The individual analysis of fluid inclusions in minerals using Laser Ablation Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS): an evaluation

Abstract

During the last decade, the possible application of laser ablation inductively coupled plasma - mass spectrometry (LA-ICP-MS) as a quantitative technique for the analysis of individual fluid inclusions has been intensely studied. The quantitative ability of this technique is, however, complicated by several fractionation processes that operate during ablation, transport and analysis in the ICP-MS. In the present study, a number of these fractionation effects were studied and the quantitative ability of LA-ICP-MS analysis of fluid inclusions in natural quartz is evaluated. Using NIST SRM 612 and 614 as reference materials, it is shown that the fractionation during transport is minimised when the sample cell is flushed with He, in contrast with the set-up where Ar is used. Calcium has been successfully applied as an internal standard to calibrate the REE in NIST-glasses. The use of Ca to calibrate other lithophile and chalcophile elements, such as K, Zn, Cu and Pb, can however be questioned. It is shown that the technique is capable of semi-quantitatively characterising different fluid inclusion populations in natural quartz, which demonstrates its importance as a tool for palaeofluidflow modelling. However, during LA-ICP-MS analysis of fluid inclusions in natural quartz, elements are reprecipitated in a glassy phase, as shown by SEM-EDX analysis of the sample surface after ablation. This process could result in a fractionation and may account for the poor precision of the analysis.