Ozzna Creek Prospect, McGrath District, Yukon-Koyukuk Borough, Alaska, USA
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Location: The Ozzna Creek prospect is located on the north facing slopes of Ozzna Creek, a westerly flowing tributary of the Windy Fork, Kuskokwim River; it is at an elevation of 4,750 feet (1,448 m) in the SE1/4 sec. 32, T. 26 N., R. 25 W., of the Seward Meridian. Location corresponds to locality number 3 of Cobb (1972). Location is accurate; the reporter investigated the prospect in 1981.
Geology: The Ozzna creek prospect consists of base metal sulfide veins and replacement deposits within an extensive quartz-sericite-pyrite halo rimming a 450 meter wide, rugged, quartz monzonite breccia pipe, which forms the core of a distinctive, precipitous, 7,205-foot -high (2,197 m) peak. A biotite separate from the quartz monzonite breccia pipe yielded a K-Ar age of 58 Ma. (Solie and others, 1991). A pronounced magnetic high rims the edge of the breccia pipe (Rob Kell, written communication, 1983). The vein and replacement deposits consist of small pods and lenses of pyrrhotite, sphalerite, argentiferous galena, and pyrite in a gangue of carbonate, epidote, and quartz along shear zones in felsic dikes and igneous breccia. Most massive sulfide pods range from 0.2 to 1.5 meters in width and 0.5 to 6.0 meters in length. Selected samples yielded 1,623.0 to 2,189.0 grams/tonne silver (Reed and Elliott, 1968, C 596). An extensive quartz-sericite-pyrite halo that surrounds the quartz monzonite breccia pipe ranges from 15 to 60 meters wide, and can be traced along strike for about 450 meters. Disseminated chalcopyrite and traces of molybdenite occur in pyrite-rich igneous breccia. Selected samples from the quartz-sericite-pyrite halo contain up to 0.08 percent copper, 150 ppm molybdenum, 1.50 percent lead, 1.00 percent zinc, 14.6 grams/tonne silver, and 2.48 grams/tonne gold (Bundtzen, Kline, and Clough, 1982; Bundtzen, Harris, and Gilbert, 1997).
Workings: Only surface sampling has been completed at the prospect. Selected samples from the quartz-pyrite-sericite halo contain up to 0.08 percent copper, 150 ppm molybdenum, 1.50 percent lead, 1.00 percent zinc, 14.6 grams/tonne silver, and 2.48 grams/tonne gold (Bundtzen, Kline, and Clough, 1982).
Age: Early Tertiary (58 Ma), based on K-Ar biotite age of intrusion.
Alteration: Pyritic and sericitic alteration in breccia pipe.
Reserves: None.
Commodities (Major) - Ag, Au, Cu, Pb, Zn; (Minor) - Mo
Development Status: No
Deposit Model: Porphyry copper molybdenum (?) (Cox and Singer, 1986; model 21a).
Mineral List
8 entries listed. 7 valid minerals.
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References
Bundtzen, T.K., Harris, E.E., and Gilbert, W.G., 1997, Geologic Map of the eastern McGrath quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Report of Investigations 97-14, 34 p., 1 sheet, scale 1:125,000. Bundtzen, T.K., Kline, J.T., and Clough, J.G., 1982, Preliminary geologiy of the McGrath B-2 quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Open-File report 149, 22 p., 1 sheet, scale 1:40,000. Cobb, E.H., 1972, Metallic mineral resources map of the McGrath quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-379, 1 sheet, 1:250,000 scale. Cobb, E.H., 1976, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Iliamna, Lake Clark, Lime Hills, and McGrath quadrangles, Alaska: U.S. Geological Survey Open-File Report 76-485, 101 p. Reed, B.L. and Elliott, R.L., 1968, Geochemical anomalies and metalliferous deposits between Windy Fork and Post River, southern Alaska: U.S. Geological Survey Circular 596, 22 pages. Smith, T.E., and Albanese, M.D., 1985, Preliminary prospect examinations in the McGrath A-2, A-3, and B-2 quadrangles, Alaska: Alaska Division of Geological and Geophysical Surveys Public Data File 85-54, 19 p. Solie, D.N., Bundtzen, T.K., and Gilbert, W.G., 1991, K/Ar ages of igneous rocks in the McGrath quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Public Data File 91-23, 7 p., 1 sheet, 1:250,000 scale.
