The Kodiak region (p1.
1, fig. 11) includes Kodiak, Afognak, and the Trinity Islands and
nearby small islands. The region, classified as a single district,
is characterized by mountains with summits 2,000—4,000 feet
in altitude and by gently rolling uplands. Long narrow inlets extend
well into the interiors of Kodiak and Afognak Islands.
Most of the region is underlain by Cretaceous graywacke, slate, and
conglomerate that rest on older Mesozoic marine and volcanic rocks
containing a few small mafic and ultramafic bodies and by Tertiary
quartz diorite plutons, some of batholithic dimen¬sions. Younger
Tertiary marine and continental rocks form the Trinity Islands and
a fringe along the southeastern coast of Kodiak Island. Quaternary
glacial and fluvial deposits mantle bedrock in low areas on western
Kodiak Island, at the heads of bays, and along some of the larger
streams. Long faults extend the length of the major islands, giving
the region a pronounced northeast-trending grain that, if prolonged,
would join generally similar features at the southwestern end of the
Kenai Peninsula. The foregoing summary is based on a recent map by
Moore (1967) and an earlier report by Capps (1937).
The Kodiak region was covered by Pleistocene ice that extended from
the crest of the Aleutian Range across the islands and sev¬eral
tens of miles into the Pacific Ocean. The ice removed most unconsolidated
material and any placer deposits that may have been formed in preglacial
valleys. Ice remains in a few cirque glaciers on the highest peaks
on Kodiak Island.
An unknown, but probably small, amount of gold was mined from several
lode deposits in the Kodiak region, mainly before World War I and
about 1935. Lode occurrences of tungsten and copper proved to be too
small and of too low grade to be mined (Berg and Cobb, 1967, p. 82—88,
The only placers that have been found in the region are in beach deposits,
where gold was concentrated from lean glacial outwash and till. Mining
was on a small scale, using rockers and portable sluice boxes operated
with water brought from nearby lakes by ditches and canvas hose. Most
of the activity was on the beaches along the west coast of Kodiak
Island (1, fig. 11), where wave action concentrated heavy minerals
in a veneer of material in transit across a planation surface cut
on glacial de¬posits. By far the greatest part (95 percent) of
the concentrates was magnetite. Other heavy minerals include pyrite,
chromite, gold, and a little platinum. Ultramafic bodies that had
been overridden by ice were the original sources of the chromite and
platinum and at least some of the magnetite. The placer at Cape Alitak
(2, fig. 11) is unusual in that the small amount of fine gold recovered
came from dune sands derived, either directly or by way of beach deposits,
from bluffs of glacial material.
The total production of gold from beaches in the Kodiak region is
not known, as records combine data from all of southwestern Alaska,
but it probably was not more than a few thousand ounces at most. The
only beach mining reported since World War II was in 1951—52,
when two men were working on the west coast of Kodiak Island.