Kougarok

Prospect in Alaska, United States with commodities Tin, Tantalum

Geologic information

Identification information

Deposit ID 10308430
Record type Site
Current site name Kougarok

Geographic coordinates

Geographic coordinates: -165.22941, 65.71032 (WGS84)
Relative position The Kougarok prospect is a 1.5 square mile area centered 2 miles north of the summit of Kougarok Mountain (2,870 feet elevation), the highest area in the Teller quadrangle outside the York Mountains. The prospect area is on the west flank of the north-south trending ridgecrest from near the Kougarok Mountain summit downslope to elevations of about 1,000 feet in the southeast headwaters of Star Creek. Star Creek is a north-flowing headwater tributary to the south fork of the Serpentine River. The prospect was discovered in 1979 (Puchner, 1986) during followup investigations of anomalous tin contents in pan concentrates from Star Creek (Marsh and others, 1972). It was not known to Cobb and Sainsbury (1972) or Cobb (1975).
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Geographic areas

Country State
United States Alaska

Commodities

Commodity Importance
Tin Primary
Tantalum Secondary

Comments on the commodity information

  • Gangue = white mica

Materials information

Materials Type of material
Cassiterite Ore
Columbite Ore
Tantalite Ore
Arsenopyrite Gangue
Fluorite Gangue
Quartz Gangue
Topaz Gangue
Tourmaline Gangue
Mica Gangue

Alteration

  • (Local) Hydrothermal alteration is extensive in the Kougarok prospect area. The country rock metapelitic schist and hornfels is extensively veined and replaced by tourmaline, axinite, and sulfide minerals (dominately pyrrhotite but including arsenopyrite and chalcopyrite) over a roughly circular area with a diameter of 3,700 feet at the surface and to a depth of almost 800 feet in the area above the zinnwaldite granite and between Chuck's dike and the Main plug (Puchner, 1986). Tin is commonly anomalous in these rocks and in places exceeds 0.1%. Sericite and tourmaline development is ubiquitous in granite intrusions of the prospect area. Puchner (1986) recognizes increasing degrees of alteration from weak sericite-tourmaline replacement to assemblages with increasing zinnwaldite contents to quartz-tourmaline-topaz greisen. Zinnwaldite-rich alteration zones peripheral to roof greisen are common.

Mineral occurrence model information

Model code 49
USGS model code 15c
Deposit model name Sn greisen

Nearby scientific data

(1) -165.22941, 65.71032

Comments on the geologic information

  • Geologic Description = A Late Cretaceous composite granite complex intrudes metapelitic schist in the Kougarok prospect area. The metapelitic schist is a highly deformed mica-quartz schist characterized by isoclinally folded quartz boudins and segregations that may be Precambrian in age (Gardner and Hudson, 1984). It is thermally metamorphosed to biotite-bearing hornfels within several hundred feet of the granite contact. Boron-rich metasomatism has altered metapelitic schist and hornfels to tourmaline-axinite-sulfide rocks throughout the main prospect area. Most of the granite complex is only present in the subsurface although a few granite dikes and a highly altered plug are exposed at the surface. Diamond drilling shows the subsurface granite to have porphyritic and eguigranular phases (Puchner, 1986) . Equigranular leucocratic phases were intruded later than the porphyritic phases and are associated with extensive alteration of the country rocks, exogreisen development in peripheral dikes and plug, and with roof greisen development in the subsurface pluton. Local and regional gravity surveys (Puchner, 1986; Barnes and Hudson, 1977) show the Kougarok granites to be part of a much larger batholithic complex at depth. Puchner (1986) reports Rb/Sr and K/Ar data that indicate the granite and associated mineralized rocks are Late Cretaceous in age (72 +/- 2 and 70.2 +/- 2.2 my respectively). These ages are consistent with that of other tin granite complexes of western Seward Peninula (Hudson and Arth, 1983). A greisen-altered granite dike (Chuck's dike, Puchner, 1984; Apel, 1984) and the Main plug are the principal exogreisen deposits. The equigranular zinnwaldite granite dike, offset locally by normal faults, is almost 3,000 feet long in the prospect area (Puchner, 1986, figure 3). This dike, with a steep east dip, varies in thickness from one to 15 feet although it is commonly 6 to 8 feet thick. It is a variably altered over most of its length but complete greisenization is present at five places at the surface (Puchner, 1986, p. 1787). The longest exposed greisen segment is 500 feet long in strike and greisen development continues downdip in the subsurface about 500 feet where it merges with a roof greisen in the subsurface pluton (Puchner, 1986, p. 1786). Tin grades in the Chuck's dike greisen are commonly 1%. Two surface trenches and 9 diamond drill holes in this part of the dike have defined a resource of 240,000 tons of 1.3% tin (0.1% tin cutoff grade; Puchner, 1984). This resource includes a higher grade portion of 110,000 tons averaging 2.3% tin. The Main plug area, exposed upslope to the east of Chuck's dike at an elevation of about 2,100 feet, is a nearly vertical composite intrusive center that is extensively altered and contains two greisen pipes. These pipes, each about 100 feet across at the surface, appear to merge at depth and extend to deep levels in the intrusive center (Puchner, 1986, p. 1786). The Main plug is
  • Geologic Description = a complex body but surface trenches and diamond drilling suggest a combined resource of 1.4 million tons averaging 0.45% tin (no cutoff); tantalum and niobium are each present in this deposit in the 0.1 to 0.03% range (Puchner, 1984). A high grade resource within this deposit (0.5% tin cutoff) is estimated to contain 100,000 tons averaging 2.1% tin. The zinnwaldite granite that forms Chuck's dike at the surface becomes a subhorizontal granite intrusion at depth whose irregular upper part is the location of a roof greisen (Puchner, 1986, p. 1786). Alteration through this intrusion increases upward to a quartz-tourmaline-topaz greisen where tin grades can exceed 1%. Limited diamond drilling suggests a resource of 1.3 million tons or more averaging 0.36% tin (0.1% cutoff) including a part that is 140,000 tons averaging 1.0% tin (0.5% cutoff; Puchner, 1984). One of the diamond drill intercepts in the roof greisen was 53 feet of 0.23% tin (0.1% cutoff) including 13 feet of 0.93% tin (0.5 % cutoff). In general, tin grade increases to as much as 3.4% upwards through the altered zinnwaldite intrusion to the roof greisen. Silver to 17 ppm, lead to 1,340 ppm, and tantalum from 20 ppm near the base to as high as 845 ppm also increase upwards to the roof greisen. Fluorine is at 1 to 2% levels in the zinnwaldite granite and arsenic is erratically high (greater than 1,000 ppm) in the upper part of this intrusion (Puchner, 1986, p. 1791). Kougarok is a boron-rich tin system characterized by abundant tourmaline and axinite replacement in the host schist and tourmaline disseminations in altered granite. Its elevated tantalum and niobium, present in discrete tantalite/columbite grains, is also notable.
  • Age = Late Cretaceous; the radiometric ages referenced by Puchner (1986) include an Rb/Sr age of 72 +/- 2 my for porphyritic biotite granite and a K/Ar age of 70.2 +/- 2.6 my for zinnwaldite granite from the Main plug.

Economic information

Economic information about the deposit and operations

Development status Prospect

Comments on exploration

  • Status = Active

Mining district

District name Serpentine

Comments on the reserve resource information

  • Reserves = Preliminay resource estimates have been made for a part of the exogreisen deposit in Chuck's dike, the exogreisen deposit in the Main plug, and the roof greisen in buried zinnwaldite granite (Puchner, 1984). The resource estimate for exogreisen in Chuck's dike is 240,000 tons averaging 1.3% tin (including a part that is 110,00 tons averaging 2.3% tin). The Main plug exogreisen resource estimate is 1.4 million tons averaging 0.45% tin and 0.1 to 0.3% of both tantalum and niobium; this includes a part that has 100,000 tons of 2.1% tin. The roof greisen estimate is 1.3 million tons of 0.36% tin including a part that is 140,000 tons of 1.0% tin. Puchner (1984) emphasizes that these estimates are preliminary and that more exploration is needed to constrain them.

Comments on the workings information

  • Workings / Exploration = Surface dozer trenching has been completed on a part of Chuck's dike and in the Main plug area. Twenty nine larger diameter diamond drill holes and 32 smaller diamond drill (Winkie) holes have been completed (Puchner, 1984). Most of these have been in the north Chuck's dike and Main plug area.

Reference information

Links to other databases

Agency Database name Acronym Record ID Notes
USGS Alaska Resource Data File ARDF TE072

Bibliographic references

  • Deposit

    Cobb, E.H., and Sainsbury, C.L., 1972, Metallic mineral resource map of the Teller quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-426, 1 sheet, scale 1:250,000.

  • Deposit

    Marsh, W.R., Sainsbury, C.L., Hamilton, J.C., and Ewing, Rodney, 1972, Tin in panned concentrates, Serpentine River, Seward Peninsula, Alaska: U.S. Geological Survey Open-File Report 536, 7 p.

  • 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., and Arth, J. G., 1983, Tin-granites of Seward Peninsula, Alaska: Geological Society of America Bulletin, v. 94, p. 768-790.

  • Deposit

    Gardner, M.C., and Hudson, T.L., 1984, Structural geology of Precambarian and Paleozoic metamorphic rocks, Seward terrane, Alaska [abs.]: Geological Society of American, Abstracts with Programs, v. 16, p. 285.

  • Deposit

    Puchner, C.C., 1984, 1983 Annual report; Kougarok Project: Anchorage, Alaska, Anaconda Minerals Company internal report (Report held by Cook Inlet Region, Inc., Anchorage, Alaska).

  • Deposit

    Puchner, C.C., 1986, Geology, alteration, and mineralization of the Kougarok Sn deposit, Seward Peninsula, Alaska; Discussion reply: Economic Geology, v. 82, p. 2201-2204.

  • Deposit

    Cobb, E.H., 1975, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Teller quadrangle, Alaska: U.S. Geological Survey Open-File Report 75-587, 130 p.

  • Deposit

    Gardner, M.C., and Hudson, T.L., 1984, Structural geology of Precambarian and Paleozoic metamorphic rocks, Seward terrane, Alaska [abs.]: Geological Society of American, Abstracts with Programs, v. 16, no. 5, p. 285.

Comments on the references

  • Primary Reference = Puchner,1984; Puchner, 1986

General comments

Subject category Comment text
Deposit Model Name = Tin greisen including exogreisen and endogreisen (roof) deposits (Cox and Singer, 1986, model 15c)

Reporter information

Type Date Name Affiliation Comment
Reporter 10-MAY-98 Travis L. Hudson Applied Geology