National mineral assessment tract AK-BR23 (Sedex Zn-Pb)

Tract AK-BR23
Geographic region Brooks Range, AK
Tract area 29,735sq km
Deposit type Sedex Zn-Pb
Deposit age Mississippian - Pennsylvanian

Estimates

Confidence Number of
deposits
90% 2
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
Shale-hosted Zn-Pb-Ag +/-Ba deposits (Briskey, 1986) occur in this tract. The geologic setting, deep-water marine sedimentary host rocks and drainage geochemistry are permissive for additional deposits.
On the delineation of permissive tracts
This tract is defined by dark, fine-grained sedimentary rocks that may host base-metal and barite mineral deposits. The most favorable units included here are Mississippian to Pennsylvanian black shale, black mudstone, black chert and some dark limestones of the Kuna Formation, Akmalik Chert, and Kayak Shale, and time-equivalent unnamed units. However, this tract also includes permissive dark fine-grained lithologies of the Cretaceous Torok Shale, and the Triassic Shublik and Otuk Formations. Tract boundaries are delineated by the outcrop areas of these strata, and by anomalously high concentrations of base metals in stream sediment samples.
Important examples of this type of deposit
Known mineral occurrences of this type include the Red Dog mine (Lange and others, 1985; Moore and others, 1986; Schmidt and Zierenberg, 1988; Zierenberg and Schmidt, 1988) and the Lik (Forrest, 1983; Forrest and others, 1983; Forrest and Sawkins, 1987), Drenchwater (Nokleberg and Winkler, 1982), and Suds prospects (Schmidt, 1997).
On the numerical estimates made
Based on the wide extent of appropriate host rocks, several known and drilled prospects, and widespread geochemical anomalies, the number of undiscovered deposits, consistent with the median grade and tonnage for the model (Menzie and Mosier, 1986), estimated for this tract is:
Percentile 90 50 10 5 1
Estimated number of deposits 2 5 7 10 15
References
Briskey, J.A., 1986, Descriptive model of sedimentary exhalative Zn-Pb, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 211-212
Forrest, Kimball, 1983, Geology and isotopic studies of the Lik deposit and the surrounding mineral district, DeLong Mountains, Western Brooks Range, Alaska: unpublished PhD thesis, Univ. of Minnesota, 161p.
Forrest, Kimball, Rye, R., and Sawkins, F.J., 1983, Sulfur and oxygen isotope systematics of sedimentary exhalative Zn-Pb-Ag deposition in a fault-bounded basin, Lik deposit, Western Brooks Range, Alaska, (abs.): Geol. Assoc. of Canada, Abstracts with Program , Victoria, B.C., v. 8, p. A23.
Forrest, Kimball, and Sawkins, F.J., 1987, Geologic setting and mineralization of the Lik deposit: Implications for the tectonic history of the western Brooks Range, in Tailleur, I.L., and Weimer, Paul, eds., Alaskan North Slope Geology: Soc. of Economic Paleontologists and Mineralogists Field Trip Guidebook 50, p. 295 -305.
Lange, I.M., Nokleberg, W.J., Plahuta, J.T., Krouse, H.R., and Doe, B.R., 1985, Geologic setting, petrology, and geochemistry of stratiform zinc-lead-barium deposits, Red Dog Creek and Drenchwater Creek areas, northwestern Brooks Range, Alaska: Economic Geology, v. 80, p. 1896-1926.
Moore, D.W., Young, L.E., Modene, J.S., and Plahuta, J.T., 1986, Geologic setting and genesis of the Red Dog zinc-lead-silver deposit, western Brooks Range, Alaska: Economic Geology, v. 81, p. 1696 - 1727.
Menzie, W.D., and Mosier, D.L., 1986, Grade and tonnage model of sedimentary exhalative Zn-Pb, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 212-215
Nokleberg, W.J., and Winkler, G.R., 1982, Stratiform zinc-lead deposits in the Drenchwater Creek area, Howard Pass quadrangle, northwestern Brooks Range, Alaska: U.S. Geological Survey Professional Paper 1209, 22p, 2 sheets, scale 1:20,000.
Schmidt, J.M., 1997, Shale-hosted Zn-Pb-Ag and barite deposits of Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 35-65.
Schmidt, J.M., and Zierenberg, R.A., 1988, Lateral variations of ore, and reconstruction of the Red Dog Zn-Pb-Ag deposit, Noatak District, Alaska [abs.]: Geol. Soc. of America Abstracts with Program, v. 20, no. 7, p. A-37.
Zierenberg, R.A., and Schmidt, J.M., 1988, Isotopic evidence for multiple sulfur sources at the Red Dog Zn-Pb-Ag deposit, Noatak District, Alaska [abs.] : Geol. Soc. of America Abstracts with Program, v. 20, no., 7, p. A-37.

Geographic coverage

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