Crooked Creek

Site Name

Primary: Crooked Creek

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Commodity

Primary: Gold
Secondary: Diamond

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Location

State: Alaska
District: Circle

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Land Status

Not available

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Holdings

Not available

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Workings

Not available

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Ownership

Not available

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Production

Not available

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Deposit

Record Type: Site
Operation Category: Past Producer
Operation Type: Unknown
Years of Production:
Organization:
Significant:

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Physiography

Not available

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Mineral Deposit Model

Model Name: Placer Au-PGE

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Orebody

Not available

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Structure

Not available

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Alterations

Not available

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Rocks

Not available

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Analytical Data

Not available

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Materials

Ore: Diamond
Ore: Gold

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Comments

Comment (Exploration): Status = Inactive

Comment (Deposit): Model Name = Placer gold deposit (Cox and Singer, 1986; model 39a)

Comment (Deposit): Other Comments = First placer diamonds documented in Alaska were found on Crooked Creek.

Comment (Production): Production Notes = Values range from 0.01 to 0.03 ounces of gold per cubic yard. Upstream from the fault, the values are lower, approximately 0.00625 ounces per cubic yard, as reported by miners on the basis of exploratory sampling (Lampright, 1996). Total amount of production is unknown.

Comment (Reference): Primary Reference = Yeend, 1991.

Comment (Workings): Workings / Exploration = Placer mining has been confined to the 8 km of the creek immediately downstream from where the Hot Springs fault crosses Crooked Creek (Yeend, 1991, p. 17). Placer mining occurred in 1952 and from 1973 through the 1980's. Bob Cacy of Points North conducted geochemical and magnetic surveys on Crooked Creek in 1993 and 1994 (Bundtzen and others, 1993; Swainbank and others, 1994).? the first diamonds in the Circle Quadrangle were discovered on Crooked Creek. In 1982, Jim Regan discovered a 0.3 ct diamond in a sluice box. Frank Warren discovered an even larger, 1.4 ct diamond, during placer mining in 1984 (Eakins and others, 1985). Subsequent exploration specifically designed to recover diamonds has been unsuccessful.

Comment (Geology): Geologic Description = Quartzitic schist is present upstream from the Hot Springs fault and along the upstream tributaries, and it makes up most of the detritus in the creek gravel. A small granite outcrop is present upstream along Mammoth Creek (Lampright, 1996). All but this uppermost part of the creek lies within the Tintina fault zone. At the Hot Springs Fault junction the Crooked Creek flood plain dissects late Pleistocene fan gravel that forms a prominent 20 meter high bench to the north. To the south, several less prominent stair-stepped bench levels of late Pleistocene fan gravel grade down to the Crooked Creek flood plain. The alluvial gravel in Crooked Creek is composed predominantly of well-rounded to subrounded clasts as much as 15 cm in diameter. A pebble count in Crooked Creek approximately 4 kilometers downstream from the Hot Springs fault reveals a composition of 43 percent quartz-mica schist, 32 percent quartzite, 21 percent quartz, and 4 percent weathered granite (Yeend, 1991). ? Gold-bearing gravel that is 2 to 5 meters thick overlies false bedrock with clay-rich, altered cobble gravel. Mining excavations in the area where the Hot Springs fault crosses the Crooked Creek valley exposed fault gouge, altered schist bedrock, and orange gravel. Locally, where river scour has eroded the intervening gray gravel, the overlying muck rests directly on the orange gravel (Yeend, 1991, p. 19). Downstream from the Hot Springs fault are many locations where the gray gravel extends vertically into the orange gravel. Gray gravel locations within the orange gravel are interpreted as former sites of ice wedges (Kline, 1985). The gray gravel was able to fill in as the ice wedges melted and the creek washed over the uneven surface (Lampright, 1996).? the gold is thought to be contained within the gray gravel that overlies the clay-rich orange gravel. Some gold extends into the upper orange gravel, but for the most part the orange gravel acts as a trap for the fine gold. ?Placer gold occurs primarily in the lower 1 to 2 meters of gray alluvial gravel, which is generally more consolidated that the overlying gravel and sometimes includes blocks of the underlying orange gravel (Yeend, 1991). The paystreak in Crooked Creek is as much as 400 meters wide and 1 to 2 meters thick (Yeend, 1991). Wood fragments are scattered through the gold bearing gravel. The upper gravel unit yielded an age from wood of approximately 1,480 B.P. This young age implies a continuous reworking of these gravels (Yeend, 1991).? Gold flakes are very flattened, commonly 1 to 3 mm in largest dimension. (Menzie, 1983) Values range from 0.01 to 0.03 ounces per cubic yard. Upstream from the fault, the values are lower, approximately 0.00625 ounces per cubic yard, as reported by miners on the basis of exploratory sampling (Lampright, 1996). ? Placer mining has been confined to the 8 km of the creek immediately downstream from where the Hot Springs fault crosses Crooked Creek (Yeend, 1991, p. 17). Placer mining occurred in 1952 and from 1973 through the 1980's. Bob Cacy of Points North conducted geochemical and magnetic surveys on Crooked Creek in 1993 and 1994 (Bundtzen and others, 1993; Swainbank and others, 1994). ? the first diamonds in the Circle Quadrangle were discovered on Crooked Creek. In 1982, Jim Regan discovered a 0.3 ct diamond in a sluice box. Frank Warren discovered an even larger, 1.4 ct diamond, during placer mining in 1984 (Eakins and others, 1985). In 1986, Paul Manuel recovered a third diamond from the Crooked Creek gravels about 1500 ft downstream from the Warren discovery (Forbes and others, 1987, p. 7). Subsequent investigations by experienced diamond producers indicated no trace minerals indicative of kimberlite or lamproite source rocks.

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References

Reference (Deposit): Forbes, R.B., Kline, J.T., and Clough, A.H., 1987, A preliminary evaluation of alluvial diamond discoveries in placer gravels of Crooked Creek, Circle district, Alaska: Alaska Division of Geological and Geophysical Surveys Report of Investigations 87-1, 26 p.

Reference (Deposit): Cobb, E.H., 1972, Metallic mineral resources map of the Circle quadrangle, Alaska: U.S. Geological Survey Misc. Field Studies Map MF-391, 1 sheet, scale 1:250,000.

Reference (Deposit): Lampright, R.L., 1996, Gold placer deposits near Fairbanks Alaska: Iron Fire Publications, Nederland, Colorado, 135 p.

Reference (Deposit): Swainbank, R.C., Bundtzen, T.K., Clough A.H., Henning, M.W., and Hansen E.W., 1994, Alaska's mineral industry 1994: Alaska Division of Geological and Geophysical Surveys Special Report 49, 77 p.

Reference (Deposit): Bundtzen, T.K., Laird, G.M., and Lockwood, M.S., 1988, Geologic map of the Iditarod C-3 quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Professional Report 96, 13 p., scale 1:63,360.

Reference (Deposit): Yeend, W.E., 1991, Gold placers of the Circle district, Alaska - past, present, and future: U.S. Geological Survey Bulletin 1943, 42 p.

Reference (Deposit): Nelson, A.E., West, W.S., and Matsko, J.J., 1954, Reconnaissance for radioactive deposits in eastern Alaska: U.S. Geological Survey Circular 348, 21 p.

Reference (Deposit): Yeend, W.E., 1985, Trace elements of placer gold: U.S. Geological Survey Circular 945, p. 4-7.

Reference (Deposit): Bundtzen, T.K., Eakins, G.R., Green, C.B. and Lueck, L.L., 1986, Alaska's mineral industry in 1985: Alaska Division of Geological and Geophysical Surveys Special Report 39, 68 p.

Reference (Deposit): Kline, J.T., 1985, Preliminary notes and observations on activities in the field during the period of June 23 to July 3: Investigations of the occurrence of diamonds in placer gravels on Crooked Creek near Central, Alaska: Alaska Division of Geological and Geophysical Surveys Public Data File 85-18, 8 p.

Reference (Deposit): Cushing, G.W., and Foster, H.L., 1984, Structural observations in the Circle quadrangle, Yukon-Tanana Upland, Alaska, in Accomplishments during 1981: U.S. Geological Survey Circular 868, p. 64-65.

Reference (Deposit): Cobb, E.H., 1976, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Circle quadrangle, Alaska: U.S. Geological Survey Open-File Report 76-633, 72 p.

Reference (Deposit): Menzie, W.D., Foster, H.L., Tripp, R.B., and Yeend, W.E., 1983, Mineral resource assessment of the Circle quadrangle, Alaska: U.S. Geological Survey Open-File Report 83-170-B, 61 p., 1 sheet, 1:250,000.

Reference (Deposit): Eakins, G.R., Bundtzen, T.K., Lueck, L.L. Green, C.B., Gallagher, J.L., and Robinson, M.S., 1985, Alaska mineral industry, 1984: Alaska Division of Geological and Geophysical Surveys Special Report 38, 57p.

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