APPLICATIONS OF RAMAN SPECTROSCOPY TO SOLID AND FLUID INCLUSION PHASE IDENTIFICATION

Raman spectroscopy is a powerful tool that has been applied widely to characterize a variety of fluid and solid materials. Whereas microspot Raman analyses have been used with great success to identify and characterize materials, it has previously been less useful for characterizing minor components in samples and for characterizing sample heterogeneities. Minerals often contain solid and fluid inclusions that have been trapped during crystal formation and thus can provide information about the conditions existing during mineralization - composition, temperature, and pressure. The size of inclusions ranges from less than a micrometer to several hundred micrometers in diameter. A Raman system coupled to a confocal microscope is required to obtain high spatial resolution and analyze inclusions below the surface without destruction.

The recent development of high-speed, high-resolution mapping capabilities apparatus makes it possible to quickly and easily obtain high spectral, high spatial resolution Raman maps quickly and easily. Many solid, fluid, and gas phases are common in inclusions, including TiO₂, H₂O, CO₂, CH₄, etc. They are easily recognized by Raman spectroscopy and, in some cases, quantified using their Raman band intensities and/or positions. Recently, there has been much interest in searching for small amounts of different phases of titania (TiO₂) and H₂O in inclusions that previously had been thought to contain only anatase, rutile, or CO₂. However, the metastable phase of titania–brookite in solid inclusions or a small amount of water in fluid inclusions are essential in understanding some mantle processes in which minerals converted to another phase (in solid inclusions), or hydrated minerals lose water that may then occupy fluid inclusion. Multivariate analysis methods are used to construct the Raman images and indicate the presence of titania polymorphs, water, and other substances.

Several examples of solid inclusions of titania with anatase, rutile, and brookite and fluid inclusions have been studied. Spectra and 3D images of solid phases and gas phases comprising a mixture of titania polymorphs and CO₂ (1285 cm^-1 and 1388 cm^-1), CH₄ (2916 cm^-1), N₂ (2330 cm^-1), solid carbon phase (amorphous carbon) (1585 cm^-1 ) and liquid H₂O phase (3200-3700 cm^-1) will be shown.