Laurent Daudin

The Pierre Süe Laboratory nuclear microprobe as a multi-disciplinary analysis tool

Abstract The nuclear microprobe at the Pierre Sue Laboratory is a facility exclusively devoted to microanalysis. The microprobe consisting of a single stage Van de Graaff accelerator and two microbeam lines will be described. Simultaneous detection (X-rays, γ-rays, charged particles, etc.) and imaging are routinely performed by a PC-based multi-parameter data acquisition system. Telescope mounting is frequently used for particle identification particularly when performing nuclear reaction analysis (NRA). A unique feature of the Pierre Sue Laboratory nuclear microprobe is the ability to analyze radioactive samples. One of the two beamlines has been specifically designed for that purpose. Radioactive environment requires suited target handling and detection setups. Main application fields of the microprobe are material, earth, planetary, environmental sciences and electronuclear related topics.

Development of “position–charge–time” tagged spectrometry for ion beam microanalysis

During sample analysis in scanning mode, our PC-based data acquisition system (MPA/PCTM) is able to record eight parameter events in a list data file. The system can acquire simultaneously collected energies from up to four detectors (X and gamma ray detectors, charged particle detectors). Each event is tagged with beam position, integrated charge and a time-code. Beam scanning control is currently upgraded. Until now, beam position tagging required a double conversion (digital-analog and analog-digital) generating supplementary dead time. The new system allows direct digital transfer with high-resolution maps and large scanning rate capabilities. RISMIN, an home made software, is used to extract maps, spectra, profiles, etc. from generated list data files. This software is developed under LabVIEWTM and IMAQTM. Beyond the classical elemental mapping capabilities, the software allows any 1D or 2D multi-filtering parameter representations and filtered events list data file generation. Map processing (standard operations and image filtering) is also integrated.

Se, As, Mo, Ag, Cd, In, Sb, Pt, Au, Tl, Re traces in biogenic and abiogenic sulfides from Black Shales (Selwyn Basin, Yukon territories, Canada): A nuclear microprobe study

Abstract Black shales can be an important source of rare metals such as Cu, Ag, As, Mo, Se, Tl, Cd, platinum group elements (PGE) and gold (Pasava et al., Econ. Geol. 91 (1996) 63). However, especially in the case of noble metals, carriers such as discrete minerals could not be identified. This nuclear microprobe study brings new data on the partition of rare metals in Fe-, Fe (Ni)-, Ni- (Fe)-, Ni- and Zn-sulfides from the Ni-Zn-Mo-PGE mineralized marin black shales (Selwyn Basin, Yukon Territories). Sulfides are present as mineralized vestimentiferan tube-worms which are pyritized. Fluid-mineral interaction led to transformation of these biogenic Fe-sulfides successively to Fe–Ni- and Ni–Fe-sulfides which is indicated by increasing Se contents. Ni-sulfides which are interstital to the tube worms represent remobilized material, they are richest in Se. Several tens to thousands ppm of Cu, Zn, As, Se, Mo were located in the biomineralized and transformed tube worms. Antimony was located in Fe–Ni and Ni-, and Zn sulfides and Ag was present in Fe–Ni and Ni–Fe-sulfides. Pt and Au can also be related to submicron-sized inclusions in Fe–Ni sulfides. Hydrothermal fluids (at least 250 °C) precipitated silica around tube worms, intercalating submicron-sized sphalerites. Larger Zn-sulfides contain about 5000 ppm Cd and locally about 60 ppm In. Ba-rich K-feldspar contains Cl-rich Ag–Cd alloys.

Biogenic and abiogenic hydrothermal sulfides: controls of rare metal distribution in black shales (Yukon Territories, Canada)

Abstract The black shales of the Selwyn basin contain relicts of worm tubes which are sulfurized and silificified. Nuclear microprobestudies on biogenic Fe Ni sulfides indicate the presence of several tenths to thousands ppm of Cu, Zn, Se, Mo, As, Sb and Tl. Several tenths of ppm of Ag. Cd and In were observed in hydrothermal sphalerite, and Pt and An of several hundreds of ppm occur as microsize inclusions in framboidal pyrite, rather than being incorporated in the sulfide structures. Mineralogical and chemical investigations prove the presence of hydrothermal fluids of acidic composition, pH of 8–8.5 and temperatures of about 260 °C which carried at least part of the metals. Nuclear reaction analyses indicate the presence of nitrogen mainly in hydrothermal feldspar.

In situ mapping of high-pressure fluids using hydrothermal diamond anvil cells

We present new results combining high pressures and temperatures attainable in a diamond anvil cell with in situ synchrotron radiation induced micro-X-ray fluorescence measurements. Hydrothermal diamond anvil cells experiments have been performed by measuring the partitioning of Pb between aqueous fluids (pure water or NaCl-enriched water) and hydrous silicate melts of haplogranite composition using synchrotron X-ray fluorescence. The in situ measurements were performed in the range 0.3–1.2 GPa and 730–850 °C both in the aqueous fluid and in the silicate melts being in equilibrium. Pb is strongly partitioned into high-pressure–temperature hydrous melts when Cl is present in either the hydrous melt or the aqueous fluid. Moreover, our comparisons of in situ results with post-mortem results show that significant changes take place during rapid quenching especially when samples are small (few hundred of microns in diameter). Water exsolution is induced by the quench in the silicate melt showing the high mobility of Pb which immediately partitions into the water vapor phase during the quench. The current in situ approach offers thus a pertinent complementary method to the classical experimental petrology investigations.

The partitioning of barium and lead between silicate melts and aqueous fluids at high pressures and temperatures

Abstract The origin of subduction-related magmas is still a matter of debate in the Earth Sciences. These magmas are characterised by their distinctive trace element compositions compared to magmas from other tectonic settings, e.g. mid-ocean ridges or rifts. The distinct trace element composition of these magmas is generally attributed to alteration of the source region by a contaminating agent: either a silicate melt or a hydrous fluid, possibly chlorine-enriched. In this study, we have used μPIXE (proton induced X-ray emission) to analyse synthetic samples obtained from a micro-experimental petrology study that aims to determine the partitioning behaviour of two key elements, Ba and Pb, between silicate melt and both pure water and saline fluids. Our experiments were performed at high-pressure (>0.34–1.53 GPa) and high-temperature (697–1082 °C) in a hydrothermal diamond anvil cell, that was used as a transparent rapid quench autoclave. We observed that at high pressure and temperature, in the presence of pure water, Ba and Pb are not strongly fractionated into one phase or the other. The partition coefficient of Pb is ranging from 0.46 to 1.28. Results from one experiment performed at 0.83 GPa and 847 °C, in the presence of a saline fluid indicate that the presence of Cl induces strong fractionation of Pb and moderate fractionation of Ba both into the silicate melt. In addition, our data indicate that Cl is strongly partitioned into the fluid phase.

A PIXE and ICP-MS Analysis of Metallic Atmospheric Contaminants in Tree Bark Tissues, A Basis for Biomonitoring Uses∗

The qualitative and quantitative metallic content of tree barks of Argania spinosa (L.) Skeels were studied. Argania spinosa is an endemic species in Morocco. This tree is adapted to semi-arid climates and exposed to specific conditions of relative humidity, temperature, wind, and particle transport. Three sites were sampled in Morocco: the large town of Rabat, the harbor of Agadir, and Aït Baha, a countryside location exposed to continuous desert wind. The methodologies included (1) in situ microanalysis with proton-induced X-ray emission (PIXE) and (2) trace element determinations by mass spectrometry with inductively coupled plasma (ICP-MS) associated with extraction procedures. Both methods allowed detection of elements coming from different bark compartments. The profile of airborne contaminants in the barks was typical of the sampling sites. The level of lead in barks sampled in Rabat reached 100 ng cm−2, or higher, while it varied between 3 and 35 ng cm−2 in Aït Baha. The in situ study of the microscopic structure of the bark provided the location of major and minor elements at various depths inside the bark. A differential between free deposit on the bark surface and penetrated content was found for the major and trace elements. The free deposit on the bark surface was suspected to be mostly the result of recent contamination. Part of the contaminants spread out on the surface penetrated the superficial suber. This long-term accumulation affected mostly Pb. In deeper levels, airborne elements at low concentrations and elements resulting from root uptake were concurrently present and resulted in a complex situation, as noted for zinc.