Iron Dome (ARDF #DN137) Cu

Iron Dome

Occurrence, Inactive

Commodities and mineralogy

Main commodities	Cu
Other commodities	Mn; Pb; Zn
Ore minerals	arsenopyrite; chalcopyrite; galena; limonite; pyrite; pyrolusite; pyrrhotite; sphalerite
Gangue minerals	calcite; clinozoisite; garnet; idocrase; quartz; serpentine

Geographic location

Quadrangle map, 1:250,000-scale	DN
Quadrangle map, 1:63,360-scale	C-2
Latitude	63.5226
Longitude	-150.988
Nearby scientific data	Find additional scientific data near this location
Location and accuracy	This occurrence is at an elevation of about 2500 feet on Iron Dome, in the SE1/4 SW1/4 section 14, T. 16 S., R. 18 W., Fairbanks Meridian. The location is accurate. The occurrence is number 70 of Hawley and Associates (1978), 16 of Bundtzen (1981), and 19 of Thornsberry, McKee, and Salisbury (1984). The site also represents a nearby mineral occurrence described by Bundtzen, Tosdal, and Smith (1976, location 11), Hawley and Associates (1978, location 68), and Thornsberry, McKee, and Salisbury (1984, location 22).

Geologic setting

Geologic description This occurrence consists of approximately stratiform tactite in marble of the Spruce Creek sequence. The marble is part of a quartzite unit that structurally underlies quartz-feldspar schist and gneiss (Thornsberry, McKee, and Salisbury, 1984, v. 2, occurrence 19). The tactite is banded and consists mostly of garnet, clinozoisite, and idocrase, along with sparsely disseminated chalcopyrite, pyrite, and pyrrhotite. It is partly oxidized and stained with limonite and a black oxide, possibly pyrolusite. The country rocks are cut by quartz-calcite-potassium feldspar veinlets. Samples collected by Bundtzen (1981) contained as much as 0.044 percent copper; samples collected by Hawley and Associates (1978) assayed more than a percent manganese, possibly originally in manganiferous carbonate or silicate that was oxidized to pyrolusite or manganiferous limonite. The tactite is superimposed on the regionally metamorphosed country rocks. It may reflect a buried Tertiary intrusive downdip to the west. Thin quartz-carbonate veins containing small amounts of arsenopyrite, galena, and sphalerite occur nearby (Bundtzen, Smith, and Tosdal, 1976, location 11; Hawley and Associates, 1978, location 68; Thornsberry, McKee, and Salisbury, 1984, v. 2, location 20).
Geologic map unit	(, )
Mineral deposit model	Cu skarn deposit (Cox and Singer, 1986; model 18b).
Mineral deposit model number	18b
Age of mineralization	The deposit is assumed to be Eocene (see record DN091).
Alteration of deposit	Development of tactite in calcareous beds of the Spruce Creek sequence. Oxidation of iron and manganese minerals.

Production and reserves

Workings or exploration	There are no workings.
Indication of production	None
Additional comments The occurrence is in Denali National Park and Preserve.

References

MRDS Number	A011297
References Bundtzen, T.K., 1981, Geology and mineral deposits of the Kantishna Hills, Mt. McKinley quadrangle, Alaska: M. S. Thesis, University of Alaska, College, Alaska, 238 p. Bundtzen, T.K., Smith, T.E., and Tosdal, R.M., 1976, Progress report--Geology and mineral deposits of the Kantishna Hills: Alaska Division of Geological and Geophysical Surveys Open-File Report AOF-98, 80 p., 2 sheets, scale 1:63,360. Cox, D.P., and Singer, D.A., eds., 1986, Mineral deposit models: U.S. Geological Survey Bulletin 1693, 379 p. Hawley, C. C. and Associates, Inc, 1978, Mineral appraisal of lands adjacent to Mt. McKinley National Park, Alaska: U. S. Bureau of Mines Open-File Report 24-78, 275 p. (paged by sections). Thornsberry, V. V., McKee, C. J., and Salisbury, W. G., eds, 1984, 1983 Mineral Resource Studies: Kantishna Hills and Dunkle Mine Areas, Denali National Park and Preserve, Alaska: U. S. Bureau of Mines Open-File Report 129-84. 3 Volumes: v. 1, Text; v. 2, Appendices; v. 3, Maps. Prepared by Salisbury & Dietz, Inc., Spokane, WA.
Reporters	C.C. Hawley
Last report date	4/20/2001