Cirque Prospect, Bonnifield Mining District, Southeast Fairbanks Census Area, Alaska, USAi

Regional Level Types
Cirque Prospect	Prospect
Bonnifield Mining District	Mining District
Southeast Fairbanks Census Area	Census Area
Alaska	State
USA	Country

Location: The Cirque prospect is at an elevation of about 5,500 feet in a cirque in the south wall of upper West Fork Little Delta River. The map site is in the SW1/4 of sec. 17, T. 13 S., R. 1 E., of the Fairbanks Meridian. The location is accurate to with 2 miles.
Geology: The country rocks at the Cirque prospect are Upper Devonian? felsic metavolcanic rocks, chiefly dark- to medium-gray, fine- to medium-grained schist and phyllite, that locally contain relict phenocrysts of quartz, orthoclase, and plagioclase (Wilson and others, 1998). The deposit generally consists of stratiform layers of massive sulfides, chiefly pyrite, chalcopyrite, galena, and sphalerite. Two ore bearing zones have been identified: the Discovery and Dol zones. The Discovery zone is hosted in carbonaceous shale and appears to follow a contact with rhyolite schist. The sulfide layer is massive to banded and can be traced in outcrop for about 20 meters with widths up to 2.8 meters. The zone remains open in both directions but is covered by talus and scree. Surface samples over a 2.4 meter width at the Discovery zone contain an average value of 3.84% zinc, 2.76% lead, and 0.49% copper, plus 3.73 grams gold and 98.5 grams silver per tonne. The Dol zone is in dolomite interbedded with shale. The zone has been traced in scattered outcrops for about 200 meters. All outcrops sampled returned anomalous base and precious metal values. Highlights include a 1-meter chip sample that assayed 5.57% zinc, 2.24% lead, and 0.31% copper, and 0.41 gram gold and 33 grams silver per tonne (The Northern Miner, v. 85, no. 24).
Workings: Surface exploration mostly includes soil grids, rock-chip sampling and trenching. In 1994, a ground geophysical survey delineated a 670-meter-long electromagnetic anomaly coincident with the Dol zone. There was unknown amount of drilling in 1999. Surface samples over a 2.4 meter width at the Discovery zone contain an average value of 3.84% zinc, 2.76% lead, and 0.49% copper, plus 3.73 grams gold and 98.5 grams silver per tonne. The Dol zone highlights include a 1-meter chip sample that assayed 5.57% zinc, 2.24% lead, and 0.31% copper, and 0.41 gram gold and 33 grams silver per tonne (The Northern Miner, v. 85, no. 24).
Age: Mineralization was probably syngenetic with the Upper Devonian host rocks.
Alteration: Pyrite and sericite.

Commodities (Major) - Ag, Cu, Pb, Zn
Development Status: None
Deposit Model: Kuroko massive sulfide (Cox and Singer, 1986; model 28a)

Other Databases

Link to USGS - Alaska:	HE104

Other Regions, Features and Areas containing this locality

References