USGS Professional Paper 1697 - Alaska Resources Library

Mount Nansen porphyry Cu-Mo deposits. If the 400 km of
right-lateral strike-slip along the Denali Fault is restored, the
area hosting the Road Metal deposit may link up with the
Southern Alaska Metallogenic Belt (described below), which
is near Chulitna and contains both Au-polymetallic greisen and
porphyry deposits as Golden Zone.
Plutonic Rocks Hosting East-Central Alaska
Metallogenic Belt
The East-Central Alaska metallogenic belt (younger part)
is hosted in Late Cretaceous (with isotopic ages of about 94
to 70 Ma) and in early Tertiary granitoid rocks (with isotopic
ages of about 74 to 55 Ma) that are the younger part of the
Yukon-Tanana igneous belt (Miller, 1994; Moll-Stalcup, 1994)
and the correlative Carmacks Plutonic Suite (Mortensen and
others, 1994). In East-Central Alaska, these granitoids intrude
the Yukon-Tanana Upland, which is underlain by the large
Yukon-Tanana terrane, and a collage of smaller, continental-margin
terranes, including the Wickershim and Manley
terranes (Nokleberg and others, 1994c, 1997). In East-Central
Alaska, most of the Late Cretaceous granitoids are calc-alkalic
and intermediate in composition, and chemical data indicate
that some of the plutons formed from magmas contaminated
by continental crust in areas underlain by the continental-margin
Yukon-Tanana terrane (Foster and others, 1987; Miller,
1994). The younger, dominantly early Tertiary granitoids generally
exhibit high initial Sr ratios and are interpreted as forming
from a mixture of mantle-derived magma and continental
crust (Foster and others, 1987; Miller, 1994).
The Late Cretaceous granitoid plutonic rocks that host
the lode deposits in the western Yukon Territory (Carmacks
area) consist of calc-alkaline granodiorite and quartz monzonite
plutons of the Carmacks Plutonic Suite, which intrude
the Yukon-Tanana and locally the Stikinia terranes (fig. 103)
(Mortensen and others, 1994).
Origin of and Tectonic Setting for East-Central Alaska
Metallogenic Belt (Younger Late Cretaceous and Early
Tertiary Part)
The younger, Late Cretaceous and early Tertiary Yukon-
Tanana igneous belt, and the Carmacks Plutonic Suite are
herein interpreted as part of the subduction-related Kluane arc,
which occurred along the Late Cretaceous and early Tertiary
continental margin of southern and southeastern Alaska
(Plafker and others, 1989; Moll-Stalcup, 1994; Nokleberg and
others, 1994b, 1997a, 2000). In Alaska, the other major parts
of the Kluane arc (Moll-Stalcup, 1994) are the Kuskokwim
Mountains sedimentary, volcanic, and plutonic belt, the Alaska
Range-Talkeetna volcanic-plutonic belt, and the Yukon-Kanuti
igneous belt. The Kluane arc is interpreted as forming immediately
after the accretion of Wrangellia superterrane in the
mid-Cretaceous and was substantially dismembered by major
dextral-slip faulting in the Cenozoic (Plafker and others,
1989; Nokleberg and others, 1994b, 2000). The Kluane arc is
Late Cretaceous and Early Tertiary Metallogenic Belts (84 to 52 Ma) (figs. 102, 103) 237
tectonically linked to the Late Cretaceous part of the Chugach
accretionary-wedge terrane (Valdez Group and equivalent
units) and to the early Tertiary part of the Prince William
accretionary-wedge terrane (Orca Group and equivalent units;
Plafker and others, 1989; Plafker and Berg, 1994; Nokleberg
and others, 1997e, 2000).
Southern Alaska Metallogenic Belt of Granitic
Magmatism Deposits (Belt SA), Central and
Northern Part of Southern Alaska
The major Southern Alaska metallogenic belt contains a
wide variety of felsic-magmatism-related deposits (fig. 103;
tables 3, 4) and occurs in the central and northern parts of
southern Alaska (Nokleberg and others, 1995a). The metallogenic
belt is hosted in the Late Cretaceous to early Tertiary
Alaska Range-Talkeetna Mountains volcanic-plutonic belt
(Nokleberg and others, 1994c, 1997c). The granitoid rocks
in this igneous belt range in age from Latest Cretaceous to
early Tertiary; the largest events occurred in the early Tertiary
(Moll-Stalcup, 1994). The significant deposits in the belt are
(table 4) (Nokleberg and others 1997a,b, 1998) (1) a porphyry
Cu deposit at Kijik River in the Bristol Bay District, (2) a
porphyry Cu-Au deposit at Pebble Copper in western-southern
Alaska, and (3) polymetallic vein, Au-Ag breccia pipe, or porphyry
Cu-Au deposit at the Golden Zone in the Chulitna district
(Nokleberg and others, 1993). Other deposits in the belt
are (1) Ag-Pb-Au (Cu) skarn deposits at Bowser, Sheep Creek,
Tin Creek, and Rat Fork Creek in the Farewell District, (2)
various Au-Ag polymetallic vein, porphyry Cu, and porphyry
Cu-Mo deposits at Nim, Nimbus, Ready Cash, and Silver
King in the Chulitna district, andat Treasure Creek, (3) various
polymetallic vein and porphyry Cu deposits at Bonanza Hills,
Nabesna Glacier, and Partin Creek, (4) a porphyry Mo deposit
at Miss Molly (Hayes Glacier), (5) a Cu-Au skarn deposit at
Zackly in the Valdez Creek district (fig. 113; table 4), (6) a Sn
greisen and Sn vein deposits at Boulder Creek (Purkeypile),
Coal Creek, Ohio Creek, and Sleitat (fig. 114; table 4), and (7)
a carbonate-hosted Hg(?) deposit at White Mountains.
Tin Creek Cu-Pb-Zn Skarn Deposit
The Tin Creek Cu-Pb-Zn skarn deposit (fig. 115) (Szumigala,
1987; Newberry and others, 1997a) consists of pyroxenerich
skarn with abundant sphalerite and minor chalcopyrite,
garnet skarn with chalcopyrite and minor sphalerite; and
locally abundant epidote and amphibole. The pyroxene skarn
is distal, and the garnet skarn is proximal to an extensive
Tertiary dacite to andesite poprhyry dike swarm that intrudes
polydeformed, middle Paleozoic contact metamorphosed clastic
and carbonate rock. The skarn forms small, discontinuous
bodies as much as 3 m wide along dikes, as manto replacement
in marble and as irregular bodies along along thrust and
high-angle faults. The skarns are zoned, with garnet-chalcopyrite-rich
skarn proximal to the dike swarm center, and pyrox-