USGS Professional Paper 1697 - Alaska Resources Library

in volcanic and volcaniclastic rocks of the Late Triassic(?) to
Early Jurassic Talkeetna Formation.
The Alaska Peninsula metallogenic belt occurs in, or adjacent
to, the Late Triassic(?) and Early to Middle Jurassic, Talkeetna
part of the Talkeetna-Bonanza island arc, which extends
for several hundred km along the strike length of the Alaska Peninsular
part of the Wrangellia superterrane (Burns, 1985; Plafker
and others, 1989; Nokleberg and others, 1994c, 1997c; DeBari
and Coleman, 1989). Abundant field, chemical, and isotopic data
indicate that the Talkeetna arc is mainly gabbro, diorite, tonalite,
and rarely granodiorite, has calc-alkaline composition and lower
initial Sr ratios, and is interpreted as having formed in an island
arc above a subduction zone (Reed and others, 1983; Burns,
1985; Plafker and others, 1985). The Jurassic(?) plutonic rocks,
which host the Alaska Peninsula metallogenic belt, form the
older part of the Alaska-Aleutian Range batholith, which along
with the Late Triassic(?) and Early Jurassic Talkeetna Formation
and Border Ranges ultramafic-mafic complex collectively
define the Talkeetna arc that is a key comlonent of the Peninsular
sequence (Nokleberg and others, 1994a).
Talkeetna Mountains-Alaska Range Metallogenic
Belt of Kuroko Massive Sulfide Deposits
(Belt TM), Northern Part of Southern Alaska
The Talkeetna Mountains-Alaska Range metallogenic
belt of kuroko massive sulfide deposits (fig. 42; tables 3, 4)
occurs in the northern part of southern Alaska. The metallogenic
belt is hosted in submarine tuff, andesite, and dacite
of the Late Triassic(?) and Early Jurassic Talkeetna Formation,
which is a major unit in the Peninsular sequence and
Talkeetna-Bonanza islanc arc of the Wrangellia superterrane
(Nokleberg and others, 1994c, 1997c). The one significant
deposit is the Johnson River prospect (table 4) (Nokleberg and
others 1997a,b, 1998).
Johnson River Massive Sulfide(?) Deposit
The Johnston River kuroko massive sulfide(?) deposit (R.
L. Detterman, oral commun., 1984; Steefel, 1987; Madelyn
Mollholyn, written commun., 1988; J. Proffett, written commun.,
1991) consists of quartz-sulfide veins and massive sulfide
lenses containing chalcopyrite, pyrite, sphalerite, galena,
and gold that occur in discordant pipe-like bodies of silicified
volcanic rock. Veins of chlorite, sericite, and anhydrite
and a cap of barite occur proximal to the four ore horizons.
The deposit occurs in pyroclastic and volcaniclastic rocks
of Portage Creek Agglomerate in the Talkeetna Formation;
similar mineralized horizons have been found along strike to
the northeast. Local stockworks, which cut the metavolcanic
rock, suggest either mobilization or additional deposition. The
deposit is interpreted as forming from deposition of sulfides
directly over a capped submarine vent system during Jurassic
volcanism. The deposit contains an estimated 997,540 tonnes
grading 10.35 g/t Au, 7.84 g/t Ag, 8.3 percent Zn, 1.1 percent
Early Jurassic Metallogenic Belts (208 to 193 Ma; fig. 42) 101
Pb, and 0.76 percent Cu (Bundtzen and others, 1994). In the
same region, in the Oshetna River drainage of the Nelchina
district, northeast of Anchorage, tuff in the Talkeetna Formation
contains disseminated chalcopyrite and barite. Also in
this region, Au-enriched massive sulfide deposits in the Eskay
Creek district contain many similar morphological features to
those described at Johnson River.
Origin of and Tectonic Controls for Talkeetna
Mountains-Alaska Range Metallogenic Belt
The Late Triassic(?) and Early Jurassic Talkeetna Formation
(fig. 42), which hosts the Talkeetna Mountains-Alaska
Range metallogenic belt consists mainly of bedded andesitic
volcaniclastic sandstone and tuff, ignimbrite, breccia, and
agglomerate; andesite and lesser rhyolite and basalt flows;
and shale (Plafker and others, 1989; Nokleberg and others,
1994a). The Talkeetna Formation is linked to Middle Jurassic
plutonic rocks that form the older part of the Alaska-Aleutian
Range batholith, which along with the Border Ranges ultramafic-mafic
complex, define the Talkeetna arc (Nokleberg and
others, 1994a). The Peninsular sequence forms a major part
of the Talkeetna-Bonanza island arc, and is one of three major
sequences in the Wrangellia superterrane. The Talkeetna arc is
tectonically linked to a discontinuous series of Early Triassic
to Jurassic(?) blueschist units and the McHugh Complex that
form a partly coeval subduction-zone complex that occurs
along the northern margin of the Chugach terrane (Nokleberg
and others, 2000).
Island Porphyry Metallogenic Belt of Porphyry
Cu-Mo, Cu Skarn, Fe Skarn and Cu Skarn
Deposits (Belt IP), Vancouver Island
The Island Porphyry metallogenic belt of porphyry Cu-
Mo; and Fe and Cu-Fe-Au skarn deposits (fig. 42; tables 3, 4)
occurs on Vancouver Island and Queen Charlotte Islands in
southern British Columbia and is hosted in the Island Plutonic
Suite rocks that are part the Gambier overlap assemblage of
the Wrangellia superterrane (Woodsworth and others, 1991;
Anderson and Reichenbach, 1991). On Vancouver Island,
the plutons are mainly Early to Middle Jurassic, whereas on
Queen Charlotte Island, the plutons are mainly Middle to
Late Jurassic. The significant deposits are the Island Copper
(Rupert Inlet), Hushamu, Red Dog, porphyry Cu-Mo and
porphyry Cu deposits, the Burnaby Iron (Jib), Jedway (Magnet,
Jessie), Kennedy Lake (Brynnor), Tasu Sound (Wesfrob,
Tasu, Garnet), Texada Iron, and Zeballos Iron (Ford) Fe skarn
deposits, the Benson area (Empire, Coast Copper) Cu-Fe skarn
deposits, and the Texada (Vananda, Marble Bay) Cu-Au skarn
deposit (table 4) (Nokleberg and others 1997a,b, 1998).
Island Copper Porphyry Cu-Mo-Au Deposit
The Island Copper (Rupert Inlet) porphyry Cu-Mo-Au
deposit (fig. 44) consists of pyrite, chalcopyrite and molyb-