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At least 973 records · Page 54Linked to original sources

USGS1977

Metamorphic rocks of the Yakutat-St. Elias area, south-central Alaska

Metamorphic rocks in the Yakutat-St. Elias area range in grade from zeolite to amphibolite facies. Radiometric age determinations on selected metamorphic rocks have helped to identify two major metamorphic events, one in Late Cretaceous time that was characterized by penetrative deformation, and one in the Miocene Epoch that resulted in widespread recrystallization and igneous intrusions. Mapped facies units show many discontinuities across major faults, and their distribution indicates major differential uplift between several structurally bound crustal blocks within a strongly deformed mobile belt west of the Art Lewis fault. Late Cretaceous metamorphic gradients indicate that the blocks have been tilted to the west or northwest parallel to their general structural grain. As mineral assemblages that were recrystallized during Miocene time occur on both sides of the Fairweather fault, large-scale, post-Miocene strike-slip movement along the fault is not indicated.

Alaska↗

USGS2011

Geophysical investigation of Red Devil mine using direct-current resistivity and electromagnetic induction, Red Devil, Alaska, August 2010

Red Devil Mine, located in southwestern Alaska near the Village of Red Devil, was the state's largest producer of mercury and operated from 1933 to 1971. Throughout the lifespan of the mine, various generations of mills and retort buildings existed on both sides of Red Devil Creek, and the tailings and waste rock were deposited across the site. The mine was located on public Bureau of Land Management property, and the Bureau has begun site remediation by addressing mercury, arsenic, and antimony contamination caused by the minerals associated with the ore deposit (cinnabar, stibnite, realgar, and orpiment). In August 2010, the U.S. Geological Survey completed a geophysical survey at the site using direct-current resistivity and electromagnetic induction surface methods. Eight two-dimensional profiles and one three-dimensional grid of direct-current resistivity data as well as about 5.7 kilometers of electromagnetic induction profile data were acquired across the site. On the basis of the geophysical data and few available soil borings, there is not sufficient electrical or electromagnetic contrast to confidently distinguish between tailings, waste rock, and weathered bedrock. A water table is interpreted along the two-dimensional direct-current resistivity profiles based on correlation with monitoring well water levels and a relatively consistent decrease in resistivity typically at 2-6 meters depth. Three settling ponds used in the last few years of mine operation to capture silt and sand from a flotation ore processing technique possessed conductive values above the interpreted water level but more resistive values below the water level. The cause of the increased resistivity below the water table is unknown, but the increased resistivity may indicate that a secondary mechanism is affecting the resistivity structure under these ponds if the depth of the ponds is expected to extend below the water level. The electromagnetic induction data clearly identified the three monofills and indicate, in conjunction with the three-dimensional resistivity data, additional possible landfill features on the north side of Red Devil Creek. No obvious shallow feature was identified as a possible source for a spring that is feeding into Red Devil Creek from the north bank. However, a discrete, nearly vertical conductive feature observed on the direct-current resistivity line that passes within 5 meters of the spring may be worth investigating. Additional deep soil borings that better differentiate between tailings, waste rock, and weathered bedrock may be very useful in more confidently identifying these rock types in the direct-current resistivity data.

Open-File Report↗

USGS1946

Trace elements investigations in the Sweepstakes Creek area, Koyuk district, Seward Peninsula, Alaska

A significant content of radioactive material was recognized in a few placer concentrates from Sweepstakes and Rube Creeks in the Koyuk district of eastern Seward Peninsula, Alaska, when old collections were scanned for radioactivity in the spring of 1945. Subsequent field investigations with a Geiger-Mueller counter were made of the creek gravels and the placer-gold paystreak on the bench ground of Sweepstakes Creek and its tributaries, the syenite stock of Granite Mountain to the north, of Sweepstakes Creek, and the creek gravels of Rube and Anzac Creeks which are tributaries of the Peace River east of the syenite stock. The content of radioactive minerals in the gravels and in the placer-gold paystreak was found to be disappointingly low. There concentration ratios were between 45 and 169 to 1, the content of concentrates from the creek gravels is only .001 to .016 percent equivalent uranium the average content of the creek gravels in place is computed as .0001 percent equivalent uranium. The placer-gold paystreak was not accessible in place, but the content was computed as .0003 percent equivalent uranium from the sluice-box concentrates and tailings at Winder's open-cut,the only active placer mine in the area in 1945. The radioactive minerals are relatively abundant in such gravity concentrates as the sluice-box concentrates, and are particularly abundant in certain size fractions of these sluice concentrates Thus the concentrates from the aluiee-fcex, after screening through 20-mesh, showed 0.04 percent equivalent uranium. An even greater concentration of radioactive minerals is obtained in the "blowings," which represent a further cleaning of the sluice-box concontrates, one saample showing 14.20 percent equivalent uranium.

Alaska↗

USGS1952

Magmatic differentiation in tertiary and quaternary volcanic rocks from Adak and Kanaga Islands, Aleutian Islands, Alaska

Samples of 17 volcanic rocks of Tertiary and Quaternary age from Adak and Kanaga islands have been chemically analyzed and studied microscopically. Spectrograms have been made of 10 of them. The rocks from Adak represent one center of possibly older Tertiary age and two centers of younger Tertiary or Quaternary age. The rocks from Kanaga Island represent both a shield volcano of possibly Tertiary age, partly destroyed by the formation of a caldera, and a young cone of Quaternary age that has grown within the caldera. All the rocks are basalt or andesite. Modally, all are characterized by relatively large crystals of plagioclase more calcic than andesine, and by one or more of the following ferromagnesian minerals: olivine, hypersthene, augite, and hornblende. Apatite and iron ores are common, and late silica minerals and orthoclase occur interstitially in the groundmasses of some rocks . As analyses of no more than four samples are available for each center, the small differences between sets of analyses representing different centers are of doubtful significance. Consequently, the analyses representing all the centers have been plotted on each of the several diagrams used. The several types of variation diagrams show that the province is a calc-alkaline one. The alkali-lime index is in the neighborhood of 63. This very high value is comparable with that for Katmai and is only slightly less than the maximum for the Japanese volcanic rock series. The quantities of minor constituents present are not exceptional for the rock types analyzed; the rocks from Adak are apparently more strontium-rich than those from Kanaga . The chemical analyses of the more basic rock types, as compared with the average analysis of plateau basalt, suggest that the Aleutian parental magma could have been derived from a plateau basalt magma by the addition of plagioclase and the subtraction of pyroxene, iron ore, and some quartz. The distribution of the minor elements can be explained more easily by postulating that, at least on Kanaga Island , some sediments have been assimilated. The derivation of the analyzed rocks from the Aleutian parental magma is most easily explained by the hypothesis that the plagioclase remained in suspension while the ferromagnesian minerals were settling out.

Alaska↗

USGS2004

Origin of the Red Dog Zn-Pb-Ag deposits, Brooks Range, Alaska: Evidence from regional Pb and Sr isotope sources

Pb and Sr isotope data were obtained on the shale-hosted Zn-Pb-Ag Red Dog deposits (Qanaiyaq, Main, Aqqaluk, and Paalaaq), other shale-hosted deposits near Red Dog, and Zn-Pb-Ag sulfide and barite deposits in the western and central Brooks Range. The Red Dog deposits and other shale-hosted Zn-Pb-Ag deposits near Red Dog are hosted in the Mississippian Kuna Formation, which is underlain by a sequence of marine-deltaic clastic rocks of the Upper Devonian to Lower Mississippian Endicott Group. Ag-Pb-Zn vein-breccias are found in the Endicott Group. Galena formed during the main mineralization stages in the Red Dog deposits and from the Anarraaq and Wulik deposits have overlapping Pb isotope compositions in the range 206Pb/204Pb = 18.364 to 18.428, 207Pb/204Pb = 15.553 to 15.621, and 208Pb/204Pb = 38.083 to 38.323. Galena and sphalerite formed during the main ore-forming stages in the Red Dog deposits define a narrow field on standard uranogenic and thorogenic Pb isotope diagrams. Lead in sulfides of the Red Dog district is less radiogenic (238U/204Pb: ?? = 9.51-9.77) than is indicated by the average crustal lead evolution model (?? = 9.74), a difference consistent with a long history of evolution at low ratios of ?? before the Carboniferous. The homogeneous regional isotopic reservoir of Pb may indicate large-scale transport and leaching of minerals with various ?? ratios and Th/Pb ratios. Younger and genetically unrelated fluids did not significantly disturb the isotopic compositions of galena and sphalerite after the main mineralization event in the Red Dog district. Some pyrite shows evidence of minor Pb remobilization. The overall lead isotope homogeneity in the shale-hosted massive sulfide deposits is consistent with three types of control: a homogeneous regional source, mixing of lead during leaching of a thick sedimentary section and fluid transport, or mixing at the site of deposition. Isotopic variability of the hydrothermal fluids, as represented by galena in the Red Dog district, appears to be consistent with a simple mixing system. Evidence indicates that galena was deposited from largely similar hydrothermal solutions throughout the Red Dog district. A shared regional isotopic reservoir is also supported by the correspondence of Pb isotope compositions of galena in deposits of the Red Dog district and galena in clastic rocks (vein-breccias). Leaching of metals and progressive extraction of radiogenic lead from the clastic rocks in the Endicott Group may account for the trend of increasing 206Pb/204Pb in galena of the Red Dog district. Galena in the Red Dog deposits is unlikely to have been derived entirely from the same isotopic reservoir as that represented by the lead in the Kuna Formation or from the igneous rocks in the Red Dog district. Sr isotope data for barite, calcite, and witherite from the Red Dog deposits are compared with data from regional barite that is associated with sulfides and from barite in sulfide-poor occurrences. Fluids with heterogeneous Sr isotope signatures are indicated. Barite in the Main deposit extends to higher ratios of 87Sr/86Sr (0.709034-0.709899) than barite in the Anarraaq deposit (0.708615-0.709256). All barite is more radiogenic than Carboniferous seawater. Other Mississippian(?) shale-hosted deposits and mineral occurrences containing barite in the Red Dog district and barite in regional occurrences east of Red Dog in the western and central Brooks Range also have heterogeneous 87Sr/86Sr ratios. Carbonate (87Sr/86Sr = 0.710319-0.713637) and witherite (87 Sr/86 Sr = 0.710513) in the Main deposit are more radiogenic than barite. In contrast, carbonate (87Sr/86Sr = 0.708196-0.709740) intergrown with massive sulfides at Anarraaq has isotopic compositions similar to that of barite. Paragenetic and isotop ic studies suggest that early barite is similar to barite typically formed in cold seeps along continental margins. This early fine-grained barite formed before the main mineralizat

Economic Geology↗

USGS2006

Water and Sediment Chemical Data and Data Summary for Samples Collected in 1999 and 2001 in the Goodpaster River Basin, Big Delta B-2 Quadrangle, Alaska

We report the chemical analysis for water and sediment collected from the Big Delta B-2 quadrangle. These data are part of a study located in the Big Delta B-2 quadrangle that focused on the integration of geology and bedrock geochemistry on with the biogeochemistry of water, sediments, soil, and vegetation. The discovery of the Pogo lode gold deposit in the northwest corner of the quadrangle was the impetus for this study. The study objectives were to create a geologic map, evaluate the bedrock geochemical influence on the geochemical signature of the surficial environment, and define landscape-level predevelopment geochemical baselines. Important to baseline development is an evaluation of what, if any, geochemical difference exists between the mineralized and non-mineralized areas within a watershed or between mineralized and non-mineralized watersheds. The analytic results for the bedrock, soils, and vegetation are reported elsewhere. Presented here, with minimal interpretation, is the analytic data for the water and sediment samples collected in the summers of 1999 and 2001, and a summary statistics of these analyses.

Open-File Report↗

USGS1968

Geology of the Golden Zone mine area, Alaska

The Golden Zone mine area, in the upper Chulitna district, is underlain mainly by siltstone and tuff, volcanic conglomerate and breccia, and limestone. These rocks were invaded, probably in the Tertiary, by dikes and a small stock of porphyry. The ore deposits of the area are the Golden Zone breccia pipe, a nearly vertical body about in the center of the porphyry stock, and steeply dipping veins. Most veins strike north to northeast and are commonly only 1-5 feet thick, but locally are as much as 15 feet thick. Both pipe and vein deposits are gold deposits of low to moderate grade that are characterized by abundant arsenopyrite; some contain possibly economic amounts of copper, lead and zinc minerals. Of the deposits of the mine area, only the Golden Zone has been explored to any extent, and both it and some of. the veins deserve further exploration to determine their potential.

Alaska↗

USGS2021

Diagenetic barite-pyrite-wurtzite formation and redox signatures in Triassic mudstone, Brooks Range, northern Alaska

Mineralogical and geochemical studies of interbedded black and gray mudstones in the Triassic part of the Triassic-Jurassic Otuk Formation (northern Alaska) document locally abundant barite and pyrite plus diverse redox signatures. These strata, deposited in an outer shelf setting at paleolatitudes of ~45 to 60°N, show widespread sedimentological evidence for bioturbation. Barite occurs preferentially in black mudstones (TOC = 0.93–6.46 wt%), forming displacive euhedral crystals with pyrite inclusions and rims, and late albite inclusions or intergrowths. Pyrite also occurs as small (3–20 μm) framboids, discontinuous laminae, euhedral and anhedral crystals, and replacements of barite and fossils (mainly radiolarians). Paragenetically early wurtzite is present as clusters of very small (1–3 μm) aggregates of radiating crystals 0.5 to 1.0 μm long with cores of organic matter that overgrow framboidal pyrite; later wurtzite forms 10- to 30-μm bladed crystals. Equant grains (3–30 μm) and small (20 μm) angular clusters of zinc sulfide that include <1-μm-long, comb-like structures are sphalerite or wurtzite, or both. Minor siderite forms euhedral crystals intergrown with albite that enclose wurtzite and barite. Illite shows intergrowths with sphalerite; rare K-feldspar is intergrown with barite. Formation of these minerals and assemblages is attributed to early diagenetic processes. Whole-rock geochemical data for 15 samples show large ranges in redox proxies including Post Archean Average Shale (PAAS)-normalized enrichment factors (EFs) for V, U, Mo, and Re, and Al-normalized ratios for V, U, and Mo. Results for most black mudstones, with or without abundant barite and/or pyrite, suggest deposition within an oxygen minimum zone. Cerium anomalies, PAAS-normalized and calculated on a detrital-free basis, range widely from 0.49 to 0.96 and may reflect diagenetic overprinting by Ce-depleted fluids. Considering data for both black and gray mudstones, the overall geochemical pattern together with evidence from pyrite framboid sizes suggest that redox conditions fluctuated greatly from euxinic to oxic, like the redox profiles reported for modern shelf sediments offshore Peru and Namibia. The euxinic redox signatures in some Otuk black mudstones may correlate with widespread Early to Middle Triassic ocean anoxic events proposed for other regions. Calculations of median EFs for trace elements in Otuk black mudstones reveal both enrichments and depletions. Normalizations to the median composition of the three least-mineralized black mudstones show that barite- and/or pyrite-rich samples display large (>50%) positive changes for Li (+80.4%), V (+75.6%), Sr (+75.9%), Ba (+790%), Cu (+92.1%), Ni (+169%), Ag (+156%), Au (+3091%), As (+109%), Sb (+476%), and Se (+205%); Zn shows a moderate positive change of +42.1%. Moderate negative changes are evident only for Ge (−47.2%) and W (−30.6%). The local enrichments may reflect one or more factors including redox variations in bottom waters and pore fluids, element mobility during diagenesis, and selective fractionation into minerals such as barite, pyrite, and wurtzite. Anomalously low U/Al and UEF values, compared to those for other modern and ancient organic-rich sediments and sedimentary rocks, are attributed to increased solubility and loss of U during bioturbation-related oxygenation in the subsurface. Physicochemical constraints on barite, pyrite, and wurtzite formation are informed by use of a pH-fO2 plot constructed at 10 °C. Based on paragenetic evidence for multistage deposition of these three minerals, together with the presence of illite intergrown with ZnS and K-feldspar with barite, proposed diagenetic trends involve an increase in pH and fO2 related to the ingress of sulfate-rich pore fluids during bioturbation, followed by a return to lower then higher pH and fO2 conditions linked to carbon, sulfur, barium, and iron cycling during diagenesis. Labile Ba of marine pelagic origin was mobilized from organic-rich sediment upward to the sulfate-methane transition zone where barite precipitated during the interaction of reduced Ba- and CH4-rich fluids with sulfate-bearing pore fluids. The formation of paragenetically early wurtzite (ZnS) crystals, as well as locally high EF values for Cu, Ni, Ag, and Au, is attributed to metal enrichment of pore fluids, with sources being derived in part from water-column deposition from hydrothermal plumes related to coeval Triassic seafloor vent systems including a volcanogenic massive sulfide deposit in British Columbia and the Wrangellia Large Igneous Province in Alaska.

Alaska↗

USGS1977

The United States Geological Survey in Alaska: Organization and status of programs in 1977

United States Geological Survey projects in Alaska include a wide range of topics of economic and scientific interest. Studies in 1976 include economic geology, regional geology, stratigraphy, environmental geology, engineering geology, hydrology, and marine geology. Discussions of the findings or, in some instances, narratives of the course of the investigations are grouped in eight subdivisions corresponding to the six major onshore geographic regions, the offshore projects, and projects that are statewide in scope. Locations of the study areas are shown. In addition, many reports and maps covering various aspects of the geology and mineral and water resources of the State were published. These publications are listed. (Woodard-USGS)

Circular↗

USGS1977

The United States Geological Survey in Alaska: Accomplishments during 1976

Circular↗

USGS1969

Results of geological and geochemical investigations in an area northwest of the Chulitna River, central Alaska Range

Sedimentary and volcanic rock units of Paleozoic and Mesozoic age, faults, and elongate bodies of intrusive rock, particularly serpentinites, have a dominant northeasterly trend in an area northwest of the Chulitna River between Eldridge Glacier and Bull River. The serpentinites locally contain abnormal (as much as 0.5 percent) concentrations of nickel, have one newly identified occurrence of chromite, and are hosts to small epigenetic lodes containing copper, gold, and silver. Other epigenetic concentrations of copper or other metals occur in interlayered basalt and limestone at Partin and Canyon Creeks in the southwestern part of the area and in porphyry near Costello Creek in the northern part of the area. Tin occurs in greisen on upper Ohio Creek, and abnormal concentrations of tin also characterize mineralized rocks along Canyon Creek and at a prospect near Long Creek. Mineralized rocks characterized by silver, lead, and zinc crop out near Lookout Mountain. Anomalous concentrations of gold and other metals occur in stream sediments at isolated sites in upper Long Creek and at Coal Creek, as well as in several areas near known lode mineral occurrences. Shotgun and McCallie Creeks both contain stream sediments with anomalous concentrations of metals and both head into the basalt-limestone unit which is the host rock at Partin and Canyon Creeks; these facts suggest that other concentrations may be found.

Circular↗

USGS1962

Lead in the United States, exclusive of Alaska and Hawaii

The productive lead districts in the United States (exclusive of Alaska and Hawaii) are shown on the accompanying map. The map is at a scale of 1: 3,168,000, (50 miles to the inch). Only those districts known or believed to contain 1,000 short tons or more of lead are shown; individual deposits within districts are not represented.

Mineral Investigations Resource Map↗

USGS2006

Effects of wildfire and permafrost on soil organic matter and soil climate in interior Alaska

The influence of discontinuous permafrost on ground-fuel storage, combustion losses, and postfire soil climates was examined after a wildfire near Delta Junction, AK in July 1999. At this site, we sampled soils from a four-way site comparison of burning (burned and unburned) and permafrost (permafrost and nonpermafrost). Soil organic layers (which comprise ground-fuel storage) were thicker in permafrost than nonpermafrost soils both in burned and unburned sites. While we expected fire severity to be greater in the drier site (without permafrost), combustion losses were not significantly different between the two burned sites. Overall, permafrost and burning had significant effects on physical soil variables. Most notably, unburned permafrost sites with the thickest organic mats consistently had the coldest temperatures and wettest mineral soil, while soils in the burned nonpermafrost sites were warmer and drier than the other soils. For every centimeter of organic mat thickness, temperature at 5cm depth was about 0.5??C cooler during summer months. We propose that organic soil layers determine to a large extent the physical and thermal setting for variations in vegetation, decomposition, and carbon balance across these landscapes. In particular, the deep organic layers maintain the legacies of thermal and nutrient cycling governed by fire and revegetation. We further propose that the thermal influence of deep organic soil layers may be an underlying mechanism responsible for large regional patterns of burning and regrowth, detected in fractal analyses of burn frequency and area. Thus, fractal geometry can potentially be used to analyze changes in state of these fire prone systems. ?? 2006 Blackwell Publishing Ltd.

Global Change Biology↗

USGS2011

Peninsular terrane basement ages recorded by Paleozoic and Paleoproterozoic zircon in gabbro xenoliths and andesite from Redoubt volcano, Alaska

Historically Sactive Redoubt volcano is an Aleutian arc basalt-to-dacite cone constructed upon the Jurassic–Early Tertiary Alaska–Aleutian Range batholith. The batholith intrudes the Peninsular tectonostratigraphic terrane, which is considered to have developed on oceanic basement and to have accreted to North America, possibly in Late Jurassic time. Xenoliths in Redoubt magmas have been thought to be modern cumulate gabbros and fragments of the batholith. However, new sensitive high-resolution ion microprobe (SHRIMP) U-Pb ages for zircon from gabbro xenoliths from a late Pleistocene pyroclastic deposit are dominated by much older, ca. 310 Ma Pennsylvanian and ca. 1865 Ma Paleoproterozoic grains. Zircon age distributions and trace-element concentrations indicate that the ca. 310 Ma zircons date gabbroic intrusive rocks, and the ca. 1865 Ma zircons also are likely from igneous rocks in or beneath Peninsular terrane basement. The trace-element data imply that four of five Cretaceous–Paleocene zircons, and Pennsylvanian low-U, low-Th zircons in one sample, grew from metamorphic or hydrothermal fluids. Textural evidence of xenocrysts and a dominant population of ca. 1865 Ma zircon in juvenile crystal-rich andesite from the same pyroclastic deposit show that this basement has been assimilated by Redoubt magma. Equilibration temperatures and oxygen fugacities indicated by Fe-Ti–oxide minerals in the gabbros and crystal-rich andesite suggest sources near the margins of the Redoubt magmatic system, most likely in the magma accumulation and storage region currently outlined by seismicity and magma petrology at ∼4–10 km below sea level. Additionally, a partially melted gabbro from the 1990 eruption contains zircon with U-Pb ages between ca. 620 Ma and ca. 1705 Ma, as well as one zircon with a U-Th disequilibrium model age of 0 ka. The zircon ages demonstrate that Pennsylvanian, and probably Paleoproterozoic, igneous rocks exist in, or possibly beneath, Peninsular terrane basement. Discovery of Pennsylvanian gabbro similar in age to Skolai arc plutons 500 km to the northeast indicates that the Peninsular terrane, along with the Wrangellia and Alexander terranes, has been part of the Wrangellia composite terrane since at least Pennsylvanian time. Moreover, the zircon data suggest that a Paleoproterozoic continental fragment may be present in the mid-to-upper crust in southern Alaska.

Alaska↗

USGS2010

Preliminary bedrock geologic map of the Seward Peninsula, Alaska, and accompanying conodont data

This 1:500,000-scale geologic map depicts the bedrock geology of Seward Peninsula, western Alaska, on the North American side of the Bering Strait. The map encompasses all of the Teller, Nome, Solomon, and Bendeleben 1:250,000-scale quadrangles, and parts of the Shishmaref, Kotzebue, Candle, and Norton Bay 1:250,000-scale quadrangles (sheet 1; sheet 2). The geologic map is presented on Sheet 1. The pamphlet includes an introductory text, unit descriptions, tables of geochronologic data, and an appendix containing conodont (microfossil) data and a text about those data. Sheet 2 shows metamorphic and tectonic units, conodont color alteration indices, key metamorphic minerals, and locations of geochronology samples listed in the pamphlet.

Alaska↗

USGS1972

Reconnaissance geologic map of the Solomon D-6 quadrangle, Seward Peninsula, Alaska

The Solomon D-6 15- by 30-minute quadrangle lies 20 miles northeast of Nome, Alaska, and adjoins on the east the Nome D-l quadrangle mapped by Hummel (1962b) and on the west the Solomon D-5 quadrangle mapped by Smith (1910). Placer gold has been produced from Iron Creek and many of its tributaries, and a small amount of copper was shipped from the Wheeler mine. Many lode prospects contain small amounts of copper in silicified limestone within and near the base of thrust plates of carbonate rocks. Other lodes consist of well-defined veins containing gold and base-metal sulfide minerals, but none has been commercially productive. Mapped rock units include the "York Slate," of Precambrian age, which consists of a highly deformed and thick sequence of graphitic calcareous siltite, which contains thin limestone beds and intercalated(?) volcaniclastic rocks, and Paleozoic carbonate rocks, which have been converted largely to marble and schistose marble. Along and near the Kigluaik Mountains in the north part of the quadrangle, quartzo-feldspathic gneisses of Precambrian age are intruded by fine-grained granite. A very thick sequence of schistose thin-bedded argillaceous and dolomitic limestone overlies the York Slate and is correlative with a similar rock originally mapped in the York Mountains. Surficial deposits, consisting principally of moraine and stream-reworked moraine, mantle large parts of the quadrangle.

Alaska↗

USGS2011

Bedrock geologic map of the Seward Peninsula, Alaska, and accompanying conodont data

This 1:500,000-scale geologic map depicts the bedrock geology of Seward Peninsula, western Alaska, on the North American side of the Bering Strait. The map encompasses all of the Teller, Nome, Solomon, and Bendeleben 1:250,000-scale quadrangles, and parts of the Shishmaref, Kotzebue, Candle, and Norton Bay 1:250,000-scale quadrangles (sh. 1; sh. 2). The geologic map is presented on Sheet 1. The pamphlet includes an introductory text, detailed unit descriptions, tables of geochronologic data, and an appendix containing conodont (microfossil) data and a text explaining those data. Sheet 2 shows metamorphic and tectonic units, conodont color alteration indices, key metamorphic minerals, and locations of geochronology samples listed in the pamphlet. The map area covers 74,000 km 2 , an area slightly larger than West Virginia or Ireland.

Alaska↗

USGS2007

Geochemical data for stream-sediment, surface-water, rock, and vegetation samples from Red Mountain (Dry Creek), an unmined volcanogenic massive sulfide deposit in the Bonnifield District, Alaska Range, east-central Alaska

North-central and northeast Nevada contains numerous large plutons and smaller stocks but also contains many small, shallowly emplaced intrusive bodies, including dikes, sills, and intrusive lava dome complexes. Decades of geologic investigations in the study area demonstrate that many ore deposits, representing diverse ore deposit types, are spatially, and probably temporally and genetically, associated with these igneous intrusions. However, despite the number and importance of igneous instrusions in the study area, no synthesis of geochemical data available for these rocks has been completed. This report presents a synthesis of composition and age data for these rocks. The product represents the first phases of an effort to evaluate the time-space-compositional evolution of Mesozoic and Cenozoic magmatism in the study area and identify genetic associations between magmatism and mineralizing processes in this region.

Alaska↗