Unnamed (north shore of outer Bertha Bay)

Prospect, Probably inactive

Commodities and mineralogy

Main commodities Cu
Ore minerals chalcopyrite; pyrrhotite

Geographic location

Quadrangle map, 1:250,000-scale SI
Quadrangle map, 1:63,360-scale D-8
Latitude 57.8067
Longitude -136.355
Nearby scientific data Find additional scientific data near this location
Location and accuracy This prospect is at sea level at the north mouth of Bertha Bay. The prospect is at the head of a small bay just east of Pt. Dougherty, and 0.4 mile southwest of the center of sec. 9, T. 47 S., R. 56 E. It is location P-41 of Bittenbender and others (1999), location 15 of Cobb (1972, 1978), and MAS no. 0021140014 (U.S. Bureau of Land Management, 2002). The location is accurate within about 0.5 mile.

Geologic setting

Geologic description

Johnson and Karl (1985) map the rocks in the area of this prospect as Cretaceous graywacke that is intruded by Tertiary gabbronorite and tonalite, and cut by high-angle faults that mainly strike northwest. The graywacke is thermally metamorphosed to hornfels near the contact of the gabbronorite and tonalite. The deposit consists of stringers of chalcopyrite and pyrrhotite in mafic intrusive rock (gabbronorite?) near its contact with the metamorphosed country rock. Bittenbender and others (1999) interpret the prospect as a magmatic segregation deposit, presumably similar to the one at Bohemia Basin (SI001).
Geologic map unit (-136.35683821723, 57.8063231228932)
Mineral deposit model Duluth Cu-Ni-PGE? (Cox and Singer, 1986; model 5a).
Mineral deposit model number 5a?
Age of mineralization Assuming that the deposit is a magmatic segregation, it is Tertiary, the age of the gabbronorite(?) host rock.
Alteration of deposit Thermal metamorphism of country rocks.

Production and reserves

Indication of production None

Additional comments

The prospect is in West Chichagof-Yakobi Wilderness.

References

MRDS Number A013251

References

Bittenbender, P., Still, J.C., Maas, K., and McDonald, M., Jr., 1999, Mineral resources of the Chichagof and Baranof Islands area, southeast Alaska: Bureau of Land Management, BLM-Alaska Technical Report 19, 222 p.
U.S. Bureau of Land Management, 2002, Alaska mineral locations database report (Sitka quadrangle), July 2, 2002, 205 p. [http://imcg.wr.usgs.gov/dem.html]
Reporters H.C. Berg (U.S. Geological Survey)
Last report date 10/16/2004