Study On The Analysis Method Of LA-ICP-MS For The Individual Fluid Inclusions Hosted In Halite

Fluid inclusions were formed during mineral crystallization by trapping the surrounding ore fluids. Therefore such trapped fluid inclusions can preserve various geochemical information during mineral growth. So the understanding of fluid inclusions provides a special significance for the geological researches.Laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS) has become a most powerful technique for the composition analysis of fluid inclusion at the moment. For the advantages such as high analysis speed, high sensitivity, good spatial resolution, less matrix effects and abilities of simultaneous multi-element analysis and isotopic ratio analysis, LA-ICP-MS can be used for the quantitative determination of major to ultra-trace element concentrations of individual fluid inclusions. In recent years, using LA-ICP-MS technique for composition analysis of individual fluid inclusions has become one of the hotspot of fluid inclusions study. Still, for the individual fluid inclusions, since the especial characteristics and complexity during the laser ablation process, unlike for the general solid geological samples, mature and systematic analysis methods are not yet well established. The reliable analysis methods for individual fluid inclusions by LA-ICP-MS is still being explored. In this paper, the analysis method of LA-ICP-MS for the individual fluid inclusions hosted in halite was studied.Artificial fluid inclusions made of pure quartz microcapillary tubes,filled with a series element concentration of standard solutions and saturated Na Cl solution as matrix, were used as calibration standards. Except for iodine, the other element results for artificial inclusions showed good precision in the process of LA-ICP-MS analysis. Using the glass reference material NIST 610 as external calibration standard,element Na as internal standard to determine the artificial fluid inclusions(using the theoretical value of saturated Na Cl solution as Na content), the relative error for all elements were ~+ 60% between the measured results and the added value of standard solution. The possible reason maybe due to crystallization of Na from saturated Na Cl solution during the ablation process. So using glass sample as external standard and Na theoretical value of saturated Na Cl solution as internal standard will cause significant systematic error. Ca or Mg were used as transition internal standard and NIST610 as external standard to get the correction coefficient for Na in the artificial fluid inclusions, and then NIST610 as external calibration standard with corrected Na as internal standard to determine the artificial fluid inclusions, The relative errors of all measured results are within 9%. Using this method to analyse the individual fluid inclusions in halite samples from Chaerhan salt lake of Qinghai province, the results are highly consistent with the analytical results using artificial fluid inclusions as external calibration standard and uncorrected Na theoretical value as internal standard.It is indicated that the method of LA-ICP-MS in-situ analysis for individual fluid inclusions is feasible and accurate. This method could greatly reduce the tedious process in preparation of the artificial fluid inclusion calibration standards(which are one-off microcapillary standards), and contribute to improve accuracy of the final results.