Hogback; Purkeypiles; Little Mountain Prospect, McGrath District, Denali Borough, Alaska, USA
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Location: Maloney and Thomas (1966) locate the Hogback prospect in the southwest quarter of Section 2, T.32 N., R.16 W., of the Seward Meridian. It is roughly 3000 feet southwest of Little Mountain on a ridge between the headwaters of Camp Creek and Canyon Creek at about 4300 feet in elevation; about 1.0 miles southwest of the Mespelt prospect (TL005). Reed and others (1978) show this prospect as locality 4.
Geology: A tractor road leads from the Mespelt prospect (TL005) to the Hogback prospect where several bulldozer cuts expose mineralized fissure veins that crosscut quartzite and limestone. The prospect consists of 3 to 4 high-grade stringers, ranging from 1.2 to 3.0 feet wide, of argentiferous galena and zinc minerals, separated by vein quartz and altered, sheared granite in a zone 32 feet wide. Quartz-fluorite alteration is developed within and adjacent to the quartz-sulfide veins. Country rocks are converted to skarn minerals (Maloney and Thomas, 1966; C.C. Hawley and Associates, Inc., 1978). Tin in the nonmagnetic heavy-mineral concentrates from stream silt samples collected by Curtin, Karlson, Tripp, and Day (1978) is in excess of 1,500 ppm from the Canyon Creek drainage to the west of this prospect. Reed and others (1978) report the veins contain 5 to 48% lead, and 32 to 70 oz/ton silver. Maloney and Thomas (1966, Table 1) collected high-grade samples that yielded 19.30 to 134.76 oz/ton silver, trace to 0.04 oz/ton gold, 2.89 to 67.2% lead, 2.32 to 36.0% zinc, 1.2% copper. The geologic setting of the Hogback lead-zinc-silver vein is described, as follows, 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 early Tertiary Tonzona granitic pluton (Tmt), part of the McKinley sequence of intrusive rocks 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 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, zinc, and silver mineralization at the Hogback prospect occurs in the lower Paleozoic metasediments and metavolcanic rocks along the north and northeast contact of the pluton. The Tonzona pluton has metamorphosed the country rocks to skarn assemblages along the contact and has formed skarn- hosted polymetallic mineralization such as at the Jiles-Knudson (TL004), Boulder Creek (TL073) and the nearby Mespelt prospect (TL005). In much of the literature, the Jiles-Knudson, Mespelt, Hogback and Boulder Creek are included as the Purkeypile group of lode claims. Despite the paucity of tin values in published analyses for the Hogback prospect, its proximity to Mespelt and the Boulder Creek tin areas and elevated tin values in streams sediment samples regionally suggests that it is part of the tin mineralizing system related to these other prospects.
Workings: Several bulldozer cuts have been made, and a tractor road leads from this prospect to the Mespelt Prospect (TL005).
Age: Tertiary; mineralization in the Boulder Creek, Jiles-Knudson, Mespelt and Hogback areas 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: Quartz-fluorite alteration developed with vein assemblage. Country rocks are converted to skarn minerals (Maloney and Thomas, 1966; C.C. Hawley and Associates, Inc., 1978).
Commodities (Major) - Ag, Pb, Zn; (Minor) - Au, Cu
Development Status: No
Deposit Model: Fringe zone of Pb, Zn, and Ag sulfide mineralization to tin veins (generally re
8 entries listed. 8 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., 1973, Grandview Exploration Company, tin and silver prospects, Talkeetna D-5 quadrangle: Alaska Divsion of Geological and Geophysical Surveys Property Examination 75-4, 42 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. Curtin, G.C., Karlson, R.C., Tripp, R.B., and Day, G.W., 1978, Geochemical and generalized geologic maps showing the distribution and abundance of tin, tungsten, and beryllium in the Talkeetna quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-870-F, 2 sheets, scale 1:250,000. 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. 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.