Lower Slate Creek Mines, Chistochina Mining District, Southeast Fairbanks Census Area, Alaska, USAi

Regional Level Types
Lower Slate Creek Mines	Group of Mines
Chistochina Mining District	Mining District
Southeast Fairbanks Census Area	Census Area
Alaska	State
USA	Country

Location: The placer mines in lower Slate Creek are mainly below Miller Gulch and above the broad flood plain of the Chistochina River. The approximate center of the mines is in the NE1/4NW1/4 section 22, T. 20 S., R. 15 E., Fairbanks Meridian. The mines correspond approximately to locality 16 on figure 6 of Cobb (1979 [OFR 79-238]) and locality 65 of MacKevett and Holloway (1977). The Slate Creek mine of Nokleberg and others (1991, locality 9, table 3) includes these mines and Miller Gulch (MH296).
Geology: Extensive mining occurred along this lower Slate Creek location in 1941 and several previous years (Moffit, 1944). Slate Creek is aligned along a graben filled with Gakona Formation of possible Eocene age. In the lower creek, the fault on the north side of the graben is largely buried by Holocene alluvium and glacial-fluvial benches of Pleistocene age; the general distribution of rock and alluvial units is shown by Rose (1967). The placer deposits of lower Slate Creek are complex (Chapin, 1919; Yeend, 1981 [C 823-B, OFR 81-355]). The ultimate source of most of the placer gold appears to be the Tertiary 'round wash' conglomerate exposed in Miller Gulch, the main south-flowing tributary of Slate Creek. A lesser amount of gold came from veins in bedrock exposed in Miller Gulch and other upstream sources. Gold was reconcentrated in high bench deposits during multiple stages of Pleistocene glaciation as Slate Creek was dammed by glaciers in the Chistochina River valley. Gold from 'round wash', glacial, and bedrock sources was also reconcentrated in rich shallow deposits of late Pleistocene and Holocene age in alluvial gravels of Slate Creek (Chapin, 1919). Rose proposed that a buried auriferous channel could lie below the high bench deposits along the north boundary fault of the Slate Creek graben. The gold in Slate Creek is generally fine grained and fairly smooth. Its fineness is about 894 (Purington, 1905). The gold is generally finer grained than the gold mined in Miller Gulch. Placer concentrates are mainly magnetite and garnet; they contain some pyrite, cinnabar, and platinum group metals (PGE). The concentrate contains about 1 part of platinum group metal per 100 parts of gold. In the early years of the district, shallow gravels along Slate Creek were mined by shovel-in methods; rich gravels were mined in Slate Creek just below Miller Gulch. In 1917, Slate Creek was mined by a fairly large scale hydraulic operation. Total production in that year was estimated at $100,000, mostly from large cuts on Slate Creek. Some of the pay was from virgin ground; the rest was from ground that had been mined earlier by hand (Chapin, 1919). In 1941 and several preceding years mining was mainly from benches 50 to 60 feet above the north side of the creek near its mouth. Most of the bench gold was recovered from loose, well-washed gravel contained in a tight brownish wash (Moffit, 1944). Extensive mining on lower Slate Creek ceased by about 1962 (Cobb, 1979 [OFR 79-238]).
Workings: Placer gold was discovered in Slate Creek in 1900 by Coles, Jacobson, Kramer, and Levell (Mendenhall and Schrader, 1903). Only a few areas of the creek were rich enough to be mined by hand; they included the first one or two claims below Miller Gulch and a bench opposite Miller Gulch, where the paystreak probably was an ancient fan from Miller Gulch (Mendenhall and Schrader, 1903). Small-scale mining took place on the creek in 1908 (Moffit, 1909), 1909 (Brooks, 1910), probably 1910, and in 1911 (Brooks, 1912). Preparation for large-scale mining began in 1912 (Brooks, 1913) with mining reported for 1914 (Brooks, 1915), 1915, (Brooks, 1916), and 1916 (Smith, 1917). The preparations for large-scale hydraulic operations were completed by 1917 when about 4,800 ounces of fine gold were produced mainly from Slate Creek on its left limit (south side) (Chapin, 1919). Platinum constituted somewhat more than 1 percent of the volume of gold recovered in 1917. Mining continued almost yearly into the 1930's, and some platinum was recovered in many years (Martin, 1920; Brooks and Martin, 1921; Brooks, 1921; Brooks, 1923; Brooks and Capps, 1924; Brooks, 1925; Moffit, 1927). Mining continued between 1926 and 1933 (Smith, 1929; Smith, 1930 [B 810-A, B 813-A]; Smith, 1932; Smith, 1933 [B 836-A]; Smith,1933 [B 844-A]; Smith, 1934 [B 857-A]; Smith, 1934 [B 864-A]. In 1934, probably reflecting the increased price of gold to $35 per ounce, extensive preparation was done for a large operation. The development work was destroyed by a flood in August 1934 (Smith, 1936); in 1935 most of the work was rehabilitation to repair flood damage (Moffit, 1937; Smith, 1937). Mining recommenced in 1936, and there was at least some mining through 1941 (Smith, 1938; Smith, 1939 [B 917-A]; Smith, 1942 [ B 933-A]). According to Moffit (1944), much of the last production was from an elevated bench on the north side of Slate Creek near its mouth. Mining of uncertain extent took place after World War II but essentially ceased by 1962.
Age: Tertiary to Holocene.
Production: Lower Slate Creek was one of the two main sources of placer gold in the Chistochina district; the other was Miller Gulch. Lower Slate Creek probably has produced at least 50,000 ounces of gold.
Reserves: A placer gold resource was postulated by Rose (1967); a channel, more or less along the north fault of the Slate Creek graben, may be buried by weakly auriferous bench deposits.

Commodities (Major) - Au; (Minor) - Ag, Hg, platinum group elements (PGE)
Development Status: Yes
Deposit Model: Placer Au-PGE, glacio-fluvial (Cox and Singer, 1986; model 39a).

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Link to USGS - Alaska:	MH295

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References