Unnamed (east-northeast of VABM Cobb)

Occurrence, Inactive

Commodities and mineralogy

Main commodities Au
Other commodities Ag; Pb; Zn
Ore minerals galena; pyrite; sphalerite
Gangue minerals carbonate minerals; quartz; tourmaline

Geographic location

Quadrangle map, 1:250,000-scale GU
Quadrangle map, 1:63,360-scale C-1
Latitude 62.73
Longitude -144.15
Nearby scientific data Find additional scientific data near this location
Location and accuracy The occurrence is on the north flank of a hill which is locally called Grizzly Hill, a broad ridge trending east-northeast of VABM Cobb. The site is approximately centered along the south half of the section line dividing sections 17 and 18, T. 11 N., R. 7 E., Copper River Meridian.

Geologic setting

Geologic description

The higher part of the area consists of Border Phase rocks of the Pennsylvanian to Permian, Ahtell pluton. These rocks are apparently underlain by the Grubstake Phase of the pluton and are cut by east-northeast-trending dikes and masses of younger Jurassic diorite (Richter, 1966; Richter and Matson, 1968).
The approximate center of the occurrence is on the east end of a locally sulfidized, silica-carbonate zone, included within the area 3a of WGM Inc. (1980, fig. 3) which is anomalous in gold. The area also has anomalous lead and zinc (Richter, 1966). A stream-sediment sample in the drainage on the north side of the occurrence contained 7,100 ppb gold (Richter and Matson, 1978). The occurrences may extend over the ridge to the south where Kirk Stanley reported (written communication, 2000) low-grade, gold-tourmaline mineral occurrences, also argentiferous galena-quartz veins. Stanley speculated that there was a large tourmaline breccia pipe in the area.
Geologic map unit (-144.152184733676, 62.7296054716771)
Mineral deposit model Polymetallic veins, Au porphyry? (Cox and Singer, 1986; model 22c).
Mineral deposit model number 22c?
Age of mineralization Uncertain; possibly composite mineralization related to both the Pennsylvanian to Permian, Ahtell pluton and the crosscutting Jurassic diorite, but could be related to either.
Alteration of deposit Silicification; formation of silica-carbonate and tourmaline-bearing rocks.

Production and reserves

Workings or exploration Most of the area has only been mapped in reconnaissance and sampled with stream sediments. Kirk Stanley (written communication, 2000) trenched a nearby area on the south flank of the Grizzly Hills in about 1970.
Indication of production None

Additional comments

Additional information can be obtained from Ahtna Minerals in Anchorage, Alaska.

References

MRDS Number 10307477

References

Reporters W.T. Ellis (Alaska Earth Sciences), C.C. Hawley (Hawley Resource Group), and W.J. Nokleberg (U.S. Geological Survey)
Last report date 12/7/2000