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

McLean Arm Porphyry Cu-Mo District
The McLean Arm porphyry Cu-Mo district (fig. 14) contains a group of porphyry copper-molybdenum deposits which
consist of precious metal stockworks and veins at Poison, Ickis, Veta, Apex, and Stone Rock Bay prospects in the central part of a
northwest-trending belt of middle Paleozoic, multi- phase plutons composed of pyroxenite, syenite, quartz monzonite, and mixed
intermediate-composition igneous rocks. The plutonic rocks intrude the clastic rocks of the Descon Formation on the extreme tip
of southern Prince of Wales Island. The central part of the complex which contains the deposits is mainly syenite. The altered and
mineralized syenite at Stone Rock Bay has a a U-Pb zircon age of436 Ma (Gehrels. 1992). The sulfide deposits occur mainly in
stockwork which occurs along joints and faults which strike 25" or 295" and dip steeply. The deposits and their host joints and
faults appear to be related to a concentric alteration zone, of about 5 km2 area, with a carbonate-albite center, and an albite and
sericite rim. The higher grade veins and stockwork range from 0.4 to 5.6% Cu, 0.01 to 0.08% Mo, and 2.1 to 1 1.0 g/t Au.
Anomalous Ag, Pt, Bi, Te, and base metals also occur in the deposits (MacKevett, 1963; F.D. Forgeron and L.W. Leroy, written
commun., 1971; T.K. Bundtzen, unpublished data, 1990; Nokleberg and others, 1995a). Soil sampling, trenching, and limited
diamond drilling done in 1972 suggests a potential for 40 million tonnes of Cu-Mo ore at the Apex zone.
Polymetallic Vein, Skarn, and Disseminated
Deposits in Paleozoic Plutons at Klakas Inlet
and Kassan Peninsula
A suite of polymetallic vein, skam, and disseminated deposits, which form part of the Prince of Wales Island
metallogenic belt, are associated with Silurian or older alaskite and granodiorite in Klakas Inlet. The granodiorite, with a minimum
K-Ar isotopic age of 428 Ma (Turner and others, 1977). contains sericite-altered veinlets of chalcopyrite, molybdenite, and galena
in a I00 mZ area. The deposit contains up to 0.23% Cu, 0.06% molybdenum, 0.05% Co, 0.05% Sn, and 0.01% W. The high Sn
and W values occur adjacent to the main Cu and Mo deposits (Herreid and others, 1978).
A suite of polymetallic Cu vein, Cu-Fe (magnetite) skam, and disseminated deposits also occurs in or near altered Late
Ordovician to Early Silurian, intermediate-composition plutons on Kasaan Peninsula. About 607,690 tonnes of Fe and Cu ore
were mined in this area prior to World War 11 (Warner and Goddard, 1961). Most of the deposits consist of irregular bodies of
magnetite, chalcopyrite, and pyrite, and contain lesser amounts of sphalerite and galena. The deposits contain minor Au and Ag,
and generally occur in skarn associated with alkali gabbro, diorite, and granodiorite. The plutonic rocks exhibit U-Pb zircon
isotopic ages ranging from the Late Ordovician to the Early Silurian (Gehrels and Berg, 1992). The largest skarn deposit in the
area occurs at the Mount Andrew-Mamie mine, the biggest Cu producer in the district (Bundtzen, 1978). The deposits in this area
are associated with peripheral polymetallic veins and stockworks which contain chalcopyrite and pyrite, and Au values.
Concentric magnetic anomalies in the area are interpreted by Warner and Goddard (1961) as reflecting as a buried porphyry Cu
deposit.
Salt Chuck Zoned Mafic-Ultramafic
CU-Au-PGE Deposit
The Salt Chuck zoned mafic-ultramafic Cu-Au-PGE deposit (fig. 15) consists of irregularly and randomly distributed
veinlets of bornite and associated minor chalcopyrite, chalcocite, covellite, native copper, and magmatic magnetite (Donald
Grybeck and David A. Brew, written commun., 1985; Loney and others, 1987; Loney and Himmelberg, 1992; Foley and others,
1997). The deposit produced about 300,000 tonnes grading 0.95% Cu, 1.2 g/t Au, 5.8 g/t Ag, 2.2 g/t PGE (mainly Pd and Pt), and
produced 610,400 g PGE from 1907 to 1941. The sulfides and oxides occur as disseminations and along cracks and fractures in
pipe-like late Paleozoic or Mesozoic gabbro-clinopyroxenite stock intruding Silurian metagraywacke. Clinopyroxenite and gabbro
grade irregularly into one another. Bornite, the principal sulfide; occurs mainly as interstitial grains in clinopyroxenite in amounts
up to 15 percent. Extensive, late magmatic or hydrothermal epidote veins occur in gabbro and clinopyroxenite. Low-K, altered
biotite from clinopyroxenite has a K-Ar isotopic age of 429 Ma. The deposit is interpreted to be magmatic, however, considerable
hydrothermal remobilization of sulfides has occurred.