The Rat Fork-Headwall prospect is part of a widespread polymetallic mineral belt similar to other deposits in the Farewell Mineral belt, including Tin Creek North (MG041), Tin Creek South (MG044), Bowser Creek-Main (MG068), Bowser Creek Northeast (MG067), and Smith Lake (MG055) prospects.
Location: The Rat Fork-Headwall prospect is located just below the crest of a steep ridgeline near the head of a glacial cirque, the headward reaches of the Rat Fork of Sheep Creek; it is at about 5,500 feet (1,676 m) elevation, in the NW1/4 sec. 27, T. 26 N., R. 25 W., of the Seward Meridian. The prospect is accurately located; the reporter visited the site in 1982.
Geology: The Rat Fork-Headwall prospect consists of disseminated to massive sulfide veins in a calc-silicate skarn zone within an extensive, east-west-trending, granodiorite dike swarm more than 1.5 kilometers wide (Bundtzen Kline, and Clough, 1982). The dike swarm cuts Lower Paleozoic clastics and carbonates of the Dillinger subterrane (Bundtzen, Harris, and Gilbert, 1997). The dikes are not dated at the prospect site, but are similar to dikes that are spatially related to the Tin Creek-Midway prospect (MG043) to the northeast, which has yielded K-Ar ages ranging in age from 25 to 35 Ma (Solie and others, 1991; Bundtzen, Harris, and Gilbert, 1997). The calc-silicate skarns, which are composed of garnet, epidote, and low temperature clinopyroxene (johannsenite) occur mainly in arenaceous, recrystallized limestone. The sulfide bearing vein parallels a pervasive joint set which cuts various calc-silicate rocks and limestone (Smith and Albanese, 1985). The sulfide vein trends N85W, dips 85S, varies from 0.5 to 3 meters thick, and can be traced for about 22 meters along strike. Principal sulfide minerals in the vein consist of pyrite, sphalerite (iron-rich marmatite), galena, and chalcopyrite. Sulfides locally compose up to 45 percent of the vein, even in thickened areas. Chip-channel samples taken across the vein at three intervals contained up to 0.56 percent copper, 11.10 percent lead, 14.10 percent zinc, 301 grams/tonne silver, 3.80 percent arsenic, 0.12 percent cadmium, and 42.40 percent iron (Smith and Albanese, 1985).
Workings: In the late 1960s and early 1970s (records are unclear), Falconbridge Minerals through exploration operator St. Eugene Mining Company, conducted a limited amount of diamond core drilling from two stations near the sulfide vein. Based on drill hole orientations, the exploration drilling attempted to intersect the vein at depth. The results of this exploration work are unknown. Surface sampling has been conducted by Reed and Elliott (1968, C 596), Bundtzen, Kline, and Clough (1982) and Smith and Albanese (1985).
Age: Unknown; inferred to be 25 to 35 Ma, based on K-Ar dating of similar granodiorite dike swarms elsewhere in McGrath quadrangle.
Alteration: Extensive oxidation of pyrite-rich areas to ferricrete gossan.
Reserves: None.

Commodities (Major) - Ag, Cu, Pb, Zn; (Minor) - As, Cd
Development Status: No
Deposit Model: Lead-zinc (copper) skarns (Cox and Singer, 1986; model 18c).

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Standard Detailed Gallery Strunz Chemical Elements

Commodity List

This is a list of exploitable or exploited mineral commodities recorded at this locality.

Mineral List

ⓘ Chalcopyrite

ⓘ 'Clinopyroxene Subgroup'

6 valid minerals.