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Opal

Prospect in Alaska, United States with commodity Gold
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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. Links to other databases
  13. Bibliographic references
  14. General comments
  15. Reporter information

Geologic information

Identification information

Deposit ID 10000960
MRDS ID A011630
Record type Site
Current site name Opal
Related records 10161026

Geographic coordinates

Geographic coordinates: -149.21269, 61.81956 (WGS84)
Relative position West of Reed Creek, 3,000 ft southwest of the confluence of Goodhope Creek with Reed Creek. Accurate within 2,000 ft. Locality 30 of Chapin (1921, plate VI), locality 28 from Cobb (1972), and locality 20 of MacKevett and Holloway (1977).

Site location context

Political divisions (FIPS codes)

Matanuska-Susitna(Borough)

Alaska(state)

United States(country)

North America(continent)

Land(continent)

USGS map quadrangles

Anchorage D-6(quadrangle 1:63,360 scale)

Anchorage NW(quadrangle 1:100,000 scale)

Anchorage(quadrangle 1:250,000 scale)

Hydrologic units (watersheds)

Lower Susitna River(hydrologic unit)

Susitna River(hydrologic accounting unit)

South Central Alaska(hydrologic subregion)

Alaska(hydrologic region)

Geographic areas

Country State
United States Alaska

Commodities

Commodity Importance
Gold Primary

Materials information

Materials Type of material
Gold Ore
Pyrite Ore
Quartz Gangue

Alteration

  • (Local) Wall-rock alteration within a few inches of the veins is intense, but seldom extends more than 10 to 12 inches beyond the quartz filling. Sericitization and carbonate alteration predominate, but there is some pyritization and in the outer parts of the alteration zone chloritization is present (Ray, 1954).

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) -149.21269, 61.81956
ListMap

Economic information

Comments on the geologic information

  • Geologic Description = Two parallel veins have been traced in the quartz diorite country rock of the Late Cretaceous Willow Creek Pluton. The veins strike N 50 E, and dip 50 NW. The upper vein is 3 to 4 ft wide and consists of quartz and gouge in altered quartz diorite. The lower vein is 3 to 5 ft wide and consists of quartz stringers and gouge in altered quartz diorite. Both veins carry pyrite and free gold, and reportedly are cut by faults (Chapin, 1921).? the Willow Creek Pluton is a zoned pluton: the outer part consists of hornblende quartz diorite and lesser hornblende tonalite; the core consists of hornblende-biotite granodiorite, and lesser hornblende-biotite quartz monzodiorite and biotite quartz monzonite. Wall-rock alteration within a few inches of the veins is intense, but seldom extends more than 10 to 12 inches beyond the quartz filling. Sericitization and carbonate alteration predominate, but there is some pyritization and in the outer parts of the alteration zone chloritization is present (Ray, 1954).
  • Age = Late Cretaceous or younger; veins cut the Late Cretaceous Willow Creek Pluton.

Economic information about the deposit and operations

Development status Prospect
Commodity type Metallic

Comments on exploration

  • Status = Inactive

Mining district

District name Willow Creek

Comments on the production information

  • Production Notes = No record of production.

Comments on the workings information

  • Workings / Exploration = Tunnels started in 1919. The prospect was explored by surface excavations and about 300 ft of underground workings as of 1923 (Brooks, 1925).

Reference information

Bibliographic references

  • Deposit

    Chapin, Theodore, 1921, Lode developments in the Willow Creek district: U.S. Geological Survey Bulletin 714-E, p. 201-206.

  • Deposit

    Brooks, A.H. and Capps, S.R., 1924, Mineral industry in Alaska, 1922: U.S. Geological Survey Bulletin 755, p. 1-56.

  • Deposit

    Brooks, A.H., 1925, Alaska's mineral resources and production, 1923: U.S. Geological Survey Bulletin 773, p. 3-52.

  • 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.

  • Deposit

    Cobb, E.H., 1972, Metallic mineral resources map of the Anchorage quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-409, 1 sheet, scale 1:250,000.

  • Deposit

    MacKevett, E.M., Jr., and Holloway, C.D., 1977, Map showing metalliferous mineral deposits in the western part of southern Alaska: U.S. Geological Survey Open-File Report 77-169-F, 38 p., 1 sheet, scale 1:1,000,000.

  • Deposit

    Cobb, E.H., 1979, Summary of references to mineral occurrences (other than mineral fuels and construction materials in the Anchorage quadrangle, Alaska: U.S. Geological Survey Open-File Report 79-1095, 184 p.

Comments on the references

  • Primary Reference = Chapin, 1921

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 30-JUL-1998 D.P. Bickerstaff U.S. Geological Survey
Reporter 30-JUL-1998 S.W. Huss U.S. Geological Survey

Beyond USGS

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

Maps centered on this site

Authoritative Alaska resources

These are landing pages for further research — the state agencies don't currently expose per-mine deep links.