Portage (ARDF #JU136) Au, Cu, Pb

Portage

Prospect, Inactive

Commodities and mineralogy

Main commodities	Au; Cu; Pb
Ore minerals	chalcopyrite; galena; pyrite
Gangue minerals	calcite; quartz

Geographic location

Quadrangle map, 1:250,000-scale	JU
Quadrangle map, 1:63,360-scale	B-3
Latitude	58.2873
Longitude	-134.8624
Nearby scientific data	Find additional scientific data near this location
Location and accuracy	The Portage prospect is at an elevation of approximately 900 feet at the head of Bear Creek, on the northeast side of Green Mountain. It is 2 miles north-northeast of Funter Bay in the SE1/4NE1/4 section 25, T. 41 S., R. 65 E. of the Copper River Meridian. The location is accurate within 1/4 mile.

Geologic setting

Geologic description The Portage prospect consists of lenticular quartz masses in slate that are sub-parallel to the cleavage (Cobb, 1978 [OFR 78-374]). The quartz contains disseminated pyrite, chalcopyrite, and minor galena. The prospect contained low gold values by 1900 standards (Cobb, 1978 [OFR 78-374]). Nearby, chlorite-mica schist is cut by quartz-calcite veinlets contain small masses of pyrite and chalcopyrite across a width of 30 to 40 feet (Wells and others, 1986). The deposit was discovered prior to 1906 and was explored by a small shaft, a tunnel that failed to reach the ore zone, open cuts, and trenches (Wright, 1907) The deposit in the mica schist resembles the one at the Mammoth prospect (JU248) (Cobb, 1978 [OFR 78-374]). The rocks in the area are mainly Ordovician and Devonian to Triassic clastic strata, mafic-intermediate volcanic rocks, and subordinate limestone. The bedded rocks are intruded and locally metamorphosed by Cretaceous granodiorite (Gehrels and Berg, 1994).
Geologic map unit	(-134.864194481273, 58.2869648810514)

Geologic description

The Portage prospect consists of lenticular quartz masses in slate that are sub-parallel to the cleavage (Cobb, 1978 [OFR 78-374]). The quartz contains disseminated pyrite, chalcopyrite, and minor galena. The prospect contained low gold values by 1900 standards (Cobb, 1978 [OFR 78-374]). Nearby, chlorite-mica schist is cut by quartz-calcite veinlets contain small masses of pyrite and chalcopyrite across a width of 30 to 40 feet (Wells and others, 1986). The deposit was discovered prior to 1906 and was explored by a small shaft, a tunnel that failed to reach the ore zone, open cuts, and trenches (Wright, 1907) The deposit in the mica schist resembles the one at the Mammoth prospect (JU248) (Cobb, 1978 [OFR 78-374]).

The rocks in the area are mainly Ordovician and Devonian to Triassic clastic strata, mafic-intermediate volcanic rocks, and subordinate limestone. The bedded rocks are intruded and locally metamorphosed by Cretaceous granodiorite (Gehrels and Berg, 1994).

Geologic map unit

(-134.864194481273, 58.2869648810514)

Production and reserves

Workings or exploration	Surface sampling, shallow shaft, tunnel, open cuts, and trenches.
Indication of production	None

References

MRDS Number	A012114
References Cobb, E.H., 1978, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Juneau quadrangle, Alaska: U.S. Geological Survey Open-File Report 78-374, 155 p. Gehrels, G.E., and Berg, H.C., 1994, Geology of southeastern Alaska, in Plafker, George, and Berg, H. C., eds., The geology of Alaska: Geological Society of America, DNAG, The geology of North America, Vol. G-1, p. 451-467. Wells, D.E., Pittman, T.L., Brew, D.A. and Douglass, S.L., 1986, Map and description of the mineral deposits in the Juneau, Taku River, Atlin, and part of the Skagway quadrangles, Alaska: U.S. Geological Survey Open-File Report 85-717, 332 p., 1 sheet, scale 1:250,000. Wright, C.W., 1907, Lode mining in southeastern Alaska, in Brooks, A.H., and others, Report on progress of investigations of mineral resources of Alaska in 1906: U.S. Geological Survey Bulletin 314, p. 47-72.
Reporters	J.C. Barnett and L.D. Miller (Juneau, Alaska )
Last report date	12/15/2001