Ross-Adams Mine, Bokan Mountain, Prince of Wales Island, Ketchikan District, Prince of Wales-Outer Ketchikan Borough, Alaska, USA
Location: The Ross-Adams Mine is about 0.7 mile southeast of Bokan Mountain. It is shown as a mine symbol on the U.S.G.S., 1:63,360-scale topographic map in the NW1/4 section 27, T. 80 S., R. 88 E. The location of the Ross-Adams mine 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 DE024 and DE026 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 Ross-Adams Mine was found in 1955 by Don Ross with an airborne radiometric survey; a radioactive anomaly over the future site of the mine was then prospected on the ground by Kelly Adams. In 1957, about 15,000 tons of ore with a grade of more than 0.80 percent U3O8 was mined from an open pit by Climax Molybdenum Company. Bay West Inc. leased the property in 1961 and began underground exploration and mining from a haulage adit beneath the open pit. Standard Metals Corporation took control of the property in 1963 and Newmont Exploration Ltd. operated the property until 1971. From 1957 to 1971, a total of 79,500 metric tons of ore was mined with an average grade of 0.76 percent U3O8 (MacKevett, 1963, Anonymous, 1980; Warner and Barker, 1989; Roppel, 1991). Thorium was not recovered. The Ross-Adams deposit is in the Bokan Mountain peralkaline complex near its southeast boundary (MacKevett, 1959, 1963; Thompson, 1980; Thompson and others, 1982; Thompson, 1988 [FIR]; Thompson 1988 [PGR]; Warner and Barker, 1989; Philpotts and others, 1996; Thompson, 1997). The ore deposit is an irregularly-shaped pipelike body about 800 feet long and 20 to 100 feet in diameter, inclined to the south. The body is gently inclined at its north end where it was mined from an open pit . The southern two-thirds inclines to a plunge of about 40 degrees to the south. This southern portion was mined over a vertical extent of about 450 feet from two haulage levels. The mineralized pipe is offset by several large faults, and cut by many smaller fractures and microfractures. The fractures tend to localize the ore body, but its general form and location is probably related to a contact between aegirine granite porphyry and aegirine syenite. The pipe typically has a core with more than 0.5 percent U3O8 and an outer shell 2-20 feet thick of lower grade material. The pipe is intensely albitized and chloritized and the effects of this alteration often extend as much as 50 feet beyond the ore body. The primary ore mineral is uranothorite; uraninite and uranothorinite also occur, and, rarely, brannerite and coffinite. The pipe is oxidized at the surface where it was mined in an open pit. Several secondary uranium minerals have been identified, including gummite, sklodowskite, beta-uranophane, bassetite, and novacekite. Sulfides commonly make up as much as 2 percent of the ore; they include pyrite, pyrrhotite, chalcopyrite, sphalerite, galena, and bornite. Thompson and others (1980, 1982, 1997) propose the following genesis of the Ross-Adams deposit: 1) emplacement of a sodium-rich oxidized magma with a normal uranium and thorium content; 2) low initial calcium and titanium, preventing the formation of early accessory minerals; 3) development of a separate volatile phase with high uranium, thorium, and REE content; 4) rapid degassing of the magma chamber, resulting in a silica-saturated magma and a volatile phase emplaced in a zone of structural weakness; and 5) precipitation of the uranium, thorium, and REE minerals. In 1980 (after the last mining), Standard Metals Corp. identified the remaining reserves as 365,000 short tons of ore with an average grade of 0.17 percent U3O8 and 0.46 percent thorium (Anonymous, 1980). Based on an analysis of drill core, Warner and Barker (1989) estimated an additional resource 'on the order of'' 2,300,000 pounds of yttrium, 537, 000 pounds of REE, and 1,752,000 pounds of zirconium.
Workings: The ore deposit is an irregularly-shaped pipelike body about 800 feet long and 20 to 100 feet in diameter, inclined to the south. The body is gently inclined at its north end where it was mined from an open pit . The southern two-thirds inclines to a plunge of about 40 degrees to the south. This southern portion was mined over a vertical extent of about 450 feet from two haulage levels.
Age: Genetically related to the Jurassic, Bokan Mountain peralkaline granite.
Production: In 1957, about 15,000 tons of ore with a grade of more than 0.80 percent U3O8 was mined from an open pit by Climax Molybdenum Company. Bay West Inc. leased the property in 1961 and began underground exploration and mining from a haulage adit beneath the open pit. Standard Metals Corporation took control of the property in 1963 and Newmont Exploration Ltd. operated the property until 1971. From 1957 to 1971, a total of 79,500 metric tons of ore was mined with an average grade of 0.76 percent U3O8 (MacKevett, 1963, Anonymous, 1980; Warner and Barker, 1989). Thorium was not recovered.
Reserves: In 1980, Standard Metals Corp. identified the remaining reserves as 365,000 short tons of ore with an average grade of 0.17 percent U3O8 and 0.46 percent thorium (Anonymous, 1980). Based on an analysis of drill core by the U.S. Bureau of Mines, they indicated an additional resource 'on the order of' 2,300,000 pounds of yttrium, 537, 000 pounds of REE, and 1,752,000 pounds of zirconium (Warner and Barker, 1989; Maas and others, 1995).
Commodities (Major) - U; (Minor) - REE, Th
Development Status: Yes; medium
Deposit Model: U-Th-REE deposit associated with a peralkaline granite.
17 entries listed. 15 valid minerals.
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Anonymous, 1980, Standard Metals Corp., Progress Report: The Mining Record, April 2, 5 p. 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. Cobb, E. H., 1978, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Dixon Entrance quadrangle, Alaska: U.S. Geological Survey Open-File Report 78-863, 34 p. 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. Denny, R. L., 1962, Operations at the Ross-Adams uranium deposit, Dixon Entrance quadrangle, in Williams, J.A., Report of the Division of Mines and Minerals for the year 1962: Alaska Division of Geological & Geophysical Surveys, Annual Report 1962, p. 89-93. Eakins, G.R., 1970, An experiment in geobotanical prospecting for uranium, Bokan Mountain area, southeastern Alaska: Alaska Division of Mines and Geology Geologic Report 41, 51 p. Eakins, G.R., 1975, Uranium investigations in southeastern Alaska: Alaska Division of Geological and Geophysical Surveys Geologic Report 44, 62 p. Freeman, V.L., 1963, Examination of uranium prospects, 1956, in Contributions to economic geology of Alaska: U.S. Geological Survey Bulletin 1155, p. 29-33. Gehrels, G. E., 1992, Geologic map of southern Prince of Wales Island, southeastern Alaska: U.S. Geological Survey Miscellaneous Investigations Series Map I-2169, 23 p., 1 sheet, scale 1:63,360. 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. Maas, K.M., Bittenbender, P E., and Still, J.C., 1995, Mineral investigations in the Ketchikan mining district, southeastern Alaska: U.S. Bureau of Mines Open-File Report 11-95, 606 p. MacKevett, E.M., Jr., 1963, Geology and ore deposits of the Bokan Mountain uranium-thorium area, southeastern Alaska: U.S. Geological Survey Bulletin 1154, 125 p. MacKevett, E. M., Jr., 1959, Geology of the Ross-Adams uranium-thorium deposit, Alaska: Mining Engineering, v. 11, no. 9, p. 915-919. Matzko, J.J., and Freeman, V.L., 1963 Summary of reconnaissance for Uranium in Alaska, 1955: U.S. Geological Survey Bulletin 1155, p. 33-49. Philpotts, J.A., Taylor, C.D., and Baedecker, P.A., 1996, Rare-earth enrichment at Bokan Mountain, southeast Alaska, in Moore, T.E. and Dumoulin, J.A., eds., Geologic studies in Alaska by the U.S. Geological Survey, 1994: U. S. Geological Survey Bulletin 2152, p. 89-100. Roppel, Patricia, 1991, Fortunes from the earth: Manhattan, Kansas, Sunflower University Press, 139 p. 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. Stephens, F. H., 1971, The Kendrick Bay Project: Western Miner, October, p. 151-158. 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. Warner, J. D., and Barker, J. C., 1989, Columbium- and rare-earth-element-bearing deposits at Bokan Mountain, southeast Alaska: U.S. Bureau of Mines Open-File Report 33-89, 196 p.
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New Locality Added: Pontével, Cartaxo, Santarém District, PortugalFrom Rui Nunes, 25th Oct 2014 21:07:20