Portland Prospect, Petersburg Mining District, Hoonah-Angoon Census Area, Alaska, USAi

Regional Level Types
Portland Prospect	Prospect
Petersburg Mining District	Mining District
Hoonah-Angoon Census Area	Census Area
Alaska	State
USA	Country

The prospect is in the Tracy Arm-Fords Terror Wilderness Area which is closed to mineral exploration and mining.
Location: 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.
Geology: 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.
Workings: 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.
Age: In schist and phyllite of Cretaceous (metamorphic) age; the age of the protolith is uncertain.
Alteration: None mentioned but schist is iron stained probably due to weathering.

Commodities (Major) - Ag, Au, Cu, Pb, Zn
Development Status: None
Deposit Model: Metamorphosed volcanogenic massive sulfide?

Other Databases

Link to USGS - Alaska:	SD026

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References