Portage Mountain Group (ARDF #PE080) Ag, Au, Cu

Portage Mountain Group

Prospect, Inactive

Commodities and mineralogy

Main commodities	Ag; Au; Cu
Ore minerals	bornite; chalcopyrite; pyrite; pyrrhotite tetrahedrite
Gangue minerals	calcite; quartz

Geographic location

Quadrangle map, 1:250,000-scale	PE
Quadrangle map, 1:63,360-scale	D-4
Latitude	56.875
Longitude	-133.2439
Nearby scientific data	Find additional scientific data near this location
Location and accuracy	There is some confusion in the old literature about the location and geology of two prospects in the area between Portage Mountain and the North Arm of Duncan Canal. Still and others (2002) spent considerable time in the field and library trying to decipher their location and descriptions. They concluded that the Portage Mountain Group consisted of 4 quartz-calcite veins that are at an elevation of between 2,000 and 3,000 feet on the west side of Portage Mountain. They could not find the old workings that they think are in the NE 1/4, NW 1/4, section 2, T. 58 S., R. 77 E. The coordinates above reflect their preferred location (The other prospect is the Silver Star prospect which consists of hornblendite with sulfides is at an elevation of about 400 feet, about 1.6 mile west-southwest of Duncan Peak; it is ARDF PE009.)

Geologic setting

Geologic description As described by Wright and Wright (1905, 1908) and Roehm (1945), the deposit consists of four, thin northeast-striking quartz-calcite veins with pyrite, pyrrhotite, chalcopyrite, bornite, and tetrahedrite. Samples of the veins contained up to 0.4 ounce of gold per ton and 2 ounces of silver per ton. The rocks have been variously mapped as metasedimentary rocks of the Jurassic to Cretaceous Seymour Canal Group by Karl and others (1999) or Cretaceous Stephens Passage Group by Brew (1997) that have been intruded by Cretaceous diorite. Roehm (1945) noted that the workings included a 130-foot adit and open cuts. However, Still and others (2002) could not locate the prospect in spite of a diligent search.
Geologic map unit	(-133.245630708051, 56.8746627495977)
Mineral deposit model	Polymetallic quartz-calcite veins.
Age of mineralization	Too little evidence to determine.

Production and reserves

Workings or exploration	Roehm (1945) noted that the workings included a 130-foot adit and open cuts. However, Still and others (2002) could not locate the prospect in spite of a diligent search.
Indication of production	None
Additional comments This prospect is now in the Petersburg Creek-Duncan Salt Chuck Wilderness which is closed to mineral exploration and mining. Some recent U.S. Geological Survey publications including Cobb (1978) Cobb (1972), Berg and Cobb (1967), and an earlier generation of ARDF probably combine two different prospects on the west side of Portage Mountain that are described separately in ARDF as this prospect and PE 009.

References

References 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. 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. Roehm, J.C., 1945, Preliminary report of investigations and itinerary of J. C. Roehm in the Wrangell and Petersburg precincts, Alaska: Alaska Territorial Department of Mines Itinerary Report 195-37, 13 p. 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. Wright, F.E., and Wright, C.W., 1905, Economic developments in southeastern Alaska, in Brooks, A.H., Report on Progress of Investigations of Mineral Resources of Alaska in 1904: U.S. Geological Survey Bulletin 259, p. 47-68. Wright, F.E., and Wright, C.W., 1908, The Ketchikan and Wrangell mining districts, Alaska: U.S. Geological Survey Bulletin 347, 210 p.
Reporters	Donald Grybeck (Port Ludlow, WA)
Last report date	4/8/2007