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, fig. 15).
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 over¬ridden 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.