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.
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