Unnamed Prospects (ARDF - PE041; in Glacier Basin), Petersburg District, Wrangell-Petersburg Borough, Alaska, USA
Gault and others, (1953) provide detailed maps of the underground workings as well as a detailed surface geologic map that covers Groundhog Basin and extends southward to Glacier Basin to include this this site.
Location: The coordinates are at the lower of two adits in an elongate mineralized area that extends southeast from Marsha Peak to Glacier Basin. The adit is near the center of section 20, T. 62 S., R. 86 E.; it includes several small mineral occurrences and two prospects that are mapped in detail on Plate 9 of Gault and others (1953).
Geology: The mineralization on the north side of Glacier Basin was first discovered in 1898 and by 1943 was prospected by three short adits and numerous cuts and pits (Gault and others, 1953; Still and others, 2002). Several companies were active in the area from 1964 to the early 1980's but most of their work was to the north and they probably did little on this prospect beyond general reconnaissance. The Glacier Basin prospects contain two distinct types of deposits that may be genetically related (Gault and others, 1953; Newberry and Brew, 1989; Still and others, 2002). The first consists of small, discontinuous, banded galena-sphalerite-magnetite lenses and layers that are probably continuous with those in Groundhog Basin (PE040) These deposits are relatively small and more scattered as compared to those in Groundhog Basin, but are essentially the same in mineralogy and origin. The host rocks are gneiss and schist that consists mainly of interlayered amphibolite, marble, and calc-silicate units. Four of these layers have been identified north of Glacier Basin below 3,000 feet in elevation. At the surface, they extend for up to 2,000 feet; they strike north-northwest and dip 50 to 60 degrees southwest. They are interpreted as replacement deposits with skarn affinities. The second type of deposit consists of quartz-fluorite veins and breccia with galena; they are exposed in two small adits where they cut a Tertiary rhyolite sill. Berryhill (1964) sampled these occurrences; he found and found found 5 widely spaced fluorite breccias north of Glacier Basin that contain beryllium which occurs as amorphous blebs of pale blue or creamy white beryl The veins average about 0.1 percent beryllium. Several other rhyolite bodies are nearby; most are conformable with the foliation of the metamorphic rocks. The rhyolite sills and dikes are probably cogenetic with the 20 Ma or younger bodies associated with the molybdenite deposits in the area (see PE043) and/or with the 15-17 Ma zinnwaldite 'tin' granite associated with the Groundhog Basin lead-zinc-silver deposits. Newberry and Brew (1989) provide analytical data for the tin content of several sulfide-rich occurrences at this site. The tin content is distinctly lower than ore samples from Groundhog Basin and their conclusion is that the Glacier Basin deposits are farther from the source of the hydrothermal fluids that formed them, i.e. from the zinnwaldite 'tin' granite at the north end of Groundhog Basin. Still and others (2002) collected several samples at the lower adit of disseminated and massive sulfides at the contact of a quartz rhyolite sill and gneiss; the best contained 3.97 to 7.98 ounces of silver per ton, 4.64 to 33.4 percent lead, and 4.32 to 7.9 percent zinc. Several samples farther north of the quartz-fluorite veins contained up to 611 parts per billion gold, 1,378 parts per million (ppm) lead, and 2,061 ppm zinc.
Workings: The mineralization on the north side of Glacier Basin was first discovered in 1898 and was prospected by three short adits and numerous cuts and pits by 1943 (Still and others, 2002). Several companies were active in the area from 1964 to the early 1980's but most of their work was to the north and they apparently did little on this prospect beyond general reconnaissance.
Age: Probably related to nearby 15-20 Ma rhyolite sills and dikes.
Alteration: Deposits locally associated with development of pyroxene-epidote-garnet skarn.
Commodities (Major) - Ag, Au, Be, Pb, Zn; (Minor) - Mo?
Development Status: None
Deposit Model: Banded Ag-Cu-Sn-Pb-Zn tabular replacement bodies, veins, and stringers; (Be-)fl
ReferencesBerryhill, R.V., 1964, Reconnaissance of Glacier Basin for beryllium minerals: U.S. Bureau of Mines unpublished draft report, 12 p., 1 plate. (available from the Bureau of Land Management, Minerals Information Center, Juneau, Alaska). Brew, D.A., 1997, Reconnaissance geologic map of the Petersburg B-1 quadrangle, southeastern Alaska: U.S. Geological Survey Open-File Report 97-156-C, 20 p., 1 sheet, scale 1:63,360. Cobb, E.H., 1972, Metallic mineral resources map of the Petersburg quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-415, 1 sheet, scale 1:250,000. Cobb, E.H., 1978, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Petersburg quadrangle, Alaska: U.S. Geological Survey Open-File Report 78-870, 53 p. Gault, H.R., Rossman, D.L., Flint, G.M., Jr., and Ray, R.G., 1953, Some lead-zinc deposits of the Wrangell district, Alaska: U.S. Geological Survey Bulletin 998-B, p. 15-58. Grybeck, D.J., Berg, H.C., and Karl, S.M., 1984, Map and description of the mineral deposits in the Petersburg and eastern Port Alexander quadrangles: U.S. Geological Survey Open-File Report 84-837, 86 p., 1 sheet, scale 1:250,000. Newberry, R.J., and Brew, D.A., 1989, Epigenetic hydrothermal origin of the Groundhog Basin-Glacier Basin silver-tin-lead-zinc deposits, southeastern Alaska: U.S. Geological Survey Bulletin 1903, p. 113-121. Roppel, P., 1987, Little to show for basin effort: Southeast Log, p. 4-5. Still, J.C., Bittenbender, P.E., Bean, K.W., and Gensler, E.G., 2002, Mineral assessment of the Stikine area, central southeast Alaska: Bureau of Land Management Technical Report 51, 560 p. Wright, F.E., and Wright, C.W., 1908, The Ketchikan and Wrangell mining districts, Alaska: U.S. Geological Survey Bulletin 347, 210 p.
6 entries listed. 6 valid minerals.
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Locality Updated: VC Quarry, Isle of Lundy, North Devon, Devon, England, UKFrom David Ifold, 20th Jun 2013 10:51:41