Unnamed (east of Brady Glacier)

Occurrence in Alaska, United States with commodities Iron, Silver, Copper, Molybdenum

Geologic information

Identification information

Deposit ID 10002280
MRDS ID A013184
Record type Site
Current site name Unnamed (east of Brady Glacier)

Geographic coordinates

Geographic coordinates: -136.61097, 58.43972 (WGS84)
Relative position This iron occurrence is at an elevation of about 1350 feet about 0.25 mile south of the southeast edge of an east-pointing arm of Brady Glacier and approximately 3.5 miles north-northwest of the head of the west arm of Dundas Bay. It is in the SW 1/4 SE 1/4 section 35, T. 39 S., R. 53 E., of the Copper River Meridian. (Kimball and others, 1978, report iron-rich skarn lenses in this vicinity from 1300 to 1700 feet elevation.) Location is accurate within 0.1 mile.? The occurrence is the same as number 54 of MacKevett and others (1971), number 53 of Cobb (1971), and number 63 of Kimball and others (1978).
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Geographic areas

Country State
United States Alaska

Commodities

Commodity Importance
Iron Primary
Silver Secondary
Copper Secondary
Molybdenum Secondary

Materials information

Materials Type of material
Chalcopyrite Ore
Magnetite Ore
Molybdenite Ore
Pyrite Ore
Garnet Gangue
Quartz Gangue

Alteration

  • (Local) Skarn, contact metasomatic deposit.

Mineral occurrence model information

Model code 62
USGS model code 18d
Deposit model name Skarn Fe

Host and associated rocks

  • Host or associated Associated
    Rock type Plutonic Rock > Mafic Intrusive Rock > Diorite
    Stratigraphic age (youngest) Pliocene
    Stratigraphic age (youngest) Late Permian
  • Host or associated Host
    Rock type Metamorphic Rock > Metasedimentary Rock > Marble

Nearby scientific data

(1) -136.61097, 58.43972

Comments on the geologic information

  • Geologic Description = The country rocks in the area of this occurrence consist of a northwest-trending belt of Paleozoic marble bounded on the west by foliated granodiorite of Cretaceous age and on the east by leucocratic biotite granite and affiliated rocks of Tertiary age (Brew and others, 1978). Magnetite lenses as much as 15 feet thick and 35 feet long occur in northwest-striking, steeply dipping bodies in limy hostrocks intermixed with leucocratic granitic rock. The limy rocks are partly converted to skarn. MacKevett and others (1971, p. 72, table 9) reported more than 10 percent iron, 1000 ppm copper, and 7 to 15 ppm molybdenum in grab and selected samples collected at the site. They also reported magnetic anomalies of as much as 5000 gammas, but believed that the iron-rich lenses were too small to be commercially significant.? A selected sample collected by the U.S. Bureau of Mines (Kimball and others, 1978, p. C267) contained 1400 ppm copper, 1.5 ppm silver, and greater than 20 percent iron. Samples of lenses that ranged from 4.5 to 35 feet across contained more than 30 percent iron and as much as 750 ppm copper.
  • Age = Tertiary.

Economic information

Economic information about the deposit and operations

Development status Occurrence
Commodity type Metallic

Comments on exploration

  • Status = Inactive

Mining district

District name Juneau

Comments on the workings information

  • Workings / Exploration = There are no workings. The Geological Survey and Bureau of Mines sampled only surface exposed occurrences. Samples collected by MacKevett and others (1971) contained 7-15 ppm molybdenum, 1000 ppm copper and greater than 10 percent iron. Kimball and others (1978) reported iron to greater than 30 percent and, in one selected sample, 1400 ppm copper.? the magnetite-rich skarn lenses are as much as 35 feet long and are traceable through a vertical range of at least 400 feet.

Reference information

Links to other databases

Agency Database name Acronym Record ID Notes
USGS Mineral Resources Data System MRDS A013184
USGS Alaska Resource Data File ARDF MF072

Bibliographic references

  • Deposit

    MacKevett, E.M., Jr., Brew, D.A., Hawley, C.C., Huff, L.C., and Smith, J.G., 1971, Mineral resources of Glacier Bay National Monument, Alaska: U.S. Geological Survey Professional Paper 632, 90 p., 12 plates, scale 1:250,000.

  • Deposit

    Brew, D.A., Johnson, B.R., Grybeck, D., Griscom, A., Barnes, D.F., Kimball, A.L., Still, J.C., and Rataj, J.L., 1978, Mineral resources of the Glacier Bay National Monument Wilderness Study Area, Alaska: U.S. Geological Survey Open-File Report 78-494, 670 p.

  • Deposit

    Kimball, A.L., Still, J.C., and Rataj, J.L., 1978, Mineral resources, in Brew, D. A., and others, Mineral resources of the Glacier Bay National Monument wilderness study area, Alaska: U.S. Geological Survey Open-File Report 78-494, p. C1-C375.

  • Deposit

    Cobb, E.H., 1972, Metallic mineral resources map of the Mount Fairweather quadrangle, AK: U.S. Geological Survey Miscellaneous Field Study Map MF-436, 1 sheet, scale 1:250,000.

Comments on the references

  • Primary Reference = Kimball and others, 1978

General comments

Subject category Comment text
Deposit Model Name = Fe skarn (Cox and Singer, 1986; model 18d).
Deposit Other Comments = Although some of the skarn bodies are rich enough to constitute iron ore, they are too small to be exploited. The proximity of this site to the Threesome Mountain (MF070) molybdenum-tungsten area, also affiliated with a Tertiary granite, suggests that the area could contain skarns having more molybdenum and copper.? the site is in Glacier Bay National Park and Preserve.

Reporter information

Type Date Name Affiliation Comment
Reporter 14-APR-99 Hawley, C.C. Hawley Resource Group