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  3. Alaska Resource Data File (ARDF)

Unnamed (northeast of Ford Arm)

Occurrence, Undetermined

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Commodities and mineralogy

Main commodities Cu
Ore minerals chalcopyrite; pyrite; secondary copper minerals

Geographic location

Quadrangle map, 1:250,000-scale SI
Quadrangle map, 1:63,360-scale C-6
Latitude 57.6217
Longitude -135.866
Nearby scientific data Find additional scientific data near this location
Location and accuracy This occurrence is at an elevation of about 1,500 feet northeast of Ford Arm, about midway between lakes 920 and 423. The occurrence is about 0.2 mile north-northeast of the center of sec. 13, T. 49 S., R. 59 E. It is location 41 of Cobb (1972, 1978). The location probably is accurate within 0.2 mile.

Geologic setting

Geologic description

Johnson and Karl (1985) map the rocks in the area of this occurrence as Triassic(?) greenstone that is intruded by a stock of Cretaceous or Jurassic gabbro and by a northwest-striking, linear sill(s) of Cretaceous(?) diorite. The rocks are cut by steeply-dipping, mainly northwest-striking faults, including the regional-scale Border Ranges Fault, whose trace is about 0.5 mile southwest of the occurrence. The fault apparently is intruded by the sill(s).
Cobb (1972, 1978), citing Loney and others (1963), describes this occurrence as chalcopyrite, pyrite, and secondary copper minerals in amygdaloidal basalt. The primary sulfides probably are about the same age as the Triassic(?) greenstone host rock.
Geologic map unit (-135.867812981216, 57.6213419604806)
Mineral deposit model Basaltic copper (Cox and Singer, 1986; model 23).
Mineral deposit model number 23
Age of mineralization The primary copper mineralization probably is Triassic(?), the age of the greenstone host rock.

Production and reserves

Indication of production None

References

MRDS Number A013286

References

Cobb, E.H., 1972, Metallic mineral resources map of the Sitka quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-467, scale 1:250,000.
Cobb, E.H., 1978, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Sitka quadrangle: U.S. Geological Survey Open-File Report 78-450, 124 p.
Loney, R.A., Berg, H.C., Pomeroy, J.S., and Brew, D.A., 1963, Reconnaissance geologic map of Chichagof Island and northwestern Baranof Island, Alaska: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-388, 1 sheet, scale 1:250,000.
Reporters H.C. Berg (U.S. Geological Survey)
Last report date 10/16/2004