Midnight Creek Mine, Ruby Mining District, Yukon-Koyukuk Census Area, Alaska, USAi

Regional Level Types
Midnight Creek Mine	Mine
Ruby Mining District	Mining District
Yukon-Koyukuk Census Area	Census Area
Alaska	State
USA	Country

Location: Midnight Creek is a southwest-flowing tributary of Long Creek. It is about 15 miles long. The coordinates given correspond to location 22 of Cobb (1972 [MF405]) and mark the approximate midpoint of tailings drawn on the Ruby (B-6) Quadrangle (USGS topographic map, 1952, minor revisions in 1972) in section 32, T. 13 S., R. 17 E of the Kateel River meridian. The location is accurate.
Geology: The bedrock underlying the head of Midnight Creek is Paleozoic phyllite and quartzite of the Ruby terrane (Puchner and others, 1998). The bedrock in the Midnight Creek valley is schist, slate, siliceous cherty rock, and greenstone (Eberlein and others, 1977). The ridge that Midnight Creek drains from is a Tertiary granitic body. The lower portion of the creek flows through Quaternary surficial deposits (Puchner and others, 1998). The gold in Midnight Creek is found under 14 to 150 feet of muck in gravel just above bedrock or on a false clay bedrock (Mertie and Harrington, 1916). The lode source for the placers in this area has not been found (Eberlein and others, 1977). The pay streak was 100 to 150 feet wide along the south side of the valley adjacent to the creek and was mined for nearly 2 miles along its length (Chapman and others, 1963). The gold is fine; there were only a few small nuggets (Mertie and Harrington, 1916). The fineness of the gold generally ranged from 883 to 885.5, but one shipment was only 857.5 parts gold per thousand (Chapman and others, 1963). The gold is accompanied by abundant cassiterite and rare scheelite (Eakin, 1914 [B578]; Chapin, 1919; Joesting, 1943). In 1911, gold was discovered in Midnight Creek (Maddren, 1912). Gravels at depths of 25 to 30 feet contained as much as $4.00 in gold (gold at $20.67 per ounce) per square foot of bedrock. There was nearly continuous mining along Midnight Creek from 1911 until about 1949 (Eberlein and others, 1977). In 1917, miners recovered 1,037 pounds of cassiterite concentrate containing 537 pounds of tin from 6,000 feet of bedrock and shipped it to Singapore for smeltering (Chapin, 1919). In 1940-42, mining averaged about $1.10 (about 0.03 ounces of gold) and 0.06 pounds of cassiterite per square yard of gravel (Chapman and others, 1963). During 1989 and 1990, Sphinx Mining Company (who became Sphinx America Company in 1990 (?)) recovered about $150,000 worth of tin in cassiterite (Jim Johnson, oral communication, 2000). There are no data on total gold production. Midnight Creek experienced nearly continuous mining between 1911 and 1990 (Bundtzen and others, 1990; Swainbank and others, 1991). In 1990, Midnight Creek was the largest operating placer mine in the Ruby district (Swainbank and others, 1991).
Workings: Midnight Creek experienced nearly continuous mining from 1911 to about 1990 (Eberlein and others, 1977; Swainbank and others, 1991).
Age: Quaternary.
Production: In 1911, gold was discovered in Midnight Creek (Maddren, 1912). Gravels at depths of 25 to 30 feet contained as much as $4.00 in gold (gold at $20.67 per ounce) per square foot of bedrock. In 1917, miners recovered 1,037 pounds of cassiterite concentrate from 6000 square feet of bedrock and shipped the ore Singapore (Chapman and others, 1963). In 1940-42, mining averaged about $1.10 of gold per cubic yard (gold at $35 per ounce), and about 7,320 pounds of cassiterite concentrate were recovered (Chapman and others, 1963). During this time mining averaged about $1.10 (about 0.03 ounces of gold) and 0.06 pounds of cassiterite per square yard of gravel (Chapman and others, 1963). During 1989 and 1990, Sphinx Mining Company (soon to be named Sphinx America Company(?) recovered about $150,000 worth of tin in cassiterite (Jim Johnson, oral communication, 2000).

Commodities (Major) - Au, Sn; (Minor) - Ag, W
Development Status: Yes; small
Deposit Model: Placer Au (Cox and Singer, 1986; model 39a).

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Link to USGS - Alaska:	RB019

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References