L. Paul Bédard

TCF selenium preconcentration in geological materials for determination at sub-μg g−1 with INAA (Se/TCF-INAA)

In geological samples, Se concentration ranges from 1x10(-9)gg(-1) up to 1x10(-3)gg(-1). The analytical difficulty at low concentration (<1mugg(-1)), is one of the main reasons why the geological cycle of Se is poorly known. The analytical method that consisted of preconcentration of Se with thiol cotton fiber (TCF) followed by graphite furnace atomic absorption spectrometry (GFAAS) has been modified by finishing with instrumental neutron activation analysis (INAA). The modified technique involves sample dissolution (HF-HNO(3)-H(2)O(2)) and evaporation to dryness at low temperature (55-60 degrees C) to avoid selenium volatilization. Se(VI) is converted to Se(IV) by adding 6M HCl to the dry residuum and the solution is then heated in a covered boiling bath (95-100 degrees C). The solution is diluted to obtain 0.6M HCl and then collected on TCF. The TCF is placed in a polyethylene vial for irradiation in the SLOWPOKE II reactor (Montréal) for 30s at a neutron flux of 10(15)m(-2)s(-1). The 162keV peak of (77m)Se (half-life 17.36s) is read for 20s after a decay of 7s. The amount of sample to be dissolved is controlled by two competing effects. To obtain low detection limits, a larger amount of sample should be dissolved. On the other hand, the TCF could become saturated with chalcophile elements when large sample is used. Sulfur is a good indicator of the amount of Se and chalcophile elements present. In S poor sample (<100mugg(-1)) 3.0g of sample was used and the L(D) was approximately 2ngg(-1). In S high samples (>1.5% S) 0.05g of sample was used and the L(D) was approximately 120ngg(-1). The present work also includes suggested Se concentration for eight international geological reference materials (IGRM) that compare favorably with literature values.

A new technique for the synthesis of geochemical reference samples for laser ablation-ICP-MS analysis of zircons

Abstract A new method for the preparation of trace element geochemical reference samples of zircons for LA-ICP-MS techniques has been developed. This method involves finely pulverising a zircon sample and sintering it with a low melting temperature phase, such as albite, at high temperatures and pressures to produce a sintered zircon compact (SZC). Such a geochemical reference sample can be homogeneous at the scale of the beam provided crushing is fine enough such that the volume sampled by the beam is representative of the whole reference sample. Based upon 32 determinations of the SZC MREE, HREE, Th, U and Y are reproducible to within 10% (relative) while LREE are reproducible within 24% (relative). LREE reproducibility is less good due to their lower concentration.

The Dolodau dykes, Canada: An example of an archean carbonatite

SummaryThe Archean Dolodau carbonatite dykes occur near a late tectonic syenite stock located in the Northern Volcanic Zone of the Abitibi greenstone belt. The biotite sovite and amphibole-biotite silicocarbonatite dykes produced fenitization of the host rocks. The Dolodau carbonatites compare favourably with Phanerozoic carbonatites in petrography, mineralogy and geochemistry. An Archean age is suggested by field geology and the isotope data available. The similarities suggest that Archean carbonatite petrogenetic processes were similar to modern day processes.ZusammenfassungDie archaischen Karbonatitgänge von Dolodau liegen in der Nähe eines spättektonischen Syenit-Stockes in der nördlichen vulkanischen Zone des Abitibi Greenstone Belts. Die Biotit-Sovit- and Amphibol-Biotit Silicokarbonatit-Gänge führten zu Fenitisierung der umgebenden Gesteine. Die Dolodau-Karbonatite lassen sich gut mit phanerozoischen Karbonatiten vergleichen, was Petrographie, Mineralogie and Geochemie betrifft. Ein archaisches Alter wird durch Geländebeziehungen and Isotopendaten belegt. Diese Ähnlichkeiten weisen darauf hin, daß archaische Karbonatit-bildende Vorgänge ihren modernen äquivalenten ähnlich sind.