National mineral assessment tract AK-EC13 (Porphyry Cu, BC-Ak type)

Tract AK-EC13
Geographic region East Central, AK
Tract area 105,247sq km
Deposit type Porphyry Cu, BC-Ak type
Deposit age Cretaceous - Tertiary


Confidence Number of
90% 1
50% 2
10% 4
5% 8
1% 10

Estimators: Grybeck, Cox, Light, Lee, Phillips


Explained by Donald Grybeck, Thomas D. Light, William J. Keith, Dennis P. Cox, Gregory K. Lee, and Jeffrey D. Phillips.
On the choice of deposit models
Several porphyry copper deposits are known in the eastern part of east-central Alaska, outside of this tract. Similar deposits may occur in Upper Cretaceous or Tertiary granitic plutons, in the western portion of the tract. These plutons, however, are consistently low in copper and have much lower potential for porphyry copper occurrences. A general porphyry copper model has been described by Hollister (1978), Beane and Titley (1981), Titley and Beane (1981), McMillan and Panteleyev (1980), and Titley (1982).
On the delineation of permissive tracts
This tract is defined by the distribution of Upper Cretaceous or Tertiary granitic plutons and adjacent areas that may contain granitic plutons of similar age. Cretaceous plutons farther to the west are consistently low in copper and have a much lower potential for porphyry Cu occurrences.
Important examples of this type of deposit
There are no porphyry deposits known in this tract, but such deposits are known in similar rocks to the south (i.e., the Taurus deposit in the Tanacross quadrangle).
On the numerical estimates made
The tonnage curve for the BC-AK type porphyry copper model (Menzie and Singer, 1993), which has a lower mean expected tonnage than the standard porphyry copper model, has been used to estimate numbers of undiscovered deposits. The grade of the undiscovered deposits is expected to be about 0.25% copper, reflecting the lower grade of Alaskan porphyry copper deposits. The estimated minimum number of undiscovered porphyry Cu-Mo deposits expected to occur in this tract is:
Percentile 90 50 10 5 1
Estimated no. of deposits 1 2 4 8 10
Beane, R.E., and Titley, S.R., 1981, Porphyry copper deposits, Part II; Hydrothermal alteration and mineralization, in Skinner, B.J., editor, Economic Geology 75th Anniversary Volume: Economic Geology Publishing Company, p. 235-269.
Holister, V.F., 1978, Geology of the porphyry copper deposits of the western hemisphere: New York, American Institute of Mining, Metallurgical, and Petroleum Engineers, 219 p.
McMillan, W.J., and Panteleyev, A., 1980, Ore deposit models-1. Porphyry copper deposits: Geoscience Canada, v. 7, p. 52-63.
Titley, S.R., 1982, Advances in geology of the porphyry copper deposits, southwestern North America: Tucson, Arizona, University of Arizona Press, 560 p.
Titley, S.R., and Beane, R.E., 1981, Porphyry copper deposits Part I; Geologic settings, petrology and tectogeneses, in Skinner, B.J., editor, Economic Geology 75th Anniversary Volume: Economic Geology Publishing Company, p. 214-234.

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