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At least 667 records · Page 37Linked to original sources
USGS1989

Can we determine the biological availability of sediment-bound trace elements?

It is clear from available data that the susceptibility of biological communities to trace element contamination differs among aquatic environments. One important reason is that the bioavailability of metals in sediments appears to be altered by variations in sediment geochemistry. However, methods for explaining or predicting the effect of sediment geochemistry upon metal bioavailability are poorly developed. Experimental studies demonstrate that ingestion of sediments and uptake from solution may both be important pathways of metal bioaccumulation in deposit/detritus feeding species. Relative importance between the two is geochemistry dependent. Geochemical characteristics of sediments also affect metal concentrations in the tissues of organisms collected from nature, but the specific mechanisms by which these characteristics influence metal bioavailability have not been rigorously demonstrated. Several prerequisites are necessary to better understand the processes that control metal bioavailability from sediments. 1) improved computational or analytical methods for analyzing distribution of metals among components of the sediments; 2) improved computational methods for assessing the influences of metal form in sediments on sediment-water metal exchange; and 3) a better understanding of the processes controlling bioaccumulation of metals from solution and food by metazoan species directly exposed to the sediments. Such capabilities would allow mechanistic explanations essential to the development of practical tools sought for determining sediment quality criteria for metals.

Hydrobiologia↗
USGS1983

Platinum-group elements in rocks from the voikar-syninsky ophiolite complex, Polar Urals, U.S.S.R.

Analyses of platinum-group elements (PGE) in rocks collected from the Voikar-Syninsky ophiolite in the Polar Urals suggest that the distribution and geochemistry of PGE in this Paleozoic ophiolite are similar to those in Mesozoic ophiolites from elsewhere. Chondrite-normalized PGE patterns for chromitite, the tectonite unit, and ultramafic and mafic cumulate unit have negative slopes. These results are similar to those found for chromitites from other ophiolites; stratiform chromities show positive slopes. If the magmas that form both types of chromitite originate from similar mantle source material with respect to PGE content, the processes involved must be quite different. However, the distinct chondrite-normalized PGE patterns may reflect differing source materials. ?? 1983 Springer-Verlag.

Mineralium Deposita↗
USGS1990

Trace-element and Sr, Nd, Pb, and O isotopic composition of Pliocene and Quaternary alkali basalts of the Patagonian Plateau lavas of southernmost South America

The Pliocene and Quaternary Patagonian alkali basalts of southernmost South America can be divided into two groups. The "cratonic" basalts erupted in areas of Cenozoic plateau volcanism and continental sedimentation and show considerable variation in 87Sr/86Sr (0.70316 to 0.70512), 143Nd/144Nd (e{open}Nd) and 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios (18.26 to 19.38, 15.53 to 15.68, and 38.30 to 39.23, respectively). These isotopic values are within the range of oceanic island basalts, as are the Ba/La, Ba/Nb, La/Nb, K/Rb, and Cs/Rb ratios of the "cratonic" basalts. In contrast, the "transitional" basalts, erupted along the western edge of the outcrop belt of the Pliocene and Quaternary plateau lavas in areas that were the locus of earlier Cenozoic Andean orogenic arc colcanism, have a much more restricted range of isotopic composition which can be approximated by 87Sr/86Sr=0.7039??0.0004, e{open}Nd, 206Pb/204Pb=18.60??0.08, 207Pb/204Pb=15.60??0.01, and 208Pb/204Pb=38.50??0.10. These isotopic values are similar to those of Andean orogenic are basalts and, compared to the "cratonic" basalts, are displaced to higher 87Sr/86Sr at a given 143Nd/144Nd and to higher 207Pb/204Pb at a given 208Pb/204Pb. The "transitional" basalts also have Ba/La, Ba/Nb, La/Nb, and Cs/Rb ratios higher than the "cratonic" and oceanic island basalts, although not as high as Andean orogenic are basalts. In contrast to the radiogenic isotopes, ??18O values for both groups of the Patagonian alkali basalts are indistinguishable and are more restricted than the range reported for Andean orogenic are basalts. Whole rock ??18O values calculated from mineral separates for both groups range from 5.3 to 6.5, while measured whole rock ??18O values range from 5.1 to 7.8. The trace element and isotopic data suggest that decreasing degrees of partial melting in association with lessened significance of subducted slabderived components are fundamental factors in the west to east transition from arc to back-arc volcanism in southern South America. The "cratonic" basalts do not contain the slab-derived components that impart the higher Ba/La, Ba/Nb, La/Nb, Cs/Rb, 87Sr/86Sr at a given 143Nd/144Nd, 207Pb/204Pb at a given 208Pb/204Pb, and ??18O to Andean orogenic arc basalts. Instead, these basalts are formed by relatively low degrees of partial melting of heterogeneous lower continental lithosphere and/or asthenosphere, probably due to thermal and mechanical pertubation of the mantle in response to subduction of oceanic lithosphere below the western margin of the continent. The "transitional" basalts do contain components added to their source region by either (1) active input of slab-derived components in amounts smaller than the contribution to the mantle below the arc and/or with lower Ba/La, Ba/Nb, La/Nb, and Cs/Rb ratios than below the arc due to progressive downdip dehydration of the subducted slab; or (2) subarc source region contamination processes which affected the mantle source of the "transitional" basalts earlier in the Cenozoic. ?? 1990 Springer-Verlag.

Contributions to Mineralogy and Petrology↗
USGS1987

Measurements of210Pb,137Cs, organic carbon and trace elements in sediments of the Illinois and Mississippi rivers

Radiometric dating of sediment accumulations by137Cs and210Pb has been successfully initiated in the Illinois and Mississippi Rivers. Sedimentation rates measured at 13 locations range from 0.7 to 3.6 cm/y. Chemical analysis has been completed for up to 45 major and trace elements in core samples. The upper Illinois River contains higher metal levels than the Mississippi River. The amount of carbon (energy) lost to sediments in large floodplain rivers is estimated between 370 and 4000 g/m2/y. ?? 1987 Akade??miai Kiado??.

Journal of Radioanalytical and Nuclear Chemistry A↗
USGS2014

Trace elements in seep waters along Whitewood Creek, South Dakota, and their toxicity to fathead minnows

Whitewood Creek, located in the Black Hills of southwestern South Dakota, has a long history of contamination from mining activity. Gold exploration began in the 1870s, and has continued since that time. Whitewood Creek received direct releases of tailings from 1870 to 1977 from Gold Run Creek in Lead, SD. It has been estimated that approximately 100 million to 1 billion tons of mining, milling, and ore processing wastes have been released by mining activity in the last century in to Whitewood Creek, the Belle Fourche river, and the Cheyenne River (Fox Consultants, Inc. 1984). Tailings deposition has altered the geomorphology of Whitewood Creek, and deposits up to 4.6 m. deep, have become stabilized by vegetation. Several other streams in the Black Hills also have been adversely affected by mining operations (Rahn 1996). As water leaches through rock strata that are disturbed by surface and subsurface mining, it dissolves inorganic elements and carries them to the groundwater. Groundwater movement through the extensive tailings deposits in the Whitewood Creek valley enter the creek at various seeps along its downstream course to the Belle Fourche river, and the Belle Fourche River itself, which empties into the Cheyenne River and eventually into Lake Oahe.

South Dakota↗
USGS2008

Metals and trace elements in giant garter snakes (Thamnophis gigas) from the Sacramento Valley, California, USA

The giant garter snake (GGS; Thamnophis gigas ) is a federally listed threatened species endemic to wetlands of the Central Valley of California. Habitat destruction has been the main factor in the decline of GGS populations, but the effects of contaminants on this species are unknown. To contribute to the recovery of these snakes, the U.S. Geological Survey (USGS) began studies of the life history and habitat use of GGSs in 1995. During a series of investigations conducted from 1995 to the present, specimens of dead GGSs were opportunistically collected from the Colusa National Wildlife Refuge (CNWR), the Natomas Basin, and other sites in northern California. Whole snakes were stored frozen for potential future analysis. As funding became available, we analyzed tissues of 23 GGSs to determine the concentrations of total mercury (Hg) and other trace elements in livers and concentrations of Hg in brains and tail clips. Mercury concentrations (μg/g, wet weight) ranged from 0.08 to 1.64 in livers, 0.01 to 0.18 in brains, and 0.02 to 0.32 in tail clips. In livers, geometric mean concentrations (μg/g, dry weight) of arsenic (25.7) and chromium (1.02) were higher than most values from studies of other snakes. Mercury concentrations in tail clips were positively correlated with concentrations in livers and brains, with the most significant correlations occurring at the Natomas Basin and when Natomas and CNWR were combined. Results indicate the value of using tail clips as a nonlethal bioindicator of contaminant concentrations.

Archives of Environmental Contamination and Toxico↗
USGS2009

On the occurrence, trace element geochemistry, and crystallization history of zircon from in situ ocean lithosphere

We characterize the textural and geochemical features of ocean crustal zircon recovered from plagiogranite, evolved gabbro, and metamorphosed ultramafic host-rocks collected along present-day slow and ultraslow spreading mid-ocean ridges (MORs). The geochemistry of 267 zircon grains was measured by sensitive high-resolution ion microprobe-reverse geometry at the USGS-Stanford Ion Microprobe facility. Three types of zircon are recognized based on texture and geochemistry. Most ocean crustal zircons resemble young magmatic zircon from other crustal settings, occurring as pristine, colorless euhedral (Type 1) or subhedral to anhedral (Type 2) grains. In these grains, Hf and most trace elements vary systematically with Ti, typically becoming enriched with falling Ti-in-zircon temperature. Ti-in-zircon temperatures range from 1,040 to 660°C (corrected for a TiO2 ≈ 0.7, a SiO2 ≈ 1.0, pressure ≈ 2 kbar); intra-sample variation is typically ~60–150°C. Decreasing Ti correlates with enrichment in Hf to ~2 wt%, while additional Hf-enrichment occurs at relatively constant temperature. Trends between Ti and U, Y, REE, and Eu/Eu* exhibit a similar inflection, which may denote the onset of eutectic crystallization; the inflection is well-defined by zircons from plagiogranite and implies solidus temperatures of ~680–740°C. A third type of zircon is defined as being porous and colored with chaotic CL zoning, and occurs in ~25% of rock samples studied. These features, along with high measured La, Cl, S, Ca, and Fe, and low (Sm/La) N ratios are suggestive of interaction with aqueous fluids. Non-porous, luminescent CL overgrowth rims on porous grains record uniform temperatures averaging 615 ± 26°C (2SD, n = 7), implying zircon formation below the wet-granite solidus and under water-saturated conditions. Zircon geochemistry reflects, in part, source region; elevated HREE coupled with low U concentrations allow effective discrimination of ~80% of zircon formed at modern MORs from zircon in continental crust. The geochemistry and textural observations reported here serve as an important database for comparison with detrital, xenocrystic, and metamorphosed mafic rock-hosted zircon populations to evaluate provenance.

Contributions to Mineralogy and Petrology↗
USGS2021

Material properties and triggering mechanisms of an andesitic lava dome collapse at Shiveluch Volcano, Kamchatka, Russia, revealed using the finite element method

Shiveluch volcano (Kamchatka, Russia) is an active andesitic volcano with a history of explosive activity, dome extrusion, and structural collapse during the Holocene. The most recent major (> 1 km 3 ) dome collapse occurred in November 1964, producing a ~ 1.5 km 3 debris avalanche that traveled over 15 km from the vent and triggered a phreatic explosion followed by a voluminous (~ 0.8 km 3 ) eruption of juvenile pyroclastic material. Seismic records suggest that the collapse was likely triggered by a magnitude 5.1 earthquake associated with the ascent of magma into the edifice. The geomechanical properties of the pre-1964 dome are unknown; accordingly, the mechanics of the collapse are poorly understood. This project employs numerical slope stability modeling using the finite element method to constrain probable ranges of geomechanical properties for the materials involved in the collapse, considering earthquake loading as the most likely triggering mechanism. Model results show good agreement with the 1964 collapse geometry considering Geological Strength Index and horizontal pseudo-static seismic coefficient ranges of 30–60 and 0.05–0.15 g, respectively, representing variably fractured and altered dome rocks under moderate earthquake loading, confirming that ground acceleration alone could have triggered the dome collapse. Deep-seated rotational sliding is the dominant failure mode, but local extension within the dome during failure appears to play an important role in the development of the collapse. The findings of this work allow for better forward modeling of potential future collapses, the results of which can be incorporated into regional hazard and risk assessments.

Shiveluch Volcano↗
USGS2007

Report of the IAU/IAG Working Group on cartographic coordinates and rotational elements: 2006

Every three years the IAU/IAG Working Group on Cartographic Coordinates and Rotational Elements revises tables giving the directions of the poles of rotation and the prime meridians of the planets, satellites, minor planets, and comets. This report introduces improved values for the pole and rotation rate of Pluto, Charon, and Phoebe, the pole of Jupiter, the sizes and shapes of Saturn satellites and Charon, and the poles, rotation rates, and sizes of some minor planets and comets. A high precision realization for the pole and rotation rate of the Moon is provided. The expression for the Sun's rotation has been changed to be consistent with the planets and to account for light travel time ?? 2007 Springer Science+Business Media B.V.

Celestial Mechanics and Dynamical Astronomy↗
USGS2010

Report of the IAU Working Group on cartographic coordinates and rotational elements: 2009

Every three years the IAU Working Group on Cartographic Coordinates and Rotational Elements revises tables giving the directions of the poles of rotation and the prime meridians of the planets, satellites, minor planets, and comets. This report takes into account the IAU Working Group for Planetary System Nomenclature (WGPSN) and the IAU Committee on Small Body Nomenclature (CSBN) definition of dwarf planets, introduces improved values for the pole and rotation rate of Mercury, returns the rotation rate of Jupiter to a previous value, introduces improved values for the rotation of five satellites of Saturn, and adds the equatorial radius of the Sun for comparison. It also adds or updates size and shape information for the Earth, Mars’ satellites Deimos and Phobos, the four Galilean satellites of Jupiter, and 22 satellites of Saturn. Pole, rotation, and size information has been added for the asteroids (21) Lutetia, (511) Davida, and (2867) Šteins. Pole and rotation information has been added for (2) Pallas and (21) Lutetia. Pole and rotation and mean radius information has been added for (1) Ceres. Pole information has been updated for (4) Vesta. The high precision realization for the pole and rotation rate of the Moon is updated. Alternative orientation models for Mars, Jupiter, and Saturn are noted. The Working Group also reaffirms that once an observable feature at a defined longitude is chosen, a longitude definition origin should not change except under unusual circumstances. It is also noted that alternative coordinate systems may exist for various (e.g. dynamical) purposes, but specific cartographic coordinate system information continues to be recommended for each body. The Working Group elaborates on its purpose, and also announces its plans to occasionally provide limited updates to its recommendations via its website, in order to address community needs for some updates more often than every 3 years. Brief recommendations are also made to the general planetary community regarding the need for controlled products, and improved or consensus rotation models for Mars, Jupiter, and Saturn.

Celestial Mechanics and Dynamical Astronomy↗
USGS2018

Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2015

This report continues the practice where the IAU Working Group on Cartographic Coordinates and Rotational Elements revises recommendations regarding those topics for the planets, satellites, minor planets, and comets approximately every three years. The Working Group has now become a “functional working group” of the IAU and its membership is open to anyone interested in participating. We describe the procedure for submitting questions about the recommendations given here or the application of these recommendations for creating a new or updated coordinate system for a given body. Regarding body orientation, the following bodies have been updated: Mercury, based on MESSENGER results; Mars, along with a refined longitude definition; Phobos; Deimos; (1) Ceres; (52) Europa; (243) Ida; (2867) Šteins; Neptune; (134340) Pluto and its satellite Charon; comets 9P/Tempel 1, 19P/Borrelly, 67P/Churyumov-Gerasimenko, and 103P/Hartley 2, noting that such information is valid only between specific epochs. The special challenges related to mapping 67P/Churyumov-Gerasimenko are also discussed. Approximate expressions for the Earth have been removed in order to avoid confusion, and the low precision series expression for the Moon’s orientation has been removed. The previously on-line only recommended orientation model for (4) Vesta is repeated with an explanation of how it was updated. Regarding body shape, text has been included to explain the expected uses of such information, and the relevance of the cited uncertainty information. The size of the Sun has been updated and notation added that the size and the ellipsoidal axes for the Earth and Jupiter have been recommended by an IAU Resolution. The distinction of a reference radius for a body (here, the Moon and Titan) is made between cartographic uses, and for orthoprojection and geophysical uses. The recommended radius for Mercury has been updated based on MESSENGER results. The recommended radius for Titan is returned to its previous value. Size information has been updated for 13 other Saturnian satellites and added for Aegaeon. The sizes of Pluto and Charon have been updated. Size information has been updated for (1) Ceres and given for (16) Psyche and (52) Europa. The size of (25143) Itokawa has been corrected. In addition, the discussion of terminology for the poles (hemispheres) of small bodies has been modified and a discussion on cardinal directions added. Although they continue to be used for planets and their satellites, it is assumed that the planetographic and planetocentric coordinate system definitions do not apply to small bodies. However, planetocentric and planetodetic latitudes and longitudes may be used on such bodies, following the right-hand rule. We repeat our previous recommendations that planning and efforts be made to make controlled cartographic products; newly recommend that common formulations should be used for orientation and size; continue to recommend that a community consensus be developed for the orientation models of Jupiter and Saturn; newly recommend that historical summaries of the coordinate systems for given bodies should be developed, and point out that for planets and satellites planetographic systems have generally been historically preferred over planetocentric systems, and that in cases when planetographic coordinates have been widely used in the past, there is no obvious advantage to switching to the use of planetocentric coordinates. The Working Group also requests community input on the question submitting process, posting of updates to the Working Group website, and on whether recommendations should be made regarding exoplanet coordinate systems.

Celestial Mechanics and Dynamical Astronomy↗
USGS2013

Environmental survey in the Tuul and Orkhon River basins of north-central Mongolia, 2010: Metals and other elements in streambed sediment and floodplain soil

Streambed sediment and subsurface floodplain soil were sampled for elemental analyses from 15 locations in river basins of north-central Mongolia during August 2010. Our primary objective was to conduct a reconnaissance-level assessment of potential inputs of toxicologically important metals and metalloids to Lake Baikal, Russia, that might originate from mining and urban activities within tributaries of the Selenga River in Mongolia. Samples were collected in triplicate from all sites, then dried, and sieved to <2 mm for analysis by portable X-ray florescence spectroscopy and by inductively coupled plasma mass spectrometry after digestion with concentrated nitric and hydrochloric acids. Arsenic, copper, and mercury were greatly elevated in sediment and floodplain soil collected from tributary streams located near two major mining operations. Lead and zinc were moderately elevated in streambed sediment and in floodplain soil obtained from a small tributary in the capital city of Ulaanbaatar, but those concentrations were considerably less than probable effects benchmarks. Historical and possibly present mining activities have led to considerable metal contamination in certain tributaries of the Orkhon River in north-central Mongolia; however, metals originating from those sources did not appear to be accumulating in sediments at our downstream-most sampling sites located near the border between Mongolia and Russia.

Environmental Monitoring and Assessment↗
USGS2008

Transport and distribution of trace elements and other selected inorganic constituents by suspended particulates in the Salton Sea Basin, California, 2001

In order to examine the transport of contaminants associated with river-derived suspended particles in the Salton Sea, California, large volume water samples were collected in transects established along the three major rivers emptying into the Salton Sea in fall 2001. Rivers in this area carry significant aqueous and particulate contaminant loads derived from irrigation water associated with the extensive agricultural activity, as well as wastewater from small and large municipalities. A variety of inorganic constituents, including trace metals, nutrients, and organic carbon were analyzed on suspended material isolated from water samples collected at upriver, near-shore, and off-shore sites established on the Alamo, New, and Whitewater rivers. Concentration patterns showed expected trends, with river-borne metals becoming diluted by organic-rich algal particles of lacustrine origin in off-shore stations. More soluble metals, such as cadmium, copper, and zinc showed a more even distribution between sites in the rivers and off-shore in the lake basin. General distributional trends of trace elements between particulate and aqueous forms were discerned by combining metal concentration data for particulates from this study with historical aqueous metals data. Highly insoluble trace metals, such as iron and aluminum, occurred almost entirely in the particulate phase, while major cations and approximately 95% of selenium were transported in the soluble phase. Evidence for greater reducing conditions in the New compared to the Alamo River was provided by the greater proportion of reduced (soluble) manganese in the New River. Evidence of bioconcentration of selenium and arsenic within the lake by algae was provided by calculating "enrichment" concentration ratios from metal concentrations on the algal-derived particulate samples and the off-shore sites. ?? 2008 Springer Science+Business Media B.V.

Hydrobiologia↗
USGS2026

Rare earth element potential in coal and coal ash in the U.S. Gulf Coast

United States heavy reliance on imports of critical minerals (CMs), including rare earth elements (REEs), underscores the importance of development of domestic sources. The study objective was to quantify CM and REE concentrations in coal and coal ash in the US Gulf Coast region. CM and REE concentrations were measured for 118 samples from outcrops and 14 mines in the Gulf Coast. Results show that total REE + Yttrium (REY) concentrations (dry coal basis) are comparable to those of the upper continental crust (UCC) with localized hot spots, such as the Texas Gibbons Creek mine (REY ≤ ~ 2860 ppm). When normalized to UCC REY concentration (169 ppm, dry coal basis), REY to UCC ratios for Gulf Coast coal samples range from 0.1 to 17 (median ratio 0.6). REE extractability from lignites is high (median: 63%–93%) using environmentally benign weak acid. In addition to raw coal, coal ash from power plants could also serve as an REE source with a median ratio of REY in ash relative to coal of 4; however, extractability from coal ash is generally much lower (≤ 5% using the same weak acid as in coal). The median basket price for extracted REY as oxides from coal, assuming 70% extractability, is $3.2 per tonne of coal and $186 billion based on 58 billion metric tonnes of dry coal in the Gulf Coast. REEs important for magnets (Pr + Nd + Tb + Dy) account for ~ 80% of the total value. The corresponding median basket price for extracted REY as oxides from coal ash, assuming ~ 30% extractability, is ~$4.4 per tonne of ash and $1.2 billion based on 258 million tonnes of ash. REE production from coal would likely require co-products, such as activated carbon or humic acids, to attain economic viability. Production of REEs from coal ash could offset remediation costs related to potential water contamination. This reconnaissance study shows the potential for REE production from coal and coal ash in the Gulf Coast; however, carbon coproducts and/or societal benefits would likely be required for socioeconomic viability.

Alabama, Florida, Louisiana, Mississippi, Texas↗
USGS1983

Rare-earth element geochemistry and the origin of andesites and basalts of the Taupo Volcanic Zone, New Zealand

Two types of basalt (a high-Al basalt associated with the rhyolitic centres north of Taupo and a "low-Al" basalt erupted from Red Crater, Tongariro Volcanic Centre) and five types of andesite (labradorite andesite, labradorite-pyroxene andesite, hornblende andesite, pyroxene low-Si andesite and olivine andesite/low-Si andesite) occur in the Taupo Volcanic Zone (TVZ), North Island, New Zealand. Rare-earth abundances for both basalts and andesites are particularly enriched in light rare-earth elements. High-Al basalts are more enriched than the "low-Al" basalt and have values comparable to the andesites. Labradorite and labradorite-pyroxene andesites all have negative Eu anomalies and hornblende andesites all have negative Ce anomalies. The former is probably due to changing plagioclase composition during fractionation and the latter to late-stage hydration of the magma. Least-squares mixing models indicate that neither high-Al nor "low-Al" basalts are likely sources for labradorite/labradorite-pyroxene andesites. High-Al basalts are considered to result from fractionation of olivine and clinopyroxene from a garnet-free peridotite at the top of the mantle wedge. Labradorite/labradorite-pyroxene andesites are mainly associated with an older NW-trending arc. The source is likely to be garnet-free but it is not certain whether the andesites result from partial melting of the top of the subducting plate or a hydrated lower portion of the mantle wedge. Pyroxene low-Si andesites probably result from cumulation of pyroxene and calcic plagioclase within labradorite-pyroxene andesites, and hornblende andesites by late-stage hydration of labradorite-pyroxene andesite magma. Olivine andesites, low-Si andesites and "low-Al" basalts are related to the NNE-trending Taupo-Hikurangi arc structure. Although the initial source material is different for these lavas they have probably undergone a similar history to the labradorite/labradorite-pyroxene andesites. All lavas show evidence of crustal contamination. ?? 1983.

Chemical Geology↗
USGS1988

The effect of mining on the sediment - trace element geochemistry of cores from the Cheyenne River arm of Lake Oahe, South Dakota, U.S.A.

Six cores, ranging in length from 1 to 2 m, were collected in the Cheyenne River arm of Lake Oahe, South Dakota, to investigate potential impacts from gold-mining operations around Lead, South Dakota. Sedimentation rates in the river arm appear to be event-dominated and rapid, on the order of 6-7 cm yr.-1. All the chemical concentrations in the core samples fall within the wide ranges previously reported for the Pierre Shale of Cretaceous age and with the exception of As, generally are similar to bed sediment levels in the Cheyenne River, Lake Oahe and Foster Bay. Based on the downcore distribution of Mn, it appears that reducing conditions exist in the sediment column of the river arm below 2-3 cm. The reducing conditions do not appear to be severe enough to produce differentiation of Fe and Mn throughout the sediment column in the river arm. Cross-correlations for high-level metal-bearing strata within the sediment column can be made for several strata and for several cores; however, cross-correlations for all the high-level metal-bearing strata are not feasible. As is the only element which appears enriched in the core samples compared to surface sediment levels. Well-crystallized arsenopyrite was found in high-As bearing strata from two cores and probably was transported in that form from reducing sediment-storage sites in the banks or floodplains of Whitewood Creek and the Belle Fourche River. It has not oxidized due to the reducing conditions in the sediment column of the Cheyenne River arm. Some As may also be transported in association with Fe- and Mn-oxides and -hydroxides, remobilized under the reducing conditions in the river arm, and then reprecipitated in authigenic sulfide phases. In either case, the As appears to be relatively immobile in the sediment column. ?? 1988.

Chemical Geology↗
USGS1988

Sr and Nd isotopic and trace element compositions of Quaternary volcanic centers of the Southern Andes

Isotopic compositions of samples from six Quaternary volcanoes located in the northern and southern extremities of the Southern Volcanic Zone (SVZ, 33–46°S) of the Andes and from four centers in the Austral Volcanic Zone (AVZ, 49–54°S) range for 87 Sr/ 86 Sr from 0.70280 to 0.70591 and for 143 Nd/ 144 Nd from 0.51314 to 0.51255. The ranges are significantly greater than previously reported from the southern Andes but are different from the isotopic compositions of volcanoes in the central and northern Andes. Basalts and basaltic andesites from three centers just north of the Chile Rise-Trench triple junction have 87 Sr/ 86 Sr , 143 Nd/ 144 Nd , La/Yb , Ba/La , and Hf/Lu that lie within the relatively restricted ranges of the basic magmas erupted from the volcanic centers as far north as 35°S in the SVZ of the Andes. The trace element and Sr and Nd isotopic characteristics of these magmas may be explained by source region contamination of subarc asthenosphere, with contaminants derived from subducted pelagic sediments and seawater-altered basalts by dehydration of subducted oceanic lithosphere. In the northern extremity of the SVZ between 33° and 34°S, basaltic andesites and andesites have higher 87 Sr/ 86 Sr , Rb/Cs , and Hf/Lu , and lower 143 Nd/ 144 Nd than basalts and basaltic andesites erupted farther south in the SVZ, which suggests involvement of components derived from the continental crust. In the AVZ, the most primitive sample, high-Mg andesite from the southernmost volcanic center in the Andes (54°S) has Sr and Nd isotopic compositions and KR/b and Ba/La similar to MORB. The high La/Yb of this sample suggests formation by small degrees of partial melting of subducted MORB with garnet as a residue. Samples from centers farther north in the AVZ show a regionally regular northward increase in SiO 2 , K 2 O, Rb, Ba, Ba/La , and 87 Sr/ 86 Sr/ and decrease in MgO, Sr, KR/b , Rb/Cs , and 143 Nd/ 144 Nd , suggesting increasingly greater degrees of fractional crystallization and associated intra-crustal contamination.

Earth and Planetary Science Letters↗