Unnamed (northwest of Smith Lake) (ARDF #MG048) Cu

Unnamed (northwest of Smith Lake)

Occurrence, Inactive

Commodities and mineralogy

Main commodities	Cu
Other commodities	Co; Pb; Zn
Ore minerals	chalcopyrite; pyrrhotite
Gangue minerals	amphibole; clinopyroxene; olivine

Geographic location

Quadrangle map, 1:250,000-scale	MG
Quadrangle map, 1:63,360-scale	B-2
Latitude	62.361
Longitude	-153.879
Nearby scientific data	Find additional scientific data near this location
Location and accuracy	The unnamed occurrence is located at the divide between the West Fork and Main Fork of Sheep creek, 8 kilometers northwest of Smith Lake, at an elevation of 5,100 feet (1,555 m) in the NE1/4 sec. 10, T. 26 N., R. 25 W., of the Seward Meridian. The reporter investigated the site in 1981.

Geologic setting

Geologic description This unnamed occurrence consists of disseminated chalcopyrite and pyrrhotite in a medium grained, phaneritic, gabbro sill thought to be a feeding system for Triassic volcanism in the Tatina River Volcanics, a unit of the Mystic subterrane (Bundtzen, Kline, and Clough, 1982). An alternative hypothesis offered by Foley (1987) is that the mafic igneous rocks that host the occurrence are flows or feeders of the Paleocene to Eocene Sheep Creek Volcanic Field as defined by Bundtzen, Harris, and Gilbert (1997). Bundtzen, Harris, and Gilbert (1997) believe that unnamed and related occurrences constitute magmatic-disseminated sulfide Cu-Ni-Co-Fe mineralization similar to deposit model 5b of Cox and Singer (1986). Selected samples of the gabbro sills in the prospect area contain up to 540 ppm copper, 190 ppm nickel, 63 ppm cobalt, and 450 ppm zinc (Foley, 1987).
Geologic map unit	(-153.881220606902, 62.3603865682726)
Mineral deposit model	Magmatic sulfide Cu-Ni-Co or polymetallic replacement (Cox and Singer, 1986; models 5b or 22c).
Mineral deposit model number	5b or 22c
Age of mineralization	Undated; inferred to be either Late Triassic or early Tertiary, based on isotopic age dates of Tatina River Volcanics and Sheep Creek Volcanic Field respectively (Bundtzen, Harris, and Gilbert, 1997).
Alteration of deposit	None.

Production and reserves

Workings or exploration	The gabbro feeders were mapped by the reporter in 1981 (Bundtzen, Kline, and Clough, 1982). Selected samples of the gabbro sills in the prospect area contain up to 540 ppm copper, 190 ppm nickel, and 450 ppm zinc (Foley, 1987).
Indication of production	None
Reserve estimates	None.
Additional comments See also Roberts PGM (MG030), Unnamed (MG045), and Chip-Loy (MG032) prospects and deposits.

References

MRDS Number	10307857
References Bundtzen, T.K., Harris, E.E., and Gilbert, W.G., 1997, Geologic Map of the eastern McGrath quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Report of Investigations 97-14, 34 p., 1 sheet, scale 1:125,000. Bundtzen, T.K., Kline, J.T., and Clough, J.G., 1982, Preliminary geologiy of the McGrath B-2 quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Open-File report 149, 22 p., 1 sheet, scale 1:40,000. Foley, J.Y., 1987, Reconnaissance strategic and critical mineral investigations in the McGrath A-3 and B-2 quadrangles, southwest Alaska: U.S. Bureau of Mines Field Report, 26 p.
Reporters	T.K. Bundtzen (Pacific Rim Geological Consulting)
Last report date	12/8/1998