Miller Gulch Mine, Chistochina District, Southeast Fairbanks Borough, Alaska, USA
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Geology: The lower part of Miller Gulch is incised in argillite of the Eagle Creek Formation of Pennsylvanian age (Richter and Dutro, 1975). This unit was previously mapped as Mankomen Formation of Permian age by Rose (1967). The upper part of the gulch is cut into a Tertiary conglomerate locally termed 'round wash' that uncomformably overlies the Eagle Creek Formation. Gabbro of Triassic (?) age crops out on the west side of Miller Gulch, and fault-controlled (?) breccia, which trends northwest, crops out near the head of Miller Gulch (Rose, 1967). The 'round wash' possibly is correlative with the Gakona Formation of Eocene (?) age. It has been deformed and dips about 20 degrees north. The conglomerate is largely composed of diorite and gabbro clasts with lesser granodiorite, slate, graywacke, white quartz, and peridotite. Finer grained facies of the 'round wash' are predominantly schist and slate with some white quartz (Rose, 1967). The unit has been altered or weathered in place, and cobbles are covered with a rind of clay or hematite; some of the cobbles are slickensided (Chapin, 1919; C.C. Hawley, unpublished field mapping, 1967). The conglomerate resembles white channel gravels of the Klondike district, Yukon Territory, which have been extensively altered since their deposition. Gold was discovered in Miller Gulch in about 1900, and mining commenced immediately. By 1903, the total production of the Chistochina district was about $365,000, of which about $175,000 came from Miller Gulch or nearby Slate Creek (Mendenhall and Schrader, 1903). Miller Gulch has been mined fairly continuously until the present. The placer deposits in the creek vary from about 5 feet wide near the head of Miller Gulch to 200 to 300 feet wide near the mouth of the gulch. The thickness of the gravel ranges from 4 to 8 feet; most of it is derived from argillite of the Eagle Creek Formation. Some of the gravel is composed of granitic material derived from the 'round wash' (Mendenhall, 1903; Mendenhall and Schrader, 1903). Gold-bearing benches are present irregularly along the creek on both walls of the canyon of Miller Gulch to as high as about 200 feet above the canyon floor. The gold in Miller Gulch is mainly flat, stained with iron and manganese, and only rarely found with remnant quartz. In the early days of the district, nuggets weighing as much as 1 ounce were common; some were as heavy as 4 ounces. The fineness of the gold varies from about 870 to 895 (Mendenhall and Schrader, 1903; Purington, 1905). Placer concentrates consist of cinnabar, native copper, and small nuggets of osmiridium with major magnetite and minor garnet. Cinnabar and native copper are probably derived locally because they occur in veinlets with chalcopyrite in the argillite bed rock (Walt Ashwill, oral communication, November 2001). The bulk of the gold in the creek appears to have been reconcentrated from the 'round wash' (Chapin, 1919; Rose, 1967; Cobb, 1973 [B 1374]; Yeend, 1981 [C 823-B, OFR 81-355]). Other sources include auriferous glacial deposits and mineralized veinlets in bedrock. Moffit (1912) proposed that most of the gold was derived from the older bedrock. The ultimate source of the 'round wash' is speculative; Rose (1967) proposed that most was from derived from an area north of the Denali Fault.
Workings: Miller Gulch was discovered in 1900. By 1903 about $175,000 (almost 8,500 fine ounces of gold) had been mined from Miller Gulch and nearby Slate Creek (Mendenhall and Schrader, 1903). The gravels along the gulch were mined extensively between 1903 and 1910 when mined slowed temporarily to allow exploitation of deposits in Slate Creek that could be covered by tailings from Miller Gulch (Moffit, 1909; Brooks, 1910; Moffit, 1912). In subsequent years production began on the higher level benches. Mining was reported in 1915 and 1916, although production in 1916 was limited by a shortage of water (Brooks, 1916). Mining activity increased in the 1930's; production was reported in 1932, 1938, and 1939 (Smith, 1934 [B 857-A], 1939 [B 917-A], 1941). The importance of the creek was recognized in summary papers by Moffit (1944, 1954). Mining on the creek was intermittently active in the 1960's (Rose, 1967). Activity increased again in the late 1970's to the mid-1980's as the price of gold rose.
Age: Eocene (?), Pleistocene, Holocene.
Alteration: The 'round wash' has been extensively weathered or altered in place; it was argillized and cobbles are coated with hematite or clay (Chapin, 1919).
Production: Total production of Miller Gulch is uncertain but considerable. According to Koschmann and Bergendahl (1968), the Chistochina district produced about 141,000 ounces of gold between 1900 and 1959. This figure is minimal because the records are incomplete between 1931 and 1945, a period of active mining. Miller Gulch and Slate Creek produced most of the gold mined in the Chistochina district, although no definite amount is assignable to Miller Gulch. It seems likely, however, that Miller Gulch has produced at least about 50,000 ounces of gold. Approximately 1 ounce of platinum group metals was produced for every 100 ounces of gold.
Reserves: No reserves have been published, but some gold still exists in bench deposits and unmined remnants of the creek gravels.
Commodities (Major) - Au; (Minor) - Ag, Cu, Hg, platinum group elements (PGE)
Development Status: Yes; medium
Deposit Model: Placer Au-PGE (Cox and Singer, 1986; model 39a).
7 entries listed. 5 valid minerals.
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Brooks, A.H., 1910, Mineral resources of Alaska, report on progress of investigations in 1909: U.S. Geological Survey Bulletin 442, 426 p. Chapin, Theodore, 1919, Platinum-bearing auriferous gravels of Chistochina River: U.S. Geological Survey Bulletin 692-C, p. 137-144. Cobb, E.H., 1972, Metallic mineral resource map of the Mount Hayes quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-414, 1 sheet, scale 1:250,000. Cobb, E.H., 1973, Placer deposits of Alaska: U.S. Geological Survey Bulletin 1374, 213 p. Cobb, E.H., 1979, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Mount Hayes quadrangle, Alaska: U.S. Geological Survey Open-File Report 79-238, 140 p. Koschmann, A.H., and Bergendahl, M.H., 1968, Principal gold producing districts of the United States: U.S. Geological Survey Professional Paper 610, 283 p. MacKevett, E.M., Jr., and Holloway, C.D., 1977, Map showing metalliferous and selected non-metalliferous mineral deposits in the eastern part of southern Alaska: U.S. Geological Survey Open-File Report 77-169-A, 99 p., 1 sheet, scale 1:1,000,000. Mendenhall, W.C., 1903, The Chistochina gold field, Alaska: U.S. Geological Survey Bulletin 213, p. 71-75. Mendenhall, W.C., and Schrader, F.C., 1903, The mineral resources of the Mount Wrangell district, Alaska: U.S. Geological Survey Professional Paper 15, 71 p. Moffit, F.H., 1909, Mining in the Kotsina-Chitina, Chistochina, and Valdez Creek regions: U.S. Geological Survey Bulletin 379-D, p. 153-160. Moffit, F.H., 1912, Headwater regions of Gulkana and Susitna Rivers, Alaska: U.S. Geological Survey Bulletin 498, 82 p. Moffit, F.H., 1944, Mining in the northern Copper River region, Alaska: U.S. Geological Survey Bulletin 943-B, p. 25-47. Moffit, F.H., 1954, Geology of the eastern part of the Alaska Range and adjacent area: U.S. Geological Survey Bulletin 989-D, p. 65-218. Nokleberg, W.J., Lange, I.M., Roback, R.C., Yeend, Warren, and Silva, S.R., 1991, Map showing locations of metalliferous lode and placer mineral occurrences, mineral deposits, prospects, and mines, Mount Hayes quadrangle, eastern Alaska Range, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-1996-C, 42 p., 1 sheet, scale 1:250,000. Purington, C.W., 1905, Methods and costs of gravel and placer mining in Alaska: U.S. Geological Survey Bulletin 263, 273 p. Richter, D.H., and Dutro, J.T., Jr., 1975, Revision of the type Mankomen Formation (Pennsylvanian and Permian), Eagle Creek area, eastern Alaska Range, Alaska: U.S. Geological Survey Bulletin 1395-B, p. B1-B25. Rose, A.W., 1967, Geology of the upper Chistochina River area, Mount Hayes quadrangle, Alaska: Alaska Division of Mines and Minerals Geologic Report 28, 41 p., 2 maps, scale 1:40,000. Smith, P.S., 1934, Mineral industry of Alaska in 1932: U.S. Geological Survey Bulletin 857-A, p. 1-91. Smith, P.S., 1939, Mineral industry of Alaska in 1938: U.S. Geological Survey Bulletin 917-A, p. 1-113. Smith, P.S., 1941, Mineral industry of Alaska in 1939: U.S. Geological Survey Bulletin 926-A, p. 1-106. Yeend, Warren, 1981, Placer gold deposits, Mount Hayes quadrangle, Alaska, IN Albert, N.R.D., and Hudson, Travis, eds., The United States Geological Survey in Alaska--Accomplishments during 1979: U.S. Geological Survey Circular 823-B, p. B68. Yeend, Warren, 1981, Placer gold deposits, Mt. Hayes quadrangle, Alaska, IN Silberman, M.L., Field, C.W., and Berry, A.L., eds., Proceedings of the symposium on mineral deposits of the Pacific Northwest: U.S. Geological Survey Open-File Report 81-355, p. 74-83.