National mineral assessment tract AK-BR02 (Cyprus massive sulfide)

Tract AK-BR02
Geographic region Brooks Range, AK
Tract area 4,203sq km
Deposit type Cyprus 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
Mafic and ultramafic complexes in the Brooks Range are geologically permissive for the occurrence of Cyprus massive sulfide deposits as described by Singer (1986). Altered basalts with pyrite and locally high copper values may suggest submarine hydrothermal activity.
Many mafic and ultramafic complexes in Alaska are geologically permissive for the occurrence of Cyprus massive sulfide deposits as described by Singer (1986).
On the delineation of permissive tracts
This tract comprises areas of known mafic and ultramafic rock complexes (i.e., the Brooks Range ophiolites) and includes dunite, layered peridotite, pyroxenite, gabbro, basalt, and minor plagiogranite. Boundaries of the permissive areas have been extended to indicate the possibility of buried ultramafic rocks where warranted by aeromagnetic data.
This tract is a composite tract which comprises all areas permissive for Cyprus massive sulfide deposits throughout the state.
Important examples of this type of deposit
No Cyprus massive sulfide deposits are known in this tract (Schmidt and Allegro, 1980).
There are several small deposits in south central and southeastern Alaska that are inferred to be Cyprus massive sulfide deposits.
On the numerical estimates made
There is not enough information available for this area to make estimates of the number of undiscovered deposits.
The lack of estimates for undiscovered Cyprus massive sulfide deposits in half of the individual permissive tracts in Alaska reflects the lack of information upon which to classify a deposit estimate, rather than a lack of deposits. We considered that most of the known deposits outside either Cyprus or the former USSR do not exceed the mean deposit tonnage or grade shown on the distribution curve. We considered the estimates already made for some regions and the areal distribution of permissive areas. The number of undiscovered Cyprus massive sulfide deposits estimated for the composite permissive tracts for the state of Alaska, based on the grade and tonnage model of Singer and Mosier (1986) is:
Percentile 90 50 10 5 1
Estimated number of deposits 1 3 5 10 12
References
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.
Singer, D.A., 1986, Descriptive model of Cyprus massive sulfide, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 131.
AK01 Cyprus Massive Sulfide Alaska
by: Thomas D. Light, Byron R. Berger, Larry J. Drew, Bruce M. Gamble, Donald Grybeck, Marti L. Miller, Jeanine M. Schmidt, and Frederick H. Wilson
Singer, D.A., 1986, Descriptive model of Cyprus massive sulfide, in, Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 131.
Singer, D.A., and Mosier, D.L., 1986, Grade and tonnage model of Cyprus massive sulfide deposits, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 131-135.

Geographic coverage

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