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

and (4) in Eocene and Oligocene granitoid plutons intruding the Valdez and Orca Groups. The deposits in this belt are of small
tonnage but locally high grade. For this widespread group of mines and deposits, a unique mineral deposit model for Chugach-
type low-sulfide Au quartz veins has been developed by Bliss (1992). The significant deposits are at Cliff, Alaska Oracle, Chalet
Mountain, Crown Point, Kilpatrick, Gold King, Granite, Jewel, Kenai-Alaska, Lucky Strike (Palmer Creek), Mineral King
(Herman and Eaton), Monarch, and Ramsey-Rutherford (table 4) (Nokleberg and others 1997a, b, 1998). Substantial Au
production occurred in this district until the early 1940's; recent exploratory work has been conducted at the Cliff Mine near
Valdez, the largest of the many known deposits.
Cliff Au Quartz Vein Deposit
The Cliff Au quartz vein deposit (Johnson, 19 15; Pickthorn, 1982; Jansons and others, 1984) consists of quartz veins, up
to 3 meters thick and 515 meters long and contain gold, pyrite, galena, sphalerite, arsenopyrite, and stibnite. The veins are hosted
in metagraywacke and minor phyllite of the Late Cretaceous Valdez Group. The veins occur in a complicated system of
intersecting faults. Sulfide minerals compose about 3 to 5% percent of the ore. The mine contains a few thousand meters of
underground workings. Production occurred mainly from 1906 to 1940. The average grade ranged from 34 to 69 g/t Au, and the
mine at the deposit produced about 1,610 kg Au from about 25,000 tonnes of ore.
Origin of and Tectonic Controls for
Chugach Mountains Metallogenic Belt
The Au quartz veins generally occur in the younger of two generations of quartz fissure veins (Richter, 1963; Goldfarb
and others, 1986, 1997, 1998; Nokleberg and others, 1989b). The older and mostly barren veins are approximately parallel to the
regional schistosity and to axial planes of minor and major folds. Their strike varies from northwest in the east to northeast in the
west. The younger Au veins generally occur in a set of tensional cross joints or fractures, and are normal to the older, barren
quartz veins. Both sets of quartz veins generally dip steeply to vertically. Hydrothermal muscovite from Au-bearing veins has
been dated at 53 Ma in the Port Valdez district (Winkler and others, 1981b), at 52 Ma in the Hope-Sunrise district (Mitchell and
others, 198 I), and at 57 Ma in the Nuka Bay district (Borden and others, 1992).
These field relations and isotopic ages are interpreted as indicating that the deposits formed during early Tertiary regional
metamorphism and anatectic granite plutonism. Regional tectonic and isotopic studies suggest that the Au veins formed in the
Orca and Valdez Groups in response to subduction of the spreading Kula-Farallon Ridge beneath the southern Alaska continental
margin (Plafker and others, 1989; Bradley and others, 1993; Haeussler and Nelson, 1993; Haeussler and others, 1995; Goldfarb
and others, 1995; 1997; Goldfarb, 1997).
Baranof Metallogenic Belt of Au Qua* Vein Deposits
Southeastern Alaska (Belt BN)
The Baranof metallogenic belt of Au quartz vein deposits occurs in Southeastern Alaska and consists of a 250-km-long belt
hosted in the Chugach subduction-zone terrane in southern and southeastern Alaska (fig. 103; tables 3,4) (Brew, 1993; Monger
and Nokleberg, 1996; Goldfarb and others, 1997, 1998). The significant deposit in the belt are Apex and El Nido, Chichagoff,
Cobol, Hirst-Chichagof, and Reid Inlet (Nokleberg and others 1997a, b, 1998). The principal deposits, at Chichagoff and Hirst-
Chichagof are quartz-sulfide veins controlled by faults in metagraywacke and argillite of the Cretaceous Sitka Graywacke of the
Valdez Group (Reed and Coats, 1941; Nokleberg and others, 1994a). The Bauer, Silver Bay, Cache, and Lucky Chance mines of
the Sitka district have similar graywacke-hosted quartz-pyrite-pyrrhotite-arsenopyrite veins (Berg and Cobb, 1967). Located near
the northern end of Chichagof Island, are the Apex-El Nido and Goldwin fissure quartz-sulfide vein mines that are hosted in
Tertiary diorite plutons and amphibolite (Reed and Coats, 194 1).
Chichagoff and Hirst-Chichagof
Au Quartz Vein Deposit
The Chichagoff and Hirst-Chichagof Au quartz vein deposit consists of tabular to lenticular quartz veins which are a few
meters thick, extend a few hundred meters along strike, and range up to a few thousand meters depth along plunge. The veins are
mainly ribbon quartz containing minor pyrite, arsenopyrite, galena, sphalerite, chalcopyrite, and some scheelite and tetrahedrite
locally (Berg, 1984; Bundtzen, Green, Deager, and Daniels, 1987; Brew and others, 1991). Ore shoots occur mainly in shear and
gouge zones along the Hirst and Chichagof faults, especially along undulations in fault planes. The deposit is hosted in
metagraywacke and argillite of the Cretaceous Sitka Graywacke. The mine produced about 24.6 million g Au, 1.24 million g Ag,
and minor Pb and Cu from 700,000 tonnes of ore. Average grade is 7.2 g/t Au and 2.0 g/t Ag. Reserves are 9 1,000 tonnes of ore
grading 4 1.2 g/t Au in several ore bodies.
Apex and El Nido Au Quattz Vein Deposit
The Apex and El Nido Au quartz vein deposit consists of quartz fissure veins up to 2 m thick and stockworks containing
sparse pyrite, arsenopyrite, chalcopyrite, galena, sphalerite, tetrahedrite, and gold (Still and Weir, 1981; Johnson and others,