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

Wheeler Creek, Clear Creek, and Zane Hills
Felsic Plutonic U Deposits
The felsic plutonic U deposits at Wheeler Creek, Clear Creek, and Zane Hills (Eakin and Forbes, 1976; Miller, 1976;
Jones, 1977; Miller and Elliott, 1977) are of two main types: (1) uranothorite and gummite in quartz-rich veinlets in altered Late
Cretaceous alaskite, uraniferous nepheline syenite and bostonite dikes which cut Early Cretaceous andesite; and (2) uranotborite,
betafite, uraninite, thorite, and allanite in veinlets in a foliated monzonite border phase, that locally grades to syenite. Grab
samples contain up to 0.027% U
Illinois Creek Manto-Replacement
(Polymetallic Pn-Zn, Au) Deposit
A structurally-controlled, plutonic-related epigentic deposit occurs at Illinois creek about 70 Km south of Galena
(Flanigan, 1998; Bundtzen and others, 2000). The Illinois Creek deposit is a supergene oxidized deposit which occurs in an east-
trending, moderately dipping shear zone. The deposit has with anomalous to ore-grade Au, Bi, AG, Cu, Pb, and Zn. The deposit
contains supergene pyrolucite, limonite, geothite, and hernetite; sulfides are rare. Ar/Ar isotopic age, petrologic, and microprobe
studies indicate that the Illinois Creek deposit is related to emplacement of the syn-collisional, 11 1.3 Ma Khotol Mountain granite
(Flaniagn, 1998). The mine produced 957 kg gold from 1.22 million tomes of ore prior to 1999 bankruptcy.
Origin of and Tectonic Controls for
Northwestern Koyukuk Basin
Metallogenic Belt
The calc-alkaline granitoid rocks which host the Northwestern Koyukuk Basin metallogenic belt extend about 300 km
from Hughes on the Koyukuk River westward to near the Seward Peninsula. The granitoid plutonic rocks are mainly ganodiorite
and lesser tonalite and high-silica granite. The granites intrude a sequence of andesitic flows, tuffs, breccia, agglomerate,
conglomerate, tuffaceous graywacke, and mudstone containing local intercalations of Early Cretaceous limestone which together
form part of the Koyukuk island-an: terrane (Patton and others, 1994). These plutons are interpreted as forming in a subduction-
related, continental-margin arc on the basis of a calc-alkaline composition, high sodium content, relatively, locally abundant mafic
xenoliths, and low initial Sr ratios (Miller, 1994). The Northwestern Koyukuk Basin metallogenic belt and the neaxby Seward
Peninsula metallogenic belt, described above, are herein interpreted as the eastern extension of the Eastern-Asian-Arctic
metallogenic belt which in the Russian Far East (figs. 102, 103). This major metallogenic belt, as described above, extends west
and southwest for 3000 km along western margin of Sea of Okhotsk.
West-Central Alaska Metallogenic Belt of
Porphyry Cu-Au Deposits (Belt WCA)
West-Central Alaska
The West-Central Aleska (Hogatza) metallogenic belt of porphyry Cu-Au deposits (fig. 103; tables 3,4) (Hollister, 1978;
Nokleberg and others, 1995a) is hosted in a suite of Late Cretaceous quartz monzonite plutons of the Hogatza plutonic belt which
intrude oceanic crust of the Yukon-Koyukuk island-arc terrane and overlapping Cretaceous flysch (Nokleberg and others, 1995a).
Most of the older intrusions of the Hogatza plutonic belt exbibit K-Ar ages generally fiom 100 to 120 Ma, and are undersaturated,
akalic igneous complexes which tend to be barren of porphyry deposits. The significant deposits in the belt are at Indian
Mountain, Purcell Mountain, and Zane Hills (table 4) (Nokleberg and others 1997a, b, 1998). All these deposib are hosted in
oval-shaped, epizonal, forcefully injected plutons with K-Ar isotopic mineral ages of 80-82 Ma wller and others, 1966).
Indian Mountain and Purcell Mountain
Porphyry Cu-Au Deposits
The Indian Mountain and Purcell Mountain porphyry Cu-Au deposits occur in the middle Koyukuk River basin. The
Indian Mountain deposit consists mainly of tourmaline-bearing breccias in the center of a quartz monzonite porphyry intrusion.
The breccias contain chalcopyrite and surrounding the breccias are concentric phyllic-argillic-propylitic alteration halos. The
quartz monzonite porphyry intrusion is approximatly 10 km2 (Miller and Ferrians, 1968; Hollister, 1978). A pyrite halo rims the
intrusion. Limited assays at Indian Mountain range from 0.07 to 0.15% g/t Cu and 0.1 to 1.5 g/t Au. Barite, galena, and sphalerite
have also been identified at the prospect. The Purcell Mountain porphyry copper deposit consists of stockwork veins in a quartz
monzonite porphyry intrusion. The veins contain chalcopyrite which are also associated with concentric phyllic-argillic-propylitic
alteration halos. The quartz monzonite porphyry intrusion is about 12 kn?(Hollister, 1978). A pyrite halo also rims the intrusion.
The deposit contains 0.07 to 0.10% Cu but no Au; however, placer Au bas been commercially recovered firom streams draining
both plutons.