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Midnight Mountain

Prospect in Alaska, United States with commodity Gold
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Geologic information

Identification information

Deposit ID 10307267
Record type Site
Current site name Midnight Mountain

Geographic coordinates

Geographic coordinates: -164.59341, 65.75933 (WGS84)
Relative position Midnight Mountain is a prominent upland reaching an elevation of 2,720 feet in the southeast part of the Bendeleben D-6 quadrangle. It is located on the continental divide which separates the drainages of the Serpentine River (Schlitz Creek) and Kougarok River (Taylor Creek) in this area. This location is on the south flank of Midnight Mountain at an elevation of about 2,100 feet.
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Geographic areas

Country State
United States Alaska

Commodities

Commodity Importance
Gold Primary

Materials information

Materials Type of material
Gold Ore
Arsenopyrite Gangue
Quartz Gangue

Alteration

  • (Local) 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.

Nearby scientific data

(1) -164.59341, 65.75933
ListMap

Comments on the geologic information

  • 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).
  • 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.

Economic information

Economic information about the deposit and operations

Development status Prospect

Comments on exploration

  • Status = Inactive

Mining district

District name Kougarok

Comments on the workings information

  • Workings / Exploration = There are no workings on this prospect.

Reference information

Links to other databases

Agency Database name Acronym Record ID Notes
USGS Alaska Resource Data File ARDF BN047

Bibliographic references

  • 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.

  • 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.

  • 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.

  • 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.

  • 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.

  • 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.

  • 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.

  • 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.

  • 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.

  • 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)

  • 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.)

  • 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.

Comments on the references

  • Primary Reference = Hudson, 1984

General comments

Subject category Comment text
Deposit Model Name = Gold-bearing quartz veins and schist

Reporter information

Type Date Name Affiliation Comment
Reporter 15-MAR-99 Travis L. Hudson Applied Geology