Midnight Mountain

The Midnight Mountain is a gold mine located in Alaska.

About the MRDS Data:

All mine locations were obtained from the USGS Mineral Resources Data System. The locations and other information in this database have not been verified for accuracy. It should be assumed that all mines are on private property.

Mine Info

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Site Name

Primary: Midnight Mountain

Commodity

Primary: Gold

Location

State: Alaska
District: Kougarok

Land Status

Not available

Holdings

Not available

Workings

Not available

Ownership

Not available

Production

Not available

Deposit

Record Type: Site
Operation Category: Prospect
Operation Type: Unknown
Years of Production:
Organization:
Significant:

Physiography

Not available

Mineral Deposit Model

Not available

Orebody

Not available

Structure

Not available

Alterations

Alteration Type: L
Alteration Text: The area contains abundant small quartz veins, veinlets, and stringers in pelitic metasedimentary rocks. Iron oxide-staining of frost-riven soils is well-developed in the area of anomalous gold and arsenic samples.

Rocks

Not available

Analytical Data

Not available

Materials

Ore: Gold
Gangue: Quartz
Gangue: Arsenopyrite

Comments

Comment (Exploration): Status = Inactive

Comment (Workings): Workings / Exploration = There are no workings on this prospect.

Comment (Deposit): Model Name = Gold-bearing quartz veins and schist

Comment (Geology): Geologic Description = Midnight Mountain is composed of Lower Paleozoic metasedimentary rocks on its northwest side and polydeformed pelitic schist of possible Precambrian age elsewhere (Hudson, 1984; Till and others, 1986). Surface material in the prospect area is frost-riven rubble; outcrops are restricted to a few places at higher elevations on Midnight Mountain. White quartz veinlets and stringers are ubiquitous in the metasedimentary rocks of this area. On the south flank of the mountain, quartz vein fragments are associated with rust-stained frost boils and some contain arsenopyrite. Here, soil and selected rock samples collected over a length of about 2,000 feet between elevations of 2,000 and 2,100 feet contain highly anomalous amounts of gold and arsenic (Hudson, 1984). Iron oxide-stained soil samples, commonly with quartz vein fragments, contain up to 725 ppb Au and greater than 1,000 ppm As. Quartz vein fragments, some with visible arsenopyrite, contain up to 765 ppb gold and greater than 1,000 ppm arsenic. This gold-bearing area seems to be mostly in altered and quartz-veined polydeformed metapelitic schist on the south side of Midnight Mountain. Bedrock exposures of this mineralization have not been observed. Lode gold deposits in the upper Kougarok River area, including this prospect on Midnight Mountain, may be associated with emplacement and crystallization of the Oonatut Granite Complex. The Midnight Mountain prospect is 4 to 4.5 miles south of outcrops of the Oonatut Granite Complex (Hudson, 1979). Regional gravity data show that the Oonatut Granite is extensively distributed in the subsurface (Barnes and Hudson, 1977); it probably extends to the south under the Midnight Mountain area (McDermott, 1983). The Oonatut Granite is part of the western Seward Peninsula tin granite suite (Hudson and Arth, 1983). K/Ar ages for the Oonatut Granite Complex are about 70 my (Hudson, 1979, p. 24).

Comment (Reference): Primary Reference = Hudson, 1984

Comment (Geology): Age = the epigenetic mineralization here is probably mid- to Late Cretaceous in age. Lode gold deposits in the upper Kougarok River area, including this prospect on Midnight Mountain, may be associated with emplacement and crystallization of the Oonatut Granite Complex. The Midnight Mountain prospect is 4 to 4.5 miles south of outcrops of the Oonatut Granite Complex (Hudson, 1979). Regional gravity data show that the Oonatut Granite is extensively distributed in the subsurface (Barnes and Hudson, 1977) and that it probably estends to the south under the Midnight Mountain area (M. McDermott, unpublished data, 1983). This large exposed granite complex is part of the western Seward Peninsula tin granite suite (Hudson and Arth, 1983). K/Ar ages for the Oonatut Granite Complex are about 70 my. Alternatively, gold-bearing mineralization here may be similar in age to some lode gold deposits of southern Seward Peninsula. The southern Seward Peninsula lode gold deposits formed as a result of mid-Cretaceous metamorphism (Apodoca, 1994; Ford, 1993, Ford and Snee, 1996; Goldfarb and others, 1997) that accompanied regional extension (Miller and Hudson, 1991) and crustal melting (Hudson, 1994). This higher temperature metamorphism was superimposed on high pressure/low temperature metamorphic rocks of the region.

References

Reference (Deposit): Hudson, T.L. 1994, Crustal melting events in Alaska, in Plafker, G., and Berg, H. C., eds., The Geology of Alaska: Boulder, Colorado, Geological Society of America, The Geology of North America, v. G-1, p. 657-670.

Reference (Deposit): Apodoca, L. E., 1994, Genesis of lode gold deposits of the Rock Creek area, Nome mining district, Seward Peninsula, Alaska: Boulder, Colorado, University of Colorado, Ph.D. dissertation, 208 p.

Reference (Deposit): Till, A.B., Dumoulin, J.A., Gamble, B. ., Kaufman, D.S., and Carroll, P.I., 1986, Preliminary geologic map and fossil data, Soloman, Bendeleben, and southern Kotzebue quadrangles, Seward Peninsula, Alaska: U.S. Geological Survey Open-File Report 86-276, 10 p., 3 plates, scale 1:250,000.

Reference (Deposit): Miller, E.L., and Hudson, T.L., 1991, Mid-Cretaceous extensional fragmentation of a Jurassic-Early Cretaceous compressional orogen, Alaska: Tectonics, v. 10, p. 781-796.

Reference (Deposit): Hudson, T.L., and Arth, J. G., 1983, Tin-granites of Seward Peninsula, Alaska: Geological Society of America Bulletin, v. 94, p. 768-790.

Reference (Deposit): Hudson, T.L., 1979, Igneous and metamorphic rocks of the Serpentine Hot Springs area, Alaska: U.S. Geological Survey Professional paper 1079, 27 p.

Reference (Deposit): Hudson, T.L., 1984, Tin systems of Seward Peninsula, Alaska: Anchorage, Anaconda Minerals Company internal report, 51 p. (Report held by Cook Inlet Region Inc., Anchorage, Alaska)

Reference (Deposit): Ford, R.C., 1993, Geology, geochemistry, and age of gold lodes at Bluff and Mt. Distin, Seward Peninsula, Alaska: Golden, Colorado School of Mines, Ph.D. dissertation, 302 p.

Reference (Deposit): McDermott, M.M., 1983, Seward Peninsula reconnaissance 1982 geophysical report: Anchorage, Anaconda Minerals Company internal report, 29 p. (Report held by Cook Inlet Region, Inc., Anchorage, Alaska.)

Reference (Deposit): Ford, R.C., and Snee, L.W., 1996, 40Ar/39Ar thermochronology of white mica from the Nome district, Alaska: The first ages of lode sources to placer gold deposits in the Seward Peninsula: Economic Geology, v. 91, p. 213-220.

Reference (Deposit): Barnes, D.F., and Hudson, T. L., 1977, Bouguer gravity map of Seward Peninsula, Alaska: U.S. Geological Survey Open-File Report 77-796-C, scale 1:1,000,000.

Reference (Deposit): Goldfarb, R.J., Miller, L.D., Leach, D.L., and Snee, L.W, 1997, Gold deposits in metamorphic rocks in Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral deposits of Alaska: Economic Geology Monograph 9, 482 p.

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