Foster

Prospect, Inactive

Commodities and mineralogy

Main commodities Ag; Au; Cu; Pb; Sn; Zn
Ore minerals anglesite; cerussite; galena
Gangue minerals clay; goethite; limonite; quartz

Geographic location

Quadrangle map, 1:250,000-scale BN
Quadrangle map, 1:63,360-scale A-2
Latitude 65.03
Longitude -162.57
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Foster prospect is in the headwaters of a north tributary of Omilak Creek at an elevation of approximately 1,250 feet. Omilak Creek flows westward from headwaters in the northern Darby Mountains to the Fish River in McCarthy's Marsh. This is locality 15 of Cobb (1972; MF 417; 1975; OFR 75-429) and locality 55 of Gamble (1988).

Geologic setting

Geologic description

The Foster prospect is a zone of massive galena-bearing gossan, 700 feet long that is localized along the vertically fractured axis of an anticline. The host rocks are bleached and partly silicified marble that is part of a high grade metasedimentary assemblage of lower Paleozoic or Precambrian age (Till and other, 1986). The deposit is extensively and deeply oxidized and the gossan material is primarily limonite, goethite, cerussite, and anglesite (Herreid, 1965). Nodules of massive galena (to 2 feet across) encased in secondary oxides and carbonates are scattered through the mineralized zone and are residually concentrated at and near the surface (Mulligan, 1962). Dozer trenching has exposed a 12 by 90 foot gossan zone to a depth of 20 feet (Mulligan, 1962). Eight, three-foot long channel samples collected in the surface trench contained a trace to 25.6 % Pb (average 9.8 % P), a trace to 7.6 % Zn (average 1.5 % Zn), 5.7 to 42.5 % Fe (average 22.2 % Fe), a trace Au, 0.14 to 14.90 ounces/ton Ag (average 4.9 ounces/ton Ag), 0.1 to 0.3 % Sn (average 0.16 % Sn) and 0.1 to 0.3 % Cu (Mulligan, 1962). Diamond drilling showed that extensive oxidation is present to depths greater than 400 feet. This drilling did not encounter massive sulfides, but sixteen assays of mixed core and sludge samples through the oxidized and mineralized zone averaged 4.6 % Pb and 0.95 ounces/ton Ag (Mulligan, 1962).
Geologic map unit (-162.572613519492, 65.0292941593812)
Mineral deposit model Polymetallic vein or replacement in marble (Cox and Singer, 1986; model 19a? or 22c?).
Mineral deposit model number 19a? or 22c?
Age of mineralization Cretaceous ?; Epigenetic mineralization in metamorphic rocks of Seward Peninsula is primarily of Cretaceous age.
Alteration of deposit Oxidation, fracturing, and leaching of wall-rock is known to a depth of 430 feet.

Production and reserves

Workings or exploration Several trenches and pits were dug in about 1890 when the nearby Omilak mine (BN097) was in operation. Initial dozer trenching took place in 1949 and the U.S. Bureau of Mines later added seven more dozer trenches. The U.S. Bureau of mines also completed 11 diamond drill holes between 201 and 430 feet in length, totalling 3,015 linear feet of drilling (Mulligan, 1962).
Indication of production None
Production notes Several tons of hand sorted, high grade ore have been collected and piled near the prospect.

References