Arm

Prospect, Probably inactive

Commodities and mineralogy

Ore minerals chalcopyrite; pyrrhotite

Geographic location

Quadrangle map, 1:250,000-scale SD
Quadrangle map, 1:63,360-scale D-5
Latitude 57.92804
Longitude -133.58755
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Arm Group of claims is in the lower part of the steep gorge that drains southeast into the sharp elbow of Tracy Arm. The site is plotted near the shoreline, about 2.1 miles southeast of the southwest end of Lower Sweetheart Lake. It is in the NE1/4 section 33, T. 45 S., R. 73 E.

Geologic setting

Geologic description

The Arm Group of claims was active as of 1974. Conspicuous iron-stained gneiss occurs along a steep gully. Samples of float from the gully contained up to 3 parts per million (ppm) silver, 230 ppm copper and 400 ppm zinc. Some pieces of the float contained visible, sparsely disseminated pyrrhotite and microscopic chalcopyrite. The rocks in the area are part of the Cretaceous biotite schist and gneiss unit of Brew and Grybeck (1984).
Geologic map unit (-133.589278894562, 57.9277078720305)
Mineral deposit model Gneiss with sparsely disseminated sulfides.
Age of mineralization In Cretaceous metamorphic rocks; the age of the protolith is uncertain.
Alteration of deposit None defined; rocks are iron stained, probably due to weathering of pyrrhotite.

Production and reserves

Workings or exploration No workings; claims were active in 1974 and possibly later.
Indication of production None

Additional comments

The prospect is in the Tracy Arm-Fords Terror Wilderness Area which is closed to mineral exploration and mining.

References

MRDS Number A013324

References

Reporters Donald Grybeck (U.S. Geological Survey)
Last report date 10/8/2004