Unnamed (southeast of confluence of Chickamin River and South Fork)

Occurrence, Undetermined

Commodities and mineralogy

Main commodities Cu
Ore minerals chalcopyrite; magnetite; pyrite

Geographic location

Quadrangle map, 1:250,000-scale KC
Quadrangle map, 1:63,360-scale D-3
Latitude 55.839
Longitude -130.675
Nearby scientific data Find additional scientific data near this location
Location and accuracy This occurrence is at an elevation of about 2900 feet, approximately 3.5 miles southeast of the confluence of the Chickamin River and the South Fork of the Chickamin. The site is in section 34, T. 69 S., R. 96 E., of the Copper River Meridian. It corresponds to area M-6 in Berg and others (1977), and to loc. 20 in Elliott and others (1978). The location is accurate within 0.1 mile.

Geologic setting

Geologic description

The country rocks in the area of this occurrence consist chiefly of Tertiary or Cretaceous foliated granodiorite of the Coast Range batholith, and of rusty-weathering pelitic paragneiss that forms roof pendants, screens, and inclusions in the batholith (Berg and others, 1977, p. 129-132; Berg and others, 1977). The paragneiss probably represents marine argillaceous and clastic strata that underwent high-grade regional metamorphism in Cretaceous or Tertiary time. The premetamorphic age of the strata is uncertain, but they probably are mainly Paleozoic and may be as old as Precambrian (Berg and others, 1988, p. 26; Gehrels and others, 1990; Crawford and others, 2000).
The occurrence consists of a conspicuous band of rusty-weathering pyritic gneiss about 1000 feet wide that strikes northwest and dips northeast, and can be traced in outcrop for about 3 miles (Berg and others, p. 129-132 and pl. 2). The rocks include quartzofeldspathic gneiss, which is gradational with the foliated plutonic rocks of the Coast Range batholith, and subordinate pelitic schist and paragneiss. The rocks contain pyrite in amounts up to several volume percent, and sparse grains of chalcopyrite. Thirty-six chip samples collected at three locations along the outcrop of the band assayed up to 700 ppm Cu, 150 ppm Pb, 200 ppm Zn, 70 ppm Mo, and 5 ppm Ag (Berg and others, 1977, table 13). A rock grab sample from the band contained up to 450 ppm Pb and 0.05 ppm Ag, and a stream-sediment sample from a creek draining the band was anomalous in Cu, Pb, Zn, Mo, Au, and Ag (Berg and others, 1977, fig. 9 and table 13).
Geologic map unit (-130.676705173041, 55.8386593733882)
Mineral deposit model Disseminated base-metal sulfides in rusty-weathering paragneiss
Alteration of deposit Conspicuous iron-staining.

Production and reserves

Workings or exploration Thirty-six chip samples collected at three locations along the outcrop of this 3-mile-long, 1000-foot-wide band of rusty-weathering gneiss assayed up to 700 ppm Cu, 150 ppm Pb, 200 ppm Zn, 70 ppm Mo, and 5 ppm Ag (Berg and others, 1977, table 13). A rock grab sample from the band contained up to 450 ppm Pb and 0.05 ppm Ag, and a stream-sediment sample from a creek draining the band was anomalous in Cu, Pb, Zn, Mo, Au, and Ag (Berg and others, 1977, fig. 9 and table 13).
Indication of production None

Additional comments

Site is in Misty Fiords National Monument Wilderness.

References