Boulder Creek

Prospect, Active

Alternative names

Death Valley

Commodities and mineralogy

Main commodities U
Ore minerals coffinite; meta-autunite; pyrite; sphalerite

Geographic location

Quadrangle map, 1:250,000-scale BN
Quadrangle map, 1:63,360-scale A-1
Latitude 65.0507
Longitude -162.2467
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Boulder Creek or Death Valley (in the early literature) uranium deposit is in the headwaters of Boulder Creek, a north tributary to the middle Tubutulik River. It is 3.5 miles south of where the Tubutulik River leaves Death Valley, and about 0.3 mile southeast of the center of section 14, T. 3 S., R. 19 W. The deposit has been explored on the east side of Boulder Creek; the discovery pits are 1.0 mile southeast of Hill 990 and 1.0 mile east of Tubutulik River.

Geologic setting

Geologic description

The Boulder Creek or Death Valley (in the early literature) sandstone-type uranium deposit (Dickinson and others, 1987) was discovered in 1977 and soon explored and drilled by Houston International Minerals Corporation.
The Death Valley deposit is in lower Eocene continental sedimentary rocks that unconformably overlie deeply weathered granitic rocks of the Darby pluton (Miller and Bunker, 1976; Johnson and others, 1979). The Eocene sediments were deposited in a graben between the uplifted Darby pluton to the west and lower Paleozoic metamorphic rocks to the east. This is probably an onshore, exposed equivalent of the deeper parts of the offshore Norton basin. Proximity to the slightly uraniferous Darby pluton seems to be an important control on the development of this deposit. The continental sedimentary rocks are conglomerate, arkosic sandstone, mudstone, and coal. The nonconformable contact between the coarse-grained, poorly sorted basal sedimentary strata and the granitic pluton is gradational and some strata in this part of the section are interpreted as mud flows in alluvial systems. The upper part of the sedimentary section contains mudstones deposited in a lacustrine environment. Eocene basalt is interbedded with and caps the sedimentary section in this area. This basalt may have created a dam that led to lacustrine sedimentation. The lacustrine mudstones contain laminated siderite but all the sediments compositionally reflect their probable source in the granitic rocks of the Darby pluton. Granitic clasts, quartz, and k-feldspar are common detrital components. Carbonized wood fragments are also common in the section which also contains bituminous coal beds up to 100 feet thick.
Uranium mineralization is both epigenetic and supergene. The epigenetic mineralization consists of coffinite, small amounts of pyrite, and trace amounts of sphalerite; it extends vertically over a stratigraphic interval of 300 feet, both above and below basalt layers. This primary mineralization, interpreted to be early Eocene in age, is formed by the reduction of oxidized groundwaters derived from areas of granitic bedrock by carbonized wood in conglomerate and arkosic sandstone. The principal mineralized zone defined by drilling covers an area of 395 by 9,850 feet and averages 10 feet thick. With an average grade of 0.27 percent U3O8, this deposit has a calculated resource of 1,000,000 pounds of U3O8 (Dickinson and others, 1987). The supergene mineralization, which is related to the present surface, consists of several varieties of meta-autunite in soil and weathered bedrock intervals. The supergene mineralization is less than 20 feet thick. The mineralized surficial materials include three zones: (1) a one-foot thick zone of organic-rich mudstone and sandstone containing basalt cobbles that may be a debris flow; (2) a zone up to 10 feet thick of arkosic sandstone containing carbonized wood fragments; and (3) a zone of granitic grus or semi-consolidated arkosic sandstone and mudstone. Some arkosic sandstone fragments contain 11 percent U3O8 and some basalt fragments have uraniferous weathering rinds. Epigenetic mineralization is considered to be early Eocene in age, a time when the climate was temperate or subtropical (Dickinson and others, 1987). This is the age of the host rocks and the mineralization must have occurred before later Tertiary faulting disrupted groundwater flow eastward from the Darby pluton. The supergene mineralization is Recent in age and may be ongoing today. The Death Valley sandstone-type uranium deposit is the farthest north of its type in the world. At the time of its formation, it was probably at an even higher latitude than it is today, 64 degrees north.
The Boulder Creek deposit is currently (2008) a joint venture between Full Metals Minerals (2007) and Triex Minerals (2007), with Triex as the operator. Triex completed a four-week reconnaissance program in 2005 and identified several geochemical anomalies in the surrounding area. In 2006, they drilled 14 core holes totaling 1,237 meters. Twelve of the holes were on the Boulder Creek deposit; the drilling did not change the known dimensions of the deposit. They drilled two additional holes on geochemical anomalies about 6 kilometers north-northwest of the Boulder Creek deposit; they did not intersect significant mineralization but they did cut rocks favorable for uranium mineralization. Triex drilled another 8 holes in 2007 that totaled 890 meters to better define the deposit. Triex noted that 'No new and continuous zones of significant radioactivity were intersected' although the drilling through 2007 confirmed the grade and thickness of the deposit.
On the basis of airborne geophysical anomalies, Triex also staked a large block of claims in 2006 about 25 kilometers to the southwest in the southeast portion of McCarthy Marsh. They followed up these anomalies in 2006 by considerable soil sampling and biogeochemical surveys.
Geologic map unit (-162.24931240958, 65.0499995412151)
Mineral deposit model Sandstone U (Cox and Singer, 1986; model 30c).
Mineral deposit model number 30c
Age of mineralization The epigenetic mineralization is considered to be early Eocene in age, a time when the climate was temperate or subtropical (Dickinson and others, 1987). This is the age of the sedimentary host rocks and mineralization must have occurred before Tertiary faulting disrupted groundwater flowing eastward from the Darby pluton. Supergene processes are at least Recent in age and may be ongoing today.
Alteration of deposit Various clays are developed in the sedimentary host rocks of the epigenetic deposit that may reflect alteration processes. The supergene enrichment accompanies alteration associated with weathering processes.

Production and reserves

Workings or exploration
The Death Valley sandstone-type uranium deposit (Dickinson and others, 1987) was discovered in 1977 and soon explored and drilled by the Houston International Minerals Corporation. Houston Oil and Minerals completed 3,300 meters of core drilling in 52 holes and about 60 m of near-surface split-tube sampling in 21 holes, focused on the Discovery Zone area. Surface grab samples reported by previous operators returned up to 34 percent U3O8; intercepts of up to 3.3 meters, averaged 0.58 percent U3O8.
As of 2008, the Boulder Creek deposit was a joint venture between Full Metals Minerals and Triex Minerals, with Triex as the operator. Triex completed a four-week reconnaissance program in 2005 and identified several geochemical anomalies in the surrounding area. In 2006, they drilled 14 core holes totaling 1,237 meters. Twelve of the holes were on the Boulder Creek deposit. They drilled two additional holes on geochemical anomalies about 6 kilometers north-northwest of the Boulder Creek deposit; they did not intersect significant mineralization but they did cut rocks favorable for uranium mineralization. Triex drilled another 8 holes in 2007 that totaled 890 meters to better define the deposit.
On the basis of airborne geophysical anomalies, Triex also staked a large block of claims in 2006 about 25 kilometers to the southwest in the southeast portion of McCarthy Marsh. They followed up these anomalies in 2006 by considerable soil sampling and biogeochemical surveys.
Indication of production None
Reserve estimates The principal mineralized zone that has been defined by drilling covers an area of 395 by 9,850 feet and averages 10 feet in thickness. This deposit has a calculated resource of 1,000,000 pounds of U3O8 at an average grade of 0.27 percent U3O8 (Dickinson and others, 1987). This is the largest presently known uranium deposit in Alaska. The work by Triex and Full Metal Minerals from 2005 to 2007 confirms the grade and thickness of the deposit but they emphasize that the historical reserve figures are not in conformity with modern standards.

References

MRDS Number A012750

References

Fisher, M.A., Patton, W.W., Jr., and Holmes, M.L., 1982, Geology of Norton Basin and continental shelf beneath northwestern Bering Sea, Alaska: American Association of Petroleum Geologists Bulletin, v. 66, p. 255-285.
Full Metal Minerals, 2007 (Boulder Creek): http://www.fullmetalminerals.com/s/bouldercreek.asp (as of April 2007).
Triex Minerals, 2007a: Boulder Creek: http://www.triexminerals.com/s/BoulderCreek.asp (as of April 15, 2007)
Triex Minerals Corp., 2007b, Triex Minerals and Full Metal Minerals: 2007, 2007 Alaska progam completed - New uranium mineralization discovered at Fireweed: http://www.triexminerals.com/s/NewsReleases.asp?ReportID=268433&_Type=News-Releases&_Title=Triex-Minerals-and-Full-Metal-Minerals-2007-Alaska-Program-Completed-New-Ur... (New release, Oct. 24, 2007).
Reporters Travis L. Hudson (Applied Geology, Inc.); D.J. Grybeck (Port Ludlow, WA)
Last report date 6/5/2008