National mineral assessment tract AK-BR07 (Kuroko massive sulfide)

Tract AK-BR07
Geographic region Brooks Range, AK
Tract area 2,423sq km
Deposit type Kuroko massive sulfide
Deposit age Cretaceous

Estimates

Confidence Number of
deposits
90% 3
50% 5
10% 7
5% 10
1% 15

Estimators: Schmidt, Kelley, Cady, Berger, Kilburn, Spanski

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
Felsic volcanic-hosted polymetallic massive sulfide deposits (Singer, 1986) occur within the tract, and the geologic setting and host rocks are favorable for additional deposits.
On the delineation of permissive tracts
This tract is defined by the distribution of the bimodal metabasalt-metarhyolite volcanic suite of the Devonian Ambler Group and correlative mafic and felsic rocks farther east in the Brooks Range. Geochemical data from stream sediment samples indicate a base metal-rich signature with a distinct lack of Sn. The aeromagnetic signature is low.
Important examples of this type of deposit
This tract contains several kuroko-type volcanogenic massive sulfide deposits, including the Arctic deposit, with indicated reserves of 36.3 million tonnes of 4% Cu, 5.5% Zn, 0.8% Pb, 55 g/T Ag and 0.69 g/T Au (Schmidt, 1986; Swainbank and others, 1995). Other deposits include Sun, Smucker, and BT, as well as numerous other drilled prospects (Hitzman and others, 1986). The large number of sulfide deposits known to crop out within the Ambler Group sensu stricto (an area of less than 800 square kilometers), even with limited exploration, suggests a deposit density higher than that of many better known districts, and may indicate unusual metallogenetic conditions.
On the numerical estimates made
Based on the number of prospects known from industry mapping and drilling, and on the volume of the host volcanic suite, the estimated minimum number of undiscovered kuroko massive sulfide deposits, of median grade and tonnage consistent with the tonnage and grade model of Singer and Mosier (1986), is:
Percentile 90 50 10 5 1
Estimated number of deposits 3 5 7 10 15
References
Hitzman, M.W., Proffett, J.M., Schmidt, J.M., and Smith, T.E., 1986, Geology and mineralization of the Ambler district, northwestern Alaska: Economic Geology, v. 81, no. 7, p. 1592-1618. Reprinted in Tailleur, I.L, and Weimer, Paul, eds., 1987
Schmidt, J.M., 1986, Stratigraphic setting and mineralogy of the Arctic volcanogenic massive sulfide deposit, Ambler district, Alaska: Economic Geology, v. 81, no. 7, p. 1619-1643. Abstract reprinted in Tailleur, I.L., and Weimer, Paul, eds., 1987.
Singer, D.A.., 1986, Descriptive model of kuroko massive sulfide, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 189-190.
Singer, D.A.., and Mosier, D.L., 1986, Grade and tonnage model of kuroko massive sulfide, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 190-197.
Swainbank, R.C., Bundtzen, T.K., Clough, A.H., Henning, M.W., and Hansen, E.W., 1995, Alaska's Mineral Industry 1994: Alaska Division of Geological and Geophysical Surveys Special Report 49, Alaska Department of Natural Resources, Juneau Alaska, 77p.

Geographic coverage

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