Portland

Prospect, Probably inactive

Commodities and mineralogy

Main commodities Ag; Au; Cu; Pb; Zn
Ore minerals chalcopyrite; galena; pyrite; pyrrhotite; sphalerite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale SD
Quadrangle map, 1:63,360-scale C-5
Latitude 57.69094
Longitude -133.37606
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Portland prospect is at an elevation of about 175 feet; it is about 2.5 miles east-southeast of the south tip of Sumdum Island and 0.3 mile north of VABM 'Not' which is shown on the USGS 1:63,360-scale topographic map. The prospect is about 0.2 mile south of the center of section 23, T. 48 S., R. 74 E.

Geologic setting

Geologic description

The Portland prospect was discovered before 1906 (Spencer, 1906; Kimble and others, 1984) and three adits were driven on it between 1890 and 1910. There is a total of 305 feet of workings in the three adits that are 7, 109, and 189 feet long. The deposit is in muscovite-quartz schist and phyllite with numerous quartz stringers and lenses parallel to the foliation. The schist contains pyrite and pyrrhotite with minor galena, sphalerite, and chalcopyrite, as disseminations and in thin stringers parallel to the foliation. The schist and phyllite are part of the Cretaceous phyllite unit of Brew and Grybeck (1984).
Kimble and others (1984) systematically sampled the adits in a series of 23 channel samples that were collected perpendicular to the trend of the mineralization. The best was a sample 8 foot long that contained 0.10 part per million (ppm) gold, 10 ppm silver, 930 ppm copper, 1,800 ppm lead, and 3,400 ppm zinc. Most samples were much leaner.
Geologic map unit (-133.377771187148, 57.6906032462191)
Mineral deposit model Metamorphosed volcanogenic massive sulfide?
Age of mineralization In schist and phyllite of Cretaceous (metamorphic) age; the age of the protolith is uncertain.
Alteration of deposit None mentioned but schist is iron stained probably due to weathering.

Production and reserves

Workings or exploration The Portland prospect was discovered before 1906 (Spencer, 1906; Kimble and others, 1984) and three adits were driven on it between 1890 and 1910. There is a total of 305 feet of workings in the three adits that are 7, 109, and 189 feet long.
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 A013334

References

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