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

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182 GEOLOGIC STUDIES IN ALASKA BY THE U.S. GEOLOGICAL SURVEY. 1992 Table 1 . Statistical summary for 436 stream-sediment samples from the Bering Glacier and Icy Bay quadrangles. Alaska [All values in are parts per million (ppm). except for Al. Ca. Fe. Mg. and Na which are in percent . Uranium was determined by delayed neutron counting; Ag. As. Bi. Cd. Cu. Ni. Pb. Sn. W. and Zr by X-ray fluorescence; and all other elements by neutron activation analysis . B. number of samples with no data reported . L. number of samples qualified with a "less than." LDL. lower determination limits (LDL) as listed in Los Alamos National Laboratory (1983. table I) . Limits were not given for Rb and Sm] Percentile Element B L LDL Minimum Median 90 95 97.5 Maximum DISCUSSION OF GEOCHEMICALLY ANOMALOUS AREAS Factor score values and plots of individual element concentrations were used to delineate the geochemically anomalous areas. which are discussed below. in the Bering Glacier and Icy Bay quadrangles (fig . 1) . Samples with high scores for factor 1 are characterized by a Hf-Lu-Cr- Mn-U-Th-La-Ti-Dy signature . Twenty samples with high scores are located along the coastline between Cape Yakataga and the Yahtse River and reflect the garnet.. chromite.. rutile.. and rare-earth-element-bearing beach placers of the Yakataga district . One sample at Cape Yakataga contained 22.6 percent Fe. 3.5 percent K. 3.7 percent Ti. 2.5 percent Zr. 15. 260 pprn Mn (probably in spessartine). 3. 234 pprn Cr. 662 pprn Hf. 639 pprn V. 299 pprn Ce. 197 pprn La. 90 pprn Th. 89 pprn Sc. 69 pprn Au. 64 pprn Yb. 55 pprn U. 21 pprn Dy. 14.9 pprn Sm. 8.2 pprn Lu. 4 pprn Tb. and 3 pprn Ta . These are the highest concentrations for most of these elements in NURE
GEOCHEMICAL EVALUATION OF STREAM-SEDIMENT DATA 183 Table 2. Factor loadings for first five factors after R-mode analysis with Varimax rotation of stream-sediment data [Variance explained by five factors equals 80 percent. -, loadings less than 0.50 that have been omitted] Element 1 2 3 4 5 A1 ................ As ............... Ba ............... Ca ............... Ce ............... Co ............... Cr ................ Cu ............... Dy ............... Eu ............... Fe ................ H f ................ K ................. La ................ Lu ............... Mg .............. Mn .............. Na ............... Ni ................ Pb ................ Sc ................ Sm .............. Th ............... Ti ................ U ................. Percent total variance .... stream-sediment samples from the two quadrangles. Samples with high scores for factor 1, collected from the toe of Yakataga Glacier and 12 km inland from the mouth of the Duktoth River, indicate that localized heavy-mineral concentrations continue inland from the coast. Eight of the 18 samples from the study area with anomalous gold were collected between Crooked Creek and the mouth of the Duktoth River. Samples with high scores for factor 2 are enriched in Co-Mg-Cu-Fe-Ni-Sc and show a strong spatial correlation with both Late Jurassic intrusive bodies and outcrops of basaltic to andesitic volcanic rocks of the Wrangellia terrane. Stream-sediment samples containing as much as 12.8 percent Fe, 3.2 percent Mg, 50 pprn Co, 123 pprn Cu, 70 pprn Ni, and 45 pprn Sc cluster along the East and North Forks of the Kiagna River and throughout the Goat Creek watershed. Samples with high factor 2 scores scat- tered along the west side of Logan Glacier suggest that the source for the element enrichments extends perhaps 25 km east of Goat Creek. Many of the 30 sediment samples in this belt also contain anomalous amounts of Ag, As, Au, Cr, Mn, Ti, and V. A sediment sample, likely collected from medial morainal material, where Baldwin Glacier joins Logan Glacier contained 149 pprn Cu and 186 pprn As, the latter being the highest arsenic concentration from the NURE survey. Some of these high element concentrations in the north-central part of the Bering Glacier quadrangle reflect high geochemical background values for many elements in mafic country rocks. But many of the anomalous samples are from drainages within the Chitina Valley bathoIith. They hint at upstream mineral occurrences similar to the porphyry-related vein systems described by MacKevett (1976) a few kilometers to the north. A number of the stream-sediment samples with high scores for factor 2 are notably enriched in pathfinder elements for the Cu-rich veins and are the most suggestive samples of upstream metallic mineral occurrences in the Bering Glacier quadrangle. One sample on Goat Creek, 8 km below the toe of the unnamed glacier at its source, contained 50 pprn Co, 123 pprn Cu, and 10.5 percent Fe; another from 12 km below the glacier contained 49 pprn Co, 107 pprn Cu, 12.8 percent Fe, and 58 pprn As; a third from 4 km below the glacier contained 82 pprn As. It is uncertain whether these samples collected during the NURE survey were taken from Goat Creek or from tributary streams, but they most likely represent pyrite, chalcopyrite, or arsenopyrite within the area. The stream-sediment sample from the head of the North Fork of the Kiagna River contained 0.12 pprn Au. Very few samples were collected in the Chitina Val- ley batholith east of Goat Creek. However, the sample described above collected from near the toe of Baldwin Glacier indicates that Cu-dominant mineral occurrences likely continue far to the east. Four of the seven samples with detected silver are in the group of anomalous samples derived from the batholith, further suggesting the presence of hydrothermal mineral occurrences. The East Fork of the Kiagna River defines the western boundary of this belt of samples with high scores for factor 2. A sample collected 2 km below the toe of the unnamed glacier at the head of the East Fork of the Kiagna River contained 108 pprn Cu, 8.8 percent Fe, 2,505 pprn Mn, 5 pprn Ag, 70 pprn As, and 0.19 pprn Au. Two other samples collected along the river were also anomalous in gold, as well as many of the siderophile and chalcophile elements. It is uncertain whether the source area for the gold-bearing sediment is also rocks of the Chitina Valley batholith, or instead may be the mafic volcanic rocks of the Wrangellia terrane and (or) rocks of the Chugach terrane near the crest of the Granite Range. A single site with a high score for factor 2, either draining Ross Green Lake or a small, unnamed glacier im- mediately to the southwest, is defined by concentrations of 79 pprn Co, 178 pprn Cu, 11.7 percent Fe, 3.6 percent Mg, 137 pprn Ni, 37 pprn Sc, 2253 pprn Ba, 194 pprn Cr, 9.6 pprn Cs, 5.0 percent K, 197 pprn Rb, and 0.96 percent Ti. These are the highest concentrations of Co, Cu, Mg, Ni, Cs, K, and Rb determined for any of the 436 sediment
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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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OSTRACODE ASSEMBLAGES FROM MODERN B
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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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