USGS Professional Paper 1697 - Alaska Resources Library

104 Metallogenesis and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera
magnetite and pyrite with minor hessite and native gold
that occur in zones of moderate to strong gneissic foliation
in diorite of the Early Jurassic Klotassin Batholith (EMR
Canada, 1989; Minto Explorations Ltd., news release, January
25, 1994). Estimated reserves are 6.55 million tonnes grading
1.87 percent Cu and 0.51 g/t Au. The deposit is interpreted
as a metamorphosed porphyry Cu deposit. The deposit age is
interpreted as Early Jurassic (Mortensen and others, 1994).
The Williams Creek porphyry Cu-Au-Ag deposit consists
of chalcopyrite, bornite, pyrite and minor arsenopyrite
and molybdenite that occur as interstitial grains parallel with
the gneissic foliation in granodiorite of the Triassic Klotassin
Batholith (EMR Canada, 1989; Western Holdings Ltd., annual
report, 1992). Estimated reserves are 14.2 million tonnes grading
1.01 percent Cu and 0.51 g/t Au. Jurassic regional metamorphism
destroyed much of the original features of the deposit. An
oxidized zone, as much as 200 meters deep, contains malachite
and azurite that replaces copper sulfides. The deposit age is
interpreted as Early Jurassic (Mortensen and others, 1994).
Origin of and Tectonic Controls for Klotassin
Metallogenic Belt
The Minto Copper and Williams Creek porphyry Cu-Au-
Ag deposits are similar, preaccretionary porphyry Cu-Au-Ag
deposits, which are hosted in foliated, gneissic granodiorite and
diorite of the Klotassin pluton (Pearson and Clark, 1979). The
original textures of the deposits were mostly destroyed during
Middle to Late Jurassic regional metamorphism and associated
deformation. These events are interpreted as occurring during
accretion of the Stikinia island arc and associated terranes
onto the North American Craton Margin (Le Couteur and
Tempelman-Kluit, 1976) after oroclinal warping of the Stikinia-Quesnellia
island arc and tectonically-linked Cache Creek
subduction-zone terrane (Mihalynuk and others; 1994; Monger
and Nokleberg, 1996; 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
Epithermal Vein and Porphyry Cu-Au 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), and
(2) the coeval and comagmatic 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 Stikine Arch. The Toodoggone
Formation forms part of the Early Jurassic, calc-alkaline
part of the Stikinia terrane and were deposited on the alkalinesubalkaline,
Late Triassic Takla Group. The Toodoggone Formation
is correlated with the Hazelton Groas much as 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 from 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 that 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
that 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 that 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 that 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 that 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