|Quadrangle map, 1:250,000-scale||JU|
|Quadrangle map, 1:63,360-scale||B-2|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||The Portland prospect is at an elevation of approximately 200 feet on Douglas Island, on the southwest side of Gastineau Channel, and about 0.2 mile west-northwest of the mouth of Ready Bullion Creek. It is near the center of the SE1/4 section 6, T. 42 S., R. 68 E. of the Copper River Meridian. The location is accurate.|
The Portland prospect was discovered before 1890 and was developed by a 118-foot adit, a 19-foot adit, and several trenches. The host rocks are black phyllite, green chlorite phyllite and amphibolite (Redman and others, 1989). The black phyllite has been intruded by two, altered, albite-diorite sills that contain quartz and disseminated pyrite. The phyllite contains disseminated pyrite and is silicified along the contact with the amphibolite. U.S. Bureau of Mines samples did not contain significant precious metal values, however a quartz sample from the amphibolite contained 164 ppm percent molybdenum (Redman and others, 1989).The rocks in the general area are Upper Jurassic or Cretaceous marine argillite and graywacke, interbedded with andesite or basalt (Brew and Ford, 1985). The bedded rocks are regionally metamorphosed to prehnite-pumpellyite or greenschist grade, and cut by diorite or gabbro dikes and sills.
|Geologic map unit||(-134.352966481926, 58.2540711778249)|
|Alteration of deposit||Altered albite-diorite sills.|
|Workings or exploration||The Portland prospect was discovered before 1890 and was developed by a 118-foot adit, a 19-foot adit, and several trenches.|
|Indication of production||None|
Brew, D.A., and Ford, A.B., 1985, Preliminary reconnaissance geologic map of the Juneau, Taku River, Atlin, and part of the Skagway 1:250,000 quadrangles, southeastern Alaska: U.S. Geological Survey Open-File Report 85-395, 23 p., 2 sheets, scale 1:250,000.
Redman, E.C., Maas, K.M., Kurtak, J.M., and Miller, L.D., 1991, Section D: Juneau Gold Belt subarea, in U.S. Bureau of Mines, Mineral investigations in the Juneau Mining District, Alaska, 1984-1988: Volume 2 - Detailed mine, prospect, and mineral occurrence descriptions: U.S. Bureau of Mines Special Publication VOL. 2D, 424 p., 19 sheets.
|Reporters||J.C. Barnett and L.D. Miller (Juneau, Alaska )|
|Last report date||12/15/2001|