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Tolstoi Prospect, Iditarod District, Yukon-Koyukuk Borough, Alaska, USA

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Location: The Tolstoi prospect is at an elevation of about 3,400 feet on a steep saddle at the head one of the headwater tributaries of Tolstoi Creek. It is about 0.5 mile south-southeast of peak 3970 and 0.1 mile northwest of the southeast corner of section 26, T. 33 N., R. 41 W., of the Seward Meridian. The location is accurate.
Geology: The Tolstoi prospect consists of several tabular-to-pipe- shaped, tourmaline-sulfide breccia zones in a cupola of the 70.3 Ma, Beaver Mountains stock (Bundtzen and Laird, 1982; Bundtzen and Miller, 1997). The tourmaline-axinite-quartz breccia bodies are from 6 to 65 feet thick and contain from 1 to 8 percent arsenopyrite, chalcopyrite, and pyrite. Stromeryite and boulangerite, possibly the source of the high silver values in samples, have been identified in polished sections. The Tolstoi prospect is similar to a nearby unnamed prospect (ID006) except that sulfides at the Tolstoi Prospect are more disseminated and the boron metasomatism in the form of tourmaline and axinite is more extensive. Grab samples of the mineralization at the Tolstoi prospect contained up to 10.0 percent copper, 500 parts per million (ppm) silver, 2.0 percent arsenic, more than 2.0 percent lead, 2.0 percent zinc, 1.0 percent antimony, 1,400 parts per billion (ppb) gold, 39 ppm bismuth, 200 ppm cadmium, and 200 ppm tin (McGimsey and others, 1988; Bundtzen and Laird, 1982). Grab samples collected by Battle Mountain Mining Company in 1990 contained up to 1,137 ppb gold, 86.1 ppm silver, 2.03 percent lead, more than 2.00 percent arsenic, and 81 ppm tin (Szumigala, 1993).
Workings: The prospect was mapped and sampled by the Alaska Division of Geological and Geophysical Surveys and the U.S. Geological Survey in from 1979 to 1986. Anaconda Minerals Company sampled and mapped the prospect in 1981 (D. Obolewicz, oral communication, 1981). Noranda Exploration examined the property in 1983 (John Dunbier, oral communication, 1983). The prospect was studied by Battle Mountain Mining Company in 1990 (Szumigala, 1993 and 1996). A geologic description of the Tolstoi prospect is in Bundtzen and Miller (1997).
Age: Undated; may be related to emplacement of the Beaver Mountains stock which has been dated at 70.3 Ma. (Bundtzen and Laird, 1982).
Alteration: Extensive greisen development with tourmaline, quartz, white mica, and fluorite.

Commodities (Major) - Ag, As, Cu; (Minor) - Au, Be, Bi, Cd, Pb, Sb, Sn
Development Status: None
Deposit Model: Sn-polymetallic veins (Cox and Singer, 1986; model 20b).

Mineral List



11 entries listed. 8 valid minerals.

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References

Bundtzen, T.K., and Laird, G.M., 1982, Geologic map of the Iditarod D-2 and eastern D-3 quadrangles, Alaska: Alaska Division of Geological and Geophysical Surveys Geologic Report 72, 1 sheet, scale 1:63,360. 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. McGimsey, R.G., Miller, M.L., and Arbogast, B.F., 1988, Paper version of analytical results, and sample locality map for rock samples from the Iditarod quadrangle, Alaska: U.S. Geological Survey Open-File Report 88-421-A, 110 p., 1 sheet, scale 1:250,000. Szumigala, D.J., 1993, Gold mineralization related to Cretaceous-Tertiary magmatism in the Kuskokwim Mountains of west-central and southwestern Alaska: Los Angeles, University of California Ph.D. dissertation, 300 p. Szumigala, D.J., 1996, Gold mineralization related to Cretaceous-Tertiary magmatism in west-central Alaska-A geochemical model and prospecting guide for the Kuskokwim region: Geological Society of Nevada Symposium Proceedings, p. 1317-1340.

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