Geoduck Occurrences, West Arm of Kendrick Bay, Kendrick Bay, Prince of Wales Island, Ketchikan Mining District, Prince of Wales-Hyder Census Area, Alaska, USAi

Regional Level Types
Geoduck Occurrences	Group of Occurrences
West Arm of Kendrick Bay	Bay
Kendrick Bay	Bay
Prince of Wales Island	Island
Ketchikan Mining District	Mining District
Prince of Wales-Hyder Census Area	Census Area
Alaska	State
USA	Country

Location: The Geoduck occurrences are south of the West Arm of Kendrick Bay. They are related to a dike system that extends N40-50W for about 10,000 feet, nearly diagonally through the center of section 36, T. 80 S., R. 88 E. and into the NW1/4 of section 2, T. 81 S., R. 89 E. The site is approximately at the midpoint of the most continuous and thickest dike, where resource calculations have been made.
Geology: This and several other nearby uranium-thorium-REE deposits (DE015 to DE030) are spatially and genetically related to a stock of Jurassic, peralkaline granite about 2 miles in outcrop diameter centered on Bokan Mountain. It commonly is referred to as the Bokan Mountain peralkakline granite or Bokan Mountain complex. The intrusion and its deposits have been mapped in detail several times using slightly different subdivisions of the granite (MacKevett, 1963; Thompson and others, 1980, 1982; Saint-Andre and others, 1983; Gehrels, 1992; Thompson, 1997). This description largely follows Gehrels' (1992) map units. The intrusion is a ring-dike complex with an outer border zone up to 14 meters thick of pegmatite and aplite; a nearly complete intermediate zone of aegirine granite porphyry, 15 to 180 meters thick; and a core of several varieties of riebeckite granite porphyry. It has been dated by several methods at 151 Ma to 191 Ma (Lanphere and others, 1964; Saint-Andre and others, 1983; Armstrong, 1985; Gehrels, 1992; Thompson, 1997). The peralkaline granite mainly intrudes a regionally extensive body of Silurian or Ordovician quartz monzonite, granite, and quartz diorite that makes up much of the southeast tip of Prince of Wales Island. The south and west sides of the peralkaline granite are in contact with a band up to about 3,000 feet wide of shale and argillite of the Silurian or Ordovician Descon Formation. The Bokan Mountain complex and surrounding Paleozoic rocks are cut by numerous pegmatite, andesite, dacite, and aplite dikes. The dikes are genetically related to the complex and commonly are associated with the uranium, thorium, and REE deposits. The deposits are marked by intense albitization, pervasive or fracture-controlled chloritization, calcite-fluorite replacement of aegirine, and hematitization. Three types of U-Th-REE deposits occur in the Bokan Mountain complex: 1) irregular cylindrical pipes; 2) steep, shear-zone-related pods or lenses ('veins'); and 3) quartz veins. The Geoduck occurrences are related to a system of eqigranular, fine- to medium-grained, andesite dikes that strike N40-50W for about 10,000 feet, west of the head of Kendrick Bay (MacKevett, 1963; Warner and Barker, 1989). The dikes have steep to vertical dips, cut Silurian or Ordovician quartz monzonite, granite, and quartz diorite, and typically have wall rocks marked by chlorite and epidote alteration. The ore mineralogy has not been worked out in detail but it is probably similar to that in the mineralized dikes at the Carol Ann/Dotson prospects (DE027), which may be extensions of the Geoduck dikes. In the northwest part of the Geoduck dike system, individual dikes average about 1.4 feet thick; in the southeast part, they average about 0.8 feet thick. Many samples contain elevated values of beryllium, thorium, yttrium, REE, columbium, uranium, and zirconium. A 3,000-foot section of the most continuous and thickest dike, which averages 1.5 feet thick, has an indicated resource of 1,378, 000 short tons of rock that contains 278,000 pounds of beryllium, 752,000 pounds of thorium, 8,116,000 pounds of yttrium, 8,786,000 pounds of REE, 2,844,000 pounds of columbium, 358,000 pounds of U, and 12,953,000 pounds of zirconium (Warner and Barker, 1989). There is a inferred reserve in 95,28,000 short tons of rock of 1,906,000 pounds of beryllium, 3,525,000 pounds of thorium, 29,975,000 pounds of yttrium, 14,864,000 pounds of columbium, 1,944,000 pounds of uranium, and 55,262,000 pounds of zirconium.
Workings: Only surface sampling by government geologists.
Age: Associated with dikes that are genetically related to the Jurassic, Bokan Mountain peralkaline granite.
Alteration: The dikes are probably albitized and chloritized; the wall rocks are marked by chlorite and epidote alteration.
Reserves: A 3,000-foot section of the most continuous and thickest dike which averages 1.5 feet thick has an indicated resource of 1,378, 000 short tons of rock that contains 278,000 pounds of beryllium, 752,000 pounds of thorium, 8,116,000 pounds of yttrium, 8,786,000 pounds of REE, 2,844,000 pounds of columbium, 358,000 pounds of U, and 12,953,000 pounds of zirconium (Warner and Barker, 1989). There is a inferred reserve in 95,28,000 short tons of rock of 1,906,000 pounds of beryllium, 3,525,000 pounds of thorium, 29,975,000 pounds of yttrium, 14,864,000 pounds of columbium, 1,944,000 pounds of uranium, and 55,262,000 pounds of zirconium.

Commodities (Major) - Be, Cb, REE, Th, U, Y, Zr
Development Status: None
Deposit Model: U-Th-REE deposit in dikes associated with peralkaline granite.

Other Databases

Link to USGS - Alaska:	DE031

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References