Unnamed high-bench deposit (Dexter Creek-Dry Creek divide)

Mine, Inactive

Commodities and mineralogy

Main commodities Au
Ore minerals gold

Geographic location

Quadrangle map, 1:250,000-scale NM
Quadrangle map, 1:63,360-scale C-1
Latitude 64.5675
Longitude -165.3429
Nearby scientific data Find additional scientific data near this location
Location and accuracy This record describes high-level, auriferous gravel deposits on the divide between Dry Creek (NM249) and Wet Gulch, a north-flowing headwater tributary to Dexter Creek (NM303). It is at a surface elevation of about 575 feet and 4,500 feet northeast of the summit of Anvil Mountain in the NE1/4 section 6, T. 11 S., R. 33 W., Kateel River Meridian. It is approximately the same location as locality 125 of Cobb (1972 [MF 463]). The location is accurate to within about 500 feet.

Geologic setting

Geologic description

Auriferous high-level gravels on the Dry Creek-Dexter Creek divide are one of three closely related ancient placer deposits; the other two are at Summit (NM247) and Dexter Station (NM246). The main deposit on the Dry Creek-Dexter Creek divide appears to have been within a nearly north-south, gently incised channel in schist bedrock. It was developed by a series of shafts for a distance of about 2,000 feet. Pay extended up the flanks of the channel, where it was successfully mined (Collier and others, 1908, p. 208-209), although the flank deposits were not as rich as the deposits near the base of the channel. Near the divide, the gravel section was approximately 72 feet thick, consisting, from the top down, of 16 feet of muck and slide rock, 12 feet of somewhat auriferous washed gravel, 2 feet of sandy soil, 22 feet of soil, peat, and slide rock, and a pay section of 10 feet of stream gravel on decomposed schist bedrock (Collier and others, 1908, p. 208). Most of the pay was within 2 to 3.5 feet of bedrock and consisted mostly of sand containing well-rounded pebbles of schist, vein quartz, and marble. Gold was fairly coarse and well rounded. Much of the gravel was thawed and could be worked year-round from shallow timbered shafts. The pay streak contained from about 6 to 12 dollars in gold per cubic yard (gold at 20.67 dollars per ounce). Toward Dry Creek, the pay streak had poorly defined rims, and bedrock generally had a gentle slope to the north.
These ancient gold deposits may be in stream channels of former drainage systems (Collier and others, 1908) or in ice-marginal drainages (Hopkins and others, 1960; Cobb, 1973 [B 1374, p. 83]; Nelson and Hopkins, 1972). The presence of erratic granite boulders and other exotic rock types suggests a glacial origin, but the exotic clasts are commonly in near-surface materials and not distributed throughout the high-level gravels (Moffit, 1913). The origin of these gravels thus still seems in question. The richness of some of the placers suggests extensive reworking, proximity to lode sources, or both.
Bedrock is mostly schist, probably of early Paleozoic protolith age (Hummel, 1962 [MF 247]; Sainsbury, Hummel, and Hudson, 1972 [OFR 72-326]; Till and Dumoulin, 1994; Bundzten and others, 1994). Bedrock under the divide belongs to the porphyroclastic micaceous graphitic schist unit of Bundtzen and others (1994). Upper Dry Creek is underlain by felsic schist, possibly in fault contact with the porphyroclastic unit.
Geologic map unit (-165.345505590129, 64.5667360162664)
Mineral deposit model Alluvial placer Au; buried high-level placer deposits (Cox and Singer, 1986; model 39a).
Mineral deposit model number 39a
Age of mineralization Quaternary or possibly late Tertiary.

Production and reserves

Workings or exploration Most of the area was mined by drifting from shafts between 1902 and 1906. Deposits in upper Dry Creek were worked from the surface or from shallow shafts.
Indication of production Yes

References

MRDS Number 10308004

References

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