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

Alkaline Magmatism and Porphyry Cu-Au Deposits at Galore Creek, Northwestern British Columbia By James M. Logan KEYWORDS: geology, 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 di rect ex plo ra tion. INTRODUCTION The Ga lore Creek camp is lo cated within the lower Stikine River region of north west ern Brit ish Co lum 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 b uted across an area measuring phyry depos it s, in par ticu 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 Cen tral, Junc tion and South west 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 Cen tral 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 con trols on miner al - spurred re-eval u ati 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 Brit ish 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 po nent of the in ter est in re fin ing the al ka line Cu-Au por phyry ex plo ra- Cu-Au Porphyry Project con ducted 1:20 000-scale field tion model (Abacus Mining and Ex plora 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 Ga lore Creek magmatic and outcrop expo sure is good. In addi ti on, regional -scale com plexes. Addi ti onal fund ing was obtained through a tra verses were started out side the main intru sive complex Rocks to Riches grant pro vided by the Brit ish Co lum bia and traced stra tig raphy back into the Galore Creek basin, and Yukon 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 stud ies will update the provincial da tabase pri mary protoliths. Mag netic sus cep ti bil i ties of in tru sive and mineral deposit mod els, and prom ote Cu-Au porphyry and vol ca nic units were measured to better uti lize the low- ex plo ra tion, all of which will ul ti mately lead to new dis cov - level air borne 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 geo logi 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 Cen tral zone; was not un til 1948 that his data were pub lished (Kerr, · ac quire a suite of samples from the var ious min er alized 1948a, b). Kerr proposed the orig inal Perm ian and pre- zones, as well as a suite of least altered volca nic and in - Perm ian sub divi sion of Paleo zoic strata and, from his work tru sive rocks, for major and trace el e ment 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 Co lumbia (NTS 104G). In set is a terrane map of north ern 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 Ju rassic 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 con ducted 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 geo logi cal maps of to Recent bim odal shield volcanism 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 ca nic is land arcs (Fig. 1) include s that of Mon ger (1970, 1977), Souther ranging in age from late Paleo zoic through Early Juras sic . (1971, 1972, 1992) and Ander son (1984, 1989). Modern analogs in clude 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 con juncti on with a study of the de- land. Recent studies suggest that the Stikine terrane de vel - posit betwee n 1973 and 1975 (Panteleyev, 1973, 1974, oped adja cent to the ances tral mar gin of North America 1975, 1976, 1983). Geo logi 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 (Lo gan 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 north ern end of Tahltan Lake map ar eas (Brown et al., 1996).

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