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Flat Creek; Marietta Mines, Iditarod District, Yukon-Koyukuk Borough, Alaska, USA

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Latitude & Longitude (WGS84): 62° 25' 30'' North , 158° 0' 21'' West
Latitude & Longitude (decimal): 62.425, -158.005833333


Location: Several mines were developed along Flat Creek, an 5-mile-long tributary of Otter Creek, in the Iditarod District. The coordinates are at the midpoint of the placered ground in about the center of the south half of section 16, T. 27 N., R. 47 W., of the Seward Meridian. Flat Creek is locality 30 of Cobb (1972 [MF 363]); also described in Cobb (1976 [OFR 76-576]).
Geology: The placer mines along Flat Creek produced the largest amount of gold in the Iditarod mining district and they were some of the richest placer mines in Alaska (Bundtzen and others, 1992). Flat Creek flows about 5 miles from the northwest slopes of Chicken Mountain to Otter Creek. Placer deposits along Flat Creek consist of: 1) rich ancestral pay channels on the east flank of Chicken Mountain and at the Marietta bench near the head of the creek; 2) limited but rich fluvial to residual placers on the steep northwest slopes of Chicken Mountain (i.e., ID107); and 3) lower grade but regionally more extensive deposits in Pleistocene to Holocene stream alluvium along the entire course of Flat Creek (Mertie, 1936; Bundtzen and others, 1992; Miller and Bundtzen, 1994: Miller, Bundtzen, and Gray, 2005). The auriferous gravel along most of Flat Creek is 6 to 10 feet thick and overlain by 10 to 13 feet of overburden. Permafrost was intermittently present, mainly on the benches. In addition to gold, the heavy minerals in concentrates include zircon, magnetite, ilmenite, chromite, cinnabar, fluorapatite, scheelite, stibnite, monazite, and traces of cassiterite (Cobb,1974; Cobb, 1976 [OFR 76-576]; Bundtzen, Cox, and Veach, 1987). The gold fineness averaged about 864. The gold was shotty and coarse; grains average 1-2 grams in size and gold nuggets are scarce. The largest gold nugget known weighed 1.6 ounces. A dredge was operated from 1912 to 1918 by the Yukon Gold Company; it mined 4.8 million cubic yards of material that averaged 0.060 ounce of gold per cubic yard. The dredge began digging on the Marietta claim and reportedly recovered 4,000 ounces of gold on its first day of operation (John Miscovich, oral communication, 2002). Subsequently, local, rich concentrations of gold were worked with scrapers and hand methods. Based on both published and unpublished records, Kimball (1969) estimated that Flat Creek alone produced at least 477,039 ounces gold. An additional 354,210 ounces of gold was was produced from a combination of Otter and Flat Creeks. Thus Flat Creek probably produced a total of about 650,000 ounces of gold from 1909 to 1992 (Bundtzen and others, 1992; Miller, Bundtzen, and Gray, 2005).
Workings: Exploration on Flat Creek has taken place mainly by churn drilling and opencuts preliminary to mining which took place continuously from 1910 to 1940s (Cobb, 1976 [OFR 76-576]). Most of the placer gold was mined with open-cut methods; there was very little drifting (Mertie, 1936). In higher areas on the Marietta bench and on Chicken Mountain, snow fences were constructed before 1920 to trap water for sluicing since there was no regular stream sources of water (Smith, 1917). From 1912 to 1918, much of the Flat Creek was worked by a large, bucket line stacker dredge operated by the Yukon Gold Company (YGC). The YGC dredge worked both virgin auriferous gravel and placer tailings that had been mined previously by small surface mines at the head of the creek. In 1941 and 1942, the North American Dredging Company operated a smaller dredge near the mouth of Flat creek and exploited part of a rich eastern bench missed by the Yukon Gold Company dredge (Bundtzen and others, 1992). After WW II, the mining on Flat creek consisted of remining tailings and small fractions of unmined gravel using bulldozers and draglines (John and Richard Fullerton, oral communication, 1986).
Age: Probably Tertiary and Quaternary by analogy with other placer deposits in Interior Alaska (Hopkins and others, 1971).
Alteration: Decomposition of monzonitic bedrock to gruss.
Production: Based on both published and unpublished records, Kimball (1969) estimated that Flat Creek alone produced at least 477,039 ounces gold. An additional 354,210 ounces of gold was was produced from a combination of Otter and Flat Creeks. Thus Flat Creek probably produced a total of about 650,000 ounces of gold from 1909 to 1992 (Bundtzen and others, 1992; Miller, Bundtzen, and Gray, 2005). The Yukon Gold Company dredge recovered 263,028 ounces of gold from Flat Creek or 20 percent of all the gold mined in the Iditarod district. From the 1930s to 1995, mechanized mining on Flat Creek was conducted by Strandberg and Company, Pat Savage, Flat Creek Placers, Inc., Ken Dahl, Awe Mining Company, and Olson and Company (Richard and Tad Fullerton, oral communication, 1986; Bundtzen and others, 1992).
Reserves: Flat Creek is largely mined out but some small gold-bearing fractions remain, especially on the eastern bench (Bundtzen and others, 1992).

Commodities (Major) - Au; (Minor) - Ag, As, Cr, Hg, Sn, U, Zr
Development Status: Yes; large
Deposit Model: Placer Au deposit (Cox and Singer, 1986; model 39a).

Mineral List


7 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: Symmetrical to irregular piles of artificially water-worked, sorted gravel and in situ slab rock derived from bedrock.

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]

Late Cretaceous
66 - 100.5 Ma
Sedimentary; Clastic: deltaic and nearshore

Age: Late Cretaceous (66 - 100.5 Ma)

Description: Interior western Alaska, Southwest Basin

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

Lithology: Sandstone, siltstone, shale, coal; plant fossils

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., Cox, B.C., and Veach, N.C., 1987, Heavy mineral provenance studies in the Iditarod and Innoko districts, western Alaska: Process Mineralogy VII, The Metallurgical Society, p. 221-246. Bundtzen, T.K., Miller, M.L., Laird, G.M., and Bull, K.F., 1992, Geology and mineral resources of Iditarod mining district, Iditarod B-4 and eastern B-5 quadrangles, southwestern Alaska: Alaska Division of Geological and Geophysical Surveys Professional Report 97, 46 p., 2 sheets, scale 1:63,360. Cobb, E.H., 1972, Metallic mineral resources map of the Iditarod quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-363, 1 sheet, scale 1:250,000. Cobb, E.H., 1974, Placer deposits of Alaska: U.S. Geological Survey Bulletin 1374, 213 pages. Cobb, E.H., 1976, Summary of references to mineral occurrences (other than mineral fuels and construction material) in the Iditarod and Ophir quadrangles, Alaska: U.S. Geological Survey Open-File Report 76-576, 101 p. Hopkins, D.M., Matthews, J.V., Wolfe, J.A., and Silberman, M.L., 1971, A Pliocene flora and insect fauna from the Bering Sea region: Paleoecology, vol. 9, p. 211-231. Kimball, A.L., 1969, Reconnaissance sampling of decomposed monzonite for gold near Flat, Alaska: U.S. Bureau of Mines Open File Report 6-69, 39 p. Mertie, J.B., Jr., 1936, Mineral deposits of the Ruby-Kuskokwim region, Alaska: U.S. Geological Survey Bulletin 864-C, p. 115-245. Miller, M.L., and Bundtzen, T.K., 1994, Generalized geologic map of the Iditarod quadrangle, Alaska showing potassium-argon, major oxide, trace element, fossil, paleocurrent, and archeological sample localities: U.S. Geological Survey Miscellaneous Field Studies Map MF-2219-A, 48 pages; 1 sheet, scale 1:250,000. Miller, M.L., Bundtzen, T.K., and Gray, J.E., 2005, Mineral resource assessment of the Iditarod quadrangle, west-central Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-2219-B, scale 1:250,000, pamphlet. Smith, S.S., 1917, The mining industry in the Territory of Alaska during the calendar year 1915: U.S. Bureau of Mines Bulletin 142, 65 p. Webber, W.J., Bjorklund, S.C., Rutledge, F.A., Thomas, B.I., and Wright, W.S., 1947, Mercury deposits of southwestern Alaska: U.S. Bureau of Mines Report of Investigations 4065, 57 p.

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