National mineral assessment tract AK-AP09 (Porphyry Cu, BC-Ak type)

Tract AK-AP09
Geographic region AK Peninsula & Aleutian Is.
Tract area 27,515sq km
Deposit type Porphyry Cu, BC-Ak type
Deposit age Tertiary


Confidence Number of
90% 5
50% 13
10% 25
5% 25
1% 25

Estimators: Wilson, Church, Saltus, Drew, Menzie


Explained by Frederic H. Wilson, Stanley E. Church, Richard W. Saltus, Lawrence J. Drew, and W. David Menzie.
On the choice of deposit models
This model (Menzie and Singer, 1993), which is defined in part on the basis of deposits in this tract, is the definitive model for Alaskan porphyry copper deposits.
On the delineation of permissive tracts
The tract is defined as the area of the Alaska Peninsula that contains known or inferred intermediate to felsic plutons of Cenozoic age. Country rocks intruded by these plutons include Jurassic and Cretaceous clastic sedimentary rocks and Cenozoic volcanic and volcaniclastic rocks. Geochemical data support consideration of large areas of the Alaska Peninsula for porphyry copper deposits, and incomplete geophysical (largely aeromagnetic) data also suggest additional areas of inferred, buried intrusions.
Important examples of this type of deposit
The Pyramid deposit near Balboa Bay has reserves of 126 million tons containing 0.413 percent Cu and 0.025 percent Mo (Christie, 1975). The Bee Creek (or Dry Creek) deposit near Chignik is reported to have an undetermined but small tonnage containing 0.25 percent Cu, 0.01 percent Mo, and 0.06 ppm Au (Fields, 1977).
On the numerical estimates made
The estimated minimum number of undiscovered porphyry Cu deposits, consistent with the grade and tonnage model of Menzie and Singer (1993), for this tract is:
Percentile 90 50 10 5 1
Estimated no. of deposits 5 13 25 25 25
Christie, J.S., 1975, Pyramid project Aleut‑Quintana‑Duval joint venture report on 1975 drill programme: Unpublished Quintana Minerals Corporation report available from The Aleut Corporation, 17 p., 1 appendix, 5 maps and figures in pocket.
Fields, E.D., 1977, 1976 Annual report, Alaska search: Chignik area‑Bristol Bay region: Unpublished report available from the Bristol Bay Native Corp., 44 p.
Menzie, W.D., and Singer, D.A., 1993, Grade and tonnage model of Porphyry Cu deposits in British Columbia, Canada, and Alaska, U.S.A.: U.S. Geological Survey Open-File Report 93-275, 7p.

Geographic coverage

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