Estimation of sedimentation rates based on the excess of radium 228 in granitic reservoir sediments

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Pb dispersion pathways in mountain soils contaminated by ancient mining and smelting activities

International audienceOver the last millennia, mining and smelting activities have produced large amounts of mine and metallurgical wastes that remain enriched in potentially toxic trace elements (PTE). A spatial distribution of Pb content was coupled to mineralogical observations and single extraction tests to characterise the Pb contamination legacy and Pb dispersion trajectories in an ancient mining and smelting site that has been abandoned for approximatively 200 years. In the Peisey-Nancroix Pb-Ag mine (Savoy, France), extreme anthropogenic Pb contamination is located close to the slag heaps and along ore and slag transport paths. The contamination gradient is restricted to a few hundred metres downhill, down to background Pb values. The Pb-bearing phases change along the contamination gradient. The most contaminated soils contain significant amounts of galena and slags that are more or less weathered into pyromorphite and cerussite. Pb-bearing Mn (hydr-)oxides are the most stable and ubiquitous forms of Pb, which proportions increase downgradient. Despite the presence of some stable Pbbearing phases (pyromorphite, Pb-bearing Mn (hydr-)oxides), extraction tests indicate that a small proportion of Pb may still be mobile over time

Les impacts environnementaux à long-terme des exploitations minières : la mine de Pb-Ag de Peisey-Nancroix (1644-1866, Alpes françaises)

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The legacy of metallurgical atmospheric contamination in a mountainous catchment: A delayed response of Pb contamination

International audienceMetal-rich fumes emitted during ore smelting contribute to widespread anthropogenic contamination. Environmental archives (such as lake sediments) record fallouts deposited on lake and terrestrial surfaces during ancient mining and smelting activities. However, very few is known about the potential buffering effect of soils upon which metal falls out, prior to be released through runoff and or/erosion, hence leading to pervasive contamination fluxes long after the ceasing of metallurgical activities. Here we aim at assessing this long-term remobilisation in a mountainous catchment area. Lake sediments and soils were collected 7 km upward a 200-year-old historic mine. The Pb-Ag mine of Peisey-Nancroix was operated between the 17 th and the 19 th centuries with a documented smelting period of 80 years. In lake sediments, the total Pb content varies from 29 mg.kg-1 prior smelting to 148 mg.kg-1 during ore smelting. Pb isotopes in lake sediments and soils provide evidence of anthropogenic Pb from the local ore (206 Pb/ 207 Pb = 1.173; 208 Pb/ 206 Pb = 2.094) during and after smelting, suggesting anthropogenic Pb remobilisation for 200 years. The accumulation rates of anthropogenic Pb calculated in lake sediments after the smelting period confirm such a remobilization. Despite

Les impacts environnementaux à long-terme des exploitations minières : la mine de Pb-Ag de Peisey-Nancroix (1644-1866, Alpes françaises)

International audienc

Collision rates estimated from exact N -body simulations of a one-dimensional plasma

In a plasma, the charged particles interact via long-range forces and this interaction causes the plasma to exhibit collective effects. If the graininess or coupling parameter g goes to zero (ideal collisionless plasma), two-body collisions are negligible while collective effects dominate the dynamics. In contrast, when g ≈ 1 collisions play a significant role. To study the transition between a collisionless and a collisional regime, a N-body code was developed and used in this work. The code solves exactly, in one spatial dimension, the dynamics of N infinite parallel plane sheets for both ion and electron populations. We illustrate the transition between individual and collective effects by studying two basic plasma phenomena, the twostream instability and Langmuir waves, for different values of g. The numerical collision rates given by the N-body code increase linearly with g for both phenomena, although with proportionality factors that differ by roughly a factor of two, a discrepancy that may be accounted for by the different initial conditions. All in all, the usual collision rates published in the literature (Spitzer collisionality) appear to compare rather well with the rates observed in our simulations

Les impacts environnementaux à long-terme des exploitations minières : la mine de Pb-Ag de Peisey-Nancroix (1644-1866, Alpes françaises)

International audienc

Collision rates estimated from exact N -body simulations of a one-dimensional plasma

International audienceIn a plasma, the charged particles interact via long-range forces, and this interaction causes the plasma to exhibit collective effects. If the graininess or coupling parameter g goes to zero (ideal collisionless plasma), two-body collisions are negligible, while collective effects dominate the dynamics. In contrast, when [Formula: see text] collisions play a significant role. To study the transition between a collisionless and a collisional regime, a N-body code was developed and used in this work. The code solves exactly, in one spatial dimension, the dynamics of N infinite parallel plane sheets for both ion and electron populations. We illustrate the transition between individual and collective effects by studying two basic plasma phenomena, the two-stream instability and Langmuir waves, for different values of g. The numerical collision rates given by the N-body code increase linearly with g for both phenomena, although with proportionality factors that differ by roughly a factor of two, a discrepancy that may be accounted for by the different initial conditions. All in all, the usual collision rates published in the literature (Spitzer collisionality) appear to compare rather well with the rates observed in our simulations

Collision rates estimated from exact N -body simulations of a one-dimensional plasma

In a plasma, the charged particles interact via long-range forces and this interaction causes the plasma to exhibit collective effects. If the graininess or coupling parameter g goes to zero (ideal collisionless plasma), two-body collisions are negligible while collective effects dominate the dynamics. In contrast, when g ≈ 1 collisions play a significant role. To study the transition between a collisionless and a collisional regime, a N-body code was developed and used in this work. The code solves exactly, in one spatial dimension, the dynamics of N infinite parallel plane sheets for both ion and electron populations. We illustrate the transition between individual and collective effects by studying two basic plasma phenomena, the twostream instability and Langmuir waves, for different values of g. The numerical collision rates given by the N-body code increase linearly with g for both phenomena, although with proportionality factors that differ by roughly a factor of two, a discrepancy that may be accounted for by the different initial conditions. All in all, the usual collision rates published in the literature (Spitzer collisionality) appear to compare rather well with the rates observed in our simulations