Lost River-skarn

Producer in Alaska, United States with commodities Fluorine-Fluorite, Tin, Tungsten, Silver, Copper, Lead

Geologic information

Identification information

Deposit ID 10308413
Record type Site
Current site name Lost River-skarn

Geographic coordinates

Geographic coordinates: -167.1594, 65.47327 (WGS84)
Relative position The Lost River Mine area includes the Cassiterite dike exogreisen deposit (TE048), the Lost River Mine skarn deposit (TE049), the Lost River Mine endogreisen deposit (TE050), and the Ida Bell dike exogreisen deposit (TE051). The Lost River skarn deposit is located 0.9 to 1 mile up Cassiterite Creek from its confluence with Lost River. This confluence is 5 miles upstream from the mouth of Lost River on the Bering Sea coast. The deposit is developed adjacent to and 800 feet south of the surface trace of the Cassiterite dike (Dobson, 1982, figure 3). It extends across Cassiterite Creek at an elevation of about 275 feet but most of the deposit (both at the surface and in the subsurface) is east of the creek. This deposit was included as part of locality 8 by Cobb and Sainsbury (1972). References were summarized under the name 'Lost River' by Cobb (1975).
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Geographic areas

Country State
United States Alaska

Commodities

Commodity Importance
Fluorine-Fluorite Primary
Tin Primary
Tungsten Primary
Silver Secondary
Copper Secondary
Lead Secondary

Comments on the commodity information

  • Gangue = white mica

Materials information

Materials Type of material
Cassiterite Ore
Chalcopyrite Ore
Fluorite Ore
Scheelite Ore
Sphalerite Ore
Wolframite Ore
Biotite Gangue
Garnet Gangue
Hornblende Gangue
Idocrase Gangue
Pyrite Gangue
Pyrrhotite Gangue
Mica Gangue

Alteration

  • (Local) There are several stages and styles of alteration in the Lost River skarn deposit; (1) early anhydrous skarn with abundant garnet and idocrase, (2) hydrous skarn with biotite and hornblende, (3) fluorite-mica veining, (4) mica-matrix breccias, and (5) clay-matrix breccias.

Mineral occurrence model information

Model code 43
USGS model code 14b
Deposit model name Sn skarn

Host and associated rocks

  • Host or associated Associated
    Rock unit name Lost River
    Chronological age 80.2
    Uncertainty 2.9
    Type of media Granite
    Stratigraphic age (youngest) Late Cretaceous

Nearby scientific data

(1) -167.1594, 65.47327

Comments on the geologic information

  • Geologic Description = The Lost River skarn is a roughly equidimensional, 10 million cubic yard volume of intense calc-silicate veining and replacement in Ordovician limestone above the apex of a fine-grained, equigranular, and leucocratic granite cupola. The buried granite cupola is known from drill core (Dobson, 1982, figure 6) and underground workings of the Lost River mine (Sainsbury, 1964, plate 10). The age of the mineralization is assumed to be related to the development of tin systems in the Lost River area and therefore Late Cretaceous, the age of the tin-mineralizing granites there (Hudson and Arth, 1983). Fine-grained, leucocratic granite collected from a Lost River Mine dump has been dated at 80.2 +/- 2.9 my (Hudson and Arth, 1983, p.769). As described by Dobson (1982), the skarn grades outward from a core of intense calc-silicate veining and replacement to a peripheral zone of fluorite-mica veining. A core of early anhydrous skarn, dominated by garnet and idocrase, was subsequently overprinted and enlarged by a hydrous skarn with abundant fluorite, biotite, and hornblende. Less intense veining, mostly fluorite-mica veins but also hydrous skarn veins, extends outward several hundred feet from the center of skarn development. Late-forming hydrothermal breccias overprint the center of the skarn. Tin was introduced with the early anhydrous skarn development where it was primarily incorporated in silicate phases such as andraditic garnet, although some cassiterite and base metal sulfide minerals did accompany later idocrase and garnet veining at this stage. Cassiterite became common as part of the hydrous skarn, which also included fluorite, scheelite, and sulfide minerals such as sphalerite, chalcopyrite, pyrrhotite, and pyrite in addition to the hydrous silicates (biotite and hornblende). Cassiterite and wolframite also accompanied the late fluorite-mica veining. Dobson (1982) points out that destruction of early calc-silicate minerals by hydrous skarn as well as later hydrothermal mica- and clay-matrix breccias appears to have remobilized and redeposited tin as cassiterite, thereby upgrading the recoverable tin content of the skarn as a whole. Extensive diamond drilling of this skarn by Lost River Mining Corporation led to a resource calculation of 23, 527,000 tons grading 16.43% fluorite, 0.26% tin, and 0.04% WO3 that could be mined by open pit methods (WGM, 1972, p. 63). However, the spatial and mineralogic complexity of the deposit documented by Dobson (1982) suggests caution in using this early estimate of tonnage and grade. Dobson (1982) developed a temporal and spatial framework for understanding relations between skarn evolution and development of veining and greisen in the subjacent granite cupola and the superjacent Cassiterite dike exogreisen deposit. In general, it appears that the overall polymetallic and aluminous character, the abundance of fluorine, and the significant potassium enrichment of the skarn reflect evolution of the highly evolved felsic magma in the subjacent granite pluton.
  • Age = the age of the mineralization is assumed to be related to the development of tin systems in the Lost River area and therefore Late Cretaceous, the age of the tin-mineralizing granites there (Hudson and Arth, 1983). Fine-grained, leucocratic granite collected from a Lost River Mine dump has been dated at 80.2 +/- 2.9 my (Hudson and Arth, 1983, p.769).
  • Age = Chronological age is for Lost River Mine.

Economic information

Economic information about the deposit and operations

Development status Producer

Comments on exploration

  • Status = Active

Mining district

District name Port Clarence

Comments on the production information

  • Production Notes = Production from the Lost River Mine has been from the Cassiterite dike exogreisen deposit (TE048).

Comments on the reserve resource information

  • Reserves = Extensive diamond drilling of this skarn by Lost River Mining Corporation led to a resource calculation of 23, 527,000 tons grading 16.43% fluorite, 0.26% tin, and 0.04% WO3 that could be mined by open pit methods and 1,275,000 tons of 11.66% fluorite, 0.15% tin, and 0.01% WO3 that would need to be mined by underground methods (WGM, 1972, p. 63). However, the spatial and mineralogic complexity of the deposit documented by Dobson (1982) suggests caution in using this early estimate of tonnage and grade.

Comments on the workings information

  • Workings / Exploration = Some of the underground workings of the Lost River mine encounter parts of the Lost River skarn and it is reasonably well exposed at the surface in outcrops and dozer trenches. However, it is primarily known from extensive diamond drilling (WGM, 1972, p. 63) which includes that of the USBM (22 holes totalling 8,693 feet), USDMEA (several underground holes totalling 1,984 feet), US Steel Corporation (15 holes totalling 5,201 feet) and Lost River Mining Corporation (68 holes totalling 36,949 feet).

Reference information

Links to other databases

Agency Database name Acronym Record ID Notes
USGS Alaska Resource Data File ARDF TE049

Bibliographic references

  • Deposit

    Lorain, S.H., Wells, R.R., Mihelich, Miro, Mulligan, J.J., Thorne, R.L., and Herdlick, J.A., 1958, Lode-tin mining at Lost River, Seward Peninsula, Alaska: U.S. Bureau of Mines Information Circular 7871, 76 p.

  • Deposit

    Sainsbury, C.L., 1964, Geology of the Lost River mine area, Alaska: U.S. Geological Survey Bulletin 1129, 80 p.

  • 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

    Dobson, D.C., 1982, Geology and alteration of the Lost River tin-tungsten-fluorine deposit, Alaska: Economic Geology, v. 77, p. 1033-1052.

  • 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

    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., 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.

Comments on the references

  • Primary Reference = Dobson, 1982.

General comments

Subject category Comment text
Deposit Model Name = Tin-bearing skarn (Cox and Singer, 1986; model 14b)

Reporter information

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