|Quadrangle map, 1:250,000-scale||KC|
|Quadrangle map, 1:63,360-scale||B-5|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||The Birdseye prospect is on the Tongass Narrows shoreline of Revillagigedo Island, about 4 miles southeast of Ketchikan and 1.3 miles northwest of Mountain Point. The site is in section 3, T. 76 S., R. 91 E., of the Copper River Meridian. It corresponds to loc. 73 in Elliott and others (1978). The location is accurate within about 0.1 mile.|
The country rocks in this part of Revillagigedo Island are mainly marine, andesitic or basaltic metavolcanic rocks and interbedded pelitic sedimentary rocks that are intruded by Cretaceous stocks, sills, and dikes of feldspar-porphyritic granodiorite, and by a stock and probably related plugs of Tertiary gabbro (Berg and others, 1988). The strata and some of the granodiorite were regionally metamorphosed to greenschist grade in Late Cretaceous time. These rocks subsequently were contact metamorphosed to hornblende hornfels: locally, near some of the Cretaceous granodiorite contacts, and, more widely, peripheral to the Tertiary gabbro. The premetamorphic age of the strata is uncertain. Berg and others (1988) note that they closely resemble Upper Jurassic to mid-Cretaceous flysch and volcanic rocks nearby on Gravina Island. The country rocks are cut by a high-angle fault along Tongass Narrows that displays about 4 miles of right-lateral offset.
The deposit consists of pyrite-bearing quartz fissure veins or lenses, 3-5 feet wide, in a porphyry dike/sill intruded parallel to the composition layering of slate and schist, which strike NW and dip 45 NE (Brooks, 1902, p. 62; Wright and Wright, 1908, p. 152. The dike/sill is 10-20 feet thick, contains many inclusions of black slate, and adjacent to the veins is impregnated with sulfide minerals. The ore minerals in the vein are pyrite, galena, sphalerite, and free gold. Pyrite-bearing quartz veins also occur in the slate and schist country rocks. These veins predate the porphyry dike and do not carry gold.The prospect, one of the first discovered in the Ketchikan area, was explored in the early 1900s by surface stripping and a 32-foot-deep shaft. A small amount of gold probably was recovered, but there is no public record of any production.
|Geologic map unit||(-131.565684833885, 55.305653879298)|
|Mineral deposit model||Polymetallic veins (Cox and Singer, 1986; model 22c)|
|Mineral deposit model number||22c|
|Age of mineralization||Cretaceous or younger.|
|Alteration of deposit||The wallrock adjacent to the veins is impregnated with sulfides.|
|Workings or exploration||The Birdseye deposit, one of the first discovered in the Ketchikan area, was explored in the early 1900s by surface stripping and a 32-foot-deep shaft.|
|Indication of production||Yes; small|
|Production notes||A small amount of gold probably was recovered in the early 1900s, but there is no public record of any production.|
Berg, H.C., Elliott, R.L., and Koch, R.D., 1988, Geologic map of the Ketchikan and Prince Rupert quadrangles, southeastern Alaska: U.S. Geological Survey Mineral Investigations Series Map I-1807, 27 p., scale 1:250,000.
Brooks, A.H., 1902, Preliminary report on the Ketchikan mining district, Alaska, with an introductory sketch of the geology of southeastern Alaska: U.S. Geological Survey Professional Paper 1, 120 p.
Elliott, R.L., Berg, H.C., and Karl, S.M., 1978, map and table describing metalliferous and selected non-metalliferous mineral deposits, Ketchikan and Prince Rupert quadrangles, Alaska: U.S. Geological Survey Open-File Report 78-73-B, 17 p., 1 sheet, scale 1:250,000.
|Reporters||H.C. Berg, USGS|
|Last report date||7/3/1999|