Rat Fork-Base prospect, Yukon-Koyukuk Census Area, Alaska, USAi

Regional Level Types
Rat Fork-Base prospect	Prospect
Yukon-Koyukuk Census Area	Census Area
Alaska	State
USA	Country

Similar to Rat Fork-Headwall (MG059), Tin Creek North (MG041), Tin Creek Midway (MG043), Smith Lake (MG055), and Bowser Creek Main (MG068) skarn deposits in the Farewell Mineral belt, McGrath Quadrangle.

Location: The Rat Fork-Base prospect is located near the base of the cirque that defines the head of the Rat Fork of Sheep Creek; it is at an elevation of 4,175 feet (1,273 m) in the NW1/4 sec. 26, T. 26 N., R. 25 W., of the Seward Meridian. An active rock glacier forms the southern boundary of the prospect area. The location is accurate; the reporter visited the site in 1982.

Geology: The Rat Fork-Base prospect consists of disseminated sulfides in a calc-silicate hornfels and marble adjacent to an extensive, east-west-trending, granodiorite sill and dike swarm, the same plutonic complex that is exposed at the Rat Fork-Headwall (MG059) prospect. At the Rat Fork-Base prospect, the calc-silicate zone, which consists of garnet, epidote, and clinopyroxene in arkosic, metaclastic rocks, has been intruded by several mafic sills that are parallel to bedding. The plutonic rocks intrude the Lower Paleozoic Dillinger subterrane (Bundtzen, Harris, and Gilbert, 1997). The zone of disseminated mineralization trends roughly east-west, varies from 1 to 10 meters thick, and can be traced along the strike for about 40 meters. Principal sulfide minerals include abundant pyrite and pyrrhotite, and minor amounts of chalcopyrite and sphalerite. Surface sampling of massive sulfide talus below a diamond drill station contained 0.31 percent copper, 1.85 percent zinc, 6.5 grams/tonne silver, 158 ppm cobalt, 161 ppm cadmium, and 41.4 percent iron (Smith and Albanese, 1985).
Workings: A single drill station was sited by Falconbridge Minerals through their operator St. Eugene Mining Company sometime in the late 1960s and early 1970s (records for time of activities are poorly known). The results of these exploration efforts are unknown. Surface sampling of massive sulfide talus below the diamond drill station contained 0.31 percent copper, 1.85 percent zinc, 6.5 grams/tonne silver, 158 ppm cobalt, 161 ppm cadmium, and 41.4 percent iron (Smith and Albanese, 1985).

Age: Unknown; inferred to be 25 to 35 Ma, based on age of similar dike swarm in Tin Creek area (Solie and others, 1991).

Alteration: Surface oxidation of massive pyrite and pyrrhotite formed a pronounced ferricrete gossan.

Commodities (Major) - Ag, Cu, Pb, Zn; (Minor) - Cd, Co, Fe

Development Status: No

Deposit Model: Lead-zinc (copper) skarn (Cox and Singer, 1986; model 18c).

Other Databases

Link to USGS - Alaska:	MG058

Other Regions, Features and Areas containing this locality

References