Cheri

Prospects, Active?

Alternative names

Cheri No. 1

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
Ore minerals allanite; hematite; magnetite; pyrite
Gangue minerals albite; quartz

Geographic location

Quadrangle map, 1:250,000-scale DE
Quadrangle map, 1:63,360-scale D-1
Latitude 54.8924
Longitude -132.1035
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Cheri prospects are centered about 0.7 mile south-southeast of the head of the West Arm of Kendrick Bay, near the center of the NE1/4 section 35, T. 80 S., R. 88 E., of the Copper River Meridian. Their locations relative to the other uranium and REE prospects in the vicinity of Bokan Mountain are best shown on Plate 1 of MacKevett (1963).

Geologic setting

Geologic description

This and several other nearby uranium-thorium-REE deposits (DE015 to DE028 and DE030 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.
MacKevett (1963) identified small pits and trenches at the Cheri prospects on several claims staked in 1956. The rocks in the vicinity consist of Ordovician, albitized quartz diorite and diorite, and a pendant of quartzite of the Descon Formation that cannot be delineated exactly in the heavily vegetated cover. The deposit at the Cheri prospects consists of system of radioactive andesite(?) dikes that strike about N 45 W and can be traced for at least 3,000 feet along strike (Warner and Barker, 1989). The zone of dikes is about 100 feet wide; it consists of several parallel dikes, 0.8 to 1.3 feet thick. The dikes are fine grained and siliceous. At one location, pyroxene-rich masses with minor pyrite, rare fluorite, and secondary uranium minerals, occur in a dike. Chlorite, magnetite, pyrite, and epidote commonly occur at the margins of the dikes. Allanite is the principal radioactive mineral and the mineralogy is probably similar to that at the nearby Carol Ann/Dotson prospects (DE027), where similar dikes occur. The radioactive minerals are mainly concentrated in quartz veinlets or along mineralized fractures. At the Cheri No. 1 prospect, allanite in the interstices of quartzite is accompanied by abundant hematite and less-abundant albite, quartz, calcite, epidote, and chlorite.
In 2009, Ucore Uranium (2010) drilled two holes near the Cheri prospect for rare-earth elements. The analyses for the samples were reported as the light rare-earth-element oxides or LREO (lanthanum, cerium, praesodymium, neodymium, and samarium) and the heavy rare-earth-element oxides or HREO (europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and yttrium); together they are termed the TREO, the total rare-earth-element oxides. The two most notable intercepts in one of the holes was 0.5 meter with 4.0 percent TREO, and 0.4 meter with 3.4 percent TREO. The ratio of the the HREO to the TREO in the two intercept was 39.4 and 46.1 percent; in other words nearly half of the rare-earth elements in the samples are the heavy rare-earth elements.
Warner and Barker (1989) estimate an indicated resource of 73,000 tons of rock in two portions of the Cheri dike system that contain 91,000 pounds of columbium, 32,000 pounds of thorium, 109,000 pounds of zirconium, 13,000 pounds of beryllium, 15,000 pounds of uranium, and 349,000 pounds of REE. There is an additional indicated resource of 458,000 short tons of rock in another portion of the dike system that contains 1,122,000 pounds of columbium, 338,000 pounds of thorium, 1,602,000 pounds of yttrium, 4,397,000 pounds of zirconium, 101,000 pounds of beryllium, 153,000 pounds of uranium, and 3,593,000 pounds of REE.
Geologic map unit (-132.105144685892, 54.8920572202075)
Mineral deposit model U-Th-REE deposit in dikes associated with peralkaline granite stock.
Age of mineralization Genetically related to the Jurassic, Bokan Mountain peralkaline granite.
Alteration of deposit 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.

Production and reserves

Workings or exploration Only a few prospect pits to 2008. In 2009, Ucore Uranium drilled two holes for rare-earth elements.
Indication of production None
Reserve estimates Warner and Barker (1989) estimate an indicated resource of 73,000 tons of rock in two portions of the Cheri dike system that contain 91,000 pounds of columbium, 32,000 pounds of thorium, 109,000 pounds of zirconium, 13,000 pounds of beryllium, 15,000 pounds of uranium, and 349,000 pounds of REE. There is an additional indicated resource of 458,000 short tons of rock in another portion of the dike system that contains 1,122,000 pounds of columbium, 338,000 pounds of thorium, 1,602,000 pounds of yttrium, 4,397,000 pounds of zirconium, 101,000 pounds of beryllium, 153,000 pounds of uranium, and 3,593,000 pounds of REE.
Production notes None.

References

MRDS Number A010269

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