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Sleitat Mountain

Prospect in Alaska, United States with commodities Tin, Tungsten, Silver
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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. Host and associated rocks
  10. Nearby scientific data
  11. Economic information about the deposit and operations
  12. Mining district
  13. Links to other databases
  14. Bibliographic references
  15. General comments
  16. Reporter information

Geologic information

Identification information

Deposit ID 10002518
MRDS ID A013460
Record type Site
Current site name Sleitat Mountain
Related records 10207786

Geographic coordinates

Geographic coordinates: -157.0827, 60.04548 (WGS84)
Relative position The Sleitat prospect is centered on a saddle at an elevation of 1,725 feet, between the two high peaks of Sleitat Mountain (1,979 and 1,903 feet elevation). Sleitat Mountain is the highest part of northeast-southwest trending uplands between the valleys of Harris Creek and the Nushagak River. This prospect is accurately located. It is locality 8 of Cobb (1972 [MF 384]; 1976 [OF 76-606]).

Site location context

Political divisions (FIPS codes)

Dillingham(Census area)

Alaska(state)

United States(country)

North America(continent)

Land(continent)

USGS map quadrangles

Taylor Mountains A-3(quadrangle 1:63,360 scale)

Taylor Mountains SE(quadrangle 1:100,000 scale)

Taylor Mountains C(quadrangle 1:250,000 scale)

Hydrologic units (watersheds)

Upper Nushagak River(hydrologic unit)

Nushagak River(hydrologic accounting unit)

Southwest(hydrologic subregion)

Alaska(hydrologic region)

Geographic areas

Country State
United States Alaska

Commodities

Commodity Importance
Tin Critical Primary
Tungsten Critical Primary
Silver Secondary

Materials information

Materials Type of material
Arsenopyrite Ore
Cassiterite Ore
Chalcopyrite Ore
Pyrite Ore
Sphalerite Ore
Stannite Ore
Wolframite Ore
Lollingite Ore
Bismite Ore
Ferrotantalite Ore
Zinnwaldite Gangue
Clay Gangue
Muscovite Gangue
Quartz Gangue
Topaz Gangue
Tourmaline Gangue

Alteration

  • (Local) Greisenization, late clay development, oxidation including iron- and scorodite-staining.

Mineral occurrence model information

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

Host and associated rocks

  • Host or associated Host
    Rock type Sedimentary Rock > Clastic Sedimentary Rock > Siltstone
    Rock unit name Kuskokwim Group;Kuskokwim Group;
    Rock description Kuskokwim Group;Kuskokwim Group;

Nearby scientific data

(1) bu
ListMap

Economic information

Comments on the geologic information

  • Geologic Description = The occurrence of granite and peripheral gold-bearing quartz gash veins was reported on Sleitat Mountain by Mertie (1938, p. 91), but subsequent exploration has shown that the principal mineral deposit is a tin-, tungsten-, and silver-bearing sheeted greisen system (Farnstrom, 1991; Burleigh, 1991; Hudson and Reed, 1997). The greisen deposit was discoverd by a Cominco Alaska regional exploration program in 1983, and subsequently evaluated in the mid-1980s by detailed surface mapping, sampling, and diamond drilling (Farnstrom, 1991).? A composite granite stock that hosts most of the greisen sharply crosscuts and thermally metamorphoses mid-Cretaceous clastic sedimentary rocks of the Kuskokwim Group. The stock has a discontinuous border zone of medium-grained biotite granite and biotite-muscovite granite, and a core of fine-grained zinnwaldite granite. Felsic porphyry dikes crosscut hornfels peripheral to the stock. A K/Ar age of 56.8 +/- 2.8 Ma on muscovite from a late veinlet was reported by Burleigh (1991, p. 6). Greisen sheets trend east-west and are developed within the biotite-muscovite granite, zinnwaldite granite, and hornfels.? the east-west trending cassiterite-bearing greisen zones are nearly vertical quartz-topaz-tourmaline +/- white mica veins and tabular bodies that vary from inches to 20 feet in thickness and coalesce to greater thicknesses in places. They are concentrated in the north half of the stock and in a second zone along the south border that includes some greisen sheets in peripheral hornfels. The individual greisen sheets are granular, massive, separated by less-altered granite, have disseminated clay-lined voids, and have cores that locally contain a few inches of coarse quartz veins carrying high concentrations (50 to 60 percent) of cassiterite (Burleigh, 1991, p. 14). Cassiterite is disseminated in the greisen, concentrated in cores of greisen veins, and in quartz-topaz veins that fill fractures in hornfels. Cassiterite-bearing veins in hornfels are up to 1.5 feet wide and a few hundred feet long. Small amounts of wolframite are disseminated in the greisen but it also occurs with arsenopyrite in quartz veins, especially in hornfels peripheral to greisen zones. Arsenopyrite is common in the greisen and veins. Up to 5 percent loellingite with inclusions of bismite has been identified as disseminations in biotite-muscovite granite (Burleigh, 1991, p. 16). Sphalerite is a minor but common constituent of the greisen and some stannite and chalcopyrite are associated with the sphalerite. One small grain of ferrotantalite was identified during SEM analysis of the greisen (Burleigh, 1991, p. 16). Individual greisen zones locally have high tin grades. For example, one 47.7 foot (true) drill intercept averaged 1.56 percent tin, and included a 5-foot (true) thick section grading 12.6 percent tin and 5.7 ounces of Ag per ton (Farnstrom, 1991; Burleigh, 1991, p. 18). An 1,800 pound bulk sample
  • Geologic Description = contained 0.37 percent tin, 0.04 percent W, and 17 ppm Ag; the Sleitat deposit is estimated to contain a total of 28.6 million tons with the average grade of this bulk sample (Burleigh, 1991). This size and grade is consistent with that found in other large cassiterite-bearing greisen deposits around the world (Menzie and Reed, 1986).? the Sleitat prospect is a deeply eroded tin-bearing system. The sheeted greisens, particularly those on the north side of the stock, are expected to diminish in size and in intensity of cassiterite mineralization at depth. However, mineralization in the relatively wide hornfels zone on the south side of the stock may indicate that the upper contact of the granite body is not steeply dipping there, or that a mineralizing zinnwaldite granite cupola could be present at depth (Hudson and Reed, 1997, p. 461). Burleigh (1991) showed that much of the eroded tin-bearing material had migrated downslope and along the small streams that head against the lode deposit.
  • Age = Early Tertiary. A composite granite stock that hosts most of the greisen sharply crosscuts and thermally metamorphoses mid-Cretaceous clastic sedimentary rocks of the Kuskokwim Group. A K/Ar age of 56.8 +/- 2.8 Ma on muscovite from a late veinlet was reported by Burleigh (1991, p. 6).

Economic information about the deposit and operations

Development status Prospect
Commodity type Metallic

Comments on exploration

  • Status = Active

Mining district

District name Bristol Bay region

Comments on the reserve resource information

  • Reserves = An 1,800 pound bulk sample contained 0.37 percent tin, 0.04 percent W, and 17 ppm Ag; the Sleitat deposit is estimated to contain a total of 28.6 million tons of ore having the average grade of this bulk sample (Burleigh, 1991).

Comments on the workings information

  • Workings / Exploration = The Sleitat prospect was discovered and explored by Cominco Alaska in the 1980s. This work included detailed surface mapping, sampling, and some diamond drilling (Farnstrom, 1991). In 1989, the U. S. Bureau of Mines conducted additional surface examinations, geochemical sampling, surface magnetometer and radiometric surveys, and a pan concentrate survey in nearby drainages (Burleigh, 1991).

Reference information

Bibliographic references

  • Deposit

    Cobb, E.H., 1972, Metallic mineral resources map of the Taylor Mountains quadrangle: U.S. Geological Survey Miscellaneous Field Studies Map MF-384, scale 1:250,000.

  • Deposit

    Cobb, E.H., 1976, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Dillingham, Sleetmute, and Taylor Mountain quadrangles, Alaska: U.S. Geological Survey Open-File Report 76-606, 92 p.

  • Deposit

    Menzie, W.D., and Reed, B.L., 1986, Grade and tonnage model of Sn greisen deposits: U.S. Geological Survey Bulletin 1693, p. 71-72.

  • Deposit

    Burleigh, R.E., 1991, Evaluation of the tin-tungsten greisen mineralization and associated granite at Sleitat Mountain, southwestern Alaska: U.S. Bureau of Mines Open-File Report 35-91, 38 p.

  • Deposit

    Hudson, T.L., and Reed, B.L., 1997, Tin deposits of Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 450-465.

  • Deposit

    Cobb, E.H., 1976, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Dillingham, Sleetmute, and Taylor Mountains quadrangles, Alaska: U.S. Geological Survey Open-File Report 76-606, 92 p.

  • Deposit

    Farnstrom, H.E., 1991, Sleitat: A new tin-silver prospect in southwestern Alaska: Alaska Miner, v. 19, p. 12-14.

  • Deposit

    Mertie, J.B., Jr., 1938, The Nushagak district, Alaska: U.S. Geological Survey Bulletin 903, 96 p.

Comments on the references

  • Primary Reference = Burleigh, 1991

General comments

Subject category Comment text
Deposit Model Name = Sn greisen deposits (Cox and Singer, 1986; model 15c)

Reporter information

Type Date Name Affiliation Comment
Reporter 30-DEC-2000 Travis L. Hudson Applied Geology

Beyond USGS

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

Maps centered on this site

Authoritative Alaska resources

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