Portland

Mine, Undetermined

Alternative names

Helm Bay King

Commodities and mineralogy

Main commodities Ag; Au
Other commodities Cu
Ore minerals gold; pyrite
Gangue minerals calcite; chlorite; quartz

Geographic location

Quadrangle map, 1:250,000-scale CR
Quadrangle map, 1:63,360-scale C-1
Latitude 55.66333
Longitude -132.02016
Nearby scientific data Find additional scientific data near this location
Location and accuracy This property, which is commonly known as the Portland Mine, is near the adit symbol on the USGS 1:63,360-scale topographic map just to the east of name 'Sleeping Beauty Mine.' (The adit is not the Sleeping Beauty Mine, which is ARDF site CR084, about 0.3 mile to the northwest.) The Portland Mine is near the southeast corner of section 35, T. 71 S., R. 87 E. The location is accurate.

Geologic setting

Geologic description

The Portland Mine was probably discovered prior to 1921, but the first published description of it is in Buddington (1925). He described the deposit as two sets of veins along shear zones in greenstone and greenschist. One set of veins is parallel to the foliation; the other set consists of gash veins oblique to the foliation. The veins consist mainly of milky white quartz with minor calcite and chlorite. In 1923, the workings consisted of a 45-foot shaft, a tunnel, and trenches. The ore zone at the bottom of the shaft was reported to contain about $14 per ton in gold (at $20.67 per ounce). Roehm (1938 [PE 119-13]) reports a mill on the property which processed a few tons of ore. He described the deposit as numerous quartz stringers up to 2 feet thick in highly folded greenstone and greenschist. Townsend (1941) visited the property when the workings consisted of a 320-foot tunnel and about 100 feet of drift along the mineralized zone. He noted some barren quartz veins, but the gold values were chiefly associated with bands of fine pyrite in greenschist. The weighted average of 11 samples collected by Townsend along 100 feet of the mineralized zone that averaged about 4.2 feet wide was 0.07 ounce of gold per ton. A mill had been in operation only a few weeks at the time of his visit. Bittenbender and others (1993) and Maas and others (1995) mapped and sampled the underground workings. They indicate that the best mineralization is along an ore shoot that plunges northwest at about 25 degrees and is localized by a deflection in the fault along the vein. The weighted average of their samples along about 270 feet of mineralization that averaged about 5 feet thick was 5,962 parts per billion gold. Maas and others (1995) indicate that mine produced 64 ounces of gold and 38 ounces of silver.
The rocks in the area consist of metamorphosed andesite, basalt, agglomerate, and tuff, and minor flysch, shale, and phyllite. Eberlein and others (1983) and Brew (1996) consider them to be Paleozoic or Mesozoic in age; Gehrels and Berg (1992) tentatively mapped them as Jurassic or Cretaceous.
Geologic map unit (-132.021844272928, 55.6629677281029)
Mineral deposit model Low-sulfide gold-quartz vein (Cox and Singer, 1986; model 36a).
Mineral deposit model number 36a
Age of mineralization The quartz veins cut country rocks that may be as young as Cretaceous or as old as Paleozoic.

Production and reserves

Workings or exploration As last described in 1941 when the mine was still active, the workings consisted of a 45-foot shaft, a 320 foot tunnel, and about 100 feet of drift along the mineralized zone.
Indication of production Yes; small
Reserve estimates None.
Production notes The mine was active intermittently from 1921 or earlier to at least 1941 and probably produced small amounts of gold in some years. Maas and others (1995) indicate that the mine produced 64 ounces of gold and 38 ounces of silver.

References

MRDS Number A010048

References

Townsend, Harry, 1941, Memorandum re Libe prospect, Helm Bay, Ketchikan District, First Division, Alaska: Anaconda Copper Mining Company, 2 p. (Unpublished report held as file 6331, Anaconda Collection, American Heritage Center, University of Wyoming, Laramie.)
Reporters D.J. Grybeck (Applied Geology)
Last report date 5/1/2004