Little Jim; Little Joe No. 1; Little Joe No. 2 Prospects, Bokan Mountain, Prince of Wales Island, Ketchikan Mining District, Prince of Wales-Hyder Census Area, Alaska, USAi

Regional Level Types
Little Jim; Little Joe No. 1; Little Joe No. 2 Prospects	Group of Prospects
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 geologically similar Little Jim and Little Joe prospects are scattered over an area about one-half mile long. The center of the prospect area is about 0.4 mile north-northeast of Bokan Mountain in the NE1/4 section 21, T 80 S., R. 88 S. The location of these prospects 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 DE019 and DE021 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 Little Jim and Little Joe prospects consist of small prospect pits on claims staked in 1956 (MacKevett, 1963; Warner and Barker, 1989). The deposits consist of pegmatite dikes and masses up to 2 feet thick and 800 feet long in riebeckite granite of the the Bokan Mountain stock. Locally the pegmatite dikes contain scattered uranium and thorium minerals. Samples of the Little Jim deposit contained up to 2,900 parts per million columbium, but only minor uranium, thorium, REE, and yttrium. Some samples of the Little Joe deposit contained elevated columbium, hafnium, titanium, yttrium, and zirconium, and lesser amounts of rare-earth elements, tantalum, and thorium. The sampling indicates that the prospects contain negligible mineral resources.
Workings: Only a few prospecting pits.
Age: Genetically related to the Jurassic, Bokan Mountain peralkaline granite.
Alteration: These prospects 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: Sampling indicates negligible resources.

Commodities (Minor) - Cb, REE, Th, Ti, U, Zr
Development Status: None
Deposit Model: U-Th-REE deposit in pegmatite associated with peralkaline granite.

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Link to USGS - Alaska:	DE020

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References