Windy Pass Prospect, McGrath District, Yukon-Koyukuk Borough, Alaska, USA
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Location: The Windy Pass Skarn prospect is situated on a north-facing spur, overlooking a prominent southern tributary of Browns Fork of the Sulukna River at an elevation of 2,280 feet in the southeast corner of Section 17, T. 21 S., R. 25 E., of the Kateel River Meridian. The reporter visited the site in 1992.
Geology: The Windy Pass Cu-Mo-(Au)-Fe skarn prospect is associated with a small, Late Cretaceous, quartz monzonite stock that has intruded Paleozoic limestone probably equivalent to the Novi Mountain Formation (Dutro and Patton, 1982). The main mineralized area is about 200 feet by 3,000 feet (61 m by 914 m) in size. Two types of skarn are identified: (1) zones of sulfides, diopside, plagioclase, and orthoclase in endoskarn; and (2) zones of chalcopyrite, molybdenite, magnetite, phlogophite, garnet, and epidote in exoskarn within the marble front (DiMarchi and others, 1992). Chalcopyrite is the main ore mineral. Molybdenite is locally abundant. Pyrite locally contains gold values. Copper and molybdenum mainly occur in exoskarn; gold values appear to be in late stage quartz veins. Windy Pass Prospect is inferred to be Late Cretaceous, based on isotopic age dating of the quartz monzonite pluton (Moll and others, 1981). DiMarchi and others (1992, 1994) reported values as high as 0.27 ounces/ton (8.4 ppm) gold in quartz veins, 0.25 percent copper in exoskarn, and 650 ppm molybdenum in exoskarn. Clautice and others (1993) reported grades as high as 0.61 percent copper, 359 ppm molybdenum, 3,160 ppb gold, 0.23 percent zinc, 0.43 percent arsenic, 236 ppm antimony, and 310 ppm tungsten, mainly exoskarn zones.
Workings: The Windy Pass Cu-Mo-(Au)-Fe skarn prospect was first reported in the literature as a result of AMRAP investigations in the Medfra quadrangle (Patton and ohers, 1980; Patton and Moll, 1983). Work by Central Alaska Gold Company from 1991 to 1994 (DiMarchi and others,1992, 1994) mapped, sampled and conducted ground geophysical surveys of the deposit. No drilling has taken place. DiMarchi and others (1992, 1994) reported values as high as 0.27 ounces/ton (8.4 ppm) gold (in quartz veins), 0.25 percent copper (in exoskarn), and 650 ppm molybdenum (in exoskarn). Clautice and others (1993) reported grades as high as 0.61 percent copper, 359 ppm molybdenum, 3,160 ppb gold, 0.23 percent zinc, 0.43 percent arsenic, 236 ppm antimony, and 310 ppm tungsten from mainly exoskarn zones.
Age: Windy Pass Prospect is inferred to be Late Cretaceous, based on isotopic age of quartz monzonite (Moll and others, 1981).
Alteration: Sericite-chlorite in intrusion.
Reserves: None reported.
Commodities (Major) - Cu, Fe, Mo; (Minor) - Ag, As, Au, Sb, Zn
Development Status: No
Deposit Model: Copper skarn deposits (Cox and Singer, 1986; model no. 18b)
Mineral List
9 entries listed. 8 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., Adams, D.D., Huber, J., and West, A.W., 1994, Annual Report for 1993--Doyon Option Lands, Volume 1: ASA Inc. Report, 187 p. (Report held by Doyon, Limited, Fairbanks, Alaska.) 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.) Dutro, J.T. Jr., and Patton,W.W. Jr., 1982, New Paleozoic formations in the northern Kuskokwim Mountains, west-central Alaska: U.S. Geological Survey Bulletin 1529-H, p. H13-H22. Patton, W.W., Jr., and Moll, E.J., 1983, Mineral resource assessment map of the Medfra quadrangle, Alaska: U.S. Geological Survey Open-File Report 80-811-G, 3 sheets, scale 1:250,000. 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.
