Jiles-Knudson; J + K; Purkeypile Prospect (s), McGrath District, Denali Borough, Alaska, USA
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Location: C.C. Hawley and Associates, Inc. (1978, Fig. 4.2-C and Fig. 4.2C(3)-A(1)) show the J+K adit in schist near the granite contact about 1/2 mile below Boulder Creek Glacier on the east bank of Boulder Creek in the southeast quarter of Section 32, T. 33 N., R. 15 W., of the Seward Meridian.
Geology: The Jiles-Knudson prospect is located on the west side of the Boulder Creek drainage, the geologic setting of which is provided, as follows, from work by C.C. Hawley and Associates, Inc. (1978) and Reed and Nelson (1980). Blocky slate, argillite, thin-bedded siliceous limestone and chert define a belt of lower Paleozoic sedimentary and metavolcanic rocks (possibly Keevy Peak, other Totalanika series, or equivalents) bordered by the Tertiary Tonzona granitic pluton (Tmt), part of the McKinley sequence of mapped by Reed and Nelson (1980). The granite has three phases: a coarse-grained, locally porphyritic biotite granite; a medium-grained biotite granite; and a late fine-grained, leucocratic, locally aplitic, muscovite- tourmaline granite in which ovoid clusters of small black tourmaline crystals give the rock a 'dalmatian' appearance. Muscovite may exceed biotite in the granite and accessory minerals include tourmaline with lesser amounts of topaz, fluorite, garnet, zircon, and apatite. Late-stage greissen veinlets contain muscovite, topaz, tourmaline, locally abundant beryl, and occasionally, cassiterite. Lead, silver and tin mineralization occurs in lower Paleozoic metasediments and metavolcanic rocks along the north and northeast contact of the pluton. At this site a short adit (J+K adit), dozer cuts and diamond drill holes have been used to explore the Jiles-Knudson property. The prospect is a lenticular body of pyrrhotite-rich skarn, 3 to 10 feet thick, that contains pods of galena, pyrite, arsenopyrite, possible tetrahedrite, and other sulfides stratabound within Paleozoic limestone (C.C. Hawley and Associates, Inc., 1978; Reed and others, 1978). The body strikes about N85E and dips 80 degrees to the north and is exposed for about 140 feet. The sulfide body has been exposed in an open cut, a 15 foot shaft, eleven-foot adit and trench. The pyrrhotite-rich skarn runs 0.7 to 0.9% copper. One sample of gossan from the shaft dump contained 3.22 oz/ton Ag. Another gossan sample contained 0.96% lead. An eleven-foot sample from pyrrhotite-rich material in place carried 0.96 oz/ton gold. (Maloney and Thomas, 1966, Table 5; C.C. Hawley and Associates, Inc., 1978). In the entire Boulder Creek area there are widely separated, mineralized outcrops. Mapping and ground geophysical surveys, including magnetics and Chrone VLF, suggest extensive skarn development and skarn mineralization across Boulder Creek from the J+K adit. Little sub-surface exploration has been completed. Although tin is not specifically reported from the Jiles-Knudson prospect, its proximity to the Boulder Creek (TL073) suggests that it is part of the same mineralizing system. In much of the published literature the Purkeypile group of lode claims includes Boulder Creek (TL073), Hogback ( TL006) and Mespelt (TL005) prospects.
Workings: F. B. Jules and Ed Knutson of Poorman, Alaska concentrated their effort on the Jiles-Knudson prospect between 1910(?) and 1923. Mr. I.W.. Purkeypile and son David Purkeypile 'rediscovered' and prospected the Boulder Creek area since the late 1940s (C.C. Hawley and Associates, Inc., 1978). The area was evaluated by numerous private mining companies in the 1970s and 1980s. Workings at the Jiles-Knudson include an open cut, a 15 foot shaft, 11 foot adit and trench ( C.C. Hawley and Associates, Inc., 1978, Fig. 4.2-C and Fig. 4.2C(3)-A(1)).
Age: Tertiary; mineralization in the Jiles-Knudson area is interpreted to be linked to the Tonzona granite (Tmt), part of the McKinley Sequence, that has been determined to range from 52.3 to 56.2 m.y. in age (Reed and Lanphere, 1972; Reed and Nelson, 1980).
Alteration: Development of skarn assemblage in Paleozoic country rocks (C.C. Hawley and Associates, Inc., 1978).
Commodities (Major) - Ag, Au, Cu, Pb; (Minor) - As, Mn, Sb, Zn
Development Status: Undetermined.
Deposit Model: Fringe zone of Pb, Zn, and Ag sulfide mineralization to tin veins (generally re
10 entries listed. 9 valid minerals.
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Berg, H.C., and Cobb, E.H., 1967, Metalliferous lode deposits of Alaska: U.S. Geological Survey Bulletin 1246, 254 p. C.C. Hawley and Associates, Inc., 1978, Mineral appraisal of lands adjacent to Mt. McKinley National Park, Alaska: U.S. Bureau of Mines Open-File Report 24-78, 277 p., 12 sheets. Capps, S.R., 1925, An early Tertiary placer deposit in the Yentna district: U.S. Geological Survey Bulletin 773-A, p. 53-61. Capps, S.R., 1927, The Toklat-Tonzona River region: U.S. Geological Survey Bulletin 792-C, p. 73-110. Clark, A.L., and Cobb, E.H., 1972, Metallic mineral resources map of the Talkeetna quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-369, 1 sheet, scale 1:250,000. Cobb, E.H., and Reed, B.L., 1980, Summaries of data on and lists of reference to metallic and selected nonmetallic mineral deposits in the Talkeetna quadrangle, Alaska: U.S. Geological Survey Open-File Report 80-884, 106 p. Conwell, C.N., 1977, Boulder Creek tin lode deposits, in Short notes on Alaskan geology, 1977: Alaska Division of Geological and Geophysical Surveys Geologic Report 55A, p. 36 -38. MacKevett, E.M., Jr., and Holloway, C.D., 1977, Map showing metalliferous and selected non-metalliferous mineral deposits in the eastern part of southern Alaska: U.S. Geological Survey Open-File Report 77-169-A, 99 p., 1 sheet, scale 1:1,000,000. Maloney, R.P., and Thomas, B.I., 1966, Investigation of the Purkeypile prospects, Kuskokwim River basin, Alaska: U.S. Bureau of Mines Open-File Report 5-66, 12 p. Nokleberg, W.J., Bundtzen, T.K., Berg, H.C., Brew, D.A., Grybeck, D.J., Robinson, M.S., Smith, T.E., and Yeend, W., 1987, Significant metalliferous lode deposits and placer districts of Alaska: U.S. Geological Survey Bulletin 1786, 104 p., 2 plates, scale 1:5,000,000. Reed, B.L., and Lanphere, M.A., 1972, Generalized geologic map of the Alaska-Aleutian range batholith showing potassium-argon ages of the plutonic rocks: U.S. Geological Survey Miscellaneous Field Studies Map MF-372, 2 sheets, scale 1:1,000,000. Reed, B.L., and Nelson, S.W., 1980, Geologic map of the Talkeetna quadrangle: U.S. Geological Survey Miscellaneous Investigations Map I-1174, 1 sheet, scale 1:250,000. Reed, B.L., Nelson, S.W., Curtin, G.C., and Singer, D.A., 1978, Mineral resources map of the Talkeetna quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-870-D, 1 sheet, scale 1:250,000. Warner, J.D., 1985, Critical and strategic minerals in Alaska--Tin, tantalum, and columbium: U.S. Bureau of Mines Information Circular 9037, 19 p.