Single fluid inclusion analysis by laser ablation inductively coupled plasma atomic emission spectrometry: quantification and validation

Abstract

Laser ablation inductively coupled plasma atomic emission spectrometry (ICP-AES) can provide quantitative determinations of element ratios in the concentrated brines contained within single fluid inclusions, larger than 30 µm in diameter, in topaz and halite. Inclusions formed at different stages can therefore be analysed separately and differentiated. This is an advantage over previous bulk methods of fluid inclusion analysis by ICP-AES that only provide composite analyses of all inclusion types present. Validation of the laser ablation ICP-AES analyses of the inclusions in topaz was obtained using scanning electron microscopy (qualitative), bulk crush–leach ICP-AES (semiquantitative) and a method of ‘geological feasibility’(semi-quantitative). Quantitative validation was achieved using synchrotron X-ray fluorescence microprobe analysis, which showed no significant bias for the determinations of the ratios between Cu, Fe, Mn, Pb and Zn. Synthetic fluid inclusions containing standard solutions were used to validate the laser ablation ICP-AES analysis of inclusions in halite. A bias of <6% was detected for the determinations of ratios between Ba, Ca, K, Li and Mg, and <20% for Sr:Ca. The precision of individual elemental ratios was 20–45%(relative standard deviation) but this could be reduced to 3–8%(standard error on the mean) by the analysis of large numbers of inclusions (e.g., 30). In some natural inclusions the geochemical variability was found to be a limiting factor in the precision of the replicate measurements. The nebulization of standard solutions was found to be an appropriate method of calibration for the determination of element ratios in this application.