Dexter High Bench

Mine, Probably inactive

Commodities and mineralogy

Main commodities Au
Other commodities Ag
Ore minerals gold

Geographic location

Quadrangle map, 1:250,000-scale NM
Quadrangle map, 1:63,360-scale C-1
Latitude 64.5866
Longitude -165.3527
Nearby scientific data Find additional scientific data near this location
Location and accuracy This record describes a complex, high-level gold placer deposit centered on the divide at the head of Deer Gulch. Other shaft mines in the Dexter divide area are described in records NM238-243. The map location is at an elevation of about 550 feet in the SW1/4 section 30, T. 10 S., R. 33 W., Kateel River Meridian. This location is included in locality 117 of Cobb (1972 [MF 463], 1978 [OFR 78-93]).

Geologic setting

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 pay streaks. The northern pay streak extends southeasterly, approximately from the Madeline mine (NM239) to the Gold Hill drift mine (NM243). The southern pay streak extends southeasterly from Nekula Gulch (lower Mattie, NM240) to upper Deer Gulch. The pay streaks were exceptionally rich, and Collier and others (1908, p. 199) proposed that if water could be gotten to the high-level gravels outside the pay streaks 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 pay streak. According to Moffit (1913, p. 102-103), the southern pay streak 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 pay streak 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.
Geologic map unit (-165.355307740786, 64.5858361355092)
Mineral deposit model Alluvial placer Au (Cox and Singer, 1986; model 39a).
Mineral deposit model number 39a
Age of mineralization Quaternary, but possibly late Tertiary.

Production and reserves

Workings or 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 feet by 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.
Indication of production Yes
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.

References

MRDS Number A012946

References

Brooks, A.H., Richardson, G.B., Collier, A.J., and W.C. Mendenhall, 1901, A reconnaissance in the Cape Nome and adjacent gold fields of Seward Peninsula, Alaska, in 1900: U.S. Geological Survey Special Publication, p. 1-185, maps.
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.
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, DNAG, The Geology of North America, v. G-1, p. 141-152.
Reporters C.C. Hawley and Travis L. Hudson
Last report date 7/10/2000