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Unnamed (southwest ridge of Bush Mountain)

Occurrence in Alaska, United States with commodities Silver, Gold, Chromium, Copper, Molybdenum, Nickel, Lead
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Geologic information

Identification information

Deposit ID 10307682
Record type Site
Current site name Unnamed (southwest ridge of Bush Mountain)

Geographic coordinates

Geographic coordinates: -131.52076, 55.21674 (WGS84)
Relative position This site represents four occurrences in a mile-long, northwest-trending line extending from about 500 feet elevation near the northwest shore of Helen Todd Lake, to about 1100 feet elevation on the southwest ridge of Bush Mountain. The occurrences are in sections 2, 3, and 11, T. 77 S., R. 92 E., of the Copper River Meridian. The map site is at the approximate center of the line of occurrences. The site corresponds to loc. 12a-d in Karl (1992). The location is accurate within about 0.1 mile.
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Geographic areas

Country State
United States Alaska

Commodities

Commodity Importance
Silver Primary
Gold Primary
Chromium Primary
Copper Primary
Molybdenum Primary
Nickel Primary
Lead Primary

Materials information

Materials Type of material
Bornite Ore
Chalcopyrite Ore
Pyrite Ore
Pyrrhotite Ore
Albite Gangue
Calcite Gangue
Quartz Gangue

Alteration

  • (Local) Country rocks are propylitized and pyritic.

Mineral occurrence model information

Model code 273
USGS model code 36a
Deposit model name Low-sulfide Au-quartz vein
Mark3 model number 27

Nearby scientific data

(1) -131.52076, 55.21674
ListMap

Comments on the geologic information

  • Geologic Description = The country rocks in the area of this site include: undivided, metamorphosed Silurian and Ordovician volcanic, sedimentary, and intrusive rocks; Silurian trondhjemite; recrystallized, Upper Triassic sedimentary and volcanic rocks; and Upper Jurassic or Cretaceous flyschlike metasedimentary rocks and metavolcanic rocks (Berg, 1972 [I 684]; Berg and others, 1988; Karl, 1992). The rocks were regionally metamorphosed to greenschist-grade phyllite and semischist in Late Cretaceous time. The mineral occurrences consist of sheared, pyritic greenstone and microgabbro containing quartz and calcite veins (Karl, 1992, loc. 12a-d). Some of the quartz veins contain pyrite, pyrrhotite, chalcopyrite, and bornite. Some of the veins are cataclastic, and the microgabbro is propylitically altered to epidote, chlorite, quartz, calcite, and sericite. . A sample of greenstone containing calcite-pyrrhotite veins assayed 500 ppm Cr and 1000 ppm Ni. Samples of greenstone, a quartz-sulfide vein, and quartz-albite-pyrite breccia contained up to 3.25 ppm Au, 70 ppm Ag, 15000 ppm Cu, 500 ppm Pb, and 10 ppm Mo. A sample of microgabbro contained 500 ppm Cr and 200 ppm Ni; samples of greenstone and quartz breccia contained up to 3 ppm Ag and 700 ppm Cu (Karl, 1992, loc. 12a-d).
  • Age = Probably Late Cretaceous or younger.

Economic information

Economic information about the deposit and operations

Development status Occurrence

Mining district

District name Ketchikan

Comments on the workings information

  • Workings / Exploration = A sample of greenstone containing calcite-pyrrhotite veins assayed 500 ppm Cr and 1000 ppm Ni. Samples of greenstone, a quartz-sulfide vein, and quartz-albite-pyrite breccia contained up to 3.25 ppm Au, 70 ppm Ag, 15000 ppm Cu, 500 ppm Pb, and 10 ppm Mo. A sample of microgabbro contained 500 ppm Cr and 200 ppm Ni; samples of greenstone and quartz breccia contained up to 3 ppm Ag and 700 ppm Cu (Karl, 1992, loc. 12a-d).

Reference information

Links to other databases

Agency Database name Acronym Record ID Notes
USGS Alaska Resource Data File ARDF KC167

Bibliographic references

  • Deposit

    Berg, H.C., 1972, Geologic map of Annette Island, Alaska: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-684, 8 p., 1 sheet, scale 1:63,360,

  • Deposit

    Berg, H.C., Elliott, R.L., and Koch, R.D., 1988, Geologic map of the Ketchikan and Prince Rupert quadrangles, southeastern Alaska: U.S. Geological Survey Mineral Investigations Series Map MF-1807,27 p., scale 1:250,000.

  • Deposit

    Karl, S.M., 1992, Map and table of mineral deposits on Annette Island, Alaska: U.S. Geological Survey Open-File Report 92-690, 57 p., 1 map, scale 1:63,360.

Comments on the references

  • Primary Reference = Karl, 1992

General comments

Subject category Comment text
Deposit Model Name = Low-sulfide Au-quartz veins (Cox and Singer, 1986; model 36a)

Reporter information

Type Date Name Affiliation Comment
Reporter 07-JUL-99 H.C. Berg U.S. Geological Survey