Japan Bay

Prospect, Undetermined

Commodities and mineralogy

Main commodities Ag; barite; Pb; Zn
Ore minerals barite; galena; pyrite; sphalerite
Gangue minerals calcite; hematite

Geographic location

Quadrangle map, 1:250,000-scale KC
Quadrangle map, 1:63,360-scale A-5
Latitude 55.178
Longitude -131.575
Nearby scientific data Find additional scientific data near this location
Location and accuracy This site, informally called the Japan Bay prospect, is on the southwest shore of inner Sylburn Harbor, about 0.5 mile from its head. The site is in section 20, T. 77 S., R. 92 E., of the Copper River Meridian. It corresponds to loc. 18 in Berg (1972 [I 684]), loc. 136 in Elliott and others (1978), and loc. 19 in Karl (1992). The location is accurate within a few hundred feet.

Geologic setting

Geologic description

The country rocks in the area of this site are recrystallized, locally intensely sheared and hematite?-altered, Upper Triassic rhyolite and limestone (Berg, 1972). The rocks are complexly folded and faulted, and were regionally metamorphosed to greenschist-grade phyllite and semischist in Late Cretaceous time.
The deposit consists chiefly of barite veins in a 10-foot-wide shear zone in brecciated rhyolite (Karl, 1992, loc. 19). The veins contain minor quartz and calcite, and clots, laminae, and stringers of hematite, galena, and sphalerite. Barite forms irregular veins and masses up to 3 feet wide. The sheared rhyolite contains disseminated sulfides.
The prospect was explored in the 1970s and 1980s by private interests (Hawley and Associates, in Karl, 1992). The work included 5 diamond drill holes, soil surveys, and other studies. The drill holes indicated that the barite zone dips 25 W, and barite was intercepted as deep as 150 feet. The soil surveys indicated that the barite zone is about 100 feet wide and extends about 1000 feet to the south. The barite lenses and veins are sparse and irregular, and barite grade is low, but the deposit size is estimated to exceed 1,000,000 tons. Karl's (1992, loc. 19a, b) samples of the barite and of variously mineralized country rocks contained as much as 0.11 ppm Au, 50 ppm Ag, 1% Pb, 700 ppm Zn, and 10 ppm Mo.
Geologic map unit (-131.576680169815, 55.1776555134306)
Mineral deposit model Polymetallic veins (Cox and Singer, 1986; model 22c)
Mineral deposit model number 22c
Age of mineralization Late Triassic or younger.
Alteration of deposit Probable local permeation of some of the country rocks by hydrothermal hematite.

Production and reserves

Workings or exploration The prospect was explored in the 1970s and 1980s by private interests (Hawley and Associates, in Karl, 1992, loc. 19). The work included 5 diamond drill holes, soil surveys, and other studies. The drill holes indicated that the barite zone dips 25 west, and barite was intercepted as deep as 150 feet. The soil surveys indicated that the barite zone is about 100 feet wide and extends about 1000 feet to the south. The barite lenses and veins are sparse and irregular, and barite grade is low, but the deposit size is estimated to exceed 1,000,000 tons. Karl's (1992, loc. 19a, b) samples of the barite and of variously mineralized country rocks contained as much as 0.11 ppm Au, 50 ppm Ag, 1% Pb, 700 ppm Zn, and 10 ppm Mo.
Indication of production None
Reserve estimates The deposit size is estimated to exceed 1,000,000 tons (Karl, 1992, loc. 19).

References