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

Zane Hills Porphyry Cu-Au Deposit
The Zane Hills porphyry Cu-Au deposit consists of a stockwork and veins containing chalcopyrite and pyrite, and trace
molybdenite and covellite that occur most commonly in a quartz gangue. The stockwork and veins occur in a small, 5 krn2
monzonite porphyry which intrudes older Jurassic andesite, and also in a mid-Cretaceous granodiorite pluton. The stockwork and
veins occurs in both the Jurassic andesite and in the monzonite porphyry which has K-Ar age of 81 Ma. Like the deposits at Indian
and Purcell Mountains, the phyllic-argillic-propylitic alteration assemblage which is annularly distributed around the core of the
monzonite porphyry (Hollister, 1978). The deposit contains up to 2.0% Cu, 0.2% Mo, and 2.4 glt Au (Miller and Fenians, 1968).
The Zane Hills deposit occurs about 4 km west of the Hog River placer deposit which has yielded about 6,842 kg of placer Au.
Origin of and Tectonic Controls for
West-Central Alaska Metallogenic Belt
Isotopic trace element (initial Sr isotopic ratios) and isotopic age data reported from the Late Cretaceous and early
Tertiary igneous rocks of western Alaska indicate a variety of source rocks for the parent magmas (Moll-Stalcup and Arth, 1991;
Moll-Stalcup, 1994; Arth, 1994), including both contaminated crustal rocks and oceanic crust. On the basis of regional geologic
relations, igneous rock composition, and ages of igneous rock, and tectonic environment, the West-Central metallogenic belt is
herein interpreted as hosted in the extreme northeastern end of the Okhotsk-Chukotka volcanic-plutonic belt. Other related
metallogenic belts to the west in Alaska are the Northwestern Koyukuk Basin metallogenic belt and the Seward Peninsula
metallogenic belt of granitic magmatism deposits (fig. 103). To the west and southwest, the Okhotsk-Chukotka volcanic-plutonic
belt, which also hosts the Northwestern Koyukuk Basin and Seward Peninsula metallogenic belts, extends for 3000 km along
western margin of Sea of Okhotsk(Nok1eberg and others, 1994c, 1997~). The Okhotsk-Chukotka belt is interpreted as a
continental-margin arc marking the Albian through Campanian and locally Paleocene active continental margin of northern Asia
(Nokleberg and others, 1994c, 1997c, 2000).
Metallogenic Belts Formed in
Late Mesozoic and Early Cenozoic Kluane
Continental-Margin Arc, Southern Alaska
Kuskokwim Mountains Metallogenic Belt of
Granitic-Magmatism-Related Deposits
(Belt SWK) Southwestern Alaska
Geologic Setting of Kuskokwim Mountains
Metallogenic Belt
A major Au-polymetallic metallogenic province associated wlth Late Cretaceous-early Tertiary granitoid plutons and
associated volcanic fields occurs in the 650 long by 350 km wide Southwestern Kuskokwim Mountians metallogenic belt in
western-southwestern Alaska (Nokleberg and others, 1995a). The metallogenic belt can be traced from Goodnews Bay in extreme
Southwestern Alaska to Cosna Dome in the northeastern Kuskokwim Mountains, a distance of more than 650 km (fig. 103).
Bundtzen and Miller (1997), have included the precious metal and related deposits of Late Cretaceous and early Tertiary age
through out much of this region into the Kuskokwim Mineral Belt which is named after the Kuskokwim Mountains where most of
the deposits occur. This name has also been adopted by other authors including Lange and others (2000) and Goldfarb and others
(2000). Smith (2000), and Flanigan and others (2000), as stated above, regard the same area as a southwest extension of the
Tintina gold belt, a belt of granitoid-related Au plutons of mainly Mesozoic age which spans the region of central Alaska and the
Yukon Territory.
During the twentieth century, lode and placer deposits derived from Cretaceous and early Tertiary igneous complexes
within the Kuskokwim Mineral Belt have produced approximately 110,000 kg Au, 9,500 kg Ag, 3,842 kg Cu, and 1.5 million kg
Hg (Bundtzen and others, 1992; Miller and Bundtzen, 1994; Nokleberg and others, 1996; Bundtzen and Miller, 1997; Bundtzen,
1999). However, some of the placer gold is interpreted as derived from older bedrock sources: (1) about 15 percent of the Au
production of 16,900 kg has been from placer deposits containing detritus from mid-Cretaceous (108 Ma) plutonic complexes in
the Nyac district; (2) one percent (970 kg) was mined from placers erodlng Jurassic ultramafic rock complexes in the Goodnews
Bay region;
The significant deposits in the belt (Nokleberg and others 1995, 1996, 1997a, 1998; Bundtzen and Miller, 1997) include:
the McLeod, and Molybdenum Mountain porphyry Mo prospects; the important Donlin Creek and Vinasale Mountain porphyry
Au-polymetallic deposits; the Chicken Mountain, Von Frank, and Golden Horn porphyry Cu-Au prospects; Au-polymetallic vein
and replacement prospects at Fortyseven Creek south of Sleetmute; the Arnold prospect near Marshall; the Mission Creek Owhat
and Headwall prospects in the Russian Mountains; Cu-Au-Bi skam deposits in the Nixon Fork area; a small Fe skarn occurrence
at Medfra; the Bismarck Creek, Win, and Won Sn-W-Ag polymetallic, greisen, vein, and skarn deposits; and epithennal Hg-Sb-