Unnamed (west of Chistochina Glacier)

Occurrence, Inactive

Commodities and mineralogy

Main commodities Au; Cu
Other commodities Ag; Ni
Ore minerals chalcopyrite; magnetite; pyrite; pyrrhotite

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale A-2
Latitude 63.1932
Longitude -144.8808
Nearby scientific data Find additional scientific data near this location
Location and accuracy This occurrence is west of the terminus of the Chistochina Glacier and about 1.6 mile north of the mouth of Slate Creek on the Chistochina River. It is about 0.2 mile southeast of the center of section 9, T. 20 S., R. 15 E. There is some question about the location of this site in the old literature but this location is accurate as described by Bittenbender and others (2007).

Geologic setting

Geologic description

The rocks in the area consist of mafic and ultramafic intrusive rocks associated with volcanic rocks, probably part of the Pennsylvanian to Permian, Slana Spur Formation (Rose, 1967; Nokleberg and others, 1992 [MF]; 1992 [Open-File]; Bittenbender and others, 2007). Nokleberg and others (2007 [MF] suggest that Cretaceous K/Ar dates (123-126 Ma) from the mafic and ultramafic rocks probably reflect regional metamorphism of rocks deposited in the Paleozoic. However, Bittenbender and others (2007) also dated the rocks as Early Cretaceous but interpret the dates as the age of primary crystallization.
As described by Rose (1967), this occurrence is in a mile-long northeast-trending body of gabbro and mafic gabbro south of quartz monzonite of probable Mesozoic age. Rose (1967) identified a 50-foot-wide zone of pyritized rocks at the contact between peridotite and monzonite. A grab sample collected contained 0.02 ounce of gold per ton, 0.18 ounce of silver per ton, 0.2 percent copper, and a trace of nickel.
Probably at or near the Rose location, Bittenbender and others (2007) identified a iron-stained, lens-shaped area about 125 feet long of coarse-grained pyroxenite, gabbro, and some dunite. The pyroxene in the gabbro is altered to amphibole and the plagioclase is saussuritized. The iron-stained area contains up to 10 percent ore minerals, mainly pyrite and magnetite with minor pyrrhotite and chalcopyrite. A composite chip sample across 54 feet contained 2.7 parts per million (ppm) gold and 837 ppm copper. No other of their samples contained more than 0.032 ppm gold and the highest copper value was 1,900 ppm.
Geologic map unit (-144.88302834752, 63.1928035049132)
Mineral deposit model Unclear; gabbro and peridotite with sulfides and anomalous gold.
Age of mineralization No definitive information.
Alteration of deposit The site is notable for its iron staining. The pyroxene in the gabbro host rock is altered to amphibole and the plagioclase is saussuritized.

Production and reserves

Workings or exploration Only limited sampling by state and federal agencies.
Indication of production None
Reserve estimates None.
Production notes None.

References

References

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