Metallogenesis and Tectonics of the Russian Far East, Alaska, and ...

and (3) the existewe of peraluminous igneous rocks and the deposits in the Kuskokwim Mountains ignaous belt. In a similar
setting, alkalic porphyry Cu-Au and polymetallic Sn deposits occur in back-arc extensional environments in South America
(Hollister, 1978), and early Tertiary peraluminous intrusions in Yukon Territory are interpreted by Sinclak (1986) as forming
during extensioaal, wrench hull lectonism related to strike-slip faulting. This interpretation is also advocated by Miller and
Bundtzen (1994) for the mineralized plutons of the Kuskokwim Mountains igneous belt.
In Alaska, the other major parts of the Kluane arc are the Alaska Range-Talkeetna volcanic-plutonic belt to the southeast,
the Yukon-Kanuli igneous belt to the northwest, and the Late Cretaceous and early Tertiary granitoid rocks of the Yukon-Tam
igneous belt to the northeast (Moll-Sblcup, 1994). The Kluane arc is interpreted as forming immediately after the accretion of
Wrangellia superterrane in the midCretaceous, and was consequently substantially dismembered by major dextral-slip faulting in
the Cenozoic (F'laker and others, 1989; Nokleberg and others, 1994d, 2000). These belts and the Kuskokwim Mouutains
sedimentary and vo~canic belt are interpreted as a subduction-related arc that was tectonically linked to the Late Cretaceous part of
the Chugacb 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) (Nokleberg and others, 2000).
Felsie Parphyry Ma Deposits -
Kuskokwh huntsins MWIaganic Belt,
Southwestem Ataska
A nortb-south-trending, linear belt of quartz monzonite to granite porphyry stocks and plutons, that host porphyry MO
deposits and profpects, intrude the Late Cretaceous flysch of the Kuskokwim Group and older metamorphic rocks of the Ruby
ten-ane in the west-cenhal Kuskokwim Mountains. From south to north along a linear distance of about 125 km, these deposits ~d
prospects include the McLeod deposit in the eastern Kaiyuh Hills along the lower lnnoko River Drainage and the Molybdenum
Mountain deposit on the Owhat River. These two felsic porphyry Mo deposits are generally similar to the model of Lowell and
Guilbert (1970). All three deposits and prospects contain concentric phyllic and argillic alteration zones, and plot in the granite
field of a normative QAPF diagram, and are peraluminous.
McLeod Porphyry Molybdenum Prospect
The McLeod porphyry Mo deposit strikes east-northeast and consists of a molybdenite-bearing quartz stockwork in a
quartz porphyry stock hut 3 km2 in area (Mertie, 1937a; Chapman, 1945; West, 1954; Nokleberg and others, 1995a). The stock
intrudes undifferentiated Cretaceous greenstone of the Kuskokwim Group and is interpreted as associated with quartz latite dikes
which occur near the eastern boundary of the pluton. In addition to quartz and molybdenite, the stockwork contains pyrite,
pyrrhotite, and chlorite. The stockwork locally comprises up to 10% of the intrusion. Veinlets also occur in adjacent penstone.
The quarlz-fabpai porphyry stock and latite dikes exhibit a phyllic alteration core flanked by oilicic and ugih wnfB in a 300 by
1,100 rn area. The stockwork averages 0.89% MoSz over a 30 by 350 m surface area. The qua porphyry stock has a K-Ar biotite
age of 69.3 Ma (T.K. Bundtzen, unpublished data, 1987).
Molybdenum Mountain Porphyry Molybderwrm Prospect
The Molybdenum Mountain porphyry Mo prospect (T.K. Bundtzen, unpublished data, 1987; Noklahg and others,
1995a) consists of a stockwork of vein quartz with massive and disseminated molybderrite, galena, and pyrite in the MolyW~mum
Mountain stock, a small, 2 km2, hypabyssal felsic intrusion which occurs about 45 km mrtheest of Amiak. Alteratiom are maialy
silicic and sericitic. A large, elongate. contact metamorphic aureole surrounds the Molybdenum Mountain stock and several
smkr intrusions which occur about 4 to 6 krn to the northeast. Selected rock samples from the Molybcknum Moutltain stock
contain up to 5.W MoS2; however, average estimates of grade are not available. The stuck intrudes conlact-rnemmxphosed, Late
Cretaceous flysch of the Kuskokwim Group along a large shear zone which is a splay of the Iditarod-Nixo*Fork Fault, a major
dextral-slip Cenozoic fault in west-central Alaska. A K-Ar white mica age of 60.9 Ma is obtained h m the stock.
Alkalic-Calcic Porphyry Cudu Pmspects -
Kuskokwim Mountaim lwefellogenk Belt
Alkdic-calcic, porphyry Cu-Au deposits and prospects have only been recently identified in the central K u~kok~h
Mountains. The general geology structure, and alteration features of the porphyry deposits in the southwestcm Kuskokwim
Mountains metallogenic belt are generally those of the alkalic porphyry Cu-Au model of Lowell and Guilbert (1970) or to the
porphyry Cu-Au deposit model of Cox (1 986b), except that the classic alteration patterns are lacking. The significant deposits are
at Chicken Mountain and Von Frank Mountain. These deposits, display similar characteristics, including tourmaline-bsaring
breccia pipes, stoekworks, metal zoning, and petrology. The host plutons for the deposits range fmm 66 to 71 Ma and intrude ]Late
Cretaceous flysch of the Kuskokwim Group.