Cooper Gulch (placer and M. Charles lode occurrence)

Mine, Inactive

Commodities and mineralogy

Main commodities Au
Ore minerals gold; limonite
Gangue minerals calcite

Geographic location

Quadrangle map, 1:250,000-scale NM
Latitude 64.556
Longitude -165.3805
Nearby scientific data Find additional scientific data near this location
Location and accuracy This site is in Cooper Gulch on the south side of Anvil Mountain. The site includes alluvial placer gold deposits in upper and lower Cooper Gulch and a calcite lode in upper Cooper Gulch (Cathcart, 1922, figure 18, location 1). The map location is about half way up the gulch from the inland margin of the coastal plain and just inside the north boundary of section 12, T. 11 S., R. 34 W., Kateel River Meridian. This is locality 103 of Cobb (1972 [MF 463], 1978 [OFR 78-93]).

Geologic setting

Geologic description

Upper Cooper Gulch was placer mined by rocker and hydraulic methods and produced a small amount of gold between 1900 and 1916 (Cobb, 1978 [OFR 78-93]). A small area near a bench where the gulch merges with the coastal plain apparently yielded good returns in gold (Moffit, 1913). Unconsolidated materials included 8 to 10 feet of low-grade gravel below 1 to 4 feet of overburden. Boulders in hydraulic tailings were mostly marble along with some greenstone and granite (Collier and others, 1908). Bedrock is mostly marble and schist that probably are of early Paleozoic protolith age (Hummel, 1962 [MF 247]; Till and Dumoulin, 1984; Bundtzen and others, 1994).
An ancestral Cooper Gulch may have been the source of gold on Fourth Beach (NM249) into shallow alluvial deposits on the coastal plain. Moffit (1913, p. 123-124) thought the lower Cooper Gulch deposit unusual enough to classify it as a 'gravel-plain placer'. The gold on lower Cooper Gulch mainly lay on clay streaks but also was distributed throughout the section. The deposit may have been a fan or delta from ancestral Cooper Gulch into the Third Beach sea.
The M. Charles lode was also reported from near the head of Cooper Gulch on the west side (Cathcart, 1922, figure 18, location 1). A short tunnel on the west bank of Cooper Gulch follows a fault zone about 4 feet wide containing brecciated schist replaced by ferruginous calcite; there is abundant limonite but no evidence of gold. Cathcart (1922) inferred the former existence of sulfide minerals from the limonite.
Geologic map unit (-165.383102638353, 64.5552347388106)
Mineral deposit model Alluvial placer Au (Cox and Singer, 1986; model 39a).
Mineral deposit model number 39a
Age of mineralization Quaternary.

Production and reserves

Workings or exploration One hydraulic pit was 100 by 300 feet in size in 1903 (Collier and others, 1908). An attempt was made to mine the lower Cooper Creek deposit by dredging (Moffit, 1913). Upper Cooper Gulch was mined by hand methods.
Indication of production Yes; small

References

MRDS Number A012910

References

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