Unnamed (north fork of Ann Creek) (ARDF #MH155) Au, Cu

Unnamed (north fork of Ann Creek)

Prospect, Inactive

Commodities and mineralogy

Main commodities	Au; Cu
Ore minerals	chalcopyrite; malachite; pyrite; pyrrhotite

Geographic location

Quadrangle map, 1:250,000-scale	MH
Quadrangle map, 1:63,360-scale	B-4
Latitude	63.3484
Longitude	-145.8777
Nearby scientific data	Find additional scientific data near this location
Location and accuracy	This prospect is at the head of the north fork of Ann Creek at an elevation of about 4,300 feet. It is about 0.6 mile south-southwest of peak 5317 and about 0.6 mile south of the center of section 17, T. 18 S., R. 10 E.

Geologic setting

Geologic description As described by W.T. Ellis (oral communication, 2001), this prospect consists of copper stained pods of pyrrhotite, chalcopyrite, and pyrite in hornfelsed sedimentary rocks of the Pennsylvanian and Permian, Slana Spur Formation. The sedimentary rocks are below serpentinized peridotite of the Upper Triassic, Rainy mafic-ultramafic complex (Rose, 1965; Nokleberg and others, 1992 [MF; 1992 [Open-File]). Samples contained up to 1.3 percent copper and 629 parts per billion gold. Bittenbender and others (2007) identified slivers of hornfelsed sedimentary rocks in faulted ultramafic rocks here. They found only sparse disseminated sulfides in both the sedimentary rocks and the ultramafic rocks and none of their samples contained nearly the metal values of the Ellis samples.
Geologic map unit	(-145.879960018663, 63.3479848758799)
Mineral deposit model	Cu in hornfels (Cox and Singer, 1986; model 18b).
Mineral deposit model number	18b
Age of mineralization	Probably related to the Late Triassic mafic and ultramafic rocks in the area.
Alteration of deposit	Peridotite is serpentinized; the sedimentary rocks are hornfelsed; copper minerals are oxidized.

Production and reserves

Workings or exploration	Limited sampling by government and industry.
Indication of production	None
Reserve estimates	None.
Production notes	None.

References

References Bittenbender, P.E., and Gensler, E.G., 2003, Mineral investigations in the Delta River Mining District, east-central Alaska, 2001-2002: U. S. Bureau of Land Management- Alaska, Open-File Report 91, 82 p. Bittenbender, P.E., Bean, K.W., Kurtak, J.M., and Deininger, James Jr., 2007, Mineral assessment of the Delta River Mining District area, east-central, Alaska: U.S. Bureau of Land Management, Alaska Technical Report 57, 675 p. Nokleberg, W. J., Aleinikoff, J. N., Dutro, J. T., Lanphere, M. A., Silberling, N. J., Silva, S. R., Smith, T. E., and Turner, D. L., 1992, Map, tables, and summary of fossil and isotopic age data, Mount Hayes Quadrangle, eastern Alaska range, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-1996-D, 43 p., 1 sheet, scale 1:250,000. Nokleberg, W.J., Aleinikoff, J. N., Lange, I. M.; Silva, S. R., Miyaoka, R. T., Schwab, C. E., Zehner, R. E., Bond, G. C., Richter, D. H., Smith, T. E., and Stout, J. H., 1992, Preliminary geologic map of the Mount Hayes quadrangle, eastern Alaska Range, Alaska: U.S. Geological Survey Open-File Report 92-594, 39 p. 1 sheet, scale 1:250,000. Nokleberg, W.J., Lange, I.M., Roback, R.C., Yeend, Warren, and Silva, S.R., 1991, Map showing locations of metalliferous lode and placer mineral occurrences, mineral deposits, prospects, and mines, Mount Hayes quadrangle, eastern Alaska Range, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-1996-C, 42 p., 1 sheet, scale 1:250,000. Rose, A.W., 1965, Geology and mineral deposits of the Rainy Creek area, Mt. Hayes quadrangle, Alaska: Alaska Division of Mines and Minerals Geologic Report 14, 57 p., 1 sheet, scale 1:36,000. Stout, J.H., 1976, Geology of the Eureka Creek area, east-central Alaska Range: Alaska Division of Geological and Geophysical Surveys Geologic Report 46, 32 p., 1 plate, scale 1:63,360.
Reporters	W.T. Ellis (Alaska Earth Sciences), C.C. Hawley (Hawley Resource Group), and W.J. Nokleberg (USGS); D.J. Grybeck (Contractor, USGS)
Last report date	5/13/2012