Location: This site consists of three, roughly E-W aligned, occurrences at 200-300 feet elevation, and 0.3-0.7 mile east of the head of Sylburn Harbor. The occurrences are in section 21, T. 77 S., R. 92 E., of the Copper River Meridian. The coordinates are for the approximate center of the line of occurrences. The site corresponds to locs. 19 and 20 in Berg (1972 [I 684]), loc. no. 137 in Elliott and others (1978), and loc. 18a-c in Karl (1992). The location is accurate within 0.2 mile.

Geology: The country rock in the area of this site is Silurian trondhjemite that was regionally metamorphosed to greenschist grade in Late Cretaceous time (Berg, 1972). The mineral occurrences consist of quartz-carbonate fissure veins in sheared, brecciated, and sericitized trondhjemite. The shear zones are up to ten feet or so wide. The veins contain chalcopyrite, pyrite, hematite, magnetite, azurite, and malachite. The mineralization extends beyond the vein margins into the trondhjemite. Of 63 rock samples collected from 1969-1975 by private interests, 8 had Cu values of more than 200 ppm, and 8 had Zn values of more than 200 ppm (Karl, 1992). One sample of a chalcopyrite-bearing quartz vein contained 6900 ppm Cu. Karl's (1992) samples of sulfide-bearing trondhjemite contained as much as 5500 ppm Cu; and a sample of a quartz-calcite-sulfide vein contained 0.08 ppm Au and 15,000 ppm Cu.

Workings: Of 63 rock samples collected from 1969-1975 by private interests, 8 had Cu values of more than 200 ppm, and 8 had Zn values of more than 200 ppm (Karl, 1992). One sample of a chalcopyrite-bearing quartz vein contained 6900 ppm Cu. Karl's (1992) samples of sulfide-bearing trondhjemite contained as much as 5500 ppm Cu; and a sample of a quartz-calcite-sulfide vein contained 0.08 ppm Au and 15,000 ppm Cu.

Age: The fissure veins probably are Late Cretaceous or younger in age.

Alteration: Local oxidation of chalcopyrite to azurite and malachite; oxidation of iron mineral(s) to hematite; sericitization of sheared trondhjemite country rock; sulfide impregnation of wallrock adjacent to veins.

Commodities (Major) - Cu

Development Status: None

Deposit Model: Polymetallic veins (Cox and Singer, 1986; model 22c)

Other Databases

Link to USGS - Alaska:	KC140

Other Regions, Features and Areas containing this locality

References