Recent developments in element concentration and isotope ratio analysis of individual fluid inclusions by laser ablation single and multiple collector ICP-MS

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has become a most powerful technique for the elemental analysis of individual, polyphase inclusions completely enclosed in minerals, be they solid or a solid–liquid–gas mixture at the time of measurement. Simultaneous, accurate quantification of major to ultra-trace element concentrations from Li to U by well-controlled ablation of the entire fluid or melt inclusion content and successful use of largely matrix-independent external calibration protocols are unique features of this method.

This contribution reviews fluid inclusion fundamentals relevant for their bulk analysis by LA-ICP-MS and discusses key aspects of the analytical protocol. Emphasis is on figures of merit (precision, accuracy) obtained from the analysis of individual inclusions and fluid inclusion assemblages, and procedures and technical developments to improving data quality are elaborated. A new equation for the calculation of detection limits for LA-ICP-MS analysis is presented, which closely follows IUPAC conventions.

Applications are reviewed with emphasis on the use of synthetic fluid inclusions in constraining metal solubility and distribution between co-existing phases. New data for natural bismuth “fluid” inclusions document the seamless transition to melt inclusion analysis by LA-ICP-MS, thus highlighting the fact that the procedures presented here are generally applicable to the analysis of inclusions in complex host minerals.

Isotope ratio analysis of individual fluid inclusions by multicollector ICP-MS (MC-ICP-MS) is a recent development that requires fast transient signals to be accurately recorded by instrumentation designed for high-precision static measurements of long-lasting stable ion beams. We address the general principles based on Pb isotopes and review a first application to the Bingham Canyon porphyry Cu–Au ± Mo deposit. A pilot study using about 50 synthetic fluid inclusions containing SRM 987 Sr and variable NaCl, Ca, and Rb concentrations demonstrates that accurate ⁸⁷Sr/⁸⁶Sr isotope ratios can be obtained on an individual Rb-poor fluid inclusion, at absolute 2 σ precisions of 0.0003 to 0.002. A residual trend in ⁸⁷Sr/⁸⁶Sr as a function of the Rb/Sr abundance ratio in the fluid inclusions suggests that interference correction of ⁸⁷Rb on mass 87 assuming identical mass bias coefficients for the two elements may be inaccurate; however, the offset can be accurately corrected for by regressing the data to zero ⁸⁷Rb.

The versatility and detection power of LA-ICP-MS makes this technique the method of choice for solute abundance and isotope ratio analysis of individual fluid inclusions. Significant future progress can be achieved by improvements in ion production, transmission and data recording efficiency and by further improving control on inclusion ablation by pulsed laser beams. Data quantification strategies may also have to be further refined to keep pace with instrumental progress and innovation.