Millet; Copper King Ledge; Millet Point Prospect, Bristol Bay Mining District, Lake and Peninsula Borough, Alaska, USAi

Regional Level Types
Millet; Copper King Ledge; Millet Point Prospect	Prospect
Bristol Bay Mining District	Mining District
Lake and Peninsula Borough	Borough
Alaska	State
USA	Country

Location: The Millet prospect on the Copper King Ledge claims extends from about 950 feet north of the shoreline of Lake Iliamna north for at least 2,500 feet. The approximate midpoint of the linear deposit is in the SW1/4 SW1/4 sec. 31, T. 4 S., R. 31 W., Seward Meridian. The Millet prospect is locality 2 of Detterman and Cobb (1972). The location is accurate within about 500 feet for the center of the prospect area.
Geology: The Millet prospect is a skarn deposit developed mainly in the Ursus Member of the Upper Triassic Kamishak Formation (Detterman and Reed, 1980, plate 1, p. 11-14). The Ursus Member consists chiefly of thin-bedded, light-gray limestone. The limestone strikes about north and dips moderately to the east, roughly parallel to its intrusive contact with Tertiary or Cretaceous, medium- to coarse-grained, light-gray quartz diorite. To the south, the diorite and limestone are overlain unconformably by locally brecciated, Tertiary basalt and andesite. The deposit is about 200-300 feet east of the quartz diorite contact, strikes about north, and consists of layers and lenses of skarn, mineralized limestone, and dikes that are roughly parallel to the quartz diorite contact. The skarn consists of amphibole, garnet, epidote, calcite, quartz, an unidentified amber-color mineral (possibly idocrase), small amounts of hematite, pyrite, and chalcopyrite, and locally other sulfide minerals. Pyrite generally is more abundant than chalcopyrite. Pyrite also is disseminated in the limestone, locally in amounts up to about 10 percent (Rutledge and Mulligan, 1952; Martin and Katz, 1910). Retherford and Hickok (1990) reported chalcocite and minor amounts of sphalerite associated with chalcopyrite in mineralized rock near an old shaft. Oxidation of the deposit extends to a depth of about 8 feet along cracks and fissures. According to Martin and Katz (1910, p. 198), the oxidized ore contains copper carbonates, presumably malachite and azurite, and black copper and iron oxides possibly including neotocite or copper pitch. Drilling and other sampling by the U.S. Bureau of Mines indicates two bodies, mainly of skarn, that aggregate about 2,500 feet of a total strike length of about 3,500 feet (Rutledge and Mulligan, 1952; Moxham and Nelson, 1952). The southern body is on Copper King Ledge Nos. 1 and 2 claims and is about 525 feet long; it parallels a dike that ranges from 3 to 80 feet thick. The body averages about 19 feet thick and grades about 1.08 percent copper. The northern body is a composite deposit about 735 feet long on the Copper King Ledge Nos. 2 and 3 claims. It comprises two mineralized zones separated by 50 feet of barren, black limestone. The larger zone is almost 30 feet thick and averages 0.64 percent copper. One U.S. Bureau of Mines drill hole (no. 3) intersected about 31 feet grading 1.44 percent copper (Rutledge and Mulligan, 1952). The original owner of the prospect (Millet) reported that a select sample that contained about 10 percent copper assayed about 0.1 ounce of gold per ton (Martin and Katz, 1910, p. 198). Later investigators found little gold. U.S. Bureau of Mines assays indicate a very low average content of gold and silver in their samples (Rutledge and Mulligan, 1952), and gold values of no more than about 600 parts per billion were reported by Retherford and Hickok (1990).
Workings: The deposit was first staked in 1906 by Millet, who patented three claims. In 1949 and 1950, the U.S. Bureau of Mines dug 6,229 feet of trenches and diamond drilled six holes totaling 2,298.5 feet (Rutledge and Mulligan, 1952). Mineralized zones contained 0.54 to 1.43 percent copper, up to 0.2 ounce of silver per ton, and less than 0.01 ounce of gold per ton At the time of the U.S. Bureau of Mines investigation, the property was leased to St. Eugene Mining Company.
Age: Late Cretaceous or Tertiary; probably nearly synchronous with intrusion of the quartz diorite.
Alteration: Replacement of limestone by garnet, amphibole, epidote, and other skarn minerals.

Commodities (Major) - Cu; (Minor) - Ag, Au
Development Status: Undetermined.
Deposit Model: Cu skarn (Cox and Singer, 1986; model 18b).

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Link to USGS - Alaska:	IL009

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References