Lost River-skarn

Site Name

Primary: Lost River-skarn

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Commodity

Primary: Tin
Primary: Tungsten
Primary: Fluorine-Fluorite
Secondary: Copper
Secondary: Silver
Secondary: Lead

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Location

State: Alaska
District: Port Clarence

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Land Status

Not available

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Holdings

Not available

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Workings

Not available

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Ownership

Not available

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Production

Not available

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Deposit

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

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Physiography

Not available

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Mineral Deposit Model

Model Name: Sn skarn

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Orebody

Not available

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Structure

Not available

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Alterations

Alteration Type: L
Alteration Text: 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.

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Rocks

Role: Associated
Age Type: Associated Rock
Age in Years: 80.200000+-2.900000
Material Analyzed: Granite
Age Young: Late Cretaceous

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Analytical Data

Not available

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Materials

Ore: Cassiterite
Ore: Chalcopyrite
Ore: Fluorite
Ore: Scheelite
Ore: Sphalerite
Ore: Wolframite
Gangue: Biotite
Gangue: Garnet
Gangue: Hornblende
Gangue: Idocrase
Gangue: Pyrite
Gangue: Pyrrhotite
Gangue: Mica

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Comments

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

Comment (Reference): Primary Reference = Dobson, 1982.

Comment (Commodity): Gangue = white mica

Comment (Geology): Age = Chronological age is for Lost River Mine.

Comment (Exploration): Status = Active

Comment (Workings): 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).

Comment (Geology): 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).

Comment (Geology): 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.

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

Comment (Reserve-Resource): 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.

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References

Reference (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.

Reference (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.

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

Reference (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.

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

Reference (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.

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.

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