Twelvemile Creek Mine (includes forks of Twelvemile Creek; Potato Creek), Koyukuk Mining District, Yukon-Koyukuk Census Area, Alaska, USAi

Regional Level Types
Twelvemile Creek Mine (includes forks of Twelvemile Creek; Potato Creek)	Mine
Koyukuk Mining District	Mining District
Yukon-Koyukuk Census Area	Census Area
Alaska	State
USA	Country

Location: Twelvemile Creek is a large western tributary to the Middle Fork, Koyukuk River. The junction of Twelvemile Creek and the Middle Fork is about 6.5 miles southwest of Coldfoot. The locations of the placer gold deposits along Twelvemile Creek are not clearly defined. Placers apparently occur intermittently along the creek from a point beginning near its mouth, extend upstream along Twelvemile Creek, and then continues up the Upper Fork (probably called Middle Fork by Reed, 1938) for an undetermined distance. The coordinates are at the junction of Upper Fork and Twelvemile Creek.
Geology: Reed (1938) states that Twelvemile Creek contains placer deposits in the modern channel, in a deep channel, and in high bench channels. Reed's descriptions of mining and prospecting efforts suggest that the gold in the deposits is sporadically distributed. The depth to bedrock in the modern channel of Twelvemile Creek (in areas that are not coincident with the deep channel) is about 5 feet. The gold-bearing gravels on the lower parts of the modern channel are relatively fine with few boulders. Those on the upper parts contain more boulders. There are two high-bench channels, an upper one, called 'primary', and a lower one, called 'secondary'. The secondary bench is about 60 feet wide and 20 feet above the modern stream; it occurs only along the left limit of the Upper Fork (the Middle Fork of Reed, 1938). The primary bench is about 125 feet above the secondary. It is 600 feet wide, and lies along the left limit of lower Upper Fork and along Twelvemile Creek downstream as far as the Lower Fork (the North Fork of Reed, 1938). Below Lower Fork, high channels occur along the right limit of Twelvemile Creek at about the same level as the primary bench. An adit into the primary channel on the lower Upper Fork explored gravels containing gold values of $0.75 per cubic yard (gold at $35 per ounce). Although a deep channel is apparently present along Twelvemile Creek it isn't clear whether it contains any gold. Reed (1938) reported only one active mining operation in 1937, along lower Upper Fork (Middle Fork). The depth to bedrock at that location was 8 to 21 feet, and very fine, flat pieces of gold were distributed throughout the gravel. The values were about $0.35 per square foot of bedrock and the average fineness was 914. According to Reed (1938), several other tributaries of Twelvemile Creek, including West Fork (West Fork and South Fork join to form Twelvemile Creek), North Fork (probably the Lower Fork on modern topographic map), and Potato Creek (a small left limit tributary about a mile below Upper Fork) have been explored and/or mined with varying degrees of success. The bedrock in the Twelvemile Creek area is mainly graphitic and quartz schist (Reed, 1938) . Dillon and others (1986) mapped it as Mississippian to Triassic metagraywacke and phyllite, and upper Devonian, Hunt Fork schist. From about 1900 to 1910, the modern creek bed was mined by hand methods. Later mining included shafts, open cuts, and drifting (Reed, 1938) There was exploration drilling in 1934 and hydraulic mining in 1937 (Reed, 1938). Some exploration work was conducted on the south fork of Twelvemile Creek in 1986.
Workings: From about 1900 to 1910, the modern creek bed was mined by hand methods. Later mining included shafts, open cuts, and drifting (Reed, 1938) There was exploration drilling in 1934 and hydraulic mining in 1937 (Reed, 1938). Some exploration work was conducted on the south fork of Twelvemile Creek in 1986.
Age: Quaternary.
Production: Maddren (1913) reported a total production of $5,000 of gold (about 260 ounces), mostly in 1900 and 1901.

Commodities (Major) - Au
Development Status: Yes
Deposit Model: Placer Au (Cox and Singer, 1986; model 39a)

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Link to USGS - Alaska:	WI147

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References