USGS Professional Paper 1697 - Alaska Resources Library

others, 1994c, 1997c). The significant deposits in the belt
are (table 4) (Crowe and others, 1992; Newberry and others,
1997; Nokleberg and others 1997a,b, 1998) (1) Besshi
massive sulfide deposits at Beatson (Latouche), Ellamar,
Fidalgo-Alaska, Midas, and Schlosser, and (2) Cyprus massive
sulfide deposits at Copper Bullion (Rua Cove), Knight
Island (Pandora), Standard Copper, and Threeman. Many of
these deposits were producing mines in the early part of the
20 th century.
Beatson (Latouche) and Ellamar Besshi Massive
Sulfide Deposits
The Beatson (Latouche), and, Ellamar Besshi massive
sulfide deposits (Johnson, 1915; Tysdal, 1978; Jansons and
others, 1984; Crowe and others, 1992) consist of massive
sulfide lenses and disseminations of mainly pyrite and pyrrhotite,
and minor chalcopyrite, cubanite, sphalerite, galena,
Ag-bearing minerals, and gold. Gangue minerals are quartz,
sericite, and ankerite. The deposits occur in graywacke
and argillite of the Paleocene and Eocene Orca Group. The
deposits are as much as 120 m thick and 300 long along
strike. The Latouche and Beatson deposits produced more
than 84 million kg Cu from 4.5 million tonnes of ore. The
average ore grade was about 1.7 percent Cu, and 9.3 g/t
Ag. The Ellamar deposit produced 7.2 million kg Cu, 1,596
kg Au, and 5,960 kg Ag from 273,760 tonnes of ore. The
deposit at Beatson (Latouche) was developed and produced
mainly from about 1903 to 1934, and the Ellamar deposit
was mined from 1897 to 1934.
Midas Besshi Massive Sulfide Deposit
The Midas deposit consists of disseminated to massive
chalcopyrite, pyrite, pyrrhotite, sphalerite, and minor galena in
a folded, lens-shaped body (Moffit and Fellows, 1950; Rose,
1965; Jansons and others, 1984; Crowe and others, 1992). The
sulfides occur in highly deformed phyllite and metagraywacke
of the Late Cretaceous Valdez Group in the southern Chugach
accretionary-wedge-turbidite terrane. Mafic metavolcanic
rocks crop out in the footwall within a few hundred meters
of the ore body. On the basis of whole rock REE analyses,
the mafic volcanic rocks in the southern Chugach terrane are
interpreted by Lull and Plafker (1990) as forming in a shortlived
island-arc environment.
Copper Bullion (Rua Cove) Cyprus Massive
Sulfide Deposit
The Copper Bullion (Rua Cove) Cyprus massive sulfide
deposit (fig. 116) (Koski and others, 1985; Crowe and others,
1992) is a lens-shaped massive body of pyrrhotite with
minor chalcopyrite and sphalerite that is hosted in sheared
pillow basalt of the lower Tertiary Orca Group of the Prince
William terrane. The lens is about 200 m long and is locally
interlayered with pillow basalt and hyaloclastite that occur
stratigraphically above sheeted dikes. The sulfides include
Late Cretaceous and Early Tertiary Metallogenic Belts (84 to 52 Ma) (figs. 102, 103) 245
pyrite, phrrhotite, chalcopyrite, sphalerite, cubanite, galena,
and marcasite. The gangue assemblage consists of abundant
quartz and chlorite, which occur as fine disseminations with
massive sulfides and in pervasive and massive zones in the
stockwork zone where fine-grained talc also occurs. The
deposit contains a well-preserved feeder zone that underlies
the massive sulfide lens is dominanted by pyrrhotite
and chalcopyrite.. The deposit contains reserves of 990,000
tonnes grading 1.25 percent Cu, and