INTEGRATED RAMAN MICROSPECTROSCOPY LASER ABLATION INDUCTIVELY COUPLED PLASMA MASS SPECTROMETRY (LA-ICP-MS) SYSTEM FOR THE ANALYSIS OF FLUID AND MELT INCLUSIONS

The composition of fluid and melt inclusions is used for the generation of ore deposit models to aid mineral resource assessments. Many chemical analysis techniques such as secondary ion mass spectrometry (SIMS), electron microprobe analysis (EMPA), LA-ICP-MS, Raman microspectroscopy, and microthermometry are used for single inclusion determinations. In this presentation, we report on an integrated Raman spectroscopy LA-ICP-MS instrument for inclusion analysis. The system is built around a petrographic microscope equipped with (1) a Raman accessory using 532 nm and 785 nm solid state lasers, edge filters for laser line removal, four gratings providing a large range of spectral resolutions, a CCD detector, and (2) a laser ablation module using a 193nm pulsed ArF eximer laser capable of creating 5 - 160 µm craters. The ablated material is swept by He gas to an ICP-MS which serves as a major, minor and trace metal detector. Additionally, the Raman spectrometer can be used as a simultaneous laser induced breakdown spectroscopy (LIBS) detector during LA-ICP-MS analysis.

The main advantage of an integrated system is the ability to analyze the same inclusions by Raman spectroscopy directly followed by elemental quantification by LA-ICP-MS. For fluid inclusions, Raman spectroscopy is used for measurement of salinity (also used for normalization of LA-ICP-MS data) and detecting gas species such as CO₂, N₂, CH₄. In melt inclusions, Raman spectroscopy provides information on the quantity of water in the melt and can also be used for determination of the oxidation states of metals (Fe²⁺ vs. Fe³⁺). By integrating these techniques in a single instrument, we expect to simplify inclusion analysis, increase throughput, and provide higher accuracy in the elemental measurements.