Three Cub Occurrence, McGrath Mining District, Bethel Census Area, Alaska, USAi

Regional Level Types
Three Cub Occurrence	Occurrence
McGrath Mining District	Mining District
Bethel Census Area	Census Area
Alaska	State
USA	Country

Location: This occurrence is on the north side of a hanging-glacier moraine in the headwaters of an unnamed south tributary to uppermost Fish Creek. It is at an elevation of about 4,800 feet, 0.9 mile north of peak 6590. The map site is in the NE1/4 section 4, T 19 N, R 24 W, of the Seward Meridian. This occurrence is sample locations 823 and 824 of Allen and others (1990), Allen and Slaughter (1990), and Allen (1991).
Geology: Thin, sulfide-bearing quartz veins, generally less than 15 cm wide, locally crosscut Jurassic or Lower Cretaceous graywacke and Upper Cretaceous or Tertiary granitic rocks at this locality (Allen, 1990; Allen and others, 1990; Allen and Slaughter, 1990). The veins consist dominantly of quartz, carbonate, pyrite, and arsenopyrite, and less commonly contain barite, chalcopyrite, stibnite, galena, and sphalerite. Some aplite dikes, quartz veins, and pyrite-bearing fracture surfaces in the granitic rocks contain scheelite and arsenopyrite. Calc-silicate skarn is very locally developed in sedimentary rocks adjacent to the granitic rock contacts. Quartz veins in graywacke contain as much as 1.3 ppm gold, 70 ppm silver, 3,000 ppm copper, and 500 ppm zinc. A sample from a sulfide-rich quartz-carbonate vein at a granitic rock contact contained 1.9 ppm gold, 150 ppm silver, 2,000 ppm arsenic, 150 ppm bismith, 1,000 ppm lead, 1,000 ppm antimony, 50 ppm tin, and 3,000 ppm zinc. Although scheelite has been reported in quartz veins from the general area, samples at this locality contained less than 20 ppm tungsten. The granitic rocks are part of the Alaska-Aleutian Range batholith (Reed and Lanphere, 1973).
Workings: Surface observation and sampling has occurred at this locality.
Age: Late Cretaceous or Tertiary. The veins crosscut Upper Cretaceous or Tertiary granitic rocks of the Alaska-Aleutian Range batholith.
Alteration: Silicification and local calc-silicate skarn.

Commodities (Major) - Ag, Au, Cu, Pb, Sb, W, Zn
Development Status: None
Deposit Model: Polymetallic veins (Cox and Singer, 1986, model 22c)

Other Databases

Link to USGS - Alaska:	LH009

Other Regions, Features and Areas containing this locality

References