Bokan Mountain

Location: Alaska, United States (54.920, -132.136 approx.)

Commodities: rare earth elements; uranium; thorium; niobium; zirconium; zinc; titanium; beryllium; tin; tantalum; lead; strontium; hafnium; zinc; tin

Deposit model: REE-Th bearing veins · Th-REE veins

Geology

The Cheri dike system consists of steeply dipping, subparallel, radioactive dikes that cut albitized quartz diorite country rock. (Long and others (2010)) The Geiger dike extends northerly from near an aplite outlier of the peralkaline granite to the north shore of South Arm Moira Sound; it is a continuous dike system of one to five or more parallel, radioactive dikes. (Long and others (2010)) The Geoduck dikes can be traced southeasterly along a strike of N. 40°–50° W. for about 2.9 km....Texturally, the dikes are fine to medium grained and granular and banded or cut by veinlets of quartz or opaque minerals. In addition, the Geoduck dike system has, for most of its strike length, chlorite- and epidote-altered pyritic quartz diorite wall rocks. (Long and others (2010)) “Staatz (1978) described the I and L vein system as consisting of at least nine veins, each rarely more than 1.5 m thick, extending northwest for 2.6 km from the east side of Bokan Mountain to the West Arm of Kendrick Bay. Vein mineralogy is complex, with at least 34 mineral species known (Wilson, 2010). The quartz-albite gangue contains U-Th minerals that vary in abundance along the vein system: uraninite, brannerite, thorite and allanite. REE occur in allanite (which is found in the southeastern part of the vein system and in transverse veins), bastnaesite, xenotime and monazite. Staatz noted that the REE mineralogy and tenor were erratic, even along the length of a single vein, from Ce-rich minerals like bastnaesite to Y-dominant species such as xenotime. The I & L veins are also rich in other elements, notably Zr. The emphasis at Bokan Mountain is on the REE but there are no suitable conceptual models at present which relate in any meaningful way to the mineralization observed on the Bokan Mountain Property.” (Robinson and others (2011)) The Ross-Adams mine extracted ore from the Ross-Adams pipe on the Cub claim, which lies along the contact between aegirine syenite and aegirine granite porphyry. An irregularly shaped north-northwest-trending body, the pipe measures 24 m (79 ft) across and was mined along strike for more than 300 m (984 ft). (Long and others (2010)) The Sunday Lake prospect…is a high-grade REE occurrence (drill intercept of 1.83 percent TREE over 4.8 m or 15.7 ft) that is apparently structurally controlled, which occurs in aegirine granite near an irregular contact with hornfels. (Barker and Van Gosen (2012)) “At Sunday Lake, mapping, prospecting and drilling defined mineralization along a north-south striking intrusive contact separating Bokan Granite on the east from older Descon Formation metasediments to the west. Shallow high grade REE mineralization is found on the east side of a roof pendant or xenolith of metasedimentary rocks approximately 50 m east of the contact. Further west, drilling intersected a zone of low grade (0.2% TREO) REE mineralization along the intrusive contact. The induced polarization survey mapped a steeply east-dipping boundary between low resistivity to the west and high resistivity to the east which likely outlines the limit of the hornfels envelope proximal to the intrusive contact. A thin, steeply dipping, NNE striking body of moderate chargeability response was mapped extending SSW from the Sunday Lake showing. This zone appears to be associated with the contact mineralization. To date, no extensive mineralization has been intersected but further work is warranted.” (Robinson and others (2011)) The Upper Cheri dikes are subparallel to and southwest of the Cheri dikes. On the whole, the dikes are very similar to those of the Cheri dike system, with comparable mineralogy, structure, setting, radioactivity, and intrusive characteristics. (Long and others (2010)) “The Dotson Zone is a steeply dipping, tabular zone of numerous veins and narrow veinlets extending from east of Bokan Mountain to the shore of Kendrick Bay. The Dotson Zone has a defined strike length of 2,140 m, an average width of 50 m and has been traced down dip over a vertical extent of 450 m. On average, the zone strikes 108deg, and dips 75 to 85deg north.” (Bentzen and others (2013))

Published resource estimates

As compiled by USGS USMIN from the cited studies. Resource classes follow the source; "approximate" flags values USMIN reports as approximations. These are not current company reserve statements.

Recorded production

• Bokan Mountain, Ross-Adams Mine: produced 77,700 metric tons of uranium oxide (U3O8) at 0.76 percent, containing about 501.1 metric tons U, 1957–1971 (Robinson and others (2011), Page 29, Table 8-1)

Exploration and site history

• Exploration — Airborne total magnetic field and radiometric surveys, 2009–2010 (Bentzen and others (2013))
• Exploration — Drilling; Newmont; 12 diamond drill holes, 1981 (Robinson and others (2011))
• Exploration — Induced polarization survey done by Aurora, 2009 (Bentzen and others (2013))
• Exploration — Ground total magnetic field and radiometric surveys performed by Aurora to map radioactive zones and REE zones prior to drilling, 2009 (Bentzen and others (2013))
• Discovery — Discovered and hand trenching and sampling completed, 1955 (Warner and Barker (1989))

Record imported from USGS USMIN ver. 4.0 (June 2019). Developments after that date appear on facility records, not here; see the methodology.