US Geological Survey research on the environmental fate of uranium mining and milling wastes

Studies by the US Geological Survey (USGS) of uranium mill tailings (UMT) have focused on characterizing the forms in which radionuclides are retained and identifying factors influencing the release of radionuclides to air and water. Selective extraction studies and studies of radionuclide sorption by and leaching from components of UMT showed alkaline earth sulfate and hydrous ferric oxides to be important hosts of radium-226 (²²⁶Ra) in UMT. Extrapolating from studies of barite dissolution in anerobic lake sediments, the leaching of²²⁶Ra from UMT by sulfate-reducing bacteria was investigated; a marked increase in²²⁶Ra release to aqueous solution as compared to sterile controls was demonstrated. A similar action of iron(III)-reducing bacteria was later shown. Ion exchangers such as clay minerals can also promote the dissolution of host-phase minerals and thereby influence the fate of radionuclides such as²²⁶Ra. Radon release studies examined particle size and ore composition as variables. Aggregation of UMT particles was shown to mask the higher emanating fraction of finer particles. Studies of various ores and ore components showed that UMT cannot be assumed to have the same radon-release characteristics as their precursor ores, nor can²²⁶Ra retained by various substrates be assumed to emanate the same fraction of radon. Over the last decade, USGS research directed at offsite mobility of radionuclides from uranium mining and milling processes has focused on six areas: the Midnite Mine in Washington; Ralston Creek and Reservoir, Colorado; sites near Canon City, Colorado; the Monument Valley District of Arizona and Utah; the Cameron District of Arizona; and the Puerco River basin of Arizona and New Mexico.     

Integration of historic groundwater data into the Continent Scale Geochemistry initiative

The groundwater dataset developed by Angela Giblin comprises over 5000 samples across much of Australia and is a useful contribution to the mapping of groundwater chemistry across Australia (the ‘Continental Scale Hydrogeochemistry’ initiative). Sampling and analytical methodology used by Giblin differed from many other protocols. In particular, water samples were not filtered in the field, or indeed prior to analysis. However, given the number of samples and their potential utility, it would be advantageous to modify data from these samples so that they can be readily integrated with other studies.

The combined data were initially sorted to ensure consistent detection limits. Data that did not pass a thorough QA/QC assessment were rejected. Correction, and where necessary removal, of data (owing to the analytical artefacts from solids contamination during analysis) was applied. The degree of contamination in bailed samples, and what data therefore to reject, is calculated using an algorithm developed and tested for Western Australian groundwaters. Geochemical changes between sampling and delayed analysis (days or weeks later) cannot be directly quantified. Other research predicted which elements should be most affected by this. This was further tested by comparing overlapping results from Giblin with more recent data from the same sites in Western Australia and Queensland. Results showed good agreement for salinities and major ions, and for the ratio indices (K:Na, etc.) determined from such data. Saturation Index calculations for sulfates gypsum, celestine and barite also closely matched between differing datasets. There was good agreement between datasets for F, HCO₃, Si, V, As, Mo, Ba and U, and moderate agreement for Li, Cr and Au. Weak agreement for pH meant that saturation indices for carbonate minerals such as calcite, dolomite, magnesite, siderite and rhodochrosite did not align, and there was very poor agreement for P, Co, Ni, Cu, Zn, Pb, Mn and Fe. However, in general, these comparisons indicate groundwater to be a robust geochemical medium.

Based on this study, this modified data should now be readily usable and ‘seamlessly’ comparable with other datasets. Combining data, across varying sources if necessary, allows hydrogeochemistry to be used to map geology, alteration, prospectivity and geomorphological factors from mine scale to the size of Australia.     

High-dispersion spectroscopic observations of Venus during 1968 and 1969 II. The carbon-dioxide band at 8689 Å

Thirty well-exposed photographic plates showing the spectrum of the carbon-dioxide band at 8689 Å in the atmosphere of Venus were obtained during 1968 and 1969. All spectra were obtained at a dispersion of 2 Å/mm for Venus phase angles varying from 10° to 126°. We find rotational temperatures ranging from 236 to 274 K. The average value of the rotational temperature is 246 ± 1 K (one standard deviation); for our 1967 observations, the rotational temperatures ranged from 222 to 248 K, with an average value of 238 ± 4 K. The variation of the equivalent width of the 8689 Å band, with Venus phase angle, was very similar for the two sets of observations (53 plates). The temporal variations, of approximately 30% were comparable with the phase variations over this limited range of phase angle.     

Sm-Nd and Zircon U-Pb ages from garnet-bearing eclogites, NE Oman: constraints on High-P metamorphism

Poly-deformed and poly-metamorphosed glaucophane-eclogite mega-boudins beneath the Samail Ophiolite, Oman record an early subduction-related high-P metamorphism as well as subsequent overprinting deformation and metamorphism related to exhumation. Previously published Rb/Sr ages of 78 Ma and ⁴⁰Ar/³⁹Ar ages of 82-79 Ma record the major NE-directed shearing event that partially exhumed the eclogites to a shallower crustal level. New Sm/Nd garnet-garnet leachate-whole rock isochron data from garnet-bearing eclogite assemblages in the As Sifah subwindow in NE Oman are 110±9 Ma (DG02-87D); 5-point isochron) and 109±13 Ma (DG02-86E; 3-point isochron). On the basis of microfabric and field structural relationships these ages are interpreted to reflect the timing of prograde, peak high-P metamorphism in the rocks structurally beneath the Samail Ophiolite. This metamorphism clearly predates the age of formation of the obducted Samail oceanic lithosphere (97-94 Ma) as well as the subsequent obduction onto the margin (80-70 Ma). A U-Pb SHRIMP zircon age from small (<200 μm in length) zircons with herring-bone textured zoning from DG02-87D indicate that rapid zircon growth associated with high-Si phengites occurred at 82±1 Ma. Zircon growth is possibly related to liberation of Zr on garnet breakdown during decompression metamorphism under high-P conditions with exhumation. These data require that crustal stacking models attendant with ophiolite obduction are inappropriate to explain the Oman high-P metamorphism.     

Interpretation of high-resolution spectra of Mars: IV. New calculations of the CO abundance

New data for carbon monoxide linewidths, pressure broadened by carbon dioxide at a temperature of 200°K, have been published since we wrote paper III of this series. The new data makes it possible to improve the accuracy of our previous estimate for the amount of CO in the atmosphere of Mars, based on the 2-0 band of CO. We now find 19.5±1.7 cm-atm_stp of carbon monoxide in the total path for Martian surface pressures in the range of 5 to 6 mb. These results are now in agreement with those obtained from the 3-0 band of CO.     

Tracing ground water input to base flow using sulfate (S, O) isotopes

Sulfate (S and O) isotopes used in conjunction with sulfate concentration provide a tracer for ground water contributions to base flow. They are particularly useful in areas where rock sources of contrasting S isotope character are juxtaposed, where water chemistry or H and O isotopes fail to distinguish water sources, and in arid areas where rain water contributions to base flow are minimal. Sonoita Creek basin in southern Arizona, where evaporite and igneous sources of sulfur are commonly juxtaposed, serves as an example. Base flow in Sonoita Creek is a mixture of three ground water sources: A, basin ground water with sulfate resembling that from Permian evaporite; B, ground water from the Patagonia Mountains; and C, ground water associated with Temporal Gulch. B and C contain sulfate like that of acid rock drainage in the region but differ in sulfate content. Source A contributes 50% to 70%, with the remainder equally divided between B and C during the base flow seasons. The proportion of B generally increases downstream. The proportion of A is greatest under drought conditions.     

Resolved OH megamaser emission in the nuclear region of the ultraluminous infrared galaxy Markarian 273

We present high angular resolution MERLIN observations of the 18-cm OH maser and continuum emission associated with the active core of the ultraluminous infrared galaxy Markarian 273. The continuum emission comes from three distinct regions in the central arcsecond of the galaxy. The brightest region of emission has a double-peaked structure which is spatially coincident with similar structures observed at 6 cm and 2.2 μm. The peak of the OH maser emission is spatially coincident with the peak in the continuum. For the first time the maser emission is spatially resolved, allowing us to measure the gas motion within the central 100 pc of the galaxy. Maser emission is found in both the 1665- and 1667-MHz lines, with no systematic offset found in the spatial locations of the two lines. The brighter component of the maser emission shows ordered motion and is aligned along the axis of the double-peaked structure in the brightest continuum region. The gas motion enables us to estimate the central mass density to be 850±50 M_⊙ pc⁻³, which corresponds to a total mass of ≈1.5×10⁸ M_⊙.