Metallogenesis and Tectonics of the Russian Far East, Alaska, and ...

Nokleberg and others, 2000). Before accretion, the Stikinia island arc is interpreted as forming on the Yukon-Tanana terrane, a
rifted and deformed fragment of the North American Craton Margin (Monger and Nokleberg, 1996; Nokleberg and others, 2000).
Several metallogenic belts formed during granitic magmatism associated with formation of the Stikinia and Quesnellia island arcs.
The metallogenic belts which formed in conjunction with the Stikinia island arc are the Copper Mountain (North), Galore Creek,
Guichon, Klotassin, Texas Creek, and Toodoggone belts. The Copper Mountain (South) and Guichon metallogenic belts formed
in conjunction with the Quesnellia island arc.
Toodoggone Metallogenic Belt of Au-Ag
Epitherrnal Vein and Porphyry CuAu
Deposits (Belt TO) Northern British Columbia
The Toodoggone metallogenic belt of Au-Ag epithermal vein and porphyry Cu-Au deposits (fig. 42; tables 3,4) occurs in
northern British Columbia and is hosted by: (1) the Toodoggone Formation, a Early Jurassic succession of subaerial, intermediate,
calc-alkaline to alkaline, predominantly pyroclastic rocks (Diakow and others, 1991, 1993; Monger and others, 1991); (2) and the
coeval and comagrnatic calc-alkaline plutons of the Black Lake Suite (Woodsworth and others, 1991). The belt and host rocks
occur in the eastern part of the Stikinia island-arc terrane along the southwestern flank of the Stikjne Arch. The Toodoggone
Formation forms part of the Early Jurassic, calc-alkaline part of the Stikinia terrane and were deposited on the alkaline-
subalkaline, Late Triassic Takla Group. The Toodoggone Formation is correlated with the Hazelton Group to the south and west.
The significant deposits are Au-Ag epithermal vein deposits in Toodoggone district, and the Kemess porphyry Cu-Au deposit
(table 4) (Nokleberg and others 1997a, b, 1998).
Toodoggone District of Au-Ag
Epithermal Vein Deposits
The Toodoggone district contains significant Au-Ag epithermal vein deposits, with production fiom four principal
deposits; Cheni (Lawyers, Cliff Creek), Chappelle (Baker), Shas, and Al.
The Lawyers Au-Ag epithermal vein deposit (fig. 46) consists of native gold, silver and electrum, with amethystine
quartz, calcite and barite occurring in veins, stockworks and breccia. The deposit is hosted in silicified, propylitized and argillized
intermediate volcaniclastic rocks which are proximally associated with plutons of the Black Lake Suite and with regional faults.
The current resource is estimated at 1.76 million tonnes grading 6.8 g/t Au and 242.7 g/t Ag (Schroeter, 1983; Vulimiri and others,
1986; Dawson and others, 1991). This and other deposits in the district display higher sulfide content and higher-temperature
alteration assemblages in relation to decreasing distance from contacts with granitoid stocks and plutons.
The Chappelle (Baker) Au-Ag epithermal vein deposit consists of a Zn-Pb-Fe-sulfide-rich mineral assemblage hosted in
calcareous sedimentary rocks of the Takla Group along the contact with the Black Lake stock (Barr, 1980). The Shasta Au-Ag
epithermal vein deposit lacks sulfides and any evidence of underlying plutons, but exhibit advanced argillic alteration assemblages
which indicate high-level deposition (MINFILE, 2002).
Kemess North and South Porphyry Cu-Au Deposit
The Kemess North, a developed prospect, and the Kemess South mine are porphyry Cu-Au deposits which consist of
pyrite, chalcopyrite, magnetite, hematite, molybdenite and digenite which occur in stockwork veinlets and fractures and as
disseminations (Diakow and others, 1991, 1993; Rebagliati and others, 1995, Diakow, 2001). The deposits are hosted in
equigranular intrusions which cut mainly mafic volcanic rock of the the Late Triassic Takla Group. At the Kemess South mine,
mineralization is related to a felsic to intermediate, mainly monzodiorite pluton of Early Jurassic age which is probably related to
the Black Lake Suite and coeval with the Toodoggone Formation. At the Kemess North prospect, several large hydothermal
alteration zones enclose six major zones of porphyry-style Cu-Au deposits, as well as several vein and skarn deposits. Oxidation
of these deposits and subsequent development of a supergene blanket are interpreted as an Early Jurassic event which occurred in
Early Jurassic volcaniclastic and epiclastic rock (Diakow, 2001). The Late Cretaceous sedimentary rock of the Sustut Group are
interpreted as capping the supergene zone.
The Kemess South porphyry Cu-Au deposit is hosted by the relatively flat-lying Maple Leaf quartz monzodiorite sill.
Higher Cu and Au grades correlate with zones of intense quartz-pyrite-chalcopyrite stockwork which contains intensely-
developed K-feldspar vein selvages and magnetite stringers. A supergene zone, which formed contemporaneously with the Late
Cretaceous Sustut Basin, forms about 20% of the deposit, and contains elevated Cu grades and contains chalcocite and native Cu.
Production commenced at Kemess South in 1998, based on estimated reserves of 442 million tonnes of hypogene and supergene
ore grading 0.23% Cu and 0.4 g/t Au (Rebagliati and others, 1995; El Condor Resources Ltd., news release, July 19, 1993).
The Kemess North porphyry Cu-Au deposit is hosted in potassic-altered, mafic volcanic rocks of the Takla Group. The
deposit is centered on Early Jurassic porphyritic monzodiorite dikes. Higher grade Cu-Au mineral assemblages in volcanic host
rocks are associated with hydrothermal biotite alteration, whereas potassium feldspar and propylitic alteration decrease zonally
outwards fiom these centers, along with decreasing Cu and Au. Estimated reserves are1 16 million tonnes grading 0.19% Cu and
0.38 g/t Au (Rebagliati and others, 1995; Northern Miner, March 10,2003).