Red Dirt

Occurrence, Inactive

Commodities and mineralogy

Main commodities As; Au; Zn
Other commodities Ag; Cu; Pb
Ore minerals pyrite; pyrrhotite

Geographic location

Quadrangle map, 1:250,000-scale MM
Quadrangle map, 1:63,360-scale C-2
Latitude 63.7323
Longitude -150.5082
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Red Dirt occurrence (Thornsberry, McKee, and Salisbury, 1984) is a mineralized area mainly in the diagonal northwest half of section 5, T. 14 S., R. 15 W., Fairbanks Meridian. The location is for the approximate center of the area and is accurate.

Geologic setting

Geologic description

The Red Dirt occurrence is at least partly controlled by the Red Dirt fault, which strikes NE and is nearly vertical. Rocks on the southeast side of the fault are calcareous mica schists of the Birch Creek Schist. Rocks on the northwest side are complexly folded and faulted graphitic and quartzitic schists, also of the Birch Creek Schist (Thornsberry, McKee, and Salisbury, 1984, v. 1, fig. K-30). Several large ferricrete 'kill' zones roughly parallel the Red Dirt fault. (Vegetation is sparse to absent in the kill zones).
The graphitic schist, which is infolded with garnet-quartz-mica schist and quartzite, is a possible host of stratabound mineralization. It contains as much as 3 percent pyrite and pyrrhotite(?), and sample assays show small amounts of copper, lead, zinc, and silver. A reddish soil zone about 800 feet long parallels the Red Dirt fault; it contains as much as 0.43 ppm gold and 120 ppm arsenic.
Zinc appears to have been mobilized by acidic surface waters. Stream- sediment samples collected immediately below the ferricrete zones contain less than 75 ppm zinc; samples collected about a mile downstream contain as much as 400 ppm zinc. The pH of waters below the ferricrete zones is about 3.5; downstream waters are less acidic.
In 1983, the U.S. Bureau of Mines conducted EM and magnetic surveys (Thornsberry, McKee, and Salisbury, 1984). There is a magnetic anomaly that could be due to pyrrhotite. The EM survey shows relatively conductive zones that could be due either to massive sulfides or to graphite.
Geologic map unit (-150.510499270038, 63.7318053968769)
Mineral deposit model The geologic setting is permissive for sedimentary-exhalative deposits.
Age of mineralization The Red Dirt occurrence might be a metamorphosed massive sulfide deposit in a protolith of late Precambrian age.
Alteration of deposit Iron-oxide(?) alteration.

Production and reserves

Workings or exploration There are no workings. In 1983, the U.S. Bureau of Mines conducted detailed mapping, soil surveys, and ground geophysical studies of the occurrence (Thornsberry, McKee, and Salisbury, 1984).
Indication of production None

Additional comments

The occurrence is in Denali National Park and Preserve.

References