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Nixon Fork; Mespelt; Crystal; Garnet; High Grade; Mespelt Inclined Shaft; Recreation; Keen; Twin Shafts; Mespelt Main Shaft; Garnet Trench; Parsons And Strand; Southern Cross Mine, McGrath District, Yukon-Koyukuk Borough, Alaska, USA

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Latitude & Longitude (WGS84): 63° 14' 20'' North , 154° 45' 50'' West
Latitude & Longitude (decimal): 63.23889,-154.76389


See Nixon Fork Crystal (MD061) and Whalen Glory Hole (MD071) mines.
Location: The Nixon Fork Mine is located at an elevation of approximately 1,400 feet (426 m) in Section 13, T. 26 S., R. 21 E., of the Kateel River Meridian. Location is precisely known as it is actively being mined. Reporter visited the site in 1996 and 1997.
Geology: The Nixon Fork gold mine is a series of small, rich contact metamorphic deposits in limestone within 100-150 m of a composite monzonite stock. The monzonite phase has yielded a 40K-40Ar biotite age of 68.0 Ma (Moll and others, 1981; Bundtzen and Miller, 1997). Younger (?) quartz porphyry bodies cut the monzonite along structures and form a distinctive border pahase of the monzonite pluton. The mineable ore bodies are copper-gold skarns that occur in irregular, structurally controlled zones in carbonate host rock with maximum dimensions of 66 feet (20 meters) along strike, 230 feet (70 meters) along rake, and are up to 16 feet (5 meters) wide (Freeman, 1996). Gangue minerals in the skarn zones include abundant garnet, diopside, epidote, and apatite. The ore bodies are lenticular, and are without well defined walls; some are probably hydrothermal replacement bodies that postdate skarn formation. Most metallic values and skarn occur as exoskarn 10 to 30 feet into the marble front; minor metallic bearing endoskarns occur within sattelite bodies of monzonite; however, most of this mineralization is not ore grade. Ore consists of auriferous chalcopyrite and pyrite with subordinate bornite and a little chalcocite that has been partly to thoroughly oxidized to a mixture of free gold and secondary copper minerals. The exception to this extensive 'supergene' oxidation process is the Crystal and Garnet Lodes (MD061), which consist mainly of unoxidized chalcopyrite, pyrite and bornite in a calcite, siderite and zeolite gangue. Gold fineness from the various Nixon Fork ore bodies range from 715 to 794 with silver being the major impurity. The Nixon Fork mine is renowned for it's high grade gold ores. Mertie (1936) and Herreid (1966) report assay values from both surface and underground workings of up to 24.34 ounces/ton gold, 17.26 ounces/ton silver, 11.69 percent copper, and 1.40 percent bismuth. From 1920 to 1997, the mine has produced (from all operators) 119,956 ounces (3,730 kg) of gold, 19,566 (608 kg) ounces of silver, 1,235,443 pounds (560,396 kg) of copper, from about 99,765 tons (90,506 tonnes) of ore. The silver and copper production figures are incomplete and considered conservative.
Workings: Exploration and development took place intermittently from 1920 to 1961. After a hiatus of about 25 years, activities resumed in 1984 when Battle Mountain Mining Company leased claims from Ted Almasy and Margaret Mespelt, the owners. In 1989, Central Alaska Gold Company took over the leases and by 1994, had defined 91,200 tons (85,348 tonnes) of ore in several high grade bodies grading 1.42 ounces/ton (48.2 grams/tonne) gold and about 2.00 percent copper. Nevada Consolidated Goldfields resumed production in October, 1995 after a production hiatus of 34 years. (Bundtzen and others, 1996). The Nixon Fork mine has been mined from at least 8 shafts with extensive branching levels and from a few pits and trenches; deepest mining was at 460-ft (140 m) level of garnet shaft in 1961 (Herreid, 1966). Some references report workings as deep as 600 ft below surface. Most shafts are about 100 ft (30 m) deep, with 2-3 levels; this includes two inclined shafts driven in early 1930's. Currently (1998) the mine is being worked through a spiral decline. The ore bodies currently being exploited are steeply inclined, structurally controlled chimneys. Maximum assays of 24.34 ounces/ton gold, 17.26 ounces/ton silver, 11.69 percent copper, and 1.4 percent bismuth have been reported in the literature (Mertie, 1936).
Age: Age is probably Late Cretaceous, based on isotopic age of monzonite (Moll and others, 1981).
Alteration: Oxidation of sulfides probably resulted in some supergene enrichment of gold values
Production: Lode deposits were soon discovered in the area after the 1917 discovery of placer gold in the Hidden Creek basin. In 1920, T.P.Aitken produced the first ore--about 370 tons (335 tonnes). In 1921, the Treadwell-Yukon Mining Company, based in Juneau, Alaska, optioned the property from Aitken and mined for four years and milled 6,922 tons (6,280 tonnes) of ore. In 1925, the property reverted to owner E.M. Whalen, who produced ore on a fairly continuous basis until 1942. The property produced intermittently for six seasons from 1946 to 1961. Total production from 1920 to 1961 is estimated to be 36,016 ounces (933 kg) gold, and 1,836 ounces (57 kg) silver from 20,200 tons (18,325 tonnes) of ore. Prior to World War II, copper production (as a byproduct) was not accurately recorded; smelter returns that report a byproduct of copper are available for five operating years. In October, 1995, Nevada Consolidated Goldfields resumed production of the Nixon Fork Mine and through the end of 1997, produced 83,940 ounces 2,610 kg) gold, 17,730 ounces (551 kg) silver, and 1,194,000 pounds (541,598 kg) copper from 79,565 tons (72,180 tonnes) of ore. From 1920 to the end of 1997, the Nixon Fork Mine has been in production for 30 seasons, and produced 119,956 ounces (3,730 kg) gold, 19,566 ounces (608 kg) silver, and 1,235,443 pounds (560,396 kg) of copper from 99,765 tons (90,506 tonnes) of ore (production data from all previous operations was complied by the reporter). Silver and copper production figures are incomplete; hence totals for these latter metals are considered conservative. Mineral production data for the Nixon Fork Mineis not yet available for 1998.
Reserves: As of late 1997, exploration has replaced most of the ore mined from 1995 to 1997. In December, 1997, reserves stood at about 85,000 tons (77,112 tonnes) grading approximately 1.2 ounces/ton (41.1 grams/tonne) gold and undisclosed copper and silver (Swainbank and others, 1997).

Commodities (Major) - Ag, Au, Cu; (Minor) - Bi, Th, U, W
Development Status: Yes; medium
Deposit Model: Copper-gold skarn (Cox and Singer, 1986; model no. 18b)

Mineral List


15 valid minerals.

Regional Geology

This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.

Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org

Maastrichtian - Tertiary
66 Ma
Granodiorite to quartz monzodiorite

Age: Paleocene (66 Ma)

Description: Includes monzonite, quartz monzonite, quartz monzodiorite, and monzodiorite. Subordinate monzogabbro and gabbro

Lithology: Igneous

Reference: Wilson, F.H., Hults, C.P., Mull, C.G, and Karl, S.M. (compilers). Geologic map of Alaska. doi: 10.3133/sim3340. U.S. Geological Survey Scientific Investigations Map 3340, pamphlet 196. [21]

Ordovician
443.8 - 485.4 Ma
Sedimentary; Carbonate

Age: Ordovician (443.8 - 485.4 Ma)

Description: Interior western Alaska, Medfra-Kantishna region

Comments: Orogen, magmatic arc/suite; Wilson & Hults, unpublished compilation, 2007-08

Lithology: Limestone, dolostone, shale, evaporites, chalk; carbonate reefs or metamorphosed equivalent

Reference: J.C. Harrison, M.R. St-Onge, O.V. Petrov, S.I. Strelnikov, B.G. Lopatin, F.H. Wilson, S. Tella, D. Paul, T. Lynds, S.P. Shokalsky, C.K. Hults, S. Bergman, H.F. Jepsen, and A. Solli. Geological map of the Arctic. doi:10.4095/287868. Geological Survey of Canada Map 2159A. [2]

Data and map coding provided by Macrostrat.org, used under Creative Commons Attribution 4.0 License



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References

Bundtzen, T.K., and Miller, M.L., 1997, Precious metals associated with Late Cretaceous-early Tertiary igneous rocks of southwestern Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 242-286. Bundtzen, T.K., Swainbank, R.C., Clough, A.H., Henning, M.W., and Charlie, K.M., 1996, Alaska's mineral industry, 1995: Alaska Division of Geological and Geophysical Surveys Special Report 50, 72 p. Bundtzen, T.K., Swainbank, R.C., Clough, A.H., Henning, M.W., and Hansen, E.W., 1994, Alaska's mineral industry, 1993: Alaska Division of Geological and Geophysical Surveys Special Report 48, 84 p. Freeman, Larry, 1996, A progress report on the Nixon Fork underground gold mine, McGrath-McKinley district, Alaska [abs]: Abstract preprint of the 15th Biennial Conference on Alaskan Mining, Alaska Miners Association, Fairbanks, Alaska, p. 36. Herreid, G.H., 1966, Geology and geochemistry of the Nixon Fork area, Medfra quadrangle, Alaska: Alaska Division of Mines and Minerals Geologic Report 22, 34 p., 1 sheet, scale 1:40,000. King, H.D., Risoli, D.A., Cooley, E.F., O'Leary, R.M., Speckman, W.A., Speisman, D.L., and Galland, D.W., 1980, Final results and statistical summary of analyses of geochemical samples from the Medfra quadrangle, Alaska: U.S. Geological Survey Open-File Report 80-811F, 134 pages. Mertie, J.B., Jr., 1936, Mineral deposits of the Ruby-Kuskokwim region, Alaska: U.S. Geological Survey Bulletin 864-C, p. 115-245. Newberry, R.J., Allegro, G.L., Cutler, S.E., Hagen-Levelle, D.D., Adams, D.D., Nicholson, L.C., Weglarz, T.B., Bakke, A.A., Clautice, K.H., Coulter, G.A., Ford, M.J., Myers, G.L., and Szumigala, D.J., 1997, Skarn deposits of Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 355-395. Patton, W.W. Jr., Moll, E.J., Dutro, J.T., Jr., Silberman, M.L., and Chapman, R.M., 1980, Preliminary geologic map of the Medfra quadrangle, Alaska: U.S. Geological Survey Open-File Report 80-811, one sheet at 1:250,000 scale. Swainbank, R.C., Bundtzen, T. K., Clough A.H., and Henning, M.W., 1997, Alaska's mineral industry 1996: Alaska Division of Geological and Geophysical Surveys Special Report 51, 68 p. Williams J.A., 1961, Report for the year 1960 of the Division of Mines and Minerals: Alaska Department of Natural Resources Special Report, 88 pages.

 
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