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Crooked Creek Mines, Circle District, Yukon-Koyukuk Borough, Alaska, USA

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Latitude & Longitude (WGS84): 65° 34' 22'' North , 145° 1' 40'' West
Latitude & Longitude (decimal): 65.5727777778, -145.027777778


First placer diamonds documented in Alaska were found on Crooked Creek.
Location: The location is at the mouth of Sawpit Creek, where mining took place in 1981. Mining in 1952 and 1973 to 1981 was near the mouth of Mammoth Creek and east for several km. Crooked Creek is the drainage below the junction of Porcupine and Mammoth Creeks. It flows 30 km in an easterly direction through the town of Central before joining Birch Creek. The Steese Highway parallels Crooked Creek between the Hot Springs Fault and the town of Central. 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).
Geology: 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.
Workings: 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.
Production: 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.

Commodities (Major) - Au; (Minor) - Diamond
Development Status: Yes; small
Deposit Model: Placer gold deposit (Cox and Singer, 1986; model 39a)

Mineral List


2 valid minerals.

Regional Geology

This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.

Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org

Quaternary
0 - 2.588 Ma
Unconsolidated surficial deposits, undivided

Age: Pleistocene (0 - 2.588 Ma)

Description: Gravel, sand, and silt, gray, buff, or brown. Unconsolidated, well-sorted, well-stratified.

Lithology: Unconsolidated

Reference: Wilson, F.H., Hults, C.P., Mull, C.G, and Karl, S.M. (compilers). Geologic map of Alaska. doi: 10.3133/sim3340. U.S. Geological Survey Scientific Investigations Map 3340, pamphlet 196. [21]

Neogene
2.588 - 23.03 Ma
Supracrustal; Sedimentary and/or volcanic: undivided

Age: Neogene (2.588 - 23.03 Ma)

Description: Eastern Alaska, Yukon, Mackenzie region, Yukon Flats, Old Crow Basin

Comments: Sedimentary basin; Gordey & Makepeace, 2003; Wilson & Hults, unpublished compilation, 2007-08

Lithology: Sedimentary and/or volcanic rock: undivided

Reference: J.C. Harrison, M.R. St-Onge, O.V. Petrov, S.I. Strelnikov, B.G. Lopatin, F.H. Wilson, S. Tella, D. Paul, T. Lynds, S.P. Shokalsky, C.K. Hults, S. Bergman, H.F. Jepsen, and A. Solli. Geological map of the Arctic. doi:10.4095/287868. Geological Survey of Canada Map 2159A. [2]

Data and map coding provided by Macrostrat.org, used under Creative Commons Attribution 4.0 License



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References

Bundtzen, T.K., Eakins, G.R., Green, C.B., and Lueck, L.L., 1986, Alaska's mineral industry, 1985: Alaska Division of Geological and Geophysical Surveys Special Report 39, 68 p. Bundtzen, T. K., Swainbank, R. C., Clough A.H., Hansen E.W., Nelson, M. G., and Henning, M. W., 1993, Alaska's mineral industry 1993: Alaska Division of Geological and Geophysical Surveys Special Report 48, 84 p. Cobb, E.H., 1972, Metallic mineral resources map of the Circle quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-391, 1 sheet, scale 1:250,000. 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. Cushing, G.W., and Foster, H.L., 1984, Structural observations in the Circle quadrangle, Yukon-Tanana Upland, Alaska, in Coonrad, W. L., and Elliott, R.L., eds., The United States Geological Survey in Alaska--Accomplishments during 1981: U.S. Geological Survey Circular 868, p. 64-65. 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, 57 p. 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. 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. [Superseded by RI 87-1] Lampright, R.L., 1996, Gold placer deposits near Fairbanks Alaska--An inventory of the gold placer mines, prospects, and deposits located within the Big Delta Charley River, Circle, Eagle, Fairbanks, and Livengood quadrangles: Nederland, Colorado, Iron Fire Publications, Anchorage, Alaska, 135 p. 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. Nelson, A.E., West, W.S., and Matsko, J.J., (1952) 1954, Reconnaissance for radioactive deposits in eastern Alaska: U.S. Geological Survey Circular 348, 21 p. 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. Yeend, W.E., 1985, Trace elements of placer gold, in Bartsch-Winkler, Susan, and Reed, K.M., eds., The United States Geological Survey in Alaska--Accomplishments during 1983: U.S. Geological Survey Circular 945, p. 4-7. Yeend, W.E., 1991, Gold placers of the Circle district, Alaska--Past, present, and future: U.S. Geological Survey Bulletin 1943, 42 p.

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