Miller Gulch Mine, Hot Springs Mining District, Yukon-Koyukuk Census Area, Alaska, USAi

Regional Level Types
Miller Gulch Mine	Mine
Hot Springs Mining District	Mining District
Yukon-Koyukuk Census Area	Census Area
Alaska	State
USA	Country

Location: The site of the Miller Gulch placer mine is at several cabins next to the creek at an elevation of about 500 feet, in the southwest quarter of section 24, T. 3 N., R. 17 W., of the Fairbanks Meridian. The site corresponds to location 27 of Cobb (1972).
Geology: The Miller Gulch mine is one of a group of cassiterite- and gold-bearing placer deposits known as the Tofty tin belt, a 12-mile-long area that trends east-northeast, between Roughtop Mountain to the north and Hot Springs Dome to the south (Thomas, 1957). Roughtop Mountain and Hot Springs Dome respectively are underlain by Cretaceous (K-Ar age date of 92 +/- 5 Ma) and Tertiary (K-Ar age date of 62 +/- 3 Ma) granitic plutons (Chapman and others, 1982). The plutons intrude and contact metamorphose Mesozoic marine sedimentary strata, which also are cut by diverse faults, including regional-scale, east-northeast-striking, thrust faults (Reifenstuhl and others, 1998). A carbonatite sill(?) is in the Triassic section of these strata and there are exposures of serpentinized, Cretaceous(?) mafic and ultramafic rock, mainly on Serpentine Ridge. The gold- and tin-bearing creeks flow normal to the trend of the tin belt. They head in the plutonic, metamorphic, and mafic/ultramafic rocks of Roughtop Mountain and Serpentine Ridge, which probably are the source(s) of some of the metalliferous minerals in the placer deposits. Concentrations of gold diminish toward the south, probably due to dispersion (Thomas, 1957). The Miller Gulch placer deposit lies on or just south of the trace of an east-northeast-striking thrust fault. High-grade placers were discovered on the United States Association claim in lower Miller Gulch in 1912. By 1914, there were three different mines operating in the area, employing 112 men. The depths to bedrock over the area of interest ranged from 85 to 120 feet over a lateral distance of only 500 feet, and to as little as 45 feet upstream. The upper portions of the creek appear to have multiple horizons of continuous pay streak (Eakin, 1915). The pay streaks reportedly were long and narrow compared to other Tofty area placers. The stream gravels consisted of angular cobbles of dark phyllite, graywacke, and metadiorite. Cobbles of brecciated quartz with tourmaline and cassiterite were also reported. Cobb (1973) reported that fine brown tourmaline replaced all micaceous layers in one piece of subangular phyllite, and dense tourmaline filled crosscutting fractures. Cassiterite tends to occur as well-rounded to subangular particles that range in size from microscopic to several inches across. The larger sizes often are accompanied by vein quartz and tourmaline, as well as by fragments of sedimentary country rock. The smaller sizes generally are free of impurities (Thomas,1957). A considerable amount of gold and silver, and cassiterite were mined from Miller Gulch. Through 1956, 17,576 ounces of gold, 2,668 ounces of silver, and 101,875 pounds of cassiterite concentrate had been recovered (Thomas, 1957). The average grade was about 0.17 ounce of gold per cubic yard. Channel sampling of tailings by the U.S. Bureau of Mines in 1954-56 showed that the efficiency of tin recovery from different workings varied dramatically. One tailings pile yielded 1.26 pounds of tin per cubic yard, while another yielded 0.29 pound of tin per cubic yard. Claims were staked at this site in 1953 and 1958 and there was mining in 1967 (Heiner and others, 1968). In addition to gold and cassiterite, other economic minerals were reported in the Miller Gulch-Idaho Gulch (TN086) area . Thomas (1957) and Barton (1962) reported that 0.2-7 percent niobium-bearing minerals were collected in pan concentrates, and Warner and others (1986) reported up to 0.6 percent CeO2 and 1.8 percent Nb2O5 in concentrates from churn drill cuttings. A calculation of possible reserves of niobium, based on this sampling and on earlier placer reserve estimates by Thomas and others (1948) and Wayland (1961), indicated that there may be 100,000 pounds of Nb2O5 reserves in the Tofty placers (Southworth, 1984). Moxham (1954) reported that the eU content of 2 [concentrate?] samples was 0.026 percent and 0.017 percent, and Cobb (1977) speculated that these values implied the presence of aeschynite, columbite, monazite, and zircon.
Workings: The workings in the Miller Gulch area were underground drift mines. They were developed around 1910-1915, after which activity waned. The tailings were reworked between 1917-20, and minor drift mining was reported in 1930-31 and 1937-40. Claims were staked at this site in 1953 and 1958 and there was mining in 1967 (Heiner and others, 1968).
Age: Quaternary.
Production: Thomas (1957) reported that 17,576 ounces of gold, 2,668 ounces of silver, and 101,875 pounds of cassiterite concentrate (averaging 60% tin), was recovered from Miller Gulch through 1956.

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

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Link to USGS - Alaska:	TN085

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References