National mineral assessment tract AK-BR01 (Besshi massive sulfide)

Tract AK-BR01
Geographic region Brooks Range, AK
Tract area 12,609sq km
Deposit type Besshi massive sulfide
Deposit age Jurassic

Rationale

Explained by Jeanine M. Schmidt, Karen D. Kelley, Richard I. Grauch, Byron R. Berger, John W. Cady, Gregory T. Spanski, James E. Kilburn.
On the choice of deposit models
Parts of the Brooks Range are permissive for Besshi massive sulfide deposits as described by Cox (1986). Altered basalts, containing pyrite and locally high copper values, may suggest submarine hydrothermal activity.
On the delineation of permissive tracts
This tract contains all of the known mafic rocks of Proterozoic(?), Paleozoic, or Mesozoic age in the Brooks Range (Murchey and Harris, 1985; Pallister and others, 1989) outside of the mafic-ultramafic complexes.
Important examples of this type of deposit
No Besshi massive sulfide deposits are known in this tract, although the Kivivik Creek prospect is possibly of this type (Schmidt and Allegro, 1988).
On the numerical estimates made
No deposits of this type are known in the area, and no estimates of the number of undiscovered deposits have been attempted.
References
Cox, D.P., 1986, Descriptive model of Besshi massive sulfide, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 136.
Murchey, B.L., and Harris, A.G., 1985, Devonian to Jurassic sedimentary rocks in the Angayucham Mountains of Alaska: possible sea mount or oceanic plateau deposits [abs]: EOS, Transactions of the American Geophysical Union, v. 66, no. 46, p. 1102.
Pallister, J.S., Budahn, J.R., and Murchey, B.L., 1989, Pillow basalts of the angayucham terrane: oceanic plateau and island crust accreted to the Brooks Range: Journal of Geophysical Research, v. 94, no. B11, p. 15,901-15,923.
Schmidt, J.M., and Allegro, G.L., 1980, Mineral occurrences and indicators in the Baird Mountains quadrangle, Alaska: USGS Miscellaneous Field Studies Map MF1992, 1 plate, scale 1:250,000, 19 p.

Geographic coverage

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