Atoll Prospect, McGrath District, Yukon-Koyukuk Borough, Alaska, USA
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Location: The Atoll prospect is situated at about 2,000 feet in elevation on the northwest slope of a ridge approximately 2.5 miles (4 km) northwest of Reef Ridge, in Section 11, T. 24 S., R. 23 E., of the Kateel River Meridian. Location is precisely known to within 100 feet (30 m).
Geology: At the Atoll prospect, smithsonite-bearing, iron-oxide gossan covers an area of 300 feet by 50 feet (91 m by 15 m) in tectonized dolomite and micritic limestone; unit probably equivalent to the Paradise Fork Formation of Dutro and Patton (1982). Mineralized rubble constitutes about one percent of float on the hillslope. Host unit is Late-Ordovician based on fossils (Dutro and Patton, 1982). Age of mineralization is not known. A large composite, chip-channel sample of 50 samples taken across the mineralized zone averaged 1.0 percent zinc and 395 ppm lead. A high-graded sample of 10 pieces of mineralized float contained 7.95 percent zinc but no lead. A strong zinc soil anomaly (1,900 to 4,000 ppm) covers a 1,000 feet by 4,000 feet (300 m by 122 m) area below the Atoll prospect (Andrews and Rishel, 1982).
Workings: The Atoll prospect was discovered by WGM Inc. and Patino Ltd. during exploration for base metals in the late 1970s on lands selected by Doyon Ltd. (Andrews and Rishel, 1982). A large composite, chip-channel sample of 50 samples taken across the mineralized zone averaged 1.0 percent zinc and 395 ppm lead. A high-graded sample of 10 pieces of mineralized float yielded 7.95 percent zinc but no lead. A strong zinc soil anomaly (1,900 to 4,000 ppm) covers a 1,000 feet by 4,00 feet (300 m by 122 m) area below the Atoll prospect.
Age: Host unit is Late-Ordovician based on fossils (Dutro and Patton, 1982). Age of mineralization is not known.
Alteration: Secondary dolomite.
Commodities (Major) - Zn; (Minor) - Pb
Development Status: No
Deposit Model: Southeast Missouri Pb-Zn, (Cox and Singer, 1986; model no. 32a)
2 entries listed. 2 valid minerals.
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Andrews, Tom, and Rishel, John, 1982, Annual Report for 1981, Reef Ridge I-to-XIII Project Areas, Kuskokwim Block, Alaska: Anchorage, Alaska, WGM Inc., Project Report 4, 45 p., 2 sheets, scales 1:63,360 and 1:20,000. (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., 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. Schmidt, J.M., 1997, Shale-hosted Zn-Pb-Ag and barite deposits of Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral deposits of Alaska, 1997: Economic Geology Monograph 9, p. 35-65.