USGS Professional Paper 1697 - Alaska Resources Library

100 Metallogenesis and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera
Southeast Asia (McCaffrey and Abers, 1991; Mihalynuk and
others, 1994). Migration of the Stikinia-Quesnellia arc and
associated terranes toward North America was accomplished
by subduction and (or) obduction of the Seventymile oceanic
plate along the continental margin.
(6) The Stikinia part of the arc consisted of the extensive
suite of the subduction-related volcanic and plutonic arc
rocks of the Hazelton Group that also formed in response to
subduction of the Cache Creek oceanic plate (CC). In central
part of the Stikinia-Quesnellia island arc, coeval subductionrelated
granitic plutonic rocks also intruded the previously
accreted passive continental-margin Yukon-Tanana terrane
(YT), which may have been the stratigraphic basement for
part of the Stikinia island arc (Mihalynuk and others, 1994).
The plutonic rocks also intrude the structurally overlying
Slide Mountain (SM) and Seventymile (SV) terranes. The
subduction-related volcanic and plutonic arc rocks of the
Quesnellia part of the arc, consisting of the Takla and Rossland
Groups, and the coeval igneous belts formed in response
to continued subduction of part of the Cache Creek oceanic
plate (CC; Mihalynuk and others, 1994).
(7) In the axial parts of the Stikinia-Quesnellia island arc,
continuing on from the Late Triassic, were the Coast (CM),
Copper Mountain (North; CMN), Copper Mountain (South;
CMS), Galore (GL), Guichon (GU), Klotassin (KL), and
Texas Creek (TC), and Toodoggone (TO) belts, which contain
granitic magmatism-related deposits.
(8) Also occurring was obduction of parts of the Seventymile
and Slide Mountain oceanic plates onto the North
American Craton Margin (NAM; Mihalynuk and others,
1994). Part of the obduction occurred by the Late Triassic
and (or) Early Jurassic when granitic plutons of the Stikinia-
Quesnellia island arc intruded across an intervening fault.
During the final stage of obduction of the Slide Mountain
terrane (SM) over the Kootenay metamorphosed continentalmargin
terrane (KO), these terranes started to obduct onto the
North American Craton Margin (NAM). Migration of the Stikinia-Quesnellia
arc and associated terranes toward the North
American Craton Margin was accomplished by subduction of
the Seventymile oceanic plate along the continental-margin
and by obduction.
(9) Outboard and perhaps at a lower paleolatitude (either
25° or 45°), the Talkeetna and Bonanza arcs continued activity
in the Wrangellia superterrane (WRA). This extensive arc
formed along most of the length of the Wrangellia superterrane
with coeval equivalents in the Cadwallader (CD) island
arc and Methow (MT) turbidite-basin terranes. Forming in
the arcs were the Talkeetna Mountains-Alaska Range metallogenic
belt, which contains kuroko massive sulfide deposits,
the Alaska Peninsula metallogenic belt (AP), which contains
Cu- and Fe-skarn deposits, and the Island Porphyry metallogenic
belt (IP), which contains granitic-magmatism-related
deposits. Associated with the Talkeetna and Bonanza arcs was
subduction of part of the Cache Creek oceanic plate to form
the Chugach (CG), Bridge River (BR), and possibly Baker
(BA) terranes.
Metallogenic Belts Formed in Middle Mesozoic
Talkeetna-Bonzana Island Arc in Wrangellia
Superterrane
Alaska Peninsula Metallogenic Belt of Granitic
Magmatism Deposits (Belt AP), Alaska Peninsula
The Alaska Peninsula metallogenic belt of granitic magmatism
deposits (fig. 42; tables 3, 4), mainly Cu-Au, Cu-Zn, and
Fe skarn deposits, occurs on the northeastern Alaska Peninsula.
The metallogenic belt is hosted in the central and northwestern
part of the Peninsular sequence of the Talkeetna-Bonanza island in
the Wrangellia superterrane where intruded by Jurassic granitoid
plutons (Nokleberg and others, 1994c, 1997c). The significant
deposits in the belt are the Crevice Creek, Glacier Fork, Kasna
Creek Cu-Fe skarn deposits, and the Magnetite Island Fe skarn
deposit (table 4) (Nokleberg and others 1997a,b, 1998).
Crevice Creek Cu-Au Skarn Deposit
The Crevice Creek Cu-Au skarn deposit (Martin and
Katz, 1912; Richter and Herreid, 1965) consists of at least ten
epidote-garnet skarn bodies that occur in limestone over a 2
km2 area adjacent to the Jurassic(?) granodiorite stock of Pilot
Knob. The skarn bodies vary from 3 to 800-m long and from
a few centimeters to 60 m wide. Local magnetite-rich skarn
occurs in isolated pods in nearby metavolcanic rocks, and
local disseminated magnetite zones occur in epidote-garnet
skarns. The garnet skarn bodies occur in limestone, chert, and
argillite of the Late Triassic Kamishak Formation and in overlying
metavolcanic rocks of the Late Triassic(?) to Early Jurassic
Talkeetna Formation (Nokleberg and others, 1994d). The
largest skarn body at Sargent Creek contains epidote, garnet,
actinolite, quartz, pyrite, and chalcopyrite. Lenses as much
as 1 m wide and 10 m long average 7 percent Cu. Numerous
airborne magnetic anomalies occur in the area surrounding the
granodiorite stock. The Crevice Creek deposit produced 11
tonnes of ore from high-grade zones, with an average grade of
4.5 g/t Au, 514 g/t Ag, and 17.5 percent Cu.
Origin of and Tectonic Controls for Alaska Peninsula
Metallogenic Belt
The Cu-Au and Cu-Zn skarn deposits of the Alaska
Peninsula metallogenic belt occur in areas where Jurassic(?)
quartz diorite and tonalite intrude calcareous sedimentary rock
and generally consist of epidote-garnet skarn in limestone or
marble, containing disseminations and layers of chalcopyrite,
sphalerite, and pyrrhotite. The Fe skarn deposits occur in
dolomite or marble and generally consist of magnetite skarn
containing lesser garnet, amphibole, and rare chalcopyrite.
The Fe skarns occur in areas where Jurassic(?) quartz diorite
and tonalite intrude calcareous sedimentary rocks. These
skarn deposits occur in marine sedimentary rocks of the Late
Triassic Kamishak Formation, in Early Triassic marble, and