Grub Gulch

Mine, Inactive

Commodities and mineralogy

Main commodities Au
Ore minerals gold
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale NM
Quadrangle map, 1:63,360-scale C-1
Latitude 64.7195
Longitude -165.3865
Nearby scientific data Find additional scientific data near this location
Location and accuracy This placer gold mine is on Grub Gulch, an east tributary to lower Goldbottom Creek. The mouth of Grub Gulch is about 1.5 miles upstream of the confluence of Goldbottom Creek and North Fork Snake River. About 1,400 feet of Grub Gluch has been placer mined upstream of the Snake River road crossing. The map location is at the approximate midpoint of the workings, in the SW1/4 section 12, T. 9 S., R. 33 W., Kateel River Meridian. This is locality 88 of Cobb (1972 [MF-463], 1978 [OFR 78-93]).

Geologic setting

Geologic description

The lower half-mile or so of Grub Gulch, at surface elevations less than 300 feet, was placer mined by hand or horse-drawn scrapers and apparently worked out before 1905 (Collier and others, 1908; Moffit, 1913). The pay streak was 40 feet wide and 5 to 6 feet thick in gravels containing schist, vein quartz, and some granite boulders. Recovered gold was coarse, rough, and reported to run 3.75 dollars (about 0.18 ounce) per cubic yard (Moffit, 1913). Grub Gulch crosses graphitic quartz schists, calcareous mica schist, and a 150-foot-thick, east-dipping, highly competent granitic orthogneiss (C.C. Hawley, written communication for Kennecott Exploration Company, 1995). The placer mainly overlies mica schist bedrock that probably has an early Paleozoic protolith age (Hummel, 1962 [MF 247]; Sainsbury, Hummel, and Hudson, 1972 [OFR 72-326]; Till and Dumoulin, 1994; Bundtzen and others, 1994). The granitic boulders in Grub Gulch probably are derived from the orthogneiss upstream. In other nearby creeks that partly traverse orthogneiss (for example, Seattle Creek, NM200), quartz boulders are abundant along and immediately downstream from, orthogneiss bedrock sections of the creek, suggesting that some of the gold may have been derived from quartz veins at the contacts of the orthogneiss.
Geologic map unit (-165.389118369039, 64.7187379543188)
Mineral deposit model Alluvial placer Au (Cox and Singer, 1986; model 39a).
Mineral deposit model number 39a
Age of mineralization Quaternary.

Production and reserves

Workings or exploration This placer deposit was worked by hand or horse-drawn scrapers mainly between 1903 and 1906. The pay averaged about 0.18 ounce of gold per cubic yard.
Indication of production Yes; small

References

MRDS Number A012886

References

Till, A.B., and Dumoulin, J.A, 1994, Geology of Seward Peninsula and St. Lawrence Island, in Plafker, G., and Berg, H.C., eds., The Geology of Alaska: Geological Society of America, DNAG, The Geology of North America, v. G-1, p. 141-152.
Reporters C.C. Hawley and Travis L. Hudson
Last report date 7/10/2000