Unnamed Prospects (ARDF - MM169; east-central tier of claims; Mt. Eielson district), Kantishna District, Denali Borough, Alaska, USA
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Location: This record describes prospects on the following claims, herein called the east-central tier of claims in the Mt. Eielson or Copper Mountain district: Carrie (Dee); Tennessee (Ruth); Georgia (Venora or Silver Mine); Jiles (Zelma); Kelly (Silver Peak), and Isobel. The claims are between Grant and Granite Creeks, which are north-flowing tributaries of Thorofare River north of Mt. Eielson. They are at elevations between 3500 to 4600 feet. For this record, the site is approximately at the center of the south-side line of the Tennessee claim, which is the northeast corner of the Georgia and the northwest corner of the Jiles claims. The location is in the NE1/4SE1/4 sec. 36, T. 17 S., R. 15 W., Fairbanks Meridian. The location is accurate within about 500 feet. The claims are included in numbers 37-40 of Cobb (1972 [MF 366], 1980 [OFR 80-363]).
Geology: The country rocks in the area of these claims generally are Paleozoic calcareous strata cut by dikes and sills of Eocene or Oligocene porphyritic granodiorite. The sills mainly strike west to west-northwest (Reed, 1933, plate 24). Outcrop is sporadic, and in many places is concealed by extensive talus fields derived from the mineralized rocks. The Jiles and adjacent claims cover the most intensely mineralized part of the area and also have been the most studied. In addition to the work summarized by Reed (1933), these claims were mapped by Gates and Wahrhaftig (1944), and sampled by the U. S. Bureau of Mines (Muir, Thomas, and Sanford, 1947). The Carrie (Dee) is the northwestern claim in the block. It was explored by small pits, some of which exposed high-grade ore relatively rich in sphalerite (Reed, 1933, p. 280). The Tennessee (Ruth) claim was also explored by pits showing 'considerable fair ore.' Strata near the SW corner of the Tennessee claim strike about N. 80 E. and dip about 50 N. The adjacent (south) Georgia (Venora or Silver Mine) claim featured good mineralization near its west side line. A composite sample across a width of about 40 feet, representing 150 feet along strike, assayed 0.02 ounce of gold and 2 ounces of silver per ton, 0.22 percent copper, 2.33 percent lead, and 5.46 percent zinc. A high-grade part of the lode contained 21 percent zinc. Mineralization is`sparse at the Isobel claim, where the wall rock contains chalcopyrite, garnet, quartz, and epidote (Reed, 1933, p. 282). The Jiles (Zelma) claim was developed by eight pits or open cuts and three short adits. Two of the adits were about 100 feet long; the third was about 70 feet long (Reed, 1933). This area was mapped in detail by Gates and Wahrhaftig (1944), and the Bureau of Mines collected seven samples near the Big Cut on the Jiles claim. The samples were 2 to12.5 feet long and assayed as much as 0.4 percent copper, 0.74 to 2.14 ounces of silver per ton, 1.46 to 4.68 percent lead, and 3.64 to 7.5 percent zinc. A representative grab sample of talus collected along 250 feet assayed 0.35 percent copper, 1.5 ounces of silver per ton, 5.09 percent lead, and 5.2 percent zinc (Muir, Thomas, and Sanford, 1947). A galena-rich zone in the middle tunnel (adit) assayed 8.7 ounces of silver per ton and 62.11 percent lead. The Bureau of Mines (1947) conducted metallurgical studies on a composite sample largely derived from the Jiles claim. The sample contained a considerable amount of oxidized ore, including cerussite and smithsonite. The head grade of the sample was 4.22 percent lead, of which 1.27 percent was in non-sulfide minerals, and 5.27 percent zinc, of which 0.37 percent was in non-sulfide minerals. Partly because of the oxidized nature of the ore, recoveries were poor. The lead concentrate contained 36.3 percent lead, representing a recovery of 59.6 percent. The zinc concentrate contained 49.5 percent zinc, representing a recovery of 76.5 percent. An unoxidized underground sample probably would give better recoveries. The mineralization is Oligocene, forming during, or shortly after, the emplacement of the Eocene or Oligocene Mt. Eielson pluton (Reed and Lanphere, 1974; Decker and Gilbert, 1978; Cole, 1998).
Workings: The claims were extensively explored by shallow pits and trenches in the 1920s and 1930s. The discoveries made by Fannie and Joe Quigley, O. M. Grant and others led to an option by Kennecott Copper Company in 1923. The area was also sampled for Kennecott Copper Corporation by W. E. Dunkle in 1923. Dunkle's crew, led by foreman Ira McCoid (written commun., W. E. Dunkle to Bradford Washburn, March 20, 1953), drove short underground workings on the Jiles claim. The claims were prospected until about 1931. During World War II, the Jiles and nearby claims were mapped by the U. S. Geological Survey (Gates and Wahrhaftig, 1944) and sampled and studied metallurgically by the U. S. Bureau of Mines (Muir, Thomas, and Sanford, 1947). The claims are inactive.
Age: The mineralization is Oligocene, forming during, or shortly after, the emplacement of the Eocene or Oligocene Mt. Eielson pluton (Reed and Lanphere, 1974; Decker and Gilbert, 1978; Cole, 1998).
Alteration: Silification and replacement of country rocks by epidote and rarely garnet. Local surface oxidation of copper, lead, and zinc minerals.
Reserves: Some of the generalized reserves or resources cited by Reed (1933), Gates and Wahrhaftig (1944), and Twenhofel (1953) must have been on the block of claims that included the Jiles. In general, resources are on the order of 100s of thousands of tons assaying about 10 percent combined lead and zinc and a few tenths percent copper.
Commodities (Major) - Pb, Zn; (Minor) - Ag, Cu
Development Status: None
Deposit Model: Polymetallic replacement deposits; Zn-Pb-(Cu) skarn deposits (Cox and Singer, 1
12 entries listed. 10 valid minerals.
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Cobb, E. H., 1972, Metallic mineral resources map of the Mount McKinley quadrangle, Alaska: U. S. Geological Survey Miscellaneous Field Studies Map MF-366, 1 sheet, scale 1:250,000. Cobb, E.H., 1980, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Mount McKinley quadrangle, Alaska: U. S. Geological Survey Open-File Report 80-363, 150 p. Cole, R. B., 1998, Early Tertiary post-subduction volcanism and deformation along the north side of the McKinley fault, Alaska [abs]: Geological Society of America. Abstracts with program, v. 30, p. 177. Cox, D.P., and Singer, D.A., eds., 1986, Mineral deposit models: U.S. Geological Survey Bulletin 1693, 379 p. Decker, J. E., and Gilbert, W. G., 1978, The Mt. Galen volcanics-A new middle Tertiary volcanic formation in central Alaska Range: Alaska Division of Geological and Geophysical Surveys Geological Report 59, 11 p. Gates, G. O., and Wahrhaftig, Clyde, 1944, Zinc deposits of the Mount Eielson district, Alaska: U. S. Geological Survey Open-File Report 16, 7 p. Muir, N. M., Thomas, B. I., and Sanford, R. S., 1947, Investigation of the Mount Eielson zinc-lead deposits, Mount McKinley National Park, Alaska: U. S. Bureau of Mines Report of Investigations RI-4121, 13 p. Reed, B.L., and Lanphere, M.A., 1974, Offset plutons and history of movement along the McKinley segment of the Denali fault system, Alaska: Geological Society of America Bulletin, v. 85, p. 1883-1892. Reed, J. C., 1933, The Mount Eielson district, Alaska: U. S. Geological Survey Bulletin 849-D, p. 231-287. Twenhofel, W.S., 1953, Potential Alaskan mineral resources for proposed electrochemical and electrometallurgical industries in the upper Lynn Canal area, Alaska: U.S. Geological Survey Circular 252, 14 p.