Atom Marietta prospect, Bokan Mountain, Prince of Wales Island, Ketchikan Mining District, Prince of Wales-Hyder Census Area, Alaska, USAi

Regional Level Types
Atom Marietta 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 Atom Marietta prospect is about 1.1 miles east-southeast of Bokan Mountain, near the center of the west boundary of the SE1/4 SE1/4 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 DE023 and DE025 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 peralkaline 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 Atom Marietta prospect consists of a few hand-dug cuts and pits on several claims located in 1955 (MacKevett, 1963). The prospect is in aplite near the southeastern edge of the Bokan Mountain peralkaline complex. The deposit is near the intersection of a major northeast-trending fault zone with a group of steep northwest faults. The deposit is associated with intensely altered and fractured dacite dikes that cut the aplite in or near the fault zones. The uranium-thorium minerals occur in narrow veinlets, as disseminations, and as irregular, sublinear masses. The primary radioactive mineral is uranothorite, although uraninite and other unidentified minerals, possibly brannerite or davidite, also occur. Secondary uranophane is present.

Workings: Only a few hand-dug pits and trenches.

Age: Genetically related to the Jurassic, Bokan Mountain peralkaline granite.

Alteration: Not specifically described; the dikes and their wallrocks are probably albitized and chloritized like those at other deposits in the area.

Commodities (Major) - Th, U

Development Status: None

Deposit Model: U-Th-REE deposit associated with peralkaline granite.

Other Databases

Link to USGS - Alaska:	DE024

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References