Prospect, Undetermined

Commodities and mineralogy

Main commodities Cu
Ore minerals chalcopyrite; pyrite
Gangue minerals jasper; quartz

Geographic location

Quadrangle map, 1:250,000-scale KC
Quadrangle map, 1:63,360-scale A-6
Latitude 55.151
Longitude -131.761
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Washington prospect is at an elevation of less than 100 feet, about 0.2 mile northwest of the southwest head of Dall Bay, and about 0.1 mile from tidewater. The site is in section 31, T. 77 S., R. 91 E., of the Copper River Meridian. It corresponds to loc. 127 in Elliott and others (1978), and to loc. 317 in Maas and others (1995). The location is accurate within 0.1 mile.

Geologic setting

Geologic description

The country rocks in the area of this prospect consist of an assemblage of undivided Silurian or Ordovician metamorphosed bedded and intrusive rocks that are intruded by stocks and dikes of Silurian trondhjemite (Berg, 1973; Berg and others, 1988), The rocks are cut by a complex system of high-angle faults that mainly strike NE and NW. Locally, they also are permeated by finely disseminated hydrothermal hematite, giving them (especially the trondhjemite) a pink or red hue commonly mistaken for potassium feldspar.
According to Elliott and others (1978), the deposit consists of a mineralized zone along a sheared and brecciated contact between diabase and pegmatite (hydrothermally altered trondhjemite?). Pyrite and chalcopyrite occur in the zone, accompanied by quartz and jasper gangue. The deposit was explored in the early 1900s by a 20-foot drift or adit (Brooks, 1902, p. 72; Maas and others, 1995, p. 229). Similarities in character and setting of the Washington deposit to those of other lodes in the Dall Bay area (see, for example, KC 131, 132) suggest that it is a polymetallic vein of Late Triassic or younger age.
Geologic map unit (-131.762677345552, 55.150653821754)
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 Probably local silicification, carbonatization, pyritization, and introduction of hydrothermal hematite.

Production and reserves

Workings or exploration The deposit was explored in the early 1900s by a 20-foot drift or adit (Brooks, 1902, p. 72; Maas and others, 1995, p. 229).
Indication of production Undetermined