Chicken Mountain Prospect, Iditarod District, Yukon-Koyukuk Borough, Alaska, USA
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Geology: The flat cryoplanation surface covering the south-facing slopes of Chicken Mountain is underlain by a crudely north-south-oriented, irregularly defined zone of thin, stockwork-like auriferous quartz veins and veinlets that cut the Chicken Mountain pluton (Bundtzen and others, 1992; Miller and Bundtzen, 1994; Bundtzen and Miller, 1997; Miller, Bundtzen, and Gray, 2005). The veins are in syenite, monzonite, and quartz monzonite in the cupola of the Chicken Mountain pluton beneath a roof pendant of thermally altered andesite and basalt. Earlier alkali gabbro and monzodiorite intrusive are present, but do not appear to host the auriferous mineralization. The Chicken Mountain pluton has been radiometrically dated at 68.7-70.9 Ma (Bundtzen and others, 1992). North of Chicken Mountain, auriferous northeast-trending quartz veinlets are present in hornfels derived from andesite that caps a monzonite phase of the pluton. This northern mineralized area has been referred to as the Golden Apex Zone (see Ventures Resources, Inc. website at http://www.venturesresource.com). The quartz veinlets in the intrusive rocks contain up to 5 percent of ore minerals including stibnite, cinnabar, arsenopyrite, chalcopyrite, ilmenorutile, molybdenite, silver-bearing sulfosalts, arsenian-pyrite, and free gold. Dolomite and ankerite breccias were formed at the same time as sulfide deposition. Bundtzen and others (1992) proposed a model of a progressive mesothermal-to- epithermal hydrothermal mineralization associated with a vertical temperature zonation. Epithermal gold-antimony-mercury mineralization crosscut older mesothermal copper-molybdenum, arsenic-copper, and tantalum-tungsten zones (Bundtzen and others, 1992). Surface and drill data suggest that the mineralization south of the summit of Chicken Mountain is at least 1,000 feet by 2,500 feet in size and extends to a depth of at least 800 feet. Based on a drill program from 1987 to 1989, Victor Hollister (oral communication, 1992) estimated that the Chicken Mountain lode contained 16.0 million tonnes of material with 0.04 ounces of gold per ton, 1.3 ounces of silver per ton, and substantial quantities of copper, molybdenum, and antimony. Beginning in 1997, Ventures Resources, Inc. initiated a core drilling program on the Chicken Mountain lode, and as well carried out soil and rock chip survey throughout the district. High grade gold mineralization was found in drill intercepts on Chicken Mountain. Intercepts include 4.6 feet with 6.18 ounces of gold per ton and 4.9 feet with 2.9 ounces of gold per ton. Their soil sampling program indicated that an area about 12,500 feet by 2,2500 feet in size has gold values that ranged from 100 to more than 1,000 parts per billion (ppb) gold. Samples from the Golden Apex zone in the north mineralized area contained up to 0.85 ounce of gold per ton (Ventures Resources, Inc.; http://www.venturesresource.com).
Workings: Lode mineralization on Chicken Mountain has been known for many years (Maddren, 1911; Mertie and Harrington 1916; Mertie; 1936). In the 1960s, the U.S. Bureau of Mines trenched parts of the deposit and conducted an auger drilling program in the soils and regolith above the bedrock (Maloney, 1962; Kimball, 1969). In 1975, Resource Associates of Alaska collected additional soil samples and drilled a few shallow holes (Ed Chipp, oral communication, 1985). The U.S. Geological Survey and the Alaska Division of Geological Surveys investigated the area from 1984 to 1988. Bull (1988) conducted trace element studies of the area in 1984 and 1985. From 1987 to 1990, Fairbanks Gold Mining Inc. and Galactic Resources, Inc. did some trenching and drilled seven holes that totaled about 5,000 feet; the results of some of their work is summarized in Bundtzen and others (1992). In 1997, Ventures Resources, Inc. initiated a core drilling program on the Chicken Mountain lode and did soil and rock chip surveys throughout the district.
Age: Unknown; the mineralization is possibly contemporaneous with the emplacement of the Chicken Mountain pluton that has been dated at 68.7 to 70.9 Ma (Bundtzen and others, 1992).
Alteration: Carbonate alteration with ankerite and dolomite in the veins; potassic alteration in the granitic rocks.
Production: None recorded.
Reserves: Based on a drill program from 1987 to 1989, Victor Hollister (oral communication, 1992) estimated that the Chicken Mountain lode contained 16.0 million tonnes of material with 0.04 ounces of gold per ton, 1.3 ounces of silver per ton, and substantial quantities of copper, molybdenum, and antimony. This estimate is probably conservative.
Commodities (Major) - Au; (Minor) - Ag, As, Bi, Cu, Hg, Mo, Nb, Sb, Ta, W
Development Status: None
Deposit Model: Porphyry Cu-Au (Cox and Singer, 1986; model 20c).
11 entries listed. 9 valid minerals.
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Bull, K.F., 1988, Genesis of the Golden Horn and related mineralization in the Flat Creek area, Alaska: Fairbanks, University of Alaska M.Sc. thesis, 300 p. 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., Cox, B.C., and Veach, N.C., 1987, Heavy mineral provenance studies in the Iditarod and Innoko districts, western Alaska: Process Mineralogy VII, The Metallurgical Society, p. 221-246. Bundtzen, T.K., Miller, M.L., Laird, G.M., and Bull, K.F., 1992, Geology and mineral resources of Iditarod mining district, Iditarod B-4 and eastern B-5 quadrangles, southwestern Alaska: Alaska Division of Geological and Geophysical Surveys Professional Report 97, 46 p., 2 sheets, scale 1:63,360. Kimball, A.L., 1969, Reconnaissance sampling of decomposed monzonite for gold near Flat, Alaska: U.S. Bureau of Mines Open File Report 6-69, 39 p. Maddren, A.G., 1911, Gold placer mining developments in the Innoko-Iditarod region: U.S. Geological Survey Bulletin 480-I, p. 236-270. Maloney, R.P., 1962, Trenching and sampling of the Rhyolite mercury prospect, Kuskokwim River basin, Alaska: U.S. Bureau of Mines Report of Investigations 6141, 43 p. Mertie, J.B., Jr., 1936, Mineral deposits of the Ruby-Kuskokwim region, Alaska: U.S. Geological Survey Bulletin 864-C, p. 115-245. Mertie, J.B., Jr., and Harrington, G.L., 1916, Mineral resources of the Ruby-Kuskokwim region, in Brooks, A.H., and others, Mineral Resources of Alaska, Report on Progress of Investigations in 1915: U.S. Geological Survey Bulletin 642-H, p. 223-266. Miller, M.L., and Bundtzen, T.K., 1994, Generalized geologic map of the Iditarod quadrangle, Alaska showing potassium-argon, major oxide, trace element, fossil, paleocurrent, and archeological sample localities: U.S. Geological Survey Miscellaneous Field Studies Map MF-2219-A, 48 pages; 1 sheet, scale 1:250,000. Miller, M.L., Bundtzen, T.K., and Gray, J.E., 2005, Mineral resource assessment of the Iditarod quadrangle, west-central Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-2219-B, scale 1:250,000, pamphlet.