Lost River

Prospect, Active

Alternative names


Commodities and mineralogy

Main commodities Ag; Be; Cu; fluorite; Pb; Sn; Zn
Ore minerals cassiterite; chrysoberyl; fluorite; galena; sphalerite; stannite
Gangue minerals arsenopyrite; diaspore; pyrite; tourmaline; white mica

Geographic location

Quadrangle map, 1:250,000-scale TE
Quadrangle map, 1:63,360-scale B-5
Latitude 65.452
Longitude -167.169
Nearby scientific data Find additional scientific data near this location
Location and accuracy This prospect is a 0.75 mile, east-west trending zone along the Rapid River fault where it crosses Lost River valley. This is approximately 4.5 miles upstream from the mouth of Lost River on the Bering Sea (21 miles west of Brevig Mission). The prospect is best exposed on a low bench on the east side of the river at elevations of 200 to 250 feet just north of the mouth of Tin Creek. This prospect was not separately identified by Cobb and Sainsbury (1972) or Cobb (1975). It is also known as the Grothe-Pearson prospect (Sainsbury, 1969, plate 5); it merges to the west with the Bessie-Maple prospect (TE038) and to the south with the Idaho prospect (TE040). The Tozer prospect (Sainsbury, 1969, plate 5) is included here as part of the Lost River valley prospect.

Geologic setting

Geologic description

Sainsbury (1969; 1972) maps the Rapid River fault as a 12-mile long east-west trending thrust fault in the southern part of the York Mountains although stratigraphic relations across the fault suggest normal displacement. Sainsbury (1969) indicates that the Rapid River fault is continuous for another 1.5 miles east of this prospect but earlier mapping (Sainsbury, 1964) suggests the possiblity that the Rapid River fault is offset by the north-south trending Lost River normal fault in the area of this prospect. Bedrock in the prospect area is Ordovician limestone locally cut by thin felsic dikes. Mineralization is probably at least locally present over about 5,000 feet of strike of the Rapid River fault including the Lost River valley and Bessie-Maple prospect (TE038) to the west. Soil samples across this prospect on the east side of Lost River are highly anomalous in base metals, tin, and beryllium (Sainsbury, 1969, plate 5).
Mineralization exposed in dozer trenches is of several types; (1) fluorite and chrysoberyl veins with diaspore, tourmaline, and white mica, (2) fluorite veins with or without fine-grained silica, (3) sulfide-bearing veins with stannite and related gossanous zones, and (4) quartz-muscovite- tourmaline-pyrite veinlets with up to 1.1% tin. Samples of the fluorite-beryllium mineralization contain 0.4 to almost 2% BeO and 50 to 59% fluorite (Sainsbury, 1963, p. 8). The complex, polymetallic character of the sulfide mineralization is well developed here as it is in the Bessie-Maple prospect to the west. Gossanous samples from trenches contain up to several percent lead, almost 1% copper, 4% zinc, 0.9% tin, 8 opt silver, and greater than 1,000 ppm arsenic (Hudson, 1983).
Geologic map unit (-167.171714287064, 65.451222144483)
Mineral deposit model Fluorite-, beryllium-, and sulfide-bearing veins and replacements in limestone (Sainsbury, 1968)
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 The veining and related replacement in this area can be thought of as distal alteration to more intense, tin metallization at depth. Mass balance calculations show significant SiO2, Al2O3, alkali, and fluorine enrichment with this type of alteration (Sainsbury, 1968, p. 1567).

Production and reserves

Workings or exploration Several surface dozer trenches and reconnaissance geochemical surveys have been completed on the bench east of Lost River.
Indication of production None
Reserve estimates Not defined
Production notes None