|Main commodities||Cb; Ce; Dy; Er; Eu; Gd; Ho; La; Lu; Nd; Pm; Pr; Sm; Tb; Th; Tm; U; Y; Yb; Zr|
|Ore minerals||aeschynite; allanite; bastnaesite; columbite-tantalite; euxenite-polycrase; fergusonite; fluorite; monazite; parisite; pyrite; samarskite; synchysite; tengerite; thalenite; thorite; unnamed ree fluorocarbonate; uranothorite; xenotime; zircon|
|Gangue minerals||albite; calcite; fluorite; hematite; quartz; tourmaline|
|Quadrangle map, 1:250,000-scale||DE|
|Quadrangle map, 1:63,360-scale||D-1|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||The three Carol Ann prospects are at the southeast end of the Dodson dike and its persistent. The coordinates are at near the center of the prospect area, about 1.9 miles southeast of Bokan Mountain, near the middle of the N1/2 section 26, T. 80 S., R. 88 E of the Copper River Meridian. The locations of the Carol Ann prospects relative to the other uranium and REE prospects in the vicinity of Bokan Mountain are best shown on Plate 1 of MacKevett (1963). The location is accurate, though degree of accuracy is not reported.|
This and several other nearby uranium-thorium-REE deposits (DE015 to DE026 and DE028 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) describes three prospects under the name Carol Ann as surface pits on three claims located in 1955. The prospects are on a series of steep, subparallel, allanite-bearing andesite dikes that strike about N60-75W for at least 3,500 feet. The dikes radiate out from the Bokan Mountain peralkaline granite into Silurian or Ordovician quartz monzonite.
Warner and Barker (1989) describes these prospects under the name Dotson and extend the dikes northwest to the I & L Nos. 3-5 prospects (DE023) at the periphery of the Bokan Mountain alkaline granite. Several parallel dikes occur over a width of less than 100 feet to 200 feet; the individual dikes vary in width from 0.6 feet to 3.1 feet. To northwest, near the Bokan Mountain granite, the dikes are pegmatitic; to the southeast, they generally are medium- to fine-grained and equigranular. The mineralization occurs in microfractures or in the interstices between silicate grains. The dominant radioactive mineral is allanite. Scanning electron microscope study shows that the REE minerals are mainly thalenite, bastnaesite, and allanite, with subordinate tengerite, parisite, synchysite, an unnamed REE flurocarbonate mineral, monazite, and xenotime. The columbium-bearing mineral is mainly euxenite-polycrase, accompanied by subordinate columbite-tantalite, samarskite, fergusonite, and aeschynite. The main radioactive mineral is thorite but uranothorite is also present.
In 2008 and 2009, Ucore Uranium drilled a line of 24 holes for rare-earth elements at roughly equal intervals from near this prospect to the Atom Marietta prospect (DE024), a distance of about 2,000 meters (Ucore Uranium, 2010). The line of holes follows the Dodson dike system. 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 (euroipium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and yttrium); together they are termed the TREO, the total rare-earth-element oxides. Some of the notable intercepts are: 0.2 meter with 5.7 percent TREO, 0.4 meter with 3.0 percent TREO, 0.3 meter with 3.3 percent TREO, 0.8 meter with 3.5 percent TREO, 0.3 meter with 3.2 percent TREO, 0.25 meter with 4.4 percent TREO, 0.33 meter with 3.0 percent TREO, 0.83 meter with 5.4 percent TREO, 0.5 meter with 6.3 percent TREO, 0.6 meter with 4.5 percent TREO), 0.4 meter with 3.4 percent TREO, 0.5 meter with 4.0 percent TREO, and 0.4 meter with 3.4 percent TREO. Several of the holes had multiple intercepts of rare-earth-element mineralization and it is notable persistent along the whole line of holes. The ratio of the the HREO to the TREO in the better intercepts varied from about 24 percent to about 70 percent, but roughly about half of the rare-earth elements in the samples are the heavy rare-earth elements.
In 2010, Ucore drilled 20 more holes, including 13 infill holes along the Dodson Dike at roughly regular intervals from the I and L prospect (DE023), through the Atom Marietta prospect (DE024), to this prospect. (Ucore, 2010 [News release]; Ucore, 2011). They also dug 45 trenches across the dike. As known in early 2011, the Dodson dike has a strike length of at least 2,180 meters, averages 50 meters wide, extends from 300 meters above sea level to at least 150 meters below sea level, has remarkably persistent mineralization, and it is open along strike and down dip.With this additional drilling on the Dodson dike, a new and considerably larger 'Conceptual Estimate' was made for the dike. The estimate was made using a model of a dike 2,425 meters long and 200 meters deep. The new figures are an 'Estimated contained mineralized tonnage' of from 3.5 to 6.5 million tonnes, with an 'Estimated grade TREO' of from 0.76 to 1.42 percent. (TREO = total rare earth elements.)
|Geologic map unit||(-132.108843972125, 54.9049574682625)|
|Mineral deposit model||U-Th-REE deposit associated with peralkaline granite.|
|Age of mineralization||Genetically related to the Jurassic, Bokan Mountain peralkaline granite (Lanphere and others, 1964; Saint-Andre and others, 1983; Armstrong, 1985; Gehrels, 1992; Thompson, 1997).|
|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.|
|Workings or exploration||
Only prospect pits to 2008. In 2008 and 2009, Ucore Uranium drilled a line of 24 holes for rare-earth elements at roughly equal intervals from near this prospect to the Atom Marietta prospect (DE024), a distance of about 2,000 meters (Ucore Uranium, 2010). In 2010, Ucore drilled 13 infill holes along the Dodson Dike at roughly regular intervals from the I and L prospect (DE023), through the Atom Marietta prospect (DE024), to this prospect. (Ucore, 2010; Ucore, 2011). They also dug 45 trenches across the dike.
In 2009 and 2010, Ucore conducted airborne total magnetic field and radiometric surveys in order to map radiogenic rocks in order to directly locate uranium and rare earth mineralization with the radiometric survey, and to map structure and stratigraphy indirectly with the total magnetic field survey. In 2009, Ground total magnetic field and radiometric surveys were performed to map these zones prior to drilling. An induced polarization (IP) survey was run to attempt to discern controls on mineralization intersected in drillholes at this site. In 2010, 3,214 m of core were drilled in 13 holes (Bentzen and others, 2013). This exploration work from 2008-2010 led to the 2013 Preliminary Economic Assessment (Bentzen and others, 2013) and a 2013 updated resource estimate (Ucore Rare Metals Inc., 2013).Although no exploration work was conducted in 2016, Ucore Rare Metals Inc. conducted mineral-separation tests on ore from their Bokan-Dotson Ridge rare-earth-element (REE) project in Southeast Alaska. The first batch of pregnant leach solution (PLS) derived from Bokan ore was treated by the SuperLig®-One Molecular Recognition Technology plant at IBC Advanced Technologies, Inc.’s Utah facility. Successful separations include: 1) separation of REE from gangue metals in the PLS; 2) greater than 99 percent purity of separation of light REE from heavy REE at greater than 99 percent recovery; 3) greater than 99 percent purity of separation and recovery of the sub-groups samarium-dysprosium (Dy sub-group) and holmium-lutetium (Ho sub-group) from the heavy REE class consisting of samarium and lutetium; and 4) greater than 99 percent separation of dysprosium from the Dy sub-group (Athey and Werdon, 2017).
|Indication of production||None|
With partial results from the 2010 infill drilling, a new and considerably larger 'Conceptual Estimate' was made for the Dodson dike. The estimate was made using a model of a dike 2,425 meters long and 200 meters deep. The new figures are an 'Estimated contained mineralized tonnage' of from 3.5 to 6.5 million tonnes, with an 'Estimated grade TREO' of from 0.76 to 1.42 percent. (TREO = total rare earth elements.)
In October 2013, an upgraded resource estimate was reported combining Carol Ann, I and L (DE023), and Atom Marietta (DE024). The estimate was made using a model via five alternative total rare earth oxide (TREO) cut-off grades with a baseline case employing a TREO cut-off of 0.4 percent. The deposit has an indicated resources of 2,936,000 tonnes containing 39,731,596 pounds of TREO composed of 0.365 percent LREO, 0.249 percent HREO, and 0.614 percent TREO with a TREO cut-off of 0.4, and an additional inferred resources of 1,995,000 tonnes containing 26,601,729 pounds of TREO composed of 0.366 percent LREO, 0.239 percent HREO, and 0.605 percent TREO with a TREO cutoff of 0.40 (Ucore Rare Minerals Inc., 2013).A 2013 preliminary economic assessment for Ucore Rare Metals’ Bokan property states an inferred resource of 5.228 million tonnes grading 0.653 percent total rare-earth oxide (Bentzen and others, 2013); it includes the Dotson (DE027), and I-and-L zones (DE023).
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.
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.
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 (Contractor, USGS); V.C. Zinno (Alaska Earth Sciences, Inc.); M.B. Werdon (DGGS)|
|Last report date||8/26/2017|