Dexter High Bench

Site Name

Primary: Dexter High Bench

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Commodity

Primary: Gold
Secondary: Silver

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Location

State: Alaska
District: Nome

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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: Gold

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Comments

Comment (Geology): Age = Quaternary, but possibly late Tertiary.

Comment (Exploration): Status = Probably inactive

Comment (Reference): Primary Reference = Collier and others, 1908

Comment (Workings): Workings / Exploration = Gold was discovered in Nekula Gulch in 1900. About 90,000 dollars worth of gold (about 4,500 ounces) was mined in 1900. The area was developed rapidly; it was active when visited by Collier and others (1908) in 1903 and by Moffit (1913) in 1905 and 1906. The Caribou Bill probably was the richest deposit ever found in the district; some pans there contained about an ounce of gold. Material excavated from that rather small deposit (30 x 50 feet x 90 feet deep) contained about 50 ounces of gold per cubic yard. Two main, largely buried paystreaks were mined. Material hoisted from most mines contained more than 0.25 ounce of gold per cubic yard.? Erosion and reworking of the high gravel deposits appears to have been a main source of gold in upper Anvil and Dexter Creeks.

Comment (Production): Production Notes = Production from the high-level gravels of the general area totaled about 100,000 ounces by 1903 (Collier and others, 1908). The high level gravels at Dexter were mostly worked out by 1906.

Comment (Geology): Geologic Description = The Dexter High Bench placer deposit is one of three similar deposits. The others are the Summit deposit (NM247) and the deposit at the head of Dry Creek (NM248). The Dexter high-level deposit includes the relatively low-grade auriferous gravel that mantles the divide between Nekula and Deer Gulches and extends southward onto the flanks of Dexter Peak and northward to Kings Mountain. It also includes two buried paystreaks. The northern paystreak extends southeasterly, approximately from the Madeline mine (NM239) to the Gold Hill drift mine (NM243). The southern paystreak extends southeasterly from Nekula Gulch (lower Mattie, NM240) to upper Deer Gulch. The paystreaks were exceptionally rich, and Collier and others (1908, p. 199) proposed that if water could be gotten to the high-level gravels outside the paystreaks then, 'all these deposits of gravel could be sluiced at a profit.' the lower Mattie in Nekula Gulch was the first discovery; it produced 90,000 dollars in gold in 1900, its first season (Collier and others, 1908, p. 201). The lower Mattie, and probably the Caribou Bill (NM238), developed the northwest end of the southern paystreak. According to Moffit (1913, p. 102-103), the southern paystreak was almost exposed in Nekula Gulch but was buried to a depth of 135 feet at Dexter Station. It was mined nearly continuously from Nekula Gulch to Deer Gulch. The northern paystreak was worked in the upper Mattie (NM239), Snowflake (NM241), Sugar (NM242), and Gold Hill (NM243) drift mines.? the presence in the Nome district of elevated benches that could contain gold was first pointed out by Schrader and Brooks (1900, p. 12, 16, and 20). The discovery of gold in the high-level gravel at Nekula Gulch followed this report. Some of the gold recovered in the Dexter deposits was crystalline; the gold also had quartz and calcite attached and was regarded as of local origin. One gold nugget having crystalline faces weighed more than 9 ounces (Collier and others, 1908, p. 204; Moffit, 1913, p. 105).? the origin of the high-level gravel deposits has been interpreted in various ways. Collier and others (1908, p. 198) regarded them as elevated remnants of deposits of an older drainage system ' . . which have been dissected and for the most part removed.' In recent years, the deposits have been interpreted as glacier-margin channels and spillways (Hopkins and others, 1960; David M. Hopkins, cited by Cobb, 1973 [B 1374], p. 83; Nelson and Hopkins, 1972). Granite boulders possibly of glacial origin, are in the deposits, but at Dexter the boulders are at the surface, not in the pay gravels (Moffit , 1913, p. 104). Collier and others (1908, p. 199) proposed that at least some of the boulders were ice-rafted during a period of submergence. The age and origin of the high-level gravels thus still seem in question. The richness of some of the placers suggests extensive reworking, proximity to lode sources, or both.? Bedrock underlying the Dexter high-level gravels possibly includes some marble and graphitic schist (Hummel, 1962 [MF 247]; Sainsbury, Hummel, and Hudson, 1972 [OFR 72-326]), rocks apparently younger than the 'mixed unit' of Till and Dumoulin (1994). Most of the saddle area, however, is underlain by feldspathic orthogneiss and metavolcanic schist (Bundtzen and others, 1994). The Dexter area was proposed as a center of silicic volcanism similar to that at Aurora Creek (NM140). The metavolcanic rocks could be the source of some of the gold in the placer deposits.

Comment (Deposit): Model Name = Alluvial placer Au (Cox and Singer, 1986; model 39a).

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References

Reference (Deposit): 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, The Geology of North America, DNAG, v. G-1, p. 141-152.

Reference (Deposit): Cobb, E.H., 1973, Placer deposits of Alaska: U.S. Geological Survey Bulletin 1374, 213 p.

Reference (Deposit): Moffit, F.H., 1913, Geology of the Nome and Grand Central quadrangles, Alaska: U.S. Geological Survey Bulletin 533, 140 p.

Reference (Deposit): Bundtzen, T.K., Reger, R.D., Laird, G.M., Pinney, D.S., Clautice, K.H., Liss, S.A., and Cruse, G.R., 1994, Progress report on the geology and mineral resources of the Nome mining district: Alaska Division of Geological and Geophysical Surveys, Public Data-File 94-39, 21 p., 2 sheets, scale 1:63,360.

Reference (Deposit): Hummel, C.L., 1962, Preliminary geologic map of the Nome C-1 quadrangle, Seward Peninsula, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-247, 1 sheet, scale 1:63,360.

Reference (Deposit): Cobb, E.H., 1978, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Nome quadrangle, Alaska: U.S. Geological Survey Open-File report 78-93, 213 p.

Reference (Deposit): Collier, A. J., Hess, F.L., Smith, P.S., and Brooks, A.H., 1908, The gold placers of parts of Seward Peninsula, Alaska, including the Nome, Council, Kougarok, Port Clarence, and Goodhope precincts: U.S. Geological Survey Bulletin 328, 343 p.

Reference (Deposit): Hopkins, D.M., MacNeil, F.S. and Leopold, E.B., 1960, The coastal plain at Nome, Alaska, A late Cenozoic type section for the Bering Sea region, in Chronology and climatology of the Quaternary: International Geological Congress, 21st, Copenhagen , Proceedings, Part 4, p. 46-57.

Reference (Deposit): Cobb, E.H., 1972, Metallic mineral resources map of the Nome quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-463, 2 sheets, scale 1:250,000.

Reference (Deposit): Schrader, F.C., and Brooks, A.H., 1900, Preliminary report on the Cape Nome gold region, Alaska: U.S. Geological Survey Special Publication, 56 p.

Reference (Deposit): Brooks, A.H., Richardson, G. B., and Collier, A. J., 1901, Reconnaissance in the Cape Nome and Norton Bay regions, Alaska, in 1900: U.S. Geological Survey Special Publication, p. 1-180.

Reference (Deposit): Sainsbury, C.L., Hummel, C.L., and Hudson, Travis, 1972, Reconnaissance geologic map of the Nome quadrangle, Seward Peninsula, Alaska: U.S. Geological Survey Open-File Report 72-326, 28 p., 1 sheet, scale 1:250,000.

Reference (Deposit): Nelson, C.H., and Hopkins, D.M., 1972, Sedimentary processes and distribution of particulate gold in the northern Bering Sea: U.S. Geological Survey Professional Paper 689, 27 p., 1 plate.

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