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Opal

Mine, Active?

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Alternative names

Tiger Mining Co.

Commodities and mineralogy

Main commodities Au
Other commodities Ag; Pb; Zn
Ore minerals arsenopyrite; galena; gold; pyrite; sphalerite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale VA
Quadrangle map, 1:63,360-scale C-2
Latitude 61.5371
Longitude -144.6462
Nearby scientific data Find additional scientific data near this location
Location and accuracy This prospect is located in the cirque at the southwest head of Liberty Creek. It is in the southeast headwall of this cirque, about nine-tenths of a mile north of elevation 5,285. It is at an elevation of 4,400 feet in the NW1/4 section 11, T. 4 S, R. 4 E., of the Copper River Meridian. This prospect is approximately located, perhaps to within one-half mile. It is locality 54 of of Cobb and Matson (1972) and locality 45 of Winkler and others (1981 [OFR 80-892-B]). The location used in this report is that shown by Winkler and others (1981 [OFR 80-892-B]); it is nine-tenths of a mile north of the location shown by Cobb and Matson (1972).

Geologic setting

Geologic description

Widely spaced quartz veins as much as 1 meter wide cut the schist of both the Liberty Creek terrane and Eocene tonalite (Winkler and others, 1981 [OFR 80-892-B]; Winkler and others, 1981 [OFR 80-892-A]). The veins contain arsenopyrite, pyrite, galena, and sphalerite.
The Opal prospect, being evaluated by Ben Porterfield, contains gold-bearing, polymetallic quartz veins hosted in a white mica-altered, 52 million-year-old tonalite sill. In 2016, exploration was conducted on high-angle shear zones cutting the sill and on pods at the wall-rock contact at the top of the sill (Athey and Werdon, 2017).
Geologic map unit (-144.648297056383, 61.5366218787844)
Mineral deposit model Polymetallic veins (Cox and Singer, 1986; model 22c)
Mineral deposit model number 22c
Age of mineralization Tertiary; the quartz veins cut tonalite with a K/Ar age of 52.4 +/- 2.6 m.y. (Winkler and others, 1981 [OFR 80-892-A]).

Production and reserves

Workings or exploration The Opal prospect, being evaluated by Ben Porterfield, contains gold-bearing, polymetallic quartz veins hosted in a white mica-altered, 52 million-year-old tonalite sill. High gold grades, up to 4 ounces of gold per ton, are present, visible gold is common, and it is associated with galena, sphalerite, pyrite, and arsenopyrite. In 2016, exploration was conducted on high-angle shear zones cutting the sill and on pods at the wall-rock contact at the top of the sill (Athey and Werdon, 2017).
Indication of production Yes; small

References

MRDS Number A011496

References

Cobb, E.H., and Matson, N.A., Jr., 1972, Metallic mineral resources map of the Valdez quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-438, 1 sheet, scale 1:250,000.
Winkler, G.R., Miller, R.J., MacKevett, E.M., Jr., and Holloway, C.D., 1981, Map and summary table describing mineral deposits in the Valdez quadrangle, southern Alaska: U.S. Geological Survey Open-File Report 80-892-B, 2 sheets, scale l:250,000.
Winkler, G.R., Silberman, M.L., Grantz, Arthur, Miller, R.J., and MacKevett, E.M., Jr., 1981, Geologic map and summary geochronology of the Valdez quadrangle, southern Alaska: U.S. Geological Survey Open-File Report 80-892-A, 2 sheets, scale 1:250,000.
Reporters Travis L. Hudson; M.B. Werdon (DGGS)
Last report date 8/26/2017