Atom Marietta

Prospect, Active

Commodities and mineralogy

Main commodities Cb; Ce; Dy; Er; Eu; Gd; Ho; La; Lu; Nd; Pm; Pr; Sm; Tb; Th; Tm; U; Y; Yb; Zr
Ore minerals brannerite; dravite; uraninite; uranophane
Gangue minerals albite; calcite; chlorite; fluorite; hematite; quartz; tourmaline

Geographic location

Quadrangle map, 1:250,000-scale DE
Quadrangle map, 1:63,360-scale D-1
Latitude 54.9122
Longitude -132.1283
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Atom Marietta prospect is about 1.1 miles east-southeast of Bokan Mountain, near the center of the west boundary of the SE1/4 SE1/4 section 22, T. 80 S., R. 88 E, of the Copper River Meridian. As known in 2011, it is one of the prospects along the Dodson dike and its persistent mineralization. Its location relative to the other uranium and REE prospects in the vicinity of Bokan Mountain is best shown on Plate 1 of MacKevett (1963). The location is accurate, though the degree of accuracy is not reported.

Geologic setting

Geologic description

This and several other nearby uranium-thorium-REE deposits (DE015 to DE023 and DE025 to DE031) are spatially and genetically related to a stock of Jurassic, peralkaline granite about 2 miles in 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 Atom Marietta prospect consists of a few hand-dug cuts and pits on several claims located in 1955 (MacKevett, 1963). The prospect is in aplite near the southeastern edge of the Bokan Mountain peralkaline complex. The deposit is near the intersection of a major northeast-trending fault zone with a group of steep northwest faults. The deposit is associated with intensely altered and fractured dacite dikes that cut the aplite in or near the fault zones. The uranium-thorium minerals occur in narrow veinlets, as disseminations, and as irregular, sublinear masses. The primary radioactive mineral is uranothorite, although uraninite and other unidentified minerals, possibly brannerite or davite, also occur. Secondary uranophane is 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 Carol Ann prospects (DE027), 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: 1) 0.2 meter with 5.7 percent TREO, 0.4 meter with 3.0 percent TREO; 2) 0.3 meter with 3.3 percent TREO, 0.8 meter with 3.5 percent TREO; 3) 0.3 meter with 3.2 percent TREO; 4) 0.25 meter with 4.4 percent TREO; 5) 0.33 meter with 3.0 percent TREO: 6) 0.83 meter with 5.4 percent TREO; 7) 0.5 meter with 6.3 percent TREO; 8) 0.6 meter with 4.5 percent TREO); 9) 0.4 meter with 3.4 percent TREO; 10) 0.5 meter with 4.0 percent TREO; and 11) 0.4 meter with 3.4 percent TREO. Several of the holes had multiple intercepts of rare-earth-element mineralization which 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 this site, to the Carol Ann prospect (DE 027) (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 it. 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 Atom Marietta, I and L (DE023), and Carol Ann (DE027). 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 1) 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 2) 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).
Geologic map unit (-132.129941513527, 54.9118581990478)
Mineral deposit model U-Th-REE deposit associated with peralkaline granite stock.
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.

Production and reserves

Workings or exploration
Only several hand-dug pits and trenches prior 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 Carol Ann prospects (DE027), a distance of about 2,000 meters (Ucore Uranium, 2010). The line of holes follows the Dodson dike system. 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 to the Carol Ann prospect (DE027) (Ucore, 2010 [News release]; 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).
Indication of production None
Reserve estimates
With the partial results of 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, and 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 Atom Marietta, I and L (DE023), and Carol Ann (DE027). 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. It has 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).

References

MRDS Number A010279

References

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.
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., 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.)
Last report date 2/25/2016