|Quadrangle map, 1:250,000-scale||PE|
|Quadrangle map, 1:63,360-scale||D-4|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||
This prospect is about 1.6 miles west-southwest of Duncan Peak at an elevation of about 400 feet. It is about 0.5 south-southeast of the center of section 10, T. 58 S., R. 77 E.There is some confusion in the old literature about the location and geology of two prospects in the area. For example, Cobb (1972 and 1978) or Berg and Cobb (1967), and an earlier generation of ARDF almost certainly combine two different prospects on the west side of Portage Mountain. Still and others (2002) spent considerable time in the field and library trying to decipher their locations and descriptions; this record is based on their location for the Silver Star prospect. The other prospect--XXX PE New A1028--which is about 2 miles to the north-northeast is a different type of deposit.
Geologic descriptionThe rocks in the vicinity of this prospect are mafic intrusions of late Cretaceous age (Brew and others, 1984). Between an elevation of 360 and 480 feet along a creek, there are outcrops of hornblendite and hornblende diorite that were examined by Still and others (2002). Disseminated pyrrhotite, pyrite, and chalcopyrite are common and there are veinlets up to 1 inch thick in the hornblendite with pyrite and pyrrhotite. Copper staining is locally prominent. Still and others (2002) took 17 samples. The maximum copper content was 4,666 parts per million but most samples contained much less. The highest platinum value was 39 parts per billion (ppb) and the highest palladium value was was 59 ppb; all other metals were in the background range. Buddington (1923) reports that the only workings were several cuts. Still and others (2002) suggest that the prospect is a magmatic segregation deposit.
|Geologic map unit||(-133.265531614355, 56.8481624230187)|
|Mineral deposit model||Magmatic segregation with copper?|
|Age of mineralization||Late Cretaceous or younger based on the age of the host rocks.|
|Workings or exploration||The only workings were several open cuts.|
|Indication of production||None|
Additional commentsThis prospect is now in the Petersburg Creek-Duncan Salt Chuck Wilderness, which is closed to mineral exploration and mining.
Berg, H.C., and Cobb, E.H., 1967, Metalliferous lode deposits of Alaska: U.S. Geological Survey Bulletin 1246, 254 p.
Brew, D.A., 1997, Reconnaissance geologic map of the Petersburg D-4 quadrangle, southeastern Alaska: U.S. Geological Survey Open-File Report 97-156-L, 21 p., 1 sheet, scale 1:63,360.
Brew, D.A., Ovenshine, A.T., Karl, S.M., and Hunt, S.J., 1984, Preliminary reconnaissance geologic map of the Petersburg and parts of the Port Alexander and Sumdum 1:250,000 quadrangles, southeastern Alaska: U.S. Geological Survey Open-File Report 84-405, 43 p., 2 sheets, scale 1:250,000.
Buddington, A.F., 1923, Mineral deposits of the Wrangell district: U.S. Geological Survey Bulletin 739-B, p. 51-75.
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., 1972, 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.
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.
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.
Still, J.C., Bittenbender, P.E., Bean, K.W., and Gensler, E.G., 2002, Mineral assessment of the Stikine area, central Southeast Alaska: U.S. Bureau of Land Management Technical Report 51, 560 p.
|Reporters||D.J. Grybeck (Port Ludlow, WA)|
|Last report date||4/8/2007|