Shore

Occurrence, Active

Commodities and mineralogy

Main commodities Be; Cb; Ce; Dy; Er; Eu; Gd; Ho; La; Lu; Nd; Pm; Pr; Sm; Tb; Th; Tm; U; Y; Yb; Zr
Other commodities Pb; Sn; Sr; Ta
Ore minerals allanite; pyrite; ree minerals
Gangue minerals albite; quartz

Geographic location

Quadrangle map, 1:250,000-scale DE
Quadrangle map, 1:63,360-scale D-1
Latitude 54.896
Longitude -132.0935
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Shore occurrence is in the intertidal zone in the vicinity of the point that juts out into the West Arm of Kendrick Bay near the northwest corner of section 36, T. 80 S., R. 88 E. The location of this occurrence 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 (DE015 to DE029 and 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 Shore occurrence is in the intertidal zone on the south side of the West Arm of Kendrick Bay (Warner and Barker, 1989). Radioactive, granitic dike rubble and a few outcrops of dike occur along about 1,000 feet of shoreline. The dikes are in a 100-foot-wide zone near the contact of quartz monzonite and quartz diorite. The dikes strike N50W and dip steeply to vertical. They are generally 0.2 to 0.5 feet thick wide and there are intervals where thinner dikes closely parallel each other. The dikes vary from coarse grained to pegmatitic and commonly contain disseminated fluorite, pyrite, allanite(?), and REE(?) minerals. The quartz monzonite near the dikes locally is cut by pyritic, siliceous zones up to 30 feet wide. Samples contained anomalously high columbium, uranium, thorium, REE, yttrium, zirconium, zinc, titanium, and beryllium. Some samples also contained elevated tin, tantalum, lead, and strontium. Three channel samples 1.1 feet long averaged 760 parts per million columbium. The dikes are unusually enriched in REE, especially cerium and neodymium; samples of dike material contained up to 2.5 percent REE.
In 2008, Ucore Uranium drilled one hole hear the Shore prospect for rare-earth elements along what they term the 'Geoduck trend' that is oriented northwest along the N50W granitic dike. In 2009, they drilled two more holes about 600 meters southeast along the trend at the Geoduck prospect (DE031).
Geologic map unit (-132.095145872906, 54.8956568673139)
Mineral deposit model U-Th-REE deposit in dikes associated with peralkaline granite.
Age of mineralization Genetically related to the Jurassic, Bokan Mountain peralkaline granite stock.
Alteration of deposit Not specifically described; the dikes and their wallrocks are probably albitized and chloritized like those at the other REE deposits in the area.

Production and reserves

Workings or exploration Only surface sampling by government geologists to 2008. In 2008, Ucore Uranium drilled one hole for rare-earth elements.
Indication of production None
Reserve estimates None.
Production notes None.

References

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.
Ucore Uranium, 2010, Bokan Mountain, Alaska: http://www.ucoreuranium.com/bokan.asp (as of February 22, 2010.)
Reporters D.J. Grybeck (Contractor, U.S. Geological Survey)
Last report date 4/2/2010