Bohemia Basin

Prospects, Undetermined

Alternative names

Basin
Takanis
Flapjack
Tunnel
Tripod
Muskeg
Side Hill

Commodities and mineralogy

Main commodities Cu; Ni
Other commodities Au; Pd; Pt
Ore minerals chalcopyrite; pentlandite; pyrite; pyrrhotite

Geographic location

Quadrangle map, 1:250,000-scale SI
Quadrangle map, 1:63,360-scale D-8
Latitude 57.976
Longitude -136.4225
Nearby scientific data Find additional scientific data near this location
Location and accuracy This site consists of several prospects in about a half-square-mile area near Bohemia Basin on Yakobi Island. The prospects have had various names. Bittenbender and others (1999, fig. 5) call them the Basin, Takanis, and Flapjack deposits. Kennedy and Walton (1946 [B 947C]) and Cobb (1978, locs. 1, 2) called them the Tunnel, Tripod, Muskeg, Side Hill, and Takanis bodies. For this record, the site is plotted near the middle of a cluster of mine (adit) symbols on the USGS D-8 topographic map (1995 ed.), about 0.5 mile south-southeast of the center of sec. 12, T. 45 S., R. 55 E. The prospects are MAS no. 0021140017 (U.S. Bureau of Land Management, 2002). The location is accurate.

Geologic setting

Geologic description

The Bohemia Basin prospects are magmatic segregation sulfide deposits in Tertiary gabbronorite and norite (Kennedy and Walton, 1946 [B 947-C] ; Johnson and Karl, 1985; Still, 1988; Foley and others, 1997; Bittenbender and others, 1999). The mineralized gabbronorite and norite form a pluglike, basin-shaped component of a compositionally gradational stock that also includes tonalite, diorite, and gabbro. The stock intrudes Mesozoic or Paleozoic metamorphic rocks and Cretaceous or Jurassic diorite, melange, and graywacke (Johnson and Karl, 1985). The sulfides are pentlandite, chalcopyrite, pyrrhotite, and pyrite that occur as disseminated grains and blebs, interstitial veinlets, and small, massive aggregates.
The prospects were first staked in 1920 and subsequently explored by a 156-foot tunnel, magnetic surveys, and extensive trenching and diamond drilling (Bittenbender and others, 1999). Much of the early exploration was conducted by the U.S. Bureau of Mines in the 1940s. The most recent work was about 5,000 feet of diamond drilling by private interests in 1984.
There has been no production. Bittenbender and others (1999), citing Thornsberry and DeWilliam (1982), report the following estimates of resources at Bohemia Basin:
1) Basin deposit (based on 73 diamond drill holes): 16,186,000 tons that average 0.31 percent nickel, 0.18 percent copper, and 0.02 percent cobalt.
2) Takanis deposit (based on 47 diamond drill holes): 3,971,500 tons that average 0.29 percent nickel, 0.18 percent copper, and 0.02 percent cobalt.
Together, the Basin and Takanis deposits have proven resources accessible by open-pit mining of 15.1 million tons grading 0.37 percent nickel, 0.22 percent copper, and 0.02 percent cobalt, at a 2.5:1 stripping ratio.
3) Flapjack deposit (based on 4 diamond drill holes): 4,000,000 tons of inferred resources that average 0.21 percent nickel and 0.12 percent copper.
They also report that small amounts of gold, platinum, and palladium are recoverable from these deposits.
Geologic map unit (-136.424342706425, 57.9756186434132)
Mineral deposit model Synorogenic Ni-Cu (Cox and Singer, 1986; model 7a).
Mineral deposit model number 7a
Age of mineralization Contemporaneous with the emplacement of the Tertiary gabbronorite and norite host rock.

Production and reserves

Workings or exploration The prospects were first staked in 1920 and subsequently explored by a 156-foot tunnel, magnetic surveys, and extensive trenching and diamond drilling (Bittenbender and others, 1999). Much of the early exploration was conducted by the U.S. Bureau of Mines in the 1940s. The most recent work was about 5,000 feet of diamond drilling by private interests in 1984.
Indication of production None
Reserve estimates
Bittenbender and others (1999), citing Thornsberry and DeWilliam (1982), report the following estimates of resources at Bohemia Basin:
1) Basin deposit (based on 73 diamond drill holes): 16,186,000 tons that average 0.31 percent nickel, 0.18 percent copper, and 0.02 percent cobalt.
2) Takanis deposit (based on 47 diamond drill holes): 3,971,500 tons that average 0.29 percent nickel, 0.18 percent copper, and 0.02 percent cobalt.
Together, the Basin and Takanis deposits have proven resources accessible by open-pit mining of 15.1 million tons grading 0.37 percent nickel, 0.22 percent copper, and 0.02 percent cobalt, at a 2.5:1 stripping ratio.
3) Flapjack deposit (based on 4 diamond drill holes): 4,000,000 tons of inferred resources that average 0.21 percent nickel and 0.12 percent copper.
They also report that small amounts of gold, platinum, and palladium are recoverable from these deposits.

References

MRDS Number AO13237; AO13238

References

Bittenbender, P., Still, J.C., Maas, K., and McDonald, M., Jr., 1999, Mineral resources of the Chichagof and Baranof Islands area, southeast Alaska: Bureau of Land Management, BLM-Alaska Technical Report 19, 222 p.
Fleming, E.E., 1917, Alaska Nickel property, Chichagof: Unpublished report, 9 p. (Report held by the Mineral Information Center, Bureau of Land Management, Juneau, Alaska.)
Foley, J.Y., Light, T.D., Nelson, S.W., and Harris, R.A., 1997, Mineral occurrences associated with mafic-ultramafic and related alkaline complexes in Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 396-449.
Healy, R L., 1918, Report on the Alaska Nickel Mines, Sitka Mining District, southeastern Alaska: Unpublished report, 15 p. (Report held by the Bureau of Land Management, Juneau, Alaska.)
Himmelberg, G.R., Loney, R.A., and Nabelek, P.I., 1987, Petrogenesis of gabbronorite at Yakobi and northwest Chichagof Islands, Alaska: Geological Society of America Bulletin v. 98, p. 265-270.
Jackson, G.T., 1918, Alaska Nickel Mines: Unpublished report, 3 p. (Report held by the Mineral Information Center, Bureau of Land Management, Juneau, Alaska.)
Jirik. R.S., 1982, Geology of the Takanis copper-nickel-cobalt prospect, Yakobi Island, southeastern Alaska: Unpublished M. S. thesis, Washington State Univ., Pullman, WA, 182 p.
Kennedy, G.C., 1944, Summary of geological survey results in connection with Bureau of Mines investigation of the nickel-copper deposits of Bohemia Basin, Yakobi Island, southeastern Alaska: Unpublished report, 22 p. (Report held by the Mineral Information Center, Bureau of Land Management, Juneau, Alaska.)
Kerr, P.F., 1924, A magmatic sulphide ore from Chichagof Island, Alaska: Economic Geology, v. 19, no. 4, p. 369-376.
Kuhn, J.G., 1978, Facts concerning copper-nickel-cobalt deposits on Yakobi Island: Company release, April 3, 3 p. (Report held by the Mineral Information Center, Bureau of Land Management, Juneau, Alaska.)
Ricker, S., 1941, Preliminary report and project set-up, Bohemia Basin Nickel, Yakobi Island, Alaska: Unpublished report, 16 p. (Report held by the Mineral Information Center, Bureau of Land Management, Juneau, Alaska.)
Rogers, J.C., 1917, Alaska Nickel Mines: Unpublished report, 7 p. (Report held by the Mineral Information Center, Bureau of Land Management, Juneau, Alaska.)
Thornsberry, V.V., and DeWilliam, P.P., 1982, Prospectus: Aleco Mining Group nickel-copper property (Bohemia Basin and Mirror Harbor) southeast Alaska: Unpublished report, 19 p. (Report held by the Mineral Information Center, Bureau of Land Management, Juneau, Alaska.)
Traver, W.M., 1942, Bohemia Basin nickel deposits, Yakobi Island, Alaska. Report to Metallurgical Division: Unpublished report, 3 p. (Report held by the Mineral Information Center, Bureau of Land Management, Juneau, Alaska.)
U.S. Bureau of Land Management, 2002, Alaska mineral locations database report (Sitka quadrangle), July 2, 2002, 205 p. [http://imcg.wr.usgs.gov/dem.html]
U. S. Bureau of Mines, 1944, Yakobi Island, Sitka Mining District, Alaska: War Minerals Report 174, 73 p. (Report held by the Mineral Information Center, Bureau of Land Management, Juneau, Alaska.)
Walton, M.S., and Kennedy, G.C., 1945, Magnetic exploration of the nickel-copper deposits of Bohemia Basin, southeastern Alaska: Economic Geology, v. 40, no.7, p.496-502.
Reporters H.C. Berg (U.S. Geological Survey)
Last report date 10/16/2004