|Quadrangle map, 1:250,000-scale||MH|
|Quadrangle map, 1:63,360-scale||A-2|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||Big Four Creek or Gulch, an informal name (not on the 1975 revision of the A-2 quadrangle), is on the south side of the Chistochina River about 1.6 miles northeast of the mouth of Slate Creek, which flows northwesterly into the Chistochina. The Big Four Creek placer mine is mainly in the E1/2NW1/4 section 14, T. 20 S., R. 15 E., Fairbanks Meridian. The location is plotted near the main site of mining, which is south of the 1966 terminus of Chistochina Glacier (Rose, 1967). Most mining has taken place between elevations of 4,300 and 4,600 feet. The location is accurate; it is approximately the same as locality 14 on figure 6 of Cobb (1979 [OFR 79-238]), locality 66 of MacKevett and Holloway (1977), and locality 8 in table 3 of Nokleberg and others (1991).|
Big Four Creek is a short, steep creek cut into Upper Triassic cumulate gabbro, argillite of the Mankomen or Eagle Creek Formations, and, at its head, the Tertiary 'round wash' conglomerate (Rose, 1967). Rose also mapped irregular breccia bodies of uncertain origin in upper Big Four Creek. The pay gravel in the creek is mainly derived from the 'round wash' conglomerate. The 'round wash' consists of gravel and partly indurated cobble and boulder 'stone' locally containing well-rounded to subangular boulders as much as a foot across. Clasts are mainly schist, greenstone, granite, and argillite (Yeend, 1981 [C 823-B]).
Gold is shotty to well-worn and is somewhat finer grained than the gold from the Miller Gulch placer (MH296; Moffit, 1912), a deposit also derived from the reworking of 'round wash' conglomerate. Gold is accompanied by some native copper and native mercury. Placer concentrates are mainly (65 to 70 percent) magnetite and 30 percent ilmenite and contain lesser amounts of chromite, pyrite, epidote, garnet, and zircon (Yeend, 1981 [C 823-B]). Small amounts of platinum-group metals (PGE) occur; iron-platinum alloy from the concentrates contained 83 percent platinum and 17 percent iron as determined by electron-microprobe analysis (Foley, 1992).The placer deposit was discovered in 1902, and mining commenced immediately (Mendenhall, 1903; Mendenhall and Schrader, 1903). Mining has continued intermittently to the present.
|Geologic map unit||(-144.823429892638, 63.1850050337006)|
|Mineral deposit model||Placer Au-PGE (Cox and Singer, 1986; model 39a).|
|Mineral deposit model number||39a|
|Age of mineralization||Tertiary to Holocene.|
|Alteration of deposit||The 'round wash' conglomerate is extensively altered to clay (Chapin, 1919).|
|Workings or exploration||Gold was discovered in Big Four Creek by 1902, and mining commenced immediately (Mendenhall, 1903; Mendenhall and Schrader, 1903). The placer deposit was worked on a small scale intermittently between 1903 and the present (Moffit, 1912, 1944; Yeend, 1981 [C 823-B]; Foley, 1992). The deposit itself is fairly small, and water has often been in short supply, minimizing production (Moffit, 1954). The creek has been mined by mechanized open-cut methods intermittently since the early 1950s (Foley, 1992).|
|Indication of production||Yes; small|
Chapin, Theodore, 1919, Platinum-bearing auriferous gravels of Chistochina River: U.S. Geological Survey Bulletin 692-C, p. 137-144.
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.
Foley, J.Y., 1992, Ophiolite and other ultramafic metallogenic provinces in Alaska (west of the 141th meridian): U.S. Geological Survey Open-File Report 92-20-B, 55 p.
Foley, J.Y., and Summers C.A., 1990, Source and bedrock distribution of gold and platinum-group metals in the Slate Creek area, northern Chistochina mining district, east-central Alaska: U.S. Bureau of Mines Open File Report 14-90, 49 p.
Mendenhall, W.C., 1903, The Chistochina gold field, Alaska, in Emmons, S.F., and Hayes, C.W., Contributions to economic geology, 1902: 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., 1 sheet.
Moffit, F.H., 1912, Headwater regions of Gulkana and Susitna Rivers, Alaska, with accounts of the Valdez Creek and Chistochina placer districts: 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.
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.
|Reporters||W.T. Ellis (Alaska Earth Sciences), C.C. Hawley (Hawley Resource Group), and W.J. Nokleberg (USGS)|
|Last report date||7/3/2003|