Unnamed (northeast of Slocum Arm)

Occurrence, Undetermined

Commodities and mineralogy

Main commodities Mo
Ore minerals malachite

Geographic location

Quadrangle map, 1:250,000-scale SI
Quadrangle map, 1:63,360-scale B-6
Latitude 57.4717
Longitude -135.7912
Nearby scientific data Find additional scientific data near this location
Location and accuracy This occurrence is at an elevation of about 1,900 feet, about a mile east-northeast of Flat Cove in Slocum Arm. The occurrence is 0.3 mile south of the center of sec. 4, T. 51 S., R. 60 E. It is location P-95 of Bittenbender and others (1999), location 45 of Cobb (1972, 1978), and MAS no. 0021140136 (U.S. Bureau of Land Management, 2002). The location is accurate within about 0.5 mile.

Geologic setting

Geologic description

Johnson and Karl (1985) map the rocks in the area of this occurrence as Triassic(?) greenstone and marble, Cretaceous(?) phyllite, and the Freeburn assemblage, a collage of kilometer-scale, fault-bounded, lozenge-shaped blocks of Cretaceous and Cretaceous(?) metasedimentary and metavolcanic rocks. The contact between the Triassic(?) strata and the Cretaceous/Cretaceous(?) strata is the Border Ranges Fault, a regional-scale, high-angle fault that strikes northwest. Other faults in the area strike northwest, north, and east-southeast. One of them appears to offset the Border Ranges Fault for about 2 miles along a right-lateral fault.
Cobb (1972, 1978), citing Loney and others (1963), describes the occurrence as disseminated sulfides and secondary copper minerals in greenstone. Bittenbender and others (1999), citing Ballard (1968) and Still and Weir (1981), describe the occurrence as a porphyry molybdenum deposit that extends over an area of at least a square mile. They specify the country rocks as greenstone intruded by granodiorite, but do not name the ore minerals.
Geologic map unit (-135.792999888003, 57.4713425221361)
Mineral deposit model Porphyry molybdenum deposit? (Cox and Singer, 1986; models 21b).
Mineral deposit model number 21b?

Production and reserves

Indication of production None

Additional comments

The occurrence is in West Chichagof-Yakobi Wilderness.


MRDS Number A013290; A013291


Bittenbender, P., Still, J.C., Maas, K., and McDonald, M., Jr., 1999, Mineral resources of the Chichagof and Baranof Islands area, southeast Alaska: Bureau of Land Management, BLM-Alaska Technical Report 19, 222 p.
Thorne, R.L., 1952, Slocum Arm molybdenum deposit, southeastern Alaska: Unpublished U. S. Bureau of Mines minerals memorandum, 2 p. (Report held by the Mineral Information Center, Bureau of Land Management, Juneau, Alaska.)
U.S. Bureau of Land Management, 2002, Alaska mineral locations database report (Sitka quadrangle), July 2, 2002, 205 p. [http://imcg.wr.usgs.gov/dem.html]
Wells, R.R., 1952, Mineral dressing report, Cobol molybdenum ore: Unpublished report, 3 p. (Report held by the Mineral Information Center, Bureau of Land Management, Juneau, Alaska.)
Williams, J.A, 1928, Cobol deposit, Slocum Arm, Chichagof Island: Unpublished report, 3 p. (Report held by the Mineral Information Center, Bureau of Land Management, Juneau, Alaska.)
Reporters H.C. Berg (U.S. Geological Survey)
Last report date 10/16/2004