Dyckman Occurrence, McGrath District, Yukon-Koyukuk Borough, Alaska, USA
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Geology: The Dyckman occurrence consists of disseminated arsenopyrite in an intensively altered, rhyolite volcanic (?) breccia. Extensive clay alteration has completely altered all feldspar minerals. The alteration zone was traceable for nearly 500 feet (152 m) along strike. The width of the zone is unknown. The mineral occurrence is inferred to be Cretaceous, based on isotopic age of host rhyolite (Moll and others, 1981). Two grab samples contained 350 ppm zinc and 234 ppm arsenic (Clautice and others, 1993). One sample contained 9 ppb gold (Clautice and others, 1993). DiMarchi and others (1992) report values of 1,630 ppm molybdenum and 574 ppm arsenic from limonitically stained zones in rhyolitic breccia on Dyckman Mountain.
Workings: Two grab samples contained 350 ppm zinc and 234 ppm arsenic (Clautice and others, 1993). One sample contained 9 ppb gold (Clautice and others, 1993). DiMarchi and others (1992) report values of 1,630 ppm molybdenum and 574 ppm arsenic from limonitically stained zones in rhyolitic breccia on Dyckman Mountain.
Age: Inferred to be Cretaceous, based on isotopic age of host rhyolite (Moll and others, 1981).
Alteration: Intensive clay alteration of feldspars; chalcedonic replacements in rhyolitic breccias.
Reserves: None.
Commodities (Major) - As, Mo, Zn; (Minor) - Au
Development Status: No
Mineral List
3 entries listed. 3 valid minerals.
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References
Clautice, K.H., Bowman, N.D., Clough, J.G., Gilbert, W.G., Kline, J.T., Smith, T.E., and Blodgett, R.B., 1993, Land selection Unit 8 (Kantishna River, Ruby, and Medfra quadrangles); References, lead isotope, geochemical and major oxide data: Alaska Division of Geological and Geophysical Surveys, 42 p., 1 sheet, scale 1:250,000. DiMarchi, J.J., Weglarz, T.B., Freeman, L.K., Nicholson, L.C., and Barker, J.C., 1992, Annual Report for 1992--Doyon Option Lands, Block 10: ASA Inc. Report, 121 p. (Report held by Doyon, Limited, Fairbanks, Alaska.) Moll, E.J., Silberman, M.L., and Patton, W.W. Jr., 1981, Chemistry, mineralogy, and K-Ar ages of igneous and metamorphic rocks of the Medfra quadrangle, Alaska: U.S. Geological Survey Open-File Report 80-811-C, 15 p., 2 sheets, scale 1:250,000.
