Lower Caribou Creek

Mines, Inactive

Alternative names

Lee bench

Commodities and mineralogy

Main commodities Au
Other commodities Ag
Ore minerals gold
Gangue minerals garnet; magnetite

Geographic location

Quadrangle map, 1:250,000-scale MM
Quadrangle map, 1:63,360-scale C-2
Latitude 63.6576
Longitude -150.936
Nearby scientific data Find additional scientific data near this location
Location and accuracy Lower Caribou Creek (Cobb, 1980 [OFR 80-363]) is the part of Caribou Creek below the Kantishna Hills. The lower Caribou Creek placer deposit is about 3 miles long. It extends from the NW1/4 of section 7, T. 15 S., R. 17 W., Fairbank Meridian, to the midpoint of sections 31 and 36 on the R. 17 W.-18 W. township line. The location marks the north limit of placer tailings shown on the 1954 (rev. 1978) edition of the Mt. McKinley C-2 quadrangle topographic map. It approximately coincides with number 47 of Cobb (1972 [MF 366]), placer resource block C-2 of Thornsberry, McKee, and Salisbury (1984, fig. K-3), and the mined area shown by Hawley and Associates (1978).

Geologic setting

Geologic description

Lower Caribou Creek has a gradient of about 150 feet per mile. It flows through a broad alluvial valley cut into bedrock of the Birch Creek Schist (Levell, 1984, v. 1 and 2; Bundtzen, 1981). The broad terrace on the east side of lower Caribou Creek is called the Lee bench. The lower Caribou Creek placer deposit consists of 4 to 7 feet of subrounded to rounded gravel on top of weathered, clayey, bedrock. The lowest 1 to 2 feet of gravel is weakly cemented. The gold was mainly in the gravel, but about 1/2 foot of bedrock was auriferous and was mined with the gravel. Most of the gold was fine and flaky, a little was nuggety, and its fineness was about 680. The gold was weakly to moderately stained with iron and manganese oxides. Garnet and magnetite were abundant in the concentrate. Grade, calculated from production, was about 0.027 ounce (0.019 fine ounce) of gold per cubic yard (Levell, 1984, v. 2, operation 6).
The nature of the Lee bench placer is uncertain, as most of it has not been tested. The deposit mainly is on schist bedrock, and consists of 4 to 10 feet of gravel overlain by 2 to 3 feet of frozen muck (Levell, 1984, v. 2). At an exposure about 1/2 mile downstream from the schist-floored deposit, 10 to 15 feet of gravel lies on false bedrock of quartz-rich, Tertiary(?) sand. Spoils from nearby pits include blue clay that is possibly Tertiary lake sediment. The average grade of the Lee bench deposit, calculated from ground mined and gold recovered in 1975, is 0.026 ounce (0.019 fine ounce) of gold per cubic yard.
Geologic map unit (-150.938300020093, 63.6570940063852)
Mineral deposit model Au-PGE placer (Cox and Singer, 1986; model 39a).
Mineral deposit model number 39a
Age of mineralization Holocene and late Pleistocene; some deposits may be as old as late Tertiary.

Production and reserves

Workings or exploration More than a mile of lower Caribou Creek was mined prior to 1951-52, probably mainly by dragline in about 1940. At least one operation worked the lower Lee bench in 1975 (Levell, 1984, v. 2; Bundtzen, Tosdal, and Smith, 1976). The alluvial deposit in and near the modern valley was mined in 1983 and probably 1984.
Indication of production Yes; small
Reserve estimates Resource block C-2 (Levell, 1984) contains about 840,000 cubic yards of alluvium on claimed ground (1983) in or adjacent to modern lower Caribou Creek. The gold resource at the calculated grade of 0.019 fine ounce of gold per cubic yard is 15,960 ounces. There is a much larger, but less quantified, resource on the Lee bench. The estimated volume of claimed (1983) gravel in the bench deposits is 4,300,000 cubic yards. Using the grade calculated from 1975 production from the bench (0.019 fine ounce of gold per cubic yard), the resource is about 81,700 ounces of gold.
Production notes Total gold production is uncertain. An operator in 1975 recovered about 70.5 ounces. An efficient 1983 operation had recovered more than 1000 ounces before the end of August, and was in production when visited by Levell (Levell, 1984, v. 2). Based on the grade of mined material, and on the extent of the mining, the lower Caribou placer deposit has probably produced at least 5000 ounces of gold.

Additional comments

Caribou Creek is in Denali National Park and Preserve.

References

MRDS Number A011264

References

Bundtzen, T.K., 1981, Geology and mineral deposits of the Kantishna Hills, Mt. McKinley quadrangle, Alaska: M. S. Thesis, University of Alaska, College, Alaska, 238 p.
Reporters C.C. Hawley
Last report date 4/19/2001