Irene-D Prospect, Bokan Mountain, Prince of Wales Island, Ketchikan Mining District, Prince of Wales-Hyder Census Area, Alaska, USAi

Regional Level Types
Irene-D Prospect	Prospect
Bokan Mountain	Mountain
Prince of Wales Island	Island
Ketchikan Mining District	Mining District
Prince of Wales-Hyder Census Area	Census Area
Alaska	State
USA	Country

Location: The Irene-D prospect is at the head of Perkins Creek at an elevation of about 850 feet. It is about 0.9 mile east-northeast of Bokan Mountain, near the center of section 22, T. 80 S., R. 88 E. Its location relative to the other uranium and REE prospects in the vicinity of Bokan Mountain is best shown on Plate 1 of MacKevett (1963).
Geology: This and several other nearby uranium-thorium-REE deposits (DE015 to DE021 and DE22 to DE031) 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 Irene-D prospect was located in the 1960's; it consists of an area about 200 feet wide of radioactive pegmatite rubble (Warner and Barker, 1989). Warner and Barker traced the pegmatite about 3,000 feet to the south by magnetometer surveys and in outcrop. The pegmatite is notable for its high content of magnetite or ilmenite, which locally makes up 15 percent of the rock. The magnetite occurs as bladed crystals up to 0.25 inch long, but more commonly as disseminated grains in the pegmatite or as masses up to 1 inch in diameter. The pegmatite commonly has a quartz core bordered by albite(?), quartz, and riebeckite phenocrysts. The riebeckite is commonly altered to aegirine which forms masses up to 1 foot in diameter. Ilmenite is more abundant than magnetite in the southern part of the pegmatite. Pyrite and unidentified radioactive minerals occur as accessory minerals in the pegmatite. The pegmatite forms a band 30 to 50 feet wide in aplite and aegirine granite. The pegmatite is bounded on the west by aegirine- and riebeckite-aegirine granite of the Bokan Mountain complex and on the east by Silurian or Ordovician quartz monzonite. Thompson and others (1982, 1997) considered this pegmatite to be the outer zone of a ring dike complex. Warner and Barker (1989) indicate that the pegmatite at the Irene-D prospect contains relatively low values of columbium, REE, yttrium, and zirconium. A few samples contained minor uranium and traces of gold. Based on their work, the values are too low to constitute a significant resource.
Workings: Only limited surface prospecting by private parties; considerable sampling and magnetometer surveys by government geologists.
Age: Genetically related to the Jurassic, Bokan Mountain peralkaline granite.
Alteration: This prospect and the other uranium, thorium, and REE deposits associated with the Bokan Mountain peralkaline granite are marked by albitization, chloritization, and argillization. Minor calcite, fluorite, quartz, sulfide minerals, and tourmaline are common in the altered rocks and hematite often occurs in the periphery of high-grade ore zones.
Reserves: Warner and Barker (1989) indicate that the pegmatite at the Irene-D prospect contains relatively low values of columbium, REE, yttrium, and zirconium. A few samples contained minor uranium and trace gold. Based on their work, the values are too low to constitute a significant resource.

Commodities (Major) - Cb, REE, U, Y, Zr
Development Status: None
Deposit Model: U-Th-REE deposit in pegmatite at the margin of a peralkaline granite intrusion.

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Link to USGS - Alaska:	DE022

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