USGS Professional Paper 1697 - Alaska Resources Library

deposits and occurrences consist of lenticular to sheet-like ore
bodies of pyrite and pyrrhotite, lesser chalcopyrite, and minor
sphalerite and magnetite (Grove, 1986; EMR Canada, 1989; Hoy,
1991; Smith, 1993). Combined production and reserves are 26.7
million tonnes grading 1.48 percent Cu, 9.6 g/t Ag, and 0.17 g/t
Au. The deposits and occurrences are located near the contact
between volcanic and sedimentary rocks in a roof pendant of
tholeiitic mafic volcanic rocks and overlying turbidites that are
intruded by the Coast Plutonic Complex. Host rock geochemistry
indicates formation along an ocean ridge. The host strata are interpreted
as Early and Middle Jurassic volcanic and sedimentary
units of the Stikinia terrane (Macdonald and others, 1996).
Origin of and Tectonic Controls for Coast Mountains
Metallogenic Belt
The Coast Mountains metallogenic belt contains a variety
of volcanogenic massive sulfide deposits, which occur in
three age-range groups of volcanic and associated rocks in
the Stikinia island-arc terrane. The following three age-range
sequences of massive sulfide deposits and host rocks are identified:
(1) The middle to upper Paleozoic Stikine assemblage
contains interbedded volcanic arc, carbonate, and fine-grained
clastic rocks. The Tulsequah Chief kuroko massive sulfide
deposit and associated occurrences formed in this age-range
of the island arc. (2) The Late Triassic Stuhini Group and
Takla Group, which unconformably overlie the Stikine assemblage,
contains volcanic arc rocks and interfingering clastic
rocks that are intruded by coeval granitoids. The Granduc
Besshi massive sulfide deposit formed in this age-range of the
island arc. (3) The unconformably-overlying Early Jurassic
Hazelton and Spatzizi Groups and the Takwahoni Formation
contain andesitic volcanic rocks and intercalated sedimentary
rocks. The kuroko massive sulfide deposits in the Alice Arm
Silver district and the Cyprus massive sulfide deposits in
the Anyox district formed in this age-range of an island arc.
Each of the three age-range groups of volcanic and associated
rocks are interpreted as parts of a long-lived volcanic arc that
were deposited on Yukon-Tanana continental-margin terrane,
a rifted fragment of the North American Craton Margin
(Gehrels and others, 1990; Monger and Nokleberg, 1996;
Nokleberg and others, 1994c, 1997c). With more detailed
study, each of the three age-range groups of volcanic rocks
and associate massive sulfide deposits might be designated as
separate metallogenic belts.
Middle Jurassic Metallogenic Belts
(193 to 163 Ma) (fig. 47)
Overview
The major Middle Jurassic metallogenic belts in Alaska
and the Canadian Cordillera are summarized in table 3 and
portrayed on figure 47. No significant Middle Jurassic metal-
Middle Jurassic Metallogenic Belts (193 to 163 Ma) (fig. 47) 107
logenic belts exist in the Russian Far East. The two major
belts are as follows: (1) In southern Alaska and the Canadian
Cordillera, continuing on from the Early Jurassic, are the
Talkeetna Mountains-Alaska Range belt, which contains
kuroko massive sulfide deposits, the Alaska Peninsula (AP)
belt, which contains Cu- and Fe-skarn deposits, and the Island
Porphyry (IP) belt, which contains granitic-magmatism-related
deposits. These belts are hosted in the Wrangellia island-arc
superterrane and are interpreted as forming in the Talkeetna-
Bonzana arc preserved in the superterrane. (2) In the Canadian
Cordillera, continuing on from the Early Jurassic were the
Coast Mountains (CM), Copper Mountain (North; CMN),
Copper Mountain (South; CMS), Galore (GL), Guichon (GU),
Klotassin (KL), Texas Creek (TC), and Toodoggone (TO)
belts, which contain either granitic magmatism-related deposits
or deposits related to felsic to mafic marine volcanism.
These belts are interpreted as forming in the axial parts of the
Stikinia-Quesnellia island arc.
Metallogenic-Tectonic Model for Middle
Jurassic (193 to163 Ma; fig. 47)
During the Middle Jurassic (Toarcian through Callovian—193
to 193 Ma), the major metallogenic-tectonic
events were (fig. 47; table 3) (1) continuation of continentalmargin
arcs and associated subduction near the North Asian
Craton in the Russian Far East, (2) beginning of assembly
of previously rifted cratonal, passive continental-margin,
and island-arc terranes between that craton and the ancestral
Pacific Ocean to form the Kolyma-Omolon superterrane,
(3) continuation of the Talkeetna, Bonanza, and Stikinia-
Quesnellia arcs, associated metallogenic belts, and formation
of companion subduction zones, (4) continued sinistral-slip
imbrication of the Stikinia-Quesnellia island arc and associated
subduction zones during oblique-sinistral convergence
between the ancestral Pacific oceanic plate and the North
American Craton Margin, and (5) with the beginning of
accretion of the Stikinia-Quesnellia arc at about 185 Ma, the
start of mountain building in the North American Cordillera.
Sedimentation continued along the passive continental margins
of North Asian and North American Cratons.
Specific Events for Middle Jurassic
(1) The Monakin continental-margin arc, consisting of
the Monakin volcanic-plutonic belt (mo) and the Umlekan
continental-margin arc, consisting of the Umlekan-Ogodzhin
volcanic-plutonic belt (uo) and associated units, commenced
activity. Associated with this arc was oblique (sinstral) subduction
of part of the Ancestral Pacific oceanic plate to form the
Samarka (SMA), Khabarovsk (KB), and Badzhal (BD) terranes.
(2) The continental-margin arc Uda arc (consisting of the
Uda volcanic-plutonic belt (ud) and Uda-Zeya Sedimentary
Basin (uz) continued to form. Associated with the arc was
subduction and sinistral transpression of part of the Mongol-