthoclase syenite megaporphyry (I-5). The early suite is orthoclase megacrysts, 10–30 mm in length, in a medium to exposed in the south part of the com plex. Intrusives I-1, I-2 rarely coarse-grained matri x. Chlorite and bi oti te pseudo-

Fig ure 5. I-4 por phyry syenite, show ing stubby orthoclase pheno - crysts and rare euhedral pseudoleucite pheno crysts, south ern part Fig ure 6. Pseudoleucite trachyte breccia flow on the ridge between of the Cen tral zone. the Anuk River Valley and the head of Galore Creek.

242 Brit ish Co lum bia Geo log i cal Sur vey morphs hornblende, and variable amounts of epidote and al ter ation. This as sem blage con sists of per va sive white garnet charac ter ize the unit. I-9b can be disti nguishe d from orthoclase, coarse bi oti te, garnet, anhydrite, di opside and I-9a in hand spec im en by the pres ence of coarse plagioclase ap atite (Fig. 8). The calcic-potassic al ter ation is cen tred and magne ti te in the matri x and com monly very large above the magm atic brec cia in Den dritic Creek at the core orthoclase pheno crysts (up to 20 cm). I-9a is also typi cal ly of the Cen tral zone and is in ter preted to have ema nated more potassically altered and py ritic. I-11 is a medium- from this cen tre. A late, lower temper ature (?) al ter ation grained, equigranular, grey to brown inter growth of (SAC), char acter ized by an as semblage of seri cite, orthoclase, bi oti te and pyroxene, with sparse, acicular anhydrite, car bon ate and py rite±he ma tite (spec u lar) is de - white orthoclase pheno crysts (2–7%). It con tains miarolitic veloped along the mar gins of the Centra l, Juncti on and cavi ti es filled with epidote and garnet. Laven der porphyry Butte zones (Fig. 9). (I-12) is a quartz-bearing (Enns et al., 1995) syenite. It is Dissem inate d pyrit e is the most abundant sulphide char acter ized by strongly aligned trachytic orthoclase mineral . Chalco py rit e and bornite, in the rati o 10:1, are the pheno crysts (50–70%) in a lav en der-col oured orthoclase main cop per miner als. Sphalerite and ga lena are as so ciated ma trix. within gar net-rich areas , and trace amounts of moly bde - Ura nium-lead ages (Mortensen et al., 1995) from in- nite, nati ve silver , nati ve gold and tetrahedrite have been trusive rocks at Galore Creek range from 210 ± 1 Ma (Pb- noted (Allen, 1966). Magne ti te oc curs in veinlets with or Pb isochron, ti tan ite) for an early intermineral syenite por - with out chal co py rite and of ten ce ments brec cias. phyry (I-4) to 197.2 ± 1.2 Ma (Pb-Pb isochron, titan it e) for Chalcocite, cu prite, na tive cop per and tenorite are sec ond - a postmineral potas sium feldspar porphyry (I-9). These ary cop per min er als (Lo gan and Koyanagi, 1994). span the Trias sic -Juras sic boundary (~200 Ma), using the Gold is gener all y as soci ate d with higher grades of cop- time scale of Palfy (2000), and suggest a protra cted mag- per miner aliza tion. There is not always a strong cor re lation; matic history for the Ga lore Creek mag matic com plex. many areas of high copper lack appre cia ble gold. However , higher gold grades are as soci ate d with bornite in the north MINERALIZATION AND ALTERATION and south parts of the Centra l zone. Ten porphyry copper -gold de posit s are known on the Galore Creek propert y. The Centra l and North Junc tion zones have drill-in di cated re serves; the re main ing de pos its are con sid er ably smaller and less well tested. The de pos its are inter preted to be high-level synvolcanic mantos re lated to al kali ne plutonic rocks that intrude and breach the volca - nic ed i fice (Allen et al., 1976).

Central Zone The al ter ation min er al ogy and zonation de vel oped around the Centra l zone have been well docu m ented and descri bed by Barr (1966), Allen et al. (1976), Panteleyev (1976) and Enns et al. (1995), and refer ence s therein. The zone extends 1800 m north-northeas terl y and varies in width from 200 to 500 m. The de posit dips steeply to the west. It is divided into a core zone and north and south zones. Although the metasomatic overprint (calcsilicate min eral as semblage) at Galore Creek is un usual, the dis tri- bu tion of sulphides, pre cious metals and mag ne tite is con - sis tent with the expect ed zoning pat tern for alkalic por- phyry depos it s (Jones and Leveille, 1989; McMillan, 1991). Prograde and ret ro grade al ter ation min eral as sem- blages char ac ter ize the hy dro ther mal sys tem that was cen - tred on the Centra l zone. Early, hot, dom inantl y magm atic flu ids caused po tas sium sil i cate al ter ation and the de po si - tion of bio ti te, magne ti te, orthoclase, bornite and chal copy - rite (Fig. 7). The po tas sium sil icate al ter ation is pre served in the northern and southern parts of the Centra l zone. Cool ing and collaps e of the hy drother mal system down- ward produced patchy propylitic alter ation (epidote, Fig ure 7. Po tas sium sil i cate al ter ation of a vol ca nic brec cia al tered chlorite, calcit e and py rite), which is devel oped periph eral and pref er en tially re placed by bi o tite, mag ne tite and orthoclase, to the miner al iza tion. This was follow ed by a late-stage (?) southern end of Cen tral Zone. In set shows enlar ge ment of bornite or sep arate hy dro ther mal fluid that caused calcic-potassic and chal co py rite min er al iza tion

Geo log i cal Field work 2004, Pa per 2005-1 243 Fig ure 9. Alteration charac ter ized by an assem blage of sericite, anhydrite, car bon ate (SAC) and py rite±he ma tite (spec u lar) over - prints an I-5 at the por tal to the North Junc tion Zone.

porphyry is sim ilar to the dark syenite por phyry at Ga lore Creek. It contai ns potas sium feldspar megacrysts up to 4 cm in length, abundant bi oti te and dissem inate d pyrit e. An intru sive breccia phase or brecciated intru sive is de vel- Fig ure 8. Calcic-potassic alter ation in the orthomagmatic breccia oped lo cally. Bio tite was col lected from the magm atic brec - lo cated on the west side of the Cen tral Zone, Den dritic Creek. Per - cia for radiometric dating; result s are pending. vasive white potas sium metasomatism, with coarse inter growths of bio tite, garnet, anhydrite and ap a tite, re place the matrix to the brec cia. STRUCTURE

The ori enta ti ons of layered rocks around the Galore Copper Canyon Creek magmatic com plex out line a broad domal struc ture, The Cop per Can yon show ing is lo cated ap prox i mately pos si bly re lated to in tru sion but prob a bly re flect ing youn- 8 km due east of the Galore Creek deposit . It is owned by ger deformational events. The Ga lore Creek area is flanked Ea gle Plains Re sources. It was tested by seven di am ond- on the east by the north-trending, east-dipping Copper Can- drill holes (1010 m) in 1957 by the Ameri can Metal Com - yon thrust fault, which forms the west-verging com ponent pany Limited. At that time, geo log ical re serves of of the regional Scud River fault, which has been inter preted 27 million tonnes with an aver age grade of 0.72% copper to repre sent a posi ti ve flower structure (Logan and and 0.43 g/t gold were inferred (Spencer and Dobell, 1958). Koyanagi, 1994). The western flank is char acter ized by In 1990, Consol i date d Rhodes Resource s Ltd. com pleted north-trending upright folds and a well-de veloped north- 3784 m of dia m ond-drilling in thirtee n holes. NovaGold, trending, west-dip ping my lon ite zone. Pen e tra tive de for- under an opti on agree ment with Eagle Plains Re sources, mation of the Tri as sic rocks is rare and re stricted to dis crete com pleted eight di am ond-drill holes total ling 3017 m in shear zones or folds in sedi m entar y rocks. Shear sense 2004. Drilling confirm ed and expanded the near-surface gives an appar ent top-to-the-west sense of moti on cop per-gold-sil ver min er al iza tion on the prop erty, which is (Fig. 10). Folds are broad, open struc tures and gener all y asso ci ate d with a syenite porphyry and a hy drother mal sys- plunge south erly. These struc tures post date min er al iza tion. tem that is simi lar to but smaller than that at Ga lore Creek. The Cone Mountai n thrust fault is a northwest -trending, The Copper Canyon area has been mapped in detail by east-dip ping my lon ite zone with sim i lar tops-to-the-west– Leary (1990) and Otto and Smithson (2004). directed thrust ing (Brown et al., 1996). The footwall to the mylon it e is foli ated granodiorite (185 Ma), which provides The de posit is hosted by Late Tri as sic al ka line flows, a lower limit to the age of thrusting. tuffs, epiclastics and syenite intrusives. To the east, Mid dle Tri as sic sed i ments and Lower Perm ian lime stones are Well-bed ded sed i men tary and wa ter-lain crys tal thrust west ward over these volcanics at the head of Copper tuffaceous rocks, exposed along the western edge of the Canyon Creek. Two northwest erly-trending dikes of com plex and at Copper Canyon, perm it a structura l analysis syenite porphyry crop out in the lower part of the creek. The of the rocks in the area. With the excep ti on of a thick pack-

244 Brit ish Co lum bia Geo log i cal Sur vey ES); and Actlabs, Ancaster, On tario for trace el em ent anal - y ses us ing in stru men tal neu tron ac ti va tion anal y sis (INAA). A sub set of these sam ples has also been sent to Me mo rial Uni ver sity, New found land for trace el e ment analysis using induc ti vely coupled plasma – mass spectrometry (ICP-MS). Results are pending.

CONCLUSIONS

A Late Tri as sic vol canic cen tre is pre served at Ga lore Creek. Sulphide de posi ti on within it was relat ed to a dy- namic system of synvolcanic faults, syenite intru sions , ex- plo sive brec cias and comagmatic extru sive volcanics. Be- cause dikes, sills and explo sive brec cias dom i nate, to gether Photo 9. Dis crete brit tle shear zone de vel oped in vol ca nic con - with pseudoleucite-bearing intrusives, this is envi sione d to glom er ates along the west ern wall of the Ga lore Creek ba sin. Ro - have taken place in a high-level setti ng, possi bly within the ta tion of clasts gives an ap par ent tops-to-the-west sense of shear. throat of a . Radio m etric ages (Mortensen et al., 1995) in di cate a pro longed al ka line mag matic his tory for age of crys tal-rich tuffs at Copper Canyon, all other bed- the intru sive com plex, with the bulk of copper -gold miner - ding measure m ents are upright . al iza tion oc cur ring early. In tense po tas sium metasomatism and copper -gold miner al iza tion are synvolcanic and latest Thrusts at Copper Can yon post date min er al iza tion and Trias sic in age (Logan and Koyanagi, 1994). Extru sive may coin cide with shears to the west of the com plex. equiva lent rocks of the potas sium porphy rit ic syenite con - Late dikes, D-1 through D-4, trend 90° and 125°, have sti tute the up per stra tig ra phy pack age of the Stuhini Group north and south dips, and crosscut alter ation, miner al iza - at Ga lore Creek (Fig. 11). These rocks are pre domi nantly tion and all I-1 through I-12 syenite dikes. po tas sium feld spar and bi o tite crys tal-rich pyroclastic and epiclastic rocks. Accretionary lapilli and depositional bed CHEMISTRY forms are interpreted to be base surge deposits and indicate subaerial deposition. Samples were steel milled at the Brit ish Co lumbia Geo log i cal Sur vey Branch Lab o ra tory in Vic to ria. Splits No sin gle min er al iza tion-al ter ation zonation pat tern is were shipped for analysis to TeckCominco Lab o ra to ries, ap par ent that would tie all the min eral oc cur rences at Ga - Van cou ver for major and trace el em ent abun dances (Ba, lore to a single centra l hy drother mal system (i.e., cen tred Rb, Sr, Nb, Zr and Y) by X-ray flu o rescence (XRF); ACME over the Centra l Zone), nor is there any appar ent rela ti on An a lyt i cal, Van cou ver for trace el e ment anal y ses us ing in - be tween el e va tion and ei ther sul phide or al ter ation min eral ducti vely couple d plasma – emiss ion spectrom e tr y (ICP- as sem blages.

Fig ure 11. Schematic repre sen ta tion of the Late Trias sic vol canic and magmatic complex at Galore Creek, show ing rela tive ages of events.

Geo log i cal Field work 2004, Pa per 2005-1 245 ACKNOWLEDGMENTS north west ern Brit ish Co lumbia (NTS 104G and 104B); in Con tri bu tions to the Ge ol ogy and Geo phys ics of North - The Ga lore Creek com ponent of the Cu-Au Porphyry west ern Brit ish Co lum bia and South east ern , An- der son, R.G., Ed i tor, Ca na dian Jour nal of Earth Sciences , Project was concei ved through discus sions with Joe Vol ume 28, pages 958–972. Piekenbrock of NovaGold Resour ces Inc., Scott Petsel Pro - ject Ge ol o gist for the Ga lore Pro ject, and the Min is try of de Rosen-Spence, A. (1985): Shoshonites and as soci ated rocks of cen tral Brit ish Co lum bia; in Geo log i cal Field work 1984, Ener gy and Mines. It was jointly funded and supple m ented BC Min istry of En ergy, Mines and Pe tro leum Re sources, by funding from a Rocks to Riches grant. Jim Muntzert and Pa per 1985-1, pages 426–442. Frank Gish are both heart ily thanked for provid ing such Enns, S.G., Thompson , J.F.H., Stanley , C.R. and Yarrow , E.W. pos i tive and cheer ful, in fact in fec tiously en thu si as tic, lo - (1995): The Ga lore Creek por phyry cop per-gold de posits, gisti cal support. Specia l thanks are extende d to John north west ern Brit ish Co lum bia; in Por phyry De pos its of Proffett, who shared his ob ser va tions and in ter pre ta tions of the North ern Cor dil lera, Schroeter, T.G., Edi tor , Ca na dian the ge ology at Galore Creek and num erous other porphyry In sti tute of Min ing and Met al lurgy, Special Vol ume 46, depos it s. Valuable discus sions in the field with Stuart pages 630–644. Moriss, Bruce Otto and Dave Smithson rein tro duced the Gabrielse, H., Monger , J.W.H., Wheeler, J.O. and Yorath, C.J. au thor to the Ga lore Creek area and its min eral oc cur rences. (1991): Part A: Morphogeological belts, tectonic as sem - blages, and ter ranes; Chap ter 2 in Ge ol ogy of the These were helpful and much appre ci ate d. Philip Gordon Cordilleran Orogen in Can ada, Gabrielse, H. and Yorath, and a num ber of the ‘core logging elite’ shared their knowl- C.J., Ed i tors, Geo log i cal Sur vey of Can ada, Ge ol ogy of edge of stra tig ra phy and al ter ation-min er al iza tion from the Can ada, Num ber 4, pages 15–28 (also Geo log i cal So ci ety North Junction, Copper Canyon and Gap zones. of America, The Ge ol ogy of North America, Vol ume G-2). Dave Lefebure visit ed the camp during the course of Geo log i cal Sur vey of Can ada (1957): Op er a tion Stikine; Map 9- fieldwork. Brian Grant is thanked for rubber sheeting the 1957. sub mis sion date and pro vid ing ed i to rial com ments and help Gill, J. and Whelan, P. 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248 Brit ish Co lum bia Geo log i cal Sur vey