Geiger

Prospect, Probably inactive

Commodities and mineralogy

Main commodities Cb; REE; Ta; Th; U; Y; Zr
Other commodities F; Ge; Pb; Zn
Ore minerals columbite-tantalite; galena; ree minerals; sphalerite; uranothorite; zircon
Gangue minerals albite; quartz

Geographic location

Quadrangle map, 1:250,000-scale DE
Quadrangle map, 1:63,360-scale D-1
Latitude 54.9511
Longitude -132.1742
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Geiger prospect is at an elevation of about 50 feet, 0.4 mile north-northeast of the mouth of Perkins Creek where it enters the South Arm of Moira Sound. The prospect is near the center of the east boundary of the NE1/4 section 8, T. 80 S., R. 88 E. The location of the Geiger prospect relative to the other uranium and REE prospects in the vicinity of Bokan Mountain is best shown on Plate 1 of MacKevett (1963).

Geologic setting

Geologic description

This and several other nearby uranium-thorium-REE deposits (DE016 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 Geiger prospect has a few small pits on claims located in 1956. The deposit consists of unidentified radioactive and REE minerals in quartz veinlets in mineralized, altered felsic dikes. The dikes, probably originally rhyolite or quartz latite, cut metavolcanic rocks of the Descon Formation outboard of the Bokan Mountain peralkaline granite (MacKevett, 1963).
Warner and Barker (1989) describe the deposit as an apparently continuous system of one to five or more, parallel felsic dikes of variable composition that strike N 15 E to N 30 W; the dikes can be traced for about 8,700 feet in float, outcrop, and test pits. Individual dikes are up to 8.5 feet thick. Warner and Barker infer that the uranium and thorium are mainly in uranothorite, and the columbium and tantalum are probably in columbite-tantalite; zircon is present, as well as minor galena, sphalerite, and fluorite.
According to Warner and Barker (1989), the indicated resources along 3,100 feet of dike are 7,497,000 pounds of columbium, 402,000 pounds of thorium, 852,000 pounds of uranium, 6,458,000 pounds of yttrium, 8,820,000 pounds of zirconium, 19,061,000 pounds of REE, and 578,000 pounds of tantalum, in 2,450,000 short tons of rock. The total inferred resource along 5,600 feet of dike is 14,361,000 pounds of columbium, 770,000 pounds of thorium, 1,652,000 pounds of uranium, 12,371,000 pounds of yttrium, 168,948,000 pounds of zirconium, 36,512,000 pounds of REE, and 1,108,000 pounds of tantalum, in 4,693,000 short tons of rock (Warner and Barker, 1989).
Geologic map unit (-132.175842972776, 54.9507582482198)
Mineral deposit model U-Th-REE deposit associated with peralkaline granite.
Age of mineralization Genetically related to the Jurassic, Bokan Mountain peralkaline granite.
Alteration of deposit 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.

Production and reserves

Workings or exploration Only a few prospect pits.
Indication of production None
Reserve estimates According to Warner and Barker (1989), the indicated resources along 3,100 feet of dike are 7,497,000 pounds of columbium, 402,000 pounds of thorium, 852,000 pounds of uranium, 6,458,000 pounds of yttrium, 8,820,000 pounds of zirconium, 19,061,000 pounds of REE, and 578,000 pounds of tantalum, in 2,450,000 short tons of rock. The total inferred resource along 5,600 feet of dike is 14,361,000 pounds of columbium, 770,000 pounds of thorium, 1,652,000 pounds of uranium, 12,371,000 pounds of yttrium, 168,948,000 pounds of zirconium, 36,512,000 pounds of REE, and 1,108,000 pounds of tantalum, in 4,693,000 short tons of rock.

References

MRDS Number A010281

References

Armstrong, R. L., 1985, Rb-Sr dating of the Bokan Mountain granite complex and its country rocks: Canadian Journal of Earth Sciences, v. 22, p. 1233-1236.
Collett, B., 1981, Le granite albitique hyperalcalin de Bokan Mountain, S.E. Alaska et ses mineralisations U-Th. Sa place dans la cordillere canadienne: Doct. 3 degree cycle theseis, Montpellier II University, Montpellier, France, 238 p.
Lanphere, M. A., MacKevett, E. M., and Stern, T. W., 1964, Potassium-argon and lead-alpha ages of plutonic rocks, Bokan Mountain area, Alaska: Science, v. 145, p. 705-707.
Saint-Andre, Bruno de, Lancelot, J. R., and Collot, Bernard, 1983, U-Pb geochronology of the Bokan Mountain peralkaline granite, southeastern Alaska: Canadian Journal of Earth Sciences, v. 20, p. 236-245.
Staatz, M. H., 1978, I and L uranium and thorium vein system, Bokan Mountain, southeastern Alaska: Economic Geology, v.73, p. 512-523.
Thompson, T. B., 1988, Geology and uranium-thorium mineral deposits of the Bokan Mountain granite complex, southeastern Alaska: Fluid Inclusion Research, v. 21, p. 193-210.
Thompson, T.B., 1988, Geology and uranium-thorium mineral deposits of the Bokan Mountain granite complex, southeastern Alaska, in Gabelman, J. W., ed., Unconventional uranium deposits: Ore Geology Reviews, v. 3, p 193-210.
Thompson, T.B., 1997, Uranium, thorium, and rare metal deposits of Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral deposits of Alaska: Economic Geology Monograph 9, p. 466-482.
Thompson, T. B., Lyttle, Thomas, and Pierson, J. R., 1980, Genesis of the Bokan Mountain, Alaska, uranium-thorium deposit: U.S.Department of Energy, Bendix Field Engineering Report GJBX-38(80), 232 p.
Thompson, T. B., Pierson, J. R., and Lyttle, T., 1982, Petrology and petrogenesis of the Bokan granite complex, southeastern Alaska: Geological Society of America Bulletin, v. 93, p. 898-908.
Reporters D.J. Grybeck (Applied Geology)
Last report date 9/1/2003