Koby

Prospect, Undetermined

Alternative names

Shepard

Commodities and mineralogy

Main commodities Au; Pb; Zn
Other commodities Bi; Cd; Cu
Ore minerals arsenopyrite; galena; gold; pyrite; sphalerite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale SI
Quadrangle map, 1:63,360-scale D-6
Latitude 57.815
Longitude -135.9441
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Koby prospect is at an elevation of about 100 feet on a trail along the southwest side of Lisianski River, about 3.5 miles from the head of Lisianski Inlet. The prospect is 0.5 mile north of the center of sec. 12, T. 47 S., R. 58 E. It is location P-31 of Bittenbender and others (1999); location 23 of Cobb (1972, 1978), who calls it Koby (and Shepard); and MAS no. 0021140051 (U.S. Bureau of Land Management, 2002). The location is accurate within 0.2 mile.

Geologic setting

Geologic description

Johnson and Karl (1985) map the rocks in the area of this prospect as part of a batholith of Cretaceous or Jurassic tonalite and gabbro. The rocks are cut by numerous high-angle faults of varying, but mainly northwest, strike. The most prominent of these is the regional-scale Peril Strait Fault that follows the Lisianski River. The prospect is on or near this fault.
Cobb (1972, 1978), citing Reed and Coats (1941) and Rossman (1959), reports that the prospect consists of quartz lenses as much as 7 feet thick along a fault zone in quartz-chlorite schist. The quartz contains about one percent sulfides, including arsenopyrite, pyrite, sphalerite, and galena; in 1959, the owners claimed that it also carries free gold. The deposit was explored by pits, trenches, and a 280-foot adit and crosscut that did not intersect mineralization.
Bittenbender and others (1999), mainly citing Kimball (1982), describe the prospect as a quartz vein in greenstone schist. It was explored by a 300-foot adit, and by surface cuts for about 300 feet along strike. Samples across 3- to 6-foot widths of the vein assayed up to 0.02 ounce of gold per ton and 0.5-0.9 ounce of silver per ton. Selected dump samples contained up to 2.96 ounces of gold per ton, 52.5 ounces of silver per ton, and 1 percent lead. They report that the deposit also contains copper, bismuth, and cadmium. There is no record of any production, but the extent of the workings suggests that some gold may have been produced.
Geologic map unit (-135.94592469127, 57.814633473029)
Mineral deposit model Polymetallic vein (Cox and Singer, 1986; model 22c).
Mineral deposit model number 22c

Production and reserves

Workings or exploration According to Cobb (1978), the deposit was explored by pits, trenches, and a 280-foot adit and crosscut that did not intersect mineralization. Bittenbender and others (1999) report that it was explored by a 300-foot adit and by surface cuts for about 300 feet along the strike of the vein.
Indication of production Undetermined
Production notes There is no record of any production, but the extent of the workings suggests that some gold may have been produced.

References