The region is classified
as a single mining district.
The region is dominated by the Aleutian Range, a series of northeast-trending
ridges 1,000—4,000 feet in altitude surmounted locally by volcanoes up
to 9,372 feet high. Northwestward, the range merges with a low sand- and gravel-mantled
plain that has local relief of 50—250 feet.
Geologically, the Alaska Peninsula region consists of two main belts that extend
for most of its length. The northwestern belt is as much as 35 miles wide near
the Ugashik Lakes but is absent on the western end of Unimak Island; it is predominantly
unconsolidated Quaternary silt, sand, and gravel. The southeastern belt is made
up mainly of Mesozoic and Cenozoic sedimentary and volcanic rocks and Tertiary
granitic plutons (Burk, 1965). A single exposure of Permian sedimentary rocks
is near Puale Bay (Hanson, 1957); some of the volcanic rocks also may be of Permian
age. The entire Alaska Peninsula was glaciated during the Pleistocene Epoch but
is now ice free except for some of the highest peaks. The region is generally
free of permafrost. Several of the volcanoes that surmount the Aleutian Range
have been active within the past few years.
Lodes in the Alaska Peninsula region (Berg and Cobb, 1967, p. 5—7, fig.
1; Cobb, 1970b) contain gold, silver, copper, lead, and zinc. Only those on Unga
Island have been worked commercially; ore worth about $2 million, chiefly in
gold and silver from the Apollo mine, was produced between 1891 and 1904.
The only placer deposit in the Alaska Peninsula region for which there is a production
record is an auriferous beach on Popof Island (4, fig. 1), where about 580 ounces
of gold was taken out with rockers in 1904 and 1905 from a belt about three-quarters
of a mile long. All gold recovered was below midtide level and most was found
around large boulders near the low-tide line. Small-scale mining was reported
in each of several years before World War I, but there is no record of more recent
activity. The source of the gold probably is nearby lodes in intensely altered
andesite. Brooks (1912, p. 37) reported beach mining on Unga Island in 1911 but
did not identify where on the island or give any idea of the success of the venture.
Titaniferous magnetite and ilmenite are widespread in beach sands along the shores
of Bristol Bay (Berryhill, 1963). Berryhill collected samples containing as much
as 100 pounds of iron per cubic yard (calculated as content of material in place)
from Mof¬fett Point (1, fig. 1), Nelson Lagoon (2), Port Moller (3), and
Port Heiden (5). The titania (Ti02) content was generally less than 25 pounds
per cubic yard. A few samples contained traces of fine gold.