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Nunatak (Muir Inlet)

Prospect in Alaska, United States with commodities Molybdenum, Silver, Gold, Copper
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Sections on this page
  1. Identification information
  2. Geographic coordinates
  3. Site location context
  4. Geographic areas
  5. Commodities
  6. Materials information
  7. Alteration
  8. Mineral occurrence model information
  9. Nearby scientific data
  10. Economic information about the deposit and operations
  11. Mining district
  12. Reserves and resources
  13. Links to other databases
  14. Bibliographic references
  15. General comments
  16. Reporter information

Geologic information

Identification information

Deposit ID 10308916
MRDS ID D000846
Record type Site
Current site name Nunatak (Muir Inlet)
Related records 10008547

Geographic coordinates

Geographic coordinates: -136.1051, 58.98973 (WGS84)
Relative position The Nunatak molybdenum deposit is on the east side of upper Muir Inlet, about one mile north of Nunatak Cove. The Cove furnishes a good anchorage for access to the deposit. The deposit trends north to northwest; the coordinates are the approximate center of the outcrop of the deposit. The deposit is mainly on the west flank of the geographic feature named the Nunatak. Mineralization extends from about 1200 feet elevation on the Nunatak northwest to the shoreline. The deposit is number 43 of Cobb (1972).

Site location context

Political divisions (FIPS codes)

Hoonah-Angoon(Census area)

Alaska(state)

United States(country)

North America(continent)

Land(continent)

USGS map quadrangles

Mount Fairweather D-1(quadrangle 1:63,360 scale)

Juneau NW(quadrangle 1:100,000 scale)

Mount Fairweather(quadrangle 1:250,000 scale)

Hydrologic units (watersheds)

Glacier Bay(hydrologic unit)

Northern Southeast Alaska(hydrologic accounting unit)

Southeast Alaska(hydrologic subregion)

Alaska(hydrologic region)

Federal lands

Glacier Bay National Park(National Park)

National Park NPS(Type of land area)

NPS(Federal land areas administered by NPS)

Geographic areas

Country State
United States Alaska

Commodities

Commodity Importance
Molybdenum Primary
Silver Secondary
Gold Secondary
Copper Secondary

Comments on the commodity information

  • Gangue = various rock
  • Gangue = alteration minerals

Materials information

Materials Type of material
Bornite Ore
Chalcopyrite Ore
Chrysocolla Ore
Enargite Ore
Magnetite Ore
Malachite Ore
Molybdenite Ore
Pyrite Ore
Pyrrhotite Ore
Tetrahedrite Ore
Calcite Gangue
Quartz Gangue

Alteration

  • The alteration consists of minor K-feldspar and pyrometasomatic conversion of calc-units to calc-hornfels and skarn. Actinolite is locally developed in the skarn and actinolitic skarns appear to be more favorable for ore The tactitic skarn consists mainly of orthoclase and clinozoisite, with lesser amounts of diopside, garnet, quartz, and plagioclase. Rocks adjacent to the quartz granodiorite porphyry are silicified. Phlogopite, montmorillonite, calcite, and feldspar occur in the altered zones flanking some veins (MacKevett and others, 1971, p. 75).

Mineral occurrence model information

Model code 80
USGS model code 21b
Deposit model name Porphyry Mo, low-F

Nearby scientific data

(1) -136.1051, 58.98973
ListMap

Economic information

Comments on the geologic information

  • Geologic Description = The deposit is in the Muir province dominated by volcanic rocks of Silurian and Devonian age and clastic, carbonate, and volcanic rocks of Permian age. Hornfels is widespread in the terrane, especially near foliated granitic rocks of Cretaceous age (Brew and others, 1978, p. B20-21). At the deposit , calc-hornfels developed in calcic argillite and limestone of probable Paleozoic age is intruded by a quartz granodiorite (rhyodacite) porphyry, generally termed quartz monzonite porphyry (MacKevett and others, 1971, p. 74). The quartz granodiorite is a massive rock composed of phenocrystic oligoclase and lesser quartz, and hornblende in a microcrystalline background of K-feldspar, plagioclase and quartz. The largest body of the granodiorite porphyry is about 1200 feet long by as much as 400 feet across. It is aligned northerly and crops out on the northwest flank of the Nunatak. The deposit and older country rocks are cut by numerous post-mineral dikes of hornblende andesite and dacite porphyry. The quartz granodiorite porphyry is enveloped by a silicfied zone that grades outward into tactitic calc-hornfels. The hornfels is succeeded outward by fine-grained 'chert' silica rock (Moerlein, 1968; Kimball and others, 1978, pl. IV, p. C275). Moerlein proposed that these facies were alteration zones or haloes related to the intrusion of the porphyry and mineralization. Previously some of the units had been mapped as primary sedimentary facies (Twenhofel, 1946). The deposit is mainly composed of quartz-molybdenite stockworks in the silicic and tactitic zones, hornfels, and quartz porphyry. Molybdenite also locally occurs in fault zones, as rosettes on joint and fracture planes in the tactized rock, and as fine-grained disseminations in the porphyry. Chalcopyrite locally occurs with molybdenite but appears to be relatively more abundant outside the main molybdenite zone. Small amonts of enargite and bornite occur locally. Chrysocolla and malachite are developed in partly oxidized facies. Rossman (1963, B 1121-K, p. K49) reported a sample from the northeast side of the Nunatak that contained 0.04 oz/ton gold and 7.07 oz/ton silver. The silver-bearing phase is uncertain, but tetrahedrite has been reported from the property. Possibly gold forms a weak distal halo, as in many other molybdenum deposits. MacKevett and others (1971, p. 75) cite communications from Amex (American Exploration & Mining) indicating the prescence of gold and silver in Amex drill holes (1971, p. 75). Diamond drill holes of the U.S. Bureau of Mines (Sanford and others, 1949) and private exploration companies indicate mineralization extends downward to at least 300 feet below sea level. The deposit is probably of Tertiary age and is genetically related to the intrusion of a high level quartz granodiorite porphyry. The haloes and pattern of alteration suggest that the intrusive is barely unroofed.
  • Age = Tertiary.

Economic information about the deposit and operations

Development status Prospect
Commodity type Metallic

Comments on exploration

  • Status = Inactive

Mining district

District name Juneau

Comments on the production information

  • Production Notes = No production.

Reserves and resources

  • Type In-situ
    Estimate year 1978
    Total resources 120000000mt
    Remarks Brew et al, 1978, as reported in Singer PorCuEX2008.xls.
    Commodity Subtype Grade units Group Importance Year
    Molybdenum 0.03 wt-pct Molybdenum Primary 1978
    Copper 0.18 wt-pct Copper Secondary 1978

Comments on the reserve resource information

  • Reserves = Approximately 145 millon tons of mineralized rock configured for surface mining and containing from 0.04 to 0.06 percent molybdenum and 0.02 percent copper exist at the Nunatak deposit. There is an inferred 9.1 million tons at or below sealevel near Muir Inlet with grades up to about 0.06 percent molybdenum and 0.02 percent Cu. The total figure (145 million tons) represents the combination of the Bureau of Mines area #1 with conspicuous molybdenite and area #2 with inconspicuous molybdenite. Rock with more molybdenum was found in the Amex No. 2 and Muir Nos. 1 & 2 drill holes. These holes indicate a discontinuous halo around the quartz granodiorite porphyry stock from 50 to 160 feet wide that grades from 0.11 to 0.143 percent molybdenum (Kimball and others, 1978, table C-53).

Comments on the workings information

  • Workings / Exploration = The area was first mapped by Reed (1938) in 1936, who recognized abundant quartz veins and described hornfels, granitic dikes, and chalcopyrite and copper-iron stained veinlet mineralization. The molybdenum deposit was found in 1941 by prospectors John Johnson and Tom Smith. It was studied jointly by the U.S. Geological Survey and Bureau of Mines in 1942 (Twenhofel, 1946; Sanford and others, 1949). The first two core holes were drilled by the Bureau of Mines in 1943 (Sanford and others, 1949). The first studies recognized and concentrated on relatively rich veins or lodes within the deposit. The area was relocated by James Walper in 1964. Amex drilled three diamond core holes in 1966. In 1968, the area was remapped by consultant George M. Moerlein (1968) for Superior Oil Company. Superior drilled seven core holes with a total footage of 5,430 feet. Maximum drill hole depth of any hole was 892 feet. Limited surface mapping and sampling, including a geochemical soil survey, was carried out by MacKevett and others, 1971 (plates 11 and 12 and p. 74-78). The area was visited and studied briefly by the U.S. Bureau of Mines in 1975 and 1977 (Kimball and others, 1978, p. C274-295).

Reference information

Bibliographic references

  • Deposit

    Twenhofel, W.S., 1946, Molybdenite deposits of the Nunatak area, Muir Inlet, Glacier Bay, in Twenhofel, W. S., Robinson, G. D., and Gault, H. R., Molybdenite investigations in southeastern Alaska: U.S. Geological Survey Bulletin 947-B, p. 7-38.

  • Deposit

    Sanford, R.S., Apell, G.A., and Rutledge, F.A., 1949, Investigations of Muir Inlet or Nunatak molybdenum deposit, Glacier Bay, southeastern Alaska: U.S. Bureau of Mines Report of Investigations 4421, 6 p.

  • Deposit

    Rossman, Darwin, 1963, Geology of the eastern part of the Mount Fairweather quadrangle, Glacier Bay, Alaska: U.S. Geological Survey Bulletin 1121-K, p. K1-K57.

  • 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

    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

    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

    Moerlein, G.A., 1968, Geology and drilling results, Nunatak molybdenum prospect, Walper property, southeastern Alaska: Unpublished report available at U.S. Bureau of Land Management Library at Juneau, Alaska.

  • 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.

  • Deposit

    Reed, J.C., 1938, Some mineral deposits of Glacier Bay and vicinity, Alaska: Economic Geology, v. 33, p. 52-80.

Comments on the references

  • Primary Reference = Kimball and others, 1978

General comments

Subject category Comment text
Deposit Model Name = Porphyry molybdenum (Cox and Singer, 1986; model 21b).
Deposit Other Comments = The site is in Glacier Bay National Park and Preserve.

Reporter information

Type Date Name Affiliation Comment
Reporter 04-APR-99 Hawley, C.C. Hawley Resource Group

Beyond USGS

Supplemental information added by qvyshift.com. Not part of the original USGS MRDS record.

Maps centered on this site

Authoritative Alaska resources

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