Post-mine metal transport and attenuation in the Keno Hill mining district, central Yukon, Canada

 The Keno Hill mining district in central Yukon was the second largest silver producer in Canada with mines operating from 1913 to 1989 on more than 65 vein silver deposits. The seven and a half decades of mining activities have generated large volumes of mine waste disposed on the land surface, resulting in elevated metal contents in numerous small drainages. To assess the extent of metal mobilization, old mine workings and the associated mine waste were examined and the water courses draining to a major river valley sampled. The results of field observations and an array of water and sediment analyses led to three major conclusions. 1. Acid mine drainage is not widespread because of galvanic protection of pyrite from oxidative dissolution and neutralization by carbonates in the country rock. 2. Mechanisms operative to limit aqueous metal transport in small streams in the district include cryogenic precipitation, coprecipitation and sorption. 3. The near-surface concentration of metals limits the options of waste disposal in future mining developments due to potential metal-leaching problems. Received: 12 December 1995 · Accepted: 26 March 1996     

Changes in Surface Morphology of Calcite Exposed to the Oceanic Water Column

Reactions occurring on the surfaces of biogenic carbonate minerals can have important consequences for the biogeochemical cycle of carbon. In this study, carbonate mineral surface reactions with ambient seawater were investigated by atomic force microscopy (AFM). A sampling method was developed in which calcite surfaces were hung at discrete depths on a sediment trap array line for a three-day deployment period in subtropical North Pacific waters. Changes in surface morphologies were examined at nanometer resolution and evaluated using as a constraint the depth profile of calcite saturation in these waters. Evidence suggests that: (1) organic films which develop on carbonate surfaces exposed to shallow seawater may be responsible for the oversaturated state of the upper oceanic water column, (2) dissolution of carbonate minerals within the shallow warm layer of the ocean could be responsible for part of the alkalinity anomaly observed in the North Pacific.     

Cosmogenic chlorine-36 production rates in terrestrial rocks

Chlorine-36 is produced in rocks exposed to cosmic rays at the earth surface through thermal neutron activation of ³⁵Cl, spallation of ³⁹K and ⁴⁰Ca, and slow negative moun capture by ⁴⁰Ca. We have measured the ³⁶Cl content of ¹⁴C-dated glacial boulders from the White Mountains in eastern California and in a ¹⁴C-dated basalt flow from Utah. Effective, time-intergrated production parameters were calculated by simultaneous solution of the ³⁶Cl production equations. The production rates due to spallation are 4160 ± 310 and 3050 ± 210 atoms ³⁶Cl yr⁻¹ mol⁻¹³⁹K and ⁴⁰Ca, respectively. The thermal neutron capture rate was calculated to be (3.07 ± 0.24) × 10⁵ neutrons (kg of rock)⁻¹ yr⁻¹. The reported values are normalized to sea level and high geomagnetic latitudes. Production of ³⁶Cl at different altitudes and latitudes can be estimated by appropriate scaling of the sea level rates. Chlorine-36 dating was performed on carbonate ejecta from Meteor Crater, Arizona, and late Pleistocene morainal boulders from the Sierra Nevada, California. Calculated ³⁶Cl ages are in good agreement with previously reported ages obtained using independent methods.     

A Proposal to Use Chlorine-36 for Monitoring the Movement of Radionuclides from Nuclear Explosions

Chlorine-36 has been produced in large amounts by hundreds of nuclear explosions on the Nevada Test Site as well as 12 off-site explosions at eight locations in five states. Continued monitoring of the redistribution of radionuclides by subsurface water is of concern in most of the areas affected by the detonations. Chlorine-36 has the following advantages as a built-in tracer for this redistribution: its mobility is equal to or greater than water, its long half-life assures its continued usefulness over long periods, collection and storage of samples is simple, it is not subject to vapor transport at ordinary temperatures, its natural background is very low, and it does not form insoluble precipitates. Chlorine-36 from the Gnome event near Carlsbad, New Mexico, illustrates how ³⁶C1 can be used to help study the redistribution of radionuclides in the soil profile. Chlorine-36 is also potentially useful as a tracer to study movement of contaminants around large nuclear reactor complexes and near respositories for radioactive waste.     

Estimation of surface heat and momentum fluxes using the flux-variance method above uniform and non-uniform terrain

Eddy-correlation measurements above an uneven-aged forest, a uniform-irrigated bare soil field, and within a grass-covered forest clearing were used to investigate the usefulness of the fluxvariance method above uniform and non-uniform terrain. For this purpose, the Monin and Obukhov (1954) variance similarity functions were compared with direct measurements. Such comparisons were in close agreement for momentum and heat but not for water vapor. Deviations between measured and predicted similarity functions for water vapor were attributed to three factors: 1) the active role of temperature in surface-layer turbulence, 2) dissimilarity between sources and sinks of heat and water vapor at the ground surface, and 3) the non-uniformity in water vapor sources and sinks. It was demonstrated that the latter non-uniformity contributed to horizontal gradients that do not scale with the vertical flux. These three factors resulted in a turbulence regime that appeared more efficient in transporting heat than water vapor for the dynamic convective sublayer but not for the dynamic sublayer. The agreement between eddy-correlation measured and flux-variance predicted sensible heat flux was better than that for latent heat flux at all three sites. The flux-variance method systematically overestimated the latent heat flux when compared to eddy-correlation measurements. It was demonstrated that the non-uniformity in water vapor sources reduced the surface flux when compared to an equivalent uniform terrain subjected to identical shear stress, sensible heat flux, and atmospheric water vapor variance. Finally, the correlation between the temperature and water vapor fluctuations was related to the relative efficiency of surface-layer turbulence in removing heat and water vapor. These relations were used to assess critical assumptions in the derivation of the flux-variance formulation.     

On the aging of comets

This study is based primarily on the calculations of comet orbits over ~ 10⁶ years for 160 short-period comets by Harold F. Levison and Martin J. Duncan from which there are calculated ablation AGES. There are positive statistical correlations (having many deviations) with radial nongravitational forces, comet activity measures, and dust-to-gas ratios in the spectra, in the sense that comets of greater AGES tend to be less active and to show less dust in their spectra than comets of lesser AGES.Harvard-Smithsonian Center for Astrophysics     

Evolution of Io's volatile inventory

Using Voyager results, we have made crude estimates of the rate at which Io loses volatiles by a variety of processes to the surrounding magnetosphere for both the current SO₂-dominated atmosphere as well as hypothetical paleoatmospheres in which other gases, such as N₂, may have been the dominant constituent. Loss rates are strongly influenced by the surface pressure on the night side, the relationship between the exobase and the Jovian magnetospheric boundary, the exospheric temperature, and the peak altitudes reached by volcanic plumes. Several mechanisms make significant contributions to the prodigious rate at which Io is currently losing volatiles. These include: interaction of the magnetospheric plasma with volcanic plume particles and the background atmosphere; sputtering of ices on the surface, if the nightside atmospheric pressure is low enough; and Jeans' escape of O, a dissociation product of SO₂ gas. For paleoatmospheres, only the first two of these mechanisms would have been effective. However, they are capable of eliminating large amounts of N₂ and other volatiles from Io over the satellite's lifetime. Io could have also lost large amounts of water over its lifetime due to the extensive recycling of water between its upper and lower crust, with the partial dissociation of water vapor in silicate magma chambers initiating this loss process. Significant amounts of water may also have been lost as a result of the interaction of the magnetospheric plasma with water ice particles in volcanic plumes. Once an SO₂-dominated atmosphere becomes established, much water may have also been lost through the sputtering of surface water ice.