Third of July

Site Name

Primary: Third of July

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Commodity

Primary: Tin

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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: Prospect
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 greisen

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Orebody

Not available

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Structure

Not available

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Alterations

Alteration Type: L
Alteration Text: Thermal recrystallization of limestone, minor skarn in limestone, minor endoskarn in granite, fluorite-bearing veins and veinlets in both limestone and granite, and local greisenization of granite are all present in the prospect area.

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Rocks

Not available

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Analytical Data

Not available

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Materials

Ore: Cassiterite
Gangue: Tourmaline
Gangue: Topaz
Gangue: Quartz
Gangue: Mica

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Comments

Comment (Exploration): Status = Inactive

Comment (Deposit): Model Name = Tin greisen in granite. (Cox and Singer, 1986; model 15c)

Comment (Reserve-Resource): Reserves = Not defined

Comment (Workings): Workings / Exploration = Surface mapping and sampling and a few shallow hand-dug surface pits have been completed here. An airborne magnetic survey and a gravity survey have been completed over the prospect (McDermott in Hudson and Wyman, 1983, p. 68-71).

Comment (Reference): Primary Reference = Hudson and Wyman, 1983.

Comment (Geology): Geologic Description = This prospect is a 500 x 500 foot area of prophyritic granite intrusion in Ordovician limestone. Sainsbury (1969, plate 1) mapped the location of the granite and noted the presence of beryllium-bearing minerals here. Anaconda Minerals Company completed detailed mapping, sampling, and gravity and magnetic surveys in the prospect area during parts of the summers of 1982 and 1983 (Hudson and Wyman, 1983). This work indicates that the exposed granite is a small part of a larger granite body at depth. The exposed intrusion is porphyritic biotite granite with quartz and feldspar phenocrysts in an aplitic groundmass. Thin, 1 to 2.5 inch wide aplite dikes, some with disseminated purple fluorite, cut the porphyritic granite. The age of the mineralization is assumed to be similar to that of tin systems in the Lost River area and therefore Late Cretaceous, the age of the tin-mineralizing granites there (Hudson and Arth, 1983). . Ordovician limestone intruded by the granite has been thermally recrystallized over large areas. Thin quartz-fluorite, calcite-fluorite, or fluorite veins and veinlet stockworks are widespread and common within 300 feet of the granite contact. Minor skarn, developed locally along the limestone-granite contact, includes light green quartz, fluorite, epidote, calcite bands with purple fluorite veins and some sulfide minerals. Sulfide minerals include pyrite and pyrrhotite in altered limestone and granite. Endoskarn is locally developed where remnant quartz phenocrysts are present within light to dark green epidote-fluorite-sericite assemblages. Intense silicification of limestone is also locally present in the contact zone. The porphyritic granite is altered to greisen along structural zones and fractures. These altered rocks typically contain vuggy clots of tourmaline crystals in a light colored, aphanitic matrix (quartz and mica?). Vuggy quartz-tourmaline veins up to one-foot wide cut granite and greisen. The exposed granite is similar to precursor granites (Hudson and Reed, 1997, figure 3) and not the fine-grained, equigranular, and leucocratic granite more directly associated with tin metallization elsewhere on Seward Peninsula (Hudson and Arth, 1983). A mineralizing granite phase could be present in the subsurface of this area. Most cassiterite mineralization is associated with altered rocks within granite. Gossan fragments have up to 0.2% tin but only weakly anomalous lead and zinc (100 to 500 ppm). Arsenic, tungsten, and base metals are generally present at low levels; elevated tin, fluorine, and boron characterize the metasomatism here. Greisen samples contain up to 0.4% tin, 5,800 ppm fluorine, and greater than 20,000 ppm boron.

Comment (Commodity): Gangue = sulfide minerals

Comment (Geology): Age = the age of the mineralization is assumed to be similar to that of tin systems in the Lost River area and therefore Late Cretaceous, the age of the tin-mineralizing granites there (Hudson and Arth, 1983).

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References

Reference (Deposit): Sainsbury, C.L., 1969, Geology and ore deposits of the central York Mountains, western Seward Peninsula, Alaska: U.S. Geological Survey Bulletin 1287, 101 p.

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): 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., 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): Hudson, T.L., and Wyman, W. F., 1983, Interim report on areas of Seward Peninsula warranting further prospecting and evaluation: Anchorage, Anaconda Minerals Company internal report, 84 p., 7 plates. (Report held by Cook Inlet Region Inc., Anchorage, Alaska.)

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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