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 MM
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 (-150.990285246317, 63.5220925676397)
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 MM091).
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