Unnamed (near Sylburn Harbor)

Occurrences, Undetermined

Commodities and mineralogy

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

Geographic location

Quadrangle map, 1:250,000-scale KC
Quadrangle map, 1:63,360-scale A-5
Latitude 55.178
Longitude -131.585
Nearby scientific data Find additional scientific data near this location
Location and accuracy This site represents 6 occurrences along about a mile of the south shore of Sylburn Harbor, about 0.7-1.0 miles east of Driest Point. The occurrences are in section 20, T. 77 S., R. 92 E., of the Copper River Meridian. The map site is at the approximate midpoint of this group of occurrences. The site corresponds to loc. 17 in Berg (1972 [I 684]), and loc. 21a-f in Karl (1992). The location is accurate within about 0.1 mile.

Geologic setting

Geologic description

The country rocks in the area of this site are recrystallized, Upper Triassic carbonate and clastic rocks, rhyolite, and basalt; Silurian trondhjemite; and greenstone derived from undivided Silurian and Ordovician volcanic, sedimentary, and intrusive rocks (Berg, 1972; Berg and others, 1988; Karl, 1992). The rocks are folded and locally intensely sheared, sericitized, silicified, dolomitized, and permeated with hydrothermal hematite. The rocks were regionally metamorphosed to greenschist-grade phyllite and semischist in Late Cretaceous time.
The occurrences consist of up to 3-foot-thick pods of barite in dolomite, and of barite-calcite fissure veins in sheared and brecciated rhyolite (Berg, 1972, loc. 17; Karl, 1992, loc. 21a-f). The dolomite and rhyolite contain galena and sphalerite; the barite contains argentiferous galena and sphalerite. The barite in the pods occurs as radial blades, with rosettes of barite up to 20 inches in diameter.
Samples of brecciated dolomite, massive dolomite, and sheared metabasite with calcite veins contained up to 100 ppm Pb, 300 ppm Zn, and 500 ppm Ba; a sample of barite contained 7 ppm Ag and 7000 ppm Zn; a sample of silicified tuff contained 1.5 ppm Ag, 1000 ppm Pb, 1500 ppm Zn, and 150 ppm Cr; samples of volcanic agglomerate with calcite veins, and of mylonitic calcareous conglomerate, contained up to 200 ppm Pb and 700 ppm Zn; and samples of pyritic rhyolite tuff-breccia and pyritic gray limestone contained up to 150 ppm Pb and 300 ppm Zn (Karl, 1992, loc. 21a-f).
A mapping and soil survey by private interests in the 1970s indicated that the barite-rich zone extends for about 210 feet along the west shore of a small peninsula, and for about 400 feet inland from there (Karl, 1992).
Geologic map unit (-131.586680146928, 55.1776554191733)
Mineral deposit model Polymetallic veins (Cox and Singer, 1986; model 22c)
Mineral deposit model number 22c
Age of mineralization The fissure veins probably are Late Cretaceous or younger.
Alteration of deposit The rocks locally are sericitized, silicified, dolomitized, and permeated with hydrothermal hematite.

Production and reserves

Workings or exploration
Samples of brecciated dolomite, massive dolomite, and sheared metabasite with calcite veins contained up to 100 ppm Pb, 300 ppm Zn, and 500 ppm Ba; a sample of barite contained 7 ppm Ag and 7000 ppm Zn; a sample of silicified tuff contained 1.5 ppm Ag, 1000 ppm Pb, 1500 ppm Zn, and 150 ppm Cr; samples of volcanic agglomerate with calcite veins, and of mylonitic calcareous conglomerate, contained up to 200 ppm Pb and 700 ppm Zn; and samples of pyritic rhyolite tuff-breccia and pyritic gray limestone contained up to 150 ppm Pb and 300 ppm Zn (Karl, 1992, loc. 21a-f).
A mapping and soil survey by private interests in the 1970s indicated that the barite-rich zone extends for about 210 feet along the west shore of a small peninsula, and for about 400 feet inland from there (Karl, 1992).
Indication of production None

References