Sheep Creek Occurrence, Koyukuk Mining District, Yukon-Koyukuk Census Area, Alaska, USAi

Regional Level Types
Sheep Creek Occurrence	Occurrence
Koyukuk Mining District	Mining District
Yukon-Koyukuk Census Area	Census Area
Alaska	State
USA	Country

See also WI014. This occurrence is located within Gates of the Arctic National Park.
Location: This occurrence is at an elevation of about 3,600 feet, about 1,00 feet northeast of the top of hill 3914, near the southeast corner of section 27, T. 32 N., R. 20 W., of the Fairbanks Meridian. The occurrence is near the midpoint of a mile-long, east-northeast belt defined by the locations of several mineralized samples (Degenhart and others, 1978). It also corresponds to the location of mineralization described by Brosge and Reiser (1960) and by Cobb (1972, MF 469, loc. 7). The location is accurate within one-half mile.
Geology: This occurrence is one of several that define a northeast trending zone of minor copper occurrences that extends for about 5 miles to the northeast from VABM Allen on the Wiseman C-5 topographic map (see also WI005, 006, and 012-014). Mineralization at this site was first described by Brosge and Reiser (1960; Cobb, 1972, locality 7 [MF 469] ), as conglomerate containing unspecified copper sulfides and malachite staining. Degenhart and others (1978) cite minor chalcopyrite, malachite, and azurite in a 5-foot-thick layer of quartz-chlorite schist. The schist underlies Middle Devonian, Skajit Limestone, which in this area is thrust over Upper Devonian shale, phyllite and schist. Degenhart and others (1978) suggested that the quartz-chlorite schist may represent the plane of a thrust fault . A select sample of mineralized talus material, collected about 0.2 mile east of the Brosge and Reiser location, contains 1,920 ppm copper and 4.2 ppm silver but no significant gold, lead, zinc, or molybdenum (Degenhart and others, 1978, sample BM1197). They interpret the mineralization as stratabound although its extent appears to be no more than 20 feet along strike and 5 feet in thickness. Dillon and others (1981; sample 304 [AOF 133B]) collected a composite rock sample about 0.5 mile west of the Brosge and Reiser's site. It consists of graphitic, chlorite-sericite-quartz schist and vein quartz with disseminated cuprite(?) and malachite; it contains 5,000 ppm copper. Kurtak and others (1999) found podiform copper mineralization in schist and marble in upper Sheep Creek that could be traced along strike for about 1,700 feet. They also observed chalcopyrite and bornite in quartz veins and in fracture fillings along a marble-schist contact. The orientation of these mineralized veins and fractures is parallel to the bedding of the overlying marble. They collected seven rock samples of float and outcrop, one of which contains an estimated 20% chalcopyrite. The samples contain 872 ppm to 16.53% copper, less than 5 to 46 ppb gold, and 0.3 to 78.6 ppm silver.
Workings: Only surface sampling.
Alteration: Local oxidation of copper minerals.
Reserves: Degenhart and others (1978) noted that a few tons of mineralized material with about 0.5% Cu may be present.

Commodities (Major) - Cu; (Minor) - Ag(?)
Development Status: None
Deposit Model: Polymetallic replacement deposit (?) (Cox and Singer, 1986; model 19a)

Other Databases

Link to USGS - Alaska:	WI016

Other Regions, Features and Areas containing this locality

References