Unnamed (on Tin Creek, tributary to Lost River)

Prospect, Inactive

Commodities and mineralogy

Main commodities Be; Sn; fluorite
Ore minerals cassiterite; chrysoberyl; fluorite; helvite; sulfide minerals
Gangue minerals idocrase; magnetite; white mica

Geographic location

Quadrangle map, 1:250,000-scale TE
Quadrangle map, 1:63,360-scale B-5
Latitude 65.459
Longitude -167.123
Nearby scientific data Find additional scientific data near this location
Location and accuracy Tin Creek is an east tributary to Lost River whose confluence is located 4.5 miles upstream from the mouth of Lost River on the Bering Sea. Fluorite and beryllium-bearing veins and tactite are mostly developed on the south flank of a hill cored by fine-grained granite (Sainsbury, 1969), that the headwaters of Tin Creek flow around. This rounded hill, between Tin Creek and its small north tributary, reaches elevations of just over 1,150 feet. Mineralization is locally present from creek level (400 feet) upslope (northward) to the contact of the Tin Creek stock at an elevation of about 850 feet. This locality was not identified separately by Cobb and Sainsbury (1972) but relevant information was summarized by Cobb (1975) under the name 'Tin Cr., trib. Lost R.'.

Geologic setting

Geologic description

The headwaters of Tin Creek are in an area where a small stock of biotite granite, the Tin Creek stock (Sainsbury, 1969; Hudson and Arth, 1983) intrudes Ordovician limestone and dolomite. The Tin Creek stock covers a 1,000 by 2,000 foot area on the crest of the rounded hill between Tin Creek and its northern tributary. The south contact of the stock is irregular and includes granite offshoots, dikes, and apophyses in the bordering carbonate rocks. Two types of mineralization are present in the carbonate country rocks on the south flank of the Tin Creek stock: (1) laminar magnetite-fluorite- idocrase skarn (wrigglite) with helvite, and (2) fluorite-diaspore-white mica veins and replacements that contain chrysoberyl. The laminar skarn forms replacement veins along fractures in limestone and larger irregular bodies adjacent to granite intrusions. The fluorite-diaspore-white mica-chrysoberyl veins, from less than an inch up to a few feet wide, are scattered through limestone and localized along borders to granite dikes. They contain cassiterite, stannite, and other sulfide minerals in places. Oxidation of the sulfide-bearing veins has produced gossanous materials at the surface. The helvite-bearing skarn is reported to carry up to 0.45% BeO (Sainsbury, 1969, p. 80). Three samples of beryllium-bearing veins contained 0.13 to 1.11% BeO (Sainsbury, 1963, p. 13). Samples of skarn from this area contained 1,020 to 4,500 ppm tin and more than 20,000 ppm fluorine; one of these samples contained 175 ppb gold (Hudson, 1983).
Geologic map unit (-167.125718083576, 65.458224991783)
Mineral deposit model Veins and tactite in limestone intruded by granite. Tin skarn model (14b) of cox and Singer (1986).
Mineral deposit model number 14b
Age of mineralization 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).
Alteration of deposit Calc-silicate, magnetite, and fluorite replacement of limestone

Production and reserves

Workings or exploration A few surface pits and trenches are present in the area.
Indication of production None
Reserve estimates Not defined