Geologic Studies in Alaska by the U.S. Geological Survey, 1992

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78 GEOLOGIC STUDIES IN ALASKA BY THE U.S. GEOLOGICAL SURVEY, 1992 eds., Guidebook to bedrock geology along the Dalton High- way, Yukon River to Prudhoe Bay, Alaska: Alaska Divi- sion of Geological and Geophysical Surveys Guidebook 7, sheet 1, scale 1:2,850,000. Mull, C.G., Roeder, D.H., Tailleur, I.L., Pessel, G.H., Grantz, Arthur, and May, S.D., 1987, Geologic sections and maps across the Brooks Range and Arctic Slope to Beaufort Sea, Alaska: Geological Society of America Maps and Charts Series MC 28-S, scale 1:500,000, 1 sheet. Murphy, J.M., and Patton, W.W., 1988, Geologic setting and pe- trography of the phyllite and metagraywacke thrust panel, north-central Alaska: Geologic studies by the U.S. Geo- logical Survey in Alaska during 1987, U.S. Geological Sur- vey Circular 1016, p.104-108. Nokleberg, W.J., Jones, D.L., and Silberling, N.J., 1985, Origin and tectonic evolution of the Maclaren and Wrangellia terranes, eastern Alaska Range, Alaska, Geological Society of America Bulletin, v. 96, p. 1251-1270. Patton, W.W., Jr., and Box, S.E., 1989, Tectonic setting of the Yukon-Koyukuk basin and its borderlands, western Alaska: Journal of Geophysical Research, v. 94, p. 15,807-15,820. Pelka, G.J., Sauve, J.A., and Walsh, T.P., 1992, Franklinian tectonic framework controls on post Devonian basin develop- ment, Chukchi Province, USA sector, in Tracy, K.V., Ankes, E.M., Ryan, C., and Hoffman, V., eds., International Conference on Arctic Margins [abs]: Abstracts, Alaska Geological Society, p. 49. Pessel, G.H., Eakins, G.R., and Garland, R.E., 1973, Geology and geochemistry of the southeastern Ambler River quadrangle, in Alaska Division of Geological and Geophysical Surveys 1972 Annual Report, p. 7-9. Sengor, A.M.C., 1990, Lithotectonic terranes and the plate tectonic theory of orogeny: a critique of the principles of terrane analysis, in Wiley, T.J., Howell, D.G., and Wong, F.L., eds., Terrane analysis of China and the Pacific rim: Houston, Circum-Pacific Council for Energy and Mineral Resources, Earth Sciences Series, v. 13, p. 9-44. Silberling, N.J., and Jones, D.L., eds., 1984, Lithotectonic terrane maps of the North American Cordillera: U.S. Geologi- cal Survey Open-File Report 84-523. Snelson, Sigmund, and Tailleur, I.L., 1968, Large-scale thrusting and migrating cretaceous foredeeps in western Brooks Range and adjacent regions of northwest Alaska [abs.]: American As- sociation of Petroleum Geologists Bulletin, v. 52, p. 567. Tailleur, I.L., and Brosgt, W.P., 1970, Tectonic history of north- ern Alaska, in Adkison, W.L., and Brosgt, M.M., eds., Pro- ceedings of the geological seminar on the North Slope of Alaska: American Association of Petroleum Geologists Pa- cific Section Meeting, Los Angeles, p. El-E19. Till, A.B., Schmidt, J.M., and Nelson, S.W., 1988, Thrust in- volvement of metamorphic rocks, southwestern Brooks Range, Alaska: Geology, v. 10, p. 930-933. Reviewers: ~wiiht C. Bradley and Steven W. Nelson
FAVORABLE AREAS FOR METALLIC MINERAL RESOURCES IN AND NEAR THE HORN MOUNTAINS, SLEETMUTE QUADRANGLE, SOUTHWESTERN ALASKA By John E. Gray, Peter M. Theodorakos, Leon A. Bradley, and John H. Bullock, Jr. ABSTRACT INTRODUCTION In a reconnaissance geochemical survey of the Horn Mountains area in the western Sleetmute quadrangle, stream-sediment and heavy-mineral-concentrate samples were collected from 138 sites. Stream-sediment samples were analyzed by semiquantitative emission spectrography, atomic absorption spectrophotometry, and visual spectrophotometry; heavy-mineral-concentrate samples were analyzed by semiquantitative emission spectrography and microscopically examined for their mineralogical content. These resulting data were interpreted to identify favorable areas for metallic mineral resources in the Horn Mountains and surrounding areas. Twelve areas were delineated as favorable for the presence of mineral deposits. In two areas within the volcanoplutonic complex of the Horn Mountains considered favorable for polymetallic vein deposits, Late Creta- ceous and Tertiary intermediate to felsic intrusive rocks of the Horn Mountains stock cut coeval mafic to felsic volcanic rocks and Cretaceous sedimentary rocks of the Kuskokwim Group. Samples collected in these two areas are geochemically anomalous in Au, Ag, As, Sb, Hg, Pb, Cu, W, Bi, Cd, B, or Te reflecting the possibility of undis- covered polymetallic vein deposits. Deposits of this type containing base-metal sulfides, sulfosalts, or gold are ob- served in these two areas, as in other volcanoplutonic complexes in southwestern Alaska. Eight areas delineated as favorable for the presence of epithennal mercury-rich vein deposits lie outside of the Horn Mountains, where Cretaceous sedimentary rocks of the Kuskokwim Group are most common, but where Late Cretaceous and Tertiary mafic to felsic volcanic rocks and intrusions are found locally. In these eight areas, the most consistent anomalies are Hg in stream-sediment samples and cinnabar in heavy-mineral-concentrate samples. These results suggest that the eight areas are favorable for undis- covered cinnabar-bearing vein deposits, a deposit type common throughout southwestern Alaska. A single site containing placer gold and an area with anomalous Au, Sn, Ba, W, and Pb were also delineated, but data are insuffi- cient to evaluate the areas further. The Horn Mountains are located about 50 km north- east of Aniak in the northwestern Sleetmute quadrangle. The Horn Mountains are considered favorable for metallic mineral resources (Miller and others, 1989), because they are similar in geology and geochemistry to the nearby Rus- sian Mountains in the Russian Mission quadrangle, and the Beaver Mountains in the Iditarod quadrangle (fig. I), where polymetallic vein deposits are known (Bundtzen and Gilbert, 1983; Bundtzen and Laird, 1991). In addition, the geology surrounding the Horn Mountains is similar to that where epithermal mercury-rich vein deposits are found such as the Red Devil deposit (MacKevett and Berg, 1963). However, few metallic mineral deposits have been discovered, probably because few geologic, geochemical, and geophysical studies have been conducted in the area. In the summer of 1992, a geochemical survey was conducted in the western part of the Sleetmute quadrangle as part of the Alaskan Mineral Resource Appraisal Program (AMRAP). The survey covered approximately 1,500 krn2 and included the Horn Mountains and surrounding areas. Reconnaissance drainage basin geochemical surveys are a rapid and efficient means of locating upstream areas with possible mineral deposits. The objective of this study was to use geochemical data from stream-sediment samples, and geochemical and mineralogical data from heavy-mineral-concentrate samples, to identify areas favorable for the presence of mineral deposits. This report de- lineates drainage basins containing samples with anomalous concentrations of a suite of elements (Au, Ag, Hg, Sb, As, Cu, Pb, Zn, Sn, Bi, Cd, Ba, B, W, or Te) considered pathfinders for mineral deposit types commonly found in southwestern Alaska such as epithermal mercury- rich vein deposits and polymetallic vein deposits (Bundtzen and Gilbert, 1983). The data used in this report are listed in Theodorakos and others (1992). GEOLOGY The Horn Mountains are underlain by one of several Late Cretaceous and Tertiary volcanoplutonic complexes
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Geologic Studies in Alaska by the U
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CONTENTS Introduction Cynthia Dusel
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CONTENTS CONTRIBUTORS TO THIS BULLE
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GEOLOGIC STUDIES IN ALASKA BY THE U
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LATE HOLOCENE LONGITUDINAL AND PARA
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DEEP-WATER LITHOFACIES AND CONODONT
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Table 1. Locality register for key
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Table 1. Locality register for key
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Page 33 and 34: DEEP-WATER LITHOFACIES AND CONODONT
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Page 37 and 38: LITHOFACIES AND CONODONTS OF CARBON
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Page 51 and 52: Table 1. Conodont faunules and lith
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Page 65 and 66: U-Pb AGES OF ZIRCON, MONAZITE, AND
Page 77 and 78: APPEAL FOR NONPROLIFERATION OF ESCA
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Page 87 and 88: FAVORABLE AREAS FOR METALLIC MINERA
Page 97 and 98: GOLD AND CINNABAR IN HEAVY-MINERAL
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RESERVOIR FRAMEWORK ARCHITECTURE, C
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GEOCHEMISTRY OF OPHIOLITIC ROCKS FR
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Table 1. Isotopic ages of intrusive
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Table 1. Isotopic ages of intrusive
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GEOCHEMICAL EVALUATION OF STREAM-SE
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Table 3. Summary of geochemical sig
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GEOCHEMICAL CHARACTER OF UPPER PALE
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RECONNAISSANCE GEOCHEMISTRY OF BASA
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OSTRACODE ASSEMBLAGES FROM MODERN B
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RUBIDIUM-STRONTIUM ISOTOPIC SYSTEMA
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RUBIDIUM-STRONTIUM ISOTOPIC SYSTEMA
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US. GEOLOGICAL SURVEY REPORTS ON AL
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U.S. GEOLOGICAL SURVEY REPORTS ON A
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U.S. GEOLOGICAL SURVEY REPOR TS ON
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REPORTS ABOUT ALASKA IN NON-USGS PU
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REPORTS ABOUT ALASKA IN NON-USGS PU
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Geologic Studies in Alaska by the U.S. Geological Survey, 1992

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