Unnamed (near Lacuna Glacier)

Occurrence in Alaska, United States with commodities Chromium, Iron

Geologic information

Identification information

Deposit ID 10000884
MRDS ID A011538
Record type Site
Current site name Unnamed (near Lacuna Glacier)

Geographic coordinates

Geographic coordinates: -151.51783, 62.78454 (WGS84)
Relative position Reed and others (1978, locality 30) locate this occurrence west of the Lacuna Glacier at about 4300 feet elevation in the southwest quarter of Section 10, T. 31 N., R. 12 N., of the Seward Meridian, approximately 3500 feet northeast of TL 055. This occurrence is within Denali National Park and Preserve.
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Geographic areas

Country State
United States Alaska

Commodities

Commodity Importance
Chromium Primary
Iron Primary

Materials information

Materials Type of material
Chromite Ore
Magnetite Ore
Pyrrhotite Ore

Mineral occurrence model information

Model code 15
USGS model code 8a
Deposit model name Podiform chromite (minor)
Mark3 model number none

Host and associated rocks

  • Host or associated Associated
    Rock type Plutonic Rock > Mafic Intrusive Rock > Diorite
    Rock unit name Foraker Pluton
    Rock description Foraker Pluton
    Stratigraphic age (youngest) Pliocene
    Stratigraphic age (youngest) Pliocene
  • Host or associated Host
    Rock type Plutonic Rock > Ultramafic Intrusive Rock > Peridotite > Dunite

Nearby scientific data

(1) -151.51783, 62.78454

Comments on the geologic information

  • Geologic Description = This is one of several chromite occurrences in a 25-mile long belt of alpine-type ultramafic bodies that are discontinuously exposed from the Dall Glacier northeast to the Lacuna Glacier which is part of the Dall Trend, described by C.C. Hawley and Associates, Inc. (1978, Fig. 4.1-(C)3 and Fig. 4.0-B). These chromite- and magnetite-bearing dunite and peridotite sills are shown by Reed and Nelson (1980) in a narrow belt of middle to upper Paleozoic sedimentary rocks that are exposed between the middle Tertiary (38 m.y.) Foraker pluton and the northwest trending fault which places the Paleozoic rocks over Mesozoic marine sedimentary rocks (KJs). Foley and others (1997, p. 431) suggest that these ultramafic bodies may be genetically related to the composite plutons (Tcp) of Reed and Nelson (1980) in the upper Yentna River. ? Reed and others (1978) describe these occurrences as magmatic segregations of podiform and disseminated chromite hosted in dunite sills. At this site a grab sample of chromite contained 0.02 ppm each ruthenium and iridium. Chromite occurs as: (1) disseminated rounded grains 1-3 mm in diameter, (2) streaks and lenses, (3) irregular pods up to 6 feet long and (4) lens-like bodies up to 6 feet thick and 60 feet long throughout the dunite. Chromium content of 0.7 to 1% from typical dunite is given in Reed and others (1978). The average of 3 microprobe analyses of one sample was 58.4% Cr2O3, 21.1% FeO, 8.9% MgO, and 9.7% Al2O3. ? Other chromite occurrences in this trend are described in TL 003, TL008 - 012, and TL055.
  • Age = Mesozoic and (or) Paleozoic (Reed and Nelson, 1980) or Late Cretaceous/early Tertiary (Foley and others, 1997).

Economic information

Economic information about the deposit and operations

Development status Occurrence
Commodity type Metallic

Comments on exploration

  • Status = Inactive

Mining district

District name Yentna

Comments on the workings information

  • Workings / Exploration = Reconnaissance mapping, stream silt and rock sampling by the U.S. Geological Survey (Reed and others, 1978; Reed and Nelson, 1980) have been done here. Chromium content of 0.7 to 1% from typical dunite is given in Reed and others (1978). The average of 3 microprobe analyses of one sample was 58.4% Cr2O3, 21.1% FeO, 8.9% MgO, and 9.7% Al2O3.

Reference information

Links to other databases

Agency Database name Acronym Record ID Notes
USGS Mineral Resources Data System MRDS A011538
USGS Alaska Resource Data File ARDF TL003

Bibliographic references

  • Deposit

    C.C. Hawley and Associates, Inc., 1978, Mineral appraisal of lands adjacent to Mt. McKinley National Park, Alaska: U.S. Bureau of Mines Open-File Report 24-78, 275 p., 7 plates.

  • Deposit

    Reed, B.L., Nelson, S.W., Curtin, G.C., and Singer, D.A., 1978, Mineral resources map of the Talkeetna Quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-870-D, 1 sheet, scale 1:250,000.

  • Deposit

    Cobb, E.H., and Reed, B.L., 1980, Summaries of data and lists of reference to metallic and selected nonmetallic mineral deposits in the Talkeetna quadrangle, Alaska: U.S. Geological Survey Open-File Report 80-884, 106 p.

  • Deposit

    Reed, B.L., and Nelson, S.W., 1980, Geologic map of the Talkeetna quadrangle: U.S. Geological Survey Miscellaneous Investigations Map I-1174, scale 1:250,000.

  • Deposit

    Foley, J.Y., Light, T.D., Nelson, S.W., and Harris, R.A., 1997, Mineral occurrences associated with mafic-ultramafic and related alkaline complexes in Alaska: Economic Geology, Monograph 9, p. 396-449.

  • Deposit

    MacKevett, E.M., Jr., and Holloway, C.D., 1977, Map showing metalliferous and selected non-metalliferous mineral deposits in the eastern part of southern Alaska: U.S. Geological Survey Open-File Report 77-169-A, 99 p., 1 sheet, scale 1:1,000,000.

Comments on the references

  • Primary Reference = Reed and others, 1978

General comments

Subject category Comment text
Deposit Model Name = Podiform chromite (Cox and Singer, 1986; model 8a).
Deposit Other Comments = Mineral occurrences in the Dall Trend are all within Denali National Park and Preserve.

Reporter information

Type Date Name Affiliation Comment
Reporter 10-AUG-1998 Madelyn A. Millholland Millholland & Associates