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

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186 GEOLOGIC STUDIES IN ALASKA BY THE U.S. GEOLOGICAL SURVEY, 1992 of epigenetic lode-gold mineralization within the Creta- ceous Valdez Group, south-central Alaska, in Keppie, J.D., Boyle, R.W., and Haynes, S.J., eds., Turbidite-hosted gold deposits: Geological Association of Canada Special Paper 32, p. 87-105. Goldfarb, R.J., O'Leary, R.M., Sutley, S.J., and Tripp, R.B., 1989, Geochemical survey of the Cordova and Middleton Island lo x 3" quadrangles, south-central Alaska: U.S. Geo- logical Survey Bulletin 1865, 32 pages, 3 plates. Goldfarb, R.J., Snee, L.W., and Pickthorn, W.J., 1993, Orogenesis, high-T thermal events, and gold vein formation within metamorphic rocks of the Alaskan Cordillera: Mineralogical Maga- zine, in press. Goldfarb, R.J., Tripp, R.B., and Smaglik, S.M., 1985, Geochemical map showing distribution of barite, galena, and sphalerite within the Chugach National Forest, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map 1645-C, scale 1:250,000. Hudson, Travis, and Plafker, George, 1982, Paleogene metamor- phism of an accretionary flysch terrane, eastern Gulf of Alaska: Geological Society of America Bulletin, v. 93, p. 1280-1290. Jansons, Uldis, Hoekzema, R.B., Kurtak, J.M., and Fechner, S.A., 1984, Mineral occurrences in the Chugach National Forest, southcentral Alaska: U.S. Bureau of Mines Mineral Land Assessment Report 5-84, 43 p., 2 map sheets. Jones, D.L., Silberling, N.J., Coney, P.J., and Plafker, George, 1987, Lithotectonic terrane map of Alaska (west of the 141st meridian): U.S. Geological Survey Miscellaneous Field Studies Map, MF-1874-A, scale 1 :2,500,000. Koschmann, A.H., and Bergendahl, M.H., 1968, Principal gold- producing districts of the United States: U.S. Geological Survey Professional Paper 610, 283 p. Los Alamos National Laboratory, 1983, The geochemical atlas of Alaska: Grand Junction, CO, Bendix Field Engineering Corp. Report GJBX-32(83), 57 p. MacKevett, E.M., Jr., 1976, Mineral deposits and occurrences in the McCarthy quadrangle, Alaska: U.S. Geological Survey Miscel- laneous Field Studies Map MF 773-B, scale 1:250,000. Maddren, A.G., 1914, Mineral deposits of the Yakataga district: U.S. Geological Survey Bulletin 592, p. 119-153. Moffit, F.H., 1914, Geology of the Hanagita-Bremner region, Alaska: U.S. Geological Survey Bulletin 576, 56 p. 1918, The upper Chitina Valley, Alaska, with a description of igneous rocks: U.S. Geological Survey Bulletin 675, 82 p. 1954, Geology of the Prince William Sound region, Alaska: U.S. Geological Survey Bulletin 989-E, p. 225-310. Moxham, R.M., and Nelson, A.E., 1952, Reconnaissance for ra- dioactive deposits in south-central Alaska: U.S. Geological Survey Circular 184, 14 p. Nelson, S.W., Miller, M.L., Barnes, D.F., Dumoulin, J.A., Goldfarb, R.J., Koski, R.A., Mull, C.G., Pickthorn, W.J., Jansons, Uldis, Hoekzema, R.B., Kurtak, J.M., and Fechner, S.A., 1984, Mineral resource potential map of the Chugach National Forest, Alaska: U.S. Geological Survey Miscella- neous Field Studies Map MF-1645-A, scale 1:250,000. Pickthorn, W.J., Goldfarb, R.J., O'Leary, R.M., Butley, S.J., and Weaver, S., 1985, Kayak Island-Analysis of a geochemical anomaly, in Bartsch-Winkler, S., and Reed, K.M., eds., The United States Geological Survey in Alaska-Accomplishments during 1983: U.S. Geological Survey Circular 945, p. 82-83. Plafker, George, 1987, Regional geology and petroleum potential of the northern Gulf of Alaska continental margin, in Scholl, D.W., Grantz, A., and Vedder, J.G., eds., Geology, and resource potential of the continental margin of western North America and adjacent ocean basins: Houston, Circum-Pacific Council for Energy and Mineral Resources Earth Sciences Series 6, p. 229-268. Plafker, George, Jones, D.L., and Pessagno, E.A., Jr., 1977, A Cretaceous accretionary flysch along the Gulf of Alaska margin, in Blean, K.M., ed., U.S. Geological Survey in Alaska-Accomplishments during 1976: U.S. Geological Survey Circular 75 lB, p. B41-B43. Plafker, George, Nokleberg, W.J., and Lull, J.S., 1989, Bedrock geology and tectonic evolution of the Wrangellia, Peninsu- lar, and Chugach terranes along the Trans-Alaska Crustal Transect in the Chugach Mountains and southern Copper River Basin, Alaska: Journal of Geophysical Research, v. 94, no. B4, p. 4255-4295. Reimnitz, Erik, and Plafker, George, 1976, Marine gold placers along the Gulf of Alaska margin: U.S. Geological Survey Bulletin 1415, 16 p. Saleeby, J.B., 1983, Accretionary terranes of the North Ameri- can Cordillera: Annual Review of Earth and Planetary Sci- ences, v. 15, p. 45-73. Singer, D.A., and MacKevett, E.M., Jr., 1977, Mineral resources of the McCarthy quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map 773-C, scale 1:250,000. Sisson, V.B., Hollister, L.S., and Onstott, T.C., 1989, Petrologic and age constraints on the origin of a low-pressureihigh- temperature metamorphic complex, southern Alaska: Jour- nal of Geophysical Research, v. 94, no. B4, p. 4392410. Thomas, B.I., and Benyhill, R.V., 1962, Reconnaissance studies of Alaskan beach sands, eastern Gulf of Alaska: U.S. Bu- reau of Mines Report of Investigations 5986, 40 p. Winkler, G.R., and Plafker, George, 1981, Geologic map and cross sections of the Cordova and Middleton Island quadrangles, southern Alaska: U.S. Geological Survey Open- file Report 8 1-1 164, 26 p. Youngquist, C.A., D'Andrea, R.F., Jr., Zinkl, R.J., Shettel, D.L., Jr., and Langfeldt, S.L., 1981, Uranium hydrogeochemical and stream sediment reconnaissance of the Bering Glacier NTMS quadrangle, Alaska: Grand Junction, Colorado, Bendix Field Engineering Corp. Report GJBX-189(81). Zinkl, R.J., Shettel, D.L., Langfeldt, S.L., Youngquist, C.A., and D' Andrea, R.F., Jr., 1981, Uranium hydrogeochemical and stream sediment reconnaissance of the Icy Bay NTMS quadrangle, Alaska: Grand Junction, Colorado, Bendix Field Engineering Corp. Report GJBX-186(8 1 ). Reviewers: John E. Gray and Cliff D. Taylor
NEWLY DISCOVERED MOLYBDENITE OCCURRENCES AT DORA BAY, PRINCE OF WALES ISLAND, SOUTHEAST ALASKA, AND PRELIMINARY SCANNING ELECTRON MICROSCOPE STUDIES By John Philpotts, Cliff Taylor, John Evans, and Poul Emsbo ABSTRACT Molybdenite was discovered at two sites that are located 3 km apart in the border facies of a syenite pluton at Dora Bay, Prince of Wales Island, southeast Alaska. At one of the localities, molybdenite is visible in a 5-m-wide zone; analyses of two molybdenite-rich bulk samples from this zone yielded 0.5 and 1.2 percent molybdenum, respec- tively. Rock samples were further studied using a scanning electron microscope with X-ray analysis capability. Chlorine-rich minerals occur at both localities. Sodic metasomatism and veining by iron-bearing minerals appear to have preceded potassic metasomatism and molybdenite crystallization. A mineral that contains potassium, iron, and molybdenum may offer insights on the transport of molybdenum and the characteristic association of potassic metasomatism with molybdenite. INTRODUCTION In support of the U.S. Geological Survey's mineral resource assessment of Alaska, enrichments of rare earths and other lithophile trace elements associated with alkalic igneous activity in the vicinity of Dora Bay, Prince of Wales Island, southeast Alaska, were examined for several days in the summers of 1991 and 1992. In 1992 we noted molybdenite in a fragment of the gravel used to surface the logging road on the mountain on the west side of Dora Bay. The road gravel at this locality was further distinguished by a reddish coloration and by an increase in count rate on the scintillometer indicative of an increase in radioactivity. An employee at the local logging camp showed us the putative source of the road gravel, a small pit having both reddish rocks and increased scintillometer counts. Examination of the face of the pit revealed molybdenite in situ. As far as we are aware, this is the first report of a molybdenite occurrence in the immediate vicinity of Dora Bay. We refer to this occurrence as "Holly Moly" (hereafter HM). Follow- ing the HM discovery, examination of other rock samples from the area resulted in the identification of molybdenite from a site 3 km to the south-southeast in a cliff face rising above the western shore of Dora Lake; we refer to this occurrence as "Cliff Moly" (CM). The HM occurrence is located on the west side of Dora Bay at about lat 55'11'54" N. and long 132'15'45" W. at an elevation of about 265 feet; the CM site is at a known occurrence of eudialyte and is located at about 55'10'23" N., 132'14'53'' W. at an elevation of about 875 feet (figs. 1, 2). Both HM and CM lie within the Tongass Figure 1. Dora Bay molybdenite localities on Prince of Wales Island in relation to known molybdenite localities ("X") in southeast Alaska. Area covered by figure 2 is outlined at center.
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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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LITHOFACIES AND CONODONTS OF CARBON
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LITHOFACES AND CONODONTS OF CARBONI
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Table 1. Conodont faunules and lith
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DEPOSITIONAL SEQUENCES IN ATIGUN SY
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U-Pb AGES OF ZIRCON, MONAZITE, AND
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APPEAL FOR NONPROLIFERATION OF ESCA
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FAVORABLE AREAS FOR METALLIC MINERA
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GOLD AND CINNABAR IN HEAVY-MINERAL
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EARLY CENOZOIC DEPOSITIONAL SYSTEMS
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EARLY CENOZOIC DEPOSITIONAL S YSTEM
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RESERVOIR FRAMEWORK ARCHITECTURE, C
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GEOCHEMISTRY OF OPHIOLITIC ROCKS FR
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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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