Island Mountain

Prospect in Alaska, United States with commodities Gold, Copper, Molybdenum, Zinc, Arsenic, Iron

Geologic information

Identification information

Deposit ID 10003510
MRDS ID A106267
Record type Site
Current site name Island Mountain

Geographic coordinates

Geographic coordinates: -152.74276, 61.77949 (WGS84)
Relative position Alaska Department of Natural Resources unpublished claim records locate these prospects on the west side of the Skwentna River, one to one-and-one half miles south of the confluence of Emerald Creek and the Skewntna River. The site covers an area of about eight square miles in Sections 28, 29, 31,32, and 33, T. 20 N., R. 19 W. Location given is in the northeast corner of the area.
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Geographic areas

Country State
United States Alaska

Commodities

Commodity Importance
Gold Primary
Copper Primary
Molybdenum Primary
Zinc Primary
Arsenic Secondary
Iron Secondary

Materials information

Materials Type of material
Arsenopyrite Ore
Chalcopyrite Ore
Gold Ore
Molybdenite Ore
Pyrite Ore
Pyrrhotite Ore
Sphalerite Ore
Magnetite Gangue
Quartz Gangue

Alteration

  • (Local) Propylitic (chlorite-epidote-carbonate +/- magnetite); argillic/sericitic; silicic.

Host and associated rocks

  • Host or associated Host
    Stratigraphic age (youngest) Early Oligocene
    Stratigraphic age (oldest) Early Cretaceous

Nearby scientific data

(1) -152.74276, 61.77949

Comments on the geologic information

  • Geologic Description = Reed and Elliott (1970) show this locality to be underlain by Mesozoic sediments (KJs) of the Kahlitna terrane that are intruded by a small body of granite and quartz monzonite (TKig). Detailed mapping in the late 1980's by Cominco American Incorporated identified veins and disseminations of pyrite-chalcopyrite and arsenopyrite-gold and stockwork quartz veins with magnetite and trace amounts of molybdenite cutting fine- to medium- grained plagioclase-hornblende porphyritic andesite and medium-grained monzonitic plutonic rocks at this site. Carbonate-rich beds in the sedimentary country rocks are locally replaced with pyrrhotite, pyrite, and sphalerite. Numerous occurrences are reported over an 8 square mile area. (Cominco American Incorporated, unpublished reports, 1987and 1988.) Host rocks are most likely Late Cretaceous or Early Tertiary(?) based on nearby K-Ar ages published by Reed and Lanphere (1972). Mineralization is probably related to these intrusions.
  • Age = Host rocks are late Cretaceous or Early Tertiary based on K-Ar ages published by Reed and Elliott (1970). The deposit is probably related to these intrusions.
  • Age = Host rocks are Eocene - Late Cretaceous.

Economic information

Economic information about the deposit and operations

Development status Prospect
Commodity type Metallic

Comments on exploration

  • Status = Inactive

Mining district

District name Yentna

Comments on the workings information

  • Workings / Exploration = Exploration included silt sampling, mapping, rock and contour soil sampling, soil grid geochemical surveys, magnetic and VLF geophysical surveys and diamond drilling by Cominco America in mid-1980's.

Reference information

Links to other databases

Agency Database name Acronym Record ID Notes
USGS Mineral Resources Data System MRDS A106267
USGS Alaska Resource Data File ARDF TY018

Bibliographic references

  • Deposit

    Reed, B.L., and Elliot, R.L., 1970, Reconnaissance geologic map, analyses of bedrock and stream sediment samples, and an aeromagnetic map of parts of the southern Alaska Range: U.S. Geological Survey Open-file Report 70-271, 24 p., 4 plates, scale 1:250,000.

  • Deposit

    Reed, B.L., and Elliott, R.L., 1970, Reconnaissance geologic map, analyses of bedrock and stream sediment samples, and an aeromagnetic map of parts of the southern Alaska Range: U.S. Geological Survey Open-file Report 70-271, 24 p., 4 sheets, scale 1:250,000.

Comments on the references

  • Primary Reference = Reed and Elliott, 1970.

General comments

Subject category Comment text
Deposit Model Name = Porphyry copper(?); porphyry copper-gold(?); polymetallic vein; replacement

Reporter information

Type Date Name Affiliation Comment
Reporter 01-JUN-1998 Madelyn A. Millholland Millholland & Associates