Lost River-Cassiterite dike exogreisen

Mine, Active

Commodities and mineralogy

Geographic location

Quadrangle map, 1:250,000-scale TE
Quadrangle map, 1:63,360-scale B-5
Latitude 65.476
Longitude -167.153
Nearby scientific data Find additional scientific data near this location
Location and accuracy Lost River Mine is located on Cassiterite Creek, one mile upstream of its confluence with Lost River. This confluence is 5 miles upstream from the mouth of Lost River on the Bering Sea. 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 Cassiterite dike exogreisen deposit crosses Cassiterite Creek about 0.9 miles upstream from its mouth (elevation approximately 300 feet). The principal surface workings in the Lost River Mine area are on the Cassiterite dike east of Cassiterite Creek between elevations of 300 and 600 feet. This is locality 8 of Cobb and Sainsbury (1972). References for this locality were summarized under the name 'Lost River' by Cobb (1975).

Geologic setting

Geologic description

The pre-mineral Cassiterite dike crosscuts Ordovician limestone and dolomite above a buried and mineralized granite cupola. The dike strikes northwest, dips moderately south, and extends at depth into parts of the Lost River skarn deposit. It ranges in thickness between 3 and 21 feet but in areas of previous stoping, widths of 5 to 10 feet are common (Sainsbury, 1964, plate 10). It is extensively altered over 2,200 feet of strike in the mine area. The dike was probably emplaced along a fault and some post mineralization displacement on this structure has occurred (Sainsbury, 1964, p. 10). Originally a leucocratic and porphyritic felsic rock, the dike is extensively replaced by quartz-topaz-fluorite greisen with disseminated cassiterite and sulfide minerals such as stannite, arsenopyrite, pyrite, galena, chalcopyrite, and sphalerite. Sulfide-rich veinlets containing cassiterite crosscut the greisen in many places. Wolframite is present in greater amounts in deeper parts of the mineralized dike where its mode of occurrence is similar to that of cassiterite, including its presence in crosscutting sulfide-bearing veins. Overprinting clay (kaolinite) alteration is common throughout the deposit. This alteration can completely obliterate preexisting textures and mineralogy, leaving only cassiterite grains in a clay matrix. Sainsbury (1964, p. 36) emphasizes that the clay alteration was superimposed on previously mineralized rock and that it did not affect tin distribution.
Mining operations in the 1950s produced 309 tons of tin from 51,000 tons of ore averaging 1.13% tin (Lorain and others, 1958). Tungsten was not recovered during these operations. Some parts of the deposit were of higher grade; distinct ore shoots with greater than 2% tin were present (Hudson and Reed, 1997, p. 458). The higher grade tungsten zones contained 0.8% WO3. Sainsbury (1964, p. 50) has calculated reserves for two types of ore; 200,500 tons grading 1.3% tin and 0.125% WO3 and 105,000 tons grading 0.76% tin and 0.6% WO3. Sainsbury (1964, p. 51) suggests that the known and inferred ore with greater than 1% combined tin and WO3 could be about 430,000 tons. The deposit is open to the southeast and potential exists to the west on the other side of Cassiterite Creek.
Geologic map unit (-167.155719909704, 65.4752248920192)
Mineral deposit model Exogreisen. This deposit has characteristics of both tin vein model (15b) and tin greisen model (15c) of Cox and Singer (1986).
Mineral deposit model number 15b, 15c
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). 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).
Alteration of deposit Greisen has extensively replaced the felsic Cassiterite dike over 2,200 feet of strike and several hundred feet of dip. Later kaolinite replacement has overprinted much of the greisen.

Production and reserves

Workings or exploration In addition to many surface trenches, significant underground workings exist at the Lost River Mine. Most of these are on the Cassiterite dike but some deeper exploratory drifts encountered the buried Lost River granite cupola. The underground workings include adits, drifts, declines, raises, and shafts that total several thousand feet in length (Sainsbury, 1964, plate 10). These workings are developed on five levels with over 500 feet of vertical extent and with individual drifts being up to 1,100 feet long. Many diamond drill holes have been completed from both the surface and underground.
Indication of production Yes
Reserve estimates Sainsbury (1964, p. 50) has calculated reserves for two types of ore; 200,500 tons grading 1.3% tin and 0.125% WO3 and 105,000 tons grading 0.76% tin and 0.6% WO3. Sainsbury (1964, p. 51) suggests that the known and inferred ore with greater than 1% combined tin and WO3 could be about 430,000 tons. The deposit is open to the southeast and potential exists to the west on the other side of Cassiterite Creek.
Production notes Lode production from the Lost River Mine is all from the Cassiterite dike exogreisen. Production includes 5.6 tons of concentrate containing 3.5 tons of tin and 0.6 tons of tungsten in 1913 and 309 tons of tin in concentrate produced between 1952 and 1955 (Lorain and others, 1958, p. 7).

References